Natural Gas Liquefaction by a High Pressure Expansion Process

A system for liquefying a feed gas stream rich in methane, the feed gas stream having a pressure of less than 1,200 psia, the system including a first heat exchanger zone and a second heat exchanger zone, the system comprising:

• a refrigerant stream having a pressure near the same pressure of the feed gas stream;
• a compressor that compresses the combined refrigerant stream and feed gas stream to a pressure of at least 1,500 psia, thereby forming a compressed second gas stream;
• a cooler that cools the compressed second gas stream by indirect heat exchange with ambient temperature air or water, to thereby form a compressed, cooled second gas stream;
• wherein the compressed, cooled second gas stream is directed to the second heat exchanger zone, to additionally cool the compressed, cooled second gas stream below ambient temperature, thereby producing a compressed, additionally cooled second gas stream;
• at least one work producing expander that expands the compressed, additionally cooled second gas stream to a pressure that is less than 2,000 psia and no greater than the pressure to which the second gas stream was compressed, to thereby form an expanded, cooled second gas stream;
• wherein the expanded, cooled second gas stream is separated into a first expanded refrigerant stream and a chilled gas stream;
• an additional at least one work producing expander that expands the first expanded refrigerant stream, thereby producing a second expanded refrigerant stream;
• wherein the second expanded refrigerant stream is passed through the first heat exchanger zone to form a first warm refrigerant stream such that the first warm refrigerant stream has a temperature that is cooler, by at least 5° F., than the highest fluid temperature within the first heat exchanger zone;
• wherein the chilled gas stream is passed through the first heat exchanger zone to cool at least part of the chilled gas stream by indirect heat exchange with the second expanded refrigerant stream, thereby forming a liquefied gas stream;
• wherein the first warm refrigerant stream is directed to the second heat exchanger zone to cool by indirect heat exchange the compressed, cooled second gas stream, thereby forming a second warm refrigerant stream;
• and
• an additional compressor that compresses the second warm refrigerant stream to produce the refrigerant stream.