(342b) An MILP Formulation for the Short-Term Scheduling of Batch and Continuous Processes Presenting Heterogeneous Processing Times

The main goal of the present work is to propose an efficient formulation that is able to address simultaneous existence of batch and continuous processes in which the batch processes are characterized by presenting lengthy processing times. The latter demands multiple units operating in parallel and the consideration of enlarged scheduling horizons that results in large models with high combinatorial complexity. These features are typical for some industries such as those for the production of phosphate fertilizer products and having fermentation steps. In particular, the phosphate fertilizer industry also features the allowance of mixed storage policies (NIS, FIS and UIS), besides requiring sequence-dependent changeover times in the continuous operations. In light of this, in this work we first propose a new model to fit continuous and batch processes that is able to tackle all requirements described above. Continuous operations are allowed to take place in a single time slot, whereas the lengthy batch operations are allowed to take place over multiple time slots. The computational results show that our model is able to efficiently solve an industrial-size problem representing a typical phosphate fertilizer plant for a one-month time horizon in reasonable time.