Hydrogen recovery from a refinery tail gas employing two stage scrubbing

摘要

1,068,982. Cold separation of gas mixtures. CONCH INTERNATIONAL METHANE Ltd. Feb. 23, 1966 [March 19, 1965], No. 7852/66. Heading F4P. Separation of hydrogen from admixture with nitrogen, carbon monoxide, methane and C 2 to C 4 hydrocarbons is effected by first condensing and separating the C 2 to C 4 hydrocarbons, then condensing the bulk of the methane by indirect heat exchange with a stream of evaporating liquid nitrogen and with a stream of cold regasified liquefied natural gas and finally by scrubbing effluent hydrogen with L.N.G. to remove nitrogen and carbon monoxide followed by further scrubbing with sub-cooled separated propane to remove residual methane. Compressed feed gas having been cooled in boiling coils (12, 18, 20, 24), Fig. 2 (not shown), of columns (10, 22, 26) hereinafter referred to is condensed at (30, 36) by L.N.G. in a coil (32). Crude ethylene is separated at (40) and is expanded at a valve (42) into a de-methanizer column (26) whilst crude vapour withdrawn from (40) is compressed at (46), cooled in boiling coils (48, 50) and is condensed at (30, 52) by L.N.G. in coils (32, 54). The wet feed gas from condenser (52) is separated at (58), Fig. 3 (not shown) into crude liquid ethylene which is expanded into de-methorizer column (26) whilst separated vapour is condensed at (62, 68, 72, 74) by re-vaporized L.N.G. traversing a line (114), by liquid methane from a scrubber (82) and by product hydrogen in a line (94). The condensate leaving (74) is separated in a column (78) into liquid methane and into hydrogenrich gas which latter is scrubbed with L.N.G. in column (82) and with sub-cooled propane in a column (86). Hydrogen withdrawn from column (86) is freed of residual nitrogen in an absorber (90) and is in part discharged as product through a consumer line (94, 96) whilst the remainder is fed along a line (92) to a hydrogen liquefier (6), Fig. 1 (not shown). Pure gaseous ethylene is withdrawn through a line (200) from a column (22) supplied with effluent gaseous ethylene and ethane from column (10) and is condensed at (162) by counterflowing L.N.G. and is discharged as product through a consumer line (204). Pure gaseous ethane is also withdrawn from column (22) through a line (206), is condensed at (184) and is discharged as product through a consumer line (210). Pure gaseous propylene is withdrawn through a line (218) from a column (214) supplied with a mixture of liquid propylene and propane from the base of column (10) and is condensed at (192) and discharged as product through a consumer line (226). Pure liquid propane is withdrawn from column (214) and is in part discharged as product through a consumer line (232) whilst the remainder is sub-cooled and supplied to column (86) for scrubbing hydrogen. L.N.G. for scrubber column (82) is withdrawn by a pump (118) from a branch (110) of a low pressure supply line (106). The minor portion of the pump delivery is fed through a line (100), the sub-cooler (74) and a line (124) leading to the column (82) whilst the major portion is further pressurized by a pump (156) and supplies cold to the condensers and columns referred to. Low pressure L.N.G. from main supply line (106) is also fed through a line (113) to a re-vaporizer (246) where it condenses gaseous nitrogen delivered by compressors (280, 294, 310, 312). The liquid nitrogen is subcooled at (258, 284) and expanded into a column (290) from which liquid nitrogen passes in part through lines (298, 78) to the reporating apparatus to effect condensation of most of the methane and sub-cooling of L.N.G. The remainder of the liquid nitrogen passes to the hydrogen liquefier (6).