Study On The Performance Of A LNG Production System Using Gas Pressure Energy In Long-distance Transport

The long-distance transport of natural gas must be decompressed by city gas gate station and district regulation station before entering the city gas pipeline network.In the conventional pressure process of the high-pressure natural gas system,throttling valve is usually used to decrease the pressure and temperature of high pressure refrigerant.This type could leads to a lot of wasted energy.In order to effectively recycle the pressure of high-pressure natural gas,the author proposes a system process flow of recovery pressure energy to produce LNG using turbine expansion agent.In this process of the system,high quality cold energy could also be well recycled,which used in the production of LNG.Pressure energy and cold energy are analyzed in the process of the expansion and decompression,according the basic principle of thermodynamics.The energy loss and energy efficiency are analysis of the main equipment according concrete engineering cases.In 6MPa gas inlet pressurek,outlet pressure is 0.4MPa,gas flow rate is 0.15kg/s condition,the energy loss of throttle valves is 412.5k W,the energy loss of turbo-expander is 265.4k W.The energy loss of throttle valves is higher than the turbo-expander.Using Aspen software system established the calculation model of LNG production technology,the parameters such as liquefied rate,energy efficiency are analyzed.The conclusions are: the method of supercharged liquefying system of before expansion is proposed using in the process of greater than 3.5MPa natural gas import pressure,and the method of after expansion using in the below 3.5MPa natural gas import pressure.Better energy efficiency is got using the correct methods.The method of supercharged liquefying system of after expansion is used according the status quo of the parameters of long distance natural gas in the station of Litun regulator station in Luoyang city of the second west-east gas pipeline project II.After the optimization of production LNG system,the temperature and pressure of liquefied natural gas temperature is-139? and 0.44 MPa,respectively.The liquefying capacity of LNG system is 13.4×104Nm3/d,the liquefying rate reached 12.2% and exergy loss is 5275.68 k W.