Air fractionation process and installation with mixing column and krypton-xenon recovery

A process for low-temperature fractionation of air in a distillation column system for nitrogen-oxygen separation (5, 6), comprising:

• introducing a first feed air stream (4) into the distillation column system for nitrogen-oxygen separation,
• pressurizing an oxygen-rich fraction (22) removed from the distillation column system for nitrogen-oxygen separation in liquid form (23) and introducing said oxygen-rich fraction (25) to a mixing column (26),
• introducing a heat transfer medium stream, in particular a second feed air stream (43, 343), into the lower region of the mixing column (26) and bringing said heat transfer medium stream into countercurrent contact with the oxygen-rich fraction (22, 25),
• removing a gaseous top product (260) from the upper region of the mixing column (26),
• introducing a liquid (38, 39, 40, 41) from the lower or middle region of the mixing column into the distillation column system for nitrogen-oxygen separation,
• introducing a krypton- and xenon-containing oxygen stream (44, 46, 47, 48) from the distillation column system for nitrogen-oxygen separation into a krypton-xenon enriching column (36),
• removing a krypton- and xenon-enriched fraction (51) from the krypton-xenon enriching column (36),
• introducing a gaseous top product (260) from the mixing column (26) into an additional column (27) and removing a krypton- and xenon-depleted top fraction (28) from the upper region of the additional column (27).