Long-term Scheduling of a Multi-stage Multi-product Bio-pharmaceutical Process

Abstract

There have been several works in the literature for scheduling of multi-product continuous processes with significant attention laid on short-term scheduling. This work presents a continuous-time model for long-term scheduling of a multi-stage multi-product process from bio-pharmaceutical industry. The overall model is a mixed-integer linear programming (MILP) formulation based on State-Task-Network (STN) representation of the process using unit-specific event-based continuous-time representation. The proposed model is an extension of model by Shaik and Floudas (Ind. Eng. Chem. Res., 2007, 46, 1764–1779) with several new constraints to deal with additional features such as unit and sequence dependent changeovers, multiple intermediate due dates, handling overproduction, shelf-life and waste disposal, and penalties on backlogs and delayed order fulfillment. Improved tightening and sequencing constraints have been presented leading to better relaxed objective values. The validity of the proposed model has been illustrated through an example from the literature.