JP2020100597A - Metan manufacturing system - Google Patents

Abstract

To efficiently utilize reaction heat generated at the time of producing methane when a methane manufacturing system produces methane using carbon dioxide contained in combustion gas.SOLUTION: A methane manufacturing system includes: a reaction pipe having a carbon dioxide storage reduction catalyst; a hydrogen supply part supplying hydrogen to the reaction pipe; and a control part controlling the supply amount of hydrogen supplied by the hydrogen supply part. The carbon dioxide storage reduction catalyst includes: a metal oxide storing and discharging the carbon dioxide; and a methanation reaction catalyst promoting the methanation reaction generating methane from hydrogen and carbon dioxide. The control part increases the supply amount more than the amount of hydrogen corresponding to a stoichiometry amount ratio based on a reaction equation of the methanation reaction.SELECTED DRAWING: Figure 1

Description

The present invention relates to a methane production system including a carbon dioxide storage reduction catalyst.

A method of producing methane by mixing carbon dioxide and hydrogen and using a methanation catalyst is known. A material containing calcium oxide is known as a catalyst for separating carbon dioxide contained in combustion gas and converting it into methane (see Non-Patent Document 1, for example). Non-Patent Document 1 discloses the composition and operating temperature of a catalyst required for carbon dioxide recovery and methanation.

M.S.Duyar et al. Dual functional materials for CO2 capture and conversion using renewable H2, Applied Catalysis B: Environmental, Volumes 168-169 (2015) pages 370-376.

The technique described in Non-Patent Document 1 discloses a method of carbon dioxide recovery and methanation, but does not disclose utilization of reaction heat of methanation generated at that time. Further, although it is possible to utilize the heat of reaction generated by the method of Non-Patent Document 1, there is a problem that the temperature of the heat is limited to 320° C. or lower which is the temperature of methanation.

The present invention has been made to solve the above-mentioned problems, and when methane is generated using carbon dioxide contained in combustion gas, a methane production system that can efficiently use reaction heat generated during generation. The purpose is to provide.

The present invention has been made to solve the above problems, and can be realized as the following modes.

(1) According to one aspect of the present invention, a methane production system is provided. This methane production system includes a reaction tube having a carbon dioxide storage reduction catalyst, a hydrogen supply unit that supplies hydrogen to the reaction tube, and a control unit that controls the supply amount of hydrogen supplied by the hydrogen supply unit. The carbon dioxide storage reduction catalyst includes a metal oxide that stores and releases carbon dioxide, and a methanation catalyst that promotes a methanation reaction that produces methane from hydrogen and carbon dioxide, and the control unit includes The supply amount is made larger than the amount of hydrogen corresponding to the stoichiometric ratio based on the reaction formula of the methanation reaction.

According to this configuration, heat is generated when the metal oxide occludes carbon dioxide and changes into a carbonate. In the reaction tube, when hydrogen is supplied to the carbonate storing carbon dioxide, carbon dioxide desorbed when the carbonate changes into a metal oxide, and hydrogen supplied by the hydrogen supply unit, Reaction on the methanation catalyst produces methane. Since the amount of hydrogen supplied is larger than the amount corresponding to the stoichiometric ratio of the methanation reaction using carbonate and hydrogen as raw materials, the desorption of carbon dioxide from the carbonate and the production of methane proceed. To do. The methanation reaction is an exothermic reaction, and the heat generated by the methanation is used for an endothermic reaction that desorbs carbon dioxide from carbonate. As a result, the reaction heat generated by the methanation reaction does not cause energy loss. Further, the methanation reaction is a reaction that easily proceeds in an environment of about 320 degrees Celsius (° C.) or less. If the temperature is higher than 320° C., the concentration of residual carbon dioxide becomes high, and the methanation reaction becomes difficult to proceed. According to this configuration, since the temperature at which the metal oxide occludes carbon dioxide is higher than 320° C., the heat of the methanation reaction is generated by passing through the occluding and releasing of carbon dioxide by the metal oxide. Can be used even under high temperature. In addition, the fuel can be downsized by generating methane, which has a smaller volume per unit heat of combustion than hydrogen, as the fuel. Further, by supplying a large amount of hydrogen during the methanation reaction, carbon dioxide occluded in the carbonate is completely desorbed, and a reversible change from the metal oxide to the carbonate is performed. Thereby, as compared with the case where the metal oxide stores carbon dioxide by chemisorption, more carbon dioxide can be stored in the metal oxide per unit volume, and the efficiency of the methane production system can be improved.

(2) In the methane production system of the above aspect, the control unit further includes a downstream concentration acquisition unit that acquires the concentration of carbon dioxide contained in the gas discharged from the reaction tube, and the control unit is the carbon dioxide storage reduction catalyst. Is occluding carbon dioxide, when the concentration of carbon dioxide acquired by the downstream side concentration acquiring unit reaches a preset allowable value, terminating the storage of carbon dioxide by the carbon dioxide occluding and reducing catalyst. You may let me.
According to this configuration, the carbon dioxide concentration in the combustion gas that passes through the reaction tube and is released into the atmosphere can be managed by the acquired value of the downstream side concentration acquisition unit. In the storage step in which the carbon dioxide storage reduction catalyst (storage reduction catalyst) stores carbon dioxide, when the carbon dioxide storage amount of the metal oxide approaches its capacity, part of the carbon dioxide passes through the reaction tube without being stored. As a result, the carbon dioxide concentration on the downstream side gradually increases. Therefore, when the acquired value of the downstream side concentration acquisition unit reaches the set allowable value of the carbon dioxide concentration, the occlusion step can be ended and it is possible to shift to another step.

(3) In the methane production system of the above aspect, a temperature acquisition unit that acquires the temperature of the reaction tube, and a temperature adjustment that heats or cools the reaction tube using the temperature acquired by the temperature acquisition unit. And a section.
According to this configuration, in the methanation step, when the temperature becomes excessively high or low, the temperature can be controlled to be a temperature suitable for the methanation reaction. Furthermore, according to this configuration, when heat is recovered by circulating the heat medium in the occlusion step, the temperature of the heat medium after heat recovery becomes a temperature suitable for heat utilization by controlling the flow rate of the heat medium. Can be managed.

(4) In the methane production system of the above aspect, the metal oxide may contain at least one of lithium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, and lead oxide.
By using these metal compounds, an exothermic reaction due to occlusion of carbon dioxide at a high temperature and an endothermic reaction due to desorption of the adsorbed carbon dioxide at a low temperature can be performed.

(5) In the methane production system of the above aspect, further, a heat transfer part for transferring the heat generated by the metal oxide by the occlusion of carbon dioxide from the reaction tube to another device, and carbon dioxide in the reaction tube. A supply pipe for supplying a gas containing the gas may be provided.
According to this configuration, carbon dioxide can be extracted from the high-temperature gas containing carbon dioxide (for example, combustion gas in a factory) by the metal oxide to generate methane. On the other hand, the heat transfer section allows the heat transfer section to transfer the heat generated when the carbon dioxide is occluded, which is generated at a temperature higher than the environment where the methanation reaction progresses, to another device.

(6) In the methane production system of the above aspect, the carbon dioxide storage reduction catalyst may be added with an oxide as the sintering suppressing material.
According to this configuration, the sintering inhibitor (also referred to as “sinter inhibitor”) added to the storage reduction catalyst prevents the metal oxide from sintering by preventing the metal oxide from sintering. Desorption can be repeated.

The present invention can be implemented in various modes, for example, a carbon dioxide separation/collection device, a methane production system, a chemical heat storage system, a carbon dioxide circulation device, a methane production method, and a carbon dioxide separation. The present invention can be implemented in the form of a collection method, a computer program for executing these devices and methods, a server device for distributing this computer program, a non-transitory storage medium storing the computer program, and the like.

It is a block diagram of the methane manufacturing system in an embodiment. It is a flowchart of methane production. It is a graph which shows the partial pressure of hydrogen, methane, and water vapor when the chemical reaction of Formula (2) is in an equilibrium state. It is explanatory drawing about the heat storage effect accompanying the methane production of this embodiment.

<Embodiment>
FIG. 1 is a block diagram of a methane production system 100 according to the embodiment. The methane production system 100 produces methane as a fuel based on carbon dioxide contained in the combustion gas of a factory. Further, the methane production system 100 supplies the reaction heat generated until the carbon dioxide is extracted from the combustion gas to generate methane to the other device 50.

As shown in FIG. 1, the methane production system 100 reacts a combustion gas containing carbon dioxide with a reaction tube 10 having a carbon dioxide storage reduction catalyst 11 (hereinafter, also simply referred to as “storage reduction catalyst 11”) therein. A combustion device 20 for supplying to the tube 10, a hydrogen supply unit 30 for storing hydrogen supplied to the reaction tube 10 at high pressure, and a gas containing methane and hydrogen produced in the reaction tube 10 are stored. A fuel tank 40, another device 50 as heat demand for supplying reaction heat generated in the reaction tube 10, a combustion gas supply path (supply tube) 29 connecting the combustion device 20 and the reaction tube 10, and hydrogen. Hydrogen supply path 39 connecting the supply unit 30 and the reaction tube 10, a fuel supply path 49 connecting the reaction tube 10 and the fuel tank 40, and a treated combustion gas connecting the reaction tube 10 and another device 50. A supply path (heat transfer section) 59 and a control section 60 for controlling the gas supplied to the reaction tube 10 and the gas discharged from the reaction tube 10 are provided.

The storage reduction catalyst 11 of the present embodiment is a composite containing calcium oxide which is a metal oxide, alumina which is a sintering inhibitor, and ruthenium which is a methanation catalyst. Calcium oxide occludes carbon dioxide contained in combustion gas and changes to calcium carbonate. When hydrogen carbonate is supplied, calcium carbonate desorbs carbon dioxide and changes to calcium oxide. The reaction from calcium oxide to calcium carbonate is an exothermic reaction, and the reaction from calcium carbonate to calcium oxide is an endothermic reaction. Ruthenium promotes the methanation reaction that produces methane from hydrogen and carbon dioxide. Alumina is used to suppress deterioration of calcium oxide due to sintering and is also called a sintering inhibitor. In addition, the storage reduction catalyst 11 in other embodiment does not need to contain the sintering prevention material.

The combustion gas supply path 29 guides the combustion gas discharged from the combustion device 20 to the reaction tube 10. In the present embodiment, the temperature of the combustion gas introduced into the reaction tube 10 is around 300°C. As shown in FIG. 1, in the middle of the supply path 29, a combustion gas flow meter 21 that detects the flow rate of the combustion gas and an upstream side dioxide that detects carbon dioxide contained in the combustion gas are sequentially provided from the combustion device 20 side. A carbon sensor 22, an upstream temperature sensor 23 that detects the temperature of the combustion gas, and a combustion gas valve 24 that opens and closes the combustion gas supply passage are arranged. The combustion gas valve 24 is opened and closed to adjust the flow rate of the combustion gas supplied to the reaction tube 10.

The hydrogen supply path 39 guides hydrogen supplied from the hydrogen supply unit 30 to the reaction tube 10. As shown in FIG. 1, in the middle of the hydrogen supply passage 39, a hydrogen flow meter 31 for detecting the amount of hydrogen flowing in the hydrogen supply passage 39 and a hydrogen supply passage 39 are opened and closed in order from the hydrogen supply unit 30 side. And a hydrogen supply valve 34 that operates. The hydrogen supply valve 34 opens and closes to control the amount of hydrogen supplied to the reaction tube 10.

The fuel supply path 49 guides the gas containing methane and hydrogen generated by the methanation reaction in the reaction tube 10 to the fuel tank 40. As shown in FIG. 1, in the middle of the fuel supply passage 49, a methane sensor 41 for detecting methane contained in a gas passing through the fuel supply passage 49 and a fuel supply passage 49 inside the reaction pipe 10 in order. A hydrogen sensor 42 for detecting hydrogen contained in the gas passing through the fuel cell and a fuel valve 44 for opening and closing the fuel supply passage 49 are provided. The fuel supply path 49 adjusts the gas containing methane and hydrogen stored in the fuel tank 40 by opening and closing.

The treated combustion gas supply path 59 guides the high-temperature gas, which is obtained by removing the carbon dioxide from the combustion gas by the storage reduction catalyst 11, from the reaction tube 10 to another device 50. As shown in FIG. 1, in the treated combustion gas supply path 59, a downstream side carbon dioxide sensor (downstream side CO ₂ sensor) 52 for detecting carbon dioxide contained in the gas and a treatment are sequentially provided from the reaction tube 10 side. An outlet valve 54 that opens and closes the spent combustion gas supply path 59, and a downstream temperature sensor 53 that detects the temperature of the gas supplied from the reaction tube 10 to the other device 50 are provided. The outlet valve 54 adjusts the flow rate of the gas supplied from the reaction tube 10 to the other device 50 by opening and closing.

The control unit 60 is connected to various sensors and various valves by wire. In addition, in FIG. 1, the connection between the control unit 60 and various valves is indicated by a broken line, but the connection between the control unit 60 and various sensors is not shown. The control unit 60 acquires detection values of various sensors and sends control signals for opening and closing various valves to the various valves. Each valve opens and closes according to the received control signal.

The control unit 60 includes a CPU (Central Processing Unit) (not shown), a RAM (Random Access Memory), a ROM (Read Only Memory), and an operation unit that receives a user operation. In accordance with the operation received by the operation unit, the CPU develops various programs stored in the ROM in the RAM to execute the various programs. The operation unit is a well-known input means such as a keyboard and a mouse. The specific processing performed by the control unit 60 will be described with reference to the flowchart shown below.

FIG. 2 is a flowchart of methane production. In methane production, the control unit 60 first performs an occlusion step (step S1). In the occlusion step, the combustion gas of the combustion device 20 flows into the reaction tube 10. The control unit 60 opens the combustion gas valve 24 and the outlet valve 54 with the hydrogen supply valve 34 and the fuel valve 44 closed. Since the combustion gas contains carbon dioxide, the storage reduction catalyst 11 in the reaction tube 10 stores carbon dioxide. The carbon dioxide flowing into the reaction tube 10 and calcium oxide cause a chemical reaction represented by the following formula (1).
CaO+CO ₂ =CaCO ₃ (1)
At this time, the chemical reaction of the above formula (1) is an exothermic reaction that raises the temperature even in an environment of 300°C.

The control unit 60 determines whether or not the concentration of carbon dioxide detected by the downstream CO ₂ sensor 52 is smaller than the allowable value that may be released into the atmosphere through the reaction tube 10 (step S2). .. When the detection value of the downstream CO ₂ sensor 52 is lower than the allowable value (step S2: YES), the control unit 60 continues the occlusion step (step S1). On the contrary, when the detection value of the downstream CO ₂ sensor 52 is equal to or more than the allowable value (step S2: NO), the control unit 60 ends the occlusion step and shifts to the next step. At this time, the control unit 60 closes the combustion gas valve 24 and the outlet valve 54.

When the occlusion step ends, the control unit 60 performs a methanation step (step S3). In the methanation step, the control unit 60 opens the hydrogen supply valve 34 and the fuel valve 44 to supply hydrogen into the reaction tube 10. The control unit 60 uses the detection value of the hydrogen sensor 42 and the detection value of the methane sensor 41 to calculate the gas composition in the fuel tank 40. In the reaction tube 10, a reaction in which methane of the following formula (2) is produced occurs.
CaCO ₃ +4H ₂ =CaO+CH ₄ +2H ₂ O (2)

FIG. 3 is a graph showing the partial pressures of hydrogen, methane, and water vapor when the chemical reaction of formula (2) is in equilibrium. The equilibrium state means that the free energy change in the reaction formula of the above formula (2) is zero. The total pressure was constant at 1 atm (atm). In FIG. 3, the scale of the vertical axis showing the partial pressure of hydrogen and the scale of the vertical axis showing the partial pressures of methane and steam are shown to be different. As shown in FIG. 3, for example, when the chemical reaction of the formula (2) is in an equilibrium state at 300° C., the partial pressure of hydrogen is 0.78 atm and the partial pressure of methane is 0.073 atm. The partial pressure of water vapor is 0.147 atm. In this case, the hydrogen utilization rate obtained by dividing the amount of hydrogen used to generate methane by the amount of hydrogen supplied is represented by the following formula (3).
0.073×4/(0.78+0.073×4)≈0.27...(3)

When hydrogen is supplied in an amount corresponding to the stoichiometric ratio based on the above formula (2), the ratio of desorption of carbon dioxide to change from calcium carbonate to calcium oxide is 0. 27. Further hydrogen needs to be supplied in order to convert 100 percent (%) of calcium carbonate to calcium oxide. That is, in order to completely desorb carbon dioxide from calcium carbonate, it is necessary to supply about 3.65 times hydrogen, which is the reciprocal of the hydrogen utilization rate of 0.27.

Therefore, in the methanation step (step S3) of FIG. 2, the control unit 60 supplies the excess amount of hydrogen to the reaction tube 10 and manages the supply amount of hydrogen using the detection value of the hydrogen flow meter 31. The control unit 60 supplies the reaction tube 10 with hydrogen, which is in excess of the amount of hydrogen corresponding to the stoichiometric ratio based on the above formula (2). However, the control unit 60 considers that the methanation reaction is stopped when the acquired value of the methane sensor 41 falls below a certain methane concentration before the supply amount reaches a predetermined amount. That is, the control unit 60 determines whether the methane concentration acquired by the methane sensor 41 exceeds a set value that is a constant methane concentration. When the acquired value of the methane sensor 41 is larger than the set value (step S4: YES), the control unit 60 continues the methanation step (step S3). When the acquired value of the methane sensor 41 is less than or equal to the set value (step S4: NO), the control unit 60 performs the next step. At this time, the control unit 60 closes the hydrogen supply valve 34 and the fuel valve 44.

After the storage of methane, the control unit 60 determines whether or not to terminate the above-described methane production process using carbon dioxide contained in the combustion gas (step S5). When the operation unit has not received a predetermined operation for ending the production of methane (step S5: NO), the control unit 60 repeats the processing from step S1 onward. When the operation unit receives a predetermined operation (step S5: YES), the control unit 60 ends the methane production.

FIG. 4 is an explanatory diagram of a heat storage effect associated with methane production according to this embodiment. FIG. 4 shows the combustion heat and the waste heat per 1 mol (mol) of hydrogen in Examples of the present embodiment and Comparative Examples 1 and 2. Example and Comparative Example 1 are the combustion heat of methane generated from 1 mol of hydrogen and the waste heat at the time of generation. Comparative Example 2 is the heat of combustion per mole of hydrogen. In the embodiment, 200 kilojoule (kJ) is generated as the combustion heat of methane, and 44 kJ is generated as the waste heat of methanation. The waste heat is used for an endothermic reaction when desorbing carbon dioxide from the calcium carbonate represented by the above formula (1). Therefore, the waste heat of methanation can be used in an exothermic reaction in which calcium oxide occludes carbon dioxide contained in combustion gas and changes to calcium carbonate. On the other hand, the waste heat of methanation of Comparative Example 1 is discarded without being used, resulting in energy loss. In Comparative Example 2, although there is no energy loss, the volume of methane is smaller than that of hydrogen when the same amount of heat as combustion heat is obtained.

As described above, the methane production system 100 according to the present embodiment is capable of storing carbon dioxide in the reaction tube 10, and at the same time, the storage reduction catalyst 11 that produces methane from supplied hydrogen and stored carbon dioxide. I have it. The control unit 60 supplies hydrogen from the hydrogen supply unit 30 into the reaction tube 10 and controls the supply amount of hydrogen to a larger amount than the above equation (2) becomes in an equilibrium state. Therefore, in the methane production system 100 of the present embodiment, since the amount of hydrogen supplied during the methanation reaction is larger than the equilibrium state of the methanation reaction, desorption of carbon dioxide from calcium carbonate and generation of methane. And proceed. The heat generated by the methanation reaction is used for the endothermic reaction when calcium carbonate changes into calcium oxide. As a result, the calorific value of the methanation reaction does not cause energy loss. Further, since the exothermic reaction when calcium oxide stores carbon dioxide contained in the combustion gas proceeds even at a temperature higher than the temperature at which the methanation reaction easily proceeds, the heat generated by the methanation reaction is used at a higher temperature. it can. Further, since the amount of hydrogen supplied during the methanation reaction is larger than that in the equilibrium state, desorption of carbon dioxide from calcium carbonate can be sufficiently performed, and the change from calcium oxide to calcium carbonate can be reversibly performed. You can do it. Thereby, as compared with the case where calcium oxide stores carbon dioxide by chemisorption, calcium oxide can store more carbon dioxide. Further, as compared with Comparative Example 2 shown in FIG. 4, when obtaining the same amount of heat as combustion heat, methane has a smaller volume than hydrogen, so that the fuel tank 40 for storing fuel can be downsized.

Further, the fuel production system 100 according to the present embodiment includes the downstream CO ₂ sensor 52 that detects carbon dioxide contained in the gas discharged from the reaction tube 10 after the methanation reaction. The control unit 60 can manage the concentration of carbon dioxide in the combustion gas that passes through the reaction tube 10 and is released to the atmosphere from the detection value of the downstream CO ₂ sensor 52. In the storage step (step S1) shown in FIG. 2, when the amount of carbon dioxide stored by calcium oxide approaches the amount that can be stored by calcium oxide, the concentration of carbon dioxide detected by the downstream CO ₂ sensor 52. Becomes higher. When the detected carbon dioxide concentration is equal to or higher than the preset allowable value, the control unit 60 ends the occlusion step and shifts to the methanation step (step S3). As a result, it is not necessary to supply more than necessary combustion gas to the storage reduction catalyst 11 that has been unable to store carbon dioxide.

Further, the control unit 60 in the present embodiment sets the amount of hydrogen supplied into the reaction tube 10 during the methanation reaction to an amount corresponding to the stoichiometric ratio based on the above equation (2) and the above equation ( It is set to the amount of the product of the reciprocal of the hydrogen utilization rate shown in 3). This supplies the hydrogen required to completely transform calcium carbonate into calcium oxide.

Further, the methane production system 100 in the present embodiment includes the combustion gas supply path 29 for supplying the combustion gas containing carbon dioxide to the reaction tube 10 and the heat generated when the storage reduction catalyst 11 stores the carbon dioxide. And a treated combustion gas supply passage 59 for supplying gas to another device 50. Therefore, the heat generated in the exothermic reaction in which the storage reduction catalyst 11 stores carbon dioxide is transferred to another device 50 which is a heat demander. Further, the storage reduction catalyst 11 is added with alumina as a sintering suppressing material. Therefore, the storage reduction catalyst 11 can repeat the storage and desorption of carbon dioxide.

<Modification of this embodiment>
The present invention is not limited to the above embodiment, and can be implemented in various modes without departing from the scope of the invention, and the following modifications are possible, for example.

[Modification]
In the above embodiment, the methane production system 100 has been described as an example, but the methane production system can be variously modified. The methane production system 100 includes a reaction tube 10 having an occlusion reduction catalyst 11 for occluding carbon dioxide and producing methane using hydrogen, and a combustion gas flow meter 21 for detecting the amount of combustion gas supplied to the reaction tube 10. It suffices to include a hydrogen supply unit 30 that supplies hydrogen to the reaction tube 10 and a control unit 60 that controls the supply amount of hydrogen. Therefore, the methane production system 100 may not include the methane sensor 41, for example. The control unit 60 determines the amount of hydrogen represented by the product of the amount corresponding to the stoichiometric ratio based on the above equation (2) and the reciprocal of the hydrogen utilization rate indicated by the above equation (3). Is preferably supplied to

The control of various valves in the methane production by the control unit 60 in the above embodiment is an example, and can be variously modified. In the methane production of the above-described embodiment, when the two valves, the combustion gas valve 24 and the outlet valve 54, and the hydrogen supply valve 34 and the fuel valve 44, are open, the other two valves are closed. In other embodiments, the opening and closing of each valve may be freely controlled within a range where adsorption and desorption of carbon dioxide by the storage reduction catalyst 11 and production of methane are performed.

Further, the control unit 60 may calculate the carbon dioxide stored in the storage reduction catalyst 11 by using the detected value of the upstream CO ₂ sensor 22 and the detected value of the downstream CO ₂ sensor 52. The control unit 60 does not have to determine the end of the occlusion step using the detection value of the downstream CO ₂ sensor 52. The control unit 60 may supply the amount of hydrogen required for the methanation reaction based on the calculated storage amount of carbon dioxide. The control of the hydrogen supply amount by the control unit 60 can be modified in various ways. For example, the control unit 60 may include the upstream CO ₂ sensor 22 or the downstream CO ₂ sensor 52, and may control the supply amount of hydrogen using the detection value of the sensor.

In the above embodiment, the control unit 60 controls the amount of hydrogen supplied into the reaction tube 10 from the amount of hydrogen corresponding to the stoichiometric ratio based on the above formula (2). The supply amount of hydrogen may be determined based on index values other than. For example, the control unit 60 uses the detection value of the methane sensor 41 to calculate the production amount of methane. The control unit 60 may control the supply amount of hydrogen based on the calculated production amount of methane. Further, the control unit 60 may open the hydrogen supply valve 34 at a predetermined opening degree for a predetermined time regardless of the detection values of various sensors.

The control unit 60 may store the relationship between the partial pressures shown in FIG. The control unit 60 may treat the average value of the detection values of the upstream temperature sensor 23 and the downstream temperature sensor 53 as the temperature inside the reaction tube 10. In this case, the control unit 60 and the upstream temperature sensor 23 and the downstream temperature sensor 53 function as a temperature acquisition unit. As a result, the supply amount of hydrogen required for advancing methanation is supplied into the reaction tube 10 in accordance with each partial pressure in the equilibrium state shown in FIG.

The means for specifying the temperature of the storage reduction catalyst 11 can be variously modified. For example, the methane production system 100 may include the upstream temperature sensor 23 or the downstream temperature sensor 53, and treat any detected value as the temperature of the storage reduction catalyst 11. Further, a temperature sensor may be attached to the reaction tube 10 or the storage reduction catalyst 11, and the detection value of the temperature sensor may be treated as the temperature of the storage reduction catalyst 11. Further, the methane production system 100 may include a temperature adjusting unit that heats or cools the reaction tube 10 using the temperature of the reaction tube 10 acquired by the upstream temperature sensor 23 or the like. A well-known heater or cooler can be used as the temperature adjusting unit.

In the above embodiment, calcium oxide has been described as an example of the metal oxide contained in the storage reduction catalyst 11, but the metal oxide can store carbon dioxide and desorbs the stored carbon dioxide by supplying hydrogen. Any compound can be used. The metal oxide preferably contains at least one of lithium oxide, magnesium oxide, strontium oxide, barium oxide, and lead oxide other than calcium oxide. The reaction tube 10 may include a plurality of metal oxides or may include metal oxides having different physical properties. Further, although alumina as a sintering suppressing material was added to the storage reduction catalyst 11, alumina may not be added, or another sintering suppressing material may be added. The other sintering suppressing material may be, for example, ceria. The storage reduction catalyst 11 is a composite of a metal oxide, a sintering suppressing material, and a methanation catalyst. However, the metal oxide added with the sintering suppressing material and the methanation catalyst are separated in the reaction tube 10. May be located at.

Although the present aspect has been described above based on the embodiment and the modified examples, the embodiment of the aspect described above is intended to facilitate understanding of the present aspect and does not limit the present aspect. The present embodiment can be modified and improved without departing from the spirit and scope of the claims, and the present embodiment includes the equivalents thereof. If the technical features are not described as essential in this specification, they can be deleted as appropriate.

10 ... the reaction tube 11 ... carbon dioxide storage-reduction catalyst 20 ... combustion device 21 ... combustion gas flowmeter 22 ... upstream CO ₂ sensor 23 ... upstream temperature sensor (temperature acquisition unit)
24... Combustion gas valve 29... Combustion gas supply path (supply pipe)
30... Hydrogen supply part 31... Hydrogen flow meter 34... Hydrogen supply valve 39... Hydrogen supply path 40... Fuel tank 41... Methane sensor 42... Hydrogen sensor 44... Fuel valve 49... Fuel supply path 50... Device 52... Downstream CO ₂ Sensor (downstream concentration acquisition unit)
53... Downstream temperature sensor (temperature acquisition unit)
54... Outlet valve 59... Treated combustion gas supply path (heat transfer section)
60... Control unit 100... Methane production system

Claims (6)

A methane production system,
A reaction tube having a carbon dioxide storage reduction catalyst;
A hydrogen supply unit for supplying hydrogen to the reaction tube,
A control unit for controlling the amount of hydrogen supplied by the hydrogen supply unit,
The carbon dioxide storage reduction catalyst,
A metal oxide that absorbs and releases carbon dioxide,
A methanation catalyst that promotes a methanation reaction that produces methane from hydrogen and carbon dioxide,
The said control part is a methane manufacturing system which makes the said supply amount larger than the amount of hydrogen equivalent to the stoichiometric ratio based on the reaction formula of the said methanation reaction. The methane production system according to claim 1, further comprising:
A downstream concentration acquisition unit for acquiring the concentration of carbon dioxide contained in the gas discharged from the reaction tube,
The control unit, when the carbon dioxide storage reduction catalyst is storing carbon dioxide, when the concentration of carbon dioxide acquired by the downstream concentration acquisition unit reaches a preset allowable value, A methane production system that terminates the storage of carbon dioxide by a carbon storage reduction catalyst. The methane production system according to claim 1 or 2, further comprising:
A temperature acquisition unit for acquiring the temperature of the reaction tube,
A temperature control unit that heats or cools the reaction tube using the temperature acquired by the temperature acquisition unit. The methane production system according to any one of claims 1 to 3,
The methane production system, wherein the metal oxide contains at least one of lithium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, and lead oxide. The methane production system according to any one of claims 1 to 4, further comprising:
A heat transfer unit for transferring the heat generated by the metal oxide by occlusion of carbon dioxide from the reaction tube to another device,
A supply pipe for supplying a gas containing carbon dioxide to the reaction pipe. The methane production system according to any one of claims 1 to 5, wherein:
The carbon dioxide occlusion reduction catalyst is a methane production system to which an oxide as the sintering suppressing material is added.

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