System and method for cryogenic air separation using four distillation columns including an intermediate pressure column

A method of air separation for production of normal purity oxygen comprising the steps of:

• rectifying one or more streams of purified, compressed feed air in a higher pressure column with a first reflux stream to yield a nitrogen-rich overhead and a kettle liquid;
• condensing all or a portion of the nitrogen-rich overhead in a main condenser-reboiler against an oxygen liquid at the bottom of a lower pressure column to yield a liquid nitrogen stream, a first portion of which is taken as the first reflux stream and another portion is taken as a second reflux stream, and an ascending vapor stream;
• rectifying a diverted liquid air stream and the ascending vapor stream in the lower pressure column with the second reflux stream to yield a low pressure nitrogen overhead, the oxygen liquid at the bottom of the lower pressure column, and an argon-oxygen containing side stream;
• rectifying the kettle liquid in an intermediate pressure kettle rectification column with a third reflux stream to yield an oxygen-rich bottoms and another nitrogen-rich overhead;
• reboiling the oxygen rich bottoms against a first part of the argon-oxygen containing side stream in a once-through kettle column reboiler disposed in the intermediate pressure kettle rectification column to produce an ascending vapor stream in the intermediate pressure kettle rectification column;
• condensing all or a portion of the nitrogen-rich overhead from the intermediate pressure kettle rectification column in a once-through kettle column condenser against a portion of the oxygen-rich bottoms to yield a liquid nitrogen stream, a portion of which is taken as the third reflux stream and another portion taken as a shelf nitrogen stream returned to the lower pressure column and a boil-off vapor stream that is returned to the lower pressure column;
• rectifying a second part of the argon-oxygen containing side stream in an argon column with an argon reflux stream to yield an argon-rich overhead and an oxygen-rich bottoms that is returned to an intermediate location of the lower pressure column;
• condensing the argon-rich overhead in a once-through argon condenser disposed in the lower pressure column against a descending liquid in the lower pressure column to yield the argon reflux stream and a crude argon stream;
• and
• producing one or more normal purity oxygen product streams from the oxygen liquid at the bottom of the lower pressure column.

An air separation unit comprising:

• a main air compression arrangement configured to receive a feed air stream and compress the feed air stream in a series of main air compression stages to yield a compressed feed air stream;
• a pre-purification unit configured to remove contaminants and water vapor from the compressed feed air stream to yield a purified, compressed feed air stream;
• wherein the purified, compressed feed air stream is split into one or more streams of purified, compressed air;
• one or more heat exchangers configured to cool the one or more streams of purified, compressed air via indirect heat exchange against an oxygen product streams and one or more nitrogen streams;
• and
• a distillation column system, wherein the distillation column system further comprises:
• 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, a kettle liquid;
• a lower pressure column configured to receive a diverted liquid air stream and a second reflux streams and yield a low pressure nitrogen overhead, an oxygen liquid at the bottom of the 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 the first reflux stream and the second reflux stream;
• an intermediate pressure kettle column arrangement comprising a kettle rectification column configured to receive the kettle liquid from the higher pressure column and yield an oxygen-rich bottoms and a nitrogen rich overhead;
• wherein the intermediate pressure kettle column arrangement further comprises a once-through kettle column reboiler configured to boil a portion of a descending liquid in the kettle rectification column against a first part of the argon-oxygen containing side stream to yield an ascending vapor stream in the kettle rectification column and an argon-oxygen liquid stream that is returned to an intermediate location of the lower pressure column;
• wherein 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 rectification column against a portion of the oxygen-rich bottoms of the kettle rectification column;
• and
• an argon column arrangement comprising one or more argon columns and a once-through argon condenser, the argon column arrangement is configured to receive a second part of the argon-oxygen containing 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 above the intermediate location of the lower pressure column and the argon-rich overhead is condensed against all or a portion of a descending liquid in the lower pressure column.