Patent GB-661888-A (GB)
Title: Improvements in or relating to processes for producing oxygen
IPC: F25J3/04
Filed: 1948-10-20
Abstract: 661,888. Production of oxygen. HYDRO-CARBON RESEARCH, Inc. Oct. 20,1948 [Nov. 1, 1947; Nov. 1, 1947]. Nos. 27259/48 and 27260/48. Class 8 (ii). In a process for the separation of oxygen from air comprising passing a stream of rectification product, e.g., nitrogen, through a flow path 17 (Fig. 1) in a heat exchanger 10b, passing a stream of air through a second path 16 in the exchanger and thereby condensing impurities such as carbon dioxide prior to rectification, and periodically switching the two streams, a stream of a second rectification product, e.g., oxygen, traverses a third flow path 15 in at least the colder end of the exchanger and in heat exchange relations with the air and nitrogen streams and a portion of this oxygen is withdrawn from the warm end of the path 15 and recirculated through the path 15; the remaining oxygen passing to a service line 33. The portion of oxygen uncontaminated by condensible constituents is recirculated by a pump 60 and is cooled at an exchanger 62 by a minor portion of the air leaving the exchanger 10b and at an exchanger 53 by returning nitrogen. In operation compressed air from a line 24 traverses a reversing valve 22, a path 12 of a preliminary heat exchanger 10a for the removal of water vapour, the path 17 and a reversing valve 23 to a line 31 where it is divided into a major portion which is cooled by returning nitrogen at an exchanger 51 and fed into the high pressure stage 35 of a rectification column 34, and into the said minor portion which after being heated at the exchanger 62 is cooled in an expansion engine 68 and is fed into the low pressure stage 36 of the column 34. The temperature of the minor air portion is controlled by a bye-pass line 70. Pure nitrogen from the stage 36 and a condenser reboiler 37 combine in a line 49 and after being heated in the exchangers 51, 53, which latter is bye-passed by a line 55, traverse the reversing valve 23, the path 17 and a path 13 in the exchanger 10a to the valve 22 and a delivery line 25. On operation of the valves 22, 23 the flow paths 12, 13 are switched as are paths 16, 17. The flow of oxygen continues in paths 15, 11 to the service line 33. In a modification air entering at a line 334 (Fig. 3) is divided into major and minor portions. The major portion traverses reversing valves 330, 331 and paths 316, 314 of an exchanger A in indirect counter current contact with returning nitrogen in paths 313, 315 and pure oxygen in a path 312. The minor air portion traverses valves 341, 342 and paths 320, 321 in indirect heat exchange with returning oxygen in paths 322, 325 and with pure oxygen, in paths 323, 326, which is delivered at a service line 355. On operation of the valves 330, 331, 341, 342 the condensed water and carbon dioxide is sublimed by the passage of nitrogen and oxygen through those paths hitherto traversed by air. The resulting contaminated nitrogen and oxygen is delivered through lines 336, 346. Pure oxygen streams from the warm ends of paths 312, 323 are combined at a line 329 and a portion is recirculated by a pump 356 through exchangers 357, 358 and a line 351. The major and minor portions of air after cooling are combined at a line 362 and are then redivided into a major portion which is cooled in exchangers 363, 364 by oxygen and nitrogen returning from a low pressure column 360 and then fed into a high pressure column 359; the minor portion after serving to cool the recirculating oxygen at exchanger 357 and being expanded is fed through a line 395 into the low pressure column 360. Pure oxygen for the non-switched paths 312, 323 is supplied through a line 351 from the base of a column 361 operating at a pressure somewhat higher than that of the low pressure column 360, and oxygen for the switched paths 321, 322, 324, 325 is supplied through a line 349 from the base of column 360. In a further modification the major and minor air streams after traversing reversing valves 330, 341 (Fig. 4) respectively are cooled and impurites condensed therefrom in paths 397, 399 of regenerators C, D and after traversing valves 331, 342 are rejoined in the line 362. Simultaneously paths 396, 398 are purged by returning nitrogen and oxygen. Pure oxygen flows continuously through lines 400, 401, 402, 403 in each regenerator and a portion of the uncontaminated oxygen delivered therefrom is recirculated as described. Instead of pure oxygen, streams rich in oxygen, krypton, xenon or relatively pure nitrogen produced in an auxiliary column may comprise the product and recirculated stream. Specification 647,483 is referred to.