A new approach for efficient rescheduling of multiproduct batch plants

In this paper, a novel solution approach to addressing the problem of effic ient reactive scheduling in multiproduct batch plants is presented. The app roach is based on a two-stage solution procedure whereby, at the first stag e, the deterministic schedule is established on the basis of data at the cu rrent time and, at the second stage, the optimal reschedule is obtained fro m the solution of a proposed formulation that systematically incorporates a ll different rescheduling alternatives. Two kinds of disturbances are consi dered-machine breakdown and rush order arrival. The rescheduling problem is formulated as a mixed integer linear programming (MILP) problem using a co ntinuous time formulation, which leads to a smaller number of binary variab les for both the deterministic and the rescheduling problems thus, resultin g in reduced computational times. It is shown that the proposed approach re sults in an efficient utilization of the plant capability as it allows the optimal selection among all rescheduling alternatives in a systematic way w ithout the use of any heuristics. Moreover, the objective function used all ows the decision maker to determine the optimal reschedule in terms of prof itability and plant operability by allowing the selection of a rescheduling policy close to the original schedule. The effectiveness of the proposed a pproach is illustrated through a number of case studies from scheduling lit erature for both single and multiple disturbances.