An interactive approach to the design of noncontinuous plants

Abstract

The design of noncontinuous plants has been an area of active research for the past 20 yr. Much of the past work has been focused on optimal equipment sizing using mathematical programming techniques, often with further restrictions on the types of equipment, intermediate storage, operating policies and so on. A more comprehensive view of the design should include equipment selection, task assignment and configuration synthesis as well as path sequencing and unit sizing, but such a design does not lend itself readily to the existing techniques. In this paper we report a novel approach to the design of noncontinuous plants. This approach is based on a design tool, BatchEx, which performs three basic functions. First, it maintains current plant configurations, production plans, path sequences and useful design indices such as equipment utilization. Second, it provides a set of design operators which are used to enter design decisions and to evaluate their consequences. Third, it provides a graphic interface for a user to access the knowledge base and the design operators. Implemented in ART, an expert system shell with schema representation and rule programming, BatchEx is applicable to both OPAT (One Product At A Time) and MPAT (Multiple Products At A Time) noncontinuous plants. It provides for task merging, task splitting and equipment reuse. It allows for nonidentical parallel units, in-phase, out-of-phase, mixed operating modes and intermediate storage. Full flexibility is available with regard to the selection and sequencing of production paths. In its present implementation a design is guided by total equipment cost minimization. Given a design BatchEx determines its feasibility and provides information which may be used to improve the design. BatchEx allows the user to enter an initial design for a given problem and information about the design is presented to the user upon request. The design is modified by the user based on his experience and analysis. Heuristics have been developed for design initialization and improvement. Examples are presented to illustrate these heuristics. A preliminary assessment of the efficacy of this approach is given.