Synchronizing Operations in Multiproduct Batch Facilities Producing Semifinished and Final Products

Integrated industrial facilities usually make semifinished (SF) products required for the production of a significant number of end products through different batch processes. Each one may involve a series of processing stages with several units running in parallel and intermediate tanks between stages. Moreover, such processes can manufacture several products but one at a time. SF products are temporarily stored in dedicated tanks from where they are supplied to the demanding production lines. Many complex process structures can be viewed as a network of interconnected linear processes. The presence of dedicated tanks allows batch mixing and splitting and changing of the batch size with the linear process. This work introduces a general precedence-based mixed-integer linear programming model for the short-term scheduling of integrated facilities producing SF and end products using different batch sequential processes. The batch facility is operated in a make-to-order environment, with several customer orders involving the same end product. A critical task is to synchronize the scheduling of the processes making SF and end products. This requires determining lot-sizing and scheduling of the processing lines all at once. In addition, the inventory of SF-products should be monitored to avoid overloading and running out conditions in their dedicated tanks. A significant number of examples have been solved to optimality in reasonable CPU times.