An Efficient MILP Model for the Short-Term Scheduling of Single Stage Batch Plants

Ignacio Grossmann, Carnegie Mellon University
Pedro Castro, INETI

Abstract or Description

This paper presents a multiple time grid continuous time MILP model for the short-term scheduling of single stage, multiproduct batch plants where the objective is the minimization of total cost or total earliness. It can handle both release and due dates and it can determine the products delivery dates explicitly if these need to be considered in the objective function. This formulation is compared to other mixed-integer linear programming approaches that have appeared in the literature, to a constraint programming model, and to a hybrid mixed integer linear/constraint programming algorithm. The results show that the proposed formulation is significantly more efficient than the MILP and CP models and comparable to the hybrid model when the objective is the minimization of total cost. For one large instance, both methods exceeded the time limit but the hybrid method failed to find a feasible solution. The results also show that a discrete-time formulation performs very efficiently even when a large number of time intervals are used.