Design, planning and scheduling of multiproduct batch plants

Efficient and accurate aggregate scheduling models are proposed in this thesis for their effective integration in higher level decision problems. Multiproduct batch plants operating with the Zero Wait and the Unlimited Intermediate Storage policies are considered.; Firstly, it is shown that the scheduling problem can be greatly simplified if the criterion of cycle time minimization is used instead of makespan minimization. An analytical model is presented for the UIS policy, while for the ZW policy a 0-1 minimax assignment model is proposed. The LP relaxation of this model is shown to yield integer solutions or else have zero gap.; It is also shown that for scheduling problems where the production involves a large number of batches of relatively few products (say 10-100), aggregation in the space of the products can be accomplished effectively. An aggregated linear programming model is derived from the 0-1 minimax assignment problem which can be used for determining the minimum cycle time and the family of schedules with the optimal cycle time. Schedules can be easily derived from the LP solution using the aggregated graph representation. The insights gained with this approximate method are used to formulate a rigorous MILP model for makespan minimization which can be solved very efficiently.; Using the compact LP based methods for scheduling, the problem of simultaneous production planning and scheduling is considered next. A multiperiod LP model is proposed for the simultaneous production planning and scheduling of multiproduct batch plants that may consist of one or several non-identical parallel lines. Inventory costs, sequence dependent cleanup times and costs, and penalties for production shortfalls are readily accounted for in this model.; The problem of simultaneous sizing and scheduling is also addressed for the case of multiproduct batch plants that involve one unit per processing stage.; Extensive numerical results are presented for all the above problems to illustrate the capabilities of the proposed methods, as well as the economic impact of anticipating scheduling at the planning, sizing and synthesis stage of multiproduct batch plants. (Abstract shortened with permission of author.)...