A mathematical programming approach including flexible recipes to batch operation rescheduling A.B. Editor et al. (Editors) © 2005 Elsevier B.V./Ltd. All rights reserved. 1 A mathematical programming approach including flexible recipes to batch operation rescheduling Sergio Ferrer-Nadal, Carlos A. Méndez, Moisès Graells, Luis Puigjaner * Chemical Engineering Department-CEPIMA, Universitat Politècnica de Catalunya ETSEIB, Av.Diagonal 647, E-08028, Barcelona, Spain Abstract The inherent dynamic nature of industrial environments often needs not only the execution of the required rescheduling actions but also the proper adjustment of the production recipe to the current process conditions. Therefore, the concept of flexible recipe becomes an important part of the rescheduling framework that allows full exploitation of the batch plant inherent flexibility. This work introduces a rigorous mathematical approach that incorporates the concept of recipe flexibility to batch operation rescheduling. Keywords: rescheduling, flexible recipe, batch operations, MILP model. 1. Introduction Batch processes have received great attention over the last years because of their higher flexibility compared to continuous processes and the increasing demand for specialty, high added-value chemical and pharmaceutical products. Within this context, the short- term scheduling deals with the optimal allocation of a set of scarce plant resources over time to manufacture one or more products following a batch recipe. Most of the scheduling approaches assume that batch processes are operated at nominal conditions following predefined fixed production recipes (Méndez and Cerdá, 2003a). However, in many cases a flexible recipe operation may result a more suitable way of incorporating systematic recipe adaptations depending on the actual process conditions. The flexible recipe concept was originally introduced by Rijnsdorp (1991) as a set of adaptable elements that controls the process output. Afterwards, Verwater-Lukszo (1994) presented a flexible recipe approach for the adjustment of control recipes during production which has been applied to several case studies (Sěl et al., 1999; Rutten and Bertrand, 1999). One of the first attempts to extent the flexible recipe approach to a plant-wide scheduling problem was carried out by Romero et al. (2001). These authors proposed to integrate a linear flexible recipe model into a multipurpose batch process scheduling model based on an S-graph algorithm. In addition to changes in nominal process conditions, frequent unexpected events can also take place during the normal batch plant operation (equipment failures, late order arrivals, order cancellations and so on). These unforeseen changes may lead the in- progress schedule to become suboptimal or even infeasible. Although rescheduling techniques have a central role in process operations, only a few developments have focused their attention on this challenging problem (Cott and Macchietto, 1988; Méndez and Cerdá, 2003b). These rescheduling approaches allow performing certain corrective * Author to whom correspondence should be addressed: Luis.Puigjaner@upc.es.