Low-temperature purification of an impurity-containing gas

摘要

884,971. Cold separation of gas mixtures. UNION CARBIDE CORPORATION. Nov. 6, 1959 [Nov. 7, 1958], No. 37751/59. Class 8(2). In process for condensing impurities e.g. water vapour and carbon dioxide contained in a compressed gas mixture e.g., air prior to rectification in a double column 255 Fig. 3 comprising passing the crude gas through one or other of switchable paths 214, 215 in countercurrent heat exchange to separated oxygen and nitrogen transversing paths 272, 274 deriming after a changeover of paths 214, 215 is effected by a reverse flow of cold purge gas at sub-atmospheric pressure drawn therethrough by a vacuum pump 220. As shown the purge gas comprises air bled from an intermediate point of the onstream path 215 through a valved duct 242, a silica gel trap 243 a duct 244 where it is augmented by a portion of cold air leaving the cold end of path 215 through a branch duct 248, and after expansion to sub-atmospheric pressure in a turbine 245 the purge gas is further cooled in a path 251 in heat exchange with cold air in a path 253 and is drawn through a duct 218, a reversing valve 216 and the path 214 being derimed. Purge gas may be augmented by a portion of cold effluent nitrogen withdrawn from a duct 273 through a valved duct 273a. In a modification purge gas comprises effluent nitrogen withdrawn from a duct 373 Fig. 4 after having been warmed in paths 366, 253 and the pressure of said withdrawn nitrogen is reduced to sub-atmospheric by a throttle valve 384 before being drawn through one or other of paths 314; 315 being derimed by a vacuum pump 320. The remaining nitrogen traverses a non- reversible path 383 whilst product oxygen traverses a path 370. The heat exchanger 313 is divided into warm and cold legs 380, 381 and a portion of incoming compressed air is bled off intermediate the legs through a duct 342 and after purification in a silica gel absorber 343 is joined by a portion of cold air leaving the cold leg is expanded in a turbine 345 before passing to the low pressure column. Alternating heat exchangers of the regenerative type may be substituted having non-reversing ducts embedded therein for uncontaminated product gas. Specifications 246,172 and 832,900 are referred to.