Methane synthesis system

Abstract

This methane synthesis system is provided with: a co-electrolysis unit for obtaining hydrogen and carbon monoxide from water and carbon dioxide by electrolysis; a methanation reaction unit for obtaining a product gas containing methane by a methanation reaction using the hydrogen and the carbon monoxide; and a cooling unit having a flow path through which a phase-changeable refrigerant flows. The cooling unit cools the methanation reaction unit by heat of gasification accompanying gasification of at least a portion of the refrigerant in the flow path.

Description

Technical Field

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

[0002] Patent Document 1 discloses a production system for producing hydrocarbons using carbon dioxide and water. The production system reduces water and carbon dioxide to obtain a mixed gas containing hydrogen and carbon monoxide. The production system generates hydrocarbons such as methane from the mixed gas.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2021 / 201192 Summary of the invention

[0006] Problems to be solved by the invention

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

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

[0009] Solutions to Solve Problems

[0010] One embodiment of the methane synthesis system disclosed herein comprises: a co-electrolysis unit for obtaining hydrogen and carbon monoxide from water and carbon dioxide by electrolysis; a methanation reaction unit for obtaining a product gas containing methane by a methanation reaction using the hydrogen and the carbon monoxide; and a cooling unit having a flow passage through which a phase-changeable refrigerant flows. The cooling unit cools the methanation reaction unit by using the heat of vaporization accompanying the vaporization of at least a portion of the refrigerant in the flow passage.

[0011] Effects of the Invention

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

[0013] Figure 1 This is a schematic diagram of a methane synthesis system according to Embodiment 1.

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

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

[0016] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In addition, the scope of the present disclosure is not limited to the following embodiments, and can be arbitrarily changed within the scope of the technical concept of the present disclosure.

[0017] Implementation Method 1

[0018] Figure 1 This is a schematic diagram showing a methane synthesis system in Embodiment 1.

[0019] like Figure 1 As shown, the methane synthesis system 1 includes a supply path 2 , a co-electrolysis unit 3 , a methanation reaction unit 4 , a cooling unit 5 , a separator 6 , a recovery path 7 , a first heat exchanger 8 , and an ejector 9 .

[0020] The supply path 2 introduces water (for example, water vapor) and carbon dioxide into the co-electrolysis section 3. Water (for example, water vapor) is supplied from the cooling section 5. Carbon dioxide is supplied from the introduction path 11. The supply path 2 introduces a mixed fluid of water and carbon dioxide into the co-electrolysis section 3, for example.

[0021] The carbon dioxide supplied from the introduction path 11 may be carbon dioxide collected from the atmosphere by DAC (Direct Air Capture) or carbon dioxide exhausted from a solid oxide fuel cell (SOFC).

[0022] The co-electrolysis unit 3 includes, for example, a solid oxide electrolysis cell (SOEC) having a cathode electrode and an anode electrode. The solid oxide electrolysis cell may use, for example, a solid oxide having oxygen ion conductivity. As an electrolyte, a zirconium oxide-based oxide or the like may be used. The co-electrolysis unit 3 is an example of an electrolysis device.

[0023] The co-electrolysis unit 3 supplies the water and carbon dioxide supplied from the supply path 2 to the cathode electrode of the solid oxide electrolysis cell. The water used for the co-electrolysis in the solid oxide electrolysis cell is preferably water vapor.

[0024] The co-electrolysis unit 3 may also be provided with a heating device for heating the solid oxide electrolysis cell. The heating device can adjust the temperature in the solid oxide electrolysis cell to a temperature suitable for the co-electrolysis reaction. The ratio of carbon dioxide and water supplied to the solid oxide electrolysis cell can be determined according to the ratio of the components (carbon monoxide and hydrogen) of the target mixed gas.

[0025] The co-electrolysis section 3 obtains a mixed gas (mixed fluid) containing hydrogen (H2) and carbon monoxide (CO) by co-electrolysis of water (H2O) and carbon dioxide (CO2). The co-electrolysis is performed, for example, according to the formula (I) shown below. This reaction is an endothermic reaction. The co-electrolysis is an electrolysis reaction in which the electrolysis of water and the electrolysis of carbon dioxide are performed simultaneously.

[0026] 3H2O+CO2→CO+3H2+2O2…(I)

[0027] In the co-electrolysis section 3, for example, electricity generated by renewable energy (such as solar power generation, wind power generation, etc.) can be used for co-electrolysis. Methane obtained by using renewable energy does not produce additional carbon dioxide even if used for combustion, so it can be considered as a carbon-neutral fuel that does not affect global warming.

[0028] The mixed gas obtained in the co-electrolysis section 3 contains not only hydrogen (H 2 ) and carbon monoxide but also unreacted water and carbon dioxide. The mixed gas is introduced into the methanogenic reaction section 4 through the outlet path 12 .

[0029] The methanation reaction unit 4 obtains a product gas (product fluid) containing water (H2O) and methane (CH4) by a methanation reaction of hydrogen (H2) and carbon monoxide (CO). The methanation reaction is carried out, for example, according to the formula (II) shown below. This reaction is an exothermic reaction.

[0030] 3H2+CO→H2O+CH4···(II)

[0031] The methanation reaction unit 4 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.

[0032] The product gas obtained in the methanation reaction unit 4 may contain not only water and methane but also unreacted hydrogen (H 2 ), carbon monoxide, carbon dioxide, etc. The product gas is introduced into the separator 6 through the discharge path 13 .

[0033] The inlet 4a of the methanation reaction unit 4 is a portion connected to the outlet path 12. The outlet 4b of the methanation reaction unit 4 is a portion connected to the discharge path 13.

[0034] The cooling unit 5 is thermally connected to the methanation reaction unit 4. The cooling unit 5 is, for example, in contact with the methanation reaction unit 4. The cooling unit 5 is, for example, formed integrally with the methanation reaction unit 4. Heat transfer can be achieved between the cooling unit 5 and the methanation reaction unit 4.

[0035] The cooling unit 5 cools the methanation reaction unit 4. A flow passage 51 through which the refrigerant flows is formed in the cooling unit 5. The flow direction of the refrigerant in the flow passage 51 (direction from the inlet 51a toward the outlet 51b) is, for example, opposite to the flow direction in the methanation reaction unit 4 (direction from the inlet 4a toward the outlet 4b).

[0036] The separator 6 separates a fluid containing methane and a fluid containing water from the product gas.

[0037] The separator 6 adopts a separation method such as liquefaction separation, membrane separation, adsorption separation, etc. The separator 6 may adopt one of these separation methods or a combination of two or more.

[0038] The separator 6 using liquefaction separation liquefies a specific component and separates it from other components (gases), for example. Specifically, for example, a component including water is liquefied by temperature adjustment and separated from other components (gases) including methane.

[0039] The separator 6 using membrane separation uses, for example, a separation membrane through which components with small molecular sizes can pass, to separate specific components from other components. Specifically, for example, a separation membrane that selectively allows water to pass is used. The separation membrane separates components including water and other components including methane from the mixed gas.

[0040] The separator 6 using adsorption separation, for example, separates a specific component by adsorbing it on an adsorbent. Examples of the adsorbent include silica gel, zeolite, activated carbon, etc. Specifically, by adsorbing a component including water on the adsorbent, the component can be separated from other components including methane.

[0041] The separator 6 using adsorption separation has the function of separating the adsorbate from the adsorbent. The separator 6 includes, for example, a heating device. The heating device separates the adsorbate from the adsorbent by heating the adsorbent. The separator 6 may also be provided with a decompression device such as a decompression pump. The decompression device promotes the separation of the adsorbate from the adsorbent by placing the adsorbent in a decompressed state.

[0042] The component containing methane is discharged from the separator 6 through the discharge path 14. The component containing methane is sent to a gas production facility or the like as a raw material of city gas or the like, for example.

[0043] The recovery path 7 connects the separator 6 and the cooling unit 5. The component containing water (fluid F1 containing water) is led out from the separator 6 through the recovery path 7 and introduced into the flow path 51 of the cooling unit 5. A pump 71 for conveying the fluid F1 to the cooling unit 5 is provided on the recovery path 7. The main component of the fluid F1 is water. The fluid F1 can undergo a phase change between liquid and gas. The fluid F1 contains not only water but also other components.

[0044] The water supply path 15 is connected to the recovery path 7. The recovery path 7 is supplied with water from the outside through the water supply path 15 as needed.

[0045] The first heat exchanger 8 is provided on the recovery path 7. The first heat exchanger 8 preheats the fluid F1 flowing through the recovery path 7 by exchanging heat with the product gas flowing through the exhaust path 13.

[0046] A known heat exchanger can be used as the first heat exchanger 8. As the first heat exchanger 8, for example, a multi-tube heat exchanger, a plate heat exchanger, a coil heat exchanger, a double-tube heat exchanger, a spiral heat exchanger, etc. can be used.

[0047] The fluid F1 flowing through the recovery path 7 is introduced into the flow path 51 of the cooling unit 5, and flows as a refrigerant in the flow path 51. The methanation reaction unit 4 is cooled by heat exchange with the fluid F1.

[0048] At least a portion of the fluid F1 is liquid at the inlet 51a of the flow passage 51. At least a portion of the fluid F1 vaporizes while flowing from the inlet 51a toward the outlet 51b through the flow passage 51. When the fluid F1 vaporizes, it cools the methanation reaction unit 4 by the heat of vaporization.

[0049] The ejector 9 is provided on the supply path 2. The ejector 9 has an inlet 9a, a suction port 9b and an outlet 9c. The fluid F1 flowing through the supply path 2 flows into the ejector 9 from the inlet 9a and flows out from the outlet 9c. The fluid F1 becomes a driving fluid. A nozzle for ejecting the driving fluid is provided inside the ejector 9. The suction port 9b is connected to an introduction path 11. Carbon dioxide flows into the ejector 9 from the suction port 9b as a suction fluid through the introduction path 11.

[0050] Next, an example of a methane synthesis method using the methane synthesis system 1 will be described.

[0051] The methane synthesis method of the present embodiment includes a supply step, an electrolysis step, a methanation step, a separation step, and a cooling step.

[0052] In the supply step, water (H 2 O) and carbon dioxide (CO 2 ) are introduced into the co-electrolysis section 3 through the supply path 2 .

[0053] In the electrolysis step, in the co-electrolysis section 3, water and carbon dioxide are co-electrolyzed to obtain a mixed gas containing hydrogen (H 2 ) and carbon monoxide (CO).

[0054] In the methanation step, a product gas containing water and methane is obtained by methanation reaction of hydrogen and carbon monoxide in the methanation reaction unit 4. The product gas contains not only water and methane but also unreacted carbon monoxide, hydrogen (H2), carbon dioxide, etc. The product gas is introduced into the separator 6 through the discharge path 13.

[0055] In the separation step, in the separator 6, a fluid comprising methane and a fluid comprising water are separated from the product gas.

[0056] In the cooling step, the fluid F1 containing water is drawn out from the separator 6 and introduced into the flow path 51 of the cooling unit 5 through the recovery path 7. The fluid F1, as a refrigerant, at least partially vaporizes while flowing from the inlet 51a toward the outlet 51b through the flow path 51. When the fluid F1 vaporizes, it cools the methanogenic reaction unit 4 by the heat of vaporization.

[0057] The cooling unit 5 forms a temperature distribution having a first region, a second region, and a third region in sequence from the inlet 51a toward the outlet 51b of the flow passage 51. The first region is a region where the temperature of the fluid F1 rises. The second region is a region where the temperature of the fluid F1 becomes substantially constant while being vaporized. The third region is a region where the temperature of the vaporized fluid F1 rises again.

[0058] The temperature of the fluid F1 at the inlet 51a of the flow passage 51 is lower than the temperature of the fluid F1 at the outlet 51b. The temperature of the fluid F1 at the inlet 51a is, for example, 200°C to 400°C. The temperature of the fluid F1 at the outlet 51b is, for example, 450°C to 650°C.

[0059] The temperature of the methanation reaction unit 4 is set to a temperature corresponding to the temperature of the cooling unit 5. That is, the temperature at the outlet 4b is lower than the temperature at the inlet 4a. The temperature in the methanation reaction unit 4 at the outlet 4b is, for example, 200°C to 400°C. The temperature in the methanation reaction unit 4 at the inlet 4a is, for example, 450°C to 650°C.

[0060] The fluid F1 containing water (water vapor) is introduced into the co-electrolysis unit 3 through the supply path 2 together with the carbon dioxide introduced by the ejector 9 .

[0061] In the methane synthesis system 1, the cooling unit 5 cools the methanogenic reaction unit 4 by using the heat of vaporization that accompanies the vaporization of at least a portion of the fluid F1 as a refrigerant in the flow passage 51. For example, the cooling unit 5 has a first region where the temperature of the fluid F1 rises, a second region where the temperature of the fluid F1 becomes substantially constant while being vaporized, and a third region where the temperature of the vaporized fluid F1 rises again. In the methanogenic reaction unit 4, the heat of reaction of the methanogenic reaction is appropriately taken away as heat of vaporization in the second region, thereby making it possible to adjust the temperature in the methanogenic reaction unit 4. Therefore, the methanogenic reaction is efficiently performed. Therefore, the efficiency of methane generation can be improved.

[0062] In the methane synthesis system 1, since the fluid F1 containing water is used as a refrigerant, an appropriate temperature distribution can be given to the methanation reaction unit 4. Therefore, the methanation reaction in the methanation reaction unit 4 can be efficiently performed.

[0063] Since the methane synthesis system 1 includes the supply path 2 for introducing the fluid F1 passing through the cooling unit 5 to the co-electrolysis unit 3, the heat obtained by the fluid F1 in the cooling unit 5 can be effectively used in the co-electrolysis unit 3. This can improve the energy efficiency of the entire system.

[0064] Since the methane synthesis system 1 includes the ejector 9 , energy saving can be achieved compared with the case where carbon dioxide is introduced into the supply path 2 using only a blower, for example.

[0065] Since the methane synthesis system 1 includes the separator 6 for separating the fluid F1 containing water from the product gas of the methanation reaction and the recovery path 7 for introducing the fluid F1 into the cooling unit 5, the water as the product of the methanation reaction can be effectively utilized, thereby improving the efficiency of the methane synthesis system.

[0066] Implementation Method 2

[0067] Next, a methane synthesis system according to Embodiment 2 will be described. The basic structure of the methane synthesis system according to this embodiment is the same as that of Embodiment 1, so the differences from Embodiment 1 will be mainly described. The same structures as those in other embodiments are denoted by the same reference numerals and description thereof will be omitted.

[0068] Figure 2 This is a schematic diagram of a methane synthesis system according to Embodiment 2.

[0069] like Figure 2 As shown, the methane synthesis system 101 is similar to the methane synthesis system 1 (see Figure 1 The second heat exchanger 17 is an example of a “heat exchanger”.

[0070] In the co-electrolysis section 3, oxygen (O2) is generated at the anode by co-electrolysis of the above-mentioned water and carbon dioxide.

[0071] The outlet path 16 outlets the fluid F2 including the oxygen (O 2 ) generated in the co-electrolysis section 3 .

[0072] The second heat exchanger 17 is provided on the recovery path 7 . The second heat exchanger 17 heats the fluid F1 flowing through the recovery path 7 by exchanging heat with the fluid F2 led out from the lead-out path 16 .

[0073] A known heat exchanger can be used as the second heat exchanger 17. As the second heat exchanger 17, for example, a multi-tube heat exchanger, a plate heat exchanger, a coil heat exchanger, a double-tube heat exchanger, a spiral heat exchanger, etc. can be used.

[0074] Methane synthesis system 101 and methane synthesis system 1 (refer to Figure 1 ) Similarly, the temperature in the methanogenic reaction unit 4 can be optimized, thereby improving the methane generation efficiency. In addition, the methane synthesis system 101 also plays a role similar to the methane synthesis system 1 (see Figure 1 )Same effect.

[0075] The methane synthesis system 101 can preheat the fluid F1 by the second heat exchanger 17. Therefore, the heat of the fluid F2 can be effectively utilized, and the energy efficiency of the entire system can be improved.

[0076] Implementation 3

[0077] A methane synthesis system according to Embodiment 3 will be described. The same components as those in other embodiments are denoted by the same reference numerals and description thereof will be omitted.

[0078] Figure 3 This is a schematic diagram of a methane synthesis system according to Embodiment 3.

[0079] like Figure 3 As shown, the methane synthesis system 201 is similar to the methane synthesis system 1 (see Figure 1 ) is different. The methane purifier 202 is provided on the derivation path 14. The derivation path 14 is a path for derivation of the component containing methane (fluid F3 containing methane) from the separator 6. The methane purifier 202 purifies the methane contained in the fluid F3 to obtain a fluid F4 with a high methane concentration. The methane purifier 202 is an example of a "methane purification unit".

[0080] The methane purifier 202 may be purified by membrane separation, liquefaction separation, adsorption separation, etc., but membrane separation is preferred. The methane purifier 202 using membrane separation includes, for example, a separation membrane that selectively permeates methane.

[0081] The return path 203 connects the outlet on the non-permeation side of the methane purifier 202 and the outlet path 12. The return path 203 returns the non-permeation side fluid F5 that has not permeated the separation membrane of the methane purifier 202 to the methanation reaction unit 4 via the outlet path 12. Alternatively, the return path 203 may be a path connecting the outlet on the non-permeation side of the methane purifier 202 and the methanation reaction unit 4.

[0082] In the methane synthesis system 201, the fluid F3 discharged from the separator 6 through the discharge path 14 is introduced into the methane purifier 202. The fluid F4 on the permeate side in which the methane concentration is increased in the methane purifier 202 is discharged to the outside of the system as a purified gas (purified fluid). The process of purifying the methane contained in the fluid F3 using the methane purifier 202 is called a "purification process".

[0083] The fluid F5 on the non-permeable side of the separation membrane of the methane purifier 202 is returned to the outlet path 12 through the return path 203. The fluid F5 is introduced from the outlet path 12 to the methanation reaction unit 4. Therefore, the methanation of the unreacted substances (such as hydrogen and carbon monoxide) contained in the fluid F5 can be promoted. Therefore, the methane generation efficiency in the methanation reaction unit 4 can be improved.

[0084] The non-permeated side fluid F5 is a remainder gas (residue fluid) obtained by separating the permeated side fluid F4 from the fluid F3.

[0085] Methane synthesis system 201 and methane synthesis system 1 (refer to Figure 1 ) Similarly, the temperature in the methanogenic reaction unit 4 can be appropriately adjusted, thereby improving the methane generation efficiency. In addition, the methane synthesis system 201 also plays a role similar to the methane synthesis system 1 (see Figure 1 )Same effect.

[0086] Since the methane synthesis system 201 includes the methane purifier 202, it is possible to obtain the fluid F4 (purified gas) having a high methane concentration.

[0087] Since the methane synthesis system 201 has the return path 203, the fluid F5 (residue gas) on the non-permeated side can be returned to the methanation reaction unit 4. Therefore, the methane production efficiency in the methanation reaction unit 4 can be improved.

[0088] In addition, the technical scope of the present disclosure is not limited to the above-mentioned embodiment, and various changes can be added without departing from the gist of the present disclosure.

[0089] For example, in the first embodiment, the co-electrolysis section 3 using a solid oxide electrolytic cell (SOEC) is exemplified, but the co-electrolysis section may adopt other forms. The co-electrolysis section may be, for example, a solid polymer type co-electrolysis section.

[0090] In the first embodiment, a co-electrolysis unit 3 is used to obtain hydrogen and carbon monoxide from water and carbon dioxide by co-electrolysis, but the device for obtaining hydrogen (H2) and carbon monoxide is not limited to the co-electrolysis unit. 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.

[0091] Description of Reference Numerals

[0092] 1, 101, 201...methane synthesis system 2...supply path 3...co-electrolysis unit 4...methanation reaction unit 4a...inlet 4b...outlet 5...cooling unit 6...separator 7...recovery path 9...ejector 17...second heat exchanger (heat exchanger) 202...methane purifier (methane purification unit) 203...return path.

Claims

1. A methane synthesis system, characterized in that: The methane synthesis system comprises: A co-electrolysis unit for obtaining hydrogen and carbon monoxide from water and carbon dioxide by electrolysis; a methanation reaction section for obtaining a product gas containing methane by a methanation reaction using the hydrogen and the carbon monoxide; and The cooling unit has a flow path for a phase-changeable refrigerant to flow through. The cooling unit cools the methanation reaction unit by using heat of vaporization associated with vaporization of at least a portion of the refrigerant in the flow passage, so that a temperature at an outlet of the methanation reaction unit is lower than a temperature at an inlet.

2. The methane synthesis system according to claim 1, characterized in that: The refrigerant is a fluid containing water.

3. The methane synthesis system according to claim 2, characterized in that: The methane synthesis system includes a supply path that introduces the refrigerant that has passed through the cooling unit into the co-electrolysis unit as the water.

4. The methane synthesis system according to claim 3, characterized in that: The supply path is provided with an ejector that uses the water as a driving fluid and sucks the carbon dioxide.

5. The methane synthesis system according to any one of claims 2 to 4, characterized in that: The methane synthesis system comprises: a separator to separate water from the product gas; and The recovery path introduces the water separated by the separator into the cooling unit as the refrigerant.

6. The methane synthesis system according to claim 5, characterized in that: The recovery path is provided with a heat exchanger for heating the water by exchanging heat with oxygen generated by co-electrolysis of the water and the carbon dioxide in the co-electrolysis section.

7. The methane synthesis system according to any one of claims 1 to 4, characterized in that: The methane synthesis system also has: a separator for separating a fluid containing the methane from the product gas; and The methane purification unit purifies the methane contained in the fluid containing the methane to obtain a purified gas.

8. The methane synthesis system according to claim 7, characterized in that: The methane synthesis system further includes a return path for returning a residue gas obtained by separating the purified product gas from the fluid containing the methane to the methanation reaction unit.

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