Scheduling of batch plants: Constraint-based approach and performance investigation

Batch processing plants are attractive due to their suitability for the manufacturing of small-volume, high-value added products. Scheduling batch plants by using computer-aided systems is important for improving the plant productivity, since it harmonizes the entire plant operation efficiently to achieve production goals. However, the current scheduling approaches for batch plants are inadequate. This research develops a constraint-based model and system for batch-process scheduling and investigates their performance. The proposed constraint model analyses and brings together many scheduling constraints, adds new constraints and categorizes them according to their functionality. A computer scheduling system, Batch Processing Scheduler, is developed in C++ to apply the model. A number of examples have been devised to study the performance of our constraint-based approach. It is found that the approach can schedule complex plants and solve large-size problems by finding feasible solutions satisfying all imposed constraints, which include some hard ones such as those of finite wait time. It is also identified that the first feasible solution can be found very quickly, but much more time, even exponentially more, is required to find the optimal solution particularly for complex and large-size problems. Feasibility and limitations of the proposed methodology are demonstrated by the results.