Aspen Plus Tutorial 1:Vinyl Chloride Monomer Production Process

Process Discription

Vinyl chloride monomer (VCM) is produced through a high-pressure, noncatalytic process

involving the pyrolysis of 1,2-dichloroethane (EDC), according to the following reactions:

CH2CI-CH2CI (EDC)" HCl + CHC1=CH2 (VCM)

The process flow diagram is shown in Figure 1.

The cracking of EDC occurs at 900oF and 300 psia in a direct-fired furnace. The pure

EDC feed enters the furnace at 60oF and 390 psia, with a rate of 2000 lbmol/hr.

Byproducts of pyrolysis consist principally of acetylene and chloroprene through the

following reactions:

EDC " C2H2 + HCl

VCM + C2H2 " C4H5Cl

Overall EDC conversion is maintained at 55%, with a selectivity of 98% for VCM

production and 2% for acetylene production. 75% of the acetylene produced is converted

to chloroprene.

The hot gases from the furnace are quenched to 10 degrees below saturation, prior to

fractionation.

Two distillation columns are used for the purification of the VCM product. In the first

column, anhydrous HCI is removed overhead and sent to the oxychlorination unit. In the

second column, VCM product is delivered overhead, and the bottoms stream containing

unreacted EDC is recycled back to the cracker. The recycle EDC stream is treated, in a

black box separator, to remove chloroprene, which could hinder pyrolysis and

fractionation.

Specifications for the two columns are:

HCl Column  

Theoretical stages 15

Condenser pressure 367 psia

Reboiler pressure 372 psia

HCl in bottoms 50 ppm (weight)

VCM recovery in bottoms 99.9 percent

 

VCM Column  

Theoretical stages 10

Condenser pressure 115 psia

Reboiler pressure 118 psia

VCM recovery in overheads 99.9 percent

EDC recovery in bottoms 99.9 percent

Tutorial

Base Case Simulation

Develop a base ASPEN PLUS simulation for the VCM flowsheet, using the following

specifications. Detailed instructions follow these general ones.

1.      Model the cracker furnace with the RSTOIC reactor model. Consider only the main

VCM reaction at this point.

2.      Model the reactor effluent quench using the HEATER model. Assume 10 degrees

subcooling, and a pressure drop of 5 psia across the quench.

3.      Model the HCI column using the DSTWU shortcut model. Specify HCI recovery of

99.9% in the overhead, VCM recovery of 99.9% in the bottoms.

4.      Model the VCM column using the DSNW shortcut model. Specify VCM recovery of

99.9% in the overhead, EDC recovery of 99.9% in the bottoms.

5.      Assume the flowrate of recycle EDC is 1600 lbmol/hr.

6.      Use the Redlich-Kwong-Soave equation of state to represent the physical

properties of the system.

Tutorial 1 introduces the use of Process flowsheet window as you create and run an

ASPEN PLUS simulation model. The tutorial uses the process flowsheet expert system

to take you step-by-step through the process of creating and running simulation. As you

create your own flowsheet, submit the run, and analyze the results, you will learn the

basics of how to use ASPEN PLUS.

You will

·        Define the problem

·        Create a simulation flowsheet using graphics

·        Enter the input specifications

·        Browse complete input

·        Run the simulation

·        Review and record the simulation results

Defining the problem

You will create a simulation flowsheet for the tutorial problem shown in Figure 1.

Figure 1: Process Flow Sheet

Logon to ASPEN PLUS. You will start with a blank flowsheet.

Creating a Simulation Flowsheet

This section of the tutorial takes you through the problem definition steps in creating the

simulation flowsheet shown in Figure 1.

Aspen Plus automatically numbers the blocks and streams you create, so you do not

have to enter IDs for these objects if you do not want to. You can change this default and

enter your own prefix. In this tutorial, you will let Aspen number the streams automatically,

using the prefix “S-“, and you will enter your own IDs for the blocks. To indicate that you

want to enter your own IDs for blocks:

On the menu bar, click on “Tools|Options”. The Options dialog window will be displayed;

click on the tab named “Flowsheet”. Uncheck the box to the left of “Automatically assign

stream name with prefix”. Make sure the option labeled “Automatically assign stream

name with prefix” is selected (there should be a check in the box þ to the left of this

label). In the text box to the left of the label enter S- . Click OK to accept the changes.

Save your work by choosing “File|Save” from the program menu. You can name the file

whatever you choose. Lets call it “Aspen Tutorial 1 – Vinyl Chloride”. Remember to

SAVE YOU WORK OFTEN! This point cannot be stressed enough. If something goes

wrong and ASPEN PLUS crashes (it does pretty often, you could loose a lot of work. Its

also a good idea to make periodic backups of your files each week or so or at major

milestones. Note: backup files (*.bkp) take up much less space than the normal “Aspen

PLUS Documents” files (*.awp).

The Model Library at the bottom of the program window is for selecting the ASPEN PLUS

unit operation models for the blocks in your simulation flowsheet. This menu is organized

as follows:

ASPEN PLUS Model Sets

Mixers and Splitters

Separators

Heat Exchangers

Columns

Reactors

Pressure Changers

Manipulators

Solids

User Models

Each of these groups has process block that can be used in your flowsheet. Many of the

blocks have other symbols that can be used on your flowsheet to make it more

descriptive. Such blocks will have a small down arrow next to the symbol. Use this to

select other icons for this block. Note that the symbol changes are completely aesthetic

and there is no change to the way Aspen will interpret the block.

If you want more information about a model before selecting it, you can use the Help

menu from the menu bar. Click on the index tab, and type “heater” to get help on the

heater block. Select double click on “Heater Model”, then double click “Heater (User

Guide Volume 1)”. You could also click on the “Arrow question mark” button on the

toolbar and then click on the item you want.

The first block in your flowsheet is a stoichiometric reactor.

Click on the “Reactors” tab to display the reactor models provided by the model manager.

Click on the “RStoic” button.

Move the mouse pointer to the middle of the screen, but do not click yet.

Notice that when the mouse pointer is on the Model Library it looks like the normal arrow,

signifying Select mode. When the pointer is on the workspace, it looks like crosshairs,

signifying Insert model. If you would like to cancel your selection of the RStoic model

without inserting it onto the flowsheet then press the arrow button at the upper left corner

of the model library or press ESC.

Move the mouse pointer to the left of center of the flowsheet, and click the left mouse

button to insert the Rstoic block.

Aspen Plus displays a dialog box asking for a block ID, or name, since you turned off the

automatic block ID numbering option.

Type the ID CRACK and press Enter or click on OK.

Aspen Plus display a RSTOIC block with the ID CRACK.

The second block in your simulation flowsheet (see Figure 1) is a reactor effluent quench

that uses the ASPEN PLUS model HEATER.

On the Model Library, select Heat Exchangers then click on Heater.

Insert the Heater block to the right of the RSTOIC block. When you insert blocks in the

flowsheet, be sure to leave about an inch and a half of space between blocks for the

connecting streams and their labels.

Type the ID QUENCH in the dialog box when asked, and press Enter.

The next block the fhowsheet is the HCL distillation column, which will be modeled by a

shortcut distillation column model, DSTWU.

On the Model Library, select Columns then click on DSTWU. Insert the DSTWU block to

the right of the HEATER. Type the ID COL1 in the dialog box when asked, and press

enter.

The last block in the flowsheet is VCM column. Initially it will be modeled using

DSTWU and later a rigorous model will be used.

Insert the DSTWU block to the right of the COL1

Type the ID COL2 in the dialog box when asked, and press enter.

If you accidentally placed an icon in the wrong location, or just want to realign a few

things, you can move the icon by using the arrow keys or by dragging it with the mouse.

Use the arrow keys for small adjustments. Use the mouse to make larger changes in

position. If you click on an ID, you can move it instead of a block or stream using the

same methods.

This is a good time to save your work again

Click on the Material STREAMS button located at the bottom of the flowsheet next to the

models. Now when you move your mouse into the flowsheet area red and blue arrows

will appear on all of the model blocks located on the flowsheet. Red arrows are required

ports and blue arrows are optional ports.

The arrows appear around the block on ports that are available. By pointing on an arrow

information about the port is given. Do this for each port to see the type of information

provided. The leftmost arrow on the CRACK block is marked “Feed (Required, 1 or

more)”, indicating that this port is required and that it can have one or more inlets

connected to it.

Click the left mouse button on this (Feeds) arrow. Move the cursor to the empty space

left of the CRACK block and press the left mouse button. A feed line labeled S-1 should

appear.

Click on the product arrow located on the right side of the CRACK block. Arrows appear

on all the possible connecting ports. Click on the arrow on the QUENCH block. The

stream ID ASPEN PLUS generated is S-2.

Next click on the Product arrow for the QUENCH block. Arrows appear on the possible

Feed ports. Click on the Feed port stream on the COL1 block. ASPEN PLUS generates

stream ID S-3.

Next click on the Distilate arrow for the COL1 block. Move the cursor above the block

and press the left mouse button. A stream labeled S-4 will be created.

Click on Bottoms arrow on COL1. Connect to Feed on COL2, ASPEN PLUS generates

stream ID S-5.

Next click on the Distillate arrow for the COL2 block. Move the cursor above the block

and press the left mouse button. A stream labeled S-6 will be created.

Next click on the Bottoms arrow for the COL2 block. Move the cursor below the block

and press the left mouse button. A stream labeled S-7 will be created.

Click on the Feeds arrow for the Rstoic block. Create a second feed line labeled S-8.

Before you continue with this tutorial, be sure that your simulation flowsheet looks

essentially like Figure 1.

Now is a good time to save.

Configuring the Input Specifications

Your ASPEN PLUS run now contains all the information about the simulation flowsheet.

Next you will enter the remaining data required to complete the problem specification,

using forms. This includes components, properties, the feed stream, and block operating

parameters.

At this point you have the choice of letting the ASPEN PLUS expert system take you

through all the steps needed to complete the problem specifications, or going through the

steps in an order you choose. When you are working from a form, you access the expert

system by using the Next function (the N® button). This button leads you through the

process of including all of the necessary information in a worksheet (See Table 1). Using

the expert system is convenient, so you will use the expert system in this tutorial.

You click the next button when Then

The sheet you are on is incomplete. Displays a message listing the input you

must provide to complete the sheet.

The sheet you are on is complete. Takes you to next required input sheet for

the current object.

You have selected an object that is

complete.

Takes you to next object or the next step in

making a run.

You have selected an object that is

incomplete.

Takes you to the next sheet you must

complete.

Table 1: Result of pressing next button.

You can also find the status of the flowsheet by looking in the lower righthand corner of

the window. If the flowsheet is not complete or more input is needed, the information will

be shown in red. See Figure 1 as an example

At this time press the Next button. Aspen will as you if you would like to display the next

input form, click on OK.

ASPEN PLUS displays the data browser window. The data browser window consists of

folders containing input fields. Folders containing all of the necessary information have a

blue check mark on them. Folders requiring additional information have a half filled red

circle. You can navigate through the folders as you would in Microsoft Explorer.

ASPEN PLUS should open the component specifications form, indicating that this is the

next form that it has encountered that requires additional information. Before we enter

the component information we would like to enter a name for the simulation. Click on the

Setup folder. This should display several icons one of which is the Specifications form.

Click on the Specifications form within the Setup folder and the Setup-Specifications form

should appear with the Global tab highlighted (see Figure 2). We would like to enter a

title for the Aspen simulation. The title will appear at the top of each page of your ASPEN

PLUS report. Enter “Vinyl Chloride Monomer Process” as the title. From this menu you

can also change many of the general Aspen parameter such as the unit of measurement.

By selecting the Description tab button you could also enter a description of the process

if you so desired.

Figure 2: Global Tab of the Setup Specification form.

One can very quickly see that Aspen offers many features for the user, many of which we

will not discuss in this tutorial. You should explore some of these features during the

course of the semester. Many of these features are very powerful, and can make

simulating any give process much easier.

We would like to return to the Components-Specifications form. We have two choices for

doing this. First of all we could select the folder using the directory tree located on the

leftmost portion of the screen, or we can use the Next button.

Components Folder

At this time you should be looking at the Components-Specifications form with the

Selection tab highlighted. We are about to enter the components to be used with this

simulation. Aspen stores the physical property data for thousands of chemicals, but only

recalls the information that you specify in this form. For this reason it is important to

specify every chemical that you plan on using in the simulation. You will also give each

chemical an arbitrary Component ID. This is the name that each chemical will be

referred to by Aspen.

Before you start to enter the chemicals used in the simulation you must activate that

appropriate databases. Click on the Databanks tab button and the currently selected

databanks are displayed along with all of the options for databanks to be used. For this

simulation the following databanks should be in the “Selected databanks” column:

Selected

Databanks

PURE10

AQUEOUS

SOLIDS

INORGANIC

If one of these is not in the selected databanks field, then select it in the “Available

databanks” field and press the > button to move it into the “Selected databanks” field.

Reselect the Selection tab. Move the highlight to the first Comp ID field using the mouse.

The first component is Hydrogen chloride. On the first Comp ID field, type HCL and

press enter.

Both the data bank Alias (the formula) and the data bank Component Name appear on

the form. ASPEN PLUS automatically searches all the data banks you have specified to

find an alias or component name that matches your component ID. If ASPEN PLUS

does not find an exact match, you must enter either the alias or the component name if

you want to retrieve data for the component from data banks. You could also use the

FIND button to locate the component you wish to add.

The folder status indicator to the left of the form has changed to a blue checkmark,

since you have specified a component for your simulation. If you were to use Next now,

ASPEN PLUS would take you to the next required step. However, your problem requires

additional components.

On the second Comp ID field below HCL, type VCM and press enter.

No Formula appears for VCM. Because VCM is simply your abbreviation for Vinyl

chloride monomer, there is no Formula or Component Name match in the data bank; so

you must enter one of them. You know that the formula for Vinyl chloride is C2H3Cl, so

on the Formula field, enter C2H3CL. ASPEN PLUS will then find the data for the

component.

On the next Comp ID field, enter the component ID EDC. Move the highlight to the

Component Name field and enter 1,2-DICHLOROETHANE.

On the next Comp ID field in the space below EDC, enter the final component C2H2.

The Formula C2H2 and the rest of the line is filled in automatically.

This completes specifications on the Components form. You can return to this form at

any time to add or delete components, or to change data bank aliases or component

names.

Save, and then hit the NEXT button.

Properties Folder

An ASPEN PLUS simulation requires physical properties, such as enthalpy and density,

of streams and other mixtures. A wide variety of methods are available in ASPEN PLUS

for calculating these properties. You specify the methods to be used by selecting

property method. A property method defines the methods and models used to calculate

each thermodynamic and transport property in a simulation.

Use the “Base Methods” box to display property methods available (click the button on

the field).

Move the highlight to SYSOP0. The prompt area below displays a description of

SYSOP0. If you want a more detailed description of the option set, use Help (type F1

after you select the method).

Select SYSOP0.

The status indicator for the folder changes to a blue checkmark, indicating that the rest of

the fields are optional; in this tutorial you will skip over them.

Save and use NEXT to display the next form requiring input. When prompted make sure

the “Go to Next required input step” is selected and click on OK.

Streams Folder

Aspen Plus displays the Stream S-1 input form.You must enter stream data for each

process feed stream in a simulation.

The blank Stream field on the form on your screen indicates a process feed stream. The

units set for the stream input data is also shown.

On the Temperature field, enter 60. The temperature for this problem is in degrees

Fahrenheit, so you can leave the default F.

On the Pressure field, enter 390 psi.

On the value field for EDC enter 2000 lbmol/hr.

This completes the information for stream S-1 (See Figure 2), you will notice that the

folder now has a blue check. Save and click the next button and the folder for stream S-

8 should appear.

Figure 3: Stream 2-1 Specification Form

Use the following stream data for the S-8 Form

·        On the Temp Field, enter 60 F.

·        On the Pressure Field, enter 390 psia.

On the Value Field for EDC enter 1600 lbmol/hr.

Save again and click Next.

Blocks Folder

The Blocks-COL1 form will appear with the specifications tab highlighted. We will enter

the following information into the appropriate blocks. The significance of these blocks will

not be explained now. That will all be done later on in the semester.

·        On the Number of Stages Field, enter 15

·        On the Pressure Condensor Field, enter 367.

·        On the Pressure Reboiler Field, enter 372.

·        On the Light key Comp Field, enter HCL (you can use List and then select HCL)

·        On the Light Key Recov Field, enter 0.999

·        On the Heavy key Comp Field, enter VCM.

On the Heavy key Recov Field, enter 0.001.

The form should look like Figure 4. Save and use the next button to get to the next form.

Figure 4: COL1 Specification form

The system takes you to the Blocks-COL2 form. Enter the following values:

·        On the Number of Stages Field, enter 10.

·        On the Pressure Condensor Field, enter 115.

·        On the Pressure Reboiler Field, enter 118.

·        On the Light key Comp Field, enter VCM

·        On the Light Key Recov Field, enter 0.999

·        On the Heavy key Comp Field, enter EDC.

On the Heavy key Recov Field, enter 0.001.

Save and click the next button. This will take you to the Blocks-Crack Specifications

form. Under operating conditions enter the following values:

·        On Pressure Field, enter 300 psi.

On Temperature Field, enter 900 F.

Save and click the next button. This takes you to the Blocks-Crack Specifications. Click

the New… at the bottom of the form. This brings up the Edit Stoichiometry window.

Set the first Reactants Component field to EDC. Then enter the coefficient of –1.

Set the first Products Component field to HCl. Then enter the coefficient of 1.

Set the first Products Component field to VCM. Then enter the coefficient of 1.

In the Products Generation section of the form, select Fractional conversion and set a

value of .55 of the component EDC.

The final result should look like Figure 5.

Figure 5: Edit Stoichiometry dialog box for reaction 1

Save and click the next button. A summary of the reaction you just input will appear.

Save and click next again. The Blocks-QUENCH Specifications form should appear.

Use your mouse to select Degrees of Subcooling where it says Temperature. Then enter

a value of 10 F.

On the Pressure field, enter –5 psi. The negative signifies this is a pressure drop

specification. A positive number would be a pressure specification.

Save and click the next button. All the required specifications for this problem are

complete so ASPEN PLUS will ask if you want to run your simulation now. You do not

want to, so select cancel. Now you can select optional input, such as a flowsheet design

specification. You could go to any of the forms and make any changes. If you were

ready to run and you remembered to save your flowsheet, you would then press OK to

run.

You can use the data browser to look at view and modify any of the input values at any

time.

Running The Simulation And Displaying The Results

The next step is to run the ASPEN PLUS simulation. Note that the status indicator in the

lower right portion of the screen reads Required Input Complete.

Save and click Next to start the simulation. Click OK when it asks if you would like to run

the simulation. Be sure to save before you Run. Aspen is most likely to crash when you

run and to savegaurd all of your hard work SAVE.

A trace of the run progress is written to the screen in the control panel window. When the

run is complete, ASPEN PLUS displays Results Available in the lower left hand corner of

the window.

Click the check results button (it looks like a blue folder with a blue check through it). A

series of folders will be displayed: Streams, Blocks and Results Summary. You can

brows through the results by clicking on any one of the various folders.  These results

can be copied and saved to other programs such as Microsoft Excel or Word or printed

directly.  You can also export a formatted report using the File|Export command.  Choose

the file type to be Aspen Plus Report (*.rpt).

For your assignment please breifly describe in a paragraph the flow rates of your product

streams and sizing/temperature/heating and cooling duty estimates for the two distillation

columns.  Also include a copy of the report file.

Please email the assignment to che473k@che.utexas.edu.

Don’t forget to save the simulation.

ChE 473K January 21, 2000

Absorption Column Simulation

Tutorial 2

1.     Insert a RADFRAC column model in the workspace.

2.     Attach two streams to the feed of the RADFRAC model. One should be labeled 1

and the other labeled 2.

 

Note: The order that you attach the feed blocks is very important. If they are not

numbered as seen in the illustration, you will have problems later.

 

3.     Attach the Vapor Distillate output from the top of the RADFRAC model to one of the

product output arrows. This arrow should be labeled 3.

4.     Attach the Bottoms output from the bottom of the RADFRAC model to one of the

product output arrows. This arrow should be labeled 4.

 

The simulation should look like this.

 

5.     Hit the Next button, enter the title of “Example Adsorption Problem”.

6.     Hit the Next button again. Enter the following in the Comp ID field:

METHANE

ETHANE

PROPANE

N-BUTANE

N-DECANE

 

The Components-Specifications form should look like this.

 

7.     Hit the Next button, and the Properties-Specifications window should appear.

8.     Choose NRTL for the Property Method.

9.     Use the Next button to get to the Stream-1-Input form.

10. In this simulation Stream 1 is the lean oil absorbing medium. This is because it is

feeding into the top, or first stage, of the RADFRAC model. Enter the following values:

 

 

Temp: 100 F

Pres: 5 ATM

Composition Basis: MOLE-FRAC

N-BUTANE: .005

N-DECANE: .995

Total MOLE-Flow: 10000 LBMOL/HR

 

Note: Make sure that you have changed the pressure units to ATM and the you have

changed the composition basis to Mole-Frac.

 

The Stream-1-Input form should look like this:

 

11. Use the Next button to get to the Stream-2-Input form.

12. Enter the following values:

 

Temp: 100 F

Pres: 5 ATM

Composition Basis: MOLE-FRAC

METHANE: .88

ETHANE: .04

PROPANE: .05

N-BUTANE: .03

Total MOLE-Flow: 5500 LBMOL/HR

 

Note: Make sure that you have changed the pressure units to ATM and the you have

changed the composition basis to Mole-Frac.

 

Note: Do not enter zero in the other component MOLE-FRAC fields, just leave them

blank.

 

Stream-2-Input should look like this:

 

13. Hit Next and the Blocks-B1-Setup-Configuration form will appear.

14. Define the number of stages as 5.

15. We do not have a condenser or a reboiler, so we enter none in the condenser field

and none in the reboiler.

 

 

Blocks-B1-Setup-Configuration should look like this:

 

16. Hit Next and the Blocks-B1-Setup-Streams form appears.

17. Make the feed location for Stream 1, Stage 1 (the top of the column) and the feed

location for Stream 2, Stage 5 (the bottom of the column).

18. Change the Convention for Stream 2 to ON-STAGE, by clicking on the field and

using the list function.

19. Product stream 3 (the exit gas) should be coming from stage 1 (the top of the

column) and should be labeled as vapor phase. Product stream 4 (the exit liquid) should

be coming from stage 5 (the bottom of the column) and should be labeled as a liquid

phase.

 

Blocks-B1-Setup-Streams should look like this:

 

20. Hit Next and the Blocks-B1-Setup-Pressure form appears.

21. In the Stage 1 / Condenser pressure enter a pressure of 5 ATM.

Blocks-B1-Setup-Pressure form should look like:

 

22. Now open the Blocks-B1-Convergance form. Select the Advanced tab.

23. Change the Absorber option from No to Yes.

Blocks-B1-Convergance-Advanced form should look like:

 

24. Next select open the Blocks-B1-DesignSpecs form.

25. Click New in the Object Manager. Hit OK and a default Spec. number of 1 will be

set.

26. This will open the Blocks-B1-DesignSpecs-Specifications form. Under Design

specification type enter Mole purity.

27. Under Specification Target enter .01.

28. The stream type should be set to Product.

 

Note: This sets the total removal of propane in the vapor stream to about 80%.

 

Blocks-B1-DesignSpecs-Specifications form should look like:

 

29. Hit the Next button and the Blocks-B1-DesignSpecs-Components form will appear.

30. Under Available components select PROPANE and move it to Selected components

using the > button.

 

Blocks-B1-DesignSpecs-Components form should look like this:

 

31. Hit the next button and the Blocks-B1-DesignSpecs-Feed/Product Streams form will

appear.

32. Under available product streams select 3 and move it to selected stream using the >

button. The completed design specification states that you wish for the mole fraction of

propane in the product stream number 3 to be equal to .01.

Blocks-B1-DesignSpecs-Feed/Product Streams form should look like this:

 

33. Click the Next button and the Blocks-B1-Vary-Object Manager will appear. Hit the

New… button and hit OK to accept the default vary ID of 1.

34. This will open the Blocks-B1-Vary-1-Specifications form. Set the Adjusted variable

type to Feed rate.

35. Set the stream name to 1. This means that you are going to vary the feed rate of

the lean oil absorbing medium.

36. Set the following values:

 

Lower bound: 5000 lbmol/hr

Upper bound: 20000 lbmol/hr

Maximum step size: 1000

 

Blocks-B1-Vary-1-Specifications form should look like this:

 

37. Save the simulation and then run the simulation. Before running the simulation you

may want to go to the Setup-Report Options-Stream form and the Mole Fraction Basis

output. This will make interpreting the results easier.

38. You will notice that the mole fraction of propane is stream 3 is .01 as we specified,

and that the molar flow basis of stream 1 is larger than the 10000 lbmol/hr value that we

initially specified. This indicates that the vary block had to increase the feed rate to meet

the desired specification.

 

Aspen Plus Tutorial 3:

Configuring a Plug Flow Reactor with Langmuir-Hinshelwood-Hougen-Watson (LHHW)

Kinetics

Todo: Simulate the vinyl acetate PFR  as described in P991 REACTION KINETICS

(Handed out in lecture) to obtain information on the initial reaction rate and compare to

results that were calculated using an Excel Spreadsheet for isothermal reactions at

212oF and 338oF.

Figure 1: Flowsheet Schematic

Figure 2: Setup Specifications

Figure 3: Component Specifications

Figure 4: Properties Specification

Figure 5: Stream 1 Input

Figure 6: Block B1 Setup Specifications

Figure 7: Block B1 Setup Configuration

Figure 8: Block B1 Setup Reactions

Figure 9: Reaction R1 Stoichiometry

Figure 10: Input forms for Reactions 1 and 2.

Figure 11: Reaction R-1 1st Reaction Kinetic Data

Figure 12: First Reaction Driving Force Expression for Terms 1 and 2

Figure 13: First Reaction Adsorption Expression

 

 Aspen Plus Tutorial 4:

Using Heat Transfer with a Plug Flow Reactor

This is an adjustment of Aspen Tutorial 3.  In that tutorial, we assumed the reactor would

operate isothermally.  Now we want to make sure that it does by adding heat transfer. 

Start from Aspen Tutorial 3 and add the "HEATX" heat exchanger and the water cooling

streams indicated in the flowsheet below.  The screenshots below illustrate how do

configure such a system in Aspen Plus.  An assignment is given below.

Assignment:

You'll probably find that the conversion of VA is pretty low.  The conversion can be

increased by reducing the feed stream inlet to 10000 lbmol/hr and increasing the pipe

diameter to 2 inches.  Make modifications to your system reflecting these changes while

still maintaining a relatively isothermal reactor. It is a good idea to try to get your cooling

water stream "COOL_OUT" to be all vapor at the same temperature of its input

counterpart. Also be sure you have enough cooling water to cool the coolant stream.

(Note: the cold water is very cold; it would be difficult to get a utility provider to

inexpensively sell you this stream)  In one page, summarize the following (you won't be

able to do this with a simple printout from Aspen):

Changes (if any) in reactor temperature (inlet vs. outlet).

VA production, overall reaction ratio (2*VAout/CO2out), and  reactor conversion

(VAout/AAin).

Coolant and cooling water flowrates.

Heat exchanger configuration.

 

Aspen Plus Tutorial 5:

Preparing and Configuring a Distillation Column using RADFRAC

We have been asked to design a C2 splitter that will give 95% recovery of the ethylene

feed, as well as a purity of 99% ethylene in the distillate.

The feed conditions are as follows:

Component 

Hydrogen- H2 

Methane-CH4 

Ethylene-C2H4 

Ethane-C2H6 

Propylene- C3H6-

2 

Mole Fraction

0.00014

0.00162

0.75746

0.24003

0.00075

We will use the DSTWU model to estimate the operating conditions. Run the DSTWU at

P=18 bar, RR=3.1, and basis=100 lbmol/hr. DSTWU performs a Winn-Underwood-

Gilliland shortcut design calculation for a single-feed, two-product distillation column, with

a partial or total condenser.

Then we will use these results to design a RADFRAC analysis. RadFrac is a rigorous tray

to tray model for simulating all types of multistage vapor-liquid fractionation operations.

Make sure that you have a total condenser, and that you have a spec. which sets the

purity of ethylene in the Distillate to 99%.

Next week we will use a sensitivity analysis to determine the optimum feed location and

number of stages. Vary number of stages from 23-35 and feed location from 12-21.

Output reflux ratio, reboiler duty, and condenser duty.

Using the DSTWU model

1. Inset a DSTWU column, one feed to the right of the column and two product streams

two the left of the column in the flowsheet space.

2. Connect the feed arrow to the Feed on the DSTWU block.

3. Connect the top product arrow to the Distillate arrow on top of the DSTWU block.

4. Connect the bottom product arrow to the Bottoms arrow on the bottom of the DSTWU

block.  Note: The stream numbers become important later, so make sure that they appear

the same as the example picture.

5. Hit the Next button and enter "DSTWU Distillation Example" as the title.

6. Hit the Next button and you should be at the Components-Specifications form.

7. Enter the components which are in the feed stream, as defined at the beginning of the

worksheet.

8. Hit the Next button, and the Properties-Specifications form should appear. For

Property method choose PENG-ROB.

9. Hit Next twice, and then OK and the Streams-1-Input-Specifications form should

appear.

10. Enter the following values:

Pressure 18 bar

Vapor Fraction 0

Composition Basis Mole Fraction

HYDROGEN 0.00014

METHANE 0.00162

ETHANE 0.24003

ETHYLENE 0.75746

PROPYLEN 0.00075

Total Mole Flow 100 lbmol/hr

11. Hit the Next button, and the Blocks-B1-Input-Specifications form should appear.

12. Enter the following values:

Reflux Ratio 3.1

Light Key:

   Component Ethylene

   Recovery 0.95

Heavy Key:

   Component Ethane

   Recovery 0.03

Condenser Pressure 17.8 bar

Reboiler Pressure 18.2 bar

Note: The Light Key Recov of .95 is to meet the 95% recovery of ethylene specification.

The Heavy Key Recov of .03 is to make the purity of the distillate stream approximately

99% ethylene. This value can be calculated by doing a material balance around the

column. The value of .03 does not account for any of the other components going into the

distillate product stream, and is therefore just an estimate.

13. Hit the Next button, and ASPEN should indicate that the required input is complete.

You should save the program before pressing OK and running it.

14. You may want to turn on the mole fraction output in the Setup-Report Options-Stream

form prior to running the simulation.

15. Run the simulation, and check the results. We will use the results from both the

Stream-Sum.Main form and the Blocks B1 (Dstwu.Results). The most important values to

note are:

a) Total Molar Flow Rate of the distillate product stream. This is one of the necessary

inputs for the RADFRAC model. This number is not completely correct since the .03

value for the Recovh specification is just an estimate.

b) Actual Equilibrium Stages, this will be used as the first guess for our RADFRAC

column.

c) Feed Stage Location, this will also be used as the first guess for the RADFRAC

column.

The rest of the information could also be useful as an initial estimate of the results from

the RADFRAC model. This information will be calculated more rigorously when we run

the RADFRAC model simulation.

Using the RADFRAC model

We can start from the DSTWU model

1. Save the last model and the save it again under a new name.  Delete the DSTWU

block.  Then add a RADFRAC block in its place

2. Connect the feed line to the center Feeds arrow on the RADFRAC block.

3. Connect the top product line to the Liquid Distillate arrow in the upper right hand

corner of the RADFRAC block.

4. Connect the bottom product line to the Bottoms arrow on the bottom of the RADRAC

block.  Note: The stream numbers become important later, so make sure that they appear

the same as the example picture.

5. The Components-Specifications-Selection, Properties-Specifications-Global, and the

Streams-1-Specifications forms should be filled out exactly as was done for the DSTWU

model.

6. After pressing NEXT you should reach the Blocks-B1-Setup-Configuration form.

7. Enter the following values:

Setup Options

Number of Stages: 32 (This value was taken from the results of the DSTWU model.)

Condenser: Total (The difference between total and partial condensors should be

discussed in class)

Reboiler: Kettle (The difference between kettle and thermosyphon reboilers should be

discussed in class)

Operating Specifications

Distillate rate (Mole): 72.68 (This is the total molar flow rate of the distillate product. This

value is close to the value in the DSTWU model, but has been calculated from the

material balance.)

Reflux ratio (Mole): 3.1 (This is the same RR in the DSTWU model.)

8. Hit the Next button, and the Blocks-B1-Setup-Streams form appears. The feed stream

1 should be set to enter Above-Stage 18. (this was also taken from the DSTWU model).

9. Be sure that product stream 2 is coming from stage 1 and that it is a liquid and that

product stream 3 is coming from stage 32 and that it is a liquid.

10. Hit the Next button, and the Blocks-B1-Setup-Pressure form appears. Enter Top

Stage pressure as 17.8 BAR.

11. Open the Blocks-B1-DesignSpecs-Object Manger form.

12. Click on the New… button.

13. Click OK to accept the default design specification number.

14. Enter the following design specification in the Blocks-B1-DesignSpecs-1-

Specifications form.

Design specification type: Mole purity

Specification Target: .99

Stream Type: Product

Note: This tells Aspen that you want the molar purity in one of the product streams to be

99%.

15. Hit the Next button and the Blocks-B1-DesignSpecs-1-Components form will open.

Select Ethylene as the component to specify.

16. Hit the Next button and the Blocks-B1-DesignSpecs-1-Feed/Product Streams form

will open. Select stream 2 (the distillate product stream) as the specified stream.

17. Hit the Next button and the Blocks-B1-Vary-Object Manager will appear. Click New…

and accept the default Vary ID number.

18. Enter the following information in the Blocks-B1-Vary-Specifications form.

Adjusted variable type: Reflux Ratio

Lower Bound: 2

Upper Bound: 20

Maximum step size (optional): 1

19. Save the simulation, then run it (don't forget to turn on the mole fraction output in the

Setup-Report Options-Stream form prior to running the simulation). Check the results.

You should have a 95% ethylene recovery, and 99% purity of ethylene in the distillate

product. Make sure that the RR seems reasonable.

Assignment

How close are the RADFRAC results to the values estimated by DSTWU?  On one page,

give relevant information to allow someone to design your final column and summarize its

performance for separating ethane from ethylene.  Some important things to show might

be (but is not restricted to) number of trays, heat duties on condenser and reboiler, reflux

rate and ratio.

Aspen Plus Tutorial 6:

Azeotropic/Extractive Distillation

This tutorial will guide you though the setup of an azeotropic distillation column using

RADFRAC.

Residue and Miscibility

Before setting up the model, the tutorial will show how to use Aspen's ability to create

residue curves based on your chose models and the add to that a liquid-liquid miscibility

curve.

Flowsheet

Start a new flowsheet in Aspen and add a FLASH3 unit and add stream FEED to the feed

stream, VAPOR to the vapor stream, 1-LIQUID to the first liquid stream and 2-LIQUID to

the second liquid stream.

Components and Properties

The components are vinyl acetate (VA, VINYL-ACETATE, C4H6O2-1), acetic acid (AA,

ACETIC-ACID, C2H4O2-1) and water (H2O, WATER, H2O).  We will use the NRTL-RK

property set.

Feed Stream

We will set up Aspen to vary this stream a short bit later.  For now define the feed stream

as having T=230F, P=65psi, VA = 1 lbmol/hr, H2O = 1 lbmol/hr.  This will be the pressure

at the top of the column.

Flash3

Define the decanter as shown below.  Here we have set the pressure to 0 denoting no

pressure drop and heat duty to zero denoting adiabatic phase separation.  Thus this unit

will have the same conditions as the inlet stream.  The key component (the majority

component) in the 2nd liquid stream will be water.

Sensitivity Analysis

We can use Aspen to get an idea of how sensitive (how much our process changes) our

process is to a changing variable.  We will use this feature to get a list of the liquid-liquid

equilibria for a water-VA-AA system.  We will later put this on a ternary diagram.

To set the sensitivity, expand "Model Analysis Tools" and click on Sensitivity.  Add a new

object.  You will then need to add FORTRAN variables to calculate your data.  Don't

despair.  We won't be using any heavy duty FORTRAN and you shouldn't need much

more than what is in this tutorial.  Just so you know, basic statements are much like any

other programming language. y = 2 (2+ 2x - sin(x)/2)x-1 would be written y = 2*(2+2*x-

sin(x)/2)**(x-1).  But again, you probably won't need all of that. 

We want to examine 6 variables, the mole fractions of each component in the 2 liquid

streams. Select new to enter in each of the variable definitions.

etc...

You should have the following variables entered in the end:

Name Type Stream Substream Component

AA1 Mole-frac 1-LIQUID MIXED AA

VA1 Mole-frac 1-LIQUID MIXED VA

WA1 Mole-frac 1-LIQUID MIXED H2O

AA2 Mole-frac 2-LIQUID MIXED AA

VA2 Mole-frac 2-LIQUID MIXED VA

WA2 Mole-frac 2-LIQUID MIXED H2O

So you know, Aspen uses an old FORTRAN convention of only having six letters for

variable names.

We will vary the flow of acetic acid.  The system forms a two phase liquid up to about

33% acetic acid.  We will collect 21 data points varying acetic acid from 0-1lbol/hr.

We will simply tabulate the variable we defined above.

Run Simulation

Everything is in, so save and run the simulation.  The results under Model Analysis Tools\

Sensitivity\S-1\Results will show you how your model reacted.  You should notice that the

final sensitivity run does not have information for the second liquid.  That point is outside

of the immiscibility region.

Ternary Diagram

We want to plot this data on a ternary diagram that Aspen will create.  To do this, in the

menu, go to Tools|Analysis|Property|Residues.  Components are VA, AA, H2O and the

pressure should be 65psi.  Valid phases should be Vapor-Liquid-Liquid.  Click Go to

make a plot.

Now you can plot the data from the 3 phase flash sensitivity run on the plot (Print it out

and do it by hand).

RADFRAC Setup

Save that project and save as a new name again.  This will be your RADFRAC file. 

Erase the unit and the product streams and delete the sensitivity run.  

Flowsheet

Set up the following flowsheet.  Be sure that VA-RICH is in the liquid distillate port and

the H2O-RICH is in the 2nd liquid distillate port. Note that RADFRAC has the appropriate

picture this time (mainly for clarity).

Feed Stream

The feed stream, like the column configuration, is taken from last year's project.

RADFRAC Setup

Set up RADFRAC using the specifications on the following sheets.  Some things of note:

The valid phases are Vapor-Liquid-Liquid

We will be extracting 2683 lbmol/hr from the bottom of the column, the same amount of

AA going in.

VA-RICH should be 1st liquid, H2O-RICH should be 2nd liquid.

Three phase calculations will happen on all stages.

Water is the key component in the 2nd liquid stream.

Run Simulation

Save and run.

Assignment

Plot a residue curve for the VA,AA,H2O system.  On the curve show the liquid-liquid

equilibrium curve and tie lines for conditions at the top of the column (230F, 65psi).  Draw

in the Feed, VA-Rich, Water-Rich, and Bottoms points on this diagram based on the

azeotropic distillation from RADFRAC.  Also indicate the material balance point, and the

distillate mixture point.  Draw lines between significant points.  Turn this page and a

printout of your stream summary in with your group number and name.