Fractionation of air by adsorption

• US 4,013,429 A
• Filed: 06/04/1975
• Issued: 03/22/1977
• Est. Priority Date: 06/04/1975
• Status: Expired due to Term

• Current Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Original Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Inventors: Sircar, Shivaji, Zondlo, John W.
• Primary Examiner(s): Spear, Jr., Frank A.
• Assistant Examiner(s): Spitzer, Robert H.
• Application Number:
  US05/583,787
• Time in Patent Office: 657 Days
• Field of Search: 55/25, 55/33, 55/58, 55/62, 55/68, 55/75
• US Class Current: 95/101
• CPC Class Codes: B01D 2253/108 Zeolites
• CPC Class Codes: B01D 2256/10 Nitrogen
• CPC Class Codes: B01D 2256/12 Oxygen
• CPC Class Codes: B01D 2257/102 Nitrogen
• CPC Class Codes: B01D 2257/504 Carbon dioxide
• CPC Class Codes: B01D 2257/80 Water
• CPC Class Codes: B01D 2259/40062 Four
• CPC Class Codes: B01D 2259/402 using two beds
• CPC Class Codes: B01D 2259/404 using four beds
• CPC Class Codes: B01D 53/0476 Vacuum pressure swing adsorption
• CPC Class Codes: B01D 53/261 by adsorption
• CPC Class Codes: C01B 21/04 Purification or separation of nitrogen by liquefying F25J
• CPC Class Codes: Y02C 20/40 of CO2
• CPC Class Codes: Y02P 20/151 Reduction of greenhouse gas [GHG] emissions, e.g. CO2

Abstract

Ambient air, during an on-stream period, is passed serially through a pretreatment adsorbent bed removing moisture and carbon dioxide therefrom and the thus dried and purified air then passed through a main adsorbent bed selective for retention of nitrogen, the oxygen-rich effluent being collected in an expandable receiving vessel. Nitrogen of high purity, is desorbed by suction from the main bed in a direction chamber to that of the initial air charge and passes from the main bed into and through the pretreatment bed to a collection vessel. Preceding the vacuum desorption step both the pretreatment bed and the main bed are rinsed with the high purity nitrogen product gas from a previous stage in the operation. Following evacuation the beds are repressured with a portion of the oxygen-rich gas drawn from the expandable receiving vessel. At least two parallel trains of adsorbent beds are employed in alternating timed sequence for continuity of operation. By operation in the described manner there are recovered for any desired use, nitrogen of high purity and an oxygen-enriched gas product.

Claims

1. The method for production of high purity nitrogen and an oxygen-enriched product from air containing water vapor and carbon dioxide, which comprises:

1. during an on-stream period carried out at substantially atmospheric pressure

a. introducing ambient air into a first bed of adsorbent effective in adsorption of said water vapor and carbon dioxide;

b. discharging unadsorbed gaseous effluent from said first adsorbent bed into a second adsorbent bed in series therewith and containing an adsorbent selective in retention of nitrogen as opposed to oxygen;

c. continuously during said on-stream period withdrawing from said second bed a primary gaseous effluent stream as an oxygen-rich product having a higher oxygen concentration than the air stream charged to said bed;

d. collecting said primary gaseous effluent in an expandable receiver;

2. discontinuing introduction of charge to said first bed of adsorbent and initiating removal of contained gases from said first and second beds by

e. first rinsing said beds with high purity nitrogen gas introduced into said first bed and flowed through said bed into and through said second bed at a rate and for a time period sufficient to effect removal of void air from both beds and short of breakthrough of adsorbed water from said first bed;

while collecting the rinse gas effluent from said second bed in a receiver separate from that in which said primary effluent was collected;

f. discontinuing introduction of said rinse gas to said first bed and the flow thereof to said second bed;

g. reducing the pressure at the air inlet end of said first bed while retaining gas flow communication between said first and second beds and causing substantially all of the nitrogen retained by said adsorbent during step (b) to flow through said first bed, thereby inducing desorption of water vapor and carbon dioxide from said first bed and desorption of nitrogen from said second bed;

h. collecting the desorbed gases rich in nitrogen in an expandable receiver, a portion of which collected gases from said receiver is employed as rinse gas in step (e);

i. thereafter discontinuing gas flow communication between said second and first bed, while continuing withdrawal of gas only from said first bed to a further reduced pressure level;

j. during said continued withdrawal of gas from said first bed introducing into said second bed a portion of the oxygen-rich primary effluent from step (d) thereby restoring said second bed to substantially its initial on-stream pressure;

k. thereafter discontinuing withdrawal of gas from said first bed and restoring gas flow communication between said second and first bed to permit flow of contained pressuring gas from said second to said first bed to bring said first bed to substantially its on-stream pressure;

3. The method as defined in claim 1 wherein at least a portion of the rinse gas effluent from step (e) is recycled for addition to the ambient air feed introduced into the adsorbent bed in step (a).

4. The method as defined in claim 1 wherein during said desorption of gas from said second bed in step (g), the pressure level in said bed is lowered to about 30-100 Torr.

5. The method as defined in claim 3 wherein desorption of gas from said first bed in step (i), is continued to a final reduced pressure level of 10-50 Torr.

6. The method as defined in claim 1 wherein desorption of gas from said first bed in step (i) is continued to a final reduced pressure level of 10-50 Torr.

7. The method as defined in claim 1 wherein the defined cycle of operations is carried out in parallel in at least two trains of such first and second series-connected beds in offset time sequence, whereby during gas removal from a first bed of one train, the first bed of another parallel train undergoes successively the steps of repressuring (k), ambient air introduction (a), and rinsing with nitrogen (e).

8. The method as defined in claim 1 wherein the defined cycle of operations is carried out in offset time sequence in parallel in two similar trains of adsorbent beds each having a first and second bed in series, whereby during gas removal at reduced pressure from the second bed of one such train, the second bed in the parallel train is subjected to the sequence;

repressuring (k), ambient air introduction (a), and rinsing with nitrogen (e).

11. The method as defined in claim 8, wherein the repressuring gas employed in operations (3) and (7) above comprises part of the unadsorbed effluent collected in operations (1) and (5) above as said oxygen-enriched product streams.

12. The method defined in claim 8, wherein the rinsing gas employed in nitrogen rinse steps (2) and (6) above, comprises part of the collected evacuated gas.

2. when said first bed has substantially reached its on-stream pressure again initiating a new cycle in the recited sequence with an on-stream period commencing with step (a).

9. The method of fractionating atmospheric air by selective adsorption for separate recovery of high purity nitrogen and oxygen-enriched product streams and wherein said atmospheric air is pretreated by contact with an adsorbent bed effective in removal of water vapor and CO₂ contained in said atmospheric air, which method comprises introducing the atmospheric air in alternate sequence into a first adsorbent train comprising a sequence of pretreatment bed and an air fractionating bed and a like second adsorbent train comprising in sequence a pretreatment bed and an air fractionating bed, each of said air fractionating beds containing molecular sieve zeolite effective in selective adsorption of nitrogen from air, said adsorbent trains being operated in a time sequence such that the respective beds simultaneously undergo during successive time periods the following operations:

1. passing atmospheric air through said first train and collecting unadsorbed effluent as an oxygen enriched product stream while said second train is being evacuated to an intermediate pressure;

2. rinsing said first train with high purity nitrogen product gas while said evacuation of the second train is continued;

3. while said rinsing of the first train is continued terminating the evacuation of the air fractionating bed of said second train and initiating the initiating the repressuring of said bed with oxygen-rich gas, while continuing evacuation of the pretreatment bed of said second train to a lower pressure level;

4. terminating nitrogen rinsing of said first train and subjecing that train to evacuation while retaining gas flow communication between the beds of said first train to cause substantially all of the nitrogen retained by said zeolite in said air fractionating bed during step (1) to flow through said pretreatment bed, during which period flow communication between the beds of said second train is established to permit flow of oxygen-rich repressuring gas from the nitrogen-adsorbent bed to the pretreatment bed of the second train;

10. during continued evacuation of said first train initiating flow of atmospheric air through said second train and collection of unadsorbed effluent as an oxygen-enriched product stream;

6. during further continued evacuation of said first train, discontinuing air introduction to said second train and rinsing said second train with high purity nitrogen product gas;

7. while said rinsing of the second train with nitrogen gas is continued, interrupting gas flow communication between the pretreatment bed and the nitrogen-adsorbing bed of said first train and repressuring the latter with oxygen-rich gas while continuing evacuation of the pretreatment bed of said first train to a lower pressure level;

8. thereafter reestablishing gas flow communication between the beds of said first train to permit flow of repressuring gas from the nitrogen adsorbent bed to the pretreatment bed of that train, while discontinuing the nitrogen rinsing of said second train and initiating evacuation of that train;

9. and thereafter repeating the foregoing sequence of operations starting with (1) above.