RELIABILITY AND MAINTENANCE CONSIDERATIONS IN-PROCESS DESIGN UNDER UNCERTAINTY

In this paper, we describe recent theoretical and algorithmic developm ents aiming at the integration of maintenance optimization in optimal life-cycle process design and development under uncertainty. Based on a mathematical description for the process model, information regardin g the reliability characteristics of equipment components and type and cost of different maintenance policies for each component, we propose an optimization formulation featuring an expected profit objective fu nction, taking into account the transitions between the different stat es of the process system (due to equipment failure and corrective main tenance). Different types of preventive maintenance strategies are dis cussed together with their resulting mathematical problems, which corr espond to mixed-integer nonlinear optimization formulations involving implicitly defined integral terms. By exploiting properties of the mai ntenance problem, a series of nonlinear optimization problems of reduc ed size is solved instead, thereby avoiding the direct solution of the original formulations. The implications of maintenance optimization o n process design are also studied. This is achieved by comparing two a pproaches, a sequential vs, a simultaneous strategy, for simultaneous design and maintenance, optimization. It is shown that the incorporati on of maintainability criteria provides new directions in proposing an d identifying optimal, over a life cycle, process designs. (C) 1998 El sevier Science Ltd. All rights reserved.