Double-mixed refrigerant circulation is used for gas liquefaction

摘要

A pressurised gas (102), especially natural gas is liquefied using high and low level heat exchangers (104, 122) in each of which is provided by a respective mixed refrigerant (110, 124) which is vaporised at a respective essentially constant pressure. The mixed refrigerant vapour (140) from the high level heat exchanger (404) is compressed in at least two stages of compression which generates an interstage compressed refrigerant. The interstage compressed refrigerant is cooled, partially condensed, and separated into an interstage refrigerant vapour and an interstage refrigerant liquid (144). The interstage refrigerant vapour is compressed to yield a further compressed refrigerant (146) which is cooled, condensed, optionally subcooled, and flashed (450) to provide the first vaporising mixed refrigerant (410) and the interstage liquid refrigerant (144) is subcooled and flashed (468) at the first essentially constant pressure to yield additional refrigeration in the first heat exchange zone (404). The process and apparatus of the invention are especially well-suited for installation on ships (including barges) and offshore platforms. IMAGE