Medium-Term Planning of Single-Stage Single-Unit Multiproduct Plants Using a Hybrid Discrete/Continuous-Time MILP Model

Abstract

The objective of this work is to develop an optimization model for the medium-term planning of single-stage continuous multiproduct plants with a single processing unit. Several types of stock keeping units (SKUs) are produced. Customers place orders that represent multiples of SKUs that must be delivered at the end of each week. When different SKU types are processed, sequence-dependent changeover times and costs are incurred. The problem is formulated as a mixed-integer linear programming (MILP) model with a hybrid time representation. The objective is to maximize profit that involves sales revenues, production costs, product changeover costs, inventory costs, and late delivery penalties. The proposed optimization-based model is validated in a real-world polymer processing plant. To improve its computational efficiency, integer cuts are developed and added in the model. The model is then applied to two literature examples, and the results are compared with other models of similar nature.