Simultaneous Scheduling and Control of Multiproduct Continuous Parallel Lines

In this work we propose a simultaneous scheduling and control optimization formulation to address both optimal steady-state production and dynamic product transitions in multiproduct parallel continuous stirred tank reactors. The simultaneous scheduling and control problem for multiproduct parallel continuous reactors is cast as a Mixed-Integer Dynamic Optimization (MIDO) problem. The reactor dynamic behavior is described by a set of nonlinear ordinary differential equations that are combined with the set of mixed-integer algebraic equations representing the optimal scheduling production model. We claim that the proposed simultaneous scheduling and control approach avoids suboptimal solutions, that are obtained when both problems are solved in a decoupled way. Hence, the proposed optimization strategy can yield improved optimal solutions. The simultaneous approach for addressing the solution of dynamic optimization problems, based on orthogonal collocation on finite elements, is used to transform the set of ordinary differential equations into a Mixed-Integer Nonlinear Programming (MINLP) problem. The proposed simultaneous scheduling and control formulation is tested using three multiproduct continuous stirred tank reactors featuring different nonlinear behavior characteristics.