Multi-stage PSA process to remove contaminant gases from raw methane streams

Abstract

A multi-stage process to remove contaminant gases from raw methane streams is provided. The present technology is an innovative solution to recover and purify biogas by use of a process having at least two pressure swing adsorption stages. Taking advantage of the presence of carbon dioxide in the raw biogas streams, nitrogen and oxygen are bulky removed in the first stage, using selective adsorbents, and a nitrogen and oxygen-depleted intermediate stream is yielded to the second stage. The second stage employs an adsorbent or adsorbents to selectively remove carbon dioxide and trace amounts of remaining nitrogen and oxygen, thus producing a purer methane stream that meets pipeline and natural gas specifications.

Claims

1. A multi-stage Pressure Swing Adsorption process to remove contaminant gases from raw methane streams, comprising at least two Pressure Swing Adsorption stages: a first stage for removing Nitrogen and Oxygen, comprising the following steps: Feed (“FD”); Adsorption (“AD”); Equalization provided (“ET”); Blowdown (“BD”); Evacuation (“EV”); Purge (“PG”); Equalization received (“E↓”), wherein the first stage comprises at least one adsorbent, or mixture thereof, with strong affinity for carbon dioxide and methane; second stage for removing Carbon Dioxide and residual Nitrogen and Oxygen comprising the following steps: Adsorption (“AD”); Co-current depressurization (“COD”); First equalization provided (“E1↑”); Second equalization provided (“E2↑”); Evacuation (“EV”); First equalization received (“E1↓”); Idle (“ID”); Second equalization received (“E2↓”); Idle (“ID”); wherein the second stage comprises at least one adsorbent, or mixture thereof, with strong affinity for carbon dioxide.

2. The process according to claim 1, wherein the second stage further comprises a Blowdown (“BD”) stage after the Second equalization provided (“E2↑”) step and before the Evacuation (“EV”) step.

3. The process according to claim 2, wherein the Co-current depressurization (“COD”) step of the second stage occurs after the Second equalization provided (“E2↑”) and before the Evacuation (“EV”) step.

4. The process according to claim 1, wherein the second stage comprises a Backfill (“BF”) stage after the Second equalization received (“E2↓”) and before the second Idle (“ID”) stage.

5. The process according to claim 1, wherein the second stage comprises a Backfill (“BF”) stage after the second Idle (“ID”) stage.

6. The process according to claim 1, wherein it comprises a pre-treatment step before the first stage.

7. The process according to claim 1, wherein the first stage operates at a temperature between −50° C. and 120° C.

8. The process according to claim 1, wherein the operating pressure during the adsorption step in the first stage is between 60 kPa and 1500 kPa.

9. The process according to claim 8, wherein the purge to feed ratio varies between 0.3 to 0.9 depending on nitrogen feed stream content.

10. The process according to claim 1, wherein the operating desorption pressure in the evacuation step of the first stage ranges from 1 kPa to 100 kPa.

11. The process according to claim 1, wherein an intermediate biogas stream resultant of the first stage is pressurized between 200 kPa to 4,000 kPa and fed to the adsorption beds of the second stage.

12. The process according to claim 1, wherein the second stage operates at a temperature between −50° C. to 150° C.

13. The process according to claim 1, wherein the operating pressure during the adsorption step of the second stage is between 200 kPa and 4,000 kPa.

14. The process according to claim 1, wherein the operating desorption pressure in the evacuation step of the second stage is between 0.001 kPa and 100 kPa.

15. The process according to claim 1, wherein adsorbents used in the first and second stage are selected from the group consisting of zeolites, titanosilicates, metal-organic frameworks, activated carbons, carbon molecular sieves, alumina, silica gel, ionic liquid zeolites and Si/Al-based mesoporous materials.

16. The process according to claim 1, wherein the first stage equalization occurs through the top of adsorbent vessels.

17. The process according to claim 1, wherein the first stage equalization occurs through the bottom of adsorbent vessels.

18. The process according to claim 1, wherein the desorption in the evacuation step of the second stage occurs with purge.

19. The process according to claim 1, wherein the desorption in the evacuation step of the second stage occurs without purge.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) For easier understanding of this application, figures are attached in the annex that represent the preferred forms of implementation which nevertheless are not intended to limit the technique disclosed herein.

(2) The illustrated embodiments are merely examples of the present invention and do not limit the scope of the invention.

(3) FIG. 1 is a diagram of the process herein disclosed to recover methane from biogas by use of a two-stage pressure swing adsorption, by removing bulk nitrogen and oxygen from raw landfill gas in the first stage, and carbon dioxide from methane in the second stage, thus yielding a pure biomethane stream. The process considers a pre-treatment stage.

(4) The references shown in FIG. 1 are as follows: 1—crude biogas feed stream 2—filter 3—biogas blower 4—biogas heat exchanger 5—biogas feed stream 6—H.sub.2S guard bed 7—biogas feed stream 8—biogas feed stream 9—first stage feed pipeline 10—first stage intermediate biogas pipeline 11—first stage bottom equalization pipeline 12—first stage adsorption bed 13—first stage adsorption bed 14—first stage top equalization pipeline 15—first stage biogas purge pipeline 16—first stage biogas exhaust pipeline 17—biogas exhaust 18—biogas vacuum pump 19—intermediate biogas low pressure storage vessel 20—biogas compressor 21—intermediate biogas high pressure storage vessel 22—intermediate biogas stream 23—second stage bottom equalization pipeline 24—second stage feed pipeline 25—second stage exhaust pipeline 26—second stage adsorption bed 27—second stage adsorption bed 28—second stage adsorption bed 29—second stage adsorption bed 30—second stage top equalization pipeline 31—second stage biogas recycle pipeline 32—second stage biomethane pipeline 33—recycle stream/off-spec biomethane product 34—biogas vacuum pump 35—exhaust biogas 36—biomethane product 37—biomethane product storage vessel 38—biomethane product

(5) FIG. 2 is an illustration of the proposed first-stage PSA steps.

(6) FIG. 3 is an illustration of one of proposed embodiments of second-stage PSA steps.

(7) FIG. 4 is an illustration of another of proposed embodiments of second-stage PSA steps.

(8) FIG. 5 is a schematic diagram of the first-stage PSA steps sequence.

(9) FIG. 6 is a schematic diagram of the second-stage PSA steps sequence.

(10) FIG. 7 is a schematic diagram of another embodiment of the second-stage PSA steps sequence.

(11) FIG. 8 is a diagram of the process herein disclosed to recover methane from biogas by use of a two-stage pressure swing adsorption.

DESCRIPTION OF THE EMBODIMENTS

(12) Hereinafter, the process will be described in detail with reference to the annexed drawings. A number of preferred embodiments will be described, but they are not intended to limit the scope of this application. Various modifications may be made in the spirit and without departing from the scope of the technology.

(13) The present application discloses a process comprising at least two PSA stages.

(14) In one embodiment, the process comprises a pre-treatment stage, before the first-stage PSA, in order to reduce water level of raw biogas feed down to 5° C. of dew point, and H.sub.2S content down to 2 ppm. This pre-stage solution comprises a filter, or a series of filters, for water and particles removal, followed by a biogas blower and a heat exchanger that reduces the temperature of the feed stream down to 5° C., thus removing moisture by condensation. The pre-stage also comprises an activated carbon adsorption filter of one or more vessels filled with an impregnated or non-impregnated activated carbon capable of removing hydrogen sulfide and other sulfur compounds.

(15) The first-stage PSA runs for each adsorber a cycle comprising the following sequence of steps in a repeating order (FIG. 2): Feed (“FD”), where the adsorber is pressurized with feed stream up to the higher operating pressure. The gas flows upwards into the adsorber, while the more-strongly adsorbed components are retained and the gas-phase is enriched in the less-adsorbed components; Adsorption (“AD”), where the feed flows through the adsorber and the more-strongly adsorbed components are retained in the bed and a gas stream enriched in the less-strongly adsorbed component leaves the column through the opposite side. In one embodiment, during the adsorption step, a fraction of the less-strongly adsorbed stream is used to counter-currently purge the bed running purge (“PG”) step at low operating pressure. The purge to feed (P/F) ratio varies between 0.3 to 0.9 depending on nitrogen feed stream content; Equalization provided (“E↑”), where the adsorber that has completed the adsorption step connects with the one that has been purged and the pressure between adsorbers is equalized. In this step, part of the gas that would be lost in the blowdown step is used to pressurize the other adsorber; Blowdown (“BD”), where the adsorber is counter-currently blowdown and some of the gas that is enriched in the more-strongly adsorbed components flows throw-out the adsorber and exits through feed end. The pressure in this step varies from the final pressure attained in equalization step to a final pressure near the low operating pressure; Evacuation (“EV”), the remaining gas that is enriched in the more-strongly adsorbed components is withdrawn from the adsorber, at low operating pressure, using a vacuum pump; Purge (“PG”), where a fraction of the less-strongly adsorbed components stream that is delivered during adsorption (“AD”) is admitted to counter-currently pass through the bed at low operating pressure conditions. This gas forces the more-strongly adsorbed components to displace the adsorption sites of the molecular sieve, thus yielding a stream enriched in the more-strongly adsorbed components that is withdraw via vacuum pump. Equalization received (“E↓”), where the adsorber that has completed the evacuation and/or purge step connects with the one that has been adsorbing and the pressure between vessels is equalized. In this step, the adsorber is pressurized with gas provided by the other adsorber, naturally richer in methane (and poorer in nitrogen and oxygen) than the raw biogas feed stream.

(16) The second-stage PSA runs, for each adsorber, a cycle comprising the following sequence of steps in a repeating order (FIG. 4): Adsorption (“AD”), where the adsorber is pressurized with feed stream to the higher operating pressure and the more-strongly adsorbed components are retained in the bed and a gas stream enriched in the less-strongly adsorbed component leaves the column through the top; Co-current depressurization (“COD”), where the adsorber is slowly co-currently depressurized and the depressurization gas is used as recycle stream that is fed to first stage; First equalization provided (“E1↑”), where the adsorber that has completed the co-current depressurization step connects with the one that has been idle after completed first equalization received step and the pressure between vessels is equalized; Second equalization provided (“E2↑”), where the adsorber that has completed the first equalization provided step connects with the one that has been evacuating and the pressure between vessels is equalized; Evacuation (“EV”), follows the blowdown step, the remaining gas that is enriched in the more-strongly adsorbed components is withdrawn from the adsorber through the feed end, at low operating pressure, using a vacuum pump; First equalization received (“E1↓”), where the adsorber that has completed the evacuation step connects with the one that has completed first equalization provided step and the pressure between vessels is equalized; Idle (“ID”), where the adsorber is on idle; Second equalization received (“E2↓”), where the adsorber that has been idle, after completed the first equalization received step, connects with the one that has completed co-current depressurization step and the pressure between vessels is equalized; Backfill (“BF”), where the adsorber that has completed the second equalization received step counter-currently receives part of the gas that leaves the adsorber that is under adsorption step; Idle (“ID”), where the adsorber is on idle.

(17) In one embodiment, the second stage further comprises a Blowdown (“BD”) stage, where the adsorber is counter-currently blowdown and a stream enriched in the more-strongly adsorbed components flows throw-out the adsorber through the feed end, which occurs after the Second equalization provided (“E2↑”) and before the Evacuation (“EV”).

(18) In one embodiment, the second stage Co-current depressurization (“COD”) step, of the second stage, occurs after the Second equalization provided (“E2↑”) and before the Evacuation (“EV”) step.

(19) In another embodiment, the second stage comprises a Backfill (“BF”) stage after the Second equalization received (“E2↓”) and before the second Idle (“ID”) stage.

(20) In yet another embodiment, the second stage comprises a Backfill (“BF”) stage after the second Idle (“ID”) stage.

(21) The previous embodiments form the following second-stage PSA sequence of steps in a repeating order (FIG. 3): Adsorption (“AD”), where the adsorber is pressurized with feed stream to the higher operating pressure, and the more-strongly adsorbed components are retained in the bed and a gas stream enriched in the less-strongly adsorbed component leaves the column through the top; First equalization provided (“E1↑”), where the adsorber that has completed the adsorption step connects with the one that has completed the first equalization received step and the pressure between vessels is equalized; Second equalization provided (“E2↑”), where the adsorber that has completed the first equalization provided step connects with the one that has been evacuating and the pressure between vessels is equalized; Co-current depressurization (“COD”), where the adsorber that has completed the second equalization provided step is co-currently depressurized, and being the depressurization gas used as recycle stream that is fed to the first stage; Evacuation (“EV”), where the adsorber is counter-currently evacuated, using a vacuum pump, and a stream enriched in the more-strongly adsorbed components is withdrawn from the adsorber, at low operating pressure; First equalization received (“E1↓”), where the adsorber that has completed the evacuation step connects with the one that has completed first equalization provided step and the pressure between vessels is equalized; Idle (“ID”), where the adsorber is on idle; Second equalization received (“E2↓”), where the adsorber that has been idle after completed the first equalization received step connects with the one that has completed adsorption step and the pressure between vessels is equalized; Idle (“ID”), where the adsorber is again on idle; Backfill (“BF”), where the adsorber that has completed the second equalization received step counter-currently receives part of the gas that leaves the adsorber that is under adsorption step.

(22) The first stage operates at a temperature between −50° C. and 120° C. In a preferred embodiment the first stage occurs at a temperature between from 0 to 70° C.

(23) The operating pressure during the adsorption step in the first stage is between ca. 60 kPa and 1500 kPa. In a preferred embodiment the pressure is between 80 kPa and 400 kPa. In a more preferred embodiment the pressure is between 100 to 150 kPa.

(24) The operating desorption pressure in the evacuation step of the first stage ranges from 1 kPa to 100 kPa. In a preferred embodiment the pressure is between 10 kPa and 80 kPa. In a more preferred embodiment the pressure is between 20 and 60 kPa.

(25) The intermediate biogas stream resultant of the first stage is pressurized between ca. 200 kPa to 4.000 kPa and fed to the adsorption beds of the second-stage PSA. In a preferred embodiment it is pressurized between 500 kPa and 1.000 kPa. In a more preferred embodiment it is pressurized between 600 to 900 kPa.

(26) The second stage operates at a temperature of −50° C. to 150° C. In a preferred embodiment the temperature is between 10 and 80° C.

(27) The operating pressure during the adsorption step of the second stage is between ca. 200 kPa and 4.000 kPa. In a preferred embodiment the pressure is between 500 kPa and 1.000 kPa. In a more preferred embodiment the pressure ranges from 600 to 900 kPa.

(28) The operating desorption pressure in the evacuation step of the second stage is between 0.001 kPa and 100 kPa. In one preferred embodiment the pressure ranges from 0.01 kPa to 20 kPa. In a more preferred embodiment the pressure ranges from 0.1 to 10 kPa.

(29) The adsorbers in the first and second stage are filled with at least one selective adsorbent, or mixture thereof, that is a molecular sieve with strong affinity to carbon dioxide and methane. Adsorbents should be selected from the group consisting of carbon molecular sieves, activated carbons, zeolites, titanosilicates, metal-organic frameworks, alumina, silica gel, novel adsorbents like ionic liquid zeolites (ILZ) or other mesoporous materials with Si/Al-based.

(30) The first stage and second stage comprise at least two adsorption beds each. In one embodiment, the second stage comprises four adsorption beds.

(31) An overview of the process of the present technology can be described by referring to FIG. 1.

(32) In one embodiment, as shown, the process comprises a pre-treatment stage. Raw biogas feed stream (1) enters the pre-treatment stage that comprises a filter or a series particle filters (2), a biogas blower (3), a heat exchanger (4) that lowers the temperature of the feed stream down to 5° C. and the condensed water is removed, and a hydrogen sulfide guard bed (6). The hydrogen sulfide guard bed (6) is filled with activated carbon that lowers the H.sub.2S content down to ppm level. The biogas feed current (7) that exits this pre-treatment stage has less than 2 ppm of H.sub.2S and less than 9000 ppm of H.sub.2O.

(33) The raw biogas feed stream (7) typically contains up to 12 mol % of N.sub.2, 5 mol % of O.sub.2, 35 mol % of CO.sub.2 and 48 mol % of CH.sub.4, and can be combined with the recycling stream (31) from the co-current depressurization of second-stage PSA, typically containing 91-97% CH.sub.4, 0.2-2.0% CO.sub.2, 3.0-6.0% N.sub.2, 0.2-1.0% O.sub.2, thus generating the stream (8) slightly methane-enriched that is fed to the first-stage PSA.

(34) The cycle steps of first-stage PSA occur as previously described (FIG. 2 and FIG. 5). In one embodiment the first-stage PSA operates at a temperature of −50° C. to 120° C., more preferably from 0 to 70° C.

(35) The adsorbent, or a combination of adsorbents, selected are nitrogen-selective molecular sieves, from the group consisting of carbon molecular sieves, activated carbons, zeolites, titanosilicates, metal-organic frameworks, alumina, silica gel, novel adsorbents like ionic liquid zeolites (ILZ) or other mesoporous materials with Si/Al-based.

(36) The adsorber (12) is pressurized with a biogas feed stream through line (9). The pressure during the adsorption is from ca. 60 kPa to 1500 kPa, preferably between 80 kPa and 400 kPa, and more preferably from 100 to 150 kPa.

(37) The gas flows upwards into the adsorber, while the more-strongly adsorbed components are retained and the gas-phase is enriched in the less-adsorbed components. Adsorption step takes place, where biogas feed flows through the adsorber (12) and the more-strongly adsorbed components are retained in the bed and a gas stream enriched in the less-strongly adsorbed component leaves the column through line (16). During this, a fraction of the less-strongly adsorbed stream is used to counter-currently purge the adsorber (13) through the line (15).

(38) After the adsorption step is completed, adsorbers are connected through line (11), at the bottom, and the pressure between adsorbers is equalized. In another embodiment, adsorbers are connected through line (14), at the top, and the pressure between adsorbers is equalized.

(39) After the equalization step, the adsorber (12) is counter-currently blowdown and evacuated through exhaust line (10) using a vacuum pump (18). The desorption pressure ranges from 1 kPa to 100 kPa, preferably from 10 kPa to 80 kPa, and more preferably from 20 to 60 kPa.

(40) An intermediate biogas stream, nitrogen and oxygen depleted, is then collected and stored in vessel (19). While adsorber (12) is evacuating, part of the less-strongly adsorbed stream exiting the adsorber (13) through top is admitted to counter-currently purge the adsorber (12). The part of raffinate stream used to purge the adsorber (12) depends on the nitrogen content of the feed stream varying, the herein designated purge to feed (P/F) ratio, between 0.3 to 0.9. Afterwards, both adsorbers (12) and (13) are connected through the line (11) and their pressure equalized. In another embodiment, adsorbers are connected through the line (14) and their pressure is equalized.

(41) The biogas intermediate stream is stored in vessel (19) and pressurized in biogas compressor (20) before fed to the second-stage PSA through line (22).

(42) The intermediate biogas stream is pressurized from ca. 200 kPa to 4.000 kPa, preferably between 500 kPa and 1.000 kPa, and more preferably from 600 to 900 kPa, and fed to the adsorption beds of the second-stage PSA.

(43) The process steps of this second-stage were previously described (FIG. 4 and FIG. 7). The second-stage PSA operates at a temperature of −50° C. to 150° C., more preferably from 10 to 80° C.

(44) Adsorbent or the combination of adsorbents selected has high CO.sub.2/CH.sub.4 selectivity, and should be selected from the group consisting of carbon molecular sieves, activated carbons, zeolites, titanosilicates, metal-organic frameworks, alumina, silica gel, novel adsorbents like ionic liquid zeolites (ILZ) or other mesoporous materials with Si/Al-based.

(45) The adsorber (26) is pressurized with intermediate biogas stream from first-stage and the gas flows upwards into the adsorber, while the more-strongly adsorbed components are retained and the gas-phase is enriched in the less-adsorbed component, that leaves the adsorber through the line (32) and is stored in vessel (36). The pressure during the adsorption is from ca. 200 kPa to 4.000 kPa, preferably between 500 kPa and 1.000 kPa, and more preferably from 600 to 900 kPa.

(46) After completing the adsorption step, the feed end is closed and the adsorber (26) co-currently depressurizes through line (31), delivering a second-grade methane-enriched stream to be recycled and fed to the first-stage PSA, that is mixed with biogas coming from feed stream (7). This enriches the feed stream (8) concentration in methane and reduces the levels of carbon dioxide, nitrogen and oxygen.

(47) After, the adsorbers (26) and (27) are connected through line (30) and pressure between them equalized. In another embodiment adsorbers are connected through line (23) and pressure between them equalized. After completing the first equalization provided step, the adsorber (26) and adsorber (29) are connected through line (30) and pressure equalized. In another embodiment the adsorbers (26) and (29) are connected through line (23) and pressure between them equalized.

(48) After, the adsorber (26) is counter-currently blowdown and evacuated through exhaust line (25) using a vacuum pump (34) and an exhaust product (35) enriched in the more-strongly adsorbed components delivered. In one embodiment the desorption step occurs with purge, through pipeline (31). In another embodiment the desorption occurs without purge. The desorption pressure ranges from 0.001 kPa to 100 kPa, preferably from 0.01 kPa to 20 kPa, and more preferably from 0.1 to 10 kPa.

(49) Afterwards, two equalization steps take place. First, adsorber (26) and (28) are connected through pipeline (30) and pressure equalized, and second, after an idle step, adsorber (26) and (27) are connected through pipe (30) and pressure equalized. In another embodiment, both equalization steps are made connecting the adsorbers through line (23). After a step in which adsorber (26) is on idle, backfill step takes place. During this step, immediately prior to adsorption, the adsorber (26) counter-currently receives part of the gas produced and stored in vessel (37) through line (32).

(50) In another embodiment, the process steps of the second-stage, previously described (FIG. 3 and FIG. 6) can be detailed as follows. The second-stage PSA operates at a temperature of −50° C. to 150° C., more preferably from 10 to 80° C. The adsorbent, or the combination of adsorbents, selected has high CO.sub.2/CH.sub.4 selectivity, and should be selected from the group consisting of carbon molecular sieves, activated carbons, zeolites, titanosilicates, metal-organic frameworks, alumina, silica gel, novel adsorbents like ionic liquid zeolites (ILZ) or other mesoporous materials with Si/Al-based.

(51) The adsorber (26) is pressurized with intermediate biogas stream from first-stage and the gas flows upwards into the adsorber, while the more-strongly adsorbed components are retained and the gas-phase is enriched in the less-adsorbed component, that leaves the adsorber through the line (32) and is stored in vessel (36). The pressure during the adsorption is from ca. 200 kPa to 4.000 kPa, preferably between 500 kPa and 1.000 kPa, and more preferably from 600 to 900 kPa.

(52) After completing the adsorption step, the adsorbers (26) and (27) are connected through line (30) and pressure between them is equalized. In another embodiment adsorbers are connected through line (23), at the bottom, and pressure between them equalized. After completing the first equalization provided step, the adsorber (26) and adsorber (29) are connected through line (30), at the top, and pressure equalized. In another embodiment the adsorbers (26) and (29) are connected through line (23) and pressure between them equalized.

(53) After, the adsorber (26) co-currently depressurizes through line (31), delivering a second-grade methane-enriched stream to be recycled and fed to the first-stage PSA, that is mixed with biogas coming from the feed stream (7). This improves and slightly enriches the feed stream (8) concentration in methane and reduces the levels of carbon dioxide, nitrogen and oxygen.

(54) After, the adsorber (26) is counter-currently blowdown and evacuated through exhaust line (25) using a vacuum pump (34) and an exhaust product (35) enriched in the more-strongly adsorbed components delivered. In one embodiment the desorption step occurs with purge, through pipeline (31). In another embodiment the desorption occurs without purge. The desorption pressure ranges from 0.001 kPa to 100 kPa, preferably from 0.01 kPa to 20 kPa, and more preferably from 0.1 to 10 kPa.

(55) Afterwards, two equalization steps take place. First, adsorber (26) and (28) are connected through pipeline (30) and pressure equalized, and second, after an idle step, adsorber (26) and (27) are connected through pipe (30) and pressure equalized. In another embodiment, both equalization steps are made connecting the adsorbers through line (23).

(56) After a step in which adsorber (26) is on idle, backfill step takes place. During this step, immediately prior to adsorption, the adsorber (26) counter-currently receives part of the gas produced and stored in vessel (37) through line (32).

(57) In preferred embodiments, the final biomethane gas contains no more than 0.5 mol % of CO.sub.2, less than 3 mol % of N.sub.2, less than 0.2 mol % of O.sub.2 and less than 2 ppm of H.sub.2S, in a dry basis.

(58) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope of the invention. Therefore, the present technology is not limited to the above-described embodiments, but the present invention is defined by the claims which follow, along with their fall scope of equivalents.

EXAMPLES

Example 1

(59) In this example, the removal of contaminant gases from a landfill biogas stream according to one embodiment of the present application is simulated computationally. According to the simulation, a biomethane stream of 174 m.sup.3/h with 96.8% of CH.sub.4, 0.1% of CO.sub.2, 3.0% of N.sub.2 and 0.1% of O.sub.2 is recovered from a raw landfill biogas stream containing 48.0% of CH.sub.4, 35.0% of CO.sub.2, 12.0% of N.sub.2 and 5.0% of O.sub.2. The flow rate of the raw landfill biogas stream is 530 m.sup.3/h.

(60) In this embodiment, the first-stage PSA comprises two adsorption beds, packed with activated carbon with 900-1200 m.sub.2/g of total surface area (B.E.T.), running the cyclic sequence of steps schematized in FIG. 5. The second-stage PSA comprises four adsorption beds, packed with a carbon molecular sieve with pore width of 3-7 Å, running the cyclic sequence of steps schematized in FIG. 7.

(61) The results obtained are listed in Table 1. This table resumes the composition as well as the pressure and temperature conditions of each crucial stream of the process illustrated in FIG. 1.

(62) TABLE-US-00001 TABLE 1 1 7 8 17 19 21 35 38 33 CH4, % 48.0 48.0 49.4 37.8 55.7 55.7 1.9 96.8 95.1 CO2, % 35.0 35.0 34.0 23.8 39.6 39.6 91.3 0.1 1.4 N2, % 12.0 12.0 11.7 27.4 3.2 3.2 3.5 3.0 3.1 O2, % 5.0 5.0 4.9 11.0 1.5 1.5 3.3 0.1 0.4 H2S, ppm 1500 0 0 0 0 0 0 0 0 H2O, ppm 28000 9600 9166 117 11300 900 2059 39 43 P/kPa 101 120 134 128 102 850 1 750 600 T/° C. 23 23 40 30 15 45 15 35 30 Flow/ 530 500 515 182 333 333 144 174 15 m3 .Math. h.sup.−1

Example 2

(63) In this example, the removal of contaminant gases from a landfill biogas stream according to one embodiment of the present application is simulated computationally. According to the simulation, a biomethane stream of 222 m.sup.3/h with 96.9% of CH.sub.4, 0.1% of CO.sub.2, 2.9% of N.sub.2 and 0.1% of O.sub.2 is recovered from a raw landfill biogas stream containing 50.0% of CH.sub.4, 39.0% of CO.sub.2, 8.0% of N.sub.2 and 3.0% of O.sub.2. The flow rate of the raw landfill biogas stream is 530 m.sup.3/h.

(64) In this embodiment, the first-stage PSA comprises two adsorption beds, packed with activated carbon with 900-1200 m.sub.2/g of total surface area (B.E.T.), running the cyclic sequence of steps schematized in FIG. 5. The second-stage PSA comprises four adsorption beds, packed with a carbon molecular sieve with pore width of 3-7 Å, running the cyclic sequence of steps schematized in FIG. 7.

(65) The results obtained are listed in Table 2. This table resumes the composition as well as the pressure and temperature conditions of each crucial stream of the process illustrated in FIG. 1.

(66) TABLE-US-00002 TABLE 2 1 7 8 17 19 21 35 38 33 CH4, % 50.0 50.0 51.7 33.4 55.9 55.9 1.6 96.9 95.3 CO2, % 39.0 39.0 37.6 28.1 39.7 39.7 92.2 0.1 1.3 N2, % 8.0 8.0 7.8 28.6 3.1 3.1 3.4 2.9 3.0 O2, % 3.0 3.0 2.9 10.0 1.3 1.3 2.9 0.1 0.4 H2S, ppm 1500 0 0 0 0 0 0 0 0 H2O, ppm 28000 9600 9166 117 11300 900 2059 39 43 P/kPa 101 120 139 128 102 850 1 750 600 T/° C. 23 23 40 30 15 45 15 35 30 Flow/ 530 500 520 96 424 424 182 222 20 m3 .Math. h.sup.−1

Example 3

(67) In this example, the removal of contaminant gases from a digestor gas stream according to one embodiment of the present application is simulated computationally. According to the simulation, a biomethane stream of 206 m.sup.3/h with 98.9% of CH.sub.4, 0.2% of CO.sub.2 and 0.9% of N.sub.2 is recovered from a raw landfill biogas stream containing 52.0% of CH.sub.4, 44.0% of CO.sub.2, 3.0% of N.sub.2 and 1.0% of O.sub.2. The flow rate of the raw landfill biogas stream is 530 m.sup.3/h.

(68) In this embodiment, the first-stage PSA comprises two adsorption beds, packed with activated carbon with 900-1200 m.sub.2/g of total surface area (B.E.T.), running the cyclic sequence of steps schematized in FIG. 5. The second-stage PSA comprises four adsorption beds, packed with a carbon molecular sieve with pore width of 3-7 Å, running the cyclic sequence of steps schematized in FIG. 6.

(69) The results obtained are listed in Table 3. This table resumes the composition as well as the pressure and temperature conditions of each crucial stream of the process illustrated in FIG. 1.

(70) TABLE-US-00003 TABLE 3 1 7 8 17 19 21 35 38 33 CH4, % 52.0 52.0 53.1 56.0 52.4 52.4 0.7 98.9 90.1 CO2, % 44.0 44.0 43.0 29.2 46.2 46.2 97.4 0.2 8.2 N2, % 3.0 3.0 2.9 11.3 1.0 1.0 1.1 0.9 1.1 O2, % 1.0 1.0 1.0 3.5 0.4 0.4 0.8 0.0 0.6 H2S, ppm 1500 0 0 0 0 0 0 0 0 H2O, ppm 28000 9600 9166 117 11300 900 2059 39 43 P/kPa 101 130 130 128 102 850 1 750 150 T/° C. 23 23 40 30 15 45 15 35 30 Flow/ 530 500 515 98 417 417 196 206 15 m3 .Math. h.sup.−1

REFERENCES

(71) [1] SOUTHERN CALIFORNIA GAS COMPANY Revised CAL. P.U.C. SHEET NO. 47193-G.