Pre-purification of air for separation

• US 5,232,474 A
• Filed: 10/17/1991
• Issued: 08/03/1993
• Est. Priority Date: 04/20/1990
• Status: Expired due to Fees

• Current Assignee: BOC Group Pty Limited (Linde Plc)
• Original Assignee: BOC Group Pty Limited (Linde Plc)
• Inventors: Jain, Ravi
• Primary Examiner(s): SPITZER, ROBERT H
• Application Number:
  US07/779,427
• Time in Patent Office: 656 Days
• Field of Search: 55/25, 55/26, 55/31, 55/33, 55/62, 55/68, 55/74, 55/75, 55/58, 62/13, 62/18
• US Class Current: 95/97
• CPC Class Codes: B01D 2253/104 Alumina
• CPC Class Codes: B01D 2253/106 Silica or silicates
• CPC Class Codes: B01D 2253/108 Zeolites
• CPC Class Codes: B01D 2253/25 Coated, impregnated or composite adsorbents
• CPC Class Codes: B01D 2253/304 Linear dimensions, e.g. particle shape, diameter
• CPC Class Codes: B01D 2257/504 Carbon dioxide
• CPC Class Codes: B01D 2257/80 Water
• CPC Class Codes: B01D 2259/40056 Gases other than recycled product or process gas
• CPC Class Codes: B01D 2259/40081 Counter-current
• CPC Class Codes: B01D 2259/402 using two beds
• CPC Class Codes: B01D 2259/4146 Contiguous multilayered adsorbents
• CPC Class Codes: B01D 2259/416 involving cryogenic temperature treatment
• CPC Class Codes: B01D 53/047 Pressure swing adsorption
• CPC Class Codes: B01D 53/261 by adsorption
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

Carbon dioxide is removed from a gas stream containing at least 250 ppm by volume of carbon dioxide by pressure swing adsorption in an alumina adsorption bed that is sized sufficiently large to remove at least 75 mole percent of the carbon dioxide in the gas stream. The process is particularly useful for removing substantially all of the carbon dioxide and water vapor from a stream of ambient air prior to separating the components of the air in a cryogenic air separation unit.

Claims

1. A process for the purification of a gas stream containing at least 250 ppm carbon dioxide by pressure swing adsorption comprising sequentially passing said gas stream through a bed of activated alumina at a superatmospheric pressure, thereby adsorbing substantially all of the carbon dioxide contained in the gas stream, depressurizing said bed and purging said bed with the gaseous effluent from said bed or with another gas that is substantially free of carbon dioxide, thereby desorbing carbon dioxide from said bed.

2. The process of claim 1, wherein said gas stream additionally contains moisture and said moisture is substantially completely adsorbed by said bed of activated alumina, and the gas used to purge said bed is substantially free of moisture.

3. The process of claim 2, wherein said gas stream is ambient air.

4. The process of claim 1, wherein the gaseous effluent from said bed of activated alumina is passed through a bed of zeolite and both of said beds are subsequently depressurized and purged with the gaseous effluent from said zeolite bed or with an other gas that is substantially free of carbon dioxide, thereby desorbing carbon dioxide from said beds.

5. A process in accordance with claim 1, wherein the particles of activated alumina in said bed are in the range of about 0.4 and 1.8 mm.

6. A process in accordance with claim 5, wherein said particles are between about 0.6 mm and 1.6 mm.

7. A process for the removal of water vapor and carbon dioxide from ambient air comprising repeating the sequential steps of:

(a) flowing a stream of ambient air at a predetermined superatmospheric pressure through a bed of activated alumina, thereby adsorbing substantially all of the water vapor and carbon dioxide contained in said ambient air stream;

(b) ceasing the flow of ambient air through said bed and venting said bed;

(c) purging said bed with the gaseous effluent from step (a) or with an other gas which is substantially free of water vapor and carbon dioxide, thereby desorbing water vapor and carbon dioxide from said bed; and

(d) repressurizing said bed to said predetermined superatmospheric pressure with a gas selected from the effluent from step (a) and ambient air.

8. The process of claim 7, wherein said bed is repressurized with the effluent from step (a) and the flow of gas in steps (b), (c) and (d) is countercurrent tot he flow of gas in step (a).

9. The process of claim 7, wherein step (d) comprises first partially pressurizing said bed with the effluent from step (a) and then further pressurizing said bed with ambient air.

10. The process of claim 7, wherein step (a) additionally comprises flowing the gaseous effluent from said bed of activated alumina through a bed of zeolite.

11. The process of claim 10, wherein the zeolite has an average particle size in the range of about 0.4 and 1.8 mm.

12. The process of claim 10, wherein the average particle side of the zeolite is in the range of about 0.6 mm and 1.6 mm.

13. The process of claim 10, wherein all adsorbent particles in said beds are between about 0.4 mm and 1.8 mm.

14. The process of claim 7, wherein the gaseous effluent from step (a) is fractionated in a cryogenic air separation unit.

15. The process of claim 14, wherein said other gas is a product gas from said cryogenic air separation unit.

16. The process of claim 14 wherein said other gas is a nitrogen-enriched waste stream from said cryogenic air separation unit.

17. A process for the removal of carbon dioxide from a gas stream comprising repeating the sequential steps of:

(a) flowing the gas stream at a predetermined superatmospheric pressure through a bed of activated alumina, thereby adsorbing substantially all of the carbon dioxide contained in said gas stream;

(b) ceasing the flow of said gas stream through said bed and venting said bed; and

(c) purging said bed with the gaseous effluent from step (a) or with an other gas which is substantially free of carbon dioxide, thereby desorbing carbon dioxide from said bed; and

(d) repressurizing said bed to said predetermined superatmospheric pressure with the effluent from step (a).