Short-Term Planning of Batch Plants in Process Industries

Abstract

The paper deals with short-term planning problems in process industries where final products are obtained by several successive chemical or physical transformations of raw materials using scarce multi-purpose equipment. In batch production mode, the total requirements for intermediate and final products are partitioned into batches. The production start of a batch at a given level requires the availability of all input products. We consider the problem of scheduling the production of given primary requirements for final products such that the makespan is minimized, where the batch sizes can be chosen within prescribed intervals. Further constraints arise from limited production and storage capacities as well as sequence-dependent cleaning times for processing units. We propose a new solution approach which is based on the decomposition of the short-term planning problem into computing appropriate batch sizes (batching) and the subsequent scheduling of batches on processing units (batch scheduling). The former problem is modelled and solved as a nonlinear mixed integer program, whereas the latter problem is addressed using models and methods of resource-constrained project scheduling. The solution procedure proposed (approximately) solves problems of industrial size within a reasonable amount of computing time.