Patent GB-771405-A (GB)
Title: Improvements in the cold separation of air
IPC: B01D53/62
Filed: 1955-05-10
Abstract: 771,405. Air rectification process. UNION CARBIDE & CARBON CORPORATION. May 10, 1955 [June 1, 1954], No. 13554/55. Class 8(2) Removal of water vapour and carbon dioxide from compressed air prior to conventional rectification in a column 30, 32, Fig. 1, is effected by first cooling air at about 3000 p.s.i. so as to condense water vapour therefrom in a path 12 of an exchanger A having a cold returning nitrogen path 50, further cooling the cold dry air in a path 15 of an exchanger B having a nitrogen path 48 to such a temperature, e.g. 140‹C. as to avoid condensation of carbon dioxide, expansion at a valve 18 to a pressure of about 270 p.s.i. and feeding to a, scrubber 17 where the stream is washed with liquid condensed by cold nitrogen traversing a coil 45, expanding the scrubber liquid at a valve 25 to about 75 p.s.i. and feeding the resulting mixture of liquid and vapour to a second scrubber 22, passing the carbon dioxide-bearing liquid from scrubber 22 through filters 27 to the low pressure column 30 and the vapour through a line 31 to the high pressure column 32. A portion of the dry compressed air leaving the path 12 is expanded to 75 p.s.i. in a turbine 54 and the resulting wet vapour is fed through a line 55 to the scrubber 22 to provide extra cold therefore. The temperature of. nitrogen traversing coil 45 is adjusted to about-180‹C. by being warmed in a path 42 of an exchanger traversed by liquid nitrogen passing from a shelf 35 through a valve 38 to the head of column 30. In a modification the nitrogen coil 60 Fig. 2 (not shown) for prodiicing washing liquid for the first scrubber is located in a chamber separate from said scrubber and the resulting liquid may be divided -between said first scrubber, the second scrubber 22 and a boiling coil at the base of the high pressure column 32. Said coil is also supplied with liquid from the first scrubber after filtration thereof in filters separate from those supplied by the second scrubber, and the so warmed carbon-dioxide free liquid after expansion is combined with that from filters 27. In a further modification on the second scrubber 122, Fig. 3 is incorporated in the base of the high pressure column 132 and is supplied with a carbon dioxide bearing liquid from the first scrubber 117 after expansion at a valve 125 to about 75 p.s.i. together with a second stream of air at 75 p.s.i. in a line 155 and after having been freed of water and carbon dioxide in a counter-current heat exchanger cooled by returning nitrogen. In operation the main air stream at 3000 p.s.i. issuing from a compressor 110 is freed of water vapour in paths 112, 80, cooled by nitrogen and a refrigerator coil 81 respectively and is then cooled to about -140‹C. in a path 115 cooled by nitrogen and oxygen in paths 148, 99 after which the cold air still containing carbon dioxide is expanded to 270 p.s.i. at a valve 118 and fed to the scrubber 117. Washing liquid for the latter is provided by condensation of vapour by cold nitrogen traversing a coil 45a and by cold gas from the column 132 in a line 83 passing along a path 82 in heat exchange with vapour path 160. Additional cold is obtained by expanding the warm gas leaving path 82 in a turbine 85 where it is joined by vapour from the scrubber 117 having been warmed in a coil 84b and expanded in a turbine 85a. A portion of the combined streams is fed through a line 87 to the column 130 and the remainder is fed through a line 88 to the effluent nitrogen line 144 which includes a coil 93a located within a liquifier 93 providing extra washing liquid for the scrubber 122. A coil 93b in the product oxygen line 97, 98 also assists in providing said extra washing liquid.