An air separation device comprises: a main heat exchanger; a nitrogen rectification column; a nitrogen condensers disposed in a top portion of the nitrogen rectification column; a high-purity oxygen rectification column; and an oxygen evaporator disposed in a bottom portion of the high-purity oxygen rectification column. An oxygen-containing fluid discharged from an intermediate stage of the nitrogen rectification column is rectified in the high-purity oxygen rectification column and is concentrated in the bottom portion of the high-purity oxygen rectification column.

An air separation unit may include: a main heat exchanger 1, a first rectification column 2, a nitrogen condenser 3, a second rectification column 4, a third rectification column 5, a crude argon condenser 6, a high-purity oxygen rectification column 8, and a high-purity oxygen reboiler 9. The air separation unit uses a portion of the feed air that has passed through the main heat exchanger 1 as a heat source in the high-purity oxygen reboiler 9.

A method for obtaining one or more air products, in which method an air fractionation plant is used which has a column system with a pressure column wherein air is fed to the column system and is fractionated in the column system, wherein at least 90% of the total amount of air supplied to the column system is compressed wherein nitrogen-rich gas is extracted from the pressure column, and wherein, at least in a first operating mode, further air is compressed to a pressure level above the base pressure level, is expanded, and is warmed without fractionation in the column system. It is provided that, at least in the first operating mode, a proportion of the nitrogen-rich gas extracted from the pressure column is fed to the further air upstream of the expansion.