(79e) A Rate-Based Equation-Oriented Parallel Column Model: Application to Dividing Wall Columns

The literature on Dividing Wall Columns (DWCs) has been growing extremely rapidly of late. Indeed, it is already sufficiently large that several review articles have been published [1-3].

With very few exceptions, simulations of DWCs are carried out using an interlinked multi-column equilibrium stage model in a commercial simulator. (A notable exception is the work of Mueller and Kenig [4-5] who used a rate-based model to describe reactive distillation in dividing wall columns. Also noteworthy (and unusual) about their work is that they used Aspen Custom Modeler, a commercial tool that employs equation-based solution techniques. This is in complete contrast to all other models (when they have been described in sufficient detail) in the published literature on dividing wall columns.)

To our knowledge, there are no commercial flowsheet simulation packages that offer a DWC as a standard model (rate-based or otherwise). (Models developed in ACM do not meet this standard.) This paper describes just such a model, which, via the CAPE-OPEN framework, can be used in any CAPE-OPEN compliant process flowsheet simulation package. We introduce a new parallel column model in ChemSep that is rate-based, equation oriented and can be used to model DWCs of arbitrary configuration.

We illustrate the model by showing the differences in design that can arise when using these two types of column model. Any DWC with an interior wall (meaning that the wall does not extend all the way to the top and bottom of the column) must have at least one side draw for the intermediate boiling product(s). The optimum location of side draws is one area of column design where a rate-based model should be superior to model based on equilibrium stages.

The model in ChemSep allows for heat transfer across the wall and we compare the predictions of the model to experimental data from the University of Texas at Austin.

References

1. Dejanović, I., Matijašević, L. & Olujić, Ž. Dividing wall column—a breakthrough towards sustainable distilling. Eng. Process. Process Intensif. 49, 5pp 59–580, 2010
2. Yildirim, Ö, Kiss, A.A., Kenig, E.Y., Dividing wall columns in chemical process industry: A review on current activities, Separation and Purification Technology, 80, pp 403-417, 2011
3. Kaibel, B. Dividing-Wall Columns, in Distillation: Equipment and Processes pp 183–199, Academic Press, 2014.
4. Mueller, I. & Kenig, E. Y. Reactive distillation in a dividing wall column: rate-based modeling and simulation. Industrial & Engineering Chemistry Research, 46, pp3709-3719, 2007
5. Mueller, I., Pech, C., Bhatia, D., & Kenig, E. Y. Rate-based analysis of reactive distillation sequences with different degrees of integration. Chemical Engineering Science, 62, 7327-7335, 2007