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

Patent metadata

Field	Value
Publication number	US-12055345-B2
Application number	US-202217875616-A
Country	US
Kind code	B2
Filing date	Jul 28, 2022
Priority date	Jul 28, 2022
Publication date	Aug 6, 2024
Grant date	Aug 6, 2024

Abstract

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 argon product as well as several nitrogen products wherein a portion of the nitrogen overhead intermediate pressure kettle column is taken as an intermediate or elevated pressure nitrogen product. The present air separation unit and associated method employs a once-through kettle column reboiler, a once-through kettle column condenser while the argon condenser condenses an argon-rich vapor stream against a pumped oxygen stream from the bottom of the lower pressure column.

First claim

What is claimed is:

1. 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.

2. The air separation unit of claim 1 , wherein the once through kettle column condenser is configured to condense a first portion of the nitrogen rich overhead of the kettle column against a first portion of the oxygen-rich bottoms of the kettle column and wherein a second portion of the nitrogen rich overhead of the kettle column is taken as an intermediate pressure nitrogen product stream.

3. The air separation unit of claim 1 , wherein a first portion of the condensate from the once through kettle column condenser is directed as reflux to the kettle column and a second portion of the condensate from the once through kettle column condenser is directed to the lower pressure column as a third reflux stream.

4. The air separation unit of claim 1 , wherein a stream of liquid oxygen is taken from the argon condenser and directed to the bottom of the lower pressure column.

5. The air separation unit of claim 4 , further comprising a gel trap disposed between the argon condenser and the lower pressure column and configured to remove heavy impurities from the stream of liquid oxygen taken from the argon condenser.

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.

7. The air separation unit of claim 1 , wherein the argon column arrangement further comprises:
a first argon column configured to receive the second part of the argon-oxygen side stream from the lower pressure column and yield the argon-rich overhead and the oxygen-rich bottoms that is directed back to the lower pressure column;
argon condenser is configured to receive the argon-rich overhead from the first argon column and condense the argon-rich overhead to produce a crude argon stream; and
a high ratio column configured to receive a portion of the crude argon stream from the 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 the bottom of the high ratio column is taken as liquid argon product.

8. The air separation unit of claim 7 , wherein the argon column arrangement further comprises:
a high ratio column reboiler is disposed at the bottom of the high ratio column and 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
a high ratio column condenser is configured to condense the overhead vapor from the high ratio column and return all or a portion of the condensate as a high ratio column reflux stream.

9. 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
a main heat exchanger configured to cool the one or more streams of purified, compressed air via indirect heat exchange against one or more nitrogen product streams and waste streams,
an upper column turbine configured to expand one of the cooled streams of purified, compressed air to produce an exhaust stream that is directed to the lower pressure column.

10. The air separation unit of claim 9 , wherein a portion of the liquid oxygen in the lower pressure column is pumped and then warmed in the main heat exchanger and taken as a gaseous oxygen product stream.

11. The air separation unit of claim 9 , wherein a portion of the nitrogen-rich overhead of the kettle column is warmed in the main heat exchanger and taken as an intermediate pressure nitrogen vapor product stream.

12. The air separation unit of claim 11 , wherein a portion of the nitrogen-rich overhead from the higher pressure column is warmed in the main heat exchanger taken as a higher pressure nitrogen vapor product stream.

Assignees

• Prosser Neil M
• Handley James R
• Praxair Technology Inc

Inventors

• Prosser Neil M
• Handley James R

Classifications

• F25J2215/58

  Argon · CPC title

• F25J2215/42

  Nitrogen or special cases, e.g. multiple or low purity N2 · CPC title

• F25J2210/40

  Air or oxygen enriched air, i.e. generally less than 30mol% of O2 · CPC title

• F25J2200/08

  in a triple pressure main column system · CPC title

• F25J3/04448

  in a double column flowsheet with an intermediate pressure column · CPC title