Planning and scheduling models for refinery operations

Abstract

The main objective of this work is to discuss planning and scheduling applications for refinery operations. Firstly, the development of a nonlinear planning model for refinery production is presented. The model is able to represent a general refinery topology and allows the implementation of nonlinear process models as well as blending relations. Considering the market limitations for each oil derivative usually supplied by the refinery, the optimization model is able to define new operating points, thus increasing the production of more valuable products, while satisfying all specification constraints. Real-world applications are developed for the planning of diesel production in the RPBC refinery in Cubatão (SP, Brazil) among others. The optimization results were compared to the current situation, where no computer algorithm is used and the stream allocation is made based on experience, with the aid of manual calculations. The new operating point represents an increase of several million dollars in annual profitability. The second part of the work addresses scheduling problems in oil refineries that are formulated as mixed integer optimization models and rely on both continuous and discrete time representations. The problem of crude oil inventory management that involves the optimal operation of crude oil unloading from pipelines, transfer to storage tanks and the charging schedule for each crude oil distillation unit will be discussed. Furthermore, the paper will consider the development and solution of optimization models for short-term scheduling of a set of operations that includes: product receiving from processing units, storage and inventory management in intermediate tanks, blending in order to attend oil specifications and demands, and transport sequencing in oil pipelines. Important real-world examples on refinery production and distribution are reported: the diesel distribution problem at RPBC refinery and the production problems related to the fuel oil/asphalt and LPG areas of the REVAP refinery in São José dos Campos (SP, Brazil), which produces approximately 80% of the national consumption.