Patent GB-1381488-A (GB)
Title: Process of and apparatus for air separation
IPC: F01K23/06
Filed: 1971-12-29
Abstract: 1381488 Air separation UNION CARBIDE CORP 29 Dec 1971 [28 Dec 1970] 60358/71 Heading F4P In an air separation process comprising high and lower pressure rectification columns 40, 42, partially separated liquid fractions from the h.p. column are fed via expansion valves 50, 56 to the lower pressure column 42 while N 2 -rich gas from the top of the h.p. column is liquefied in a heat exchanger 58 at the bottom of the l.p. column to provide heating therefor, before being injected into the l.p. column via expansion valve 62, the l.p. column operating at a pressure in the range 45-140 p.s.i. so that the pure product gases require little or no further compression. Feed air is compressed at 11 to 97 p.s.i. and led via lines 12, 14 to a heat exchanger (h.e.), 14b to remove some of the heat of compression before being compressed to 335 p.s.i. at 20 and fed via line 30 through one of a pair of adsorption traps 31, 32 to remove impurities using, e.g calcium zeolite A, after which it is passed through a second h.e. 35 to reduce its temperature to about 134‹ K. prior to being introduced to the h.p. column 40. O 2 -rich liquid is withdrawn from the bottom of this column 40 and separated into two portions for feeding through third and fourth h.e.s 43, 46 respectively before injecting into the l.p. column 42 via valve 50. Similarly a N 2 -rich liquid fraction is drawn off through line 51 and fed through a fifth h.e. 52 and expansion valve 56. Some of the N 2 -rich liquid from the h.e. 58 is refluxed to the h.p. column 40 via line 59, the remainder passing through the fifth h.e. 52. Pure O 2  gas is drawn off through line 65 at 115‹ K, and 111 p.s.i. and is used as coolant in second h.e. 35 before being led off. Product N 2  gas and N 2 -rich waste gas are drawn off in lines 63, 66 respectively and provide the coolant for the fifth and fourth h.e.s 52, 46, the product N 2  gas is work expanded at 64 before cooling the third h.e. 43, and both gas streams are used to cool second h.e. 35. The waste gas is then used to cool the first h.e. 14b, a portion being drawn off compressed and heated to purge the off-line adsorption trap 31, 32. The waste gas is now used to cool the gases issuing from a combustion chamber 15 in which some of the originally compressed air is used as oxidant to burn a fuel, the combustion gases driving a turbine 19 to provide some of the work for the compressors. In a modification, Fig. 2, the fifth h.e. 52 incorporates the fourth h.e., and the N 2 -rich liquid from h.e. 58 is divided into two additional streams 73, 77 which are fed through further h.e.s 71 and 76, both cooled by product N 2  gas after it has passed through a further work expander 70. Liquid O 2  may be drawn off from the base of column 42. In Fig. 3 (not shown), the N 2  separation portion at the top of the column 42 is omitted, a portion of the N 2 -rich waste gas being work expanded to cool third h.e. 43. In Fig. 4 (not shown), some of the compressed air is diverted from within second h.e. 35 and work expanded to the pressure of the l.p. column 42 then partially rewarmed by cooling the O 2 -rich liquid in third h.e. 43, further rewarmed in heat exchange with a portion of the compressed air being fed to the h.p. column 40 and then added to the N 2 -rich waste gas. In Fig. 5 (not shown), the feed air is compressed to an excess pressure and is work expanded to provide the necessary cooling before introduction to the h.p. column 40. A portion of the feed air bi-passes this work expander and' is liquefied in heat exchange with the N 2 -rich waste gas before passing into column 40 via a throttle valve.