INTEC   05402
INSTITUTO DE DESARROLLO TECNOLOGICO PARA LA INDUSTRIA QUIMICA
Unidad Ejecutora - UE
artículos
Título:
Material Transfer Operations in Batch Scheduling: A Critical Modeling Issue
Autor/es:
S. FERRER-NADAL; E. CAPON-GARCIA; C.A. MÉNDEZ; L. PUIGJANER
Revista:
INDUSTRIAL & ENGINEERING CHEMICAL RESEARCH
Editorial:
American Chemical Society
Referencias:
Lugar: Columbus; Año: 2008 vol. 47 p. 7721 - 7732
ISSN:
0888-5885
Resumen:
An effective short-term scheduling formulation must simultaneously deal with several problem difficulties commonly arising in batch processes. A critical feature to be considered when dealing with multi-stage batch plants is the movement of material through the process. A non-zero time as well as certain conditions are always required to move the material from one processing stage to the next one according to the specified product recipe. The transfer task consumes a period of time during which a proper synchronization of the equipment units supplying and receiving the material is enforced. Synchronization implies that during the execution of the transfer task, one unit will be supplying the material whereas the other one will be receiving it and consequently, no other task can be simultaneously performed in both units. Most of the existing mixed-integer linear programming (MILP) optimization approaches have traditionally dealt with the batch scheduling problem assuming zero transfer times, and consequently no synchronization, between consecutive processing stages. The problem simplification relying on negligible transfer times may work properly for the scheduling of multiproduct batch plants with similar product recipes. However, it is demonstrated in this work that ignoring the important role of transfer times may seriously compromise the feasibility of the scheduling whenever shared units and storage tanks, material recycles or bidirectional flows of products are to be considered. In order to overcome the serious limitations of current MILP-based scheduling approaches, a general precedence based framework accounting for non-zero transfer times is introduced. Also, two alternative methods that avoid generating unfeasible schedules are proposed and tested in different case studies involving zero transfer times.