JP2019108302A - Methane manufacturing device, controlling method of methane manufacturing device, and methane manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for reducing a methane production cost in a methane production apparatus. SOLUTION: A methane production apparatus for producing methane from carbon dioxide and hydrogen accommodates a catalyst containing a metal having a methaneation catalyst performance and a metal having a carbon dioxide storage performance, and takes out an internal gas. A plurality of reactors provided with outlets, a supply destination switching unit provided on a gas flow path between a supply source of carbon dioxide-containing raw material gas and a plurality of reactors, and a supply destination switching unit for switching the supply destination of the raw material gas, and each reaction. A control unit including a measurement unit that measures the carbon dioxide concentration at the outlet of the reactor and a control unit that can control the supply destination switching unit to supply the raw material gas to a specific reactor among a plurality of reactors. Switches the supply destination of the raw material gas to another reactor when the carbon dioxide concentration at the outlet of the reactor supplying the raw material gas reaches a predetermined value. [Selection diagram] Fig. 1

Description

  The present invention relates to a methane production apparatus, a control method of the methane production apparatus, and a methane production method.

Conventionally, techniques for producing methane CH ₄ from hydrogen H ₂ and carbon dioxide CO ₂ are known (see Patent Documents 1 and 2 and Non-patent Documents 1 and 2). For example, in Patent Document 1, carbon is deposited on the surface of ferrite by passing CO ₂ and H ₂ through ferrite in a temperature range of 300 to 400 ° C., and then ferrite is added in H ₂ without supplying CO _2. There is disclosed a technology for converting deposited carbon into methane by raising the temperature to 600 ° C. or higher. Further, in the cited document 2, a CO ₂ decomposition step of contacting the CO ₂ containing gas in the activation ferritic iron oxide obtained by removing the oxygen O ₂ in the ferritic iron oxide crystals, with CO ₂ decomposition step There is disclosed a technique of alternately repeating a process for producing methane, in which a gas containing H ₂ is brought into contact with the obtained activated ferritic iron oxide.

JP-A-5-193920 Japanese Patent Application Laid-Open No. 9-110731

Applied catalysis B: Environmental, 2015, 370-376 Catalysts, 2017, 88

In recent years, in order to suppress global warming, improvement of a technology for reducing CO ₂ emissions is desired by methanizing CO ₂ contained in combustion exhaust gas, biogas and the like. However, even with the above prior art, there is still room for improvement in the technology for producing methane from CO ₂ at low cost. For example, in the technology of Patent Document 1, since the reduction of carbon generated by the Bosch reaction requires a high temperature of 600 ° C. or more, the external energy needs to be supplied by the heater, and the cost reduction is not easy. In addition, since the carbon dioxide separator and the reactor are separately provided, there is a problem that the apparatus becomes complicated and large. In the technique of reference document 2, methane is obtained by circulating ferrite after CO ₂ decomposition by a closed circulation device for 10 to 12 times by a single-cylinder reactor, and therefore, it corresponds to continuous CO ₂ supply. Is difficult and there is a risk that the manufacturing efficiency may be reduced.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a technique for reducing the cost of producing methane in a methane producing apparatus for producing methane from H ₂ and CO ₂ .

  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 accommodates a catalyst containing a metal having methanation catalytic performance and a metal having carbon dioxide storage performance, and comprises a plurality of reactors provided with outlets for taking out internal gas, carbon dioxide A supply destination switching unit provided on a gas flow path between a supply source of a source gas to be contained and the plurality of reactors, and switching a supply destination of the source gas; and a carbon dioxide concentration at the outlet of each of the reactors And a control unit capable of supplying the source gas to a specific reactor among the plurality of reactors by controlling a measurement unit to be measured and the supply destination switching unit; When the carbon dioxide concentration at the outlet of the reactor supplying the gas reaches a predetermined value, the source gas supply destination is switched to the other reactor.

  According to this configuration, when the carbon dioxide concentration at the outlet of the reactor supplying the source gas reaches a predetermined value, the source gas is continuously continued to switch the source gas supply destination to another reactor. It can be fed to the reactor. Since the catalyst storing carbon dioxide by the supply of the source gas also has methanation catalyst performance, methane can be easily produced by supplying hydrogen to the reactor after the source gas has been supplied. it can. Further, since the separation and methanation reaction of carbon dioxide can be performed in the same reactor, the heat generated by the methanation reaction can be used as energy required for the separation of carbon dioxide. From the above, according to this configuration, it is possible to reduce the production cost of methane by improving the production efficiency of methane. Moreover, since it is not necessary to provide a carbon-dioxide separation apparatus and a reactor separately, size reduction of a manufacturing apparatus can be achieved.

  (2) The methane production apparatus according to the above aspect further includes a hydrogen supply unit that supplies hydrogen to the plurality of reactors, and the control unit controls the hydrogen supply unit so that the hydrogen is supplied to the plurality of reactors. Hydrogen may be supplied to a specific reactor, and hydrogen may be supplied to the reactor whose carbon dioxide concentration at the outlet has reached the predetermined value by the supply of the raw material gas. According to this configuration, since hydrogen can be sequentially supplied to the reactor in a state where the catalyst sufficiently stores carbon dioxide by the supply of the raw material gas, methane can be continuously manufactured, and the production efficiency is further improved. Can be

(3) In the methane production apparatus of the above aspect, the control unit satisfies the following formula (1) for the reactor in which the carbon dioxide concentration at the outlet has become the predetermined value by the supply of the source gas. A mole number of hydrogen may be supplied.
1 <M _H2 / (4 × M _CO2 + 0.1 × M _CA ) <1.2 (1)
(In the formula (1), M _H2 is the number of moles of hydrogen to be supplied, M _CO2 is the number of moles of carbon dioxide stored in the catalyst in the reactor to which hydrogen is supplied, and M _CA is hydrogen It is the number of metal moles of the catalyst in the reactor to be supplied.)
According to this configuration, the amount of unreacted carbon dioxide or hydrogen contained in the reaction mixture gas in the reactor after the hydrogen supply can be reduced, and the purity of the produced methane can be improved. As a result, the processing time for removing hydrogen from the reaction mixture gas can be shortened to reduce the manufacturing cost. In addition, the decrease in the activity of the catalyst due to the accumulation of carbon dioxide can be suppressed.

(4) In the methane production apparatus according to the above aspect, the control unit satisfies the following formula (2) for the reactor in which the carbon dioxide concentration at the outlet has reached the predetermined value by the supply of the source gas. A mole number of hydrogen may be supplied.
4.1 <M _H2 / M _CO2 <5.5 (2)
(In the formula (2), M _H2 is the number of moles of hydrogen to be supplied, and M _CO2 is the number of moles of carbon dioxide stored in the catalyst in the reactor to which hydrogen is supplied.)
This configuration also can reduce the amount of unreacted carbon dioxide or hydrogen contained in the reaction mixture gas, and can improve the purity of methane to be produced.

  (5) In the methane production apparatus of the above aspect, when the carbon dioxide concentration at the outlet of the reactor supplying the source gas becomes greater than 100 ppm, the control unit causes the source gas to be supplied to the other reaction source. You may switch to the According to this configuration, it is possible to reduce the amount of carbon dioxide that is in the gas phase without being occluded by the catalyst in the reactor after the raw material gas is supplied, so that it is included in the reaction mixture gas after the methanation reaction. The amount of unreacted carbon dioxide can be further reduced, and the purity of the produced methane can be further improved.

  (6) The methane production apparatus of the above aspect may further include a hydrogen separation unit for separating hydrogen from the reaction mixture gas extracted from the plurality of reactors. According to this configuration, the purity of the produced methane can be further improved by separating hydrogen contained in the reaction mixture gas.

  The present invention can be realized in various aspects. For example, a control method of a methane production apparatus, a computer program that causes a computer to execute the control method, a methane production method, a production method of a methane production apparatus, methane It can be realized in the form of an organic catalyst system, a carbon dioxide recovery device, etc.

It is an explanatory view showing a schematic structure of a methane production device. It is a flowchart which shows gas path control processing. It is a figure for demonstrating the distribution state of gas in step S11. It is an explanatory view showing the distribution state of gas in Steps S13-S14. It is an explanatory view showing the distribution state of gas in Steps S17-S18. It is the figure which showed the composition of the reaction mixed gas obtained by Example 1 and Comparative Examples 1-3.

First Embodiment
FIG. 1: is explanatory drawing which showed schematic structure of the methane production apparatus 1 in 1st Embodiment. The methane production apparatus 1 includes a first reactor 10, a second reactor 20, a raw material gas supply unit 30, a hydrogen supply unit 40, a first outlet CO ₂ sensor 50, and a second outlet CO ₂ sensor 60. , A control unit 70, and a hydrogen separation unit 80.

The first reactor 10 is a container for producing methane by a methanation reaction inside, and the catalyst 11 is accommodated inside. A raw material gas inlet 12, an H ₂ inlet 13, and a gas outlet 14 are formed on the container wall surface of the first reactor 10. The catalyst 11 contains a metal having methanation catalytic performance and a metal having carbon dioxide storage performance. As a metal which has methanation catalyst performance, Ru and Ni can be illustrated, for example. Examples of metals having carbon dioxide storage performance include alkali metal oxides such as CaO and Al ₂ O ₃ , and alkaline earth metal oxides. The catalyst 11 may contain a metal oxide support.

The source gas inlet 12 is an opening to which a source gas containing CO ₂ used for the methanation reaction is supplied, and the first source gas supply pipe 33 is connected. The H ₂ inlet 13 is an opening to which H ₂ used for the methanation reaction is supplied, and the first hydrogen supply pipe 41 is connected. The gas outlet 14 is an opening from which a reaction mixture gas containing methane generated by the methanation reaction is taken out, and the first outlet pipe 51 is connected.

The second reactor 20 is a container having the same shape and volume as the first reactor 10, and the catalyst 21 is accommodated therein, and the raw material gas inlet 22, the H ₂ inlet 23, and the gas outlet 24 are accommodated in the container wall. And are being formed. Similarly to the catalyst 11, the catalyst 21 contains a metal having methanation catalytic performance and a metal having carbon dioxide storage performance. Here, the catalyst 11 contained in the first reactor 10 and the catalyst 21 contained in the second reactor 20 will be described as having almost equal methanation catalyst performance and carbon dioxide storage performance.

The source gas inlet 22 is an opening through which the source gas is supplied, and the second source gas supply pipe 35 is connected. The H ₂ inlet 23 is an opening to which H ₂ is supplied, and the second hydrogen supply pipe 43 is connected. The gas outlet 24 is an opening from which the reaction mixture gas generated inside the second reactor 20 is taken out, and the second outlet pipe 61 is connected.

The source gas supply unit 30 is a supply source capable of supplying a source gas containing CO ₂ , and is constituted of, for example, a combustion furnace or a source gas tank. The source gas may contain O ₂ , N ₂ , H ₂ 0, etc. in addition to CO ₂ . The raw material gas supplied from the raw material gas supply unit 30 is supplied to the first reactor 10 via the upstream side raw material gas supply pipe 31 and the first raw material gas supply pipe 33 at a temperature of 350 ° C. or less. Further, the gas is supplied to the second reactor 20 via the upstream side raw material gas supply pipe 31 and the second raw material gas supply pipe 35.

  The first raw material gas supply valve 32 is a gate valve provided between the upstream side raw material gas supply pipe 31 and the first raw material gas supply pipe 33, and the raw material gas is supplied to the first reactor 10 when the valve is opened. Supply is stopped when the valve is closed. The second raw material gas supply valve 34 is a gate valve provided between the upstream side raw material gas supply pipe 31 and the second raw material gas supply pipe 35, and the raw material gas is supplied to the second reactor 20 when the valve is opened. Supply is stopped when the valve is closed. The opening and closing of each of the first source gas supply valve 32 and the second source gas supply valve 34 is performed by the control of the control unit 70. The first source gas supply valve 32 and the second source gas supply valve 34 correspond to the “supply destination switching unit” in the claims.

In the first raw material gas supply pipe 33, a first temperature sensor 91, a first gas flow meter 92, and a first inlet CO ₂ sensor 93 are disposed. The first temperature sensor 91 measures the temperature of the source gas supplied to the first reactor 10. The first gas flow meter 92 measures the flow rate of the source gas supplied to the first reactor 10. The first inlet CO ₂ sensor 93 measures the CO ₂ concentration of the raw material gas supplied to the first reactor 10. In the second source gas supply pipe 35, a second temperature sensor 94, a second gas flow meter 95, and a second inlet CO ₂ sensor 96 are disposed. The second temperature sensor 94 measures the temperature of the source gas supplied to the second reactor 20. The second gas flow meter 95 measures the flow rate of the source gas supplied to the second reactor 20. The second inlet CO ₂ sensor 96 measures the CO ₂ concentration of the source gas supplied to the second reactor 20.

The hydrogen supply unit 40 is, for example, a device capable of supplying H ₂ constituted by a water electrolysis device or a hydrogen tank. H ₂ supplied from the hydrogen supply unit 40 is supplied to the first reactor 10 via the first hydrogen supply pipe 41, and is supplied to the second reactor 20 via the second hydrogen supply pipe 43. . The first hydrogen supply valve 42 is a gate valve provided in the first hydrogen supply pipe 41. When the valve is opened, H ₂ is supplied to the first reactor 10, and when the valve is closed, the supply is stopped. The second hydrogen supply valve 44 is a gate valve provided in the second hydrogen supply pipe 43. When the valve is opened, H ₂ is supplied to the second reactor 20, and when the valve is closed, the supply is stopped. The opening and closing of each of the first hydrogen supply valve 42 and the second hydrogen supply valve 44 is performed by the control of the control unit 70. The hydrogen supply unit 40, the first hydrogen supply valve 42, and the second hydrogen supply valve 44 correspond to the "hydrogen supply unit" in the claims.

The first outlet CO ₂ sensor 50 is provided in the first outlet pipe 51 at a position close to the gas outlet 14 of the first reactor 10, and from the first reactor 10 to the first outlet pipe 51 via the gas outlet 14. Measure the concentration of CO ₂ contained in the gas coming out. The first outlet CO ₂ sensor 50 and the second outlet CO ₂ sensor 60 correspond to the “measurement unit” in the claims. The gas coming out of the first reactor 10 to the first outlet pipe 51 via the gas outlet 14 is discharged to the outside of the methane production apparatus 1 via the first external discharge pipe 53 or reaction mixture The hydrogen is supplied to the hydrogen separation unit 80 via the gas pipe 81.

  The first exhaust valve 52 is a gate valve provided between the first outlet pipe 51 and the first external discharge pipe 53, and when the valve is opened, the first outlet pipe 51 and the first external discharge pipe 53 communicate with each other. The gas flowing through the first outlet pipe 51 can be discharged to the outside of the methane production apparatus 1. The first reaction gas valve 54 is a gate valve provided between the first outlet pipe 51 and the reaction mixture gas pipe 81, and when the valve is opened, the first outlet pipe 51 and the reaction mixture gas pipe 81 communicate with each other. The gas flowing through the first outlet pipe 51 can be supplied to the hydrogen separation unit 80.

The second outlet CO ₂ sensor 60 is provided in the second outlet pipe 61 at a position close to the gas outlet 24 of the second reactor 20, and from the second reactor 20 to the second outlet pipe 61 via the gas outlet 24. Measure the concentration of CO ₂ contained in the gas coming out. The gas coming out of the second reactor 20 to the second outlet pipe 61 via the gas outlet 24 is discharged to the outside of the methane production apparatus 1 via the second external discharge pipe 63 or reaction mixture The hydrogen is supplied to the hydrogen separation unit 80 via the gas pipe 81.

  The second exhaust valve 62 is a gate valve provided between the second outlet pipe 61 and the second external discharge pipe 63, and when the valve is opened, the second outlet pipe 61 and the second external discharge pipe 63 communicate with each other. The gas flowing through the second outlet pipe 61 can be discharged to the outside of the methane production apparatus 1. The second reaction gas valve 64 is a gate valve provided between the second outlet pipe 61 and the reaction mixture gas pipe 81, and when the valve is opened, the 2 outlet pipe 61 and the reaction mixture gas pipe 81 communicate with each other. The gas flowing through the second outlet pipe 61 can be supplied to the hydrogen separation unit 80.

  The control unit 70 is a computer configured to include a ROM, a RAM, and a CPU, and controls the entire methane producing apparatus 1. The control unit 70 includes eight valves 32, 34, 42, 44, 52, 54, 62, 64, two temperature sensors 91, 94, two gas flow meters 92, 95, and four CO2 sensors 50, 60. , 93, 96, and performs open / close control of eight valves based on the measurement values output from the sensor and the flow meter. The gas path control process of the control unit 70 including the opening and closing of eight valves will be described later with reference to FIGS.

The hydrogen separation unit 80 is an apparatus provided with a polyamide-based polymer membrane or the like, and separates H ₂ from the reaction mixture gas containing methane and H ₂ supplied from the reaction mixture gas pipe 81. The separated H ₂ is returned to the hydrogen supply unit 40 via the recycling pipe 82 and reused. The reaction gas from which H ₂ has been separated is taken out from the reaction gas pipe 83. The removed reaction gas may be supplied to, for example, the raw material gas supply unit 30 as a combustion furnace.

  The gas path control process of the control unit 70 will be described using FIGS. 2 to 5. FIG. 2 is a flowchart showing the gas path control process. FIG. 3 is an explanatory view showing the flow of gas in step S11. FIG. 4 is an explanatory view showing the flow of gas in steps S13 to S14. FIG. 5 is an explanatory view showing the flow of gas in steps S17 to S18.

As shown in FIG. 2, after the start of the methane production apparatus 1, the control unit 70 first opens the first source gas supply valve 32 and closes the second source gas supply valve 34 (step S11). At the same time, the control unit 70 opens the first exhaust valve 52 and closes the first reaction gas valve 54. By this control, as shown in FIG. 3, the source gas is supplied from the source gas supply unit 30 to the first reactor 10. At this time, the temperature, flow rate, and CO ₂ concentration of the raw material gas supplied to the first reactor 10 are measured by the first temperature sensor 91, the first gas flow meter 92, and the first inlet CO ₂ sensor 93. Ru. A part of CO ₂ contained in the raw material gas supplied to the first reactor 10 is stored in the catalyst 11, and the remaining raw material gas containing O ₂ , N ₂ , H ₂ 0, etc. And is discharged to the outside through the first external discharge pipe 53.

Next, the control unit 70 determines whether the CO ₂ concentration at the gas outlet 14 of the first reactor 10 exceeds the threshold Th1 (step S12). Specifically, the control unit 70 uses the measurement value of the first outlet CO ₂ sensor 50 as the CO ₂ concentration of the gas outlet 14, and whether the measurement value of the first outlet CO ₂ sensor 50 exceeds the threshold Th 1 It is determined whether or not. Here, 100 ppm is set as the threshold value Th1. Since part of the CO ₂ contained in the raw material gas supplied to the first reactor 10 is stored in the catalyst 11, the CO _{2 at} the gas outlet 14 of the first reactor 10 is kept for a while after the start of the supply of the raw material gas. The concentration is less than 100 ppm. On the other hand, when a certain amount of CO ₂ is stored in the catalyst 11, the storage rate of CO ₂ by the catalyst 11 decreases, and the CO ₂ concentration at the gas outlet 14 gradually increases. The inventors of the present invention have found that the CO ₂ concentration of the gas outlet 14 is 100 ppm just before the CO ₂ storage of the catalyst 11 is saturated. Therefore, by setting the threshold value Th1 to 100 ppm, the state of the catalyst 11 can be brought to a state slightly before saturation of the stored amount of CO ₂ . The control unit 70 continues the supply of the source gas to the first reactor 10 until the CO ₂ concentration at the gas outlet 14 of the first reactor 10 exceeds the threshold Th1 (step S12: NO).

When the CO ₂ concentration at the gas outlet 14 of the first reactor 10 exceeds the threshold Th1 (step S12: YES), the control unit 70 closes the first source gas supply valve 32, and the second source gas supply valve 34 The open state is made (step S13). By this control, the supply of the source gas to the first reactor 10 is stopped, and the supply of the source gas to the second reactor 20 is started. At the same time, the control unit 70 opens the second exhaust valve 62 and closes the second reaction gas valve 64. By this control, as shown in the second reactor 20 of FIG. 4, the source gas is supplied to the second reactor 20. At this time, the temperature, flow rate, and CO ₂ concentration of the raw material gas supplied to the second reactor 20 are measured by the second temperature sensor 94, the second gas flow meter 95, and the second inlet CO ₂ sensor 96. Ru. Part of the CO ₂ contained in the source gas supplied to the second reactor 20 is stored in the catalyst 21, and the remaining source gas containing O ₂ , N ₂ , H ₂ 0, etc. And the second external discharge pipe 63 are discharged to the outside. On the other hand, in the first reactor 10, the supply of the raw material gas is stopped, and the catalyst 11 is in a state where CO ₂ is sufficiently absorbed.

The controller 70 opens the first hydrogen supply valve 42 (step S14). At the same time, the control unit 70 closes the first exhaust valve 52 and opens the first reaction gas valve 54. By opening the first hydrogen supply valve 42, H ₂ is supplied to the first reactor 10 as shown in the first reactor 10 of FIG. As a result, CO ₂ stored in the catalyst 11 is reduced by H ₂ to generate methane. In the control unit 70, the remaining number of moles of H ₂ consumed after reduction of the catalyst 11 is the stoichiometric ratio of the methanation reaction to the number of moles of absorbed CO _{2 of the} catalyst 11 (H ₂ moles / CO _The number of moles of H ₂ satisfying the following equation (1) is supplied to the first reactor 10 so that the number of moles is ₂ ).

1 <M _H2 / (4 × M _CO2 + 0.1 × M _CA ) <1.2 (1)
Here, M _H2 is the number of moles of H ₂ supplied to the first reactor 10, M _CO2 is the number of moles of absorbed CO _{2 of the} catalyst 11, and M _CA is the mole of the metal contained in the catalyst 11 It is a number. The _MCAs are specified in advance at the time of manufacture.

M _CO2 can be estimated, for example, by the following equation (3).
M _CO2 = C × F × t × 273 / (0.224 × (273 + T)) (3)
Here, C is the average CO ₂ concentration [% / sec] of the source gas in the period of steps S11 to S13, that is, the period when the first source gas supply valve 32 is open, and F is the period Average gas flow rate [F / sec], t is the length of the period [seconds], and T is the average temperature [° C.] of the source gas in the period. C is the average of the measurements of the first inlet CO ₂ sensor 93 in that period, F is the average of the measurements of the first gas flow meter 92 in that period, and T is the first in that period It is an average of the measurement values of the temperature sensor 91.

After the number of moles of H ₂ satisfying the formula (1) is supplied to the first reactor 10, the control unit 70 closes the first hydrogen supply valve 42 (step S15). After H ₂ supply, the reaction mixture gas containing methane and residual H ₂ generated inside the first reactor 10 is taken out of the first reactor 10 to the first outlet pipe 51 via the gas outlet 14. The removed reaction mixture gas is supplied to the hydrogen separation unit 80 via the reaction mixture gas pipe 81. In the hydrogen separation unit 80, residual H ₂ is separated from the reaction mixture gas, and methane is taken out. The residual H ₂ is supplied to the hydrogen supply unit 40 via the recycle pipe 82, and methane is taken out from the reaction gas pipe 83. On the other hand, in the second reactor 20, the supply of the source gas is continued.

The control unit 70 determines whether the CO ₂ concentration at the gas outlet 24 of the second reactor 20 exceeds the threshold value Th2 (step S16). Specifically, the control unit 70 uses the measurement value of the second outlet CO ₂ sensor 60 as the CO ₂ concentration of the gas outlet 24, and the measurement value of the second outlet CO ₂ sensor 60 exceeds the threshold value Th 2 It is determined whether or not. Here, 100 ppm is set as the threshold value Th2. The control unit 70 continues the supply of the source gas to the second reactor 20 until the CO2 concentration at the gas outlet 24 of the second reactor 20 exceeds the threshold Th2 (step S16: NO).

When the CO ₂ concentration at the gas outlet 24 of the second reactor 20 exceeds the threshold Th2 (step S16: YES), the control unit 70 opens the first source gas supply valve 32, and the second source gas supply valve 34 The closed state is set (step S17). By this control, the supply of the source gas to the second reactor 20 is stopped, and the supply of the source gas to the first reactor 10 is started. At the same time, the control unit 70 opens the first exhaust valve 52 and closes the first reaction gas valve 54. By this control, as shown in the first reactor 10 of FIG. 5, the source gas is supplied again to the first reactor 10, CO ₂ is absorbed in the catalyst 11, and the remaining source gas is subjected to the second exterior. It is discharged from the discharge pipe 63 to the outside. On the other hand, in the second reactor 20, the supply of the source gas is stopped, and the catalyst 21 is in a state where CO ₂ is sufficiently absorbed.

The controller 70 opens the second hydrogen supply valve 44 (step S18). At the same time, the control unit 70 closes the second exhaust valve 62 and opens the second reaction gas valve 64. By opening the second hydrogen supply valve 44, H ₂ is supplied to the second reactor 20 as shown in the second reactor 20 of FIG. Thus, CO ₂ stored in the catalyst 21 is reduced by H ₂ to generate methane. The control unit 70 supplies, to the second reactor 20, the number of moles of H ₂ satisfying the formula (1), as in step S14. Here, M _H2 is the number of moles of H ₂ supplied to the second reactor 20, M _CO2 is the number of moles of absorbed CO _{2 of the} catalyst 21, and M _CA is a metal contained in the catalyst 21. The number of moles of M _CO2 can be estimated from the measurement values of the second inlet CO ₂ sensor 96, the second gas flow meter 95, and the second temperature sensor 94 according to equation (3).

After the number of moles of H ₂ satisfying the formula (1) is supplied to the second reactor 20, the control unit 70 closes the second hydrogen supply valve 44 (step S19). After the H ₂ supply, the reaction mixture gas in the second reactor 20 is supplied to the hydrogen separation unit 80 through the reaction mixture gas pipe 81 and separated into residual H 2 and methane. On the other hand, in the first reactor 10, the supply of the source gas is continued. The control unit 70 repeatedly executes the process of step S12 again in order. The above is the description of the gas path control process.

Here, in the gas path control process described above, an example of an effect of the number of moles of H ₂ supplied to the catalysts 11 and 12 satisfying the equation (1) will be described. In order to show this example of the effect, after actually preparing the catalyst of the present embodiment and occluding CO ₂ , H ₂ of four moles is supplied to this catalyst, and the composition of the reaction mixture gas obtained Was analyzed. The composition of the prepared catalyst (CO ₂ storage reduction catalyst) is Ru (5 wt%), CaO (10 wt%), Al ₂ O ₃ , and the composition of the used source gas is CO ₂ (10 vol%), O ₂ And the composition of the reducing gas is H ₂ (100%).

H ₂ of the number of moles of the following four (Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3) was supplied to the prepared catalyst under the same conditions.
Example 1: M _{H 2} / (4 × M _{CO 2} + 0.1 × M _CA ) = 1.1
Comparative Example 1: M _H2 / (4 × M _CO2 + 0.1 × M _CA ) = 0.6
Comparative Example 2: M _H2 / (4 × M _CO2 + 0.1 × M _CA ) = 0.95
Comparative Example 3: M _H2 / (4 × M _CO2 + 0.1 × M _CA ) = 2.1

FIG. 6 is a diagram showing the composition of the reaction mixture gas obtained in Example 1 and Comparative Examples 1 to 3. In Example 1, a little more H ₂ than the stoichiometric ratio (H ₂ mole number / CO ₂ mole number = 4) in the methanation reaction is supplied. Therefore, when a part of H ₂ is consumed for the reduction of the catalytic metal, the number of moles of H ₂ remaining becomes a value close to the above-described stoichiometric ratio with respect to the number of moles of CO ₂ stored. . As a result, the stored CO ₂ is almost methanated, so the proportion of unreacted CO ₂ contained in the reaction mixture gas is reduced.

In Comparative Example 1, compared with Example 1, the number of moles of H ₂ supplied is smaller, and the proportion of unreacted CO ₂ is greatly increased. Comparative Example 2 has a stoichiometric ratio in the methanation reaction (H ₂ mole number / CO ₂ mole number = 4), so the proportion of unreacted CO ₂ is reduced more than in Comparative Example 1. However, since the amount of H ₂ is consumed for the reduction of the catalyst metal, the ratio of unreacted CO ₂ is higher than that of Example 1. Therefore, it can be said from Comparative Examples 1 and 2, the number of moles M _H2 which supplies to the catalyst H _2, and preferably satisfy the _{M H2 / (4 × M CO2} + 0.1 × M CA)> 1. In Comparative Example 3, since the excess of H ₂ is supplied, the proportion of unreacted CO ₂ decreases as in Example 1. However, the reaction time required for methanation is increased while H _{2 is} removed from the reaction mixture gas. It increases the processing time to separate, causing a decrease in the processing speed of generating methane from C0 _2. Therefore, it can be said from the Comparative Example 3, the number of moles M _H2 which supplies to the catalyst H _2, and preferably satisfy the _{M H2 / (4 × M CO2} + 0.1 × M CA) <1.2. From the above, it is preferable that the number of moles of H ₂ supplied to the catalyst satisfies the formula (1).

As described above, the inventors of the present invention can reduce the number of moles of H ₂ supplied to the reactor slightly more than the stoichiometry ratio in the methanation reaction to reduce the remaining amount consumed for the reduction of the catalytic metal. It has been found that the number of moles of H ₂ is a value close to the stoichiometric ratio described above. In addition, it was found that about 10% of the number of moles of metal was consumed for reduction, and it was found that by supplying H ₂ in consideration of that value, methane of high purity can be more stably produced. . Furthermore, since there is a range that can be taken by a general catalyst in MCA of formula (1), the number of moles of H ₂ supplied to the reactor satisfies the following formula (2). It was found that the same effect as that of the formula (1) can be obtained.
4.1 <M _H2 / M _CO2 <5.5 (2)

According to the methane production apparatus 1 of the present embodiment described above, the raw material gas is supplied to one of the reactors to cause CO ₂ to be absorbed by the catalyst, while H ₂ is supplied to the other of the reactors for methanation. The reaction can occur and these can be repeated alternately to produce methane. Therefore, while being able to supply source gas continuously to a reactor continuously, methane can be manufactured continuously. Therefore, according to the methane production apparatus 1 of this embodiment, methane can be continuously produced at low cost from raw material gases containing CO ₂ such as combustion exhaust gas and biogas which are continuously supplied.

Conventionally, in systems that methanate gases containing CO ₂ and O ₂ such as fuel exhaust gas and biogas, CO ₂ separation and recovery equipment (chemical adsorption method, physical adsorption method, etc.) and methanation catalyst device (reactor) And are separately configured, and they are operated in combination. CO ₂ in the separation recovery apparatus, the thermal energy of the separation and recovery CO ₂ is necessary, also, CO ₂ separation if recovery device and methanation catalyst device separate from the complex structure of the system, larger overall size Was a problem. On the other hand, according to the methane production apparatus 1 of the present embodiment, the raw material gas containing CO ₂ and O ₂ is made to flow directly to the reactor to separate and recover the CO ₂ , and thereafter, reduction to methane by supply of H ₂ It can be converted. Thereby, simplification and size reduction of a manufacturing apparatus can be achieved. In the case of the methane production apparatus 1 of the present embodiment in particular, the energy necessary for the separation and recovery of CO ₂ can be covered by the heat generated by the exothermic reaction, the methanation reaction. Therefore, the reaction can be allowed to proceed at a temperature of about 300 to 350 ° C. without supplying energy from the outside.

Further, according to the methane production apparatus 1 of the present embodiment, when the CO ₂ concentration at the gas outlet of the reactor supplying the source gas becomes greater than 100 ppm, the source gas supply destination is switched to another reactor. The purity of the produced methane can be improved. When CO ₂ is absorbed to the catalyst to the saturated storage amount (maximum storage amount), unreacted CO ₂ is released from the reactor together with the produced methane when H _{2 is} supplied, and the concentration of methane in the product is descend. On the other hand, according to this embodiment, since CO ₂ is not stored up to the saturated storage amount, high purity methane can be produced.

<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]
The methane production apparatus 1 of the first embodiment has been described as including two reactors (the first reactor 10 and the second reactor 20). However, the methane production apparatus 1 may be equipped with three or more reactors. Further, the first reactor 10 and the second reactor 20 of the first embodiment have the same shape and the same capacity. However, the first reactor 10 and the second reactor 20 may have different shapes and volumes.

[Modification 2]
In the gas production line control process, the methane production apparatus 1 according to the first embodiment always supplies the source gas to any one of the first reactor 10 and the second reactor 20. However, when the feed gas supply is switched from one reactor to the other, there may be a period in which no feed gas is supplied to both reactors. Alternatively, there may be a period in which both the first reactor 10 and the second reactor 20 are simultaneously supplied.

[Modification 3]
The raw material gas supply unit 30 according to the first embodiment is configured of a combustion furnace and a supply source of a raw material gas tank. However, the source gas supply unit 30 may be configured not as a supply source but as a pipe into which the exhaust gas discharged from a fuel furnace such as a factory flows. That is, the methane production apparatus 1 may not include the source of the source gas.

[Modification 4]
In the gas path control process of the first embodiment, the threshold value Th1 is 100 ppm. However, the threshold value Th1 is not limited to 100 ppm as long as it is a value smaller than the concentration of CO ₂ in the atmosphere, and can be an arbitrary value. However, the threshold value Th1 is preferably in the range of 20 to 400 ppm, and more preferably in the range of 20 to 150 ppm. The same applies to the threshold value Th2. The threshold Th1 and the threshold Th2 may be different from each other.

[Modification 5]
In the gas path control process of the first embodiment, the M _CO2 is estimated from the measurement values of the inlet CO ₂ sensor on the side of the source gas supply pipe, the gas flow meter, and the temperature sensor. However, M _CO2 may be estimated in other ways. For example, M _CO2 may be estimated from the measurement values of the outlet CO ₂ sensor on the outlet pipe side, the gas flow meter, and the temperature sensor. Further, in the gas path control process, the number of moles of H ₂ not satisfying the formula (1) or the formula (2) may be supplied to the reactor. However, it is preferable that the number of moles of H ₂ satisfying the formula (1) or the formula (2) be supplied.

[Modification 6]
The configuration of the methane production apparatus 1 according to the first embodiment is an example, and may not have a part of the configuration or may have another configuration. For example, the methane production apparatus 1 may include a dewatering unit on the downstream side of the source gas supply unit 30. Moreover, the methane production apparatus 1 may not have the hydrogen separation unit 80. Further, instead of the first source gas supply valve 32 and the second source gas supply valve 34, a three-way valve may be provided.

  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.

DESCRIPTION OF SYMBOLS 1 ... Methane manufacturing apparatus 10 ... 1st reactor 20 ... 2nd reactor 11, 21 ... Catalyst 12, 22 ... Raw material gas inlet 13, 23 ... H ₂ inlet 14 and 24 ... Gas outlet 30 ... Raw material gas supply part 31, 33, 35 ... source gas supply pipe 32, 34 ... source gas supply valve 40 ... hydrogen supply unit 41, 43 ... hydrogen supply pipe 42, 44 ... hydrogen supply valve 50, 60 ... outlet CO ₂ sensor 51, 61 ... outlet pipe 52 62: Exhaust valve 53, 63: External exhaust pipe 54, 64: Reaction gas valve 70: Control unit 80: Hydrogen separation part 81: Reaction mixed gas pipe 82: Reuse pipe 83: Reaction gas pipe 91, 94: Temperature sensor 92 , 95 ... gas flow meter 93, 96 ... inlet CO ₂ sensor

Claims (8)

A methane production apparatus that produces methane from carbon dioxide and hydrogen,
A plurality of reactors containing a catalyst comprising a metal having methanation catalytic performance and a metal having carbon dioxide storage performance and provided with an outlet for taking out an internal gas;
A supply destination switching unit provided on a gas flow path between a supply source of a raw material gas containing carbon dioxide and the plurality of reactors, and switching a supply destination of the raw material gas;
A measurement unit for measuring the carbon dioxide concentration at the outlet of each of the reactors;
And a control unit capable of supplying the source gas to a specific reactor among the plurality of reactors by controlling the supply destination switching unit;
The control unit switches the supply destination of the source gas to another reactor when the carbon dioxide concentration at the outlet of the reactor supplying the source gas reaches a predetermined value.
Methane production equipment. The methane production apparatus according to claim 1 further comprises
A hydrogen supply unit for supplying hydrogen to the plurality of reactors;
The control unit
Among the plurality of reactors, it is configured to be able to supply hydrogen to a specific reactor by controlling the hydrogen supply unit,
Supplying hydrogen to the reactor whose carbon dioxide concentration at the outlet has reached the predetermined value by supplying the source gas;
Methane production equipment. In the methane production apparatus according to claim 2,
The control unit supplies a number of moles of hydrogen satisfying the following equation (1) to the reactor in which the carbon dioxide concentration at the outlet has reached the predetermined value by the supply of the source gas.
Methane production equipment.
1 <M _H2 / (4 × M _CO2 + 0.1 × M _CA ) <1.2 (1)
(In the formula (1), M _H2 is the number of moles of hydrogen to be supplied, M _CO2 is the number of moles of carbon dioxide stored in the catalyst in the reactor to which hydrogen is supplied, and M _CA is hydrogen It is the number of metal moles of the catalyst in the reactor to be supplied.) In the methane production apparatus according to claim 2,
The control unit supplies a number of moles of hydrogen satisfying the following formula (2) to the reactor in which the carbon dioxide concentration at the outlet has reached the predetermined value by the supply of the source gas.
Methane production equipment.
4.1 <M _H2 / M _CO2 <5.5 (2)
(In the formula (2), M _H2 is the number of moles of hydrogen to be supplied, and M _CO2 is the number of moles of carbon dioxide stored in the catalyst in the reactor to which hydrogen is supplied.) The methane production apparatus according to any one of claims 1 to 4.
The control unit switches the supply destination of the source gas to another reactor when the carbon dioxide concentration at the outlet of the reactor supplying the source gas becomes higher than 100 ppm.
Methane production equipment. The methane production apparatus according to any one of claims 1 to 5, further,
A hydrogen separation unit for separating hydrogen from the reaction mixture gas extracted from the plurality of reactors;
Methane production equipment. A plurality of reactors containing a catalyst comprising a metal having methanation catalytic performance and a metal having carbon dioxide storage performance and provided with an outlet for taking out an internal gas;
A supply destination switching unit provided on a gas flow path between a supply source of a raw material gas containing carbon dioxide and the plurality of reactors, and switching a supply destination of the raw material gas;
A control unit configured to measure a carbon dioxide concentration at the outlet of each of the reactors;
The control method of the methane manufacturing apparatus which switches the supply destination of the said source gas to another said other reactor, if the carbon dioxide density | concentration in the exit of the said reactor which is supplying the said source gas becomes predetermined value. A process for producing methane,
A raw material gas containing carbon dioxide is supplied to a reactor containing a catalyst containing a metal having methanation catalytic performance and a metal having carbon dioxide storage performance, and carbon dioxide is stored in the catalyst And a process of
Measuring the concentration of carbon dioxide at the outlet of the reactor to which the source gas is supplied;
Switching the supply destination of the raw material gas to another reactor when the concentration of the carbon dioxide reaches a predetermined value.
Methane production method.

Images