Patent GB-798921-A (GB)
Title: Process and apparatus for separating gaseous mixtures by rectification
IPC: F25J3/08
Filed: 1956-12-12
Abstract: 798,921. Cold separation of gas mixtures. UNION CARBIDE CORPORATION, [formerly UNION CARBIDE & CARBON CORPORATION.]. Dec. 12, 1956 [Jan. 4, 1956], No. 38008/56. Class 8(2). In a gas mixture e.g. air rectification process wherein relatively high boiling impurities e.g. carbon dioxide and hydrocarbons are condensed in one or other of a pair of interchangeable paths 18, 20, Fig. 1 of a heat exchanger 14 and are afterwards revaporized by returning nitrogen on switching the paths 18, 20 by conventional valves 15, R.V., the excess cold required to effect complete reevaporation of condensed impurities is effected by withdrawing through a duct 50 separated constituent e.g., oxygen vapour from the column 32 passing it through a separate non-reversing path 19 in at least the colder portion of the exchanger 14 and returning at least a portion thereof through a duct 68 to the column 32 at a point of lower pressure than that prevailing at the point of withdrawal. The head of pressure h necessary to effect this recycling of oxygen vapour is provided by a diaphram 74 extending across the column between the ducts 50, 68 and a throttle valve 76 in a bypass 78. The cold requirements of the process are met by an external reservoir 60 of liquid oxygen discharging by gravity through a duct 64 to the reboiler 36 of the column 32 which forms the low pressure section of a conventional twostage column 30. In operation compressed air leaving the exchanger 14 which comprises two portions in series traverses a duct 26, and an absorbent trap 24 before passing to the high pressure column 28, nitrogen-rich liquid from shelf 38 is subcooled in a coil 56 surrounded by effluent nitrogen from the head of column 32 before being expanded at a valve 42 and fed to the column 32 as reflux, and the recycle portion of oxygen vapour which may be bled from the warm end of either of the two portions of the exchanger 14 according to the setting of valves 71, 72 traverses a duct 68 and an optional cooler 86 before being returned to the column 32 ; pure product oxygen being discharged through a valved duct 69. In a modification the recycled oxygen path is completely closed and includes a separate pass 162, Fig. 4 (not shown) in the colder portion of the heat exchanger 14. In a further modification the main heat exchanger comprises alternating nitrogen regenerators 102, 104, Fig. 2 and the recycle oxygen is bled from the oxygen passes 106, 108 through the duct 68 and heat exchangers 116, 86 back to the column 32. The cold requirements of the column are met by passing air vapour from a liquifier-scrubber 110 through a pass 114 of the exchanger 116 where it is warmed before expansion in a turbine 118 and passage through a duct 120 leading to the column 32. A portion of such expanded air may be fed through a duct 122 to join effluent nitrogen in a duct 52, leading to a liquefying coil 110a and the regenerators 102, 104. In a still further modification for the production of low purity oxygen both nitrogen and oxygen regenerators are used and the recycled oxygen traverses paths within the regenerators and is uncontaminated by condensed impurities. Reference has been directed by the Comptroller to Specification 742,779.