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Method for liquefying a gas which comprises cooling a feed gas stream successively through first and second temperature ranges to provide a liquefied product, wherein refrigeration for cooling the feed gas stream in the first temperature range is provided by a first vaporizing refrigerant and refrig

Method for liquefying a gas which comprises cooling a feed gas stream successively through first and second temperature ranges to provide a liquefied product, wherein refrigeration for cooling the feed gas stream in the first temperature range is provided by a first vaporizing refrigerant and refrigeration for cooling the stream in the second temperature range is provided by a second vaporizing refrigerant, and further wherein the second vaporizing refrigerant provides additional refrigeration by vaporization at temperatures above a lowest temperature in the first temperature range.

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1. A method for liquefying a gas which comprises cooling a feed gas stream successively through first and second temperature ranges to provide a liquefied product, wherein refrigeration for cooling the feed gas stream in the first temperature range is provided by a first vaporizing refrigerant and r

1. A method for liquefying a gas which comprises cooling a feed gas stream successively through first and second temperature ranges to provide a liquefied product, wherein refrigeration for cooling the feed gas stream in the first temperature range is provided by a first vaporizing refrigerant and refrigeration for cooling the stream in the second temperature range is provided by a second vaporizing refrigerant, and further wherein the second vaporizing refrigerant provides additional refrigeration by vaporization at temperatures above a lowest temperature in the first temperature range. 2. A method for liquefying a gas which comprises cooling a feed gas stream ( 1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream in the first temperature range is provided by a first vaporizing refrigerant (117), refrigeration for cooling the stream in the second temperature range is provided by a second vaporizing refrigerant (213), and refrigeration for cooling the stream in the third temperature range is provided by a third vaporizing refrigerant (315), and further wherein the third vaporizing refrigerant provides additional refrigeration by vaporization (317) at temperatures above a lowest temperature in the second temperature range.3. The method of claim 2 wherein the first refrigerant (117) is a single component refrigerant.4. The method of claim 2 wherein the second (213) and third (315) refrigerants are multi-component refrigerants.5. The method of claim 2 wherein the first temperature range is between 35 and −70° C., the second temperature range is between 0 and −140° C., and the third temperature range is between −90 and −165° C.6. The method of claim 2 wherein the feed gas stream (1) is natural gas.7. The method of claim 2 wherein the cooling of the feed gas stream (1) is effected by: (a) cooling the feed gas stream ( 1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101); (b) further cooling the partially cooled feed stream ( 5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and (c) further cooling the second partially cooled feed stream ( 9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316).8. The method of claim 7 wherein the third refrigerant (315) is a multi-component mixture comprising two or more components selected from the group consisting of nitrogen and hydrocarbons having from one to five carbon atoms.9. A method for liquefying a gas which comprises cooling a feed gas stream ( 1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by: (a) cooling the feed gas stream ( 1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101); (b) further cooling the partially cooled feed stream ( 5) in the second temperature range by ind irect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and (c) further cooling the second partially cooled feed stream ( 9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two phase refrigerant stream (316); wherein the third refrigerant ( 315) is a multi-component mixture comprising two or more components selected from the group consisting of nitrogen and hydrocarbons having from one to five carbon atoms and comprises (in mole %) 5-15% nitrogen, 30-60% methane, 10-30% ethane, 0-10% propane, and 5-15% i-pentane.10. The method of claim 8 wherein the third refrigerant comprises i-pentane and one or more hydrocarbons having four carbon atoms, wherein the molar ratio of i-pentane to the one or more hydrocarbons having four carbon atoms is greater than one.11. The method of claim 8 wherein the third refrigerant comprises i-pentane and n-pentane and wherein the molar ratio of i-pentane to n-pentane in the third refrigerant is greater than one.12. A method for liquefying a gas which comprises cooling a feed gas stream ( 1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by: (a) cooling the feed gas stream ( 1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101); (b) further cooling the partially cooled feed stream ( 5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and (c) further cooling the second partially cooled feed stream ( 9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316); wherein the third refrigerant ( 315) is a multi-component mixture comprising two or more components selected from the group consisting of nitrogen and hydrocarbons having from one to five carbon atoms, wherein the third refrigerant comprises i-pentane and n-pentane and wherein the molar ratio of i-pentane to i-pentane in the third refrigerant is greater than one, wherein the i-pentane and n-pentane are obtained from the feed gas stream, and wherein the molar ratio of i-pentane to n-pentane in the third refrigerant is greater than the molar ratio of i-pentane to n-pentane in the feed gas stream.13. A method for liquefying a gas which comprises cooling a feed gas stream ( 1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by: (a) cooling the feed gas stream ( 1) in the first temperature range by in direct heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101); (b) further cooling the partially cooled feed stream ( 5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); an (c) further cooling the second partially cooled feed stream ( 9) in the third temperature range by indirect heat exchange with the third refrigerant ( 315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316); wherein the third refrigerant ( 315) is a multi-component mixture comprising two or more components selected from the group consisting of nitrogen and hydrocarbons having from one to five carbon atoms, wherein the third refrigerant comprises i-pentane and one or more hydrocarbons having four carbon atoms, wherein the i-pentane and one or more hydrocarbons having four carbon atoms in the third refrigerant are obtained from the feed gas stream, and wherein the molar ratio of i-pentane to the one or more hydrocarbons having four carbon atoms in the third refrigerant is greater than the molar ratio of i-pentane to one or more hydrocarbons having four carbon atoms in the feed gas stream.14. A method for liquefying a gas which comprises cooling a feed gas stream ( 1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range ,a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by: (a) cooling the feed gas stream ( 1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101); (b) further cooling the partially cooled feed stream ( 5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and (c) further cooling the second partially cooled feed stream ( 9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316); and wherein the third refrigerant ( 315) is provided in a third recirculating refrigeration process that comprises vaporizing the two-phase refrigerant stream (316) in a fourth heat exchange zone (317) at temperatures greater than a lowest temperature in the second temperature range to provide a third refrigerant vapor (318), compressing (319,324) the third refrigerant vapor (318) to yield a compressed third refrigerant stream (328), cooling the compressed third refrigerant stream (328) in the fourth heat exchange zone (317) by indirect heat exchange with the two-phase refrigerant stream (316) to provide a cooled third refrigerant stream (329), and further cooling the cooled third refrigerant (329) stream to provide the third refrigerant (315) in (c).15. The method of claim 14 wherein the further cooling of the cooled third refrigerant stream (329) is effected by indirect heat exchange with the third refrigerant (315) vaporizing in the third heat exchange zone (312).16. The method of claim 14 wherein the compressed third refrigerant stream (328) is provided by compressing the third refrigerant vapor (318) in a first compression stage (319) to provide a first compressed vapor, cooling (320) the first compressed vapor to yield a two-phase stream, separating (321) the two-phase stream into a vapor stream (322) and a liquid stream (323), compressing the vapor stream (322) to yield a further compressed vapor, pumping (325) the liquid stream (323) to provide a pressurized liquid, combining the further compressed vapor and the pressurized liquid to yield a combined refrigerant stream (326), and cooling the combined refrigerant stream (326) to provide the compressed third refrigerant stream (328).17. A method for liquefying a gas which comprises cooling a feed gas stream ( 1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by: (a) cooling the feed gas stream ( 1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101); (b) further cooling the partially cooled feed stream ( 5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and (c) further cooling the second partially cooled feed stream ( 9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316); and wherein the third refrigerant ( 315) is provided in a third recirculating refrigeration process that comprises vaporizing the two-phase refrigerant stream (316) in a fourth heat exchange zone (355) at temperatures greater than a lowest temperature in the second temperature range to provide a third refrigerant vapor (348), compressing (349) and cooling (350) the third refrigerant vapor (348) to yield a compressed third refrigerant stream (351), cooling the compressed third refrigerant stream (351) in the first heat exchange zone (353) by indirect heat exchange (352) with the first vaporizing refrigerant (117) and in the fourth heat exchange zone (355) by indirect heat exchange with the vaporizing two-phase refrigerant stream (316) to provide a cooled third refrigerant stream (329), and further cooling the cooled third refrigerant stream (329) to provide the third refrigerant (315) in (c).18. A method for liquefying a gas which comprises cooling a feed gas stream ( 1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by: (a) cooling the feed gas stream ( 1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101); (b) further cooling the partially cooled feed stream ( 5) in the second tempe rature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and (c) further cooling the second partially cooled feed stream ( 9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316); and wherein the third refrigerant ( 315) is provided in a third recirculating refrigeration process that comprises combining the two-phase refrigerant stream (316) with a cooled reduced-pressure liquid refrigerant stream to provide a combined two-phase refrigerant stream (347), vaporizing the combined refrigerant stream (347) in a fourth heat exchange zone (344) at temperatures greater than a lowest temperature in the second temperature range to provide a third refrigerant vapor (330), compressing (331) and cooling (332) the third refrigerant vapor (330) to provide a partially-condensed third refrigerant, separating (333) the partially-condensed third refrigerant into a refrigerant vapor stream (334) and a refrigerant liquid stream (335), compressing (336) and cooling (337) the refrigerant vapor stream (334) to form a partially-condensed stream and separating (338) the partly-condensed stream into a compressed third refrigerant vapor (339) and a liquid refrigerant (340), reducing the pressure (341) of the liquid refrigerant to provide a reduced-pressure liquid refrigerant (342), combining the reduced-pressure liquid refrigerant (342) with the refrigerant liquid stream (335) to provide a combined refrigerant liquid (343), subcooling the combined refrigerant liquid stream (343) in the fourth heat exchange zone (344) to provide a subcooled liquid refrigerant, combining the subcooled liquid refrigerant and the two-phase refrigerant stream (316) to provide a combined two-phase refrigerant (347), vaporizing the combined two-phase refrigerant (347) in the fourth heat exchange zone (344) to provide refrigeration therein, cooling compressed third refrigerant vapor (339) in the fourth heat exchange zone (344) to provide a cooled third refrigerant stream (329), and further cooling (356) and reducing the pressure (314) of the cooled third refrigerant stream (329) to provide the third refrigerant (315).19. A system for liquefying a gas stream which comprises first ( 310), second (311), and third (312) heat exchange zones for cooling the gas stream successively through first, second, and third temperature ranges, respectively, to provide a liquefied product, a first refrigeration system for providing a first refrigerant in a first refrigerant line (117) to the first heat exchange zone (310), a second refrigeration system for providing a second refrigerant in a second refrigerant line (213) to the second heat exchange zone (311), and a third refrigeration system for providing a third refrigerant in a third refrigerant line (315) to the third heat exchange zone (312), wherein the third refrigeration system comprises piping means (318) to provide a vaporized third refrigerant to compression means for compressing the vaporized third refrigerant, piping means (328) to provide a compressed third refrigerant to a fourth heat exchange zone (317), piping means (329) for providing a cooled compressed third refrigerant from the fourth heat exchange zone (317) to the third heat exchange zone (312), means to further cool (356) the cooled compressed third refrigerant in the third heat exchange zone (312) to provide a condensed third refrigerant, and pressure reduction means (314) to reduce the pressure of the condensed third refrigerant to provide the third refrigerant to the third refrigerant line (315) and the third heat exchange zone (312).20. The system of claim 19 wherein the compression means for compressing the vaporized third refrigerant comprises a firs t stage compressor (319), an intercooler (320) to cool and partially condense a first compressed refrigerant stream to yield a partially condensed first compressed refrigerant stream, a separator (321) to separate the partially condensed first compressed refrigerant stream into a vapor refrigerant stream and a liquid refrigerant stream, a second stage compressor (324) to compress the vapor refrigerant stream to provide a compressed vapor refrigerant stream, a pump (325) to pressurize the liquid refrigerant stream to provide a pressurized liquid refrigerant stream, piping means (326) to combine the compressed vapor refrigerant stream and the pressurized liquid refrigerant stream and provide a combined refrigerant stream to an aftercooler (327) to cool the combined refrigerant stream to provide the compressed third refrigerant.21. The system of claim 19 wherein the fourth heat exchange zone (344) includes means for subcooling a refrigerant liquid to provide a subcooled refrigerant liquid, pressure reduction means (346) for reducing the pressure of the subcooled refrigerant liquid to provide a reduced-pressure refrigerant, piping means (347) for combining the reduced-pressure refrigerant with the further vaporizing third refrigerant from the third heat exchange zone (312) to provide a combined vaporizing refrigerant stream to the fourth heat zone (344), wherein the combined vaporizing refrigerant stream vaporizes in the fourth heat exchange zone (344) to provide the vaporized third refrigerant.22. The system of claim 19 wherein the compression means for compressing the vaporized third refrigerant comprises a first stage compressor (331), an intercooler (332) to cool and partially condense a first compressed refrigerant stream to yield a partially condensed first compressed refrigerant stream, a first separator (333) to separate the partially condensed first compressed refrigerant stream into a first vapor refrigerant stream and a first liquid refrigerant stream, a second stage compressor (336) to compress the vapor refrigerant stream to provide a compressed vapor refrigerant stream, an aftercooler (337) to cool the compressed vapor refrigerant stream to provide a cooled two-phase refrigerant stream, a second separator (338) to provide a second liquid refrigerant stream and the compressed third refrigerant, pressure reduction means (341) to reduce the pressure of the second liquid refrigerant stream to provide a reduced-pressure second liquid refrigerant stream, and piping means (335,342,343) to combine the reduced-pressure second liquid refrigerant stream and the first liquid refrigerant stream to provide the refrigerant liquid to the fourth heat exchange zone (344).23. A system for liquefying a gas stream which comprises first ( 353), second (311), and third (312) heat exchange zones for cooling the gas stream successively through first, second, and third temperature ranges, respectively, to provide a liquefied product, a first refrigeration system for providing a first refrigerant vaporizing in the first heat exchange zone (353), a second refrigeration system for providing a second refrigerant vaporizing in the second heat exchange zone (311), and a third refrigeration system for providing a third refrigerant vaporizing in the third heat exchange zone (312), wherein the third refrigeration system comprises compression means (349) for compressing a vaporized third refrigerant to provide a compressed third refrigerant, cooling means (352) in the first heat exchange zone (353) for cooling the compressed third refrigerant by indirect heat exchange with the first refrigerant vaporizing in the first heat exchange zone (353) to provide a cooled compressed third refrigerant, a fourth heat exchange zone (355) to further cool the cooled compressed third refrigerant by indirect heat exchange with a vaporizing third refrigerant from the third heat exchange zone (312) to provide the vaporized third refrigerant and a further cooled compresse d third refrigerant, means to further cool (356) the cooled compressed third refrigerant in the third heat exchange zone (312) to provide a condensed third refrigerant, and pressure reduction means (314) to reduce the pressure of the condensed third refrigerant to provide the third refrigerant vaporizing in the third heat exchange zone (312).24. A refrigerant comprising i-pentane, one or more hydrocarbons having four carbon atoms, and one or more components selected from the group consisting of nitrogen, methane, ethane, ethylene, propane, and propylene, wherein the molar ratio of i-pentane to the one or more hydrocarbons having four carbon atoms is greater than one. 25. The refrigerant of claim 24 wherein the refrigerant also contains n-pentane and wherein the molar ratio of i-pentane to n-pentane is greater than one.26. A refrigerant comprising i-pentane, one or more hydrocarbons having four carbon atoms, and one or more components selected from the group consisting of nitrogen, methane, ethane, ethylene, propane, and propylene, wherein the molar ratio of i-pentane to the one or more hydrocarbons having four carbon atoms is greater than one, and wherein the refrigerant has a composition comprising (in mole %) 5-15% nitrogen, 30-60% methane, 10-30% ethane, 0-10% propane, and 5-15% i-pentane.