Patent ID: 6269655
Filing Date: 2001-08-07
Classification: F25J,Y02C

Abstract:
A method for liquefying a pressurized feed gas which comprises:(a) cooling the pressurized feed gas by indirect heat exchange in a first heat exchange zone with a first vaporizing mixed refrigerant which is vaporized at a first essentially constant pressure to yield a cooled feed gas and a first mixed refrigerant vapor;(b) further cooling and condensing the cooled feed gas by indirect heat exchange in a second heat exchange zone with a second vaporizing mixed refrigerant which is vaporized at a second essentially constant pressure to yield a liquid product and a second mixed refrigerant vapor;(c) compressing the first mixed refrigerant vapor; and cooling, condensing and flashing the resulting compressed first mixed refrigerant vapor to provide the first vaporizing mixed refrigerant; and(d) compressing the second mixed refrigerant vapor; and cooling condensing and flashing the resulting compressed second mixed refrigerant vapor to provide the second vaporizing mixed refrigerant, wherein at least a portion of the refrigeration for the cooling and condensing of the second mixed refrigerant vapor is provided by indirect heat exchange in the first heat exchange zone with the first vaporizing liquid mixed refrigerant;wherein the compressing of the first mixed refrigerant vapor in (c) is carried out 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 vapor and an interstage refrigerant liquid; the interstage refrigerant vapor is compressed to yield a further compressed refrigerant which is cooled, condensed, optionally subcooled, and flashed to provide the first vaporizing mixed refrigerant in (a); and the interstage liquid refrigerant is subcooled and flashed at the first essentially constant pressure to yield additional refrigeration in the first heat exchange zone.