An integrated scheduling/planning environment for petrochemical production processes

Abstract Production planning/scheduling is a very difficult task because it has to deal with many conflicting constraints. Some attempts have been made to obtain an optimal solution that satisfies all constraints, but this approach is not practical, because the scheduling problem is NP-complete. This paper proposes a practical approach to actual scheduling and planning problems and describes its application to creating monthly schedules for synthetic rubber production, a typical petrochemical process. Cooperative scheduling is a new approach in which procedures, rules, and the user cooperate to make feasible schedules efficiently. The procedures, collectively called a “scheduling engine,” work as a local constraint satisfier to solve general primitive constraints. Rules that represent domain-dependent knowledge then solve domain-specific constraints by means of a pattern-matching function. Finally, the user evaluates the schedule and modifies it via a user-friendly interface with direct-manipulation functions. The user interaction is therefore included in the system architecture as a global constraint satisfier. The integrated planning and scheduling environment described here was designed within this cooperative framework. The system produces a production plan that satisfies a due date limitation, taking account of stock shortages; the plan is checked concurrently to determine whether it leads to a realizable schedule. The prototype system has been transferred to one of the major petrochemical companies in Japan, and is being tested and evaluated in an actual environment for operational use.