An air separation process using warm and cold expanders

摘要

The energy consumption of cryogenic distillation of air in a distillation column system having a higher pressure distillation column (196) and a lower pressure distillation column (198), wherein cooled feed air (114, 120) is fed to the higher pressure column (196), the boil-up at the bottom of the lower pressure column is provided by condensing (193) a stream (150; 152 Figs. 2-5) having a nitrogen concentration at least equal to that of the feed air stream (100) and at least two expanders (182,139; 139,277 Fig. 2; 182,339 Fig. 3; 182,439 Fig. 4; 539,582 Fig. 5) are employed to provide refrigeration to the distillation column system, the first expander (182; 277 Fig. 2; 582 Fig. 5) having an inlet temperature near or above ambient and the second expander (139; 339 Fig. 3; 439 Fig. 4; 529 Fig. 5) having an inlet temperature colder than ambient, is reduced by employing at least one of the following steps in at least one of the two expanders: (a) work expanding a portion (102) of the feed air; (b) work expanding a process stream (438 Fig. 4; 538 Fig. 5) with a nitrogen content at least equal to that of the feed air, and, then, condensing at least a portion of the expanded stream (440 Fig. 4; 540 Fig. 5) by a latent heat exchange (394 Fig. 4 & 5) with (i) a liquid at an intermediate height in the lower pressure column and/or (ii) one of the liquid feeds (334 Fig. 4 & 5) to the low pressure column (198) which has an oxygen concentration of at least equal to that in the feed air (100); (c) condensing at least one process stream (354 Fig. 3) with nitrogen content at least equal to that in the feed air (100) by latent heat exchange (394 Fig. 3) which vaporizes at least a portion (334 Fig. 3) of a liquid stream with oxygen concentration at least equal to that in the feed air and which is at a pressure greater than the pressure of the lower pressure column (198), and work expanding at least a portion (338 Fig. 3) of the resulting vapor stream; and (d) work expanding a process stream (274 Fig. 2) from the higher pressure column (196) with nitrogen content at least equal to that in the feed air and withdrawing the expanded stream as gaseous product stream (278 Fig. 2).