GB732448A - Improvements in or relating to method and apparatus for deriming a heat interchangeand for fractionating air - Google Patents

Abstract

732,448. Cold separation of gases. AIR PRODUCTS, Inc. June 11, 1952 [June 12, 1951], No. 14666/52. Addition to 666,914. Class 8 (2). In a method of deriming a heat interchanger 221 having a common passage 227 in which there is alternate flow in opposite directions of compressed gas, e.g. air, to be rectified in a two-stage column 270 and a cold low pressure returning component e.g. nitrogen, from the low pressure column 272 and comprising passing through a passage 257 of the interchanger high pressure component gas in the direction opposite to that of the compressed gas and in heat exchange therewith and then expanding the warmed high pressure component gas, e.g. in a turbine 261, and adding it at a point 265 to the same low pressure component gas flowing to the common passage, the supplemental passage 257 is confined to adjacent the cold end of the common passage 227. As shown, the interchanger 221 has common passages 227, 237 traversed by air and low pressure nitrogen and a passage 247 traversed by product oxygen. A second interchanger 222 has similar passages 228, 238, 248 and a supplemental passage 258, one or other of the common passages of each interchange being traversed by air or returning nitrogen according to the setting of switching valves 220, 231, 229. In a modification incoming air is divided prior to compression and preliminary separation of carbon-dioxide into a 33 : 67 ratio and the portions traverse heat interchangers in parallel ; the minor portion only being cooled by cold high pressure nitrogen traversing a supplemental path at the cold end of the interchanger traversed by said minor portion, the mass of which is greater than that of the cold low pressure nitrogen flowing in the opposite direction. In a further modification wherein the incoming air is divided at a point 301, Fig. 4, into a 33 : 67 ratio and wherein said minor portion only is cooled by cold returning high pressure nitrogen traversing a path 346 at the cold end of the interchanger 333, about 5 per cent of the cold returning low pressure nitrogen traversing the exchanger 309 and serving to cool said major portion of incoming air is bled off through a valved duct 376 and a passage 374 at the warm end of the exchanger 333. The cold low pressure nitrogen enters the interchangers 309, 333 in the proportions 72 and 28 per cent. respectively.