Study On Liquefaction Process Of Coal - Based Natural Gas

Coal-based natural gas, a synthesis gas, is made up of coal through gasification, purification, methanation and so forth. Compared with direct combustion, the conversion of coal to coal-based natural gas can increase the use efficiency of coal to relief environmental pollution. Generally speaking, coal-based natural gas factories are located in less-development areas where the incomplete pipeline network will cause difficulties in gas transportation. However, the liquefaction of coal-based natural gas before delivery to customers is a simple and convenient method to solve this problem. Therefore, the study on liquefaction technique of coal-based natural gas is significant. This paper will conduct simulation study on the liquefaction of natural gas according to the properties of the coal-based natural gas made by a coal-based natural gas factory.This paper discusses the liquefaction process for the coal-based natural gas processing flow by Aspen Hysys. According to the analysis result, C3/MRC liquefaction technique is better than cascaded liquefaction technique in refrigerant flow, performance per Watt, movement dynamic equipment numbers, but it still need further optimization because there is areas with big temperature differences in its heat transfer curve and some hydrogen components in its LNG products.Thus, relative optimization is conducted to solve the problems above. In the propane pre-refrigeration process after optimization, the propane compressor uses three stage inspiration and three stage compression" structure and adds a low temperature distillation tower in the process. The research analyzes mixing refrigerant components and pressure, temperature distribution of cooling boxes in pre-cooling section, temperature distribution of cooling boxes in cryogenic section and the throttling pressure of coal-based natural gas and compares the performance per Watt, refrigerant dosage, liquefaction ratio and heat transfer curve. After analyzing the main operating parameters, this paper optimizes the main operating parameters in optimized N2-CH4swelling and liquefaction process by using performance per Watt as objective function:the refrigerated containers’ temperature of Ti, T2, T3, T4, T5are-5℃,-15℃,-35℃,-110℃,-160℃, components of mixing refrigerants are N2:CH4:C2H4:C3H8=0.3820:0.4132:0.1609:0.0439, throttling pressure of coal-based natural gas is200kPa, and the performance per Watt is0.34kW·h/kg LNG. Compared with the original process, the performance per Watt is reduced by29%without hydrogen components. Under the optimal parameters, this paper studies the influence of the fluctuation of coal-based natural gas components on the heat transfer temperature difference, power dissipation, liquefaction ratio and so forth. As the study shows, the fluctuation of coal-based natural gas would increase the power dissipation, and the liquefaction ratio would increase as the hydrogen components decreasing, particularly, over6.5%hydrogen components would cause the invalidation of the process.At last, this paper analyzes the exergy consumption in optimized liquefaction process, conducting selective calculation of main equipment and preliminarily economic evaluation in the whole process.