IMPROVED CASCADE REFRIGERATION PROCESS FOR LIQUEFACTION OF NATURAL GAS

摘要

This invention relates to a process for liquefying a pressurized gas stream (10) rich in methane with a heat exchanger being cooled by a cascade refrigeration system to produce a methane-rich liquid product (20) having a temperature above about -112 °C (-170 °F). In this process, a pressurized gas stream (10) is introduced into heat exchange contact with a first refrigerant cycle (32) comprising at least one refrigeration stage (30-31), whereby the gas stream is cooled against 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 (33), comprising at least one refrigeration stage (37-39), whereby the temperature of the cooled gas stream is cooled to produce a liquefied methane-rich stream (20) having a temperature above about -112 °C (-170 °F) and a pressure sufficient for the liquefied stream to be at or below its bubble point.