Enhancements to a dual column nitrogen producing cryogenic air separation unit

An air separation unit comprising:

• a main air compression system configured for receiving a stream of incoming feed air and producing a compressed air stream;
• an adsorption based pre-purifier unit configured for removing impurities from the compressed air stream and producing a compressed, purified air stream;
• a main heat exchange system configured to cool the compressed and purified air stream to temperatures suitable for fractional distillation;
• a distillation column system comprises a higher pressure column and a lower pressure column linked in a heat transfer relationship via a first condenser-reboiler;
• wherein the higher pressure column is configured to receive the cooled, compressed, purified air stream and produce a nitrogen enriched overhead and an oxygen-enriched kettle stream;
• wherein the lower pressure column is configured and produce a lower pressure nitrogen product stream, an overhead stream and an oxygen-enriched bottoms;
• wherein the first condenser-reboiler is configured to condense a first portion of the nitrogen enriched overhead from the higher pressure column against the oxygen-enriched bottoms from the lower pressure column to produce a nitrogen reflux stream for the higher pressure column and an ascending vapor stream in the lower pressure column from the boil-off of the oxygen-enriched bottoms;
• wherein the distillation column system further comprises a second condenser-reboiler operatively associated with the higher pressure column and configured to condense a second portion of the nitrogen enriched overhead from the higher pressure column against a first split portion of the oxygen-enriched kettle stream from the higher pressure column to produce a liquid nitrogen stream and a recycle stream from the boil-off of the oxygen-enriched kettle stream;
• wherein a second split portion of the oxygen-enriched kettle stream is introduced into the lower pressure column at an intermediate location;
• wherein a third portion of the nitrogen enriched overhead from the higher pressure column is taken as a medium/high nitrogen product stream;
• wherein the distillation column system further comprises a third condenser-reboiler operatively associated with the lower pressure column and configured to condense the nitrogen overhead from the lower pressure column against the oxygen bottoms from the lower pressure column to produce a nitrogen reflux stream for the lower pressure column, a reverse reflux stream for the higher pressure column, and a waste stream;
• and
• wherein the recycle stream is recycled to:
• (i) the main air compression system and combined with the incoming feed air stream;
• (ii) a location upstream of the main heat exchange system and combined with the compressed, pre-purified air stream;
• or (iii) to the main heat exchanger system.