Hysys Unit Operations v10 Reference Guide

Aspen HYSYS Unit Operations

Reference Guide

Version Number: V10 June 2017 Copyright (c) 1981-2017 by Aspen Technology, Inc. All rights reserved. Aspen Plus®, Aspen Air Cooled Exchanger™, AirCooled™, Aspen Rate-Based Distillation™, Aspen Custom Modeler®, Aspen HTFS Research Network™, Aspen HYSYS®, Aspen HYSYS Petroleum Refining®, Aspen Process Economic Analyzer, Aspen In-Plant Cost Estimator, Aspen Capital Cost Estimator, Aspen OnLine®, Aspen PIMS™, Aspen Plus Optimizer™, Aspen Process Manual™, Aspen Properties®, Aspen Shell & Tube Exchanger™, Shell&Tube™, SLM™, and the Aspen leaf logo are trademarks or registered trademarks of Aspen Technology, Inc., Burlington, MA. All other brand and product names are trademarks or registered trademarks of their respective companies. This document is intended as a guide to using AspenTech's software. This documentation contains AspenTech proprietary and confidential information and may not be disclosed, used, or copied without the prior consent of AspenTech or as set forth in the applicable license agreement. Users are solely responsible for the proper use of the software and the application of the results obtained. Although AspenTech has tested the software and reviewed the documentation, the sole warranty for the software may be found in the applicable license agreement between AspenTech and the user. ASPENTECH MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THIS DOCUMENTATION, ITS QUALITY, PERFORMANCE, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE. Aspen Technology, Inc. 20 Crosby Drive Bedford, MA 01730 USA Phone: (1) (781) 221-6400 Toll Free: (1) (888) 996-7100 URL: http://www.aspentech.com

Contents

Contents 1 Unit Operations Overview About this Guide Integrated Steady State and Dynamics Simulation Multi-Flowsheet Architecture Extensibility and Customization Model Categories Degrees of Freedom Adding Unit Operations Basic Unit Operation Property View Object Inspect Menu Logical Connections For... Property View 2 Unit Operation Common Property Views Graph Control Property View Heat Exchanger Page Duty Radio Button Options Heater Type Group Duty Source/Source Group Tube Bundle Radio Button Holdup Page Holdup Property View Nozzles Page Notes Pages or Tabs Notes Manager Holdup Model Assumptions of Holdup Model Accumulation Non-Equilibrium Flash Heat Loss Model Chemical Reactions Related Calculations Advanced Holdup Properties Stripchart Page Adding a Strip Chart from the Navigation Pane or Ribbon

Contents

iii 1 1 2 2 3 3 4 5 11 12 12 15 15 16 16 16 17 18 21 22 22 23 23 24 24 25 25 28 31 31 32 34 34

iii

Adding a Strip Chart from a Unit Operation Using the Data Logger Property View Controls in the Displayed Strip Chart User Variables Page Adding a User Variable Variable Navigator (Multi-Select) Variable Navigator (Single-Select) Select Type Dialog Box Using the Select Type Dialog Box Changing the Fluid Package for Multiple Unit Operations Worksheet Tab Stream Conditions Stream Properties Stream Compositions PF Specs 3 Column Input Experts Column Reboiler Pre-configurations Reboiler Once-Through Reboiler Circulation Without Baffle Reboiler Circulation With Baffle Reboiler Circulation with Auxiliary Baffle Absorber Distillation Column Liquid-Liquid Extractor Reboiled Absorber Refluxed Absorber Three Phase Distillation 4 Side Operations Input Expert Reboiled Side Stripper Steam Stripped Side Stripper Side Rectifier Pump-Around Vapor Bypass 5 Column Operations Using Column Subflowsheets Isolation of the Column Solver Independent Fluid Package Ability to Construct Custom Column Configurations Use of Simultaneous Solution Algorithm Dynamic Mode Column Property View Main Flowsheet and Column Subflowsheet Relationship Main Flowsheet / Subflowsheet Concept HYSYS Column Theory Three Phase Theory

iv

34 35 35 37 38 39 40 41 42 42 42 43 43 43 43 45 45 46 47 48 48 50 52 55 57 59 62 65 66 68 70 72 74 77 77 78 78 79 79 79 80 81 81 82 86

Contents

Basic Column Parameters Pressure Flow Condensers and Reboilers Column Installation Input Experts Templates Column Specification Types Cold Property Specifications Component Flow Rate Component Fractions Component Ratio Component Recovery Cut Point Draw Rate Delta T (Heater/Cooler) Delta T (Streams) Duty Duty Ratio Feed Ratio Gap Cut Point Liquid Flow Physical Property Specifications Pump Around Specifications Reboil Ratio Recovery Reflux Feed Ratio Reflux Fraction Ratio Reflux Ratio Stream Property Tee Split Fraction Tray Temperature Transport Property Specifications User Property Vapor Flow Vapor Fraction Vapor Pressure Specifications Column Stream Specifications Column-Specific Operations Condenser Unit Operation Reboiler Unit Operation Column Tower Tee Running the Column Run Reset Column Troubleshooting Heat and Spec Errors Fail to Converge Equilibrium Error Fails to Converge Equilibrium Error Oscillates

Contents

88 89 93 95 96 97 103 103 103 104 104 105 105 106 106 106 107 107 107 108 109 109 109 110 110 111 111 111 112 113 113 114 114 114 115 115 115 116 117 130 139 151 152 152 153 154 154 157 157

v

References 6 Column Property View Column Runner Column Convergence Sequence Design Tab Connections Page (Main Flowsheet) Tower Details Property View Connections Page (Column Runner) Monitor Page Specs Page Specification Property View Advanced Solving Options Specs Summary Page Subcooling Page Notes Page Parameters Tab Profiles Page Estimates Page Efficiencies Page Solver Page Col Dynamic Estimates Property View 2/3 Phase Page Fluid Pkgs Page Amines Page Side Ops Tab Side Strippers Page Side Rectifiers Page Pump Arounds Page Vap Bypasses Page Side Draws Page Internals Tab Rating Tab Towers Page Vessels Page Equipment Page Pressure Drop Page Worksheet Tab Performance Tab Summary Page Column Profiles Page Feeds/Products Page Plots Page Properties View for Plots and Tables Data Control Property View Condenser/Reboiler Page Flowsheet Tab Setup Page Flowsheet Variables Page (Main)

vi

158 159 159 160 160 160 162 163 163 167 168 169 172 172 172 172 173 174 175 178 186 188 190 190 192 193 194 194 194 195 195 196 197 198 198 198 199 199 200 200 200 201 215 216 218 218 218 220

Contents

Internal Streams Page Mapping Page Lock Page Reactions Tab Stages Page Column Reaction Property View Results Page Dynamics Tab Vessels Page Equipment Page Holdup Page Perturb Tab Column Internals Tab Adding a New Internals Option Creating Column Sections Duplicating Column Sections Using Auto Sectioning Selecting an Active Option Adding a New Geometry Option Updating Pressure Drops Calculating the Pressure Drop Across a Sump Including Static Vapor Head Correction Viewing Internals Summary Results Initializing from the Rating Tab Sending to the Rating Tab Importing and Exporting Column Section Templates Viewing Internals Results 7 Column Analysis Overview Column Analysis Workflow Column Internals Manager Column Design Ribbon Column Analysis Flowsheet Icons Removing Column Analysis Flowsheet Icons Creating a Column Internals Configuration Creating Column Sections Duplicating Column Sections Using Auto Sectioning Updating Pressure Drops Calculating the Pressure Drop Across a Sump Including Static Vapor Head Correction Viewing Internals Summary Results Initializing from the Rating Tab Sending to the Rating Tab Importing Column Section Templates Exporting Column Section Templates Geometry Details Tray Geometry Workflow Packing Geometry Workflow

Contents

221 222 222 222 224 224 226 227 228 228 228 228 229 230 230 233 234 234 234 234 235 235 236 236 236 237 238 241 241 242 243 243 246 246 247 250 251 252 252 253 253 253 254 254 255 255 255 256

vii

Specifying Tray Geometry Specifying Picket Fence Weirs or Swept Back Weirs Viewing the Tray Geometry Summary Specifying Tray Geometry Design Parameters Viewing Tray Summary Results Viewing Tray Geometry Results By Tray Specifying Packing Geometry Specifying Packing Geometry Design Parameters Specifying Packing Constants Viewing Packing Summary Results Viewing Packing Results By Stage Geometry Messages Hydraulic Plots Accessing Hydraulic Plots Trayed Hydraulic Plots Packing Hydraulic Plots Hydraulic Plots Ribbon Tab Importing Column Analysis Variables into a Spreadsheet Exporting Column Results to Vendor Packages Using Column Analysis Report Builder Methods Used in Column Analysis Swept-Back Weir Calculations Chan and Prince Dump Point Correlation Liquid Entrainment Correlations Discharge Coefficient Downcomer Relative Froth Density Tray and Downcomer Area Calculations Downcomer Backup Calculations Maximum Capacity Calculations for Packing Liquid Holdup Calculations for Packing Foaming Calculations Packing Types and Packing Factors Downcomer Choke Flooding Flooding Calculations for Trays Kister & Haas Jet Flood Correlation Fair and Fair72 Jet Flood Correlations Smith, Dresser, and Ohlswager Jet Flood Correlation Pressure Drop Calculations for Packing in Column Analysis Sherwood/Leva/Eckert GPDC Pressure Drop Correlation for Packing Aspen GPDC85 Pressure Drop Correlation for Packing Wallis Pressure Drop Correlation for Packing Billet-99 Correlation for Packing Pressure Drop Calculations for Trays 8 Electrolyte Operations Introduction Electrolyte Operations

viii

256 281 284 284 288 290 293 294 297 298 298 300 300 300 301 304 306 308 308 310 312 312 312 313 315 316 318 325 326 328 328 331 331 332 333 334 336 337 338 341 343 347 348 351 351 351

Contents

9 Crystallizer Operation Theory Boundary Condition Equations Design Tab Connections Page Parameters Page Solver Page User Variables Page Notes Page Rating Tab Worksheet Tab Dynamics Tab 10 Neutralizer Operation Theory Boundary Condition Solving Options Equations Design Tab Connections Page Parameters Page Solver Page Rating Tab Dynamic Tab 11 Precipitator Operation Theory Boundary Condition Solving Options Equations Design Tab Connections Page Parameters Page Solver Page User Variables Page Notes Page Rating Tab Worksheet Tab Dynamic Tab

353 353 354 354 354 355 355 356 356 356 357 357 357 359 359 360 360 360 361 361 361 362 362 363 365 365 366 366 366 367 367 367 368 368 368 369 369 369

12 Heat Transfer Operations

371

13 Air Cooler

373

Theory Steady State Rigorous Air Cooler Functionality Dynamics

Contents

373 373 374 374

ix

Heat Transfer Dynamic Specifications Pressure Drop Air Cooler Property View Design Tab Connections Page Parameters Page Specs Page User Variables Page Notes Page Rating Tab Sizing Page (Simple Design) Sizing Page Rigorous Air Cooler Nozzles Page Worksheet Tab Performance Tab Performance Results Page Performance Profiles Page Performance Plots Page Performance Tables Page Performance Setup Page Dynamics Tab Model Page Specs Page Holdup Page Stripchart Page Rigorous Air Cooler Tab Simulation Calculation Options Exchanger Page Process Data Page Property Range Page Results Summary Page Setting Plan Page Tube Layout Page Profiles Page 14 Cooler/Heater Theory Steady State Operation Dynamic Operation Pressure Drop Dynamic Specifications Heater or Cooler Property View Design Tab Connections Page Parameters Page User Variables Page Notes Page Rating Tab

x

374 375 375 376 376 377 377 378 378 378 378 378 379 380 380 380 380 381 381 381 382 382 382 383 384 385 385 385 386 386 387 388 389 389 389 391 391 391 391 392 392 393 393 393 393 394 394 394

Contents

Nozzles Page Heat Loss Page Worksheet Tab Performance Tab Profiles Page Plots Page Tables Page Setup Page Dynamics Tab Specs Page Duty Fluid Page Holdup Page Stripchart Page

394 394 395 395 396 396 396 397 397 398 400 401 401

15 Fired Heater (Furnace)

403

Fired Heater Steady State Operation Fired Heater Dynamic Operation Switching Modes Fired Heater Theory Combustion Reaction Heat Transfer Radiant Heat Transfer Convective Heat Transfer Conductive Heat Transfer Pressure Drop Minimum Specifications Fired Heater Property View Design Tab Connections Page Parameters Page User Variables Page Notes Page Rating Tab Sizing Page Nozzles Page Heat Loss Page Worksheet Tab Performance Tab Performance Details Page Performance Plots Page Performance Tables Page Performance Setup Page Dynamics Tab Tube Side PF Page Flue Gas PF Page Holdup Page EDR Fired Heater Tab Summary Page Streams Page

Contents

404 405 405 405 405 406 409 409 410 410 411 411 411 412 412 413 413 413 413 417 417 417 417 417 417 418 418 418 418 419 420 420 420 421

xi

Fuel Page Flue Gas Page Tube Banks Page Operation Page Property Table Page 16 Heat Exchanger Heat Exchanger Theory Steady State Dynamic Pressure Drop Dynamic Specifications Heat Exchanger Property View Design Tab Connections Page Parameters Page Specs Page Specification Property View User Variables Page Notes Page Worksheet Tab Heat Exchanger Rating Tab Sizing Page Parameters Page Detailed Heat Model Properties Property View Nozzles Page Heat Loss Page Performance Tab Details Page Plots Page Tables Page Setup Page Error Msg Page Dynamics Tab Model Page Specs Page Holdup Page Stripchart Page Rigorous Shell&Tube Tab Specifying Application Information for Rigorous Shell&Tube Specifying Exchanger Information for Rigorous Shell&Tube Specifying Process Information for Rigorous Shell&Tube Specifying Property Ranges for Rigorous Shell&Tube Viewing Results Summary for Rigorous Shell&Tube Viewing a Setting Plan for Rigorous Shell&Tube Viewing Tube Layout Information for Rigorous Shell&Tube Viewing Rigorous Shell&Tube Profiles Information Specifying Find Fouling Calculation Options for Rigorous Shell&Tube

xii

421 421 421 421 421 423 424 424 425 425 426 426 427 427 427 432 433 436 436 437 437 437 441 445 448 448 448 449 451 451 451 452 452 452 455 458 459 459 460 462 468 469 470 470 471 472 472

Contents

17 Liquefied Natural Gas (LNG) Exchanger Theory Heat Transfer Pressure Drop Convective (U) & Overall (UA) Heat Transfer Coefficients Dynamic Specifications LNG Property View Design Tab Connections Page Parameters Page Specs Page Specification Property Views User Variables Page Notes Page Rating Tab Sizing (dynamics) Page Layers (dynamic) Page Heat Transfer (dynamics) Page Worksheet Tab Performance Tab Results Page Plots Page Tables Page Setup Page Summary Page Layers Page Dynamics Tab Model Page Specs Page Holdup Page Estimates Page Stripchart Page About the LNG Wound Coil Heat Exchanger Wound Coil Heat Exchanger (WCHE) Reference Page Wound Coil Heat Exchanger - Plate Fin Equivalents Reference LNG EDR PlateFin Overview EDR PlateFin Tab Exchanger Design Ribbon Options EDR PlateFin Process Page EDR PlateFin Property Ranges Page EDR PlateFin Results Summary Page EDR PlateFin Results Geometry LNG EDR CoilWound Overview EDR CoilWound Tab Exchanger Design Ribbon Options Specifying LNG EDR CoilWound Process Information Specifying LNG EDR CoilWound Property Ranges Viewing LNG EDR CoilWound Results Summary Viewing LNG EDR CoilWound Results Geometry

Contents

475 476 476 477 477 478 479 479 479 479 481 482 484 484 484 485 486 487 489 489 489 491 491 492 492 493 493 493 495 496 497 497 497 498 500 507 508 508 509 511 512 513 515 516 516 517 519 520 522

xiii

Modifying LNG EDR CoilWound Convergence Parameters References

523 524

18 Plate Exchanger

525

Theory

525 525 526 526 526 527 527 528 528 529 530 531 532 532

Heat Transfer Plate Exchanger Design Tab Specifying Plate Exchanger Connections Specifying Plate Exchanger Parameters Plate Exchanger Specifications Rigorous Plate Overview EDR Rigorous Plate Tab Exchanger Design Ribbon Options Specifying Rigorous Plate Process Information Specifying Rigorous Plate Property Ranges Viewing Rigorous Plate Results Summary Viewing Rigorous Plate Setting Plan Viewing Rigorous Plate Profiles 19 Logical Operations Common Options ATV Tuning Technique Controller Face Plate 20 Adjust Operation Connections Tab Connections Page Notes Page Parameters Tab Parameters Page Simultaneous Adjust Manager Options Page Monitor Tab Tables Page Plots Page User Variables Tab Starting the Adjust Individual Adjust Multiple Adjust 21 Balance Balance Property View Connections Page Parameters Tab Worksheet Tab Stripchart Tab User Variables Tab

xiv

533 533 533 534 537 537 538 538 539 539 540 542 543 543 543 543 544 544 545 547 548 548 548 552 552 552

Contents

22 Boolean Operations Boolean Logic Blocks Property View Logical Operation Face Plate Property View Boolean Connections Tab Adding/Editing Process Variable (PV) Source Adding/Editing Output Target Boolean Monitor Tab Not Gate Xor Gate On Delay Gate Off Delay Gate Latch Gate Counter Up Gate Counter Down Gate Boolean And Gate Specifying Boolean And Gate Connections Monitoring Boolean And Gate Input and Output Values Boolean Or Gate Specifying Boolean Or Gate Connections Monitoring Boolean Or Gate Input and Output Values Cause and Effect Matrix Configuring a Cause and Effect Matrix Connecting the Inputs Connecting the Outputs Changing the Order of the Inputs or Outputs Viewing the Inputs and Outputs Specifications Viewing Status Messages Viewing Trace Messages

553 554 554 555 555 555 556 556 556 557 557 558 559 559 560 560 561 561 562 562 563 564 565 567 568 568 569 570

23 Control Ops

571

24 Split Range Controller

573

Connections Tab Parameters Tab Operation Page Configuration Page Advanced Page Autotuning Page IMC Design Page Scheduling Page Alarms Page Signal Processing Page Initialization Page Split Range Setup Tab Stripchart Tab User Variables Tab

Contents

574 574 575 576 577 581 582 583 583 584 585 585 586 586

xv

25 Ratio Controller Connections Tab Parameters Tab Configuration Page Range Page Advanced Page Autotuning Page IMC Design Page Scheduling Page Alarms Page Signal Processing Page Initialization Page Stripchart Tab User Variables Tab 26 PID Controller Connections Tab Process Variable Source Remote Setpoint Source Output Target Object Parameters Tab Configuration Page Advanced Page Autotuner Page IMC Design Page Scheduling Page Alarms Page PV Conditioning Page Signal Processing Page FeedForward Page Model Testing Page Initialization Page Monitor Tab Stripchart Tab User Variables Tab Algorithm References HYSYS PID Controller Algorithms Foxboro PID Controller Algorithms Discrete Time Domain Implementation of the Foxboro Algorithms Honeywell PID Controller Algorithms Discrete Time Domain Implementation of the Honeywell Algorithms Yokogawa PID Controller Algorithms 27 MPC Controller Connections Tab Process Variable Source Remote Setpoint Output Target Object

xvi

587 588 588 589 591 592 595 596 597 597 598 599 599 600 601 602 602 602 603 603 603 608 611 614 614 615 616 618 619 619 620 620 621 621 621 621 623 624 626 627 629 631 632 632 632 633

Contents

Parameters Tab Operation Page Configuration Page Advanced Page Alarms Page Signal Processing Page MPC Setup Tab Basic Page Advanced Page Process Models Tab Basic Page Advanced Page Stripchart Tab User Variables Tab 28 DMCplus Controller Connections Tab Controlled Variable (CV) Manipulated Variable (MV) Feed Forward (FF) Model Test Tab Performing DMCplus Model Testing Operation Tab Operation Page FF Variable Page Stripchart Tab User Variables Tab Control Valve Window Control OP Port 29 Digital Point Connections Tab Parameters Tab Off Mode Manual Mode Auto Mode Stripchart Tab User Variables Tab Alarm Levels Tab 30 External Data Linker Connections Page Configuration Page Properties Page Revision History Tab 31 Recycle Recycle Property View

Contents

633 633 634 635 637 639 639 640 641 643 643 644 644 644 645 647 647 647 648 648 650 652 652 653 654 654 654 656 657 657 658 658 658 659 661 662 662 663 663 663 664 664 665 666

xvii

Connections Tab Connections Page Notes Page Parameters Tab Variables Page Numerical Page Convergence Page Worksheet Tab Monitor Tab User Variables Tab Calculations Reducing Convergence Time Recycle Advisor Using the Recycle Advisor Recycle Setup Tab 32 Selector Block Connections Tab Parameters Tab Selection Mode Page Scaling Factors Page Monitor Tab Stripchart Tab User Variables Tab 33 Set

677 677 678 678 680 680 681 681 683

Set Property View Connections Tab Parameters Tab User Variables Tab 34 Spreadsheet Spreadsheet Functions General Math Functions Calculation Hierarchy Logarithmic Functions Trigonometric Functions Logical Operators IF/THEN/ELSE Statements Spreadsheet Interface Importing and Exporting Variables by drag and drop Enumeration in Spreadsheet Importing Variables by Browsing Exporting Formula Results View Associated Object Spreadsheet Tabs Connections Tab Parameters Tab

xviii

666 666 666 666 667 668 672 672 672 673 673 673 674 674 675

683 683 684 684 685 686 686 687 688 688 689 689 690 690 690 691 691 692 692 692 693

Contents

Formulas Tab Spreadsheet Tab Calculation Order Tab User Variables Tab Function Help and Spreadsheet Only Buttons 35 Stream Cutter Stream Cutter Property View Changing the Fluid Package Changing the Fluid Package in the Unit Operation Property View Changing the Fluid Package Using the Object Inspect Menu Changing the Fluid Package from the Fluid Package Manager Design Tab Connections Page Specifying Stream Cutter Transition Information Fluid Package Transitions True to Apparent Transition 36 Black Oil Translator Connections Tab Transitions Tab Simple Method Three Phase Method Infochem Multiflash Transition Types 37 Transfer Function Transfer Function Property View Connections Tab Parameters Tab Configuration Page Integrator Page Delay Page Lag Page Lead Page 2nd Order Page Ramp Page Rate Limiter Page Stripchart Tab User Variables Tab 38 Piping Operations Piping References 39 Compressible Gas Pipe Model for a Single Phase Compressible Flow Governing Equations

Contents

695 695 696 696 696 699 699 699 700 703 704 704 704 705 706 708 709 709 709 710 711 711 712 713 714 714 714 715 716 716 717 718 719 720 721 721 721 723 723 725 725 725

xix

Algorithm Compressible Gas Pipe Property View Design Tab Connections Page Parameters Page User Variables Page Notes Page Rating Tab Sizing Page Heat Transfer Page Worksheet Tab Performance Tab Profiles Page Properties Tab Dynamics Tab Specs Page Stripchart Page 40 Liquid-liquid Hydrocyclone Theory Oil Droplet Distribution Hydrocyclone Liner Dimensions Hydrocyclone Hydraulics Oil Droplet Migration Probability Hydrocyclone Separation Efficiency Liquid-liquid Hydrocyclone Property View Design Tab Connections Page Parameters Page Liner Details Page Droplet Distribution Page User Variables Page Notes Page Performance Tab General Page Geometric Page Overflow Page Underflow Page Tables Page Plots Page Worksheet Tab Dynamics Tab Nomenclature 41 Mixer Mixer Property View Design Tab Connections Page

xx

726 726 726 727 727 727 727 728 728 729 729 729 729 730 730 731 731 733 733 734 734 735 737 738 738 739 739 739 741 742 743 743 743 743 743 743 744 744 744 744 744 744 747 748 748 748

Contents

Parameters Page User Variables Page Notes Page Rating Tab Nozzles Page Worksheet Tab Dynamics Tab Specs Page Holdup Page Stripchart Page 42 Pipe Segment Calculation Modes Pressure Drop Mode Length Mode Diameter Mode Flow Mode Incremental Material and Energy Balances Mode Pipe Segment Property View Design Tab Connections Page Parameters Page Summary of Methods Emulsions Page User Variables Page Notes Page Pipe Segment Rating Tab Sizing Page Pipe Fittings Property View Dynamics Tab Parameters Page Holdup Page Stripchart Page Rating Tab Heat Transfer Page Pipe Segment Heat Model Page Pipe Segment Performance Tab Profiles Page Pipe Profile View Property View Insulation Page Pipe Segment Performance Tab (Dynamics Mode) Viewing Segments Performance Results Viewing Holdups Performance Results HYSYS Piping Flow Assurance Pipe Flow Assurance - CO2 Corrosion Pipe Flow Assurance - Erosion Pipe Flow Assurance - Hydrates Specifying P/T Options: Hydrate Formation Profile Pipe Flow Assurance - Slug Analysis

Contents

748 749 749 749 749 749 749 750 750 751 753 753 754 755 756 756 757 758 758 758 759 760 787 787 787 787 788 798 801 801 802 802 803 803 809 816 816 816 818 819 819 820 820 821 823 823 824 825

xxi

Pipe Flow Assurance - Wax Deposition Profes Wax Property View References CO2 Corrosion Rate Correlations Reference Pipe Flow Correlations Fitting Pressure Loss Pipe Emulsion Viscosity Methods 43 Relief Valve Design Tab Connections Page Parameters Page User Variables Page Notes Page Rating Tab Sizing Page Nozzles Page Worksheet Tab Dynamics Tab Specs Page Holdup Page Advanced Page Stripchart Page 44 Tee Tee Property View Design Tab Connections Page Parameters Page User Variables Page Notes Page Rating Tab Nozzles Page Dynamics Tab Specs Page Holdup Page Stripchart Page 45 Valve Operation Valve Property View Design Tab Connections Page Parameters Page User Variables Page Notes Page Rating Tab Sizing Page Characteristic Curve Property View

xxii

828 831 838 838 843 844 846 851 851 851 852 852 852 852 853 856 856 856 856 857 858 858 859 859 859 859 860 861 861 861 861 861 861 862 863 865 866 866 866 866 867 867 867 867 873

Contents

Control Valve Calculation Theory Nozzles Page Options Page Flow Limits Page Worksheet Tab Dynamics Tab Specs Page Pipe Page Holdup Page Actuator Page Flow Limits Page Stripchart Page

874 890 890 890 890 891 891 893 894 895 897 899

46 Reactor Operations

901

47 Reactor Operations: CSTR and General Reactors

903

General Reactors Property Views Design Tab Connections Page Parameters Page Conversion Reactor Reactions Tab Details Page Results Page CSTR Reactions Tab Details Page Results Page Equilibrium Reactor Reactions Tab Details Page Results Page Gibbs Reactor Reactions Tab Overall Page Details Page Rating Tab Sizing Page Nozzles Page Heat Loss Page Worksheet Tab Dynamics Tab Specs Page Holdup Page Stripchart Page Heat Exchanger Page 49 Yield Shift Reactor Theory Product Stream Mass Fractions Yield Shift Reactor Property View Design Tab Connections Page

Contents

905 905 905 906 908 908 909 911 911 912 913 914 915 916 917 917 918 918 921 921 921 921 922 923 924 924 925 925 925 927 927 927

xxiii

Parameters Page Model Config Tab Design Parameters Page Design Variables Page Heat of Reaction Page Composition Shift Tab Design Data Page Design Data: Base Page Design Data: Datasets Page Base Yields Page Base Shifts Page Efficiencies Page Results Page Property Shift Tab Properties Page Design Data Page Design Data: Base Page Design Data: Datasets Page Base Shifts Page Efficiencies Page Results Page Worksheet Tab Dynamics Tab Specs Page 50 Plug Flow Reactor Newton’s Method Plug Flow Reactor (PFR) Property View PFR Design Tab Connections Page Parameters Page Heat Transfer Page User Variables Page Notes Page Reactions Tab Overall Page Details Page Results Page Rating Tab Sizing Page Nozzles Page Worksheet Tab Performance Tab Conditions Page Flows Page Reaction Rates Page Transport Page Compositions Page Dynamics Tab

xxiv

928 928 929 929 930 930 931 931 933 935 936 937 937 937 938 939 939 939 940 940 940 941 941 941 943 943 945 945 946 946 948 950 951 951 951 953 954 955 955 956 957 957 957 958 958 958 959 959

Contents

Specs Page Holdup Page Duty Page Stripchart Page

959 961 961 961

51 Rotating Equipment

963

References

963

52 Centrifugal Compressor or Expander Unit Operations Typical Solution Methods Compressor - Expander Theory Steady State Dynamics Equations Used Compressor Efficiencies Expander Efficiencies Compressor Heads Expander Heads Using Momentum Equations References Methods Used Compressor Performance Curves: Off Design Corrections Compressor Curve Interpolation Details Huntington Method Multiple IGV Curves Multiple MW Curves Quasi-Dimensionless and Non-Dimensional Curves Schultz Method Reference Compressor - Reference Method Single Curve Compressor Options Compressor or Expander Design Tab Connections Page Parameters Page Surge Analysis Links Page User Variables Page Notes Page Compressor or Expander Rating Tab Curves Page Flow Limits Page Nozzles Page Inertia Page Electric Motor Page Compressor or Expander Performance Tab Results Page Power Page Compressor or Expander Dynamics Tab Specs Page

Contents

965 966 967 967 968 969 969 970 971 971 972 973 973 973 976 977 978 980 981 984 985 985 986 986 987 988 988 989 990 990 990 997 998 999 999 1002 1003 1003 1003 1004

xxv

Surge Controller Holdup Page Stripchart Page

1006 1009 1009

53 Reciprocating Compressor Unit Operation

1011

Reciprocating Compressor Theory Rod Loading Maximum Pressure Flow Reciprocating Compressor Design Tab Connections Page Parameters Page Links Page Settings Page User Variables Page Notes Page Reciprocating Compressor Rating Tab Nozzles Page Inertia Page Reciprocating Compressor Performance Tab Results Page Power Page Reciprocating Compressor Dynamics Tab

1012 1014 1015 1015 1015 1016 1016 1016 1016 1017 1017 1018 1018 1018 1018 1018 1019 1019

54 Screw Compressor Workflow Screw Compressor Theory Volumetric Efficiency and Leakage Flow Calculation Performance Curve Calculation References Screw Compressor: Design Tab Connections Page Parameters Page Links Page Settings Page Screw Compressor: Rating Tab Curves Page Nozzles Page Inertia Page Screw Compressor: Performance Tab Results Page Power Page Screw Compressor: Dynamics Tab Specs Page Holdup Page Stripchart Page

xxvi

1021 1021 1021 1022 1023 1023 1024 1024 1024 1026 1027 1029 1030 1032 1032 1032 1032 1033 1034 1034 1036 1036

Contents

55 Pump Unit Operation Pump Theory Pump Design Tab Connections Page Parameters Page Curves Page Links Page User Variables Page Notes Page Pump Rating Tab Curves Page Curve Property View Curves Profiles Property View Generate Curve Options Property View NPSH Page Nozzles Page Inertia Page Electric Motor Page Design Page Pump Performance Tab Results Page Power Page Pump Dynamics Tab Specs Page Holdup Page Stripchart Page References 56 Separation Operations

1037 1037 1038 1039 1039 1039 1041 1042 1042 1042 1043 1045 1046 1047 1048 1050 1051 1051 1054 1054 1055 1055 1055 1055 1058 1058 1058 1059

References

1059

57 Component Splitter

1061

Theory Component Splitter Property View Design Tab Connections Page Parameters Page Splits Page TBP Cut Point Page User Variables Page Notes Page Rating Tab Nozzles Page Worksheet Tab Dynamics Tab Specs Page

Contents

1061 1062 1062 1062 1062 1063 1064 1065 1065 1065 1066 1066 1066 1066

xxvii

58 Separator, 3-Phase Separator, and Tank Theory Energy Balance Physical Parameters Separator Ops General Property Views Design Tab Connections Page Parameters Page User Variables Page Notes Page Reactions Tab Results Page Rating Tab Sizing Page Nozzles Page Heat Loss Page Level Taps Page Option Page C.Over Setup Page C. Over Results Page Worksheet Tab Dynamics Tab Specs Page Holdup Page Stripchart Page Heat Exchanger Page 59 Shortcut Column Shortcut Column Property View Design Tab Connections Page Parameters Page Rating Tab Worksheet Tab Performance Tab Dynamics Tab

1067 1068 1069 1069 1071 1071 1071 1071 1072 1072 1072 1072 1073 1073 1075 1076 1082 1084 1084 1090 1090 1090 1091 1093 1093 1093 1095 1095 1095 1095 1096 1096 1096 1096 1097

60 Solid Separation Operations

1099

61 Baghouse Filter

1101

Design Tab Connections Page Parameters Page Notes Page Rating Tab Sizing Page Worksheet Tab Performance Tab

xxviii

1101 1101 1101 1102 1102 1102 1102 1102

Contents

Results Page Dynamics Tab 62 Cyclone Design Tab Connections Page Parameters Page Solids Page User Variables Page Rating Tab Sizing Page Constraints Page Worksheet Tab Performance Tab Results Page Dynamics Tab 63 Hydrocyclone Design Tab Connections Page Parameters Page Solids Page User Variables Page Notes Page Rating Tab Sizing Page Constraints Page Worksheet Tab Performance Tab Results Page Dynamics Tab 64 Rotary Vacuum Filter Design Tab Connections Page Parameters Page User Variables Page Notes Page Rating Tab Sizing Page Cake Page Worksheet Tab Dynamics Tab 65 Simple Solid Separator Design Tab Connections Page Parameters Page

Contents

1103 1103 1105 1105 1105 1105 1106 1107 1107 1107 1108 1108 1108 1108 1109 1111 1111 1111 1111 1112 1112 1112 1112 1112 1113 1113 1113 1114 1114 1115 1115 1115 1115 1116 1116 1116 1116 1116 1117 1117 1119 1119 1119 1119

xxix

Splits Page User Variables Page Notes Page Rating Tab Worksheet Tab Dynamics Tab 66 Material Streams The "Spec Stream As..." Property View Worksheet Tab Conditions Page Properties Page Composition Page Input Composition Property View Oil & Gas Feed Page Petroleum Assay Page K Value Page User Variables Page Notes Page Cost Parameters Page Normalized Yields Page Acid Gas Page PSD Properties Page Sulfur Recovery Page Attachments Tab Unit Ops Page Analysis Page Dynamics Tab Specs Page Stripchart Page 67 Energy Streams Stream Tab Unit Ops Tab Dynamics Tab Stripchart Tab User Variables Tab 68 Subflowsheet Operations Introduction Subflowsheet Property View Adding a Subflowsheet Connections Tab Parameters Tab Transfer Basis Tab Variables Tab Notes Tab Lock Tab

xxx

1119 1120 1120 1120 1120 1120 1121 1122 1122 1123 1125 1130 1131 1132 1134 1136 1137 1137 1137 1137 1138 1138 1139 1139 1140 1140 1141 1141 1142 1143 1143 1144 1144 1144 1144 1145 1145 1146 1146 1147 1148 1148 1151 1151 1151

Contents

Index

Contents

1153

xxxi

xxxii

Contents

1 Unit Operations Overview

About this Guide The Aspen HYSYS Unit Operations Guide provides detailed information regarding: l

Common Property Views

l

Input Experts

l

Column Operations

l

Columns

l

Column Analysis

l

Electrolyte Operations

l

Heat Transfer Operations

l

Logical Operations

l

Piping Operations

l

Reactor Operations

l

Rotating Equipment

l

Separation Operations

l

Solid Separation Operations

l

Streams

l

Subflowsheet Operations

For information related to other aspects of HYSYS: l

l

l

For information regarding HYSYS Petroleum Refining operations, please refer to the Aspen HYSYS Petroleum Refining Unit Operations & Reactor Models Reference Guide or the HYSYS Help. For information on using Assay Management in HYSYS, please refer to the Assay Management in Aspen HYSYS Petroleum Refining Reference Guide or the HYSYS Help. For information regarding the Properties Environment, HYSYS Upstream operations, Sulsim (Sulfur Recovery) operations, Acid Gas Cleaning, Simulation and Analysis Tools, Safety Analysis, BLOWDOWN Technology,

1 Unit Operations Overview

1

HYSYS Dynamics, and HYSYS Equation Oriented (EO) Solving, please refer to the HYSYS Help.

Integrated Steady State and Dynamics Simulation HYSYS uses an integrated steady state and dynamic modeling capability in which the same model can be evaluated from either perspective with full sharing of process information. The components that comprise HYSYS provide a powerful approach to steady state process modeling. The comprehensive selection of operations and property methods lets you model a wide range of processes with confidence. Perhaps even more important is how the HYSYS approach to modeling maximizes your return on simulation time through increased process understanding. The key to this is the Event Driven operation. By using a ‘degrees of freedom’ approach, calculations in HYSYS are performed automatically. HYSYS performs calculations as soon as unit operations and property packages have enough required information. Any results, including passing partial information when a complete calculation cannot be performed, is propagated bi-directionally throughout the flowsheet. What this means is that you can start your simulation in any location using the available information to its greatest advantage. Since results are available immediately - as calculations are performed - you gain the greatest understanding of each individual aspect of your process.

Multi-Flowsheet Architecture The multi-flowsheet architecture of HYSYS is vital to this overall modeling approach. Although HYSYS is designed to allow the use of multiple property packages and the creation of pre-built templates, the greatest advantage of using multiple flowsheets is that they provide an extremely effective way to organize large processes. By breaking flowsheets into smaller components, you can easily isolate any aspect for detailed analysis. Each of these sub-processes is part of the overall simulation, automatically calculating like any other operation. The design of the HYSYS interface is consistent, if not integral, with this approach to modeling. Access to information is the most important aspect of successful modeling, with accuracy and capabilities accepted as fundamental requirements. Not only can you access whatever information you need when you need it, but the same information can be displayed simultaneously in a variety of locations. Just as there is no standardized way to build a model, there is no unique way to look at results. HYSYS uses a variety of methods to display

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1 Unit Operations Overview

process information - individual property views, the PFD, Workbook, graphical Performance Profiles, and Tabular Summaries. Not only are all of these display types simultaneously available, but through the object-oriented design, every piece of displayed information is automatically updated whenever conditions change.

Extensibility and Customization The inherent flexibility of HYSYS allows for the use of third party design options and custom-built unit operations. These can be linked to HYSYS through OLE Extensibility. This section covers the various unit operations, template and column subflowsheet models, optimization, and dynamics. Since HYSYS is an integrated steady state and dynamic modeling package, the steady state and dynamic modeling capabilities of each unit operation are described successively, illustrating how the information is shared between the two approaches. In addition to the physical operations there is a chapter for logical operations, which do not physically perform heat and material balance calculations, but that impart logical relationships between the elements that make up your process.

Model Categories The following is a brief definition of categories used in this volume: Term

Definition

Physical Operations

Governed by thermodynamics and mass/energy balances, as well as operation-specific relations.

Logical Operations

The Logical Operations presented in this volume are primarily used in Steady State mode to establish numerical relationships between variables. Examples include the Adjust and Recycle. There are, however, several operations such as the Spreadsheet and Set operation which can be used in Steady State and Dynamic mode.

Subflowsheets

You can define processes in a subflowsheet, which can then be inserted as a “unit operation” into any other flowsheet. You have full access to the operations normally available in the main flowsheet.

Columns

Unlike the other unit operations, the HYSYS Column is contained within a separate subflowsheet, which appears as a single operation in the main flowsheet.

Integrated into the steady state modeling is multi-variable optimization. Once you have reached a converged solution, you can construct virtually any objective function with the Optimizer. There are five available solution algorithms for both unconstrained and constrained optimization problems, with an automatic

1 Unit Operations Overview

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backup mechanism when the flowsheet moves into a region of non-convergence. HYSYS offers an assortment of analysis tools which can be attached to process streams and unit operations. These tools interact with the process model and provide additional information. In this guide, each operation is explained in its respective chapters for steady state and dynamic modeling. A separate guide has been devoted to the principles behind dynamic modeling. HYSYS is the first simulation package to offer dynamic flowsheet modeling backed up by rigorous property package calculations. Note: The HYSYS Dynamics license is required to use the features in the HYSYS dynamics mode.

HYSYS has a number of unit operations, which can be used to assemble flowsheets. By connecting the proper unit operations and streams, you can model a wide variety of oil, gas, petrochemical, and chemical processes. Included in the available operations are those which are governed by thermodynamics and mass/energy balances, such as Heat Exchangers, Separators, and Compressors, and the logical operations like the Adjust, Set, and Recycle. A number of operations are also included specifically for dynamic modeling, such as the Controller, Transfer Function Block, and Selector. The Spreadsheet is a powerful tool, which provides a link to nearly any flowsheet variable, allowing you to model “special” effects not otherwise available in HYSYS.

Degrees of Freedom In modeling operations, HYSYS uses a Degrees of Freedom approach, which increases the flexibility with which solutions are obtained. For most operations, you are not constrained to provide information in a specific order, or even to provide a specific set of information. As you provide information to the operation, HYSYS calculates any unknowns that can be determined based on what you have entered. For example, consider the Pump operation. If you provide a fully-defined inlet stream to the pump, HYSYS immediately passes the composition and flow to the outlet. If you then provide a percent efficiency and pressure rise, the outlet and energy streams is fully defined. If, on the other hand, the flowrate of the inlet stream is undefined, HYSYS cannot calculate any outlet conditions until you provide three parameters, such as the efficiency, pressure rise, and work. In the case of the Pump operation, there are three degrees of freedom, thus, three parameters are required to fully define the outlet stream.

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1 Unit Operations Overview

All information concerning a unit operation can be found on the tabs and pages of its property view. Each tab in the property view contains pages which pertain to the unit operation, such as its stream connections, physical parameters (for example, pressure drop and energy input), or dynamic parameters such as vessel rating and valve information.

Adding Unit Operations You can use the Model Palette to add HYSYS unit operations, streams, and subflowsheets to the main flowsheet or a sub-flowsheet. Operations can also be installed and set up from the Workbook, which is a spreadsheet style view of the simulation environment. Note: The standard Model Palette is available for the main flowsheet and the Standard Sub-Flowsheet. However, Column Sub-Flowsheets, EO Sub-Flowsheets, Aspen Hydraulics Sub-Flowsheets, and Sulfur Recovery Unit (SRU) Sub-Flowsheets feature different model palettes. These palettes feature different unit operations depending on the sub-flowsheet type.

To access the Model Palette: l

Press F4.

l

Press F12. -or-

l

From the View ribbon tab | Show group, click the Model Palette

button. To add a stream: l

On the Model Palette, in the upper-right corner, click the desired stream type. Name

Icon

Material Stream Energy Stream

The upper-right corner of the model palette also allows you to add a Standard Sub-Flowsheet or an EO Sub-Flowsheet.

1 Unit Operations Overview

5

Name

Icon

Standard Sub-Flowsheet

EO Sub-Flowsheet

To add other unit operations or sub-flowsheets: 1. On the Model Palette, select one of the following Views: o

Text View : Display the icon, name, and description for each unit operation.

o

Grid View : Displays only the icon for each unit operation. You can hover over a unit operation to view the associated tooltip.

2. You can either: o

Type a search term in the search bar, and then click . Searches are filtered based on the name and description. -or-

o

6

Select one of the categories on the left-hand side. Category

Associated Unit Operations/Sub-Flowsheets

All

Shows all available unit operations and sub-flowsheets.

1 Unit Operations Overview

Category Dynamics & Control

External Model

1 Unit Operations Overview

Associated Unit Operations/Sub-Flowsheets o

Split-Range Controller

o

Ratio Controller

o

PID Controller

o

MPC Controller

o

DMCPlus Controller

o

Selector

o

Digital Control Point

o

Transfer Function Block

o

Boolean Not Gate

o

Boolean And Gate

o

Boolean Or Gate

o

Boolean XOr Gate

o

Boolean Off Delay Gate

o

Boolean On Delay Gate

o

Boolean Latch Gate

o

Boolean Count Up Gate

o

Boolean Count Down Gate

o

Cause-and-Effect Matrix

o

CAPE-OPEN 1.0 Unit

o

CAPE-OPEN 1.1 Unit

o

Equilibrium Unit

o

External Data Linker

o

ACM Operation

o

User Unit Op

o

Mach Number Unit

o

Virtual Stream

o

Wellhead PQ Unit Operation

o

SULSIM Extension

7

Category Heat Transfer

Manipulator

Piping & Hydraulics

8

Associated Unit Operations/Sub-Flowsheets o

Heater

o

Cooler

o

Heat Exchanger

o

Fired Heater

o

Air Cooler

o

LNG Exchanger

o

Plate Exchanger

o

Adjust

o

Spreadsheet

o

Recycle

o

Set

o

Stream Saturator

o

Balance

o

Stream Cutter

o

Petroleum Feeder

o

Assay Manipulator

o

Product Blender

o

Black Oil Translator

o

Lumper

o

Delumper

o

Mixer

o

Tee

o

Pipe Segment

o

Gas Pipe

o

Aspen Hydraulics Sub-Flowsheet

o

OLGA Link

o

Petroleum Experts GAP

o

PIPESIM

o

PipeSim Link Unit

o

PipeSim Net Unit

1 Unit Operations Overview

Category Pressure Changer

Reactor

1 Unit Operations Overview

Associated Unit Operations/Sub-Flowsheets o

Pump

o

Control Valve

o

Relief Valve

o

Compressor

o

Expander

o

Continuously Stirred Tank

o

Plug Flow Reactor

o

Conversion Reactor

o

Equilibrium Reactor

o

Gibbs Reactor

o

Yield Shift Reactor

o

Neutralizer

o

HF Alkylation

o

H2SO4 Alkylation

o

Isomerization

o

Naphtha Hydrotreater

o

Catalytic Reformer

o

Hydrocracker

o

Hydroprocessing Bed

o

Fluidized Catalytic Cracking (FCC)

o

CatGas Hydrotreater SHU

o

CatGas Hydrotreater HDS

o

Delayed Coker

o

Visbreaker

o

Sulfur Recovery Unit (SRU) Sub-Flowsheet

o

Petroleum Shift Reactor

o

HYPlan Model

9

Category Separator

Associated Unit Operations/Sub-Flowsheets o

Separator

o

3 Phase Separator

o

Tank

o

Distillation Column

o

Blank Column

o

Component Splitter

o

Absorber

o

Refluxed Absorber

o

Reboiled Absorber

o

Three Phase Distillation

o

Shortcut Column

o

Refining Short-Cut Column

o

Liquid-Liquid Extractor

o

3 Stripper Crude

o

4 Stripper Crude

o

Vacuum Resid Tower

o

FCCU Main Frac

o

Simple Solid Separator

o

Cyclone

o

Hydrocyclone

o

Liquid-liquid Hydrocyclone

o

Baghouse Filter

o

Rotary Vacuum Filter

o

Precipitator

o

Crystallizer

Note: The electrolyte operations are only available if your case is an electrolyte system; the selected fluid package must support electrolytes.

3. Select the desired unit operation or sub-flowsheet. To add it to the PFD: o

Drag and drop the icon onto the PFD. -or-

o

10

Double-click the icon.

1 Unit Operations Overview

Basic Unit Operation Property View Although each unit operation differs in functionality and operation, in general, the unit operation property view remains consistent in its overall appearance. Most operation property views contain the following common objects: l

l

l

Delete button. This button lets you delete the unit operation from the current simulation case. Only the unit operation is deleted, any streams attached to the unit operation is left in the simulation case. Status bar. This bar displays messages associated to the calculation status of the unit operation. The messages also indicate the missing or incorrect data in the operation. Ignore check box. This check box lets you toggle between including and excluding the unit operation in the simulation process calculation. o

To ignore the operation during calculations, select the check box. HYSYS completely disregards the operation until you restore the operation to an active state by clearing the check box. Note: You can also right-click and select the Ignore/Restore Unit Operation command to ignore or restore multiple selected flowsheet operations.

The Operation property view also contain several different tabs which are operation specific, however the Design, Rating, Worksheet, and Dynamics tabs can usually be found in each unit operation property view and have similar functionality. Tab

Description

Design

Connects the feed and outlet streams to the unit operation. Other parameters such as pressure drop, heat flow, and solving method are also specified on the various pages of this tab.

Rating

Rates and Sizes the unit operation vessel. Specification of the tab is not always necessary in Steady State mode, however it can be used to calculate vessel hold up.

Worksheet

Displays the Conditions, Properties, Composition, and Pressure Flow values of the streams entering and exiting the unit operation.

Dynamics

Sets the dynamic parameters associated with the unit operation such as valve sizing and pressure flow relations. Not relevant to steady state modelling. For information on dynamic modeling implications of this tab, refer to the HYSYS Dynamics section.

Note: If negative pressure drop occurs in a vessel, the operation will not solve and a warning message appears in the status bar.

1 Unit Operations Overview

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Object Inspect Menu To access the Object Inspect menu of a unit operation property view, right-click on any empty area of the property view. The unit operation property view all have the following common commands in the Object Inspect menu: Command

Description

Print Datasheet

Lets you access the Select DataBlocks to Print property view.

Open Page

Lets you open the active page into a new property view.

Find in PFD

Lets you locate and display the object icon in the PFD property view. This command is useful if you already have access to an object's property view and want to see where the object is located in the PFD. This command is only available in the Object Inspect menu of the HYSYS stream & operation property views.

Connections

Lets you access the Logical Connections For... Property View.

Logical Connections For... Property View The Logical Connections for... property view lets you determine simulation dependencies between objects which are not otherwise shown via connecting lines on the PFD. Certain HYSYS operations can write to any other object and if the user is looking at the object being written to, they have no way of telling this, other than that the value might be changing. For example, one can determine if one spreadsheet is writing to another. Note: The Logical Connections for... property view is different if accessed from a Spreadsheet property view since there is an additional column (This Name) in the table. The This Name column displays the spreadsheet cell that contains the information/variable connected to the spreadsheet.

The table in the Logical Connections for... property view contains the following columns: l

Remote Name column displays the name of the operation or stream being written to or read from the active object. o

l

12

Double-click on a particular entry of the Remote Name column to open the property view of the operation or stream.

Remote Type column displays the operation type (pump, valve, stream, and so forth) of the remote object from the current/active property view.

1 Unit Operations Overview

The Show All check box lets you toggle between displaying or hiding all the other operations and streams that the selected object knows about. Duplicate connectivity information may be shown otherwise (either via a line on the PFD or elsewhere in a Logical operations property view, for example). Usually, you do not need to select this check box. Note: There is only one Show All check box for your HYSYS session. When the check box is changed, the current setting is effective for all Logical Connections For... property view.

To access the Logical Connections for… view of a HYSYS PFD object: 1. Open the object's property view. 2. Right-click in an empty area of the object's property view. The Object Inspect menu associated to the object appears. 3. Select Connections command from the Object Inspect menu. Note: The information displayed in the Logical Connections for... property view is primarily use for the Spreadsheet, Cause and Effect Matrix operation, Event Scheduler operation, and any other operations that read/write from/to these property views.

1 Unit Operations Overview

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1 Unit Operations Overview

2 Unit Operation Common Property Views

Each unit operation in HYSYS contains some common information and options grouped into common property views, tabs, and pages. The following sections describe the common objects in HYSYS operation property view.

Graph Control Property View The Graph Control property view and its options are available for all plots in HYSYS. The options are grouped into five tabs: l

l

l

l

l

Data - Modify the variable characteristics (type, name, color, symbol, line style, and line thickness) of the plot. Axes - Modify the axes characteristics (label name, display format, and axes value range) of the plot. Title - Modify the title characteristics (label, font style, font color, borders, and background color) of the plot. Legend - Modify the legend characteristics (border, background color, font style, font color, and alignment) of the plot. Plot Area - Modify the plot characteristics (background color, grid color, frame color, and cross hair color) of the plot.

To access the Graph Control property view, do one of the following: l

l

Right-click any spot on an active plot and select the Graph Control command from the Object Inspect menu. Click in the plot area to make the plot the active object. Then, either double-click on the plot Title or Legend to access the respective tab of the Graph Control property view.

2 Unit Operation Common Property Views

15

Heat Exchanger Page The Heat Exchanger page on the Dynamics tab for most vessel unit operations in HYSYS contains the options use to configure heat transfer method within the unit operation. There are three options to choose from: l

l

l

None radio button option indicates that there is no energy stream or heat exchanger in the vessel. The Heat Exchanger page is blank and you do not have to specify an energy stream for the unit operation to solve. Duty radio button option indicates that there is an energy stream in the vessel. The Heat Exchanger page contains the HYSYS standard heater or cooler parameters and you have to specify an energy stream for the unit operation to solve. Tube Bundle radio button option indicates that there is heat exchanger in the vessel and lets you simulate a kettle reboiler or chiller. The Heat Exchanger page contains the parameters used to configure a heat exchanger and you have to specify material streams of the heat exchanger for the unit operation to solve.

Note: The Tube Bundle option is only available in Dynamics mode. Note: The Tube Bundle option is only available for the following unit operations: Separator, Three Phase Separator, Condenser, and Reboiler.

Duty Radio Button Options When you select the Duty radio button the following options are available.

Heater Type Group In the Heater Type group, there are two heating methods available to the general vessel operation: l

Vessel Heater

l

Liquid Heater

If you select the Vessel Heater radio button, 100% of the duty specified or calculated in the SP field is applied to the vessel’s holdup. (1) where: Q = total heat applied to the holdup QTotal = duty calculated from the duty source

16

2 Unit Operation Common Property Views

If you select the Liquid Heater radio button, the duty applied to the vessel depends on the liquid level in the tank. You must specify the heater height in the Top of Heater and Bottom of Heater cells that appear with Heater Height as % Vessel Volume group. The heater height is expressed as a percentage of the liquid level in the vessel operation. The default values are 5% for the Top of the Heater and 0% for the Bottom of the Heater. These values are used to scale the amount of duty that is applied to the vessel contents. (2)

where: L = liquid percent level (%) T = top of heater (%) B = bottom of heater (%) The Percent Heat Applied can be calculated as follows: (3) It is shown that the percent of heat applied to the vessel’s holdup directly varies with the surface area of liquid contacting the heater.

Duty Source/Source Group In the Duty Source/Source group, you can choose whether HYSYS calculates the duty applied to the vessel from a direct energy source or from a utility source. l

If you select the Direct Q radio button, the Direct Q group appears, and you can directly specify the duty applied to the holdup in the SP field.

2 Unit Operation Common Property Views

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The following table describes the purpose of each object in the Direct Q group.

l

Object

Description

SP

The heat flow value in this cell is the same value specified in the Duty field of the Parameters page on the Design tab. Any changes made in this cell are reflected on the Duty field of the Parameters page on the Design tab.

Min. Available

Lets you specify the minimum amount of heat flow.

Max. Available

Lets you specify the maximum amount of heat flow.

If you select the Utility radio button, the Utility Properties group appears, and you can specify the flow of the utility fluid. o

The duty is then calculated using the local overall heat transfer coefficient, the inlet fluid conditions, and the process conditions. The calculated duty is then displayed in the SP field or the Heat Flow field.

o

If you select the Heating radio button, the duty shown in the SP field or Heat Flow field is added to the holdup. If you select the Cooling radio button, the duty shown in the SP field or Heat Flow field is subtracted from the holdup.

o

For more information regarding how the utility option calculates duty, refer to the Logical Operations.

Tube Bundle Radio Button When you select the Tube Bundle radio button, the Tube Bundle options are available. Note: The Tube Bundle option is only available in Dynamics mode. Note: If you had an energy stream attached to the unit operation, HYSYS automatically disconnects the energy stream when you switch to the Tube Bundle option.

The Tube Bundle option lets you configure a shell tube heat exchanger (for example, kettle reboiler or kettle chiller). l

l

18

In the kettle reboiler, the process fluid is typically on the shell side and the process fluid is fed into a liquid "pool" which is heated by a number of tubes. A weir limits the amount of liquid in the pool. The liquid overflow is placed under level control and provides the main liquid product. The vapor is circulated back to the vessel. In the kettle chiller, the process fluid is typically on the tube side with a refrigerant on the shell side. The refrigerant if typically pure and cools by evaporation. The setup is similar to the reboiler except that there is no weir or level control.

2 Unit Operation Common Property Views

The unit operation icon in the PFD also changes to indicate that a heat exchanger has been attached to the unit operation.

The following table lists and describes the options available to configure the heat exchanger: Object

Description

Parameters group Tube Volume cell

Lets you specify the volume of the tubes in the heat exchanger.

Vessel Liquid U cell

Lets you specify the heat transfer rate of the liquid in the shell.

Vessel Vapor U cell

Lets you specify the heat transfer rate of the vapor in the shell.

Tube Liquid U cell

Lets you specify the heat transfer rate of the liquid in the tube.

Tube Vapor U cell

Lets you specify the heat transfer rate of the vapor in the tube.

Heat Transfer Area cell

Lets you specify the total heat transfer area between the fluid in the shell and the fluid in the tube.

Bundle Top Height cell

Lets you specify the location of the top tube/bundle based on the height from the bottom of the shell.

Bundle Bottom Height cell

Lets you specify the location of the bottom tube/bundle based on the height from the bottom of the shell.

Specs group Tube Dp cell

Lets you specify the pressure drop within the tubes. You have to select the associate check box in order to specify the pressure drop.

Tube K cell

Lets you specify the pressure flow relationship value within the tubes. You have to select the associate check box in order to specify the pressure flow relationship value.

2 Unit Operation Common Property Views

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Object

Description

Tube UA Reference Flow cell

Lets you set a reference point that uses HYSYS to calculate a more realistic UA value. If no reference point is set then UA is fixed. UA is the product of overall heat transfer multiply with overall heat transfer area, and depends on the flow rate. If a value is specified for the Reference Flow, the heat transfer coefficient is proportional to the (mass flow ratio)0.8. The equation below is used to determine the actual UA:

Reference flows generally help to stabilize the system when you do shut downs and startups as well. Minimum Flow Scale Factor cell

The ratio of mass flow at time t to reference mass flow is also known as flow scaled factor. The minimum flow scaled factor is the lowest value which the ratio is anticipated at low flow regions. This value can be expressed in a positive value or negative value. l

A positive value ensures that some heat transfer still takes place at very low flows.

l

A negative value ignores heat transfer at very low flows.

A negative minimum flow scale factor is often used in shut downs if you are not interested in the results or run into problems shutting down the heat exchanger. If the Minimum Flow Scale Factor is specified, the actual UA is calculated using the  ratio if the ratio is greater

than the Min Flow Scale Factor. Otherwise the Min Flow Scale Factor is used. Calculate K button

Lets you calculate the K value based on the heat exchanger specifications.

Shell Dp cell

Lets you specify the pressure drop within the shell.

Summary group

20

Actual UA cell

Displays the calculated UA in Dynamics mode.

Shell Liq. Percent Level cell

Displays the calculated liquid level in the shell at percentage value.

Tube Liq. Volume Percent cell

Lets you specify in percentage value the volume of liquid in the tube.

Shell Duty cell

Displays the calculated duty value in the shell.

2 Unit Operation Common Property Views

Object

Description

Use Tube Trivial Level and Fraction Calc. radio button

Lets you select the volume percent level variable for the vessel fraction calculation.

Use Tube Normal Level and Fraction Calc. radio button

Lets you select the liquid percent level variable for the vessel fraction calculation.

View Tube HoldUp button

Lets you access the tube HoldUp Property View.

This option uses a variable that is independent of the vessel shape or orientation.

This option uses a variable that is dependent of the vessel shape and orientation.

Holdup Page Each unit operation in HYSYS has the capacity to store material and energy. The Holdup page contains information regarding the properties, composition, and amount of the holdup. Most Holdup pages contains the following common objects/options: Objects

Description

Phase column

Displays the phase of the fluid available in the unit operation’s holdup volume. Each available phase occupies a volume space within the unit operation.

Accumulation column

Displays the rate of change of material in the holdup for each phase.

Moles column

Displays the amount of material in the holdup for each phase.

Volume column

Displays the holdup volume of each phase.

Total row

Displays the sum of the holdup accumulation rate, mole value, and volume value.

Advanced but- Lets you access the unit operation’s HoldUp Property View that ton provides more detailed information about the holdup of that unit operation.

2 Unit Operation Common Property Views

21

Holdup Property View The Holdup property view displays the detailed calculated results of the holdup data in the following tabs: l

l

l

l

l

General tab. Displays the phase, accumulation, moles, volume, duty and holdup pressure of the heat exchanger. o

Select the Active Phase Flip Check check box to enable HYSYS to check if there is a phase flip between Liquid 1 (light liquid) and Liquid 2 (heavy liquid) during simulation and generate a warning message whenever the phase flip occur. If the check box is clear, HYSYS generates a warning only on the first time the phase flip occur.

o

Refer to Advanced Holdup Properties in the HYSYS Dynamic Modeling section for more information.

Nozzles tab. Lets you modify nozzle configuration attached to the heat exchanger. Efficiencies tab. Lets you modify the efficiency of the recycle, feed nozzle, and product nozzle of the heat exchanger. Properties tab. Displays the temperature, pressure, enthalpy, density, and molecular weight of the holdup in the heat exchanger. Compositions tab. Displays the composition of the holdup in the heat exchanger.

For detailed technical information on the Holdup Model is, refer to Holdup Model.

Nozzles Page The Nozzles page (from the Rating Tab) in most of the operations property view lets you specify the elevation and diameter of the nozzles connected to the operation. Note: The Nozzles page is only available if the HYSYS Dynamics license is activated.

Depending on the type of operation, the options in the Nozzles page varies. The following table lists and describes the common options available in the page:

22

Object

Description

Base Elevation Relative to Ground Level field

Lets you specify the height/elevation between the bottom of the operation and the ground.

Diameter row

Lets you specify the diameter of the nozzle for each material stream flowing into and out of the operation.

2 Unit Operation Common Property Views

Object

Description

Elevation (Base) row

Lets you specify the height/elevation between the nozzle and the base of the operation.

Elevation (Ground) row

Lets you specify the height/elevation between the nozzle and the ground.

Notes Pages or Tabs Use the Notes tab or any Notes page to enter or revise notes. Notes can be useful for informing other people working with your case about changes and assumptions you have made. You can: l l

l

Enter notes in the Notes window. Make use of all common formatting options, bold, italic, indents, fonts, etc. Use the Notes Manager to search across multiple notes locations.

To enter notes: 1. Click anywhere in the Notes window to make it active. 2. Type in any relevant notes you have regarding such things as fluid packages, assays, user properties, operations, and so on.

Notes Manager The Notes Manager lets you survey and edit notes associated all objects on the Flowsheet from a central location. 1. From the View ribbon tab > Show group, select Notes Manager. 2. In the list of available objects select the object that contains the note you want to view. Click the Plus icon to expand the tree browser revealing more selections. 3. If a valid note is present in the object the note appears in the Note group. From here you can view and modify the note. Tip: You can also access the Notes Manager by pressing the CTRL G hot key. l

Select the View Objects with Notes Only check box to display only objects that contain a valid note.

l

Click Clear to delete the entire note from the selected object.

l

Click View to open the property view of the selected object.

l

l

Select the Search notes containing the string check box and enter a string in the corresponding field to filter the list of available objects to objects that contain the specified string. Select the Search notes modified since check box and enter month,

2 Unit Operation Common Property Views

23

day and year to filter the list of available objects to objects whose notes modified since the specified date.

Holdup Model Dynamic behavior arises from the fact that many pieces of plant equipment have some sort of material inventory or holdup. A holdup model is necessary because changes in the composition, temperature, pressure or flow in an inlet stream to a vessel with volume (holdup) are not immediately seen in the exit stream. The model predicts how the holdup and exit streams of a piece of equipment respond to input changes to the holdup over time. In some cases, the holdup model corresponds directly with a single piece of equipment in Aspen HYSYS. For example, a separator is considered a single holdup. In other cases, there are numerous holdups within a single piece of equipment. In the case of a distillation column, each tray can be considered a single holdup. Heat exchangers can also be split up into zones with each zone being a set of holdups. Calculations included in the holdup model are: l

Material and energy accumulation

l

Thermodynamic equilibrium

l

Heat transfer

l

Chemical reaction

The new holdup model offers certain advantages over the previous HYSYS dynamic model: l

l

l

An adiabatic PH flash calculation replaces the bubble point algorithm used in the previous holdup model. Adiabatic flashes also allow for more accurate calculations of vapor composition and pressure effects in the vapor holdup. Flash efficiencies can be specified allowing for the modeling of non-equilibrium behavior between the feed phases of the holdup. The placement of feed and product nozzles on the equipment has physical meaning in relation to the holdup. For example, if the vapor product nozzle is placed below the liquid level in a separator, only liquid exits from the nozzle.

Assumptions of Holdup Model There are several underlying assumptions that are considered in the calculations of the holdup model:

24

l

Each phase is assumed to be well mixed.

l

Mass and heat transfer occur between feeds to the holdup and material

2 Unit Operation Common Property Views

already in the holdup. l

Mass and heat transfer occur between phases in the holdup.

Accumulation The lagged response that is observed in any unit operation is the result of the accumulation of material, energy, or composition in the holdup. To predict how the holdup conditions change over time, a recycle stream is added alongside the feed streams. For example, the material accumulation in a holdup can be calculated from: (1)

The recycle stream is not a physical stream in the unit operation. Rather, it is used to introduce a lagged response in the output. Essentially, the recycle stream represents the material already existing in the piece of equipment. It becomes apparent that a greater amount of material in the holdup means a larger recycle stream and thus, a greater lagged response in the output.

The holdup model is used to calculate material, energy, and composition accumulation. Material accumulation is defaulted to calculate at every integration time step. The energy of the holdup is defaulted to calculate at every second time step. The composition of the holdup is defaulted to calculate at every tenth time step.

Non-Equilibrium Flash As material enters a holdup, the liquid and vapor feeds can associate in different proportions with the existing material already in the holdup. For instance, a separator’s vapor and liquid feeds can enter the column differently. It is very likely that the liquid feed mixes well with the liquid already in the holdup. The vapor feed is not mixed as well with the existing material in the vessel since the residence time of the vapor holdup is much smaller than that of the liquid. If the feed nozzle is situated close to the vapor product nozzle, it is possible that even less mixing occurs. In the physical world, the extent of mixing the feeds with a holdup depends on the placement of the feed nozzles, the amount of holdup, and the geometry of the piece of equipment.

2 Unit Operation Common Property Views

25

Efficiencies In HYSYS, you can indirectly specify the amount of mixing that occurs between the feed phases and the existing holdup using feed, recycle, and product efficiencies. These feed efficiency parameters can be specified on the Efficiencies tab of the unit operation’s Advance property view. Click the Advance button on the Holdup page under the Dynamics tab to open the Advance property view. Essentially, the efficiencies determine how rapidly the system reached equilibrium. If all efficiencies are 1, then all feeds reach equilibrium instantaneously. If the values are lower, it takes longer and the phases cannot be in equilibrium and can have different temperatures. A flash efficiency can be specified for each phase of any stream entering the holdup. A conceptual diagram of the non-equilibrium flash is shown for a two phase system in the figure below:

As shown, the flash efficiency, η, is the fraction of feed stream that participates in the rigorous flash. If the efficiency is specified as 1, the entire stream participates in the flash; if the efficiency is 0, the entire stream bypasses the flash and is mixed with the product stream. The recycle stream (and any streams entering the holdup) participates in the flash. You can specify the flash efficiency for each phase of the recycle stream and any feed entering the holdup. The flash efficiency can also be specified for each phase of any product streams leaving the holdup. Note: Product flash efficiencies are only used by the holdup model when reverse flow occurs in the product flow nozzles. In such cases, the product nozzle effectively becomes a feed nozzle and uses the product flash efficiencies that you provided.

The default efficiencies for the feed, product, and recycle streams is 1, and this value is sufficient in the vast majority of cases. The flash efficiencies can be changed to model non-equilibrium conditions. For example, the efficiency of vapor flowing through a vessel containing liquid can be reduced if the residence time of the vapor is very small and there is little time for it to reach thermodynamic equilibrium with the liquid. Also, in some narrow boiling systems,

26

2 Unit Operation Common Property Views

lower efficiencies can be used to reduce the rate at which material can condense or evaporate. This can help to stabilize the pressure in certain difficult cases such as narrow boiling systems like steam. For example, a water system is heated by pure steam (no inerts) can encounter problems if the stream efficiency is specified as 1. If the holdup material is significantly larger than the stream flow, all the steam condenses and the holdup temperature increases accordingly. No vapor is present which can complicate pressure control of the system. In the physical world, typically not all of the steam condenses in the water and there are also some inerts (e.g., nitrogen or air) present in the system. Using lower efficiencies can help to model this system better.

Nozzles In HYSYS, you can specify the feed and product nozzle locations and diameters. These nozzle placement parameters can be specified in the unit operation’s Nozzles page under the Rating tab.

The placement of feed and product nozzles on the equipment has physical meaning in relation to the holdup. The exit stream’s composition depends partially on the exit stream nozzle’s location in relation to the physical holdup level in the vessel. If the product nozzle is located below the liquid level in the vessel, the exit stream draws material from the liquid holdup. If the product nozzle is located above the liquid level, the exit stream draws material from the vapor holdup. If the liquid level sits across a nozzle, the mole fraction of liquid in the product stream varies linearly with how far up the nozzle the liquid is.

Static Head Contributions When the Static Head Contributions check box is selected on the Options tab of the Integrator property view, Aspen HYSYS calculates static head using the following contributions: l

Levels inside separators, Towers, and so forth

l

Elevation differences between connected equipment

Note: Including static head contributions in the modeling of pressure-flow dynamics is an option in Aspen HYSYS.

2 Unit Operation Common Property Views

27

For unit operations with negligible holdup, such as the valve operation, Aspen HYSYS incorporates only the concept of nozzles. There is no static head contributions for levels, unless the feed and product nozzles are specified at different elevations. You can specify the elevation of both the feed and product nozzles. If there is a difference in elevation between the feed and product nozzles, Aspen HYSYS uses this value to calculate the static head contributions. It is recommended that static head contributions not be modeled in these unit operations in this way since this is not a realistic situation. Static head can be better modeled in these unit operations by relocating the entire piece of equipment. Static head is important in vessels with levels. For example, consider a vertical separator unit operation that has a current liquid level of 50%. The static head contribution of the liquid holdup makes the pressure at the liquid outlet nozzle higher than that at the vapor outlet nozzle. Nozzle location also becomes a factor. The pressure-flow relationship for the separator is different for a feed nozzle which is below the current liquid holdup level as opposed to a feed which is entering in the vapor region of the unit. It is important to notice that exit stream pressures from a unit operation are calculated at the exit nozzle locations on the piece of equipment and not the inlet nozzle locations of the next piece of equipment.

Heat Loss Model The heat loss experienced by any piece of plant equipment is taken into consideration in Aspen HYSYS. The heat loss influences the boundaries and holdups inside the equipment by contributing extra terms to the energy balance equations. There are two heat loss models available: Simple and Detailed. These models can be specified for most unit operations under the Rating tab | Heat Loss page. You can choose to neglect the heat loss calculation in the energy balance by selecting the None radio button.

Simple Model The Simple model allows you to have the heat loss calculated from specified values: Overall U value and Ambient temperature. The heat transfer area A and the fluid temperature Tf are calculated or available to HYSYS. The resulting heat loss is then: (1)

Detailed Model: Cartesian one-dimensional version Heat is lost (or gained) from the holdup fluid through the wall and insulation to the surroundings. There are several underlying assumptions that are considered during a heat loss calculation:

28

2 Unit Operation Common Property Views

l

l

l

l

l

l

There is heat capacity associated with the wall (metal) and with insulation housing the fluid There is thermal conductivity associated with the wall and with insulation housing the fluid The temperature across the wall and the temperature across the insulation are assumed to be constant (lumped parameter analysis) You can have different heat transfer coefficients on the inside of a vessel for the vapor and the liquid: the heat transfer coefficients between the holdup and the wall are not the same for the vapor and liquid The calculation assumes natural convection heat transfer on the inside and outside of the vessel The calculations do not take into account that temperatures vary along the height of the vessel depending on the phase they are in contact with at the corresponding height: this is what is meant by a one-dimensional model

In the figure above, we show the heat flow through the different material layers.  A first balance can be performed across the wall: (2) and the balance across the insulation: (3) with: (4) (5) (6) (7) (8) where:

2 Unit Operation Common Property Views

29

A

heat transfer area

Δx

thickness

ρ cp

mass density heat capacity

k

thermal conductivity

h

convective heat transfer coefficient

r

thermal resistance for conductive h. transfer

q

rate of heat transfer

T

temperature

t

time

The temperature at the wall/insulation interface is calculated using a pseudo steady state assumption for viewing purposes

Detailed Model: radial one-dimensional version Since HYSYS V7.3.1, HYSYS has used a radial model for pipe segments which yields considerably different predictions from those of the Cartesian model when the insulation thickness is comparable to the wall thickness. The radial model is active by default in all newly created pipe segments in dynamics mode, in the pipe segment property view, Rating tab | Heat Model page, as shown below.

In the analysis below, the Cartesian one-dimensional version figure is still useful if representing a small angular section of a long pipe. A balance across the wall would be: (9) and the balance across the insulation: (10) with: (11) (12)

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2 Unit Operation Common Property Views

(13) (14)

where: pipe length

L

pipe inner radius

ri

pipe outer radius

ro rins ρ

insulation outer radius mass density

cp

heat capacity

k

thermal conductivity

h

convective heat transfer coefficient

R

thermal resistance for conductive h. transfer

q

rate of heat transfer

T

temperature

t

time

Chemical Reactions Chemical reactions that occur in plant equipment are considered by the holdup model in HYSYS. Reaction sets can be specified in the Results page of the Reactions tab. The holdup model is able to calculate the chemical equilibria and reactions that occur in the holdup. In a holdup, chemical reactions are modeled by one of four mechanisms: l

Reactions handled inside thermophysical property packages

l

Extent of reaction model

l

Kinetic model

l

Equilibrium model

Related Calculations There are calculations which are not handled by the holdup model itself, but can impact the holdup calculations. The following calculations require information

2 Unit Operation Common Property Views

31

and are solved in conjunction with the holdup model as described in the following table: Calculations

Description

Vessel Level Calculations

The vessel level can be calculated from the vessel geometry, the molar holdup and the density for each liquid phase.

Vessel Pressure

The vessel pressure is a function of the vessel volume and the stream conditions of the feed, product, and the holdup. The pressure in the holdup is calculated using a volume balance equation. Holdup pressures are calculated simultaneously across the flowsheet.

Tray Hydraulics

Tray Hydraulics determines the rate from which liquid leaves the tray, and hence, the holdup and the pressure drop across the tray. The Francis Weir equation is used to determine the liquid flow based on the liquid level in the tray and the tray geometry.

Advanced Holdup Properties Each Dynamics tab | Holdup page on the unit operation property view contains an Advanced button. This button accesses the Holdup property view that provides more detailed information about the holdup of that unit operation. Right-click anywhere in the property view to bring up the object inspect menu. Selecting the Open Page command displays the information on the Holdup page in a separate property view.

General Tab This tab provides the same information as shown in the Holdup page of the Dynamics tab. The accumulation, moles, and volume of the holdup appear on this tab. The holdup pressure also appears on this tab. Select the Active Phase Flip Check check box to enable Aspen HYSYS to check if there is a phase flip between Liquid 1 (light liquid) and Liquid 2 (heavy liquid) during simulation and generate a warning message whenever the phase flip occur. If the check box is clear, Aspen HYSYS generates a warning only on the first time the phase flip occur.

Nozzles Tab Note: The Nozzles tab requires HYSYS Dynamics license.

The Nozzles tab displays the same information as shown in the Nozzles page of the Ratings tab. The nozzle diameters and elevations for each stream attached to the holdup appear on this tab. This section also displays the holdup elevation which is essentially equal to the base elevation of the piece of equipment relative to the ground. Changes to nozzle parameters can either be made in this tab or in the Nozzles page of the Ratings tab.

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2 Unit Operation Common Property Views

Efficiencies Tab Note: The Efficiencies tab requires HYSYS Dynamics license.

The nozzle efficiencies can be specified in this tab. In Aspen HYSYS, you can indirectly specify the amount of mixing that occurs between the feed phases and existing holdup using feed, recycle and product efficiencies. A flash efficiency, η, is the fraction of feed stream that participates in the rigorous flash. If the efficiency is specified as 100, the entire stream participates in the flash; if the efficiency is 0, the entire stream bypasses the flash and is mixed with the product stream. Nozzle Efficiency

Description

Feed Nozzle Efficiency

The efficiencies of each phase for each feed stream into the holdup can be specified in these cells. These efficiencies are not used by the holdup model if there is flow reversal in the feed streams.

Product Nozzle Efficiency

Product nozzle efficiencies are used only when there is flow reversal in the product streams. In this situation, the product nozzles act as effective feed nozzles.

Recycle Efficiency

Essentially, the recycle stream represents the material already existing in the holdup. Recycle efficiencies represent how much of the material in the holdup participates in the flash.

Properties Tab The following fluid properties for each phase in the holdup appear on the Properties tab: l

Temperature

l

Pressure

l

Flow

l

Molar Fraction of the specific phase in the holdup

l

Enthalpy

l

Density

l

Molecular Weight

Compositions Tab The compositional molar fractions of each phase in the holdup appears on the Compositions tab.

2 Unit Operation Common Property Views

33

Stripchart Page Strip charts let you monitor the behavior of process variables in a graphical format during dynamics calculations. Current and historical values for each strip chart are also tabulated for further examination. You can create strip charts directly from a unit operation property view, or in the Strip Charts folder on the navigation pane. You can have multiple strip charts, each having an unlimited number of variables charted. The same variable can be used in more than one Strip Chart. Tips: l

To delete a variable from a strip chart, select the variable you want delete from the list of available variables and press DELETE. To replace the variable deleted, reselect the variable set from the Variable Set drop-down list.

l

Right-click anywhere within the plot area to access the plot’s object inspection menu.

Adding a Strip Chart from the Navigation Pane or Ribbon This method lets you select objects and variables from the Variable Navigator: 1. Click Strip Charts in the Simulation navigation pane, or in the Dynamics ribbon tab | Tools | Strip Charts. 2. Click the Add button. A new strip chart is added to the list of available strip charts. 3. In the Sample Int. field, specify the amount of time in between taking data samples. The HYSYS default value is 20 seconds 4. Select the new strip chart and click Edit. 5. Use the Add button and the Variable Navigator to set up each variable that you want to appear in this strip chart.

Adding a Strip Chart from a Unit Operation Depending on the object property view, the strip chart sets contain variables appropriate for the object. For example, the strip chart set ToolTip Properties for a mixer will contain the following variables: Product Temperature, Product Pressure, and Product Molar Flow. The strip chart set ToolTip Properties for a separator will contain the following variables: Vessel Temperature, Vessel Pressure, and Liquid Volume Percent, as shown below. 1. Open the object’s property view, and access the Stripchart page or tab. 2. From the Variable Set drop-down list, select the desired strip chart. 3. Click the Create Stripchart button. The new strip chart property view

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2 Unit Operation Common Property Views

appears. By default, the new stripchart is named DL (n). To display the stripchart itself, click Display.

Using the Data Logger Property View When you first create a strip chart, the Data Logger property view appears. For the new strip chart, or any existing stripchart, this lets you display the results in tabular or chart form. Use this view to add or remove variables from the strip chart. l

Use the Edit button to edit a selected variable.

l

Click Display to view the actual strip chat.

Historical Tab To view data points stored in the strip chart in tabular format, click Historical. The Historical Data property view appears, which allows you to you to save/export the results to a CSV file and to a DMP file.

Current Tab To view the current conditions reflected in the strip chart, select the Current tab.

Controls in the Displayed Strip Chart Showing the Strip Chart 1. Select the strip chart under the Strip Charts folder in the navigation pane. 2. In the strip chart’s Data Logger window click Display. Note: Right click within the strip chart for display-specific commands.

Selecting Curves 1. Right-click in the strip chart. The object inspect menu appears. 2. Click the Select Curve command. The Select Curve sub-menu appears. 3. From the sub-menu click the variable curve you want to select. Tip: You can click on any part of the variable curve in the plot to select that curve.

Manipulating the X-axis Range 1. Place the cursor over any part of the x-axis. 2. Left-click and hold the mouse button. Drag the strip chart right if you want to display a lower range of values on the x-axis. Drag the strip chart left if you want to display a higher range of values.

2 Unit Operation Common Property Views

35

Note: Using the Log Controller bar, you can also manipulate the range of sampled data displayed in the strip chart. A set of colors indicates what range of sampled data is displayed in the strip chart. You can increase or decrease the range of sampled data or you can scroll the strip chart over a range of recorded strip chart data. The following colors make up the Log Controller bar: l

Gray - No data in that section of the strip chart.

l

Dark blue - Data recorded in that section of the strip chart.

l

l

l

Red - The Red marker labels where the first data point displayed in your strip chart is located in the overall data set. You can expand the range of display by "dragging" the red marker to the left (away from the yellow marker) and decrease the displayed range by dragging the red marker right (towards the yellow marker). Light blue - Indicates where the data displayed on the strip chart is located in the overall data set. Yellow - The Yellow marker labels where the last data point displayed in your strip chart is located in the overall data set. You can expand the displayed range by "dragging" the yellow marker to the right (away from the red marker) and decrease the displayed range of data by dragging the yellow marker left (towards the red marker).

Manipulating the Y-axis Range 1. Place the cursor over any part of the y-axis. 2. Left-click and hold the mouse button. Drag the strip chart up if you want to display a lower range of values on the y-axis. Drag the strip chart down if you want to display a higher range of values. Notes l

l

By default, strip chart curves are grouped into their unit sets. For instance, all temperature variables are associated and displayed with the same y-axis range and units. By manipulating the range of a temperature variable in the strip chart, you change the range of all temperature variables associated with that axis. If you want to associate a different range to a variable in the strip chart, you must first create your own axis. Refer to the Graph Control section for more information.

Creating Interval Markers 1. Ensure that the most recent strip chart data is displayed on the strip chart. (The light blue part of the Log Controller Bar should be located at the far right of the x-axis.) 2. Place the cursor on the right edge of the strip chart. 3. Press the left mouse button and drag the interval marker across the strip chart. Release the mouse button when the interval marker is in the desired location. Notes

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2 Unit Operation Common Property Views

l

l l

Interval markers are used to measure variables at certain instances in the strip chart. The strip chart variable value appears next to where the interval marker intersects the strip chart variable curve. You can add up to four interval markers to the strip chart. To remove the interval marker, drag the marker back the right hand edge of the strip chart.

Saving the Data to a .CSV File 1. From the list of available strip charts, select the strip chart you want to view. 2. Click the Historical button. The Historical Data window appears. 3. Click the Save To .CSV File button. The Save File window appears. 4. From the Save File window, specify a name of your CSV history file and the location of your file. 5. Click Save.

User Variables Page The User Variables page or tab lets you create and implement custom variables in the HYSYS simulation. The following table outlines options in the user variables toolbar: Object

Icon

Current Variable Filter drop-down list

Function Lets you filter the list of variables in the table based on the following types: l

All

l

Real

l

Enumeration

l

Text

l

Code Only

l

Message

Create a New User Variable icon

Lets you create a new user variable and access the Create a New User Variable property view.

Edit the Selected User Variable icon

Lets you edit the configuration of an existing user variable in the table.

2 Unit Operation Common Property Views

You can also open the edit property view of a user variable by double-clicking on its name in the table.

37

Object

Icon

Function

Delete the Selected User Variable icon

Lets you delete the select user variable in the table.

Sort Alphabetically icon

Lets you sort the user variable list in ascending alphabetical order.

Sort by Execution Order icon

Lets you sort the user variable list according to the order by which they are executed by HYSYS.

HYSYS requires confirmation before proceeding with the deletion. If a password has been assigned to the User Variable, the password is requested before proceeding with the deletion.

Sorting by execution order is important if your user variables have order dependencies in their macro code. Generally, we recommend that you avoid these types of dependencies. Move Selected Variable Up In Execution Order icon

Lets you move the selected user variable up in execution order.

Move Selected Variable Down In Execution Order icon

Lets you move the selected user variable down in the execution order.

Show/Hide Variable Enabling Check box icon

Lets you toggle between displaying or hiding the Variable Enabling check boxes associated with each user variable. By default, the check boxes do not appear.

Adding a User Variable 1. Access the User Variables page or tab in the object property view. 2. Click the Create a New User Variable icon. The Create New User Variable property view appears. 3. In the Name field, type in the user variable name. 4. Specify the rest of the user variable parameters, such as data type, dimension type, and unit type. You can define your own filters on the Filters tab of the User Variable property view, or set a password to lock it for security purposes.

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2 Unit Operation Common Property Views

Variable Navigator (MultiSelect) The Variable Navigator property view lets you browse for and select variables to add to operations; for example, a process variable for a controller or a strip chart. You can add multiple variables at a time and easily search for specific variables. Note: Depending on the position in the flowsheet from which you access the Variable Navigator, the user interface may differ from the below description.

To use the Variable Navigator: 1. From the Context drop-down list, from the following options, select the area/location containing the variable you want: o

Flowsheet: This is the default value.

o

Properties

o

Analysis

2. From the list below the Context drop-down list, select the flowsheet/case/basis object/utility containing the variable(s) that you want. The type of objects available in this list depends on your selection from the Context drop-down list. 3. From the Object Type drop-down list, you either: o

Filter by general type by selecting Streams, UnitOps, Logicals, or ColumnOps. -or-

o

Select Custom and select a specific unit operation from the Select Type window. When you select an object type in this window and click OK, the objects available in the Variable Navigator are limited to those contained within the object type you selected.

4. Perform one of the following tasks: o

In the Objects field, type part of the object name. Objects that match the text appear in the Objects list. -or-

o

From the Objects list, select the desired object.

5. Select or clear the Input and Output check boxes depending on whether you want to view Input variables, Output variables, or both. 6. From the Physical Type drop-down list, select a physical type by which to filter the Variables list. The available options may vary depending on the position in the flowsheet from which you access the Variable Navigator. The default selection is All, which shows all objects. 7. You can either:

2 Unit Operation Common Property Views

39

o

In the Variables field, type part of the variable name. Variables that match the text appear in the Variables tree. -or-

o

From the Variables tree, select the desired variables. You can use the Ctrl key to select multiple variables. You can use the Shift key to select a range of variables. Variables appear in the Selected list corresponding to the order in which you added them. Note: Within the Object list, when switching from one Object to another of the same type (such as moving from one stream to another), any Variables that were selected in the Variable tree will remain selected. This makes it easy to add the same set of Variables for several objects of the same type.

8. Click the

button to add the selected variables to the Selected list.

Note: To remove variables from the Selected list, click the

button.

9. Click the Done button. 10. The Description field is automatically populated with the default name of the Variable that is selected in the Selected list. You can provide a custom name for this selected variable by editing the default name. Note: When a variable is selected in the Variable Navigator property view, a Disconnect button may appear. You can use the Disconnect button to remove/disconnect the selected variable and close the property view.

Variable Navigator (Single-Select) The Variable Navigator property view lets you browse for and select variables to add to operations; for example, a process variable for a controller or a strip chart. You can easily search for specific variables. Note: Depending on the position in the flowsheet from which you access the Variable Navigator, the user interface may differ from the below description.

To use the Variable Navigator: 1. From the Context drop-down list, from the following options, select the area/location containing the variable you want: o

Flowsheet: This is the default value.

o

Properties

o

Analysis

2. From the list below the Context drop-down list, select the flowsheet/case/basis object/utility containing the variable that you want. The type of objects available in this list depends on your selection from the Context drop-down list. 3. From the Object Type drop-down list, you either:

40

2 Unit Operation Common Property Views

o

Filter by general type by selecting Streams, UnitOps, Logicals, or ColumnOps. -or-

o

Select Custom and select a specific unit operation from the Select Type window. When you select an object type in this window and click OK, the objects available in the Variable Navigator are limited to those contained within the object type you selected.

4. Perform one of the following tasks: o

In the Objects field, type part of the object name. Objects that match the text appear in the Objects list. -or-

o

From the Objects list, select the desired object.

5. Select or clear the Input and Output check boxes depending on whether you want to view Input variables, Output variables, or both. 6. From the Physical Type drop-down list, select a physical type by which to filter the Variables list. The available options may vary depending on the position in the flowsheet from which you access the Variable Navigator. The default selection is All, which shows all objects. 7. You can either: o

In the Variables field, type part of the variable name. Variables that match the text appear in the Variables tree. -or-

o

From the Variables tree, select the desired variable. You can only select a single variable.

8. The Description field is automatically populated with the default name of the Variable that is selected in the Selected list. You can provide a custom name for this selected variable by editing the default name. 9. Click the Select button. Note: When a variable is selected in the Variable Navigator property view, a Disconnect button may appear. You can use the Disconnect button to remove/disconnect the selected variable and close the property view.

Select Type Dialog Box Use the Select Type dialog box to fine tune a selection within an object picker such as the Variable Navigator, the Object Navigator, or any Add or View Variable or Object function with a Custom option. The Select Type list, sorted by object type, (for example, Vessel, Reactor, Column, and so on) lets you select specific objects to use in defining the filter mechanism for the Object, Variable, or other Navigator in use.

2 Unit Operation Common Property Views

41

Notes: l

The objects within the Select Type list are always limited to the types of objects relevant to the current case or environment.

l

When you select an object from the Select Type view, only the selections associated with that object are allowed into the parent selector.

Example In the case of the Variable Navigator, for example, if you wanted to limit the Variable Navigator Variables pane to show only variables associated with a certain mixer, you would use the Select Type dialog box to select the Mixer type of object from the Piping Equipment selections. Your Variable Navigator Object selections would then be limited to only the mixer or mixers in the case. You would then make your variable selections from those objects.

Using the Select Type Dialog Box To use the Select Type dialog box: 1. On the Navigator window, select Custom (or Setup Custom depending upon the parent navigator type) in the Object Filter field. 2. On the Select Type dialog box, expand the top-level options to view potential variables. Select the object type to which you want to limit your object search, and then click OK.

Changing the Fluid Package for Multiple Unit Operations To change the fluid package for multiple unit operations at the same time: 1. Select the desired objects on the flowsheet. 2. Right-click one of the unit operations and select Change Fluid Package. 3. On the Change Fluid Pkg dialog box, from the drop-down list, select the fluid package that you want to apply to the selected objects. 4. Click OK. Note: Any changes you make within the Change Fluid Pkg dialog box are applied to all highlighted unit operations except columns.

Worksheet Tab The Worksheet tab presents a summary of the information held by a stream or an operation object. The Worksheet tab on each unit operation provides access to the streams attached to the unit.

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2 Unit Operation Common Property Views

Worksheet pages contain analytical information on the Worksheet and/or Performance tabs. The type of analytical information found in operation property views depends on the operation type. Regardless of what the operation is, the displayed information is automatically updated as conditions change. For Streams, you can use the Worksheet tab Composition page to define a material stream. The Worksheet tab Properties page contains detailed property correlation information. The Conditions page is a subset of the information provided in the Properties page. The pages are described below:

Stream Conditions This page lets you define streams that are incomplete, or modify stream values if you require changes in the simulation. Any blue colored value may be modified. This lets you easily define or modify a stream without opening the property view of each stream that is attached to the unit operation. This page also lets you quickly see how the streams connected to the unit operation are acting throughout the simulation. Any changes made to this page are reflected in the stream’s property view. The PF Specs page is relevant to dynamics cases only.

Stream Properties This page lets you quickly see how the streams connected to the unit operation are acting throughout the simulation. Any value that is blue in color indicates that the value may be modified. Any changes made to this page are reflected in the stream’s property view.

Stream Compositions This page lets you define or modify the composition of streams attached to the unit operation. Any value that is blue in color indicates that the value may be modified. This lets you easily define or modify a stream’s composition without opening the property view of each stream that is attached to the unit operation. When you define or modify a composition, the Input Composition property view property view appears. Any changes made to this page are reflected in the stream’s property view.

PF Specs PF (Pressure Flow) applies to dynamic simulations only. Note: The Heat of Vaporization for a stream in HYSYS is defined as the heat required for the stream to go from saturated liquid to saturated vapor.

2 Unit Operation Common Property Views

43

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2 Unit Operation Common Property Views

3 Column Input Experts

The Column Input Experts guide you through the installation of a Column. The Input Expert is available for the following standard column templates: l

Absorber

l

Liquid-Liquid Extractor

l

Reboiled Absorber

l

Refluxed Absorber

l

Distillation

l

Three Phase Distillation

The Input Expert contains a series of input pages. You must supply the required information for the page before advancing to the next one. When you have worked through all the pages, you will have supplied the basic information required to build your column, and the Column property view appears. It is not necessary to use the Input Experts to install a column. You can disable the use of Input Experts by deactivating the Use Input Experts check box on the Options page in the Simulation tab of the Session Preferences property view. If you do not use the Input Expert, the Column property view appears when you install a new column.

Column Reboiler Pre-configurations For the distillation column and the reboiled absorber, the following predefined reboiler pre-configurations (below) are available on page 2 of the column configuration wizard. Depending on the configuration you can specify a HYSYS Reboiler, a Heater, or a heat exchanger model as the reboiler type. Thermosiphon reboilers can be simulated rigorously using Aspen Shell & Tube Exchanger (formerly Tasc+). Using this operation as the reboiler, you can select different types of EDR-Shell and Tube heat exchangers such as thermosiphon, kettle, and forced circulation.

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The heat exchanger is integrated with the column so that rigorous calculations can be done in both the column and the reboiler. The heat exchanger is treated as part of the column, and both the column and the heat exchanger are solved simultaneously. When the selections are complete, move to the next page to specify top and last stage pressures. Notes: l

For a thermosiphon reboiler, both fixed-flow and find-flow options are implemented.

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Some specs related to the EDR-Shell and Tube heat exchanger are automatically defined to minimize user input.

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A damping factor is added for EDR-Shell and Tube heat exchangers inside the column sub-flowsheet to improve the convergence of the solver.

Each configuration is shown both as an approximation of the way it might be arranged in an actual column and in detail showing how it is represented using heat exchangers, flash drums, mixers, and splitters. In these diagrams, NT represents the number of trays (stages). l

Reboiler Once-through

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Reboiler Circulation without baffle

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Reboiler Circulation with baffle

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Reboiler Circulation with auxiliary baffle

When done, click Next to proceed to page 3.

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This configuration is available when using the kettle reboiler. The liquid coming from the stage above the reboiler passes through the reboiler once and is returned to the bottom of the column as a mixture of liquid (which goes into the sump, to be drawn as bottom product) and vapor (which goes up to the stage above).

Reboiler Circulation Without Baffle The liquid coming from the stage above the reboiler enters the sump, from which the bottoms and the reboiler feed are both drawn (with the same composition). The reboiler product is returned above the sump. Vapor may also be produced when the hot liquid return from the reboiler contacts the liquid in the sump.

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Reboiler Circulation With Baffle The sump is divided into two sections with different compositions. The liquid from above the reboiler enters one section, from which the reboiler feed is drawn. The reboiler liquid product enters the other section, from which the bottoms stream is drawn. Excess reboiler liquid return (above the flow rate of the bottoms stream) overflows into the first section. Vapor from the first section (along with that from the reboiler product) passes up to the stage above.

Reboiler Circulation with Auxiliary Baffle

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The sump is divided into three sections by a main baffle and an auxiliary baffle. Liquid from the tray above enters the section from which the reboiler feed is drawn. Reboiler return enters above the middle section, overflowing over the main baffle into the section from which the bottoms stream is drawn. Liquid can flow under the auxiliary baffle into or out of the middle section, depending on flow rates. The composition of the middle section is the same as one of the other two sections, depending on the direction of flow. In this configuration, the sump is modeled as two stages, representing the different compositions of the reboiler feed and the bottoms stream.

Because the flow under the baffle is reversible, the effective flowsheet pattern depends on the direction of this flow. This diagram shows both possible configurations, with the dashed lines representing one configuration and the dashdot lines representing the other. In the case when the liquid is flowing upward in the middle section, this overflowing liquid mixes with the reboiler return liquid and both of these enter stage NT. In this case, vapor may be produced by the mixing of these two streams (the vapor stream shown leaving the sump middle section). Since the sump's middle section is not a stage in and of itself, this vapor stream is reported as a vapor flow from stage NT. Since such a flow would normally go to stage NT-1 but in this case goes to stage NT-2, it is treated as a total vapor draw from stage NT returned above stage NT-1 (so that it enters stage NT-2), and this appears as a vapor product and vapor feed in the column results.

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These two diagrams show the separate configurations for the different directions of the reversible middle section flow. Note that only two vapor streams enter stage NT-2, one from the reboiler return and one from the meeting of cold sump and hot sump liquid, but the location for the meeting of this liquid varies; at the other point liquid is meeting liquid flowing away from it and assumed to be at the same conditions as the entering liquid. The switch between the two configurations is handled via a smoothing equation. Though only one of the two vapor streams from stage NT-1 or from stage NT-2 actually exist, a trace amount of vapor may be seen in the other stream due to this smoothing method. The flow in the middle section is reported as Cold sump to hot sump flow or Hot sump to cold sump flow, as appropriate.

Absorber Absorber Input Expert Connections Page This is the first page in the Absorber Input Expert. 1. In the Column Name field, specify a name for the Absorber. 2. In the # Stages field, specify the number of stages (or trays) in the column. 3. In the Top Stg. Reflux group, click either the Liquid Inlet or Pumparound radio button.

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o

If you click the Liquid Inlet radio button, either type the name of the stream in the Top Stage Inlet field or, if you have predefined your stream, select it from the Top Stage Inlet dropdown list.

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If you click the Pump-around radio button, select the stage you want to draw the pump-around stream from the Draw Stage drop-down list.

4. In the Bottom Stage Inlet drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. 5. In the Ovhd Vapor Outlet drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. 6. In the Bottoms Liquid Outlet drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. At this point, you can click on the Next > button to proceed to the Pressure Profile page or you can specify any extra inlet streams or draws streams you may require for your Absorber. 7. In the Optional Inlet Stream list, click the cell. A drop-down list appears. From the drop-down list, either select a predefined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step if you have multiple feed streams. 8. For each optional inlet stream, select the stage the stream is entering the column from the Inlet Stage drop-down list. 9. In the Optional Side Draws list, click the cell. A dropdown list appears. From the drop-down list, either select a pre-defined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step if you have multiple side draw streams. 10. For each optional side draw stream, select the type of draw stream from the Type drop-down list and select the stage the stream is leaving the column from the Draw Stage drop-down list. 11. Click the Next > button to proceed to the Pressure Profile page. Tips: l

The radio buttons in the Stage Numbering group are used to specify the way the column is numbered.

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Click the Top Down radio button to set the top stage as stage 1 and the bottom stage as stage n.

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Click the Bottom Up radio button to set the bottom stage as stage 1 and the top stage as stage n.

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Absorber Input Expert Pressure Profile Page This is the second page in the Absorber Input Expert. 1. In the Top Stage Pressure field, specify the pressure of the overhead vapor stream. 2. In the Bottom Stage Pressure field, specify the pressure of the bottoms liquid stream. 3. Click the Next > button to proceed to the Estimates page. Tip: Click the < Prev button to return to the Connections page.

Absorber Input Expert Estimates Page This is the third page in the Absorber Input Expert. On this page, you can provide initial temperature estimates. These estimates are optional values that help the HYSYS algorithm converge to a solution. The better your estimates, the quicker HYSYS converges. 1. In the Optional Top Stage Temperature Estimate field, specify the temperature of the top stage of the column. 2. In the Optional Bottom Stage Temperature Estimate field, specify the temperature of the bottom stage of the column. Tips: l

Click the Done button to accept the entries made in the input expert and proceed to the Absorber property view.

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Click the < Prev button to return to the Pressure Profiles page.

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Click the Side Ops > button to access the Side Operations Input Expert.

Distillation Column Distillation Input Expert Connections Page This is the first page in the Distillation column input expert. 1. In the Column Name field, specify a name for the Distillation column. 2. In the # Stages field, specify the number of stages (or trays) in the column. 3. In the Inlet Streams list, click the cell. A drop-down list appears. From the drop-down list, either select a pre-defined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step if you have multiple feed streams. 4. For each inlet stream, select the stage the stream is entering column from the Inlet Stage drop-down list. 5. In the Condenser Energy Stream drop-down list, either type in the

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name of the stream or, if you have pre-defined your stream, select it from the drop-down list. 6. In the Condenser group click one of the following radio buttons: Total, Partial, or Full Rflx. o

If you click the Total radio button, either type in the name of the stream in the Ovhd Liquid Outlet field or, if you have predefined your stream, select it from the Ovhd Liquid Outlet drop-down list.

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If you click the Partial radio button, either type in the name of the streams in both Ovhd Outlets fields or, if you have predefined your streams, select them from the Ovhd Outlets dropdown lists.

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If you click the Full Rflx radio button, either type in the name of the stream in the Ovhd Vapor Outlet field or, if you have predefined your stream, select it from the Ovhd Vapor Outlet drop-down list.

7. The Water Draw check box appears when either the Total or Partial radio button is selected. Select this check box to add a water draw to your condenser. In the corresponding drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. 8. In the Reboiler Energy Stream drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. 9. In the Bottoms Liquid Outlet drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. At this point you can click on the Next > button to proceed to the Column Reboiler Pre-configurations page. 10. In the Optional Side Draws list, click the cell. A dropdown list appears. From the drop-down list, either select a pre-defined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step if you have multiple side draw streams. 11. For each optional side draw stream, select the type of draw stream from the Type drop-down list and select the stage the stream is leaving the column from the Draw Stage drop-down list. You are given three options: L (Liquid), V (Vapor), and W (Water). 12. Click the Next > button to proceed to the Reboiler Configuration page.

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Tips: l

The radio buttons in the Stage Numbering group are used to specify the way the column is numbered.

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Click the Top Down radio button to set the top stage as stage 1 and the bottom stage as stage n.

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Click the Bottom Up radio button to set the bottom stage as stage 1 and the top stage as stage n.

Distillation Input Expert Pressure Profile Page This is the second page in the Distillation column input expert. 1. In the Condenser Pressure field, specify the pressure at the condenser. 2. In the Condenser Pressure Drop field, specify the pressure drop across the condenser. 3. In the Reboiler Pressure field, specify the pressure at the reboiler. 4. Click the Next > button to proceed to the Optional Estimates page.

Distillation Input Expert Estimates Page This is the third page in the Distillation column input expert. On this page, you can provide initial temperature estimates. These estimates are optional values that help the HYSYS algorithm converge to a solution. The better your estimates, the quicker HYSYS converges. 1. In the Optional Condenser Temperature Estimate field, specify the temperature at the condenser. 2. In the Optional Top Stage Temperature Estimate field, specify the temperature of the top stage of the column. 3. In the Optional Reboiler Temperature Estimate field, specify the temperature at the reboiler. Tips: l

Click the Next > button to proceed to the Specifications page.

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Click the < Prev button to return to the Pressure Profile page.

Distillation Input Expert Specifications Page This is the fourth page in the Distillation column input expert. This page suggests possible specifications that can be set for the column. These specifications are optional and not exhaustive. See the Specs page of the Design tab for more information regarding column specifications. 1. To add the reflux ratio specification, specify a value in the Reflux Ratio field.

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2. To add the liquid draw rate specification, specify a value in the Liquid Rate field. (Available when a total and partial condenser is modeled.) 3. To add the vapor draw rate specification, specify a value in the Vapor Rate field. (Available when a full reflux and partial condenser is modeled.) Tips: l

The Flow Basis drop-down list allows you to specify the basis for the reflux ratio, liquid rate and vapor rate specifications. You are given the following options: Molar, Mass, and Volume.

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Click the Done button to accept the entries made in the input expert and proceed to the Distillation column property view.

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Click the < Prev button to return to the Estimates page.

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Click the Side Ops > button to access the Side Operations Input Expert.

Liquid-Liquid Extractor Liquid-Liquid Extractor Input Expert Connections Page This is the first page in the Liquid-Liquid Extractor input expert. 1. In the Column Name field, specify a name for the Liquid-Liquid Extractor. 2. In the Number of Stages field, specify the number of stages (or trays) in the column. 3. In the Top Stage Inlet drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the dropdown list. 4. In the Bottom Stage Inlet drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. 5. In the Ovhd Light Liquid drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the dropdown list. 6. In the Bottoms Heavy Liquid drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. At this point you can click on the Next > button to proceed to the Pressure Profile page or you can specify any extra inlet streams or draws streams you may require for your Liquid-Liquid Extractor. 7. In the Optional Inlet Streams list, click the cell. A drop-down list appears. From the drop-down list, either select a predefined stream or click the empty space at the top of the list and type in

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the name of the stream. Repeat this step if you have multiple feed streams. 8. For each optional inlet stream, select the stage the stream is entering the column from the Inlet Stage drop-down list. 9. In the Optional Side Draws list, click the cell. A dropdown list appears. From the drop-down list, either select a pre-defined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step if you have multiple side draw streams. 10. For each optional side draw stream, select the type of draw stream from the Type drop-down list and select the stage the stream is leaving the column from the Draw Stage drop-down list. You are given three options: L (Liquid), V (Vapor), and W (Water). 11. Click the Next > button to proceed to the Pressure Profile page. Tip: l

The radio buttons in the Stage Numbering group are used to specify the way the column is numbered.

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Click the Top Down radio button to set the top stage as stage 1 and the bottom stage as stage n.

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Click the Bottom Up radio button to set the bottom stage as stage 1 and the top stage as stage n.

Liquid-Liquid Extractor Input Expert Pressure Profile Page This is the second page in the Liquid-Liquid Extractor input expert. 1. In the Top Stage Pressure field, specify the pressure of the overhead vapor stream. 2. In the Bottom Stage Pressure field, specify the pressure of the bottoms liquid stream. 3. Click the Next > button to proceed to the Optional Estimates page.

Liquid-Liquid Extractor Input Expert Estimates Page This is the third page in the Liquid-Liquid Extractor input expert. On this page, you can provide initial temperature estimates. These estimates are optional values that help the HYSYS algorithm converge to a solution. The better your estimates, the quicker HYSYS converges. 1. In the Optional Top Stage Temperature Estimate field, specify the temperature of the top stage of the column. 2. In the Optional Bottom Stage Temperature Estimate field, specify the temperature of the bottom stage of the column.

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Tip: Click the Done button to accept the entries made in the input expert and proceed to the column property view.

Reboiled Absorber Reboiled Absorber Input Expert Connections Page This is the first page in the Reboiled Absorber input expert. 1. In the Column Name field, specify a name for the Reboiled Absorber. 2. In the # Stages field, specify the number of stages (or trays) in the column. 3. In the Top Stg. Reflux group, click either the Liquid Inlet or Pumparound radio button. 4. If you click the Liquid Inlet radio button, either type in the name of the stream in the Top Stage Inlet drop-down list or, if you have predefined your stream, select it from the Top Stage Inlet drop-down list. 5. If you click the Pump-around radio button, select the stage you want to draw the pump-around stream from the PA Draw Stage drop-down list. 6. In the Ovhd Vapor Outlet drop-down list either type in the name of the stream or if you have pre-defined your stream select it from the dropdown list. 7. In the Reboiler Energy Stream drop-down list either type in the name of the stream or if you have pre-defined your stream select it from the drop-down list. 8. In the Bottoms Liquid Outlet drop-down list either type in the name of the stream or if you have pre-defined your stream select it from the drop-down list. 9. At this point, you can click on the Next > button to proceed to the Reboiler Configuration page, or you can specify any extra inlet streams or draws streams you may require for your Reboiled Absorber. 10. In the Optional Inlet Streams list, click the cell. A drop-down list appears. From the drop-down list, either select a predefined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step if you have multiple feed streams. 11. For each optional inlet stream, select the stage the stream is entering the column from the Inlet Stage drop-down list. 12. In the Optional Side Draws list, click the cell. A dropdown list appears. From the drop-down list, either select a pre-defined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step if you have multiple side draw streams. 13. For each optional side draw stream, select the type of draw stream from

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the Type drop-down list and select the stage the stream is leaving the column from the Draw Stage drop-down list. You are given three options: L (Liquid), V (Vapor), and W (Water). 14. Click the Next > button to proceed to the Reboiler Configuration page. Tip: l

The radio buttons in the Stage Numbering group are used to specify the way the column is numbered.

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Click the Top Down radio button to set the top stage as stage 1 and the bottom stage as stage n.

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Click the Bottom Up radio button to set the bottom stage as stage 1 and the top stage as stage n.

Reboiled Absorber Input Expert Pressure Profile Page This is the third page in the Reboiled Absorber input expert. 1. In the Top Stage Pressure field, specify the pressure of the overhead vapor stream. 2. In the Reboiler Pressure field, specify the pressure of the Reboiler energy stream. 3. Click the Next > button to proceed to the Optional Estimates page.

Reboiled Absorber Input Expert Estimates Page This is the fourth page in the Reboiled Absorber input expert. On this page you can provide initial temperature estimates. These estimates are optional values that help the HYSYS algorithm converge to a solution. The better your estimates, the quicker HYSYS converges. 1. In the Optional Top Stage Temperature Estimate field, specify the temperature of the top stage of the column. 2. In the Optional Reboiler Temperature Estimate field, specify the temperature of the Reboiler energy stream. 3. Click the Next > button to proceed to the Specifications page.

Reboiled Absorber Input Expert Specifications Page This is the fifth page in the Reboiled Absorber input expert. This page suggests possible specifications that can be set for the column. These specifications are optional and not exhaustive. (See the Specs page of the Design tab for more information regarding column specifications.)

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To add the boilup ratio specification to the Reboiled Absorber, specify a value in the Boil-up Ratio field. Tips: l

Click Done to accept the entries made in the input expert and proceed to the Reboiled Absorber property view.

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Click the < Prev button to return to the Estimates page.

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Click the Side Ops > button to access the Side Operations Input Expert.

Refluxed Absorber Refluxed Absorber Input Expert Connections Page This is the first page in the Refluxed Absorber input expert. 1. In the Column Name field, specify a name for the Reboiled Absorber. 2. In the # Stages field, specify the number of stages (or trays) in the column. 3. In the Condenser Energy Stream drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. 4. In the Bottom Stage Inlet drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. 5. In the Condenser group, click one of the following radio buttons: Total, Partial, or Full Rflx. o

If you click the Total radio button, either type in the name of the stream in the Ovhd Liquid Outlet field or, if you have pre-defined your stream, select it from the Ovhd Liquid Outlet drop-down list.

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If you click the Partial radio button, either type in the name of the streams in both Ovhd Outlets fields or, if you have pre-defined your streams, select them from the Ovhd Outlets drop-down lists.

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If you click the Full Rflx radio button, either type in the name of the stream in the Ovhd Vapor Outlet field or, if you have predefined your stream, select it from the Ovhd Vapor Outlet dropdown list.

6. The Water Draw check box appears when either the Total or Partial radio button is selected. Select this check box to add a water draw to your condenser. In the corresponding drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. 7. In the Bottoms Liquid Outlet drop-down list, either type in the name

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of the stream or, if you have pre-defined your stream, select it from the drop-down list. At this point you can click on the Next > button to proceed to the Pressure Profile page or you can specify any extra inlet streams or draws streams you may require for your Reboiled Absorber. 8. In the Optional Inlet Streams list, click the cell. A drop-down list appears. From the drop-down list, either select a predefined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step if you have multiple feed streams. 9. For each optional inlet stream, select the stage the stream is entering column from the Inlet Stage drop-down list. 10. In the Optional Side Draws list, click the cell. A dropdown list appears. From the drop-down list, either select a pre-defined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step if you have multiple side draw streams. 11. For each optional side draw stream, select the type of draw stream from the Type drop-down list and select the stage the stream is leaving the column from the Draw Stage drop-down list. You are given three options: L (Liquid), V (Vapor), and W (Water). 12. Click the Next > button to proceed to the Pressure Profile page. Tips: l

The radio buttons in the Stage Numbering group are used to specify the way the column is numbered.

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Click the Top Down radio button to set the top stage as stage 1 and the bottom stage as stage n.

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Click the Bottom Up radio button to set the bottom stage as stage 1 and the top stage as stage n.

Refluxed Absorber Input Expert Pressure Profile Page This is the second page in the Refluxed Absorber input expert. 1. In the Condenser Pressure field, specify the pressure at the condenser. 2. In the Condenser Pressure Drop field, specify the pressure drop across the condenser. 3. In the Bottom Stage Pressure field, specify the pressure of the bottom stage of the column. 4. Click the Next > button to proceed to the Optional Estimates page.

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Refluxed Absorber input expert estimates page This is the third page in the Refluxed Absorber input expert. On this page, you can provide initial temperature estimates. These estimates are optional values that help the HYSYS algorithm converge to a solution. The better your estimates, the quicker HYSYS converges. 1. In the Optional Condenser Temperature Estimate field, specify the temperature at the condenser. 2. In the Optional Top Stage Temperature Estimate field, specify the temperature of the top stage of the column. 3. In the Optional Bottom Stage Temperature Estimate field, specify the temperature of the bottom stage of the column. Tips: l

Click the Next > button to proceed to the Specifications page.

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Click the < Prev button to return to the Pressure Profiles page.

Refluxed Absorber input expert specifications page This is the fourth page in the Refluxed Absorber input expert. This page suggests possible specifications that can be set for the column. These specifications are optional and not exhaustive. Refer to the Specs page of the Design tab for more information regarding column specifications. 1. To add the reflux ratio specification, specify a value in the Reflux Ratio field. 2. To add the liquid draw rate specification, specify a value in the Liquid Rate field. Available when a total and partial condenser is modeled. 3. To add the vapor draw rate specification, specify a value in the Vapor Rate field. Available when a full reflux and partial condenser is modeled. Tips: l

The Flow Basis drop-down list allows you to specify the basis for the reflux ratio, liquid rate, and vapor rate specifications. You are given the following options: Molar, Mass and Volume.

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Click the Done button to accept the entries made in the input expert and proceed to the Refluxed Absorber property view.

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Click the < Prev button to return to the Estimates page.

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Click the Side Ops > button to access the Side Operations Input Expert.

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Three Phase Distillation Three Phase Distillation configuration page This is the first page in the Three Phase Distillation input expert. 1. Click one of the following radio buttons to specify the type of column you want to model: Distillation, Refluxed Absorber, Reboiled Absorber, or Absorber. 2. Click the Next > button to proceed to the Liquid Phase Check page. Tip: Click the Cancel button to close the input expert without accepting any entries made.

Three Phase Distillation liquid phase check page This is the second page in the Three Phase Distillation input expert. 1. In the Column Name field, specify a name for the column. 2. In the Number of Stages field, specify the number of stages (or trays) in the column. 3. In the Two Liquid Phase Check group, select the Check check boxes for the stages that you want to check for two liquid phases. Tips: l

The radio buttons in the Stage Numbering group are used to specify the way the column is numbered.

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Click the Top Down radio button to set the top stage as stage 1 and the bottom stage as stage N.

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Click the Bottom Up radio button to set the bottom stage as stage 1 and the top stage as stage N.

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Click the Next > button to proceed to the Three Phase Condenser Setup page. (This page is only available if the column model has a condenser.)

Three Phase Distillation condenser setup page This is the third page in the Three Phase Distillation input expert. This page is only available if the column model has a condenser. 1. In the Condenser Energy Stream drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the drop-down list. There are a number of ways that you can model the column’s condenser. 2. The Condenser Type group enables you to model the following condenser types: Total, Partial, or Full Reflux. o

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If you click the Total radio button there is no vapor product stream. Refer to step 3 for configuring the outlet streams.

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o

If you click the Partial radio button, the condenser has both a vapor stream and a liquid stream leaving it. To define the vapor stream, either type in the name of the stream in the Vapor Outlet field or, if you have pre-defined your stream, select it from the Vapor Outlets drop-down list. To define the liquid streams, refer to step 3.

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If you click the Full Reflux radio button, there are no liquid product streams. To define the vapor stream, either type in the name of the stream in the Vapor Outlet field or, if you have pre-defined your stream, select it from the Vapor Outlet dropdown list. The Outlet Streams group is hidden when this radio button is selected.

3. The Outlet Streams group enables you to model the following outlet stream configurations: Light, Heavy, or Both. o

If you click the Light radio button, either type in the name of the light liquid stream in the Light Outlet field or, if you have predefined your stream, select it from the Light Outlet drop-down list. You cannot select this radio button if the Light radio button in the Reflux Streams group is selected.

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If you click the Heavy radio button, either type in the name of the heavy liquid stream in the Heavy Outlet field or, if you have pre-defined your stream, select it from the Heavy Outlet drop-down list. You cannot select this radio button if the Heavy radio button in the Reflux Streams group is selected.

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If you click the Both radio button, either type in the name of the light and heavy liquid streams in the Light Outlet and Heavy Outlet fields or, if you have pre-defined your streams, select them from the Light Outlet and Heavy Outlet drop-down lists.

4. The Reflux Streams group enables you to model the following reflux stream configurations: Light, Heavy, or Both. o

If you click the Light radio button, either type in the name of the light reflux stream in the Light Reflux field or, if you have predefined your stream, select it from the Light Reflux drop-down list. HYSYS provides a default stream name for you. You cannot select this radio button if the Light radio button in the Outlet Streams group is selected.

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If you click the Heavy radio button, either type in the name of the heavy reflux stream in the Heavy Reflux field or, if you have pre-defined your stream, select it from the Heavy Reflux drop-down list. HYSYS provides a default stream name for you. You cannot select this radio button if the Heavy radio button in the Outlet Streams group is selected.

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If you click the Both radio button, either type in the name of the light and heavy reflux streams in the Light Reflux and Heavy Reflux fields or if you have pre-defined your streams, select

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them from the Light Reflux and Heavy Reflux drop-down lists. HYSYS provides default stream names for you. 5. Once you have specified all of the condenser streams, click the Next > button to proceed to the Condenser Specs page. Click the button on the last page of the Absorber, Reboiled Absorber, Refluxed Absorber and Distillation input experts accesses Side Operations Input Expert property view. It is not necessary to use the Side Operations Input Experts to install a side operation. If you do not use the Side Operation Input Expert, you can install column side equipment from the Side Ops tab in the columns property view. The Side Operations Input Expert provides templates for following operations: l

Reboiled Side Stripper Connections Page

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Reboiled Side Stripper Pressure Specifications Page

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Reboiled Side Stripper Specifications Page

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Steam Stripped Side Stripper Connections Page

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Steam Stripped Side Stripper Pressure Specifications Page

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Steam Stripped Side Stripper Specifications Page

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Side Rectifier Connections Page

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Side Rectifier Pressure Specifications Page

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Side Rectifier Specifications Page

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Pump-Around Connections Page

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Pump-Around Pressure Specifications Page

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Pump-Around Specifications Page

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Vapor Bypass Connections Page

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Vapor Bypass Specifications Page

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Reboiled Side Stripper Reboiled Side Stripper Connections Page This is the first page in the Side Operations Input Expert. 1. Click the Add Side Stripper button. 2. In the Name field, specify a name for the Side Stripper. 3. In the k= field, specify the number of stages (or trays) in the Side Stripper. 4. In the Return Stage drop-down list, select the stage you are returning the stream to. This stage can be located in the column, a side stripper, or a side rectifier. 5. In the Draw Stage drop-down list, select the stage you are drawing the stream from. This stage can be located in the column, a side stripper, or a side rectifier. 6. In the Draw Product drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the dropdown list. 7. Click the Install button. The Side Stripper appears in the Reboiled Side Strippers group. 8. You can then click the Add Side Stripper button to add another Side Stripper or click the Next > button to proceed to the Steam Stripped Side Stripper Connections page. Tips: l

Click the Clear button, before the Side Stripper is installed, to delete the current Side Stripper from the column.

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Click the Return > button to return to the Column Input Expert property view.

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Click the Cancel button to close the input expert without accepting any entries made.

Note: The Reboiled Side Strippers group displays all of the Reboiled Side Strippers attached to the column. For each Side Stripper listed, you can modify the number of stages, the draw stage, and the return stage.

Reboiled Side Stripper Specifications Page This page only appears when one or more Reboiled Side Strippers have been added to the column. You must proceed through the Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around, and Vapor Bypass connection pages to access this page. Perform the following steps for each Reboiled Side Stripper listed in the Reboiled Side Stripper Specs group. These specifications are optional. 1. From the Flow Basis drop-down list, select the flow basis for the draw stream. You are given the following options: Molar, Mass, Volume and

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Std Volume. 2. In the Draw Spec field, specify the rate that material is drawn from the column. 3. From the 2nd Spec Type drop-down list, select the type specification you want to use for the remaining degree of freedom. You are given the following options: Boilup and Duty. 4. In the 2nd Spec Value field, specify either the boilup rate in the reboiler or the duty of the reboiler. 5. Click the Next > button to proceed to the next side operation’s specification page. Tips: l

Click the Prev > button to return to the Vapor Bypass Connections page.

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Click the Cancel button to close the input expert without accepting any entries made.

Reboiled Side Stripper Pressure Specifications Page This page only appears when one or more Reboiled Side Strippers have been added to the column. You must proceed through the following pages to access this page: l

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Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass connection pages Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass specifications pages (not all of the specification pages may be available)

Perform the following steps for each Reboiled Side Stripper listed in the Reboiled Side Stripper Pressure Specs group. 1. In the Top Stg. Pressure field, specify the pressure at the top stage of the side stripper. 2. In the Reb. dP field, specify the pressure drop across the reboiler. 3. Click the Next > button to proceed to the next side operation’s pressure specification page or click the Done button to close the Side Operations Input Expert property view and access the Column property view. Tips: l

Click the Prev > button to return to the next available side operation’s specification page or the next available side operation’s pressure specifications page.

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Click the Cancel button to close the input expert without accepting any entries made.

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Steam Stripped Side Stripper Steam Stripped Side Stripper Connections Page This is the second page in the Side Operations Input Expert. You must proceed through the Reboiled Side Stripper Connections page to access this page. 1. Click the Add Side Stripper button. 2. In the Name field, specify a name for the Side Stripper. 3. In the k= field, specify the number of stages (or trays) in the Side Stripper. 4. In the Return Stage drop-down list, select the stage you are returning the stream to. This stage can be located in the column, a side stripper, or a side rectifier. 5. In the Draw Stage drop-down list, select the stage you are drawing the stream from. This stage can be located in the column, a side stripper, or a side rectifier. 6. In the Stream Feed drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the dropdown list. 7. In the Draw Product drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the dropdown list. 8. Click the Install button. The Side Stripper appears in the Steam Stripped Side Strippers group. 9. You can then click the Add Side Stripper button to add another Side Stripper or click the Next > button to proceed to the Side Rectifier Connections page. Tips: l

Click the Clear button, before the Side Stripper is installed, to delete the current Side Stripper from the column.

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Click the Prev > button to return to the Reboiled Side Stripper Connections page.

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Click the Cancel button to close the input expert without accepting any entries made.

Note: The Steam Stripped Side Strippers group displays all of the Steam Stripped Side Strippers attached to the column. For each Side Stripper listed, you can modify the number of stages, the draw stage, and the return stage.

Steam Stripped Side Stripper Specifications Page This page only appears when one or more Steam Stripped Side Strippers have been added to the column. You must proceed through the following pages to access this page:

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l

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Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass connection pages Reboiled Side Stripper specifications page (if available)

Perform the following steps for each Steam Stripped Side Stripper listed in the Steam Stripped Side Stripper Specs group. These specifications are optional. 1. From the Flow Basis drop-down list, select the flow basis for the draw stream from the following options: Molar, Mass, Volume, and Std Volume. 2. In the Draw Spec field, specify the rate that material is drawn from the column. 3. Click the Next > button to proceed to the next side operation’s specification page. Tips:  l

Click the Prev > button to return to the Reboiled Side Stripper Specifications page (if available) or the Vapor Bypass Connections page.

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Click the Cancel button to close the input expert without accepting any entries made.

Steam Stripped Side Stripper Pressure Specifications Page This page only appears when one or more Steam Stripped Side Strippers have been added to the column. You must proceed through the following pages to access this page: l

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Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass connection pages Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass specifications pages (not all of the specification pages may be available) Reboiled Side Stripper pressure specification page (if available).

Perform the following steps for each Steam Stripped Side Stripper listed in the Steam Stripped Side Stripper Pressure Specs group. 1. In the Top Stg. Pressure field, specify the pressure at the top stage of the side stripper. 2. Click the Next > button to proceed to the next side operation’s pressure specification page or click the Done button to close the Side Operations Input Expert property view and access the Column property view. Tips: l

Click the Prev > button to return to the next available side operation’s specification page or the next available side operation’s pressure specifications page.

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Click the Cancel button to close the input expert without accepting any entries made.

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Side Rectifier Side Rectifier Connections Page This is the third page in the Side Operations Input Expert. You must proceed through the Reboiled Side Stripper Connections page and the Steam Stripped Side Stripper Connections page to access this page. 1. Click the Add Side Rectifier button. 2. In the Name field, specify a name for the Side Rectifier. 3. In the k= field, specify the number of stages (or trays) in the Side Rectifier. 4. In the Draw Stage drop-down list, select the stage you are drawing the stream from. This stage can be located in the column, a side stripper, or a side rectifier. 5. In the Return Stage drop-down list, select the stage you are returning the stream to. This stage can be located in the column, a side stripper, or a side rectifier. 6. In the Vapor Product drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the dropdown list. 7. In the Liquid Product drop-down list, either type in the name of the stream or, if you have pre-defined your stream, select it from the dropdown list. 8. Click the Install button. The Side Rectifier appears in the Side Rectifiers group. 9. You can then click the Add Side Rectifier button to add another Side Rectifier or click the Next > button to proceed to the Pump-Around Connections page. Tips: l

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Click the Clear button, before the Side Rectifier is installed, to delete the current Side Rectifier from the column. Click the Prev button to return to the Steam Stripped Side Stripper Connections page. Click the Cancel button to close the input expert without accepting any entries made.

Note: The Side Rectifiers group displays all of the Side Rectifiers attached to the column. For each Side Rectifier listed, you can modify the number of stages, the draw stage, and the return stage.

Side Rectifier Specifications Page This page only appears when one or more Side Rectifiers have been added to the column. You must proceed through the following pages to access this page:

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Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass connection pages Reboiled Side Stripper and Steam Stripped Side Stripper specifications pages (not all of the specification pages may be available)

Perform the following steps for each Side Rectifier listed in the Side Rectifier Specs group. These specifications are optional. 1. From each of the Flow Basis drop-down lists, select the flow basis for the vapor outlet and liquid outlet streams. You are given the following options: Molar, Mass, Volume and Std Volume. 2. In the Vap. Rate field, specify the flow rate of the outlet vapor stream. 3. In the Liq. Rate field, specify the flow rate of the outlet liquid stream. 4. In the Ref. Ration field, specify the reflux ratio. 5. Click the Next > button to proceed to the next side operation’s specification page. Tips: l

Click the Prev > button to return to the next available side operation’s specification page or the Vapor Bypass Connections page.

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Click the Cancel button to close the input expert without accepting any entries made.

Side Rectifier Pressure Specifications Page This page only appears when one or more Side Rectifiers have been added to the column. You must proceed through the following pages to access this page: l

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Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass connection pages Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass specifications pages (not all of the specification pages may be available) Reboiled Side Stripper and Steam Stripped Side Stripper pressure specification pages (not all of the specification pages may be available).

Perform the following steps for each Side Rectifier listed in the Side Rectifier Pressure Specs group. 1. In the Top Stg. Press. field, specify the pressure at the top stage of the side stripper. 2. In the Cond. dP field, specify the pressure drop across the condenser. 3. Click the Next > button to proceed to the next side operation’s pressure specification page or click the Done button to close the Side Operations Input Expert property view and access the Column property view.

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Tips:  l

Click the Prev > button to return to the next available side operation’s specification page or the next available side operation’s pressure specifications page.

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Click the Cancel button to close the input expert without accepting any entries made.

Pump-Around Pump-Around Connections Page This is the fourth page in the Side Operations Input Expert. You must proceed through the Reboiled Side Stripper Connections page, the Steam Stripped Side Stripper Connections page, and the Side Rectifier Connections page to access this page. 1. Click the Add Pump-Around button. 2. In the Name field, specify a name for the Pump-Around. 3. In the Return Stage drop-down list, select the stage you are returning the stream to. This stage can be located in the column, a side stripper, or a side rectifier. 4. In the Draw Stage drop-down list, select the stage you are drawing the stream from. This stage can be located in the column, a side stripper, or a side rectifier. 5. Click the Install button. The Pump-Around appears in the PumpArounds group. 6. Click the Add Pump-Around button to add another Pump-Around or click the Next > button to proceed to the Vapor Bypass Connections page. Tips:  l

Click the Clear button, before the Pump-Around is installed, to delete the current Pump-Around from the column.

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Click the Prev > button to return to the Side Rectifier Connections page.

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Click the Cancel button to close the input expert without accepting any entries made.

Note: The Pump-Arounds group displays all of the Pump-Arounds attached to the column. For each Pump-Around listed, you can modify the draw stage and the return stage.

Pump-Around Specifications Page This page only appears when one or more Pump-Arounds have been added to the column. You must proceed through the following pages to access this page:

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Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass connection pages Reboiled Side Stripper, Steam Stripped Side Stripper and Side Rectifier specifications pages (not all of the specification pages may be available)

Perform the following steps for each Pump-Around listed in the Pump-Around Specs group. These specifications are optional. 1. From the Flow Basis drop-down list, select the flow basis for the draw stream from the following options: Molar, Mass, Volume and Std Volume. 2. In the PA Rate field, specify the rate that material is drawn from the column. 3. From the 2nd Spec Type drop-down list, select the type specification you want to use for the remaining degree of freedom. You are given the following options: Temperature Difference, Return Temperature, Duty, and Return Vapor Fraction. 4. In the 2nd Spec Value field, specify a value for the selected specification. 5. Click the Next > button to proceed to the next side operation’s specification page. Tips:  l

Click the Prev > button to return to the next available side operation’s specification page or the Vapor Bypass Connections page.

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Click the Cancel button to close the input expert without accepting any entries made.

Pump-Around Pressure Specifications Page This page only appears when one or more Pump-Arounds have been added to the column. You must proceed through the following pages to access this page: l

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Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass connection pages Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass specifications pages (not all of the specification pages may be available) Reboiled Side Stripper, Steam Stripped Side Stripper and Side Rectifier pressure specification pages (not all of the specification pages may be available).

Perform the following steps for each Pump-Around listed in the Pump-Around Pressure Specs group. 1. In the Cooler dP field, specify the pressure drop across the cooler. 2. Click the Done button to close the Side Operations Input Expert property view and access the Column property view.

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Tips: l

Click the Prev > button to return to the next available side operation’s specification page or the next available side operation’s pressure specifications page.

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Click the Cancel button to close the input expert without accepting any entries made.

Vapor Bypass Vapor Bypass Connections Page This is the fifth page in the Side Operations Input Expert. You must proceed through the Reboiled Side Stripper Connections page, the Steam Stripped Side Stripper Connections page, the Side Rectifier Connections page, and the PumpAround Connections page to access this page. 1. Click the Add Vapor Bypass button. 2. In the Name field, specify a name for the Vapor Bypass. 3. In the Return Stage drop-down list, select the stage you are returning the stream to. This stage can be located in the column, a side stripper, or a side rectifier. 4. In the Draw Stage drop-down list, select the stage you are drawing the stream from. This stage can be located in the column, a side stripper, or a side rectifier. 5. Click the Install button. The Vapor Bypass appears in the Vapor Bypasses group. 6. You can then click the Add Vapor Bypass button to add another Vapor Bypass or click the Next > button to proceed to the side operation’s specification pages. The page that appears next depends on the side operations that have been added to the column. If no side operations have been added, then the Column property view appears. Tips: l

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Click the Clear button, before the Vapor Bypass is installed, to delete the current Vapor Bypass from the column. Click the Prev button to return to the Pump-Around Connections page. Click the Cancel button to close the input expert without accepting any entries made.

Note: The Vapor Bypasses group displays all of the Vapor Bypasses attached to the column. For each Vapor Bypass listed, you can modify the draw stage and the return stage.

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Vapor Bypass Specifications Page This page only appears when one or more Vapor Bypasses have been added to the column. You must proceed through the following pages to access this page: l

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Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier, Pump-Around and Vapor Bypass connection pages Reboiled Side Stripper, Steam Stripped Side Stripper, Side Rectifier and Pump-Around specifications pages (not all of the specification pages may be available)

Perform the following steps for each Vapor Bypass listed in the Vapor Bypass Specs group. These specifications are optional. 1. From the Flow Basis drop-down list, select the flow basis for the draw stream from the following options: Molar, Mass, Volume and Std Volume. 2. In the VBP Rate field, specify the rate that material is drawn from the column. 3. Click the Next > button to proceed to the next side operation’s pressure specification page. Tips: l

Click the Prev > button to return to the next available side operation’s specification page or the Vapor Bypass Connections page.

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Click the Cancel button to close the input expert without accepting any entries made.

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5 Column Operations

Using Column Subflowsheets The Column is a special type of subflowsheet in HYSYS. A subflowsheet contains equipment and streams, and exchanges information with the parent flowsheet through the connected internal and external streams. From the main simulation environment, the Column appears as a single, multi-feed multi-product operation. In many cases, you can treat the column in exactly that manner. You can also work inside the Column subflowsheet. You can do this to focus your attention on the Column. When you move into the Column build environment, the main simulation is cached. All aspects of the main environment are paused until you exit the Column build environment. When you return to the Main Environment, the Desktop re-appears as it was when you left it. You can also enter the Column build environment when you want to create a custom column configuration. Side equipment such as pump arounds, side strippers, and side rectifiers can be added from the Column property view in the main simulation. However, if you want to install multiple Towers or multiple columns, you need to enter the Column build environment. Once inside, you can access the Column-specific operations (Towers, Heaters/Coolers, Condensers, Reboilers, and so forth) and build the column as you would any other flowsheet. Note: By design, the parent flowsheet does not solve when you are in the subflowsheet environment. You must instead go to the parent flowsheet to let the solver run, and then return to the subflowsheet and run the solver.

If you want to create a custom column template for use in other simulations, from the File menu, select New | Column. Since this is a column template, you can access the Column build environment directly from the Properties environment. Once you have created the template, you can store it on disk. Before you install the template in another simulation, make sure that the Use Input Experts check box in the Session Preferences property view is cleared. Note: In this section, the use of the Column property view and Column Templates are explained. Column-Specific Operations describes the unit operations available in the Column build environment.

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Having a Column subflowsheet provides a number of advantages: l

Isolation of the Column Solver.

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Optional use of different Property Packages.

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Construction of custom templates.

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Ability to solve multiple towers simultaneously.

Isolation of the Column Solver One advantage of the Column build environment is that it allows you to make changes, and focus on the Column without requiring a recalculation of the entire flowsheet. When you enter the Column build environment, HYSYS clears the Desktop by caching all property views that were open in the parent flowsheet. Then the property views that were open when you were last in the Column build environment are re-opened. Once inside the Column build environment, you can access profiles, stage summaries, and other data, as well as make changes to Column specifications, parameters, equipment, efficiencies, or reactions. When you have made the necessary changes, simply run the Column to produce a new converged solution. The parent flowsheet cannot recalculate until you return to the parent build environment. The subflowsheet environment permits easy access to all streams and operations associated with your column. l l

Click the PFD icon to view the column subflowsheet. If you want to access information regarding column product streams, click the Workbook icon to view the Column workbook, which displays the Column information exclusively.

Independent Fluid Package HYSYS allows you to specify a unique fluid package for the Column subflowsheet. Here are some instances where a separate fluid package is useful: l

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If a column does not use all of the components used in the main flowsheet, it is often advantageous to define a new fluid package with only the components that are necessary. This speeds up the column solution. In some cases, a different fluid package can be better suited to the column conditions. For example, if you want to redefine Interaction Parameters such that they are applicable for the operating range of the column. In Dynamic mode, different columns can operate at very different temperatures and pressures. With each fluid package, you can define a different dynamic model whose parameters can be regressed in the appropriate temperature and pressure range, thus, improving the accuracy and stability of the dynamic simulation.

5 Column Operations

Ability to Construct Custom Column Configurations Custom column configurations can be stored as templates, and recalled into another simulation. To create a custom template, select File | New | Column. When you store the template, it has a *.col extension. Note: Complex custom columns and multiple columns can be simulated within a single subflowsheet using various combinations of subflowsheet equipment.

There exists a great deal of freedom when defining column configurations, and you can define column setups with varying degrees of complexity. You can use a wide array of column operations in a manner which is straightforward and flexible. Column arrangements are created in the same way that you build the main flowsheet: l

Accessing various operations.

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Making the appropriate connections.

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Defining the parameters.

Use of Simultaneous Solution Algorithm The Column subflowsheet uses a simultaneous solver whereby all operations within the subflowsheet are solved simultaneously. The simultaneous solver permits you to install multiple unit operations within the subflowsheet (interconnected columns, for example) without the need for Recycle blocks.

Dynamic Mode There are several major differences between the dynamic column operation and the steady state column operation. One of the main differences is the way in which the Column subflowsheet solves. In steady state if you are in the Column subflowsheet, calculations in the main flowsheet are put on Hold until the focus is returned to the main flowsheet. When running in dynamics, calculations in the main flowsheet proceed at the same time as those in the Column subflowsheet. Another difference between the steady state column and the dynamic column is with the column specifications. Steady state column specifications are ignored in dynamics. To achieve the column specifications when using dynamics, control schemes must be added to the column. Finally, although it is possible to turn off static head contributions for the rest of the simulation, this option does not apply to the column. When running a column in Dynamic mode, the static head contributions are always used in the column calculations.

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Column Property View The Column property view (the representation of the Column within the main or parent flowsheet) essentially provides you with complete access to the Column.

From the Column property view, you can change feed and product connections, specifications, parameters, pressures, estimates, efficiencies, reactions, side operations, and view the Profiles, Work Sheet, and Summary. You can also run the column from the main flowsheet just as you would from the Column subflowsheet. Note: Side equipment (for example, pump arounds and side strippers) is added from the Column property view.

If you want to make a minor change to a column operation (for example, resize a condenser) you can call up that operation using the Object Navigator without entering the Column subflowsheet. Major changes, such as adding a second Tower, require you to enter the Column subflowsheet. To access to the Column build environment, click the Column Environment button at the bottom of the Column property view. Note: Enter the Column subflowsheet to add new pieces of equipment, such as additional Towers or Reboilers.

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Main Flowsheet and Column Subflowsheet Relationship Unlike other unit operations, the Column contains its own subflowsheet, which in turn, is contained in the Parent (usually the main) flowsheet. When you are working in the parent flowsheet, the Column appears just as any other unit operation, with multiple input and output streams, and various adjustable parameters. Note: If you make a change to the Column while you are working in the parent, or main build environment, both the Column and the parent flowsheets are automatically recalculated.

When you install a Column, HYSYS creates a subflowsheet containing all operations and streams associated with the template you have chosen. This subflowsheet operates as a unit operation in the main flowsheet. Figure 2.2 shows this concept of a Column subflowsheet within a main flowsheet.

Main Flowsheet / Subflowsheet Concept Consider a simple absorber in which you want to remove CO2 from a gas stream using H2O as the solvent. A typical approach to setting up the problem would be as follows: 1. Create the gas feed stream, FeedGas, and the water solvent stream, WaterIn, in the main flowsheet. 2. Click the Absorber icon from the Object Palette. 3. Specify the stream names, number of stages, pressures, estimates, and specifications. You must also specify the names of the outlet streams, CleanGas and WaterOut. 4. Run the Column from the main flowsheet Column property view. When you connected the streams to the tower, HYSYS created internal streams with the same names. The Connection Points or “Labels” serve to connect the main flowsheet streams to the subflowsheet streams and facilitate the information transfer between the two flowsheets. Note: A subflowsheet stream that is connected to a stream in the main flowsheet is automatically given the same name with “@subflowsheet tag” attached at the end of the name. An example is the stream named “WaterIn” has a subflowsheet stream named “WaterIn@Col1”.

For instance, the main flowsheet stream WaterIn is connected to the subflowsheet stream WaterIn.

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Note: The connected streams do not necessarily have the same values. All specified values are identical, but calculated stream variables can be different depending on the fluid packages and transfer basis (defined on the Flowsheet tab).

When working in the main build environment, you “see” the Column just as any other unit operation, with a property view containing parameters such as the number of stages, and top and bottom pressures. If you change one of these parameters, the subflowsheet recalculates (just as if you had clicked the Run button); the main flowsheet also recalculates once a new column solution is reached. However, if you are inside the Column subflowsheet build environment, you are working in an entirely different flowsheet. To make a major change to the Column such as adding a reboiler, you must enter the Column subflowsheet build environment. When you enter this environment, the main flowsheet is put on “hold” until you return. Note: If you delete any streams connected to the column in the main flowsheet, these streams are also deleted in the Column subflowsheet.

HYSYS Column Theory Multi-stage fractionation towers, such as crude and vacuum distillation units, reboiled demethanizers, and extractive distillation columns, are the most complex unit operations that HYSYS simulates. Depending on the system being simulated, each of these towers consists of a series of equilibrium or nonequilibrium flash stages. The vapor leaving each stage flows to the stage above and the liquid from the stage flows to the stage below. A stage can have one or more feed streams flowing onto it, liquid or vapor products withdrawn from it, and can be heated or cooled with a side exchanger.

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The following figure shows a typical stage j in a Column using the top-down stage numbering scheme. The stage above is j-1, while the stage below is j+1. The stream nomenclature is shown below.

More complex towers can have pump arounds, which withdraw liquid from one stage of the tower and typically return it to a stage farther up the column. Small auxiliary towers, called sidestrippers, can be used on some towers to help purify side liquid products. With the exception of Crude distillation towers, very few columns have all of these items, but virtually any type of column can be simulated with the appropriate combination of features. It is important to note that the Column operation by itself is capable of handling all the different fractionation applications. HYSYS has the capability to run cryogenic towers, high pressure TEG absorption systems, sour water strippers, lean oil absorbers, complex crude towers, highly non-ideal azeotropic distillation columns, and so forth. There are no programmed limits for the number of components and stages. The size of the column which you can solve depends on your hardware configuration and the amount of computer memory you have available. The column is unique among the unit operations in the methods used for calculations. There are several additional underlying equations which are used in the column. The Francis Weir equation is the starting point for calculating the liquid flowrate leaving a tray: (1) where:  LN = liquid flowrate leaving tray N C = units conversion constant ρ = density of liquid on tray lw = weir length h = height of liquid above weir The vapor flowrate leaving a tray is determined by the resistance equation: (2) where:

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Fvap = vapor flowrate leaving tray N k = conductance, which is a constant representing the reciprocal of resistance to flow ΔPfriction = dry hole pressure drop Note: For columns the conductance, k, is proportional to the square of the column diameter. Note: The pressure drop across a stage is determined by summing the static head and the frictional losses.

It is possible to use column stage efficiencies when running a column in dynamics. The efficiency is equivalent to bypassing a portion of the vapor around the liquid phase, as shown in the figure below, where n is the specified efficiency.

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HYSYS has the ability to model both weeping and flooding inside the column. If ΔPfriction is very small, the stage exhibits weeping. Therefore it is possible to have a liquid flow to the stage below even if the liquid height over the weir is zero. For the flooding condition, the bulk liquid volume approaches the tray volume. This can be observed on the Dynamics tab | Holdup page of either the Column Runner or the Tower property view.

Three Phase Theory For non-ideal systems with more than two components, boundaries can exist in the form of azeotropes, which a simple distillation system cannot cross. The formation of azeotropes in a three phase system provides a thermodynamic barrier to separating chemical mixtures. Distillation schemes for non-ideal systems are often difficult to converge without very accurate initial guesses. To aid in the initialization of towers, a Three Phase Input Expert is available to initialize temperatures, flows, and compositions. Note: For non-ideal multicomponent systems, DISTIL is an excellent tool for determining process viability. This conceptual design software application also determines the optimal feed tray location and allows direct export of column specifications to HYSYS for use as an initial estimate. Contact your local AspenTech representative for details.

Detection of Three Phases Whenever your Column converges, HYSYS automatically performs a Three Phase Flash on the top stage. If a second liquid phase is detected, and no associated water draw is found, a warning message appears. Note: View the Trace Window for column convergence messages.

If there is a water draw, HYSYS checks the next stage for a second liquid phase, with the same results as above. This continues down the Tower until a stage is found that is two phase only. Note: If there is a three phase stage below a stage that was found to be two phase, the three phase stage is not detected because the checking would have ended in the previous two phase stage.

HYSYS always indicates the existence of the second liquid phase. This continues until the Column reverts to VLE operation, or all applicable stages have water draws placed on them. Refer to the Section Templates for further details on the three phase capabilities in HYSYS.

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Initial Estimates Initial estimates are optional values that you provide to help the HYSYS algorithm converge to a solution. The better your estimates, the quicker HYSYS converges. There are three ways for you to provide the column with initial estimates: l l

l

Provide the estimate values when you first build the column. Go to the Profiles or Estimates page on the Parameters tab to provide the estimate values. Go to the Monitor or Specs page on the Design tab to provide values for the default specifications or add your own specifications.

It is important to remember, when the column starts to solve for the first time or after the column has been reset, the specification values are also initial estimates. So if you replaced one of the original default specifications (overhead vapor flow, side liquid draw or reflux ratio) with a new active specification, the new specification value is used as initial estimates. For this reason it is recommended you provide reasonable specification values initially even if you can replace them while the column is solving or after the column has solved. Note: Although HYSYS does not require any estimates to converge to a solution, reasonable estimates help in the convergence process.

Temperatures Temperature estimates can be given for any stage in the column, including the condenser and reboiler, using the Profiles page in the Parameters tab of the Column property view. Intermediate temperatures are estimated by linear interpolation. When large temperature changes occur across the condenser or bottom reboiler, we recommend that you provide an estimate for the top and bottom column sections in the Tower. Note: If the overhead product is a subcooled liquid, it is best to specify an estimated bubble-point temperature for the condenser rather than the subcooled temperature.

Mixing Rules at Feed Stages When a feed stream is introduced onto a stage of the column, the following sequence is employed to establish the resulting internal product streams: 1. The entire component flow (liquid and vapor phase) of the feed stream is added to the component flows of the internal vapor and liquid phases entering the stage. 2. The total enthalpy (vapor and liquid phases) of the feed stream is added to the enthalpies of the internal vapor and liquid streams entering the stage. 3. HYSYS flashes the combined mixture based on the total enthalpy at the

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stage Pressure. The results of this process produce the conditions and composition of the vapor and liquid phases leaving the stage. In most physical situations, the vapor phase of a feed stream does not come in close contact with the liquid on its feed stage. However if this is the case, the column allows you to split material inlet streams into their phase components before being fed to the column. The Split Inlets check box can be selected in the Setup page of the Flowsheet tab. You can also set all the feed streams to a column to always split, by selecting the appropriate check box in the Options page from the Simulation tab of the Session Preferences property view.

Basic Column Parameters Regardless of the type of column, the Basic Column Parameters remain at their input values during convergence.

Pressure The pressure profile in a Column Tower is calculated using your specifications. You can either explicitly enter all stage pressures or enter the top and bottom tray pressures (and any intermediate pressures) such that HYSYS can interpolate between the specified values to determine the pressure profile. Simple linear interpolation is used to calculate the pressures on stages which are not explicitly specified. You can enter the condenser and reboiler pressure drops explicitly within the appropriate operation property view. Default pressure drops for the condenser and reboiler are zero, and a non-zero value is not necessary to produce a converged solution. If the pressure of a Column product stream (including side vapor or liquid draws, side stripper bottom streams, or internal stream assignments) is set (either by specification or calculation) prior to running the Column, HYSYS “backs” this value into the column and uses this value for the convergence process. If you do specify a stream pressure that allows HYSYS to calculate the column pressure profile, it is not necessary to specify another value within the column property view. If you later change the pressure of an attached stream, the Column is rerun. Note: Recall that whenever a change is made in a stream, HYSYS checks all operations attached to that stream and recalculates as required.

Number of Column Sections The number of column sections that you specify for the Tower does not include the condenser and bottom reboiler, if present. If sidestrippers are to be added to the column, their column sections are not included in this number. By default, HYSYS numbers column sections from the top down. If you want, you

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can change the numbering scheme to bottom-up by selecting this scheme on the Connections page of the Design tab. HYSYS initially treats the column sections as being ideal. If you want your column sections to be treated as real stages, you must specify efficiencies on the Efficiencies page of the Parameters tab. Once you provide efficiencies for the column sections, even if the value you specify is 1, HYSYS treats the stages as being real.

Stream The feed stream and product stream location, conditions, and composition are treated as Basic Column Parameters during convergence.

Pressure Flow In the following sections, the pressure flow specifications presented are the recommended configurations if no other equipment, such as side strippers, side draws, heat exchanger, and so forth, are connected. Other combinations of pressure flow specifications are possible, however they can lead to less stable configurations. Regardless of the pressure flow specification configuration, when performing detailed dynamic modeling it is recommended that at least valves be added to all boundary streams. Once valves have been added, the resulting boundary streams can all be specified with pressure specifications, and, where necessary, flow controlled with flow controllers.

Absorber The basic Absorber column has two inlet and two exit streams. When used alone, the Absorber has four boundary streams and so requires four Pressure Flow specifications. A pressure specification is always required for the liquid product stream leaving the bottom of the column. A second pressure specification should be added to the vapor product of the column, with the two feed streams having flow specifications. The column below shows the recommended pressure flow specifications for a standalone absorber column.

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If there are downstream unit operations attached to the liquid product stream, then a column sump needs to be simulated. There are several methods for simulating the column sump. A simple solution is to use a reboiled absorber, with the reboiler duty stream specified as zero in place of the absorber. Another option is to feed the liquid product stream directly into a separator, and return the separator vapor product to the bottom stage of the column.

Refluxed Absorber The basic Refluxed Absorber column has a single inlet and two or three exit streams, depending on the condenser configuration. When used alone, the Refluxed Absorber has three or four boundary streams (depending on the condenser) and requires four or five pressure-flow specifications; generally two pressure and three flow specifications. A pressure specification is always required for the liquid product stream leaving the bottom of the column. The extra specification is required due to the reflux stream and is discussed in Column-Specific Operations. The column below shows the recommended pressure flow specifications for a standalone refluxed absorber with a partial condenser.

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If there are downstream unit operations attached to the liquid product stream, then a column sump needs to be simulated. There are several methods for simulating the column sump. A simple solution is to use a distillation column, with the reboiler duty stream specified as zero in place of the refluxed absorber. Another option is to feed the liquid product stream directly into a separator, and return the separator vapor product to the bottom stage of the column.

Reboiled Absorber A Reboiled Absorber column has a single inlet and two exit streams. When used alone, the Reboiled Absorber has three boundary streams and so requires three Pressure Flow specifications; one pressure and two flow specifications. A pressure specification is always required for the vapor product leaving the column. The column below shows the recommended pressure flow specifications for a standalone reboiled absorber.

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Distillation Column The basic Distillation column has one inlet and two or three exit streams, depending on the condenser configuration. When used alone, the Distillation column has three or four boundary streams but requires four or five pressure-flow specifications; generally one pressure and three or four flow specifications. The extra pressure-flow specification is required due to the reflux stream, and is discussed in Column-Specific Operations.

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The column above shows the The column below shows the recommended pressure flow spe-recommended pressure flow specifications for a standalone dis- cifications for a standalone three tillation column with a partial phase distillation column with a condenser. partial condenser.

The Three Phase Distillation column is similar to the basic Distillation column except it has three or four exit streams. So when used alone, the Three Phase Distillation column has four to five boundary streams, but requires five or six pressure-flow specifications; generally one pressure and four to five flow specifications.

Condensers and Reboilers The following sections provide some recommended pressure-flow specifications for simple dynamic modeling only. The use of flow specifications on reflux streams is not recommended for detailed modeling. If the condenser liquid level goes to zero, a mass flow specification results in a large volumetric flow because the stream is a vapor. It is highly recommended that the proper equipment be added to the reflux stream (for example pumps, valves, and so forth). In all cases, level control for the condenser should be used to ensure a proper liquid level.

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Partial Condenser The partial condenser has three exit streams: l

overhead vapor

l

reflux

l

distillate

All three exit streams must be specified when attached to the main Tower. One pressure specification is recommended for the vapor stream, and one flow specification for either of the liquid product streams. The final pressure flow specification can be a second flow specification on the remaining liquid product stream, or the Reflux Flow/Total Liquid Flow value on the Specs page of the Dynamics tab of the condenser can be specified.

Fully-Refluxed Condenser The Fully-Refluxed condenser has two exit streams: l

overhead vapor

l

reflux

A pressure specification is required for the overhead vapor stream, and a flow specification is required for the reflux stream.

Total Condenser A Total condenser has two exit streams: l

reflux

l

distillate

There are several possible configurations of pressure flow specifications for this type of condenser. A flow specification can be used for the reflux stream and a pressure flow spec can be used for the distillate stream. Two flow specifications can be used, however, it is suggested that a vessel pressure controller be setup with the condenser duty as the operating variable.

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Reboiler The Reboiler has two exit streams: l

boilup vapor

l

bottoms liquid

Only one exit stream can be specified. If a pressure constraint is specified elsewhere in the column, this exit stream must be specified with a flow rate.

Column Installation The first step in installing a Column is deciding which type you want to install. Your choice depends on the type of equipment (for example, reboilers and condensers) your Column requires. HYSYS has several basic Column templates (pre-constructed column configurations) which can be used for installing a new Column. The most basic Column types are described in the table below. Basic Column Types

Icon

Description

Absorber

Tower only.

LiquidLiquid Extractor

Tower only.

Reboiled Absorber

Tower and a bottom stage reboiler.

Refluxed Absorber

Tower and an overhead condenser.

Distillation

Tower with both a reboiler and condenser.

Three Phase Distillation

Tower, three-phase condenser, reboiler. Condenser can be either chemical or hydrocarbon specific.

There are also more complex Column types, which are described in the table below.

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Complex Column Types

Description

3 Sidestripper Crude Column

Tower, reboiler, condenser, 3 sidestrippers, and 3 corresponding pump around circuits.

4 Sidestripper Crude Column

Tower, reboiler, condenser, an uppermost reboiled sidestripper, 3 steamstripped lower sidestrippers, and 3 corresponding pump around circuits.

FCCU Main Fractionator

Tower, condenser, an upper pump around reflux circuit and product draw, a mid-column two-product-stream sidestripper, a lower pump around reflux circuit and product draw, and a quench pump around circuit at the bottom of the column.

Vacuum Reside Tower

Tower, 2 side product draws with pump around reflux circuits and a wash oil-cooled steam stripping section below the flash zone.

Input Experts Input Experts guide you through the installation of a Column. The Input Experts are available for the following six standard column templates: l

Absorber

l

Liquid-Liquid Extractor

l

Reboiled Absorber

l

Refluxed Absorber

l

Distillation

l

Three Phase Distillation

Details related to each column template are outlined in Templates. Each Input Expert contains a series of input pages whereby you must specify the required information for the page before advancing to the next one. When you have worked through all the pages, you have specified the basic information required to build your column. You are then placed in the Column property view which gives comprehensive access to most of the column features. It is not necessary to use the Input Experts to install a column. You can disable and enable the Input Experts option on the Options page in the Simulation tab of the Session Preferences property view. If you do not use the Input Experts, you move directly to the Column property view when you install a new column.

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Templates HYSYS contains a number of column templates which have been designed to simplify the installation of columns. A Column Template is a pre-constructed configuration or “blueprint” of a common type of Column, including Absorbers, Reboiled and Refluxed Absorbers, Distillation Towers, and Crude Columns. A Column Template contains the unit operations and streams that are necessary for defining the particular column type, as well as a default set of specifications. All Column templates can be accessed using the Model Palette. When you add a new Column HYSYS gives you a choice of the available templates. Simply select the template that most closely matches your column configuration, provide the necessary input in the Input Expert property view (if applicable), and HYSYS installs the equipment and streams for you in a new Column subflowsheet. Stream connections are already in place, and HYSYS provides default names for all internal streams and equipment. You can then make modifications by adding, removing or changing the names of any streams or operations to suit your specific requirements. Clicking the Side Ops button on the final page of the Column Input Expert opens the Side Operations Input Expert wizard, which guides you through the process of adding a side operation to your column. In addition to the basic Column Templates which are included with HYSYS, you can create custom Templates containing Column configurations that you commonly use.

HYSYS Column Conventions Column Towers, Overhead Condensers, and Bottom Reboilers are each defined as individual unit operations. Condensers and Reboilers are not numbered stages, as they are considered to be separate from the Tower. Note: By making the individual components of the column separate pieces of equipment, there is easier access to equipment information, as well as the streams connecting them.

The following are some of the conventions, definitions, and descriptions of the basic columns: Column Component

Description

Tower

A HYSYS unit operation that represents the series of equilibrium stages in a Column.

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Column Component

Description

Stages

Stages are numbered from the top down or from the bottom up, depending on your preference. The top stage is 1, and the bottom stage is N for the top-down numbering scheme. The stage numbering preference can be selected on the Connections page of the Design tab on the Column property view.

Overhead Vapor Product

The overhead vapor product is the vapor leaving the top stage of the Tower in simple Absorbers and Reboiled Absorbers. In Refluxed Absorbers and Distillation Towers, the overhead vapor product is the vapor leaving the Condenser.

Overhead Liquid Product

The overhead liquid product is the Distillate leaving the Condenser in Refluxed Absorbers and Distillation Towers. There is no top liquid product in simple Absorbers and Reboiled Absorbers.

Bottom Liquid Product

The bottom liquid product is the liquid leaving the bottom stage of the Tower in simple Absorbers and Refluxed Absorbers. In Reboiled Absorbers and Distillation Columns, the bottom liquid product is the liquid leaving the Reboiler.

Overhead Condenser

An Overhead Condenser represents a combined Cooler and separation stage, and is not given a stage number.

Bottom Reboiler

A Bottom Reboiler represents a combined heater and separation stage, and is not given a stage number.

Default Replaceable Specifications Replaceable specifications are the values which the Column convergence algorithm is trying to meet. When you select a particular Column template or as you add side equipment, HYSYS creates default specifications. You can use the specifications that HYSYS provides or replace these specifications with others more suited to your requirements. The available default replaceable specifications are dependent on the Basic Column type (template) that you have chosen. The default specifications for the four basic column templates are combinations of the following: l

Overhead vapor flowrate

l

Distillate flowrate

l

Bottoms flowrate

l

Reflux ratio

l

Reflux rate

Note: The specifications in HYSYS can be set as specifications or changed to estimates.

The provided templates contain only pre-named internal streams (streams which are both a feed and product). For instance, the Reflux stream, which is named by HYSYS, is a product from the Condenser and a feed to the top stage of the Tower.

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Note: The pressure for a Tower column section, condenser, or reboiler can be specified at any time on the Pressures page of the Column property view.

In the following schematics, you specify the feed and product streams, including duty streams.

Absorber Template The only unit operation contained in the Absorber is the Tower, and the only streams are the overhead vapor and bottom liquid products. The following is a schematic representation of the Absorber:

There are no available specifications for the Absorber, which is the base case for all tower configurations. The conditions and composition of the column feed stream, as well as the operating pressure, define the resulting converged solution. The converged solution includes the conditions and composition of the vapor and liquid product streams. Note: The Liquid-Liquid Extraction Template is identical to the Absorber Template. Note: The remaining Column templates have additional equipment, thus increasing the number of required specifications.

Reboiled Absorber Template The Reboiled Absorber template consists of a Tower and a bottom reboiler. Two additional streams connecting the Reboiler to the Tower are also included in the template. Figure 2.11

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When you install a Reboiled Absorber (in other words, add only a Reboiler to the Tower), you increase the number of required specifications by one over the Base Case. As there is no overhead liquid, the default specification in this case is the overhead vapor flow rate. Note: The Column Input Expert for Reboiled Absorber offers advanced pre-configurations for the reboiler including the HYSYS Shell and Tube Heat Exchanger. See the Reboiled Absorber section of the Aspen HYSYS online help for updated information on these functions.

Refluxed Absorber Template The Refluxed Absorber template contains a Tower and an overhead Condenser (partial or total). Additional material streams associated with the Condenser are also included in the template. For example, the vapor entering the Condenser from the top stage is named to Condenser by default, and the liquid returning to the Tower is the Reflux. Figure 2.12

When you install a Refluxed Absorber, you are adding only a Condenser to the base case. Specifying a partial condenser increases the number of required specifications by two over the Base Case. The default specifications are the overhead vapor flow rate, and the side liquid (Distillate) draw. Specifying a total condenser results in only one available specification, since there is no overhead vapor product. Either of the overhead vapor or distillate flow rates can be specified as zero, which creates three possible combinations for these two specifications. Each combination defines a different set of operating conditions. The three possible Refluxed Absorber configurations are listed below: l

Partial condenser with vapor overhead but no side liquid (distillate) draw.

l

Partial condenser with both vapor overhead and distillate draws.

l

Total condenser with distillate but no vapor overhead draw.

Distillation Template If you select the Distillation template, HYSYS creates a Column with both a Reboiler and Condenser. The equipment and streams in the Distillation tem-

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plate are therefore a combination of the Reboiled Absorber and Refluxed Absorber Templates Figure 2.13

Note: The Column Input Expert for the Distillation column offers advanced pre-configurations for the reboiler including the HYSYS Shell and Tube Heat Exchanger. Refer to Column Property View for further details.

Reflux Ratio The number of specifications for a column with both a Reboiler and Condenser depends on the condenser type. For a partial condenser, you must specify three specifications. For a total condenser, you must specify two specifications. The third default specification (in addition to Overhead Vapor Flow Rate and Side Liquid Draw) is the Reflux Ratio. (1) The Reflux Ratio is defined as the ratio of the liquid returning to the Tower divided by the total flow of the products (see the figure above). If a water draw is present, its flow is not included in the ratio. As with the Refluxed Absorber, the Distillation template can have either a Partial or Total Condenser. Choosing a Partial Condenser results in three replaceable specifications, while a Total Condenser results in two replaceable specifications. The pressure in the tower is, in essence, a replaceable specification, in that you can change the pressure for any stage from the Column property view. Note: The pressure remains fixed during the Column calculations.

The following table gives a summary of replaceable column (default) specifications for the basic column templates. Templates Reboiled Absorber

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Vapor Draw

Distillate Draw

Reflux Ratio

X

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Templates

Vapor Draw

Distillate Draw

Reflux Ratio

Refluxed Absorber Total Condenser Partial Condenser

X X

X

Distillation Total Condenser Partial Condenser

X

X

X

X

X

Three Phase Distillation Template If you select the Three Phase Distillation template, HYSYS creates a Column based on a three phase column model. Note: The same standard column types exist for a three phase system that are available for the “normal” two phase (binary) systems.

Using the Three Phase Column Input Expert, the initial property view allows you to select from the following options: l

Distillation

l

Refluxed Absorber

l

Reboiled Absorber

l

Absorber

Each choice builds the appropriate column based on their respective standard (two phase) system templates. If the Input Expert is turned off, installing a Three Phase column template opens a default Column property view for a Distillation type column equipped with a Reboiler and Condenser. The key difference between using the standard column templates and their three phase counterparts lies in the solver that is used. The default solver for three phase columns is the “Sparse Continuation” solver which is an advanced solver designed to handle three phase, non-ideal chemical systems, that other solvers cannot. When using the Three Phase Column Input Expert some additional specifications can be required when compared with the standard (binary system) column setups. Clicking the Side Ops button on the final page of the Three Phase Column Input Expert opens the Side Operations Input Expert wizard, which guides you through the process of adding a side operation to your column.

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Column Specification Types This section outlines the various Column specification (spec) types available along with their relevant details. Specs are added and modified on the Specs Page or the Monitor Page of the Design tab. Adding and changing Column specifications is straightforward. If you have created a Column based on one of the templates, HYSYS already has default specifications in place. The type of default specification depends on which of the templates you have chosen.

Cold Property Specifications

Cold Property

Description

Flash Point

Allows you to specify the Flash Point temperature (ASTM D93 flash point temperature closed cup) for the liquid or Vapor flow on any stage in the column.

Pour Point

Allows you to specify the ASTM Pour Point temperature for the liquid or Vapor flow on any stage in the column.

RON

Allows you to specify the Research Octane Number for the liquid or Vapor flow on any stage.

Component Flow Rate The flow rate (molar, mass or volume) of any component, or the total flow rate for any set of components, can be specified for the flow leaving any stage. If a side liquid or Vapor draw is present on the selected stage, these are included with the internal Vapor and liquid flows.

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Component Fractions The mole, mass or volume fraction can be specified in the liquid or Vapor phase for any stage. You can specify a value for any individual component, or specify a value for the sum of the mole fractions of multiple components.

Component Ratio The ratio (molar, mass or volume fraction) of any set of components over any other set of components can be specified for the liquid or Vapor phase on any stage.

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Component Recovery Component recovery is the molar, mass or volume flow of a component (or group of components) in any internal or product stream draw divided by the flow of that component (or group) in the combined tower feeds. As the recovery is a ratio between two flows, you specify a fractional value.

Cut Point This option allows a cut point temperature to be specified for the liquid or Vapor leaving any stage. The types are TBP, ASTM D86, D1160 Vac, D1160 ATM, and ASTM D2887. For D86, you are given the option to use ASTM Cracking Factor. For D1160, you are given an Atmospheric Pressure option. The cut point can be on a mole, mass or volume fraction basis, and any value from 0 to 100 percent is allowed.

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Note: While initial and final cut points are permitted, it is often better to use 5 and 95 percent cut points to minimize the errors introduced at the extreme ends of boiling point curves.

Draw Rate The molar, mass or volume flowrate of any product stream draw can be specified.

Delta T (Heater/Cooler) The temperature difference across a Heater or Cooler unit operation can be specified. The Heater/Cooler unit must be installed in the Column subflowsheet, and the HYSIM Inside-Out, Modified HYSIM Inside-Out or Sparse Continuation solving methods must be selected on the Solver page of the Parameters tab.

Delta T (Streams) The temperature difference between two Column subflowsheet streams can be specified.

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Duty You can specify the duty for an energy stream.

Duty Ratio You can specify the duty ratio for any two energy streams. In addition to Column feed duties, the choice of energy streams also includes pump around duties (if available).

Feed Ratio The Feed Ratio option allows you to establish a ratio between the flow rate on or from any stage in the column, and the external feed to a stage. You are prompted for the stage, flow type (Vapor, Liquid, Draw), and the external feed stage.

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Note: This type of specification is useful for turn down or overflash of a crude feed.

Gap Cut Point The Gap Cut Point is defined as the temperature difference between a cut point (Cut Point A) for the liquid or Vapor leaving one stage, and a cut point (Cut Point B) on a different stage.

Note: This specification is best used in combination with at least one flow specification; using this specification with a Temperature specification can produce non-unique solutions.

You have a choice of specifying the distillation curve to be used: l

TBP

l

ASTM D86

l

D1160 Vac

l

D1160 ATM

l

ASTM D2887

You can define Cut Point A and Cut Point B, which together must total 100%. The cut points can be on a mole, mass or volume basis.

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Liquid Flow The net molar, mass or volume liquid (Light or Heavy) flow can be specified for any stage.

Physical Property Specifications The mass density can be specified for the liquid or Vapor on any stage.

Pump Around Specifications

Specification

Description

Flow Rate

The flow rate of the Pump Around can be specified in molar, mass, or liquid volume units.

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Specification

Description

Temperature Drop

Allows you to specify the temperature drop across a Pump Around exchanger. The conditions for using this specification are the same as that stated for the Pump Around return temperature.

Return Temperature

The return temperature of a Pump Around stream can be specified. Ensure that you have not also specified both the pump around rate and the duty. This would result in the three associated variables (flow rate, side exchanger duty, and temperature) all specified, leaving HYSYS with nothing to vary in search of a converged solution.

Duty

You can specify the duty for any Pump Around.

Return Vapor Fraction

You can specify the return Vapor fraction for any Pump Around.

Duty Ratio

To specify a Pump Around duty ratio for a Column specification, add a Column Duty Ratio spec instead, and select the Pump Around energy streams to define the duty ratio.

Note: The Pump Around Rate, as well as the Pump Around Temperature Drop are the default specifications HYSYS requests when a pump around is added to the column.

Reboil Ratio You can specify the molar, mass or volume ratio of the Vapor leaving a specific stage to the liquid leaving that stage.

Recovery The Recovery spec is the recovery of the total feed flow in the defined outlet streams (value range between 0 and 1). (1)

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Reflux Feed Ratio The Reflux Feed Ratio spec is the fraction of the reflux flow divided by the reference flow for the specified stage and phase. (1)

Reflux Fraction Ratio The Reflux Fraction Ratio spec is the fraction or % of liquid that is being refluxed on the specified stage (value range between 0 and 1).

Reflux Ratio The Reflux Ratio is the molar, mass or volume flow of liquid (Light or Heavy) leaving a stage, divided by the sum of the vapor flow from the stage plus any side liquid flow.

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The Reflux Ratio specification is normally used only for top stage condensers, but it can be specified for any stage. For a Partial Condenser: l

Selecting the Include Vapor check box, gives the following equation for the reflux ratio: (1)

l

Clearing the Include Vapor check box, gives the following equation for the reflux ratio: (2)

where: R = liquid reflux to column V = vapor product D = distillate product

Stream Property To be able to add a specification to a stream: l

l

The Modified HYSIM Inside-out solving method must be chosen for the solver. The stream must be a draw stream.

Note: Only one stream specification can be created per draw stream.

See Column Stream Specifications for more information.

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Tee Split Fraction The split fraction for a Tee operation product stream can be specified. The Tee must be installed within the Column subflowsheet and directly attached to the column, for example, to a draw stream, in a pump around circuit, and so forth. Also, the Modified HYSIM Inside-Out solving method must be selected. Tee split fraction specifications are automatically installed as you install the tee operation in the Column subflowsheet; however, you can select which specifications become active on the Monitor page or Specs page. Changes made to the split fraction specification value are updated on the Splits page of the tee operation.

Tray Temperature The temperature of any stage can be specified.

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Transport Property Specifications The viscosity, surface tension or thermal conductivity can be specified for the liquid leaving any stage. The viscosity or thermal conductivity can be specified for the vapor leaving any stage. A reference temperature must also be given. Note: The computing time required to satisfy a Vapor viscosity specification can be considerably longer than that needed to meet a liquid viscosity specification.

User Property A User Property value can be specified for the flow leaving any stage. You can choose any installed user property in the flowsheet, and specify its value. The basis used in the installation of the user property is used in the spec calculations.

Vapor Flow The net molar, mass or volume vapor flow can be specified for any stage. Feeds and draws to that tray are taken into account.

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Vapor Fraction The vapor fraction of a stream exiting a stage can be specified.

Vapor Pressure Specifications

Two types of vapor pressure specifications are available: l

True vapor pressure (@100 °F)

l

Reid vapor pressure.

Vapor Type

Description

Vapor Pressure

The true Vapor pressure at 100 °F can be specified for the Vapor or liquid leaving any stage.

Reid Vapor Pressure

Reid Vapor pressure can be specified for the Vapor or liquid leaving any stage. The specification must always be given in absolute pressure units.

Column Stream Specifications Column stream specifications must be created in the Column subflowsheet. Unlike other specifications, the stream specification is created through the stream’s property view, and not the Column Runner Specs page. To be able to add a specification to a stream: l

The Modified HYSIM Inside-out solving method must be chosen for the solver. Note: Only one stream specification can be created per draw stream.

l

The stream must be a draw stream.

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The Create Column Stream Spec button on the Conditions page of the Worksheet tab is available only on Stream property views within the Column subflowsheet. When you click on the Create Column Stream Spec button, the Stream Spec property view appears. l

l

l

For draw streams from a separation stage (Tower, condenser, or reboiler) only a stream temperature specification can be set. For a non-separation stage streams (from pumps, heaters, and so forth) either a temperature or a vapor fraction specification can be set. For any given stage, only one draw stream specification can be active at any given time. Note: Creating a new stream specification for a stage, or activating a specification automatically deactivates all other existing draw stream specifications for that stage.

Once a specification is added for a stream, the button on the Conditions page of the Worksheet tab changes from Create Column Stream Spec to View Column Stream Spec, and can be clicked to view the Stream Specification property view. Note: You can only add Column Stream Specifications via the Stream property view of a draw stream within the Column subflowsheet.

Column-Specific Operations To install unit operations in a Column subflowsheet, press F4 or F12 to access the Model Palette. The unit operations available within the Column subflowsheet are listed in the following table. Operation Category

Types

Vessels

3-Phase Condenser, Partial Condenser, Reboiler, Separator, Total Condenser, Tower

Heat Transfer Equipment

Cooler, Heater, Heat Exchanger

Rotating Equipment

Pump

Piping Equipment

Valve

Logicals

Balance, Digital Pt, PID Controller, Selector Block, Transfer Function Block

Most operations shown here are identical to those available in the main flowsheet in terms of specified and calculated information, property view structure, and so forth.

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Note: Only the operations which are applicable to a Column operations are available within the Column subflowsheet.

There are also additional unit operations which are not available in the main flowsheet. They are: l

Condenser (Partial, Total, 3-Phase)

l

Reboiler

l

Tower

The Bypasses and Side Operations (side strippers, pump arounds, and so forth) are available on the Side Ops page of the Column property view. Note: You can open a property view of the Column PFD from the main build environment. This PFD only provides you with the ability to modify stream and operation parameters. You cannot add and delete operations or break stream connections. These tasks can only be performed in the Column subflowsheet environment.

Condenser Unit Operation The Condenser is used to condense vapor by removing its latent heat with a coolant. In HYSYS, the condenser is used only in the Column Environment, and is generally associated with a Column Tower There are four types of Condensers: Condenser Type

Description

Partial

Feed is partially condensed; there are vapor and liquid product streams. The Partial Condenser can be operated as a total condenser by specifying the vapor stream to have zero flowrate. The Partial Condenser can be used as a Total Condenser simply by specifying the vapor flowrate to be zero.

Total

Feed is completely condensed; there is a liquid product only.

Three-Phase - Chemical

There are two liquid product streams and one vapor product stream.

Three-Phase - Hydrocarbon

There is a liquid product streams and a water product stream and one vapor product stream.

When you add a Column to the simulation using a pre-defined template, there can be a condenser attached to the tower (for example, in the case of a Distillation Column). To add a Condenser: l

In the Column environment, press F4 or F12 and select a Condenser icon from the Column Palette.

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The Condenser property view uses a Type drop-down list, which lets you switch between condenser types without having to delete and re-install a new piece of equipment. When you switch between the condenser types, the pages change appropriately. For example, the Connections page for the Total Condenser does not show the vapor stream. If you switch from the Partial to Total Condenser, the vapor stream is disconnected. If you then switch back, you have to reconnect the stream. The Condenser property view has the same basic five tabs that are available on any unit operation: l

Design

l

Rating

l

Worksheet

l

Performance

l

Dynamics

It is necessary to specify the connections and the parameters for the Condenser. The information on the Dynamics tab are not relevant in steady state.

Condenser Design Tab The Design tab contains options to configure the Condenser.

Condenser Connections Page On the Connections page, you can specify the operation name, as well as the feed(s), vapor, water, reflux, product, and energy streams. The Connections page shows only the product streams, which are appropriate for the selected condenser. For example, the Total Condenser does not have a vapor stream, as the entire feed is liquefied. Neither the Partial nor the Total Condenser has a water stream. The Condenser is typically used with a Tower, where the vapor from the top stage of the column is the feed to the condenser, and the reflux from the condenser is returned to the top stage of the column.

Condenser Parameters Page The condenser parameters that can be specified are: l

Pressure Drop

l

Duty

l

Subcooling Data

Note: It is better to use a duty spec than specifying the heat flow of the duty stream.

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Pressure Drop The Pressure Drop across the condenser (Delta P) is zero by default. It is defined in the following expression: (1) where: P = vessel pressure Pv = pressure of vapor product stream Pl = pressure of liquid product stream Pfeed = pressure of feed stream to condenser ΔP = pressure drop in vessel (Delta P) Note: You typically specify a pressure for the condenser during the column setup, in which case the pressure of the top stage is the calculated value.

Duty The Duty for the energy stream can be specified here, but this is better done as a column spec (defined on the Monitor page or Specs page of the Column property view). This allows for more flexibility when adjusting specifications, and also introduces a tolerance. Note: If you specify the duty, it is equivalent to installing a duty spec, and a degree of freedom is used.

The Duty should be positive, indicating that energy is being removed from the Condenser feed. The steady state condenser energy balance is defined as: (2) where: Hfeed = heat flow of the feed stream to the condenser Hvapor = heat flow of the vapor product stream Hliquid = heat flow of the liquid product stream(s)

SubCooling In some instances, you want to specify Condenser SubCooling. In this situation, either the Degrees of SubCooling or the SubCooled Temperature can be specified. If one of these fields is set, the other is calculated automatically. Note: In steady state, SubCooling applies only to the Total Condenser. There is no SubCooling in dynamics.

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Condenser Estimate Page On the Estimate page, you can estimate the flows and phase compositions of the streams exiting the Condenser. You can enter any value for fractional compositions, and click the Normalize Composition button to have HYSYS normalize the values such that the total equals 1. This button is useful when many components are available, but you want to specify compositions for only a few. HYSYS also specifies any compositions as zero. HYSYS re-calculates the phase composition estimates when you click the Update Comp. Est. button. Clicking this button also removes any of the estimated values you entered for the phase composition estimates. Click the Clear Comp. Est. button to clear the phase compositions estimated by HYSYS. This button does not remove any estimate values you entered. You can clear the all estimate values by clicking the Clear All Comp. Est. button.

Condenser User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Condenser Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Condenser Rating Tab The Rating tab contains options that are applicable in both Steady State and Dynamics mode.

Condenser Sizing Page The Sizing page contains all the required information for correctly sizing the condenser. You can select either vertical or horizontal orientation, and cylinder or sphere. You can either enter the volume or dimensions for your condenser. You can also indicate whether or not the condenser has a boot associated with it. If it does, then you can specify the boot dimensions.

Condenser Nozzles Page The Nozzles page contains information regarding the elevation and diameter of the nozzles. The information provided in the Nozzles page is applicable only in Dynamic mode.

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Condenser Heat Loss Page The Heat Loss page allows you to specify the heat loss from individual sections in the Tower. You can choose either a Direct Q, Simple, or Detailed heat loss model or no heat loss from the Heat Loss Mode group.

Direct Q Heat Loss Model The Direct Q model allows you to either specify the heat loss directly, or have the heat loss calculated from the Heat Flow for the condenser.

Simple Heat Loss Model The Simple model allows you to calculate the heat loss from these specified values: l

Overall U value

l

Ambient Temperature

Detailed Heat Loss Model The Detailed model allows you to specify more detailed heat transfer parameters.

Condenser Level Taps page The information on this page is relevant only to dynamics cases. Since the contents in a vessel can be distributed in different phases, the Level Taps page lets you monitor the level of liquid and aqueous contents that coexist within a specified zone in a tank or separator. Level Tap

Name of the level tap

PV High (m)

Upper limit to be monitored. (Meters)

PV Low (m)

Lower limit to be monitored. (Meters)

OP High

Upper limit of the output of the normalization scale

OP Low

Lower limit of the output of the normalization scale

The normalization scale can be expressed in negative values. In some cases, the output normalization scale is manually set between -7% to 100% or -15%100% so that there is a cushion range before the level of the content becomes unacceptable (i.e., too low, or too high). By default, a new level tap is set to the total height of the vessel, and the height is normalized in percentage (100-0). All the upper limit specifications should not be smaller than or equal to the lower limit specifications and vice versa; otherwise no calculations will be performed. In the Calculated Level Taps Values (Dynamics) group, the level of liquid and aqueous are displayed in terms of the output normalization scale you specified.

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Whenever the level of a content exceeds PV High, HYSYS automatically outputs the OP High value as the level of that content. If the level is below the PV Low, HYSYS outputs the OP Low value. The levels displayed are always entrained within the normalized zone.

Condenser Options Page Use this page to specify the PV Work Term Contribution in percent. It is approximately the isentropic efficiency. A high PV work term contribution value results in lower pressures and temperatures. The PV work term contribution value should be between 87% to 98%. Use the check box to enable or disable the factor.

Condenser Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the Condenser. Note: The PF Specs page is relevant to dynamics cases only.

Condenser Performance Tab The Performance tab has the following pages: l

Plots

l

Tables

l

SetUp

From these pages you can select the type of variables you want to calculate and plot, view the calculated values, and plot any combination of the selected variables. The default selected variables are temperature, pressure, heat flow, enthalpy, and vapor fraction. At the bottom of the Plots or Tables page, you can specify the interval size over which the values should be calculated and plotted. (The same instructions apply to the Reboiler operation.) Note: In steady state, the displayed plots are all straight lines. Only in Dynamic mode, when the concept of zones is applicable, do the plots show variance across the vessels.

Plots Page This page lets you view results for the unit operation displayed in plot format. l

l

From the X Variable drop-down list, select the variable you want to use for the x-axis. From the Y Variable drop-down list, select the variable you want to use for the y-axis.

Tip: Right-click anywhere within the plot area to access the plot’s object inspection menu. Note: Use the Performance > Setup Page to determine number of plot points (intervals) and the variables that may be read into the X or Y axis of the Plot. The page lists all available variables in the simulation, and lets you select which ones to use within the plot.

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The same instructions apply to the Reboiler operation.

Tables Page This page lets you view results for the unit operation displayed in table format. Use the Phase Viewing Options to selectively examine results for a particular phase or phases. Note: Use the Performance > Setup Page to determine number of plot points (intervals) and the variables that may be read into the X or Y axis of the Plot. The page lists all available variables in the simulation, and lets you select which ones to use within the plot.

The same instructions apply to the Reboiler operation.

Plots Setup Page Use the Performance - Setup Page to determine number of plot points (intervals) and the variables that may be read into the X or Y axis of the Plot. The page lists all available variables in the simulation, and lets you select which ones to use within the plot. The table below describes the options for the heat curve. Curve Option

Description

Intervals

Number of points on the plot

Dew/Bubble Pts

Include or exclude dew/bubble points in the curves

Step Type

Set the points on the plot to be based on equal temperature or equal enthalpy intervals

Pressure Profile

Set heat curves to be calculated at a specific constant pressure independent of the feed or product pressures. Specify Linear, Inlet Pressure, or Outlet Pressure.

Properties Selection Windows Use the arrow buttons to add or remove calculated variables from the results set. You can single select, drag a series to group select, or hold down the Ctrl key to create a multiple selection of individual variables. Once selected, click the Add arrow to add them to the Selected Viewing variables list. The same instructions apply to the Reboiler operation.

Condenser Dynamics Tab The Dynamics tab contains the following pages: l

Specs

l

Holdup

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l

StripChart

l

Heat Exchanger

You are not required to modify information on the Dynamics tab when working in Steady State mode.

Condenser Dynamics Specs Page The Specs page contains information regarding initialization modes, condenser geometry, and condenser dynamic specifications.

Model Details In the Model Details group, you can specify the initial composition and amount of liquid that the separator should start with when you start dynamics. This is done via the initialization mode which is discussed in the table below. Initialization Mode

Description

Initialize from Products

The composition of the holdup is calculated from a weighted average of all products exiting the holdup. A PT flash is performed to determine other holdup conditions. The liquid level is set to the value indicated in the Liq Volume Percent field.

Dry Startup

The composition of the holdup is calculated from a weighted average of all feeds entering the holdup. A PT flash is performed to determine other holdup conditions. The liquid level in the Liq Volume Percent field is set to zero.

Initialize from User

The composition of the liquid holdup in the condenser is user specified. The molar composition of the liquid holdup can be specified by clicking the Init Holdup button. The liquid level is set to the value indicated in the Liq Volume Percent field.

Note: The Initialization Mode can be changed any time when the integrator is not running. The changes cause the vessel to re-initialize when the integrator is started again.

The condenser geometry can be specified in the Model Details group. The following condenser geometry parameters can be specified in the same manner as the Geometry group on Sizing page of the Rating tab: l

Volume

l

Diameter

l

Height (Length)

l

Geometry (Level Calculator)

The Liquid Volume Percent value is also displayed in this group. You can modify the level in the condenser at any time. HYSYS then uses that level as an initial value when the integrator is run.

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The Fraction Calculator determines how the level in the condenser and the elevation and diameter of the nozzle affects the product composition. There is only one Fraction Calculation mode available, it is called Use Levels and Nozzles. The calculations are based on how the nozzle location and vessel liquid level affect the product composition.

Dynamic Specifications The Dynamic Specifications group contains fields, where you can specify what happens to the pressure and reflux ratio of the condenser when you enter dynamic mode. The Fixed Pressure Delta P field allows you to impose a fixed pressure drop between the vessel and all of the feed streams. This is mostly supported for compatibility with Steady State mode. In Dynamic mode, you are advised to properly account for all pressure losses by using the appropriate equipment such as valves or pumps or static head contributions. A zero pressure drop should preferably be used here otherwise you may get unrealistic results such as material flowing from a low to a high pressure area. The Fixed Vessel Pressure field allows you to fix the vessel pressure in Dynamic mode. This option can be used in simpler models where you do not want to configure pressure controllers and others, or if the vessel is open to the atmosphere. In general the specification should not be used, because the pressure should be determined by the surrounding equipment. The Reflux Flow/Total Liquid Flow field provides you with a simple reflux ratio control option, and the ratio determines the reflux flow rate divided by the sum of the reflux and distillate flow rates. Note: This option allows you to set up simple models without having to add the valves, pumps, and controller that would normally be present. This option does not always give desirable results under all conditions such as very low levels or reversal of some of the streams.

The Add/Configure Level Controller button installs a level controller on the distillate (liquid) outlet stream if one is not already present. If this stream has a valve immediately downstream of the vessel, the controller is configured to control the valve rather than the stream directly. In any case, the controller is configured with some basic tuning parameters, but you can adjust those. The default tuning values are as follows: l

Kp = 1.8

l

Ti = 4 * Residence time / Kp

Condenser Holdup Page The Holdup page contains information regarding the properties, composition, and amount of the holdup.

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The Levels group displays the following variables for each of the phases available in the vessel: l

Level. Height location of the phase in the vessel.

l

Percent Level. Percentage value location of the phase in the vessel.

l

Volume. Amount of space occupied by the phase in the vessel.

Condenser StripChart Page The Stripchart page allows you to select and create default strip charts containing various variable associated to the operation.

Condenser Heat Exchanger Page The Heat Exchanger page opens a list of available heating methods for the unit operation. This page contains different objects depending on which configuration you select. l

l

l

If you select the None radio button, this page is blank and the Condenser has no cooling source. If you select the Duty radio button, this page contains the standard cooling parameters and you have to specify an energy stream for the Condenser. If you select the Tube Bundle radio button, this page contains the parameters used to configure a kettle chiller and you have to specify the required material streams for the kettle chiller. Note: The Tube Bundle options are only available in Dynamics mode. Note: If you switch from Duty option or Tube Bundle option to None option, HYSYS automatically disconnects the energy or material streams associated to the Duty or Tube Bundle options.

Duty Radio Button When the Duty radio button is selected, the following heat transfer options are available.

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The Heater Type group has two radio buttons: Gas Heater. When you select this radio button, the duty is linearly reduced so that it is zero at liquid percent level of 100%, unchanged at liquid percent level of 50%, and doubled at liquid percent level of 0%. The following equation is used: (3) where: Q = total heat applied to the holdup L= liquid percent level QTotal = duty calculated from the duty source The heat applied to the Condenser operation directly varies with the surface area of vapor contacting the vessel wall.

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Note: The Gas Heater method is available only for condensers, because the heat transfer in the Condenser depends more on the surface area of the vapor contacting the cooling coils than the liquid.

Vessel Heater. When you select this radio button, 100% of the duty specified or calculated in the SP cell is applied to the vessel’s holdup. That is: (4) where: Q = total heat applied to the holdup QTotal = duty calculated from the duty source Note: The Vessel Heater method is a non-scaling method.

The Duty Source group has two radio buttons: l

Direct Q

l

From Utility

When you select the Direct Q radio button, the Direct Q Data group appears. The following table describes the purpose of each object in the group. Object

Description

SP

The heat flow value in this cell is the same value specified in the Duty field on the Parameters page of the Design tab. Any changes made in this cell are reflected on the Duty field on the Parameters page of the Design tab.

Min. Available

Allows you to specify the minimum amount of heat flow.

Max. Available

Allows you to specify the maximum amount of heat flow.

When you select the From Utility radio button, the Utility Flow Properties group appears.

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In the cells: l

l

l

Black text indicates that the value is calculated by HYSYS and cannot be changed. Blue text indicates that the value is entered by you, and you can change the value. Red text indicates that the value is calculated by HYSYS, and you can change the value.

The following table describes the purpose of each object that appears when the From Utility radio button is selected. Utility Flow Property

Description

Heat Flow

Displays the heat flow value.

UA

Displays the overall heat transfer coefficient.

Holdup

Displays the amount of holdup fluid in the condenser.

Flow

Displays the amount of fluid flowing out of the condenser.

Min. Flow

Displays the minimum amount of fluid flowing out of the condenser.

Max. Flow

Displays the maximum amount of fluid flowing out of the condenser.

Heat Capacity

Displays the heat capacity of the fluid.

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Utility Flow Property

Description

Inlet Temp.

Displays the temperature of the stream flowing into the condenser.

Outlet Temp.

Displays the temperature of the stream flowing out of the condenser.

Temp Approach

Displays the value of the operation outlet temperature minus the outlet temperature of the Utility Fluid. It is only used when one initializes the duty valve via the Initialize Duty Valve button.

Initialize Duty Valve

Allows you to initialize the UA, flow, and outlet temperature to be consistent with the duty for purposes of control.

Reboiler Unit Operation If you choose a Reboiled Absorber or a Distillation column template, it includes a Reboiler which is connected to the bottom stage in the Tower with the streams to reboiler and boilup. The Reboiler is a column operation, where the liquid from the bottom stage of the column is the feed to the reboiler, and the boilup from the reboiler is returned to the bottom stage of the column. The Reboiler is used to partially or completely vaporize liquid feed streams. You must be in a Column subflowsheet to install the Reboiler. To install the Reboiler operation: l

In the Column environment, press F4 or F12 and select the Reboiler icon from the Column Palette.

It is necessary to specify the connections, and the parameters for the Reboiler. The information on the Dynamics tab are not relevant in steady state.

Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

User Variables

l

Notes

Reboiler Connections Page On the Connections page, you must specify the Reboiler name, as well as the feed(s), boilup, vapor draw, energy, and bottoms product streams. The vapor

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draw stream is optional.

Reboiler Parameters Page On the Parameter page, you can specify the pressure drop and energy used by the Reboiler. The pressure drop across the Reboiler is zero by default. The Duty for the energy Stream should be positive, indicating that energy is being added to the Reboiler feed(s). If you specify the duty, a degree of freedom is used. Note: It is recommended to define a duty specification on the Monitor page or Specs page of the Column property view, instead of specifying a value for the duty stream.

The steady state reboiler energy balance is defined as: (1) where: Hfeed = heat flow of the feed stream to the reboiler Hvapor = heat flow of the vapor draw stream Hbottoms = heat flow of the bottoms product stream Hboilup = heat flow of the boilup stream

Reboiler User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Reboiler Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Reboiler Rating Tab The Rating tab contains the following pages: l

Sizing

l

Nozzles

l

Heat Loss

l

Level Taps

l

Options

Note: The Rating tab for a Reboiler is the same as the Rating tab for the Condenser.

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Reboiler Sizing Page The Sizing page contains all the required information for correctly sizing the reboiler. You can select either vertical or horizontal orientation, and cylinder or sphere. You can either enter the volume or dimensions for your reboiler. You can also indicate whether or not the reboiler has a boot associated with it. If it does, you can specify the boot dimensions.

Reboiler Nozzles Page The Nozzles page contains information regarding the elevation and diameter of the nozzles. The information provided in the Nozzles page is applicable only in Dynamic mode.

Reboiler Heat Loss Page The Heat Loss page allows you to specify the heat loss from individual sections in the Tower. You can choose either a Direct Q, Simple or Detailed heat loss model or no heat loss from the Heat Loss Mode group.

Direct Q Heat Loss Model The Direct Q model allows you to either specify the heat loss directly, or have the heat loss calculated from the Heat Flow for the reboiler.

Simple Heat Loss Model The Simple model allows you to calculate the heat loss from these specified values: l

Overall U value

l

Ambient Temperature

Detailed Heat Loss Model The Detailed model allows you to specify more detailed heat transfer parameters.

Reboiler Level Taps page The information on this page is relevant only to dynamics cases. Since the contents in a vessel can be distributed in different phases, the Level Taps page lets you monitor the level of liquid and aqueous contents that coexist within a specified zone in a tank or separator.

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Level Tap

Name of the level tap

PV High (m)

Upper limit to be monitored. (Meters)

PV Low (m)

Lower limit to be monitored. (Meters)

OP High

Upper limit of the output of the normalization scale

OP Low

Lower limit of the output of the normalization scale

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The normalization scale can be expressed in negative values. In some cases, the output normalization scale is manually set between -7% to 100% or -15%100% so that there is a cushion range before the level of the content becomes unacceptable (i.e., too low, or too high). By default, a new level tap is set to the total height of the vessel, and the height is normalized in percentage (100-0). All the upper limit specifications should not be smaller than or equal to the lower limit specifications and vice versa; otherwise no calculations will be performed. In the Calculated Level Taps Values (Dynamics) group, the level of liquid and aqueous are displayed in terms of the output normalization scale you specified. Whenever the level of a content exceeds PV High, HYSYS automatically outputs the OP High value as the level of that content. If the level is below the PV Low, HYSYS outputs the OP Low value. The levels displayed are always entrained within the normalized zone.

Reboiler Options Page Use this page to specify the PV Work Term Contribution in percent. It is approximately the isentropic efficiency. A high PV work term contribution value results in lower pressures and temperatures. The PV work term contribution value should be between 87% to 98%. Use the check box to enable or disable the factor.

Reboiler Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the Reboiler. Note: The PF Specs page is relevant to dynamics cases only.

Reboiler Performance Tab The Performance tab of the Reboiler has the same pages as the Performance tab of the Condenser. Click on a page for instructions: l

Plots

l

Tables

l

Setup

From these pages you can select the type of variables you want to calculate and plot, view the calculated values, and plot any combination of the selected variables. The default selected variables are temperature, pressure, heat flow, enthalpy, and vapor fraction. At the bottom of the Plots or Tables page, you can specify the interval size over which the values should be calculated and plotted.

Reboiler Dynamics Tab The Dynamics tab contains the following pages:

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l

Specs

l

Holdup

l

StripChart

l

Heat Exchanger

Notes: The Dynamics tab for a Reboiler is the same as the Dynamics tab for the Condenser. You are not required to modify information on the Dynamics tab of the Reboiler when working in Steady State mode.

Reboiler Specs Page The Specs page contains information regarding initialization modes, reboiler geometry, and reboiler dynamic specifications.

Model Details In the Model Details group, you can specify the initial composition and amount of liquid that the separator should start with when you start dynamics. This done via the initialization mode which is discussed in the table below. Initialization Mode

Description

Initialize from Products

The composition of the holdup is calculated from a weighted average of all products exiting the holdup. A PT flash is performed to determine other holdup conditions. The liquid level is set to the value indicated in the Liq Volume Percent field.

Dry Startup

The composition of the holdup is calculated from a weighted average of all feeds entering the holdup. A PT flash is performed to determine other holdup conditions. The liquid level in the Liq Volume Percent field is set to zero.

Initialize from User

The composition of the liquid holdup in the reboiler is user specified. The molar composition of the liquid holdup can be specified by clicking the Init Holdup button. The liquid level is set to the value indicated in the Liq Volume Percent field.

Note: The Initialization Mode can be changed any time when the integrator is not running. The changes cause the vessel to re-initialize when the integrator is started again.

The reboiler geometry can be specified in the Model Details group. The following reboiler geometry parameters can be specified in the same manner as the Geometry group on the Sizing page of the Rating tab:

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l

Volume

l

Diameter

l

Height (Length)

l

Geometry (Level Calculator)

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The Liquid Volume Percent value is also displayed in this group. You can modify the level in the condenser at any time. HYSYS then uses that level as an initial value when the integrator is run. The Fraction Calculator determines how the level in the condenser, and the elevation and diameter of the nozzle affects the product composition. There is only one Fraction Calculation mode available, it is called Use Levels and Nozzles. The calculations are based on how the nozzle location and vessel liquid level affect the product composition.

Dynamic Specifications The Dynamic Specifications group contains fields where you can specify what happens to the pressure of the reboiler when you enter dynamic mode. The Feed Delta P field allows you to impose a fixed pressure drop between the vessel and all of the feed streams. This is mostly supported for compatibility with Steady State mode. In Dynamic mode, you are advised to properly account for all pressure losses by using the appropriate equipment such as valves or pumps or static head contributions. A zero pressure drop should preferably be used here otherwise you may get unrealistic results such as material flowing from a low to a high pressure area. The Fixed Vessel Pressure field allows you to fix the vessel pressure in Dynamic mode. This option can be used in simpler models where you do not want to configure pressure controllers and others, or if the vessel is open to the atmosphere. In general the specification should not be used, because the pressure should be determined by the surrounding equipment.

Reboiler Holdup Page The Holdup page contains information regarding the properties, composition, and amount of the holdup. Refer to the Holdup Page section for more information. The Levels group displays the following variables for each of the phases available in the vessel: l

Level. Height location of the phase in the vessel.

l

Percent Level. Percentage value location of the phase in the vessel.

l

Volume. Amount of space occupied by the phase in the vessel.

Reboiler StripChart Page The Stripchart page allows you to select and create default strip charts containing various variable associated to the operation.

Reboiler Heat Exchanger Page The Heat Exchanger page opens a list of available heating methods for the unit operation. This page contains different objects depending on which radio button

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you select. l

l

l

If you select the None radio button, this page is blank and the Condenser has no cooling source. If you select the Duty radio button, this page contains the standard heating parameters and you have to specify an energy stream for the Reboiler. If you select the Tube Bundle radio button, this page contains the parameters used to configure a kettle reboiler and you have to specify the required material streams for the kettle reboiler.

Note: The Tube Bundle options are only available in Dynamics mode. Note: If you switch from the Duty option or Tube Bundle option to the None option, HYSYS automatically disconnects the energy or material streams associated to the Duty or Tube Bundle options.

Duty Radio Button When the Duty radio button is selected the following heat transfer options are available. The Heater Type group has two radio buttons: l

Liquid Heater

l

Vessel Heater

When you select the Liquid Heater radio button, the Heater Height as % Vessel Volume group appears. This group contains two cells used to specify the heater height: l

Top of Heater

l

Bottom of Heater

For the Liquid Heater method, the duty applied to the vessel depends on the liquid level in the tank. The heater height value must be specified. The heater height is expressed as a percentage of the liquid level in the vessel operation. The default values are 5% for the top of the heater, and 0% for the bottom of the heater. These values are used to scale the amount of duty that is applied to the vessel contents. (2)

where: L = liquid percent level (%) T = top of heater (%) B = bottom of heater (%)

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The Percent Heat Applied may be calculated as follows: (3) It is shown that the percent of heat applied to the vessel’s holdup directly varies with the surface area of liquid contacting the heater.

When you select the Vessel Heater radio button, 100% of the duty specified or calculated in the SP cell is applied to the vessel’s holdup: (4) where: Q = total heat applied to the holdup QTotal = duty calculated from the duty source The Duty Source group has two radio buttons: l

Direct Q

l

From Utility

When you select the Direct Q radio button, the Direct Q Data group appears. The following table describes the purpose of each object in the group. Object

Description

SP

The heat flow value in this cell is the same value specified in the Duty field of the Parameters page on the Design tab. Any changes made in this cell is reflected on the Duty field of the Parameters page on the Design tab.

Min. Available

Allows you to specify the minimum amount of heat flow.

Max. Available

Allows you to specify the maximum amount of heat flow.

When you select the From Utility radio button, the Utility Flow Properties group appears.

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In the cells: l

l

l

Black text indicates that the value is calculated by HYSYS and cannot be changed. Blue text indicates that the value is entered by you, and you can change the value. Red text indicates that the value is calculated by HYSYS, and you can change the value.

The following table describes the purpose of each object that appears when the From Utility radio button is selected.

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Object

Description

Heat Flow

Displays the heat flow value.

Available UA

Displays the overall heat transfer coefficient.

Utility Holdup

Displays the amount of holdup fluid in the reboiler.

Mole Flow

Displays the amount of fluid flowing out of the reboiler.

Min Mole Flow

Displays the minimum amount of fluid flowing out of the reboiler.

Max Mole Flow

Displays the maximum amount of fluid flowing out of the reboiler.

Heat Capacity

Displays the heat capacity of the fluid.

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Object

Description

Inlet Temp.

Displays the temperature of the stream flowing into the condenser.

Outlet Temp.

Displays the temperature of the stream flowing out of the condenser.

Initialize Duty Valve

Allows you to initialize the UA, flow, and outlet temperature to be consistent with the duty for purposes of control.

Column Tower At the very minimum, every Column Template includes a Tower. An individual stage has a vapor feed from the stage below, a liquid feed from the stage above, and any additional feed, draw or duty streams to or from that particular stage. The property view for the Tower of a Distillation Column template is shown in the figure below.

The Tower property view contains the five tabs that are common to most unit operations. You are not required to change anything on the Rating tab and Dynamics tab, if you are operating in Steady State mode.

Design Tab The Design tab contains the following pages: l

Connections

l

Side Draws

l

Parameters

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l

Pressures

l

User Variables

l

Notes

Tower Connections Page The Connections page of the Tower is used for specifying the names and locations of vapor and liquid inlet and outlet streams, feed streams, and the number of stages (see Figure above). When a Column template is selected, HYSYS inserts the default stream names associated with the template into the appropriate input cells. For example, in a Distillation Column, the Tower vapor outlet stream is To Condenser and the Liquid inlet stream is Reflux. l

l

l

A number of conventions exist for the naming and locating of streams associated with a Column Tower: When you select a Tower feed stream, HYSYS by default feeds the stream to the middle stage of the column (for example, in a 20-stage column, the feed would enter on stage 10). The location can be changed by selecting the desired stage from the drop-down list, or by typing the stage number in the appropriate field. Streams entering and leaving the top and bottom stages are always placed in the Liquid or Vapor Inlet/Outlet fields.

Note: Specifying the location of a column feed stream to be either the top stage (stage 1 or stage N, depending on your selected numbering convention) or the bottom stage (N or 1) automatically results in the stream becoming the Liquid Inlet or the vapor Inlet, respectively. If the Liquid Inlet or vapor Inlet already exists, your specified feed stream is an additional stream entering on the top or bottom stage , displayed with the stage number (1 or N). A similar convention exists for the top and bottom stage outlet streams (vapor Outlet and Liquid Outlet).

Tower Side Draws Page On the Side Draws page, you can specify the name and type of side draws taken from the Tower of your column. Use the radio buttons to select the type of side draw: l

Vapor

l

Liquid

l

Water

Select the cells to name the side draw stream, and specify the stage from which it is taken.

Tower Parameters Page You can input the number of stage on the Parameters page. Note: By default, the Use Tower Name for Stage Name check box is selected.

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The stages are treated as ideal if the fractional efficiencies are set to 1. If the efficiency of a particular stage is less than 1, the stage is modeled using a modified Murphree Efficiency. You can add or delete stages anywhere in the column by clicking the Customize button and entering the appropriate information in the Custom Modify Number of Stages group. This feature makes adding and removing stage simple, especially if you have a complex column, and you do not want to lose any feed or product stream information. The figure below shows the property view that appears when the Customize button is clicked.

You can add and remove stages by: l

l

Specifying a new number of stages in the Current Number of Stages field. This is the same as changing the number of theoretical stages on the Connections page. All inlet and outlet streams move appropriately; for example, if you are changing the number of stages from 10 to 20, a stream initially connected to stage 5 is now stage 10, and a stream initially connected at stream 10 is now at stages 20. Adding or removing stages into or from an individual Tower.

Note: When you are adding or deleting stages, all Feeds remain connected to their current stages.

Adding Stages To add stages to the Tower: 1. Type the number of stages you want to add in the Number of Stages to Add/Delete field. 2. In the Stage to add after or delete first field, specify the stage number after which you want to add the stage. 3. Click the Add Stages button, and HYSYS inserts the stages in the appropriate place according to the stage numbering sequence you are using. All streams (except feeds) and auxiliary equipment below (or above, depending on the stage numbering scheme) the stage where you inserted is moved down (or up) by the number of stages that were inserted.

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Removing Stages To remove stages from the Tower: 1. Enter the number of stages you want to delete in the Number of Stages to Add/Delete field. 2. In the Stage to add after or delete first field, type the first stage in the section you want to delete. 3. Click the Remove Stages button. All stages in the selected section are deleted. If you are using the top-down numbering scheme, the appropriate number of stages below the first stage (and including the first stage) you specify are removed. If you are using the bottom-up scheme, the appropriate number of stages above the first stage (and including the first stage) you specify are removed. 4. Streams connected to a higher stage (numerically) are not affected; for example, if you are deleting 3 stages starting at stage number 6, a side draw initially at stage 5 remains there, but a side draw initially connected to stage 10 is now at stage 7. Any draw streams connected to stages 6, 7, or 8 are deleted with your confirmation to do so. If you select the Side Stripper radio button or Side Rectifier radio button at the bottom of the property view, this affects the pressure profile. The pressure of the main Tower column section from which the liquid feed stream is drawn is used as the side stripper pressure, which is constant for all column sections. The pressure of the main Tower column section from which the vapor feed stream is drawn is used as the Side Rectifier pressure, which is constant for all column sections.

Tower Pressures Page The Pressures page displays the pressure on each stage. Whenever two pressures are known for the Tower, HYSYS interpolates to find the intermediate pressures. For example, if you enter the Condenser and Reboiler Pressures through the Column Input Expert or Column property view, HYSYS calculates the top and bottom stage pressures based on the Condenser and Reboiler pressure drops. The intermediate stage pressures are then calculated by linear interpolation.

Tower User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Tower Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

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Tower Rating Tab The Rating tab contains the following pages: l

Sizing

l

Nozzles

l

Heat Loss

l

Efficiencies

l

Pressure Drop

Tower Sizing Page The Sizing page contains the required information for correctly sizing column tray and packed sections. If the Sieve, Valve, Bubble Cap radio button with the Uniform Tray Data are selected, the following property view is shown.

The Tower diameter, weir length, weir height, and the tray spacing are required for an accurate and stable dynamic simulation. You must specify all of the information on this page. The Quick Size button allows you to automatically and quickly size the tray parameters. The Quick Size calculations are based on the same calculations that are used in the Tray Sizing Analysis. Note: The required size information for the Tower can be calculated using the Tray Sizing Analysis.

HYSYS only calculates the tray volume, based on the weir length, tray spacing, and tray diameter. For multipass trays, simply enter the column diameter and the appropriate total weir length.

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When you select the Packed radio button and the Uniform Tray Data radio button, the Sizing page changes to the property view shown below.

The stage packing height, stage diameter, packing type, void fraction, specified surface area, and Robbins factor are required for the simple dynamic model. HYSYS uses the stage packing dimensions and packing properties to calculate the pressure flow relationship across the packed section.

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Packing Properties (Dynamics)

Description

Void Fraction

Packing porosity, in other words, m3 void space/m3 packed bed.

Specific Surface Area

Packing surface area per unit volume of packing (m-1).

Robbins Factor

A packing-specific quantity used in the Robbins correlation, which is also called the dry bed packing factor (m-1). The Robbins correlation is used to predict the column vapor pressure drop. For the dry packed bed at atmospheric pressure, 2 the Robbins or packing factor is proportional to the vapor pressure drop.

Static Holdup

Static liquid, h st, is the m 3 liquid/ m 3 packed bed remaining on the packing after it has been fully wetted and left to drain. The static liquid holdup is a constant value.

Include Loading Regime Term

Loading regime term is the second term in the Robbins pressure drop equation, which is limited to atmospheric pressure and under vacuum but not at elevated pressures. When pressure is high, (in other words, above 1 atm), inclusion of the loading regime term may cause an unrealistically high pressure drop prediction.

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To specify Chimney and Sump tray types, the Non Uniform Tray Data Option must be selected from the Section Properties group. The Non Uniform Tray Data Option allows you to model a column with high fidelity by adjusting tray rating parameters on a tray by tray basis. For a Trayed section of a column, you can adjust the Internal Type of tray, Tray Spacing, Diameter, Weir Height, Weir Length, DC Volume, Flow Path and Weeping factor. For a Packed section of a column, you can adjust the Stage Packing Height, and Diameter. From the Internal Type drop-down list in the Detailed Sizing Information group, you can select alternative internal tray types on a tray by tray basis. The Chimney and Sump internals along with the weeping factor details are mentioned below. Detailed Sizing Information

Description

Internal Type

Chimney - This allows a higher liquid level and does not have any liquid going down to the tray below. Although vapor can go up through it but it does not contact the liquid. The Chimney tray type can be designated on any tray. By default, the weeping factor is set to 0 and the stage efficiency is set to 5% on the Efficiencies page. The weir height and tray spacing is increased for a Tower. For a packed section, stage packing height is increased. Sump - Only the bottom tray can be designated as a sump. By default, the efficiency is set to 5%. The tray spacing for a Tower and the stage packing height in a packed section are increased when using a Sump.

Weeping Factor

The weeping factor can be adjusted on a tray by tray basis. It is used to scale back or turn off weeping. By default the weeping factor is set to 1 for all internal types except the sump.

Tower Nozzles Page The Nozzles page contains the elevations at which vapor and liquid enter or leave the Tower.

Tower Heat Loss Page The Heat Loss page allows you to specify the heat loss from individual sections in the Tower. You can select from either a Direct Q, Simple or Detailed heat loss model or have no heat loss from the Towers.

Direct Q Heat Flow Model The Direct Q model allows you to input the heat loss directly where the heat flow is distributed evenly over each Tower. Otherwise, you have the heat loss calculated from the Heat Flow for each specified Tower.

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Using the check box, you can temporarily disable heat loss calculations without losing any Heat Loss data that is entered.

Simple Heat Flow Model The Simple model allows you to calculate the heat loss by specifying: l

The Overall U value

l

The Ambient Temperature

l

°C

Detailed Heat Flow Model The Detailed Heat Flow model allows you to specify more detailed heat transfer parameters. The detailed properties can be used on a tray to tray basis based on the temperature profile, conduction, and convection data specified.

Tower Level Taps Page The information on this page is relevant only to dynamics cases. Since the contents in a vessel can be distributed in different phases, the Level Taps page lets you monitor the level of liquid and aqueous contents that coexist within a specified zone in a tank or separator. Level Tap

Name of the level tap

PV High (m)

Upper limit to be monitored. (Meters)

PV Low (m)

Lower limit to be monitored. (Meters)

OP High

Upper limit of the output of the normalization scale

OP Low

Lower limit of the output of the normalization scale

The normalization scale can be expressed in negative values. In some cases, the output normalization scale is manually set between -7% to 100% or -15%100% so that there is a cushion range before the level of the content becomes unacceptable (i.e., too low, or too high). By default, a new level tap is set to the total height of the vessel, and the height is normalized in percentage (100-0). All the upper limit specifications should not be smaller than or equal to the lower limit specifications and vice versa; otherwise no calculations will be performed. In the Calculated Level Taps Values (Dynamics) group, the level of liquid and aqueous are displayed in terms of the output normalization scale you specified. Whenever the level of a content exceeds PV High, HYSYS automatically outputs the OP High value as the level of that content. If the level is below the PV Low, HYSYS outputs the OP Low value. The levels displayed are always entrained within the normalized zone.

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Tower Efficiencies Page As with steady state, you can specify stage efficiencies for columns in dynamics. However, you can only specify the overall stage efficiency; component stage efficiencies are only available in steady state. To specify the efficiency of the overall stage: 1. Click the Overall radio button. 2. For each stage in the Overall Efficiencies table, specify the efficiency of the stage in the appropriate field. Values must be between 0 and 1, with 1 corresponding to 100% efficiency. To specify the component specific efficiencies: 1. Click the Component radio button. 2. Specify tray by tray component efficiencies in the Component Efficiencies table. Values must be between 0 and 1, with 1 corresponding to 100% efficiency.

Tower Pressure Drop Page The Pressure Drop page displays the information associated with the pressure drops (or pressures) across the Tower. In the Pressure column, specify the pressure for each of the stages in the column. You are only required to specify a top stage (or condenser) and bottom stage (or reboiler) pressure in order for HYSYS to solve the column (This normally done through the Column Input Expert or Column Property view). However, the more data you can input, the faster the column will solve. The remaining stage pressures are calculated by linear interpolation. The same calculation in the Tray Sizing analysis is used to calculate the pressure drop for the Towers when the column is running (in other words, using the traffics and geometries to determine what the pressure drop is). The Tray Sizing analysis calculates a pressure drop across each tray, but you need to fix one end of the column (top or bottom), allowing the other trays to float with the calculations. Select the end of the column to be fixed by selecting the Top Tray Fixed For Update or Bottom Tray Fixed For Update radio button. The Tower Pressure Drop field displays the calculated pressure drop across the Tower. Selecting the Rating Enabled check box turns on the pressure drop calculations as part of the column solution.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the Tower. Note: The PF Specs page is relevant to dynamics cases only.

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Performance Tab The Performance tab contains the following pages: l

Pressure

l

Temperature

l

Flow

l

Summary

l

Hydraulics

Tower Performance - Pressure Page The Pressure page contains a table that lists all the pressure for each stage. The table also includes the names of any inlet streams associated to a stage and the inlet stream’s pressure.

Tower Performance - Temperature Page The Temperature page contains a table that lists all the temperature for each stage. The table also includes the names of any inlet streams associated to a stage and the inlet streams’ temperature.

Flow Performance - Page The Flow page contains a table that lists all the liquid and vapor flow rates for each stage. The table also includes the names of any inlet streams associated to a stage and the inlet stream's flow rate. You can also change the unit of the flow rates displayed by selecting the unit from the Flow Basis drop-down list. There are four possible units: l

Molar

l

Mass

l

Standard Liquid Volume

l

Actual Volume

Tower Performance - Summary Page The Summary page contains a table that displays the flow rates, temperature, and pressure for each stage.

Tower Performance - Hydraulics Page The Hydraulics page contains a table that displays the height and pressure of Dry Hole DP, Static Head, and Height over Weir, and tray residence time. The tray residence time is computed as: (1)

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Where the Tray Liquid Molar Flow Rate is the maximum between the liquid molar flow rate from above the tray plus the liquid side feed molar flow rates and the liquid molar flow rate to below the tray plus the liquid side product molar flow rates. The residence time of every tray is permanently compared against the column (composition) integrating step size to verify the accuracy of the dynamic simulation. The adopted criterion is: Note: Every tray residence time must be at least four times as long as the column integrating step.

Tower Dynamics Tab The Dynamics tab contains the following pages: l

Specs

l

Holdup

l

Static Head

l

StripChart

Tower Specs Page The Specs page contains the Nozzle Pressure Flow k Factors for all the stages in the Tower. 1. In the Calculate K Values group: o

Click the All Stages button to have HYSYS calculate the k value for all of the stages.

o

If you want HYSYS to calculate the k values for certain stages only, select the desired stages and click the Selected Stages button. HYSYS only calculates the k values for the selected stages.

2. Select the Use tower diameter method check box if you want HYSYS to assume k is proportional to the diameter squared and use the tower actual diameter to calculate k values. When the Use tower diameter method check box is cleared, the k values are calculated using the results obtained from the steady state model, providing a smoother transition between your steady state model and dynamic model. 3. Select the Use detailed internal method check box if you want HYSYS to calculate k values based on each stage's fluid information, such as vapor flow rate, pressure drop, and density. 4. Select the Model Weeping check box if you want HYSYS to take into account any weeping that occurs on the Towers and add the effects to your model. Note: Weeping can start to occur on a tray when the dry hole pressure loss drops below 0.015 kPa. It allows liquid to drain to the stage below even if the liquid height is below the weir height.

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5. In the Initialization Options group: o

The Perform dry start up check box allows you to simulate a dry start up. Selecting this check box removes all the liquid from all the trays when the integrator starts.

o

The Initialize From User check box allows you to start the simulation from conditions you specify. Selecting this check box activates the Init HoldUp button. Click the Init HoldUp button to specify the initial liquid mole fractions of each component and the initial flash conditions.

o

The Fixed Pressure Profile check box allows you to simulate the column based on the fixed pressure profile.

Pressure Profile The Fixed Pressure Profile check box lets you run the column in Dynamic mode using the steady state pressure profile. This option simplifies the column solution for inexperienced users, and makes their transition from the steady state to dynamics simulation a bit easier. Note: You do not have to configure pressure control systems with this option. This option is not recommended for rigorous modeling work where the pressure can typically change on response to other events.

The pressure profile of a Tower is determined by the static head, which is caused mostly by the liquid on the trays, and the frictional pressure losses, which are also known as dry hole pressure loses. The frictional pressure losses are associated with vapor flowing through the Tower. The flowrate is determined by the following equation. (2) In HYSYS, the k-value is calculated by assuming: (3) However, if the Fixed Pressure Profile option is selected, then the static head contribution can be subtracted and hence the vapor flow and the frictional pressure loss is known. This allows the k-values to be directly calculated to match steady state results more closely.

Tower Holdup Page The Holdup page contains a summary of the dynamic simulation results for the column. The holdup pressure, total volume, and bulk liquid volume results on a stage basis are contained in this property view. Double-clicking on a stage name in the Holdup column opens the stage property view. You can double-click on any cell within each row to view the advanced holdup properties for each specific Tower.

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Tower Static Head Page The Static Head page enables you to select how the static head contributes to the calculation. Since static head contributions are often essential for proper column modeling, internal static head contributions are generally considered for the column model in any case, and should only be disabled under special circumstances. Refer to the Static Head Section in the HYSYS Dynamics section for more information.

Tower StripChart Page The Stripchart page allows you to select and create default strip charts containing various variable associated to the operation.

Tee The property view for the Tee operation in the Column subflowsheet has all of the pages and inherent functionality contained by the Tee in the Main Environment with one addition, the Estimates page. On the Estimates page, you can help the convergence of the Column subflowsheet's simultaneous solution by specifying flow estimates for the tee product streams. To specify flow estimates: 1. Select one of the Flow Basis radio buttons: Molar, Mass or Volume. 2. Enter estimates for any of the product streams in the associated fields next to the stream name. There are four buttons on the Estimates page, which are described in the table below. Button

Related Setting

Update

Replaces all estimates except user specified estimates (in blue) with values obtained from the solution.

Clear Selec- Deletes the highlighted estimate. ted Clear Calculated

Deletes all calculated estimates.

Clear All

Deletes all estimates.

If the Tee operation is attached to the column (for example, via a draw stream), one tee split fraction specification is added to the list of column specifications for each tee product stream that you specify. As you specify the split fractions for the product streams, these values are transferred to the individual

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column specifications on the Monitor page and Specs page of the column property view. The additional pieces of equipment available in the Column subflowsheet are identical to those in the main flowsheet. For information on each piece of equipment, refer to its respective chapter. All operations within the Column subflowsheet environment are solved simultaneously. Refer to Piping Operations for more details on the property view of the Tee. Refer to the section on the General Features of the Solving Methods for information on which method supports the Tee operation.

Running the Column Once you are satisfied with the configuration of your Column subflowsheet and you have specified all the necessary input, the next step is to run the Column solution algorithm. The iterative procedure begins when you click the Run button on the Column property view. The Run/Reset buttons can be accessed from any page of the Column property view. Note: When you are inside the Column build environment, a Run icon also appears on the toolbar, which has the same function as the Run button on the Column property view. Note: On the toolbar, the Run icon and Stop icon are two separate icons. Whichever icon is toggled on has light gray shading.

When the Run button on the Column property view is clicked, the Run/Reset buttons are replaced by a Stop button which, when clicked, terminates the convergence procedure. The Run button can then be clicked again to continue from the same location. Similarly, the Stop icon switches to a gray shading with the Run icon on the toolbar after it is activated. When you are working inside the Column build environment, the Column runs only when you click the Run button on the Column property view, or the Run icon on the toolbar. When you are working with the Column property view in the Main build environment, the Column automatically runs when you change: l l

A specification value after a converged solution has been reached. The Active specifications, such that the Degrees of Freedom return to zero.

Run The Run command begins the iterative calculations necessary to simulate the column described by the input. On the Monitor page of the Column property view, a summary showing the iteration number, equilibrium error, and the heat

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and specification errors appear. Detailed messages showing the convergence status are shown in the Trace Window. The default basis for the calculation is a modified “inside-out” algorithm. In this type of solution, simple equilibrium and enthalpy models are used in the inner loop, which solve the overall component and heat balances, vapor-liquid equilibrium, and any specifications. The outer loop updates the simple thermodynamic models with rigorous calculations. When the simulation is running, the status line at the bottom of the screen first tracks the calculation of the initial properties used to generate the simple models. Then the determination of a Jacobian matrix appears, which is used in the solution of the inner loop. Next, the status line reports the inner loop errors and the relative size of the step taken on each of the inner loop iterations. Finally, the rigorous thermodynamics is again calculated and the resulting equilibrium, heat, and spec errors reported. The calculation of the inner loop and the outer loop properties continues until convergence is achieved, or you determine that the column cannot converge and click Stop to terminate the calculation. If difficulty is encountered in converging the inner loop, the program occasionally recalculates the inner loop Jacobian. If no obvious improvement is being made with the printed equilibrium and heat and spec errors, click Stop to terminate the calculations and examine the available information for clues. Refer to the Column Troubleshooting section for solutions to some common troubles encountered while trying to achieve the desired solution. Any estimates which appear in the Column Profile page and Estimates page are used as initial guesses for the convergence algorithm. If no estimates are present, HYSYS begins the convergence procedure by generating initial estimates.

Reset The Reset command clears the current Column solution, and any estimates appearing on the Estimates page of the Column property view. If you make major changes after converging the Column, it is a good idea to Reset to clear the previous solution. This allows the Column solver to start fresh and distance itself from the previous solution. If you make only minor changes to the Column, try clicking Run before Resetting. Once the column calculation has started it continues until it has either converged, has been terminated due to a mathematically impossible condition, (for example being unable to invert the Jacobian matrix), or it has reached the maximum number of iterations. Other than these three situations, calculations continue indefinitely in an attempt to solve the column unless the Stop button is clicked. Unconverged results can be analyzed, as discussed in Column Troubleshooting.

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Column Troubleshooting Although HYSYS does not require any initial estimates for convergence, good estimates of top and bottom temperatures and one product accelerate the convergence process. Detailed profiles of vapor and liquid flow rates are not required. However, should the column have difficulty, the diagnostic output printed during the iterations provides helpful clues on how the tower is performing. If the equilibrium errors are approaching zero, but the heat and spec errors are staying relatively constant, the specifications are likely at fault. If both the equilibrium errors and the heat and spec errors do not appear to be getting anywhere, then examine all your input (for example the initial estimates, the specifications, and the tower configuration). In running a column, keep in mind that the Basic Column Parameters cannot change. By this, it is meant that column pressure, number of trays, feed tray locations, and extra attachments such as side exchanger and pump around locations remain fixed. To achieve the desired specifications the Column only adjusts variables which have been specified as initial estimates, such as reflux, side exchanger duties, or product flow rates. This includes values that were originally specifications but were replaced, thereby becoming initial estimates. It is your responsibility to ensure that you have entered a reasonable set of operating conditions (initial estimates) and specifications (Basic Column Parameters) that permit solution of the column. There are obviously many combinations of column configurations and specifications that makes convergence difficult or impossible. Although all these different conditions could not possibly be covered here, some of the more frequent problems are discussed in the following sections.

Heat and Spec Errors Fail to Converge This is by far the most frequent situation encountered when a column is unable to satisfy the allowable tolerance. The following section gives the most common ailments and remedies.

Poor Initial Estimates Initial estimates are important only to the extent that they provide the initial starting point for the tower algorithm. Generally, poor guesses simply cause your tower to converge more slowly. However, occasionally the effect is more serious. Consider the following: l

154

Check product estimates using approximate splits. A good estimate for the tower overhead flow rate is to add up all the components in your feed which are expected in the overheads, plus a small amount of your heavy key component. If the tower starts with extremely high errors, check to see that the overhead estimate is smaller than the combined feed rates.

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l

l

Poor reflux estimates usually do not cause a problem except in very narrow boiling point separations. Better estimates are required if you have high column liquid rates relative to vapor rates, or vice versa. Towers containing significant amounts of inert gases (for example, H2, N2, and so forth), require better estimates of overhead rates to avoid initial bubble point problems. A nitrogen rejection column is a good example. Note: To see the initial estimates, click the View Initial Estimates button on the Monitor page of the column property view.

Input Errors It is good practice to check all of your input just before running your column to ensure that all your entries, such as the stage temperatures and product flow rates, appear reasonable: l

l

l

l

Check to ensure that your input contains the correct values and units. Typical mistakes are entering a product flow rate in moles/hr when you really meant to enter it in barrels/day, or a heat duty in BTU/hr instead of E+06 BTU/hr. When specifying a distillate liquid rate, make sure you have specified the Distillate rate for the condenser, not the Reflux rate. If you change the number of trays in the column, make sure you have updated the feed tray locations, pressure specifications, and locations of other units such as side exchangers on the column. If the tower fails immediately, check to see if all of your feeds are known, if a feed was entered on a non-existent tray, or if a composition specification was mistakenly entered for a zero component. Note: Clicking the Input Summary button on the Monitor page of the column property view displays the column input in the Trace Window.

Incorrect Configuration For more complex tower configurations, such as crude columns, it is more important that you always review your input carefully before running the tower. It is easy to overlook a stripping feed stream, side water draw, pump around or side exchanger. Any one of these omissions can have a drastic effect on the column performance. As a result, the problem is not immediately obvious until you have reviewed your input carefully or tried to change some of the specifications. l

Check for trays which have no counter-current vapor-liquid traffic. Examples of this are having a feed stream on a tray that is either below the top tray of an un-refluxed tower or a tower without a top lean oil feed, or placing a feed stream above the bottom stage of a tower that does not have a bottom reboiler or a stripping feed stream below it. In both cases the trays above or below the feed tray become single phase. Since they do not represent any equilibrium mass transfer, they should be removed or the feed should be moved. The tower cannot converge

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with this configuration. l

l

l

The tower fails immediately if any of the sidestrippers do not have a stripping feed stream or a reboiler. If this should occur, a message is generated stating that a reboiler or feed stream is missing in one of the sidestrippers. Make sure you have installed a side water draw if you have a steamstripped hydrocarbon column with free water expected on the top stage. Regardless of how you have approached solving crude columns in the past, try to set up the entire crude column with your first run, including all the side strippers, side exchangers, product side draws, and pump arounds attached. Difficulties arise when you try to set up a more simplified tower that does not have all the auxiliary units attached to the main column, then assign product specs expected from the final configuration.

Impossible Specifications Impossible specifications are normally indicated by an unchanging heat and spec error during the column iterations even though the equilibrium error is approaching zero. To get around this problem you have to either alter the column configuration or operating pressure or relax/change one of the product specifications. l

l

l

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You cannot specify a temperature for the condenser if you are also using subcooling. If you have zero liquid flows in the top of the tower, either your top stage temperature spec is too high, your condenser duty is too low, or your reflux estimate is too low. If your tower shows excessively large liquid flows, either your purity specs are too tight for the given number of trays or your Cooler duties are too high. Dry trays almost always indicate a heat balance problem. Check your temperature and duty specifications. There are a number of possible solutions: fix tray traffic and let duty vary; increase steam rates; decrease product makes; check feed temperature and quality; check feed location. A zero product rate could be the result of an incorrect product spec, too much heat in the column which eliminates internal reflux, or the absence of a heat source under a total draw tray to produce needed vapor.

Conflicting Specifications This problem is typically the most difficult to detect and correct. Since it is relatively common, it deserves considerable attention. l l

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You cannot fix all the product flow rates on a tower. Avoid fixing the overhead temperature, liquid and vapor flow rates because this combination offers only a very narrow convergence

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envelope. l l

l

l

l

l

l

You cannot have subcooling with a partial condenser. A cut point specification is similar to a flow rate spec; you cannot specify all flows and leave one unspecified and then specify the cut point on that missing flow. Only two of the three optional specifications on a pump around can be fixed. For example, duty and return temperature, duty and pump around rate, and so forth. Fixing column internal liquid and vapor flows, as well as duties can present conflicts since they directly affect each other. The bottom temperature spec for a non-reboiled tower must be less than that of the bottom stage feed. The top temperature for a reboiled absorber must be greater than that of the top stage feed unless the feed goes through a valve. The overhead vapor rate for a reboiled absorber must be greater than the vapor portion of the top feed.

Heat and Spec Error Oscillates While less common, this situation can also occur. It is often caused by poor initial estimates. Check for: l

l

l

Water condensation or a situation where water alternately condenses and vaporizes. A combination of specifications that do not allow for a given component to exit the column, causing the component to cycle in the column. Extremely narrow boiling point separations can be difficult since a small step change can result in total vaporization. First, change the specifications so that the products are not pure components. After convergence, reset the specifications and restart.

Equilibrium Error Fails to Converge This is almost always a material balance problem. Check the overall balance. l

Check the tower profile. If the overhead condenser is very cold for a hydrocarbon-steam column, you need a water draw. o

l

Normally, a side water draw should be added for any stage below 200 °F.

If the column almost converges, you may have too many water draws.

Equilibrium Error Oscillates This generally occurs with non-ideal towers, such as those with azeotropes. Decreasing the damping factor or using adaptive damping should correct this problem.

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References 1. Sneesby, Martin G. Simulation and Control of Reactive Distillation, Curtin University of Technology, School of Engineering, March 1998. 2. Kister, Henry. Distillation Design, (1992), pp 497-499.

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6 Column Property View

The column property view is sectioned into tabs containing pages with information pertaining to the column. The column property view is accessible from the main flowsheet or Column subflowsheet. The column property view is used to define specifications, provide estimates, monitor convergence, view stage-by-stage and product stream summaries, add pump-arounds and side-strippers, specify dynamic parameters and define other Column parameters such as convergence tolerances, and attach reactions to column stages. l

l

The column property view is essentially the same when accessed from the main flowsheet or Column subflowsheet. However, there are some differences: The Connections page in the main flowsheet column property view displays and allows you to change all product and feed stream connections. In addition, you can specify the number of stages and condenser type. Note: The number of stages specified should be equal to the actual number of stages installed or built, rather than theoretical stages, since HYSYS calculates stage efficiencies.

l

The Connections page in the subflowsheet Column property view (Column Runner) allows you to change the product and feed stream connections, and gives more flexibility in defining new streams.

In the main flowsheet Column property view, the Flowsheet Variables and Flowsheet Setup pages allow you to specify the transfer basis for stream connections, and permit you to view selected column variables.

Column Runner When you are inside the column subflowsheet environment, the column properties can be viewed using the Column Runner. The Column Runner lets you access the column property view from inside the column subflowsheet, so you don't have to continuously go back and forth between the parent and subflowsheet environments for the column.

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To show the column runner from the column subflowsheet, click Column > Runner > Show Column Runner on the subflowsheet Ribbon options. Note: In order to make changes or additions to the Column in the main simulation environment, the Solver should be active. Otherwise HYSYS cannot register your changes.

Column Convergence Sequence The Run and Reset buttons are used to start the convergence algorithm and reset the Column, respectively. HYSYS first performs iterations toward convergence of the inner and outer loops (Equilibrium and Heat/Spec Errors), and then checks the individual specification tolerances. The Monitor page displays a summary of the convergence procedure for the Equilibrium and Heat/Spec Errors. An example of a converged solution is shown in the following figure:

A summary of each of the tabs in the Column property view are in the following sections.

Design Tab The following sections detail information regarding the Column property view pages. All pages are common to both the Main Column property view and the Column Runner, unless stated otherwise. Note: Column Runner is another name for the subflowsheet Column property view.

Connections Page (Main Flowsheet) The main flowsheet Connections page allows you to specify the name and location of feed streams, the number of stages in the Tower, the stage numbering scheme, condenser type, names of the Column product streams, and Condenser/Reboiler energy streams. Note: If you have modified the Column Template (for example if you added an additional Tower), the Connections page appears differently than what is shown below.

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Note: Click the Design and Specify Column Internals button to hydraulically design and rate tray or packing internals for your column. We recommend that you select this option for rigorous column analysis.

The streams shown in this property view reside in the parent or main flowsheet; they do not include Column subflowsheet streams, such as the Reflux or Boilup. In other words, only feed and product streams (material and energy) appear on this page. When the column has complex connections, the Connections page changes to the property view shown in the figure below, an example of the Connections page for an atmospheric crude tower.

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You can also split the feed streams by selecting the Split check box associated to the stream. Note: Click the Design and Specify Column Internals button to hydraulically design and rate tray or packing internals for your column. We recommend that you select this option for rigorous column analysis.

Tower Details Property View Click the Edit Trays button on the (Complex) Column Design / Connections page to open the Tower Details property view. You can edit the number of trays in the column, and add or delete trays after or before the tray number of your choice in this property view. In the example below, ten trays are being added after the 12th stage of the main tower.

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Connections Page (Column Runner) The Connections page displayed in the Column Runner (inside the Column subflowsheet) appears as shown in the following figure.

All feed and energy streams, as well as the associated stage, appear in the left portion of the Connections page. Liquid, vapor, and water product streams and locations appear on the right side of the page.

Monitor Page The Monitor page is primarily used for editing specifications, monitoring Column convergence, and viewing Column profile plots. An input summary, and a property view of the initial estimates can also be accessed from this page.

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Optional Checks Group The Optional Checks group displays the iteration number, step size, and equilibrium and heat / spec errors during the iteration process. You will also find the following two buttons: Button

Function

Input Summary

Provides a column input summary in the Trace Window. The summary lists vital tower information including the number of trays, the attached fluid package, attached streams, and specifications. You can click the Input Summary button after you make a change to any of the column parameters to view an updated input summary. The newly defined column configuration appears.

View Initial Estimates

Opens the Summary page of the Column property view, and displays the initial temperature and flow estimates for the column. You can then use the values generated by HYSYS to enter estimates on the Estimates page. These estimates are generated by performing one iteration using the current column configuration. If a specification for flow or temperature has been provided, it is included in the displayed estimates.

Profile Group During the column calculations, a profile of temperature, pressure or flow appears, and is updated as the solution progresses. Select the appropriate radio button to display the desired variable versus tray number profile.

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Specifications Group Each specification, along with its specified value, current value, weighted error, and status is shown in the Specifications group. You can change a specified value by typing directly in the associated Specified Value cell. Specified values can also be viewed and changed on the Specs and Specs Summary pages. Any changes made in one location are reflected across all locations. Note: New specifications can also be added via the Specs page.

Double-clicking on a cell within the row for any listed specification opens its property view. In this property view, you can define all the information associated with a particular specification. Each specification property view has three tabs: l

Parameters

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Summary

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Spec Type

This property view can also be accessed from both the Specs and Specs Summary pages.

Spec Status Check Boxes The status of listed specifications are one of the following types: Status

Description

Active

The active specification is one that the convergence algorithm is trying to meet. An active specification always serves as an initial estimate (when the Active check box is selected, HYSYS automatically selects the Estimate and Current check boxes). An active specification always exhausts one degree of freedom. An Active specification is one which the convergence algorithm is trying to meet initially. An Active specification has the Estimate check box selected also.

Estimate

An Estimate is considered an Inactive specification because the convergence algorithm is not trying to satisfy it. To use a specification as an estimate only, clear the Active check box. The value then serves only as an initial estimate for the convergence algorithm. An estimate does not exhaust an available degree of freedom. An Estimate is used as an initial “guess” for the convergence algorithm, and is considered to be an Inactive specification.

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Status

Description

Current

This check box shows the current specs being used by the column solution. When the Active check box is selected, the Current check box is automatically selected. You cannot alter this check box. When Alternate specs are used and an existing hard to solve spec has been replaced with an Alternate spec, this check box shows you the current specs used to solve the column. A Current specification is one which is currently being used in the column solution.

Completely Inactive

To disregard the value of a specification entirely during convergence, clear both the Active and Estimate check boxes. By ignoring a specification rather than deleting it, you are always able to use it later if required. The current value appears for each specification, regardless of its status. An Inactive specification is therefore ideal when you want to monitor a key variable without including it as an estimate or specification. A Completely Inactive specification is ignored completely by the convergence algorithm, but can be made Active or an Estimate at a later time.

The degrees of freedom value appears in the Degrees of Freedom field on the Monitor page. When you make a specification active, the degrees of freedom is decreased by one. Conversely, when you deactivate a specification, the degrees of freedom is increased by one. You can start column calculations when there are zero degrees of freedom. Variables such as the duty of the reboiler stream, which is specified in the Workbook, or feed streams that are not completely known can offset the current degrees of freedom. If you feel that the number of active specifications is appropriate for the current configuration, yet the degrees of freedom is not zero, check the conditions of the attached streams (material and energy). You must provide as many specifications as there are available degrees of freedom. For a simple Absorber there are no available degrees of freedom, therefore no specifications are required. Distillation columns with a partial condenser have three available degrees of freedom.

Specification Group Buttons The four buttons which align the bottom of the Specifications group allow you to manipulate the list of specs. The table below describes the four buttons. Button

Action

View

Move to one of the specification cells and click the View button to display its property view. You can then make any necessary changes to the specification. To change the value of a specification only, move to the Specified Value cell for the specification you want to change, and type in the new value. You can also double-click in a specification cell to open its property view.

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Button

Action

Add Spec

Opens the Column Specifications menu list, from which you can select one or multiple (by holding the CTRL key while selecting) specifications, and then click the Add Spec(s) button. The property view for each new spec is shown and its name is added to the list of existing specifications.

Update Inactive

Updates the specified value of each inactive specification with its current value.

Group Active

Arranges all active specifications together at the top of the specifications list.

Specs Page Adding and changing Column specifications is straightforward. If you have created a Column based on one of the templates, HYSYS already has default specifications in place. The type of default specification depends on which of the templates you have chosen. Note: The active specification values are used as initial estimates when the column initially starts to solve.

Column Specifications Group The following buttons are available: Button

Action

View

Opens the property view for the highlighted specification. Alternatively, you can object inspect a spec name and select View from the menu. Refer to the section on the Specification Property View for more details.

Add

Opens the Add Specs property view, from which you can select one or multiple (by holding the CTRL key while selecting) specifications, and then click the Add Spec(s) button. The property view for each new spec is shown, and its name is added to the list of existing specifications. Refer to Column Specification Types for a description of the available specification types.

Delete

Removes the highlighted specification from the list.

From the Default Basis drop-down list, you can choose the basis for the new specifications to be Molar, Mass or Volume. The Update Specs from Dynamics button replaces the specified value of each specification with the current value (lined out value) obtained from Dynamics mode.

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Specification Property View The figure below is a typical property view of a specification. In this property view, you can define all the information associated with a particular specification. Each specification property view has three tabs: l

Parameters

l

Summary

l

Spec Type

This example shows a component recovery specification which requires the stage number, spec value, and phase type when a Target Type of Stage is chosen. Specification information is shared between this property view and the specification list on both the Monitor and Specs Summary pages. Altering information in one location automatically updates across all other locations. For example, you can enter the spec value in one location, and the change is reflected across all other locations.

The Summary tab is used to specify tolerances, and define whether the specification is Active or simply an Estimate.

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The Spec Type tab (as shown above) can be used to define specifications as either Fixed/Ranged or Primary/Alternate. A ranged spec allows the solver to meet a spec over an interval (defined according to the upper and lower spec values.) An alternate spec can replace another hard-to-solve spec in situations where the column is not converging. By default, all specifications are initially defined as Fixed and Primary. Advanced solving options available in HYSYS allow the use of both Alternate and Ranged Spec types. The following section further details the advanced solving options available in HYSYS.

Advanced Solving Options Ranged and Alternate Specs The reliability of any solution method depends on its ability to solve a wide group of problems. Some specs like purity, recovery, and cut point are hard to solve compared to a flow or reflux ratio spec. The use of Alternate and/or Ranged Specs can help to solve columns that fail due to difficult specifications. Note: If the Column solves on an Alternate or Ranged Spec, the status bar reads “Converged - Alternate Specs” highlighted in purple.

Configuration of these advanced solving options are made by selecting the Advanced Solving Options button located on the Solver page. The advanced solving options are only available for use with either the Hysim I/O or Modified I/O solving methods.

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Fixed/Ranged Specs For a Fixed Spec, HYSYS attempts to solve for a specific value. For a Ranged Spec, the solver attempts to meet the specified value, but if the rest of the specifications are not solved after a set number of iterations, the spec is perturbed within the interval range provided for the spec until the column converges. Note: When the solver attempts to meet a Ranged spec, the Wt. Error becomes zero when the Current Value is within the Ranged interval (as shown on the Monitor page).

Any column specification can be specified over an interval. A Ranged Spec requires both lower and upper specification values to be entered. This option (when enabled), can help solve columns where some specifications can be varied over an interval to meet the rest of the specifications.

Primary/Alternate Specs A Primary Spec must be met for the column solution to converge. An Alternate Spec can be used to replace an existing hard to solve specification during a column solution. The solver first attempts to meet an active Alternate spec value, but if the rest of the specifications are not solved after a minimum number of iterations, the active Alternate spec is replaced by an inactive Alternate spec. Note: When an existing spec is replaced by an alternate spec during a column solution, the Current check box is cleared for the original (not met) spec and is selected for the alternate spec. Note: The number of active Alternate specs must always equal the number of inactive Alternate specs.

This option (when enabled), can help solve columns where some specifications can be ignored (enabling another) to meet the rest of the specifications and converge the column. Note: Both Ranged or Alternate Specs must be enabled and configured using the Advanced Solving Options Button located on the Solver page of the Parameters tab before they can be applied during a column solution.

 Specification Tolerances for Solver The Solver Tolerances feature allows you to specify individual tolerances for your Column specifications. In addition to HYSYS converging to a solution for the Heat/Spec and Equilibrium Errors, the individual specification tolerances must also be satisfied. HYSYS first performs iterations until the Heat/Spec (inner loop), and Equilibrium (outer loop) errors are within specified tolerances. The Column specifications do not have individual tolerances during this initial iteration process; the specification errors are “lumped” into the Heat/Spec Error. Once the Heat/Spec and Equilibrium conditions are met, HYSYS proceeds to compare the error with the tolerance for each individual specification. If any

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of these tolerances are not met, HYSYS iterates through the Heat/Spec, and Equilibrium loops again to produce another converged solution. The specification errors and tolerances are again compared, and the process continues until both the inner/outer loops and the specification criteria are met. Specific Solver Tolerances can be provided for each individual specification. HYSYS calculates two kinds of errors for each specification: l

an absolute error

l

a weighted error Note: When the Weighted and Absolute Errors are less than their respective tolerances, an Active specification has converged.

The absolute error is simply the absolute value of the difference between the calculated and specified values: (1) The Weighted Error is a function of a particular specification type. When a specification is active, the convergence algorithm is trying to meet the Weighted Tolerances (Absolute Tolerances are only used if no Weighted Tolerances are specified, or the weighted tolerances are not met). Therefore, both the weighted and absolute errors must be less than their respective tolerances for an active specification to converge. HYSYS provides default values for all specification tolerances, but any tolerance can be changed. For example, if you are dealing with ppm levels of crucial components, composition tolerances can be set tighter (smaller) than the other specification tolerances. If you delete any tolerances, HYSYS cannot apply the individual specification criteria to that specification, and Ignore appears in the tolerance input field. The specification tolerance feature is simply an “extra” to permit you to work with individual specifications and change their tolerances if desired.

Specification Details Group For a highlighted specification in the Column Specifications group, the following information appears: l l

l

l

l

Spec Name Convergence Condition. If the weighted and absolute errors are within their tolerances, the specification has converged and Yes appears. Status. You can manipulate the Active and Use As Estimate check boxes. Dry Flow Basis. Draw specifications are calculated on a dry flow basis by selecting the Dry Flow Basis check box. This option is only available for draw specifications. The check box is grayed out if it does not apply to the specification chosen. Spec Type. You can select between Fixed/Ranged and Primary/Alternate specs.

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l

Specified and Current Calculated Values.

l

Weighted/Absolute Tolerance and Calculated Error.

Note: You can edit any specification values (in the Column property view) shown in blue.

Specs Summary Page The Specs Summary page lists all Column specifications available along with relevant information. This specification information is shared with the Monitor page and Specs page. Altering information in one location automatically updates across all other locations. Note: You can edit any specification details shown in blue. Note: You can double-click in a specification cell to open its property view.

Refer to the section on the Specification Property View for more details.

Subcooling Page The Subcooling page allows you to specify subcooling for products coming off the condenser of your column. You can specify the condenser product temperature or the degrees to subcool. For columns without condensers, such as absorbers, this page requires no additional information. Note: The Subcooling page is not available for Liquid-Liquid Extractor.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Parameters Tab The Parameters tab shows the column calculation results, and is used to define some basic parameters for the Column solution. The Parameters tab consists of six pages:

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Profiles

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Estimates

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Efficiencies

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Solver

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2/3 Phase

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Amine

6 Column Property View

Profiles Page The Profiles page shows the column pressure profile, and provides estimates for the temperature, net liquid and net vapor flow for each stage of the column. You can specify tray estimates in the Temperature column, Net Liquid column and Net vapor column, or view the values calculated by HYSYS. The graph below depicts the pressure profile across the column.

Use the radio buttons in the Flow Basis group to select the flow type you want displayed in the Net Liquid and Net vapor columns. The Flow Basis group contains three radio buttons: l

Molar

l

Mass

l

Volume

Note: At least one iteration must have occurred for HYSYS to convert between bases. In this way, values for the compositions on each tray are available.

The buttons in the Steady State Profiles group are defined as follows: Button

Function

Update from Solution

Transfers the current values that HYSYS has calculated for the trays into the appropriate cells. Estimates that have been Locked (displayed in blue) are not updated. The Column Profiles page on the Performance tab allows you to view all the current values.

Clear

Deletes values for the selected tray.

Clear All Trays

Deletes values for all trays.

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Button

Function

Lock

Changes all italicized values for Optional Estimates (unlocked estimates, current values, and interpolated values) to bold (locked), which means that they cannot be overwritten by current values when you click the Update from Solution button.

Unlock

Changes all bold values (locked) to italicized (unlocked). Unlocked values are overwritten by current values when you click the Update from Solution button.

Stream Estimates

Displays the temperature, molar flow, and enthalpy of all streams attached to the column operation.

Although the Profiles page is mainly used for steady state simulation, it does contain vital information for running a column in dynamics. One of the most important aspects of running a column in dynamics is the pressure profile. While a steady state column can run with zero pressure drop across a Tower, the dynamic column requires a pressure drop. In dynamics, an initial pressure profile is required before the column can run. This profile can be from the steady state model or can be added in dynamics. If a new Tower is created in Dynamic mode, the pressure profile can be obtained from the streams if not directly specified. In either case, the closer the initial pressure profile is to the one calculated while running in dynamics, the fewer problems you encounter. Note: If you opt to use the Internals tab to analyze different column Internals configurations with Column Analysis, all liquid results apply to the liquid leaving a tray and include any liquid draw from the tray. All vapor results apply only to vapor entering a tray.

Estimates Page The Estimates page allows you to view and specify composition estimates. Note: To see the initial estimates generated by HYSYS, click the View Initial Estimates button on the Monitor page.

When you specify estimates on stages that are not adjacent to each other, HYSYS cannot interpolate values for intermediate stages until the solution algorithm begins. Note: Estimates are not required for column convergence.

You can specify tray by tray component composition estimates for the vapor phase or liquid phase. Each composition estimate is on a mole fraction basis, so values must be between 0 and 1. HYSYS interpolates intermediate tray component values when you specify compositions for non-adjacent trays. The interpolation is on a log basis. Unlike the temperature estimates, the interpolation for the compositions does not wait for the algorithm to begin. Select either the Vap or Liq radio button in the Phase group to display the table for the vapor or liquid phase, respectively.

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The Composition Estimates group has the following buttons: Button

Action

Clear Tray

Deletes all values, including user specified (blue) and HYSYS generated (red), for the selected tray. HYSYS does not ask for confirmation before deleting estimates.

Clear All Trays

Deletes all values for all trays.

Update

Transfers the current values which HYSYS has calculated for tray compositions into the appropriate cells. Estimates that have been locked (shown in blue) cannot be updated.

Restore

Removes all HYSYS updated values from the table, and replaces them with your estimates and their corresponding interpolated values. Any cells that did not contain estimates or interpolated values are shown as . This button essentially reverses the effect of the Update button.

HYSYS does not ask for confirmation before deleting estimates.

If you had entered some estimate values, click the Unlock Estimates button, and click the Update button. All the values in the table appear in red. You can restore your estimated values by clicking the Restore button. Normalize Trays

Normalizes the values on a tray so that the total of the composition fractions equals 1. HYSYS ignores cells, and normalizes the compositions on a tray provided that there is at least one cell containing a value.

Lock Estimates

Changes all red values (unlocked estimates, current values, interpolated values) to blue (locked), which means that they cannot be overwritten by current values when the Update button is clicked.

Unlock Estimates

Changes all blue values (locked) to red (unlocked). Unlocked values are overwritten by current values when the Update button is clicked.

Efficiencies Page The Efficiencies page allows you to specify Column stage efficiencies on an overall or component-specific basis. Efficiencies for a single stage or a section of stages can easily be specified. Note: Fractional efficiencies cannot be given for the condenser or reboiler stages. Note: The functionality of this page is slightly different when working with the Amine Property Package.

HYSYS uses a modified Murphree stage efficiency. All values are initially set to 1.0, which is consistent with the assumption of ideal equilibrium or theoretical stages. If this assumption is not valid for your column, you have the option of specifying the number of actual stages, and changing the efficiencies for one or more stages. The modified Murphree stage efficiency equation is as follows:

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(1)

Where: l l

l

E = Efficiency Vn = Total vapor flow leaving stage n (if the stage has a side vapor draw, then the side vapor draw flow is included) y = Vapor mole fraction

l

Kn × xn = Composition of vapor in equilibrium with the stage liquid x = Liquid mole fraction

l

n = Stage number (measured top-down)

l

This equation applies to both component and overall stage efficiencies. If you specify an overall stage efficiency, HYSYS will assign each component the same efficiency. Note: If the vapor flow is constant (in other words, Vn = Vn+1, constant molar overflow), then the modified efficiency reduces to the standard Murphree stage efficiency.

To specify an efficiency to multiple cells, highlight the desired cells, enter a value in the Eff. Multi-Spec field, and click the Specify button. The data table on the Efficiencies page gives a stage-by-stage efficiency summary. Note: The efficiencies are fractional. In other words, an efficiency of 1.0 corresponds to 100% efficiency.

Overall stage efficiencies can be specified by selecting the Overall radio button in the Efficiency Type group, and entering values in the appropriate cells. Component-specific efficiencies can be specified by selecting the Component radio button, and entering values in the appropriate cells.

Application Considerations for Murphree Efficiencies Stage efficiencies or component efficiencies can be calibrated to match a given set of column operating data. You can adjust the Murphree efficiency to match column operating data when: l

Efficiency is unknown

l

Actual column operating data is available

Note: Adjusted efficiencies are not predictive and will not necessarily give good results if column operating conditions change.

Use of Murphree efficiencies has certain limitations and implications. Non-judicious specification of these efficiency values can lead to unrealistic column results. They should be used with care. Whenever possible, efficiency values should be calibrated against plant data. The following implications should be considered:

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l

l

When stage Murphree efficiencies are specified, the calculated vapor phase may not be at saturation. When component Murphree efficiencies are specified, both the calculated vapor and liquid phases may not be at saturation.

Special Case - Amine Property Package Starting in HYSYS V8.3, you can no longer add an Amine property package when creating a new case. For cases created prior to V8.3 that include an Amine package, you can opt to continue using the Amine package. However, we recommend that you switch to the Acid Gas - Chemical Solvents package. Note: HYSYS now offers seamless conversion from the Amine package to the Acid Gas Chemical Solvents package. When you open a HYSYS case which includes the Amine Pkg selection, a dialog box appears, recommending that you switch to the new Acid Gas package for gas treating. The Acid Gas package provides an easy to set up and accurate column solver and offers superior thermodynamics and mass transfer rate-based distillation. l

If you select the Switch Amines to Acid Gas button, your case is converted to Acid Gas. A backup of your current case is created, ensuring that none of your data is lost in this conversion. A conversion report is also logged, informing you about any warnings or errors that occurred during the conversion.

l

Only Amine property packages that are used in the flowsheet are converted, since for an unused package, there is no unit operation with which to associate it. Depending on the unit operation, either Acid Gas - Chemical Solvents or Acid Gas - Liquid Treating may be used.

When solving a column for a case using the Amine Property Package, HYSYS always uses stage efficiencies for H2S and CO2 component calculations. If these are not specified on the Efficiencies page of the Column property view, HYSYS calculates values based on the tray dimensions. Tray dimensions can be specified on the Amines page of the Parameters tab. If column dimensions are not specified, HYSYS uses its default tray values to determine the efficiency values. If you specify values for the CO2 and H2S efficiencies, these are the values that HYSYS uses to solve the column. If you want to solve the column again using efficiencies generated by HYSYS, click the Reset H2S, CO2 button, which is available on the Efficiencies page. Run the column again, and HYSYS calculates and displays the new values for the efficiencies. Select the Transpose check box to change the component efficiency matrix so that the rows list components and the columns list the stages. Note: The Reset H2S, CO2 button, and the Transpose check box are available only if the Efficiency Type is set to Component.

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Solver Page You can manipulate how the column solves the column variables on the Solver page. Note: The Solving Method Group, Acceleration Group, and Damping Group will have different information displayed according to the options selected within the group.

Solving Options Group Specify your preferences for the column solving behavior in the Solving Options group.

Maximum Number of Iterations The Column convergence process terminates if the maximum number of iterations is reached. The default value is 10000, and applies to the outer iterations. If you are using Newton's method, and the inner loop does not converge within 50 iterations, the convergence process terminates.

Equilibrium and Heat/Spec Tolerances Convergence tolerances are pre-set to very tight values, thus ensuring that regardless of the starting estimates (if provided) for column temperatures, flow rates, and compositions, HYSYS always converges to the same solution. However, you have the option of changing these two values if you want. Default values are: l

Inner Loop. Heat and Spec Error: 5.000e-04

l

Outer Loop. Equilibrium Error: 1.000e-05

Because the default values are already very small, you should use caution in making them any smaller. You should not make these tolerances looser (larger) for preliminary work to reduce computer time. The time savings are usually minor, if any. Also, if the column is in a recycle or adjust loop, this could cause difficulty for the loop convergence.

Equilibrium Error The value of the equilibrium error printed during the column iterations represents the error in the calculated vapor phase mole fractions. The error over each stage is calculated as one minus the sum of the component vapor phase mole fractions. This value is then squared; the total equilibrium error is the sum of the squared values. The total equilibrium error must be less than 0.00001 to be considered a converged column.

Heat and Spec Error The heat and specification error is the sum of the absolute values of the heat error and the specification error, summed over each stage in the tower.

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This total value is divided by the number of inner loop equations. The heat error contribution is the heat flow imbalance on each tray divided by the total average heat flow through the stage. The specification error contribution is the sum of each individual specification error divided by an appropriate normalization factor. l

For component(s) flow, the normalization factor is the actual component (s) flow.

l

For composition, it is the actual mole fraction.

l

For vapor pressure and temperature, it is a value of 5000.

l

And so forth.

The total sum of heat and spec errors must be less than 0.0005 to be considered a converged column. The allowed equilibrium error and heat and spec error are tighter than in most programs, but this is necessary to avoid meta-stable solutions, and to ensure satisfactory column heat and material balances.

Save Solution as Initial Estimate This option is on by default, and it saves converged solutions as estimates for the next solution.

Super Critical Handling Model Supercritical phase behavior occurs when one or more Column stages are operating above the critical point of one or more components. During the convergence process, supercritical behavior can be encountered on one or more stages in the Column. If HYSYS encounters supercritical phase behavior, appropriate messages appear in the Trace Window. HYSYS cannot use the equation of state or activity model in the supercritical range, so an alternate method must be used. You can specify which method you want HYSYS to use to model the phase behavior. There are three choices for supercritical calculations: Model

Description

Simple K

The default method. HYSYS calculates K-values for the components based on the vapor pressure model being used. Using this method, the K-values which are calculated are ideal K-values.

Decrease Pressure

When supercritical conditions are encountered, HYSYS reduces the pressure on all trays by an internally determined factor, which can be seen in the Trace Window when the Verbose option is used. This factor is gradually decreased until supercritical conditions no longer exist on any tray, at which point, the pressure in the column is gradually increased to your specified pressure. If supercritical conditions are encountered during the pressure increase, the pressure is once again reduced and the process is repeated.

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Model

Description

Adjacent Tray

When supercritical conditions are encountered on a tray, HYSYS searches for the closest tray above which does not have supercritical behavior. The non-supercritical conditions are substituted in the phase calculations for the tray with supercritical conditions.

Trace Level The Trace Level defines the level of detail for messages displayed in the Trace Window, and can be set to Low, Medium, or High. The default is Low.

Initialize from Ideal K’s When this check box is selected, HYSYS initializes its column solution using ideal K values which are calculated from vapor pressure correlations. The ideal K-value option, which is also used by HYSIM, increases the compatibility between HYSIM and HYSYS. By default, the Initialize from Ideal K's check box is cleared. HYSYS uses specified composition estimates or generates estimates to rigorously calculate K-values.

Two Liquids Check The Two Liquids Check drop-down list lets you specify a check for two liquid phases in the column. You can select from the following options: l l

No 2 Liq Check: Disables the two liquid check. 2 Liquid Check: The calculation is based on the overall composition of the fluid in the column.

Tighten Water Tolerance When this check box is selected, HYSYS increases the contribution of the water balance error to the overall balance error in order to solve columns with water more accurately. The default setting for this check box is cleared.

Solving Method Group The Solving Method drop-down list allows you to select the column solution method. The display field, which appears below the drop-down list, provides explanations for each method, and is restated here:

180

Method

Explanation

HYSIM Inside-Out

General purpose method, which is good for most problems.

6 Column Property View

Method

Explanation

Modified HYSIM Inside-Out

General purpose method, which allows mixer, tee, and heat exchangers inside the column subflowsheet.

Newton Raphson InsideOut

General purpose method, which allows liquid-phase kinetic reactions inside the Column subflowsheet.

Sparse Continuation Solver

An equation based solver. It supports two liquid phases on the trays, and its main use is for solving highly non-ideal chemical systems and reactive distillation.

Simultaneous Correction

Simultaneous method using dogleg methods. Good for chemical systems. This method also supports reactive distillation.

OLI Solver

Only used to calculate the column unit operation in an electrolyte system.

Only a simple Heat Exchanger Model (Calculated from Column) is available in the Column subflowsheet. The Simple Rating, End-Point, and Weighted models are not available.

Inside-Out With the “inside-out” based algorithms, simple equilibrium and enthalpy models are used in the inner loop to solve the overall component and heat balances as well as any specifications. The outer loop updates the simple thermodynamic models with rigorous model calculations.

Sparse Continuation Solver Control Panel When the Sparse Continuation Solver is selected, the Control button becomes available. This button brings up the Sparse Continuation Solver Control Panel. This panel gives you the following options: l

l

l

l

Liquid Fugacity Model o

Temp Only

o

Temp and Composition

o

Property Package

Vapor Fugacity Model o

Temp Only

o

Temp and Composition

o

Property Package

Liquid Enthalpy Model o

Simple Liquid Model

o

Property Package

Vapor Enthalpy Model o

Simple Liquid Model

o

Property Package

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Select the Chemical Defaults radio button in the Phase Fugacity Models group to use the following default settings: l

Liquid Fugacity Model - Property Package

l

Vapor Fugacity Model - Temp and Composition

l

Liquid Enthalpy Model - Simple Liquid Model

l

Vapor Enthalpy Model - Simple vapor Model

Select the Hydrocarbon Defaults radio button in the Phase Fugacity Models group to use the following default settings: l

Liquid Fugacity Model - Temp and Composition

l

Vapor Fugacity Model - Temp Only

l

Liquid Enthalpy Model - Simple Liquid Model

l

Vapor Enthalpy Model - Simple vapor Model

Note: Whenever you modify any of the default settings, the User Specified radio button becomes active.

General Features of the Solving Methods The following table displays the general features of all the HYSYS column solving methods.

182

HYSIM I/O

Modified HYSIM I/O

Newton Raphson I/O

Sparse Continuation

Simultaneous Correction

OLI

Component Efficiency Handling

Yes

Yes

No

Yes

No

Yes

Total Efficiency Handling

Yes

Yes

No

Yes

No

Yes

Additional Side Draw

Yes

Yes

Yes

Yes

Yes

Yes

Vapor Bypass

Yes

Yes

No

Yes

No

No

Pump Arounds

Yes

Yes

No

Yes

No

Yes

Side Stripper

Yes

Yes

No

Yes

No

No

Side Rectifier

Yes

Yes

No

Yes

No

No

6 Column Property View

HYSIM I/O

Modified HYSIM I/O

Newton Raphson I/O

Sparse Continuation

Simultaneous Correction

OLI

Mixer & Tee in Sub-flowsheet

No

Yes

No

No

No

No

Three Phase

Yes (water draw)

Yes (water draw)

No

Yes

No

Yes

Chemical (reactive)

No

No

Yes

Yes

Yes

Internal reactions

Acceleration Group When selected, the Accelerate K value & H Model Parameters check box displays two fields, which relate to an acceleration program called the Dominant Eigenvalue Method (DEM). The DEM is a numerical solution program, which accelerates convergence of the simple model K values and enthalpy parameters. It is similar to the Wegstein accelerator, with the main difference being that the DEM considers all interactions between the variables being accelerated. The DEM is applied independently to each stage of the column. Note: Use the acceleration option if you find that the equilibrium error is decreasing slowly during convergence. This should help to speed up convergence. Notice that the Accelerate K value & H Model Parameters check box should NOT be selected for Azeotropic columns, as convergence tends to be impeded.

The listed DEM parameters include: Parameter

Description

Acceleration Mode

Select either Conservative or Aggressive. With the Conservative approach, smaller steps are taken in the iterative procedure, thus decreasing the chance of a bad step.

Maximum Iterations Queued

Allows you to choose the number of data points from previous iterations that the accelerator program uses to obtain a solution.

Damping Group Choose the Damping method by selecting either the Fixed or Adaptive radio button.

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Fixed Damping If you select the Fixed radio button, you can specify the damping factor. The damping factor controls the step size used in the outer loop when updating the simple thermodynamic models used in the inner loop. For the vast majority of hydrocarbon-oriented towers, the default value of 1.0 is appropriate, which permits a full adjustment step. However, should you encounter a tower where the heat and specification errors become quite small, but the equilibrium errors diverge or oscillate and converge very slowly, try reducing the damping factor to a value between 0.3 and 0.9. Alternatively, you could enable Adaptive Damping, allowing HYSYS to automatically adjust this factor. Note: Changing the damping factor has an effect on problems where the heat and spec error does not converge.

There are certain types of columns, which definitely require a special damping factor. Use the following table as a guideline in setting up the initial value. Type of Column   

Damping Factor

All hydrocarbon columns from demethanizers to debutanizers to crude distillation units

1.0

Non-hydrocarbon columns including air separation, nitrogen rejection

1.0

Most petrochemical columns including C2= and C3= splitters, BTX columns   

1.0

Amines absorber   

1.0

Amines regenerator, TEG strippers, sour water strippers   

0.25 to 0.50

Highly non-ideal chemical columns without azeotropes   

0.25 to 0.50

Highly non-ideal chemical columns with azeotropes

0.50 to -1.0*

Note: The Azeotropic check box on the Solver page of the Parameters tab must be selected for an azeotropic column to converge.

As shown in the table above, an azeotropic column requires the azeotrope check box to be enabled. There are two ways to indicate to HYSYS that you are simulating an azeotropic column: l

l

Enter a negative damping factor, and HYSYS automatically selects the Azeotropic check box. Enter a positive value for the damping factor, and select the Azeotropic check box.

Note: The absolute value of the damping factor is always displayed.

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6 Column Property View

Adaptive Damping If you select the Adaptive radio button, the Damping matrix displays three fields. HYSYS updates the damping factor as the column solution is calculated, depending on the Damping Period and convergence behavior. Damping Period

Description

Initial Damping Factor

Specifies the starting point for adaptive damping.

Adaptive Damping Period

The default Adaptive Damping Period is ten. In this case, after the tenth iteration, HYSYS looks at the last ten errors to see how many times the error increased rather than decreased. If the error increased more than the acceptable tolerance, this is an indication that the convergence is likely cycling, and the current damping factor is then multiplied by 0.7. Every ten iterations, the same analysis is done to see if the damping factor should be further decreased. Alternatively, if the error increased only once in the last period, the damping factor is increased to allow for quicker convergence.

Reset Initial Damping Factor

If this check box is selected, the current damping factor is used the next time the column is solved. If this check box is cleared, the damping factor before adaptive damping was applied is used.

Initialization Algorithm Radio Buttons There are two types of method for the initialization algorithm calculation: l

l

Standard Initialization radio button uses the traditional initialization algorithm in HYSYS. Program Generates Estimations radio button uses a new functionality that handles the cases where the traditional initialization does not.

The following list situations when the Program Generates Estimations (PGE) initialization method is used: l

l

The PGE initialization handles systems with more than 25 components while the standard initialization does not handle systems with more than 25 components without the user’s initial estimation. When column does not converge with the standard initialization method (default), switching to PEG may converge the column. The new algorithm eliminates the discrepancy in the temperature and component estimates, which may exist in standard initialization.

Initial Estimate Generator Parameters You can enable the initial estimate generator (IEG) by selecting the Dynamic Integration for IEG check box. The IEG then performs iterative flash

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185

calculations (NRSolver, PV, and PH) to provide initial estimates for the temperature and composition profiles. No user estimates are required when the Dynamic Integration for IEG check box is selected. Click the Dynamic Estimates Integrator button, and the Col Dynamic Estimates property view appears.

Col Dynamic Estimates Property View The Col Dynamic Estimates property view allows you to further define the dynamic estimates parameters. You can set parameters for the time period over which the dynamic estimates are calculated, as well as set the calculation tolerance. A selected Active check box indicates that the Dynamic Integration for IEG is on. Select either the Adiabatic or Isothermal radio button to set the dynamic initialization flash type. If you want to generate the dynamic estimates without running the column, you can do so from this property view by clicking the Start button. If you want to stop calculations before the specified time has elapsed, click the Stop button. You do not have to manually click the Start button to generate the estimates; if the Dynamic Integration for IEG option is active, HYSYS generates them automatically whenever the column is running. The Shortcut Mode check box allows you to bypass this step once a set of estimates is generated, that is, once the column has converged. Note: If you are running simulation with an iterative solving procedure where the column has to be calculated several times, it is a good idea to select this option to save on calculation time.

Advanced Solving Options Button When you click the Advanced Solving Options button, the Advanced Solving Options property view appears.

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6 Column Property View

The Sequence to Apply Advanced Options is the order in which the solving options are executed is based on the priority. The “Can be used” check boxes must be selected in order to enable a particular option. These check boxes are only enabled if the corresponding spec type exists. All the Alternate active specs can be replaced on an individual spec basis or all specs simultaneously. The alternative (active) spec with the larger error is replaced with an alternative inactive spec with minimum error. Note: If the Column converges on an Alternate or Ranged Spec, the status bar reads “Converged - Alternate Specs” highlighted in purple.

On the Advanced Solving Options property view, each solving option (for example, Alternate, Ranged, and Autoreset) has a solving priority and also a check box option. To use a particular solving option, you have to select the corresponding check box. You must also specify the priority of the solving method. This is the order in which the solving options are executed (either first, second or third).

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187

Advanced solving options cannot be used until the minimum number of iterations are met. If the column is not solved after the minimum number of iterations, the solver switches to an advanced solving option according to the solving priority. This process is repeated until all the solving options have been attempted or the column converges. Note: When a column is in recycle, by default, the solver switches to the original set of specs after each recycle iteration or the next time the column solves.

2/3 Phase Page The 2/3 Phase page is relevant only when you are working with three-phase distillation. On this page, you can check for the presence of two liquid phases on each stage of your column. Note: This page is not available for Liquid-Liquid Extractor.

The Liquid Phase Detection table lists the liquid molar flow rates on each tray of the Tower, including the reboiler and the condenser. In order for HYSYS to check for two liquid phases on any given stage, select the check box in the Check column. If a second liquid phase is calculated, this is indicated in the Detected column, and by a calculated flowrate value in the L2Rate column. The buttons in the Liquid Phase Detection group serve as aids in selecting and clearing the trays that you want to check. Note: Checking for liquid phases in a three phase distillation tower greatly increases the solution time. Typically, checking the top few stages only, provides reasonable results.

The 2nd Liquid Type group allows you to specify the type of calculation HYSYS performs when checking for a second liquid phase. When the Pure radio button is selected, HYSYS checks only for pure water as the second phase. This helps save calculation time when working with complex hydrocarbon systems. When you want a more rigorous calculation, select the Rigorous radio button. Note: By default, HYSYS selects Pure for all hydrocarbon, and Rigorous for all chemical based distillations. This default selection criteria is based on the type of fluid package used but you can always change it.

Auto Water Draws Button The Auto Water Draws (AWD) option allows for the automatic adding and removing of total aqueous phase draws depending on the conditions in the converged column. Note: The Auto Water Draws facility is available for IO and MIO solvers.

AWD updating process is based on direct check of stage fluid phases. The direct check follows the Two Liquids Check Based on control criteria for detecting the aqueous phase. AWD mode is not available if No 2 Liq Check option is selected.

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6 Column Property View

Note: The Two Liquids Check Based on drop-down list is located in the Parameters tab of the Solver page in the Solving Options group.

To manipulate the AWD option, click the Auto Water Draws button to open the Auto Water Draws property view. Note: The Auto Water Draws button is available in both column subflowsheet and main flowsheet.

The Auto Water Draws property view contains the following objects: Object

Description

On

Select this check box to activate the Auto Water Draws mode.

Threshold

The threshold value allows variation of the condition for 2nd liquid phase. The default value in this cell is 0.001 (same as for Two Liquids Check based on control). If you delete the value in this cell, the threshold is set to minimum possible value.

Keep draws

If this check box is selected, the added draws are not removed.

Preserve estimates

If this check box is selected, the converged values are preserved as estimates for the next column run.

Reset

If this check box is selected, the column Reset option is performed before each column run.

Strategy

There are three options of strategy to select from in the Strategy group: l

All. All required changes in water draw configuration are done simultaneously.

l

From Top. Updates on the topmost stage from required is performed.

l

From Bottom. Updates on the bottommost stage from required is performed.

The All option results typically in multiple water draws with small flows, and the From Top or From Bottom option results typically in fewer water draws. To AWD

All existing water draws are converted to AWDs.

From AWD

Converts all AWDs to regular draws.

Restore

Restores the last successful (in other words, column equation were solved) AWD configuration.

Delete

Deletes all AWDs.

Two more columns are added in the table on the 2/3 Phase page when in Auto Water Draws mode. These two columns are called AWD and No AWD

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189

l

l

Set AWD mode for attached water draw by selecting the check boxes under the AWD column. If the check box in the No AWD column is selected, no AWD will be attached to corresponding stage.

Fluid Pkgs Page A column can use different fluid packages for different stages, including the condenser and the reboiler. The Parameters tab | Fluid Pkgs page property view lets you change the fluid package for each stage. Use the Change Fluid Pkgs button to change the fluid packages for a range of stages in one click. Note: Multiple fluid packages must be assigned the same component list to be substituted within the column.

Change Fluid Package Property View On the parameters - Fluid Pkgs page, click Change Fluid Pkgs... Use this dialog to highlight a target tower and select the range of trays, starting and ending, to accept the new fluid package.

Amines Page The Amines page appears on the Parameters tab only when working with the Amines Property Package. Starting in HYSYS V8.3, you can no longer add an Amine package when creating a new case. For cases created prior to V8.3 that include an Amine package, you can opt to continue using the Amine Package. However, we recommend that you switch to the Acid Gas package. Note: HYSYS now offers seamless conversion from the Amine package to the Acid Gas package. When you open a HYSYS case which includes the Amine Pkg selection, a dialog box appears, recommending that you switch to the new Acid Gas package for gas treating. The Acid Gas package provides an easy to set up and accurate column solver and offers superior thermodynamics and mass transfer rate-based distillation. If you select the Switch Amines to Acid Gas button, your case is converted to Acid Gas. A backup of your current case is created, ensuring that none of your data is lost in this conversion. A conversion report is also logged, informing you about any warnings or errors that occurred during the conversion.

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6 Column Property View

There are two groups on the Amine page: l

Tower Dimensions for Amine Package

l

Approach to Equilibrium Results

Tower Dimensions for Amine Package When solving the column using the Amines package, HYSYS always takes into account the tray efficiencies, which can either be user-specified, on the Efficiencies page, or calculated by HYSYS. Calculated efficiency values are based on the tray dimensions specified. The Amines page lists the Tower dimensions of your column, where you can specify these values that are used to determine the tray efficiencies in the Tower Dimensions for Amine Package group. The list includes: l

Tower

l

Weir Height

l

Weir Length

l

Tray Volume

l

Tray Diameter

If tray dimensions are not specified, HYSYS uses the default tray dimensions to determine the efficiency values.

Approach to Equilibrium Results Approach to Equilibrium values are used for the design, operation, troubleshooting, and de-bottlenecking for the absorption and regeneration columns in an amine plant. When you are modeling an amine column in HYSYS, you can calculate the Approach to Equilibrium values after the column converges. With this capability, you can adjust the flowrate of amine to achieve a certain Approach to Equilibrium value recommended by literature or in-house experts for the amine column. The extension is compatible with all of the major amine and mixtures of amines (in other words, MEA, DEA, TEA, DGA, DIPA, MDEA, and any mixtures of these amines). Note: The extension can only be used on a pre-converged amine treating unit simulation with the Amine Property Package.

The Approach to Equilibrium extension calculates the Approach to Equilibrium value of rich amine from the bottom of the absorber column in two methods: l

Partial Pressure

l

Amine Molar Loading

Method 1 Partial Pressure In this method, the Approach to Equilibrium is defined as the partial pressure of the acid gas in the rich amine stream exiting the absorber relative to the partial pressure of the acid gas in the main feed gas stream entering the absorber.

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The Approach to Equilibrium calculation are as follows: (1)

(2)

The Approach to Equilibrium results based on H2S and CO2 are expressed in percentages. When both H2S and CO2 are present, the highest Approach to Equilibrium percentage is usually reported, although both values should be reported.

Amine Molar Loading Amine Molar Loading is defined as the loading of the rich amine solution leaving the absorber divided by the equilibrium amine loading, assuming that the amine is at equilibrium with the feed gas and is at the same temperature as the rich amine leaving the absorber. The temperature of the rich amine and the amine in equilibrium with the feed gas are the same. The result is expressed as a percentage as follows: (3)

In general, the Approach to Equilibrium value calculated by the Partial Pressure method is greater than the one calculated by the Amine Molar Loading method.

Side Ops Tab Side strippers, side rectifiers, pump arounds, and vapor bypasses can be added to the Column from this tab. To install any of these Side Operations, click the Side Ops Input Expert button or on the appropriate Side Ops page, click the Add button. l

l

192

If you are using the Side Ops Input Expert, a wizard guides you through the entire procedure of adding a side operation to your column. If you are using the Add button, complete the form which appears, and then click the Install button. o

Specifications that are created when you add a side operation are automatically added to the Monitor page and Specs page.

o

For instance, when you add a side stripper, product draw and boilup ratio specs are added. As well, all appropriate operations are added; for example, with the side stripper (reboiled configuration), a side stripper Tower and reboiler are installed in the Column subflowsheet.

6 Column Property View

You can view or delete any Side Operation simply by positioning the cursor in the same line as the Operation, and clicking the View or Delete button. Note: If you are specifying Side Operations while in the Main simulation environment, make sure that the Solver is Active. Otherwise, HYSYS cannot register your changes. Note: The Side Ops tab is not available in the Liquid-Liquid Extractor. Note: Some solver methods do not allow side ops.

Side Strippers Page You can install a reboiled or steam-stripped side stripper on this page. You must specify the number of stages, the liquid draw stage (from the Main Column), the vapor return stage (to the Main Column), and the product stream and flow rate (on a molar, mass or volume basis). For the reboiled configuration, you must specify the boilup ratio, which is the ratio of the vapor to the liquid leaving the reboiler. For the steam-stripped configuration it is necessary to specify the steam feed. The property view of the side stripper is shown in the figure below.

When you click the Install button, a side stripper Tower is installed, as well as a reboiler if you selected the Reboiled configuration.

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193

By default, the Tower is named SS1, the reboiler is named SS1_Reb, and the reboiler duty stream is named SS1_Energy. As you add additional Side strippers, the index increases (for example SS2, SS3, and so forth). Note: To change the side stripper draw and return stages from the Column property view, the Solver must be Active in the Main simulation environment.

Side Rectifiers Page As with the side stripper, you must specify the number of stages, the liquid draw stage, and the vapor return stage. The vapor and liquid product rates, as well as the reflux ratio are also required. These specifications are added to the Monitor page and Specs page of the Column property view. When you install the side rectifier, a side rectifier Tower and partial condenser are added. By default, the Tower is named SR_1, the condenser is named SR_ 1_Cond, and the condenser duty stream is named SR_1_Energy.

Pump Arounds Page When you install the pump around, a Cooler is also installed. The default pump around specifications are the pump around rate and temperature drop. These are added on the Monitor page and Specs page of the Column property view. After you click the Install button, the Pump Around property view allows you to change pump around specifications, and view pump around calculated information. Note: When installing a Pump Around, it is necessary to specify the draw stage, return stage, molar flow, and duty.

Vap Bypasses Page As with the Pump Around, it is necessary to specify the draw and return stage, as well as the molar flow and duty for the vapor bypass. When you install the vapor bypass, the draw temperature and flowrate appear on the vapor bypass property view. The vapor bypass flowrate is automatically added as a specification. The figure below shows the vapor bypass property view once the side operation has been installed.

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Side Draws Page The Side Draws page allows you to view and edit information regarding the side draw streams in the column. The following information is included on this page: l

Draw Stream

l

Draw Stage

l

Type (Vapor, Liquid, or Water)

l

Mole Flow

l

Mass Flow

l

Volume Flow

Internals Tab Refer to Column Internals Tab for information regarding the Internals tab.

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Rating Tab The Rating tab has several pages, which are described in the table below. Page

Description

Towers

Provides information regarding Tower sizing. On this page, you can specify the following: l

Tower (Name)

l

Uniform Section. When this option is selected all tray stages have the same physical setup (diameter, tray type, and so forth).

l

Internal Type (tray type)

l

Diameter

l

Tray/Packed Space

l

Tray/Packed Volume

l

Disable Heat Loss Calcs

l

Heat Model

l

Rating Calculations

l

Hold Up (ft3). If you delete the weir height, you can then enter the hold up value, and the weir height is back-calculated.

l

Weeping Factor. The value is used to adjust the weeping in dynamic mode for low pressure drops.

l

Tray Sizing Analysis for Costing. Select which tray sizing utility Aspen Process Economic Analyzer needs to use for sizing. Note: No HYSYS calculations change as a result of selecting a tray sizing utility associated with costing.

Vessels

Equipment

196

Provides information regarding vessel sizing. On this page, you can specify the following: l

Vessel (Name)

l

Diameter

l

Length

l

Volume

l

Orientation

l

Vessel has a Boot

l

Boot Diameter

l

Boot Length

l

Hold Up (ft3)

Contains a list of Other Equipment in the Column flowsheet.

6 Column Property View

Page

Description

Pressure Drop

Contains information regarding pressure drop across the column. On this page you can specify the following information: l

Pressure Tolerance

l

Pressure Drop Tolerance

l

Damping Factor

l

Maximum Pressure Iterations

l

Top and Bottom column pressures

Towers Page The Towers page contains all the required information for correctly sizing the column Towers. Note: The required size information for the Tower can be calculated using the Tray Sizing Analysis.

The Tower diameter, weir length, weir height, and the tray spacing are required for an accurate and stable dynamic simulation. You must specify all the information on this page. With the exception of the tray volume, no other calculations are performed on this page. (The required size information for the Tower can be calculated using a Tray Sizing Analysis.) For multipass trays, simply enter the column diameter and the appropriate total weir length. To complete the Tower Sizing form: 1. Specify the following sizing information for each Tower: Diameter and Tray/Packed Space. The Tray Volume is calculated from these parameters. 2. Select the Disable Heat Loss Calcs check box to ignore the effects of heat loss. 3. From the Heat Model drop-down list, select one of the following models: None, Direct Q, Simple, or Detailed. 4. Select the Rating Calculations check box to enable rating calculations. 5. Use the Tray Sizing Analysis for Costing drop down list to select the tray sizing utility Aspen Process Economic Analyzer (APEA) must use for sizing for a particular tray / packed section. Note: This entry is only relevant to APEA - no HYSYS calculations change as a result of selecting a tray sizing utility associated with costing.

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Vessels Page The Vessels page contains the necessary sizing information for the different vessels in the column subflowsheet. To complete the Vessels form: 1. From the Orientation drop-down list, select one of the following vessel orientations for each vessel in the Vessel Sizing table: Horizontal or Vertical. 2. For each vessel in the Vessel Sizing table, specify two of the following sizing parameters: Diameter, Length/Height, or Volume. 3. Select the Vessel has a Boot check box to simulate the vessel with a boot. Specify the Boot Diameter and Boot Length in the appropriate fields.

Equipment Page The Equipment page contains a list of all the additional equipment, which is part of the column subflowsheet. The list does not contain equipment, which is part of the original template. Any extra equipment, which is added to the subflowsheet (pump arounds, side strippers, and so forth) is listed here. Doubleclicking on the equipment name opens its property view on the Rating tab. Note: This page is not available in the Liquid-Liquid Extractor.

Pressure Drop Page The Pressure Drop page allows you to specify the pressure drop across individual trays in the Towers. The pressure at each individual stage can also be specified. The Pressure Solving Options group allows you to adjust the following parameters: l

Pressure Tolerance

l

Pressure Drop Tolerance

l

Damping Factor

l

Maximum Pressure Iterations

To specify the tray pressure profile: 1. In the Pressure column, specify the pressure for each of the stages in the column. You are only required to specify a top stage (or condenser) and bottom stage (or reboiler) pressure in order for HYSYS to solve the column. However, the more data you can input, the faster the column will solve. The remaining stage pressures are calculated by HYSYS. 2. In the Pressure Tolerance field, specify the tolerance you want to use when calculating the pressures of each stage. 3. In the Pressure Drop Tolerance field, specify the tolerance you want

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to use when calculating the pressure drops of each stage. 4. In the Damping Factor field, specify the damping factor. 5. In the Max Press Iterations field, specify the maximum number of iterations you want the solver to try before failing.

Damping Factor Guidelines

Type of Column

Damping Factor

All hydrocarbon columns from demethanizers to debutanizers to crude distillation units.

1.0

Non-hydrocarbon columns including air separation, nitrogen rejection.

1.0

Most petrochemical columns including C2= and C3= splitters, BTX columns.

1.0

Amines absorber

1.0

Amines regenerator, TEG strippers, sour water strippers

0.25 to 0.50

Highly non-ideal chemical columns without azeotropes.

0.25 to 0.50

Highly non-ideal chemical columns with azeotropes.

0.50 to -1.0

Note: This page is not available in the Liquid-Liquid Extractor.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the unit operation. The PF Specs page contains a summary of the stream property view’s Dynamics tab. Note: The Column Environment also has its own Workbook.

Performance Tab On the Performance tab, you can view the results of a converged column on the Summary page, Column Profiles page, and Feeds/Products page. You can also view the graphical and tabular presentation of the column profile on the Plots page. Note: You can view the results in molar, mass or liquid volume, by selecting the appropriate basis radio button.

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Summary Page The Summary page gives a tabular summary of the feed and product stream compositions, flows or the % recovery of the components in the product streams. When you select the Recovery radio button, the Feed table displays the feed stream flowrate. The Products table displays the flow rate of each of the column product streams and either the composition (Composition radio button is active), flow rate (Flows radio button is active), or percent recovery (Recovery radio button is active) of each of the components in the product streams.

Column Profiles Page The Column Profiles page gives a tabular summary of Column stage temperatures, pressures, flows, and duties. l

l

l

l

The Reflux Ratio and Reboil Ratio are displayed in the upper left corner of the page. If the Flows radio button is selected, the table displays the Temperature, Pressure, Net Liquid Flow, Net Vapor Flow, Net Feed Rate, Net Draw Rates, and Duty. If the Energy radio button is selected, the table displays the Temperature, Liquid Enthalpy, Vapor Enthalpy, and Heat Loss. The Heat Loss column is empty if no heat loss model has been selected (see the Towers page on the Rating tab). You can change the basis for which the data appears by selecting the appropriate radio button from the Basis group.

Note: The liquid and vapor flows are net flows for each stage. Note: The Heat Loss column is empty unless you select a heat flow model in the column subflowsheet of Main TS property view on the Rating tab.

Feeds/Products Page The Feeds/Products page gives a tabular summary of feed and product streams tray entry/exit, temperatures, pressures, flows, and duties. You can change the basis of the data by selecting the appropriate radio button from the Basis group. For the feeds and draw Streams, the VF column to the right of each flow value indicates whether the flow is vapor (V) or liquid (L). If the feed has been split, a star (*) follows the phase designation. If there is a duty stream on a stage, “Energy” appears in the Type column. The direction of the energy stream is indicated by the sign of the duty. Note: You can split a feed stream into its phase components either on the Setup page of the Flowsheet tab in the column property view or on the Options page of the Simulation tab in the Session Preferences property view.

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Plots Page On the Plots page, you can view various column profiles or assay curves in a graphical or tabular format. Select the Live Updates check box to update the profiles with every pass of the solver (in other words, a dynamic update). This check box is cleared by default, because the performance of the column can be a bit slower if the check box is selected and a profile is open.

Tray by Tray Properties Group To view a column profile, follow this generalized procedure: 1. Select a profile from the list in the Tray by Tray Properties group. The choices include: Temperature, Pressure, Flow, Transport Properties, Composition, K Value, Light/Heavy Key, and Electrolyte Properties. Note: Electrolyte Properties are only available for cases with an electrolyte system.

2. In the Column Tray Ranges group, select the appropriate radio button: Radio Button

Action

 All

Displays the selected profile for all trays connected to the column (for example, main Tower, side strippers, condenser, reboiler, and so forth).

Single Tower

From the drop-down list, select a Tower.

From/To

Use the drop-down lists to specify a specific range of the column. The first field contains the tray that is located at a higher spot in the tower (for example, for top to bottom tray numbering, the first field could be tray 3 and the second tray 6).

The main Tower along with the condenser and reboiler are considered one section, as is each side stripper.

3. After selecting a tray range, click either the View Graph button or the View Table button to display a plot or table respectively. To make changes to the plot, right-click in the plot area, and select Graph Control from the object inspect menu. Note: Plots and tables are expandable property views that can remain open without the column property view.

Depending on the profile selected, you have to make further specifications. For certain profiles, there is a Properties button on both the profile plot and table. By clicking this button, the Properties property view appears, where you can customize the display of your profile. Changes made on the Properties property view affect both the table and plot.

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A description of the specifications available for each profile type are outlined in the following table.

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Profile Type

Description

Temperature Profile

Displays the temperature for the tray range selected. No further specification is needed.

Pressure Profile

Displays the pressure of each tray in the selected range. No further specification is needed.

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Profile Type

Description

Flow Profile

Displays the flow rate of each tray in the selected range. You can customize the data displayed using the Properties property view. In the Basis group, select molar, mass or liquid volume for your flow profile basis. In the Phase group, select the check box for the flow of each phase that you want to display. Multiple flows can be shown. If three phases are not present in the column, the Heavy Liquid check box is not available, and thus, the Light Liquid check box represents the liquid phase. In the Tray Flow Basis group, you can specify the stage tray flow basis by selecting the appropriate radio button: l

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Net.

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Profile Type

Description The net basis option only includes interstage flow. l

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Total. The total basis option includes draw and pump around flow.

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Profile Type

Description

Transport Properties Profile

Displays the selected properties from each tray in the selected range. You can customize the data displayed using the Properties property view:

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l

In the Basis group, select molar or mass for the properties profile basis.

l

In the Phase group, select the check box for the flow of each phase that you want to display on the graph. Multiple flows can be shown. If three phases are not present in the colum-

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Profile Type

Description n, the Heavy Liquid check box is not available. The Properties Profile table displays all of the properties for the phase (s) selected. l

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In the Axis Assignment group, by selecting a radio button under Left, you assign the values of the appropriate property to the left y-axis. To dis-

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Profile Type

Description play a second property, choose the radio button under Right. The right yaxis then shows the range of the second property. If you want to display only one property on the plot, select the None radio button under Right.

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Profile Type

Description

Composition Profile

Displays the selected component’s mole fraction for each stage in the selected range. You can customize the data displayed using the Properties property view. l

In the Basis group, select molar, mass or liquid volume for the composition profile basis.

l

In the Phase group, select the check box for the flow of each phase that you want to display. Multiple flows can be shown. If the three phases are not present

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Profile Type

Description in the column, the Heavy Liquid check box is not available, and thus, the Light Liquid check box represents the liquid phase.

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l

Choose either Fractions or Flows in the Comp Basis group by selecting the appropriate radio button.

l

The Components group displays a list of all the compon-

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Profile Type

Description ents that enter the tower. You can display the composition profile of any component by selecting the appropriate check box. The plot displays any combination of component profiles.

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Profile Type

Description

K Values Profile

Displays the K Values for each stage in the selected range. You can select which components you want included in the profile using the Properties property view.

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Profile Type

Description

Light/Heavy Key Profile

Displays the fraction ratio for each stage. You can customize the data displayed using the Properties property view. l

In the Basis group, select molar, mass or liquid volume for the profile basis.

l

In the Phase group, select vapor, Light Liquid or Heavy Liquid for the profile phase.

l

In the Light Key(s) and Heavy Key(s) groups, you can select the key component (s) to include in your profile.

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Profile Type

Description

Electrolyte Properties Profile

Displays the pH and ionic strength or the scale index depending on which radio button you select in the Graph Type group. When you select the pH, Ionic Strength radio button, you can see how the pH value and ionic strength decrease or increase from stage to stage. The Solid Components group displays a list of the solids that could form in the distillation column. You can select or clear the check boxes to display or hide the scale tendency index value for the solid components in the table or graph. The scale tendency index value refers to its tendency to form at the given conditions. Solids with a scale tendency

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Profile Type

Description index greater than 1 form, if the solid formation is governed by equilibrium (as oppose to kinetics), and if there are no other solids with a common cation or anion portion which also has scale tendency greater than 1.

Assay Curves Group From the Assay Curves group, you can create plots and tables for the following properties: l

Boiling Point Assay

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Molecular Weight Assay

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Density Assay

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User Properties

For each of the options, you can display curves for a single tray or multiple trays. To display a plot or table, make a selection from the list, and click either the View Graph button or the View Table button. The figure below is an example of how a Boiling Point Properties plot appears.

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Properties View for Plots and Tables The Properties view is available to certain plots and tables generated from the Tray By Tray field. Use it to control the contents of the generated table or plot. Click the Properties button on the lower left corner of these tables or plots to open the Properties view. The Properties view options change depending on the property type of plot or table you are generating. For example, the figure below shows the dialog when Composition is the selected property. For a selected property, all changes made on the Properties view effect the data of both the plot and the table. See the table above for specifics on each property plot type.

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Data Control Property View Click the Profile Data Control button on the bottom of every generated assay curve plot and table to open the Data Control property view. For the selected curve, all changes made on the Data Control property view affect the data of both the plot and table. The Data Control property view consists of the groups as shown in the figure below.

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The following table describes each data control option available according to group name. Group

Description

Style

Select either the Multi Tray or Single Tray radio button. The layout of the Data Control property view differs slightly for each selection. For the Single Tray selection, you must open the drop-down list and select one tray. If you select Multi Tray, the drop-down list is replaced by a list of all the trays in the column. Each tray has a corresponding check box, which you can select to display the tray property on the plot or table.

Properties

Displays the properties available for the plot or table. Each Curve option has its own distinct Properties group. For a single tray selection, you can choose as many of the boiling point curves as required. Select the check box for any of the following options: TBP, ASTM D86, D86 Crack Reduced, D1160 Vac, D1160 ATM, and D2887. When multiple trays have been chosen in the Style group, the check box list is replaced by a drop-down list. You can only choose one boiling point curve when displaying multiple trays.

Basis

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Select molar, mass or liquid volume for the composition basis.

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Group

Description

Phase

Select the check box for the flow of each phase that you want displayed. Multiple flows can be shown. If there are not three phases present in the column, the Heavy Liquid check box is not available, and thus, the Light Liquid check box represents the liquid phase.

Visible Points

The radio buttons in the Visible Points group apply to the plots only. Select either the 15 Points or 31 Points option to represent the number of data points which appear for each curve.

TBP Envelope Group The TBP Envelope group contains only the View Graph button. You can click the View Graph button to display a TBP Envelope curve. Note: The curve allows you to view product stream distillation overlaid on the column feed distillation. This gives a visual representation of how sharp the separations are for each product. The sharpness of separation is adjusted using section and stripper efficiencies and front and back end shape factors.

Click the Profile Data Control button located on the property view above to open a property view for customizing your TBP Envelope curve.

Condenser/Reboiler Page Use this page to view the performance of condensers or reboilers associated with the column.

Flowsheet Tab The Flowsheet tab contains the following pages: l

Setup

l

Variables

l

Internal Streams

l

Mapping

l

Lock

Setup Page The Setup page defines the connections between the internal (subflowsheet) and external (Parent) flowsheets. To split all material inlet streams into their phase components before being fed to the column, select the Split All Inlets check box. l

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If one of the material feed stream Split check box is clear, the Split All Inlets check box is cleared also.

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l

If you clear the Split All Inlets check box, none of the material inlet stream Split check boxes are affected.

Note: Split functions are incompatible with the Sparse Continuation solver, and are grayed out when Sparse Continuation is selected as the solving method.

The Labels, as noted previously, attach the external flowsheet streams to the internal subflowsheet streams. They also perform the transfer (or translation) of stream information from the property package used in the parent flowsheet into the property package used in the Column subflowsheet (if the two property packages are different). The default transfer basis used for material streams is a P-H Flash.

Setup Page Fields l

l

l

l

l

l

The Inlet Streams group displays the name of the internal stream (subflowsheet stream), the name of the external stream (parent flowsheet stream), and the transfer basis for each of the streams entering the column. By default, both the internal and external streams are the same. The Inlet Streams group also enables you to add new streams to the Column or modify existing streams using the drop-down lists in the External Stream and Transfer Basis columns. The Outlet Streams group displays the name of the internal stream (subflowsheet stream), the name of the external stream (parent flowsheet stream), and the transfer basis for each of the streams exiting the column. By default, both the internal and external streams are the same. The Outlet Streams group also enables you to add new streams to the Column or modify existing streams using the drop-down lists in the External Stream and Transfer Basis columns. The Transfer Basis is significant only when the subflowsheet and parent flowsheet Property Packages are different. The Transfer Basis dropdown lists contain the following options: T-P Flash, VF-T Flash, VF-P Flash, P-H Flash, User Specs, and None Required. The Flowsheet Topology group displays stage information for each element in the Column’s flowsheet.

The Transfer Basis is significant only when the subflowsheet and parent flowsheet Property Packages are different. Flash Type

Action

T-P Flash

The pressure and temperature of the material stream are passed between flowsheets. A new vapor fraction is calculated.

VF-T Flash

The vapor fraction and temperature of the material stream are passed between flowsheets. A new Pressure is calculated.

VF-P Flash

The vapor fraction and pressure of the material stream are passed between flowsheets. A new temperature is calculated.

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Flash Type

Action

P-H Flash

The pressure and enthalpy of the material stream is passed between flowsheets. This is the default transfer basis.

User Specs

You can specify the transfer basis for a material Stream.

None Required

No calculation is required for an energy stream. The heat flow is simply passed between flowsheets.

When the Split check box for any of the inlet material streams is selected, the stream is split into its vapor and liquid phase components. The liquid stream is then fed to the specified tray, and the vapor phase to the tray immediately above the specified feed tray. Note: See the Summary page of the Performance tab to verify the split feed streams. An asterisk (*) following the phase indicator in the VF column indicates a split stream.

Energy streams and material streams connected to the top stage (condenser) cannot be split. The check boxes for these variables appear grayed out. The Flowsheet Topology group provides stage information for each element in the flow sheet.

Flowsheet Variables Page (Main) The Variables page allows you to select and monitor any flowsheet variables from one location. You can examine subflowsheet variables from the outside Column property view, without actually having to enter the Column subflowsheet environment. You can add, edit or delete variables in the Selected Column flowsheet Variables group. Note: You can also use the Specifications page to view certain variables. Select the variable by adding a specification, and ensure that the Active and Estimate check boxes are clear. The value of this variable appears in the Current value column, and this “pseudospecification” do not affect the solution.

Adding a Variable To add a variable in the Selected Column Flowsheet Variables group: 1. Click the Add button. 2. From the Variable Navigator, select each of the parameters for the variable. 3. Click the OK button. 4. The variable is added to the Selected Column Flowsheet Variables group.

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Editing a Variable You can edit a variable in the Selected Column Flowsheet Variables group as follows: 1. Highlight a variable. 2. Click the Edit button. 3. Make changes to the selections in the Variable Navigator. 4. Click the OK button. If you decide that you do not want to keep the changes made in the variable navigator, click the Cancel button.

Deleting a Variable You can remove a variable in any of the following ways: l

Select a variable, and click the Delete button. -or-

l

Select a variable, click the Edit button, and then click the Disconnect button on the Variable Navigator.

Internal Streams Page On the Internal Streams page, you can create a flowsheet stream that represents any phase leaving any stage within the Column. Streams within operations attached to the main Tower (for example, side strippers, condenser, reboiler, and so forth) can also be targeted. Each time changes occur to the column, new information is automatically transferred to the stream which you have created. Example: add a stream representing the liquid phase flowing from stage 7 to stage 8 in the main Tower of a column: 1. Click the Add button. 2. In the Stream drop-down list, type the name of the stream named Liquid. 3. In the Stage drop-down list, select stage 6 or simply type 6, which locates the selection in the list. 4. In the Type drop-down list, select the phase that you want to represent. The options include Vapor, Liquid or Aqueous. Select Liquid in this case. 5. From the Net/Total drop-down list, select either Net or Total. For the stage 6 liquid, select Net. o

Net represents the material flowing from the Stage you have selected to the next stage (above for vapor, below for liquid or aqueous) in the column.

o

Total represents all the material leaving the stage (for example, draws, pump around streams, and so forth).

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Mapping Page The Mapping page contains a table that displays the inlet and outlet streams from the column subflowsheet, and component maps for each boundary stream. If the fluid package of the column is the same as the main flowsheet, component maps are not needed (because components are the same on each side of the column boundary). None Req'd is the only option in the drop-down list of the Into Sub-Flowsheet and Out of Sub-Flowsheet columns. If the fluid packages are different, you can choose a map for each boundary stream. HYSYS lists appropriate maps based on the fluid package of each stream across the boundary. Click the Overall Imbalance Into Sub-Flowsheet button or Overall Imbalance Out of Sub-Flowsheet button to view any mole, mass, or liquid volume imbalance due to changes in fluid package. If there are no fluid package changes, then there are no imbalances.

Lock Page The Lock page lets you lock or unlock the subflowsheet and displays the lock status of the subflowsheet. When the flowsheet is locked, you cannot create or delete objects, or change the topology. You can add Set, Adjust, and Spreadsheet operations; manipulate variable values; or copy the contents of the flowsheet and create your own modifiable version. Note: Subflowsheets inside a locked subflowsheet have to be specifically locked. l

l

To lock a subflowsheet, enter a password in the Lock Status field and press ENTER. To unlock a subflowsheet, enter the correct password in the Lock Status field and press ENTER.

Reactions Tab Note: This tab is not available for the Liquid-Liquid Extractor.

Reactive distillation has been used for many years to carry out chemical reactions, in particular esterification reactions. The advantages of using distillation columns for carrying out chemical reactions include: l

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The possibility of driving the reaction to completion (break down of thermodynamic limitations for a reversible reaction), and separating the products of reactions in only one unit, thus eliminating recycle and reactor costs. The elimination of possible side reactions by continuous withdrawal of

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one of the products from the liquid phase. l

l

The operation at higher temperatures (boiling liquid), thus increasing the rate of reaction of endothermic reactions. The internal recovery of the heat of reaction for exothermic reactions, thereby replacing an equivalent amount of external heat input required for boil-up.

You can only use reactions with the following Column solving methods: Sparse Continuation Solver, Newton Raphson Inside-Out, and Simultaneous Correction. Note: For any column in an electrolyte flowsheet, there is no option to add any reaction (reaction set) to the column. Conceptually, electrolyte thermo conducts a reactive and phase flash all together. HYSYS does not provide options to allow you to add external reactions to the unit operation.

The Reactions tab allows you to attach multiple reactions to the column. The tab consists of two pages: l

l

Stages. Allows you select the reaction set, and its scope across the column. Results. Displays the reaction results stage by stage.

Before adding a reaction to a column, you must first ensure that you are using the correct column Solving Method. HYSYS provides three solving methods which allow for reactive distillation. Solving Method

Reaction Type

Reaction Phase

Sparse Continuation Solver

Kinetic Rate, Simple Rate, Equilibrium Reaction

Vapor, Liquid

Newton Raphson InsideOut

Kinetic Rate, Simple Rate

Simultaneous Correction

Kinetic Rate, Simple Rate, Equilibrium Reaction

This is an equation based solver. It supports two liquid phases on the trays, and its main use is for solving highly non-ideal chemical systems and reactive distillation

Liquid

General purpose method that allows liquid-phase kinetic reactions inside the Column subflowsheet.

Simultaneous method using dogleg methods, good for chemical systems. This method also supports reactive distillation.

Vapor, Liquid, Combined Phase

Note: The Sparse Continuation Solver method allows you to attach a reaction set to your column, which combines reaction types. Other solvers require that the attached reactions are of a single type.

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Stages Page The Stages page consists of the Column Reaction Stages group. The group contains the Column Reaction Stages table and three buttons.

Column Reaction Stages Table The table consists of four columns, which are described in the table below. Column

Description

Column Reaction Name

The name you have associated with the column reaction. This is not the name of the reaction set you set in the fluid package manager.

First Stage

The highest stage of the stage range over which the reaction is occurring.

Last Stage

The lowest stage of the stage range over which the reaction is occurring.

Active

Activates the associated reaction thereby enabling it to occur inside the column.

The property view also contains three buttons that control the addition, manipulation, and deletion of column reactions. Button

Description

New

Allows you to add a new column reaction set via the Column Reaction property view.

Edit

Allows you to edit the column reaction set whose name is currently selected in Column Reaction Stages table. The selected reaction’s Column Reaction property view appears.

Delete

Allows you to delete the column reaction set whose name is currently selected in the Column Reaction Stages table.

Column Reaction Property View The Column Reaction property view allows you to add and revise column reactions. The Column Reaction property view consists of two groups: l

l

The Reaction Set Information group allows you to select the reaction set, and the scope of its application. The Reaction Information group contains thermodynamic and stoichiometric information about the reaction you are applying to the selected section of the column.

Reaction Set Information Group The Reaction Set Information group consists of six objects:

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Objects

Description

Name

The name you would like to associate with the column reaction. This is the name that appears in the Column Reaction Name column of the Column Reaction Stages table.

Reaction Set

Allows you to select a reaction set from a list of all the reaction sets attached to the fluid package.

First Stage

The upper limit for the reaction that is to occur over a range of stages.

Last Stage

The lower limit for the reaction that is to occur over a range of stages.

Delete

Deletes the Column Reaction from the column.

Active

Allows you to enable and disable the associated column reaction.

Reaction Information Group The Reaction Information group contains the Reaction field, which allows you to select a reaction from the reaction set selected in the Reaction Set field. Click the View Reaction button to open the selected reaction’s Reaction property view. This group also contains three sub-groups, which allow you to view or specify the selected reactions properties. Sub-group

Description

Stoichiometry

Allows you to view and make changes to the stoichiometric formula of the reaction currently selected in the Reaction drop-down list. The group contains three columns:

Basis

l

Components. Displays the components involved in the reaction.

l

Mole Wt. Displays the molar weight of each component involved in the reaction.

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Stoich Coeff. Stoichiometric coefficients associated with the reaction.

Consists of two fields: l

Base Component. Displays the reactant to which the reaction extent is calculated. This is often the limiting reactant.

l

Reaction Phase. Displays the phase for which the kinetic rate equations for different phases can be modeled in the same reactor. To see the possible reactions, click the Reaction Information button in the View Reaction group.

You can make changes to the fields in these groups. These changes affect all the unit operations associated with this reaction. Click the View Reactions button for more information about the attached reaction.

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Sub-group

Description

Heat and Balance Error

Consists of two fields: l

Reaction Heat. Displays the reaction heat.

l

Balance Error. Displays any error in the mass balance around the reaction.

Results Page The Results page displays the results of a converged column. The page consists of a table containing six columns. The columns are described in the following table: Column

Description

1st column

Displays the name/number of the column stage.

Rxn Name

The name of the reaction occurring at this stage.

Base Comp

The name of the reactant component to which the calculated reaction extent is applied.

Rxn Extent

The consumption or production of the base component in the reaction.

Spec % Conv

Displays the percentage of conversion specified by you.

Act % Conv

Displays the percentage of conversion calculated by HYSYS.

If you have more than one reaction occurring at any particular stage, each reaction appears simultaneously. Note: The Rxn Extent results appear only if the Sparse Continuation Solver is chosen as the Solving Method.

Design Tips for Reactive Distillation Although the column unit operations allows for multiple column reactions and numerous column configurations, a general column topography can be subdivided into three sections:

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Rectifying Section

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Reactive Section

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Stripping Section

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While the Rectifying and Stripping Sections are similar to ordinary distillation, a reactive distillation column also has a Reactive Section. The Reactive Section of the column is where the main reactions occur. There is no particular requirement for separation in this section. There are several unique operational considerations when designing a reactive distillation column: l

l

l

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The operating pressure should be predicated on the indirect effects of pressure on reaction equilibrium. The optimum feed point to a reactive distillation column is just below the reactive section. Introducing a feed too far below the reactive section reduces the stripping potential of the column and results in increased energy consumption. Reflux has a dual purpose in reactive distillation. Increasing the reflux rate enhances separation and recycles unreacted reactants to the reaction zone thereby increasing conversion. Reboiler Duty is integral to reactive distillation as it must be set to ensure sufficient recycle of unreacted, heavy reactant to the reaction zone without excluding the light reactant from the reaction zone, if the reboiler duty is too high or too low, conversion, and purity can be compromised.

Dynamics Tab The Dynamics tab contains the following pages: l

Vessels

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Equipment

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Holdup

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If you are working exclusively in Steady State mode or your version of HYSYS does not support dynamics, you are not required to change any information on the pages accessible through this tab.

Vessels Page The Vessels page contains a summary of the sizing information for the different vessels contained in the column subflowsheet. In addition, it contains the possible dynamic specifications for these vessels.

Equipment Page The Equipment page displays the same information as the Equipment page on the Rating tab. The difference is that double-clicking on the equipment name opens its property view on the Dynamics tab. Note: This page is not available for the Liquid-Liquid Extractor.

Holdup Page The Holdup page contains a summary of the dynamic information calculated by HYSYS. Column

Description

Pressure

Displays the calculated stage pressure.

Total Volume

Displays the stage volume.

Bulk Liq Volume

Displays the liquid volume occupying the stage.

Refer to the Holdup Page section for more information.

Perturb Tab The Perturb tab is only available in the Column Runner property view. To show the Perturb tab: 1. From the PFD, double-click the Column icon. The Column property view appears. 2. Click the Column Environment button. The Column build environment appears. 3. Click Column > Runner > Show Column Runner in the Ribbon. The Column Runner property view appears. 4. Click the Perturb tab.

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The Perturb tab allows you to control the way column solver calculates the partial derivatives. There are two types of independent controls. Control

Description

Low The Analytic property derivatives check box allows you to turn On and Off Level Ana- low level analytic derivatives support (in other words, derivatives of therlytic modynamic properties like Fugacity, Enthalpy, and Entropy by Temperature, Pressure, and Composition). At present this facility is available for Peng Robinson or Soave-RedlichKwong property packages in Sparse Continuation Solver context. Optimizer HYSYS Optimizer (RTO+) allows calculation of column analytic derivatives Level Ana- by stream Temperature, Pressure, Component Flow, Column Spec spelytic cified value, and Tear Variables.

The Sparse Analytic page allows you to select a particular method of column analytic derivatives calculation. The Perturb method parameters group provides tuning parameters for analytic column derivatives calculator. l

l

l

Rigorous properties check box. If active, rigorous thermodynamic properties are applied in Jacobi matrix calculation. If inactive, simple models (controlled by Control panel of Sparse solver) are applied instead for Enthalpy and Fugacity of thermodynamic phases. The last option may expedite derivative calculations. Warm restart check box. If active, additional Sparse linear solver information is preserved between Analytic derivative calculator calls (faster solution of linear system). If inactive, no Sparse linear solver information is stored (memory economy). Skip Sparse Solve check box. If active, Column solution phase is skipped (may allow faster execution).

Column Internals Tab You can use the Internals tab for the Column to explore multiple column configurations. The Internals tab includes pages for each tower within your column subflowsheet: l

Main Tower

l

Side Strippers

l

Side Rectifiers

To learn more about the fields/buttons on this page, refer to the following table.

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Field/Button

Refer to

Active drop-down list

Selecting an Active Option

Add New button

Creating Column Sections

Auto Section button

Using Auto Sectioning

Duplicate button

Duplicating Column Sections

Import Template button

Importing and Exporting Column Section Templates

Export Template button

Importing and Exporting Column Section Templates

View Internals Summary button

Viewing Internals Results

Include Static Vapor Head in Pressure Drop Calculations check box

Including Static Vapor Head Corrections

Calculate Pressure Drop Across Sump check box

Calculating the Pressure Drop Across a Sump

View Hydraulic Plots button

Hydraulic Plots

Export Pressure Drop from Top button

Updating Pressure Drops

Export Pressure Drop from Bottom button

Updating Pressure Drops

Initialize from Rating button

Initializing from the Rating Tab

Send to Rating button

Sending to the Rating Tab

Adding a New Internals Option On the Internals tab of the Column property view, you can add a new option. l

From the Active drop-down list, select the option. An empty Internals form appears. The new option will also appear in the Internals Manager. You can rename this option in the Internals Manager. For further details, refer to Column Internals Manager.

Creating Column Sections Note: If there are two liquid phases in a column, the total liquid flow rate (light and heavy liquids) is used in calculations. The transport properties are weighted averages of the light and heavy liquids for each liquid phase.

To create column sections within your column: 1. Select the Internals tab. 2. Click the Add New button to create a new internals section. A row appears, named CS-1 by default. 3. Optionally, type a Column Description for the Column Internals configuration. You can use this to record the purpose for this internals configuration when you have multiple configurations that may implement different design choices.

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4. Specify the desired Start Stage and End Stage for the section from the list of available stages. To complete the Column Internals configuration, you must define a set of sections which include all stages (except for the condenser and reboiler). If you previously specified a particular stage, it will no longer be available as an option unless you modify the previous section to not include that stage. The column diagram on the left displays the layout of the column with adjacent sections in alternating colors. Any gaps in the column are visible as white sections. A message at the top right of the sheet indicates where these gaps are located. If the column sections are of different diameters, the sections are depicted with widths proportional to those diameters. Arrows left and right of the diagram indicate feeds, products, side draws, and pumparounds (which are indicated with blue connected arrows on the right side of the diagram). When there are multiple feeds, draws, and/or pumparound returns on the same or near stages such that the arrows would overlap, you can hover the mouse over the arrow to see information about the connections there.

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o

If all stages are accounted for and there are no gaps in the column, an Internals Input Complete message appears.

o

If you specified section boundaries but there are gaps within the column, a message appears, indicating where the gaps are located.

5. Specify the Mode: o

Interactive Sizing: If the mode is Interactive Sizing, which is the default, once you specify the start and end stages, HYSYS generates reasonable defaults for the section: Trays: HYSYS calculates a default for:

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o

Diameter

o

Number of passes

o Downcomer geometry and locations Refer to Tray and Downcomer Area Calculations for further details. Packing: HYSYS calculates a default for: o

Section diameter Note: You must specify section packing height.

Rating: Diameter and downcomer geometry and location are not calculated by HYSYS. This will apply to all sections in this object. o

6. In the Details column, click the View button to specify detailed geometry information on the Geometry form. Notes: l

When you create sections adjacent to one another, they will be shaded in different colors in the diagram on the Internals tab or form.

l

Click the X to delete a section.

l

Click the View button in the Details column to specify Geometry details on the Geometry form.

l

Click the View Hydraulic Plots button to view hydraulic operating diagrams for the current Internals configuration.

l

Click the Import Template button to: o

Create a new section using the geometry and design parameters specified in a template.

o

Update an existing section using the geometry and design parameters specified in a template.

You can import the same template to multiple sections at a time. l

Click the Export Template button to export an XML template with geometry and design parameters based on an existing internals section.

Duplicating Column Sections You can duplicate geometry and design parameters from a selected column section to a new column section. To duplicate an existing column section: 1. On the Internals tab or form, select the desired section to duplicate. Note: If you select multiple sections, HYSYS duplicates the first section.

2. Click Duplicate. A new row appears in the table, with a new name that you can change by clicking its cell and typing over it in the grid. Values of appear for the Start Stage and End Stage. All other user-specified values will be duplicated. 3. If desired, modify the Description and Mode for the new section.

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4. Double-click the row and make changes to the sections to complete specifications for the new section.

Using Auto Sectioning If you click the Auto Section button, HYSYS automatically creates column sections based on feed and draw locations or internal flow rates. Note: You can only click the Auto Section button if there are no internal sections defined already.

If you click the arrow next to the Auto Section button, you can opt to auto section the column: l

Based on Feed/Draw Locations (default)

l

Based on Flows

Selecting an Active Option To select an active option: l

From the Active drop-down list, select the primary internals configuration for analysis.

Note: Only one internals configuration can be set as Active.

Adding a New Geometry Option To add a new geometry option without accessing the Internals Manager: l

From the Active drop-down list, select . A new option is automatically created, and an empty Internals form appears. You can rename this option on the Internals Manager.

Updating Pressure Drops You can update pressure drops in your column using results from the hydraulic calculations. Your column must be converged and cannot include any overlapping sections or gaps. To update pressure drops in your simulation: 1. Specify sections and geometry for the entire column. 2. On the Internals form or tab, click the Export Pressure Drop from Top button or the Export Pressure Drop from Bottom button. The column's pressure profile is updated based on the calculated pressure drops, and the pressure specification for the each stage is overwritten.

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When Export Pressure Drop from Top is selected, the condenser/top stage pressure is retained, and the pressures for the other stages are updated using the calculated pressure drops. When Export Pressure Drop from Bottom is selected, the reboiler pressure is retained, and the pressures for the other stages are updated using the calculated pressure drops.

Calculating the Pressure Drop Across a Sump Since sumps are commonly used at the bottom of distillation towers, HYSYS allows you to specify liquid holdup and a sump diameter on the Internals form or tab. To calculate the pressure drop across a sump: 1. Open the Internals form or tab for your column. 2. Select the Calculate Pressure Drop Across Sump check box. 3. In the Sump section, you can specify the Diameter. The default value is the diameter of the section adjacent to the sump. 4. In the Sump section, select one of the following radio buttons and specify a value in the corresponding field: o

Liquid Residence Time: This is the default selection. The default value is 60 seconds. -or-

o

Liquid Level

When Liquid Residence Time is specified:

Including Static Vapor Head Correction If you want to include the static vapor head in the pressure drop calculations, select the Include Static Vapor Head in Pressure Drop Calculations check box. The rating results will account for the static vapor head. The pressure drop due to the static vapor head on a particular stage is calculated as follows: l

l

Trays: Static vapor contribution to pressure drop = Vapor mass density * Gravitational acceleration * Tray Spacing Packing: Static vapor contribution to pressure drop = Vapor mass density * Gravitational acceleration * Packed Height per stage

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Viewing Internals Summary Results Click the View Internals Summary Results button to view Internals results data for the entire Tower. Refer to Viewing Internals Results for further details.

Initializing from the Rating Tab You can use specified column geometry information from the column's Rating tab as an initial estimate for the Column Internals for Hydraulic Analysis. Before performing this workflow, you must specify geometry information on the Rating tab. To initialize from the Rating tab: 1. Open the Internals tab or form. 2. Click the Initialize from Rating button. Information from the Sieve, Bubble Cap, and Valve tray types are transferred to Internals. Sump Trays and some HYSYS packing types are not transferred; a message notifies you that you cannot initialize from these internal types.

Sending to the Rating Tab You can use Geometry information specified in the Internals to populate the Rating tab of the Column property view. Notes:  l

The Send to Rating button is enabled when no gaps currently exist and you have specified the necessary information for the Tower.

l

When Send to Rating is used for an Acid Gas column, the column is resolved using the updated geometry information from the Internals tab/form. This could lead to a change in the vapor-liquid traffic in the column. If the Internals section is in Interactive Sizing mode, this triggers a recalculation of the diameter and other results on the Internals tab/form.

To send information to the Rating tab:

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1. Open the Internals tab or form. 2. Specify Internals information for a given HYSYS Tower. There must be no gaps or overlaps between Tower sections. 3. Click the Send to Rating button. For a column with one section that encompasses every stage: o

HYSYS populates the Rating tab for that column with the Tray/Packing Type and other parameters, such as Diameter and Tray Spacing.

The Uniform Section check box is selected, indicating that all stages of the column share the same geometry characteristics. For a column with multiple sections with different characteristics: o

o

HYSYS populates the Internal Type, Diameter Fields, and the Tray/Packed Space and Volume fields for that column with Multiple if there are multiple options selected for each parameter.

o

The Uniform Section check box is cleared.

o

A message on the Rating tab indicates that multiple Sections are detected and lets you know where to locate further information. Refer to Rating Tab for further details.

Importing and Exporting Column Section Templates You can: l

l

l

Import a template with geometry and design parameters into an existing internals section. Create a new internals section with the geometry and design parameters from a template. Export a template with geometry and design parameters based on the internals section that is currently selected.

A section template is an .xml file containing: l

User-specified geometry for a section

l

User-specified design parameters for a section

To import an existing template: 1. Open the Internals tab or form for your column. 2. Click the Import Template button. 3. On the Import Template dialog box, click the button next to the Import To field. On the Import Template dialog box, navigate to the desired template, and then click Open. 4. Perform one of the following tasks: o

6 Column Property View

Select the Create new section from imported template radio button to create an entirely new section based on your

237

selected template. -oro

Select the Import to section radio button, and then select the check boxes for sections which you want to be overwritten with the geometry and design parameters saved in the selected template.

5. Click the Import button. To export an existing template: 1. Open the Internals tab or form for your column. 2. Click the Export Template button. 3. On the Export as Template dialog box, from the Export section dropdown list, select the section that you want to export as a template. 4. Click the button next to the to File field. On the Save Template dialog box, navigate to the desired location, and the click Open. 5. Click the Export button. Geometry and design parameter information for the selected template is saved as an .xml file in the specified location.

Viewing Internals Results On the Performance tab | Internals Results page for your column, you can view Internals results data for the entire Tower when you use Column Analysis. Note: If you did not specify internals, this page is empty.

To view Internals results: 1. From the Tower drop-down list, selected the Tower for which you want to view Internals results. 2. From the Selected Internals drop-down list, select the Internals configuration for which you want to view results. 3. In the Column Internals Summary section, you can view the following values:

238

o

Number of Stages: Total number of trays or packed stages in the selected tower

o

Total Height: Height of tower = Sum of the height of all defined sections

o

Total Head Loss: Total head loss across the tower = Sum of head loss over all defined sections

o

Total Pressure Drop: Total pressure drop across the tower = Sum of pressure drop over all defined sections

o

Number of Sections: Number of defined sections

o

Number of Diameters: Number of sections with different

6 Column Property View

diameters o

Pressure Drop Across Sump: HYSYS calculates this value using the values that you specified for Diameter of Sump and either Liquid Residence Time or Liquid Level.

4. In the Sections Summary section, you can view the following values for each section in the selected Tower. Click the View button to access the Geometry form for the section. o

Section

o

Start

o

End

o

Diameter

o

Height

o

Internal Type

o

Tray or Packing Type

o

Section Pressure Drop

o

Approach to Flood: Highest approach to flood in the section

o

Limiting Stage: Stage number of the stage with the highest Approach to Flood

Note: Click the View button in a row to open the Results tab of the Geometry form for the selected row.

Viewing Transport Properties 1. On the Performance tab | Internals Results page, click the Transport Properties button. Note: If there are two liquid phases in a column, the total liquid flow rate (light and heavy liquids) is used in calculations. The transport properties are weighted averages of the light and heavy liquids for each liquid phase.

2. On the Profile Table: Properties Profile form, you can view the following physical properties for each stage: o

Surface Ten

o

Mole Weight

o

Density

o

Viscosity

o

Therm Cond

o

Heat Cap

Note: Click the Properties button to adjust the Basis, Phase, and/or Axis Assignment.

Viewing the Total Flow Profile 1. On the Performance tab | Internals Results page, click the Flows button. 2. On the Profile Table: Total Flow Profile form, you can view the profile of vapor and mass flows for each stage.

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Note: Click the Properties button to adjust the Basis, Phase, and/or Tray Flow Basis.

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Column Analysis lets you analyze different column Internals configurations. Notes: l

You can use Column Analysis for Acid Gas columns.

l

If there are two liquid phases in a column, the total liquid flow rate (light and heavy liquids) is used in calculations. The transport properties are weighted averages of the light and heavy liquids for each liquid phase.

Column Analysis Workflow 1. Create a Column Internals configuration. 2. Specify Sections within the column internals. 3. Click the View button in the Geometry column to specify Geometry details on the Geometry form. 4. View results on the Geometry form. 5. Use the Hydraulic Plots form to view tray operability diagrams for the column. 6. Export column hydraulics results and internals geometry to vendor packages. 7. Use the Column Analysis Report Builder. Note: If you are using Activated Economics, information from Column Analysis is picked up by APEA, including: l

Tray/Packing Type

l

Tray Spacing

l

Packed Spacing

l

Diameter

l

Packing Material

l

Valve Material for Valve Trays

l

Tray Thickness

APEA uses the geometry for the Active column option in Column Internals.

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Column Internals Manager You can use the Internals Manager to create and analyze multiple Internals configurations within the same HYSYS simulation. To access the Internals Manager: 1. From the Column Design ribbon tab, click the Internals Manager

button. 2. You can click the Add button to add a new configuration option. From the Tower drop-down list, select the desired Tower. The default Status is Active if no Internals are defined for the column. The default Status is Inactive there are already Internals defined for the column. 3. Double-click the row to access the Internals form and create a Column Internals configuration. When you set up a HYSYS column, an Internals Manager option is automatically created for each tower associated with the column flowsheet.

Note: Click the X in the Delete column to delete a Column Internals configuration.

You can also create a new Column Internals configuration by duplicating an existing one. To do so: 1. Click the existing object in the table. 2. Click Duplicate. A new row appears in the table, with a new name that you can change by clicking its cell and typing over it in the grid. 3. If desired, you can modify the Description for the new configuration. 4. Double-click the row and make changes to the sections to complete specifications for the new configuration.

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Column Design Ribbon If you double-click a HYSYS column, the Column Design ribbon appears.

Click

To

Hydraulic Plots button

View the hydraulic operating diagram for the active column option. Refer to Hydraulic Plots for further details.

Reports button

Customize and create printable reports for this column. Refer to Using Column Analyzer Report Builder for further details.

Internals Manager button

Create and analyze multiple Internals configurations within the same HYSYS simulation. Refer to Column Internals Manager for further details.

Export to Vendor button

Export geometry and column results from Column Internals to thirdparty vendor software (KG Tower, SulCol, and FRI-DRP). Refer to Exporting Column Results to Vendor Packages for further details.

Plots gallery

View the following plots: l

Temperature

l

Pressure

l

Transport

l

Composition

l

Flow Rate

l

K-Values

l

Light-Heavy

l

Boiling Point

Column Analysis Flowsheet Icons When you open a HYSYS case that includes a column, icons on the flowsheet indicate whether: l

No internals are specified

l

Internals have been specified and Column Analysis has not detected any

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errors l

Internals have been specified and Column Analysis has detected errors

Columns without Internals Specified For columns without internals, a gray icon appears to the left of the column.

Double-click the gray icon to open the Internals tab and begin configuring Column Internals.

Columns with Internals Specified (No Errors) For columns with internals specified and without errors, a blue icon appears to the left of the column. This indicates that the Column Internals are configured and the column is operating within specified hydraulic limits.

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Double-click the blue icon to open the Internals tab and review Internals results.

Columns with Internals Specified, with Errors For columns with internals specified and with errors, a red icon appears to the left of the column. This indicates that the Column Internals are configured, but the column is operating outside specified hydraulic limits.

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Double-click the blue icon to open the Internals tab and review Internals results in order to resolve the errors.

Removing Column Analysis Flowsheet Icons If desired, you can remove the icons on the flowsheet that provide information regarding Internals using the Preferences form. To remove the column flowsheet icons: 1. Click File | Options. 2. Select the Equipment page. 3. Clear the Display Decoration on PFD check box.

Creating a Column Internals Configuration You can use the Internals form to explore multiple column Internals configurations.

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The Internals form includes the complete configuration of tray and/or packing specifications for an entire column. This configuration consists of one or more sections, each of which represents trays or packing of a single type and size. To learn more about the fields/buttons on this page, refer to the following table. Field/Button

Refer to

Add New button

Creating Column Sections

Auto Section button

Using Auto Sectioning

Duplicate button

Duplicating Column Sections

Import Template button

Importing and Exporting Column Section Templates

Export Template button

Importing and Exporting Column Section Templates

View Internals Summary button

Viewing Internals Results

Include Static Vapor Head in Pressure Drop Calculations check box

Including Static Vapor Head Corrections

Calculate Pressure Drop Across Sump check box

Calculating the Pressure Drop Across a Sump

View Hydraulic Plots button

Hydraulic Plots

Export Pressure Drop from Top button

Updating Pressure Drops

Export Pressure Drop from Bottom button

Updating Pressure Drops

Initialize from Rating button

Initializing from the Rating Tab

Send to Rating button

Sending to the Rating Tab

Creating Column Sections Note: If there are two liquid phases in a column, the total liquid flow rate (light and heavy liquids) is used in calculations. The transport properties are weighted averages of the light and heavy liquids for each liquid phase.

To create column sections within your column: 1. Select the Internals tab or form. 2. Click the Add New button. A row appears, named CS-1 by default. 3. Optionally, type a Column Description for the Column Internals configuration. You can use this to record the purpose for this object when you have multiple configurations which may implement different design choices. 4. Specify the desired Start Stage and End Stage from the list of available stages. To complete the Column Internals configuration, you must define a set of sections which include all stages (except for the condenser and reboiler). If you previously specified a particular stage, it will no longer be available as an option unless you modify the previous

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section to not include that stage. The column diagram displays the layout of the column with adjacent sections in alternating colors. Any gaps in the column are visible as white sections. A message at the top right of the sheet indicates where these gaps are located. If the column sections are of different diameters, the sections are depicted with widths proportional to those diameters. Arrows left and right of the diagram indicate feeds, products, side draws, and pumparounds (which are indicated with blue connected arrows on the right side of the diagram). When there are multiple feeds, draws, and/or pumparound returns on the same or near stages such that the arrows would overlap, you can hover the mouse over the arrow to see information about the connections there.

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o

If all stages are accounted for and there are no gaps in the column, an Internals Input Complete message appears.

o

If you specified section boundaries but there are gaps within the column, a message appears, indicating where the gaps are located.

5. Specify the Mode: o

Interactive Sizing: If the mode is Interactive Sizing, which is the default, once you specify the start and end stages, HYSYS generates reasonable defaults for the section: Trays: HYSYS calculates a default for:

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o

Diameter

o

Number of passes

o Downcomer geometry and locations Refer to Tray and Downcomer Area Calculations for further details. Packing: HYSYS calculates a default for: o

Section diameter Note: You must specify section packing height.

o

Rating: Diameter and downcomer geometry and location are not calculated by HYSYS.

6. In the Details column, click the View button to specify Geometry details on the Geometry form. Notes: l

When you create columns adjacent to one another, they will be shaded in different colors in the diagram on the Internals tab or form.

l

Click the X in the Delete column to delete a Column Internals section.

l

Click the View Hydraulic Plots button to view hydraulic operating diagrams for the current Internals configuration.

l

Click the Import Template button to: o

Create a new section using the geometry and design parameters specified in a template.

o

Update an existing section using the geometry and design parameters specified in a template.

You can import the same template to multiple sections at a time. l

Click the Export Template button to export an XML template with geometry and design parameters based on an existing internals section.

Duplicating Column Sections You can duplicate geometry and design parameters from a selected column section to a new column section. To duplicate an existing column section: 1. On the Internals tab or form, select the desired section to duplicate. Note: If you select multiple sections, HYSYS duplicates the first section.

2. Click Duplicate. A new row appears in the table, with a new name that you can change by clicking its cell and typing over it in the grid. Values of appear for the Start Stage and End Stage. All other user-specified values will be duplicated. 3. If desired, modify the Description and Mode for the new section. 4. Double-click the row and make changes to the sections to complete specifications for the new section.

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Using Auto Sectioning If you click the Auto Section button, HYSYS automatically creates column sections based on feed and draw locations or internal flow rates. Note: You can only click the Auto Section button if there are no internal sections defined already.

If you click the arrow next to the Auto Section button, you can opt to auto section the column: l

Based on Feed/Draw Locations (default)

l

Based on Flows

Auto Sectioning Based on Feed Draw Locations If you select Auto Section | Based on Feed/Draw Locations, HYSYS uses the following logic to auto section the column: 1. HYSYS starts Section 1 from the top tray. 2. The Stage Number is increased by 1 until a Feed, Product, Pump Around Draw, or Pump Around Return is encountered. o

If a Feed or Pump Around Return is encountered at Stage I, HYSYS ends Section 1 at Stage I-1 and starts Section 2 at Stage I.

o

If a Product or Pump Around Draw is encountered at Stage I, HYSYS ends Section 1 at Stage I and starts Section 2 at Stage I+1.

3. HYSYS repeats the same logic until the bottom tray is reached. If there is no reboiler, this is the Nth stage. Otherwise, it is the (N - 1)th stage. Note: If a Feed or Pump Around Return and a Product or Pump Around Draw exist in the same tray: o

The Feed logic is used if the Feed has a higher flow than the Product flow.

o

The Product logic is used if the Product has a higher flow than the Feed flow.

Auto Sectioning Based on Flows If you select Auto Section | Based on Flows, HYSYS uses the following logic to auto section the column: 1. HYSYS starts Section 1 from the top tray. If there is no condenser, it starts with Stage 1. Otherwise, it starts with Stage 2. 2. The Stage Number is increased by 1. 3. If the liquid flow from Stage I differs from the flow of stage I-1 by more than 20%, a new section is started at Stage I. 4. HYSYS repeats the same logic until the bottom tray is reached.

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Updating Pressure Drops You can use information calculated from Column Analyzer to update pressure drops in your simulation. Your column must be converged and cannot include any overlapping sections or gaps. To update pressure drops in your simulation: 1. Specify sections and geometry for the entire column. 2. On the Internals form or tab, click the Export Pressure Drop from Top button or the Export Pressure Drop from Bottom button. The column's pressure profile is updated based on the calculated pressure drops, and the pressure specification for the each stage is overwritten. When Export Pressure Drop from Top is selected, the condenser/top stage pressure is retained, and the pressures for the other stages are updated using the calculated pressure drops. When Export Pressure Drop from Bottom is selected, the reboiler pressure is retained, and the pressures for the other stages are updated using the calculated pressure drops.

Calculating the Pressure Drop Across a Sump Since sumps are commonly used at the bottom of distillation towers, HYSYS allows you to specify liquid holdup and a sump diameter on the Internals form or tab. To calculate the pressure drop across a sump: 1. Open the Internals form or tab for your column. 2. Select the Calculate Pressure Drop Across Sump check box. 3. In the Sump section, you can specify the Diameter. The default value is the diameter of the section adjacent to the sump. 4. In the Sump section, select one of the following radio buttons and specify a value in the corresponding field: o

Liquid Residence Time -or-

o

Liquid Level

When Liquid Residence Time is specified:

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Including Static Vapor Head Correction If you want to include the static vapor head in the pressure drop calculations, select the Include Static Vapor Head in Pressure Drop Calculations check box. The rating results will account for the static vapor head. The pressure drop due to the static vapor head on a particular stage is calculated as follows: l

l

Trays: Static vapor contribution to pressure drop = Vapor mass density * Gravitational acceleration * Tray Spacing Packing: Static vapor contribution to pressure drop = Vapor mass density * Gravitational acceleration * Packed Height per stage

Viewing Internals Summary Results Click the View Internals Summary Results button to view Internals results data for the entire Tower. Refer to Viewing Internals Results for further details.

Initializing from the Rating Tab You can use specified column geometry information from the column's Rating tab as an initial estimate for the Column Internals for Hydraulic Analysis. Before performing this workflow, you must specify geometry information on the Rating tab. To initialize from the Rating tab: 1. Open the Internals tab or form. 2. Click the Initialize from Rating button. Tray types, including Sieve, Bubble Cap, and Valve, are mapped to the Column Analyzer. Sump chimney trays and some HYSYS packing types will not be mapped; a message appears, notifying you that you cannot initialize from these internal types.

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Sending to the Rating Tab You can use Geometry information specified using the Column Analyzer to populate the Rating tab of the Column property view. Note:  l

The Send to Rating button is enabled when no gaps currently exist and you have specified the necessary information for the Tower.

l

When Send to Rating is used for an Acid Gas column, the column is resolved using the updated geometry information from the Internals tab/form. This could lead to a change in the vapor-liquid traffic in the column. If the Internals section is in Interactive Sizing mode, this triggers a recalculation of the diameter and other results on the Internals tab/form.

To send information to the Rating tab: 1. Open the Internals tab or form. 2. Specify Internals information for a given HYSYS Tower. There must be no gaps or overlaps between Tower sections. 3. Click the Send to Rating button. For a column with one section that encompasses every stage: o

HYSYS populates the Rating tab for that column with the Tray/Packing Type and other parameters, such as Diameter and Tray Spacing.

The Uniform Section check box is selected, indicating that all stages of the column share the same geometry characteristics. For a column with multiple sections with different characteristics: o

o

HYSYS populates the Internal Type, Diameter Fields, and the Tray/Packed Space and Volume fields for that column with Multiple if there are multiple options selected for each parameter.

o

The Uniform Section check box is cleared.

o

A message on the Rating tab indicates that multiple Sections are detected and lets you know where to locate further information. Refer to Rating Tab for further details.

Importing Column Section Templates You can import a template with geometry and design parameters into a column section. A section template is an .xml file containing: l

User-specified geometry for a section

l

User-specified design parameters for a section

To import an existing template:

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7 Column Analysis Overview

1. Open the Internals tab or form for your column. 2. Click the Import Template button. 3. On the Import Template dialog box, click the button next to the Import To field. On the Import Template dialog box, navigate to the desired template, and then click Open. 4. Perform one of the following tasks: o

Select the Create new section from imported template radio button to create an entirely new section based on your selected template. -or-

o

Select the Import to section radio button, and then select the check boxes for sections which you want to be overwritten with the geometry and design parameters saved in the selected template.

5. Click the Import button.

Exporting Column Section Templates You can export a template with geometry and design parameters based on a column section. A section template is an .xml file containing: l

User-specified geometry for a section

l

User-specified design parameters for a section

To export an existing template: 1. Open the Internals tab or form for your column. 2. Click the Export Template button. 3. On the Export as Template dialog box, from the Export section dropdown list, select the section that you want to export as a template. 4. Click the button next to the to File field. On the Save Template dialog box, navigate to the desired location, and the click Open. 5. Click the Export button. Geometry and design parameter information for the selected template is saved as an .xml file in the specified location.

Geometry Details You can use the Geometry form to specify Geometry details for the column.

Tray Geometry Workflow On the Tray Geometry form, you can perform the following tasks:

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255

l

Specify tray geometry.

l

Specify Picket Fence Weirs or Swept Back Weirs.

l

View the tray geometry summary.

l

Specify tray geometry design parameters.

l

View tray geometry summary results.

l

View tray geometry results by stage.

l

Troubleshoot potential issues.

Packing Geometry Workflow On the Packing Geometry form, you can perform the following tasks: l

Specify packing geometry.

l

Change packing geometry design parameters.

l

Specify packing constants.

l

View packing geometry summary results.

l

View packing geometry results by stage.

l

Troubleshoot potential issues.

Specifying Tray Geometry On the Geometry tab | Geometry page, you can specify tray geometry. Note: If you opted to initialize the Tower from the Rating tab using the Initialize from Rating button, the default values on this page may differ from those described below.

To specify tray geometry: 1. On the Geometry form, select the Geometry tab | Geometry page. 2. For Section Type, select the Trayed radio button. 3. From the Tray Type drop-down list, select the desired valve or tray type. The default option is Sieve. If you are using Activated Economics, this information is sent to APEA. Refer to the table below to view a list of subtypes for valves and how the valve or tray types are mapped within APEA. Note: Dump point calculations are performed for Sieve trays only. The dump point is determined using the Chan and Prince Dump Point Correlation. Liquid entrainment correlations are performed for Bubble Cap trays and Sieve trays only. To learn more about liquid entrainment correlations, refer to Liquid Entrainment Correlations.

Tray Type

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7 Column Analysis Overview

Valve or Tray Type

Valve Subtype

Mapped to in APEA

Sieve

Sieve

Bubble Cap

Bubble Cap

Sulzer-Nutter Koch-Glistch Ballast Koch-Glistch Flexitray

o

BDP

o

BDH

o

V-1

o

V-4

o

AO

o

A14

o

A16

o

A18

o

TO

o

T-14

o

T-16

o

T-18

o

S

Valve

Valve

Valve Note: Koch-Glitsch S valves are made of the same material and thickness as the tray.

4. In the Number of Passes combo box, if desired, you can specify a value between 1 and 4. In Interactive Sizing Mode, HYSYS automatically determines the default Number of Passes so that the weir loading does not exceed the Maximum Weir Loading specified on the Geometry tab | Design Parameters page. If you specified the Diameter, HYSYS uses the following heuristic to determine if an increase in the number of passes is justified: o

Number of Passes = 2, Minimum Diameter = 5 ft

o

Number of Passes = 3, Minimum Diameter = 8 ft

o

Number of Passes = 4, Minimum Diameter = 10 ft

Note: In Interactive Sizing Mode, if the column is in a sized model, the model is resized whenever the value for Number of Passes is changed.

5. Specify the Mode: o

Interactive Sizing: This is the default mode. If you do not specify Diameter, Number of Passes, Downcomer Width, and Downcomer Location, these values will be calculated by HYSYS.

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Note: You can specify the Diameter and have HYSYS calculate the downcomer widths/locations and number of passes based on standard column design rules. When you specify diameter, number of passes and downcomer geometry and locations, the Interactive Sizing mode effectively behaves the same as the Rating mode. o

Rating: Diameter and downcomer geometry and location are not calculated by HYSYS.

Note: When you switch from Interactive Sizing mode to Rating mode, the calculated values for Diameter, Downcomer Widths, and Downcomer Locations fields are retained and appear as defaults (in blue italics). If you delete one or more of these values in Rating mode, the simulation becomes incomplete. You can specify your own values or switch to Interactive Sizing and back to Rating to populate these fields and make the simulation complete.

6. Adjust values for the following, if desired. The fields are dependent upon your Tray Type selection. Field

Default

Description

Hole Diameter

0.5 inches

Applicable for Sieve tray types.

Number of Holes

Hole Area To Active Area

Applicable for Sieve tray types. Calculated when the Hole Area To Active Area is specified. When you update the Hole Diameter, this value changes. 0.1

Cap Diameter Number of Caps -orNumber of Caps Per Active Area

Applicable for Sieve tray types. Value must be less than 1. This value is not impacted when you change the Hole Diameter. Refer to Discharge Coefficient to learn how this value impacts the discharge coefficient. Applicable for Bubble Cap tray types.

50 (for 3 in cap diameter), (28 (for 4 in cap diameter), 12 (for 6 in cap diameter)

Applicable for Bubble Cap tray types. Select the radio button to specify this value. If you specify Number of Caps, the Number of Caps Per Active Area is calculated by HYSYS. Applicable for Bubble Cap tray types. Select the radio button to specify this value. If you specify Number of Caps Per Active Area, the Number of Caps is calculated by HYSYS.

258

Skirt Height

Applicable for Bubble Cap tray types.

Leg Length

Applicable for all Sulzer-Nutter, KochGlistch Ballast, or Koch-Glistch Flexitray tray types, except Flex-S.

Valve Material

Applicable for all Sulzer-Nutter, KochGlistch Ballast, or Koch-Glistch Flexitray tray types, except Flex-S.

7 Column Analysis Overview

Valve Thickness

Applicable for all Sulzer-Nutter, KochGlistch Ballast, or Koch-Glistch Flexitray tray types, except Flex-S (since the FlexS Valve Thickness is equivalent to Deck Thickness).

Number of Valves

Applicable for all Sulzer-Nutter, KochGlistch Ballast, or Koch-Glistch Flexitray tray types.

-or-

Select the radio button to specify this value. If you specify Number of Valves, the Number of Valves Per Active Area is calculated by HYSYS.

Number of Valves Per Active Area 75/sqm

Applicable for all Sulzer-Nutter, KochGlistch Ballast, or Koch-Glistch Flexitray tray types. Select the radio button to specify this value. If you specify Number of Valves Per Active Area, the Number of Valves is calculated by HYSYS.

Note: You can click the View Hydraulic Plots button to view hydraulic operating diagrams for the column.

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For 1-pass trays:

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l

Adjust values for the following, if desired: Field

Default

Description

Deck Thickness

10 gauge

If you specify a deck gauge, the thickness is automatically calculated. If you select Other, you must manually type the thickness.

Active Area Under Downcomer check box

When this check box is selected, the area under the downcomer is included in the active (bubbling) area.

Weir Modifications

You can select between the following options:

Refer to Tray and Downcomer Area Calculations for further details.

o

No weir modifications: This is the default selection.

o

Picket weirs: Used to accommodate lower loads.

o

Swept-back weirs: Used to accommodate higher loads.

Refer to Specifying Picket Fence Weirs or Swept Back Weirs for further details. Side Downcomer Width: Top

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details. The limits on side downcomer width for 1-pass trays are as follows: o

0.025D to 0.4D

where D is the diameter of the column. Side Downcomer Width: Bottom

Defaults to the same value as the Side Downcomer Width: Top. When the top width is modified, the bottom width will change accordingly unless explicitly modified by the user. Refer to Tray and Downcomer Area Calculations for further details. The limits on side downcomer width for 1-pass trays are as follows: o

0.025D to 0.4D

where D is the diameter of the column

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261

Side Weir Length

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Length of outlet weir of side downcomer. Refer to Tray and Downcomer Area Calculations for further details.

Weir Height

(Tray Spacing)/12

Downcomer Clearance

0.75 * Weir Height

Diameter

Refer to Tray and Downcomer Area Calculations for further details.

In Interactive Sizing Mode, for Sieve and Bubble Cap trays, the calculation of the Diameter is performed based on the following parameters specified on the Geometry tab | Design Parameters page: o

the Jet Flood Method (where the default is Glitsch6)

o

the Percent Jet Flood by Design (where the default is 80%)

o

the Minimum Downcomer Area / Total Tray Area (where the default is 0.1)

Refer to Tray and Downcomer Area Calculations for further details. Note: Weeping is not accounted for in the sizing calculation. Tray Spacing

0.6096 m (2 ft)

Refer to Tray and Downcomer Area Calculations for further details. In Rating Mode, if you update the Tray Spacing, the tray section is automatically re-rated with the new tray spacing. The maximum value is 2 m (6.562 ft). Note: We do not recommend a Tray Spacing value larger than 1 m, since the correlations may not be reliable in this case.

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7 Column Analysis Overview

For 2-pass trays:

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263

l

Adjust values for the following, if desired: Field

Default

Description

Deck Thickness

10 gauge

Available options: If you specify a deck gauge, the thickness is automatically calculated. If you select Other, you must manually type the thickness.

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7 Column Analysis Overview

Balance Downcomers Based On

Adjusts downcomer widths/locations to balance load among downcomers. This drop-down list is only available in the Interactive Sizing mode and is enabled only if downcomers are not balanced. You can select: o

Maximum Downcomer Loading: Downcomer widths and locations will be adjusted to ensure that the top and bottom areas for all downcomers are equal and loading for each downcomer equals the maximum loading. For Sieve and Bubble Cap trays, the maximum downcomer loading will be computed using the Maximum Downcomer Loading Method selected on the Geometry tab | Design Parameters page. For the other tray types, vendor specified correlations will be used. All user-specified downcomer geometry will be overwritten by HYSYS.

o

Side Downcomer: Widths and locations will be adjusted for the center and off-center downcomers to ensure that the top and bottom areas (and hence the loading) are equal to that of the side downcomer. User-specified downcomer geometry/locations for the Center and OffCenter downcomers will be overwritten by HYSYS.

o

Center Downcomer: Widths and locations will be adjusted for the side and off-center downcomers to ensure that the top and bottom areas (and hence the loading) are equal to that of the center downcomer. User-specified downcomer geometry/locations for the Side and OffCenter downcomers will be overwritten by HYSYS.

Click the Rebalance Downcomers button to update the downcomer geometry and layout to ensure an equal liquid load (flow per unit area) across all downcomers. The diagram updates to display the new dimensions, and the graphs displaying downcomer and weir data update.

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265

Active Area Under Downcomer check box

When this check box is selected, the area under the downcomer is included in the active (bubbling) area.

Weir Modifications

You can select between the following options:

Refer to Tray and Downcomer Area Calculations for further details.

o

No weir modifications: This is the default selection.

o

Picket weirs: Used to accommodate lower loads.

o

Swept-back weirs: Used to accommodate higher loads.

Refer to Specifying Picket Fence Weirs or Swept Back Weirs for further details. Side Downcomer Width: Top

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details. The limits on side downcomer width for 2-pass trays are as follows: o

0.025D to 0.25D

where D is the diameter of the column Side Downcomer Width: Bottom

Defaults to the same value as the Side Downcomer Width: Top. When the top width is modified, the bottom width will change accordingly unless explicitly modified by the user. Refer to Tray and Downcomer Area Calculations for further details. The limits on side downcomer width for 2-pass trays are as follows: o

0.025D to 0.25D

where D is the diameter of the column Side Weir Length

266

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details.

7 Column Analysis Overview

Center Weir Length

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details.

Center Downcomer Width: Top

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details.

Center Downcomer Width: Bottom

Refer to Tray and Downcomer Area Calculations for further details.

Weir Height

(Tray Spacing)/12

The default value is 2 inches. Refer to Tray and Downcomer Area Calculations for further details.

Downcomer Clearance

0.75 * Weir Height

The default value is 1.5 inches. Refer to Tray and Downcomer Area Calculations for further details.

Diameter

In Interactive Sizing Mode, for Sieve and Bubble Cap trays, the calculation of the Diameter is performed based on the following parameters specified on the Geometry tab | Design Parameters page: o

the Jet Flood Method (where the default is Glitsch6)

o

the Percent Jet Flood by Design (where the default is 80%)

o

the Minimum Downcomer Area / Total Tray Area (where the default is 0.1)

Refer to Tray and Downcomer Area Calculations for further details. Note: Weeping is not accounted for in the sizing calculation.

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267

Tray Spacing

0.6096 m (2 ft)

Refer to Tray and Downcomer Area Calculations for further details. In Rating Mode, if you update the Tray Spacing, the tray section is automatically re-rated with the new tray spacing. The maximum value is 2 m (6.562 ft). Note: We do not recommend a Tray Spacing value larger than 1 m, since the correlations may not be reliable in this case.

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7 Column Analysis Overview

For 3-pass trays:

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269

l

Adjust values for the following, if desired: Field

Default

Description

Deck Thickness

10 gauge

If you specify a deck gauge, the thickness is automatically calculated. If you select Other, you must manually type the thickness.

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7 Column Analysis Overview

Balance Downcomers Based On

Adjusts downcomer widths/locations to balance load among downcomers. This drop-down list is only available in the Interactive Sizing mode and is enabled only if downcomers are not balanced. You can select: o

Maximum Downcomer Loading: Downcomer widths and locations will be adjusted to ensure that the top and bottom areas for all downcomers are equal and loading for each downcomer equals the maximum loading. For Sieve and Bubble Cap trays, the maximum downcomer loading will be computed using the Maximum Downcomer Loading Method selected on the Geometry tab | Design Parameters page. For the other tray types, vendor specified correlations will be used. All user-specified downcomer geometry will be overwritten by HYSYS.

o

Side Downcomer: Widths and locations will be adjusted for the center and off-center downcomers to ensure that the top and bottom areas (and hence the loading) are equal to that of the side downcomer. User-specified downcomer geometry/locations for the Center and OffCenter downcomers will be overwritten by HYSYS.

o

Center Downcomer: Widths and locations will be adjusted for the side and off-center downcomers to ensure that the top and bottom areas (and hence the loading) are equal to that of the center downcomer. User-specified downcomer geometry/locations for the Side and OffCenter downcomers will be overwritten by HYSYS.

Click the Rebalance Downcomers button to update the downcomer geometry and layout to ensure an equal liquid load (flow per unit area) across all downcomers. The diagram updates to display the new dimensions, and the graphs displaying downcomer and weir data update.

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Active Area Under Downcomer check box

When this check box is selected, the area under the downcomer is included in the active (bubbling) area.

Weir Modifications

You can select between the following options:

Refer to Tray and Downcomer Area Calculations for further details.

o

No weir modifications: This is the default selection.

o

Picket weirs: Used to accommodate lower loads.

o

Swept-back weirs: Used to accommodate higher loads.

Refer to Specifying Picket Fence Weirs or Swept Back Weirs for further details. Side Downcomer Width: Top

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details. The limits on side downcomer width for 3-pass trays are as follows: o

0.025D to 0.25D

where D is the diameter of the column Side Downcomer Width: Bottom

Defaults to the same value as the Side Downcomer Width: Top. Refer to Tray and Downcomer Area Calculations for further details The limits on side downcomer width for 3-pass trays are as follows: o

0.025D to 0.25D

where D is the diameter of the column Side Weir Length

272

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details.

7 Column Analysis Overview

Weir Lengths: Inside

For Off-Center downcomer, two of the following must be specified: o

Top width

o

Inside weir length

o

Outside weir length

o

Off-Center Downcomer Location (distance from center) When any one of these fields is selected for modification, all four fields will be highlighted in yellow to indicate the relationship.

Refer to Tray and Downcomer Area Calculations for further details. Weir Lengths: Outside

For Off-Center downcomer, two of the following must be specified: o

Top width

o

Inside weir length

o

Outside weir length

o

Off-Center Downcomer Location (distance from center) When any one of these fields is selected for modification, all four fields will be highlighted in yellow to indicate the relationship.

Refer to Tray and Downcomer Area Calculations for further details. Off-Center Downcomer Width: Top

For Off-Center downcomer, two of the following must be specified: o

Top width

o

Inside weir length

o

Outside weir length

o

Off-Center Downcomer Location (distance from center) When any one of these fields is selected for modification, all four fields will be highlighted in yellow to indicate the relationship.

Refer to Tray and Downcomer Area Calculations for further details. Off-Center Downcomer Width: Bottom Weir Height

7 Column Analysis Overview

Refer to Tray and Downcomer Area Calculations for further details.

(Tray Spacing)/12

The default value is 2 inches. Refer to Tray and Downcomer Area Calculations for further details.

273

Downcomer Clearance

0.75 * Weir Height

Diameter

The default value is 1.5 inches. Refer to Tray and Downcomer Area Calculations for further details. In Interactive Sizing Mode, for Sieve and Bubble Cap trays, the calculation of the Diameter is performed based on the following parameters specified on the Geometry tab | Design Parameters page: o

the Jet Flood Method (where the default is Glitsch6)

o

the Percent Jet Flood by Design (where the default is 80%)

o

the Minimum Downcomer Area / Total Tray Area (where the default is 0.1)

Refer to Tray and Downcomer Area Calculations for further details. Note: Weeping is not accounted for in the sizing calculation. Tray Spacing

0.6096 m (2 ft)

Refer to Tray and Downcomer Area Calculations for further details. In Rating Mode, if you update the Tray Spacing, the tray section is automatically re-rated with the new tray spacing. The maximum value is 2 m (6.562 ft). Note: We do not recommend a Tray Spacing value larger than 1 m, since the correlations may not be reliable in this case.

Off-Center Downcomer Location

For Off-Center downcomer, two of the following must be specified: o

Top width

o

Inside weir length

o

Outside weir length

o

Off-Center Downcomer Location (distance from center) When any one of these fields is selected for modification, all four fields will be highlighted in yellow to indicate the relationship. Refer to Tray and Downcomer Area Calculations for further details.

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7 Column Analysis Overview

For 4-pass trays:

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275

l

Adjust values for the following, if desired: Field

Default

Description

Deck Thickness

10 gauge

If you specify a deck gauge, the thickness is automatically calculated. If you select Other, you must manually type the thickness.

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7 Column Analysis Overview

Balance Downcomers Based On

Adjusts downcomer widths/locations to balance load among downcomers. This drop-down list is only available in the Interactive Sizing mode and is enabled only if downcomers are not balanced. You can select: o

Maximum Downcomer Loading: Downcomer widths and locations will be adjusted to ensure that the top and bottom areas for all downcomers are equal and loading for each downcomer equals the maximum loading. For Sieve and Bubble Cap trays, the maximum downcomer loading will be computed using the Maximum Downcomer Loading Method selected on the Geometry tab | Design Parameters page. For the other tray types, vendor specified correlations will be used. All user-specified downcomer geometry will be overwritten by HYSYS.

o

Side Downcomer: Widths and locations will be adjusted for the center and off-center downcomers to ensure that the top and bottom areas (and hence the loading) are equal to that of the side downcomer. User-specified downcomer geometry/locations for the Center and OffCenter downcomers will be overwritten by HYSYS.

o

Center Downcomer: Widths and locations will be adjusted for the side and off-center downcomers to ensure that the top and bottom areas (and hence the loading) are equal to that of the center downcomer. User-specified downcomer geometry/locations for the Side and OffCenter downcomers will be overwritten by HYSYS.

Click the Rebalance Downcomers button to update the downcomer geometry and layout to ensure an equal liquid load (flow per unit area) across all downcomers. The diagram updates to display the new dimensions, and the graphs displaying downcomer and weir data update.

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Active Area Under Downcomer check box

When this check box is selected, the area under the downcomer is included in the active (bubbling) area.

Weir Modifications

You can select between the following options:

Refer to Tray and Downcomer Area Calculations for further details.

o

No weir modifications: This is the default selection.

o

Picket weirs: Used to accommodate lower loads.

o

Swept-back weirs: Used to accommodate higher loads.

Refer to Specifying Picket Fence Weirs or Swept Back Weirs for further details. Side Downcomer Width: Top

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details. The limits on side downcomer width for 4-pass trays are as follows: o

0.025D to 0.2D

where D is the diameter of the column Side Downcomer Width: Bottom

Defaults to the same value as the Side Downcomer Width: Top. When the top width is modified, the bottom width will change accordingly unless explicitly modified by the user. Refer to Tray and Downcomer Area Calculations for further details. The limits on side downcomer width for 4-pass trays are as follows: o

0.025D to 0.2D

where D is the diameter of the column Side Weir Length

278

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details.

7 Column Analysis Overview

Center Weir Length

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details.

Off-Center Weir Lengths: Inside

Refer to Tray and Downcomer Area Calculations for further details.

Off-Center Weir Lengths: Outside

Refer to Tray and Downcomer Area Calculations for further details.

Off-Center Downcomer Width: Top

Refer to Tray and Downcomer Area Calculations for further details.

Off-Center Downcomer Width: Bottom

Refer to Tray and Downcomer Area Calculations for further details.

Center Downcomer Width: Top

For the Side and Center downcomers, either top width or weir length can be specified. If top width is specified, the weir length is calculated and vice versa. When any one of these mutually exclusive fields (say top width) is selected for modification, the related field (say weir length) will be highlighted in yellow. Refer to Tray and Downcomer Area Calculations for further details.

Center Downcomer Width: Bottom

Refer to Tray and Downcomer Area Calculations for further details.

Weir Height

(Tray Spacing)/12

The default value is 2 inches.

Downcomer Clearance

0.75 * Weir Height

The default value is 1.5 inches. Refer to Tray and Downcomer Area Calculations for further details.

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279

Diameter

In Interactive Sizing Mode, for Sieve and Bubble Cap trays, the calculation of the Diameter is performed based on the following parameters specified on the Geometry tab | Design Parameters page: o

the Jet Flood Method (where the default is Glitsch6)

o

the Percent Jet Flood by Design (where the default is 80%)

o

the Minimum Downcomer Area / Total Tray Area (where the default is 0.1)

Refer to Tray and Downcomer Area Calculations for further details. Note: Weeping is not accounted for in the sizing calculation. Tray Spacing

0.6096 m (2 ft)

Refer to Tray and Downcomer Area Calculations for further details. In Rating Mode, if you update the Tray Spacing, the tray section is automatically re-rated with the new tray spacing. The maximum value is 2 m (6.562 ft). Note: We do not recommend a Tray Spacing value larger than 1 m, since the correlations may not be reliable in this case.

Off-Center Downcomer Location

Refer to Tray and Downcomer Area Calculations for further details.

Rebalancing Downcomers Note: The Rebalance Downcomers button is only enabled when Interactive Sizing Mode is selected and the downcomers are not balanced.

To rebalance downcomers for multi-pass trays: 1. Adjust the desired dimensions. 2. From the Balance Downcomers Based On drop-down list, select the parameter from which downcomer loading is balanced. o

280

Maximum Downcomer Loading: Downcomer widths and locations will be adjusted to ensure that the top and bottom areas for all downcomers are equal and loading for each downcomer equals the maximum loading. For Sieve and Bubble Cap trays, the maximum downcomer loading will be computed using the Maximum Downcomer Loading Method selected on the Geometry tab | Design Parameters page. For the other tray types, vendor specified correlations will be used.

7 Column Analysis Overview

All user-specified downcomer geometry will be overwritten by HYSYS. o

Side Downcomer: Widths and locations will be adjusted for the center and off-center downcomers to ensure that the top and bottom areas (and hence the loading) are equal to that of the side downcomer. User-specified downcomer geometry/locations for the Center and Off-Center downcomers will be overwritten by HYSYS.

o

Center Downcomer: Widths and locations will be adjusted for the side and off-center downcomers to ensure that the top and bottom areas (and hence the loading) are equal to that of the center downcomer. User-specified downcomer geometry/locations for the Side and Off-Center downcomers will be overwritten by HYSYS.

3. Click the Rebalance Downcomers button to update the downcomer geometry and layout to ensure an equal liquid load (flow per unit area) across all downcomers. The geometry is calculated with balanced downcomers. The diagram updates to display the new dimensions, and the graphs displaying downcomer and weir data update.

Specifying Picket Fence Weirs or Swept Back Weirs When Picketed or Swept-back is selected as a Weir Modifications option on the Geometry tab | Geometry page, use this sheet to specify the geometry information for picketed or swept-back weirs. Swept-back weirs are used to accommodate higher loads, whereas Picketed weirs are used to accommodate lower loads.

Specifying Picket Fence Weirs Use Picketing to increase the weir loading for single-pass trays or balance the weir loading for multi-pass trays. The picketing fraction represents the fraction of the weir length that is “blocked” by the picket. Picketing reduces the effective weir length exposed to the liquid and increases the weir loading: Effective picketed weir length = (1 – Picketing fraction) * Actual weir length

Single-Pass Tray In Interactive Sizing mode, a default Picketing Fraction is calculated as follows: l

If the weir loading for the unpicketed weir is less than the Minimum Weir Loading specified on the Geometry tab | Design Parameters page, the picketing fraction is calculated based on the extent of picketing

7 Column Analysis Overview

281

required to raise the weir loading to the specified Minimum Weir Loading: Picketing Fraction = 1 - Liquid Volumetric Flow Across Weir/(Unpicketed weir length * Minimum Weir Loading) l

If the weir loading for the unpicketed weir is greater than the Minimum Weir Loading, the picket fraction defaults to 0.

Multi-Pass Trays In Interactive Sizing mode, a default Picketing Fraction is calculated as follows: l

The picketing fraction for center and of-center weirs are calculated based on the extent of picketing required to make the weir loading across all weirs equal: Picketing Fraction = 1 - Side Weir Length/Unpicketed weir length

Rating Mode In Rating Mode, a default value of 0 is used for the Picketing Fraction.

Specifying Picket Fence Weirs To specify picket fence weirs: 1. On the Geometry tab | Geometry page of the Geometry form, in the Weir Modifications section, select Picketed. 2. Select the Picketed/Swept-Back Weirs page. 3. Specify the Picketing Fraction according to the following guidelines: o

For one-pass trays, update the Side Picketing Fraction as desired. The default value is the fraction required to move the load on each weir above the Minimum Weir Loading. Note: If the weir loading is higher than the minimum weir loading, the calculated Picketing Fraction will be 0.

282

o

For two-pass trays, update the following as desired: Side Picketing Fraction and Center Picketing Fraction. The default value for the Side Picketing Fraction is 0.

o

For three-pass trays, update the following as desired: Side Picketing Fraction, Off-Center Outside Picketing Fraction, and Off-Center Inside Picketing Fraction. The default value for the Side Picketing Fraction is 0.

o

For four-pass trays, update the following as desired: Side Picketing Fraction, Off-Center Outside Picketing Fraction, OffCenter Inside Picketing Fraction, and Center Picketing Fraction. The default value for the Side Picketing Fraction is 0.

7 Column Analysis Overview

Specifying Swept-Back Weirs Use swept-back weirs to increase the effective length of the side weirs and decrease the weir loading. To specify swept-back weirs: 1. On the Geometry tab | Geometry page of the Geometry form, in the Weir Modifications section, select Swept-back weirs. 2. Select the Picketed/Swept-Back Weirs page. 3. Specify values depending on your selection in the Compatibility section. Refer to Swept-Back Weir Calculations for further details. Three different shapes for swept-back weirs are available, corresponding with designs offered in vendor programs SulCol, KG-Tower, and FRI-DRP. Choose one of these shapes, and then specify the geometry parameters in the diagram. o

SulCol: This is the default selection. For SulCol, you can specify lengths A, B, and S, which define the size and shape of the swept-back portion of the weir. Notes: o

o

o

In Interactive Sizing mode, if the side weir loading exceeds the Maximum Weir Loading, S is calculated to ensure that: o

Effective weir loading of the swept-back weir = Maximum weir loading

o

Effective weir loading of the swept-back weir = Volumetric flow rate of liquid across the weir/ Projected weir length

A and B are defaulted as follows: o

A = (2/3) * Width of side downcomer

o

B = (2/3) * A

KG Tower: In the Swept Back Weir field, specify the depth from the main part of the weir at the point where it is most swept back. The other geometry parameters are defined relative to this specification. Note: In Interactive Sizing mode, if the side weir loading exceeds the Maximum Weir Loading, the Swept Back Weir is calculated to ensure that: o

Effective weir loading of the swept-back weir = Maximum weir loading

o

Effective weir loading of the swept-back weir = Volumetric flow rate of liquid across the weir/ Projected weir length

FRI-DRP: Specify the lengths of the three different segments of the weir: Parallel Chord Segment, Swept-Back Weir Chord, and Angled Chord Segment. The following calculated values appear below the diagram: o

o

Tray with Maximum Weir Loading

o

Maximum Weir Loading

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283

o

Maximum Allowable Loading in Section: The value for the Maximum Weir Loading specified on the Geometry tab | Design Parameters page is used. For further details, refer to Specifying Tray Geometry Design Parameters.

o

Actual Side Weir Length

o

Effective Side Weir Length: Considered in the hydraulic calculations.

o

Lost Area: The percentage of tray area lost due to the sweptback weirs

Viewing the Tray Geometry Summary On the Geometry tab | Geometry Summary page of the Tray Geometry form, you can view the results for values specified on the Geometry tab | Geometry page.

Specifying Tray Geometry Design Parameters To specify design parameters: 1. Select the Geometry tab | Design Parameters page. 2. In the Sizing Criterion section, adjust the following values as desired: Field

Default

Description

Percent Jet Flood and Downcomer Choke Flood

80%

Percentage approach to jet flood and downcomer choke flood used to compute diameter in Interactive Sizing mode. Refer to Flooding Calculations for Trays.

Minimum Downcomer Area / Total Tray Area

0.1

Minimum fraction of total tray area occupied by downcomers. Used in Interactive Sizing mode.

3. In the Hydraulic Plots / Limits section, adjust the following values as desired. Changing these parameters will affect the boundaries drawn on the stability (operating) diagrams.

284

Field

Default

Description

Maximum Acceptable Pressure Drop

0.3626 psi

Maximum acceptable pressure drop per stage. The final pressure drop reported for a stage also includes static vapor head losses. This and other limits below determine the stability region on the hydraulic plot, and violations of the limits are indicated there.

7 Column Analysis Overview

Maximum Percent Jet Flood

100%

Maximum acceptable approach to jet flooding on any stage, in percent; 100 indicates the vapor velocity equals the velocity at which flooding is predicted to begin.

Maximum Percent Downcomer Backup

100%

Maximum acceptable height of aerated froth in any downcomer compared to the height of the downcomer (sum of tray spacing and weir height), in percent. Refer to Downcomer Backup Calculations for further details.

Maximum Percent Liquid Entrainment

10%

Maximum acceptable percentage of liquid entrained in the rising vapor as droplets. This limit is only applied where information is available from experiments on liquid entrainment as a function of tray hydraulics (currently bubble cap and sieve trays).

Minimum Weir Loading

0.5 gal/min per inch

Minimum acceptable volumetric flow rate of aerated liquid per unit length of weir, calculated on the basis of total liquid flow divided by total weir length. Changing the Minimum Weir Loading affects the boundaries drawn on the stability (operating) diagrams for the Picketing Fraction. Refer to Specifying Picket Fence Weirs or Swept Back Weirs for further information.

Maximum Weir Loading

Maximum acceptable weir loading, calculated in the same way as for the minimum. Default is based on the tray spacing (Resetarits & Ogundeji, 2009): o

When tray spacing is 12 in., maximum weir loading is 3 gal/min per inch.

o

When tray spacing is 15 in., maximum weir loading is 5 gal/min per inch.

o

When tray spacing is 18 in., maximum weir loading is 8 gal/min per inch.

o

When tray spacing is 21 in., maximum weir loading is 10 gal/min per inch.

o

When tray spacing is 24 in., maximum weir loading is 13 gal/min per inch.

When you update the Tray Spacing on the Geometry tab | Geometry page, HYSYS recalculates the Maximum Weir Loading. Changing the Maximum Weir Loading affects the boundaries drawn on the stability (operating) diagrams for the swept-back weir dimensions. Warning Status (Percent to Limit)

7 Column Analysis Overview

10%

For each of the specified maximum or minimum values, if the value is within this percentage of the limit, a warning appears (indicated in yellow) in the hydraulic plots. Refer to Hydraulic Plots for further details.

285

4. In the Design Factors section, adjust the following values as desired: Field

Default

Description

System Foaming Factor

1

Adjustment factor to the maximum density-corrected vapor load at flood, CSf , calculated from a jet flood correlation. Typical non-foaming systems should use a value of 1. Lower values indicate more foaming. See Foaming Calculations for typical values.

Aeration Factor Multiplier

1

Adjustment factor to the aeration parameter β used in the calculation of pressure drop through the aerated liquid on a tray. Adjust this parameter to get better agreement between calculated and measured tray pressure drops.

Over-Design Factor

1

Multiplier to adjust the liquid flow leaving a tray and the vapor flow going to a tray. This parameter can be used to examine turnup/turndown behavior.

Override Downcomer Froth Density (0 to 1) check box

Cleared

Select this check box to override the calculated value for the downcomer froth density. This is a dimensionless value which represents the volume fraction of liquid in the froth. To learn how HYSYS calculates downcomer relative froth density, refer to Downcomer Relative Froth Density.

5. In the Calculation Methods section, adjust the following values as desired: Field

286

Default

Description

7 Column Analysis Overview

Weep

Hsieh

Method used to calculate weeping. For sieve trays, select between correlations suggested by Hsieh & McNulty (Hsieh) or Lockett (Lockett). Weeping on valve trays is calculated by modifications to the Hsieh & McNulty equation for sieve trays which these researchers suggested. Bubble cap trays do not weep significantly. Lockett and Banik (56) and Hsieh and McNulty (63) proposed correlations for predicting weep rates from sieve trays. Both correlations are based on pilot scale data, mainly with the air water system. The Hsieh and McNulty correlation is based on a broader data bank, which includes the experimental data by Lockett and Banik. Hsieh and McNulty used an even wider, non-airwater, proprietary data bank for testing some of their predicted trends. Note: HYSYS does not explicitly calculate the weep rate. The above correlations are used to determine the vapor load at which weeping starts (weep rate = 0).

Jet Flood

GLITSCH6

Method used to calculate jet flooding. This is not available for certain tray types where a method provided by the vendor is always used. Available options:

7 Column Analysis Overview

o

GLITSCH6: Refer to Flooding Calculation for Trays for further details.

o

KISTER: Refer to Kister & Haas Jet Flood Correlation for further details.

o

FAIR72: Refer to Fair and Fair72 Jet Flood Correlations for further details.

o

SDO72: Refer to Smith, Dresser, and Ohlswager Jet Flood Correlation for further details.

287

Maximum Downcomer Loading

Glitsch

Method used to calculate downcomer loading. For bubble cap and sieve trays, select between correlations suggested by Glitsch, Koch, or Nutter. For specific valve tray types, the correlation appropriate to the valve type is used. Ballast Tray Design Manual, Glitsch, Inc. Bulletin No. 4900, 3rd ed. Dallas, 1980. Koch Flexitray Design Manual, Koch Engineering Co., Inc. Bulletins No. 960, 960-1, Wichita. Nutter Float Valve Design Manual, Tulsa: Nutter Engineering Co., 1976.

References Lockett, M. J. and Banik, S., “Weeping from sieve trays,” Ind. Eng. Chem. Process Des. Dev., 25(2), pp. 561-569, 1986. Hsieh, C. Li. and McNulty, K. J., “Predict weeping of sieve and valve trays,” Chem. Eng. Prog., V. 89, No. 7, p. 71-77, 1993. Hsieh, C. L., and McNulty, K. J., Paper presented at the annual Meeting of the AICHE, Miami Beach, Florida, November 2-7, 1986. Resetarits, M.R. and Ogundeji, A.Y. "On Distillation Tray Weir Loading." AIChE Spring National Meeting, Tampa, FL (April 26-30, 2009).

Viewing Tray Summary Results On the Results tab | Summary page of the Tray Geometry form, you can view the following results for the section. Field

Description

Section Starting Stage

You can change this value on the Internals tab.

Section Ending Stage

You can change this value on the Internals tab.

Tray Type

This value is set on the Geometry tab | Geometry page.

Number of Passes

This value is set on the Geometry tab | Geometry page.

Tray Spacing Section Diameter Section Height Section Pressure Drop Section Head Loss

288

7 Column Analysis Overview

Trays With Weeping

Lists the trays (if any) that include weeping. If there are no trays with weeping, None appears in this field.

Limiting Conditions Maximum % Jet Flood

Lists the maximum acceptable approach to jet flooding on any stage, in percent, and the tray in which it occurs. 100 indicates the vapor velocity equals the velocity at which flooding is predicted to begin. Refer to Flooding Calculations for Trays.

Maximum % Downcomer Backup

Lists the maximum downcomer backup in percent, and the tray in which it occurs. Refer to Downcomer Backup Calculations. The Location column lists one of the following results:

Maximum Downcomer Loading

l

Side

l

Center

l

Off-Center Inside

l

Off-Center Outside

Lists the maximum downcomer loading and the tray in which it occurs. The Location column lists one of the following results: l

Side

l

Center

l

Off-Center

Maximum Weir Loading

Lists the maximum weir loading and the tray in which it occurs.

Maximum Aerated Height Over Weir

Lists the maximum aerated height over weir and the tray in which it occurs.

Maximum % Approach To System Limit

Lists the maximum % approach to system limit and the tray in which it occurs. System Limit, or ultimate capacity, for a given system represents an upper limit of the superficial vapor velocity beyond which a column cannot operate without flooding. The System Limit is independent of column diameter and internals design and depends only on the physical properties and the liquid load. Percent Approach to system limit = (Capacity factor / Capacity factor at system limit) * 100

Maximum Cs Based On Bubbling Area

7 Column Analysis Overview

Lists the maximum Cs based on bubbling area and the tray in which it occurs.

289

Maximum % Downcomer Choke Flood (%)

Lists the highest calculated downcomer choke flood and the tray and location in which it occurs. Downcomer choke flood is a problem in high liquid rate applications in trayed columns. It occurs when the downcomer top area is not large enough to handle the froth flow, and vapor cannot disengage properly from the liquid. Choke flooding on certain trays reduces the capacity and efficiency of the trays and other trays in the immediate vicinity, which can sometimes lead to serious operability issues for the entire column.

References Stupin, W. J. and Kister, H. Z., “System Limit: The Ultimate Capacity of Fractionators,” Chemical Engineering Research and Design, Volume 81, Issue 1, 136 – 146, 2003.

Viewing Tray Geometry Results By Tray You can use the Results tab | By Tray page to view tray-by-tray results for tray rating calculations. For each tray in this section, many results are shown. Use the View drop-down list to select which results are shown. Selecting All shows all of these results. You can scroll, filter, and sort the tabular results.

State Conditions All liquid results apply to the liquid leaving a tray and include any liquid draw from the tray. All vapor results apply to vapor entering a tray. l

Liquid Temperature

l

Vapor Temperature

l

Liquid Mass Flow (liquid from tray, including any liquid draw from the tray)

l

Vapor Mass Flow (vapor to tray)

l

Liquid Volume Flow (liquid from tray)

l

Vapor Volume Flow (vapor to tray)

Physical Properties All liquid results apply to the liquid leaving a tray. All vapor results apply to vapor entering a tray.

290

l

Liquid Molecular Weight

l

Vapor Molecular Weight

l

Liquid Mass Density

l

Vapor Mass Density

l

Liquid Viscosity

7 Column Analysis Overview

l

Vapor Viscosity

l

Surface Tension

Hydraulic Results This is the default selection. Hydraulic results are reported on a tray-by-tray basis. l l

l

l

l

l

l

l

l

% Jet Flood: Refer to Flooding Calculations for Trays. Dry Pressure Drop: Average pressure drop for a tray when the liquid flow is zero, reported in pressure drop units. Total Pressure Drop: The sum of dry pressure drop, clear liquid height on the tray, and any residual pressure drop terms that might apply. Reported in pressure drop units. Dry Pressure Drop (Head Loss): Average pressure drop for a tray when the liquid flow is zero, reported in liquid head units. Total Pressure Drop (Head Loss): The sum of dry pressure drop, clear liquid height on the tray, and any residual pressure drop terms that might apply. Reported in liquid head units. Downcomer Backup (Aerated): Average height of aerated liquid in the downcomers. Refer to Downcomer Backup Calculations for further details. Downcomer Backup (Unaerated): Average height of unaerated liquid in the downcomers. Refer to Downcomer Backup Calculations for further details. % Downcomer Backup (Aerated): Downcomer backup divided by the total of tray spacing and weir height, expressed as a percentage, reported for aerated liquid. Refer to Downcomer Backup Calculations for further details. % Downcomer Backup (Unaerated): Downcomer backup divided by the total of tray spacing and weir height, expressed as a percentage, reported for unaerated liquid. Refer to Downcomer Backup Calculations for further details.

l

Mass Rate/Column Area

l

Volume Rate/Column Area

l

Fs (Net Area):

l

Fs (Bubbling Area):

l

Cs (Net Area):

l

Cs (Bubbling Area):

l

Approach to System Limit (as a percentage): System Limit, or

7 Column Analysis Overview

291

ultimate capacity, for a given system represents an upper limit of the superficial vapor velocity beyond which a column cannot operate without flooding. The System Limit is independent of column diameter and internals design and depends only on the physical properties and the liquid load. Percent Approach to system limit = (Capacity factor / Capacity factor at system limit) * 100 l

Height Over Weir (Aerated)

l

Height Over Weir (Unaerated)

l

For each downcomer type (depending on number of tray passes): Refer to Downcomer Backup Calculations for further details. o

Volume

o

Residence Time

o

Velocity from Top

o

Velocity from Bottom

o

Exit Velocity

o

Downcomer Choke Flood [%]: Downcomer choke flood is a problem in high liquid rate applications in trayed columns. It occurs when the downcomer top area is not large enough to handle the froth flow, and vapor cannot disengage properly from the liquid. Choke flooding on certain trays reduces the capacity and efficiency of the trays and other trays in the immediate vicinity, which can sometimes lead to serious operability issues for the entire column. The reported Downcomer Choke Flood [%] is the percentage of the maximum acceptable liquid velocity at the downcomer entrance.

Hydraulic Results (Short) Hydraulic results are reported on a tray-by-tray basis. l l

l

292

% Jet Flood: Refer to Flooding Calculations for Trays. Total Pressure Drop: The sum of dry pressure drop, clear liquid height on the tray, and any residual pressure drop terms that might apply. Reported in pressure drop units. Downcomer Backup (Aerated): Average height of aerated liquid in the downcomers. Refer to Downcomer Backup Calculations for further details.

l

Liquid Mass Flow

l

Vapor Mass Flow

l

Liquid Mass Density

l

Vapor Mass Density

l

Liquid Viscosity

l

Vapor Viscosity

l

Surface Tension

7 Column Analysis Overview

References Stupin, W. J. and Kister, H. Z., “System Limit: The Ultimate Capacity of Fractionators,” Chemical Engineering Research and Design, Volume 81, Issue 1, 136 – 146, 2003.

Specifying Packing Geometry To specify packing geometry: 1. On the Geometry form, select the Geometry tab | Geometry page. 2. For Section Type, select the Packed radio button. 3. Specify the Mode: o

Interactive Sizing: This is the default selection. If you specify Packing Type, Vendor, and Dimension, HYSYS calculates the Diameter. If you specify the Diameter, the column behavior is the same as in Rating mode.

o

Rating: You must specify the Section Diameter.

4. From the Packing Type drop-down list, select the desired packing type. The default selection is Pall. 5. If desired, select values for the following: Field

Description

Vendor

If you do not change the default Packing Type, the default selection is Generic. Options are dependent on the Packing Type selected.

Material

If you do not change the default Packing Type, the default selection is Metal. Options are dependent on the Packing Type selected.

Dimension

If you do not change the default Packing Type, the default selection is 1.5-in or 38-mm. Options are dependent on the Packing Type selected.

Section Diameter

In Interactive Sizing Mode, the diameter is calculated based on the constraints that you specified on the Geometry tab | Design Parameters page. For further details, refer to Specifying Packing Geometry Design Parameters. By default, HYSYS uses a Fractional Approach to Maximum Capacity of 0.8 to calculate the diameter.

Packing Factor (>0)

If you choose a GPDC-based Pressure Drop Calculation Method on the Design Parameters page, and the Packing Factor is missing, you must specify it.

6. You must perform one of the following tasks: o

Select the Section Packed Height radio button and adjust the value in the field. Packed Height per Stage (HETP) is automatically calculated. -or-

7 Column Analysis Overview

293

o

Select the Packed Height per Stage (HETP) radio button and adjust the value in the field. Section Packed Height is automatically calculated.

Note: You can click the View Hydraulic Plots button to view hydraulic operating diagrams for the column.

Specifying Packing Geometry Design Parameters To specify Packing Geometry design parameters: 1. Select the Geometry tab | Design Parameters page. 2. Specify or view values for the following fields: Field

Default

Description

% Approach to Maximum Capacity

80%

If selected, in Interactive Sizing Mode, the section diameter is computed such that the maximum value of the fractional approach to maximum capacity in the section equals this value.

Design Capacity Factor

N/A

If selected, in Interactive Sizing Mode, the section diameter is computed such that the maximum capacity factor in the section equals this value.

Sizing Criterion

Note: The Design Capacity Factor is used for sizing (diameter) calculations, which are performed using the conditions from the stage with the highest flow. Design Factors

294

Optional Capacity Factor at Flooding



If desired, you can type a value in this field. If you do not specify a value, HYSYS calculates the capacity factor at flooding from the correlations.

System Foaming Factor

1

Specifies the degree of foaming which occurs. Typical non-foaming systems should use a value of 1. Lower values indicate more foaming. See Foaming Calculations for typical values.

7 Column Analysis Overview

Over-Design Factor

1

Factor used to multiply column loadings to reflect expected minimum of maximum loadings. Cannot be used if HYSYS updates the pressure drop during calculations.

Hydraulic Plot/Pressure Drop Minimum Liquid Flow Rate per Unit Area

Pressure Drop at Flood per Unit Packed Height

7 Column Analysis Overview

o

0.25 gpm/ft2 for sheet metal structured packings, glass, ceramic, or carbon

o

0.5 gpm/ft2 for random packings

o

0.1 gpm/ft2 for wire gauze structured packings

o

0.5 gpm/ft2 for metal random packings

o

1 gpm/ft2 for plastic random packings

o

0.5 gpm/ft2 for plastic structured packings

Determines the minimum liquid flow rate boundary on the hydraulic plot. The default depends on the type of packing, but can be overridden by specifying a value here.

Displays the calculated value of pressure drop at flooding per unit packed height. This value cannot be edited, but see below.

295

Allowable Pressure Drop per Unit Packed Height

296

Pressure Drop at Flood

Limit on pressure drop per unit packed height. By default, this is the pressure drop at flooding (see above). Depending on the option selected for Pressure Drop Calculation Method: o

Wallis or Stichlmair: You cannot exceed the maximum suggested Pressure Drop at Flood.

o

Any of the GPDC methods: You can overwrite the maximum pressure drop value up to 4" H2O/ft.

Minimum Pressure Drop per Unit Packed Height

0.05 in-water/ft

Lower limit on pressure drop per unit packed height. Determines a limit on the stability plot.

Number of Curves ( 1.8 lb/ft3)

1.21/ρG0.32

Low Foaming Systems Depropanizers

0.9

H2S strippers

0.85-0.9

Fluorine systems

0.9

Hot carbonate regenerators

0.9

Moderate Foaming Systems Demethanizers and deethanizers, top section (refrigerated type)

0.8-0.85

Demethanizers and deethanizers, top section (absorbing type)

0.85

Demethanizers and absorbing type deethanizers, bottom section

1.0

Refrigerated type deethanizers, bottom section

0.85-1.0

Oil absorbers

0.85 (0.8-0.95 below 0°F)

Crude towers, crude vacuum towers

0.85-1.0

Furfural refining towers

0.8-0.85

Sulfolane systems

0.85-1.0

Amine regenerators

0.85

Glycol regenerators

0.65-0.85

Hot carbonate absorbers

0.85

Caustic wash

0.65

Heavy Foaming Systems Amine absorbers

0.73-0.8

Glycol contactors

0.5-0.73

Sour water strippers

0.5-0.7

Oil reclaimer

0.7

MEK units

0.6

Stable Foam Systems

330

7 Column Analysis Overview

System

System Foaming Factor

Caustic regenerators

0.3-0.6

Alcohol synthesis absorbers

0.35

Packing Types and Packing Factors HYSYS can handle a wide variety of packing types, including different sizes and materials from various vendors. For random packings, the calculations require packing factors. HYSYS stores packing factors for the various sizes, materials, and vendors allowed in a databank. If you provide the following information, HYSYS retrieves these packing factors automatically for calculations: l

Packing type

l

Size

l

Material

Is the vendor specified?

Aspen uses

Yes

The packing factor published by the vendor. Packing factors for Koch-Glitsch packings were updated in Aspen 2006.5 using KGLP Bulletins KRP-5 (2000), KRP-6 (2000), KCP-7 (2003), KMF-6 (2003), KG-IMTP2 (2003), KGMRP-1 (2003), KGSS-1 (2003), and KGPP1 (2003).

No

A value compiled from various literature sources (also updated in 2006.5): J.R. Fair, et al., "Liquid-Gas Systems," Perry's Chemical Engineers' Handbook, R.H. Perry and D. Green, ed., 6th ed. (New York: McGraw Hill, 1984). Tower Packings, Bulletin No. 15 (Tokyo: Tokyo Special Wire Netting Company). H. Kister, Distillation Design. S.M. Walas, Chemical Process Equipment. And other sources in the open literature

You can enter the packing factor directly to override the built-in values. Aspen uses the packing type to select the proper calculation procedure.

Downcomer Choke Flooding Downcomer choke flooding is a problem in high-liquid-rate applications in trayed columns. It occurs when the downcomer top area is not large enough to

7 Column Analysis Overview

331

handle the froth flow, and vapor cannot disengage properly from the liquid. Choke flooding on certain trays reduces the capacity and efficiency of those trays and other trays in the immediate vicinity, which can sometimes lead to serious operability issues for the entire column. If avoiding downcomer choke flood requires that the downcomer area exceeds 25% of the cross-sectional area of the column, a warning will appear, as this limit is a standard good design practice.

Flooding Calculations for Trays HYSYS provides the following procedures for calculating the approach to jet flooding.

Methods available for sieve and bubble cap trays The Fair72 method. This is a new, much better fit to the original graphical correlation by Fair. The Glitsch ballast tray procedure. All hydraulic calculations besides the approach to flooding are based on the Fair and Bolles methods. The original Glitsch method (available only for rating) is based on version 3 of Glitsch bulletin 4900. Version 6 is also available. For sizing, Glitsch refers to version 6. The Kister & Haas method (not for bubble cap trays). The Smith, Dresser, and Ohlswager method.

Methods available for Glitsch Ballast trays Only the Glitsch version 3 (rating only) and version 6 methods, described above under sieve and bubble cap trays.

Methods available for Koch Flexitray and Nutter Float Valve trays For Koch Flexitray and Nutter Float Valve trays, HYSYS uses procedures from vendor design bulletins. Two versions of vendor design bulletins are available for Koch Flexitray: l

Bulletin 960

l

Bulletin 960-1

Note: These bulletins apply to earlier versions of Koch Flexitrays. Koch-Glitsch does not release information which would allow their current tray designs to be precisely modeled in HYSYS.

Footnotes Ballast Tray Design Manual, Glitsch, Inc. Bulletin No. 4900, 3rd ed. and 6th ed. Dallas.

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7 Column Analysis Overview

Smith, B.D., "Tray Hydraulics: Bubble Cap Trays" and "Tray Hydraulics: Perforated Trays," Design of Equilibrium Stage Processes, New York: McGraw Hill, 1963, pp. 474-569. Ballast Tray Design Manual, Glitsch, Inc. Bulletin No. 4900, 3rd ed. Dallas, 1980. Koch Flexitray Design Manual, Koch Engineering Co., Inc. Bulletins No. 960, 960-1, Wichita. Nutter Float Valve Design Manual, Tulsa: Nutter Engineering Co., 1976.

Kister & Haas Jet Flood Correlation Kister & Haas developed a correlation for jet flooding on sieve or valve trays. The correlation takes into account the effects both of physical properties and of tray geometry. Its predictions more closely match experimental data that those of Fair or Smith, Dresser, and Ohlswager. The correlation is given below:

Where: Variable

Description

Units

CSF

=

Density-corrected superficial vapor velocity at flooding, based on the net area of the tray

m/sec

h cl

=

Clear liquid height on the tray, calculated by the correlation of Jeronimo and Sawistowski

mm

dh

=

Hole diameter

mm

σ

=

Liquid surface tension

dyn/cm

ρL, ρV

=

Liquid and vapor densities

kg/m3

ts

=

Tray spacing

mm

ϕ

=

Fractional hole area per unit active bubbling area

-

QL

=

Liquid load per length of weir

m3/mhr

The Kister & Haas correlation is applicable over the following ranges: l

Pressure 1.5 to 1500 psia (10.3 kPa to 10.3 MPa)

l

Vapor velocity 1.5 to 13 ft/s (0.46 to 3.96 m/s)

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333

l

Liquid Load 0.5 to 12 gpm/in of outlet weir (1.24 to 29.8 liters/sec per meter of outlet weir)

l

Vapor density 0.03 to 10 lb/ft3 (0.48 to 160 kg/m3)

l

Surface tension 5 to 80 dyn/cm

l

Liquid viscosity 0.05 to 2.0 cP

l

Tray spacing 14 to 36 in (0.36 to 0.91 m)

l

Hole diameter 1/8 to 1 in (3.2 to 25.4 mm)

l

Fractional hole area 0.06 to 0.20

l

Weir height 0 to 3 in (0 to 76.2 mm)

If any of these conditions is violated, HYSYS uses the Glitsch method instead, and prints messages in the history file indicating which conditions were violated. If hole diameter is not available, the correlation uses a hole diameter of 3/8 inch (9.5 mm). In sizing mode, the Glitsch correlation for maximum downcomer velocity is used to establish the area of the downcomers. The design velocity (in gpm/ft2, multiply by 0.679 for liters/sec-m2) is set to the smallest of:

Where ts is the tray spacing in inches.

Reference H.Z. Kister and J.R. Haas, Chem. Eng. Prog. 86(9), 1990, p. 63.

Fair and Fair72 Jet Flood Correlations The Fair72 correlation is a greatly improved fit to the graphical correlation by Fair. The Fair correlation uses this equation:

The Fair72 correlation uses this equation:

Where:

334

X

=

Flow parameter (minimum 0.01 for Fair72)

TS

=

Tray spacing, meters

7 Column Analysis Overview

CSB

=

Reduced flooding velocity

A1

=

-0.00667

A2

=

0.0192

A3

=

-0.434

A4

=

1.466

B1

=

0.024837

B2

=

0.33586

B3

=

-0.049623

B4

=

0.48029

B5

=

-0.63132

B6

=

0.0094263

B7

=

1.3165

B8

=

-0.31952

The following plot compares the Fair72 and original Fair methods to the graphical correlation over a range of typical conditions:

7 Column Analysis Overview

335

References J.R. Fair, Petro/Chem Eng. 33(10), 1961, p. 45. J.R. Fair, et al., "Liquid-Gas Systems," Perry's Chemical Engineers' Handbook, R.H. Perry and D. Green, ed. 6th ed., New York: McGraw Hill, 1984.

Smith, Dresser, and Ohlswager Jet Flood Correlation The Smith, Dresser, and Ohlswager jet flood correlation is represented as the SDO72 jet flood method in HYSYS. The following equation to fit the curves they presented (1963):

Where: X

=

Flow parameter ≥ 0.02

S

=

Settling height, inches = tray spacing - weir height - height of liquid over the weir ≥ 2 inches. Height of liquid over the weir is calculated by HYSYS based on tray geometry.

CSF

=

Density-corrected superficial vapor velocity at flooding, based on the net area of the tray, ft/sec

a

=

0.018776

b

=

0.23291

c

=

0.12365

d

=

0.00032439

f

=

2.7995

g

=

-0.076557

h

=

0.0063109

j

=

0.58541

k

=

3.7316

l

=

-0.070155

m

=

2

n

=

-0.0024265

p

=

0.94794

The following plot compares the SDO72 method to the graphical correlation over a range of typical conditions:

336

7 Column Analysis Overview

Reference R.B. Smith, T. Dresser, and S. Ohlswager. Hydrocarb. Proc. & Pet. Ref., 40(5), 1963, p. 183.

Pressure Drop Calculations for Packing in Column Analysis HYSYS provides several built-in methods to compute the pressure drop. Vendor correlations for random packing: Raschig, Sulzer Vendor correlations for structured packing: Sulzer BX, CY, Mellapak, Kerapak, BXPlus, MellapakPlus, MellaCarbon, and MellaGrid; Raschig Super-Pak, RaluPak, Sheet-Pack, Wire-Pack, and Grid-Pack To specify one of these vendor correlations, specify the appropriate packing type and vendor, and leave Pressure drop calculation method blank. See below for details on which methods are used for each packing. Note: These correlations are based on vendor bulletins that apply to earlier versions of Koch and Sulzer packings. Koch-Glitsch and Sulzer do not release information which would allow their current packing designs to be precisely modeled in HYSYS.

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337

Other methods: Eckert GPDC, Norton GPDC, Prahl GPDC, Tsai GPDC, Aspen GPDC-85, Sherwood/Leva/Eckert GPDC (SLE), Robbins GPDC, Wallis, Stichlmair If you choose one of the GPDC-based methods, a packing factor is required. If you specify vendor Sulzer, the vendor correlation will be used unless you select the User method. If you specify vendor Raschig, only the vendor correlation is available. If you specify a vendor other than Raschig or Sulzer, the Wallis method is the default. The pressure drop calculated for stage N is the pressure difference between stage N and stage N+1. In columns without reboilers where the last stage is included in a pressure update section, the pressure drop for the last stage is not used because there is no stage below to receive the updated pressure.

Footnotes R. Billet & M. Schultes, I. Chem. E. Symp. Ser. 104, p. B255, 1987. R. Billet & M. Schultes, I. Chem. E. Symp. Ser. 104, p. A159, 1987. Fair, J.R. et al., "Liquid-Gas Systems," Perry's Chemical Engineers' Handbook, R.H. Perry and D. Green, ed., 6th ed. (New York: McGraw Hill, 1984), pp. 1822. McNulty, K.J. and Hsieh, C. L., "Hydraulic Performance and Efficiency of Koch Flexipac Structured Packings." Paper presented at American Institute of Chemical Engineers Annual Meeting in Los Angeles, 1982. This is a cubic spline interpolation, a 6th order polynomial representation of curves. Correlation supplied by the Norton Company, subsequently acquired by SaintGobain, and then sold to Koch-Glitsch. Uses a log-log interpolation. Robbins, L.A., "Improved Pressure Drop Prediction with a New Correlation," Chemical Engineering Progress, May 1991, pp. 87-91. Tsai, T. C., "Packed Tower Program Has Special Features," Oil and Gas Journal, Vol. 83 No. 35 (September, 1985), p. 77. See usage in, for example, Unit Operations Handbook: Volume 1 - Mass Transfer, 2nd Edition, edited by John J. McKetta, CRC Press, Boca Raton, FL, 1993, p. 265.

Sherwood/Leva/Eckert GPDC Pressure Drop Correlation for Packing The Sherwood/Leva/Eckert (SLE) correlation is a fit to the graphical correlation in Packed Tower Design and Applications; Random and Structured Packings.

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7 Column Analysis Overview

Where: X

=

Flow parameter

Δp

=

Pressure drop in inches of water per foot

Y

=

Capacity parameter

a

=

0.13443

b

=

0.76042

c

=

2.0952

d

=

0.69665

f

=

1.7438

g

=

0.0052937

h

=

0.51819

Plots comparing model predictions with actual data for Sherwood/Leva/Eckert GPDC Pressure Drop Correlation for Packing:

7 Column Analysis Overview

339

Reference R.F. Strigle Jr., Packed Tower Design and Applications; Random and Structured Packings, 2nd ed. Gulf Publishing Co., 1994 p. 19.

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7 Column Analysis Overview

Aspen GPDC85 Pressure Drop Correlation for Packing The GPDC85 is a fit to the graphical correlation in Applied Process Design for Chemical and Petrochemical Plants. (1)

Where: X

= Flow parameter

Δp

= Pressure drop in inches of water per foot

Y

= Capacity parameter

a

= 7.8282

b

= 1.087

c

= 2.5292

d

= 0.34185

f

= 1.7976

g

= 1.0557

h

= -0.95216

Plot comparing model predictions with actual data for Aspen GPDC85:

7 Column Analysis Overview

341

Reference Applied Process Design for Chemical and Petrochemical Plants, Vol. 2, 3rd Edition, Gulf Professional Publishing, Houston, 1997, p. 285. Figure 9-21E"

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7 Column Analysis Overview

Wallis Pressure Drop Correlation for Packing The new model for pressure drop and flood in packed columns is based upon the observation that renormalizing air/water pressure drop data to the flood point generally collapses that data onto a single curve. This behavior is shown below for 1/2-inch ceramic INTALOX saddles [1].

The pressure drop has also been rescaled by the liquid static head, ρLg, so that the functional form taken by the data is dimensionless. The pressure drop for any system can now be determined quite accurately so long as a good method for estimating flood points in that system is available. HYSYS uses this form:

7 Column Analysis Overview

343

Where the Ai are the fitting coefficients (built into HYSYS) and x is the approach to flood at constant liquid load:

Here CS is the density-corrected superficial vapor velocity, and CSF is the density-corrected vapor velocity that would flood the column at the liquid load in question.

Prediction of Flood Points The Wallis equation, originally derived for two phase flow in pipes, has been found to correlate flooding data for packed columns quite well [2].

Here, CL is the liquid load. The Wallis parameters c and m have been found to vary with the physical properties of the liquid. Therefore semi-empirical corrections based on the liquid’s physical properties are usually applied to the air/water values of c and m. Unfortunately, these corrections do not always work well. The air/water values of c and m vary in a predictable way with the size of the packing within a given packing family. This has profound implications. If a dimensionless parameter, like m, changes in response to a parameter that has dimensions, then m must depend on other physical quantities in such a way that their product has no dimensions. Similarly, c has dimensions of , but it depends on a parameter with dimensions of length. Again, it can be inferred that c must depend on other physical quantities in such a way that the net result is a quantity with the dimensions of

344

.

7 Column Analysis Overview

It is not too difficult to show, via dimensional analysis, that

where g is the acceleration due to gravity, ρL is the liquid phase density, and σ is the interfacial tension. The analysis suggests no form for the functions Φc and Φm so we are free to choose any form that reproduces the data best. In general, Φc and Φm can be adequately represented by power laws. Thus, a complete description for the flood point has been developed by application of renormalization and scaling principles. Aspen Technology has collected and analyzed air-water pressure drop data for a great number of packing styles and sizes, resulting in better pressure drop estimates for packed sections. For other fluids, using the proportionality above:

7 Column Analysis Overview

345

Where c1W and m1W are the values of c and m for air-water systems, and POWC and POWM are exponents in the power laws. Aspen Technology has also verified the predictive capabilities of the new model. Shown below are some comparisons of experimental data taken on different systems with different packings with estimates of the pressure drop based on the new Aspen model as well as on the GPDC [3]. While the GPDC predicts reasonable pressure drops it misses flooding rather severely. On the other hand, the new Aspen model succeeds in predicting both pressure drop and flood point, even for historically difficult systems, like high pressure debutanizers.

346

7 Column Analysis Overview

References 1. http://www.rauschert-vt.de/cms/upload/td_fk_en/Saddles_12_ Stonew.pdf 2. McNulty, K.; Hsieh, C.; Hydraulic Performance and Efficiency of Koch Flexipac Structured Packings, presented at the 1982 AIChE National Meeting, Los Angeles, CA. 3. Data taken from the following sources: "Distillation Pilot Plant Design, Operating Parameters, and Scale-Up Considerations" http://www.cheresources.com/distillationmodel4.shtml; Sulzer structured packing brochure; Fitz Jr., C.W; Shariat, A.; Kunesh, F.G.; Performance of Structured packing in a Commercial Scale Column at Pressures of 0.02 to 27.6 Bar, Distillation and Absorption ’97, Maastricht, the Netherlands, 8-10 September 1997.

Billet-99 Correlation for Packing HYSYS supports the following correlations:

7 Column Analysis Overview

347

l

Billet-99 correlation for pressure drop

l

Billet-99 correlation for mass transfer

l

Billet-99 correlation for mass interfacial area

l

Billet-99 correlation of holdup

The Billet-99 correlation is supported for the packings described in the table below. Packing Type

Vendor

Material

Dimension

PALL

GENERIC

PLASTIC

1-IN OR 25-MM

PALL

GENERIC

PLASTIC

2-IN OR 50-MM

PALL

GENERIC

METAL

1-IN OR 25-MM

PALL

GENERIC

METAL

2-IN OR 50-MM

RASCHIG

GENERIC

CERAMIC

1-IN OR 25-MM

RASCHIG

GENERIC

CERAMIC

2-IN OR 50-MM

SUPER-PAK

GENERIC

METAL

250

SUPER-PAK

GENERIC

METAL

300

SHEET-PACK

GENERIC

METAL

250X

SHEET-PACK

GENERIC

METAL

250Y

SHEET-PACK

GENERIC

METAL

250Y-HC

SHEET-PACK

GENERIC

METAL

350Y

WIRE-PACK

GENERIC

METAL

500Y

GRID-PACK

GENERIC

METAL

P40Y

GRID-PACK

GENERIC

METAL

P64X

GRID-PACK

GENERIC

METAL

P64Y

GRID-PACK

GENERIC

METAL

P90X

Pressure Drop Calculations for Trays Normally, Columns treat the stages you enter as equilibrium stages. You must enter overall efficiency to: l

l

Convert the calculated pressure drop per tray to pressure drop per equilibrium stage Compute the column pressure drop

If you do not enter overall efficiency, these models assume 100% efficiency. If you specify Murphree or vaporization efficiency, you should not enter overall efficiency. The Column will treat the stages as actual trays. The pressure drop calculated for stage N is the pressure difference between stage N and stage N+1. In columns without reboilers where the last stage is

348

7 Column Analysis Overview

included in a pressure update section, the pressure drop for the last stage is not used because there is no stage below to receive the updated pressure.

References B.D. Smith, Design of Equilibrium Stage Processes, Chap. 14, McGraw-Hill, New York, 1963. Perry’s Chemical Engineers’ Handbook, 5th ed., Chap. 18, McGraw-Hill, New York, 1973.

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349

350

7 Column Analysis Overview

8 Electrolyte Operations

Introduction Most HYSYS unit operations can be used when working with the OLI_Electrolyte property package. The following HYSYS unit operations are not available in the OLI_Electrolyte property package: l

Pipe Segment

l

Reactors

l

Short Cut Column

l

Three Phase Distillation

l

Compressible Gas Pipe

Electrolyte Operations There are three electrolyte simulations specific to OLI Electrolyte property package. The electrolyte operations are only available if your case is an electrolyte system (the selected fluid package must support electrolytes). The table below describes the electrolyte simulations. Operation

Icon

Description

Neutralizer

Neutralizer operation is used to control PH value for a process material stream.

Precipitator

Precipitator operation is used to achieve a specified aqueous ionic species concentration in its product stream.

Crystallizer

Crystallizer operation is used to estimate and control solid concentration in a product stream.

8 Electrolyte Operations

351

352

8 Electrolyte Operations

9 Crystallizer Operation

The Crystallizer operation models the crystallization of a fully defined inlet stream to attain a specified amount of selected solids concentration that is present in the effluent. The Crystallizer operation contains four tabs: l

Design

l

Rating

l

Worksheet

l

Dynamics

Theory The figure below represents the crystallizer model. A Crystallizer has a product stream that contains liquid and solid. By adjusting the operation condition like Crystallizer temperature and pressure or heat duty, the amount of solid or solid component product in the liquid stream can be controlled or estimated.

The Crystallizer vessel is modeled as a perfect mixing in HYSYS. Heat can be added or removed from the Crystallizer, and a simple constant duty model is assumed.

9 Crystallizer Operation

353

Boundary Condition Since the electrolyte flow sheet implements a forward calculation only, the Crystallizer does not solve until the Inlet Stream is defined. If the energy stream is not specified, the crystallizer is treated as an adiabatic one. You must specify two of the following to define the boundary condition for crystallizer solver to proceed: l

T: Crystallizer temperature

l

P or DeltP: Crystallizer’s pressure or pressure drop

l

E. Heat Duty

l

Fcry. Crystal product flow rate (total or a specific component)

l

Fvap. Vapor flow

Equations The crystallizer solves under the constraint of mass and energy balance equations: (1) (2) (3) with the target solid equation: where: Fsolid(product stream) = solid flow rate in the outlet liquid stream Fsolid(specified) = desired solid flow rate in the outlet liquid stream E = energy/heat transfer rate M = mass flow rate

Design Tab The Design tab contains the following pages:

354

l

Connections

l

Parameters

l

Solver

l

User Variables

l

Notes

9 Crystallizer Operation

Connections Page You can specify the inlet stream, outlet stream, and energy stream on the Connections page. Object

Description

Name

You can change the name of the operation by typing a new name in the field.

Inlet

You can enter one or more inlet streams in this table, or use the dropdown list to select the streams you want.

Vapor Out- You can enter the name of the vapor product stream or use the drop-down let list to select a pre-defined stream. Liquid Outlet

You can enter the name of the product stream in this field or use the dropdown list to select a pre-defined stream.

Energy (Optional)

You can add an energy stream to the operation by selecting an energy stream from the drop-down list or typing the name for a new energy stream.

Fluid Pack- Displays the fluid package currently being used by the operation. You can age select a different fluid package from the drop-down list.

Parameters Page On the Parameters page, you can specify the pressure drop and solid output flow rate. Note: The flow rate of crystal product depends on the solubility of the product at the crystallizer’s operation condition.

The four radio buttons allow you to control the specified solid output in the liquid stream by crystallization operation: l

l

l

l

Mole Flow. Select this radio button to specify the flow rate value in mole basis. Mass Flow. Select this radio button to specify the flow rate value in mass basis. Component. Select this radio button to control a specified solid component in the operation. Total. Select this radio button to control the total solid flow rate in the liquid stream.

This page also displays the degrees of freedom for the operation at the current setting.

9 Crystallizer Operation

355

Solver Page On the Solver page, you can specify the upper and lower bounds of the manipulated variable, the tolerance of specified variable, and the maximum iterations/steps of calculations the solver performs before stopping. Crystallizer operates on various boundary conditions. The following table lists all the possible options. As soon as the operation condition (as listed in the Specified Variables column) is known, the crystallizer will start to solve. The Crystallizer Calculates column lists some of the calculation variables for the operation. Specified Variables

Crystallizer Calculates

Temperature & Pressure

Heat Duty, Crystal product flow rate, Vapor flow rate

Temperature & Heat Duty

Pressure, Crystal product flow rate, Vapor flow rate

Temperature & Crystal product flow rate

Pressure, Heat Duty, Vapor flow rate

Temperature & Vapor flow rate

Pressure, Crystal product flow rate, Heat Duty

Pressure & Heat Duty

Temperature, Crystal product flow rate, Vapor flow rate

Pressure & Crystal product flow rate

Temperature, Heat Duty, Vapor flow rate

Pressure & Vapor flow rate

Temperature, Crystal product flow rate, Heat Duty

The bounds for the Manipulated Variables and tolerances for the Target Variables are shown on the Solver tab and are user-modifiable. As well, the Active status for the Manipulated Variable used by the solver is shown. However, this flag is meant for displaying information only thus cannot be changed.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation. Click here for more information.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general. Click here for more information.

356

9 Crystallizer Operation

Rating Tab The Crystallizer operation currently does not support any rating calculations.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the Crystallizer. Click here for more information. Note: The PF Specs page is relevant to dynamics cases only.

The Crystallizer Worksheet tab also has one extra page called the Solids page. On the Solids page, you can view the precipitate molar and mass flow rates.

Dynamics Tab The Crystallizer operation does not support dynamic mode.

9 Crystallizer Operation

357

358

9 Crystallizer Operation

10 Neutralizer Operation

The Neutralizer operation models the neutralization of a fully defined inlet stream, and allows you to adjust the pH value in the effluent stream. The Neutralizer property view contains four tabs: l

Design

l

Rating

l

Worksheet

l

Dynamics

Theory The figure below represents the neutralizer model. Through adjusting the Reagent Stream variables (flow rate), the PH value for the targeting stream (Liquid Stream) could be controlled at the level as required.

l l

l

l

Inlet Stream. At least one inlet stream. Reagent Stream. Reagent stream must be a free stream, that is, not attached to any other unit operations. Product Stream. A Neutralizer has two product streams, a vapor stream and a liquid stream. The liquid stream controls the pH value. pH. The liquid stream’s pH value that is to be controlled must fall in the range between the pH values of the Reagent and inlet streams to guarantee the solution.

10 Neutralizer Operation

359

l

Q. The energy stream is optional. When no energy stream is attached, an adiabatic operation is assumed.

The Neutralizer vessel is modeled as perfect mixing. Heat can be added or removed from the Neutralizer, and a simple constant duty model is assumed.

Boundary Condition Since the electrolyte flow sheet implements a forward calculation only, the Neutralizer does not solve until both inlet and Reagent streams are defined. If the energy stream is not specified, the neutralizer is treated as an adiabatic one. If the energy stream is specified, you must specify either the Neutralizer temperature or the duty of the energy stream. Pressure drop of the neutralizer must be specified or can be calculated out from the inlet and product streams.

Solving Options The Neutralizer has two different solving options, depending on what you specify.

Option 1 (Targeting pH Value is Not Specified) If the targeting pH value is not specified, the Neutralizer operates as a mixer for the inlet and Reagent streams. The product stream accepts the mixed result as is.

Option 2 (Targeting pH Value is Specified) If the targeting pH value is specified, the flow rate of the Reagent stream must be left unspecified. The Reagent stream is used as an adjusting variable for neutralizer solver to search for a solution to meet the targeting pH value at the outlet stream.

Equations The Neutralizer solves under the constraint of the following equations. (1) (2) (3) (4) where: E = energy/heat transfer rate

360

10 Neutralizer Operation

M = mass flow rate

Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

Solver

l

User Variables

l

Notes

Connections Page You can specify the inlet stream, outlet stream, and energy stream on the Connections page. Object

Description

Name

You can change the name of the operation by typing a new name in the field.

Inlet

You can enter one or more inlet streams in this table, or use the dropdown list to select the streams you want.

Reagent Stream

You can enter a name for the reagent stream or use the drop-down list. Reagent stream must be a free stream, that is, not attached to any other unit operations.

Vapor Out- You can type the name of the vapor product stream or use the drop-down let list to select a pre-defined stream. Liquid Outlet

You can type the name of the product stream in this field or use the dropdown list to select a pre-defined stream.

Energy (Optional)

You can add an energy stream to the operation by selecting an energy stream from the drop-down list or typing the name for a new energy stream.

Fluid Pack- Displays the fluid package currently being used by the operation. You can age select a different fluid package from the drop-down list.

Parameters Page On the Parameters page, you can specify the pressure drop and an initial pH value. This page also displays the degrees of freedom for the operation at the current setting, and the actual pH balance in the operation when the operation reaches a solution.

10 Neutralizer Operation

361

Object

Description

Delta P

You must specify the pressure drop for the Neutralizer or specify inlet and product streams with known pressure.

pH Spec

You can specify the product stream’s pH value in this field. The pH value that is to be controlled must fall in the range between the pH values of the Reagent and Inlet Streams for calculations to converge.

The pH value in a solution is defined in a mathematical format: (1) where: [H+] = concentration of H+ in a solution, mol/l According to Equation (2), the pH (specified) value must be specified between the pH values of the inlet and the Reagent streams. An adjustment of Reagent Stream’s variables, for example, temperature, pressure, and compositions, can bracket the pH (specified) value to meet the constraint Equation (2). As soon as the specified pH value is bracketed according to Equation (2), the pH value of the product stream in Equation (1) can be obtained by adjusting the flow rate of the Reagent stream.

Solver Page On the Solver page, you can specify the upper and lower bounds of the manipulated variable, the tolerance of specified variable, and the maximum iterations/steps of calculations the solver performs before stopping. Currently only the flow rate of a defined Reagent stream is used as an adjustable variable to the solver. Here a defined Reagent stream means that the stream can be flashed to get a solution with the specified variables meeting the degree of freedom. According to HYSYS, a defined stream can have the following variables: l

T. Stream Temperature

l

P. Stream Pressure

l

F. Stream Flow Rate

l

x. Stream Component Compositions

l

H. Stream Enthalpy

l

V. Stream Vapor Fraction

Rating Tab The Neutralizer operation currently does not support any rating calculations.

362

10 Neutralizer Operation

Dynamic Tab The Neutralizer operation currently does not support dynamic mode.

10 Neutralizer Operation

363

364

10 Neutralizer Operation

11 Precipitator Operation

The Precipitator models the precipitation of a selected ion in a stream entering the operation to achieve a specified target concentration in the effluent stream. The Precipitator operation contains four tabs: l

Design

l

Rating

l

Worksheet

l

Dynamics

Theory The figure below represents the precipitator model.

Through adjusting the flow rate of the Reagent stream, the concentration of the targeting ion could be controlled at the desired level as you require in the outlet stream. To ensure that the Precipitator functions properly, the ions in the Reagent stream must be capable of reacting with the target ion under the specified operation condition. The formation of a precipitate in the outlet stream reduces the target ion concentration that entered the operation in the inlet stream. l

Inlet Stream. At least one inlet stream.

l

Reagent Stream. Reagent stream must be a free stream, that is, not

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attached to any other unit operations. l

l

l

Liquid Stream. A Precipitator must have one liquid stream (contains liquid and solid) that is a targeting stream for the control of ion concentration through precipitation. Ion Concentration. The product stream’s ion concentration value can be controlled by dilution or precipitation. Q. The energy stream is optional.

The Precipitator is modeled as a perfect mixing in HYSYS. Heat can be added or removed from the precipitator through a duty stream, and a simple constant duty model is assumed.

Boundary Condition Since the electrolyte flow sheet implements a forward calculation only, the Precipitator does not solve until both inlet and Reagent streams are defined. If the energy stream is not specified, the precipitator is treated as an adiabatic one. If the energy stream is specified, you must specify either the Precipitator temperature or the duty of the energy stream. Pressure drop of the Precipitator must be either specified or can be calculated from the inlet and product streams.

Solving Options The Precipitator has two different solving options, depending on what you specify. Option 1 (Targeting Ionic Species Not Specified) If the targeting ionic species is not specified, the Precipitator simply mixes the inlet stream with the Reagent stream. The product stream accepts the mixed result as is. Option 2 (Targeting Ionic Species is Specified) If the targeting ionic species is specified for the control of its concentration, the flow rate of the Reagent stream is used as iterative variables for the precipitator solver to search for a solution.

Equations The precipitator solves under the constraint of the following equations: (1) (2) (3) where:

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11 Precipitator Operation

Cion = concentration of the targeting ion species E = energy/heat transfer rate M = mass flow rate

Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

Solver

l

User Variables

l

Notes

Connections Page You can specify the inlet stream, outlet stream, and energy stream on the Connections page. Object

Description

Name

You can change the name of the operation by typing a new name in the field.

Inlet

You can enter one or more inlet streams in this table, or use the dropdown list to select the streams you want.

Reagent Stream

You can enter a name for the reagent stream or use the drop-down list. Reagent stream must be a free stream, that is, not attached to any other unit operations.

Vapor Out- You can enter the name of the vapor product stream or use the drop-down let list to select a pre-defined stream. Liquid Outlet

You can enter the name of the product stream in this field or use the dropdown list to select a pre-defined stream.

Energy (Optional)

You can add an energy stream to the operation by selecting an energy stream from the drop-down list or typing the name for a new energy stream.

Fluid Pack- Displays the fluid package currently being used by the operation. You can age select a different fluid package from the drop-down list.

Parameters Page On the Parameters page, you can specify the pressure drop, select the ion to be controlled, and specify the ion concentration in the liquid stream. This page also displays the degrees of freedom for the operation at the current setting, and

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the actual ion concentration value in the operation when the operation has reached a solution. Object

Description

Delta P

You must specify the pressure drop for the Precipitator or specify inlet and product streams with known pressure.

Controlled Ion

Select the ion component you want to control from the drop-down list, or type the name of the ion component in the field.

Ion Spec

The concentration of ion from the inlet stream can be controlled via the following exercises:

Heating/Cooling

l

Dilution. If the mixing of reagent and inlet streams does not produce the ion to be controlled and the ion concentration in the Reagent stream is less than that in the inlet stream, an increase of flow rate of the Reagent stream can achieve the target. In this case, the Chemistry Model does not have to include Solid.

l

Precipitation. Form precipitator by mixing inlet and Reagent streams. The change of Regent stream variables: temperature, pressure, flow rate or composition may achieve the target. To form precipitator, OLI chemistry model must include Solid.

If an energy stream is attached to the Precipitator select either the Heating or Cooling radio button. If you know the duty of the energy stream specify the value in the Duty field.

Solver Page On the Solver page, you can specify the upper and lower bounds of the manipulated variable, the tolerance of specified variable, and the maximum iterations/steps of calculations the solver performs before stopping. Currently, the flow rate of the Reagent stream is the manipulated variable used by the precipitator solver to search for a solution.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation. Click here for more information.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general. Click here for more information.

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Rating Tab Precipitator operation currently does not support any rating calculations.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the Precipitator. Click here for more information. Note: The PF Specs page is relevant to dynamics cases only.

Dynamic Tab Precipitator operation currently does not support dynamic mode.

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12 Heat Transfer Operations

The next chapters will describe the following Heat Transfer Operations: l

Air Cooler

l

Cooler/Heater

l

Fired Heater

l

Heat Exchanger

l

LNG

l

Plate Exchanger

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371

372

12 Heat Transfer Operations

13 Air Cooler

The Air Cooler unit operation uses an ideal air mixture as a heat transfer medium to cool (or heat) an inlet process stream to a required exit stream condition. One or more fans circulate the air through bundles of tubes to cool process fluids. The air flow can be specified or calculated from the fan rating information. The Air Cooler can solve for many different sets of specifications, including: l

Overall heat transfer coefficient, UA

l

Total air flow

l

Exit stream temperature

Theory Steady State The Air Cooler uses the same basic equation as the Heat Exchanger unit operation; however, the Air Cooler operation can calculate the flow of air based on the fan rating information. The Air Cooler calculations are based on an energy balance between the air and process streams. For a cross-current Air Cooler, the energy balance is calculated as follows: (1) where: Mair = air stream mass flow rate Mprocess = process stream mass flow rate H = enthalpy The Air Cooler duty, Q, is defined in terms of the overall heat transfer coefficient, the area available for heat exchange, and the log mean temperature difference:

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(2) where: U = overall heat transfer coefficient A = surface area available for heat transfer ΔTLM = log mean temperature difference (LMTD) Ft = correction factor The LMTD correction factor, Ft, is calculated from the geometry and configuration of the Air Cooler.

Rigorous Air Cooler Functionality In Steady State mode, you can also access certain Aspen Exchanger Design and Rating functions on the Rigorous Air Cooler tab. You must install and license the EDR functions.

Dynamics In dynamics, the Air Cooler tube is capable of storing inventory like other dynamic unit operations. The direction of the material flowing through the Air Cooler operation is governed by the pressures of the surrounding unit operations.

Heat Transfer The Air Cooler uses the same basic energy balance equations as the Heat Exchanger unit operation. The Air Cooler calculations are based on an energy balance between the air and process streams. For a cross-current Air Cooler, the energy balance is shown as follows: (1)

where: Mair = air stream mass flow rate Mprocess = process stream mass flow rate ρ = density H = enthalpy V = volume of Air Cooler tube

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Dynamic Specifications HYSYS requires three overall specifications in order for the Air Cooler unit operation to fully solve in Dynamic mode: Dynamic Specifications

Description

Overall UA

The Overall UA is the product of the Overall Heat Transfer Coefficient (U) and the total area available for heat transfer (A). You can specify the value of UA on the Parameters page of the Design tab.

Fan Rating Information

The Fan Rating information characterizes the flow rate and cooling properties of the air flowing through the Air Cooler. HYSYS provides two methods to determine the Fan Rating information. For the Air Cooler Simple Design method, specify the following variables in the Sizing page of the Rating tab: l

Demanded Speed

l

Design Speed

l

Design Flow

l

Max Acceleration (optional)

For the ACOL Design method, specify:

Pressure Drop

l

 The Air Mass Flow Rate variable in the Sizing page of the Rating tab

l

The various Fan parameters in the HTFS - ACOL tab

HYSYS provides two options to determine the pressure difference between the inlet and outlet process streams: l

Specified pressure drop (constant value)

l

Calculated pressure drop from K-value (value may vary with time)

These pressure drop specifications can be made on the Specs page of the Dynamics tab.

Pressure Drop The pressure drop of the Air Cooler can be determined in one of two ways: l

l

13 Air Cooler

Specify the pressure drop. This method assumes the pressure difference between the inlet process stream and outlet process stream is constant. This method is applicable to both Steady State and Dynamic modes. Define a pressure flow relation in the Air Cooler by specifying a k-value. This method assumes the pressure difference between the inlet process stream and outlet process stream varies with time. This method is applicable only to Dynamic mode.

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If the pressure flow option is chosen for pressure drop determination in the Air Cooler, a k-value is used to relate the frictional pressure loss and flow through the exchanger. This relation is similar to the general valve equation: (1) The general flow equation uses the pressure drop across the Heat Exchanger without any static head contributions. The quantity, P1 - P2, is defined as the frictional pressure loss which is used to “size” the Air Cooler with a k-value. Using the pressure flow option, you must have an accurate k-value to generate valid/accurate results. HYSYS also provides a feature than enables you to calculate the k-value of the Air Cooler at steady state. This k-value can then be used in Dynamic mode to calculate the varying pressure difference between the inlet and outlet process streams. The Calculate K option is located on the Dynamics tab | Specs page of the Air Cooler property view. The following information is required for HYSYS to calculate the k-value in Steady State mode: l

Completely defined inlet or outlet process stream (to obtain the flow and density variable value)

l

Pressure difference between the inlet and outlet stream

l

Solved Air Cooler operation

HYSYS assumes no pressure difference in the air flowing through the Air Cooler operation.

Air Cooler Property View Design Tab The Design tab contains the following pages:

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l

Connections

l

Parameters

l

User Variables

l

Notes

13 Air Cooler

Connections Page On the Connections page, you can specify the feed and product streams attached to the Air Cooler. You can change the name of the operation in the Name field. You can also select the fluid package you want to use for the air cooler. The fluid package that is associated with the flowsheet is selected by default. If you want to take advantage of the activated Aspen Exchanger Design and Rating calculations, you can quickly convert the air cooler to a rigorous heat exchanger model using the Convert to Rigorous Model options. l

l

Size Air Cooler lets you size the model automatically or interactively, optionally starting with a template file for either choice. Specify Geometry lets you use the EDR interface to directly enter key geometry to the model, or select values saved in an .edr file.

Parameters Page On the Parameters page, the following information appears: Parameters

Description

Air Cooler Model

Allows you to select the air cooler model from Air Cooler Simple Design and Rigorous Air Cooler. HTFS - ACOL or EDR models are available if they are installed and licensed as options. To use these models, select the Rigorous Air Cooler option.

13 Air Cooler

Process Stream Delta P

Allows you to specify the pressure drops (DP) for the process stream side of the Air Cooler. The pressure drop can be calculated if both the inlet and exit pressures of the process stream are specified. There is no pressure drop associated with the air stream. The air pressure through the Cooler is assumed to be atmospheric.

Overall UA

Contains the value of the Overall Heat Transfer Coefficient multiplied with the Total Area available for heat transfer. The Air Cooler duty is proportional to the log mean temperature difference, where UA is the proportionality factor. The UA can either be specified or calculated by HYSYS.

Configuration

Displays the possible tube pass arrangements in the Air Cooler. There are eight different Air Cooler configurations to choose from. HYSYS determines the correction factor, Ft, based on the selected Air Cooler configuration.

Air Intake/Outlet Temperatures

The inlet and exit air stream temperatures can be specified or calculated by HYSYS.

Air Intake Pressure

The inlet air stream pressure has a default value of 1 atm.

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Specs Page Use the Air Cooler Design tab Specs page to enter values for the solver controls Max Iterations and Tolerance. Current Iteration and Current Error are read out as the solver progresses.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation or the simulation case in general.

Rating Tab The Rating tab allows you to specify the fan rating information. The steady state and dynamic Air Cooler operations share the same fan rating information. Note: In dynamics, the air flow must be calculated using the fan rating information.

The Rating tab contains the following pages: l

l

Sizing page. The content of this page differs depending on which option you selected in the Air Cooler Model drop-down list on the Parameters page of the Design tab. If you selected ERD or HTFS-Engines, this page displays only one field: Air Mass Flow Rate. Nozzles page. This page appears only if the HYSYS Dynamics license is activated.

Sizing Page (Simple Design) In the Sizing page, the following fan rating information appears for the Air Cooler operation when the HYSYS-Engines option is selected on the Parameters page of the Design tab.

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Fan Data

Description

Number of Fans

Number of fans in the Air Cooler.

Speed

Actual speed of the fan in rpm (rotations per minute).

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Fan Data

Description

Demanded speed

Desired speed of the fan. l

Steady State mode. The demanded speed is always equal the speed of the fan. The desired speed is either calculated from the fan rating information or user-specified.

l

Dynamic mode. The demanded speed should either be specified directly or from a Spreadsheet operation. If a control structure uses the fan speed as an output signal, it is the demanded speed which should be manipulated.

Max Acceleration

Applicable only in Dynamic mode. It is the rate at which the actual speed moves to the demanded speed.

Design speed

The reference Air Cooler fan speed. It is used in the calculation of the actual air flow through the Cooler.

Design air flow

The reference Air Cooler air flow. It is used in the calculation of the actual air flow through the Cooler.

Current air flow

This can be calculated or user-specified. If the air flow is specified no other fan rating information needs to be specified.

Fan Is On

By default, this check box is selected. You have the option to turn on or off the air cooler as desired. When you clear the check box, the temperature of the outlet stream of the air cooler will be identical to that of the inlet stream. The Fan Is On check box has the same function as setting the Speed to 0 rpm.

The air flow through the fan is calculated using a linear relation: (1) In dynamic mode only, the actual speed of the fan is not always equal to the demanded speed. The actual fan speed after each integration time step is calculated as follows: (2)

Each fan in the Air Cooler contributes to the air flow through the Cooler. The total air flow is calculated as follows: (3)

Sizing Page Rigorous Air Cooler The Sizing page for the Rigorous Air Cooler appears when the Rigorous Air Cooler option is selected on the Parameters page of the Design tab. HYSYS

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air coolers can have multiple fans, and HYSYS calculates the airflow from the sum of the airflows of each fan. For the Rigorous Air Cooler, you can only enter the total air mass flow rate for the air cooler.

Nozzles Page The Nozzles page contains information regarding the elevation and diameter of the nozzles. The information provided in the Nozzles page is applicable only in Dynamic mode.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the Air Cooler. Note: The PF Specs page is relevant to dynamics cases only.

Performance Tab The Performance tab contains pages that display the results of the Air Cooler calculations. Note: The Profiles page is relevant to dynamics cases only.

Performance Results Page The information from the Results page is shown as follows: Results

Description

Working Fluid Duty

This is defined as the change in duty from the inlet to the exit process stream: (1)

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LMTD Correction Factor, Ft

The correction factor is used to calculate the overall heat exchange in the Air Cooler. It accounts for different tube pass configurations.

UA

The product of the Overall Heat Transfer Coefficient, and the Total Area available for heat transfer. The UA can either be specified or calculated by HYSYS.

13 Air Cooler

Results

Description

LMTD

The LMTD is calculated in terms of the temperature approaches (terminal temperature difference) in the exchanger, using the following uncorrected LMTD equation: (2) where: ΔT1 = Thot,out - Tcold,in ΔT2 = Thot,in - Tcold,out

Inlet/Outlet Process Temperatures

The inlet and outlet process stream temperatures can be specified or calculated in HYSYS.

Inlet/Outlet Air Temperatures

The inlet and exit air stream temperatures can be specified or calculated in HYSYS.

Air Inlet Pressure

The inlet air stream pressure has a default value of 1 atm.

Total Air flow

The total air flowrate appears in volume and mass units.

Performance Profiles Page The Dynamic Results table displays the temperature and vapor fraction of each zone in the Air Cooler.

Performance Plots Page l

l

From the X Variable and Y Variable drop-down lists, select the variables you want to use for the x and y-axes. Use the Setup page to determine number of plot points (intervals) and the variables that may be read into the X or Y axis of the Plot. The page lists all available variables in the simulation, and lets you select which ones to use within the plot.

Performance Tables Page l

l

13 Air Cooler

Use the Setup page to determine the intervals (plot points) and variables to be made available to the Performance Table x and y axes. The page lists all available variables in the simulation, and lets you select which ones to use within the table. Use the Phase Viewing Options to selectively examine results for a particular phase or phases.

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Performance Setup Page Use the Setup page to determine the intervals (plot points) and variables to be made available to the Performance Table x and y axes. The page lists all available variables in the simulation, and lets you select which ones to use within the table.

Dynamics Tab The Dynamics tab contains the following pages: l

Model

l

Specs

l

Holdup

l

Stripchart

In dynamics, the air flow must be calculated using the fan rating information. Note: If you are working exclusively in Steady State mode, you are not required to change any of the values on the pages accessible through this tab.

Model Page The Model page allows you to define how UA is defined in Dynamic mode. The value of UA is calculated as follows: (1) where: UAsteadystate = UA value entered on the Parameters page of the Design tab (2)

(3)

(4)

The Model page contains the UA Calculation group, which contains four fields:

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Field

Description

UA

The steady state value of UA. This should be the same as the value entered on the Parameters tab.

Reference air flow

The reference flowrate for air. It is used to calculate the value of f1 as shown in Equation (3).

Reference fluid flow

The reference flowrate for the fluid. It is used to calculate the value of f2 as shown in Equation (4).

Minimum flow scale factor

The minimum scale factor used. If the value calculated by Equation (2) is smaller than this value, this value is used.

Specs Page The Specs page contains information regarding the calculation of pressure drop across the Air Cooler. You can specify how the pressure drop across the Air Cooler is calculated in the Dynamic Specifications group. Dynamic Specifications

Description

Overall Delta P

A set pressure drop is assumed across the valve operation with this specification. The flow and the pressure of either the inlet or exit stream must be specified or calculated from other operations in the flowsheet. The flow through the valve is not dependent on the pressure drop across the Air Cooler. To use the overall delta P as a dynamic specification, select the corresponding check box. The Air Cooler operations, like other dynamic unit operations, should use the k-value specification option as much as possible to simulate actual pressure flow relations in the plant.

Overall k Value

13 Air Cooler

The k-value defines the relationship between the flow through the Air Cooler and the pressure of the surrounding streams. You can either specify the k-value or have it calculated from the stream conditions surrounding the Air Cooler. You can “size” the Cooler with a kvalue by clicking the Calculate K button. Ensure that there is a nonzero pressure drop across the Air Cooler before the Calculate K button is clicked. To use the k-value as a dynamic specification, select the corresponding check box.

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Dynamic Specifications

Description

Pressure Flow Reference Flow

The reference flow value results in a more linear relationship between flow and pressure drop. This is used to increase model stability during startup and shutdown where the flows are low. If the pressure flow option is chosen the k value is calculated based on two criteria. If the flow of the system is larger than the k Reference Flow the k value remains unchanged. It is recommended that the k reference flow is taken as 40% of steady state design flow for better pressure flow stability at low flow range. If the flow of the system is smaller than the k Reference Flow, the k value is given by: (1) where Factor is determined by HYSYS internally to take into consideration the flow and pressure drop relationship at low flow regions.

The Dynamic Parameters group contains information about the holdup of the Air Cooler, which is described in the table below. Dynamic Parameters

Description

Fluid Volume

Specify the Air Cooler holdup volume.

Mass Flow

The mass flow of process stream through the Air Cooler is calculated.

Exit Temperature

The exit temperature of the process stream.

Holdup Page The Holdup page contains information regarding the properties, composition, and amount of the holdup. The Overall Holdup Details group displays the following information for each phase contained within the volume space of the unit operation: l

Accumulation: The rate of change of material in the holdup.

l

Moles: The amount of material in the holdup for each phase.

l

Volume: The holdup volume of each phase.

The Zone drop-down list enables you to select and view the holdup data for each zone in the operation. Click the Advanced button to access the Advanced Holdup view for the selected zone. Note: The Air Cooler operation only has one zone.

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Stripchart Page The Stripchart page allows you to select and create default strip charts containing various variable associated to the operation.

Rigorous Air Cooler Tab The Rigorous Air Cooler tab contains the following pages: l

Exchanger

l

Process Data

l

Property Range

l

Result Summary

l

Setting Plan

l

Tube Layout

l

Profiles

You can use the Import - Export buttons to use data saved in an .edr file format from Aspen Exchanger Design and Rating. The View EDR Browser button lets you use the Exchanger Design and Rating program interface to access advanced settings for the model parameters.

Simulation Calculation Options The Simulation calculation option is an EDR option that does not appear on the HYSYS form. This option helps the EDR engine determine which type of output (temperature or mass flow) EDR should calculate. If you open the EDR Browser within a rigorous air cooled exchanger by clicking View EDR Browser, and then select Air Cooled | Input | Problem Definition | Application Options and select the X-side flow and X-side outlet temperature option from the Simulation calculation drop-down list, HYSYS will keep that option unless you manually change it. If the X-side flow and Xside outlet temperature option is no longer selected, HYSYS will automatically select the most appropriate option. When the X-side flow and Xside outlet temperature option is selected, the air cooler is expected to have specified inlet and outlets for the tube side. EDR will calculate an outside air temperature and flow rate based on that information. If you import an EDR file with the X-side flow and X-side outlet temperature option selected under Application Options, the option will be changed to the default. You must manually change the Simulation calculation option to X-side flow and X-side outlet temperature within the EDR Browser.

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Exchanger Page On the Rigorous Air Cooler tab | Exchanger page: l

l

Use the Transfer UA to simple design button to send the effective UA to the simple design model. Use the Unit, Tubes, and Bundle radio buttons to set up their respective geometries for the air cooler:

Unit

Tubes

Bundle

Number of Bays per Unit

Tube OD

Number of Passes

Bundles per bay

Tube Wall Thickness

Number of Rows

Fans per bay

Tube Length

Number of Tubes

Frame Type

Fin Type

Type of Bundle

Fan diameter

Fin Frequency

Transverse Pitch

Fan configuration

Fin Tip diameter

Tube layout angle

Tube Side Flow Orientation

Fin Thickness

Note: You can specify any size for the tube outside diameter. However, the correlations have been developed based on tube sizes from 10 to 50 mm (0.375 to 2.0 inch). The most common sizes in the U.S. are 0.625, 0.75, and 1.0 inch. In many other countries, the most common sizes are 16, 20, and 25 mm.

If you do not know what tube diameter to use, start with a 20 mm diameter (ISO standards) or a 0.75 inch diameter (American standards). This size is readily available in nearly all tube materials. The primary exception is graphite, which is made in 32, 37, and 50 mm, or 1.25, 1.5, and 2 inch, outside diameters. For integral low fin tubes, the tube outside diameter is the outside diameter of the fin.

Process Data Page On the Rigorous Air Cooler tab | Process Data page, you can specify or view the following process information for the streams: l

Total Mass Flow: You should normally enter the total flow rates for the hot and cold side streams. You can omit a flow rate if the stream inlet and outlet conditions are specified, and the heat load is known, either because it has been input, or it can be deduced from the implicit heat load of the other stream. In the special variant of Simulation, where the flowrate is to be calculated, any value specified in this field is treated as an initial estimate. This type of Simulation is used in thermosiphon reboilers, where the flowrate of the thermosiphon stream must be calculated, or for

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simulating condensing steam where the flowrate adjusts itself to give complete condensation to liquid water, according the heating requirements of the cold stream. l

Inlet Temperature

l

Estimated Outlet Temperature

l

Inlet Mass Quality

l

Inlet Pressure

l

Estimated Pressure Drop: You can enter an estimated pressure drop for each side. This can be important in low pressure and vacuum applications, where outlet pressures can significantly affect outlet pressures. In other cases, the program-supplied default is usually acceptable. Supplying an outlet pressure is an alternative to supplying an estimated pressure drop. One will be calculated from the other, once the inlet pressure (mandatory) is specified. If you specify neither outlet pressure nor pressure drop, default values will be calculated using the Allowable Pressure Drop. The exchanger inlet and outlet pressure will be used to set defaults for the range of pressures at which physical properties are calculated. If you are unsure of the pressure drop, a higher rather than a lower estimate may be appropriate. If the pressure range is large, additional default pressure levels for properties will be defaulted. You can add more pressure levels for properties yourself, but this is rarely necessary. In the unusual case of a vertical exchanger with liquid down flow, gravitational pressure increases could exceed frictional losses. The outlet pressure would be above the inlet pressure, and the pressure change would be negative. Negative pressure change inputs are allowed; a warning message appears, but you can ignore it if the case described above occurs.

l l

Allowable Pressure Drop Fouling Resistance: Enter the process-side fouling resistance. This resistance is assumed to apply wherever the process fluid flows, in convection banks or the firebox. This is required for the calculation of the effective (dirty) heat transfer coefficient. The fouling resistance is based on the inside surface area of the tubes. If omitted, the program will assume that the surface of the tubes is clean, so that the fouling resistance is 0.0.

Property Range Page The following numerical ranges for the shell side and the tube side appear on the Property Ranges page:

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l

Temp. Range (End)

l

Temp. Range (Start)

l

Number of Temperatures

387

l

No. of Pressure Levels

l

Pressure Level 1

l

Pressure Level 2

l

Pressure Level 3

l

Pressure Level 4

l

Pressure Level 5

Results Summary Page The following results appear on the Rigorous Air Cooler | Results Summary page: l

Total Heat Load

l

Effective Surface Area

l

Effective MTD: The Effective MTD is calculated using the following equation: (1)

You can check the calculation of the Effective MTD using the values reported. The LMTD (log mean temperature difference) may appear on the Performance tab | Results page. This value is calculated after the heat load is passed from the Rigorous Air Cooler model to HYSYS. The LMTD and Effective MTD may have different values, since they are calculated using different formulas. The LMTD is calculated using the following equation: (2) where: ΔT1 = Thot,out - Tcold,in ΔT2 = Thot,in - Tcold,out l

Overall Dirty Coeff

l

Overall Clean Coeff

The following results appear for the Tube Side and Air Side:

388

l

Film Coefficient

l

Calculated Pressure drop

l

Allowable Pressure drop

l

Velocity In (Highest)

l

Velocity Out (Highest)

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Setting Plan Page The Rigorous Air Cooler tab | Setting Plan page lets you view a dimensional drawing of the heat exchanger. To view further details, click View EDR Browser and navigate to Results | Mechanical Summary | Setting Plan / Tube Layout for a more detailed and configurable view of the mechanical layout of the exchanger.

Tube Layout Page The following is an example of the information shown on the Rigorous Air Cooler tab | Setting Plan page.

Right-click within the display to show the diagram configuration and printing options.

Profiles Page The following is an example of the display on the Rigorous Air Cooler tab | Profiles page.

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389

Right-click within the plot and select Properties to access the Plot properties dialog box for plot customization.

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14 Cooler/Heater

The Cooler and Heater operations are one-sided heat exchangers. The inlet stream is cooled (or heated) to the required outlet conditions, and the energy stream absorbs (or provides) the enthalpy difference between the two streams. These operations are useful when you are interested only in how much energy is required to cool or heat a process stream with a utility, but you are not interested in the conditions of the utility itself. Note: The difference between the Cooler and Heater is the energy balance sign convention.

Theory Note: The Cooler and Heater use the same basic equation.

Steady State Operation The primary difference between a cooler and a heater is the sign convention. You specify the absolute energy flow of the utility stream, and HYSYS then applies that value as follows: l

For a Cooler, the enthalpy or heat flow of the energy stream is subtracted from that of the inlet stream: (1)

l

For a Heater, the heat flow of the energy stream is added: (2)

Dynamic Operation The Cooler duty is subtracted from the process holdup while the Heater duty is added to the process holdup. For a Cooler, the enthalpy or heat flow of the energy stream is removed from the Cooler process side holdup:

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391

(1)

For a Heater, the enthalpy or heat flow of the energy stream is added to the Heater process side holdup: (2)

where: M = process fluid flow rate ρ = density H = enthalpy Qcooler = cooler duty Qheater = heater duty V = volume shell or tube holdup

Pressure Drop The pressure drop of the Cooler/Heater can be determined in one of two ways: l l

Specify the pressure drop manually. Define a pressure flow relation in the Cooler or Heater by specifying a kvalue.

If the pressure flow option is chosen for pressure drop determination in the Cooler or Heater, a k value is used to relate the frictional pressure loss and flow through the Cooler/Heater. The relation is similar to the general valve equation: (1)

This general flow equation uses the pressure drop across the heat exchanger without any static head contributions. The quantity, P1 - P2, is defined as the frictional pressure loss which is used to “size” the Cooler or Heater with a k-value.

Dynamic Specifications In general, two specifications are required by HYSYS in order for the Cooler/Heater unit operation to fully solve in Dynamic mode:

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Dynamic Specifications

Description

Duty Calculation

The duty applied to the Cooler/Heater can be calculated using one of three different models: l

Supplied Duty

l

Product Temp Spec

l

Duty Fluid

Specify the duty model in the Model Details group on the Specs page of the Dynamics tab. Pressure Drop

Either specify an Overall Delta P or an Overall K-value. Specify the Pressure Drop calculation in the Dynamic Specifications group on the Specs page of the Dynamics tab.

Heater or Cooler Property View Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

User Variables

l

Notes

Connections Page The Connections page is used to define all of the connections to the Cooler/Heater. You can specify the inlet, outlet, and energy streams attached to the operation on this page. The name of the operation can be changed in the Name field.

Parameters Page The applicable parameters are the pressure drop (Delta P) across the process side, and the duty of the energy stream. Both the pressure drop and energy flow can be specified directly or can be determined from the attached streams. HYSYS uses the proper sign convention for the unit you have chosen, so you can enter a positive duty value for both heater and cooler. You can specify a negative duty value, however, be aware of the following:

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l

l

For a Cooler, a negative duty means that the unit is heating the inlet stream. For a Heater, a negative duty means that the unit is cooling the inlet stream.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor that allows you to record any comments or information regarding the specific unit operation, or the simulation case in general.

Rating Tab You must specify the rating information only when working with a dynamics simulation.

Nozzles Page On the Nozzles page, you can specify nozzle parameters on both the inlet and outlet streams connected to a Cooler or Heater. The addition of nozzles to Coolers and Heaters is relevant when creating dynamic simulations.

Heat Loss Page Rating information regarding heat loss is relevant only in Dynamic mode. The Heat Loss page contains heat loss parameters that characterize the amount of heat lost across the vessel wall. In the Heat Loss Model group, you can choose either a Simple or Detailed heat loss model or no heat loss through the vessel walls.

Simple Model The Simple model allows you to either specify the heat loss directly, or have the heat loss calculated from the specified values: l

Overall U value

l

Ambient Temperature

The heat transfer area, A, and the fluid temperature, Tf, are calculated by HYSYS using the following equation:

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(1) For a Cooler, the parameters available for the Simple model appear in the figure below. The simple heat loss parameters are as follows: l

Overall Heat Transfer Coefficient

l

Ambient Temperature

l

Overall Heat Transfer Area

l

Heat Flow

The heat flow is calculated as follows: (2) where: U = overall heat transfer coefficient A = heat transfer area TAmb = ambient temperature T = holdup temperature Heat flow is defined as the heat flowing into the vessel. The heat transfer area is calculated from the vessel geometry. The ambient temperature, TAmb, and overall heat transfer coefficient, U, can be modified from their default values shown in red.

Detailed Model The Detailed model allows you to specify more detailed heat transfer parameters. For further information, refer to Detailed Heat Loss Model. Note: The HYSYS Dynamics license is required to use the Detailed Heat Loss model.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the unit operation. Note: The PF Specs page is relevant to dynamics cases only.

Performance Tab The Performance tab contains pages that display calculated stream information. By default, the performance parameters include the following stream properties:

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l

Pressure

l

Temperature

l

Vapor Fraction

l

Enthalpy

Other stream properties can be viewed by adding them to the Viewing Variables group on the Setup page. All information appearing on the Performance tab is read-only. The Performance tab contains the following pages: l

Profiles

l

Plots

l

Tables

l

Setup

Profiles Page In Steady State mode, HYSYS calculates the zone conditions for the inlet zone only, regardless of the number of zones specified. The pressure, temperature, vapor fraction, and enthalpy are calculated for each zone in the cooler. For a heater, you can specify the number of zones you want on the Specs page on the Dynamics tab.

Plots Page On the Plots page, you can graph any of the default performance parameters to view changes that occur across the operation. In Steady State mode, stream property readings are taken only from the inlet and outlet streams for the plots. As such, the resulting graph is always a straight line. The property values are not calculated incrementally through the operation. All default performance parameters are listed in the X Variable and Y Variable drop-down lists below the graph. Select the axis and variables you want to compare, and the plot appears. To graph other variables, select the Setup page and add them to the Selected Viewing Variables group from the Available Variables list. You can right-click on the graph area to access the graph controls and manipulate the graph appearance.

Tables Page The Tables page displays the results of the Cooler/Heater in a tabular format. All default values for the pressure, temperature, vapor fraction, and enthalpy calculated for each interval are listed here. Note: Information on the Tables page is read-only, except the Intervals value.

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Setup Page The Setup page allows you to filter and add variables to be viewed on the Plots and Tables pages. l

In the Curve Options section, you can edit values for the following: Field

Description

Intervals

The default value is 10.

Dew/Bubble Pts check box

This check box is cleared by default.

Step Type

The following options are available: o

Equal Temp: This is the default selection.

o

Equal Heat Flow

o

Equal Vap Frac

Note: Only Equal Temp and Equal Heat Flow are available within an SRU sub-flowsheet. Pressure Profile

l l

The following options are available: o

Linear: This is the default selection

o

Inlet Press.

o

Outlet Press.

In the Additional Const Pressures field, you can specify a value. The variables that are listed in the Selected Viewing Variables group are available in the X and Y drop down list for plotting on the Plots page. The variables are also available for tabular plot results on the Tables page based on the Phase Viewing Options selected.

Dynamics Tab Note: If you are working exclusively in Steady State mode, you do not need to change any of the values on the pages accessible on the Dynamics tab.

In the Dynamic mode, the values you enter in the Dynamics tab affects the calculation. The Dynamics tab contains the following pages: l

Specs

l

Duty Fluid

l

Holdup

l

Stripchart

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Specs Page The Specs page contains information regarding the calculation of pressure drop across the Cooler or Heater:

Zone Information HYSYS has the ability to partition heat transfer operations into discrete sections called zones. By dividing the unit operation into zones, you can make different heat transfer specifications for individual zones, and therefore more accurately model the physical process. Specifying the Cooler/Heater with one zone provides optimal speed conditions, and is usually sufficient in modeling accurate exit stream conditions.

Model Details The Model Details group must be completed before the simulation case solves. The number of zones and the volume of a Cooler/Heater can be specified in this group. HYSYS can calculate the duty applied to the holdup fluid using one of the three different methods described in the table below.

398

Model

Description

Supplied Duty

If you select the Supplied Duty radio button, you must specify the duty applied to the Cooler/Heater. It is recommended that the duty supplied to the unit operation be calculated from a PID Controller or a Spreadsheet operation that can account for zero flow conditions.

Product Temp Spec

If you select the Product Temp Spec radio button, you must specify the desired exit temperature. HYSYS back calculates the required duty to achieve the specified desired temperature. This method does not run as fast as the Supplied Duty model.

Duty Fluid

If you select the Duty Fluid radio button, you can model a simple utility fluid to heat or cool your process stream. The following parameters must be specified for the utility fluid on the Duty Fluid page of the Dynamics tab: l

Mass Flow

l

Holdup Mass

l

Mass Cp

l

Inlet temperature

l

Average UA

14 Cooler/Heater

Dynamic Specifications Group The Dynamic Specifications group allows you to specify how the pressure drop is calculated across the Cooler or Heater unit operation. The table below describes the specifications. Specification

Description

Overall Delta P

A set pressure drop is assumed across the Cooler or Heater operation with this specification. The flow and the pressure of either the inlet or exit stream must be specified, or calculated from other unit operations in the flowsheet. The flow through the valve is not dependent on the pressure drop across the Cooler or Heater. To use the overall delta P as a dynamic specification, select the corresponding check box in the Dynamic Specifications group

Overall k Value

The k-value defines the relationship between the flow through Cooler or Heater and the pressure of the surrounding streams. You can either specify the k-value, or have it calculated from the stream conditions surrounding the unit operation. You can “size” the Cooler or Heater with a kvalue by clicking the Calculate k button. Ensure that there is a non-zero pressure drop across the Cooler or Heater before you click the Calculate k button. To use the k-value as a dynamic specification, select the corresponding check box in the Dynamic Specifications group.

Note: The Cooler or Heater unit operation, like other dynamic unit operations, should use the k-value specification option as much as possible to simulate actual pressure flow relations in the plant.

Zone Dynamic Specifications If the Cooler or Heater operation is specified with multiple zones, you can click the Spec Zones button to define dynamic specifications for each zone. In the Delta P Specs and Duties group, you can specify the following parameters:

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Dynamic Specification

Description

dP Value

Allows you to specify the fixed pressure drop value.

dP Option

Allows you to either specify or calculate the pressure drop across the Cooler or Heater. Specify the dP Option with one of the following options:

Duty

l

user specified. The pressure drop across the zone is specified by you in the dP Value field.

l

non specified. Pressure drop across the zone is calculated from a pressure flow relationship. You must specify a kvalue, and activate the specification for the zone in the Zone Conductance Specifications group.

A fixed duty can be specified across each zone in the Cooler or Heater unit operation.

In the Zone Conductance Specifications group, you can specify the following parameters: Dynamic Specification

Description

k

The k-value for individual zones can be specified in this field. You can either specify the k-value or have it calculated by clicking the Calculate k button.

Specification

Activate the specification if the kvalue is to be used to calculate pressure across the zone.

Duty Fluid Page The Duty Fluid page becomes visible if the Duty Fluid radio button is selected on the Specs page. The Duty Fluid page allows you to enter the following parameters to define your duty fluid:

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l

Mass Flow

l

Holdup mass

l

Mass Cp

l

Inlet Temperature

l

Average UA

The Counter Flow check box allows you to specify the direction of flow for the duty fluid. When the check box is selected, you are using a counter flow. The View Zones button displays the duty fluid parameters for each of the zones specified on the Specs page.

Holdup Page The Holdup page contains information regarding the Cooler or Heater holdup properties, composition, and amount. The Overall Holdup Details group displays the following information for each phase contained within the volume space of the unit operation: l

Holdup Accumulation is the rate of change of material in the holdup.

l

Holdup Moles are the amount of material in the holdup for each phase.

l

Holdup Volume is the holdup volume of each phase.

The Individual Zone Holdups group contains detailed holdup properties for each holdup in the Cooler or Heater. In order to view the advanced properties for individual holdups, you must first choose the individual zone in the Zone drop-down list. Click the Advanced button to access the Advanced Holdup view for the selected zone.

Stripchart Page The Stripchart page allows you to select and create default strip charts containing various variable associated to the operation.

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15 Fired Heater (Furnace)

The Fired Heater (Furnace) operation performs energy and material balances in steady state or dynamic modes to model a direct Fired Heater type furnace. This type of equipment requires a large amount of heat input. Heat is generated by fuel combustion and transferred to process streams. A simplified schematic of a direct Fired Heater is illustrated in the figure below.

In general, a Fired Heater can be divided into three zones:

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l

Radiant zone

l

Convective zone

l

Economizer zone Note: To define the number of zones required by the Fired Heater, enter the number in #External Passes field on Connections page of the Design tab.

The Fired Heater operation allows multiple stream connections at tube side in each zone and optional economizer, and convection zone selections. The operation incorporates a single burner model, and a single feed inlet and outlet on the flue gas side.

Fired Heater Steady State Operation The Fired Heater in steady state is based only on the energy balance and the system is limited to one degree of freedom. Fuel and air streams: The steady state fired heater supports multiple, simultaneous fuel streams and an independent air stream. Note: The dynamic mode does not support multiple fuel streams, but uses one combined fuel/air stream. If there are multiple fuel streams defined for steady state, when switching from steady state to dynamics a new stream is created from the sum of the fuel streams and the air stream defined in steady state. When switching back to steady state, one fuel and one air stream is created from the dynamic settings.

Variables supported as possible unknown/calculated variables are: l

Outlet temperature of the process streams

l

Flow rate of the process streams

l

Flow rate of one fuel stream. The ratio fuel/air as well as the fuel compositions should be fully defined by the user.

l

Flue gas temperature

l

Efficiency

Economizer and Convection Zone - In steady state mode, by default the external passes in the economizer and convection zone are set to zero and the number of external passes in the radiant zone is set to 1. If you set more than one external pass in the radiant zone, the heat energy is divided equally between all the process streams in the radiant zone.

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Fired Heater Dynamic Operation The following are some of the major features of the dynamic Fired Heater operation: l

l

l

l

l

Flexible connection of process fluid associated in each Fired Heater zone. For example, radiant zone, convective zone, or economizer zone. Different Fired Heater configurations can be modeled or customized using tee, mixer, and heat exchanger unit operations. A pressure-flow specification option on each side and pass realistically models flow through Fired Heater operation according to the pressure gradient in the entire pressure network of the plant. Possible flow reversal situations can therefore be modeled. A comprehensive heat calculation inclusive of radiant, convective, and conduction heat transfer on radiant zone enables the prediction of process fluid temperature, Fired Heater wall temperature, and flue gas temperature. A dynamic model which accounts for energy and material holdups in each zone. Heat transfer in each zone depends on the flue gas properties, tube and Fired Heater wall properties, surface properties of metal, heat loss to the ambient, and the process stream physical properties. A combustion model which accounts for imperfect mixing of fuel, and allows automatic flame ignition or extinguished based on the oxygen availability in the fuel air mixture.

Switching Modes When switching the fired heater to dynamic mode, any fuel streams and the air stream in steady state will be combined into one stream. When switching from dynamic to steady state, a yellow warning message states that only the radiant zone in considered in the steady state heat balance. The combined fuel/air stream in Dynamics is split into two streams for the fuel and the air.

Fired Heater Theory Combustion Reaction The combustion reaction in the burner model of the Fired Heater performs pure hydrocarbon (Cx Hy ) combustion calculations only. The extent of the combustion

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depends on the availability of oxygen which is usually governed by the air to fuel ratio. Air to fuel ratio (AF) is defined as follows: (1)

You can set the combustion boundaries, such as the maximum AF and the minimum AF, to control the burner flame. The flame cannot light if the calculated air to fuel ratio falls below the specified minimum air to fuel ratio. The minimum air to fuel ratio and the maximum air to fuel ratio can be found on the Parameters page of the Design tab. The heat released by the combustion process is the product of molar flowrate, and the heat of formation of the products minus the heat of formation of the reactants at combustion temperature and pressure. In the Fired Heater unit operation, a traditional reaction set for the combustion reactions is not required. You can choose the fuels components (the hydrocarbons and hydrogen) to be considered in the combustion reaction. You can see the mixing efficiency of each fuel component on the Parameter page of the Design tab.

Heat Transfer The Fired Heater heat transfer calculations are based on energy balances for each zone. The shell side of the Fired Heater contains five holdups: l

Three in the radiant zone

l

A convective zone

l

An economizer zone holdup as outlined previously in the simplified schematic above.

For the tube side, each individual stream passing through the respective zones is considered as a single holdup. Major heat terms underlying the Fired Heater model are illustrated in the figure below.

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15 Fired Heater (Furnace)

The heat terms related to the tubeside are illustrated in the figure below.

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Taking Radiant zone as an envelope, the following energy balance equation applies: (1)

where:  = energy accumulation in radiant zone holdup shell side  = energy accumulation in radiant zone process fluid holdup (tube side) (MRPFHRPF)IN = total heat flow of process fluid entering radiant zone tube (MRPFHRPF)OUT = total heat flow of process fluid exiting radiant zone tube (MFG HFG )IN = total heat flow of fuel gas entering radiant zone (MFG HFG )OUT = total heat flow of fuel gas exiting radiant zone QRadToCTube = radiant heat of radiant zone to convective zone’s tube bank

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Qrad_wall_sur = radiant heat loss of Fired Heater wall in radiant zone to surrounding Qcon_wall_sur = convective heat loss of Fired Heater wall in radiant zone to surrounding Qrad_wall_to_tube = radiant heat from inner Fired Heater wall to radiant zone’s tube bank Qrad_flame_wall = radiant heat from flue gas flame to inner Fired Heater wall Qcon_to_wall = convective heat from flue gas to Fired Heater inner wall Qreaction = heat of combustion of the flue gas

Radiant Heat Transfer For a hot object in a large room, the radiant energy emitted is given as: (1) where: δ = Stefan-Boltzmann constant, 5.669 × 10-8 W/m2K4 ε = emissivity, (0-1), dimensionless A = area exposed to radiant heat transfer, m2 T1 = temperature of hot surface 1, K T2 = temperature of hot surface 2, K

Convective Heat Transfer The convective heat transfer taking part between a fluid and a metal is given in the following: (1) where: U = overall heat transfer coefficient, W/m2K A = area exposed to convective heat transfer, m2 T1 = temperature of hot surface 1, K T2 = temperature of surface 2, K The U actually varies with flow according to the following flow-U relationship if this Flow Scaled method is used: (2)

where:

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Uspecified = U value at steady state design conditions. The ratio of mass flow at time t to reference mass flow is also known as flow scaled factor. The minimum flow scaled factor is the lowest value, which the ratio is anticipated at low flow region. For the Fired Heater operation, the minimum flow scaled factor can be expressed only as a positive value. For example, if the minimum flow scaled factor is +0.001 (0.1%), when this mass flow ratio is achieved, the Uused stays as a constant value. Therefore: (3)

Conductive Heat Transfer Conductive heat transfer in a solid surface is given as: (1) where: k = thermal conductivity of the solid material, W/mK ΔT = thickness of the solid material, m A = area exposed to conductive heat transfer, m2 T1 = temperature of inner solid surface 1, K T2 = temperature of outer solid surface 2, K

Pressure Drop The pressure drop across any pass in the Fired Heater unit operation can be determined in one of two ways: l

Specify the pressure drop - delta P.

l

Define a pressure flow relation for each pass by specifying a k-value

If the pressure flow option is chosen for pressure drop determination in the Fired Heater pass, a k value is used to relate the frictional pressure drop and molar flow, F through the Fired Heater. This relation is similar to the general valve equation: (1) This general flow equation uses the pressure drop across the Fired Heater pass without any static head contribution. The quantity, (P1-P2) is defined as the frictional pressure loss which is used to “size” the flow. The k value is calculated based on two criteria: l

410

If the flow of the system is larger than the value at kref (k reference flow), the k value remains unchanged. It is recommended that the kreference

15 Fired Heater (Furnace)

is taken as 40% of steady state design flow for better pressure flow stability at low flow range. flow l

If the flow of the system is smaller than the kref, the k value is given by: (2) where: Factor = value is determined by HYSYS internally to take into consideration the flow and pressure drop relationship for low flow regions.

The effect of kref is to increase the stability by modeling a more linear relationship between flow and pressure. This is also more realistic at low flows.

Minimum Specifications The following is a list of the minimum specifications required for the Fired Heater operation to solve: Dynamic Specifications

Description

Connections

At least one radiant zone inlet stream and the respective outlet zone, one burner fuel/air feed stream and one combustion product stream must be defined. There is a minimum of one inlet stream and one outlet stream required per zone. Complete the connections group for each zone of the Design tab.

(Zone) Sizing

The dimensions of the tube and shell in each zone in the Fired Heater must be specified. All information in the Sizing page of the Rating tab must be completed.

Heat Transfer

For each zone, almost all parameters in the Radiant Zone Properties group and Radiant/Convective/Economizer Tube Properties groups are required, except the Inner/Outer Scaled HX Coefficient.

Nozzle

Nozzle elevation is defaulted to 0. Elevation input is required when static head contribution option in Integrator property view is selected.

Pressure Drop

Either specify an overall delta P or an overall K value for the Fired Heater. Specify the pressure drop calculation method on the Tube Side PF page and Flue Gas PF page of the Dynamics tab.

Fired Heater Property View Design Tab The Design tab of the Fired Heater property view contains the following pages:

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l

Connections

l

Parameters

l

User Variables

l

Notes

Connections Page On the Connections page, you can specify the name of the operation, and inlet and outlet streams. Object

Description

Econ Zone Inlet/Outlet

You can specify multiple inlet and outlet streams for the Economizer zone. (Dynamics only.) To add stream connections to Econ zone and Conv zone, enter the desired number in the corresponding External Passes field and then attach the streams.

Conv Zone Inlet/Outlet

You can specify multiple inlet and outlet streams for the Convective zone. (Dynamics only.)

Radiant Zone Inlet/Outlet

You can specify multiple inlet and outlet streams for the Radiant zone.

Fuel Streams

Specifies the stream or streams to be used for the burner fuel.

Air Feed

Source for the burner air. Note: If you switch to dynamics mode, all fuel streams and air will be combined in one stream named Air/Fuel Mix.

Combustion Product

The stream that contains the products from the combustion.

# External Passes

Defines the number of zones required by the Fired Heater

Fluid Package

The associated fluid package

Parameters Page The Parameters page is used to specify the Fired Heater combustion options. This page is divided into parameter groups.

412

Object

Description

Flame Status

Toggles between a lit flame and an extinguished flame.

15 Fired Heater (Furnace)

Object

Description

Combustion Boundaries

Sets the combustion boundary based on a range of air fuel ratios.

Efficiency

Sets a steady state efficiency percentage. The heater will heat all the radiant zone streams equally using energy from the combustion. If the efficiency is 0, then all the energy from the combustion will go into heating the flue gas. If the efficiency is 100%, then all the energy will go to heating the radiant zone process streams and the flue gas stream will not be heated.

Excess Air Percent

HYSYS calculates the required Air flow using a percentage value.

Oxygen

Specifies the oxygen mixing efficiency.

Fuels

Selects the components present in your fuel as well as set their mixing efficiencies.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor that allows you to record any comments or information regarding the specific unit operation, or the simulation case in general.

Rating Tab The Rating tab contains the following pages: l

Sizing

l

Nozzles

l

Heat Loss

Each page is discussed in the following sections.

Sizing Page On the Sizing page, you can specify the geometry of the radiant, convective, and economizer zones in the Fired Heater. From the Zone group on the Sizing page, you can choose between Radiative, Convective, and Economizer zone property views. These property views contain information regarding the tube and shell properties. To edit or enter

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parameters within these property views, click the individual cell and make the necessary changes. The figure below shows an example of the Fired Heater setup with one radiant zone/firebox only with four tube passes. This is the simplest type.

The figure below shows an example of the Fired Heater setup with a radiant, convective and economizer section.

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Tube Properties Group The Tube Properties group displays the following information regarding the dimension of the tube: l

stream pass

l

tube inner diameter, Din

l

tube outer diameter, Dout

l

tube thickness

l

# tubes per external pass

l

tube length, L

l

tube inner area

l

tube outer area

l

tube inner volume

A pass in the Fired Heater is defined as a path where the process fluid flows through a distinctive inlet nozzle and outlet nozzle. The figure below illustrates the various dimensions of the tube and shell.

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Shell Properties Group The Shell Properties group displays the following information regarding the dimension of the shell:

416

l

shell inner diameter, Dsin

l

shell outer diameter, Dsout

l

wall thickness, ts

l

zone height, H

l

shell inner area

l

shell outer area

l

shell net volume

l

shell total volume

15 Fired Heater (Furnace)

Nozzles Page The information provided in the Nozzles page is applicable only in Dynamic mode. You can define the base elevation to ground level of the Fired Heater in the Nozzles page.

Heat Loss Page The information provided in the Heat Loss page is applicable only in Dynamic mode. This page displays the radiant heat transfer properties, heat transfer coefficients of the Fired Heater wall and tube, and shell area, tube area, and volume in each individual zone. Click here for more information on the Heat Loss Models. Note: You may improve numeric stability in certain depressuring studies by using Prevent Temperature Cross.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the heat exchanger unit operation. To view the stream parameters broken down per stream phase, open the Worksheet tab of the stream property view. Note: The PF Specs page is relevant to dynamics cases only.

Performance Tab The performance tab contains tables which highlight the calculated temperature, duty, and pressure of the Fired Heater operation.

Performance Details Page The Overall Performance table displays the duty readout for each zone in the Fired Heater.

Performance Plots Page From the X or Y Variable drop-down lists, select the variables you want to use for the x and y-axes. Use the Setup Page to determine number of plot points (intervals) and the variables that may be read into the X or Y axis of the Plot. The page lists all available variables in the simulation, and lets you select which ones to use within the plot.

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Performance Tables Page Use the Phase Viewing Options to selectively examine results for a particular phase or phases.

Performance Setup Page Use the Setup page to determine the intervals (plot points) and variables to be made available to the Performance Table x and y axes. The page lists all available variables in the simulation, and lets you select which ones to use within the table. The table below describes the options for the heat curve. Curve Option

Description

Intervals

Number of points on the plot

Dew/Bubble Pts

Include or exclude dew/bubble points in the curves

Step Type

Set the points on the plot to be based on equal temperature or equal enthalpy intervals

Pressure Profile

Set heat curves to be calculated at a specific constant pressure independent of the feed or product pressures. Specify Linear, Inlet Pressure, Outlet Pressure, or a value you enter in the Additional Const Pressures table.

Dynamics Tab The Dynamics tab contains information pertaining to pressure specifications for the dynamic calculations. The information is sorted into the following pages: l

Tube Side PF

l

Flue Gas PF

l

Holdup

Tube Side PF Page The Tube Side PF page lets you specify how the pressure drop in each pass is calculated. The following table outlines the tube side PF options available on this page.

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Option

Description

Use K’s?

If this check box is selected, the K method is used to calculate Delta P across the pass.

15 Fired Heater (Furnace)

Option

Description

Use Delta P Spec?

If this check box is selected, the pressure drop is fixed at this specified value. Specify the pressure drop across the tube in the Delta P field.

Calculate K’s

If this button is clicked, HYSYS calculates the K required to maintain a specified Delta P across a defined flow condition.

l

l

The reference flow value results in a more linear relationship between flow and pressure drop. This is used to increase model stability during startup and shutdown where the flows are low. It is recommended that the k reference flow be taken as 40% of steady state design flow for better pressure flow stability at low flow range. Specify a k reference flow in the K Reference flow field. The k-value defines the relationship between the flow through the Fired Heater and the pressure of the surrounding streams. Specify the k value in the K Values field. If you do not know the k value, click the Calculate K’s button to have HYSYS calculate the k value for you. Make sure that there is a non-zero pressure drop across the Fired Heater before clicking the Calculate K's button.

Note: Use the k-value specification option as much as possible to simulate actual pressure flow relations in the plant.

Flue Gas PF Page On the Flue Gas PF page, you can specify how the pressure drop in each pass is calculated. The following table outlines the tube side PF options available on this page. Option

Description

Use PF K’s

If this check box is selected, the K method is used to calculate Delta P across the pass.

Use Delta P

If this check box is selected, the pressure drop is fixed at this specified value.

Calculate K’s

If this button is clicked, HYSYS calculates the K required to maintain a specified Delta P across a defined flow condition.

l

l

The reference flow value results in a more linear relationship between flow and pressure drop. This is used to increase model stability during startup and shutdown where the flows are low. It is recommended that the k reference flow be taken as 40% of steady state design flow for better pressure flow stability at low flow range. Specify a k reference flow in the K Reference flow field. The k-value defines the relationship between the flow through the Fired Heater and the pressure of the surrounding streams. Specify the k value

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in the K Values field. If you do not know the k value, click the Calculate K’s button to have HYSYS calculate the k value for you. Make sure that there is a non-zero pressure drop across the Fired Heater before clicking the Calculate K's button. Note: Use the k-value specification option as much as possible to simulate actual pressure flow relations in the plant.

Holdup Page The Holdup page contains information regarding each stream’s holdup properties and composition. The Individual Holdups group contains two dropdown lists (Zone and Holdup) that enable you to select and view information on individual zone and holdup section. l

l

l

l

From the Stream drop-down list, select the stream for which you want to view the holdup details. The table in the Overall Stream Holdup Details group displays the following information for each phase contained within the selected stream: o

Accumulation: Holdup Accumulation is the rate of change of material in the holdup

o

Moles: Holdup Moles is the amount of material in the holdup for each phase.

o

Volume: Holdup Volume is the holdup volume of each phase.

From the Zone drop-down list, select the zone for which you want to view data. From the Holdup drop-down list, select the tube in the selected zone you want to view data for. Click the Advanced button to access the Advanced Holdup view for the selected zone/holdup combination.

EDR Fired Heater Tab For all pages of the Fired heater EDR tab, you can use the Import - Export buttons to bring in or read out .edr format data files. You can also use the View EDR Browser button to open the configuration in the Aspen Exchanger Design and Rating interface, for more advanced view and configuration options.

Summary Page Use the EDR Fired Heater Summary Page to examine the overall performance of the heater and of the firebox and bank.

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Streams Page Use the EDR Fired Heater Streams Page to examine calculations for selected streams in the firebox.

Fuel Page Use the EDR Fired Heater Fuel Page to specify the air to oxidant ratio, the fuel source and the calculation mode.

Flue Gas Page Use the Flue Gas Page to examine EDR fired heater flue gas composition calculation

Tube Banks Page Use the Tube Banks Page to define the convection bank flow sequence.

Operation Page Use the Operation Page to set operating limits for the fired heater unit operation.

Property Table Page Use the Property Table Page to examine or set values within property tables generated for each process stream (excluding fuel and oxidant streams) entering the fired heater based on the stream composition held by HYSYS. These property tables are used within the FiredHeater to calculate the physical properties of the stream at any set of conditions.

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The Heat Exchanger performs two-sided energy and material balance calculations. The Heat Exchanger is very flexible, and can solve for temperatures, pressures, heat flows (including heat loss and heat leak), material stream flows, or UA. In HYSYS, you can choose from different Heat Exchanger models for your analysis. The choices include an End Point analysis design model, an ideal (Ft=1) counter-current Weighted design model, a steady state rating method, Rigorous Shell and Tube, and a dynamic rating method for use in dynamic simulations. The dynamic rating method is available as either a Basic, Intermediate, or Detailed model, and can also be used in Steady State mode for Heat Exchanger rating. The unit operation also allows the use of third party Heat Exchanger design methods via OLE Extensibility. The following are some of the key features of the dynamic Heat Exchanger operation: l

A pressure-flow specification option which realistically models flow through the Heat Exchanger according to the pressure network of the plant. Possible flow reversal situations can therefore be modeled. Note: In Dynamic mode, the shell and tube of the Heat Exchanger is capable of storing inventory like other dynamic vessel operations. The direction of flow of material through the Heat Exchanger is governed by the pressures of the surrounding unit operations.

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l

l

16 Heat Exchanger

The choice between a Basic, Intermediate, and Detailed Heat Exchanger model. Detailed Heat Exchanger rating information can be used to calculate the overall heat transfer coefficient and pressure drop across the Heat Exchanger. A dynamic holdup model which calculates level in the Heat Exchanger shell based on its geometry and orientation. A heat loss model which accounts for the convective and conductive heat transfer that occurs across the Heat Exchanger shell wall.

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Heat Exchanger Theory The Heat Exchanger calculations are based on energy balances for the hot and cold fluids.

Steady State In the following general relations, the hot fluid supplies the Heat Exchanger duty to the cold fluid: (1) where: M = fluid mass flow rate H = enthalpy Qleak = heat leak Qloss = heat loss Balance Error = a Heat Exchanger Specification that equals 0 for most applications hot and cold in and out

= hot and cold fluids

= inlet and outlet stream

Note: The Heat Exchanger operation allows the heat curve for either side of the exchanger to be broken into intervals. Rather than calculating the energy transfer based on the terminal conditions of the exchanger, it is calculated for each of the intervals, then summed to determine the overall transfer.

The total heat transferred between the tube and shell sides (Heat Exchanger duty) can be defined in terms of the overall heat transfer coefficient, the area available for heat exchange, and the log mean temperature difference: (2) where: U = overall heat transfer coefficient A = surface area available for heat transfer ΔTLM = log mean temperature difference (LMTD) Ft = LMTD correction factor The heat transfer coefficient and the surface area are often combined for convenience into a single variable referred to as UA. The LMTD and its correction factor are defined in the Performance section.

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Dynamic The following general relation applies to the shell side of the Basic model Heat Exchanger. (1) For the tube side: (2) where: Mshell = shell fluid flow rate Mtube = tube fluid flow rate ρ = density H = enthalpy Qloss = heat loss Q = heat transfer from the tube side to the shell side V = volume shell or tube holdup The term Qloss represents the heat lost from the shell side of the dynamic Heat Exchanger.

Pressure Drop The pressure drop of the Heat Exchanger can be determined in one of three ways: l l

l

Specify the pressure drop. Calculate the pressure drop based on the Heat Exchanger geometry and configuration. Define a pressure flow relation in the Heat Exchanger by specifying a kvalue.

If the pressure flow option is chosen for pressure drop determination in the Heat Exchanger, a k value is used to relate the frictional pressure loss and flow through the exchanger. This relation is similar to the general valve equation: (1) This general flow equation uses the pressure drop across the Heat Exchanger without any static head contributions. The quantity, P1 - P2, is defined as the frictional pressure loss which is used to “size” the Heat Exchanger with a k-value.

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Dynamic Specifications The following tables list the minimum specifications required for the Heat Exchanger unit operation to solve in Dynamic mode. The Basic Heat Exchanger model requires the following dynamic specifications: Specification

Description

Volume

The tube and shell volumes must be specified.

Overall UA

The Overall UA must be specified.

Pressure Drop

Either specify an Overall Delta P or an Overall K-value for the Heat Exchanger. Specify the Pressure Drop calculation method in the Dynamic Specifications group on the Specs page of the Dynamics tab. You can also specify the Overall Delta P values for the shell and tube sides on the Sizing page of the Rating tab.

The Detailed Heat Exchanger model requires the following dynamic specifications: Specification

Description

Sizing Data

The tube and shell sides of the Heat Exchanger must be completely specified on the Sizing page of the Rating tab. The overall tube/shell volumes, and the heat transfer surface area are calculated from the shell and tube ratings information.

Overall UA

Either specify an Overall UA or have it calculated from the Shell and Tube geometry. Specify the U calculation method on the Parameters page of the Rating tab. The U calculation method can also be specified on the Model page of the Dynamics tab.

Pressure Drop

Either specify an Overall Delta P or an Overall K-value for the Heat Exchanger. Specify the Pressure Drop calculation method on the Parameters page of the Rating tab. You can also specify the Pressure Drop calculation method in the Pressure Flow Specifications group on the Specs page of the Dynamics tab.

Heat Exchanger Property View On the Heat Exchanger property view, the Update button lets you update the heat exchanger calculation when in Dynamic mode. For example, if you make a configuration change to the heat exchanger, click this button to reset the equations around the heat exchanger before running the simulation calculation in Dynamic mode.

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Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

Specs

l

User Variables

l

Notes

Connections Page The Connections page allows you to specify the operation name, and the inlet and outlet streams of the shell and tube. The main flowsheet is the default flowsheet for the Tube and Shell side. You can select a subflowsheet on the Tube and/or Shell side which allows you to choose inlet and outlet streams from that flowsheet. This is useful for processes such as the Refrigeration cycle, which require separate fluid packages for each side. You can define a subflowsheet with a different fluid package, and then connect to the main flowsheet Heat Exchanger.

Convert to Rigorous Model If you want to take advantage of the activated Aspen Exchanger Design and Rating calculations, you can quickly convert the heat exchanger to a rigorous heat exchanger model using the Convert to Rigorous Model fields. Size Exchanger lets you size the model automatically or interactively, optionally starting with a template file for either choice. Specify Geometry lets you use the EDR interface to directly enter key geometry to the model, or select values saved in an .edr file.

Parameters Page The Parameters page allows you to select the Heat Exchanger Model and specify relevant physical data. The parameters that appear on the Parameters page depend on the selected Heat Exchanger Model. Note: When a heat exchanger is installed as part of a column subflowsheet (available when using the Modified HYSIM Inside-Out solving method) these Heat Exchanger Models are not available. Instead, in the column subflowsheet, the heat exchanger is “Calculated from Column” as a simple heat and mass balance.

From the Heat Exchanger Model drop-down list, select the calculation model for the Heat Exchanger. The following Heat Exchanger models are available: l

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Rigorous Shell & Tube (Requires Aspen Exchanger Design and Rating (EDR).)

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l

Simple End Point

l

Simple Steady State Rating

l

Simple Weighted

l

"Dynamic Rating Model" on page 431

Note: When you add a Heat Exchanger within an SRU sub-flowsheet, the Simple End Point model is the only available option.

For both the Simple End Point and Simple Weighted models, you can specify whether your Heat Exchanger experiences heat leak/loss. l

l

Heat Leak: Loss of cold side duty due to leakage. Duty gained to reflect the increase in temperature. Heat Loss: Loss of hot side duty due to leakage. Duty lost to reflect the decrease in temperature.

The table below describes the radio buttons in the Heat Leak/Loss group of the Simple End Point and Simple Weighted models. Radio Button

Description

None

By default, the None radio button is selected.

Extremes

On the hot side, the heat is considered to be “lost” where the temperature is highest. Essentially, the top of the heat curve is being removed to allow for the heat loss/leak. This is the worst possible scenario. On the cold side, the heat is gained where the temperature is lowest.

Proportional

The heat loss is distributed over all of the intervals.

All Heat Exchanger models allow for the specification of either Counter or CoCurrent tube flow.

Simple End Point Model The Simple End Point model is based on the standard Heat Exchanger duty equation, Equation (2), defined in terms of overall heat transfer coefficient, area available for heat exchange, and the log mean temperature difference (LMTD). The main assumptions of the model are as follows: l

Overall heat transfer coefficient, U is constant.

l

Specific heats of both shell and tube side streams are constant.

The Simple End Point model treats the heat curves for both Heat Exchanger sides as linear. For simple problems where there is no phase change and CP is relatively constant, this option may be sufficient to model your Heat Exchanger. For non-linear heat flow problems, use the Simple Weighted model instead.

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The following parameters are available when the Simple End Point model is selected. Parameters

Description

Tubeside and Shellside Delta P

The pressure drops (DP) for the tube and shell sides of the exchanger can be specified here. If you do not specify the Delta P values, HYSYS calculates them from the attached stream pressures.

UA

The product of the Overall Heat Transfer Coefficient, and the Total Area available for heat transfer. The Heat Exchanger duty is proportional to the log mean temperature difference, where UA is the proportionality factor. The UA can either be specified, or calculated by HYSYS. Note: With Heat Exchangers within an SRU sub-flowsheet, the UA is always calculated by HYSYS.

Use Ft check box

Select this check box to use the LMTD (log mean temperature difference) correction factor, Ft. The Ft is calculated as a function of the Number of Shell Passes and the temperature approaches. For a counter-current Heat Exchanger, Ft is 1.0. For the Simple End Point rating method, Ft = 1. This selection impacts the LMTD and Uncorrected LMTD results on the Performance tab | Details page.

Exchanger Geometry

The Exchanger Geometry is used to calculate the Ft Factor using the End Point Model. Refer to the Rating tab for more information on the Exchanger Geometry.

Simple Weighted Model The Simple Weighted model is an excellent model to apply to non-linear heat curve problems such as the phase change of pure components in one or both Heat Exchanger sides. With the Simple Weighted model, the heating curves are broken into intervals, and an energy balance is performed along each interval. A LMTD and UA are calculated for each interval in the heat curve, and summed to calculate the overall exchanger UA. The Simple Weighted model is available only for counter-current exchangers, and is essentially an energy and material balance model. The following table describes the parameters available on the Parameters page when the Simple Weighted model is selected. Parameters

Description

Tube-side and Shellside Delta P

The pressure drops (DP) for the tube and shell sides of the exchanger can be specified here. If you do not specify the DP values, HYSYS calculates them from the attached stream pressures.

UA

The product of the Overall Heat Transfer Coefficient and the Total Area available for heat transfer. The Heat Exchanger duty is proportional to the log mean temperature difference, where UA is the proportionality factor. The UA can either be specified, or calculated by HYSYS.

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Parameters

Description

Use Ft check box

Select this check box to use the LMTD (log mean temperature difference) correction factor, Ft. The Ft is calculated as a function of the Number of Shell Passes and the temperature approaches. For a counter-current Heat Exchanger, Ft is 1.0. For the Simple Weighted rating method, Ft = 1. This selection impacts the LMTD and Uncorrected LMTD results on the Performance tab | Details page.

Exchanger Geometry

The Exchanger Geometry is used to calculate the Ft Factor using the End Point Model. Refer to the Rating tab for more information on the Exchanger Geometry.

Individual Heat Curve Details For each side of the Heat Exchanger, the following parameters appear. All but the Pass Names can be modified. Pass Name

Identifies the shell and tube side according to the names you provided on the Connections page.

Intervals

The number of intervals can be specified. For non-linear temperature profiles, more intervals are necessary.

Dew/Bubble Pt.

Select this check box to add a point to the heat curve for the dew and/or bubble point. If there is a phase change occurring in either pass, the appropriate check box should be selected.

Step Type

There are three choices for the Step Type:

Pressure Profile

l

Equal Enthalpy. All intervals have an equal enthalpy change.

l

Equal Temperature. All intervals have an equal temperature change.

l

Auto Interval. HYSYS determines where points should be added to the heat curve. This is designed to minimize error using the least number of intervals.

The Pressure Profile is updated in the outer iteration loop, using one of the following methods: l

Constant dPdH. Maintains constant dPdH during update.

l

Constant dPdUA. Maintains constant dPdUA during update.

l

Constant dPdA. Maintains constant dPdA during update. This is not currently applicable to the Heat Exchanger, as the area is not predicted.

l

Inlet Pressure. Pressure is constant and equal to the inlet pressure.

l

Outlet Pressure. Pressure is constant and equal to the outlet pressure.

Simple Steady State Rating Model The Steady State Rating model is an extension of the End Point model to incorporate a rating calculation, and uses the same assumptions as the End Point model. If you provide detailed geometry information, you can rate the

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exchanger using this model. As the name suggests, this model is only available for steady state rating. When dealing with linear or nearly linear heat curve problems, the Steady State Rating model should be used. Due to the solver method incorporated into this rating model, the Steady State Rating model can perform calculations exceptionally faster than the Dynamic Rating model. The following parameters are available on the Parameters page when the Steady State Rating model is selected: Parameters

Description

Tubeside and Shellside Delta P

The pressure drops (DP) for the tube and shell sides of the exchanger can be specified here. If you do not specify the Delta P values, HYSYS calculates them from the attached stream pressures.

UA

The product of the Overall Heat Transfer Coefficient, and the Total Area available for heat transfer. The Heat Exchanger duty is proportional to the log mean temperature difference, where UA is the proportionality factor. In Steady State, the UA is calculated by HYSYS.

Dynamic Rating Model Three models are available for Dynamic Rating using the Heat Exchanger unit operation: Basic, Intermediate, and Detailed. If you specify three temperatures or two temperatures and a UA, you can rate the exchanger with the Basic model. If you want to perform zone analysis and model tube thermal inertia without providing geometric details such as tube ID, OD, length, shell diameter, and baffles, you can rate the exchanger using the Intermediate model. If you provide detailed geometry information, you can rate the exchanger using the Detailed model.

Dynamic Basic Model The Basic model is based on the same assumptions as the End Point model, which uses the standard Heat Exchanger duty equation, Equation (2), defined in terms of overall heat transfer coefficient, area available for heat exchange, and the log mean temperature difference. The Basic model is actually the counterpart of the End Point model for dynamics and dynamic rating. The Basic model can also be used for steady state Heat Exchanger rating.

Dynamic Intermediate Model The Intermediate model option enables a level of fidelity for dynamic modeling that is higher than the Basic model but lower than the Detailed model. You can perform zone analysis and model tube thermal inertia without providing geometric details such as tube ID, OD, length, shell diameter, and baffles. Instead of detailed exchanger geometry, you must provide lumped parameters, such as shell/tube volume, tube mass/heat capacity, and heat transfer area.

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Dynamic Detailed Model The Detailed model is based on the same assumptions as the Weighted model, and divides the Heat Exchanger into a number of heat zones, performing an energy balance along each interval. This model requires detailed geometry information about your Heat Exchanger. The Detailed model is actually the counterpart of the Weighted model for dynamics and dynamic rating, but can also be used for steady state Heat Exchanger rating. The Basic, Intermediate, and Detailed Dynamic Rating models share rating information with the Dynamics Heat Exchanger model. Any rating information entered using these models is observed in Dynamic mode. Once the Dynamic Rating model is selected, no further information is required on the Parameters page of the Design tab. You can choose the model (Basic, Intermediate, Detailed) on the Parameters page of the Rating tab.

Rigorous Shell and Tube Model This mode accesses the Aspen Exchanger Design and Rating (EDR) program and lets you set up a rigorous shell and tube exchanger model within it. You can also import existing information for the model from EDR in the .edr file format. Using this model also allows advanced analysis and error checking through the EDR activated analysis environment. You must have Aspen Exchanger Design and Rating (EDR) installed to access this model.

Specs Page The Specs page includes three groups that organize various specifications and solver information. The information provided on the Specs page is only valid for the Weighted, Endpoint, and Steady State Rating models. Note: If you are working with a Dynamic Rating model, the Specs page does not appear on the Design tab.

Solver Group The following parameters are listed in the Solver group:

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Parameters

Details

Tolerance

The calculation error tolerance can be set.

Current Error

When the current error is less than the calculation tolerance, the solution is considered to have converged.

Iterations

The current iteration of the outer loop appears. In the outer loop, the heat curve is updated and the property package calculations are performed. Non-rigorous property calculations are performed in the inner loop. Any constraints are also considered in the inner loop.

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Unknown Variables Group HYSYS lists all unknown Heat Exchanger variables according to your specifications. Once the unit has solved, the values of these variables appear.

Specifications Group The Heat Balance (specified at 0 kJ/h) is considered to be a constraint. Note: Without the Heat Balance specification, the heat equation is not balanced.

This is a Duty Error spec, which you cannot turn off. Without the Heat Balance specification, you could, for example, completely specify all four Heat Exchanger streams, and have HYSYS calculate the Heat Balance error which would be displayed in the Current Value column of the Specifications group. The UA is also included as a default specification. HYSYS displays this as a convenience, since it is a common specification. You can either use this spec or deactivate it.

Specification Property View You can add edit or delete highlighted specifications by using the View, Add, or Delete buttons at the right of the group. A specification property view appears automatically each time a new spec is created via the Add button. The figure below shows a typical property view of a specification, which is accessed via the View or Add button.

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Each specification property view has the following tabs: l

Parameters

l

Summary

The Summary page is used to define whether the specification is Active or an Estimate. The Spec Value is also shown on this page. Note: Information specified on the specification property view also appears in the Specifications group.

All specifications are one of the following three types: Specification Type

Description

Active

An active specification is one that the convergence algorithm is trying to meet. An active specification always serves as an initial estimate (when the Active check box is selected, HYSYS automatically selects the Estimate check box). An active specification exhausts one degree of freedom. An Active specification is one that the convergence algorithm is trying to meet. An Active specification is on when both check boxes are selected.

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Specification Type

Description

Estimate

An Estimate is considered an Inactive specification because the convergence algorithm is not trying to satisfy it. To use a specification as an estimate only, clear the Active check box. The value then serves only as an initial estimate for the convergence algorithm. An estimate does not use an available degree of freedom. An Estimate is used as an initial “guess” for the convergence algorithm, and is considered to be an inactive specification.

Completely Inactive

To disregard the value of a specification entirely during convergence, clear both the Active and Estimate check boxes. By ignoring rather than deleting a specification, it remains available if you want to use it later. A Completely Inactive specification is one that is ignored completely by the convergence algorithm, but can be made Active or an Estimate at a later time.

The specification list allows you to try different combinations of the above three specification types. For example, suppose you have a number of specifications, and you want to determine which ones should be active, which should be estimates and which ones should be ignored altogether. By manipulating the check boxes among various specifications, you can test various combinations of the three types to see their effect on the results. Caution: If your Heat Exchanger is located within an SRU sub-flowsheet: l

You can only add Temperature and Delta Temp specifications.

l

The default Heat Balance specification, which is a Duty specification, still appears; however, you cannot add any new Duty specifications.

l

The default UA specification also appears, but you must clear the Active check box in order for the Heat Exchanger to solve. You cannot create any new UA specifications.

l

For Temperature and Delta Temp specifications, Cold Inlet Equilibrium and Hot Inlet Equilibrium do not appear as selectable streams.

The available specification types include the following: (View Button) Specification

Description

Temperature

The temperature of any stream attached to the Heat Exchanger. The hot or cold inlet equilibrium temperature can also be defined.

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l

The Hot Inlet Equilibrium temperature is the temperature of the inlet hot stream minus the heat loss temperature drop.

l

The Cold Inlet Equilibrium temperature is the temperature of the inlet cold stream plus the heat leak temperature rise.

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Specification

Description

Delta Temp

The temperature difference at the inlet or outlet between any two streams attached to the Heat Exchanger. The hot or cold inlet equilibrium temperatures (which incorporate the heat loss/heat leak with the inlet conditions) can also be used.

Minimum Approach

Minimum internal temperature approach. The minimum temperature difference between the hot and cold stream (not necessarily at the inlet or outlet).

UA

The overall UA (product of overall heat transfer coefficient and heat transfer area).

LMTD

The overall log mean temperature difference.

Duty

The overall duty, duty error, heat leak or heat loss. The duty error should normally be specified as 0 so that the heat balance is satisfied. The heat leak and heat loss are available as specifications only if the Heat Loss/Leak is set to Extremes or Proportional on the Parameters page.

Duty Ratio

A duty ratio can be specified between any two of the following duties: overall, error, heat loss, and heat leak.

Flow

The flowrate of any attached stream (molar, mass or liquid volume).

Flow Ratio

The ratio of the two inlet stream flowrates. All other ratios are either impossible or redundant (in other words, the inlet and outlet flowrates on the shell or tube side are equal).

Subcooling

Subcools the LNG or heat exchanger to the temperature of any of the attached stream. Select the stream you want to use from the Stream drop-down list.

Superheating

Superheats the LNG or heat exchanger to the temperature of any of the attached stream. Select the stream you want to use from the Stream drop-down list.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor that allows you to record any comments or information regarding the specific unit operation or the simulation case in general.

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Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the Heat Exchanger unit operation. To view the stream parameters broken down per stream phase, select the Worksheet tab of the stream property view. Note: The PF Specs page is relevant to dynamics cases only.

Heat Exchanger Rating Tab The Rating tab contains the following pages: l

Sizing

l

Parameters Note: The Parameters page is used exclusively by the dynamics Heat Exchanger, and only becomes active either in Dynamic mode or while using the Dynamic Rating model.

l

Nozzles

l

Heat Loss

Sizing Page The Sizing page provides Heat Exchanger sizing related information. Based on the geometry information, HYSYS is able to calculate the pressure drop and the convective heat transfer coefficients for both Heat Exchanger sides and rate the exchanger. The information is grouped under three radio buttons: l

Overall

l

Shell

l

Tube

Overall When you select the Overall radio button, the overall Heat Exchanger geometry appears. In the Configuration group, you can specify whether multiple shells are used in the Heat Exchanger design. The following fields appear, and can be modified in, the Configuration group.

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Field

Description

Number of Shell Passes

You have the option of HYSYS performing the calculations for Counter Current (ideal with Ft = 1.0) operation, or for a specified number of shell passes. Specify the number of shell passes to be any integer between 1 and 7. When the shell pass number is specified, HYSYS calculates the LMTD correction factor (Ft) for the current exchanger design. A value lower than 0.8 generally corresponds to inefficient design in terms of the use of heat transfer surface. More passes or larger temperature differences should be used in this case. For n shell passes, HYSYS solves the heat exchanger on the basis that at least 2n tube passes exist. Charts for Shell and Tube Exchanger LMTD Correction Factors, as found in the GPSA Engineering Data Book, are normally in terms of n shell passes and 2n or more tube passes.

Number of Shells in Series

If a multiple number of shells are specified in series, the configuration is shown as follows:

Number of Shells in Parallel

If a multiple number of shells are specified in parallel, the configuration is shown as follows:

Currently, multiple shells in parallel are not supported in HYSYS. Tube Passes per Shell

The number of tube passes per shell. The default setting is 2 (in other words, the number of tubes equal to 2n, where n is the number of shells.)

Exchanger Orientation

The exchanger orientation defines whether or not the shell is horizontal or vertical. Used only in dynamic simulations. When the shell orientation is vertical, you can also specify whether the shell feed is at the top or bottom via the Shell Feed at Bottom check box. The Shell Feed at Bottom check box is only visible for the vertical oriented exchanger.

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Field

Description

First Tube Pass Flow Direction

Specifies whether or not the tube feed is co-current or counter-current.

Elevation (base)

The height of the base of the exchanger above the ground. Used only in dynamic simulations.

You can specify the number of shell and tube passes in the shell of the Heat Exchanger. In general, at least 2n tube passes must be specified for every n shell pass. The exception is a counter-current flow Heat Exchanger which has 1 shell pass and one tube pass. The orientation can be specified as a vertical or horizontal Heat Exchanger. The orientation of the Heat Exchanger does not impact the steady state solver, however, it is used in the Dynamics Heat Exchanger Model in the calculation of liquid level in the shell. Note: For a more detailed discussion of TEMA-style shell-and-tube heat exchangers, refer to page 11-33 of the Perry’s Chemical Engineers’ Handbook (1997 edition).

The shape of Heat Exchanger can be specified using the TEMA-style drop-down lists. The first list contains a list of front end stationary head types of the Heat Exchanger. The second list contains a list of shell types. The third list contains a list of rear end head types. In the Calculated Information group, the following Heat Exchanger parameters are listed: l

Shell HT Coeff

l

Tube HT Coeff

l

Overall U

l

Overall UA

l

Shell DP

l

Tube DP

l

Heat Trans. Area per Shell

l

Tube Volume per Shell

l

Shell Volume per Shell

Shell Selecting the Shell radio button allows you to specify the shell configuration and the baffle arrangement in each shell. In the Shell and Tube Bundle Data group, you can specify whether multiple shells are used in the Heat Exchanger design. The following fields appear, and can be modified in, the Shell and Tube Bundle Data group.

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Field

Description

Shell Diameter

Diameter of the shell(s).

Number of Tubes per Shell

Number of tubes per shell. You can change the value in this field.

Tube Pitch

Shortest distance between the centers of two adjacent tubes.

Tube Layout Angle

In HYSYS, the tubes in a single shell can be arranged in four different symmetrical patterns: l

Triangular (30°)

l

Triangular Rotated (60°)

l

Square (90°)

l

Square Rotated (45°)

For more information regarding the benefits of different tube layout angles, refer to page 139 of Process Heat Transfer by Donald Q. Kern (1965) Shell Fouling

The shell fouling factor is taken into account in the calculation of the overall heat transfer coefficient, U.

The following fields appear, and can be modified in, the Shell Baffles group: Field

Description

Shell Baffle Type

You can choose from four different baffle types: l

Single

l

Double

l

Triple

l

Grid

Shell Baffle Orientation

You can choose whether the baffles are aligned horizontally or vertically along the inner shell wall.

Baffle cut (Height %)

The baffle cut is expressed as a percent of the baffle window height to the shell diameter. You can use the baffle cut to specify the percent of net free area, which is defined as the total cross-sectional area in the flow direction parallel to the tubes minus the area blocked off by the tubes (essentially the percentage of open area).

Baffle Spacing

You can specify the space between each baffle.

Tube Selecting the Tube radio button allows you to specify the tube geometry information in each shell.

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The Dimensions group allows you to specify the following tube geometric parameters: Field l

Outer Tube

l

Inner Tube Diameter (ID)

l

Tube Thickness

Tube Length

Description Two of the three listed parameters must be specified to characterize the tube width dimensions.

Heat transfer length of one tube in a single Heat Exchanger shell. This value is not the actual tube length.

In the Tube Properties group, the following metal tube heat transfer properties must be specified: l

Tube Fouling Factor

l

Thermal Conductivity

l

Wall Specific Heat Capacity, Cp

l

Wall Density

Parameters Page The Parameters page of the Rating tab is used to define rating parameters for the Dynamic Rating model. On the Parameters page, you can specify a Basic, Intermediate, or Detailed model. For the Basic model, you must define the Heat Exchanger overall UA and pressure drop across the shell and tube. For the Intermediate model, you must provide lumped parameters, such as shell/tube volume, tube mass/heat capacity, and heat transfer area. For the Detailed model, you must define the geometry and heat transfer parameters of both the shell and tube sides in the Heat Exchanger operation. In order for either the Basic, Intermediate, or Detailed Heat Exchanger Model to completely solve, the Parameters page must be completed.

Basic Model When you select the Basic model radio button on the Parameters page in Dynamic mode, the Basic Model Parameters property view appears. The Dimensions group contains the following information: l

Tube Volume

l

Shell Volume

l

Elevation (Base)

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The tube volume, shell volume, and heat transfer area are calculated from Shell and Tube properties specified by selecting the Shell and Tube radio buttons on the Sizing page. The elevation of the base of the Heat Exchanger can be specified but does not impact the steady state solver. The Parameters group includes the following Heat Exchanger parameters. All but the correction factor, F, can be modified: Field

Description

Overall UA

The product of the Overall Heat Transfer Coefficient, and the Total Area available for heat transfer. The Heat Exchanger duty is proportional to the log mean temperature difference, where UA is the proportionality factor. The UA can either be specified, or calculated by HYSYS.

Tubeside and Shellside Delta P

The pressure drops (DP) for the tube and shell sides of the exchanger can be specified here. If you do not specify the DP values, HYSYS calculates them from the attached stream pressures.

Intermediate Model The Intermediate model option enables a level of fidelity for dynamic modeling that is higher than the Basic model but lower than the Detailed model. You can perform zone analysis and model tube thermal inertia without providing geometric details such as tube ID, OD, length, shell diameter, and baffles. Instead of detailed exchanger geometry, you must provide lumped parameters, such as shell/tube volume, tube mass/heat capacity, and heat transfer area. The Heat Transfer Coefficient Information (Intermediate Model), Zone Information (Detailed and Intermediate Models), and Delta P (Detailed and Intermediate Models) sections below describe how to specify inputs for the Intermediate model, Note: No geometry information is required for the Intermediate model.

Heat Transfer Coefficient Information (Intermediate Model) The Heat Transfer coefficients group contains the following information: Field

Description

Shell/Tube Heat Transfer Coefficient

The local Heat Transfer Coefficients, h o and h i , can be specified or calculated.

Shell/Tube HT Coefficient Calculator

The Heat Transfer Coefficient Calculator allows you to either specify or calculate the local Heat Transfer Coefficients. Specify the cell with one of following options: l

U flow scaled

l

U specified: The local heat transfer coefficients, h o and h i , are specified by you. Note: The Hysim-Correlation option is not supported.

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Detailed Model The Detailed model option allows you to specify the zone information, heat transfer coefficient, and Delta P details. When you select the Detailed model radio button on the Parameters page, the Detailed property view contains:

Zone Information (Detailed and Intermediate Models) HYSYS can partition the Heat Exchanger into discrete multiple sections called zones. Because shell and tube stream conditions do not remain constant across the operation, the heat transfer parameters are not the same along the length of the Heat Exchanger. By dividing the Heat Exchanger into zones, you can make different heat transfer specifications for individual zones, and therefore more accurately model an actual Heat Exchanger. In the Zone Information group you can specify the following: Field

Description

Zones per Shell Pass

Enter the number of zones you want for one shell. The total number of zones in a Heat Exchanger shell is calculated as:

Zone Fraction

The fraction of space the zone occupies relative to the total shell volume. HYSYS automatically sets each zone to have the same volume. You can modify the zone fractions to occupy a larger or smaller proportion of the total volume. Click the Normalize Zone Fractions button in order to adjust the sum of fractions to equal one.

(1)

Heat Transfer Coefficients (Detailed Model) The Heat Transfer Coefficients group contains information regarding the calculation of the overall heat transfer coefficient, U, and local heat transfer coefficients for the fluid in the tube, hi , and the fluid surrounding the tube, ho. The heat transfer coefficients can be determined in one of two ways: l

l

The heat transfer coefficients can be specified using the rating information provided on the Parameters page and the stream conditions. You can specify the heat transfer coefficients.

For fluids without phase change, the local heat transfer coefficient, hi , is calculated according to the Sieder-Tate correlation: (2)

where: Gi = mass velocity of the fluid in the tubes (velocity*density) μ i = viscosity of the fluid in the tube μ i,w = viscosity of the fluid inside tubes, at the tube wall

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Cp,i = specific heat capacity of the fluid inside the tube The relationship between the local heat transfer coefficients, and the overall heat transfer coefficient is shown in Equation (3). (3)

where: U = overall heat transfer coefficient ho = local heat transfer coefficient outside tube hi = local heat transfer coefficient inside tube ro = fouling factor outside tube ri = fouling factor inside tube rw = tube wall resistance Do = outside diameter of tube Di = inside diameter of tube The Heat Transfer coefficients group contains the following information: Field

Description

Shell/Tube Heat Transfer Coefficient

The local Heat Transfer Coefficients, h o and h i , can be specified or calculated.

Shell/Tube HT Coefficient Calculator

The Heat Transfer Coefficient Calculator allows you to either specify or calculate the local Heat Transfer Coefficients. Specify the cell with one of following options: l

Shell & Tube: The local heat transfer coefficients, h o and h i , are calculated using the heat exchange rating information and correlations.

l

U specified: The local heat transfer coefficients, h o and h i , are specified by you.

Delta P (Detailed and Intermediate Models) The Delta P group contains information regarding the calculation of the shell and tube pressure drop across the exchanger. In Steady State mode, the pressure drop across either the shell or tube side of the Heat Exchanger can be calculated in one of two ways: l

l

The pressure drop can be calculated from the rating information provided in the Sizing page and the stream conditions. The pressure drop can be specified.

The Delta P group contains the following information:

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Field

Description

Shell/Tube Delta P

The pressure drop across the Shell/Tube side of the Heat Exchanger can be specified or calculated.

Shell/Tube Delta P Calculator

The Shell/Tube Delta P Calculator allows you to either specify or calculate the shell/tube pressure drop across the Heat Exchanger. Specify the cell with one of following options: l

Shell & Tube Delta P Calculator. The pressure drop is calculated using the Heat Exchanger rating information and correlations.

l

User specified. The pressure drop is specified by you.

l

Non specified. This option is only applicable in Dynamic mode. Pressure drop across the Heat Exchanger is calculated from a pressure flow relation.

Detailed Heat Model Properties Property View When you click the Specify Parameters for Individual Zones button, the Detailed Heat Model Properties property view appears. The Detailed Heat Model Properties property view displays the detailed heat transfer parameters and holdup conditions for each zone. HYSYS uses the following terms to describe different locations within the Heat Exchanger. Location Term

Description

Zone

HYSYS represents the zone using the letter “Z”. Zones are numbered starting from 0. For instance, if there are 3 zones in a Heat Exchanger, the zones are labeled: Z0, Z1, and Z2.

Holdup

HYSYS represents the holdup within each zone with the letter “H”. Holdups are numbered starting from 0. “Holdup 0” is always the holdup of the shell within the zone. Holdups 1 through n represents the n tube holdups existing in the zone.

Tube Location

HYSYS represents tube locations using the letters “TH”. Tube locations occur at the interface of each zone. Depending on the number of tube passes per shell pass, there can be several tube locations within a particular zone. For instance, 2 tube locations exist for each zone in a Heat Exchanger with 1 shell pass and 2 tube passes. Tube locations are numbered starting from 1.

Consider a shell and tube Heat Exchanger with 3 zones, 1 shell pass, and 2 tube passes. The following diagram labels zones, tube locations, and hold-ups within the Heat Exchanger:

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Heat Transfer (Individual) Tab Information regarding the heat transfer elements of each tube location in the Heat Exchanger appears on the Heat Transfer (Individual) tab. Heat transfer from the fluid in the tube to the fluid in the shell occurs through a series of heat transfer resistances or elements. There are two convective elements, and one conductive element associated with each tube location. This tab organizes all the heat transfer elements for each tube location in one spreadsheet. You can choose whether Conductive or Convective elements will appear by selecting the appropriate element type in the Heat Transfer Type drop-down list. The following is a list of possible elements for each tube location: Heat Transfer Element

Description

Convective Element

The Shell Side element is associated with the local heat transfer coefficient, h o, around the tube. The Tube Side is associated with the local heat transfer coefficient, h i , inside the tube. These local heat transfer coefficients can be calculated by HYSYS, or you can modify them.

Conductive Element

This element is associated with the conduction of heat through the metal wall of the tube. The conductivity of the tube metal, and the inside and outside metal wall temperatures appear. You can modify the conductivity.

Heat Transfer (Global) Tab The Heat Transfer (Global) tab displays the heat transfer elements for the entire Heat Exchanger. You can choose whether the overall Conductive or Convective elements are to appear by selecting the appropriate element type in the Heat Transfer Type drop-down list.

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Tabular Results Tab The Tabular Results tab displays the following stream properties for the shell and tube fluid flow paths. The feed and exit stream conditions appear for each zone. l

Temperature

l

Pressure

l

Vapor Fraction

l

Molar Flow

l

Enthalpy

l

Cumulative UA

l

Cumulative Heat Flow

l

Length (into Heat Exchanger)

Note: You can choose whether the flow path is shell or tube side by selecting the appropriate flow path in the Display which flow path? drop-down list.

Specs (Individual) Tab The Specs (Individual) tab displays the pressure drop specifications for each shell and tube holdup in one spreadsheet. Note: You can choose whether the shell or tube side appears by selecting the appropriate flow path in the Display which flow path? drop-down list.

The Pressure Flow K and Use Pressure Flow K columns are applicable only in Dynamic mode.

Specs (Global) Tab The Specs (Global) tab displays the pressure drop specifications for the entire shell and tube holdups. The Pressure Flow K and Use Pressure Flow K columns are applicable only in Dynamic mode. You can choose whether the shell or tube side appears by selecting the appropriate flow path from the Display which flow path? drop-down list.

Plot Tab The information displayed on the Plots tab is a graphical representation of the parameters provided on the Tabular Results tab. You can plot the following variables for the shell and tube side of the Heat Exchanger: l

Vapor Fraction

l

Molar Flow

l

Enthalpy

l

Cumulative UA

l

Heat Flow

l

Length

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Nozzles Page The Nozzles page contains information regarding the elevation and diameter of the nozzles. The placement of feed and product nozzles on the Detailed Dynamic Heat Exchanger operation has physical meaning. The exit stream’s composition depends on the exit stream nozzle’s location and diameter in relation to the physical holdup level in the vessel. If the product nozzle is located below the liquid level in the vessel, the exit stream draws material from the liquid holdup. If the product nozzle is located above the liquid level, the exit stream draws material from the vapor holdup. If the liquid level sits across a nozzle, the mole fraction of liquid in the product stream varies linearly with how far up the nozzle the liquid is. Essentially, all vessel operations in HYSYS are treated the same. The compositions and phase fractions of each product stream depend solely on the relative levels of each phase in the holdup and the placement of the product nozzles, so a vapor product nozzle does not necessarily produce pure vapor. A 3-phase separator may not produce two distinct liquid phase products from its product nozzles.

Heat Loss Page The Heat Loss page contains heat loss parameters which characterize the amount of heat lost across the vessel wall. You can choose either to have no heat loss model, a Simple heat loss model or a Detailed heat loss model.

Simple Heat Loss Model When you select the Simple radio button, the following parameters appear: l

Overall U

l

Ambient Temperature

l

Overall Heat Transfer Area

l

Heat Flow

Detailed Heat Loss Model The Detailed model allows you to specify more detailed heat transfer parameters. The HYSYS Dynamics license is required to use the Detailed Heat Loss model found on this page.

Performance Tab The Performance tab has pages that display the results of the Heat Exchanger calculations in overall performance parameters, as well as using plots and tables.

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The Performance tab contains the following pages: l

Details

l

Plots

l

Tables

l

Setup

l

Error Msg

Details Page The information from the Details page appears in the figures below.

Steady State

Dynamic State

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Note: The appearance of this page is slightly different for the Dynamic Rating model.

The Overall Performance and Detailed Performance groups contain the following parameters that are calculated by HYSYS. Parameter

Description

Overall Performance Duty

Heat flow from the hot stream to the cold stream.

Heat Leak

Loss of cold side duty due to leakage. Duty gained to reflect the increase in temperature.

Heat Loss

Loss of the hot side duty to leakage. The overall duty plus the heat loss is equal to the individual hot stream duty defined on the Tables page.

UA

Product of the Overall Heat Transfer Coefficient, and the Total Area available for heat transfer. The UA is equal to the overall duty divided by the LMTD.

Min. Approach

The minimum temperature difference between the hot and cold stream.

Mean Temp Driving Force

The average temperature difference between the hot and cold stream.

LMTD

The uncorrected LMTD multiplied by the Ft factor. When the Use Ft check box is cleared for the Simple Weighted or Simple End Point model, this is equal to the Uncorrected LMTD.

Detailed Performance UA Curvature Error

The LMTD is ordinarily calculated using constant heat capacity. An LMTD can also be calculated using linear heat capacity. In either case, a different UA is predicted. The UA Curvature Error reflects the difference between these UAs.

Hot Pinch Temperature

The hot stream temperature at the minimum approach.

Cold Pinch Temperature

The cold stream temperature at the minimum approach.

Ft Factor

The LMTD (log mean temperature difference) correction factor, Ft, is calculated as a function of the Number of Shell Passes and the temperature approaches. For a counter-current Heat Exchanger, Ft is 1.0. When the Use Ft check box is cleared, this appears as .

Uncorrected LMTD

Applicable only for the Simple Weighted or Simple End Point models. The LMTD is calculated in terms of the temperature approaches (terminal temperature differences) in the exchanger, using the Equation (1). When the Use Ft check box is cleared, this appears as .

The Uncorrected LMTD equation is as follows:

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(1) where: ∆T1 = Thot, out - Tcold, in ∆T2 = Thot, in - Tcold, out

Plots Page You can plot curves for the hot and/or cold fluid. Use the Plot check boxes to specify which side(s) of the exchanger should be plotted. Note: You can modify the appearance of the plot via the Graph Control property view.

The following default variables can be plotted along either the X or Y-axis: l

Temperature

l

UA

l

Delta T

l

Enthalpy

l

Pressure

l

Heat Flow

Select the combination from the Plot Type drop-down list. To plot other available variables, you need to add them on the Setup page. Once the variables are added, they are available in the X and Y drop-down lists.

Tables Page On the Tables page, you can view (default variables) interval temperature, pressure, heat flow, enthalpy, UA, and vapor fraction for each side of the Exchanger in a tabular format. Select either the Shell Side or Tube Side radio button. To view other available variables, you need to add them on the Setup page. Variables are displayed based on Phase Viewing Options selected.

Setup Page The Setup page allows you to filter and add variables to be viewed on the Plots and Tables pages. The variables that are listed in the Selected Viewing Variables group are available in the X and Y drop down list for plotting on the Plots page. The variables are also available for tabular plot results on the Tables page based on the Phase Viewing Options selected.

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Error Msg Page The Error Msg page contains a list of the warning messages on the Heat Exchanger. You cannot add comments to this page. Use it to see if there are any warnings in modeling the Heat Exchanger.

Dynamics Tab The Dynamics tab contains the following pages: l

"Model Page" below

l

Specs

l

"Holdup Page" on page 458

l

Stripchart

Note: If you are working exclusively in Steady State mode, you are not required to change any information on the pages accessible through the Dynamics tab.

Any information specified on the Rating tab also appears in the Dynamics tab.

Model Page In the Model page, you can specify whether HYSYS uses a Basic, Intermediate, or Detailed model.

Basic Model The Model Parameters group contains the following information for the Heat Exchanger unit operation:

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Field

Description

Tube/Shell Volume

The volume of the shell and tube must be specified in the Basic model.

Elevation

The elevation is significant in the calculation of static head around and in the Heat Exchanger.

Overall UA

Product of the Overall Heat Transfer Coefficient and the Total Area available for heat transfer. The Heat Exchanger duty is proportional to the log mean temperature difference, where UA is the proportionality factor. The UA must be specified if the Basic model is used.

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Field

Description

Shell/Tube UA Reference Flow

Since UA depends on flow, these parameters allow you to set a reference point that uses HYSYS to calculate a more realistic UA value. If no reference point is set then UA is fixed. If the UA is specified, the specified UA value does not change during the simulation. The UA value that is used, however, does change if a Reference Flow is specified. Basically, as in most heat transfer correlations, the heat transfer coefficient is proportional to the (mass flow ratio)0.8. The equation below is used to determine the UA used: (1)

Reference flows generally help to stabilize the system when you do shut downs and startups as well. Minimum Flow Scale Factor

The ratio of mass flow at time t to reference mass flow is also known as flow scaled factor. The minimum flow scaled factor is the lowest value which the ratio is anticipated at low flow regions. This value can be expressed in a positive value or negative value. l

A positive value ensures that some heat transfer still takes place at very low flows.

l

A negative value ignores heat transfer at very low flows.

A negative factor is often used in shut downs if you are not interested in the results or run into problems shutting down an exchanger. If the Minimum Flow Scale Factor is specified, Equation (1) uses the

ratio if the ratio is greater than the Min Flow Scale Factor. Otherwise the Min Flow Scale Factor is used. In some cases you can use a negative value for minimum flow scale factor. If you use -0.1, then if the scale factor goes below 0.1, the Minimum Flow Scale Factor uses 0.

The Summary group contains information regarding the duty of the Heat Exchanger shell and tube sides.

Intermediate Model The Intermediate model lets you model the heat exchanger dynamics with a level of fidelity higher than Basic model but lower than the Detailed model. l l

l

l

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One shell pass and one tube pass is assumed. No detailed geometry is required. Instead, you can specify the shell side and tube side heat transfer area. Thermal inertia can be modeled by specifying the tube mass and tube wall heat capacity Zone analysis is supported.

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When you select the Intermediate radio button, you can edit the following information. The Model Data group contains the following information: Field

Description

Tube/Shell Volume

(Required) The volume of the shell and tube must be specified.

Heat Transfer Area

(Required) Tube/shell side heat transfer area must be specified.

Elevation

The elevation is significant in the calculation of static head around and in the Heat Exchanger.

Tube mass

Required

Tube wall Cp

Required

The Model Parameters group contains the local and overall heat transfer coefficients for the Heat Exchanger. Depending on how the Heat Transfer Coefficient Calculator is set on the Parameters page of the Rating tab, the local and overall heat transfer coefficients can either be calculated or specified in the Model Parameters group. HT Coefficient Calculator Setting

Description

Shell & Tube

Overall heat transfer coefficient, U, is calculated using the exchanger rating information.

U Specified

Overall heat transfer coefficient, U, is specified by you.

Detailed Model When you select the Detailed radio button, a summary of the rating information specified on the Rating tab appears. The Model Data group contains the following information:

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Field

Description

Tube/Shell Volume

The volume of the shell and tube is calculated from the Heat Exchanger rating information.

Heat Transfer Area

The heat transfer area is calculated from the Heat Exchanger rating information.

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Field

Description

Elevation

The elevation is significant in the calculation of static head around and in the Heat Exchanger.

Shell/Tube Passes

You can specify the number of tube and shell passes in the shell of the Heat Exchanger. In general, at least 2n tube passes must be specified for every n shell pass. The exception is a counter-current flow Heat Exchanger which has 1 shell pass and one tube pass

Orientation

The orientation may be specified as a vertical or horizontal Heat Exchanger. The orientation of the Heat Exchanger does not impact the steady state solver. However, it used in the dynamic Heat Exchanger in the calculation of liquid level in the shell.

Zones per Shell Pass

Enter the number of zones you would like for one shell pass. The total number of zones in a Heat Exchanger shell is calculated as: (2)

The Model Parameters group contains the local and overall heat transfer coefficients for the Heat Exchanger. Depending on how the Heat Transfer Coefficient Calculator is set on the Parameters page of the Rating tab, the local and overall heat transfer coefficients can either be calculated or specified in the Model Parameters group. HT Coefficient Calculator Setting

Description

Shell & Tube

Overall heat transfer coefficient, U, is calculated using the exchanger rating information.

U Specified

Overall heat transfer coefficient, U, is specified by you.

The Startup Level group appears only if the Heat Exchanger is specified with a single shell and/or tube pass having only one zone. The Startup level cannot be set for multiple shell and/or tube pass exchangers for multiple shell or tube passes. You can specify an initial liquid level percent for the shell or tube holdups. This initial liquid level percent is used only if the simulation case re-initializes.

Specs Page The Specs page contains information regarding the calculation of pressure drop across the Heat Exchanger. Note: The information that appears on the Specs page depends on the model (Basic or Detailed) selected on the Model page.

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Basic Model When you select the Basic model radio button on the Model page, the Specs page opens. The pressure drop across any pass in the Heat Exchanger operation can be determined in one of two ways: l

Specify the pressure drop.

l

Define a pressure flow relation for each pass by specifying a k value.

The following parameters are used to specify the pressure drop for the Heat Exchanger.

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Dynamic Specification

Description

Shell/Tube Delta P

The pressure drop across the Shell/Tube side of the Heat Exchanger may be specified (check box active) of calculated (check box inactive).

k

Activate this option if to have the Pressure Flow k values used in the calculation of pressure drop.

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Dynamic Specification

Description

k Reference Flow

If the pressure flow option is chosen the k value is calculated based on two criteria. If the flow of the system is larger than the k Reference Flow, the k value remains unchanged. If the flow of the system is smaller than the k Reference Flow, the k value is given by: (1) where: Factor = value is determined by HYSYS internally to take into consideration the flow and pressure drop relationship at low flow regions. At low flow range, it is recommended that the k reference flow is taken as 40% of steady state design flow for better pressure flow stability. The Factor involved in the equation above is given by: (2) bounded between 0.001 and 1. Next, the kused is damped to avoid oscillations. If we consider the damping as a first order filtering operation, the way to update these kused values is, assuming continuous time: (3) where τ is the filter time constant. In discrete time, we approximate the derivative as: (4) with h the integrating step. So we come out with the damping equation in its familiar form: (5) where α =θ / (1+θ) θ= τ / h An instantaneous update corresponds to θ = 0 and a very slow update to a large θ, so 0 < α < 1. For this application, we have selected α = 0.8.

Effectively, the k Reference Flow results in a more linear relationship between flow and pressure drop, and this is used to increase model stability during startup and shutdown where the flows are low. Use the Calculate k button to calculate a k value based on the Delta P and k Reference flow. Make sure that there is a non-zero pressure drop across the Heat Exchanger before you click the Calculate k button.

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Detailed Model When you select the Basic model radio button on the Model page, the Specs page appears. The following parameters are used to specify the pressure drop for the Heat Exchanger. Dynamic Specification

Description

Pressure Flow k

The k-value defines the relationship between the flow through the shell or tube holdup and the pressure of the surrounding streams. You can either specify the k-value or have it calculated from the stream conditions surrounding the Heat Exchanger. You can “size” the exchanger with a k-value by clicking the Calculate K’s button. Ensure that there is a non-zero pressure drop across the Heat Exchanger before the Calculate k button is clicked.

Pressure Flow Option

Activate this option to have the Pressure Flow k values used in the calculation of pressure drop. If the Pressure Flow option is selected, the Shell/Tube Delta P calculator must also be set to non specified.

Shell/Tube Delta P

The pressure drop across the Shell/Tube side of the Heat Exchanger may be specified or calculated.

Shell/Tube Delta P Calculator

The Shell/Tube Delta P calculator allows you to either specify or calculate the shell/tube pressure drop across the Heat Exchanger. Specify the cell with one of the following options: l

Shell & Tube Delta P Calculator. The pressure drop is calculated using the Heat Exchanger rating information and correlations.

l

User specified. The pressure drop is specified by you.

l

Not specified. This option is only applicable in Dynamic mode. Pressure drop across the Heat Exchanger is calculated from a pressure flow relationship. You must specify a k-value and activate the Pressure Flow option to use this calculator.

Click the K Summary button to open the Detailed Heat Model Properties property view.

Holdup Page The Holdup page contains information regarding the shell and tube holdup properties, composition, and amount.

Basic Model When you select the Basic model radio button on the Model page, the Holdup page appears. The Shell Holdup group and Tube Holdup group contain information regarding the shell and tube side holdup parameters.

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Detailed Model When you select the Detailed model radio button on the Model page, the Holdup page includes the following: l

l

The Overall Holdup Details group contains information regarding the shell and tube side holdup parameters. The Individual Zone Holdups group contains detailed holdup properties for every layer in each zone of the Heat Exchanger unit operation. In order to view the advanced properties for individual holdups, you must first choose the individual holdup.

To choose individual holdups, you must specify the Zone and Layer in the corresponding drop-down lists.

Stripchart Page The Stripchart page allows you to select and create default strip charts containing various variable associated to the operation.

Rigorous Shell&Tube Tab The Rigorous Shell&Tube tab of the Heat Exchanger contains the following pages: l

Application

l

Exchanger

l

Process

l

Property Ranges

l

Results Summary

l

Setting Plan

l

Tube Layout

l

Profiles

l

Fouling

You can use the Import - Export buttons to use data saved in .edr file format from the Aspen Exchanger Design and Rating program. The View EDR Browser button lets you use the Exchanger Design and Rating program interface to access advanced settings for the model parameters.

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Notes: l

When you click the View EDR Browser button and enter the Exchanger Details form, on the Geometry Summary page, if the Use existing layout option is selected, this indicates that you want to retain your current geometry settings; as a result, no changes are made to the geometry based on any updates or changes you make. Select the New (optimum) layout option if you want to view changes to the geometry.

l

If there are two liquid phases, HYSYS sometimes premixes properties before sending them to EDR. As a result, two liquid phases may not appear in the EDR Properties table in instances where two phases would be expected.

Specifying Application Information for Rigorous Shell&Tube To specify application information for a Rigorous Shell&Tube Heat Exchanger: 1. Select the Rigorous Shell&Tube tab | Application page. 2. From the Hot Fluid Allocation drop-down list, select one of the following options: o

Not Specified: Shell&Tube provides a guess regarding the most appropriate value and issues a warning indicating the level of confidence in this guess.

o

Shell Side: Select this option if the shell side of the exchanger contains the hot stream.

o

Tube Side: Select this option if the tube side of the exchanger contains the hot stream. Note: It is strongly recommended that you specify this information in all calculation modes. If you are Simulating or Rating an existing exchanger, and you get this item wrong, the program results may be of little value. If you are Designing an exchanger and are unsure which is the best option, we recommend that you try both Shell Side and Tube Side and assess which option gives the best design. Allocation of a stream to the shell side or tube side is influenced by factors of safety, reliability, company practice, maintenance requirements and capital cost. Some general guidelines are:

460

o

Hazardous fluids should not go on the shell side of exchangers with expansion bellows or with P or W type rear end heads.

o

Heavily fouling fluids go by preference on the tube side, which is much easier to clean.

o

Fluids that need to be in contact with expensive materials go by preference on the tube side.

o

High pressure fluids go by preference on the tube side.

o

Fluids with a high volume flow rate go by preference on the shell side, which offers more geometrical options to avoid excessive pressure drop than the tube side.

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3. From the Calculation method drop-down list, select one of the following options: o

Set Default

o

Advanced method: The Advanced method defines a set of physical locations within the exchanger and calculates the state (enthalpy and pressure) of the shell side stream and all the tube side passes at that point. Endspaces are dealt with explicitly, and in other points of detail approximation needed in the Standard method are avoided. The Advanced method is available in all calculation modes: Design, Rating, Simulation, and Maximum Fouling. It is available for most shell types; the exceptions are Kettles, Double pipes and Flooded evaporators. The Advanced method is the only available method for some new options, such as variable baffle pitch. The options for Convergence algorithm, Tolerances, and Number of iterations are only available for the Advanced method in Shell&Tube. Other Advanced method options let the calculation grid resolution be selected, as Low, Medium, High, or Very high. This changes the number of calculation points. The actual number of points cannot be set explicitly. It depends on the complexity.

o

Standard method: The Standard method is based on defining a set of shell side enthalpy/pressure points, and then determining their location, together with a consistent set of tube side points. Corrections are made to allow for endspaces in baffled exchangers, where shell side mass fluxes differ from those in the standard baffle space.

Note: The calculation methods will normally provide very similar results, but in exchangers where end-spaces occupy a significant fraction of the tube length, the Advanced method is likely to give better results.

4. From the Condenser Type drop-down list, select one of the following options. Most condenser types have the vapor and condensate flow in the same direction. o

Set Default

o

Normal

o

Knockback reflux: The Knockback (reflux) condenser, which is often used to separate high and low boilers with minimal subcooling, has vapor entering the bottom of the unit with condensate falling back against the incoming vapor. With this type of condenser, you should consider using the differential condensation option if the program calculates the condensation curve.

5. From the Vaporizer Type drop-down list, select one of the following options. The Vaporizer Type identifies the various equipment types, each of which requires special design considerations.

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461

o

Set Default

o

Flooded evaporator or kettle

o

Thermosiphon

o

Forced circulation

o

Falling film evaporator

6. From the Calculation Options drop-down list, select one of the following options: o

Simulation Mode: This is the default mode.

o

Find Fouling: The Find Fouling calculation mode provides the ability to estimate fouling factors given a set of process conditions. Specify calculation options and view results on the Find Fouling page. Notes: o

When you switch from Simulation Mode to Find Fouling, the Heat Exchanger may be underspecified due to differing requirements for the calculation modes. In this case, you must manually specify outlet stream data to obtain an accurate heat balance in order for the Heat Exchanger to solve.

o

When you switch from Find Fouling to Simulation Mode, the Heat Exchanger may be over-specified due to differing requirements for the calculation modes. In this case, you must manually remove the extraneous specifications in order for the Heat Exchanger to solve.

Specifying Exchanger Information for Rigorous Shell&Tube To specify exchanger information for a Rigorous Shell&Tube Heat Exchanger: 1. Select the Rigorous Shell&Tube tab | Exchanger page. 2. In the TEMA Type group, you can specify the information described in the table below. TEMA is the U.S. Tubular Exchanger Manufacturers' Association, which produces a regularly updated set of standards, relating (primarily) to mechanical design considerations for shell and tube heat exchangers. Front and rear end heads for a shell and tube exchanger come in a range of types identified by a letter, designated by TEMA. The choice of front and rear end head is primarily a mechanical design consideration. It affects whether the bundle (and tubesheet) are fixed or can be withdrawn from the shell for cleaning, and whether there is simple access to the tubes for cleaning.  It can also impact the thermal design, insofar as it affects the clearance between the bundle and the shell.

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16 Heat Exchanger

Field

Description

Front End Head Type

The front end is the tube side inlet end.  It is also the tube side outlet end, if there is an even number of tube side passes.  Since the front end always has a nozzle, it is also referred to as the stationary head. o

Set default

o

A - channel &removable cover: Fixed tubesheet; access to tubes for cleaning.

o

B - bonnet bolted or integral with tubesheet: Fixed tubesheet

o

C - integral tubesheet & removable bundle: Channel integral with tubesheet, removable cover; access to tubes for cleaning.

o

N - integral tubesheet & nonremovable bundle: Channel integral with shell and (fixed) tubesheet. Removable cover for access to tubes.

o

D - high pressure enclosure: High pressure version of C.

463

Field

Description

Shell T- The shell type determines the shell side flow arrangement and the ype place of the shell side nozzles. The default is type E (except for K type shell side pool boilers).

464

o

Set default

o

E - one pass shell: Generally provides the best heat transfer but also the highest shell side pressure drop. Used for temperature cross applications where pure counter current flow is needed.

o

F - two pass shell with long. baffle: This two pass shell can enhance shell side heat transfer and also maintain counter current flow if needed for temperature cross applications.

o

G - split flow: Enhances the shell side film coefficient for a given exchanger size.

o

H - double split flow: A good choice for low shell side operating pressure applications. Pressure drop can be minimized. Used for shell side thermosiphons.

o

J - divided flow (nozzles: 1 in, 2 out): Used often for shell side condensers. With two inlet vapor nozzles on top and the single condensate nozzle on bottom, vibration problems can be avoided.

o

I - divided flow (nozzles: 2 in, 1 out)

o

K - kettle: Used for kettle type shell side reboilers.

o

X -crossflow: Good for low shell side pressure applications. Unit is provided with support plates that provide pure cross flow through the bundle. Multiple inlet and outlet nozzles or flow distributors are recommended to assure full distribution of the flow along the bundle.

o

Multi-tube hairpin:

o

Double pipe:

16 Heat Exchanger

Field

Description

Rear End Head Type

Rear end heads do not have nozzles if there are an even number of shell side of tube side passes. L, M, and N have fixed tubesheets. Other tubesheets can be withdrawn through the shell with the bundle. o

Set default

o

L - removable channel with flat cover: Fixed tubesheet, like A type.

o

M - bonnet: Fixed tubesheet, like B type.

o

N - integral channel with flat cover: Fixed tubesheet, as N type stationary head.

o

P - outside packed floating head: Removable tubesheet. External packing. Cover for access to tubes

o

S - floating head with backing device: Removable tubesheet. Internal packing. No cover for access to tubes.

o

T - pull through floating head: Removable tubesheet. Pull through floating head; no packing.

o

U - U-tube bundle: Shell closed at this end, but shape of end is not defined.

o

W - floating head with lantern ring: Externally sealed floating tubesheet. Do not use with hazardous fluids.

Certain Front/Rear head combinations are customarily used together.

3. In the Tubes group, you can specify the information described in the table below.

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Field

Description

Tube OD

You can specify any size for the tube outside diameter. However, the correlations have been developed based on tube sizes from 10 to 50 mm (0.375 to 2.0 inch). The most common sizes in the U.S. are 0.625, 0.75, and 1.0 inch. In many other countries, the most common sizes are 16, 20, and 25 mm. If you do not know which tube diameter to use, start with a 20 mm diameter (ISO standards) or a 0.75 inch diameter (American standards). This size is readily available in nearly all tube materials. The primary exception is graphite, which is made in 32, 37, and 50 mm, or 1.25, 1.5, and 2 inch outside diameters. For integral low fin tubes, the tube outside diameter is the outside diameter of the fin.

Tube Length

Tube Length (straight)

Effective Tube Count

The tube count is the total number of tubes in an exchanger. For this purpose, a U-tube is counted as two-tubes, so the tube count still gives the total number of holes in the tubesheet. Since tubes are laid out in a regular array, calculating the approximate number of tubes in an exchanger is relatively straightforward. Allowance can be made for tubes removed adjacent to nozzles, pass partition lanes, and so on. An exact tube count, however, can only be performed when the position of every tube in the exchanger is fixed, and allowance has to be made for tubes removed to give space for tie-rods. Shell&Tube uses an approximate tube count in Design mode but performs an exact tube count in all other modes. The diagram on the Shell&Tube tab | Tube Layout page shows an exact tube count, and, if desired, you can modify this to correspond exactly to the exchanger that you are modeling. You can do this by making sure that all the Bundle Layout input items are set correctly, and then, if necessary, making additional revisions by editing the diagram, by adding or deleting tubes, or moving tubepass regions. Alternatively, you can explicitly specify a tube count in the input, and this value will be used in the heat transfer and pressure drop calculations. If your specified value differs from the calculated value, a warning appears. As long as the Tube Layout calculated by Shell and Tube roughly matches your exchanger, using such a specified tube count is a very good approximation and eliminates the need for detailed editing of the diagram.

Tube Thickness Tubes Pitch Tube Pattern

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16 Heat Exchanger

4. In the Shell group, you can specify the information described in the table below. Field

Description

Orientation

Select one of the following options:

Exchangers in Parallel

Exchangers in Series

o

Set default

o

Horizontal

o

Vertical

o

In Rating/Checking, Simulation, or Maximum Fouling modes, specify the number of shells in parallel.

o

For all modes, the default is 1 exchanger (shell) in parallel, and the maximum number allowed is 50.

o

In order to specify a hairpin multi-tube exchanger or a hairpin-type double pipe exchanger (M or D type), where one exchanger consists of two shells, specify the number of Exchangers in parallel.  The number of tube side passes per shell in such exchangers is 1.

o

In Design mode, values can be set for Minimum and Maximum Number of Shells in Parallel.

o

In Rating/Checking, Simulation, or Maximum Fouling modes, specify the number of shells (or sets of parallel shells) in series.

o

The default is one exchanger (shell) in series.

o

For all modes, the maximum number is 12 for E, I, and J shells or 6 for D, F, G, H and M shells. Only one shell in series is permitted for K and X shells.

o

In order to specify a hairpin multi-tube exchanger or a hairpin-type double pipe exchanger (M or D type), where one exchanger consists of two shells in series, specify the number of Exchangers in series.  The number of tube side passes per shell in such exchangers is 1.

o

In Design mode, values can be set for Minimum and Maximum Number of Shells in Series.

Tubeside Passes

Notes: l

Click the Transfer Geometry from HYSYS button to use the settings from the simple rating model.

l

Click the Transfer UA to End Point button to send the effective UA to the heat exchanger end point model.

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467

Specifying Process Information for Rigorous Shell&Tube To specify process information for a Rigorous Shell&Tube Heat Exchanger: 1. Select the Rigorous Shell&Tube tab | Process page. 2. View or edit the process information for the streams: o

Total Mass Flow: You should normally specify the total flow rates for the hot and cold side streams. You can leave this field blank if the stream inlet and outlet conditions are specified and the heat load is known, either because it has been specified or can be deduced from the implicit heat load of the other stream. In the special variant of Simulation, where the flowrate is to be calculated, any value specified in this field is treated as an initial estimate. This type of Simulation is used in thermosiphon reboilers, where the flowrate of the thermosiphon stream must be calculated, or for simulating condensing steam where the flowrate adjusts itself to give complete condensation to liquid water, according the heating requirements of the cold stream.

468

o

Inlet Temperature

o

Estimated Outlet Temperature

o

Inlet Mass Quality

o

Inlet Pressure: This is a mandatory specification.

o

Estimated Pressure Drop: You can specify an estimated pressure drop for each side. This can be important in low pressure and vacuum applications, where outlet pressures can significantly affect outlet pressures. In other cases, the default value is usually acceptable. o

You can specify an outlet pressure as an alternative to specifying the Estimated Pressure Drop. One value will be calculated from the other value, once the Inlet Pressure (mandatory) is specified.

o

If you specify neither outlet pressure nor pressure drop, defaults are calculated using the Allowable Pressure Drop.

o

The exchanger inlet and outlet pressure are used to set defaults for the range of pressures at which physical properties are calculated. If you do not know the pressure drop, a higher rather than a lower estimate may be appropriate. If the pressure range is large, additional default pressure levels for properties are defaulted. You can manually add more pressure levels for properties, but this is rarely necessary.

o

In the unusual case of a vertical exchanger with liquid down flow, gravitational pressure increases can exceed

16 Heat Exchanger

frictional losses. The outlet pressure would be above the inlet pressure, and the pressure change would be negative. Negative pressure change inputs are permissible; a warning message appears, but you can ignore the message if the described case occurs. o

Allowable Pressure Drop: If you specify neither outlet pressure nor pressure drop, defaults are calculated using the Allowable Pressure Drop.

o

Fouling Resistance: Specify the process-side fouling resistance. This resistance is assumed to apply wherever the process fluid flows, in convection banks or the firebox. This is required for the calculation of the effective (dirty) heat transfer coefficient. The fouling resistance is based on the inside surface area of the tubes. If you leave this field blank, the surface of the tubes is assumed to be clean, so that the Fouling Resistance is 0.

Specifying Property Ranges for Rigorous Shell&Tube Numerical ranges for the shell side and the tube side appear on the Property Ranges page. To specify property ranges for a Rigorous Shell&Tube Heat Exchanger: 1. Select the Rigorous Shell&Tube tab | Property Ranges page. 2. Specify the information described in the table below.

16 Heat Exchanger

Field

Description

Temp. Range (Start)

One of two points defining the range of temperatures included in the property table. This value does not necessarily need to be the lower temperature. Expanding the temperature range may resolve properties errors preventing the unit operation from successfully solving.

Temp. Range (End)

One of two points defining the range of temperatures included in the property table. This value does not necessarily need to be the higher temperature. Expanding the temperature range may resolve properties errors preventing the unit operation from successfully solving.

Number of Temperatures

Specify the number of temperatures points in the property table. The range of input is between 2 and 24. A higher number enhances the resolution of properties in the property table and can improve the accuracy of the calculations. The program determines the spacing between temperatures.

469

Field

Description

No. of Pressure Levels

Specify the number of pressure points to be transferred to EDR. The range of input is between 1 and 5. A higher number enhances the resolution of properties transferred and can improve the accuracy of the calculations.

Pressure Level 1 - 5

You can specify the pressures in the property table. You can manually control spacing for pressures sent to the property table. Modifying these values can improve calculation accuracy, especially for exchangers experiencing significant pressure drops. Pressures should be specified in descending order; Pressure Level 1 should be highest pressure.

Viewing Results Summary for Rigorous Shell&Tube The following results appear on the Rigorous Shell&Tube tab | Results Summary page: l

Duty

l

Effective Surface Area

l

Effective MTD

l

Overall Clean Coeff

l

Overall Dirty Coeff

l

Vibration Problem

l

RhoV2 Problem

and for Shell-Side and Tube-Side: l

Film Coefficient

l

Calculated Pressure Drop

l

Allowable Pressure Drop

l

Velocity (Highest)

Viewing a Setting Plan for Rigorous Shell&Tube The Rigorous Shell&Tube tab | Setting Plan page lets you view a dimensional drawing of the heat exchanger. The image below shows a sample of a display. Click View EDR Browser and navigate to the Mechanical Summary | Setting Plan and Tubesheet Layout sheet for a more detailed and configurable view of the mechanical layout of the exchanger.

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16 Heat Exchanger

Viewing Tube Layout Information for Rigorous Shell&Tube The following is an example of the information on the Rigorous Shell&Tube tab | Tube Layout page of the Heat Exchanger.

Right-click the display to show the diagram configuration and printing options.

16 Heat Exchanger

471

Viewing Rigorous Shell&Tube Profiles Information The following is an example of the display for the Rigorous Shell&Tube tab | Profiles page of the Heat Exchanger.

Right-click the plot and select Properties to access the Plot properties dialog box for plot customization.

Specifying Find Fouling Calculation Options for Rigorous Shell&Tube The Find Fouling calculation mode provides the ability to estimate fouling factors given a set of process conditions. You can specify calculation options and view results on the Rigorous Shell&Tube tab | Find Fouling page. Notes: l

When you switch from Simulation Mode to Find Fouling, the Heat Exchanger may be underspecified due to differing requirements for the calculation modes. In this case, you must manually specify outlet stream data to obtain an accurate heat balance in order for the Heat Exchanger to solve.

l

When you switch from Find Fouling to Simulation Mode, the Heat Exchanger may be over-specified due to differing requirements for the calculation modes. In this case, you must manually remove the extraneous specifications in order for the Heat Exchanger to solve.

To specify Find Fouling calculation options:

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16 Heat Exchanger

1. On the Rigorous Shell&Tube tab | Application page of the Heat Exchanger, from the Calculation Options drop-down list, select Find Fouling. 2. Select the Rigorous Shell&Tube tab | Find Fouling page. 3. From the Fouling Calculation Options drop-down list, select one of the following options: o

Set default

o

Adjust hot side fouling only: Only adjusts the hot side fouling and retains your specifications for the cold side.

o

Adjust cold side fouling only: Only adjusts the cold side fouling and retains your specifications for the hot side.

o

Adjust both sides based on fouling input: Adjusts the fouling based on the ratio between the hot and cold sides currently specified.

o

Adjust both sides using equal fouling: Attempts to set the fouling resistances to be equal.

4. You can adjust the following values for both the Hot side and Cold side. If you edit any of these values, the flowsheet re-solves. o

Fouling Layer Thickness

o

Fouling Thermal Conductivity

o

Fouling Resistance

5. In the Fouling Calculation Results group, you can view the following results:

16 Heat Exchanger

o

Overall fouled

o

Overall clean

o

Tube side film

o

Tube side fouling

o

Tube wall

o

Outside fouling

o

Outside film

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16 Heat Exchanger

17 Liquefied Natural Gas (LNG) Exchanger

The LNG (Liquefied Natural Gas) exchanger model solves heat and material balances for multi-stream heat exchangers and heat exchanger networks. The solution method can handle a wide variety of specified and unknown variables. For the overall exchanger, you can specify various parameters, including heat leak/heat loss, UA or temperature approaches. Two solution approaches are employed; in the case of a single unknown, the solution is calculated directly from an energy balance. In the case of multiple unknowns, an iterative approach is used that attempts to determine the solution that satisfies not only the energy balance, but also any constraints, such as temperature approach or UA. Note: The LNG allows for multiple streams, while the heat exchanger allows only one hot side stream and one cold side stream.

The dynamic LNG exchanger model performs energy and material balances for a rating plate-fin type heat exchanger model. The dynamic LNG is characterized as having a high area density, typically allowing heat exchange even when low temperature gradients and heat transfer coefficients exist between layers in the LNG operation. Some of the major features in the dynamic LNG operation include: l

l

l

A pressure-flow specification option which realistically models flow through the LNG operation according to the pressure network of the plant. Possible flow reversal situations can therefore be modeled. A dynamic model, which accounts for energy holdup in the metal walls and material stream layers. Heat transfer between layers depends on the arrangement of streams, metal properties, and fin and bypass efficiencies. Versatile connections between layers in a single or multiple zone LNG operation. It is possible to model cross and counter flow, and multipass flow configurations within the LNG operation.

17 Liquefied Natural Gas (LNG) Exchanger

475

l

A heat loss model, which accounts for the convective and conductive heat transfer that occurs across the wall of the LNG operation.

Theory Heat Transfer The LNG calculations are based on energy balances for the hot and cold fluids. The following general relation applies any layer in the LNG unit operation. (1)

where:  M = fluid flow rate in the layer ρ = density H = enthalpy Qinternal = heat gained from the surrounding layers Qexternal = heat gained from the external surroundings V = volume shell or tube holdup LNG dynamics constructs and builds the conductive heat transfer equations into the dynamic solvers to account for the metal thermal inertia for both plates and fins. (2)

(3) where: Mw = wall mass Cpw = wall heat capacity Tw = average wall temperature t = time Qin/Qout = the heat transfer to/from the wall Qcond = conductive heat transfer k = metal thermal conductivity x = wall thickness A = heat transfer area Tw1 and Tw2 = temperature of the two sides of the wall

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17 Liquefied Natural Gas (LNG) Exchanger

Pressure Drop The pressure drop across any layer in the LNG unit operation can be determined in one of two ways: l

Specify the pressure drop.

l

Define a pressure flow relation for each layer by specifying a k-value.

If the pressure flow option is chosen for pressure drop determination in the LNG, a k value is used to relate the frictional pressure loss and flow through the exchanger. This relation is similar to the general valve equation: (1) This general flow equation uses the pressure drop across the heat exchanger without any static head contributions. The quantity, P1 - P2, is defined as the frictional pressure loss which is used to “size” the LNG with a k-value.

Convective (U) & Overall (UA) Heat Transfer Coefficients It is important to understand the differences between steady state and dynamics LNG models. The Steady State model is based on heat balances, and a number of specifications related to temperatures and enthalpy. In this model, the UA values are calculated based on heat curves. Whereas, the dynamic LNG model is a rating model, which means the outlet streams are determined by the physical layout of the exchanger. Note: Several of the pages in the LNG property view indicate whether the information applies to steady state or dynamics.

In steady state the order of the streams given to the LNG is not important but in the dynamics rating model the ordering of streams inside layers in each zone is an important consideration. The U value on the dynamics page of LNG refers to the convective heat transfer coefficient for that stream in contact with the metal layer. For convenience, you can also specify a UA value in Dynamic mode for each layer, and it is important to note that this value is not an overall UA value as it is in steady state but accounts merely for the convective heat transfer of the particular stream in question with its immediate surroundings. These UA values are thus not calculated in the same way as in Steady State mode. In Dynamic mode the U and UA value refers to the convective heat transfer (only) contribution between a stream and the metal that immediately surrounds it. The overall duty of each stream, in dynamic mode, is influenced by the presence of metal fins, fin efficiencies, direct heat flow between metal layers, and other factors, as it would be in a real plate-fin exchanger.

17 Liquefied Natural Gas (LNG) Exchanger

477

Note: If you specify the convective UA values in Dynamic mode, than the size and metal holdup of the LNG are still considered.

Ideally in Dynamic mode the convective heat transfer coefficient, U, for each stream is specified. An initial value can be estimated from correlations commonly available in the literature or from the steady state UA values. The values specified can be manipulated by a spread sheet if desired. If the shut down and start up of the LNG is to be modeled, then the U flow scaled calculator should be selected on the Heat Transfer page, of the Rating tab, as it correctly scales the U values based on the flow. If the streams in the rating model are properly laid to optimize heat transfer (in other words, arranged in the fashion hot-cold-hot-cold and not hot-hot-coldcold on the Model page of the Dynamics tab), and the metal resistance is not significant and significant phase change is not taking place, then the UA values reported by steady state approximates the convective UA values that can be specified in Dynamic mode for the same results.

Dynamic Specifications The following table lists the minimum dynamic specifications required for the LNG unit operation to solve: Specification

Description

Zone Sizing

The dimensions of each zone in the LNG operation must be specified. All information in the Sizing page of the Rating tab must be completed. You can modify the number of zones in the Model page of the Dynamics tab.

Layer Rating

The individual layer rating parameters for each zone must be specified. All information on the Layers page of the Rating tab must be completed.

Heat Transfer

Specify an Overall Heat Transfer Coefficient, U, or Overall UA. These specifications can be made on the Heat Transfer page of the Rating tab.

Pressure Drop

Either specify an Overall Delta P or an Overall K-value for the LNG. Specify the Pressure Drop calculation method on the Specs page of the Dynamics tab.

Layer Connections

478

Every layer in each zone must be specified with one feed and one product. Complete the Connections group for each zone on the Model page of the Dynamics tab.

17 Liquefied Natural Gas (LNG) Exchanger

LNG Property View On the LNG property view, select the Ignored check box ignore to the LNG during calculations. HYSYS completely disregards the operation (and cannot calculate the outlet stream) until you restore it to an active state by clearing the check box.

Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

Specs

l

User Variables

l

Notes

Connections Page For each exchanger side: l

An inlet stream and outlet stream are required.

l

A Pressure Drop is required.

l

The Hot/Cold designation can be specified. This is used as an estimate for calculations and is also used for drawing the PFD. If a designated hot pass is actually cold (or vice versa), the operation still solves properly. The actual Hot/Cold designation (as determined by the LNG) can be found on the Side Results page. Note: Any number of Sides can be added simply by clicking the Add Side button. To remove a side, select the side to be deleted and click the Delete Side button.

l

The main flowsheet is the default shown in the flowsheet column.

The LNG status appears on the bottom of the property view, regardless of which page is currently shown. It displays an appropriate message such as Under Specified, Not Converged, or OK.

Parameters Page On the Parameters page, you have access to the exchanger parameters, heat leak/loss options, the exchanger details, and the solving behavior.

17 Liquefied Natural Gas (LNG) Exchanger

479

Exchanger Parameters Group

Parameters

Description

Rating Method

Select one of the following options:

Shell Passes

l

Simple End Point

l

Simple Weighted: For the Simple Weighted method, the heating curves are broken into intervals, which then exchange energy individually. An LMTD and UA are calculated for each interval in the heat curve and summed to calculate the overall exchanger UA.

l

EDR - CoilWound: When you switch to this rating method, the LNG unit operation uses EDR CoilWound rigorous calculations, and the pages on the EDR CoilWound tab are enabled. This differs from the Wound Coil tab, which uses a lumped sum heat calculation; instead, EDR - Coil Wound calculates the heat load rigorously based on geometry.

l

EDR PlateFin

You have the option of having HYSYS perform the calculations for Counter Current (ideal with Ft = 1.0) operation or for a specified number of shell passes. You can specify the number of shell passes to be any integer between 1 and 7.

Heat Leak/Loss Group By default, the None radio button is selected. The other two radio buttons incorporate heat loss/heat leak: Radio Button

Description

Extremes

The heat loss and heat leak are considered to occur only at the end points (inlets and outlets) and are applied to the Hot and Cold Equilibrium streams.

Proportional

The heat loss and heat leak are applied over each interval.

Note: The Heat Leak/Loss group is available only when the Rating Method is Weighted.

Exchange Details Group For each side, the following parameters can be specified:

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17 Liquefied Natural Gas (LNG) Exchanger

Parameter

Description

Intervals

The number of intervals, applicable only to the Weighted Rating Method, can be specified. For non-linear temperature profiles, more intervals are necessary.

Dew/Bubble Point

Select this check box to add a point to the Heat curve for a phase change. Temperature is on the y-axis, and heat flow is on the x-axis

Equilibrate

All sides that are checked comes to thermal equilibrium before entering into the UA and LMTD calculations. If only one hot stream or cold stream is checked, then that stream is by definition in equilibrium with itself and the results are not affected. If two or more hot or cold streams are checked, then the effective driving force is reduced. All unchecked streams enter the composite curve at their respective temperatures.

Step Type

There are three choices, which are described below.

Pressure Profile

l

Equal Enthalpy. All intervals have an equal enthalpy change.

l

Equal Temperature. All intervals have an equal temperature change.

l

Auto Interval. HYSYS determines where points should be added to the heat curve. This is designed to minimize the error, using the least amount of intervals.

The Pressure Profile is updated in the outer iteration loop, using one of the following methods described below. l

Constant dPdH. Maintains constant dPdH during update.

l

Constant dPdUA. Maintains constant dPdUA during update.

l

Constant dPdA. Maintains constant dPdA during update. This is not currently applicable to the LNG Exchanger in steady state, as the area is not predicted.

l

Inlet Pressure. The pressure is constant and equal to the inlet pressure.

l

Outlet Pressure. The pressure is constant and equal to the pressure.

Specs Page On the Specs page, there are three groups which organize the various specification and solver information.

Solver Group The Solver group includes the solving parameters used for LNGs:

17 Liquefied Natural Gas (LNG) Exchanger

481

Solver Parameter

Specification Description

Tolerance

You can set the calculation error tolerance.

Current Error

When the current error is less than the calculation tolerance, the solution is considered to have converged.

Maximum Iterations

You can specify the maximum number of iteration before HYSYS stops the calculations.

Iteration

The current iteration of the outer loop appears. In the outer loop, the heat curve is updated and the property package calculations are performed. Non-rigorous property calculations are performed in the inner loop. Any constraints are also considered in the inner loop.

Unknown Variables

Displays the number of unknown variables in the LNG.

Constraints

Displays the number specifications you have placed on the LNG.

Degrees of Freedom

Displays the number of Degrees of Freedom on the LNG. To help reach the desired solution, unknown parameters (flows, temperatures) can be manipulated in the attached streams. Each parameter specification reduces the Degrees of Freedom by one. The number of Constraints (specs) must equal the number of Unknown Variables. When this is the case, the Degrees of Freedom is equal to zero, and a solution is calculated.

Unknown Variables Group HYSYS lists all unknown LNG variables according to your specifications. Once the unit has solved, the values of these variables appear.

Specifications Group Notice the Heat Balance (specified at 0 kJ/h) is considered to be a constraint. This is a Duty Error spec; if you turn it off, the heat equation cannot balance. Without the Heat Balance spec, you can, for example, completely specify all four heat exchanger streams, and have HYSYS calculate the Heat Balance error, which would be displayed in the Current Value column of the Specifications group. Note: The Heat Balance specification is a default LNG specification that must be active for the heat equation to balance.

You can view or delete selected specifications by using the buttons that align the right of the group. A specification property view appears automatically each time a new spec is created via the Add button.

Specification Property Views Each specification property view has two tabs:

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17 Liquefied Natural Gas (LNG) Exchanger

l

Parameters

l

Summary

The Summary page is used to define whether the specification is Active or an Estimate. The Spec Value is also shown on this page. Note: Information specified on the Summary page of the specification property view also appears in the Specifications group.

   All specifications are one of the following three types: Specification Type

Action

Active

An active specification is one which the convergence algorithm is trying to meet. Notice an active specification always serves as an initial estimate (when the Active check box is selected, HYSYS automatically selects the Estimate check box). An active specification exhausts one degree of freedom. An Active specification is one which the convergence algorithm is trying to meet. Both check boxes are selected for this specification.

Estimate

An estimate is considered an Inactive specification because the convergence algorithm is not trying to satisfy it. To use a specification as an estimate only, clear the Active check box. The value then serves only as an initial estimate for the convergence algorithm. An estimate does not use an available degree of freedom. An Estimate is used as an “initial guess” for the convergence algorithm, and is considered to be an Inactive specification.

Completely Inactive

To disregard the value of a specification entirely during convergence, clear both the Active and Estimate check boxes. By ignoring rather than deleting a specification, it is available if you want to use it later or simply view its current value. A Completely Inactive specification is one which is ignored completely by the convergence algorithm, but can be made Active or an Estimate at a later time.

The specification list allows you to try different combinations of the above three specification types. For example, suppose you have a number of specifications, and you want to determine which ones should be active, which should be estimates and which ones should be ignored altogether. By manipulating the check boxes among various specifications, you can test various combinations of the three types to see their effect on the results. The available specification types are: Specification

Description

Temperature

The temperature of any stream attached to the LNG. The hot or cold inlet equilibrium temperature can also be defined.

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Specification

Description

Delta Temp

The temperature difference at the inlet or outlet between any two streams attached to the LNG. The hot or cold inlet equilibrium temperatures can also be used.

Minimum Approach

The minimum temperature difference between the specified pass and the opposite composite curve. For example, if you select a cold pass, this is the minimum temperature difference between that cold pass and the hot composite curve. l

The Hot Inlet Equilibrium temperature is the temperature of the inlet hot stream minus the heat loss temperature drop.

l

The Cold Inlet Equilibrium temperature is the temperature of the inlet cold stream plus the heat leak temperature rise.

UA

The overall UA (product of overall heat transfer coefficient and heat transfer area).

LMTD

The overall log mean temperature difference. It is calculated in terms of the temperature approaches (terminal temperature differences) in the exchanger. See Equation (1).

Duty

The overall duty, duty error, heat leak or heat loss. The duty error should normally be specified as 0 so that the heat balance is satisfied. The heat leak and heat loss are available as specifications only if Heat Loss/Leak is set to Extremes or Proportional on the Parameters page.

Duty Ratio

A duty ratio can be specified between any two of the following duties: overall, error, heat loss, heat leak or any pass duty.

Flow

The flowrate of any attached stream (molar, mass or liquid volume).

Flow Ratio

The ratio of any two inlet stream flowrates.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Rating Tab Note: While working exclusively in Steady State mode, you are not required to change any information on the pages accessible through this tab.

The Rating tab contains the following pages:

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l

Sizing (dynamics)

l

Layers (dynamics)

l

Heat Transfer (dynamics)

Sizing (dynamics) Page On the Sizing (dynamics) page, you can specify the geometry of each zone in the LNG unit operation. You can partition the exchanger into a number of zones along its length. Each zone features a stacking pattern with one feed and one product connected to each representative layer in the pattern. In practice, a plate-fin heat exchanger may have a repeating pattern of layers in a single exchanger block. A set is defined as a single pattern of layers that are repeated over the height of an exchanger block. Each zone can be characterized with a multiple number of sets each with the same repeating pattern of layers. The figure below displays an LNG exchanger block (zone) with 3 sets, each containing 3 layers:

The Zone Sizing and Configuration group contains information regarding the geometry, heat transfer properties, and configuration of each zone in the LNG

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unit operation. To edit a zone, select the individual zone in Zone group, and make the necessary changes to the other groups. The Zone Geometry group displays the following information regarding the dimensions of each zone: l

Width

l

Length

This length refers to the actual length of the exchanger, which is used for heat transfer. The remainder is taken up by the flow distributors. The flow of material travels in the direction of the length of the exchanger block. The fins within each layer are situated across the width of the exchanger block. The Zone Metal Properties group contains information regarding the metal heat transfer properties: l

Thermal Conductivity

l

Specific Heat Capacity, Cp

l

Density

The Zone Layers group contains the following information regarding the configuration of layers in the zone: l

Number of Layers in a Set

l

Repeated Sets

Layers (dynamic) Page The Layers (dynamics) page contains information regarding the plate and fin geometry: Each of the following plate and fin properties should be specified for every layer in each zone if the LNG operation is to solve:

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Plate and Fin Property

Description

Fin Perforation

The perforation percentage represents the area of perforation relative to the total fin area. Increasing the Fin Perforation decreases the heat transfer area.

Height

The height of the individual layers. This affects the volume of each layer holdup.

Pitch

The pitch is defined as the fin density of each layer. The pitch can be defined as the number of fins per unit width of layer.

Fin thickness

The thickness of the fin in the layer.

17 Liquefied Natural Gas (LNG) Exchanger

Plate and Fin Property

Description

Plate thickness

The thickness of the plate.

Heat Transfer (dynamics) Page The Heat Transfer (dynamics) page displays the heat transfer coefficients associated with the individual layers of the LNG unit operation. You can select internal or external heat transfer by selecting the appropriate Heat Transfer radio button. HYSYS accounts for the heating and cooling of the metal fins and plates in the LNG unit operation. The calculation of heat accumulation in the metal is based on the conductive heat transfer properties, fin efficiencies, and various other correction factors. An initial metal temperature can be specified for each zone in the Initial Metal Temperature field. Since a repeating stacking pattern is used, the top most layer of a set is assumed to exchange heat with the bottom layer of the set above. You can also select the Brazed Aluminum Plate-Fin heat transfer calculation standards by selecting the Calculate fin area using the standards of the Brazed Aluminium Plate-Fin HX Manufacturer’s Association check box. Select the Auto Prevent Temp. Cross check box to enter two parameters for split steps, and prevent the temperature from crossing along the heat transfer passes. Select the Automatically Update k’s check box to automatically update the k’s based on current relationships between P-F flow rates and pressure drops for all the heat transfer layers, making the LNG steam flow rates more stable.

LNG Temperature Crossing Project The LNG Temperature Crossing Project redistributes the zone length fractions among the total flow pass length and multiple zones to prevent the temperature from crossing along the heat transfer passes. It uses a cascade of lumping heat zones to incorporate the distributed systems, and requires at least 10 zones to automatically remove the big temperature wiggle profiles within the flow passes. Under certain conditions, such as zone number and the changes in temperature and flow rates, the original function of Auto Prevent Temp Cross could smooth the small temperature waves. But it also made the dynamic processes unstable. To minimize temperature and flow instability in the LNG dynamic processes: 1. Specify 10 or more heat zones to remove the wiggle temperature profiles.

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2. Select the Automatically Update k’s check box to make the LNG flow rates more stable if your LNG flow rates are not too small. 3. Select the Auto Prevent Temp Cross check box to prevent temperature cross and lessen small temperature waves. 4. Use the following parameters for the Auto Prevent Temperature Crossing: l

Reach small split steps o

l

A smaller value (0.001-1000) helps to prevent small temperature crossing.

Reach even split steps o

A small value (0.1-1000) leads to a quick speed.

Internal Heat Transfer If you select the Internal radio button, the internal heat transfer coefficient associated with each layer appears. Currently, the internal heat transfer coefficient, U, or the overall UA must be specified for the LNG unit operation. HYSYS cannot calculate the heat transfer coefficient from the geometry/configuration of the plates and fins. The Internal Heat Transfer group contains the following parameters: Parameter

Description

U Calculator

The heat transfer calculator currently available in HYSYS are U specified and U flow scaled. If U specified is selected, you must specify the internal heat transfer coefficient, U. Alternatively, you can select U flow scaled calculator and a reference flow rate is used to calculate U. If you are modeling a shut-down or a start-up LNG process, select U flow scaled calculator to correctly scale the U values based on the flow condition.

U

The internal heat transfer coefficient is specified in this cell.

Ref. Flow

The Reference Flow is used to calculate U when the U Flow Scaled calculator is selected.

Min Scale

The minimum scale factor is applied to U by the U Flow Scaled calculator when the flow changes.

Override UA

The overall UA can be specified if the Override UA check box is selected. The specified UA value is used without the consideration or back calculation of the internal heat transfer coefficient, U.

Convective UA

The overall UA is specified in this cell.

External Heat Transfer If you select the External radio button, the overall UA associated with heat loss to the atmosphere appears.

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Like the internal heat transfer coefficients, the external overall UA must be specified. The External Heat Transfer group contains the following parameters: Parameter

Description

External T

The ambient temperature surrounding the plate-fin heat exchanger. This parameter may be specified or can remain at its default value.

UA

The overall UA is specified in this field. The heat gained from the ambient conditions is calculated using the overall UA.

Q1

Q1 is calculated from the overall UA and the ambient temperature. If heat is gained in the holdup, Q1 is positive; if heat is lost, Q1 is negative.

Q fixed

A fixed heat value can be added to each layer in the LNG unit operation. Since Q fixed does not vary, a constant heat source or sink is implied (for example, electrical tracing). If heat is gained in the holdup, Q fixed is positive; if heat is lost, Q fixed is negative.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the LNG unit operation. Note: The PF Specs page is relevant to dynamics cases only.

Performance Tab The Performance tab contains detail performance results of the LNG exchanger. The calculated results are displayed in the following pages: l l

l l

l

Results (SS). Contains information relevant only to Steady State mode. Plots (SS/Dyn). Contains information relevant to both Steady State and Dynamics mode. Tables (SS). Contains information relevant only to Steady State mode. Summary (dynamics). Contains information relevant only to Dynamics mode. Layers (dynamics). Contains information relevant only to Dynamics mode.

Results Page The Results page displays the calculated values generated by HYSYS. These values are split into three groups for your convenience.

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Overall Performance Group

Parameter

Description

Duty

Combined heat flow from the hot streams to the cold streams minus the heat loss. Conversely, this is the heat flow to the cold streams minus the heat leak.

Heat Leak

Loss of cold side duty to leakage.

Heat Loss

Loss of hot side duty to leakage.

UA

Product of the Overall Heat Transfer Coefficient and the Total Area available for heat transfer. The LNG Exchanger duty is proportional to the overall log mean temperature difference, where UA is the proportionality factor. That is, the UA is equal to the overall duty divided by the LMTD.

Minimum Approach

The minimum temperature difference between the hot and cold composite curves.

LMTD

The LMTD is calculated in terms of the temperature approaches (terminal temperature differences) in the exchanger, using Equation (1).

The equation used to calculate LMTD is: (1)

Where: ΔT1 = Thot, out - Tcold, in ΔT2 = Thot, in - Tcold, out

Detailed Performance Group

490

Parameter

Description

Estimated UA Curvature Error

The LMTD is ordinarily calculated using constant heat capacity. An LMTD can also be calculated using linear heat capacity. In either case, a different UA is predicted. The UA Curvature Error reflects the difference between these UAs.

Hot Pinch Temperature

The hot stream temperature at the minimum approach between composite curves.

Cold Pinch Temperature

The cold stream temperature at the minimum approach between composite curves.

Cold Inlet Equilibrium Temperature

The Equilibrium Temperature for the cold streams. When streams are not equilibrated (see the Parameters page), the Equilibrium temperature is the coldest temperature of all cold inlet streams.

17 Liquefied Natural Gas (LNG) Exchanger

Parameter

Description

Hot Inlet Equilibrium Temperature

The Equilibrium Temperature for the hot streams. When streams are not equilibrated (see the Parameters Page), the Equilibrium temperature is the hottest temperature of all hot inlet streams.

Side Results Group The Side Results group displays information on each Pass. For each side, the inlet and outlet temperatures, molar flow, duty, UA, and the hot/cold designation appear.

Plots Page On the Plots page, you can plot composite curves or individual pass curves for the LNG. The options available on this page varies, depending on the type of mode (Steady State or Dynamics) your simulation case is in. Note: You can modify the appearance of the plot via the Graph Control property view.

Use the check boxes under the Plot column to select which curve(s) you want to appear in the plot. l

l

In Steady State mode, all the check boxes under the Plots column are active. In Dynamics mode, the Cold Composite and Hot Composite check boxes are unavailable.

The data displayed in the plot varies depending on the simulation mode: l

In Steady State mode, the information in the plot is controlled by the selection in the Plot Type drop-down list. Note: The Plot Type drop-down list is only available at Steady State mode. o

l

The Plot Type drop-down list enables you to select any combination of the following data for the x and y axes: Temperature, UA, Delta T, Enthalpy, Pressure, and Heat Flow.

In the Dynamics mode, the plot only displays the Temperature vs. Zone data.

Use the View Plot button to open the plot area in a separate property view.

Tables Page On the Table page, you can examine the interval Temperature, Pressure, Heat Flow, Enthalpy, UA, Vapor Fraction, and Delta T for each side of the Exchanger in a tabular format. Choose the side, Cold Composite or Hot Composite, by making a selection from the Side drop-down list located above the table.

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Setup Page This page lets you set up the results displayed in the unit operation result plots and tables. The table below explains the options available for each pass. Curve Option

Description

Intervals

Number of points on the plot

Dew/Bubble Pts

Include or exclude dew/bubble points in the curves

Step Type

Set the points on the plot to be based on equal temperature or equal enthalpy intervals

Pressure Profile

Set heat curves to be calculated at a specific constant pressure independent of the feed or product pressures. Specify Linear, Inlet Pressure, Outlet Pressure, or a value you enter in the Additional Const Pressures table.

Properties Selection Windows Use the arrow buttons to add or remove calculated variables from the results set. You can single select, drag a series to group select, or hold down the Ctrl key to create a multiple selection of individual variables. Once selected, click the Add arrow to add them to the Selected Viewing variables list.

Summary Page The Summary page displays the results of the dynamic LNG unit operation calculations. On this page, the following zone properties appear for each layer:

492

l

Layer

l

Inlet Temperature

l

Exit Temperature

l

Inlet Enthalpy

l

Exit Enthalpy

l

Inlet Flow rate

l

Outlet Flow rate

l

Fluid Duty

l

Fluid Volume

l

Surface Area

l

Metal Mass

17 Liquefied Natural Gas (LNG) Exchanger

The Fluid Duty is defined as the energy specified to the holdup. If the fluid duty is positive, the layer gains energy from its surroundings; if the fluid duty is negative, the layer loses energy to its surroundings. Note: If the Combine Layers check box is selected on the Model page of the Dynamics tab, some parameters on the Summary page of the Performance tab include contributions from multiple layers.

Layers Page The Layers page displays information regarding local heat transfer and fluid properties at endpoint locations in each layer of each zone. Use the Zone, Layer, and Point drop-down list to select the zone, layer, and endpoint location you want to see. Click the Diagram button to access the Layer Point Conditions property view.

Layer Point Conditions Property View The Layer Point Conditions property view displays the detailed temperatures and overall heat transfer values for both endpoints of the selected layer. You can select a different layer using the Layer drop-down list. Click the View Holdup button to access the Holdup property view.

Dynamics Tab The Dynamics tab contains the following pages: l

Model

l

Specs

l

Holdup

l

Estimates

l

Stripchart Note: If you are working exclusively in steady state mode, you are not required to change any information on the pages accessible through this tab.

Model Page On the Model page, you can specify how each layer in a multi-zone LNG unit operation is connected.

Main Settings The Main Settings group displays the following LNG model parameters:

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Parameter

Description

Number of Zones

The number of zones in a LNG unit operation can be specified in this field.

Elevation

You can specify the elevation of the LNG in this field. The elevation is significant in the calculation of static head in and around the LNG unit operation.

Combine Layers Check box

With the Combine Layers check box selected, individual layers (holdups) carrying the same stream in a single zone is calculated using a single holdup. The Combine Layers option increases the speed of the dynamic solver, and usually yields results that are similar to a case not using the option.

The Connections group displays the feed and product streams of each layer for every zone in the LNG unit operation. Every layer must have one feed stream and one product stream in order for the LNG operation to solve. A layer’s feed or product stream can originate internally (from another layer) or externally (from a material stream in the simulation flowsheet). Thus, various different connections can be made allowing for the modeling of multi-pass streams in a single zone.

Connections Group Every zone in the LNG unit operation is listed in the Zone drop-down list in the Connections group. All the layers in the selected zone in one set appear. For every layer’s feed and product, you must specify one of the following: l

An external material stream.

l

The zone and layer of an internal inlet or exit stream.

You can specify the relative direction of flow in each layer in the zone. Layers can flow counter (in the opposite direction) or across the direction of a reference stream. The reference stream is defined as a stream which does not have either the Counter or Cross check box selected in the Connections group. The following table lists three possible flow configurations:

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Description

Flow Direction

Flow Setting

Counter Current Flow

Parallel Flow

Cross Flow

Note: To implement counter current flow for two streams in a single exchanger block, ensure that the Counter check box is selected for only one of the streams. If the Counter check box is selected for both streams, the flow configuration is still parallel, and in the opposite direction.

Specs Page The Specs page contains information regarding the calculation of pressure drop across the LNG unit operation. The following parameters appear for every layer in each zone in the LNG unit operation in the Dynamic Specification groups. Dynamic Specification

Description

Delta P Calculator

The Delta P Calculator allows you to either specify or calculate the pressure drop across the layer in the LNG operation. Specify the cell with one of following options:

Delta P

l

user specified. You specify the pressure drop.

l

not specified. Pressure drop across the layer is calculated from a pressure flow relationship. You must specify a k-value, and select the Flow Eqn check box if you want to use this non specified Delta P calculator.

The pressure drop across the layer of the LNG operation can be specified or calculated.

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Dynamic Specification

Description

Flow eqn

Activate this option, if you want to have the Pressure Flow k value used in the calculation of pressure drop. If the Flow Eqn check box is selected, the Delta P calculator must also be set to not specified.

Laminar

HYSYS is able to model laminar flow conditions in the layer. Select the Laminar check box if the flow through the layer is in the laminar flow regime.

Pressure Flow k Value

The k-value defines the relationship between the flow through layer and the pressure of the surrounding streams. You can either specify the k-value or have it calculated from the stream conditions surrounding the layer. You can “size” each layer in the zone with a kvalue by clicking the Calculate k’s button. Ensure that there is a nonzero pressure drop across the LNG layer before the Calculate k button is clicked. Each zone layer can be specified with a flow and set pressure drop by clicking the Generate Estimates button. The LNG unit operation, like other dynamic unit operations, should use the k-value specification option as much as possible to simulate actual pressure flow relations in the plant.

When you click the Generate Estimates button, the initial pressure flow conditions for each layer are calculated. HYSYS generates estimates using the assumption that the flow of a particular stream entering the exchanger block (zone) is distributed equally among the layers. The generated estimates appear on the Estimates page of the Dynamics tab. It is necessary to complete the Estimates page in order for the LNG unit operation to solve. It is strongly recommended that you specify the same pressure drop calculator for layers that are connected together in the same exchanger block or across adjacent exchanger blocks. Complications arise in the pressure flow solver if a stream’s flow is set in one layer, and calculated in the neighboring layer. The Automatically Update k’s check box automatically updates the k’s based on current relationships between P-F flow rates and pressure drops for all the heat transfer layers, making the LNG steam flow rates more stable.

Holdup Page The Holdup page contains information regarding each layer’s holdup properties, composition, and amount. The Details group contains detailed holdup properties for every layer in each zone of the LNG. In order to view the advanced properties for individual holdups, you must first select the individual holdup. To choose individual holdups you must specify the Zone and Layer in the corresponding drop-down lists.

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Estimates Page The Estimates page contains pressure flow information surrounding each layer in the LNG unit operation: The following pressure flow information appears on the Estimates page: l

Delta P

l

Inlet Pressure

l

Outlet Pressure

l

Inlet Flow

l

Outlet Flow

It is necessary to complete the Estimates page in order for the LNG unit operation to completely solve. The simplest method of specifying the Estimates page with pressure flow values is having HYSYS estimate these values for you. This is achieved by clicking the Generate Estimates button on the Specs page of the Dynamics tab. HYSYS generates estimates using the assumption that the flow of a particular stream entering the exchanger block (zone) is distributed equally among the layers.

Stripchart Page The Stripchart page allows you to select and create default strip charts containing various variable associated to the operation.

About the LNG Wound Coil Heat Exchanger The LNG Wound Coil Heat Exchanger tab lets you use the LNG with Plate Fin as the rating method to model a wound-coil heat exchanger, a large multiple-pass heat exchanger often used as the cold box in a Liquefied Natural Gas facility. The WCHE operation is similar in principle to that of a Plate Fin exchanger, except that there are several different fluids in the WCHE tubes. Aspen HYSYS translates the geometric configuration of a WCHE into an equivalent configuration for the HYSYS LNG Exchanger block in Plate Fin mode. The process to pass the Wound Coil geometry to the plate fin model is as follows: l

l

l

Use the WCHE Geometry page to define the properties of the Wound Coil exchanger. Use the Calculate Plate Fin button on the Plate Fin Equivalents page to conduct the conversion calculations and display the results. Use the Transfer to Plate Fin button to pass the translated values to the Plate Fin parameters for modeling.

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From this point forward, you can interact with the standard Plate Fin inputs on the LNG model forms.

Wound Coil Heat Exchanger (WCHE) Reference Page To model a Wound Coil (or Spiral Wound) Heat Exchanger (WCHE) in a LNG unit operation, HYSYS translates the specified geometric configuration of the WCHE into an equivalent exchanger configuration in Plate Fin mode. Use the instructions and guidelines below to define the WCHE.

Specifying the WCHE Geometry In the LNG property view, click the Wound Coil tab. Click the WCHE geometry page. Select the Enable WCHE Configuration check box to specify details of the shell and tube geometry of the heat exchanger. Refer to the tables below for descriptions of the specification fields.

Tube Properties

Property

Value

Tube side fluid number Tube outer diameter

498

Comment Specify how many fluids on the tube side

D

Specified

17 Liquefied Natural Gas (LNG) Exchanger

Property

Value

Comment

Tube wall thickness

ht

Specified, should be smaller than half of tube outer diameter

Tube pitch

pt

Specified

Tube length

L

Specified

Tube metal density

ρ

Specified

Single tube area

Single inner cross-sectional area

Single tube holdup

Single tube inner volume

Single tube mass

Single tube metal mass

Shell Properties

Property

Value

Shell side fluid

Comment Specify the shell side fluid name

Shell diameter

Ds

Specified

Shell height

Hs

Specified

Shell wall thickness

hs

Specified

Metal density

ρs

Specified

Shell metal mass

Total metal mass of shell

Shell inside surface area

Shell inner surface area

Shell holdup

Shell inner volume

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Tube Side Fluid Information

Property

Value

Comment

Fluid name

Specify names of each fluid on the tube side

Number of tubes for each fluid

Ntube, i Total number of tubes:

Number of layers for each fluid

Nlayer, i By default:

Specify the number of tubes that carries each kind of fluids

n tube = sum (Ntube, i)

 Nlayer, I = Ntube, I /min(Ntube, i) (for example, if fluid 1 has 100 tubes, and fluid 2 has 500 tubes, then in plate-fin mode, fluid 1 has 1 hot layer/set, fluid 2 has 5 hot layers/set) Hot layers:   n hot = sum(Nlayer, I) Cold layers:  n cold = n hot + 1

The number of layers per fluid in Plate-Fin configuration, which corresponding to the number of tubes per fluid in WCHE. The default value is calculated based on the ratio of each fluid tubes number to the smallest number of tubes.

Total outside surface area of tubes

Total tube outer surface area

Total inside surface area of tubes

Total tube inner surface area

Total fluid holdup in tubes

Total fluid volume in tubes

Total tube holdup

Total tube volume

Total amount of metal in tubes

Total metal mass of tubes

Wound Coil Heat Exchanger - Plate Fin Equivalents Reference To derive the equivalent geometry of a Plate Fin Heat Exchanger (PFHE), four tuning factors, fm, fa, ft, and fs, are introduced to balance the total metal mass, the total inner and outer surface areas, the total fluid holdup in tubes, and the

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total fluid holdup in shell side, between the WCHE and the PFHE.  By default, they are set to 1.0. Any change to specified parameters on the WCHE geometry and Plate Find Equivalent pages will result in a mismatch of the two configurations.  Click the Calculate Plate Fin button to recalculate the tuning factors. You can select a linear or non-linear model to use when figuring the plate-fin equivalents. A table below shows the differences between the linear and non linear approaches to finding tuning factors.

Tuning Factors Reference

Factor

Description

Surface area balance:

F2 (fm , fa , ft , fs) = sum of total WCHE tube inner and outer surface area – total PHFE surface area of cold layers and hot layers

Mass bal- F1 (fm , fa , ft , fs) = total WCHE tube metal mass – total PHFE plate metal ance mass Tube side fluid holdup balance:

F3 (fm , fa , ft , fs) = total fluid holdup in WCHE tube side – total fluid holdup in PHFE hot layers

Shell side fluid holdup balance

F4 (fm , fa , ft , fs) = total fluid holdup in WCHE shell side – total fluid holdup in PHFE cold layers

Sum of Square Error (SSE)

SSE = F12 + F22 + F32 + F42

Upper and Lower Bound

By default the lower bound for all tuning factors is 0.5, and the upper bound is 2.0. If a converged set of tuning factors cannot be found with default tuning factors and lower/upper bounds in nonlinear model, you can either try different initial values by specifying the tuning factors or relax the bounds of existing tuning factors.

Plate-Fin zone information

Parameter

Description

Number of zones

Specified number of zones in plate fine

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Parameter

Description

Zone length

Specified zone length

Zone width

Layer Length x layer width / (number of zones x zone length)

Number of layers

Total number of layers in set

Adjusted layer length

Actual layer length in plate fin = Specified zone length x number of zones

Adjusted layer width

Actual layer width in plate fin = Calculated zone width

Linear vs. Non-Linear Plate Fin Equivalent Calculations Linear Model Solve for the linear system consisting of F1, F2, F3, and F4, mass tuning factor and area tuning factor can be obtained directly: fm = 1.0, fa = 2.0.

Nonlinear Model The optimization method is used to find tuning factors.  The objective function is:

subject to: 0.5 ≤ fi ≤ 2.0

Models Compared:

502

Plate Fin Geometry

Linear model

Nonlinear model

Layer width

By default: Square root of shell cross sectional area; Can be specified by user

By default: Square root of shell cross sectional area; Can be specified by user

Layer length

Tube length

Tube length

17 Liquefied Natural Gas (LNG) Exchanger

Plate Fin Geometry

Linear model

Nonlinear model

Metal density

Tube metal density

Tube metal density

Fin perforation

Default: zero (can be specified)

Default: zero (can be specified)

Fin height

Cold layer: Tube outer diameter x shell holdup tuning factor(fs)

Cold layer: Tube outer diameter x shell holdup tuning factor(fs)

Hot layer: Tube outer diameter x tube holdup tuning factor (ft)

Hot layer: Tube outer diameter x tube holdup tuning factor(ft)

Fin pitch

Cold layer:

Cold layer:

Hot layer:

Hot layer:

Number of sets

Fin thickness

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Plate Fin Geometry

Linear model

Nonlinear model

Layer width x layer length x 2

Layer width x layer length x 2

Plate thickness Horizontal area per layer

Equivalent Plate-Fin Geometry Refer to the notation section at the bottom of the page for a guide to notation conventions. Parameter

Value

Total number of layers

Sum of cold layers # + hot layers#, where cold layer # = hot layer # + 1

Layer width

By default:

Layer length

Equal to the length of tubes.

Number of sets

Linear model:

Nonlinear model:

Fin height

Cold layer: Hot layer: 

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17 Liquefied Natural Gas (LNG) Exchanger

Parameter

Value

Fin pitch

Linear model: (cold layer) (hot layer) Nonlinear model: (cold layer) (hot layer)

Fin thickness

Linear model:

Nonlinear model:

Plate thickness

Vertical fin mass per layer Horizontal fin mass per layer Plate mass per layer Fluid holdup per layer

Horizontal area per layer Vertical fin area per layer Total area in layer

Volume/area ratio

Fluid holdup in layer/total area in layer

Equivalent tube diameter

 Volume/area ratio × 1000 × 4

Transfer to Plate Fin: Populate Derived Plate Fin Geometry Once the equivalent Plate Fin geometry of a WCHE is derived, click the Transfer to Plate Fin button to populate the calculated PHFE configuration to the corresponding parameter fields on the Rating and Dynamics pages.  You can

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then start to configure the PHFE-equivalent WCHE from there by connecting inlet/outlet streams and specifying zones and connections.

Notation Reference

506

Symbol

Parameter

Ah

Horizontal area per layer

Av

Vertical fin area per layer

Alayer

Total surface area in layer

Aid

Total inside surface area of tubes

Aod

Total outside surface area of tubes

Acold

Total surface area of cold layers

Ahot

Total surface area of hot layers

D

Tube outer diameter

Ds

Shell inner diameter

fa

Area tuning factor

fm

Mass tuning factor

fs

Shell side holdup tuning factor

ft

Tube side holdup tuning factor

H

Fin height

Hs

Shell height

hf

Fin thickness

hp

Plate thickness

ht

Tube wall thickness

L

Tube length or layer length

mh

Horizontal fin mass per layer

mv

Vertical fin mass per layer

mp

Plate mass per layer

n set

Number of sets

n tube

Number of tubes

17 Liquefied Natural Gas (LNG) Exchanger

Symbol

Parameter

ρ

Tube metal density or plate fin metal density

ρs

Shell metal density

pf

Fin pitch

pr

Fin perforation

pt

Tube pitch

Vlayer

Fluid holdup per layer

Vtube

Total tube fluid holdup

W

Layer width

LNG EDR PlateFin Overview EDR PlateFin is an optional Rating Method that can be selected on the Design tab | Parameters page. When you switch to this rating method, the LNG unit operation uses EDR PlateFin rigorous calculations, and the pages on the EDR PlateFin tab are enabled. When choosing EDR PlateFin, some HYSYS functionalities may not be supported for the LNG unit operation. These functionalities include: l

l

l

Design tab | Specs page: The Heat Balance specification is set as Active for the LNG. Other specifications, including UA, Delta Temp, and Flow, are not supported. Rating tab: The Rating tab is not supported for the LNG. Any information on this tab is not relevant to PlateFin calculations. Detailed geometry information is located on the EDR PlateFin tab. Performance tab: The Performance tab, including thermodynamic values and plots, may not be accurate. Accurate thermodynamic information is located on the EDR PlateFin tab.

l

Dynamics: PlateFin does not support dynamics.

l

Wound Coil: PlateFin does not support Wound Coil.

The benefit of using EDR PlateFin is access to rigorous calculations and the ability to define detailed geometry for PlateFin exchangers. Detailed results tables and plots are available in the EDR Browser, providing a more in-depth look at stream behavior in the PlateFin exchanger. PlateFin and the HYSYS LNG exchanger allow multiple process stream connections. PlateFin allows up to 20 inlet streams. Conditions (P, T, H, and Vapor fraction) are passed from each connected HYSYS stream to PlateFin. A property table is generated for each process stream entering the PlateFin exchanger based on the stream composition held by HYSYS, using the current property

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package. These property tables are used within PlateFin to calculate the physical properties of the stream at any set of conditions. At the end of the PlateFin calculation, output data is passed back to HYSYS, and HYSYS variables are updated.

EDR PlateFin Tab The EDR PlateFin tab is the primary way to view information related to PlateFin calculations. The EDR PlateFin tab contains four pages: l

Process (contains inputs)

l

Property Ranges (contains inputs)

l

Results Summary (contains results)

l

Results Geometry (contains results)

On the bottom of each page of the EDR PlateFin tab, the following buttons are available: l

l

l

Import: Click the Import button to import geometries from EDR PlateFin files. This is the primary way to define EDR PlateFin geometry. Export: Click the Export button to export stream data and geometries of the current PlateFin exchanger to an EDR file. View EDR Browser: Click the View EDR Browser button to open a dockable window containing more detailed input parameters and results. Press F1 within the EDR Browser to view EDR-specific help.

Exchanger Design Ribbon Options When you click the View EDR Browser button, the Exchanger Design contextual ribbon appears.

Ribbon Group

Description

Set Units

Units shown in the EDR browser are EDR unit sets. HYSYS custom unit sets are currently not supported.

Model Readiness

508

l

When the EDR browser is connected to HYSYS, changing input values will re-solve the LNG block in the flowsheet. When disconnected, changing input values will not resolve the LNG in the flowsheet.

l

Disconnect from HYSYS if you want to modify geometries without having HYSYS re-solve after every input. You can reconnect after you finish making changes.

17 Liquefied Natural Gas (LNG) Exchanger

Ribbon Group

Description

Run Control

Runs the EDR case in the EDR browser. This may cause HYSYS to resolve.

Run Mode

There are four calculation modes available for PlateFin. For all calculation modes, PlateFin assumes inlet streams are fully defined or calculated and will not run otherwise. l

Stream by stream simulation: Evaluates the outlet conditions achievable for each process stream with a defined exchanger geometry, assuming a common wall temperature. Stream by stream simulation assumes no outlet temperatures, pressures, vapor mass fractions, or enthalpies are specified or defined for the LNG block.

l

Layer by layer simulation: Evaluates the outlet conditions achievable for each process stream with a defined exchanger geometry taking account of actual arrangement of layers. Layer by layer simulation assumes no outlet temperatures, pressures, vapor mass fractions, or enthalpies are specified or defined for the LNG block. Layer by layer simulations may take significantly more time to converge compared to stream by stream calculations.

l

Checking/Rating: Estimates the degree to which a defined exchanger geometry is over-surfaced or under-surfaced to meet the process requirements for each stream. Checking/Rating requires enough thermodynamic information to determine inlet and outlet stream states.

l

Design: Locates the number of exchangers or cores, the arrangement of streams, and the number of layers required for each stream to satisfy the stream process requirements. Design requires enough thermodynamic information to determine inlet and outlet stream states.

Export

Supports exporting predefined PlateFin-specific results to Excel. This option is separate from and unavailable for use with standard HYSYS Excel reporting.

Print

Supports printing PlateFin-specific reports. These reports are not available when printing standard HYSYS reports.

EDR PlateFin Process Page The EDR PlateFin Process page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR - PlateFin. This page presents a basic set of input process data sent to EDR PlateFin. Changing values on this page does change values for material streams (on the Worksheet tab | Connections page). However, changes to material streams may override values entered in this page.

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For more specialized operations, you can click the View EDR Browser button to launch the EDR PlateFin Browser from within the page.

510

Field

Description

LNG Pass Name

LNG Pass Names are pairs of inlet and outlet streams, also called sides, defined on the Design tab | Connections page. Geometry in EDR Plate Fin is defined relative to EDR Stream Numbers. You must map EDR Stream numbers and sides before the LNG can solve.

EDR Stream Number

All inputs on the EDR PlateFin tab | Process page are shown relative to EDR Stream Numbers. This ordering of streams may be different compared to the Worksheet tab | Conditions page. LNG Pass Names map EDR Stream Numbers to streams on the Worksheet tab | Conditions page.

Total Mass Flow Rate

Specify the Total Mass Flow Rate. This information is usually provided by the stream.

Inlet Temperature

Specify the Inlet Temperature. This information is usually provided by the stream.

Outlet Temperature

Specify the Outlet Temperature. If an outlet temperature will be determined during calculation, an initial estimate can be specified.

Inlet Mass Quality

Specify the Inlet Mass Quality. This is the vapor mass fraction and is usually provided by the stream.

Outlet Mass Quality

Specify the Outlet Mass Quality or vapor mass fraction. Vapor mass fractions are important for streams that are boiling or condensing isothermally, where temperature alone is not adequate to define the stream conditions.

Inlet Pressure

Specify the Inlet Pressure. This information is usually provided by the stream.

Outlet Pressure

Specify the Outlet Pressure. If this pressure will be determined during the calculation, an initial estimate can be given. If you leave this field blank, a default value will be determined using the inlet pressure and the estimated pressure drop. Explicitly specifying the exchanger outlet pressure can be useful when gravitational effects are significant.

Allowed Pressure Drop

Specify the maximum permitted pressure drop in the exchanger.

Estimated Pressure Loss

Specify the estimated pressure loss. This is the difference between the inlet and outlet pressures in the exchanger.

Heat Load

Stream heat load (in the absence of partial draw-off) is the stream mass flowrate multiplied by the difference in specific enthalpy between inlet and outlet.

17 Liquefied Natural Gas (LNG) Exchanger

Field

Description

Fouling Resistance

You can specify a fouling resistance for each stream. This is a resistance based on full local heat transfer area and assumed to apply throughout the exchanger and on both primary and secondary surfaces. On the fins, it is used to determine the overall local heat transfer coefficient used to calculate fin efficiency. In cryogenic equipment, the fluids are normally clean and non-corrosive, so it is common for fouling resistances to be set to zero.

EDR PlateFin Property Ranges Page The EDR PlateFin Property Ranges page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR - PlateFin. This page presents parameters affecting how properties are sent to EDR Plate Fin. Properties are sent through a property table of temperature and pressure points. If you leave these values blank, default values will be determined using inlet stream temperatures and pressures. You may need to expand the ranges of temperatures or pressures on this page, especially for streams with three phases if the unit operation does not converge. Field

Description

LNG Pass Name

Pairs of inlet and outlet streams. This value is determined on the EDR PlateFin tab | Process page.

EDR Stream Number

All inputs on the EDR PlateFin tab | Property Ranges page are shown relative to EDR Stream Numbers. This ordering of streams may be different compared to the Worksheet tab | Conditions page. LNG Pass Names map EDR Stream Numbers to streams on the Worksheet tab | Conditions page.

Temp. Range (Start)

One of two points defining the range of temperatures included in the property table. This value does not necessarily need to be the lower temperature. Expanding the temperature range may resolve properties errors preventing the unit operation from successfully solving.

Temp. Range (End)

One of two points defining the range of temperatures included in the property table. This value does not necessarily need to be the higher temperature. Expanding the temperature range may resolve properties errors preventing the unit operation from successfully solving.

Number of Temperatures

Specify the number of temperatures points in the property table. The range of input is between 2 and 24. A higher number enhances the resolution of properties in the property table and can improve the accuracy of the calculations. The program determines the spacing between temperatures.

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Field

Description

No. of Pressure Levels

Specify the number of pressure points to be transferred to EDR. The range of input is between 1 and 5. A higher number enhances the resolution of properties transferred and can improve the accuracy of the calculations.

Pressure Level 1 - 5

You can specify the pressures in the property table. You can manually control spacing for pressures sent to the property table. Modifying these values can improve calculation accuracy, especially for exchangers experiencing significant pressure drops. Pressures should be specified in descending order; Pressure Level 1 should be highest pressure.

EDR PlateFin Results Summary Page The EDR PlateFin Results Summary page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR - PlateFin. This page shows stream-specific calculation results.

512

Field

Description

LNG Pass Name

Pairs of inlet and outlet streams. This value is determined in EDR PlateFin | Process.

EDR Stream Number

All inputs on the EDR PlateFin tab | Results Summary page are shown relative to EDR Stream Numbers. This ordering of streams may be different compared to the Worksheet tab | Conditions page. LNG Pass Names map EDR Stream Numbers to streams on the Worksheet tab | Conditions page.

Stream Type

Identifies whether the stream is hot or cold.

Flow Direction

Identifies the flow direction of a stream. Flow direction can be End A to B (down), End B to A (up), no flow, or Crossflow. Normal design practice is for hot streams to flow away from end A (which is at the top of the exchanger), while cold streams flow towards end A.

Number of Layers

Identifies the total number of layers a stream occupies in the exchanger. If there is more than one exchanger in parallel, the number of layers applies throughout.

Total Mass Flow Rate

Identifies the mass flow rate of the stream.

Heat Load

Stream heat load (in the absence of partial draw-off) is the stream mass flowrate multiplied by the difference in specific enthalpy between inlet and outlet.

17 Liquefied Natural Gas (LNG) Exchanger

Field

Description

Area Ratio

An area ratio can be defined for each stream in a PlateFin exchanger. This term is more commonly used with shell and tube exchangers. It is the ratio of the actual stream heat transfer area to the area required for a specified duty. For two-stream exchangers such as shell and tube, the ratio must be the same for both streams and is taken as a simple measure of the acceptability of exchanger performance. An area ratio of more than 1 means that an exchanger can more than achieve a specified duty. In a multi-stream exchanger, the position is more complicated, since each stream can have a different area ratio. An area ratio above unity does not necessarily indicate that all of the area is in the right place to achieve the desired heat transfer. Nevertheless, the area ratio can be useful as a parameter indicating how well an exchanger is performing. Area ratios are the primary result of Checking calculations. For two-stream exchangers, the area ratio of each stream will be the same. For a Simulation calculation, the area ratio should in principle be unity. Values slightly different from unity sometimes occur when the overall heat load (based on stream exit conditions) has converged more rapidly that the local stream heat transfer at all points between inlet and outlet.

Inlet Temperature

Identifies the inlet temperature of the stream.

Outlet Temperature

Identifies the outlet temperature of the stream.

Inlet Pressure

Identifies the inlet pressure of the stream.

Outlet Pressure

Identifies the outlet pressure of the stream.

Pressure Loss

Identifies the pressure drop across the stream.

EDR PlateFin Results Geometry The EDR PlateFin Results Geometry page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR - PlateFin. Use the Results Geometry page to review results of the PlateFin geometry calculations. Many of these geometry parameters cannot be changed without using the EDR Browser. To access the EDR Browser, click the View EDR Browser button. Within the EDR browser, press F1 to access EDR-specific help.

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Field

Description

No. of exchangers in parallel

Identifies the number of Plate Fin exchangers in parallel. More than one exchanger in parallel can be used when stream flow rates or thermal duties are too large to be handled by a single exchanger. In all cases, the exchangers are assumed to be identical, and no calculations are performed on pressure losses in connecting pipe work.

No. of exchangers per unit

Identifies the number of exchangers per unit. A unit is a set of exchanger cores welded together so that stream headers can each span the entire set, while a single nozzle can feed each header. Grouping exchangers together in this way affects the nozzle pressure loss, but not any other part of the calculation.

514

No. of layers per exchanger

The total number of layers in the exchanger.

No. of Xflow passes

Identifies the number of cross flow passes. A maximum of one crossflow pass is permitted for Simple Crossflow and Plate-fin Kettles. This item refers to the exchanger as a whole. It is not used for axial flow exchangers, where one dimensional modeling (axially along the exchanger) is for each stream or layer – even if some streams are in multi-pass cross counterflow or flow in a short crossflow pass somewhere along the exchanger.

Orientation

Plate Fin heat exchangers are normally vertical with flow up or down.

Exchanger metal

Plate Fin exchangers for LNG and other cryogenic duties are made of aluminum.

Weight empty

The empty exchanger weight. It includes the core, headers, and nominal length nozzles. If there are multiple exchangers in parallel, this is the weight of all of them combined.

Weight full of water

The weight of all exchangers with the core and headers filled with water.

Weight operating

The weight of all exchangers with the core and headers filled with process fluid. This is based on mean fluid densities.

Core length

The full external length of the plate fin exchanger core. This does not include any allowance for headers and stubs/nozzles welded on to the core.

Core width

The full external width of the plate fin exchanger core. This does not include any allowance for headers and stubs/nozzles welded on to the core. This width is the width of each layer, measured transversely to the axial (flow) direction and is the same for each layer type.

17 Liquefied Natural Gas (LNG) Exchanger

Field

Description

Core depth

The exchanger depth (stack height) is the third dimension, alongside the exchanger width and length that defines the rectangular core of the exchanger. The stack height is the sum of the thicknesses of every layer (fin height plus parting sheet), plus the thickness of the cap sheets. The term stack height applies to the orientation of the exchanger during construction, when layers are laid horizontally on top of each other prior to brazing, rather than during operation, when the layers are normally vertical.

Distributor length end A

The length of the distributor-only region at end A.

Main heat transfer length

The heat transfer length of the exchanger.

Distributor length end B

The length of the distributor-only region at end B.

Internal (effective) width

The Internal (effective) width is the total width of the exchanger less the widths of the two side bars.

Side bar width

Identifies the side bar width.

Parting sheet thickness

The thickness of the separating plates (parting sheets) between layers.

Cap sheet thickness

On the outside of the plate fin core, Cap Sheets are used; these are thicker than the parting sheets that separate layers internally.

LNG EDR CoilWound Overview EDR CoilWound is an optional Rating Method that can be selected on the Design tab | Parameters page. When you switch to this rating method, the LNG unit operation uses EDR CoilWound rigorous calculations, and the pages on the EDR CoilWound tab are enabled. When choosing EDR CoilWound, some HYSYS functionalities are hidden and unsupported for the LNG unit operation. These functionalities include: l

Design tab | Specs page

l

Rating tab

l

Performance tab

l

Dynamics tab

l

Wound Coil tab

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The benefit of using EDR CoilWound is access to rigorous calculations and the ability to define detailed geometry for CoilWound exchangers. Detailed results tables and plots are available in the EDR Browser, providing a more in-depth look at stream behavior in the CoilWound exchanger. To help you easily create flowsheets with CoilWound, CoilWound HYSYS templates are available in the Template folder.

EDR CoilWound Tab The EDR CoilWound tab is the primary way to view information related to CoilWound calculations. The EDR CoilWound tab contains five pages: l

Process (contains inputs)

l

Property Ranges (contains inputs)

l

Results Summary (contains results)

l

Results Geometry (contains results)

l

Convergence

On the bottom of each page of the EDR CoilWound tab, the following buttons are available: l

l

l

Import: Click the Import button to import geometries from EDR CoilWound files. This is the primary way to define EDR CoilWound geometry. Export: Click the Export button to export stream data and geometries of the current CoilWound exchanger to an EDR file. View EDR Browser: Click the View EDR Browser button to open a dockable window containing more detailed input parameters and results. Press F1 within the EDR Browser to view EDR-specific help.

Exchanger Design Ribbon Options When you click the View EDR Browser button, the Exchanger Design contextual ribbon appears.

516

Ribbon Group

Description

Set Units

Units shown in the EDR browser are EDR unit sets. HYSYS custom unit sets are currently not supported.

17 Liquefied Natural Gas (LNG) Exchanger

Ribbon Group Model Readiness

Description

l

When the EDR browser is connected to HYSYS, changing input values will re-solve the LNG block in the flowsheet. When disconnected, changing input values will not resolve the LNG in the flowsheet.

l

Disconnect from HYSYS if you want to modify geometries without having HYSYS re-solve after every input. You can reconnect after you finish making changes.

Run Control

Runs the EDR case in the EDR browser. This may cause HYSYS to resolve.

Run Mode

There are two calculation modes available for CoilWound. For both calculation modes, CoilWound assumes inlet streams are fully defined or calculated and will not run otherwise. l

Simulation: Evaluates the outlet conditions achievable for each process stream with a defined exchanger geometry. Assumes no outlet temperatures, pressures, vapor mass fractions, or enthalpies are specified or defined for the LNG block.

l

Checking/Rating: Estimates the degree to which a defined exchanger geometry is over-surfaced or under-surfaced to meet the process requirements for each stream. Checking/Rating requires enough thermodynamic information to determine inlet and outlet stream states.

Export

Supports exporting predefined CoilWound-specific results to Excel. This option is separate from and unavailable for use with standard HYSYS Excel reporting.

Print

Supports printing CoilWound-specific reports. These reports are not available when printing standard HYSYS reports.

Specifying LNG EDR CoilWound Process Information The EDR CoilWound tab | Process page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR - CoilWound. This page presents a basic set of input process data sent to EDR CoilWound. Changing values on this page does change values for material streams (on the Worksheet tab | Connections page). However, changes to material streams may override values entered in this page. For more specialized operations, you can click the View EDR Browser button to launch the EDR CoilWound Browser from within the page. To specify EDR CoilWound process information for the LNG Exchanger: 1. On the Design tab | Parameters page, from the Rating Method dropdown list, select EDR - CoilWound.

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2. Select the EDR CoilWound tab | Process page. 3. Specify the information described in the table below.

518

Field

Description

LNG Pass Name

LNG Pass Names are pairs of inlet and outlet streams, also called sides, defined on the Design tab | Connections page. Geometry in EDR CoilWound is defined relative to EDR Stream Numbers. You must map EDR Stream numbers and sides before the LNG can solve.

EDR Stream Number

All inputs on the EDR CoilWound tab | Process page are shown relative to EDR Stream Numbers. This ordering of streams may be different compared to the Worksheet tab | Conditions page. LNG Pass Names map EDR Stream Numbers to streams on the Worksheet tab | Conditions page.

Total Mass Flow Rate

Specify the Total Mass Flow Rate. This information is usually provided by the stream.

Inlet Temperature

Specify the Inlet Temperature. This information is usually provided by the stream.

Outlet Temperature

Specify the Outlet Temperature. If an outlet temperature will be determined during calculation, an initial estimate can be specified.

Inlet Mass Quality

Specify the Inlet Mass Quality. This is the vapor mass fraction and is usually provided by the stream.

Outlet Mass Quality

Specify the Outlet Mass Quality or vapor mass fraction. Vapor mass fractions are important for streams that are boiling or condensing isothermally, where temperature alone is not adequate to define the stream conditions.

Inlet Pressure

Specify the Inlet Pressure. This information is usually provided by the stream.

Outlet Pressure

Specify the Outlet Pressure. If this pressure will be determined during the calculation, you can provide an initial estimate. If you leave this field blank, a default value will be determined using the inlet pressure and the estimated pressure drop. Explicitly specifying the exchanger outlet pressure can be useful when gravitational effects are significant.

Allowed Pressure Drop

Specify the maximum permitted pressure drop in the exchanger.

Est. Pressure Loss

Specify the estimated pressure loss. This is the difference between the inlet and outlet pressures in the exchanger.

Heat Load

Stream heat load (in the absence of partial draw-off) is the stream mass flowrate multiplied by the difference in specific enthalpy between inlet and outlet.

17 Liquefied Natural Gas (LNG) Exchanger

Field

Description

Fouling Resistance

You can specify a fouling resistance for each stream. This is a resistance based on full local heat transfer area and is assumed to apply throughout the exchanger and on both primary and secondary surfaces. On the fins, it is used to determine the overall local heat transfer coefficient used to calculate fin efficiency. In cryogenic equipment, the fluids are normally clean and noncorrosive, so it is common for fouling resistances to be set to zero.

Specifying LNG EDR CoilWound Property Ranges The EDR CoilWound tab | Property Ranges page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR CoilWound. This page presents parameters affecting how properties are sent to EDR CoilWound. Properties are sent through a property table of temperature and pressure points. If you leave these values blank, default values will be determined using inlet stream temperatures and pressures. You may need to expand the ranges of temperatures or pressures on this page, especially for streams with three phases when the unit operation does not converge. To specify EDR CoilWound property ranges for the LNG Exchanger: 1. On the Design tab | Parameters page, from the Rating Method dropdown list, select EDR - CoilWound. 2. Select the EDR CoilWound tab | Property Ranges page. 3. Specify the information described in the table below. Field

Description

LNG Pass Name

Pairs of inlet and outlet streams. This value is determined on the EDR CoilWound tab | Process page.

EDR Stream Number

All inputs on the EDR CoilWound tab | Property Ranges page are shown relative to EDR Stream Numbers. This ordering of streams may be different compared to the Worksheet tab | Conditions page. LNG Pass Names map EDR Stream Numbers to streams on the Worksheet tab | Conditions page.

Temp. Range (Start)

One of two points defining the range of temperatures included in the property table. This value does not necessarily need to be the lower temperature. Expanding the temperature range may resolve properties errors preventing the unit operation from successfully solving.

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Field

Description

Temp. Range (End)

One of two points defining the range of temperatures included in the property table. This value does not necessarily need to be the higher temperature. Expanding the temperature range may resolve properties errors preventing the unit operation from successfully solving.

Number of Temperatures

Specify the number of temperatures points in the property table. The range of input is between 2 and 24. A higher number enhances the resolution of properties in the property table and can improve the accuracy of the calculations. The program determines the spacing between temperatures.

No. of Pressure Levels

Specify the number of pressure points to be transferred to EDR. The range of input is between 1 and 5. A higher number enhances the resolution of properties transferred and can improve the accuracy of the calculations.

Pressure Level 1 - 5

You can specify the pressures in the property table. You can manually control spacing for pressures sent to the property table. Modifying these values can improve calculation accuracy, especially for exchangers experiencing significant pressure drops. Pressures should be specified in descending order; Pressure Level 1 should be highest pressure.

Viewing LNG EDR CoilWound Results Summary The EDR CoilWound tab | Results Summary page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR CoilWound. This page shows stream-specific calculation results. To view EDR CoilWound results summary information for the LNG Exchanger: 1. On the Design tab | Parameters page, from the Rating Method dropdown list, select EDR - CoilWound. 2. Select the EDR CoilWound tab | Results Summary page. 3. View the results described in the table below.

520

Field

Description

LNG Pass Name

Pairs of inlet and outlet streams. This value is determined on the EDR CoilWound tab | Process page.

EDR Stream Number

All inputs on the EDR CoilWound tab | Results Summary page are shown relative to EDR Stream Numbers. This ordering of streams may be different compared to the Worksheet tab | Conditions page. LNG Pass Names map EDR Stream Numbers to streams on the Worksheet tab | Conditions page.

17 Liquefied Natural Gas (LNG) Exchanger

Field

Description

Stream Type

Identifies whether the stream is hot or cold.

Flow Direction

Identifies the flow direction of a stream. Flow direction can be Up, Down, or No Flow. Normal design practice is for hot streams to flow up and cold streams to flow down.

Number of Tubes

Identifies the total number of tubes that a stream occupies in the exchanger. If there is more than one exchanger in parallel, the number of tubes applies throughout.

Total Mass Flow Rate

Identifies the mass flow rate of the stream.

Heat Load

Stream heat load (in the absence of partial draw-off) is the stream mass flowrate multiplied by the difference in specific enthalpy between the inlet and outlet.

Area Ratio

An area ratio can be defined for each stream in a CoilWound exchanger. This term is more commonly used with shell and tube exchangers. It is the ratio of the actual stream heat transfer area to the area required for a specified duty. For two-stream exchangers such as shell and tube, the ratio must be the same for both streams and is taken as a simple measure of the acceptability of exchanger performance. An area ratio of more than 1 means that an exchanger can more than achieve a specified duty. In a multi-stream exchanger, the position is more complicated, since each stream can have a different area ratio. An area ratio above unity does not necessarily indicate that all of the area is in the right place to achieve the desired heat transfer. Nevertheless, the area ratio can be useful as a parameter indicating how well an exchanger is performing. Area ratios are the primary result of Checking calculations. For two-stream exchangers, the area ratio of each stream will be the same. For a Simulation calculation, the area ratio should in principle be unity. Values slightly different from unity sometimes occur when the overall heat load (based on stream exit conditions) has converged more rapidly that the local stream heat transfer at all points between inlet and outlet.

Inlet Temperature

Identifies the inlet temperature of the stream.

Outlet Temperature

Identifies the outlet temperature of the stream.

Inlet Pressure

Identifies the inlet pressure of the stream.

Outlet Pressure

Identifies the outlet pressure of the stream.

Pressure Loss

Identifies the pressure drop across the stream.

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Viewing LNG EDR CoilWound Results Geometry The EDR CoilWound tab | Results Geometry page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR CoilWound. Use the Results Geometry page to review results for the CoilWound geometry calculations. Many of these geometry parameters cannot be changed without using the EDR Browser. To access the EDR Browser, click the View EDR Browser button. Within the EDR browser, press F1 to access EDR-specific help. To review the EDR CoilWound geometry calculations for the LNG Exchanger: 1. On the Design tab | Parameters page, from the Rating Method dropdown list, select EDR - CoilWound. 2. Select the EDR CoilWound tab | Results Geometry page. 3. View the results described in the table below. Field

Description

Bundle Num- Bundle Number has a range from 1 to 3. The top bundle is ber labeled Bundle 1. Bundle height

Indicates the height of the coiled bundle. The bundle height is related to the length of the tube in a bundle and the helix angle by the following equation:

where: θ = helix angle L = length of tube in bundle h = height of bundle

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Bundle diameter

Indicates outside diameter of the bundle. This value is from the outside of the tube OD.

Number of tubes

Indicates the total number of tubes in each bundle.

Number of layers

Indicates the total number of layers in each bundle.

Longitudinal pitch

Indicates the longitudinal pitch. The longitudinal pitch is the distance from the center of a tube in one layer to the center of the tube directly above or below it in the same layer. All layers in a bundle will have the same longitudinal pitch.

Transverse pitch

Indicates the transverse pitch. The transverse pitch is the distance from the center of a tube in one layer to the center of a tube in an adjacent layer. The transverse pitch is the same for all layers in a bundle.

17 Liquefied Natural Gas (LNG) Exchanger

Field

Description

Total surface area

Total surface area for heat transfer, based on tube OD, and the length of each tube within the main coil.

Shell side flow area

The total shell side area for flow, including space occupied by spacing wires.

Tube OD

Outside diameter of tubes forming the bundle. Each tube in a bundle has the same outside diameter, wall thickness, and material.

Tube wall thickness

Indicates the thickness of tube wall.

Tube metal

Indicates the tube material, which can be Aluminum, Stainless Steel, or Titanium.

Helix angle

Indicates the helix angle measured from the horizontal in degrees. This is also sometimes referred to as the winding angle.

Mandrel diameter

Indicates the outside diameter of the mandrel on which the coil is wound. The mandrel is also called the central axial cylinder.

Shell ID

Indicates the internal diameter of the shell.

Modifying LNG EDR CoilWound Convergence Parameters The EDR CoilWound tab | Convergence page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR CoilWound. Use the Convergence page to modify convergence parameters. Modifying default convergence patterns can be useful when default settings do not lead to a full convergence. To modify the EDR CoilWound convergence parameters for the LNG Exchanger: 1. On the Design tab | Parameters page, from the Rating Method dropdown list, select EDR - CoilWound. 2. Select the EDR CoilWound tab | Convergence page. 3. Modify the parameters described in the table below. Field

Description

Calculation grid resolution

Changes grid resolution for calculations. Increasing grid resolution is useful for exchangers with large temperature swings and can improve convergence at the cost of calculation time.

Maximum number of iterations

Specify the maximum number of iterations to be performed.

Convergence tolerance heat load

Specify the required convergence accuracy of the overall exchanger heat load.

17 Liquefied Natural Gas (LNG) Exchanger

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Field

Description

Convergence tolerance pressure

Specify the required convergence accuracy of the outlet pressure of any stream.

Relaxation parameter

Determines how fast the calculation converges. For exchangers where the duty is close to the maximum possible value for each stream, large values can lead to instability in the calculation and failure to converge. Very low values can give false positives for convergence.

Maximum step: heat load

Changing the maximum permitted step size for heat load can converge the solution more smoothly, especially in the early stages, when discrepancies from the true solution are large.

Max. iterations in prelim checking

Checking iterations are performed prior to a simulation calculation. This helps establish good initial temperature profiles for the simulation calculations. You must provide accurate stream outlet conditions; if the conditions are inaccurate, checking will be counterproductive. In this case, reduce or eliminate iterations in preliminary checking.

References 1.

Perry, R.H. and D.W. Green. Perry’s Chemical Engineers’ Handbook (Seventh Edition) McGraw-Hill (1997) p. 11-33

2. Perry, R.H. and D.W. Green. Perry’s Chemical Engineers’ Handbook (Seventh Edition) McGraw-Hill (1997) p. 11-42 3. Kern, Donald Q. Process Heat Transfer McGraw-Hill International Editions: Chemical Engineering Series, Singapore (1965) p. 139

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17 Liquefied Natural Gas (LNG) Exchanger

18 Plate Exchanger

The Plate Exchanger unit operation solves heat and material balances for two stream plate heat exchangers. Plate heat exchangers consist of plates packed in a frame. Two streams, one hot and one cold, flow in alternate channels between these plates. Plate unit operations can solve for heat loads using either a basic heat and material balance or a rigorous calculation based on geometry.

Theory Heat Transfer Plate calculations are based on energy balances for the hot and cold fluid. The following general relation applies to plate heat exchangers. (1) Where: H = Enthalpy M = Mass flow rate The plate duty for the simple end point method, Q, is defined in terms of the overall heat transfer coefficient, the area available for heat exchanger, and the log mean temperature difference. (2) Where: U = Overall heat transfer coefficient A = Surface area available for heat transfer ΔTLM = log mean temperature difference (LMTD) The plate duty for the EDR - Plate rating method is rigorously calculated incorporating geometry.

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Plate Exchanger Design Tab The Design tab of the Plate Exchanger contains the following pages: l

Connections

l

Parameters

l

Specs

l

User Variables

l

Notes

Specifying Plate Exchanger Connections The Design tab | Connections page of the Plate Exchanger lets you specify the following information: l

Name

l

Hot Side Inlet stream

l

Hot Side Outlet stream

l

Hot Side Fluid Pkg

l

Cold Side Outlet stream

l

Cold Side Inlet stream

l

Cold Side Fluid Pkg

l

Switch Sides

Red lines represent the hot side material stream, and blue lines represent the cold side material stream.

Specifying Plate Exchanger Parameters The Design tab | Parameters page of the Plate Exchanger lets you select the Rating Model and specify relevant heat transfer data. To specify parameters for the Plate Exchanger: 1. Select the Design tab | Parameters page. 2. From the Rating Method drop-down list, select the plate rating method. o

Simple End Point: Solves for heat loads using a basic heat and material balance.

o

EDR - Plate: Solves for heat loads using a rigorous calculation based on geometry. If you select this option, specify information on the Rigorous Plate tab.

3. Specify the following values.

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18 Plate Exchanger

Field

Description

Overall UA

Appears for the Simple End Point model. This is the overall heat transfer coefficient multiplied by the total area for heat transfer.

Area

Appears for the Simple End Point model. This is the total heat transfer area. The default area is 100 m2.

Heat Transfer Coefficient

Appears for the Simple End Point model. This is the overall heat transfer coefficient.

Pressure Drop

Hot Side and Cold Side pressure drop for the plate heat exchanger. o

For the Simple End Point rating method, specify this value.

o

For the EDR - Plate rating method, this appears as a calculated value.

Plate Exchanger Specifications On the Design tab | Specs page of the Plate Exchanger, specify the following values: l

Max. Iterations

l

Tolerance

The following values are calculated as the solver progresses: l

Current Iteration

l

Current Error

Note: The specifications on this page only appear if you selected Simple End Point as the Rating Method on the Design tab | Parameters page.

Rigorous Plate Overview EDR - Plate is an optional Rating Method that can be selected on the Design tab | Parameters page. When you switch to this rating method, the Plate Exchanger unit operation uses EDR Plate rigorous calculations, and the pages on the Rigorous Plate tab are enabled. The benefit of using EDR Plate is access to rigorous calculations and the ability to define detailed geometry for Plate Exchangers. Detailed results tables and plots are available in the EDR Browser, providing a more in-depth look at stream behavior in the Plate Exchanger.

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EDR Rigorous Plate Tab The Rigorous Plate tab is the primary way to view information related to Plate calculations. The Rigorous Plate tab contains five pages: l

Process (contains inputs)

l

Property Ranges (contains inputs)

l

Results Summary (contains results)

l

Setting Plan

l

Profiles

On the bottom of each page of the Rigorous Plate tab, the following buttons are available: l

l

l

Import: Click the Import button to import geometries from EDR Plate files. This is the primary way to define EDR Plate geometry. Export: Click the Export button to export stream data and geometries of the current Plate exchanger to an EDR file. View EDR Browser: Click the View EDR Browser button to open a dockable window containing more detailed input parameters and results. Press F1 within the EDR Browser to view EDR-specific help.

Exchanger Design Ribbon Options When you click the View EDR Browser button, the Exchanger Design contextual ribbon appears.

Ribbon Group

Description

Set Units

Units shown in the EDR browser are EDR unit sets. HYSYS custom unit sets are currently not supported.

Model Readiness

Run Control

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l

When the EDR browser is connected to HYSYS, changing input values will re-solve the Plate block in the flowsheet. When disconnected, changing input values will not resolve the Plate block in the flowsheet.

l

Disconnect from HYSYS if you want to modify geometries without having HYSYS re-solve after every input. You can reconnect after you finish making changes.

Runs the EDR case in the EDR browser. This may cause HYSYS to resolve.

18 Plate Exchanger

Ribbon Group

Description

Run Mode

There are four calculation modes available for Plate. EDR Plate primarily runs in Simulation mode, but other modes can be accessed through the EDR Browser temporarily to design or check the exchanger. l

Design: Generates a design given sufficient process conditions. Uses average heat transfer coefficients and linear temperatureenthalpy relations. Works well for single phase streams.

l

Design (given plate): Generates a design given sufficient process conditions. Plate details are required as a geometry input. Uses average heat transfer coefficients and linear temperatureenthalpy relations. Works well for single phase streams.

l

Rating / Checking: Checking calculations estimate if a specified geometry will achieve a required duty. The result of this calculation is the ratio of the actual to required surface area. Requires enough thermodynamic information to determine inlet and outlet stream state.

l

Simulation: Evaluates the outlet conditions achievable for each process stream with a defined exchanger geometry. Assumes no outlet temperatures, pressures, vapor mass fractions, or enthalpies are specified or defined for the Plate block.

Export

Supports exporting predefined Plate-specific results to Excel. This option is separate from and unavailable for use with standard HYSYS Excel reporting.

Print

Supports printing Plate-specific reports. These reports are not available when printing standard HYSYS reports.

Specifying Rigorous Plate Process Information The Rigorous Plate tab | Process page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR - Plate. This page presents a basic set of input process data sent to EDR Plate. Changing values on this page does change values for material streams (on the Worksheet tab | Connections page). However, changes to material streams may override values entered in this page. For more specialized operations, you can click the View EDR Browser button to launch the EDR Plate Browser from within the page. To specify Rigorous Plate process information for the Plate Exchanger: 1. On the Design tab | Parameters page, from the Rating Method dropdown list, select EDR - Plate. 2. Select the Rigorous Plate tab | Process page. 3. Specify the information described in the table below.

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Field

Description

EDR Stream

Indicates the type of stream (hot stream or cold stream).

Total Mass Flow Rate

Specify the Total Mass Flow Rate. This information is usually provided by the stream.

Inlet Temperature

Specify the Inlet Temperature. This information is usually provided by the stream.

Outlet Temperature

Specify the Outlet Temperature. If an outlet temperature will be determined during calculation, an initial estimate can be specified.

Inlet Mass Quality

Specify the Inlet Mass Quality. This is the vapor mass fraction and is usually provided by the stream.

Outlet Mass Quality

Specify the Outlet Mass Quality or vapor mass fraction. Vapor mass fractions are important for streams that are boiling or condensing isothermally, where temperature alone is not adequate to define the stream conditions.

Inlet Pressure

Specify the Inlet Pressure. This information is usually provided by the stream.

Allowed Pressure Drop

Specify the maximum permitted pressure drop in the exchanger.

Est. Pressure Loss

Specify the estimated pressure loss. This is the difference between the inlet and outlet pressures in the exchanger.

Fouling Resistance

You can specify a fouling resistance for each stream. Fouling resistances for plate exchangers are generally low and much less than the TEMA recommended values for shell and tube exchangers. Fouling in plate exchangers is often dealt with using an overall fouling margin rather than individual fouling resistances for each stream.

Specifying Rigorous Plate Property Ranges The Rigorous Plate tab | Property Ranges page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR - Plate. This page presents parameters affecting how properties are sent to EDR Plate. Properties are sent through a property table of temperature and pressure points. If you leave these values blank, default values will be determined using inlet stream temperatures and pressures. You may need to expand the ranges of temperatures or pressures on this page, especially for streams with vaporliquid phases when the unit operation does not converge. To specify Rigorous Plate property ranges for the Plate Exchanger: 1. On the Design tab | Parameters page, from the Rating Method dropdown list, select EDR - Plate.

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18 Plate Exchanger

2. Select the Rigorous Plate tab | Property Ranges page. 3. Specify the information described in the table below. Field

Description

EDR Stream

Indicates hot side or cold side.

Temp. Range (Start)

One of two points defining the range of temperatures included in the property table. This value does not necessarily need to be the lower temperature. Expanding the temperature range may resolve properties errors preventing the unit operation from successfully solving.

Temp. Range (End)

One of two points defining the range of temperatures included in the property table. This value does not necessarily need to be the higher temperature. Expanding the temperature range may resolve properties errors preventing the unit operation from successfully solving.

Number of Temperatures

Specify the number of temperatures points in the property table. The range of input is between 2 and 24. A higher number enhances the resolution of properties in the property table and can improve the accuracy of the calculations. The program determines the spacing between temperatures.

No. of Pressure Levels

Specify the number of pressure points to be transferred to EDR. The range of input is between 1 and 5. A higher number enhances the resolution of properties transferred and can improve the accuracy of the calculations.

Pressure Level 1 - 5

You can specify the pressures in the property table. You can manually control spacing for pressures sent to the property table. Modifying these values can improve calculation accuracy, especially for exchangers experiencing significant pressure drops. Pressures should be specified in descending order; Pressure Level 1 should be highest pressure.

Viewing Rigorous Plate Results Summary The Rigorous Plate tab | Results Summary page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR - Plate. This page shows stream-specific calculation results. To view Rigorous Plate results summary information for the Plate Exchanger: 1. On the Design tab | Parameters page, from the Rating Method dropdown list, select EDR - Plate. 2. Select the Rigorous Plate tab | Results Summary page. 3. View the results described in the table below.

18 Plate Exchanger

Field

Description

Duty

Total heat exchanged between the hot side and cold side.

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Field

Description

Effective Surface Area

Effective surface area for heat transfer calculations.

MTD

MTD for heat transfer calculations.

The following equation gives you the heat exchanged for the plate heat exchanger:

The following equation gives you the heat exchanged for the plate heat exchanger:

Overall Clean Coeff

Overall heat transfer coefficient without fouling resistance.

Overall Dirty Coeff

Overall heat transfer coefficient with fouling resistance.

Stream Name

Indicates the stream name for the plate heat exchanger.

Allowable Pressure Drop

Indicates the maximum allowable pressure drop that you can specify for the plate heat exchanger.

Calculated Pressure Drop

Indicates the calculated pressure drop.

Risk of Maldis- Indicates the risk of flow maldistribution (Yes or No). tribution Velocity (Port)

Velocity of fluid at the ports based on average density.

Velocity (Plate)

Velocity of fluid through the plates based on average density.

Film Coefficie- Weighted coefficients for any sensible cooling/heating and nt phase change that occurred in the Plate heat exchanger.

Viewing Rigorous Plate Setting Plan The Rigorous Plate tab | Setting Plan page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR - Plate. The Setting Plan page shows a schematic of a plate heat exchanger.

Viewing Rigorous Plate Profiles The Rigorous Plate tab | Profiles page is visible when the Rating Method on the Design tab | Parameters page is changed to EDR - Plate. The Profiles page provides a plot of the sectional hot and cold stream temperatures versus distance of the plate heat exchanger.

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18 Plate Exchanger

19 Logical Operations

The next chapters will describe the following Logical Operations: l

Adjust

l

Balance

l

Boolean Operations

l

Control Operations

l

Split Range Controller

l

Ratio Controller

l

PID Controller

l

MPC Controller

l

DMCplus Controller

l

Digital Point

l

External Data Linker

l

Recycle

l

Selector Block

l

Set

l

Spreadsheet

l

Stream Cutter

l

Black Oil Translator

l

Transfer Function

Common Options ATV Tuning Technique The ATV (Auto Tune Variation) Technique is one of a number of techniques used to determine two important system constants known as the Ultimate Period, and the Ultimate Gain. From these constants, tuning values for proportional, integral, and derivative gains can be determined.

19 Logical Operations

533

Note: The Tuning option only sets up the limit cycle; it does not calculate the tuning parameters for you.

A small limit-cycle disturbance is set up between the Control Output and the Controlled Variable, such that whenever the process variable crosses the set point, the controller output is changed. The ATV Tuning Method is as follows: 1. Determine a reasonable value for the valve change (OP). Let h represent this value. In HYSYS, h is 5%. 2. Move the valve +h%. 3. Wait until the process variable starts moving, then move valve -2h%. 4. When the PV crosses the set point, move the OP +2h%. 5. Continue this procedure until the limit-cycle is established. From the cycle, two key parameters can be observed: Observed Parameter

Description

Amplitude (a)

The amplitude of the PV curve, as a fraction of the PV span.

Ultimate Period (PU)

Peak-to-Peak period of the PV curve.

The Ultimate Gain can be calculated from the following relationship: (1)

where: KU = ultimate gain h = change in OP (0.05) a = amplitude Finally, the Controller Gain and Integral Time can be calculated as follows: Controller Gain = KU / 3.2 Controller Integral Time = 2.2*PU Note: The ATV Tuning Method only works for systems with dead time.

Controller Face Plate To access the controller Face Plate: 1. Press CTRL F. The Face Plates property view appears. 2. From the list of available flowsheets, select the flowsheet that contains the logical operation you want to view the face plate for. 3. From the list of available logical operations, select the logical operation you want to view the face plate for.

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19 Logical Operations

4. Click the Open button. The Face Plates property view closes and the face plate for the selected logical operation appears. OR 1. Open the property view of a Controller operation. 2. Click the Face Plate button located at the bottom of the Controller’s property view. Each controller’s Face Plate varies in appearance; however, the functionality remains the same. This section provides a general description of how to use the controller Face Plate. The Face Plate provides all pertinent information about the controller when the simulation is running. The Setpoint is shown as a red pointer, and the actual value of the Process Variable appears in the current default unit. Output is always displayed as a percentage of the span you defined on the Valve tab. The Face Plate also displays the execution type and the setpoint source. Also, you can change the mode of the Controller by selecting the mode from the drop-down list at the bottom left of the Face Plate. The mode choices are identical to those on the Parameters tab. Clicking the Tuning button returns you to the Tuning tab of the Controller property view.

Changing the Setpoint and Output You can change the SP or OP of the Controller (depending on the current mode) at any time during the simulation without returning to the Parameters tab, by using the Face Plate. To change the SP while in Automatic mode, or to change the OP while in Manual mode, use any one of the following three methods: 1. Move to the field for the parameter you want to change. For this example, the Setpoint (top field) is changed. Start entering a new value for the SP, and HYSYS displays a field with a drop-down list containing the default units. Once you have entered the value, press ENTER and HYSYS accepts the new Setpoint. Note: If you select an alternate unit, your value appears in the face plate using HYSYS display units.

2. Place the mouse pointer near the red Setpoint indicator, and the cursor changes to a double-ended arrow. Click and hold, a fly-by appears below, showing the current value of the SP (in this case, 50%). 3. Click and drag the double-ended arrow to the new SP of 60%. The fly-by displays the SP value as you drag. Release the mouse button to accept the new SP. 4. Place the pointer at either end of the field, and the pointer changes to a single-ended arrow. Click once to increase or decrease the value by 1%. For example, switch to Manual mode and adjust the OP. To increase the OP, move the pointer to the right end of the field and the single-ended arrow pointing to the right appears. Click to increase the OP by 1%.

19 Logical Operations

535

Note: You can click the button consecutively to repeatedly increase (or decrease) the OP.

Object Inspect Menu of Face Plates The options for the Object Inspect menu for a Fixed Size Face Plate are described below. The options associated with this menu are: Command

Description

Turn Off

Turns the Controller Mode to Off.

Start Ramp

Starts Setpoint Ramping

Auto-Tune

Puts the Controller into a cycling mode. This can be used for tuning the Controller.

Tuning

Returns you to the Tuning page of the Controller property view.

Connections

Returns you to the Connections page of the Controller property view.

Parameters

Returns you to the Parameters page of the Controller property view.

Print Datasheet

Allows you to print the Datasheet for the controller.

Print Specsheet

Allows you to print the controller Specsheet.

The additional menu options in the Object Inspection menu for a Scalable Face Plate are:

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Command

Description

Font

Allows you to choose the Font for the text on the Face Plate.

Hide Values/Show Values

Hides the values for SP, PV, and OP. When the values are hidden, the Show Values option appears. Choose this to display the values.

Hide Units/Show Units

Hides the units for SP and PV. When the units are hidden, the Show Units option appears in the menu. Choose this to display the units.

19 Logical Operations

20 Adjust Operation

The Adjust operation varies the value of one stream variable (the independent variable) to meet a required value or specification (the dependent variable) in another stream or operation. Note: The Adjust is a steady state operation; HYSYS ignores it in dynamic mode.

In a flowsheet, a certain combination of specifications may be required, which cannot be solved directly. These types of problems must be solved using trialand-error techniques. To quickly solve flowsheet problems that fall into this category, the Adjust operation can be used to automatically conduct the trial-anderror iterations for you. The Adjust is extremely flexible. It allows you to link stream variables in the flowsheet in ways that are not possible using ordinary “physical” unit operations. It can be used to solve for the desired value of just a single dependent variable, or multiple Adjusts can be installed to solve for the desired values of several variables simultaneously. Note: The Independent variable cannot be a calculated value; it must be specified.

The Adjust can perform the following functions: l

l

Adjust the independent variable until the dependent variable meets the target value. Adjust the independent variable until the dependent variable equals the value of the same variable for another object, plus an optional offset.

Connections Tab The first tab of the Adjust property view, as well as several other logicals, is the Connections tab. The tab contains the following pages: l

Connections

l

Notes

20 Adjust Operation

537

Connections Page The Connections page comprises the following groups: l

Adjusted Variable

l

Target Variable

l

Target Value

Adjusted/Target Variable Groups The Adjusted Variable and Target Variable groups are similar in appearance, each containing an Object field, Variable field, and a Select Var button. l

l

l

The Adjusted Object is the owner of the independent variable which is manipulated in order to meet the specified value of the Target variable. The Target Object is the owner of the dependent variable whose value you are trying to meet. A Target Object can be a unit operation, stream, or a utility. The Select Var button enables you to select a variable for the Adjusted and Target objects.

Target Value Group Once the target object and variable are defined, there are three choices for how the target is to be satisfied: l

l

l

If the target variable is to meet a certain numerical value, select User Supplied and enter the appropriate value in the Specified Target Value field. If the target variable is to meet the value (or the value plus an offset) of the same variable in another stream or operation, select Another Object and select the stream or operation of interest from the Matching Value Object drop-down list. If applicable, enter an offset in the available field. If the target variable is to meet the value (or the value plus an offset) of the same variable specified in the spreadsheet, select SpreadSheetCell Object and select the cell that you want from the Matching Value Object drop-down list. This allows the SpreadSheetCell to be attached as an adjusted variable, and source to the target variable. You can also specify the offset in the available field.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the operation or to your simulation case in general.

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20 Adjust Operation

Parameters Tab Once you have chosen the dependent and independent variables, the convergence criteria must be defined. This is usually done on the Parameters tab. The Parameters tab has two pages: l

Parameters

l

Options

Parameters Page The Parameters page allows you to specify the adjust parameters: Solving Parameter

Description

Simultaneous Solution

Solves multiple Adjust loops simultaneously. There is only one simultaneous solving method available therefore when this check box is selected the Method field is no longer visible.

Method

Sets the (non-simultaneous) solving method: Secant or Broyden.

Tolerance

Sets the absolute error. In other words, the maximum difference between the Target Variable and the Target Value.

Step Size

The initial step size employed until the solution is bracketed.

Maximum / Minimum

The upper and lower bounds for the independent variable (optional) are set in this field.

Maximum Iterations

The number of iterations before HYSYS quits calculations, assuming a solution has not been obtained.

Sim Adj Manager

Opens the Simultaneous Adjust Manager allowing you to monitor and modify all Adjusts that are selected as simultaneous.

Optimizer Controlled

Passes a variable and a constant to the optimizer. When activated the efficiency of the simultaneous Adjust is increased. This option requires RTO.

Choosing the Solving Methods Adjust loops can be solved either individually or simultaneously. If the loop is solved individually, you have the choice of either a Secant (slow and sure) or Broyden (fast but not as reliable) search algorithm. The Simultaneous solution method uses modified Levenberg-Marquardt method search algorithm. A single Adjust loop cannot be solved in the Simultaneous mode. In Simultaneous mode, the adjust variable is adjusted after the last operation in the flowsheet has solved. The calculation level has no effect on the Adjust operation in the Simultaneous mode.

20 Adjust Operation

539

Note: The Calculation Level for an Adjust (accessed under Main Properties) is 3500, compared to 500 for most streams and operations. This means that the Adjust is solved last among unknown operations. You can set the relative solving order of the Adjusts by modifying the Calculation Level.

When the Simultaneous Solution check box is selected, the Method field is no longer visible.

Simultaneous Adjust Manager The Simultaneous Adjust Manager (SAM) property view allows you to monitor, and modify all Adjusts that are selected as simultaneous. This gives you access to a more efficient method of calculation, and more control over the calculations. Note: All adjusts from old cases in Simultaneous mode are automatically added to the SAM.

The SAM property view is launched by clicking the Sim Adj Manager button on the Parameters tab, or by selecting Simultaneous Adjust Manager command from the Simulation menu. Note: The SAM requires two or more active (in other words, not ignored) adjusts to solve. If you are using only one adjust, you cannot use the SAM.

The SAM property view contains the following tabs: l

Configuration

l

Parameters

l

History

The SAM property view also contains the following common objects: l l

l

The status bar, which displays the status of the SAM calculation. The Stop and Start buttons, which are used to start and stop the SAM calculations respectively. The Ignored check box, which enables you to toggle on and off the SAM feature and all of the selected Adjusts simultaneously.

SAM Configuration Tab The Configuration tab displays information regarding Adjusts that have been selected as simultaneous. You can view the individual Adjusts by double-clicking on the Adjust name. You can also modify the target value or matching value object, value, and offset. This tab also allows you to ignore individual Adjusts.

SAM Parameters Tab The Parameters tab allows you to modify the tolerance, step size, max, and min values for each Adjust, as well as, displays the residual, number of iter-

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20 Adjust Operation

ations the SAM has taken, and the iteration status. This tab also allows you to specify some of the calculation parameters as described in the table below. Parameter

Description

Type of Jacobian Calculation

Allows you to select one of three Jacobian calculations:

Type of Convergence

l

ResetJac. Jacobian is fully calculated and values reset to initial values after each Jacobian calculation step. Most time consuming but most accurate.

l

Continuous. Values are not recalculated between Jacobian calculation steps. Quickest, but allows for “drift” in the Jacobian therefore not as accurate.

l

Hybrid. Hybrid of the above two methods.

Allows you to select one of three convergence types: l

Specified. SAM is converged when all Adjusts are within the specified tolerances.

l

Norm. SAM is converged when the norm of the residuals (sums of squares) is less than a user-specified value.

l

Either. SAM is converged with whichever of the above types occurs first.

Max Step Fraction

The number x step size is the maximum that the solver is allowed to move during a solve step.

Perturbation Factor

The number x range (Max - Min) or the number x 100 x step size (if no valid range). This is the maximum that the solver is allowed to move during a Jacobian step.

Max # of Iter- Maximum number of iterations for the SAM. ations

History Tab The History tab displays the target value, adjusted value, and residual value for each iteration of the selected Adjust(s). One or more Adjusts can be displayed by clicking on the check box beside the Adjust name. The Adjusts are always viewed in order from left to right across the page. For example, if you are viewing Adjust 2 and add Adjust 1 to the property view, Adjust 1 becomes the first set of numbers, and Adjust 2 is shifted to the right. Note: The History tab only displays the values from a solve step. The values calculated during a Jacobian step can be seen on the Monitor tab of the adjust for the individual results.

Tolerance For the Adjust to converge, the error in the dependent variable must be less than the Tolerance. (1)

20 Adjust Operation

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It is sometimes a good idea to use a relatively loose (large) tolerance when initially attempting to solve an Adjust loop. Once you determine that everything is working properly, you can reset the tolerance to the final design value. Note: The tolerance and error values are absolute (with the same units as the dependent variable) rather than relative or percentage-type.

Step Size The step size you enter is used by the search algorithm to establish the maximum step size adjustment applied to the independent variable. This value is used until the solution has been bracketed, at which time a different convergence algorithm is applied. The value which is specified should be large enough to permit the solution area to be reached rapidly, but not so large as to result in an unreasonable overshoot into an infeasible region. A positive step size initially increments the independent variable, while a negative value initially decrements the independent variable. Note: A negative initial step size causes the first step to decrement the independent variable.

If the Adjust steps away from the solution, the direction of the steps are automatically reversed. Note: Before installing the Adjust module, it is often good practice to initialize the independent variable, and perform one adjust “manually”. Solve your flowsheet once, and notice the value for the dependent variable, then self-adjust the independent variable and re-solve the flowsheet. This assures you that one variable actually affects the other, and also gives you a feel for the step size you need to specify.

Maximum/Minimum These two optional criteria are the allowable upper and lower bounds for the independent variable. If either bound is encountered, the Adjust stops its search at that point. Note: The Independent variable must be initialized (have a starting value) in order for the Adjust to work.

Maximum Iterations The default maximum number of iterations is 10. Should the Adjust reach this many iterations before converging, the calculations stop, and you are asked if you want to continue with more iterations. You can enter any value for the number of maximum iterations.

Options Page The Options page contains two groups of settings:

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20 Adjust Operation

l

Secant Solver Options

l

Generic Solver Options

The Secant Solver Options group offers the Relax Internal Bounds option as well as two settings: Bounds Tolerance and Relaxation Percentage. If the secant solver takes a step and is above the target value, it sets the adjusted variable at that time as an internal maximum or minimum. However, HYSYS is not solving problems of the nature F(x)=y, but rather F(x) = G(x), so that the response surface changes as the adjusted variable changes. This can lead to a situation where we have an internal minimum and internal maximum set to the same value. By using Relax Internal Bounds, you can allow these internal bounds to move out (within the specified minimum and maximum) if the adjusted variable is within the Bounds Tolerance of the local minimum or maximum. The bound can be relaxed by a Relaxation Percentage. The Generic Solver Option group has one option that allows you to specify the solver to Always Stop At Maximum Iterations.

Monitor Tab The Monitor tab contains the following pages: l

Tables

l

Plots

Tables Page For each Iteration of the Adjust, the number, adjusted value, target value, and residual appear. If necessary, use the scroll bar to view iterations which are not currently visible. Note: You can also use the Solver Trace Window to view the Iteration History.

Plots Page The Plots page displays the target and adjusted variables like on the Tables page, except the information is presented in graph form.

User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

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Starting the Adjust There are two ways to start the Adjust: If you have provided values for all the fields on the Parameters tab, the Adjust automatically begins its calculations. If you have omitted one or both values in the Minimum/Maximum fields (on the Parameters tab) for the independent variable (which are optional parameters), and you would like the Adjust to start calculating, simply click the Start button. Note: With the exception of the minimum and maximum values of the independent (adjusted) variable, all parameters are required before the Adjust begins its calculations.

The Start button then disappears, indicating the progress of the calculations. When the error is less than the tolerance, the status bar displays in green the “OK” message. If the Adjust reaches the maximum number of iterations without converging, the “Reached iteration Limit without converging” message appears in red on the status bar. If you click the Start button when all of the required parameters are not defined, the status bar displays in yellow the “Incomplete” message, and calculations cannot begin. Once calculations are underway, you can view the progress of the convergence process on the Iterations tab. Note: The Start button only appears in the initialization stage of the Adjust operation. It disappears from the property view as soon as it is pressed. Any changes made to the Adjust or other parts the flowsheet automatically triggers the Adjust calculation. Note: To stop or disable the Adjust select the Ignored check box.

Individual Adjust The Individual Adjust algorithm, either Secant or Broyden, uses a step-wise trial-and-error method, and displays values for the dependent and independent variables on each trial. The step size specified on the Parameters tab is used to increment, or decrement the independent variable for its initial step. The algorithm continues to use steps of this size until the solution is bracketed. At this point, depending on your choice, the algorithm uses either the Secant search (and its own step sizes) or Broyden search to quickly converge to the desired value. If a solution has not been reached in the maximum number of iterations, the routine pauses, and asks you whether another series of trials should be attempted. This is repeated until either a solution is reached, or you abandon the search. The Secant search algorithm generally results in good convergence once the solution has been bracketed.

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20 Adjust Operation

Multiple Adjust The term Multiple Adjust typically applies to the situation where all of the Adjusts are to be solved simultaneously. In this case, where the results of one Adjust directly affect the other(s), you can use the Simultaneous option to minimize the number of flowsheet iterations. Examples where this feature is very valuable include calculating the flow distribution of pipeline looping networks, or in solving a complex network of UAconstrained heat exchangers. In these examples, you must select the stream parameters which HYSYS is to manipulate to meet the desired specifications. For a pipeline looping problem, the solution may be found by adjusting the flows in the branched streams until the correct pressures are achieved in the pipelines downstream. In any event, it is up to you to select the variables to adjust to solve your flowsheet problem. HYSYS uses the modified Levenberg-Marquardt algorithm to simultaneously vary all of the adjustable parameters defined in the Adjusts until the desired specifications are met. The role of step size with this method is quite different. With the single Adjust algorithm, step size is a fixed value used to successively adjust the independent variable until the solution has been bracketed. With the simultaneous algorithm, the step size for each variable serves as an upper limit for the adjustment of that variable. In solving multiple UA exchangers, the starting point should not be one that contains a temperature crossover for one of the heat exchangers. If this occurs, a warning message appears informing you that a temperature crossover exists, and a very large UA value is computed for that heat exchanger. This value is insensitive to any initial change in the value of the adjustable variable, and therefore the matrix cannot be solved. Note: One requirement in implementing the Multiple Adjust feature is that you must start from a feasible solution.

Install all Adjusts using the simultaneous option on the Parameters tab, then click the Start button to begin the calculations.

20 Adjust Operation

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20 Adjust Operation

21 Balance

The Balance operation provides a general-purpose heat and material balance facility. The only information required by the Balance is the names of the streams entering and leaving the operation. For the General Balance, component ratios can also be specified. Since HYSYS permits streams to enter or leave more than one operation, the Balance can be used in parallel with other units for overall material and energy balances. Note: The Balance overrides the filtering of streams that HYSYS typically performs.

The Balance Operation solves in both the forward and backward directions. For instance, it backs out the flowrate of an unknown feed, given that there are no degrees of freedom. There are six Balance types which are defined in the table below:

21 Balance

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Balance Type

Definition

Mole

An overall balance is performed where only the molar flow of each component is conserved. It can be used to provide material balance envelopes in the flowsheet, or to transfer the flow and composition of a process stream into a second stream.

Mass

An overall balance is performed where only the mass flow is conserved. A common application would be for modeling reactors with no known stoichiometry, but for which analyses of all feeds and products are known.

Heat

An overall balance is performed where only the heat flow is conserved. An application would be to provide the pure energy difference in a heat balance envelope.

Mole and Heat

An overall balance is performed where the heat and molar flow are conserved. The most common application for this unit operation would be to perform overall material (molar basis) and energy balance calculations of selected process streams to either check for balances, or force HYSYS to calculate an unknown variable, such as flow. Most of the unit operations in HYSYS perform the equivalent of a Mole and Heat Balance besides their other more specialized calculations.

Mass and Heat

An overall balance is performed where the overall mass flow and heat flow are conserved.

General

HYSYS solves a set of n unknowns in the n equations developed from the streams attached to the operation. Component ratios can be specified on a mole, mass or liquid volume basis.

Balance Property View Connections Page On the Connections page of the Balance property view, you must specify the following information: l

Name. The name of the balance operation.

l

Inlet Streams. Attach the inlet streams to the balance.

l

Outlet Streams. Enter the outlet streams to the balance operation. You can have an unlimited number of inlet and outlet streams. Use the scroll bar to view streams that are not visible.

Parameters Tab The Parameters tab contains two groups:

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21 Balance

l

Balance Type

l

Ratio List

The Balance Type group contains a series of radio buttons, which allow you to choose the type of Balance you want to use. The radio buttons are shown above. Note: The Ratio List group applies only to the General balance. This is discussed in the General Balance section.

Component Mole Flow This operation performs an overall mole balance on selected streams; no energy balance is made. It can be used to provide material balance envelopes in the flowsheet or to transfer the flow and composition of a process stream into a second stream. l l

l

The composition does not need to be specified for all streams. The direction of flow of the unknown is of no consequence. HYSYS calculates the molar flow of a feed to the operation based on the known products, or vice versa. This operation does not pass pressure or temperature.

Mass Flow This operation performs an overall balance where only the mass flow is conserved. An application is the modeling of reactors with no known stoichiometry, but for which analyses of all feeds and products are available. If you specify the composition of all streams, and the flowrate for all but one of the attached streams, the Mass Balance operation determines the flowrate of the unknown stream. This is a common application in alkylation units, hydrotreaters, and other non-stoichiometric reactors. l l

l

l

The composition must be specified for all streams. The flowrate must be specified for all but one of the streams. HYSYS determines the flow of that stream by a mass balance. Energy, moles, and chemical species are not conserved. The Mass Balance operation determines the equivalent masses of the components you have defined for the inlet and outlet streams of the operation. This operation does not pass pressure or temperature.

Heat Flow This operation performs an overall heat balance on selected streams. It can be used to provide heat balance envelopes in the flowsheet or to transfer the enthalpy of a process stream into a second energy stream. l

21 Balance

The composition and material flowrate must be specified for all material streams. The heat flow is not passed to streams which do not have the composition and material flowrate specified, even if there is only one unknown heat flow.

549

l

The direction of flow for the unknown stream is of no consequence. HYSYS calculates the heat flow of a feed to the operation based on the known products, or vice versa.

l

This operation does not pass the pressure or temperature.

l

You cannot balance the heat into a Material Stream.

Component Mole and Heat Flow The most common application for this balance is to perform overall material (molar basis), and energy balance calculations of selected process streams to either check for balances or force HYSYS to calculate an unknown variable, such as a flowrate. l l

l

l

l

The Mole and Heat Balance independently balance energy and material. The Mole and Heat Balance calculate ONE unknown based on a total energy balance, and ONE unknown based on a total material balance. The operation is not directionally dependent for its calculations. Information can be determined about either a feed or product stream. The balance remains a part of your flowsheet and as such defines a constraint; whenever any change is made, the streams attached to the balance always balances with regard to material and energy. As such, this constraint reduces by one the number of variables available for specification. Since the Mole and Heat Balance work on a molar basis, it should not be used in conjunction with a reactor where chemical species are changing.

Mass and Heat Flow Similar to the Mass balance mode, this balance mode performs a balance on the overall mass flow. In addition, however, energy is also conserved. l l

l

l

The composition must be specified for all streams. Flow rate must be specified for all but one of the streams. HYSYS determines the flow of that stream by a mass balance. Enthalpy must be specified for all but one of the streams. HYSYS determines the enthalpy of that stream by a heat balance. Moles and chemical species are not conserved.

General Balance The General Balance is capable of solving a greater scope of problems. It solves a set of n unknowns in the n equations developed from the streams attached to the operation. This operation, because of the method of solution, is extremely powerful in the types of problems that it can solve. Not only can it solve unknown flows and compositions in the attached streams (either inlet or outlet can have unknowns), but ratios can be established between components

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21 Balance

in streams. When the operation determines the solution, the prescribed ratio between components are maintained. l

l

l

The General balance solves material and energy balances independently. An Energy Stream is an acceptable inlet or outlet stream. The operation solves unknown flows or compositions, and can have ratios specified between components in one of the streams. Ratios can be specified on a mole, mass or liquid volume basis.

Ratios A Ratio, which is unique to the general Balance, is defined between two components in one of the attached streams. Multiple ratios within a stream (for example 1:2 and 1:1.5) can be set with a single Ratio on a mole, mass or liquid volume basis. Each individual ratio (1:2, 1:1, and 1:1.5), however uses a degree of freedom. To set a ratio: 1. On the Parameters tab of the Balance operation property view, select the General Balance radio button. The Ratio List group should now be visible. 2. Click the Add Ratio button to access the Ratio property view. In the Ratio property view, specify the following information: o

Name. The name of the Ratio.

o

Stream. The name of the stream.

o

Ratio Type. Allows you to specify the Ratio Type: Mole, Mass, or Volume.

o

Component/Ratio. Provides the relative compositions of two or more components. Other components in the stream are calculated accordingly, and it is not necessary nor advantageous to include these in the table. All ratios must be positive; non-integer values are acceptable.

Number of Unknowns The general Balance determines the maximum number of equations, and hence unknowns, in the following manner (notice that the material and energy balances are solved independently): l l

l

One equation performing an overall molar flow balance. {Number of Components (nc)} equations performing an individual molar balance. {Number of Streams (ns)} equations, each performing a summation of individual component fractions on a stream by stream basis.

This is the maximum number of equations (1 + nc + ns), and hence unknowns, which can be solved for a system. When ratios are specified, they reduce the available number of unknowns. For each ratio, the number of unknowns used is

21 Balance

551

one less than the number of components in the ratio. For example, for a threecomponent ratio, two unknowns are used.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the operation.

Stripchart Tab The Stripchart tab allows you to select and create default strip charts containing various variable associated to the operation.

User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

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21 Balance

22 Boolean Operations

The Boolean Logic block is a logical operation which takes in a specified number of Boolean inputs and then applies the Boolean operation to calculate an output. A typical use of the Boolean Logic is to apply emergency shutdown of an exothermic reactor, such as closing the valves on the fuel and air line to the reactor when the reactor core temperature exceeds its setpoint. It is also used to simulate the ladder diagrams, which are found in most of the electrical applications. The following Boolean Logic blocks are available in HYSYS: l

And Gate

l

Or Gate

l

Not Gate

l

Xor Gate

l

On Delay Gate

l

Off Delay Gate

l

Latch Gate

l

Counter Up Gate

l

Counter Down Gate

l

Cause And Effect Matrix

Note: To evaluate the Boolean Logic blocks at each time step, open the Integrator property view and go to the Execution tab. In the Calculation Execution Rates group, change the Control and Logical Ops field value to 1. This change ensures that your time sensitive Boolean Logic blocks like On Delay and Off Delay are executed at the required time instead of a one-time step delay. This change also slows down the HYSYS calculation rate and is noticeable for large cases.

22 Boolean Operations

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Boolean Logic Blocks Property View Boolean Logic

Icon

Not Gate

And Gate

Or Gate

Xor Gate

Off Delay Gate

On Delay Gate

Latch Gate

Counter Up Gate

Counter Down Gate

Cause And Effect Matrix

The property view for all the Boolean Logic blocks in HYSYS contains four tabs (Connections, Monitor, Stripchart, and User Variables), a Delete button, and a Face Plate button.

Logical Operation Face Plate Property View The Face Plate button lets you access the Face Plate property view. The Face Plate property view lets you see the Boolean type and output value at a glance.

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22 Boolean Operations

On the PFD property view, the Digital/Boolean and Boolean/Boolean logical connections have the capability to display the change of logical state by changing the line color to either green (1) or red (0).

The output is set up to have a default initial value of 1 for all the Boolean Logic blocks.

Boolean Connections Tab Use the Connections tab for any Boolean operation to connect operations to the Boolean Logic block. Boolean unit operations can make logical connections with the Digital Point operation as well as among themselves. The connections can either be made from the Connections tab or through the PFD. If the Boolean type supports multiple process variable sources, the Process Variable Sources group contains a table with three buttons with the same functions as the buttons in the Output Target group. l

Use the Edit OP button to change the output connection

l

Use the Add OP button to add an output connection

l

Use the Delete OP button to remove the output connection

Adding/Editing Process Variable (PV) Source Depending on the Boolean type, you must click the Select PV button, the Edit PV button or the Add PV button to open the Select Input PV property view. The Select Input PV property view is similar to the Variable Navigator property view. If you want to delete a process variable, click the Delete PV button.

Adding/Editing Output Target Click the Edit OP button or Add OP button to open the Select Output PV property view. Use the object filter to narrow the search in the object list. When an object is selected to receive the output value, click OK. You can also use Disconnect to disconnect the connection.

22 Boolean Operations

555

Boolean Monitor Tab The Monitor tab for any Boolean operation lets you monitor the input and output values of the Boolean Logic block. The contents of this tab varies from one Boolean Logic type to another. For example, the Monitor tab of an On Delay Gate Boolean also contains a field where you can specify the time delay.

Not Gate This unit operation perform a logical NOT function on an input. The output is the negative of the input. In other words, when the input is high the output is low and vice versa. The table below displays the function logic for the Not Gate. Input

Output

1

0

0

1

The Monitor tab of the Not Gate displays the following information: l l

Input Value. Displays the value received by the Boolean Logic block. Output Value. Displays the output value of the Boolean Logic block, based on the input value from the input connection.

Xor Gate This unit operation performs an exclusive or function on two inputs. The output state is always High (1) whenever anyone of the input is high (1), but it is low (0) when all of the inputs are high (1). The table below displays the function logic for Xor Gate. Input 1

Input 2

Output

1

1

0

1

0

1

0

1

1

0

0

0

Note: The input and output values can only be 1 or 0. This unit operation can only have two input connections. The output in this unit operation can also be fanned out.

The Monitor tab of the Xor Gate displays the following information:

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22 Boolean Operations

l

l l

l

Input. Contains the name and number used to designate the input connection. Object. Displays the operation name of the input connection. Initial State. Displays the input value received by the Boolean Logic block. Output Value. Displays the output value of the Boolean Logic block, based on the Boolean type and the input values from the input connections.

On Delay Gate This unit operation performs an on time delay function on a single input. The output’s signal is delayed for a specified time delay (θ) only when the input is set to be 1. The following logical expression is used to calculate the output (y) for an input (x) change. For x = 1: (1)

The Monitor tab of the On Delay Gate displays the following information: l

l l

Delay Time. Lets you specify the amount of time you want for the time delay function. The default value is 10 minutes. Input Value. Displays the value received by the Boolean Logic block. Output Value. Displays the output value of the Boolean Logic block, based on the input value from the input connection.

Notes: l

The input and output values can only be 1 or 0.

l

The output in this unit operation can also be fanned out.

Off Delay Gate This unit operation performs an off time delay function on a single input. The output’s signal is delayed for a specified time delay (θ) only when the input is set to be 0. The following logical expression is used to calculate the output (y) for an input (x) change. For x = 0: (1)

The Monitor tab of the Off Delay Gate displays the following information:

22 Boolean Operations

557

l

l l

Delay Time. Lets you specify the amount of time you want for the time delay function. The default value is 10 minutes. Input Value. Displays the value received by the Boolean Logic block. Output Value. Displays the output value of the Boolean Logic block, based on the input value from the input connection.

Note: l

The input and output values can only be 1 or 0.

l

The output in this unit operation can also be fanned out.

Latch Gate This unit operation provides a latch functionality. It requires two input signals; one for set and other one for reset. The second input is the prevailing input meaning that it specify the output to be set to high (1), reset to low (0), or left unchanged. The table below displays the function logic for the Latch Gate. Input 1

Input 2

Output

1

1

override state

1

0

1

0

1

0

0

0

previous state

Notes: By definition the latch gate lets you select the OP value when both of its inputs are high. So this state is known in the industry as override state.

The Monitor tab of the Latch Gate displays the following information: l

l

Prevailing Input. The radio buttons come into play when both of the inputs are high(1). It lets you specify what you want the output value to be. Selecting Set makes the OP value to be high(1), and Reset makes it low(0). Input. Contains the name and number used to designate the input connection.

Notes: l

The input and output values can only be 1 or 0.

l

This unit operation can only have two input connections.

l

The output in this unit operation can also be fanned out.

l l

558

Object. Displays the operation name of the input connection. Initial State. Displays the input value received by the Boolean Logic block.

22 Boolean Operations

l

Output Value. Displays the output value of the Boolean Logic block, based on the input value from the input connection.

Counter Up Gate This unit operation acts as an up counter. It counts up to a maximum counter value which is specified by the users. It is triggered every time the input is switched to a desired state. After reaching the maximum counter limit, it sets the output to a predefined value. The counter and output value is reset with the second input by switching it to high (1). The Monitor tab of the Counter Up Gate displays the following information: l

l l

l

l

l l

l

Maximum Counter. Lets you specify the counter limit value. The default value is 10. Current Counter. Displays the current counter value. PV Alarm. Lets you select which PV value triggers the counter to increase a step. You can only choose 0 or 1. Desired Output Value. Lets you select what the output value should be when the counter reaches maximum. You can only choose 0 or 1. Input. Contains the name and number used to designate the input connection. Object. Displays the operation name of the input connection. Initial State. Displays the input value received by the Boolean Logic block. Output Value. This field displays the output value of the Boolean Logic block, based on the input value from the input connection.

Notes: l

The input and output values can only be 1 or 0.

l

The output in this unit operation can also be fanned out.

Counter Down Gate This unit operation acts as a down counter. It counts down to a maximum counter value which is specified by the users. It is triggered every time the input 1 is switched to a desired state. After the counter has reached zero, it sets the output to a predefined value. The counter and output value is reset with the second input by switching it to High (1). The Monitor tab of the Counter Down Gate displays the following information: l

l

Maximum Counter. lets you specify the counter limit value. The default value is 10. Current Counter. Displays the current counter value.

22 Boolean Operations

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l

l

l

l l

l

PV Alarm. Lets you select which PV value triggers the counter to decrease a step. You can only choose 0 or 1. Desired Output Value. Lets you select what the output value should be when the counter reaches 0. You can only choose 0 or 1. Input. Contains the name and number used to designate the input connection. Object. Displays the operation name of the input connection. Initial State. Displays the input value received by the Boolean Logic block. Output Value. Displays the output value of the Boolean Logic block, based on the input value from the input connection. 

Notes: l

The input and output values can only be 1 or 0.

l

The output in this unit operation can also be fanned out.

Boolean And Gate The Boolean And Gate performs a logical AND function on a set of inputs. The output is always low as long as any one of the input is low and it is high when all of the inputs are high. The table below displays the function logic for the And Gate. Input 1

Input 2

Input 3

Output

1

1

1

1

1

0

0

0

0

1

0

0

0

0

1

0

0

0

0

0

Notes: l

The input and output values can only be 1 or 0.

l

The output in this unit operation can also be fanned out.

Specifying Boolean And Gate Connections Use the Connections tab for the Boolean And Gate to connect operations to the Boolean Logic block. Boolean unit operations can make logical connections with the Digital Point operation, as well as among themselves. The connections can either be made from the Connections tab or through the PFD. l

560

Click the Add PV button to open the Select Input PV property view. The Select Input PV property view is similar to the Variable Navigator

22 Boolean Operations

property view. l

If you want to delete a process variable, click the Delete PV button.

If the Boolean type supports multiple process variable sources, the Process Variable Sources group contains a table with three buttons with the same functions as the buttons in the Output Target group. l l

l

Use the Edit OP button to change the output connection. Use the Add OP button to add an output connection. The Select Output PV property view appears. Use the object filter to narrow the search in the object list. When an object is selected to receive the output value, click OK. You can also use Disconnect to disconnect the connection. Use the Delete OP button to remove the output connection.

Monitoring Boolean And Gate Input and Output Values The Monitor tab for the Boolean And Gate lets you monitor the input and output values of the Boolean Logic block. The Monitor tab of the And Gate displays the following information: l

l l

l

Input. Contains the name and number used to designate the input connection. Object. Displays the operation name of the input connection. Initial State. Displays the input value received by the Boolean Logic block. Output Value. Displays the output value of the Boolean Logic block, based on the Boolean type and the input values from the input connections.

Boolean Or Gate The Boolean Or Gate performs a logical OR function on a set of inputs. The output is always high as long as any one of the input is high and it is low when all of the inputs are low. The table below displays the function logic for the Or Gate. Input 1

Input 2

Input 3

Output

1

1

1

1

1

0

0

1

0

1

0

1

0

0

1

1

22 Boolean Operations

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Input 1

Input 2

Input 3

Output

0

0

0

0

Notes: l

l

The Or Boolean Logic block can have any number of inputs and a single output, which can be fanned out. The input and output values can only be 1 or 0.

Specifying Boolean Or Gate Connections Use the Connections tab for the Boolean Or Gate to connect operations to the Boolean Logic block. Boolean unit operations can make logical connections with the Digital Point operation, as well as among themselves. The connections can either be made from the Connections tab or through the PFD. l

l

Click the Add PV button to open the Select Input PV property view. The Select Input PV property view is similar to the Variable Navigator property view. If you want to delete a process variable, click the Delete PV button.

If the Boolean type supports multiple process variable sources, the Process Variable Sources group contains a table with three buttons with the same functions as the buttons in the Output Target group. l l

l

Use the Edit OP button to change the output connection. Use the Add OP button to add an output connection. The Select Output PV property view appears. Use the object filter to narrow the search in the object list. When an object is selected to receive the output value, click OK. You can also use Disconnect to disconnect the connection. Use the Delete OP button to remove the output connection.

Monitoring Boolean Or Gate Input and Output Values The Monitor tab for the Boolean Or Gate lets you monitor the input and output values of the Boolean Logic block. The Monitor tab of the Or Gate displays the following information: l

l l

l

562

Input. Contains the name and number used to designate the input connection. Object. Displays the operation name of the input connection. Initial State. Displays the input value received by the Boolean Logic block. Output Value. Displays the output value of the Boolean Logic block,

22 Boolean Operations

based on the Boolean type and the input values from the input connections.

Cause and Effect Matrix The Cause and Effect Matrix unit operation replicates a Cause and Effect matrix commonly used in designing and operating the safety system of many processing plants. It looks at process values throughout the process and, based upon safety thresholds, determines if certain equipment and/or valves should be shutdown. The unit operation is similar to a spreadsheet. It takes inputs called Causes and sends outputs called Effects. The input can be any simulation variable from your case or a simple switch that does not need to be connected to an object’s variable. Each input generates either a Healthy (1) or Tripped (0) state. The output is a Boolean (1 or 0) result from processing one of the Cause and Effect Matrix columns. The output may write or export its result to any simulation variable within your case. You must specify a variable of discrete type (1 or 0). The output is not required to be connected to an object or variable. The same 1 or 0 result is produced from the matrix column, and then any other object in the simulation may read or use this value. l

l

l

It is important that you clarify the 1 and 0 convention of the Cause and Effect Matrix for Healthy/Tripped, On/Off, Start/Stop, and so forth. For both the inputs and outputs, a result of 0 indicates Tripped, whereas a result of 1 indicates Healthy, except where the Invert check box is selected. When the Invert check box is selected, a result of 0 indicates Healthy, whereas a result of 1 indicates Tripped.

The matrix is processed one column at a time to determine the resultant state of the output associated with that column. The associated input state is reviewed for each element (or row entry) of a particular column having a nonblank user-specified matrix element. All of the matrix elements of that column (and their associated input state) are compared based upon their respective and collective meaning to determine the Cause result. Note: You can access the Cause and Effect Matrix Help property view by clicking on the Cause and Effect Help button on the C&E Matrix tab.

The Boolean inputs enter through logical gate type operations (and, or, not, and so forth) with each other to determine the resultant Boolean value. Each matrix element type is described in the following table.

22 Boolean Operations

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Matrix Elements

Description

X

TRIP

One or more zero input(s) causes a zero output.

R

RESET

One or more 1 inputs causes a 1 output (as long as there are no X, T or C active and ALL P must be 1) There is no requirement to have a reset on a particular output. If you want a reset, this can either be done with one or more R matrix element entries or a local reset switch. In the case of both R and a local reset, then both reset features must be reset for the output to return to normal, and the local reset must be done last.

T

TIMED TRIP

Same as the TRIP but the input must have remained zero for at least the time period. The T matrix element should be followed by an integer representing the number of seconds of time delayed trip.

C

COINCIDENT TRIP

In contrast to all other trips, a zero input for ALL the coincident signals of the same grouping causes a zero output. The C matrix element should be followed by an integer representing the Coincident group number. There should be more than one in each group.

P

PERMISSIVE

All P inputs must be 1 to permit an R to have the desired effect. Also required for a STANDBY 1 effect, a local reset and a local switch ON.

I

INHIBIT

A 1 will inhibit any trip of the output which would normally be caused by an X, T or C.

S

STANDBY

A 1 will cause a 1 (as long as there are no X, T or C active and ALL P must be 1), and a zero will cause a zero output (no INHIBIT applicable). Normally one would not want more than one Standby input designation per output. If you have more than one Standby, ALL Standby inputs must have a 1 for the output to be started (1 result). Otherwise, a zero output result is produced. All Permissive inputs must be 1 for the Standby 1 action to occur.

Note: It is recommended that you build a dynamics case first with all the specifications in place before adding and configuring a Cause and Effect Matrix.

Configuring a Cause and Effect Matrix There are no PFD streams or lines that connect to or from the Cause and Effect Matrix operation. Hence you can place it anywhere and on any flowsheet. You can also view all simulation variables across flowsheets, the same as with a Spreadsheet. To add a new Cause and Effect Matrix unit operation to the flowsheet, refer to Boolean Logic Blocks Property View.

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22 Boolean Operations

You can set the global defaults and controls on the Parameters tab. l

You can specify the global defaults by selecting the appropriate check boxes.

Check Box

Description

Input Invert

Lets you set the invert check box on for all new inputs.

Output Invert

Lets you set the invert check box on for all new outputs.

Hand Switch Pulse Duration

You can specify the pulse duration for any hand Switch inputs that are pulsed.

Always Update Output Objects

You can select this check box, if you want to ensure that the results from the logic calculations are sent every timestep to the output objects.

Use Output Resets

Select this check box if you want the Use Reset check box selected for all new outputs.

Use Local Switches for Outputs

You can select this check box if you want the Use Local Switch check box selected for all new outputs.

Insert New Above/To Left

When you add a new row or column and this check box is selected, the row or column will be added above (to the left) of that currently selected row or column.

l

You can specify the global control by selecting the appropriate check boxes.

Check Box

Description

Reset All Outputs

If you want to reset all individual outputs, select this check box.

Bypass All Outputs

When you select this check box, the Bypass check box of each output is selected.

Trace Alarms & Trips

If you want to trace the occurrence of input alarms, input trips and output trips, select this check box. The Trace Alarms & Trips check box affects all Cause and Effect matrix instances in your model.

You can view all the input and output configuration information on the Parameters tab.

Connecting the Inputs 1. On the Connections tab or the C&E Matrix tab, click the Add Input button to add and connect an input. The Simulation Navigator

22 Boolean Operations

565

appears. 2. From the Simulation Navigator, select the input variable. Then click OK. By default, the new input is added at the bottom of any existing inputs. From the Parameters tab, select the Insert New Above/To Left check box. The new input is added above the currently selected row. You have to select the bottom blank input row to add to the bottom of the existing inputs. 3. Alternatively, if you want to add switch inputs, click the Add Switch button on the C&E matrix tab. A new input row is added, but no simulation variable needs to be selected. You can manually change the switch during the operation of the dynamic model. A switch input is useful for a R(eset) matrix element entry. You should make this a Pulse On type switch. Switches can also be useful as an emergency shutdown push button if you want to test your dynamic model response to the trip of a collection of outputs. You can change the state of the switch by clicking on the appropriate radio buttons. (In the Inputs (Causes) table, click on a row with the SW check box selected.) 4. Enter the description, tag, and comment (if any) for the Inputs (Causes). The description appears to the left of each input row, and its associated matrix elements on the C&E Matrix tab. 5. For all inputs with a simulation variable (not a switch), except for the Digital Point’s OP State or an output result from a Cause and Effect matrix, specify the trip threshold. Select the High? check box if a value higher than the threshold will result in a tripped input. Otherwise, a low threshold trip is assumed. Note: The input can also be a time delayed Trip resulting to zero by entering a non-zero time in the Off Delay field.

You can also specify an Alarm threshold, which acts as a pre-alarm prior to the trip actually occurring. Click the Invert check box, if you want to invert the meaning of the matrix elements. Note: The inversion (1 to 0 or 0 to 1) occurs at the completion of the normal input processing just before the input result is passed on for matrix processing. Hence the input status, trace messages, and so forth, occur as normal regardless of inversion.

6. You can also override the effect of any tripped inputs by clicking on the OR (Override) check box in the Inputs (Causes) table on the C&E Matrix tab or the Inputs (Causes) group on the Parameters tab. You can use this as a startup override. If a trip requires a reset, you will have to activate the input(s), which resets it or you may have to reset the local reset.

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22 Boolean Operations

Connecting the Outputs 1. In the Outputs (Effects) group, click the Add Output button to create a new Cause and Effect Matrix column. Specify the simulation variable that you want the resultant 1 or 0 exported to. By default, the new output is added to the right (end) of any existing outputs. From the Parameters tab, select the Insert New Above/To Left check box. The new output is added to the left of the currently selected column. You can select the last blank output column to add to the right of the existing outputs. You can add a new column without connecting a simulation variable, if you want to just display a trip. You can also access the outputs result using the input in other logical operations including other Cause and Effect Matrices or using a Spreadsheet Import. Use the Simulation Navigator from that unit operation to select the Cause and Effect Matrix Output Result. 2. If you want to add a new column without connecting an object’s variable, click the Add Effect button in the Outputs (Effects) group. 3. Select the Reset? check box if you want to specify the output has its own local reset switch. This could perhaps represent a solenoid on a shutdown valve in the field. Once the Reset? check box is selected, then the Reset check box becomes active and relevant. Note: It is not recommended to configure an output without a reset. This can be a matrix element R(eset) or a local reset.

You can also specify the presence of a local or field switch for the controlled equipment that the output is associated with. To specify the presence, select the SW (Switch) check box. Click on the appropriate radio button to set the local switch state. Note: This switch has as its permissive any inputs with a P matrix element. Also, the switch is interlocked with any inputs affecting a trip of this output. An output must be reset before the local switch state can be changed from off.

You can click the Invert check box in the Outputs (Effects) group if the object being controlled expects a 1 to shutdown rather than a zero. This output inversion is done at the completion of the output processing, therefore the Outputs (Effects) group status bar and property view status window will show a Tripped status when sending a 1. If the trace option is turned on, a Tripped message will be traced, but a final value of 1 will be sent out. Note: When a certain input trips, causing a resulting trip in an output, there is also likely to be a cascading set of trips including other inputs which may appear to cause a trip of the original output. To detect what was the first input to cause the output's trip, you will see the relevant first out matrix element which caused the trip turn red. This color only returns to the default of blue when the output trip has cleared and been reset.

Once you have your Cause and Effect Matrix configured, you may want to use

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the Bypass check box of some or all outputs. This then makes the resultant value in the Outputs (Effects) group at the bottom of the C&E Matrix tab turn blue. This value should initialize to 1 and will remain at this until the bypass is released and matrix output processing proceeds. You can bumplessly prevent initialization trips in this manner.

Changing the Order of the Inputs or Outputs If the inputs or outputs are not in the order that you want, you can re-sort either the rows or columns of the Cause and Effect Matrix: 1. In the Inputs (Causes) or Outputs (Effects) tables of the C&E Matrix tab, select the row or column you want to move. 2. In the Inputs (Causes) or Outputs (Effects) groups, click the row or column number displayed in the # field. Note: The row or column number is displayed in blue indicating that you can change the value.

3. Type the new number that you want the row or column to be located at. If you type a number that is smaller than the number of the row (or column) you are moving, all rows (or columns) below the new number will be moved down (to the right) hence filling in the empty row (or column). Alternatively, if the new number is greater than the number of the row (or column) you are moving, the rows (or columns) will be moved up (to the left).

Viewing the Inputs and Outputs Specifications You can view all the specifications for the inputs and outputs on the C&E Matrix tab. If you want to view the specifications for the Input: l

On the C&E Matrix tab, select the row of the Cause data in the Inputs table. The information for that input is shown in the Inputs group at the bottom of the tab.

If you want to view the specifications for the Output: l

On the C&E Matrix tab, select the column of the Effect data in the Outputs table. The information for that output is shown in the Outputs group at the bottom of the tab.

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22 Boolean Operations

When you click a matrix element, the specifications for the selected row and column appear in the Inputs and Outputs groups at the bottom of the tab. You can drag and drop input or output object/variables to the object or variable columns of the selected row or column in the Inputs (Causes) or Outputs (Effects) groups. Select the variable from another unit operation, and then right-click to drag the selection to the desired location. When you drag the variable, the appearance of the cursor changes. The functionality is similar to dragging the variable in the Spreadsheet. The C&E Matrix tab also shows the state of each input and output. State

Description Healthy (1 result)

Tripped (0 result)

For an input this means alarm. For an output this indicates some other state. Refer to the Output status at the bottom of the property view for an indication of the exact status. For both inputs and outputs, this indicates that attention is most likely required.

Viewing Status Messages While integrating, the status window and the Cause and Effect Matrix's status bar may update to show the following three states: l

One or more outputs have tripped

l

One or more inputs are in alarm

l

One or more outputs require reset (either via an input with an R matrix element or via a local output reset).

The status of the inputs and outputs is shown in the table below: State

Inputs

Outputs

Healthy

1

1

Alarm

2

Tripped

0

0

Reset

2

LocalReset

3

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State

Inputs

Outputs

ManualOff

4

AutoOff

5

Viewing Trace Messages Note: The Cause and Effect Matrix tracing is turned on by selecting the Trace & Alarms check box on the Global group of the Parameters tab.

You can also add a timestamp to the trace messages. 1. Click File | Options. The Simulation Options property view appears. 2. In the Errors section, select the Prefix data and time to error and trace messages check box to add the timestamp to the trace messages.

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22 Boolean Operations

23 Control Ops

HYSYS has the following Control operations: l

Split Range Controller

l

Ratio Controller

l

PID Controller

l

MPC Controller

l

DMCplus Controller

Control Operation

Icon

Control Operation

Split Range Controller

MPC Controller

Ratio Controller

DMCplus Controller

Icon

PID Controller

All Control operations contain the following buttons at the bottom of the property view: l l

l

Delete. You can remove the Control ops by clicking this button. Face Plate. You can access the Face Plate property view by clicking this button. Control Valve. You can access the Control Valve property view by clicking this button. or

l

23 Control Ops

Control OP Port. You can access the Control OP Port property view by clicking this button.

571

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23 Control Ops

24 Split Range Controller

In the Split Range Controller, several manipulated variables are used to control a single process variable. Here both manipulated variables are driven by the output of a single controller. However, the range of operation for the manipulated variables can be independent of each other. Typical examples include the control of the pressure in a chemical reactor by manipulating the inflow and outflow from the reactor. Another classic example is the temperature control of a vessel by manipulating both the cooling water flow and steam flow to the vessel. When there is more than one controller in the strategy, for example, one single process variable with two controllers and two manipulated variables, the control is referred to as a multiple controller strategy. In the present implementation in HYSYS there are two outputs that you have to choose. The outputs can be configured as having negative or positive gains with ranges that are independent of each other. In other words, there can be an overlap of the ranges. The figure below shows the Split Range Controller property view.

24 Split Range Controller

573

The Split Range Controller property view contains the following tabs: l

Connections

l

Parameters

l

Split Range Setup

l

Stripchart

l

User Variables

Connections Tab On the Connections tab, you can select the process variable source and the output target objects. Object

Description

Name field

Allows you to change the name of the operation.

Process Variable Source group

Output Target Object group

Remote Setpoint group

l

Select PV button enables you to access the Select Input PV property view and select the source object of the Process Variable.

l

Object field displays the Process Variable object (stream or operation) that owns the variable you want to compare.

l

Variable field displays the variable of the selected object.

l

Select OP button enables you to access the Select OP Object property view and select the source object of the Output Target.

l

Object field displays the object (stream or operation) that is controlled by the operation.

l

Variable field displays the variable of the selected object.

l

Select RSP button enables you to access the Select Remote Setpoint property view and select the source object of the Remote Setpoint.

l

Remote Setpoint field displays the selected master controller.

Parameters Tab The Parameters tab contains the following pages:

574

l

Operation

l

Configuration

l

Advanced

l

Autotuning

l

IMC Design

24 Split Range Controller

l

Scheduling

l

Alarms

l

Signal Processing

l

Initialization

Operation Page On the Operation page, you can manipulate how the operation reacts to the process variable inputs. Object

Description

Action

You can select one of the two types of action available for the operation to take when the process variable value deviates from the setpoint value:

Controller Mode

Execution

l

Direct: When the PV rises above the SP, the OP increases. When the PV falls below the SP, the OP decreases.

l

Reverse: When the PV rises above the SP, the OP decreases. When the PV falls below the SP, the OP increases.

You can select from four types of controller modes: l

Off: The operation does not manipulate the control valve, although the appropriate information is still tracked.

l

Manual: Manipulate the operation output manually.

l

Automatic: The operation reacts to fluctuations in the Process Variable and manipulates the Output according to the logic defined by the tuning parameters.

l

Casc: The main controller reacts to the fluctuations in the Process Variable and sends signals to the slave controller (Remote Setpoint Source).

You can select from two types of execution. l

Internal: Confines the signals generated to stay within HYSYS.

l

External: Sends the signals to a DCS, if a DCS is connected to HYSYS.

Sp

Allows you to specify the setpoint value.

Pv

Displays the process variable value.

Op

Displays the output value.

Split Range Output

Displays the current OP value in percent for each output.

Kc (Gain)

Allows you to specify the proportional gain of the operation.

Ti (Reset)

Allows you to specify the integral (reset) time of the operation.

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575

Object

Description

Td (Derivative)

Allows you to specify the derivative (rate) time of the operation.

Tuning Parameters Group The Tuning Parameters group allows you to define the constants associated with the PID control equation. The characteristic equation for a PID Controller is given below: (1)

where: OP(t) = controller output at time t OPss = steady state controller output (at zero error) E(t) = error at time t Kc = proportional gain of the controller Ti = integral (reset) time of the controller Td = derivative (rate) time of the controller The error at any time is the difference between the Setpoint and the Process Variable: (2) Depending on which of the three tuning parameters you have specified, the Controller responds accordingly to the error. A Proportional-only controller is modeled by providing only a value for Kp, while a PI (Proportional-Integral) Controller requires values for Kp and Ti. Finally, the PID (Proportional-IntegralDerivative) Controller requires values for all three of Kp, Ti, and Td.

Configuration Page The Configuration page allows you to specify the process variable, setpoint, and output ranges.

PV: Min and Max Group For the operation to become operational, you must: 1. Define the minimum and maximum values for the PV (the operation cannot switch from Off mode unless PVmin and PVmax are defined). 2. Once you provide these values (as well as the Control Valve span), you can select the Automatic mode and give a value for the Setpoint. Note: HYSYS uses the current value of the PV as the set point by default, but you can change this value at any time.

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24 Split Range Controller

Note: Without a PV span, the Controller cannot function.

HYSYS converts the PV range into a 0-100% range, which is then used in the solution algorithm. The following equation is used to translate a PV value into a percentage of the range: (1)

SP Low and High Limits Group In this group, you can specify the higher and lower limits for the setpoints to reflect your needs and safety requirements. The setpoint limits enforce an acceptable range of values that could be entered via the interface or from a remote source. By default, the PV min. and max values are used as the SP low and high limits, respectively.

Op Low and High Limits Group In this group, you can specify the higher and lower limits for all the outputs. The output limits ensure that a predetermined minimum, or maximum output value is never exceeded. By default 0% and 100% is selected as a low and a high of limit, respectively for all the outputs. Note: When the Enable Op Limits in Manual Mode check box is selected, you can enable the set point and output limits when in manual mode.

Advanced Page The Advanced page contains the following four groups described in the table below:

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Group

Description

Control Interval

The time step between successive executions of the controller. When a new Split Range Controller is added to the PFD, the control interval is set to the product of the integration Step Size and Control and Logical Ops execution rates. You can change this value, but the new value must be a multiple of the current Step Size and Control and Logical Ops execution rates, or HYSYS will round it to the nearest multiple. Also, if you change the time step or Control and Logical Ops execution rates in the Integrator, the Control Interval value is updated upon running the Integrator as follows. l

If you have never changed the Control Interval value, it is updated to the product of Step Size and Control and Logical Ops execution rates.

l

Otherwise, it is updated to the multiple of Step Size and Control and Logical Ops execution rates that is nearest to your choice.

The readjustments of the Control Interval are performed to ensure the inputs to the control algorithm are consistent. Setpoint Ramping

Allows you to specify the ramp target and duration.

Setpoint Mode

Contains the options for setpoint mode and tracking, as well as, the option for remote setpoint.

Setpoint Options

Contains the option for setpoint tracking only in manual mode.

The setpoint signal is specified in the Selected Sp Signal # field by clicking the up or down arrow button, or by typing the appropriate number in the field. Depending upon the signal selected, the page displays the respective setpoint settings.

Setpoint Ramping Group The setpoint ramping function has been modified in the present MPC controllers. Now it is continuous, in other words, when set to on by clicking the Enable button, the setpoint changes over the specified period of time in a linear manner. Note: Setpoint ramping is only available in Auto mode.

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24 Split Range Controller

The Setpoint Ramping group contains the following two fields: l

l

Target SP. Contains the Setpoint you want the Controller to have at the end of the ramping interval. When the ramping is turn off, the Target SP field display the same value as SP field on the Configuration page. Ramping. Contains the time interval you want to complete setpoint change in.

Besides these two fields there are also two buttons available in this group: l

Enable. Activates the ramping process.

l

Disable. Stops the ramping process.

While the controller is in ramping mode, you can change the setpoint as follows: l

Enter a new setpoint in the Target SP field

l

Enter a new setpoint in the SP field, on the Operation page.

During the setpoint ramping the Target SP field shows the final value of the setpoint whereas the SP field, on the Operation page, shows the current setpoint seen internally by the control algorithm. Note: During ramping, if a second setpoint change has been activated, then Ramping Duration time would be restarted for the new setpoint.

Setpoint Mode Group You have now the ability to switch the setpoint from local to remote using the Setpoint mode radio buttons. Essentially, there are two internal setpoints in the controller, the first is the local setpoint where the you can manually specify the setpoint via the property view (interface), and the other is the remote setpoint which comes from another object such as a spreadsheet or another controller cascading down a setpoint, in other words, a master in the classical cascade control scheme. The Sp Local option allows you to disable the tracking for the local setpoint when the controller is placed in manual mode. You can also have the local setpoint track the remote setpoint by selecting the Track Remote radio button.

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The Remote Sp option allows you to select either the Use% radio button (for restricting the setpoint changes to be in percentage) or Use Pv units radio button (for setpoint changes to be in Pv units). l

l

If the Remote Sp is set to Use%, then the controller reads in a value in percentage from a remote source, and using the Pv range calculates the new setpoint. If the Remote Sp is set to Use Pv units, then the controller reads in a value from a remote source, and sets a new setpoint. The remote source’s setpoint must have the same units as the controller Pv.

SetPoint Options Group If you select the Track PV radio button then there is automatic setpoint tracking in manual mode, that sets the value of the setpoint equal to the value of the Pv prior to the controller being placed in the manual mode. This means that upon switching from manual to automatic mode the values of the setpoint and Pv were equal and, therefore, there was an automatic bumpless transfer. Also you have the option not to track the Pv, by selecting the No Tracking radio button, when the controller is placed in manual mode. However, when the controller is switched into the automatic mode from manual, there is an internal resetting of the controller errors to ensure that there is an instantaneous bumpless transfer prior to the controller recognizing a setpoint that is different from the Pv.

Algorithm Selection Group In the Algorithm Selection group you can select one of the three available controller update algorithms: l

PID Velocity Form

l

PID Positional Form (ARW = Anti-Reset Windup)

l

PID Positional Form (noARW)

Velocity or Differential Form Note: The velocity or differential form of the controller should be applied when there is an integral term. When there is no integral term a positional form of the controller should be used.

In the velocity or differential form, the controller equation is given as: (1)

where: u(t) = controller output and t is the enumerated sampling instance in time u(t-1) = value of the output one sampling period ago Kc, Ti, and Td = controller parameters

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24 Split Range Controller

h = sampling period Positional Form In the positional form of the algorithm, the controller output is given by: (2)

Here it is important to handle properly the summation term associated with the integral part of the control algorithm. Specifically, the integral term could grow to a very large value in instances where the output device is saturated, and the PV is still not able to get to the setpoint. For situations like the one above, it is important to reset the value of the summation to ensure that the output is equal to the limit (upper or lower) of the controller output. As such, when the setpoint is changed to a region where the controller can effectively control, the controller responds immediately without having to decrease a summation term that has grown way beyond the upper or lower limit of the output. This is referred to as an automatic resetting of the control integral term commonly called anti-reset windup. In HYSYS both algorithms are implemented as presented above with one key exception, there is no derivative kick. This means that the derivative part of the control algorithm operates on the process variable as opposed to the error term. As such the control equation given in Equation (1) is implemented as follows: (3)

Autotuning Page You can set the autotuning parameters on the Autotuning page. This page consists two groups: l

l

Autotuner Parameters. Contains the parameters required by the Autotuner to calculate the controller parameters. Autotuner Results. Displays the resulting controller parameters. You have the option to accept the results as the current tuning parameters.

Autotuner Parameters Group Note: In the present version of the software there are default values specified for the PID tuning. Before starting the autotuner, you must ensure that the controller is in the manual or automatic mode, and the process is relatively steady. Note: If you move the cursor over the tuning parameters field, the Status Bar displays the parameters range.

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In this group, you can specify the controller type by selecting the PID radio button or the PI radio button for the Design Type. In the present autotuner implementation there are five parameters that you must specify which are as follows: Parameter Ratio (Ti/Td) (Alpha)

Range 3.0 ≤ α ≤ 6.0

Gain ratio (Beta)

0.10 ≤ β ≤ 1.0

Phase angle (Phi)

30° ≤ ɸ ≤ 65°

Relay hysteresis (h)

0.01% ≤ h ≤ 5.0%

Relay amplitude (d)

0.5% ≤ d ≤ 10.0%

Autotuner Results Group This group displays the results of the autotuner calculation, and allows you to accept the results as the current controller setting. The Start Autotuner button activates the tuning calculation, and the Stop Autotuning button aborts the calculations. After running the autotuner, you have the option to accept the results either automatically or manually. Selecting the Automatically Accept check box sets the resulting controller parameters as the current value instantly. If the Automatically Accept check box is inactive, you can specify the calculated controller parameters to be the current setting by clicking the Accept button.

IMC Design Page The IMC Design page allows you to use the internal model control (IMC) calculator to calculate the operation parameters based on a specified model of the process one is attempting to control. The IMC method is quite common in most of the process industries and has a very solid theoretical basis. In general, the performance obtained using this design methodology is superior to most of the existing techniques for tuning PIDs. As such, when there is a process model available (first order plus delay) this approach should be used to determine the controller parameters. You must specify a design time constant, which is usually chosen as three times that of the measured process time constant. The IMC Design page has the following two groups:

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24 Split Range Controller

Group

Description

Process Model

Contains the parameters for the process model, which are required by the IMC calculator.

IMC PID Tuning

l

Process Gain

l

Process Time Constraint

l

Process Delay

l

Design To

Displays the operation parameters.

As soon as you enter the parameters in the Process Model group, the operation parameters are calculated and displayed in the IMC PID Tuning group. You can accept them as the current tuning parameters by clicking the Update Tuning button.

Scheduling Page The Scheduling page gives you the ability to do parameter scheduling. This feature is quite useful for nonlinear processes where the process model changes significantly over the region of operation. The parameter scheduling is activated through the Parameter Schedule check box. You can use three different sets of PID parameters, if you so desires for three different regions of operation. The following regions of operation can be specified from the Selected Range drop-down list. l

Low Range

l

Middle Range

l

High Range

These regions of operations can be based either on the setpoint, or PV of the controller. The ranges can also be specified, the default values are 0-33%, 33%-66%, and 66%-100% of the selected scheduling signal. You need to specify the middle range limit by defining the Upper and Lower Range Limits. Note: The values of 0 and 100 cannot be specified for both the Lower and the Upper Range Limits.

Alarms Page The Alarms page allows you to set alarm limits on all exogenous inputs to and outputs from the controller. The Alarms page contains two groups:

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583

l

Alarm Levels

l

Alarms

Alarm Levels Group The Alarm Level group allows you to set, and configure the alarm points for a selected signal type. There are four alarm points that could be configured: l

LowLow

l

Low

l

High

l

HighHigh

The alarm points should be specified in the descending order from HighHigh to LowLow points. You cannot specify the value of the Low and LowLow alarm points to be higher than the signal value. Similarly, the High and HighHigh alarm points cannot be specified to a value lower than the signal value. Also, no two alarm points can be specified to a similar value. In addition, you can specify a deadband for a given set of alarms. This can be helpful in situations where the signal is “noisy” to avoid constant triggering of the alarm. If a deadband is specified, you have to specify the alarm points so that their difference is greater than the deadband. At present the range for the allowable deadband is as follows: 0.0% ≤ deadband ≤ 1.5% of the signal range. Note: The above limits are set internally, and are not available for adjustment by the user.

Alarms Group The Alarms group displays the recently violated alarm for the following signals: Signal

Description

PV

Process Variable

OP

Output

SP

Setpoint

Signal Processing Page The Signal Processing page allows you to add filters to any signal associated with the operation, as well as test the robustness of any tuning on the controller. This page consists of two groups:

584

l

Signal Filters

l

Noise Parameters

24 Split Range Controller

Both of these groups allow you to filter, and test the robustness of the following tuning parameters: l

Pv

l

Op

l

Sp

l

Dv

l

Rs

To apply the filter select the check box corresponding to the signal you want to filter. Once active, you can specify the filter time. As you increase the filter time you are filtering out frequency information from the signal. For example, the signal is noisy, there is a smoothing effect noticed on the plot of the PV. Notice that it is possible to add a filter that makes the controller unstable. In such cases the controller needs to be returned. Adding a filter has the same effect as changing the process, which the controller is trying to control. Activating a Noise Parameter is done the same way as adding a filter. However, instead of specifying a filter time you are specifying a variance. Notice that if a high variance on the PV signal is chosen the controller may become unstable. As you increase the noise level for a given signal you observe a somewhat random variation of the signal.

Initialization Page The Initialization page allows you to initialize an appropriate OP value to start the controller smoothly. To back initialize the controller, click on the Back Initialization button and HYSYS will initialize the controller output based on the current position of the executor (for example, a valve or another controller). The current back initialization OP value is displayed in the OP value field. Since the split controller has two outputs (two OP values), you can click on the Output1 or Output2 radio button to choose which OP value you want to use to back initialize the controller.

Split Range Setup Tab The Split Range Setup tab allows you to specify the split ranges for the controller. The Split Range Setup tab consists of three groups: Split Range Setup, PID Values, and Split Range Outputs.

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Stripchart Tab The Stripchart tab allows you to select and create default strip charts containing various variable associated to the operation.

User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

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25 Ratio Controller

The Ratio Controller’s objective is to keep the ratio of two variables, the load variable and the manipulated variable, constant.

The Ratio Controller is a special type of feedforward control, and can be implemented in two ways: l

l

Method 1. The actual ratio of the two variables is calculated using a divider, and is sent on to the ratio controller in which the setpoint is the required ratio. Method 2. The value of the load variable is measured and sent to a ratio station, which then calculates the setpoint of the manipulated (second) variable.

The inclusion of a divider in approach (method 1) renders the methodology less desirable since it results in a loop in which the process gain varies in a nonlinear manner as a result of the included divider. As such, method (2) is the preferred way of doing the ratio implementation, and is the approached followed in this implementation for HYSYS. The Ratio Controller property view contains the following tabs:

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l

Connections

l

Parameters

l

Stripchart

l

User Variables

Connections Tab On the Connections tab, you can select the process variable source, and the output target object. You can also select a remote setpoint value. Object

Description

Name

Allows you to change the name of the operation.

Process Variable Source: Object

Contains the Process Variable Object (stream or operation) that owns the variable you want to compare.

Process Variable Source: Variable

Contains the Process Variable you want to compare.

PV

From the PV drop-down list, you can specify the Controlled or Reference process variable.

Output Target Object

The stream or valve, which is controlled by the operation.

Select PV/OP

These two buttons open the Variable Navigator which selects the Process Variable and the Output Target Object respectively.

Remote Setpoint Source

If you are using set point from a remote source, select the remote Setpoint Source associated with the Master controller

Parameters Tab The Parameters tab contains the following pages:

588

l

Configuration

l

Range

l

Advanced

l

Autotuning

l

IMC Design

l

Scheduling

l

Alarms

l

Signal Processing

l

Initialization

25 Ratio Controller

Configuration Page On the Configuration page, you can manipulate how the operation reacts to the process variable inputs. Object

Description

Action

You can select one of the two types of action available for the operation to take when the process variable value deviates from the setpoint value:

SP Mode

Mode

Execution

l

Direct. When the PV rises above the SP, the OP increases. When the PV falls below the SP, the OP decreases.

l

Reverse. When the PV rises above the SP, the OP decreases. When the PV falls below the SP, the OP increases.

You have the ability to switch the setpoint from Local to Remote. Essentially, there are two internal setpoints in the controller: l

Local: the local setpoint where you can manually specify the setpoint via the property view (interface).

l

Remote: the remote setpoint which comes from another object such as a spreadsheet or another controller cascading down a setpoint. In other words, a master in the classical cascade control scheme.

You can select from three types of controller mode: l

Off. The operation does not manipulate the control valve, although the appropriate information is still tracked.

l

Manual. Manipulate the operation output manually.

l

Automatic. The operation reacts to fluctuations in the Process Variable and manipulates the Output according to the logic defined by the tuning parameters.

You can select from two types of execution. l

Internal. Confines the signals generated to stay within HYSYS.

l

External. Sends the signals to a DCS, if a DCS is connected to HYSYS.

Ref. PV

The value in this field is used to calculate the setpoint along with the ratio.

PV

Displays the process variable value.

Ratio

Displays the set or calculated ratio value between the selected the two process variables.

Current Ratio

Displays the current ratio (a calculated value).

OP

Displays the output value.

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Tuning Parameters Group The Tuning Parameters group allows you to define the constants associated with the PID control equation. The characteristic equation for a PID Controller is given below: (1)

where: OP(t) = controller output at time t OPss = steady state controller output (at zero error) E(t) = error at time t Kc = proportional gain of the controller Ti = integral (reset) time of the controller Td = derivative (rate) time of the controller The error at any time is the difference between the Setpoint and the Process Variable: (2) Depending on which of the three tuning parameters you have specified, the Controller responds accordingly to the error. A Proportional-only controller is modeled by providing only a value for Kp, while a PI (Proportional-Integral) Controller requires values for Kp and Ti. Finally, the PID (Proportional-IntegralDerivative) Controller requires values for all three of Kp, Ti, and Td.

Algorithm Selection Group In the Algorithm Selection group you can select one of three available controller update algorithms: l

PID Velocity Form

l

PID Positional Form (ARW = Anti-Reset Windup)

l

PID Positional Form (noARW)

Velocity or Differential Form Note: The velocity or differential form of the controller should be applied when there is an integral term. When there is no integral term a positional form of the controller should be used.

In the velocity or differential form the controller equation is given as: (3)

where: u(t) = controller output and t is the enumerated sampling instance in time

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25 Ratio Controller

u(t-1) = value of the output one sampling period ago Kc, Ti, and Td = controller parameters h = sampling period Positional Form In the positional form of the algorithm, the controller output is given by: (4)

Here it is important to handle properly the summation term associated with the integral part of the control algorithm. Specifically, the integral term could grow to a very large value in instances where the output device is saturated and the PV is still not able to get to the setpoint. For situations like the one above, it is important to reset the value of the summation to ensure that the output is equal to the limit (upper or lower) of the controller output. As such, when the setpoint is changed to a region where the controller can effectively control, the controller responds immediately without having to decrease a summation term that has grown way beyond the upper or lower limit of the output. This is referred to as an automatic resetting of the control integral term commonly called anti-reset windup. In HYSYS both algorithms are implemented as presented above with one key exception, there is no derivative kick. This means that the derivative part of the control algorithm operates on the process variable as opposed to the error term. As such, the control equation given in the Velocity or Differential Form equation above is implemented as follows: (5)

Range Page The Range page allows you to specify the process variable, setpoint, and output ranges.

PV: Min and Max Group For the operation to become operational, you must: 1. Define the minimum and maximum values for the PV (the operation cannot switch from Off mode unless PVmin and PVmax are defined). 2. Once you provide these values (as well as the Control Valve span), you can select the Automatic mode and give a value for the Setpoint. Note: HYSYS uses the current value of the PV as the set point by default, but you can change this value at any time.

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Note: Without a PV span, the Controller cannot function.

3. HYSYS converts the PV range into a 0-100% range, which is then used in the solution algorithm. The following equation is used to translate a PV value into a percentage of the range: (1)

SP Low and High Limits Group In this group, you can specify the higher and lower limits for the Setpoints to reflect your needs and safety requirements. The Setpoint limits enforce an acceptable range of values that could be entered via the interface or from a remote source. By default the PV min. and max values are used as the SP low and high limits, respectively.

Op Low and High Limits Group In this group, you can specify the higher and lower limits for all the outputs. The output limits ensure that a predetermined minimum or maximum output value is never exceeded. By default 0% and 100% is selected as a low and a high of limit, respectively for all the outputs. When the Enable Op Limits in Manual Mode check box is selected, you can enable the set point and output limits when in manual mode.

Advanced Page The Advanced page contains the following four groups:

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Group

Description

Control Interval

The time step between successive executions of the controller. When a new Ratio Controller is added to the PFD, the control interval is set to the product of the integration Step Size and Control and Logical Ops execution rates. You can change this value, but the new value must be a multiple of the current Step Size and Control and Logical Ops execution rates, or HYSYS will round it to the nearest multiple. Also, if you change the time step or Control and Logical Ops execution rates in the Integrator, the Control Interval value is updated upon running the Integrator as follows. l

If you have never changed the Control Interval value, it is updated to the product of Step Size and Control and Logical Ops execution rates.

l

Otherwise, it is updated to the multiple of Step Size and Control and Logical Ops execution rates that is nearest to your choice.

The readjustments of the Control Interval are performed to ensure the inputs to the control algorithm are consistent. Setpoint Ramping

Allows you to specify the ramp target and duration.

Setpoint Mode

Contains the options for setpoint mode and tracking as well as the option for remote setpoint.

Setpoint Options

Contains the option for setpoint tracking only in manual mode.

The setpoint signal is specified in the Selected Sp Signal # field by clicking the up or down arrow button or typing the appropriate number in the field. Depending upon the signal selected, the Advanced page displays the respective setpoint settings.

Setpoint Ramping Group The setpoint ramping function has been modified in the present MPC controllers. Now it is continuous, in other words, when set to on by clicking the Enable button, the setpoint changes over the specified period of time in a linear manner. The Setpoint Ramping group contains the following two fields: Field

Input Required

Target SP

Contains the Setpoint you want the Controller to have at the end of the ramping interval. When the ramping is turn off, the Target SP field display the same value as SP field on the Configuration page.

Ramping Duration

Contains the time interval you want to complete setpoint change in.

Note: Setpoint ramping is only available in Auto mode.

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Besides these two fields there are also two buttons available in this group: l

Enable. Activates the ramping process.

l

Disable. Stops the ramping process.

While the controller is in ramping mode, you can change the setpoint as follows: l

Enter a new setpoint in the Target SP field.

l

Enter a new setpoint in the SP field, on the Operation page.

During the setpoint ramping the Target SP field shows the final value of the setpoint whereas the SP field, on the Operation page, shows the current setpoint seen internally by the control algorithm. Note: During ramping, if a second setpoint change has been activated, then Ramping Duration time would be restarted for the new setpoint.

Setpoint Mode Group You have now the ability to switch the setpoint from local to remote using the Setpoint mode radio buttons. Essentially, there are two internal setpoints in the controller, the first is the local setpoint where you can manually specify the setpoint via the property view (interface), and the other is the remote setpoint which comes from another object such as a spreadsheet or another controller cascading down a setpoint, in other words, a master in the classical cascade control scheme. The Sp Local option allows you to disable the tracking for the local setpoint when the controller is placed in manual mode. You can also have the local setpoint track the remote setpoint by selecting the Track Remote radio button. The Remote Sp option allows you to select either the Use% radio button (for restricting the setpoint changes to be in percentage) or Use Pv units radio button (for setpoint changes to be in Pv units). l

l

594

If the Remote Sp is set to Use%, then the controller reads in a value in percentage from a remote source, and using the Pv range calculates the new setpoint. If the Remote Sp is set to Use Pv units, then the controller reads in a value from a remote source and sets a new setpoint. The remote source’s setpoint must have the same units as the controller Pv.

25 Ratio Controller

SetPoint Options Group If you select the Track PV radio button, then there is automatic setpoint tracking in manual mode, that sets the value of the setpoint equal to the value of the Pv prior to the controller being placed in the manual mode. This means that upon switching from manual to automatic mode the values of the setpoint and Pv were equal and, therefore, there was an automatic bumpless transfer. Also you have the option not to track the pv, by clicking the No Tracking radio button, when the controller is placed in manual mode. However, when the controller is switched into the automatic mode from manual, there is an internal resetting of the controller errors to ensure that there is an instantaneous bumpless transfer prior to the controller recognizing a setpoint that is different from the Pv.

Autotuning Page You can set the autotuning parameters on the Autotuning page. This page consists of two groups: l

l

Autotuner Parameters. Contains the parameters required by the Autotuner to calculate the controller parameters. Autotuner Results. Displays the resulting controller parameters. You have the option to accept the results as the current tuning parameters.

Autotuner Parameters Group In this group, you can specify the controller type by selecting the PID radio button or the PI radio button for the Design Type. In the present autotuner implementation there are five parameters that you must specify, which are as follows: Parameter Ratio (Ti/Td) (Alpha)

Range 3.0 ≤ α ≤ 6.0

Gain ratio (Beta)

0.10 ≤ β ≤ 1.0

Phase angle (Phi)

30° ≤ ϕ ≤ 65°

Relay hysteresis (h)

0.01% ≤ h ≤ 5.0%

Relay amplitude (d)

0.5% ≤ d ≤ 10.0%

In the present version of the software there are default values specified for the PID tuning. Before starting the autotuner, you must ensure that the controller is in the manual or automatic mode, and the process is relatively steady. If you move the cursor over the tuning parameters field, the Status Bar displays the parameters range.

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Autotuner Results Group This group displays the results of the autotuner calculation and allows you to accept the results as the current controller setting. The Start Autotuner button activates the tuning calculation, and the Stop Autotuning button abort the calculations. After running the autotuner, you have the option to accept the results either automatically or manually. Selecting the Automatically Accept check box sets the resulting controller parameters as the current value instantly. If the Automatically Accept check box is inactive, you can specify the calculated controller parameters to be the current setting by clicking the Accept button.

IMC Design Page The IMC Design page allows you to use the internal model control (IMC) calculator to calculate the operation parameters based on a specified model of the process one is attempting to control. The IMC method is quite common in most of the process industries, and has a very solid theoretical basis. In general, the performance obtained using this design methodology is superior to most of the existing techniques for tuning PIDs. As such, when there is a process model available (first order plus delay) this approach should be used to determine the controller parameters. You must specify a design time constant, which is usually chosen as three times that of the measured process time constant. The IMC Design page has the following two groups described in the table below: Group

Description

Process Model

Contains the parameters for the process model which are required by the IMC calculator.

IMC PID Tuning

l

Process Gain

l

Process Time Constraint

l

Process Delay

l

Design To

Displays the operation parameters.

As soon as you enter the parameters in the Process Model group, the operation parameters are calculated and displayed in the IMC PID Tuning group. You can accept them as the current tuning parameters by clicking the Update Tuning button.

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25 Ratio Controller

Scheduling Page The Scheduling page gives you the ability to do parameter scheduling. This feature is quite useful for nonlinear processes where the process model changes significantly over the region of operation. The parameter scheduling is activated through the Parameter Schedule check box. You can use three different sets of PID parameters if you so desire for three different regions of operation. The following regions of operation can be specified from the Selected Range drop-down list. l

Low Range

l

Middle Range

l

High Range

These regions of operations can be based either on the setpoint, or PV of the controller. The ranges can also be specified, the default values are 0-33%, 33%-66%, and 66%-100% of the selected scheduling signal. You need to specify the middle range limit by defining the Upper and Lower Range Limits. Note: The values of 0 and 100 cannot be specified for both the Lower and the Upper Range Limits.

Alarms Page The Alarms page allows you to set alarm limits on all exogenous inputs to and outputs from the controller. The Alarms page contains two groups: l

Alarm Levels

l

Alarms

Alarm Levels Group The Alarm Level group allows you to set, and configure the alarm points for a selected signal type. There are four alarm points that could be configured: l

LowLow

l

Low

l

High

l

HighHigh

The alarm points should be specified in the descending order from HighHigh to LowLow points. You cannot specify the value of the Low and LowLow alarm points to be higher than the signal value. Similarly, the High and HighHigh alarm points cannot be specified to a value lower than the signal value. Also, no two alarm points can be specified to a similar value. In addition, you can specify a deadband for a given set of alarms. This can be helpful in situations where the signal is “noisy” to avoid constant triggering of the alarm. If a

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deadband is specified, you have to specify the alarm points so that their difference is greater than the deadband. At present the range for the allowable deadband is as follows: 0.0% ≤ deadband ≤ 1.5% of the signal range. Note: The above limits are set internally and are not available for adjustment by the user.

Alarms Group The Alarms group displays the recently violated alarm for the following signals: Signal

Description

PV

Process Variable

OP

Output

SP

Setpoint

Signal Processing Page The Signal Processing page allows you to add filters to any signal associated with the operation, as well as test the robustness of any tuning on the controller. This page consists of two groups: l

Signal Filters

l

Noise Parameters

Both of these groups allow you to filter, and test the robustness of the following tuning parameters: l

Pv

l

Op

l

Sp

l

Dv

l

Rs

To apply the filter select the check box corresponding to the signal you want to filter. Once active you can specify the filter time. As you increase the filter time you are filtering out frequency information from the signal. For example, the signal is noisy, there is a smoothing effect noticed on the plot of the PV. Notice that it is possible to add a filter that makes the controller unstable. In such cases the controller needs to be returned. Adding a filter has the same effect as changing the process the controller is trying to control. Activating a Noise Parameter is done the same way as adding a filter. However, instead of specifying a filter time you are specifying a variance. Notice that if a high variance on the PV signal is chosen the controller may become unstable.

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As you increase the noise level for a given signal you observes a somewhat random variation of the signal.

Initialization Page The Initialization page allows you to set up a sophisticated controller by taking into account the problem of saturation in cascade control, and the need for an appropriate initial output value to ensure a smooth start-up. The Initialization page consists of two features: l

Back Initialization

l

Cascade Control Anti Windup

Back Initialization A proper initial OP Value is supplied to the controller to ensure the integration runs smoothly during start up. The Back Initialization button is used to initialize the controller output based on the current position of the executor (for example, a valve, a stream, or another controller). This prevents disturbances in the system during the initial switch-over.

Cascade Control Anti Windup A common problem associated with cascade control is saturation. Saturation occurs when the primary controller continues to integrate and send out correction signals to the secondary controller even when the output of the secondary controller is already at its designed limit. As a result, when the primary offset changes (decreases or increases), the primary controller cannot respond accordingly until it overcomes the saturation. By the time this happens, the primary offset is once again too large to be adjusted. This severely reduces the controller performance and even creates an unstable system as the output is always fluctuating. The Cascade Control Anti Windup check box allows you to prevent saturation by having the primary controller automatically calculate the feasible output that can be executed by the secondary controller. Once the primary controller detects that the output of the secondary controller has reached its limit (upper or lower), the primary controller will not integrate any further from getting into saturation. Thus, when the offset changes, both the primary and secondary controllers can react immediately without having to wait for the saturation to clear.

Stripchart Tab The Stripchart tab allows you to select and create default strip charts containing various variable associated to the operation.

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User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

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26 PID Controller

The Proportional-Integral-Derivative Controller operation is the primary means of manipulating the model in Dynamic mode. It adjusts a stream (OP) flow to maintain a specific flowsheet variable (PV) at a certain value (SP).

Note: The Controller can cross the boundaries between flowsheets, enabling you to sense a process variable in one flowsheet and control a valve in another.

The PID Controller property view contains the following tabs: l

Connections

l

Parameters

l

Monitor

l

Stripchart

l

User Variables

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Connections Tab The Connections tab allows you to select both the PV and OP. It is comprised of six objects described in the table below: Object

Description

Name

Contains the name of the controller. It can be edited by selecting the field and entering the new name.

Process Variable Source Object

Contains the Process Variable Object (stream or operation) that owns the variable you want to control. It is specified via the Variable Navigator.

Process Variable

Contains the Process Variable you want to control.

Output Target Object

The stream or valve, which is controlled by the PID Controller operation

Select PV/OP

These two buttons open the Variable Navigator which selects the Process Variable and the Output Target Object respectively.

Remote Setpoint Source

If you are using set point from a remote source, select the remote Setpoint Source associated with the Master controller

Process Variable Source Common examples of PVs include vessel pressure and liquid level, as well as stream conditions such as flow rate or temperature. Note: The Process Variable, or PV, is the variable that must be maintained, or controlled at a desired value.

To attach the Process Variable Source, click the Select PV button. Then select the appropriate object and variable simultaneously using the Variable Navigator.

Remote Setpoint Source The Remote Setpoint Source drop-down list allows you to select the remote sources from a list of existing operations. Note: A Spreadsheet cell can also be a Remote Setpoint Source.

The “cascade” controller mode is replaced by the ability to switch the setpoint from local to remote. The remote setpoint can come from another object such as a spreadsheet, or another controller cascading down a setpoint - in other words, a master in the classical cascade control scheme.

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26 PID Controller

Output Target Object The Controller compares the Process Variable to the Setpoint, and produces an output signal which causes the manipulated variable to open or close appropriately. Note: The Output of the Controller is the control valve which the Controller manipulates in order to reach the set point. The output signal, or OP, is the desired percent opening of the control valve, based on the operating range which you define in the Control Valve property view.

Selecting the Output Target Object is done in a similar manner to selecting the Process Variable Source. You are also limited to objects supported by the controller and not currently attached to another controller. The information regarding the control valve or control op port sizing is contained on a sub-view accessed by clicking the Control Valve or Control OP Port button found at the bottom of the PID Controller property view. Note: The Control Valve button (at the bottom right corner of the controller operation property view) appears if the OP is a stream. Note: The Control OP Port button (at the bottom right corner of the controller operation property view) appears when the OP is not a stream and there a range of specified values is required.

Parameters Tab The Parameters tab contains the following pages: l

Configuration

l

Advanced

l

Autotuner

l

IMC Design

l

Scheduling

l

Alarms

l

PV Conditioning

l

Signal Processing

l

FeedForward

l

Model Testing

l

Initialization

Configuration Page The Configuration page allows you to set the process variable range, controller action, operating mode, and depending on the mode, either the SP or OP, as well as tune the controller.

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SP and PV The PV (Process Variable) is the measured variable, which the controller is trying to keep at the Setpoint. The SP (Setpoint) is the value of the Process Variable, which the Controller is trying to meet. Depending on the Mode of the Controller, the SP is either entered by the user or displayed only. For the Controller to become operational, you must: 1. Define the minimum and maximum values for the PV (the Controller cannot switch from Off mode unless PVmin and PVmax are defined). 2. Once you provide these values (as well as the Control Valve span), you may select the Automatic mode, and give a value for the Setpoint. Note: HYSYS uses the current value of the PV as the set point by default, but you may change this value at any time. Note: Without a PV span, the Controller cannot function.

HYSYS converts the PV range into a 0-100% range, which is then used in the solution algorithm. The following equation is used to translate a PV value into a percentage of the range: (1)

OP The OP (or Output) is the percent opening of the control valve. The Controller manipulates the valve opening for the output stream in order to reach the set point. HYSYS calculates the necessary OP using the controller logic in all modes with the exception of Manual. In Manual mode, you may input a value for the output, and the setpoint becomes whatever the PV is at the particular valve opening you specify.

Modes The Controller operates in any of the following modes:

604

Controller Mode

Description

Off

The controller does not manipulate the control valve, although the appropriate information is still tracked.

Manual

Manipulates the controller output manually.

Auto

The controller reacts to fluctuations in the Process Variable, and manipulates the output according to the logic defined by the tuning parameters.

26 PID Controller

Controller Mode

Description

Casc

The main controller reacts to the fluctuations in the Process Variable, and sends signals to the slave controller (Remote Setpoint Source).

Indicator

Allows you to simulate the controller without controlling the process.

The mode of the controller can also be set on the Face Plate.

Execution You can select where the signal from the controller is sent using the drop-down list in the Execution field. You have two selections: l

Internal. Confines the signals generated to stay within HYSYS.

l

External. Sends the signals to a DCS, if a DCS is connected to HYSYS.

Action There are two options for the Action of the controller, which are described in the table below: Controller Action

Description

Direct

When the PV rises above the SP, the OP increases. When the PV falls below the SP, the OP decreases.

Reverse

When the PV rises above the SP, the OP decreases. When the PV falls below the SP, the OP increases.

That is, when the PV rises above the SP, the error becomes negative and the OP decreases. For a Direct-response Controller, the OP increases when the PV rises above the SP. This action is made possible by replacing Kp with -Kp in the Controller equation. A typical example of a Reverse Acting controller is in the temperature control of a Reboiler. In this case, as the temperature in the vessel rises past the SP, the OP decreases, in effect closing the valve and hence the flow of heat. Some typical examples of Direct-Acting and Reverse-Acting control situations are given below. l

Direct - Acting Controller Example 1: Flow Control in a Tee Suppose you have a three-way tee in which a feed stream is being split into two exit streams. You want to control the flow of exit stream Product 1 by manipulating the flow of stream Product 2: Process Variable and Setpoint

26 PID Controller

Product 1 Flow

605

l

Output

Product 2 Flow

When Product 1 Flow rises above the SP

The OP increases, in effect increasing the flow of Product 2 and decreasing the flow of Product 1.

When Product 1 Flow falls below the SP

The OP decreases, in effect decreasing the flow of Product 2 and increasing the flow of Product 1.

Direct - Acting Controller Example 2: Pressure Control in a Vessel Suppose you were controlling the pressure of a vessel V-100 by adjusting the flow of the outlet vapor, SepVapour:

l

Process Variable and Setpoint

V-100 Vessel Pressure

Output

SepVapour Flow

When V-100 Pressure rises above the SP

The OP increases, in effect increasing the flow of SepVapour and decreasing the Pressure of V-100.

When V-100 Pressure falls below the SP

The OP decreases, in effect decreasing the flow of SepVapour and increasing the Pressure of V-100.

Reverse - Acting Controller Example 1: Temperature Control in a Reboiler Reverse-Acting control may be used when controlling the temperature of reboiler R-100 by adjusting the flow of the duty stream, RebDuty:

l

606

Process Variable and Setpoint

R-100 Temperature

Output

RebDuty Flow

When R-100 Temperature rises above the SP

The OP decreases, in effect decreasing the flow of RebDuty and decreasing the Temperature of R-100.

When R-100 Temperature falls below the SP

The OP increases, in effect increasing the flow of RebDuty and increasing the Temperature of R-100.

Reverse - Acting Controller Example 2: Pressure Control in a Reboiler

26 PID Controller

Another example where Reverse-Acting control may be used is when controlling the stage pressure of a reboiler R-100 by adjusting the flow of the duty stream, RebDuty: Process Variable and Setpoint

R-100 Stage Pressure

Output

RebDuty Flow

When R-100 Stage Pressure rises above the SP

The OP decreases, in effect decreasing the flow of RebDuty and decreasing the Stage Pressure of R-100.

When R-100 Stage Pressure falls below the SP

The OP increases, in effect increasing the flow of RebDuty and increasing the Stage Pressure of R-100.

SP Mode: Local or Remote You have the ability to switch the setpoint from local to remote. Essentially, there are two internal setpoints in the controller, the first is the local setpoint where you can manually specify the setpoint via the property view (interface), and the other is the remote setpoint which comes from another object such as a spreadsheet or another controller cascading down a setpoint. In other words, a master in the classical cascade control scheme.

Tuning Parameters and Algorithm Selection Groups From the Algorithm Type selector, you can choose PID algorithms of four possible types or vendors: l

HYSYS

l

Honeywell

l

Foxboro

l

Yokogawa

Each of them offers a set of options or Algorithm Subtypes.

OP Override The INIT box usually indicates that the OP value displayed on the controller has been back-calculated either from another controller. The OP value is determined based on the Kc term and the PV range specified on the controller. See An example of an override controller in Aspen HYSYS Dynamics. A controller can show INIT under the following circumstances. Note: For certain DCS vendors, the INIT message appears as IMAN, or Initialization Manual mode. l

26 PID Controller

The controller is the master controller in a master-slave configuration and the slave controller is not in cascade mode. The OP for the master controller is back calculated, allowing for bumpless transfer when switching controller modes. The INIT message serves to notify the user that

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the OP is being calculated elsewhere. If a Selector Block or Transfer Function block is placed between the master and slave PIDs, the master controller enters INIT mode if the slave block is in Local (Non-Cascade) Mode. l

The controller is one of two (or more) controllers feeding their respective OPs into a selector block. The controller whose OP has not been selected will display an Unselected message to indicate that its OP has been calculated by the selector. Again, this is to facilitate a bumpless transfer when the selected controller changes.

External/Dynamic Reset Feedback When the Selector Block has multiple input signals from PID blocks and you selected the Minimum, Maximum, or Median radio buttons in the Mode section, the Output (OP) of unselected PIDs is tracked closely to the selected output, or OP. If the PID Controller is using the HYSYS PID Velocity Algorithm (selected on the Parameters tab | Configuration page of the PID Controller when you select Hysys from the Algorithm Type drop-down list and PID Velocity Form from the Algorithm Subtype drop-down list), HYSYS uses time-dependent reset feedback. The following equation is used: (2)

Where: n = current time step n-1 = previous time step h = control interval (time step) Ti = reset time, chosen to be the same as Integral time OPvel = OP calculated using the HYSYS Velocity algorithm (refer to the HYSYS PID Velocity Form equation for further information. For other algorithms, the steady state version of the above equation is used: (3)

Advanced Page The Advanced page contains the following four groups:

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Group

Description

Set Point Ramping

Allows you to specify the ramp target and duration.

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Group

Description

Set Point / OP Options

Contains the options for setpoint tracking.

Limit Setting

Allows you to set the upper and lower limits for set point and output targets.

Set Point Ramping Group The setpoint ramping function has been modified in the present PID controllers. Now it is continuous (in other words, when enabled by clicking the Enable button), the setpoint changes over the specified period of time in a linear manner. Note: Setpoint ramping is only available in Auto mode.

The Set Point Ramping group contains the following two fields: l

l

Target SP. Contains the Setpoint you want the Controller to have at the end of the ramping interval. When the ramping is disabled, the Target SP field displays the same value as the SP field on the Configuration page. Ramp Duration. Contains the time interval you want to complete setpoint change in.

There are also two buttons available in this group: l

Enable. Activates the ramping process

l

Disable. Stops the ramping process.

While the controller is in ramping mode, you can change the setpoint as follows: l

Enter a new setpoint in the Target SP field on this page.

l

Enter a new setpoint in the SP field on the Configuration page.

During the setpoint ramping, the Target SP field shows the final value of the setpoint, whereas the SP field on the Configuration page shows the current setpoint seen internally by the control algorithm.

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Note: During ramping, if a second setpoint change has been activated, then Ramping Duration time would be restarted for the new setpoint.

An example, if you click the Enable button and enter values for the two parameters in the Set Point Ramping group, the Controller switches to Ramping mode and adjust the Setpoint linearly (to the Target SP) during the Ramp Duration. See Figure 5.72. For example, suppose your current SP is 100, and you want to change it to 150. Rather than creating a sudden, large disruption by manually changing the SP while in Automatic mode, click the Enable button and enter an SP of 150 in the Target SP input cell. Make the SP change occur over, say, 10 minutes by entering this time in the Ramp Duration cell. HYSYS adjusts the SP from 100 to 150 linearly over the 10 minute interval.

Set Point / OP Options Group In the past, the PID controllers implemented an automatic setpoint tracking in manual mode. In other words, the value of the setpoint was set equal to the value of the PV when the controller was placed in manual mode. This meant that upon switching, the values of the setpoint and PV were equal, and therefore there was an automatic bumpless transfer. In the present controller setup, the SP Man option allows PV tracking, by selecting the No Tracking radio button, when the controller is in manual mode. However, when the controller is switched into the automatic mode from manual, there is an internal resetting of the controller errors to ensure that there is an instantaneous bumpless transfer prior to the controller recognizing a setpoint that is different from the PV. If the Track PV radio button is selected, an automatic setpoint tracking occurs. If the SP INIT option is not grayed out, it is because this PID controller is the Master controller in a Master-Slave or Cascade configuration. The SP INIT feature comes into play when the Slave controller is switched out of the Cascade mode. Then, its SP is no longer equal to the OP of the Master controller, so the Master and Slave are disconnected and the external control loop is open. Under these conditions the Master SP has the option of tracking or not tracking its own PV. Keeping the originally specified SP is important in some applications. Note: By default, the No Tracking radio button is selected for both SP Man and SP INIT.

The Remote SP option allows you to select either the Use % radio button (for restricting the setpoint changes to be in percentage) or Use PV units radio button (for setpoint changes to be in PV units). l

l

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Use %: If this radio button is selected, then the controller reads in a value in percentage from a remote source and uses the PV range to calculate the new setpoint. Use PV units: If this radio button is selected, then the controller reads

26 PID Controller

in a value from a remote source, and is used as the new setpoint. The remote sources setpoint must have the same units as the controller PV. An example, it is desired to control the flowrate in a stream with a valve. A PID controller is used to adjust the valve opening to achieve the desired flowrate that is set to range between 0.2820 m3/h and 1.75 m3/h. A spreadsheet is used as a remote source for the controller setpoint. A setpoint change to 1 m3/h from the current Pv value of 0.5 m3/h is made. The spreadsheet internally converts the new setpoint as m3/s (in other words, 1/3600 = 0.00028 m3/s) and pass it to the controller, which converts it back into m3/h (in other words, 1 m3/h). The controller uses this value as the new setpoint. If the units are not specified, then the spreadsheet passes it as 1 m3/s, which is the base unit in HYSYS, and the controller converts it into 3600 m3/h and pass it on to the SP field as the new setpoint. Since the PV maximum value cannot exceed 1.75 m3/h, the controller uses the maximum value (1.75 m3/h) as the new setpoint. If the PID is Master Controller in a Cascade Loop, the INIT Mode OP option becomes available. Select one of the following radio buttons: l

l

Track SP: This is the default selection. In most cases, we recommend that you retain this selection. If the Slave PID is in Local (or Non-Cascade), based on this selection, the Master Controller's OP (Output) will track the SP of the slave PID. Track PV: If the Slave PID is in Local (or Non-Cascade), based on this selection, the Master Controller's OP (Output) will track the PV of the slave PID.

Limit Setting Group This group enables you to specify the output and setpoint limits. The output limits ensure that a predetermined minimum or maximum output value is never exceeded. In the case of the setpoint, the limits enforce an acceptable the range of values that could be entered via the interface or from a remote source. When the Enable OP Limits in Manual Mode check box is selected, you can enable the set point and output limits when in manual mode.

Autotuner Page To make plantwide control less tedious, recent contributions have made it possible to do automated tuning for controllers where no general heuristics apply. These ideas are based on a widely used experimental technique that can back calculate the transfer function of the controlled system as long as it is expressed in a two-parameter form. The basic principle was the use of a P-only controller to take the closed loop system to the limit of stability by increasing the controller gain until what is known as the ultimate gain. The period of the self-sustained oscillations of the system at these conditions is called the ultimate period and, once the connection between these two values to the system

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parameters was made, suitable tuning parameters for a PID controller were proposed. Since taking a process to the limit of stability is not always recommended, an open loop step test was also given as alternative by the same authors, Ziegler and Nichols [1]. With time, Åström and Hägglund [2] realized that these two values –amplitude and frequency of the self-sustained oscillations- could be predicted from an independent theory based on a linearization technique developed for the analysis of non-linear systems: the describing function method. From this theory, the following expression of the ultimate gain was available when using an ONOFF or relay controller. (1)

Where h is the maximum percentile output amplitude allowed to the relay controller with respect to the OP span of the regular controller it substitutes, and a is the amplitude –also expressed in percentile units of the controller PV span- of the main or first harmonic of the periodic signal generated by the overall closed loop system. During the test, the PID controller is actually internally replaced by a built-in relay controller. This alternative identification technique, known also as ATV (or automatic tuning variation), can be applied with little risk in practice because (a) the amplitude a of the self-sustained oscillations does not represent a danger to the plant since it is usually smaller than h, which in most cases equals 5% of the OP span, (b) the test is done in closed-loop, and most transfer functions in open loop are not necessarily the same after the loop is closed. In other words, the main drawbacks of the original testing techniques from the mid 40’s were overcome. The last step in these developments was to adapt the relationships between the ultimate gain and ultimate period to actual controller parameters for the case of chemical processes, since Ziegler and Nichols relationships were optimized for the case of servomechanisms. This is what Tyréus and Luyben did in the mid 90’s [3]. The page contains two groups: l

l

Autotuner Parameters. Contains the parameters required by the Autotuner to calculate the controller parameters. Autotuner Results. Displays the resulting Ku and ultimate period Pu. You have the option to load the tuning parameters computed from these values.

Autotuner Parameters Group In this group, you can specify the controller type by selecting the PID or PI radio button for the Design Type. In the present autotuner implementation the following parameters must be specified:

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Parameter

Range

Relay hysteresis (h)

0.1 to 1.0 %

Relay amplitude (d)

2 TO 15%

Note: Before starting the ATV test, you must ensure that the process is stable. It is recommended the controller be automatic mode. If you move the cursor over the tuning parameters field, the Status Bar displays the parameters range.

Autotuner Results Group This group displays the ultimate gain and ultimate period of the autotuner calculation and lets you accept these results as the basis for the internal controller autotuning computations. The Start Autotuner button activates the tuning calculation, and the Stop Autotuning button aborts the calculations. The PID tuning parameters are computed from the ultimate gain and ultimate period as follows, as per Tyréus-Luyben. (2)

For a PI controller, we have: (3)

The formulas for the PID above correspond to a non-interactive implementation. Conversion of the PID tuning parameters between non- interactive and interactive algorithms is made internally as follows: (4)

References [1] “Optimum settings for automatic controllers”. J. G. Ziegler and N. B. Nichols. Transactions ASME, 64, pp. 759-768. 1942

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[2] “Automatic tuning of simple regulators with specifications on phase and amplitude margins”. K. J. Åström and T. Hägglund. Automatica, 20 (5), pp. 645651. 1984 [3] “Tuning PI controllers for integrator/deadtime processes”. B. D. Tyréus and W. L. Luyben. Industrial and Engineering Chemistry Research, 31, pp. 26252628. 1992

IMC Design Page The IMC Design page allows you to use the internal model control (IMC) calculator to calculate the PID parameters based on a specified model of the process one is attempting to control. The IMC method is quite common in most of the process industries and has a very solid theoretical basis. In general, the performance obtained using this design methodology is superior to most of the existing techniques for tuning PIDs. As such, when there is a process model available (first order plus delay) this approach should be used to determine the controller parameters. You must specify a design time constant, which is usually chosen as three times that of the measured process time constant. The IMC Design page has the following two groups: Group

Description

IMC Design Parameters

Contains the parameters for the process model which are required by the IMC calculator.

IMC PID Tuning

l

Process Gain

l

Process Time Constraint

l

Process Delay

l

Design To

Displays the PID controller parameters.

As soon as you enter the parameters in the IMC Design Parameters group, the controller parameters are calculated and displayed in the IMC PID Tuning group. You can accept them as the current tuning parameters by clicking the Update Tuning button.

Scheduling Page The Scheduling page gives you the ability to do parameter scheduling. The parameter scheduling is quite useful for nonlinear processes where the process model changes significantly over the region of operation. The parameter scheduling is activated through the Parameter Schedule check box. You can use three different sets of PID parameters, if you so desire for three different

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regions of operation. The following regions of operation can be specified from the Selected Range drop-down list. l

Low Range

l

Middle Range

l

High Range

These regions of operations can be based either on the setpoint or PV of the controller. The ranges can also be specified, the default values are 0-33%, 33%66%, and 66%-100% of the selected scheduling signal. You need to specify the middle range limit by defining the Upper and Lower Range Limits. Note: The values of 0 and 100 cannot be specified for both the Lower and the Upper Range Limits.

Alarms Page The Alarms page allows you to set alarm limits on all exogenous inputs to and outputs from the controller. The page contains two groups and one button: l

Alarm Levels

l

Alarms

l

Reset Alarm button

Alarm Levels Group The Alarm Level group allows you to set, and configure the alarm points for a selected signal type. There are four alarm points that can be configured: l

LowLow

l

Low

l

High

l

HighHigh

The alarm points should be specified in the descending order from HighHigh to LowLow points. You cannot specify the value of the Low and LowLow alarm points to be higher than the signal value. Similarly, the High and HighHigh alarm points cannot be specified a value lower than the signal value. Also, no two alarm points can have a similar value. In addition, you can specify a deadband for a given set of alarms. This can be helpful in situations where the signal is “noisy” to avoid constant triggering of the alarm. If a deadband is specified, you have to specify the alarm points so that their difference is greater than the deadband. At present the range for the allowable deadband is as follows: 0.0% ≤ deadband ≤ 1.5% of the signal range. Note: The above limits are set internally and are not available for adjustment by the user.

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Alarms Group The Alarms group display the recently violated alarm for the following signals: Signal

Description

PV

Process Variable

OP

Output

SP

Setpoint

DV

Disturbance Variable

RS

Remote Setpoint

Reset Alarm Button When the deadband has been set, it is possible that an alarm status is triggered and the alarm does not disappear until the band has been exceeded. The Reset Alarm button allows the alarm to be reset when within the deadband. An example, it is desired to control the flowrate through a valve within the operating limits. Multiple alarms can be set to alert you about increases or decreases in the flowrate. For the purpose of this example, you are specifying low and high alarm limits for the process variable signal. Assuming that the normal flowrate passing through the valve is set at 1.2 m3/h, the low alarm should get activated when the flowrate falls below 0.7 m3/h. Similarly, when the flowrate increases to 1.5 m3/h the high alarm should get triggered. To set the low alarm, first make sure that the Pv Signal is selected in the Signal drop-down list. Specify a value of 0.7 m3/h in the cell beside the Low alarm level. Follow the same procedure to specify a High alarm limit at 1.5 m3/h. If you want to re-enter the alarms, click the Reset Alarm button to erase all the previously specified alarms.

PV Conditioning Page The PV Conditioning page allows you to simulate the failure of the controller input signal. This page consists of three groups: l

PV Sampling Failure

l

Sample and Hold PV

l

Stream Temperature Filter

PV Sampling Failure Group The PV Sampling Failure group consists of three radio buttons: None, Fixed Signal, and Bias. The options presented to you changes with respect to the radio button chosen.

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l

l

When the None radio button is selected, the property view is as seen in the figure above, with only the Actual PV and Failed PV values displayed. When Fixed Signal radio button is selected, the PV Sampling Failure group appears as follows.

The Failed Input Signal To parameter allows you to fix the failed input signal using either the PV units or a Percentage of the PV range. l

When the Bias radio button is selected, the PV Sampling Failure group appears as follows.

The PV Sampling Failure group allows you to drift the input signal. The parameters allow you to bias the signal and create a drift over a period of time. To start the drift simply click the Start Drift button.

Sample and Hold PV Group The Sample And Hold PV group allows you to take a PV sample and hold this value for a specified amount of time.

Stream Temperature Filter Group The Stream Temperature Filter group allows you to calculate the temperature of a low flow rate stream by applying a first order transient filter with a userspecified ambient time constant. By default, the Apply Filter check box is cleared. You can apply the temperature filter by selecting the Apply Filter check box. To set the conditions for the filter, you will need to specify the following: l

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First Order Time Constant. First order exponential time constant applied to the filter when the flow rate is within the acceptable range (in other words, above the Cut Off Flow value). By default, the First Order Time Constant is 15 seconds. If the field is empty, or you enter a value of zero, then no filtering is applied.

617

l

l

Ambient Time Constant. Time constant applied to the filter when the flow rate of a stream drops below the Cut Off Flow value. It determines how long it takes for the actual temperature of the stream to reach the ambient temperature. By default, the ambient time constant is 3600 seconds. If the field is empty, or you enter a value of zero, the temperature value is calculated from the flash and no filtering is applied. Cut Off Flow. Switch-over point at which the temperature filter applies the ambient time constant in calculating the temperature of the stream. The Cut Off Flow value is expressed in molar flow, and the default value is 1e-5 kmol/s.

If the stream flow rate is above the Cut Off Flow value, the controller automatically switches back to the normal flash calculations which only apply the First Order Time Constant. The Ambient Time Constant is applied when the flow rate drops below the Cut Off Flow value with the temperature ramping to ambient over some slow periods.

Signal Processing Page The Signal Processing page allows you to add filters to any signal associated with the PID controller, as well as test the robustness of any tuning on the controller. This page is made up of two groups: Signal Filters and Noise Parameters. Both of these groups allows you to filter and test the robustness of the following tuning parameters: l

Pv

l

Op

l

Sp

l

Dv

l

Rs

To apply the filter, select the check box corresponding to the signal you want to filter. Once active you can specify the filter time. As you increase the filter time you are filtering out frequency information from the signal. It is possible to add a filter that makes the controller unstable. In such cases the controller needs to be returned. Adding a filter has the same effect as changing the process the controller is trying to control. For example, if the signal is noisy, there is a smoothing effect noticed on the plot of the PV when the filter is applied. Activating a Noise Parameter is done the same way as adding a filter. However, instead of specifying a filter time you are specifying a variance. Notice that if a high variance on the PV signal is chosen the controller may become unstable. As you increase the noise level for a given signal you observe a somewhat random variation of the signal.

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FeedForward Page The FeedForward page enables you to design a controller that takes into account measured disturbances. Note: To enable feedforward control you must select the Enable FeedForward check box.

The Disturbance Variable Source group allows you to select a disturbance variable, and minimum and maximum variables. The disturbance variable is specified by clicking the Select Dv button. This opens the Variable Navigator. The FeedForward Parameters group allows you to set the Operating Mode for both the PID controller and the FeedForward controller and tune the controller. All FeedForward controllers require a process model in order for the controllers to work properly. Presently HYSYS uses a model that results in a lead-lag process. The transfer function equation model for the FeedForward controller is as follows: (1)

where: τp1 = Lead time constant τp2 = Lag time constant U= FeedForward model input or PID Controller disturbance variable value (scaled between 0 and 100). Y = Corresponds to FeedForward output (FFWD OP) (scaled between -50 and 50) Controller Output = FFWD OP + PID OP

Model Testing Page The Model Testing page allows you to set the following parameters for generating data from the plant model. l

l

l

26 PID Controller

Signal Type offers two options. o

PRBS is simple to use for model identification.

o

STEP is more recognized in practical process applications.

Signal Variation Amplitude determines how much the output variables are changed to identify the model. The default value is 5%. Time Interval determines how often data points are recorded during the testing phase.

619

l

Testing Time Length determines the total time period to apply the testing. The value should be larger than the time constant of the system.

Select the Enable Test check box in the Monitor table to perform the model testing when the integrator starts. Click Reset Test to reset the model testing back to the beginning. After the testing is complete, click Save Test Result to save the testing results. The results will be saved as three files: l

*_sp.vec for SP

l

*_pv.vec for PV

l

*_op.vec for OP

Initialization Page The Initialization page of the PID controller contains the same information as the one for the ratio controller.

Monitor Tab A quick monitoring of the response of the Process Variables, Setpoint, and Output can be seen on the Monitor tab. This tab allows you to monitor the behavior of process variables in a graphical format while calculations are proceeding. The Monitor tab displays the PV, SP, and Op values in their relevant units versus time. You can customize the default plot settings using the object inspection menu, which is available only when you right-click on any spot on the plot area. The object inspection menu contains the following options:

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Item

Description

Graph Control

Opens the Graph Control Property View to modify many of the plot characteristics.

Turn Off/On Cross Hair

Turns the cross hair either on or on.

Turn Off/On Vertical Cross Hair

Turns the vertical cross hair either on or on.

Turn Off/On Horizontal Cross Hair

Turns the horizontal cross hair either on or on.

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Item

Description

Values Off/On

Displays the current values for each of the variables, if turned on.

Copy to Clipboard

Copies the current plot to the clipboard with the chosen scale size.

Print Plot

Prints the plot as it appears on the screen.

Print Setup

Allows you to access the typical Windows Print Setup. The Windows Print Setup allows you to select the printer, the paper orientation, the paper size, and paper source.

A quick way to customize your plot is to use the Monitor Properties property view, which can be access by clicking the Properties button. There are three group available on the Monitor Properties property view, which are described as follows: l

l

l

Data Capacity. Allows you specify the type and amount of data to be displayed. You can also select the data sampling rate. Left Axis. Gives you an option to display either the PV and SP or the Error data on the left axis of the plot. You can also customize the scale or let HYSYS auto scale it according to the current values. Right Axis. Gives you an option to either customize the right axis scale or let HYSYS auto scale it according to the current OP value.

Stripchart Tab The Stripchart tab allows you to select and create default strip charts containing various variable associated to the operation.

User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

Algorithm References HYSYS PID Controller Algorithms The HYSYS PID algorithm implements a two degrees of freedom PID Controller via setpoint weighting. The equations are as follows.

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PID Velocity Form (1)

where: l

l l

u(t) = controller output and t is the enumerated sampling instance in time u(t - k) = value of the controller output k sampling periods before e(t - k) = sp(t - k) - pv(t - k) = value of the error signal k sampling periods before

l

ep(t - k) = b × sp(t - k) - pv(t - k)

l

eD(t - k) = c × sp(t - k) - pv(t - k)

l

pv(t - k) = value of the process variable k sampling periods before

l

Kc, Ti, Td = controller parameters

l

h = sampling period

l

sp = setpoint

l

0 ≤ b, c ≤ 1 o

b = setpoint weight for proportional action

o

c = setpoint weight for derivative action

The actual control output is non-linear since saturation must be applied.

PID Positional Form (ARW) Here, the control output is: (2)

Where uss is the steady-state controller output (at zero error) and ui(t) is the controller, the integral term is given by: (3) The Anti-reset windup (ARW) will adjust the term ui(t) for use in the next control execution (t + 1) if the calculated control output u(t) has exceeded the OP limits. In case Feedforward is also enabled, the total control output, u{total}(t) = u(t) + u{ff}(t) will be considered and checked against the OP limits. Two ARW methods are implemented in the HYSYS algorithm, as follows: l

ARW-Clamp: When u{total}(t) exceeds the OP limits, the integral con-

←

tribution ui(t) is reset instantaneously by clamping it as ui(t) ui(t) – he (t) so as to prevent the control output from further exceeding the limits. Note: Clamping of u i will only affect the control output calculated in the next control execution. The current control execution still uses the unclamped u i as seen in Eq. (3). l

622

ARW-BkCalc: This is the back-calculation[1] method, in which the

26 PID Controller

integral contribution is reset dynamically by adjusting it as: (4) Where usat is the saturated control output that finally goes to the control element, and Tt is the back-calculation time constant. Again, the adjustment will only affect the control output calculated in the next control execution, not the current one.

PID Positional Form (NoARW) The same algorithm is used as above, with the difference that no antireset windup action is implemented.

PID Manual Loading In the manual loading station algorithm, the output u(t) is equal to the input y (t).

Reference Åström, K. and T. Hägglund. PID Controllers: Theory, Design, and Tuning (2nd ed.) Instrument Society of America, 1995.

Foxboro PID Controller Algorithms The PID algorithms supported by the Foxboro I/A Series System are

1. Interacting PID In the continuous time domain: (1)

where: (2)

(3) and: (4)

μ(t)

Controller output

sp(t)

Controller setpoint

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pv(t)

process variable

u f (t)

Butterworth filtered process variable

u i(t)

integral action

A

setpoint lead/lag ratio

τ

Butterworth filter time constant

Kd

Derivative gain

fr

additional scaling parameter

P

proportional band

I

integral time

D

derivative time

The Interacting PID can be reduced to a PI algorithm if D = 0 or to a P-only algorithm if parameter I is let undefined () in the corresponding tuning group of the property view. In the latter, case the integral part becomes: (5) A PD implementation is obtained in case D ≠ 0 for undefined I, since parameter τ defaults to: (6)

2. Non-Interacting PID The changes with respect to the previous expressions are in: (7)

(8)

3. Pure Integral In this case: (9)

Discrete Time Domain Implementation of the Foxboro Algorithms

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Interacting PID The composed variable time equations is implemented numerically as:

used in the continuous

(1) Where t is just an index that refers to the current sampling instant. For a backward-difference approximation: (2) (3) (4) On the other hand, the numerical version of the integral part is: (5) Once ug and ui are known, the corresponding discrete time domain expression of the output is: (6)

Non-Interacting PID The numerical implementation of uf is done through: (7) so: (8) and u(t) is computed as before. The P-only, PI, or PD Non-Interacting equations reduce to the same expressions as in the corresponding Interacting cases. This should be expected, since the interacting principle refers to the fact that derivative and integral actions interact or not, which is meaningful only when both actions are in operation

Pure Integral In this case: (9)

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Antireset windup for all of the Foxboro algorithms is implemented by tracking of the controller output, as explained in the Honeywell algorithm section which, if applied to any of the above equations, yields: (10) and u*(t) can be uf (t), ug (t), or pv(t), depending on the algorithm subtype.

Honeywell PID Controller Algorithms The PID algorithms supported by the Honeywell TDC3000 distributed control system are presented in Laplace notation:

1. Interacting Form, Equation A (1)

2. Interacting Form, Equation B (2)

3. Interacting Form, Equation C (3)

4. Non-Interacting Form, Equation A (4)

5. Non-Interacting Form, Equation B (5)

6. Non-Interacting Form, Equation C (6)

7. Pure Integral (7)

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Where: l

OP(s) = controller output, s the Laplace variable

l

E(s) = deviation signal or E(s) = SP(s) - PV(s)

l

SP(s) = controller set point

l

PV(s) = process variable

l

K = controller gain

l

T1 = integral time constant

l

T2 = derivative time constant

l

α = high frequency gain or rate amplitude, ranging from 0.05 to 0.5

Discrete Time Domain Implementation of the Honeywell Algorithms Here: u(t) controller output, t the enumerated sampling instance in time u i(t) controller integral term u d(t) depending on the form, output to lead-lag filter or to derivator e(t) deviation signal sp(t) controller set point pv(t) process variable K

controller gain

T1

integral time constant

T2

derivative time constant

a

high frequency gain or rate amplitude, ranging from 0.05 to 0.5

The numerical, linear implementations of the Interacting Form equations are: (1) where: (2)

and ud(t) is the output of a lead/lag filter, written as follows in state-space form using the state variable xd(t): (3)

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The variable xd(t+1) represents the state xd value to be used at the next iteration. The input i0 depends also of the equation selected: (4)

and constants a and b correspond to what is called the ramp-invariant approximation, a stable, high fidelity discretization option commonly used for the derivative part of a continuous algorithm: (5)

(6)

Finally, the integral term ui in the first of this series of equations is expressed as: (7)

with: (8)

Just slight variations to the above are needed to express the Non-Interacting Form equations. Variable i2(t) is now: (9)

And variables a and b now correspond not to a lead-lag but to a filtered derivative action, so b is substituted by: (10)

Finally, in the case of the Pure Integral control equation, we simply have:

Antireset windup for the above algorithms is based not on conditional integration (as is the case of the HYSYS Positional Form ARW) but on the tracking of the actuator output –or, actually, the output of a saturator model of the actuator– which means that the integral action u1(t) has a non-linear implementation like this:

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26 PID Controller

(11)

with:

Tracking of the actuator output is much better than conditional integration to avoid windup. It may still fail by resetting the integrator accidentally if the derivative or proportional actions –rather than the integral action– tend to saturate the actuator.

Yokogawa PID Controller Algorithms The Yokogawa Centum CS3000 control system PID algorithms are of three kinds: l

PID

l

PI-D

l

I-PD

All of the Yokogawa algorithms are in the velocity or incremental form. The PID subtype assumes all three actions working on the error signal whereas, in the PI-D subtype, the derivative action works on the process variable and the Pand I-actions on the error. The I-PD algorithm, in turn, has P- and D- actions working both on the process variable and the integral part on the error. The numerical implementation of the algorithm is as follows. For the proportional action: (1) (2)

For the integral action: (3)

and, finally, for the derivative action: (4) (5)

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(6) This derivative action comes with a low-pass filter of time constant TD / N, where N can vary from 2 and 20. The final control output is then computed from: (7) The relevant parameters and variables in these equations are: u(t)

controller output

Δu p(t), Δu i(t), Δu d(t)

increments to the proportional, integral, and derivative actions

sp(t)

controller setpoint

pv(t)

process variable

e(t) = sp(t) - pv(t)

error signal or control deviation

Kp

integral action

TI

reset or integral time

TD

derivative time

N

maximum derivative gain, ranging from 2 to 20 Tip: The velocity algorithms, which include all the Yokogawa types just discussed and the HYSYS Velocity subtype, offer the most effective antireset windup by simple saturation of the output. As a drawback, P-only and PD actions are not easily implemented by these algorithms and an internal switching to a positional form will take place when required.

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27 MPC Controller

The “Model Predictive Control” (MPC) controller addresses the problem of controlling processes that are inherently multi-variable and interacting in nature, in other words, one or more inputs affects more than one output.

Note: The current version of the MPC implementation does not handle the problem of processes with constraints.

The MPC property view contains the following tabs: l

Connections

l

Parameters

l

MPC Setup

l

Process Models

l

Stripchart

l

User Variables

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Connections Tab The Connections tab Operation page is comprised of six objects that allow you to select the Process Variable Source, Output Target Object, and Remote SP. Object

Description

Name

Contains the name of the controller. It can be edited by selecting the field and entering the new name.

Process Variable Source Object

Contains the Process Variable Object (stream or operation) that owns the variable you want to control. It is specified via the Variable Navigator.

Process Variable

Contains the Process Variable you want to control.

Output Target Object

The stream or valve which is controlled by the MPC Controller operation

Remote Setpoint Source

If you are using set point from a remote source, select the remote Setpoint Source associated with the Master controller

Select PV/OP/SP

These three buttons open the Variable Navigator, which selects the Process Variable, the Output Target Object, and the Remote Setpoint Source respectively.

PV/OP/SP

These three fields allow you to select a specific Process Variable, Output Target Object, and Remote Setpoint Source respectively.

Process Variable Source Common examples of PVs include vessel pressure and liquid level, as well as stream conditions such as flow rate or temperature. Note: The Process Variable, or PV, is the variable that must be maintained or controlled at a desired value.

To attach the Process Variable Source, click the Select PV button. Then select the appropriate object and variable simultaneously, using the Variable Navigator. The Variable Navigator allows you to simultaneously select the Object and Variable.

Remote Setpoint The “cascade” mode of the controller no longer exits. Instead what is available now is the ability to switch the setpoint from local to remote. The remote setpoint can come from another object such as a spread-sheet or another controller cascading down a setpoint. In other words, a master in the classical cascade control scheme. Note: A Spreadsheet cell can also be a Remote Setpoint Source.

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The Select Sp button allows you to select the remote source using the Variable Navigator.

Output Target Object The Controller compares the Process Variable to the Setpoint, and produces an output signal which causes the manipulated variable to open or close appropriately. Note: The Output of the Controller is the control valve which the Controller manipulates in order to reach the set point. The output signal, or OP, is the desired percent opening of the control valve, based on the operating range which you define in the Control Valve property view.

Selecting the Output Target Object is done in a similar manner to selecting the Process Variable Source. You are also limited to objects supported by the controller and not currently attached to another controller. The information regarding the control valve or control op port sizing is contained on a sub-view accessed by clicking the Control Valve or Control OP Port button found at the bottom of the MPC Controller property view. Note: The Control Valve button (at the bottom right corner of the logical operation property view) appears if the OP is a stream. Note: The Control OP Port button (at the bottom right corner of the logical operation property view) appears when the OP is not a stream and there a range of specified values is required.

Parameters Tab The Parameters tab contains the following pages: l

Operation

l

Configuration

l

Advanced

l

Alarms

Operation Page The Operation page allows you to set the execution type, controller mode and depending on the mode, either SP or OP.

Mode Group The Controller operates in any of the following modes: l

l

27 MPC Controller

Off. The Controller does not manipulate the control valve, although the appropriate information is still tracked. Manual. Manipulates the Controller output manually.

633

l

Automatic. The Controller reacts to fluctuations in the Process Variable and manipulates the Output according to the logic defined by the tuning parameters.

You can select where the signal from the controller is sent using the drop-down list in the Execution field. You have two selections: l

Internal. Confines the signals generated to stay within HYSYS.

l

External. Sends the signals to a DCS, if a DCS is connected to HYSYS.

SPs and PVs Group Displays the Setpoint (SP) and Process Variable (PV) for each of the controller inputs. Depending on the Mode of the controller the SP can either be input by you or is determined by HYSYS.

Outputs Group The Output (OP) is the percent opening of the control valve. The Controller manipulates the valve opening for the Output Stream in order to reach the set point. HYSYS calculates the necessary OP using the controller logic in all modes with the exception of Manual. In Manual mode, you may enter a value for the Output, and the Setpoint becomes whatever the PV is at the particular valve opening you specify. This can be done for all of the inputs to the controller.

Configuration Page The Configuration page allows to specify the process variable, setpoint, and output ranges.

PV: Min and Max For the Controller to become operational, you must: 1. Define the minimum and maximum values for the PV (the Controller cannot switch from Off mode unless PVmin and PVmax are defined). 2. Once you provide these values (as well as the Control Valve span), you can select the Automatic mode and give a value for the Setpoint. Note: HYSYS uses the current value of the PV as the set point by default, but you can change this value at any time. Note: Without a PV span, the Controller cannot function.

HYSYS converts the PV range into a 0-100% range, which is then used in the solution algorithm. The following equation is used to translate a PV value into a percentage of the range: (1)

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27 MPC Controller

SP Low and High Limits You can specify the higher and lower limits for the Setpoints to reflect your needs and safety requirements. The Setpoint limits enforce an acceptable range of values that could be entered via the interface or from a remote source. By default, the PV min and max values are used as the SP low and high limits, respectively.

Op Low and High Limits You can specify the higher and lower limits for all the outputs. The output limits ensure that a predetermined minimum or maximum output value is never exceeded. By default 0% and 100% is selected as a low and a high of limit, respectively for all the outputs. Note: When the Enable Op Limits in Manual Mode check box is selected, you can enable the set point and output limits when in manual mode.

Advanced Page  The Advanced page contains the following three groups: Group

Description

Setpoint Ramping

Allows you to specify the ramp target and duration.

Setpoint Mode

Contains the options for setpoint mode and tracking, as well as the option for remote setpoint.

Setpoint Options

Contains the option for setpoint tracking only in manual mode.

The setpoint signal is specified in the Selected Sp Signal # field by clicking the up or down arrow button, or by typing the appropriate number in the field. Depending upon the signal selected, the page displays the respective setpoint settings.

Setpoint Ramping Group The setpoint ramping function has been modified in the present MPC controllers. Now it is continuous, in other words, when set to on by clicking the Enable button, the setpoint changes over the specified period of time in a linear manner. Note: Setpoint ramping is only available in Auto mode.

The Setpoint Ramping group contains the following two fields: l

27 MPC Controller

Target SP. Contains the Setpoint you want the Controller to have at the end of the ramping interval. When the ramping is turn off, the Target SP field display the same value as SP field on the Configuration page.

635

l

Ramping Duration. Contains the time interval you want to complete setpoint change in.

Besides these two fields there are also two buttons available in this group: l

Enable. Activates the ramping process.

l

Disable. Stops the ramping process.

While the controller is in ramping mode, you can change the setpoint as follows: l

Enter a new setpoint in the Target SP field.

l

Enter a new setpoint in the SP field, on the Operation page.

During the setpoint ramping the Target SP field shows the final value of the setpoint whereas the SP field, on the Operation page, shows the current setpoint seen internally by the control algorithm. Note: During ramping, if a second setpoint change has been activated, then Ramping Duration time would be restarted for the new setpoint.

An example, if you click the Enable button and enter values for the two parameters in the Setpoint Ramping group, the Controller switches to Ramping mode and adjusts the Setpoint linearly (to the Target SP) during the Ramp Duration, see Figure 5.90. For example, suppose your current SP is 100, and you want to change it to 150. Rather than creating a sudden large disruption by manually changing the SP while in Automatic mode, click the Enable button and enter the SP of 150 in the Target SP input field. Make the SP change occur over, say, 10 minutes by entering this time in the Ramp Duration field. HYSYS adjusts the SP from 100 to 150 linearly over the 10 minute interval.

Setpoint Mode Group You now have the ability to switch the setpoint from local to remote using the Setpoint mode radio buttons. Essentially, there are two internal setpoints in the controller, the first is the local setpoint where you can manually specify the setpoint via the property view (interface), and the other is the remote setpoint which comes from another object such as a spreadsheet or another controller cascading down a setpoint. In other words, a master in the classical cascade control scheme.

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27 MPC Controller

The Sp Local option allows you to disable the tracking for the local setpoint when the controller is placed in manual mode. You can also have the local setpoint track the remote setpoint by selecting the Track Remote radio button. The Remote Sp option allows you to select either the Use% radio button (for restricting the setpoint changes to be in percentage) or Use Pv units radio button (for setpoint changes to be in Pv units). l

l

Use%. If the Remote Sp is set to Use%, then the controller reads in a value in percentage from a remote source, and using the Pv range calculates the new setpoint. Use Pv units. If the Remote Sp is set to Use Pv units, then the controller reads in a value from a remote source and sets a new setpoint. The remote source’s setpoint must have the same units as the controller Pv.

SetPoint Options Group If the Track PV radio button is selected, then there is automatic setpoint tracking in manual mode, that sets the value of the setpoint equal to the value of the Pv prior to the controller being placed in the manual mode. This means that upon switching from manual to automatic mode the values of the setpoint and Pv were equal and, therefore, there was an automatic bumpless transfer. Also you have the option not to track the pv, by clicking the No Tracking radio button, when the controller is placed in manual mode. However, when the controller is switched into the automatic mode from manual, there is an internal resetting of the controller errors to ensure that there is an instantaneous bumpless transfer prior to the controller recognizing a setpoint that is different from the Pv. An example, it is desired to control the flowrate in a stream with a valve. A MPC controller is used to adjust the valve opening to achieve the desired flowrate, that is set to range between 0.2820 m3/h and 1.75 m3/h. A spreadsheet is used as a remote source for the controller setpoint. A setpoint change to 1 m3/h from the current PV value of 0.5 m3/h is made. The spreadsheet internally converts the new setpoint as m3/s (1/3600 = 0.00028 m3/s) and passes it to the controller, which reads the value and converts it back into m3/h (1 m3/h). The controller uses this value as the new setpoint. If the units are not specified, then the spreadsheet passes it as 1 m3/s, which is the base unit in HYSYS, and the controller converts it into 3600 m3/h and passes it on to the SP field as the new setpoint. Since the PV maximum value cannot exceed 1.75 m3/h, the controller uses the maximum value (1.75 m3/h) as the new setpoint.

Alarms Page The Alarms page allows you to set alarm limits on all exogenous inputs to and outputs from the controller. The page contains two groups:

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l

Alarm Levels

l

Alarms

Alarm Levels Group The Alarm Level group allows you to set, and configure the alarm points for a selected signal type. There are four alarm points that could be configured: l

LowLow

l

Low

l

High

l

HighHigh

The alarm points should be specified in the descending order from HighHigh to LowLow points. You cannot specify the value of the Low and LowLow alarm points to be higher than the signal value. Similarly, the High and HighHigh alarm points cannot be specified a value lower than the signal value. Also, no two alarm points can be specified a similar value. In addition, you can specify a deadband for a given set of alarms. This can be helpful in situations where the signal is “noisy” to avoid constant triggering of the alarm. If a deadband is specified, you have to specify the alarm points so that their difference is greater than the deadband. At present, the range for the allowable deadband is as follows: 0.0% ≤ deadband ≤ 1.5% of the signal range. Note: The above limits are set internally and are not available for adjustment by the user.

Alarms Group The Alarms group displays the recently violated alarm for the following signals: Signal

Description

PV

Process Variable

OP

Output

SP

Setpoint

An example, it is desired to control the flowrate through a valve within the operating limits. These limits can be monitored using the Alarms feature in MPC Controller. Multiple alarms can be set to alert you about increase or decrease in the flowrate. For the purpose of this example, you are specifying low and high alarm limits for the process variable signal. Assuming that the normal flowrate passing through the valve is set at 1.2 m3/h, the low alarm should get activated when the flowrate falls below 0.7 m3/h. Similarly, when the flowrate increases to 1.5 m3/h the high alarm should get triggered. To set the low alarm, first make sure that the Pv Signal is selected in the Signal drop-down list. Specify a value of 0.7 m3/h in the cell beside the Low

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alarm level. Follow the same procedure to specify a High alarm limit at 1.5 m3/h. If you want to re-enter the alarms, click the Reset Alarm button to erase all the previously specified alarms.

Signal Processing Page The Signal Processing page allows you to add filters to any signal associated with the MPC controller, as well as test the robustness of any tuning on the controller. This page is made up of two groups: l

Signal Filters

l

Noise Parameters

Both of these groups allow you to filter, and test the robustness of the following tuning parameters: l

Pv

l

Op

l

Sp

l

Rs

To apply the filter select the check box corresponding to the signal you want to filter. Once active you can specify the filter time. As you increase the filter time you are filtering out frequency information from the signal. For example the signal is noisy, there is a smoothing effect noticed on the plot of the PV. Notice that it is possible to add a filter that makes the controller unstable. In such cases the controller needs to be returned. Adding a filter has the same effect as changing the process the controller is trying to control. Activating a Noise Parameter is done the same way as adding a filter. However, instead of specifying a filter time you are specifying a variance. Notice that if a high variance on the PV signal is chosen the controller may become unstable. As you increase the noise level for a given signal you observe a somewhat random variation of the signal.

MPC Setup Tab The MPC controller has a number of setup options available. These options are available on the Basic and Advanced pages of the Setup tab. In order to change any of the default values specified on these pages it is necessary to enable the MPC modifications check box. Whatever the option chosen, it is important to establish a sampling period (control interval) first. Specifically, the sampling period must be chosen to be consistent with the sampling theorem (see Shannon's Sampling Theorem). As such, it should be about 1/5 to 1/10 of the smallest time-constants. If the process is heavily dominated by process deadtime then the sampling period should be based on the deadtime. In situations where

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the process models are a mix of fast and slow process dynamics care should be taken in selecting the sampling period. A carefully designed MPC controller is an effective and efficient controller.

Basic Page The Basic page divides the setup settings into MPC Control Setup and MPC Process Model Type groups.

MPC Control Setup Group In the MPC Control Setup group you are required to specify the following: l

l

l

Num of Inputs. Allows you to specify the number of process input. Up to a maximum of 12 process inputs can be specified. The default value is 1. Num of Outputs. Allows you to specify the number of process output. Up to a maximum of 12 process inputs can be specified. The default value is 1. Control Interval. Allows you to specify the control or sampling interval. The default value is 30 seconds. Note: Anytime one of the MPC setting is changed, a new MPC object has to be created internally-this is automatically achieved by clicking on the Create MPC button.

MPC Process Model Type Group You have the option to specify the model to be either Step response data or a First order model. If the Step response data radio button is selected, then a text file can be used to input the process model. The input file must follow a specific format in terms of inputs and outputs, as well as columns of data. The following is a description of the ASCII text file required for the input:

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The step response data is typically obtained either directly from plant data, or they are deducted from other so-called parametric model forms such as Discrete State-Space and Discrete Transfer Function Models.

Advanced Page The Advanced page divides the setup settings into MPC Control Setup, MPC Process Model Type, and MPC Control Type groups.

MPC Control Setup Group Note: Anytime one of the MPC setting is changed, a new MPC object has to be created internally-this is automatically achieved by clicking on the Create MPC button.

In the MPC Control Setup group you are required to specify the following: Field

Description

Num of Inputs

The number of process input. Up to a maximum of 12 process inputs can be specified. The default value is 1.

Num of Out- The number of process output. Up to a maximum of 12 process outputs puts can be specified. The default value is 1. Control interval

The control or sampling interval. The default value is 30 seconds.

Step Resp. length

The number of sampling intervals that is necessary to reach steady state when an input step is applied to the process model. The range of acceptable values are from 15 to 100. The default value is 50.

Prediction Horizon

Allows you to specify how far into the future the predictions are made when calculating the controller output. The Prediction Horizon should be less than or equal to the Step Response Length. The default value is 25.

Control hori- The number of control moves into the future that are made to achieve zon the final setpoint. A small control horizon generally means a less aggressive controller. The Control Horizon should be less than or equal to the Prediction Horizon. The default value is 2. Reference trajectory

The time constant of a first order filter that operates on the true setpoint. A small reference trajectory lets the controller see a pure step as the setpoint is changed. The default value is 1.

Gamma_ U/Gamma_ Y

The positive-definite weighting functions, which are associated with the optimization problem that is solved to produce the controller output every control interval. The value of Gamma_U and Gamma_Y should be between 0 and 1. The default value is 1.

Step Response Length This value represents the number of sampling intervals that is necessary to reach steady state when an input step is applied to the process model. You

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should consider all of the process models and the sampling interval when selecting step response length. At present, the maximum step response is limited to 100 sampling intervals. Also, the fact that you are specifying the process models in terms of step response means that you are only considering stable processes in this MPC design. Prediction Horizon and Control Horizon The prediction horizon represents how far into the future the controller makes its predictions, based on the specified process model. The prediction horizon is limited to the length of the step response, and should be greater than the minimum process model delay. A longer prediction horizon means that the controller looks further into the future when solving for the controller outputs. This may be better if the process model is accurate. In general, you want to take full advantage of the process model by using longer predictions. The control horizon is the number of control moves into the future the controller considers when making its predictions. In general, the larger the number of moves, the more aggressive the controller is. As a rule of thumb a control horizon of less than 3 is used quite often. Sampling Interval and reference trajectory Once you have determined the control interval, other parameters like reference trajectory can be chosen. This value affects the reference setpoint of the predictions used by the MPC problem when solving for the control outputs. Essentially, the reference trajectory represents the time constant of a first order filter that operates on the true setpoint. Hence, a very small value for the reference trajectory implies that the setpoint used in the MPC calculations are close to the actual setpoint. The minimum value for the reference trajectory that can be selected is 1 second. One of the problems that could arise in setting this value “too large” is that the final setpoint reference value, which is used in the predictions, would not be seen by the control algorithm in a given iteration. Therefore, it is important that the reference trajectory value be chosen such that the time constant is smaller than the smallest time constant of the user specified process model set. At present, there is a limit placed on the reference trajectory that is based on the sampling interval and the maximum step-response. However, you should use the process model set as a guide when selecting this value. In the present version the limits for the reference trajectory is as follows: (1)

MPC Process Model Type Group You have the option to specify the model to be either Step response data or First order model. If the Step response data is selected, then a text file can be used to input the process model. The input file must follow a specific format in terms of inputs and outputs, as well as columns of data.

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MPC Control Type Group This group allows you to select the MPC Control Algorithm that is used by the controller. At Present, the only option available for selection is the MPC Unconstrainted (No Int). This algorithm does not consider constraints on either controlled and manipulated variables.

Process Models Tab The Process Models tab allows you to either view the step response data, or specify the first order model parameters.

Basic Page Step Response Data If the Step response data radio button is selected on the MPC Setup tab, the Process Model tab displays the Model Step Response matrix. Note: You cannot modify the model step response data on the Process Model tab.

Depending on the number of inputs (i) and outputs (o) the system’s dynamics matrix should be an i × o matrix. The number of process models is equal to the number of outputs or controlled variables. If the Step response data is selected, then the First order model parameters fields are grayed out.

First Order Model If the First order model is selected on the MPC Setup tab, the Process Model table appears. You can specify the first order model parameters for each of the process models, as follows: 1. Select the input and output variable number in the Input # and Output # selection field by clicking the up or down arrow button, or by typing the appropriate number in the field. 2. Depending upon the input and output variable selected, the relevant process model appears. 3. Specify the process gain (Kp), process time constant (Tp) and delay for the selected process model in the available matrix. 4. Repeat step# 1-2 for the remaining process models. 5. Click the Update Step Response button to calculate the step response data for the process models.

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Advanced Page The Advanced page lists all of the Process Models, and their associated tuning parameters in a table.

Stripchart Tab The Stripchart tab allows you to select and create default strip charts containing various variable associated to the operation.

User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

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28 DMCplus Controller

The DMCplus Controller engine runs in Aspen DMCplus Online. HYSYS communicates to DMCplus using the DMCplus API. You are required to have the following licenses to run DMCplus in HYSYS: l

DMCplus Link

l

DMCplus Online

l

Cim-IO Kernel

l

ACO Base

The figure below shows the HYSYS and DMCplus connection. HYSYS works like a Real Plant.

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Note: You must install DMCplus Online and DMCplus Desktop for the DMCplus Controller to operate properly. l l

DMCplus Online is required to run the DMCplus Controller. DMCplus Desktop allows you to configure the model used by the DMCplus Controller.

The DMCplus Desktop allows you to configure the models. Each DMCplus Controller requires a Model File (MDL) and a Controller Configuration File (CCF) to operate properly with the Aspen DMCplus. l

l

The MDL file determines the size of the control problem and all the dynamic relationships between each independent and dependent variables. The CCF file determines where the input and output parameters for the controller will reside, which optional capabilities will be used, and the values assigned to all of its parameters such as limits, switches, and tuning.

HYSYS can generate the MDL file automatically or record the independent and dependent variable in the collection files (CLC), which contains model testing data. The data in the CLC files are used by the DMCplus Model to create the MDL file. The MDL file is then used by the Aspen DMCplus Build to create a CCF file. You can add the DMCplus Controller to an existing HYSYS simulation case or to a new HYSYS simulation case that you have created. Note: If the DMCplus Controller is not loaded, it appears in yellow in the HYSYS flowsheet. The status bar on the DMCplus Controller property view will also appear in yellow and indicate that the DMCplus has not been loaded.

The DMCplus property view contains the following tabs: l

Connections

l

Model Test

l

Operation

l

Stripchart

l

User Variables

The DMCplus Controller property view also contains an Enable DMCplus check box at the bottom right corner. This check box allows you to enable or disable

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the DMCplus Controller. When the Enable DMCplus check box is disabled, the model testing features can be enabled in the Model Test tab.

Connections Tab The Connections tab allows you to define and edit the Controlled, Manipulated and Feed Forward variables for the plant model. You can specify the name of the DMCplus Controller in the Controller Name field. You have to select the Enable DMCplus Modifications check box to add and edit the Controlled, Manipulated, and Feed Forward variables. Note: When editing the Controlled and Manipulated variables in the DMCplus Model, ensure that the variable order is the same as in HYSYS.

Controlled Variable (CV) You must specify a controlled variable for the DMCplus Controller. The controlled variables are the dependent variables that will be controlled by the DMCplus controller. The CV table contains the stream or operation that owns the variable you want to control. The stream or operation is specified using the Select Input property view, which appears when you click the Add CV button or Insert CV button. l

l

The Add CV button adds the stream or operation after the last defined stream or operation in the table. The Insert CV button adds the stream or operation before the currently selected stream or operation in the table.

You can select the appropriate object and variable simultaneously using the Select Input property view.

Manipulated Variable (MV) You must specify a manipulated variable for the DMCplus Controller. The manipulated variables are the independent variables that will be manipulated by the DMCplus controller. The MV table contains the stream or operation which is controlled by the controller operation. l

l

The Add MV button adds the stream or operation after the last defined stream or operation in the table. The Insert MV button adds the stream or operation before the currently selected stream or operation in the table.

The stream or operation is specified using the Select Object property view, which appears when you click the Add MV button or Insert MV button.

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When you add a stream to the MV table the Control Valve button is enabled.

Feed Forward (FF) You can add the Feed Forward variables if needed. The variable takes into account measured disturbances which you can view on the Feed Forward page of the Operation tab. You can add the Feed Forward variables using the Select Input property view similar to when you are adding a controlled variable. l

l

The Add FF button adds the stream or operation after the last defined stream or operation in the table. The Insert FF button adds the stream or operation before the currently selected stream or operation in the table.

The Feed Forward variables are used as independent variables in the DMCplus Model, and they cannot be manipulated by the DMCplus Controller.

Model Test Tab The Model Test tab allows you to set up the DMCplus Controller for model testing. The Model Test page is the only page available on this tab. The following table lists and describes the objects available in the Model Test tab: Object

Description

Model Test Setting group Test Signal Type cell

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Enables you to select the signal type for the DMCplus model test. There are two types of signal to choose from: l

PRBS is simple to use for model identification.

l

STEP is more recognized in practical process applications.

Control/Sampling Time Interval cell

Enables you to specify the amount of time between recorded data points during the testing phase.

TTSS cell

Enables you to specify the total time period available for the model testing. The value should at least be larger than the setting time of the system.

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Object

Description

Auto Test check box

Enables you to toggle between activating and deactivating the Auto Test option. This option performs test for each of the selected Manipulated and Feed Forward variables one by one. The test results are used to generate an MDL file (which contains the DMCplus controller model). If this check box is clear, you need to manually save the testing data to CLC files.

Conf. Ramp button

Enables you to access the Configure Ramp Response property view. The Configure Ramp Response property view enables you to select the ramp type for each CV tag using the drop-down list available under the Ramp Type column. There are three types of ramp type to choose from: l

non-ramp

l

ramp

l

pseudo ramp

The Conf. Ramp button is only available if you selected the Auto Test option. Auto test file root name field

Enables you to specify the location and name of the testing data files containing the auto test results and the date and time when the test was performed. This field is only available if the Auto Test check box is selected.

Ellipses icon ...

Enables you to access the File Selection for Saving Test results property view and select the location to save the test result files. This icon is only available if the Auto Test check box is selected.

Monitor table Time left cell

Displays the amount of time left in the model testing.

Current Interval cell

Displays the current interval value during the model testing calculation.

Total Intervals cell

Displays the total number of intervals required to complete the model testing.

Ready cell

Displays an icon to indicate whether the selected model is ready for testing:

Enable Test cell

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l

Red x X indicates the model is not ready.

l

Green check mark ✓ indicates the model is ready for testing.

Enables you to activate the model testing when the Start Test button is clicked.

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Object

Description

Model Test Help icon

Enables you to access the help property view that displays the steps required to develop the DMCplus controller.

Start Test button

Enables you to first reset the test and then start the model testing.

Continue Test button

Enables you to continues the last test if it has not been finished.

Stop Test button

Enables you to stop the model testing before the test is complete

Select tag to apply the testing signal table No. column

Displays an integer number for each MV and FF variables in the DMCplus controller.

MV & FF Tag column

Displays the name of the MV and FF variables in the DMCplus controller. If a Feed Forward variable (FF) is a dependent (or calculated) variable, HYSYS cannot perform the test at the default/current setting.

Selected column

Contains check boxes that enable you to toggle between selecting and ignoring the variables for the test. By default, all the Manipulated variables (MV) and Feed Forward variables (FF) are selected to apply the test signal.

Tested column

Display the status of the variable, whether it has been tested or not, during the testing process.

Step Up column

Contains check boxes that enable you to toggle between step up testing or step down testing for each variable. By default, the check boxes are set to step up.

Amplitude column

Enables you to specify the percentage value of testing signal amplitude for each variable. By default, the signal amplitude is set at 1.00%.

Reset Test button

Enables you to reset the model testing back to the beginning.

Save Test Results button

Enables you to save the test data results in a *.clc file or a set of *.rec files.

Load DMC Controller button

Enables you to load and run the configured DMCplus controller model in the HYSYS simulation case. This button is disabled if you do not have the configuration (.ccf) and model (.mdl) files in the correct directory.

Performing DMCplus Model Testing After selecting the controlled, manipulated, and feed forward variables, data needs to be generated from the plant model to develop the controller model.

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28 DMCplus Controller

Follow the steps below to develop the controller model: 1. From the Model Testing Setting group, select the test setting parameters. o

In the Test Signal Type drop-down list, select STEP or PRBS.

o

In the Control/Sampling Time Interval cell, specify the time used to determine how often the data points are recorded during the testing phase.

o

In the TTSS cell, specify the total time period during which to apply the testing.

o

In the Auto Test cell, use the check box to toggle between activating and deactivating the Auto Test option.

o

Click the Conf. Ramp button to access the Configure Ramp Response property view. In the Configure Ramp Response property view, select the ramp characteristic/option for each CV data using the drop-down list under the Ramp Type column.

o

In the Auto test file root name field, specify the location and name for the generated testing data files. This field is only available if the Auto Test check box is selected.

2. The Select tag to apply the testing signal table contains several options to configure the variable to be tested. Note: It is recommended that the default setting in the Select tag to apply the testing signal table be modified by advance users for special case.

3. In the Monitor table, select the Enable Test check box, to automatically activate the model testing when the Start Test button is clicked. 4. Click the Start Test button to start the testing. Note: Before you start the testing, ensure that all the related slave PID Controllers are set to the remote mode.

When the Time left field displays zero, the testing is finished. o

If you had selected the Auto Test option, you can skip steps #5 to #6 because HYSYS will automatically generate an MDL file.

o

If you did not select the Auto Test option, you have to manually save the test results in a file.

5. Click the Save Test Result button, and save the testing results to a *.clc file or a set of *.rec files. The CLC or REC file(s) can be processed by the Aspen DMCplus Model to generate a MDL file. 6. Start the Aspen Model application, load the saved data and build the DMCplus model (*.mdl). In the DMCplus Model you will import the Collect file (*.clc) to vectors by saving the project first and then adding the CLC file. Note: When adding the independent (MV) and dependent (CV) variables to a case, ensure that the order you are adding the variables is the same as on the Connections tab in HYSYS.

28 DMCplus Controller

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If HYSYS has already generated the MDL file, you can still import the file into the DMCplus Model to review the generated model. The MDL file determines the size of the control problem and all the dynamic relationships between each independent and dependent variables. 7. Start the Aspen Build application and build the DMCplus configuration file (*.ccf). The CCF file determines where the input and output parameters for the controller will reside, which optional capabilities will be used, and the values assigned to all of its parameters such as limits, switches, and tuning. 8. Open the app folder in the DMCplus Online installation directory. 9. Create a folder with the controller name (for example DMC_100) and copy the *.mdl and *.ccf files into the folder. 10. Return to HYSYS program. 11. Click the Load DMCplus Controller button. You should now be able to run the simulation using the newly created DMCplus Controller. You can set the low and high variable limits for MVs and CVs (similar to setpoint range). Note: The DMCplus Controller requires that the DMCplus Online and DMCplus Desktop programs are installed. Refer to the Aspen Manufacturing Suite Installation Guide for information on installing DMCplus Online and DMCplus Desktop.

Operation Tab The Operation Tab contains the following pages: l

Operation

l

FF Variable

Operation Page The Operation page allows you to set the controller mode and the low/high limit parameters. Note: All DMCplus Controllers created can be viewed using the DMCplus GUI. The DMCplus GUI provides more functionality on using the DMCplus Controller.

DMCplus uses these low/high parameters to optimize the controlled variable (CV) and manipulated variable (MV) setpoints (steady state target) based on its tuning parameters. The CV SS target is similar to the MPC Controller setpoint except:

652

l

In MPC controller, you specify the CV SS target value.

l

In DMCplus controller, you specify the lowest and highest setpoint val-

28 DMCplus Controller

ues, and DMCplus calculates the CV SS target value based on the provided range. The Update CCF File button enables you to export any update configuration results from the Operation page into the *.ccf file. The Set Default Low/High Parameters button enables you to populate the CV and MV parameters with default values (refer to the table below). For CV: Low Limit

= current value

High Limit

= current value

For MV: Low Limit

=0

High Limit

= highest value limited by the variable span

The CV and MV SS targets are fixed, if the low/high limit values are the same.

Mode The DMCplus Controller operates in any of the following modes: l

l

l

Off. The DMCplus Controller does not manipulate the control valve, although the appropriate information is still tracked. Manual. Manipulates the DMCplus Controller output manually. In the Manual mode you can enter a value for the Manipulated Variable (MV). Automatic. The DMCplus Controller reacts to fluctuations in the Controlled Variable (CV) and manipulates the Manipulated Variable (MV) according to the DMCplus algorithm.

The mode of the controller may also be set on the Face Plate. Note: On the Face Plate, you can also view the current value of the CV and MV. You cannot change the low/high limit using the Face Plate.

FF Variable Page The Feed Forward Variable page allows you to view the controller measured disturbance. Note: The Feed Forward Variable page will only show the Feed Forward value if the variable has been added on the Connections tab.

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653

Stripchart Tab The Stripchart tab allows you to select and create default strip charts containing various variables associated to the operation.

User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

Control Valve Window The Control Valve button appears if the OP is a stream. The information shown on the Control Valve property view is specific to the associated valve. For instance, the information for a Vapor Valve is different than that for an Energy Stream. To access the Control Valve property view, click the Control Valve button located at the bottom right corner of the controller operation property view.

FCV for a Liquid/Vapor Product Stream from a Vessel The FCV property view for a material stream consists of two groups: l

Valve Parameters

l

Valve Sizing

The Valve Parameters group contains flowrate information about the stream with which the Control Valve is associated. The Valve Sizing group is usually part of the property view that requires specification. This group contains three fields, which are described in the table below:

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Field

Description

Flow Type

The type of flow you want to specify: l

molar flow

l

mass flow

l

liquid volume flow

l

actual volume flow

Min. Flow

The Minimum flow through the control valve.

Max. Flow

The Maximum flow through the valve.

28 DMCplus Controller

The Minimum and Maximum flow values define the size of the valve. To simulate a leaky valve, specify a Minimum flow greater than zero. The actual output flow through the Control Valve is calculated using the OP signal (% valve opening): (1)

For example, if the Controller OP is 25%, the Control Valve is 25% open, and is passing a flow corresponding to 25% of its operating span. In the case of a liquid valve, if the Minimum and Maximum flow values are 0 and 150 kgmole/h, respectively, the actual flow through the valve is 25% of the range, or 37.5 kgmole/h.

FCV for Energy Stream The FCV property view that appears is dependent on the type of duty stream selected. There are two types of duty streams: l l

Direct Q duty consists of a simple power value (in other words, BTU). Utility Fluid takes the duty from a utility fluid (in other words, steam) with known properties.

The type of Duty Source specified can be changed at any time by clicking the appropriate radio button in the Duty Source group.

Direct Q Duty Source This is the Flow Control Valve (FCV) view, when the Duty Source is set to Direct Q in the Duty Source group. The Attached Stream and Controller appear in the upper left corner of the property view in the Control Attachments group. The specifications required by the property view are all entered into the Direct Q group. In this group, Setpoint (SP) appears, and you may specify the minimum (Min. Available) and maximum (Max. Available) cooling or heating available.

From Utility Fluid Duty Source As with the Direct Q Duty Source, the attached stream, and controller appear in the upper left corner of the property view. Note: The application of the Utility Fluid information is dependent on the associated operation.

There are several Utility Fluid Parameters, which can be specified in the Utility Properties group: Parameter

Description

UA

The product of the local overall heat-transfer coefficient and heattransfer surface area.

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655

Parameter

Description

Holdup

The total amount of Utility Fluid at any time. The default is 100 kgmole.

Flow

The flowrate of the Utility Fluid.

Min and Max Flow

The minimum and maximum flowrates available for the Utility Fluid.

Heat Capacity

The heat capacity of the Utility Fluid.

Inlet and Outlet Temp

The inlet and outlet temperatures of the Utility Fluid.

T Approach

The operation outlet temperature minus the outlet temperature of the Utility Fluid.

Available to Controller check box. When you make the controller connections, and move to the Control Valve property view (by clicking the Control Valve button on the PID Controller property view), the Available to Controller check box is automatically selected. HYSYS assumes that because you installed a new controller on the valve, you probably want to make it available to the Controller.

Control OP Port To access the Control OP Port property view, click the Control OP Port button at the bottom right corner of the control operation property view. Note: The Control OP Port button appears when the OP is not a stream and a range of specified values is required.

The following table describes the common options in the Control OP Port property view.

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Object

Description

Attached Object cell

Displays the name of the output target object attached to the controller.

Attached Controller cell

Displays the name of the controller attached to the output target object.

Current Value cell

Displays the current value of the output target object variable.

Minimum Value cell

Enables you to specify the minimum value for the output target object variable.

Maximum Value cell

Enables you to specify the maximum value for the output target object variable.

28 DMCplus Controller

29 Digital Point

The Digital Point is an On/Off Controller. You specify the Process Variable (PV) you want to monitor, and the output (OP) stream which you are controlling. When the PV reaches a specified threshold value, the Digital Point either turns the OP On or Off, depending on how you have set up the Digital Point.

Note: The PV is optional; if you do not attach a Process Variable Source, the Digital Point operates in Manual mode.

Connections Tab The Process Variable Source and Output Target are both optional connections. No error is shown when these are not connected nor does an error appear in the Status List Window. The Object: is the stream or operation that owns the variable you want to control. The "Variable:" is the process variable you want to control. The Output Object: is the stream that is controlled by the digital point. The optional connections feature allows the controller to be in Manual mode, and have its OPState imported into a Spreadsheet and used in further calculations in the model. This configuration can only be used for Manual mode. To run the controller in Automatic mode, you require a Process Variable Source input. With only the input connected, the Digital Point acts as a digital input indicator. With both the input and output specified the Digital Point can be used to determine its state from its PV and then take a discrete action. To specify the controller input, use the Select PV button to access the Variable Navigator property view, which allows you to simultaneously target the PV

29 Digital Point

657

Object and Variable. Similarly, use the Select OP button to choose the Output Target. Note: The flow of the OP Output is manipulated by the Digital Point Controller.

Parameters Tab The Parameters tab provides three different modes of operation: l

Off

l

Manual

l

Auto

For each of these modes the Parameters tab is made up of a number of groups: Output, Manual/Auto Operational Parameters, and Faceplate PV Configuration.

Off Mode When Off mode is selected, you cannot adjust the OP State. Notice that if you turn the controller Off while running the simulation, it retains the current OP State (Off or On). Thus, turning the Controller off is not necessarily the same as leaving the Controller out of the simulation. Only the Output group, displaying the current OP State, is visible when in the Off mode.

Manual Mode When Manual mode is selected you can adjust the OP State from the Faceplate or this tab. Two groups are visible when in this mode: Output and Manual Operation Parameters. The Output group allows you to toggle the OP state on and off. The Operational Parameters group allows you to select one of the three options described in the table below.

658

Option

Description

Latch

Holds the current OP State to what is specified in the Output group.

Pulse On

Allows the OP State to Pulse On for a specified period and fall back to the Off state.

Pulse Off

Allows the OP State to Pulse Off for a specified period and fall back to the On state.

29 Digital Point

Auto Mode When Auto mode is selected, HYSYS automatically operates the Digital Point, setting the OP State Off or On when required, using the information you provided for the Threshold and OP Status. Three groups are visible when in this mode: Output, Auto Operational Parameters, and Faceplate PV Configuration. Since HYSYS is automatically adjusting the controller, the Output group simply displays the OP State. Like Manual mode, the Auto Operation Parameters group allows you to select one of the three options: l

Latch

l

Pulse On

l

Pulse Off

When Latch is selected, the following parameters appear. Parameter

Description

PV

The actual value of the PV (Process Variable).

Threshold

The value of the PV which determines when the controller switches the OP on or off.

Higher Deadband

Allows you to specify the upper deviation of the threshold value.

Lower Deadband

Allows you to specify the lower deviation of the threshold value.

OP On/Off when

Allows you to set the condition when the OP state is on or off.

For both the Pulse On and Pulse Off options the parameters are the same as the Latch option. However the pulse options both require you to specify a Pulse Duration. The Face Plate PV Configuration group allows you to specify the minimum and maximum PV range. This is the range shown on the controllers Face Plate.

Threshold and Dead Band for Latch For the Latch option, the OP (output) switches states (on or off) when the PV (Process Variable) value reaches the set point value. The set point value is accompanied with an adjustable differential gap or dead band value, this value allows small deviations to occur in the PV value without triggering changes to the OP state. The following is an example of how the Latch option operates. Assume you have a Digital Point operation with the following parameters:

29 Digital Point

659

Parameter

Value

Threshold

100

Higher dead band

45

Lower dead band

20

OP is on when

PV >= Threshold

l

Red line indicates the path of the OP vs. time.

l

Blue line indicates the path of the PV vs. time.

The following situations illustrates when the OP is turned on or off. l

l

l

Initial State. If PV value starts at 70 and OP is off, the OP stays off until the PV value rises above or to equal 145, than OP is turned on. Intermediate State. If PV value rises and falls above value 80 and OP state is already on, then OP remains on. Intermediate State. If PV value falls below or equal value 80, OP is turned off. Note: If PV value starts at 150 and OP state is off, then OP remains off until the PV value falls below 80 and rises above 145, after PV reaches or rises above 145 the OP state is turned on.

The above situation is the same for Latch option with OP is on when PV = Threshold

Pulse Duration

2 seconds

l

Red line indicates the path of the OP vs. time.

l

Blue line indicates the path of the PV vs. time.

The following situations illustrates when the OP is turned on or off. l

l

If PV value starts at 70, the OP is off until the PV value rises to equal 145, than OP is on for 2 seconds. After OP state has pulsed on once, OP remains off if PV value rises and falls above the value 80. Note: If PV value starts at 150, OP is off until the PV value falls below 80 and rises above 145, after PV reaches 145 the OP state is on for 2 seconds.

Stripchart Tab The Stripchart tab allows you to select and create default strip charts containing various variable associated to the operation.

29 Digital Point

661

User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

Alarm Levels Tab The Alarms tab allows you to set alarm limits for the controller. The Alarm Level group allows you to set and configure the alarm points for a selected signal type. There are four alarm points that can be configured: l

LowLow

l

Low

l

High

l

HighHigh

The alarm points should be specified in the descending order from HighHigh to LowLow points. You cannot specify the value of the Low and LowLow alarm points to be higher than the signal value. Similarly, the High and HighHigh alarm points cannot be specified a value lower than the signal value. Also, no two alarm points can have a similar values. In addition, the user can specify a deadband for a given set of alarms. This can be helpful in situations where the signal is “noisy” to avoid constant triggering of the alarm. If a deadband is specified, you have to specify the alarm points so that their difference is greater than the deadband. At present the range for the allowable deadband is as follows: 0.0% ≤ deadband ≤ 1.5% of the signal range. Note: The above limits are set internally and are not available for adjustment by the user.

The Alarm Status displays the recently violated alarm for each alarm point.

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29 Digital Point

30 External Data Linker

The External Data Linker operation lets you connect Internal streams (streams that exist within the active simulation) to External streams (previously published streams that exist on the RTI Data Server). A valid connection to the RTI Data Server must exist before you can use the External Data Linker operation.

Connections Page Specifying External Data Linker Connections 1. From the PFD, double-click the External Data Linker icon. The External Data Linker property view appears. 2. Click on the Design tab. 3. Click on the Connections page. 4. In the Name field, specify a name for the External Data Linker. 5. In the External Stream column, click the cell. A drop-down list appears. From the drop-down list, either select a pre-defined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step if you have multiple external streams. 6. In the Internal Stream column, click the cell. A drop-down list appears. From the drop-down list, either select a pre-defined stream or click the empty space at the top of the list and type in the name of the stream. Repeat this step for each external stream you have specified. Notes: l

You must select an external stream before you can select an internal stream.

l

If the Live Link check box is active, the internal stream’s conditions change as changes are made to the external stream’s published data. If the check box is not active, the conditions are read in initially at connection only.

Configuration Page To Specify the External Data Linker Transfer Type

30 External Data Linker

663

1. From the PFD, double-click the External Data Linker icon. The External Data Linker property view appears. 2. Click on the Design tab. 3. Click on the Configuration page. 4. From the Transfer Specifications drop-down list, select one of the following transfer types: Temperature-Pressure, Pressure-Vapor Fraction, Temperature-Vapor Fraction, or Pressure-Enthalpy. Repeat this step for each external stream.

Properties Page On the Properties page, you can modify any of the External Data Linker’s properties.

Revision History Tab To view Revision History: 1. From the PFD, double-click the External Data Linker icon. The External Data Linker property view appears. 2. Select the Revision History tab. 3. From the list of external streams, select the stream for which you want to view the revision history. The Refinery Information group displays the number of revisions and the For Stream GUID. The Revision Data group displays the author of the revision, the date of the revision and the revision notes. Use the Currently in Use Revision drop-down list to select the revision you want to use. Click the View Raw Data button to open the Published Data property viewer. Activate the Use as Default Revision check box to use the selected revision as the default revision. Activate the Warn if Higher Revision is Available check box to be informed if the revision you selected is not the latest revision.

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30 External Data Linker

31 Recycle

The capability of any flowsheet simulator to solve recycles reliably and efficiently is critical. HYSYS has inherent advantages over other simulators in this respect. It has the unique ability to back-calculate through many operations in a non-sequential manner, allowing many problems with recycle loops to be solved explicitly. For example, most heat recycles can be solved explicitly (without a Recycle operation). Material recycles, where downstream material mixes with upstream material, require a Recycle operation. The Recycle installs a theoretical block in the process stream. The stream conditions can be transferred either in a forward or backward direction between the inlet and outlet streams of this block. In terms of the solution, there are assumed values and calculated values for each of the variables in the inlet and outlet streams. Depending on the direction of transfer, the assumed value can exist in either the inlet or outlet stream. For example, if the user selects Backward for the transfer direction of the Temperature variable, the assumed value is the Inlet stream temperature and the calculated value is the Outlet stream temperature. The following steps take place during the convergence process: 1. HYSYS uses the assumed values and solves the flowsheet around the recycle. 2. HYSYS then compares the assumed values in the attached streams to the calculated values in the opposite stream. 3. Based on the difference between the assumed and calculated values,

31 Recycle

665

HYSYS generates new values to overwrite the previous assumed values. 4. The calculation process repeats until the calculated values match the assumed values within specified tolerances. Note: The Recycle Adviser can ensure that flowsheets contain the minimum number of recycles at their optimal locations. The Adviser picks the best location for recycles and assigns the best calculation order for optimized convergence.

Recycle Property View The Continue button at the bottom of the Recycle property view enables you to run the calculation after the maximum iteration has been reached.

Connections Tab The Connections tab contains the following pages: l

Connections

l

Notes

Connections Page  The Connections page consists of the four fields: l l

l

l

Name. The name of the Recycle operation. Inlet. Holds the inlet stream, which is the latest calculated recycle; it is always a product stream from a unit operation. Outlet. Contains the outlet stream, which is the latest assumed recycle; it is always a feed stream to a unit operation. Fluid Package. The fluid package associated to the operation can be selected by entering the fluid package name or using the drop-down list.

Notes Page The Notes page provides a text editor, where you can record any comments or information regarding the operation or to your simulation case in general.

Parameters Tab The Parameters tab contains the following pages:

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l

Variables

l

Numerical

31 Recycle

If HYSYS petroleum Refining is installed, the Parameters tab has a Convergence page.

Variables Page HYSYS allows you to set the convergence criteria factor for each of the variables and components listed. The sensitivities values you enter actually serve as a multiplier for HYSYS internal convergence tolerances. The internal absolute tolerances, except flow which is a relative tolerance, are shown in the table below. HYSYS Internal Tolerances Variable

Internal Tolerance

Vapor Fraction

0.01

Temperature

0.01

Pressure

0.01

Flow

0.001*

Enthalpy

1.00

Composition

0.0001

Entropy

0.01

*Flow tolerance is relative rather than absolute Note: The internal Vapor Fraction tolerance, when multiplied by the recycle tolerance, is 0.1 which appears to be very loose. However, in most situations, if the other recycle variables have converged, the vapor fraction in the two streams are identical. The loose Vapor Fraction tolerance is critical for close-boiling mixtures, which can vary widely in vapor fraction with minimal difference in other properties.

For example, the internal tolerance for temperature is 0.01 and the default multiplier is 10, so the absolute tolerance used by the Recycle convergence algorithm is 0.01*10 = 0.1. Therefore, the assumed temperatures and the calculated temperature must be within 0.1 °C (where C is the internal units) of each other if the Recycle is to converge. HYSYS always convert the values entered to the internal units before performing calculations. A multiplier of 10 (default) is normal, and is recommended for most calculations. Values less than 10 are more stringent; that is, the smaller the multiplier, the tighter the convergence tolerance. Note: It is not required that each of the multipliers be identical. For example, if you are dealing with ppm levels of crucial components, you can set the Composition tolerance multiplier much tighter (smaller) than the others.

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The Transfer Direction column allows you to select the transfer direction of the variable. There are three selections: l

not to transfer

l

transfer forward

l

transfer backward

Not Transferred option can be used if you only want to transfer certain stream variables. For example, if you only want to transfer P, T composition and flow, the other variables could be set to Not Transferred. When you select the Take Partial Steps check box, the Recycle operation takes calculation steps on any variables whenever the calculations are possible. When you clear the check box, the Recycle operation waits until all of the inlet stream flowing into the operation is complete before performing the next calculation step. The default setting for this check box is clear. In addition to converging on physical properties basis, the Recycle operation also converges on individual component tolerances. The components in the recycle stream are automatically added to the Recycle logical operation. When you select the Use Component Sensitivities check box, the single composition sensitivities value is automatically overridden by the individual component sensitivities values and the Recycle operation takes calculation steps on each value when applicable. The default setting for this check box is inactive. Once you select the Use Component Sensitivities check box, the tolerances for each component in the recycle stream are listed in the table. By default, the sensitivities value is set at 10.00 for each component. Any changes that you make to the sensitivities value are automatically saved.

Numerical Page The Numerical page contains the options related to the Wegstein Acceleration Method. This method is used by the Recycle to modify the values it passes from the inlet to outlet streams, rather than using direct substitution. The table below describes the parameters on the Numerical page. Parameter

Description

Calculation Mode

Nested: The Nested option results in the Recycle being called whenever it is encountered during the calculations. If your Flowsheet has a single Recycle operation, or if you have multiple recycles that are not connected, use the Nested option. Simultaneous: The Simultaneous option causes all Recycles to be invoked at the same time once all recycle streams have been calculated. If your Flowsheet has multiple inter-connected recycles, use the Simultaneous option.

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31 Recycle

Parameter

Description

Acceleration Method

Wegstein: Ignores interactions between variables being accelerated.

Maximum Iterations

The number of iterations before the Recycle stops. You can continue with the calculations by clicking the Continue button.

Iteration Count

The number of iterations before an acceleration step is applied to the next iteration.

Flash Type

The flash method to be implemented by the Recycle operation.

Wegstein Parameters

Acceleration Frequency: Tells the recycle how many steps to go before putting in acceleration (the lower the value the more variables get accelerated).

Dominant Eigenvalue: Includes interactions between variables being accelerated. Further, the Dominant Eigenvalue option is superior when dealing with non-ideal systems or systems with strong interactions between components.

Q Maximum: Damping factors for the acceleration step (defaults are 0 and 20). Q Minimum: Damping factors for the acceleration step (defaults are 0 and 20). Acceleration Delay: This delays the acceleration until the specified step. PSD Properties

Particle size distribution - To have PSD properties in a stream (and recycle) you must have solids in the components list. (You can create hypo solids in the Properties environment, the same way you create hypo components).

There are several additional points worth noting about the Recycle: l

l

31 Recycle

When the Recycle cannot be solved in the number of iterations you specify, HYSYS stops. If you decide that the problem may converge with more iterations, simply click the Continue button. The Recycle initializes the iteration counter and continues until a solution is found or it again runs out of iterations. If your problem does not converge in a reasonable number of iterations, there are probably constraints in your flowsheet which make it impossible to solve. In particular, if the size of the recycle stream keeps growing, it is likely that the flowsheet does not permit all of the material entering the flowsheet to leave. An example of this occurs in gas plants when you are trying to make a liquid product with a low vapor pressure and a vapor product which must remain free of liquids even at cold temperatures. Often, this leaves no place for intermediate components like propane and butane to go, so they accumulate in the plant recycle streams. It is also possible that the tolerance is too tight for one or more of the Recycle variables and cannot be satisfied. This can readily be determined by examining the convergence history, and comparing the unconverged variable deviations with their tolerances.

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Note: The Monitor tab provides a history of the Recycle calculations. l

l

The logical operations (such as the Recycle, Adjust and Controller) are different from other operations in that they actually modify the specifications of a stream. As a result, if you remove any of these operations, the outlet stream specifications remain. Thus, nothing in the flowsheet is “forgotten” for these operations. You can Delete or Ignore a Recycle when you want to make flowsheet modifications, but do not want to invoke the iterative routines. Tolerance settings are important to a successful Recycle solution. This is especially true when multiple recycles are involved. If there is no interaction among the recycles, or if they are inter-connected and are being solved simultaneously, tolerance values can be identical for all Recycles if desired. However, if the Recycles are nested, tolerances should be made increasingly tighter as you go from the outermost to the innermost Recycle. Without this precaution, the outside Recycle may not converge.

Maximum Number of Iterations When HYSYS has reached the maximum number of iterations, a warning message appears stating that the Recycle failed to converge in the specified number of iterations. You can then choose whether or not to continue calculations. If you are starting a new flowsheet, use a small number of Maximum Iterations, such as 3. Once it is evident that the calculations are proceeding well, the count can be increased. The iterations required depend not only on the complexity of your flowsheet, but also on your initial estimate and the convergence tolerances you use.

Damping Factors - Qmax and Qmin The Wegstein acceleration method uses the results of previous iterations in making its guesses for the recycle stream variables. Assumed values are calculated as follows: (1) where: X = assumed value Y = calculated value n = iteration number Q = acceleration factor HYSYS determines the actual acceleration (Q) to apply based on the amount of change between successive iterations. The values for Qmax  and Qmin set bounds on the amount of acceleration applied. Note from the equation that when Q = 0, direct replacement is used. When Q is negative, acceleration is used. When Q is positive and smaller than 1, damping occurs.

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31 Recycle

Note: If the Recycle is still oscillating, even with the Iteration Count set to ensure direct replacement, you can specify a slightly larger value for Qmax to damp the direct replacement.

Iteration Count The Iteration Count is the number of Recycle iterations before an acceleration step is applied when calculating the next assumed recycle value. The default count is 3; after three iterations (assuming the Acceleration Delay is less than 3), the assumed and calculated recycle values are compared and the Wegstein acceleration factor is determined and applied to the next assumed value. When the acceleration factor is not being used (in all iterations up to the Iteration Count), the next assumed value is determined by direct replacement. Notice that Acceleration Delay takes precedence over the Iteration Count. This means that for an Acceleration Delay value of x, the initial x iterations use direct replacement, even if the Iteration Count is set to less than x. The x+1 iteration uses the acceleration after which the Iteration Count applies.

Although acceleration generally works well for most problems, in some cases it may result in over-correction, oscillation, and possibly non-convergence. Examples of this type of problem include highly-sensitive recycles and multiple recycle problems with strong interactions among recycles. In cases such as these, direct replacement may be the best method for all iterations. To eliminate the use of acceleration, simply set the Iteration Count (or Acceleration Delay) to a very high number of iterations (for example, 100) which is never reached. In the rare instance where even direct replacement causes excessive over-corrections, damping is required. Use the set of parameters discussed below to control this.

Acceleration Delay The Acceleration Delay parameter delays the acceleration until the specified step. This delay applies to the initial set of iterations and once the specified step is reached the Iteration Count is applied. That is to say no acceleration is performed until the delay value is reached and after that iteration the acceleration is applied according to the Iteration count. The default is specified as 2 but now it can be specified to any value. For example, if the 'delay' is set to 5 and the Iteration Count is 3 then the first 5 iterations use direct replacement and the sixth uses acceleration then after every third iteration the acceleration step is applied.

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Convergence Page The Convergence page contains information about transferring and converging petroleum properties across the recycle. On this page, you can l

individually set each property as an active specification during the recycle convergence

l

adjust the tolerance for each property

l

view the current value for each property Note: The Convergence page only appears when HYSYS Petroleum Refining is installed.

Worksheet Tab The Worksheet tab displays the various Conditions, Properties, and Compositions of the Feed and Product streams.

Monitor Tab The Monitor tab contains the following pages: l

Setup

l

Tables

l

Plots

The Setup page allows you to specify which variables you want to view or monitor. To view a variable, select the View check box corresponding to the variable of interest. The Tables page and Plots page display the convergence information as the calculations are performed in tabular and graphical format respectively. The inlet value, outlet value, and variable are shown, along with the iteration number. On the Tables page: l

Use the Raw Data, Sort by Iteration, and Sort by Variable radio buttons to organize the presentation of the information.

On the Plots page: l

l

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Right-click anywhere within the plot area to access the plot’s object inspect menu. The variables listed in the Left Axis and Right Axis drop-down lists are selected on the Setup page.

31 Recycle

User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

Calculations HYSYS provides a very simple means of solving recycle problems, and its interactive nature provides a high degree of control and feedback to the user as to how the solution is proceeding. Note: In Dynamic mode, HYSYS ignores the Recycle operation. So in the case of the outlet stream, it is identical to the inlet stream.

The Recycle can be set up as a single unit operation to represent a single recycle stream in a process flowsheet, or a number of them can be installed to represent multiple recycles, interconnected or nested, as well as a combination of interconnected and nested recycle loops. Similar to the Adjust operation, the Recycle solves all the recycle loops simultaneously, if requested to do so. The step-by-step procedure for setting up a recycle is as follows: 1. Make a guess for the assumed values in the stream attached to the recycle operation (temperature, pressure, flow rate, composition). The flow rate can generally be zero, but, obviously, better estimates results in faster convergence.  Note: If the recycle is a feed to a tower, a reasonable estimate is needed to ensure that the column converges the first time it is run.

2. Build your flowsheet until the calculated values in the connected streams can be determined by HYSYS. Note: The outlet and inlet recycle streams must have different names.

3. Install the Recycle block.

Reducing Convergence Time Selection of the recycle tear location is vitally important in determining the computer run time to converge the Recycle. Although the physical recycle stream itself is often selected as the tear stream, the flowsheet can be broken at virtually any location. In simulating a complex system, a number of factors must be considered. The following are some general guidelines: l

Choose a Tear Location to Minimize the Number of Recycles o

31 Recycle

Reducing the number of locations where the iterative process is required save on total convergence time. Choosing the location of the Recycle depends on the flowsheet topology. Attempt to choose a point such that specifying the assumed values defines

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as many streams downstream as possible. It generally occurs downstream of gathering points and upstream of distribution points. Examples include downstream of mixers (often mixing points where the physical recycle combines with the main stream), and upstream of tees, separators, and columns. l

Choose a Tear Location to Minimize the Number of Recycle Variables o

Variables include vapor fraction, temperature, pressure, flow, enthalpy, and composition. Choose the tear stream so that as many variables as possible are fixed, thus effectively eliminating them as variables and increasing convergence stability. Good choices for these locations are at separator inlets, compressor aftercooler outlets, and trim heater outlets. Note: Avoid choosing tear streams which have variables determined by an Adjust operation.

l

Choose a Stable Tear Location o

The tear location can be chosen such that fluctuations in the recycle stream have a minimal effect. For example, by placing the tear in a main stream, instead of the physical recycle, the effect of fluctuations are reduced. The importance of this factor depends on the convergence algorithm. It is more significant when successive substitution is used. Choosing stable tear locations is also important when using simultaneous solution of multi-recycle problems.

Recycle Advisor When a flowsheet contains a number of recycle blocks, it is difficult to know simply by examining the topology what the ideal placement and configuration of the recycle would be. The Recycle Advisor can ensure that flowsheets contain the minimum number of recycles at their optimal locations. The Advisor picks the best location for recycles and assigns the best calculation order for optimized convergence. When you approve the new suggested configuration, the Advisor automatically disconnects the old recycles and creates the new ones. The Recycle Advisor lets you edit recycle settings and apply changes to one or all recycles. You can also use the tool to return to the original recycle configuration.

Using the Recycle Advisor The Recycle Advisor icon is located on the Flowsheet/Modify ribbon, Tools section. It is also available from the Recycle operation interface. To start the analysis, select Recycle Advisor from the ribbon. On the Recycle Advisor view, click Run Advisor.

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31 Recycle

When the analysis is run, you can use check boxes to selectively accept or reject suggested changes. When you click Accept Suggested Actions, the new recycle scheme is implemented.

Recycle Setup Tab Use the Recycle Setup tab to edit one or several selected recycle operations on the flowsheet. The Recycle Advisor lets you configure all major settings for a recycle, including l

l

l

Sensitivities for vapor fraction, temp., pres., flow, enthalpy, composition, and entropy. Recycle type, calculation level, maximum iterations, ignore/unignored state, convergence state. Petroleum assay initialization setting.

You can copy these settings to selected recycles or all recycles.

31 Recycle

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31 Recycle

32 Selector Block

The Selector Block is a multiple-input single-output controller that provides signal conditioning capabilities. It determines an Output value based on a user-set Input function. For instance, if you want the maximum value of a specific variable for several Input streams to dictate the Output, you would use the Selector Block. A simple example would be where a Selector Control chooses the average temperature from several temperature transmitters in a Column, so that the Reboiler duty can be controlled based on this average.

Connections Tab The Connections tab consists of three objects described in the table below: Objects

Description

Selector Name

Contains the name of the Selector Block, which can be edited at any time.

Process Variable Sources

Contains the variables the Selector Block considers and inserted into the input function. The Process Variables for the various inputs are targeted by clicking the Add PV button, accessing the Variable Navigator. You can edit or delete any current PV by positioning the cursor in the appropriate row, and clicking the Edit PV or Delete PV buttons. If you add a Variable whose type is inconsistent with the current Input Variables, HYSYS displays an error message. However, you are allowed to retain that Variable.

OP Target

Contains the process variable, which is manipulated by the Selector Block. To select the OP Target, click the Select OP button. This button also accesses the Variable Navigator. Notice that it is not necessary for the Target Variable type to match the Input Variable type.

32 Selector Block

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Parameters Tab The Parameters tab contains the following pages: l

Selection Mode

l

Scaling Factor

Selection Mode Page The Selection Mode page allows you to select the mode and parameters of the operation. When the Apply Unit Set check box is cleared, no real unit conversions are done for calculations. When the Apply Unit Set check box is selected, you can select a unit set and variable type for the calculations and output respectively.

In the Mode group, you can choose from the following modes:

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Modes

Description

Off

Select this mode to disable the Selector Block. The function of this mode is similar to the Ignored check box in the unit operations.

Minimum

The minimum value from the list of Input Variables is passed to the Output stream.

Maximum

The maximum value from the list of Input Variables is passed to the Output stream.

32 Selector Block

Modes

Description

Median

The median value of the Input Variables is passed to the Output stream. If there are an even number of Input Variables, then the higher of the two middle values is passed to the Output stream.

Average

The average of the Input Variables is passed to the Output stream.

Sum

The sum of the Input Variables is passed to the Output stream.

Product

The product of the Input Variables is passed to the Output stream.

Quotient

The quotient of the Input Variables is passed to the Output stream.

Manual

This mode is similar to Manual mode in the PID controller. This mode allows you to specify the OP directly.

Hand Sel

Allows you to select which Input Variable value is written to the OP. You can select the PV value using the Selected Input field.

In the Parameters group, you can specify the following parameters: l

l

Calculation Unit Set. You can select the unit set you want the calculations done with using the drop-down list. There are three standard selections: SI, EuroSI, and Field. You can create your own unit set in the Session Preferences property view. Selected Input. You can select the PV source using the drop-down list in this field. This field is only available for the Minimum, Maximum, and Hand Sel modes.

External/Dynamic Reset Feedback When the Selector Block has multiple input signals from PID blocks and you selected the Minimum, Maximum, or Median radio buttons in the Mode section, the Output (OP) of unselected PIDs is tracked closely to the selected output, or OP. If the PID Controller is using the HYSYS PID Velocity Algorithm (selected on the Parameters tab | Configuration page of the PID Controller when you select Hysys from the Algorithm Type drop-down list and PID Velocity Form from the Algorithm Subtype drop-down list), HYSYS uses time-dependent reset feedback. The following equation is used: (1) Where: n = current time step n-1 = previous time step h = control interval (time step) Ti = reset time, chosen to be the same as Integral time

32 Selector Block

679

OPvel = OP calculated using the HYSYS Velocity algorithm (refer to the HYSYS PID Velocity Form equation for further information. For other algorithms, the steady state version of the above equation is used: (2)

Scaling Factors Page The Scaling Factors page allows you to manipulate the input and output parameters. The Output is a function of the Mode, Gain, and Bias, where the Input function is dependent on the mode: (1) The Input function is multiplied by the Gain. In effect, the gain tells how much the output variable changes per unit change in the input function. The Bias is added to the product of the Input function and Gain. Note: If you want to view the Input function without any Gain or Bias adjustment, set the Gain to one and the Bias to zero.

Inputs can be individually scaled before the output calculations. (2) The Inverse Cond. check box is used when the selector is writing back to its PV, and you are required to scale the input value backwards. (3)

Monitor Tab The Monitor tab displays the results of the Selector Block. It consists of two objects: l

l

Input PV Data. This group contains the current values of the input process variable. Output Value. This display field contains the current value of the PV for each of the input variables and the Output Value is also displayed on the Parameters tab. Note: The Output value is not displayed until the Integrator has been started.

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32 Selector Block

Example In the simple example shown here, the median value of Stream 1, Stream 2, and Stream 3 is passed to the Output, after a Gain of 2 and a Bias of 5 have been applied. These are the steps: 1. Determine f(Inputs), which in this case is the median of the Input Variables. The median (middle value) temperature of the three streams (10 °C, 15 °C, 20 °C) is 15 °C. 2. Determine the Output Value, from the Gain and Bias. The Gain is 2, and the Bias is 5 °C. 3. The Output is calculated as follows: (1)

Stripchart Tab The Stripchart tab allows you to select and create default strip charts containing various variable associated to the operation.

User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

32 Selector Block

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32 Selector Block

33 Set

The Set is an operation used to set the value of a specific Process Variable (PV) in relation to another PV. The relationship is between the same PV in two like objects; for instance, the temperature of two streams or the UA of two exchangers. Note: The Set unit operation can be used in both Dynamic and Steady State mode.

The dependent, or target, variable is defined in terms of the independent, or source, variable according to the following linear relation: (1) where: Y = dependent (target) variable X = independent (source) variable M = multiplier (slope) B = offset (intercept)

Set Property View Connections Tab On the Connections tab, you can specify the following information: l

l

33 Set

Target Object. The stream or operation to which the dependent variable belongs. This is chosen by clicking the Select Var button. This brings up the Variable Navigator property view. Target Variable. The type of variable you want to set, for example, temperature, pressure, and flow. The available choices for Variable are dependent on the Object type (stream, heat exchanger, and so forth) Your choice of Variable is automatically assigned to both the Target and Source object.

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l

Source Object. The stream or operation to which the independent variable belongs.

Notice that when you choose an object for the Target, the available objects for the Source are restricted to those of the same object type. For example, if you choose a stream as the Target, only streams are available for the Source. HYSYS solves for either the Source or Target variable, depending on which is known first (bi-directional solution capabilities).

Parameters Tab On the Parameters tab, you can specify values for the slope (Multiplier) and the intercept (Offset). The default values for the Multiplier and Offset are 1 and 0, respectively.

User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

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33 Set

34 Spreadsheet

The Spreadsheet applies the functionality of spreadsheet programs to flowsheet modeling. With essentially complete access to all process variables, the Spreadsheet is extremely powerful and has many applications in HYSYS. Note: The HYSYS Spreadsheet has standard row/column functionality. You can import a variable, or enter a number or formula anywhere in the spreadsheet.

The Spreadsheet can be used to manipulate or perform custom calculations on flowsheet variables. Because it is an operation, calculations are performed automatically; Spreadsheet cells are updated when flowsheet variables change. In Dynamics mode, the Spreadsheet cells are updated when the integrator is running. One application of the Spreadsheet is the calculation of pressure drop during dynamic operation of a Heat Exchanger. In the HYSYS Heat Exchanger, the pressure drop remains constant on both sides regardless of flow. However, using the Spreadsheet, the actual pressure drop on one or both sides of the exchanger could be calculated as a function of flow. Complex mathematical formulas can be created, using syntax which is similar to conventional Spreadsheets. Arithmetic, logarithmic, and trigonometric functions are examples of the mathematical functionality available in the Spreadsheet. The Spreadsheet also provides logical programming in addition to its comprehensive mathematical capabilities. Boolean logic is supported, which allows you to compare the value of two or more variables using logical operators, and then perform the appropriate action depending on that result. You can import virtually any variable in the simulation into the Spreadsheet, and you can export a cell's value to any specifiable field in your simulation. There are two methods of importing and exporting variables to and from the Spreadsheet:

34 Spreadsheet

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Methods

Description

Using the Variable Navigator

Do one of the following: l

On the Connections tab, click the Add Import or Add Export button.

l

On the Spreadsheet tab, right-click the cell you want and select the import/export command from the object inspection menu.

Then using the Variable Navigator, select the variable you want to import or export. Dragging Variables

Simply right-click the variable value you want to import, and drag it to the desired location in the Spreadsheet. If you are exporting the variable, drag it from the Spreadsheet to an appropriate location. When using the Dragging Variables method, the property views have to be non-modal.

When you are using the Spreadsheet to return a result back to the flowsheet, you must consider its application in terms of the overall calculation sequence, particularly when Recycles are involved. If the Spreadsheet performs a calculation and sends the results back upstream, the potential exists for creating inconsistencies as the full effect of the previous Recycle loop has not propagated through the flowsheet. By using the Calculation Sequencing option, you can minimize the potential for problems of this nature.

Spreadsheet Functions The HYSYS Spreadsheet has extensive mathematical and logical function capability. To view the available Spreadsheet Functions and Expressions, click the Function Help button to open the Available Expressions and Functions property view. Note: All functions must be preceded by “+” (straight math) or “@” (special functions like logarithmic, trigonometric, logical, and so forth). Note: Examples are "+A4/B5" and "@ABS(A4-B5)".

The Available Expressions and Functions property view contains the following tabs: l

Mathematical Expressions

l

Logical Expressions

l

Mathematical Functions

General Math Functions The following arithmetic functions are supported:

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34 Spreadsheet

General Operations

Method of Application

Addition

Use the “+” symbol.

Subtraction

Use the "-" symbol.

Multiplication

Use the “*” symbol.

Division

Use the “/” symbol, typically located on the numeric keypad, or next to the right SHIFT key. (Do not use the “\” symbol).

Absolute Value

 “@Abs”.

Several other mathematical functions are also available: Advanced Operations

Method of Application

Power

Use the “^” symbol. Example: +3^3 = 27 Example 2: +27^(1/3)=3 Notice that the parentheses are required in this case, since the cube root of 27 (or 27 to the power of one-third) is desired.

Square Root

"@SQRT". Example: @sqrt(16) = 4 Notice that capitalization is irrelevant. You can also use “@RT” to calculate a square root. (Example: @rt(16)=4)

Pi

Simply enter "+pi" to represent the number 3.1415...

Factorial

Use the “!” symbol. Example: +5!-120=0

Calculation Hierarchy The usual hierarchy of calculation is used (Brackets, Exponents, Division and Multiplication, Addition and Subtraction). For example: +6+4/2 = 8 (not 5) since division is performed before addition. However, +(6+4)/2 = 5 because any expressions in parentheses are calculated first.

34 Spreadsheet

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Logarithmic Functions Log Function

Method of Application

Natural Log

“@ln”. Example: @ln(2.73)=1.004

Base 10 Log

"@log". Example: @log(1000)=3

Exponential

“@exp”. Example: @exp(3)=20.09

Hyperbolic

 “@sinh”, “@cosh”, “@tanh”. Example: @tanh(2) = 0.964

Expression within Range

“@Inrange” Returns a 1 if the number is within the range specified within the function. Example: A1 = 5

Expression within Limit

l

@Inrange(A1,4,7) = 1

l

@Inrange(A1,6,10) = 0

“@Inlimit” Returns a 1 if the number is within the range, on either side of the number, specified within the function. Example: A1 = 5

Expression within Percentage

l

@Inlimit(A1,7,2) = 1

l

@Inlimit(A1,7,1) = 0

“@Inpercentage” Returns a 1 if the number is within the percentage, on either side of the number, specified within the function. Example: A1 = 5 l

@Inpercentage(A1,8,40) = 1

l

@Inpercentage(A1,8,35) = 0

Trigonometric Functions All of the trigonometric functions are supported, including inverse and hyperbolic functions:

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34 Spreadsheet

Trig Function

Method of Application

Standard

“@sin”, “@cos”, “@tan”. Example: @cos(pi) =-1 (Radian Angles)

Inverse

“@asin”, “@acos”, “@atan”. In this case, the number to which the function is being applied must be between -1 and 1. Example: @asin(1) = 1.571 (Radian Angles)

Trigonometric functions can be calculated using radian, degree or grad units, by selecting the appropriate type from the Angles in drop-down list in the Current Cell group. Note: Parentheses are required for all logarithmic and trigonometric functions. The capitalization is irrelevant; HYSYS calculates the function regardless of how it is capitalized.

Logical Operators The Spreadsheet supports Boolean logic. For example, suppose cell A1 had a value of 5 and cell A2 had a value of 10. Then, in cell A3, you entered the formula (+A1”

Less Than

“=”

Less Than or Equal to

“ Curves pages. b. If the compressor speed is not the same as the curve design speed, a new curve is calculated based on FanLaw, and the new head is calculated for the current flow using the linear or quadratic method from the FanLaw curve. 3. If multiple compressor curves are available: a. If the compressor speed is the same as one of the curve speeds, the new head will be calculated from the current flow of the linear or quadratic method from this curve. b. If the compressor speed is not equal to any speed of the curves, a new table is calculated with each row as a pair of curve speeds and the head based on current flow. The head is calculated using the linear or

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52  Centrifugal Compressor or Expander Unit Operations

quadratic method if the flow is within the data range, or extrapolation if the flow is outside the range. Then the head for compressor speed is calculated by interpolating from this table.

Dynamics Mode 1. If one compressor curve is available: b. The compressor speed is the same as the curve design speed. Curve will be fitted into this equation:  Q**2 = aa * N**2 - bb * H, where Q is the flow, N is the speed and H is the head. The parameter aa and bb will be used to calculate the derivative and the right hand side value of this equation: Rhs = Q**2 - (aa * N**2 - bb * H) b. If the compressor speed is not the same as the curve design speed, a new curve will be calculated based on FanLaw, and the calculation will be the same as above base on the FanLaw curve. c. If multiple compressor curves are available: a. If the compressor speed is the same as one of the curve speed, the calculation will be the same as the single curve method base on this curve. b. If compressor speed is not equal to any speed of the curves: i. If the compressor speed is lower than the lowest speed of the curve collection, the curve with lowest speed is used as the single available curve. ii. If the compressor speed is higher than the highest speed of the curve collection, the curve with highest speed is used as the single available curve. iii. Find the two curves with the compressor speed in the middle. Fit these two curves into the same equation: Q**2 = aa * N**2 - bb * H, where Q is the flow, N is the speed and H is the head. Then: 1. Select one set of aa and bb from the closest curve based on speed. Calculate the heads for each curves from current flow. 2. Calculate the head of the compressor using a linear interpolation based on speed, like this: (1) 3. Then modify the parameter from the compressor head, current flow and speed as: (2)

Huntington Method

52  Centrifugal Compressor or Expander Unit Operations

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This method tries to use the definition of the polytropic path (constant value of e in Equation H = edh along the polytropic path). Combining equations H = Vdp and H = edh with the Maxwell equation dh = Tds + Vdp yields the general relationship of the entropy derivative along the polytropic path: (1) In this method, a general relationship of the compressibility factor and pressure is assumed along the polytropic path of compression for a simple analytical integration. It is important to point out that Huntington tried several functional relationships Z(P) in his work and checked them against the results obtained in the reference method. The following relationship showed the most accurate results: (2)

where the constants a, b, and c are evaluated from the compressibility factor found at the endpoints of the compression path and at one intermediate pressure along the path as follows: (3)

And the first estimated intermediate temperature, T3 is assumed below: (4) The initial T3 defined above may be improved by using recursive calculations as described in Huntington’s paper. With the Z(P) given by Equation (2), Huntington integrates Equation (1). After rearranging some terms, the following equation is obtained for the polytropic efficiency: (5)

Multiple IGV Curves For Multiple IGV Curves, the following options are available:

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52  Centrifugal Compressor or Expander Unit Operations

Option

Description

Efficiency group

Select the efficiency model for the compressor: Adiabatic or Polytropic

Compressor Speed field

Specify the speed for the compressor.

Enable Curves check box

Use all the curves (that have selected Activate check box) in the compressor calculations.

Curve table

Display a list of curve data available for the compressor. You can specify the curve name under the Curve Name column, and activate or ignore the curve data by selecting the appropriate check box under the Activate column.

View Curve button

Access the selected curve property view.

Add Curve button

Add/create a curve.

Delete Curve button

Delete the selected curve.

Clone Curve button

Clone the selected curve.

Plot Curve button

Plot and view the curve data.

Plot All Collections check box

Allow you to see all the curves from all the curve collection (in the compressor) in one plot. This option is particularly useful if all the curves data are based on one speed.

Curve Collections list

Displays the names of all the curve collection available in the compressor.

Curve Collection name field

Modify the name of the selected curve collection.

Curve IGV cell

Specify the inlet guide vane position that the entered curve set data is at (or for).

Current IGV cell

Specify the current position that the compressor is operating at. You can specify this value to different values during operation or specify this value in controllers during Dynamics mode.

Add Curve Collection button

Create a collection of curve data.

52  Centrifugal Compressor or Expander Unit Operations

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Option

Description

Del. Curve Collection button

Delete the selected curve collection.

Set Simple Curves button

Generates five curve collections of data based on the selected curve data. The curve collections data have hypothetical curve data values for lighter and heavier components.

Off-Design Correction check box

If On is checked, you are allowed to specify the Ref. Temperature and Ref. Molec. Weight.

Extrapolation group

The Extrapolation group contains the Linear and Quadratic radio buttons. These radio button are used to select the extrapolation method for the compressor.

Multiple MW Curves For the Multiple MW Curves, the following options are available:

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Option

Description

Efficiency group

Select the efficiency model for the compressor: Adiabatic or Polytropic

Compressor Speed field

Specify the speed for the compressor.

Enable Curves check box

Use all the curves (that have selected Activate check box) in the compressor calculations.

Curve table

Display a list of curve data available for the compressor. You can specify the curve name under the Curve Name column, and activate or ignore the curve data by selecting the appropriate check box under the Activate column.

View Curve button

Allow you to access the selected curve property view.

Add Curve button

Add/create a curve.

Delete Curve button

Delete the selected curve.

Clone Curve button

Clone the selected curve.

Plot Curve button

Plot and view the curve data.

Plot All Collections check box

Allow you to see all the curves from all the curve collection (in the compressor) in one plot. This option is particularly useful if all the curves data are based on one speed.

Curve Collections list

Displays the names of all the curve collection available in the compressor.

52  Centrifugal Compressor or Expander Unit Operations

Option

Description

Curve Collection name field

Modify the name of the selected curve collection.

Design MW cell

Specify the design average molecular weight for the compressor.

Curve MW cell

Specify the molecular weight for the selected curve collection.

Actual MW cell

Displays the actual molecular weight of the stream (calculated by HYSYS) within your case.

Add Curve Collection button

Create a collection of curve data.

Del. Curve Collection button

Delete the selected curve collection.

Set Simple Curves button

Generates two curve collections of data based on the selected curve data. The curve collections data have hypothetical curve data values for lighter and heavier components.

Off-Design Correction check box

If On is checked, you are allowed to specify the Ref. Temperature and Ref. Molec. Weight. Note: Ref. Molec. Weight specification is allowed only when Single MW Curves or IGV Curves are used and Off-Design Correction is enabled. You cannot specify Ref. Molec. Weight when using Off-Design Correction with Multiple MW Curves since HYSYS already provides various curves at different MWs.

Extrapolation group

Select the extrapolation method for the compressor: Linear or Quadratic

Quasi-Dimensionless and Non-Dimensional Curves Dimensional analysis is used in cases where experimental data is used for compressor characteristic curves. It performs ideally when the experimental equipment differs from actual equipment. Non-dimensional curves (below) and Quasi-dimensional curves serve this purpose in HYSYS.

Quasi-Dimensionless Curves The quasi-dimensionless groups are derived from dimensionless groups that exclude constant terms, such as gas constant or equipment sizes. The quasidimensionless curves are expressed in the following form: (1)

(2)

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(3) And if the gas constant R is included: (4)

(5)

(6) Where : Pin = Pressure at inlet conditions Tin = Temperature at inlet conditions R = Gas constant Note: The conversion formula uses mass flows. The conversion utility provided works for both volume flow and mass flow.

Non Dimensional Curves Non-dimensional curves can include information about the surge conditions. You can input surge operating data to model the surge behavior and design a new surge controller. The dimensionless mass-flow, ϕ, dimensionless pressure difference Ψ et. are defined as: (7)

and (8)

Where is the mass-flow, ∆p is the pressure difference between inlet and outlet, ρa is the density of the inlet gas stream, Ac is the compressor duct area, and Ut is the rotor tip speed. Note: The conversion formula uses mass flows. The conversion utility provided works for both volume flow and mass flow.

The compressor characteristics are approximated by a cubic approximation of Ψ c (φc) (Moore and Greitzer, 19861): (9)

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52  Centrifugal Compressor or Expander Unit Operations

where Ψ c(0) is the valley point of the characteristic located at the compressor pressure rise axis, and Ψ c = 2F corresponds to the dimensionless compressor mass flow at the top of the characteristic.

In many cases, this top coincides with the surge point at each speed line. A best fit of all measurements is determined in a least square sense. The above equation can be rewritten as: (10) with:

For each compressor characteristic, the parameters c0(N), c1(N), and c2(N) are determined. The dependence of these parameters on rotational speed N is approximated by a quadratic polynomial in N: c0(N) = b01 +b02N + b03N2 c1(N) = b11 +b12N + b13N2 c2(N) = b21 +b22N + b23N2 In the region where compressor data is available, the compressor characteristics is approximated well. The valley point Ψ c(0) can be input in the non-dimensional curve form. If this point is provided, it will be used in the fitting process.

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References 1. Moore, F. K. and Greitzer, E. M. (1986). A theory of post stall transient in axial compression systems: Part I—Development of equations. ASME J. Engineering for Gas Turbines and Power, 108, 68–76.

Schultz Method Reference This is the method currently used by HYSYS to calculate the polytropic head and efficiency in centrifugal compressors. This method is based on a simple polytropic path from inlet to discharge conditions. Schultz method (Schultz, J.M., ASME Journal of Engineering For Power, Jan. 1962, pp. 69-82) is based on the assumption that the gas compression follows a simple polytropic path as shown below: (1) Where n is calculated based on the conditions at the beginning and end of the polytropic path. This equation is combined with the definition of polytropic head: (2) That upon integration between P1 and P2 > gives: (3) or (4)

The polytropic efficiency can then be calculated from: (5) Notice that a real compression is not reversible and it must be path-dependent instead of endpoints dependent. To compensate this effect Schultz introduced a correction factor usually called the polytropic head (Schultz, J.M., ASME Journal of Engineering For Power, Jan. 1962, pp. 69-82). (6) Where f, the polytropic head factor, is defined as: (7)

That for an isentropic compression/expansion gives

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and e = 1.

52  Centrifugal Compressor or Expander Unit Operations

The Schultz method has long been recognized as required by the ASME Power Test Code 10, and it is well accepted by industry.

Compressor - Reference Method The definition of polytropic path (R.A. Huntington, Journal of Engineering for Turbines and Power, 1985) is for a real gas the path where the ratio of reversible work input to the enthalpy increase along the path is constant: H = Vdp

(1)

H = edh

(2)

Where e is a constant along the path. This equation can be integrated numerically dividing the pressure range in sufficiently small intervals such as V can be assumed to be constant in this interval. An iterative procedure can be implemented where temperature and pressure are known at the beginning of the interval but only pressure is known at the end. Then we iterate on the temperature till equation (2) is satisfied. Also an alternative procedure can be used where equation PVn = C is used in each integration interval instead of assuming a constant volume. It is important to point out that this method does not make any assumption regarding the pressure-volume relationship along the path can be used as a reference to check the accuracy of the other methods, e.g. the Schultz method and the new method suggested by Huntington in the paper. Although probably it was not the intention of Huntington in the paper the reference/integration method can be directly implemented. And they are indeed implemented in Aspen: piece-wise integration and nmethod piece wise integration, the latter being the approach where equation PVn = C substitutes the assumption of constant volume in the integration interval.

Single Curve Compressor Options For the Single Curve option, the following settings are available: Option

Description

Efficiency group

The Efficiency group contains the Adiabatic and Polytropic radio buttons. These radio buttons are used to select the efficiency model for the compressor.

Compressor Speed field

Allows you to specify the speed for the compressor.

Enable Curves check box

Allows HYSYS to use all the curves (that have selected Activate check box) in the compressor calculations.

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Option

Description

Curve table

Display a list of curve data available for the compressor. You can specify the curve name under the Curve Name column, and activate or ignore the curve data by selecting the appropriate check box under the Activate column.

View Curve button

Allows you to access the selected curve property view.

Add Curve button

Allows you to add/create a curve.

Delete Curve button

Allows you to delete the selected curve.

Clone Curve button

Allows you to clone the selected curve.

Plot Curve button

Allows you to plot and view the curve data.

Off-Design Correction check box

If On is checked, you are allowed to use quasi-dimensionless performance curves for off-design corrections and specify the Ref. Temperature and Ref. Molec. Weight.

Extrapolation group

The Extrapolation group contains the Linear and Quadratic radio buttons. these radio button are used to select the extrapolation method for the compressor.

Compressor or Expander Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

Links

l l

User Variables Notes

Connections Page The Connections page of the Centrifugal Compressor property view lets you specify the name of the operation, as well as the inlet stream, outlet stream, and energy stream. Note: For the Screw Compressor operating mode, refer to Screw Compressor: Connections Page.

The information required on the Connections page of the Expander is identical; the only difference is that the Expander icon is shown rather than the Compressor icon.

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Parameters Page You can specify the duty of the attached energy stream on the Parameters page, or allow HYSYS to calculate it. Note: For the Screw Compressor operating mode, refer to Screw Compressor: Parameters Page.

The adiabatic (for the compressor) / isentropic (for the expander) and polytropic efficiencies appear on this page. Note: You can specify only one efficiency, either adiabatic/isentropic or polytropic. If you specify one efficiency and a solution is obtained, HYSYS back calculates the other efficiency, using the calculated duty and stream conditions.

The Parameters page for the Compressor and the Expander are similar. However, the following items are not available for the Expander: l

Polytropic method selection

l

Operating Mode group

l

Multiple MW Curves in the Curve Input Option group

Centrifugal or Reciprocating Compressor In the Operating Mode group, you can switch between a Centrifugal, Reciprocating, and Screw Compressor by selecting the corresponding radio button. If you choose the Centrifugal radio button, the radio buttons in the Curve Input Option group are enabled. In the Curve Input Option group, the following radio buttons are available: l

Select the Single Curve radio button to model your compressor with a single pair of head vs. flow and efficiency vs. flow curves.

The Single Curve radio button still allows multiple curves as a function of speed, but not MW or IGV position. l

l

Select the Multiple MW Curves radio button if you have a set of curves that describe the compressor performance as a function of the flowing gas molecular weight (MW). Select the Multiple IGV Curves radio button if you have a set of curves that describe the compressor performance as a function of inlet guide vane (IGV) position.

To learn more about the Screw Compressor options, refer to Screw Compressor: Parameters Page.

Polytropic Methods l

l

Select Schultz to use the Schultz method to calculate the polytropic head and efficiency in centrifugal compressors. Select Huntington to use the Huntington method to calculate the

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polytropic head and efficiency in centrifugal compressors. l

Select Reference for an integration of the Schultz and Huntington methods.

Curve Input Options l

l

l

l

Use Single MW to model your compressor with a single pair of head vs. flow and efficiency vs. flow curves. Use Multiple MW if you have a set of curves that describe the compressor performance as a function of the flowing gas molecular weight (MW). Use Multiple IGV if you have a set of curves that describe the compressor performance as a function of inlet guide vane (IGV) position. Use Non-Dimensional or Quasi-Dimensionless curves where experimental data is used for compressor characteristic curves.

Pressure Specs Use the DeltaP and Pressure Ratio areas to enter Pressure Specs for the unit operation. You can type them or they can be calculated by HYSYS, if Inlet Pressure and Outlet pressures are available.

aspenONE Exchange

Click the aspenONE Exchange icon (pictured to the left) to access known manufacturer specifications. aspenONE Exchange is a websourced library that includes pre-built models and partial flowsheets that you can download to speed creating simulations. If you select a model, it will populate the fields on the Parameters page with known values.

Surge Analysis You can select the Surge Analysis button to perform compressor surge analysis under different emergency scenarios quickly and easily by running a dynamic simulation of a compressor with a recycle, controller, pipes, valves, and knock out drums included, using very few inputs. Dynamic results display on pre-made stripcharts, compressor curves profiles, and additional results forms to help you discover the best anti-surge configuration for your compressor.

Links Page Compressors and expanders modeled in HYSYS can have shafts that are physically connected to the unit operation. Linking compressors and expanders in HYSYS means the:

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52  Centrifugal Compressor or Expander Unit Operations

n

Speed of each linked unit operation is the same.

n

Sum of the duties of each linked Compressor or Expander and the total power loss equals zero.

Note: For the Screw Compressor, refer to Screw Compressor: Links Page.

The rotational linker operates both in Steady State and Dynamic mode. It is not significant which order the Compressors or Expanders are linked. The notion of upstream and downstream links is arbitrary and determined by the user. A list of available compressors or expanders can be displayed by clicking the down arrow in the Downstream Link field. In most cases, one additional specification for any of the linked operations is required to allow the simulation case to completely solve. Ideally, you should specify one of the following for any of the linked unit operations. l

Duty

l

Speed

l

Total Power Loss

It is also possible to link an Expander to a Compressor, and use the Expander to generate kinetic energy to drive the Compressor. If this option is chosen, the total power loss is typically specified as zero.

Dynamic Specification In Dynamics mode, at least one curve must be specified in the Curves page of the Rating tab for each linked unit operation. Ideally, a set of linked compressor or expanders should only have the Use Characteristic Curves check box selected in the Specs page of the Dynamics tab. In addition, the total power loss for the linked operations should be specified. Usually, total power input to the linked compressors or expanders is calculated in a Spreadsheet operation and specified by you in the Total Power Loss field. If you want to provide the total power input to a set of linked compressors or expanders, the total power input to the linked operations is defined in terms of a total power loss. The relationship is as follows: (1)

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

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Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Compressor or Expander Rating Tab The Rating tab contains following pages: l

" Curves Page" below

l

Flow Limits

l

l

Nozzles (The Nozzles page is only visible if you have the HYSYS Dynamics license.) "Inertia Page" on page 999

Curves Page One or more Centrifugal Compressor or Expander curves can be specified on the Curves page. You can create adiabatic (for the compressor) / isentropic (for the expander) or polytropic plots for values of efficiency and head. The efficiency and head for a specified speed can be plotted against the capacity of the Centrifugal Compressor or Expander. Multiple curves can be plotted to show the dependence of efficiency and head on the speed of Centrifugal Compressors or Expanders. Note: For the Screw Compressor, refer to Screw Compressor: Curves Page.

If you do not use curves, then specify four of the following variables and HYSYS will calculate the fifth variable and the duty: l

Inlet Temperature

l

Inlet Pressure

l

Outlet Temperature

l

Outlet Pressure

l

Efficiency

Optionally, you can enter an Offset value to apply to the head and efficiency results. The specified offsets are applied to the head and efficiency that come out of the curve calculation to get the desired plant head and efficiency. It is assumed that you have specified the composition and flow.

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Single MW (Molecular Weight) If you choose the Single Curve radio button on the Parameters page of the Design Tab, the only group visible on the Curves page is the Compressor Curves group. Note: This option is only relevant for compressors and not expanders.

Entering Curve Data The following are steps to add a curve to the compressor or expander: 1. Select either the Adiabatic / Isentropic or Polytropic radio button in the Efficiency group. This determines the basis of your input efficiency values. The efficiency type must be the same for all input curves. 2. Optionally you can enter an Offset Value to apply to the head and efficiency results.  The specified offsets are applied to the head and efficiency that come out of the curve calculation to get the desired plant head and efficiency. 3. Two parameters can be entered for performance curves: Design Temperature and Design Molecular Weight. When these are supplied, HYSYS corrects the inlet volumetric flow rate to the equivalent design conditions flow rate. 4. Click the Add Curve button and the Curve property view appears. You can specify the following data in the Curve property view. Curve Data

Description

Name

Name of the curve.

Speed

The rotational speed of the Centrifugal Compressor or Expander. This is optional if you specify only one curve. HYSYS can interpolate values for the efficiency and head of the Centrifugal Compressor or Expander for speeds that are not plotted.

Flow Units/Head Units

Units for the flow and head.

Flow/Head/% Efficiency

One row of data is equivalent to one point on the curve. For better results, you should enter data for at least three (or more) points on the curve.

5. Click the Close icon to return to the Curves page. 6. Select the corresponding Activate check box to use that curve in calculations. 7. For each additional curve, repeat steps #2 to #5. 8. Click the Enable Curves check box. You can remove a specific curve from the calculation by clearing its Activate check box.

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HYSYS uses the curve(s) to determine the appropriate efficiency for your operational conditions. If you specify curves, ensure the efficiency values on the Parameters page are empty or a consistency error will be generated. Once a curve has been created, the following buttons on the Curves page are enabled: l

l

l l

View Curve: Allows you to view or edit your input data in the Curve property view. Delete Curve: Allows you to delete the selected curve from the simulation. Clone Curve: Allows you to duplicate an existing curve. Plot Curves: Allows you to view a graph of activated curves by accessing the Compressor Curves Profiles.

You can access the Curve property view of an existing curve by clicking the View Curve button or by double-clicking the curve name.

Deleting Curve Data The following are two ways you can delete information within a curve: 1. Double-click the curve name to open the Curve property view. 2. Highlight the data you want to delete and click the Erase Selected button to delete the Flow, Head, and % Efficiency values for a selected row. OR 1. Select the curve within the table and click the View Curve button. 2. Click the Erase All button to delete all of the information within the Curve property view.

Single Curve When you have a single curve, the following combinations of input allow the operation to completely solve (assuming the feed composition and temperature are known): l

Inlet Pressure and Flow Rate

l

Inlet Pressure and Duty

l

Inlet Pressure and Outlet Pressure

l

Inlet Pressure and Efficiency corresponding to the Curve type (for example, if the Curve is Adiabatic you need to provide an Adiabatic Efficiency).

Multiple Curves If multiple curves have been installed, an operating speed is specified on the Curves page, and one of the multiple curves’ speed equals the operating speed, then only the curve with the corresponding speed is used. For example, if you provide curves for two speeds (1000/min and 2000/min), and you specify an

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52  Centrifugal Compressor or Expander Unit Operations

operating speed of 1000/min, then only the curve with the speed of 1000/min is used within the calculation. If multiple curves have been installed, an operating speed has been specified, and none of the multiple curves’ speed equals the operating speed, then all of the curves will be used within the calculation. For example, if you provide curves for two speeds (1000/min and 2000/min), and you specify an operating speed of 1500/min, HYSYS interpolates between the two curves to obtain the solution. Conversely, if you specify an operating speed outside the range of speeds provided by the curves, HYSYS uses an extrapolation method to obtain the solution. Currently, HYSYS supports both Linear and Quadratic extrapolation methods and the user has the option to pick which method to use for extrapolation. Linear extrapolation method is set as the default option and is highly encouraged since extrapolation in general will yield unpredictable results, especially when one does not know the actual form of the data. If multiple curves are used, you need to provide: l

Feed Composition

l

Pressure

l

Temperature

l

Inlet Flow Rate

Only one of the following variables: o

Duty

o

Outlet Pressure

o

Operating Speed

HYSYS then calculates the other two variables.

Curve Plots in Dynamics Mode In order to run a stable and realistic dynamics model, HYSYS requires you to input reasonable curves. If compressors or expanders are linked, it is a good idea to ensure that the curves plotted for each unit operation span a common speed and capacity range. Typical Compressor curves are plotted below.

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For an Expander, the head is only zero when the speed and capacity are zero. Note: The Plot All Calculations check box is useful if you want to see all of the curves for the curves collection (in the compressor) appear in one plot. This is very useful if all of the curves data is based on one speed.

Multiple MW (Molecular Weight) The Multiple MW (molecular weight) option is for more advanced users of HYSYS. This option allows the performance of the compressor to vary with the flowing gas molecular weight based upon the performance map you specified. Note: This option is only relevant for compressors and not expanders.

When you choose the Multiple MW Curves radio button on the Parameters page of the Design tab, the MW Curve Collections group and the Plot All Collections check box are added to the Curves page. The following is a brief description of the fields and buttons found within the MW Curve Collections group. Fields

Description

MW Curve Collections list

Displays the list of curve collection available in the unit operation. Each curve collection contains a set of data curves at a particular molecular weight.

Curve Collection name

Allows you to rename the selected curve collection in the list.

Design MW

The Design MW is the design average molecular weight for the compressor. Its default value is the same as the value for the Actual MW. This value is only used as a reference point and does not affect the Compressor calculation.

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52  Centrifugal Compressor or Expander Unit Operations

Curve MW

Each curve collection has its corresponding set of curves at a particular molecular weight.

Actual MW

This value is calculated by HYSYS. The field displays the actual MW of the stream within your case. The following are descriptions of three potential operating situations:

Buttons

o

If the Actual MW is the same as the Design MW, it means the compressor is operating with components at your designed MW.

o

If the Actual MW is less than the Design MW value, it means the compressor is operating with lighter components.

o

If the Actual MW is more than the Design MW value, it means the compressor is operating with heavier components.

Description

Add Adds another empty curve collection to the MW Curve Collections list. Curve Collection Del. Deletes the selected curve collection in the MW Curve Collections list. Curve Collection Set Simple Curves

Creates two more curve collections with curve data based on the selected curve collection in the MW Curve Collections list. The data values within the two new curve collections are estimated values for testing purposes only. You should modify this data accordingly to specify your actual curve values.

Creating Multiple Curve Collections The following are methods on how you can create multiple curve collections: 1. Enter the data for the curve(s). All of these values will be stored under a curve collection named CurveCollection-1. 2. Click the Set Simple Curves button. 3. Two hypothetical curve collections will appear (named CurveCollection-2 and CurveCollection-3). These two new collections will provide you with rough data for curves generated with lighter or heavier components. These estimated values are based on the values entered for CurveCollection-1. Note: The values given in CurveCollection-2 and CurveCollection-3 are for testing purposes only. You need to modify the data accordingly in order to determine the definite curve values.

OR

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1. Enter the data for the curve(s). All of these values will be stored under a curve collection. 2. Click the Add Curve Collection button. Repeat step #1 to enter the data for the new curve collection

Multiple IGV (Inlet Guide Vane) The Multiple IGV (inlet guide vane) Curves option allows you to model a compressor with adjustable guide vanes. The guide vanes are modulated to control the capacity of the compressor. Note: To use the Multiple IGV Curves feature, you need a manufacturer's performance map of curves at different IGV operating conditions.

When you choose the Multiple IGV Curves radio button on the Parameters page of the Design tab, the IGV Curve Collections group and the Plot All Collections check box are added to the Curves page. This can be useful if all of the curve data is based on one speed. The following is a brief description of the fields and buttons found within the IGV Curve Collections group. Fields

Description

IGV Curve Collections list

Displays the list of curve collection available in the unit operation. Each curve collection contains a set of data curves at a particular inlet guide vane.

Curve Collection name

Allows you to rename the selected curve collection in the list.

Curve IGV

Allows you to specify the inlet guide vane position that the entered curve set data is at (or for).

Current IGV

Allows you to specify the current position that the compressor is operating at. You can specify this value to different values during operation or specify this value in controllers during Dynamics mode.

Buttons

Description

Add Adds another empty curve collection to the IGV Curve Collections list. Curve Collection Del. Deletes the selected curve collection in the IGV Curve Collections list. Curve Collection

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Set Simple Curves

Creates five more curve collections with curve data based on the curve collection in the IGV Curve Collections list. The data values within the five new curve collections are estimated values for testing purposes only. You should modify this data accordingly to specify your actual curve values.

Creating Multiple Curve Collections The following are methods on how you can create multiple curve collections: 1. Enter the data for the curve(s). All of these values will be stored under a curve collection named CurveCollection-1. 2. Click the Set Simple Curves button. Two hypothetical curve collections will appear (named CurveCollection-2 and CurveCollection-3). These two new collections will provide you with rough data for curves generated with lighter or heavier components. These estimated values are based on the values entered for CurveCollection-1. Note: The values given in CurveCollection-2 and CurveCollection-3 are for testing purposes only. You need to modify the data accordingly in order to determine the definite curve values.

OR 1. Enter the data for the curve(s). All of these values will be stored under a curve collection. 2. Click the Add Curve Collection button. Repeat steps to enter the data for a new curve collection.

Wegstein Solver In the Wegstein Solver section, you can select the Enable acceleration bounds check box if you want to limit the Wegstein method's acceleration factor to upper and lower bounds to help convergence. If you select the check box, you can manually edit the default values in the Lower bound and Upper bound fields.

Flow Limits Page There is a certain range in which the dynamic Centrifugal Compressors or Expanders can operate, depending on operating speed. The lower flow limit of a Centrifugal Compressor is called the surge limit, whereas the upper flow limit is called the stonewall limit. In HYSYS, you can specify the flow limits of a Centrifugal Compressor or Expander by plotting surge and stonewall curves.

Entering Surge or Stonewall Curves From the Flow Limits page, it is possible to add Surge or Stonewall curves for the Centrifugal Compressor. (See explanation above.) The procedure for adding

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or editing a Stonewall curve is similar to the procedure for adding or editing a Surge curve. Note: If you are working exclusively in Steady State mode, you are not required to change any information on the Flow Limits page.

When a dynamic Centrifugal Compressor reaches its stonewall limit, HYSYS fixes the flow at that Centrifugal Compressor speed. When a Centrifugal Compressor reaches the surge limit, the flow reverses and cycles continuously causing damage to the Centrifugal Compressor. This phenomenon is modeled in HYSYS by causing the flow rate through the Centrifugal Compressor to fluctuate randomly below the surge flow.

Adding or Editing a Surge Curve To add or edit a Surge curve, follow this procedure: 1. Click the Surge Curve button. The Surge flow curve property view appears. 2. From the Speed Units drop-down list, select the units you want to use for the speed measurements. 3. From the Flow Units drop-down list, select the units you want to use for the flow measurements. 4. Specify the speed and flow data points for the curve. Once you have entered all the data points, click the Close icon to return to the Compressor or Expander property view.

Deleting data of a Surge Curve To delete data within a surge curve, do the following: Click the Surge Curve button. The Surge flow curve property view appears. Do one of the following: l

l

To remove a certain data point, select either the speed cell or flow cell, and click the Erase Selected button. To remove all the data points, click the Erase All button.

Nozzles Page The Nozzles page contains information regarding the elevation and diameter of the nozzles. Note: If you are working exclusively in Steady State mode, you are not required to change any information on the Nozzles page.

For a Centrifugal Compressor or Expander unit operation it is strongly recommended that the elevation of the inlet and exit nozzles are equal. If you want to

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52  Centrifugal Compressor or Expander Unit Operations

model static head, the entire piece of equipment can be moved by modifying the Base Elevation relative to Ground Elevation field. Note: For the Screw Compressor, refer to Screw Compressor: Nozzles Page.

Inertia Page Note: For the Screw Compressor, refer to Screw Compressor: Inertia Page.

The inertia modeling parameters and the friction loss associated with the impeller in the Centrifugal Compressor can be specified on the Inertia page. Note: If you are working exclusively in Steady State mode, you are not required to change any information on the Inertia page. The HYSYS Dynamics license is required to use the Inertia features found on this page.

Electric Motor Page The Electric Motor page allows you to drive your rotating unit operation through the designation of a motor torque versus speed curve. These torque vs. speed curves can either be obtained from the manufacturer for the electric motor being used or from a typical curve for the motor type. For most process industry applications, a NEMA type A or B electric motor is used. When you use the Electric Motor option the torque (and power) generated by the motor is balanced against the torque consumed by the rotating equipment. Notes: l l

l

The Electric Motor functionality is only relevant in Dynamics mode. The Electric Motor option uses one degree of freedom in your dynamic specifications. The results of the Electric Motor option are presented on the "Power Page" on page 1055 in the "Pump Performance Tab" on page 1054 of the rotating equipment operation.

When you activate the Electric Motor option: o

An On check box will appear at the bottom of the Compressor property view, which can be used to turn the motor on and off.

o

The Compressor operation icon in the PFD changes to include a motor.

The following table lists and describes the objects in the Electric Motor page: Object

Description

Synchronous Speed cell

Allows you to specify the synchronous speed of the motor.

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999

Full Load Speed cell

Allows you to specify the design speed of the motor.

Full Load Torque cell

Allows you to specify the design torque of the motor.

Full Load Power cell

Allows you to specify the design power of the motor.

Gear Ratio cell

Allows you to manipulate the gear ratio. The gear ratio is the rotating equipment’s speed divided by the motor speed.

Motor Inertia cell

Allows you to specify the motor inertia.

Motor Friction Factor cell

Allows you to specify the motor friction factor.

User Electric Motor check box

Allows you to toggle between using or ignoring the electric motor functionality.

Speed vs Torque Curve button

Allows you to view the plot and specify the data in the "Speed vs. Torque Curve Property View" on page 1054.

Size Inertia button

Allows you to calculate the inertia based on the following equation (Thorley A. R. D. Fluid Transients in Pipeline Systems. D & L George Ltd. England, 1991):

I = inertia (kg • m3) P = full load power of the motor (kW) N = full load speed of the motor (rpm/1000) Simple radio button

Allows you to select the Simple model for the modelling option.

Breakdown radio button

Allows you to select the Breakdown model for the modelling option.

Electric Brake check box

Allows you to model the torque force on the rotating equipment simply by changing the sign of the produced torque value.

Gearing check box

Allows the gear ratio to be updated during integration. A zero value for the gear ratio indicates a decoupling of the equipment.

Theory The definition of torque is found from the following equation: (1)

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52  Centrifugal Compressor or Expander Unit Operations

Where: P = power consumption (kW) T = torque (Nm) ω = synchronous speed (rpm) The synchronous electric motor speed can be found from: (2) Where: f = power supply frequency (Hz), typically either of 50 or 60 p = number of poles on the stator The number of poles is always an even number of 2, 4, 6, 8, 10, and so forth. In North America, common motor speeds are always 3600, 1800, 1200, 900, 720, and so forth. The relationships of inertia and friction loss in the total energy balance are the same as for the pump and compressor operations.

Operation Model There are three ways to use the Electric Motor curve, each with progressing rigor. l

l

l

Simple Model. The easiest calculation is the Simple modeling option (default). This model is useful if you just want to model the startup/shutdown transient and want to keep the equipment at the fixed full load speed once operating. In this mode, once the speed has accelerated enough to become larger than the last (largest) curve speed value entered, the motor speed immediately is set to the full load speed and remains there until the motor is turned off. If the process invokes a larger torque than the motor curve suggests the motor can produce, the speed still remains synchronous and remains at its full load value. Breakdown Model. The Breakdown modeling option allows the speed to reduce if the system torque or resistance gets too large. To use this option, the largest (last) curve speed value entered should be just less than the full load speed value. This provides for a smooth transition in operation. You can drop the curve to a lower torque than the breakdown torque if desired. Simple Model Modified. The third modeling approach is to use the Simple model option, but enter the speed vs torque curve up to a speed value of 99.99% of the synchronous speed. In this case the full load speed entered is only used, if necessary, to calculate the full load torque and is not used otherwise. With this approach, the speed vs torque curve must ascend or drop from the breakdown torque to approach zero torque at 100% speed. For most motor types, this approach is nearly vertical (asymptotic). This modelling approach allows for the simulation of the

52  Centrifugal Compressor or Expander Unit Operations

1001

slippage of the motor speed based upon the actual and current system resistance. The operating speed of the motor will then move based upon the process model operation. Use a near vertical curve to keep a constant speed or level it off more to allow greater slip. This performance should be predicted by using an accurate manufacturer's torque vs speed curve. Note: The speed and torque are not solved simultaneously with the pressure flow solution but instead is lagged by a time step. You may need to use a smaller time step to ensure accuracy and pressure flow solver convergence.

Speed vs. Torque Curve Property View The Speed vs. Torque Curve property view displays the data curve of speed versus torque in both table and plot format. To access the Speed vs. Torque Curve property view, click the Speed vs Torque Curve button on the Electric Motor page of the Rating tab. Notes: l

l l

l

The values under the Speed and Torque columns are entered as a percent of the Full Load values. The Speed vs. Torque curve must always contain a 0% speed value. The maximum table speed cannot be greater than the value in the Maximum X value field. The Maximum X value is the ratio of the full load speed to the synchronous speed. During integration, the current operating point appears on the Torque vs. Speed curve.

The following table lists and describes the objects available in the Speed vs. Torque Curve property view: Object

Description

Maximum X value display field

Displays the ratio of the full load speed to the synchronous speed.

Speed column

Allows you to specify speed percentage values you want to plot.

Torque column

Allows you to specify the torque percentage values associated with the speed.

Erase Selected button

Allows you to delete the row containing both speed and torque percentage values of the selected cell.

Erase All button

Allows you to delete all the values in the table.

Compressor or Expander Performance Tab 1002

52  Centrifugal Compressor or Expander Unit Operations

The Performance page contains the calculated results of the compressor or expander.

Results Page On the Results page, you can view a table of calculated values for the Centrifugal Compressor or Expander: n

Adiabatic Head

n

Polytropic Head

n

Adiabatic Fluid Head

n

Polytropic Fluid Head

n

Adiabatic Efficiency (for the Compressor) or Isentropic Efficiency (for the Expander)

n

Polytropic Efficiency

n

Power Produced

n

Power Consumed

n

Friction Loss

n

Rotational inertia

n

Fluid Power

n

Polytropic Head Factor

n

Polytropic Exponent

n

Isentropic Exponent

n

Speed

Note: For the Screw Compressor, refer to Screw Compressor: Results Page.

Power Page The Power page is only available for the compressor. The following information appears on this page: n

Compressor rotor power

n

Compressor rotor torque

n

Electric motor power

n

Electric motor torque

n

Electric motor speed

Note: For the Screw Compressor, refer to Screw Compressor: Power Page.

Compressor or Expander Dynamics Tab The Dynamics tab contains the following pages:

52  Centrifugal Compressor or Expander Unit Operations

1003

l

Specs

l

Holdup

l

Stripchart

l

Surge Controller Window

Note: If you are working exclusively in Steady State mode, you are not required to change any information on the pages accessible through this tab.

Specs Page The dynamic specifications of the Centrifugal Compressor or Expander can be specified on the Specs page. Note: For the Screw Compressor, refer to Screw Compressor: Specs Page.

In general, two specifications are required in the Dynamics Specifications group. You should be aware of specifications which may cause complications or singularity in the pressure flow matrix. Some examples of such cases are: o

The Pressure Increase check box should not be selected if the inlet and exit stream pressures are specified.

o

The Speed check box should not be selected if the Use Characteristic Curves check box is not selected.

The possible dynamic specifications are as follows:

Duty The duty is defined, in the case of the Centrifugal Compressor operation, as the power required to rotate the shaft and provide energy to the fluid. The duty has three components: (1)

The duty in a Centrifugal Compressor should be specified only if there is a fixed power available to be used to drive the shaft.

Efficiency (Adiabatic/Isentropic and Polytropic) For a dynamic Centrifugal Compressor, the efficiency is given as the ratio of the isentropic power required for compression to the actual energy imparted to the fluid. The efficiency, η, is defined as: (2)

W = isentropic power F1 = molar flow rate of the inlet gas stream

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52  Centrifugal Compressor or Expander Unit Operations

MW = molecular weight of the gas h1 = inlet head h2 = outlet head For a dynamic Expander, the efficiency, η, is defined as: (3)

If a polytropic efficiency definition is required, the polytropic work should be provided in one of the above two equations. If an isentropic efficiency definition is required, the isentropic work should be provided. The general definition of the efficiency does not include the losses due to the rotational acceleration of the shaft and seal losses. Therefore, the efficiency equations in dynamics are not different from the general efficiency equations defined in Theory. This is true since the actual work required by a steady state Centrifugal Compressor is the same as the energy imparted to the fluid. If the Centrifugal Compressor or Expander curves are specified in the Curves page of the Rating tab, the adiabatic/isentropic or polytropic efficiency can be interpolated from the flow of gas and the speed of the Centrifugal Compressor or Expander.

Pressure Increase A Pressure Increase specification can be selected if the pressure drop across the Centrifugal Compressor is constant.

Head The isentropic or polytropic head, h, can be defined as a function of the isentropic or polytropic work. The relationship is: (4) Where: W = isentropic or polytropic power MW = molecular weight of the gas CF = correction factor (For a compressor, this factor is the inverse value of the adiabatic/polytropic efficiency; for an expander, it is the isentropic/polytropic efficiency.) F1 = molar flow rate of the inlet gas stream g = gravity acceleration If the Centrifugal Compressor or Expander curves are provided in the Curves page of the Rating tab, the isentropic or polytropic head can be interpolated from the flow of gas and the speed of the Centrifugal Compressor or Expander.

52  Centrifugal Compressor or Expander Unit Operations

1005

Fluid Head The Fluid Head is the produced head in units of energy per unit mass.

Capacity The capacity is defined as the actual volumetric flow rate entering the Centrifugal Compressor or Expander. A capacity specification can be selected if the volumetric flow to the unit operation is constant.

Speed The rotational speed of the shaft, ω, driving the Centrifugal Compressor or being driven by the Expander can be specified.

Shift to Reciprocating Compressor (Positive Displacement) Select the Reciprocating (Positive Displacement) check box if you want to change the Centrifugal Compressor to a Reciprocating Compressor. You can change the Centrifugal Compressor to a Reciprocating Compressor at any time. The reciprocating check box option is only available with the compressor unit operation.

Use Characteristic Curves Select the Use Characteristic Curves check box if you want to use the curve (s) specified in the Curves page of the Rating tab. If a single curve is specified in a dynamics Centrifugal Compressor, the speed of the Centrifugal Compressor is not automatically set to the speed of the curve (unlike the steady state Centrifugal Compressor or Expander unit operation). A different speed can be specified and HYSYS extrapolates values for head and efficiency.

Linker Power Loss To specify the power loss (negative for a power gain) of the linked operations, select the Linker Power Loss check box.

Electric Motor Select the Electric Motor check box if you want to use the electric motor functionality.

Surge Controller The Create Surge Controller button on the Specs page of the Dynamics tab opens a Surge Controller property view (which is owned by the Centrifugal Compressor). The surge controller also works exclusively with Centrifugal Compressor and Expander unit operations. As mentioned, a Centrifugal Compressor surges if its capacity falls below the surge limit. The surge controller determines a minimum volumetric flow rate that the Centrifugal Compressor should operate at without surging. This is called the surge flow. The surge controller then attempts to control the flow to

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52  Centrifugal Compressor or Expander Unit Operations

the Centrifugal Compressor at some percent above the surge flow (this is typically 10%). The surge controller essentially acts like PID Controller operations. The control algorithms used to prevent Centrifugal Compressors from surging are extensions of the PID algorithm. Two major differences distinguish a surge from a regular controller: o

The setpoint of the surge controller is calculated and not set.

o

More aggressive action is taken by the surge controller if the Centrifugal Compressor is close to surging.

Surge Controller Connections Tab The Connections tab is very similar to a PID controller’s Connections tab. The inlet volumetric flow to the Centrifugal Compressor is automatically defaulted as the process variable (PV) to be measured. You must select a Control Valve operation as an operating variable (OP), which has a direct effect on the inlet flow to the Centrifugal Compressor. The Upstream Surge Controller Output field contains a list of the other surge controllers in the simulation flowsheet. If you select an upstream surge controller using the Upstream Surge Controller Output field, HYSYS ensures that the output signal of the Centrifugal Compressor’s surge controller is not lower than an upstream surge controller’s output signal. Consider a situation in which two compressors are connected in series.

As shown in the previous figure, both surge controllers must use the same valve for surge control. If the surge controllers are connected in this manner HYSYS, automatically selects the largest controller output. This is done to ensure that surge control is adequately provided for both compressors.

Surge Controller Parameters Tab The parameters tab consists of the following pages: o

Configuration

o

Surge Control

52  Centrifugal Compressor or Expander Unit Operations

1007

Configuration Page If the process variable (PV) is operating above a certain margin over the surge flow limit, the surge controller operates exactly as a PID Controller. Therefore, PID control parameters should be set on the Configuration page. The process variable range, the controller action, operation mode, and the tuning parameters of the controller can be set in this page.

Surge Control Page Various surge control parameters can be specified on the Surge Control page. A head versus quadratic flow expression relates the surge flow to the head of the Centrifugal Compressor. (1)

Where Fs = surge flow (m3/s) hm = head of the Centrifugal Compressor A, B, C = parameters used to characterize the relationship between surge flow and head You can enter surge flow parameters A, B, and C in order to characterize the relationship between the surge flow and head. The next three parameters in the Surge Control Parameters section are defined as follows: Surge Con- Description trol Parameter

1008

Control Line (%)

The primary setpoint for the surge controller. This line is defaulted at 10% above the surge flow. If the flow is above the backup line then the surge controller acts as a normal PID controller.

Backup Line (%)

Set somewhere between the control line and the surge flow. This line is defaulted at 5% above the surge flow. If the flow to the Centrifugal Compressor falls below the backup line, more aggressive action is taken by the controller to prevent a surge condition.

Quick Opening (%/sec)

Aggressive action is taken by increasing the desired actuator opening at a rate specified in this field until the volumetric flow to the Centrifugal Compressor rises above the backup line.

52  Centrifugal Compressor or Expander Unit Operations

Surge Controller Monitor Tab The Monitor tab displays a chart that graphs the three variables (PV, SP, and OP) of the surge controller.

Surge Controller User Variables Tab The User Variables tab enables you to create and implement your own user variables for the current operation.

Holdup Page Holdup volume could be considered in Compressors and Expanders. In the model implementation, the holdup volume is located at the product side (i.e. after compression or expansion). However, typical Centrifugal Compressors and Expanders in actual plants usually have significantly less holdup than most other unit operations in a plant. Therefore, the volume of the Centrifugal Compressor or Expander operation in HYSYS is generally assumed to be zero on the Holdup page. Note: For the Screw Compressor, refer to Screw Compressor: Holdup Page.

Stripchart Page The Stripchart page allows you to select and create default strip charts containing various variable associated to the operation.

52  Centrifugal Compressor or Expander Unit Operations

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52  Centrifugal Compressor or Expander Unit Operations

53 Reciprocating Compressor Unit Operation

The following section discusses a Reciprocating Compressor. A Reciprocating Compressor is a type of compressor used for applications where higher discharge pressures and lower flows are needed. It is known as a positive displacement type. Reciprocating Compressors have a constant volume and variable head characteristics, as compared to the Centrifugal Compressor that has a constant head and variable volume. Note: For Reciprocating Compressors, there is no direct relationship between the head and flow capacity.

In HYSYS, Centrifugal and Reciprocating Compressors are accessed via the same compressor unit operation. However, the solution methods differ slightly as a Reciprocating Compressor does not require a compressor curve and the required geometry data. The present capability of Reciprocating Compressors in HYSYS is focused on a single stage compressor with a single or double acting piston. A typical solution method for a Reciprocating Compressor is as follows: n

Always start with a fully defined inlet stream, in other words, inlet pressure, temperature, flow rate, and compositional data are known.

n

Specify compressor geometry data, for example, number of cylinders, cylinder type, bore, stroke, and piston rod diameter. HYSYS provides default values too.

n

Compressor performance data, in other words, adiabatic efficiency or polytropic efficiency, and constant volumetric efficiency loss are specified.

n

HYSYS calculates the duty required, outlet temperature if the outlet pressure is specified.

Some of the features in the dynamic Reciprocating Compressor unit operation include: n

Dynamic modeling of friction loss and inertia.

n

Dynamic modeling which supports shutdown and startup behavior.

n

Dynamic modeling of the cylinder loading.

53  Reciprocating Compressor Unit Operation

1011

n

Linking capabilities with other rotational equipment operating at the same speed with one total power.

Reciprocating Compressor Theory In a single stage Reciprocating Compressor, it comprises of the basic components like the piston, the cylinder, head, connecting rod, crankshaft, intake valve, and exhaust valve. This is illustrated below, HYSYS is capable of modeling a multi-cylinder in one Reciprocating Compressor with a single acting or double acting piston.

A single acting compressor has a piston that is compressing the gas contained in the cylinder using one end of the piston only. A double acting compressor has a piston that is compressing the gas contained in the cylinder using both ends of the piston. The piston end that is close to the crank is called crank end, while the other is named as outer. The thermodynamic calculations for a Reciprocating Compressor are the same as a Centrifugal Compressor. Basically, there are two types of compression being considered: l

l

Isentropic/adiabatic reversible path. A process during which there is no heat added to or removed from the system, and the entropy remains constant. PVk =constant, where k is the ratio of the specific heat (Cp/Cv). Polytropic reversible path. A process in which changes in the gas characteristic during compression are considered.

Details of the equation are found in the Theory section. The reference: Gas Processors Association. Gas Processors Suppliers Association (1998) p. 13-1 to p. 13-20 contains the information about the operation of the Reciprocating Compressor. The performance of the Reciprocating Compressor is evaluated based on the volumetric efficiency, cylinder clearance, brake power, and duty. Cylinder clearance, C, is given as:

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53  Reciprocating Compressor Unit Operation

(1)

Where: PD = positive displacement volume The sum of all clearance volume for all cylinders includes both fixed and variable volume. C is normally expressed in a fractional or percentage form. The piston displacement, PD, is equal to the net piston area multiplied by the length of piston sweep in a given period of time. This displacement can be expressed as follows: For a single-acting piston compressing on the outer end only: (2)

For a single-acting piston compressing on the crank end only: (3)

For a double-acting piston (other than tail rod type): (4)

For a double-acting piston (tail rod type): (5)

Where: d = piston rod diameter D = piston diameter PD includes the contributions from all cylinders and both ends of any double acting. If a cylinder is unloaded then its contribution does not factor in. The volumetric efficiency is one of the important parameters used to evaluate the Reciprocating Compressor's performance. Volumetric efficiency, VE, is defined as the actual pumping capacity of a cylinder compared to the piston displacement volume. VE is given by:

53  Reciprocating Compressor Unit Operation

1013

Where: Pd = discharge pressure Ps = suction pressure L = effects of variable such as internal leakage, gas friction, pressure drop through valves, and inlet gas preheating k = heat capacity ratio, Cp/Cv Zd = discharge compressibility factor Zs = suction compressibility factor C = clearance volume To account for losses at the suction and discharge valve, an arbitrary value about 4% VE loss is acceptable. For a non-lubricated compressor, an additional 5% loss is required to account for slippage of gas. If the compressor is in propane, or similar heavy gas service, an additional 4% should be subtracted from the volumetric efficiency. These deductions for non-lubricated and propane performance are both approximate, and if both apply, cumulative. Thus, the value of L varies from (0.04 to 0.15 or more) in general.

Rod Loading Rod loads are established to limit the static and inertial loads on the crankshaft, connecting rod, frame, piston rod, bolting, and projected bearing surfaces.

It can be calculated as follows: Load in compression, Lc: (1)

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53  Reciprocating Compressor Unit Operation

Load in tension, Lt: (2)

Maximum Pressure The maximum pressure that the Reciprocating Compressor can achieve is: (1) Where the maximum discharge pressure ratio, PRmax , is calculated from: (2)

Flow Flow into the Reciprocating Compressor is governed by the speed of the compressor. If the speed of the compressor is larger than zero then the flow rate is zero or larger than zero (but never negative). The molar flow is then equal to: (1)

Where: N = speed, rpm ρ = gas density MW = gas molecular weight If the speed of the compressor is exactly zero, then the flow through the unit is governed by a typical pressure flow relationship, and you can specify the resistance in zero speed flow resistance, kzero speed. The flow equation is as follows: (2)

Where: ΔPfriction = frictional pressure drop across the compressor

Reciprocating Compressor Design Tab 53  Reciprocating Compressor Unit Operation

1015

The Design tab contains the following pages: n

Connections

n

Parameters

n

Links

n

Settings

n

User Variables

n

Notes

Connections Page The Connections page allows you to specify the inlet stream, outlet stream, and energy stream. The Connections page is identical to the Connections page for the Centrifugal Compressor property view.

Parameters Page The Parameters pages is basically identical to the Centrifugal Compressor.. The difference between the Centrifugal and Reciprocating compressors are the Curve Input Options, which are missing from the reciprocating mode. Instead, use the Settings page on the Design tab to set up the reciprocating model. You can switch between Centrifugal and Reciprocating Compressor by selecting one of the radio buttons in the Operating Mode group. You can specify the duty of the attached energy stream on this page, or allow HYSYS to calculate it. The adiabatic and polytropic efficiencies appear as well. Notes: l

l

l

You can specify only one efficiency, either adiabatic or polytropic. If you specify one efficiency and a solution is obtained, HYSYS back calculates the other efficiency, using the calculated duty and stream conditions. The Reciprocating Compressor has a higher adiabatic efficiency than the Centrifugal Compressor, normally in the range of 85% - 95%. Maximum pressure ratio can be achieved at zero volume efficiency.

Links Page The Links page is identical to the Centrifugal Compressor Links page. .

Settings Page The Settings page is used to size the Reciprocating Compressor. The Settings page is only visible when you have activated the Reciprocating Compressor option either from the Parameters page on the Design tab or the Specs page on the Dynamics tab. Note: For the Screw Compressor, refer to Screw Compressor: Settings Page.

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53  Reciprocating Compressor Unit Operation

A Reciprocating Compressor does not require a characteristic curve, however the following compressor geometry information is required: n

Number of Cylinders

n

Cylinder Type

n

Bore - Bore is the diameter of the cylinder.

n

Stroke - Stroke is the distance head of piston travels.

n

Piston Rod Diameter

n

Constant Volumetric Efficiency Loss

n

Default Fixed Clearance Volume

n

Zero Speed Flow Resistance (k) - dynamics only

n

Typical Design Speed - Typical Design Speed is the estimated speed for the rotor. Speed is the actual speed of the rotor

n

Volumetric Efficiency

Depending on the cylinder type selected, you have four parameters that can be specified. If the cylinder type is of double action, you need to specify the fixed clearance volume for the crank side and the outer side. n

Fixed Clearance Volume

n

Variable Clearance Volume

n

Variable Volume Enabled

n

Cylinder is Unloaded - dynamics only

If the Variable Volume Enabled check box is selected, you need to specify a variable clearance volume. Note: The variable clearance volume is used when additional clearance volume (external) is intentionally added to reduce cylinder capacity.

If the Cylinder is Unloaded check box is selected, the total displacement volume is not considered and is essentially zero. The Size k button allows you to access the Reciprocating Pressure-Flow Sizing property view, and specify a pressure drop and mass flow rate that is used to calculate the zero speed flow resistance of the Reciprocating Compressor.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

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Reciprocating Compressor Rating Tab The Rating tab contains the following pages:

Nozzles Page If you are working exclusively in Steady State mode, you are not required to change any information on the Nozzles page. The Nozzles page in the Reciprocating Compressor is identical to the Nozzles page in the Centrifugal Compressor.

Inertia Page If you are working exclusively in Steady State mode, you are not required to change any information on this page. The Reciprocating Compressor Inertia page is identical to the one for the Centrifugal Compressor.

Reciprocating Compressor Performance Tab The Performance tab consists of the Results page and the Power Page

Results Page On the Results page, you can view a table of calculated values for the Compressor. In the Results group, the following fields appear:

1018

n

Adiabatic Head

n

Polytropic Head

n

Adiabatic Efficiency

n

Polytropic Efficiency

n

Power Consumed

n

Friction Loss

n

Rational Inertia

n

Fluid Power

n

Polytropic Head Factor

n

Polytropic Exponent

n

Isentropic Exponent

n

Speed

53  Reciprocating Compressor Unit Operation

In the Reciprocating group, the following fields appear: n

Total Effective Piston Displacement Volume

n

Total Effective Fractional Clearance Volume

n

Maximum Pressure Ratio

n

Load in Compression

n

Load in Tension

Power Page l

l

l

l

l

The Compressor Rotor Power group displays the following parameters: Total Rotor power, Transient Rotational power, Friction Loss power, and Fluid power. The Compressor Rotor Torque group displays the following parameters: Total Rotor torque, Transient Rotational torque, Friction Loss torque, and Fluid torque. The Electric Motor Power group displays the following parameters: Total Electric Motor power, Transient Rotational power, and Friction Loss power. The Electric Motor Torque group displays the following parameters: Total Electric Motor torque, Transient Rotational torque, and Friction Loss torque. The Other Electric Motor Data group displays the Motor Speed.

Note: The information displayed in the Electric Motor Power, Electric Motor Torque, and Other Electric Motor Data groups are blank if no electric motor is attached.

Reciprocating Compressor Dynamics Tab The Dynamics tab is identical to the one for the Centrifugal Compressor. However, when using a Reciprocating Compressor, you cannot use the Characteristic Curves specification or create a Surge Controller. Note: If you are working exclusively in Steady State mode, you are not required to change any information on the pages accessible through the Dynamics tab.

53  Reciprocating Compressor Unit Operation

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53  Reciprocating Compressor Unit Operation

54 Screw Compressor

The Screw Compressor is a new compressor model introduced as a part of the Compressor Unit operation in HYSYS V9. Similar to the Reciprocating Compressor, it is a positive displacement machine. The performance of the Screw Compressor can be calculated using either the Leakage flow or Performance curve method. The Leakage flow method uses the geometric configuration of the compressor, and the Performance curve method uses user-specified curves between volumetric flow, pressure change, and power at different suction pressures to calculate compressor performance.

Workflow To use the Screw Compressor: 1. Add a Compressor unit operation. 2. On the Design tab | Parameters page, select the Screw Compressor operating mode and specify parameters. 3. On the Design tab | Connections page, specify connections for the Screw Compressor. 4. On the Design tab | Links page, specify links to other compressors and expanders. 5. On the Design tab | Settings page, specify settings for the Screw Compressor. 6. On the Rating tab, edit values on the Nozzles and Inertia pages, if desired. For Performance curve calculations, you can also specify curves on the Curves page. 7. On the Performance tab, view performance results for the Screw Compressor. 8. On the Dynamics tab | Specs page, set dynamic specifications, if necessary.

Screw Compressor Theory 54 Screw Compressor

1021

Volumetric Efficiency and Leakage Flow Calculation In the reciprocating compressor, the volumetric efficiency is reduced due to the presence of clearance volume (that is, the piston is not able to use the entire volume for compression). In the rotary screw compressor, the volumetric efficiency is reduced because of the presence of leakages through various clearances present in the complex rotor assembly. HYSYS uses a simplified model for the leakage flow calculation under the following assumptions: l

l

Only gas is assumed to leak. This "leaked" gas is not getting recompressed, that is, this solely acts to lower the volumetric efficiency and reduce the gas molar flow rate. The clearances remain constant. Flow out of these clearance is modeled as isentropic flow out of convergent nozzles [1] [2].

Two different types of leakages are modeled based on the literature. l

Interlobe leakage

l

Blowhole leakage

Gas mass flow out of these leakages has the following form [3]: (1)

(2)

Where: C = Clearance coefficient A = Area of clearance r = Pressure ratio at the site of leakage. Note: This is not the overall compression ratio of the compressor, but is related to the overall compression ratio via an exponent.

T1 = Gas temperature at the leakage point k = Gas Cp/Cv Overall Volumetric Efficiency is calculated as: (3)

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54 Screw Compressor

(4) Note: You can vary Blowhole Area and Interlobe Area to manipulate the volumetric efficiency as a function of overall compression ratio.

Where the subscripts imply: VC = Constant volumetric efficiency loss (as specified in the Const. Vol. Efficiency Loss field on the Design tab | Settings page). This shifts the overall volumetric efficiency up or down by a constant term. You can keep it at 0, if desired. L = Efficiency loss due to leakage flow (see above) (5)

Gas Leakage flow = Interlobe Leakage flow + Blowhole Leakage flow The Compressor is divided into N chambers based on the number of lobes. For Interlobe leakage, the r in the leakage flow equations shown above corresponds to the pressure in a given chamber and suction pressure. For Blowhole leakage, the r corresponds to pressure in subsequent chambers. The overall volumetric flow (or volumetric efficiency) has a dependency on the overall compression ratio via the leakage flow through various clearances. You can change the areas of these clearances to tune the volumetric flow rate.

Performance Curve Calculation For the Performance curve calculation method, user-input curves representing the dependence of volumetric flow rate, pressure change, and power at different suction pressures are used to calculate the performance of the compressor. The leakage flow and volumetric efficiency values become implicit quantities in the data input in the form of curves.

References [1] Fujiwara, M.; Mori, H.; and Suwama, T., "Prediction of the Oil Free Screw Compressor Performance Using Digital." (1974). International Compressor Engineering Conference. Paper 119. [2] Seshaiah, N., Sahoo, R., Sarangi, S. (2010). “Theoretical and experimental studies on oil injected twin-screw air compressor when compressing different light and heavy gases.” Journal of Applied Thermal Engineering, 30 (4), pg. 327-339. [3] Yahya, S. M. Fundamentals of compressible flow. New Age International, 2003.

54 Screw Compressor

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[4] Wennemar, Jurgen. "Dry Screw Compressor Performance and Application Range." [5] Sjoholm, L. “Variable Volume-Ratio and Capacity Control in Twin-Screw Compressors.” (1986). International Compressor Engineering Conference. [6] Boldvig, V., and Villadsen, V. “A Balanced View of Reciprocating and Screw compressor Efficiencies.” (1980). International Compressor Engineering Conference.

Screw Compressor: Design Tab Connections Page On the Design tab | Connections page of the Screw Compressor, you can specify connections. To specify connections for the Screw Compressor: 1. In the Inlet field, specify the Inlet stream. 2. In the Outlet field, specify the Outlet stream. 3. In the Energy field, specify the Energy stream. 4. In the Oil Feed field, specify an oil stream if you selected the Oil-Injected radio button from the Oil Feed group on the Design tab | Parameters page. 5. From the Fluid Package drop-down list, edit the fluid package used for the compressor, if desired.

Parameters Page On the Design tab | Parameters page, you can select the Screw Compressor as the Operating Mode and specify parameters. Click the aspenONE Exchange icon (pictured to the left) to access known manufacturer specifications for compressors. aspenONE Exchange is a web-sourced library that includes pre-built models and partial flowsheets that you can download to speed creating simulations. If you select a model, it will populate the fields on the Parameters page with known values.

Selecting the Screw Compressor and Specifying Parameters To select the Screw Compressor and specify parameters: 1. In the Operating Mode group, select the Screw Compressor radio button. 2. In the Oil Feed group, select one of the following radio buttons:

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54 Screw Compressor

o

Dry: When you select this option, the Screw Compressor behaves similarly to the Reciprocating Compressor, except in the calculation of volumetric efficiency based on geometric parameters. -or-

o

Oil-Injected: If you select this option, you must specify the oil feed stream on the Design tab | Connections page. Typically, heavy oil or lubricants are used for this purpose. In the HYSYS model, oil does not interfere with the actual compression process. Internally, it is flashed with compressed gas at the discharge to create a mixed vapor-liquid stream at the outlet. Oil acts as a lubricant and a coolant for the compressor. You must model gas-oil separation in a separate unit-operation.

3. In the Performance Calculation group, select one of the following radio buttons: o

Leakage flow: This option uses the geometric parameters of the compressor for performance calculation.

o

Performance curve: This option allows you to use the Rating tab | Curves page to provide multiple curves of Volumetric Flow vs. Pressure Change vs. Power at different Suction Pressure values or provide one curve at a single Suction Pressure value.

Note: If you select the Performance curve option and the Input Power Curves check box on the Rating tab | Curves page is selected, the Adiabatic Efficiency, Polytropic Efficiency, Duty, Delta P, and Pressure Ratio will be calculated by HYSYS.

4. In the Efficiency group, specify one of the following if the Leakage flow calculation method is selected. This input is also necessary when the Performance curve method is selected and the Input Power Curve option is cleared on the Ratings tab | Curves page. o

Adiabatic Efficiency -or-

o Polytropic Efficiency If you specify one efficiency and a solution is obtained, HYSYS back-calculates the other efficiency, using the calculated duty and stream conditions.

5. In the Duty field, you can specify the duty of the attached energy stream. Alternately, you can allow HYSYS to calculate this value. 6. In the Pressure Specs group, you can specify pressure specifications for the unit operation in the following fields: o

Delta P

Pressure Ratio These values can also be calculated by HYSYS if the inlet pressure and outlet pressures are available either from user-specified values or from performance curves. o

54 Screw Compressor

1025

Oil-Injected Screw Compressor Necessary Inputs

Leakage Flow Calculation Method

Performance Curve Calculation Method

Feed gas composition, pressure, and temperature

Feed gas composition, pressure, and temperature

Oil feed composition, pressure, temperature, and volumetric, mass, or molar flow

Oil feed composition, pressure, temperature, and volumetric, mass, or molar flow

Either Adiabatic Efficiency or Polytropic Efficiency (on the Design tab | Parameters page)

Either Adiabatic Efficiency or Polytropic Efficiency (on the Design tab | Parameters page) if the Input Power Curve check box is cleared on the Ratings tab | Curves page

Speed (specified on the Design tab | Settings page) or Feed Molar Flow. For the Duty specification described below, you must always specify Feed Molar Flow.

Speed or Volumetric Efficiency on the Design tab | Settings page

One of the following: Discharge Temperature, Discharge Pressure, or Compressor Duty. We recommend that you specify Discharge Pressure. If you specify Duty, then clear the Speed field on the Design tab | Settings page and specify Feed Molar Flow.

One of the following: Flow (Volumetric/Mass/Molar), Discharge Pressure, Duty if the Input Power Curves check box is selected.

For the Leakage flow calculation method, HYSYS solves for the following sets of unknown values: 1. T2, P2, Duty, and either Adiabatic Efficiency or Polytropic Efficiency 2. T2, P2, Speed, and either Adiabatic Efficiency or Polytropic Efficiency 3. T2, Duty, Gas Molar Flow, and either Adiabatic Efficiency or Polytropic Efficiency 4. P2, Duty, Molar Flow, and either Adiabatic Efficiency or Polytropic Efficiency 5. T2, Duty, Speed, and either Adiabatic Efficiency or Polytropic Efficiency 6. P2, Duty, Speed, and either Adiabatic Efficiency or Polytropic Efficiency

Links Page Compressors and expanders modeled in HYSYS can have shafts that are physically connected to the unit operation. Linking compressors and expanders in

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54 Screw Compressor

HYSYS means that the: l l

Speed of each linked unit operation is the same. Sum of the duties of each linked Compressor or Expander and the total power loss equals zero.

The rotational linker operates both in Steady State and Dynamic mode. It is not significant which order the Compressors or Expanders are linked. Since the notion of upstream and downstream links is arbitrary, you can determine the links on the Design tab | Links page. 1. From the Previous Link and/or Next Link drop-down list, select from the list of available compressors or expanders. In most cases, one additional specification for any of the linked operations is required to allow the simulation case to completely solve. Ideally, you should specify one of the following for any of the linked unit operations. o

Duty

o

Speed

o

Total Power Loss Note: It is also possible to link an Expander to a Compressor, and use the Expander to generate kinetic energy to drive the Compressor. If this option is selected, the total power loss is typically specified as zero.

2. In the Gear Ratio field, specify the gear ratio for the linked operations. 3. Select the Dynamic Specification check box if you want to specify the Total Power Loss for the linked operations. Usually, total power input to the linked compressors or expanders is calculated in a Spreadsheet operation and specified by you in the Total Power Loss field. If you want to provide the total power input to a set of linked compressors or expanders, the total power input to the linked operations is defined in terms of a total power loss. The relationship is as follows: (1)

Settings Page Editing Screw Compressor Settings To edit Screw Compressor Settings: 1. Select the Design tab | Settings page. 2. In the Screw Compressor Settings table, view or edit the following fields: Field

54 Screw Compressor

Default

Description

1027

Suction Volume

0.01

The volume of non-compressed gas at the inlet per rotation. Equivalent to total piston displacement volume in reciprocating. If Volumetric Efficiency was 100%, then the volumetric flow rate of gas would equal suction volume * Speed.

Zero Speed Flow Resistance (k)

0

Only used in Dynamics Mode.

Typical Design Speed



Only used in Dynamics Mode.

Volumetric Efficiency

Calculated variable. For the relevant equation, refer to Screw Compressor Theory.

Speed [rpm]

Can be calculated by HYSYS or specified.

3. If desired, you can click the Size k button. The Screw Compressor Pressure-Flow Sizing dialog box appears, allowing you to specify the following values: o

Pressure Drop

Mass Flow Rate Click Size and Close. o

Note: The calculated Size k value is also used in Dynamics mode when the speed falls below 10% of the Typical Design Speed.

4. In the Leakage Flow Settings table, if you selected the Leakage flow option on the Design tab | Parameters page, you can specify parameters related to the leakage flow calculation. If you view the leakage flow equations in Screw Compressor Theory, these input parameters are used to evaluate CA for two types of leakages.

1028

Field

Default

Description

Number of Lobes

5

Number of helical lobes on male/female rotors.

Const. Vol. Efficiency Loss

4

If you are not satisfied with the leakage flow calculations, you can manipulate this variable to obtain the desired volumetric efficiency and gas molar flow rate.

54 Screw Compressor

Blowhole Area

Interlobe Area

5

25

Note: HYSYS uses a flow clearance coefficient of 0.7 in the program. You can vary Blowhole Area and Interlobe Area to manipulate the volumetric efficiency as a function of overall compression ratio. o

Interlobe leakage: Leakage of gas from the interlobe region to the suction chamber.

o

Blowhole leakage: Blowhole is the small triangular area formed between the two rotors and the housing. The leaked gas flows from a working chamber of higher pressure to its neighboring lower pressure region.

Note: HYSYS uses a flow clearance coefficient of 0.7 in the program. You can vary Blowhole Area and Interlobe Area to manipulate the volumetric efficiency as a function of overall compression ratio. o

Interlobe leakage: Leakage of gas from the interlobe region to the suction chamber.

o

Blowhole leakage: Blowhole is the small triangular area formed between the two rotors and the housing. The leaked gas flows from a working chamber of higher pressure to its neighboring lower pressure region.

5. If the Leakage flow calculation option is selected, you can either select or clear the Enable Slide Valve check box as desired. This check box allows you to model the Capacity Control Slide Valve found in most compressors in the industry. o

If you clear this check box, the volumetric flow rate remains unchanged and is equivalent to Speed × Suction Volume × Volumetric Efficiency.

o

If you select this check box, in the Slide Valve Characteristics group, you can specify Valve Opening (%) vs. Capacity Load %. The Capacity (%) corresponds to the effect on actual volumetric flow rate. By default, the relationship is linear, and the slide valve is at its maximum position (100%). You can edit the Current Slide Valve Position (%) to edit this value. In the table, you can model the relationship between the two parameters.

Note: The slide valve position can be used as a controllable variable in Dynamics mode.

Screw Compressor: Rating Tab

54 Screw Compressor

1029

Curves Page When the Performance curve calculation option is selected on the Design tab | Parameters page, the Curves page becomes available on the Rating tab, allowing you to specify one or more Screw Compressor curves. You can either: l

Provide multiple curves at different Suction Pressure values -or-

l

Provide one curve at a single Suction Pressure value

Specifying Curve Data To specify curve data for the Screw Compressor: 1. On the Design tab | Parameters page, in the Performance Calculation group, select the Performance curve radio button. 2. On the Rating tab | Curves page, if you select the Input Power Curves check box, you should enter the Power information for each curve. If you clear this check box, and efficiency specification may be needed. 3. You can edit the Compressor Speed value. 4. Click the Add Curve button. The ScrewCurve view appears. 5. On the ScrewCurve view, you can specify the following information: Curve Data

Description

Name

Name of the curve.

Vol Flow Units

Units for the volumetric flow.

Power Units

Units for the power.

Delta P Units

Units for the Delta P.

Suction Pressure

Suction Pressure of the Screw Compressor. This is optional if you specify only one curve. HYSYS can interpolate values for Delta P and Power for Suction Pressures that are not plotted.

Volumetric Flow / Delta P / Power

One row of data is equivalent to one point on the curve. For better results, enter data for at least three (or more) points on the curve.

6. Click the Close icon to return to the Curves page. 7. Select the corresponding Activate check box to use the curve in calculations. 8. For each additional curve, repeat steps #4 through #6.

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54 Screw Compressor

You can remove a specific curve from the calculation by clearing the corresponding Activate check box. Once a curve has been created, the following buttons on the Curves page are enabled: l

l

l l

View Curve: Allows you to view or edit your input data in the Curve property view. Delete Curve: Allows you to delete the selected curve from the simulation. Clone Curve: Allows you to duplicate an existing curve. Plot Curves: Allows you to view a graph of activated curves by accessing the Compressor Curves Profiles.

You can access the ScrewCurve view for an existing curve by clicking the View Curve button or by double-clicking the curve name.

Deleting Curve Data To delete information within a curve: 1. Double-click the curve name or click the View Curve button to open the ScrewCurve view. 2. Either: o

Highlight the data that you want to delete and click the Erase Selected button to delete the values for a selected row. -or-

o

Click the Erase All button to delete all of the information within the ScrewCurve property view.

Plotting Curves To view and edit Compressor Curves Profiles plots: 1. On the Rating tab | Curves page, click the Plot Curves button. The Compressor Curves Profiles view appears. 2. Select one of the following radio buttons: o

Delta P

o

Power

3. In the Curves group, select or clear the Show Operating Pt. check box as desired. 4. Select the Plot check boxes for the compressor curves that you want to display on the plot. You can select as many compressor curves as desired. Tip: Right-click anywhere within the plot area to access the plot’s object inspection menu.

54 Screw Compressor

1031

Nozzles Page On the Rating tab | Nozzles page of the Screw Compressor, you can specify information regarding the elevation and diameter of the nozzles. l

l

You can specify the Base Elevation Relative to Ground Level. If you want to model static head, the entire piece of equipment can be moved by modifying this value. In the Nozzle Parameters table, you can view or edit the following values: o

Diameter

o

Elevation (Base)

o

Elevation (Ground)

Note: If you are working exclusively in Steady State mode, you are not required to change any information on the Nozzles page. We recommend that the elevation of the inlet and exit nozzles are equal.

Inertia Page On the Rating tab | Inertia page, you can specify the inertia modeling parameters and the friction loss associated with the impeller in the Screw Compressor. l

l

In the Inertia Modeling Parameters (Dynamics) table, you can view or edit the following values: o

Rotational Inertia

o

Radius of Gyration

o

Mass

In the Friction Loss table, specify one of the following: o

Friction Loss Factor

o

First Order Time Constant

Note: If you are working exclusively in Steady State mode, you are not required to change any information on the Inertia page.

Screw Compressor: Performance Tab Results Page On the Performance tab | Results page, you can view the calculated results for the Screw Compressor. In the Results table, you can view the following calculated values:

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54 Screw Compressor

l

Adiabatic Head

l

Polytropic Head

l

Adiabatic Fluid Head

l

Polytropic Fluid Head

l

Adiabatic Efficiency

l

Polytropic Efficiency

l

Power Consumed

l

Polytropic Head Factor

l

Polytropic Exponent

l

Isentropic Exponent

l

Speed

In the Screw Compressor table, you can view the following calculated values: l

l

Maximum Pressure Ratio: The value of Discharge Pressure / Suction Pressure at which the molar flow rate becomes 0, or the Volumetric Efficiency equals 0. Volumetric Efficiency [%]: For the relevant equation, refer to Screw Compressor Theory.

l

Const. Vol. Efficiency Loss [%]

l

Vol. Eff. Loss due to Interlobe [%]

l

Vol. Eff. Loss due to Blowhole [%]

Note: For the Dry Screw Compressor, the sum of these 3 losses (Const. Vol. Efficiency Loss, Vol. Eff. Loss due to Interlobe, and Vol. Eff. Loss due to Blowhole) equals 100% - Volumetric Efficiency [%]. For the Oil-Injected Screw Compressor, there would be miniscule difference due to the volume occupied by the oil.

Power Page On the Performance tab | Power page, you can view the following results for the Screw Compressor. In the Compressor Rotor Power table, you can view the following calculated values: l

Total Rotor

l

Transient Rotational

l

Friction Loss

l

Fluid

In the Compressor Rotor Power table, you can view the following calculated values: l

Total Rotor

l

Transient Rotational

54 Screw Compressor

1033

l

Friction Loss

l

Fluid

Screw Compressor: Dynamics Tab Note: If you are working exclusively in Steady State mode, you are not required to change any information on the pages on the Dynamics tab.

Specs Page You can set the dynamic specifications for the Screw Compressor on the Dynamics tab | Specs page. In general, two specifications are required in the Dynamics Specifications group. You should be aware of specifications which may cause complications or singularity in the pressure flow matrix. For example, the Pressure Increase check box should be cleared if the inlet and exit stream pressures are specified. The possible dynamic specifications are as follows: Field

Description

Duty

The duty is defined, in the case of the Screw Compressor, as the power required to rotate the shaft and provide energy to the fluid. The duty has three components: Duty = Power imparted to the fluid + Power required to change the rotational speed of the shaft + Power lost due to mechanical friction loss The duty in a Screw Compressor should be specified only if there is a fixed power available to be used to drive the shaft.

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54 Screw Compressor

Adiabatic Efficiency or

For a dynamic Screw Compressor, the efficiency is given as the ratio of the isentropic power required for compression to the actual energy imparted to the fluid. The efficiency, η, is defined as:

Polytropic Efficiency Where: W = isentropic power F1 = molar flow rate of the inlet gas stream MW = molecular weight of the gas h 1 = inlet head h 2 = outlet head If a polytropic efficiency definition is required, the polytropic work should be provided in one of the above two equations. If an adiabatic efficiency definition is required, the isentropic work should be provided. The general definition of the efficiency does not include the losses due to the rotational acceleration of the shaft and seal losses. Therefore, the efficiency equations in dynamics are not different from the general efficiency equations defined in Screw Compressor Theory. This is true since the actual work required by a steady state Screw Compressor is the same as the energy imparted to the fluid. Pressure Increase

You can select a Pressure Increase specification if the pressure drop across the Screw Compressor is constant.

Head

The isentropic or polytropic head, h, can be defined as a function of the isentropic or polytropic work. The relationship is: (1) Where: W = isentropic or polytropic power MW = molecular weight of the gas CF = correction factor. For a compressor, this factor is the inverse value of the adiabatic/polytropic efficiency. F1 = molar flow rate of the inlet gas stream g = gravity acceleration

Fluid Head

The Fluid Head is the produced head in units of energy per unit mass

Capacity

The Capacity is defined as the actual volumetric flow rate entering the Screw Compressor. You can select a Capacity specification if the volumetric flow to the unit operation is constant.

Speed

The rotational speed of the shaft, ω, driving the Screw Compressor can be specified.

Linker Power Loss

To specify the power loss (negative for a power gain) of the linked operations, select the Linker Power Loss check box.

54 Screw Compressor

1035

Holdup Page Holdup volume could be considered in Compressors. In the model implementation, the holdup volume is located at the product side (that is, after compression). However, typical Compressors in actual plants usually have significantly less holdup than most other unit operations in a plant. Therefore, the Volume of the Screw Compressor in HYSYS is generally assumed to be zero on the Dynamics tab | Holdup page.

Stripchart Page The Dynamics tab | Stripchart page allows you to select and create default strip charts containing various variable associated to the operation.

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54 Screw Compressor

55 Pump Unit Operation

The Pump operation is used to increase the pressure of an inlet liquid stream. Depending on the information specified, the Pump calculates either an unknown pressure, temperature or pump efficiency. The dynamics Pump operation is similar to the Compressor operation in that it increases the pressure of its inlet stream. The Pump operation assumes that the inlet fluid is incompressible. Some of the features in the dynamic Pump include: l

Dynamic modeling of friction loss and inertia.

l

Dynamic modeling which supports shutdown and startup behavior.

l

Multiple head and efficiency curves.

l

l

Modeling of cavitation if Net Positive Suction Head (NPSH) is less than a calculated NPSH limit. Linking capabilities with other rotational equipment operating at the same speed with one total power.

Pump Theory HYSYS uses the following assumptions and equations in calculating the unknown Pump unit operation variables. l

Calculating the ideal power of the pump required to raise the pressure of the liquid: The calculations are based on the standard pump equation for power, which uses the pressure rise, the liquid flow rate, and density: (1) Where: Pout = pump outlet pressure Pin = pump inlet pressure

l

Calculating the actual power of the pump:

55  Pump Unit Operation

1037

The actual power requirement of the Pump is defined in terms of the Pump Efficiency: (2) When the efficiency is less than 100%, the excess energy goes into raising the temperature of the outlet stream. Combining the above equations leads to the following expression for the actual power requirement of the Pump: (3)

The actual power is also equal to the difference in heat flow between the outlet and inlet streams: (4) Where: The pump calculations that HYSYS performs assume that the liquid is incompressible. The density is constant, and the liquid volume is independent of pressure. This is the usual assumption for liquids well removed from the critical point, and the standard pump equation given above is generally accepted for calculating the power requirement. However, if you want to perform a more rigorous calculation for pumping a compressible liquid (for example, one near the critical point), you should install a compressor to represent the pump. The ideal power required, W, to increase the pressure of an incompressible fluid is: (5) Where: P1 = pressure of the inlet stream P2 = pressure of the exit stream ρ = density of the inlet stream F = molar flow rate of the stream MW = molecular weight of the fluid Note: For a pump, an efficiency of 100% does not correspond to a true isentropic compression of the liquid.

Pump Design Tab 1038

55  Pump Unit Operation

The Design tab consists of the following pages: l

Connections

l

Parameters

l

Curves

l

Links

l

User Variables

l

Notes

Connections Page On the Connections page, you can specify the pump name, fluid package, and inlet, outlet, and energy streams of the Pump.

Parameters Page The Parameters page enables you to specify the adiabatic efficiency, Delta P, and pump energy (power) parameters. However, if the inlet stream is fully defined, only two of the following variables need to be specified for the Pump to calculate all unknowns: o

Outlet Pressure or Pressure Drop (pressure difference between inlet and outlet stream)

o

Efficiency (pump efficiency)

o

Pump Energy or Duty (actual power)

HYSYS can also back-calculate the inlet pressure. Use the Delta P and Pressure Ratio fields to enter pressure specifications for the unit operation. You can specify these values, or they can be calculated by HYSYS, if Inlet Pressure and Outlet pressures are available.

Curves Page The Curves page allows you to configure the pump based on the pump curve. On the Curves page, you can create the pump curve using the equation provided by the pump manufacturer.

55  Pump Unit Operation

1039

To generate a pump curve: 1. Enter the coefficients for the quadratic pump equation. The coefficient values come from the pump manufacture. 2. Select the Activate Curves check box. The Activate Curves check box can only be selected if the Use Curves check box in the Curves page of the Rating tab is cleared. Based on the calculated pump curve results, HYSYS determines the pressure rise across the Pump for the given flowrate. To avoid a consistency error, ensure that you have not specified the pressure rise across the Pump, either in the attached streams or in the operation itself.

Notes on Pre-2004 curve calculations The curve equation function was originally provided in older versions of HYSYS (before 2004). The function was limited to a pump curve data generated by the curve equation, which may not accurately reflect the actual pump operating behavior. The current curve characteristics function lets users directly describe the pump operating behavior in terms of Flow, Head, Efficiency, and speed issues. By entering these variable values, a more accurate pump curve data is achieved. If an old case is loaded into HYSYS containing converged pumps that use curve equation to generate the pump curves, HYSYS automatically populates a curve characteristic set to generate a new pump curve similar to the old pump curve based on the curve equation specifications.

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55  Pump Unit Operation

Note: HYSYS does not automatically replace the new pump curve with the old pump curve. A warning message also appears informing you about the new pump curve and suggesting that you switch to the curve characteristic method.

To switch to the curve characteristic method: 1. Open the Pump property view. 2. Click the Design tab and select the Curves page. 3. Clear the Activate Curves check box. 4. Click the Rating tab and select the Curves page. 5. Select the Use Curves check box. 6. Click the Design tab and select the Parameters page. 7. Delete any specified values in the Adiabatic Efficiency field or Duty field.

Links Page In HYSYS, Pumps can have shafts which are physically connected. The rotational equipment linker operates both in Steady State and Dynamic mode. The following table lists and describes the objects in the Links page: Object

Description

Previous Link field

Displays the HYSYS rotating equipment operation connected on one side of the shaft.

Next Link dropdown list

Allows you to select a rotating equipment operation to connect on the other side of the shaft.

Gear Ratio field

Displays the ratio of the speed from the next linked operation divided by the speed of the current pump.

Total Power Loss field

Depending on the configuration of the pump and the information specified, you can either:

Dynamic Specification check box

o

View the total power loss of the linked operation.

o

Specify the total power loss of the linked operation.

Allows you to specify the total power loss (or power gain by entering a negative value) for the linked operation. You can ignore this option in Steady State mode.

Notes: l

l

It is not significant which order the Pumps are linked. The notion of previous and next links is arbitrary and determined by the user. Linked Pump operations require curves. In Dynamics mode, to fully define a set of linked operations, you must select the Use the Characteristic Curves check box for each of the linked Pumps in the Specs page of the Dynamics tab.

55  Pump Unit Operation

1041

In Dynamics mode when you link rotating operation, the pressure flow equations are affected as follow: o

An energy conservation equation is set such that the sum of the operation powers equals the total power.

o

Each pair of operation has their speeds set to equal.

One additional dynamic specification is usually required for the set. The total power loss from the linked operations can be specified. For a series of linked Pumps, it is desired to input a total power: (1) An electric motor connected to the current operation or a linked operation can also supply the total power. Note: It is possible to link a Pump to a Compressor and use the Pump as a turbine to generate kinetic energy to drive the Compressor. If this option is selected, the total power loss is typically specified as zero.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Pump Rating Tab If you are working exclusively in Steady State mode, you are not required to change any information on most of the pages accessible through the Rating tab. The Rating tab consists of the following pages:

1042

l

Curves

l

NPSH

l

Nozzles

l

Inertia

l

Electric Motor

l

Design

55  Pump Unit Operation

Curves Page The Curves page on the Rating tab allows you to configure the pump based on pump curve characteristics generated by the pump manufacturer. Note: The pump curve characteristics method works in both steady state and dynamic mode.

The curve characteristics consist of pump efficiency, pump head, pump flow rate, and pump speed variables. The pump can be configured based on multiple pump curves and speeds. The following table lists and describes the objects in the Curves page: Object

Description

Curve Name column

Displays the names of the curve data for the pump.

View Curve button

Allows you to open the " Curve Property View " on page 1045 and modify the curve characteristic of the selected curve.

Add Curve button

Opens the " Curve Property View " on page 1045and allows you to create a curve.

Delete Curve button

Allows you to delete the selected curve in the Curve Name column.

Clone Curve button

Allows you to duplicate an existing curve.

Plot Curves button

Allows you to generate a plot of all the curve in the " Curves Profiles Property View" on page 1046.

Generate Curves button

Allows you to manipulate and generate the curve using the " Generate Curve Options Property View" on page 1047. This option should be used only if the pump curve data is not provided by the manufacturer.

Pump Speed field

Enables you to specify a pump speed for all the curve data.

Use Curves check box

Enables you to accept the pump curve data generated by the curve characteristics.

55  Pump Unit Operation

This button is only available if there is a curve available in the Curve Name column.

This button is only available if there is a curve available in the Curve Name column.

The Use Curves check box can only be selected if the Activate Curves check box is clear in the Curves page of the Design tab.

1043

Object

Description

Offset Values Field

Optionally you can enter an Offset Value to apply to the head and efficiency results.  The specified offsets are applied to the head and efficiency that come out of the curve calculation to get the desired plant head and efficiency.

Depending on the type of pump curve you want to generate the following information needs to be supplied for the pump to solve: l

l

For a performance curve (one curve), the feed temperature and pressure must be supplied along with one of flow, duty, outlet pressure or efficiency. For normalized curves, the feed temperature and pressure must be specified along with two of flow, speed, duty, outlet pressure, and efficiency.

Note: For the two variables, either flow and/or speed must be specified. A pump with duty and efficiency specified cannot be solved using the curve characteristic option.

In addition, if outlet pressure or efficiency is supplied as one of the variables (for performance or normalized curves) and their corresponding curve is a parabola or has multiple flows for a given pressure or efficiency, then there may be multiple solutions. HYSYS will notify you of this possibility but will still solve to the first solution only. If iterations are required, basically any problems that do not have both flow and speed specified for a normalized problem or no flow for a performance problem, then HYSYS deploys the Secant method to converge to a solution. The number of maximum iterations is set at 10000 and is not modifiable. To specify data for a pump curve: 1. On the Curves page, click the Add Curve button. The Curve property view appears. 2. On the Curve property view, specify the pump speed in the Speed field. 3. Specify the flow, head, and % efficiency data points for a single curve in the appropriate cells. For each additional curve, repeat steps 1 and 2. l

l

Click the Erase Selected button to delete the entire row (Flow, Head or Efficiency) of the selected cell. Click the Erase All button to delete all Flow, Head, and Efficiency data for the curve.

After entering all your curve data, click the Close icon to return to the Pump property view. HYSYS uses the curve(s) to determine the appropriate efficiency for your operational conditions. If you specify curves, ensure the Efficiency values on the

1044

55  Pump Unit Operation

Parameters page of the Design tab are empty, or a consistency error will be generated.

Curve Property View You can access the Curve property view by: l

Clicking the Add Curve button. -or-

l

Selecting curve data and clicking the View Curve button.

In the Curve property view, you can specify the following data: Object

Description

Name field

Enables you to designate a name for particular curve characteristic data.

Speed field

Enables you to specify the rotation speed of the pump. This value is only required if you specify more than one set of curve characteristic data. Each set of curve characteristic data is associated to a specific pump rotation speed.

Flow Units field

Enables you to select the unit of the flow rate for the curve characteristic data.

Head Units field

Enables you to select the unit of the head for the curve characteristic data.

Flow column

Enables you to specify the flow rate data of the pump curve. The flow rate values appear along the x-axis of the pump curve plot.

Head column

Enables you to specify the head data of the pump curve. The head values appear along the y-axis of the pump curve plot.

Efficiency column

Enables you to specify the efficiency data of the pump curve. The pump efficiency values appear along the y-axis of the pump curve plot.

Erase Selected button

Enables you to select a cell and erase the data in the entire row associated to the selected cell.

Erase All button

Enables you to delete all the flow, head, and efficiency data of the curve.

Note: The curve characteristics data is normally provided by the pump manufacturer. HYSYS can interpolate values for the efficiency and head of the Compressor or Expander for speeds that are not plotted.

In order to run a stable and realistic dynamic model, HYSYS requires you to input reasonable curves. If Compressors or Expanders are linked, it is a good

55  Pump Unit Operation

1045

idea to ensure that the curves plotted for each unit operation span a common speed and capacity range. Typical curves are plotted in the figure below.

Where: h = pump head η = pump efficiency Capacity = pump flow rate

Curves Profiles Property View The Curves Profiles property view allows you to see the plot of the curve data. To access the Curves Profiles property view, click the Plot Curves button on the Curves page in the Rating tab of the Pump property view. The following table lists and describes the objects available in the Curves Profiles property view:

1046

Object

Description

Plot

Displays the selected curve data in plot format.

Head radio button

Allows you to view the Head vs. Flow curve data plot.

Efficiency radio button

Allows you to view the Efficiency vs. Flow curve data plot.

Curve Name column

Displays the names of the curve data available for the plot.

55  Pump Unit Operation

Object

Description

Plot check boxes

Allows you to toggle between displaying and hiding the associate curve data in the plot.

Show Operating Pt check box

Allows you to toggle between displaying and hiding the curve data generated by the Pump’s current operating conditions and specifications.

Generate Curve Options Property View The Generate Curve Options property view allows you to generate curve data based on the specified pump design parameters. HYSYS automatically generates three curves based on three different speeds: user specified speed, user specified speed multiplied by low speed %, and user specified speed multiplied by low low speed %. Each curve is generated using the following data point assumptions: l

l

A point based on the Head of the pump, Capacity of the pump, and the assumption that shutoffhead (0 flow rate) occurs at 110% of the Design Head value (the 110% comes from the Design Head Factor variable). A point based on the Head of the pump, Capacity of the pump, and the assumption that maximum flow (0 Head) occurs at 200% of the design capacity flow rate (the 200% comes from the Design Flow Factor variable).

l

A point based on the following expression:

l

A point based on the following expression:

l

A point based on the following expression:

To access the Generate Curve Options property view, click the Generate Curves button on the Curves page in the Rating tab of the Pump property view. The following table lists and describes the objects available in the Generate Curve Options property view: Object

Description

Design Efficiency Factor cell

Allows you to manipulate the pump design efficiency factor. Default value is 0.90.

55  Pump Unit Operation

1047

Object

Description

Design Efficiency cell

Allows you to manipulate the design efficiency of the pump. HYSYS provides a default value of 70%.

Design Flow Factor cell

Allows you to manipulate the pump design flow factor. Default value is 2.

Design Flow cell

Allows you to manipulate the pump design flow. Default value is 10.

Design Head Factor cell

Allows you to manipulate the pump design Head factor. Default value is 1.10.

Design Head cell

Specify the design Head of the pump.

Design Speed cell

Specify the design speed of the pump.

Low Speed cell

Allows you to manipulate the pump low speed based on the percentage value of the pump design speed. Default value is 60%.

Low Low Speed cell

Allows you to manipulate the pump low low speed based on the percentage value of the pump design speed. Default value is 30%.

Generate Curves button

Allows you to generate the curve data based on the specified pump design.

Cancel button

Allows you to exit the Generate Curves Options property view without generating any curve data.

Any previous specified curve data in the Curves page of the Rating tab will be deleted, when you generate the new curve data.

Note: The default values in the Required Data table are provided as an example. The variable values must be changed to reflect the data of the pump the user wants to simulate. The user data is normally provided by the pump manufacturer or by the design specifics for the simulation.

The default values in the Optional Curve Shape Data table are for a typical pump used in a plant.

NPSH Page Net Positive Suction Head (NPSH) is an important factor to consider when choosing a Pump. Sufficient NPSH is required at the inlet of the Pump to prevent the formation of small bubbles in the pump casing which can damage the Pump. This is known as cavitation. For a given Pump, the net positive suction head required to prevent cavitation, NPSHrequired, is a function of the capacity (volumetric flowrate) and speed of the Pump. In HYSYS, NPSH curves can be specified like regular pump curves on the NPSH page.

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55  Pump Unit Operation

To add or edit a NPSH curve from the NPSH page: 1. Select the Enable NPSH curves check box. 2. Click the Add Curve button. The NPSH Curve property view appears. 3. Specify the speed for each curve. 4. Enter a capacity and NPSH for two points on the curve. Only two points are required for the NPSH curves since: (1) 5. To remove all the data points, click the Erase All button. 6. For each additional curve, repeat steps 1 to 4. The NPSH required value can either be taken from the NPSH curves or specified directly in the NPSH required field. To directly specify the NPSHrequired, you must first clear the Enable NPSH curves check box. NPSHavailable can be explicitly calculated from the flowsheet conditions by clicking the Calculate Head button. The NPSHavailable is calculated as follows: (2)

Where: P1 = inlet stream pressure to the pump Pvap = vapor pressure of the inlet stream ρ = density of the fluid V1 = velocity of the inlet stream g = gravity constant To prevent pump cavitation, the NPSHavailable must be above the NPSHrequired. If a pump cavitates in HYSYS, it is modeled by scaling the density of the fluid, ρ, randomly between zero and one.

Thoma Estimation On the Rating | NPSH page, in the NPSH Curves section, you can select the Thoma Estimation radio button. The relevant calculations for this option are described below. The NPSH is estimated based on the PSN correlation for the Thoma’s cavitation parameter (Reference: “Fluid Mechanics for Engineers” by BARNA, p. 323-331). Theory The Net Positive Suction Head (NPSH) is the difference between the static inlet head and the head corresponding to the vapor pressure of the liquid. The term used for describing the effects of cavitation on pump performance or similarity of cavitation conditions between machines having similar geometry and hydraulic characteristics is described as the Thoma sigma:

55  Pump Unit Operation

1049

(3) Where: H=head developed by pump (m) NPSH= net positive suction head at some location (m) σcr = the Critical Sigma value at which there is an abrupt decrease in performance of the hydraulic machine. The NPSH required may be calculated by the Eqn (1) if the critical sigma and the head developed by pumps are known. The specific speed (X) determines the general shape or class of the impeller and it is calculated using the following formula: (4)

Where: N = Pump speed in rpm Q = Capacity in ft3/sec H = Total head per stage or the operating head in feet. The critical sigma is then calculated from Figure 11.51: Cavitation chart for centrifugal pumps (Reference: “Fluid Mechanics for Engineers” by BARNA, p. 323-331) that gives a plotted Critical Sigma (Y) against the pump’s Specific Speed (X). In the cavitation chart (Fig. 11.51, Barna), the relationship between log(sigma) and log(Ns) is linear. So a simple linear relationship is regressed from the cavitation chart. (5)

Calculation Procedure The calculation procedure is as follows: 1. Specific speed is calculated based on Eq (4). 2. The critical sigma with the specific speed known is calculated based on Eq (5). 3. The NPSH required is calculated based on Eq (3).

Nozzles Page The Nozzles page contains information regarding the elevation and diameter of the nozzles.

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55  Pump Unit Operation

For a Pump unit operation it is strongly recommended that the elevation of the inlet and exit nozzles are equal. If you want to model static head, the entire piece of equipment can be moved by modifying the Base Elevation relative to Ground Elevation field.

Inertia Page The inertia modeling parameters and the frictional loss associated with the impeller in the Pump can be specified on this page. The HYSYS Dynamics license is required to use the Inertia features.

Electric Motor Page The Electric Motor page allows you to drive your rotating unit operation through the designation of a motor torque versus speed curve. These torque vs. speed curves can either be obtained from the manufacturer for the electric motor being used or from a typical curve for the motor type. For most process industry applications, a NEMA type A or B electric motor is used. When you use the Electric Motor option the torque (and power) generated by the motor is balanced against the torque consumed by the rotating equipment. Notes: o

The Electric Motor functionality is only relevant in Dynamics mode.

o

The Electric Motor option uses one degree of freedom in your dynamic specifications.

o

The results of the Electric Motor option are presented on the "Power Page" on page 1055 in the "Pump Performance Tab" on page 1054 of the rotating equipment operation.

The following table lists and describes the objects in the Electric Motor page: Object

Description

Synchronous Speed cell

Specify the synchronous speed of the motor.

Full Load Speed cell

Specify the design speed of the motor.

Full Load Torque cell

Specify the design torque of the motor.

Full Load Power cell

Specify the design power of the motor.

Gear Ratio cell

Allows you to manipulate the gear ratio. The gear ratio is the rotating equipment’s speed divided by the motor speed.

55  Pump Unit Operation

1051

Object

Description

Motor Inertia cell

Specify the motor inertia.

Motor Friction Factor cell

Specify the motor friction factor.

User Electric Motor check box

Allows you to toggle between using or ignoring the electric motor functionality.

Speed vs Torque Curve button

Allows you to view the plot and specify the data in the "Speed vs. Torque Curve Property View" on page 1054.

Size Inertia button

Allows you to calculate the inertia based on the following equation:

I = inertia (kg • m3) P = full load power of the motor (kW) N = full load speed of the motor (rpm/1000) Simple radio but- Allows you to select the Simple model for the modelling option. ton Breakdown radio button

Allows you to select the Breakdown model for the modelling option.

Electric Brake check box

Allows you to model the torque force on the rotating equipment simply by changing the sign of the produced torque value.

Gearing check box

Allows the gear ratio to be updated during integration. A zero value for the gear ratio indicates a decoupling of the equipment.

Theory The definition of torque is found from the following equation: (1)

Where: P = power consumption (kW) T = torque (Nm) ω = synchronous speed (rpm) The synchronous electric motor speed can be found from: (2)

Where:

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55  Pump Unit Operation

f = power supply frequency (Hz), typically either of 50 or 60 p = number of poles on the stator The number of poles is always an even number of 2, 4, 6, 8, 10, and so forth. In North America, common motor speeds are always 3600, 1800, 1200, 900, 720, and so forth. The relationships of inertia and friction loss in the total energy balance are the same as for the pump and compressor operations.

Operation Model There are three ways to use the Electric Motor curve, each with progressing rigor. l

l

l

Simple Model. The easiest calculation is the Simple modelling option (default). This model is useful if you just want to model the startup/shutdown transient and want to keep the equipment at the fixed full load speed once operating. In this mode, once the speed has accelerated enough to become larger than the last (largest) curve speed value entered, the motor speed immediately is set to the full load speed and remains there until the motor is turned off. If the process invokes a larger torque than the motor curve suggests the motor can produce, the speed still remains synchronous and remains at its full load value. Breakdown Model. The Breakdown modelling option allows the speed to reduce if the system torque or resistance gets too large. To use this option, the largest (last) curve speed value entered should be just less than the full load speed value. This provides for a smooth transition in operation. You can drop the curve to a lower torque than the breakdown torque if desired. Simple Model Modified. The third modelling approach is to use the Simple model option, but enter the speed vs torque curve up to a speed value of 99.99% of the synchronous speed. In this case the full load speed entered is only used, if necessary, to calculate the full load torque and is not used otherwise. With this approach, the speed vs torque curve must ascend or drop from the breakdown torque to approach zero torque at 100% speed. For most motor types, this approach is nearly vertical (asymptotic). This modelling approach allows for the simulation of the slippage of the motor speed based upon the actual and current system resistance. The operating speed of the motor will then move based upon the process model operation. Use a near vertical curve to keep a constant speed or level it off more to allow greater slip. This performance should be predicted by using an accurate manufacturer's torque vs speed curve.

The speed and torque are not solved simultaneously with the pressure flow solution but instead is lagged by a time step. You may need to use a smaller time step to ensure accuracy and pressure flow solver convergence.

55  Pump Unit Operation

1053

Speed vs. Torque Curve Property View The Speed vs. Torque Curve property view displays the data curve of speed versus torque in both table and plot format. To access the Speed vs. Torque Curve property view, click the Speed vs Torque Curve button on the Electric Motor page of the Rating tab. Notes: l

l l

l

The values under the Speed and Torque columns are entered as a percent of the Full Load values. The Speed vs. Torque curve must always contain a 0% speed value. During integration, the current operating point appears on the Torque vs. Speed curve. The maximum table speed cannot be greater than the value in the Maximum X value field. The Maximum X value is the ratio of the full load speed to the synchronous speed.

The following table lists and describes the objects available in the Speed vs. Torque Curve property view: Object

Description

Maximum X value display field

Displays the ratio of the full load speed to the synchronous speed.

Speed column

Specify speed percentage values you want to plot.

Torque column

Specify the torque percentage values associated with the speed.

Erase Selected button

Allows you to delete the row containing both speed and torque percentage values of the selected cell.

Erase All button

Allows you to delete all the values in the table.

Design Page The Design page allows you to specify the typical or design operating capacity, pump speed, and power consumption. l

l

l

Typical operating capacity cell allows you to specify a value used to assist pump start up priming when vapor is present in the inlet stream. The Design Speed cell allows you to specify the speed value used for the Auto Pump Curve generation feature and the pump inertia sizing. The Design Power cell allows you to specify the power value used for the Auto Pump Curve generation feature and for pump inertia sizing.

Note: The HYSYS Dynamics license is required to use the options in the Design page.

Pump Performance Tab 1054

55  Pump Unit Operation

The Performance tab contains the calculated results of the pump.

Results Page The Results page contains pump head information. The values for total head, pressure head, velocity head, Delta P excluding static head, total power, friction loss, rotational inertia, and fluid power are calculated values. The Total Head field is used only for dynamic simulation.

Power Page The Power page displays the following calculated values: n

pump rotor power variables

n

pump rotor torque variables

n

electric motor power variables (if applicable)

n

electric motor torque variables (if applicable)

n

other electric motor data (if applicable)

Pump Dynamics Tab The Dynamics tab is used only for dynamic simulation. The Dynamic tab contains the following pages: n

Specs

n

Holdup

n

Stripchart

Note: If you are working exclusively in Steady State mode, you are not required to change any of the values on the pages accessible through the Dynamics tab.

Specs Page The dynamic specifications of the Pump can be specified on the Specs page.

55  Pump Unit Operation

1055

In general, two specifications should be selected in the Dynamics Specifications group in order for the Pump operation to fully solve. You should be aware of specifications, which may cause complications or singularity in the pressure flow matrix. Some examples of such cases are: n

The Pressure rise check box should be cleared if the inlet and exit stream pressures are specified.

n

The Speed check box should be cleared if the Use Characteristic Curves check box is cleared.

The possible dynamic specifications are as follows:

Head The ideal head, h, can easily be defined as a function of the isentropic or polytropic work. The relationship is: (1) Where: W = ideal pump power MW = molecular weight of the gas F = molar flow rate of the inlet stream g = gravity acceleration or using the Pump Theory Equation for W, the head is defined as:

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55  Pump Unit Operation

(2)

If pump curves are provided in the Curves page of the Rating tab, the ideal head can be interpolated from the flow of gas and the speed of the pump.

Fluid Head The Fluid Head is the produced head in units of energy per unit mass.

Speed The rotational speed of the shaft, ω, driving the Pump can be specified.

Efficiency The efficiency is given as the ratio of the ideal power required by the pump to the actual energy imparted to the fluid. The efficiency, η, is defined as: (3)

The ideal power required by the pump is provided in the Pump Theory Equation for W. The general definition of the efficiency does not include the losses due to the rotational acceleration of the shaft and seal losses. Therefore, the efficiency equations in dynamics are not different at all from the general efficiency equations defined in the Pump Theory section. If pump curves are provided in the Curves page of the Rating tab, the efficiency can be interpolated from the flow of gas and the speed of the Pump.

Pressure Rise A Pressure Rise specification can be selected, if the pressure drop across the Pump is constant.

Power The duty is defined as the power required to rotate the shaft and provide energy to the fluid. The duty has three components: (4)

The duty should be specified only if there is a fixed rate of energy available to be used to drive the shaft.

Capacity The capacity is defined as the actual volumetric flow rate entering the Pump.

55  Pump Unit Operation

1057

Use Characteristic Curves Select the Use Characteristic Curves check box if you want to use the curve (s) specified in the Curves page of the Rating tab. If a single curve is specified in a dynamics Pump, the speed of the Pump is not automatically set to the speed of the curve. A different speed can be specified, and HYSYS extrapolates values for head and efficiency.

Pump is acting as turbine Select the Pump is acting as turbine check box if you want the pump to act as a turbine with a pressure drop from inlet to outlet.

Linker Power Loss Select the Linker Power Loss check box if you want to specify the power loss (negative for a power gain) of the linked operations.

Electric Motor Select the Electric Motor check box if you want to use the electric motor functionality.

Holdup Page Typical pumps in actual plants usually have significantly less holdup than most other unit operations in a plant. Therefore, the volume of the Pump operation in HYSYS cannot be specified, and is assumed to be zero on the Holdup page.

Stripchart Page The Stripchart page allows you to select and create default strip charts containing various variable associated to the operation.

References 1. Gas Processors Association. Gas Processors Suppliers Association (1998), p.13-1 to p. 13-20. 2. Campbell M.John. Gas Conditioning and Processing (vol. 2) 7th ed. 1994, p. 213-221, 3. Thorley A. R. D. Fluid Transients in Pipeline Systems. D & L George Ltd. England, 1991.

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55  Pump Unit Operation

56 Separation Operations

The next chapters will describe the following Separation Operations: l

Component Splitter

l

Separator, 3-Phase Separator, & Tank

l

Shortcut Column

References 1. GPSA, Vol 1, 10th Ed., January 1990. 2. Separation Mechanism of Liquid-Liquid Dispersions in a deep-layer Gravity, Settler, E. Barnea and J Mizrahi, Trans. Instn. Chem. Engrs, 1975, Vol 53. 3. Droplet size spectra generated in turbulent pipe flow of dilute liquidliquid dispersions, A J Karabelas, AIChE, 1978, vol. 24, No. 2, pages 170181. 4. Society of Petroleum Engineers papers: SPE36647 – Separator Design and Operation: Tools for Transferring "Best Practice" SPE21506 – Proseparator – a novel separator/scrubber design program 5. Aspen Process Manuals – Mini Manual 1: Gas & Particle Properties; Part 8 – Particle Size 6. Aspen Process Manuals – Gas Cleaning Manual: Vol 1 – Introduction Vol 2 – Demisting Vol 10 – Applied Technology

56 Separation Operations

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56 Separation Operations

57 Component Splitter

With a Component Splitter, a material feed stream is separated into two component streams based on the parameters and split fractions that you specify. You must specify the fraction of each feed component that exits the Component Splitter into the overhead product stream. Use it to approximate the separation for proprietary and non-standard separation processes that are not handled elsewhere in HYSYS.

Theory The Component Splitter satisfies the material balance for each component: (1) where: fi = molar flow of the ith component in the feed ai = molar flow of the ith component in the overhead bi = molar flow in the ith component in the bottoms The molar flows going to the overhead and bottoms are calculated as: (2) (3) where: xi = split, or fraction of component i going to the overhead Once the composition, vapor fraction, and pressure of the outlet streams are know, a P-VF flash is performed to obtain the temperatures and heat flows. An overall heat balance is performed to obtain the energy stream heat flow: (4) where: 

57 Component Splitter

1061

hE = enthalpy of unknown energy stream hF = enthalpy of feed stream hO = enthalpy of overhead stream hB = enthalpy of bottoms stream

Component Splitter Property View Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

Splits

l

TBP Cut Point

l

User Variables

l

Notes

Each of the pages are discussed in the following sections.

Connections Page You can specify an unlimited number of inlet streams to the Component Splitter on the Connections page. You must specify the overhead outlet stream, bottoms outlet stream, and an unlimited number of energy streams. One of the attached energy streams should have an unspecified energy value to allow the operation to solve the energy balance.

Parameters Page The Parameters page displays the stream parameters. You must specify the stream parameters, which include the vapor fraction, pressure of the overhead stream, and pressure of the bottoms stream. To specify the Component Splitter parameters: 1. Click one of the following radio buttons to calculate the outlet stream parameters: o

1062

Calculate Equal Temperatures – HYSYS calculates equal temperatures for both the Overhead and Bottoms streams. You cannot select this option if you have multiple overhead streams.

57 Component Splitter

o

Use Stream Flash Specifications – HYSYS uses the stream specifications to calculate the outlet stream conditions.

2. Click one of the following radio buttons to calculate the Overhead and Bottoms stream pressures: o

Use Stream Pressure Specifications – You must supply the pressure for each of the outlet streams.

o

Equalize All Stream Pressures – HYSYS gives all the attached streams the same pressure after one of the attached streams is known.

o

Use Lowest Feed Pressure for All Products – HYSYS assigns the lowest inlet pressure to the outlet stream pressure. All but one outlet stream pressure must be known.

To avoid consistency errors, remember to delete relevant specifications when choosing your Component Splitter parameters.

Splits Page The Splits page lets you specify the separation fraction of the outlet streams. The Splits, or separation fractions ranging from 0 to 1, must be specified for each component in the overhead stream exiting the Component Splitter. For each component you can set the Basis (Mass or Molar) and Fraction Type to Feed Fraction in Products, Fraction in Products or Flow in Products. (See next heading.) You can also set the Bottom Stream fraction value. To solve, the feed component flows must be known. There can only be one unknown split fraction per component. The Splitter does forward calculation only. For backward calculation, use a Mixer instead. The two buttons on the Splits page, Set to 1 and Set to 0, let you specify overhead fractions of one (100%) or zero (0%), respectively, for all components. These buttons are useful if many components are leaving entirely in either the overhead stream or bottoms stream. For example, if the majority of your components are going overhead, simply click Set to 1, rather than repeatedly entering fractions of 1. Then, correct the splits appropriately for the components not leaving entirely in the overhead.

Split Fractions Type Calculations As stated above, using the Splits page on the Design tab, you can define the split fractions type for each component. Calculations are made according to the following formulas for each type: For the FeedFrac to Products option, the molar flows going to the overhead and bottoms are calculated as: (1) (2)

57 Component Splitter

1063

Where: xi = FeedFrac to Products, or fraction of component i going to each overhead Once the composition, vapor fraction, and pressure of the outlet streams are know, a P-VF flash is performed to obtain the temperatures and heat flows. For the Fraction to Products option, the molar flows going to the overhead and bottoms are calculated as: (3) Where: xi= "Fraction in Products", fraction of the ith component in each overhead, Σ xi=1 yi=" Fraction in Products", fraction of component in bottom, Σ yi=1 a = molar flow of the overhead b = molar flow of the bottom For the Flow in Products option, the following applies: ai = "Flow in Products," molar flow of the ith component in each overhead bi = "Flow in Products," molar flow of the ith component in the bottom An overall heat balance is performed to obtain the energy stream heat flow: (4) Where: hE = enthalpy of unknown energy stream hF = enthalpy of feed stream hO = enthalpy of overhead stream hB = enthalpy of bottoms stream

TBP Cut Point Page The TBP Cut Point page lets you specify the compositions of the product streams by providing the TBP Cut Point between the streams, and assuming that there is sharp separation at the cut point. You can specify a temperature cut point of 0 K and higher. On the TBP Cut Point page, the upper table lets you specify the initial TBP Cut Point on the Feed for each product stream except for the overhead. The Initial Cut Point values are expressed in temperature and they are listed in ascending order. Consecutive streams can have the same Initial Cut Point value, implying that the second or subsequent stream has zero flow. Note: The TBP Cut Point page is designed for streams with hypothetical components.

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57 Component Splitter

The bottom table lets you specify the split fraction for each component in the stream. The split fraction values are also available on the Splits page of the Design tab. Pure components are distributed according to their NBP (Natural Boiling Point) while the TBP (True Boiling Point) of the pure components defines the boundaries of distribution. The NBP for each component is displayed in the NBP table for reference. The TBP Cut Point page is designed for handling streams that carry hypocomponents. The hypocomponents are treated as a continuum and they are distributed according to their FBP (Final Boiling Point). The FBP of each hypocomponent is first calculated by sorting the NBP of the hypocomponents in ascending order. Then with the sorted order, the FBP of the last hypocomponent is calculated as follows: (1) The FBPs for other hypocomponents is calculated by: (2) The hypocomponents are then distributed according to where the cut point lies. The boiling range for each hypocomponent is defined by the FBP of the previous component to the FBP of the current component. The boiling range for each product stream is from its Initial TBP Cut Point to the Initial TBP Cut Point of the next stream.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Rating Tab You cannot provide any information for the Component Splitter on the Rating tab when in steady state.

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1065

Nozzles Page The Nozzles page usually contains information regarding the elevation and diameter of the nozzles. For this unit they are not shown as this operation usually models a large plant where it makes less sense and accounting for internal elevations differences is not simple, Streams commonly have the pressure specifications.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the operation. Note: The PF Specs page is relevant to dynamics cases only.

Dynamics Tab Information available on this page is relevant only to cases in Dynamic mode. The Dynamics tab consists of the Specs page.

Specs Page The Specs page contains information regarding pressure specifications of the streams. The Equal Pressures check box lets you propagate the pressure from one stream to all others. If you want to equalize the pressures you have to free up the pressure specs on the streams that you want the pressure to be propagated to. The Vessel Volume is also specified on this page. This volume is only used to affect the compositional affects in this operation. The Pressure - Flow and hydraulics are not affected by this value. This volume is only a simplified and synthetic way of getting some lag in the compositional affects. The thermal state (temperature and enthalpy) of the outlet streams may or may not be affected by this value depending on the other specifications of this operation. For example, if you have specified the outlet stream temperatures directly, then this volume has no effect, on the other hand if the operation is doing some flash with an external duty (of value zero or otherwise), then this volume has an effect.

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57 Component Splitter

58 Separator, 3-Phase Separator, and Tank

The property views for the Separator, 3-Phase Separator, and Tank are similar, therefore, the three unit operations are discussed together in this section. All information in this section applies to the Separator, the 3-Phase Separator, and the Tank operation, unless indicated otherwise. There is an Operation Type toggle option on the Parameters page of the Design tab that allows you to easily switch from one of these operations to another. For example, you may want to change a fully defined Separator to a 3-Phase Separator. Simply, select the appropriate radio button in the Operation Type toggle option. The only additional information required would be to identify the additional liquid stream. All of the original characteristics of the operation (Parameters, Reactions, and so forth) are retained. The key differences in the three separator operations are the stream connections (related to the feed separation), which are described in the table below. Unit Operation

Description

Separator

Multiple feeds, one vapor and one liquid product stream. In Steady State mode, the Separator divides the vessel contents into its constituent vapor and liquid phases.

3-Phase Separator

Multiple feeds, one vapor and two liquid product streams. The 3-Phase Separator operation divides the vessel contents into its constituent vapor, light liquid, and heavy liquid phases.

Tank

Multiple feeds, one liquid and one vapor product stream. The Tank is generally used to simulate liquid surge vessels.

In Dynamic mode, the following unit operations all use the holdup model and therefore, have many of the same properties. Vessel operations in HYSYS have the ability to store a significant amount of holdup. The key differences in the vessel operations are outlined in the table below.

58 Separator,

3-Phase Separator, and Tank

1067

Unit Operation

Description

Separator

The Separator can have multiple feeds. There are two product nozzles:

3-Phase Separator

l

liquid

l

vapor

The 3-Phase Separator can have multiple feeds. There are 3 product nozzles: l

light liquid

l

heavy liquid

l

vapor

Tank

The Tank can have multiple feeds. There are two product nozzles which normally removes liquid and vapor from the Tank.

Condenser

The condenser has one vapor inlet stream. The number and phase of each exit stream depends on the type of condenser. The condenser has a unique method of calculating the duty applied to its holdup.

Reboiler

The reboiler has one liquid inlet stream. The reboiler can have a number of liquid and vapor exit streams.

Reactors

Reactor operations can have multiple inlet and exit streams.

Heat Exchanger (Simple Rating Model, Detailed)

A shell or tube with a single pass in the heat exchanger unit operation can be modeled with a liquid level. Both the shell and tube sides of the heat exchanger have one inlet and one exit stream.

Every dynamic vessel operation in HYSYS has some common features including: l

l

l

l

The geometry of the vessel and the placement and diameter of the attached feed and product nozzles have physical meaning. A heat loss model which accounts for the convective and conductive heat transfer that occurs across the vessel wall. Various initialization modes which allow you to initialize the vessel at user-specified holdup conditions before running the integrator. Various Heater types which determine the way in which heat is transferred to the vessel operation.

Theory A P-H flash is performed to determine the product conditions and phases. The pressure at which the flash is performed is the lowest feed pressure minus the

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58 Separator,

3-Phase Separator, and Tank

pressure drop across the vessel. The enthalpy is the combined feed enthalpy plus or minus the duty (for heating, the duty is added; for cooling, the duty is subtracted). As well as standard forward applications, the Separator and 3-Phase Separator have the ability to back-calculate results. In addition to the standard application (completely defined feed stream(s) being separated at the vessel pressure and enthalpy), the Separator can also use a known product composition to determine the composition(s) of the other product stream(s), and by a balance the feed composition. In order to back-calculate with the Separator, the following information must be specified: l

One product composition.

l

The temperature or pressure of a product stream.

l

Two (2-phase Separators) or three (3-phase Separators) flows

Note: If you are using multiple feed streams, only one feed stream can have an unknown composition in order for HYSYS to back-calculate.

Energy Balance In Steady State mode Separator energy balance is defined below: (1) where: Hfeed = heat flow of the feed stream(s) Hvapor = heat flow of the vapor product stream Hlight = heat flow of the light liquid product stream Hheavy = heat flow of the heavy liquid product stream

Physical Parameters The Physical Parameters associated with this operation are the pressure drop across the vessel and the vessel volume. Note: The default pressure drop across the vessel is zero.

The pressure drop across the vessel is defined as: (1) where: P = vessel pressure Pv = pressure of vapor product stream

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Pl = pressure of liquid product stream(s) Pfeed = pressure of feed stream - the pressure is assumed to be the lowest pressure of all the feed streams ΔP = pressure drop in vessel Phead = pressure of the static head The vessel volume, together with the set point for liquid level/flow, defines the amount of holdup in the vessel. The amount of liquid volume, or holdup, in the vessel at any time is given by the following expression: (2) where: PV(%Full) = liquid level in the vessel at time t Note: The Vessel Volume is necessary in steady state when modeling a Reactor (CSTR), as it determines the residence time.

Ideal vs. Real

In ideal separators, complete/perfect separation between the gas and liquid phases is assumed. In real world separators, separation is not perfect: liquid can become entrained in the gas phase and each liquid phase may include entrained gas or entrained droplets of the other liquid phase. Recent years have seen increasing use of vessel internals (for example, mesh pads, vane packs, weirs) to reduce the carry over of entrained liquids or gases. By default the HYSYS separators are ideal separators, however, you can modify the separators to model imperfect separation by using the HYSYS Real Separator capabilities. The real separator offers you a number of advantages: l

l

Carry Over options so that your model matches your process mass balance or separator design specifications. Options to predict the effect of feed phase dispersion, feed conditions, vessel geometry, and inlet / exit devices on carry over.

Refer to Rating Tab for information on the options used to configure a real separator.

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Separator Ops General Property Views Design Tab The Design tab contains options for configuring the separator operation.

Connections Page The Connections page allows you to specify the streams flowing into and out of the separator operation, the name of the separator operation, and the fluid package associated to the separator operation. Note: Any of the HYSYS separator operations accept multiple feed streams, as well as an optional energy stream.

Depending on the type of heat transfer you want to make available for the separator operation, the options available in the Connections page varies. You are required, however, to always specify the following variables: l

Name of the separator operation

l

Name of the feed streams

l

Name of the vapor product stream

l

Name of the liquid product stream(s)

l

Name of the fluid package of the separator operation

Parameters Page The Parameters page lets you specify the pressure drop across the vessel. The following table lists and describes the options available in this page:

58 Separator,

Object

Description

Inlet cell

Allows you to specify the pressure difference across the vessel.

Vapor outlet cell

Allows you to specify the static head pressure of the vessel.

Volume Field

Allows you to specify the volume of the vessel. The default vessel volume is 2 m3.

Liquid Volume Display Field

Not set by the user. The Liquid Volume is calculated from the product of the Vessel Volume and Liquid Level fraction.

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Object

Description

Liquid Level SP Field

Allows you to specify the starting point of the liquid level in the vessel. This value is expressed as a percentage of the Full (Vessel) Volume.

Type Group

Allows you to toggle between the Separator, 3-Phase Separator, and Tank by clicking the appropriate radio button.

Notes: l

The Liquid Volume is calculated from the product of the Vessel Volume and Liquid Level fraction.

l

The Separator, 3 Phase Sep, and Tank radio buttons in the Type group allow you to change the type of vessel without having to add a new unit operation.

l

If you toggle from a 3 Phase Separator operation to a Separator or Tank operation, you permanently lose the heavy liquid stream connection. If you change back to the 3 Phase Separator, you have to reconnect the heavy liquid stream.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation. Note: If you select an alternate unit, your value appears in the face plate using HYSYS display units.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Reactions Tab The Reactions tab contains options for applying chemical reactions that can take place in the vessel.

Results Page The Results page allows you to attach a reaction set to the Separator, 3-Phase Separator, or Tank Operations. In the Reaction Set drop-down list, select the reaction set you want to use. Reaction and component information can also be examined in the Reaction Results group. Select the Reaction Balance radio button to view the total

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inflow, total reaction, and total outflow for all of the components in the reaction. Select the Reaction Extents radio button to view the Percent Conversion, Base Component, Equilibrium Constant, and Reaction Extent. You can also view information for specific reactions by clicking the View Global Rxn button. Tips: l

Click the View Global Rxn button to open the reaction's property view. By default, the property view from the first reaction defined in the reaction set appears.

l

To open another reaction’s property view, click the Reaction Extents radio button, select the reaction you want to view from the list of available reactions, and then click the View Global Rxn button.

l

Select the Ignore Reactions when unable to Solve check box if you want HYSYS to ignore the reactions if the solver cannot solve the separator.

Rating Tab The Rating tab includes options relevant in both Steady State and Dynamics modes. The options available are: l

Configuring and calculating the separator’s vessel size.

l

Specifying and calculating heat loss.

l

Configuring level taps to observe relative levels of different liquid phases.

l

Specifying the PV work term contribution.

l

Configuring and calculating the Carry Over model.

You must provide the following information for the separator operation when working in Dynamics mode: l

vessel geometry

l

nozzle geometry

l

heat loss

Sizing Page You can define the geometry of the unit operation on the Sizing page. Also, you can indicate whether or not the unit operation has a boot associated with it. If it does, then you can specify the boot dimensions. After you specify the vessel’s shape and orientation information in the appropriate field, click the Quick Size button to initiate the HYSYS sizing calculation for the vessel.

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Vessel Geometry In the Geometry group, you can specify the vessel orientation, shape, and volume. The geometry of the vessel is important in determining the liquid height in the vessel. There are four possible vessel shapes as described in the table below. Vessel Shape

Description

Flat Cylinder

A cylindrical shape vessel that is available for either horizontal or vertical oriented vessel. You can either specify the total volume or any two of the following for the vessel: l

total volume

l

diameter

l

height (length)

If only the total cylindrical volume of the vessel is specified, the height to diameter ratio is defaulted as 3:2. Sphere

A sphere shape vessel that is available for either horizontal or vertical oriented vessel. You can either specify the total volume or the diameter of the sphere.

Ellipsoidal Cylinder

An ellipsoidal cylindrical shape vessel that is only available for horizontal oriented vessel. You can either specify the total volume or any three of the following for the vessel: l

total volume

l

diameter

l

length

l

ellipsoidal head height

If only the total cylindrical volume of the vessel is specified, the height to diameter ratio is defaulted as 3:2. If the diameter or length is already specified, the only other variable that can be specified is the Ellipsoidal Head Height. Hemispherical Cylinder

A hemispherical cylindrical shape vessel that is only available for horizontal oriented vessel. You can either specify the total volume or any two of the following for the vessel: l

total volume

l

diameter

l

length

If only the total cylindrical volume of the vessel is specified, the height to diameter ratio is defaulted as 3:2.

The liquid height in a vertical cylindrical vessel varies linearly with the liquid volume. There is a nonlinear relationship between the liquid height, and the liquid volume in horizontal cylindrical and spherical vessels.

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Weir A weir can be specified for the horizontal flat cylinder separator by selecting the Enable Weir check box and clicking the Weir button. The Initial Holdup property view appears. Note: The Enable Weir check box is only available for Flat Cylinder vessel shape option.

The Initial Holdup property view allows you to specify the weir height and position. The weir position is the distance the weir is from the vessel feed side. HYSYS calculates the Levels and Phase Moles in each chamber using the specified values for the weir height and position. When HYSYS simulates, the weir has two volumes inside the Separator, called chamber 1 and chamber 2; but there is still only one enhanced holdup volume and moles as far as the pressure flow solver is concerned. This means that the compositions and properties of the phases in the two volumes are the same.

Boot Geometry Any vessel operation can be specified with a boot. A boot is typically added when two liquid phases are present in the holdup. Normally, the heavy liquid exits from the boot exit nozzle. The lighter liquid can exit from another exit nozzle attached to the vessel itself. In HYSYS, a boot can be added to the vessel geometry by selecting the This Separator has a Boot check box. The boot height is defaulted to one third the vessel height. The boot diameter is defaulted to one third the vessel diameter.

Nozzles Page The Nozzles page contains information regarding the elevation and diameter of the nozzles. Note: The HYSYS Dynamics license is required to use the Nozzle features found on the Nozzles page.

Unlike steady state vessel operations, the placement of feed and product nozzles on a dynamic vessel operation has physical meaning. The composition

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of the exit stream depends on the exit stream nozzle location and diameter in relation to the physical holdup level in the vessel. l

l

l

If the product nozzle is located below the liquid level in the vessel, the exit stream draws material from the liquid holdup. If the product nozzle is located above the liquid level, the exit stream draws material from the vapor holdup. If the liquid level sits across a nozzle, the mole fraction of liquid in the product stream varies linearly with how far up the liquid is in the nozzle.

Essentially, all vessel operations in HYSYS are treated the same. The compositions and phase fractions of each product stream depend solely on the relative levels of each phase in the holdup and the placement of the product nozzles. So, a vapor product nozzle does not necessarily produce pure vapor. A 3-Phase Separator may not produce two distinct liquid phase products from its product nozzles.

Heat Loss Page The Heat Loss page contains heat loss parameters which characterize the amount of heat lost across the vessel wall. In the Heat Loss Model group, you can select one of the radio buttons to use as a model: l

l

l

Simple: Allows you to either specify the heat loss directly or have it calculated from specified values Detailed: Allows you to specify a more detailed set of heat loss parameters None: No heat loss through the vessel walls.

The Simple and Detailed heat loss models are discussed in the following sections.

Simple Model The Heat Transfer Area is the cylindrical area of the vessel with no allowance for head area. This value is calculated using the vessel dimensions specified on the Rating tab | Sizing page. Using the Simple Heat Loss Model, heat loss from the vessel is calculated using the following formula. The heat transfer area, A, and the fluid temperature, Tfluid, are calculated by HYSYS. (1) Where: U = Overall heat transfer coefficient A = Heat transfer area

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Tambient = Ambient temperature Note: The duty calculated can be applied to the vessel wall or directly to the fluid. The former would be used to model a fire and the latter to model a heater.

The Heat flow is calculated as follows: (2) where: U = overall heat transfer coefficient A = heat transfer area TAmb = ambient temperature T = holdup temperature As shown, Heat flow is defined as the heat flowing into the vessel. The heat transfer area is calculated from the vessel geometry. The Ambient Temperature, TAmb, and overall heat transfer coefficient, Overall U, can be modified from their default values.

Detailed Model The Detailed model allows you to specify more detailed heat transfer parameters. It considers heat transfer through natural convection between the vessel fluid and the wall, conduction through the wall and the insulation, and natural convection from the insulation to the environment. The HYSYS Dynamics license is required to use the Detailed Heat Loss model on the Heat Loss page. There are three portions of the model that you must set up. l

Temperature Profile

l

Conduction

l

Convection

The radio buttons switch the view to allow you to configure these options. Note: The total area in the Detailed model consists of the cylindrical area and the head areas (flat or non-flat). During a fire case, the vessel is covered with flame. In this case, heat loss to the surrounding atmosphere determined by taking a normal atmospheric temperature is generally not correct, since the vessel surrounding temperature is very high. Using the detailed heat loss model to the environment assumes natural convection, which is an invalid assumption for a fire case scenario. You should not use the detailed heat loss model for a fire case.

Temperature Profile Option When you select the Temperature Profile radio button, you can set the ambient temperature per segment. This can be added directly to the holdup or applied on the outside wall in the form of an energy stream.

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Conduction Option The Conduction section lets you manipulate the conductive properties of the wall and insulation. To model a vessel without insulation, the insulation value thickness should be zero. You are also required to enter the specific heat capacity of the materials, the density of the materials, and their conductivity. Default values are provided by HYSYS. The metal wall thickness must always have a finite value (that is, it cannot be ). Some typical values for metals are: Metal

Density kg/m 3

Specific Heat kJ/kg K

Thermal Conductivity W/m K

Mild Steel

7860

0.420

63

Stainless steel

7930

0.510

150

Aluminum

2710

0.913

201

Titanium

4540

0.523

23

Copper

8930

0.385

385

Brass

8500

0.370

110

Convection Option The Convection section lets you directly manipulate the heat transfer coefficients for the inside and the outside of the vessel, as well as between vapor and liquid material inside the vessel. If these values are unknown, click the Estimate Coefficients Using Current Conditions button so HYSYS can determine them. HYSYS computes heat transfer coefficients for the vessel outer wall to outside air, vessel contents to inner wall, and vapor to liquid inside the vessel. These coefficients are computed according to Holman [1] and will be used in the detailed heat loss mathematical model. You can either use these defaults or edit the values. The values are used as follows: l

l

1078

Outside Heat Loss U: These parameters go directly into Equations (5) or (6), depending on the value of Grf × Prf. Notice that these C value is the same regardless of the vessel orientation. Inside Vap Phase Heat Loss U, Inside Liq Phase Heat Loss U, and Vapor to Liquid Heat Loss U: Equations (8) and (7) are used. Since the C and m values are independent of the vessel orientation, we have plotted Eq. (8) below.

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Above: Nusselt correlation assuming default values

When the Update while Integrating check box is selected, HYSYS updates the heat transfer coefficients while the Integrator is running. During Dynamics simulations, the heat transfer coefficient values will slowly change depending on the in/out temperatures. When this check box is cleared, HYSYS assumes a constant heat transfer coefficient.

Auto Selected Correlations between the External Vessel Wall and the Ambient The assumed external ambient is air at atmospheric pressure and zero speed. In HYSYS, we begin by computing the Prandlt and Grashof numbers for the air

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at the film temperature Tf, which is the average between the outer wall temperature and the ambient temperature: (3)

(4)

where: : heat capacity cp v : viscosity

J/kg-K

κ : thermal conductivity

W/m-K

g

: 9.8

kg/m-s m/s2

: thermal expansion coefficient K-1 β ∆T : temperature difference K X : vessel orientation dependent m ρ

: mass density

kg/m3

The characteristic length X depends on the vessel orientation: it is the vessel axial length, for the vertical vessel case, or the vessel diameter, for horizontal vessels. From here, the product Grf × Prf determines the type of natural convection regime. For values of Grf × Prf lower than 109, we are in laminar regime and: (5)

with C : vessel orientation dependent kW/m2-K m :¼ ∆T : temperature difference

K

X : vessel orientation dependent m

The constant C equals 1.42 x10-3 for vertical vessels and 1.32 x10-3 for horizontal vessels. For values of Grf x Prf higher than 109, we are in turbulent regime, so: (6) with C : vessel orientation dependent kW/m2-K m :⅓ ∆T : temperature difference

1080

K

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where: C equals 1.31 x10-3 for vertical vessels and 1.24 x10-3 for horizontal vessels.

Auto Selected Correlations for the Inner Vessel Wall and the Vessel Contents The heat transfer coefficient for each phase inside the vessel towards the portion of the inner vessel wall in contact with that particular phase is calculated by means of the Nusselt number Nuf which, in turn, depends on the vessel orientation and the fluid conditions, since it is a function of the corresponding Grf × Prf. The way Nuf is correlated to this product is described in detail in Holman’s book and depicted in the curves below. Once the Nuf is available, the heat transfer coefficient is obtained from: (7) with κ : fluid thermal conductivity

W/m-K

X : vessel orientation dependent m

Auto Selected Correlations for Heat Transfer from Vapor to Liquid in Vessel In situations where the phase temperatures are different, the following formula: (8) is used in combination with equation (5) for C = 0.16 and m = ⅓. The reference phase is the vapor phase, so equations (1), (2), and (5) are at the vapor phase conditions. One way the phases can exhibit different temperatures –or set into non-equilibrium conditions– is by adjusting the recycle efficiencies of the vessel.

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Above: Nusselt number correlated to the product Grashof times Prandlt numbers References [1] Holman, J.P.: “Heat Transfer”, 3rd ed. McGraw-Hill Book Company, New York, 1972.

Level Taps Page Since the contents in a vessel can be distributed in different phases, the Level Taps page allows you to monitor the level of liquid and aqueous contents

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that coexist within a specified zone in a tank or separator. The information available on this page is relevant only to dynamics cases. You can also define Level Taps for the lowest stage of a distillation column, as long as it is a Sump type. In the column subflowsheet, column property view, use the rating tab, level taps page.

Level Taps Specifications (Dynamics) The Level Tap Specifications (Dynamics) group allows you to specify the boundaries to be monitored within the vessel, and to normalize that section in a desired scale. A level tap can be specified for any horizontal or vertical vessel by clicking the New Level Tap button. Note: You can add/configure multiple level taps.

To set the boundaries of the section concerned, specify the following fields: Field

Description

Level Tap

Name of the level tap.

PV High (m)

Upper limit of the section to be monitored. It is expressed in meters.

PV Low (m)

Lower limit of the section to be monitored. It is expressed in meters.

OP High

Upper limit of the output of the normalization scale.

OP Low

Lower limit of the output of the normalization scale.

The normalization scale can be negative values. In some cases, the output normalization scale is manually set between -7% to 100% or -15%-100% so that there is a cushion range before the level of the content becomes unacceptable (in other words, too low or too high). By default, a new level tap is set to the total height of the vessel, and the height is normalized in percentage (100-0). All the upper limit specifications should not be smaller than or equal to the lower limit specifications and vice versa; otherwise no calculations will be performed.

Calculated Level Taps Values (Dynamics) The level of liquid and aqueous are displayed in terms of the output normalization scale you specified. Whenever the level of a content exceeds PV High, HYSYS automatically outputs the OP High value as the level of that content. If the level is below the PV Low, HYSYS outputs the OP Low value. The levels displayed are always entrained within the normalized zone.

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Option Page The Options page allows you to specify and enable the PV Work Term Contribution. The PV Work Term Contribution is expressed in percent. It is approximately the isentropic efficiency. A high PV work term contribution value results in lower pressures, and temperatures. The PV work term contribution value should be between 87% to 98%.

C.Over Setup Page The C.Over Setup page allows you to modify the separator operation from an ideal model to a real model. To achieve a real model separator, the C. Over Setup page enables you to configure the carry over effect in real separator operations. Carry over refers to the conditions when the liquid gets entrained in the vapor phase and/or when the gas gets entrained in the liquid phase. The effect is mainly caused by the disturbances created as the inlet stream enters the vessel. In HYSYS, the carry over effect is modeled using the entrainment fraction in the feed or product stream, or using the available correlations that calculate carry over based on the vessel configuration. On the C. Over Setup page, you can select the type of carry over calculation model by clicking one of the following four radio buttons: l

None (indicates that there is currently no carry over model applied to the associated vessel).

l

Feed Basis

l

Product Basis

l

Correlation Based

There are two check boxes available at the bottom of the page: l

l

Carry Over to Zero Flow Streams. When you select this check box, the calculated carry over will be added to the product stream even if it has no flow. Use PH Flash for Product Streams. When you select this check box, you apply a PH flash calculation to the product streams. This option is slower but it may be required to eliminate inconsistencies when one product flow is much less than the others.

These two check boxes are available in the Feed Basis, Product Basis, and Correlation Based models. The Feed Basis, Product Basis, and Correlation Based models are discussed in the following sections.

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Feed Basis Model The Feed Basis Model allows you to specify the entrainment of each phase in each product as a fraction of the feed flow of the phase. There are six types of carry over flow (in the feed and product streams) available for you to specify: l

Light liquid in gas

l

Heavy liquid in gas

l

Gas in light liquid

l

Heavy liquid in light liquid

l

Gas in heavy liquid

l

Light liquid in heavy liquid Note: The terms light liquid and heavy liquid refer to oil and water, respectively. No assumptions are made as to the actual composition of the two liquid phases.

The fractions containing non-zero values indicates the product streams exiting the separator will have multiple liquid and gas phases. For example, if you specify Fraction of Feed as 0.1 for light liquid in gas, this means that 10 mol% of the light liquid phase in the feed will be carried over into the gas product leaving the separator. As a result the gas product vapor fraction will be less than 1.0 and contain a liquid phase.

Product Basis Model The Product Basis model allows you to specify the carry over entrainment in the product streams on fraction or flow basis. You can select the desired basis by clicking on one of the following radio buttons in the Specification By group: l

l

Fraction. Allows you to specify the entrainment in the product stream as a fraction. The fraction basis is selected from the Basis drop-down list and may be either Mole, Mass, Liq. Volume or Actual Volume. Flow. Allows you to specify the entrainment in the product streams as a flow. The flow basis may be specified using the Flow Basis drop-down list. The options are Mole, Mass, Liq. Volume or Actual volume.

There are six types of carry over flow (in the feed and product streams) available for you to specify:

58 Separator,

l

Light liquid in gas

l

Heavy liquid in gas

l

Gas in light liquid

l

Heavy liquid in light liquid

l

Gas in heavy liquid

l

Light liquid in heavy liquid

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The terms light liquid and heavy liquid refer to oil and water, respectively. No assumptions are made as to the actual composition of the two liquid phases. For example, if you specify Frac in Product (Mole Basis) as 0.1 for the light liquid in gas, this means that the gas product will contain 10 mol% light liquid. In Steady State mode, if a phase is missing from the feed stream, selecting the Use 0.0 as product spec if phase feed flow is zero allows the separator to continue to calculate the carry over effect (in this example, carry over model calculation ignores any product fraction or flow specification for that phase). In Dynamics mode, the Use 0.0 as product spec if phase feed flow is zero feature is automatically and always active.

Correlation Based Model The Correlation Based model allows you to calculate the expected carry over based on the configuration of the vessel, the feed conditions, and the operating conditions. The options available in the Correlation Based model allows you to configure the type of the correlation, dimensions and geometry of vessel, pressure drop methods, and nozzle location.

Correlation Setup The Correlation Setup group allows you to select the Correlation Calculation Type, and how you want to apply the correlation. l

l

You can apply one correlation for all of the carry over calculations by clicking on the Overall Correlation radio button. If you want to select a different correlation for each carry over calculation steps (Inlet Device, Gas/Liq Separation, Liq/Liq Separation, and Vapor Exit Device), you can select the Sub Calculations radio button to activate the appropriate options.

A schematic of these steps is shown in the figure below:

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Only those parts of the correlation in use that apply to the particular sub-calculation will be used. For example, if the Generic correlation is used for the Inlet device and ProSeparator is used for primary L-L and G-L separation calculations, then the user supplied data for the generic inlet calculations (in other words, inlet split and Rossin Rammler parameters) will be used to generate the inlet droplet dispersion. The ProSeparation primary separation calculations will then be performed using this inlet dispersion. As ProSeparator correlations will not be used to calculate the inlet conditions, any ProSeparator inlet setup data is ignored. Likewise, any critical droplet sizes entered in the Generic correlation will be ignored as the ProSeparator is being used for the primary separation calculations. There are three correlations available: Generic, Horizontal Vessel, and ProSeparator. After you have selected the type of correlation, you can click on the View Correlation button to view its calculation parameters.

Generic The Generic correlation provides a general correlation for generating the phase dispersions in the feed and defining the separation criteria. It is a generic calculation that is independent of the vessel dimensions, geometry, and operating levels. l

l

58 Separator,

For the Inlet Calculations, you must define the percentage of each feed phase dispersed in each other phase. You must also define the maximum droplet sizes and Rosin Rammler index for each dispersion. The dispersions are then calculated using Rosin Rammler methods to give the amount of each phase in each droplet size range. For the rest of the carry over calculation, all droplets smaller than a

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user-specified critical droplet size are assumed to be carried over. l

The Generic correlation can be used for gas-liquid, liquid-liquid, and gas exit separation calculations. You must define the critical droplet size for each type of separation. Any droplets that are smaller than the specified critical droplet size will be carried over; the droplets that are larger than the critical droplet size will be separated.

Horizontal Vessel

1 2 3

The Horizontal Vessel correlations were developed for a horizontal three-phase separator. For the Inlet Calculations, the correlations calculate the six types of dispersions in the feed according to an assumed efficiency of a user-defined inlet device, and user-defined dispersion fractions (termed Inlet Hold up; these parameters are found on the General page in the Setup tab of the Horizontal Vessel Correlation property view). The droplet distribution of the dispersed phase (s) is then calculated using user-supplied Rosin-Rammler parameters just as for the Generic correlation. Note: The droplet d95 of the liquid-liquid dispersions (in other words, heavy liquid in light liquid and light liquid in heavy liquid) is not specified but calculated using the inlet droplet d95 and the densities of the 2 liquid phases.

The Primary Gas-Liquid Separation is calculated from the settling velocities for each liquid (light and heavy) droplet size in the gas phase and the residence time for the gas in the vessel. A droplet is carried over if the vertical distance traveled during its residence in the vessel is less than the vertical distance required to rejoin its bulk phase. The Primary Liquid-Liquid Separation is also calculated using settling velocities for each droplet of liquid or gas in the liquid phases and residence time for each liquid phase. The settling velocities are calculated using the GPSA correlations for all dispersions, except for the water in oil dispersion for which the settling velocity is calculated by the method of Barnea and Mizrahi. A user defined liquid phase inversion point is used in the calculation of the appropriate liquid phase viscosities (in other words, water-in-oil and oil-in-water). A residence time correction factor can also be applied. A droplet is carried over if the vertical distance traveled during its residence in the vessel is less than the vertical distance required to rejoin its bulk phase. The Secondary Separation calculations for the gas phase are defined by a userdefined critical droplet size. The gas loading factor for each device is used to calculate the size of the exit device. 4

ProSeparator

The ProSeparator correlations are rigorous but are limited to calculating liquid carry over into gas. There are no calculations of liquid-liquid separation or gas entrainment in the liquid phases (they are set to zero). Light liquid and heavy

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liquid entrainments are calculated separately and the total carry over is the sum of the separate light and heavy liquid carry over calculations. For Inlet Calculations, minimum and maximum droplet diameter are calculated based on inlet flow conditions (inlet gas flow rate and gas-liquid phase physical properties) and inlet pipe size. The droplet distribution of light and heavy liquids in the inlet gas is then calculated using a Rosin-Rammler type distribution. Note: ProSeparator effectively calculates its own Rossin Rammler parameters5 (droplet diameters) and does not require the user to specify these parameters. The only user input in the inlet calculations is the ability to limit the amount of phase dispersion calculated.

Primary Gas-Liquid Separation is based on critical droplet size; however, the critical droplet size is not user-specified but calculated using gas velocity through the vessel. Secondary Gas-Liquid Separation accomplished using exit devices (for example, demisting pad) are calculated by device specific correlations. The user can choose from vane pack or mesh pad devices. There are 2 different calculation methods available for each type of device.

Dimensions Setup The Dimensions Setup group allows you to set the orientation, and the geometry of the vessel. You can also set the operating levels for the light and heavy liquid in the vessel. You have the option to model the horizontal vessel with weir or a boot by selecting the Has Weir check box and Has Boot check box, respectively.

DP/Nozzle Setup The Pressure Drop/Nozzle Setup group allows you to model the method of DP (pressure drop), and the geometry of the nozzles. Since the dynamic pressure and the pressure drop of the feed stream and vessel are specified in the Specs page of the Dynamics tab, the Pressure Drop table is not available when the separator is operating in dynamics mode.

In the Pressure Drop table, after you have selected a DP method from the dropdown list, you can activate the Inlet Device DP Method, and the Vapor Exit DP Method by selecting the Active check box. You can click on the View Method button to view the parameters of the DP method you have selected. In the Nozzle Diameter/Location table, you can set the diameter, height, and location for all the streams connected to the vessel. If a Correlation Based carry over model is selected: l

58 Separator,

The options on the DP / Nozzles Setup page can be used to calculate the inlet and exit nozzle pressure drop.

3-Phase Separator, and Tank

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l

The user-specified pressure drops on the Parameters page of the Design tab can be used instead.

C. Over Results Page The C. Over Results page allows you to view the carry over results in the feed, and product streams based on what you specified in the C. Over Setup page. There are four columns of data in the Carry Over Results table: l

Frac. of Feed

l

Frac. in Product

l

Product Flow

l

Prod. Mass/Vol

The C. Over Results page information is also available in Dynamic mode. The units for Frac. of Feed, and Prod. Mass/Vol are set by default. You can change the unit for the Frac. in Product and Product Flow column by selecting one of the four units from the Product Basis drop-down list (Mole, Mass, Liq. Volume, and Actual Volume).

View Dispersion Results Property View You can view the carry over dispersion results by clicking on the View Dispersion Results button. The Carry Over Dispersion Results property view has two tabs: l

l

Table. Displays the dispersion results for a single phase at a given point in the vessel. The radio buttons allow you to select the results of the corresponding phase. You can select the unit to be displayed from the Dispersion Basis drop-down list. Plot. Provides a graphically interpretation of the dispersed quantity against the droplet size for a single dispersion. The Select Plot check boxes allow you to select one or more dispersions to be plotted. You can select the dispersion basis from the Dispersion Basis drop-down list.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the operation. Note: The PF Specs page is relevant to dynamics cases only.

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58 Separator,

3-Phase Separator, and Tank

Most of the options available on this tab is relevant only to cases in Dynamics mode. There is one exception: the Heat Exchanger Page allows you to specify whether or not the separator operation contains an energy stream used to heat or cool the vessel.

Specs Page The Specs page contains information regarding initialization modes, vessel geometry, and vessel dynamic specifications.

Model Details You can determine the composition and amount of each phase in the vessel holdup by specifying different initialization modes. HYSYS forces the simulation case to re-initialize whenever the initialization mode is changed. The radio buttons in the Model Details group are briefly described in the table below. Initialization Mode

Description

Initialize from Products

The composition of the holdup is calculated from a weighted average of all products exiting the holdup. A PT flash is performed to determine other holdup conditions. The liquid level is set to the value indicated in the Liq Volume Percent field.

Dry Startup

The composition of the holdup is calculated from a weighted average of all feeds entering the holdup. A PT flash is performed to determine other holdup conditions. The liquid level in the Liq Volume Percent field is set to zero.

Initialize from User

The composition of the liquid holdup in the vessel is user specified. The molar composition of the liquid holdup can be specified by clicking the Init Holdup button. The liquid level is set to the value indicated in the Liq Volume Percent field.

l

l

Select the Lag Rxn Temperature check box if you want HYSYS to assume no temperature lag for reactions. Click the Add/Configure Level Controller button to quickly add a level controller to the vessel.

In the Model Details group, you can specify the vessel geometry parameters: l

Vessel Volume

l

Vessel Diameter

l

Vessel Height (Length)

l

l

58 Separator,

Liq Volume Percent: You can modify the level in the vessel at any time. HYSYS then uses that level as an initial value when the integrator is run. Liq Percent Level: Specify the level of the liquid as a percentage of the full vessel volume. The default value is 50.0%.

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l

l

Vessel Geometry (Level Calculator): The vessel geometry parameters can also be specified in the Geometry group on the Sizing page of the Rating tab. Fraction Calculator

If you selected the When the Initialize From User radio button, the Init HoldUp button becomes available. Click this button to specify the conditions you want to use for initializing the vessel. The Initial Holdup property view appears.

Initial Holdup l

l l

l

In the Initial Liquid Mole Fractions group, specify the initial mole fractions of each of the components in the vessel. Click the Normalize button to normalize the total composition to 1. In the Temperature field, specify the temperature you want HYSYS to use to determine the initial holdup conditions. In the Pressure field, specify the pressure you want HYSYS to use to determine the initial holdup conditions.

Tips: l

Click the Nitrogen button to specify a Nitrogen mole fraction of 1.0 if Nitrogen is present in the unit operation.

l

Click the Erase button to delete all of the compositions from the Initial Liquid Mole Fractions group. Note: You can determine the composition and amount of each phase in the vessel holdup by specifying different initialization modes. HYSYS forces the simulation case to re-initialize whenever the initialization mode is changed.

Fraction Calculator Note: The Fraction Calculator defaults to the correct mode for all unit operations and does not typically need to be changed.

The Fraction Calculator determines how the levels in the tank, and the elevation and diameter of the nozzles affect the product composition. The following is a description of the Fraction Calculator options: l

Use Levels and Nozzles. The nozzle location and vessel phase (liquid/vapor) level determines how much of each phase, inside the vessel, will exit through that nozzle. For example, if a vessel contained both liquid and vapor phases and the nozzle is below the liquid level, then liquid will flow out through it. If the nozzle is above the liquid level, then vapor will flow out through it.

l

1092

Emulsion Liquids. This behaves like the Use Levels and Nozzles option, except it simulates a mixer inside the vessel that mixes two liquid phases together so they do not separate out. For example, if a

58 Separator,

3-Phase Separator, and Tank

nozzle is below the lighter liquid level and the vessel has two liquid phases, the product is a mixture of both liquid phases.

Dynamic Specifications l

The frictional pressure loss at the feed nozzle is a dynamic specification in HYSYS. You can specify this value in the Feed Delta P field. The frictional pressure losses at each product nozzle are automatically set to zero by HYSYS.

Note: We recommend that you enter a value of zero in the Feed Delta P field, because a fixed pressure drop in the vessel is not realistic for all flows. If you want to model friction loss at the inlet and exit stream, it is suggested you add valve operations. In this case, flow into and out of the vessel is realistically modeled. l

You can specify the vessel pressure by selecting the check box beside the Vessel Pressure field. This specification is typically not set, since the pressure of the vessel is usually a variable and determined from the surrounding pieces of equipment. Once the check box is selected, you can modify this value in the field next to the check box.

Holdup Page The Holdup page contains information regarding the properties, composition, and amount of the holdup. The Vessel Levels group displays the following variables for each of the phases available in the vessel: l

Level. Height location of the phase in the vessel.

l

Percent Level. Percentage value location of the phase in the vessel.

l

Volume. Amount of space occupied by the phase in the vessel.

Stripchart Page The Stripchart page allows you to select a default strip chart containing various variable associated to the operation.

Heat Exchanger Page The Heat Exchanger page allows you to select whether the unit operation is heated, cooled, or left alone. You can also select the method used to heat or cool the unit operation. The options available in the Heat Exchanger page depends on which radio button you select: l

l

58 Separator,

If you select the None radio button, this page is blank and you do not have to specify an energy stream in the Connections page (from the Design tab) for the separator operation to solve. If you select the Duty radio button, this page contains the standard

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heater or cooler parameters and you have to specify an energy stream in the Connections page (from the Design tab) for the separator operation to solve. Note: The Tube Bundle options are only available in Dynamics mode and for Separator and Three Phase Separator. If you switch from Duty option or Tube Bundle option to None option, HYSYS automatically disconnects the energy or material streams associated to the Duty or Tube Bundle options.

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58 Separator,

3-Phase Separator, and Tank

59 Shortcut Column

The Shortcut Column performs Fenske-Underwood short cut calculations for simple refluxed towers. The Fenske minimum number of trays and the Underwood minimum reflux are calculated. A specified reflux ratio can then be used to calculate the vapor and liquid traffic rates in the enriching and stripping sections, the condenser duty and reboiler duty, the number of ideal trays, and the optimal feed location. The Shortcut Column is only an estimate of the Column performance and is restricted to simple refluxed Columns. For more realistic results the rigorous Column operation should be used. This operation can provide initial estimates for most simple Columns.

Shortcut Column Property View Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

User Variables

l

Notes

Connections Page You must specify the feed stream, overhead product, bottoms product, condenser, and reboiler duty name on the Connections page. The overhead product can either be an overhead vapor or a distillate stream, depending on the radio button selected in the Top Product Phase group. The operation name can also be changed on this page. Note: You can specify the top product to be either liquid or vapor using the radio buttons in the Top Product Phase group.

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Parameters Page The Shortcut Column requires the light key and heavy key components to be defined. The light key is the more volatile component of the two main components that are to be separated. The compositions of the keys are used to specify the distillation products. Note: The composition of the light key in the bottoms and the heavy key in the overhead are the only composition specifications required. l

l

l

l

In the Components group, select the light key in bottoms and heavy key in distillation component from the drop-down list in the component cell, and specify their corresponding mole fraction. The specification must be such that there is enough of both keys to be distributed in the bottoms and overhead. It is possible to specify a large value for the light key composition such that too much of the light key is in the bottoms, and the overhead heavy key composition spec cannot be met. If this problem occurs, one or both of the key specs must be changed. In the Pressures group, you can define the column pressure profile by specifying a value in the Condenser Pressure field and a Reboiler Pressure field. In the Reflux Ratios group, the calculated minimum reflux ratio appears once streams are attached on the Connections page, and the required parameters are specified in the Components group and Pressures group. You can then specify an external reflux ratio, which is used to calculate the tray traffic, the condenser and reboiler duties, the ideal number of trays, and the optimum tray location. The external reflux ratio must be greater than the minimum reflux ratio.

Rating Tab You currently cannot provide any rating information for the Shortcut Column.

Worksheet Tab The Worksheet tab displays a summary of the information contained in the stream property view for all the streams attached to the operation.

Performance Tab The Performance tab allows you to examine the results of the Shortcut Column calculations. The results correspond to the external reflux ratio value that you specified on the Parameters page. The following results are available on the:

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59 Shortcut Column

Column Result

Description

Minimum Number of Trays

The Fenske minimum number of trays, which is not affected by the external reflux ratio specification.

Actual Number of Trays

Calculated using a using the Gilliland method.

Optimal Feed Stage

Top down feed stage for optimal separation.

Condenser and Reboiler Temperatures

These temperatures are not affected by the external reflux ratio specification.

Rectifying Section Vapor and Liquid traffic flow rates

The estimated average flow rates above the feed location.

Stripping Section Vapor and Liquid traffic flow rates

The estimated average flow rates below the feed location.

Condenser and Reboiler Duties

The duties, as calculated by HYSYS.

Dynamics Tab The Shortcut Column currently runs only in Steady State mode. As such, there is no information available on the Dynamics tab.

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59 Shortcut Column

60 Solid Separation Operations

The next chapters will describe the following Solid Separation Operations: l

Baghouse Filter

l

Cyclone

l

Hydrocyclone

l

Rotary Vacuum Filter

l

Simple Solid Separator

60 Solid Separation Operations

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60 Solid Separation Operations

61 Baghouse Filter

The Baghouse Filter model is based on empirical equations. It contains an internal curve relating separation efficiency to particle size. Based on your particle diameter, the reported separation efficiency for your solids is determined from this curve. The solids being separated must be previously specified and installed as components in the stream attached to this operation.

Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

User Variables

l

Notes

Connections Page On the Connections page, you can specify the name of the operation, as well as the feed, vapor product, and solid product streams.

Parameters Page On the Parameters page, you must specify the following information: Parameter

Description

Configuration

When you make a change to any of the parameters, the configuration changes to User Defined. Select Default to revert to the HYSYS defaults.

Clean Bag Pressure Drop

The pressure drop across a clean bag.

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1101

Parameter

Description

Dirty Bag Pressure Drop

The pressure drop across a dirty bag. This value must be greater than the Clean Bag Pressure Drop.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Rating Tab The Rating tab consists of the Sizing page.

Sizing Page On the Sizing page, the following parameters can be specified: Parameter

Description

Maximum Gas Velocity

Maximum velocity of gas in the Baghouse Filter.

Bag Filter Area

Filter Area for each bag.

Bag Diameter

Bag Diameter.

Bags per Cell

Number of bags per filter cell.

Bag Spacing

Spacing between the bags.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the operation.

Performance Tab The Performance tab consists of the Results page.

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61 Baghouse Filter

Results Page The following Filtration results appear on this page: l

Filtration Time

l

Number of Cells

l

Area/Cell

l

Total Cell Area

l

Particle Diameter

Dynamics Tab This unit operation is currently not available for dynamic simulation.

61 Baghouse Filter

1103

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61 Baghouse Filter

62 Cyclone

The Cyclone is used to separate solids from a gas stream and is recommended only for particle sizes greater than 5 microns. The Cyclone consists of a vertical cylinder with a conical bottom, a rectangular inlet near the top, and an outlet for solids at the bottom of the cone. It is the centrifugal force developed in the vortex which moves the particles toward the wall. Particles which reach the wall, slide down the cone, and so become separated from the gas stream. The solids being separated must be previously specified and installed as components in the stream attached to this operation.

Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

Solids

l

User Variables

l

Notes

Connections Page You can specify the name of the operation, as well as the feed, vapor product, and solid product streams, on the Connections page.

Parameters Page  On the Parameters page, you can specify the following parameters:

62 Cyclone

Parameter

Description

Configuration

Select either High Efficiency, High Output or User Defined.

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Parameter

Description

Efficiency Method

Select one of the following methods:

Particle Efficiency

l

Lapple

l

Leith/Licht method: The more rigorous calculation, since it considers radial mixing effects.

The percent recovery of the specified solid in the bottoms stream.

The diameter provided, either from the selected component or from the particle characteristics, is used in the efficiency calculations. For example, if you select an 85% efficiency, 85% of the solids of the specified diameter is recovered. All other solids in the inlet stream are removed at an efficiency related to these parameters.

Solids Page You can specify the solid characteristics on the Solids page. This page contains different data, depending on the radio button selected in the Efficiency Basis group. When you select the Single Particle Diameter radio button, the following solids information can be specified: Parameter

Description

Solid Name

You must provide either the name of a solid already installed in the case, or provide a particle diameter and density.

Particle Diameter and Particle Density

If you do not choose a solid component, provide the particle diameter and density.

When you select the Particle Size Distribution radio button, the following solids information can be specified:

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Parameter

Description

Solid Name

You must provide either the name of a solid already installed in the case, or provide a particle diameter and density.

Particle Density

If you do not choose a solid component, provide the particle density.

Particle Size Distribution

If you do not choose a solid component, provide the minimum or maximum particle size.

62 Cyclone

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Rating Tab The Rating tab contains the following pages: l

Sizing

l

Constraints

Sizing Page The Sizing page contains two groups: l

l

Design Mode. Contains two radio buttons: On and Off. o

The radio buttons enables you to toggle between turning on or turning off the Design Mode option.

o

When you select the Off radio button, the Specify Number of Parallel Cyclones check box appears in the Sizing page. Select the check box if you want to specify the number of parallel Cyclones in the flowsheet.

Sizing Ratios. Contains a table. The table below describes the parameters available on the page: Parameter

Description

Configuration

Select High Output, High Efficiency, or User Defined. This is also defined on the Parameters page.

Inlet Width Ratio

The ratio of the inlet width to the body diameter (must be between 0 and 1). The value must be less than the Total Height Ratio

62 Cyclone

Inlet Height Ratio

The ratio of the inlet height to the body diameter.

Cyclone Height Ratio

The ratio of the Cyclone height to the body diameter. The Cyclone is the conical section at the bottom of the entire operation.

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Parameter

Description

Gas Outlet Length Ratio

The ratio of the gas outlet length to the body diameter.

Gas Outlet Diameter Ratio

The ratio of the gas outlet diameter to the body diameter (must be between 0 and 1).

Total Height Ratio

The ratio of the total height of the apparatus to the body diameter.

Solids Outlet Diameter Ratio

The ratio of the solids outlet diameter to the body diameter.

Body Diameter

If Design Mode is on, this is automatically calculated, within the provided constraints. If Design Mode is off, then you can specify this value.

The value must be less than the Total Height Ratio

# Parallel Cyc- If Design Mode is on, this field displays the number of parallel Cyclones lones (if any) attached to the unit operation. If Design Mode is off and the Specify Number of Parallel Cyclones check box is selected, you can specify this value.

Constraints Page On the Constraints page, you can specify the minimum and maximum diameter for the Cyclone. The page is also applicable only when the On radio button is selected in the Design Mode group. The Maximum Pressure Drop and Maximum Number of Cyclones is set on this page. These are used in the calculations to determine the minimum number of Cyclones needed to complete the separation.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the operation.

Performance Tab The Performance tab contains the Results page.

Results Page The Results page displays the calculated pressure drop, overall efficiency, and the number of parallel Cyclones.

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62 Cyclone

Dynamics Tab This unit operation is currently not available for dynamic simulation.

62 Cyclone

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62 Cyclone

63 Hydrocyclone

The Hydrocyclone is essentially the same as the cyclone, the primary difference being that this operation separates the solid from a liquid phase, rather than a gas phase. The solids being separated must be previously specified and installed as components in the stream attached to this operation.

Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

Solids

l

User Variables

l

Notes

Connections Page On the Connections page, you can specify the name of the operation, as well as the feed, liquid product, and solid product streams.

Parameters Page On the Parameters page, you can specify the following parameters: Parameter

Description

Configuration

Select either Mode 1, Mode 2, or User Defined.

Particle Efficiency

The percent recovery of the specified solid in the bottoms stream.

The diameter provided, either from the selected component or from the particle characteristics, is used in the efficiency calculations. For example, if you select an 85% efficiency, 85% of the solids of the specified diameter are recovered.

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1111

All other solids in the inlet stream are removed at an efficiency related to these parameters.

Solids Page On the Solids page, the following solids information can be specified: Parameter

Description

Solid Name

You must provide either the name of a solid already installed in the case, or provide a particle diameter and density.

Particle Diameter and Particle Density

If you do not specify a Solid Name, provide the particle diameter and density.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation. Note: The object in which the user variable is created owns the user variable.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Rating Tab The Rating tab contains the following pages: l

Sizing

l

Constraints

Sizing Page The Sizing page contains two groups: l

l

Design Mode. Contains two radio buttons: On and Off. The radio buttons enable you to toggle between turning on or turning off the Design Mode option. Sizing Ratio. Contains a table.

The table below describes the parameters available on the page:

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63 Hydrocyclone

Parameter

Description

Configuration

Select Mode 1, Mode 2 or User Defined. This is also defined on the Parameters page.

Inlet Diameter Ratio

The ratio of the inlet diameter to the body diameter.

Included Angle (Degrees)

The angle of the cyclone slope to the vertical.

Overflow Length Ratio

The ratio of the overflow length to the body diameter.

Overflow Diameter Ratio

The ratio of the overflow diameter to the body diameter.

Total Height Ratio

The ratio of the total height of the apparatus to the body diameter.

Underflow Diameter Ratio

The ratio of the underflow diameter to the body diameter.

Body Diameter

If Design Mode is on, then this is automatically calculated, within the provided constraints. If Design Mode is off, then you can specify this value.

Constraints Page You can specify the minimum and maximum diameter for the Cyclone, applicable only when the On radio button is selected in the Design Mode group. The Maximum Pressure Drop and Maximum Number of Cyclones can also be set on this page.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the operation.

Performance Tab The Performance tab consists of the Results page.

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Results Page The calculated pressure drop, overall efficiency, and the number of parallel cyclones appear on this page.

Dynamics Tab This unit operation is currently not available for dynamic simulation.

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63 Hydrocyclone

64 Rotary Vacuum Filter

The Rotary Vacuum Filter assumes that there is 100% removal of the solid from the solvent stream. This operation determines the retention of solvent in the particle cake, based on the particle diameter and sphericity of your defined solid(s). The diameter and sphericity determines the capillary space in the cake and thus the solvent retention. The solids being separated must be previously specified and installed as components in the stream attached to this operation.

Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

User Variables

l

Notes

Connections Page On the Connections page, you can define the operation name, as well as the feed, liquid product, and solids product streams.

Parameters Page The Rotary Vacuum Filter parameters are described in the table below:

64 Rotary

Parameter

Description

Cycle Time

The complete time for a cycle (one complete revolution of the cylinder).

Dewatering [% of cycle]

The portion of the cycle between the time the cake comes out of the liquid to the time it is scraped, expressed as a percentage of the overall cycle time.

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Parameter

Description

Submergence [% of cycle]

The percentage of the overall cycle for which the cake is submerged.

Pressure Drop

Pressure drop across the filter.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Rating Tab The Rating tab contains the following pages: l

Sizing

l

Cake

Sizing Page You can specify the following filter size parameters: Parameter

Description

Filter Radius

The radius of the filter. This defines the circumference of the drum.

Filter Width

The horizontal filter dimension.

Filter Area

The area of the filter.

Cake Page The Cake page consists of two groups: l

Cake Properties

l

Resistance

You can define the cake properties in the Cake Properties group.

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64 Rotary

Vacuum Filter

Property

Description

Mass Fraction of Cake

The final solid mass fraction.

Thickness

The thickness of the cake.

Porosity

The overall void space in the cake.

Irreducible Saturation

The solvent retention at infinite pressure drop.

Permeability

If you do not provide a value, HYSYS calculates this from the sphericity and diameter of the solid.

You can define the resistance or use a resistance equation in the Resistance group. Selecting the Use Resistance Equation check box, which allows HYSYS to calculate the resistance value based on the Filtration Resistance equation. The Filtration Resistance equation is as follows: (1) where: a, s = constants dP = pressure drop

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the operation.

Dynamics Tab This unit operation is currently not available for dynamic simulation.

64 Rotary

Vacuum Filter

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64 Rotary

Vacuum Filter

65 Simple Solid Separator

The Simple Solid Separator (Simple Filter) performs a non-equilibrium separation of a stream containing solids. This operation does not perform an energy balance, as the separation is based on your specified carry over of solids in the vapor and liquid streams, and liquid content in the solid product. It should be used when you have an existing operation with known carry over or entrainment in the product streams. The solids being separated must be previously specified and installed as components in the stream attached to this operation.

Design Tab The Design tab contains the following pages: l

Connections

l

Parameters

l

Splits

l

User Variables

l

Notes

Connections Page You can specify the name of the operation, feed stream, and product streams (Vapor, Liquid, Solids) on the Connections page.

Parameters Page You can specify the pressure drop on the Parameters page.

Splits Page  On the Splits page, you must choose the split method by defining a Type of Fraction. The types of fraction are described in the table below.

65 Simple Solid Separator

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Object

Definition

Split Frac- Specify the fractional distribution of solids from the feed into the vapor and tions liquid product streams. The solids fraction in the bottoms are calculated by HYSYS. You must also specify the fraction of liquid in the bottoms (solid product). Stream Fractions

Enter the mole, mass or liquid volume fraction specification for each of the following: l

Total vapor product solids fraction on the specified basis.

l

Total liquid product solids fraction on the specified basis.

l

Liquid phase fraction in the bottom product.

   In the flowsheet, the streams are not reported as single phase, due to the solid content in the vapor and liquid streams, and the liquid content in the solid product stream.

User Variables Page The User Variables page enables you to create and implement your own user variables for the current operation.

Notes Page The Notes page provides a text editor where you can record any comments or information regarding the specific unit operation, or your simulation case in general.

Rating Tab This unit operation currently does not have rating features.

Worksheet Tab The Worksheet tab contains a summary of the information contained in the stream property view for all the streams attached to the operation.

Dynamics Tab This unit operation is currently not available for dynamic simulation.

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65 Simple Solid Separator

66 Material Streams

Material streams are used to simulate the material traveling in and out of the simulation boundaries and passing between unit operations. For the material stream you must define their properties and composition so HYSYS can solve the stream. To add a Material stream: 1. Press F4 to open the Unit Operations palette. 2. Double-click the Material Stream icon

.

The Material Stream property view contains three tabs and associated pages that allow you to define parameters, view properties, add utilities, and specify dynamic information. If you want to copy properties or compositions from existing streams within the flowsheet, click the Define from Stream button. The Spec Stream As property view appears, which lets you select the stream properties and/or compositions you want to copy to your stream. Note: When you click the Define from Stream button and specify a stream with a property slate, HYSYS copies both the composition and property slate. If you only want to use the property slate, you must manually delete the composition values or adjust them as desired.

The left green arrow is the View Upstream Operation icon, which indicates the upstream position. The right green arrow is the View Downstream Operation icon, which indicates the downstream position. If the stream you want is attached to an operation, clicking these icons opens the property view of the nearest upstream or downstream operation. If the stream is not connected to an operation at the upstream or downstream end, then these icons open a Feeder Block or a Product Block. Note: The stream pressure represents the pressure at the inlet side of the stream, that is, the side that is connected to the upstream equipment. This becomes important when analyzing pressure-flow behavior of connected pieces of equipment that have different relative elevations. The pressure shown for the inlet stream of a unit operation belongs to the upstream unit operation and can be different than the actual inlet pressure if the two nozzles on both sides of the stream have different elevations.

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The "Spec Stream As..." Property View The Spec Stream As property view lets you select properties/information from other streams and use that information to define a stream. l

l

l

l

l

l

l

l

The Available Streams list lets you select the stream containing the properties you want to copy. You can only select one stream. In defining the basic stream properties, you can only select the check boxes of two of the following stream properties for the new stream: vapor fraction, temperature, pressure, molar enthalpy, or molar entropy. The Composition check box lets you copy the composition fraction values of the selected stream into the new stream. The Correlations check box lets you copy the selected stream’s correlation configuration into the new stream. The Flow check box lets you copy the selected stream’s flow rate value into the new stream. You can select the flow rate basis you want to copy into the new stream by selecting the appropriate radio button on the Flow Basis group. The Cost Parameters check box lets you copy the cost parameters values of the selected stream into the new stream. The Cancel button lets you exit the property view without accepting any changes. The OK button lets you exit the property view and accepts any changes made.

Worksheet Tab The Worksheet tab has pages that display information relating to the stream properties:

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l

Conditions

l

Properties

l

Compositions

l

Oil and Gas Feed

l

Petroleum Assay

l

K Value

l

Electrolytes (In use if the stream is in an electrolyte system.)

l

Cost Parameters

l

Normalized Yields

l

Acid Gas (Active when Acid Gas property package is in use)

l

PSD Properties (Active for solids simulations)

66 Material Streams

Conditions Page The Conditions page displays all of the default stream information as it is shown on the Material Streams tab of the Workbook property view. The names and current values for the following parameters appear below: l

Stream Name

l

Vapor/Phase Fraction

l

Temperature

l

Pressure

l

Molar Flow

l

Mass Flow

l

Std Ideal LiqVol Flow

l

Molar Enthalpy

l

Molar Entropy

l

Heat Flow

l

LiqVol Flow @ Std Cond

l

Fluid Package

l

Utility Type Note: In the electrolyte system, the Conditions page contains an extra column. This column displays the property parameters of the stream after electrolyte flash calculations. For the reactions involved in the flash and the model used for the flash calculation, refer to Section 1.6.9 - Electrolyte Stream Flash in the HYSYS OLI Interface Reference Guide.

HYSYS uses degrees of freedom in combination with built-in intelligence to automatically perform flash calculations. In order for a stream to “flash”, the following information must be specified, either from your specifications or as a result of other flowsheet calculations: l

Stream Composition

Two of the following properties must also be specified; at least one of the specifications must be temperature or pressure: l

Temperature (At least one of the temperature or pressure properties must be specified for the material stream to solve.)

l

Pressure

l

Vapor Fraction

l

l

Entropy (In the electrolyte system, the entropy (S) is always a calculated property.) Enthalpy (If you specify a vapor fraction of 0 or 1, the stream is assumed to be at the bubble point or dew point, respectively. You can also specify vapor fractions between 0 and 1.)

Depending on which of the state variables are known, HYSYS automatically performs the correct flash calculation.

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Once a stream has flashed, all other properties about the stream are calculated as well. You can examine these properties through the additional pages of the property view. A flowrate is required to calculate the Heat Flow. Note: For an electrolyte material stream, HYSYS conducts a simultaneous phase and reaction equilibrium flash on the stream.

The stream parameters can be specified on the Conditions page or in the Workbook property view. Changes in one area are reflected throughout the flowsheet. While the Workbook displays the bulk conditions of the stream, the Conditions page, Properties page, and Compositions page also show the values for the individual phase conditions. HYSYS can display up to five different phases. l

Overall

l

Vapor

l

Liquid. If there is only one hydrocarbon liquid phase, that phase is referred to as liquid.

l

Liquid 1. This phase refers to the lighter liquid phase.

l

Liquid 2. This phase refers to the heavier liquid phase. Note: In HYSYS, the liquid phase, and aqueous phase are internally recognized as Liquid 1, and Liquid 2, respectively. Liquid 1 refers to the lighter phase whereas the heavier phase is recognized as Liquid 2.

l

Aqueous. In the absence of an aqueous phase, the heavier hydrocarbon liquid is treated as aqueous. When there is only one aqueous phase, that phase is labeled as aqueous. Note: If there is only one hydrocarbon liquid phase, that phase is referred to as liquid.

l

Mixed Liquid. This phase combines the Liquid phases of all components in a specified stream, and calculates all liquid phase properties for the resulting fluid. Note: The Mixed Liquid phase does not add its composition or molar flow to the stream it is derived from. This phase is only another representation of existing liquid components.

For example, if you expand the width of the default material stream property view, you can view the hidden phase properties. In this case, the vapor phase and liquid phase properties appear beside the overall stream properties. If there were another liquid phase, it would appear as well. Note: Rather than expanding the property view, you can use the horizontal scroll bar to view the hidden phase properties. Note: When you are viewing a stream property view in the column subflowsheet, there is an additional Create Column Stream Spec button on the Conditions page.

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66 Material Streams

Dynamic Mode In Dynamic mode, the Manipulate Conditions button appears on the Conditions page of the Material Stream property view. The Manipulate Conditions button lets you change the values in a stream if you want to provide a different set of values for when the integrator is started. Normally, you would not have to use this feature. The Manipulate Conditions button is an advanced troubleshooting feature that you can use when you encounter problems, and you want to change the stream values temporarily to affect a downstream operation. You can use this feature, for example, if you ran the simulation and you got really cold temperatures out of a heat exchanger that is causing problems downstream. Note: This feature can be used on streams that feed into the flowsheet (sits on the boundary) and those that connect operations together. If the stream being changed flows out of a unit operation, its contents are likely overwritten by the upstream operation as soon as you start the integrator. Note: If the downstream operation is new or had problems solving, changing its feed stream may allow HYSYS to solve the downstream operation or initialize and solve a replacement unit operation.

If you click the Manipulate Conditions button, the stream values in the table appear in red. You can then enter in a new temperature (even if the stream had no specifications before). The Manipulate Conditions button is also replaced by the Accept Stream Conditions button. If you click the Accept Stream Conditions button, HYSYS performs flash calculations again with the initial values you provided. The stream values in the table appear in black as before.

Properties Page The Properties page displays the properties for each stream phase. The options in the Property Correlation Controls group lets you manipulate the property correlations displayed on this page for an individual stream. By default the properties from the Conditions page are not available on this page. Note: You can also manipulate the property correlations displayed in the Properties page using the Correlation Manager.

The Properties page contains a table, a Preference Option display field, and a group of icons. l l

The table displays the property correlations you select for the stream. The Preference Option display field is Active if the Activate Property Correlations check box is selected.

This check box can be found on the Options page, Simulation tab of the Session Preferences property view.

66 Material Streams

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l

The Property Correlation Controls group contains ten icons. These icons are used to manipulate the property correlations displayed in the table below. Note: You can modify and over-write any existing correlation set using the stream’s Property Correlation Controls.

Name

Icon

Description

View Correlation Set List

Lets you select a correlation set.

Append New Correlation

Lets you add a property correlation to the end of the table.

Move Selected Correlation Down

Lets you move the selected property correlation one row down the table.

Move Selected Correlation Up

Lets you move the selected property correlation one row up the table.

Sort Ascending

Lets you sort the property correlations in the table by ascending alphabetic order.

Remove Selected Correlation

Lets you remove the selected property correlation from the table.

Remove All Correlations

Lets you remove all the property correlations from the table.

Save Correlation Set to File

Lets you save a set of property correlations.

View Selected Correlation

Lets you view the parameters and status of the selected property correlation.

View All Correlation Plots

Lets you view all correlation plots for the selected stream.

Adding a Property Correlation To add a property correlation to the table: 1. Click the Append New Correlation icon property view appears.

.The Correlation Picker

HYSYS property correlations have been grouped into categories which target the specific reporting needs of the various process industries. The field at the bottom of the form shows the name of the stream to which the property correlation will be appended. 2. Select a property correlation that you want to view from the branch list. Click the Plus icon  to expand the available correlations list. 3. Click the Apply button to append the selected property correlation to the

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66 Material Streams

stream. If the selected correlation cannot be calculated by that stream’s fluid, a message will be sent to the trace window informing the user that this property correlation cannot be added to the stream. 4. Repeat steps #2 to #3 to add another property correlation. 5. When you have completed appending property correlations to the stream, click the Close button to return to the stream property view. To select a different stream to append the property correlations to: 1. Click the Select Material Stream to Append

icon.

The Select Material Stream property view appears. 2. Select the appropriate stream from the object list. 3. Click the OK button to return to the Correlation Picker property view. You can now add a property correlation to the selected stream. The new selected stream’s name also appears in the display field located beside the Select Material Stream to Append icon.

Removing a Property Correlation from the table To remove property correlations from the table: 1. Select the property correlation you want to remove in the table. 2. Click the Remove Selected Correlation icon. HYSYS removes the selected property correlation from the table. You can remove all property correlations in the table by clicking the Remove All Correlations icon.

Creating a Correlation Set To save the property correlations in the table as a set: 1. Add all the property correlations you want to the table. 2. Click the Save Correlation Set to File icon. The Save Correlation Set Name property view appears. HYSYS automatically enters a name for the property list based on the stream name. 3. Enter the name you want for the property list in the Set Name (Global) field. Each correlation set name must be unique. 4. Click the Save button to save the property list. Note: If you are creating a correlation set for the first time, you are also creating the default file (Support\StreamCorrSets.xml) which will hold all these sets. You can change the name of the file on the Locations page, Files tab of the Session Preferences property view.

The saved correlation set can then be added to other streams using the View Correlation Set List icon displayed in each stream property view. You can

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also add the saved correlation set to all of the streams within the case by using the Correlation Manager.

Displaying a Correlation Set To display a correlation set: 1. Click the View Correlation Set List icon. The Correlation Set Picker property view appears. 2. Select the desired correlation set from the property view. To see the list of correlations contained within the correlation set, click the associated icon. 3. Click the Apply button. The Correlation Set Picker property view closes, and the property correlations contained in the selected correlation set will appear in that streams properties table. HYSYS will check each correlation’s type against the fluid type of the stream. If a problem occurs while appending a correlation from the set, a warning will be sent to the Trace window. 4. Repeat steps to apply additional correlation sets to your stream. You can expand the property view or use the scroll bar to view any property correlation phase values.

Deleting a Correlation Set To delete a correlation set: 1. Click the View Correlation Set List icon. 2. The Correlation Set Picker property view appears. 3. Select the correlation set you want to delete. 4. Click the Delete button. A window will appear asking you if you are sure you want to delete the set because it cannot be undone. 5. Click the Yes button and the Correlation Set Picker property view appears with the chosen set deleted from the list. 6. Click the Close icon to close the Correlation Set Picker property view and return to the stream property view.

Viewing a Property Correlation When you select a property correlation from the table and click the View Selected Correlation icon, , the following property view appears. The values shown on the correlation property view cannot be edited. Any configuration parameters available to each property correlation can only be edited using the Correlation Manager property view.

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66 Material Streams

The following table describes the status bars contained in the Status group. Status Bar

Description

Stream

Indicates that the correlation can only be applied to material streams.

Point/Plottable

Indicates whether the property correlation is a point or plottable property.

Black Oil/Electrolyte/Gas/Petroleum/ RFG/RVP/Solid/Standard/User/Clone

Indicates which correlation type the property correlation resides within in the Available Correlations list.

Active/Inactive

Indicates whether the property correlation has been activated by the correlation manager. If the status bar is green, any new stream added to the flowsheet with the same fluid type as the correlation will automatically have the property correlation added.

In Use/Not in Use

Indicates whether the property correlation is being used by a stream in the case.

Available/Unavailable

Indicates whether the property correlation exists in the window registry of the system.

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In the Parameters group, you can view the parameters used to calculate the property correlation. Note: To manipulate the parameter values, you have to access the Correlation Manager property view.

In the Stream Connections group, a list of all the material streams currently using the property correlation appears.

Viewing All Correlation Plots The View All Correlation Plots icon opens the Correlation Plots property view which displays all plottable properties for the stream. Only plottable properties appear on the plots property view, while both point and plot properties appear on the stream properties property view. The plot property view can show only one plot property at a time.

Composition Page The Composition page lets you view and edit the stream composition. In the figure below, the page shows the mole fractions for each component in the overall phase, vapor phase, and aqueous phase.

To view the composition in a different basis, click the Basis button, and select the basis you want on the Stream property view.

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66 Material Streams

Button

Description

Edit

Open the Input Composition property to edit the stream composition. (The Edit button is disabled if the stream’s composition is calculated by other unit operations connected to the stream.)

View Properties

View table of stream properties

Basis

View the composition in a different basis

Input Composition Property View The Input Composition property view lets you edit the stream compositions. Click the Edit button, or specify a value in a component cell on the Composition page and press ENTER to access the Input Composition property view. (The Edit button is disabled if the stream’s composition is calculated by other unit operations connected to the stream.) In the Composition Basis group, select the radio button that corresponds to the basis for your stream. In the list of available components, specify the composition of the stream. The Composition Controls group has two buttons that can be used to manipulate the compositions. Button

Action

Erase

Clears all compositions.

Normalize

Lets you enter any value for fractional compositions and have HYSYS normalize the values such that the total equals 1. This button is useful when many components are available, but you want to specify compositions for only a few. When you enter the compositions, click the Normalize button and HYSYS ensures the Total is 1.0, while also specifying any  compositions as zero. If compositions are left as , HYSYS cannot perform the flash calculation on the stream. The Normalize button does not apply to flow compositional bases, since there is no restriction on the total flowrate.

The OK button closes the Input Composition property view and accepts any specified changes to the stream composition. The Cancel button closes the property view without accepting any changes. Note: For fractional bases, clicking the OK button automatically normalizes the composition if all compositions contain a value.

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Oil & Gas Feed Page Use the Oil & Gas Feed page to define stream composition as a mixture of oil and gas.

From the drop-down list at the top of the page, you can select one of the following options: l l

l

No Oil & Gas Feed: This is the default selection. Oil & Gas Feed with Bulk Oil Properties: You can define the feed makeup as an oil and gas feed using bulk properties. Oil & Gas Feed with Oil Assay Info: You can define the feed makeup as an oil and gas feed using information from an imported oil assay.

Oil & Gas Feed with Bulk Oil Properties To define an Oil & Gas Feed with Bulk Oil Properties: 1. In the Oil Properties section, specify the following values: o

Density

o

Gas-Oil Ratio (GOR)

2. Specify a value in one of the following fields: o

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Water-Oil Ratio (WOR): If you specified the Water Cut, this value is calculated by HYSYS. If you want to edit the Water-Oil Ratio, you must delete the value that you specified for the Water Cut.

66 Material Streams

-oro

Water Cut: If you specified the Water-Oil Ratio, this value is calculated by HYSYS using the following formula: Water Cut = WOR / (WOR + 1) If you want to edit the Water Cut, you must delete the value that you specified for the Water-Oil Ratio.

3. In the Gas Composition section, specify the gas composition in the table. Click the Edit button if you want to edit the Composition Basis. 4. In the Gas-Oil Flash Calculation section, adjust the Number of Stages as desired. Note: When the stages are initialized, HYSYS always initializes one stage at atmospheric conditions.

5. In the table below, you can edit the Temperature and Pressure for each stage. You can also view the following for each stage: o

Total GOR

o

Stg GOR

o

Total WOR

o

Stg WOR

o Liq Density The Oil & Gas Feed solves once you specify this information.

6. In the Viscosity section, adjust the Number of Inputs as desired. Your viscosity input information is assumed to be based on measurements made at standard pressure (1 atm). 7. For each input, specify the following: o

At Temp: Specify the temperature at the viscosity curve.

o

Value: The value of the viscosity curve at the At Temp.

8. In the Additional Inputs section, specify or edit values for the following: o

Watson K:

o

Oil Flow Target: When you specify the Oil Flow Target value at stock tank conditions, the stream calculates its total molar flow to match the oil flow target value specified.

Oil & Gas Feed with Oil Assay Info To define an Oil & Gas Feed with Oil Assay Info: 1. In the Oil Properties section, specify the following values: o

Density

o

Gas-Oil Ratio (GOR)

2. Specify a value in one of the following fields: o

66 Material Streams

Water-Oil Ratio (WOR): If you specified the Water Cut, this value is calculated by HYSYS. If you want to edit the Water-Oil Ratio, you must delete the value that you specified for the Water Cut.

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-oro

Water Cut: If you specified the Water-Oil Ratio, this value is calculated by HYSYS using the following formula: Water Cut = WOR / (WOR + 1) If you want to edit the Water Cut, you must delete the value that you specified for the Water-Oil Ratio.

3. In the Assay Info section, click the Select Assay button to select the desired assay. On the Select Assay To Import dialog box, select the assay that you want to import, and then click the Import Selected Assay button. You can click the View Details button to view Macrocut Data. 4. In the Gas-Oil Flash Calculation section, adjust the Number of Stages as desired. Note: When the stages are initialized, HYSYS always initializes one stage at atmospheric conditions.

5. In the table below, you can edit the Temperature and Pressure for each stage. You can also view the following for each stage: o

Total GOR

o

Stg GOR

o

Total WOR

o

Stg WOR

o

Liq Density

Petroleum Assay Page Use the Petroleum Assay page on the Stream Worksheet tab to define stream composition as a HYSYS Petroleum Assay.

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66 Material Streams

You can select one of the assays that you have added to the case, (existing) or import one to attach to the stream from the assay library or from a file. You can also click Create to define a new assay for the stream using data tables to enter the boiling points, number of cuts, cut range temperatures, and so on. In HYSYS V9, new options were added to control how Assay Manager characterizes input data. When characterizing streams in the Simulation environment, the default options are always used: matching all cuts (including overlapping cuts), enforcing pure component consistency, 10% warning threshold, ignoring Freeze>Cloud>Pour rules of thumb if input data contradicts, and using default GC distribution. If you want to use an assay in a stream and you want to use non-default options, you must add the assay in the Properties environment and attach it to the stream, rather than adding the assay on the stream directly.

Detaching an Assay From the Stream Assays estimate stream compositions and determine the component property slate for the stream. When an assay is detached from a stream or deleted from the case, the composition estimated by the assay is considered system-estimated and is retained. However, the component property slate becomes the default fluid package slate. So when detaching an assay from a stream the stream remains flashed, however, because the property slate has changed the flash results will change as well. Similarly, if you change the assay input data invalidating the char-

66 Material Streams

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acterization, this assay will no longer provide its property slate to the connected stream.”

K Value Page The K Value page displays the K values or distribution coefficients for each component in the stream. A distribution coefficient is a ratio between the mole fraction of component i in the vapor phase and the mole fraction of component i in the liquid phase: (1)

where: Ki = distribution coefficient yi = mole fraction of component i in the vapor phase xi = mole fraction of component i in the liquid phase

Electrolytes Page If the stream is associated with an OLI-Electrolyte property package, the Electrolytes page displays electrolytic information. The Electrolytes page is available only if the stream is in an electrolyte system. You can view the electrolyte stream properties or the electrolyte stream composition for aqueous or solid phase. In the True Species Info group, select the appropriate radio button to view the electrolyte stream properties. The Properties radio button displays the stream fluid phase properties for an electrolyte system. l

Use the radio buttons in the Phase group to switch between the Aqueous phase and the Solid phase.

When you click the Aqueous phase radio button, the following aqueous phase related properties appear: l

pH value

l

Osmotic Pressure

l

Ionic Strength

l

Heat Capacity

l

Viscosity

When you click the Solid phase radio button, you can include or exclude a particular solid in the current stream equilibrium flash calculation. The value of Scale Tendency Index shown in the table is a measure of the tendency of a solid species forming at the specified conditions. A solid with a scaling tendency greater than one forms if the solid formation is governed by

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66 Material Streams

equilibrium (as opposed to kinetics), and if there are no other solids with a common cation or anion portion which also has a scaling tendency greater than one. The Composition radio button displays the component name, molar fraction, molar flow, or molality and molarity of all the components in the stream for aqueous or solid phase in a table. l

l

If you select the Aqueous radio button, the component list including ionic component(s) appears in the table. If you select the Solid radio button, a component list including precipitate (PPT) and hydrated (-nH2O) solid appears with only mole fraction and mole flow.

User Variables Page The User Variables page lets you create and implement your own user variables for all material streams.

Notes Page The Notes page provides a text editor that lets you record any comments or information regarding the material stream or the simulation case in general.

Cost Parameters Page You can enter a cost factor value for the stream on the Cost Parameters page. You can also choose the flow basis associated with the cost factor from the Flow Basis drop-down list.

Normalized Yields Page The Normalized Yields page reports a selected product stream flow as a fraction of a reference stream. Normalized yields can be assembled in the HYSYS Workbook feature for convenient reports. You can report a product (current stream) to feed (reference stream) ratio in unusual units such as SCF/BBL, etc. that appear as Key Performance Indicators (KPIs) in process units. Normalized Yields simplifies support of Planning and Scheduling models like Aspen PIMS and Aspen Petroleum Scheduler that may need stream units normalized against a feed stream or use unusual KPI style yield ratios. To examine Normalized Yields: 1. Double click the target material stream on the PFD. 2. In the Material Stream view, click the Worksheet tab 3. Click Normalized Yields in the Worksheet column

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4. Use the Reference Stream row to select the stream for comparison. The calculations are updated immediately. Note: You can also compare these yields side by side by importing them into the HYSYS workbook. When updating refinery planning models in Aspen PIMS from Aspen HYSYS, these easily-available yields will be very helpful. You can directly access these yield variables in the PIMS Support Utility rather than indirectly calculating these values in a spreadsheet.

Acid Gas Page The Acid Gas worksheet page displays the results of acid gas calculations. It is present in the stream form only when the stream uses the Acid Gas property package in the simulation basis.

Units Some results, for example, Amine Strength, Recirculation Rate, Temperature, and Pressure, appear in units determined by the user-defined dimension set. Other results, for example, compositions and flow rates, appear in default units regardless of the active dimension set.

PSD Properties Page  You must have a solid component installed in the stream to access this page. Use the list of available solid components to select the component for which you want to specify particle size distribution parameters. l

1138

Click the Edit button and from the Input PSD group use the radio buttons to select the data input method you want to use. You have three options

66 Material Streams

to choose from: User-Defined Discrete, Log Probability, or RosinRammler. l

l

From the Fit Type group, click one of the following radio buttons: AutoFit, Standard Interpolation, Probability Interpolation, Log Probability Fit, Rosin Rammler Fit, or Not Fit. Specify the number of points in the distribution in the Number of Desired Points field (the default value of 25 is provided) and specify the density of the particle in the Particle Density field.

Notes: Click the Calculate PSD button. If the AutoFit radio button is selected, the PSD Fit Comparison view appears. Clicking the Basis button on the PSD Property page and the PSD Input property view accesses the Basis property view. This property view lets you specify the input basis (InSize, Undersize, or Oversize) and the composition basis (Mass Percent or Number Percent). Click the Default button to return all the values the default settings.

Sulfur Recovery Page Note: The Sulfur Recovery page only appears for material streams located within an SRU sub-flowsheet.

The following results appear on the Worksheet tab | Sulfur Recovery page: l

Temperature

l

Pressure

l

Mass Flow

l

Molar Flow

l

Dewpoint Temperature

l

Dewpoint Margin

l

Sx Mass Fraction

l

Sx Mole Fraction

l

Sx Mass Flow

l

Sx Mole Flow

l

Sx Average Species Number

l

Air Demand [%]

l

H2S/SO2 Ratio

l

H2S Mole % (Dry) [%]

l

H2S Mole % (Wet) [%]

l

SO2 Mole % (Dry) [%]

l

SO2 Mole % (Wet) [%]

Attachments Tab The Attachments tab displays the names and types of unit and logic operations attached to the inlet and outlet of the stream Double-click in either the

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name or type cells to open the property view for the specific unit or logical operation.

Unit Ops Page The Unit Ops page lets you view the names and types of unit and logical operations to which the stream is attached. The property view uses three groups: l

The units from which the stream is a product.

l

The units to which the stream is a feed.

l

The logical operations to which the stream is connected.

You can access the property view for a specific unit operation or logical by double-clicking in the Name cell or Type cell.

Analysis Page Analyses are specialized tools that can monitor and report on a wide range of stream calculation activity. The Analysis page lets you do the following: l

Attach an analysis to the current stream.

l

View an existing analysis attached to the stream.

l

Delete an existing analysis attached to the stream.

Use the Create button to add analyses to the stream. The choices are limited to those pertaining to streams. Once added, use the View... button to view or edit the analysis.

DRU Stream Page The DRU stream facilitates running a given set of unit operations under different stream conditions. The information gathered from the run are stored within the DRU stream, and can be either user input or acquired from the RTO system directly. Note: The DRU stream is applicable for data reconciliation problems.

The DRU stream is used for data reconciliation to hold different states of streams. During data reconciliation, measured data of DCS tags can be obtained under different stream states (for example, temperature or pressure). The DRU stream can also perform flash calculations as other HYSYS streams do. If you want to use the DRU stream to hold data, the number of data sets needs to be equal to the number of data sets of DCS tags. You can create data sets for streams and set values to stream states. Note: Each data set behaves as a stream (for example, the data set contains automatic flash calculation and freedom control).

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66 Material Streams

The Data Rec utility controls the updating of its associated streams with the correct data corresponding to the data set being evaluated at that point in time. The Add Transfer Stream button and Delete Transfer Stream button are solely for On-Line applications. l

l

Clicking the Add Transfer Stream button creates a DRU Stream (Data Reconciliation Stream) such that you can move the information for the stream as a block between HYSYS cases, or instances of HYSYS. Clicking the Delete Transfer Stream button removes the DRU Stream.

Dynamics Tab The Dynamics tab displays the pressure and flow specifications for the material stream, and lets you generate the strip chart for a set of variables. Note: You must be in dynamic mode for any of these specifications to have an effect on the simulation.

Specs Page The Specs page lets you add a pressure and a flow specification for the stream. If the Active check box is selected for a specification, the value of the specification appears in blue and you can modify the value. If the Active check box is cleared, the value is appears in black and is calculated by HYSYS. Default stream conditions are shown in red.

Feed and Product Blocks A flowsheet boundary stream is a stream which has only one unit operation attached to it. If a material stream is a flowsheet boundary stream, a Feeder block button or Product block button appears in the Specs page of the Dynamics tab. A flowsheet boundary stream can be the feed or product of the model. Depending on whether the flowsheet boundary stream is a feed or a product, the Dynamics tab contains either a Feeder block button or a Product block button. You can also access the Feeder Block property view by clicking the View Upstream Operation icon on the stream property view. Similarly, you can also access the Product Block property view by clicking the View Downstream Operation icon. The Product Block property view displays flow reversal conditions of the material stream which you can specify. If simulation conditions are such that the product stream flow becomes negative, HYSYS recalls the stream conditions stored in the Product block and performs a rigorous flash on the product stream to determine the other stream conditions.

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When process conditions in the simulation cause the feed flow to reverse, the feed stream conditions are calculated by the downstream operation. The Feeder Block property view is used to restore desired feed conditions and compositions if the feed stream reverses and then becomes feed again. The Feeder Block and Product Block have similar property views. You can specify the stream conditions as follows: Required Feed and Product Block Specifications Conditions Tab

Composition Tab

Specify one of the following: l

Temperature

l

Vapor Fraction

l

Entropy

l

Enthalpy

Specify the stream composition.

Since the pressure of the stream remains the same after the product stream flow reverses, the pressure value does not need to be specified. With this information, the stream is able to perform flash calculations on the other stream properties. Both the Feeder Block property view and Product Block property view have three buttons that allow you to manipulate the direction of stream conditions between the material stream and the block. The table below briefly describes each button. Block Button

Action

Export Conditions to Stream

Copies stream conditions stored in the block to the material stream.

Update From Stream

Copies the current stream conditions from the material stream to the block.

Update from Current Com- Copies only the stream composition from the material position stream to the block.

Stripchart Page The Stripchart page lets you select and create strip charts containing various variables associated with the material stream.

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67 Energy Streams

Energy streams are used to simulate the energy traveling in and out of the simulation boundaries and passing between unit operations. To add an energy stream: 1. Press F4 to open the Unit Operations palette. 2. Double-click the Energy Stream icon

.

The Energy Stream property view appears. The Energy Stream property view contains the following tabs that allow you to define stream parameters, view objects to which the stream is attached, and specify dynamic information: l

Stream

l

Unit Ops

l

Dynamics

l

Stripchart

l

User Variables

As with the material streams, the energy stream property view has the View Upstream Operation and the View Downstream Operation arrow icons that allow you to view the unit operation to which the stream is connected. Energy streams differ from material streams in that if there is no upstream or downstream connection on the stream (which is often the case for the energy stream) the associated icon is not active.

Stream Tab The Stream tab allows you to specify the Stream Name and Heat Flow for the stream. Note: When converting an energy stream to a material stream, all material stream properties are unspecified, except for the stream name.

67 Energy Streams

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Unit Ops Tab The Unit Ops tab displays the Names and Types of all objects to which the energy stream is attached. Both unit operations and logicals are listed. The Unit Ops tab either shows a unit operation in the Product From cell or in the Feed To cell, depending on whether the energy stream receives or provides energy respectively. Note: You can double-click on either the Product From or Feed To cell to access the property view of the operation attached to the stream.

Dynamics Tab The options on the Dynamics tab allow you to set the dynamic specifications for a simulation in dynamic mode. In dynamic mode, two different heating methods can be chosen for an energy stream. When the Direct Q radio button is selected, you can specify a duty value. When the Utility Fluid radio button is selected, the duty is calculated from specified properties of a utility fluid. The Utility Valve button opens the Flow Control Valve (FCV) view for the energy stream. For a detailed description of the Direct Q and Utility Fluid Heating methods, refer to the Valve Operation.

Stripchart Tab The Stripchart tab currently does not have any functions.

User Variables Tab The User Variables tab lets you create and implement your own user variables for all energy streams.

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67 Energy Streams

68 Subflowsheet Operations

Introduction The subflowsheet operation uses the multi-level flowsheet architecture and provides a flexible, intuitive method for building the simulation. Suppose you are simulating a large processing facility with a number of individual process units and instead of installing all process streams and unit operations into a single flowsheet, you can simulate each process unit inside its own compact subflowsheet. Once a subflowsheet operation is installed in a flowsheet, its property view becomes available just like any other flowsheet object. Think of this property view as the “outside” property view of the “black box” that represents the subflowsheet. Some of the information contained on this property view is the same as that used to construct a Template type of Main flowsheet. Naturally this is due to the fact that once a Template is installed into another flowsheet, it becomes a subflowsheet in that simulation. Whether the flowsheet is the Main flowsheet of a simulation case, or it is contained in a subflowsheet operation, it possesses the following components: l

l

l

l

l

Fluid Package. An independent fluid package, consisting of a Property Package, Components, and so forth. It is not necessary that every flowsheet in the simulation have its own separate fluid package. More than one flowsheet can share the same fluid package. Flowsheet Objects. The inter-connected topology of the flowsheet. Unit operations, material and energy streams, utilities, and so forth. A Dedicated PFD. A HYSYS property view presenting a graphical representation of the flowsheet, showing the inter-connections between flowsheet objects. A Dedicated Workbook. A HYSYS property view of tabular information describing the various types of flowsheet objects. A Dedicated Desktop. The PFD and Workbook are home property views for this Desktop, but also included are a menu bar and a toolbar specific to either regular or Column subflowsheets.

68 Subflowsheet Operations

1145

Note: By design, the parent flowsheet does not solve when you are in the subflowsheet environment. You must instead go to the parent flowsheet to let the solver run, and then return to the subflowsheet and run the solver.

Subflowsheet Property View The Subflowsheet property view consists of the following tabs: l

Connections

l

Parameters

l

Transfer Basis

l

Transition

l

Variables

l

Notes

l

Lock

Adding a Subflowsheet To add a subflowsheet to your simulation, use the Model Palette. The Sub-Flowsheet Option property view appears. The Sub-Flowsheet Option property view contains the following options, explained below: l

Read an Existing Template

l

Start with a Blank Flowsheet

l

Paste exported objects

l

Cancel

Read an Existing Template If you want to use a previously constructed Template that has been saved on disk, click the Read an Existing Template button on the Sub-Flowsheet Option property view.

Start with a Blank Flowsheet If you want to start with a blank subflowsheet, click the Start with a Blank Flowsheet button on the Sub-Flowsheet Option property view, HYSYS will install a subflowsheet operation containing no unit operations or streams. On the Connections tab of the property view of the blank subflowsheet, there will be no feed or product connections (boundary streams) to the subflowsheet. You can connect feed streams in the External Stream column by either typing in the name of the stream to create a new stream or selecting a pre-defined stream from a drop-down list. When an external feed connection is made by selecting a pre-defined stream from the drop-down list, a stream similar to the pre-defined stream is created inside the subflowsheet environment.

1146

68 Subflowsheet Operations

In order to fully define the flowsheet, you have to enter the subflowsheet environment. Click the Sub-Flowsheet Environment button on the property view to transition to the subflowsheet environment and its dedicated Desktop. The subflowsheet is constructed using the same methods as the main flowsheet. When you return to the Parent environment, you can connect the subflowsheet boundary streams to streams in the Parent flowsheet.

Paste Exported Objects If you want to import previously exported objects into a new subflowsheet, click the Paste Exported Objects button on the Sub-Flowsheet Option property view. Note: The objects that are selected and exported via the PFD can be imported back into a flowsheet without creating a new subflowsheet first.

You copy and paste selected objects inside the same subflowsheet or another subflowsheet. You can also copy and paste subflowsheets and column subflowsheets. Objects can also be moved into or out of a subflowsheet.

Connections Tab  You can enter the name of the subflowsheet, as well as its Tag name, on the Connections tab. All feed and product connections appear on the Connections tab.

Flowsheet Tags These short names are used by HYSYS to identify the flowsheet associated with a stream or operation when that flowsheet object is being viewed outside of its native flowsheet scope. The default Tag name for a subflowsheet operation is TPL1 (for Template). When more than one subflowsheet operation is installed, HYSYS ensures unique tag names by incrementing the numerical suffix; the subflowsheets are numbered sequentially in the order they were installed. For example, if the first subflowsheet added to a simulation contained a stream called Comp Duty, it would appear as Comp Duty@TPL1 when viewed from the Main flowsheet of the simulation.

Feed and Product Connections Internal streams are the boundary streams within the subflowsheet that can be connected to external streams in the Parent flowsheet. Internal streams cannot be specified on this tab, they are automatically determined by HYSYS. Basically, any streams in the subflowsheet that are not completely connected (in other words, "open ended") can serve as a feed or product. Note: Subflowsheet streams that are not connected to any unit operations in the subflowsheet appear in the property view as well (and are termed "dangling streams").

68 Subflowsheet Operations

1147

To connect the subflowsheet, specify the appropriate name of the external streams, which are in the Parent flowsheet, in the matrix opposite the corresponding internal streams, which are in the subflowsheet. The stream conditions are passed across the flowsheet boundary via these connections. Note: It is not necessary to specify an external stream for each internal stream.

Parameters Tab You can view the exported subflowsheet variables on the Parameters tab, which allows you to keep track of several key variables without entering the subflowsheet environment. It is also useful when dealing with a subflowsheet as a black box. The user who created the subflowsheet can set up an appropriate Parameters tab, and another user of the subflowsheet can be unaware of the complexities within the subflowsheet. These variables display values, which have been calculated or specified by the user. If changes to the specified values are made here, the subflowsheet is updated accordingly. For each variable, the description, value, and units are shown. Note: These variables are actually added on the Variables Tab of the property view, but are viewed in full detail on the Parameters tab. l

l

The Ignore check box is used to bypass the subflowsheet during calculations, just as with all HYSYS unit operations. The Update Outlets check box lets you toggle between transferring or not transferring updated values from the subflowsheet to the external streams.

Transfer Basis Tab The transfer basis for each Feed and Product Stream is listed on the Transfer Basis tab. Note: The Transfer Basis is also useful in controlling VF, T, or P calculations in column subflowsheet boundary streams with close boiling or nearly pure compositions.

The transfer basis only becomes significant when the subflowsheet and Parent flowsheet's fluid packages consist of different property methods. The transfer

1148

68 Subflowsheet Operations

basis is used to provide a consistent means of switching between the different basis of the various property methods. The table below list all the possible transfer basis provided by HYSYS: Transfer Basis

Description

T-P Flash

The Pressure and Temperature of the Material stream are passed between flowsheets. A new Vapor Fraction is calculated.

VF-T Flash

The Vapor Fraction and Temperature of the Material stream are passed between flowsheets. A new Pressure is calculated.

VF-P Flash

The Vapor Fraction and Pressure of the Material stream are passed between flowsheets. A new Temperature is calculated.

P-H Flash

The Pressure and Enthalpy of the Material stream are passed between flowsheets.

User Specs

You define the properties passed between flowsheets for a Material stream.

None Required

No calculation is required for an Energy stream. The heat flow is simply passed between flowsheets.



No transfer basis has been selected.

Transition Tab The Transition tab allows you to select and modify the stream transfer and map methods for the fluid component composition across fluid package boundaries. You may choose between three transition types: FluidPkg Transition, Basis Transition, and Black Oil Transition.

Fluid Package Transition Composition values for individual components from one fluid package can be mapped to a different component in an alternate fluid package. Mapping is especially useful when dealing with hypothetical oil components where like components from one fluid package can be mapped across the subflowsheet boundary to another fluid package. Note: Component Maps can also be created and edited in the Properties environment.

Basic Transition The Basic Transition view outlines the value of each component within the Inlet Stream Molar Composition and the Outlet Stream Molar Composition.

Black Oil Transition The Black Oil Transition view allows you to:

68 Subflowsheet Operations

1149

l

Choose between three separate Black Oil Transition Methods: o

Simple

o

Three Phase

o

Infochem Multiflash

l

Select the Oil Phase Cut Options from the drop-down list.

l

View/Edit the Composition of the stream.

l

Erase the Composition of the stream.

l

Normalize the Composition of the stream.

For every pairing of different fluid packages, a collection of maps exists. Component maps can be added to each collection on the Component Maps tab in the Simulation Basis Manager property view. To select a transfer and map method for the inlet and outlet streams: 1. In the appropriate cell under the Transition column, click the down arrow icon to open the drop-down list. 2. In the drop-down list, select the transition type you want to apply to the stream. Note: Some of the transition method require the RefSYS or Upstream license to run.

3. Repeat the above steps for all the streams that require a transition method. To modify the type of transfer and map method for inlet and outlet streams: 1. Under the Stream column, click on the cell containing the stream you want to modify. 2. Click the appropriate View Transition button in the group. The Transition property view of the selected stream appears. 3. In the Transition property view, you can make the following changes: o

modify the fluid package of the streams

o

edit, add, or delete a component map method

o

modify the transfer basis

4. Click the Imbalance button to view the component imbalance in the selected stream. To view overall component imbalance for streams flowing through the subflowsheet: 1. Click the Overall Imbalance Into Sub-Flowsheet button or Overall Imbalance Out of Sub-Flowsheet button to open the Untransferred Component Info property view. The Untransferred Component Info property view allows you to confirm that all of the components have been transferred into or out of the subflowsheet.

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68 Subflowsheet Operations

2. Click the appropriate radio button to view the imbalance in molar, mass, or liquid volume basis.

Variables Tab The Variables tab of the Main flowsheet property view allows you to create and maintain the list of externally accessible variables. Although you can access any information inside the subflowsheet using the Variable Navigator, the features on the Variables tab allow you to target key process variables inside the subflowsheet and display their values on the property view. Then, you can conveniently view this whole group of information directly on the subflowsheet property view in the Parent flowsheet. To add variables: 1. Click the Add button. The Variable Navigator property view appears. 2. On the Variable Navigator property view, select the flowsheet object and variable you want. You can also over-ride the default variable description displayed in the Variable Description field of the Variable Navigator property view. Note: Any subflowsheet variables added in the Variables tab will appear on the Parameters tab.

Notes Tab The Notes tab provides a text editor where you can record any comments or information regarding the material stream or to your simulation case in general.

Lock Tab The Lock tab lets you lock or unlock the subflowsheet and displays the lock status of the subflowsheet. When the flowsheet is locked, you cannot create or delete objects, or change the topology. You can add Set, Adjust, and Spreadsheet operations; manipulate variable values; or copy the contents of the flowsheet and create your own modifiable version. Note: Subflowsheets inside a locked subflowsheet have to be specifically locked. l

l

To lock a subflowsheet, enter a password in the Lock Status field and press ENTER. To unlock a subflowsheet, enter the correct password in the Lock Status field and press ENTER.

68 Subflowsheet Operations

1151

1152

68 Subflowsheet Operations

Index B A Absorber See Column 89 Absorber Template (Column) 99 Accumulation 25 Actuator 895 Adiabatic Efficiency 1003, 1018 Adjust 537 individual 544 maximum iterations 542 multiple 545 solving methods 539 start 544 step size 542 tolerance 541 Advanced Holdup 32 compositions tab 33 efficiencies tab 33 general tab 32 nozzles tab 32 properties tab 33 Advanced Holdup Properties 32 Air Cooler 373 duty 373 dynamic 374 dynamic specifications 375 holdup 384 pressure drop 375 steady state 373 theory 373 Annular Mist 783 Aspen GPDC85 correlation 341 Assay curves 214 Assay Curves (Column) 214 ATV Tuning 533

Index

Baghouse Filter 1101 parameters 1101 sizing 1102 Balance 547 general 550 mass 549 mass and heat 550 mole 549 mole and heat 550 types 547 Beggs and Brill Correlation 779 Broyden Method (Adjust) 539 C Col Dynamic Estimates 186 Cold Property Specifications (Column) 103 Column 77 3-phase detection 86 absorber 89 acceleration 183 advanced solving options 169 build environment 81 composition estimates 174 conflicting specifications 156 conventions 97 convergence 165 damping 183 design tab 160 dynamics tab 227 equilibrium error 157, 178 flowsheet tab 218 flowsheet variables 220 fluid package 78 heat and spec error 154, 178 impossible specifications 156 initial estimates 87 inner loop errors 153

1153

input errors 155 installation 95 k value 84 operations 116 parameters tab 172 partial condenser 94 performance tab 199 plots 201 poor initial estimates 154 property view 80 rating tab 196 reactions tab 222 reboiled absorber 91 refluxed absorber 90 run / reset buttons 160 runner 159 running 152 side ops tab 192 solver 78 solver tolerance 170 specification types 103 specifications 103 stream specification 115 tee 151 theory 82 transfer basis 159 troubleshooting 154 worksheet tab 199 Column Analysis 229, 241, 243, 246, 254-255, 300, 308, 310 Column Input Expert 45 Column Runner 228 Column Subflowsheet 77 relationship with main flowsheet 81 Columns Column Input Expert Absorber 50, 52 Distillation 52, 54 Liquid-Liquid Extractor 55-56 Reboiled Absorber 57-58 reboiler configurations 45 Refluxed Absorber 59-61, 61 Three Phase Distillation 62, 64

1154

types of column Absorber 50, 52 Distillation 52, 54 Liquid-Liquid Extractor 55-56 Reboiled Absorber 57-58 Refluxed Absorber 59-61 Three Phase Distillation 62, 64 Component Map 1149 Component Splitter 1061 splits page 1063 theory 1061 Components Flow Rate Specification (Column) 103 Fractions Specification (Column) 104 Ratio Specification (Column) 104 Recovery Specification (Column) 105 Compressor, Centrifugal 965 curves 990 isentropic efficiency 967 solution methods 966 theory 967 Compressor, Reciprocating 1011 maximum pressure 1015 piston displacement 1013 rod loading 1014 theory 1012 Compressor/Expander capacity 1006 duty 1004 efficiency 1004 features 965 head 1005 holdup 1009, 1036 speed 1006 surge control 1006 Condenser fully-condensed 94 fully-refluxed 94 partial 94 See Vessels 1068 Condenser (Column) 117

Index

Conduction through insulation/pipe 808 Control Valve 654 See Valve 654 Controller See PID Controller or Digital Point 571 Cooler 391 duty 394 pressure drop 393 theory 391 zones 396 Cooler/Heater dynamic specifications 399 holdup 401 pressure drop 392 zones 398 Create Column Stream Spec Button 1124 CSTR 905 reactions 911 Cut Point Specification 105 Cyclone 1105 constraints 1108 parameters 1105 sizing 1107 solids information 1106 D Damping Factors recycle 670 Darcy friction factor 893 Delta Temp Specification column 106 heat exchanger 436 LNG exchanger 484 Digital Point connections 657 parameters 658 Direct Action 605 direct energy stream 16 Distillation Column See Column 92 Distillation Column Template 100 Dittus and Boelter Correlation 806 Draw Rate Specification (Column) 106 Duty Ratio Specification

Index

(Column) 107 Duty Specification column 107 heat exchanger 436 Dynamic Estimates Integrator 186 dynamics mode license 4 E Efficiencies 26 Energy Stream 1143 convert to material stream 1143 Equilibrium Reactor 913 Ergun Equation 947 Examples pipe segment 789 Expander 965 curves 990 isentropic efficiency 967 solution methods 966 theory 967 F Face Plate 535 Face Plates object inspection 536 Fair72 jet flood correlation 334 Feed Ratio Specification (Column) 107 Feeder Block 1141 Filters baghouse 1101 rotary vacuum 1115 Fired Heater (Furnace) combustion reaction 405 conductive heat transfer 410 convective heat transfer 409 duty 418 dynamic specifications 411 features 405 flue gas pf 419 heat transfer 406 holdup 420 nozzles 417 radiant heat transfer 409 sizing 417 theory 405 tube side pf 418

1155

Fittings Database modifying 789 Flash 24 non-equilibrium 25 Flow Control Valve (FCV) 654 Flowsheet tags 1147 G Gap Cut Point Specification 108 General Balance 550 ratios 551 Gibbs Reactor 916 Gregory Aziz Mandhane Correlation 782 H Heat Exchanger 423 basic model (dynamic rating) 431, 441 delta pressure 444 detailed model (dynamic rating) 432, 443 dynamic rating 431 dynamic specifications 426 end point design model 428 heat balance 433 heat loss 448 holdup 458 intermediate model (dynamic rating) 442 plots 451 pressure drop 425 See also Vessels 1068 steady state rating model 430 theory 424 weighted design model 429 Heat Exchangers zones 443 Heat Loss Model 28 detailed 1077 heat exchanger 448 simple 394, 1076 Heat Transfer coefficients 443 conductive elements 446 convective elements 446 duty parameters 16

1156

kettle chiller 18 kettle heat exchanger 18 kettle reboiler 18 PFR 948 reactors 924 separator 1069 tank 1069 three-phase separator 1069 Heater 391 duty 394 pressure drop 393 theory 391 zones 396 Heavy Key (Shortcut Column) 1096 Holdup Model 24 advantages of 24 assumptions 24 Hydraulic Plots 300 Hydrocyclone 1111 constraints 1113 parameters 1111 sizing 1112 solids information 1112 Hysteresis 857 HYSYS Dynamics License 4 I If/Then/Else Statements 689 Input Experts 96 Inside Film Convection 805 Isentropic Power 969 Iteration Count recycle 671 K k Values See also specific Unit Operations 496 Kister & Haas correlation 333 L Lag Function second order 719 Lapple Efficiency Method (Cyclone) 1106 Leith/Licht Efficiency Method (Cyclone) 1106

Index

Light Key (Shortcut Column) 1096 Liner parameters 741 Liquid-liquid Hydrocyclone add 738 attach streams 739 characteristic diameter 735 configure Liner type 741 configure parameters 739 Connections page 739 create 738 cumulative distribution 734 dense dispersion 737 Design tab 739 dimensions schematic 734 Droplet Distribution page 742 Dynamics tab 744 General page 743 general results 743 Geometric page 743 geometric results 743 graphical representation 738 hydraulics 735 Hydrocyclone Number 736 inlet diameter 735 Liner Details page 741 Liner dimensions 734 Migration Probability 737 Migration Probability results 744 MP 737 nomenclature 744 Notes page 743 oil droplet distribution 734 Oil Droplet Distribution results 744 overflow diameter 735 Overflow page 743 overflow results 743 Parameters page 739 Performance tab 743 Plots page 744 property view 738 Reduced Migration Probability 737 Reynolds Number 736 RMP 737 Rosin Rammler distribution 742 Rosin Rammler modal diameter 734 Rossin Rammler 734 separation efficiency 738 Serck Baker OilSpin 741

Index

split ratio 736 Tabular page 744 Taper angles 735 theory 733 underflow diameter 735 Underflow page 744 underflow results 744 User Variables page 743 Vortoil G-liners 741 Worksheet tab 744 Liquid Flow Specification (Column) 109 Liquid Heater 17 LMTD air cooler 374 heat exchanger 424 LNG exchanger 484 LNG counter current flow 495 cross flow 495 dynamic specifications 495 features 475 heat transfer 487 holdup 496 k values 496 laminar flow 496 layers 485 parallel flow 495 pressure drop 477 zones 485 LNG Exchanger 475 heat balance 482 plots 491 Logical Operations See Digital Point, PID Controller, Selector Block, Set, Spreadsheet and Transfer Function 657 M Main Flowsheet relationship with column subflowsheet 77 Mapping 1149 Mass Balance 549 Material Stream 1121 Mixer 747 holdup 750 nozzles 749

1157

Mole and Heat Balance 550 Mole Balance 549 MPC Controller output target object 633 N Net Positive Suction Head (NPSH) 1048 Normalizing Compositions 1131 Notes Manager 23 Nozzles 27 O object inspect menu 12 OLGAS Correlation 784 Operation(s) installing 5 property view 11 Outside Conduction/Convection 806 P packings 326, 328 Paste Exported Objects 1147 Percent Heat Applied 17 Petukov Correlation 806 PFR. See Plug Flow Reactor 943 Physical Property Specification (Column) 109 PID Controller ATV tuning 533 configuration 604, 634 connections 571 control valve 654 controller action 605 Faceplate 657 flow control valve 654 modes 604 output target object 603 process variable source 602, 632 set point ramping 608 tuning 605 Pipe Contribution 893 Pipe Material Type 797 Pipe Segment 753 adding 794 calculation modes 753 example 789

1158

flow calculation 756 heat transfer 801 length calculation 755 material and energy balances 757 pressure drop calculation 754 removing 800 roughness factor 796 sizing 788 Pipe. See Pipe Segment 753 Plate Exchanger 525-526, 531-532 Plug Flow Reactor 943 catalyst data 952 duty 947 heat transfer 948 physical parameters 957 pressure drop 946 reaction balance 955 reaction extents 954 reactions 951 sizing 955 Plug Flow Reactors (PFR) duty 961 k values 961 segment holdup 961 Polytropic Efficiency 1003, 1018 Polytropic Power 969 Pourable Fraction Specification (Column) 115 Pourable Pressure Specifications (Column) 115 Power Requirement pump 1037 Pressure Flow 24 pipe contribution 893 Pressure Profile LNG exchanger 481 Product Block 1141 Pump 1037 capacity 1057 curve data 1045 curve profiles 1046 curves 1039 dynamic specifications 1055 efficiency 1057 features 1037 generate curve options 1047 head 1056 holdup 1058 inertia 1051

Index

linked 1041 nozzles 1050 NPSH 1048 power 1057 pressure rise 1057 pump efficiency 1038 speed 1057 theory 1037 Pump Around 194 column specifications 109 Q Quasi-Dimensionless Curves 981 R Reactions 31 Reactors 903 CSTR 905 duty parameters 924 equilibrium 913 general 905 Gibbs 916 heat transfer 924 holdup 923 nozzles 921 parameters 906 PFR 943 See also Vessels 1068 Reboiled Absorber See Column 91 Reboiled Absorber Template (Column) 99 Reboiler 95 See Vessels 1068 Reboiler (Column) duty 131 Reciprocating Compressor features 1011 Recycle 665 calculations 673 damping factors 670 maximum iterations 670 Reflux Ratio Specification (Column) 111 Refluxed Absorber See Column 90 Refluxed Absorber Template (Column) 100

Index

Relief Valve 851 capacity correction 853 flow equations 853 holdup 857 nozzles 856 types 853 valve lift 856 Resistance Equation rotary vacuum filter 1117 Reverse Action 605 Rosin Rammler distribution 742 Rotary Vacuum Filter 1115 cake properties 1116 parameters 1115 resistance equation 1117 sizing 1116 Roughness Factor (Pipe) 796 S Secant Method (Adjust) 539 Selector Block 677 connections 677 Separator 1067 duty parameters 126, 1093 kettle heat exchanger 126 physical parameters 1069 reaction sets 1072 See Vessels 1068 theory 1068 Serck Baker Oilspin liners 733 Set 683 Set Point Ramping 608 Shells baffles 440 diameter 440 fouling 440 in parallel 438 in series 438 shell and tube bundle data 439 Sherwood/Leva/Eckert GPDC pressure drop correlation 338 Shortcut Column 1095 Side Operations Input Expert 192 Side Rectifier 194 Side Stripper 193 Sieder and Tate Correlation 806 Simple Filter. See Simple Solid Separator 1119

1159

Simple Solid Separator 1119 splits page 1119 slug analysis 825 Smith, Dresser, and Ohlswager jet flood correlation 336 Solid Operations baghouse filter 1101 cyclone 1105 hydrocyclone 1111 rotary vacuum filter 1115 simple solid separator 1119 Specifications active 165, 434 advanced solving options 169 alternate 166 completely inactive 434 current 166 estimate 165, 434 fixed and ranged 170 heat exchanger 413, 433 LNG Exchanger 482 primary and alternate 170 property view 168 types 103 Splits component splitter 1063 Simple Solid Separator 1119 Spreadsheet 685 exporting variables 685 general math functions 686 importing variables 685 logarithmic functions 688 logical operations 689 trigonometric functions 688 Static Head Contributions 27 Steady State Mode terminology 3 Stopping/Resetting Column Calculations 153 Streams Column Specifications 115 energy (See Energy Stream) 1143 material (See Material Stream) 1121 Subflowsheets 1146 blank flowsheets 1146 connections 1147 feed and product connections 1147 installing 1146

1160

mapping 1149 parameters 1148 transfer basis 1148 variables 1151 Surge Control 1006 T Tank 1067 duty parameters 126, 1093 kettle heat exchanger 126 physical parameters 1069 reaction sets 1072 See Vessels 1068 TBP Envelope 218 Tear Location (Recycle) 673 Tee 859 holdup 862 splits 860 Tee (Column) 151 Tee Split Fraction Specification (Column) 112 Templates 3 sidestripper crude column 96 4 sidestripper crude column 96 absorber 99 column 97, 159 distillation 100 FCCU main fractionator 96 liquid-liquid extractor 95 reading existing 1146 reboiled absorber 99 refluxed absorber 100 vacuum reside tower 96 Three-Phase Separator 1067 physical parameters 1069 reaction sets 1072 See Vessels 1068 theory 1068 Three Phase Distillation detection of three phases 86 three phase theory 86 Three Phase Separator duty parameters 126, 1093 kettle heat exchanger 126 Tower efficiencies 147 heat loss 145 holdup 150

Index

Tower (Column) 139 Performance page 147 Transfer Function 713 integrator 716 lag function 717 lead function 718 sine wave function 719 Transitions Fluid Package Transition 707 property view 707 Transport Property Specifications (Column) 114 Tray Residence time 149 Tray Temperature Specification (Column) 113 Tubes (Heat Exchanger) dimensions 441 heat transfer length 441 U UA LNG exchanger 484 Unit Operations Compressor Non Dimensional Curves 981 EDR PlateFin 507 External Data Linker 663-664 property view 664

User Property Specification (Column) 114 V Valve 865 actuator 895 friction factor 893 holdup 894 manufacturer 870 nozzles 890 pipe contribution 893 sizing 867 sizing method 868 types 870 Vapor Flow Specification (Column) 114 Vessel duty parameters 16 kettle chiller 18 kettle heat exchanger 18 kettle reboiler 18 Vessel Heater 16 Vessels boot 1075 features 1068 geometry 1074 heater type 16 holdup 1093 liquid heater 17 nozzles 1075 Vortoil G-liners 733

LNG PlateFin 507 PID Controller Foxboro PID Controller Algorithm 623 HYSYS PID Controller Algorithm 621 Pipe Segment 825, 829

W Wallis-Aspen pressure drop correlation 343 Wave Flow (Pipe Segment) 782 Z Zones 398 cooler/heater 396 heat exchanger 443

deposition method 828 slug calculation 825 Stream Cutter 707, 712 fluid package transition 707

Index

1161