Air separation unit and method for production of high purity nitrogen product using a distillation column system with an intermediate pressure kettle column

An air separation unit for production of oxygen, nitrogen and argon from a purified, compressed feed air stream, the air separation unit comprising:

• a main heat exchanger configure to cool the purified, compressed feed air stream via indirect heat exchange against one or more product streams, a recycle stream and a waste stream to yield a liquid air stream;
• a higher pressure column configured to receive the liquid air steam, a nitrogen recycle stream, and a first reflux stream and yield a nitrogen-rich overhead, a kettle liquid, and a dirty shelf nitrogen stream;
• a lower pressure column configured to receive the dirty shelf nitrogen stream from the higher pressure column as a second reflux stream, and yield a nitrogen overhead stream, a nitrogen waste stream, an oxygen liquid bottoms, an oxygen waste stream, and an argon-oxygen side stream;
• a main condenser-reboiler disposed in the lower pressure column and configured for thermally coupling the higher pressure column and the lower pressure column by liquefying at least a portion of the nitrogen-rich overhead from the higher pressure column against the oxygen liquid bottoms in the lower pressure column to yield the first reflux stream and the oxygen waste stream;
• an intermediate pressure kettle column configured to receive the kettle liquid from the higher pressure column at an intermediate location of the kettle rectification column and yield an oxygen-rich bottoms and a nitrogen rich overhead;
• a once-through kettle column reboiler configured to boil a portion of the oxygen-rich bottoms in the intermediate pressure kettle column against a first part of the argon-oxygen side stream to yield an ascending vapor stream in the intermediate pressure kettle column and an argon-oxygen liquid stream that is returned to an intermediate location of the lower pressure column;
• a once through kettle column condenser configured to condense all or a portion of the nitrogen rich overhead of intermediate pressure kettle column against a portion of the oxygen-rich bottoms of the intermediate pressure kettle column;
• and
• an argon column arrangement comprising one or more argon columns and an argon condenser, the argon column is configured to receive a second part of the argon-oxygen side stream from the lower pressure column and yield an argon-rich overhead and an oxygen-rich liquid stream that is returned to the intermediate location of the lower pressure column;
• a nitrogen recycle circuit configured to recycle all or a portion of the nitrogen overhead from the lower pressure column to the higher pressure column as the nitrogen recycle stream;
• and
• wherein a portion of the nitrogen-rich overhead from the higher pressure column is warmed in the main heat exchanger and taken as a higher purity nitrogen product stream and a portion of the oxygen liquid bottoms is taken as an oxygen product stream.