38997683 Methyl Tertiary Butyl Ether MTBE Full Report
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
MEMBER OF GROUP AND SUPERVISORS
1
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
ACKNOWLEDGEMENT
First and foremost, thank you to Allah S.W.T for giving us the strength to finish up this project report. Without Your Willingness we would not be able to complete this project. It would be impossible to acknowledge adequately all the people who have been influential, directly or indirectly in forming this project. We would like to take this opportunity to express our deepest gratitude to our supervisors, Encik Mohd Imran Bin Zainuddin and Puan Sunita Binti Jobli who has given us his constant encouragement constructive advises and his patient in monitoring our progress in this project. Our appreciation and special thanks goes, Puan Hasnora Binti Jafri, Puan Junaidah Binti Jai, Encik Aziz Bin Ishak for supplying the valuable information and guidance for this project. We greatly indebted to Encik Napis Bin Sudin for his cooperation and willingness to be interviewed and for provide us with invaluable information and for his resourcefulness in gathering material. Special thanks owe to Puan Masni Bt Ahmad for her willingness to be interviewed and for the painstaking care she has shown in assisting us throughout the project. We also would like to express our appreciation to the Malaysia Industrial Development Authority (MIDA), Pusat Informasi Sirim Berhad, Petronas Resource Center, Jabatan Perangkaan Malaysia and Tiram Kimia Sdn.Bhd. (Kuala Lumpur) for their generous supply of relevant documents and material needed research. Last but not least to all my lecturers, family, friends and collegues for their encouragement and kind support when we need it most.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
ABSTRACT
The purpose for this MTBE or Methyl tertiary Butyl Ether plant is to produce 300,000 metric tonne/year. MTBE is the simplest and most cost effective oxygenate to produce, transport and deliver to customers. The additive works by changing the oxygenate / fuel ratio so that gasoline burns cleaner, reducing exhaust emissions of carbon monoxide, hydrocarbons, oxides of nitrogen, fine particulates and toxic. Two units will be considered which are the fluidizations, (Snamprogetti) Unit and the Etherification Unit. The raw materials used are isobutane, methanol, and water as feedstock. In addition, two types of catalysts are chromia alumina catalyzed compound in Snamprogetti Unit, while sulphonic ion exchanged resin catalyzed is used in the MTBE reactor. A good deal of catalyst has been devoted to improve the activity, selectivity, and the lifetime of the catalysts. In the Design Project 2, we emphasize in the individual chemical and mechanical designs for selected equipments in the plant. The chosen equipments are Catalytic Cracking Reactor, Multitubular Fixed Bed Reactor, MTBE Distillation Column, LiquidLiquid Extraction Column and Heat Exchanger. Design Project 2 also includes Process Control, Safety, Economic Evaluation, Process Integration and as well as Waste Treatment, which are considered as group works.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
CONTENTS
TITLE
PAGE
DECLARATION
II
CERTIFICATION
III
ACKNOWLEDGEMENT
V
ABSTRACT
VI
LIST OF TABLES LIST OF FIGURES LIST OF NOMENCLATURES
REPORT 1 CHAPTER 1 PROCESS BACKGROUND AND INTRODUCTION 1.1 Introduction 1.2 Historical Review of MTBE Production Process 1.2.1 UOP Oleflex Process 1.2.2 Philips Star Process 1.2.3 ABB Lummus Catofin Process 1.2.4 Snmprogetti Yartsingtez FBD Process
1 2 3 3 3 4
CHAPTER 2 PROCESS SELECTION 2.1 2.2
Method Consioderation Detailed Process Description 2.2.1 Snaprogetti Yarsingtez fbd Process 2.2.2 MTBE Unit 2.2.3 Distillation Column Unit 2.2.4 Liquid-Liquid Extraction Unit
5 7 7 8 8 9
CHAPTER 3 ECONOMIC SURVEY 3.1 3.2 3.3
3.4
Market Survey 3.1.1 World Market Asia Market Demand Production Capacity
10 10 11 11 14
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.5 3.6
3.7
Supply Market Price 3.6.1 Methanol 3.6.2 Isobutane 3.6.3 Catalyst 3.6.4 Conclusion Economic Analysis 3.7.1 Break Even Analysis 3.7.2 Data Calculation1
14 15 15 16 16 16 17 17 20
CHAPTER 4 PLANT LOCATIONS & SITE SELECTION 4.1 4.2
4.3
4.4
Plant Location 24 General Consideration On the site Selection 24 4.2.1 Location with Respect To Marketing Area 25 4.2.2 Raw Material supply 25 4.2.3 Transport Facilities 25 4.2.4 Availability Of Labor 25 4.2.5 Availability Of Utilities 26 4.2.6 Environmental Impact and Effluent Disposal 26 4.2.7 Local Community Considerations 26 4.2.8 Land (Site Consideration) 26 4.2.9 Political and Strategic Consideration 27 Overview on Prospective Locations 27 4.3.1 Teluk Kalong 28 4.3.2 Tanjung Langsat 28 4.3.3 Bintulu 29 Conclusion 33
CHAPTER 5 ENVIRONMENTAL CONSIDERATION 5.1 5.2 5.3
Introduction Stack gas 5.2.1 Gas Emission treatment Wastewater Treatment 5.3.1 Wastewater characteristic 5.3.1a) Priority pollutants 5.3.1b) Organic 5.3.1c) Inorganic 5.3.1d) pH and Alkalinity 5.3.1e) Temperature 5.3.2 Liquid waste treatment 5.3.2a) Equalization treatment 5.3.2b) Solid waste treatment 5.3.3 Waste Minimization
34 35 35 35 35 36 36 37 37 38 38 38 39 41
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
CHAPTER 6 SAFETY CONSIDERATION 6.1 6.2
6.3
Introduction 42 Material Safety Data Sheet 43 6.2.1 Isobutane 43 6.2.1.1 Product Information 43 Physical & Chemical Properties 43 6.2.1.2 Immediate Health Effects 44 6.2.1.3 First Aid Measure 44 6.2.2 N-Butane 44 6.2.2.1 Handling and Storage 45 6.2.3 Methanol 45 6.2.4 MTBE 46 6.2.4.1 Physical State and Appearance46 6.2.4.2 Physical Dangers 46 6.2.4.3 Chemical Dangers 47 6.2.4.4 Inhalation Risks 47 6.2.5 TBA 47 6.2.5.1 Recognition 48 6.2.5.2 Evaluation 48 6.2.5.3 Controls 48 Hazard Identification & Emergency Safety & Health Risk 49
CHAPTER 7 MASS BALANCE 7.1 7.2 7.3 7.4
7.5 7.6
7.7 7.8 7.9
Snamprogetti -Yarsingtez FBD Unit Separator Mixer MTBE Reactor 7.4.1 1st Reaction in rector 7.4.2 2nd Reaction in reactor 7.4.3 3rd Reaction in reactor 7.4.4 Overall reaction Distillation Column Liquid Extraction Column Distillation Column Overall reaction system; flow diagram Scales Up Factor
51 53 53 54 55 56 57 58 59 60 61 62 63
CHAPTER 8 ENERGY BALANCES 8.1 8.2
Energy Equation Energy balance: Sample of calculation 8.2.1 Pump 1 8.2.2 Cooler 1 8.2.3 Separator 8.2.4 MTBE Reactor 8.2.5 Pump 2
64 65 73 75 76 78 79
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
8.2.6 8.2.7 8.2.8 8.2.9 8.2.10 8.2.11 8.2.12 8.2.13 8.2.14 8.2.15 8.2.16
Mixer Expander 1 Cooler 1 Distillation Column 1 Cooler 2 Pump 3 Extraction Column Pump 4 Pump 5 Distillation Column 2 Cooler 3
CHAPTER 9 HYSYS
80 81 82 84 86 87 88 89 91 92 93
95
APPENDICES
REPORT 2 CONTENTS PAGE
CHAPTER 1 CHEMICAL DESIGN AND MECHANICAL DESIGN SECTION 1 CATALYTIC CRACKING DESIGN
2.2
1.1 Introduction 1.2 Estimation of Cost Diameter of Reactor 1.3 Calculation of TDH Height 1.4 Minimum Fluidization Velocity 1.5 Calculation for Terminal Velocity 1.6 Find the Value Kih 1.7 Find the value Eo 1.8 Calculation of Solid Loading 1.9 Calculation for Holding Time 1.10 Calculation for Pressure Drop 1.11 Determine the Direction and Flowrate 1.12 Design of Cyclone 1.13 Calculation for Mechanical Design Mechanical Design 2.2.1 Introduction 2.2.2 Design stress 2.2.3 Welded Joint Efficiency
1 3 4 4 5 8 9 10 12 14 15 17 21 58 59 59
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
2.2.4 2.2.5 2.2.6 2.2.7 2.2.7.1
2.2.8 2.2.9 2.2.10 2.2.11 2.2.12 2.2.13 2.2.14 2.2.15 2.2.16 2.2.17 2.2.18 2.2.19 2.2.20 2.2.21
Corrosion allowance Minimum thickness of cylindrical section of shell Minimum thickness of domed head Loading stress Dead weight load 1.2.7.1 Dead Weight of Vessel 1.2.7.2 Weight of the Tubes 1.2.7.3 Weight of Insulation 1.2.7.4 Weight of Catalyst 1.2.7.5 Total Weight 1.2.7.6 Wind Loading 1.2.7.7 Analysis of Stresses Dead Weight Stress Bending Stress Radial Stress Check Elastic Stability Vessel Support Skirt Thickness Height of the Skirt Bending Stress at Base of the Skirt Bending Stress in the Skirt Base Ring and Anchor Bolt Design Compensation for Opening and Branches Compensation for Other Nozzles Bolted Flange Joint 2.2.20.1 Type of Flanges Selected 2.2.20.2 Gasket Flange face
SECTION 3 3.1 3.2 3.3
3.4
59 59 60 61 61 61 62 62 63 63 63 64 65 65 66 67 68 68 69 70 70 71 73 74 74 74 75 75
MTBE DISTILLATION COLUMN
Introduction Selection f Construction Material Chemical Design 3.3.1 Determine the Number of Plate 3.3.2 Determination of Number of Plate 3.3.3 Physical Properties 3.3.4 Determination of Column Diameter 3.3.5 Liquid Flow Arrangements 3.3.7 Plate Layout 3.3.8 Entrainment Evaluation 3.3.9 Weeping Rate Evaluation 3.3.13 Number of Holes 3.3.14 Column size Mechanical Design 3.4.1 Material construction 3.4.2 Vessel Thickness 3.4.3 Heads and closure 3.4.4 Total Column Weight
78 79 79 81 88 89 89 90 91 91 94 95 96 98 98 99
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.5
3.4.5 Wind Loads 3.4.6 Stiffness Ring Vessel Support Design
SECTION 4 4.1 4.2
4.3
5.1 5.2
5.3
DESIGN OF LIQUID-LIQUID EXTRACTION COLUMN
Introduction Chemical Design 4.2.1 Choice of Solvent 4.2.2 Estimation the Physical Properties 4.2.3 Determination the Number of Stage 4.2.4 Sizing of Sieve Tray 4.2.5 Number of Holes 4.2.6 Column Parameter 4.2.7 Weeping Evaluation Mechanical Design 4.3.1 Material Construction 4.3.2 Vessel Thickness 4.3.3 Design of Domed Ends 4.3.4 Column Weight 4.3.4.1 Dead Weight of Vessel 4.3.4.2 Weight of Plate 4.3.4.3 Weight of Insulation 4.3.4.4 Total weight 4.3.4.5 Wind Loading 4.3.5 Analysis of Stress 4.3.5. 1 Longitudinal & Circumferential Pressure Stress 4.3.5.2 Dead weight 4.3.5.3 Bending Stress 4.3.5.4 Buckling 4.3.6 Vessel Support Design 4.3.6.1 Skirt Support 4.3.6.2 Base Ring and Anchor 4.3.7 Piping Sizing
SECTION 5
100 100 100
103 104 104 104 105 107 107 107 108 110 111 111 112 112 113 113 113 114 114 115 115 115 115 116 117 117 119 122
HEAT EXCHANGER DESIGN
Introduction 5.1.1 Designing the heater Chemical Design 5.2.1 Physical Properties of the Stream 5.2.2 The Calculation 5.2.3 Number of Tubes Calculation 5.2.4 Bundle and Shell Diameter 5.2.5 Tube Side Coefficient 5.2.6 Shell Side Coefficient 5.2.7 Overall Heat Transfer Coefficient 5.2.8 Tube Side Pressure Drop 5.2.9 Shell Side pressure Drop Mechanical Design 5.3.1 Design Pressure
127 129 130 130 131 133 134 135 137 139 140 140 142 142
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
5.3.2 5.3.3 5.3.4 5.3.5 5.3.6 5.3.7 5.3.8 5.39 5.3.10 5.3.11 5.3.12 5.3.13 5.3.14 5.3.15
Design Temperature Material of Construction Exchanger Type Minimum Thickness Longitudinal Stress Circumferential Stress Minimum Thickness of Tube wall Minimum Thickness of Head and Closure Minimum Thickness of the Channel Cover Design Load Pipe Size Selection for the Nozzle Standard Flanges Design Of Saddles Baffles
142 142 143 143 144 144 144 145 146 147 150 150 152 152
CHAPTER 2 PROCESS CONTROL AND INSTRUMENTATION 2.1 2.2 2.3
Introduction Objective of control Control system design sheet 2.3.1 Heat Exchanger 2.3.2 Catalytic cracking fluidized bed reactor 2.3.3 Compressor 2.3.4 Condenser 2.3.5 Separator 2.3.6 Fixed bed reactor 2.3.7 Distillation Column 2.3.8 Liquid -liquid extraction Column 2.3.9 Distillation Column 2.3.10 Mixer 2.3.11 Expander
154 155 156 156 157 158 159 160 161 162 163 164 165 166
CHAPTER 3 SAFETY CONSIDERATION 3.1 3.2 3.3
3.4
Introduction Hazard and Operability Study Plant Start Up and Shut Down Procedure 3.3.1 Normal Start Up and Shut Down the Plant 3.3.1.1 Operating Limits 3.3.1.2 Transient Operating and Process Dynamic 3.3.1.3 Added Materials 3.3.1.4 Hot Standby 3.3.1.5 Emergency Shut Down 3.3.2 Start up and Shut down Procedure for the main Equipment 3.3.2.1 Reactor 3.3.2.2 Distillation Column 3.3.2.3 Liquid-Liquid Extraction Column 3.3.2.4 Heat Exchanger Emergency Response Plan (ERP)
167 168 170 171 171 172 172 172 172 172 172 173 174 175 175
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.5
3.4.1 Emergency Response Procedures 3.4.2 Evacuation Procedures 3.4.3 Fires 3.4.4 Explosion, Line Rupture or Serious Leak 3.4.5 Other Emergencies Plant Layout
176 176 177 177 177 178
CHAPTER 4 ECONOMIC EVALUATION 4.1 4.2 4.3
4.4
Introduction Cost Estimation Profitability Analysis 4.3.1 Discounted Cash flow 4.3.2 Net Present Value 4.3.3 Cumulative Cash flow Diagram 4.3.4 Rate of Return 4.3.5 Sensitivity Analysis 4.3.6 Payback Period Conclusion
184 187 199 199 202 203 204 205 206 208
CHAPTER 5 PROCESS INTEGRATION AND PINCH TECHNOLOGY 5.1 5.2 5.3 5.4 5.5
Introduction Pinch Technology The Problem Table Method The Heat Exchanger Network Minimum number of exchangers
209 209 210 214 216
CHAPTER 6 WASTE TREATMENT 6.1 6.2 6.3 6.4 6.5 6.6
Introduction Wastewater Treatment Wastewater Treatment Plant Design Sludge Treatment Waste Treatment Plant Layout Absorption tank using granular activated carbon 6.6.1 Analysis of the absorption process 6.6.2 Breakthrough Absorption capacity
220 221 224 229 230 231 232 233
APPENDICES
11
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
LIST OF TABLES OF DESIGN I
TABLE
TITLE
1.1
The Physical and Chemical Properties of MTBE
2.1
The Comparison of the UOP Oleflex, Philips Star
PAGE 2
SP-Isoether FBD Process
6
3.1
Trade Balance of MTBE in Asia and Pacific
12
3.2
MTBE Balances for Asia and Pacific
13
3.3
Production, Import, Export & Consumption in Europe in Year 2000
14
3.4
Supplies MTBE Plant in Asia & Pacific
15
3.5
Standard Price for Isobutane
16
3.6
Cost of Producing MTBE 500000 tonne/year
18
3.7
Value in US Dollar Converted to RM
20
3.8
Value in US Dollar Converted to RM per tonne
20
3.9
Data Calculation by using Microsoft Excel in RM
23
4.1
The Comparison of the Potential Site Location
30
4.2
The Comparison of Location in term of Weightage Study
31
4.3
The Electricity Tariffs (Industrial Tariff) for Peninsular Malaysia and Sarawak
33
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
LIST OF TABLES OF DESIGN II
TABLE
TITLE
PAGE
Chapter 1 Section 1 1.1
Calculation for Terminal Velocity in Different Size of dp.
8
1.2
Correlation of Three Investigators
10
1.3
Data Calculation to Find Solid Loading
12
1.4
Summary of Mechanical Design
40
3.1
The Composition in Feed Stream
80
3.2
The Composition in Top Stream
80
3.3
The Composition in Bottom Stream
80
3.4
The Average Relative Volatility,
3.5
The Non-key Flow of the Top Stream
82
3.6
The Non-key Flow of the Bottom Stream
83
3.7
MTBE Equilibrium Curve
85
3.8
Provisional Plate Design Specification
97
3.9
Summarized Results of Mechanical Design
101
3.10
Design Specification of the Support Skirt
102
4.1
Provisional Plate Design Specification
106
4.2
Summary of the Mechanical Design
118
4.3
Stress Analysis for Liquid-Liquid Extraction Column
119
4.4
Design Specification of the Support Skirt
119
4.5
Piping Sizing for Liquid-liquid Extraction Column
120
Section 3
α
82
Section 4
Section 5 5.1
Properties of Raw Material (Isobutane and N-butane) and Steam for (E100)
5.2 5.3
130
Summary of Chemical Design For Heat Exchanger In Series
141
By taking D = 100 mm, the selected tube nozzle
149
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
TABLE
TITLE
PAGE
5.4
By taking D = 500 mm, the selected tube nozzle is:
149
5.5
Standard Flange for Inlet isobutene
150
5.6
Standard Flange for Outlet isobutene
151
5.7
Standard Flange for Inlet Steam
151
5.8
Standard Flange for Outlet Steam
151
5.9
Using Ds = 600mm, the Standard Steel Saddles for Vessels up to 1.2m
5.10
152
Summary of Mechanical Design For Heat Exchanger in Series
153
2.1
Parameter at Heat Exchanger
151
2.2
Parameter at Catalytic Cracking Fluidized Bed Reactor
152
2.3
Parameter at Compressor
153
2.4
Parameter at Condenser
154
2.5
Parameter at Separator
154
2.6
Parameter at Fixed Bed Reactor
155
2.7
Parameter at MTBE Distillation Column
156
2.8
Parameter at Liquid-liquid Extraction Column
157
2.9
Parameter at Distillation Column
158
2.10
Parameter at Mixer
159
2.11
Parameter for Expander
160
Important Features in a HAZOP Study
170
4.1
Labor Cost
189
4.2
Estimation Cost of Purchase Equipment
197-198
4.3
Annual Cash flow Before Tax
200
4.4
Annual Cash flow After Tax
201
4.5
Present Worth Value
202
Chapter 2
Chapter 3 3.1 Chapter 4
14
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.6
After Tax Cumulative Cash Flow
TABLE
203
TITLE
PAGE
4.7
Present Value (RM) When i = 30% & i = 40%
204
4.8
Future Value (RM) When MARR = 15%
205
4.9
Simple Payback Period
206
4.10
The Interpolation Simple Payback Period
206
4.11
Discounted Payback Period
207
4.12
The Interpolation Discounted Payback Period
207
5.1
Shows the process data for each stream.
210
5.2
Interval Temperature for ΔTmin = 10oC
211
5.3
Ranked order of interval temperature
212
5.4
Problem Table
213
Chapter 5
Chapter 6 6.1
Parameter Limits for Wastewater and Effluent under the Environmental Quality Act 1974
6.2
208
Functions of Pumps in the Waste Treatment Plant
215
15
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
LIST OF FIGURES OF DESIGN I
FIGURE 3.1
TITLE
PAGE
MTBE’s Role in US Gasoline grew rapidly Through 1995
10
3.2
World MTBE Demand (1998-2010) – Mod Scenario
11
3.3
MTBE supply & Demand Asia and Pacific
13
3.4
Breakeven Analysis Chart Calculated by using Excel
19
5.1 .
Functional Elements in a Solid-Waste Treatment System
40
16
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
LIST OF FIGURES OF DESIGN II
FIGURE
TITLE
PAGE
Chapter 1 Section 1 1.1
Illustration Diagram of the Reactor
2
1.2
CDRe2 and CD/Re vs. Reynolds Number
6
Analysis of Stresses
67
3.1
MTBE Distillation Column
78
3.2
McCabe-Thiele Diagram
86
5.1
Heat Exchanger in Series for the Heating Process
129
5.2
Steel Pipe Nozzle
149
5.3
Standard Flange
150
2.1
Control Scheme for the Heat Exchanger
156
2.2
Control Scheme for Catalytic Cracking
Section 2 2.1 Section 3
Section 5
Chapter 2
Fluidized Bed Reactor
157
2.3
Control Scheme for the Compressor
158
2.4
Control Scheme for the Condenser
159
2.5
Control Scheme for the Separator
160
2.6
Control Scheme for the Fixed Bed Reactor
161
2.7
Control Scheme for the MTBE Distillation Column
162
2.8
Control Scheme for the Liquid-liquid Extraction Column
163
2.9
Control Scheme for the Distillation Column
164
2.10
Control Scheme for the Mixer
165
2.11
Control Scheme for the Expander
166
17
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
FIGURE
TITLE
PAGE
Chapter 3 3.1
Methyl tert-Butyl Ether (MTBE) Plant Layout
180
3.2
Methyl tert-Butyl Ether (MTBE) Plant Evacuation Routes
181
3.3
PID before HAZOP
182
3.4
PID after HAZOP
183
Cumulative Cash Flow (RM) Versus Year
203
5.1
Diagrammatically representation of process stream
210
5.2
Intervals and streams
211
5.3
Heat Cascade
212
5.4
Grid for 4 stream problem
213
5.5
Grid for 4 Stream Problem
214
5.6
Proposed Heat Exchanger Network
216
6.1
The Sludge Treatment System
229
6.2
Waste Treatment Plant Layout
231
Chapter 4 4.1 Chapter 5
Chapter6
18
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Ar
-
Archimedes number
a
-
acceleration
B
-
settling chamber longitudinal cross-sectional area
b
-
dimension
C
-
constant
CD
-
drag coefficient
c
-
concentration
D
-
system diameter
d
-
particle diameter
de
-
effective fiber diameter
E,
-
field intensity
F
-
cross-sectional area
Pr
-
Fronde number
g
-
gravitational acceleration
H
-
height
K
-
precipitation constant ,
A
-
Cross sectional area of catalytic reactor
Aor
-
Area of orifice
C Ag
-
Concentration of gas reactant
CD
-
Drag coefficient
d Bv
-
Diameter of bubble in the bed
dp
-
Particle diameter
D
-
Diffusivity
Dt
-
Diameter of catalytic reactor
e
-
Thickness
E
-
Activation energy
19
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
FBo
-
Mass flow of coal to the catalytic reactor
FC
-
Fixed carbon mass fraction
Hbed
-
Height of bed
Hh
-
Height of Catalytic reactor
J
-
Joint factor
k”
-
Reaction rate constant
k
-
Reaction rate constant
K eq
-
Equilibrium constant
L
-
Height above the bed
n
-
Total no of orifice
N
-
No of holes in 1 m2 area
Nor
-
No of orifice in 1 m2 area
PCO , PH 2 O
-
Pi
Design stress
-
Partial pressure
rC , rS -
Rate of reaction
R
-
Ideal gas constant
Ret
-
Reynolds number
Rp
-
Radius of particle
t
-
Total holding time
T
-
Temperature
Uo
-
Superficial gas velocity
Umf
-
Minimum fluidization velocity
Ut
-
Terminal velocity
VBed
-
Volume of bed
WBed
-
Weight of coal in bed
WC
-
Total mass of carbon
X
-
Conversion factor
α
-
Fitting parameter (for this design is 0.21)
β
-
Fitting parameter (for this design is 0.66)
ρg
-
Gas density
ρB
-
Molar density
ρs
-
Bulk density of catalyst
ρp
-
Particle density
20
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
µg
-
Gas viscosity
τ
-
Time for complete conversion of reactant particle
∆p
-
Pressure drop
E
-
total elutriation rate of particles
Ef
-
frictional force of particles
Ei
-
entrainment rate of panicle size i
Ei∞
-
elutriation rate of particle size i
Eo
-
total entrainment rate at bed surface
E∞
-
total elutriation rate of particles
g
-
gravitational acceleration constant
gc
-
gravitational conversion constant, m kg/s2 kg -force
Gi
-
solids flow rate
h
-
height above dense bed surface
Rep
-
particle Reynolds Number = ρ g (U o − U ts ) d p / µ
Ret
-
dpU ρg / µ
t
-
time
Umf
-
minimum fluidization velocity
Uo
-
superficial gas velocity
Usi
-
solid velocity (upward)
Us
-
single particle terminal velocity of particle size i
W
-
weight fraction of bed
Ws
-
weight of solid particles in verlical pipe having length h
Xi
-
weight fraction of particle size i in bed
Greek Symbols
ε
-
voidage in freeboard
21
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
εi
-
voidage in freeboard for system having only particle size i
λ
-
solid friciion coefficient
ρg
-
gas density
ρp
-
particle density
22
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
CHAPTER 1
PROCESS BACKGROUND AND INTRODUCTION
1.1
INTRODUCTION
Methyl tertiary butyl ether (MTBE) is produced by reacting isobutene with methanol over a catalyst bed in the liquid phase under mild temperature and pressure. Isobutene can be obtained from stream cracker raffinate or by the dehydrogenation of isobutane from refineries. Ether in general is a compound containing an oxygen atom bonded to two carbon atoms. In MTBE one carbon atom is that of a methyl group – CH3 and the other is the central atom of a tertiary butyl group, -C (CH3)). At room temperature, MTBE is a volatile, flammable, colorless liquid with a distinctive odour. It is miscible with water but at high concentrations it will form an air-vapour explosive mixture above the water, which can ignite by sparks or contact with hot surfaces. MTBE has good blending properties and about 95% of its output is used in gasoline as an octane booster and an oxygenate (providing oxygen for cleaner combustion and reduced carbon monoxide emissions). It is also used to produce pure isobutene from C4 streams by reversing its formation reaction. It is a good solvent and extractant.
Table 1.1: The Physical and chemical properties of MTBE
23
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Chemical formula Molecular structure Oxygen content Physical state (at normal
C5H12O (CH3)4CO 18.2 wt% Colorless liquid
temperature and pressure) Boiling point Melting point Flash point Autoignition temperature Flammable limits in air Relative density Vapour pressure Reactive index Color Water solubility
55.2oC -108.6 oC 30 oC 425 oC 1.5 – 8.5% 0.7405g/ml at 20 oC 245 mm Hg at 25 oC 1.3690 at oC Colorless 42000mg/l at 25 oC (1
65
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
6.2.1.3 Immediate Health Effects: Eye: Because the liquid product evaporates quickly, it can have a severe chilling effect on eyes and can cause local freezing of tissues (frostbite). Symptoms may include pain, tearing, reddening, swelling and impaired vision. Skin: Because the liquid product evaporates quickly, it can have a severe chilling effect on skin and can cause local freezing of tissues (frostbite). Symptoms may include pain, itching, discoloration, swelling, and blistering. Not expected to be harmful to internal organs if absorbed through the skin. Ingestion: Material is a gas and cannot usually be swallowed. Inhalation: This material can act as a simple asphyxiant by displacement of air. Symptoms of asphyxiation may include rapid breathing, in coordination, rapid fatigue, excessive salivation, disorientation, headache, nausea, and vomiting. Convulsions, loss of consciousness, coma, and/or death may occur if exposure to high concentrations continues. 6.2.1.4 First Aid Measures Eye: Flush eyes with water immediately while holding the eyelids open. Remove contact lenses, if worn, after initial flushing, and continue flushing for at least 15 minutes. Get immediate medical attention. Skin: Skin contact with the liquid may result in frostbite and burns. Soak contact area in tepid water to alleviate the immediate effects and get medical attention. Ingestion: No specific first aid measures are required because this material is a gas and cannot usually be swallowed. Inhalation: For emergencies, wear a niosh approved air-supplying respirator. Move the exposed person to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get immediate medical attention. 6.2.2
N-Butane
N-Butane synonym with I-Butane, Butane, and Normal Butane is a flammable gas. NButane is heavier than air and may travel considerable distance to an ignition source.
66
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
N-Butane is listed under the accident prevention provisions of section 112(r) of the Clean Air Act (CAA) with threshold quantity (TQ) of 10000 pounds.
Physical and Chemical Properties Parameter
value
Physical state
units
: Gas o
Vapor pressure at 70 F
: 31
psia
Vapor density at STP
: 2.07
Evaporation point
: not available
Boiling point
: 31.1
o
Freezing point
: -0.5
o
pH
: not available
Solubility
: insoluble
Odor and appearance
: a colourless and odourless gas
Stability
: stable
Condition to avoid
: high temperature
F
C
6.2.2.1 Handling and storage Protect cylinders from physical damage. Store in cool, dry, well- ventilated area away from heavily trafficked areas and emergency exits. Do not allow the temperature where cylinders are stored to exceed 130oF. Cylinders should be stored upright and firmly secured to prevent falling or being knocked over. Full and empty cylinders should be segregated. Use a “first in first out” inventory systems to prevent full cylinders from being stored for excessive periods of time. Never carry a compressed gas cylinder or a container of a gas in cryogenic liquid form in an enclosed space such as a car trunk, van or station wagon. A leak cans re4sult in a fire, explosion, asphyxiation or a toxic exposure. 6.2.3
Methanol
Methanol synonyms with Methyl alcohol and in chemical family alcohol with the formula CH3OH. Methanol is a clear, colourless, mobile, volatile, flammable liquid and it’s soluble in water, alcohol and ether.
67
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Physical and Chemical properties: Parameter
value
Physical state
: liquid
Boiling Point
: 64.7oc
Vapor Pressure (20oc)
: 128 mb
Vapor Density (air=1)
: 1.11
Solubility in water ,%wt
: full
Specific Gravity
: 0.792 g/cm3
Appearance and odor
: liquid-colorless-odor specific
Fire and Explosion Hazard data: Flash point
: closed cup: 12oc
Flammable limits, % vol
: Lel: 6, Uel : 36.5
Extinguishing media
: Foam – CO2 –halogenated agents
Special fire fighting
: Avoid contact with oxidizing materials
Unusual fire and explosion : Moderate Reactivity Data: Stability
: Medium
Conditions to avoid
: Oxidizing materials
Incompatibility
: Sulfo-chromic mixtures
Special Precautions Precaution to be taken in handling and storing Methanol: store in iron or steel containers or tanks. Small quantities can be stored in reinforced glass containers. 6.2.4
MTBE
6.2.4.1 Physical state, appearance MTBE is chemically stable; it does not polymerize, nor will decompose under normal conditions of temperature and pressure. Unlike most ether, MTBE does not tend to form peroxides (auto-oxidize). The physical state of MTBE is that MTBE is in the form of liquid at room temperature (25oC). It is a colourless liquid with the billing point at
68
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
55.2oC 131.4oF. The freezing point of MTBE is –108.6oC –163.5oC. The density of MTBE at 25oC is 735g/cm3. 6.2.4.2 Physical dangers MTBE is non-reactive. It does not react with air, water, or common materials of construction. The reactivity of MTBE with oxidizing materials is probably low. However, without definitive information, it should be assumed that MTBE reacts with strong oxidizers, including peroxides. 6.2.4.3 Chemical dangers MTBE is highly flammable and combustible when exposed to heat or flame or spark, and it is a moderate fire risk. Vapours may form explosive mixtures with air. It is unstable in acid solutions. Fire may produce irritating, corrosive or toxic gases. Runoff from fire control may contain MTBE and its combustion products. Occupational exposure limits (OELs) Routes of Exposure 6.2.4.4 Inhalation risk Like other ethers, inhalation of high levels of MTBE by animals or humans results in the depression of the central nervous system. Symptoms observe red in rats exposed to 4000 or 8000 ppm in air included labored respiration, ataxia, decreased muscle tone, abnormal gait, impaired treadmill performance, and decreased grip strength. These symptoms were no longer evident 6 hours after exposure ceased. A lower level of MTBE, 800ppm did not produce apparent effects (Daughtrey et al., 1997). A number of investigations have been conducted to examine the self-reported acute MTBE in gasoline vapors during use by consumers. This research includes both epidemiological studies and studies involving controlled exposure of volunteers to MTBE at concentrations similar to those encountered in refueling an automobile (Reviewed in USEPA, 1997, and California EPA, 1998). In general, the studies involving controlled human exposures in chambers to levels of MTBE similar to those experienced during refueling and driving an automobile have not shown effects of
69
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
MTBE on physical symptoms (e.g. irritation), mood, or performance based tests of neurobehavioral function. 6.2.5
TBA (TERT - BUTYL ACOHOL)
CAS Number: 75-65-0 Synonyms:
tert-Butanol 2-methyl-2-propanol TBA t-butylhydroxide 1,1-dimethylethanol trimethylmethanol trimethylcarbinol
6.2.5.1 Recognition NIOSH/OSHA Health Guideline. Summarizes pertinent information about for workers and employers as well as for physicians, industrial hygienists,and other occupational safety and health professionals who may need such information to conduct effective occupational safety and health programs. 6.2.5.2 Evaluation
1. Health Hazards. Routes of exposure, summary of toxicology, signs and symptoms, emergency procedure.
2. Workplace Monitoring and Measurement. 3. Medical Surveillance. Workers who may be exposed to chemical hazards should be monitored in a systematic program of medical surveillance that is intended to prevent occupational injury and disease. The program should include education of employers and workers about work-related hazards, placement of workers in jobs that do not jeopardize their safety or health, early detection of adverse health effects, and referral of workers for diagnosis and treatment.
70
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
6.2.5.3 Controls
1. Exposure Sources and Control Methods. 2. Personal Hygiene Procedures. 3. Respiratory Protection. Conditions for respirator use, respiratory protection program.
4. Personal Protective Equipment. Protective clothing should be worn to prevent any possibility of skin contact. Chemical protective clothing should be selected on the basis of available performance data, manufacturers' recommendations, and evaluation of the clothing under actual conditions of use.
5. Emergency Medical Procedures. Material Safety Data Sheets (MSDS's) include chemical specific information on emergency medical and first aid procedures as referenced under the OSHA Hazard Communication standard, 29 CFR 1910.1200, (g)(2)(X). This standard requires chemical manufacturers and importers to obtain or develop an MSDS for each hazardous chemical they produce or import. Employers shall have an MSDS in the workplace for each hazardous chemical, which they use.
6. Storage. 7. Spills and Leaks. In the event of a spill or leak, persons not wearing protective equipment and clothing should be restricted from contaminated areas until cleanup has been completed.
6.3
HAZARD IDENTIFICATION & EMERGENCY SAFETY & HEALTH RISK ASSESSMENT
Safety & Health Risks vary with the type of industry & the magnitude of the emergency. The severity of the risk too will vary with especially where there are chemicals, combustible gases, potential for fire & explosion etc. These hazards may not only pose a danger to the health of working in a particular plant but also the adjacent community. In the event of a major disaster property both within and outside the plant will be damaged. The real and potential hazards at the work place must be identified and the Safety & Health Risks that they pose assessed. This will require a close scrutiny of all
71
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
work place buildings, their design, electrical wiring, transport and storage facilities, the work processes, workstation design, safe operating procedures, list of chemicals substances used, their quantity, storage, daily transfer, safe usage and disposal. MSDS’s of the chemical too have to be studied as regards their toxicity, volatility, and their potential for a fire and/or explosion and adverse health affects both short term and long term. The possible emergencies/disaster in a industry could be: •
Fire/ explosion
•
Chemical spill
•
Radioactive material spill
•
Biological material spill
•
Personal injury The best action plan is prevention from an emergency. This is where one has to
work closely with operation personnel to make sure that all operations are safe and comply with OSH Legislations. All persons at work are aware of the safe procedure and also follow those procedures. Unfortunately in the real world, mostly human factors- accident & emergency do occur. This is why emergency response plans have to be written up, communicated to all concerned and tested for effectiveness. Depending on the gravity the workplace emergency can be categorized in to Level 1, Level 2, or Lever 3 emergency. Level 1 Emergency- the first responder without having to call the disaster response team or outside help can effectively manage such incident. Examples; a small fire easily smothered, chemical spill easily contained and cleaned, injury minor and treated at site by rendering first aid. Level 2 Emergency - an incident that requires technical assistance from the disaster response team and may need outside help. Examples; fire that need technical from trained personnel and specialized equipment spill that can only be properly contained by specialized equipment.
72
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Level 3 Emergency- these are major disaster that are difficult to contain even with trained personnel and outside help. Examples, spill that cannot be properly contained or abated even by highly trained team and the use of sophisticated special equipment. Fire involving toxic material that is too large to control and are to burn. This may require the evacuation of civilians across jurisdictional boundaries
73
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
CHAPTER 7
MASS BALANCE
7.1
SNAMPROGETTI UNIT (REACTOR AND REGENERATOR)
Stream S5 = 164.74 kgmole/hr 0.393 C4H8 0.393 H2 0.212 iC4H10 0.002 nC4H10
100 kgmole/hr 0.996 iC4H10 0.004 nC4H10
S2 Given from MSDS
Assume steady-state system, Basis = 100 kgmole/hr of S2
74
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
The fraction at stream S2 acquired from isobutane instrument grade, MSDS. Reaction occurred in the reactor, iC4H10
C4H8
+
H2
Flowrate in kgmole/hr of iC4H10 in the feed stream of S2
= 0.996 (100)
= 99.6 kgmole/hr iC4H10 Balanced Based upon the stoichoimetric ratio with 65% conversion of iC4H10 to obtain C4H8. Since, 65% conversion in the reactor, ∴ kgmole/hr of C4H8 obtained
= 0.65 (99.6) = 64.74 kgmole/hr
∴ 35% of iC4H10 unreacted
= 99.6
-
64.74
= 34.86 kgmole/hr Based upon stoichiometric ratio (inert)
(unreacted)
n C4H10
+ iC4H10
0.4
C4H8
99.6
H2
64.74
(kgmole/hr)
+
iC4H10
64.74
+ n C4H10
34.86
0.4
(kgmole/hr)
Input S2
Stream Component
+
(inert)
MW
Molar flow
Output S5
Mass flow kg/hr
Molar flow
Mass flow kg/hr
kg/kgmole
kgmole/hr
C4H8
56
-
-
kgmole/hr
64.74
3625.44
H2
2
-
-
64.74
129.4
iC4H10
58
99.6
5776.8
34.86
2021.88
n C4H10 Total
58
0.4
23.2 5800
0.4
23.4 5800
75
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
7.2
SEPARATOR
Stream S10 = 64.74 kgmole/hr 1 H2
Stream S9 = 164.74 kgmole/hr 0.393 C4H8 0.393 H2 0.212 iC4H10
Stream S11 = 100 kgmole/hr
0.002 nC4H10
0.6474 C4H8 0.3486 iC4H10 0.0040 nC4H10
Input S9
Stream Component
Output S10
S11
MW
Molar flow
Mass flow
Molar flow
Mass flow
Molar flow
Mass flow
kg/kgmole
kgmole/hr
kg/hr
kgmole/hr
kg/hr
kgmole/hr
kg/hr
C4H8
56
-
-
-
-
64.74
3625.44
H2
2
-
-
64.74
129.4
64.74
129.4
iC4H10
58
99.6
5776.8
-
-
34.86
2021.88
n C4H10 Total
58
0.4
23.2 5800
-
129.4
0.4
23.4 5670.6
7.3
MIXER
S13 = 64.74kgmole/hr
S14 = 71.62 kgmole/hr
1 CH3OH
0.996 CH3OH 0.004 H2O
S27 = 0.406 kgmole/hr 0.3596 CH3OH 0.6404 H2O
76
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Input Stream Component
S13 MW
Molar flow
Output S14
S27
Mass flow
Molar flow
Mass flow
Molar flow
Mass flow
kg/kgmole
kgmole/hr
kg/hr
kgmole/hr
kg/hr
kgmole/hr
kg/hr
CH3OH
32
71.214
2278.848
0.146
4.67
71.36
2283.52
H2O Total
18
-
2278.848
0.26
4.68 9.356
0.26
4.685 2288.205
7.4
MTBE REACTOR Assumption : 98% conversion of C4H8 (2% remains unconverted) Reactions involve in the reactor,
1. C4H8
+
CH3OH
2. 2CH3OH 3. C4H8
+
C5H12O
C2H6O H2O
+
H2O
C4H10O
Stream S11 = 100 kgmole/hr 0.6474 C4H8 0.3486 iC4H10 0.0040 nC4H10
R e ac to r
S15
kgmole/hr C4H8 iC4H10 nC4H10
S14 = 71. 214 kgmole/hr CH3OH
CH3OH
H2O
C5H12O C4H10O C2H6O H2O
7.4.1
1st REACTION IN REACTOR C4H8
+
CH3OH
C5H12O
77
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
kgmole/hr of C4H8 in the stream S11 = 100(0.6474) =
64.74 kgmole/hr C4H8
Balance based upon stoichiometric ratio with 98% conversion. CH3OH is classified an excess. The unreacted of CH3OH (excess) = (71.36 - 64.74) =
6.62 kgmole/hr
Since 98% conversion in the reactor, kgmole/hr of C5H12O obtained = 0.98 (64.74) = 63.44 kgmole/hr C5H12O obtained From the stoichiometric ratio, 98%
C4H8 64.74
+
CH3OH
conv.
71.214
C5H12O +
C4H8
63.44
1.3
+
CH3OH 7.92
unconverted
kgmole/hr
kgmole/hr
64.74 kgmole/hr 1 C4H8 R e ac to r
kgmole/hr C4H8 CH3OH C5H12O
64.74 kgmole/hr 1 CH3OH
Component
MW
Input Molar flow Mass flow
Output Molar flow Mass flow
78
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
C4H8
(kg/kgmole) 56
(kgmole/hr) 64.74
(kg/hr) 3625.44
(kgmole/hr) 1.3
(kg/hr) 72.8
CH3OH
32
71.36
2283.52
7.92
253.44
C5H12O Total
88
-
5908.96
63.44
5582.72 5908.96
7.4.2
2nd REACTION IN REACTOR
From 2nd reaction, stoichiometric ratio shown below: Since the ratio between methanol and dimethylether is 2CH3OH : 1C2H6O , 98% conversion methanol (CH3OH) into dimethylether (C2H6O) = 1.3 (0.98) 2 =
0.637 kgmole/hr
98%
2CH3OH
conv.
7.92
C2H6O + 3.88
H2O
+
2CH3OH
3.88
0.16 unconverted
kgmole/hr
7.92 kgmole/hr 1 CH3OH
kgmole/hr R e ac to r
kgmole/hr CH3OH C2H6O H2O
Input
Output
79
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Component
MW
Molar flow
Mass flow
Molar flow
Mol
Mass flow
kg/kgmole
kgmole/hr
(kg/hr)
(kgmole/hr)
Fraction
(kg/hr)
CH3OH
32
7.92
253.44
0.16
0.02
5.12
C2H6O
46
-
-
3.88
0.49
178.48
H2O
18
-
-
3.88
0.49
69.84
1.0
253.44
Total
7.4.3
253.44
3rd REACTION IN REACTOR
The 3rd reaction and its stoichiometric below, From 1st reaction, kgmole/hr of C4H8 remain is 1.3 and 3.88 kgmole/hr of H2O is obtained in 2nd reaction. Since C4H8 is limiting reactant to react with H2O, only 1.3 kgmole/hr of H2O needed to react with C4H8 H2O is classified an excess. The unreacted of H2O (excess) = (4.14 - 1.3) = C4H8
+
1.3
H2O 4.14
2.84 kgmole/hr C4H10O + 1.274
C4H8 0.026
+
H2O 2.866
unconverted
kgmole/hr
kgmole/hr
1.3 kgmole/hr 1
C4H8
80
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
R e ac to r
4.166 kgmole/hr 0.3058C4H8 0.3058C4H10O 0.688H2O
4.14 kgmole/hr 1 H2O
Input Component
MW
Molar flow
Mass
Molar
Mass
Molar
Mass
kg/kgmole
kgmole/hr
flow
flow
flow
flow
flow
kgmole/hr -
(kg/hr) -
kgmole/hr 0.026
(kg/hr) 1.456
4.14
74.52
2.866
51.588
1.274
94.276
4.166
147.32
C4H8
56
1.3
(kg/hr) 72.8
H2O
18
-
-
C4H10O
74
Total
7.4.4
Output
1.3
72.8
4.14
74.52
OVERALL MASS BALANCE ON MTBE REACTOR
S11 = 100 kgmole/hr 0.6474 C4H8 0.3486 iC4H10 0.0040 nC4H10
81
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
R e ac to r
S15 = 100.676 kgmole/hr 0.0002 C4H8 0.3261 iC4H10 0.0037 nC4H10 0.0015CH3OH 0.5934 C5H12O
S14 = 71.36 kgmole/hr
0.0119 C4H10O
1 CH3OH
0.0363 C2H6O 0.0268 H2O
Input
Input
Output
S11
S14
S15
MW
Molar flow
Mass
Molar flow
Mass
Molar flow
Mass
(kg/kg
(kgmole/hr)
flow
(kgmole
flow
(kgmole/h
flow
C4H8
mole) 56
64.74
(kg/hr) 3625.44
/hr) -
(kg/hr) -
r) 0.026
(kg/hr) 1.456
iC4H10
58
34.86
2021.88
-
-
34.860
2021.88
n C4H10
58
0.4
23.2
-
-
0.4
23.2
CH3OH
32
-
-
71.36
2283.52
0.16
5.12
C5H12O
88
-
-
63.44
5582.72
C2H6O
46
-
-
3.88
178.48
C4H10O
74
-
-
1.274
94.276
H2O
18
-
0.26
2.866
51.588
106.906
7958.72
Component
Total
7.5
100
5670.52
71.62
4.68 2288.2
DISTILLATION COLUMN Assume that 90% of methanol in bottom.
82
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
S17 = 40.321 kgmole/hr 0.0006 C4H8
S15 = 100.906 kgmole/hr 0.0002 C4H8
0.8646 iC4H10
0.3261 iC4H10
0.0099 nC4H10
0.0037 nC4H10
0.0037 CH3OH
0.0015 CH3OH
0.0249 H2O
0.5934 C5H12O
0.0962 C2H6O
0.0119 C4H10O
S16 = 66.585 kgmole/hr
0.0363 C2H6O
0.9528 C5H12O
0.0268 H2O
0.0191 C4H10O 0.0279 H2O 0.0002 CH3OH
S15 Component
MW kg/kgmole
Molar
Mass
S16 Molar flow Mass
S17 Molar flow Mass
flow
flow
(kgmole/hr)
flow
(kgmole/hr)
flow
C4H8
56
kgmole/hr 0.026
(kg/hr) 1.456
-
(kg/hr) -
0.026
(kg/hr) 1.456
iC4H10
58
34.86
2021.88
-
-
34.86
2021.88
n C4H10
58
0.4
23.2
-
-
0.4
23.2
CH3OH
32
0.16
5.12
0.011
0.352
0.003
4.768
C5H12O
88
63.44
5582.72
63.44
5582.72
-
-
C2H6O
46
3.88
178.48
-
-
3.88
178.48
C4H10O
74
1.274
94..276
1.274
94..276
-
-
H2O Total
18
2.866 106.906
51.588 7958.72
1.860 66.585
33.48 5710.828
0.013 40.321
18.108 2247.892
7.6
LIQIUD –LIQUID EXTRACTION
S 20 = 12.029 kgmole/hr 1 H2O
S 21 = 39.166 kgmole/hr 0.0007 C4H8 0.8901 iC4H10 0.0102 nC4H10 0.0991 C2H6O
83
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
S18 = 40.321 kgmole/hr
S23 = 13.184 kgmole/hr
0.0006 C4H8
0.0113 CH3OH
0.8646 iC4H10
0.9887 H2O
0.0099 nC4H10 0.0037 CH3OH
0.0962C2H6O 0.0249 H2O
Input
Output
S18
S20 Mass
MW
Molar flow
kg/kgmole
(kgmole/hr)
C4 H8
56
0.026
(kg/hr) 1.456
Component
flow
Molar flow (kgmole/hr)
S21 Mass flow
-
(kg/hr) -
Molar flow (kgmole/hr)
S23 Mass flow
0.026
(kg/hr) 1.456
Mass
Molar flow
flow
(kgmole/hr) -
(kg/hr) -
iC4H10
58
34.86
2021.88
-
-
34.86
2021.88
-
-
n C4H10
58
0.4
23.2
-
-
0.4
23.2
-
-
CH3OH
32
0.149
4.768
-
-
-
-
0.149
4.768
C5H12O
88
-
-
-
-
-
-
-
-
C2H6O
46
3.88
178.48
-
-
3.88
178.48
-
C4H10O
74
-
-
-
-
-
-
-
-
H2O Total
18
1.006 40.321
18.108 2247.892
12.029 12.029
216.522 216.522
39.166
2225.016
13.035 13.184
234.63 239.398
7.7
DISTILLATION COLUMN
S26 = 0.407 kgmole/hr S24 = 13.185 kgmole/hr 0.0113 CH3OH 0.9887 H2O
0.146 CH3OH 0.260 H2O
84
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
S25 = 12.778 kgmole/hr 1 H2O
S24 Component
MW kg/kgmole
Molar
Mass
S25 Molar flow Mass
S26 Molar flow Mass
flow
flow
(kgmole/hr)
flow
(kgmole/hr)
flow
C4H8
56
kgmole/hr -
(kg/hr) -
-
(kg/hr) -
-
(kg/hr) -
iC4H10
58
-
-
-
-
-
-
n C4H10
58
-
-
-
-
-
-
CH3OH
32
0.149
4.776
0.003
0.096
0.146
4.680
C5H12O
88
-
-
-
-
-
-
C2H6O
46
-
-
-
-
-
-
C4H10O
74
-
-
-
-
-
-
H2O Total
18
13.035 13.185
234.63 239.411
12.775 12.778
229.95 230.046
0.260 0.407
4.685 9.365
OVERALL REACTION SYSTEM, FLOW DIAGRAM
S3
S17
S18
S9 Liquid d– liquid liquid extra extrac ction tion
Liqui
Distill ation colu mn
S11
Distill ation colu mn
7.8
85
Re act or
R Se ea pa rat ct or or
Ca tal ytic rea cto r
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
S2
S10
S12
S15
Overall mass balance is shown below: Input
S4 Molar flow
Mass flow
kgmole/hr
(kg/hr) 5800
=
output
Input S13 Molar flow Mass flow
Molar flow
(kgmole/hr)
(kgmole/hr)
(kg/hr)
2278.848
Total input
S20 Mass flow (kg/hr) 216.522
8295.37
Output S10 Molar flow Mass (kgmole/hr
flow
)
(kg/hr) 129.48
S16 Molar flow (kgmole/hr)
Total
S26 Mass flow (kg/hr) 5710.828
Molar flow (kgmole/hr)
S21 Mass flow (kg/hr) 230.046
Molar flow (kgmole/hr)
Mass flow (kg/hr) 2225.016
8295.37
output
7.6 SCALE-UP FACTOR Determination of the scale-up factor for the end product (MTBE) With a basis 100 kgmole/hr of feed at stream S2, the product at stream S12 acquired is 5658.934 kg/hr. This amount if converted to kg/yr, by conversion unit, 5582.72kg/hr * 7920 hr/yr = 44.215142 * 106 kg/yr of MTBE Targeted production of MTBE = 300 X106 kg/yr (300,000 metric tonnes/yr)
86
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
∴ Therefore, the scale-up factor = Targeted Amount Actual Amount = 300,000 x103 kg/yr 44.8188 x106 kg/yr = 6.785005854 ≈ 6.785 To determined whether the scale-up factor can proceed or not, Target amount
=
Actual Production x Scale-up factor
=
44.215 x 106 x 6.785
=
299.9997385 x106
≈
300 x106 kg/yr at stream S14
Therefore, the scale-up factor of 6.785 is acceptable for this process.
CHAPTER 8
ENERGY BALANCE 8.1
ENERGY EQUATION
The equation that we used to calculate the power Q or W at each equipment is:
87
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Q – W = ∆HR + (-∆Hin) + (∆Hout) + (∆KE) + (∆PE) To calculate ∆H, first we need to find the Cp values for every component in each of the stream. To find the Cp values, we need to use this equation to find the values of Cp
C
o
P
= a + bT + cT2 + dT3
The values of a, b, c and d are taken from Appendix D, Coulson and Richardson Chemical Engineering, Volume 6. If the temperature and pressure is more than the critical temperature and pressure of the component, we need to find the (C p – Cpo) for that specific component. But as for all of our temperatures and pressures none of them exceed the critical temperature and pressure; we need not to find the (Cp – Cpo). To find the value of ∆H, we use this equation:
∆H =
T2
∫ C T1
P
dT x (n)
Should there is any reaction in the process; we need also to find the values of ∆HR which takes place in the equipment. The equation, which we used to find ∆HR is:
∆HR = (∆ĤF product - ∆ĤF reactant) x n and if the equipment has ∆KE and ∆PE, we also need to calculate the values by using this equation: ∆KE = 0.5 m(vout2 - vin2) ∆PE = mg x (zout – zin) so, after we have calculated all the values of the energy for each and every of the stream, we then can calculate the value of Q or W. And for this sample of calculations, listed are the values of constants in the ideal gas heat capacity equation based on R. K Sinnot, Coulson & Richardson, Chemical Engineering, Volume 6, Third Edition, Butterworth Heinemann:
88
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 8.1 Table of Constant in the Ideal Heat Capacity Component C5H12O CH3OH H2O C4H8 i-C4H8 i-C4H10 C4H10O n-C4H10 (CH3)2O H2 8.2
a
b
c
d
Delta HF kJ/kmol.K kJ/kmol -1 -4 -8 2.53 5.14 x 10 -2.60 x 10 4.30 x 10 -292990 2.12 x 101 7.09 x 10-2 2.59 x 10-5 -2.85 x 10-8 -201300 32.243 1.93 x 10-3 1.06 x 10-5 -3.60 x 10-9 -242000 -2.994 3.53 x 10-1 -1.98 x 10-4 4.46 x 10-8 -130 16.052 2.8043 x 10-1 -1.091 x 10-4 9.098 x 10-9 -16900 -1.39 3.85 x 10-1 -1.85 x 10-4 2.90 x 10-8 -134610 1 -4.86 x 10 7.17 x 10-1 -7.08 x 10-4 2.92 x 10-7 -312630 9.85 3.31 x 10-1 -1.11 x 10-4 -2.82 x 10-9 -126.23 1.70 x 101 1.79 x 10-1 -5.23 x 10-5 -1.92 x 10-9 -184180 2.71 x 101 9.27 x 10-3 -1.38 x 10-5 7.65 x 10-9 0
ENERGY BALANCE: SAMPLE OF CALCULATIONS
(Methods of calculations are based on, Coulson & Richardson, Chemical Engineering, Volume 6, page 78). 8.2.1
P-100 (Pump 1) S2 T = -150C P = 750 Kpa (liquid)
S1 T = -180C P = 450 Calculations are Kpa based on Yunus A. Cengel, Micheal A. Boles, Thermodynamics: (Liquid) An Engineering Approach, WCB/Mc Graw-Hill, 1989, page, 354-355. Assumptions: 1. Steady operating conditions exist 2. Kinetic and potential energy negligible 3. The process is to be isentropic Specific volume: Isobutane = 0.255 m3/mol n-butane = 0.263 m3/mol
89
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
(Data of these specific volumes are based on Coulson & Richardson, Chemical Engineering, Volume 6, Third Edition, Butterworth Heinemann, page 947) Isobutane 0.255m3/mol x 1000mol/kmol x 1kmol/58kg = 9.11 m3/kg n-butane 0.263m3/mol x 1000mol/kmol x 1kmol/58kg = 4.53 m3/kg Vavg = (9.11 + 4.53) m3/kg / 2 = 6.82 m3/kg (Which remains essentially constant during the process) 2
∴Win = ∫ Vdp 1
= V1 (P2 − P1 ) = 6.82m 3 /kg(750 − 450)kpa(1k J/1kpa.m = 6.82(300)
3
)
= 2046.00kJ/ kg ∴2046kJ/kg x 39353kg/hr = 80516238kJ /hr = 22365.62kW
8.2.2
E-100 (Heat Exchanger 1)
S2 T = -15 oC P = 750Kpa (Liquid)
S3 T = 117 oC P = 450Kpa (Gas)
Stream 2 Component i-C4H10 n-C4H10
Flowrates Kmol/hr 675.786 2.714
∆ĤF kJ/Kmol -1.35 x105 -1.26 x105
To K 298 298
T, K 258 258
∆H kJ/hr -690.04 -2.81
90
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
∑ ∆H = -692.86
Stream 3 Component i-C4H10 n-C4H10
Flowrates Kmol/hr 676.786 2.714
∆ĤF kJ/Kmol -1.35 x105 -1.26 x105
To K 298 298
T, K 390 390
∆H kJ/hr 1902.85 7.66
∑ ∆H = 1910.51
Sample of calculations for i-C4H10 at stream 3 ∆H =
T2
∫ C T1
T2
∫ C T1
P
P
dT =
dT x (n) T2
∫
T1
a + bT + cT 2 + dT 3
b(T 2 − T1 ) 2 c(T 2 − T1 )3 d(T 2 − T1 ) 4 a(T − T ) + + + = 2 1 2 3 4
= ( 1.390 )( 390 − 298 ) + +
38 .473 ×10 2 (390 - 298 ) 2 2
+
( 1.846 ×10 4 )( 390 - 298 )3 3
28 .952 ×10 9 (390 - 298 ) 4 4
= 10100 kJ/kmol ∆H
= 10100 kJ/kmol x 675.786 kmol/hr = 6825438.6 kJ/hr = 1902.85 kW (for i-C4H10)
And as for n-C4H10, the ∆H
So
= 7.66 kW
∑ ∆H = 1910.51
Energy balance,
91
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Q=(
∑ H)
out
–(
∑ H)
in
= 1910.51- (-692.86) = 2603.37kW Steam flowrate, Q = mCpΔT Cp of isobutane, 2155 J/kg oC (Elementary Principles of Chemical Processes,
W.
Rousseau et. al)
m=
Q Cp ∆T
2603370 J/s 2155J/g o C x (117 - (-15)) = 9.152g/s =
o
C
Therefore the supply of steam flow rate required is 9.152 g/s. 8.2.3
E-101 (Heat Exchanger 2)
S3 T = 117 oC P = 450 kPa (Gas)
S4 T = 250 oC P = 325 kPa (Gas)
Stream 3 Component i-C4H10 n-C4H10
Flowrates Kmol/hr 676.786 2.714
∆ĤF kJ/Kmol -1.35 x105 -1.26 x105
To K 298 298
T, K 390 390
∆H kJ/hr 1902.85 7.66
∑ ∆H = 1910.51
Stream 4 Component i-C4H10 n-C4H10
Flowrates Kmol/hr 676.786 2.714
∆ĤF kJ/Kmol -1.35 x105 -1.26 x105
To K 298 298
T, K 523 523
∆H kJ/hr 5356.57 21.46
92
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
∑ ∆H = 5378.03
Sample of calculations for i-C4H10 at stream 4 ∆H =
T2
∫ C T1
T2
∫ C T1
P
P
dT x (n) T2
∫
dT =
T1
a + bT + cT 2 + dT 3
b(T 2 − T1 ) 2 c(T 2 − T1 )3 d(T 2 − T1 ) 4 a(T − T ) + + + = 2 1 2 3 4
= ( 1.390 )( 523 − 298 ) + +
38 .473 ×10 2 (523 - 298 ) 2 2
+
( 1.846 ×10 4 )( 523 - 298 )3 3
28 .952 ×10 9 (523 - 298 ) 4 4
= 28500 kJ/kmol ∆H
= 28500 kJ/kmol x 675.786 kmol/hr = 19259901 kJ/hr = 5349.97 kW (for i-C4H10)
And as for n-C4H10, the ∆H
So
= 21.46 kW
∑ ∆H t = 5371.43kW ou
Energy balance, Q=(
∑ H)
out
–(
∑ H)
in
= 5371.43- (1910.51) = 3460.92kW Steam flowrate, Q = mCpΔT
93
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Cp of isobutane, 2155 J/kg oC (Elementary Principles of Chemical Processes,
W.
Rousseau et. al)
m=
Q Cp ∆T
3460920 J/s 2155J/g o C x (250 - 118) o C = 12.17g/s =
Therefore the supply of steam flow rate required is 12.17 g/s. 8.2.4
R-101 (Snamprogetti Fluidized Bed Reactor)
S5 Air Out S4 T=250oC P=325kPa (gas)
S6 Air In
S7 T=180oC P=110kPa (Liquid) Stream 4 Component i-C4H10 n-C4H10
Flowrates Kmol/hr 676.786 2.714
∆ĤF kJ/Kmol -1.35 x105 -1.26 x105
To K 298 298
T, K 523 523
∆H kJ/hr 5356.57 21.46
∑ ∆H = 5378.03
Stream 7
94
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Component i-C4H8 i-C4H10 n-C4H10 H2
Flowrates Kmol/hr 237 2.71 439 439
∆ĤF kJ/Kmol -1.30 x10-1 -1.35 x105 -1.26 x105 0.00
To K 298 298 298 298
T, K 453 453 453 453
∆H kJ/hr 1056.59 13.82 2236.41 549.84
∑ ∆H = 3856.66
To calculate the value of ∆HR: 1) i-C4H10 →C4H8 + H2 so, ∆ĤR = (∆ĤF C4H8) + (∆ĤF H2) -(∆ĤF i-C4H10) = (-130) + (0) – (-134610) = 134480 kJ/kmol therefore, ∆HR = (∆ĤR kJ/kmol x 236.53 kmol/hr) = (134480 kJ/kmol x 236.53 kmol/hr) = 31808554.4 kJ/hr = 8835.71 kJ/s = 8835.71 kW Although there is stream flow, but the ∆KE is too small and negligible and there is also now work so, W is zero and as for the ∆PE, the value is neglected, as it is also too small. Now we calculate the value of Q, Q – W 0= ∆HR + (-∆Hin) +(∆Hout) +∆KE 0+ ∆PE0 Q = ∆HR + (∆Hout) - (∆Hin) Q = 8835.71 + (1980.66) - (3856.66) Q = 6959.71kW (heat have been absorbed) 8.2.5
C-100 (Compressor 1)
95
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
S7 T = 1800C P = 110 Kpa (Gas)
S8 T = 1930C P = 120 Kpa (Gas-liquid)
T7 = 453K
T8 =?
P7 = 1.1 bar
P8 = 1.2 bar
T4 = 453K,
P4 = 1.1 bar,
P8 = 1.2 bar is based on the literature review of process
Snamprogetti fluidized bed. By assuming polytropic and ideal gas condition: T7= T6(P7/P6)m (Coulson & Richardson, Chemical Engineering, Volume 6, page 85) m = α – 1/ αEp
α = CPmean/CV = CPm/CPm – R
Where R = 8.314 kJ/kmol.K For hydrogen, a = 27.143, b = 97.38 x 10-4, c = -1.31 x 10-5, d = 76.451 x 10-10 1000K
∫
CPHydrogen =
453K
a + bT + cT 2 + dT 3 = 16200 kJ/kmol.K
For butene, a = -2.994 , b = 3.53 x 10-1 , c = -1.98 x 10-4 , d = 4.46 x 10-8 , CPbutene =
1000K
∫
453K
a + bT + cT 2 + dT 3 = 89400 kJ/kmol.K
For Isobutane, a = -1.39 , b = 3.85 x 10-1 , c = -1.85 x 10-4 , d = 2.90 x 10-8 , CPisobutane =
1000K
∫
453K
a + bT + cT 2 + dT 3 = 103000 kJ/kmol.K
For n-butane, a = 9.85 , b = 3.31 x 10-1 , c = -1.11 x 10-4 , d = -2.82 x 10-9, 1000K
CPn-butane =
∫
Cpmean =
0.25 (Cp , Hydrogen + Cp , butene + Cpisobu tan e + Cp , n − bu tan e) (466 − 453 )
=
453K
a + bT + cT 2 + dT 3 = 103000 kJ/kmol.K
0.25(16200 + 89400 + 103000 + 103000) = 167.5kJ/km ol.K 1000 − 453
So , α = CPm/CPm – R = 167.5/(167.5-8.314) = 1.07
96
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
To find Ep(efficiency), Flow rate =
1117.76kmo l 453 1 x22.4x x 3600s 273 0.5
= 23 .08 m 3 / s From Figure 3.6, Coulson & Richardson, Chemical Engineering, Volume 6, page 83, Ep = 75% m = α – (1/ αEp) = 1.07-(1/1.07 (0.75) ) = 0.3690 To determine T6, T8 = T7(P8/P7)m = 453(1.2/1.1)0.3690 = 466.83K (193oC) Tc and Pc for H2, isobutene, isobutane and n-butane, Tc = 417.07K, Pc = 38.17 bar Trmean = (T7 + T8)/2Tc = (453+ 466.83K)/2(417.07) = 1.10 K Prmean = (P5 + P6)/2Pc = (1.1+1.2)/2(38.17) = 0.030 bar From Figure 3.8, Compressibility factors (Coulson & Richardson, Chemical Engineering, Volume 6, page 87). Z = 1.00 Then find n, n = 1/(1-m) = 1/(1-0.3456) = 1.53 Polytropic work = zRT1(n/n-1)x((P1/P2)(n-1/n) – 1) =
1.53 1.00 (8.314 )( 453 )( 0.53
0.53 1.2 1.53 ) x −1 1.1
= 332.69 kJ/kmol Actual work = Polytropic work / Ep = 332.69 /0.75 = 443.60 kJ/kmol Compressor power = 443.60 kJ/kmol x 1117.76 kmol/hr x 1hr/3600s = 137.73 kW Therefore the compressor power required to increase the pressure from 1.1 bar to 1.2 bar is 137.73kW.
8.2.6
E-102 (Cooler 1) S8 T = 193oC P = 120 Kpa (Liquid)
S9 T = 530C P = 100 Kpa (Liquid)
97
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Sample of Calculation for Cooler 1 Stream 8 Component C4H8 i-C4H10 n-C4H10 H2
Flowrates Kmol/hr 4.39x1002 2.37x102 2.71x100 4.39x102
∆ĤF kJ/Kmol -1.69x10-4 -1.35x105 -1.26x105 0.00
To K 298 298 298 298
T, K 466 466 466 466
∆H kJ/hr 2155.41 1323.43 15.15 596.20
∑ ∆H = 4090.20
Stream 9 Component i-C4H8 i-C4H10 n-C4H10
Flowrates Kmol/hr 6.47x101 3.49x 101 4.00x101
∆ĤF kJ/Kmol -1.69x104 -1.35 x104 -1.26 x105
To K 298 298 298
T, K 326.3 326.3 326.3
∆H kJ/hr 47.45 27.84 0.32
∑ ∆H = 75.61
Energy balance, Q=(
∑ H)
out
–(
∑ H)
in
= 75.61– 4090.20 = -4014.59 kW (heat is being released to the surrounding) Steam flowrate, Q = mCpΔT
98
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Cp of pure water, 4.184 J/g oC (Elementary Principles of Chemical Processes, W.Rousseau et. al) Q mCp ∆T 4014590J/s = 4.184J/g o C x (193 - 53.3) =6869.36 g/s
m=
o
C
Therefore the supply of steam flow rate required is 6869.36 g/s.
8.2.7 V-100 (Separator) S10 T = 53.3oC P = 90 kPa (gas) S9 T= 53.3oC P= 100kPa (liquid-gas) S11 T=53.3oC P=100kPa
Sample of Calculation for Hydrogen Splitter Vessel Stream 9 Component C4H8
Flowrates Kmol/hr 2.37x102
i-C4H10 n-C4H10 H2
2.71x102 4.39x102 4.39x102
∆ĤF kJ/Kmol -1.69x104 1.35Ex105 -1.26x105 0.00
To K 298
T, K 326.3
∆H kJ/hr 166.03
298 298 298
326.3 326.3 326.3
2.17 353.50 99.88
99
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
∑ ∆H = 621.57
Stream 10 Component
H2
Flowrates Kmol/hr
∆ĤF kJ/Kmol
To K
T, K
∆H kJ/hr
4.39x102
0.00
298
326.3
99.88
Flowrates Kmol/hr 439.26 236.53 2.71
∆ĤF kJ/Kmol -16910 -134610 -126230
To K 298 298 298
T, K
∆H kJ/hr 321.92 188.89 2.18
∑ ∆H =
Stream 11 Component C4H8 i-C4H10 n-C4H10
326.3 326.3 326.3
∑ ∆H = 512.99
Energy balance, Q=(
∑ H)
out
–(
∑ H)
in
= (512.99)-(621.57+99.88) = -208.46 (heat is being released to the surroundings) 8.2.8
R-102 (MTBE Reactor) S11 T = 53.3oC P = 2000kPa (liquid)
S14 T = 27oC P = 100kPa (liquid)
S15 T = 101oC P = 2000kPa (liquid)
100
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
The pressure increases from 100kPa to 2000kPa. As there is a heat exchanger (heater) in the MTBE reactor. Stream 11 Component C4H8 i-C4H10 n-C4H10
Flowrates Kmol/hr 439.26 236.53 2.71
∆ĤF kJ/Kmol -16910 -134610 -126230
To K 298 298 298
T, K 326.3 326.3 326.3
∆H kJ/hr 321.92 188.89 2.18
∑ ∆H = 512.99
Stream 14 Component CH3OH H2O
Flowrates Kmol/hr 4.84x102 1.76
∆ĤF kJ/Kmol -2.01x104 -2.42x105
To K 298 298
T, K 300 300
∆H kJ/hr 11.81 -4.79
∑ ∆H = 7.02
Stream 15 Component C5H12O CH3OH
Flowrates Kmol/hr 4.30x102 1.09
∆ĤF kJ/Kmol -2.93x105 -2.01 x105
To K 298 298
T, K 374 374
∆H kJ/hr 1339.10 1.07
101
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
H2O i-C4H8 i-C4H10 C4H10O n-C4H10 (CH3)2O
1.94 0.176 2.37x102 8.64 2.71 26.3
-2.44 x105 -0.123 -1.35 x105 -3.13 x105 -1.26 x105 -1.84 x105
298 298 298 298 298 298
374 374 374 374 374 374
13.94 0.35 539.59 22.49 6.22 39.56
∑ ∆H = 1962.32
Q=(
∑ H)
out
–(
∑ H)
in
= 1962.32 – 7.02 – 512.99 = 1442.31 kW To calculate the value of ∆HR: 1.) C4H8 + CH3OH 2.) 2CH3OH
C5H12O C2H6O + H2O
3.) C4H8 + H2O
C4H10O
so, ∆ĤR 1 = (∆ĤF C5H12O) - (∆ĤF CH3OH) + (∆ĤF C4H8) = (-292990) – ((-201300) + (-130)) = -91820 kJ/kmol ∆ĤR 2 = (∆ĤF C2H6O) + (∆ĤF H2O) -(2 ∆ĤF CH3OH ) = (-242000) + (-184180) – (2 x -201300) = -23580 kJ/kmol ∆ĤR 3 = (∆ĤF C4H10O) – (∆ĤF H2O) -(∆ĤF C4H8) = (-312630) - (-184180) – (-130) = -128270 kJ/kmol Therefore, ∆HR = (∆ĤR 1kJ/kmol x (63.44kmol/hr) + (∆ĤR 2kJ/kmol x 0.039kmol/hr) + (∆ĤR 3kJ/kmol x 0.624kmol/hr) =(-91820kJ/kmolx63.44kmol/hr)+(-23580kJ/kmolx0.039kmol/hr) + 102
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
(-128270 kJ/kmol x 0.624kmol/hr) = -5906020.9 kJ/hr = -1640.56 kW Although there is stream flow, but the ∆KE is too small and negligible and there is also now work so, W is zero and as for the ∆PE, the value is neglected, as it is also too small Now we calculate the value of Q Q – W 0= ∆HR + (-∆Hin) +(∆Hout) +∆KE 0+ ∆PE0 Q = ∆HR + (-∆Hin) +(∆Hout) Q = -1640.56 + 1442.31 = -198.25 kW 8.2.9
P-101 (Pump 2)
S13 T = 270C P = 115 Kpa (liquid) S12 T = 270C P = 110 Kpa (Liquid) Calculations are based on Yunus A. Cengel, Micheal A. Boles, Thermodynamics: An Engineering Approach, WCB/Mc Graw-Hill, 1989, page, 354-355. Assumptions: 4. Steady operating conditions exist, 5. Kinetic and potential energy negligible 6. The process is to be isentropic Specific volume:
103
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
methanol = 0.118 m3/mol (Data of these specific volumes are based on Coulson & Richardson’s) Methanol 0.118m3/mol x 1000mol/kmol x 1kmol/32kg = 3.6875 m3/kg Vavg = 1.78 m3/kg Which remains essentially constant during the process 2
∴Win = ∫ Vdp 1
= V1 (P2 − P1 ) = 3.6875m 3 /kg(115 −110)kpa(1k J/1kpa.m = 18 .44 kJ/kg ∴18.44kJ/kg x 15462 kg/hr = 285080.63k J/hr = 79.19 kW
3
)
8.2.10 M-101 (Mixer)
S13
S14
T= 27oC P=115kPa (liquid)
T= 27oC P= 115kPa (liquid)
S29 T=27oC P=130kPa (liquid) Stream 13 Component
CH3OH
Flowrates
∆ĤF
To
Kmol/hr
kJ/Kmol
K
4.83 x102
-2.01 x102
298
T, K
∆H kJ/hr
∑ ∆H = 300
11.79
104
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Stream 29 Component CH3OH
Flowrates
∆ĤF
Kmol/hr
kJ/Kmol
9.91 x10
H20
1
1.76
To
T, K
K
∆H kJ/hr
-2.01 x10
5
298
300
0.02
-2.42 x10
5
298
300
0.03
∑ ∆H = 0.06
Stream 14 Component CH3OH
Flowrates
∆ĤF
Kmol/hr
kJ/Kmol
4.84 x10
H20
1.76
5
To
T, K
K
∆H kJ/hr
-2.01 x10
5
298
300
11.81
-2.42 x10
5
298
300
0.03
∑ ∆H = 11.84
Energy balance = out - in Q=(
∑ H)
out
–(
∑ H)
in
= 11.84 – 0.06 – 11.79 = 0.04 kW 8.2.11 EX-100 (Expander 1)
S15
S16
T = 1010C P = 2000 kPa (liquid)
T = ?0C P = 450 Kpa (Gas-liquid)
T15 = 453K
T16 =?
P15 = 2 bar
P16 = 0.45 bar
105
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
By assuming polytropic and ideal gas condition: T16= T15(P16/P15)m (Coulson & Richardson, Chemical Engineering, Volume 6, page 85) m = α – 1/ αEp
α = CPmean/CV = CPm/CPm – R
Where R = 8.314 kJ/kmol.K For MTBE, a = 2.533 , b = 51.372 x 10-2 , c = -2.59 x 10-4 , d = 43.04 x 10-9 , CPMTBE =
1000K
∫
374K
a + bT + cT 2 + dT 3 = 151000 kJ/kmol.K
For TBA, a = 3.266 , b = 41.80 x 10-2 , c = -2.242 x 10-4 , d = 46.85 x 10-9 , CP(TBA) =
1000K
∫
374K
a + bT + cT 2 + dT 3 = 126000 kJ/kmol.K
For DME, a = 17.015 , b = 19.907x 10-2 , c = -5.23 x 10-5 , d = -1.918 x 10-9 , CP(DME) =
1000K
∫
374K
a + bT + cT 2 + dT 3 = 70700 kJ/kmol.K
For CH3OH, a = 21.152 , b = 70.924 x 10-3 , c = 25.870 x 10-6 , d = -2.852 x 10-8 , CP(methanol) =
1000K
∫
374K
a + bT + cT 2 + dT 3 = 44900kJ/km ol.K
For H2O, a = 27.143 , b = 92.738 x 10-4 , c = -1.381 x 10-5 , d = 76.451 x 10-10 , CP(water) =
1000K
∫
374K
a + bT + cT 2 + dT 3 = 23500kJ/km ol.K
For butene, a = -2.994 , b = 3.53 x 10-1 , c = -1.98 x 10-4 , d = 4.46 x 10-8 , CPbutene =
1000K
∫
374K
a + bT + cT 2 + dT 3 = 113000 kJ/kmol.K
For Isobutane, a = -1.39 , b = 3.85 x 10-1 , c = -1.85 x 10-4 , d = 2.90 x 10-8 , CPisobutane =
1000K
∫
374K
a + bT + cT 2 + dT 3 = 126000 kJ/kmol.K
For n-butane, a = 9.85 , b = 3.31 x 10-1 , c = -1.11 x 10-4 , d = -2.82 x 10-9, CPn-butane =
Cpmean= =
1000K
∫
374K
a + bT + cT 2 + dT 3 = 113000 kJ/kmol.K
0.125(Cp, M TBE+ Cp, TBA + Cp, DM E+ Cp, methanol+ Cp, H2 + Cp, butene+ Cpisobu (1000− 453)
0.125(1510 00 + 126000 + 70700 + 44900 + 23500 + 113000 + 126000 + 113000) = 153.37kJ/k mol.K 1000 − 374
So , α = CPm/CPm – R = 153.37/(153.37-8.314) = 1.06
106
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
To find Ep(efficiency), Flow rate =
53999.92km ol 374 1 x22.4x x 3600s 273 0.5
= 920 .61m 3 / s From Figure 3.6, Coulson & Richardson, Chemical Engineering, Volume 6, page 83, Ep = 85% m = α – 1/ αEp = (1.06-1/1.06 (0.85)= 0.0665 To determine T6, T16 = T15(P16/P15)m = 374(0.45/2.0)0.0665 = 338.68K (65.6oC) Tc = 417.07K, Pc = 38.17 bar Trmean = (T15 + T16)/2Tc = (374+ 228.68K)/2(417.07) = 0.723 K Prmean = (P15 + P16)/2Pc = (2+0.45)/2(38.17) = 0.0321 bar From Figure 3.8, Compressibility factors (Coulson & Richardson, Chemical Engineering, Volume 6, page 87). Z = 0.8 Then find n, n = 1/(1-m) = 1/(1-0.0665) = 1.07 Polytropic work = zRT1(n/n-1)x((P15/P16)(n-1/n) – 1) =
1.07 1.00 (8.314 )( 374 )( 0.07
0.07 2 1.07 ) x −1 0.45
= 4872.06 kJ/kmol Actual work = Polytropic work / Ep = 4872.06 /0.80 = 6090.07 kJ/kmol Compressor power = 6090.07 kJ/kmol x 53999.12x 1hr/3600s = 91349kW Therefore the compressor power required to decrease the pressure from 2 bar (2000kPa) to 0.45 bar (450kPa) is 91349kW. 8.2.12 E-103 (Cooler 1) S16 T = 193oC P = 120 Kpa (Liquid)
S17 T = 64.50C P = 100 Kpa (Liquid)
107
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Sample of Calculation for Cooler 1 Stream 16 Component C5H12O CH3OH H2O i-C4H8 I-C4H10 C4H10O n-C4H10 (CH3)2O
Flowrates Kmol/hr 4.30 x102 5.02 1.21 x102 8.16 2.37 x102 6.65 x101 2.71 1.21 x102
∆ĤF kJ/Kmol -2.93 x105 -2.01 x105 -2.42 x105 -1.69 x105 -1.35 x105 -3.13 x105 -1.26 x105 -1.84 x105
To K 298 298 298 298 298 298 298 298
T, K 466 466 466 466 466 466 466 466
∆H kJ/hr 3270.13 11.81 194.19 40.93 1323.40 4.26 15.17 438.54
∑ ∆H = 5298.44
Stream 17 Component C5H12O CH3OH H2O i-C4H8 I-C4H10 C4H10O n-C4H10 (CH3)2O
Flowrates Kmol/hr 4.30 x102 5.02 x102 1.21 x102 8.16 2.37 x102 0.665 2.71 1.21 x105
∆ĤF kJ/Kmol -2.93 x105 -2.01 x105 -2.42 x105 -1.69 x105 -1.35 x105 -3.13 x105 -1.26 x105 -1.84 x105
To K 298 298 298 298 298 298 298 298
T, K 337.5 337.5 337.5 337.5 337.5 337.5 337.5 337.5
∆H kJ/hr 665.50 2.50 44.96 8.45 267.64 0.85 3.09 91.16
∑ ∆H = 1084.15
Energy balance,
108
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Q=(
∑ H)
out
–(
∑ H)
in
= 1084.15– 5298.44 = -4214.29 kW (heat is being released to the surrounding) Steam flowrate, Q = mCpΔT Cp of pure water, 4.184 J/g oC (Elementary Principles of Chemical Processes, W.Rousseau et. al) Q mCp ∆T 4214290J/s = 4.184J/g o C x (193 - 64.5) =7838.44 g/s
m=
o
C
Therefore the supply of steam flow rate required is 7838.44 g/s. 8.2.13 T-101 (Distillation Column 1)
S19 P = 305 Kpa T = 53.3 oC (gas) S17 P = 450 Kpa T =64.5 oC ( liquid ) S18 P = 400 Kpa T = 103.3oC ( liquid ) Sample of Calculations: R = L/D Overall: (NL), L = D x 1.5
109
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
= 451.779 x 2.5 = 1129.45 kmol/hr (NV), V = L + D = 1129.45+ 451.779 = 1581.23 kmol/hr
Stream 17 Component C5H12O CH3OH H2O i-C4H8 I-C4H10 C4H10O n-C4H10 (CH3)2O
Flowrates Kmol/hr 4.30 x102 5.02 1.21 x102 8.16 2.37 x102 0.665 2.71 1.21 x102
∆ĤF kJ/Kmol -2.93 x105 -2.01 x105 -2.42 x105 -1.69 x105 -1.35 x105 -3.13 x105 -1.26 x105 -1.84 x105
To K 298 298 298 298 298 298 298 298
T, K 337.5 337.5 337.5 337.5 337.5 337.5 337.5 337.5
∆H kJ/hr 665.50 2.50 44.96 8.45 267.64 0.85 3.09 91.16
∑ ∆H = 1084.15
Stream 19 Component
Flowrates
∆ĤF
To
T, K
∆H
CH3OH H2O i-C4H8 (CH3)2O i-C4H10 n-C4H10
Kmol/hr 1.01E+00 6.83E+00 1.76E-01 2.63E+01 2.37E+02 2.71E+00
kJ/Kmol -2.01 x105 -2.42 x105 -1.69 x104 -1.84E+05 -1.35 x105 -1.26 x105
K 298 298 298 298 298 298
376.3 376.3 376.3 376.3 376.3 376.3
kJ/hr 1.03 5.04 0.38 40.85 557.49 6.42
∑ ∆H = 611.21
Stream 18 Component
Flowrates Kmol/hr
∆ĤF kJ/Kmol
To K
T, K
∆H kJ/hr
110
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
CH5H12O CH3OH C4H10O H2O
4.30E+02 7.50E-02 8.64E+00 1.26E+01
-2.93 x105 -2.01 x105 -3.13 x105 -2.42 x105
298 298 298 298
326.3 326.3 326.3 326.3
469.97 0.03 7.82 3.35
∑ ∆H = 481.17
Energy balance, Q=(
∑ H)
out
–(
∑ H)
in
= (481.17 + 611.21)– 1084.15 = 8.23 kW 8.2.14 Cooler 2 (E-104)
S19 T = 53.3oC P = 305 Kpa (Liquid)
S20 T = 400C P =100 Kpa (Liquid)
Sample of Calculation for Cooler 1 Stream 19 Component
Flowrates
∆ĤF
To
T, K
∆H
CH3OH H2O i-C4H8 (CH3)2O i-C4H10 n-C4H10
Kmol/hr 1.01E+00 6.83E+00 1.76E-01 2.63E+01 2.37E+02 2.71E+00
kJ/Kmol -2.01 x105 -2.42 x105 -1.69 x104 -1.84x105 -1.35 x105 -1.26 x105
K 298 298 298 298 298 298
376.3 376.3 376.3 376.3 376.3 376.3
kJ/hr 1.03 5.04 0.38 40.85 557.49 6.42
∑ ∆H = 611.21
Stream 20 Component
Flowrates Kmol/hr
∆ĤF kJ/Kmol
To K
T, K
∆H kJ/hr
111
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
CH3OH
1.01E+00
H2O
6.83E+00
i-C4H8
1.76E-01
(CH3)2O
2.63E+01
I-C4H10
2.37E+02
N-C4H10
2.71E+00
-2.01 x105 -2.42 x105 -1.69 x104 -1.84 x105 -1.35 x105 -1.26 x105
298
313
0.19
298
313
0.96
298
313
0.07
298
313
7.33
298
313
98.29
298
313
1.14
∑ ∆H = 107.97
Energy balance, Q=(
∑ H)
out
–(
∑ H)
in
= 107.97– 611.21 = -503.24 kW Steam flowrate, Q = mCpΔT Cp of pure water, 4.184 J/g oC (Elementary Principles of Chemical Processes, W.Rousseau et. al) Q mCp ∆T 503240J/s = 4.184J/g o C x (53.3 - 40) o C =9043.40 g/s
m=
Therefore the supply of steam flow rate required is 9043.40 g/s. 8.2.15 P-102 (Pump 3)
S22 T = 270C P = 30 kPa (liquid) S21 T = 270C P = 25 kPa (Liquid)
112
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Calculations are based on Yunus A. Cengel, Micheal A. Boles, Thermodynamics: An Engineering Approach, WCB/Mc Graw-Hill, 1989, page, 354-355. Assumptions: 7. Steady operating conditions exist, 8. Kinetic and potential energy negligible 9. The process is to be isentropic Specific volume: Water = 0.056m3/mol (Data of these specific volumes are based on Coulson & Richardson’s) (Which remains essentially constant during the process) Water 0.056m3/mol x 1000 mol/kmol x 1 kmol/18kg = 3.11 m3/kg Which remains essentially constant during the process. 2
∴Win = ∫ Vdp 1
= V1 (P2 − P1 ) = 3.11m 3 /kg(30 − 25)kpa(1kJ /1kpa.m 3 ) = 3.11(5) = 15.55kJ/kg ∴15.55kJ/kg x 1469kg/hr = 22851 kJ/hr = 22.85kW
8.2.16 T-102 (Extraction Column)
113
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
S22 T=27oC P=30kPa (liquid)
S23 T=40oC P=250kPa (liquid)
S20 T=40oC P=100kPa (liquid)
S25 T=27oC P=100kPa (liquid)
Sample of Calculation for Extraction Column Stream 20 Component
Flowrates Kmol/hr
CH3OH
1.01E+00
H2O
6.83E+00
i-C4H8
1.76E-01
(CH3)2O
2.63E+01
I-C4H10
2.37E+02
N-C4H10
2.71E+00
∆ĤF kJ/Kmol -2.01 x105 -2.42 x105 -1.69 x104 -1.84 x105 -1.35 x105 -1.26 x105
To K
T, K
∆H kJ/hr
298
313
0.19
298
313
0.96
298
313
0.07
298
313
7.33
298
313
98.29
298
313
1.14
∑ ∆H = 107.97
Stream 22 Component
H2O
Flowrates Kmol/hr
∆ĤF kJ/Kmol
To K
T, K
8.16E+01
-2.42 x105
298
300
∆H kJ/hr
∑ ∆H = 1.53
114
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Stream 23 Component
Flowrates Kmol/hr
i-C4H8
1.76E-01
(CH3)2O
2.63E+01
i-C4H10
2.37E+02
n-C4H10
2.71E+00
∆ĤF kJ/Kmol -1.69 x104 -1.84 x105 -1.35 x105 -1.26 x105
To K
T, K
∆H kJ/hr
298
313
0.07
298
313
7.33
298
313
98.30
298
313
1.14
∑ ∆H = 106.83
Stream 25 Component CH3OH H2O
Flowrates Kmol/hr 1.01E+00 8.84E+01
∆ĤF kJ/Kmol -2.01 x105 -2.42 x105
To K 298 298
T, K 300 300
∆H kJ/hr 0.02 1.65
∑ ∆H = 1.68
Energy balance, Q=(
∑ H)
out
–(
∑ H)
in
= (106.83+1.68) – (107.97+1.53) = -0.91 kW 8.2.17 Pump 4 (P-103)
S24 T = 40OC P= 300 Kpa (liquid) 115
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Calculations are based on Yunus A. Cengel, Micheal A. Boles, Thermodynamics: An Engineering Approach, WCB/Mc Graw-Hill, 1989, page, 354-355. Assumptions: 1. Steady operating conditions exist, 2. Kinetic and potential energy negligible 3. The process is to be isentropic Specific volume: (Data of these specific volumes are based on Coulson & Richardson’s)
Specific volumes: DME = 0.178m3/mol Butene = 0.240 m3/mol Isobutane = 0.255m3/mol n-butane =0.263 m3/mol
DME 0.178m3/mol x 1000mol/kmol x 1kmol/46kg = 3.87 m3/kg
butene 0.240m3/mol x 1000mol/kmol x 1kmol/56kg = 4.29 m3/kg Isobutane 0.255m3/mol x 1000mol/kmol x 1kmol/58kg = 9.11 m3/kg n-butane 0.263m3/mol x 1000mol/kmol x 1kmol/58kg = 4.53 m3/kg Vavg = (3.87 + 4.29 + 9.11 + 4.53) m3/kg / 4 = 5.45 m3/kg Which remains essentially constant during the process
116
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
2
∴Win = ∫ Vdp 1
= V1 (P2 − P1 ) = 5.45m 3 /kg(300 − 250)kpa(1k J/1kpa.m = 5.45(50)
3
)
= 272.50kJ/k g ∴272.50kJ/k g x kg/hr = 4113932.50 kJ/hr = 1142.76kW
8.2.18 Pump 5 (P-104)
S26 T = 27OC P= 150 Kpa ( liquid ) on Yunus A. Cengel, Micheal A. Boles, Thermodynamics: An Calculations are based Engineering Approach, WCB/Mc Graw-Hill, 1989, page, 354-355. Assumptions: 4. Steady operating conditions exist, 5. Kinetic and potential energy negligible 6. The process is to be isentropic Specific volume: Water = 0.056 m3/mol Methanol = 0.118m3/mol (Data of these specific volumes are based on Coulson & Richardson’s) Water 0.056 m3/mol x 1000mol/kmol x 1kmol/18kg = 4.26 m3/kg Methanol 0.118m3/mol x 1000mol/kmol x 1kmol/32kg = 3.6875 m3/kg
117
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Vavg = (4.26 m3/kg + 3.6875 m3/kg)/2 = 3.974 m3/kg Which remains essentially constant during the process. 2
∴Win = ∫ Vdp 1
= V1 (P2 − P1 ) = 3.974m 3 /kg(150 −100)kpa(1k J/1kpa.m = 3.974(50)
3
)
= 198.7kJ/kg ∴198.7kJ/kg x 1624.32kg/ hr = 322752.384 kJ/hr = 322 .75 kW
8.2.19 T-102 (Distillation Column 2)
S28 T=530C P=100kPa (liquid) S26 T=27oC P=150kPa (Liquid)
Sample of Calculations:
S27 T=30oC P=70kPa (liquid)
R = L/D Overall: (NL), L = D x 1.5 = 88.44 x 1.5 = 132.66 kmol/hr (NV), V = L + D
118
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
= 132.66 + 88.64 = 221.30 kmol/hr Stream 26 Component
Flowrates
∆ĤF
To
T, K
∆H
CH3OH H2O
Kmol/hr 9.91E-01 1.76E+00
kJ/Kmol -2.01 x105 -2.42 x105
K 298 298
300 300
kJ/hr 0.02 -4.79
∑ ∆H = -4.77
Stream 27 Component
Flowrates
∆ĤF
To
T, K
∆H
CH3OH H2O
Kmol/hr 2.00E-02 8.67E+01
kJ/Kmol -2.01 x105 -2.42 x105
K 298 298
300 300
kJ/hr 0.00 -235.48
∑ ∆H = -235.48
Stream 28 Component
Flowrates
∆ĤF
To
T, K
∆H
CH3OH H2O
Kmol/hr 1.10E-02 8.84E+01
kJ/Kmol -2.01 x105 -2.42 x105
K 298 298
326 326
kJ/hr 0.00 -240.26
∑ ∆H = -240.26
Energy balance, Q=(
∑ H)
out
–(
∑ H)
in
= (-235.48+(-240.26))– (-4.77) = -470.97 kW 8.2.20 Cooler 3 (E-105)
S28 T = 53oC P = 100Kpa (Liquid)
S29 T = 270C P = 130 Kpa (Liquid)
119
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Sample of Calculation for Cooler 1 Stream 28 Component
Flowrates
∆ĤF
To
T, K
∆H
CH3OH H2O
Kmol/hr 1.10E-02 8.84E+01
kJ/Kmol -2.01 x105 -2.42 x105
K 298 298
300 300
kJ/hr 0.00 -240.26
∑ ∆H = -240.26
Stream 29 Component
Flowrates
∆ĤF
To
Kmol/hr
kJ/Kmol
K
T, K
∆H
CH3OH
9.91E-01
-2.01 x105
298
300
0.02
H20
1.76E+00
-2.42 x105
298
300
0.03
kJ/hr
∑ ∆H = 0.06
Energy balance, Q=(
∑ H)
out
–(
∑ H)
in
= 0.06– (-240.26) = 240.32 kW Steam flowrate, Q = mCpΔT Cp of pure water, 4.184 J/g oC (Elementary Principles of Chemical Processes, W.Rousseau et. al) Q mCp ∆T 240320 J/s = 4.184J/g o C x (53 - 27) o C = 2209.15 g/s
m=
120
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Therefore the supply of steam flow rate required is 2209.15 g/s.
CHAPTER 9
121
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
HYSYS
9.0
THE DESIGN MADE BASED ON HYSYS SIMULATION
There are two method that was used in calculating the mass balance and energy balance for the process which is: i)
Manual calculation
ii)
Hysys simulation
Hysys program was used to see whether the design could be run or not. Using Hysys the calculation of the process was calculated automatically when the parameter that needed was insert. Then if the parameter that was insert is logic so Hysys program can calculated the result and the equipment can converge. If the data that was inserted was illogical the equipment cannot converge and the calculation cannot be done. At the back of this page show the simulation using Hysys that was converge and include with the manual log book.
REFERENCES Alber V.G Hahn (1970). The Petrochemical Industry – Market & Economics, USA Mc Graw Hill Book Company. 363- 372.
122
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Coulson & Richardson’s, Chemical Engineering Volume 6 Third Edition, Butterworth Heinemann. Norman N. Barish and Seymour Kaplan, Economic Analysis for Engineering and Managerial Decision Making, Second Edition, Mc Graw Hill Robert H. Perry and Don W. Green, Perry’s Chemical Engineering’s Handbook, Seventh Edition, Mc Graw Hill. Encik Mohd Napis Bin Sudin. 2003, Production of MTBE, Malaysia, Kuantan. Interview, 8 July Puan Masri. 2003. Information of MTBE production, Malaysia, Kuantan. Interview, 28 Jun. Lanny P. Schmidt (1998), The Engineering of Chemical Reaction, Oxford University Press. James, G. Speight, Baki Ozum (1985). Petroleum Refining Process, Apex Engineering Inc. Marcell Dekkir New York. MTBE and Oxygenates (1990), An International Marketing Guide Dewitt & Company Incorporated 16800 Greenport park, Suite 120N Houston, Texas 77060-2386. Page 51-62. The 1992-1995 Worldwide Catalyst Product, Process Licensing & Service DirectoryTechnical articl-1992/3. Page 9. Annual Report 1994, Section 4. Area Summary for asia and the Pacific. Page 135-169. Ray/Johnston (1989). Chemical Engineering Design Project, a case study approach, volume 6. Gordon and Breach Science Publishers. Wentz (1998). Safety, Health, And Environmental Protection, Mc Graw Hill Companies, Inc. Wiley (2000). Elementary Principles of Chemical Processes, John Willey & sons, Inc. Chemical Week June 11, 2003 Volume 165 page 31 George S. Brandy ,Henry R.Clauser & John A. Vaccari. ”Material Handbook – 4th edition”Joshua D.Tayloy, Jerrey I. Steinfeld and Jefferson W.Tester “ Ind. Eng. Chem. Res 2001,40, 67-74 page 71. Monica Bianchi & Rachl Uctas,ECN “ACN/CMR/ ECN NPRA Supplement, March 2002. Petronas Resource Center, Tingkat 4, Menara 2, Menara Berkembar Petronas, Kuala Lumpur City Center.
123
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Malaysia Industrial Development Authority
(MIDA), Plaza Central, K L Sentral. Kuala
Lumpur. Pusat Informasi SIRIM Berhad. 1, Persiaran Dato’ Menteri, PO Box 7035, Seksyen 2, 40911 Shah Alam. Jabatan Perangkaan Malaysia, Pusat Pentadbiran Kerajaan, Putrajaya. Tiram Kimia Sdn. Bhd, Tingkat 1, Bangunan Shell, Off Jalan Semantan, Damansara Heights, 50490 Kuala Lumpur. http://www.Manufacturing.net/pur/index.asp http://www.ceh.sric.sri.com/Public…html http://ww2.cemr.wvu/edu/~wwwche/publications/project/index.html http://www.illallc.com/engarticle.html http://www.huntsman.com/pertochemicals/ShowPage.cfm http://www.cmt.anl.gov/science_technology/basicci/onestep_phenol.shtml http://www.illallc.com/engpatent3am.html http://www.wikipedia.org/w/wiki.phtml http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/acetone/basic_ace http://www.atsdr.ede.gov/toxfag.html http://www.shellchemicals.com/chemicals/products/1,1184,806,00.html http://www.mida.gov.my http://eneken.ieej.or.jp/en/data/pdf/142.pdf http://www.matheson-trigos.com/mathportal/-pdfs/product/isobutane.pdf http://www.specialgas.com/isobutane.html http://www.gas.com.pdf/gas.pdf http://www.boc.com/microsite/america/products/gases/mixed/isobutane.html http://www.boc.com/microsite/america/products/gases/aps/geiger.html http://www.airliquide.com/safety/msds/en/129-AlEn.pdfhttp://www.cpchem/msds/specchem/isobutaneinstrumengradi.pdf
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
DESIGN PROJECT II
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
SECTION 1
Catalytic Cracking Design
1.1 INTRODUCTION A bed of solid particles can be fluidized by a stream of gas through it. The fluidization of solids in a stream of gas occurs only if the gas velocity achieved a certain value which is called minimum fluidization velocity Umf. Once the gas velocity achieved this value, the bed expands and pressure drop across the fluidized bed remains constant once fluidization occurred. In this commercial fluidized-bed catalytic cracking reactor, catalysts flow up through the reaction regeneration section in a riser type of flow regime. The over head catalyst captured by cyclones is returned to the hopper where it is fluidized with air to recapture any entrained hydrocarbon vapor. The catalyst was then discharged from the hopper, down through a standpipe. The solids flow through the standpipe was controlled by slide valve located at the base. From there, the solids went into the riser where they are carried by stream of air to the regenerator vessel. The regenerator operation in these plants resembled that of the reactor except for the system’s use of air instead of oil vapor. A portion of the catalyst from the regenerated catalyst hopper was returned to the regenerator through catalyst fresh feed exchangers. This action controlled the regenerator temperature and served to preheat the feed. Another bypass line from the hopper to the regenerator was used to control the dense bed level or holdup in the regenerator. Catalyst from the regenerated catalyst hopper flowed through a standpipe back into riser where the feed was injected. The commercial cracking catalysts used most widely is silica-alumina. High content catalysts are characterized by higher equilibrium activity level and surface area. These
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
catalysts could be offered at a lower price. An advantage of this catalyst grade is that a lesser amount of adsorbed, unconverted, heavy products on the catalyst were carried over to the stripper zone and regenerator. As a result, a higher yield of more valuable products and also smoother operation of the regenerator was achieved. Basically the design of the fluidized bed system can be divided into several sections: 1. Reaction vessel which included: Fluidized bed portion Gas disengaging space or freeboard Gas distributor 2. Solids feeder or flow control 3. Solids discharge 4. Dust separator for the exit gas 5. Instrumentation and control 6. Gas supply
Figure 1.1 : Illustration diagram of the reactor
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
1.2
Estimation of diameter of reactor
The fluidized bed diameter depends on the operating gas velocity. A larger diameter is required for a low gas velocity while for a high gas velocity, a small diameter is required. However the gas velocity must exceed the terminal velocity (Ut) of the particle transport of solid particles may occur. The operating velocity should be between minimum fluidization velocity and terminal falling velocity to maintain fluidization of solids.
Operating gas velocity, Uo = Where
d p2 g ( ρ p − ρg ) 18 µg
dp = diameter of particle
ρ
p
= density of particle
ρ
g
= density of gases
µ = viscosity of gases g = gravitational acceleration so, the value of Uo =
(80 ×10 −6 ) 2 × 9.81 × (1282 −1.484 ) 18 × (1.15 ×10 −5 )
= - 0.388 m/s (rising) = 0.388 m/s Flowrate of gas stream , Q = 39353 kg/hr =
39353 m3/s 1.484 ×3600
= 7.366 m3/s The bed diameter will be depending on the area of reactor used: Cross sectional area, A = =
Q V 7.366 0.388
= 18.985 m2
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Diameter of bed, D =
=
4×A
π 4 ×18 .985
π
= 4.9164 m ≈5m 1.3
Calculation of the Transport disengagement height, TDH
According to M. Rhodes (1998), the TDH region is considered as the region where located above the bed surface to the top of disengagement zone. While the disengagement zone is the region above the splash zone or region just above the bed surface in which the upward flux and suspension concentration of fine particles decrease with increasing in height. There are so many correlations that can be used to find the TDH value. For this design Amitin et al. (1968) was used.
TDH ( F ) = 0.85U 0 TDH ( F ) = 7.740968
1 .2
( 7.33 − 1.2 log 10 U 0 )
(1.1)
≅ 8m
1.4 Minimum fluidization Velocity The minimum fluidization velocity (Umf) is determined from Ergun equation: For Reynolds number, 0.01 < Re < 1000: According to the Martin Rhodes (1999), Ar =
Re =
d p2 g ( ρ p − ρ g ) ρ g 18 µg
and
U mf D p ρ f
µ
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Ar = 150
And
(1 − ε ) Re + 1.75 ε
3
1 Re 2 3 ε
(1.2)
By rearranging the equation (1.2) above we can get the new equation for minimum fluidization, Umf. As a result, the equation is becomes: Re =
U mf D p ρ f
U mf =
µ
=
µ ρg d p
(1135 .7 + 0.0408 Ar ) 0.5 − 33 .7
1.15 ×10 −5 (1135 .7 + 0.0408 × 72 .44 ) 0.5 − 33 .7 −6 1.484 × 80 ×10
U mf = 0.00425 m / s
1.5
Calculation for the value of terminal velocity U t
The value of Re
t
need to be calculated first, then the value of U t can be calculated.
The range of particle size is 65 μm to 95 μm. The mean particle size is 250 μm. −6 When d p = 80 ×10 m
4 ρ g ( ρ p − ρ g ) gd p C D Ret = 2 3 µg
3
2
C D Re t
2
(
4 1.484 × (1282 − 1.484 ) × 9.81 × 80 ×10 −6 = × 2 3 1.15 ×10 −5
(
)
)
3
2
C D Re t = 96.227883 2
From the chart of C D Re t and
CD vs Reynolds number, for value of Re t
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Figure 1.1 : CDRe2 and CD/Re versus Reynold number 2 C D Re t = 96.227883 the value of Re t = 3
Now from this we can calculate the value of U t , where
Re t =
3=
ρg U t d p µg
1.484 ×U t ×8 ×10 −6 1.15 ×10 −5
U t = 0.290599 ms −1
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
−6 when d p = 85 ×10 m
C D Re t
2
C D Re t
2
4 ρ g ( ρ p − ρ g ) gd p = 3 µ2
3
(
4 1.484 × (1282 −1.484 ) × 9.81 × 85 ×10 −6 = × 2 3 1.15 ×10 −5
(
)
)
3
2
C D Re t = 115.421775 5
2
From the chart of C D Re t and
CD vs Reynolds number from figure 1.1 for value Re t
2 of C D Re t = 115.421775 5 the value of Re t = 3.5
Now from this we can calculate the value of U t , where
Re t =
3=
ρg U t d p µg
5.54 ×U t ×85 ×10 −6 5.0 ×10 −5
U t = 0.3190899 ms −1
Table 1.1 : Calculation for terminal velocity in different size of dp.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Sieve
Weight,
Weight
size dp,
%, xi
fraction,
3.5 7.5 24 44 9.5 7 4.5
xi 0.035 0.075 0.24 0.44 0.095 0.07 0.045
m 0.000095 0.00009 0.000085 0.00008 0.000075 0.00007 0.000065
1.6
CDReT2 161.1394175 137.0119672 115.4217755 96.22788368 79.28933286 64.46516426 51.61441905
Reynold
Terminal
number 4.5 4 3.5 3 2.5 2 1.8
velocity, Vt 0.367073344 0.344414495 0.3190899 0.29059973 0.258310872 0.221409318 0.214596724
Find the value of K i*∞
Using the correlation for estimating entrainment rates are reported in the literature. The entrainment rate can be expressed by the following equation, as follows: Ei = Ei∞ + (Eio -Ei∞)exp (-afh)
( 1.3)
Where Ei = entrainment rate at a point h above bed surface af = a constant in freeboard Ei∞ = rate of elutriation of the fines with diameter dpi above the TDH Ei∞ = K i∞ Xi
(1.4)
Where Ki∞ is the elutriation rate constant for which numerous correlations have been reported. Table 2.2 from Appendix lists various published correlations for the elutriation rate constant. The constant, af, in equation (1.2) is independent of the bed’s composition and can be evaluated from experimental data for Fi as a function of h. Following Chen et al. (1979), is the entrainment rate of particles at the bed surface, where: Eio = KoXi
(1.5)
Where Ko = Elutriation rate constant at bed surface Xi = weight fraction of the particle cut size dpiA
1.7
Find the value of Eo
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.07 ×10 −9 ρ g Eo = Ad eqmt µ 2 .5
Eo =
3.5
g 0 .5
(U − U )
2..5
mf
3.07 ×10 −9 × (1.484 ) 3.5 (9.81) 0.5 ( 0.388 − 0.00425416 7 ) (1.15 ×10 −5 ) 2..5
2.5
(18 .98 )( 5)
Eo = 10.676 kg/m2s The following correlation is used to calculate the value of E i*∞ by using three different investigators which is : Merrick and Highley (1974) 0.5 E i∞ v U mf = A +130 exp −10 .4 t ρg U U U −U mf
0.25
Geldart et al. (1979) revised
E i∞ v = 23 .7 exp − 5.4 t ρgU U and Colakyan et al (1979)
E i∞
v = 331 − t U
2
From this correlation we find that the average of the correlation for these three investigators, shown in the table below:
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 1.2 : Correlation of three investigators Merrick and Highley
Geldart et al.
(1974) Ki*∞ 2.810456563 3.115064954 3.509080841 4.035580234 4.76909596 5.849694145 6.085514067
(1981) Ki*∞ 0.008247282 0.011304929 0.016081902 0.023907858 0.037471784 0.062625124 0.068853496
Colakyan (1979) Ki*∞ 10.27741771 8.238989106 6.227114828 4.299839595 2.545780992 1.100824216 0.8993437
1.8
Ki*∞, average 4.36537385 3.788452996 3.25075919 2.786442562 2.450782912 2.337714495 2.351237088
Calculation of solid loading
First find the value of Kih , K ih = K i*∞ + ( E o − K i*∞ ) exp( −a i h) = 4.36537385 = 4.36537385
+ (10.676996 53 - 4.36537385
)(2.69398E
- 12)
kg/m 2 s
R = Σ Ri = Σ RmRi
m Bi =
Fm Fi ( F − R ) + K i∞ A
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
m Bi =
10 .93 × 0.035 (10 .93 − R ) + 4.36537385
×18 .98
+
10 .93 × 0.075 (10 .93 − R ) + 3.78845299 6 ×18 .98
+
10 .93 × 0.024 (10 .93 − R ) + 3.25075919
+
10 .93 × 0.0095 10 .93 × 0.07 + (10 .93 − R ) + 2.45078291 2 ×18 .98 (10 .93 − R ) + 2.33771449 5 ×18 .98
+
10 .93 × 0.0045 (10 .93 − R ) + 2.35123708 8 ×18 .98
×18 .98
+
10 .93 × 0.044 (10 .93 − R ) + 2.78644256 2 ×18 .98
So the value of Rih calculated by excel is = 0.564147556 kg/s
Eih =
RT A 0.5641475 = 18.98 = 0.0297 kg / m 2 s
Rti = Kih* A
= 4.36537385
×1 8.98
2.78644256
2 ×1 8.98
2.35123708
8 ×1 8.98
+ 3.78845299 + 2.45078291
6 ×1 8.98 2 ×1 8.98
+ 3.25075919 + 2.33771449
×1 8.98
+
5 ×1 8.98
+
= 404.8578835 kg/s Ri = Kih A. Xi = 4.36537385 2.78644256 2.35123708 = 55.90386
×18.98 ×0.035 + 3.78845299 6 ×18.98 ×0.075 + 3.25075919 ×18.98 × 2 ×18 .98 ×0.44 +2.45078291 2 ×18.98 ×0.095 + 2.33771449 5 ×18.98 ×0 8 ×18.98 ×0.045 kg/s
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 1.3 : Data calculation to find solid loading
Total
Mbi 0.004103705 0.009964059 0.03640034 0.076031739 0.018254549 0.013978087 0.008943974 0.167676452
MRi 0.602699773 1.269994045 3.981014237 7.127685256 1.505148839 1.099367014 0.707506537 16.2934157
Ki*η 4.36537385 3.788452996 3.25075919 2.786442562 2.450782912 2.337714495 2.351237088
Rti 82.85479568 71.90483787 61.69940943 52.88667983 46.51585967 44.36982112 44.62647993
Ri 2.899918 5.392863 14.80786 23.27014 4.419007 3.105887 2.008192 55.90386
a) Solid loading unreturned = 0.029723 / 0.388 = 0.076606351kg/s b) solid loading return = =
55.90386 / 18.98 2.94540903 kg/s
1.9 Calculation of holding time and residence time The outlet concentration of a plug flow reactor is related to the inlet concentration of the reactant by the same equation as in a batch reactor with the same residence time -. For an equilibrium reaction between A and B, is first order. Based on studied of Khabtou, S., Chevreau, T., and Lavalley, J.C., Micropor. Mat. 3, 133 (1994), express the rate per catalyst mass instead of reactor volume.
k mA = − =
1 0.75 0.35 ⋅ ⋅ ln 1 − 0.35 − 151 .92 0.75 +1 0.75 4.785 ×10 −3 m 3 kg
−1
hr
−1
where x is the conversion in this process,
x = ([A] 0 - [A]) / [A]0 = 0.35,
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
[A] is experssed in concentration in mol/m3, K the rate mol m-3 s-1, kA in s-1. The value K = [i-C4=]eq/[i-C4]eq = 0.75 and ST = 151.94 g.hr/m3 based on study by Yamamoto, S. Asaoka, et al (1997). Then from below equation given, w can find τ : kτ = (1 − ε A ) ln
1 −ε A X A 1− X A
1 − 0.41(065 ) 1 − 0.65
τ
= (1 − 0.41 ) ln
τ
= 2256.48/ 4.785x10-3
τ
= 417574.39 hr
τ
= 115.99 s
when the total holding time are calculate then the weight of the bed of fluidized bed can be calculated. The formula used is as below:
t=
W Bed FB 0
WBed 830 = 3600 39353 W Bed = 95679.7761 7 kg
1.10
Calculation for the pressure drop ∆PB
The equation that can be used to calculate the pressure drop across the bed is:
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
ρg W Bed − W Bed ρp ( − ∆p ) = A
( − ∆p ) =
( 95679.78
1.484 × 9.81 ) − ( 95679.78 ×9.81 ) × 1282 18 .985
( − ∆p ) = 49382 .78 Pa
≅ 49 .383 kPa
According to Kunii and Levenspield, the pressure drop across the distributor ∆p d is
10% from the value of pressure drop across the bed when fluidized ∆PB . So the value of ∆p d is:
( ∆p d ) = 10 %( − ∆p B ) ( ∆p d ) = 10 % × (49 .382 kPa ) ( ∆Pd ) = 4.938 kPa
≅ 0.5035 kgm −2
According to Kunii and Levenspield (1991), to determine the number of holes in the distributor the Re
t
need to be calculated first:
Re t =
ρg U 0 Dt µg
Re t =
1.484 ×0.388 ×5.0 1.15 ×10 −5
Re t = 250344
1.11
Determine the direction and flow rate of gas passing between the vessels.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Assuming that in fluidized flow the apparent weight of the solids will be supported by the gas flow, the equation below gives the pressure gradient for fluidized bed flow:
( − ∆P ) = (1 − ε ) × ( ρ − ρ ) × g p g H
( − ∆P )
= (1 − 0.42 ) ×(1282 −1.484 ) ×9.81
H
= 7411.499
Pa / m
Actual pressure gradient =
( 3.25 − 2.89 ) ×10 5 10
= 3600 Pa / m
Since the actual pressure gradient is well below that for fluidized flow, the standpipe is operating in packed bed flow. The pressure gradient in packed bed flow is generated by the upward flow of gas through the solids in the standpipe. The Ergun equation above provides the relationship between gas flow and pressure gradient in packed bed. Knowing the required pressure gradient, the packed bed voidage and the particle and gas properties, equation below can solve for IUrelI, the magnitude of the relative gas velocity:
( − ∆P ) H
2 ρ f (1 − ε ) µ (1 − ε ) 2 = 150 2 ! U ! + 1 . 75 !U rel ! rel 2 x sv ε x sv ε
For standpipes it is to take downward velocities as positive. In order to create the pressure gradient in the required direction, the gas must flow upwards relative to the solids. Hence, IUrelI is negative: IUrelI = -0.291 m/s
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
From the continuity for the solid,
Solid flux, =
Gp A
= U p (1 − ε ) ρ p
The solid flux calculated is 55.9 kg/m2s as and so Up =
55 .9 (1 −0.41 ) ×1282
= 0.072715 m /s
Solids flow is downward, so Up = + 0.072715 m/s The relative velocity, Urel = Uf - Up Hence, actual gas velocity, Uf = - 0.291 + 0.072715 = - 0.21829 m/s (upwards)
Therefore the gas flows upwards at a velocity of 0.21829 m/s relative to the standpipe walls. The superficial gas velocity is therefore : U = ε Uf = -0.0895 m/s (upward ) From the continuity for the gas, mass flow rate of gas, Mf = ε U f ρp A = -0.10431 kg/s So, for the standpipe operate as required, 0.10431 kg/s of gas must flow from the lower vessel to the upper vessel.
1.12
Design of cyclone
Size a cyclone separator for removing particles above 80µ m in diameter entrained in a flue gas stream. The following information is supplied:
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
α
= β
0.21
=
0.66 dp = 0.00008 m gas volumetric flow = 1.8 m3/s particle density = 1282 kg/m3 gas density = 1.484 kg/m3 viscosity gas = 0.0000115 Ns/m kinematic viscosity v = 0.0000278 m2/s inlet gas velocity = 0.388 m/s specific wall thickness δ = 5 mm The particles are approximately round with a shape factor of 0.77 All dimensions of a cyclone of any design are selected depending on the width of inlet duct b or on the diameter of cyclone Dc. The problem is to properly select one of these dimensions from which the other dimensions are proportionally evaluated. The cyclone diameter, settling velocity, gas velocity, and parameters of the suspension to be separated are all interrelated parameters. Therefore, we select a preliminary diameter for approximate calculations and then refine our estimate to a more exact design. According Nicholas P. Cheremisinoff at al. (1984), the relative dimensions of the cyclone are specified as: b = α DC
and
hin = β DC
For the chosen cyclone α = 0.21 and β = 0.66 The continuity equation for the inlet nozzle is:
bh =
Vsec Win
(1.5)
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
where win is the inlet gas velocity; which for a primary cyclone operation is typically 18 to 22 m/s. Expressing b and hin in terms of diameter DC, equation above is rearranged to solve for the cyclone diameter:
Vsec DC = w in
0.5
0.5
1.8 = 0.21 × 0.66 ×18 = 0.85 m
For design purposes, assume a value of 0.9 m for DC. The diameter of the discharge pipe is: Dd = 0.58Dc = 0.58 x 0.9 = 0.52 m The gas velocity in discharge pipe is thus:
Wd =
4 Vsec 4 × 1.8 = 2 πDd 3.142 × 0.52 2
= 8.5m / s
Specifying a wall thickness δ = 5 mm for the gas discharge pipe, its outside diameter will be: Dd ,out
=
Dd + 2δ
= 0.52 + 2(0.005 )
= 0.53 m
The width of the circular gap between the pipe and cyclone shell is:
=
Dc Dd ,out − 2 2
= 0.45 − 0.265
= 0.185 m
The height of the circular gap from a spiral surface to the lower edge of discharge pipe is: H = 0.775 Dc = 0.775 X 0.9
= 0.7 m
The calculated dimensions of the cyclone can be checked by comparing the particle settling time:
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
τ0 =
Rc − Rd ,out wo
=
wo
to the residence time of gas in the cyclone:
τ=
2 π Rav n wg
where Rc and Rd,out are the radii of the cyclone and discharge pipe, respectively; n = number of gas rotations around the discharge pipe (we may assume n = 1.5) The peripheral velocity of gas is: wg =
Vsec = H
1 .8 0.7 × 0.185
= 13 .9 m / s
For this cyclone, this value must be in the range of 12 to 14 m/s The average radius of the gas rotation is :
Rav =
Dd ,out
+
2
2
=
0.53 0.185 + 2 2
= 0.357 m
The centrifugal acceleration (at the average radius) is:
a=
w g2 Rav
2
=
13.9 = 542 m / s 2 0.357
The separation criterion is: Ks
=
a g
=
542 9.81
= 55 .2
In this case, the centrifugal field in the cyclone is 55.2 times more intensive than the gravitational. The Archimedes number is:
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
g d 3 ρ p − ρg × Ar = ρg ν2
9.81 × (80 ×10 −5 ) 3 × (1282 −1.484 ) ×1.484 = (1.15 ×10 −5 ) 2 = 77.44 The settling number is: S1 = Ar x 1 x
Ks = 72.44 x
55.08843
= 3999 Because
3.6 < S1 < 82,500 the flow regime through the cyclone is transitional.
Therefore, the theoretical velocity of the particles is:
(
α ρf 2 w = 0.22 d µρ
)
0.333
(
α ρf 2 = 0.22 d µρ
)
0.333
5.42 ×10 2 ×1282 = 0.22 ×10 ×10 −5 1.15 ×10 =
4.638 m / s
The particles have a shape factor ofψ = 0.77 and the gas inlet gas stream contains a low volume of solid particles. Based on the operating conditions specified, the settling velocity is Ws = R ψ w = 0.77 x 4.634 = 3.568 m/s
Because the concentration of the suspension is low, we may assume R = 1
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
The settling time is therefore: w
τ0 =
= 0.0518s
The residence time for the gas is:
τ=
2πRavg n wg
=
2 × 3.142 × 0.357 ×1.5 = 0.2424 s 13 .9
Since τ0 < τ
the diameter of the cyclone selected is acceptable and we may now
specify the other dimensions as based on the recommended proportions. As a final calculation for the design, we evaluate the hydraulic resistance of the cyclone: ∆ P=
1 C D ρ win2 Where CD is the typical number of cyclone. 2
= 0.5 x 1 x 1.484 x 182 = 240.4 N/m2
1.13
Calculation for mechanical design
For mechanical design, the temperature and pressure are imperative properties in calculate the thickness and the stress of the material. For that reason, the safety factor also required as safeguard and determined by certain consideration such as corrosion factor, location and process characteristic. From Hysys data, the operating temperature inlet into the reactor is 250oC and regenerator is 180oC. The design temperature is related to the operating temperature. The design pressure and temperature for this reactor are showed as follow: Reactor 1. Design Pressure Operating pressure
=
2.89 bar
=
0.289 N/mm2
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
For safety reason take pressure 10% above operating pressure Design Pressure, Pi Design Temp. , T
=
0.289 N/mm2x 1.1
=
0.3179 N/mm2
=
200ºC
2. Material Construction
The material used is stainless steel (18Cr/8Ni, 304). For this material, the design stress at 200 ºC, R.K.Sinnot (1999). Design stress, f
=
115 N/mm2
Diameter vessel, Di
=
5.0 m
Tensile strength,
=
510 N/mm2
3. Vessel Thickness e
=
Pi Di 2 jf − Pi
=
(0.3179 )( 5000 ) 2(1)(115 ) − (0.3179 )
=
7 mm + 4 mm
=
11 mm
From R.K.Sinnot (1999), this value should not be less than 12 mm (including 2 mm of corrosion allowance). For vessel diameter around 5 m, this take e = 15 mm. A much thicker wall will be needed at the column base to withstand the wind and dead weight loads.
4.
Heads and Closure
This section covers the choice of closure to be used in the design. Basically there are two types of ends, which are domed ends. A standard torispherical heads and ellipsoidal heads as well as the flat heads are calculated in order to select the most economical head regarding its thickness. All the calculation is referring to the R.K. Sinnot, Coulson and Richardson Vol.6 page 815-817. Take, crown radius, Rc
= Di
= 5.0 m
147
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Knuckle radius, Rk
= 6% Rc
= 0.03 m
A head of this size would be form by pressing: no joints, so J = 1.0
Cs
=
1 3+ 4
Rc Rk
=
1 3 + 4
5 .0 0 .3
= 1.77 Therefore, minimum thickness:
e
= =
Pi Di 2 Jf − Pi ( Cs − 0.2)
( 0.3179 )( 5000 ) 2(1)(115 ) − 0.3179 (1.77 − 0.2 )
= 11 mm 5.
Column Weight
Dead weight of vessel, Wv For a steel vessel, Wv
=
240 Cv Dm (Hv + 0.8Dm) t
=
mean diameter, m
=
(Di + t)
Cv
=
a factor, take 1.15
Hv
=
height or length between tangent lines, m
t
=
wall thickness, m
Where, Dm
148
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
To get a rough estimate of the weight of this vessel is by using the average thickness, 11mm Therefore, Dm
=
5 + 2 x 0.011
=
5.022 m
=
240 (1.15) (5.022) [7.6 + 0.8(5.022)] 0.011
=
177.13 N
=
0.17713 kN
So, Wv
Weight of insulation, WI Assume material is Mineral wool. ρ of Mineral wool
=
thickness
75 mm
=
130 kg/m3
Volume of insulation =
π
=
π (5.022) (7.622) (0.075)
=
9.018967m3
x Dm x Hv x thickness of insulation
Weight of insulation, WI =
Volume of insulation x ρ x g
=
9.018967 x 130 x 9.81
=
11501.89N
=
11.50189kN
Double this value to allow fittings, so weight of insulation will be = 23.004 kN Weight of bed
149
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Weight of bed in reactor WB
= 95679.78 x 9.81 = 938618.6 N = 938.6186 kN
Weight of cyclone Volume of cyclone in reactor = 2.438 m3 Weight of cylone = 2.438 x 9.81 x 1282 = 30661.31 N = 30.661 kN There fore, Total weight
= Wv +WI +WB + Wc = (177.1311 + 23003.78 + 938618.6 + 30661.31)N = 992.461 kN
For Regenerator 1.
Design Pressure Operating pressure
=
2.6 bar
=
0.26 N/mm2
For safety reason take pressure 10% above operating pressure Design Pressure, Pi Design Temp. , T 2.
=
0.26 N/mm2x 1.1
=
0.286 N/mm2
=
180ºC
Material Construction
The material used is stainless steel (18Cr/8Ni, 304). For this material, the design stress at 200 ºC, R.K.Sinnot (1999). Design stress, f
=
121 N/mm2
Diameter vessel, Di
=
6.5 m
150
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Tensile strength, 3. e
4
510 N/mm2
=
Vessel Thickness =
Pi Di 2 f − Pi
=
(0.286 )( 6500 ) 2(1)(121 ) − (0.286 )
=
8 mm + 4 mm
=
12 mm
Heads and Closure
This section covers the choice of closure to be used in the design. Basically there are two types of ends, which are domed ends. A standard torispherical heads and ellipsoidal heads as well as the flat heads are calculated in order to select the most economical head regarding its thickness. All the calculation is by referring to the R.K. Sinnot, Coulson and Richardson Vol.6 page 815-817 Take, crown radius, Rc
= Di
= 6.5 m
Knuckle radius, Rk
= 6% Rc
= 0.39 m
A head of this size would be form by pressing: no joints, so J = 1.0
Cs
=
1 3+ 4
Rc Rk
=
1 3 + 4
6.5 0.39
= 1.77
Therefore, minimum thickness:
e
=
Pi Di 2 Jf − Pi ( Cs − 0.2)
151
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
=
( 0.286 )( 5000 ) 2(1)(121 ) − 0.286 (1.77 − 0.2 )
= 14 mm
5.
Column Weight
Dead weight of vessel, Wv For a steel vessel, Wv
=
240 Cv Dm (Hv + 0.8Dm) t
=
mean diameter, m
=
(Di + t)
Cv
=
a factor, take 1.15
Hv
=
height or length between tangent lines, m
t
=
wall thickness, m
Where, Dm
To get a rough estimate of the weight of this vessel is by using the average thickness, 12 mm Therefore, Dm
=
6.5 + 2 x 0.012
=
6.524 m
=
240 (1.15) (6.524) [8 + 0.8(6.524)] 0.012
=
285.6337 N
=
0.2856 kN
So, Wv
Weight of insulation, WI Assume material is Mineral wool. ρ of Mineral wool
=
130 kg/m3
152
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
thickness
=
75 mm
Volume of insulation =
π
=
π (6.524) (8) (0.075)
=
12.29745 m3
x Dm x Hv x thickness of insulation
Weight of insulation, WI =
Volume of insulation x ρ x g
=
12.29745 x 130 x 9.81
=
15682.94N
=
15.68294kN
Double this value to allow fittings, so weight of insulation will be = 31.36588kN Weight of bed Weight of bed in reactor WB
= 75060.19 x 9.81 = 736340.5 N = 736.3405 kN
Weight of cyclone Volume of cyclone in reactor = 2.438 m3 Weight of cylone = 2.438 x 9.81 x 1282 = 30661.31 N = 30.661 kN There fore, Total weight
= Wv +WI +WB + Wc = 0.2856 + 31.36588 + 736.3405 + 30.661 = 798.652 kN
153
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Total weight for reactor and regenerator = 992.461 + 798.652 kN = 1791.113 kN 6.
Wind Loads
Take, Win speed, Uw =
160 km/hr
For a smooth cylindrical column stack, the following semi-empirical equation can be used to estimate wind pressure. Pw
=
0.05Uw2
=
0.05(160)2
=
1280 N/m2
Loading per Unit Length of column, Fw Fw
=
Pw Deff]
Where, Deff
= Effective column diameter = Diameter + 2(tshell + tinsulation ) = 6.5 + 2(12 + 75 ) x 10-3 = 6.68 m
Therefore, Fw
=
1280 x 6.68
=
8550.4 N/m
Bending Moment
Mx
=
Fw ( X ) 2 2
154
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Where, X
= Distance measure from the free end =8m
Therefore, Mx
7.
=
8550 .4 (18 ) 2 2
=
1385164.8 Nm
=
1385.1648 kNm
Analysis of Stress
From bottom tangent line, Longitudinal pressure stress,
σ
h
=
Pi Deff 2t
=
(0.286 )( 6680 ) 2(12 )
=
79.6033N/mm2
Circumferential pressure stress, σ
L
=
Pi Deff 4t
=
(0.286 )( 6680 ) 4(12 )
=
39.802 N/mm2
Dead weight stress, σ
w
=
W
π( Di + t )t
155
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
=
1791 .113 ×10 3 π(6500 +12 )12
=
7.2958 N/mm2
Bending Stress,
σ
b
±
=
M Di + t Iv 2
where, M
= total bending moment
Iv
=
Iv
= second moment of area
π 64
(D
4
o
− Di
4
)
which, Di
= 6500 mm
Do
= (6500+ 2(12)) = 6524 mm
so, Iv
π
=
(6524 64
=
1.3013 x 1012 mm4
4
− 6500 4 )
Therefore, σ
b
1385164 .8 ×1000 6500 + 12 12 1.3013 ×10 2
=
±
=
± 3.47 N/mm2
The resulted longitudinal stress, σ z is: σ
z(upwind)
=
σ
=
39.802 - 7.2958 + 3.47
=
35.9762 N/mm2
L
- σ
w
+ σ
b
156
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
σ
σ
=
z(downwind)
L
- σ
=
w
- σ
b
39.802 - 7.2958 - 3.47
29.0363 N/mm2
= 8. Elastic Stability Critical bulking stress
σ
1
t = 2 x 104 D m
12 = 2 x 104 6512 = 36.855 N/mm2 Maximum compressive stress will occurs when the vessel not under pressure =σ
w
+ σ
b
= 7.2958 + 3.472 = 10.768 N/mm2 This is below critical bulking stress, so acceptable. 9. Vessel Support Design (Skirt Design) Type of support
: Straight cylindrical skirt
θs
: 80º
Material construction : Carbon steel Design stress, fs
: 135 N/mm2 at ambient temperature, 20ºC
Skirt height
: 4.0 m
Young modulus
: 200, 000 N/mm2
Therefore, The total weight of vessel from calculation before = 1791.113 kN Wind load, Fw
= 8550.4 N/m = 8.5504 kN/m
157
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Bending moment at skirt base,
Ms
( H v + H skirt ) 2 = Fw 2 (18 + 2 ) 2 = 8.5504 2
= 1710.08 kNm As a first trial, take skirt thickness as same as the thickness of the bottom section of the vessel, ts = 12 mm Bending stresses in skirt, σ
=
bs
4 Ms [π ( Ds + ts )ts Ds ]
Where, Ms
= maximum bending moment (at the base of the skirt)
ts
= skirt thickness
Ds
= inside diameter of the skirt base = 3.0 m
Therefore, σ
bs
=
4(1710 .08 )(1000 )(1000 ) [π ( 6500 +12 ) (12 )( 6500 )]
= 4.287 N/mm2 Dead weight stress in the skirt,
σ
ws
=
2W [π ( D s + t s ) t s ]
Where,
158
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
W
= Total weight of the vessel and content = 1791.113 kN
Therefore,
σ
(test)
ws
=
2 ×1791 .113 ×1000 [π( 6.5 + 0.012 ) (0.012 )]
= 14591753.05 N/m2 = 14.592 N/mm2
σ
bs,
(operating)
=
1791 .113 ×1000
[π( 6.5 + 0.012 ) (0.012 )]
= 7295876.525 N/m2 = 7.2958 N/mm2
Thus, the resulting stress in the skirt, σ Maximum σ s (compressive) = σ
ws
s
:
(test) + σ
bs
= 14.592 + 4.287 = 18.879 N/mm2 Maximum σ s (tensile)
=σ
bs
- σ
ws
(operating)
= 4.287 - 7.2958 = 0.0323 N/mm2
10.
General consideration for design
Take the joint factor J as 0.85,
159
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
σ s (tensile)
< fs J sin θ s
σ s (compressive)
< 0.125 E
ts sin θs Ds
Where , fs
= maximum allowable design stress for the skirt material = 135 N/mm2
J
= weld joint factor
θs
= base angle of a conical skirt
E
= modulus young = 200, 000 N/mm2
Therefore, σ s (tensile)
< 135 x 0.85 sin 80
0.1892 N/mm2
< 113.007 N/mm2
σ s (compressive)
< (0.125)(200,000)
0.4014 N/mm2
< .1214.473 N/mm2
148 sin 80 3000
Both criteria are satisfied, add 2 mm for corrosion, give design thickness of 150 mm
11.
Base Rings and Anchor Bolts
Assume pitch circle diameter
= 5.0 m
Circumference of bolt circle
= 5000π
Bolt stress design, fb
= 125 N/ mm2
Recommended spacing between bolts
= 600 mm
160
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Minimum number bolt required, Nb
=
5000 π 600
= 26.18 Closest multiple of 4
= 28
Bending moment at base skirt, Ms
= 212.101 kNm
Total weight of vessel, W
= 236.7534 kN
Area of bolt,
Ab
=
4M s − W N b f b Db
=
1 4( 212 .101 )(1000 ) − (184 .046 )(1000 ) 28 (125 ) 3. 0
1
… E.1.19
= 28.22 mm2 bolt root diameter,
d
28 .22 × 4
=
π
= 6 mm Total compressive load on the base ring per unit length,
Fb
4M s
=
πDs
2
+
W πDs
4 (212 .101 ) ×1000 236 .7534 ×1000 + = 2 π (3) π (3.0)
= 55.12 kN/m
Assuming that a pressure of 4 N/mm2 is one of the concrete foundation pad, fc Minimum width of the base ring,
Lb
=
Fb 1 × 3 fc 10
161
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
=
55 .12 ×10 3 4 ×10 3
= 13.78 mm
12.
Feed Nozzle Sizing
Optimum duct diameter, dopt,t
= 293G0.53ρ
-0.37
Where, G
= flow rate
= 1.32121 x 105kg/hr = 36.7 kg/s
ρ
= density
= 30.698 kg/ m3
Therefore, Dopt
= 293 (36.7)0.53 (30.698)-0.37 = 500 mm
Nozzle thickness,
t
=
Ps d opt 20 σ + Ps
Where, Ps
= Operating pressure
= 2.74945 N/mm2
σ
= Design stress at working temperature
= 30 N/mm2
Therefore
162
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
t
=
( 2.74945 )(118 ) 20 (30 ) + 2.74945
= 0.2 mm So, thickness of nozzle
= corrosion allowance + 0.2 mm = 4 + 0.2 mm = 4.2 mm ∼ 5 mm
13.
Top Product Nozzle Sizing
Optimum duct diameter, dopt,t
= 260G0.52ρ
-0.37
Where, G
= flowrate
= 223938.68 kg/hr = 62.205 kg/s
ρ
= density
= 56.69 kg/m3
Therefore, dopt
= 226(62.205)0.50 (56.69)-0.35 = 500 mm
Nozzle thickness,
t
=
Ps d opt 20 σ + Ps
σ
163
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Where Ps
= Operating pressure
= 2.74945 N/mm2
σ
= Design stress at working temperature
= 30 N/mm2
Therefore
t
=
( 2.74945 )(1000 ) 20 (30 ) + 2.74945
= 2 mm So, thickness of nozzle
= corrosion allowance +2 mm =4 +2 = 6 mm ∼ 6 mm
Table 1.4 : Summary of the Mechanical Design Design Pressure Reactor Operating Pressure
2.89 bar
Reactor Operating Temperature
160
Reactor Design Pressure
0
C
3.179 bar
164
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
0
Reactor Design Temperature
200
C
Regenerator Operating Pressure
2.6 bar
Regenerator Operating Temperature
150
Regenerator Design Pressure
2.86 bar
Regenerator Design Temperature
180
Safety Factor
0.10
0
C
0
C
Design of Domed Ends Types
Torispherical head
Crown Radius Knuckle Radius Joint Factor Stress Concentration Factor Minimum Thickness Corrosion Allowance Column Weight Dead Weight of Vessel Weight of Bed Weight of cyclone Weight of Insulation Total Weight reactor and regenerator Wind Pressure Loading Bending Moment
6.5 0.039 1 1.77 14 4 389 736.34 30.66 31.366 1791.11 1280 8550.4 1385.1648
m m mm mm kN kN kN kN kN N/m2 N/m kNm
REFERENCES
Cheremisinoff, Nicholas P., 1984, Hydrodynamics of Gas-Solids Fluidization, 279 - 231 Amitin et al. 1985, The Hydrodynamic of Fluidization, Powder Technology,(42):
67-78
Geldart, D ,. et al., 1979, Transition Institute Chemical Engineers, 57-269. Dolignier J. C, Marty E., Martin G. & Delfosse L., 1998, Modelling of gaseous pollutants emission in circulating fluidized bed of municipal refuse. Elsevier Science Ltd(77): 1399-1409 Gregory et al, 1985, The design of distributor for gas-fluidized bed, Powder Technology. (42): 100-145
165
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Horio et al. 1980, The Hydrodynamic of Fluidization, Powder Technology,(42): 67-78 Sinclair, J.L. and R. Jackson, “Gas-Particle Flow in a Vertical Pipe with Particle-Particle Interactions, AIChE J., 35, 1473-1486 (1989) Sinclair, J.L., “Hydrodynamic Modeling”, in “Circulating Fluidized Beds”, ed. Grace, J.R., Avidan, A.A. and T. M. Knowlton, Chapman and Hall, Great Britain (1997) Wang, Z., D. Bai and Y. Jin, "Hydrodynamics of Concurrent Downflow Circulating Fluidized Bed (CDCFB)", Powder Technology, 70, 271-275 (1992) Wei, F., Wang, Z., Jin, Y., Yu, Z. and W. Chen, “Dispersion of Lateral and Axial Solids in a Cocurrent Downflow Circulating Fluidized Bed”, Powder Technology, 81, 2530 (1994) Himmelblau M. D. 1996, Basic Principles and calculation in Chemical Engineering. Sixth edition. United States of America: Prentice Hall International, Inc. Levinspiel O. 1999. Chemical reaction engineering. Third edition. United States of America: John Wiley & Sons. Rhodes, M. 1998. Introduction to particle technology. Chichester England. John Wiley & Sons 97-130. Sinnot, R.K. 1999.Chemical engineering volume 6. Third edition. Great Britain: Butterworth-Heinemann. Zhang H, “Hydrodynamics of a Gas-Solids Downflow Fluidized Bed Reactor”, Ph.D. thesis, The University of Western Ontario (1999) Zhang, H., Zhu, J-X., “Hydrodynamics in Downflow Fluidized Beds (2): Particle Velocity and Solids Flux Profiles”, Chemical Engineering Science, 55, 4367-4377 (2000) Matsen, J. M. "Some Characteristics of Large Solids Circulation Systems". In Fluidization Technology, Keairns, D. L., Ed.; Hemisphere: New York, Vol. 2, Chapter1 (1976)
166
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Ouyang, S. Potter, S.E., “Consistency of Circulating Fluidized Bed Experimental Data”, Ind. Eng. Chem. Res., 32, 1041-1045 (1993) Wei, F., R. Xing, Z. Rujin, L. Guohua, J. Yong, “A Dispersion Model for Fluid Catalytic Cracking Riser and Downer Reactors”, Ind. Eng. Chem. Res., 36, 5049-5053 (1997) Yang Y.L., Y. Jin, Z.Q. Yu, Wang, Z.W., “Investigation on Slip Velocity Distribution in the Riser of Dilute Circulating Fluidized Bed”, Powder Tech., 73, 67-73 (1992) http://thor.tech.chemie.tu_muenchen.de/~tc2/eng/teaching/industr_chem_process/crac king%20lecture%201.pdf http://www.refiningonline.com/EngelhardKB/npra/NPR8851.htm http://iglesia.cchem.berkeley.edu/ChemicalCommunications_1764_2003.pdf http://www.caer.uky.edu/energeia/PDF/vol10-3.pdf http://www.netl.doe.gov/publications/proceedings/96/96ps/ps_pdf/96ps3_2.pdf http://tetra.mech.ubc.ca/CFD03/papers/paper29AF3.pdf http://www.netl.doe.gov/products/r&d/annual_reports/2001/stpt/cfb%20operating %20regimes%20cork.pdf http://www.flotu.org/~weifei/twophase-ces.pdf http://www.gtchouston.com/articles/GTC%20online%20reprint%2011-99.pdf
167
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
SECTION 2
MULTITUBULAR FIXED BED REACTOR
2.1
CHEMICAL DESIGN
2.1.1 INTRODUCTION
168
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Fixed bed reactors are the most important type of the reactor for the synthesis of large scale basic chemicals and intermediates. In these reactors, the reaction takes place in the form a heterogeneous catalyst. In addition to the synthesis of valuable chemicals, fixed bed reactors have been increasingly used in recent years to treat harmful and toxic substances. The most common arrangement is the multi tubular fixed bed reactor, in which the catalyst is arranged in the tubes, and the heat carrier circulates externally around the tubes. Fixed bed reactor for industrial synthesis are generally operated in a stationary mode under constant operating conditions over prolonged production runs, and design therefore concentrates on achieving an optimum stationary operation. However, the non stationary dynamic operation mode is also great importance for industrial operation control.
CATALYST FORM FOR FIXED BED REACTOR The heart of fixed bed reactor and the site of the chemical reaction is the catalyst. The processes taking place on the catalyst may formally be subdivided into the following separate steps: 1. Mass transfer of reactants from the main body of the fluid to the gross exterior surface of the catalyst particle. 2. Molecular diffusion /Knudsen flow of reactants from the exterior surface of the catalyst particle into the interior pore structure. 3. Chemisorption of at least of the reactants on the catalyst surface. 4. Reaction of the surface 5. Desorption of absorbed species from the surface of the catalyst. 6. Transfer of products from the interior catalyst pores to the gross exterior surface of the catalyst by ordinary molecular diffusion/Knudsen flow. 7. Mass transfer of products from the exterior surface3 of the particle into the bulk of the fluid.
169
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
For industrial use, a particle size is a compromise between the speed of the exchange reaction (which is greater with small beds) and high flow rates (which require coarse particles to minimize the head loss). Standard resins contain particle with diameter from 0.3 to 1.2 mm, but coarser or finer grades are available. For the MTBE production process, the fine sulphonic ion exchange resin particles with its size less than 1.0 mm have to be enveloped in various conceivable shapes The catalyst properties are as below: Shape of Catalyst
=
Spheres
Diameter of catalyst (dc)
=
0.6 mm (ref: Jon J.Ketta)
Effective Diameter surface d’p
=
0.5mm
Bulk Density of Catalyst (ρb)
=
810 kg/m3
Specific Solid Sphere surface
=
34.25 m2/g (ref:Perry’sHandbook,pg 16.10)
2.1.2
Voidage (εb)
=
0.32 (ref:Tech Info.Buletin)
Surface Area (Sa)
=
45 m2/g
Specific Surface
=
0.034 m2/g
Specific Gravity
=
in range 1 to 1.4
Internal Void Fraction (εp)
=
0.54
Molecular Weight
=
98 g/mole
PARTICLES SOLID DENSITY
Particle solid density (ρp) can be obtained from the equation below (ref: Particle Technology’s book):
ρp
=
ρb 1-εb
=
810 1 - 0.32
=
1191.2
kg/m3
170
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
2.1.3
VOID VOLUME OF CATALYST
Void volume of catalyst, Vg can be determined as below: Vg
2.1.5
=
εp ρp
=
0.32 1191.2
=
0.268 cm3/g
(2.1)
PORE RADIUS OF CATALYST
Pore radius of particle, r is the determined, r
2.1.6
=
2. Vg Sa
=
2 * 0.268 45 x 104
=
1.194 x10-5 m
(2.2)
KNUDSEN DIFFUSIVITY
Knudsen Diffusivity is given by the equation below: Dk where M T
Dk
=
9.7 x103 r (T)1/2 (M)
=
molecular weight of the catalyst
=
98 g/mole
=
operating temperature
=
393 K
=
9.7 * 103 * 1.194 *10-5 *( 393)1/2
(2.3)
171
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
98 =
0.013 cm2/ s
The effectiveness factor is given in term of Thiele Modulus as: η
=
η
2.1.7
=
3 (Φ - 1) Φ2 tan h Φ
(ref: Jon J.Mc Ketta) (2.4)
0.928 where Φ = 1.1 (ref: Perry,s Handbook)
REACTION RATE
The synthesis of MTBE from methanol and isobutylene catalyzed by Amberlyst-15 or similar sulphonic ion exchange resin catalyst is a reversible etherification as shown in equation 1: iC4H8 (isobutene) + CH3OH (methanol)
C5H12O (MTBE) k1
CH3C(CH3)=CH2(B) + CH3OH
CH3C(CH3)2OCH3 (M) K2
Reaction kinetics: According to Yang et al, the forward reaction of reaction above is first order with respect to the isobutylene concentration and zero order with respect to the methanol concentration, respectively, and the reverse reaction is first order with respect to the MTBE concentration as shown below: Table 1:
Arhenius parameters of rate constant K1 and K2 for MTBE
synthesis catalyzed by Sulphonic ion exchange acidic resin catalyst. (Ref: Chem. Eng. Journal)
172
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
A1
A2
E1(J/mole)
E2(J/mole)
6.50E+05
1.36E+08
4.74E+04
7.04E+04
-rB = k1CB – k2CM where: k1 = A1 exp (-E1/RT) & k2 = A2 exp (-E2/RT) k1 = A1 exp (-E1/RT)
(2.5)
= 6.5 * 105 exp (-4.74*104/ 8.314 * 326 K) = 0.0165 / min k2 = A2 exp (-E2/RT)
(2.6)
= 1.36 * 108 exp (-7.04 * 104 / 8.314 * 326 K) = 0.00071/ min
The main side reactions are the dimerization of isobutylene to diisobutylene, and the hydration of isobutylene to tert-butyl-alcohol (TBA) as shown below: 2CH3C(CH3)=CH2 CH3C(CH3)=CH2 + H2O
CH2=C(CH3)CH2C(CH3)2CH3 (DIB) CH3C(CH3)2OH (TBA)
(3) (4)
The kinetic study shows that reaction (3) can only take place when the addition of methanol is unsufficient. Since the methanol addition is carefully arranged to allow the molar ratio of methanol to isobutylene to be higher than 0.8, the reaction (3) can be
173
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
neglected. For reaction (4), the minor water in hydrocarbon and methanol feedstock is consumed in the pre-reactor before it is fed into reactor. Therefore, reaction (4) can also neglect. The products of the two side reaction are considered in the vapor-liquid equilibrium calculation, whereas the reaction kinetics is not included in the calculation. -rB = k1CB – k2CM = k1(CBo –CBXB) – k2( MCBo –CBXB) CB = CBo since Pi = 2000Kpa and Ti = 326 K CBo = Pi /RT = 73.79 mol /m3 M = CMo / CBo = 0.138 Substitute all the value, -rB = 173.8 mole/ m3hr 2.1.8 WEIGHT OF CATALYST The weight of catalyst can be determined from the equation, W = ∫ dX F r
2.7)
Where r = overall reaction rate W = weight of catalyst needed for the conversion F = mole flow rate of the feed to the reactor Substitute all the value and the by integration, the weight of catalyst is found to be 2998 kg. 2.1.9 DETAIL DESIGN OF THE REACTOR 2.1.9.1 Heat Exchanger for Reactor
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
For isothermal operation, heat may be supplied or removed continuously along with the reaction path. In order to accomplish effective heat transfer with the packed bed, the width of the bed must be small. In other words, isothermal reactors usually consist of a number tube arranged as in large heat exchangers with the catalyst inside the tubes and the cooling or heating medium outside the tubes. 2.1.9.2 Direction of the Reactant Flow For the fixed bed reactor to be designed so that reactants remain isothermal, the rate of heat required for the exothermic reaction must be exactly balance the heat transfer from the heating medium. For any isothermal reaction of positive order, the reaction rate falls as the reaction approaches equilibrium. Therefore a more rapid heating is need at the reactant entrance than the reactant exit. Therefore the reactors have to be designed as co-current to match the requirement and heat transfer. 2.1.9.3 Volume of Catalyst Bed Volume of catalyst bed (Vb)
= W / ρb = 2998 810 = 3.70 m3
(2.8)
2.1.9.4 Pressure Drop in the Bed Pressure drop is an important variable in the rate equations. The maximum allowable pressure drop criteria below have to be concerned. 1. The resulting force must not be exceeding the crushing strength of the particle. For the down flow bed this force created by the pressure drop is transmitted by contacting solid to the bottom of the bed. 2. Mass velocity through the bed must be high enough to minimize interphase gradients and assure good distribution. Incremental increases in pressure
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
drop however should not exceed savings release from improved reactor performance. In many bed systems the maximum economical pressure drop is in the range of 3 to 5% of the total pressure. 2.1.9.5 Estimating Pressure Drop (ΔP) L Where ƒ
=
ƒ u2 ρf d’p
(2.9)
= friction factor, the correlation of Ergun (1952) will be used = [1.75 + 150 / (1-εb) / Re] (1-εb)/ εb3
Re
= d’p u ρf = d’p G μf μf
(2.10)
Where G is mass velocity = m/ A since m= 12.12 kg/s and G = 1.968 kg/m2s μf
= ( 0.28 E-6 + 1.001 E-3 +7.86 E-6)/3 = 3.36 E-4 kg/ms
Substitute the value, so Re = 2.928 (transition region) and ƒ = 73.75. Since ρf = 796.57 kg/m3 and u= 0.0178x4/ πx2.82 =0.003 m/s, (ΔP) will be 1060 N/m2 2.1.9.6 Height of Bed From the criteria shown above, the optimum value of pressure drop is between 3 to 15% of the total pressure. Let the height of bed equals to 4 m, the pressure drop in the bed is 4240 N/m2 which is equal to 4.2% of the operating pressure. Therefore, the height of bed is taken as 4m 2.1.9.7 Total cross Section Area of the Tube Total cross section area of the tube can be obtained by dividing the volume of the bed with the height of the bed. At
=
3.70
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4
=
0.925 m2
(2.11)
2.1.9.8 Tube Diameter If the tube diameter to particle diameter ratio is less than 10, the effect of wall can become predominate, the void fraction and thus fluid velocity near the wall become more dominant. However, if high value of tube to particle diameter ratio is obtained, the heating effects through the tube wall will not be efficient. Therefore, tube with the inside diameter Di =0.1143m and thickness 0.005m is used in this reactor, where the ratio is approximately 11.5. The inside diameter of the tube (Di) = =
0.1143 – 2 x 0.005 0.1043 m
The cross section of the tube is then obtained from the equation: At
=
π Di 2 /4
=
0.009 m2
(2.12)
2.1.9.9 Total Number of Tubes Total number of tube can then obtained by dividing the total cross section area of one tube. Nt
=
0.925 0.009
=
103 tubes
(2.13)
2.1.9.10 Tube Arrangement The tubes in an exchanger are usually arranged in an equilateral triangular, square or rotated square pattern. Since the triangular pattern gives higher heat transfer rates, it is recommended for this reactor.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
2.9.1.11 Pitch of the Tube From reference (Process Heat Transfer’s book), the pitch of the tube is recommended to be 1.25 times of the outside tube diameter Do. Therefore, Pitch of the tube (Pt)
=
1.25Do
=
1.25 x 0.1143
=
0.143 m
(2.14) 2.1.9.12 Bundle Diameter The bundle diameter depends not only on the number of tubes but also can also on the number of tube passes. For a single pass heat exchanger type reactor, the bundle diameter can be obtained from the empirical equation base on standard tube layout as shown: Bundle diameter, Db =
Do ( Nt)n-1 K1
(2.15)
Where n1 and K1 = constant for use in the equation above given in reference (Process Heat Transfer’s book). For single pass, n1 and K1 is given as 2.142 and 0.319 respectively. Hence, Db = =
0.1143 x (103 / 0.319) (1/2.142) 1.70 m
2.1.9.13 Number of Tubes In the Centre Row The number of tubes in the centre row is then given by equation: Nc = =
Db / Pt 1.70/ 0.143
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
=
11.8 or 12 tubes
(2.16)
2.1.9.14 Shell Diameter By using split ring floating head type from Fig 12.6 in Reference (Chem. Eng. Vol.6’s book), Ds – Db
=
95.14 mm
Where Ds
=
Shell Diameter
Ds
=
1.7 + 0.09
=
1.79 m
2.1.10 Baffles Baffles are used in the shell to direct the fluid stream across the tubes, increase the fluid viscosity and create turbulence so as to improve the rate of heat transfer. The baffles used in this reactor are a common type i.e the single segmented baffles with baffles cut 35 %.
2.1.11 Baffles Spacing The optimum baffles spacing will usually be between 0.3 to 0.5 times of the shell diameter. Here, it is taken as 0.3 times of the shell diameter. Bs
=
0.3 Ds
=
0.3 x 1.79
=
0.55 m say 0.6 m
(2.17)
2.1.12 Number of Crosses Number of crosses in the shell side,
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Nc
= =
L -1 Bs 4
(2.18)
(Pt – Do) * Ds * Bs Pt
(2.19)
Area for Cross Flow As
=
= =
(0.143 - 0.114) * 1.79 * 0.6 0.143 2 0.218 m
2.1.14 Shell side heat transfer and pressure drop calculation The flow pattern in the shell of a segmental baffled heat exchanger type of reactor is complex, and this makes the prediction of the shell side heat transfer coefficient and pressure drop much more difficult than for the tube side. However, Kern has developed a method base on experimental work on commercial exchangers with standard tolerances and gives a reasonably satisfactory prediction of the heat transfer coefficient and pressure drop for standard design.
2.1.15 Shell side Mass Velocity Mass velocity, Gs Gs =
Ws As
G =
2.211 0.218
G s =10.14 kg / m 2 s
(2.20) Shell side velocity
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Gs
us =
us =
ρ
10.14 1209
u s = 0.01 m / s
(2.21) Shell side equivalent diameter for triangular pitch arrangement = 4(Pt/2).0.87.Pt – π.Do2/8 π. Do/2
Das
= 0.084 m
(2.22)
Reynolds number Re =
Re =
G s d as
µ
(10.14)(0. 084) 0.00034
(2.23)
Re = 2505
Prandtl number Pr =
Pr =
CP µ kf (3124.5)(0 .00034) 0.086
(2.24)
Pr =12.3
Choose buffle cut of 35%, from figure 12.30 (Coulson & Richardson’s Chemical Engineering), we can obtained Jf
=1.3 x 10-1
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Assumed that the viscosity correction is negligible
hs =
k f jf Re Pr 1 / 3 de
hs =
(0.086)(0. 13)(2505)( 12.3 1/3 ) 0.084
h s = 763.2 W / m 2
o
(2.25)
C
Shell side pressure drop Reynolds number Re = 2505 From figure 12.30 (Coulson & Richardson’s Chemical Engineering), Jf = 1.3 x 10-1
Shell side pressure drop can be calculated using equation below ∆P =8j f ( D d / d e )( L/I B )( ρµs / 2 )( µ / µw ) ∆P =8.93kPa
-0.14
(2.26)
2.1.16 Tube side coefficient, hi Mean temperature of the tube
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
t mean =
t1 + t 2 2
t mean =
53 + 27 2
(2.27)
t mean = 80 o C
cross sectional area = π d12/ 4 = (3.142)(0.10432) / 4 = 0.009 m2 Tube / pass = 103 / 1 = 103 tube / pas
(2.28)
Total flow rate area = (cross sectional area)(tube / pass) = (0.009)(103) = 0.927 m2 velocity, Gt
= (2.211)/(0.927) = 2.05 kg / sm2
v
= 0.002 kg / ms
Ratio of L / di = 4 / 0.104
(2.29)
= 38.46 Reynolds number, Re
Re =
ρν d i µ
Re =
(1209) (0.002 ) (0.1043) 0.00034
Re =1000
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Heat transfer factor figure 12.31 (Coulson & Richardson’s Chemical Engineering), Jh = 2 x 10-2 Prandtl number, as 12.3
Pr =12.3 Tube side coefficient, hi can be calculated using equation below.
hi =
jh k f Re Pr 0.33 di
hi =
(2x 10 -1 )(0.086)(1 000)(12.3) 0.104
(2.30)
0.33
h i = 393 W / m o C
Tube side pressure drop Reynolds number, Re = 1000
From figure 12.24 (Coulson & Richardson’s Chemical Engineering), jf = 2 x 10-1 Neglect the viscosity correction term
[
∆Pt = N p 8 jf ( L/d i )( µ / µW ) - m + 2.5
[
∆Pt = 2 8(5 x 10 -3 )(4/0.104) + 2.5
] ρ 2µ i
2
i
] (1209 )( 02.00034 )
2
(2.31)
∆Pt =10.89 kPa
2.1.17 Correction for Tube Heat Transfer Coefficient
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Since the tube side heat transfer coefficient calculated is based on the inside diameter of the tube, correction has to be done to obtain the heat transfer coefficient for outside diameter of tube.
HO
= =
hI . Di Do 192 W/ moC
(2.32)
2.1.18 Overall Heat Transfer Coefficient Uc
=
HO . hS HO + hS
=
100.1 W/ moC
(2.33)
2.1.19 Reactor cooling system mfCPf (t1 - t2)
=
mcCpc (t1 - t2)
(2.34)
Log Mean Temperature difference (LMTD) : TLMTD
=
=
Ti –To ln(Ti-To)/(Ti-To)
(2.35)
45 oC
From this value can get mc = 39.63 kg/s where CPc=4220 and ti-t2 =135 oC
2.2
MECHANICAL DESIGN
2.2.1 INTRODUCTION The mechanical design of chemical plant are of particular interest to chemical engineers, but not usually be called on to undertake the detailed mechanical design of
185
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
the plant, especially the reactor vessels. However, the chemical engineer will be responsible for developing and specifying the elementary design information for the reactor, and need to have a general appreciation of pressure vessel design to work effectively with the specialist designer. Therefore, the design of wall thickness, head, column support, flange joint, reinforcement and maximum allowable pressure are considered here. Material of construction: In this design, reference will mainly be based on the current British Standard BS 5500 and Bs 1515 where the current addition of Bs 5500 covers vessels fabricated in carbon steel. The most common types used in the petroleum industry are Types 304, 316,321, and 347.Because of their inherent high temperature strength propertied and high corrosion resistance, they are particularly suitable for use in this process, in areas of moderate and high temperature, and where substantial resistance such as in heater tubes, reactors, reactor effluent exchangers and piping. In this design, material of construction: can be constructed by using carbon steel. Type 304
DESIGN STRESS It is necessary to decide a value for the maximum allowable stress that can be accepted in the material of construction, for example, it can withstand without failure under standard test conditions. The nominal design strengths (allowable design stress) for the range of materials covered are listed in BS 5500. By using carbon steel (semi killed or silicon Killed), the design stress is given, σD as 125 N /mm2 at design temperature. WELDED JOINT EFFICIENCY The strength of a welded joint will be depending on the type of joint and the quality of the welding. The soundness of welds is checked by visual inspection and non destructive testing (radiography). For the reactor, it is assumed that the joint is equally as strong as the virgin plate; this is achieved by radio graphing the complete weld length and cutting out and remarking
186
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
any defects. Therefore, the non destructive testing is assumed to be 100% and the joint efficiency, J is taken as 1.0. 2.2.4 CORROSION ALLOWANCE
1. Corrosion and erosion or scaling will cause material lost, so an additional thickness of material called “corrosion allowance” must be added to be calculated wall thickness. MINIMUM THICKNESS OF CYLINDRICAL SECTION OF SHELL The minimum thickness of cylindrical section of shell to resist the internal pressure can be determined by using equation below: e
=
PD DIs 2J σD - PD
=
2.0*1.8 2.125-2
=
0.015 m
(2.36)
By adding corrosion allowance 2 mm, e
=
0.015 + 0.002m
=
0.017 m
MINIMUM THICKNESS OF DOMED HEAD There are three types of commonly used domed head: 1. Hemispherical heads 2. Ellipsoidal heads 3. Torispherical heads
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
The selection of head depends on the cost and the thickness required for the head. The design equations and charts for the various types of domed head are given in the codes and standards (BS 5500) used in this design. A standard dished head (torisphere) is used as first trial. The crown radius of this head equals to the diameter of the shell, DIS. On the other hand, the knuckle radius is taken as 6% of the crown radius. Since this type of head is formed by pressing, no joint is needed. Therefore, the joint factor is taken as 1. For the torispherical head, the minimum thickness of the head can be determined from equation below: eh
=
P D RC CS 2 J TD + PD(CS – 0.2)
(2.37)
where Rc is the crown radius, equal to DIS in this case. CS = stress concentration factor for torispheriical head. It is given by equation below: CS
=
1 / 4(3 + (Rc + Rk) 1/2)
(2.38)
Since Rk is 0.06 of Rc, CS
=
1 / 4 (3 + (1/ 0.06)1/2)
=
1.771
=
2.0 x1.8 x1.771 2 x 1x125 + 2.0 (1.771 - 0.2)
=
0.025 m
Therefore, eh
However, for a standard ellipsoidal head, eh
=
PDDIs 2J σD - 0.2PD
=
0.014 m
(2.39)
Therefore, an ellipsoidal head would probably be the most economical to be used. For convenience, the thickness is taken to be as same of wall thickness 17 mm.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
LOADING STRESSES 2.2.7.1 Dead Weight of Loading 2.2.7.2 Dead Weight Of vessel The major source of dead weight loads are: 1. vessel shell 2. vessel fitting : manway, nozzles 3. internal fittings: where the main item is tube 4. insulation 5. catalyst The preliminary calculation of the approximate weight of a cylindrical vessel with domed ends, and uniform wall thickness can be estimated from the following equation, Wv
=
Cv.Л.ρm.Dm.g.(Hv + 0.8Dm)t x 10-3
Where Wv
=
total weight of the shell, excluding internal fitting
Cv
=
a factor to account for the weight of nozzles, internal support etc. Cv is given as 1.08 for vessels with only a few internal fitting.
Hv
=
height between 2 tangent lines, 4m in this case
g
=
gravitational acceleration, 9.81 m/s2
t
=
wall thickness, mm
ρm
=
density of vessel material, kg/m3. by using carbon steel, ρm = 6870 kg/m3
Dm
=
mean diameter of vessel
=
DIs + t * 10-4
Since the wall thickness = 0.017 m Therefore, Dm = 1.8 + 0.014 = 1.817 m As a result, by substituting into the equation above: Wv
=
39000 N
=
39 KN
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Weight of the Tubes From BS 3059, the mass per length of tubes is equal to 13.5 kg/ m for carbon steel. Therefore, the weight of one tube =
13.5 x 3 x g
=
4.529 * 104 N
≈
45 KN
(2.40)
Total weight of the tubes, Wt
=
103 x 13.5 x3 x9.81
=
4.1x104
Weight of Insulation
To avoid heat loss from the surface of the shell, mineral wool is used as the insulator. From (Chem. Eng. Vol. 6’s book),
Density of mineral wool
= 130 kg/m3
Let the thickness of mineral wool
= 75 mm
The approximate weight of the insulator, Wi
=
2ЛHvtiρig
=
2 Л x3 x0.075 x30 x9.81
=
1.803 x103 N
(2.41)
This value should be double to allow for fittings, etc. =
3.6 x103 N
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Weight of Catalyst
Weight of catalyst, Wc = 2998 kg = 2.998 x104 N
Total Weight Since only 4 baffles are used in the reactor, their weight is neglected compared to others. W
=
Wv + Wi + Wt +Wc
=
39000N+ 4.1x104 N+ 3.6x103 N +2.998x104 N
=
1.1x 105 N
Wind Loading Take dynamic wind pressure as 1300 N/m2 Mean Diameter, including insulation = 2+2(17+75) x10-3 = 2.18 m
The wind loading is then given by equation below: Fw
=
P w Dm
=
1300 x2.18 m
=
2.8 x 103 N/m
(2.42)
Therefore, the bending moment at bottom tangent line can be determined from equation below: Mx
=
Fw L2
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
2
(2.43)
=
2.8 x 103 x 42 2
=
2.24 x104 N
2.2.7.8 ANALYSIS OF STRESSES Uniform thickness is used for analyzing stresses in the column. If it is found satisfactory at the bottom of the vessel which is the highest loading point, then the entire column structure is feasible. At bottom tangent line, the longitudal and circumferential stresses due to pressure is given by: Longitudal,
σL
Circumrerential, σh
=
P i Di 4t
=
2.0 x1.8 4 x 0.017
=
53 N /mm2
=
P i Di 4t
=
2.0 x1.8 2 x 0.017
=
106 N /mm2
(2.44)
Dead Weight Stress The direct stress is mainly due to the weight of vessel, its contents and any attachment which is often called the dead weight stress. The stress is compressive since it is at the bottom of the vessel to support the direct loading.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Dead Weight stress, σW =
= =
W Л (Di + ti) * t 1.1 x 105 Л (1800 + 17) x 17
(2.45)
1.13 N /mm2 (compressive)
Bending Stress The second moment of area of the vessel about the plane of bending, Iv
Where Do
Iv
=
Л (Do4 – Di4) 64
=
outer diameter of vessel
=
Di + 2t
=
1.8 + 2 x 0.017
=
1.834 m
=
Л (18344 – 18004) 64 4.0 x1010 mm4
=
(2.46)
Therefore, the bending stress is then given by equation below: σb
= =
± Mx (Di /2 + t) Iv
(2.47)
± 0.51 N/mm2
The resultant longitudal stress σZ
=
σ L + σW + σb
σZ
=
53 – 1.13 + 0.51
=
52.38 N/mm2
For upwind,
For downwind,
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
σZ
=
53– 1.13 - 0.51
=
51.36 N/mm2
=
Pi = 2.0 2 2
Radial Stress
(2.48)
1.0 N/mm2
=
Since radial stress obtained is a small value and there are torsional stress in the system, therefore the principle stress will be σZ and σh
52.38 N/mm2
Figure 2.1:
51.36 N/mm2
Analysis of Stresses
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Therefore, the greatest difference between the principles stresses, σd
=
σh - σZ ( downward)
=
106 – 51.36
=
54.64 N/mm2
The value obtained is well bellow the maximum allowable design, 125 N/mm2. 2.2.11 CHECK ELASTIC STABILITY The design of this vessel have to be checked to ensure that the maximum value of the resultant axial stress does not exceed the critical value at which buckling will occur. By applying a factor of safety of 12, the critical buckling stress gives: σC
=
2x104 (t/Do)
=
185.4 N/mm2
(2.49)
The maximum compressive stress will occur when the vessel is not under pressure, =
σ W + σb
=
1.13 + 0.51
=
1.64 N/mm2
Which is well below the critical buckling stress, σC . 2.2.12 VESSEL SUPPORT The method used to support a vessel will depend on the size, shape and weight of the vessel; the design temperature and pressure; the vessel location and arrangement; and the internal and external fittings and attachment. Since the reactor is a vertical vessel, skirt support is used in this design.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
A skirt support consists of a cylindrical or conical shell welded to the base of the vessel. A flange at the bottom of the skirt transmits the load to the foundations. The skirt may be welded to the bottom, level of the vessel. Skirt supports are recommended for vertical vessels as they do not imposed concentrated loads on the vessel shells; they are particularly suitable for use with tall columns subject to wind loading. 2.2.13 SKIRT THICKNESS The skirt thickness must be sufficient to withstand the dead weight loads and bending moments imposed on it by the vessel; it will not be under the vessel pressure. The resultant stresses in the skirt will be: σS (tensile)
=
σbS - σWS
σS (compressive)
=
σbS + σWS
and
where σbS
= =
σWS
= =
bending stress in the skirt 4Ms Л(Ds + ts) tsDs
(2.50)
the dead weight stress in the skirt W Л(Ds + ts) ts
Where Ms
=
maximum bending moment, evaluated at the base of the skirt.
W
=
total weight of the vessel and contents
Ds
=
inside diameter of the skirt, at the base
ts
=
skirt thickness
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
The skirt thickness should be such that under the worst combination of wind and dead weight loading the following design criteria are followed: σS (tensile)
< fs.J sin θs
σS (compressive)
< 0.125 E (ts/Ds) sin θs
Where fs is the maximum allowable design stress for the skirt material, normally taken at ambient temperature, 20oC. J
=
weld joint factor
θs
=
base angle of conical skirt, 90o is used in this design
The maximum thickness should not less than 6mm. 2.2.14 HEIGHT OF THE SKIRT The height of the skirt, Hs is taken to be 1m.
2.2.15 BENDING STRESS AT BASE OF THE SKIRT Mbs
=
= =
Fw (Hv + Hs)21 2
(2.51)
2.8x 103 (4 + 1)2 2 3.5 x 104 Nm
BENDING STRESS IN THE SKIRT As the first trial, the thickness of skirt is taken to be 20 mm. Substitute into the equation (19), σbS
=
=
4 x 2.24 x104 Л (1.9 + 0.020) 1.9x0.020 3.9 x 105 N/m2
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
σWS
=
1.1 x 105 Л (1.9 +0.020)*0.020
=
9.1 x 105 N/m2
The maximum stress (compressive), σS
=
σbS + σWS
=
3.9 x 105 N/m2 +9.1x 105 N/m2
=
1.3 x 106 N/m2
The maximum stress (tensile), σS
=
σbS - σWS
=
3.9 x 105 N/m2 – 9.1 x 105 N/m2
=
5.2 x 105 N/m2 (negative)
Let the joint factor for skirt support, J = 0.85 Criteria for design, fs.J sin θs
=
125 x 0.85 xsin( 90o)
=
10.63 * 107 N/m2
>
σS (tensile) , therefore it satisfied.
(2.52)
Modulus Young = 200,000 N/mm2 at ambient temperature, (from Bs 5500:1998), 0.125 E (ts/Ds) sin θs =
0.125x2x105 (0.02/1.9) sin 90o
=
26.3 x 107 N/m2
>
σS (compressive) , therefore it satisfied
Both criteria are satisfied, add 2mm for corrosion allowance, and give a design thickness of 22 mm.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
BASE RING AND ANCHOR BOLT DESIGN The loads carried by the skirt are transmitted to the foundation slab by the skirt base ring (bearing plate). The moment produced by wind and other lateral loads will tend to overturn the vessel. Since the reactor can be considered as the small vessel, the simplest types, rolled angle ring are used. The preliminary design of base ring is done by using Scheiman’s short cut method. The anchor bolts are assumed to share the overturning load equally, and the bolt area required is given by: =
1 (4.Mbs – W) Nbfb Db
(2.53)
Where Ab
=
area of one bolt at the root of the thread, mm2
Nb
=
number of bolts
fb
=
maximum allowable bolts stress, typical design = 125 N/mm2
Mbs
=
bending (overturning) moment at the base, Nm
W
=
weight of the vessel, N
Db
=
bolt circle diameter, m
Scheiman gives the following guide rules which can be used for the selection of the anchor bolts. 1. bolts smaller than 25 mm diameter should not be used 2. minimum number of bolts = 8 3. use multiples of 4 bolts 4. bolts pitch should not be less than 600 mm The base ring must be sufficiently wide to distribute the load to the foundation. The total compressive load on the base ring is given by: fb
=
(4 Mbs + W ) = 28255 N/mm ЛDs2 ЛDs
(2.54)
Where Fb is the compressive load on the base ring and Ds = skirt diameter, m The minimum width of the base ring is given by:
199
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Lb
Where Lb fc
=
fb fc
1 103
(2.55)
= base ring width, mm = the maximum allowable fc on the concrete foundation pad, And typically range from 3.5 to 7 N/mm2
fb
= 28255 N/mm
Take the bearing pressure as 5 N/mm2, fc = 5 N/mm2 Substitute into the equation above, Lb
= =
28255 5 x103 5.65 mm
This is the minimum width required; actual width will depend on the chair design Actual width required= Lr + ts +50 mm Where Lr = the distance from the edge of the skirt to the outer edge of the ring, mm = 64 mm (from BS 4190:1967) Therefore, actual width required = 64 + 22 +50 = 136 mm Actual bearing pressure on concrete foundation: f’c
= =
tb
=
28255 136 x103 0.21 N/mm 64 ( 3 x 0.21) ½ 140
(2.56)
200
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
=
4.3 mm
COMPENSATION FOR OPENING AND BRANCHES All process vessels will have opening for connections, man ways, sight holes, hand holes and instrument fittings. The presence of an opening weakens the shell, and gives rise to stress concentrations. The stress at edge of a hole will be considerably higher than the average stress in the surrounding plate. To compensate for the effect of an opening, the wall thickness is increased in the region adjacent to the opening. Sufficient reinforcement must be provided to compensate for the weakening effect of opening without altering the general dilation pattern of the vessel opening.
2.2.19 COMPENSATION FOR OTHER NOZZLES Pipe size for inlet and outlet of the reactor are all less than 10 mm, therefore, the reinforcement area can be usually is provided by increasing the wall thickness of the branch pipe. This already done on piping, where extra thickness is provided, thus no compensation area needed. 2.2.20 BOLTED FLANGE JOINT Flanged joints are used to connect pipes and instruments to vessels and from removable vessel heads when ease of access is required. Flanges may also be used on the vessel body, when it is necessary to divide the vessel into section for transport or maintenance. Flanged joints are also used to connect pipes to other equipment, such as pumps, valves. 2.2.20.1 Type of Flanges Selected a) Welding neck Flanges
201
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Have a long tapered lub between the flange ring and the welded joint. This gradual transition of the section reduces discontinuity stresses between flange and branch, and increases the strength of the flange assembly. Welding neck flanges are suitable for extreme service conditions, where the flange is likely to be subjected to temperature, shear and vibration loads.. For this reactor, the welding neck flanges are suitable for use in connecting the inlet and outlet piping of reactor. b) Gasket Gaskets are used to make a leak tight joint between two surfaces. It is impractical to machine flanges to the degree of surface finish that would be required to make a satisfactory seal under pressure without a gasket. Gasket are made from “semi plastic” materials, which will deform and flow under load to fill the surface inequalities between the flange faces, yet retain sufficient elasticity to take up the changes in the flange arrangement that occur under load. Several factors must be considered when selecting a gasket material: 1. The process condition: pressure, temperature, corrosive nature of process fluid.
2. Whether repeated assembly and disassembly of the joint is required 3. The type of flange and flange face. Judging from process conditions, where the operating temperature is quite high, 393K, metal reinforced gaskets is recommended, since it have a quite good heat resistance property. 2.2.21 Flange Face The raised face, narrow feed flange are used for all the flanges. Where the flange has a plain face, as for the flange faces mentioned above, the gasket is held in place by friction between the gasket and flange surface.
202
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
S
SUMMARY OF CHEMICAL DESIGN PARAMETERS
Reactor Design Catalyst weight required
2998 kg
Volume of Catalyst bed
3.7 m3
Height of Bed
4.0 m
Diameter of Bed
1.817 m
Tube inside pressure drop
1.06E-4 N/m2
% of pressure drop
0.042
Tube inner diameter
0.1043 m
Total number of tubes
103 tubes
Tube arrangement
equivalent triangular pitch
Tube side heat transfer coefficient
293 W/moC
Pitch of tube
0.143 m
Bundle diameter
1.70 m
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Shell diameter
1.79 m
Baffles cuts
0.35
Baffles Spacing
0.6 m
Number of crosses
4
Inlet flow rate
0.647 kg/s
Inlet temperature
326 K
Outlet temperature
373 K
Shell side heat transfer coefficient
191 W/moC
Shell side pressure drop
0.557 kPa
Design overall heat transfer area
100.1 W/moC
SUMMARY OF MECHANICAL DESIGN PARAMETERS
204
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Operating Conditions and Material of construction Design pressure
2.0 bar
Design temperature
323 K
Material of construction
Carbon Steel plate (Type 304)
Design Stress
125 N/mm2
Welded joint efficiency
1
Corrosion allowance
2 mm
Designed Column Diameter Shell thickness
17 mm
Domed end thickness(ellipsoidal heads)
17 mm
Vessel Support (skirt) Skirt thickness
22 mm
Skirt diameter
1.9 m
Skirt height
1m
Base Ring and Anchor Bolt Base ring
Rolled angle rings
Minimum ring thickness
4.5 mm
Minimum base ring width
7.06 mm
Anchor bolt
M24
Number of bolts
8
Bolt root diameter
21.2 m
205
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
SECTION 3
MTBE DISTILLATION COLUMN 3.1
INTRODUCTION
Distillation is a method used to separate the components of a liquid solution, which depends upon the distribution of these various components between a vapor and a liquid phase. All components are present in both phases. The vapor phase is created from the liquid phase by vaporization at the boiling point. MTBE is our main product that needs to be separated. For individual design, MTBE distillation column was chosen. The characteristics required in the chosen types of distillation column are the separation objective satisfied in the column, the cost of construction and the design of the selected distillation column.
R e lief Va lve
C on den se r
T=53.3oC T=6 4.5oC
TC
LC
R e bo iler
T=10 3.3oC
Figure 3.1 MTBE Distillation Column 3.2
SELECTION OF CONSTRUCTION MATERIAL
206
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Materials chosen are based on the characteristics of the component in the distillation column, the location and the environmental consideration of the MTBE plant. Stainless steel 304 is used in construction of the MTBE distillation column - ‘The stainless steels are the most frequently used corrosion resistant materials in the chemical industry’ – Coulson & Richardson, Chemical Engineering, Volume 6, page 295. Carbon steel is used in skirt support material and the insulation material used is fiberglass. The selection is based on the chemical and mechanical design as stated in Coulson & Richardson, Chemical Engineering, Volume 6. Most parameters used in design were referred to mass, energy balance data and also data generated by Chemical Engineering Simulation Software; HYSIS Version 3.2. Other materials chosen were based on the British Standard BS 5500, BS4505 and BS 750.
3.3
CHEMICAL DESIGN In the MTBE distillation column design, the McCabe-Thiele method in
determining the number of stages needed was used.
The McCabe-Thiele method is
based upon representation of the material-balance equations as operating lines on the X-Y diagram. The lines are made straight (and the need for the energy balance obviated) by the assumption of constant molar overflow. The liquid-phase flow is assumed to be constant from tray to tray in each section of the column between addition (feed) and withdrawal (product) points. If the liquid rate is constant, the vapour rate must also be constant.
Table 3.1 The Composition in Feed Stream FEED
Component
T (K)
Operating
Op Pressure,
Feed Flowrate
Fraction, zi
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
T (K)
kPa kmol/hr
i-C4H10
313
337.5
450
34.860
0.3261
n-C4H10
313
337.5
450
0.400
0.0037
C4H8 DME
313 313
337.5 337.5
450 450
0.026 3.880
0.0002 0.0363
CH3OH
313
337.5
450
0.160
0.0015
H2O
313
337.5
450
2.866
0.0268
MTBE TBA
380 380
337.5 337.5
450 450
63.44 1.274 ∑ =106.906
0.5934 0.0119 ∑ = 1.0000
Table 3.2 The Compositions in Top Stream Top
Component
T (K)
Operating T (K)
Op Pressure, kPa
Top Flowrate
Yi
kmol/hr
S16 (top)
i-C4H10
313
326.3
305
33.860
0.839760919
n-C4H10
313
326.3
305
0.400
0.009920389
C4H8
313
326.3
305
0.026
0.000644825
DME
313
326.3
305
3.880
0.096227772
CH3OH
313
326.3
305
0.149
0.003695345
H2O
313
326.3
305
1.006
0.024949778
MTBE
313
326.3
305
1.000
0.024800972
∑ =40.321
∑ =1.0000
Table 3.3 The Composition in Bottom Stream Bttm
S14 (bttm)
Component
T (K)
Operating T (K)
Op Pressure, kPa
Bttm Flowrate kmol/hr
Xi
i-C4H10
380
376.3
400
1.000
0.015018398
MTBE
380
376.3
400
62.44
0.937748742
TBA
380
376.3
400
1.274
0.019133438
CH3OH
380
376.3
400
0.011
0.000165202
H2O
380
376.3
400
1.860 ∑ =66.59
0.027934219 ∑ =1.0000
* The T(K) is the stream temperature, while the Operating T(K) temperature is the temperature which should be achieved by controlling the pressures.
208
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.3.1
DETERMINATION OF THE NUMBER OF PLATES USING McCABETHIELE METHOD
The components in the feed to the MTBE distillation column are i-C4H10, n-C4H10, C4H8, DME, CH3OH, H2O, MTBE and TBA, and the feed is assumed as multicomponents feed. By using the Hengstebeck’s and McCabe-Thiele method, the number of stages required and the position of the feed in the MTBE distillation column can be determined. The determination of the plate by using McCabe-Thiele method was simply because as explained in J.M Coulson, J.F Richardson, Chemical Engineering Volume 2, Third Edition, the Pergamon Textbook, page 429, which stated that “This method is one of the most important concepts in chemical engineering and is an invaluable tool for the solution of distillation column. The assumptions of constant molar overflow is not limiting since in very few systems do the molal heats of vaporizations differ by more than 10 percent. The method does have limitations, however, and should not be employed when the relative volatility is less than 1.3 or greater than 5, when the reflux ratio is less than 1.1 times the minimum, or when more than twenty-five theoretical trays are required. In these circumstances, the Ponchon-Savarit method should be employed”.
The vapor pressure can be determined by using the Antoine’s equation as follows:
Log10 P* = A -
B T +C
(3.1)
With related at equilibrium, constant K, Ki = P* x P
(3.2)
And related with concentration,
209
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Ki =
yi xi
(3.3)
Where yi = concentration in vapor phase xi = concentration in liquid phase Calculation for the relative volatility, α , α = KLK / KHK
(3.4)
Where KLK = Light key component KHK = Heavy key component In this case, MTBE is as the heavy key and i-C4H10 is as the light key components. By using goal seek in the excel programme, the value of the bubble point at bottom column = 103.3oC and dew point at the top column is = 53.3 oC, from the values of Ki related to the pressure, the values of relative volatilities could be determined, listed are values of the relative volatilities for components at the top and bottom of the distillation column. Table 3.4 Average Relative Volatility,
α
α
Bttm,
α
Top,
i-C4H10 (LK)
7.699631
n-C4H10
5.654994
-
2.827496955
C4H8 DME MTBE (HK) TBA
6.948741 14.10614 1.00000 -
1.0000 0.149333
3.474370398 7.05306993 1.00000 0.074666444
CH3OH
0.67395
0.99561
0.834780143
H2O
0.152422
0.288322
0.220371796
5.084017
Avg,
α
Component
6.39182391
Calculations for the non-key flows, Table 3.5 The Non-key Flow of the Top Stream
210
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
αi 2.827497 3.47437 7.05307 0.83478 0.220372
TOP n-C4H10 C4H8 DME CH3OH H2O
di 0.4 0.026 3.88 0.149 1.006
li = di / (α i-1) 0.218878614 0.010507724 0.640997055 -0.901828648 -1.290358653
Vi = li + di 0.618878614 0.036507724 4.520997055 -0.75282865 -0.28435865
∑ = -1.321803909
∑ = 4.139
Table 3.6 The Non-Key Flow of the Bottom Stream BOTTOM
αi
bi
TBA CH3OH H2O
0.074666 0.83478 0.220372
1.27 0.01 1.86
Vi’=α ibi / (α
-
LK
li’ = vi’ + bi’
α i) 0.01506000 0.001652422 0.066417357 ∑ = 0.083127984
1.2900 0.0100 1.9300 ∑ = 3.23
Flows of combine key, Le
= L - ∑ li
(3.5)
= (2.5 X 40.321) – (- 1.3218) = 102.1243 Ve
= V - ∑Vi
(3.6)
= (2.5+1) x 40.321 – 4.139 = 136.985 Calculation of the slope for top operating line, Le Ve
=
102 .1243 136 .984
(3.7)
= 0.7455 Ve’
= V’ - ∑ Vi’
(3.8)
= (2.5+1) x 40.321 – 0.08313 = 141.04 Le’
= L’ - ∑ li’
(3.9)
= (2.5+1) x 40.321 + 66.59 – 3.23 = 204.48
211
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Calculation of the slope for bottom operating line, Le ' Ve '
=
141 .04 204 .48
(3.10)
= 1.45
Xb
=
flow .LK flow ( LK + HK )
=
1 (1 +62 .47 )
at bottom,
(3.11)
at top,
(3.12)
at feed,
(3.13)
= 0.016
Xd
=
flow .LK flow ( LK + HK )
Xd
=
33 .86 (33 .86 +1)
= 0.9713
Xf
=
Xf
=
flow .LK flow ( LK + HK ) 34 .86 (34 .86 +63 .44 )
= 0.3546 For vapor – liquid equilibrium curve, we use the equation of
Y
=
α.x [1 + (α − 1) x]
=
6.391 x [1 + ( 5.391 ) x]
α
from LK component
(3.14)
Table 3.7 MTBE Equilibrium Curve
y= x
6.391 x 1 + 5.391 x y
212
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0 0.41527398 0.61508201 0.73257407 0.80992987 0.86471539 0.9055511 0.93716326 0.96235974 0.9829137 1.0000
So from the data as above, the McCabe-Thiele diagram was constructed to determine the number of plates. The top operating line and the bottom operating line were determined first before the number of plates required could be calculated. And from the graph plotted, the number of stages needed for the MTBE distillation column is 11 with the feed point location is at stage number six from bottom.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
McCabe-Thiele Diagram 1
0.9
0.8
Top Operating Line
0.7
Y
0.6
Equilibrium Curve
0.5
Line for Number Stages
0.4
0.3 Bottom Operating Line
0.2
0.1
0 0
0.2
0.4
0.6
0.8
1
X
Xb = 0.016
Xf = 0.35
Xd = 0.97
At bottom
At feed
At top
214
the of
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Figure 3.2 McCabe-Thiele Diagram From the graph plotted, the number of plate can be determined by calculating the stage plotting at graph and the number of stages needed is 11 stages. The feeding stage also can be determined from the graph, feed at stage 6 from bottom. Calculation for minimum reflux ratio, Rmin, To get the value of minimum reflux ratio, use the Underwood equation was used, (J. Douglas, 1988),
Rmin
1 = α −1
X D.L K X D.H K −α X F .H K X F .H K
(3.15)
1 1.0 33 .86 − 6.391 = 6.391 −1 63 .44 63 .44 = 0.0803 Optimum reflux ratio is 0.0803 x 1.5 = 0.1204 Where, XD.LK
= Light key component at top flow
XD.HK
= Heavy key component at top flow
XF.LK
= Light key component at feed flow
XF.HK
= Heavy key component at feed flow
In the calculation, the optimum reflux ratio as 2.5 was used (based on Coulson & Richardson, Chemical Engineering, Volume 6, and J.M Coulson, J.F Richardson, Chemical Engineering, Volume Two, Third Edition) as 0.1204 is too low for the calculation, based on statement from R. K. Sinnot, Coulson & Richardson, Chemical Engineering, Volume 6, Butterworth Heinemann, 2001, page 495 – “At low reflux ratios the calculated number of stages will be very dependent on the accuracy of the vapor-liquid equilibrium data available. If the data are suspect a higher than normal ratio should be selected to give more confidence in the design”.
215
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.3.2
DETERMINATION OF THE NUMBER OF PLATES USING FENSKE’S EQUATION
The Fenske’s equation (1932) can be used to estimate the minimum stages required at total reflux. The derivation of the equation is for binary system and applies equally to multicomponents system. But in the design only the calculation of plates using McCabe-Thiele method as the design plate number was taken into consideration.
Nmin
Nmin
=
x x log LK HK x HK d x LK b log α LK
=
33 .86 62 .44 log 1.000 1.000 log 6.392
=
4.13
≈
5 stages
(3.16)
Normally after using the Fenske’s Equation, the value of Nmin is given by the equation below to get the number of stages, NT, NT
=
2 (Nmin)
=
2 (5)
=
10 stages
To get the real number of stages, the efficiency of the process must be considered, and the efficiency is calculated based on the equation by O’Connell’s (J. Douglas, 1988), Eo
=
0.5
( µ α) 0.25
=
0.5 ( 0.224 x 6.392 ) 0.25
=
0.457
(3.17)
216
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
N
3.3.3
=
NT Eo =
11 0.457
=
24.07
≈
24 plates
THE PHYSICAL PROPERTIES
The properties consider in this design are liquid flow rate, LW, vapor flow rate, VW, liquid surface tension, σ, liquid density, ρl and vapor density, ρv. This physical properties evaluated at the system temperature by using HYSIS generated data or by manual calculations the from mass and energy balance data. The useful properties data are from HYSIS, mass and energy balance data is given as below: Liquid flow rate, LW
=
38747.97 kg/hr (10.7633 kg/s)
Vapor flow rate, VW
=
15251.95 kg/hr (4.2367 kg/s)
Liquid surface tension, σ
=
0.0351 N/m
Liquid density, ρl
=
746.74 kg/m3
Vapor density, ρv
=
3.8402 kg/m3
Data evaluated are at system temperatures and pressures.
3.3.4
DETERMINATION OF COLUMN DIAMETER
The principal factor that determines the columns diameter is the vapour flow-rate. The vapour velocity must be below that which would cause excessive liquid entrainment or a high-pressure drop. The equation below which is based on the well-known Souders and Brown equation, Lowenstein (1961), Coulson & Richardson, Chemical Engineering, Volume 6, page 556, can be used to estimate the maximum allowable superficial vapour velocity, and hence the column area and diameter,
217
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
( σ L −σ v) u = (− 0.171 l2t + 0.27 lt − 0.047 ) σ v
1/ 2
(3.18)
v
2 ( 746 .74 −3.8402 = −0.171 ( 0.9 ) +0.27 ( 0.9) −0.047 3.8402
1/ 2
)
= 0.7997 m/s
Where,
u
v
= maximum allowable vapour velocity, based on the gross (total) column cross-sectional area, m/s,
l
t
= plate spacing, m (range 0.5 – 1.5).
Based on the equation below, the column diameter could be determined,
Dc
=
Dc
=
Dc
4 vw
π vρu v
(3.19)
4(0.6244 )
π(3.8402 )( 0.7997 )
=
0.51 m
=
0.51 x 1.5
=
0.765 m
For safety reason, the approximate diameter was increased 50% more than the calculated value, as it deals with vapour, which is in high pressure.
218
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.3.5
DETERMINATION OF PLATE SPACING
The overall height of the column will depend on the plate spacing. Plate spacings from 0.15 m (6 in.) to 1m (36 in.) are normally used. The spacing chosen will depend on the column diameter and the operating conditions. Close spacing is used with smalldiameter columns, and where head room is restricted, as it will be when a column is installed in a building. In the MTBE distillation column, the plate spacing was assumed 0.9 m as it is in the range of 0.5 m to 1 m recommended by Coulson and Richardson, Chemical Engineering, Volume 6.
3.3.6
LIQUID FLOW ARRANGEMENTS
Before deciding liquid flow arrangement, maximum volumetric liquid rate were determined by using equation below,
VL
=
Lw
ρ
(3.20)
L
VL
=
38747 .97 746 .74
VL
=
51.89 m3/hr
=
0.0144 m3/s
Based on the values of volumetric flow rate and column diameter, Dc. Figure 11.28 from Coulson & Richardson, Chemical Engineering, Volume 6, page 568. Therefore, types of liquid flow could be considered as single pass.
3.3.7
PLATE LAYOUT
The value of downcomer area, active area, hole area, hole size, and weir height were determined based on above value calculated, trial plate layout column area determined by using the equation below,
219
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Column area, Ac
Where Um
=
Um Uv (0.9)
=
4.181 0.7997 (0.9)
=
5.81 m2
=
Velocity at below plate,
(3.21)
Down comer area were found by assume 20% of column area and using equation below, Down comer Area Ad
=
0.2 Ac
=
0.2(5.81 m2)
=
1.162 m2
Net area and active area were determined by using equations below, Net Area, An
Active area, Aa
=
Ac - Ad
=
5.181 -1.162
=
4.02 m2
=
Ac - 2Ad
=
5.181 - 2(1.162)
=
2.857 m2
Hole Area, AH are determine with trial value of 10% active area by equation below, Hole Area, Ah
=
0.10(Aa)
=
0.10(2.857)
=
0.2857 m2
Weir Length, lw was calculated by referring Figure 11.31 from Coulson Richardson, Chemical Engineering, Volume 6, page 572 which was determined based on the value of the ratio of Ad/Ac to get the ratio of lw/ Dc . The weir height determined and other dimensions are as below:
220
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.3.8
Weir Height, hw
=
50 mm (standard)
Hole diameter, dh
=
5 mm (standard)
Plate Thickness
=
5 mm (standard)
Weir Length, Iw
=
612 mm (80% x 765)
ENTRAINMENT EVALUATION
The entrainment checking can be done by determine actual flooding percentage, Uv by using equation below, Uv
=
Um Ac
=
4.181 5.181
=
0.807 m/s
(3.22)
Liquid flow rate were determine by using below equation by using liquid vapor flow factor.
FLV
0.5
ρv ρl
=
Lw Vw
=
38747 .97 3.8402 15251 .95 746 .74
=
0.182
(3.23) 0.5
Where FLV is liquid vapor factor.
Based on value of FLV and assumption made for initial tray spacing (0.9m) by referring to Figure 11.27 from Coulson & Richardson, Chemical Engineering, Volume 6, page 567, the data were used to determine the constant, K1 for the estimation of flooding velocity. Before that, correction factor are used as equation below: 0.2
K1 =
σ k1 0.02
(3.24)
221
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
0 .2
=
0.0351 0.1 0.02
=
0.112
And flooding velocity, Uf determine by equation below (correlation given by Fair, Coulson & Richardson, Chemical Engineering, Volume 6, page 567, Uf
=
ρl − ρv K1 ρv
=
ρl − ρv 0.112 ρv 0.5
=
746 .74 − 3.8402 3.8402 0.112
=
1.56 m/s
(3.25)
0 .5
Actual % of flooding =
Uv ×100 Uf
=
0.807 ×100 1.560
=
51.8%
(3.26)
Fractional entrainment is calculated based on this percentage and FLV by referring to Figure 11.29 from Coulson & Richardson, Chemical Engineering, Volume 6, page 570, if unsatisfied, recalculation were done based on chosen diameter and plate spacing acceptable to determine the lowest value. However, fractional entrainment Ψ = 0.02, is below the initial guest of 0.1 and entrainment is acceptable.
3.3.9
WEEPING RATE EVALUATION
222
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Weir liquid crest were determined by using values of maximum liquid flow rate and minimum flow rate based on the process condition and also assumption of turndown percentage based on the liquid characteristic. Each weir liquid crest value was determined by using equations as follow, the Francis weir formula (see also Volume 1, Chapter 5),
Max how
Min how
2/3
=
Lw max 750 ρl (lw )
=
750
=
13.49 mm liquid
=
Lw min 750 ρl (lw )
=
10 .7633 750 (746 .74 )( 0.88 )
=
48.37 mm liquid
(3.27) 2/3
1.5860 (746 .74 )( 0.88 )
2/3
(3.28) 2/3
Where, Iw
=
Weir length, 0.88 (standard)
how
=
weir crest
Lw
=
liquid flow rate
At minimum liquid flow rate, the value was determined by adding weir height H w and weir crest, how the constant, K2 where it is found based on the value by referring to Figure 11.30 from Coulson & Richardson, Chemical Engineering, Volume 6, page 571. Minimum vapor velocity Uh, were determined by using the equation as below, Uh
=
K 2 − 0.90 ( 25 .4 − d h ) ρv 0.5 =
=
(3.29)
28 .60 − 0.90 (25 .4 − 0.005 ) (3.8402 ) 0.5
2.931 m/s
(3.3.10, 3.3.11 and 3.3.12: Please refer to the Appendix)
223
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.3.13 NUMBER OF HOLES Area of hole, AH
= =
Number of Holes
3.3.14
πd h 4
2
(3.30)
π × (0.05 ) 2 4
=
1.9634 x 10-3 m2
=
Ah AH
=
0.2857 1.9634 ×10 −3
=
145.49
≈
146 units (at every sieve plate).
(3.31)
COLUMN SIZE
The column height will be calculated based on the equation given below. The equation determines the height of the column without taking the skirt or any support into consideration. Its determination is based on condition in the column. Column Height
=
(No stage –1) (tray spacing) +(Tray spacing x 2) +(No stage-1) (Thickness of Plate)
=
(11 -1)(0.9)+(0.9)(2) + (11-1)(0.005)
=
10.85 m
≈
12.00 m (including 10% safety factor)
The overall height from the calculation is 10.85 m, but in a real construction it will be added slightly more (about 10%) because of vapor and liquid area at top and bottom column. The space for vapor and liquid are required if uncertain condition occur
224
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
in the column, such as over flooding, over vapor pressure or upset in reaction situation. The calculated result is tabulated in the Table 5.8 as below. Table 3.8
Provisional Plate Design Specification
Item Column Diameter, Dc No of Plates Plate Spacing Plate Thickness Total Column Height, Ht Plate Pressure Drop, ht Plate Material Down Comer Area, Ad Down Comer Material Column Area, Ac Net Area, An Active Area, Aa Hole Area, Ah Number of Holes Weir Length Weir Height (standard) Resident Time
Value 0.765 m 11 units 0.9 m 5 mm* 12.00 m 192.81 mm liquid* SS 304 0.8348 m2 SS 304 5.181 m2 4.020 m2 2.857 m2 0.2857 m2 146 units 0.612 m 0.05 m 13.37 seconds*
* For the determination of these values, they are shown in the Appendix section.
3.4
MECHANICAL DESIGN
In the mechanical design, the temperature and pressure are important properties in evaluating the thickness and the stress of material. Therefore, the safety factor also is
225
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
also added as precaution and determined by certain consideration such as corrosion factor, location and process characteristic. The safety factor is usually 10% above the operating pressure and as for this MTBE distillation column, the operating pressure is 450 kPa. The chosen safety factor is based on the process characteristics of the system. The design temperature is related to the operating temperature. Based on the calculated result, the temperature at the top of the column is 53.3oC and the temperature at the bottom of the column is 107oC. Design Pressure, Pi
Design Temperature, T
3.4.1
=
0.450 N/mm2 x 110%
=
0.495 N/mm2
=
117.70 ºC (10% more than design temp.)
MATERIAL OF CONSTRUCTION
The material used in the construction of the distillation column is stainless steel (18Cr/8Ni, 304) as the material is suitable in high temperature and less corrosive. For this material, the design stress at 150 ºC is obtained from Table 13.2, page 809 Coulson & Richardson, Chemical Engineering, Volume 6.
3.4.2
Design stress, f
=
130 N/mm2
Diameter vessel, Di
=
860 mm
Tensile strength,
=
510 N/mm2
VESSEL THICKNESS
The minimum thickness of column required and other designs are calculated based on equation below (Coulson & Richardson, Chemical Engineering, Volume 6, page 812):
226
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
e
=
Pi Di 2Jf − Pi
=
(0.495 )( 765 ) 2(1)(145 ) −(0.495 )
=
1.31 mm
(3.32)
Based on Table 13.4, Coulson & Richardson, Chemical Engineering, Volume 6, page 811, this minimum thickness should be added 5 mm to withstand its own weight and any incidental loads. e Assumed
=
1.31 mm + 5 mm
=
6.31 mm
≈
7.00 mm
Where, Pi
=
Design pressure
Di
=
Column diameter
f
=
Design Stress
J
=
Joint factor (assumed = 1)
From Table 13.4, Coulson and Richardson, Chemical Engineering, Volume 6, page 811, for diameter 1 m to 2 m the minimum thickness should not be less than 7 mm (including 2 mm of corrosion allowance). For vessel diameter around 0.5 m to 1 m, a much thicker wall will be needed at the column base to withstand the wind and dead weight loads. A much thicker wall is needed at the column base to withstand the wind and dead weight loads. As a first trial, divide the column into five sections, with the thickness increasing by 2 mm per section. Try 7, 9, 11, 13 and 15 mm. The average wall thickness is 11 mm. 3.4.3
HEADS AND CLOSURE
227
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Torispherical head had been chosen because of operating pressure below 10 bars and suitable for liquid vapor phase process in inconsistent high pressure. The calculations as below is considered, Crown radius, Rc
= Di
= 0.765 m
Knuckle radius, Rk
= 6% Rc
= 0.046 m
Minimum Thickness =
Pi R c C s 2Jf + Pi (C s − 0.2)
= 0.2137mm
(The method of calculations is shown in the Appendix section)
3.4.4
TOTAL COLUMN WEIGHT
Total Weight, Tw Total weight is the summation of the weight of dead weight, the weight of plates and the weight of insulation. The calculations for the dead weight, the weight of plates and the weight of the insulation are shown in the Appendix. Total weight, Wt
3.4.5
=
W v + Wp + WI
=
(28.46 + 68.53 + 10.63) kN
=
107.62 kN
WIND LOADS The wind load is calculated based on location and the weather of surrounding.
Therefore, the value of wind speed is assumed as below and wind load is calculated shown in the appendix. The wind load for the MTBE column is 62.91kN (methods of calculation in shown in the appendix. 3.4.6 – STIFFNESS RING (Please refer to the Appendix) Table 3.9
Summarized Results of Mechanical Design
228
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Operating pressure, Po
0.45 N/mm2
Design Pressure, Pi
0.495 N/mm2
Safety factor
0.15
Design Temperature, TD
88.78 oC
Operating Temperature, To
80.71 oC
Heads and Closure Types
Torispherical head.
Crown Radius, Rc = Di
0.765 m
Knuckle Radius, Rk = 6% Rc
0.046 m
Joint Factor, J
1.00
Cs
1.77
Minimum thickness head, e
0.2317 mm
Column Weight Dead weight of vessel, Wv
28.46 kN
Weight of a plate, Wp
6.23 kN
Weight of 11 plates,Wp
68.53 kN
Weight of insulation, WI
10.63 kN
Total weight
107.62 kN
Win speed, Uw
160 km/hr
Wind pressure. Fw
1068.8 N/m2
Bending Moment (Mx)
62.91 kN
Stiffness Ring Critical buckling pressure for ring, Pc
15 x 106 N/m2
229
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.5
VESSEL SUPPORT DESIGN (SKIRT DESIGN)
Type of Support
:
Straight cylindrical skirt
θs
:
90º
Material of Construction
:
Carbon steel
Design Stress, fs
:
135 N/mm2 at ambient temp. 20ºC
Skirt Height, Hv
:
2.5 m (standard)
Young’s Modulus
:
200, 000 N/mm2
Approximate Weight
:
8.418 kN
Total Weight
:
36.88 kN
230
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
(The method of calculations for other parameters in the vessel support design in shown in the Appendix section)
Table 3.10
Design Specification of the Support Skirt Support Data Type of Support
Straight cylindrical skirt
Material of Construction
Carbon steel
Design Stress, at T 20ºC (ambient)
135 N/mm2
Skirt Height
2.50 m
Young’s Modulus
200000 N/mm2
σ
746.74 kg/m3
L
Approximate Weight, Wapprox
8.418 kN
Total Weight
107.62 kN
Wind Load, Fw
1068.8 N/m2
Skirt Thickness, ts
15 mm
REFERENCES J. M. Coulson, J. F. Richardson, Chemical Engineering, Volume Two, Third Edition, The Pergamon Press, 1977. R. K Sinnot, Coulson & Richardson’s Chemical Engineering, Chemical Engineering Design, Volume Six, Butterworth Heinemann, 1999. Robert H. Perry, Don W. green, Perry’s Chemical Engineer’s Handbook, Seventh Edition, McGraw-Hill, 1998. James, M. Douglas, Conceptual Design of Chemical Processes, McGraw-Hill Book Company, 1988. Martyn S. Ray and David, W. Johnston, Chemical Engineering, Design Project: A Case Study Approach, Gordon and Breach Science Publishers, 1989. Carl R. Branan, Rules of Thumb for Chemical Engineers, Gulf Publishing Company, 1994.
231
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Billet, R., Distillation Engineering, Heydon Publishing, 1979. King, C. J., Separation Processes, Second Edition, McGraw-Hill, 1992. Kister, H. Z., Distillation Design, McGraw-Hill, 1992. Lockett, M. J., Distillation Tray Fundamentals, Cambridge University Press, 1986. Normans, W. S., Absorption, Distillation and Cooling Towers, Longmans, 1961. Oliver, E. D., Diffusional Separation Procesess, John-Wiley, 1966. Robinson, C.S., and Gilliland, E.R., Elements of Fractional Distillation, McGrawHill, 1950. Smith, R., Chemical Process Design, McGraw-Hill, 1995. Van Winkle, M., Distillation, McGraw-Hill, 1967. Micheal J. Barber, Handbook of Hose, Pipes, Couplings and Fittings, First Edition, The Trade & Technical Press Limited, 1985. Louis Gary Lamit, Piping Systems: Drafting and Design, Prentice-Hall, Inc., 1981. David H. F. Liu, Bela. G. Liptak, Wastewater Treatment, Lewis Publishers, 2000.
SECTION 4
DESIGN OF LIQUID-LIQUID EXTRACTION COLUMN
4.1
INTRODUCTION
Liquid-liquid extraction has become an important separation technique in modern process technology. This is has resulted in the rapid development of a great variety of
232
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
extractor types, in the evaluation of which the chemical engineer must primarily depend on manufacturers’ literature. To the design, only three components that are considered, - methanol, water and isobutene- this is because of for most system containing more than four components, the display of equilibrium data and the computation of stages is very difficult. In such cases, the requirements are best obtained in the laboratory without detail study of the equalibria. (Treybal, Mass Transfer Operations, 1987). Beside that for multicomponent separations also, special computer programs for these multistage operations embodying heat and material balances and sophisticated phase equilibrium relations are best left to professionals. Most such work is done by service organizations that specialize in chemical engineering process calculations or by specialize in chemical engineering organizations. (Stanley M. Walas, Chemical Process Equipment, 1988). Sieve tray (perforated plate) Column were choose for the extraction of these components. These multistage, countercurrent columns are very effective, both with respect to liquid-handling capacity and with respect to extraction efficiency, particularly for system of low interfacial tension, which do not require mechanical agitation for good dispersion. 4.2
CHEMICAL DESIGN OF LIQUID – LIQUID EXTRACTION COLUMN
4.2.1
Choice of Solvents
There is usually a wide choice of liquids to be used as solvent for extraction operations. It is unlikely that any particular liquid will exhibit all the properties considered desirable for extraction, and some compromise is usually necessary. The following factors need to be considered when selecting a suitable solvent for a given extraction – affinity for solute, partition ratio, density, miscibility, safety and cost. Based on the factors that need to be considered water was choosing as a solvent in this system. 4.2.2
Estimation or Gather the Physical Properties
233
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Most of the design parameter used were refer to mass balance, energy balance data and generated by chemical Engineering Simulation Software, HYSIS. The properties data as state below: Flowrate at the dispersed phase, QD
=
1254.92 ft3/hr
Flowrate at the continuous phase, QC
=
1.785 ft3/hr
Density at the dispersed phase, ρD
=
24.10 lb/ ft3
Density at the continuous phase ρC
=
41.45 lb/ft3.
The data was evaluated at system temperature and pressure. 4.2.3
Determination of Number of Stages
To determine the theoretical stages required, by assuming the minimum solvent to feed ratio required to remove all the minimum component, so that is the extraction factor, ε = 1(Schweitzer, Separation Handbook). Equation 4.1 was used. The value for X f = 0.0195 kg CH3OH/ kg water, Ys = 1.57 x 10-6 kg CH3OH/ kg water was compute from the mass balance at this system. Number of theoretical stage, Nf = Xf – Ys/m Xr – Ys/m
Nf = 0.0195 – (1.57 x 10-6 / 0.001) (1.57 x 10-6 / 0.001)
-1
(4.1)
-1
= 10.42 stages = 10 stages Where,
Xf
= weight solute /weight feed solvent in the feed phase
Ys
= weight solute / weight extraction solvent in extract
Xr
= weight solute /weight feed solvent in the raffinate phase
m
= slope at the equilibrium line dY/dX
234
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
The number of mass transfer unit, Nor is identical to the number of the theoretical stages when extraction factor, ε = 1. Nor
= Xf – Ys/m
-1
(4.2)
Xr – Ys/m Nor
= 10 units
By assuming column efficiency, E is 80%, the number of real stages, N was determining by using equation 4.3. N = (Nf -1)/ E
(4.3)
= (10 – 1)/ 0.8 = 11 stages 4.2.4
Sizing of Sieve Tray
The sieve tray sizing was base on the manufacturer’s literature. Usually the tray spacing is from (6 to 24) in, and perforation diameter, do usually from (0.32 to 0.64) cm or (1/8 to 1/4) in diameter. By take 2 ft tray spacing, Zt, 0.25 in holes on 0.75 in triangular spacing. The downcomer area is found with equation 4.4. h
= 4.5 Vd2 ρC / 2gc
∆h = 2
(4.4)
= 4.5 Vd2 ρC / 2gc ∆ρ
2
=
4.5(41.45) 2(4.18 x 108) 17.35
Vd
= 12471 ft/hr
Ad
= QD/ Vd
Vd2
(4.5)
= 1254.92 / 12471 = 0.1006 ft2
235
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Dd
Where,
= 4.2948 in (Downcomer diameter)
Vd
= Velocity of the dowmcomer
ρC
= Density at the continuous phase
gc
= gravitational constant
To determine the total holes area in a tray used equation 4.6 and set the velocity through the holes, Uh are kept below 0.8 ft/sec or 2880ft/ hr to avoid formation of very small droplet. Total hole area, AHT
= QD/ Uh
(4.6)
= (1254.92 / 2880) = 0.4357 ft2 To find the tray area, by using ratio of the tray area to hole area as state below: Tray area, AT
=
½ (Л/4) (do) 2
Hole area, AH =
2.21( ds/ do) 2
=
2.21 (0.75/0.25)2
=
19.89
=
19.89(0.4357)
=
8.666 ft2
=
3.32 ft
do
=
perforation diameter
ds
=
triangular spacing
Tray Area, AT Tray Diameter, DT
Where,
4.2.5
0.866 (ds) 2
Number of Holes Hole area, AH
= ½ (Л/4) (do) 2
(4.7)
236
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
=½ (Л/4) (0.25) 2 =0.0245 in2 Number of hole, NH
= AHT/AH
(4.8) 2
= 0.4357ft / 0.0245 in
2
= 2560 units 4.2.6
Column Parameter
Number of tray, NT required and the tower high, HT is determining by using equation 4.9 and 4.10 respectively. The efficiency of the tray is base on assumption of the column efficiency. Number of trays, NT
= Nf / ET
(4.9)
= 10 / 0.8 = 13 trays Column Height, CT
= Zt x NT
(4.10)
= 2 (13) = 26 ft + 3 ft (including 1.5 ft at each end) = 29 ft Column diameter same with the tray diameter, so Column diameter, DC
= 3.32 ft.
Column area, AC
= 8.67 ft2
Net area and active are were determined by using equation 4.11 and 4.12 respectively. Net area, AN
= AC - Ad
(4.11)
= 8.67 – 0.1739 = 28.4961ft 2 Active area, Aa
=
AC - 2Ad
(4.12)
= 8.67 – (2 x 0.1739) = 8.322 ft2 Where,
Ad = downcomer area
237
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
The height equivalent to theoretical stages, (HETS) and height of transfer unit, Hor are calculated by using equation 4.13 and 4.14 respectively. HETS
Hor
4.2.7
=
CH / Nf
(4.13)
=
29 / 10
=
2.9
=
CH / Nor
=
2.9
(4.14)
Weeping Evaluation
By analogy with distillation. Weir length, lw is calculated by referring to Figure 11.31 from Coulson and Richardson Vol.6 page 572, which determined the value is base on the ratio of Ad/AC to get the ratio of lw/DC. The weir height determine from standard form as follows: Weir height
= 50 mm
Hole diameter
= 5 mm
Plate thickness
= 5 mm
Weir crest were determined by using value of maximum flowrate and minimum flowrate based on process condition. Each weir crest value determine by using equation 4.15 and equation 4.16 respectively. Max how
Min how
2/3
=
750
Lw max / ρD( lw)
=
750
3.8106/ (380.048 x 1.2705)
=
29.73 mm liquid
=
750
Lw min / ρD( lw)
=
750
0.4512/ (380.048 x 1.2705)
(4.15) 2/3
2/3
(4.16) 2/3
238
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
=
7.17 mm liquid
At minimum rate hw + how = 50 + 7.17 =57.17 mm Where,
lw
= weir length
how = weir crest Lw
= liquid flowrate
Orifice coefficient, Co was referring from figure 11.34 Coulson and Richardson Vol. 6 pg 576 and by assuming.
1.
Plate thickness : hole diameter
=1
2.
Ah/Ap
=5
Plate pressure drop, h h
=
51 (Uh / Co)2 (ρC/ρD)
(4.17)
2
=
51 (0.2438/0.805) (640/380.048)
=
7.88 mm liquid
=
(12.5 x 103) / ρD
Residual head, hr hr
(4.18)
3
=
12.5 x 10 / 380.048
=
32.89 mm liquid
Total plate pressure drop, ht ht
=
h + (hw + how) + hr
=
7.88 + 57.17 + 32.89
=
97.94 mm liquid
(4.19)
Plate pressure drop, ∆Pt ∆Pt =
9.81 x 10-3 ht ρD
(4.20)
=
9.81 x 10-3 (97.94) (380.048)
=
365.147 Pa (N/m2)
Table 4.1: Provisional Plate Design Specification Column Diameter
1011
mm
239
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Number of Trays Tray Spacing Plate Thickness Total Column Height Plate Pressure Drop Plate Material Downcomer Area Column Area Net Area Active Area Hole Area Number of Holes Weir Length Weir Height (standard) Number of manhole Manhole Diameter (BS 470:1984) 4.3
13 0.6 5 9 7.88 SS304 9.3 x 10-3 0.805 2.647 0.773 1.58 x 10-5 2560 1.2705 50 2 700
trays m mm m mm liquid m2 m2 m2 m2 m2 units m mm mm
MECHANICAL DESIGN OF LIQUID – LIQUID EXTRACTION COLUMN
In mechanical design, the temperature and the pressure are important properties in evaluate the thickness and the stress of material. Therefore, the safety factor also need as precaution and determined by certain consideration such as corrosion factor, location and process characteristic. Based on Hysis data, the operating pressure is 2.75 kPa and the safety factor is 10% above operating pressure. The design temperature related to the operating temperature. The temperature of column operated in 400C at top of column and 270C at the bottom of the column. The design pressure and design temperature of the system as follows: Design Pressure, Pi Design Temperature, T 4.3.1
=
0.275 N/mm2 x 1.1
=
0.3025 N/mm2
=
500C
Material Construction
The material used is stainless steel (18Cr/8Ni, 304). Design stress at 500C is gain from table 13.2, pg 809 Coulson & Richardson Vol.6.
240
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.3.2
Design stress, f
=
165 N/mm2
Diameter Vessel, Di
=
1011 mm
Tensile Strength,
=
510 N/mm2
Vessel Thickness
The thickness of column is calculated based on the equation below: e
=
PiDi
(4.21)
2f – Pi =
0.3025(1011) 2(165) – 0.3025
=
0.9276 mm
Add corrosion allowance 4mm, so the thickness: e
=
4.9276 mm
=
5 mm
From Coulson & Richardson, value for vessel diameter (m), 1 m, the minimum wall thickness required should not be less than 5mm including corrosion allowance. A much thicker wall will be needed at the column base to withstand the wind and dead weight loads. As a first trial, divide the column into five sections (courses) with thickness increasing by 2mm per section. Try 10,12,14,16, and 18mm. The average is 14 mm. 4.3.3
Design of Domed Ends
Standard torispherical head are the most commonly used end closure for vessel up to operating pressure of 15 bar. Torispherical head had been choose because of operating pressure below 10 bar. Crown Radius, RC
=
Di
=
1.011m
Knuckle Radius, Rk
=
6%RC =
0.061 m
241
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
A head of this size would be formed by pressing: no joint, so J = one. Stress concentration factor for torispherical heads, Cs: Cs
=
¼ (3 + √ (RC / Rk))
=
¼ (3 + √ (1.011/0.061))
=
3.053
(4.22)
Therefore the minimum thickness: e
=
PiRCCs
(4.23)
2fJ + Pi (Cs – 0.2) =
0.3025(1011) (3.053) (2 x 165) + (0.3025(3.053 -0.2))
= 4.3.4
2.821 mm
Column Weight
4.3.4.1
Dead Weight of Vessel, Wv Wv
=
240 Cv Dm(Hv + 0.8Dm) t
Where;Cv
=
a factor take 1.15, vessel with plates
Dm
=
mean diameter, m
=
(Di + t)
Hv
=
height or length between tangent line
t
=
wall thickness, m
(4.24)
To get a rough estimate of the weight of this vessel by using the average thickness 14 mm. Dm
=
1.011 + 0.014
=
1.025 m
=
240(1.15) (1.025) (9 +0.8(1.025)) 14
=
38933.69N
Hence, Wv
242
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
= 4.3.4.2
389 kN
Weight of plate, Wp
From Nelson (1963) pg 833 in Coulson & Richardson Vol. 6 rough guide to weight of fittings, take contacting plates, steel including typical liquid loading, 1.2 kN/m2 plate areas. The total of weight of plate determine by multiply the value with number of tray design. Tray area, AT
=
0.805 m2
Weight of plate
=
1.2 x AT
=
1.2(0.805)
=
0.966 kN
Weight of 13 trays, Wp
4.3.4.3
=
0.966(13)
=
12.558 kN
(4.25)
Weight of Insulation, Wi
The insulating material is mineral wool; Density of mineral wool
=
130 kg/m3
Thickness of insulation, ti
=
75 mm
Volume of insulation, Vi
=
ЛDiHv x ti
=
Л (1.0110) (9) (75 x 10-3)
=
2.144m3
=
Viρg
=
2.144(130) (9.81)
=
2734.11 N
Weight of Insulation, Wi
(4.26)
(4.27)
Double this value to allow fittings, so weight of insulation, Wi = 5.468 kN 4.3.4.4
Total weight, W
243
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
W
4.3.4.5
=
Wv + Wp + Wi
=
389 + 12.56 + 5.47
=
407.03 kN
(4.28)
Wind Loading
Take dynamic wind pressure, Pw as 1280 N/m2. Mean diameter, including insulation, Deff: =
1.011 + 2(0.014 + 0.075)
=
2.791 m
Loading (per linear meter) Fw; Fw
=
PwDeff
(4.29)
=
1280 (2.791)
=
3572.48 N/m
Bending moment at bottom tangent line. MX MX
=
FwX2
(4.30)
2 =
3572.48 (9)2 2
Where; X
=
144685 Nm
=
Distance measured from the free end
The calculated value as the result tabulated in table 4.2. The value requires determining in strength and suitability of column while in construction and operation. It also required the safety consideration operation. The operating procedure of the column should base on this value. 4.3.5
Analysis of Stress
At bottom tangent line,
244
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.3.5.1
Longitudinal and Circumferential Pressure Stress; σh
=
PiDi
(4.31)
2t =
0.3025 (1011) 2 (14)
σL
=
10.92 N/mm2
=
PiDi
(4.32)
4t =
0.3025 (1011) 4 (14)
= 4.3.5.2
5.46 N/mm2
Dead Weight Stress σL
=
W
(4.33)
Л (Di + t) t =
407030 Л (1011 + 14) 14
= 4.3.5.3
9.03 N/mm2
Bending Stress σb
=
± MX / IV ((Di/2) + t)
Where;MX
=
Total bending moment
=
Second bending moment
=
Л / 60 (Do4 –Di4)
=
1011 + 2(14)
=
1039 mm
=
Л / 60 (10394 –10114)
=
6.32 x 109 mm4
IV
(4.34)
Which; Do IV Therefore,
245
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
σb
=
± 144685000
((1011 / 2) + 14)
6.32 x 109 =
± 11.89N/mm2
The result longitudinal stress, σZ is: σZ
=
σ L + σW ± σ b
σZ (upwind)
=
σ L - σ W + σb
=
5.46 – 11.15 + 11.89
=
6.2 N/mm2
=
σL - σW - σb
=
5.46 – 11.15 – 11.89
=
-17.58 N/mm2
σZ(downwind)
4.3.5.4
Elastic Stability (Buckling)
Critical buckling stress, σC: σC
=
2 x 104 (t / Do)
(4.35)
4
=
2 x 10 (14 / 1039)
=
269.48 N/mm2
The maximum compressive stress will occurs when the vessel is not under pressure: σ W + σb
=
11.15 + 11.89
=
23.04N/mm2
This value is below critical buckling stress, so design is satisfactory. Stresses analysis is tabulate in the table 4.3. 4.3.6 4.3.6.1
Vessel Supports Design Skirt Supports
At ambient temperature.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Type of support
:
Straight cylindrical skirt (θS = 900)
Material construction :
Plain carbon steel
Design stress
:
135 N/mm2
Young’s Modulus
:
200000 N/mm2
Skirt height, Hs
:
3m
The maximum dead weight load on the skirt will occur when the vessel is full of the mixture. Approximate weight, Wapprox
Total weight
(Л / 4) Di2 HVρLg
=
(4.36)
2
=
(Л / 4) (1.011 ) (9) (380.048) (9.81)
=
26936.56 N
=
26.9 kN
=
W + Wapprox
=
407.03 + 26.9
=
433.93kN
Bending moment at base of skirt, MS: MS
=
Fw
(HV + HS)2
(4.37)
2 2
=
3.572 (12 / 2)
=
257.184 kNm
As a first trial, take the skirt thickness as the same as that of the bottom section of the vessel, ts = 14 mm. Bending stresses in skirt, σbs Where; Ms
= 4Ms / (Л (Ds + ts) tsDs)
=
Maximum bending moment at the base of the skirt.
ts
=
Skirt thickness
Ds
=
Inside diameter of the skirt at the base
(4.38)
So,
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
σbs
=
4 (257184 x 103) / Л (1011+14) (14) (1011)
=
22.5710 N/mm2
Dead weight stress in the skirt, σWs: σWs(test)
σWs(operating)
=
W / (Л (Ds + ts) ts)
=
26900 / Л (1011+14) (14)
=
0.60 N/mm2
=
407030 / Л (1011+14) (14)
=
9.03 N/mm2
(4.39)
Thus, the resulting stress in the skirt, σs: Max σs (compressive) =
σWs(test) + σbs
=
0.60 + 22.57
=
23.17 N/mm2
=
σbs - σWs(operating)
=
22.57 – 9.03
=
13.54 N/mm2
Max σs (tensile)
(4.40)
(4.41)
Take the joint factor, J as 0.85. Criteria for design σs (tensile)
> fs J sin θ
13.54
> 0.85 (135 sin 900)
13.54
> 114.75 248
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
σs (compressive)
> 0.125 E (ts/DS) sin θ
23.17
> 0.125 (200000) (14/1011) sin 900
23.17
> 346.19
Both criteria are satisfied; add 2mm for corrosion gives a design thickness of 16 mm. 4.3.6.2
Base Ring and Anchor Bolt
Approximate pitch circle diameter, say 2.2 m. Circumferences of bolt circle = 2200 Л Л of bolt required, at minimum recommended bolt spacing: =
2200 Л / 600
=
11.5
Closet multiple of 4
=
12 bolts
Take bolt design stress
=
125 N/mm2
Bending moment at skirt, MS =
301.834 kNm
Total weight vessel, W
502.53 kN
Area of bolt, Ab
=
=
1 Nbfb
Where:Nb
4MS - W
(4.42)
Db
=
Number of bolts
fb
=
Maximum allowable bolt stress
MS
=
Bending moment at the base
W
=
Weight of the vessel
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Db
=
Bolt Circle diameter
Therefore, Ab
=
1
4 (257184)
12 (125) = Bolt root diameter
- 407030
2.2
40.35 mm2 =
√ (40.38 x 4) / Л
=
7.17 mm
Total compressive load on the base ring per unit length. Fb
=
4MS
+
Л DS2 =
(4.43)
Л DS
4 (257184) + Л (1.0112)
=
W
407030 Л (1.011)
448.5 x 103 N/m
By taking the bearing pressure as 5 N/mm2. The minimum width of the base ring, Lb: Lb
=
Fb Fc
+
1 103
=
448.5 x 103
(4.44)
5000 =
89.7 mm
Actual width can be calculated from this minimum width. Use M24 bolts (BS 4190:1967) root area = 353 mm2 (Figure 13.30 Coulson & Richardson Vol. 6)
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Actual width required =
Lr + ts + 50mm
=
150 + 14 + 50
=
214 mm
Actual bearing pressure on concrete foundation: f’c
=
Fb actual width
=
448500 214000
=
2.10 N/mm2
Actual minimum base thickness: tb
Where: fr
=
Lr √ (3 f’c / fr)
=
150 √ ((3 x 2.1) / 140)
=
25.98 mm
(4.45)
= Allowable design stress in the ring material, typically 140 N/mm2
The design specifications of support are summarized in the table 4.4.
4.3.7
Piping Sizing
The optimum diameter for carbon steel pipe: d, optimum =
293 G 0.53 ρ-0.37
Where:G
=
Flowrate (kg/s)
ρ
=
Density (kg/m3)
Pipe thickness, t
=
P d, optimum
(4.46)
(4.47)
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
20σ + P Where:P
=
Internal pressure, bar
σ
=
Design stress at working temperature, N/mm2
The piping sizing for this system are shown in table 4.5
Table 4.2 : Summary of the Mechanical Design Design Pressure Operating Pressure
2.75 kPa
Operating Temperature
40
0
C
0.3025 N/mm2
Design Pressure Design Temperature
50
Safety Factor
0
C
0.10
Design of Domed Ends Types Crown Radius Knuckle Radius Joint Factor Stress Concentration Factor Minimum Thickness Column Weight Dead Weight of Vessel Weight of Plate (per plate) Weight of Insulation Total Weight Wind Pressure Loading Bending Moment
Torispherical head 1.011 m 0.061 m 1 3.053 2.821 mm 389 0.966 2734.11 407.03 1280 3572.48 144.685
kN kN N kN N/m2 N/m kNm
252
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 4.3: Stress Analysis for Liquid-Liquid Extraction Column Longitudinal Pressure Stress Circumferential Pressure Stress Dead Weight Stress Bending Stress σZ (upwind) σZ(downwind) Critical Buckling Stress
10.92 N/mm2 5.46 N/mm2 9.03 N/mm2 ± 11.89 6.2 -17.58 269.48
N/mm2 N/mm2 N/mm2 N/mm2
Table 4.4: Design Specification of the Support Skirt Types of Support θ Material Construction Design Stress Skirt Height Young Modulus ρL Approximate Weight Total weight Bending Moment at Skirt Skirt Thickness Bending Stress in Skirt σ ws (test) σ ws (operating) Maximum σs (compressive) Maximum σs (tensile)
Straight cylindrical skirt 90 Plain Carbon steel 135 3 200000 380.048 26.9 433.93 257.184 14 22.57 0.60 9.03 23.17 13.54
0
C
N/mm2 m N/mm2 kN kN kN kNm m N/mm2 N/mm2 N/mm2 N/mm2 N/mm2
253
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 4.5: Piping Sizing for Liquid-liquid Extraction Column Feed Pipe Sizing Flowrate, G Density, ρ Internal Pressure, P Design Stress, σ Diameter Optimum, d optimum Corrosion Allowance Pipe Thickness, t Solvent Pipe Sizing Flowrate, G Density, ρ Diameter Optimum, d optimum Extract Pipe Sizing Flowrate, G Density, ρ Diameter Optimum, d optimum Raffinate Pipe Sizing Flowrate, G Density, ρ Diameter Optimum, d optimum
4.4
13873.67 567.0445 2.75 165 55 4 4.05
kg/hr kg/hr bar N/mm2 mm mm mm
1469.1 kg/hr 998 kg/hr 15 mm 1624.37 kg/hr 992.8161 kg/hr 15 mm 15096.74 kg/hr 564.7173 kg/hr 30 mm
PROCESS CONTROL AND INSTRUMENTATION OF THE LIQUID-LIQUID EXTRACTION COLUMN
Control systems are very important in any of the chemical industries. It is essential for a process to meet the design specification and products purity that imposed by the designer or by external constrains such as government regulations and standards.
254
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Process parameters control is to compensate for the process changes with the existence of external disturbances. Normally, an overall control strategy is design to meet the following objectives: 1. Ensure stable plant operation conductive to power optimization 2. Maintain product quality according to specification 3. Operate the process and machinery in such a way as to estimate or minimize the possibility of activating last resort safety measures such as relief valve and surge system, thus ensuring safe plant operation. Compensate for perturbations cause by external factors such as ambient and cooling water temperature variations. Provide an intelligent man-machine interface capable of presenting process and control system information and interactive format. Typically, there are two types of control systems- feedback control and feed forward control. In this case, the feedforward control is applied; in feedforward control its take corrective action before they upset the process. In this system also, solvent use is lighter than the material being extract, the two input indicated are of course interchanged. Both inputs are on flow control. The light phase is removing from the tower on LC (level control) or at the top of level maintain with an internal weir. The bottom stream is removed on interfacial level control (ILC). The relative elevations of feed and solvent input nozzles depend on the nature of the extraction process. The temperature of an extraction process ordinarily is controlled by regulating the temperature of the feed stream.
REFERENCES
Buford D.Smith, 1963. Design of Equilibrium Stage Processes, United State of America. McGraw-Hill. Robert C.Reid,Prausnitz & Poling,1987.The properties of Gases and Liquid, United State of America. McGraw-Hill.
255
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Erneat J.Henley & J.D Seader, 1968.Equilibrium-Stages Separation Operations in Chemical Engineering. Canada. John Wiley & Sons Philip A.Schweitzer,1988. Handbook of Separations Techniques for Chemical Engineers,2nd Edition. United State of America. McGraw-Hill. J.D Seader & Erneat J.Henley, 1998.Separation Process Principles, United State of America. John Wiley & Sons R.K.Sinnott, 1999.Chemical Engineering Design, Coulson & Richardson Chemical Engineering .3rd Edition. Volume 6 .Britain. Butterworth Heinemann Robert H. Perry, Don W. Green, 1998 Perry’s Chemical Engineer’s Handbook, Seventh Edition, McGraw-Hill. J.R Backhurst & J.H Harker.1987.Chemical Engineering Design, Coulson & Richardson Chemical Engineering .3rd Edition. Volume 2 .United Kingdom. Pergamon Press. Stanley M. Walas. 1988. Chemical Process Equipment Selection and Design. United State of America. Butterworth’s Series in Chemical Engineering. Robert E.Treybal.1988. Mass-Transfer Operations,3rd Edition. Singapore, McGraw-Hill International Series. K.H Reissinger & Jurgen Schroter. 1980. Selections Criteria for Liquid-liquid Extractors. Chemical Engineering Magazine, November: 274-256. P.J Bailes,C.Hanson & M.A Hughes.1976. .Liquid-liquid Extraction: The process, the equipment. Chemical Engineering Magazine, January 217-231. Ariffin Marzuki & Nurul Izzi, 2004. PETRONAS Research Centre, Bangi. Interview,19 January.
SECTION 5
256
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
DESIGN OF HEAT EXCHANGER
INTRODUCTION Shell and tube heat exchangers are the most versatile type of heat exchangers. They are used in process industries, in conventional and nuclear power stations as condensers, in steam generators in pressurized water reactor power plants, in feed water heaters and in some air conditioning and refrigeration systems. They are also proposed for many alternative energy applications including ocean, thermal and geothermal. Shell and tube heat exchangers provide relatively large ratios of heat transfer area to volume and weight and they can be easily cleaned. Shell and tube heat exchangers offer great flexibility to meet almost any service requirement. The reliable design methods and shop facilities are available for their successful design and construction. Shell and tube heat exchangers can be designed for high pressures relative to the environment and high pressure differences between the fluid streams. Shell and tube heat exchangers are built of round tubes mounted in a cylindrical shell with the tubes parallel to the shell. One fluid flows inside the tubes, while the other fluid flows across and along the axis of the exchanger. The major components of this exchanger are tubes (tube bundle), shell, front-end head, baffles and tube sheets. Shell types-various front and rear head types and shell types have been standardized by Tubular Exchanger manufacturers Association (TEMA). The E-shell is the most common due to its cheapness and simplicity. In this shell, the shell fluid enters at one end of the shell and leaves at the other end that is there is one pass on the shell side. The tubes may have a single or multiple passes and are supported by transverse baffles. This shell is the most common for singlephase shell fluid applications. With a single-tube pass, a nominal counter flow can be obtained. The design of a shell and tube heat exchanger is an iterative process because heat transfer coefficients and pressure drop depend on many geometric factors, including shell and tube diameters, tube length, tube layout, baffle type and
257
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
spacing and the numbers of tube and shell passes, all of which are initially unknown and are determined as part of the design process. In production of MTBE, heat exchanger is very important equipment. Heat exchanger is used to increase or to decrease the mixture to the desired temperature. In order to make the process of production of MTBE taking place in the system, it is important to make the system at the correct environment. The heat exchanger that we used here is the shell and tube exchanger. Shell and tube heat exchanger is the most common type of heat exchanger used in the industry. This is because it has many advantages. The advantages are: 1.
It provided a large transfer area in a small space.
2.
Good mechanical layout: a good shape for pressure operation.
3.
Used well-established fabrication techniques.
4.
It can be constructed from a wide range of materials.
5.
It can be clean easily.
6.
Well-established design procedures.
7.
Single phases, condensation or boiling can be accommodated in either the tubes or the shell, in vertical or horizontal positions.
8.
Pressure range and pressure drop are virtually unlimited and can be adjusted independently for the two fluids.
9.
Thermal stresses can be accommodated inexpensively.
10.
A great variety of materials of construction can be used and may be different for the shell and tubes.
DESIGNING THE HEATER In the production of MTBE, a heater is the most important heat exchanger in the system. Therefore this chapter is going to describes details for this heater and the design of this piece of equipment.
258
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Heater is used in the process to heated the raw material of MTBE consist of isobutane and a bit of normal butane. Isobutane and normal butane from the storage is in liquid form. The heating process is because to produce the isobutane and normal butane in the gases form before this material is feed to the Snamprogetti Fluidized Bed Reactor. Here the mixtures of this component initially are in the liquefied gas form at temperature of -15 oC. It will be heated in the Heater (E-100) and Heater (E101) until it converted into gas form at temperature of 250 oC using steam. For this heat exchanger we use the counter current process. The temperature difference between liquid and gas phase is quit big, so we need two heat exchanger in series. The shell and tube heat exchanger is the floating head type.
T = 250OC
T = 350OC
STEAM IN
T = -15 OC
STREAM 2
STEAM IN
STREAM 3
STREAM 4 T = 250 OC
O
T = 117 C
E100
E101 STEAM OUT
T = 120 OC
STEAM OUT T = 250OC
Figure 5.1 : Heat Exchanger In Series For The Heating Process
5.1
CHEMICAL DESIGN OF HEAT EXCHANGER
The chemical engineering design for the heat exchanger is also known as thermal. The design requires the calculation of the heat transfer area required. From this value, design features of the unit such as the tube and shell size, tube counts and layout is determined. In addition, then pressure loss of the fluids across the unit is also calculated by determined the pumping capacity required. The calculation of the design
259
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
is base on the first heat exchanger (E100). The chemical design is based on Bell’s and Kern method. Bell’s method accounts for the major bypass and leakage streams. Kern method was based on experimental work on commercial exchangers with standard tolerances and will give a reasonably satisfactory prediction of heat-transfer coefficient for standard design. 5.1.1
Physical Properties Of The Stream
Table 5.1:
Properties of Raw material (Isobutane and N-butane) and
Steam for (E100) Component
Raw material (Isobutane
Steam
Temperature inlet, oC Temperature outlet, oC Specific heat, j/kg oC Thermal conductivity, W/mK Density, kg/m3 Viscosity, kg/ms Feed flowrate, kg/s
and normal butane) t1 = -15 t2 = 117 2155 0.07 485 1.30005 x 10-4 10.9314
T1 = 250 T2 = 120 2010 0.0306575 0.49375 1.55263 x 10-5 1.7649
5.1.2 The Calculation Of ∆ Tm To determine the mean temperature, Tm ∆Tm = Ft ∆Tlm
(5.1)
Where ∆ Tm = true temperature difference
260
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Ft = temperature correction factor Before ∆ Tm can be obtained, logarithmic mean temperature ∆ Tlm must be calculated Using the equation:
∆Tlm =
(T1 - t 2 ) - (T2 - t1 ) (T - t ) ln 1 2 (T2 - t1 )
(5.2)
Where ∆ Tlm = log mean temperature difference T1
= inlet shell-side fluid temperature
T2
= outlet shell-side fluid temperature
t1
= inlet tube-side temperature
t2
= outlet tube-side temperature
∆Tlm =
( 250 - 117 ) - (120 + 15 ) (250 - 117) ln (120 - (-15))
∆Tlm = 134.00
0
C
the temperature correction factor can be obtain by using figure 12.19 (Coulson & Richardson’s Chemical Engineering)
261
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
R=
T1 - T2 t 2 - t1
R=
(250 - 120) (117 - (-15))
(5.3)
R = 0.98
S=
t 2 - t1 T1 - t1
S=
(117 - (-15)) (250 - (-15))
(5.4)
S = 0.50
Using figure 12.19, (Coulson & Richardson’s Chemical Engineering) Ft = 0.82 Substitute the above value into equation (1.1) below : ∆Tm = Ft ∆Tlm ∆Tm = ( 0.82 )(134 .00 ∆Tm = 109.88
0
0
C)
C
From table 12.1 (Coulson & Richardson’s Chemical Engineering), we take overall Coefficient, U = 300 W/m2 0 C Duty for this heat exchanger is obtain from the energy balance. The duty is, Q = 3109542.883 W
262
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Then we need to calculate the surface area using equation below.
A=
Q U∆Tm
A=
3109542.88 3 (300 )(109 .88 )
(5.5)
A = 94.33 m2
5.1.3
Number Of Tubes Calculation
From table 12.3 (Coulson & Richardson’s Chemical Engineering), we take standard pipe of: Inside diameter, di
= 16 mm
Outside diameter, do
= 20 mm
Length of pipe is assumed as 16 ft. Length, L
= 4.88 m
Area of the pipe can be calculated using equation below area = Lπ D
(5.6)
area = (4.88)(3.142)(0.02) area = 0.3067 m2 Using the area needed from the duty and area for each tube, the number of Tube, Nt that we get is,
Nt =
Nt =
A a
(5.7)
94.33 0.3067
Nt = 307.56
Therefore the number of tube, Nt = 308 tubes
263
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
5.1.4
Bundle And Shell Diameter Calculation
The tubes in heat exchanger are usually arranged in an equilateral triangular, square or rotated pattern. The triangular and rotated square patterns give higher heat transfer rates. Here we use the triangular pattern. The triangular pitch of 1.25 is chosen as the tube arrangement. Bundle diameter
Db = do (Nt / K1 )1 / n1
(5.8)
From table 12.4 (Coulson & Richardson’s Chemical Engineering), for 1.25 triangular pitch, number of passes = 2, then we can obtain K1 = 0.249 n1 = 2.207 Db = do (Nt / K1 )1 / n1 Db = 0.02 (308 / 0.249 )1 / 2.207 Db = 0.50m
Assume using pull-through floating head type. From figure 12.10 (Coulson & Richardson’s Chemical Engineering), for bundle diameter 0.33, bundle clearance is 93 mm. Shell diameter, Ds Ds = 0.50 + 0.093 = 0.60m
5.1.5 Tube Side Coefficient, hi
264
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Mean temperature of the tube t mean =
t1 + t 2 2
t mean =
- 15 + 117 2
(5.9)
t mean = 51 o C
cross sectional area = π d12/ 4
(5.10) 2
= (3.142)(0.016 ) / 4 = 0.0002 m2 Tube / pass = 308 / 2
(5.11)
= 154 tube / pass Total flow rate area = (cross sectional area)(tube / pass)
(5.12)
= (0.0002)(154) = 0.0308 m2 Steam mass velocity, Gt = (steam flow rate)/(total flow rate area)
(5.13)
= (1.7649)/(0.0308) = 57.30 kg / sm2 Steam linear velocity, u1 = (Gt)/(steam density)
(5.14)
= (57.30)/(0.49375) = 116.05 kg / ms Ratio of L / di = 4.88 / 0.016
(5.15)
= 305
Reynolds number, Re
265
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Re =
ρ ν di µ
Re =
(0.49375) (116 .05 ) (0.016) 1.55263 x 10 - 5
(5.16)
Re = 59047.87
Heat transfer factor figure 12.31 (Coulson & Richardson’s Chemical Engineering), Jh = 4.1 x 10-3 Prandtl number,
Pr =
Pr =
Cp µ
(5.17)
kf (2.010 x 10 3 )(1.55263 x 10 - 5 ) 0.0306575
Pr = 1.0180
Tube side coefficient, hi can be calculated using equation below. jhk f Re Pr 0.33 hi = di
hi =
(4.1 x 10 - 3 )(0.030657 5)(59047.8 7)(1.0180) 0.016
(5.18)
0.33
hi = 466.62 W / mo C
266
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
5.1.6 Shell Side Coefficient, hs Take baffle spacing as 1/3 from the shell diameter, so Baffle spacing: lB
= Ds / 3
(5.19)
= 0.60 / 3 = 0.20 m Tube pitch, pt
= 1.25 do
(5.20)
= (1.25)(0.02) = 0.025 m Flow area, As
As =
As =
(Pt - do )(D s )(IB ) Pt
(5.21)
(0.025 - 0.02)(0.60 )(0.20) 0.025
A s = 0.0240 m2
Mass velocity, Gs Gs =
Ws As
Gs =
10.9314 0.0240
(5.22)
Gs = 455.48 kg / m 2 s
Shell side velocity
267
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
us =
Gs ρ
us =
455.48 485
(5.23)
us = 0.9391 m / s
Shell side equivalent diameter for triangular pitch arrangement de =
1.10 2 (p t - 0.917d o 2 ) do
de =
1.10 (0.025 2 - 0.917(0.02 )2 ) 0.02
(5.24)
de = 0.0142 m
Calculate the Reynolds number Re =
Re =
Gs de μIsobutane
(5.25)
(455.48)(0 .0142) 0.00013000 5
Re = 49750.52
Prandtl number Pr =
Pr =
CpIsobutane μIsobutane kf
(5.26)
(2155)(0.0 00130005) 0.07
Pr = 4.0023
268
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Choose baffle cut of 25%, from figure 12.30 (Coulson & Richardson’s Chemical Engineering), we can obtained Jf
= 2.70 x 10-2
Assumed that the viscosity correction is negligible
hs =
k f jf Re Pr 1 / 3 de
hs =
(0.07)(2.7 0 x 10 - 2 )(49750.52 )(4.0023 1/3 ) 0.0142
hs = 10513.35 W / m2
(5.27)
o
C
5.1.7 Overall Heat Transfer Coefficient, Uo Material of construction = carbon Steel Thermal conductivity of the tube wall Kw
= 38 W/moC
Assumed dirt coefficient as hid = 8500 W/m2 oC hod = 8500 W/m2 oC 1 1 1 d ln(d o /di ) 1 ( do /di ) + 1 (do /di ) = + + o + Uo hs hod 2k w hid hi 1 = 0.0039738 m2 Uo Uo = 322.85 W / m2
5.1.8
o
C/W
o
C
(5.28)
Tube Side Pressure Drop
269
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Reynolds number , Re = 59047.87 From figure 12.24 (Coulson & Richardson’s Chemical Engineering), jf = 3.10 x 10-3 Neglect the viscosity correction term
∆Pt = Np [ 8 jf (L/d i )(μ/μ W )- m + 2.5 ]
ρiμi 2 2
∆Pt = 2[ 8(3.10 x 10 - 3 )(4.88/0.0 16) + 2.5 ]
(5.29) ( 0.49375 )(116 .05 )2 2
∆Pt = 66921.86 N / m2 ∆Pt = 66.92 kPa
5.1.9
Shell Side Pressure Drop
Reynolds number Re = 49750.52 From figure 12.30 (Coulson & Richardson’s Chemical Engineering), Jf = 2.70 x 10-2 Shell side pressure drop can be calculated using equation below ∆P = 8j f ( Dd / de ) ( L/I B ) ( ρμ s / 2) ( μ/μ w ) -0.14
(5.30)
∆P = 47.63 kPa
Table 5.2: Summary Of Chemical Design For Heat Exchanger In Series
270
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Heat Exchanger Temperature range, (o C) Feed flow rate, (kg/hr) Steam flow rate, (kg/hr) Log mean temperature
E100 Shell side 250 →150 Tube side -15 → 117 39353 6353.64 134.00
difference, ,∆ Tm (o C) True temperature
109.88
difference, ∆ Tm (o C) Overall coefficient, U (W/m2 300 o
C) Duty, Q (w) Surface are, A (m2) Length of tube or shell, L Tube diameter di (mm) Tube diameter do (mm) Area of pipe, a (m2) Number of tube, Nt Bundle diameter, Db(m) Shell diameter, Ds(m) Baffles spacing, IB(m) Tube side coefficient, hi
3109542.883 94.33 4.88m or 16 ft 16 20 0.3067 308 0.50 0.60 0.2000 466.62
(W/m2 o C) Shell side coefficient,
10513.35
hs(W/m2 o C) Overall heat transfer
322.85
coefficent, Uo (W/m2 o C) Tube side pressure drop,
66.92
∆ P (kPa) Shell side pressure drop,
47.63
∆ P (kPa) 5.2
MECHANICAL DESIGN OF HEAT EXCHANGER
The mechanical engineering design of heat exchanger determines the physical elements that make up the unit as well as their respective dimensions. This design follows the procedures specified by the Tubular Heat Exchanger association (TEMA) Mechanical Standards. It is applicable to shell and tube exchangers with internal diameter not exceeding 60 in. (1524mm), a maximum design pressure of 3000psi (204 bar) or a maximum product of nominal diameter (in) and design pressure (psi) of
271
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
60000. In addition, the design also complies with the American Society of mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section VIII, Division 1.
5.2.1
Design Pressure
For the design of tube and shell parts, a safety factor of 10% is included to determine the design pressures. Operating pressure = 1.1 bar 10% above the pressure for safety Pi = 1.1 x 10 = 11 bar = 1.1 N / mm2 5.2.2
Design Temperature
For the shell side and tube side the operating temperature is at 250 oC, so: Shell-side design temperature = 1.1x 250 oC = 275 oC Adding 2 oC for uncertainties in temperature prediction TD
= 275 + 2 = 277 oC
5.2.3
Material Of Construction
For the heat exchanger, the material used for construction is carbon steel. This selection of material is depending on the economic factor and also level of corrosiveness of the fluid used. Since the properties of the fluid both in the tube and also in the shell are not corrosive fluid, therefore the carbon steel is used because it is more economics compared to stainless steel. 5.2.4
Exchanger Type
For the heater design, pull through floating head exchanger is chosen as the exchanger type. Internal floating head is versatile than other type and also suitable for
272
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
high temperature different between shell and tubes. The tube for internal floating head also can be rod from end to ends and the bundle are easier to clean. 5.2.5
Minimum Thickness Of Cylindrical Section Of The Shell
The minimum thickness of the cylindrical section of the shell to stand the pressure can be obtained from the calculation below.
e=
PiDi 2jf - Pi
(5.30)
Where, Pi = design pressure Di = shell diameter F = design stress (from table 13.2, Coulson & Richardson’s Chemical Engineering)
e=
(1.1)(600) 2(1)(85) - (1.1)
e = 3.91 mm
adding the corrosion allowance = 2 mm e = 3.91 + 2
e = 5.91 mm Take the round number of the thickness e = 6.00 mm
5.2.6
Longitudinal Stress
σh =
σh =
PiDi 2t
(5.31)
(1.1)(600) 2(6)
σ h = 55.00 / mm 2
273
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
5.2.7
Circumferential Stress
σh =
PiDi 4t
(5.32)
σ h = (1.1)(600) / 4(6) σ h = 27.50 N / mm 2 5.2.8
Minimum Thickness Of Tube Wall
Minimum thickness of the tube wall can be calculated using the equation
e=
(5.30):
PiDi 2jf - Pi
e=
(1.1)(600) 2(1)(85) - (1.1)
e = 3.91 mm
adding the corrosion allowance = 2 mm e = 3.91 + 2 e = 5.91 mm 5.2.9
Minimum Thickness Of Head And Closure
The minimum thickness of the torispherical head can be calculated by ,
e=
PiR c Cs 2jf + Pi (Cs - 0.2)
(5.33)
Rc = crown radius Rk = knuckle radius Cs = stress concentration factor for torispherical head
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
[
Cs = 1/4 3 + R c / Rk
]
(5.34)
Rc = Ds = 600 mm Rk = 0.06(500) = 36 mm Cs = 1.77 e=
(1.1)(600) (1.77) 2(1)(85) + 1.1(1.77 - 0.2)
e = 6.80 mm
Adding corrosion allowance e = 6.80 + 2 = 8.80 mm 5.2.10 Minimum Thickness Of The Channel Cover e = (C p )(D e )(Pi /f) 1/2
(5.35)
where Cp = a design constant, depend on the edge constraint (0.45) De = nominal plate diameter f
= design stress
e = (0.45)(600)(1.1/85)1/2 = 30.72 mm
Adding corrosion allowance = 2 mm E = 30.72 + 2 = 32.72 ≈ 33 mm 5.2.11 Design Load Dead weight of vessel
275
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
W v = C v πρ mDm g(H v + 0.8D m )t x 10 -3
(5.36)
where Wv = total weight of the shell Cv = 1.08 for vessels with only few internal fitting Wv = (1.08)π (7700)(0.602)(9.81)(4.88+0.8(0.602))(2 x 10-3) = 1654.45 N Weight of tubes W t = Nt π(do2 - d12 )Lρmg W t = 308 π(0.02
2
(5.37)
- 0.016 2 )(4.88)(77 00)(9.81)
W t = 51362.08 N
Weight of insulation Material used = mineral wool insulation Insulation thickness = 50 mm = 0.05 m Density = 130 kg / m3 Approximate volume of insulation
V = πH v [ (r + r1 )2 - r 3 ]
(5.38)
V = π (4.88) [ (0.60 + 0.05) - (0.50) 2
2
]
V = 2.64 m3 W t = Vρ g
(5.39)
W t = (2.64)(130 )(9.81) W t = 3366.79 N
Total weight of heat exchanger WT = Wv + Wt + Wi
(5.40)
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
WT = 1654.45 + 51362.08 + 3366.79 = 56383.32 N = 56.38 kN 5.2.12 Pipe Size Selection For The Nozzle pipe size for isobutane inlet material of construction
= carbon steel
density inlet isobutane, ρ
= 600 kg / m3
flow rate isobutane at inlet, Gisobutane = 10.9314 kg / s Diameter pipe for isobutane inlet, Disobutane Disobutane (in) = 293G0.53ρ
-0.37
(5.41)
Disobutane (in) = 293(10.9314) 0.53(600)-0.37 Disobutane (in) = 97.60 mm Pipe size for isobutane at outlet, material of construction
= carbon steel
density outlet isobutane, ρ
= 370 kg / m3
flow rate isobutane at outlet, Gisobutane = 10.9314 kg / s Diameter pipe for isobutane outlet, Disobutane Disobutane (out) = 293G0.53ρ
-0.37
Disobutane (out) = 293(10.9314) 0.53(370)-0.37 Disobutane (out) = 116.72 mm Diameter pipe for steam at inlet stream
277
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
material of construction
= carbon steel
density inlet steam, ρ
= 0.5654 kg / m3
flow rate steam at inlet, Gsteam
= 1.7649 kg / s
Diameter of pipe Dsteam (in) = 293G0.53ρ
-0.37
Dsteam (in) = 293(1.7649) 0.53(0.5654)-0.37 Dsteam (in) = 488.94 mm
Diameter pipe for steam at outlet stream material of construction density outlet steam, ρ
= carbon steel = 0.4221 kg / m3
flow rate steam at outlet, Gsteam = 1.7649 kg / s Diameter of pipe Dsteam (out) = 293G0.53ρ
-0.37
Dsteam (out) = 293(1.7649) 0.53(0.4221)-0.37 Dsteam (out) = 544.79 mm
278
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Figure 5.2 : Steel pipe nozzle Table 5.3 : by taking D = 100 mm, the selected tube nozzle is : Nominal pipe size, inch 4
Outside diameter, inch 4.5 (114.30)
Schedule no. 4OST
Wall thickness, inch 0.237 (6.02 mm)
Inside diameter, inch 4.026 (102.26 mm)
Table 5.4 : by taking D = 500 mm, the selected tube nozzle is : Nominal pipe size, inch 20
Outside diameter, inch 20 (508)
Schedule no. 4OST
Wall thickness, inch 0.375 (9.53 mm)
Inside diameter, inch 19.250 (488.95 mm)
(From Perry R.H and Green, Don (1984), “Perry’s Chemical Engineer’s Handbook”, 7th Edition, McGraw-Hill Book)
5.2.13 Standard Flanges
279
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Flanges used in this design are chosen from the standard flanges. Here standard flanges are adapted from the British standard (BS 4504), nominal pressure 10 bar.
Figure 5.3 Standard Flange Standard flange for inlet isobutane Diameter isobutane inlet pipe = 97.60 mm Used standard o.d pipe
= 114.3 mm
Table 5.5 : Standard Flange for Inlet isobutane nom. size
100
pipe o.d d1
D
114.3
210
Flange b
16
hi
Raised face Bolting Drilling d4 f No. d2
45
148
3
M16
4
18
k
d3
170
130
Neck h2
r
10
8
Standard flange for outlet isobutane Diameter isobutane outlet pipe
= 116.72 mm
Used standard o.d pipe
= 114.3 mm
280
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 5.6 : Standard Flange for Outlet isobutane nom. size
100
pipe o.d d1
D
114.3
210
Flange b
16
hi
45
Raised face Bolting Drilling d4 f No. d2
148
3
M16
4
18
k
d3
170
130
Neck h2
r
10
8
Standard flange for inlet steam Diameter steam inlet pipe
= 488.94 mm
Used standard o.d pipe
= 508 mm
Table 5.7 : Standard Flange for Inlet Steam nom. size
pipe o.d d1
500
508
Flange D b
645
24
hi
68
Raised face Bolting Drilling d4 f No. d2
570
4
M20
20
22
Neck h2
k
d3
600
538
15
r
12
Standard flange for outlet steam Diameter steam outlet pipe
= 544.79 mm
Used standard o.d pipe
= 508 mm
Table 5.8 : Standard Flange for Outlet Steam nom. size
pipe o.d d1
500
508
Flange D b
645
24
hi
68
Raised face Bolting Drilling d4 f No. d2
570
4
M20
20
22
Neck h2
k
d3
600
538
5.2.14 Design of Saddles
Table 5.9: Using Ds = 600mm, the standard steel saddles for vessels up to 1.2m : 281
15
r
12
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Vessel
Maximum
diamete
weight
r (m) 0.9
(kN) 56.38
V
Y
Dimension (m) C E J
G
t2
0.63 0.15 0.81 0.34 0.275 0.095 10
t1
mm Bolt diameter
6
20
5.2.15 Baffles
Type : transverse baffle
Baffle diameter for plate shell is given as, Ds = the nominal diameter of the shell for plate shell. So baffle diameter = 0.600 m = 23.63’ = 600 mm
Diameter of tube holes in baffles, Dh
Dh = outer diameter of the tube = (0.16 + 1/32) x 20.2 = 3.86 mm
Number of baffle segmental, Nb
Nb = length tube / inside diameter shell = 4880 / 600 = 8.13 ≈ 8 baffles
Vent and drain -A drain and vent connection shall be provided on the shell side
Table 5.10: Summary Of Mechanical Design For Heat Exchanger In Series Heat Exchanger
E100
282
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Design pressure, bar
11
design temperature, oC
277
Material Of Construction
Tube side: Carbon steel Shell side : Carbon steel 6.0
Minimum Thickness Of Cylindrical Section Of The Shell, mm Longitudinal Stress,
55.0
N/mm2 Circumferential Stress
27.5
N/mm2 Minimum Thickness Of Tube Wall, mm Minimum Thickness Of Head And Closure,
5.91 8.80
Minimum Thickness Of The Channel Cover,mm
33.0
Design Load, kN Diameter pipe for isobutene inlet and outlet, mm Diameter pipe for steam inlet and outlet, mm Vessel diameter, m Types of baffles Number of baffle segmental, Nb
56.38 100 500 0.9 transverse 8
REFERENCES D. Brian Spalding, J.Taborek, “Heat Exchanger Design Handbook, Volume 1 - Heat Exchanger Theory”, Hemisphere Publishing Corporation, Washington, New York, London, 1983.
283
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
D. Brian Spalding, J.Taborek, “Heat Exchanger Design Handbook, Volume 2 -
Fluid Mechanics and Heat Transfer”, Hemisphere Publishing Corporation,
Washington, New York, London, 1983. J. M. Chenoweth, D. Chisholm, R. C. Cowie, D. Harris, A. Illingworth, J. F. Lancaster, M. Morris, I. Murray, C. North, C. Ruiz, E. A. D. Sauders, K. V. Shipes, J. Dennis Usher, R. L. Webb, “Heat Exchanger Design Handbook, Volume 4 Mechanical Design of Heat Exchangers”, Hemisphere Publishing Corporation 1983, Washington, New York, London, 1983. D. K. Edwards, P. E. Liley, R. N. Maddox, Robert Matavosian, S. F. Pugh, M. Schunk, K. Schwier, Z. P. Shulman, “Heat Exchanger Design Handbook, Volume 5 - Physical Properties”, Hemisphere Publishing Corporation 1983, Washington, New York, London, 1983. E. A. D. Saunders, B. Sc. C. Eng., M. I. Mech. E. “Heat Exchangers, Selection, Design and Construction”, Longman Scientific and Technical, 1998. Yokell, Stanley, “A working Guide to Shell and Tube Heat Exchangers”, McGraw-Hill Publishing Company, 1990. Sadik Kakac, Hongtan Cin, “ Heat Exchangers, Selection, Rating, and Thermal Design”, CRC Press, Boca Raton, Boston London New York, Washington, D.C, 1998. Gupta, J. P., “Working With Heat Exchangers: question and answers”, Hemisphere Publishing Corporation, A member of the Taylor and Francis Group, 1990. Warren D. Seider, J.D. Seider, Daniel R. Lewin, “Process Design Principles, Synthesis, Analysis and Evaluation”, 1997. Stanley M. Wales, “Chemical Process Equipment, Selection and Design” , Butterworths Series in Chemical Engineering, 1990. Frank P. Incropera, David P. Dewitt, “Fundamentals of Heat and mass Transfer”, 5th Edition, John Wiley & Sons, Inc, 2002. Holman, J.P, “Heat Transfer”, 7th Edition, McGraw-Hill, Inc, 1992. Kern. D.Q, “Process Heat Transfer”, International Editions, McGraw-Hill, Inc, 1965. Perry R.H and Green, Don, “Perry’s Chemical Engineer’s Handbook”, 7th Edition, McGraw-Hill Book Company, Singapore, 1984. Bhattacharya,
B.B,
“Introduction
to
Chemical
Equipment
Design,
Mechanical Aspects”, Indian Institute of Technology, 1976.
284
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Holman, J.P. “Heat Transfer”, 7th Edition, McGraw-Hill, Inc, 1992. Kern. D. Q “Process Heat Transfer”, International Editions, McGraw-Hill, Inc, 1965. Perry R.H and Green, Don, “Perry’s Chemical Engineer’s Handbook”, 7th Edition, McGraw-Hill Book Company, Singapore, 1984. Sinnott, R. K., Coulson & Richardson, “Chemical Engineering Volume 6, Chemical Engineering Design”, Butterworth Heinemann, 1999. Carl R. Branon, “Rules Of Thumb For Chemical Engineers”, Gulf Publishing Company, 1994. Perry R.H and Green, Don, “Perry’s Chemical Engineer’s Handbook”, 7th Edition, McGraw-Hill Book Company, Singapore, 1984. Sinnott, R. K., Coulson & Richardson, “Chemical Engineering Volume 6, Chemical Engineering Design”, Butterworth Heinemann, 1999. Peters, max Stone, “Plant Design and Economics for Chemical Engineers”, 2nd Edition, McGraw-Hill Chemical Engineering Series, 1968.
CHAPTER 2
285
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
PROCESS CONTROL AND INSTRUMENTATION
2.1
INTRODUCTION
All processes are subject to disturbances that tend to change operating conditions, compositions and physical properties of the streams. In order to minimize those ill effects that could result from such disturbances, chemical plants are implemented with substantial amounts of instrumentation and automatic control equipment. In critical cases and in especially large plants, moreover, the instrumentation is computer monitors for convenient, safety and optimization. A chemical plant is an arrangement of processing unit. The plant overall objective is to convert the raw materials into desired product using available sources of energy in the most economical way. All operating unit should be monitored. Methods of limiting hazard levels by control features include sensoring control on limits and various aspects of sequential and continuous monitoring. In control situations, the demand for speed of response may not be realizable with an overly elaborate mathematical system. Moreover, in practice, not all disturbances are measurable and the process characteristics are not known exactly. Accordingly, feedforward control is supplemented in most instances with feedback. In a well-designed system, typically, 90% of the corrective action is provided by feed forward and 10% by feedback with the result that the integrated error is reduces by a factor 10%. The main types of instrument used for chemical process plants are flow controller, temperature controller, pressure controller and level controller. 2.2
OBJECTIVES OF CONTROLL
The most important objectives of the designer when specifying control and instrumentation schemes are: 1.
Safe Plant Operation
286
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
•
To keep the process variables within known safety operating limits and within allowable limits.
•
To detect dangerous situations as they develop and to provide alarms and automatic shut down system.
•
To provide interlocks and alarms to prevent unsafe operating procedures.
2.
Production Specification •
To achieve the design product output
•
To produce the desired quality of final product
•
To keep the product composition within the specified quality standards.
3.
Economics •
To operate at the lowest production cost, commensurate with the other objectives.
•
The operation of the plant must conform to the market condition, which is availability of raw materials and demand of the final product.
4.
Environmental Regulations •
Variable controlled must not exceed the allowable limits set by various federal and state laws.
5.
Operational Constraint •
Various type of equipments used in chemical plant have constrains inherent to their operation. Such constraints should be satisfied throughout the operation of plant.
•
Control systems are needed to satisfy all these operational constrains.
In a typical chemical processing plant these objectives are achieve by combination of automatic control, manual monitoring and laboratory analysis.
2.3
CONTROL SYSTEM DESIGN SHEET
2.3.1
Heat Exchanger (E-100)
287
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Figure 2.1: Control Scheme for the Heat Exchanger Table 2.1: Parameter at Heat Exchanger Intention: To Heat Up the reactant Before Entering Reactor Objective : To heat up the reactants to 250 oC Objective Measurable Disturbances Action Variable 1. To control Temperature at Change in Control temperature temperature of outlet stream flow rate of the heating by V3 at outlet stream S4 feed steam inlet S3
2.3.2
Set Point E-100 Temperature 250oC
Catalytic Cracking Fluidized Bed Reactor (op-100)
288
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Figure 2.2: Control Scheme for Catalytic Cracking Fluidized Bed Reactor Table 2.2: Parameter at Catalytic Cracking Fluidized Bed Reactor Intention: To Separate Vapor and Liquid from Stream Leaving Heat Exchanger Set Point Objective Measurable Disturbances Action 1. To control flow inside phase reactor 2. To control solid flow to relate speed and flow rate 3. To control pressure between reactor and regenerator 4. To control temperature in reactor
2.3.3
Variable Flow of gas in phase to reactor Solid in and out in the reactor and regenerator flow rate of feed into reactor and regenerator Temperature in reactor and regenerator
Change in flow of gas in phase of reactor Change of solid flow rate moving to reactor and regenerator Change of feed flow rate
Control flowrate of the Input stream S4 by controlling V3 Control solid in and solid out in the reactor and regenerator Control pressure by opening or closing valve by adjusting V5
Stream S4
Change of temperature In reactor and regenerator
Control temperature by opening or closing valve at the air feed V4 and product V6
180oC
95679.8kg
2.89 bar
Control at Compressor (C-101)
S7
289
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
S8
Figure 2.3: Control Scheme for the Compressor
Table 2.3: Parameter at Compressor
Objective To maintain pressure inside compressor
2.3.4
Intention: To maintain the pressure inside the compressor Objective : To keep pressure maintain at bar Measurable Disturbances Action Variable Pressure Power or duty Control pressure inside of the by adjusting V8 at compressor compressor steam inlet S7
Set Point C-101 pressure bar
Control at Condenser
290
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Figure 2.4: Control Scheme for the Condenser Table 2.4: Parameter at Condenser Intention: To maintain the pressure inside the compressor Objective : To keep pressure maintain at bar Objective Measurable Disturbances Action Variable 1. To control Temperature at Change in Control temperature temperature of outlet stream flow rate of the heating by V9 at outlet stream S9 feed steam inlet S8
Set Point E-100 Temperature 50oC
2.3.5 Separator (V-100)
291
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Figure 2.5: Control Scheme for the Separator Table 2.5: Parameter at Separator Intention: To Separate Vapor and Liquid from Stream Leaving Heat Exchanger Objective Measurable Disturbances Action Set Point Variable 1. To control level Level of liquid Change in level Control level by Stream inside phase in phase of liquid in phase V10 at inlet stream S9 of separator separator separator S9 liquid height 1. To control Maintain Change in Control pressure by Pressure pressure pressure pressure opening and closing 0.5 bar phase separator in phase of liquid in phase valve by V28 at separator separator stream S10 1. To control Flow rate at Change in the Control Flow at the Flow into Flow rate the bottom of flowrate of bottom by V27 at The feed inside phase the separator the separator stream S11 At stream separator S11
292
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
2.3.6 Fixed Bed Reactor (R-101)
V29
V13
Figure 2.6: Control Scheme for the Fixed Bed Reactor Table 2.6: Parameter at Fixed Bed Reactor Objective
Intention: To React Isobutene with Methanol to Produce MTBE Measurable Disturbances Action
Set Point
To regulate
Variable Cooling
Reactant feed
Control temperature
Set the
reactor
water make
temperature and
by V13
temperature
temperature To maintain
up rate Pressure in
composition Pressure feed to
Control the pressure
at 53.3 oC Pressure at
constant
the fed of
the reactor
in the reactor by
1 bar
pressure at the
stream S15
control of V29
feed stream
2.3.7
Distillation Column (T-101)
293
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Figure 2.7: Control Scheme for the MTBE Distillation Column Table 2.7: Parameter at MTBE Distillation Column Intention: To Separate MTBE from Mixture Leaving Reactor Objective Measurable Disturbances Action Variable 1. To control level Level of liquid Change of level Control level by inside column in column of column Adjusting V17 valve at raffinate outlet Stream S19 2. To control Temperature Change of Control temperature by temperature inside column temperature Control V16 inside column in column 3. To control Level in drum Change of level Control level by V15 level in drum in drum to maintain the Product output
2.3.8
Set Point Stream S19 at 15251.9kg/hr 61.2oC
Stream S17 at 38747.97kg/hr
Liquid-Liquid Extraction Column (T-100)
294
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Figure 2.8: Control Scheme for the Liquid-liquid Extraction Column Table 2.8: Parameter at Liquid-liquid Extraction Column Objective To control flow at stream S20 To
control
flow
at
Intention: To Extract Methanol and Water from Hydrocarbon Measurable Disturbances Action Variable flow of liquid Change of level Control flow by adjust in column of column Valve V19 at bottom outlet stream Flow of liquid in Change of flow of Control at V20 to keep
stream S21 To control level at the
column Level of
raffinate
Set Point Stream S20 at 40.32kg/hr Flow inlet
at
liquid extraction Change of level in
the flow inlet maintain Maintain the level by
stream S21 Level output at
going out of the
the column
control V21 at stream
raffinate section
Product of S24 To control the density
column Density level
Change of the
S24 The bottom stream
S24 Interfacial level
intermediate between
change between
removed by control
at bottom
methanol and water
water and
between two
V22
product at
methanol
phase
2.3.9
liquid
interfacial of level
stream S26
Distillation Column (T-102)
295
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Figure 2.9: Control Scheme for the Distillation Column Table 2.9: Parameter at Distillation Column Objective 1. To control level inside column
2. To control temperature inside column 3. To control level in drum
Intention: To Separate Methanol and water Measurable Disturbances Action Variable Level of liquid Change of level Control level by in column of column opening and closing valve V25 at bottom outlet stream Temperature Change of Control temperature by inside column temperature opening or closing in column Valve 24 at top outlet stream Level in drum Change of level Control level by V23 in drum opening or closing valve at reflux stream
Set Point Stream S28 : at 63.4453kg/hr 62.17oC
Stream S27
296
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
2.3.10 Mixer (MIX-100)
Figure 2.10: Control Scheme for the Mixer
Table 2.10: Parameter at Mixer Intention: To Mix Methanol from Recycle and Make Up Methanol Measurable Disturbances Action Set Point Variable 1. To control the Flowrate of Change of Control flowrate M - 101 flowrate the reactant flowrate to the bypass valve Stream S14 reactor V12 at 2.88 m3/hr Objective
297
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
2.3.11 Expander (EX-100)
Figure 2.11: Control Scheme for the Expander
Table 2.11: Parameter for Expander Intention: To Expand the Pressure Leaving the Reactor Measurable Disturbances Action Variable 1. To expand the Pressure Change of Control pressure by pressure inside the pressure adjusting valve V14 expander Objective
Set Point Pressure 0.45
38
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
Figure 2.13 : PFD Diagram Before Control
39
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
Legend TC
-
Process Flow
PC
-
Pressure Control
Control Flow
FC
-
Flow Control
LC
ILC -
Temperature Control
TI
-
Temperature Indicator
DPC -
-
Interfacial Level Control
Level control Differential Pressure Control
Figure 2.13 : Process Control P and ID Diagram
40
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
41
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
REFERENCES
Luyben, W. l., (1990), Process Modelling simulation and Control for Chemical Engineers, 2nd Edition, McGraw-Hill Chemical Engineering Series Ogunnaike, B. A. and Ray, W. H. (1994), Process Dynamics, Modeling and Control, New York, Pxford. R.K.Sinnott, 1999.Chemical Engineering Design, Coulson & Richardson Chemical Engineering .3rd Edition. Volume 6 .Britain. Butterworth Heinemann J.R Backhurst & J.H Harker.1987.Chemical Engineering Design, Coulson & Richardson Chemical Engineering .3rd Edition. Volume 2 .United Kingdom. Pergamon Press. Stanley M. Walas. 1988. Chemical Process Equipment Selection and Design. United State of America. Butterworth’s Series in Chemical Engineering. Chemical Engineering Progress, February 2001, American Institute of Chemical Engineering.
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PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
CHAPTER 3
SAFETY CONSIDERATION
3.1 INTRODUCTION Any organization has a legal and moral obligation to safe guard the health and welfare of its employees and the public. Safety is also good business: the good management practices needed to ensure safe operation would also ensure efficient operation. All manufacturing processes there are additional, special, hazard associated with the chemical used and the process condition. The designer must be aware of these hazards and ensure through the application of sound engineering practices that the risks are reduced to acceptable levels. Safety and loss prevention in process design can be considered under the following broad headings :( Coulson and Richardson’s Volume 6) 1. Identification and assessment of the hazards 2. Control of the hazards; for example by containment of flammable and toxic materials 3. Control the process. Prevention of hazardous deviation in the process variables, (pressure, temperature, flow) by provision of automatic control system interlocks, alarms, trips, together with good operating practices and management. 4. Limitation of the loss. The damage and injury caused if an incident occurs, pressure relief, plant layout, provision of fire-fighting equipment. In Malaysia, The Occupational Safety and Health Act, 1994 is a tool which provided a new legal and administrative as a driving force to promote, encourage and stimulate the high quality standards of health and safety at work place. Both parties such as employers and employees must give their support and cooperate to
43
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
comply the law and not misuse safety in order to increasing the promotion of safety awareness and effective safety organization and performance in companies.
3.2 HAZARD AND OPERABILITY STUDY HAZOP stands for “hazard and operability studies.” This is asset of formal hazard identification and elimination procedures designed to identify hazard to people, process plants and the environment. The techniques aim to stimulate in a systematic way the imagination of designers and people who operate plants or equipment so they can identify potential hazard. In effect, HAZOP studies make the assumption that hazard or operating problem can arise when there is a deviation from the design or operating intention. Corrective actions can then be made before a real accident occurs. The primary goal in performing a HAZOP study is to identify, not analyse or quantify, the hazard process. The end product of a study is a list of concerns and recommendation for prevention of the problem, not an analysis of the occurrence, frequency, overall effects, and the definite solution. If HAZOP is started too late in a project, it can lose effectiveness because: 1. There may be a tendency not to challenge an already existing design. 2. Changes may come too late, possibly requiring redesign of the process. 3. There may be loss of operability and design decision data used to generate the design. HAZOP is a formal procedure that offers a great potential to improve the safety, reliability and operability of process plants by recognizing and eliminating potential problems at the design stage. It is not limited to the design stage, however. It can be applied anywhere that a design intention. (Perry’s Handbook, 1998) When using the operability study technique to vet a process design, the action to be taken to deal with a potential hazard will often be modification to the control system and instrumentation, the inclusion of additional alarms, trips or interlock. If major hazard are identified, major design changes may be necessary, alternatives processes, material and equipment. In order to have a safe process successfully producing to specification to the required product, a sound control system is necessary but not sufficient. (Coulson & Richardson’s, 1999).
44
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
The objectives of HAZOP study are: 1. To identify areas of the design that may posses a significant hazard potential
2. To identify and study features of the design that influences the probability of a hazardous incident occurring. 3. To familiarize the study team with the design information available. 4. To ensure that a systematic study is made of the areas of significant hazard potential. 5. To identify design information not currently available to the team. 6. To provide a mechanism for feedback to the client of the study team’s detailed comments. (Sydney Lipton and Jeremiah Lynch, 1994) The advantages of HAZOP study to the design application: •
Early identification of problems areas when conceptual design stage.
•
Identifies need for emergency procedures to mitigate.
•
Provide essential information for safety case, such as on the hazards identified and effectiveness of safety systems.
•
Through examination of hazard and operability problems when applied at detailed stage.
•
Meets legislative requirements.
•
Identifies need for commissioning, operating and maintenance procedures for safe and reliable operations.
45
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
Table 3.1: A HAZOP study contains the following important features: Features : Intention Guide words Deviations Causes Consequences Action
Meaning : Defines how the part or process is expected to operate. Simple word used to qualify the intention in order to guide and stimulate creative thinking. Departures from the intention discovered by systematic application of guide words. Reasons that deviations might occur. Results of deviations if they occur. Prevention, mitigation and control -
Prevent causes.
-
Mitigate the consequences.
-
Control action such as provide alarms to indicate things getting out of control: define control actions to get back into control.
The MTBE Plant HAZOP Study is included at Appendix: Safety.
3.3
PLANT START UP AND SHUT DOWN PROCEDURE
Safe procedures must be well known for the start up and shut down of plant and deviations from normal operating conditions. Whenever process conditions are changed, opportunities are presented for hazardous situations to arise. Building up the process consistency may reduce the investigating breakdown and malfunction, availability, the design cycle, operability, flexibility including blending and recycling experience and known how personnel. The start-up and shutdown of the plant must proceed safely and easily, yet be flexible enough to be carried out in several ways. The operating limits of the plant must not exceed and dangerous mixtures must not be formed because of abnormal states of concentration, temperature, phase, reactant, catalyst and products. During start-up, the catalyst in the reactor should be activated and sufficiently warm for reaction to begin when the flow of reactant is started. Contaminants often enter the system at this stage. Materials are added by operations such as purging, drying and flushing. Water and other materials may
46
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
condense in unplanned location causing process levels to get out of control and other problems. The ignition of fuel to heat the high temperature fluid during start-up must be designed to accomplish this safely Some typical errors that could occur during start-up of the plant include : 1. Wrong routing, involving failure to ensure that correct valves are closed. This is especially crucial in the adsorption section where three different processes are occurring at any one time. 2. Drain valves are left open resulting in loss of material and possibly endangering the lives of workers. 3. Valves left closed resulting in over pressure in the vessel. 4. Failure to complete purging cycle before admission of fuel air mixture. 5. Backflow of material from high pressure to low pressure system.
6. Setting of wrong valves for operating parameters such as jacket temperature in the reactor and reflux in the distillation column. 3.3.1
Normal Start up and Shut down the Plant
The study of the plant start up and shut down must include investigation of the operating limits, transient operating conditions, process dynamics, contamination and added material, emissions, hot standby and emergency shut down with plant protection control systems and alarms. 3.3.1.1 Operating Limits The operating limits of the plant are imposing by mechanical, electrical, civil and process design. Where necessary, it has to be introduce additional equipment, sampling points, instrumentation and lines, and identify their use on the engineering line diagram,
3.3.1.2 Transient Operating and Process Dynamic The transient operating conditions must be studied to safe time and operating cast. The process dynamics that to be investigated includes excessive heat transfer
47
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
when more or less floe in either energy exchanging streams through activations and warming of catalyst when the flow of reactant starts to entrance of contamination and others 3.3.1.3 Added Materials Materials are added by operations may not be tolerated in part of the system or clean material may be needed for the start up of the plant. Residues or unwanted products such as out of specification may be discharged or hold in tank for further treatment. 3.3.1.4 Hot Standby Time is save during restart up if plant are kept partially working such as when other unit operation are ceased to function temporarily, the converter can be left in hot standby conditions. 3.3.1.5 Emergency Shut Down Special plant protection known as process trip system or emergency shut down system is design to affect the emergency shut down through the push button by operator or from automatic activation of a relay when necessary. The trip systems should be reliable and operate when required to avoid a nuisance shut down of plant. 3.3.2
Start up and Shut down Procedure for the Main Equipment
3.3.2.1 Reactor 1. It is recommended that the internal reactor vessel measurements (ID, Bed Depth – not the overall vessel height, etc.) be verified, so that product loading is consistent with the "Estimated Performance Sheet" (EPS). 2. Prior to any loading, it is necessary to make an internal and external inspection of the reactor vessel. In other words, there should not be any pipes or hollow devices in the vessel, which could allow the gas to travel without contacting the product.
48
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
3. There are two vessel types of bed supports that can be used; (1) has a support grid permanently installed about 2 inches below the throat of the lower manway; or (2) uses a level bed of washed gravel, ceramic balls, or pawl rings. The bed support must be leveled. 4. Close and secure the bottom manway. 5. Through the top manway, load the remaining feed to level as stated in the EPS. During the latter stages of loading level off the cone of the filled product bed and continue loading until finished. 6. Close and secure the top manway. Upon operational start-up, record the required measurements – temperature, pressure, and flow rate - from each bed (if applicable). This data should be kept on some routine basis (daily, weekly bi-weekly, etc.) so that any problems that might develop can be identified and corrected. 3.3.2.2 Distillation Column Start-Up Procedure 1. Turn the switch box indicator to Distillation Control setting. 2. Switch the column power source lever to the "on" position. Turn the Reboiler Heater Control knob clockwise. This prevents over heating of the reboiler. 3. Turn on the cold water supply ( CWS )valve until the computer stops telling the user to increase the volume of the CWS valve. 4.
Adjust the Reflux Control to the desired setting.
5.
Assure all computer settings are as desired.
6. Allow the tray temperatures to reach a steady-state value. 7. Turn on the feed and reboiler pumps as applicable. The pump settings can be adjusted on the computer. Caution: DO NOT ALLOW THE WATER LEVEL TO FALL BELOW THE CALROD HEATERS.
49
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
This will result in damage to the heaters. If the heaters are exposed turn off the column, this allows the vapor in the column to condense and return to the reboiler. If the liquid level is still below the heaters, more liquid must be added to the reboiler. Shut-Down Procedure 1. Turn the Reboiler Heater Control knob to zero. 2. Turn off the pumps (feed and reboiler). 3. Turn off the CWS valve when the temperature of the distillate is below the boiling point of the light component of the mixture. 4.
Press the stop button.
5. Shut off the computer, by selecting the "Shut-down" option from the Special menu. 3.3.2.3 Liquid-Liquid Extraction Column Start Up Procedure 1. Check to see that all the drainage valves are closed. 2. Check to be sure the top water vent valve is open. 3. When the liquid level in the column reaches the top right nozzle(water in nozzle), turn the water flowrate down to the desired setpoint. Turn on and set the feed flowrate to the desired setpoint by adjusting the pump speed, and close the top water vent. 4. Allow the interface to form between the top mesh and the top left nozzle. 5. Small adjustments should be made in order to keep the interface constant.
Shut down procedure 1. Turn off all inlet flowrates on the right control panel. 2. Shut off the stirrer on the right control panel.
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PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
3. Open the top water in vent valve. 4. Open the bottom centre black valve to drain the column. 3.3.2.4 Heat Exchanger Start up Procedure When putting a heat exchanger in operation, open the vent connections and slowly start to circulate the cold medium only. Be sure that the entire cold side of the exchanger is completely flooded before closing its vents. The hot medium should then be gradually introduced until all passages are filled with fluid. Then close the hot side vents and slowly bring the unit up to its operating temperature. Shut down Procedure When heat exchanger is required to be shutdown, the hot fluid should be turned off first. If it is necessary to stop the circulation of the cold fluid, the hot medium should also be stopped by by-passing the heat exchanger.
3.4
EMERGENCY RESPONSE PLAN (ERP)
It is expected that every person who working in this plant will act responsibly in any Department of Emergency. ERP procedures were state in Appendix: Safety. In most cases, the observer of an emergency is faced with decision to leave the scene to summon help or stay and provide help. The basic rule is as follows. “Unless we are sure that we are not putting ourselves in any danger and we know we can make a difference, summon help.
3.4.1
Emergency Response Procedures
General Procedures
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PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
When alarm system is activated whether by break glass or by smoke detector, the alarm that is siren sound will be triggered throughout plant. The following general procedures should be followed if there is no immediate emergency in your area. •
Do not panic and stay alert: Stay calm and be alert and ready to response to any emergency according to the Plant Emergency Organization Programmed. The shift manager should go to the security guard to identify the location of the alarm.
•
Access the situation around your area :
Look around and ensure that your immediate area is not in danger or affected by the emergency. Stop all contractors from working immediately. •
Wait for instruction from Supervisor/Shift Manager :
Do no evacuate from one’s post unless one is immediate danger or when instructed by one’s supervisor or the shift manager. •
Avoid using the telephone :
Do not use the telephone unless it is absolutely necessary, as the telephone lines must be reserved for calling emergency services. All incidents resulting in injuries, property damage and/ or productions loss shall be investigated and reported for within 24 hours. Corrective action to prevent the recurrence of the incident shall be initiated 48 hours. 3.4.2 •
Evacuation Procedures: Exit building via the stairways : It takes time to the person familiarize with evacuation routes in advance. The maps showing the location of all emergency exits and extinguishers are posted on all floors.
•
Assist the injured when possible : Do not move the seriously injured unless there is danger of further injury. If it is necessary to leave someone in the building, try to leave him in a relatively secure place (example, the stairwell is one of the safer places to be in fire). After someone has been evacuated the building, find the proper officials and report the location and condition of persons who need assistance.
•
Designed persons are responsible for clearing the production floors and offices :
52
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
Efforts to clear the production floor and offices should be limited to 5 minutes. As the areas are cleared, all doors should be closed. •
Once outside the building : Keep at least 50 feet away from the building to avoid danger from falling glass, example “Evacuate to the Emergency Assembly Area “.
•
Do not re – enter the building until safety officer or fire personnel have been determined that it is safe.
3.4.3
•
Fires:
If the fire alarm sounds or a fire broke out in the plant, turn off any electrical equipment that been operating and evacuate the building immediately. Close all doors to help prevent fires from spreading. Exit via stairwells.
•
Call 994 to give location and extent of fire and notify the management to report the fire : State if there are any special circumstances, such as the presence of dangerous chemicals.
•
Don’t attempt to fight a fire unless we have been trained in fire extinguisher use and the fire is very small : When fighting a fire, always position ourselves between the exit and the fire to ensure an escape route. IF THE FIRE CANNOT BE CONTAINED, GET OUT QUICKLY!
3.4.4 •
Explosion, Line Rupture or Serious Leak Do the following if possible. 1. Turn the “Emergency Stop” switch to “Off” position 2. Isolate the effected area of the limit. Block in high-pressure source as required accomplishing this. 3. Complete the shut down
3.4.5 •
Other Emergencies : Injuries :
53
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
For life – threatening emergencies, CALL 991 for medical aid and for transportation to hospital and at same time notify the management as listed on the Notification Lists. For less serious injuries or illness, first aid can be obtained at the nearest clinic. Report all injuries to the management. •
Equipment failures : Any equipment failures, which may harm or injured the workers, should be reported to the Production Supervisors or the management for further action to be taken.
3.5
PLANT LAYOUT
The process units and ancillary buildings should be laid out to give the most economical flow of material and personnel around the site. Hazardous process must be located at a safe distance from other buildings. Consideration must be also being given to the future expansion of the site. The ancillary buildings and services required on site, in addition to the main processing units (building) will include: (Coulson and Richardson’s 1999) 1. Storage for raw materials and products; tank farms and warehouses 2. Maintenance workshop 3. Stores, for maintenance and operating supplies 4. Laboratories for process control 5. Fire stations and other emergency services 6. Utilities: steam boilers, compressed air, power generation, refrigeration, transformer stations. 7. Effluent disposal plant 8. Offices for general administration 9. Canteens and other amenity buildings, such as medical centres 10. Car parks Normally, the process units will be sited first and arranged to give a smooth flow of materials through various processing steps, from raw material to final product storage. It is normally spaced at least 30 apart and for hazardous processes, the greater spacing may be needed. Then, the principal ancillary buildings to be located and arranged in order to minimize the time spent by the personnel in travelling between the buildings. The administration offices and
54
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
laboratory should be located well away from potentially hazardous processes since a many people be in here. The control rooms normally are located adjacent to the process units but if it with the potentially hazardous processes has to be sited at safer distance. Besides that, the layout of the plant roads, pipe alleys and drains also must be considered to locate the main process units. Easy access roads will be needed to each building for construction and for operation and maintenance. The utilities buildings should be sited to give most economical run of pipes to and from the process units. Finally, the main storage areas should be placed between loading and unloading facilities and the process units they serve. Storage tanks containing hazardous materials should be sited at least 70 m (200 ft) from the site boundary. There are 7 principal factors to be considered : 1. Economic considerations: construction and operating costs. 2. The process requirements. 3. Convenience of operation. 4. Convenience of maintenance. 5. Safety. 6. Future expansion. 7. Modular construction. The MTBE site layout have shown in Figure 3.1.
55
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
Figure 3.1 Methyl tert-Butyl Ether (MTBE) Plan Layout U
56
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
Figure 3.2: Methyl tert-Butyl Ether (MTBE) Plant Evacuation Routes
U
Legand Evacuation Routes
57
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
Figure 3.3 PID before HAZOP
58
PRODUCTION OF 300,000 METRIC TON MTBE PER YEAR
Figure 3.4 PID after HAZOP
59
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
REFERENCES
Clarles A.Wentz, 1998. Safety, Health and Environmental Protection. United State of America:McGraw-Hill. R.K.Sinnot, 1999. Chemical Engineering Design. Coulson & Richardson’s Chemical Engineering 3rd Edition. Volume 6. Britain; Butterworth Heinemann. Robert H. Perry, Don W. Green, 1998 Perry’s Chemical Engineer’s Handbook, Seventh Edition, McGraw-Hill. http://www.sulfatreat.com/Documents/HTML/St/startup.html http://www.amberjet.com/IP/start_up.htm http://www.sulfatreat.com/Documents/PDF/SulfaTreat/ST-Start_Up_Procedure.pdf http://chem.engr.utc.edu/Webres/435F/Proc.htm http://www.eng.buffalo.edu/Courses/ce428/Distillation/procedure.htm http://users.rowan.edu/~savelski/uol/liqliq.html http://pharmaflo.com/heatexch/
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
CHAPTER 4
ECONOMIC EVALUATION
INTRODUCTION Economic evaluation is very important for a proposed plant. We have to be able to estimate and decide between alternative designs and for project evaluation. Chemical plants are built to make a profit an estimate of the investment required and the cost of production are needed before the profitability of a project can be assessed. The total investment needed for a project is the sum of the fixed and working capital. Fixed capital is the total cost of the plant ready for start up. It is the cost paid to the contractors. Working capital is the additional investment needed, over and above the fixed capital, to start the plant up and operate it to the point when income is earned. Most of the working capital is recovered at the end of the project.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.1.1 The Specification Of Plant In this chapter, the costing of equipment which has been designed will be estimated and the feasibility of MTBE production will be evaluated by profitability analysis to make sure the project is economically attractive. There are some general assumptions to this chapter; i.
The plant life span is fifteen years.
ii.
The currency exchange rate of US dollar to Ringgit Malaysia is fixed at 3.8 as fixed by Malaysian Government.
iii.
The price of raw materials, catalyst and product is fixed for the whole period of operation.
Price of raw material
: Isobutane - RM 0.8094 / kg : Methanol - RM 0.988 / kg
Price of product
: MTBE - RM 1.320 / kg : TBA - RM 1.035 / kg : DME - RM 0.655 / kg
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.1.2
Revenue From Sales
i.
MTBE
=
37878.76 kg/h =
300000 tonne year
Price: RM 1.320/kg =
37878 .76 kg 24 hr 365 day RM 1.320 × × × ×0.90 hr day year kg
= ii.
TBA
=
RM 394199710/yr
639.663 kg/h Price: RM 1.035/kg
=
639 .663 kg 24 hr 365 day RM 1.035 × × × ×0.90 hr day year kg
= iii.
DME
=
RM 5219612/yr
1210.9868 kg/h Price: RM 0.655/kg
=
1210 .9868 kg 24 hr 365 day RM 0.655 × × × ×0.90 hr day year kg
= iv.
Isobutane
=
RM 6253560/yr
13718.4558 kg/h Price: RM 0.8094/kg
= 13718 .4558 kg 24 hr 365 day RM 0.8094 × × × ×0.90 hr day year kg
=
RM
87541714/yr v.
n-butane
=
157.412 kg/h Price: RM 0.35/kg
Total revenue
=
157 .412 kg 24 hr 365 day RM 0.35 × × × ×0.90 hr day year kg
=
RM 434363/yr
=
RM 493648959/yr
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.2 COST ESTIMATION 4.2.1 Capital cost estimation Capital cost estimates are essentially “paper and pencil” studies. The cost of making an estimate indicates the personnel hours required in order to complete the estimate.
The capital needed to supply the necessary manufacturing and plant facilities is called the fixed capital investment (FC), while the additional investment needed for the plant operation (for plant start-up and operation to the point when income is earned) form the working capital (WC). Capital cost estimates for chemical process plants are often based on an estimate of the purchase cost of the major equipment items required for the process, the other costs being estimated as factors of the equipment cost. The accuracy of this type of estimate will depend on what stage the design has reached at the time estimate is made and on the reliability of the data available on equipment cost.
The cost of the purchased equipment is used as the basis of the factorial method of cost estimation and must be determined as accurately as possible. It should preferably be based on recent prices paid for similar equipment. Calculation of total module cost and gross roots cost (based on table 4.2) CTC = CFC + CWC + CL Where, CTC
=
total capital cost
CFC
=
fixed capital cost
CWC
=
working capital cost
CL
=
cost of land & other non-depreciable costs
FP
=
Pressure factor to account for high pressure
FM
=
Material factor to account for material of constructions
CP
=
Purchase cost for base condition
FBM
=
Bare module cost factor
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
CBM
=
Bare module equipment cost for base condition
C°BM
=
Bare module equipment cost for actual condition
Total Module Cost, CTM
Grass Root Cost, CGR
=
1.18 (∑C°BM )
=
1.18 (3223841)
=
RM 3804132 x 3.8
=
RM 14455703
=
CTM + 0.35 ( ∑ CBM)
= =
14455703 + 0.35 (12659343) x 3.8 RM 31292629
Since, Grass Root Cost (CGR) is: CGR
=
CFC + CL
Area for 1 lot of land = 200000 m2 The price of land is RM 60 per m2 CL
=
RM 12000000
CFC
=
CGR - CL
=
RM 31292629 - RM 12000000
=
RM 19292629
Working capital is the additional investment needed over and above the fixed capital to start the plant up and operate it to the point when income is earned. Working capital cost = 5% of fixed capital costs CWC
=
5% fixed capital cost (CFC)
(Coulson & Richardson,
=
RM 964631
1990)
Thus, Total capital cost (CTC)
=
CFC + CL + CWC
=
RM 19292629+ RM 12000000+ RM 964631
=
RM 32257260
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.2.2
Manufacturing Cost Estimation
The cost of associated with the day to day operation of a chemical plant must be estimated before the economic feasibility of a proposed process can be assessed. The equation below is used to evaluate the cost of manufacture:
Cost of manufacture (COM) =
Direct Manufacturing Cost (DMC) + Fixed Manufacturing Cost (FMC) + General Expenses (GE)
COM = 0.304FCI + 2.73COL + 1.23(CUT + CWT + CRM) The cost of manufacturing (COM) can be determined when the following costs are known or can be estimated:
1. Fixed Capital Investment (FCI): (CTM or CGR) 2. Cost of Operating Labor (COL) 3. Cost of Utilities (CUT) 4. Cost of Waste Treatment (CWT) 5. Cost of Raw Material (CRM) 4.2.2.1 Cost of Operating Labor (COL) Table 4.1 Labor Cost Equipment type Heat exchangers Reactor Vessels Pumps Compressor
No of
Operators per shift per
Operator per
equipment 6 2 1 5 2
equipment 0.1 0.5 0.0 0.0 0.15
shift 0.6 1.0 0.0 0.0 0.3
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Towers Waste Treatment
3 1
0.35 0.5
1.05 0.5 3.45 Since, a single operators works on the average 48 weeks (3 weeks time off for vacation and sick leave) a year, five 8-hour shifts a week.
1 operator
=
48 week 5 shift × Year week
=
240 shift Year
Working days for MTBE plant is 7920 hour = 330 days Operating shift per Year
=
330 days 3 operating × Year days
=
990 operating shift Year
Working days for MTBE plant is 7920 hour
So, the number operator needed
=
=
990 operating shift Year 240 shift Year 4.125 operators
Thus, Operating Labor
=
4.125 operators x 3.45 operator per shift
=
14.23 operator
=
15 operator
A mechanical engineers maximum wages per year (MIDA 2002) RM 60,000.00 Thus, Labor Cost (1996)
=
15 x RM 60,000.00
=
RM 900,000.00
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.2.2.2 Cost of Utilities (CUT) Yearly costs
=
flowrate x costs x period x steam factor
Since, assuming the plants operating days per year = 330 days So, Steam factor (SF)
=
no . of day ' s plant operates per year no . of days per year
=
330 = 0.90 365
1. Heater (E-100) Duty
=
3109542
J s = 11 .16 G J hr
From table 8.5 (W.R Wan Daud, Princip Reka bentuk Proses Kimia, 2002, page 285) cost of heater RM 19.6 / GJ. Thus , Yearly cost
= (Q) (C steam) (t) = 11 .16
GJ 19 .6 hr day × RM × 24 ×365 ×0.90 hr GJ day yr
= RM 1724515 2. Heater (E-101) Duty
=
3423874
J s = 12 .24 G J hr
From table 8.5 (W.R Wan Daud, Princip Reka bentuk Proses Kimia, 2002, page 285) cost of cooling water RM 0.6 / GJ. Thus , Yearly cost
= (Q) (C steam) (t) = 12 .24
GJ 19 .6 hr day × RM × 24 ×365 ×0.90 hr GJ day yr
= RM1891403
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3. Compressor (C-100) Power (shaft)
=
137.73kW
Effeciency of drives, ξdr
=
92.28% (refer to table 3.7) Appendix
Electric Power, Pr
=
Power output ξdr
=
137 .73 0.9228
=
149.25 kW
Yearly cost 149 .25 kW ×
=
0.228 hr day ×24 ×365 ×0.90 kWh day yr
= RM 268285 4. Cooler 1 (E-102) Duty
= 4014590
KJ s = 14 .4 GJ hr
From table 8.5 (W.R Wan Daud, Princip Reka bentuk Proses Kimia, 2002, page 285) cost of cooling water RM 0.6 / GJ. Thus , Yearly cost
= (Q) (C steam) (t) = 14 .4
GJ 0.6 hr day × RM × 24 ×365 ×0.90 hr GJ day yr
= RM 68118 5. Cooler 2 (E-103) Duty
= 4204290
J s = 15 .12 G J hr
From table 8.5 (W.R Wan Daud, Prinsip Reka bentuk Proses Kimia, 2002, page 285) cost of cooling water RM 0.6 / GJ. Thus , Yearly cost
= (Q) (C steam) (t) = 15 .12
GJ 0.6 hr day × RM × 24 ×365 ×0.90 hr GJ day yr
= RM71524
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
6. Cooler 3 (E-104) Duty
=
J s = 1.8 G J hr
503240
From table 8.5 (W.R Wan Daud, Princip Reka bentuk Proses Kimia, 2002, page 285) cost of cooling water RM 0.6 / GJ. Thus , Yearly cost
= (Q) (C steam) (t) GJ
0.6
hr
day
= 1.8 hr × RM GJ ×24 day ×365 yr ×0.90 = RM 8514 7. Cooler 4 (E-105) Duty
=
J s = 0.72 G J hr
240320
From table 8.5 (W.R Wan Daud, Princip Reka Bentuk Proses Kimia, 2002, page 285) cost of cooling water RM 0.6 / GJ. Thus , Yearly cost
= (Q) (C steam) (t) = 0.72
GJ 0.6 hr day × RM × 24 ×365 ×0.90 hr GJ day yr
= RM 3406 8. Pump 1(P100) Power (shaft)
=
327.94kW
Effeciency of drives, ξdr
=
93.71% (refer to table 3.7) Appendix
Electric Power, Pr
=
Power output ξdr
Yearly cost 349 .95 kW ×
=
327 .94 0.9371
=
349.95kW
=
0.228 hr day × 24 ×365 ×0.90 kWh day yr
= RM 629053
70
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
9. Pump 2(P101) Power (shaft)
=
79.19kW
Effeciency of drives, ξdr
=
91.58% (refer to table 3.7) Appendix
Electric Power, Pr
=
Power output ξdr
=
79 .19 0.9158
=
86.47kW
Yearly cost
= 86 .47 kW ×
0.228 hr day × 24 ×365 ×0.90 kWh day yr
= RM 155434 10. Pump 3(P102) Power (shaft)
=
22.85kW
Effeciency of drives, ξdr
=
86.93% (refer to table 3.7) Appendix
Electric Power, Pr
=
Power output ξdr
Yearly cost
=
22 .85 0.8693
=
26.29kW
= 26 .29 kW ×
0.228 hr day × 24 ×365 ×0.90 kWh day yr
= RM 47258 11. Pump 4(P103) Power (shaft)
=
685.64kW
Effeciency of drives, ξdr
=
95.37% (refer to table 3.7) Appendix
Electric Power, Pr
=
Power output ξdr
=
685 .64 0.9537
=
718.93kW
71
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Yearly cost 718 .93 kW ×
=
0.228 hr day × 24 ×365 ×0.90 kWh day yr
= RM 1292314 12. Pump 5(P104) Power (shaft)
=
322.75kW
Effeciency of drives, ξdr
=
93.67% (refer to table 3.7) Appendix
Electric Power, Pr
=
Power output ξdr
Yearly cost 344 .56 kW ×
=
322 .75 0.9367
=
344.56kW
=
0.228 hr day × 24 ×365 ×0.90 kWh day yr
= RM 619366 Total cost of utilities (CUT)
= RM 6779190
4.2.2.3Cost of Raw Material (CRM) 1.
Isobutane
=
39353 kg/h Price RM 0.8094/kg
2.
Methanol
=
39353 kg 24 hr 365 day RM 0.8094 × × × ×0.90 hr day year kg
=
RM 251123677/yr
=
15462 kg/hr Price RM 0.988/kg (Chemical week, June 2003)
=
15462 kg 24 hr 365 day RM 0.988 × × × ×0.90 hr day year kg
=
RM 120439579/yr
72
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
3.
Catalyst (Alumina silica)
=
95679 kg ×
RM 9.5 1 tonne × tonne 1000 kg
=
RM909
=
RM 251123677/yr + RM 120439579/yr
=
RM 371563256/yr
Total cost of catalyst (for 3 year)
=
RM 909
Total cost
=
RM 371564165
Total cost of raw material
The estimation of total manufacturing cost (with catalyst): COM = 0.304FCI + 2.73COL + 1.23(CUT + CWT + CRM) COM = 0.304 (31292629) + 2.73 (900000) + 1.23 (6779190 + 371564165) COM = RM 477332286/yr The estimation of total manufacturing cost (without catalyst): COM = 0.304FCI + 2.73COL + 1.23(CUT + CWT + CRM) COM = 0.304 (31292629) + 2.73 (900000) + 1.23 (6779190 + 371563256) COM = RM 477331168/yr
73
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 4.2: Estimation Cost Of Purchased Equipment Equipment
Capacity/Size
Operating Pressure 0.0 barg
Area =94.33m2 (floating head)
Material Of Construction Carbon Steel Carbon Steel Tube-CS Shell-CS
C100
W=137.73kW
C101
W = 22.85kW
E 100 Heat Exchanger E 101 Heat exchanger E 102 Heat Exchanger E 103 Heat Exchanger E 104 Heat Exchanger E 105 Heat Exchanger
FP
Tube- 9 barg Shell- 9 barg
1.0 1.0
Area =95.71m2 (floating head)
Tube-CS Shell-CS
Tube- 9 barg Shell- 9 barg
Area =94.33m2 (floating head)
Tube-CS Shell-CS
Area =94.33m2 (floating head)
FM
FBM
Cp
CBM
2.2
16000
264000
3.0
3536676
10610028
1.0 1.0
3.2 3.2
15000 15000
48000
1.0 1.0
1.0 1.0
3.2 3.2
16000 16000
51200
Tube- 9 barg Shell- 9 barg
1.0 1.0
1.0 1.0
3.2 3.2
15000 15000
48000
Tube-CS Shell-CS
Tube- 9 barg Shell- 9 barg
1.0 1.0
1.0 1.0
3.2 3.2
15000 15000
48000
Area =94.33m2 (floating head)
Tube-CS Shell-CS
Tube- 9 barg Shell- 9 barg
1.0 1.0
1.0 1.0
3.2 3.2
15000 15000
48000
Area =94.33m2 (floating head)
Tube-CS Shell-CS
Tube- 9 barg Shell- 9 barg
1.0 1.0
1.0 1.0
3.2 3.2
15000 15000
48000
0.1 barg
Co BM
74
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 4.2: Estimation Cost Of Purchased Equipment Equipment
Capacity/Size
P100
W = 327.94kW
P101 P102
W = 79.19kW W = 22.85kW
Material Of Construction Cass Steel Cass Steel Cass Steel
Operating Pressure 3.5 barg 0.1 barg 0.0 barg
P103
W = 685.64kW
Cass Steel
1.50 barg
P104
W = 322.75kW
Cass Steel
0.0 barg
R100
R101 T100 Sieve tray T101 T102 Sieve tray V100 Total
D = 6.512 H = 18m D = 1.814m H = 4m D = 0.765 m H = 10.85 11 trays D = 1.01 m H =9 m D = 0.765 m H = 10.85 11 trays
Stainless Steel
1.75 barg
Carbon Steel
1.0 barg
Stainless Steel Stainless Steel Stainless Steel Stainless Steel
3.5 barg
1.75 barg 3.5 barg
FP
FM
FBM
Cp
1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.3 1.0 1.0 1.0 1.2 1.0
1.8 1.0 1.8 1.0 1.8 1.0 1.8 1.0 1.8 1.0 4.0 1.0 1.0 1.0 4.0 1.0
4.518 3.31 4.518 3.31 4.518 3.31 4.518 3.31 4.518 3.31 11.5 4.2 4.2 4.2 11 4 2.0 1.0 2.0 1.2 11 4 2.0 1.0
36881
1.2 1.0 1.2 1.0
4.0 1.0 4.0 1.0
CBM
Co BM 333257
244152 8571
77448 56740
1429
12912 9460
52276
472366 346067
36593
330654 121123
200000
840000 230000
19000
79800 79800
40000
440000 160000
294
9702 5821
17000
178000 68000
40000
440000 160000
294
9702 5821 7131 12659343
3223841
75
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.3
PROFITABILITY ANALYSIS Profitability is used as the general term for the measure of the amount of profit
that can be obtained from a given situation. Profitability therefore, is the common denominator for all business activities. The feasibility of MTBE production in Malaysia is evaluated by profitability analysis. The profitability of the project will be the largest factor that makes a project economically attractive.
To this stage, almost all the design and cost information
required for the profitability analysis were obtained.
Based on the information
available, the best methods assessing the profitability of alternatives are based on projections of the cash flows during the project file. A proposed capital investment / project and its associated expenditures can be recovered by revenue (or savings) over time in addition to a return on the capital that is sufficiently attractive in view of the risks involved of the potential alternatives uses. There are 5 common methods in performing engineering economic analysis: 1) Present Worth (PW) 2) Future Worth (FW) 3) Annual Worth (AW) 4) Internal Rate Of Return (IRR) 5) Benefits / Cost Ratio (B/C) 4.3.1
Discounted Cash Flow
The economic feasibility of this plant is evaluated using the Discounted Cash Flow Analysis (DCF), which is the most frequently used method of economic evaluation in the chemical industry. This method measures the profitability of the project taking into account the time value of money. From this method, the internal rate of return (IRR) of the project can be determined which indicates the feasibility of the project. The value of IRR is calculated using the information obtained in the sections.
76
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 4.3: Annual Cash Flow Before Tax Year
Gross Income (RM) 0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 15
Annual Expenses (RM)
1
2
493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959
-477332286 -477331168 -477331168 -477332286 -477331168 -477331168 -477332286 -477331168 -477331168 -477332286 -477331168 -477331168 -477332286 -477331168 -477331168
Estimated salvage value
Investment & Salvage Value (RM) 3 -19292629 -964631 -12000000
1929262.9
=
10%CFC
=
0.1 x RM 19292629
=
RM 1929262.9
Before Tax Cash Flow (RM) (4)= (1)+(2)+(3) -19292629 -964631 -12000000 16316673 16317791 16317791 16316673 16317791 16317791 16316673 16317791 16317791 16316673 16317791 16317791 16316673 16317791 16317791 1929262.9
(Coulson & Richardson, 1990)
77
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 4.4 : Annual Cash Flow After Tax Taxes rate at 38% is chosen referring to reference from MIDA Year
Gross Income (RM) 1
0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 15 15
Expenses (RM) 2
Investment & Salvage Value (RM) 3
Depreciation Cost Basis * MACRS Rates 4
Taxable Income (RM)
Taxes (RM) Taxes rates = 38%
After Tax Cash Flow (RM)
(5)=(1)+(2)(4)
(6)=(5)*0.38
2756916.69 4724764.84 3374280.81 2409649.36 1722831.77 1720902.50 1722831.77 860451.25 0 0 0 0 0 0 0
13559756.32 11593026.16 12943510.19 13907023.64 14594959.23 14596888.49 14593841.23 15457339.75 16317791 16316673 16317791 16317791 16316673 16317791 16317791 1929262.9
5152707.4 4405349.94 4918533.871 5284668.982 5546084.508 5546817.627 5545659.668 5873789.104 6200760.58 6200335.74 6200760.58 6200760.58 6200335.74 6200760.58 6200760.58 733119.902
(7)=(1)+(2)+ (3)-(6) -19292629 -964631 -12000000 11163965.6 11912441.06 11399257.13 11032004.02 10771706.49 10770973.37 10771013.33 10444001.9 10117030.42 10116337.26 10117030.42 10117030.42 10116337.26 10117030.42 10117030.42 1929262.9 12964631
-19292629 -964631 -12000000 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959 493648959
-477332286 -477331168 -477331168 -477332286 -477331168 -477331168 -477332286 -477331168 -477331168 -477332286 -477331168 -477331168 -477332286 -477331168 -477331168 1929262.9 12964631
Cumulative Cash Flow (RM)
-32257260 -21093294.4 -9180853.34 2218403.789 13250407.81 24022114.3 34793087.67 45564101 56008102.9 66125133.32 76241470.58 86358501 96475531.42 106591868.7 116708899.1 126825929.5 128755192.4 141719823.4
78
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.3.2 Net Present Value 4.3.2.1 Present Worth MARR is the rate set by an organization to designate the lowest level that makes an investment acceptable. For a risky investment, MARR should be set higher. However, for public purpose (government, public utility), MARR is lower. For this proposed plant, MARR that has been selected is 15%.
By using present worth, we can determine either this proposed plant is profitable and acceptable or not. Table 4.4 shows the value of present worth by using 15%, therefore this proposed plant is profitable because the value of PW is > 0. PW when MARR = 15% Table 4.5: Present Worth Value Year 0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 15 PW
After Tax Cash Flow (RM) -19292629 -964631 -12000000 11163965.6 11912441.06 11399257.13 11032004.02 10771706.49 10770973.37 10771013.33 10444001.9 10117030.42 10116337.26 10117030.42 10117030.42 10116337.26 10117030.42 10117030.42 13697750.9
MARR = 15%
0.86957 0.75614 0.65752 0.57175 0.49718 0.43233 0.37594 0.3269 0.28426 0.24718 0.21494 0.18691 0.16253 0.14133 0.12289 0.12289
Present Worth (PW), (RM) -19292629 -964631 -12000000 9707849.57 9007473.18 7495239.55 6307548.3 5355477.03 4656614.92 4049254.75 3414144.22 2875867.07 2500556.24 2174554.52 1890974.16 1644208.29 1429839.91 1243281.87 1683316.61 33178940.2
MARR = 15% PW = RM 33178940.2 This project is attractive and acceptable because PW > 0
79
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
4.3.3 Cumulative Cash Flow Diagram For The Evaluation Of A New Project Table 4.6: After Tax Cumulative Cash Flow Year 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 15
After Tax Cash Flow (RM) -32257260 11163965.6 11912441.06 11399257.13 11032004.02 10771706.49 10770973.37 10771013.33 10444001.9 10117030.42 10116337.26 10117030.42 10117030.42 10116337.26 10117030.42 10117030.42 13697750.9
Cumulative Cash Flow -32257260 -21093294.4 -9180853.34 2218403.789 13250407.81 24022114.3 34793087.67 45564101 56008102.9 66125133.32 76241470.58 86358501 96475531.42 106591868.7 116708899.1 126825929.5 140523680.4
Cumulative Cash Flow vs Year 150000000 125000000 100000000 Cumulative 75000000 Cash Flow 50000000 25000000 (RM) 0 -25000000 0 -50000000
2
4
6
8
10
12
14
16
Year Figure 4.1: Cumulative Cash Flow (RM) Versus Year
4.3.4
Rate Of Return (ROR)
4.3.4.1 Internal Rate Of Return
80
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
In theory, the Minimum Attractive Rate of Return (MARR) is chosen higher than the rate expected from the bank or some safe investment that involved minimal investment risk. The MARR for after taxes is selected at 15%. (Analysis, and Design of Chemical Processes)
IRR is a method that produces an annual rate of profit, or return, resulting from an investment and compared with the MARR. In determining the internal rate of return, trial and error has been done based on the MARR that mentioned before. By trial and error, the IRR for this plant has been found as 34.94%. Table 4.7: Present Value (RM) when i = 30% and i = 40% Year 0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 15 PW
After Tax Cash Flow (RM) -19292629 -964631 -12000000 11163965.6 11912441.06 11399257.13 11032004.02 10771706.49 10770973.37 10771013.33 10444001.9 10117030.42 10116337.26 10117030.42 10117030.42 10116337.26 10117030.42 10117030.42 13697750.9
i = 30%
0.76923 0.59172 0.45517 0.35013 0.26933 0.20718 0.15937 0.12259 0.0943 0.07254 0.0558 0.04292 0.03302 0.0254 0.01954 0.01954
Present Value (RM)
i = 40%
-19292629 -964631 -12000000 8587657.26 7048829.62 5188599.87 3862635.57 2901143.71 2231530.26 1716576.39 1280330.19 954035.969 733839.105 564530.297 434222.946 334041.456 256972.573 197686.774 267654.053 4303026.05
0.71129 0.5102 0.36443 0.26031 0.18593 0.13281 0.09486 0.06776 0.0484 0.03457 0.02469 0.01764 0.0126 0.009 0.00643 0.00643
Present Value (RM) -19292629 -964631 -12000000 7940817.092 6077727.429 4154231.275 2871740.966 2002783.388 1430492.974 1021738.325 707685.5685 489664.2723 349721.7791 249789.4811 178464.4166 127465.8495 91053.27378 65052.5056 88076.5383 -4410754.867
By interpolation, IRR value is 34.94% when P is at 0 value. IRR (34.94%) > MARR (15%). This project is profitable and acceptable.
4.3.5 Sensitivity Analysis A sensitivity analysis is a way of examining the effects of uncertainties in the forecasts on the viability of a project. AW = PW (A/P, 15%, 15)
81
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
= 33178940.2 (0.17102) = RM 5674262.32
FW = PW (F/P, 15%, 15) = 33178940.2 (8.13706) = RM 269979027.1 Table 4.8: Future Worth (RM) when MARR = 15% Year 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 15
After Tax Cash Flow (RM) -32257260 11163965.6 11912441.06 11399257.13 11032004.02 10771706.49 10770973.37 10771013.33 10444001.9 10117030.42 10116337.26 10117030.42 10117030.42 10116337.26 10117030.42 10117030.42 13697750.9
MARR = 15% 8.13706 7.07571 6.15279 5.35025 4.65239 4.04556 3.51788 3.05902 2.66002 2.31306 2.01136 1.74901 1.52088 1.3225 1.15 -
FW
4.3.6
Future Worth (FW), (RM) -262479260.1 78992983.04 73294748.23 60988875.45 51325185.17 43577584.92 37890991.81 32948745.2 27781253.92 23401298.38 20347596.11 17694787.37 15386789.23 13378856.03 11634584.98 10117030.42 13697750.9 269979801.1
Payback Period
The payback period analysis is a more simplistic method of calculating the economic feasibility of a project. This method determines the period in number of years required for the project to recover back the initial capital investment of the plant. In using this method, the assumptions stated above such as below still applies: 1) The plant life is taken as 15 years. 2) The annual net profit of the plant is taken as constant. 3) The class life or recovery period is 7 years. 4) The working capital is taken as 5% of the total fixed capital cost.
4.3.6.1
Simple Payback Period
Table 4.9 : Simple Payback Period
82
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Year 0 1 2
After Tax Cash Flow -32257260 16316673 16317791
Cumulative Cash Flow -32257260 -15940587 377204
By interpolation, Table 4.10 : The Interpolation Simple Payback Period Cumulative Cash Flow -15940587 0 377204
Year 1 1.97 2
Therefore, MTBE plant can have payback period with: Payback period = (1 + 0.97) years = 1 years 12 month ≈ 2 years
4.3.6.2
Discounted Payback Period
Normally, the interest in Malaysia standardized for chemical plant. By referring to Hong Leong Bank, the interest is 15% and use as a basis for discounted payback period. Table 4.11 : Discounted Payback Period Year
Annual Cash Flow After Tax
0 1 2 3
-32257260 16316673 16317791 16317791
Cumulative Cash Flow
Cumulative Cash Flow After Tax
-32257260 -15940587 -2013884.05 14001824.34
-18331675.05 -2315966.658 16102097.99
By interpolation, Table 4.12 : The Interpolation Discounted Payback Period Cumulative Cash Flow -2315966.658 0 16102097.99
Year 2 2.03 3
Therefore, MTBE plant can have payback period with: = 2 + (0.03) years
83
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
= 2 year 1 month
4.4 CONCLUSION Based on this chapter, the economic evaluation of MTBE plant are made through study in all aspect including feasibility study, process synthesis and flow sheeting and designed of major equipment. From the cash flow analysis, the payback period for the MTBE plant is about 2 years. Furthermore, it should be stated that the present work is primarily illustrated based on the method of engineering economic analysis of chemical processes. PW is positive value so the project is attractive and acceptable same as when IRR is bigger than MARR. By estimate the value of PW, FW and AW by using relationship between PW and FW the answer of FW same with estimate direct from CFAT.
REFERENCES
84
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Perry R.H and Green, Don, “Perry’s Chemical Engineer’s Handbook”, 7th Edition, McGraw-Hill Book Company, Singapore, 1984. Sinnott, R. K., Coulson & Richardson, “Chemical Engineering Volume 6, Chemical Engineering Design”, Butterworth Heinemann, 1999. Peters, max Stone, “Plant Design and Economics for Chemical Engineers”, 2nd Edition, McGraw-Hill Chemical Engineering Series, 1968.
85
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
CHAPTER 5
PROCESS INTEGRATION AND PINCH TECHNOLOGY
5.1
INTRODUCTION
Process integration can lead to a substantial reduction in the energy requirements of a process. One of the most successful and generally useful techniques is that developed by Bodo Linnhoff and other workers: pinch technology. The term derives from the fact that in a plot of the system temperatures versus the heat transferred, a pinch usually occurs between the hot stream and cold stream curves. It has been shown that the pinch represents a distinct thermodynamic break in the system and that, for minimum energy requirements, heat should not be transferred across the pinch, Linhoff and Townsend (1982) (Ref: Coulson & Richardson’s vol. 6) 5.2
PINCH TECHNOLOGY
There are four streams to consider the problem of integrating the utilization of energy. Two hot streams which require cooling and two cold streams that have to be heated. Each streams starts from a source temperature Ts, and is to be heated or cooled to a target temperature, Tt. The heat capacity of each stream is shown as CP. CP is given by: CP = mCp (5.1) Where,
m = mass flow rate, kg/s Cp = average specific heat capacity between Ts and Tt, (KJ/kgoC)
Table 5.1:
Shows the process data for each stream.
86
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Heat Stream number
Type
1 2 3 4
HOT HOT COLD COLD
Heat capacity Cp(KW/ oC) 3.2 1.3 2 4
Ts(oC)
Tt (oC)
180 150 20 75
50 30 140 135
Load (KW) 416 156 240 240
The heat load shown in the table is the total heat required to heat or cools the stream from the source to target temperature. The stream are shown diagrammatically below,
Stream 1
180°C
CP = 3.2 kW/°C
50°C
Stream 2
150°C
CP = 1.3kW/°C
30°C
Stream 3
20°C
CP = 2 kW/°C
140°C
Stream 4
75°C
CP = 4 kW/°C
135°C
Figure 5.1: 5.3
Diagrammatically representation of process stream
THE PROBLEM TABLE METHOD
The problem table is a numerical method for determining the pinch temperature and the minimum utility requirements. Firstly, it needs to convert the actual stream temperature Tact into the interval temperatures Tint. Hot streams Tint
=
Tact – (ΔTmin/2)
Cold streams Tint
=
Tact – (ΔTmin/2)
The minimum temperature difference taken from composite curve as, ΔTmin = 10 oC
87
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Hot a nd Cold Com posite curve s 350
Temperature
o
C
300 250 200
Hot Stre am s
150
Cold Stre am s
100 50 0 1
2
3
4
2
Enthalpy,1 0kW
Figure 5.2: Hot and cold streams composite curves Table 5.2: Interval Temperature for ΔTmin = 10oC
Actual Temp. oC
Stream
Interval Temp. oC
1
180
50
175
45
3
150
30
145
25
9
20
140
25
145
10
75
135
80
140
The heat balance for the streams falling within each temperature interval: For the nth interval: ΔHn
=
(∑CPc - ∑CPh) (ΔTn)
=
net heat required in the nth interval
(5.2) Where, ΔHn
∑CPc =
sum of the heat capacities of all the cold streams in interval
∑CPh =
sum of the heat capacities of all the hot streams in the interval
ΔTn
=
interval temperature difference=(Tn-1-Tn)
88
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
175 Interval 1:
145 1
Interval 2:
4
140 2
Interval 3:
80
Interval 4:
45
Interval 5:
25
Figure 5.3: Table 5.3:
3
Intervals and streams
Ranked order of interval temperature
Rank,oC
Interval, ΔTn oC
Stream in interval
145
30
-1
140
5
4-(2+1)
80
60
(3+4)-(1+2)
45
35
3-(1+2)
25
20
(3-2)
175
Cascading the heat from one interval to the next implies that the temperature difference is such that the heat can be transferred between the hot and cold streams. A negative value in the column indicates the temperature gradient is in the wrong direction and that the exchange is not thermodynamically possible.
Table 5.4:
Problem Table ∑CPc - ∑CPh
Interval
o
Tint, C
o n
ΔT ,C
(Kw/oC)
ΔHn (KW)
surplus/deficit
89
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
175 1
145
30
-3.2
-96
S
2
140
5
0.5
2.5
D
3
80
60
2.1
126
D
4
45
35
-2.0
-87.5
S
5
25
20
1.0
14
D
Interval temperature Rank oC 175oC
0kW
145oC
-96kW
96 kW
-96 kW
128.5 kW
140oC
2.5 kW
93.5 kW
2.5 kW
126 kW
80oC
126 kW
-32.5 kW
126 kW
0 kW
45oC
-87.5 kW
55 kW
-87.5 kW
87.5 kW
25oC
14 kW
-41 kW
14 kW
73.5 kW
32.5 kW
Figure 5.4 Heat Cascade From figure 5.4: pinch occurs at interval temperature 80oC At the pinch, hot stream
=
80 + 5
=
85 oC
=
80 – 5
=
75oC
(5.3)
Cold stream (5.4)
5.4
THE HEAT EXCHANGER NETWORK
The grid representation of the stream is shown in Figure 5 CP
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
(KW/ oC) o
o
85 C75 C 180oC
50 oC 3.2
1 150 oC
30 oC 1.3
2 140 oC
20 oC 2.0
3 135 oC
75 oC 4.0
4
Figure 5.5 Grid for 4 stream problem For maximum energy recovery (minimum utility consumption) the best performance is obtained if no cooling is used above the pinch. This means the hot streams above the pinch should be brought it the pinch temperature solely by exchange with the cold streams. THE NETWORK DESIGN ABOVE THE PINCH CP hot ≤ CP cold Applying this condition at the pinch, stream 1 can be matched with stream 4, but not with 3. Matching streams 1 and 4 and transferring the full amount of heat required to bring stream 1 to the pinch temperature gives; ΔHex
=
CP (T pinch - Ts)
=
304 kW
(5.5)
This will also satisfy the heat load required to bring stream 4 to its target temperature.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Stream 2 can be matched with stream 3, whilst satisfying the heat capacity restriction. Transferring the full amount to bring stream 3 to the pinch temperature: ΔHex
=
CP (T pinch- Ts)
=
97.5 kW
The heat required to bring stream 3 to its target temperature, from the pinch temperature, is: ΔH
=
2.0(140-75)
=
130 kW
So a heater will have to be included to provide the remaining heat load: ΔHhot
=
130-97.5 kW
=
32.5 kW
(5.6)
THE NETWORK DESIGN BELOW THE PINCH Stream 1 is matched with stream 3 transferring the full amount to bring stream 1 to its target temperature; transferring: ΔHex
=
3.2(85-50)
=
112 kW
Stream 3 requires more heat to bring it to pinch temperature; amount needed: ΔH
=
2.0(75-20)-85kW
=
25 kW
So transferring 25 kW will raise the temperature from the source temperature to: 20+ 25/2 =32.5 kW and gives a stream temperature difference on the outlet side of the exchanger of: 85-32.5 = 52.5 kW
So the minimum temperature difference condition, 10oC will not be violet by this match. Stream 2 will need further cooling to bring its to its target temperature, so a cooler must be included; cooling required. ΔHcold = =
1.3 (85-50)-25 73.5 kW
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
The proposed network for maximum energy recovery is shown in Figure 5.5
B
1
2
C
A
D
A
D
B
C
3
4
Figure 5.6 Proposed heat exchanger network 5.5
MINIMUM NUMBER OF EXCHANGERS
The network shown in figure 5.5 was designed to give the maximum heat recovery, and therefore give the minimum consumption, and cost of the hot and cold utilities. In figure 5.5 it is clear that there is scope for reducing the number of exchangers. Exchanger D can be deleted and the heat loads of the cooler and heater increased to bring stream 2 and 3 to their target temperatures. Heat would across the pinch and the consumption of the utilities would be increased For complex networks a more general expression is needed to determine the number of exchangers: Zmin = N’ +L’ – S
(5.7)
Where L’= the number of internal loops present in the network S= the number of independence branches (subsets) that exist in the network N= the number of streams including the utilities
93
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
In a final design, there are 3 exchangers, rather than 4 before the process integration and pinch technology, with the minimum heating and cooling loads, 32.5 kW and 73.5 kW, respectively, match those predicted from the problem table, compare with the loads for heating and cooling before process integration: 416 kW and 240 kW.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
CHAPTER 6
WASTE TREATMENT
6.1
INTRODUCTION
Pollution is something that should be taken into serious consideration in any petrochemical plant especially the MTBE plant. Pollution, no matter what kind of the pollution is has serious negative effects not only to human beings, but also to animals, plants and to the environment. Therefore, it is the responsibility of each individual to ensure that their activities are not harmful to the environment. This includes activities and works involved in designing a plant. Waste from any petrochemical plant should be treated according to the local and international standards before being released to the environment. In the MTBE plant, the wastes are only the in liquid form and gas form. The liquid will be treated in the wastewater treatment plant. The hydrogen gas leaving the reactor is sent to a gas cylinder which it is then sold to interested company at market price. The treatment processes and systems employed by the MTBE plant is the typical processes and systems based on Howard S. Peavy, Donald R. Rowe, George Tchobanoglous; Environmental
Engineering, McGraw-Hill, 1985 and
David H. F. Liu, Bela G. Liptak, Wastewater Treatment, Lewis Publishers, 1999.
6.2
WASTEWATER TREATMENT
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Wastewater treatment is a must in any plant. The wastewater from plant cannot be channeled into the sewage system without being treated. The wastewater from the MTBE plant may contains a small amount of the feed and product and a small quantity of by-products such as butene, TBA and dimethylether. According to the site location selected, the wastewater from the plant is to be treated and should comply with Standard B which is shown Table 6.1. In the design of the wastewater treatment plant for the production of MTBE, the COD value used is based of the COD value of wastewater from other plants that are in operation. The COD value of 3000 mg/l will be used for design purposes. The design of the plant consists of preliminary, primary and secondary treatment where each treatment unit chosen is based on the characteristics of the influent to be treated. Before being treated, all the wastewater is channeled to the holding tank. It is then ferried for screening and the next process is the primary settling tank. The effluent leaving this tank is sent to the active sludge reactor. After that, it will be sent to the secondary settling tank. Finally, the effluent undergoes adsorption by activated carbon before leaving the wastewater treatment plant.
6.2.1 Denitrification Process (Chemical Treatment)
96
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
To remove methanol in the waste water, we use the denitrification process in our plant waste treatment. In the denitrification process, nitrate is reduced to nitrogen gas by the same facultative, heterotrophic bacteria involved in the oxidization of carbonaceous material. For reduction to occur the dissolved oxygen level must be at or near zero and a carbon supply must be available to the bacteria. Because low carbon content is required for the previous nitrification step, carbon must be added before denitrification can proceed. A small amount of primary effluent, bypassed around secondary and nitrification reactors, can be used to supply the carbon. However, the unnitrified compounds in this water will be unaffected by the denitrification process and will appear in the effluent. When essentially complete nitrogen removal is required, an external source of carbon containing no nitrogen will be required. The most commonly used external carbon source is methanol, CH3OH. When methanol is added, the denitrification reaction is:
NO3- +
5 CH3OH 6
1 5 7 N2 + CO2+ H2O +OH2 6 6
Theoretically, each milligram per liter of nitrate should require 1.9 mg/L of methanol. Under treatment plant conditions, however about 3.0 mg/L of methanol is required for each milligram per litre of nitrate, making this process an expensive one.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Table 6.1 Parameter Limits for Wastewater and Effluent Under the Environmental Quality Act 1974. PARAMETER Temperature pH BOD5 at 20oC COD Suspended solid Mercury Cadmium Chromium Hexavalent Arsenic Cyanide Lead Copper Manganese Nickel Tin Zinc Boron Iron Phenol Free Chlorine Sulfide Oil and grease
UNIT o C mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l
STANDARD A 40 6.0-9.0 20 50 50 0.005 0.01 0.05 0.05 0.05 0.10 0.20 0.20 0.20 0.20 1.0 1.0 1.0 0.001 1.0 0.5 None
STANDARD B 40 5.5-9.0 50 100 100 0.05 0.02 0.05 0.10 0.10 0.5 1.0 1.0 1.0 1.0 1.0 4.0 5.0 1.0 2.0 0.5 10
* Both standards could be used and acceptable, but only one is chosen, Standard B for the wastewater treatment for the MTBE plant.
6.3
WASTEWATER TREATMENT PLANT DESIGN
The design of the wastewater treatment plant consists of the holding tank, the design of the screening device, then the design of the settling tank, the design of the primary and secondary sedimentation tanks, and lastly the design for the activated sludge process.
98
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
The next step is the sludge treatment which consists of the sludge thickening by centrifugation, condensation by using heat treatment and lastly dehydration by using vacuum filter. Since the gas produced only hydrogen and no other gases, so the gas needs no treatment. The hydrogen gas produced is stored to be sold to interested companies like MOX Sdn. Bhd..
6.3.1
Design of Holding Tank The purpose of the holding tank is to hold and accumulate the wastewater
before it undergoes further treatment. The design of the holding tank is as follows: Wastewater flow rate
Volume of wastewater per day
m 3 24 hr × hr day
=
1.5642
=
37 .54
=
37.54 m3
m3 day
By taking into consideration the depth of the holding tank as 3 m, and the ratio of the length to the width as 3:1, the dimensions of the holding tank are as follows: Depth of holding tank
=
3.0 m
Width of holding tank
=
3.0 m
Length of holding tank
=
9.0 m
Volume of holding tank
=
81.0 m3
This means that the holding time is about two days (81m3/37.54m3) and it is acceptable.
6.3.2
Design of Screening Device In the preliminary treatment of the wastewater, the treatment chosen is by
using screening. Fine screens made of woven-wire cloth are used. The screen is used to remove small particles which might be in the wastewater. A screen with small sized openings is chosen because the wastewater does not contain large particles. The head loss is calculated by using the following equation:
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
1 Q hL = C( 2g ) A
2
(6.1)
Where hL
=
head loss, m
C
=
waste constant for screen
=
0.6 for clean screen (Metcalf & Eddy, 1979)
g
=
gravity, ms-2
Q
=
Flow through screen, m3s-1
A
=
Effective opening area for submerged screen, m2
=
take as 9m2
Thus, h L =
1 0.6 ×2 ×9.81
2 4.345 x10 −4 9
h L = 1.9799 ×10 −10 m
6.3.3
Design of Settling Tank For the wastewater treatment, sulfide precipitation treatment is used to
remove heavy metals from the wastewater. The precipitant used is sodium sulfide, which will react with the metal ions and will form non-soluble sulfide metal. However, extra care is required in this process to avoid sulfide poisoning. Pretreatment which involves the increasing of the pH of the wastewater is required to minimize the release of hydrogen sulfide gas. The design of the settling tank is as follows: Take holding time
=
15 minutes (standard holding time)
Average flow rate
=
1.5642
Holding time
=
15 minutes
=
0.25 hr
=
Average flow rate
=
1.5642
=
0.391 m 3
Tank volume
m3 hr
× Holding time
m3 × 0.25 hr hr
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
By taking the depth as L=0.8m, and using a square tank, Length of tank
=
V L
=
0.391 0.8
= 6.3.4
0.70 m
Design of Primary and Secondary Sedimentation Tank Primary sedimentation is a unit operation designed to concentrate and
remove suspended organic
solids
from the wastewater. The secondary
sedimentation tank is designed as a unit operation for the activated sludge process. The design for the sedimentation tanks are as follows: Take holding time
=
2 hr
Average flow rate
=
1.5642
Holding time
=
2 hr
Tank Volume
=
Average flow rate
=
1.5642
=
3.1284 m 3
m3 hr
× Holding time
m3 × 2hr hr
By taking the depth as L=2m, Length of tank
6.3.5
=
2×
V L
=
2×
3.1284 2
=
2.50 m
Design for Activated Sludge Process
The activated sludge process is a treatment process that involves the production of a living or active microorganism which is used to stabilize the waste aerobically. A completely mixed reactor is used in this process. This reactor is used as it is suitable for general wastewater treatment and it has a high efficiency (85-95%) to reduce high COD or BOD. This process involves a completely mixed reactor followed by a secondary sedimentation tank. Part of the sludge from the secondary
101
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
sedimentation tank is recycled to the influent reactor. The design for the reactor is as follows: m3 hr
Average flow rate
=
1.5642
Holding time
=
3 hr
Tank Volume
=
Average flow rate
=
1.5642
=
4.693 m 3
× Holding time
m3 ×3hr hr
By taking the depth as L=2m, Length of tank
6.3.6
=
V L
=
4.69 2
=
1.53 m
Oxygen Demand and Aerator
COD (kg/day)
=
Influent COD
=
3
=
112 .62
× wastewater flow rate
kg m3 × 37 . 54 m3 day kg day
By assuming that 1kg COD requires 1kg of oxygen, thus 112.62 kg/day COD requires 112.62 kg O2/day. The aerator used is a mechanical aerator with an oxygen transfer rate of 1.8 kg O2/day. Power needed
=
Oxygen needed per hour
O2 needed per hour / O2 transfer rate
=
112 .62
=
4.69
kg 1day × day 24 hr
kg hr
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Thus, power needed
=
4.69 kg day 1.8 hr kg
=
2.61 kW
An aerator unit provides 10kW of power. Thus, one unit is sufficient to provide enough power for the activated sludge process.
6.4
SLUDGE TREATMENT In this wastewater treatment plant, sludge is formed in the primary and
secondary sedimentation tank. This sludge needs to be treated and disposed. For the MTBE plant, the following operations are used for the sludge treatment system: i.
Sludge thickening by centrifugation
ii.
Condensation by using heat treatment
iii.
Dehydration by using vacuum filter
Wastes from the sludge treatment system, for example the filtrate from the vacuum filter, are sent to the influent treatment plant to undergo further treatment. Dehydrated sludge is sent to the sludge dump site. The flow chart for the sludge treatment is shown in Figure 6.1. Although the treatment is expensive, it is necessary for our plant.
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
S l udge P la nt
C EN TR IFU G ATIO N TH IC K EN IN G
H EA T TR E ATM EN T
T o influ ent plant
S l udge to dis pos al s ite
SL U D G E STO R AG E
D ehy dr ated s lud ge
VAC U U M FIL TE R
F iltrate to influen t pl an t
Figure 6.1 The Sludge Treatment System
6.5
WASTE TREATMENT PLANT LAYOUT Generally, the layout of a waste treatment plant depends on the process
requirements. The treatment plant covers an area of 800m2. The plant layout is shown in Figure 6.3. The waste treatment plant consists of the following units: 1.
1 holding tank
2.
1 primary sedimentation tank
3.
1 secondary sedimentation tank
4.
1 activated sludge reactor
5.
1 screening device
6.
1 power house
7.
4 pumps
8.
1 sludge store
9.
Units in the sludge treatment process Table 6.2 Functions of Pumps in the Waste Treatment Plant Pump
Function
104
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
1
To pump sludge from the sedimentation tank to the sludge treatment tank.
2
To pump sludge from the secondary sedimentation tank to be recycled to the activated sludge reactor.
3
To pump sludge from the secondary sedimentation tank to the sludge treatment process.
4
To pump wastewater from the sludge treatment system to be recycled to the influent plant.
U LEG END Pum p P R IM A R Y S E D IM E N T A T IO N T A N K
1
1
S lu d g e f ro m p r im a ry s e d im e n t a t io n t a n k to b e t re a t e d
2
S lu d g e f ro m s e c o n d a ry s e d im e n t a t io n t a n k to b e r e c y c le d
3
4
S lu d g e f ro m s e c o n d a ry s e d im e n t a t io n t a n k to b e t r e a te d W a s t e w a te r f r o m s lu d g e t r e a tm e n t s y s te m to in flu e n t p la n t
F lo w S lu d g e F lo w
S E T T L IN G T A N K
W a ste w a te r F lo w
POW ER HOUSE A E R A T IO N T A N K
S C R E E N IN G D E V IC E 2
3
S LU D G E TR EA TM E N T PR O C E SS
SECO NDARY S E D IM E N T A T IO N T A N K H O L D IN G T A N K
4
Figure 6.2 Waste Treatment Plant Layout 6.6
ABSORPTION TANK USING GRANULAR ACTIVATED CARBON
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
In the operation of absorption tank, granular activated carbon (GAC) is used which has a diameter between 0.1-2.0 mm. The contact system for GAC consists of cylindrical tanks, which contain a bed of the carbon material (refer the design given). The water is passed through the bed with sufficient residence time allowed for completion of the adsorption process. The system is operating in a fixed bed mode. Fixed bed systems are batch operations that are taken off the line when the adsorptive capacity of the carbon in used up. Although fixed granular carbon beds can be cleaned in a place with superheated steam, the most common practice is to remove the carbon for cleaning in a furnace. The regeneration process is essentially the same as the original activation process. The adsorbed organics are first burned at about 800 oC in the absence of oxygen. An oxidizing agent, usually stream, is then applied at slightly higher temperatures to remove the residue and reactivated carbon.
6.6.1 Analysis of the Absorption Process The adsorption process takes place in the three steps, macrotransport, microtransport and sorption. The quantities of adsorbate that can be taken up by an adsorbent are function of both the characteristics and concentration of adsorbate and the temperature. Generally, the amount of material absorbed is determined as a function of the concentration at a constant temperature and the resulting function is called an absorption isotherm. Equation that are often used to described the experimental isotherm data where developed by Freundlich by Langmuir and by Brunauer, Emmet and Teller (BET isotherm). Freundlich Isotherm Equation: x = K f Ce1 n m Where x/m
= amount adsorbate absorbed per unit weight of absorbent (activated carbon)
Ce
= equilibrium concentration of absorbed in solution after absorption K f , n = empirical constant
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
The constants in the Freundlich isotherm can be determined by plotting (x/m) versus C and making use of above equation rewritten as: 1 x log = log K f + log Ce n m 6.6.2
Breakthrough Absorption Capacity In the field, the breakthrough adsorption capacity, ( x m )b , of the GAC in a
full-scale column is some percentage of the theoretical absorption capacity found from the isotherm. The
(x
m )b of a single column can be assumed to be
approximately 25 to 50 percent of the theoretical capacity ( x m ) o . Once ( x m )b is known, time to breakthrough can be calculated by solving the following equation for tb
X C t x = b = Q Ci − b b [8.34 lb Mgal .( mg L ) ] 2 Mc m b M c x Where = field breakthrough adsorption capacity, lb/lb or g/g m b X b = mass of organic material absorbed in the GAC column at breakthrough, lb or g M c = mass of carbon in the column, lb or g
Q = flow rate, Mgal/d Ci = influent organic concentration, mg/L Cb = breakthrough organic concentration, mg/L tb = time to breakthrough, day
Equation above was developed assuming that Ci is constant and that the effluent concentration increases linearly with time from 0 to Cb value. The time breakthrough can be calculated using the rearranging equation above. From the test data by Freundlich adsorption isotherm plotted,
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PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
x 3.56 = 0.0015 Ce m x = 0.0015(3.250)3.56 m 0
= 0.0996 mg/mg say 0.10 mg/mg = 0.10 Ib/Ib Determination of breakthrough time,
tb =
( x / m) b M c Q (Ci − Cb / 2[8.34 Ib / Mgal .( mg / L)]
Following condition apply:
(x
m )b =50 percent of ( x m ) o =o.5 (0.10 lb/lb) = 0.050 lb/lb
Assuming from the data testing by Freundlich adsorption isotherm, Surface area = 10 ft 2 = 0.929m2 M c = (10 ft 2 ) × ( 5.0 ft ) × 38 lb ft 3 = 1,900 lb Q = 5.0 gal ft 2 . min ×1440 min d ×10 ft 2 = 72000 gal d = 0.072 Mgal d Ci = 3.2 mg L Cb = 0.75 mg L
the time to breakthrough is
tb =
( x / m) b M c Q (Ci − Cb / 2[8.34 Ib / Mgal .( mg / L)]
tb = 56 day
Therefore, results from our study based on Freundlich adsorption isotherm the activated carbon in our design waste treatment column vessel can long lasting for 56 day. Therefore, our estimation is changing the activated carbon in the vessel waste treatment in every 56 day to make sure the efficiency capacity of adsorption carbon is in the maximum capacity.
REFERENCES
108
PRODUCTION OF 300,000 METRIC TON OF MTBE PER YEAR
Howard S. Peavy, Donald R. Rowe, George Tchobanoglous; Environmental Engineering, McGraw-Hill, 1985. David H. F. Liu, Bela G. Liptak, Wastewater Treatment, Lewis Publishers, 1999.
109
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