METHANE SYNTHESIS SYSTEM

Abstract

A methane synthesis system according to the present invention comprises: a supply path for supplying carbon dioxide and water, a carbon dioxide consumption reaction part configured to obtain a product by using at least the carbon dioxide and the water, a methane production reaction part configured to be thermally connected to the carbon dioxide consumption reaction part and to produce methane from a reacted material and hydrogen, and a first heat recovery part configured to recover heat by heat exchange with the carbon dioxide consumption reaction part.

Description

Technical FieldThe present invention relates to a system for methane synthesis.Background ArtPatent Document 1 discloses an apparatus for methane production that produces methane using hydrogen carbonate and hydrogen.List of ReferencesPatent DocumentsPatent Document 1: Japanese Unexamined Patent Application, First Publication JP 2021-17 409 ASUMMARY OF THE INVENTIONProblem to be Solved by the InventionIn the above technique, there is a possibility that the energy efficiency of the entire apparatus is lowered.In view of the foregoing circumstances, the object of the present invention is to provide a system for methane synthesis capable of improving energy efficiency.Means for Solving the ProblemAccording to an aspect of the present invention, a system for methane synthesis includes a supply path for supplying carbon dioxide and water, a carbon dioxide consumption reaction part configured to obtain a product by using at least the carbon dioxide and the water, a methane generation reaction part configured to be thermally connected to the carbon dioxide consumption reaction part and generate methane from a reacted material and hydrogen, and a first heat recovery part configured to recover heat by heat exchange with the carbon dioxide consumption reaction part.Effects of the InventionAccording to the present invention, it is possible to provide a system for methane synthesis that can improve energy efficiency.Brief Description of the DrawingsFIG. 1 is a schematic view of a system for methane synthesis according to an embodiment.DESCRIPTION OF THE EMBODIMENTSHereinafter, an embodiment of the present invention will be described with reference to the drawings. The scope of the present invention is not limited to the following embodiment, and may be changed in any manner within the technical ideas of the present invention.FIG. 1 is a schematic view showing a system for methane synthesis in the embodiment.As illustrated in FIG. 1, a methane synthesis system 1 includes a raw material supply path 2, a carbon dioxide consumption reaction part 3, a methane generation reaction part 4, a first heat recovery part 5, a hydrogen production part 6, a separator 7, a second heat recovery part 8, an ejector 9, an exhaust path 11, a water recovery path 12, a hydrogen supply path 13, a circulation path 14, a recirculation path 15, and a water supply path 16.The raw material supply path 2 supplies water (e.g., water vapor) and carbon dioxide to the carbon dioxide consumption reaction part 3. carbon dioxide is supplied via an introduction path 21. The raw material supply path 2 supplies, for example, a mixed fluid of water and carbon dioxide to the carbon dioxide consumption reaction part 3.The carbon dioxide supplied via the introduction path 21 may be carbon dioxide that has been recovered from the atmosphere by direct air capture (DAC). The carbon dioxide supplied via the introduction path 21 may be carbon dioxide derived from a solid oxide fuel cell (SOFC). The carbon dioxide supplied via the introduction path 21 may be carbon dioxide derived from a gas water heater, a boiler, or the like.The carbon dioxide consumption reaction part 3 contains carbonate in a reactor, for example. In the carbon dioxide consumption reaction part 3, hydrogen carbonate is produced as a product by the reaction between water and carbon dioxide from the raw material supply path 2 and carbonate. This reaction is a reaction that consumes carbon dioxide. This reaction proceeds, for example, according to formula (I) shown below. This reaction is an exothermic reaction. K 2 CO 3+ CO 2+ H 2 O→2KHCO 3( I)The carbonate is not limited to potassium carbonate, and may also be sodium carbonate, lithium carbonate, ammonium carbonate, or the like. The hydrogen carbonate is not limited to potassium hydrogen carbonate, and may also be sodium hydrogen carbonate, lithium hydrogen carbonate, ammonium hydrogen carbonate, or the like.The carbon dioxide consumption reaction part 3 is thermally connected to the methane production reaction part 4. Therefore, the carbon dioxide consumption reaction part 3 can adjust the temperature by heat exchange with the methane production reaction part 4. Accordingly, the temperature in the carbon dioxide consumption reaction part 3 can be adjusted to a temperature suitable for the reaction shown in formula (I).The hydrogen carbonate (KHCO 3) produced as a product is mainly in a solid state and is held in the reactor of the carbon dioxide consumption reaction part 3. In the carbon dioxide consumption reaction part 3, a fluid F2 (non-reactant fluid, e.g., non-reactant gas) containing a non-reactant such as water (e.g., water vapor) is formed.Formula (I) is the reaction of absorbing carbon dioxide. The carbon dioxide consumption reaction part is also referred to as a "carbon dioxide absorption reaction part".The methane production reaction part 4 contains, for example, the hydrogen carbonate in the reactor. In the methane generation reaction part 4, carbonate, methane and water are generated by the reaction between hydrogen (H 2) from the hydrogen supply path 13 and the hydrogen carbonate (reacted material). This reaction is a methane production reaction. The methane production reaction proceeds according to, for example, formula (II) shown below. This reaction is an endothermic reaction. 2KHCO 3+4 H 2 →K 2 CO 3+ CH 4+3 H 2 O (II)The hydrogen carbonate is not limited to potassium hydrogen carbonate, and may also be sodium hydrogen carbonate, lithium hydrogen carbonate, ammonium hydrogen carbonate, or the like. The carbonate is not limited to potassium carbonate, and may also be sodium carbonate, lithium carbonate, ammonium carbonate, or the like.In the methane generation reaction part 4, a reactant fluid F 3 (e.g., a reactant gas) containing methane and water is formed. Carbonate (K 2 CO 3) is mainly a solid and is held in the reactor of the methane production reaction part 4.The methane generating reaction part 4 is thermally connected to the carbon dioxide consumption reaction part 3. Therefore, the methane generation reaction part 4 can provide thermal energy by heat exchange with the carbon dioxide consumption reaction part 3. Accordingly, the temperature in the methane generation reaction part 4 can be adjusted to a temperature suitable for the methane formation reaction.The carbon dioxide consumption reaction part 3 and the methane production reaction part 4 preferably have the same shape.The first heat recovery part 5 recovers the heat of the carbon dioxide consumption reaction part 3 by heat exchange with the carbon dioxide consumption reaction part 3. Specifically, the first heat recovery part 5 heats a heat medium fluid by heat exchange with the carbon dioxide consumption reaction part 3. The water as the heat medium fluid is supplied from, for example, the water recovery path 12.As the first heat recovery part 5, a known heat exchanger can be used. As the heat exchanger, for example, a multi-tube heat exchanger, a plate heat exchanger, a coil type heat exchanger, a double-tube heat exchanger, a spiral heat exchanger, or the like can be used.The first heat recovery part 5 may be configured to recover the heat of the methane generation reaction part 4 by heat exchange with the methane generation reaction part 4.The carbon dioxide consumption reaction part 3 and the methane production reaction part 4 form a composite reaction part 100. The assembled reaction part 100 includes a first reaction part 101 and a second reaction part 102. In the example shown in FIG. 1, the first reaction part 101 (left part in FIG. 1 ) is the carbon dioxide consumption reaction part 3. the second reaction part 102 (right part in FIG. 1 ) is the methane generation reaction part 4.The reactant fluid F 3 (reactant gas) containing methane and water obtained in the methane generation reaction part 4 is supplied to the separator 7 via the discharge path 11. The separator 7 separates the methane-containing fluid F 4 and the water-containing fluid F 1 from the reactant fluid F 3.The separator 7 uses, for example, a separation method such as liquefaction separation, membrane separation, or adsorption separation. In the separator 7, one of these separation methods may be used, or two or more of these separation methods may be combined.The separator 7 using liquefaction separation liquifies a specific component and separates the specific component from, for example, other components (gases). Specifically, for example, a water-containing component is liquefied by temperature adjustment and separated from other methane-containing components (gases).The separator 7 using membrane separation separates a specific component from other components, for example, by a separation membrane through which a small-molecule component can pass. Specifically, for example, a separation membrane that selectively allows water to pass therethrough is used. This separation membrane separates a water-containing component and other methane-containing components from a mixed gas.For example, the separator 7 using adsorption separation separates a specific component by adsorbing the specific component to an adsorbent. Examples of the adsorbent include silica gel, zeolite and activated carbon. By adsorbing a water-containing component to an adsorbent, this component can be separated from other methane-containing components.The separator 7 using adsorption separation has a function of desorption of an adsorbed substance from the adsorbent. The separator 7 includes, for example, a heater. The heater heats the adsorbent to desorb the adsorbed substance from the adsorbent. In the separator 7, a pressure reducing device, for example, a pressure reducing pump is provided. The pressure reducing device is configured to promote desorption of the adsorbed substance from the adsorbent by exposing the adsorbent to a reduced pressure.The methane-containing component (fluid F4) is discharged from the separator 7 via the discharge path 22. The methane-containing component is passed on to a gas production plant, for example, as raw material, such as city gas.The water recovery path 12 connects the separator 7 and the first heat recovery part 5. A pump 121 for delivering the fluid F 1 to the first heat recovery part 5 is provided in the water recovery path 12. The main component of the fluid F1 is water. The fluid F1 serves as a heat medium fluid for recovering the heat of the carbon dioxide consumption reaction part 3.The water supply path 23 is connected to the water recovery path 12. Water is supplied to the water recovery path 12 from the outside as needed via the water supply path 23.The second heat recovery part 8 is provided in the discharge path 11. The second heat recovery part 8 recovers the heat of the reactant fluid F 3 that is guided to the separator 7 via the discharge path 11. Specifically, the fluid F 1 flowing through the water recovery path 12 is heated by heat exchange with the reactant fluid F 3.As the second heat recovery part 8, a known heat exchanger may be used. As the second heat recovery part 8, for example, a multi-tube heat exchanger, a plate heat exchanger, a coil type heat exchanger, a double-tube heat exchanger, a spiral heat exchanger, or the like can be used.The hydrogen production part 6 performs electrolysis with water (e.g., water vapor) supplied from the water supply path 16 to obtain hydrogen (H 2) and oxygen (O 2).In the hydrogen production part 6, electrolysis may be performed using, for example, power generated from renewable energy (e.g., solar energy generation, wind energy generation, or the like). The methane obtained by utilizing renewable energy can be considered as CO 2- neutral fuel, which has no effect on global warming, because the methane does not generate additional carbon dioxide even when the methane is used for combustion.The hydrogen supply path 13 supplies the hydrogen (H 2) obtained in the hydrogen production part 6 to the methane production reaction part 4.The circulation path 14 guides the fluid F 1 (heat medium fluid) discharged from the first heat recovery part 5 to the raw material supply path 2.The return path 15 returns the non-reactant fluid F 2 discharged from the carbon dioxide consumption reaction part 3 to the raw material supply path 2 via the ejector 9.The water supply path 16 supplies a part (fluid F 5) of the fluid F 1 flowing through the circulation path 14 to the hydrogen production part 6.The ejector 9 is provided in the raw material supply path 2. The ejector 9 has an inlet port 9 a, a first suction port 9 b, a second suction port 9 c, and an outlet port 9 d. The fluid F 1 flowing through the raw material supply path 2 flows from the inlet port 9 ainto the ejector 9 and flows out of the outlet port 9 d. The fluid F 1 is a motive fluid. Inside the ejector 9, a nozzle that discharges the motive fluid is provided. An introduction path 21 is connected to the first suction port 9 b. Carbon dioxide flows as suction fluid from the first suction port 9 bthrough the introduction path 21 into the ejector 9.The recirculation path 15 is connected to the second suction port 9 c. The non-reactant fluid F 2 discharged from the carbon dioxide consumption reaction part 3 flows as a suction fluid from the second suction port 9 cthrough the return path 15 into the ejector 9.Next, an example of a process for methane synthesis using the system for methane synthesis 1 will be described.The methane synthesis method according to the present embodiment includes a supplying step, a carbon dioxide consumption reaction step, a methane generation reaction step, a separating step, and a hydrogen generation step.In the supplying step, water (H 2 O) and carbon dioxide (CO 2) are supplied to the carbon dioxide consumption reaction part 3 via the raw material supply path 2.In the carbon dioxide consumption reaction step, in the carbon dioxide consumption reaction part 3, hydrogen carbonate is obtained as a product by the reaction between water and carbon dioxide from the raw material supply path 2 and carbonate. In the carbon dioxide consumption reaction step, the fluid F2 (non-reactant fluid, e.g., non-reactant gas) containing a non-reactant such as water (for example, water vapor) is produced.In the methane generation reaction step, in the methane generation reaction part 4, carbonate, methane and water are generated by the reaction between hydrogen (H 2) from the hydrogen supply path 13 and hydrogen carbonate (reacted material). In the methane generation reaction step, the reactant fluid F 3 (e.g., reactant gas) containing methane and water is generated. The reactant fluid F 3 (reactant gas) is supplied to the separator 7 via the discharge path 11.In the separation step, the separator 7 separates the methane-containing fluid F 4 and the water-containing fluid F 1 from the reactant fluid F 3.The fluid F 1 is discharged from the separator 7 via the water recovery path 12 and conducted as heat medium fluid to the first part for heat recovery 5. The first heat recovery part 5 heats the fluid F 1 by heat exchange with the carbon dioxide consumption reaction part 3.The fluid F 1 discharged from the first heat recovery part 5 is supplied to the raw material supply path 2 via the circulation path 14. The fluid F 1 is supplied to the carbon dioxide consumption reaction part 3 together with the carbon dioxide introduced through the ejector 9.A part (fluid F 5) of the fluid F 1 flowing through the circulation path 14 is introduced into the hydrogen production part 6 via the water supply path 16. A part of the water contained in the fluid F 1 is electrolysed in the hydrogen production part 6.The hydrogen (H 2) obtained in the hydrogen generating part 6 is supplied to the methane generating reaction part 4 via the hydrogen supply path 13. The oxygen (O 2) obtained in the hydrogen production part 6 is discharged to the outside of the system via the discharge path 24.The switching between the carbon dioxide consumption reaction part 3 and the methane generation reaction part 4 will be described below.After the carbon dioxide consumption reaction step and the methane generation reaction step, the hydrogen carbonate (KHCO 3) and the carbonate (K 2 CO 3) may be exchanged between the carbon dioxide consumption reaction part 3 and the methane generation reaction part 4.For example, the hydrogen carbonate (KHCO 3) of the carbon dioxide consumption reaction part 3 for each reactor is transferred to the methane production reaction part 4. The carbonate (K 2 CO 3) of the methane production reaction section 4 is transferred to the carbon dioxide consumption reaction section 3 for each reactor. This method enables switching between the carbon dioxide consumption reaction part 3 and the methane production reaction part 4.In order to switch between the carbon dioxide consumption reaction part 3 and the methane generation reaction part 4, the carbonate (K 2 CO 3) may be taken out of the reactor and transferred to the carbon dioxide consumption reaction part 3, and the hydrogen carbonate (KHCO 3) may be taken out of the reactor and transferred to the methane generation reaction part 4.In the form shown in FIG. 1, the first reaction part 101 (left part in FIG. 1 ) of the assembled reaction part 100 is the carbon dioxide consumption reaction part 3.The carbon dioxide consumption reaction part 3 and the methane generation reaction part 4 can be changed in arrangement. That is, the first reaction part 101 may be the methane generation reaction part 4 and the second reaction part 102 may be the carbon dioxide consumption reaction part 3.The carbon dioxide consumption reaction part 3 and the methane production reaction part 4 can also be changed or replaced by changing the route.The raw material supply path 2 and the return path 15 are connected to the first reaction part 101 (carbon dioxide consumption reaction part 3). The hydrogen supply path 13 and the discharge path 11 are connected to the second reaction part 102 (methane generation reaction part 4).The second raw material supply path 2A is branched from the raw material supply path 2 and connected to the second reaction part 102. In the raw material supply path 2, a valve V 1 is provided. In the second raw material supply path 2A, a valve V 2 is provided. In the form shown in FIG. 1, the valve V 1 is open. The valve V2 is closed.The second return path 15A is branched from the return path 15 and is connected to the second reaction part 102.A second hydrogen supply path 13A is branched from the hydrogen supply path 13 and is connected to the first reaction part 101. In the hydrogen supply path 13, a valve V3 is provided. In the second hydrogen supply path 13A, a valve V 4 is provided. In the form shown in FIG. 1, the valve V 3 is open. The valve V 4 is closed.The second discharge path 11A is branched from the discharge path 11 and is connected to the first reaction part 101.When the carbon dioxide consumption reaction step is completed, the first reaction part 101 (carbon dioxide consumption reaction part 3) contains hydrogen carbonate (KHCO 3), which is a product. When the methane generation reaction step is completed, the second reaction part 102 (methane generation reaction part 4) contains carbonate (K 2 CO 3).When the valve V 1 is closed and the valve V 2 is opened, water and carbon dioxide may be supplied to the second reaction part 102 via the second raw material supply path 2A. Accordingly, the second reaction part 102 can be used as a reaction part for carbon dioxide consumption. The non-reactant fluid F 2 is discharged via the second return path 15A and guided to the raw material supply path 2 via the return path 15.When the valve V 3 is closed and the valve V 4 is opened, hydrogen (H 2) can be supplied to the first reaction part 101 via the second hydrogen supply path 13A. Accordingly, the first reaction part 101 can be used as a reaction part for methane generation. The reactant fluid F 3 is discharged via the second discharge path 11A and guided to the separator 7 via the discharge path 11.The first reaction part 101 can be returned to the carbon dioxide consumption reaction part by a valve operation opposite to the above. The second reaction part 102 can also be recycled into the methane production reaction part 4.In this way, the carbon dioxide consumption reaction part and the methane generation reaction part can be interchanged.Since the carbon dioxide consumption reaction part 3 and the methane generation reaction part 4 are thermally connected in the methane synthesis system 1, heat generated in the carbon dioxide consumption reaction part 3 can be utilized in the methane generation reaction part 4. The methane synthesis system 1 recovers the heat of the carbon dioxide consumption reaction part 3 through the first heat recovery part 5. By supplying the fluid F 1 to the carbon dioxide consumption reaction part 3 via the raw material supply path 2, the recovered heat in the carbon dioxide consumption reaction part 3 can be utilized. In this way, it is possible to improve the energy efficiency of the entire system.In the methane synthesis system 1, the carbon dioxide consumption reaction part 3 and the methane generation reaction part 4 can be changed from each other by the above-described method. By appropriately changing according to the progress of the reaction, the methane synthesis system 1 can be operated for a long time.In the methane synthesis system 1, the heat between the carbon dioxide consumption reaction part 3 and the methane generation reaction part 4 can be effectively utilized by switching between the carbon dioxide consumption reaction part 3 and the methane generation reaction part 4.Since the methane synthesis system 1 has a recycle path 15 configured to recycle the non-reactant fluid F 2 (non-reactant gas) obtained in the carbon dioxide consumption reaction part 3 to the carbon dioxide consumption reaction part 3 via the raw material feed path 2, the reaction efficiency in the carbon dioxide consumption reaction part 3 can be improved.The heat medium fluid used in the first heat recovery part 5 is the fluid F 1 containing water. Therefore, the fluid F 1 can be supplied to the carbon dioxide consumption reaction part 3 as a raw material. Accordingly, the reaction heat in the carbon dioxide consumption reaction part 3 can be effectively used. In this way, the energy efficiency can be improved.Since the methane synthesis system 1 has the second heat recovery part 8, the fluid F 1 flowing through the water recovery path 12 can be heated by heat exchange with the reactant fluid F 3 supplied to the separator 7 via the discharge path 11. Accordingly, the heat of the methane generation reaction part 4 can be effectively utilized. In this way, the energy efficiency can be improved.Since the methane synthesis system 1 includes the ejector 9, it is possible to save energy, for example, as compared with a case where carbon dioxide is supplied into the raw material supply path 2 only using a blower.The technical scope of the present invention is not limited to the above embodiments, and various modifications may be made without departing from the gist of the present invention.For example, in the methane synthesis system 1, in a case where the first reaction part 101 and the second reaction part 102 are alternately changed and used as a carbon dioxide consumption reaction part and a methane generation reaction part, it is desirable that the first heat recovery part 5 be configured to recover heat from both the first reaction part 101 and the second reaction part 102.For example, a configuration may be adopted in which the first heat recovery part 5 is thermally connected to both the first reaction part 101 and the second reaction part 102. According to this configuration, even in a case where either the first reaction part 101 or the second reaction part 102 is the carbon dioxide consumption reaction part, heat can be efficiently recovered by the first heat recovery part 5.List of reference characters1 Methane Synthesis System 2 Raw Material Supply Path (Supply Path) 3 Carbon Dioxide Consumption Reaction Part 4 Methane Generation Reaction Part 5 First Heat Recovery Part 8 Second Heat Recovery Part 9 Ejector 15 Recirculation Path F 1 FluidReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 2021-17 409 A

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Claims

A system for methane synthesis, comprising: a supply path for supplying carbon dioxide and water; a carbon dioxide consumption reaction part configured to obtain a product by using at least the carbon dioxide and the water; a methane generation reaction part configured to be thermally connected to the carbon dioxide consumption reaction part and generate methane from a reacted material and hydrogen; and a first heat recovery part configured to recover heat by heat exchange with the carbon dioxide consumption reaction part.The system for methane synthesis according to claim 1, wherein the carbon dioxide consumption reaction part and the methane generation reaction part are capable of exchanging each other.The system for methane synthesis according to claim 1 or 2, further comprising: a recycle path configured to recycle a non-reactant obtained in the carbon dioxide consumption reaction part to the carbon dioxide consumption reaction part.The system for methane synthesis according to any one of claims 1 to 3, wherein the first heat recovery part heats a heat medium fluid by heat exchange with the carbon dioxide consumption reaction part, and wherein the heat medium fluid is a fluid containing water.The methane synthesis system according to claim 4, further comprising: a second heat recovery part configured to heat the heat medium fluid by heat exchange with a fluid containing the methane obtained in the methane generation reaction part.The system for methane synthesis according to any one of claims 1 to 5, wherein an ejector that draws in the carbon dioxide with the water as a motive fluid is disposed in the supply path.

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