Introduction to Aspen Plus Speaker ZongYan Li r

Introduction to Aspen Plus Speaker: Zong-Yan Li(李宗諺) r 07524013@ntu. edu. tw PSE Laboratory Department of Chemical Engineering National Taiwan University (化 館RM 307, 02 -33663068) Editors : 程建凱/吳義章/余柏毅/陳怡均/潘晧人/李宗諺 Figures in the slides are based on Aspen Plus V 10 1

Outline • Part 1 : Introduction and start-up Aspen Plus software • Part 2 : Properties analysis 2 -1: Select compounds needed 2 -2: Select thermodynamics model 2 -3: Plotting phase diagram/ thermodynamics validation 2 -4: System without build-in parameter • Part 3 : “Mixing-heating” process simulation • Part 4 : Reaction simulation • Part 5 : Simple distillation simulation • Part 6 : Separating azeotrope: Pressure Swing Distillation (PSD) 2

Part 1 Introduction & start-up of Aspen Plus software 3

What course Aspen Plus can be employed for • MASS AND ENERGY BALANCES • PHYSICAL CHEMISTRY • CHEMICAL ENGINEERING THERMODYNAMICS • CHEMICAL REACTION ENGINEERING • UNIT OPERATIONS • PROCESS DESIGN • PROCESS CONTROL 4

How Aspen Plus Work Process Inlet(s) Mass balance Energy balance Thermodynamics User define models outlet(s) Simulate a process based on principles above 5

Initializing Aspen Plus Aspen. Tech>>Aspen Plus V 10 6

Creating Simulation File 7

Starting up Interface 8

Guideline for starting a simulation 1. Select chemical compound in the system we want to simulate 2. Select suitable thermodynamics model to describe the system 3. Try your best to validate thermodynamic data First rule of simulation: Garbage in, garbage out 9

Part 2 Property analysis 10

2 -1 Select compounds needed Example: water & n-butanol (n-BUOH) mixture system 1 2 Every compound with “water” appears in its name shows in searching result Ø Choose “Equals” instead! 11

1 ü Searching with compound name 2 ü Searching with chemical formula Double click on the compound Or click “Add selected compounds” 12

Select n-butanol (n-BUOH) Add n-butanol, not replace You can change Component ID (name appears in simulation) 13

Example: Building Dimethyl Adipate (DIMA) Find DIMA (Dimethyl Adipate) 14

Example: Building Dimethyl Adipate (DIMA) No DIMA in the databanks 15

Example: Building Dimethyl Adipate (DIMA) • Check NIST chemistry webbook for those information you need to build a user defined component. (http: //webbook. nist. gov/chemistry/) Searching Method 16

Example: Building Dimethyl Adipate (DIMA) Searching for DIMA 17

Example: Building Dimethyl Adipate (DIMA) All information you can find in NIST Download the 2 -d molecular structure file 18

Example: Building Dimethyl Adipate (DIMA) 19

Example: Building Dimethyl Adipate (DIMA) 20

Example: Building Dimethyl Adipate (DIMA) 21

Example: Building Dimethyl Adipate (DIMA) 22

Example: Building Dimethyl Adipate (DIMA) 23

Example: Building Dimethyl Adipate (DIMA) 24

Example: Building Dimethyl Adipate (DIMA) Import the 2 -d molecular file you downloaded from NIST 25

Example: Building Dimethyl Adipate (DIMA) (Calculate bond for UNIFAC model estimation) 26

Example: Building Dimethyl Adipate (DIMA) Check the formula again. Then the component is successfully built. 27

Example: Building Dimethyl Adipate (DIMA) 28

Example: Building Dimethyl Adipate (DIMA) 29

Example: Building Dimethyl Adipate (DIMA) 30

Example: Building Dimethyl Adipate (DIMA) 31

Example: Building Dimethyl Adipate (DIMA) 32

2 -2 Select Thermodynamics Model Choose suitable model to describe behavior of liquid/gas phase (a) Relationship between pressure/temperature/volume of gas (b) Phase diagram of liquid mixture EOS: Equation of State (ex: Van der Waal equations) 33

Typical Equation of States Peng-Robinson (PR) EOS Redlich-Kwong (RK) EOS Haydon O’Conell (HOC) EOS 34

Typical Activity Coefficient Models Non-Random-Two Liquid Model (NRTL) UNIQUAC Model UNIFAC Model 35

Water & Bu. OH: polar compounds Ø Choose activity coefficient model; NRTL in this demonstration to describe liquid phase Ø Select NRTL in Methods: use ideal gas law to describe vapor phase 1 2 36

3 See one binary parameter set Red semicircle turns to blue circle with check 2 1 Click on red semicircle 37

2 -3 Plotting Phase Diagram/ Thermodynamics Validation Analysis Binary Txy or Pxy Define x-axis 38

You can set unit of temperature/pressure (Please switch the temperature unit to K for next step) T-xy diagram for WATER/BUOH 118 x 1. 0133 bar y 1. 0133 bar 116 114 112 Temperature, K 110 108 106 104 Liquid-liquid-vapor Phase equilibrium 102 100 98 96 94 92 0. 000 0. 025 0. 050 0. 075 0. 100 0. 125 0. 150 0. 175 0. 200 0. 225 0. 250 0. 275 0. 300 0. 325 0. 350 0. 375 0. 400 0. 425 0. 450 0. 475 0. 500 0. 525 0. 550 0. 575 0. 600 0. 625 0. 650 0. 675 0. 700 0. 725 Liquid/vapor mole fraction, WATER 0. 750 0. 775 0. 800 0. 825 0. 850 0. 875 0. 900 0. 925 0. 950 0. 975 1. 000 39

1 Experimental Data Validation 2 3 4 40

1 2 Choose one experimental data Then double click on it (later in year; more data point) Look up “Binary VLE” Isobaric (Txy plot) 41

2 1 3 42

Now the data have been saved! Click “T-xy” in “Plot” Temperature, K T-xy diagram for WATER/BUOH Liquid/vapor mole fraction, WATER 43

Merge two plot (simulation/exp. data) 2 Merge plots 3 1 Switch to exp. data Txy plot You will see a plot with 2 y-axis; use “Y axis map” to merge them 4 44

T-xy diagram for WATER/BUOH 392 x 1. 0133 bar y 1. 0133 bar Exp. y BVLE 067 (101300 N/sqm) Exp. x BVLE 067 (101300 N/sqm) 390 388 386 384 Simulation data fit the exp. ones fairly well! 382 Temperature, K 380 378 376 374 372 370 368 366 364 0. 000 0. 025 0. 050 0. 075 0. 100 0. 125 0. 150 0. 175 0. 200 0. 225 0. 250 0. 275 0. 300 0. 325 0. 350 0. 375 0. 400 0. 425 0. 450 0. 475 0. 500 0. 525 0. 550 Liquid/vapor mole fraction, WATER 0. 575 0. 600 0. 625 0. 650 0. 675 0. 700 0. 725 0. 750 0. 775 0. 800 0. 825 0. 850 0. 875 0. 900 0. 925 45 0. 950 0. 975 1. 000

Save the Simulation File Save the file in Aspen Plus Documents (. apw) 46

Error demonstration: If we intentionally delete thermodynamics parameters… Aspen Plus treat the liquid phase as ideal liquid mixture Bad simulation result! 47

2 -4 System without Build-in Parameter Practice: open a new file and choose glycerol, water, acetic acid (HAC) 48

Choose “NRTL-HOC” thermodynamics model Method filter: ALL NRTL-HOC: Use NRTL model to describe the liquid phase Use HOC equation of state to describe behavior of carboxylic acid dimer (acetic acid in this case) in gas phase 49

Check parameters… 3 -components system: should have 3 sets of parameter, but no build-in parameter for GLYCEROL and HAC… “Required Properties Input Complete” still be at lower-left corner! 50

To solve the problem, use “UNIFAC” to estimate parameters we need UNIFAC: Predict thermodynamics data by examining functional groups in molecule 2 Run 1 3 Click “Estimate using UNIFAC” Estimated parameters appear! 51

Part 3 Mixing-heating process 52

Process to be simulated 1 5 atm 50 °C 5 atm 2 Mixing tank Pump Heater Stream 1 2 Temperature (°C) 30 30 Pressure (bar) 1 1 Glycerol (kmol/hr) 0 100 Water (kmol/hr) 50 0 HAc (kmol/hr) 50 0 Q: What are the value of pump work and heater duty? 53

Switch to “Simulation” mode Many type of units are available here 54

Construct “Mixer” (tank) in flowsheet There are 12 different icons representing mixer You can arbitrarily use any of them without affecting simulation result! 55

2 Click on “Main Flowsheet” to build a mixer 1 Click on “Mixer” icon 56

Add stream on block Red arrow: required stream Blue arrow: optional stream 2 1 Click on arrow and construct Inlet stream Click on “Material” 3 Repeat step 2 (2 inlets, 1 outlet) Tips: click on the stream then press “ctrl+B” can make the stream straight 57

Define inlet stream 1 Click on stream/block name and rename them 2 Double click on stream 1, then the following screen appears 58

Key in temperature/pressure/flowrate Red semicircle turns to blue circle No need to specify total flow rate since the value has been assigned in “Composition” 59

Another way Specify mole fraction (“Mole-frac”) here Specify total flow rate Note: mass base is also available (depend on what you need!) 60

Define stream 2 “Required Input Complete” in bottom-left corner All setting are complete and we can start simulation 61

1 2 Click “Run” “Result Available” simulation is successful! 62

Check the simulation result 3 1 Right click on stream 2 Click “Results” All stream information are available in the table 63

Construct pump (can be found in “Pressure Changers”) on the flowsheet Reconnect Destination: reconnect “to” somewhere To connect the outlet stream of mixer to pump, right click on the stream then choose “Reconnect Destination” Reconnect Source: Reconnect “from” somewhere 64

Pump setting: Double click on pump icon Set the outlet pressure to be 5 bar 65

Construct outlet stream of pump then run simulation 66

Check the pump work Right click on pump icon Then click on “Results” The work required is 2. 77791 k. W 67

Practice: Construct heater (can be found in “Exchangers”) Try to set parameters of heater by yourself. What’s the duty of heater? 68

Solution 69

Part 4 Reaction Simulation 70

Example: isomerization reaction of butane 71

Try to select components and thermodynamics model by yourself 72

2 1 3 Click “New” in Reactions 4 Select “POWERLAW” reaction type (ID can be given arbitrarily) 5 Click “New” in Stoichiometry Click “Reaction” Switch to “Simulation” mode 73

In Aspen Plus, we need to define forward/reverse reaction respectively Reactant: N-C 4 H 10 Coefficient in reaction equation = -1 Product: I-C 4 H 10 Coefficient in reaction equation = 1 2 1 Switch to “Kinetic” 74

1 Select reaction 2 Reacting phase/rate basis 3 Key in kinetics parameters 75

Practice: Define the reverse reaction 76

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Back to Main Flowsheet and select PFR (RPlug in “Reactors”) 78

PFR Setting: adiabatic, 1 meter in diameter and length 1 3 2 Move defined reaction set (R-1) to “Selected reaction sets” Be careful about reacting phase!! 79

PFR Inlet setting 80

Check simulation result 1 2 Right click on PFR icon Click “Stream Results” to check the inlet and outlet streams simultaneously 81

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Temp. /Concentration profile in PFR Blocks B 1 (block name of PFR) Profiles 83

Temp. /Concentration profile plot in PFR You can make Temperature/Pressure/Composition plot by clicking here 84

Example: Temperature profile plot; use length as x-axis 85

Part 5 Simple distillation simulation 86

Example: flash benzene and toluene Saturated Feed: Liquid phase itself, but start vaporizing if heated. Saturated Feed P=1 atm F=100 kmol/hr z. Ben=0. 5 z. Tol=0. 5 T=95 °C P=1 atm What are flowrates and compositions of the two outlets? 87

Try to select components and thermodynamics model by yourself 88

Add Block: Flash 2 89

Add Material Stream 90

Specify Feed Condition 91

Block Input: Flash 2 92

Flash 2: Specification T=95 °C P=1 atm 93

Stream Results 94

Stream Results (cont’d) 43. 008 kmol/hr z. BEN=0. 627 z. TOL=0. 373 Saturated Feed P=1 atm F=100 kmol/hr z. BEN=0. 5 z. TOL=0. 5 T=95 °C P=1 atm 56. 992 kmol/hr z. BEN=0. 404 z. TOL=0. 596 95

System Containing Benzene/Toluene Example : • Reflux ratio: 3 • Pressure at top: 100 kpa • Assume no pressure drop Distillate should be completely condensed in the column Find: 1. Minimum number of stages needed 2. Corresponding feed stage (Problem is taken from Coulson & Richardson’s Chemical Engineering, vol 2, Ex 11. 7, p. 564) 96

1. By what you learned in Material balance and unit operation From Overall Material Balance: 100 = D+B 37. 5 From Benzene Balance: 100*0. 4 = 0. 9 * D+ 0. 1* B Thus, D=37. 5 and B=62. 5. 62. 5 97

1. By what you learned in Material balance and unit operation From thermodynamic phase equilibrium, and the calculation of operating line: We can get the number of theoretical plate to be 7. 98

By the shortcut method in Aspen Plus (DSTWU) DSTWU: Use Winn-Underwood-Gilliland method to estimate the minimum stage/reflux ratio needed Ref: http: //www. just. edu. jo/~yahussain/files/Equilibrium%20 Separation%20 Columns. pdf 99

Add the unit “DSTWU” The red arrows are the required material stream! 100

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DSTWU column specification “Feed 1” Stream specification 102

From the problem Assume no pressure drop Inside the column 103

Light Key recovery = (mol of light component in distillate) / (mol of light component in feed) = (37. 5*0. 9)/(100*0. 4) = 0. 84375 104

Heavy Key recovery = (mol of heavy component in distillate) / (mol of heavy component in feed) = (37. 5*0. 1)/(100*0. 6) = 0. 0625 105

Get results by varying the number of stages. (Initial Guess) 106

Run the simulation… Right click on the unit, and select “Stream Results” 107

Stream Results Required product quality 108

Column Results Estimated result from Winn-Underwood. Gilliland method (Reason why the values are not integer) 109

RR vs number of stage For RR=3, at least 7 theoretical stages are required. 110

More rigorous method in Aspen Plus (RADFRAC) Add the unit “RADFRAC” The red arrows are the required material stream! 111

Connect the required material stream 112

Same as Case 2 113

Double left click on the unit 114

RADFRAC column specification 7 stages from previous calculation. Total condenser is used RR=3 from the problem, distillate rate = 37. 5 (kmol/h) from previous calculation 115

Specify the feed stage 116

Specify the pressure at the top of column 117

Click right button on the unit, and select “Stream Results” 118

The result is slightly different with result of DSTWU column (Not at optimal feed stage) 119

Exercise Adjust reflux ratio so that the distillate contains 90 mol% benzene. Number of stages, distillate rate, and feed stage remain unchanged. ? ? ? 120

It’s tedious to manually adjust the input variable… Ø Use “Design Specification”! Design Specification: Automatically calculate value of input variable (reflux ratio in this case) to make the product stream meets spec. 121

Click “Design Specification” first 1 2 Spec in this case: mole purity = 90% 122

3 Numerator Denominator Definition of mole purity = (BEN)/ (BEN+TOL) 4 Distillate (DST 1) should meet the spec 123

Switch to “Vary” (1 Design Specification 1 Vary) Vary: set input variable that are going to be adjust automatically 1 2 124

By using Design Spec, even we set the value of reflux ratio to be 3 in RADFRAC “ 3” serves as initial guess here The result of reflux ratio is still the value that make the product meet spec. (with very small difference due to error tolerance) 125

Note: If your “initial guess” is outside the range of upper/lower bound in “Vary” Red semi-circle appears and you cannot run simulation 126

Comments: It’s not easy to get converged value when using Design Specification. Here are some tips: 1. It’s okay to use two Design Specification on a RADFRAC column, but I suggest you do that one-by-one; Setting Design Spec 1, getting converged, then setting the other one. 2. Adjust the input variables manually in the beginning to understand the trend. 3. Do not set interval between upper/lower bound in “Vary” to be too large or small (need experience!) 4. If you keep getting error message, try to understand if there is anything wrong in your idea (Example: try to separate binary mixture with azeotrope on phase diagram) 127

Part 6 Separating azeotrope: Pressure Swing Distillation (PSD) 128

Introduction to PSD It’s useful when separating azeotropes that the composition are sensitive to pressure. Example: acetone/methanol (Me. OH) 1 atm Bottom: Pure Me. OH Distillate: (nearly) azeotropic composition at 1 atm X-axis: Me. OH mol fraction 10 atm Bottom: Pure Acetone Distillate: (nearly) azeotropic composition at 10 atm Feed 129

Example: Please reproduce the following flowsheet 10 atm 1 atm Mixer • All fraction in molar base • Product spec: 99. 9 mol % • Thermodynamics model: UNIQUAC • Assume no pressure drop in distillation column • 50 stages, feed at 25 th stage , reflux ratio = 3 for both column 130

Whenever you want to connect recycle stream… • Make initial guess (temperature/pressure/flowrate/composition) first • DO NOT connect recycle stream in the beginning of simulation 1 atm 10 atm Mixer Flowrate = F 131

Start from HP column: feed + (fake) recycle stream That’s helpful for convergence 132

Key in estimated value 133

Set Design Specification on HP column after first run 3 1 2 134

Set ”Vary” Run the simulation… Result available 135

Build up LP column That’s helpful for convergence 136

4 Run the simulation again Value changed from “initial guess” (30) to actual values (29. 709) Reason for reconciling: 3 Click Ok “Input changed” in lower-left corner Reduce the iteration times for Aspen Plus and make it easier to converge. (Useful for complicated simulation especially!) 139

Add pump to transport distillate of LP column back to HP column 1 Tips: Flip the pump icon to make the direction of inlet right-hand side 2 Connect inlet and outlet of pump Caution: DO NOT connect recycle stream now 140

3 Set the discharge pressure of pump to be 10 atm then run the simulation Temperature/flowrate/composition of pump outlet are slightly different with initial guess of recycle flow 141

Manually copy the result of pump outlet and paste it on input specification of recycle stream Run the simulation and do the manual iteration again Until the difference between pump outlet and recycle stream is small 142

After 4 rounds… 143

Tear the pump outlet stream and connect recycle stream back to pump outlet Run the simulation… 144

Tips: Use backup document to erase past error record If you save the simulation file as “. apw” format Several document appears including “Aspen Plus Backup File” . apw document. bkp document (Backup file) 145

Open the backup file and you will see the same flowsheet you done before Run the simulation, save the file, and close it Size of. apw file decreased! (error record has been eliminated) Prevent the file from crashed 146

Thanks for your attention! 147