Air separation unit and method for cryogenic separation of air using a distillation column system including an intermediate pressure kettle column
An air separation unit and associated method for separating air by cryogenic distillation using a distillation column system including a higher pressure column, a lower pressure column, an intermediate pressure kettle column, and an argon column arrangement is provided. The disclosed air separation unit and method is particularly suited for production of an oxygen product as well as several nitrogen products wherein a portion of the nitrogen overhead intermediate pressure kettle column is taken as an intermediate pressure nitrogen product. The present air separation unit and associated method employs a once-through kettle column reboiler, a once-through kettle column condenser, and a once-through argon condenser. The once through argon condenser is disposed within the lower pressure column where an argon-rich vapor stream is condensed against the descending liquid in the lower pressure column.
1 . 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.
2 . The air separation unit of claim 1 , further 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 the purified, compressed feed air stream;
wherein the purified, compressed feed air stream is split into one or more streams of purified, compressed air; and
the one or more heat exchangers are configured to cool the one or more streams of purified, compressed air via indirect heat exchange against an oxygen product stream from the lower pressure column and one or more nitrogen streams from the lower pressure column, the higher pressure column and/or the intermediate pressure kettle column.
3 . The air separation unit of claim 2 , wherein at least one of the one or more purified, compressed air streams exiting the one or more heat exchangers is a feed liquid air stream.
4 . The air separation unit of claim 3 , wherein the one or more heat exchangers comprise a main heat exchanger configured for cooling the one or more streams of purified, compressed air via indirect heat exchange with streams selected from the group consisting of: a higher pressure gaseous nitrogen stream from the higher pressure column, a waste nitrogen stream from the lower pressure column; the low pressure nitrogen overhead stream from the lower pressure column; a pumped liquid oxygen stream from the lower pressure column; and a pumped high pressure liquid nitrogen stream.
5 . The air separation unit of claim 2 , wherein the one or more heat exchangers further comprise a nitrogen superheater configured to subcool one or more streams selected from the group consisting of: the kettle liquid, the second reflux stream, and the liquid air stream from the intermediate location of the higher pressure column against a waste nitrogen stream from the lower pressure column and the low pressure nitrogen overhead stream from the lower pressure column.
6 . The air separation unit of claim 1 , wherein the kettle column is configured to receive the kettle liquid at an intermediate location of the kettle column several separation stages above a bottom section.