Workshop 12 Simulators for Design Across the Curriculum ASEE Summer School, Colorado, August 2002

Transcription

1 Workshop 12 Simulators for Design Across the Curriculum ASEE Summer School, Colorado, August 2002 Workshop Leaders: Daniel R. Lewin (DRL), Dept. of Chemical Engineering, Technion. Warren D. Seider (WDS), Dept. of Chemical Engineering, Penn. Workshop Objective: During the senior year design project, teams of students carry out an integrated process design, determining its technical, environmental, safety, and economic feasibility. Due to the problem scale, this inevitably involves the use of a process simulator to formulate and solve the material and energy balances, with phase and chemical equilibria and chemical kinetics, for cost estimation and economic evaluation. The availability of a reliable process model allows the design team to assess rapidly the economic potential for alternative designs, as well as to derive operating conditions using optimization methods that incorporate economics. To ensure that students are prepared to meet the challenges of the design project, they should be prepared for the competent and critical use of the process simulators. This is best achieved by a gradual exposure to aspects of their use through various exercises in the core courses. This workshop, which is intended for chemical engineering faculty, shows one way to achieve this objective. Contents: This document is an assembly of: (1) suggested instruction sequences, using the multimedia CD-ROM (Using Process Simulators in Chemical Engineering: A Multimedia Guide for the Core Curriculum), henceforth referred to as the multimedia, and (2) problem statements and solutions for class exercises and projects using process simulators to support many of the chemical engineering core courses. Materials are included for courses on: Material and Energy Balances, Thermodynamics, Heat Transfer, Separation Principles, and Reactor Design. ASPEN PLUS, HYSYS.Plant, BATCH PLUS, and IPE files used for the solutions of the exercises are also available on this CD. In addition, each participant of Workshop 12 will receive a CD Containing Version 1.2 of Using Process Simulators in Chemical Engineering: A Multimedia Guide for the Core Curriculum. 1

2 HYSYS.Plant Chemical Engineering Principles and Material and Energy Balances 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 the students to bring themselves 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: Session 1: 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). Students should review all three modules in the first section on the fluid package, and the first three modules in the second section on setting up the simulation. Session 2: At this point, the student 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. The student should follow the multimedia while at the same time develop his/her version of the simulation using HYSYS.Plant. 2

3 Session 3: Begin by reviewing material learned so far review the module Do It Yourself (the fifth module under Getting Started in HYSYS - 2. Set Up the Simulation). Next briefly review the section Getting Started in HYSYS - 3. Convergence of Simulation, paying particular attention to the section on Recycle Implementation. Session 4: At this point, the student 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. The student should follow the multimedia while at the same time develop his/her version of the simulation using HYSYS.Plant. Session 5: If additional time is available, the student can complete the review of materials supporting initial use of HYSYS.Plant, i.e., the remaining 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. If time is available, the student should also cover the use of Set and Adjust (in Part 3) and the Optimizer (in Part 4). A project should be assigned to groups of up to three students, to reinforce their acquired capabilities. A typical project definition is provided. 3

4 ASPEN PLUS Chemical Engineering Principles and Material and Energy Balances 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 the students to bring themselves 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. Note that this sequence has not been class-tested using ASPEN PLUS. However, a similar sequence using HYSYS.Plant, on the previous two pages, has been class-tested successfully: Session 1: Under Principles of Process Flowsheet Simulation, access Getting Started in ASPEN PLUS (overview). Its main menu consists of five sections (1. Brief Introduction, 2. Setting Up, 3. Convergence, 4. Sensitivity Analysis, and 5. Sample Problem). Students should review modules 1-3 and 5. Session 2: At this point, the student 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. The student should follow the multimedia while at the same time develop his/her version of the simulation using ASPEN PLUS. 4

5 Session 3: Briefly review the section ASPEN -Getting Started - 3. Convergence, paying particular attention to the section on Recycle. Session 4: At this point, the student 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. The student should follow the multimedia while at the same time develop his/her version of the simulation. Session 5: If additional time is available, the student can complete the review of materials supporting initial use of ASPEN PLUS, i.e., the remaining items in ASPEN - Getting Started - 3. Convergence (especially, Control Blocks), and ASPEN - Getting Started - 4. Sensitivity Analysis. A project should be assigned to groups of up to three students, to reinforce their acquired capabilities. A typical project definition is provided. Three homework problems are suggested: (Exercise A.1) (Exercise A.2) (Exercise A.3) BATCH PLUS BATCH PLUS, an Aspen Tech product, carries out material and energy balances for batch plants and prepares operating schedules (Gantt charts). In the second edition of SSL, we have added material on the synthesis of a process to manufacture tissue plasminogen activator (tpa). Then, a simulation of the tpa process is carried out using BATCH PLUS. For a course on chemical engineering principles and material and energy balances at the sophomore level, this material could be presented with the exercise provided below. The file TPA SYNTHESIS.PDF provide the text that covers the synthesis and simulation steps. 5

6 Material and Energy Balances Example Project Methanol is manufactured in a synthesis loop, in which a mixture of carbon dioxide and hydrogen is reacted to form the methonal product at high pressure: CO H 2 CH 3OH + H 2O S-6 Adiabatic Heater Converter Feed 50 0 C P s S-1 S C S-3 S-5 Purge Cooler S-4 T s Separator Product The synthesis gas fed to the process, illustrated above, is largely composed of hydrogen and carbon dioxide, but with traces of inert gases as in Table 1. Additional specifications for the process are: SRK property predictions should be employed Pressure drops is all units can be neglected Converter feed temperature is set to 400 o C The converter can be approximated as a conversion reactor, operating adiabatically. The reactor conversion depends of the operating pressure, according to Table 2. The reactor effluent is cooled to a temperature of T S using a cooler, and fed to a flash unit, modeled by a separator. Table 1. Process feed stream specification. Composition ( mol %) Hydrogen Carbon dioxide CH Argon 0.1 Flow rate (kgmol/hr) 1000 Temperature ( o C) 50 Pressure (MPa) P S Table 2. Conversion as a function of pressure P S [MPa] CO 2 conversion [%] P S [MPa] CO 2 conversion [%]

7 Your tasks: 1. Solve the material and energy balances for the flowsheet for a purge flow rate of 600 kg/h, and values for P S and T S by group, according to Table 3. Ensure an accuracy of 3 significant figures. Table 3. Operating specifications by student group. Group No. T S ( C) P S (MPa) Group No. T S ( C) P S (MPa) An operating window for the process is defined by a closed polygon in T S Purge space, within which, the following constraints are met: 200 < Purge < 1000 kg/h 0 < T S < 40 o C Mass flow rate of recycle 35 T/hr CO 2 mol. fraction in product 2.5 mol % Mass flow rate of methanol in product 7,200 kg/hr Determine the operating window for the operating pressure for your group in Table 3. Try and estimate the limits of the operating window as accurately as possible, and plot the result as a function of T S and Purge flow rate, as shown below. Ts [ o C] Operating Window Purge [kg/h] HYSYS.Plant Solution 7

8 Exercise A.1 Flash with Recycle Problem (Exercise 3.1, SSL) a. Consider the flash separation process shown below: If using ASPEN PLUS, solve all three cases using the MIXER, FLASH2, FSPLIT, and PUMP subroutines and the RK-SOAVE option set for thermophysical properties. Compare and discuss the flow rates and compositions for the overhead stream produced by each of the three cases. b. Modify Case 3 of Exercise 3.1a to determine the flash temperature necessary to obtain 850 lb/hr of overhead vapor. If using ASPEN PLUS, a design specification can be used to adjust the temperature of the flash drum to obtain the desired overhead flow rate. ASPEN PLUS Solution 8

9 Exercise A.2 Ammonia Synthesis Loop Problem (Example 4.3, SSL) For the ammonia process in Example 4.3, consider operation of the reactor at 932 F and 400 atm. Use a simulator to show how the product, recycle, and purge flow rates, and the mole fractions of argon and methane, vary with the purge-to-recycle ratio. How do the power requirements for compression increase? Example 4.3 Ammonia Process Purge In this example, the ammonia reactor loop: is simulated using ASPEN PLUS to examine the effect of the purge-to-recycle ratio on the purge stream and the recycle loop. For the ASPEN PLUS flowsheet below, the followingspecifications are made: Simulation Unit Subroutine T, F P,atm R1 REQUIL F1 FLASH and the Chao-Seader option set is selected to estimate the thermophysical properties. Note that the REQUIL subroutine calculates chemical equilibria at the temperature and pressure specified, as discussed in the REQUIL module on the multimedia CD-ROM. The combined feed stream, at 77 F and 200 atm, is comprised of: lbmole/hr Mole fraction H N Ar CH ASPEN PLUS Solution 9

10 Exercise A.3 Near-isothermal Distillation (Cavett) Problem (Exercise 3.7, SSL) A near-isothermal distillation process, having multiple recycle loops formulated by R. H. Cavett (Proc. Am. Petrol. Inst., 43, 57 (1963)), has been used extensively to test tearing, sequencing, and convergence procedures. Although the process flowsheet requires compressors, valves, and heat exchangers, a simplified ASPEN PLUS flowsheet is (excluding the recycle convergence units): In this form, the process is the equivalent of a four-theoretical-stage, near-isothermal distillation (rather than the conventional near-isobaric type), for which a patent by A. Gunther (U.S. Patent 3,575,077, April 13, 1971) exists. For the specifications shown on the flowsheet, use a process simulator to determine the component flow rates for all streams in the process. ASPEN PLUS Solution 10

11 Exercise A.4 Scheduling Batch Reactors Problem (New Exercise 4.19, SSL) Debottlenecking Reactor Train. To prepare for this exercise, read the background materials in TPA SYNTHESIS.PDF. These new sections are for the second edition of SSL. When the third tpa cultivator in Section 3.4 is added to the two cultivators in Example 4.1, as shown in Figure 4.25a, a significant time strain is placed on the process because the combined feed, cultivation, harvest, and cleaning time in this largest vessel is long and rigid. Consequently, the remainder of the process is designed to keep this cultivator in constant use, so as to maximize the yearly output of product. Note that, in many cases, when an equipment item causes a bottleneck, a duplicate is installed so as to reduce the cycle time. For this exercise, the third cultivator is added to the simulation in Example 4.1, with the specifications for the mixer, filter, holding tank, heat exchanger 1, and first two cultivators identical to those in Example 4.1. After the cultivation is completed in Cultivator 2, its cell mass is transferred as inoculum to Cultivator 3 over 0.5 day. Then, the remaining media from the mixing tank is heated to 37 F and added over 1.5 day, after which cultivation takes place over eight days. Immediately after the transfer from Cultivator 2 to Cultivator 3, Cultivator 2 is cleaned-in-place using 600 Kg of water over 20 hours. The yield of the cultivation in Cultivator 3 is 11.4 wt% tpa-cho cells, wt% endotoxin, 88.9 wt% water, and wt% tpa. When the cultivation is completed in Cultivator 3, its contents are cooled in a heat exchanger to 4 C and transferred to the centrifuge holding tank over one day, and Cultivator 3 is cleaned using 600 Kg of water over 67 hours and sterilized using the procedure for Cultivators 1 and 2. To eliminate an undesirable bottleneck(s), and reduce the cycle time to 14 days (total operation time of Fermenter 3), it may be necessary to add an equipment unit(s). Print and submit the text recipes and 3-batch schedules for both the original process and the modified process, if debottlenecking is necessary, as prepared by BATCH PLUS. For background materials and BATCH PLUS solution, see TPA SYNTHESIS.PDF 11

12 Material and Energy Balances Solution Sketch of Example Project using HYSYS.Plant 1. The flowsheet is set up and its material and energy balance solved using HYSYS.Plant is a straight-forward fashion. A sample solution file is given as METHANOL_PART1.hsc. 2. The second part of the problem is more interesting. This involves the use of the Spreadsheet, to generate Boolean variables corresponding to the feasibility of each of the three constraints: Recycle: Mass flow rate of recycle 35 T/hr Purity: CO 2 mol. fraction in product 2.5 mol % Production: Mass flow rate of methanol in product 7,200 kg/hr Subsequently, the Databook is used to construct 3D plots involving the Boolean variables as a function of T S and Purge. Sample operating windows in T S Purge space, for flowsheets designed for P S = 5 and 30 MPa are shown in Figure 1, noting that the interpretation of the operating widows is given schematically in Figure 2. In general, the recycle and production constraints lead to lower and upper limits on the allowed purge flow rate, both of which are relatively independent on the separation temperature, T S. In constrast, the purity constraint leads to a lower limit on T S, whose value increases with increasing purge flow rate. As seen in Figure 1, the operating window is significantly more limited for operation at lower pressures. The files METHANOL_PART2_05.hsc and METHANOL_PART2_30.hsc provide sample solutions. (a) (b) Figure 1: Operating windows for (a) P S = 5 MPa; (b) P S = 30 MPa 12

13 T S 40 o C Operating Window Purity Production Recycle 0 o C Purge Figure 2: Interpretation of constraints bounding the operating window. The selection of operating point should consider the cost of energy, which increases significantly as T S decreases, and the equipment costs, which increase exponentially with decreasing purge flow rate. An appropriate choice would be at the top right-hand corner of the operating window. 13

14 Exercise A.1 Solution using ASPEN.PLUS 3.1 a. ASPEN PLUS Flowsheet simulation results can be reproduced using the file EXER3-1A.BKP on the CD-ROM. VP FEED1 M1 F1 FEED2 S2 S5 S3 S4 S1 LP P1 ASPEN PLUS Simulation Flowsheet VP FEED1 FEED2 M1 MIXER S2 F1 FLASH2 S5 S3 P1 PUMP S4* $OLVER01 S4 S1 FSPLIT LP 14

15 ASPEN PLUS Program IN-UNITS ENG DEF-STREAMS CONVEN ALL DATABANKS PURE93 / AQUEOUS / SOLIDS / INORGANIC / & NOASPENPCD PROP-SOURCES PURE93 / AQUEOUS / SOLIDS / INORGANIC COMPONENTS METHANE CH4 METHANE / ETHANE C2H6 ETHANE / PROPANE C3H8 PROPANE / N-BUTANE C4H10-1 N-BUTANE / 1-BUTENE C4H8-1 1-BUTENE / 1,3-BUTA C4H6-4 1,3-BUTA FLOWSHEET BLOCK M1 IN=S5 FEED2 FEED1 OUT=S2 BLOCK F1 IN=S2 OUT=VP S3 BLOCK S1 IN=S3 OUT=LP S4 BLOCK P1 IN=S4 OUT=S5 PROPERTIES RK-SOAVE PROP-DATA RKSKIJ-1 IN-UNITS ENG PROP-LIST RKSKIJ BPVAL METHANE ETHANE E-3 BPVAL METHANE PROPANE E-3 BPVAL METHANE N-BUTANE E-3 BPVAL ETHANE PROPANE E-3 BPVAL ETHANE N-BUTANE E-3 BPVAL ETHANE METHANE E-3 BPVAL PROPANE ETHANE E-3 BPVAL PROPANE N-BUTANE 0.0 BPVAL PROPANE METHANE E-3 BPVAL N-BUTANE ETHANE E-3 BPVAL N-BUTANE PROPANE 0.0 BPVAL N-BUTANE METHANE E-3 BPVAL N-BUTANE 1-BUTENE E-3 BPVAL N-BUTANE 1,3-BUTA E-3 BPVAL 1-BUTENE N-BUTANE E-3 BPVAL 1-BUTENE 1,3-BUTA E-3 STREAM FEED1 SUBSTREAM MIXED TEMP=85 <C> PRES=100 MASS-FLOW METHANE 50 / ETHANE 100 / PROPANE 700 STREAM FEED2 SUBSTREAM MIXED TEMP=85 <C> PRES=100 MOLE-FLOW N-BUTANE 15 / 1-BUTENE 21 / 1,3-BUTA 95 BLOCK M1 MIXER BLOCK S1 FSPLIT FRAC S4 0.5 BLOCK F1 FLASH2 PARAM TEMP=5 <C> PRES=25 BLOCK P1 PUMP PARAM PRES=100 Calculation Sequence SEQUENCE USED WAS: $OLVER01 P1 M1 F1 S1 (RETURN $OLVER01) 15

16 Stream Variables FEED1 FEED2 LP S2 S STREAM ID FEED1 FEED2 LP S2 S3 FROM : S1 M1 F1 TO : M1 M F1 S1 SUBSTREAM: MIXED PHASE: VAPOR VAPOR LIQUID MIXED LIQUID COMPONENTS: LBMOL/HR METHANE ETHANE PROPANE N-BUTANE BUTENE ,3-BUTA TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F PRES PSI VFRAC LFRAC SFRAC ENTHALPY: BTU/LBMOL BTU/LB BTU/HR ENTROPY: BTU/LBMOL-R BTU/LB-R DENSITY: LBMOL/CUFT LB/CUFT AVG MW S4 S5 VP STREAM ID S4 S5 VP FROM : S1 P1 F1 TO : P1 M SUBSTREAM: MIXED PHASE: LIQUID LIQUID VAPOR COMPONENTS: LBMOL/HR METHANE ETHANE PROPANE N-BUTANE BUTENE ,3-BUTA TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F

17 PRES PSI VFRAC LFRAC SFRAC ENTHALPY: BTU/LBMOL BTU/LB BTU/HR ENTROPY: BTU/LBMOL-R BTU/LB-R DENSITY: LBMOL/CUFT LB/CUFT AVG MW Selected Process Unit Output BLOCK: F1 MODEL: FLASH INLET STREAM: S2 OUTLET VAPOR STREAM: VP OUTLET LIQUID STREAM: S3 PROPERTY OPTION SET: RK-SOAVE STANDARD RKS EQUATION OF STATE *** MASS AND ENERGY BALANCE *** IN OUT RELATIVE DIFF. TOTAL BALANCE MOLE(LBMOL/HR) E-15 MASS(LB/HR ) E-10 ENTHALPY(BTU/HR ) E E *** INPUT DATA *** TWO PHASE TP FLASH SPECIFIED TEMPERATURE F SPECIFIED PRESSURE PSI MAXIMUM NO. ITERATIONS 30 CONVERGENCE TOLERANCE *** RESULTS *** OUTLET TEMPERATURE F OUTLET PRESSURE PSI HEAT DUTY BTU/HR E+06 VAPOR FRACTION V-L PHASE EQUILIBRIUM : COMP F(I) X(I) Y(I) K(I) METHANE E E E ETHANE E E E PROPANE E E N-BUTANE E BUTENE ,3-BUTA

18 The results above are for Case 1 (50% bottoms recycle) in Figure For Cases 2 (25% bottoms recycle) and 3 (no recycle), the vapor and liquid product streams are identical to those for Case 1. That is, the product streams and the heat removed from the flash vessel are identical regardless of the amount of recycle. This is because the vapor and liquid product streams are in phase equilibrium at the conditions of the flash vessel. Acyclic Simulation Flowsheet Since the product streams do not change with recycle flow rate, they can be computed at the conditions of the flash vessel. Then, given the recycle fraction, the other streams can be computed. This is accomplished using the following ASPEN PLUS simulation flowsheet. MUL2 MULT S3 VP FEED1 FEED2 MIX1 MIXER S1 D1 DUPL S1A F1 FLASH2 MUL1 MULT S4 P1 PUMP S5 M1 MIXER S2 LP S1B D2 DUPL LPB LPA Using this flowsheet, identical results are obtained. 3.1 b. ASPEN PLUS Flowsheet identical to that in Exer. 3.1a. The recycle flow rate is zero. Simulation results can be reproduced using the file EXER3-1B.BKP on the CD- ROM. ASPEN PLUS Simulation Flowsheet 850 lb/hr VP F T $OLVER02 FEED1 FEED2 M1 MIXER S2 $OLVER01 S2* F1 FLASH2 T S5 S3 P1 PUMP S4 S1 FSPLIT LP 18

19 ASPEN PLUS Program identical to that in Exer. 3.1a with following change and addition: BLOCK S1 FSPLIT FRAC S4 0 DESIGN-SPEC OVHD DEFINE OVHD STREAM-VAR STREAM=VP SUBSTREAM=MIXED & VARIABLE=MASS-FLOW SPEC "OVHD" TO "850" TOL-SPEC "0.01 " VARY BLOCK-VAR BLOCK=F1 VARIABLE=TEMP SENTENCE=PARAM LIMITS "0" "100" Calculation Sequence SEQUENCE USED WAS: $OLVER01 *P1 M1 $OLVER02 F1 (RETURN $OLVER02) S1 (RETURN $OLVER01) Stream Variables FEED1 FEED2 LP S2 S STREAM ID FEED1 FEED2 LP S2 S3 FROM : S1 M1 F1 TO : M1 M F1 S1 SUBSTREAM: MIXED PHASE: VAPOR VAPOR LIQUID VAPOR LIQUID COMPONENTS: LBMOL/HR METHANE ETHANE PROPANE N-BUTANE BUTENE ,3-BUTA TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F PRES PSI VFRAC LFRAC SFRAC ENTHALPY: BTU/LBMOL BTU/LB BTU/HR ENTROPY: BTU/LBMOL-R BTU/LB-R DENSITY: LBMOL/CUFT LB/CUFT

20 AVG MW S4 S5 VP STREAM ID S4 S5 VP FROM : S1 P1 F1 TO : P1 M SUBSTREAM: MIXED PHASE: MISSING MISSING VAPOR COMPONENTS: LBMOL/HR METHANE ETHANE PROPANE N-BUTANE BUTENE ,3-BUTA TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F MISSING MISSING PRES PSI MISSING VFRAC MISSING MISSING LFRAC MISSING MISSING 0.0 SFRAC MISSING MISSING 0.0 ENTHALPY: BTU/LBMOL MISSING MISSING BTU/LB MISSING MISSING BTU/HR MISSING MISSING ENTROPY: BTU/LBMOL-R MISSING MISSING BTU/LB-R MISSING MISSING DENSITY: LBMOL/CUFT MISSING MISSING LB/CUFT MISSING MISSING AVG MW MISSING MISSING Selected Process Unit Output BLOCK: F1 MODEL: FLASH INLET STREAM: S2 OUTLET VAPOR STREAM: VP OUTLET LIQUID STREAM: S3 PROPERTY OPTION SET: RK-SOAVE STANDARD RKS EQUATION OF STATE *** MASS AND ENERGY BALANCE *** IN OUT RELATIVE DIFF. TOTAL BALANCE MOLE(LBMOL/HR) E-15 MASS(LB/HR ) E-11 ENTHALPY(BTU/HR ) E E *** INPUT DATA *** TWO PHASE TP FLASH SPECIFIED TEMPERATURE F SPECIFIED PRESSURE PSI MAXIMUM NO. ITERATIONS 30 CONVERGENCE TOLERANCE *** RESULTS *** 20

21 OUTLET TEMPERATURE F OUTLET PRESSURE PSI HEAT DUTY BTU/HR E+07 VAPOR FRACTION V-L PHASE EQUILIBRIUM : COMP F(I) X(I) Y(I) K(I) METHANE E E ETHANE E E PROPANE E N-BUTANE E E BUTENE E ,3-BUTA

22 Exercise A.2 Solution using ASPEN.PLUS Several variables are tabulated as a function of the purge/recycle ratio: Purge/Recycle Ratio PROD flow rate, lbmole/h Recycle flow rate, lbmole/h Purge flow rate, lbmole/h Purge Mole fraction Ar Purge Mole fraction CH In all cases, the mole fraction of Ar and CH 4 in the purge are significantly greater than in the feed. As the purge/recycle ratio is decreased, the vapor effluent from the flash vessel becomes richer in the inert species and less H 2 and N 2 are lost in the purge stream. However, this is accompanied by a significant increase in the recycle rate and the cost of recirculation, as well as reactor volume. Note that the EXAM4-3.BKP file on this CD-ROM can be used to reproduce these results. Although not implemented in this file, the purge/recycle ratio can be adjusted parametrically by varying the fraction of stream S5 purged in a sensitivity analysis, which is one of the model analysis tools in ASPEN PLUS. The capital and operating costs can be estimated and a profitability measure optimized as a function of the purge/recycle ratio. 22

23 Exercise A.3 Solution using ASPEN.PLUS ASPEN PLUS Flowsheet - simulation results can be reproduced using the file EXER3-7.BKP on the CD-ROM. V1 F1 FLASH2 V2 L1 FEED F2 FLASH2 V3 L2 F3 FLASH2 V4 L3 F4 FLASH2 L4 ASPEN PLUS Program IN-UNITS ENG DEF-STREAMS CONVEN ALL DESCRIPTION "General Simulation with English Units : F, psi, lb/hr, lbmol/hr, Btu/hr, cuft/hr. Property Method: None Flow basis for input: Mole Stream report composition: Mole flow " DATABANKS PURE10 / AQUEOUS / SOLIDS / INORGANIC / & NOASPENPCD PROP-SOURCES PURE10 / AQUEOUS / SOLIDS / INORGANIC COMPONENTS NITROGEN N2 NITROGEN / CO2 CO2 CO2 / H2S H2S H2S / METHANE CH4 METHANE / ETHANE C2H6 ETHANE / PROPANE C3H8 PROPANE / ISOBU-01 C4H10-2 ISOBU-01 / 23

24 N-BUT-01 C4H10-1 N-BUT-01 / 2-MET-01 C5H MET-01 / N-PEN-01 C5H12-1 N-PEN-01 / N-HEX-01 C6H14-1 N-HEX-01 / N-HEP-01 C7H16-1 N-HEP-01 / N-OCT-01 C8H18-1 N-OCT-01 / N-NON-01 C9H20-1 N-NON-01 / N-DEC-01 C10H22-1 N-DEC-01 / N-DOD-01 C12H26 N-DOD-01 FLOWSHEET BLOCK F1 IN=V2 OUT=V1 L1 BLOCK F2 IN=FEED L1 V3 OUT=V2 L2 BLOCK F3 IN=L2 V4 OUT=V3 L3 BLOCK F4 IN=L3 OUT=V4 L4 PROPERTIES RK-SOAVE PROP-DATA RKSKIJ-1 IN-UNITS ENG PROP-LIST RKSKIJ BPVAL NITROGEN CO BPVAL NITROGEN H2S BPVAL NITROGEN METHANE BPVAL NITROGEN ETHANE BPVAL NITROGEN PROPANE BPVAL NITROGEN ISOBU BPVAL NITROGEN N-BUT BPVAL NITROGEN 2-MET BPVAL NITROGEN N-PEN BPVAL NITROGEN N-HEX BPVAL NITROGEN N-HEP BPVAL NITROGEN N-OCT BPVAL CO2 H2S BPVAL CO2 METHANE BPVAL CO2 ETHANE BPVAL CO2 PROPANE BPVAL CO2 ISOBU BPVAL CO2 N-BUT BPVAL CO2 2-MET BPVAL CO2 N-PEN BPVAL CO2 N-HEX BPVAL CO2 N-HEP BPVAL CO2 NITROGEN BPVAL H2S CO BPVAL H2S ETHANE BPVAL H2S PROPANE BPVAL H2S ISOBU BPVAL H2S N-PEN BPVAL H2S NITROGEN BPVAL METHANE CO BPVAL METHANE ETHANE E-3 BPVAL METHANE PROPANE E-3 BPVAL METHANE ISOBU BPVAL METHANE N-BUT E-3 BPVAL METHANE 2-MET E-3 BPVAL METHANE N-PEN BPVAL METHANE N-HEX BPVAL METHANE N-HEP BPVAL METHANE N-OCT BPVAL METHANE NITROGEN BPVAL METHANE N-NON BPVAL ETHANE CO BPVAL ETHANE H2S BPVAL ETHANE METHANE E-3 BPVAL ETHANE PROPANE E-3 BPVAL ETHANE ISOBU BPVAL ETHANE N-BUT E-3 24

25 BPVAL ETHANE N-PEN E-3 BPVAL ETHANE N-HEX BPVAL ETHANE N-HEP E-3 BPVAL ETHANE N-OCT BPVAL ETHANE NITROGEN BPVAL PROPANE CO BPVAL PROPANE H2S BPVAL PROPANE METHANE E-3 BPVAL PROPANE ETHANE E-3 BPVAL PROPANE ISOBU BPVAL PROPANE N-BUT BPVAL PROPANE 2-MET E-3 BPVAL PROPANE N-PEN BPVAL PROPANE N-HEX E-3 BPVAL PROPANE N-HEP E-3 BPVAL PROPANE NITROGEN BPVAL ISOBU-01 CO BPVAL ISOBU-01 H2S BPVAL ISOBU-01 METHANE BPVAL ISOBU-01 ETHANE BPVAL ISOBU-01 PROPANE BPVAL ISOBU-01 N-BUT E-3 BPVAL ISOBU-01 NITROGEN BPVAL N-BUT-01 CO BPVAL N-BUT-01 METHANE E-3 BPVAL N-BUT-01 ETHANE E-3 BPVAL N-BUT-01 PROPANE 0.0 BPVAL N-BUT-01 ISOBU E-3 BPVAL N-BUT-01 N-PEN BPVAL N-BUT-01 N-HEX BPVAL N-BUT-01 N-HEP E-4 BPVAL N-BUT-01 NITROGEN BPVAL 2-MET-01 CO BPVAL 2-MET-01 METHANE E-3 BPVAL 2-MET-01 PROPANE E-3 BPVAL 2-MET-01 N-PEN BPVAL 2-MET-01 NITROGEN BPVAL N-PEN-01 CO BPVAL N-PEN-01 H2S BPVAL N-PEN-01 METHANE BPVAL N-PEN-01 ETHANE E-3 BPVAL N-PEN-01 PROPANE BPVAL N-PEN-01 N-BUT BPVAL N-PEN-01 2-MET BPVAL N-PEN-01 N-HEP E-3 BPVAL N-PEN-01 N-OCT E-3 BPVAL N-PEN-01 NITROGEN BPVAL N-HEX-01 CO BPVAL N-HEX-01 METHANE BPVAL N-HEX-01 ETHANE BPVAL N-HEX-01 PROPANE E-3 BPVAL N-HEX-01 N-BUT BPVAL N-HEX-01 N-HEP E-3 BPVAL N-HEX-01 NITROGEN BPVAL N-HEP-01 CO BPVAL N-HEP-01 METHANE BPVAL N-HEP-01 ETHANE E-3 BPVAL N-HEP-01 PROPANE E-3 BPVAL N-HEP-01 N-BUT E-4 BPVAL N-HEP-01 N-PEN E-3 BPVAL N-HEP-01 N-HEX E-3 BPVAL N-HEP-01 NITROGEN BPVAL N-OCT-01 METHANE BPVAL N-OCT-01 ETHANE BPVAL N-OCT-01 N-PEN E-3 25

26 BPVAL N-OCT-01 NITROGEN BPVAL N-NON-01 METHANE STREAM FEED SUBSTREAM MIXED TEMP=120. PRES=284.7 MOLE-FLOW NITROGEN / CO / H2S / & METHANE / ETHANE / PROPANE / & ISOBU / N-BUT / 2-MET / & N-PEN / N-HEX / N-HEP / N-OCT / N-NON / N-DEC / & N-DOD BLOCK F1 FLASH2 PARAM TEMP=100. PRES=814.7 BLOCK F2 FLASH2 PARAM TEMP=120. PRES=284.7 BLOCK F3 FLASH2 PARAM TEMP=96. PRES=63.7 BLOCK F4 FLASH2 PARAM TEMP=85. PRES=27.7 & Calculation Sequence SEQUENCE USED WAS: $OLVER01 F2 F1 F3 F4 (RETURN $OLVER01) Stream Variables FEED L1 L2 L3 L STREAM ID FEED L1 L2 L3 L4 FROM : ---- F1 F2 F3 F4 TO : F2 F2 F3 F SUBSTREAM: MIXED PHASE: MIXED LIQUID LIQUID LIQUID LIQUID COMPONENTS: LBMOL/HR NITROGEN CO H2S METHANE ETHANE PROPANE ISOBU N-BUT MET N-PEN N-HEX N-HEP N-OCT N-NON N-DEC N-DOD TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F PRES PSI VFRAC LFRAC SFRAC ENTHALPY: 26

27 BTU/LBMOL BTU/LB BTU/HR ENTROPY: BTU/LBMOL-R BTU/LB-R DENSITY: LBMOL/CUFT LB/CUFT AVG MW V1 V2 V3 V STREAM ID V1 V2 V3 V4 FROM : F1 F2 F3 F4 TO : ---- F1 F2 F3 SUBSTREAM: MIXED PHASE: VAPOR VAPOR VAPOR VAPOR COMPONENTS: LBMOL/HR NITROGEN CO H2S METHANE ETHANE PROPANE ISOBU N-BUT MET N-PEN N-HEX N-HEP N-OCT N-NON N-DEC N-DOD TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F PRES PSI VFRAC LFRAC SFRAC ENTHALPY: BTU/LBMOL BTU/LB BTU/HR ENTROPY: BTU/LBMOL-R BTU/LB-R DENSITY: LBMOL/CUFT LB/CUFT AVG MW

28 HYSYS.Plant Thermodynamics The materials that support a course in thermodynamics have not yet been class-tested. However, it is recommended that thermodynamics instructors consider allotting three hours of computer laboratory time for the exercises. A self-paced approach using the multimedia allows the students to bring themselves up-to-speed on the selection of property prediction methods, and their applications in VLE calculations, and to perform chemical equilibrium calculations. The following sequence of modules is recommended: Session 1: Under HYSYS Physical Property Estimation Package selection, students are provided with a guide to the correct selection of physical property methods, and their impact on VLE calculations. It is recommended that students be assigned an exercise that allows them to test the recommendations, which are implemented as decision-trees (e.g., Exercise B.2). Session 2: Under HYSYS Separators, the main menu refers to item 1, Flash. Students should review the background material on K-value computations for VLE computations and see the video of an industrial flash vessel. They will also find helpful the section on the use of the HYSYS Separator, modeling the flash unit. 28

29 Session 3: Under HYSYS Chemical Reactors, the main menu refers to item 3, Setting up Reactors. Students can review the modules on the Equilibrium Reactor, for calculations involving the mass-action equations, and on the Gibbs Reactor for calculations involving the direct minimization of the Gibbs free energy. To reinforce their acquired capabilities, students should be assigned a homework exercise. Three typical exercises are provided: Exercise B.1 Refrigerator Design Problem Exercise B.2 VLLE Problem Exercise B.4 Chemical Equilibrium Problem 29

30 ASPEN PLUS The materials that support a course in thermodynamics have not yet been class-tested. However, it is recommended that thermodynamics instructors consider allotting four hours of computer laboratory time for the exercises. A self-paced approach using the multimedia allows the students to bring themselves up-to-speed on the use of a process simulator to carry out the energy balances in a refrigerator, to perform VLE calculations, and to perform chemical equilibrium calculations. The following sequence of modules is recommended: Session 1: Under ASPEN Pumps & Compressors, the main menu refers to item 2, Compressors and Expanders. Students should see the video of an industrial compressor and review the module on ASPEN PLUS (COMPR, MCOMPR). Then, under ASPEN PLUS Heat Exchangers, the main menu refers to item 2, Heat Requirement Models. Students should review this module. For the refrigerator process, the multimedia doesn t have a module on valves. Students can use the ASPEN PLUS VALVE subroutine with little preparation. Session 2: Under ASPEN Separators, the main menu refers to item 3, Phase Equil. and Flash. Students should see the video of an industrial flash vessel and review the two modules on FLASH 2 and FLASH 3. In addition, under Physical Property Estimation, the main menu refers to item 3, Property Estimation. Students can review the basis for VLE calculations in module on Phase Equilibria, methods for using ASPEN PLUS to draw equilibrium 30

31 diagrams in the modules on Binary Phase Diagrams and Phase Envelopes, and methods for regressing VLE data in the module Property Data Regression. Session 3: Under ASPEN Reactors, the main menu refers to item 3, Equilibrium Reactors. Students can review the modules on the Equilibrium Reactor (REQUIL), for calculations involving the mass-action equations, and on the Gibbs Reactor (RGIBBS) for calculations involving the direct minimization of the Gibbs free energy. To reinforce their acquired capabilities, students should be assigned a homework exercise. Five typical exercises are provided: Exercise B.1 Refrigerator Design Problem Exercise B.2 VLLE Problem Exercise B.3 VLE Data Regression Problem Exercise B.4 Chemical Equilibrium Problem Exercise B.5 Selection of an Environmentally-friendly Refrigerant 31

32 Exercise B.1 Refrigerator Design Problem This is extension of Example 6.2 in Seider, Seader, and Lewin (1999), which involves a refrigeration loop: In this problem, it is desired to: a. simulate the refrigeration cycle assuming that the compressor has an isentropic efficiency of 0.9. For the evaporator and condenser, do not simulate the heat exchangers. Instead, use models that compute the heat required to be absorbed by the evaporating propane and to be removed from the condensing propane. Use the Soave-Redlich-Kwong equation and a propane flow rate of 5,400 lb/hr. Set the pressure levels as indicated above, but recognize that the temperatures may differ due to the VLE model. b. calculate the lost work and the thermodynamic efficiency for the refrigeration cycle. HYSYS.Plant Solution ASPEN PLUS Solution 32

33 Exercise B.2 VLLE Problem An equimolar stream of benzene, toluene, and water at 150 kgmole/hr, 100 C, and 7 bar enters a flash vessel. It is expanded to 0.5 bar and cooled to 60 C. Use a process simulator with the UNIFAC method, having liquid-liquid interaction coefficients, for estimating liquid-phase activity coefficients to compute the flow rates and compositions of the three product streams. Also, determine the heat added or removed. If using ASPEN PLUS, the FLASH3 subroutine and the UNIF-LL property option are appropriate. If using HYSYS.Plant, use the 3-phase Separator, and select the appropriate physical property method as guided by the multimedia. HYSYS.Plant Solution ASPEN PLUS Solution 33

34 Exercise B.3 VLE Data Regression Problem The following vapor-liquid equilibrium data for ethanol and benzene at 1 atm have been taken from the Gmehling and Onken data bank: x y T, C

35 For the design of a distillation column to produce nearly pure ethanol, it is desired to obtain a close match between the computed VLE and the Gmehling and Onken data. a. Use the binary interaction coefficients for the UNIQUAC equation for liquid-phase interaction coefficients, in the data bank of a process simulator, to prepare T-x-y and x-y diagrams. b. Use data points having ethanol mole fractions above its azeotropic mole fraction with a regression program in a process simulator. Determine interaction coefficients that give better agreement with the Gmehling and Onken data at high ethanol concentrations. Show how the T-x-y and x-y diagrams compare using these data points. ASPEN PLUS Solution Exercise B.4 Chemical Equilibrium Problem An equimolar stream of ammonia, oxygen, nitrogen oxide (NO), nitrogen dioxide (NO 2 ), and water at 100 lbmole/hr, 300 F, and 1 atm enters a tank reactor. Determine the flow rate and composition of the reactor effluent, assuming that chemical equilibrium is attained. Use a process simulator, assuming that the ideal gas law applies. a. Determine the number of independent reactions. Then, determine a set of independent reactions. b. Obtain chemical equilibrium by solving the mass-action equations (using K-values). If using ASPEN PLUS, the REQUIL subroutine is appropriate. c. Obtain chemical equilibrium by minimizing the Gibbs free energy. Note that it is not necessary to specify an independent reaction set. If using ASPEN PLUS, the RGIBBS subroutine is appropriate. ASPEN PLUS Solution Exercise B.5 Selection of an Environmentally-friendly Refrigerant It is desired to find a refrigerant that removes heat at -20 C and rejects heat at 32 C. Desirable refrigerants should have P s {-20 C} > 1.4 bar, P s {32 C} < 14 bar, H v {-20 C} > 18.4 kj/mol, and c pl {6 C} > 18.4 kj/mol. For the candidate groups, CH 3, CH, F, and S, formulate a mixed-integer nonlinear program and use GAMS to solve it. Hint: maximize the objective function, H v {-20 C}. 35

36 Exercise B.1 Solution using HYSYS.Plant Refrigerator Design Problem Solution a. Solution using HYSYS.Plant. This solution can be reproduced using the file, REFRIG.HSC. HYSYS.Plant Report. Fluid Package: Basis-1 Property Package: SRK Material Stream: S-1 Overall Vapour Phase Liquid Phase Vapour / Phase Fraction Temperature: (F) 8.44E E E-02 Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -4.61E E E+04 Molar Entropy (Btu/lbmole-F) Heat Flow (Btu/hr) -5.65E E+06 0 Material Stream: S-2 Overall Vapour Phase Vapour / Phase Fraction 1 1 Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -4.45E E+04 Molar Entropy (Btu/lbmole-F) Heat Flow (Btu/hr) -5.45E E+06 Material Stream: S-3 Overall Liquid Phase Vapour Phase Vapour / Phase Fraction

37 Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -5.10E E E+04 Molar Entropy (Btu/lbmole-F) Heat Flow (Btu/hr) -6.25E E+06 0 Material Stream: S-4 Overall Vapour Phase Liquid Phase Vapour / Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -5.10E E E+04 Molar Entropy (Btu/lbmole-F) Heat Flow (Btu/hr) -6.25E E E+06 Cooler: E-100 Pressure Drop: psi Duty: 7.920e+005 Btu/hr Volume: ft3 Heater: E-101 PARAMETERS Pressure Drop: psi Duty: 5.970e+005 Btu/hr Volume: ft3 Compressor: K-100 Duty: e+05 Btu/hr Adiabatic Eff.: PolyTropic Eff.: Speed: Adiabatic Head: 2.501e+004 ft Polytropic Head: 2.535e+004 ft Polytropic Exp Isentropic Exp Poly Head Factor User Variables Valve: VLV-100 Pressure Drop: psi b. Lost work (see Eq. (6.23), Seider, Seader, Lewin (1999)): LW T W 1 Q Evap = 70 kw + (1 537/470) kw = = 44.9 kw = in + 0 TEvaporator Thermodynamic efficiency (see Eq. (6.27), Seider, Seader, Lewin (1999)): main goal 25.1 η ( ) goal = = = main goal LW See SSL for calculations of the lost work in each process unit. Also, see Example 6.3 in which the valve is replaced by a power recovery turbine. 37

38 Exercise B.1 Solution using ASPEN.PLUS a. Solution using ASPEN PLUS. This solution can be reproduced using the file, REFRIG.BKP. S1 C1 S2 EVAP1 COND1 V1 S4 S3 ASPEN PLUS Program TITLE 'PROPANE REFRIGERATION LOOP' IN-UNITS ENG DEF-STREAMS CONVEN ALL DESCRIPTION " General Simulation with English Units : F, psi, lb/hr, lbmol/hr, Btu/hr, cuft/hr. Property Method: None Flow basis for input: Mole Stream report composition: Mole flow " DATABANKS PURE11 / AQUEOUS / SOLIDS / INORGANIC / & NOASPENPCD PROP-SOURCES PURE11 / AQUEOUS / SOLIDS / INORGANIC COMPONENTS PROPANE C3H8 FLOWSHEET BLOCK EVAP1 IN=S4 OUT=S1 BLOCK COND1 IN=S2 OUT=S3 BLOCK C1 IN=S1 OUT=S2 BLOCK V1 IN=S3 OUT=S4 PROPERTIES RK-SOAVE STREAM S3 SUBSTREAM MIXED PRES=185. VFRAC=0. MASS-FLOW=5400. MOLE-FRAC PROPANE 1. BLOCK COND1 HEATER PARAM PRES=185. VFRAC=0. BLOCK EVAP1 HEATER PARAM PRES=38.37 VFRAC=1. BLOCK C1 COMPR PARAM TYPE=ISENTROPIC PRES=187. SEFF=0.9 BLOCK V1 VALVE PARAM P-OUT=40. EO-CONV-OPTI STREAM-REPOR MOLEFLOW Stream Variables S1 S2 S3 S

39 STREAM ID S1 S2 S3 S4 FROM : EVAP1 C1 COND1 V1 TO : C1 COND1 V1 EVAP1 MAX CONV. ERROR: SUBSTREAM: MIXED PHASE: VAPOR VAPOR LIQUID MIXED COMPONENTS: LBMOL/HR PROPANE TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F PRES PSI VFRAC LFRAC SFRAC ENTHALPY: BTU/LBMOL BTU/LB BTU/HR ENTROPY: BTU/LBMOL-R BTU/LB-R DENSITY: LBMOL/CUFT LB/CUFT AVG MW Selected Process Unit Output BLOCK: C1 MODEL: COMPR *** RESULTS *** INDICATED HORSEPOWER REQUIREMENT HP BRAKE HORSEPOWER REQUIREMENT HP NET WORK REQUIRED HP ISENTROPIC HORSEPOWER REQUIREMENT HP CALCULATED OUTLET TEMP F ISENTROPIC TEMPERATURE F EFFICIENCY (POLYTR/ISENTR) USED HEAD DEVELOPED, FT-LBF/LB 25,101.0 MECHANICAL EFFICIENCY USED INLET HEAT CAPACITY RATIO INLET VOLUMETRIC FLOW RATE, CUFT/HR 14,708.6 OUTLET VOLUMETRIC FLOW RATE, CUFT/HR 3, INLET COMPRESSIBILITY FACTOR OUTLET COMPRESSIBILITY FACTOR AV. ISENT. VOL. EXPONENT AV. ISENT. TEMP EXPONENT AV. ACTUAL VOL. EXPONENT AV. ACTUAL TEMP EXPONENT

40 BLOCK: COND1 MODEL: HEATER *** RESULTS *** OUTLET TEMPERATURE F OUTLET PRESSURE PSI HEAT DUTY BTU/HR E+06 BLOCK: EVAP1 MODEL: HEATER *** RESULTS *** OUTLET TEMPERATURE F OUTLET PRESSURE PSI HEAT DUTY BTU/HR E+06 BLOCK: V1 MODEL: VALVE *** RESULTS *** VALVE PRESSURE DROP PSI b. Lost work (see Eq. (6.23), Seider, Seader, Lewin (1999)): LW W 1 T = in + 0 TEvaporator Q Evap = 70 kw + (1 537/470) kw = = 44.9 kw Thermodynamic efficiency (see Eq. (6.27), Seider, Seader, Lewin (1999)): η ( ) goal = main goal main goal LW 25.1 = = See SSL for calculations of the lost work in each process unit. Also, see Example 6.3 in which the valve is replaced by a power recovery turbine. 40

41 Exercise B.2 Solution using HYSYS.Plant Solution using 3-phase Separator in HYSYS.Plant. This solution can be reproduced using the file, VLLE.HSC. Note that the physical properties are predicted using the NRTL activity method, with UNIFAC-LL binary interaction coefficients, and assuming ideal vapor, as recommended by both Eric Carlson and Bob Seader (Both indicate that the UNIFAC LL estimation method is appropriate). The option to check for the possibility of two liquid phases should be activated. NAME FEED VAP LIQ1 LIQ2 SEP-DUTY Vapor Fraction Temperature [C] Pressure [bar] Molar Flow [kgmol/h] Mass Flow [kgl/h] Liquid Volume Flow [m3/h] Heat Flow [kcal/h] Molar Enthalpy [kcal/kgmol] Comp Molar Flow (Benzene) [kgmol/h] E-03 Comp Molar Flow (Toluene) [kgmol/h] E-03 Comp Molar Flow (Water) [kgmol/h] In the above table, values in blue are the process specifications, with the remaining values being computed results. Note that the organic liquid product is LIQ1 and the aqueous liquid product is LIQ2. To satisfy the energy balance, HYSYS.Plant computes MMKcal/hr are added to the flash vessel. 41

42 Exercise B.2 Solution using ASPEN.PLUS Solution using the FLASH3 subroutine in ASPEN PLUS. This solution can be reproduced using the file, VLLE.BKP. VAP F1 FEED LIQ1 LIQ2 ASPEN PLUS Program TITLE 'VLLE - BENZENE, TOLUENE, WATER' IN-UNITS MET VOLUME-FLOW='cum/hr' ENTHALPY-FLO='MMkcal/hr' & HEAT-TRANS-C='kcal/hr-sqm-K' PRESSURE=bar TEMPERATURE=C VOLUME=cum DELTA-T=C HEAD=meter MOLE-DENSITY='kmol/cum' MASS-DENSITY='kg/cum' MOLE-ENTHALP='kcal/mol' & MASS-ENTHALP='kcal/kg' HEAT=MMkcal MOLE-CONC='mol/l' & PDROP=bar DEF-STREAMS CONVEN ALL SIM-OPTIONS NPHASE=3 DESCRIPTION " General Simulation with Metric Units : C, bar, kg/hr, kmol/hr, MMKcal/hr, cum/hr. Property Method: None Flow basis for input: Mole Stream report composition: Mole flow DATABANKS PURE10 / AQUEOUS / SOLIDS / INORGANIC / & NOASPENPCD PROP-SOURCES PURE10 / AQUEOUS / SOLIDS / INORGANIC COMPONENTS BENZENE C6H6 / TOLUENE C7H8 / WATER H2O FLOWSHEET BLOCK F1 IN=FEED OUT=VAP LIQ1 LIQ2 PROPERTIES UNIF-LL PROPERTIES IDEAL / UNIFAC STREAM FEED SUBSTREAM MIXED TEMP=100. PRES=7. MOLE-FLOW=150. MOLE-FLOW BENZENE 50. / TOLUENE 50. / WATER 50. BLOCK F1 FLASH3 PARAM TEMP=60. PRES=0.5 STREAM-REPOR MOLEFLOW & & 42

43 Stream Variables FEED LIQ1 LIQ2 VAP STREAM ID FEED LIQ1 LIQ2 VAP FROM : ---- F1 F1 F1 TO : F SUBSTREAM: MIXED PHASE: LIQUID LIQUID LIQUID VAPOR COMPONENTS: KMOL/HR BENZENE TOLUENE WATER TOTAL FLOW: KMOL/HR KG/HR CUM/HR STATE VARIABLES: TEMP C PRES BAR VFRAC LFRAC SFRAC ENTHALPY: KCAL/MOL KCAL/KG MMKCAL/HR ENTROPY: CAL/MOL-K CAL/GM-K DENSITY: KMOL/CUM KG/CUM AVG MW Note that the stream LIQ1 contains the organic phase and the stream LIQ2 contains the aqueous phase. Selected Process Unit Output BLOCK: F1 MODEL: FLASH PROPERTY OPTION SET: UNIF-LL UNIFAC / REDLICH-KWONG *** RESULTS *** OUTLET TEMPERATURE C OUTLET PRESSURE BAR HEAT DUTY MMKCAL/HR VAPOR FRACTION ST LIQUID/TOTAL LIQUID V-L1-L2 PHASE EQUILIBRIUM : COMP F(I) X1(I) X2(I) Y(I) K1(I) K2(I) BENZENE E E+04 TOLUENE E E+04 WATER E To satisfy the energy balance, MMKcal/hr are added to the flash vessel. 43

44 Exercise B.3 Solution using ASPEN.PLUS Solution obtained using ASPEN PLUS with the UNIQUAC method for estimating liquid-phase activity coefficients. Results can be reproduced using the file, VLEREG.BKP. a. From the ASPEN PLUS data banks, the following binary interaction coefficients are used: a ij = , a ji = , b ij = 137.8, b ji = -1,001.7 Using these interaction coefficients, T-x-y and x-y graphs are prepared. b. Using the data points for ethanol concentrations greater than or equal to 0.6 from the Gmehling and Onken data bank, the binary interaction coefficients are adjusted by the ASPEN PLUS data regression program to: a ij = , a ji = , b ij = 14.96, b ji = In this case, just small changes are observed in the T-x-y and x-y diagrams. 44

45 Exercise B.4 Solution using ASPEN PLUS Chemical Equilibrium Problem Solution a. N C = 5, R = rank of atom matrix = 3. Hence, N R = no. of independent chemical reactions = N C R = 5 3 = 2. For the atom matrix, see the solution to part c. b. Solution using the REQUIL subroutine in ASPEN PLUS. This solution can be reproduced using the file, REQUIL.BKP. VAP FEED R1 LIQ Note that when using the REQUIL subroutine, streams for both vapor and liquid effluents must be defined, even when one doesn t exist. The two independent reactions are selected arbitrarily: ASPEN PLUS Program NO + 1/2O 2 = NO 2 4NH 3 + 5O 2 = 4NO + 6H 2 O TITLE 'CHEMICAL EQUILIBRIUM - K-VALUES' IN-UNITS ENG DEF-STREAMS CONVEN ALL DATABANKS PURE10 / AQUEOUS / SOLIDS / INORGANIC / & NOASPENPCD PROP-SOURCES PURE10 / AQUEOUS / SOLIDS / INORGANIC COMPONENTS AMMON-01 H3N / OXYGE-01 O2 / NITRI-01 NO / NITRO-01 NO2 / WATER H2O FLOWSHEET BLOCK R1 IN=FEED OUT=VAP LIQ PROPERTIES IDEAL STREAM FEED SUBSTREAM MIXED TEMP=300. PRES=1. <atm> MOLE-FLOW=100. MOLE-FRAC AMMON / OXYGE / NITRI / NITRO / WATER 0.2 BLOCK R1 REQUIL PARAM NREAC=2 TEMP=300. PRES=1. <atm> NPHASE=2 STOIC 1 NITRI * / OXYGE * / NITRO * STOIC 2 AMMON * / OXYGE * / NITRI * / WATER 6. * TAPP-SPEC / STREAM-REPOR MOLEFLOW 45 & & &

46 Stream Variables FEED LIQ VAP STREAM ID FEED LIQ VAP FROM : ---- R1 R1 TO : R SUBSTREAM: MIXED PHASE: VAPOR MISSING VAPOR COMPONENTS: LBMOL/HR AMMON OXYGE NITRI NITRO WATER TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F MISSING PRES PSI VFRAC MISSING LFRAC 0.0 MISSING 0.0 SFRAC 0.0 MISSING 0.0 ENTHALPY: BTU/LBMOL MISSING BTU/LB MISSING BTU/HR MISSING ENTROPY: BTU/LBMOL-R MISSING BTU/LB-R MISSING DENSITY: LBMOL/CUFT MISSING LB/CUFT MISSING AVG MW MISSING Selected Process Unit Output *** RESULTS *** OUTPUT TEMPERATURE F OUTPUT PRESSURE PSI HEAT DUTY BTU/HR E+07 VAPOR FRACTION REACTION EQUILIBRIUM CONSTANTS: REACTION EQUILIBRIUM NUMBER CONSTANT c. Solution using the RGIBBS subroutine in ASPEN PLUS. This solution can be reproduced using the file, RGIBBS.BKP. 46

47 R1 FEED VAP LIQ Note that when using the REQUIL subroutine, streams for both vapor and liquid effluents must be defined, even when one doesn t exist. ASPEN PLUS Program only those paragraphs that differ from the program above are included. TITLE 'CHEMICAL EQUILIBRIUM - MINIMIZATION OF G' BLOCK R1 RGIBBS PARAM TEMP=300. PRES=1. <atm> Stream Variables FEED LIQ VAP STREAM ID FEED LIQ VAP FROM : ---- R1 R1 TO : R SUBSTREAM: MIXED PHASE: VAPOR MISSING VAPOR COMPONENTS: LBMOL/HR AMMON OXYGEN NITRO NITRI WATER TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F MISSING PRES PSI MISSING VFRAC MISSING LFRAC 0.0 MISSING 0.0 SFRAC 0.0 MISSING 0.0 ENTHALPY: BTU/LBMOL MISSING BTU/LB MISSING BTU/HR MISSING ENTROPY: BTU/LBMOL-R MISSING BTU/LB-R MISSING DENSITY: LBMOL/CUFT MISSING LB/CUFT MISSING AVG MW MISSING Note that these results are nearly identical to those for part a. Tight convergence tolerances are satisfied by the RGIBBS subroutine, while small material balance differences between the inlet and outlet streams are reported by the REQUIL subroutine. 47

48 Selected Process Unit Output FLUID PHASE SPECIES IN PRODUCT LIST: AMMON-01 OXYGEN NITRO-01 NITRI-01 WATER ATOM MATRIX: ELEMENT H N O AMMON OXYGEN NITRO NITRI WATER *** RESULTS *** TEMPERATURE F PRESSURE PSI HEAT DUTY BTU/HR E+07 VAPOR FRACTION NUMBER OF FLUID PHASES 1 FLUID PHASE MOLE FRACTIONS: PHASE VAPOR OF TYPE VAPOR PHASE FRACTION PLACED IN STREAM VAP AMMON E+00 OXYGEN E-07 NITRI WATER

49 HYSYS.Plant Heat Transfer The materials supporting a course in heat transfer assume that two hours of computer laboratory time is allocated to the exercises. 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. The following sequence is suggested: Session 1: In the first part of the exercise session, the student should review the entire section on HYSYS Heat Exchangers in the multimedia. This consists of modules describing the simple heater/cooler and the more rigorous heat exchanger. The modules each illustrate the use of the models in example applications. Session 2: The tutorial Toluene Manufacture should be reviewed, while at the same time, the student should develop his/her version of the simulation using HYSYS.Plant. To reinforce their acquired capabilities, students should be assigned a homework exercise. Two typical exercises are provided: (a) The rating of a 2-8 heat exchanger for process heat transfer; (b) Completing the Toluene Manufacture heat-integrated process to determine the optimum preheat temperature. 49

50 ASPEN PLUS Heat Transfer The materials supporting a course in heat transfer assume that two hours of computer laboratory time is allocated to the exercises. The multimedia includes a section that provides a self-paced overview on heat transfer equipment in general and the models available in ASPEN PLUS in particular. The following sequence is suggested. Note that this sequence has not been class-tested using ASPEN PLUS. However, a similar sequence using HYSYS.Plant, on the previous page, has been class-tested successfully: Session 1: In the first part of the exercise session, the student should review the first three sections on Heat Exchangers in the multimedia (1. Introduction with Videos, 2. Heat Requirement Modules, and 3. Shell-and-Tube Heat Exchangers.) These consist of modules describing the simple heater/cooler and the more rigorous heat exchanger. The modules each illustrate the use of the models in example applications. Note that videos are provided of industrial 1-2 shell-and-tube heat exchangers and fin-fan heat exchangers. Session 2: The student should review the tutorial involving Toluene Manufacture, while at the same time, develop his/her version of the simulation using ASPEN PLUS. To reinforce their acquired capabilities, students should be assigned a homework exercise. Two typical exercises are provided: (a) The rating of a 2-8 heat exchanger for process heat transfer; (b) Completing the Toluene Manufacture heat-integrated process to determine the optimum preheat temperature. 50

51 Exercise C.1 Heat Exchanger Rating Problem An existing 2-8 shell-and-tube heat exchanger is to be used to transfer heat to a toluene feed stream from a styrene product stream. The toluene enters the exchanger on the tube side at a flow rate of 125,000 lb/hr at 100 o F and 90 psia. The styrene enters on the shell side at a flow rate of 150,000 lb/hr at 300 o F and 50 psia. The exchanger shell and tubes are carbon steel. The shell has an inside diameter of 39 in. and contains 1,024 3/4-in., 14 BWG, 16-ft-long tubes on a 1-in. square pitch. Thirty-eight segmental baffles are used with a baffle cut of 25%. Shell inlet and outlet nozzles are 2.5-in., schedule 40 pipe, and tube-side inlet and outlet nozzles are 4-in., schedule 40 pipe. Fouling factors are estimated to be (hr-ft 2 - o F)/Btu on each side. Determine the exit temperatures of the two streams, the heat duty, and the pressure drops. In ASPEN PLUS, use the HEATX subroutine, and in HYSYS.Plant, use Heat Exchanger. Note that this problem is solved in Example 8.7 of Seider, Seader, and Lewin (1999). HYSYS.Plant Solution ASPEN PLUS Solution Exercise C.2 Heat Exchanger Design Problem Complete the class exercise in which a heat integrated process was developed for the manufacture of toluene from n-heptane. You are required to determine the optimum pre-heat temperature to minimize the annual cost, involving both the cost of the preheater and the energy costs associated with preheating the feed stream. The following data is provided: U = 65 Btu/h ft 2 F (assumed constant) Cost of Super-heater Fuel = 0.02 $/Btu h -1 y -1 Bare Modules Cost (for kettle reboiler), in $: C = exp ln( A) ln( A) 2, B { [ ] [ ] } where A is the exchanger surface area in ft 2. The annualized equipment cost, assuming 20% depreciation, is C A = C B /5 It is suggested that you use the Spreadsheet to compute the annual costs based on the above data and the Databook to carry out a sensitivity analysis to show the effect of preheat temperature on annual cost. Your solution should include the following: a) A plot showing the annual cost as a function of the super-heater feed temperature. What is the maximum possible temperature attainable? b) A definition of the optimal value of the super-heater feed temperature, optimal pre-heater heat exchange area, and the corresponding annual cost. c) Comparison of the optimal annual cost incurred with that of the cases where (a) no preheater installed; (b) a preheater is installed to bring the n-heptane to its dew point. HYSYS.Plant Solution 51

52 Exercise C.1 Solution using HYSYS.Plant These results can be reproduced using the file HEATEX.hsc The heat exchanger in HYSYS.Plant is used to make the calculations. In its rating mode, it uses built-in correlations of the type described in Chapter 8 (Seider, Seader, and Lewin) for estimating shell-side and tube-side heat-transfer coefficients and pressure drops. The following results are obtained (both streams are liquid): Toluene exit temperature = o F Styrene exit temperature = o F Tube-side pressure drop = 0.02 psi (this is well-below expected) Toluene exit pressure = psia Shell-side pressure drop = psia (this is well-below expected) Styrene exit pressure = psia Heat-transfer area (tube outside) = Two shells, with 1,608 ft 2 per shell. Heat duty = Btu/hr Estimated shell-side film coefficient =110.3 Btu/hr-ft 2 -R Estimated tube-side film coefficient = 393.7Btu/hr-ft 2 -R Estimated overall heat transfer coefficient = 58.1 Btu/hr-ft 2 -R Log-mean temperature difference based on countercurrent flow = 46.5 o F Correction factor for 2-8 exchanger, F T =

53 Exercise C.1 Solution using ASPEN.PLUS The HEATX subroutine (block) of the ASPEN PLUS simulator is used to make the calculations. It has built-in correlations of the type described in Chapter 8 (Seider, Seader, and Lewin) for estimating shell-side and tube-side heat-transfer coefficients and pressure drops. The following results are obtained (both streams are liquid): Toluene exit temperature = o F Styrene exit temperature = o F Tube-side tube pressure drop = 3.59 psi Tube-side nozzle pressure drop = 0.55 psi Toluene exit pressure = psia Shell-side baffled pressure drop = 4.55 psia Shell-side nozzle pressure drop = 5.18 psia Styrene exit pressure = psia Heat-transfer area (tube outside) = 3,217 ft 2 Heat duty = 8,625,200 Btu/hr Estimated (U o ) clean = 90.4 Btu/hr-ft 2 -R Estimated (U o ) dirty = 64.0 Btu/hr-ft 2 -R Log-mean temperature difference based on countercurrent flow = 41.9 o F Correction factor for 2-8 exchanger, F T = Velocity in the tubes = 3.02 ft/s Maximum Reynolds number in the tubes = 45,700 Crossflow velocity in the shell = 2.59 ft/s Maximum crossflow Reynolds number in the shell = 50,300 Flow regime on tube and shell sides = turbulent ASPEN PLUS Program TITLE 'HEAT EXCHANGER DESIGN - EXAMPLE 13.7 (OLD 8.7)' IN-UNITS ENG DEF-STREAMS CONVEN ALL DESCRIPTION " General Simulation with English Units : F, psi, lb/hr, lbmol/hr, Btu/hr, cuft/hr. Property Method: None Flow basis for input: Mole 53

54 Stream report composition: Mole flow DATABANKS PURE11 / AQUEOUS / SOLIDS / INORGANIC / & NOASPENPCD PROP-SOURCES PURE11 / AQUEOUS / SOLIDS / INORGANIC COMPONENTS TOLUENE C7H8 / STYRENE C8H8 FLOWSHEET BLOCK H1 IN=HOTIN COLDIN OUT=HOTOUT COLDOUT PROPERTIES RK-SOAVE PROPERTIES BWR-LS / BWRS / CHAO-SEA / IDEAL / LK-PLOCK / PENG-ROB STREAM COLDIN SUBSTREAM MIXED TEMP=100. PRES=90. MASS-FLOW= & FREE-WATER=NO NPHASE=2 PHASE=V MOLE-FRAC TOLUENE 1. / STYRENE 0. STREAM HOTIN SUBSTREAM MIXED TEMP=300. PRES=50. MASS-FLOW= MOLE-FRAC TOLUENE 0. / STYRENE 1. BLOCK H1 HEATX PARAM CALC-TYPE=SIMULATION AREA=3217. TYPE=COUNTERCURRE & NPOINTS=5 P-UPDATE=YES U-OPTION=FILM-COEF & F-OPTION=GEOMETRY CALC-METHOD=DETAILED FC-USE-AVTD=YES FEEDS HOT=HOTIN COLD=COLDIN PRODUCTS HOT=HOTOUT COLD=COLDOUT HEAT-TR-COEF SCALE=1. FLASH-SPECS HOTOUT NPHASE=1 PHASE=L FREE-WATER=NO FLASH-SPECS COLDOUT NPHASE=1 PHASE=L FREE-WATER=NO EQUIP-SPECS TUBE-NPASS=8 TEMA-TYPE=F SHELL-DIAM=39. <in> & SHELL-BND-SP=0.25 <in> TUBES TOTAL-NUMBER=1024 PATTERN=SQUARE LENGTH=16. & INSIDE-DIAM=0.584 <in> OUTSIDE-DIAM=0.75 <in> PITCH=1. <in> TCOND=25. NOZZLES SNOZ-INDIAM=2.469 <in> SNOZ-OUTDIAM=2.469 <in> & TNOZ-INDIAM=4.026 <in> TNOZ-OUTDIAM=4.026 <in> SEGB-SHELL NBAFFLE=38 NSEAL-STRIP=1 BAFFLE-CUT=0.25 & SHELL-BFL-SP=0.1 <in> TUBE-BFL-SP=0.1 <in> IN-BFL-SP=0.6 & OUT-BFL-SP=0.6 HOT-HCURVE 1 NPOINT=20 COLD-HCURVE 1 NPOINT=20 HOT-SIDE H-OPTION=GEOMETRY H-SCALE=1. FOUL-FACTOR=0.002 & SHELL-TUBE=SHELL DP-OPTION=GEOMETRY COLD-SIDE H-OPTION=GEOMETRY H-SCALE=1. FOUL-FACTOR=0.002 & DP-OPTION=GEOMETRY REPORT PROFILE EO-CONV-OPTI STREAM-REPOR MOLEFLOW Stream Variables 54 &

55 COLDIN COLDOUT HOTIN HOTOUT STREAM ID COLDIN COLDOUT HOTIN HOTOUT FROM : ---- H H1 TO : H H SUBSTREAM: MIXED PHASE: LIQUID LIQUID LIQUID LIQUID COMPONENTS: LBMOL/HR TOLUENE STYRENE TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F PRES PSI VFRAC LFRAC SFRAC ENTHALPY: BTU/LBMOL BTU/LB BTU/HR ENTROPY: BTU/LBMOL-R BTU/LB-R DENSITY: LBMOL/CUFT LB/CUFT AVG MW Selected Process Unit Output BLOCK: H1 MODEL: HEATX FLOW DIRECTION AND SPECIFICATION: COUNTERCURRENT HEAT EXCHANGER SPECIFIED EXCHANGER AREA SPECIFIED VALUE SQFT EQUIPMENT SPECIFICATIONS: NUMBER OF SHELL PASSES 2 NUMBER OF TUBE PASSES 8 TEMA SHELL TYPE F ORIENTATION HORIZONTAL BAFFLE TYPE SEGMENTAL SHELL INSIDE DIAMETER FT SHELL TO BUNDLE CLEARANCE FT SPECIFICATIONS FOR TUBES: TOTAL NUMBER OF TUBES 1024 TUBE TYPE BARE TUBE PATTERN SQUARE TUBE MATERIAL CARBON-STEEL TUBE LENGTH FT TUBE INSIDE DIAMETER FT TUBE OUTSIDE DIAMETER FT TUBE PITCH FT TUBE THERMAL CONDUCTIVITY BTU-FT/HR-SQFT-R SPECIFICATIONS FOR SEGMENTAL BAFFLE SHELL: NUMBER OF BAFFLES 38 NUMBER OF SEALING STRIP PAIRS 1 TUBES IN WINDOW YES BAFFLE CUT SHELL TO BAFFLE CLEARANCE FT TUBE TO BAFFLE CLEARANCE FT CENTRAL BAFFLE SPACING FT INLET BAFFLE SPACING FT

56 OUTLET BAFFLE SPACING FT SPECIFICATIONS FOR NOZZLES: SHELL INLET NOZZLE DIAMETER FT SHELL OUTLET NOZZLE DIAMETER FT TUBE INLET NOZZLE DIAMETER FT TUBE OUTLET NOZZLE DIAMETER FT *** OVERALL RESULTS *** STREAMS: HOTIN -----> HOT (SHELL) -----> HOTOUT T= D+02 T= D+02 P= D+01 P= D+01 V= D+00 V= D+00 COLDOUT <----- COLD (TUBE) <----- COLDIN T= D+02 T= D+02 P= D+01 P= D+01 V= D+00 V= D DUTY AND AREA: CALCULATED HEAT DUTY BTU/HR CALCULATED (REQUIRED) AREA SQFT ACTUAL EXCHANGER AREA SQFT PER CENT OVER-DESIGN HEAT TRANSFER COEFFICIENT: AVERAGE COEFFICIENT (DIRTY) BTU/HR-SQFT-R AVERAGE COEFFICIENT (CLEAN) BTU/HR-SQFT-R LOG-MEAN TEMPERATURE DIFFERENCE: THERMAL EFFECTIVENESS (XI) NUMBER OF TRANSFER UNITS (NTU) LMTD CORRECTION FACTOR LMTD (CORRECTED) F STREAM VELOCITIES: SHELLSIDE MAX. CROSSFLOW VEL. FT/SEC SHELLSIDE MAX. CROSSFLOW REYNOLDS NO SHELLSIDE MAX. WINDOW VEL. FT/SEC SHELLSIDE MAX. WINDOW REYNOLDS NO TUBESIDE MAX. VELOCITY FT/SEC TUBESIDE MAX. REYNOLDS NO PRESSURE DROP: SHELLSIDE, BAFFLED FLOW AREA PSI SHELLSIDE, NOZZLE PSI SHELLSIDE, TOTAL PSI TUBESIDE, TUBES PSI TUBESIDE, NOZZLE PSI TUBESIDE, TOTAL PSI PRESSURE DROP PARAMETER: SHELL SIDE: TUBE SIDE: ZONE 1: *** ZONE PROFILES *** SHELLSIDE: CROSSFLOW/WINDOW CROSSFLOW/WINDOW TEMPERATURE VELOCITY REYNOLDS NUMBER PRANDTL NUMBER POINT F FT/SEC / / / / / / / / / /

57 TUBESIDE: TEMPERATURE VELOCITY REYNOLDS NUMBER PRANDTL NUMBER POINT F FT/SEC HEAT TRANSFER: WALL TEMP. HS HT U AREA POINT F <---- BTU/HR-SQFT-R ----> SQFT HEATX COLD-HCURVE: H1 HCURVE INDEPENDENT VARIABLE: DUTY PRESSURE PROFILE: CONSTANT PROPERTY OPTION SET: RK-SOAVE STANDARD RKS EQUATION OF STATE ! DUTY! PRES! TEMP! VFRAC!!!!!!!!!!!!!!!!! BTU/HR! PSI! F!!!!!!!!============!============!============!============!! 0.0! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! !! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! !! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! !! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! !! ! ! ! 0.0!! ! ! ! 0.0! HEATX HOT-HCURVE: H1 HCURVE INDEPENDENT VARIABLE: DUTY PRESSURE PROFILE: CONSTANT PROPERTY OPTION SET: RK-SOAVE STANDARD RKS EQUATION OF STATE ! DUTY! PRES! TEMP! VFRAC!!!!!!!!!!! 57

58 !!!!!! BTU/HR! PSI! F!!!!!!!!============!============!============!============!! 0.0! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! !! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! !! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! !! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! ! ! ! 0.0!! !! ! ! ! 0.0!! ! ! ! 0.0!

59 Exercise C.2 Solution using HYSYS.Plant These results can be reproduced using the file: TOLUENE_MANUFACTURE_EX.HSC a) The annual costs computed using HYSYS is plotted below. The maximum possible preheat temperature is 617 o F (here the temperature profiles in the heat exchanger are almost pinched). b) From the above results, it is noted that the optimal pre-heat temperature is 600 o F, at which the annual cost is $369,500. For this value of pre-heat temperature, the required heat transfer area is 7,110 ft 2 c) The total annual cost with no pre-heating is $1,173,000. To bring the n-heptane to its dew point, the pre-heat temperature needs to be o F (computed by setting the vapor fraction to unity), for which the annual cost is $765,

60 HYSYS.Plant Separations The materials supporting a course in separations assume that the students have already covered most of the theory on multicomponent separations (flash and distillation). It is recommended that 1-2 hours of computer laboratory time be allocated to allow students to review the multimedia support available. The following sequence of modules is recommended: Session 1: Cover all of the material under HYSYS Separations in the multimedia: Click on Overview, and the cover all of the materials supporting Flash and Distillation. The latter provides a framework for systematic multicomponent distillation column design, 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. Session 2: Many students require assistance in the correct selection of property estimation methods. It may be helpful to review the module on Physical Property Estimation Package Selection. Advanced students are encouraged to also review the tutorial on multi-draw tower optimization. To reinforce their acquired capabilities, students should be assigned one or more homework exercises. Two example exercises are provided: (a) The design of a series of two columns for the separation of a mixture of alcohols; (b) A single multicomponent column. 60

61 ASPEN PLUS Separations The materials supporting a course in separations assume that the students have already covered most of the theory on multicomponent separations (flash and distillation). It is recommended that 1-2 hours of computer laboratory time be allocated to allow students to review the multimedia support available. The following sequence of modules is recommended: Session 1: Under ASPEN Tutorials Separations, the main menu refers to item 2. Distillation. Students should see the videos of an industrial distillation complex and a laboratory tower. Then, they should review the module on Split-fraction Model (SEP2), which shows how to set the tower pressure, given specifications of the split fractions. Then, they should refer to the module on FUG Shortcut Design (DSTWU) to review methods for estimating the number of trays, the feed tray, and the reflux ratio. Finally, they should review the module on MESH Equations (RADFRAC) Session 2: Many students require assistance in the correct selection of property estimation methods. It may be helpful to review the module on Physical Property Estimation Package Selection. To reinforce their acquired capabilities, students should be assigned one or more homework exercises. Two typical exercises are provided: (a) The design of a series of two columns for the separation of a mixture of alcohols; (b) A single multicomponent column. ICARUS Process Evaluator (IPE) IPE, an Aspen Tech product, takes results from any of the major process simulators, involving many kinds of equipment items, and estimates equipment sizes, purchase costs and installation costs leading to the total capital investment, operating costs, and profitability measures. WDS has developed a set of course notes, which are provided with these materials. Also, he is developing multimedia materials to provide instruction on the use of IPE. Eventually, these can be used in the separations course to estimate the investment costs for a distillation complex, as well as other separators. In these materials, we are providing Exercise 9.1 (SSL), which involves the sizing and costing of a distillation complex. Exercise 9.1 has been modified to include the usage of IPE. 61

62 Exercise D.1 Multicomponent Distillation Design Problem 1 In the manufacture of higher alcohols from carbon monoxide and hydrogen, a mixture of alcohols is obtained, which must be separated into desired products. A feed mixture of: mol% ethanol 25 n-propanol 50 iso-butanol 10 n-butanol 15 has been isolated from methanol and heavier alcohols in prior distillation steps. It is a saturated liquid at the pressure of the first distillation column, to be determined in a below. The three desired products are streams containing: 1. At least 98% of the ethanol at a purity of 98 mol%. 2. N-propanol with essentially all of the remaining ethanol and no more than 2% of the isobutanol in the feed mixture. 3. At least 98% of the iso-butanol, all of the n-butanol, and no more than 1% of the n-propanol, in the feed mixture. Two distillation towers are used. The first receives the feed mixture. Its distillate is fed to the second tower, which produces ethanol-rich and n-propanol-rich products. Use a process simulator to: a. Determine the tower pressures that permit cooling water to be used in the condensers; that is, let the cooling water be heated from F and the bubble-point of the condensed overhead vapor be 130 F or higher. This assures that the minimum approach temperature difference is 10 F. Use total condensers. To avoid vacuum operation, pressures in the towers must exceed 20 psia. Assume no pressure drop in the towers. In ASPEN PLUS, use the SEP2 subroutine. In HYSYS.Plant, use Splitter. b. Determine the minimum number of trays and the minimum reflux ratio. Then, let the actual reflux ratio be 1.3 R min and use the Gilliland correlation to determine the theoretical number of trays and the location of the feed tray. In ASPEN PLUS, use the DSTWU subroutine. In HYSYS.Plant, use Short-cut Column. c. Using the design determined in a and b, simulate the towers; that is, solve the MESH equations. In ASPEN PLUS, use the RADFRAC subroutine. In HYSYS.Plant, use Column. HYSYS.Plant Solution ASPEN PLUS Solution 62

63 Exercise D.2 Multicomponent Distillation Design Problem 2 The composition of a stream of 100 kgmol/hr at of a multicomponent mixture is: mol% benzene 12.5 toluene 22.5 o-xylene 37.5 n-propylbenzene 27.5 It is required to design a distillation column to separate the mixture such that the distillate contains at least 99% of the toluene and the bottoms at least 99.4% of the o-xylene, given that the stream is supplied at its bubble point, and both of the product streams are to be drawn as liquids. Use a process simulator to: (a) (b) (c) (d) Determine the tower pressure that permit cooling water to be used in the condenser; that is, let the cooling water be heated from C and the bubble-point of the condensed overhead vapor 50 C, with a lower bound on the operating pressure being 20 psia. You may neglect the pressure drop in the column throughout this exercise. In ASPEN PLUS, use the SEP2 subroutine. In HYSYS.Plant, use Splitter. Determine the minimum number of trays and the minimum reflux ratio. Then, let the actual reflux ratio be 1.3 R min and use the Gilliland correlation to determine the theoretical number of trays and the location of the feed tray. In ASPEN PLUS, use the DSTWU subroutine. In HYSYS.Plant, use Short-cut Column. Using the design determined in a and b, simulate the towers; that is, solve the MESH equations. In ASPEN PLUS, use the RADFRAC subroutine. In HYSYS.Plant, use Column. Following fouling of the heat transfer surface in the reboiler, it is estimated that the available heat transfer duty has dropped by 40%. Is it possible to make a design change in the column to allow the two specifications met previously to be maintained? Alternatively, without changing the number of trays or the location of the feed tray determined previously, what is the reflux ratio that will allow at recovery of at least 90% of the toluene and 90% of the o-xylene for the fouled reboiler? HYSYS.Plant Solution 63

64 Exercise D.3 Distillation Sizing and Costing Problem (Exercise 9.1 (SSL) Revised for IPE) The feed to a sieve-tray distillation column operating at 1 atm is 700 lbmol/hr of 45 mol% benzene and 55 mol% toluene at 1 atm and its bubble-point temperature of 201 F. The distillate contains 92 mol% benzene and boils at 179 F. The bottoms product contains 95 mol% toluene and boils at 227 F. The column has 23 trays spaced 18 in. apart, and its reflux ratio is Column pressure drop is neglected. Tray efficiency is 80%. Estimate the total bare-module cost of the column, condenser, reflux accumulator, condenser pump, reboiler, and reboiler pump. Also, estimate the total permanent investment. Results should be computed using: (1) the cost charts in Chapter 9, and (2) IPE (ICARUS Process Evaluator). Compare the results. Data Molal heat of vaporization of distillate = 13,700 Btu/lbmol Molal heat capacity of distillate = 40 Btu/lbmol F Overall U of condenser = 100 Btu/hr ft 2 F Cooling water from 90 F to 120 F Heat flux for reboiler = 12,000 Btu/hr ft 2 Saturated steam at 60 psia Reflux accumulator residence time = 5 minutes at half full; L/D = 4 Pump heads = 50 psia; suction pressure = 1 atm, efficiency = 1 Calculate the flooding velocity of the vapor using the procedure in Example Use 85 percent of the flooding velocity to determine the column diameter. Notes The file, BENTOLDIST.BKP, is included on the CD-ROM that accompanies these notes. It contains the simulation results using the RADFRAC subroutine in ASPEN PLUS. This file should be used to prepare the report file for IPE. Note that the simulation was carried out using 20 stages (18 trays plus the condenser and reboiler). When using IPE, set the tray efficiency to 0.8 and IPE will adjust the number of trays to 23. Since IPE does not size and cost a reboiler pump, a centrifugal pump should be added. Also, since Chapter 9 does not include the cost charts for a pump, copies from Ulrich (1984) are attached. IPE estimates the physical properties and heat-transfer coefficients. Do not adjust these. In IPE, reset the temperatures of cooling water (90 and 120 F) and add a utility for 60 psia steam. Use the steam tables to obtain the physical properties. Use a kettle reboiler with a floating head. 64

65 IPE sizes the tower using a 24 in tray spacing as the default. After sizing (mapping) is complete, adjust the tray spacing to 18 in. Note that the height of the tower must be adjusted accordingly. Note that IPE estimates the costs of Direct Material and Manpower for each equipment item. These are also referred to as the costs of direct materials and labor, C DML = C P + C M + C L. To Be Submitted Include your hand calculations using the cost charts and the methods in Chapter 9. (Note that these methods are identical to those in Example 10.2). Do not submit the entire IPE Capital Estimate Report. Instead, prepare a table showing a comparison of the equipment sizes and purchased costs. When using the methods in Chapter 9, show the bare module cost. For IPE, show the direct cost of materials and labor. It is sufficient to take the numbers from IPE. For both methods, show the calculations leading to the total permanent investment. Discuss the results. ASPEN PLUS Solution 65

66 Exercise D.1 Solution using HYSYS.Plant Solution reproduced in: DISTIL_EX_1.hsc Based upon the specifications, the desired product streams are determined by material balance: FEED D1 B1 D2 B2 Ethanol Propanol i-butanol Butanol Total a. In HYSYS.Plant, the column pressures are determined using the Component Splitter, adjusting the distillate pressure to achieve distillate bubble points at 130 F, with lower bounds of 20 psia to avoid vacuum operation. Note that because the most volatile species, ethanol, is present in the distillate of both towers, the pressure is adjusted to its lower bound in both towers. Component Splitter: X-100 PARAMETERS Stream Specifications Overhead Pressure: psia Overhead Vapour Fraction: Bottoms Pressure: psia Bottoms Vapour Fraction: SPLITS Component Fraction To Overhead Component Overhead Fraction Ethanol 1 1-Propanol 0.99 PROPERTIES 66

67 F1 Overall Liquid Phase Vapour Phase Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -1.24E E E+05 Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) Heat Flow (Btu/hr) -1.24E E+07 0 D1 Overall Liquid Phase Vapour Phase Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -1.21E E E+05 Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) Heat Flow (Btu/hr) -9.06E E+06 0 B1 Overall Liquid Phase Vapour Phase Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -1.31E E E+05 Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) Heat Flow (Btu/hr) -3.32E E

68 Component Splitter: X-101 PARAMETERS Stream Specifications Overhead Pressure: psia Overhead Vapour Fraction: Bottoms Pressure: psia Bottoms Vapour Fraction: SPLITS Component Fraction To Overhead Component Overhead Fraction Ethanol Propanol PROPERTIES Overall Liquid Phase Vapour Phase D Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) -1.21E E E+05 Molar Enthalpy (Btu/lbmole) Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) -9.06E E+06 0 Heat Flow (Btu/hr) Overall Vapour Phase Liquid Phase D Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) -9.95E E E+05 Molar Enthalpy (Btu/lbmole) Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) -2.49E E+06 0 Heat Flow (Btu/hr) Overall Liquid Phase Vapour Phase B Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) -1.24E E E+05 Molar Enthalpy (Btu/lbmole)

69 Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) -6.15E E+06 0 Heat Flow (Btu/hr) b. Using the tower pressures determined in a, the numbers of trays and the reflux ratios are determined using short-cut column in HYSYS.Plant, for splits specified to give the desired products. For the first column, the minimum number of trays is 22. For 1.3R min, the design calls for 44 trays with reflux ratio of For the second column, N min = 12, with a design for 1.3R min giving 23 trays and a reflux ratio of Shortcut Column: T-100B Parameters Component Mole Fraction Light Key 1-Propanol 1.98E-02 Heavy Key i-butanol 2.70E-03 Pressures (psia) Reflux Ratios Condenser Pressure 20 External Reflux Ratio Reboiler Pressure 20 Minimum Reflux Ratio User Variables Results Summary Trays / Temperatures Flows Minimum # of Trays Rectify Vapour (lbmole/hr) Actual # of Trays Rectify Liquid (lbmole/hr) Optimal Feed Stage 24.7 Stripping Vapour (lbmole/hr) Condenser Temperature (F) Stripping Liquid (lbmole/hr) Reboiler Temperature (F) Condenser Duty (Btu/hr) -4.11E+06 Reboiler Duty (Btu/hr) 4.14E+06 69

70 Shortcut Column: T-101B Parameters Component Mole Fraction Light Key Ethanol 1.01E-02 Heavy Key 1-Propanol 2.00E-02 Pressures (psia) Reflux Ratios Condenser Pressure 20 External Reflux Ratio Reboiler Pressure 20 Minimum Reflux Ratio User Variables Results Summary Trays / Temperatures Flows Minimum # of Trays Rectify Vapour (lbmole/hr) Actual # of Trays Rectify Liquid (lbmole/hr) Optimal Feed Stage Stripping Vapour (lbmole/hr) Condenser Temperature (F) Stripping Liquid (lbmole/hr) Reboiler Temperature (F) Condenser Duty (Btu/hr) -1.88E+06 Reboiler Duty (Btu/hr) 1.89E+06 c. Using the design determined in a and b, the MESH equations are solved using column in HYSYS.Plant. Note that minor adjustments in the the reflux ratios in both columns are made by the internal design specification to achieve the required component molar flow rates: In the first column, the reflux ratio is decreased from to 2.192, while in the second column, it is reduced from 3.60 to Distillation: MONITOR Specifications Summary Specified Value Current Value Wt. Error Wt. Tol. Abs. Tol. Active E Iso-prop in D lbmole/hr lbmole/hr 2.62E E lbmole/hr On O Iso-butanol in B lbmole/hr lbmole/hr 1.39E E lbmole/hr On O Distillate Rate lbmole/hr lbmole/hr 5.28E E lbmole/hr Off O Reflux Ratio E E E-02 Off O Reflux Rate lbmole/hr 1.00E lbmole/hr Off O Btms Prod Rate lbmole/hr 1.00E lbmole/hr Off O 70

71 SPECS Column Specification Parameters Iso-prop in D Draw: D1C Flow Basis: Molar Phase: Liquid Components: 1-Propanol Iso-butanol in B Draw: B1C Flow Basis: Molar Phase: Liquid Components: i-butanol Distillate Rate Stream: D1C Flow Basis: Molar Reflux Ratio Stage: Condenser Flow Basis: Molar Liquid Specification: Reflux Rate Stage: Condenser Flow Basis: Molar Liquid Specification: Btms Prod Rate Stream: B1C Flow Basis: Molar User Variables PROFILES General Parameters Sub-Flow Sheet: T-100C (COL1) Number of Stages: 44 SOLVER Column Solving Algorithm: HYSIM Inside-Out Solving Options Acceleration Parameters Maximum Iterations: Accelerate K Value & H Model Parameters: Off Equilibrium Error Tolerance: 1.000e-07 Heat/Spec Error Tolerance: 1.000e-007 Save Solutions as Initial Estimate: On Super Critical Handling Model: Simple K Trace Level: Low Init from Ideal K's: Off Damping Parameters Initial Estimate Generator Parameters Azeotrope Check: Off Iterative IEG (Good for Chemicals): Off Fixed Damping Factor: 1 PROPERTIES Properties : F3 Overall Vapour Phase Liquid Phase Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) E Mass Flow (lb/hr) E Liquid Volume Flow (barrel/day) E Molar Enthalpy (Btu/lbmole) -1.24E E+05 Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) Heat Flow (Btu/hr) -1.24E E+07 71

72 Properties : D1C Overall Vapour Phase Liquid Phase Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -1.21E E E+05 Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) Heat Flow (Btu/hr) -9.06E E+06 Properties : B1C Overall Vapour Phase Liquid Phase Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -1.31E E E+05 Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) Heat Flow (Btu/hr) -3.32E E+06 Tray Summary Flow Basis: Molar Reflux Ratio: Temp. Pressure Liquid Vapour Feeds Draws Duties (F) (psia) (lbmole/hr) (lbmole/hr) (lbmole/hr) (lbmole/hr) (Btu/hr) Condenser L -3.98E+06 1 Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS

73 18 Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS L 26 Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Reboiler L 4.01E+06 73

74 Distillation: MONITOR Specifications Summary Specified Value Current Value Wt. Error Wt. Tol. Abs. Tol. Ab Ethanol in D lbmole/hr lbmole/hr 5.99E E lbmole/hr 2.2 Iso-propanol in B lbmole/hr lbmole/hr -1.58E E lbmole/hr 2.2 Distillate Rate lbmole/hr lbmole/hr 5.68E E lbmole/hr 2.2 Reflux Ratio E E E-02 Reflux Rate lbmole/hr 1.00E lbmole/hr 2.2 Btms Prod Rate lbmole/hr 1.00E lbmole/hr 2.2 SPECS Column Specification Parameters Ethanol in D Draw: Flow Basis: Molar Phase: Liquid Components: Ethanol Iso-propanol in B Draw: Flow Basis: Molar Phase: Liquid Components: 1-Propanol Distillate Rate Stream: Flow Basis: Molar Reflux Ratio Stage: Condenser Flow Basis: Molar Liquid Specification: Reflux Rate Stage: Condenser Flow Basis: Molar Liquid Specification: Btms Prod Rate Stream: Flow Basis: Molar User Variables PROFILES General Parameters Sub-Flow Sheet: T-101C (COL2) Number of Stages: 24 SOLVER Column Solving Algorithm: HYSIM Inside-Out Solving Options Acceleration Parameters Maximum Iterations: Accelerate K Value & H Model Parameters: Off Equilibrium Error Tolerance: 1.000e-07 Heat/Spec Error Tolerance: 1.000e-007 Save Solutions as Initial Estimate: On Super Critical Handling Model: Simple K Trace Level: Low Init from Ideal K's: Off Damping Parameters Initial Estimate Generator Parameters Azeotrope Check: Off Iterative IEG (Good for Chemicals): Off Fixed Damping Factor: 1 PROPERTIES Properties : Overall Liquid Phase Vapour/Phase Fraction

75 Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -1.21E E+05 Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) Heat Flow (Btu/hr) -9.06E E+06 Properties : Overall Vapour Phase Liquid Phase Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -1.16E E E+05 Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) Heat Flow (Btu/hr) -2.90E E+06 Properties : Overall Vapour Phase Liquid Phase Vapour/Phase Fraction Temperature: (F) Pressure: (psia) Molar Flow (lbmole/hr) Mass Flow (lb/hr) Liquid Volume Flow (barrel/day) Molar Enthalpy (Btu/lbmole) -1.24E E E+05 Mass Enthalpy (Btu/lb) Molar Entropy (Btu/lbmole-F) Mass Entropy (Btu/lb-F) Heat Flow (Btu/hr) -6.15E E+06 Tray Summary Flow Basis: Molar Reflux Ratio: Temp. Pressure Liquid Vapour Feeds Feeds Draws Duties (F) (psia) (lbmole/hr) (lbmole/hr) (lbmole/hr) (lbmole/hr) (lbmole/hr) (Btu/hr) Condenser L -1.85E+06 1 Main TS Main TS Main TS Main TS Main TS Main TS Main TS

76 8 Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Reboiler L 1.86E+06 76

77 Exercise D.1 Solution using ASPEN.PLUS Based upon the specifications, the desired product streams are determined by material balance: FEED DIS1 BOT1 DIS2 BOT2 EtOH npoh iboh nboh Total a. The column pressures are determined using the SEP2 subroutine in ASPEN PLUS with design specifications that adjust the distillate pressure to achieve distillate bubble points at 130 F. The lower bound of 20 psia to avoid vacuum operation. Note that because the most volatile species, ethanol, is present in the distillate of both towers, the pressure is adjusted to its lower bound in both towers. The results below can be reproduced using the file SEP2.BKP. DIS1 DIS2 FEED D1 D2 BOT1 BOT2 ASPEN PLUS Program TITLE 'PRESSURE DETERMINATION' IN-UNITS ENG DEF-STREAMS CONVEN ALL DESCRIPTION " General Simulation with English Units : F, psi, lb/hr, lbmol/hr, Btu/hr, cuft/hr. Property Method: None Flow basis for input: Mole Stream report composition: Mole flow DATABANKS PURE11 / AQUEOUS / SOLIDS / INORGANIC / & NOASPENPCD PROP-SOURCES PURE11 / AQUEOUS / SOLIDS / INORGANIC COMPONENTS ETHANOL C2H6O-2 / PROPANOL C3H8O-1 / ISOBU-01 C4H10O-3 / 77

78 N-BUT-01 C4H10O-1 FLOWSHEET BLOCK D1 IN=FEED OUT=DIS1 BOT1 BLOCK D2 IN=DIS1 OUT=DIS2 BOT2 PROPERTIES IDEAL STREAM FEED SUBSTREAM MIXED PRES=20. <psia> VFRAC=0. MOLE-FLOW=100. MOLE-FRAC ETHANOL 0.25 / PROPANOL 0.5 / ISOBU / & N-BUT BLOCK D1 SEP2 FRAC STREAM=DIS1 SUBSTREAM=MIXED COMPS=ETHANOL PROPANOL & ISOBU-01 N-BUT-01 FRACS= FLASH-SPECS DIS1 PRES=20. VFRAC=0. FLASH-SPECS BOT1 PRES=20. VFRAC=0. BLOCK D2 SEP2 FRAC STREAM=DIS2 SUBSTREAM=MIXED COMPS=ETHANOL PROPANOL & ISOBU-01 N-BUT-01 FRACS= FLASH-SPECS DIS2 PRES=20. VFRAC=0. FLASH-SPECS BOT2 PRES=20. VFRAC=0. DESIGN-SPEC DS-1 DEFINE DIS1T STREAM-VAR STREAM=DIS1 SUBSTREAM=MIXED & VARIABLE=TEMP SPEC "DIS1T" TO "130" TOL-SPEC "0.001" VARY BLOCK-VAR BLOCK=D1 VARIABLE=PRES SENTENCE=FLASH-SPECS & ID1=DIS1 LIMITS "20" "100" DESIGN-SPEC DS-2 DEFINE DIS2T STREAM-VAR STREAM=DIS2 SUBSTREAM=MIXED & VARIABLE=TEMP SPEC "DIS2T" TO "130" TOL-SPEC "0.001" VARY BLOCK-VAR BLOCK=D2 VARIABLE=PRES SENTENCE=FLASH-SPECS & ID1=DIS2 LIMITS "20" "100" EO-CONV-OPTI STREAM-REPOR MOLEFLOW Stream Variables BOT1 BOT2 DIS1 DIS2 FEED STREAM ID BOT1 BOT2 DIS1 DIS2 FEED FROM : D1 D2 D1 D TO : D D1 SUBSTREAM: MIXED PHASE: LIQUID LIQUID LIQUID LIQUID LIQUID COMPONENTS: LBMOL/HR ETHANOL PROPANOL ISOBU N-BUT TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F PRES PSI VFRAC LFRAC SFRAC ENTHALPY: BTU/LBMOL

79 BTU/LB BTU/HR ENTROPY: BTU/LBMOL-R BTU/LB-R DENSITY: LBMOL/CUFT LB/CUFT AVG MW b. Using the tower pressures determined in a, the numbers of trays and the reflux ratios are determined using the DSTWU subroutine in ASPEN PLUS, for splits specified to give the desired products. The towers have 41 and 23 stages and reflux ratios of 2.39 and The results below can be reproduced using the file DSTWU.BKP. ASPEN PLUS Program paragraphs that differ from above. TITLE 'DESIGN CALCULATIONS' BLOCK D1 DSTWU PARAM LIGHTKEY=1-PRO-01 RECOVL=0.99 HEAVYKEY=ISOBU-01 & RECOVH=0.02 PTOP=20. PBOT=20. RDV=0.0 RR=-1.3 BLOCK D2 DSTWU PARAM LIGHTKEY=ETHAN-01 RECOVL=0.98 HEAVYKEY=1-PRO-01 & RECOVH= PTOP=20. PBOT=20. RR=-1.3 Selected Process Unit Output BLOCK: D1 MODEL: DSTWU *** INPUT DATA *** HEAVY KEY COMPONENT ISOBU-01 RECOVERY FOR HEAVY KEY LIGHT KEY COMPONENT 1-PRO-01 RECOVERY FOR LIGHT KEY TOP STAGE PRESSURE (PSI ) BOTTOM STAGE PRESSURE (PSI ) REFLUX RATIO DISTILLATE VAPOR FRACTION 0.0 *** RESULTS *** DISTILLATE TEMP. (F ) BOTTOM TEMP. (F ) MINIMUM REFLUX RATIO ACTUAL REFLUX RATIO MINIMUM STAGES ACTUAL EQUILIBRIUM STAGES NUMBER OF ACTUAL STAGES ABOVE FEED DIST. VS FEED CONDENSER COOLING REQUIRED (BTU/HR ) 4,381,070. NET CONDENSER DUTY (BTU/HR ) -4,381,070. REBOILER HEATING REQUIRED (BTU/HR ) 4,409,900. NET REBOILER DUTY (BTU/HR ) 4,409,900. BLOCK: D2 MODEL: DSTWU *** INPUT DATA *** HEAVY KEY COMPONENT 1-PRO-01 RECOVERY FOR HEAVY KEY LIGHT KEY COMPONENT ETHAN-01 RECOVERY FOR LIGHT KEY

80 TOP STAGE PRESSURE (PSI ) BOTTOM STAGE PRESSURE (PSI ) REFLUX RATIO DISTILLATE VAPOR FRACTION 0.0 *** RESULTS *** DISTILLATE TEMP. (F ) BOTTOM TEMP. (F ) MINIMUM REFLUX RATIO ACTUAL REFLUX RATIO MINIMUM STAGES ACTUAL EQUILIBRIUM STAGES NUMBER OF ACTUAL STAGES ABOVE FEED DIST. VS FEED CONDENSER COOLING REQUIRED (BTU/HR ) 1,918,790. NET CONDENSER DUTY (BTU/HR ) -1,918,790. REBOILER HEATING REQUIRED (BTU/HR ) 1,932,040. NET REBOILER DUTY (BTU/HR ) 1,932,040. c. Using the design determined in a and b, the MESH equations are solved using the RADFRAC subroutine in ASPEN PLUS. The results below can be reproduced using the file RADFRAC.BKP. Note that the reflux ratio in the second column is increased using an internal design specification to achieve a molar flow rate of n-pentanol in the distillate of 0.5 lbmole/hr. The reflux ratio is increased from 3.64 to ASPEN PLUS Program paragraphs that differ from above. TITLE 'RADFRAC SIMULATION' BLOCK D1 RADFRAC PARAM NSTAGE=41 COL-CONFIG CONDENSER=TOTAL FEEDS FEED 19 PRODUCTS DIS1 1 L / BOT1 41 L P-SPEC COL-SPECS DP-COL=0. MOLE-D=74.7 MOLE-RR=3.65 SC-REFLUX DEGSUB=0. BLOCK D2 RADFRAC PARAM NSTAGE=23 COL-CONFIG CONDENSER=TOTAL FEEDS DIS1 12 PRODUCTS DIS2 1 L / BOT2 23 L P-SPEC COL-SPECS DP-COL=0. MOLE-D=25. MOLE-RR=3.64 SC-REFLUX DEGSUB=0. SPEC 1 MOLE-FLOW 0.5 COMPS=1-PRO-01 STREAMS=DIS2 VARY 1 MOLE-RR Stream Variables BOT1 BOT2 DIS1 DIS2 FEED STREAM ID BOT1 BOT2 DIS1 DIS2 FEED FROM : D1 D2 D1 D TO : D D1 80

81 SUBSTREAM: MIXED PHASE: LIQUID LIQUID LIQUID LIQUID LIQUID COMPONENTS: LBMOL/HR ETHAN PRO ISOBU N-BUT TOTAL FLOW: LBMOL/HR LB/HR CUFT/HR STATE VARIABLES: TEMP F PRES PSI VFRAC LFRAC SFRAC ENTHALPY: BTU/LBMOL BTU/LB BTU/HR ENTROPY: BTU/LBMOL-R BTU/LB-R DENSITY: LBMOL/CUFT LB/CUFT AVG MW Selected Process Unit Output BLOCK: D1 MODEL: RADFRAC INLETS - FEED STAGE 19 OUTLETS - DIS1 STAGE 1 BOT1 STAGE 41 **** COL-SPECS **** MOLAR VAPOR DIST / TOTAL DIST 0.0 MOLAR REFLUX RATIO MOLAR DISTILLATE RATE LBMOL/HR DIST + REFLUX DEG SUBCOOLED F 0.0 *** COMPONENT SPLIT FRACTIONS *** OUTLET STREAMS DIS1 BOT1 COMPONENT: ETHAN E-09 1-PRO E-02 ISOBU E N-BUT E *** SUMMARY OF KEY RESULTS *** TOP STAGE TEMPERATURE F BOTTOM STAGE TEMPERATURE F TOP STAGE LIQUID FLOW LBMOL/HR BOTTOM STAGE LIQUID FLOW LBMOL/HR TOP STAGE VAPOR FLOW LBMOL/HR 0.0 BOTTOM STAGE VAPOR FLOW LBMOL/HR MOLAR REFLUX RATIO MOLAR BOILUP RATIO CONDENSER DUTY (W/O SUBCOOL) BTU/HR -6,046,320. REBOILER DUTY BTU/HR 6,075,370. DIST + REFLUX SUBCOOLED TEMP F

82 SUBCOOLED REFLUX DUTY BTU/HR 0.0 ENTHALPY STAGE TEMPERATURE PRESSURE BTU/LBMOL HEAT DUTY F PSI LIQUID VAPOR BTU/HR E E SUBC E E E E E E E E E E E E E E E E E STAGE FLOW RATE FEED RATE PRODUCT RATE LBMOL/HR LBMOL/HR LBMOL/HR LIQUID VAPOR LIQUID VAPOR MIXED LIQUID VAPOR E+00 SUBC X (mole frac) Block D1: Liquid Composition Profiles ETHAN-01 1-PRO-01 ISOBU-01 N-BUT Stage BLOCK: D2 MODEL: RADFRAC INLETS - DIS1 STAGE 12 OUTLETS - DIS2 STAGE 1 BOT2 STAGE 23 **** COL-SPECS **** MOLAR VAPOR DIST / TOTAL DIST 0.0 MOLAR REFLUX RATIO MOLAR DISTILLATE RATE LBMOL/HR DIST + REFLUX DEG SUBCOOLED F

83 *** COMPONENT SPLIT FRACTIONS *** OUTLET STREAMS DIS2 BOT2 COMPONENT: ETHAN E-01 1-PRO E ISOBU E N-BUT E *** SUMMARY OF KEY RESULTS *** TOP STAGE TEMPERATURE F BOTTOM STAGE TEMPERATURE F TOP STAGE LIQUID FLOW LBMOL/HR BOTTOM STAGE LIQUID FLOW LBMOL/HR TOP STAGE VAPOR FLOW LBMOL/HR 0.0 BOTTOM STAGE VAPOR FLOW LBMOL/HR MOLAR REFLUX RATIO MOLAR BOILUP RATIO CONDENSER DUTY (W/O SUBCOOL) BTU/HR -2,180,430. REBOILER DUTY BTU/HR 2,193,610. DIST + REFLUX SUBCOOLED TEMP F SUBCOOLED REFLUX DUTY BTU/HR ENTHALPY STAGE TEMPERATURE PRESSURE BTU/LBMOL HEAT DUTY F PSI LIQUID VAPOR BTU/HR E SUBC E E E E E E E E E E E E E E E STAGE FLOW RATE FEED RATE PRODUCT RATE LBMOL/HR LBMOL/HR LBMOL/HR LIQUID VAPOR LIQUID VAPOR MIXED LIQUID VAPOR E+00 SUBC

84 X (mole frac) Block D2: Liquid Composition Profiles ETHAN-01 1-PRO-01 ISOBU-01 N-BUT Stage 84

85 Exercise D.2 Solution using HYSYS.Plant Solution reproduced in: DISTIL_EX_2.hsc Based upon the specifications, the desired product streams (in kgmol/hr) are determined by material balance: FEED D1 B1 Benzene Toluene o-xylene n-pbenzene Total a. In HYSYS.Plant, the column pressures are determined using the Component Splitter, adjusting the distillate pressure to achieve distillate bubble points at 50 C, with lower bounds of 20 psia to avoid vacuum operation. Note that due to volatiles in the overhead, the column pressure is dictated by this lower bound. Component Splitter: X-100 PARAMETERS Stream Specifications Overhead Pressure: psia Overhead Vapor Fraction: 0.00 Bottoms Pressure: psia Bottoms Vapor Fraction: 0.00 SPLITS Component Fraction To Overhead Component Overhead Fraction Benzene 1 Toluene 0.99 PROPERTIES 85

86 F1 Overall Liquid Phase Vapor Phase Vapour/Phase Fraction Temperature: (C) Pressure: (psig) Molar Flow (kgmole/h) Mass Flow (kg/h) 1.03E E+04 0 Liquid Volume Flow (m3/h) Molar Enthalpy (kj/kgmole) 1.06E E E+04 Mass Enthalpy (J/kg) 1.03E E E+05 Molar Entropy (kj/gmole-c) 3.66E E E-02 Mass Entropy (kj/g-c) 3.54E E E-04 Heat Flow (kj/h) 1.06E E+06 0 D1 Overall Liquid Phase Vapor Phase Vapour/Phase Fraction Temperature: (C) Pressure: (psig) Molar Flow (kgmole/h) Mass Flow (kg/h) Liquid Volume Flow (m3/h) Molar Enthalpy (kj/kgmole) 3.81E E E+04 Mass Enthalpy (J/kg) 4.37E E E+05 Molar Entropy (kj/gmole-c) -7.86E E E-03 Mass Entropy (kj/g-c) -9.01E E E-05 Heat Flow (kj/h) 1.33E E+06 0 B1 Overall Liquid Phase Vapor Phase Vapour/Phase Fraction Temperature: (C) Pressure: (psig) Molar Flow (kgmole/h) Mass Flow (kg/h) Liquid Volume Flow (m3/h) Molar Enthalpy (kj/kgmole) E+04 Mass Enthalpy (J/kg) E+05 Molar Entropy (kj/gmole-c) 9.96E E Mass Entropy (kj/g-c) 8.89E E E-03 Heat Flow (kj/h) -1.70E E+04 0 d. Using the tower pressures determined in a, the numbers of trays and the reflux ratios are determined using short-cut column in HYSYS.Plant, for splits specified to give the desired products. The minimum number of trays is 13. For 1.3R min, the design calls for 26 trays, with feed entering on the 13 th tray, with a reflux ratio of

87 Shortcut Column: T-100 Component Mole Fraction Light Key Toluene 3.46E-03 Heavy Key o-xylene 6.43E-03 Pressures (psig) Reflux Ratios Condenser Pressure 20 External Reflux Ratio Reboiler Pressure 20 Minimum Reflux Ratio User Variables Results Summary Trays / Temperatures Flows Minimum # of Trays Rectify Vapour (kgmole/h) Actual # of Trays 26.1 Rectify Liquid (kgmole/h) Optimal Feed Stage 12.9 Stripping Vapour (kgmole/h) Condenser Temperature (C) Stripping Liquid (kgmole/h) Reboiler Temperature (C) Condenser Duty (kj/h) -3.57E+06 Reboiler Duty (kj/h) 3.82E+06 e. Using the design determined in a and b, the MESH equations are solved using column in HYSYS.Plant. Note that a minor adjustment in the reflux ratio is made by the internal design specification to achieve the required component molar flow rates: to

88 Distillation: T-101 MONITOR Specifications Summary Specified Value Current Value Wt. Error Wt. Tol. Abs. Tol. Active Estimate Toluene Recovery E E E-03 On On Xylene Recovery E E E-03 On On Distillate Rate kgmole/h kgmole/h 3.36E E kgmole/h Off On Reflux Ratio E E-02 Off On Reflux Rate kgmole/h 1.00E kgmole/h Off On Btms Prod Rate kgmole/h 1.00E kgmole/h Off On SPECS Column Specification Parameters Toluene Recovery Draw: Components: Xylene Recovery Draw: Components: Distillate Rate Stream: Flow Basis: Molar Toluene Flow Basis: Molar o-xylene Flow Basis: Molar Reflux Ratio Stage: Condenser Flow Basis: Molar Liquid Specification: Reflux Rate Stage: Condenser Flow Basis: Molar Liquid Specification: Btms Prod Rate Stream: Flow Basis: Molar User Variables PROFILES General Parameters Sub-Flow Sheet: T-101 (COL1) Number of Stages: 26 SOLVER Column Solving Algorithm: HYSIM Inside-Out Solving Options Acceleration Parameters Maximum Iterations: Accelerate K Value & H Model Parameters: Off Equilibrium Error Tolerance: 1.000e-07 Heat/Spec Error Tolerance: 1.000e-007 Save Solutions as Initial Estimate: On Super Critical Handling Model: Simple K Trace Level: Low Init from Ideal K's: Off Damping Parameters Initial Estimate Generator Parameters Azeotrope Check: Off Iterative IEG (Good for Chemicals): Off Fixed Damping Factor: 1 88

89 PROPERTIES Properties : Overall Liquid Phase Vapour/Phase Fraction 0 1 Temperature: (C) Pressure: (psig) Molar Flow (kgmole/h) Mass Flow (kg/h) 1.03E E+04 Liquid Volume Flow (m3/h) Molar Enthalpy (kj/kgmole) 1.59E E+04 Mass Enthalpy (J/kg) 1.54E E+05 Molar Entropy (kj/gmole-c) 4.92E E-02 Mass Entropy (kj/g-c) 4.76E E-04 Heat Flow (kj/h) 1.59E E+06 Properties : Overall Vapour Phase Liquid Phase Vapour/Phase Fraction Temperature: (C) Pressure: (psig) Molar Flow (kgmole/h) Mass Flow (kg/h) Liquid Volume Flow (m3/h) Molar Enthalpy (kj/kgmole) 4.19E E E+04 Mass Enthalpy (J/kg) 4.80E E E+05 Molar Entropy (kj/gmole-c) -6.90E E E-02 Mass Entropy (kj/g-c) -7.91E E E-04 Heat Flow (kj/h) 1.47E E+06 Properties : Overall Vapour Phase Liquid Phase Overall Vapour Phase Liquid Phase Vapour/Phase Fraction Temperature: (C) Pressure: (psig) Molar Flow (kgmole/h) Mass Flow (kg/h) Liquid Volume Flow (m3/h) Molar Enthalpy (kj/kgmole) E Mass Enthalpy (J/kg) 5.22E E E+04 Molar Entropy (kj/gmole-c) Mass Entropy (kj/g-c) 1.01E E E-03 Heat Flow (kj/h) 3.80E E+05 89

90 SUMMARY Tray Summary Flow Basis: Molar Reflux Ratio: Temp. Pressure Liquid Vapour Feeds Draws Duties (C) (psig) (kgmole/h) (kgmole/h) (kgmole/h) (kgmole/h) (KJ/h) Condenser L -3.89E6 1 Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS L 14 Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Main TS Reboiler L 4.14E+06 90

91 f. It is noted from the solution for (c) that the heat duty for the reboiler needed to meet the design specifications is 4.14E+06 KJ/h. If this value is reduced by 20%, that is, to KJ/h, then clearly, this new specification is substituted for one of the others. It is not possible to meet both of the product specifications simultaneously for the lower level of reboiler heat duty. The following table indicates the impact of possible alternative design specifications accounting for fouling. Note that cases B and C, in which one of the two product specifications is maintained leads to a serious reduction in the recovery of the species whose specification is sacrifices. In contrast, with case D, it is possible to back off both of the specifications simultaneously, and to recover at least 93% of both of the desired products even when the reboiler is fouled (20% less duty). Case Specification 1 Specification 2 Outcome A Toluene recovery, 0.99 o-xylene recovery, Base case design, with RR = B Reboiler Duty, KJ/h o-xylene recovery, RR = 2.02, and toluene recovery drops to C Reboiler Duty, KJ/h Toluene recovery, 0.99 RR = 1.03, and toluene recovery drops to D Reboiler Duty, KJ/h o-xylene recovery, 0.93 RR = 1.62, and toluene recovery drops to

92 9.1 Mass balances Exercise D.3 Solution using ASPEN.PLUS Benzene = D B Overall 700 = D + B Solving: D = lbmole/hr, B = lbmole/hr L = R D = = lbmole/hr V = D + L = = lbmole/hr Tower dimensions Diameter Vapor density assume ideal gas at highest temperature = 227 F P 1atm lbmole lb ρ v = = = RT 3 3 ft atm ft lbmole R lbmole R lb = ft 3 Flooding velocity see Example 10.2 U f = F F ST ST C FP = F ρ L ρv ρv σ 18.2 = = = Note: σ is for toluene at 227 F L V ρv ρ L Note: 48.7 is the density of toluene at 227 F U f U = mm TS = 18 in = mm in ( ) ( 457.2) C F = e m = = s = = 3.85 ft s 1 2 = 1.38 m s = ft 4.53 s 92

93 Height 4V D = 0.9πρ v U 1 2 lbmole lb 1hr = hr lbmole 3600 s lb ft 0.9( 3.14) ft s = 6.09 ft = 1.86 m ( 23 1) = 47 ft 14.3 m H = 4 + = 1 2 Costs Column Eqs. (9.7) F M = 1 (Fig. 9.3(c)) C P = 1, ( ) ( 1.86) = $38, 640 From Figs 9.3(c) and 9.3(d) F P = 1, F BM = 4.5 C BM = 38, = $173,900 Trays Figure 9.4 f q = 1, N act = 23, F BM = 1.2 C BM = [ (1.86) (1.86) 2 ] (1.2)(23)(1) = $12,300 / tray Tower C BM = 173, ,300 = $186,200 Condenser lbmole Btu 6 Q C = ,700 = hr lbmole ( ) ( ) T LM = = F ln A C = = 1,360ft = m Btu hr Eqs. (9.5) 0.7 C P = 450( 126.3) = $13, 300 Fig. 9.1(a) - F M = 1, Fig 9.1(b) - F P = 1, Fig. 9.1(c) F BM = 3. 2 C = 13, = $42,600 BM 93

94 Reboiler Overall energy balance FH + Q = DH + Q + BH Q R F R = DH D + BH D B + Q C C FH Let H D = 0 (sat d liq. at 179 F) lbmole Btu Q R = ( ) F hr lbmole F ( ) 6 Btu = hr A = = 842 ft = 78.2 m 12,000 Eqs. (9.5) 0.7 C P = 450( 78.2) = $9, 510 Fig. 9.1(a) - F M = 1, Fig 9.1(b) - F P = 1, Fig. 9.1(c) - F BM = 3. 2 C = 9, $30,400 BM = Reflux Accumulator lbmole lb lb V = = 56,480 hr lbmole hr ben. condensate lb 1ft ft ft = 56,480 = 1,110 = 18.5 hr 50.7 lb hr min Note: 50.7 is the density of benzene at 179 F For a residence time = 5 min at half full: 3 Volume = = 185 ft = 5.24 m For L D = 4 : 1 3 V D = π L = 4.76 m = π Fig. 9.3(a) C P = $6, (c) F M = 1, FP = 1 9.3(d) F BM = 3. 0 B F = 1.19 m C BM = 6, = $18,

95 Reflux Pump centrifugal & W s 1 lbmole = m& P = ρ hr 2 lbf in in ft = 1.7 KW lb lbmole 1hr 3,600 s ft lb 1 W ft lb s F Figs Ulrich C P = $3,800, FM = 1, FP = 1, FBM = 3. 2 C = 3, $12,200 BM = Reboiler Pump centrifugal lbmole m& = L + F = hr lbmole = 1,102.3 hr W& s = m& P = 1, W ρ , = 5.6 KW Figs Ulrich C P = $5,500, FM = 1, FP = 1, FBM = 3. 2 C = 5, $17,600 Total Bare Module Cost BM = Tower 186,200 Condenser 42,600 Reboiler 30,400 Reflux accumulator 18,000 Reflux pump 12,200 Reboiler pump 17,600 $307,000 - mid-1982 In mid-1999: C TBM 392 = 307,000 = $382,

96 Total Permanent Investment C TBM = 382,000 C site + C serv = 0.1C TBM = 38,200 C DPI $420,200 C cont = 0.15 C DPI = 63,000 C TDC $483,200 C land = 0.02 C TDC = 9,700 C royal = - C start = 0.10 C TDC = 48,300 C TPI $541,200 (mid-1999) IPE Results Distillation Tower IPE Cost Charts in Chapter Costs Diameter (ft) Height (ft) C P ($) 81,100 48,760 (392/315) = 60,700 C DML ($) 214,000 C BM ($) 186,200 (392/315) =231,700 Condenser Area (ft 2 ) 555 1,360 C P ($) 15,000 13,300 (392/315) = 16,600 C DML ($) 57,100 C BM ($) 42,600 (392/315) = 53,000 Reboiler Area (ft 2 ) 1, C P ($) 26,900 9,510 (392/315) = 11,800 C DML ($) 87,700 C BM ($) 30,400 (392/315) =37,800 Reflux Accumulator Volume (gal) ,384 96

97 Diameter (ft) Height (ft) C P ($) 10,000 6,000 (392/315) = 7,500 C DML ($) 70,500 C BM ($) 18,000 (392/315) =22,400 Reflux Pump Power (KW) C P ($) 3,400 3,800 (392/315) = 4,700 C DML ($) 22,600 C BM ($) 12,200 (392/315) =15,200 Reboiler Pump Power (KW) C P ($) 4,500 5,500 (392/315) = 6,800 C DML ($) 32,100 C BM ($) 17,600 (392/315) =21,900 The equipment sizes and purchased costs are comparable with the exception of the reboiler. IPE does not design for the heat flux of 12,000 Btu/hr ft 2. IPE estimates the direct materials and labor costs, C DML, for each equipment item. These estimates do not include the indirect project expenses, while the bare module factors from the cost charts include these expenses. Note, however, that the IPE estimates of C DML are considerably higher than C BM for the reboiler and reflux accumulator. Total Permanent Investment The total permanent investment is calculated in the table below. Note that the purchased equipment cost, $145,800, is obtained from line 1 of the Contract Summary in the IPE Capital Estimate Report. The total direct materials and labor costs are obtained from line 11, $450,300 and $146,500, respectively. These sum to C DML = $596,800. The direct installation cost is obtained by difference. The material and manpower costs associated with G&A Overhead and Contract Fees are obtained by adding the entries on lines 13 and 14; that is, $52,200. The Contractor Engineering and Indirect Costs are obtained from line

98 Cost $ Source IBL (Inside Battery Limits) Purchased Equipment Cost Direct Installation Cost Total Direct Materials and Labor Cost, C DML =C DI 145,800 IPE Equipment List 451,000 By difference 596,800 IPE Contract Summary Pipe Racks (10% of C DML ) 59,700 Recommended by Instructor Sewers/Sumps (10% of C DML ) 59,700 Recommended by Instructor Mat l and Labor G&A Overhead and Contract Fees 52,200 IPE Contract Summary Contractor Engineering 390,400 IPE Contract Summary Indirects 358,900 IPE Contract Summary IBL Total Bare Module Cost, C TBM 1,517,700 98

99 OBL (Outside Battery Limits) Site Preparation & Service Facil. (10% of C TBM ) 151,800 Allocated Costs for Utilities 0 Storage 0 Environmental 0 OBL Total 151,800 Direct Permanent Investment, C DPI 1,669,500 Contingencies (15% of C DPI ) 250,400 Total Depreciable Capital, C TDC 1,919,900 Land (2% of C TDC ) 38,400 Royalty 0 Start Up (10% of C TDC ) 192,000 Total Permanent Investment, C TPI 2,150,300 Comparison of Results Using the cost charts in Chapter 9, the total bare module cost, C TBM = $382,000, as compared with the IPE estimate for the total direct materials and labor cost of $596,800. This is partially due to the increase in reboiler area due to IPE s inability to design for a heat flux of 12,000 Btu/hr ft 2. The remaining difference is likely due to IPE s detailed estimates of installation costs. Of greater consequence, the IPE estimate for the total permanent investment, C TPI = $2,150,300, is substantially greater than that obtained using the cost charts, $541,200. Although the IPE Project Type is Plant addition suppressed infrastructure, the IPE estimates for the contractor engineering and indirect costs are substantial. These cause the total permanent investment to far exceed that computed using the cost charts. This is probably because the bare module factors in the cost charts are not sufficiently large to represent the contractor engineering and indirect costs. However, some of the IPE estimates may be large for this distillation plant, which has only six equipment items. When added to the costs for more typical plants, with an order-ofmagnitude more equipment items, these large estimates would have a less significant impact on the total permanent investment. 99

100 HYSYS.Plant Reactor Design The materials supporting a course in heat transfer assume that 2-3 hours of computer laboratory time is allocated to the exercises. The multimedia includes a section that provides a self-paced overview on reactors in general and the models available in HYSYS.Plant in particular. The following sequence is suggested: Session 1: In the first part of the exercise session, the student should review the entire section on Reactors in the multimedia. This consists of modules describing all of the reactor models available in HYSYS.Plant, each illustrated by an example application. The students should ensure that they have covered the modules describing the PFR and the CSTR. Session 2: The tutorial Ammonia Converter Design should be reviewed, while at the same time, the student should develop his/her version of the simulation using HYSYS.Plant. To reinforce their acquired capabilities, students should be assigned a homework exercise. A typical exercise is provided. 100

101 ASPEN PLUS Reactor Design The materials supporting a course in heat transfer assume that 2-3 hours of computer laboratory time is allocated to the exercises. The multimedia includes a section that provides a self-paced overview on reactors in general and the models available in ASPEN PLUS in particular. The following sequence is suggested: Session 1: In the first part of the exercise session, the student should review the entire section on Reactors in the multimedia. This consists of modules describing all of the reactor models available in ASPEN PLUS, each illustrated by an example application. The students should ensure that they have covered the modules describing the PFR and the CSTR. Session 2: The tutorial Ammonia Converter Design should be reviewed, while at the same time, the student should develop his/her version of the simulation using ASPEN PLUS. To reinforce their acquired capabilities, students should be assigned a homework exercise. A typical exercise is provided. 101

102 Exercise E.1 Reactor Design Problem Maleic anhydride is manufactured by the oxidation of benzene over vanadium pentoxide catalyst (Westerlink and Westerterp, 1988), with excess air. The following reactions occur: Reaction 1: Reaction 2: Reaction 3: C H + O C H O + 2CO + 2H O (1) H O + 3O 4CO + H O (2) C C H + O 6CO + 3H O (3) Since air is supplied in excess, the reaction kinetics are approximated as first-order rate laws: r 1 r 2 A P B r 3 C r1 k1c A,r2 = k2c P = and r3 = k3ca (4) In the above, A is benzene, P is maleic anhydride (the desired product), and B and C are the undesired byproducts (H 2 O and CO 2 ), with kinetic rate coefficients in s -1 : k k 2 1 = 4, 300 exp = 70, 000 exp k 3 = 26 exp [ 25, 000 RT] [ 30, 000 RT] [ 21000, RT] In Eq. (5), the activation energies are in kcal/kgmol. (5) The objective of this exercise is to design a plug flow reactor to maximize the yield of MA, for a feed steam of 200 kgmol/hr of air (21 mol % O 2 and 79 mol % N 2 ) and 2 kgmol/hr of benzene, at 200 o C and 1.5 Bar. Assume a reactor diameter of 2 m, neglect pressure drops, and design for adiabatic operation. a) For fixed reactor tube length of 7 m, define the optimum reactor feed temperature to maximize MA yield (Hint: check values in the range o C) b) Investigate the effect of both reactor tube length, in the range 5-15 m, and feed temperature, in the range o C, on the MA yield. Define the optimum combination of both of these variables. HYSYS.Plant Solution 102 ASPEN PLUS Solution

103 Exercise E.1 Solution using HYSYS.Plant Solution reproduced in: REACT_EX_1.hsc a) The process is simulated using the Antoine equation for vapor pressure estimation (in the reaction conditions, the system is in the vapor phase, so that VLE calculations are not performed anyway). A PFD for the process is set up as below, noting that a heater, E-101, is installed to bring the reactor feed to the desired temperature. The Databook is used to investigate the sensitivity of yield (computed as the ratio of the molar flow rate of MA in PRODUCTS and the molar flow rate of benzene in S-2, 2 kgmol/hr), and selectivity (computed as the ratio of MA in PRODUCTS and the molar flow rates in the same stream of the byproducts, H 2 O and CO 2 ). A parametric run for a reactor of length 7 m is shown next. 103

104 b) It is noted that for a reactor tube length of 7 m, the optimal feed temperature appears to be 780 o C; here the yield is just over 22% and the selectivity is about 16%. An additional sensitivity analysis, testing the variation of both feed temperature and reactor tube length, gives the following result: The peak in yield occurs approximately at a reactor tube length of 14 m, with a feed temperature of 710 oc. Complete results for these operating conditions are listed below. Fluid Package: Basis-1 Property Package: Antoine Plug Flow Reactor: PFR-100 PARAMETERS Physical Parameters 104 Pressure Drop: bar Type : User Specified Heat Transfer : Heating Type : Direct Q Value Energy Stream : Duty : kcal/h Dimensions Total Volume: m3 Length: m Diameter: m Number of Tubes: 1 Wall Thickness: 5.000e-003 m Void Fraction: Void Volume: m3 Reaction Info

105 Reaction Set: Global Rxn Set Integration Information Number of Segments: 30 Initialize From: Current Minimum Step Fraction: 1.0e-06 Minimum Step Length: 1.4e-05 m Length (m) Temperature (C)

106 Mole Fractions Length (m) Oxygen CO2 H2O Benzene MaleicAnhydr Nitrogen PROPERTIES S-2 Overall Vapour Phase Vapour/Phase Fraction 1 1 Temperature: (C) Pressure: (bar) Molar Flow (kgmole/h) Mass Flow (kg/h) Liquid Volume Flow (m3/h) Molar Enthalpy (kcal/kgmole) Mass Enthalpy (kcal/kg) Molar Entropy (kj/kgmole-c) Mass Entropy (kj/kg-c) Heat Flow (kcal/h) 1.11E E

107 PRODUCTS Overall Vapour Phase Vapour/Phase Fraction 1 1 Temperature: (C) Pressure: (bar) Molar Flow (kgmole/h) Mass Flow (kg/h) Liquid Volume Flow (m3/h) Molar Enthalpy (kcal/kgmole) Mass Enthalpy (kcal/kg) Molar Entropy (kj/kgmole-c) Mass Entropy (kj/kg-c) Heat Flow (kcal/h) 1.11E E