Optimization algorithms for design and scheduling of batch processes

Abstract

This thesis deals with the development of mixed integer optimization algorithms for the sizing and scheduling of batch processes that are involved in multiproduct or multipurpose plants. The goal is to develop mathematical models and efficient solution techniques. A new mixed-integer linear program (MILP) model in which makespan is minimized for the multiproduct batch processes are developed. Specifically, the Zero Wait (ZW) scheduling with transfer and sequence-dependent setup times is analyzed. Not only idle times between the successive products but also heads and tails are used to select a possible production sequence with the minimum makespan. To determine the suitable head and tail, new binary variables are defined, and aggregated to the assignment constraints of Traveling Salesman Problems (TSP). Although the number of binary variables increases, the mathematical formulation can yield a very compact MILP model. The effectiveness of the proposed model is demonstrated through several examples. Also, the proposed model is extended to solve the scheduling problems for productions with Single Product Campaigns (SPC) and Mixed Product Campaigns (MPC) explained by Birewar and Grossmann (I&EC R. 28(9), 1333, 1989b). As in the scheduling problem, the design decisions regarding sizes of the processing units, structure of the batch plant (e.g. use of parallel units), and functionality of various units (e.g. task assignment to various units) will depend on their estimate of the scheduling performance. The problem of simultaneous sizing and scheduling of multiproduct batch processes with one equipment per stage is analyzed. For most of NLP or MINLP formulations, in general, a potential problem is that integer variables cannot be handled by existing solvers. In the case when the solution of the integer variables is not in integer, the solution may be under- or over-estimated. In order to estimate the optimal solution in which integer variables are included, two a...