Patent GB-1012443-A (GB)
Title: Improvements in or relating to the liquifaction of one or more constituents of a gaseous mixture
IPC: C07C7/09
Filed: 1962-05-31
Abstract: 1,012,443. Cold separation of gas mixtures. L'AIR LIQUIDE S.A. POUR I'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE. May 31, 1962 [June 1, 1961; Sept. 5, 1961], No. 21107/62. Heading F4P. In the cold separation of a compressed gas mixture, e.g. natural gas containing methane, ethane, propane, butane and nitrogen to yield a liquefied product containing at least one component, e.g. propane and butane, the feed mixture is condensed in steps by cooling in exchangers 10-13 and associated liquid separators 4, 7, 20 and 23, the condensed components are supercooled in an exchanger 26 and coil 27 at the base of a degasification column 15 into which the supercooled condensate is expanded at a valve 28 to 15 kg./cm.<SP>2</SP> and the condensate from separators 4, 7 is expanded at values 85, 88, 91 vaporized in exchangers 12, 11, 10 in counterflow to feed mixture and passed through a duct 57 to the second stage of a compressor 83 which delivers through a water condenser 36 and a duct 2 to the feed inlet duct 1 at the pressure thereof via. 30 kg./cm.<SP>2</SP>. The column 15 is also fed with cold liquid propane and butane from a rectification column 17 connected thereto by valvecontrolled ducts 58, 63, 65 and exchangers 62, 64 wherein the liquid propane and butane is cooled by reverse flowing separated nitrogen and methane derived as later explained. Furthermore, the column 15 is supplied with methane and nitrogen which having been withdrawn from separator 20 through a duct 21 cooled in exchanger 13 and liquefied in an exchanger 14 connected thereto by a duct 30 and expanded at a valve 31. A portion of said liquid methane and nitrogen is expanded at a valve 32 into a condenser 33 to provide reflux. Liquid propane and butane withdrawn from the base of column 15 is expanded at a valve 74 into a separator 75 having a gas outlet duct 76 leading to the effluent outlet 69 of the column 15, and having a liquid outlet containing an expansion valve 77 leading to a separator 78 from which product liquid propane and butane is discharged through a duct 79 and from which uncondensed methane and nitrogen is discharged through a duct 80 which is connected through exchangers 64, 54 and a duct 82 to the inlet of the first stage of compressor 83. A portion of the effluent from column 15 serves to cool exchangers 26, 62, 54 and is discharged as fuel gas through ducts 73A, 73B. A further portion of the effluent is expanded at a valve 68 from 15 to 7 kg./cm.<SP>2</SP> after which it is joined by gas leaving condenser 33, by a small portion of feed liquid which by-passes valve 28 and is expanded at a valve 29 to 7 kg./cm.<SP>2</SP>, and by methane gas from separator 75. The combined flow then serves to cool exchangers 14, 13 after which the combined stream is added to liquid propane having been expanded at valve 85. The stream then cools exchanger 12 after which it is joined by butane having been withdrawn from separator 4 through a duct 6 cooled in exchanger 11 in co-current flow with feed mixture and expanded at valve 88. The combined streams are warmed in exchanger 11 and enter a duct 90 where they are joined firstly by liquid butane from the condenser 36 and having been expanded at a valve 39, cooled in exchanger 10 and expanded at a valve 91 and secondly by a mixture of methane, propane, butane and nitrogen from columns 16, 17, heat exchanger 54 and an expansion valve 55. The combined streams then serve to cool exchanger 10 and pass along said duct 57 to the second stage of the compressor 83. Liquid propane and butane may be obtained by closing valves 49, 61 and opening a valve 51 in a duct 52 leading from the base of column 17. Liquid ethane may be obtained by feeding ethane-rich condensate from separator 20 to a rectification column (not shown). In a modified process for obtaining a mixture of liquid propane and butane and for obtaining fuel gas the recycle gas is separately cooled in a series of exchangers 145, 120, 121 and 122, Fig. 2 (not shown). In a further modification for the production of liquid methane the latter after being withdrawn from a column 17, Fig. 3 (not shown) is supercooled before being expanded to storage in the liquid phase.