What can go wrong in a dividing wall column and how to detect it

Abstract

Dividing wall columns are state of the art distillation arrangements performing three separation tasks within one unit. Compared to using two conventional columns in series this saves both capital costs and energy but on the other hand it brings a higher risk of malfunction. This simulation study analyses what can go wrong during the operation of dividing wall columns. The emphasis is on the operation of the prefractionator section, that is, on the choice on the liquid and vapor splits, which is crucial for the overall performance. The resulting two-way flows between the prefractionator and main column gives a broader feasible operating range than in a conventional column arrangement. This can lead to peculiar behavior, including circulation of components around the dividing wall. This paper identifies 15 non-optimal operating regions for the prefractionator with specific internal flow patterns, characteristic temperature and composition profiles for the separation of a fairly ideal mixture of benzene, toluene and p-xylene. From these results it is possible to identify and hopefully rectify wrong choices for the liquid and vapor splits in a dividing wall column.