Divided Wall Columns: Usefulness and Challenges

Distillation systems are responsible for the highest amount of energy consumption in the chemical industry. Therefore, in recent years, fully thermally coupled distillation sequences have become increasingly of interest. The realization of such an intensified system for the separation of a multicomponent feed into three fractions in one column shell with one or more dividing walls and in general with one reboiler and one condenser is called a dividing wall column (DWC). Since the first reported implementation of a DWC by BASF in 1985, the number of these columns has been significantly increased. The position of the divided wall is not limited to the middle of the column. Installation of the wall at either bottom or top of the column is possible. Additionally, concerning to the column design, various papers have been published analyzing the operability and controllability of DWCs. Nevertheless, the design and operation of a DWC sill seems to be a domain of specialists. In this contribution, starting with the discussion of systematic design methods for DWCs and the generation of robust process control concepts, industrial examples will be presented. The presented examples, e.g. a multipurpose DWC and a DWC for extractive distillation, demonstrate, that a straightforward design and a flexible as well as robust control strategy for DWCs is possible. As a result, DWCs can be assumed to be “conventional” distillation systems today.