Energy-use Analysis And Optimization Of Hydrocracking Processes

With the rapid development of the world economy, the demand for light fuel oil, especially the high quality light fuel oil, increases rapidly. In the world's crude oil reserves, the shallow less sulfur and light crude become less and less, remaining the high sulfur heavy crude oil. While more and more attention was paid to environmental protection, the quality requirements of light fuel oil, such as gasoline and diesel is becoming higher and higher. Therefore, hydrocracking, such an important refining mean for processing heavy oil and producing high quality light fuel oil, is getting more and more attention, and the processing capacity of hydrocracking is increasing annually.Hydrocracking is a high energy consumption process as it involves high pressure and high temperature reactions. The energy-use level for domestic hydrocracking units is uneven, and the difference between the highest and the lowest energy-use level is up to more than two times, which indicates that the energy-saving potential is very large. Nowadays, the energy situation is so severe that it is important to save energy for hydrocracking units.In this paper, a hydrocracking benchmark process (single-stage, single pass, cold high pressure separation flowsheet) was used as the research object, to establish the process simulation, and adjust the parameters of simulation model (such as conversion of the theoretical plate number, the adjustment of properties of the reaction product), so the simulation can accurately reproduce the actual process. Based on the simulation, energy analysis and exergy analysis with "three-link model" were conducted. The results obtained show that the energy-use bottlenecks for the existing process flow is the cold high pressure separation flowsheet, in which the reaction products repeat the process of cooling and heating, which resulting in a great energy loss, and limiting the reaction heat getting into the distillation system.A higher distillation system heating load is required for the distillation separation. In addition, the high pressure energy of the high-temperature reaction products is not recycled also. Against to this bottleneck, two energy saving and optimizing strategies was proposed. One is based on the cold high pressure separation process and the other is based on hot high pressure separation process.The optimization strategy based on cold high pressure separation process is optimizing the heat exchanger network which combined with distillation system optimization, to improving the recovery part of the energy recovery efficiency to reduce energy conversion part of the output energy. The main optimization measures include: optimization of distillation tower, optimization of de-butanizer tower, optimization of the heat exchanger network which combined with the distillation system optimization and pressure energy recovery. Through simulation, the improved energy efficiency decreases the energy consumption by about 4kgEo/t.The optimization strategy based on cold high pressure separation process is to completely change the existing process, and improved distillation system optimization processes, as well as heat exchanger network optimization design. The energy save is obtained by reducing the total process energy consumption in fundamental aspects. The simulation results show that it has at least 10kgEO/t save potential by reduce fuel use.