Patent ID: 6141989
Filing Date: 2000-11-07
Classification: F25J

Abstract:
A method of separating air comprising:introducing the air into a double rectification column comprising a higher pressure rectification column, a lower pressure rectification column, and a first condenser-reboiler, of which the condensing passages communicate with an upper region of the higher pressure rectification column so as to condense nitrogen, and the reboiling passages communicate with a lower region of the lower pressure rectification column;operating a second condenser-reboiler so as to reboil a liquid fraction obtained in the higher pressure rectification column, the second condenser-reboiler being heated either by means of a first stream of compressed air to be separated, the first stream of air thereby being partially or totally condensed, or by a flow of nitrogen-rich vapour formed by pre-separating the first stream of air in a further rectification column operating at a higher pressure than any obtaining in the higher pressure rectification column, the nitrogen-rich vapour thereby being partially or totally condensed;partially or totally condensing a second stream of compressed air to be separated by indirect heat exchange with a stream of the condensed nitrogen; andtaking at least part of the stream of condensed nitrogen as product downstream of its heat exchange with the second stream of compressed air.