Methane producing apparatus

Abstract

To provide a methane producing apparatus having a plurality of stages of reaction tubes, in which downsizing of the apparatus is realized.SOLUTION: A methane producing apparatus 1 at least comprises: a reaction tube 10 of a first stage into which raw material gas flows; a reaction tube 20 of a second stage which is positioned on a downstream side of the reaction tube 10 of the first stage; and flow rate control means for adjusting the flow rate of the raw material gas flowing into the reaction tube 10 of the first stage and the reaction tube 20 of the second stage. The volume of the reaction tube 20 of the second stage is smaller than the volume of the reaction tube 10 of the first stage, and the flow rate of gas passing through the reaction tube 20 of the second stage is smaller than the flow rate of gas passing through the reaction tube 10 of the first stage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a methane production apparatus that produces methane using a plurality of stages of reaction tubes.

Background Art

[0002] Methanation is a technique in which hydrogen and carbon dioxide are chemically reacted to produce methane. A methane production technique using this methanation is known (see, for example, Patent Documents 1 and 2).

[0003] In the methane production method disclosed in Patent Document 1, the methanation reaction step has a multi-stage configuration, a bypass step connecting the inlets of the first reaction step and the subsequent reaction step is provided, and the flow rates of the reaction step and the bypass step are controlled so that each reaction step is in an equilibrium state.

[0004] Patent Document 2 discloses a reaction apparatus including one or a plurality of reaction tubes in which an input gas is subjected to a methanation reaction in the presence of a catalyst, and the reaction tube is characterized in that it has an inlet for the input gas not only at one end but also at an intermediate portion.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The methane production technologies disclosed in Patent Documents 1 and 2 both perform the methanation reaction using a reaction tube or reactor with a multi-stage configuration. Usually, in such a methane production apparatus with a multi-stage configuration, the latter-stage reactor is made larger to stabilize the reaction throughout the apparatus. However, this results in an increase in the size of the methane production apparatus.

[0007] An object of the present invention is to realize downsizing of a methane production apparatus having a plurality of reaction tubes.

Means for Solving the Problems

[0008] The methane production apparatus according to one aspect of the present invention produces methane from a raw material gas using a catalyst. This methane production apparatus includes at least a first-stage reaction tube into which the raw material gas flows, a second-stage reaction tube located downstream of the first-stage reaction tube, and a flow rate control means for adjusting the flow rate of the raw material gas flowing into the first-stage reaction tube and the second-stage reaction tube. The volume of the second-stage reaction tube is smaller than the volume of the first-stage reaction tube, and the flow rate of the gas passing through the second-stage reaction tube is smaller than the flow rate of the gas passing through the first-stage reaction tube.

[0009] According to the above configuration, the amount of methanation reaction in the first-stage reaction tube can be made larger. As a result, since the amount of methanation reaction in the second-stage reaction tube becomes relatively small, the size of the second-stage reaction tube can be made smaller compared to the size of the first-stage reaction tube. Therefore, the second-stage reaction tube can be made space-saving. Accordingly, downsizing of the methane production apparatus having a plurality of reaction tubes can be realized.

[0010] In the methane production apparatus according to one aspect of the present invention, the space velocity of the gas in the first-stage reaction tube may be set within a range of 2400 (1 / hour) or more and 7500 (1 / hour) or less.

[0011] According to the above configuration, methane with an appropriate concentration can be generated without heating the first-stage reaction tube.

[0012] In the methane production apparatus according to one aspect of the present invention, the concentration of the catalyst contained in the first-stage reaction tube may be smaller than the concentration of the catalyst contained in the second-stage reaction tube.

[0013] According to the above configuration, the methanation reaction in the first-stage reaction tube can be further promoted.

[0014] In the methane production apparatus according to one aspect of the present invention, the first-stage reaction tube may not have a heating means around itself.

[0015] According to the above configuration, the methane production apparatus can be further miniaturized. Also, in the methane production apparatus, the energy required for methane generation can be made smaller.

[0016] In the methane production apparatus according to one aspect of the present invention, the first-stage reaction tube and the second-stage reaction tube each include a plurality of unit reaction tubes, and the number of unit reaction tubes contained in the first-stage reaction tube may be larger than the number of unit reaction tubes contained in the second-stage reaction tube.

[0017] According to the above configuration, when the volumes of the respective unit reaction tubes included in the first-stage reaction tube and the second-stage reaction tube are the same, the volume of the second-stage reaction tube can be made smaller than the volume of the first-stage reaction tube 10.

Advantages of the Invention

[0018] According to the methane production apparatus according to one aspect of the present invention, the apparatus can be made more compact.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a methane production apparatus 1 having a two-stage reaction tube will be described as an example. Note that the methane production apparatus according to the present invention is not limited to having a two-stage reaction tube, and may have three or more reaction tubes.

[0021] The methane production apparatus 1 is an apparatus that produces methane from a raw material gas using a catalyst. The process of methane production performed in the methane production apparatus 1 is called a methanation process. The raw material gas is carbon dioxide (CO 2 ) and hydrogen (H 2 ). Examples of the catalyst used in the methane production apparatus 1 include catalysts used in general methanation processes (for example, nickel (Ni) catalysts, ruthenium (Ru) catalysts, etc.).

[0022] In the methanation process, the reaction shown in the following [Reaction Formula 1] is carried out to produce methane. [Reaction Formula 1] CO 2 + 4H 2 → CH 4 + 2H 2 O In the above [Reaction Formula 1], theoretically 4 moles of H 2 react with 1 mole of CO 2 . Therefore, carbon dioxide (CO 2 ) and hydrogen (H 2 ) as the raw material gas may be supplied at a molar ratio of CO 2 : H 2 = 1: 4. Since it is considered that the reaction is promoted in equilibrium by supplying H 2 in an amount equal to or greater than the stoichiometric ratio, the supply amount (volume) is H2 / CO 2 It is desirable that it be ≥4. In the methanation process, in addition to methane, water and heat are generated.

[0023] (Configuration of Methane Production Apparatus) With reference to FIG. 1, the configuration of the methane production apparatus 1 will be described. In FIG. 1, the configuration related to the methanation process among the overall configuration of the methane production apparatus 1 is mainly illustrated. In FIG. 1, the configuration of the pre-process portion of the first-stage reaction tube (the portion where the raw material gas is introduced and mixed) and the post-process portion of the second-stage reaction tube (the portion where the generated methane is recovered) are not illustrated.

[0024] The methane production apparatus 1 includes a plurality of stages of catalytic reaction tubes. Specifically, as shown in FIG. 1, the methane production apparatus 1 includes, as catalytic reaction tubes, a first-stage reaction tube 10 and a second-stage reaction tube 20. The first-stage reaction tube 10 is composed of an aggregate of one or more (for example, N1) unit reaction tubes 11. Further, the second-stage reaction tube 20 is composed of an aggregate of one or more and a number (for example, N2) of unit reaction tubes 21 that is less than the number of unit reaction tubes 11 constituting the first-stage reaction tube 10.

[0025] Raw material gas (specifically, CO 2 and H 2 ) flows into the first-stage reaction tube 10. More specifically, the raw material gas flows into each of the unit reaction tubes 11 constituting the first-stage reaction tube 10. The second-stage reaction tube 20 is disposed on the downstream side of the first-stage reaction tube 10. Gas that has passed through the first-stage reaction tube 10 flows into the second-stage reaction tube 20. More specifically, the gas that has passed through the first-stage reaction tube 10 flows into each of the unit reaction tubes 21 constituting the second-stage reaction tube 20.

[0026] As components other than the reaction tubes 10 and 20, the methane production apparatus 1 includes a flow rate control unit (flow rate control means) 41, a cooler 34, a gas-liquid separator 35, and a cooler 39, etc. These respective components and devices are connected to each other by a gas pipe 50.

[0027] The flow control unit 41 is disposed upstream of the reaction tube 10 in the first stage. The flow control unit 41 adjusts the flow rate of the gas flowing into the reaction tube 10 in the first stage.

[0028] The flow control unit 41 has, for example, a pump 31 and a flow meter 32. The pump 31 can adjust the pressure. The flow meter 32 measures the flow rate of the raw material gas passing through the gas pipe 50 and flowing into the reaction tube 10 in the first stage.

[0029] The cooler 34 and the gas-liquid separator 35 are disposed between the reaction tube 10 in the first stage and the reaction tube 20 in the second stage.

[0030] The cooler 34 is connected to the downstream end of the reaction tube 10 in the first stage. The cooler 34 cools the gas discharged from the reaction tube 10 in the first stage. As a result, the water vapor (H 2 O) contained in the gas becomes liquid water. The gas-liquid separator 35 is disposed downstream of the cooler 34. The gas-liquid separator 35 separates and discharges the liquid (specifically, the water liquefied in the cooler 34) contained in the gas in the gas pipe 50.

[0031] The cooler 39 is disposed downstream of the reaction tube 20 in the second stage. The cooler 39 cools the gas discharged from the reaction tube 20 in the second stage. The gas that has passed through the cooler 39 undergoes subsequent processes. As a result, the methane contained in the gas is recovered. The recovered methane is sent to a storage tank or the like.

[0032] The methane production apparatus 1 according to the present embodiment includes a gas-liquid separator 35 between the reaction tube 10 in the first stage and the reaction tube 20 in the second stage as described above. According to this configuration, the water contained in the gas that has passed through the reaction tube 10 in the first stage can be removed. That is, the water component (2H 2O) is removed. As a result, in the reaction of [Reaction Formula 1] in the second-stage reaction tube 20, the equilibrium conversion rate to the product side can be increased. Therefore, the methane production in the second-stage reaction tube 20 can be further promoted.

[0033] (Configuration of the first-stage and second-stage reaction tubes) Subsequently, a more detailed configuration of the first-stage reaction tube 10 and the second-stage reaction tube 20 will be described. FIG. 2 shows the configuration of the first-stage reaction tube 10. FIG. 3 shows the configuration of the second-stage reaction tube 20. In FIG. 2, the configuration of the unit reaction tube 11 included in the first-stage reaction tube 10 is schematically shown. In FIG. 3, the configuration of the unit reaction tube 21 included in the second-stage reaction tube 20 is schematically shown.

[0034] As shown in FIG. 2, around each unit reaction tube 11 included in the first-stage reaction tube 10, a gas pipe 50a and a gas pipe 50b are provided in order from the upstream side. The first-stage reaction tube 10 has a heater 12 and a preheater 13 as heating means.

[0035] The heater 12 is provided around each unit reaction tube 11 constituting the first-stage reaction tube 10. The preheater 13 is arranged adjacent to the upstream end of the unit reaction tube 11 (see FIG. 2).

[0036] In addition, by increasing the space velocity of the raw material gas passing through the first-stage reaction tube 10 and increasing the reaction amount of [Reaction Formula 1] in the first-stage reaction tube 10, more reaction heat is generated. In such a case, a sufficient reaction amount can be ensured in the first-stage reaction tube 10 without heating by the heater 12 and the preheater 13.

[0037] Therefore, in another embodiment, the first-stage reaction tube 10 may not have a heating means. This is because in the first-stage reaction tube 10 located more upstream in the methane production apparatus 1, the proportion (concentration) of the raw material gas contained in the gas passing through the reaction tube is large, so the reaction of the above [Reaction Formula 1] proceeds more violently and the amount of heat generated also increases. That is, by appropriately controlling the flow rate and volume of the raw material gas flowing into the first-stage reaction tube 10, the reaction heat generated in the reaction tube can be utilized to promote the methanation reaction, so heating by a heater can be made unnecessary. Thus, the equipment of the methane production apparatus 1 can be made smaller and more energy-saving.

[0038] As shown in FIG. 3, around each unit reaction tube 21 included in the second-stage reaction tube 20, a gas pipe 50c and a gas pipe 50d are provided in order from the upstream side. The second-stage reaction tube 20 has a heater 22 and a preheater 23 as heating means.

[0039] The heater 22 is provided around each unit reaction tube 11 constituting the first-stage reaction tube 10. The preheater 23 is disposed adjacent to the upstream end of the unit reaction tube 21 (see FIG. 3).

[0040] The gas pipe 50c located downstream of the first-stage reaction tube 10 is connected to the gas inlet to the unit reaction tube 21. A preheater 23 is provided around a part of the gas pipe 50c. The gas pipe 50d is connected to the gas outlet from the unit reaction tube 21.

[0041] When the reaction in the reaction tube 10 of the first stage starts, reaction heat is generated. Therefore, the heating means of the reaction tube 10 of the first stage may be omitted. However, it is desirable not to omit the preheating means for heating the raw material until the reaction starts. On the other hand, it is preferable not to omit the heating means for the reaction tube 20 of the second stage. This is because in the reaction tube 20 of the second stage, the reaction of the above [Reaction formula 1] proceeds more gently compared to the reaction tube 10 of the first stage. Therefore, by having the heater 22 in the reaction tube 20 of the second stage, the reaction of the above [Reaction formula 1] can be promoted.

[0042] In the methane production apparatus 1 according to the present embodiment, the volume of the reaction tube 20 of the second stage is smaller than the volume of the reaction tube 10 of the first stage. Here, the volume of the reaction tube 10 of the first stage means the total volume of the reaction tube 10 of the first stage, which is an aggregate of one or more (for example, N1) unit reaction tubes 11. Similarly, the volume of the reaction tube 20 of the second stage means the total volume of the reaction tube 20 of the second stage, which is an aggregate of one or more (for example, N1) unit reaction tubes 21. Further, the volume of the unit reaction tube 11 or 21 is the internal volume of the tubular unit reaction tube, and is determined by the diameter (D) of the unit reaction tube and the height (H) of the catalyst layer introduced into the unit reaction tube.

[0043] The diameter (D1) of the unit reaction tube 11 of the reaction tube 10 of the first stage can be, for example, 0.25 inches or more and 3 inches or less (more specifically, about 1 inch). Further, the height (H1) of the catalyst layer introduced into the unit reaction tube can be, for example, 300 mm or more and 5000 mm or less (more specifically, about 800 mm). Further, the reaction tube 10 of the first stage includes, for example, 2 or more and 20 or less (more specifically, 4) unit reaction tubes 11.

[0044] In addition, the diameter (D2) of the unit reaction tube 21 of the second-stage reaction tube 20 can be, for example, 0.25 inches or more and 3 inches or less (more specifically, about 1 inch). Further, the height (H1) of the catalyst layer introduced into the unit reaction tube can be, for example, 30 mm or more and 5000 mm or less (more specifically, about 800 mm). In addition, the second-stage reaction tube 20 includes, for example, 1 or more and 10 or less (more specifically, 2) unit reaction tubes 21.

[0045] The number of unit reaction tubes 11 included in the first-stage reaction tube 10 is preferably larger than the number of unit reaction tubes 21 included in the second-stage reaction tube 20. Thereby, when the volumes of the respective unit reaction tubes 11 and 21 are the same, the volume of the second-stage reaction tube 20 can be made smaller than the volume of the first-stage reaction tube 10. In this way, by adjusting the volumes of the first-stage reaction tube 10 and the second-stage reaction tube 20 by changing the number of unit reaction tubes respectively, unit reaction tubes of the same size can be used for the first-stage reaction tube 10 and the second-stage reaction tube 20.

[0046] As described above, the flow rate control unit 41 adjusts the flow rate of the gas flowing into the first-stage reaction tube 10.

[0047] By adjusting the flow rates of the gas flowing into the first-stage reaction tube 10 and the second-stage reaction tube 20 as described above, the space velocity of the gas passing through the first-stage reaction tube 10 and the space velocity of the gas passing through the second-stage reaction tube 20 can be changed.

[0048] Here, the space velocity (H -1 , or 1 / hour) is a numerical value obtained by dividing the amount of gas (gas passing speed) per hour passing through the processing device (for example, the first-stage reaction tube 10, the second-stage reaction tube 20, etc.) by the volume of the catalyst in the device.

[0049] In the process of methane production including the methanation step, by ensuring a space velocity of the reaction tube to a certain extent or more, a relatively large amount of reaction heat is generated, so there is no need to heat the reaction tube. However, if the space velocity is increased too much, the raw material gas will be discharged from the reaction tube in an unreacted state, resulting in a decrease in the concentration of the generated methane.

[0050] In one example, the gas space velocity of the first-stage reaction tube 10 and the gas space velocity of the second-stage reaction tube 20 are both set to be 10,000 or less. According to this configuration, the concentration of methane generated by the methane production apparatus 1 can be made higher (for example, 50% or more).

[0051] Also, the gas space velocity in the first-stage reaction tube 10 is preferably set within the range of 2,400 (1 / hour) or more and 7,500 (1 / hour) or less.

[0052] By setting the gas space velocity in the first-stage reaction tube 10 to 2,400 (1 / hour) or more, the methane generation reaction in the first-stage reaction tube 10 is promoted and the heat generation amount increases, so heating using a heater 12 or the like in the first-stage reaction tube 10 can be made unnecessary.

[0053] By setting the gas space velocity in the first-stage reaction tube 10 to 7,500 (1 / hour) or less, the concentration of methane generated by the methane production apparatus 1 can be made even higher (for example, 60% or more).

[0054] Note that the space velocity of the first-stage reaction tube 10 and the space velocity of the second-stage reaction tube 20 are preferably set to be substantially the same. Thereby, the gas flow in the first-stage reaction tube 10 and the second-stage reaction tube 20 connected via the gas pipe 50 can be made smoother.

[0055] The reaction amount of the above [Reaction Formula 1] in the reaction tube 10 of the first stage and the reaction tube 20 of the second stage is also changed depending on the concentration of the catalyst introduced into each unit reaction tube. That is, the higher (greater) the concentration of the catalyst introduced into each unit reaction tube, the greater the reaction amount of [Reaction Formula 1].

[0056] Note that the concentration of the catalyst can be adjusted by changing the dilution ratio of the catalyst. In one example, the dilution ratio of the catalyst contained in the reaction tube 10 of the first stage may be made larger than the dilution ratio of the catalyst contained in the reaction tube 20 of the second stage. In other words, the concentration of the catalyst contained in the reaction tube 10 of the first stage may be lower than the concentration of the catalyst contained in the reaction tube 20 of the second stage. Thereby, it is possible to suppress the methanation reaction from proceeding too far in the reaction tube 10 of the first stage where a relatively intense reaction can occur, and to suppress the temperature of the reaction tube 10 of the first stage from rising.

[0057] (Summary of Embodiment) The methane production apparatus 1 according to the present embodiment includes at least a reaction tube 10 of the first stage into which a raw material gas flows, a reaction tube 20 of the second stage located downstream of the reaction tube 10 of the first stage, and a flow rate control means (specifically, a flow rate control unit 41) for adjusting the flow rate of the raw material gas flowing into the reaction tube 10 of the first stage and the reaction tube 20 of the second stage.

[0058] The methane production apparatus 1 according to the present embodiment is a multi-stage methane production apparatus having two reaction tubes, namely, a reaction tube 10 of the first stage and a reaction tube 20 of the second stage. Usually, in such a multi-stage methane production apparatus, the reaction tube in the latter stage is made larger in size to stabilize the reaction throughout the apparatus. However, this results in an increase in the size of the methane production apparatus.

[0059] Therefore, in the methane production apparatus 1 according to the present embodiment, the volume of the second-stage reaction tube 20 is configured to be smaller than the volume of the first-stage reaction tube 10. Further, the flow rate control means of the methane production apparatus 1 controls the gas flow rate so that the flow rate of the gas passing through the second-stage reaction tube 20 is smaller than the flow rate of the gas passing through the first-stage reaction tube 10.

[0060] According to the above configuration, the amount of methanation reaction in the first-stage reaction tube 10 can be increased. Therefore, the size of the second-stage reaction tube 20 relative to the size of the first-stage reaction tube 10 can be made smaller. As a result, the amount of heat generated in the first-stage reaction tube 10 increases. The heat generated here can be used, for example, to heat the raw material gas flowing into the first-stage reaction tube 10.

[0061] This can reduce the space occupied by the second-stage reaction tube 20 and the amount of heater and electric power required for heating the second-stage reaction tube 20. Also, with the above configuration, the conversion rate of methane in the first-stage reaction tube 10 can be made higher than the conversion rate of methane in the second-stage reaction tube 20.

[0062] As described above, the present invention adopts the technical idea of maximizing the utilization of the first-stage reaction tube that reacts more vigorously. Then, the second-stage reaction tube is made as small as possible to miniaturize the entire apparatus.

[0063] Also, in the present invention, the heating means for the second-stage reaction tube that requires heating means can be made smaller. As a result, the methane production apparatus can be miniaturized (the installation area can be made as small as possible), and the amount of heater and electric power required for heating can be reduced.

[0064] The methanation reaction for generating methane gas is a process that generates a large amount of heat. In the present invention, the heat generated in the methanation reaction can be effectively utilized as much as possible to provide a methane production apparatus with a small environmental load.

[0065] 〔Example〕 Hereinafter, examples of the present invention will be described. Note that the present invention is not limited to the following examples.

[0066] In this example, a methane production experiment was conducted using the methane production apparatus 1. In this experiment, by varying the space velocity of the gas in the first-stage reaction tube 10 and the second-stage reaction tube 20 in various ways, it was confirmed how the concentration of the generated methane changes. The results are shown in Table 1.

[0067]

Table 1

[0068] In Table 1 above, the "space velocity" is the average value of the space velocity of the first-stage reaction tube 10 and the space velocity of the second-stage reaction tube 20. Note that this space velocity is determined by calculation using the flow rate of the input gas raw material and the volume filled with the catalyst in the reaction tube.

[0069] Also, in Table 1 above, "presence or absence of heating" means the presence or absence of heating using a heater in the first-stage reaction tube 10. Also, in Table 1 above, "methane concentration" means the concentration of methane in the final product by the methane production apparatus 1.

[0070] Table 1 shows the experiments in ascending order of the space velocity of each experiment. Specifically, the space velocities of each example and each comparative example are as follows. Comparative Example 1: 1,200 Example 1: 2,400 Example 2: 2,500 Example 3: 5,000 Example 4: 7,500 Comparative Example 2: 10,000

[0071] As shown in Table 1, it was confirmed that as the space velocity increased, the concentration of methane in the final product decreased. And when the space velocity reached 10,000, it was confirmed that the methane concentration decreased to about 50% (see Comparative Example 2). Also, in Comparative Example 1 where the space velocity was 1,200, it was confirmed that heating by a heater was required for the progress of the reaction in the first-stage reaction tube 10.

[0072] From the above, by setting the space velocity of the first-stage reaction tube 10 within the range of 2,400 (1 / hour) or more and 7,500 (1 / hour) or less, it was confirmed that methane with an appropriate concentration can be generated without heating the first-stage reaction tube 10.

[0073] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included. Also, the configurations obtained by combining the configurations of different embodiments described in this specification with each other are also included in the scope of the present invention.

Explanation of Reference Numerals

[0074] 1: Methane production apparatus 10: First-stage reaction tube 11: Unit reaction tube 12: Heater (heating means) 20: Second-stage reaction tube 21: Unit reaction tube 22: Heater (heating means) 31: Pump 32: Flowmeter 35: Gas-liquid separator 41: Flow control unit (flow control means)

Claims

1. A methane production apparatus for producing methane from a raw material gas using a catalyst, comprising: a first-stage reaction tube into which the raw material gas flows; a second-stage reaction tube located downstream of the first-stage reaction tube; flow control means for adjusting the flow rate of the raw material gas flowing into the first-stage reaction tube and the second-stage reaction tube; and at least comprising: the volume of the second-stage reaction tube is smaller than the volume of the first-stage reaction tube; the flow rate of the gas passing through the second-stage reaction tube is smaller than the flow rate of the gas passing through the first-stage reaction tube. Methane production apparatus.

2. The space velocity of the gas in the first-stage reaction tube is set within a range of 2400 (1 / hour) or more and 7500 (1 / hour) or less. The methane production apparatus according to Claim 1.

3. The concentration of the catalyst contained in the first-stage reaction tube is smaller than the concentration of the catalyst contained in the second-stage reaction tube. The methane production apparatus according to Claim 1 or 2.

4. The first-stage reaction tube does not have heating means around itself. The methane production apparatus according to Claim 1 or 2.

5. The first-stage reaction tube and the second-stage reaction tube each include a plurality of unit reaction tubes. The number of unit reaction tubes contained in the first-stage reaction tube is larger than the number of unit reaction tubes contained in the second-stage reaction tube. The methane production apparatus according to Claim 1 or 2.

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