Continuous Time Representation Approach to Batch and Continuous Process Scheduling. 1. MINLP Formulation

Abstract

The problem of decision timing in the context of batch and continuous process scheduling is addressed in this paper. Representation of time in any scheduling model affects the number of integer variables and the convexity of the model. The usual procedure in batch and continuous process scheduling is to divide the scheduling interval into equal size intervals so as to achieve the required accuracy. This construction generates a formulation with a potentially very large number of binary variables. In this paper, the time events arising in the schedule are modeled directly, and thus the use of binary variables over periods during which no real changes in system state occur is avoided. Furthermore, such a representation of time offers the potential for direct integration of operations scheduling and control which is difficult to achieve in the usual equal size interval approach. The problem is formulated as a mixed integer nonlinear program (MINLP). Issues pertaining to the efficient solution of this problem...