This tutorial will guide you though the setup of an azeotropic distillation column using RADFRAC.
Residue and Miscibility
Before setting up the model, the tutorial will show how to use Aspen's ability to create residue curves based on your chose models and the add to that a liquid-liquid miscibility curve.
Flowsheet
Start a new flowsheet in Aspen and add a FLASH3 unit and add stream FEED to the feed stream, VAPOR to the vapor stream, 1-LIQUID to the first liquid stream and 2-LIQUID to the second liquid stream.
Components and Properties
The components are vinyl acetate (VA, VINYL-ACETATE, C4H6O2-1), acetic acid (AA, ACETIC-ACID, C2H4O2-1) and water (H2O, WATER, H2O). We will use the NRTL-RK property set.
Feed Stream
We will set up Aspen to vary this stream a short bit later. For now define the feed stream as having T=230F, P=65psi, VA = 1 lbmol/hr, H2O = 1 lbmol/hr. This will be the pressure at the top of the column.
Flash3
Define the decanter as shown below. Here we have set the pressure to 0 denoting no pressure drop and heat duty to zero denoting adiabatic phase separation. Thus this unit will have the same conditions as the inlet stream. The key component (the majority component) in the 2nd liquid stream will be water.
Sensitivity Analysis
We can use Aspen to get an idea of how sensitive (how much our process changes) our process is to a changing variable. We will use this feature to get a list of the liquid-liquid equilibria for a water-VA-AA system. We will later put this on a ternary diagram.
To set the sensitivity, expand "Model Analysis Tools" and click on Sensitivity. Add a new object. You will then need to add FORTRAN variables to calculate your data. Don't despair. We won't be using any heavy duty FORTRAN and you shouldn't need much more than what is in this tutorial. Just so you know, basic statements are much like any other programming language. y = 2 (2+ 2x - sin(x)/2)x-1 would be written y = 2*(2+2*x-sin(x)/2)**(x-1). But again, you probably won't need all of that.
We want to examine 6 variables, the mole fractions of each component in the 2 liquid streams. Select new to enter in each of the variable definitions.
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