The Numerical Simulation Of Natural Gas Liquefaction Process With Precooling Transcritical Carbon Dioxide Cycle

The transcritical carbon dioxide refrigeration cycle is used instead of the propane refrigeration cycle to make the natural gas liquefaction process pre-cooled in this article.The physical properties of the gas components have to be considered and the physical parameters of the relevant components are collected in this article.At the same time,the PR equation is used to calculate the phase equilibrium in the natural gas liquefaction process,and the LKP equation is used to calculate the enthalpy and entropy of the natural gas.In order to calculate the thermodynamic properties of carbon dioxide in subcritical and supercritical states more accurately,the thermodynamic properties of carbon dioxide were calculated by PR equation of state,Tong Jingshan equation,Martin-Hou state equation and Exp-RK equation.The results show that the four equations are all suitable,and the accuracy of the PR equation in the process of calculating the thermodynamic properties of the carbon dioxide in the supercritical state is also feasible.Considering the simple and easy to solve the problem,this article determines using the PR state equation to calculate the thermodynamic properties of carbon dioxide in transcritical states.Two kinds of transcritical carbon dioxide cycle which used to pre-cooled natural gas liquefaction processes are established by two kinds of transcritical carbon dioxide single-stage compression refrigeration cycle and transcritical carbon dioxide single-stage compression expander cycle with regenerator in this paper.And the numerical simulation of the liquefaction process is carried out with natural gas extracted from Tarim.The simulation results show that the specific power consumption of the pre-cooled natural gas liquefaction process with the subcritical carbon dioxide single stage compression refrigeration cycle with regenerator 1.8141/(kW*h/kg);the specific power consumption of the recirculating natural gas liquefaction process of the transcritical carbon dioxide single-stage compression expander with regenerator 1.2976/(kW*h/kg).The latter is less energy-consuming than the former 39.80%.But the power consumption is still higher than the propane pre-cooling natural gas liquefaction process.This study shows that transcritical carbon dioxide cycles can be used as a pre-cooling method in natural gas liquefaction processes.Although the energy consumption of the two transcritical carbon dioxide refrigeration cycles studied are higher than the propane cycle,the character that carbon dioxide does not burn eliminates the potential risk of propane flammability;and the use of carbon dioxide as a working mass provides a means for the capture of carbon dioxide.It have a certain practical significance which for safe production and reduce carbon emissions.