Cyclic short-term scheduling of multiproduct batch plants using continuous-time representation

Abstract

The idea of cyclic scheduling is commonly utilized to address short-term scheduling problems for multiproduct batch plants under the assumption of relatively stable operations and product demands. It requires the determination of optimal cyclic schedule, thus greatly reducing the size of the overall scheduling problems with large time horizon. In this paper a new cyclic scheduling approach is proposed based on the state-task network (STN) representation of the plant [Comput. Chem. Eng. 17 (1993) 211] and a continuous-time formulation [Ind. Eng. Chem. Res. 37 (1998a) 4341]. Assuming that product demands and prices are not fluctuating along the time horizon under consideration, the proposed formulation determines the optimal cycle length as well as the timing and sequencing of tasks within a cycle. This formulation corresponds to a non-convex mixed integer nonlinear programming (MINLP) problem, for which local and global optimization algorithms are used and the results are illustrated for various case studies.