Generating binary and ternary phase diagrams using HYSYS or UniSim

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Generating McCabe-Thiele diagrams using HYSYS or UniSim

The procedure outlined here allows one to easily generate a McCabe-Thiele diagram from a converged column in HYSYS or UniSim. In addition to its pictorial value, such a diagram is useful in optimization of stripping, absorption, and distillation columns. The method was developed by Hyprotech engineers prior to the acquisition of HYSYS by Aspen and Honeywell. It is useful for any number of components, not just binaries under the ideal conditions usually assumed. Follow this procedure:

You must be logged on to the computer as an Administrator, because registering an extension modifies the HYSYS code on the C drive, and this is permitted only for Administrators. Thus, you may require the assistance of one of your IT people to do this.
Right click on mto.dll and Save Target to a convenient location on your computer. You may also need to download and save mto.edf.
Open HYSYS.
Go to Tools/Preferences/Extensions and Click on Register an Extension. Find EqPlots.dll and open it. This will remain part of HYSYS on your machine until it is Unregistered. Close Preferences.
Open or create a HYSYS case with at least one converged column. This must not be a short-cut column or component splitter.
Go to Flowsheet/Add Operation. Select the Extensions category and Add McCabe-Thiele Plot Generator.
Click on Refresh Col Lists. This should display a list of converged columns in this case. Click on the one you want and the Start and End Stages. These would normally be at the top and bottom of the column, e.g. the Condenser and Reboiler for a distillation column.
Click on a Light Key component and a heavy Key component. The light key is the component whose concentration you want to limit in the bottoms, while the heavy key is the component whose concentration you want to limit in the overhead. One useful procedure is to order the components by vapor pressure and decide where you want to make the split. Usually more volatile (higher vapor pressure) component adjacent to the split would be the light key, while the less volatile would be the heavy key. A better procedure is probably to look at the column’s worksheet composition and see where the split is. One can choose more than one heavy key and light key, but this makes interpretation more difficult.
Click on Run and then Plot. If you have more than 2 components, the mole fractions on the plot equal the sum of the mole fractions of light key components divided by the sum of the mole fractions of both light and heavy key components. Notice that the blue “equilibrium line” is not smooth. That’s because it actually shows vapor and liquid compositions leaving each tray (which are in equilibrium only for 100% tray efficiencies). The red operating line is actually a plot of the vapor and liquid compositions entering each tray, i.e. the liquid from the tray above and the vapor from the tray below. It is controlled by the relative molar rates of liquid and vapor entering the tray.
This diagram enables you to see the effectiveness of each tray, and particularly to see if the feed tray is at the optimal location.

Created June 25, 2007. Updated January 29, 2009. Please email questions, comments and suggestions to W.R. Wilcox

Disclaimer: The material on these pages is intended for instructional purposes by Clarkson University students only. Neither Clarkson University nor Professor Wilcox is responsible for problems caused by using this information.