Process for the production of nitrogen by cryogenic distillation of atmospheric air

A process for producing gaseous nitrogen from a mixture to be treated in a distillation column, said mixture comprising nitrogen and oxygen, said process comprising:

• (a) compressing the mixture to be treated to a pressure at least equal to the column pressure;
• (b) further compressing a first portion of said compressed gas mixture into a compressor driven by a turbine, cooling said further compressed gas mixture and expanding it through said turbine and thereafter fractionating by distillation said expanded gas mixture in the column to obtain, at the bottom of the column, and oxygen-enriched fraction and, at the top of the column, a nitrogen-enriched fraction;
• (c) drawing off at least a portion of the nitrogen-enriched fraction as nitrogen product;
• (d) compressing the remaining portion of the nitrogen-enriched fraction;
• (e) recycling at least a portion of the compressed remaining portion of the nitrogen-enriched fraction to the bottom reboiler of the column where it condenses to provide reboil for the column;
• (f) introducing at least a portion of the condensed nitrogen stream of step (e) to the column as additional reflux;
• and
• (g) drawing off an oxygen-enriched fraction in liquid form from the bottom of the column and expanding at least a portion of the fraction to a pressure less than the column pressure and vaporizing this portion by heat exchange with the condensing nitrogen-enriched fraction at the top of the column, and wherein said process further comprises:
• expanding compressed gas mixture in the turbine for refrigeration of the column, and venting the expanded gas mixture with waste steam from the column after heat exchange in a main heat exchanger.