Patent GB-862944-A (GB)
Title: Process and apparatus for purifying and separating compressed gas mixtures
IPC: F25J3/04
Filed: 1959-03-17
Abstract: 862,944. Cold separation of gas mixtures. UNION CARBIDE CORPORATION. March 17, 1959 [March 28, 1958], No. 9268/59. Class 8 (2). Unbalance flow necessary to reduce the temperature difference between incoming compressed gas mixture e.g. air and returning separated constituent e.g. nitrogen at the cold end of conventional reversible heat exchangers and in order to completely sublime condensed high boiling impurities is provided by passing through a separate passage within the cold end of the exchangers flash-off vapour obtained by throttling a cold liquid derived from the inlet air after passage through the exchangers. In operation air is forced by a compressor 11, Fig. 1, through one or other of alternating regenerators 14 not traversed by reversely flowing nitrogen leaving the head of the low pressure chamber 26 of a conventional two-stage rectification column 21, 26 a duct 18 leading to a silica gel trap 19 from which liquid air passes in part to the high pressure chamber 21 and in part through a valved duct 21a where it is joined by flash-off vapour from a phase separator 29 fed through a duct 27 and throttle valve 28 with oxygen-rich liquid from the base 20a of the chamber 21. The combined flow then traverses one or both coils 34 located within the cold ends 17 of exchangers 14, a pair of oxygen regenerators (not shown) are supplied with compressed air and reversely flowing product gaseous oxygen through ducts 12a, 48 respectively and also with flash-off vapour through separate passages therein. The so warmed flash-off vapour is fed through ducts 35, 36 and a valve 37 and also through a coil 39 to different levels of the low pressure chamber 26 together with a portion of flash-off vapour leaving the separator 29 through a valved duct 32. Cold is supplied to low pressure chamber 26 by liquid oxygen stored in an insulated container 43a. In a modification flash-off vapour is obtained by throttling nitrogen-rich liquid from a shelf at the upper end of the high pressure chamber and the cold requirements are met by turbine-expansion of a portion of liquid air leaving the silica gel absorber and having been preheated by the warmed unbalance gas. In a further modification using reversing countercurrent heat exchangers having warm and cold legs 214a, 214b, Fig. 2, within which are interchangeable compressed air and returning nitrogen passages 260, 261, 264 and 265, non-interchangeable returning oxygen passages 261a, 264a, flash-off vapour is obtained by throttling at a valve 228 contaminated liquid from a scrubber 267 and leading the clean vapour from a phase separator 229 through a valved duct 231 and a coil 266 within the cold end 217 of the cold leg 214b. The so-warmed flash-off vapour traverses a path 272 of an exchanger 271 to warm scrubber vapour in a path 270 prior to its expansion in a turbine 273. Scrubber liquid is provided by feeding oxygenrich liquid from the base of high pressure chamber 221 through a valve 291 and by passing cold nitrogen product gas from the head of low pressure chamber 226 through a coil 269 which acts as a condenser. Contaminated scrubber liquid from separator 229 is filtered at 274 and fed to the chamber 226 as reflux.