Computers & Chemical Engineering, Vol.20, No.11, 1335-1360, 1996
Milp Model for Scheduling and Design of a Special-Class of Multipurpose Batch Plants
In this paper we propose a method for the integrated scheduling and design for a special class of multipurpose batch proceses. The type of plants considered are the ones where not all the products use the same processing stages, and manufacturing of the products can be characterized through production routes. A novel representation for cyclic schedules is proposed that has the effect of aggregating the number of batches for each product. It is shown that the no-wait characteristics of substrains can be exploited with a reduction scheme that has the effect of greatly decreasing the dimensionality of the problem. This reduction scheme can be complemented with a tight formulation of the underlying disjunctions in the MILP to reduce the computational expense. The proposed MILP model for scheduling is extended to design problems in which the potential existence of intermediate storage in the production paths is also considered. In addition to the rigorous scheduling of the process, the sizes of the equipment constituting the various production stages are determined. By using exact linearization schemes it is shown that the problem can be reformulated as an MILP model and solved rigorously to global optimality. Application of the proposed model is illustrated with several example problems.