INTEGRATED PROCESS TO RECOVER HIGH QUALITY NATIVE CO2 FROM A SOUR GAS COMPRISING H2S AND CO2

Abstract

The invention concerns a method for treating a hydrocarbon feed gas stream containing at least CO.sub.2 and H.sub.2S to recover a high quality purified CO.sub.2 gas stream, comprising a. Separating said hydrocarbon feed gas stream into a sweetened hydrocarbon gas stream, and an acid gas stream; b. Introducing said gas stream into a Claus unit, c. Introducing the tail gas into a hydrogenation reactor and then into a quench contactor of the Tail Gas Treatment Unit (TGTU); d. Contacting said tail gas stream with a non-selective amine-based solvent into a non-selective acid gas absorption unit of the TGTU; e. Sending the off gas to an incinerator; f. Contacting said enriched gas stream (vii) with a selective H.sub.2S-absorption solvent into a selective H.sub.2S-absorption unit thereby recovering a highly purified CO.sub.2 gas stream and a H.sub.2S-enriched gas stream, as well as the device for carrying said method.

Claims

1. A device for treating a hydrocarbon feed gas stream containing at least carbon dioxide and hydrogen sulfide to recover a high quality purified CO.sub.2 gas stream, the device comprising in the direction of flow: an acid gas removal unit; a Claus unit; a tail gas treatment unit for removing sulfur components; a selective H.sub.2S-absorption unit; and an incinerator; wherein said process comprising the following steps: separating said hydrocarbon feed gas stream into (i) a sweetened hydrocarbon gas stream, and (ii) an acid gas stream comprising at least carbon dioxide and hydrogen sulfide; introducing said acid gas stream (ii) into the Claus unit, thereby recovering (iii) a liquid stream of elemental sulfur and (iv) a tail gas mainly comprising nitrogen, carbon dioxide, sulfur dioxide and hydrogen sulfide; introducing the tail gas (iv) into a hydrogenation reactor and then into a quench contactor of the Tail Gas Treatment Unit (TGTU) thereby recovering (v) a hydrogenated tail gas stream comprising nitrogen, hydrogen, carbon monoxide, carbon dioxide and hydrogen sulfide; contacting said hydrogenated tail gas (v) with a non-selective amine-based solvent into a non-selective acid gas absorption unit of the TGTU thereby recovering (vi) an off gas comprising nitrogen, hydrogen and carbon monoxide and (vii) a gas stream enriched in carbon dioxide and hydrogen sulfide; sending the off gas (vi) to the incinerator; and contacting said enriched gas stream (vii) with a selective H2S-absorption solvent into the selective H2S-absorption unit thereby recovering (viii) a highly purified CO.sub.2 gas stream and (ix) a H2S-enriched gas stream;

2. The device according to claim 1, wherein the tail gas treatment unit further comprises a feed inline burner or a tail gas heater before the hydrogenation reactor.

3. The device according to claim 1, wherein the selective H.sub.2S-absorption unit comprises a recycle line for recycling the H2S-enriched gas stream upstream of or directly to the Claus furnace.

4. The device according to claim 1, wherein the tail gas treatment unit further comprises a hydrogenation reactor, a quench contactor and a non-selective acid gas absorption unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 is a schematic view of a classical CO2 recovery unit, as known in the prior art.

[0039] FIG. 2 is a schematic view of the high-quality native CO2 recovery unit for performing the method of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0040] The process according to the invention applies to the treatment of a hydrocarbon feed gas stream containing acid contaminants, such as a natural gas stream. The acid contaminants are mainly composed of carbon dioxide and hydrogen sulfide. However, the gas stream may also contain other acid contaminants, such as mercaptans, and/or carbonyl sulfide, and/or carbon disulfide, etc.

[0041] Typically, the hydrocarbon feed gas stream may contain from 5% to 70% of CO.sub.2, in particular from 7% to 40% of CO.sub.2, more particularly from 10% to 20% of CO.sub.2, and from 1% to 40% of H.sub.2S, in particular from 2% to 20% of H.sub.2S, more particularly from 3% to 10% of H.sub.2S.

[0042] According to step a) of the method of the invention, the hydrocarbon gas stream is separated into (i) a sweetened hydrocarbon gas stream, and (ii) an acid gas stream comprising at least carbon dioxide and hydrogen sulfide.

[0043] 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.

[0044] 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 cryogenic treatment or solvent treatment, such as chemical, physical or hybrid solvent.

[0045] Typically, the acid gas stream (ii) contains from 15% to 75% of CO.sub.2, in particular from 30% to 65% of CO.sub.2, more particularly from 40% to 60% of CO.sub.2, and from 20% to 80% of H.sub.2S, in particular from 40% to 70% of H.sub.2S, more particularly from 50% to 70% of H.sub.2S.

[0046] According to step b) of the method of the invention, the acid gas stream (ii) is then introduced into a Claus unit thereby recovering (iii) a liquid stream of elemental sulfur and (iv) a tail gas mainly comprising nitrogen, carbon dioxide, sulfur dioxide and hydrogen sulfide.

[0047] A Claus unit allows the conversion of hydrogen sulfide into elemental sulfur according to the following reactions:

2 H.sub.2S+3 O.sub.2.fwdarw.2 SO.sub.2+2 H.sub.2O  (1)

2 H.sub.2S+SO.sub.2⇄3 S+2 H.sub.2O  (2)

[0048] According to the invention, the tail gas (iv) recovered at the exit of the Claus unit mostly contains nitrogen, carbon dioxide, sulfur dioxide, hydrogen sulfide and water. Said tail gas (iv) generally contains at least 40% of N2, preferably from 40% to 70% of N2, and at least 10% of CO2, in particular from 10% to 75% of CO2 as main components, and less than 4% of SO2, in particular less than 2% of SO2, and less than 4% of H2S, in particular less than 2% of H2S.

[0049] In one embodiment of step c) of the method of the invention, the tail gas (iv) exiting the Claus unit is introduced into a feed inline burner or a tail gas heater before being introduced into the hydrogenation reactor of the Tail Gas Treatment Unit (TGTU) thereby recovering (v) a hydrogenated tail gas stream mainly comprising nitrogen, hydrogen, carbon monoxide, carbon dioxide and hydrogen sulfide.

[0050] According to the invention, the hydrogenated tail gas (v) recovered at the exit of the hydrogenation unit mostly contains nitrogen, hydrogen, carbon monoxide, carbon dioxide and hydrogen sulfide. Said tail gas (iv) generally contains at least 20% of N.sub.2, preferably from 60% to 90% of N.sub.2, and at least 5% of CO.sub.2, in particular from 10% to 20% of CO.sub.2 as main components, and less than 1.0% of CO, in particular less than 0.5% of CO, and less than 5% of H.sub.2S, in particular less than 3% of H.sub.2S.

[0051] In one embodiment, the TGTU comprises four main equipments in the direction of flow:

[0052] a feed inline burner or a tail gas heater for heating the tail gas stream,

[0053] a hydrogenation reactor for converting the sulfur compounds of the tail gas stream into H.sub.2S,

[0054] a quench contactor for removing water from the gas stream and,

[0055] a non-selective acid gas absorption unit for separating the acid gases (mainly CO.sub.2 and H.sub.2S) from the other constituents of the hydrogenated tail gas stream.

[0056] The hydrogenation reactor typically comprises a catalytic bed where sulfur compounds such as SO.sub.2, S, COS and CS.sub.2 are converted into H.sub.2S. Furthermore, the feed inline burner or tail gas heater positioned before the input of the hydrogenation reactor heats the tail gas to a temperature suitable for performing the hydrogenation, generally from 130° C. to 240° C., preferably around 225° C. The burner generally operates with air and fuel.

[0057] The converted gas stream recovered at the exit of the hydrogenation reactor is then passed through a quench contactor, preferably a water-quench tower, in order to remove all or part of water from the gas stream. The proportion of water removed from the gas stream is at least 60%, preferably at least 70%.

[0058] The water saturated gas stream exiting the quench tower is then passed through a non-selective acid gas absorption unit, wherein acidic compounds, mainly CO.sub.2 and H.sub.2S, are absorbed by a non-selective acid gas absorbing solution. The non-selective acid gas absorption unit is an amine-based unit. A gas stream enriched in carbon dioxide and hydrogen sulfide (vii) is thus recovered from the non-selective acid gas absorption unit, that contains less than 500 ppm of H.sub.2S, preferably less than 100 ppm of H.sub.2S.

[0059] The lean solution containing carbon dioxide and hydrogen sulfide and some other sulfur contaminants, such as carbonyl sulfide, carbon disulfide and mercaptans, is recovered and passed through a stripping column in order to separate the absorbing solution from the acidic contaminants. The absorbing solution is recovered at the bottom of the stripping column and may be recycled to the acid gas absorption unit. A gas stream enriched with sulfur compounds is recovered at the head of the column and may be recycled upstream of or directly in the Claus furnace.

[0060] According to step d) of the method of the invention, the hydrogenated tail gas (v) exiting the quench contactor is introduced into a non-selective acid gas absorption unit thereby separating said hydrogenated tail gas into (vi) an off gas mainly comprising nitrogen, hydrogen, and carbon monoxide, and (vii) a gas stream enriched in carbon dioxide and hydrogen sulphide. According to the invention, the off gas (vi) recovered at the exit of the non-selective acid gas absorption unit generally contains at least 70% of N.sub.2, preferably from 70% to 80% of N.sub.2, and at least 2% of H.sub.2, in particular from 2% to 5% of H.sub.2, and at least 0.1% of CO, in particular from 0.1% to 1% of CO.

[0061] According to the invention, the gas stream (vii) recovered at the exit of the acid gas absorption unit generally contains at least 90% of CO.sub.2, preferably from 85% to 97% of CO.sub.2, and at least 3% of H.sub.2S, in particular from 0% to 10% of H.sub.2S.

[0062] According to step e) of the method of the invention, the off gas (vi) is sent to an incinerator.

[0063] According to step f) of the method of the invention, the enriched gas stream (vii) is introduced into a selective H.sub.2S-absorption unit, wherein H.sub.2S is selectively absorbed by a selective H.sub.2S-absorption solvent. Preferably, the selective H.sub.2S-absorption solvent is an amine-based solvent but any other suitable solvent may be used. More preferably, the amine-based solvent is a MDEA-based solvent.

[0064] According to the invention, the highly purified CO.sub.2 gas stream (viii) exiting the selective H.sub.2S-absorption unit generally contains at least 90% of CO.sub.2 (wet basis), preferably from 90% to 97% of CO.sub.2, and less than 250 ppm of H.sub.2S, in particular less than 100 ppm of H.sub.2S.

[0065] In one embodiment, the H.sub.2S-enriched gas stream (ix) exiting the selective H.sub.2S-absorption unit is recycled upstream of or directly to the Claus furnace.

[0066] According to the invention, the H.sub.2S-enriched gas stream (ix) exiting the selective H.sub.2S-absorption unit generally contains at least 15% of H.sub.2S, preferably from 15% to 30% of H.sub.2S, and less than 80% of CO.sub.2, in particular less than 70% of CO.sub.2.

[0067] 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: [0068] an acid gas removal unit; [0069] a Claus unit; [0070] a tail gas treatment unit comprising a hydrogenation reactor, a quench contactor and a non-selective acid gas absorption unit; [0071] a selective H.sub.2S-absorption unit; and [0072] an incinerator.

[0073] In one embodiment, the tail gas treatment unit (TGTU) further comprises a feed inline burner or a tail gas heater before the hydrogenation reactor.

[0074] The hydrogenation reactor preferably comprises a CoMo catalyst.

The quench contactor may comprise distillation trays or a column packing (random or structured) for direct contact of water.

[0075] The non-selective acid gas absorption unit preferably comprises a non-selective amine-based solvent. More preferably the non-selective amine-based solvent used in said non-selective absorption unit is an alcanolamine, in particular MonoEthanolAmine (MEA).

[0076] In one embodiment, the device comprises a selective H.sub.2S-absorption unit based on a selective H.sub.2S-absorption solvent. Preferably, said selective H.sub.2S-absorption solvent is an alcanolamine. More preferably, said solvent is MDEA (MethylDiEthanolAmine).

[0077] In one embodiment, the device comprises a recycle line for recycling the H.sub.2S-enriched gas exiting the selective H.sub.2S-absorption unit upstream of or directly into the Claus furnace.

[0078] The absorbing units usually comprise a regeneration system for the absorbing solution that comprises a stripping column with a reboiler and reflux drum. The absorbing solution is recovered at the bottom of the stripping column and is recycled into the absorbing unit. A gas stream enriched with acidic compounds is recovered at the head of the column and may be recycled upstream of or directly in the Claus unit. Therefore, the device may further comprise a recycling line for injecting the gas stream enriched with acidic compounds which is recovered at the head of the column upstream of or directly into the Claus unit.

[0079] The invention is further described in the FIGS. 1 and 2. These examples are offered to illustrate the invention and should in no way be viewed as limiting the invention.

[0080] FIG. 1 provides a schematic view of a classical CO.sub.2 recovery unit, as known in the prior art. In FIG. 1, a sour gas is introduced into an acid gas removal unit (AGRU), thereby providing a sweet gas and an acid gas containing 50% of carbon dioxide and 50% of hydrogen sulfide. The acid gas then enters a Claus unit at a pressure of 2 bar wherein the hydrogen sulfide is converted into elemental sulfur. Then, the exiting mixture enters the hydrogenation reactor and then the quench contactor of the Tail Gas Treatment Unit (TGTU) to reduce the sulfur compounds leading to a hydrogenated tail gas mixture composed of 80% of nitrogen, 5% of hydrogen, 1% of carbon monoxide and 10% of carbon dioxide. At the outlet of quench contactor, said mixture enters the selective H.sub.2S-absorption unit wherein it is contacted with an H.sub.2S-selective amine based solvent in order to selectively capture H.sub.2S.

[0081] Typically, MethylDiEthanolAmine (MDEA) is used as a common H.sub.2S-selective amine solvent to capture the CO.sub.2 from flue gas. After the step of absorption, the chemical amine solvent enriched in hydrogen sulfide is sent to a regenerator operating at a pressure comprised between 2 bara to recover the amine solvent depleted in acidic compounds (mainly H.sub.2S) and to provide a stream which comprises 33% of H.sub.2S and 66% of co-absorbed CO.sub.2. Said stream is then recycled to the Claus furnace.

[0082] The off gas exiting the selective H.sub.2S-absorption step is then introduced into an acid gas absorption unit wherein it is contacted with a non-selective amine-based solvent. Typically, MonoEthanolAmine (MEA) is used as a common non-selective amine-based solvent to capture the acid gases from the 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 2 bara to recover the amine solvent depleted in acid gases and to provide a stream which comprises 500 ppm of H.sub.2S and 99.95% of CO.sub.2 (dry basis).

[0083] The off gas exiting the acid gas absorption unit is then sent to the incinerator.

[0084] FIG. 2 provides a schematic view of a high-quality native CO.sub.2 recovery unit for performing the method of the present invention.

[0085] In FIG. 2, a sour gas is introduced into an acid gas removal unit (AGRU), thereby providing a sweet gas and an acid gas containing 50% of carbon dioxide and 50% 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 then enters a Claus unit at a pressure of 2 bar wherein the hydrogen sulfide is converted into elemental sulfur. Two streams exit from the Claus unit: a stream of elemental sulfur and a tail gas mainly comprising N.sub.2, CO.sub.2 and sulfur compounds. Then, the tail gas enters the hydrogenation reactor and then the quench contactor of a Tail Gas Treatment Unit (TGTU) in order to reduce the sulfur compounds present in the tail gas, leading to a hydrogenated tail gas mixture composed of 80% of nitrogen, 5% of hydrogen, 1% of carbon monoxide and 10% of carbon dioxide. At the outlet of quench contactor, said mixture enters the acid gas absorption unit wherein it is contacted with a non-selective amine-based solvent. Typically, MonoEthanolAmine (MEA) is used as a common non-selective amine-based solvent to capture the acid gases from the hydrogenated tail gas. The off gas exiting the acid gas absorption unit is then sent to the incinerator.

[0086] The regenerated acid gas from the absorption unit which comprises 5% of H.sub.2S and 95% of CO.sub.2 then enters the selective H.sub.2S-absorption unit wherein it is contacted with an H.sub.2S-selective amine based solvent in order to selectively capture H.sub.2S.

[0087] Typically, MethylDiEthanolAmine (MDEA) is used as a common H.sub.2S-selective amine solvent to capture the H2S from the previously mentioned acid gas mixture. After the step of absorption, the chemical amine solvent enriched in hydrogen sulfide is sent to a regenerator operating at a pressure comprised between 2 bara to recover the amine solvent depleted in acid gases and to provide a stream which comprises 20% of H.sub.2S and 80% of co-absorbed CO.sub.2. Said stream is then recycled to the Claus unit.

[0088] The treated gas exiting the selective H.sub.2S-absorption unit comprises 100 ppm of H.sub.2S and 99.99% of CO.sub.2 (dry basis).

[0089] The embodiments above are intended to be illustrative and not limiting. Additional embodiments may be within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

[0090] Various modifications to the invention may be apparent to one of skill in the art upon reading this disclosure. For example, persons of ordinary skill in the relevant art will recognize that the various features described for the different embodiments of the invention can be suitably combined, un-combined, and re-combined with other features, alone, or in different combinations, within the spirit of the invention. Likewise, the various features described above should all be regarded as example embodiments, rather than limitations to the scope or spirit of the invention. Therefore, the above is not contemplated to limit the scope of the present invention.