Manual de Simulación de Procesos Químicos en Aspen Plus

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

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Part 1 | 공정모사에 필요한 열역학 11

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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.



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


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:

Part 2 | 공정모사기 실습 19

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.


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.


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


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.


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.


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


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.


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


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.


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.


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.


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).


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


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.


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.


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





Unknown in the Database

Click on the Find Button



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.




column theentering feed theof flowratecolumn theof top theleaving vapor theof flowrate









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




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


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.


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


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


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.


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


SelectThisIcon








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.


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


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


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


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


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.




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.


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.


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










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



Workshop #6 Heat Exchangers


Fig. .1 HeatX Flowsheet

Fig. . 2. Two Heater Blocks


Hints

Fig. .3. Block Specifications

Fig. . 4. Hcurve Option


Fig. .5. Drawing Units and Material Streams

Fig. . 6. Selection of a Heat Stream


Fig. . 7. Connection of the Two Sides of the Exchanger via a Heat Stream


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.


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.


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,


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.


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:


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:


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.


Fig. .8.

Fig . .9.


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.


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.


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.


Fig. .4.

This will bring you to figure 8.5 seen below:

Fig . .5.


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.


Fig. .9.

Fig. .10.


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.).


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


Turn In:


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










PART 3단위공정 모델의 종류


Part 3 | 단위공정 모델의 종류 123




































































Documents

Manual de Simulación de Procesos Químicos en Aspen Plus