Patent ID: 6347531
Filing Date: 2002-02-19
Classification: F25J

Abstract:
A method for gas liquefaction which comprises:(a) cooling an essentially water-free feed gas by indirect heat exchange with one or more vaporizing liquid mixed refrigerant streams in a first cooling zone, wherein at least one of the liquid mixed refrigerant streams in the first cooling zone is vaporized at a first pressure level, and withdrawing from the first cooling zone an intermediate cooled feed gas and a first vaporized mixed refrigerant; (b) further cooling the intermediate cooled feed gas by indirect heat exchange with one or more vaporizing liquid mixed refrigerant streams in a second cooling zone, wherein at least one of the liquid mixed refrigerant streams in the second cooling zone is vaporized at a second pressure level, and withdrawing from the second cooling zone a liquefied gas and a second vaporized mixed refrigerant; and (c) compressing and cooling the first vaporized mixed refrigerant and the second vaporized mixed refrigerant to yield one or more liquid mixed refrigerant streams, wherein the cooling is ambient cooling effected by heat transfer to an ambient heat sink; wherein the one or more vaporizing liquid mixed refrigerant streams utilized to cool the feed gas in the first cooling zone of (a) are derived solely from the one or more liquid mixed refrigerant streams of (c), and wherein the vaporizing liquid mixed refrigerant streams in the first and second cooling zones are provided in a recirculating refrigeration process which includes the steps of:(1) compressing the second vaporized mixed refrigerant to a first pressure level to yield a pressurized second mixed refrigerant; (2) combining the pressurized second mixed refrigerant with the first vaporized mixed refrigerant and compressing the resulting combined refrigerant stream to yield a compressed mixed refrigerant stream; (3) cooling and partially condensing the compressed mixed refrigerant stream by ambient cooling to yield a mixed refrigerant vapor and a mixed refrigerant liquid; (4) subcooling and reducing the pressure of the mixed refrigerant liquid to provide a vaporizing liquid mixed refrigerant stream in the first cooling zone at the first pressure level; and (5) cooling, at least partially condensing, and reducing the pressure of the mixed refrigerant vapor to provide a vaporizing liquid mixed refrigerant which is vaporized in the second cooling zone at a second pressure level; wherein the compression of the combined refrigerant stream in (2) is effected in multiple stages of compression, and wherein an interstage vapor refrigerant stream is cooled and partially condensed by ambient cooling to yield an additional mixed refrigerant liquid.