A control perspective on process intensification in dividing-wall columns

During the last decades, process intensification led to major developments also in separation technology. Particularly in distillation, dividing-wall column (DWC) is the next best thing as it allows significant energy savings combined with reduced investment costs. However, in spite of these clear advantages and the steady increase of DWC applications, the spreading of DWC at industrial scale is still limited to only a few companies. One of the major reasons for this status quo is the insufficient insight with regard to the operation and control of a DWC – this lack of knowledge making most chemical companies reticent to large-scale implementations. This study gives an overview of the available control strategies for DWC, varying from the classic three-point control structure and PID controllers in a multi-loop framework to model predictive control (MPC) and other advanced control strategies (LQG, LSDP, H∞ and μ-synthesis). The previous studies prove that the DWC is not difficult to control providing that an appropriate control structure is selected. The available results show that MIMO controllers perform better than multi-loop PID controllers. However, among the decentralized multivariable PI structured controllers, LSV and DSV are the best control structures being able to handle persistent disturbances in reasonably short times. All things considered, this study clearly concludes that the DWC controllability is only perceived as a problem, but in fact there are no real solid grounds for concern.