Process for obtaining gaseous and liquid nitrogen with a variable proportion of liquid product

A process for obtaining gaseous and liquid nitrogen with a variable proportion of the liquid product by low-temperature separation of air in a distillation column system having a single column, said process comprising:

• cooling compressed feed air in a main heat exchanger and introducing the resultant cooled feed air to said single column operating under pressure;
• withdrawing a nitrogen-rich fraction from the distillation column system and compressing said nitrogen-rich fraction, at least in a part in a circulation compressor;
• passing a part of said nitrogen-rich fraction downstream from said circulation compressor to a liquefaction chamber of a condenser-evaporator and condensing said first part of said nitrogen-rich fraction under a pressure higher than the operating pressure of said single column so as to form a nitrogen-rich liquid;
• passing a liquid, oxygen-enriched fraction from the distillation column system to an evaporation chamber of the condenser-evaporator so as to at least partially evaporate said liquid, oxygen-enriched fraction;
• passing a first oxygen-enriched gas (234, 533) formed in the evaporation chamber, as ascending vapor into the single column;
• and
• withdrawing a second portion of nitrogen-rich fraction at least at times as gaseous nitrogen product,
• characterized in that
• a part of said nitrogen-rich liquid is withdrawn from the condenser-evaporator at least at times as liquid product, the evaporation chamber of condenser-evaporator is operated at least at times under a pressure higher than the operating pressure of the single column, and
• a second oxygen-enriched gas is withdrawn from at least one of (1) a column in the distillation system and (2) the evaporation chamber of the condenser-evaporator, and the resultant withdrawn second oxygen enriched gas is machine expanded and then heated in the main heat exchanger.