Liquefaction of natural gas employing multiple-component refrigerants

Claim 1

A method of liquefying and subcooling a methane-rich stream comprising: a. compressing said methane-rich stream to a first pressure and passing said stream through a first heat exchange zone, b. expanding said stream to a lower pressure after passage through said first heat exchange zone, c. passing said expanded stream through a second heat exchange zone, d. compressing a multicomponent refrigerant comprising a plurality of components having different boiling points, e. partially condensing said multicomponent refrigerant to form a first vapor fraction and a first liquid fraction, expanding said first liqUid fraction and passing some of said expanded first liquid fraction in countercurrent heat exchange with said multicomponent refrigerant undergoing partial condensation, f. passing another portion of said expanded first liquid fraction through said first heat exchange zone to condense said methane-rich stream, g. partially condensing said first vapor fraction to form a second liquid fraction, expanding said second liquid fraction and passing some of said expanded second liquid fraction in countercurrent heat exchange with said first vapor fraction undergoing partial condensation, and h. passing another portion of said second expanded liquid fraction through said second heat exchange zone to subcool said condensed methane-rich stream.

Claim 2

A system for liquefying a methane-rich stream comprising: a. means forming an elongated, vertically extending heat exchanger having a warm end and a cold end, b. first fluid passage means extending through said exchanger from said warm end to said cold end, c. first compressor means for compressing said methane-rich stream and passing said stream through said first fluid passage means from said warm end to said cold end, d. second compressor means for compressing a multicomponent refrigerant comprising a plurality of components having different boiling points, e. a series of phase separators, each of said separators having an inlet, a liquid fraction outlet and a vapor fraction outlet, f. passage means connecting said second compressor means to the first separator of said series, g. a series of refrigerant passage means located in said exchanger and positioned along the vertical length thereof, h. passage means connecting said vapor fraction outlet of each separator to one of said refrigerant passage means, i. passage means connecting each of said refrigerant passage means to the inlet of the next separator for progressive partial condensation of said multicomponent refrigerant to form a plurality of liquid refrigerant fractions, j. means for spraying each of said liquid refrigerant fractions in countercurrent heat exchange with said first fluid passage means for progressively vaporizing each liquid fraction and liquefying said methane-rich stream, and k. closed cycle passage means for collecting all of said vaporized liquid fractions at the warm end of said exchanger and returning them to said second compressor means.

Claim 3

A system for liquefying a feed stream composed primarily of methane comprising: a. first compressor means for compressing a multicomponent refrigerant comprising a plurality of components having different boiling points, b. a plurality of heat exchange means and phase separator means connected in series for progressively condensing and separating said compressed multicomponent refrigerant into a plurality of liquid condensates of decreasing temperatures, c. expansion means for expanding each of said liquid condensates, d. multistage heat exchanger means for passing each of said expanded liquid condensates in countercurrent heat exchange with said feed stream at progressively lower temperature stages for liquefying said feed stream, said multistage heat exchanger means including a final lowest temperature stage, at least said lowest temperature stage comprising a vertically extending coil through which said feed stream is passed upwardly, and means for spraying said lowest temperature liquid condensate downwardly over said coil.

Claim 4

A method of liquefying a compressed natural gas stream comprising the steps of: a. precooling and partially condensing said compressed natural gas stream to form a first liquid fraction and a first vapor fraction, b. separating said vapor and liquid fractions, c. passing said first vapor fraction through a confined passageway of a heat exchange zone from the warm end thereof to the cold end thereof, d. passing said first liquid fraction through independent fraCtionation means to fractionate said liquid into a plurality of substantially pure hydrocarbon components, e. combining selected amounts of each of said plurality of hydrocarbon components to maintain a multicomponent refrigerant of selected composition, f. maintaining independently of said natural gas stream and said fractionation means a separate source of a nonhydrocarbon component having a boiling point substantially below that of methane, g. introducing selected amounts of said nonhydrocarbon component from said separate source into said multicomponent refrigerant so as to substantially reduce the boiling point of said multicomponent refrigerant, h. forming a series of multicomponent liquids fractions of said multicomponent refrigerant at progressively lower temperatures by successive partial liquefaction of said multicomponent refrigerant in heat exchange with expanded liquid fractions thereof in closed cycle passage means, the lowest temperature multicomponent liquid fraction so formed being rich in said nonhydrocarbon component having a boiling point substantially below methane, i. introducing said multicomponent liquid fractions, including said lowest temperature liquid fraction, into said heat exchange zone at a plurality of locations intermediate said warm and cold ends thereof and flowing each of said multicomponent liquid fractions in countercurrent heat exchange with said first vapor fraction in said confined passageway, j. progressively vaporizing each of said multicomponent liquid fractions in countercurrent heat exchange with said first vapor fraction so as to liquefy said first vapor fraction, k. withdrawing all of said vaporized multicomponent fractions from said heat exchange zone, and l. recombining all of said withdrawn vaporized multicomponent fractions to reconstitute the major portion of said multicomponent refrigerant.