An effective MIDO approach for the simultaneous cyclic scheduling and control of polymer grade transition operations

In this work we propose a scheduling and control formulation for simultaneously addressing scheduling and control problems by explicity incorporating process dynamics in the form of system constraints that ought to be met. The formulation takes into account the interactions between such problems and is able to cope with nonlinearities embedded into the processing system. The simultaneous scheduling and control problems is cast as a Mixed-Integer Dynamic Optimization (MIDO) problem where the simultaneous approach, based on orthogonal collocation on finite elements, is used to transform it into a Mixed-Integer Nonlinear Programming (MINLP) problem. The proposed simultaneous scheduling and control formulation is tested using a Methyl-Methacrylate CSTR where four different types of grades are manufactured. It is shown that the proposed methodology provides the best grade scheduling policy and optimal transition trajectories leading to maximum process profit.