Effective MILP model for oil refinery-wide production planning and better energy utilization

Generally, a refinery complex consists of process system and utility system. Process system not only produces liquefied petroleum gas, gasoline, diesel and so on, but also some byproducts, such as fuel gas and residual fuel oil, which supply utility system as fuel. The utility system converts fuel gas and fuel oil to high pressure or medium pressure steam and electricity to meet the energy demand of the process system. A novel approach to the integration of the process system and utility system for better energy utilization is presented in this paper. A plant-wide multi-period planning mathematical model is proposed and three improvements are identified. First, the process unit energy-consumed model is reformulated, because energy consumed by a unit not only relates the throughput of the unit, but also varies with the operation modes of the unit and season. Second, The MILP (Mixed Integer linear Programming) model of utility system is embedded in the plant-wide model to gain the overall optimization and for better energy efficiency. Third, steam, fuel oil and fuel gas are balanced in the whole plant. Finally, the proposed approach was used in a real industrial example to determine the optimal mass and energy flow and some important results have been obtained and are presented.