Abstract: Air is separated in an arrangement of rectification columns comprising a double rectification column (which has a higher pressure column and a lower pressure column), an intermediate pressure rectification column, and a side rectification column communicating with the lower pressure column. The side rectification column is provided with a condenser, and the intermediate pressure rectification column with a reboiler and a further condenser. A stream of oxygen-enriched liquid is withdrawn from the bottom of the higher pressure column through an outlet and is separated in the intermediate pressure rectification column. The reboiler is heated by a stream typically withdrawn from the side rectification column through an outlet. A stream of liquid is withdrawn from the bottom of the intermediate pressure rectification column, is employed to cool the further condenser of the intermediate pressure rectification column, and is partially vaporised therein.

Abstract: A stream of precooled and purified air is introduced into a double rectification column comprising a higher pressure rectification column and a lower pressure rectification column and is separated therein into an oxygen-rich fraction and a nitrogen-rich fraction. A stream of argon-enriched oxygen vapor flows from an outlet of the lower pressure rectification column into a side column in which argon is separated therefrom. An oxygen-enriched liquid air stream is taken from an outlet at the bottom of the higher pressure rectification column. A vaporous oxygen-enriched air stream is introduced into the lower pressure rectification column through an inlet above the outlet. At least part of the oxygen-enriched liquid is separated in a further or intermediate pressure rectification column provided with a reboiler, thereby forming a vapor depleted of oxygen and a liquid air stream further enriched in oxygen.

Abstract: A stream of precooled and purified air is introduced into a double rectification column comprising a higher pressure rectification column and a lower pressure rectification column and is separated therein into an oxygen-rich fraction and a nitrogen-rich fraction. A stream of argon-enriched oxygen vapour flows from the lower pressure rectification column into a side column in which argon is separated therefrom. An oxygen-enriched liquid air stream is taken from the bottom of the higher pressure rectification column. A vaporous oxygen-enriched air stream is introduced into the lower pressure rectification column above the point at which argon-enriched oxygen vapour is removed. At least part of the oxygen-enriched liquid is partially reboiled in a reboiler and is separated in a further rectification column, thereby to form a vapour depleted of oxygen and a liquid air stream further enriched in oxygen.