Plantwide control: The search for the self-optimizing control structure

The following important question is frequently overlooked: Which variables should we control? The answer is related to finding a simple and robust way of implementing the optimal operating policy. The task is to translate the economic operating objectives into control objectives, and it is argued that the controlled variables should be those that give “self-optimizing control”, which is when acceptable operation is achieved with constant setpoints for the controlled variables. A systematic procedure for finding controlled variables based on only steady-state information is presented and tested on a CSTR and a distillation case study