Crude Tower Simulation Using Aspen HYSYS

Bangladesh University of Engineering and Technology

Course No: CHE-306 Course title: Chemical Engineering Laboratory-IV

Report on

Crude Tower Simulation Using Aspen HYSYS Submitted To:

Mr. Ahaduzzaman

Mr. Md. Nazibul Islam

Lecturer,

Lecturer,

Department of Chemical Engineering,

Department of Chemical Engineering,

BUET

BUET

Mr. Rajesh Paul

Dr. Md. Iqbal Hossain

Lecturer,

Assistant Professor,

Department of Chemical Engineering,

Department of Chemical Engineering,

BUET

BUET

Noor Mohammad Lecturer, Department of Chemical Engineering, BUET

Crude Tower Simulation Using Aspen HYSYS Md. Touhidul Islam Ummay Hani Rifat Hasan Reza Zannatul Ferdous Mahe Jabeen Taohid Bin Ahmed

1202011 1202012 1202013 1202014 1202015 0902058

Email address: [email protected]

Chemical engineering department Bangladesh University of Engineering and Technology, Dhaka -1000

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Abstract Crude Tower is a crude distillation unit (CDU) system which is the most fundamental process of petroleum refining. This work aimed at the fundamental design of crude tower using Aspen HYSYS.In this project, Crude distillation unit system constituted a furnace, a three phase separator and an atmospheric distillation tower. The atmospheric distillation aims to fraction the crude oil in their products: naphtha, kerosene, gas oil, etc. Steady state simulation of a real crude tower was performed using Aspen HYSYS.

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Acknowledgements First and foremost we would like to thank God because without him none of this would have ever been possible. We would also love to thank our wonderful parents, friends and benefactors who have wished nothing but the best for us. We would also like to give special thanks to our teachers who were constantly patient with us as we were doing the project.

Date: 6.11.2016

Md. Touhidul Islam Student ID: 1202011 Department of Chemical Engineering Bangladesh University of engineering & technology, Dhaka -1000

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Contents Abstract ….……………………………………………………………………………………………...iii Acknowledgements……………………………………………………………………………………...iv Contents……………………………………………………………………………………………….....v List of Figures………………………………………………………………………………………..….vi List of Tables ………………………………………………………………………………………...…vii Chapter 1: Introduction………………………………….…………………………………………….…1 Chapter 2: Process Description…………………………………………………………………………..2 Chapter 3: Simulation Process Description………………………………………………………………3 3.1 Crude Assay…………………………………………………………………………….……4 3.2 Defining Simulation Basis………………………………………………………………..….7 3.3 Oil Characterization……………………………………………………………………….…7 3.4 Preheat furnace……………………………………………………………………………...13 3.5 Three-phase separator………………………………………………………………………..14 3.6 Atmospheric Distillation Unit………………………………………………………………..15

Chapter 4: Process Block Diagram……………………………………………………...……………….18 Chapter 5: Process Flow Diagram………………………………………………………………………..19 Chapter 6: Results and Discussions………………………………………………………………………20 Chapter 7: Conclusion ……………………………………………………………………………………24 References …………………………………………………………..………………………25

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List of Figures Figure 1: TBP vs percent liquid volume. .............................................................................................8 Figure 2: Critical temperature vs percent liquid volume. ....................................................................8 Figure 3: Critical pressure vs percent liquid volume…………………………....................................9 Figure 4: Distribution plot of the oil………………………………………………………...............10 Figure-5: Kerosene Boiling Point Curve……………………………………………………….........11 Figure-6: Diesel Boiling Point Curve………………………………………………………………..12 Figure-7: Installing heater………………………………………………………………………........13 Figure-8: Overview of the heater…………………………………………………………………….13 Figure-9: Installing three-phase separator……………………………………………………………14 Figure-10: Overview of the three-phase separator…………………………………………………...15 Figure-11: Overview of the distillation unit streams………………………………………………....16 Figure 12: Overview of the atmospheric Distillation tower……………………………………….....17 Figure 13: Process block diagram....……………………………………………………………..…..18 Figure 14: Process flow diagram……………………………………………………………………..19 Figure-15: Kerosene Product Stream Properties for the simulation………………………………….20 Figure-16: Diesel Product Stream Properties for the simulation……………………………………..21 Figure-17: Temperature vs tray position in the distillation column…………………………………..22 Figure-18: Flow rate vs tray position in the distillation column……………………………………...22 Figure-18: Overview of the process……………………………………………………………….….23

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List of Tables Table 1: Assay Data for Light Crude………………………...........................................................4 Table 2: Assay Data for Medium Crude………………………………..........................................5 Table 3: Assay Data for Heavy Crude………………………………….........................................6

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Introduction Today, distillation of crude oil is an important process in almost all the refineries. Crude distillation is the process of separating the hydrocarbons in crude oil based on their boiling point. The crude oil fractioning is very intensive process. The complexity due to large number of products, side stripper, and pump around made the task of improving energy efficiency into tedious. Aspen HYSYS Engineering is a market leading suite of products focused on process engineering and optimization. Process modelling analysis and design tools are integrated and accessible through Aspen HYSYS and Aspen Plus. Steady state simulation of a real crude tower was performed using Aspen HYSYS.

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Process Description Distillation of crude oil or petroleum refers to fractioning crude oil into the following cuts: gas, naphtha, JP or kerosene, light and heavy gas oil and atmospheric residue. Generally, it is used to make the separation in one single column, which operates under a pressure slightly higher than the atmospheric one, possessing side extractions. Nowadays, distillation unit of crude oil is a fractionation single unit, on contrast with a set of units that were the first fractionation units. The crude oil feed to a fractional distillation tower is heated by flow through pipe arranged within a large furnace. The heating unit is known as a pipe-still furnace, and the heating unit and the fractional distillation tower make up the essential parts of a distillation unit. The crude oil feed is heated by furnace to a predetermined temperature. The vapor is held under pressure in the pipe-still furnace until it discharges as a foaming stream into the fractional distillation tower. Here the vapors pass up the tower to be fractionated into light and heavy gas oil, JP or kerosene, and naphtha. While the nonvolatile or liquid portion of the feed descends to the bottom of the tower to be pumped away as a bottom product. The stripping section is the part of the tower below the point at which the feed is introduced, the more volatile components are stripped from the descending liquid. Above the feed point, the rectifying section, the concentration of the less volatile components in the vapor is reduced. The tower is divided into a number of horizontal sections by metal trays, and each of them is equivalent to a distillation unit. The feed to a tower may be at any point from top to bottom with trays above and below the entry point, depending on the kind of feedstock and the characteristics desired in the products. The temperature of the trays is progressively cooler from bottom to top. The bottom tray is heated by the incoming heated crude oil feed. As the hot vapors pass upward in the tower, condensation occurs onto the trays until refluxing (simultaneous boiling of a liquid and condensing of the vapor) occurs on the trays. Vapors pass upward through the tower, whereas the liquids spill onto the tray below, and so on. Until the heat at a particular point is too intense for that fluid to remain in liquid condition; then it becomes vapor and joins the other vapors passing upward through the tower. The whole tower thus simulates a set of several distillers, with the composition of the liquid at any point or any tray remained fairly constant. This allows part of the refluxing liquid can be collected at various points as side stream product.

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Simulation Process Description Aspen HYSYS was used for the simulation of this process. The Aspen HYSYS software application performs process simulation by carrying out material and energy balances over the process unit. In addition, the Aspen Process Economic Analyzer (Aspen-PEA) tool can be used to obtain an economic analysis of any proposed design. In using Aspen HYSYS, project goals was achieved within a certain degree of accuracy. Aspen HYSYS is an application that provides models for the analysis of the feasibilities of processes. It is often applied in the study and investigation of several operating parameters on various processes. It is an effective tool, offering a high degree of efficiency in accomplishing process design. The flexibility accompanying the logical and consistent approach to how HYSYS delivers its capabilities makes it an extremely efficient multipurpose simulation process tool. The preferred fluid package for the process under consideration is Peng-Robinson equation of state (EOS) since it can handle the hypothetical components (pseudo-components). Pseudo-components are coded variables used to simplify design construction and model fitting. The crude oil feed properties are provided as a crude assay which is essentially the chemical evaluation of crude oil feedstock by petroleum testing laboratories. Once the crude oil feed has been specified in Aspen HYSYS, it undergoes some pre-treatment after which it is fed into the atmospheric distillation tower. Within the distillation unit, it is distilled into naphtha, diesel kerosene, AGO and heavy distillate (atmospheric residue). The main purpose of the project is designing a crude tower. In order to reduce the complexity of the design project, a three phase separator has been used in place of pre-flash process. Pre-treating of crude oil feed Figure 1 shows our proposed process flow diagram (PFD) developed using Aspen HYSYS. A crude oil stream is fed to the furnace at the rate of 5893 lbmol/h, a temperature of 100°F and a pressure of 314.7 psia. The exiting crude stream enters then enters a three phase separator where three streams of vapor, light liquid and heavy liquid are withdrawn to form the feed for the atmospheric tower T-100. Light liquid which is named as Oil enters the atmospheric distillation column at a molar flow rate of 5893 lbmol/hr, pressure of 294 psia and temperature of 100°F. The atmospheric tower T-100 is a column having 30 trays in which the feed enters the tower at the 15th tray.

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Table-1: Assay Data for Light Crude

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Table-2: Assay Data for Medium Crude

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Table-3: Assay Data for Heavy Crude

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Defining the Simulation Basis The foremost step is the selection of lighter components and the appropriate thermodynamic method. The thermodynamic fluid package selected is Peng Robinson, equation of state which is recommended for the petroleum components. Since the exact composition of the crude is unknown and is defined in terms of distillation temperatures the feed developed is a combination of pure library components (lighter components) and pseudo components. The lighter components, methane, propane, i-butane, n- butane, i-pentane, n-pentane and hexane are added to the pure component library. Developing Crude Oil Feed or Oil Characterization The data from the crude assay is used to define the petroleum pseudo-components. The pseudo components are the theoretical components that are not readily available in the component library and have to be defined. The data from the pure component library are used to represent the defined light components in the crude oil. It is required to input the laboratory distillation curve (TBP or ASTM data) and any bulk property such as Molecular Weight, Density, or Watson K Factor. It should be noted that the more the information is provided to the simulation, the accuracy of the property prediction is improved. In this study, the light end composition, TBP distillation curve, density, viscosity are used in characterizing the oil. Each crude type is characterized separately and finally the required crude oil blend is defined and installed into the flow sheet. The calculated TBP data by HYSYS for the given crude is compared to the input data to identify any inaccuracies.

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Figure-1: Temperature vs percent liquid volume

Figure-2: Critical temperature vs percent liquid volume

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Figure-3: Critical pressure vs percent liquid volume

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Figure-4: Distribution plot of the oil

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Figure-5: Kerosene Boiling Point Curve

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Figure-6: Diesel Boiling Point Curve

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Installing the Preheat furnace The furnace is an important constituent in the crude distillation unit. Typically in refineries, the crude oil is heated to a temperature that enables overflash conditions in the main crude distillation column. The concept of overflash is that the crude is heated to such a temperature that enables an additional 5 % vaporization with respect to the residue product. In other words, the residue fraction vapors amounting to 5 % of the total volume of the crude oil are desired.

Figure-7: Installing heater

Figure-8: Overview of the heater

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Installing the three-phase separator

In this case a 3-phase separator is used to simulate the Desalter. A 3-phase separator in general is used to separate the feed into vapor light liquid and heavy liquid (aqueous phase). The water phase is considered as the pure phase and thereby we neglect any effects of salt in both water and oil phase. A calculation block can be used to set the proper flow of another water stream based on the desired residual water content of the treated crude oil. It can also be simulated using a component splitter.

Figure-9: Installing three-phase separator

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Figure-10: Overview of the three-phase separator

Installing the Atmospheric Distillation Unit Crude oil is a mixture of light molecular weight hydrocarbons to high molecular weight components. In petroleum refining usually boiling point ranges are used instead of mole fractions. The crude oil refineries are highly nonlinear, complex and integrated system used for the refining and production of crude oil into end products such as gasoline, naphtha, kerosene, diesel, and vacuum gas oil.

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Figure-11: Overview of the distillation unit streams

Adding the side operations to the column Side Strippers are added to the column in order to improve the quality of the four products (Kerosene-I & II, Diesel, and AGO). The steam is specified to enter at the bottom of the side stripper and the vapor from the top of the stripper is fed to the column again. The side stripper is simulated using the prebuilt side operations available in the simulation. For each stripper, the product flow is specified to meet the degrees of freedom. In some cases the column also consists of side rectifiers. In addition three pumparounds are defined by adding the pump around coolers each for the Heavy Naphtha, kerosene-I and Diesel.

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Figure 12: Overview of the atmospheric Distillation tower

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Process Block Diagram

Figure 13: Process block diagram

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Process Flow Diagram

Figure 14: Process flow diagram

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Results and Discussion

Figure-15: Kerosene Product Stream Properties for the simulation

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Figure-16: Diesel Product Stream Properties for the simulation

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Figure-17: Temperature vs tray position in the distillation column

Figure-18: Flow rate vs tray position in the distillation column

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Figure-1 shows true boiling point vs liquid volume percent by which crude oil can be characterized. Figure-2 and figure-3 shows critical temperature vs percent liquid volume and Critical pressure vs percent liquid volume.Figure-4 shows the distribution plot of the crude oil.Figure-17 and figure18 shows the temperature and molar flow rate variation of crude oil in the different stage of distillation column

Figure-18: Overview of the process

Figure-18 shows the input output stream specifications of different unit operation.

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Conclusion This work has considered a fundamental design of crude tower consisting of a furnace, a three phase separator and an atmospheric distillation tower with minimal number of stages/plates, pump around and strippers of the columns. Simulation software is one of the best tools for a crude oil refinery. This can be used during the conceptual design as well during the entire lifespan of the equipment's. Aspen HYSYS enables the simulation of very complex crude distillation systems in an easy manner. The goal is achieved by using Aspen, which provide capability to design the entire process accurately. For the analysis of the crude distillation unit simulated and experimental curves of kerosene, light gas oil and true boiling point curve of atmospheric residue is taken into account. The optimization can be done very easily, together with the advanced process control tools, make it profitable in the operation in real time. The goal is achieved by using Aspen, which provide capability to design the entire process accurately.

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References 1. K. Liebmann, V. R. Dhole. Integrated Crude Distillation Design.European Symposium on Computer aided Process Engineering. Vol. 5, pp. 119-124, New Jersey, 1995. 2. Chiyoda. “Process and Operating Manual for Crude Distillation Unit” Chiyoda Chemical Engineering, pp. 84-125. Tokyo, 1980. 3. www.aspentech.com.paper 4. D.M. Himmeblau. “Basic Principles and Calculation in Chemical Engineering, Prentice Hall, pp. 76-82, New Jersey, 2001. 5. S.M. Brown. The drive for Refining Energy Efficiency, Global Technology Forum. The European Refining Technology Conference, pp. 14-30, Berlin, 1998. 6. C.D. Holland. “Multicomponent Distillation” Prentice Hall Englewood Cliff, pp. 6089, New Jersey, 1963. 7. M.J. Box. “A New Method of Constrained Optimization and a Comparison with other Methods,” Computer J., Vol. 8, pp. 42-4, Ontario, 1965. 8. J.L. Kuesterand, J.H. Mize. “Optimization Techniques with FORTRAN,” McGrawHill Book Co., pp. 35-108, New York, 1973. 9. D.M. Himmeblau, E. Thomas. “Process Optimization and Simulation, Prentice Hall, pp. 45-90, New Jersey, 2005.