Patent GB-939409-A (GB)
Title: Separation of the elements of air
Inventor: SMITH DONALD EDWARD
IPC: F25J5/00
Filed: 1962-02-07
Abstract: 939,409. Cold separation of air. AIR REDUCTION CO. Inc. Feb. 7, 1962, No. 4781/62. Class 8(2). Effluent nitrogen withdrawn from the head of the high pressure column 400, Fig. 4a, of a two stage air rectification plant is liquefied and the major portion withdrawn as product through a valve 404 whilst the remainder is forced by a pump 444 through a duct 446 for use as reflux in said column 400 and effluent nitrogen from the head of the low pressure column 10 is also liquefied and returned as reflux to said column 10. As shown the high pressure nitrogen effluent is liquefied in the coil 438 of the oxygen reboiler 440 of column 10 from which product liquid oxygen is withdrawn through a valve 406, and the high pressure liquid nitrogen after being freed of uncondensed gases in a chamber 442 is fed through a duct 36 to the outlet 404 and through said pump 444 to the head of column 400 The low pressure nitrogen effluent from column 10 serves to subcool the high pressure liquid nitrogen in ar exchanger 24 and thereafter traverses one or other of the outer passages of switchable exchangers 418, 420 in countercurrent to feed air from a compressor 412. The so contaminated nitrogen gas is fed through a duct 468 to a two-stage compressor 472, Fig. 4b, and after traversing a caustic scrubber 476, a cooler 478, a drier 60, a refrigerated chamber 482, an oil absorber 484, heat exchangers 486, 488, a further refrigerator 490 and coolers 492, 494 is expanded at a valve 496 into a separator 108 from which liquid nitrogen after being sub-cooled at 498 is returned through a duct 500 and expansion valve 501 to the head of column 10 to serve as reflux. The cold requirements of condenser chamber 442 and for refluxing the column 400 are provided by a closed auxiliary nitrogen cycle comprising a compressor 540 and an oil filter 542 from which a first portion of compressed nitrogen is passed through the coil of a warm exchanger 544 whilst a second portion is cooled in a refrigerator 546 and is added to the first portion before being cooled in the coil of a cold exchanger 548, and the two portions are then passed through the reboiler 550 of column 400 before being passed through a surge drum 551 and the condenser 442. Vapour from the latter traverses a conduit 552 and the middle non- switchable passages of exchangers 418, 420 and a conduit leading to the inlet of compressor 540. Extra cold for the cycle is obtained by expanding a portion of nitrogen leaving the coil of exchanger 544 in an engine 554 and using the so-cooled nitrogen in exchangers 548, 544 before returning it to the compressor 540. Make-up nitrogen for the cycle is provided through a valved conduit 556. Argon rich vapour is withdrawn from column 10 through a conduit 461 and is passed up a column 402 containing a condenser 458 and rectified crude argon vapour is passed through a conduit 464 to a condenser 456 where the argon is condensed in heat exchange with liquid withdrawn from the base of the column 400. Product liquid argon is withdrawn through a valve 408. In a modification a portion of the effluent nitrogen from the oxygen column 10, Fig. 1 (not shown), is used to scavenge reversible heat exchangers serving to cool and purify incoming air and the fouled nitrogen is then cleaned, compressed, cooled and expanded and used to liquefy the remainder of the said effluent nitrogen for use as reflux.