Methane generation system

Abstract

A methane production system according to the present disclosure is provided with: a supply pathway for supplying carbon dioxide and water; an electrolytic apparatus for obtaining carbon monoxide and hydrogen from the carbon dioxide and the water through electrolysis; a methane reactor for obtaining a product gas containing methane from a gas mixture containing the carbon monoxide and the hydrogen; a first separator for separating, from a returned fluid that is one portion of the product gas, a first separated fluid containing water and a second separated fluid containing hydrogen; and a first circulation pathway. The first circulation pathway includes a first return path for guiding the first separated fluid to the electrolytic apparatus, and a second return path for guiding the second separated fluid to the methane reactor.

Description

Technical Field

[0001] This disclosure relates to a methane production system.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above technology, the production efficiency of methane may be low.

[0005] In view of the above circumstances, an object of this disclosure is to provide a methane production system capable of enhancing the production efficiency of methane.

Means for Solving the Problems

[0006] One aspect of the methane production system according to this disclosure includes a supply path for supplying carbon dioxide and water, an electrolyzer for obtaining carbon monoxide and hydrogen by electrolyzing the carbon dioxide and the water, a methane reactor for obtaining a product gas containing methane from a mixed gas containing the carbon monoxide and the hydrogen, a first separator for separating a first separated fluid containing water and a second separated fluid containing hydrogen from a return fluid that is a part of the product gas, a first return path for guiding the first separated fluid to the electrolyzer, and a second return path for guiding the second separated fluid to the methane reactor, and a first circulation path.

Effects of the Invention

[0007] According to this disclosure, a methane production system that can increase the efficiency of methane production can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of the methane production system according to Embodiment 1. [Figure 2] This is a schematic diagram of the methane production system according to Embodiment 2. [Figure 3] This is a schematic diagram of the methane production system according to Embodiment 3. [Figure 4] This is a schematic diagram of the methane production system according to Embodiment 4. [Figure 5] This is a schematic diagram of the methane production system according to Embodiment 5. [Figure 6] This is a schematic diagram of the methane production system according to Embodiment 6. [Figure 7] This is a schematic diagram of the methane production system according to Embodiment 7. [Figure 8] This is a schematic diagram of the methane production system according to Embodiment 8. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described below with reference to the drawings. However, the scope of this disclosure is not limited to the embodiments described below and can be modified at will within the scope of the technical idea of ​​this disclosure.

[0010] Embodiment 1. Figure 1 is a schematic diagram showing the methane production system in Embodiment 1. As shown in Figure 1, the methane production system 1 comprises a supply path 10, a co-electrolytic device 20, a methane reactor 30, a first separator 40, and a first circulation path 50.

[0011] The supply path 10 guides carbon dioxide and water supplied from a supply source (not shown) to the electrolytic apparatus 20. The supply path 10 guides, for example, a mixed fluid of carbon dioxide and water to the electrolytic apparatus 20. The supply path 10 may include a first supply path for guiding carbon dioxide and a second supply path for guiding water. The supply path 10 may be provided with an evaporator (water vapor generation unit) for vaporizing water.

[0012] The co-electrolytic apparatus 20 includes, for example, a solid oxide type electrolytic cell having a cathode electrode and an anode electrode. For example, a solid oxide having oxygen ion conductivity is used in the solid oxide type electrolytic cell. Zirconia-based oxides are used as the electrolyte. The co-electrolytic apparatus 20 is an example of an electrolytic apparatus.

[0013] The co-electrolysis apparatus 20 supplies carbon dioxide and water supplied from the supply path 10 to the cathode electrode of the solid oxide electrolytic cell. The water used for co-electrolysis in the solid oxide electrolytic cell is preferably water vapor.

[0014] The co-electrolytic apparatus 20 may include a heating device for heating the solid oxide electrolytic cell. The heating device can adjust the temperature inside the solid oxide electrolytic cell to a temperature suitable for the co-electrolytic reaction. The ratio of carbon dioxide to water supplied to a solid oxide electrolytic cell can be determined according to the ratio of the components of the desired mixed gas (carbon monoxide, hydrogen).

[0015] The co-electrolytic apparatus 20 obtains a mixed gas containing carbon monoxide (CO) and hydrogen (H2) from carbon dioxide (CO2) and water (H2O) through co-electrolysis. Co-electrolysis proceeds, for example, according to equation (I) shown below. This reaction is an endothermic reaction. CO2 + H2O → CO + H2 + O2···(I)

[0016] In the co-electrolysis device 20, for example, co-electrolysis can be performed using electric power generated using renewable energy (for example, solar power generation, wind power generation, etc.). Methane obtained using renewable energy can be considered a carbon-neutral fuel that does not affect global warming because no additional carbon dioxide is generated even when it is used for combustion.

[0017] In the present embodiment, a co-electrolysis device 20 that obtains carbon monoxide and hydrogen by co-electrolysis from carbon dioxide and water is used, but the device for obtaining carbon monoxide and hydrogen (H2) is not limited to a co-electrolysis device. For example, an electrolysis device that independently performs a step of electrolyzing carbon dioxide to obtain carbon monoxide and a step of electrolyzing water to obtain hydrogen (H2) can also be used.

[0018] The mixed gas obtained in the co-electrolysis device 20 contains not only carbon monoxide and hydrogen (H2), but also unreacted carbon dioxide and water. The inlet of the co-electrolysis device 20 is the location where the supply path 10 is connected. The outlet of the co-electrolysis device 20 is the location where the mixed gas is led out.

[0019] The methane reactor 30 obtains a product gas containing methane (CH4) and water (H2O) from carbon monoxide (CO) and hydrogen (H2) by a methanation reaction. The methanation reaction proceeds, for example, according to the following formula (II). This reaction is an exothermic reaction. CO + 3H2 → CH4 + H2O ···(II)

[0020] The methane reactor 30 preferably includes a methanation catalyst with which the mixed gas comes into contact. Examples of the methanation catalyst include a Ni catalyst and a Ru catalyst. The methanation catalyst promotes the methanation reaction. The methane reactor 30 may generate methanol from the mixed gas and generate methane from the methanol.

[0021] The product gas obtained in the methane reactor 30 contains not only methane and water, but also unreacted carbon monoxide, hydrogen (H2), carbon dioxide, and the like. The generated gas is discharged out of the system through the discharge path 60. The discharged generated gas is sent to gas production facilities, for example, as a raw material for city gas. The inlet of the methane reactor 30 is where the mixed gas is introduced from the electrolytic device 20. The outlet of the methane reactor 30 is where the discharge path 60 is connected.

[0022] The first separator 40 separates a first separation fluid F2 containing water and a second separation fluid F3 containing hydrogen (H2) from the return fluid F1, which is part of the product gas. The first separator 40 employs separation methods such as adsorption separation, membrane separation, cooling separation, centrifugal separation, gravity separation, and gas-liquid separation. The first separator 40 may employ one of these separation methods, or a combination of two or more.

[0023] The first separator 40, which uses adsorption separation, separates specific components by adsorbing them onto an adsorbent, adsorbent solution, etc. Examples of adsorbents include silica gel, zeolite, and activated carbon. Specifically, by adsorbing water-containing components onto the adsorbent, these components can be separated from other components containing hydrogen (H2). The adsorbent may be granular, powdery, or otherwise. Granular adsorbents may be, for example, bead-shaped (spherical) or pellet-shaped (cylindrical). When using a powdery adsorbent, the adsorbent may be supported on the surface of a substrate. The substrate may be, for example, honeycomb-shaped.

[0024] The first separator 40, which uses adsorption separation, has the function of separating the adsorbent from the adsorbent. The first separator 40 is equipped with, for example, a heating device. The heating device separates the adsorbent from the adsorbent by heating the adsorbent. The first separator 40 may also be equipped with a vacuum device such as a vacuum pump. The vacuum device separates the adsorbent from the adsorbent by placing the adsorbent under reduced pressure.

[0025] The first separator 40, which uses membrane separation, separates specific components from other components using, for example, a permeable membrane that allows low molecular weight components to pass through. Specifically, for example, a component containing hydrogen (H2) can be separated from a component containing water using a palladium permeable membrane. The first separator 40, which uses cooling separation, separates a specific component from other components (gases) by liquefying it through cooling. Specifically, for example, it can liquefy a component containing water and separate it from a gas containing hydrogen (H2).

[0026] The first separator 40 using centrifugal separation liquefies a specific component (a component containing water) by cooling, for example, and separates this component from other components (a gas containing hydrogen (H2)) by centrifugal force. The first separator 40 using gravity separation liquefies a specific component (a component containing water) by cooling, for example, and separates this component from other components (a gas containing hydrogen (H2)) by gravity. The first separator 40 using gas-liquid separation liquefies a specific component (a component containing water) by cooling, for example, and separates this component from other components (a gas containing hydrogen (H2)) by gravity, centrifugal force, surface tension, etc.

[0027] The first circulation path 50 includes an outlet path 51, a first return path 52, and a second return path 53. The outlet 51 connects the methane reactor 30 and the first separator 40. The starting end (first end) of the outlet 51 is connected to a position close to the outlet of the methane reactor 30. The ending end (second end) of the outlet 51 is connected to the first separator 40. The outlet 51 extracts a portion of the product gas from the methane reactor 30 as a return fluid F1. The outlet 51 leads the return fluid F1 to the first separator 40.

[0028] The first return path 52 connects the first separator 40 and the supply path 10. The starting end (first end) of the first return path 52 is connected to the first separator 40. The ending end (second end) of the third return path 552 is connected to the supply path 10. The first return path 52 can guide the first separated fluid F2 to the co-electrolytic device 20 through the supply path 10. The first return path 52 may also connect the first separator 40 and the co-electrolytic device 20.

[0029] The second return channel 53 connects the first separator 40 and the methane reactor 30. The starting end (first end) of the second return channel 53 is connected to the first separator 40. The ending end (second end) of the second return channel 53 is connected to a position close to the inlet of the methane reactor 30. The ending end (second end) of the second return channel 53 is located closer to the inlet of the methane reactor 30 than the starting end (first end) of the outlet channel 51. The second return channel 53 leads the second separated fluid F3 to the methane reactor 30.

[0030] The discharge path 60 may be equipped with a separator to remove impurities from the product gas. These impurities may include, for example, components other than methane (such as carbon dioxide, water, and hydrogen (H2)). The separator may employ separation methods such as adsorption, membrane separation, cooling, centrifugal separation, gravity separation, or gas-liquid separation. The separator may employ one of these separation methods, or a combination of two or more.

[0031] Separators using adsorption separation separate substances such as carbon dioxide and water by adsorbing them onto an adsorbent or adsorbent solution. Examples of adsorbents include silica gel, zeolite, and activated carbon. Separators using membrane separation, for example, use a permeable membrane that allows low-molecular-weight components to pass through to separate specific components from other components. Specifically, low-molecular-weight components such as hydrogen (H2) can be separated using a palladium permeable membrane. A separator using cooling separation, for example, liquefies a specific component by cooling and separates it from other components (gases).

[0032] A separator using centrifugal separation, for example, liquefies a specific component by cooling and separates this component from other components (gases) by centrifugal force. A separator using gravity separation, for example, liquefies a specific component by cooling and separates this component from other components (gases) by gravity. A separator using gas-liquid separation, for example, liquefies a specific component by cooling and separates this component from other components (gases) by gravity, centrifugal force, surface tension, etc.

[0033] Next, an example of a methane production method using methane production system 1 will be described. The methane production method according to this embodiment comprises a supply step, an electrolysis step, a methanation step, and a circulation step.

[0034] In the supply process, carbon dioxide (CO2) and water (H2O) are introduced to the co-electrolysis device 20 via the supply path 10. In the electrolysis process, a co-electrolytic apparatus 20 obtains a mixed gas containing carbon monoxide (CO) and hydrogen (H2) from carbon dioxide and water through co-electrolysis.

[0035] In the methanation process, methane (CH4) and a product gas containing water are obtained from carbon monoxide and hydrogen in the methane reactor 30 through a methanation reaction. The product gas contains not only methane and water, but also unreacted carbon monoxide, hydrogen (H2), carbon dioxide, etc. The product gas is discharged out of the system through the discharge path 60.

[0036] In the circulation process, a portion of the product gas is removed from the methane reactor 30 through the outlet 51 and guided to the first separator 40 as a return fluid F1. In the first separator 40, the return fluid F1 is separated into a first separation fluid F2 containing water (e.g., water vapor) and a second separation fluid F3 containing hydrogen (H2). The concentration of water (e.g., water vapor) in the first separation fluid F2 is higher than the concentration of water (e.g., water vapor) in the return fluid F1. The concentration of hydrogen (H2) in the second separation fluid F3 is higher than the concentration of hydrogen (H2) in the return fluid F1.

[0037] The first separated fluid F2 is led to the co-electrolytic device 20 through the first return path 52 and the supply path 10. The second separated fluid F3 is led to the methane reactor 30 through the second return path 53.

[0038] The methane production system 1 includes a first return channel 52 that leads the first separated fluid F2 to the co-electrolytic device 20, and a second return channel 53 that leads the second separated fluid F3 to the methane reactor 30. According to the methane production system 1, the second separation fluid F3 containing unreacted hydrogen (H2) is returned to the methane reactor 30, thereby increasing the efficiency of the methanation reaction in the methane reactor 30. Therefore, the methane production efficiency can be increased. According to the methane production system 1, the first separation fluid F2, which contains unreacted water (e.g., water vapor), is returned to the co-electrolytic device 20. Therefore, the efficiency of the electrolytic reaction in the co-electrolytic device 20 can be increased. Since the first separation fluid F2 is returned to the co-electrolytic device 20, the heat generated in the methane reactor 30 can be utilized in the co-electrolytic device 20. Thus, energy efficiency can be increased. In the methane production system 1, water (e.g., water vapor) is discharged from the methane reactor 30, thereby increasing the efficiency of the methane reaction in the methane reactor 30.

[0039] Embodiment 2. Next, a methane production system according to Embodiment 2 will be described. Since the basic configuration of the methane production system according to this embodiment is the same as that of Embodiment 1, we will mainly describe the differences from Embodiment 1. Components that are the same as those in other embodiments are denoted by the same reference numerals and their description is omitted.

[0040] Figure 2 is a schematic diagram of the methane production system according to Embodiment 2. As shown in Figure 2, the methane production system 101 is equipped with a cooler 70 in the second return passage 53. The cooler 70 may be a heat exchanger. The cooler 70 may be a water-cooled, air-cooled, or other type of cooler. The cooler 70 cools the second separation fluid F3 flowing through the second return passage 53.

[0041] The methane production system 101 cools the second separation fluid F3 with the cooler 70, thereby allowing the temperature in the methane reactor 30 to be set to a temperature suitable for the methanation reaction. Therefore, the methane production efficiency in the methane reactor 30 can be increased.

[0042] Embodiment 3. Next, a methane production system according to Embodiment 3 will be described. Components that are the same as those in the other embodiments are denoted by the same reference numerals and their description is omitted.

[0043] Figure 3 is a schematic diagram of the methane production system according to Embodiment 3. As shown in Figure 3, the methane production system 201 is equipped with a supply path 210 instead of the supply path 10 (see Figure 1). The supply path 210 includes a first supply path 211 and a second supply path 212. The first supply path 211 leads carbon dioxide to the co-electrolysis device 20. The second supply path 212 leads water to the first supply path 211. Therefore, the second supply path 212 can lead water to the co-electrolysis device 20 via the first supply path 211.

[0044] The methane production system 201 includes a heat exchanger 270. The heat exchanger 270 spans both the second supply channel 212 and the outlet channel 51. The heat exchanger 270 can cool the return fluid F1 by exchanging heat with the water flowing through the second supply channel 212. As the return fluid F1 is cooled, certain components (including water) liquefy.

[0045] The methane production system 201 is equipped with a gas-liquid separator 240 in place of the first separator 40 (see Figure 1). The gas-liquid separator 240 separates liquid and gas by means of gravity, centrifugal force, surface tension, etc. The gas-liquid separator 240 is an example of the first separator. The liquid obtained in the gas-liquid separator 240 becomes a first separated fluid F2 containing water. The first separated fluid F2 is led to the co-electrolytic device 20 through the first return path 52 and the first supply path 211. The gas obtained in the gas-liquid separator 240 becomes a second separated fluid F3 containing hydrogen (H2). The second separated fluid F3 is led to the methane reactor 30 through the second return path 53.

[0046] The methane production system 201 is equipped with a heat exchanger 270, which allows the return fluid F1 to be cooled using water supplied by the second supply channel 212. This improves the energy efficiency of the gas-liquid separator 240. The methane production system 201 obtains a second separated fluid F3 with a controlled temperature through the heat exchanger 270, which allows the temperature in the methane reactor 30 to be set to a temperature suitable for the methanation reaction. Therefore, the methane production efficiency in the methane reactor 30 can be improved.

[0047] Embodiment 4. Next, a methane production system according to Embodiment 4 will be described. Components that are the same as those in the other embodiments are denoted by the same reference numerals and their description is omitted.

[0048] Figure 4 is a schematic diagram of the methane production system according to Embodiment 4. As shown in Figure 4, the methane production system 301 is equipped with a supply path 310 instead of supply path 10 (see Figure 1). The supply path 310 leads a mixed fluid of carbon dioxide and water to the co-electrolytic device 20. Most of the carbon dioxide is gaseous, and most of the water is liquid. Therefore, the mixed fluid flowing through the supply path 310 is a gas-liquid two-phase fluid.

[0049] The methane production system 301 includes a heat exchanger 370. The heat exchanger 370 spans the supply path 310 and the outlet path 51. The heat exchanger 370 can cool the return fluid F1 by exchanging heat with the mixed fluid flowing through the supply path 310. As the return fluid F1 is cooled, certain components (including water) liquefy.

[0050] The methane production system 301 is equipped with a heat exchanger 370, which allows the return fluid F1 to be cooled using the mixed fluid supplied from the supply path 310. This improves the energy efficiency of the gas-liquid separator 240. The methane production system 301 obtains a second separated fluid F3 with a controlled temperature through the heat exchanger 370, which allows the temperature in the methane reactor 30 to be set to a temperature suitable for the methanation reaction. Therefore, the methane production efficiency in the methane reactor 30 can be increased.

[0051] In the methane production system 301, a mixed fluid, which is a gas-liquid two-phase fluid, is used as the heat transfer medium, thereby improving heat transfer performance. As a result, the return fluid F1 can be efficiently cooled in the heat exchanger 370.

[0052] Embodiment 5. Next, a methane production system according to Embodiment 5 will be described. Components that are the same as those in other embodiments are denoted by the same reference numerals and their description is omitted.

[0053] Figure 5 is a schematic diagram of the methane production system according to Embodiment 5. As shown in Figure 5, the methane production system 401 is equipped with a supply path 410 instead of the supply path 10 (see Figure 1). The supply path 410 includes a first supply path 411, a second supply path 412, and a confluence path 413. The first supply path 411 introduces carbon dioxide. The second supply path 412 introduces water. The confluence path 413 combines the carbon dioxide from the first supply path 411 and the water from the second supply path 412 and leads them to the co-electrolysis device 20.

[0054] The methane production system 401 includes a heat exchanger 470. The heat exchanger 470 spans the first supply channel 411, the second supply channel 412, and the outlet channel 51. The heat exchanger 470 can cool the return fluid F1 by exchanging heat with carbon dioxide and water flowing through the supply channels 411 and 412. As the return fluid F1 is cooled, certain components (including water) liquefy.

[0055] The methane production system 401 is equipped with a heat exchanger 470, which allows the return fluid F1 to be cooled using carbon dioxide and water supplied from supply lines 411 and 412. This improves the energy efficiency of the gas-liquid separator 240. The methane production system 401 obtains a second separated fluid F3 with a controlled temperature through the heat exchanger 470, which allows the temperature in the methane reactor 30 to be set to a temperature suitable for the methanation reaction. Therefore, the methane production efficiency in the methane reactor 30 can be increased.

[0056] The supply path 410 includes a first supply path 411 for introducing carbon dioxide and a second supply path 412 for introducing water. Although carbon dioxide and water may have different pressures and other properties, the methane production system 401 allows for setting appropriate conditions for each fluid.

[0057] Embodiment 6. Next, a methane generation system according to Embodiment 6 will be described. Components that are the same as those in other embodiments are denoted by the same reference numerals and their description is omitted.

[0058] Figure 6 is a schematic diagram of the methane production system according to Embodiment 6. As shown in Figure 6, the methane production system 501 includes a supply path 10, a co-electrolytic device 20, a methane reactor 530, a first separator 40, a first circulation path 50, a second separator 540, and a second circulation path 550.

[0059] The methane reactor 530 comprises a first methane reaction section 531 and a second methane reaction section 532. The first methane reaction unit 531 generates methane from the mixed gas from the co-electrolytic device 20 through a methanation reaction to obtain an intermediate gas. The second methane reaction unit 532 generates methane from the intermediate gas through a methanation reaction to obtain a product gas. In this way, the methane reactor 530 obtains a product gas through a two-stage methanation reaction.

[0060] The first circulation path 50 includes an outlet path 51, a first return path 52, and a second return path 53. The outlet 51 connects the second methane reaction section 532 and the first separator 40. The starting end (first end) of the outlet 51 is connected to a position close to the outlet of the second methane reaction section 532. The ending end (second end) of the outlet 51 is connected to the first separator 40. The outlet 51 extracts a portion of the product gas from the second methane reaction section 532 as a return fluid F1. The outlet 51 guides the return fluid F1 to the first separator 40.

[0061] The first return path 52 connects the first separator 40 and the supply path 10. The first return path 52 can guide the first separated fluid F2 to the co-electrolytic device 20 through the supply path 10. The first return path 52 may also connect the first separator 40 and the co-electrolytic device 20.

[0062] The second return channel 53 connects the first separator 40 and the second methane reaction section 532. The starting end (first end) of the second return channel 53 is connected to the first separator 40. The ending end (second end) of the second return channel 53 is connected to a position close to the inlet of the second methane reaction section 532. The ending end (second end) of the second return channel 53 is located closer to the inlet of the second methane reaction section 532 than the starting end (first end) of the outlet channel 51. The second return channel 53 guides the second separated fluid F3 to the second methane reaction section 532.

[0063] Similar to the first separator 40, the second separator 540 employs separation methods such as adsorption separation, membrane separation, cooling separation, centrifugal separation, gravity separation, and gas-liquid separation.

[0064] The second circulation path 550 includes an outlet path 551, a third return path 552, and a fourth return path 553. The outlet 551 connects the first methane reaction section 531 and the second separator 540. The starting end (first end) of the outlet 551 is connected to a position close to the outlet of the first methane reaction section 531. The ending end (second end) of the outlet 551 is connected to the second separator 540. The outlet 551 extracts a portion of the intermediate gas from the first methane reaction section 531 as a return fluid F4. The outlet 551 leads the return fluid F4 to the second separator 540.

[0065] The third return path 552 connects the second separator 540 and the supply path 10. The starting end (first end) of the third return path 552 is connected to the second separator 540. The ending end (second end) of the third return path 552 is connected to the supply path 10. The third return path 552 can guide the third separation fluid F5 to the co-electrolytic device 20 through the supply path 10. The third return path 552 may also connect the second separator 540 and the co-electrolytic device 20.

[0066] The fourth return channel 553 connects the second separator 540 and the first methane reaction section 531. The starting end (first end) of the fourth return channel 553 is connected to the second separator 540. The ending end (second end) of the fourth return channel 553 is connected to a position close to the inlet of the first methane reaction section 531. The ending end (second end) of the fourth return channel 553 is located closer to the inlet of the first methane reaction section 531 than the starting end (first end) of the outlet channel 551. The fourth return channel 553 guides the fourth separated fluid F6 to the first methane reaction section 531.

[0067] In the methane production system 501, a portion of the intermediate gas is taken out of the first methane reaction section 531 through the outlet passage 551 and guided to the second separator 540 as a return fluid F4. In the second separator 540, a third separation fluid F5 containing water (e.g., water vapor) and a fourth separation fluid F6 containing hydrogen (H2) are separated from the return fluid F4. The concentration of water (e.g., water vapor) in the third separation fluid F5 is higher than the concentration of water (e.g., water vapor) in the return fluid F4. The concentration of hydrogen (H2) in the fourth separation fluid F6 is higher than the concentration of hydrogen (H2) in the return fluid F4.

[0068] In the methane production system 501, a portion of the product gas is taken out of the second methane reaction section 532 through the outlet passage 51 and guided to the first separator 40 as a return fluid F1. In the first separator 40, the return fluid F1 is separated into a first separation fluid F2 containing water (e.g., water vapor) and a second separation fluid F3 containing hydrogen (H2). The concentration of water (e.g., water vapor) in the first separation fluid F2 is higher than the concentration of water (e.g., water vapor) in the return fluid F1. The concentration of hydrogen (H2) in the second separation fluid F3 is higher than the concentration of hydrogen (H2) in the return fluid F1.

[0069] In the methane production system 501, not only is the first separated fluid F2 containing water returned to the co-electrolytic device 20 via the first circulation path 50, but the third separated fluid F5 containing water is also returned to the co-electrolytic device 20 via the second circulation path 550. In the methane production system 501, water is discharged from the methane reactor 530 at multiple locations, so water can be effectively removed. Therefore, the efficiency of the methanation reaction in the methane reactor 530 can be increased.

[0070] Embodiment 7. Next, a methane production system according to Embodiment 7 will be described. Components that are the same as those in other embodiments are denoted by the same reference numerals and their description is omitted.

[0071] Figure 7 is a schematic diagram of the methane production system according to Embodiment 7. As shown in Figure 7, the methane production system 601 includes a supply path 10, a co-electrolytic device 20, a methane reactor 530, a first separator 40, a first circulation path 50, a second separator 540, a second circulation path 550, and an ejector 680. The methane production system 601 differs from the methane production system 501 (see Figure 6) in that it includes an ejector 680.

[0072] The ejector 680 has an inlet 681, a first suction port 682, a second suction port 683, and an outlet 684. The ejector 680 is installed in the supply path 10. Carbon dioxide and water flowing through the supply path 10 flow into the ejector 680 from the inlet 681 and out from the outlet 684. Carbon dioxide and water serve as the driving fluid. The water serving as the driving fluid may be a gas (water vapor) or a liquid.

[0073] The first suction port 682 is connected to the end (second end) of the first return passage 52. The first separation fluid F2 flows into the ejector 680 from the first suction port 682 as a suction fluid. The second suction port 683 is connected to the end (second end) of the third return passage 552. The second suction port 683 is located downstream of the first suction port 682 in the flow direction. The "flow direction" is the direction in which carbon dioxide and water flow from the inlet 681 to the outlet 684. The third separation fluid F5 flows into the ejector 680 from the second suction port 683 as a suction fluid. Inside the ejector 680, there is a nozzle for ejecting the drive fluid.

[0074] The ejector 680 uses carbon dioxide and water flowing in from the inlet 681 as driving fluids to draw in the first separation fluid F2 and the third separation fluid F5 into the ejector 680. The first separation fluid F2 and the third separation fluid F5, along with the driving fluids carbon dioxide and water, flow out of the ejector 680 through the outlet 684 and are supplied to the co-electrolytic device 20 through the supply path 10.

[0075] Pumps or the like may be provided in the first return path 52 and the third return path 552 to send the first separated fluid F2 and the third separated fluid F5 to the supply path 10.

[0076] The methane production system 601 is equipped with an ejector 680, which can guide the first separated fluid F2 and the third separated fluid F5 to the supply path 10. Therefore, compared to, for example, a case where only a pump is used to guide the first separated fluid F2 and the third separated fluid F5 to the supply path 10, energy savings are possible.

[0077] The methane production system 601 uses an ejector 680 with multiple suction ports, thus reducing the number of ejectors required. This offers advantages in terms of miniaturization and cost reduction of the device.

[0078] Embodiment 8. Next, a methane production system according to Embodiment 8 will be described. Components that are the same as those in other embodiments are denoted by the same reference numerals and their description is omitted.

[0079] Figure 8 is a schematic diagram of the methane production system according to Embodiment 8. As shown in Figure 8, the methane production system 701 comprises a supply path 10, a co-electrolytic device 20, a methane reactor 530, a first separator 40, a first circulation path 50, a second separator 540, a second circulation path 550, and an ejector 780. The methane production system 701 differs from the methane production system 601 (see Figure 7) in that it is equipped with an ejector 780 instead of an ejector 680.

[0080] The ejector 780 comprises a first ejector section 781 and a second ejector section 782. The first ejector unit 781 has an inlet 783, a suction port 784, and an outlet 785. The first ejector unit 781 is provided in the supply path 10. Carbon dioxide and water flowing through the supply path 10 flow into the first ejector unit 781 from the inlet 783 and out from the outlet 785. Carbon dioxide and water become the driving fluid. The water that serves as the driving fluid may be a gas (water vapor) or a liquid. A nozzle for ejecting the driving fluid is provided inside the first ejector unit 781.

[0081] The suction port 784 is connected to the end (second end) of the first return path 52. The first separation fluid F2 flows into the first ejector section 781 from the suction port 784 as a suction fluid.

[0082] The first ejector unit 781 uses carbon dioxide and water flowing in from the inlet 783 as driving fluids to draw in the first separated fluid F2. The first separated fluid F2, along with the driving fluids carbon dioxide and water, flows out of the first ejector unit 781 through the outlet 785.

[0083] The second ejector unit 782 has an inlet 786, a suction port 787, and an outlet 788. The second ejector unit 782 is provided in the supply path 10. The second ejector unit 782 is provided downstream of the first ejector unit 781 in the flow direction of carbon dioxide and water in the supply path 10. Carbon dioxide and water flowing in the supply path 10 flow into the second ejector unit 782 from the inlet 786 and out from the outlet 788. Carbon dioxide and water become the driving fluid. The water that serves as the driving fluid may be a gas (water vapor) or a liquid. A nozzle for ejecting the driving fluid is provided inside the second ejector unit 782. The second ejector unit 782 is a separate unit from the first ejector unit 781.

[0084] The suction port 787 is connected to the end (second end) of the third return path 552. The third separation fluid F5 flows into the second ejector section 782 from the suction port 787 as the suction fluid.

[0085] The second ejector unit 782 uses carbon dioxide, water, and the first separation fluid F2 that flow in from the inlet 786 as driving fluids to draw in the third separation fluid F5. The third separation fluid F5, along with the driving fluids carbon dioxide, water, and the first separation fluid F2, flows out of the second ejector unit 782 through the outlet 788. The carbon dioxide, water, the first separation fluid F2, and the third separation fluid F5 are supplied to the co-electrolytic device 20 through the supply path 10.

[0086] The methane production system 701 is equipped with an ejector 780, which can guide the first separated fluid F2 and the third separated fluid F5 to the supply path 10. Therefore, compared to, for example, a case where only a pump is used to guide the separated fluids F2 and F5 to the supply path 10, energy savings are possible.

[0087] The methane production system 701 includes an ejector 780 comprising a first ejector section 781 for drawing in the first separation fluid F2 and a second ejector section 782 for drawing in the third separation fluid F5. The first ejector section 781 and the second ejector section 782 can have their operating conditions set independently of each other. Therefore, even if conditions such as flow rates differ between the first separation fluid F2 and the third separation fluid F5, the first ejector section 781 and the second ejector section 782 can be operated appropriately.

[0088] The technical scope of this disclosure is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of this disclosure. For example, in Embodiment 6, the methane reactor 530 has two methane reaction units 531 and 532, but the number of methane reaction units is not particularly limited. The number of methane reaction units may be any number of two or more. The methane production system 501 has two circulation paths 50 and 550 because it has two methane reaction units, but the number of circulation paths may be any number of two or more.

[0089] In Embodiment 7, the methane production system 601 draws in the first separation fluid F2 and the third separation fluid F5 using carbon dioxide and water flowing through the supply path 10 as driving fluids, but the driving fluid may be at least one of carbon dioxide and water. In Embodiment 8, the ejector 780 includes two first ejector units 781 and 782, but the number of ejector units may be any number of two or more. [Explanation of Symbols]

[0090] 1,101,201,301,401,501,601,701…Methane production system 10,210,310,410…Supply path 20…Co-electrolytic device (electrolyte) 30,530…Methane reactor 40…First separator 50…First circulation path 51…Outlet path 52…First return path 53…Second return path 70…Cooler 240…Gas-liquid separator 270,370…Heat exchanger 411…First supply path 412…Second supply path 531…First methane reaction section 532…Second methane reaction section 540…Second separator 550…Second circulation path 551…Outlet path 552…Third return path 553…Fourth return path 680,780…Ejector 781...First ejector section 782...Second ejector section F1...Return fluid F2...First separated fluid F3...Second separated fluid F5...Third separated fluid F6...Fourth separated fluid

Claims

1. Supply routes for supplying carbon dioxide and water, An electrolytic apparatus that obtains carbon monoxide and hydrogen from carbon dioxide and water by electrolysis, A methane reactor that obtains a product gas containing methane from a mixed gas containing carbon monoxide and hydrogen by an exothermic reaction, A first separator separates a first separation fluid containing water and a second separation fluid containing hydrogen from a return fluid which is part of the product gas, The first circulation path includes a first return path that leads the first separated fluid to the electrolytic device, and a second return path that leads the second separated fluid to the methane reactor, The return fluid is cooled by heat exchange with the carbon dioxide and water supplied in the supply path, or with the water. Methane production system.

2. A cooler for cooling the second separation fluid is provided in the second return path. The methane production system according to claim 1.

3. The system further includes a heat exchanger that cools the return fluid by heat exchange with the water supplied through the aforementioned supply path, The first separator is a gas-liquid separator. The methane production system according to claim 1.

4. The system further includes a heat exchanger that cools the return fluid by heat exchange with the mixed fluid of carbon dioxide and water supplied through the supply path, The first separator is a gas-liquid separator. The methane production system according to claim 1.

5. The supply path comprises a first supply path for supplying carbon dioxide and a second supply path for supplying water. The system further includes a heat exchanger that cools the return fluid by heat exchange with the carbon dioxide and water supplied by the first and second supply channels, The first separator is a gas-liquid separator. The methane production system according to claim 1.

6. Supply routes for supplying carbon dioxide and water, An electrolytic apparatus that obtains carbon monoxide and hydrogen from carbon dioxide and water by electrolysis, A methane reactor that obtains a product gas containing methane from a mixed gas containing carbon monoxide and hydrogen by an exothermic reaction, A first separator separates a first separation fluid containing water and a second separation fluid containing hydrogen from a return fluid which is part of the product gas, The first circulation path includes a first return path that leads the first separated fluid to the electrolytic device, and a second return path that leads the second separated fluid to the methane reactor, The aforementioned methane reactor is A first methane reaction unit that generates methane from the mixed gas to obtain an intermediate gas, The system comprises a second methane reaction unit that generates methane from the intermediate gas to obtain the product gas, A second separator separates a third separation fluid containing water and a fourth separation fluid containing hydrogen from a portion of the aforementioned intermediate gas, The system further comprises a second circulation path having a third return path for guiding the third separated fluid to the electrolytic device, and a fourth return path for guiding the fourth separated fluid to the first methane reaction section. Methane production system.

7. The supply path is provided with an ejector that draws in the first separated fluid and the third separated fluid using at least one of the carbon dioxide and the water as the driving fluid. The methane production system according to claim 6.

8. The ejector comprises a first ejector section for sucking in the first separated fluid and a second ejector section for sucking in the third separated fluid. The methane production system according to claim 7.

Images