Air Separation Process

1,180,904. Cold separation of air. BRITISH OXYGEN CO. Ltd. 23 May, 1967 [1 June, 1966], No. 24522/66. Heading F4P. In a two-stage air rectification process comprising passing compressed air through reversing heat exchangers 6A, 6B in series traversed by reverse flowing high purity oxygen and waste nitrogen product streams 27, 29 withdrawn from the low-pressure column 10, feeding the socooled compressed air stream 20 into the highpressure column 12, withdrawing from the latter an oxygen-rich fraction 21 and expanding it at a valve 22 into column 10, withdrawing a relatively pure nitrogen fraction from column 12 and expanding at least a portion of it at a valve 26 into column 10, substantially the whole of the cold requirements of the process are met by work-expansion to one atmosphere of at least one of the product streams, e.g. waste nitrogen in a turbine 7 and prior to expansion all or part of the streams are heated, e.g. in a pass of heatexchanger 6B thereby effecting thermal balancing of the exchangers 6A, 6B. That portion of the relatively pure high-pressure nitrogen stream not expanded at 26 into column 10 is returned through the heat-exchangers 6B, 6A. A gaseous argon-rich fraction may be withdrawn from column 10 and fed through a line 31 to a side column 13 to which is also fed a portion of the oxygen-rich liquid stream 21 after expansion at a valve 32. The resulting argon-rich gas is withdrawn through a line 34.