Patent GB-1125182-A (GB)
Title: Improvements in or relating to the liquefaction of gaseous mixtures
IPC: F25J1/00
Filed: 1965-09-17
Abstract: 1,125,182. Cold separation of gas mixtures. L'AIR LIQUIDE SOC. ANON. POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE. 17 Sept., 1965 [18 Sept., 1964], No. 39872/65. Divided out of 1,012,443. Heading F4P. In the cold separation of a first gas mixture, e.g. compressed natural gas containing methane, ethane, propane, butane and nitrogen, to yield a liquid product containing at least one component, e.g. a mixture of methane and propane, wherein the first gas mixture at 50 ats. pressure admitted through a line is condensed in steps in indirect heat exchangers 10-13 and associated liquid separators 25, 33 from which latter liquid is fed through a line 34, a supercooler 15, a line 35 and an expansion valve 38 to a de gassing column 16 at 7 ats. pressure to which is also fed gas from separator 33 after being condensed in a heat exchanger 14 of the reflux type and expanded at a valve 43, cooling of exchangers 10-14 is effected by counter-current flow of a second gas mixture comprising a low pressure recycle gas mixture derived in part from the head of column 16 through a line 64, in part by expanding at a valve 36 a portion of supercooled feed liquid leaving exchanger 15 and in part by condensed incoming high pressure mixture withdrawn from separator 25 and expanded at a valve 28, and the so-formed low pressure recycle gas mixture having cooled exchangers 14, 13 is combined at the cold ends of exchangers 12, 11 with liquid having been condensed from the recycle gas having left the warm end of exchanger 10 through a line 128, recompressed to 30 ats. at 70 to provide a high pressure recycle gas which is re-cooled in exchangers 10-12 co-currently with feed mixture, separated at 106, 112 and expanded in valves 114, 108; uncondensed high pressure recycle gas withdrawn from separator 112 being cooled in exchanger 12 and added to the feed mixture after expansion of the latter at a valve 23 to 30 ats. The compressor 70 discharges into a water cooler 72 and a separator 75, and heavy hydrocarbon liquid withdrawn through a line 76 and cooled in exchanger 10 is in part expanded at a valve 78 to 15 ats. into a column 82 and is in part expanded at a valve 83 to 7 ats. and fed through a line 89 to the low pressure re-cycle gas at the cold end of exchanger 10 where it is joined by effluent withdrawn from column 82 and expanded to 7 ats. at a valve 88. Liquid propane and butane withdrawn from column 82 is expanded to 12 ats. at a valve 91 and is separated in a column 92 into liquid butane which is expanded at a valve 100 and added to the low pressure recycle gas at the cold end of exchanger 10 and into liquid propane which is withdrawn through a line 93, cooled in exchangers 86, 57 expanded to 7 ats. at a valve 95 and added to liquid methane withdrawn from the base of column 16, and the methane-propane mixture having been cooled in an exchanger 52 is expanded to atmospheric pressure and fed as product to a storage container. The boiling coil 46 of column 16 is heated by a portion of uncondensed nitrogenrich methane gas withdrawn from exchanger 14 through lines 43, 45 and the resulting condensed mixture is under-cooled in exchanger 48, a portion is expanded at a valve 50 to 7 ats. and fed through a line 4 to be added to the effluent in line 64, whilst the remainder in a line 51 is cooled in exchanger 52 expanded to 1 at. pressure at a valve 54, re-heated in said exchanger 52, and added to the mixture of gases in line 43 after expansion of the latter to 1 at. at a valve 44. The combined gases are then warmed in exchangers 58, 86 and fed through a line 59 to serve as fuel gas.