Methane production method

Abstract

Provided is a methane production method capable of efficiently producing methane and excellent in safety. The methane production method according to one embodiment produces methane from a raw material gas containing carbon dioxide gas, oxygen gas, and hydrogen gas. The methane production method comprises: a step of preparing the raw material gas by adding hydrogen gas to a mixed gas containing carbon dioxide gas and oxygen gas; and a step of supplying the raw material gas to a gas flow path of a methane production apparatus. In the methane production method, when the oxygen concentration is 5 vol. % or more and the temperature in the gas flow path exceeds 450°C in the raw material gas to be supplied to the gas flow path, the addition of the hydrogen gas to the mixed gas is stopped.

Description

Methane production method

[0001] The present invention relates to a method for producing methane.

[0002] In recent years, from the viewpoint of reducing environmental load, studies have been conducted on recovering carbon dioxide and reusing it as a raw material for carbon compounds. For example, a method for producing methane has been proposed in which a raw material gas containing hydrogen gas, oxygen gas, and carbon dioxide gas is supplied to a reactor equipped with a catalyst, and a methanation reaction is initiated and continued by heat including reaction heat from catalytic combustion of the hydrogen gas (see, for example, Patent Document 1).

[0003] International Publication No. 2021 / 045101

[0004] Exhaust gases emitted from various industrial facilities may contain carbon dioxide gas and oxygen gas. Therefore, it has been considered to use a mixed gas obtained by adding hydrogen gas to the exhaust gas as a feed gas for the method for producing methane described in Patent Document 1. However, when hydrogen gas is added to the exhaust gas, depending on the oxygen concentration in the exhaust gas, the feed gas may become an explosive mixture, posing a risk of explosion during methane production. A primary object of the present invention is to provide a methane production method that can efficiently produce methane and is highly safe.

[0005] [1] A methane production method according to one embodiment of the present invention produces methane from a feed gas containing carbon dioxide gas, oxygen gas, and hydrogen gas. The methane production method includes the steps of: preparing a feed gas by adding hydrogen gas to a mixed gas containing carbon dioxide gas and oxygen gas; and supplying the feed gas to a gas flow path of a methane production apparatus. In the methane production method, when the oxygen concentration in the feed gas supplied to the gas flow path is 5% by volume or more and the temperature in the gas flow path exceeds 450°C, the addition of hydrogen gas to the mixed gas is stopped. [2] The methane production method described in [1] above may further include the steps of measuring the oxygen concentration in an exhaust gas discharged from the gas flow path; and measuring the hydrogen concentration in the exhaust gas. In the methane production method, the addition of hydrogen gas to the mixed gas may be stopped when the oxygen concentration in the exhaust gas is 5% by volume or more and the hydrogen concentration in the exhaust gas is 4% by volume or more. [3] In the methane production method described in [1] or [2] above, a dilution gas may be supplied to the gas flow path after stopping the addition of the hydrogen gas to the mixed gas. [4] In the methane production method described in any of [1] to [3] above, the methane production apparatus may have a vent. The vent communicates with the upstream end of the gas flow path in the supply direction of the raw material gas. The vent is capable of releasing pressure within the gas flow path. [5] In the methane production method described in any of [1] to [4] above, in the step of adding hydrogen to the mixed gas, the amount A of hydrogen gas added may satisfy the following formula (1): A = (z × c1 × x) + (z × c2 × y) ... (1) (In formula (1), A represents the amount of hydrogen gas added. z represents the flow rate of the mixed gas. c1 represents the oxygen concentration in the mixed gas. c2 represents the carbon dioxide concentration in the mixed gas. x represents 2.0. y represents a numerical value of 4.0 or more.) [6] In the methane production method according to any one of [1] to [5] above, the methane production apparatus may include a honeycomb substrate and a catalyst layer. The honeycomb substrate includes partition walls that form a plurality of cells. At least a portion of the plurality of cells includes the gas flow path. The catalyst layer is provided on the surface of the partition walls.The catalyst layer contains a methanation catalyst. The methanation catalyst may be capable of promoting a first reaction of reacting oxygen gas with hydrogen gas to produce water and a second reaction of reacting carbon dioxide gas with hydrogen gas to produce methane. [7] In the methane production method described in [6] above, the thermal conductivity of the honeycomb substrate may be 8 W / m·K or more. [8] In the methane production method described in any one of [1] to [7] above, the methanation catalyst may contain a transition metal as an active component. [9] In the methane production method described in [8] above, the transition metal may include Co, Fe, Pt, Ru, Rh, Pd, Ni, Cu, Ag, Au, Ir, or a combination thereof.

[10] In the methane production method described in [8] or [9] above, the transition metal may include Ni.

[11] In the method for producing methane according to any one of [8] to

[10] above, the methanation catalyst may further contain a carrier supporting the transition metal. The carrier may contain cerium oxide, silicon oxide, zirconium oxide, yttrium oxide, aluminum oxide, or a composite oxide thereof.

[12] In the method for producing methane according to

[11] above, the carrier may contain cerium oxide.

[0006] According to an embodiment of the present invention, a method for producing methane that can efficiently produce methane and is highly safe can be realized.

[0007] FIG. 1 is a process flow diagram illustrating a methane production method according to one embodiment of the present invention. FIG. 2 is a process flow diagram illustrating a hydrogenation step included in the methane production method of FIG. 1. FIG. 3 is a process flow diagram illustrating a reaction step included in the methane production method of FIG. 1. FIG. 4 is a process flow diagram illustrating an abnormal shutdown step included in the methane production method of FIG. 1. FIG. 5 is a process flow diagram illustrating a normal shutdown step included in the methane production method of FIG. 1. FIG. 6 is a schematic configuration diagram of a methane production apparatus used in the methane production method according to one embodiment of the present invention. FIG. 7 is a schematic perspective view of a honeycomb structure provided in the methane production apparatus of FIG. 6. FIG. 8 is a schematic cross-sectional view of the honeycomb structure of FIG. 7. FIG. 9 is a schematic configuration diagram of a methane production system in which the methane production method according to one embodiment of the present invention can be implemented.

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In addition, in order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiment, but these are merely examples and do not limit the interpretation of the present invention.

[0009] A. Overview of Methane Production Method A methane production method according to one embodiment of the present invention is capable of producing methane from a feed gas containing carbon dioxide gas, oxygen gas, and hydrogen gas, and includes a hydrogenation step and a reaction step. In the hydrogenation step, hydrogen gas is added to a mixed gas containing carbon dioxide gas and oxygen gas to prepare a feed gas. In the reaction step, the feed gas prepared in the hydrogenation step is supplied to a gas flow path of a methane production apparatus. As a result, a first reaction represented by the following formula (I) and a second reaction represented by the following formula (II) can each proceed in the gas flow path of the methane production apparatus. O ２ +2H ２ →2H ２ O...(I) CO ２ +4H ２ →CH ４ +2H ２O... (II) The first reaction is a combustion reaction of hydrogen gas, in which oxygen and hydrogen react to produce water. The second reaction is a methanation reaction of carbon dioxide gas, in which carbon dioxide and hydrogen react to produce methane. Because both the first and second reactions are exothermic, the generated heat (heat of reaction) can be effectively utilized to promote and continue these reactions. Therefore, methane gas can be efficiently produced in the reaction process while saving energy, resulting in efficient methane production. Furthermore, in this methane production method, the addition of hydrogen gas to the mixed gas is stopped when the oxygen concentration in the feed gas is 5% by volume or more and the temperature in the gas flow path exceeds 450°C (hereinafter referred to as the first stop condition). This prevents the feed gas supplied to the gas flow path of the methane production apparatus from becoming an explosive mixture and prevents explosions in the gas flow path. As a result, the safety of the methane production method can be improved. Therefore, a methane production method that can efficiently produce methane and is highly safe can be realized. Such a methane production method can be suitably applied to the continuous industrial production of methane.

[0010] The mixed gas is typically exhaust gas emitted from various industrial products or industrial facilities (hereinafter referred to as "industrial products / facilities"). Examples of industrial products / facilities include combustion equipment, thermal power plants, and factories. The composition of the mixed gas emitted from such industrial products / facilities may change over time. Therefore, if the oxygen concentration in the mixed gas increases, there is a risk that the mixed gas will become explosive when hydrogen gas is added to the mixed gas. In contrast, in one embodiment, the addition of hydrogen gas to the mixed gas is stopped when the first stop condition described above is satisfied, thereby ensuring the safety of the methane production method even when exhaust gas from industrial products / facilities is used.

[0011] In one embodiment, the methane production method includes an exhaust gas oxygen concentration measuring step and an exhaust gas hydrogen concentration measuring step. In the exhaust gas oxygen concentration measuring step, the oxygen concentration in the exhaust gas discharged from a gas flow path of the methane production apparatus is measured. In the exhaust gas hydrogen concentration measuring step, the hydrogen concentration in the exhaust gas is measured. In the methane production method, the addition of hydrogen gas to the mixed gas is stopped when the oxygen concentration in the exhaust gas is 5% by volume or more and the hydrogen concentration is 4% by volume or more (hereinafter referred to as the second stop condition). This can prevent the exhaust gas from becoming an explosive mixture, further improving the safety of the methane production method.

[0012] B. Details of the Methane Production Method Next, details of the methane production method according to one embodiment will be described with reference to Figures 1 to 5. As shown in Figure 1, in one embodiment, the methane production method includes the above-mentioned hydrogenation step (S1), the above-mentioned reaction step (S2), a stop determination step (S3), and a normal stop step (S4).

[0013] B-1. Hydrogen Addition Process As shown in Figure 2, the hydrogen addition process typically includes a mixed gas flow rate measurement process (S1-1), a mixed gas oxygen concentration measurement process (S1-2), a mixed gas carbon dioxide concentration measurement process (S1-3), a hydrogen gas addition amount calculation process (S1-4), a gas flow path initial temperature measurement process (S1-5), and a hydrogen gas addition start determination process (S1-6). The mixed gas flow rate measurement process, oxygen concentration measurement process, and carbon dioxide concentration measurement process are typically performed before the hydrogen gas addition amount calculation process. Furthermore, the gas flow path initial temperature measurement process and hydrogen gas addition start determination process are typically performed after the hydrogen gas addition amount calculation process.

[0014] B-1-1. Mixed gas flow rate measurement step (S1-1) A mixed gas containing carbon dioxide gas and oxygen gas is typically discharged from the above-mentioned industrial products and facilities and then transported toward the gas flow path of the methane production equipment. In the mixed gas flow rate measurement step, the flow rate z of the mixed gas [unit: m ３ / hr] is measured by any suitable method.

[0015] The mixed gas flow rate measurement process may be performed before the mixed gas oxygen concentration measurement process and carbon dioxide concentration measurement process, after the mixed gas oxygen concentration measurement process and carbon dioxide concentration measurement process, or between the mixed gas oxygen concentration measurement process and the carbon dioxide concentration measurement process.

[0016] In the illustrated example, the step of measuring the flow rate of the mixed gas is performed before the step of measuring the oxygen concentration and the step of measuring the carbon dioxide concentration of the mixed gas.

[0017] The flow rate z of the mixed gas can be measured using, for example, a thermal flow meter, a differential pressure flow meter, or a Coriolis flow meter. The temperature of the mixed gas is, for example, 25°C to 500°C, and preferably 50°C to 300°C.

[0018] B-1-2. Oxygen concentration measurement step of mixed gas (S1-2) In the oxygen concentration measurement step of mixed gas, the oxygen concentration c1 [unit: vol%] in the mixed gas is measured by any appropriate method. The oxygen concentration measurement step of mixed gas may be performed before or after the carbon dioxide concentration measurement step of mixed gas.

[0019] In the illustrated example, the oxygen concentration measurement step of the mixed gas is performed after the flow rate measurement step of the mixed gas and before the carbon dioxide concentration measurement step of the mixed gas. The first reaction (combustion reaction of hydrogen gas) shown in formula (I) above typically proceeds before the second reaction (methanation reaction of carbon dioxide gas) shown in formula (II). In one embodiment, the second reaction (methanation reaction of carbon dioxide gas) shown in formula (II) above proceeds after the completion of the first reaction (combustion reaction of hydrogen gas) shown in formula (I). Therefore, if the oxygen concentration c1 in the mixed gas is measured before the carbon dioxide concentration c2, the amount of hydrogen gas required for the first reaction (combustion reaction of hydrogen gas) can be accurately calculated from the oxygen concentration c1 in the hydrogen gas addition amount calculation step. As a result, in the reaction step, the first reaction (combustion reaction of hydrogen gas) can be completed early, and sufficient reaction time can be ensured for the second reaction (methanation reaction of carbon dioxide gas).

[0020] The oxygen concentration c1 in the mixed gas may be measured by, for example, a zirconia method, a laser method, a porcelain method, or an electrode method. The oxygen concentration c1 in the mixed gas is, for example, 0.5% to 5.0% by volume, and preferably 1.0% to 4.0% by volume.

[0021] B-1-3. Step of measuring carbon dioxide concentration of mixed gas (S1-3) In the step of measuring carbon dioxide concentration of mixed gas, the carbon dioxide concentration c2 [unit: vol%] in the mixed gas is measured by any appropriate method. In the illustrated example, the step of measuring carbon dioxide concentration of mixed gas is performed after the step of measuring oxygen concentration of mixed gas and before the step of calculating the amount of added hydrogen gas.

[0022] The carbon dioxide concentration c2 in the mixed gas is, for example, 0.1% by volume to 20% by volume, and preferably 1.0% by volume to 15% by volume, by non-dispersive infrared absorption, etc.

[0023] B-1-4. Hydrogen Gas Addition Amount Calculation Step (S1-4) In one embodiment, in the hydrogen addition step, the amount of hydrogen gas added A [unit: m ] to the mixed gas is calculated from the following formula (1) using the flow rate z measured in the flow rate measurement step, the oxygen concentration c1 measured in the oxygen concentration measurement step, and the carbon dioxide concentration c2 measured in the carbon dioxide concentration measurement step. ３ In addition, in the hydrogen gas addition amount calculation step, the oxygen concentration c3 and hydrogen concentration c4 in the source gas are calculated together with the hydrogen addition amount A.

[0024] A = {z × (c1 / 100) × x} + {z × (c2 / 100) × y} (1) (In formula (1), A is the amount of hydrogen gas added [unit: m ３ / hr], z is the flow rate of the mixed gas [unit: m ３ / hr]. c1 represents the oxygen concentration in the mixed gas [unit: volume %]. c2 represents the carbon dioxide concentration in the mixed gas [unit: volume %]. x represents 2.0. y represents a value of 4.0 or more.) According to this method, the amount of hydrogen gas added to the mixed gas is adjusted to satisfy the above formula (1), so even if the composition of the mixed gas fluctuates, an appropriate amount of hydrogen gas according to the composition of the mixed gas can be added to the mixed gas. Therefore, in the reaction process, the first reaction (combustion reaction of hydrogen) represented by the above formula (I) and the second reaction (methanation reaction of carbon dioxide) represented by the following formula (II) can each proceed smoothly.

[0025] In the above formula (1), y is, for example, 10.0 or less, preferably 7.0 or less, and more preferably 5.0 or less.

[0026] B-1-5. Gas Flow Path Initial Temperature Measurement Step (S1-5) In the gas flow path initial temperature measurement step, the initial temperature T1 [unit: °C] in the gas flow path of the methane production apparatus is measured by any appropriate method. The gas flow path initial temperature measurement step may be performed before the hydrogen gas addition start determination step, or may be performed after the hydrogen gas addition start determination step. In the illustrated example, the gas flow path initial temperature measurement step is performed before the hydrogen gas addition start determination step. Note that if the initial temperature T1 in the gas flow path is 300°C or lower, the methane production apparatus may be heated in advance to the reaction initiation temperature. The reaction initiation temperature is, for example, 100°C or higher, preferably 150°C or higher. On the other hand, the upper limit of the reaction initiation temperature is typically 400°C.

[0027] B-1-6. Hydrogen gas addition start determination step (S1-6) In the hydrogen gas addition start determination step, it is determined whether the initial temperature T1 is less than 450°C and the oxygen concentration c1 in the mixed gas is less than 5% by volume (hereinafter referred to as the addition start condition).

[0028] If the addition start condition is satisfied (yes in S1-6), hydrogen gas is supplied to the mixed gas flowing at the flow rate z at the same pressure as the mixed gas and at the calculated addition amount A. As a result, carbon dioxide gas, oxygen gas, and hydrogen gas are mixed in an appropriate ratio to prepare a source gas.

[0029] On the other hand, if the addition start conditions are not met (if the initial temperature T1 is 450°C or higher and / or the oxygen concentration c1 in the mixed gas is 5% by volume or higher, the answer is no in S1-6), the oxygen concentration measurement step (S1-2) of the mixed gas, the carbon dioxide concentration measurement step (S1-3) of the mixed gas, the hydrogen gas addition amount calculation step (S1-4), and the initial temperature measurement step (S1-5) of the gas flow path are repeated until the addition start conditions are met.

[0030] This completes the hydrogenation step.

[0031] B-2. Reaction Step As shown in FIG. 1, the reaction step (S2) is initiated upon completion of the hydrogenation step. In the reaction step, the raw material gas prepared in the hydrogenation step is supplied to a gas flow path of the methane production apparatus. As a result, the first reaction (hydrogen combustion reaction) and the second reaction (carbon dioxide methanation reaction) described above proceed within the gas flow path. Typically, the first reaction (hydrogen combustion reaction) proceeds prior to the second reaction (carbon dioxide methanation reaction). At this time, reaction heat is generated by the first reaction and is used to continue the first reaction and to start the second reaction (carbon dioxide methanation reaction). Once the second reaction starts, reaction heat is also generated by the second reaction. As a result, the first and second reactions are continued using the reaction heat, and the second reaction continues stably even after the first reaction is completed. Therefore, in one embodiment, external heating of the methane production apparatus is stopped.

[0032] When external heating of the methane production apparatus is stopped, the temperature (reaction temperature) in the gas flow passage of the methane production apparatus is typically maintained at 300°C or higher and lower than 450°C by the heat of reaction. Therefore, in one embodiment, the methane production apparatus is capable of methanation. When the reaction temperature is in this range, the second reaction (the methanation reaction of carbon dioxide) can be continued more stably.

[0033] As a result, carbon dioxide and hydrogen react in the gas flow path of the methane production apparatus to produce methane gas. Thereafter, methane-containing gas is continuously discharged as exhaust gas from the gas flow path of the methane production apparatus. The methane conversion rate in the reaction step is the percentage of the amount of methane gas contained in the exhaust gas relative to the amount of carbon dioxide contained in the raw material gas, and is, for example, 65% or more, preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more. Meanwhile, the methane conversion rate is, for example, 100% or less, or, for example, 95% or less. When the methane conversion rate is within this range, it is possible to suppress the remaining unreacted carbon dioxide gas in the exhaust gas. Therefore, it is possible to reduce the energy and cost required for the separation / purification step described below. The pressure range of the exhaust gas is, for example, the same as the reaction pressure range described above. The temperature range of the exhaust gas is, for example, the same as the reaction temperature range described above.

[0034] The exhaust gas may contain water vapor in addition to methane gas. The content of methane gas in the exhaust gas is, for example, 1% by volume or more, preferably 10% by volume or more.

[0035] In addition to methane gas and water vapor, the exhaust gas may contain raw material gases (oxygen, hydrogen, and / or carbon dioxide) remaining from the reaction process.

[0036] B-2-1. Methane Production Apparatus A methanation reaction catalyst is typically disposed in the gas flow path of a methane production apparatus. The methanation reaction catalyst can promote the first reaction and the second reaction described above.

[0037] The methanation catalyst contains any suitable metal element as an active component. The methanation catalyst may contain a metal element in a metallic state, a salt of the metal element, or an oxide of the metal element. The methanation catalyst preferably contains a metal element in a metallic state.

[0038] Examples of metal elements include alkali metals, alkaline earth metals, and transition metals, and preferably transition metals. Specific examples of transition metals include Co, Fe, Pt, Ru, Rh, Pd, Ni, Cu, Ag, Au, and Ir. These transition metals may be used alone or in combination. In one embodiment, the methanation catalyst contains Ni. When the methanation catalyst contains Ni, the first reaction (combustion reaction of hydrogen gas) and the second reaction (methanation reaction of carbon dioxide gas) can be further promoted.

[0039] The methanation catalyst may further contain a support in addition to the above-described active component. The support is capable of supporting the active component (typically a transition metal). The support is composed of any appropriate inorganic material depending on the application. Examples of inorganic materials include oxides, carbides, nitrides, sulfides, halides, hydrogen compounds, and hydroxides. The inorganic materials may be used alone or in combination.

[0040] Among such inorganic materials, oxides are preferred. Specific examples of oxides include cerium oxide, silicon oxide, zirconium oxide, yttrium oxide, aluminum oxide, and composite oxides thereof. In one embodiment, the support contains cerium oxide. When the above-mentioned active component (particularly Ni) is supported on a support containing such an oxide, the activity of the methanation reaction catalyst can be stably improved.

[0041] When the methanation catalyst contains an active component and a support, the content of the active component is 0.01 to 50 parts by mass, and preferably 1 to 20 parts by mass, per 100 parts by mass of the support. When the content of the active component is within this range, the activity of the methanation catalyst can be improved more stably.

[0042] The mass of the methanation catalyst per unit volume of the gas flow passage is, for example, 30 g / L or more, preferably 50 g / L or more, while the upper limit of the mass of the methanation catalyst per unit volume of the gas flow passage is typically 1000 g / L or less.

[0043] 6, in one embodiment, the methane production apparatus 1 has a flow-through structure. The methane production apparatus 1 includes a honeycomb structure 10, a case 17, and a thermometer 19.

[0044] As shown in FIGS. 7 and 8 , the honeycomb structure 10 includes a honeycomb substrate 11 and a catalyst layer 12. The honeycomb substrate 11 includes partition walls 13 that define a plurality of cells 14. At least some of the cells 14 include gas flow channels 15. In the illustrated example, all of the cells 14 include the gas flow channels 15. The catalyst layer 12 is provided on the surface of the partition walls 13. The catalyst layer 12 includes the methanation catalyst described above. With this configuration, a methane production apparatus can efficiently contact the raw material gas with the methanation catalyst in the catalyst layer when the raw material gas passes through the gas flow channels. This allows the first reaction (combustion reaction of hydrogen gas) and the second reaction (methanation reaction of carbon dioxide gas) to proceed smoothly, further improving the methane conversion rate.

[0045] The honeycomb substrate 11 has any appropriate shape (overall shape). Examples of the shape of the honeycomb substrate 11 include a cylindrical shape with a circular bottom, an elliptical cylindrical shape with an elliptical bottom, a rectangular prism with a polygonal bottom, and a cylindrical shape with an irregular bottom. In one embodiment, the honeycomb substrate 11 has a cylindrical shape. The outer diameter and length of the honeycomb substrate 11 can be appropriately set depending on the purpose.

[0046] In the illustrated example, the honeycomb substrate 11 includes outer walls 16 and partition walls 13 located inside the outer walls 16. The outer walls 16 and the partition walls 13 may be integrally formed or may be separate bodies. In the illustrated example, the outer walls 16 and the partition walls 13 are integrally formed.

[0047] The outer wall 16 has a cylindrical shape. The thickness of the outer wall 16 is set arbitrarily and appropriately. The thickness of the outer wall 16 is, for example, 1 mm to 10 mm, or, for example, 2 mm to 8 mm.

[0048] As described above, the partition walls 13 define a plurality of cells 14. The cells 14 extend in the longitudinal direction (axial direction) of the honeycomb substrate 11 from the first end face E1 (inlet end face) to the second end face E2 (outlet end face) of the honeycomb substrate 11 (see FIG. 8 ). The cells 14 have any appropriate shape in a cross section perpendicular to the longitudinal direction of the honeycomb substrate 11. Examples of the cross-sectional shape of the cells include a triangle, a rectangle, a pentagon, a polygon having hexagons or more, a circle, and an ellipse. The cross-sectional shapes and sizes of the cells may all be the same, or at least some of them may be different. Among such cross-sectional shapes of the cells, a rectangle is preferred, and a square or rectangle is more preferred.

[0049] The cell density of the honeycomb substrate 11 is, for example, 40 cpsi or more, preferably 50 cpsi or more, and more preferably 100 cpsi or more. On the other hand, the cell density of the honeycomb substrate 11 is, for example, 1000 cpsi or less, and preferably 900 cpsi or less. When the cell density is in this range, the raw material gas can be brought into contact with the catalyst layer more efficiently. In this specification, the "cell density of the honeycomb substrate" means the cell density of the cross section in the length direction (direction in which the cells extend) of the honeycomb substrate, and "cpsi" means the cell density of 6.4516 cm of the cross section. ２ This refers to the number of cells per square inch.

[0050] In the illustrated example, the partition walls 13 have first partition walls 13a and second partition walls 13b that are perpendicular to each other, and the first partition walls 13a and the second partition walls 13b define a plurality of cells 14. The cross-sectional shape of the cells 14 is quadrangular except for the portions where the first partition walls 13a and the second partition walls 13b contact the outer wall 16. The configuration of the partition walls is not limited to the above-described partition walls 13. The partition walls may have first partition walls extending in the radial direction and second partition walls extending in the circumferential direction, which define a plurality of cells.

[0051] The thickness of the partition walls 13 can be set arbitrarily and appropriately. The thickness of the partition walls 13 is typically thinner than the thickness of the outer walls 16. The thickness of the partition walls 13 is, for example, 0.0508 mm or more, preferably 0.0635 mm or more. On the other hand, the thickness of the partition walls 13 is, for example, 1.52 mm or less, preferably 1.27 mm or less. When the thickness of the partition walls is in this range, the mechanical strength of the honeycomb substrate can be sufficient, and the cell density can be adjusted to the above-mentioned range. The thickness of the partition walls is measured, for example, by cross-sectional observation using a scanning electron microscope (SEM).

[0052] The partition walls 13 may or may not have pores. The porosity of the partition walls 13 can be appropriately set depending on the purpose. The porosity of the partition walls 13 is, for example, 70% or less, and preferably 65% ​​or less. On the other hand, the porosity of the partition walls 13 is, for example, 0% or more. The porosity is measured by, for example, mercury intrusion porosimetry.

[0053] The bulk density of the partition walls 13 can be appropriately set depending on the purpose. The bulk density of the partition walls 13 is, for example, 1.0 g / cm ３ ~3.0 g / cm ３ and preferably 2.0 g / cm ３ ~3.0 g / cm ３ The bulk density is measured by, for example, the Archimedes method.

[0054] Examples of materials that can be used to form the honeycomb substrate 11 include ceramic materials. Specific examples of ceramic materials include zirconia-based materials, alumina-titanium carbide-based composite materials, Si-SiC-based composite materials, aluminum nitride, aluminum oxide, silicon nitride, silicon carbide, zirconia, cordierite, and mullite. These ceramic materials can be used alone or in combination. Of these ceramic materials, cordierite and Si-SiC-based composite materials are preferred.

[0055] The thermal conductivity of such a honeycomb substrate 11 is, for example, 1 W / m·K or more, preferably 5 W / m·K or more, and more preferably 8 W / m·K or more. If the thermal conductivity of the honeycomb substrate (each of the partition walls and outer walls) is equal to or greater than this lower limit, the occurrence of local high-temperature areas (hot spots) in the honeycomb structure during the reaction step can be suppressed, and the safety of the methane production method can be further improved. On the other hand, the upper limit of the thermal conductivity of the honeycomb substrate 11 is not limited, but is typically 1000 W / m·K. The thermal conductivity is measured, for example, using an optical alternating current thermal diffusivity measuring device.

[0056] The catalyst layer 12 is formed on the surface of the partition wall 13. In the methane production apparatus 1, gas flow paths 15 are formed in portions (typically central portions) of the cross section of the cells 14 where the catalyst layer 12 is not formed. The catalyst layer 12 may be formed on the entire inner surface of the partition wall 13 (i.e., so as to surround the gas flow path 15) as in the illustrated example, or may be formed on a portion of the surface of the partition wall. When the catalyst layer 12 is formed on the entire inner surface of the partition wall 13, the methane conversion rate can be improved more stably.

[0057] The gas flow channels 15 are spaces formed inside the cells 14, and extend from a first end face E1 (inlet end face) to a second end face E2 (outlet end face) similarly to the cells 14 (see FIG. 8 ). The cross-sectional shape of the gas flow channels 15 may be the same as that of the cells 14 described above, preferably a quadrangle, and more preferably a square or rectangle. The cross-sectional shapes and sizes of the gas flow channels 15 may all be the same, or at least some may be different.

[0058] As described above, the catalyst layer 12 contains a methanation catalyst. The methanation catalyst contained in the catalyst layer 12 may have any appropriate shape. The methanation catalyst is typically in a particulate form. Hereinafter, particulate methanation catalysts may be referred to as catalyst particles. In one embodiment, the catalyst layer 12 contains aggregates formed by aggregating a plurality of catalyst particles. The aggregates of the plurality of catalyst particles may form mesopores in the catalyst layer 12.

[0059] The content of the methanation catalyst in the catalyst layer 12 is, for example, 10% by mass to 100% by mass, and preferably 50% by mass to 100% by mass. When the content of the methanation catalyst is within this range, the mass of the methanation catalyst per unit volume of the gas flow channel can be stably adjusted within the above range.

[0060] The catalyst layer 12 may contain an additive in addition to the methanation catalyst. Examples of the additive include a filler, a binder, and a heat transfer material. The additives may be used alone or in combination. The additive is added in an amount of, for example, 0.1 to 90 parts by mass, and preferably 0.1 to 50 parts by mass, per 100 parts by mass of the methanation catalyst.

[0061] The thickness of the catalyst layer 12 is, for example, 0.1 μm to 3000 μm, and preferably 20 μm to 300 μm. The average pore diameter of the catalyst layer 12 is, for example, 0.01 μm to 30 μm, and preferably 1 μm to 20 μm. The porosity of the catalyst layer 12 is, for example, 1% to 80%, and preferably 2% to 50%.

[0062] Such a honeycomb structure 10 is typically grounded, thereby removing static electricity from the honeycomb structure.

[0063] As shown in Fig. 6, the case 17 houses the honeycomb structure 10. In the illustrated example, the case 17 has a cylindrical shape extending in the same direction as the gas flow path 15. One end of the case 17 is configured as an inlet 171, and the other end of the case 17 is configured as an outlet 172. In other words, the case 17 has the inlet 171 and the outlet 172. In the supply direction of the raw material gas to the gas flow path, the inlet 171 is located at the upstream end of the case 17, and the outlet 172 is located at the downstream end of the case 17.

[0064] In one embodiment, the case 17 has a vent 18. The vent 18 is connected to the upstream end of the gas flow path 15 in the supply direction of the raw material gas. The vent 18 is capable of releasing pressure within the gas flow path 15. The first reaction (hydrogen combustion reaction) described above can proceed in the upstream portion of the gas flow path. Therefore, if the vent is connected to the upstream end of the gas flow path, the pressure within the gas flow path can be smoothly released when the first reaction (hydrogen combustion reaction) proceeds explosively. As a result, the safety of the methane production method can be further improved.

[0065] In one embodiment, the explosion vent 18 is provided in the side wall of the case 17. The explosion vent 18 is typically an opening formed in the side wall of the case 17. The explosion vent 18 is located between the inlet 171 and the honeycomb structure 10 in the direction in which the gas flow path 15 extends.

[0066] The thermometer 19 is capable of measuring the temperature inside the gas flow path 15 of the methane production apparatus 1. More specifically, the thermometer 19 is capable of measuring the temperature of the exhaust gas discharged from the gas flow path 15 as the temperature inside the gas flow path 15. At least a part of the thermometer 19 is typically located in the internal space of the case 17. In the illustrated example, at least a part of the thermometer 19 is located between the honeycomb structure 10 and the outlet 172 in the extension direction of the gas flow path. The thermometer 19 may have any appropriate configuration. An example of the thermometer 19 is a temperature sensor.

[0067] B-2-2. Gas Flow Channel Reaction Temperature Measurement Step (S2-1) As shown in Fig. 3, in one embodiment, the reaction step includes a gas flow channel reaction temperature measurement step (S2-1), a first stop determination step (S2-2), an exhaust gas oxygen concentration measurement step (S2-3), an exhaust gas hydrogen concentration measurement step (S2-4), a second stop determination step (S2-5), and an emergency stop step (S5).

[0068] In the reaction step, first, a gas flow path reaction temperature measurement step is carried out. In the gas flow path reaction temperature measurement step, a reaction temperature T2 (unit: ° C.) in the gas flow path of the methane production apparatus is measured by any appropriate method. Typically, the reaction temperature T2 in the gas flow path 15 is measured by a thermometer 19 (see FIG. 6 ).

[0069] B-2-3. First stop determination step (S2-2) Next, it is determined whether the above-mentioned first stop condition (oxygen concentration c3 in the raw material gas is 5% by volume or more and reaction temperature T2 in the gas flow path exceeds 450°C) is met.

[0070] More specifically, if the oxygen concentration c3 of the source gas calculated in the hydrogen gas addition amount calculation step is 5% by volume or more and the reaction temperature T2 in the gas flow path exceeds 450°C (no in S2-2), the first stop condition is met. In this case, an emergency stop step (S5) is performed. The emergency stop step will be described in detail later.

[0071] On the other hand, if at least one of the oxygen concentration c3 of the raw material gas being less than 5% by volume and the reaction temperature T2 in the gas flow path being 450°C or less is satisfied (yes in S2-2), the first stop condition is not met, and the process proceeds to the oxygen concentration measurement step (S2-3) in the exhaust gas.

[0072] B-2-4. Exhaust Gas Oxygen Concentration Measurement Step (S2-3) In the exhaust gas oxygen concentration measurement step, the exhaust gas oxygen concentration c5 [unit: volume %] is measured by any appropriate method. Examples of methods for measuring the oxygen concentration c5 include a zirconia method, a laser analysis method, a porcelain method, and an electrode method. The exhaust gas oxygen concentration measurement step may be performed before the exhaust gas hydrogen concentration measurement step, or may be performed after the exhaust gas hydrogen concentration measurement step. In the illustrated example, the exhaust gas oxygen concentration measurement step is performed after the first stop determination step and before the exhaust gas hydrogen concentration measurement step.

[0073] B-2-5. Exhaust Gas Hydrogen Concentration Measurement Step (S2-4) In the exhaust gas hydrogen concentration measurement step, the hydrogen concentration c6 [unit: vol%] in the exhaust gas is measured by any appropriate method. Examples of methods for measuring the hydrogen concentration c6 include catalytic combustion, semiconductor, electrochemical, and infrared absorption spectroscopy. In the illustrated example, the exhaust gas hydrogen concentration measurement step is performed after the exhaust gas oxygen concentration measurement step and before the second stop determination step.

[0074] B-2-6. Second Shutdown Determination Step (S2-5) Next, it is determined whether the above-mentioned second shutdown condition (oxygen concentration c5 in the exhaust gas is 5% by volume or more and hydrogen concentration c6 is 4% by volume or more) is met.

[0075] More specifically, if the oxygen concentration c5 in the exhaust gas is 5% by volume or more and the hydrogen concentration c6 is 4% by volume or more (No in S2-5), the second stop condition is met. In this case, an emergency stop step (S5) is performed. The emergency stop step will be described in detail later.

[0076] On the other hand, if the oxygen concentration c5 of the exhaust gas is less than 5% by volume and / or the hydrogen concentration c6 of the exhaust gas is less than 4% by volume (yes in S2-5), the second stop condition is not met. In this case, the reaction process is completed.

[0077] B-3. ​​Emergency Shutdown Process (S5) As shown in Figure 4, in one embodiment, the emergency shutdown process includes, in this order, a hydrogen gas shutdown process (S5-1), a diluent gas supply process (S5-2), a gas flow path shutdown temperature measurement process (S5-3), a safety assessment process (S5-4), and a diluent gas shutdown process (S5-5).

[0078] In the hydrogen gas stopping step, the supply of hydrogen gas to the mixed gas is stopped. Next, in the dilution gas supplying step, a dilution gas is supplied to the gas flow path of the methane production apparatus. Examples of the dilution gas include air and nitrogen. Next, in the gas flow path stopping temperature measuring step, the stopping temperature T3 [unit: °C] in the gas flow path of the methane production apparatus is measured by any appropriate method. Typically, the stopping temperature T3 of the gas flow path 15 is measured by a thermometer 19 (see FIG. 6 ).

[0079] Thereafter, in a safety determination step, it is determined whether the stop temperature T3 in the gas flow path is less than 450°C. If the stop temperature T3 is 450°C or higher (no in S5-4), the supply of diluent gas to the gas flow path is maintained, and the stop temperature measurement step for the gas flow path and the safety determination step are repeated until the stop temperature T3 becomes less than 450°C. On the other hand, if the stop temperature T3 is less than 450°C (yes in S5-4), the process proceeds to a diluent gas stop step, in which the supply of diluent gas to the gas flow path is stopped. This completes the emergency shutdown step and the reaction step (see FIG. 3).

[0080] B-4. Stop Determination Step (S3) As shown in Fig. 1, when the reaction step is completed, the process proceeds to the stop determination step. In the stop determination step, the presence or absence of a stop signal is confirmed, and if there is no stop signal (no in S3), the hydrogenation step and the reaction step are repeated. On the other hand, if there is a stop signal (yes in S3), the process proceeds to the normal stop step (S4).

[0081] B-5. Normal Shutdown Process (S4) As shown in Fig. 5, in one embodiment, the normal shutdown process (S4) includes, in this order, an abnormal shutdown determination process (S4-1), a hydrogen gas shutdown process (S4-2), a stabilization process (S4-3), and a mixed gas shutdown process (S4-4).

[0082] In the abnormal shutdown determination step, first, it is determined whether the abnormal shutdown step has been performed. If the abnormal shutdown step has not been performed (yes in S4-1), the process proceeds to a hydrogen gas shutdown step, in which the supply of hydrogen gas to the mixed gas is stopped, and this is maintained until the time X that has elapsed since the hydrogen gas supply was stopped in the stabilization step reaches or exceeds a specified time (no in S4-3). Furthermore, if the abnormal shutdown step has been performed (no in S4-1), or if the time X that has elapsed since the hydrogen gas supply was stopped in the stabilization step reaches or exceeds a specified time (yes in S4-3), the process proceeds to a mixed gas shutdown step, in which the supply of the mixed gas is stopped. This completes the methane production method.

[0083] B-6. Separation / Purification Step In one embodiment, the methane production method further includes a separation / purification step. The separation / purification step is typically carried out together with the reaction step. In the separation / purification step, methane is separated and purified from the exhaust gas discharged from the gas flow path by any appropriate method. Examples of methods for separating and purifying methane include membrane separation using a methane separation membrane and pressure swing adsorption (PSA) using an adsorbent. The separation and purification methods may be carried out alone or in combination of two or more. Among the methods for separating and purifying methane, membrane separation is preferred. This makes it possible to recover high-purity methane. The methane recovered in the separation / purification step may be in a gaseous state or a liquid state. The purity of the methane is, for example, 50% to 100% by volume.

[0084] C. Methane Production System Next, a methane production system 100 capable of implementing a methane production method according to one embodiment will be described with reference to Figure 9. The methane production system 100 includes an industrial product / facility 2, a mixed gas supply unit 3, a hydrogen addition unit 4, a dilution gas supply unit 7, a methane production apparatus 1, an exhaust gas conveyance unit 6, a methane recovery unit 5, and a control unit 9.

[0085] C-1. Industrial Product / Facility The industrial product / facility 2 is any of various industrial products or industrial facilities that discharge a mixed gas containing carbon dioxide gas and oxygen gas. The industrial product / facility 2 is not particularly limited. The industrial product / facility 2 typically has an exhaust port that discharges the mixed gas.

[0086] C-2. Mixed Gas Supply Unit In one embodiment, the mixed gas supply unit 3 includes a first gas supply line 31. The first gas supply line 31 is typically a pipe for supplying the mixed gas discharged from the industrial product / facility 2 to the methane production apparatus 1. The upstream end of the first gas supply line 31 in the supply direction of the raw material gas is connected to the industrial product / facility 2 so as to communicate with the exhaust port. The downstream end of the first gas supply line 31 in the supply direction of the mixed gas is connected to the methane production apparatus 1 so as to communicate with the inlet 171 (see FIG. 6 ).

[0087] In one embodiment, the first gas supply line 31 is provided with a flow meter 32 , a first oxygen concentration meter 33 , a carbon dioxide concentration meter 34 , and a pressure meter 35 .

[0088] The flow meter 32 is capable of performing the mixed gas flow rate measuring step (S1-1) described above. The flow meter 32 is capable of measuring the flow rate z of the mixed gas passing through the first gas supply line 31. Typical examples of the flow meter 32 include a thermal flow meter, a differential pressure flow meter, and a Coriolis flow meter.

[0089] The first oxygen concentration meter 33 is capable of performing the mixed gas oxygen concentration measuring step (S1-2) described above. The first oxygen concentration meter 33 is capable of measuring the oxygen concentration c1 in the mixed gas passing through the first gas supply line 31. In the illustrated example, the first oxygen concentration meter 33 is provided on the first gas supply line 31 on the opposite side of the flow meter 32 from the industrial product / facility 2. Representative types of the first oxygen concentration meter 33 include zirconia type, laser type, porcelain type, and electrode type.

[0090] The carbon dioxide concentration meter 34 is capable of carrying out the above-described step (S1-3) of measuring the carbon dioxide concentration of the mixed gas. The carbon dioxide concentration meter 34 is capable of measuring the carbon dioxide concentration c2 in the mixed gas passing through the first gas supply line 31. In the illustrated example, the carbon dioxide concentration meter 34 is provided on the first gas supply line 31 on the opposite side of the flow meter 32 with respect to the oxygen concentration meter 33. A representative example of the carbon dioxide concentration meter 34 is a gas sensor that uses a non-dispersive infrared absorption method.

[0091] The pressure gauge 35 can measure the pressure of the source gas passing through the first gas supply line 31. In the illustrated example, the pressure gauge 35 is provided on the first gas supply line 31 on the opposite side of the carbon dioxide concentration meter 34 from the first oxygen concentration meter 33. Representative examples of the pressure gauge 35 include an absolute pressure gauge, a differential pressure gauge, and a Bourdon tube pressure gauge.

[0092] In the illustrated example, the mixed gas supply unit 3 further includes a flashback valve 36. If the mixed gas supply unit includes a flashback valve, when an explosion occurs in the gas flow path, the explosion can be prevented from spreading upstream of the flashback valve. The flashback valve 36 is provided in the first gas supply line 31. In the illustrated example, the flashback valve 36 is provided in the first gas supply line 31, between the pressure gauge 35 and the methane production apparatus 1. Typical examples of the flashback valve 36 include a dry safety device and a water-sealed safety device.

[0093] C-3. Hydrogen Addition Unit In one embodiment, the hydrogen addition unit 4 includes a hydrogen production unit 42 , a second gas supply line 41 , and a pump 43 .

[0094] The hydrogen production unit 42 is capable of producing hydrogen gas. Examples of the hydrogen production unit 42 include a water electrolysis device that produces hydrogen gas by electrolyzing water, an ammonia decomposition device that produces hydrogen gas by cracking ammonia, and a dehydrogenation device that releases hydrogen gas from a liquid organic carrier.

[0095] The second gas supply line 41 is typically a pipe for supplying hydrogen gas produced in the hydrogen production unit 42 to the first gas supply line 31. An upstream end of the second gas supply line 41 in the supply direction of hydrogen gas is connected to the hydrogen production unit 42. A downstream end of the second gas supply line 41 in the supply direction of hydrogen gas is connected to the gas supply line 31. In the illustrated example, the downstream end of the second gas supply line 41 is connected to a portion of the gas supply line 31 between the carbon dioxide concentration meter 34 and the pressure gauge 35.

[0096] The pump 43 is provided on the second gas supply line 41. The pump 43 is capable of adjusting the flow rate of the hydrogen gas passing through the second gas supply line 41. The pump 43 has any appropriate configuration.

[0097] C-4. Dilution Gas Supply Unit The dilution gas supply unit 7 is capable of carrying out the above-described dilution gas supply step (S5-2) and dilution gas stop step (S5-5). The dilution gas supply unit 7 is configured to be able to supply dilution gas to the gas flow path 15 of the methane production apparatus 1. The dilution gas supply unit 7 has any appropriate configuration. In one embodiment, the dilution gas supply unit 7 is connected to the first gas supply line 31. In the illustrated example, the dilution gas supply unit 7 is connected to a portion of the first gas supply line 31 between the flashback valve 36 and the methane production apparatus 1.

[0098] C-5. Methane Production Apparatus In one embodiment, the methane production apparatus 1 includes the above-described honeycomb structure 10, the above-described case 17, and the above-described thermometer 19. Therefore, a description of the methane production apparatus 1 will be omitted. The thermometer 19 can perform the above-described gas flow path initial temperature measurement step (S1-5), reaction temperature measurement step (S2-1), and stop temperature measurement step (S5-3).

[0099] C-6. Exhaust Gas Transporting Section In one embodiment, the exhaust gas transporting section 6 includes a connecting line 61 , a second oxygen concentration meter 62 , and a hydrogen concentration meter 63 .

[0100] The connecting line 61 is typically a pipe for transporting the exhaust gas (methane-containing gas) discharged from the methane production apparatus 1 to the methane recovery section 5. The upstream end of the connecting line 61 in the supply direction of the methane-containing gas is connected to the methane production apparatus 1 so as to communicate with the outlet 172 (see FIG. 6 ). The downstream end of the connecting line 61 in the supply direction of the methane-containing gas is connected to the methane separation device 51, which will be described later.

[0101] The second oxygen concentration meter 62 is capable of carrying out the above-described exhaust gas oxygen concentration measuring step (S2-3). The second oxygen concentration meter 62 is capable of measuring the oxygen concentration c5 in the exhaust gas passing through the connecting line 61. Representative types of the second oxygen concentration meter 62 include zirconia type, laser type, porcelain type, and electrode type.

[0102] The hydrogen concentration meter 63 is capable of carrying out the above-described hydrogen concentration measurement step (S2-4) of the exhaust gas. The hydrogen concentration meter 63 is capable of measuring the hydrogen concentration c6 in the exhaust gas passing through the connecting line 61. In the illustrated example, the hydrogen concentration meter 63 is located on the connecting line 61 on the opposite side of the methane production apparatus 1 from the second oxygen concentration meter 62. Representative hydrogen concentration meters 63 include catalytic combustion type, semiconductor type, electrochemical type, and infrared absorption spectrum type.

[0103] C-7. Methane Recovery Section The methane recovery section 5 is capable of carrying out the separation / purification process described above. In one embodiment, the methane recovery section 5 includes a methane separation device 51, a methane recovery line 52, and a discharge line 53. The methane separation device 51 is capable of separating methane from a methane-containing gas. Examples of the methane separation device 51 include a membrane separator equipped with a methane separation membrane and a PSA gas adsorption device. The methane recovery line 52 is typically a pipe through which the methane separated in the methane separation device 51 can pass. The upstream end of the methane recovery line 52 in the direction in which methane passes is connected to the methane separation device 51. The downstream end of the methane recovery line 52 in the direction in which methane passes is typically connected to a methane storage tank (not shown). The discharge line 53 is typically a pipe for discharging the residual gas after methane separation. The upstream end of the discharge line 53 in the direction in which the residual gas is discharged is connected to the methane separation device 51.

[0104] C-8. Control Unit In one embodiment, the control unit 9 is capable of performing the above-described hydrogen gas addition amount calculation step (S1-4), hydrogen gas addition start determination step (S1-6), first stop determination step (S2-2), second stop determination step (S2-5), abnormal stop occurrence determination step (S4-1), and safety determination step (S5-4). The control unit 9 is capable of controlling the operation of the methane production system 100. The control unit 9 includes, for example, a central processing unit (CPU), ROM, and RAM. In one embodiment, the control unit 9 is communicatively connected to the flow meter 32, the first oxygen concentration meter 33, the carbon dioxide concentration meter 34, the pump 43 of the hydrogen addition unit 4, the second oxygen concentration meter 62, the hydrogen concentration meter 63, and the thermometer 19 of the methane production apparatus 1.

[0105] Therefore, the control unit 9 can receive the flow rate z of the mixed gas from the flow path meter 32, the oxygen concentration c1 of the mixed gas from the oxygen concentration meter 33, and the carbon dioxide concentration c2 of the mixed gas from the carbon dioxide concentration meter 34. In the illustrated example, when the control unit 9 receives the flow rate z, oxygen concentration c1, and carbon dioxide concentration c2 of the mixed gas, it calculates the amount A of hydrogen gas to be added based on the above-described formula (1). Thereafter, the control unit 9 adjusts the output of the pump 43 to adjust the flow rate of hydrogen gas flowing through the second gas supply line 41 to the amount A of addition. As a result, hydrogen gas is supplied at the amount A of addition to the mixed gas flowing through the first gas supply line 31.

[0106] The control unit 9 can also receive the temperature of the gas flow path 15 from the thermometer 19, can receive the oxygen concentration c5 in the exhaust gas from the second oxygen concentration meter 62, and can receive the hydrogen concentration c6 from the hydrogen concentration meter 63. In the illustrated example, the control unit 9 receives the temperature, oxygen concentration c5, and hydrogen concentration c6 of the gas flow path 15, and can perform the first stop determination step and the second stop determination step described above.

[0107] The methane production method according to the embodiment of the present invention can be used for producing methane, and is particularly suitable for continuous production of methane using exhaust gas emitted from various industrial products or industrial facilities as a raw material.

[0108] REFERENCE SIGNS LIST 1 methane production device 11 honeycomb substrate 12 catalyst layer 13 partition wall 14 cell 15 gas flow path 12 partition wall 13 cell 14 gas flow path

Claims

1. A methane production method for producing methane from a feed gas containing carbon dioxide gas, oxygen gas, and hydrogen gas, comprising: a step of adding hydrogen gas to a mixed gas containing carbon dioxide gas and oxygen gas to prepare the feed gas; and a step of supplying the feed gas to a gas flow path of a methane production apparatus, wherein the addition of the hydrogen gas to the mixed gas is stopped when the oxygen concentration in the feed gas supplied to the gas flow path is 5% by volume or more and the temperature within the gas flow path exceeds 450°C.

2. The methane production method according to claim 1, further comprising the steps of: measuring the oxygen concentration in the exhaust gas discharged from the gas flow path; and measuring the hydrogen concentration in the exhaust gas, wherein the addition of the hydrogen gas to the mixed gas is stopped when the oxygen concentration in the exhaust gas is 5% by volume or more and the hydrogen concentration is 4% by volume or more.

3. The methane production method according to claim 1 or 2, wherein a dilution gas is supplied to the gas flow path after the addition of the hydrogen gas to the mixed gas is stopped.

4. A methane production method as described in claim 1 or 2, wherein the methane production apparatus has an explosion vent that communicates with the upstream end of the gas flow path in the supply direction of the raw material gas and is capable of releasing pressure within the gas flow path.

5. The methane production method according to claim 1 or 2, wherein in the step of adding hydrogen to the mixed gas, the amount A of hydrogen gas added satisfies the following formula (1): A = (z × c1 × x) + (z × c2 × y) (1) (In formula (1), A represents the amount of hydrogen gas added; z represents the flow rate of the mixed gas; c1 represents the oxygen concentration in the mixed gas; c2 represents the carbon dioxide concentration in the mixed gas; x represents 2.0; and y represents a value of 4.0 or more).

6. The methane production method according to claim 1 or 2, wherein the methane production apparatus comprises: a honeycomb substrate having partition walls that form a plurality of cells, at least some of the plurality of cells including the gas flow path; and a catalyst layer provided on the surface of the partition walls, the catalyst layer including a methanation reaction catalyst, wherein the methanation reaction catalyst is capable of promoting a first reaction of producing water by reacting oxygen with hydrogen, and a second reaction of producing methane by reacting carbon dioxide with hydrogen.

7. The methane production method according to claim 6, wherein the thermal conductivity of the honeycomb substrate is 8 W / m·K or more.

8. The method for producing methane according to claim 1 or 2, wherein the methanation catalyst contains a transition metal as an active component.

9. The method for producing methane according to claim 8, wherein the transition metal comprises Co, Fe, Pt, Ru, Rh, Pd, Ni, Cu, Ag, Au, Ir, or a combination thereof.

10. The method for producing methane according to claim 9, wherein the transition metal comprises Ni.

11. The method for producing methane according to claim 8, wherein the methanation catalyst further comprises a support that supports the transition metal, and the support comprises cerium oxide, silicon oxide, zirconium oxide, yttrium oxide, aluminum oxide, or a composite oxide thereof.

12. The method for producing methane according to claim 11, wherein the support comprises cerium oxide.

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