Short-term Scheduling of Non-sequential Multipurpose Batch Processes with Transfer and Set-up Times Under Various Intermediate Storage Policies

Abstract

In this paper, a mixed integer linear programming (MILP) model for short-term scheduling of non-sequential multipurpose batch processes is presented. The processes consist of a single production line, i.e. one unit per stage. The intermediate storage policies considered are unlimited intermediate storage (UIS), no intermediate storage (NIS), zero-wait (ZW) and finite intermediate storage (FIS) policies. Transfer and sequence dependent setup times are also taken into account under four intermediate storage policies. The objective of this study is to determine the optimal production sequence for minimizing makespan under the different storage policies. The basic idea of the proposed MILP model comes from the fact that the production sequence can be determined by comparing the orders of all pairs of products. In contrast to previously published models, the proposed model has fewer binary and continuous variables and fewer constraints, and can be solved in significantly less computational time. The effectiveness of the proposed formulation is illustrated by several examples, and the numerical results and comparisons are provided.