IMPROVED CASCADE REFRIGERATION PROCESS FOR LIQUEFACTION OF NATURAL GAS

摘要

This invention relates to a process for liquefying a pressurized gas stream rich in methane in which the liquefication of the gas stream occurs in a heat exchanger being cooled by a cascade refrigeration system to produce a methane-rich liquid product having a temperature above about -112 DEG C. (-170 DEG F.). In this process, a pressurized gas stream is introduced into heat exchange contact with a first refrigerant cycle comprising at least one refrigeration stage whereby the temperature of the gas stream is reduced by heat exchange with a first portion of a first refrigerant to produce a cooled gas stream. The cooled gas stream is then introduced into heat exchange contact with a second refrigerant cycle comprising at least one refrigeration stage whereby the temperature of the cooled gas stream is further reduced by heat exchange with a second refrigerant to produce a liquefied methane-rich stream having a temperature above about -112 DEG C. (-170 DEG F.) and a pressure sufficient for the liquefied stream to be at or below its bubble point.