An optimal control approach to scheduling maintenance and production in parallel lines of reactors using decaying catalysts

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In this work, an optimal control approach for scheduling maintenance and production in a process using decaying catalysts, originally developed in a previous study for a single reactor, is extended to parallel lines of reactors. Unlike traditional mixed-integer optimisation methods, this approach involves formulating this problem as a multistage mixed-integer optimal control problem (MSMIOCP) and using a methodology that enables solution as a standard nonlinear optimisation problem. The methodology’s features of a feasible path approach and scheduling catalyst changeovers without combinatorial optimisation techniques can be advantageous in providing reliable, robust and efficient solutions in comparison to mixed-integer methods. The MSMIOCP formulation is applied to the case study of an industrial process that operates a single feed over a set of 4 parallel reactors and produces a single product. The solutions obtained using the proposed methodology are of high quality and highlight the potential advantages of this approach over mixed-integer techniques.