JP2019123678A - Methane manufacturing device, and methane manufacturing method - Google Patents

Abstract

To simplify a device configuration and make a methane production amount stationary in manufacturing methane using a catalyst having occlusion of carbon dioxide and reduction performance.SOLUTION: A methane manufacturing device for manufacturing methane from carbon dioxide and hydrogen, has a first reactor and a second reactor housing a slurry containing a catalyst having occlusion of carbon dioxide and reduction performance, a raw material gas supply part for supplying a raw material gas containing carbon dioxide to the first reactor, a reduction gas supply part for supplying a reduction gas containing hydrogen to the second reactor, a first flow channel formation part for forming a first flow channel for transporting a slurry from the first reactor to the second reactor, a second flow channel formation part for forming a second flow channel for transporting the slurry from the second reactor to the first reactor and a pump for circulating the slurry between the first reactor and the second reactor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a methane production apparatus.

Techniques for producing methane (CH ₄ ) from carbon dioxide (CO ₂ ) and hydrogen (H ₂ ) are known. For example, Non-Patent Document 1 discloses a first step of storing carbon dioxide from a raw material gas, and reduction of stored carbon dioxide in a single reactor containing a catalyst having a carbon dioxide storage and reduction performance. It is described to carry out both of the second step of producing methane. For example, Patent Document 1 includes a plurality of reactors (reactor), and in one reactor, carries out the first step of simultaneously supplying carbon dioxide and hydrogen to convert carbon dioxide into carbon (C). In another reactor, the second step of stopping the supply of carbon dioxide and continuing the supply of hydrogen to convert carbon to methane is performed, and it is described to switch the role of these reactors at regular intervals. There is.

Zheng, Qinghe, Robert Farrauto, and Anh Chau Nguyen, "Adsorption and methanation of exhaust gas CO2 by dual-function catalytic materials: A parametric study of adsorption and methanation of Flue gas with dual functional catalytic materials: A Parametric Study." Industrial & Engineering Chemistry Research, American Chemical Society, June 2016, 55 (24), p. 6768-6776

JP-A-5-193920

In Non-Patent Document 1, a raw material gas containing carbon dioxide is supplied into the reactor in the first step, and a reducing gas containing hydrogen is supplied into the reactor in the second step. That is, in Non-Patent Document 1, it is necessary to switch the gas to the reactor between the first and second steps, so it is necessary to provide a large number of valves in the reactor, and there is a problem that the apparatus configuration becomes complicated. The Specifically, at least the valve for supplying the source gas and the valve for supplying the reducing gas are required upstream of the reactor, and at least the valve for discharging oxygen and the valve for discharging methane are required downstream of the reactor It is. Further, in the case of providing a purge step of discharging the residual gas in the reactor between the first and second steps, an additional valve for supplying and discharging nitrogen (N ₂ ) gas for purge is required.

  Furthermore, in Non-Patent Document 1, the first step of storing carbon dioxide and the second step of producing methane are sequentially performed while switching the type of gas supplied to the reactor. For this reason, in the nonpatent literature 1, the quantity (methane production amount) of the methane produced | generated by the storage and reduction | restoration of a carbon dioxide fluctuate | varies with time, and the subject that it could not be stabilized was occurred.

  In Patent Document 1, since the catalyst moves between a plurality of reactors, switching of the gas to the reactors is not necessarily required, and it is not always necessary to provide a large number of valves. However, Patent Document 1 does not describe at all the production of methane using a catalyst having carbon dioxide storage and reduction performance. Furthermore, in Patent Document 1, since the gas containing carbon dioxide serves as a carrier for catalyst transport between reactors, the amount of carbon recovered in a reactor that carries out the first step of converting carbon dioxide to carbon becomes a trend . Along with this, the amount of methane generated by the reaction of carbon and hydrogen (the amount of generated methane) also becomes the same as the amount of recovered carbon, and there is a problem that the amount of generated methane can not be stabilized.

  The present invention has been made to solve the above-mentioned problems, and in the production of methane using a catalyst having a carbon dioxide storage and reduction performance, simplification of the apparatus configuration and stabilization of the amount of methane production are realized. The purpose is to

  The present invention has been made to solve at least a part of the above-mentioned problems, and can be realized as the following modes.

(1) According to one aspect of the present invention, there is provided a methane production apparatus for producing methane from carbon dioxide and hydrogen. This methane production apparatus supplies a first reactor and a second reactor containing a slurry containing a catalyst having a carbon dioxide storage and reduction performance, and supplies a raw material gas containing carbon dioxide to the first reactor. A source gas supply unit, a reduction gas supply unit supplying a reduction gas containing hydrogen to the second reactor, and transferring the slurry from the first reactor to the second reactor A first flow passage forming portion forming a first flow passage, and a second flow passage forming portion forming a second flow passage for transferring the slurry from the second reactor to the first reactor; And a pump for circulating the slurry between the first reactor and the second reactor.

  According to this configuration, in the first reactor, carbon dioxide contained in the raw material gas supplied from the raw material gas supply unit is stored in the catalyst. In the second reactor, hydrogen contained in the reducing gas supplied from the reducing gas supply unit reacts with carbon dioxide stored in the catalyst to generate methane. In this configuration, the catalyst contained in the first and second reactors is in the form of a slurry capable of flowing, and the slurry between the first reactor and the second reactor by the first and second flow passage forming portions and the pump. Circulate. For this reason, it is not necessary to carry out both the storage step of carbon dioxide from the raw material gas and the methanation step of carbon dioxide using a reducing gas in a single reactor as in the prior art. The same gas can always be supplied to the two reactors. As a result, according to the present configuration, switching of the gas to the reactor and a mechanism (such as a valve) for switching the gas are not necessary, so the apparatus configuration of the methane production apparatus can be simplified. Furthermore, according to this configuration, it is not necessary to switch the gas to the reactor, so the flow rate of the source gas from the source gas supply unit to the first reactor and the reducing gas from the reducing gas supply unit to the second reactor By stabilizing the flow rate of methane, it is possible to make methane production steady. As described above, according to the present configuration, simplification of the device configuration and steadyization of the amount of generated methane can be achieved in the production of methane using a catalyst having storage and reduction performance of carbon dioxide. Furthermore, according to this configuration, the residence time of the catalyst in the first and second reactors can be controlled by changing the flow rate of the pump. Therefore, for example, even when the flow rate and the composition (content of carbon dioxide) of the raw material gas supplied from the raw material gas supply unit to the first reactor change, the target carbon dioxide recovery rate is to be achieved. The residence time required for the

(2) In the methane production apparatus of the above aspect, further, a first concentration acquisition unit that acquires the concentration of carbon dioxide in the source gas, a first flow rate acquisition unit that acquires the flow rate of the source gas, and the first reaction A second concentration acquisition unit that acquires a carbon dioxide concentration in the exhaust gas discharged from the processing unit; a second flow rate acquisition unit that acquires a flow rate of the exhaust gas discharged from the first reactor; May be provided. The control unit is configured to control the pump according to at least a part of the values acquired by the first concentration acquisition unit, the first flow amount acquisition unit, the second concentration acquisition unit, and the second flow amount acquisition unit. At least one of the reducing gas from the reducing gas supply unit may be controlled. According to this configuration, the control unit, for example, responds to at least a portion of the carbon dioxide concentration in the source gas, the flow rate of the source gas, the carbon dioxide concentration in the exhaust gas, and the flow rate of the exhaust gas, for example It is possible to control the flow rate and presence / absence of operation of a pump for circulating the slurry containing the catalyst, the flow rate and concentration of the reducing gas supplied from the reducing gas supply unit, and the like. For this reason, according to the present configuration, it is possible to further stabilize the amount of generated methane in methane production using a catalyst having storage and reduction performance of carbon dioxide.

(3) In the methane production apparatus of the above aspect, the control unit is configured to control the concentration of carbon dioxide in the raw material gas acquired by the first concentration acquisition unit and the raw material gas acquired by the first flow rate acquisition unit. The flow rate of the pump may be changed in inverse proportion to both the flow rate. According to this configuration, the control unit changes the flow rate of the pump in inverse proportion to both the carbon dioxide concentration in the raw material gas and the flow rate of the raw material gas, so that carbon dioxide is sufficiently absorbed by the catalyst in the first reactor. The catalyst can be allowed to stay in the first reactor for a period of time until it is done. As a result, the carbon dioxide recovery amount in the first reactor can be improved.

(4) In the methane production apparatus of the above aspect, the control unit is configured to control the concentration of carbon dioxide in the raw material gas acquired by the first concentration acquisition unit and the raw material gas acquired by the first flow rate acquisition unit. The amount of carbon dioxide in the source gas determined from the flow rate, the concentration of carbon dioxide in the exhaust gas acquired by the second concentration acquisition unit, and the flow rate of the exhaust gas acquired by the second flow rate acquisition unit The carbon dioxide recovery amount in the first reactor is determined by reducing the carbon dioxide amount in the exhaust gas determined from the above and proportional to both the determined carbon dioxide recovery amount and the flow rate of the pump. Alternatively, the amount of supply of the reducing gas from the reducing gas supply unit may be changed. According to this configuration, the control unit changes the supply amount of the reducing gas in proportion to both of the carbon dioxide recovery amount in the first reactor and the flow rate of the pump, so that the carbon dioxide in the second reactor is changed each time. It is possible to supply just enough amount of hydrogen for the reduction of As a result, the amount of generated methane in the second reactor can be improved, and the amount of consumption of reducing gas can be suppressed.

(5) In the methane production apparatus of the above aspect, a third reactor provided on the first channel and containing the slurry, and a fourth reaction provided on the second channel and containing the slurry are further provided. And / or a purge gas supply unit for supplying a purge gas to at least one of the third reactor and the fourth reactor. According to this configuration, the third reactor can be used to discharge the gas (oxygen, nitrogen, etc.) remaining in the catalyst contained in the slurry transferred on the first flow path. In addition, the fourth reactor can be used to discharge the gas (such as hydrogen) remaining in the catalyst contained in the slurry transferred on the second flow path.

(6) In the methane production apparatus of the above aspect, of the first gas-liquid separator provided on the first flow path and the second gas-liquid separator provided on the second flow path, At least one of them may be provided. According to this configuration, the gas (oxygen, nitrogen, etc.) remaining in the catalyst contained in the slurry transferred on the first flow path can be discharged using the first gas-liquid separator. In addition, the second gas-liquid separator can be used to discharge the gas (such as hydrogen) remaining in the catalyst contained in the slurry transferred on the second flow path.

(7) In the methane production apparatus of the above aspect, the catalyst is at least one of an alkali metal which forms carbonate and stores carbon dioxide, an alkaline earth metal, and a metal having methanation catalytic performance. May be included. According to this configuration, various catalysts can be used as a catalyst having carbon dioxide storage and reduction performance.

(8) According to one aspect of the present invention, there is provided a methane production method for producing methane from carbon dioxide and hydrogen. This methane production method comprises the steps of: supplying a raw material gas containing carbon dioxide to a first reactor containing a slurry containing a catalyst having a carbon dioxide storage and reduction performance; and a second reaction containing the slurry Supplying a reducing gas containing hydrogen to the reactor, a first flow path for transferring the slurry from the first reactor to the second reactor, and the second flow from the second reactor Circulating the slurry between the first reactor and the second reactor using the second flow path for transferring the slurry to the one reactor.

  The present invention can be realized in various aspects, for example, a methane production apparatus for producing methane from carbon dioxide and hydrogen, a methane production method, a methane production system, and control of these apparatuses and systems. The present invention can be realized in the form of a computer program, a server device for distributing the computer program, and a non-temporary storage medium storing the computer program.

It is a figure explaining schematic structure of the methane production apparatus in a 1st embodiment. It is a figure showing the time change of the amount of methane production. It is a figure explaining schematic structure of the methane production apparatus in a 2nd embodiment. It is a figure explaining schematic structure of the methane production apparatus in a 3rd embodiment. It is a figure explaining schematic structure of the methane production apparatus in a 4th embodiment. It is a conceptual diagram of a pump flow rate map and a reduction gas flow rate map. It is a flowchart which shows the procedure of flow control by a control part.

First Embodiment
FIG. 1 is a view for explaining a schematic configuration of the methane production apparatus 1 in the first embodiment. The methane production apparatus 1 of the present embodiment is an apparatus for producing methane (CH ₄ ) from carbon dioxide and hydrogen (H ₂ ) using a catalyst having storage and reduction performance of carbon dioxide (CO ₂ ). The methane production apparatus 1 includes a first reactor 10, a second reactor 20, a source gas supply unit 15, a reducing gas supply unit 25, and a slurry pump 30.

The methane production apparatus 1 uses a catalyst (hereinafter, also simply referred to as “catalyst”) having CO ₂ storage and reduction performance. For example, in the present embodiment, a catalyst containing at least one of an alkali metal that forms carbonate and stores CO ₂ , an alkaline earth metal, and a metal having methanation catalytic performance. Can be used. In the methane production apparatus 1, the above-mentioned powdery catalyst is mixed with a fluid such as silicone oil to make a slurry (hereinafter, also simply referred to as "slurry"), used for CO ₂ storage and reduction Do. That is, the catalyst used in the methane production apparatus 1 is in the form of fluid (slurry).

The first reactor 10 is a reactor (container) for storing CO ₂ contained in the raw material gas in the catalyst. The slurry is contained inside the first reactor 10. The first reactor 10 includes a supply pipe 11 through which the raw material gas from the raw material gas supply unit 15 flows, and a discharge pipe 12 through which the exhaust gas (O ₂ , N _2, etc.) from the first reactor 10 flows. The second flow path forming unit 31 for transferring the slurry from the slurry pump 30 to the first reactor 10, and the first flow path formation for transferring the slurry from the first reactor 10 to the second reactor 20 The units 13 are connected to one another.

The second reactor 20 is a reactor (container) for the methanation reaction. In the second reactor 20, CH ₄ is produced by the Sabatier reaction using CO ₂ stored in the slurry and H ₂ contained in the reducing gas. The slurry is contained in the second reactor 20 in the same manner as the first reactor 10. In the second reactor 20, a supply pipe 21 through which the reduction gas from the reduction gas supply unit 25 flows, an exhaust pipe 22 through which the reaction mixture gas (CH ₄ etc.) in the second reactor 20 flows, and A first flow path forming portion 13 for transferring slurry from the reactor 10 to the second reactor 20, and a second flow path forming portion 23 for transferring slurry from the second reactor 20 to the slurry pump 30 And are connected respectively.

The sizes (diameter and height of the container) of the first reactor 10 and the second reactor 20 may be the same or different. The sizes of the first reactor 10 and the second reactor 20 are preferably determined according to the characteristics of the catalyst. For example, when the reduction rate of CO ₂ is slower than the storage rate, the first reactor 10 is It is preferable to design the size of the second reactor 20 larger than that. Then, the time for which the catalyst stays in the second reactor 20 can be made longer than the time for staying in the first reactor 10.

The raw material gas supply unit 15 is a device for supplying a raw material gas to the first reactor 10, and is constituted of, for example, a combustion furnace or a raw material gas tank. The source gas may contain oxygen (O ₂ ), nitrogen (N ₂ ), and the like in addition to CO ₂ used for the generation of CH ₄ . The raw material gas supply unit 15 is connected to a supply pipe 11 through which the raw material gas from the raw material gas supply unit 15 flows to the first reactor 10. The source gas supply unit 15 of the present embodiment always supplies the source gas to the first reactor 10. Therefore, the supply pipe 11 may not be provided with a mechanism (valve or the like) that switches between supply and shutoff of the source gas.

The reducing gas supply unit 25 is a device for supplying a reducing gas to the second reactor 20, and is constituted of, for example, a water electrolysis device or a hydrogen tank. The reducing gas may contain N ₂ or the like in addition to H ₂ used to generate CH ₄ . The reduction gas supply unit 25 is connected to a supply pipe 21 through which the reduction gas from the reduction gas supply unit 25 to the second reactor 20 flows. The reducing gas supply unit 25 of the present embodiment constantly supplies the reducing gas to the second reactor 20. Therefore, like the supply pipe 11, the supply pipe 21 may not be provided with a mechanism (such as a valve) that switches between the supply and shutoff of the reducing gas.

  Between the first reactor 10 and the second reactor 20, the slurry pump 30 is provided on the second flow path, and transfers the slurry in the direction of the white arrow and the dashed hatching arrow (FIG. 1). Is a pump that circulates the slurry. In addition, a "1st flow path" is a flow path for transferring a slurry from the 1st reactor 10 to the 2nd reactor 20, and is formed of the 1st flow path formation part 13 (FIG. 1: White arrow). The “second flow passage” is a flow passage for transferring the slurry from the second reactor 20 to the first reactor 10, and is formed by the second flow passage forming portion 23 and the second flow passage forming portion 31. (Figure 1: hatched arrows).

A methane production method using the methane production apparatus 1 will be described. As described above, each of the first reactor 10 and the second reactor 20 contains a catalyst having an ability to store and reduce CO ₂ . First, in the first reactor 10, CO ₂ contained in the source gas supplied from the source gas supply unit 15 is stored in the catalyst. The other components (for example, O ₂ , N _2, etc.) contained in the source gas are discharged from the discharge pipe 12 as an exhaust gas. The exhaust gas may be discharged to the outside, for example, may be separated into gas types and stored in a gas tank (not shown).

The catalyst in a state in which CO ₂ is stored is transferred by the slurry pump 30 from the first reactor 10 to the second reactor 20 through the first flow path (FIG. 1: white arrow). That is, the catalyst in a state in which CO ₂ is stored is supplied to the second reactor 20.

Next, in the second reactor 20, H ₂ contained in the reducing gas supplied from the reducing gas supply unit 25 reacts with CO ₂ stored in the catalyst (Sabatier reaction), and a reaction containing CH ₄ A mixed gas is produced. The reaction mixed gas is discharged from the discharge pipe 22 and separated as it is or by the type of gas, and accumulated in a gas tank (not shown).

The catalyst after CO ₂ storage is transferred from the second reactor 20 to the first reactor 10 through the second flow path (FIG. 1: hatched arrows) by the slurry pump 30. . That is, the catalyst in a state where CO ₂ is not stored is supplied to the first reactor 10.

As described above, in the methane production apparatus 1 of the present embodiment, the catalyst contained in the first and second reactors 10 and 20 is made in the form of a slurry capable of flowing, and the first and second flow passage forming portions 13, 23 and 31 The slurry is circulated between the first reactor 10 for storing CO ₂ in the catalyst and the second reactor 20 for the methanation reaction by the slurry pump 30. For this reason, in the methane production apparatus 1 of the present embodiment, as in the prior art, the storage step of carbon dioxide (CO ₂ ) from the raw material gas and methane of CO ₂ using the reducing gas in a single reactor It is not necessary to carry out both the (CH ₄ ) conversion step, and the first and second reactors 10 and 20 can always be supplied with the same gas. As a result, according to the methane production apparatus 1 of the present embodiment, it is possible to simplify the apparatus configuration of the methane production apparatus 1 because it is not necessary to switch the gas to the reactor and a large number of valves associated therewith.

FIG. 2 is a diagram showing time change of methane (CH ₄ ) production amount. The vertical axis represents CH ₄ production [mol / min], and the horizontal axis represents time. In FIG. 2, the change S of the CH ₄ production amount by the methane production apparatus 1 of this embodiment, the change S 1 of the CH ₄ production amount by the methane production apparatus of the first comparative example, and the methane production apparatus of the second comparative example CH ₄ production amount of change S2 (1) and showing the (2). The first comparative example, in a single reactor containing a solid catalyst layer having absorbing and reduction performance of CO _2, a first step of storing CO ₂ from the raw material gas, the occluded CO ₂ reduced to methane production apparatus for sequentially carrying out a second step of generating a CH _4. The second comparative example is a methane production apparatus in which reactors are multi-staged in the same configuration as the first comparative example.

As apparent from the change S1 (one-dot chain line) in FIG. 2, in the first comparative example, the CH ₄ is performed during the time t _n to t _{n + 1} when the first step of storing CO ₂ from the source gas is performed. Does not occur. In addition, "n" means arbitrary time after the process start. Furthermore, in the first comparative example, the methane production amount is parabolic even during time t _{n + 1} to t _{n + 2} in which the second step of reducing occluded CO ₂ to generate CH ₄ is performed. It does not take a fixed value. This is because there is a time delay between the opening and closing of the reducing gas supply valve and the stabilization of the reducing gas flow rate, and the total amount and distribution of CO ₂ stored in the catalyst layer with the passage of time. Cause changes, etc.

A change S2 (1) indicated by a broken line in FIG. 2 represents the amount of methane produced by the first stage reactor of the second comparative example, and a change S2 (2) occurs by the second stage reactor of the second comparative example. Represents methane production. For example, CH ₄ is generated by the first stage reactor between time t _n and t _{n + 1} by shifting the timings of the first and second steps by multi-staging the reactor, and from time t _{n + 1} During t _{n +2} , continuous processing is possible such that CH ₄ is produced by the second stage reactor. However, also in the second comparative example, as in the first comparative example, the methane production amount in each reactor is parabolic and does not take a constant value. The reason is as described above. In addition, when the reactor is multistaged, although it becomes possible to continuously process the source gas as described above, the total amount and distribution of CO ₂ stored in the catalyst layer change with the passage of time. The changes S2 (1) and S2 (2) of the methane production amount do not necessarily have the same locus of parabola.

On the other hand, in the methane production apparatus 1 of the present embodiment, as described above, it is not necessary to switch the gas to the reactor, the flow rate of the source gas from the source gas supply unit 15 to the first reactor 10; The flow rate of the reducing gas from the reducing gas supply unit 25 to the second reactor 20 can be made steady. The catalyst contained in the first and second reactors 10 and 20 is in the form of a fluidizable slurry. Therefore, the slurry flows not only between the first and second reactors 10 and 20 but also in each of the reactors 10 and 20, so that the total amount and distribution of CO ₂ stored in the catalyst are equalized. In addition, the temperature in the reactor can be made uniform. As a result of these, in the methane production apparatus 1 of the present embodiment, as is apparent from the change S (solid line) in FIG. 2, the methane production amount can be made steady. That is, in the methane production apparatus 1 of the present embodiment, the steady generation of CH ₄ which is difficult in the conventional configuration can be realized, and the robustness against load fluctuation can be improved.

As described above, according to the methane production apparatus 1 of the present embodiment, simplification of the apparatus configuration and stabilization of the methane production amount are achieved in production of methane using a catalyst having CO ₂ storage and reduction performance. be able to. Furthermore, according to the methane production apparatus 1, the residence time of the catalyst in the first and second reactors 10 and 20 can be controlled by changing the flow rate of the slurry pump 30. Therefore, for example, even when the flow rate and the composition (content of CO ₂ ) of the raw material gas supplied from the raw material gas supply unit 15 to the first reactor 10 change, the target CO ₂ in the first reactor 10 The residence time required to achieve the recovery rate can be easily secured.

Second Embodiment
FIG. 3 is a view for explaining the schematic configuration of a methane production apparatus 1a in the second embodiment. In the second embodiment, a configuration in which the gas remaining in the catalyst moving to the next reactor can be discharged will be described. The methane production apparatus 1a of the second embodiment further includes a third reactor 40, a fourth reactor 50, a first purge gas supply unit 45, and a second purge gas, in addition to the components of the first embodiment described above. And a supply unit 55. The differences from the first embodiment will be described below.

The third reactor 40 is provided on the first flow path, and the gas (O ₂ , N _2, etc.) remaining in the catalyst contained in the slurry transferred from the first reactor 10 to the second reactor 20 is It is a reactor (container) for discharging. The slurry is contained in the third reactor 40 as in the first reactor 10. The third reactor 40 includes a supply pipe 41 through which the purge gas from the first purge gas supply unit 45 flows, an exhaust pipe 42 through which the exhaust gas from the third reactor 40 flows, and the first reactor 10 to the third reactor 40. A first flow passage forming portion 13a for transferring the slurry to the reactor 40 and a first flow passage forming portion 43 for transferring the slurry from the third reactor 40 to the second reactor 20 are respectively provided. It is connected.

The fourth reactor 50 is provided on the second flow path and is for discharging a gas (such as H ₂ ) remaining in the catalyst contained in the slurry transferred from the second reactor 20 to the first reactor 10. Reactor (container). The slurry is contained in the fourth reactor 50 in the same manner as the first reactor 10. In the fourth reactor 50, the supply pipe 51 through which the purge gas from the second purge gas supply unit 55 flows, the discharge pipe 52 through which the exhaust gas from the fourth reactor 50 flows, and the second reactor 20 to the fourth A second flow passage forming portion 23a for transferring the slurry to the reactor 50 and a second flow passage forming portion 53 for transferring the slurry from the fourth reactor 50 to the slurry pump 30 are connected, respectively. ing.

The first purge gas supply unit 45 is a device for supplying a purge gas to the third reactor 40, and is constituted of, for example, a nitrogen gas generator or a nitrogen tank. The purge gas may contain CO ₂ , O _{2 and the} like in addition to N ₂ used for discharging the residual gas. The supply pipe 41 through which the purge gas from the first purge gas supply unit 45 to the third reactor 40 flows is connected to the first purge gas supply unit 45. The first purge gas supply unit 45 of the present embodiment always supplies the purge gas to the third reactor 40. Therefore, like the supply pipe 11, the supply pipe 41 may not be provided with a mechanism (valve or the like) that switches between supply and shutoff of the purge gas. The second purge gas supply unit 55 is an apparatus for supplying a purge gas to the fourth reactor 50, and the details thereof are the same as the first purge gas supply unit 45. The second purge gas supply unit 55 is connected to a supply pipe 51 through which the purge gas from the second purge gas supply unit 55 to the fourth reactor 50 flows.

  In the second embodiment, the first flow passage forming portion 13a and the first flow passage forming portion 43 form a "first flow passage", and the second flow passage forming portion 23a, the second flow passage forming portion 53, and the second The two flow passage forming portion 31 forms a "second flow passage". In the configuration described above, at least one of the third reactor 40 and the first purge gas supply unit 45, and the fourth reactor 50 and the second purge gas supply unit 55 may be omitted. Further, the first purge gas supply unit 45 and the second purge gas supply unit 55 may be configured by a single purge gas supply unit. In this case, both a supply pipe 41 for supplying the purge gas to the third reactor 40 and a supply pipe 51 for supplying the purge gas to the fourth reactor 50 are connected to a single purge gas supply unit.

Thus, in the methane production apparatus 1a of the second embodiment, the same effect as that of the above-described first embodiment can be obtained. Furthermore, in the methane production apparatus 1a of the second embodiment, the third reactor 40 is used to discharge the gas (O ₂ , N _2, etc.) remaining in the catalyst contained in the slurry transferred on the first flow path. it can. Moreover, the gas (H ₂ , N _2, etc.) remaining in the catalyst contained in the slurry transferred on the second flow path can be discharged using the fourth reactor. As a result, in the methane production apparatus 1a of the second embodiment, the mixture of O ₂ and H _{2 in the first} and _second reactors 10 and 20 can be suppressed.

Third Embodiment
FIG. 4 is a view for explaining the schematic configuration of a methane production apparatus 1b in the third embodiment. In the third embodiment, as in the second embodiment, a configuration capable of discharging the gas remaining in the catalyst moving to the next reactor will be described. The methane production apparatus 1b of the third embodiment further includes a first gas-liquid separator 60 and a second gas-liquid separator 70 in addition to the components of the first embodiment described above.

The first gas-liquid separator 60 is provided on the first flow path, and the gas (O ₂ , N _2, etc.) remaining in the catalyst contained in the slurry transferred from the first reactor 10 to the second reactor 20 ) Is a gas-liquid separator for separating and discharging. The slurry is contained in the first gas-liquid separator 60 as in the first reactor 10. In the first gas-liquid separator 60, a first flow path forming portion 13b for transferring the slurry from the first reactor 10 to the first gas-liquid separator 60, and a second gas-liquid separator 60 from the first gas-liquid separator 60 A first flow path forming unit 61 for transferring the slurry to the reactor 20 is connected to each other.

The second gas-liquid separator 70 is provided on the second flow path, and the gas (H ₂ , N _2, etc.) remaining in the catalyst contained in the slurry transferred from the second reactor 20 to the first reactor 10 ) Is a gas-liquid separator for separating and discharging. The slurry is contained in the second gas-liquid separator 70 as in the first reactor 10. In the second gas-liquid separator 70, a second flow path forming portion 23b for transferring the slurry from the second reactor 20 to the second gas-liquid separator 70, and a slurry pump from the second gas-liquid separator 70. A second flow path forming portion 71 for transferring the slurry to the surface 30 is connected to each other.

  In the third embodiment, the first flow passage forming portion 13 b and the first flow passage forming portion 61 form the “first flow passage”, and the second flow passage forming portion 23 b, the second flow passage forming portion 71, and the second flow passage forming portion The two flow passage forming portion 31 forms a "second flow passage". In the configuration described above, at least one of the first gas-liquid separator 60 and the second gas-liquid separator 70 may be omitted.

Thus, in the methane production apparatus 1b of the third embodiment, the same effect as that of the above-described first embodiment can be obtained. Furthermore, in the methane production apparatus 1b of the third embodiment, using the first gas-liquid separator 60, gas (O ₂ , N ₂ etc.) remaining in the catalyst contained in the slurry transferred on the first flow path Can be discharged. In addition, the second gas-liquid separator 70 can discharge the gas (H ₂ , N _2, etc.) remaining in the catalyst contained in the slurry transferred on the second flow path. As a result, also in the methane production apparatus 1b of the third embodiment, coexistence of O ₂ and H _{2 in the first} and _second reactors 10 and 20 can be suppressed.

Fourth Embodiment
FIG. 5 is a view for explaining the schematic configuration of a methane production apparatus 1c in the fourth embodiment. In the fourth embodiment, a configuration capable of controlling the flow rate of the slurry pump 30 and the supply amount of reducing gas from the reducing gas supply unit 25 will be described. The methane production apparatus 1c according to the fourth embodiment further includes a first flow meter 91, a second flow meter 92, a first concentration meter 95, and a second concentration meter, in addition to the components of the first embodiment described above. A mass flow controller 80 and a control unit 100 are provided.

  The first flow meter 91 is a flow sensor that measures the flow rate of the source gas supplied from the source gas supply unit 15 to the first reactor 10, and is provided in the supply pipe 11. Various types can be adopted as the first flow meter 91, and for example, a Karman vortex type, a thermal type, an ultrasonic type, etc. can be adopted. The first flow meter 91 functions as a “first flow rate acquisition unit” that acquires the flow rate of the source gas. When the control unit 100 can obtain information on the flow rate of the raw material gas from an apparatus (for example, a combustion furnace or a raw material gas tank) constituting the raw material gas supply unit 15, the control unit 100 functions as a first flow rate acquisition unit The first flow meter 91 may be omitted.

The first densitometer 95 is a concentration sensor that measures the CO ₂ concentration of the raw material gas supplied from the raw material gas supply unit 15 to the first reactor 10, and the gas jet port of the raw material gas supply unit 15 in the supply pipe 11 In the vicinity of the The first concentration meter 95 functions as a “first concentration acquisition unit” that acquires the CO ₂ concentration in the source gas. When the control unit 100 can obtain information on the concentration of CO ₂ in the raw material gas from the apparatus constituting the raw material gas supply unit 15, the control unit 100 functions as a first concentration acquisition unit to make the first concentration meter 95 may be omitted.

The second flow meter 92 is a flow sensor that measures the flow rate of the exhaust gas discharged from the first reactor 10, and is provided to the discharge pipe 12. Similar to the first flow meter 91, the second flow meter 92 can adopt various types. The second flow meter 92 functions as a “second flow rate acquisition unit” that acquires the flow rate of the exhaust gas. The second concentration meter 96 is a concentration sensor that measures the concentration of CO ₂ in the exhaust gas discharged from the first reactor 10, and is provided in the vicinity of the gas outlet of the first reactor 10 in the discharge pipe 12 There is. The second concentration meter 96 functions as a “second concentration acquisition unit” that acquires the CO ₂ concentration in the exhaust gas.

  The mass flow controller 80 is a device that includes a flow rate sensor, a flow rate control valve, and the like (not shown) and controls the flow rate of the reducing gas supplied from the reducing gas supply unit 25 to the second reactor 20. ing.

  The control unit 100 is a computer configured to include a ROM, a RAM, and a CPU, and controls each unit of the methane production apparatus 1c. The control unit 100 is electrically connected to the first and second flow meters 91 and 92, and the first and second densitometers 95 and 96, and acquires measurement values of each flow meter and each densitometer. Further, the control unit 100 is electrically connected to the slurry pump 30 and the mass flow controller 80, and controls the slurry pump 30 and the mass flow controller 80. The control unit 100 stores in advance a pump flow rate map 101 used to control the slurry pump 30 and a reducing gas flow rate map 102 used to control the mass flow controller 80.

FIG. 6 is a conceptual view of the pump flow rate map 101 and the reduction gas flow rate map 102. As shown in FIG. FIG. 6A shows a conceptual diagram of the pump flow rate map 101. As shown in FIG. In pump flow map 101, the vertical axis represents the concentration of CO ₂ in the feed gas (X _CO2 _ _in), the abscissa represents the flow rate of the source gas (Q _in [slm]). The density of the map represents the flow rate of the slurry pump 30, and the darker the color, the higher the flow rate of the slurry pump 30, and the thinner the color, the smaller the flow rate of the slurry pump 30.

As the concentration of CO ₂ in the source gas is higher, and as the flow rate of the source gas supplied to the first reactor 10 per unit time is larger, it takes more time for CO ₂ storage by the catalyst, The flow rate of the slurry pump 30 needs to be reduced. Therefore, in the pump flow rate map 101, the flow rate of the slurry pump 30 is inversely proportional to both the CO ₂ concentration in the source gas and the flow rate of the source gas. The pump flow rate map 101 is obtained in advance by an experiment or the like, and stored in a storage unit (ROM or the like) in the control unit 100.

FIG. 6B shows a conceptual diagram of the reducing gas flow rate map 102. As shown in FIG. In the reducing gas flow rate map 102, the vertical axis represents the amount of recovered CO ₂ (Q _ad [slm]) in the first reactor 10, and the horizontal axis represents the flow rate (Q _s [slm]) of the slurry pump 30. The density of the map represents the flow rate of the reducing gas controlled by the mass flow controller 80. The darker the color, the higher the flow rate of the reducing gas, and the thinner the color, the smaller the flow rate of the reducing gas.

CO ₂ recovery amount in the first reactor 10 (the amount of CO ₂ that is occluded in the catalyst) is meant the amount of CO ₂ that requires reduction in the second reactor 20. Further, the flow rate of the slurry pump 30 means the amount of catalyst supplied to the second reactor 20 per unit time. Therefore, as the amount of recovered CO ₂ in the first reactor 10 increases and as the flow rate of the slurry pump 30 increases, more H ₂ for CO ₂ reduction is consumed, so the flow rate of the reducing gas Need to do more. Therefore, in the reducing gas flow rate map 102, the flow rate of the reducing gas is made proportional to both the CO ₂ recovery amount in the first reactor 10 and the flow rate of the slurry pump 30. Similar to the pump flow rate map 101, the reduction gas flow rate map 102 is obtained in advance by experiments and the like, and is stored in a storage unit (ROM or the like) in the control unit 100.

The pump flow rate map 101 and the reduction gas flow rate map 102 shown in FIG. 6 indicate the CO ₂ storage rate and reduction rate in the catalyst used, the size of the first reactor 10 and the second reactor 20 used, and the target It fluctuates depending on the recovery rate of CO ₂ and the composition of the source gas and the reducing gas. Therefore, when it is desired to change each of these conditions in the subsequent flow control, the pump flow map 101 and the reduction gas flow map 102 need to be re-created.

FIG. 7 is a flowchart showing the flow control procedure by the control unit 100. The flow control is performed after the start of the operation of the methane production apparatus 1c, and is constantly performed during the operation of the methane production apparatus 1c. In the following description, a combustion furnace is illustrated as the source gas supply unit 15, and the case where the concentration of CO ₂ in the source gas and the flow rate of the source gas constantly fluctuate is illustrated.

In step S10, the control unit 100 initializes a time variable t [seconds] used for control to zero. Control unit in step S12 100 includes a flow rate Q _in (t) [slm] of the raw material gas measured by the first flow meter 91, CO ₂ concentration in the feed gas measured by the first densitometer 95 X _CO2 _ _{Get in} (t) and In step S14, the control unit 100 refers to the pump flow rate map 101 and obtains the flow rate Q _s (t) [slm] of the slurry pump 30 using each acquired value in step S12. In step S16, the control unit 100 changes the flow rate of the slurry pump 30 to the flow rate Q _s (t) obtained in step S14.

In step S18, the control unit 100 controls the flow rate Q _out (t) [slm] of the exhaust gas from the first reactor 10 measured by the second flow meter 92 and the first reaction measured by the second densitometer 96. and CO ₂ concentration in the exhaust gas from the vessel _{10 X CO2 _ out (t)} , to obtain the. In step S20, the control unit 100 obtains the CO ₂ recovery amount Q _ad (t) [slm] in the first reactor 10 from the following equation 1 using each acquired value in step S18.

In step S22, the control unit 100 refers to the reducing gas flow rate map 102 and calculates the CO ₂ recovery amount Q _ad (t) determined in step S20 and the flow rate Q _s (t) of the slurry pump 30 determined in step S14. Using this, the flow rate Q _r (t) [slm] of the reducing gas is obtained. In step S24, the control unit 100 changes the flow rate of the reducing gas from the mass flow controller 80 to the flow rate Q _r (t) obtained in step S22.

  In step S26, the control unit 100 determines whether the first time (Δt) [seconds] has elapsed. The first time Δt can be arbitrarily determined in advance, and can be an arbitrary value of, for example, about 0.1 to 5 seconds. If the first time has not elapsed (step S26: NO), the control unit 100 shifts the process to step S26 and monitors the elapse of the first time. When the first time has elapsed (step S26: YES), the control unit 100 shifts the process to step S28.

In step S28, the control unit 100 sets the flow rate Q _in (t + Δt) of the source gas after the first time has elapsed and the CO ₂ concentration X _CO2 _ _in (t + Δt) _{in the} source gas to the first flow meter 91 and the first flow meter. Acquired from a densitometer 95. In step S30, the control unit 100 increases or decreases the flow rate Q _in (t + Δt) of the source gas after the first time elapses from each acquired value in step S12 and each acquired value in step S28, and the first time elapses. the increase or decrease in the feed gas of CO ₂ concentration _{X CO2 _ in (t + Δt} ) after, it is judged whether or not the condition shown in the following equation 2. Here, α is a threshold value representing an increase / decrease amount [%] of the flow rate and concentration, and can be an arbitrary value of, for example, about 1 to 20. In Equation 2, the increase and decrease of the raw material gas flow rate Q _in (t + Δt), but to the increase or decrease in the raw material gas of the CO ₂ concentration _{X CO2 _ in (t + Δt} ) using the same threshold alpha, it has different thresholds It may be used.

If the condition shown in Formula 2 is satisfied (step S30: YES), the control unit 100 shifts the process to step S14, and the flow rate Q _in (t + Δt) of the source gas after the first time elapses, and CO ₂ in the source gas The flow rate Q _s (t + Δt) of the slurry pump 30 based on the concentration X _{CO 2 — in} (t + Δt) is determined, and the flow rate of the slurry pump 30 is changed. After that, the control unit 100 continues the processing after step S16.

On the other hand, when the condition shown in Formula 2 is not satisfied (step S30: NO), the control unit 100 shifts the process to step S32 and determines whether a second time (Δt _w ) [seconds] has elapsed. The second time Δt _w can be arbitrarily determined in advance, and can be an arbitrary value of, for example, about 30 to 600 seconds. When the second time has not elapsed (step S32: NO), the control unit 100 shifts the process to step S32 and monitors the elapse of the second time. When the second time has elapsed (step S32: YES), the control unit 100 shifts the process to step S28, and again using the acquired values of the first flow meter 91 and the first densitometer 95 at that time, It is determined whether the condition shown in Formula 2 is satisfied.

Thus, in the methane production apparatus 1c of the fourth embodiment, the same effect as that of the above-described first embodiment can be obtained. Furthermore, according to steps S12 to S16 of the flow control (FIG. 7) of the methane production apparatus 1c, the control unit 100 controls the CO ₂ concentration in the source gas acquired by the first densitometer 95 (first concentration acquisition unit). The flow rate of the pump is changed in inverse proportion to both the flow rate of the raw material gas acquired by the first flow meter 91 (first flow rate acquisition unit) (FIG. 6A). For this reason, according to the methane production apparatus 1c of the fourth embodiment, the catalyst can be kept in the first reactor 10 for a time until the CO ₂ is sufficiently stored in the catalyst in the first reactor 10. As a result, the CO ₂ recovery amount in the first reactor 10 can be improved.

Further, according to steps S18 to S24 of the flow control of the methane production apparatus 1c (FIG. 7), the control unit 100 controls the CO ₂ concentration in the raw material gas acquired by the first concentration meter 95 (first concentration acquisition unit). And “the amount of CO ₂ in the source gas” determined from the flow rate of the source gas acquired by the first flow meter 91 (first flow rate acquiring unit) by the second concentration meter 96 (second concentration acquisition unit) By reducing “the amount of carbon dioxide in the exhaust gas” obtained from the acquired CO ₂ concentration in the exhaust gas and the flow rate of the exhaust gas acquired by the second flow meter 92 (second flow rate acquisition unit) ( Formula 1) The CO ₂ recovery amount Q _ad in the first reactor 10 is determined. The control unit 100 changes the flow rate of the mass flow controller 80 in proportion to both the obtained amount of recovered CO ₂ in the first reactor 10 and the flow rate of the slurry pump 30, thereby changing the flow rate from the source gas supply unit 15 Change the reduction gas supply amount. For this reason, according to the methane production apparatus 1c of the fourth embodiment, it is possible to supply an amount of H ₂ that is just enough for reduction of CO ₂ in the second reactor 20 each time. As a result, the methane production amount in the second reactor 20 can be improved, and the consumption amount of the reducing gas can be suppressed.

The control content of the control unit 100 described in FIG. 7 is merely an example. Control unit 100, and the flow rate Q _in the feed gas obtained from the first flow meter 91, and the CO ₂ concentration X _CO2 _ _in the feed gas obtained from the first concentration meter 95, obtained from the second flow meter 92 and the flow rate Q _out of the exhaust gas from the first reactor 10, the CO ₂ concentration X _CO2 _ _out in the exhaust gas from the first reactor 10 acquired from the second densitometer 96, at least a portion of the Various controls for the slurry pump 30 and the mass flow controller 80 can be implemented using this. For example, instead of changing the flow rate of the slurry pump 30, the control unit 100 may control the drive and stop of the slurry pump 30. For example, instead of changing the flow rate of the reducing gas, the control unit 100 may change the concentration and the composition of the reducing gas, or may change the flow rate, the concentration, and the composition of the source gas. In this way, in methane production using a catalyst having CO ₂ storage and reduction performance, it is possible to further stabilize the methane production amount.

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

[Modification 1]
In the said 1st-4th embodiment, an example of a structure of the methane production apparatus was shown. However, the configuration of the methane production apparatus can be variously modified. For example, a plurality of at least one of the first reactor and the second reactor may be provided. When a plurality of first reactors or second reactors are provided, these reactors may be connected in series or in parallel. For example, when a plurality of second reactors are connected in series, for example, a gas-liquid separator is provided between the first reactor of the second stage and the second reactor of the second stage to obtain a reaction mixture gas. H ₂ O may be separated. For example, in the methane production apparatus of the fourth embodiment, a mass flow controller for controlling the flow rate of the source gas may be provided in the supply pipe from the source gas supply unit to the first reactor.

[Modification 2]
In the said 4th Embodiment, an example of the control content by the control part of the methane production apparatus was shown. However, the control contents by the control unit can be variously modified. For example, at least one of the flow rate control of the slurry pump in steps S12 to S16 and the flow rate control of the reducing gas in steps S18 to S24 may be omitted. When the flow control of the reducing gas in steps S18 to S24 is omitted, the mass flow controller may be omitted in the methane production apparatus shown in FIG. For example, additional processing not described may be added. As the further processing, for example, flow rate control of the source gas, concentration control of the reducing gas, composition control of the reducing gas, and the like can be adopted.

[Modification 3]
You may combine suitably the structure of the methane production apparatus of 1st-4th embodiment, and the structure of the methane production apparatus of the said modification 1-2. For example, in the methane production apparatus of the second and third embodiments, the first and second flow meters, the first and second densitometers, and the control unit are provided, and the control by the control unit described in the fourth embodiment is performed. It is also good. For example, the methane production apparatus of the second embodiment may further include the gas-liquid separator described in the third embodiment.

  As mentioned above, although this aspect was demonstrated based on embodiment and a modification, embodiment of the above-mentioned aspect is for making an understanding of this aspect easy, and does not limit this aspect. The present embodiment can be modified and improved without departing from the spirit and the scope of the claims, and the present embodiment includes the equivalents thereof. In addition, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

1, 1a to 1c: Methane production apparatus 10: first reactor 11: supply pipe 12: discharge pipe 13, 13a, 13b: first flow path forming unit 15: raw material gas supply unit 20: second reactor 21: supply Pipe 22 ... discharge pipe 23, 23a, 23b ... second flow path forming part 25 ... reducing gas supply part 30 ... slurry pump 31 ... second flow path forming part 40 ... third reactor 41 ... supply pipe 42 ... discharge pipe 43 ... 1st flow path formation part 45 ... 1st purge gas supply part 50 ... 4th reactor 51 ... supply pipe 52 ... discharge pipe 53 ... 2nd flow path formation part 55 ... 2nd purge gas supply part 60 ... 1st gas-liquid separation 61: First flow path forming portion 70: second gas-liquid separator 71: second flow path forming portion 80: mass flow controller 91: first flow meter 92: second flow meter 95: first densitometer 96: first density meter 2 Concentration meter 100 ... Control section 101 ... Pump flow map 102 ... Reduction gas flow rate map

Claims (8)

A methane production apparatus that produces methane from carbon dioxide and hydrogen,
A first reactor and a second reactor containing a slurry containing a catalyst having carbon dioxide storage and reduction performance;
A source gas supply unit configured to supply a source gas containing carbon dioxide to the first reactor;
A reducing gas supply unit for supplying a reducing gas containing hydrogen to the second reactor;
A first flow passage forming part forming a first flow passage for transferring the slurry from the first reactor to the second reactor;
A second flow passage forming part forming a second flow passage for transferring the slurry from the second reactor to the first reactor;
A pump for circulating the slurry between the first reactor and the second reactor;
, A methane production unit. The methane production apparatus according to claim 1, further comprising:
A first concentration acquisition unit that acquires a carbon dioxide concentration in the raw material gas;
A first flow rate acquiring unit that acquires a flow rate of the raw material gas;
A second concentration acquisition unit configured to acquire a carbon dioxide concentration in the exhaust gas discharged from the first reactor;
A second flow rate acquiring unit for acquiring a flow rate of the exhaust gas discharged from the first reactor;
The pump and the reduction gas supply according to at least a part of the values acquired by the first concentration acquisition unit, the first flow rate acquisition unit, the second concentration acquisition unit, and the second flow rate acquisition unit. A control unit that controls at least one of the reducing gas from the control unit;
, A methane production unit. The methane production apparatus according to claim 2, wherein
The control unit is inversely proportional to both the carbon dioxide concentration in the source gas acquired by the first concentration acquisition unit and the flow rate of the source gas acquired by the first flow rate acquisition unit. Methane production equipment that changes the flow rate of the pump. The methane production apparatus according to claim 2 or 3, wherein
The control unit
The amount of carbon dioxide in the source gas determined from the concentration of carbon dioxide in the source gas acquired by the first concentration acquisition unit and the flow rate of the source gas acquired by the first flow rate acquisition unit By reducing the amount of carbon dioxide in the exhaust gas determined from the concentration of carbon dioxide in the exhaust gas acquired by the second concentration acquisition unit and the flow rate of the exhaust gas acquired by the second flow rate acquisition unit Determining the carbon dioxide recovery amount in the first reactor,
The methane production apparatus which changes the supply amount of the said reduction gas from the said reduction gas supply part in proportion to both the calculated | required amount of said carbon dioxide collection | recovery and the flow volume of the said pump. The methane production apparatus according to any one of claims 1 to 4, further comprising:
A third reactor provided on the first channel and containing the slurry;
A fourth reactor provided on the second flow path and containing the slurry;
And at least one of the
A purge gas supply unit for supplying a purge gas to at least one of the third reactor and the fourth reactor;
, A methane production unit. The methane production apparatus according to any one of claims 1 to 5, further comprising:
A first gas-liquid separator provided on the first flow path;
A second gas-liquid separator provided on the second flow path;
An apparatus for producing methane, comprising at least one of the following. A methane production apparatus according to any one of claims 1 to 6, wherein
The said catalyst is a methane production apparatus containing at least any one of the alkali metal which forms carbonate, and occludes a carbon dioxide, alkaline-earth metal, and the metal which has methanation catalyst performance. A methane production method for producing methane from carbon dioxide and hydrogen, comprising:
Supplying a raw material gas containing carbon dioxide to a first reactor containing a slurry containing a catalyst having carbon dioxide storage and reduction performance;
Supplying a reducing gas containing hydrogen to a second reactor containing the slurry;
A first flow path for transferring the slurry from the first reactor to the second reactor, and a second flow path for transferring the slurry from the second reactor to the first reactor Circulating the slurry between the first reactor and the second reactor using
A method for producing methane, comprising:

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