Integrated process for native CO2 recovery from a sour gas comprising H2S and CO2

Abstract

The invention relates to a method for treating a hydrocarbon feed gas stream containing CO.sub.2 and H.sub.2S to recover a purified CO.sub.2 gas stream (vii), comprising: a. Separating said feed gas stream into a sweetened gas stream (i), and an acid gas stream (ii); b. Introducing stream (ii) into a Claus unit wherein an oxygen-rich stream is used as a combustive agent in the Claus furnace, thereby recovering a liquid stream of elemental sulfur (iii) and a tail gas stream (iv); c. Introducing the stream (iv) into a Tail Gas Treatment Unit (TGTU) thereby separating said tail gas stream into a CO.sub.2 enriched gas stream (v), and a stream enriched in sulfur compounds (vi); d. Compressing stream (v) exiting the TGTU; e. Passing the compressed CO.sub.2 enriched gas through a CO.sub.2 purification unit thereby recovering a purified CO.sub.2 gas stream (vii), and the device for carrying out said method.

Claims

1. A method for treating a hydrocarbon feed gas stream containing at least carbon dioxide and hydrogen sulfide to recover a purified CO.sub.2 gas stream (vii), said process comprising the following steps: a. Separating said hydrocarbon feed gas stream into a sweetened hydrocarbon gas stream (i), and an acid gas stream (ii) comprising at least carbon dioxide and hydrogen sulfide; b. Introducing said acid gas stream (ii) into a Claus unit wherein an oxygen-rich stream is used as a combustive agent in a Claus furnace, thereby recovering a liquid stream of elemental sulfur (iii) and a tail gas stream (iv) mainly comprising carbon dioxide, hydrogen and sulfur compounds; c. Introducing the exiting tail gas stream (iv) into a Tail Gas Treatment Unit (TGTU) thereby separating said tail gas stream into a CO.sub.2 enriched gas stream also containing hydrogen and sweetened in sulfur compounds (v), and a stream enriched in sulfur compounds (vi); d. Compressing the CO.sub.2 enriched gas stream (v) exiting the TGTU and performing dehydration of the CO.sub.2 enriched gas stream exiting the compression unit, thereby obtaining a dehydrated and compressed CO.sub.2 enriched gas; e. Passing the dehydrated and compressed CO.sub.2 enriched gas through a CO.sub.2 purification unit thereby recovering a purified CO.sub.2 gas stream (vii) and a lean CO.sub.2 stream (viii).

2. The method according to claim 1, wherein the combustive agent used in the Claus furnace of the Claus unit is an oxygen-rich stream, wherein the amount of nitrogen does not exceed 50%.

3. The method according to claim 1, wherein the tail gas stream (iv), the CO.sub.2 enriched gas stream (v) and the purified CO.sub.2 gas stream (vii) also contain nitrogen.

4. The method according to claim 1, wherein the acid gas stream (ii) is enriched in H.sub.2S by an acid gas enrichment unit located upstream the Claus unit.

5. The method according to claim 1, wherein the TGTU comprises a feed inline burner or a tail gas heater, a hydrogenation reactor, a quench contactor and optionally an absorber unit.

6. The method according to claim 1, wherein the CO.sub.2 purification unit is a cryogenic separation unit producing the purified CO.sub.2 gas stream (vii) and the lean CO.sub.2 stream (viii).

7. The method according to claim 1, wherein the CO.sub.2 purification unit is a membrane unit producing the purified CO.sub.2 gas stream (vii) on the residue side and the lean CO.sub.2 stream (viii) on the permeate side.

8. The method according to claim 1, wherein the CO.sub.2 purification unit is an adsorption unit producing the purified CO.sub.2 gas stream (vii) and the lean CO.sub.2 stream (viii).

9. The method according to claim 1, wherein the CO.sub.2 purification unit is an absorption unit producing the purified CO.sub.2 gas stream (vii) and the lean CO.sub.2 stream (viii).

10. The method according to claim 1, wherein the CO.sub.2 purification unit is a combination of CO.sub.2 purification units.

11. The method according to claim 1, wherein part of the gas stream exiting the Claus unit is recycled into the Claus furnace before introduction to the TGTU.

12. The method according to claim 1, wherein part of the gas stream inside the Claus unit is recycled into the Claus furnace by internal recycling.

13. The method according to claim 5, wherein part of the gas stream exiting the quench contactor is recycled into the Claus furnace before introduction to the absorber unit.

14. The method according to claim 1, wherein part of the purified CO.sub.2 gas stream (vii) exiting the CO.sub.2 purification unit is recycled into the Claus furnace.

15. The method according to claim 1, wherein part of the lean CO.sub.2 stream (viii) exiting the CO.sub.2 purification unit is recycled upstream of or directly in the Claus furnace.

16. The method according to claim 1, wherein part of the lean CO.sub.2 stream (viii) exiting the CO.sub.2 purification unit is recycled between the Claus unit and the hydrogenation reactor of the TGTU.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a schematic view of a classical native CO.sub.2 recovery unit, as known in the prior art.

(2) FIG. 2 is a schematic view of the native CO.sub.2 recovery unit for performing the method of the present invention.

(3) FIG. 3 is a schematic view of the native CO.sub.2 recovery unit for performing the method of the present invention, wherein the CO.sub.2 purification uses a membrane unit.

(4) FIG. 4 is a schematic view of the native CO.sub.2 recovery unit for performing the method of the present invention, wherein the CO.sub.2 purification uses a cryogenic separation unit.

DETAILED DESCRIPTION OF THE INVENTION

(5) The process according to the invention applies to the treatment of a hydrocarbon gas stream containing acid contaminants, such as a natural gas stream or refinery gas stream. The acid contaminants are mainly composed of carbon dioxide and hydrogen sulfide. However, the gas stream may also contain other acid contaminants, like sulfur compounds, in particular mercaptans.

(6) Typically, the hydrocarbon feed gas stream may contain (on a dry basis) from 1% to 70% of CO.sub.2, in particular from 2% to 40% of CO.sub.2, more particularly from 3% to 20% of CO.sub.2, and from 0.5% to 50% of H.sub.2S, in particular from 0.5% to 40% of H.sub.2S, more particularly from 0.5% to 20% of H.sub.2S.

(7) According to step a) of the method of the invention, the hydrocarbon feed gas stream is separated into a sweetened hydrocarbon gas stream (i), and an acid gas stream (ii) comprising at least carbon dioxide and hydrogen sulfide.

(8) By sweetened hydrocarbon gas stream, it is meant a hydrocarbon gas stream containing less acid contaminants than the hydrocarbon feed gas stream. The acid gas stream (ii), on the other hand, is enriched in acid contaminants compared to the hydrocarbon feed gas stream.

(9) Methods for obtaining a sweetened hydrocarbon gas stream (i) and acid gas stream (ii) from a hydrocarbon feed gas stream containing acid contaminants are well known by the person skilled in the art. Any sweetening method may be used for performing step a) of the present invention. Such methods include solvent treatment, such as chemical solvent treatment, in particular amine based solvent treatment, hybrid solvent treatment or physical solvent treatment.

(10) Typically, the acid gas stream (ii) contains (on a dry basis) from 10% to 90% of CO.sub.2, in particular from 25% to 75% of CO.sub.2, and from 10% to 90% of H.sub.2S, in particular from 25% to 75% of H.sub.2S.

(11) According to step b) of the method of the invention, the acid gas stream (ii) is then introduced into a Claus unit wherein an oxygen-rich stream (also named oxygen or oxygen plus air) is used as a combustive agent in the Claus furnace (also named combustion furnace), thereby recovering (iii) a liquid stream of elemental sulfur (iii) and a tail gas stream (iv) mainly comprising carbon dioxide, hydrogen and sulfur compounds.

(12) In one embodiment, the acid gas stream (ii) is enriched in an acid gas enrichment unit located upstream the Claus unit to increase the H.sub.2S content in the acid gas stream (ii).

(13) As explained previously, a Claus unit allows the conversion of hydrogen sulfide into elemental sulfur according to the following reactions:
2H.sub.2S+3O.sub.2.fwdarw.SO.sub.2+2H.sub.2O(1)
2H.sub.2S+SO.sub.2?3S+2H.sub.2O.(2)

(14) In a Claus unit, air is generally used as a combustive agent for the conversion of hydrogen sulfide into sulfur dioxide. However, since air contains around 80% of nitrogen and 20% of oxygen, the use of air as a combustive agent results in large volume of nitrogen in the process gas stream, which in turn requires equipments of large size.

(15) According to the present invention, an oxygen-rich stream is used as a combustive agent, instead of air, in order to reduce the process gas volume. By oxygen-rich stream, it is meant a stream containing an amount of oxygen from 20% to 100%, preferably from 70% to 100% and more preferably from 97% to 100%. The balanced components can be CO.sub.2, N.sub.2, Ar, Xe, H.sub.2, H.sub.2O, etc. . . .

(16) In one embodiment, the combustive agent used in the Claus furnace of the Claus unit is an oxygen-rich stream, wherein the amount of nitrogen does not exceed 50%, is preferably less than 40%, more preferably less than 20%, and more preferably less than 10%.

(17) The oxygen-rich stream may be obtained from atmospheric air by using an air separation unit (ASU) which separates atmospheric air into its primary components: mostly nitrogen and oxygen, and sometimes also argon and other rare inert gases. Any suitable method of separation may used in the process of the invention, for instance cryogenic distillation.

(18) The above described Claus reactions are strongly exothermic. Typically, the pressure in the Claus furnace is from 1.7 to 1.9 bara and the temperature should be maintained between 900? C. and 1450? C. The hot gas from the combustion chamber passes through steps of reaction and condensation to produce liquid elemental sulfur (iii).

(19) The use of an oxygen-rich stream as a combustive agent in the Claus furnace promotes side reactions resulting in the formation of hydrogen. The tail gas stream (iv) downstream the Claus unit thus contains minor amounts of hydrogen.

(20) Thus, according to the invention, the tail gas stream (iv) recovered at the exit of the Claus unit mostly contains carbon dioxide and water, but also contains a certain amount of hydrogen, nitrogen and possibly carbon monoxide, as well as traces of sulfur compounds, such as hydrogen sulfide and sulfur dioxide.

(21) Depending on the CO.sub.2 purification technology, the nitrogen content in the oxygen-rich stream may be adjusted depending on the content of nitrogen that can be accepted in the purified CO.sub.2 stream.

(22) The tail gas stream (iv) exiting the Claus unit generally contains (on a dry basis) at least 40% of CO.sub.2, preferably from 50% to 90% of CO.sub.2. Balanced components can be H.sub.2, N.sub.2, H.sub.2S, SO.sub.2, CO, Ar, COS, etc. . . .

(23) According to step c) of the method of the invention, the tail gas stream (iv) exiting the Claus unit is introduced into a Tail Gas Treatment Unit (TGTU), thereby separating said tail gas stream (iv) into a CO.sub.2 enriched gas stream (v) containing hydrogen and sweetened in sulfur compounds, and a gas stream enriched in sulfur compounds (vi).

(24) The TGTU allows the conversion of the sulfur compounds of the tail gas stream (iv) into H.sub.2S.

(25) In one embodiment, the TGTU comprises four main equipments in the direction of flow: a feed inline burner or a tail gas heater for heating the tail gas stream (iv), a hydrogenation reactor for converting the sulphur compounds of the tail gas stream (iv) into H.sub.2S, a quench contactor removing extra water from the gas stream and an absorber unit (amine-based) for separating the sulfur compounds (mainly H.sub.2S) from the other constituents of the tail gas stream (iv).

(26) The TGTU includes amine based tail gas treatment units or subdew point tail gas treatment or direct oxidation based tail gas treatment units. The TGTU used to implement the method of the invention is not limited to these TGTUs. Any type of TGTU may be suitable for implementing the method of the invention.

(27) As a result, two streams are recovered at the exit of the TGTU: a CO.sub.2 enriched gas stream containing hydrogen (v), and a gas stream enriched in sulfur compounds (vi) (i.e. containing more sulfur compounds than the tail gas (iv)) in the other hand.

(28) Typically, the gas stream enriched in sulfur compounds (vi) is introduced into the Claus unit.

(29) The feed inline burner/or tail gas heater positioned upstream of the hydrogenation reactor provides the heat and hydrogenation/or heat.

(30) The hydrogenation reactor typically comprises a catalyst bed where sulphur compounds such as SO.sub.2, S, COS and CS.sub.2 are converted into H.sub.2S. The hydrogenated stream is then passed through a quench contactor, preferably a water-quench tower, in order to reduce temperature and remove extra water.

(31) The gas stream at quench outlet exiting the quench tower is then passed through an absorber unit, wherein sulfur compounds, mainly H.sub.2S, are absorbed by an absorbing solution. Preferably, the absorber unit is an amine-based. A CO.sub.2 enriched gas stream (v) is thus recovered from the absorber unit, that contains less than 500 ppm of H.sub.2S, preferably less than 100 ppm of H.sub.2S. The sulfur-containing stream is separated from the absorbing solution and recycled back to the Claus furnace.

(32) Alternatively, the gas stream recovered at quench outlet may not be passed through the absorber unit if the content of H.sub.2S in the CO.sub.2 stream is lower than the required H.sub.2S specification in the purified CO.sub.2 stream. In that case, the TGTU only comprises a feed inline burner or a tail gas heater, a hydrogenation reactor and a quench contactor.

(33) At the exit of the TGTU, the CO.sub.2 enriched gas stream (v) generally contains (on a dry basis) at least 40% of carbon dioxide, preferably from 50% to 90% of carbon dioxide.

(34) In one embodiment, the CO.sub.2 enriched gas stream (v) also comprises nitrogen due to the presence of nitrogen in the oxygen-rich stream used as a combustive agent.

(35) In other embodiments, according to step d) of the method of the invention, the CO.sub.2 enriched gas stream (v) exiting the TGTU is compressed, preferably at a pressure from 10 bar to 100 bar, more preferably from 20 bar to 60 bar. Of course, the compression step may be eliminated if the purification technology does not require it.

(36) In one embodiment, the compressed CO.sub.2 enriched gas stream is passed through a dehydration unit in order to complete the removal of water contained in the CO.sub.2 stream. Preferably, the dehydration unit is a glycol or an adsorption unit but any other suitable dehydration technique may be used.

(37) According to step e) of the method of the invention, the compressed CO.sub.2 enriched gas stream is then passed through a CO.sub.2 purification unit, such as CO.sub.2/H.sub.2 separation unit, thereby recovering a purified CO.sub.2 gas stream (vii) in one hand and a lean CO2 stream (viii) in the other hand, which comprises hydrogen.

(38) Any suitable CO.sub.2 purification unit may be used. Preferably, the CO.sub.2 purification unit is a cryogenic separation unit, a membrane unit, an adsorption unit, an absorption unit or a combination thereof.

(39) The cryogenic separation unit produces a purified CO.sub.2 gas stream (vii) and a non-condensable stream (viii) containing H.sub.2, CO.sub.2, N.sub.2, Ar, etc. . . . which may be thus recovered for further use.

(40) As for membrane separation, the CO.sub.2 recovery rate is generally lower than that of cryogenic separation. However, since the membrane permeate comprises a large amount of carbon dioxide, it may be advantageously recycled to the Claus furnace in order to facilitate the oxygen-rich operations. In the case of membrane separation, the CO.sub.2 recovery rate may be increased by recycling totally or part of the membrane permeate into the Claus furnace.

(41) In case of low CO.sub.2 content in the compressed CO.sub.2 enriched gas stream, a combination of CO.sub.2 purification units can be advantageously implemented to increase CO.sub.2 recovery.

(42) The CO.sub.2 stream may be required to control the Claus furnace temperature and recycled at different stages of the process. Preferably, the recycled CO.sub.2 stream is collected as upstream as possible in order to reduce the volume of gas to be treated by the downstream units.

(43) In one embodiment, part of the gas stream exiting the quench tower of the TGTU is recycled into the Claus furnace before introduction to the absorber unit.

(44) In one embodiment, part of the gas stream (iv) exiting the Claus unit is recycled into the Claus furnace before introduction to the TGTU.

(45) In one embodiment, part of the gas stream inside the Claus unit is recycled into the Claus furnace by internal recycling.

(46) In one embodiment, part of the purified CO.sub.2 gas stream (vii) exiting the CO.sub.2 purification unit is recycled into the Claus furnace.

(47) In one embodiment, part of the lean CO.sub.2 stream (viii) exiting the CO.sub.2 purification unit is recycled between the Claus unit and the hydrogenation reactor of the TGTU.

(48) In one embodiment, part of the lean CO.sub.2 stream (viii) exiting the CO.sub.2 purification unit is recycled upstream of or directly in the Claus furnace.

(49) A combination of these recycles may be also performed.

(50) The purified CO.sub.2 stream (vii) obtained by the method of the invention may contain from 90% to 100% of CO.sub.2, preferably from 97% to 99.9% of CO.sub.2. It may be then sequestered or used for enhanced oil recovery (EOR).

(51) In one embodiment, the purified CO.sub.2 gas stream (vii) also contains nitrogen due to the presence of nitrogen in the oxygen-rich stream used as a combustive agent.

(52) As previously mentioned, the purity of the CO.sub.2 stream obtained by the method of the invention will depend on the type of combustive agent used in the Claus furnace, on the TGT technology and on the CO.sub.2 purification technology. To obtain a CO.sub.2 stream of high purity (98% or more), it is preferable to use high purity oxygen-rich stream (to Claus furnace). However, for a lower purity of produced CO.sub.2 rich stream, lower purity of oxygen-rich stream (to Claus furnace) may be preferable because it is less expensive to implement.

(53) Another object of the present invention is a device for carrying the method of the invention as previously described, said device comprising in the direction of flow: an acid gas removal unit providing an acid gas stream; a Claus unit operated with an oxygen-rich stream; a tail gas treatment unit removing sulfur components; a compression device; and a CO.sub.2 purification device.

(54) The acid gas removal unit may be a unit performing a classical sweetening method such as chemical, hybrid or physical solvent. It may be for instance an amine washing unit. Amine solutions are well known by the person skilled in the art. According to the desired specification, the amine solutions may include DEA (di-ethanol amine), MDEA (methyl-di-ethanol amine) or activated MDEA or any other solution.

(55) As previously mentioned, the combustive agent for the Claus unit may be an oxygen-rich stream. The oxygen-rich stream may be produced by an air separation unit. In addition, part of the purified CO.sub.2 stream (vii) may be recycled into the Claus unit to facilitate the oxygen-rich operations.

(56) In one embodiment, the device further comprises an acid gas enrichment unit located between the acid gas removal unit and the Claus unit to increase the H.sub.2S content in the stream.

(57) In one embodiment, the tail gas treatment unit (TGTU) comprises in the direction of flow a feed inline burner/or a tail gas heater, a hydrogenation reactor, a quench contactor and optionally an absorber unit, in particular an absorber unit based on amine. As previously explained, it may not be necessary to include an absorber unit in the TGTU if the content of H.sub.2S in the CO.sub.2 stream at the exit of the hydrogenation reactor is lower than the required specification in the purified CO.sub.2 stream. In that case, the TGTU only comprises a feed inline burner/or a tail gas heater, a hydrogenation reactor and a quench contactor.

(58) In one embodiment, TGTU includes subdew point tail gas treatment or direct oxidation based tail gas treatment units. The TGTU used to implement the method of the invention is not limited to these TGTUs. Any type of TGTU may be suitable for implementing the method of the invention.

(59) In one embodiment, the device further comprises a dehydration device located upstream the CO.sub.2 purification device. Depending on the compression configuration, dehydration can be located between two compression stages. Preferably, the CO.sub.2 purification device is a cryogenic separation unit, a membrane unit, an adsorption unit or an absorption unit.

(60) In one embodiment, the CO.sub.2 purification device is a combination of CO.sub.2 purification technologies.

(61) The device may further comprise a one or several recycle lines as follows: a recycle line for collecting part of the gas stream (iv) between the Claus unit and the TGTU and injecting into the Claus furnace; a recycle line for collecting part of the gas stream inside the Claus unit is recycled into the Claus furnace, a recycle line for collecting part of the gas stream between the quench tower of the TGTU and the absorber unit and injecting into the Claus furnace, a recycle line for collecting part of the purified CO.sub.2 gas stream (vii) exiting the CO.sub.2 purification unit and injecting into the Claus furnace, a recycle line for collecting part of the lean CO.sub.2 stream (viii) exiting the CO.sub.2 purification unit and injecting between the Claus unit and the hydrogenation reactor of the TGTU, a recycle line for collecting part of the lean CO.sub.2 stream (viii) exiting the CO.sub.2 purification unit and injecting upstream of or directly into the Claus furnace.

(62) The invention is further described in the FIGS. 1, 2, 3 and 4. These examples are offered to illustrate the invention and should in no way be viewed as limiting the invention.

(63) FIG. 1 provides a schematic view of a classical CO.sub.2 recovery unit, as known in the prior art.

(64) In FIG. 1, a sour gas stream is introduced into an acid gas removal unit (AGRU), thereby providing a sweet gas stream and an acid gas stream containing 48% of carbon dioxide and 43% of hydrogen sulfide. The acid gas stream then enters a Claus unit at a pressure of 1-2 bar. In the Claus unit the hydrogen sulfide is converted into elemental sulfur using air containing 20% of oxygen and 80% of nitrogen as a combustive agent, therefore leading to the dilution of carbon dioxide with nitrogen. Then, this mixture enters a Tail Gas Treatment Unit (TGTU) to remove remaining traces of sulfur compounds, leading to a tail gas stream mixture composed of 60% of nitrogen, 30% of carbon dioxide and 10% of water. At the outlet of the TGTU, said mixture is then contacted with an amine-based solvent in order to capture the carbon dioxide, thereby separating the carbon dioxide from remaining nitrogen.

(65) Typically, MethylEthanolAmine (MEA) is used as the most common amine solvent to capture the CO.sub.2 from TGT off gas. After the step of absorption, the chemical amine solvent enriched in carbon dioxide is sent to a regenerator operating at a pressure comprised between 1 and 2 bara to recover the amine solvent depleted in carbon dioxide and to provide a stream of gaseous carbon dioxide saturated with water. After the steps of compression and dehydration (typically using a TEG unit), a stream composed of about 99.9% of carbon dioxide and 600 ppm of hydrogen sulfide is obtained.

(66) The remaining mixture exiting the CO.sub.2 capture absorber comprising 87% of nitrogen, 4% of carbon dioxide, 6% of water and 3% of hydrogen is sent to the incinerator.

(67) As a result typical native CO.sub.2 recovery of such capture is about 90%.

(68) FIG. 2 provides a schematic view of a native CO.sub.2 recovery unit for performing the method of the present invention.

(69) In FIG. 2, a sour gas stream is introduced into an acid gas removal unit (AGRU), thereby providing a sweet gas stream (i) and an acid gas stream (ii) containing 48% of carbon dioxide and 43% of hydrogen sulfide. A classical sweetening method using a chemical, a hybrid or a physical solvent is used as an Acid Gas Removal Unit (AGRU). The acid gas stream (ii) then enters a Claus unit using oxygen-rich stream at a pressure of 1.7-1.9 bar. Matter of fact, the hydrogen sulfide is transformed into elemental sulfur in the Claus unit using oxygen-rich stream as a combustive agent. Two streams exit from the Claus unit: a stream of elemental sulfur (iii) and a tail gas stream (iv) mainly comprising CO.sub.2, H.sub.2 and sulfur compounds. Then, the tail gas stream (iv) enters a Tail Gas Treatment Unit (TGTU) in order to remove remaining traces of sulfur compounds, thereby producing a gas effluent (v) composed of 85% of carbon dioxide, 10% of hydrogen, 5% of water and 100 ppm of hydrogen sulfide. Then, this gas effluent (v) enters the compression unit, then a CO.sub.2 purification unit, thereby forming, on the one hand, a purified carbon dioxide stream (vii) and, on the other hand, a lean carbon dioxide stream (viii) comprising carbon dioxide and hydrogen.

(70) The composition of the purified carbon dioxide stream (vii) and of the lean CO.sub.2 stream (viii) will depend on the type of separation technology.

(71) One or several recycle lines may be included in the process: recycle line {circle around (1)}, wherein part of the gas stream exiting the quench tower is recycled into the Claus furnace before introduction to the absorber unit, recycle line {circle around (2)}, wherein part of the gas stream (iv) exiting the Claus unit is recycled into the Claus furnace before introduction to the TGTU, recycle line {circle around (3)}, wherein part of the gas stream inside the Claus unit is recycled into the Claus furnace by internal recycling, recycle line {circle around (4)}, wherein part of the purified CO.sub.2 gas stream (vii) exiting the CO.sub.2 purification unit is recycled into the Claus furnace, recycle line {circle around (5)}, wherein part of the lean CO.sub.2 stream (viii) exiting the CO.sub.2 purification unit is recycled between the Claus unit and the hydrogenation reactor of the TGTU, recycle line {circle around (6)}, wherein part of the lean CO.sub.2 stream (viii) exiting the CO.sub.2 purification unit is recycled upstream of or directly into the Claus furnace.

(72) FIG. 3 provides a schematic view of a native CO.sub.2 recovery unit for performing the method of the present invention, wherein the CO.sub.2 purification unit is a membrane.

(73) In FIG. 3, a sour gas stream is introduced into an acid gas removal unit (AGRU), thereby providing a sweet gas stream (i) and an acid gas stream (ii) containing 48% of carbon dioxide and 43% of hydrogen sulfide. A classical sweetening method using a chemical, a hybrid or a physical solvent is used as an Acid Gas Removal Unit (AGRU). The acid gas stream (ii) then enters a Claus unit using oxygen-rich stream as a combustive agent in the Claus furnace, at a pressure of 1.7-1.9 bar. Two streams exit from the Claus unit: a stream of elemental sulfur (iii) and a tail gas stream (iv) mainly comprising CO.sub.2, H.sub.2 and sulfur compounds. Then, the tail gas stream (iv) enters a Tail Gas Treatment Unit (TGTU), said TGTU being an amine based technology, thereby producing a gas effluent (v) composed of 85% of carbon dioxide, 8% of hydrogen, 7% of water and 100 ppm of hydrogen sulfide. Then, this gas effluent (v) enters a compression unit and a dehydration unit, then a membrane unit for CO.sub.2 purification, thereby forming a purified carbon dioxide residue and a permeate stream containing carbon dioxide and hydrogen.

(74) The purified carbon dioxide residue stream (vii), at a pressure close to the compression unit discharge pressure, is composed of 98% of carbon dioxide, 1.7% of hydrogen, 0.3% of carbon monoxide and less than 100 ppm of hydrogen sulfide. The permeate stream (viii), at about 2 bara is composed of approximately 70% of carbon dioxide and 30% of hydrogen. Said membrane permeate stream (viii) is totally or partially recycled upstream of or directly in the Claus unit. As a result of total recycle, typical native CO.sub.2 recovery of this process scheme is about 100%.

(75) FIG. 4 provides a schematic view of a native CO.sub.2 recovery unit for performing the method of the present invention, wherein the CO.sub.2 purification unit is a cryogenic unit.

(76) In FIG. 4, a sour gas stream is introduced into an acid gas removal unit (AGRU), thereby providing a sweet gas stream (i) and an acid gas stream (ii) containing 18% of carbon dioxide and 73% of hydrogen sulfide. A classical sweetening method using a chemical, a hybrid or a physical solvent is used as an Acid Gas Removal Unit (AGRU). The acid gas stream (ii) then enters a Claus unit using oxygen-rich stream as a combustive agent in the Claus furnace, at a pressure of 1.7-1.9 bar. Two streams exit from the Claus unit: a stream of elemental sulfur (iii) and a tail gas stream (iv) mainly comprising CO.sub.2, H.sub.2 and sulfur compounds. Then, the tail gas stream (iv) enters a Tail Gas Treatment Unit (TGTU), said TGTU being an amine based technology. Part of the gas stream after the quench tower is recycled to the Claus furnace, with a composition of 59% CO.sub.2, 20% H.sub.2 and 4% H.sub.2S. Downstream the TGT amine, a gas effluent (v) is produced, composed of 58% of carbon dioxide, 23% of hydrogen, 15% of water and 500 ppm of hydrogen sulfide. Then, this gas effluent (v) enters a compression unit and a dehydration unit, then a cryogenic unit for CO.sub.2 purification, thereby forming a purified carbon dioxide product (vii) and a lean CO.sub.2 stream (viii) containing hydrogen and some carbon dioxide.

(77) The purified carbon dioxide stream (vii), at around 10 bara, is composed of 99.9% of carbon dioxide and less than 0.1% of hydrogen sulfide. The lean CO.sub.2 stream (viii) rich in hydrogen (viii), at about 1.3 bara is composed of approximately 72% of hydrogen and 14% of carbon dioxide, remaining components being argon, carbon monoxide, nitrogen.