Aspen Plus7 - Chemical Engineering

Aspen Plus7 - Chemical Engineering
Version
Aspen Plus
10
7
STE ADY STATE SIMUL ATION
Building and Running
a Process Model
GETTING STARTED
AspenTech7
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Contents
About Getting Started Building and Running a Process Model
Why Use Process Simulation?........................................................................................vii
What is an Aspen Plus Process Simulation Model?.................................................... viii
Sessions in this Book .......................................................................................................ix
For More Information ......................................................................................................ix
Technical Support.............................................................................................................x
1
Aspen Plus Basics
Starting Aspen Plus .......................................................................................................1-2
The Aspen Plus Main Window ......................................................................................1-2
Opening a File................................................................................................................1-3
Selecting Flowsheet Objects ...........................................................................................1-6
Using a Shortcut Menu .................................................................................................1-7
Opening Input Forms ....................................................................................................1-8
Using Help .....................................................................................................................1-9
Entering Data on a Form .............................................................................................1-11
Expert Guidance—the Next Function .........................................................................1-12
Running the Simulation ..............................................................................................1-16
Examining Stream and Block Results........................................................................1-17
Modifying and Rerunning Your Model ........................................................................1-19
Exiting Aspen Plus .......................................................................................................1-20
2
Building and Running a Process Simulation Model
Building the Process Model...........................................................................................2-2
Defining the Problem: Methylcyclohexane Recovery Column ....................................2-2
Starting Aspen Plus.......................................................................................................2-3
Creating a New Simulation...........................................................................................2-3
The Aspen Plus Main Window ......................................................................................2-4
Defining the Flowsheet..................................................................................................2-5
Adding Data to the Process Model..............................................................................2-11
Specifying Title, Stream Properties, and Units .........................................................2-13
Entering Components..................................................................................................2-14
Selecting Thermodynamic Methods............................................................................2-16
Entering Stream Data .................................................................................................2-18
Entering Unit Operation Block Data .........................................................................2-20
Running the Simulation ..............................................................................................2-25
Examining Simulation Results ...................................................................................2-26
Examining Block Results ............................................................................................2-26
Examining Stream Results .........................................................................................2-29
Changing Input Specifications....................................................................................2-30
Rerunning the Simulation...........................................................................................2-31
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Creating Reports ......................................................................................................... 2-32
Exiting Aspen Plus...................................................................................................... 2-33
3
Performing a Sensitivity Analysis
Starting Aspen Plus ...................................................................................................... 3-2
Opening an Existing Simulation ................................................................................... 3-2
Saving a Simulation under a New Name .................................................................... 3-3
Defining the Sensitivity Analysis.................................................................................. 3-4
Entering Sensitivity Specifications ............................................................................... 3-4
Defining Sampled Variables .................................................................................. 3-5
Defining Manipulated Variables ........................................................................... 3-9
Defining Tabulated Variables.............................................................................. 3-11
Running the Simulation .............................................................................................. 3-14
Displaying Sensitivity Analysis Results.................................................................... 3-15
Plotting Sensitivity Results ......................................................................................... 3-16
Exiting Aspen Plus ...................................................................................................... 3-17
4
Meeting Process Design Specifications
Starting Aspen Plus....................................................................................................... 4-2
Opening an Existing Simulation.................................................................................. 4-2
Saving a Simulation Under a New Name ..................................................................... 4-3
Defining the Design Specification ................................................................................. 4-4
Entering Design Specifications ..................................................................................... 4-4
Running the Simulation ................................................................................................ 4-9
Examining Design Specification Results .................................................................... 4-10
Exiting Aspen Plus ...................................................................................................... 4-11
5
Creating a Process Flow Diagram
Starting Aspen Plus....................................................................................................... 5-2
Opening an Existing Simulation ................................................................................... 5-2
Switching to PFD Mode ................................................................................................. 5-3
Adding Equipment Icons and Streams ......................................................................... 5-4
Displaying Stream Data ................................................................................................ 5-8
Adding a Stream Table ............................................................................................... 5-11
Adding Text ................................................................................................................. 5-13
Printing a Process Flow Diagram................................................................................ 5-15
Leaving PFD Mode...................................................................................................... 5-16
Exiting Aspen Plus ...................................................................................................... 5-16
6
Estimating Physical Properties for a Non-Databank Component
Thiazole Physical Property Data................................................................................... 6-2
Starting Aspen Plus....................................................................................................... 6-3
Creating a Property Estimation Simulation ............................................................... 6-3
Entering Components Information ............................................................................... 6-4
Specifying Properties to Estimate ................................................................................. 6-5
Entering Molecular Structure ....................................................................................... 6-7
Entering Property Data............................................................................................... 6-10
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Running a Property Constant Estimation (PCES) ......................................................6-14
Examining Property Constant Estimation Results .....................................................6-14
Creating a Property Backup File .................................................................................6-16
Exiting Aspen Plus .......................................................................................................6-16
7
Analyzing Properties
Starting Aspen Plus........................................................................................................7-2
Entering Components and Properties............................................................................7-2
Generating a Txy Diagram ............................................................................................7-5
A
Connecting to the Aspen Plus Simulation Engine
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About Getting Started
Building and Running a
Process Model
Aspen Plus makes it easy to build and run a process simulation model by
providing you with a comprehensive system of online prompts, hypertext help,
and expert system guidance at every step. In many cases, you will be able to
develop an Aspen Plus process simulation model without referring to printed
manuals.
If you are new to Aspen Plus, you should do all of these Getting Started sessions.
To familiarize yourself with Aspen Plus basics, first do the brief hands-on session
in Chapter 1. Then do the six other sessions in this book to learn step-by-step
how to use the full power and scope of Aspen Plus. Each session requires only 20
to 30 minutes.
This guide assumes only that you have an installed copy of the software. If you
have not installed the software, please see the appropriate installation guide.
Why Use Process Simulation?
Process simulation allows you to predict the behavior of a process by using basic
engineering relationships, such as mass and energy balances, and phase and
chemical equilibrium. Given reliable thermodynamic data, realistic operating
conditions, and rigorous equipment models, you can simulate actual plant
behavior. Process simulation enables you to run many cases, conduct "what if"
analyses, and perform sensitivity studies and optimization runs. With simulation,
you can design better plants and increase profitability in existing plants.
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Process simulation is useful throughout the entire lifecycle of a process, from
research and development through process design to production.
What is an Aspen Plus Process Simulation
Model?
A process consists of components being mixed, separated, heated, cooled, and
converted by unit operations. These components are transferred from unit to unit
through process streams.
You can translate a process into an Aspen Plus process simulation model by
doing the following steps:
1. Define the process flowsheet configuration. To do this step, you:
−
−
−
Define the unit operations in the process
Define the process streams that flow between these unit operations
Select unit operation models from the Aspen Plus model library to
describe each unit operation
2. Specify the chemical components in the process. You can take these
components from the Aspen Plus databanks, or you can define them.
3. Choose appropriate thermodynamic models from those available in Aspen
Plus, to represent the physical properties of the components and mixtures in
the process.
4. Specify the component flow rates and the thermodynamic conditions (for
example, temperature and pressure) of feed streams to the process.
5. Specify the operating conditions for the unit operations in the flowsheet.
When you have specified this information, you have defined an Aspen Plus
process simulation model of your process. You can use the Aspen Plus process
simulation model to predict process behavior.
With Aspen Plus you can interactively change specifications, such as flowsheet
configuration, operating conditions, and feed compositions, to run new cases and
analyze alternatives.
In addition to process simulation, Aspen Plus allows you to perform a wide range
of other tasks such as estimating and regressing physical properties, generating
custom graphical and tabular output results, data-fitting plant data to
simulation models, costing your plant, optimizing your process, and interfacing
results to spreadsheets.
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Sessions in this Book
The hands-on sessions in this book are described in the following table:
Follow the steps in Chapter
To learn how to
1 Aspen Plus Basics
Start Aspen Plus, use the Aspen Plus user interface, exit Aspen Plus
2 Building and Running a Process Simulation
Model
Build and run a typical Aspen Plus process simulation model.
3 Performing a Sensitivity Analysis
Use Aspen Plus to study the sensitivity of process performance to changes
in process feeds and operating variables.
4 Meeting Process Design Specifications
Use Aspen Plus to make your process model meet a design specification
by manipulating a process feed or operating variable.
5 Creating a Process Flow Diagram
Add stream tables, graphics, and text to your graphical simulation
flowsheet.
6 Estimating Physical Properties for a NonDatabank Component
Use Aspen Plus to enter and estimate missing physical properties required
for simulation.
7 Analyzing Properties
Use Aspen Plus to generate tables and plots of physical properties,
computed over a range of values.
For More Information
Online Help Aspen Plus has a complete system of online help and
context-sensitive prompts. The help system contains both context-sensitive help
and reference information. For more information about using Aspen Plus help, see
the Aspen Plus User Guide, Chapter 3.
Aspen Plus Getting Started Building and Running a Process Model This
tutorial includes several hands-on sessions to familiarize you with Aspen Plus.
The guide takes you step-by-step to learn the full power and scope of Aspen Plus.
Aspen Plus Getting Started Modeling Processes with Electrolytes This
tutorial includes several hands-on sessions to familiarize you with simulating
electrolyte systems with Aspen Plus.
Aspen Plus Getting Started Modeling Petroleum Processes This tutorial
includes several hands-on sessions to familiarize you with simulating petroleum
processes with Aspen Plus.
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Aspen Plus Getting Started Customizing Unit Operation Models This
tutorial includes several hands-on sessions to familiarize you with the
customization of unit operation models with Aspen Plus.
Aspen Plus User Guide The three-volume Aspen Plus User Guide provides
step-by-step procedures for developing and using an Aspen Plus process
simulation model. The guide is task-oriented to help you accomplish the
engineering work you need to do, using the powerful capabilities of Aspen Plus.
Aspen Plus reference manual series Aspen Plus reference manuals provide
detailed technical reference information. These manuals include background
information about the unit operation models and the physical properties methods
and models available in Aspen Plus, tables of Aspen Plus databank parameters,
group contribution method functional groups, and a wide range of other reference
information. The set comprises:
• Unit Operation Models
• Physical Property Methods and Models
• Physical Property Data
• User Models
• System Management
• System Administration
• Summary File Toolkit
Aspen Plus application examples A suite of sample online Aspen Plus
simulations illustrating specific processes is delivered with Aspen Plus.
Aspen Plus Installation Guides These guides provide instructions on
platform and network installation of Aspen Plus. The set comprises:
•
•
•
Aspen Plus Installation Guide for Windows
Aspen Plus Installation Guide for OpenVMS
Aspen Plus Installation Guide for UNIX
The Aspen Plus manuals are delivered in Adobe portable document format (PDF)
on the Aspen Plus Documentation CD.
Technical Support
World Wide Web For additional information about AspenTech products and
services, check the AspenTech World Wide Web home page on the Internet at:
http://www.aspentech.com/
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Technical resources To obtain in-depth technical support information on the
Internet, visit the Technical Support homepage. Register at:
http://www.aspentech.com/ts/
Approximately three days after registering, you will receive a confirmation e-mail
and you will then be able to access this information.
The most current Hotline contact information is listed. Other information
includes:
• Frequently asked questions
• Product training courses
• Technical tips
AspenTech Hotline If you need help from an AspenTech Customer Support
engineer, contact our Hotline for any of the following locations:
If you are located in:
Phone Number
Fax Number
E-Mail Address
North America & the
Caribbean
+1-617/949-1021
+1-617/949-1724
[email protected]
+54-11/4393-5308
+54-11/4394-8621
[email protected]
+55-11/5506-0756
+55-11/5506-0567
[email protected]
+32-2/724-0100
+32-2/705-4034
+44-1223/312220
+44-1223/366980
+81-3/3262-1743
+81-3/3262-1744
+1-888/996-7001
(toll free)
South America
(Argentina office)
(Brazil office)
Europe, Gulf Region, & Africa
(Brussels office)
[email protected]
(UK office)
Japan
Asia & Australia
[email protected]
(Hong Kong office)
+85-2/2838-6077
+85-2/2833-5642
(Korea office)
+82-2/761-5800
+82-2/761-5803
❖
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[email protected]
❖
❖
❖
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Chapter 1
1
Aspen Plus Basics
The best way to learn basic Aspen Plus concepts is by using Aspen Plus. This
session leads you through an example Aspen Plus simulation to explain how to
open a file, enter data, run a simulation, and examine results
Allow about 20 minutes for this session.
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Aspen Plus
Basics
Starting Aspen Plus
To start Aspen Plus:
➤ From your Windows desktop, click Start and then select Programs.
➤ Click AspenTech, select Aspen Plus 10.1-0, and click Aspen Plus User Interface.
The Aspen Plus Startup dialog box appears. You can use this dialog box to open an
existing simulation or to create a new simulation using a template or a blank
simulation.
➤ Select the Blank Simulation option and click OK to start the new Aspen Plus
simulation.
Note
If the Connect to Engine dialog box appears, see Appendix A.
Aspen Plus starts a new simulation with the default name, Simulation 1.
Tip
You can create a shortcut icon for your Windows desktop that you
double-click to start Aspen Plus. To create this icon, use Windows
Explorer to navigate to the xeq folder of your Aspen Plus User
Interface installation. Next, select the apwn.exe program and
drag it onto your Windows desktop.
The Aspen Plus Main Window
The Aspen Plus main window (shown in Figure 1.1) is displayed when you start
Aspen Plus. In the workspace of this window you create and display your
simulation flowsheet. The workspace remains blank until you enter problem
specifications.
Aspen Plus displays context-dependent definitions and information in the prompt
area of the main window. Whenever you need information about the currently
highlighted field or item, refer to the prompt for guidance.
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Figure 1.1 Aspen Plus Main Window
Help button
Next button
Menu bar
Toolbar
Flowsheet
work space
Scroll bars
Select Mode
button
Model Library
Prompt area
Status indicator
Opening a File
You can open a file for an Aspen Plus simulation by either:
• Double-clicking the file from Windows Explorer
• Selecting the Open command from the File menu in Aspen Plus
In this section you will use the Open command on the File menu to open a
partially completed Aspen Plus simulation stored in a backup file.
➤ To display the File menu, click File on the menu bar.
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Aspen Plus
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Aspen Plus displays the File menu:
➤ From the File menu select Open.
The Open dialog box appears. Your default working directory is displayed in the Look
In box. You can navigate to the folder containing a file by using the Look In box or the
Look In Favorites button
.
➤ Click the Look in Favorites button.
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A list of folders is displayed in the Open dialog box:
By default, the Favorites list contains five folders that are provided with Aspen
Plus. The files in these folders are designed to assist you in creating suitable
simulation models in Aspen Plus.
Tip
You can add folders to the Favorites list by navigating to the
appropriate folder and clicking the Add to Favorites
button.
➤ Double-click the Examples folder.
➤ From the files list, select flash.bkp and click Open.
➤ Click Yes when Aspen Plus prompts "Do you want to close current run before opening
new run?"
➤ Click No when Aspen Plus prompts "Save changes to Simulation 1?"
While Aspen Plus opens the simulation model, the mouse pointer shows the busy
symbol, to indicate that Aspen Plus is finishing an operation. When the operation
is complete, the mouse pointer returns to the Select arrow shape.
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Aspen Plus
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Selecting Flowsheet Objects
In the main window workspace, Aspen Plus displays the graphical flowsheet for
the opened Flash simulation:
The graphical simulation flowsheet shows the feeds, products, unit operation
blocks, and process streams. The Flash simulation has one feed stream (stream
1), two product streams (streams 2 and 3), and one unit operation block (B1).
In this section, you will select the feed stream (stream 1) on the simulation
flowsheet and enter specifications.
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➤ To select stream 1, place the mouse pointer over stream 1 in the graphical simulation
flowsheet and click.
Stream 1 is selected and highlighted, as shown in the following figure:
Using a Shortcut Menu
A shortcut menu of commands is available for the flowsheet objects. To display the
shortcut menu for stream 1:
➤ Place the mouse pointer over stream 1 and click with the right mouse button.
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Aspen Plus
Basics
The stream shortcut menu appears, listing the commands that you can execute for
stream 1:
➤ Use the Up and Down arrow keys to highlight the commands in the shortcut menu.
The prompts at the bottom of the main window change as you highlight each
command.
Opening Input Forms
To open the input forms for a stream, you can do any of the following:
•
Select Streams from the Data menu.
•
•
Click the Streams button
on the main window toolbar.
Select Input on the shortcut menu for the stream.
➤ To open the input forms for stream 1, select Input on the shortcut menu.
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Tip
Alternatively, to open a stream or block input form quickly,
double-click the object from the graphical simulation flowsheet in
the Process Flowsheet window.
The input forms for stream 1 (Material) appear in a Data Browser window, which is
displayed on top of the Aspen Plus main window:
Data Browser
menu tree
The Data Browser is a sheet and form viewer with a hierarchical menu tree view
(on the left side of the window) of the available simulation input, results, and
objects that have been defined.
Using Help
When you view a form or a dialog box, you can get context-sensitive help in any of
the following ways:
•
•
•
on the main
Click the box you want information on and the Help button
window toolbar
From Help on the main window menu bar, select What’s This? from the Help
menu
Press the Help key (F1)
➤ Click the Help button
in the Data Browser.
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on the main window toolbar, then click the Specifications tab
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Aspen Plus
Basics
Aspen Plus displays a Help window that explains how to use the current sheet, the
Stream Input Specifications Sheet:
In Help, green underlined words identify topics with additional or related help.
In this example there is a link to help on the Stream Input Form at the end of
the Help topic.
➤ Scroll to the end of this Help topic and click the underlined text Input Form Help.
Help on this topic appears.
➤ When you finish reading the help, close the Help window by clicking the Close button
on the upper right corner of the Help window.
You can also get help on any topic at any time by using the Help menu. For
example:
➤ Click Help on the main window menu bar.
➤ Use the arrow keys to move through the menu, and read the prompts at the bottom of
the screen to see a description of each item .
➤ To learn more about the Aspen Plus online help system, select Help Topics.
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➤ From the Contents tab, double-click Using Aspen Plus Help and select a help topic to
display.
➤ When you are finished, close the Help window by clicking the Close button.
Entering Data on a Form
You use the Data Browser to enter data on forms. In this section, you will enter
missing temperature, pressure, and component flow data for stream 1.
To move from box to box on a form, use the Tab key or the mouse.
➤ Click the open Data Browser window to make it active. This returns you to the Streams
Input Specifications sheet.
Tip
Alternatively, you can select streams 1 (Material) - Data Browser
from the Window menu in the main window to make the Data
Browser window active.
➤ Enter the following specifications:
Temperature
Pressure
Methanol component flow
Water component flow
180°F
20 psi
50 lbmol/hr
50 lbmol/hr
Since the default units are appropriate for this simulation, you will need to enter only
the values.
Note
If you make a mistake while typing, use the Backspace key to
erase the previous characters.
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Aspen Plus
Basics
The completed Streams Input Specifications sheet is shown in the following
figure:
When you enter values in boxes or change default options on Input forms, the
specifications you enter and the defaults you modify are shown in black text, and
will appear next to the sheet name. On the Specifications sheet,
a check mark
the temperature, pressure, and component flow specifications are black,
indicating user input.
Expert Guidance—the Next Function
The Aspen Plus expert system, known as the Next function, guides you through all
the steps for entering specifications for your simulation model. The Next function:
• Guides you through the required and optional input for a simulation by
displaying the appropriate forms
• Displays messages informing you what you need to do next
• Ensures that you do not enter incomplete or inconsistent specifications even
when you change options and specifications you have already entered
➤ To use the Next function to complete the simulation model, click the Next button
on the Data Browser window toolbar. (When the Data Browser window is not open,
you can also click the Next button on the main window toolbar.)
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Aspen Plus displays the next sheet on which input data is required for the simulation
model, the Flash2 Input Specifications sheet for Block B1:
The input data for Block B1 on the Specifications tab is incomplete as indicated by the
symbol on the Specifications tab.
➤ Click the Next button
again.
Aspen Plus displays a Completion Status window that indicates additional data are
required:
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Basics
➤ Close the Completion Status window.
➤ Move to the first flash specification box and click the Down arrow to display the list of
flash specification types.
➤ Select Heat Duty from the list.
➤ In the Heat Duty value box , enter 0. Press Enter.
➤ To specify the flash conditions of 1 atmosphere, move the pointer to the Pressure
value box, and type 1. Press Enter.
➤ To change the input units from psi to atm, move to the Pressure Units box, which
currently displays units of psi.
➤ Click the arrow on the pressure units box to display the available options.
The units list for pressure appears:
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➤ Select atm from the list.
The input data on the Specifications tab is now complete, as indicated by the check
mark on the Specifications tab:
The input for Block B1 is complete as indicated by the check mark on the B1
folder in the menu tree view on the left side of the Data Browser window.
The input specifications for the simulation are complete as indicated by the
message in the status bar at the bottom of the main window.
➤ Close the Data Browser window by clicking the Close button
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Aspen Plus
Basics
Running the Simulation
With the input specifications for this simulation model complete, the simulation is
ready to be run. You can run the simulation in any of the following ways:
• Select Run from the Run menu in the main window menu bar
•
Click the Start button
toolbar
•
Click the Run Control Panel button
click the Start button
on the Simulation Run toolbar in the main window
to open the Control Panel and then
on the Control Panel toolbar
➤ Click Run on the menu bar.
Aspen Plus displays the Run menu:
➤ Select Run.
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While Aspen Plus performs calculations for the simulation, the mouse pointer has
a stop sign shape. The block being executed is also highlighted in the simulation
flowsheet in the Process Flowsheet window. When the calculations are complete,
the mouse pointer returns to the Select arrow shape. In the status bar at the
bottom of the main window, the prompt message "Simulation run completed"
appears on the left and on the right, the status message "Results Available"
appears in blue.
Note
If the calculations are completed with errors or warnings, the
status message indicates "Results Available with Errors" and
"Results Available with Warnings," respectively.
Examining Stream and Block Results
In this section you will view the results for the flash overhead vapor stream
(stream 2) and the summary results for the Flash block (Block B1).
➤ To display the flash overhead vapor (stream 2) results, click stream 2 in the graphical
flowsheet to select the stream.
➤ With stream 2 selected, right-click on the stream to display the shortcut menu for the
stream.
➤ Select Results from the menu.
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Aspen Plus
Basics
Aspen Plus displays the thermodynamic state and composition flows of the vapor
stream, stream 2, on the Streams 2 (Material) Results Sheet in a Data Browser
window:
➤ Use the vertical scrollbar to the right of the results to scroll down the stream results.
➤ To display the results for the Flash Block B1, double-click Blocks on the Data Browser
menu tree and then double-click B1.
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Aspen Plus displays the results forms for Block B1 in a Data Browser window. The
Block B1 (Flash2) Results Summary sheet displays the overall results for the block.
You can see the calculated flash outlet temperature and overall vapor fraction:
➤ Click the Next Form button
through the results.
on the toolbar of the Data Browser window to browse
➤ Close the Data Browser window by clicking
.
Modifying and Rerunning Your Model
To simulate changing the composition of the feed stream to 60 lbmol/hr methanol
and 40 lbmol/hr water:
➤ Click stream 1 in the graphical simulation flowsheet to select it.
➤ Right-click to display the stream shortcut menu.
➤ Select Input from the menu.
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The input form for stream 1 appears.
➤ Move to the Value boxes in the Composition group box and enter a component flow of
60 for METHANOL and 40 for WATER.
➤ Close the Data Browser window.
➤ To run the simulation, select Run from the Run menu.
➤ When the run is completed, select and display results for the outlet streams and the
flash block to examine the new process results. (See Examining Stream and Block
Results, this chapter, to review how to do this.)
Exiting Aspen Plus
To exit Aspen Plus:
➤ Click File on the main window menu bar to display the File menu.
➤ Select Exit.
Aspen Plus displays a dialog box asking if you want to save your simulation.
➤ Select No to exit without saving the simulation.
Congratulations! You have successfully completed an Aspen Plus simulation.
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Building and Running a
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In this session you will create an Aspen Plus process model for a
methylcyclohexane (MCH) recovery column.
This session is divided into three sections:
• Building the Process Model
• Adding Data to the Process Model
• Running the Simulation
Allow about 50 minutes to complete the entire session.
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Building the Process Model
In this section, you will build the process model by performing these tasks:
• Define the problem to be simulated
• Start Aspen Plus
• Create a new simulation
• Define the flowsheet using the graphical interface
Defining the Problem: Methylcyclohexane
Recovery Column
The process flow diagram, operating conditions, and problem definition are shown
in Figure 2.1.
Figure 2.1 Problem Definition: MCH Recovery Column
MCH and toluene form a close-boiling system that is difficult to separate by
simple binary distillation. In the recovery column in Figure 2.1, phenol is used to
extract toluene, allowing relatively pure methylcyclohexane to be recovered in
the overhead.
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In this session, you will evaluate the performance of an existing column for
recovering MCH from a feed stream with a lower concentration than the original
design conditions. You can increase the phenol solvent rate to improve MCH
recovery. However, you need to simulate the column to determine the product
purity, column flow, and composition profiles, and the condenser and reboiler
duties, for a given solvent rate.
Starting Aspen Plus
To start Aspen Plus:
➤ Start Aspen Plus from the Windows Start menu or by double-clicking the Aspen Plus
icon on your desktop.
For more detailed information, see Starting Aspen Plus in Chapter 1.
The Aspen Plus Startup dialog box appears.
Creating a New Simulation
Aspen Plus provides built-in templates for applications such as chemicals,
petroleum, electrolytes, specialty chemicals, pharmaceuticals, and metallurgy.
➤ On the Aspen Plus Startup dialog box, select the Template option. Click OK to
continue.
The New dialog box appears.
Use the New dialog box to specify the template and Run Type for the new
simulation. Use the Run Type option to select the type of calculations you want to
perform. For example, you can perform flowsheet simulation, data regression,
and property estimation calculations.
➤ On the New dialog box, click any item in the list of templates.
A brief description of the selected template appears in the Preview box on the right
side of the dialog box.
➤ Select the General with English Units template for this session.
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The default Run Type, Flowsheet, is appropriate for this session.
➤ Click OK to start the new Aspen Plus simulation.
Note
If the Connect to Engine dialog box appears, see Appendix A.
Aspen Plus starts a new simulation with the default name, Simulation 1.
The Aspen Plus Main Window
The Aspen Plus main window is displayed when you start Aspen Plus. Because you
have not entered any problem specifications yet, the workspace is blank:
For more information about the main window, refer to the section, The Aspen
Plus Main Window, in Chapter 1.
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➤ Click the Next button on the Aspen Plus main window toolbar.
Next button
Aspen Plus displays the Flowsheet Definition dialog box telling you that the first step is
to define the flowsheet in the graphics workspace:
➤ Click OK to close the dialog box.
Defining the Flowsheet
In the flowsheet for the MCH process shown in Figure 2.1, there are two feed
streams (MCH-toluene feed and phenol solvent), one unit operation (an extractive
distillation column), and two product streams (distillate and bottoms).
In this session, you will define the process flowsheet by placing unit operation
blocks in the workspace and connecting streams to the blocks.
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First you will select a unit operation model to simulate the extractive distillation
column.
➤ From the Aspen Plus main window, click the Columns tab on the Model Library.
➤ The list of available distillation columns is displayed. Move the mouse over any model
in the Model Library and read the description in the lower left of the window.
➤ Move the mouse over the RadFrac block and read the prompt.
The prompt for RadFrac suggests this is the right model for this problem.
➤ Click RadFrac, then press the Help key (F1).
The help information confirms that RadFrac is suitable for extractive distillation.
➤ Close the Help window.
The RadFrac model can be represented on the flowsheet by a number of pictorial
icons. You can select the default displayed in the Model Library or select a
different icon from the icon list:
➤ To choose a different icon for RadFrac, click the down arrow to the right of RadFrac in
the Model Library.
The available icons for RadFrac are displayed:
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➤ Move the mouse pointer over the displayed icons to view the label for each icon.
In this session, you will use the icon labeled FRACT1 for the RadFrac block.
➤ Select the RadFrac icon that you want to place in your process flowsheet.
Note
The icon you select becomes the default icon for the model, until
you select a different icon.
➤ Click the icon and drag it to the Process Flowsheet window.
The mouse pointer is in the shape of a box with an arrow, which indicates that only
one block will be placed.
➤ In the Process Flowsheet window, release the mouse button where you want to place
the block. The icon that you selected appears on the flowsheet.
Tip
Alternatively, you can click the icon in the Model Library and
then click the area in the process flowsheet window where you
want to place the block. This method allows you to place multiple
blocks by clicking different locations in the process flowsheet
window.
Aspen Plus automatically assigns a block ID, B1, to your RadFrac block.
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Tip
To stop the automatic naming of blocks, select Options from the
Tools menu, click the Flowsheet tab and deselect the
Automatically Assign Block Name option.
The inserted RadFrac block is shown below:
Next, place the streams for the RadFrac column by doing the following:
➤ Click the Material Stream icon on the left side of the Model Library.
Tip
To select a Heat or Work stream, click the down arrow next to the
Material Stream icon and choose Heat or Work stream.
➤ Move the cursor to the Process Flowsheet window.
For each block in the Process Flowsheet window, all ports that are compatible with the
stream type you selected are highlighted.
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Ports that must have at least one stream connected are shown in red. Optional
ports are shown in blue. If you position the mouse pointer over a port for a few
seconds, the arrow is highlighted and a description of the port appears.
➤ Four required ports, shown with red arrows, appear on the RadFrac block B1. Move
the mouse over the red arrows; the port labels indicate the types of port that are
required to be connected to at least one stream.
To connect the feed streams:
➤ Point to the RadFrac Feed (Required; one or more) port on the RadFrac icon in the
process flowsheet window. Click once to select it.
➤ Move the mouse pointer to a blank part of the process flowsheet window where you
want the feed stream to originate in your graphical flowsheet and click once.
A feed stream connecting the selected inlet port is created. Aspen Plus automatically
assigns the ID 1 to this stream.
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➤ Similarly, connect a second feed stream to the same feed port on the RadFrac icon.
To connect the overhead liquid distillate product stream:
➤ Move the mouse pointer through the ports until the port labeled Liquid Distillate
(Required if Distillate Vapor Fraction < 1(Setup Condenser sheet)) appears. Click the
left mouse button once to select it.
➤ Move the mouse pointer to a blank part of the process flowsheet window where you
want the product stream to terminate in your graphical flowsheet, and click.
Product stream 3 is created, connected to the selected outlet port.
To connect the bottoms product stream:
➤ Move the mouse pointer through the ports until the port labeled Bottoms (Required)
appears. Click once to select it.
➤ Move the mouse pointer to a blank part of the Process Flowsheet window and click
once to create Stream 4.
➤ When you have finished placing streams, click the Select Mode button
upper left corner of the Model Library.
Tip
in the
To cancel connecting the stream at any time, press ESC.
To delete a stream, select the stream in the graphical flowsheet
and press the Delete key.
Your graphical simulation flowsheet is now complete. The status indicator in the
bottom right of the main window says "Required Input Incomplete" indicating
that further input specifications are required for the simulation.
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Adding Data to the Process Model
Now that you have defined your flowsheet graphically, use the Data Browser input
forms to enter the remaining required information for this run.
You can rely on the Aspen Plus Next function to display the required input forms.
As an alternative, you can display the input forms by:
• Selecting the appropriate forms from the Data menu
•
•
on the Data Browser toolbar
Clicking the appropriate button
in the main window
Selecting an object in the graphical flowsheet and clicking Input on the
shortcut menu
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•
Double-clicking an object in the graphical flowsheet
(For more information on opening Input forms, see Chapter 1.)
For this section, you will use the Next function.
➤ Click the Next button in the main window toolbar.
Aspen Plus displays a dialog box telling you that your flowsheet is complete and
that you are now ready to provide remaining specifications through the input
forms.
➤ Click OK to display the first required input form.
Aspen Plus displays a Data Browser window containing the Setup Specifications
forms. The Data Browser window title bar contains the form name.
In the following sections, you will enter input specifications for your model.
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Specifying Title, Stream Properties, and
Units
The Setup Specifications form displays some of the defaults Aspen Plus uses for the
other simulation forms. (Global defaults appear on all subsequent forms, but you
can override them.) You will use the Global sheet to give your simulation a title.
You can also review the other global options that were set when you selected
General with English Units as the Application Type.
➤ Use either the mouse, or the Tab key to move from box to box on the form and read
the prompts at the bottom of the main window.
➤ When you are finished reading about the boxes on this form, click the Title box.
➤ In the Title box, enter Methylcyclohexane Recovery Process and then press Enter.
The values for the remaining boxes on this sheet establish global defaults for
your simulation input. For this session you will use English units and the other
defaults, so you do not need to specify anything else on this sheet.
➤ In the menu tree of the Data Browser window, click the Report Options form in the
Setup folder to review the report options specified in the selected Template.
Aspen Plus always calculates temperature, pressure, vapor fraction, molecular
weight and total flow, enthalpy, entropy, and density for the simulation streams.
Because you selected the General with English Units Application Type when you
created this run, Aspen Plus will also calculate component mole flow by default.
➤ Click the Stream tab to view the Stream sheet.
On the Stream sheet, you can specify which additional properties you want
Aspen Plus to calculate and report. The component flow and fraction bases and
additional properties requested on this form will be included in the StreamSummary reports.
➤ To specify that you would like to have Aspen Plus calculate mole fractions, click the
Fraction Basis Mole checkbox.
You can also request that Aspen Plus calculate and report additional stream
properties. A number of sets of additional properties are built in to Aspen Plus for
each application type, as Property Sets.
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➤ Click the Property Sets button.
You can use the Property Sets dialog box to enter additional property sets for your
calculations.
The Available Property Set, TXPORT, contains transport properties and density.
➤ To specify that you want Aspen Plus to calculate transport properties, select the
TXPORT Property Set in the Available Property Sets list.
➤ Click the right arrow button
list it to the Selected list.
to move TXPORT Property Set from the Available
➤ Click Close to close the Property Sets dialog box.
➤ Click the Next button on the Data Browser window toolbar, to move to the next
required input form.
The Components Specifications form appears.
Entering Components
You use the Components Specifications Selection sheet to select the chemical
components present in the simulation.
The components for the process in this example are toluene, phenol, and
methylcyclohexane. For each component, you must enter a unique component ID.
➤ In the first Component ID box, type TOLUENE and press Enter.
(If you make a mistake while typing, use the Backspace key to erase. )
Because Aspen Plus recognizes the component name Toluene as an Aspen Plus
databank component, Aspen Plus fills in the Type, Component Name, and
Formula boxes automatically.
➤ Click the next blank Component ID box, below TOLUENE. Type PHENOL and press
Enter.
Aspen Plus again fills in the Type, Component Name, and Formula boxes.
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For methylcyclohexane, use the abbreviation MCH for the component ID:
➤ Move to the next blank Component ID box for MCH. Type MCH and press Enter.
Because you have used an abbreviation, MCH, to represent methylcyclohexane,
you must also enter a databank formula or databank name to retrieve the
appropriate component data from the Aspen Plus databank.
➤ Click the blank Component Name box. Type the partial name METHYLCYC and
press Enter.
The Find dialog box appears, listing all the components in the Aspen Plus
databank that have a name containing the letters you typed, METHYLCYC:
Use the Find dialog box to choose the component you need.
Tip
To view the complete component name, click and slide the right
edge of the component name column label to the right.
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➤ Using the mouse, or the Up and Down arrow keys, look through the list until you find
METHYLCYCLOHE... The corresponding Formula, Databank, Molecular Weight,
Boiling Point, CAS Number, and Component Class are displayed in the searched list.
➤ Select the component METHYLCYCLOHEXANE from the list and click Add to add it to
the component list.
Note
You can continue adding components from this dialog box or close
it.
Tip
If you need to search for components based on molecular weight
range, boiling point range, or CAS numbers, you should use the
Advanced sheet in the Find dialog box.
➤ Click Close to return to the Components Specifications Selection sheet.
You have now specified the three components required for this process
simulation model, Toluene, Phenol, and Methylcyclohexane.
➤ Click the Next button on the Data Browser window toolbar.
The Aspen Plus expert system displays the next required sheet, the Properties
Specifications Global sheet.
Selecting Thermodynamic Methods
Use the Properties Specifications Global sheet to select the thermodynamic
methods used to calculate properties such as K-values, enthalpy, and density.
Property methods in Aspen Plus are arranged according to Process Types and in
logical groupings called Base Method.
For this simulation, use the UNIFAC activity coefficient model to estimate
liquid-phase nonideality.
To find the appropriate type of base method for this simulation:
➤ Click the arrow to the right of the Base Method box to display the available
thermodynamic property methods in Aspen Plus.
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You can get basic information about a base method by using the mouse or the
arrow keys to move to the base method and reading the prompt. For more
information about a base method, you can move to the base method name and
use Help.
To select the UNIFAC property method:
➤ Move the highlight down the list to the UNIFAC property method. The information in
the prompt indicates this is the appropriate property method for this simulation.
➤ Select UNIFAC by clicking it.
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➤ Click the Next button on the Data Browser window toolbar.
The Required Properties Input Complete dialog box appears. This dialog box
allows you to select additional input forms for physical property parameters and
estimation.
However, the property specifications for this problem are complete, so you can
continue to the next required input.
➤ Click OK to close the dialog box.
Entering Stream Data
The Stream Input Specifications sheet for Stream 1 appears, as indicated in the
Data Browser window title bar. Stream 1 will be the MCH-toluene feed stream.
➤ Enter the following state variable and component flow specifications for the MCHtoluene feed stream:
Temperature
Pressure
Toluene flow value
MCH flow value
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220
20
200
200
F
psi
lbmol/hr
lbmol/hr
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Because the default units are correct for this simulation, you will need to only enter the
values. (Refer to Entering Data on Forms in Chapter 1 for more information.)
You have now finished entering data for Stream 1, as indicated by the Input
Complete message in the Data Browser status bar, at the lower left of the
window.
➤ Click Next on the Data Browser window toolbar to guide you to the next form.
The Stream Specifications form for Stream 2 appears, as indicated in the Data
Browser window title bar. Stream 2 will be the phenol feed stream.
➤ Enter the following stream specifications for the phenol solvent stream:
Temperature
Pressure
Phenol flow value
220
20
1200
F
PSI
lbmol/hr
The feed stream specifications for the model are now complete.
➤ Click Next on the Data Browser window toolbar.
The RadFrac Setup form for block B1 appears.
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Entering Unit Operation Block Data
On the RadFrac Setup Configuration sheet, you enter the number of theoretical
stages, the valid phases in the column, the distillate vapor fraction, and other
operating specifications for the column.
➤ Use the TAB key to move through the boxes on the form, and read the descriptive
prompts for each box.
The red Incomplete status indicator
next to the Configuration tab tells you
that the sheet is not yet complete and you must enter some additional
specifications.
➤ To learn what specifications this sheet requires, click the Next button on the Data
Browser window title bar.
The Aspen Plus expert system displays a Completion Status window, stating that
you need to enter Number of stages, Condenser type, and two out of a list of
specifications, in order to complete this sheet:
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➤ Close the Completion Status window.
➤ Now enter the operating specifications for the column:
Number of stages 22
Click the Condenser list box and select Total
Distillate Rate 200 lbmol/hr
Reflux ratio 8
The default of Vapor-Liquid for Valid phases is correct for this problem because
we expect only a vapor phase and one liquid phase.
The blue check mark next to the Configuration tab indicates the sheet is
complete.
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➤ Click the Next button on the Data Browser window toolbar.
The RadFrac column model requires more than one sheet to enter the necessary
information. The expert system displays the Streams sheet, on which you specify
feed and product stage locations.
In the RadFrac model, stage 1 is the top stage (condenser) and stage N (where N
is the number of stages) is the bottom stage (reboiler). For the process that you
are simulating (shown in Figure 2.1), the MCH-toluene feed (stream 1) enters
above stage 14, and the phenol solvent stream (stream 2) enters above stage 7.
➤ For stream 1, enter a feed stage location of 14.
➤ For stream 2, enter a feed stage location of 7 and press Enter.
The Streams sheet is now complete:
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➤ Click the Next button to view the next required input sheet.
On the next required sheet, the Pressure sheet, you will enter the column
pressure profile. You may enter a stage-by-stage profile, or specify a top-stage
pressure and a pressure drop for the rest of the column. For the MCH recovery
column in this example, use a condenser pressure of 16 psia, and a reboiler
pressure of 20.2 psia. In the simulation, Aspen Plus will interpolate the pressure
of the intermediate stages.
➤ Click the arrow to the right of the View box to display a list of available views, and
select Pressure profile.
➤ In the Stage box, enter 1 to indicate the top stage (condenser). Enter 16 psi for the
pressure of this stage.
➤ In the next Stage box enter 22 to indicate the bottom stage (reboiler). Enter 20.2 psi
for the pressure and press Enter.
The Pressure sheet is now complete.
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The Input Complete message in the Data Browser status bar in the lower left of
the window, indicates that you have completed the required specifications for the
column model.
All the required forms for the flowsheet are now complete. You can still enter
specifications on optional input forms. You can also go back to any of the required
forms and make changes.
➤ To see what optional input forms are available, use the scroll bar on the left side of the
Data Browser window to view all the folders.
The blue check marks on the Setup, Components, Properties, Streams, and
Blocks folders indicate that these required forms are complete.
The remaining input folders Reactions, Convergence, Flowsheeting Options, and
Model Analysis Tools are optional
For this example, there is no additional input.
➤ Click the Next button on the Data Browser window toolbar.
The Required Input Complete dialog box confirms that all required specifications
are complete, and prompts you to run the simulation:
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Running the Simulation
To run the simulation:
➤ Click OK on the Required Input Complete dialog box.
Aspen Plus displays the Control Panel.
The Control Panel allows you to monitor and interact with the Aspen Plus
simulation calculations. For more information on how to control the simulation
through the Control Panel, you can either see the Aspen Plus User Guide,
Volume 1, Chapter 11, or see the topic Control Panel:about in the on-line Help.
The simulation calculations occur in three sequential steps:
•
•
•
Processing input specifications
Calculations begin
Generating results
As Aspen Plus executes the simulation, status messages appear in the Control
Panel. When the simulation has completed, the message Results Available
appears in the status bar at the bottom of the main window.
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Examining Simulation Results
When the Results Available message appears in the status area, you can examine
the results of your flowsheet simulation run.
➤ If the Control Panel window obscures your view of the graphical simulation flowsheet,
close the window by clicking
.
Examining Block Results
To display the results for block B1:
➤ Click Block B1 in the simulation flowsheet.
The Block icon is surrounded by square bullets, indicating it is selected.
➤ Continue to point to the column and click (or press and hold) the right mouse button.
The Block menu appears, showing all the commands that apply to a block.
➤ Select Results from the menu.
The RadFrac ResultsSummary form appears in a Data Browser window.
For this run, results are reported on several forms, as indicated by the check
next to the form names in the menu tree. The Summary sheet reports a
mark
summary of column results, such as condenser and reboiler duties:
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➤ To examine the RadFrac profile results, click the Next Form button
Browser window toolbar.
on the Data
-or-
➤ Click the Profiles form in the menu tree on the left side of the Data Browser window.
The displayed Profiles TPFQ sheet reports temperature, pressure, enthalpies,
and flow profiles for the RadFrac column:
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➤ Use the scroll bars at the bottom of the window and to the right to view up and down,
and left and right, through the displayed profiles. You can also resize the window to
expand the view.
By default, the Summary view of the TPFQ profile results is shown. You can use the
View box to select a different view of the TPFQ profile results.
➤ Click the arrow on the right of the View box to display a list of available views, and
select Stage Flows.
You can use the Basis box to specify the flow basis for the displayed results.
➤ Click the arrow on the right of the Basis box to display a list of available flow bases.
➤ To display the RadFrac Composition results, click the RadFrac Profiles Compositions
tab.
On the Composition sheet, when the Liquid View is selected, liquid composition
(as mole fraction) profiles are shown for the RadFrac column:
➤ Check the purity of the methylcyclohexane overhead product (about 97%) by
examining the composition at the top of the column (stage 1).
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Examining Stream Results
You can display calculated stream results by selecting a stream directly from the
graphical simulation flowsheet.
To display the graphical flowsheet, first close the Data Browser window:
➤ Click the command icon
display the command menu.
in the upper left corner of the Data Browser window to
➤ Select Close to close the Data Browser window.
To display the results for Stream 3:
➤ On the flowsheet, click in the rectangle that displays the stream ID 3 to select it.
➤ Display the Stream shortcut menu by right-clicking Stream 3 while it is selected.
➤ Select Results from the menu.
The Material sheet is displayed, showing the results for Stream 3. In addition to
the thermodynamic state and flow results for the stream, the properties you
requested on the Setup Report Options sheet are also displayed.
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To display the results for Streams 1 and 4 on the same form as the results for
Stream 3:
➤ Move to the blank box next to 3 (in the next column).
➤ Click the list box and select 4 from the dropdown list to display results for stream 4.
➤ To display results for stream 1, repeat the preceding step and select 1 in the next
column of the table.
The Material sheet displays results for Streams 3, 4, and 1:
From the component flow rates reported in the stream results, you can determine
that the methylcyclohexane recovery overhead is 97%.
Changing Input Specifications
In this section, you want to see the effect of increasing the solvent flow rate on the
purity and recovery of methylcyclohexane. To increase the phenol solvent stream
flow rate from 1200 lbmol/hr to 1800 lbmol/hr:
➤ Close the Stream Results form by clicking the
Browser window.
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➤ Select Stream 2 on the graphical simulation flowsheet.
➤ From the Stream shortcut menu, select Input to display the Stream Input
Specifications sheet.
➤ Use the Tab key to move to the PHENOL flow value box, or click in the box.
➤ Change the PHENOL flow rate from 1200 to 1800 lbmol/hr by entering 1800.
Rerunning the Simulation
To rerun the model with the changed input:
➤ Click the Next button on the main window toolbar.
The Required Input Complete dialog box appears telling you that you input is
complete and asking if you want to run the simulation with the new
specifications.
➤ Select OK to run the simulation.
The Control Panel appears again, and the column calculations are completed
using the new phenol flow rate.
Display the block and stream results for the new conditions, as previously
described. You will observe that increasing the solvent flow rate from 1200 to
1800 lbmol/hr increases the MCH purity in the overhead product to 98.4% and
the MCH recovery to 98.4%.
To choose the optimal conditions, it would be helpful to generate a sensitivity
table of MCH recovery and purity versus phenol flow rate. This example is in
Chapter 3.
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Creating Reports
To generate a report of the simulation specifications, calculations, and results:
➤ From the File menu in the main window, select Export.
➤ On the Export dialog box, select Report File (*.rep) in the Save As Type box.
➤ Type the filename mch in the File name box.
➤ Click Save to generate the report file, mch.rep.
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You can open this file with a text editor or you can print the file. By default, the
report file mch.rep is saved in your working directory (displayed in the Save In
box). You can select another directory by navigating to it using the Save In box.
Tip
You can also examine the report by selecting Report from the
View menu on the main window. The Report dialog box allows
you to select which section of the report you want displayed in a
text editor (selecting the simulation will display the entire
report).
Exiting Aspen Plus
When you are finished working with this model, you can exit Aspen Plus as follows:
➤ From the File menu, select Exit.
➤ When the dialog box appears, select YES to save the simulation.
➤ In the Save As dialog box, enter the Run ID mch in the File name box.
Aspen Plus saves the simulation as the Aspen Plus Document file, mch.apw, in your
default working directory (displayed in the Save In box). This saved simulation will be
used as the starting point for the exercises in Chapters 3 and 4.
Congratulations! You have just built and run a complete simulation model using
Aspen Plus.
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3
Performing a Sensitivity
Analysis
One of the benefits of using a process simulation model is that you can quickly
study the sensitivity of process performance to changes in process operating
variables. With Aspen Plus, you can allow simulation inputs to vary, and can
tabulate the effect on a set of results of your choice.
In this session, you will learn how to perform sensitivity analysis with
Aspen Plus.
Allow about 20 minutes for this session.
This session assumes that you have successfully completed the
methylcyclohexane (MCH) recovery column simulation in Chapter 2, and that
you have saved the simulation as the Aspen Plus document file, mch.apw. If you
have not created the Chapter 2 example, you can open a backup file from the
Aspen Plus Examples folder as described in Opening an Existing Simulation, this
chapter.
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Starting Aspen Plus
To start Aspen Plus:
➤ Start Aspen Plus from the Windows Start menu or by double-clicking the Aspen Plus
icon on your desktop.
For more details, see Starting Aspen Plus in Chapter 1.
The Aspen Plus Startup dialog box appears.
Opening an Existing Simulation
If you saved the methylcyclohexane (MCH) recovery column simulation created in
Chapter 2:
➤ Select the option Open an Existing Simulation on the Aspen Plus Startup dialog box.
If your saved file mch.apw is displayed in the list box:
➤ Select mch.apw in the list and click OK.
If your saved file mch.apw is not displayed in the list box:
➤ Double-click on More Files… in the list box.
➤ In the Open dialog box that appears, use the Look In box to navigate to the directory
that contains your saved file mch.apw.
➤ Select mch.apw in the list of files and click Open.
Note
If the Connect to Engine dialog box appears, see Appendix A.
Aspen Plus displays the graphical flowsheet for the MCH column simulation.
If you did not create the MCH simulation in Chapter 2, you can open the backup
file mch.bkp in the Examples folder.
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➤ From the Aspen Plus Startup dialog box, select the option Open an Existing Simulation
and then click OK.
The Open dialog box appears.
➤ Using the Look In box and the list of files and folders displayed, navigate to the
Examples folders in the Aspen Plus user interface installation directory (e:\Program
Files\AspenTech\Aspen Plus 10.1-0\Favorites\Examples by default).
➤ Double-click the Examples folder.
➤ Select mch.bkp and click OK.
Note
If the Connect to Engine dialog box appears, see Appendix A.
Aspen Plus displays the graphical flowsheet for the MCH column simulation.
Saving a Simulation under a New Name
Before you create a sensitivity simulation starting from the MCH column
simulation, create and save a copy of the MCH simulation file with a new file
name, MCHSENS. Then you can modify this new file.
➤ From the File menu, click Save As.
➤ In the Save As dialog box, choose the directory where you want to save the simulation.
➤ In the Filename box, enter the new filename mchsens.
➤ From the Save as Type list, select Aspen Plus Documents (*.apw).
➤ Click Save to save the simulation and continue.
Aspen Plus creates a new simulation model, MCHSENS, which is a copy of the
base case simulation, MCH.
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Defining the Sensitivity Analysis
In the base case MCH simulation in Chapter 2, you simulated the MCH recovery
column performance at two values for the phenol solvent flow rate (1200 and 1800
lbmol/hr). In the sensitivity analysis, you will want to tabulate methylcyclohexane
(MCH) distillate product purity (mole fraction), as well as condenser duty and
reboiler duty, for several different flow rates of phenol.
Entering Sensitivity Specifications
To enter sensitivity specifications, use Sensitivity forms, which you access from the
Data menu:
➤ To display the Data menu, click Data on the main window menu bar.
➤ Drag the mouse through the Data menu and read the prompts at the bottom of the
window for each type of form.
➤ Select Model Analysis Tools and then select Sensitivity from the submenu.
Aspen Plus displays the Sensitivity Object Manager from which you can create new
Sensitivity blocks, as well as edit input, display results, or perform other operations on
existing Sensitivity blocks.
➤ On the Sensitivity Object Manager, click New.
The Create New ID dialog box appears, displaying an automatically generated
Sensitivity ID, S-1. You can accept the default ID or replace it with an ID of your
choice.
➤ In the Create New ID dialog box, click OK to accept the default ID and continue.
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The Sensitivity Input Define sheet for S-1 appears:
Each sensitivity analysis generates a table. You will define the results you want
to look at, the inputs you want to vary, and how Aspen Plus tabulates the results.
Defining Sampled Variables
On the Input Define sheet, you select the simulation variables you want to
sample for the sensitivity analysis and give each variable a unique name. In this
example you will define the MCH distillate product purity, the condenser duty,
and the reboiler duty as sampled variables.
To select the MCH distillate product purity as a sampled variable:
➤ Click the New button.
The Create New Variable dialog box appears.
➤ Type XMCH in the Variable Name field and click OK to continue.
The Variable Definition dialog box appears. MCH distillate product purity is the mole
fraction of component MCH in the distillate product, stream 3. This sampled variable
belongs to the Streams category and is of type Mole fraction.
➤ Under Category, click the Streams button to select the variable category.
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➤ In the Reference frame, click the arrow to the right of the Type box to display a list of
flowsheet variable types that can be accessed for streams.
➤ Move through the list using the arrow keys, and look at the descriptive prompts.
➤ Select the Type Mole-Frac, since the variable is a component mole fraction.
Aspen Plus displays the other fields necessary to complete the variable definition. In
this case, the Stream list box appears.
➤ Select stream 3, the liquid distillate stream from the dropdown list in the Stream list
box.
The Substream and Component list boxes appear. In this example, you do not need to
modify the default choice of MIXED in the Substream list box.
➤ Click the Component list box to display a list of valid components. Select MCH.
The blue check mark next to XMCH in the Variable Name list box indicates that the
definition of variable XMCH is complete.
➤ Click the Close button to close the Variable Definition dialog box and return to the
Define sheet.
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You have specified the first sampled variable, XMCH:
To select the condenser duty as a sampled variable:
➤ Click the New button.
➤ In the Create New Variable dialog box, enter QCOND in the Variable Name box. Click
OK to continue.
Since condenser duty is a scalar result for the RadFrac block B1, this sampled
variable belongs to the Blocks category and is of type Block-Var.
➤ Click the Blocks option under Category.
➤ Click the Type list box to display the flowsheet variable types that can be accessed for
blocks.
➤ Select Block-Var for Type.
➤ In the Blocks list box that appears, select block B1.
➤ Click the Variable list box to display the list of variables. Move through the list and look
at the descriptive prompts.
➤ Select COND-DUTY for Variable since it represents the result of interest.
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Aspen Plus automatically fills the Sentence box based on your choice of variable.
The definition of the variable QCOND is now complete.
You have created two new sampled variables (XMCH and QCOND) using the
New button on the Define sheet. To illustrate another way to create sampled
variables, you will now use the Variable Name list box in the Variable Definition
dialog box to define the column reboiler duty as a sampled variable.
➤ Click the Variable Name box and select New.
Tip
You can also right-click on the Variable Name box and select
Create from the popup menu.
The New item dialog box appears.
➤ In the Create a New Item box enter QREB, the name of the new variable that you want
to define. Click OK to continue.
You are returned to the Variable Definition dialog box with QREB displayed in the
Variable Name box.
Reboiler duty is also a Block variable of type Block-Var.
➤ Click the Blocks option button under Category.
➤ Select Block-Var in the Type list box.
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➤ Select B1 for Block and REB-DUTY for Variable.
The definition of variable QREB is now complete.
➤ Click Close to close the Variable Definition dialog box and to return to the Define
sheet.
You have identified the three process variables to sample for the sensitivity
analysis and given each a unique name.
➤ Click the Next button.
The expert system displays the next required sheet, the Vary sheet.
Defining Manipulated Variables
On the Input Vary sheet, you define the simulation variable to be manipulated
for the sensitivity analysis, identify the variable values to be used, and specify
the labels for the variable to be used in the tabulated results. In this example,
you will manipulate the molar flow rate of the phenol feed stream (stream 2).
➤ Click the Variable Number list box, select <New> to create a new manipulated
variable.
Aspen Plus creates the manipulated variable and displays the ID 1 in the Variable
Number list box.
➤ Click the Type box to display a list of valid variable types.
➤ Select Stream-Var for the Type.
Aspen Plus displays the remaining fields necessary to uniquely identify the flowsheet
variable.
➤ Select 2 for the Stream.
➤ Select MOLE-FLOW for the Variable.
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For this session, you will vary the flow rate between 1200 and 2000 lbmol/hr at
increments of 100 lbmol/hr:
➤ Click the Overall Range option button.
➤ Move to the Lower box and enter 1200 for the bottom of the range.
➤ On the Upper box, enter 2000 for the top of the range.
➤ On the Incr field, enter 100 for the increment size.
For this session, you will specify PHENOL FLOWRATE as the label for the
manipulated variable.
➤ Enter the label PHENOL for Line1 and FLOWRATE for Line2 of the Report labels.
You have specified the information for the manipulated process variable:
➤ Click the Next button.
The Tabulate sheet appears.
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Defining Tabulated Variables
On the Tabulate sheet, you specify the variables to be tabulated by the sensitivity
analysis, and supply optional headings for the table columns. You can choose
from among the variables that you defined on the Sensitivity Input Define sheet.
You can also tabulate any algebraic combinations of those variables.
To tabulate MCH distillate composition:
➤ In the Column Number box, enter 1, indicating that this is the first tabulated variable.
A second row opens up in the table to define a second tabulated variable.
➤ On the Tabulate variable or expression box, in the first row enter XMCH.
To specify column labels for the tabulated MCH distillate composition:
➤ Click the Table Format button, the Table Format dialog box appears.
➤ Enter the label MCH PURITY IN DIST on the column label field in the first column, as
shown:
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➤ Click Close to close the Table Format dialog box.
To tabulate the column condenser duty and reboiler duty:
➤ On the Column Number box in the second row, enter 2.
➤ Enter QCOND for the Tabulate variable or expression field.
➤ On the next Column Number field, enter 3.
➤ Enter QREB for the Tabulate variable or expression field.
You have now defined the three variables to be tabulated in your Sensitivity
analysis.
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To specify the column labels for condenser duty and reboiler duty:
➤ Click the Table Format button.
➤ Enter the label CONDENS DUTY in the column label boxes under Column Number 2.
➤ Enter the label REBOILER DUTY in the Column label boxes under Column Number 3.
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➤ Close the Table Format dialog box.
The Input Status for Sensitivity block S-1 (the blue check mark on folder S-1 in
the left pane of Data Browser window) shows that all required input is complete.
Running the Simulation
➤ Click the Next button.
The Required Input Complete dialog box appears.
➤ Click OK to run the simulation.
Aspen Plus displays the Control Panel. As the simulation executes, status messages
appear in the Control Panel.
➤ When the Simulation Run Completed and Results Available messages appear in the
status bar at the bottom of the main window, close the Control Panel window.
You can now examine the results of your simulation.
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Displaying Sensitivity Analysis Results
The Sensitivity Analysis Results consist of a table of the values you requested on
the Input Tabulate sheet, shown as a function of the manipulated variable defined
on the Input Vary sheet.
To view the Sensitivity results:
➤ On the menu tree of the Data Browser window, click Results under Sensitivity block,
S-1.
The Summary sheet appears.
Note
The above results were obtained by using the Aspen Plus
document file, mch.apw, as described in Opening an Existing
Run, this chapter. If you used the Aspen Plus backup file,
mch.bkp, from the Examples folder, your results may be slightly
rd
different (the 3 significant digit). These differences occur because
the starting point for the calculations are different. When you use
an .apw file, Aspen Plus starts calculating from the previous
results. When you use a .bkp file, Aspen Plus reinitializes before
starting calculations.
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Plotting Sensitivity Results
In addition to displaying the sensitivity results in tabular form, you can plot the
results.
To generate a plot of MCH distillate purity versus phenol flow rate:
➤ Click the column label you want to plot on the X-Axis. In this case, click the VARY 1
column label.
➤ From the Plot menu, select X-Axis Variable.
➤ Click the column label on the MCH PURITY IN DIST column.
➤ From the Plot menu, select Y-Axis Variable.
To create the plot:
➤ Select Display Plot from the Plot menu.
The plot of MCH distillate purity versus phenol flow rate appears in a Plot window:
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You can use the Maximize button in the Plot window title bar to obtain a
maximized full-screen plot. You can also customize the plot by using the Plot
popup menu (displayed by right-clicking in the plot window).
Exiting Aspen Plus
When you finish examining the plot, exit Aspen Plus:
➤ From the File menu, select Exit.
➤ In the dialog box that appears select Yes to save the simulation.
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4
Meeting Process Design
Specifications
In Chapter 3, you used Aspen Plus to tabulate the sensitivity of MCH distillate
purity and column duties to changes in phenol solvent flow rate. You can also use
Aspen Plus to meet a specific process design target (or design specification) by
manipulating any simulation input variable.
In this session, you will learn how to use Aspen Plus to make your process model
meet a process design specification.
Allow about 20 minutes for this session.
This session assumes that you have successfully completed the
methylcyclohexane (MCH) recovery column simulation in Chapter 2, and that
you have saved the simulation as the Aspen Plus document file, mch.apw. If you
have not created the Chapter 2 example, you can open a backup file from the
Aspen Plus Examples folder as described in Opening an Existing Simulation, this
chapter.
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Starting Aspen Plus
To start Aspen Plus:
➤ Start Aspen Plus from the Start menu or by double-clicking the Aspen Plus icon on
your desktop.
For more details, see Starting Aspen Plus in Chapter 1.
The Aspen Plus Startup dialog box appears.
Opening an Existing Simulation
If you saved the methylcyclohexane (MCH) recovery column simulation created in
Chapter 2:
➤ Select the option Open an Existing Simulation on the Aspen Plus Startup dialog box.
If your saved file mch.apw is displayed in the list box:
➤ Select mch.apw in the list and click OK.
If your saved file mch.apw is not displayed in the list box:
➤ Double-click on More Files… in the list box.
➤ In the Open dialog box that appears, navigate to the directory that contains your saved
file mch.apw.
➤ Select mch.apw in the list of files and click Open.
Note
If the Connect to Engine dialog box appears, see Appendix A.
Aspen Plus displays the graphical flowsheet for the MCH column simulation.
If you did not create the MCH simulation in Chapter 2, you can open the backup
file mch.bkp in the Examples folder.
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➤ From the Aspen Plus Startup dialog box, select the option Open an Existing Simulation
and then click OK.
The Open dialog box appears.
➤ Click the Look in Favorites button
.
By default, the Favorites list contains five folders that are provided with Aspen Plus.
➤ Double-click the Examples folder.
➤ Select mch.bkp and click OK.
Note
If the Connect to Engine dialog box appears, see Appendix A.
Aspen Plus displays the graphical flowsheet for the MCH column simulation.
Saving a Simulation Under a New Name
Before you create a new simulation starting from the MCH base case simulation,
create and save a copy of the MCH simulation file with a new filename,
MCHSPEC. Then you can modify this new file.
➤ From the File menu, click Save As.
➤ In the Save As dialog box, choose the directory where you want to save the simulation.
➤ In the Filename box, enter the new filename mchspec.
➤ From the Save as Type list, select Aspen Plus Documents (*.apw).
➤ Click Save to save the simulation and continue.
Aspen Plus creates a new simulation model, MCHSPEC, which is a copy of the
base case simulation, MCH.
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Defining the Design Specification
In the base case MCH simulation in Chapter 2, you simulated the MCH recovery
column performance at two values for the phenol solvent flow rate (1200 and 1800
lbmol/hr). In the sensitivity analysis in Chapter 3, you tabulated MCH distillate
product purity, and condenser and reboiler duties, as a function of phenol solvent
flow rate.
In this session you will run a simulation to determine the exact phenol solvent
feed rate required to maintain a MCH distillate purity of 98.0%.
Entering Design Specifications
To enter design specifications, use the Design Specs forms.
➤ From the Data menu select Flowsheeting Options and then select Design Specs.
The Design Specs Object Manager appears.
➤ In the Design Specs Object Manager, click New.
A Create New ID dialog box appears, displaying an automatically generated
Design Specs ID, DS-1. You can accept the default ID or replace it with an ID of
your choice.
➤ In the Create New ID dialog box, click OK to accept the default ID and continue.
The Design Specs Input Define sheet for DS-1 appears:
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On this Define sheet, you select the simulation variables that you want to sample
to calculate the process design specification target. You will identify each
sampled variable and give it a unique variable name.
To select the MCH distillate product purity as a sampled variable:
➤ Click the New button.
The Create New Variable dialog box appears.
➤ Type XMCH in the Variable Name field and click OK to continue.
The Variable Definition dialog box appears.
➤ Since MCH purity in the distillate product stream is a stream variable, click the
Streams option under Category.
Tip
If you are not sure of the appropriate category for the sampled
variable, use the default ALL option. This option will list all
accessible flowsheet variables in the Type list box.
➤ In the Reference frame, click the Type list box to display a list of flowsheet variable
types.
➤ Move through the list using the arrow keys, and look at the descriptive prompts.
➤ Because MCH distillate product purity is a component mole fraction, select the Type
MOLE-FRAC.
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Aspen Plus displays the other fields necessary to complete the variable definition. In
this case, the Stream list box appears.
➤ Select stream 3, the liquid distillate stream, in the Stream list box.
➤ Click the Component list box to display a list of valid components. Select MCH.
The blue check mark next to XMCH in the Variable Name list box indicates that the
definition of variable XMCH is complete.
➤ Click the Close button to close the Variable Definition dialog box and return to the
Define sheet.
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You have specified the sampled variable XMCH:
➤ Click the Next button.
The Spec sheet appears.
On the Spec sheet you define the process design specification target. For this
example, you want to meet a target MCH distillate purity of 98.0% by
manipulating the total mole flow for the phenol feed stream.
➤ On the Spec box, enter XMCH*100.
The multiplicative factor of 100 converts the sampled mole fraction to a mole
percentage.
➤ Enter 98.0 in the Target box to assign a target value of 98.0%.
➤ Enter 0.01 in the Tolerance box to signify that you want the specification satisfied to
within 98.0% +/- .01%.
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➤ Click the Next button.
The Design Specs Vary sheet appears. On this sheet, you identify the input
variable to be manipulated (varied) to meet the target. For the MCH column
specification, you want to vary the total mole flow for the phenol feed stream
(stream 2).
➤ Click the Type list box to display a list of valid variable types.
➤ Select STREAM-VAR for the Type.
➤ Select 2 for the stream name.
➤ Select MOLE-FLOW for the Variable.
Next you specify the upper and lower limits for your manipulated variable. From
the sensitivity analysis in Chapter 3, you saw that the appropriate phenol flow
rate is somewhere between 1200 and 2000 lbmol/hr.
➤ Move to the Lower field and enter 1200.
➤ On the Upper field, enter 2000.
Aspen Plus will search for a value of the phenol feed rate within this range that
results in a 98.0% MCH distillate purity.
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You can also supply optional labels for the manipulated variable to be used in
reporting results.
➤ Enter the label PHENOL for Line1 and FLOWRATE for Line 2 of the Report labels
area.
You have specified the information for the manipulated process variable:
The input for this Design Specification is complete.
➤ Click the Next button.
The Required Input Complete dialog box appears.
Running the Simulation
From the Required Input Complete dialog box:
➤ Click OK to run the simulation.
Aspen Plus displays the Control Panel. As the simulation executes, you will see
status messages displayed in the Control Panel.
Soon the messages Simulation Run Completed and Results Available appear in
the status bar at the bottom of the main window. In the Control Panel, you can
see a message that the design specification has converged.
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➤ When the Simulation Run Completed message appears in the status bar, close the
Control Panel window.
You can now examine the results of your simulation.
Examining Design Specification Results
You can determine how well your design specification has been satisfied by
examining the Results Summary Convergence DesignSpec Summary form.
➤ From the Data menu, select Results Summary, then Convergence.
The results on the DesignSpec Summary sheet show that the error is less than
the specified tolerance and that the target specification was converged to
successfully. The required phenol flow is 1519.2 lbmol/hr.
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Note
The above results were obtained by using the Aspen Plus
document file, mch.apw, as described in Opening an Existing
Run, this chapter. If you used the Aspen Plus backup file,
mch.bkp, from the Examples folder, your results may be slightly
rd
different (the 3 significant digit). These differences occur because
the starting point for the calculations are different. When you use
an .apw file, Aspen Plus starts calculating from the previous
results. When you use a .bkp file, Aspen Plus reinitializes before
starting calculations.
Exiting Aspen Plus
When you are finished examining the results, exit Aspen Plus:
➤ From the File menu, select Exit.
➤ When the dialog box appears select Yes to save the simulation.
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5
Creating a Process Flow
Diagram
In this example, you will learn how to generate a customized Process Flow
Diagram (PFD) from your Aspen Plus simulation.
Allow about 20 minutes for this session.
Aspen Plus has two modes for displaying graphics:
• Simulation
• PFD
In both modes, you can modify your graphical flowsheet to prepare customized
drawings for reports by:
• Adding text and graphics
• Displaying global data for streams and blocks
• Displaying stream results tables
• Adding OLE objects
Also, in PFD mode, you can add or delete blocks and streams to or from the
flowsheet, and you can modify the flowsheet connectivity to match your plant.
These changes are graphical only and do not affect the simulation flowsheet you
developed to model your process,
This session assumes that you have successfully completed the
methylcyclohexane (MCH) recovery column simulation in Chapter 2, and that
you have saved the simulation as the Aspen Plus document file, mch.apw. If you
have not created the Chapter 2 example, you can open a backup file from the
Aspen Plus Examples folder as described in Opening an Existing Simulation, this
chapter.
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Creating a
PFD-Style
Simulation
Drawing
Starting Aspen Plus
To start Aspen Plus:
➤ Start Aspen Plus from the Windows Start menu or double-click the Aspen Plus icon on
your desktop.
For more details, see Starting Aspen Plus in Chapter 1.
The Aspen Plus Startup dialog box appears.
Opening an Existing Simulation
If you saved the methylcyclohexane (MCH) recovery column simulation created in
Chapter 2:
➤ Select the option Open an Existing Simulation on the Aspen Plus Startup dialog box.
If your saved file mch.apw is displayed in the list box:
➤ Select mch.apw in the list and click OK.
If your saved file mch.apw is not displayed in the list box:
➤ Double-click on More Files… in the list box.
➤ In the Open dialog box that appears, navigate to the directory that contains your saved
file mch.apw.
➤ Select mch.apw in the list of files and click Open.
Note
If the Connect to Engine dialog box appears, see Appendix A.
Aspen Plus displays the graphical flowsheet for the MCH column simulation.
If you did not create the MCH simulation in Chapter 2, you can open the backup
file mch.bkp in the Examples folder.
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➤ From the Aspen Plus Startup dialog box, select the option Open an Existing Simulation
and then click OK.
The Open dialog box appears.
➤ Click the Look in Favorites button
.
By default, the Favorites list contains five folders that are provided with Aspen Plus.
➤ Double-click the Examples folder.
➤ Select mch.bkp and click Open.
Note
If the Connect to Engine dialog box appears, see Appendix A.
Aspen Plus displays the graphical flowsheet for the MCH column simulation.
Switching to PFD Mode
Simulation mode is the Aspen Plus default mode that you use to create a
simulation flowsheet model and run a simulation. In this example, you will use
PFD mode to create a customized drawing of the MCH column simulation by:
• Adding equipment icons and streams
• Displaying global stream data
• Displaying a stream results table
• Adding a title
To switch from Simulation mode to PFD mode:
➤ From the View menu select PFD Mode.
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Creating a
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Drawing
The check mark next to PFD Mode in the View menu and the status bar at the
bottom of the main window indicate that PFD mode is on. Also, the graphical
flowsheet workspace displays a thick blue border when you are using PFD mode.
To switch back to Simulation mode, from the View menu, select PFD mode again
to clear the check mark. For this example, keep PFD mode on.
Tip
The PFD-style drawing is separate from the graphical simulation
flowsheet. You must return to simulation mode if you want to
make changes to the simulation flowsheet.
Adding Equipment Icons and Streams
In a PFD-style drawing, you may want to add pieces of equipment that you did not
include in the simulation. For example, in the MCH simulation, you did not model
the feed pump to the column, because the pressure is set in the feed stream to the
column. However, you may want to include a feed pump in the PFD-style drawing.
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To add the feed pump to the PFD diagram, choose and place the pump icon by
doing the following:
➤ Click the Pressure Changers tab in the Model Library.
➤ In the Model Library, select the unit operation model, Pump, that you want to place in
your process flowsheet.
You can choose a different icon for the model:
➤ Click the down arrow next to the Pump block icon to display all the icons available for
the Pump model.
➤ Move the mouse over the icons to see a name (or label) for each.
In this exercise, you will select the pump icon named ICON1.
➤ Click and hold down the mouse button on the Pump Icon1, and drag it to the Process
Flowsheet window. Release the mouse button when it is on top of Stream 1.
Note
The pump icon you select remains the default icon for that model,
until you change the icon.
➤ Use the + and - keys to adjust the size of the pump icon.
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Your drawing should look approximately like this:
Next, disconnect stream 1 from block B1:
➤ Select stream 1 and then click with the right mouse button on the stream.
➤ From the menu that appears, select Reconnect Destination.
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Stream 1 is now disconnected from block B1. Your drawing should look
approximately like this:
➤ To reconnect stream 1 to the inlet of the pump block, point to an inlet feed port of the
pump. Click the left mouse button to connect stream 1.
Finally, connect the pump to the column:
➤ Click the Material Stream icon on the left side of the Model Library.
➤ Move the cursor to the Process Flowsheet window. Point to a Product port of the pump
and click to create a new stream.
➤ Point to the middle Feed port of block B1 and click to connect the stream.
➤ To stop placing streams, click the Select Mode button
the Model Library, or click the right mouse button.
Tip
in the upper left corner of
To cancel connecting the stream at any time, press ESC.
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Creating a
PFD-Style
Simulation
Drawing
Displaying Stream Data
To display stream temperature and pressure in the PFD-style drawing:
➤ From the View menu, ensure Global data is selected.
➤ From the Tools menu, click Options.
➤ Click the Results View tab.
➤ In the Stream results frame, select Temperature and Pressure.
A check mark appears next to each one.
➤ Click OK to close the dialog box and display the data.
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The temperature and pressure calculated by Aspen Plus during the MCH
simulation run are shown on each stream. Aspen Plus also displays a legend box
in the lower left corner of the screen. The legend box shows the symbols and
units for the global data. You can move and resize the legend in the same way
that you move and resize blocks.
Tip
If you do not see the legend box, from the View menu, select Zoom
and then select Zoom Full.
Your drawing should look approximately like this:
The stream data may be in a very small font on your screen display. However,
you can zoom in on any section of the PFD-style drawing to read the values. To
zoom in on the legend:
➤ With the mouse pointer above and to the left of the legend box, press and hold the left
mouse button until the mouse pointer changes to the drag select shape
.
➤ Drag down and to the right, until you have enclosed the legend box, and then release
the mouse button.
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➤ With the mouse pointer inside the selected region, right-click to display the menu.
➤ From the menu, select Zoom In.
Aspen Plus displays an enlarged view of the legend box:
➤ To display the full drawing again, select Zoom and then Zoom Full from the View
menu.
You can use the Zoom In function on any portion of a PFD-style drawing.
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Adding a Stream Table
PFD-style drawings frequently include a table of stream results (the heat and
material balance table, or birdcage). In Aspen Plus, you can generate such a table
by doing the following.
➤ From the View menu, ensure Annotation is selected.
➤ From the Data menu, select Results Summary, then select Streams.
Aspen Plus displays the Results Summary Streams Material sheet. You generate
your stream table from this sheet. By default Aspen Plus displays all streams on
the Stream Summary sheet.
➤ Click the Stream Table button.
Aspen Plus displays a birdcage-style stream table in the Process Flowsheet window
showing the stream results from the simulation.
➤ Close the Data Browser window.
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The table is scaled for printing. If you cannot read its contents on the screen, you
can zoom in on it, or resize it.
➤ Drag a region around the upper left quarter of the table.
➤ Right-click inside the selected region to display the popup menu.
➤ From the menu, select Zoom In to display an enlarged view.
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➤ From the View menu, select Zoom Full to restore your PFD-style drawing.
Adding Text
To add the finishing touches to the PFD-style drawing, you can add text and other
graphics objects. In this session you will complete the drawing by adding a title.
The Draw toolbar provides some simple Aspen Plus drawing tools for adding text
and graphics to the drawing. To display the Draw toolbar:
➤ From the View menu, select Toolbar.
➤ In the Toolbars dialog box, click the Draw checkbox to select it.
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Creating a
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Drawing
➤ Click OK to close the Toolbars dialog box.
The Draw toolbar is displayed on the main window toolbar.
➤ From the Draw toolbar, click the text button
.
➤ Move the cursor to where you want to place the text and click the mouse button.
A rectangular box with a blinking cursor appears.
➤ Type Methylcyclohexane Recovery Column, then click outside the rectangular box.
If you want to reformat the text, you can do the following:
➤ To resize the title, select the text and format it by using the options in the Draw toolbar,
for example Font and Font Size.
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➤ To move the title, hold the left mouse button down anywhere on the title, until the
pointer changes to the move shape, then drag the title to the new position, and release
the mouse button.
➤ From the View menu, select Zoom Full to view the entire drawing.
Your completed PFD-style drawing should look like this:
Printing a Process Flow Diagram
Before you print, make sure that your printer is set up correctly. Refer to the online
help topic, Using Aspen Plus, Annotating Process Flowsheets, or to the Aspen Plus
User Guide, Chapter 14, for more information on printing options.
You can preview your drawing before you print it.
➤ From the File menu, select Print Preview.
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Creating a
PFD-Style
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Drawing
The block and stream IDs and the global data in your drawing are now scaled
approximately as they will appear in print.
➤ In the Preview window, click Zoom In or Zoom out to see how your printout will look.
A gray margin appears around the drawing workspace. The drawing workspace
is now the shape and orientation of the paper size and page orientation currently
selected, so you can see how the drawing will be positioned on the page. You
could also lay out and print your drawing on multiple pages, but will not do so in
this session.
To print the PFD-style drawing:
➤ In the Preview window, select Print.
A dialog box appears asking you where you want the output directed.
➤ Select the appropriate printer and click OK.
Leaving PFD Mode
You have seen how straightforward it is to create a PFD-style drawing from a
simulation flowsheet. Remember that the flowsheet modifications you have made
for the PFD-style drawing have no effect on the simulation flowsheet and will not
be included in it. You can go back to Simulation mode at any time by turning off
PFD mode:
➤ From the View menu, select PFD mode to turn PFD Mode off.
The original graphical simulation flowsheet is displayed. The stream data, the stream
table, and the title that you added in PFD mode are also displayed in Simulation mode.
Note
If you make changes to the flowsheet in Simulation mode, these
changes will not be automatically included in the PFD-style
drawing.
Exiting Aspen Plus
When you are finished working with this run, exit Aspen Plus:
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➤ From the File menu, select Exit
➤ When the dialog box appears, select YES to save the simulation.
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Chapter 6
6
Estimating Physical
Properties for a
Non-Databank Component
This session guides you through the procedure for estimating physical properties
for a component that is not present in the Aspen Plus databank.
Allow about 30 minutes for this session.
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Estimating
Physical
Properties
for a NonDatabank
Component
Thiazole Physical Property Data
In this session, you are dealing with a process involving thiazole and water, among
other components.
Thiazole (C3H3NS) is not in the Aspen Plus databank. The following information
is available in various sources:
Molecular structure for thiazole:
HC=CH
S
N=CH
Molecular weight: 85
Normal boiling point: 116.8 °C
Vapor pressure correlation:
oL
ln p i
=
16.445 - 3281.0/(T+216.255)
oL
p i in mmHg, T in °C for 69 °C < T < 118°C
By checking the manual Aspen Plus Physical Property Methods and Models,
Chapter 2, you see that you do not have data for all the required pure component
property parameters for thiazole. You are missing data for the following property
parameters (required for calculating enthalpies and densities):
Parameter
Description
TC
Critical temperature
PC
Critical pressure
CPIG
Ideal gas heat capacity coefficients
DHFORM
Heat of formation
DGFORM
Gibbs free energy formation
DHVLWT
Watson heat-of-vaporization coefficients
VC
Critical volume
ZC
Critical compressibility factor
You will run a Property Estimation simulation in Aspen Plus to estimate the
missing property parameters for thiazole required to run your simulation.
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Starting Aspen Plus
To start Aspen Plus:
➤ Start Aspen Plus from the Windows Start menu or double-click the Aspen Plus icon on
your desktop.
For more details, see Starting Aspen Plus in Chapter 1.
The Aspen Plus Startup dialog box appears.
➤ On the Aspen Plus startup dialog box, select the Template option and click OK to
continue.
The New dialog box appears.
Creating a Property Estimation
Simulation
You use the New dialog box to specify the Application Type and the Run Type for
the new simulation.
➤ Select General with English Units for the Application Type.
➤ Choose Property Estimation from the Run Type list.
➤ Click OK.
Note
If the Connect to Engine dialog box appears, see Appendix A.
The Aspen Plus graphics workspace is shaded, because you do not use a
graphical simulation flowsheet in specifying a Property estimation simulation.
You will use the Aspen Plus expert system (the Next function) to guide you
through this session.
➤ Click the Next button.
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Estimating
Physical
Properties
for a NonDatabank
Component
A dialog box appears telling you that the graphics workspace is not used in this type of
run and that you enter all specifications on input forms.
➤ Click OK to continue.
The Setup Specifications Global sheet appears. The Run Type Property Estimation is
already selected.
➤ Type Property Estimation for Thiazole in the Title box and press Enter.
➤ Click the Next button.
The Components Specifications Selection sheet appears.
Entering Components Information
On the Components Specifications Selection sheet:
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➤ Enter THIAZOLE in the Component ID field.
Because THIAZOLE is not in the Aspen Plus databank, do not fill in the
Component Name or Formula boxes.
➤ Click the Next button.
The Properties Estimation Input Setup sheet appears.
Specifying Properties to Estimate
On the Properties Estimation Input Setup sheet you specify the parameters to
estimate. For this session, the default option to estimate all missing parameters is
appropriate.
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Estimating
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You can use the remaining sheets to optionally select specific estimation methods
for each property. Since you are using default methods for this session, you will
not need to provide this input.
➤ Click the Next button.
The Non-Databank Components dialog box appears.
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Entering Molecular Structure
The Non-Databank Components dialog box indicates that your simulation has
some non-databank components, for which you can enter additional information.
➤ To enter the molecular structure information for thiazole, select Enter molecular
structure for estimation.
➤ Click OK.
The Molecular Structure Object Manager appears.
➤ From the Molecular Structure Object Manager, select the component ID THIAZOLE
for which you want to specify the molecular structure, then click Edit.
The Molecular Structure General sheet for THIAZOLE appears:
In Aspen Plus, you can define the molecular structure either by using a general
method based on atoms and bonds, or by specifying the functional groups specific
to a particular estimation method. For this session, you will use the General
method.
On the General sheet, you specify the molecular structure of the component to be
estimated, by describing the atomic connectivity. You do not need to define
hydrogen atoms or bonds to hydrogen. Aspen Plus decides the hydrogen atom
connectivity automatically. Before using this sheet, it is helpful to sketch the
structure of the component and to number all the non-hydrogen atoms:
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Estimating
Physical
Properties
for a NonDatabank
Component
C1 = C2
N5 = C4
S3
To specify the atomic connectivity for thiazole:
➤ On the Atom 1 Number box, enter 1.
➤ Click the Type list box to display a list of atoms available. Select C for carbon.
➤ On the Atom 2 Number box, enter 2.
➤ Click the Type list box to display a list of atoms available. Select C for carbon.
➤ Click the Bond Type list box to display a list of bond types available. Select Double
bond.
The entries you have just made specify that atoms 1 and 2 in your molecule are
carbon atoms linked by a double bond.
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➤ Complete the structure for thiazole by entering the atomic connectivity as you did for
the carbon double bond, starting with the Number box in the next row of the table.
Atom 1
Atom 2
Number
Type
Number
Type
Bond type
2
C
3
S
Single bond
3
S
4
C
Single bond
4
C
5
N
Double bond
5
N
1
C
Single bond
For this cyclical structure, atom 1 and atom 5 are linked to form a ring. Aspen
Plus displays the atom number and corresponding atom type in the bottom
section of the sheet.
The Molecular Structure General sheet is now complete.
➤ Click the Next button.
The Non-Databank Components dialog box appears.
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Estimating
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Component
Entering Property Data
You have already entered the structure for thiazole. This information is sufficient
for Aspen Plus to estimate component properties. However, you also have
molecular weight, boiling point, and vapor pressure data for thiazole. Aspen Plus
can use your data for these properties in the estimation of other properties. This
should improve the accuracy of the estimation. As a general guideline, use
available data whenever possible, and use Property Constant Estimation (PCES)
to estimate only properties that are missing.
You will use the Parameters forms to enter the property parameters that you know
from various literature sources, as described in the first section of this chapter.
➤ In the Non-Databank Components dialog box, select Enter additional property
parameters.
➤ Click OK.
The Properties Parameters Types dialog box appears.
To enter pure component boiling point and molecular weight for thiazole:
➤ Select Pure Component Parameters.
➤ Click OK.
The Properties Parameters Pure Component Object Manager appears.
➤ Click New.
➤ Select Scalar in the New Pure Component Parameters dialog box. You can accept the
default name that Aspen Plus automatically generates or enter a name of your choice.
➤ Enter the name TBMW and click OK.
The Properties Parameters Pure Component Input sheet appears.
➤ Click the Component list box and select THIAZOLE.
On this sheet, you will enter your pure component property data for boiling point
and molecular weight.
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➤ Click the first Parameters list box to display the available pure component parameters.
Use the arrow keys to move through the list and view the descriptive prompt for each
parameter.
➤ Select TB (normal boiling point) from the list.
The default temperature units for Normal Boiling Point are degrees Fahrenheit.
To specify a boiling point in degrees Celsius:
➤ Click the Units list box for TB and select C.
➤ In the data column where you selected THIAZOLE for Component, enter a value of
116.8 for TB.
➤ On the Parameter list box in the next row of the table, use the arrow keys to move
through the list and select MW (molecular weight).
➤ In the data column for component THIAZOLE, enter a value of 85 for MW.
You have entered the pure component property data for thiazole:
Now you will specify the coefficients for the Antoine vapor pressure correlation.
➤ Click the Next button.
The Non-Databank Components dialog box appears.
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Estimating
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Component
➤ Select Enter additional property parameters, and click OK.
The Properties Parameter Types dialog box appears.
➤ Select Pure Component Parameters.
➤ Click OK.
The Properties Parameters Pure Component Object Manager appears.
➤ Click New.
➤ Select T-Dependent Correlation in the New Pure Component Parameters dialog box.
➤ Scroll down the list and select PLXANT-1 for the Antoine vapor pressure correlation.
➤ Click OK.
The Properties Parameters Pure Component Input sheet for PLXANT-1 appears:
➤ Click the Component list box and select THIAZOLE.
Your vapor pressure parameters are valid for units of mmHg for pressure, and
degrees Celsius for temperature.
➤ Click the Temperature Units list box and select C.
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➤ Click the Property Units list box and select mmHg.
➤ Enter the Antoine coefficients for thiazole:
Element
Coefficient
1:
16.445
2:
-3281
3:
216.255
4:
0
5:
0
6:
0
7:
0
8:
69
9:
118
You have completed the Properties Parameters Pure Component PLXANT-1
Input sheet:
➤ Click the Next button.
The Non-Databank Component dialog box appears.
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Estimating
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Properties
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Component
➤ Click OK to go to the next required input step.
The Required Properties Input Complete dialog box appears.
➤ Click OK to go to the next required input step.
The Required PCES Input Complete dialog box appears.
Running a Property Constant Estimation
(PCES)
You can now run PCES.
➤ Click OK in the Required PCES Input Complete dialog box.
The Control Panel appears.
As the run executes, you will see status messages displayed in the Control Panel.
Soon you will see the message Results Available with Warnings in the status bar
at the bottom of the main window.
To analyze the PCES warnings, you can look at the Control Panel.
➤ Use the vertical scroll bar to the right of the Control Panel window to see the
messages.
You can see that there were warnings that the functional groups for the
UNIFAC, UNIF-LBY, UNIF-DMD, UNIF-R4, Lydersen, Ambrose, Reichienb,
Orrick-E, and Ruzicka methods cannot be automatically generated from the
general structure. In this session, you can ignore these warnings since these
methods were not used to estimate properties.
Examining Property Constant Estimation
Results
You can now examine the results of your PCES simulation. You will view the
Pure Component and T-dependent properties estimated by Aspen Plus.
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➤ Click the Check Results button
on the Control Panel.
The Results Summary Run-Status form appears and indicates that the calculations
were completed normally with warnings. To view the Property estimation results, you
from the Data Browser toolbar to browse the
can use the Next Form button
various results forms.
➤ Click the Next Form button
.
The Properties Estimation Results Pure Component sheet appears, with the
estimated pure component parameters for thiazole.
➤ Use the scroll bars to examine the tabulated results.
➤ Click the Next Form button
to continue reviewing results.
The T-Dependent sheet appears, with the estimated temperature-dependent
parameters such as Ideal Gas Heat Capacity (CPIG) and Heat of Vaporization
(DHVLWT).
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Creating a Property Backup File
Once you are satisfied with your property estimation results, you can save this
simulation as a backup file. You could then retrieve the properties you have
developed for thiazole into another Aspen Plus simulation.
To save this simulation as a backup file:
➤ From the File menu, select Save As.
➤ In the Save As dialog box, select Aspen Plus Backup Files for the Save as type.
➤ Enter THIAZOLE in the File Name field.
Your working directory is displayed in the Save In box.
➤ Click the Save button to save the Aspen Plus backup file.
Your simulation is now saved as thiazole.bkp.
➤ Click No in the dialog box that prompts you to also save the simulation as an Aspen
Plus Document file.
Exiting Aspen Plus
➤ From the Aspen Plus File menu, select Exit.
➤ When the dialog box appears, select No, because you have already saved the
simulation as a backup file.
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Chapter 7
7
Analyzing Properties
Before starting a simulation study, it is important to understand the physical
property and phase equilibrium behavior of the fluids in your process, and to
confirm that the behavior predicted by the property models and data you are
using is reasonable. In this session you will use the interactive property analysis
features in Aspen Plus to obtain a binary T-xy diagram for the
acetone-chloroform system, using the NRTL activity coefficient model with
parameters from the built-in binary pair databank. You will check your results
against the following literature data:
Acetone boiling point
Chloroform boiling point
Acetone-chloroform azeotrope
56 °C
61 °C
64.5 °C
(From Mass-Transfer Operations, Treybal, 3rd Ed., McGraw-Hill p. 356, and from
Properties of Gases and Liquids, Reid, Sherwood and Prausnitz, 3rd Ed.
McGraw-Hill, Appendix A.)
Allow about 20 minutes for this session.
The Aspen Plus Analysis commands are available to interactively generate tables
and plots of a pre-defined set of properties for pure components, binary mixtures,
and streams. The Analysis commands allow you to conveniently generate the
most common types of property analyses. You can use the Properties Analysis
forms to set up generic property analysis and to report additional properties.
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Analyzing
Properties
Starting Aspen Plus
To start Aspen Plus:
➤ Start Aspen Plus from the Windows Start menu or double-click the Aspen Plus icon on
your desktop.
The Aspen Plus Startup dialog box appears.
➤ On the Aspen Plus startup dialog box, select the Template option and click OK to
continue.
The New dialog box appears.
➤ Select General_with_English_Units for the Application Type.
➤ Choose Property Analysis in the Run Type list.
➤ Click OK.
Note
If the Connect to Engine dialog box appears, see Appendix A.
The Aspen Plus main window appears. Aspen Plus starts a new simulation with the
default name, Simulation 1.
Entering Components and Properties
You do not need a graphical simulation flowsheet to perform a property analysis.
You require information only about chemical species and physical properties.
➤ Click the Next button in the main window toolbar.
The Non-Flowsheet Simulation dialog box appears.
➤ Click OK to display the next input form.
The Setup Specifications Global sheet appears. The next step is to select a units set
consistent with the literature data.
➤ Click the Input data units list box to display the available units sets. Select METCBAR
for Metric Units with Celsius for temperature units and Bar for pressure units.
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➤ Click the Next button.
The Components Specifications Selection sheet appears.
➤ On the first Component ID field, enter ACETONE.
➤ On the second Component ID field, enter CHCL3 for chloroform and press Enter.
Aspen Plus matches the component against the ID’s, Component names, or
Formulas in the Aspen Plus databank, and displays the information on the sheet.
The Components form is complete.
➤ Click the Next button.
The Properties Specifications Global sheet appears.
For this session, you will use the NRTL physical property model to generate the
vapor-liquid equilibrium properties.
➤ Click the Base Method list box to display the available property methods, then select
NRTL.
➤ Click the Next button.
The Properties Parameter Binary Interaction Input sheet for the NRTL method
appears:
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This sheet shows the default binary parameters for acetone-chloroform retrieved
from the Aspen Plus databank. These parameters were determined from
literature data for this binary system between 15 °C and 64.47 °C. You can find
additional information on the range of data used and the quality of the fit by
using the online help.
➤ Move the highlight to the AIJ field or the Source field. Click the What’s This button or
press F1.
➤ Review the help to confirm that you will use these default parameters for your analysis.
➤ Click the Next button.
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A dialog box appears telling you that you have to specify the property analysis to be
generated. Because you will perform an ad-hoc property analysis in this session, you
will not continue with the next simulation input.
➤ Click Cancel to close the dialog box.
➤ Close the Data Browser window.
Generating a Txy Diagram
You can use the Analysis capability even before the Flowsheet Simulation input
specifications are complete. (Note the Required Input Incomplete message on the
status bar.)
You can generate Property analysis; pure, binary, residue, and stream analysis.
However, with the given input, only Pure and Binary Analysis are available. In
this session, you want to study VLE behavior of the acetone-chloroform binary
system, so you will perform a binary analysis.
➤ From the Tools menu, select Analysis, then Property, then Binary.
The Binary Analysis dialog box appears.
➤ On the Binary Analysis dialog box, click in the Analysis Type list box to view the type of
Analysis available.
As the prompts indicate, Txy and Pxy analysis are used to study nonideality of
vapor-liquid systems to check for azeotrope formation and Gibbs Energy of
Mixing Analysis is used to see if the system will form two liquid phases.
➤ Select Txy.
Default options for the Txy analysis are displayed in the Binary Analysis dialog
box. You can change the defaults or use the values shown. For this session, you
will use the defaults.
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➤ Click Go to apply the defaults and to start the analysis.
Calculations begin for the Txy diagram. When the calculations are finished the
results appear in tabular form. In addition, a Txy plot is automatically displayed,
as shown in the following figure:
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You can use the Maximize button in the Plot window title bar to obtain a
maximized plot screen.
This plot indicates that this system contains an azeotrope at an acetone mole
fraction of about 0.34 and a temperature of 64.14°C (147.5°F). The temperature
of the azeotrope agrees with the literature value within 0.5%, so you could feel
confident using the Aspen Plus default data in a simulation.
➤ Click the Binary Analysis Results window, behind the Plot window.
The table shows that Aspen Plus has calculated activity coefficients and K-values
as well as temperature and composition. Several additional built-in plots are
available using the Plot Wizard.
➤ In the Binary Analysis Results Window, click the Plot Wizard button at the bottom of
the window.
➤ The Plot Wizard Step 1 window appears. Read the description on the Welcome page
and click Next> to continue.
The available plots are displayed.
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➤ To plot activity coefficients versus mole fraction of acetone, select Gamma.
➤ Click Next> to continue.
The Plot Wizard Step 3 dialog box appears.
➤ Specify ACETONE in the Component to Plot box.
➤ Click Finish to accept defaults for the remaining plot settings and generate the plot.
The activity coefficient plot appears.
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From this plot you can see the infinite dilution activity coefficients.
➤ Close the Plot window and the Binary Analysis Results window.
Tip
In the Binary Analysis dialog box, click the Save As Form button
at the bottom of the window to save your interactive Property
Analysis to forms within the Data Browser. Saving an interactive
Property Analysis as forms enables you to preserve the input and
results of this Property Analysis to view or modify at a later time.
➤ Close the Binary Analysis dialog box.
At this point you could change the Run Type in the Setup Specifications Global
sheet to Flowsheet, define a flowsheet, and proceed with a simulation. However,
for this session, you will stop here.
➤ From the File menu, select Exit.
➤ Click No when the dialog box prompts you to save the changes to your simulation.
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Appendix A
A
Connecting to the
Aspen Plus Simulation
Engine
If either of the following conditions exist, you will be prompted to specify the host
computer for the Aspen Plus simulation engine after you start the Aspen Plus
User Interface:
• The simulation engine is not installed on your PC.
• The simulation engine is installed on your PC, but the Activator security
device is not connected to your PC.
In these cases, the Connect to Engine dialog box appears.
➤ Click the Server Type list box and select the type of host computer for the simulation
engine.
If you choose Local PC as the server for the simulation engine, you do not need to
enter any more information into the dialog box.
➤ Click OK to continue.
If you choose UNIX host, OpenVMS host, or Windows NT server as the server for
the simulation engine:
➤ Enter the node name of the computer on which the Aspen Plus simulation engine will
execute.
➤ Enter your User Name, Password, and Working Directory, and click OK.
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Connecting
to the
Aspen Plus
Simulation
Engine
When the network connection is established, a message box appears saying
Connection Established.
If the Connection Established message does not appear, see your Aspen Plus
system administrator for more information on network protocols and host
computers for the Aspen Plus simulation engine.
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A-2
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