Methane production system

Abstract

To provide a methane production system capable of producing high concentration methane while suppressing a cost increase and an installation space.SOLUTION: A methane production system 1 produces methane and includes: a methanation reaction section 4 to which a first gas containing hydrogen and at least one of carbon monoxide and carbon dioxide is supplied; and a methane separation section 5 to which a second gas containing methanation reaction outlet components including at least methane obtained in the methanation reaction section 4 is supplied. The methane separation section 5 separates the second gas using a methane separation membrane into a target gas containing methane as a main component and a recycle gas containing other residual components as main components, and the recycle gas is supplied to the methanation reaction section 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a methane production system. [Background technology]

[0002] In recent years, from the perspective of carbon neutrality, research and development has been conducted on processes for producing methane using carbon dioxide as a raw material. For example, a process has been proposed in which hydrogen is produced from water by an electrolysis reaction, and then methane is produced by a methanation reaction using the hydrogen and carbon dioxide as raw materials. Furthermore, Patent Document 1 discloses a process in which an electrolysis reaction unit and a reverse water gas shift reaction unit are combined to produce a gas containing hydrogen and carbon monoxide from water and carbon dioxide by an electrolysis reaction, and methane is produced by a methanation reaction using the hydrogen and carbon monoxide as raw materials. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-50700 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to use methane produced by the above process by injecting it into a pipeline, the impurity concentrations must be 4 vol% or less for hydrogen, 0.05 vol% or less for carbon monoxide, and 0.5 vol% or less for carbon dioxide.

[0005] Here, when producing methane by methanation reaction, by preparing multiple methanation reaction devices and adopting a method (multi-stage method) in which exhaust gas containing unreacted substances is supplied to the reaction devices again, it is possible to produce high-concentration methane with a reduced concentration of impurities in the final gas obtained.

[0006] However, methanation reactors require appropriate temperature control, which requires a control system. Therefore, the cost increases as the number of methanation reactors increases when a multi-stage system is adopted. Furthermore, the multi-stage system requires sufficient space to install multiple methanation reactors, which increases the installation space of the entire system.

[0007] In other words, when a multi-stage system is adopted in a system for producing methane by a methanation reaction, there is a problem that an increase in cost and an expansion of installation space are unavoidable in order to improve the methane yield and produce highly concentrated methane.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a methane production system that can produce highly concentrated methane while suppressing increases in cost and installation space. [Means for solving the problem]

[0009] The methane production system according to the present invention for achieving the above object has the following characteristic configuration: A methane production system for producing methane, comprising: a methanation reaction section to which a first gas containing hydrogen and at least one of carbon monoxide and carbon dioxide is supplied; a methane separation section to which a second gas containing a methanation reaction section outlet component containing at least methane obtained in the methanation reaction section is supplied, The methane separation unit separates the second gas into a target gas containing methane as a main component and a recycled gas containing other remaining components as main components using a methane separation membrane, The recycled gas is supplied to the methanation reaction section.

[0010] According to the above-described characteristic configuration, methane produced in the methanation reaction unit can be separated in a methane separation unit that can be installed in a space smaller than the methanation reaction unit and is low-cost to operate. This reduces the cost and installation space of the methane production system compared to when multiple methanation reaction units are installed. Furthermore, the recycled gas after separation can be supplied to the methanation reaction unit to reuse unreacted material in the methanation reaction, improving the methane yield and producing high-concentration methane. In other words, a methane production system having the above-described characteristic configuration can produce high-concentration methane while reducing the cost and installation space.

[0011] Further characteristic configurations of the methane production system according to the present invention include: The methanation reaction section outlet component further contains water, The second gas and the recycled gas contain water vapor formed by vaporization of the water in the components at the outlet of the methanation reaction section.

[0012] According to the above characteristic configuration, a second gas containing water generated in the methanation reaction section in the form of steam is supplied to the methane separation section. The second gas is then separated in the methane separation section into a target gas and a recycled gas containing steam, and the recycled gas is supplied again to the methanation reaction section. In other words, in a methane production system having the above characteristic configuration, it is not necessary to lower the temperature of the second gas to cause a phase transition of the water from gas to liquid in order to separate the water generated in the methanation reaction section. Therefore, energy is not required to reheat the gas from which methane has been separated to a predetermined temperature when it is supplied to the methanation reaction section. Therefore, the above methane production system can reduce the energy required for methane production.

[0013] Further characteristic configurations of the methane production system according to the present invention include: The first gas having a temperature of 25°C or higher and 350°C or lower is supplied to the methanation reaction section, The second gas having a temperature of 200°C or higher and 600°C or lower is supplied to the methane separation unit, The recycled gas having a temperature of 200°C or higher and 600°C or lower is supplied to the methanation reaction section.

[0014] According to the above-mentioned characteristic configuration, the recycle gas at a temperature at which the methanation reaction easily proceeds can be directly supplied to the methanation reaction section and reused without temperature adjustment. Therefore, a methane production system having the above-mentioned characteristic configuration eliminates the need to adjust the gas temperature during methane production, and can reduce energy loss caused by increasing and decreasing the gas temperature.

[0015] Further characteristic configurations of the methane production system according to the present invention include: The methane separation section is of a multi-stage type.

[0016] According to the above characteristic configuration, the yield of methane can be further improved, and methane with a higher concentration can be produced.

[0017] Further characteristic configurations of the methane production system according to the present invention include: The electrolysis reactor further includes an electrolysis reactor to which water and carbon dioxide are supplied. The first gas contains components obtained in the electrolytic reaction section and discharged from the electrolytic reaction section, the components including at least hydrogen and carbon monoxide.

[0018] According to the above-described characteristic configuration, the hydrogen and carbon monoxide required for producing methane can be produced in the electrolysis reaction unit. Therefore, in the methane production system, methane can be produced through a series of processes using water and carbon dioxide, which are relatively easily available as raw materials.

[0019] Further characteristic configurations of the methane production system according to the present invention include: a water separation section is provided between the electrolysis reaction section and the methanation reaction section, The first gas is supplied to the methanation reaction section after water has been separated from the first gas in the water separation section.

[0020] According to the above characteristic configuration, water is separated from the first gas supplied to the methanation reaction section, which facilitates the progress of the methanation reaction. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a diagram showing a schematic configuration of a methane production system according to an embodiment. [Figure 2] FIG. 1 is a schematic diagram showing a methane separation membrane. [Figure 3] FIG. 1 is a diagram showing a schematic configuration of a methane production system according to a first comparative example. [Figure 4] FIG. 10 is a diagram showing a schematic configuration of a methane production system according to a second comparative example. [Figure 5] FIG. 10 is a diagram showing a schematic configuration of a methane production system according to a third comparative example. [Figure 6] 1 is a graph showing the change in methane concentration in an example. [Figure 7] 10 is a graph showing the change in methane concentration over time in Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0022] A methane production system 1 according to an embodiment will be described below.

[0023] [Outline of the methane production system] First, an overview of the methane production system 1 will be described. Fig. 1 is a diagram showing the configuration of the methane production system 1 according to this embodiment. As shown in Fig. 1, in this embodiment, the methane production system 1 is a system that produces methane from water and carbon dioxide, and includes an electrolysis reaction unit 2, a water separation unit 3, a methanation reaction unit 4, and two methane separation units 5 (a first methane separation unit 5a and a second methane separation unit 5b).

[0024] [Electrolytic reaction section] The electrolysis reaction unit 2 is a unit that electrolyzes water and carbon dioxide to produce carbon monoxide and hydrogen. Specifically, water and carbon dioxide are supplied as raw materials to the electrolysis reaction unit 2, and these are electrolyzed, with water being decomposed into hydrogen and oxygen, and carbon dioxide being decomposed into carbon monoxide and oxygen. A known solid oxide electrolysis cell (SOEC) can be used.

[0025] The reaction in the electrolytic reaction section 2 can be summarized as follows: (Formula 1) CO2+3H2O→CO+3H2+2O2

[0026] A gas (first gas) containing hydrogen and carbon monoxide obtained in the electrolytic reaction unit 2 and water vapor formed by vaporization of unreacted carbon dioxide and water is supplied to the downstream water separation unit 3. In this embodiment, some of the components other than carbon dioxide out of the gas discharged from the electrolytic reaction unit 2 are supplied to the electrolytic reaction unit 2. In this embodiment, hydrogen, carbon monoxide, water, and carbon dioxide correspond to the "electrolytic reaction unit outlet components."

[0027] [Water separation section] The water separation unit 3 is a unit that removes at least a portion of the water contained in the gas flowing therein, and is composed of a gas-liquid separation cooler and the like. The water separation unit 3 lowers the temperature of the first gas supplied from the preceding electrolysis reaction unit 2, and liquefied water is removed. The first gas from which water has been removed in the water separation unit 3 is heated to a predetermined temperature and then supplied to the following methanation reaction unit 4.

[0028] [Methanation reaction section] The methanation reaction section 4 is a section to which a first gas containing hydrogen and carbon monoxide is supplied from the previous stage and which produces methane from the hydrogen and carbon monoxide. Specifically, in the methanation reaction section 4, methane is produced from hydrogen and carbon monoxide by a methanation reaction using a catalyst. From the viewpoint of facilitating the methanation reaction, it is preferable that the first gas supplied to the methanation reaction section 4 be at a temperature of 25°C or higher and 350°C or lower. Examples of the catalyst used include a Ni-based catalyst and a Ru-based catalyst.

[0029] The reaction in the methanation reaction section 4 is represented by the following formula 2. (Formula 2) CO+3H2⇔CH4+H2O

[0030] A gas (second gas) containing methane obtained in the methanation reaction section 4, water vapor formed by vaporization of water as a by-product, and unreacted carbon monoxide, hydrogen, and carbon dioxide is supplied to the downstream methane separation section 5. In this embodiment, methane, water, carbon monoxide, hydrogen, and carbon dioxide correspond to the "methanation reaction section outlet components."

[0031] [Methane separation section] As described above, the methane production system 1 according to this embodiment includes the first methane separation unit 5a and the second methane separation unit 5b as the methane separation unit 5. In other words, the methane production system 1 includes a multi-stage methane separation unit 5. The methane separation units 5a and 5b have the same configuration except that the gases supplied thereto are different.

[0032] Each of the methane separation units 5a, 5b has a methane separation membrane C. Each of the methane separation units 5a, 5b separates the gas supplied from the previous stage by the methane separation membrane C into a target gas mainly composed of methane and a recycle gas mainly composed of other remaining components. In this application, "mainly composed" means that the proportion of methane in a certain gas as a whole exceeds 50 vol%, specifically exceeds 80 vol%, and more specifically exceeds 90 vol%.

[0033] [Methane separation membrane] FIG. 2 is a schematic diagram showing a methane separation membrane C. Note that the thick arrows in FIG. 2 indicate the flow of gas containing the separation target (methane). In this embodiment, the methane separation membrane C is a so-called zeolite membrane composite. As shown in FIG. 2, the methane separation membrane C of this embodiment has a metal support K and a zeolite membrane M formed on the surface of the metal support K.

[0034] The metal support K is generally plate-shaped and serves to support the zeolite membrane M and maintain the strength of the methane separation membrane C. In this embodiment, the metal support K is made of ferritic stainless steel, but is not limited to this. The thickness H1 of the metal support K may be appropriately set based on the fluid permeability and the strength required for the methane separation membrane C, and is preferably, for example, 0.1 mm to 2 mm.

[0035] The metal support K has a plurality of through holes K1 formed therein, penetrating from the surface (front surface) on which the zeolite membrane M is formed to the back surface. The through holes K1 can be formed by mechanical, chemical, or optical perforation processes such as punching, etching, or laser processing. The diameter of the through holes K1 is not particularly limited, but is preferably, for example, 0.1 μm or more and 7.5 μm or less. In this embodiment, the shape of the opening edge of the through holes K1 is circular, but is not limited thereto.

[0036] [Zeolite membrane] The zeolite membrane M serves to separate specific molecules by utilizing the molecular sieving action of zeolite (aluminosilicate). The zeolite constituting the zeolite membrane M can be appropriately selected from known zeolite species having various skeletal structures depending on the molecular size of the object to be separated (i.e., methane). In this embodiment, since the object to be separated is methane, LTA, CHA, FAU, or the like, which have a crystal pore diameter of less than 0.38 nm, is used.

[0037] The thickness H2 of the zeolite membrane M may be appropriately set in consideration of the permeability of the fluid. Specifically, if the thickness H2 of the zeolite membrane M is too thick, the permeability decreases, making it difficult for the fluid to pass through the zeolite membrane M. Conversely, if the thickness H2 is too thin, the permeability increases too much, resulting in a decrease in the efficiency of separation of the target from the fluid. Therefore, the thickness H2 of the zeolite membrane M is preferably 0.1 μm or more and 100 μm or less.

[0038] In the methane separation unit 5 (first methane separation unit 5a and second methane separation unit 5b) having the above configuration, when a gas containing methane to be separated is supplied from the back side of the metal support K, as shown in Fig. 2, the supplied gas passes through the through holes K1 and is supplied to the zeolite membrane M. As the gas passes through the zeolite membrane M, the methane is separated by the molecular sieving action of the zeolite. In other words, the methane separation membrane C separates the target gas, which is mainly composed of methane, into the non-permeation side of the methane separation membrane C (the back side of the zeolite membrane M in Fig. 2), and the recycled gas, which is mainly composed of residual components such as hydrogen and carbon monoxide, which have smaller molecular sizes than methane, into the permeation side (the front side of the zeolite membrane M in Fig. 2). From the viewpoint of enabling the recycle gas at a temperature at which the methanation reaction easily proceeds to be supplied to the methanation reaction section 4 without temperature adjustment, it is preferable that the second gas at a temperature of 200°C or higher and 600°C or lower be supplied to the methane separation section 5 (first methane separation section 5a and second methane separation section 5b).

[0039] [Methane production flow using a methane production system] Next, a process for producing methane using the methane production system 1 having the above configuration will be described.

[0040] As shown in FIG. 1, carbon dioxide and water are supplied to an electrolysis reaction section 2, and carbon monoxide and hydrogen are produced from the carbon dioxide and water by an electrolysis reaction at a predetermined temperature (for example, 800° C.).

[0041] Next, a portion of the components other than carbon dioxide of the first gas discharged from the electrolysis reaction section 2 is supplied to the electrolysis reaction section 2, and the remainder is supplied to the water separation section 3, where the temperature of the gas is lowered to a temperature (e.g., 35°C) at which the water in the gas liquefies, and the liquefied water is removed.

[0042] Next, the first gas after water separation is heated to a predetermined temperature (for example, 260° C.) and then supplied to the methanation reaction section 4, where methane and water are produced from carbon monoxide and hydrogen by a methanation reaction.

[0043] Thereafter, the second gas discharged from the methanation reaction section 4 is supplied to the first methane separation section 5a. The temperature of the second gas supplied to the first methane separation section 5a is higher (for example, 400°C) than the first gas supplied to the methanation reaction section 4 due to the heat generated by the methanation reaction, which is an exothermic reaction.

[0044] The second gas supplied to the first methane separation section 5a is separated by the methane separation membrane C into a target gas mainly composed of methane and a recycled gas mainly composed of the remaining components. The target gas separated by the first methane separation section 5a contains trace amounts of hydrogen, carbon monoxide, and carbon dioxide in addition to methane. The recycled gas also contains trace amounts of methane that have permeated the methane separation membrane C, in addition to the remaining components hydrogen, carbon monoxide, carbon dioxide, and water vapor.

[0045] Since component separation by the methane separation membrane C is driven by a pressure difference, it may be necessary to increase the pressure of the supplied gas. In this embodiment, the second gas discharged from the methanation reaction section 4 is at high pressure (for example, about 0.8 MPa or higher), and the pressure increase process can be omitted, so that equipment required for increasing the pressure of the second gas is not required. Note that if the pressure difference is insufficient, the pressure difference required for component separation may be generated by providing a means for increasing the pressure of the second gas or a blower downstream of the second methane separation section.

[0046] Next, the target gas separated in the first methane separation section 5a is supplied to the second methane separation section 5b, while the recycled gas separated in the first methane separation section 5a is supplied to the methanation reaction section 4 without undergoing temperature adjustment treatment.

[0047] The target gas supplied to the second methane separation unit 5b is then separated into a target gas and a recycled gas in the same manner as described above. The target gas separated in the second methane separation unit 5b contains methane as well as traces of carbon dioxide, which has a molecular size similar to that of methane. The recycled gas also contains residual components such as hydrogen, carbon monoxide, and carbon dioxide, as well as traces of methane that have permeated the methane separation membrane C.

[0048] As described above, according to the methane production system 1, the methane produced in the methanation reaction unit 4 can be efficiently separated by the methane separation unit 5, and the recycled gas can be reused in the methanation reaction unit 4. This improves the methane yield and enables the production of highly concentrated methane. Furthermore, the methane separation unit 5 requires less installation space than the methanation reaction unit 4, and does not require temperature management or other controls, allowing for low-cost operation. Therefore, it is possible to produce highly concentrated methane while suppressing increases in cost and installation space compared to adopting a multi-stage system in which multiple methanation reaction units 4 are provided.

[0049] In particular, in the methane production system 1, the methane separation unit 5 separates water contained in the gas as water vapor and supplies it again to the methanation reaction unit 4 as part of the recycled gas. In other words, in the methane production system 1, there is no need to lower the temperature of the second gas to cause a phase transition of water from gas to liquid in order to separate the water produced as a by-product in the methanation reaction unit. Therefore, the methane production system does not require lowering the gas temperature as in the separation of water in the water separation unit 3, and does not require energy to heat the recycled gas to a predetermined temperature before resupplying it to the methanation reaction unit 4. In other words, the methane production system can reduce energy loss caused by temperature increases and decreases in the gas, thereby reducing the energy required for methane production.

[0050] [Examples and Comparative Examples] Examples and comparative examples will be described below. In the examples, a methane production process using the above-described methane production system was simulated, and the compositions of the target gas and recycled gas were calculated. In Comparative Examples 1 to 3, a methane production process using each of the methane production systems shown in Figs. 3 to 5 was simulated, and the composition of the final gas obtained was calculated. Fig. 3 is a diagram showing a schematic configuration of a methane production system according to Comparative Example 1. Fig. 4 is a diagram showing a schematic configuration of a methane production system according to Comparative Example 2. Fig. 5 is a diagram showing a schematic configuration of a methane production system according to Comparative Example 3.

[0051] [Example] In Example 1, a simulation was performed to calculate the composition of the target gas by producing methane using the process shown below. First, water and carbon dioxide were supplied to the electrolysis reaction section, and carbon monoxide and water were produced from the water and carbon dioxide at 800°C. The conversion rate in the electrolysis reaction section was assumed to be approximately 98.4%.

[0052] The gas containing hydrogen and carbon monoxide obtained in the electrolysis reaction section, as well as unreacted carbon dioxide and water vapor, was then cooled to 35°C in the water separation section, where the water was liquefied and separated. The water removal rate in the water separation section was assumed to be approximately 74.7%.

[0053] Next, the gas after water separation, heated to 260°C, was supplied to the methanation reactor, where methane and water were produced from carbon monoxide and hydrogen. The conversion rate in the methanation reactor was assumed to be approximately 95.7%.

[0054] Thereafter, the gas containing the methane and water vapor obtained in the methanation reaction section, as well as the unreacted hydrogen, carbon monoxide, and carbon dioxide, was supplied to the first methane separation section, where it was separated by a methane separation membrane into a target gas mainly composed of methane and a recycled gas mainly composed of the remaining components. It was assumed that the gas discharged from the methanation reaction section had reached 400°C due to the heat generated in the methanation reaction, and the temperature of the gas supplied to the first methane separation section was 400°C. The permeability of the methane separation membrane for each gas was approximately 8.0 x 10 for methane. -8 mol / m 2 / s / Pa, and hydrogen is approximately 5.0 × 10 -6 mol / m 2 / s / Pa, and carbon monoxide is approximately 3.0 × 10 -6 mol / m 2 / s / Pa, and carbon dioxide is approximately 2.7 × 10 -6 mol / m 2 / s / Pa, and water is approximately 2.0 × 10 -5 mol / m 2The pressure was measured as / s / Pa. The composition of the recycled gas obtained by collecting the permeate gases separated in the first methane separation section and the second methane separation section is shown in the "Permeate Side" column in Table 1.

[0055] The target gas was then fed to the second methane separation section, where it was separated into target gas and recycled gas using the same methane separation membrane. The composition of the target gas separated in the second methane separation section was as shown in the "non-permeate side" in Table 1.

[0056] Figure 6 is a graph summarizing the transition of methane concentration in gas in the examples. In Figure 6, the plot "between the methanation reaction section and the first methane separation section" is the second gas supplied from the methanation reaction section to the first methane separation section, the plot "between the first methane separation section and the second methane separation section" is the target gas supplied from the first methane separation section to the second methane separation section, and the plot "after the second methane separation section" is data (methane concentration) related to the target gas discharged from the second methane separation section.

[0057] Comparative Example 1 The methane production system according to Comparative Example 1 is a system equipped with an electrolysis reaction unit, a first water separation unit, a methanation reaction unit, and a second water separation unit. The electrolysis reaction unit, the first water separation unit, and the methanation reaction unit correspond to the electrolysis reaction unit, the water separation unit, and the methanation reaction unit of the methane production system according to the embodiment. As with the first water separation unit, the second water separation unit cools the methane obtained in the methanation reaction unit, water vapor formed by vaporizing water as a by-product, and a gas containing unreacted substances such as hydrogen, carbon monoxide, and carbon dioxide, and liquefies and separates the water. The methane production system according to Comparative Example 1 is a system equipped with a second water separation unit instead of the methane separation unit 5 of the methane production system 1 according to the embodiment.

[0058] In Comparative Example 1, the processes from the electrolysis reaction section to the methanation reaction section were carried out in the same manner as in the Examples, and a simulation was performed in which the gas discharged from the methanation reaction section was cooled to 35°C in the second water separation section, and water was liquefied and separated to produce methane. It was assumed that the water removal rate from the gas discharged from the methanation reaction section was approximately 99.1%. The composition of the final gas obtained was as shown in Table 1.

[0059] Comparative Example 2 The methane production system according to Comparative Example 2 is a system including an electrolysis reaction unit, a first water separation unit, a first methanation reaction unit, and a second methanation reaction unit. In other words, the methane production system according to Comparative Example 2 is a system in which one methanation reaction unit is added to the methane production system according to Comparative Example 1.

[0060] In Comparative Example 2, the processes from the electrolysis reactor to the first methanation reactor were carried out in the same manner as in the Example. The gas discharged from the first methanation reactor was then supplied to a second methanation reactor under the same conditions. The gas discharged from the second methanation reactor was then cooled to 35°C in a second water separation unit, and the water was liquefied and separated to produce methane. The conversion rate in the second methanation reactor was assumed to be the same as that in the first methanation reactor, and the water removal rate from the gas discharged from the methanation reactor was assumed to be approximately 99.1%. The composition of the final gas obtained was as shown in Table 1.

[0061] Comparative Example 3 The methane production system according to Comparative Example 3 is a system including an electrolysis reaction section, a first water separation section, a first methanation reaction section, a second water separation section, a second methanation reaction section, a third methanation reaction section, and a third water separation section. In other words, the methane production system according to Comparative Example 3 is a system in which one more water separation section and one more methanation reaction section are added to the methane production system according to Comparative Example 2.

[0062] In Comparative Example 3, the process from the electrolysis reaction section to the first methanation reaction section was the same as in Comparative Example 2. The gas discharged from the first methanation reaction section was cooled to 35°C in the second water separation section, and the heated gas obtained by liquefying and separating water was supplied to the second methanation reaction section under the same conditions. The gas discharged from the second methanation reaction section was then supplied to the third methanation reaction section under the same conditions. The gas discharged from the third methanation reaction section was then cooled to 35°C in the third water separation section, and the water was liquefied and separated to produce methane. A simulation was conducted. The conversion rate in the third methanation reaction section was assumed to be the same as the conversion rates in the first methanation reaction section and the second methanation reaction section. The water removal rate from the gas discharged from the methanation reaction section was assumed to be approximately 99.1%. The composition of the final gas obtained was as shown in Table 1.

[0063] Fig. 7 is a graph summarizing the changes in methane concentration in the gas in Comparative Example 3. In Fig. 7, the plot "between the first methanation reaction section and the second water separation section" represents gas discharged from the first methanation reaction section and supplied to the second water separation section, the plot "between the second water separation section and the second methanation reaction section" represents gas supplied to the second methanation reaction section after water has been removed in the second water separation section, the plot "between the second methanation reaction section and the third methanation reaction section" represents gas discharged from the second methanation reaction section and supplied to the third methanation reaction section, the plot "between the third methanation reaction section and the third water separation section" represents gas discharged from the third methanation reaction section and supplied to the third water separation section, and the plot "after the third water separation section" represents data (methane concentration) related to the gas after water has been removed in the third water separation section.

[0064] [Table 1]

[0065] As shown in Table 1, in all of Comparative Examples 1 to 3, the methane concentration in the final gas obtained was below 70 vol%, and the concentrations of hydrogen and carbon dioxide were also high. In contrast, in the Examples, the concentrations of hydrogen, water, and carbon dioxide in the recycled gas (permeation side) were higher than the methane concentration, indicating that the methane separation section could efficiently separate the target gas, which is primarily composed of methane, from the recycled gas, which is primarily composed of the remaining components. Furthermore, in the Examples, by undergoing two stages of methane separation, the methane concentration in the final target gas (non-permeation side) was extremely high at 99.7 vol%, and the carbon dioxide concentration was extremely low at 0.3 vol%.

[0066] From the above, it was confirmed that by adopting a method in a methane production system in which the gas discharged from the methanation reaction section is supplied to the methane separation section and the target gas, which is mainly composed of methane, can be produced with high concentration while suppressing increases in costs and installation space.

[0067] 6, in the example, the methane concentration of the gas supplied from the methanation reaction section to the first methane separation section is approximately 64%, and then, by passing the gas through a methane separation membrane once in the first methane separation section, the methane concentration increases significantly to approximately 89%.Then, by passing the gas through a methane separation membrane again in the second methane separation section, the methane concentration increases to 99.7%.

[0068] On the other hand, as shown in FIG. 7, in Comparative Example 3, the methane concentration of the gas supplied from the first methanation reaction section to the second methanation reaction section is approximately 64%, but even after further methanation reactions in the second methanation reaction section and the third methanation reaction section and water removal in the second water separation section, the increase in methane concentration is small, and the methane concentration of the gas finally obtained is only 66.3%.

[0069] From the above, it can be seen that even if a methane production system uses a multi-stage method with multiple methanation reaction sections, additional processing is required to increase the methane concentration to a level that can be injected into a pipeline and used.In contrast, by incorporating a method that separates methane using a methane separation membrane into a methane production system, it is possible to produce highly concentrated methane that can be injected into a pipeline and used.

[0070] [Another embodiment] [1] In the above embodiment, the methanation reaction section produces methane from hydrogen and carbon monoxide. However, the present invention is not limited to this. For example, the methanation reaction section may produce methane from hydrogen and carbon dioxide as raw materials. Even in this case, the gas discharged from the methanation reaction section may be supplied to a methane separation section, and the gas may be separated into a target gas and a recycled gas using a methane separation membrane. This configuration reduces the installation space, improves the methane yield, and produces high-concentration methane.

[0071] [2] In the above embodiment, the electrolysis reactor 2 and the water separation unit 3 are provided, but the present invention is not limited to this. The electrolysis reactor 2 and the water separation unit 3 may not be provided, or a reverse water gas shift reactor may be provided in addition to the electrolysis reactor.

[0072] [3] In the above embodiment, an embodiment including two methane separation units 5 (the first methane separation unit 5a and the second methane separation unit 5b) has been described, but the present invention is not limited to this embodiment. An embodiment including one methane separation unit or an embodiment including three or more methane separation units may also be used.

[0073] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradictions arise. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Explanation of symbols]

[0074] 1: Methane production system 2: Electrolytic reaction section 3:Water separation section 4: Methanation reaction section 5: Methane separation section 5a: First methane separation section 5b: Second methane separation section C: Methane separation membrane

Claims

1. A methane production system for producing methane, comprising: a methanation reaction section to which a first gas containing hydrogen and at least one of carbon monoxide and carbon dioxide is supplied; a methane separation section to which a second gas containing a methanation reaction section outlet component containing at least methane obtained in the methanation reaction section is supplied, The methane separation unit separates the second gas into a target gas containing methane as a main component and a recycled gas containing other remaining components as main components using a methane separation membrane, The methane production system, wherein the recycled gas is supplied to the methanation reaction section.

2. The methanation reaction section outlet component further contains water, 2. The methane production system according to claim 1, wherein the second gas and the recycled gas contain water vapor formed by vaporizing the water contained in the components at the outlet of the methanation reaction section.

3. The first gas having a temperature of 25°C or higher and 350°C or lower is supplied to the methanation reaction section, the second gas having a temperature of 200°C or higher and 600°C or lower is supplied to the methane separation section, The methane production system according to claim 2 , wherein the recycled gas having a temperature of 200° C. or higher and 600° C. or lower is supplied to the methanation reaction section.

4. The methane production system according to claim 1 , wherein the methane separation section is a multi-stage type.

5. The electrolysis reactor further includes an electrolysis reactor to which water and carbon dioxide are supplied.

2. The methane production system according to claim 1, wherein the first gas contains an electrolysis reaction section outlet component containing at least hydrogen and carbon monoxide obtained in the electrolysis reaction section.

6. a water separation section is provided between the electrolysis reaction section and the methanation reaction section, The methane production system according to claim 5 , wherein the first gas is supplied to the methanation reaction section after water has been separated from the first gas in the water separation section.

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