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

Patent metadata

Field	Value
Publication number	US-12209802-B2
Application number	US-202217875583-A
Country	US
Kind code	B2
Filing date	Jul 28, 2022
Priority date	Jul 28, 2022
Publication date	Jan 28, 2025
Grant date	Jan 28, 2025

Abstract

A system and method for separating air by cryogenic distillation using a four column arrangement including a higher pressure column, a lower pressure column, an intermediate pressure column, and an argon column is provided. The disclosed system and method is particularly suited for production of normal purity oxygen and 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.

First claim

What is claimed is:

1. A distillation column system for production of oxygen, nitrogen and argon from a source of purified, compressed feed air, the distillation column system 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, 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;
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;
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 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.

2. The distillation column system of claim 1 , wherein the diverted liquid air stream is a synthetic liquid air stream taken from an intermediate location of the higher pressure column.

3. The distillation column system of claim 1 , wherein the kettle rectification column is configured to receive the kettle liquid at an intermediate location of the kettle rectification column.

4. The distillation column system of claim 1 , wherein the argon column arrangement further comprises:
a first argon column configured to receive the second part of the argon-oxygen containing 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;
the once-through 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 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 the bottom of the high ratio column is taken as liquid argon product.

5. The distillation column system of claim 4 , wherein the argon column arrangement further comprises:
a high ratio column reboiler 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;
a high ratio column condenser 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.

6. The distillation column system of claim 5 , wherein a first portion of the oxygen-rich bottoms from the kettle column is directed to the once-through kettle column condenser and a second portion of the oxygen-rich bottoms from the kettle column is directed to the high ratio column condenser.

7. The distillation column system of claim 6 , wherein a ratio of first portion of the oxygen-rich kettle bottoms to the second portion of the oxygen-rich kettle bottoms from the kettle column is between about 25:1 to 100:1.

8. The distillation column system of claim 5 , wherein the kettle liquid is subcooled in a heat exchanger and in the high ratio column reboiler.

9. The distillation column system of claim 8 , wherein the intermediate pressure kettle column yields one or more intermediate pressure nitrogen product streams.

10. The distillation column system of claim 1 , wherein the kettle rectification column is spatially disposed above the intermediate location of lower pressure column.

11. 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

Assignees

• Prosser Neil M
• Praxair Technology Inc

Inventors

• Prosser Neil M

Classifications

• F25J2245/40

  the recycled stream being air · CPC title

• F25J2200/92

  Details relating to the feed point · CPC title

• F25J2200/54

  in the low pressure column of a double pressure main column system · CPC title

• F25J3/04884

  Arrangement of reboiler-condensers · CPC title

• F25J3/04727

  using an auxiliary pure argon column for nitrogen rejection (F25J3/04739 takes precedence) · CPC title