Unit Slots Based Short-Term Scheduling for Multipurpose Batch Plants

In chemical process industries, scheduling of multipurpose batch plants is challenging and has received tremendous attention so far. Recently, Susarla et al. ( 2009) explored the concept of unit- (asynchronized) slots for scheduling multipurpose batch processes and successfully reduced number of slots required for the optimal solution of a given problem. In this paper, we extend the work of Susarla et al. ( 2009) and utilize unit- slots to formulate a continuous-time mixed integer linear programming (MILP) model for the short-term scheduling of multipurpose batch processes. In addition to Susarla et al. ( 2009), our model is capable of handling various utility resources ( other than the processing units and material resources) and sequence dependent changeover/setup times. Also, our model is capable of handling various storage configurations explicitly ( Classes: UIS, LIS, and FIS with policies: UW, LW, and NW, Liu & Karimi, 2007). We demonstrate the performance of our model through an extensive numerical evaluation with some of the best known models from the literature. This rigorous comparison further elucidates that our model uses fewer binary variables, continuous variables and constraints.