Abstract
Dividing wall columns (DWC) are attractive for the significant potential savings in energy requirements compared to conventional distillation sequences. Challenges in control have been reported as an obstacle that may hamper the number of industrial applications. In practice, sub-optimal operation normally shows up as inability to obtain the designed product purity and not as increased energy consumption. Herein, we address the practical optimising control of DWC by applying a regulatory layer where the focus is on controlling the top (lights) and bottom (heavies) products to their purity specification. This allows for several approaches for the optimisation layer where the key task is to adjust the prefractionator operation such that high purity can be obtained in all three products including the side product (intermediates). A promising optimisation approach is the model-free Perturb and Observe method which is within the class of extremum seeking algorithms. The proposed structure may also be applied to the so-called liquid transfer only LOT-DWC.