Patent ID: 7127914

Claim:
A method for gas liquefaction comprising: (a) cooling a feed gas in a first heat exchange zone by indirect heat exchange with one or more refrigerant streams provided in a first refrigeration system, and withdrawing a substantially liquefied stream from the first heat exchange zone; (b) further cooling the substantially liquefied stream in a second heat exchange zone by indirect heat exchange with one or more work-expanded refrigerant streams provided by a second refrigeration system and withdrawing a further cooled, substantially liquefied stream from the second heat exchange zone; and (c) work expanding two or more cooled compressed refrigerant streams in the second refrigeration system to provide at least one of the one or more work-expanded refrigerant streams in the second heat exchange zone, wherein the operation of the second refrigeration system includes the steps of (1) compressing one or more refrigerant gases to provide a compressed refrigerant stream; (2) cooling all or a portion of the compressed refrigerant stream in a third heat exchange zone to provide a cooled, compressed refrigerant stream; and (3) work expanding the cooled, compressed refrigerant stream to provide one of the one or more work-expanded refrigerant streams; wherein the flow rate of a work-expanded refrigerant stream in the second heat exchange zone is less than the total flow rate of one or more work-expanded refrigerant streams in the third heat exchange zone.