COMBINATORIAL TECHNIQUE FOR SHORT-TERM SCHEDULING OF MULTIPURPOSE BATCH PLANTS BASED ON SCHEDULE-GRAPH REPRESENTATION

This paper deals with the production scheduling of multipurpose batch plants. A navel graph representation is proposed that takes into consi deration the specific characteristics of chemical processes in schedul ing. In this graphs, the nodes represent the production tasks and the arcs the precedence relationships among them. The representation is fl exible enough to consider a great variety of production structures (re cipes with branches, alternative units,...). Both NIS and UIS transfer policies can be considered simply by choosing the appropriate precede nce relationships. This representation provides the opportunity of inc orporating highly efficient graph algorithms together with an appropri ate branch-and-bound (B&B) algorithm for serving multipurpose scheduli ng problems effectively. The B&B algorithm takes care of the combinato rial optimization problem involved in each scheduling problem, while t he graph algorithms allow to obtain the lower bounds that control the branching strategy. The efficiency of the proposed method is establish ed by comparing it with the application of a generic B&B solving an eq uivalent MILP scheduling model. (C) 1998 Elsevier Science Ltd. All rig hts reserved.