Time scale separation and the link between open-loop and closed-loop dynamics

This paper aims at combining two different approaches ([1] and [2]) into a method for control structure design for plants with large recycle. The self-optimizing approach ([1]) identifies the variables that must be controlled to achieve acceptable economic operation of the plant, but it gives no information on how fast these variables need to be controlled and how to design the control system. A detailed controllability and dynamic analysis is generally needed for this. One alternative is the singular perturbation framework proposed in [2] where one identifies potential controlled and manipulated variables on different time scales. The combined approaches has successfully been applied to a reactor-separator process with recycle and purge.