An improved process for liquid nitrogen production by cryogenic air separation using a distillation column system to enhance the product recovery.

An air product is produced in an air separation plant having a heat exchanger, an expansion/compression unit, a rectification unit, liquid storage, cold storage and an air compressor. The air supplied to the rectification unit is conducted through the main air compressor at a pressure level at least 3 bar above the highest operation pressure for the rectification unit. Cryogenic liquids are produced in a first production amount by a first operating mode, a lower second production amount by a second operating mode and a higher third production amount by a third operating mode. Cryogenic liquid is stored in the liquid storage in the third operating mode and removed from storage in the second operating mode. Cryogenic liquid is evaporated in different amounts in each operating mode, which amounts differ by no more than 10%.

An apparatus for separating air by cryogenic distillation comprises N air compressors (C1, C2, C3) connected so as to receive air at ambient pressure and designed to produce air at a first pressure above 12 bar absolute, N being at least 3, each of the compressors being driven by a single asynchronous motor (M1, M2, M3), the total power of the compressors being at least 10 MW.