During the last 15 years, many mathematical models have been developed in order to solve process operation scheduling problems, using discrete or continuous time representations. In this paper, we present a unified representation and modeling approach for process scheduling problems. Four different time representations are presented, compared, and applied to single-stage and multi-stage batch scheduling problems, as well as crude-oil operations scheduling problems. We introduce three solution methods that can be used to achieve global optimality or obtain near-optimal solutions depending on the stop criterion used. Computational results show that the Multi-Operation Sequencing time representation is superior to the others as it allows efficient symmetry-breaking and requires fewer priority-slots, thus leading to smaller model sizes.
Sylvain Mouret, Ignacio E. Grossmann, Pierre Pesti