1. Introduction to Aspen Plus
Speaker: Zong-Yan Li(李宗諺)
PSE Laboratory
Department of Chemical Engineering
National Taiwan University
(化工館RM307, )
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 V10

2. 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)

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

4. 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 

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

6. Initializing Aspen Plus
AspenTech>>Aspen Plus>>Aspen Plus V10

7. Creating Simulation File

8. Starting up Interface

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

10. Part 2
Property analysis

11. 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
Choose “Equals” instead!

12. Searching with compound name1 2
Double click on the compound
Or click “Add selected compounds”
Searching with chemical formula

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

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

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

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

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

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

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)

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

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

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

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. Example: Building Dimethyl Adipate (DIMA)

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

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

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

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

37. Check parameter pairs:
For N components system, there should be 𝐶 2 𝑁 pairs of binary parameters 3
See one binary parameter set
Red semicircle turns to blue circle with check 2 1
Click on red semicircle

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

39. You can set unit of temperature/pressure
(Please switch the temperature unit to K for next step)
T-xy diagram for WATER/BUOH
Liquid/vapor mole fraction, WATER
Temperature, K
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
0.750
0.775
0.800
0.825
0.850
0.875
0.900
0.925
0.950
0.975
1.000 92 94 96 98
100
102
104
106
108
110
112
114
116
118
x bar
y bar
Liquid-liquid-vapor
Phase equilibrium

40. Experimental Data Validation1 2 3 4

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

42. 2 3 1

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

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

45. Simulation data fit the exp. ones fairly well!
T-xy diagram for WATER/BUOH
Liquid/vapor mole fraction, WATER
Temperature, K
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
0.750
0.775
0.800
0.825
0.850
0.875
0.900
0.925
0.950
0.975
1.000
364
366
368
370
372
374
376
378
380
382
384
386
388
390
392
x bar
y bar
Exp. y BVLE067 ( N/sqm)
Exp. x BVLE067 ( N/sqm)
Simulation data fit the exp. ones fairly well!

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

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

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

49. 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

50. 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!

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

52. Mixing-heating process
Part 3
Mixing-heating process

53. Process to be simulated1
5 atm
50 °C
5 atm 2
Mixing
tank
Pump
Heater
Stream 1 2
Temperature (°C) 30
Pressure (bar)
Glycerol (kmol/hr)
100
Water (kmol/hr) 50
HAc (kmol/hr)
Q: What are the value of pump work and heater duty?

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

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

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

57. Add stream on block Red arrow: required stream
Blue arrow: optional stream 2
Click on arrow and construct
Inlet stream 1
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

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

59. 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”

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

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

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

63. Check the simulation result1
Right click on stream 2
Click “Results” 3
All stream information are available in the table

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

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

66. Construct outlet stream of pump then run simulation

67. Check the pump work
Right click on pump icon
Then click on “Results”
The work required is kW

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

69. Solution

70. Part 4
Reaction Simulation

71. Example: isomerization reaction of butane
Normal butane (A) is to be isomerized to isobutane (B) in a plug-flow reactor
𝑛− 𝐶 4 𝐻 10 (𝐴)↔𝑖− 𝐶 4 𝐻 10 (𝐵)
Rate expression: 𝑟= 𝑘 𝑓 𝐶 𝐴 − 𝑘 𝑏 𝐶 𝐵 ; 𝐶 𝐴 and 𝐶 𝐵 are in molarity (M)
𝑘 𝑓 =3.0× exp − 𝑅𝑇 [1/s]
𝑘 𝑏 =1.2× exp − 𝑅𝑇 [1/s]
Unit of 𝐸 𝐴 is 𝑘𝐽 𝑘𝑚𝑜𝑙
Feed: 20 atm, 30 °C, 20 kmol/hr, 90 mol % (A) and 10 mol %(B)
(high pressure for liquid phase reaction)
Reactor: 1 meter in diameter and length, adiabatic PFR
Thermodynamics model: Peng-Robinson (PENG-ROB) equation of state

72. Try to select components and thermodynamics model by yourself

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

74. In Aspen Plus, we need to define forward/reverse reaction respectively
𝑟=3.0× exp − 𝑅𝑇 𝐶 𝐴 [M/s]
Forward: 𝑛− 𝐶 4 𝐻 10 (𝐴)→𝑖− 𝐶 4 𝐻 10 (𝐵)
Reactant: N-C4H10
Coefficient in reaction equation = -1
Product: I-C4H10
Coefficient in reaction equation = 1 1 2
Switch to “Kinetic”

75. 𝑟=3.0× exp − 𝑅𝑇 𝐶 𝐴 [M/s]
Forward: 𝑛− 𝐶 4 𝐻 10 (𝐴)→𝑖− 𝐶 4 𝐻 10 (𝐵) 1
Select reaction 2
Reacting phase/rate basis 3
Key in kinetics parameters
Note:
there is no 𝑇 0 in kinetics expression  left the 𝑇 0 blank being empty
(2) Unit of k in Aspen Plus is [ (𝑀) 𝑎 /𝑠] (𝑎 depends on expression of rate law)

76. Practice: Define the reverse reaction

77. 𝑟=1.2× exp − 𝑅𝑇 𝐶 𝐵 [M/s]
reverse: 𝑖− 𝐶 4 𝐻 10 (𝐴)→𝑛− 𝐶 4 𝐻 10 (𝐵)

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

79. PFR Setting: adiabatic, 1 meter in diameter and length3 2
Move defined reaction set (R-1) to “Selected reaction sets”
Be careful about reacting phase!!

80. PFR Inlet setting

81. Check simulation result1
Right click on PFR icon 2
Click “Stream Results” to check the inlet and outlet streams simultaneously

83. Temp./Concentration profile in PFR
Blocks  B1 (block name of PFR) Profiles

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

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

86. Simple distillation simulation
Part 5
Simple distillation simulation

87. Example: flash benzene and toluene
Saturated Feed:
Liquid phase itself, but start vaporizing if heated.
T=95 °C
P=1atm
Saturated Feed
P=1atm
F=100 kmol/hr
zBen=0.5
zTol=0.5
What are flowrates and compositions of the two outlets?

88. Try to select components and thermodynamics model by yourself

89. Add Block: Flash2

90. Add Material Stream

91. Specify Feed Condition

92. Block Input: Flash2

93. Flash2: Specification
T=95 °C
P=1atm

94. Stream Results

95. Stream Results (cont’d)
kmol/hr
zBEN=0.627
zTOL=0.373
T=95 °C
P=1atm
Saturated Feed
P=1atm
F=100 kmol/hr
zBEN=0.5
zTOL=0.5
kmol/hr
zBEN=0.404
zTOL=0.596

96. System Containing Benzene/Toluene
Example :
Reflux ratio: 3
Pressure at top: 100 kpa
Assume no pressure drop in the column
Find:
Minimum number of stages needed
Corresponding feed stage
Distillate should be completely condensed
(Problem is taken from Coulson & Richardson’s Chemical Engineering, vol 2, Ex 11.7, p.564)

97. 1. By what you learned in Material balance and unit operation
From Overall Material Balance:
100 = D+B
From Benzene Balance:
100*0.4 = 0.9 * D+ 0.1* B
Thus, D=37.5 and B=62.5.
37.5
62.5

98. 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.

99. By the shortcut method in Aspen Plus (DSTWU)
DSTWU: Use Winn-Underwood-Gilliland method to estimate the minimum stage/reflux ratio needed
Ref:

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

102. “Feed1” Stream specification
DSTWU column specification
“Feed1” Stream specification

103. From the problem
Assume no pressure drop
Inside the column

104. Light Key recovery
= (mol of light component in distillate) / (mol of light component in feed)
= (37.5*0.9)/(100*0.4) =

105. Heavy Key recovery
= (mol of heavy component in distillate) / (mol of heavy component in feed)
= (37.5*0.1)/(100*0.6) =

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

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

108. Stream Results
Required product quality

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

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

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

112. Connect the required material stream

113. Same as Case 2

114. Double left click on the unit

115. 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

116. Specify the feed stage

117. Specify the pressure at the top of column

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

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

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

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

122. Click “Design Specification” first1 2
Spec in this case: mole purity = 90%

123. 3
Numerator
Denominator
Definition of mole purity =
(BEN)/ (BEN+TOL) 4
Distillate (DST1) should meet the spec

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

125. 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)

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

127. Comments:
It’s not easy to get converged value when using Design Specification. Here are some tips:
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.
Adjust the input variables manually in the beginning to understand the trend.
Do not set interval between upper/lower bound in “Vary” to be too large or small (need experience!)
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)

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

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

130. Example: Please reproduce the following flowsheet
𝑋 𝑎𝑐𝑒𝑡𝑜𝑛𝑒 = 0.753
𝑋 𝑀𝐸𝑂𝐻 = 0.247
1 atm
10 atm
𝑋 𝑎𝑐𝑒𝑡𝑜𝑛𝑒 = 0.4
𝑋 𝑀𝐸𝑂𝐻 = 0.6
Mixer
100 kmol/hr
Saturated liquid
𝑋 𝑎𝑐𝑒𝑡𝑜𝑛𝑒 = 0.7
𝑋 𝑀𝐸𝑂𝐻 = 0.3
𝑋 𝑎𝑐𝑒𝑡𝑜𝑛𝑒 = 0.999
𝑋 𝑀𝐸𝑂𝐻 = 0.001
𝑋 𝑎𝑐𝑒𝑡𝑜𝑛𝑒 = 0.001
𝑋 𝑀𝐸𝑂𝐻 = 0.999
All fraction in molar base
Product spec: 99.9 mol %
Thermodynamics model: UNIQUAC
Assume no pressure drop in distillation column
50 stages, feed at 25th stage , reflux ratio = 3 for both column
Azeotrope at 1 atm: 𝑋 𝑀𝐸𝑂𝐻 =0.2225, °C
Azeotrope at 10 atm: 𝑋 𝑀𝐸𝑂𝐻 =0.6252, °C

131. 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
𝑋 𝑎𝑐𝑒𝑡𝑜𝑛𝑒 = 0.753
𝑋 𝑀𝐸𝑂𝐻 = 0.247
1 atm
10 atm
𝑋 𝑎𝑐𝑒𝑡𝑜𝑛𝑒 = 0.4
𝑋 𝑀𝐸𝑂𝐻 = 0.6
Mixer
Flowrate = F
100 kmol/hr
Saturated liquid
𝑋 𝑎𝑐𝑒𝑡𝑜𝑛𝑒 = 0.7
𝑋 𝑀𝐸𝑂𝐻 = 0.3
𝑋 𝑎𝑐𝑒𝑡𝑜𝑛𝑒 = 0.999
𝑋 𝑀𝐸𝑂𝐻 = 0.001
𝑋 𝑎𝑐𝑒𝑡𝑜𝑛𝑒 = 0.001
𝑋 𝑀𝐸𝑂𝐻 = 0.999
MEOH Mole balance for LP column: assume bottom product is pure MEOH
0.6F = 0.247(F-30) + 30
F = ; estimated recycle flowrate ≈

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

133. Key in estimated value

134. Set Design Specification on HP column after first run3 1 2

135. Set ”Vary”
Run the simulation…  Result available

136. Build up LP column
That’s helpful for convergence

137. 4
Run the simulation again
Value changed from “initial guess” (30) to actual values (29.709)
Reason for reconciling:
Reduce the iteration times for Aspen Plus and make it easier to converge.
(Useful for complicated simulation especially!) 3
Click Ok
“Input changed” in lower-left corner

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

139. Set the discharge pressure of pump to be 10 atm then run the simulation3
Temperature/flowrate/composition of pump outlet are slightly different with initial guess of recycle flow

140. 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

141. After 4 rounds…

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

143. 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)

144. 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

145. Thanks for your attention!