Methane production apparatus and method for producing methane using the same

Abstract

To provide a methane generator capable of obtaining a methanation reaction under absence of a catalyst and a manufacturing method using the same.SOLUTION: A methane generator 1 includes a housing 2 having a reaction space 7 therein, an intake part 4 capable of supplying a premixed gas of carbon dioxide and hydrogen to the reaction space 7, and a movable body 3 provided movably within the housing 2 to compress the premixed gas supplied into the space 7 to generate methane by reacting the premixed gas, and an exhaust portion 5 for exhausting the methane from the reaction space 7.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a methane production apparatus and a method for producing methane using the same. Background Art

[0002] In recent years, global warming caused by carbon dioxide emissions has become a problem, and for example, a transition to a low-carbon society that does not depend on fossil fuels such as petroleum and coal is required. For example, in Japan, the government has declared that it will achieve carbon neutrality by 2050, which reduces net carbon dioxide emissions to zero after excluding amounts absorbed by forests and the like.

[0003] To achieve carbon neutrality, it is necessary to increase the use of renewable energy such as solar power and wind power, for example. However, solar power is affected by daytime sunshine duration, and wind power requires a certain wind speed; in both cases, output is unstable due to daily changes or seasonal fluctuations throughout the year. Furthermore, when surplus power is generated in power generation by solar power, wind power, or the like, electricity can be stored in storage batteries, but storage batteries cannot store electric power for long periods of time.

[0004] Accordingly, in recent years, efforts toward Power to Gas (hereinafter referred to as "PtG"), which produces gaseous fuel using surplus power from renewable energy, have attracted attention. As a fuel, hydrogen, which can be obtained relatively easily by electrolyzing water, has been considered. However, at present, the use of hydrogen is limited to automobiles, stationary fuel cells, and the like.

[0005] Patent Document 1 discloses a method for synthesizing methane from carbon dioxide and hydrogen, which comprises: a first reaction step of reacting carbon dioxide and hydrogen to obtain a gas containing carbon monoxide as a main component; and a second reaction step of reacting the carbon monoxide generated in the first reaction step with hydrogen to obtain methane.

[0006] This offers several advantages, including the ability to utilize carbon dioxide, expand the range of hydrogen applications, and use methane as an alternative fuel to natural gas. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 5562873 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, in the technology described in Patent Document 1, a catalyst is required to react hydrogen with carbon dioxide, but simply using a catalyst may lead to catalyst degradation.

[0009] The present invention aims to provide a methane production apparatus capable of performing a methanation reaction in the absence of a catalyst, and a method for producing methane using the same. [Means for solving the problem]

[0010] Section 1. A housing having a reaction space inside, The reaction space includes an intake section capable of supplying a premixed gas of carbon dioxide and hydrogen, A movable body is provided within the housing and compresses the premixed gas supplied into the reaction space to react the premixed gas and produce methane; An exhaust unit for exhausting the methane from the reaction space, A methane generator equipped with the following features.

[0011] Section 2. A housing having a reaction space inside, A first intake section capable of supplying either carbon dioxide or hydrogen gas to the reaction space, and a movable body provided movably within the housing for compressing the gas supplied to the reaction space, The movable body compresses the gas supplied into the reaction space, and a second intake section supplies either carbon dioxide or hydrogen to the reaction space to produce methane. An exhaust unit for exhausting the methane from the reaction space, A methane generator equipped with the following features.

[0012] Section 3. The housing has a cylinder, The movable body has a piston that can reciprocate axially relative to the cylinder. The methane generating apparatus described in item 1 or item 2 above.

[0013] Section 4. The piston is supported by a catalyst. A methane generating apparatus according to any one of the preceding items 1 to 3.

[0014] Section 5. The housing is further equipped with a spark plug that ignites the reaction space when the methane is produced, A methane generating apparatus according to any one of the preceding items 1 to 4.

[0015] Section 6. A method for producing methane using the methane production apparatus described in item 1 above, An intake stroke in which a premixed gas of carbon dioxide and hydrogen is supplied from the intake section into the reaction space, After the intake stroke, a compression stroke is performed in which the premixed gas supplied into the reaction space is compressed by the movable body, The reaction step involves the premixed gas reacting under compression to produce methane, After the reaction step, an exhaust step is performed in which the methane is exhausted from the reaction space through the exhaust section, A method for producing methane, including

[0016] Item 7. A method for producing methane using the methane production apparatus according to Item 2 above, comprising: an intake step of supplying either one of carbon dioxide and hydrogen gas into the reaction space from the first intake section; after the intake step, a compression step of compressing the gas supplied into the reaction space by the movable body; a reaction step of, in a state where said gas is compressed, supplying the other of carbon dioxide and hydrogen into the reaction space from the second intake section to cause a reaction and generate methane; after the reaction step, an exhaust step of exhausting the methane from the exhaust section; A method for producing methane, comprising the above steps.

[0017] Item 8. The method for producing methane according to Item 6 or 7 above, wherein the exhaust step is performed after repeating the compression step and the reaction step a plurality of times. Effects of the Invention

[0018] The methane production apparatus of the above aspect according to the present invention and the method for producing methane using the same have an advantage that a methanation reaction can be obtained in the absence of a catalyst. Brief Description of the Drawings

[0019] [Figure 1] FIGS. 1(A) to 1(D) are cross-sectional views illustrating a production method using a methane production apparatus according to an embodiment of the present invention. [Figure 2] FIGS. 2(A) to 2(D) are cross-sectional views illustrating a production method using a methane production apparatus according to Modified Example 1. [Figure 3] FIGS. 3(A) to 3(D) are cross-sectional views illustrating a production method using a methane production apparatus according to Modified Example 2. [Figure 4]These are graphs of the methanation reaction when a premixed gas of carbon dioxide and hydrogen is compressed. Figure 4(A) shows the relationship between compressibility and temperature, and Figure 4(B) shows the relationship between compressibility and conversion rate. [Figure 5] These are graphs of the methanation reaction in which carbon dioxide is supplied after hydrogen is compressed. Figure 5(A) shows the relationship between compressibility and temperature, and Figure 5(B) shows the relationship between compressibility and conversion rate. [Figure 6] These are graphs of the methanation reaction in which hydrogen is supplied after compressing carbon dioxide. Figure 6(A) shows the relationship between compressibility and temperature, and Figure 6(B) shows the relationship between compressibility and conversion rate. [Figure 7] This is a cross-sectional view illustrating a modified example of the embodiment. [Figure 8] This is a cross-sectional view illustrating a further variation of Variation 1. [Figure 9] This is a cross-sectional view illustrating a further variation of variation 2. [Modes for carrying out the invention]

[0020] <Embodiment> The present invention will be described in detail below with reference to the accompanying drawings.

[0021] (1) Methanation technology The methane production method according to this embodiment is a production method using a synthetic methane production technology (methanation technology) that synthesizes methane from carbon dioxide and hydrogen. The chemical reaction equation for the methanation technology is as follows.

[0022] CO2 + 4H2 → CH4 + 2H2O

[0023] In this specification, the chemical reaction that produces methane by reacting carbon dioxide and hydrogen is referred to as the "methanation reaction."

[0024] In the methane production method according to this embodiment, the methanation reaction is carried out in the absence of a catalyst (under conditions where a catalyst is not required). Furthermore, in the methanation technology, it is preferable to carry out the methanation reaction at a temperature of 300°C to 600°C. In addition, in the methanation technology, the raw materials for the methanation reaction (raw materials containing carbon dioxide and hydrogen) may be gaseous or liquid. When the raw materials are gaseous (raw material gas), the temperature of the raw material gas before the reaction (before compression) is preferably above room temperature, for example, 20°C to 30°C. When the raw material gas is above room temperature, the methanation reaction is more likely to occur. Even if the raw materials are liquid, they can be used if they vaporize when compressed after the raw materials are supplied.

[0025] In terms of stoichiometry for the methanation reaction, 4 moles of hydrogen (H2) react with 1 mole of carbon dioxide (CO2). In other words, 0.25 moles of carbon dioxide (CO2) react with 1 mole of hydrogen (H2). The molar ratio of carbon dioxide to hydrogen (CO2 / H2) is preferably between 0.2 and 0.5, and more preferably between 0.2 and 0.3. By setting the molar ratio of carbon dioxide to hydrogen to 0.2 or higher, the conversion rate to methane can be increased to a high level. Here, "conversion rate" refers to the proportion of hydrogen and carbon dioxide that are converted into methane through reaction.

[0026] Furthermore, although the methane production method of this embodiment does not use a catalyst, for example, by supplying a small amount of oxygen to the raw material gas before the methanation reaction and burning it with hydrogen, the reaction of the mixture containing hydrogen and carbon dioxide can be promoted. This makes it possible to improve the conversion rate of the product, methane.

[0027] As mentioned above, in the methanation reaction, carbon dioxide and hydrogen react. Generally, since hydrogen is a fuel, supplying oxygen allows some of the hydrogen, which is the raw material gas for the methanation reaction, to react with oxygen (combustion reaction), thereby raising the temperature of the raw material gas. In this case, since the reaction with hydrogen involves carbon dioxide (CO2) and oxygen (O2), the ratio of oxygen to the total molar amount of carbon dioxide and oxygen (molar concentration, O2 / (CO2+O2)) is preferably between 0.02 and 0.1.

[0028] The methane produced in the methanation reaction may react with the remaining unreacted oxygen, but methane requires a large amount of oxygen to burn, and the remaining oxygen is insufficient. In the methane production method according to this embodiment, when supplying oxygen, the amount of oxygen supplied can be adjusted to an amount that reacts with hydrogen in the compound (reactant) gas but does not react with methane, thereby preventing the combustion of methane.

[0029] In the methane production method according to this embodiment, methane can be synthesized from hydrogen and carbon dioxide with a conversion rate of approximately 80%.

[0030] (2) Methane generator The methane generator 1 according to this embodiment is a manufacturing apparatus that produces methane by realizing the methanation technology described above. As shown in Figure 1(A), the methane generator 1 according to this embodiment comprises a housing 2, an intake section 4, a movable body 3, and an exhaust section 5. The methane generator 1 can produce methane by performing an intake stroke (Figure 1(A)), a compression stroke (Figure 1(B)), a reaction stroke (Figure 1(C)), and an exhaust stroke (Figure 1(D)).

[0031] For the sake of explanation, in the following, the direction of movement of the movable body 3 will be defined as the "up and down direction," and within the up and down direction, the direction from the movable body 3 toward the exhaust section 5 or intake section 4 will be defined as the "up direction," and the opposite direction will be defined as the "down direction." However, these definitions of directions are not intended to specify the mode of use of the methane generator 1 according to the present invention.

[0032] (2.1) Housing Housing 2 is the case for the methane generator 1, which has a reaction space 7 inside. Housing 2 has a cylinder. The reaction space 7 is formed inside the cylinder. Specifically, the reaction space 7 refers to the space enclosed by the inner circumferential surface of the cylinder and the movable body 3. The cylinder comprises a cylinder liner 21 and a cylinder head 22.

[0033] The cylinder liner 21 is a cylindrically formed portion. A movable body 3, described later, is movably housed inside the cylinder liner 21. The movable body 3 can move along the central axis of the cylinder liner 21.

[0034] The cylinder head 22 closes one of the central axial openings (in this case, the upper opening) of the cylinder liner 21. The cylinder head 22 has an upper base surface that forms the reaction space 7. The upper base surface is formed in a substantially conical cross-section, with the diameter decreasing towards the top.

[0035] The cylinder head 22 has an intake port 23 and an exhaust port 24. The intake port is an opening that connects the intake passage 41 to the inside of the cylinder. The exhaust port 24 is an opening that connects the inside of the cylinder to the exhaust passage 51. The intake port 23 and the exhaust port 24 penetrate the cylinder head 22.

[0036] (2.2) Movable body The movable body 3 is a component that is movably mounted within the housing 2. The movable body 3 can repeatedly compress and expand the gas in the reaction space 7. The movable body 3 comprises a piston 31 and a plurality of piston rings 32.

[0037] The piston 31 is configured to reciprocate axially relative to the cylinder. In the methane generator 1 according to this embodiment, the movement of the piston 31 along the central axis of the cylinder allows the gas in the reaction space 7 to be compressed or expanded.

[0038] A rod 33 is connected to the piston 31. The piston 31 and the rod 33 are rotatably connected by a pin. The rod 33 is rotatably connected to a crankshaft (not shown).

[0039] It is preferable that a catalyst is supported on the piston 31. Preferably, the catalyst supported on the piston 31 is, for example, Ni / ZrO2. In the methane generator 1 according to this embodiment, hydrogen and carbon dioxide can be reacted even without a catalyst, but methane can be obtained with higher efficiency by using a catalyst. However, if a catalyst is used without a catalyst, there is a possibility that the catalyst will deteriorate due to the heat generated during the reaction. Therefore, in this embodiment, the catalyst is supported on the piston 31, and the methanation reaction is carried out at a temperature lower than the temperature condition of 300°C to 600°C. This suppresses the deterioration of the catalyst due to heat.

[0040] The piston rings 32 are components that maintain an airtight seal in the reaction space 7 between the piston 31 and the cylinder. The piston rings 32 are mounted on the outer circumferential surface of the piston 31. Multiple piston rings 32 are arranged at intervals in the vertical direction.

[0041] With hydrogen and carbon dioxide supplied into the reaction space 7, the piston 31 moves and the reaction space 7 is compressed (Figure 1(B)), causing the hydrogen and carbon dioxide to be pressurized and reach a high temperature. Then, a methanation reaction occurs in the reaction space 7, and methane is produced (Figure 1(C)).

[0042] (2.3) Intake section The intake section 4 supplies the raw material gas to the reaction space 7. In the methane generator 1 according to this embodiment, a premixed gas of carbon dioxide and hydrogen is supplied as the raw material gas. The premixed gas contains carbon dioxide and hydrogen, but as mentioned above, it may also contain oxygen. As also mentioned above, the molar ratio of carbon dioxide to hydrogen in the premixed gas (CO2 / H2) is preferably 0.2 or more and 0.5 or less, and more preferably 0.2 or more and 0.3 or less. Furthermore, the temperature of the premixed gas before compression is preferably, for example, between room temperature of about 20°C to 30°C and 300°C.

[0043] The intake section 4 comprises an intake passage 41 and an intake valve 42. The intake passage 41 is connected to the intake port 23 of the housing 2 and is a passage that connects the gas supply source to the inside of the housing 2. The intake valve 42 can open and close the intake passage 41. The intake valve 42 closes the intake passage 41 during the compression stroke, reaction stroke, and exhaust stroke, and opens the intake passage 41 during the intake stroke. Here, "closing the intake passage 41" includes not only closing the inside of the intake passage 41 but also closing the intake port 23. The same applies to the expression "opening the intake passage 41".

[0044] The intake valve 42 and the exhaust valve 52, described later, may open and close in conjunction with the rotation of the crankshaft, for example, or each may be connected to a drive unit (for example, a motor).

[0045] (2.4) Exhaust section The exhaust unit 5 exhausts the methane generated in the reaction space 7 from the reaction space 7. The exhaust unit 5 comprises an exhaust passage 51 and an exhaust valve 52. The exhaust passage 51 is connected to the exhaust port 24 of the housing 2 and is a passage that connects the methane supply port (not shown) to the inside of the housing 2. The exhaust valve 52 can open and close the exhaust passage 51. The exhaust valve 52 closes the exhaust passage 51 during the intake stroke, compression stroke and reaction stroke, and opens the exhaust passage 51 during the exhaust stroke. "Closing the exhaust passage 51" here includes not only closing the inside of the exhaust passage 51 but also closing the exhaust port 24. The same applies to the expression "opening the exhaust passage 51".

[0046] (3) Manufacturing method Using a methane generator 1 with this configuration, methane can be produced by going through an intake stroke, a compression stroke, a reaction stroke, and an exhaust stroke.

[0047] The intake stroke is the process of supplying raw material gas from the intake section 4 into the reaction space 7. In the intake stroke according to this embodiment, a premixed gas of carbon dioxide and hydrogen is supplied as the raw material gas. In the intake stroke, as shown in Figure 1(A), as the piston 31 moves from top dead center to bottom dead center, the intake valve 42 opens the intake passage 41 and the premixed gas is supplied into the reaction space 7. As a result, the reaction space 7 is filled with the premixed gas.

[0048] The compression stroke is the process in which the raw material gas (premixed gas) supplied into the reaction space 7 is compressed by the movable body 3 after the intake stroke. During the compression stroke, as shown in Figure 1(B), the piston 31 moves from bottom dead center to top dead center, and at this time, the volume of the reaction space 7 decreases. At this time, the premixed gas in the reaction space 7 is compressed. Due to the compression stroke, the temperature of the premixed gas rises to, for example, between 300°C and 600°C.

[0049] The reaction process involves the reaction of a premixed gas to produce methane. During the compression process, the premixed gas, which has become hot, undergoes a methanation reaction in the reaction space 7. This generates methane within the reaction space 7. After the reaction, the hot gas expands, and as shown in Figure 1(C), the piston 31 moves from top dead center to bottom dead center.

[0050] Here, since the methanation reaction is an exothermic reaction, a force can be applied to the piston 31 toward the bottom dead center. Therefore, it is also possible to extract work to the outside from the rod 33 or the crankshaft.

[0051] Furthermore, it is preferable to monitor the amount of methane produced through the reaction process using sensors, for example, or to verify the reaction amount in advance, in order to understand the amount of methane obtained in a single reaction process. This allows for the option of repeating the compression and reaction processes without proceeding to the exhaust process after the reaction process. In other words, by repeating the compression and reaction processes multiple times before performing the exhaust process, the desired amount of methane can be secured, thereby improving the methane conversion rate.

[0052] The choice of whether to perform the compression and reaction processes once each, or to repeat them multiple times, may be made by the operator depending on the amount of methane to be obtained, or it may be determined by the control program based on the amount of methane produced as determined by monitoring.

[0053] The exhaust stroke is the process that follows the reaction stroke in which methane is exhausted from the reaction space 7 through the exhaust section 5. During the exhaust stroke, as shown in Figure 1(D), the piston 31 moves from bottom dead center to top dead center. At this time, the exhaust valve 52 opens the exhaust passage 51, and the methane filling the reaction space 7 is discharged.

[0054] After the exhaust stroke, the intake stroke can be performed again. Therefore, according to the methane production method of this embodiment, methane can be produced continuously.

[0055] (4) Effects As described above, the methane generator 1 according to this embodiment comprises a housing 2 having a reaction space 7 inside, an intake section 4 capable of supplying a premixed gas of carbon dioxide and hydrogen to the reaction space 7, a movable section that compresses the premixed gas supplied to the reaction space 7 to cause the premixed gas to react, and an exhaust section 5 that exhausts methane from the reaction space 7. Therefore, efficient methane production can be achieved. Furthermore, since the methanation reaction can be obtained in the absence of a catalyst, cost reduction can be achieved, and there is the advantage that there are no restrictions on the composition of the raw material gas.

[0056] Conventional methanation technology has several technical challenges, such as the need for a catalyst to synthesize methane, the need to raise the temperature to the reaction temperature, the fact that the methanation reaction is an exothermic reaction and the catalyst layer deteriorates due to heat, and the fact that the catalyst becomes poisoned (catalyst poisoning) if the carbon dioxide contains sulfur or other substances.

[0057] In contrast, the methane generator 1 according to this embodiment synthesizes methane without a catalyst, allowing hydrogen and carbon dioxide to react at a relatively low temperature. Furthermore, since no catalyst is used, there is no need to consider catalyst degradation, nor is there any need to consider adjustments such as arranging catalysts with different activities in a tiered configuration. Moreover, while catalysts are made of expensive precious metals, synthesizing methane without a catalyst reduces costs, and because there are no restrictions on the gas composition of the reactants, biogas containing sulfur can also be used.

[0058] Furthermore, since the housing 2 has a cylinder and the movable body 3 has a piston 31 that can reciprocate axially relative to the cylinder, methane can be produced using a mechanism similar to a reciprocating engine, enabling continuous methane production. In addition, due to its simple structure, the housing 2 can be easily miniaturized, which is advantageous because it can be owned by companies with limited installation space. Moreover, since the raw materials are carbon dioxide and hydrogen, transportation costs can be reduced.

[0059] Furthermore, since the methane production method according to this embodiment includes an intake stroke, a compression stroke, a reaction stroke, and an exhaust stroke, it is possible to achieve efficient methane production and continuous methane production.

[0060] Furthermore, since the compression and reaction processes can be repeated multiple times before the exhaust process is executed, the conversion rate can be improved, enabling efficient methane production.

[0061] <Variation> The above embodiments are merely one of many embodiments of the present invention. The embodiments can be modified in various ways depending on the design, etc., as long as the objectives of the present invention are achieved. The modifications described below can be combined and applied as appropriate.

[0062] (1) Variation 1 The methane generator 1 according to Modification 1 differs from Embodiment 1 in that it has a second intake section 6. The "intake section 4" of Embodiment 1 will be referred to as the "first intake section 4" to distinguish it from the second intake section 6. The other components of Modification 1 are the same as those of Embodiment 1, so they are denoted by the same reference numerals and their descriptions are omitted.

[0063] The methane generator 1 according to modified example 1, as shown in Figure 2, comprises a housing 2, a first intake section 4, a second intake section 6, a movable body 3, and an exhaust section 5. The housing 2 has a cylinder, similar to embodiment 1, and the movable body 3 has a piston 31.

[0064] The first intake section 4 is configured to supply either carbon dioxide or hydrogen (sometimes referred to as the "first gas") to the reaction space 7. In this invention, the gas supplied to the reaction space 7 by the first intake section 4 may be either carbon dioxide or hydrogen, but from the viewpoint of methane conversion rate, it is preferable to supply carbon dioxide.

[0065] The phrase "either carbon dioxide or hydrogen" here means that the dominant gas is one of the two gases, and does not exclude the possibility of a small amount of hydrogen being present when the dominant gas is carbon dioxide. In other words, "either carbon dioxide or hydrogen" includes the possibility of a small amount of hydrogen being present when the dominant gas is carbon dioxide. Furthermore, other gases such as oxygen may also be present in this gas.

[0066] A second intake section 6 is provided in the cylinder head 22. Specifically, a second intake port 25 is formed in the cylinder head 22, and the flow path 61 of the second intake section 6 is connected to it. The second intake section 6 supplies a gas to the reaction space 7 that is different from the gas supplied from the first intake section 4 (sometimes called the "second gas"), which is either carbon dioxide or hydrogen. That is, if the first intake section 4 supplies a gas containing carbon dioxide, the second intake section 6 supplies a gas containing hydrogen. On the other hand, if the first intake section 4 supplies a gas containing hydrogen, the second intake section 6 supplies a gas containing carbon dioxide.

[0067] The second intake section 6 comprises a flow path 61 and a nozzle 62. The flow path 61 is connected to the second intake port 25. The nozzle 62 is connected to the flow path 61 and can eject the gas flowing through the flow path 61 into the reaction space 7. When the first gas supplied from the first intake section 4 is compressed and heated to a high temperature, and the second gas is supplied from the second intake section 6, a methanation reaction occurs in the reaction space 7, producing methane.

[0068] In this modified example, methane can be produced by performing an intake stroke, a compression stroke, a reaction stroke, and an exhaust stroke, similar to Embodiment 1.

[0069] The intake stroke is the process of supplying the first gas from the intake section 4 into the reaction space 7. During the intake stroke, as shown in Figure 2(A), as the piston 31 moves from top dead center to bottom dead center, the intake valve 42 opens the intake passage 41, and the first gas is supplied into the reaction space 7. As a result, the reaction space 7 is filled with the first gas.

[0070] The compression stroke is the process in which the first gas supplied into the reaction space 7 after the intake stroke is compressed by the movable body 3. During the compression stroke, as shown in Figure 2(B), the piston 31 moves from bottom dead center to top dead center, and at this time, the volume of the reaction space 7 decreases. At this time, the first gas in the reaction space 7 is compressed. Due to the compression stroke, the temperature of the first gas rises, for example, to between 300°C and 600°C.

[0071] The reaction process involves supplying a second gas from the second intake section 6 into the reaction space 7 while the first gas is compressed, thereby inducing a methanation reaction. Methane can be produced through this reaction process. When the second gas is ejected into the atmosphere of the first gas, which has become hot due to the compression process, the methanation reaction occurs. As a result, methane is produced in the reaction space 7. After the reaction, the hot gas expands, and as shown in Figure 2(C), the piston 31 moves from top dead center to bottom dead center.

[0072] In this modified example, as in the above embodiment, the compression stroke and reaction stroke may be performed again after the reaction stroke without proceeding to the exhaust stroke.

[0073] The exhaust stroke is the process that follows the reaction stroke in which methane is exhausted from the reaction space 7 through the exhaust section 5. During the exhaust stroke, as shown in Figure 2(D), the piston 31 moves from bottom dead center to top dead center. At this time, the exhaust valve 52 opens the exhaust passage 51, and the methane filling the reaction space 7 is discharged.

[0074] After the exhaust stroke, the intake stroke can be performed again. Therefore, according to the methane production method of this modified example, methane can be produced continuously.

[0075] (2) Modification example 2 In the methane generator 1 according to the above embodiment, the intake stroke, compression stroke, reaction stroke, and exhaust stroke are realized using a cylinder and a piston 31, but they may also be realized with a structure such as those shown in Figures 3(A) to (D).

[0076] The modified methane generator 1, like the embodiment 1, comprises a housing 2, an intake section 4, a movable body 3, and an exhaust section 5. However, while the methane generator 1 according to embodiment 1 utilizes volume changes due to the reciprocating motion of a piston 31 as the movable body 3, this modified version utilizes volume changes due to the rotational movement of a rotor 34 as the movable body 3 to generate the methanation reaction.

[0077] The housing 2 is a hollow body and has a reaction space 7 inside. The reaction space 7 is formed between the inner surface of the housing 2 and the movable body 3. When the inner surface of the housing 2 is viewed along the axis of rotation, the inner surface of the housing 2 is formed in the shape of a 2-node peritrochoidal curve.

[0078] The movable body 3 is a rotor 34 formed in a substantially triangular shape. The rotor 34 can rotate within the housing 2. Preferably, the movable body 3 supports a catalyst, similar to the piston 31 in Embodiment 1.

[0079] During the intake stroke, as shown in Figure 3(A), the rotor 34 is positioned such that a reaction space 7 is formed facing the intake section 4. In this state, a premixed gas is supplied.

[0080] During the compression stroke, as shown in Figure 3(B), the rotor 34 rotates, reducing the volume of the reaction space 7. At this time, the premixed gas in the reaction space 7 is compressed.

[0081] During the compression stroke, as shown in Figure 3(C), the rotor 34 rotates further, and the high-temperature premixed gas undergoes a methanation reaction in the reaction space 7.

[0082] During the exhaust stroke, as shown in Figure 3(D), the rotor 34 rotates further, causing the reaction space 7 to move to a position facing the exhaust section 5. This allows the methane filling the reaction space 7 to be discharged through the exhaust passage 51.

[0083] In this modified example, for the sake of explanation, we focused on a single reaction space 7, but multiple (three in this case) reaction spaces 7 exist within a single housing 2, and the intake stroke, compression stroke, reaction stroke, and exhaust stroke can be performed in each reaction space 7.

[0084] Furthermore, in this modified example, the premixed gas is supplied from the intake section 4, but the configuration of Modified Example 1 may also be combined. That is, the first gas may be supplied from the intake section 4 as the first intake section 4, and during the compression stroke, a second supply section may be provided to supply the second gas to the reaction space 7, thereby supplying the second gas.

[0085] (3) Modification example 3 As shown in Figures 7 and 8, a spark plug 8 may be attached to the housing according to the above embodiment and modification 1. The spark plug 8 ignites in the reaction space 7 when methane is produced. The spark plug 8 may be, for example, a spark plug or a glow plug. During the reaction process, ignition in the reaction space 7 by the spark plug 8 can generate H radicals, thereby promoting the methanation reaction.

[0086] The spark plug 8 may be attached to the cylinder head 22 or provided on the cylinder liner 21, as long as it can ignite the reaction space 7.

[0087] It is preferable to add oxygen to the reaction space 7 before ignition by the spark plug 8. When the spark plug 8 ignites, H radicals are generated as described above, but in the presence of oxygen, the reactions (Equations 1) to (3) occur, and the H radicals react with CO2 to produce carbon monoxide (Equation 4). The reaction between the generated carbon monoxide and hydrogen proceeds, and the methanation reaction is promoted (Equation 5). The chemical reaction equation at this time is as follows. Note that "·" indicates a radical.

[0088] O2+H·=OH·+O· (Formula 1) H2+O·=OH·+H· (Formula 2) H2+OH·=H2O+H· (Formula 3) CO2+H·=CO+OH· (Formula 4) CO+3H2=CH4+H2O (Formula 5)

[0089] The spark plug 8 is also applicable to the methane generator 1 of the modified example 2, as shown in Figure 9. There may be multiple spark plugs 8 or there may be one.

[0090] (4) Other variations Although the movable body 3 in the above embodiment is equipped with a piston ring 32, the piston ring 32 may be omitted.

[0091] In the methane generator 1 according to the above embodiment, the intake section 4 has an intake valve 42 and the exhaust section 5 has an exhaust valve 52. However, if a structure like that of Modification 2 is adopted, the intake valve 42 and exhaust valve 52 may be omitted in the present invention.

[0092] In the above embodiment, force may be applied to at least one of the piston 31, rod 33, and crankshaft to actively move the piston 31 and control the temperature and pressure of the gas in the reaction space 7.

[0093] In the above embodiment, when work is extracted from the rod 33 or crankshaft to the outside, it is also possible to generate electricity and store it in a battery, for example.

[0094] The housing 2 in the above embodiment has one cylinder, but it may have, for example, multiple cylinders. If there are multiple cylinders, multiple rods 33 may be connected to a single crankshaft so that multiple pistons 31 can move in conjunction, or each piston 31 may operate independently.

[0095] <Examples> The embodiments of the present invention will be described more specifically below based on the examples. However, the present invention is not limited to the scope of the examples.

[0096] (1) Methanation reaction of a premixed gas of carbon dioxide and hydrogen

[0097] A premixed gas at 1 atmosphere was subjected to adiabatic compression to induce a methanation reaction. Under conditions where there was no heat exchange with the surroundings and no work was done on the surroundings, methane was produced, and the conversion rate to methane was calculated.

[0098] Figure 4(A) shows a graph with compressibility on the horizontal axis and temperature on the vertical axis. Figure 4(B) shows a graph with compressibility on the horizontal axis and the conversion rate to methane on the vertical axis. The compressibility ε is expressed as ε = V1 / V2, where V1 is the volume of the reaction chamber when piston 31 is at bottom dead center and V2 is the volume of the reaction chamber when piston 31 is at top dead center after compressing the premixed gas. This allows us to evaluate the methane conversion rate obtained when the temperature after compression is changed. T0 is the initial temperature after compression, and T adは、 This is the temperature after the methanation reaction.

[0099] As can be seen from Figures 4(A) and 4(B), the initial temperature after compression and the temperature after the methanation reaction increase with compressibility. As a result, it was found that the higher the compressibility, the lower the conversion rate to methane.

[0100] (2) Methanation reaction in which carbon dioxide is supplied after hydrogen has been compressed. After adiabatic compression of hydrogen at 1 atmosphere, carbon dioxide was injected into the reaction space in a stoichiometric ratio to induce a methanation reaction. Under conditions where there was no heat exchange with the surroundings and no work was done on the surroundings, methane was produced, and the conversion rate to methane was calculated.

[0101] Figure 5(A) shows a graph with compressibility on the horizontal axis and temperature on the vertical axis. Figure 5(B) shows a graph with compressibility on the horizontal axis and conversion rate to methane on the vertical axis.

[0102] As can be seen from Figures 5(A) and 5(B), the initial temperature after compression and the temperature after the methanation reaction increase with the compressibility. As a result, similar to (1) above, it was found that the higher the compressibility, the lower the conversion rate to methane.

[0103] (3) Methanation reaction in which hydrogen is supplied after the carbon dioxide has been compressed. After adiabatic compression of carbon dioxide at 1 atmosphere, hydrogen was injected into the reaction space in a stoichiometric ratio to induce a methanation reaction. Under conditions where there was no heat exchange with the surroundings and no work was done on the surroundings, methane was produced, and the conversion rate to methane was calculated.

[0104] Figure 6(A) shows a graph with compressibility on the horizontal axis and temperature on the vertical axis. Figure 6(B) shows a graph with compressibility on the horizontal axis and conversion rate to methane on the vertical axis.

[0105] As can be seen from Figures 6(A) and (B), the initial temperature after compression does not change significantly with respect to the compressibility ratio. On the other hand, the temperature after the methanation reaction increases slightly with respect to the compressibility ratio. As a result, it was found that the conversion rate to methane increases as the compression ratio increases.

[0106] Based on the results of (1) to (3) above, it was found that the methanation reaction in which only carbon dioxide was supplied from the first intake and compressed, and then hydrogen was supplied from the second intake, was superior in terms of the conversion rate to methane. [Explanation of Symbols]

[0107] 1. Methane generator 2 Housing 3 Movable body 31 pistons 4. Intake section 5. Exhaust section 6. Second intake section 7 Reaction space

Claims

1. A housing having a reaction space inside, A first intake section capable of supplying either carbon dioxide or hydrogen gas to the reaction space, A movable body is provided within the housing to be movable and compress the gas supplied into the reaction space, The movable body compresses the gas supplied into the reaction space, and a second intake section supplies either carbon dioxide or hydrogen to the reaction space to produce methane. An exhaust unit for exhausting the methane from the reaction space, Equipped with, Methane generator.

2. The housing has a cylinder, The movable body has a piston that can reciprocate axially relative to the cylinder. The methane generating apparatus according to claim 1.

3. The piston is supported by a catalyst. The methane generating apparatus according to claim 2.

4. The housing is further equipped with a spark plug that ignites the reaction space when the methane is produced, The methane generating apparatus according to claim 1.

5. A method for producing methane using the methane production apparatus described in claim 1, An intake stroke in which either carbon dioxide or hydrogen gas is supplied from the first intake section into the reaction space, After the intake stroke, a compression stroke is performed in which the gas supplied into the reaction space is compressed by the movable body, A reaction step in which, while the aforementioned gas is compressed, either carbon dioxide or hydrogen is supplied from the second intake section into the reaction space to cause a reaction and produce methane, After the reaction step, an exhaust step is performed in which the methane is exhausted from the exhaust section, including, A method for producing methane.

6. After repeating the compression stroke and the reaction stroke multiple times, the exhaust stroke is performed. The method for producing methane according to claim 5.

7. The movable body is a rotor that rotates within the housing. The methane generating apparatus according to claim 1.

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