An air separation unit for production of oxygen and nitrogen from a source of purified, compressed feed air, the air separation unit comprising:
- a higher pressure column configured to receive one or more streams of compressed, purified air and a first reflux stream and yield a nitrogen-rich overhead and a kettle liquid;
- a lower pressure column configured to receive a liquid air stream from an intermediate location of the higher pressure column and a second reflux stream and yield a low pressure nitrogen overhead, an oxygen liquid at a bottom of the lower pressure column, and an argon-oxygen containing 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 at the bottom of the lower pressure column to yield a high pressure nitrogen product, 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 and yield an oxygen-rich bottoms and a nitrogen-rich overhead, and wherein a first portion of the nitrogen-rich overhead of the kettle column is an intermediate pressure nitrogen vapor product and directed to one or more heat exchangers configured to cool the purified, compressed feed air;
- the intermediate pressure kettle column arrangement further comprises a once-through kettle column reboiler disposed in the kettle column and configured to boil a 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 a second portion of the nitrogen-rich overhead of the kettle column against a first major portion of the oxygen-rich bottoms of the kettle column;
- and
- an argon column arrangement comprising an argon column, a once-through argon condenser, a high ratio column, a high ratio column reboiler, and a high ratio column condenser;
- wherein 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 bottoms that is returned to the intermediate location of the lower pressure column;
- wherein the argon condenser is disposed within the lower pressure column at a location below a location where the liquid air is received and above the intermediate location of the lower pressure column and configured to receive the argon-rich overhead from the argon column and condense the argon-rich overhead to produce the crude argon stream;
- wherein the high ratio column configured to receive a portion of a crude argon stream from the once-through argon condenser and rectify the portion of the crude argon stream to yield an argon-rich liquid and an overhead vapor;
- wherein a portion of the argon-rich liquid at a bottom of the high ratio column is a liquid argon product;
- wherein the high ratio column reboiler is disposed at a bottom of the high ratio column and is configured for reboiling another portion of the argon-rich liquid at the bottom of the high ratio column to produce an ascending vapor stream in the high ratio column;
- and
- wherein the high ratio column condenser is configured to condense the overhead vapor from the high ratio column against a second minor portion of the oxygen-rich bottoms of the kettle column, the high ratio column condenser is further configured to return all or a portion of a condensate as a high ratio column reflux stream.