Research On Production Of LNG By Pressure Of Natural Gas Pipeline Network

With the gas pipeline network developing to the high pressure transmission, there is huge available pressure energy in the gas-distributing station of the long-distance pipeline of natural gas. Therefore, the recovery of the pressure of natural gas pipeline network has been gradually attracted people’s attention. Meanwhile, the liquefied natural gas which is a clean energy resource will be the main force of the natural gas market. Synthetically, the recycling natural gas pipe network pressure to liquefy the natural gas will have the great significance for energy-saving and emission-reducing and improving the economic benefits of the long-distance pipeline of natural gas.First of all, based on "the choice of the liquefaction process using differential pressure in the gas-distributing station of the long-distance pipeline of natural gas", the author establishes the mathematical models about the steady-state simulation of pressure liquefaction processes by the theory of simultaneously modular method and does simulation under the guidance of those models. Secondly, the author sets up the maximum annual total profit of the liquefaction process as the objective function to choose the optimal process. In order to further ptimization to achieve higher economic performance, the author chooses the compressor stages of refrigerant cycle of the optimal pressure liquefaction process used in the gas-distributing station of natural gas. At the last, the author establishes the optimization model of refrigerant cycle which the minimize energy consumption is an objective function to optimize the following parameters:the compositions and ratio of pre-cold refrigerant; pre-cooling temperature; high pressure and low pressure of refrigerant cycle.The processes of recovering pressure energy of the gas-distributing station to liquefy the natural gas involve the following three categories:the one of only utilizing gas pressure energy; the one with refrigerant cycle before the expander; the one with refrigerant cycle after the expander. The natural gas liquefaction rate of the former process is up to about18%. The latter two processes have improved the liquefaction rate on the basis of the refrigeration cycle, but have the power consumption in liquefaction system. Based on the maximum economic benefits of the gas-distributing station, the natural gas liquefaction process with refrigerant cycle before the expander is optimal pressure liquefaction process.Meanwhile, to improve economic benefits of producing LNG by recovery of pressure energy of the gas-distributing station, the structure pre-cooling cycle in the natural gas liquefaction process with refrigerant cycle before the expander was three-stage compression. The pre-cooling refrigerant is mixture, and the best compositions are C2H6, C3H8, i-C4H10,. Moreover, pre-cooling temperature should not be too low.