Methane synthesis system

Abstract

To provide a methane synthesis system capable of enhancing methane generation efficiency.SOLUTION: A methane synthesis system comprises: a co-electrolytic part; a methanation reaction part using hydrogen and carbon monoxide acquired from the co-electrolytic part for acquiring a product gas including methane; a separator for separating water from the product gas; a water supply path for supplying water from an external part; a cooling part which has a circulation path in which, a refrigerant whose phase can be varied, is circulated, the cooling part cooling the methanation reaction part; and a collection path for guiding water separated at the separator with water supplied from the water supply path to the cooling part, as the refrigerant. The collection path introduces the refrigerant into the circulation path which is at inside of the cooling part. The cooling part cools the methanation reaction part by evaporation heat following evaporation in the circulation path of at least a part of the refrigerant introduced from the external part by the collection path, and lowers a temperature on an outlet of the methanation reaction part relative to a temperature on an inlet. The refrigerant passed through the cooling part is introduced to the co-electrolytic part as water used for electrolysis.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a methane synthesis system.

Background Art

[0002] Patent Document 1 discloses a production system for producing hydrocarbons using carbon dioxide and water. This production system reduces water and carbon dioxide to obtain a mixed gas containing hydrogen and carbon monoxide. This production system generates hydrocarbons such as methane from the mixed 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 the present disclosure is to provide a methane synthesis system capable of enhancing the production efficiency of methane.

Means for Solving the Problems

[0006] One aspect of the methane synthesis system according to the present disclosure includes a co-electrolysis unit that obtains hydrogen and carbon monoxide by electrolyzing water and carbon dioxide, a methanation reaction unit that obtains 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 the heat of vaporization associated with vaporization of at least a part of the refrigerant in the flow path.

Effects of the Invention

[0007] According to this disclosure, a methane synthesis 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 synthesis system according to Embodiment 1. [Figure 2] This is a schematic diagram of the methane synthesis system according to Embodiment 2. [Figure 3] This is a schematic diagram of the methane synthesis system according to Embodiment 3. [Modes for carrying out the invention]

[0009] 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 synthesis system in Embodiment 1. As shown in Figure 1, the methane synthesis system 1 comprises a supply path 2, a co-electrolysis section 3, a methanation reaction section 4, a cooling section 5, a separator 6, a recovery path 7, a first heat exchanger 8, and an ejector 9.

[0011] Supply path 2 guides water (e.g., water vapor) and carbon dioxide to the co-electrolysis unit 3. Water (e.g., water vapor) is supplied from the cooling unit 5. Carbon dioxide is supplied from the introduction path 11. Supply path 2 guides, for example, a mixed fluid of water and carbon dioxide to the co-electrolysis unit 3.

[0012] The carbon dioxide supplied from the introduction route 11 may be carbon dioxide recovered from the atmosphere by DAC (Direct Air Capture). The carbon dioxide supplied from the introduction route 11 may also be carbon dioxide exhausted from a solid oxide fuel cell (SOFC).

[0013] The co-electrolysis unit 3 includes, for example, a solid oxide electrolytic cell (SOEC) having a cathode electrode and an anode electrode. For example, a solid oxide having oxygen ion conductivity is used for the solid oxide electrolytic cell. Zirconia-based oxides are used as the electrolyte. The co-electrolysis unit 3 is an example of an electrolytic device.

[0014] The co-electrolysis unit 3 supplies water and carbon dioxide supplied from the supply path 2 to the cathode electrode of the solid oxide electrolytic cell. It is preferable that the water used for co-electrolysis in the solid oxide electrolytic cell be water vapor.

[0015] The co-electrolytic unit 3 may be equipped with 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 the solid oxide electrolytic cell can be determined according to the ratio of the components (carbon monoxide, hydrogen) of the desired mixed gas.

[0016] The co-electrolysis unit 3 obtains a mixed gas (mixed fluid) containing hydrogen (H2) and carbon monoxide (CO) from water (H2O) and carbon dioxide (CO2) through co-electrolysis. Co-electrolysis proceeds, for example, according to equation (I) shown below. This reaction is an endothermic reaction. Co-electrolysis is an electrolytic reaction that simultaneously performs the electrolysis of water and the electrolysis of carbon dioxide. 3H2O+CO2→CO+3H2+2O2···(I)

[0017] In the co-electrolysis unit 3, co-electrolysis can be performed using electricity generated from renewable energy sources (e.g., 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, as combustion does not generate additional carbon dioxide.

[0018] The mixed gas obtained in the co-electrolysis unit 3 contains not only hydrogen (H2) and carbon monoxide, but also unreacted water and carbon dioxide. The mixed gas is led to the methanation reaction unit 4 through the derivation path 12.

[0019] The methanation reaction unit 4 obtains a product gas (product fluid) containing water (H2O) and methane (CH4) from hydrogen (H2) and carbon monoxide (CO) by a methanation reaction. The methanation reaction proceeds, for example, according to the following formula (II). This reaction is an exothermic reaction. 3H2 + CO → H2O + CH4 ··· (II)

[0020] The methanation reaction unit 4 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.

[0021] The product gas obtained in the methanation reaction unit 4 may contain not only water and methane, but also unreacted hydrogen (H2), carbon monoxide, carbon dioxide, etc. The product gas is led to the separator 6 through the discharge path 13. The inlet 4a of the methanation reaction unit 4 is the location where the derivation path 12 is connected. The outlet 4b of the methanation reaction unit 4 is the location where the discharge path 13 is connected.

[0022] 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, integrally formed with the methanation reaction unit 4. Heat transfer is possible between the cooling unit 5 and the methanation reaction unit 4.

[0023] The cooling unit 5 cools the methanation reaction unit 4. A flow path 51 through which a refrigerant flows is formed in the cooling unit 5. The flow direction of the refrigerant in the flow path 51 (the direction from the inlet 51a to the outlet 51b) is, for example, opposite to the flow direction in the methanation reaction unit 4 (the direction from the inlet 4a to the outlet 4b).

[0024] The separator 6 separates the product gas into a fluid containing methane and a fluid containing water. The separator 6 employs separation methods such as liquefaction separation, membrane separation, and adsorption separation. The separator 6 may employ one of these separation methods, or a combination of two or more.

[0025] The separator 6, which uses liquefaction separation, separates a specific component by liquefying it, for example, and separating it from other components (gases). Specifically, for example, it liquefies a water-containing component by temperature control and separates it from other components (gases) that contain methane.

[0026] The separator 6, which uses membrane separation, separates specific components from other components by using a separation membrane that allows components with small molecular sizes to pass through. Specifically, for example, it uses a separation membrane that selectively allows water to pass through. This separation membrane separates the water-containing component from the other components, including methane, from the mixed gas.

[0027] The separator 6, which uses adsorption separation, separates components by adsorbing them onto an adsorbent, for example. 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, including methane.

[0028] The separator 6, which uses adsorption separation, has the function of desorbing the adsorbent from the adsorbent. Separator 6 may be equipped with, for example, a heating device. The heating device desorbs the adsorbent from the adsorbent by heating the adsorbent. Separator 6 may also be equipped with a vacuum device such as a vacuum pump. The vacuum device promotes the desorption of the adsorbent from the adsorbent by placing the adsorbent under reduced pressure.

[0029] The methane-containing components are discharged from the separator 6 through the discharge path 14. The methane-containing components are then sent to gas production facilities, for example, as a raw material for city gas.

[0030] The recovery path 7 connects the separator 6 and the cooling unit 5. The water-containing component (water-containing fluid F1) is discharged from the separator 6 through the recovery path 7 and guided to the flow passage 51 of the cooling unit 5. The recovery path 7 is equipped with a pump 71 for sending the fluid F1 to the cooling unit 5. The main component of fluid F1 is water. Fluid F1 is capable of phase changes between liquid and gas. Fluid F1 may contain other components in addition to water.

[0031] A water supply route 15 is connected to the recovery route 7. Water is supplied to the recovery route 7 from an external source via the water supply route 15 as needed.

[0032] The first heat exchanger 8 is located in 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 discharge path 13. Any known heat exchanger can be used 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 as the first heat exchanger 8.

[0033] The fluid F1 flowing through the recovery path 7 is introduced into the flow passage 51 of the cooling unit 5 and circulates through the flow passage 51 as a refrigerant. The methanation reaction unit 4 is cooled by heat exchange with the fluid F1.

[0034] At the inlet 51a of the flow passage 51, at least a portion of the fluid F1 is liquid. As the fluid F1 flows through the flow passage 51 from the inlet 51a to the outlet 51b, at least a portion of it vaporizes. When the fluid F1 vaporizes, the heat of vaporization cools the methane reaction section 4.

[0035] The ejector 9 is located in 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 out from the outlet 9c. The fluid F1 is the driving fluid. Inside the ejector 9, there is a nozzle that ejects the driving fluid. The introduction path 11 is connected to the suction port 9b. Carbon dioxide flows into the ejector 9 as the suction fluid through the introduction path 11 and the suction port 9b.

[0036] Next, an example of a methane synthesis method using methane synthesis system 1 will be described. The methane synthesis method according to this embodiment comprises a supply step, an electrolysis step, a methanation step, a separation step, and a cooling step.

[0037] In the supply process, water (H2O) and carbon dioxide (CO2) are introduced to the co-electrolysis unit 3 via supply path 2. In the electrolysis process, a mixed gas containing hydrogen (H2) and carbon monoxide (CO) is obtained from water and carbon dioxide by co-electrolysis in the co-electrolysis section 3.

[0038] In the methanation process, in the methanation reaction section 4, a product gas containing water and methane is obtained from hydrogen and carbon monoxide through a methanation reaction. The product gas contains not only water and methane, but also unreacted carbon monoxide, hydrogen (H2), carbon dioxide, etc. The product gas is led to the separator 6 through the discharge path 13.

[0039] In the separation process, the separator 6 separates the product gas into a fluid containing methane and a fluid containing water.

[0040] In the cooling process, the water-containing fluid F1 is discharged from the separator 6 and guided to the flow passage 51 of the cooling section 5 via the recovery path 7. As the fluid F1 flows through the flow passage 51 from the inlet 51a to the outlet 51b, at least a portion of it vaporizes. When the fluid F1 vaporizes, the heat of vaporization cools the methane reaction section 4.

[0041] The cooling section 5 forms a temperature distribution having a first region, a second region, and a third region in that order, from the inlet 51a to the outlet 51b of the flow passage 51. The first region is the region where the temperature of the fluid F1 rises. The second region is the region where the temperature of the fluid F1 becomes almost constant as it vaporizes. The third region is the region where the temperature of the vaporized fluid F1 rises again. 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. For example, the temperature of the fluid F1 at the inlet 51a is 200°C to 400°C. For example, the temperature of the fluid F1 at the outlet 51b is 450°C to 650°C.

[0042] The temperature of the methanation reaction section 4 corresponds to the temperature of the cooling section 5. That is, the temperature at outlet 4b is lower than the temperature at inlet 4a. The temperature inside the methanation reaction section 4 at outlet 4b is, for example, 200°C to 400°C. The temperature inside the methanation reaction section 4 at inlet 4a is, for example, 450°C to 650°C.

[0043] The fluid F1, which contains water (water vapor), is introduced into the co-electrolysis unit 3 through the supply path 2, along with the carbon dioxide introduced by the ejector 9.

[0044] In the methane synthesis system 1, the cooling unit 5 cools the methanation reaction unit 4 by the heat of vaporization that occurs when at least a portion of the refrigerant fluid F1 vaporizes 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 remains almost constant while it vaporizes, and a third region where the temperature of the vaporized fluid F1 rises again. In the methanation reaction unit 4, the heat of reaction of the methanation reaction is appropriately removed as heat of vaporization in the second region, thereby optimizing the temperature inside the methanation reaction unit 4. As a result, the methanation reaction proceeds efficiently. Thus, the efficiency of methane production can be increased.

[0045] In the methane synthesis system 1, a fluid F1 containing water is used as a refrigerant, which allows for an appropriate temperature distribution in the methane reaction section 4. Therefore, the methane reaction in the methane reaction section 4 can proceed efficiently.

[0046] The methane synthesis system 1 is equipped with a supply path 2 that guides the fluid F1, which has passed through the cooling section 5, to the co-electrolysis section 3. Therefore, the heat obtained by the fluid F1 in the cooling section 5 can be effectively utilized in the co-electrolysis section 3. As a result, the energy efficiency of the entire system can be improved.

[0047] Because the methane synthesis system 1 is equipped with an ejector 9, it is possible to save energy compared to, for example, a system that uses only a blower to guide carbon dioxide to the supply path 2.

[0048] The methane synthesis system 1 includes a separator 6 that separates a fluid F1 containing water from the product gas of the methanation reaction, and a recovery path 7 that guides the fluid F1 to a cooling section 5. Therefore, it can effectively utilize the water that is a product of the methanation reaction and increase the efficiency of the methane synthesis system.

[0049] Embodiment 2. Next, a methane synthesis system according to Embodiment 2 will be described. Since the basic configuration of the methane synthesis 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.

[0050] Figure 2 is a schematic diagram of the methane synthesis system according to Embodiment 2. As shown in Figure 2, the methane synthesis system 101 differs from the methane synthesis system 1 (see Figure 1) in that it includes an outlet path 16 and a second heat exchanger 17. The second heat exchanger 17 is an example of a "heat exchanger".

[0051] In the co-electrolysis section 3, oxygen (O2) is generated at the anode through the co-electrolysis of water and carbon dioxide as described above. The drainage path 16 drains the fluid F2 containing oxygen (O2) generated in the co-electrolysis section 3.

[0052] The second heat exchanger 17 is located in 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 discharged through the outlet path 16. Any known heat exchanger can be used 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 as the second heat exchanger 17.

[0053] Similar to methane synthesis system 1 (see Figure 1), methane synthesis system 101 can optimize the temperature within the methanation reaction section 4, thereby increasing the efficiency of methane production. In addition, methane synthesis system 101 provides the same effects as methane synthesis system 1 (see Figure 1).

[0054] The methane synthesis system 101 can preheat the fluid F1 using the second heat exchanger 17. Therefore, the heat of the fluid F2 can be effectively utilized, improving the overall energy efficiency of the system.

[0055] Embodiment 3. A methane synthesis system according to Embodiment 3 will now be described. Components identical to those in other embodiments are denoted by the same reference numerals and their descriptions are omitted.

[0056] Figure 3 is a schematic diagram of the methane synthesis system according to Embodiment 3. As shown in Figure 3, the methane synthesis system 201 differs from the methane synthesis system 1 (see Figure 1) in that it includes a methane purifier 202 and a return path 203. The methane purifier 202 is located in the outlet path 14. The outlet path 14 is the path through which the methane-containing component (fluid F3 containing methane) is discharged 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".

[0057] The methane purifier 202 can employ various purification methods, including membrane separation, liquefaction separation, and adsorption separation, but membrane separation is preferred. The methane purifier 202 using membrane separation is equipped with, for example, a separation membrane that selectively permeates methane.

[0058] The return route 203 connects the impermeable outlet of the methane purifier 202 to the discharge route 12. The return route 203 returns the impermeable fluid F5 that has not permeated the separation membrane of the methane purifier 202 to the methanation reaction unit 4 via the discharge route 12. Alternatively, the return route 203 may be a route connecting the impermeable outlet of the methane purifier 202 to the methanation reaction unit 4.

[0059] In the methane synthesis system 201, the fluid F3 discharged from the separator 6 via the discharge path 14 is led to the methane purifier 202. The permeate fluid F4, whose methane concentration has been increased in the methane purifier 202, is discharged from the system as purified gas (purified fluid). The process of purifying the methane contained in the fluid F3 using the methane purifier 202 is called the "purification process".

[0060] The fluid F5 that has not permeated the separation membrane of the methane purifier 202 is returned to the outlet path 12 via the return path 203. The fluid F5 is then introduced into the methanation reaction section 4 from the outlet path 12. This promotes the methanation of unreacted substances (e.g., hydrogen, carbon monoxide) contained in the fluid F5. Thus, the efficiency of methane production in the methanation reaction section 4 can be increased. The impermeable fluid F5 is the residual gas (residual fluid) obtained by separating the permeable fluid F4 from the fluid F3.

[0061] Similar to methane synthesis system 1 (see Figure 1), methane synthesis system 201 can optimize the temperature within the methanation reaction section 4, thereby increasing the efficiency of methane production. In addition, methane synthesis system 201 provides the same effects as methane synthesis system 1 (see Figure 1).

[0062] The methane synthesis system 201 is equipped with a methane purifier 202, which allows it to obtain a fluid F4 (purified gas) with a high methane concentration. Since the methane synthesis system 201 has a return path 203, the impermeable fluid F5 (residual gas) can be returned to the methane reaction section 4. Therefore, the efficiency of methane production in the methane reaction section 4 can be increased.

[0063] 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 1, a co-electrolytic unit 3 using a solid oxide electrolytic cell (SOEC) was illustrated, but other methods may be adopted for the co-electrolytic unit. The co-electrolytic unit may be, for example, a solid polymer type co-electrolytic unit.

[0064] In Embodiment 1, a co-electrolytic unit 3 is used to obtain hydrogen and carbon monoxide from water and carbon dioxide by co-electrolysis. However, the apparatus for obtaining hydrogen (H2) and carbon monoxide is not limited to a co-electrolytic unit. For example, an electrolytic apparatus can be used that independently performs the steps of obtaining carbon monoxide by electrolyzing carbon dioxide and obtaining hydrogen (H2) by electrolyzing water. [Explanation of Symbols]

[0065] 1,101,201…Methane synthesis system 2…Supply route 3…Co-electrolysis unit 4…Methanation reaction unit 4a…Inlet 4b…Outlet 5…Cooling unit 6…Separator 7…Recovery route 9…Ejector 17…Second heat exchanger (heat exchanger) 202…Methane purifier (methane purification unit) 203…Return route

Claims

1. A co-electrolytic unit that obtains hydrogen and carbon monoxide from water and carbon dioxide by electrolysis, A methanation reaction unit that obtains a methane-containing product gas by a methanation reaction using the hydrogen obtained from the co-electrolysis unit and the carbon monoxide, A separator for separating water from the aforementioned product gas, A water supply route that supplies water from the outside, A cooling section having a flow passage through which a phase-changeable refrigerant flows, and which cools the methane reaction section, A recovery path connected to the water supply path, which guides the water separated by the separator together with the water supplied from the water supply path to the cooling section as the refrigerant, Equipped with, The recovery path introduces the refrigerant into the flow passage located inside the cooling unit. The cooling unit is thermally connected to the methanation reaction unit, and cools the methanation reaction unit by the heat of vaporization that occurs when at least a portion of the refrigerant introduced from the outside by the recovery path vaporizes in the flow passage, thereby lowering the temperature at the outlet of the methanation reaction unit to a lower temperature at the inlet. The refrigerant that has passed through the cooling section is led to the co-electrolytic section as water used for electrolysis. Methane synthesis system.

2. The system includes a supply path that guides the refrigerant, which has passed through the cooling section, to the co-electrolysis section as water. The methane synthesis system according to claim 1.

3. The supply path is provided with an ejector that uses the water as the driving fluid to draw in the carbon dioxide. The methane synthesis system according to claim 2.

4. A pump is provided in the recovery path to send the water to the cooling section. The methane synthesis system according to claim 1.

5. The recovery path is provided with a heat exchanger that heats the water by heat exchange with oxygen produced by the co-electrolysis of the water and carbon dioxide in the co-electrolysis section. The methane synthesis system according to claim 4.

6. The separator separates the fluid containing the methane from the product gas. The system further comprises a methane purification unit that purifies the methane contained in the methane-containing fluid to obtain a purified gas. A methane synthesis system according to any one of claims 1 to 4.

7. The system further includes a return path for returning the residual gas obtained by separating the purified gas from the fluid containing methane back to the methanation reaction unit. The methane synthesis system according to claim 6.

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