Method and apparatus for separating air by cryogenic distillation

Patent metadata

Field	Value
Publication number	US-11852408-B2
Application number	US-202117308750-A
Country	US
Kind code	B2
Filing date	May 5, 2021
Priority date	May 20, 2020
Publication date	Dec 26, 2023
Grant date	Dec 26, 2023

Abstract

In a method for separating air by cryogenic distillation using a column system consisting of a higher pressure column operating at a first pressure and a lower pressure column operating at a second pressure, a first air flow constituting between 75% and 98% of the air sent to the column system compressed to a third pressure above the first pressure, is sent to the higher pressure column, a second air flow constituting between 5% and 25% of the air sent to the column system is compressed to a fourth pressure above the second pressure but lower than the third pressure, is sent to the lower pressure column, a third column separates an argon-enriched flow and the air sent to the lower pressure column constitutes between 10% and 25% of the total air sent to the column system.

First claim

We claim:

1. A method for separating air by cryogenic distillation using a column system comprising of a higher pressure column operating at a first pressure and a lower pressure column operating at a second pressure lower than the first pressure, the top of the higher pressure column being thermally coupled to the bottom of the lower pressure column, in which:
i. compressing a first air flow constituting between 75% and 98% of the air sent to the column system to a third pressure above the first pressure, and then cooling and sending the first air flow at the third pressure to a first adsorption unit in order to be purified of water and of carbon dioxide and the purified first flow before sending at least a first portion of first air flow to the higher pressure column and optionally to the lower pressure column;
ii. compressing a second air flow constituting between 2% and 25% of the air sent to the column system to a fourth pressure between 1.2 and 2 bar abs and above the second pressure but lower than the third pressure, preferably cooled by direct contact in an air cooling tower, and then sending at the fourth pressure to a second adsorption unit in order to be purified of water and of carbon dioxide and the purified second flow before being sent to the lower pressure column;
iii. separating air in the higher pressure column to form an oxygen-enriched liquid and a nitrogen-enriched gas;
iv. sending the oxygen-enriched liquid and the nitrogen-enriched liquid from the higher pressure column to the lower pressure column;
v. withdrawing a liquid with a purity of greater than 99% of oxygen from the column system, pressurizing the liquid in a pump and then vaporizing said liquid by heat exchange with at least one portion of the first air flow;
vi. sending an argon-enriched gas from the lower pressure column to a third column and withdrawing an argon-rich fluid at the top of the third column; and
vii. sending air the lower pressure column constitutes between 10% and 25% of the total air sent to the column system;
wherein the argon-rich fluid contains between 20% and 80% of the argon contained in the first and second air flows.

2. The method according to claim 1 , wherein the argon-rich fluid contains between 45% and 75% of the argon contained in the first and second air flows.

3. The method according to claim 1 , wherein the oxygen yield of the apparatus is greater than 95%.

4. The method according to claim 1 , wherein the first air flow is cooled by direct contact with a first flow of water in a first cooling tower and the second air flow is cooled by direct contact with a second flow of water in a second cooling tower, nitrogen gas originating from the column system is sent to a water cooling tower and the cooled water in the water cooling tower is sent to the first and second air cooling towers.

5. The method according to claim 4 , wherein the cooled water is cooled between the water cooling tower and the second air cooling tower so that the water sent to the second air cooling tower is colder than that sent to the first air cooling tower.

6. The method according to claim 4 , wherein the air is cooled in the first air cooling tower to a temperature at least 5° C. above the temperature to which the air is cooled in the second air cooling tower.

7. The method according to claim 4 , wherein the air is cooled in the first cooling tower to a temperature at most 30° C., preferably at most 12° C., above the temperature to which the air is cooled in the second cooling tower.

8. The method according to claim 1 , wherein the first purified flow is cooled upstream of the column system in a first heat exchanger by heat exchange with a first nitrogen gas flow originating from the column system and the second purified flow is cooled upstream of the column system in a second heat exchanger by heat exchange with a second nitrogen gas flow originating from the column system.

9. The method according to claim 8 , wherein the second purified flow is cooled upstream of the column system in the second heat exchanger by heat exchange with only the second nitrogen gas flow originating from the column system.

10. The method according to claim 8 , wherein the second nitrogen flow is introduced into the second heat exchanger at a temperature without being passed through another heat exchanger after it has left the column.

11. The method according to claim 1 , wherein the second air flow is not expanded or boosted between the second adsorption unit and the lower pressure column.

12. The method according to claim 1 , wherein at least one portion of the first air flow is not expanded or boosted between the first adsorption unit and the higher pressure column.

13. The method according to claim 1 , wherein a portion of the first air flow is boosted then expanded between the first adsorption unit and the higher pressure column.

14. The method according to claim 1 , wherein a portion of the first air flow is expanded in a turbine then sent to the higher pressure column in gaseous and/or liquid form.

15. The method according to claim 1 , wherein at least 14 mol % of the total air is sent to the lower pressure column.

16. The method according to claim 1 , wherein the purified second flow is sent to the lower pressure column in order to be separated at the same level of the column as a flow of oxygen-enriched liquid originating from the higher pressure column or as a flow of oxygen-enriched liquid originating from the higher pressure column and vaporized in an overhead condenser of the third column.

17. An apparatus for separating air by cryogenic distillation using a column system comprising a higher pressure column operating at a first pressure and a lower pressure column operating at a second pressure lower than the first pressure, the top of the higher pressure column being thermally coupled to the bottom of the lower pressure column, a first adsorption unit, a second adsorption unit, means for sending a first air flow constituting between 75% and 98% of the air sent to the column system, compressed to a third pressure above the first pressure, to cooling means and then, at the third pressure, to the first adsorption unit in order to be purified of water and of carbon dioxide and means for sending the whole of the purified first flow to the higher pressure column and optionally to the lower pressure column, means for sending a second air flow constituting between 2% and 25% of the air sent to the column system, compressed to a fourth pressure between 1.2 and 2 bar abs and above the second pressure but lower than the third pressure, at the fourth pressure, to the second adsorption unit in order to be purified of water and of carbon dioxide and means for sending the whole of the purified second flow to the lower pressure column, the higher pressure column comprising heat and mass exchange means in order to separate the air to form an oxygen-enriched liquid and a nitrogen-enriched gas, means for sending oxygen-enriched liquid and nitrogen-enriched liquid from the higher pressure column to the lower pressure column, means for drawing off a liquid with a purity of greater than 99%, preferably 99.5% of oxygen from the column system, a pump for pressurizing this liquid, means for vaporizing the pressurized liquid by heat exchange with at least one portion of the first air flow and means for sending an argon-enriched gas from the lower pressure column to the third column and means for drawing off an argon-rich fluid at the top of the third column.

Assignees

• Air Liquide

Inventors

• Tranier Jean-Pierre
• Dubettier-Grenier Richard
• Rozieres Maxime

Classifications

• F25J3/04412 Primary

  in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column · CPC title

• F25J3/04018

  of main feed air · CPC title

• F25J3/04169

  by adsorption of the impurities (adsorption in general B01D53/02) · CPC title

• F25J3/04248

  Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion · CPC title

• F25J3/04466

  for producing oxygen as a mixing column overhead gas by mixing gaseous air feed and liquid oxygen · CPC title