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

An air separation unit for production of nitrogen and argon from a source of purified, compressed feed air, the air separation unit comprises a distillation column system comprising:

• a higher pressure column configured to receive the air steam and a first reflux stream and yield a nitrogen-rich overhead and a kettle liquid;
• a lower pressure column configured to receive the exhaust stream and a second reflux stream and yield a low pressure product grade nitrogen overhead, an oxygen liquid bottoms, 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 oxygen liquid bottoms in the lower pressure column to yield the first reflux stream and the second reflux stream;
• an intermediate pressure kettle column arrangement comprising a kettle column configured to receive the kettle liquid from the higher pressure column at an intermediate location of the kettle column and yield an oxygen-rich bottoms and a nitrogen rich overhead;
• the intermediate pressure kettle column arrangement further comprises a once-through kettle column reboiler configured to boil a portion of the descending liquid in the kettle column against a first part of the argon-oxygen side stream to yield an ascending vapor stream in the kettle column and an argon-oxygen liquid stream that is returned to an intermediate location of the lower pressure column;
• the intermediate pressure kettle column arrangement further comprises a once through kettle column condenser configured to condense all or a portion of the nitrogen rich overhead of the kettle column against a portion of the oxygen-rich bottoms of the 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;
• wherein the argon condenser is configured to condense the argon overhead against a portion of the oxygen liquid bottoms from the lower pressure column.