ASPEN Tutorial _ Chemical Reactors

ASPEN Tutorial | Chemical Engineering & Materials Science

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ASPEN Tutorial

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1. Aspen Introduction

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ASPEN is a process simulation software package widely used in industry today. Given a process design and an appropriate selection of thermodynamic models, ASPEN uses mathematical models to predict the performance of the process. This information can then be used in an iterative fashion to optimize the design. This accurate modeling of thermodynamic properties is particularly important in the separation of non-ideal mixtures, and ASPEN has a large data bases of regressed parameters. ASPEN can handle very complex processes, including multiple-column separation systems, chemical reactors, distillation of chemically reactive compounds, and even electrolyte solutions like mineral acids and sodium hydroxide solutions.

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ASPEN does not design the process. It takes a design that the user supplies and simulates the performance of the process specified in that design. Therefore, a solid understanding of the underlying chemical engineering principles is required to supply reasonable values of input parameters and to evaluate the suitability of the results obtained. For instance, a user should have some idea of the column behavior before attempting to use ASPEN. This information could come from an approximate method, such as the McCabe-Thiele approach, general modeling of the T-x-y behavior, or residue curve maps. ASPEN cannot tell you how many stages to use for a given separation. You must set the number of stages and see what type of separation results. Some preliminary or 'back of the envelope' calculations are generally recommended. MSU has a variety of Aspen packages for different simulations. Briefly, here are the programs and capabilities: Aspen Adsim - Fixed bed adsorption for pressure swing adsorption, etc. Aspen Chromatography Chromatography - Fixed bed adsorption, simulated moving bed chromatography. Runs independent of Aspen Plus. Aspen Custom Modeler - A utility to permit the creation of user unit operations. Aspen Distil - Aspen's 'Conceptual Engineering Product' for planning for processing schemes. Runs independent of Aspen Plus. Aspen Dy namics namics - Unsteady-state simulator. Aspen Plus - Steady-state process simulator. Aspen Properties - Modeling of properties and phase equilibria. Incorporated into most other components, though it can be run as a stand-alone subset. All of the phase equilibria and mixture property methods discussed on this site are accessible in either Aspen Plus or Aspen Properties. Aspen Polymers - Modeling of polymerization reactors and polymer thermodynamics. This package is available within Aspen Plus or Aspen Properties rather than via an external menu. BatchSep - Batch distillations. Runs independently of Aspen Plus. Normally undergraduate student projects will involve Aspen Plus or Aspen Pr operties . To start either of these packages, be sure to look for the corresponding User Interface Interface on the start menu.

1.1 Getting Getting more h elp This document is intended to be an overview. ASPEN has extensive online help. Do not try to contact ASPEN directly. They do not respond to student requests. Work through your instructor and TA for getting answers to your questions. If your questions are not answered with online help, see the pdf documents available from the ASPEN documentation folder folder available on the START menu. Most common tasks are covered. To find descriptions/equations for the thermodynamic models and parameter variables, are in online Properties Help, Chapter 3.

2. Getting Started with Aspen Plus or Aspen Properties Normally undergraduate student projects will involve Aspen Plus or Aspen Pr operties . To start either of these packages, be sure to look for the corresponding User Interface Interface on the start menu. When you are prompted to connect to the engine (license) configure the window as shown, and click OK.


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Figure 2.1 - Connection dialog

3. Specification of Flowsheet in Aspen Plus If you are working with Aspen Properties, you may skip to section 4 of this document. To demonstrate how to build a process simulation using ASPEN, we will develop a distillation column for separation of ethanol and water. The first step in developing a simulation is to develop the process flow diagram (PFD), which consists of the unit operations (blocks) and streams that feed and connect the blocks. The blocks are listed by category at the bottom of the main window (columns, reactors, etc.) in a toolbar known as the 'Model Library', a portion is shown in Figure 3.1. There are a wide variety of block available. Documentation for the algorithm for each block is provided in the ASPEN documentation.

The first step is to choose the column type for the ethanol-water separation. Click on columns to view the different column simulations available. The two types of common interest are 'DSTWU', which is the multicomponent shortcut distillation method, and 'RadFrac', which is the rigorous simulation of a single column.

Figure 3.1 - Column and Stream menu

For the ethanol + water system, the short-cut will not be appropriate since the system has an azeotrope. Choose 'RadFrac'. Click on the small arrow on the right side of 'RadFrac' to select the column icon that you want to use on the PFD. The menu will disappear; move the crosshairs to the desired location on the main flowsheet window and click the mouse button.

Next you have to add streams to the block. Click on the small arrow to the right of the STREAMS button at the lower left corner of your screen (as shown in Figure 3.1), and choose the stream icon you want from the menu (material, energy or work). For this example, set up the feed stream: choose the Material stream by clicking on it. The column will now show arrows where the stream can be connected; red arrows indicate required streams as shown in Figure 3.2

Figure 3.2 - Required and optional stream connection points

To set up the feed stream to the column, move the crosshair on top of the red feed position and left click once. Now, move the mouse to the left and click again. You should now have a defined feed stream (Stream 1). For the outlet streams click the column outlet first to connect the bottoms (Stream 2) and liquid distillate (Stream 3). If you make a mistake and want to delete a stream or block, click on the arrow (select) button at the upper left of the Model Library toolbar, then click on the stream or block you want to delete and hit the DELETE key.

Figure 3.3 - Column after connection of material streams

Now that you have defined the unit operations to be simulated and set up the streams into and out of the process, you must enter the rest of the information required to complete the simulation. Within Aspen Plus, the easiest way to find the next step is to use one of the following equivalent commands: (1) click the Next icon (blue N ->); (2) find 'Next' in the Tools menu; or (3) use keyboard shortcut F4. Any option will open the Data Browser.

4. Configuring Units and Settings

SPEN Tutorial | Chemical Engineering & Materials Science


CHEMS Links Department Links In the Data Browser, you are required to enter information at locations where there are red semicircles. When you have finished a section, a blue checkmark CHEMS will appear. However, providing some 'Setup' settings is often desirable. Home College Of Engineering About CHEMS Applied Engineering Sciences You can change default units by opening the ‘Setup’ FolderProgram as shown below. Biosystems & Agricultural Engineering Undergraduate Graduate Program Chemical Engineering & Materials Science Friends And Alumni Civil & Environmental Engineering Research Computer Science & Engineering People Electrical & Computer Engineering Resources Mechanical Engineering W e b S t a n d a r d s : X H T M L 1 .0 S t r i c t | C S S | W C A G A A | D e v e l o p e d B y D EC S © M i c h i g an S t a te U n i v e r s i ty . A l l R i g h t s R e s e r v e d

You can browse the unit sets to see the choices. The base 'unit-set' names shown above are reserved names and you cannot modify them. However, if you right-click on a unit set, you can ‘rename’ it and then modify it. Once you have viewed the units you can specify the choice by using the drop down boxes.

If you are running Aspen Plus, you may wish to have stream results summarized with mole fractions or some other basis that is not set by default. Use the 'Report Options' as shown below.

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ASPEN Tutorial _ Chemical Reactors

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