Harry reminded everyone that BASF is a pioneer in installing Dividing Wall Columns (DWCs) and is now operating more than 70 of them. Modelling a DWC in a process simulator requires often to develop a complex flowsheet of several simple columns and to interconnect them. Such a multi-column model is cumbersome to develop and often difficult to get to converge. By using an equation-oriented Parallel Column Model (PCM), it is possible to easily model a DWC of any configuration. In ChemSep such an algorithm has been implemented. The implementation includes both equilibrium stage and rate-based models. In addition, and independently, the PCM can be used to model maldistribution in packed columns.
A movie was presented showing how easy it is to study how a DWC may replace a section made of several distillation columns.
Harry made the point that, if a model of a DWC may be developed in such modelers as Aspen Custom Modeler, gPROMS or MOSAIC, changing the configuration of the column requires changing the model, while, when designing a DWC, it may be required to change its configuration a number of times to improve the separation efficiency. Therefore proposing a software tool creating DWC models that are easily configurable and behaving as CAPE-OPEN Unit Operations fulfills a need.
To further facilitate the identification of column sections in a DWC, a color coding has been developed in ChemSep. An accurate rate-based model of a DWC must take into account heat transfer through walls. Heat transfer may be extremely important for small columns, often used in experimental studies. While it is very difficult to include heat transfer in a multi-column flowsheet representing a DWC, the Parallel Column Model easily deals with it.
Validation of the PCM in ChemSep was conducted against a set of experimental data collected for her PhD by Bailey ROACH at the University of Texas at Austin.
Several well-documented maldistribution models can also be used in ChemSep in order to take into account the effect of redistributors on the efficiency of separation. Harry ended by giving the history of development of ChemSep as a CAPE-OPEN Unit Operation, going back to version 5.0 that was presented at the CAPE-OPEN Meeting held in Como, Italy. A new release was announced for later in October 2018 of a Chemsep Lite version including the Parallel Column Model for DWCs with one wall, no heat transfer, one condenser, one reboiler.