Simultaneous Batching and Scheduling of Single Stage Batch Plants with Parallel Units

This article deals with the optimal short-term scheduling of single stage batch plants with sequence-dependent changeovers together with the optimal selection of the number of batches to produce. The novelty of the article is that instead of following the traditional approach of considering one processing task per batch, all batches of the product are now aggregated into a single task. Integer variables that hold the number of batches to produce are used to characterize these aggregated tasks. Two conceptually different continuous-time models are proposed. They rely on either multiple time grids or global precedence sequencing variables for event representation and generate a mixed integer linear program. The new formulations are compared to a traditional resource-task network multiple time grid approach as well as to a recent bounding model with immediate precedence sequencing variables. The results for several example problems show the new multiple time grid formulation as the best overall performer. When compared to the traditional approach, one order of magnitude savings in computational effort are achieved due to the need of fewer event points to get to the global optimal solutions. © 2007 American Institute of Chemical Engineers AIChE J, 2008

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