2020 Virtual AIChE Annual Meeting
(648b) A General Model for Periodic Chemical Production Scheduling
In this work, we present a general model for periodic chemical production scheduling that can be applied to address problems in all production environments considering various features. We first define the concept of âperiodic schedulingâ, which is a generalization of âcyclic schedulingâ, in that it considers a broader set of solutions (interestingly, the generalization is analogous to the way a cycle in a graph is a special case of a closed trail). Second, we propose a model that does not rely on five commonly made assumptions in previous works: (1) each product can be produced in only one unit; (2) unlimited storage policy; (3) no task crossover between the execution of the periodic solutions; and (4) final products are shipped at constant rates. The relaxation of these assumptions allows us to find solutions that are very different, and better, than the solutions obtained by the previous approaches. We also discuss alternative types of constraints for sequence-independent setups and sequence-dependent changeovers to study the tradeoffs between switchover costs and inventory costs, one of the fundamental trade-offs in periodic scheduling. Further, we propose a method to systematically convert shipment information to parameters that can be used in the inventory balance constraints, where detailed product demand profiles are considered. Finally, the model is extended to handle continuous processes.
We provide illustrative examples to demonstrate how the relaxation of the previously made assumptions can lead to better solutions and/or solutions that remain feasible when, for example, detailed (periodic) demand profiles are taken into account. We close with a number of large-scale instances to illustrate the computational efficiency of the proposed models.
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