Inequalities for Continuous-time Model for Scheduling of Continuous Processes

This paper presents a mathematical formulation for large-scale continuous process scheduling problem using unit-specific event-based continuous-time representation. The formulation is based on the work of Ierapetritou et al., (1999). The model considers the changeovers for multi-purpose units and tanks, setup constraints for parallel units and tanks, and includes product tanks that satisfy demand of products with intermediate due-date requirements. The main objective of the model is to satisfy the demand by respecting the due-dates and maximize the performance by minimizing changeovers and setup costs. For the large-scale scheduling problem, the resulting formulation is a complex mixed-integer linear programming model that is difficult to solve to global optimality. A set of valid inequalities are proposed that improves the computational performance of the model significantly. Applicability of the proposed valid inequalities is demonstrated by studying a case study.