Simultaneous Batching and Scheduling of Single Stage Batch Plants

This paper presents a new mixed integer linear program (MILP) for the optimal short-term scheduling of single stage batch plants with sequence dependent changeovers and optimal selection of the number of batches to produce. It is a continuous-time formulation employing multiple time grids that is based on the resource-task network (RTN) process representation. The main novelty is that aggregated processing and changeover tasks are considered that account for the time required to produce all batches of the product, plus the changeover time to the next product in the sequence. When compared to the traditional approach of considering a single processing task per batch, fewer event points are needed, which results in significantly lower computational effort as illustrated through the solution of several example problems. The new formulation is further compared to a continuous-time model with global precedence sequencing variables to a bounding model with immediate precedence sequencing variables and to a constraint programming model. * To whom correspondence should be addressed. Tel.: +351-210924643. Fax: +351-217167016. Email: [email protected]