Patent ID: 6293126
Filing Date: 2001-09-25
Classification: F25J

Abstract:
A method of separating air, wherein a first stream of compressed air is cooled in a heat exchanger and downstream of the cooling is rectified in an arrangement of rectification columns comprising a higher pressure column and a lower pressure column; a stream of oxygen-enriched liquid is withdrawn from the higher pressure column, is expanded and is introduced into the lower pressure column; a second stream of compressed air is cooled at a higher pressure than the first stream of compressed air; the first and second streams of compressed air are cooled in indirect countercurrent heat exchange with a gaseous nitrogen stream taken from the lower pressure column; the first stream of compressed air passes out of heat exchange relationship with the gaseous nitrogen stream at a higher temperature than the second stream; at least part of the second stream of air downstream of its heat exchange with the nitrogen stream is expanded and is introduced into the lower pressure column; and the stream of oxygen-enriched liquid passes essentially isenthalpically from the higher pressure column to its expansion, wherein the entire cooling of the second stream of compressed air from 0.degree. C. is performed in the same heat exchanger as the cooling of the first stream of compressed air, and the second stream of air passes out of heat exchange with the nitrogen stream at a temperature at least 5K lower than the bubble point temperature of air at the pressure prevailing at the inlet for the first stream of compressed air to the higher pressure column.