A novel network-based continuous-time representation for process scheduling: Part I. Main concepts and mathematical formulation

• Published in: Computers & chemical engineering Vol. 33; no. 9; pp. 1511 - 1528
• Main Authors: Giménez, Diego M., Henning, Gabriela P., Maravelias, Christos T.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 09.09.2009
• Subjects: Mixed-integer linear programming; Network-based continuous-time representation; Process scheduling; Process scheduling; Network-based continuous-time representation; Mixed-integer linear programming
• ISSN: 0098-1354; 1873-4375
• DOI: 10.1016/j.compchemeng.2009.03.007

A novel network-based framework for the short-term scheduling of multi-purpose batch processes is presented. The novelty of the proposed approach lies in five key concepts. First, it is based on a new continuous-time representation that does not require tasks to start (end) exactly at a time point; thus reducing the number of time points needed to represent a solution. Second, processing units are modeled as being in different activity states to allow storage of input/output materials. Third, time variables for “idle” and “storage” periods of a unit are introduced to enable the matching between tasks and time points without big-M constraints. Fourth, material transfer variables are introduced to explicitly account for unit connectivity. Fifth, inventory variables for storage in processing units are incorporated to model non-simultaneous and partial material transfers. The proposed representation leads to MILP formulations which address limitations of existing scheduling methods.