| Production scheduling defines what products should be produced and what products should be consumed at each point in time over a short period; hence, it defines which run-mode to use and when to perform changeovers in order to meet the market needs and to satisfy the demand. The study presented in this paper focuses on the scheduling of the loading and unloading of crude oil in intermediate storage tanks, between ports and crude distillation units. Analysis of this activity gives rise to better use of a system’s resources, as well as improved total visibility and control of production units and the entire supply chain. It is very important that the crude oil is loaded and unloaded continuously, primarily for security reasons but also to reduce the setup costs incurred when flow between a port and a tank or between a tank and a crude distillation unit is reinitialized. The aim of the present paper is to develop an exact solution approach based on a generic mixed integer model, which provides not only the optimal schedule of loading and unloading of crude oil minimizing the setup cost but also the optimal type of mixture preparation. Comparison between the approach applied in a real refinery and the developed exact approach is presented in order to justify the advantage of optimization tools. A series of valid inequalities are developed in order to speed-up the convergence of the resolution approach of the model. Finally a comparison between the two classical types of mixture preparation and the proposed combination type mixture preparation is provided to illustrate the advantages of the proposed method. |