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Tips & Tricks: Use Model Regression Tool to Adjust Hypothetical Components

Adjust hypothetical component properties for more accurate modeling by using your plant data. The Model Regression tool was added to VMGSim 6.0, it has proven to be a very powerful tool that is ideal for these types of tasks. This article also features the Structure Builder, used to create hypothetical components.

This simple example demonstrates how easy is to regress properties of hypothetical components. Data extracted from our case study was used as experimental data for the regression example. In this case a stream of Naphthalene is cooled down.

The specification of the case are:
/Dp.In.VapFrac = 1
/Dp.In.P = 250 kPa
/Dp.In.Fraction.NAPHTHALENE = 1
/C1.DeltaP = 200 kPa
/Bp.In.VapFrac = 0

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This case also demonstrates how to use the Structure Builder to re-create the Naphthalene compound. Start by setting the Normal Boiling Point of 218 °C and naming the hypo to My-Naphthalene. Now, open the Structure Builder. 

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First, add the functional groups by selecting them on the left hand side and then clicking on the design area.

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First, add the functional groups by selecting them on the left hand side and then clicking on the design area.

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With the information provided by the structure builder, the hypo compound is ready to be created. Click Ok on both forms and then Click Apply on the Basis form.

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Here is the comparison of the properties between hypo and Naphthalene.

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In the same case, duplicate the streams and the cooler to use the hypo instead of the original Naphthalene. Note the differences in temperature.

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Now is time to set up the Model Regression tool to adjust the hypo component. First, add the regressed variables. Open the Model Regression to activate the right click short cut menus.

The properties to be adjusted are: Critical Pressure, Critical Temperature and the Acentric Factor. Right click on the critical pressure and select the option to Add to Regression: Case 1. In the pop-up window that appears select Add variable as “Regressed Variable”.

Repeat this process for the other two properties.

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Now, add the experimental variables.  /Dp_1.In.P,  /Dp_1.In.T,  /Bp_1.In.T 

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The regressed and experimental variables are now in the model regression Case 1.

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The experimental data is currently in Excel®. Adjust the Number of Points to 21 and then copy/paste the data to the Model Regression Input Data.

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The Model Regression is ready to run. Click Run and wait until is done.

Now compare the fit between calculated and the input data before and after the regression.

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The  regressed values of the properties can be seen in the optimizer value column of the set up section as well as in the results tab. Click the button “Set Regressed Vals as Specs” to apply the values to the hypothetical component.

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My-Napthalene* now has the regressed values. Using these values the temperatures align to the ones of the original section.

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Please contact your local VMG office for more information.

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