Analysis of commonly used scheduling models for multistage biopharmaceutical processes

Several works have been reported in the literature over the past two decades to schedule a multiproduct facility in the biopharmaceutical industry. The present work attempts to analyze a few commonly used scheduling models, based on different time representations, for midterm planning or long-term scheduling of multistage, multiproduct biopharmaceutical facilities for multiperiod demand. Several model inconsistencies/limitations in the published literature and in the reported Gantt charts, such as (i) real-time storage violation, (ii) early product delivery, (iii) inadequate mapping of upstream and downstream tasks, (iv) no initial setup time, and (v) incomplete sequencing/modelling of storage tasks, thus (iv) overestimating the reported objective values in their results, are identified. Accordingly, one of the unit-specific-event-based literature models is improved in this work to address these limitations. An improved model is proposed with enhanced/new features such as modified material balances, proper sequencing of storage based on storage bypassing allowed for intermediates and bypassing not allowed for products, modified shelf-life constraints, initial setup time constraints, and updated bounds on storage, giving better results compared to the published literature models.