Patent ID: 7308805

Claim:
A method for liquefying a gas ( 1 ) which comprises cooling a feed gas stream successively through at least two heat exchange zones ( 310 , 311 , 312 ; 353 ) at respective temperature ranges to provide a liquefied product ( 13 ), wherein refrigeration for cooling the feed gas stream in the temperature ranges is provided by respective vaporizing refrigerants ( 117 , 213 , 315 ), wherein the refrigerant ( 315 ) in the coldest temperature range is only partially vaporized in the coldest heat exchange zone ( 312 ) to form a partially vaporized refrigerant ( 316 ), and wherein the refrigerant is recirculated in a recirculating refrigeration process that comprises further vaporizing the partially vaporized refrigerant ( 316 ) in a further heat exchange zone ( 317 , 355 ) at temperatures above the highest temperature of the coldest heat exchange zone ( 312 ) to form a totally vaporized refrigerant ( 318 , 348 ), compressing ( 319 , 324 ; 349 ) the totally vaporized refrigerant ( 318 , 348 ) to yield a compressed refrigerant stream, and cooling the compressed refrigerant stream to provide a coldest refrigerant ( 315 ), characterized in that the entire compressed refrigerant stream is cooled by either (i) cooling the entire compressed refrigerant stream ( 328 ) in the further heat exchange zone ( 317 ) by indirect heat exchange with the further vaporizing partially vaporized refrigerant ( 316 ) to provide a cooled refrigerant stream ( 329 ), thereby providing self-refrigeration for the recirculating refrigeration process, and then by further cooling ( 312 ) the cooled refrigerant stream ( 329 ) to provide the coldest refrigerant ( 315 ), or (ii) cooling the entire compressed refrigerant stream ( 351 ) in a heat exchange zone ( 353 ) preceding the coldest heat exchange zone ( 312 ) by indirect heat exchange ( 352 ) with a respective vaporizing refrigerant ( 117 ), further cooling the refrigerant in the further heat exchange zone ( 355 ) by indirect heat exchange with the partially vaporized refrigerant ( 316 ) to provide a cooled refrigerant stream ( 329 ), and then further cooling ( 312 ) the cooled refrigerant stream ( 329 ) to provide the coldest refrigerant ( 315 ).