Online Optimizing Control: the Link Between Plant Economics and Process Control

In chemical process operation, the purpose of control is to achieve optimal process operation despite the presence of significant uncertainty about the plant behavior and distur-bances. Tracking of set-points is often required for lower level control loops, but on the process level in most cases this is not the primary concern and may even be counterproductive. In this survey, different approaches how to realize optimal process operation by feedback control are reviewed. The emphasis is on direct online optimizing control by optimizing an economic cost criterion online over a finite horizon where the usual control specifications in terms of e.g. product purities enter as constraints and not as set-points. The potential of this approach is demonstrated by its application to a complex process which combines a chemical reaction with chromatographic separation. Issues for further research are outlined in the final part.