HDA Simulation Laboratory - 054330

045330 – Simulation Laboratory

© D. R. Lewin 2004

Objectives. This course provides students with the knowledge and experience to use a process simulator effectively for the analysis and synthesis of process flowsheets. The topics covered are:

1. Getting started with HYSYS. 2. Solving material and energy balances for recycle processes. 3. Selection the appropriate thermodynamic package. 4. Modeling heat exchangers using HYSYS. 5. Modeling PFRs using HYSYS. 6. Modeling CSTRs using HYSYS. 7. Modeling separation devices using HYSYS: from flash to distillation.

Note that topics 1-4 cover material for which you have already learned the theory, while topics 5-7 support courses that you are learning this semester. You are expected to progress through the course material at your own pace, using multimedia instruction modules in a pre-arranged order. At the end of each lesson, you will be able required to pass a computerized quiz. If you pass the test, you can continue to the next lesson. During the course of the semester, you will assemble portions of a flowsheet for the manufacture of a commodity chemical. The course grade will be given for an engineering report describing the overall project. At least five lab sessions, including the last two weeks of the semester, will be spent working on the project in class time. Exercises. The course has been designed so that you make the best use of your time in the exercise sessions. Most of the instruction on the usage of HYSYS, and a large part of the course-work will be carried out during these sessions. Attendance of the exercise sessions is mandatory, and you will be given a score of 20% just for attending classes (this must be a first at the Technion...). Quizzes. Most exercise sessions end with a quiz, which is intended to check that you have adsorbed and understood the material in the exercise. You need to score sufficiently high in the quiz to be eligible to continue to the next session. However, you can take the quiz as many times as you need to, noting that some of the questions may change. Note also, that your scores on the quizzes do not affect your final grade. Homework. There will be no homework set, but you are expected to complete the tasks associated with each exercise before the next one. Project. The main part of the course grade (80%) will be given for a simulation project, which will be submitted in pairs on the last day of term. You will be given portions of this project to work on as the semester progresses. Reserve Duty and other Unfortunate Occurrences. Students called to reserve duty should contact Prof. Lewin as soon as possible on receipt of the call-up papers. Please seek help either with your exercise demonstrator or with Prof. Lewin to make up for missed exercises.


© D. R. Lewin 2004

Lesson 1: Getting Started with HYSYS.Plant.

The materials supporting a course in material and energy balances assume that that at least four hours of computer laboratory time is allocated to the exercises. A self-paced approach using the multimedia allows you to bring yourself “up-to-speed” on the use of a process simulator to develop and solve material and energy balances of process flowsheets involving simple models of unit operations and recycles. The following sequence of modules is recommended (to be continued next week):

1st step: Under Principles of Process Flowsheet Simulation, access Getting Started in HYSYS (overview). Its main menu consists of four sections (1. Define the Fluid Package, 2. Set Up the Simulation, 3. Convergence of Simulation, and 4. Advanced Techniques). You should review the module Property Package in the first section, and the first three modules in the second section on Setting Up the Simulation.

2nd step: At this point, you should be ready to construct and solve a relatively simple example. The first tutorial supporting a course in M&E balances, Ammonia/Water Separation, is appropriate. You should follow the multimedia while at the same time develop your version of the simulation using HYSYS.Plant. Make sure that you save a copy of your simulation, for possible future use.

3rd step: Complete WebCT Quiz 1 to acquaint yourself with their usage.


© D. R. Lewin 2004

Lesson 2: Chemical Engineering Principles and Material and Energy Balances

We continue the coverage of basic skills for the solution of material and energy balances started last week:

1st step: Begin by reviewing the section Getting Started in HYSYS - 3. Convergence of Simulation. Study the three modules that cover the implementation of recycles: Setting up Recycle, Setting Convergence Parameters, and Dealing with Multiple Loops.

2nd step: At this point, you should try to set up and solve a flowsheet involving material

recycle. The second tutorial supporting a course in M&E balances, Ethylchloride Manufacture, is appropriate. You should follow the multimedia while at the same time develop your version of the simulation using HYSYS.Plant. Make sure that you save a copy of your simulation, for possible future use.

3rd step: Continue reviewing items in Getting Started in HYSYS - 3. Convergence of Simulation, and Getting Started in HYSYS - 4. Advanced Techniques. The most important features that should be covered are the materials that support for the use of the Spreadsheet and Databook, to assist in sensitivity analysis, covered in the modules: Spreadsheet and Case Study (HYSYS Databook).

4th step: Complete WebCT Quiz 2, to test what you have learned so far. You need to pass this test to be able to move onto more advanced materials next week.


© D. R. Lewin 2004

Lesson 3: Selecting Thermo Package/Adjust The selection of the correct method to estimate VLE (vapor-liquid equilibrium) and

VLLE (vapor-liquid-liquid equilibrium) thermodynamic relationships is crucial for meaningful process simulation. In this lesson, we shall learn how to apply several recommendations to help us get this right. In the second part of the lesson, we shall review more methods to control the results of simulations, namely the usage of Adjust.

1st step: Start by reviewing the module on Physical Property Estimation – Package Selection. Compare the recommendations suggested by Bob Seader and Eric Carlson for the appropriate thermo package for a mixture of water- and ethanol at 2 bar. For this mixture, construct a T-x-y diagram using the HYSYS-Excel macro. Make sure that you save a copy of your simulation, for possible future use.

2nd step: It is often desirable to force HYSYS to converge a process at a desired value of an output or parameter. For example, we can manipulate the length of a plug flow reactor so that the conversion is at the desired value, or to manipulate the purge stream in a recycle process to fix the amount of impurities in the recycle stream. These manipulations are performed in HYSYS using the adjust object. Review the module describing its use (Review the module Getting Started in HYSYS – Convergence of Simulation – Adjust):

3rd step: Complete WebCT Quiz 3, to test what you have learned so far. You need to pass this test to be able to move onto more advanced materials next week.


© D. R. Lewin 2004

Lesson 4: Heat Exchanger Design

The multimedia includes a section that provides a self-paced overview on heat

transfer equipment in general and the models available in HYSYS.Plant in particular. Follow this sequence:

1st step: In the first part of the exercise session, you should review the entire section on Heat Exchangers in the multimedia. This consists of modules describing the simple heater/cooler and the more rigorous heat exchangers. The modules each illustrate the use of the models in example applications.

2nd step: Review the tutorial Toluene Manufacture, while at the same time, develop your

own version of the simulation using HYSYS.Plant. Make sure that you save a copy of your simulation, for possible future use.

3rd step: Complete WebCT Quiz 4, to test what you have learned so far. You need to pass this test to be able to move onto more advanced materials next week – the simulation of a part of your final project!


© D. R. Lewin 2004

Lesson 5: Project – Part 1

Now that you have mastered the basics of HYSYS.Plant, you are ready to tackle something more challenging. We will use this lesson to build a simulation of the reaction section of a process for the manufacture of benzene from toluene. This portion of the process will later be integrated with other portions that you will construct in the course of the semester.

SIMULATION OF THE TOLUENE HYDRODEALKYLATION PROCESS

This process was used actively following World War II, when it became favorable to

convert large quantities of toluene, which was no longer needed to make the explosive TNT, to benzene for use in the manufacture of cyclohexane, a precursor of nylon. The main reaction path is: C7H8 + H2 → C6H6 + CH4, which is accompanied by the side reaction: 2C6H6 → C12H10 + H2. Laboratory data indicate that the reactions proceed irreversibly without a catalyst at temperatures in the range of 1,200 - 1,270 oF with approximately 75 mol% of the toluene converted to benzene and approximately 2 mol% of the benzene produced in the hydrodealkylation reaction converted to biphenyl. Since the reactions occur in series in a single processing unit, just a single reaction operation is positioned in the flowsheet, as shown in Figure 1. The plant capacity is based on the conversion of 274.2 lbmol/hr of toluene, or approximately 200 MMlb/yr, assuming operation 330 days per year.

Figure 1. Reaction operations for the hydrodealkylation of toluene.

One distribution of chemicals involves a large excess of hydrogen gas to prevent

carbon deposition and absorb much of the heat of the exothermic hydrodealkylation reaction. Furthermore, to avoid an expensive separation of the product methane from the hydrogen gas, a purge stream is utilized in which methane leaves the process, unavoidably with a comparable amount of hydrogen. Because the performance of the separation system, to be added in the next synthesis step, is unknown, the amount of hydrogen that accompanies methane in the purge stream is uncertain at this point in synthesis. Hence, the distribution of

Hydrodealkylation

H2CH4C6H6C7H8C12H10

C7H8 + H2 → C6H6 + CH4

2C6H6 → C12H10 + H2

H2549 lb/h

C7H825,262 lb/h

CH44398 lb/h

C6H620,989 lb/h

C12H10423 lb/h


© D. R. Lewin 2004

chemicals in Figure 2 is known incompletely. Note, however, that the sources and sinks of the chemicals can be connected and an estimate for the toluene recycle prepared based on the assumption of 75 mol% conversion and complete recovery of toluene from the effluent stream. Also, at 1,268 oF and 494 psia, a typical operating pressure, the heat of reaction is 5.84×106 Btu/hr, as computed by HYSYS.Plant using the Conversion Reactor object and the SRK equation of state.

Figure 2. Distribution of chemicals for the hydrodealkylation of toluene.

One selection of separation operations, shown in Figure 3, involves a flash separator at 100 oF and a slightly reduced pressure, to account for anticipated pressure drops, at 484 psia. The liquid product is sent to a distillation train in which H2 and CH4 are recovered first, followed by C6H6 and then C7H8. Note that the pressures of the distillation columns have not yet been entered. These are computed to permit the usage of cooling water in the condensers; that is, the pressures are adjusted to set the bubble- or dew-point temperatures of the vapor streams to be condensed at 130 oF or greater.

H2549 lb/h

+ ?

C7H825,262 lb/h

Hydrodealkylation1268°F

Heat liberatedby reaction5.84x106 Btu/h

H2CH4C6H6C7H8C12H10

}

CH4 4398 lb/hH2 ?

C6H620,989 lb/h

C12H10423 lb/h

8,421 lb/h


© D. R. Lewin 2004

Figure 3. Flowsheet including the separation operations for the hydrodealkylation of toluene.

The next synthesis step involves task integration, that is, the combination of operations into process units. In one task integration, shown in Figure 4, reactor effluent is quenched rapidly to 1,150 oF, primarily to avoid the need for a costly high-temperature heat exchanger, and is sent to a feed/product heat exchanger. There, it is cooled as it heats the mixture of feed and recycle chemicals to 1,000 oF. The stream is cooled further to 100 oF, the temperature of the flash separator. The liquid from the quench is the product of the reactor section, yet a portion of it is recycled to quench the reactor effluent. The vapor product is recycled after a portion is purged to keep methane from building up in the process. This recycle is compressed to the pressure of the feed chemicals, 569 psia. Returning to the feed/product heat exchanger, the hot feed mixture leaves at 1,000 oF and is sent to a gas-fired furnace for further heating to 1,200 oF, the temperature of the feed to the reactor. Note that the gases are heated in a tube bank that resides in the furnace, and hence a high pressure drop is estimated (70 psia). On the other hand, the hydrodealkylation reactions take place in a large-diameter vessel that has negligible pressure drop. Clearly, at a later stage in the process design, these pressure drops, along with pressure drops in the connecting pipes, can be estimated. Normally, however, small errors in the pressure drops have only a small impact on the equipment sizes and costs as well as the operating costs.

H2549 lb/h+ ?70°F 569 psia

C7H825,262 lb/h75°F, 569 psia

Hydrodealkylation1268°F, 494 psia

Flash100°F484psia

5.84x106 Btu/h

C7H8

8,421 lb/h

C12H10423 lb/h

PurgeCH4 4398 lb/hH2 ?

FuelCH4 ?H2 ? C6H6

20,989 lb/h


© D. R. Lewin 2004

Figure 4. Flowsheet showing task integration for the toluene hydrodealkylation process.

The process will be simulated in parts. The first simulation involves the reactor section

of the proposed process, and the objective of the simulation is to provide a better understanding of its performance. Note that several assumptions are made concerning the recycle streams, so as not to complicate the analysis. Subsequently, in Lessons 9 and 10, the separation section is examined, with specifications made for the flow rates and compositions of the product streams. Finally, after obtaining a better understanding of the performance of these two sections, the entire process will be simulated in Lessons 12 and 13. In this simulation, the flow rates and compositions of the recycle and purge streams are computed to satisfy material and energy balances. Of course, during any of these simulations, the specifications can be varied to gain a better understanding of the performance of the process.

494 psia

1200°F1000°F 564 psia

H2 549 lb/h + ? 70°F 569 psia

C7H8 25,262 lb/h 75°F, 569

Flash 100°F484 psia

C7H8

8,421 lb/h

C12H10 423 lb/h

Purge CH4 4398 lb/h H2 ?

Fuel CH4 ? H2 ? C6H6

20,989 lb/h

1268°FReactor

Pump

Furnace ∆P=70 psia

∆P=0 psiaHeat Exchanger

1150°F

494psia

CW 90°F

120°F

Compressor

484 psia

569 psia


© D. R. Lewin 2004

Your task for today - Simulation of the Reactor Section!

1st step: The reactor section of the process is shown in Figure 5, as are the conditions for the feed and two recycle streams. The flow rate of the quench stream should be such that the reactor effluent is quenched to 1,150 oF. Conversion of toluene in the reactor is 75 mol%. Two mole percent of the benzene present after the first reaction occurs is converted to biphenyl. Use HYSYS.Plant to perform material and energy balances with the SRK equation of state.

100 F

Figure 5. Reactor section of the toluene hydrodealkylation process.

2nd step: Complete WebCT Quiz 5, which will test the accuracy of your solution. You need to pass this test to be able to move onto more advanced materials next week.

mailto:[email protected]



© D. R. Lewin 2004

Lesson 6: Reactors, Part 1

The materials supporting the usage of HYSYS.Plant for the simulation of chemical reactors will cover two weeks of the course. Today, we will follow this sequence:

1st step: Up until now, we have approximated reactors as stoichiometric reactors, defined by their conversion only. In the first part of the exercise session, you should review the section on the more realistic equilibrium and kinetic reactions.

2nd step: Begin to review the section on chemical reactors. Cover equilibrium and Gibbs

reactors, and PFRs.

3rd step: Review the tutorial Ammonia Converter, while at the same time, develop your

own version of the simulation using HYSYS.Plant. Make sure that you save a copy of your simulation, for possible future use. There is no quiz today, kids!


© D. R. Lewin 2004

Lesson 7: Reactors, Part 2

We continue the coverage of chemical reactors that we started last week. Today, we will follow this sequence:

1st step: Complete the coverage of chemical reactors, focusing on CSTRs. Cover also CSTR Theory, accessed from the module covering how to set up CSTR models using HYSYS (CSTR Setup). As you work through the module, set up your own simulation of a CSTR for the production of propylene glycol. Make sure that you save a copy of your simulation, for possible future use.

2nd step: Complete WebCT Quiz 7, to test what you have learned so far. Once you pass this quiz you are ready to move onto the next phase of the course – learning how to set up separation systems with HYSYS.Plant.


© D. R. Lewin 2004

Lesson 8: Separations – From Flash to Distillation

The materials supporting a course in separations assume that the students have already

covered most of the theory on multicomponent separations (flash and distillation). The following sequence of modules is recommended:

1st step: Under Separations - Overview, review the material covering flash. See the module on VLE K-values, to review how VLE calculations are carried out. Then, access the module of Flash theory, to see how a flash unit works (also shown in a video). Finally, you can see how a flash unit is setup in HYSYS (this is a do-it-yourself module).

2nd step: Under Separations - Overview, review the material covering distillation. The

sequence of modules shows how a multicomponent distillation column is designed in which the Component Splitter assists in the selection of operating pressure, the Short-cut Column, using FUG methods, is employed to estimate the number of stages, the location of the feed tray, and the required reflux ratio, and finally the Column is used for the rigorous solution of MESH equations.

3rd step: Complete WebCT Quiz 8, to test what you have learned so far. You need to pass this test to be able to continue working on the next stage of the project.


© D. R. Lewin 2004

Lessons 9 and 10: Project – Part 2

Now that you have mastered modeling separation units in HYSYS.Plant, you are ready to apply this knowledge to the simulation of a separation system. We will use this lesson to build a simulation of the separations section of a process for the manufacture of benzene from toluene. This portion of the process will later be integrated with the reaction section that you simulated in Lesson 5.

SIMULATION OF THE TOLUENE HYDRODEALKYLATION PROCESS (CONT’D)

As discussed in Lesson 5, a feed stream of 1.5 lbmol/hr H2, 19.3 lbmol/hr CH4, 262.8

lbmol/hr C6H6, 84.7 lbmol/hr C7H8, and 5.1 lbmol/hr C12H10, at 100 oF and 484 psia, is to be

separated by two distillation columns into the following products:

Product 1: containing 99% of the feed methane content, and a methane mole fraction of no

less than 0.9.

Product 2: rich in benzene with a benzene mole fraction of no less than 0.99.

Product 3: rich in toluene and bi-phenyl with a pollutant mole fraction of no more than 1%

Using HYSYS.Plant, simulate a sequence of two columns in which H2 and CH4 are removed

in the first column as Product 1, followed by Products 2 and 3 in the second column. Use the

SRK equation of state to estimate VLE equilibrium. Specify a reflux ratio equal to 1.3 times

the minimum. Use design specifications to adjust the isobaric column pressures so as to

obtain distillate temperatures of 130 oF or more; however, no column pressure should be less

than 20 psia. Also, specify total condensers except note that a partial condenser is used when

H2 and CH4 are taken overhead.

Explore alternative separation sequences. Note that the two columns above can be sequenced

in the opposite order (i.e., Remove the products in the opposite order – Product 3 first, and

then Products 2 and 1). Furthermore, the possibility of using three distillation columns was

discussed in Lesson 5. Try our at least one of these alternatives and discuss the results.


© D. R. Lewin 2004

Lesson 11: Optimization

HYSYS includes an optimizer, which can assist you to improve the quality of simulated results. To use this effectively, you should know which process parameters can be changed to effect the intended result. Today’s lesson will provide instruction on how to use the HYSYS optimizer effectively.

1st step: In the main menu of Getting Started in HYSYS, access the module Optimizer, which provides instruction on the basic usage of the HYSYS optimizer. The module shows how to maximize the venture profit for the Ethylchloride process, which was simulated in Lesson 2. As you review it, develop your own version of the simulation using HYSYS.Plant, and make sure that you save a copy of your simulation, for possible future use.

2nd step: After having mastered basic optimization, now try a more advanced example,

which optimizes the operating conditions in a multi-draw distillation column to maximize the separation of a feed of alkanes. This module is the tutorial Tower Optimization, and as you review it, you should develop your own version of the simulation using HYSYS.Plant. Make sure that you save a copy of your simulation, for possible future use.

3rd step: Complete WebCT Quiz 11, to test what you have learned today. Once you pass this quiz you are ready to start working on the final project!


© D. R. Lewin 2004

Lessons 12 - 13: Project – Part 3

Now that you have mastered all of the building blocks in HYSYS.Plant, and you have developed the reaction and separation sections of the process for the manufacture of benzene from toluene, you will now integrate both parts of the process into a single flowsheet, while applying some engineering judgement. Here is what you have to do:

1. Complete a simulation of the entire process for the hydrodealkylation of toluene. The process must satistfy ALL of the following specifications (simultaneously):

a. Benzene product flow rate must be at least 20,000 lb/hr b. Benzene product must have a benzene mole fraction of 0.99 c. Feed stream to the heat exchanger (after the quench) must be at 1150 oF. d. Molar ratio of hydrogen/toluene entering the reactor must be 1.5. e. Fuel gas product (methane and hydrogen) – which is the combination of the purge

after the separator and the overhead product of the first distillation column – must have no more than 1% (molar) pollutants.

2. Bonus sections: To qualify for bonuses, you need to do at least one of the following modifications:

a) Suggest an alternative plant structure (additional separation between toluene and biphenyl or a side draw in the second column). Discuss the differences and relative advantages of the different structures (heat requirements, equipment sizes, etc.)

b) Suppose the reboiler of the benzene column develops a fault, and only 70% of its design duty is available. Discuss the effect of this fault on the five specifications you were able to satisfy in Part 1. What requirements can still be met in light of this problem

c) Replace the reactor with a PFR, referring to the Appendix of this document, and discuss the results. How does the dependence on concentrations influence the solution. Are the assumptions for the conversions (75% and 2%) accurate?

d) Setting the hydrogen feed flowrate to 450 lbmoles/hr, perform a case study changing the two purge ratios (between 0.05 and 0.95 each) to find the range of feasibility such that the following sepecifications are met:

a. Gas recycle mass flow of no more than 2,000 lb/hr. b. Liquid recycle mass flow (rich in toluene) no larger than 5,000 lb/hr. c. Benzene product mass flow rate no less than 16,500 lb/hr. d. Molar ratio between hydrogen and toluene entering the reactor no less than 1.5. e. Benzene product contains no less than 99% benzene by moles.

The project will be completed by students working in pairs. The project will be submitted as a report in WORD, completed according to a report format as given (see the website for more information, and please follow the instruction carefully). The following items need to be submitted to the webct site as a zipped file, named group_xy.zip (where xy is your group number) to to course website:


© D. R. Lewin 2004

1. Report in WORD. A template for the report is provided on the website.

2. A separate HYSYS case file for each part of your solution.

The report should include the following items:

a. Cover page, including the names and i.d. numbers of the group members and the group number.

b. Contents page. c. Detailed list of HYSYS file names and a brief description of their contents. d. Executive summary of up to 1,000 words, which summarize the work accomplished and

describe the main results. This summary should be sufficient to judge the quality of your work, so make it good!

e. Main body of the report (refererred to in the execuitive summary), containing: i. Description of work-steps, namely, the reactor and separation sections

and their combination in the overall flowsheet. ii. Description on the completion each of the bonus sections attempted, and

the conclusions obtained. iii. Presentation of graphs and tables as needed.

Note: we are looking for evidence of the correct use of engineering judgement in all steps of the project. Show us that you know what you are doing!

You must request a group number by sending a list of two names to Alex by email to: [email protected]

The deadline for submission of your project to the website is 15th JULY, 12:00. Note that the site not be available for project submissions after that time.

Grading: As you know, the project is worth 80% of the course grade. The maximum project grade depends on whether or not a group attempts at least one of the bonus sections, as per the table below.

Maximum Project Grade Possible No bonus questions attempted 60 One bonus question attempted 80

At least two bonus questions attempted 100

Warning: Copied work is unacceptable. In the event that copies of the same work, or variations of the same piece of work, is submitted by two or more groups, all groups will receive a grade of zero for the project.



© D. R. Lewin 2004

Appendix: Kinetic Data for Reactions for Hydrodealkylation of Toluene. Source: http://www.che.ttu.edu/classes/che5000/EmetsThesis.pdf

Gas Constant: R= 3.57458 [BTU/lbmole-K] -------------------------------------------------------- E1=2.5616×104×3.57458 = 91,566 [BTU/lbmole] E2=1.5362×104×3.57458 = 54,913 [BTU/lbmole] E3=1.2237×104×3.57458 = 43,742 [BTU/lbmole]

http://www.che.ttu.edu/classes/che5000/EmetsThesis.pdf

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