A novel continuous time MILP formulation for multipurpose batch plants-integrated planning, design and scheduling

Abstract

This chapter presents a methodology for the integration of planning, design, and scheduling in multipurpose batch plants. In dealing with this problem, the method presented exploits the mathematical structure of the overall plant model. The overall model exhibits a block angular structure that is decomposed by raw material allocation. If raw materials can be allocated optimally to individual plants, solving individual models for each plant can produce same results as solving an overall model for the site. This discovery leads to a decomposition strategy that consists of two levels. In the first level, only planning decisions are made, and the objective function is the maximization of the overall profit. The results from solving the planning model give optimal raw material allocation to different plants. In the second level, the raw material targets from the first (planning) level are incorporated into the scheduling submodels for each plant that are solved independently without compromising global optimality. The objective function for each scheduling submodel is the maximization of product throughput. The planning model acts as coordination for scheduling models for individual plants. An industrial case study with three chemical processes is presented to demonstrate the effectiveness of this approach.