Patent ID: 6484533
Filing Date: 2002-11-26
Classification: F04D,F25J

Abstract:
A method of liquefying a gas to produce a liquid cryogen comprising:compressing a gas stream comprising a recycle gas stream in a compressor to provide at least one compressed gas stream; cooling at least a portion of said compressed gas stream to a first temperature; work expanding said cooled compressed gas stream in a â€œwarmâ€  expansion turbine to provide a first expanded gas stream, said warm expansion turbine being mechanically linked to the compressor to provide a portion of the mechanical power required to drive the compressor; cooling a compressed gas stream, selected from a remaining portion of said compressed gas stream and said first expanded gas stream, to a second temperature below said first temperature to provide a further cooled compressed gas stream; work expanding said further cooled compressed gas stream in a â€œcoldâ€  expansion turbine to provide a second expanded gas stream, said cold expansion turbine being mechanically linked to the compressor to provide a further portion of the mechanical power required to drive the compressor; cooling and at least partially condensing the gas to be liquefied by heat exchange with an expanded gas stream, selected from said first and second expanded gas streams, providing refrigeration duty for said cooling and condensation thereby producing a heat-exchanged expanded gas stream; and recycling said heat-exchanged expanded gas stream to the compressor.