Optimization Simulation Of Natural Gas Liquefaction Process With Double Mixed Refrigerant Cycle

The mixed refrigerant liquefied natural gas process has been widely used in large LNG plants due to its advantages of high liquefaction efficiency and low energy consumption.In many kinds of mixed refrigerant processes,the double mixed refrigerant cycle natural gas liquefaction process?DMR?is more suitable for large-scale natural gas liquefaction plant than SMR,C3MR,ap-x and other processes.Therefore,this paper studies the DMR process.According to the different stages of mixed refrigerant cycle throttling in DMR liquefaction process,three kinds of processes were selected for optimization simulation:second-order throttling DMR liquefaction process,third-order throttling DMR liquefaction process and fourth-order throttling DMR liquefaction process.Three simulation models of DMR process optimization were established in HYSYS.Taking the minimum energy consumption of the process as the objective function,the process parameters and mix refrigerant ratio of the three DMR processes were optimized by using the optimizer in HYSYS,and the optimal process parameters and mix refrigerant ratio,as well as the load distribution curve of the cold and hot logistics in the plate-fin heat exchanger were obtained.According to the optimized simulation to get the process of power consumption,calculated the process than the power consumption and the exergy efficiency.The adaptability of three DMR processes to natural gas pressure and component changes was studied.Secondary throttle DMR liquefaction process than power range is 268.2 kw/t³31.5 kw/t,the exergy efficiency changes in the range of 42.01%⁴3.83%;Level 3 throttling DMR liquefaction process than power range is 263.7 kw/t³17.3 kw/t,the exergy efficiency changes in the range of 44.16%⁴5.51%;Level 4 throttling DMR liquefaction process than power range is 250.6 kw/t³03.5 kw/t,the exergy efficiency changes in the range of 46.63%t⁴7.57%.Simulation results show that for the same three DMR process of natural gas inlet conditions,with the increase of mixed refrigerant cycle throttling series,the average heat transfer temperature difference in plate-fin heat exchanger is reduced,so the heat exchange process of the exergy loss,improve the energy efficiency of the process,reduces the process than the total energy consumption and power consumption.When three DMR process in natural gas component is constant,as the rise of the gas pressure,the process than the total power consumption and power consumption are decreased,the exergy efficiency.When three DMR process in natural gas pressure is constant,as the rise of the CH₄ content in natural gas,the decrease in the total process power consumption than the rise in power consumption,the exergy efficiency.In conclusion,by adjusting the circulation amount and proportion of precooled mixed refrigerant and cryogenic mixed refrigerant,three DMR processes can be guaranteed to operate with low energy consumption under high liquefaction rate.Therefore,the DMR process has good adaptability.