PRODUCTION PLANNING FOR THE RATIONAL USE OF ENERGY IN MULTIPRODUCT CONTINUOUS PLANTS

This paper presents an optimal algorithm for the planning of multiproduct energy-intensive continuous operations when the cost of energy is time-dependent, whilst the amount of energy required for the production of a unit amount of material depends on the product being produced and the equipment being used. A typical example of such a process is provided by cement milling operations. Here, demands on the available resources (processing equipment, storage capacity and electricity) are placed simultaneously by a number of final products. Significant change-over costs and delays may be incurred whenever a mill is switched from one type of cement to another. Furthermore, the cost of electricity varies over a 24 hour cycle. The methodology presented formulates the planning problem as a mixed integer linear program, the solution of which is guaranteed to produce the optimal production plan. The system developed is currently being used for planning the production of an industrial cement plant.