Optimization Study Of Operation Parameters Propane Pre-cooling Natural Gas Liquefaction Process And Layer Pattern Of Plate-fin Heat

Natural gas,with its advantages of clean,safe and high calorific value,has become a green and clean energy source of great concern in the 21st century.Natural gas liquefaction industry is the basis of natural gas transportation and storage.China's natural gas liquefaction industry started late,and there is still a big gap of natural gas liquefaction technology with developed countries.By optimizing the process of natural gas liquefaction,the investment cost of natural gas liquefaction plant can be reduced,the production efficiency can be improved,and the development of natural gas liquefaction industry in China can be promoted.This paper simulates and optimizes the process parameters include low pressure refrigerant's pressure and high pressure refrigerant's pressure,the composition ratio of mixed refrigerant and the layer pattern of plate-fin heat exchanger,and analyses the influence of various parameters on the process of C3/MRC process.Aspen HYSYS software was used to simulate the liquefaction process of 1 million Nm3/d with propane precooled mixed refrigerant,and the influence of the process parameters on the process power consumption was analyzed.The gas-liquid content of the mixed refrigerant at the three heat exchanger inlets in the mixed refrigerant cycle was obtained.The function of each component in the mixed refrigerant was analyzed.The flow rate of the mixed refrigerant at the three heat exchanger inlets was simulated when the composition of the mixed refrigerant changed.The flow rate of low-pressure refrigerant in the first heat exchanger is the total flow rate of mixed refrigerant,which is not affected by component content;the flow rate of low-pressure refrigerant in the second heat exchanger increases with the increase of CH4 and N2 content in mixed refrigerant,and decreases with the increase of C3H8 and C2H4 content;the flow rate of low-pressure refrigerant in the third heat exchanger increases with the increase of N2 content and decreases with the increase of C3H8 and C2H4 content.By using the optimizer,the process was optimized with the minimum power consumption as the objective function and the process parameters and refrigerant ratio as variables.The matching of the heat and cold fluid composite curve was better,heat exchanger was improved,the logarithmic mean temperature difference of the heat exchanger was reduced,and the process power consumption was reduced by 4.24%.By analyzing the gas phase mass fraction and heat load distribution in heat exchanger,the influence of refrigerant ratio on the composite curve of heat and cold fluids in heat exchanger was obtained.The obtained process parameters and the influence of refrigerant ratio on the process can be used as a reference for the optimization of natural gas liquefaction process in engineering practice.Aspen EDR software was used to simulate the deep-cooling heat exchanger in the mixed refrigerant cycle.The influence of the fluid flow-maldistribution on the liquefaction rate of natural gas was obtained.The characteristics of the difference between the layers of the heat exchanger and the flow direction along the heat exchanger were analyzed.Taking heat load and zigzag diagram of heat exchanger as evaluation indexes,the layer pattern scheme of heat exchanger is evaluated.It is found that the performance of heat exchanger using single-stack layer pattern scheme conforming to periodicity and symmetry is better.Then comparing the layer pattern schemes considering the flow-maldistribution,it is found that the gas passage in heat exchanger is arranged in the middle of the heat exchanger,and the high-pressure refrigerant passage in the edge of the heat'exchanger can improve the liquefaction rate of natural gas.