Combustion system

Abstract

Provided is a combustion system that makes it possible to use methane gas as fuel for a combustion device in an energy-saving manner. A combustion system according to one embodiment comprises a combustion device, a methane production device, a raw-material gas supply unit, a hydrogen gas supply unit, a product gas supply unit, and an oxygen gas supply unit. The combustion device is configured to combust methane. The methane production device is configured to promote a methane conversion reaction of carbon oxide. The raw-material gas supply unit is configured to supply a raw-material gas that contains carbon oxide gas and nitrogen gas to the methane production device. The hydrogen gas supply unit is configured to supply hydrogen gas to the methane production device. The product gas supply unit is configured to supply a reaction product gas that contains methane gas and nitrogen gas from the methane production device to the combustion device. The oxygen gas supply unit is configured to supply oxygen gas to the reaction product gas.

Description

Combustion system 【0001】 This invention relates to a combustion system. 【0002】 In recent years, from the perspective of reducing environmental impact, the recovery of carbon dioxide and its use as a raw material for carbon compounds has been considered. 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 the methanation reaction is started and continued by the heat, including the reaction heat from the catalytic combustion of hydrogen gas (see, for example, Patent Document 1). 【0003】 International Publication No. 2021 / 045101 【0004】 In methane production methods such as those described in Patent Document 1, a reaction product gas containing methane gas and other gaseous components is usually discharged from the reactor. Therefore, when methane gas is used for various purposes, it is separated from other gaseous components by separation methods such as membrane separation. Such methane gas is expected to be used as fuel for combustion devices. In this case, the methane gas is supplied to the combustion device together with air. However, in this method, since the methane gas is supplied to the combustion device after being separated from other gaseous components, there is room for improvement in energy saving for the entire combustion system. The main object of the present invention is to provide a combustion system that can utilize methane gas as fuel for a combustion device in an energy-saving manner. 【0005】[1] A combustion system according to one embodiment of the present invention comprises a combustion device, a methane production device, a raw material gas supply unit, a hydrogen gas supply unit, a product gas supply unit, and an oxygen gas supply unit. The combustion device is configured to burn methane. The methane production device is configured to carry out the methane conversion reaction of carbon oxide. The raw material gas supply unit is configured to supply a raw material gas containing carbon oxide gas and nitrogen gas to the methane production device. The hydrogen gas supply unit is configured to supply hydrogen gas to the methane production device. The methane production device discharges a reaction product gas. The reaction product gas contains methane gas and nitrogen gas. The product gas supply unit is configured to supply the reaction product gas from the methane production device to the combustion device. The oxygen gas supply unit is configured to supply oxygen gas to the reaction product gas. [2] In the combustion system described in [1] above, the combustion device may be configured to supply exhaust gas to the methane production device. [3] In the combustion system described in [1] or [2] above, the methane production apparatus is configured such that H in the methane conversion reaction ２ It may be configured to produce O. The above-mentioned product gas supply unit may include a separation unit. The separation unit separates H from the above-mentioned reaction product gas. ２ It is configured to separate O. [4] In the combustion system described in [3] above, the oxygen gas supply unit may be configured to supply oxygen gas to the reaction product gas between the separation unit and the combustion device. [5] In the combustion system described in [3] or [4] above, the product gas supply unit may further include a methane measuring instrument. The methane measuring instrument is configured to measure the concentration of methane gas in the reaction product gas. The combustion system may further include a control unit. The control unit is configured to receive measurement results from the methane measuring instrument. The control unit is configured to control the operation of the oxygen gas supply unit and to adjust the amount of oxygen gas supplied to the reaction product gas according to the measurement results from the methane measuring instrument. [6] In the combustion system described in any of [1] to [5] above, the hydrogen gas supply unit is H ２It may be provided with an H2O decomposition device. The H2O ２ decomposition device is configured to decompose H2O ２ into oxygen gas and hydrogen gas. The H2O ２ decomposition device is configured to discharge an oxygen-containing gas and a hydrogen-containing gas. The oxygen gas supply unit may be configured to supply the oxygen-containing gas from the H2O ２ decomposition device to the product gas supply unit. [7] In the combustion system according to [6] above, the hydrogen gas supply unit may be configured to supply the hydrogen-containing gas from the H2O ２ decomposition device to the methane production device. [8] In the combustion system according to [6] or [7] above, the content ratio of oxygen gas in the oxygen-containing gas may be 94% to 100% by volume. Also, the content ratio of hydrogen gas in the hydrogen-containing gas may be 96% to 100% by volume. 【0006】 According to an embodiment of the present invention, methane gas can be used as fuel for a combustion device with energy savings. 【0007】 FIG. 1 is a schematic configuration diagram of a combustion system according to one embodiment of the present invention. FIG. 2 is a schematic perspective view of a methane production device included in the combustion system of FIG. 1. FIG. 3 is a schematic cross-sectional view of the methane production device of FIG. 2. FIG. 4 is a schematic configuration diagram of a combustion system according to another embodiment of the present invention. 【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. Also, for the sake of clarity in the explanation, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the embodiments, but this is merely an example and does not limit the interpretation of the present invention. 【0009】A. Schematic diagram 1 of the combustion system is a schematic diagram of a combustion system according to one embodiment of the present invention. In one embodiment, the combustion system 100 includes a raw material gas supply unit 2, a hydrogen gas supply unit 3, a methane production device 1, a product gas supply unit 4, an oxygen gas supply unit 6, and a combustion device 5. The raw material gas supply unit 2 is configured to supply a raw material gas containing carbon oxide gas and nitrogen gas to the methane production device 1. The hydrogen gas supply unit 3 is configured to supply hydrogen gas to the methane production device 1. The methane production device 1 is configured to carry out the methane conversion reaction of carbon oxide and to discharge the reaction product gas. The reaction product gas contains methane gas and nitrogen gas. The product gas supply unit 4 is configured to supply the reaction product gas from the methane production device 1 to the combustion device 5. The oxygen gas supply unit 6 is configured to supply oxygen gas to the reaction product gas. The combustion device 5 is configured to burn methane. With this configuration, the raw material gas supply unit supplies raw material gas containing carbon oxide gas and nitrogen gas to the methane production unit, and the hydrogen gas supply unit supplies hydrogen gas to the methane production unit. As a result, the methane production unit can produce methane gas by reacting carbon oxide gas and hydrogen gas. On the other hand, nitrogen gas does not react substantially in the methane production unit. Therefore, the methane production unit discharges a reaction product gas containing methane gas and nitrogen gas. Oxygen gas is supplied to this reaction product gas from the oxygen gas supply unit, and a mixture of the reaction product gas and oxygen gas is supplied to the combustion unit. As a result, the methane gas is supplied to the combustion unit without being separated from the reaction product gas, and it reacts with oxygen gas and burns in the combustion unit. Consequently, in a combustion system according to one embodiment, methane gas can be used as fuel for the combustion unit in an energy-saving manner compared to a combustion system in which methane gas is separated before being supplied to the combustion unit. Furthermore, since the reaction product gas supplied to the combustion device contains nitrogen gas, conventional combustion devices that supply methane gas and air can be suitably adopted in the combustion system. 【0010】The raw material gas supply unit 2 is typically configured to supply a raw material gas containing carbon dioxide gas, nitrogen gas, and oxygen gas to the methane production apparatus 1. As the carbon dioxide gas, for example, carbon monoxide (CO) gas, carbon dioxide (CO ２ ), gas may be mentioned, and preferably carbon dioxide gas may be mentioned. 【0011】 The hydrogen gas supply unit 3 is typically configured to supply a hydrogen-containing gas containing hydrogen gas to the methane production apparatus 1. The hydrogen-containing gas may contain other gas components in addition to hydrogen gas. 【0012】 In one embodiment, the methane production apparatus 1 is configured to generate H ２ O in the methane conversion reaction. In this specification, "H ２ O" typically has a gaseous state or a liquid state. Hereinafter, gaseous H ２ O is distinguished from water vapor, and liquid H ２ O is distinguished from water. More specifically, the methane production apparatus 1 is configured to cause the first reaction represented by the following formula (I) and the second reaction represented by the following formula (II) to proceed. O ２ + 2H ２ → 2H ２ O... (I) CO ２ + 4H ２ → CH ４ + 2H ２ O... (II) The first reaction is a combustion reaction of hydrogen gas, in which oxygen and hydrogen react to generate water. The second reaction is a methanation reaction of carbon dioxide gas, in which carbon dioxide and hydrogen react to generate methane. Since both the first reaction and the second reaction are exothermic reactions, the generated heat (reaction heat) can be effectively used for the progress and continuation of these reactions. That is, the methane production apparatus is direct methanation capable. Therefore, methane gas can be efficiently generated with energy savings in the methane production apparatus. 【0013】 In the methane production apparatus 1, H ２When oxygen is produced, the methane production apparatus 1 typically discharges a reaction product gas containing methane gas, nitrogen gas, and water vapor. The product gas supply unit 4 is configured to supply the reaction product gas from the methane production apparatus 1 to the combustion apparatus 5. In one embodiment, the product gas supply unit 4 further comprises a separation unit 42. The separation unit 42 separates H from the reaction product gas. ２ It is configured to separate O. With this configuration, H is separated from the reaction product gas before the reaction product gas is supplied to the combustion device. ２ Since oxygen (typically water vapor) can be removed, the combustion efficiency of methane in combustion devices can be improved. 【0014】 In one embodiment, the product gas supply unit 4 further comprises a methane meter 43. The methane meter 43 is configured to measure the concentration of methane gas in the reaction product gas. The methane meter 43 is installed at any suitable location. If the product gas supply unit 4 comprises a separation unit 42, the methane meter 43 is H ２ The concentration of methane gas in the reaction product gas before O separation may be measured, and H ２ The concentration of methane gas in the reaction product gas after O separation may also be measured. In the illustrated example, the methane measuring instrument 43 is H ２ The system is configured to measure the concentration of methane gas in the reaction product gas after O separation. The methane measuring instrument 43 is located on the opposite side of the methane production apparatus 1 from the separation unit 42. With this configuration, the methane measuring instrument measures H ２ Compared to measuring the concentration of methane gas in the reaction product gas before O separation, this method allows for smoother and more accurate measurement of the methane gas concentration in the reaction product gas. 【0015】 In one embodiment, the generated gas supply unit 4 further includes an oxygen meter 44. The oxygen meter 44 is capable of measuring the concentration of oxygen gas in the reaction product gas. The oxygen meter 44 is installed at any suitable location. If the generated gas supply unit 4 includes a separation unit 42, the oxygen meter 44 is H ２ The concentration of oxygen gas in the reaction product gas before O separation may be measured, and H ２The concentration of oxygen gas in the reaction product gas after O separation may also be measured. In the illustrated example, the oxygen meter 44 measures H ２ The system is configured to measure the concentration of oxygen gas in the reaction product gas after O separation. The oxygen meter 44 is located on the opposite side of the methane production apparatus 1 from the separation unit 42. With this configuration, the oxygen meter measures H ２ Compared to measuring the oxygen gas concentration in the reaction product gas before O separation, this method allows for smoother and more accurate measurement of the oxygen gas concentration in the reaction product gas. Furthermore, when the product gas supply unit 4 includes a separation unit 42 and a methane measuring instrument 43, the oxygen measuring instrument 44 may be located between the separation unit 42 and the methane measuring instrument 43, or it may be located on the opposite side of the separation unit 42 from the methane measuring instrument 43. In the illustrated example, the oxygen measuring instrument 44 is located on the opposite side of the separation unit 42 from the methane measuring instrument 43. 【0016】 The oxygen gas supply unit 6 is typically configured to supply an oxygen-containing gas, including oxygen gas, to the reaction product gas. The oxygen-containing gas may also contain other gaseous components in addition to oxygen gas. 【0017】 The oxygen gas supply unit 6 may supply oxygen gas to the reaction product gas being transported to the generated gas supply unit 4, or it may supply oxygen gas to the reaction product gas in the combustion device 5. In one embodiment, the oxygen gas supply unit 6 is configured to supply oxygen gas to the reaction product gas being transported to the generated gas supply unit 4. In the illustrated example, the oxygen gas supply unit 6 is configured to supply oxygen gas to the reaction product gas between the separation unit 42 and the combustion device 5. With this configuration, H in the separation unit ２ This can reduce the energy required to separate oxygen. 【0018】 The combustion device 5 has any suitable configuration capable of burning methane. More specifically, in the combustion device 5, the methane gas contained in the reaction product gas supplied from the product gas supply unit 4 burns using the oxygen gas supplied from the oxygen gas supply unit 6 as a combustion support. At this time, the reaction between methane and oxygen produces carbon dioxide and H ２O is generated. Therefore, the combustion device 5 is typically configured to discharge exhaust gas (combustion gas) containing carbon dioxide and water vapor. In one embodiment, the combustion device 5 is configured to supply the exhaust gas to the methane production device 1. With such a configuration, the exhaust gas from the combustion device can be effectively utilized as a raw material for methane. Therefore, the combustion system can be operated stably and continuously, and the amount of carbon dioxide emitted from the combustion system can be reduced. 【0019】 In one embodiment, the combustion system 100 further includes a control unit 7. The control unit 7 is configured to receive measurement results from a methane measuring instrument 43 and control the operation of the oxygen gas supply unit 6. The control unit 7 is configured to adjust the amount of oxygen gas supplied by the oxygen gas supply unit 6 to the reaction product gas according to the measurement results from the methane measuring instrument 43. With this configuration, an appropriate amount of oxygen gas can be supplied for methane combustion according to the concentration of methane in the reaction product gas, thereby further improving the combustion efficiency of methane in the combustion device. 【0020】 The control unit 7 may be configured to receive measurement results from the oxygen meter 44. In this case, the control unit 7 can adjust the amount of oxygen gas supplied by the oxygen gas supply unit 6 to the reaction product gas according to the measurement results from the methane meter 43 and the oxygen meter 44, respectively. This can further improve the combustion efficiency of methane in the combustion device. 【0021】 B. Details of the Combustion System Next, with reference to Figure 1, the details of a combustion system according to one embodiment will be described. In one embodiment, the combustion system 100 includes the above-mentioned raw material gas supply unit 2, the above-mentioned hydrogen gas supply unit 3, the above-mentioned methane production apparatus 1, the above-mentioned generated gas supply unit 4, the above-mentioned oxygen gas supply unit 6, the above-mentioned combustion apparatus 5, and the above-mentioned control unit 7. 【0022】 B-1. Raw material gas supply unit In one embodiment, the raw material gas supply unit 2 comprises a raw material gas source 21 and a raw material gas supply line 22. 【0023】The raw material gas source 21 is configured to discharge a raw material gas containing carbon oxide gas and nitrogen gas. In one embodiment, the raw material gas discharged by the raw material gas source 21 further contains oxygen gas. Any suitable industrial product or facility can be used as the raw material gas source 21. Examples of industrial products or facilities include carbon oxide adsorption devices (typically DACs) capable of adsorbing and desorbing carbon oxide gas from the atmosphere, combustion devices, thermal power plants, and factories. 【0024】 The raw material gas supply line 22 is typically a pipe for supplying raw material gas discharged from the raw material gas source 21 to the methane production apparatus 1. In the illustrated example, the upstream end of the raw material gas supply line 22 in the direction of raw material gas supply is connected to the raw material gas source 21. The downstream end of the raw material gas supply line 22 in the direction of raw material gas supply is connected to the methane production apparatus 1 so as to be connected to a gas flow path described later. 【0025】 B-2. Hydrogen Gas Supply Unit In one embodiment, the hydrogen gas supply unit 3 includes a hydrogen gas source 31 and a hydrogen gas supply line 32. 【0026】 The hydrogen gas source 31 is typically configured to produce a hydrogen-containing gas that includes hydrogen gas. For example, the hydrogen gas source 31 is H ２ H is produced by electrolyzing oxygen. ２ Examples include electrolytic devices, ammonia decomposition devices that crack ammonia to produce hydrogen gas, and dehydrogenation devices that release hydrogen gas from liquid organic carriers. 【0027】 The hydrogen gas supply line 32 is typically a piping system for supplying hydrogen-containing gas produced by the hydrogen gas source 31 to the methane production apparatus 1. In the illustrated example, the upstream end of the hydrogen gas supply line 32 in the direction of hydrogen-containing gas supply is connected to the hydrogen gas source 31. The downstream end of the hydrogen gas supply line 32 in the direction of hydrogen-containing gas supply is connected to the methane production apparatus 1 so as to be connected to a gas flow path described later. The downstream end of the hydrogen gas supply line 32 in the direction of hydrogen-containing gas supply may also be connected to the raw material gas supply line 22. 【0028】B-3. ​​Methane Production Apparatus The methane production apparatus 1 has any suitable configuration having a gas flow path. Typically, a methanation reaction catalyst is placed in the gas flow path of the methane production apparatus 1. 【0029】 The methanation catalyst contains any suitable metal element as an active ingredient. The methanation catalyst may contain a metal element in its metallic state, a salt of a metal element, or an oxide of a metal element. Preferably, the methanation catalyst contains a metal element in its metallic state. 【0030】 Examples of metallic elements include alkali metals, alkaline earth metals, and transition metals, with transition metals being preferred. Examples of transition metals include Co, Fe, Pt, Ru, Rh, Pd, Ni, Cu, Ag, Au, and Ir. These transition metals can be used individually or in combination. In one embodiment, the methanation catalyst contains Ni. The presence of Ni in the methanation catalyst can further accelerate the methane conversion reaction, particularly the first reaction (combustion of hydrogen gas) and the second reaction (methanation of carbon dioxide gas). 【0031】 The methanation catalyst may further contain a support in addition to the active component described above. The support is capable of supporting the active component (typically a transition metal). The support is composed of any suitable inorganic material depending on the application. Examples of inorganic materials include oxides, carbides, nitrides, sulfides, halides, hydrogen compounds, and hydroxides. The inorganic materials can be used individually or in combination. 【0032】 Among such inorganic materials, oxides are preferred. 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 such an oxide-containing support bears the above-mentioned active component (particularly Ni), the activity of the methanation reaction catalyst can be stably improved. 【0033】When the methanation catalyst contains an active ingredient and a support, the content ratio of the active ingredient is 0.01 to 50 parts by mass, preferably 1 to 20 parts by mass, per 100 parts by mass of the support. Within this range of active ingredient content, the activity of the methanation catalyst can be improved more stably. 【0034】 The mass of the methanation catalyst per unit volume of the gas flow path is, for example, 30 g / L or more, preferably 50 g / L or more. On the other hand, the upper limit of the mass of the methanation catalyst per unit volume of the gas flow path is typically 1000 g / L or less. 【0035】 As shown in Figures 2 and 3, in one embodiment, the methane production apparatus 1 has a flow-through structure. The methane production apparatus 1 comprises a honeycomb substrate 11 and a catalyst layer 12. The honeycomb substrate 11 has partition walls 13 that define a plurality of cells 14. At least some of the plurality of cells 14 include a gas flow path 15. In the illustrated example, all of the plurality of cells 14 include a gas flow path 15. The catalyst layer 12 is provided on the surface of the partition walls 13. The catalyst layer 12 contains the methanation reaction catalyst described above. If the methane production apparatus has such a configuration, when the mixed gas of the raw material gas and the hydrogen-containing gas passes through the gas flow path, the mixed gas and the methanation reaction catalyst in the catalyst layer can be efficiently brought into contact. Therefore, the methane conversion reaction in the methane production apparatus can proceed smoothly, and the methane conversion rate can be stably improved. 【0036】 The honeycomb-shaped substrate 11 has any suitable shape (overall shape). Examples of the shapes of the honeycomb-shaped substrate 11 include a cylindrical shape with a circular base, an elliptical columnar shape with an elliptical base, a prismatic columnar shape with a polygonal base, and a columnar shape with an irregular base. In one embodiment, the honeycomb-shaped substrate 11 has a cylindrical shape. The outer diameter and length of the honeycomb-shaped substrate 11 can be appropriately set depending on the purpose. 【0037】In the illustrated example, the honeycomb-shaped substrate 11 comprises an outer wall 16 and a partition wall 13 located inside the outer wall 16. The outer wall 16 and the partition wall 13 may be formed integrally or as separate components. In the illustrated example, the outer wall 16 and the partition wall 13 are formed integrally. 【0038】 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. 【0039】 As described above, the partition wall 13 defines a plurality of cells 14. The cells 14 extend from the first end face E1 (inlet end face) to the second end face E2 (outlet end face) of the honeycomb substrate 11 in the longitudinal direction (axial direction) of the honeycomb substrate 11 (see Figure 3). The cells 14 have any suitable shape in a cross section perpendicular to the longitudinal direction of the honeycomb substrate 11. Examples of cell cross-sectional shapes include triangles, quadrilaterals, pentagons, polygons with hexagons or more, circles, and ellipses. The cross-sectional shapes and sizes of the cells may all be the same, or at least some may differ. Among such cell cross-sectional shapes, quadrilaterals are preferred, and squares or rectangles are more preferred. 【0040】 The cell density in 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 in the honeycomb substrate 11 is, for example, 1000 cpsi or less, preferably 900 cpsi or less. When the cell density is within this range, the raw material gas can be efficiently brought into contact with the catalyst layer. In this specification, "cell density of the honeycomb substrate" means the cell density of the cross-section in the longitudinal direction (direction in which the cells extend) of the honeycomb substrate, and "cpsi" means 6.4516 cm² of the said cross-section. ２ This refers to the number of cells per square inch. 【0041】In the illustrated example, the partition wall 13 has a first partition wall 13a and a second partition wall 13b that are perpendicular to each other, and the first partition wall 13a and the second partition wall 13b define a plurality of cells 14. The cross-sectional shape of the cells 14 is rectangular, except for the parts where the first partition wall 13a and the second partition wall 13b are in contact with the outer wall 16. Note that the configuration of the partition wall is not limited to the partition wall 13 described above. The partition wall may have a first partition wall extending in the radial direction and a second partition wall extending in the circumferential direction, and these may define a plurality of cells. 【0042】 The thickness of the partition wall 13 can be set arbitrarily and appropriately. Typically, the thickness of the partition wall 13 is thinner than the thickness of the outer wall 16. For example, the thickness of the partition wall 13 is 0.0508 mm or more, preferably 0.0635 mm or more. On the other hand, the thickness of the partition wall 13 is, for example, 1.52 mm or less, preferably 1.27 mm or less. If the thickness of the partition wall is within this range, the mechanical strength of the honeycomb substrate can be made sufficient, and the cell density can be adjusted to the above range. The thickness of the partition wall can be measured, for example, by cross-sectional observation using an SEM (scanning electron microscope). 【0043】 The partition wall 13 may or may not have pores. The porosity of the partition wall 13 can be appropriately set depending on the purpose. The porosity of the partition wall 13 is, for example, 70% or less, preferably 65% ​​or less. On the other hand, the porosity of the partition wall 13 is, for example, 0% or more. The porosity is measured, for example, by the mercury intrusion method. 【0044】 The bulk density of the partition wall 13 can be appropriately set depending on the purpose. For example, the bulk density of the partition wall 13 is 1.0 g / cm³. ３ ~3.0 g / cm ３ Preferably 2.0 g / cm³ ３ ~3.0 g / cm ３ The bulk density is measured, for example, by the Archimedes method. 【0045】Examples of materials that constitute the honeycomb-shaped 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 individually or in combination. Among these ceramic materials, cordierite and Si-SiC-based composite materials are preferred. 【0046】 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 above this lower limit, it is possible to suppress the occurrence of localized high-temperature areas (hot spots) in the methane production apparatus and improve the safety of the combustion system. On the other hand, there is no upper limit to the thermal conductivity of the honeycomb substrate 11, but it is typically 1000 W / m·K. The thermal conductivity is measured, for example, by an optical AC thermal diffusivity measuring device. 【0047】 The catalyst layer 12 is formed on the surface of the partition wall 13. In the methane production apparatus 1, the gas flow path 15 is formed in the portion of the cell 14's cross-section where the catalyst layer 12 is not formed (typically the central portion). The catalyst layer 12 may be formed on the entire inner surface of the partition wall 13 (i.e., surrounding the gas flow path 15) as shown in the illustrated example, or it may be formed on a part 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. 【0048】The gas flow path 15 is a space formed inside the cell 14 and extends from the first end face E1 (inlet end face) to the second end face E2 (outlet end face), similar to the cell 14 (see Figure 3). In the illustrated example, the end of the gas flow path 15 on the first end face E1 side is connected to the downstream end in the raw material gas supply direction of the raw material gas supply line 22 and the downstream end in the hydrogen gas supply direction of the hydrogen-containing gas supply line 32 (see Figure 1). The end of the gas flow path 15 on the second end face E2 side is connected to the upstream end in the reaction product gas supply direction of the product gas supply line 41, which will be described later. 【0049】 The cross-sectional shape of the gas flow path 15 can be the same as that of the cell 14 described above, preferably a rectangle, and more preferably a square or rectangle. The cross-sectional shape and size of the gas flow path 15 may all be the same, or at least some of them may be different. 【0050】 As described above, the catalyst layer 12 contains a methanation reaction catalyst. The methanation reaction catalyst contained in the catalyst layer 12 may have any suitable shape. Typically, the methanation reaction catalyst is in particulate form. Hereinafter, particulate methanation reaction catalyst may be referred to as catalyst particles. In one embodiment, the catalyst layer 12 contains aggregates formed by the aggregation of multiple catalyst particles. Aggregates of multiple catalyst particles can form mesopores in the catalyst layer 12. 【0051】 The content of the methanation reaction catalyst in the catalyst layer 12 is, for example, 10% to 100% by mass, preferably 50% to 100% by mass. When the content of the methanation reaction catalyst is within this range, the mass of the methanation reaction catalyst per unit volume of the gas flow path can be stably adjusted to the above range. 【0052】 The catalyst layer 12 may contain additives in addition to the methanation reaction catalyst. Examples of additives include fillers, binders, and heat transfer materials. Additives can be used alone or in combination. The addition ratio of additives is, for example, 0.1 to 90 parts by mass, preferably 0.1 to 50 parts by mass, per 100 parts by mass of the methanation reaction catalyst. 【0053】 The thickness of the catalyst layer 12 is, for example, 0.1 μm to 3000 μm, preferably 20 μm to 300 μm. The average pore size in the catalyst layer 12 is, for example, 0.01 μm to 30 μm, preferably 1 μm to 20 μm. The porosity in the catalyst layer 12 is, for example, 1% to 80%, preferably 2% to 50%. 【0054】 B-4. Generated Gas Supply Unit As shown in Figure 1, in one embodiment, the generated gas supply unit 4 includes a generated gas supply line 41, the separation unit 42 described above, the methane measuring instrument 43 described above, and the oxygen measuring instrument 44 described above. 【0055】 The product gas supply line 41 is typically a pipe for supplying reaction product gas discharged from the methane production plant 1 to the combustion plant 5. In the illustrated example, the upstream end of the product gas supply line 41 in the direction of supply of reaction product gas is connected to the methane production plant 1 so as to be connected to the gas flow path 15. The downstream end of the product gas supply line 41 in the direction of supply of reaction product gas is connected to the combustion plant 5. More specifically, the downstream end of the product gas supply line 41 in the direction of supply of reaction product gas is connected to the combustion furnace 51, which will be described later. 【0056】 The separation unit 42 is located in the middle of the product gas supply line 41. The separation unit 42 has any suitable configuration. Examples of the separation unit 42 include a membrane separator equipped with a water vapor separation membrane and a gas-liquid separator. In one embodiment, the separation unit 42 is a gas-liquid separator 42a. Typically, the gas-liquid separator 42a is configured to cool the reaction product gas and condense the water vapor contained in the reaction product gas. In this way, the gas-liquid separator can smoothly separate water from gaseous components (typically methane gas and nitrogen gas). 【0057】The methane analyzer 43 is typically configured to measure the methane concentration in the reaction product gas passing through the product gas supply line 41. The methane analyzer 43 is installed in the product gas supply line 41. In the illustrated example, the methane analyzer 43 is installed in the portion of the product gas supply line 41 between the separation unit 42 and the combustion device 5. Examples of methane analyzers 43 include non-dispersive infrared absorption (NDIR) gas analyzers. 【0058】 The oxygen meter 44 is typically configured to measure the oxygen concentration in the reaction product gas passing through the product gas supply line 41. The oxygen meter 44 is installed in the product gas supply line 41. In the illustrated example, the oxygen meter 44 is installed in the portion of the product gas supply line 41 between the methane meter 43 and the combustion device 5. Examples of oxygen meters 44 include zirconia type, laser fractional formula, magnetic type, and electrode type. 【0059】 B-5. Oxygen Gas Supply Unit In one embodiment, the oxygen gas supply unit 6 includes an oxygen gas source 61 and an oxygen gas supply line 62. 【0060】 The oxygen gas source 61 is typically configured to produce an oxygen-containing gas. For example, the oxygen gas source 61 may be H ２ H is produced by electrolyzing O to create oxygen gas. ２ One example is an electrolytic device. 【0061】 The oxygen gas supply line 62 is typically a pipe for supplying oxygen-containing gas produced by the oxygen gas source 61 to the reaction product gas. In the illustrated example, the upstream end of the oxygen gas supply line 62 in the direction of oxygen-containing gas supply is connected to the oxygen gas source 61. In one embodiment, the downstream end of the oxygen gas supply line 62 in the direction of oxygen-containing gas supply is connected to the portion of the product gas supply line 41 downstream of the separation section 42. As a result, the oxygen gas supply section 6 is H ２Oxygen gas is supplied to the reaction product gas after O separation. Therefore, if the separation unit is a gas-liquid separator, the amount of reaction product gas to be cooled in the gas-liquid separator can be reduced, and as a result, the cooling energy of the reaction product gas (= gas amount × specific heat) can be stably reduced. In the illustrated example, the downstream end of the oxygen gas supply line 62 in the direction of oxygen-containing gas supply is connected to the portion of the product gas supply line 41 between the oxygen measuring instrument 44 and the combustion device 5. 【0062】 B-6. Combustion device In one embodiment, the combustion device 5 comprises a combustion furnace 51 and an exhaust line 52. 【0063】 The combustion furnace 51 has any suitable configuration capable of burning methane. Examples of the combustion furnace 51 include a calcination furnace, a boiler, a turbine, and the like. 【0064】 The exhaust line 52 is typically a pipe for discharging exhaust gas from the combustion device 5. The upstream end of the exhaust line 52 in the exhaust gas discharge direction is connected to the combustion furnace 51 so as to communicate with the internal space of the combustion furnace 51. The downstream end of the exhaust line 52 in the exhaust gas discharge direction is connected to any appropriate location in the combustion system. In the illustrated example, the downstream end of the exhaust line 52 in the exhaust gas discharge direction is connected to the raw material gas supply line 22 of the raw material gas supply unit 2. This allows the exhaust gas from the combustion device to be stably supplied to the methane production device via the exhaust line and the raw material gas supply line, enabling more stable and continuous operation of the combustion system. 【0065】B-7. Control Unit The control unit 7 can control the operation of the methane production system 100. The control unit 7 includes, for example, a central processing unit (CPU), ROM, and RAM. In one embodiment, the control unit 7 is communicatively connected to the methane meter 43, the oxygen meter 44, and the oxygen gas supply unit 6. Therefore, the control unit 7 is configured to receive measurement results from the methane meter 43 and / or the oxygen meter 44. In the illustrated example, when the control unit 7 receives the measurement results from the methane meter 43 and / or the oxygen meter 44, it calculates the amount of oxygen gas to be added to the reaction product gas. Then, based on the calculation result, the control unit 7 adjusts the operation of the oxygen gas supply unit 6 to supply oxygen-containing gas to the reaction product gas flowing through the product gas supply line 41 in an appropriate amount. 【0066】 C. Methane Combustion Method Next, a methane combustion method will be described with reference to Figure 1. In one embodiment, the methane combustion method includes a reaction step, an oxygen gas supply step, and a combustion step. 【0067】 C-1. Reaction Process In the reaction process, the methane production apparatus 1 is typically heated to the reaction start temperature beforehand. The reaction start temperature is, for example, 100°C or higher, preferably 150°C or higher. On the other hand, the upper limit of the reaction start temperature is typically 600°C. 【0068】 Next, the methane production apparatus 1 is supplied with raw material gas and hydrogen-containing gas. In the illustrated example, the raw material gas supply unit 2 supplies raw material gas to the methane production apparatus 1, and the hydrogen gas supply unit 3 supplies hydrogen-containing gas to the methane production apparatus 1. 【0069】In one embodiment, the raw material gas contains carbon dioxide gas and nitrogen gas. The carbon dioxide gas content in the raw material gas is, for example, 0.1% by volume or more, preferably 5% by volume or more. On the other hand, the carbon dioxide gas content in the raw material gas is, for example, 20% by volume or less, preferably 15% by volume or less. The nitrogen gas content in the raw material gas is, for example, 0.1% by volume or more, preferably 80% by volume or more. On the other hand, the nitrogen gas content in the raw material gas is, for example, 99% by volume or less, preferably 95% by volume or less. 【0070】 Furthermore, the raw material gas may also contain oxygen gas. The oxygen gas content in the raw material gas is, for example, 0% by volume or more, preferably 1% by volume or more. On the other hand, the oxygen gas content in the raw material gas is, for example, 20% by volume or less, preferably 5% by volume or less. 【0071】 The flow rate of the raw material gas is adjusted arbitrarily and appropriately. 【0072】 The hydrogen gas content in the hydrogen-containing gas is, for example, 96% to 100% by volume, or 98% to 100% by volume. The hydrogen gas flow rate is 10,000 Nm³ of the raw material gas flow rate. ３ When set to / hr, for example, 1300 Nm ３ / hr~8000Nm ３ The value is / hr, preferably 2000 Nm ３ / hr~6000Nm ３ It is / hr. 【0073】As a result, carbon dioxide gas and hydrogen gas are supplied to the gas flow path 15 of the methane production apparatus 1 and come into contact with the methanation reaction catalyst heated to the reaction start temperature (see Figure 3). Typically, the first reaction (combustion reaction of hydrogen) proceeds preferentially over the second reaction (methanization reaction of carbon dioxide). At this time, reaction heat is generated by the first reaction and used to continue the first reaction and to start the second reaction (methanization reaction of carbon dioxide). 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 this reaction heat, and the second reaction continues stably even after the completion of the first reaction. For this reason, in one embodiment, external heating of the methane production apparatus is stopped. 【0074】 When external heating to the methane production apparatus is stopped, the temperature in the gas flow path of the methane production apparatus (reaction temperature) is maintained, for example, between 250°C and 450°C by the heat of reaction. When the reaction temperature is within this range, the second reaction described above (the methane reaction of carbon dioxide) can be continued more stably. 【0075】 In the reaction process, the pressure in the gas channel 15 (reaction pressure) is, for example, 0.5 MPaA (absolute pressure) or higher, preferably 1.0 MPaA or higher, more preferably 2.0 MPaA or higher, and even more preferably 2.5 MPaA or higher. On the other hand, the pressure inside the gas channel 15 is, for example, 7.0 MPaA or lower, preferably 5.5 MPaA or lower. When the reaction pressure is within this range, the second reaction (methane reaction of carbon dioxide) can be continued more stably. 【0076】 As a result, carbon dioxide gas and hydrogen gas react in the gas flow path of the methane production plant to produce a reaction product gas containing methane gas. Subsequently, the reaction product gas is continuously discharged from the gas flow path of the methane production plant. 【0077】The methane conversion rate in the reaction process is the percentage of the amount of methane gas produced relative to the amount of carbon dioxide supplied, and is, for example, 65% or more, preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more. On the other hand, the methane conversion rate is, for example, 100% or less, and also, for example, 95% or less. When the methane conversion rate is within this range, it is possible to suppress the residue of unreacted carbon dioxide gas in the reaction product gas. Therefore, it is possible to stably improve the combustion efficiency in the combustion device. The temperature range of the reaction product gas is, for example, the same as the reaction temperature range described above. The pressure range of the reaction product gas is, for example, the same as the reaction pressure range described above. 【0078】 As described above, the reaction product gas contains methane gas and nitrogen gas. The methane gas content in the reaction product gas is, for example, 0.1 volume% or more, preferably 5 volume% or more. On the other hand, the methane gas content in the reaction product gas is, for example, 100 volume% or less, and also, for example, 10 volume% or less. The nitrogen gas content in the reaction product gas is, for example, 50 volume% or more, preferably 60 volume% or more. On the other hand, the nitrogen gas content in the reaction product gas is, for example, 90 volume% or less, preferably 75 volume% or less. 【0079】 The reaction product gas may contain water vapor in addition to methane and nitrogen gas. The water vapor content in the reaction product gas is, for example, 0% to 40% by volume, or for example, 10% to 30% by volume. 【0080】 The reaction product gas may further contain hydrogen gas and / or carbon oxide gas that remained unreacted in the reaction process. The hydrogen gas content in the reaction product gas is, for example, 10% by volume or less, preferably 5% by volume or less. On the other hand, the lower limit of the hydrogen gas content in the reaction product gas is typically 0% by volume. The carbon oxide gas content in the reaction product gas is, for example, 3% by volume or less, preferably 1% by volume or less. On the other hand, the lower limit of the carbon oxide gas content in the reaction product gas is typically 0% by volume. 【0081】Furthermore, the reaction product gas is substantially free of oxygen gas. The oxygen gas content in the reaction product gas is, for example, 1% by volume or less, preferably 0.5% by volume or less. On the other hand, the lower limit of the oxygen gas content in the reaction product gas is typically 0% by volume. 【0082】 The flow rate of the reaction product gas is 10,000 Nm³ of the flow rate of the raw material gas. ３ When set to / hr, for example, 10000 Nm ３ / hr~16000Nm ３ The value is / hr, preferably 12000 Nm ３ / hr~15000Nm ３ It is / hr. 【0083】 C-2. Dehydration step: If the reaction product gas contains water vapor, the methane combustion method preferably further includes a dehydration step. In the dehydration step, water vapor is separated from the reaction product gas. In the illustrated example, the separation unit 42 separates the water vapor from the reaction product gas. Hereinafter, the reaction product gas from which water vapor has been separated may be referred to as the dehydrated gas. 【0084】 The methane gas content in the dehydrated gas is, for example, 1 volume% or more, preferably 5 volume% or more, and more preferably 7 volume% or more. On the other hand, the methane gas content in the dehydrated gas is, for example, 100 volume% or less, and also, for example, 15 volume% or less. The nitrogen gas content in the dehydrated gas is, for example, 70 volume% or more, preferably 80 volume% or more. On the other hand, the nitrogen gas content in the dehydrated gas is, for example, 99 volume% or less, and preferably 90 volume% or less. 【0085】 The range of hydrogen gas content in the dehydrated gas is, for example, the same as the range of hydrogen gas content in the reaction product gas described above. The range of carbon oxide gas content in the dehydrated gas is, for example, the same as the range of carbon oxide gas content in the reaction product gas described above. 【0086】Furthermore, the dehydrated gas contains substantially no water vapor. The water vapor content in the dehydrated gas is, for example, 1% by volume or less, preferably 0.5% by volume or less. On the other hand, the lower limit of the water vapor content in the dehydrated gas is typically 0% by volume. 【0087】 The flow rate of the dewatered gas is 10,000 Nm³ of the flow rate of the raw material gas. ３ When set to / hr, for example, 1000 Nm ３ / hr~5000Nm ３ The value is / hr, preferably 2000 Nm ３ / hr~4000Nm ３ It is / hr. 【0088】 C-3. Oxygen Gas Supply Process In one embodiment, the oxygen gas supply process first measures the methane gas concentration and / or oxygen gas concentration in the reaction product gas (preferably the dehydrated gas). In the illustrated example, the methane meter 43 measures the methane gas concentration in the dehydrated gas. The oxygen meter 44 measures the oxygen gas concentration in the dehydrated gas. This allows for an accurate determination of the amount of oxygen gas that can efficiently burn the methane gas contained in the reaction product gas (preferably the dehydrated gas). 【0089】 Next, an oxygen-containing gas is supplied to the reaction product gas (preferably the dehydrated gas). In the illustrated example, the oxygen gas supply unit 6 supplies the oxygen-containing gas to the reaction product gas. The oxygen content in the oxygen-containing gas is, for example, 94% to 100% by volume, or for example, 98% to 100% by volume. 【0090】This process mixes the reaction product gas and the oxygen-containing gas to prepare a methane-oxygen combined gas. The range of methane gas content in the methane-oxygen combined gas is, for example, the same as the range of methane gas content in the reaction product gas described above. The range of nitrogen gas content in the methane-oxygen combined gas is, for example, the same as the range of nitrogen gas content in the reaction product gas described above. The oxygen gas content in the methane-oxygen combined gas is, for example, 5% by volume or more, preferably 10% by volume or more. On the other hand, the oxygen gas content in the methane-oxygen combined gas is, for example, 40% by volume or less, preferably 30% by volume or less. When the methane-oxygen combined gas has such a composition, it can undergo a stable and sufficient combustion reaction. 【0091】 The range of hydrogen gas content in methane-oxygen combined gas is, for example, the same as the range of hydrogen gas content in the reaction product gas described above. The range of carbon oxide gas content in methane-oxygen combined gas is, for example, the same as the range of carbon oxide gas content in the reaction product gas described above. 【0092】 C-4. Combustion Process In the combustion process, typically, methane-oxygen gas is heated to burn the methane gas contained in it. In the illustrated example, methane-oxygen gas is supplied to the combustion device 5, and the methane gas is burned in the combustion furnace 51. In other words, the methane gas is supplied to the combustion device 5 and burned without being separated from the reaction product gas produced in the methane production device 1. Therefore, methane gas can be used as fuel for the combustion device in an energy-saving manner. 【0093】 When methane burns, it produces carbon dioxide and H ２O is produced. Therefore, in the combustion process, exhaust gas (combustion gas) containing carbon dioxide and water vapor is typically produced. The range of carbon dioxide content in the exhaust gas is, for example, 0.1 volume% or more, preferably 5 volume% or more. On the other hand, the range of carbon dioxide content in the exhaust gas is, for example, 20 volume% or less, preferably 15 volume% or less. The range of water vapor content in the exhaust gas is, for example, 0.1 volume% or more, preferably 10 volume% or more. On the other hand, the range of water vapor content in the exhaust gas is, for example, 25 volume% or less, preferably 20 volume% or less. The range of nitrogen gas content in the exhaust gas is, for example, the same as the range of nitrogen gas content in the reaction product gas described above. 【0094】 The exhaust gas may contain oxygen gas remaining from the combustion process. The oxygen gas content in the exhaust gas is, for example, 0% by volume or more, preferably 1% by volume or more. On the other hand, the oxygen gas content in the exhaust gas is, for example, 7% by volume or less, preferably 5% by volume or less. 【0095】 Furthermore, the exhaust gas is substantially free of methane gas. The methane gas content in the exhaust gas is, for example, 1 volume% or less, preferably 0.5 volume% or less. On the other hand, the lower limit of the oxygen gas content in the exhaust gas is typically 0 volume%. 【0096】 The exhaust gas flow rate is calculated by multiplying the raw gas flow rate by 10,000 Nm³. ３ When set to / hr, for example, 10000 Nm ３ / hr~15000Nm ３ The value is / hr, preferably 11000 Nm ３ / hr~14000Nm ３ It is / hr. 【0097】 Such exhaust gases are used as raw material gases in the reaction process, if necessary. In the illustrated example, the exhaust gas is returned to the raw material gas supply line 22 via the exhaust line 52. This allows the exhaust gases generated in the combustion process to be effectively utilized as raw material for methane. 【0098】D. Modified Example As shown in Figure 4, in one embodiment, the hydrogen gas supply unit 3 uses H as the hydrogen gas source. ２ It is equipped with an O decomposition device 31a. ２ O Decomposition apparatus 31a is H ２ It is configured to decompose O into oxygen gas and hydrogen gas. ２ The oxygen decomposition apparatus 31a is configured to discharge oxygen-containing gas and hydrogen-containing gas. In the illustrated example, the hydrogen gas supply unit 3 supplies hydrogen-containing gas to H ２ The system is configured to supply oxygen from the oxygen decomposition unit 31a to the methane production unit 1. More specifically, the hydrogen-containing gas is supplied to the methane production unit 1 by passing through the hydrogen gas supply line 32 of the hydrogen gas supply unit 3. The oxygen gas supply unit 6 also supplies oxygen-containing gas to the H ２ It is configured to supply the generated gas from the O decomposition device 31a to the generated gas supply unit 4. More specifically, the upstream end in the oxygen-containing gas supply direction of the oxygen gas supply line 62 is H ２ It is connected to the O decomposition device 31a. With this configuration, H ２ The hydrogen-containing gas and oxygen-containing gas produced in the oxygen decomposition unit can be effectively used in the combustion system. Furthermore, even if the hydrogen content in the hydrogen-containing gas and / or the oxygen content in the oxygen-containing gas are within the above-mentioned ranges, the combustion system can operate stably. 【0099】 The combustion system according to the embodiment of the present invention is suitably used in various industrial facilities that utilize methane by combustion. 【0100】 1. Methane production apparatus 2. Raw material gas supply unit 3. Hydrogen gas supply unit 31a H ２ 4 O decomposition unit 42 Production gas supply unit 43 Separation unit 43 Methane measuring instrument 5 Combustion unit 6 Oxygen gas supply unit 7 Control unit 100 Combustion system

Claims

1. A combustion system comprising a combustion device configured to burn methane, the system comprising: a methane production device configured to carry out a methane conversion reaction of carbon oxide; a raw material gas supply unit configured to supply a raw material gas containing carbon oxide gas and nitrogen gas to the methane production device; a hydrogen gas supply unit configured to supply hydrogen gas to the methane production device; a product gas supply unit configured to supply a reaction product gas discharged from the methane production device, which contains methane gas and nitrogen gas, from the methane production device to the combustion device; and an oxygen gas supply unit configured to supply oxygen gas to the reaction product gas.

2. The combustion system according to claim 1, wherein the combustion device is configured to supply exhaust gas to the methane production device.

3. The methane production apparatus uses H in the methane conversion reaction. ２ The system is configured to produce O, and the product gas supply unit supplies H from the reaction product gas. ２ The combustion system according to claim 1, comprising a separation unit capable of separating oxygen.

4. The combustion system according to claim 3, wherein the oxygen gas supply unit is configured to supply oxygen gas to the reaction product gas between the separation unit and the combustion device.

5. The combustion system according to claim 3 or 4, wherein the product gas supply unit further comprises a methane measuring instrument configured to measure the concentration of methane gas in the reaction product gas, the combustion system further comprises a control unit configured to receive measurement results from the methane measuring instrument, and the control unit is configured to control the operation of the oxygen gas supply unit and to adjust the amount of oxygen gas supplied to the reaction product gas according to the measurement results from the methane measuring instrument.

6. The hydrogen gas supply unit is H ２ H is configured to decompose O into oxygen gas and hydrogen gas. ２ Equipped with an O decomposition device, the H ２ The oxygen decomposition apparatus is configured to discharge oxygen-containing gas and hydrogen-containing gas, and the oxygen gas supply unit supplies the oxygen-containing gas to the H ２ The combustion system according to claim 1, configured to supply the generated gas from the oxygen decomposition device to the generated gas supply unit.

7. The hydrogen gas supply unit supplies the hydrogen-containing gas to the H ２ The combustion system according to claim 6, configured to supply from an oxygen decomposition device to a methane production device.

8. The combustion system according to claim 6 or 7, wherein the oxygen content in the oxygen-containing gas is 94% to 100% by volume, and the hydrogen content in the hydrogen-containing gas is 96% to 100% by volume.

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