Methane generation system

Abstract

A methane generation system according to the present disclosure is provided with: a methane generation unit having an electrolysis device for obtaining hydrogen by electrolyzing water, and a methane reactor for obtaining a fuel gas containing methane by a methanation reaction using the hydrogen; the reformer is used for reforming the fuel gas to obtain reformed gas; a fuel cell that generates power by a reaction in which a product gas is obtained from the reformed gas and an oxygen-containing gas; a recovery device that separates a recovery gas containing carbon dioxide from a return fluid that is part of the product gas; and a circulation path through which the recovered gas is introduced into the methane generation unit.

Description

Technical Field

[0001] The present disclosure relates to methane generation systems. Background Art

[0002] Patent Document 1 discloses an apparatus for producing methane using carbon dioxide and water. The apparatus reduces water and carbon dioxide to obtain a synthesis gas containing hydrogen and carbon monoxide. The apparatus generates methane from the synthesis gas.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2022-22978 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In the above-mentioned techniques, the efficiency of generating methane may be reduced.

[0008] In view of the above-mentioned circumstances, an object of the present disclosure is to provide a methane production system capable of improving the production efficiency of methane.

[0009] Means for solving problems

[0010] One scheme of the methane generation system involved in the present disclosure comprises: a methane generation unit, which has an electrolysis device for obtaining hydrogen by electrolyzing water, and a methane reactor for obtaining a fuel gas containing methane by a methanation reaction using the above-mentioned hydrogen; a reformer, which reforms the above-mentioned fuel gas to obtain a reformed gas; a fuel cell, which generates electricity by a reaction of obtaining a product gas from the above-mentioned reformed gas and an oxygen-containing gas; a recovery device, which separates a recovery gas containing carbon dioxide from a return fluid that is a part of the above-mentioned product gas; and a circulation path, which introduces the above-mentioned recovery gas into the above-mentioned methane generation unit.

[0011] Effects of the Invention

[0012] According to the present disclosure, it is possible to provide a methane production system capable of improving the production efficiency of methane. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the methane production system involved in embodiment 1.

[0014] Figure 2 This is a schematic diagram of a methane production system according to Embodiment 2.

[0015] Figure 3 This is a schematic diagram of a methane production system according to Embodiment 3.

[0016] Figure 4 This is a schematic diagram of a portion of a methane generation system according to a fourth embodiment.

[0017] Figure 5 This is a schematic diagram of a portion of a methane generation system according to Embodiment 5.

[0018] Figure 6 This is a schematic diagram of a methane generation system according to a sixth embodiment.

[0019] Figure 7 This is a schematic diagram of a methane generation system according to Embodiment 7. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. It should be noted that the scope of the present disclosure is not limited to the following embodiments, and any changes can be made within the scope of the technical concept of the present disclosure. Implementation method 1.

[0021] Figure 1 Schematic diagram showing the methane production system in Embodiment 1.

[0022] like Figure 1 As shown in FIG. 1 , a methane generation system 1 includes a methane generation unit 2, a reformer 3, a fuel cell 4, a recovery device 5, a circulation path 6, and a return path 7. The methane generation system is also referred to as a "fuel cell system".

[0023] The methane production unit 2 includes a supply path 110 , an electrolysis device 120 , and a methane reactor 130 .

[0024] The supply path 110 introduces water (steam) supplied from a supply source (not shown) to the electrolysis device 120. The supply path 110 may be provided with an evaporator (steam generator) for vaporizing water.

[0025] The electrolysis device 120 electrolyzes water (H2O) to obtain a mixed gas containing hydrogen (H2) and oxygen (O2). The electrolysis is performed, for example, according to the following formula (I).

[0026] 2H2O→2H2+O2···(I)

[0027] In the electrolysis device 120, for example, electricity generated by renewable energy (such as solar power generation, wind power generation, etc.) can be used for electrolysis. Even if methane obtained by using renewable energy is burned, no additional carbon dioxide is generated, and it can be considered as a carbon-neutral fuel that has no effect on global warming.

[0028] The methane reactor 130 produces a fuel gas containing methane (CH4) and water (H2O) by a methanogenic reaction of carbon dioxide (CO2) supplied from the circulation path 6 and hydrogen (H2) from the electrolysis device 120. The methanogenic reaction proceeds, for example, according to the following formula (II).

[0029] CO2+4H2→CH4+2H2O···(II)

[0030] The methane reactor 130 preferably includes a methanation catalyst with which the mixed gas contacts. Examples of the methanation catalyst include a Ni catalyst and a Ru catalyst. The methanation catalyst promotes the methanation reaction.

[0031] The fuel gas obtained in the methane reactor 130 contains not only methane and water but also unreacted carbon dioxide, hydrogen (H 2 ), and the like.

[0032] The fuel gas is introduced into the reformer 3 through the discharge path 60. The water contained in the fuel gas introduced into the reformer 3 is preferably water vapor.

[0033] The reformer 3 obtains a reformed gas containing carbon monoxide (CO) and hydrogen (H 2 ) through a reforming reaction from methane and water (steam) contained in the fuel gas. The reforming reaction proceeds, for example, according to the following formula (III).

[0034] CH4+H2O→CO+3H2···(III)

[0035] The reformer 3 preferably includes a reforming catalyst with which the fuel gas contacts. Examples of the reforming catalyst include a Ni catalyst and a Ru catalyst. The reforming catalyst promotes the reforming reaction.

[0036] The reformer 3 preferably includes a carbon monoxide generator and a carbon monoxide remover. The reformed gas can reduce the concentration of carbon monoxide by passing through the carbon monoxide generator and the carbon monoxide remover. The carbon monoxide generator includes a carbon monoxide generation catalyst such as a Cu catalyst and an Fe catalyst. In the carbon monoxide generator, a part of the carbon monoxide becomes carbon dioxide. The carbon monoxide remover includes a methanation catalyst that methanates the carbon monoxide. Examples of the methanation catalyst include Ru catalysts and the like. In the carbon monoxide remover, a part of the carbon monoxide becomes methane.

[0037] The reformed gas passes through the carbon monoxide generator and the carbon monoxide remover, whereby the concentration of carbon monoxide is reduced, and thus becomes a gas containing hydrogen (H 2 ) as a main component.

[0038] The oxygen-containing gas (gas containing an oxidant) is supplied from the supply path 8, passed through the reformer 3, and introduced into the fuel cell 4. The oxygen-containing gas contains oxygen (O 2 ) as an oxidant. The oxygen-containing gas is, for example, air.

[0039] The reformed gas is supplied to the anode of the fuel cell 4. The oxygen-containing gas is supplied to the cathode of the fuel cell 4. In the fuel cell 4, power generation is performed by the reaction of the reformed gas containing hydrogen (H2) and the oxygen-containing gas. This reaction is an exothermic reaction. In the fuel cell 4, a product gas containing water (water vapor) is obtained by the reaction of the reformed gas and the oxygen-containing gas. The product gas contains not only water (water vapor) but also unreacted hydrogen (H2) and carbon dioxide.

[0040] A part of the product gas is discharged from a discharge path (not shown).

[0041] The recovery device 5 separates and recovers the recovery gas F2 containing carbon dioxide from the return fluid F1 which is a part of the product gas.

[0042] In the recovery device 5, for example, separation methods such as adsorption separation, membrane separation, cooling separation, centrifugal separation, gravity separation, gas-liquid separation, etc. are used. In the recovery device 5, one of these separation methods may be used, or two or more of them may be combined.

[0043] In the case of the recovery device 5 using adsorption separation, for example, a specific component is adsorbed on an adsorbent, an adsorbent liquid, etc. to perform separation. As the adsorbent, silica gel, zeolite, activated carbon, etc. can be cited. Specifically, by adsorbing the component containing carbon dioxide on the adsorbent, the component can be separated from other components. The adsorbent can be granular, powdery, etc. Granular, for example, is beaded (spherical), pelletized (cylindrical), etc. In the case of using a powdered adsorbent, the adsorbent can be loaded on the surface of a substrate. The substrate can be, for example, in a honeycomb shape.

[0044] The recovery device 5 using adsorption separation has the function of separating carbon dioxide from the adsorbent. For example, the recovery device 5 is provided with a heating device. The heating device separates carbon dioxide from the adsorbent by heating the adsorbent. The recovery device 5 may be provided with a decompression device such as a decompression pump. The decompression device separates carbon dioxide from the adsorbent by placing the adsorbent under reduced pressure.

[0045] The recovery device 5 using membrane separation can separate specific components from other components using a permeable membrane through which low molecular weight components can permeate, for example. Specifically, for example, a component containing hydrogen (H2) can be separated from a component containing carbon dioxide using a palladium permeable membrane.

[0046] In the recovery device 5 using cooling separation, for example, a specific component is liquefied by cooling and separated from other components (gases). Specifically, for example, a component containing water can be liquefied and separated from a gas containing carbon dioxide.

[0047] In the case of the recovery device 5 using centrifugal separation, for example, a specific component (component containing water) is liquefied by cooling, and the component is separated from other components (gas containing carbon dioxide) by centrifugal force. In the case of the recovery device 5 using gravity separation, for example, a specific component (component containing water) is liquefied by cooling, and the component is separated from other components (gas containing carbon dioxide) by gravity. In the case of the recovery device 5 using gas-liquid separation, for example, a specific component (component containing water) is liquefied by cooling, and the component is separated from other components (gas containing carbon dioxide) by gravity, centrifugal force, surface tension, etc.

[0048] In the recovery device 5, a recovery gas F2 having a higher carbon dioxide concentration than the return fluid F1 can be obtained.

[0049] The circulation path 6 includes a lead-out path 61 and a return path 62 .

[0050] The lead-out path 61 connects the fuel cell 4 and the recovery device 5 . The lead-out path 61 takes out a part of the product gas as the return fluid F1 from the fuel cell 4 . The lead-out path 61 guides the return fluid F1 to the recovery device 5 .

[0051] The return path 62 connects the recovery device 5 and the methane reactor 130. The return path 62 introduces the recovered gas F2 containing carbon dioxide into the methane reactor 130.

[0052] The return path 7 connects the fuel cell 4 and the reformer 3. In the return path 7, a part of the product gas is taken out from the fuel cell 4 as a return fluid F3 and is returned to the reformer 3.

[0053] The methane generation system 1 includes: a recovery device 5 for separating a recovery gas F2 containing unreacted carbon dioxide from a part of the product gas (return fluid F1) discharged from the fuel cell 4; and a circulation path 6 for introducing the recovery gas F2 to the methane generation unit 2. According to the methane generation system 1, the recovery gas F2 containing carbon dioxide is returned to the methane generation unit 2, so that the efficiency of the methanogenic reaction in the methane generation unit 2 can be improved. Therefore, the methane generation efficiency can be improved.

[0054] Since the methane production system 1 includes the return path 7 for introducing the return fluid F3 to the reformer 3, the heat generated in the fuel cell 4 can be utilized in the reformer 3. Therefore, the energy efficiency can be improved.

[0055] Since the methane generation system 1 includes the return path 7, the amount of carbon dioxide generated in the reformer 3 can be increased. Therefore, the concentration of carbon dioxide in the product gas discharged from the fuel cell 4 can be increased. Therefore, the recovery efficiency of carbon dioxide in the recovery device 5 can be improved. Implementation method 2.

[0056] Next, a methane generation system according to Embodiment 2 will be described. The methane generation system according to this embodiment has a common configuration with Embodiment 1, so the description will focus on differences from Embodiment 1. The same configurations as those in Embodiment 1 are denoted by the same reference numerals, and description thereof will be omitted.

[0057] Figure 2 This is a schematic diagram of a methane production system according to Embodiment 2.

[0058] like Figure 2 As shown in FIG. 1 , the methane generation system 201 includes a methane generation unit 202 instead of the methane generation unit 2. The methane generation system 201 includes a circulation path 206 instead of the circulation path 6. The methane generation system 201 is different from the methane generation system 1 of the first embodiment (see FIG. 1 ). Figure 1 )different.

[0059] The methane production unit 202 includes a supply path 10 , a co-electrolysis device 20 , a methane reactor 30 , and a circulation path 50 .

[0060] The supply path 10 introduces water (water vapor) supplied from a supply source (not shown) to the co-electrolysis device 20. An evaporator (water vapor generator) for vaporizing water may be provided in the supply path 10. The supply path 10 may supply only water or both water and carbon dioxide.

[0061] The co-electrolysis device 20 is, for example, provided with a solid oxide electrolytic cell having a cathode electrode and an anode electrode. In the solid oxide electrolytic cell, for example, a solid oxide having oxygen ion conductivity is used. As an electrolyte, a zirconium oxide-based oxide or the like is used. The co-electrolysis device 20 is an example of an electrolysis device.

[0062] In the co-electrolysis device 20, water (or water and carbon dioxide) supplied from the supply path 10 is supplied to the cathode electrode of the solid oxide electrolytic cell. The water used in the co-electrolysis in the solid oxide electrolytic cell is preferably water vapor. In the co-electrolysis device 20, the recovered gas F2 containing carbon dioxide introduced from the circulation path 206 is supplied to the cathode electrode of the solid oxide electrolytic cell.

[0063] The co-electrolysis device 20 may include a heating device for heating the solid oxide electrolytic cell. The heating device can adjust the temperature in the solid oxide electrolytic cell to a temperature suitable for the co-electrolysis reaction.

[0064] The ratio of carbon dioxide and water supplied to the solid oxide electrolytic cell can be determined based on the ratio of the components (carbon monoxide and hydrogen) of the target mixed gas.

[0065] The co-electrolysis device 20 produces a mixed gas containing carbon monoxide (CO) and hydrogen (H2) by co-electrolysis of carbon dioxide (CO2) and water (H2O). The co-electrolysis is carried out, for example, according to the following formula (IV). This reaction is an endothermic reaction.

[0066] CO2+H2O→CO+H2+O2···(IV)

[0067] In the co-electrolysis device 20, for example, electricity generated by renewable energy (such as solar power generation, wind power generation, etc.) can be used to perform co-electrolysis. Even if methane obtained by using renewable energy is burned, no additional carbon dioxide is generated, so it can be considered as a carbon-neutral fuel that has no effect on global warming.

[0068] In the present embodiment, a co-electrolysis device 20 is used to obtain carbon monoxide and hydrogen from carbon dioxide and water by co-electrolysis, but the device for obtaining carbon monoxide and hydrogen (H2) is not limited to the co-electrolysis device. For example, an electrolysis device that independently performs a process of electrolyzing carbon dioxide to obtain carbon monoxide and a process of electrolyzing water to obtain hydrogen (H2) can also be used.

[0069] The mixed gas obtained in the co-electrolysis device 20 contains not only carbon monoxide and hydrogen (H 2 ) but also unreacted carbon dioxide and water.

[0070] The inlet of the co-electrolysis device 20 is a portion where the supply path 10 and the return path 262 are connected. The outlet of the co-electrolysis device 20 is a portion where the mixed gas is led out.

[0071] In the methane reactor 30 , carbon monoxide (CO) and hydrogen (H 2 ) are reacted by methanation to obtain a fuel gas containing methane (CH 4 ) and water (H 2 O). The methanation reaction is performed, for example, according to the following formula (V). This reaction is an exothermic reaction. CO+3H2→CH4+H2O···(V)

[0072] The methane reactor 30 preferably includes a methanation catalyst with which the mixed gas contacts. Examples of the methanation catalyst include a Ni catalyst and a Ru catalyst. The methanation catalyst promotes the methanation reaction.

[0073] The methane reactor 30 can generate methanol from the mixed gas, and can also generate methane from methanol.

[0074] The fuel gas obtained in the methane reactor 30 contains not only methane and water but also unreacted carbon monoxide, hydrogen (H 2 ), carbon dioxide, and the like.

[0075] The fuel gas passes through the discharge path 60 and is introduced into the reformer 3 .

[0076] The inlet of the methane reactor 30 is a portion where the mixed gas is introduced from the co-electrolysis device 20. The outlet of the methane reactor 30 is a portion where the discharge path 60 is connected.

[0077] The circulation path 50 connects the methane reactor 30 and the co-electrolysis device 20. The starting end (first end) of the circulation path 50 is connected to a position close to the outlet of the methane reactor 30. The terminal end (second end) of the circulation path 50 is connected to the co-electrolysis device 20. The circulation path 50 introduces a part of the fuel gas obtained in the methane reactor 30 into the co-electrolysis device 20.

[0078] The circulation path 206 includes a lead-out path 61 and a return path 262. The return path 262 connects the recovery device 5 and the co-electrolysis device 20. The return path 262 introduces the recovered gas F2 containing carbon dioxide into the co-electrolysis device 20.

[0079] The methane generation system 201 includes: a recovery device 5 for separating a recovery gas F2 containing carbon dioxide from a product gas (return fluid F1) discharged from a fuel cell 4; and a circulation path 206 for introducing the recovery gas F2 into a methane generation unit 202. According to the methane generation system 1, the recovery gas F2 containing carbon dioxide as an unreacted product is returned to the methane generation unit 202, so that the efficiency of the methanogenic reaction in the methane generation unit 202 can be improved. Therefore, the methane generation efficiency can be improved.

[0080] In the methane generation system 201, the co-electrolysis device 20 is used as the electrolysis device, so a mixed gas containing carbon monoxide and hydrogen (H2) can be obtained by co-electrolysis. Therefore, the efficiency of the methanogenic reaction in the methane reactor 30 can be improved compared to the case of using a mixed gas containing carbon dioxide and hydrogen.

[0081] Since the methane production system 201 includes the circulation path 6 for introducing the recovered gas F2 into the methane production unit 2, the heat generated in the fuel cell 4 can be utilized in the co-electrolysis device 20. Therefore, the energy efficiency can be improved. Implementation method 3.

[0082] Next, a methane generation system according to Embodiment 3 will be described. The same components as those in Embodiment 2 are denoted by the same reference numerals, and description thereof will be omitted.

[0083] Figure 3 This is a schematic diagram of a methane production system according to Embodiment 3.

[0084] like Figure 3 As shown in FIG. 3 , the methane generation system 301 includes an auxiliary supply path 302. The auxiliary supply path 302 supplies an auxiliary gas F4 supplied from a supply source not shown to the recovery device 5. The auxiliary gas F4 contains carbon dioxide. The auxiliary gas F4 is, for example, air. The auxiliary gas F4 may be a gas having a carbon dioxide concentration higher than that of air.

[0085] In the methane generation system 301, the auxiliary gas F4 containing carbon dioxide can be supplied to the recovery device 5 through the auxiliary supply path 302, so that the amount of carbon dioxide recovered in the recovery device 5 can be increased. Therefore, the amount of carbon dioxide supplied to the methane generation unit 202 can be increased. Therefore, the methane generation efficiency can be improved. Implementation method 4.

[0086] Next, a methane generation system according to Embodiment 4 will be described. The same components as those in Embodiment 2 are denoted by the same reference numerals, and description thereof will be omitted.

[0087] Figure 4 This is a schematic diagram of a portion of a methane generation system according to a fourth embodiment.

[0088] like Figure 4 As shown in FIG. 4 , the methane generation system 401 includes an auxiliary supply path 402 , an auxiliary recovery device 403 , an auxiliary concentrator 404 , and a concentrator 405 .

[0089] The auxiliary supply path 402 introduces the auxiliary gas F4 supplied from a supply source (not shown). The auxiliary supply path 402 is connected to the circulation path 206 (return path 262). The auxiliary gas F4 contains carbon dioxide. The auxiliary gas F4 may be air or a gas having a higher carbon dioxide concentration than air.

[0090] The auxiliary recovery device 403 is provided in the auxiliary supply path 402. The auxiliary recovery device 403 separates and recovers the auxiliary recovery gas F5 containing carbon dioxide from the auxiliary gas F4. In the auxiliary recovery device 403, for example, separation techniques such as adsorption separation, membrane separation, cooling separation, centrifugal separation, gravity separation, gas-liquid separation, etc. are used. The auxiliary recovery device 403 can be connected to the recovery device 5 (see Figure 1In the auxiliary recovery device 403, an auxiliary recovery gas F5 having a higher carbon dioxide concentration than the auxiliary gas F4 can be obtained.

[0091] The auxiliary concentrator 404 is provided in the auxiliary supply path 402. As for the auxiliary concentrator 404, similarly to the auxiliary recovery device 403, for example, the carbon dioxide concentration of the auxiliary recovery gas F5 can be increased by separation techniques such as adsorption separation, membrane separation, cooling separation, centrifugal separation, gravity separation, gas-liquid separation, etc. The auxiliary recovery gas F5 with increased carbon dioxide concentration is introduced into the circulation path 206 (return path 262) through the auxiliary supply path 402. The auxiliary recovery gas F5 merges with the recovery gas F2 flowing in the circulation path 206 (return path 262).

[0092] The concentrator 405 is provided in the circulation path 206 (return path 262). The concentrator 405 can increase the carbon dioxide concentration of the gas flowing in the circulation path 206 (return path 262) by separation techniques such as adsorption separation, membrane separation, cooling separation, centrifugal separation, gravity separation, gas-liquid separation, etc., similarly to the auxiliary recovery device 403. The gas with increased carbon dioxide concentration is introduced into the methane generation unit 202 through the circulation path 206 (return path 262).

[0093] In the methane generation system 401, the amount of carbon dioxide recovered can be increased by the auxiliary supply path 402. In the methane generation system 401, the gas with an increased carbon dioxide concentration can be supplied to the methane generation unit 202 through the auxiliary concentrator 404 and the concentrator 405. Therefore, the methane generation efficiency can be improved. Since the gas with an increased carbon dioxide concentration can be supplied to the methane generation unit 202, the energy efficiency can be improved. Implementation method 5.

[0094] Next, a methane generation system according to Embodiment 5 will be described. The same components as those in Embodiment 2 are denoted by the same reference numerals, and description thereof will be omitted.

[0095] Figure 5 This is a schematic diagram of a portion of a methane generation system according to Embodiment 5.

[0096] like Figure 5 As shown in FIG. 5 , a methane generation system 501 includes an auxiliary supply path 502 , an auxiliary recovery device 503 , an auxiliary concentrator 504 , a second recovery device 505 , and a concentrator 506 .

[0097] The assist supply path 502 introduces the assist gas F4 supplied from a supply source (not shown).

[0098] The auxiliary recovery device 503 is provided in the auxiliary supply path 502. The auxiliary recovery device 503 separates and recovers the auxiliary recovery gas F5 having a high carbon dioxide concentration from the auxiliary gas F4.

[0099] The auxiliary concentrator 504 is provided in the auxiliary supply path 502 . The auxiliary concentrator 504 can increase the carbon dioxide concentration of the auxiliary recovered gas F5 . The auxiliary recovered gas F5 with increased carbon dioxide concentration is introduced into the methane generator 202 through the auxiliary supply path 502 .

[0100] The second recovery device 505 is provided in the circulation path 206 (the return path 262 ). The second recovery device 505 obtains a recovered gas F6 having an increased carbon dioxide concentration from the recovered gas F2 .

[0101] The concentrator 506 is provided in the circulation path 206 (return path 262 ). The carbon dioxide concentration of the recovered gas F6 can be further increased in the concentrator 506 . The recovered gas F6 with increased carbon dioxide concentration is introduced into the methane generator 202 through the circulation path 206 (return path 262 ).

[0102] In the methane generation system 501, the amount of carbon dioxide recovered can be increased through the auxiliary supply path 502. In the methane generation system 501, the gas with an increased carbon dioxide concentration can be supplied to the methane generation unit 202 through the auxiliary recovery device 503, the auxiliary concentrator 504, the second recovery device 505 and the concentrator 506. Therefore, the methane generation efficiency can be improved. Since the gas with an increased carbon dioxide concentration can be supplied to the methane generation unit 202, the energy efficiency can be improved. Implementation method 6.

[0103] Next, a methane generation system according to Embodiment 6 will be described. The same components as those in Embodiment 2 are denoted by the same reference numerals, and description thereof will be omitted.

[0104] Figure 6 This is a schematic diagram of a methane generation system according to a sixth embodiment.

[0105] like Figure 6 As shown in FIG. 6 , the methane generation system 601 includes an auxiliary supply path 302 (see Figure 3 ). The auxiliary supply path 302 supplies the auxiliary gas F4 to the recovery device 5 .

[0106] The auxiliary gas F4 has a higher concentration of carbon dioxide than air. The auxiliary gas F4 is, for example, indoor air. Indoor air contains exhaled breath of indoor users, so it has a higher concentration of carbon dioxide than outdoor air. The auxiliary gas F4 may be exhaust gas discharged from a ventilator installed in a building for indoor ventilation.

[0107] In the methane generation system 601, the auxiliary gas F4 containing high carbon dioxide can be supplied to the recovery device 5 through the auxiliary supply path 302, so that the amount of carbon dioxide recovered in the recovery device 5 can be increased. Therefore, the amount of carbon dioxide supplied to the methane generation unit 202 can be increased. Therefore, the methane generation efficiency can be improved. Implementation method 7.

[0108] Next, a methane generation system according to Embodiment 7 will be described. The same components as those in Embodiment 2 are denoted by the same reference numerals, and description thereof will be omitted.

[0109] Figure 7 This is a schematic diagram of a methane generation system according to Embodiment 7.

[0110] like Figure 7 As shown in FIG. 1 , the methane generation system 701 includes a recovery device 705 instead of the recovery device 5. In this respect, it is different from the methane generation system 201 of the second embodiment (see FIG. 1 ). Figure 2 The recovery device 705 is provided on the air conditioner 702.

[0111] The air conditioner 702 can deliver conditioned air to the room. The air conditioner 702 performs at least one of cooling operation and heating operation. The air conditioner 702 includes a heat exchanger 703 and a blower 704. The heat exchanger 703 is, for example, a heat exchanger for an indoor unit. The heat exchanger 703 adjusts the temperature of the air. The blower 704 sends the air whose temperature has been adjusted by the heat exchanger 703 to the room.

[0112] As for the recovery device 705, its characteristics are affected by temperature and humidity according to the separation method. For example, in the case of adsorption separation using an adsorbent, the adsorption characteristics of the adsorbent can be improved by rationalizing the temperature and humidity. Even when the adsorbate (carbon dioxide) is separated from the adsorbent, the separation characteristics can be improved by rationalizing the temperature and humidity. Therefore, as for the recovery device 705, the heat exchanger 703 of the air conditioner 702 is used to adjust the temperature and humidity, thereby obtaining a recovered gas F2 with a high carbon dioxide concentration.

[0113] The recovery device 705 can adjust the temperature using the heat of the return fluid F1 from the fuel cell 4. Therefore, by adjusting the temperature using the exhaust heat of the fuel cell 4, a recovery gas F2 having a high carbon dioxide concentration can be obtained.

[0114] In the methane generation system 701, the temperature and humidity are adjusted using the existing air conditioner 702, so the device cost can be suppressed compared with the case of using a temperature adjustment means dedicated to the recovery device.

[0115] As for the recovery device 705, its characteristics are affected by the flow of the return fluid F1 according to the separation method. For example, in the case of adsorption separation using an adsorbent, the adsorption characteristics of the adsorbent can be improved by rationalizing the flow rate of the return fluid F1 in contact with the adsorbent. Even when the adsorbate (carbon dioxide) is separated from the adsorbent, the separation characteristics from the adsorbent can be improved by rationalizing the flow rate of the return fluid F1. Therefore, as for the recovery device 705, the air supply volume can be adjusted using the air blower 704 of the air conditioner 702, thereby obtaining a recovered gas F2 with a high carbon dioxide concentration.

[0116] It should be noted that the technical scope of the present disclosure is not limited to the above-described embodiments, and various changes can be made without departing from the gist of the present disclosure.

[0117] For example, the number of the recovery device, the auxiliary recovery device, the concentrator, and the auxiliary concentrator may each be 1, or may be plural (any number of 2 or more).

[0118] In the electrolysis device 120 (refer to Figure 1 ) and the co-electrolysis device 20 (refer to Figure 2 ) is electrolyzed to generate oxygen (O2). This oxygen can be supplied to the reformer 3 (see Figure 1 and Figure 2 As the oxygen-containing gas, a mixed gas containing oxygen and air obtained from an electrolysis device may be used. That is, the oxygen-containing gas may be a gas containing oxygen obtained from an electrolysis device.

[0119] According to this method, the concentration of components other than oxygen (nitrogen, etc.) in the oxygen-containing gas can be reduced. Therefore, the carbon dioxide concentration of the product gas from the fuel cell 4 can be increased. Therefore, the carbon dioxide concentration of the recovered gas F2 obtained in the recovery device 5 can be increased. Description of Reference Numerals

[0120] 1, 201, 301, 401, 501, 601, 701...methane generation system 2, 202...methane generation unit 3...reformer 4...fuel cell 5...recovery device 6...circulation path 7...return path 20...co-electrolysis device (electrolysis device) 30, 130...methane reactor 120...electrolysis device 302, 402, 502...auxiliary supply path 404, 504...auxiliary concentrator 405, 506...concentrator 702...air conditioner 703...heat exchanger 704...blower F1...return fluid F2...recovered gas F4...auxiliary gas

Claims

1. A methane generation system comprising: a methane generating unit including an electrolysis device for obtaining hydrogen by electrolyzing water, and a methane reactor for obtaining a fuel gas containing methane by a methanogenic reaction using the hydrogen; a reformer that reforms the fuel gas to obtain a reformed gas; A fuel cell that generates electricity by reacting the reformed gas and the oxygen-containing gas to obtain a product gas; a recovery device that separates a recovery gas containing carbon dioxide from a return fluid that is a portion of the product gas; and A circulation path introduces the recovered gas into the methane generating unit.

2. The methane generation system according to claim 1, wherein: The electrolysis device is a co-electrolysis device for obtaining the hydrogen and carbon monoxide by electrolysis of the water and carbon dioxide. 3 . The methane production system according to claim 1 , further comprising: a return path for introducing a part of the product gas into the reformer. 4 . The methane production system according to claim 1 , further comprising: an auxiliary supply path for supplying an auxiliary gas containing carbon dioxide to the recovery device.

5. The methane generation system according to claim 1, wherein: The circulation path is provided with a concentrator for increasing the concentration of carbon dioxide contained in the gas flowing in the circulation path.

6. The methane generation system according to claim 1, further comprising: An auxiliary supply path for supplying an auxiliary gas containing carbon dioxide to the circulation path; and An auxiliary concentrator is provided to increase the concentration of carbon dioxide contained in the auxiliary gas.

7. The methane generation system according to claim 5, further comprising: an auxiliary supply path for supplying an auxiliary gas containing carbon dioxide to the methane generating unit; and An auxiliary concentrator is provided to increase the concentration of carbon dioxide contained in the auxiliary gas.

8. The methane generation system according to claim 4, wherein: The auxiliary supply path supplies air in the chamber as the auxiliary gas.

9. The methane generation system according to claim 1, wherein: The recovery device obtains the recovered gas by temperature adjustment caused by a heat exchanger of an air conditioner.

10. The methane generation system according to claim 1, wherein: The recovery device obtains the recovered gas by using the air blown by a blower of an air conditioner.

11. The methane generation system according to claim 1, wherein: The recovery device obtains the recovered gas by utilizing a heat exchanger with air conditioning and adjusting the temperature of the fuel cell.

12. The methane generation system according to claim 1, wherein: The oxygen-containing gas includes oxygen obtained by electrolysis of the water in the electrolysis device.

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