(520f) Equation-Based Model for Dividing Wall Column Simulations

The literature on Dividing Wall Columns (DWCs) has been growing extremely rapidly of late. Indeed, it is already sufficiently large that more than one review article has been published (Dejanović, I., Matijašević, L. & Olujić, Ž. Dividing wall column—a breakthrough towards sustainable distilling. Chem. Eng. Process. Process Intensif. 49, 5pp 59–580, 2010; 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; Kaibel, B. Dividing-Wall Columns, in Distillation: Equipment and Processes pp 183–199, Academic Press, 2014).

With apparently few exceptions, simulations of DWCs are done using an interlinked multi-column model in a commercial simulator and it is not hard to find statements lamenting the degree of difficulty of simulating DWCs in this way. For example: Dejanovic et al. (2010) wrote:

Carrying out DWC performance simulations requires great experience and these are more or less computationally very demanding. … well established commercial software packages still do not contain a DWC as a standard model. This however will occur sooner or later, most probably as a simultaneous, equation based model.

The sooner or later mentioned by Dejanovic et al., in fact, means now. An imminent release of the freely available column simulation program ChemSep will include an equation based equilibrium-stage model for simulating DWCs of arbitrary complexity (this means with multiple walls in any configuration).

In fact, it has long been recognized that a simultaneous equation based model is probably the smart tool to use. Many investigators cite a paper by Becker et al. (Becker, H., Godorr, S., Kreis, H. & Vaughan, J. Partitioned Distillation Columns–Why, When & How. Chem. Eng. 108, 68–68, 2001) who make such a recommendation, but they provide no evidence at all of having done so. Nor do any of the many other writers that cite Becker’s work. Thus, one goal of this work is provide definitive evidence that a simultaneous column model can converge quickly and easily, even in cases where the multi-column models fail.

In addition, the model in ChemSep is compared to experimental data from the University of Texas at Austin. Finally, we demonstrate that the ChemSep standalone DWC model can be used as a single unit operation model within commercial process simulation tools via the CAPE-OPEN mechanism, thereby greatly simplifying the task of building DWC models.