Optimal periodic scheduling of multipurpose plants

This paper considers the problem of deriving an optimal periodic schedule f or general multipurpose plants comprising batch, semi-batch and continuous operations. This involves the determination both of the optimal duration of the operating cycle, and of the precise nature and timing of operations ta king place within it. The basis of our formulation is the general resource- task network (RTN) process representation coupled with a continuous represe ntation of time; The presented mathematical formulation results in a mixed integer non-linear programming (MINLP) problem which cannot be linearized e xactly. We describe a special branch-and-bound algorithm for solving this p roblem by branching on both discrete and continuous variables. The overall approach can be parallelized in an effective manner as demonstrated by the examples presented. (C) 1999 Elsevier Science Ltd. All rights reserved.