Aspen Plus Tutorial 6
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Aspen Plus Tutorial 6: Azeotropic/Extractive Distillation
This tutorial will guide you though the setup of an azeotropic distillation column using RADFRAC.
Residue and Miscibility
Before setting up the model, the tutorial will show how to use Aspen’s ability to create residue curves based on your chose models and the add to that a liquid-liquid miscibilitycurve.
Flowsheet
Start a new flowsheet in Aspen and add a FLASH3 unit and add stream FEED to the feed stream, VAPOR to the vapor stream, 1-LIQUID to the first liquid stream and 2-LIQUID to the second liquid stream.
Components and Properties
The components are vinyl acetate (VA, VINYL-ACETATE, C4H6O2-1), acetic acid (AA, ACETICACID, C2H4O2-1) and water (H2O, WATER, H2O). We will use theNRTL-RK property set.
http://www.che.utexas.edu/~che473k/aspen/aspentutor6.htm
2005-2-24
Aspen Plus Tutorial 6
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Feed Stream
We will set up Aspen to vary this stream a short bit later. For now define the feed stream as having T=230F, P=65psi, VA = 1 lbmol/hr, H2O = 1 lbmol/hr. This will be the pressure at the top of the column.
Flash3
Define the decanter as shown below.Here we have set the pressure to 0 denoting no pressure drop and heat duty to zero denoting adiabatic phase separation. Thus this unit will have the same conditions as the inlet stream. The key component (the majority component) in the 2nd liquid stream will be water.
http://www.che.utexas.edu/~che473k/aspen/aspentutor6.htm
2005-2-24
Aspen Plus Tutorial 6
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Sensitivity AnalysisWe can use Aspen to get an idea of how sensitive (how much our process changes) our process is to a changing variable. We will use this feature to get a list of the liquid-liquid equilibria for a waterVA-AA system. We will later put this on a ternary diagram. To set the sensitivity, expand «Model Analysis Tools» and click on Sensitivity. Add a new object. You will then need to add FORTRANvariables to calculate your data. Don’t despair. We won’t be using any heavy duty FORTRAN and you shouldn’t need much more than what is in this tutorial. Just so you know, basic statements are much like any other programming language. y = 2 (2+ 2x sin(x)/2)x-1 would be written y = 2*(2+2*x-sin(x)/2)**(x-1). But again, you probably won’t need all of that. We want to examine 6 variables, the molefractions of each component in the 2 liquid streams. Select new to enter in each of the variable definitions.
http://www.che.utexas.edu/~che473k/aspen/aspentutor6.htm
2005-2-24
Aspen Plus Tutorial 6
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etc… You should have the following variables entered in the end: Name AA1 VA1 WA1 AA2 VA2 WA2 Type Mole-frac Mole-frac Mole-frac Mole-frac Mole-frac Mole-frac Stream 1-LIQUID 1-LIQUID1-LIQUID 2-LIQUID 2-LIQUID 2-LIQUID Substream MIXED MIXED MIXED MIXED MIXED MIXED Component AA VA H2O AA VA H2O
http://www.che.utexas.edu/~che473k/aspen/aspentutor6.htm
2005-2-24
Aspen Plus Tutorial 6
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So you know, Aspen uses an old FORTRAN convention of only having six letters for variable names. We will vary the flow of acetic acid. The system forms a two phase liquid upto about 33% acetic acid. We will collect 21 data points varying acetic acid from 0-1lbol/hr.
http://www.che.utexas.edu/~che473k/aspen/aspentutor6.htm
2005-2-24
Aspen Plus Tutorial 6
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We will simply tabulate the variable we defined above.
http://www.che.utexas.edu/~che473k/aspen/aspentutor6.htm
2005-2-24
Aspen Plus Tutorial 6
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Run SimulationEverything is in, so save and run the simulation. The results under Model Analysis ToolsSensitivityS-1Results will show you how your model reacted. You should notice that the final sensitivity run does not have information for the second liquid. That point is outside of the immiscibility region.
Ternary Diagram
We want to plot this data on a ternary diagram that Aspen will create. To do this, in…