A Novel Multi-Grid Formulation for Scheduling Semi-Continuous Plants

Abstract

Semi-continuous plants are abundant in bulk manufacturing chemical process industries. However, scheduling of semi-continuous plants has received rather lower attention as compared to batch plants in the literature. In this paper, we develop a novel continuous-time formulation for short-term scheduling of semi-continuous processes using a multi-grid approach. For this, we adopt the unit-slots framework proposed by Susarla et al. (2010) to ensure accurate resource balances. We allow a number of storage configurations (no, constrained, and unconstrained) with either dedicated or multipurpose storage units. Also, we consider various wait policies (no, limited, and unlimited) for all materials. In addition, we consider resources such as utilities, equipment, etc. and allow operational scenarios such as sequence-dependent transition times. Numerical evaluation shows gains in solution efficiency as compared to the literature models in terms of better solutions, fewer variables, constraints and computation time. © 2012 Elsevier B.V.