Scheduling with Equipment Redesign in Multipurpose Batch Plants

The objective of this paper is to present a new formulation for the optimal scheduling of multipurpose batch plants where equipment redesign is considered simultaneously with the scheduling decisions. The equipment redesign is characterized by the implementation of modifications in the existent processing units so as to change their suitability to perform certain tasks, while regarding tasks’ characteristics inside a given scheduling horizon. This approach may be advantageous in cases where no schedule solutions are found with the existent equipments and where, with minor technology modifications on the processing units, feasible schedules can be obtained. Each of these changes has a cost and requires a certain time to be implemented. In order to model such problem a simple Mixed Integer Linear Programing formulation (MILP) is proposed having as basis the unified Resource-Task Network (RTN) representation presented by Pantelides (1994). An example motivated by a chemical-pharmaceutical industry is used to demonstrate the applicability of the proposed formulation.