Process and apparatus for air fractionation by rectification

In an air fractionation process by rectification, wherein air (1) is compressed, purified, cooled (36), and preliminarily fractionated in a high pressure column (3) of a two-stage rectification column (2) into an oxygen-rich liquid (6) and into a nitrogen-rich fraction (5), the oxygen-rich liquid (6) and/or nitrogen-rich fraction (5) being fed at least in part to the medium pressure column (4) of the rectification column (2) and separated into oxygen and nitrogen, and wherein an argon-containing oxygen stream (17) and an oxygen product stream (40) are withdrawn from the medium pressure column (4), the argon-containing oxygen stream being introduced into a crude argon column (20) operated under a pressure lower than the pressure of the medium pressure column (4), and gaseous crude argon (21) being removed from an upper zone of said crude argon column, the improvement wherein the oxygen product stream (40) is discharged in the liquid condition from the medium pressure column (4), at least a portion (31) of the gaseous crude argon withdrawn from the crude argon column (20) is condensed in indirect heat exchange (34) against the liquid oxygen product stream (40), the oxygen product stream (40) being at least partially vaporized, and resultant condensed crude argon (35) is reintroduced into the crude argon column (20).