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An improved two stage pressure swing adsorption process for producing enriched oxygen and separating nitrogen or oxygen from a feed air stream. The process utilizes two-stage pressure swing adsorption plants which are serially connected. In the first stage, carbon dioxide, water and part of nitrogen

An improved two stage pressure swing adsorption process for producing enriched oxygen and separating nitrogen or oxygen from a feed air stream. The process utilizes two-stage pressure swing adsorption plants which are serially connected. In the first stage, carbon dioxide, water and part of nitrogen are removed and nitrogen is concentrated. In the second stage nitrogen is further separated from the effluent intermediate gas from the adsorption step in the adsorption towers of the first stage and oxygen is concentrated to the desired concentration. In the first stage the adsorption towers go through the steps in turn in a cycle: Adsorption, Purge, evacuation, countercurrent pressure equalization rising of the second stage gas, purge gas pressurization, and final pressurization. In the second stage the adsorption towers go through the steps in turn in a cycle: Adsorption, countercurrent pressure equalization falling, and final pressurization.

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1. An improved method of making enriched oxygen with two-stage pressure-swing adsorption, wherein oxygen and nitrogen are separated from air; the production can be oxygen or nitrogen or both of them; the method adopts two-stage pressure-swing adsorption device operating in series, wherein the first

1. An improved method of making enriched oxygen with two-stage pressure-swing adsorption, wherein oxygen and nitrogen are separated from air; the production can be oxygen or nitrogen or both of them; the method adopts two-stage pressure-swing adsorption device operating in series, wherein the first stage pressure-swing adsorption device is used to remove carbon dioxide and water as well as partial nitrogen and enrich nitrogen, and the second stage pressure-swing adsorption device is used to further remove the nitrogen in interim gas which is discharged from the adsorption tower in the adsorption step of the first stage and increase the concentration of oxygen up to the desired level; the adsorption tower of the first stage sequentially undergoes the following steps in one circulation period: adsorption A, purge P′, evacuation VC, the second stage gas backward equalization repressurization 2ER, purge gas repressurization R′, final repressurization FR; the adsorption tower of the second stage sequentially undergoes the following steps in one circulation period: adsorption A, backward equalization depressurization BD′, and final repressurization FR. 2. The method of claim 1, wherein the adsorption tower of the second stage adds the cocurrent equalization depressurization ED step after the adsorption A step, and adds the backward repressurization ER step after the backward equalization depressurization BD′ step in the meantime; the gas mixture of the repressurization ER step comes from the depressurization ED step. 3. The method of claim 1, wherein the adsorption tower of the first stage adds the two-end equalization depressurization 2ED′ step after the adsorption A step, and adds the two-end equalization repressurization 2ER′ step after the second stage gas backward equalization repressurization 2ER step in the meantime; the gas mixture of the two-end equalization repressurization 2ER′ step comes from the equalization depressurization 2ED′ step. 4. The method of claim 3, wherein the adsorption tower of the first stage adds backward depressurization BD step after the purge P′ step. 5. The method of claim 1, wherein the gas mixture discharged from the backward equalization depressurization BD′ step in the adsorption tower of the second stage enters into a buffer vessel V until pressure balance; in the meantime, the adsorption tower of the first stage is connected with the buffer vessel V, while proceeding the second stage gas backward equalization repressurization 2ER, until pressure balance. 6. The method of claim 3, wherein the gas mixture discharged from the backward equalization depressurization BD′ step in the adsorption tower of the second stage enters into a buffer vessel V until pressure balance; in the meantime, the adsorption tower of the first stage is connected with the buffer vessel V, while proceeding the second stage gas backward equalization repressurization 2ER, until pressure balance. 7. The method of claim 4, wherein the gas mixture discharged from the backward equalization depressurization BD′ step in the adsorption tower of the second stage enters into a buffer vessel V until pressure balance; in the meantime, the adsorption tower of the first stage is connected with the buffer vessel V, while proceeding the second stage gas backward equalization repressurization 2ER step, until pressure balance. 8. The method of claim 1, wherein the average concentration of oxygen in outlet gas, which comes from the adsorption tower in the adsorption step of the first stage, is 21 to 80 V %. 9. The method of claim 3, wherein the average concentration of oxygen in outlet gas, which comes from the adsorption tower in the adsorption step of the first stage, is 21 to 80 V %. 10. The method of claim 5, wherein the average concentration of oxygen in outlet gas, which comes from the adsorption tower in the adsorption step of the first stage, is 21 to 80 V %. 11. The method of claim 9, wherein the average concentration of oxygen in outlet gas, which comes from the adsorption tower in the adsorption step of the first stage, is 21 to 25V %. 12. The method of claim 10, wherein the average concentration of oxygen in outlet gas, which comes from the adsorption tower in the adsorption step of the first stage, is 21 to 25V %. 13. The method of claim 1, wherein the pressure of adsorption step A of two-stage pressure-swing adsorption device is 0.001 to 0.1 Mpa(g). 14. The method of claim 3, wherein the pressure of adsorption step A of two-stage pressure-swing adsorption device is 0.001 to 0.6 Mpa(g). 15. The method of claim 4, wherein the pressure of adsorption step A of two-stage pressure-swing adsorption device is 0.001 to 0.6 Mpa(g). 16. The method of claim 1, wherein the adsorbents which are packed in the adsorption tower of the first stage are activated alumina and molecular sieve from the bottom up, and the adsorbent which is packed in the adsorption tower of the second stage is molecular sieve only. 17. The method of claim 1, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are more than or equal to 1. 18. The method of claim 3, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are more than or equal to 1. 19. The method of claim 4, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are more than or equal to 1. 20. The method of claim 17, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are 3 to 7. 21. The method of claim 18, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are 3 to 7. 22. The method of claim 19, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are 3 to 7. 23. An improved method of making enriched oxygen with two-stage pressure-swing adsorption, wherein oxygen and nitrogen are separated from air; the production can be oxygen or nitrogen or both of them; the method adopts two-stage pressure-swing adsorption device operating in series, wherein the first stage pressure-swing adsorption device is used to remove carbon dioxide and water as well as partial nitrogen and enrich nitrogen, and the second stage pressure-swing adsorption device is used to further remove the nitrogen in interim gas which is discharged from the adsorption tower in the adsorption step of the first stage and increase the concentration of oxygen up to the desired level; the adsorption tower of the first stage sequentially undergoes the following steps in one circulation period: adsorption A, two-end equalization depressurization 2ED′, purge P′, backward depressurization BD, the second stage gas backward equalization repressurization 2ER, two-end equalization repressurization 2ER′, purge gas repressurization R′, final repressurization FR; the adsorption tower of the second stage sequentially undergoes the following steps in one circulation period: adsorption A, cocurrent equalization depressurization ED, backward equalization depressurization BD′, backward equalization repressurization ER, and final repressurization FR. 24. The method of claim 23, wherein the pressure of adsorption A step of two-stage pressure-swing adsorption device is 0.3 to 0.6 Mpa(g). 25. An improved method of making enriched oxygen with two-stage pressure-swing adsorption, wherein oxygen and nitrogen are separated from air; the production can be oxygen or nitrogen or both of them; the method adopts two-stage pressure-swing adsorption device operating in series, wherein the first stage pressure-swing adsorption device is used to remove carbon dioxide and water as well as partial nitrogen and enrich nitrogen, and the second stage pressure-swing adsorption device is used to further remove the nitrogen in interim gas which is discharged from the adsorption tower in the adsorption step of the first stage and increase the concentration of oxygen up to the desired level; the adsorption tower of the first stage sequentially undergoes the following steps in one circulation period: adsorption A, two-end equalization depressurization 2ED′, evacuation VC, the second stage gas backward equalization repressurization 2ER, two-end equalization repressurization 2ER′, final repressurization FR; the adsorption tower of the second stage sequentially undergoes the following steps in one circulation period: adsorption A, backward equalization depressurization BD′, and final repressurization FR. 26. The method of claim 25, wherein the adsorption tower of the second stage adds the cocurrent equalization depressurization ED step after the adsorption A step, and adds the backward repressurization ER step after the backward equalization depressurization BD′ step in the meantime; the gas mixture of the repressurization ER step comes from the depressurization ED step. 27. The method of claim 25, wherein the adsorption tower of the first stage adds the backward depressurization BD step after the two-end equalization depressurization 2ED′ step. 28. The method of claim 25, wherein the gas mixture discharged from the backward equalization depressurization BD′ step in the adsorption tower of the second stage enters into a buffer vessel V1 until pressure balance; in the meantime, the adsorption tower of the first stage is connected with the buffer vessel V1, while proceeding the second stage gas backward equalization repressurization 2ER, until pressure balance. 29. The method of claim 25, wherein the pressure of adsorption A step of two-stage pressure-swing adsorption device is 0.005 to 0.6 Mpa(g). 30. The method of claim 2, wherein the adsorption tower of the first stage adds the two-end equalization depressurization 2ED′ step after the adsorption A step, and adds the two-end equalization repressurization 2ER′ step after the second stage gas backward equalization repressurization 2ER step in the meantime; the gas mixture of the two-end equalization repressurization 2ER′ step comes from the equalization depressurization 2ED′ step. 31. The method of claim 30, wherein the adsorption tower of the first stage adds backward depressurization BD step after the purge P′ step. 32. The method of claim 2, wherein the gas mixture discharged from the backward equalization depressurization BD′ step in the adsorption tower of the second stage enters into a buffer vessel V until pressure balance; in the meantime, the adsorption tower of the first stage is connected with the buffer vessel V, while proceeding the second stage gas backward equalization repressurization 2ER, until pressure balance. 33. The method of claim 30, wherein the gas mixture discharged from the backward equalization depressurization BD′ step in the adsorption tower of the second stage enters into a buffer vessel V until pressure balance; in the meantime, the adsorption tower of the first stage is connected with the buffer vessel V, while proceeding the second stage gas backward equalization repressurization 2ER, until pressure balance. 34. The method of claim 31, wherein the gas mixture discharged from the backward equalization depressurization BD′ step in the adsorption tower of the second stage enters into a buffer vessel V until pressure balance; in the meantime, the adsorption tower of the first stage is connected with the buffer vessel V, while proceeding the second stage gas backward equalization repressurization 2ER step, until pressure balance. 35. The method of claim 2, wherein the average concentration of oxygen in outlet gas, which comes from the adsorption tower in the adsorption step of the first stage, is 21 to80 V %. 36. The method of claim 30, wherein the average concentration of oxygen in outlet gas, which comes from the adsorption tower in the adsorption step of the first stage, is 21 to 80 V %. 37. The method of claim 32, wherein the average concentration of oxygen in outlet gas, which comes from the adsorption tower in the adsorption step of the first stage, is 21 to 80 V %. 38. The method of claim 36, wherein the average concentration of oxygen in outlet gas, which comes from the adsorption tower in the adsorption step of the first stage, is 21 to 25V %. 39. The method of claim 37, wherein the average concentration of oxygen in outlet gas, which comes from the adsorption tower in the adsorption step of the first stage, is 21 to 25V %. 40. The method of claim 2, wherein the pressure of adsorption step A of two-stage pressure-swing adsorption device is 0.001 to 0.1 Mpa(g). 41. The method of claim 30, wherein the pressure of adsorption step A of two-stage pressure-swing adsorption device is 0.001 to 0.6 Mpa(g). 42. The method of claim 31, wherein the pressure of adsorption step A of two-stage pressure-swing adsorption device is 0.001 to 0.6 Mpa(g). 43. The method of claim 2, wherein the adsorbents which are packed in the adsorption tower of the first stage are activated alumina and molecular sieve from the bottom up, and the adsorbent which is packed in the adsorption tower of the second stage is molecular sieve only. 44. The method of claim 2, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are more than or equal to 1. 45. The method of claim 30, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are more than or equal to 1. 46. The method of claim 31, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are more than or equal to 1. 47. The method of claim 44, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are 3 to 7. 48. The method of claim 45, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are 3 to 7. 49. The method of claim 46, wherein the frequency of the backward equalization depressurization BD′ step in the adsorption tower of the second stage and the frequency of the second stage gas backward equalization repressurization 2ER step in the adsorption tower of the first stage are 3 to 7. 50. The method of claim 26, wherein the adsorption tower of the first stage adds the backward depressurization BD step after the two-end equalization depressurization 2ED′ step. 51. The method of claim 26, wherein the gas mixture discharged from the backward equalization depressurization BD′ step in the adsorption tower of the second stage enters into a buffer vessel V1 until pressure balance; in the meantime, the adsorption tower of the first stage is connected with the buffer vessel V1, while proceeding the second stage gas backward equalization repressurization 2ER, until pressure balance. 52. The method of claim 26, wherein the pressure of adsorption A step of two-stage pressure-swing adsorption device is 0.005 to 0.6 Mpa(g).