manual de simulación de procesos químicos en aspen plus
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아스펜 플러스 공정 모사기 실습
아스펜 플러스 공정 모사기 실습
초판 1쇄 인쇄 2010년 06월 16일
초판 1쇄 발행 2010년 06월 23일
편편저 | 김병직
펴낸이 | 손형국
펴낸곳 | (주)에세이퍼블리싱
출판등록 | 2004. 12. 1(제315-2008-022호)
주소 | 157-857 서울특별시 강서구 방화3동 316-3번지 102호
홈페이지 | www.book.co.kr
전화번호 | (02)3159-9638~40
팩스 | (02)3159-9637
ISBN 978-89-6023-387-4 13430
이 책의 판권은 지은이와 (주)에세이퍼블리싱에 있습니다.
내용의 일부와 전부를 무단 전재하거나 복제를 금합니다.
아스펜 플러스공정 모사기 실습
김병직 편저
아스펜 플러스는 범용 화학공정모사기이다. 본서의 구성은
Part I ~ Part III로 구성되어 있고 Part I에는 공정모사 필요한
열역학을 설명하고 Part II에서는 11개의 예제 문제로 구성되어
있다. Part III는 아스펜모사기의 대표적 단위공정 모델을 소개
하고 있다. 본서는 화학공학 학부 4학년생이나 대학원 학생이
쉽게 아스펜 공정모사기에 쉽게 익숙해 질 수 있도록 설계된
입문서에 해당된다. 아스펜 플러스를 사용법은 세 단계로 나눌
수 있다.
1단계 : Process Flowsheet 을 완성하는 법
2단계: input(입력사항)의 입력하는 법 및 모사
3단계: 모사 결과를 효과적으로 확인하는 방법
Part II에서 알기 쉬운 설명과 함께 제공한 11개의 workshop을
따라 하다 보면 1단계 Process Flowsheet을 완성하는 법은 쉽
게 익힐 수 있을 것으로 생각된다. 2 단계 input을 입력하는 방
법 역시 11가지 예제 문제의 입력을 따라 하면 모사기를 실행시
킬 수 있게 된다.
Part III 에는 아스펜 플러스에서 제공하는 다양한 단위공정 모
델들을 설명한다.
서론
그러나 응용문제 또는 다른 문제에 적용하려면 화학공학의 기
본과목인 화공양론, 열역학, 반응공학, 분리공정에 대한 기본
지식이 필요하다. 더하여 그러한 화학공학의 원리와 물리의 이
론 및 실험 data, 화학의 실험 및 이론 data를 모두 포함하고
있는 Aspen Plus 범용 모사기를 적절하게 활용하려면 아스펜
플러스 manual을 참조하여야 한다. 아스펜 플러스에 내장되어
있는 ‘Help’ 기능을 활용하면 manual로부터 많은 궁금증에 대
한 답을 얻을 수 있다.
화학공학과 학생들이 휴대용 컴퓨터를 가지고 다니면서 모든 과
목의 과제를 아스펜 플러스를 사용하여 해결하고 conceptual
design에 익숙해질 날이 곧 올 것이라 생각하며 서론을 마치고
자 한다.
2010년 6월
김병직
Contents
PART 1
PART 2
공정모사에 필요한 열역학
공정모사기 실습
서론 _ 4
Physical Properties and selection of thermodynamic models _ 10
Simulation of an Air Compressor _ 18
Flash Separation _ 34
Introduction to Simulation with RadFrac _ 54
Design Specifications and Sizing _ 67
Sensitivity Analysis _ 75
Heat Exchangers _ 88
Production of Cyclohexane _ 93
Simulating a Distillation Column for Crude Oil _ 101
Simulating a Stripper for Wastewater Treatment _ 108
An Absorber-Stripper Process for CO2 Capture Using MEA _ 110
Phase equilibrium (azeotrope case) _ 112
PART 3단위공정 모델의 종류
Unit Operation Model Types _ 122
Reactor Models _ 133
Calculator Blocks _ 150
Customizing the look of your flowsheet _ 168
Optimization _ 180
PART 1공정모사에 필요한 열역학
10 아스펜 플러스 공정 모사기 실습
0if
oi
Pf oii
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oi
0,vii
vi fyf 0
, LiiL
i fxf
Pyf iviv
i ,
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Part 1 | 공정모사에 필요한 열역학 11
oi
ii f
fa
ivivi ya ,, iLiLi xa ,,
0.1,, Livi
12 아스펜 플러스 공정 모사기 실습
Part 1 | 공정모사에 필요한 열역학 13
1 An example of a strong polar compound is water. The following is a list of relative polarities of functional groups starting with most polar and ending with least polar: water organic acids amines alcohols esters ketones aldehydes ethers aromtics olefins paraffins.
14 아스펜 플러스 공정 모사기 실습
Part 1 | 공정모사에 필요한 열역학 15
Do You Have AnyPolarComponents in Your System?
Use EOS Model Are the operating conditionsnear the critical region of the mixture
Do you have light gases orsupercritical components
in your system
Use activity coefficientmodel with Henry’s law
Use activity coefficient model
No Yes
Yes
Yes
No
No
PART 2공정모사기 실습
18 아스펜 플러스 공정 모사기 실습
Workshop #1
Simulation of an Air Compressor
An isentropic compressor is used to compress 100 lbmole/hr of air (21% oxygen and
79% nitrogen) at 60 F and 14.7 psia to a pressure of 147 psia. Use Aspen Plus to model
this system. The flowsheet is shown below (Fig I.1)
Air100 lbmole/hr21% Oxygen79% Nitrogen14.7 psia60 oF
147.0 psia
IsentropicCompressor
Horsepower?
Temperature?
Figure I.1. Isentropic Compression Process
Turn In:
1) A memo with answers to the following:
a) How much power is needed to achieve the compression (in hp)?
b) What is the outlet air temperature in F?
Step By Step Instructions For Workshop #1:
Initiating the Aspen Plus User Interface on the PC:
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Open the Aspen Plus User Interface from the start bar
Figure I.2 below shows the location of the Aspen Plus User Interface on the start bar.
Figure I.2. Starting ASPEN Plus
After clicking on Aspen Plus User Interface, Aspen Plus will open and prompt you to select
one of three options: blank simulation, template, or open an existing simulation.
Select blank simulation and click on “OK”
The Aspen Plus startup screen can be seen in Figure I.3.
20 아스펜 플러스 공정 모사기 실습
Figure I.3. ASPEN Plus Startup
The program will now connect to the server2, this will take a few seconds. You are now
ready to begin your simulation.
Creating a Simulation Flowsheet
The bottom of the Aspen Plus window contains several tabs, which can be seen in Figure I.4.
These tabs allow the user to select the type of equipment or stream to be placed in their
simulation flowsheet.
Figure I.4. Model Menu Tabs
This brings up several choices of equipment.
2 If the program asks you about connecting to engine, use the local PC as the default server.
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This brings up four options for compressor icons. Figure I.5 below shows the selection of the
compressor tab and the proper compressor icon.
Figure I.5. Selecting an Icon for the Compressor
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Drag and drop (with left button)
Next, feed and product streams must be connected.
Once selecting the material stream icon the compressor block in the simulation flowsheet
will show three arrows, two red and one blue. These arrows indicate inlet and outlet
locations. The red arrows are feed and product locations that require streams to be attached.
The blue arrow is for collecting any liquid that is formed during compression. This is an
optional outlet that you don't have to connect to an outlet stream.
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The inlet feed stream to the compressor icon is now complete and labeled “1”
The same procedure can be used to insert the product stream.
Move the mouse pointer over to the bottom red arrow until highlighted. With the
left mouse button click once.
The simulation flowsheet is now complete and should look like Fig. I.7.
24 아스펜 플러스 공정 모사기 실습
Figure I.7. Process Flowsheet
From the File pull down menu, select Save As. It is advisable that you save your file
as a .bkp file (Fig. I.8a).
Fig. I.8a. File Saving
Part 2 | 공정모사기 실습 25
You may get a warning message as shown in Fig. I.8b, click No indicating that you
still want to save it in the backup format.
Fig. I.8b. Warning Message
Entering Input Specifications
The run now contains all the information about the simulation flowsheet. Next, the data
required to complete the problem specification must be entered. These data include
components, properties, the feed streams, and block operating parameters. To input these
data the setup button is used. The setup button is located at the top of the screen and can be
seen in Figure I.9a.
SetupButton
Figure 1.9a The Setup Button
Move the mouse pointer to the setup button and click once with the left mouse
button.
26 아스펜 플러스 공정 모사기 실습
Alternatively, you can go from the Data menu to the Setup option as shown in Fig. I.9b.
Fig. I.9b. Setup Option
This will bring up a new window, setup specifications, that can be seen in Figure I.10.
Figure I.10. Setup Specification
Part 2 | 공정모사기 실습 27
On this window, you can enter a title of your simulation (e.g., title of the workshop, your
name).
Left click once in the “Title” box then enter Workshop #1: Compressor by Ready T.
Graduate.
On the Setup Specification window, you can also choose the units to display your
input and output data (e.g. molar, mass, SI, metric, Engineering, etc.) as shown in Fig. I.11.
Fig. I.11. Entering Data on Setup Specification Window
The program will help guide you through the setup with the use of the Next button.
The Next button is a very useful advancement guide (an on-line artificial intelligence guide).
Left click once on the advancement button.
You will get the Component Specifications Window Alternatively, you could have clicked on
the Component Folder then the Specifications Form as shown in Fig. I.12.
28 아스펜 플러스 공정 모사기 실습
Fig. I.12. Using Folders and Forms to Access Component Specifications Window
In our simulation, we have two components, oxygen and nitrogen.
Left click in the Component ID Field and type Oxygen. When you hit return, the
program will recognize that it is oxygen and will display its type, name, and chemical
formula (Fig. I.13). You can do the same for Nitrogen.
Fig. I.13. Component Specifications Window
Left click on the Next button, you will get the Properties Specifications Window.
Part 2 | 공정모사기 실습 29
On
this form, you need to specify the type of thermodynamic model that will be used to estimate
the physical properties of the components and streams. Click on the drop-down arrow to get a
menu of choice. Select RK-Soave4 as your thermodynamic model (see Fig. I.14).
Fig. I.14. Selection of a Thermodynamic Property Method
Click on the Next button, you will get the Properties Parameters Binary Interaction
Window. This window is used when you have thermodynamic binary parameters that
you would like to use to override ASPEN's data. No need to do that today (save your
binary parameters for a rainy day)!. Click on Next button, you will get a couple of
windows for thermodynamic databases and parameters. Again, skip both and click on
Next. You will get the window shown in Fig. I.15 indicating that you are done with
properties and ready to proceed to the next required input step. Click on O.K.
4 Redlich-Kwong-Soave (RK-Soave) is a cubic equation of state. This property method is recommended for air compression, gas-processing, refinery, and petrochemical applications. Example applications include gas plants, crude towers, and ethylene plants.
30 아스펜 플러스 공정 모사기 실습
Fig. I.15. Required Input for Properties is Complete
You are now on the Stream Input Window (Fig. I.16).
Enter the values of temperature (60 oF), pressure (14.7 psi), and molar flowrate (100
lbmol/hr) for the entering air stream.
Fig. I.16. Entering Stream Data
If the units were not what we wanted, we could have used the drop-down menu to change the
units (Fig. I.17).
Part 2 | 공정모사기 실습 31
Fig. I.17. Changing Units
In the composition field, use the drop-down arrow to display the menu for
compositions. Choose Mole-Fraction (Mole-Frac) option (Fig. I.18) and enter the
data for air (0.21 Oxygen and 0.79 Nitrogen as shown in Fig. I.19).
Fig. I.18. Selection of Mole Fraction
Fig. I.19. Entering Mole Fractions
Click on Next, you will get the Block Setup window (Fig. I.20). The Isentropic
compressor model is already selected (which is our compressor type). We also need to
32 아스펜 플러스 공정 모사기 실습
enter the data for the outlet of the compressor. Since the outlet pressure is 147 psia, you
can click on Discharge pressure and enter 147 psia (or click on pressure ratio and enter
10).
Fig. I.20. Block Setup Window
Click on Next, you will get a window indicating that all required input has been
provided and are complete5. Do you want to run simulation? Click on O.K.
Fig. I.21. Required Input Complete
5 Notice that the symbol now appears next to all input forms indicating that they are complete.
Part 2 | 공정모사기 실습 33
Once the simulation converges, click on the Display Results Button (Fig. I.22).
Alternatively, you could you click on the Next button. Also, you could have gone to
the Data menu then to the Results Option.
DisplayResultsButton
Fig. I.22. Display Results Button
Use the browsing buttons (>> and <<) to browse through the results forward
and backward. You can also click on the Blocks folder then click on B1 form you will
get the results as shown in Fig. I.23. Record/print the required results, save your file,
and exit.
Yournumbers
Fig. I.23. Viewing Results
Congratulations! You have performed your first ASPEN simulation.
34 아스펜 플러스 공정 모사기 실습
Workshop #2
Flash Separation
A flash column is used to separate a gas mixture into liquid and vapor fractions. The
feed is at 400oF and 21 atm (Fig. II.1). It contains hydrogen (30.0 lbmol/hr), nitrogen (15.0
lbmol/hr), methane (43.0 lbmol/hr), cyclohexane (144.2 lbmol/hr), and benzene (0.2
lbmol/hr). The flash column operates at 120oF and there is no pressure drop in it. The liquid
entrainment in the vapor phase from the separator is 0.012.
The flash column can be modeled by ASPEN Plus' model FLASH2 and the thermodynamic
properties can be estimated using the Redlich-Kwong-Soave equation.
Part I: What is the flowrate and composition of the vapor phase
Part II: Develop the heating curve for the separator and use it to determine the dew point of
the feed.
Part III: If we wish to split the molar flowrate of the feed equally between the vapor and the
liquid products, what should the column temperature be (while keeping all other operating
conditions the same)? Verify your answer by running a new simulation with the new column
temperature.
Your report should include a memo, your input files, and supporting graphs.
FeedS1400 oF21 atm.Hydrogen = 30.0 lbmol/hrNitrogen = 15.0 lbmol/hrMethane = 43.0 lbmol/hrCyclohexane = 144.2.0 lbmol/hrBenzene = 0.2 lbmol/hr
High Pressure
Flash120 oF
(no pressuredrop)
VaporS2
LiquidS3
Part 2 | 공정모사기 실습 35
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Part 2 | 공정모사기 실습 37
38 아스펜 플러스 공정 모사기 실습
Unknown in the Database
Click on the Find Button
Part 2 | 공정모사기 실습 39
40 아스펜 플러스 공정 모사기 실습
6 Entering a positive number for pressure corresponds to the actual pressure, entering zero indicates no pressure drop in the unit, and entering a negative number corresponds to the pressure drop inside the unit.
Part 2 | 공정모사기 실습 41
42 아스펜 플러스 공정 모사기 실습
Part 2 | 공정모사기 실습 43
column theentering feed theof flowratecolumn theof top theleaving vapor theof flowrate
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Part 2 | 공정모사기 실습 51
Block HP-SEP (Flash2) Hcurves 1 Results
Vapor fraction
TEM
PE
RA
TUR
E F
0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1
150
200
250
300
350
400
TEMP
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54 아스펜 플러스 공정 모사기 실습
Workshop #3
Introduction to Simulation with RadFrac
RadFrac is a rigorous ASPEN Plus model for simulating various types of multistage
vapor-liquid fractionation operations. These operations include:
Ordinary distillation
Absorption
Reboiled absorption
Stripping
Reboiled stripping
Extractive and azeotropic distillation
RadFrac numbers stages from the top down, starting with the condenser (or starting
with the top stage if there is no condenser). Figure III.1 illustrates the various flowsheet-
connectivity options for RadFrac.
Fig. III.1. Flowsheet Connectivity Options for RadFrac
RadFrac can have any number of:
Feeds
Stages
Part 2 | 공정모사기 실습 55
Interstage heaters/coolers
Decanters
Pumparounds
Material Streams
Required:
Inlet: At least one inlet material stream
Outlet: One vapor or liquid distillate product stream, or both
One bottoms liquid product stream
Optional:
One water distillate product stream (optional)
Up to three side product streams per stage (optional)
Any number of pseudo-product streams (optional)
Each stage can have:
Any number of inlet streams
Up to three outlet streams (one vapor and two liquid)
Outlet streams can be partial or total drawoffs of the stage flows.
Heat Streams
Inlet: One inlet heat stream per stage (optional)
One heat stream per pumparound (optional)
Outlet:One outlet heat stream per stage (optional)
One heat stream per pumparound (optional)
RadFrac uses an inlet heat stream as a duty specification for all stages except the
condenser, reboiler, and pumparounds. If you do not give two column operating
specifications on the Setup Configuration sheet, RadFrac uses a heat stream as a specification
for the condenser and reboiler. If you do not give two specifications on the Pumparounds
Specifications sheet, RadFrac uses a heat stream as a specification for pumparounds.
56 아스펜 플러스 공정 모사기 실습
Partial Condenser, Total Condenser, Partial Reboiler, Stage, Tray …… (I thought I was
done with this stuff in my junior year)?
In a total condenser (Fig. III.2) , the overhead vapor is entirely condensed and split
into two portions: a liquid distillate which leaves the column and a liquid reflux which is
returned to the top plate. The reflux ratio is defined as L/D. In a total condenser, the
compositions of the overhead vapor, the distillate, and the reflux are all the same. Therefore,
there is no separation achieved. That is why a total condenser is not counted as a
separation/equilibrium stage.
OverheadVapor
Vy1
LiquidDistillate
DxD
Reflux Accumulator(Drum)
RefluxLxD
TotalCondenser
Fig. III.2. Total Condenser
On the other hand, in a partial condenser (Fig. III.3) , the overhead vapor is partially
condensed. The condensate may be completely returned as reflux or may be split into two
portions: a liquid distillate which leaves the column and a liquid reflux which is returned to
the top plate. The reflux ratio is now defined L/(vapor distillate + liquid distillate).
Furthermore, the vapor fraction of the distillate is defined as flowrate of vapor
distillate/flowrate of liquid distillate (e.g., a vapor fraction = 1 corresponds to no liquid
distillate). In a partial condenser, the compositions of the distillate vapor and the liquid
Part 2 | 공정모사기 실습 57
distillate or the reflux are different (actually are in equilibrium if the condenser is considered
to be an equilibrium stage). Therefore, a partial condenser is counted as an equilibrium
stage.
OverheadVapor
V2y2
LiquidDistillate
DxD
Reflux Accumulator(Drum)
RefluxLxD
PartialCondenser Vapor
DistillateV1y1
Fig. III.3. Partial Condenser
Most reboilers (Fig. III.4) accept liquid and produce liquid and vapor streams, thereby
causing separation. Therefore, a reboiler is counted as one stage.
LiquidBottoms
BxB
Boilupvapor
Reboiler Fig. III.4. Reboiler
58 아스펜 플러스 공정 모사기 실습
Now what about ASPEN's terminology. In all cases (whether the
condenser is total or partial), ASPEN will assign it as Stage #1
(don't worry, ASPEN Plus is smart enough to recognize that if it is a total condenser, it
is an idle stage not achieving any separation). The reboiler will always be the last stage.
Let us now proceed to Workshop #3. A distillation column is used to fractionate
methanol and water mixture (Fig. III.5). The feed has 63.2 wt% water and 36.8 wt%
methanol. The flowrate of the feed is 120,000 lb/hr. Its pressure is 18 psia and is a saturated
liquid (vapor fraction of the feed = 0). The column has 38 trays. The feed is introduced above
tray #23 (Now, remember according to ASPEN's terminology: stage #1 is the condenser,
therefore the feed tray is stage #24). The top-stage pressure is 16.1 psia and the pressure drop
per stage is 0.1 psi. The column uses a total condenser. The distillate flowrate is 39,885 lb/hr
and the reflux ratio is 1.3. Use NRTL-RK property method.
Part 2 | 공정모사기 실습 59
Reboiler(Stage #40)
Feed:63.2 wt% Water36.8 wt% MethanolFlowrate = 120,000 lb/hrPressure = 18 psiaSaturated Liquid
38Trays
FeedTray =
23i.e., stage
#24
39,885 lb/hrReflux ratio = 1.3
Pressure = 16.1 psia
TotalCondenser
Fig. III.5. Methanol Separation from Water
60 아스펜 플러스 공정 모사기 실습
SelectThisIcon
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Workshop #4
DESIGN SPECIFICATIONS AND SIZING
(RadFrac DesignSpecs and Vary, Efficiencies, and Tray Sizing)
Sometimes, it is necessary to specify desired values of some of the output variables.
In this case, you should allow one of the input variables to vary such that the design
specification is met. In ASPEN Plus, this is handled through two important options that work
in tandem; DesignSpec and Vary. Design-Spec blocks allow you to set a process variable
which is normally calculated during the simulation. For each specification, you must identify
which process variable can be adjusted to meet that specification. For this reason, Design-
Spec blocks can be used as feedback controllers.
To use this block you must specify which model variables must be fixed, what values
they must be fixed at, and which model input variables can be manipulated (varied). In
general, number of DesignSpec variables = number of Vary variables.
Let us do an example by revisiting Workshop #3. Again, we have a distillation
column used to fractionate methanol and water mixture (Fig. IV.1). The feed has 63.2 wt%
water and 36.8 wt% methanol. The flowrate of the feed is 120,000 lb/hr. Its pressure is 18.0
psia and is a saturated liquid (vapor fraction of the feed = 0). The column has 38 trays. The
feed is introduced above tray #23 (Now, remember according to ASPEN's terminology: stage
#1 is the condenser, therefore the feed tray is stage #24). The top-stage pressure is 16.1 psia
and the pressure drop per stage is 0.1 psi. The column uses a total condenser.
PART A
Now, we would like to reach a 99.95 wt% purity for methanol in the distillate and
99.90 wt% purity for water in the bottoms. Since we have two design specifications, we must
vary two variables. Let us allow the distillate flowrate and reflux ratio to vary. We should
provide ASPEN Plus with a range for the potential variations. Let us choose a variation range
for the distillate flowrate between 25,000 and 55,000 lb/hr and a reflux ratio between 0.8 and
2.0. Solve this problem and note the condenser and reboiler duties. Discuss your results.
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PART B
For the same design specifications, specify a 65% Murphree efficiency for each tray.
Assume the reboiler to have a stage efficiency of 90%.
Note the condenser and reboiler duties. Discuss your results.
PART C
Perform tray sizing calculation for the entire column, given that Bubble Cap trays are
used. Describe the diameter profile throughout the column.
Reboiler(Stage #40)
Feed:63.2 wt% Water36.8 wt%MethanolFlowrate = 120,000 lb/hrPressure = 18 psiaSaturated Liquid
38Trays
FeedTray =
23i.e., stage
#24
Pressure =16.1 psia
TotalCondenser
99.95 wt.% methanolDistillate flowrate?Reflux ratio ?
99.90 wt.% water
Fig. IV.1. DesignSpec - Vary Problem
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Start by opening your file from Workshop #3. From the Data Browser, go to Blocks
DIST-COL Design Specs (Fig. IV.2).
Fig. IV.2. Design Specs Form
Click on New, you'll get the window shown in Fig. IV.3.
Fig. IV.3. Create New ID
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Click on OK. You will get the window shown in Fig. IV.4.
Fig. IV.4. Selection of First Design Specification
Select mass purity as your first design specification and enter 0.9995 as a target.
Click on the Next button, you will get the Components sheet. Use this sheet to select
components and base components for the purity specification. The available components and
base components appear on the left side of the list. The selected components appear on the
right side of the list. Highlight methanol and click on > to move it to the left hand side.
Methanol is selected since the purity (0.9995) is for methanol. It is defined as 0.9995 =
methanol in distillate/(methanol + water) in distillate. Therefore, our base components are
methanol and water. To select both as the base components, use the >> button (Fig. IV.5).
.
Fig. IV.5. Selection of Components
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Click on Next button to go to the Stream sheet. Since the 0.9995 methanol purity is
in the distillate, select stream S2 (Fig. IV.6).
Fig. IV.6. Selection of Distillate
Now, we can move to the Vary sheet by clicking on Next. Follow procedure (Fig.
IV.7) and choose Distillate Rate between 25,000 and 55,000 lb/hr.
If you click Next, ASPEN Plus will indicate that you are ready to run the simulation.
Do not click on OK since we still need to enter another design specification (water purity in
the bottoms). Click on Cancel, then go to the Design Specs sheets (as before) and choose
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water purity in the bottoms to be 0.999. Similarly, select the second Vary variable to be
reflux ratio between 0.8 and 2.0. Now, you are ready to run the simulation.
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Workshop #5
SENSITIVTY ANALYSIS
Sensitivity analysis is a useful tool for examining how a process responds to changes
in design and operating variables. You can use it to vary one or more process variables and
observe the effect of such variation on other process variables. It is a valuable tool for
performing "what if" studies. In a sensitivity analysis, you will have two types of variables:
1. Manipulated variables: These are the ones you would like to vary (i.e., they are your
input7 variables).
2. Sampled (or measured) variables: These are the ones you would like to see how they
change in response to the changes you made in the manipulated variables (i.e., they are your
output of variables).
Here is an example on how sensitivity analysis works:
PART A:
Let us revisit the flash column of Workshop II which is used to separate a gas mixture
into liquid and vapor fractions. The feed is at 400oF and 21 atm (Fig. V.1a). It contains
hydrogen (30.0 lbmol/hr), nitrogen (15.0 lbmol/hr), methane (43.0 lbmol/hr), cyclohexane
(144.2 lbmol/hr), and benzene (0.2 lbmol/hr). The flash column operates at 120oF and there is
no pressure drop in it. The liquid entrainment in the vapor phase from the separator is 0.012.
The flash column can be modeled by ASPEN Plus' model FLASH2 and the thermodynamic
properties can be estimated using the Redlich-Kwong-Soave equation.
7 The flowsheet variables that are varied must be inputs to the flowsheet. They can not be variables that are calculated during the simulation.
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column theentering feed theof flowratecolumn theof top theleaving vapor theof flowrate
). Use the plot to determine the dew point
of the feed. Compare with results of the heating curve of Workshop #2.
FeedS1400 oF21 atm.Hydrogen = 30.0 lbmol/hrNitrogen = 15.0 lbmol/hrMethane = 43.0 lbmol/hrCyclohexane = 144.2 lbmol/hrBenzene = 0.2 lbmol/hr
HighPressure
Flash
(no pressuredrop)
VaporS2
LiquidS3
This part is open ended and is based on Workshop #3. A distillation column is used to
fractionate methanol and water mixture (Fig. V.1b). The feed has 63.2 wt% water and 36.8 wt%
methanol. The flowrate of the feed is 120,000 lb/hr. Its pressure is 18 psia and is a saturated
liquid (vapor fraction of the feed = 0). The column has 38 trays. The feed is introduced above
tray #23 (Now, remember according to ASPEN's terminology: stage #1 is the condenser,
therefore the feed tray is stage #24). The top-stage pressure is 16.1 psia and the pressure drop
per stage is 0.1 psi. The column uses a total condenser. The distillate flowrate is 39,885 lb/hr
and the reflux ratio is 1.3. Use NRTL-RK property method.
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Reboiler(Stage #40)
Feed:63.2 wt% Water36.8 wt% MethanolFlowrate = 120,000 lb/hrPressure = 18 psiaSaturated Liquid
38Trays
FeedTray =
23i.e., stage
#24
39,885 lb/hrReflux ratio = 1.3
Pressure = 16.1 psia
TotalCondenser
Fig. V.1b. Methanol Separation from Water
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8 If you forgot what the name(s) of your measured variable(s), click on the right button of the mouse to get a list
of variables
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Workshop #6 Heat Exchangers
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Fig. .1 HeatX Flowsheet
Fig. . 2. Two Heater Blocks
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Hints
Fig. .3. Block Specifications
Fig. . 4. Hcurve Option
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Fig. .5. Drawing Units and Material Streams
Fig. . 6. Selection of a Heat Stream
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Fig. . 7. Connection of the Two Sides of the Exchanger via a Heat Stream
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Workshop #7 Production of Cyclohexane
A plant produces cyclohexane by the hydrogenation of benzene according to the
following reaction:
The process is shown below in Figure 7.1:
Fig. .1.
This workshop will demonstrate the capability to merge two smaller simulations into one complex simulation. Workshops #2 and #3 will be the basis for this simulation. RK-Soave model can be used to predict the properties. Assume molar basis unless specified otherwise.
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Stream S2: 100 F, 15psia, 100 lbmol/hr (100%C6H6).
Heater (HEATER): Mixes the recycle and feed streams and preheats them to 300 F and 330 psia.
Operates at 400 F and has a pressure drop of 15 psia. Conversion of benzene is 99.8% considering only the main reaction, Equation 1. Separator (FLASH2): Splits the product stream into two streams: vapor and liquid (cyclohexane rich) streams. It is operated at 120 F and has a pressure drop of 5 psia. Distillation Column (RADFRAC): Purifies the content of cyclohexane in the liquid stream. The column has 15 stages including a partial condenser and reboiler. The feed stream is located above the 8th tray. The column operates at 200 psia. Assume the condenser temperature is 20 F and the reflux ratio is 1.2 (molar basis). In the bottom product, it is desired to recover 99.99% (mol recovery) of cyclohexane from the feed. The bottom flowrate is estimated to lie between 97.0 and 101.0 lbmol/hr (initial guess 97.0 lbmol/hr). Flow Splitters (SSPLIT): Vapor Stream (Split 1): Splitting ratio of recycle is 0.92. Liquid Stream (Split 2): Splitting ratio of recycle is 0.30 Misc: To increase the conversion of benzene to cyclohexane in the reactor it is desired to have 10% excess of H2 in the feed stream to the reactor (S3). The flowrate of makeup H2 (S1) can be adjusted to satisfy the excess requirement. Turn In:
1. The Aspen Plus flowsheet and stream table.
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2. The heat duties of the heater and reactor.
3. The heating curve of the heater and the flash separator.
4. The actual flowrates of make-up H2 and cyclohexane product.
Merging the Flowsheets:
1. In order to avoid any conflicts in nomenclature you should first modify workshops #2 and #3 by renaming the streams and blocks so that they do not have the same ID’s. (You may still have some problems merging the flowsheets. However, Aspen Plus will allow you to change any duplicate information prior to merging the files.
2. Select Export from the File pulldown menu and then export one of the files as a
BKP file. (If you have been saving your files in backup format as you should have then skip this step).
3. Open the other workshop and then import the BKP file created in step 2 by
selecting Import from the File pulldown menu.
4. Modify the data and connections based on Figure 7.1 and the data provided. To modify connections you can either double click on a stream end if it is not connected to anything or at anytime you can highlight and right click on the stream and choose either reconnect source or reconnect destination.
5. Finally, after merging the two simulations save your modified flowsheet as
Wkshop7. (This will preserve workshops 2 and 3 as separate entities and allow you to access them again if something were to go wrong in this workshop).
To complete the flowsheet you will have to use several icons you have not previously
used. In the information provided about each unit the name in parenthesis shows you the icon set to choose from. For example, to select your reactor you would go to the Reactors tab and then the RSTOIC icon. This provides you with several choices of icons; simply choose the one that looks like the one seen in Figure 7.1. Also, when choosing the splitters be sure to use the DOT icon under SSPLIT. Remember, if you place your pointer over an icon or feed/product arrow it will tell you the name or information about the connection. Filling in the Forms: Because this workshop is designed to show you that two workshops can be merged a considerable amount of information in your data browser will be incorrect. For example,
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the number of stages in your distillation column will probably be 40 or some optimized number other than 15. Also, you will have chemicals specified from previous workshops that are unnecessary (i.e. methanol, water), you will have to remove them from your simulation. Because of this it is your job to judiciously go through all the tabs in the data browser to ensure that all the information is correct. This will not be done using the Next button; rather you should use the advance button >> so that every form is checked. Reactors: When you reach the reactor block you will need to specify several pieces of information. The specifications tab will ask for temperature and pressure, information provided to you at the beginning of this workshop. The second tab reactions (Figure 7.2) will require you to input in the reaction (Equation 1) and the stoichiometric coefficients.
Fig . .2.
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Fig . 3.
From this window you can select the reactants, products, coefficients and percent conversion. When you click on the component box a drop down arrow appears that allows you to select components. When this information is inputted properly it will look like Figure 7.4.
Fig. .4.
Note that reactant coefficients are negative and product coefficients are positive. Click the Next button or the Close button to proceed past the reactors form. Splitters:
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The split blocks will also need some information specified in them, which was provided earlier in the workshop. Figure 7.5 shows the specifications tab of Split1 properly completed.
Fig . .5.
To make sure that there is 10% excess Hydrogen present in the reactor feed you can again use the Design Spec feature of Aspen. Recall that Design Spec is located in the Flowsheeting Options folder. From the Design Spec folder start a new design spec (DS-1) and define two variables, MH2 and MC6H6. These variables can be defined as: Type (Mole Flow), Stream (S3), and Component (Hydrogen or Benzene) depending on the variable name. Next, Figure 7.6 shows the spec tab properly filled in:
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Fig. .6.
Fig .7.
Some results are seen below in Figures 7.8 and 7.9. These results should only be used for comparison to determine if you are on the right track with your simulation.
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Fig. .8.
Fig . .9.
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Simulating a Distillation Column for Crude Oil
A forty-stage distillation column (including a reboiler and a total condenser) is used to fractionate a crude oil stream with a flowrate of 100 lb/hr. The stream enters the column on stage 20 at 250 F and 23 psia. The column has two side draws, both for fuel grade products, one of them above the feed stream (use stage 10 as an initial guess) and one below the feed stream (use stage 30 as an initial guess). The reflux ratio of the column is 2.0, the bottoms rate is 32.5 lb/hr, and the column operates at 23 psia. The flowsheet is shown in fig 8.1. The RK-SOAVE method can be used to model this system.
15.2 % 250-350 F
Fig .1.
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1) The Aspen Plus flowsheet and stream summary table.
Flowsheet
To simulate the column described you will need to use a RADFRAC column, Icon FRAC1, with one feed stream and four product streams (distillate, bottoms, and two side draws). When attaching the side draws you will notice two blue arrows that you can attach streams to in the middle of the column, be sure to attach both side draws to the upper blue arrow. This arrow is for side products, the lower blue arrow is for psuedo-streams and will not be used in this workshop (note if you place your mouse icon over the arrow when you have material streams selected it will specify the stream to be attached). The flowsheet is shown in fig 8.1. Setup Now that the flowsheet is ready you can enter the data browser and begin setting up the simulation. By using the next button you will come to the component specifications section. Instead of specifying components for this lab we will be specifying an Assay Blend. Directly below component specifications on the data browser you will see a folder Assay/Blend. Double click this folder and select new, then select Assay and click O.K, fig 8.2.
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Fig. .2.
This will bring you to fig 8.3 where you can specify the API gravity, distillation method and characterize your Assay blend.
Fig. . 3.
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Fig. .4.
This will bring you to figure 8.5 seen below:
Fig . .5.
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Fig . .6.
Having defined the crude you can now allow aspen to guide you through the rest of the setup. When you reach the column streams setup you will need to specify a stage, phase and flowrate for your two side streams. These should be specified as 10, liquid, and 8.3 lb/hr for SID1, and 30, liquid, and 44 lb/hr for SID2, see figure 8.7.
Fig . .7.
Finally, when you have completed entering in your data and aspen tells you “all required input is complete, you can run the simulation now” hit cancel. Aspen has a wide variety of convergence methods available, however, the standard method is not the best for this particular situation. To change the convergence method on the data browser go to your block setup, figure 8.8, and select Custom.
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Fig. .9.
Fig. .10.
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Fig. .11.
You are now ready to run your simulation!
Column Definition
It is desired to break the crude stream into four valuable product streams as defined by the analysis data – naphtha (BP 250 F – 350 F), jet fuel (BP 350 F – 450 F), diesel (BP 450 F - 650 F), and heavy crudes (BP > 650 F). To achieve this you will need to fine-tune your column.
The amount of each component in the feed can be determined by examining the analysis data. For example, the percent of diesel would be the 67.5 % less the amount of naphtha and jet fuel, 23.5 %, giving 44 %. Therefore, this percent of the feed stream needs to be withdrawn from the column on a stage where the temperature is between 450 F and 650 F. Similarly, the heavy crudes can be determined to be 32.5 % of the feed, which can then be specified as the bottoms flowrate. The jet fuel, calculated like the diesel (8.3 %), and the diesel are specified as side draws at approximate locations. To get the correct feed and side draw locations, the simulation can be run repeatedly, varying a side draw or the feed’s location one stage at a time (in this simulation only vary the side draws.) until the side draws pull from the correct temperature ranges, and the distillate and bottom’s flows match their expected values. Examining the temperature profile in a column without side streams is often a way to determine an approximate location for the initial guesses for the locations of the side draws. (Possible solutions include side draws at 10 and 31, 10 and 32, 11 and 31, etc. Start at 10 and 30.).
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Workshop #9 Simulating a Stripper for Wastewater Treatment
Fig. .1. Stripper Flowsheet
The RADFRAC model should be used with icon ABSBR1 (the icon shows no condenser or reboiler). Also, the UNIFAC thermodynamic property model should be used.
Column Specifications
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Turn In:
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Fig. .1 . An Absorber-Stripper Process for CO2 Capture Using MEA
FLUEGAS
LEANIN
PUREGAS
RICHOUT
LEANOUTPURGE
RECYCLE
COOL
REFLUXRICHIN
VAPOR
CO2
ADD
ABSORBER
SPLITTER
COOLER
STRIPPER
FLASH
MIXER
PUMP
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174 아스펜 플러스 공정 모사기 실습
Part 3 | 단위공정 모델의 종류 175
176 아스펜 플러스 공정 모사기 실습
Part 3 | 단위공정 모델의 종류 177
178 아스펜 플러스 공정 모사기 실습
Part 3 | 단위공정 모델의 종류 179
180 아스펜 플러스 공정 모사기 실습
Part 3 | 단위공정 모델의 종류 181
182 아스펜 플러스 공정 모사기 실습
Part 3 | 단위공정 모델의 종류 183
184 아스펜 플러스 공정 모사기 실습
Part 3 | 단위공정 모델의 종류 185
186 아스펜 플러스 공정 모사기 실습
Part 3 | 단위공정 모델의 종류 187
188 아스펜 플러스 공정 모사기 실습
Part 3 | 단위공정 모델의 종류 189
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