(A) continuous-domain MILP for short-term scheduling of multipurpose batch plants

Abstract

The present study concerns novel mathematical formulation for the short-term scheduling of a special class of multipurpose batch plants. In particular, the scheduling problems of the multipurpose batch plants under mixed-product-campaign (MPC) are addressed here. An MILP model is developed based on the definition of an event slot. It is used to determine the production sequence and to select the production path for each batch of product. Every batch of products is assigned to an event slot. The number of event slot is the same as the number of batch operations. By introducing the event slots, the scheduling model of sequential multipurpose batch plants can be achieved and the number of binary variables, as a consequence, the computational load can be reduced compared to established models. Furthermore, the proposed MILP model for scheduling of sequential multipurpose batch plants can be extended to treat sequence dependent changeovers. The changeover times are considered for each time slot of a unit when a product is assigned to the event slot and a different product is assigned to the adjacently next event slot. By considering sequence dependent changeovers in modeling, we can reduce makespan to some degree and more complex problems abound in usual industrial practice can be handled with reduced computational expense. Finally, two examples are shown to illustrate the performance of the models, respectively.