Methane production device, methane production method, and power generation system

Abstract

To provide: a methane production device and a methane production method which, in production of methane gas by bio-methanation, enable supply of the methane gas at a proper concentration required on a use place where the methane gas is used; and a power generation system utilizing the methane production device.SOLUTION: A methane production method according to the present invention, which is for performing methane production based on bio-methanation, includes: a reaction step of performing a methanation reaction with hydrogen gas and biogas being supplied; and a control step of controlling the efficiency of the methanation reaction to obtain methane gas having any methane concentration. According to the methane production method, the methane gas can be supplied at a proper concentration adapted to a use place of the methane gas. A power generation system according to the present invention utilizes the methane gas obtained from a methane production device according to the present invention. The power generation system enables the methane production device to have a high efficiency without replacing an existing gas power generator.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a methane generation apparatus and a methane generation method for generating methane by biomethanation, and a power generation system that utilizes methane gas obtained by the methane generation apparatus. [Background technology]

[0002] In recent years, there has been active development of technologies for treating various organic wastes and wastewater by decomposing and reducing their volume through methane fermentation using microorganisms, as well as recovering and utilizing the methane gas generated during this process.

[0003] For example, Patent Document 1 describes an apparatus for generating methane gas by methane fermentation of organic waste, which is equipped with a means for measuring the hydrogen partial pressure in the digester gas generated from a methane fermentation tank, a means for removing hydrogen from the digester gas, and a means for returning the residual gas from which hydrogen has been removed to the methane fermentation tank. This reduces the hydrogen partial pressure in the methane fermentation tank, promotes the decomposition of organic acids into acetic acid, and eliminates the accumulation of organic acids, thereby preventing the occurrence of rancidity and enabling stable methane fermentation with a high decomposition rate over a long period of time. It also describes how the generated methane gas can be sent to a power generation facility and effectively utilized as fuel for electricity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-998 Summary of the Invention [Problem to be solved by the invention]

[0005] As described in Patent Document 1, in the past, in technologies for generating methane gas through methane fermentation and then utilizing the generated methane gas, efforts have focused on stably progressing methane fermentation and increasing its processing efficiency.

[0006] It is also known that the gas produced by methane fermentation (known as biogas) contains carbon dioxide in addition to methane, and that some methanogens, the microorganisms involved in methane fermentation, produce methane by oxidizing hydrogen and reducing carbon dioxide. By supplying hydrogen to the carbon dioxide in the biogas produced by methane fermentation, methane production can be further promoted, thereby increasing the methane yield in the biogas produced by the anaerobic process as a whole. The technology of producing methane from carbon dioxide and hydrogen using methanogens is called biomethanation. Because it produces methane, which is useful as an energy source, by consuming carbon dioxide, it is expected to not only improve the methane yield in biogas, but also contribute to decarbonization efforts by reducing carbon dioxide emissions into the environment.

[0007] On the other hand, when considering the utilization of methane gas generated by methane fermentation (including biomethanation), it is not necessarily the case that the higher the concentration of methane gas generated and supplied by methane fermentation, the better; it is desirable to supply the methane gas at a concentration appropriate for the point of use (various devices and facilities that use methane gas). For example, there are gas power generation devices on the market that use methane gas as fuel whose specifications stipulate an appropriate range of methane gas concentration, and it is required that the concentration of the methane gas supplied conform to this appropriate range. However, in the technologies related to methane generation and supply through methane fermentation to date, little attention has been paid to the methane concentration required at the point of use. In particular, even with biomethanation technology, which is expected to contribute to the high concentration of methane gas and decarbonization, in order to widely and effectively utilize the generated methane gas, it is necessary to make it possible to easily and stably adjust the concentration of methane gas rather than simply increasing the concentration of methane gas.

[0008] The problem to be solved by the present invention is to provide a methane generation device and a methane generation method that enable the supply of methane gas at an appropriate concentration required at the point of use where the methane gas is utilized in the generation of methane gas by biomethanation, as well as to provide a power generation system that utilizes this methane generation device. [Means for solving the problem]

[0009] As a result of extensive research into the above-mentioned problems, the inventors have discovered that in a methane generation device and methane generation method that generate methane based on biomethanation, and in a power generation system that utilizes a methane generation device, by performing control to suppress the reaction efficiency related to biomethanation, it is possible to obtain methane gas that satisfies any methane concentration range, and to supply methane gas at an appropriate concentration required at the point of use where methane gas is utilized, and have completed the present invention.

[0010] In order to solve the above problems, the methane generation apparatus of the present invention is a methane generation apparatus that generates methane based on biomethanation, and is characterized by comprising: a reaction section to which hydrogen gas and biogas are supplied and which performs a methanation reaction; and a control means that suppresses the efficiency of the methanation reaction in order to obtain methane gas with a desired methane concentration. The methane generator of the present invention makes it possible to easily and stably supply methane gas at the appropriate concentration required at the point of use while taking advantage of the benefits of methane gas generation by biomethanation, such as contributing to decarbonization. This makes it possible to effectively utilize the generated methane gas.

[0011] In one embodiment of the methane generation apparatus of the present invention, the control means controls the amount of hydrogen gas supplied to the reaction section. This methane generator can supply methane gas at an appropriate concentration depending on the location where the methane gas is used.

[0012] In one embodiment of the methane generation apparatus of the present invention, the control means continues to supply hydrogen gas to an extent that methanogens can be maintained in the reaction section. This methane generator can continue biomethanation in a resource-saving manner even if the hydrogen supply volume decreases, and can quickly return to normal operation when the hydrogen supply volume recovers.

[0013] In one embodiment of the methane generation apparatus of the present invention, the control means controls the amount of biogas supplied to the reaction section. This methane generator can supply methane gas at an appropriate concentration depending on the location where the methane gas is used.

[0014] In order to solve the above problems, the methane generation method of the present invention is a methane generation method that performs methane generation based on biomethanation, and is characterized by including a reaction step in which hydrogen gas and biogas are supplied and a methanation reaction is performed, and a control step in which the efficiency of the methanation reaction is suppressed in order to obtain methane gas with a desired methane concentration. According to this methane generation method, methane gas can be supplied at an appropriate concentration depending on the location where the methane gas is used.

[0015] In order to solve the above problems, the power generation system according to the present invention is characterized by utilizing methane gas obtained from the methane generator according to the present invention. This power generation system makes it possible to increase the efficiency of the methane generator without replacing the existing gas generator. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a methane generation device and a methane generation method that enable the supply of methane gas at an appropriate concentration required at the point of use where the methane gas is utilized in the generation of methane gas by biomethanation, as well as a power generation system that utilizes this methane generation device. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram illustrating a methane generation apparatus according to an embodiment of the present invention. [Figure 2] 1 is a schematic explanatory diagram of a power generation system according to an embodiment of the present invention. [Figure 3] FIG. 2 is a schematic explanatory diagram of a reaction section in an embodiment of the present invention. [Figure 4] FIG. 1 is a schematic explanatory diagram of a modified example of a methane generation apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a methane generator, a methane generation method, and a power generation system according to the present invention will be described in detail with reference to the drawings. The methane generation apparatus and power generation system described as embodiments are merely examples for explaining the methane generation apparatus and power generation system according to the present invention, and are not limited thereto. The methane generation method of this embodiment is replaced by the following description of the configuration and operation of the methane generation apparatus.

[0019] [Methane generator] FIG. 1 shows a schematic diagram of a methane generating apparatus 1 according to an embodiment of the present invention. A methane generator 1 according to this embodiment will be described with reference to FIG. As shown in Fig. 1, the methane generator 1 in this embodiment includes a reaction section 90 in which a methanation reaction occurs, and a control means 80 that suppresses the methanation reaction. The methane generator 1 in this embodiment also includes a hydrogen supply section 5 that supplies hydrogen to the reaction section 90, and a biogas supply section 4 that supplies biogas to the reaction section 90. The dashed dotted lines in Fig. 1 indicate controllable connections.

[0020] In the methane generation apparatus 1 of this embodiment, hydrogen gas and biogas are supplied into the reaction section 90 via the hydrogen supply section 5 and the biogas supply section 4, and methane is generated by causing a methanogenic reaction to proceed using methanogens in the reaction section 90.At this time, the reaction efficiency of the methanation reaction is suppressed by the control means 80 in order to obtain methane gas with a desired methane concentration. Each component of the methane generator 1 in this embodiment will be described below.

[0021] [Reaction section] An anaerobic treatment tank for biomethanation is preferably used as the reaction section 90. The anaerobic treatment tank is a reaction tank for anaerobic treatment of starting materials (hydrogen and carbon dioxide) introduced into the tank by methanogens.

[0022] The anaerobic treatment tank in this embodiment will be described with reference to FIG. As shown in FIG. 3, the anaerobic treatment tank 2 contains a liquid S containing methanogens, and is connected to a hydrogen supply unit 4, a biogas supply unit 5, and a methane recovery unit 6.

[0023] The anaerobic treatment tank 2 in this embodiment can have the structure of a reaction tank used in general anaerobic treatment. For example, it is preferable that the anaerobic treatment tank 2 be a closed system to maintain an anaerobic environment.

[0024] The liquid S containing methanogens contained in the anaerobic treatment tank 2 of this embodiment may be any liquid containing methanogens and a certain amount of water, such as a liquid consisting mainly of a solution (water) containing methanogens dispersed therein, or a liquid containing a large amount of solids known as sludge or sludge. The liquid S may be a liquid containing isolated methanogens, or seed sludge from other wastewater treatment facilities. Alternatively, a reaction tank used after anaerobic treatment of the water to be treated may be reused as the anaerobic treatment tank 2 of this embodiment, utilizing the sludge (including granules) present in the tank.

[0025] The anaerobic treatment that takes place in the anaerobic treatment tank 2 mainly includes methane production (biomethanation) by hydrogen-utilizing methanogens that produce methane from hydrogen and carbon dioxide, as well as methane fermentation by methanogens that produce methane from organic acids. During normal methane fermentation, carbon dioxide is produced along with methane. Therefore, by adding hydrogen from an external source, it is possible to consume carbon dioxide and produce methane from hydrogen and carbon dioxide (a process called biomethanation). In the present invention, attention is focused on this reaction, and biomethanation can be promoted.

[0026] [Hydrogen supply unit] The hydrogen supply unit 5 is for supplying hydrogen as a starting material into the anaerobic treatment tank 2. The hydrogen supply unit 5 in this embodiment may be any unit capable of introducing hydrogen into the anaerobic treatment tank 2, and may include, for example, a unit equipped with a pipe 51 connected to a hydrogen source (not shown), as shown in Figure 1. It is preferable to provide a flow rate adjustment mechanism 85 (such as an on-off valve or a valve) on the pipe 51 to adjust the amount of hydrogen supplied.

[0027] Here, the hydrogen supplied into the anaerobic treatment tank 2 via the hydrogen supply unit 5 of this embodiment may be hydrogen (H2) gas as the main component, or may be a mixed gas containing components other than hydrogen. However, in consideration of the yield of methane produced, it is preferable that the hydrogen supplied has a high H2 purity; for example, the H2 content is preferably greater than 50%, and more preferably 70% or greater. The hydrogen to be supplied may also be hydrogen produced by electrolysis of water using renewable energy (green hydrogen) or hydrogen obtained by technology to recover hydrogen from fossil resources without emitting carbon dioxide into the atmosphere (blue hydrogen), which would also enable decarbonization of the procurement of hydrogen sources.

[0028] [Biogas Supply Department] The biogas supply unit 4 is for supplying carbon dioxide as a starting material into the anaerobic treatment tank 2. The biogas supply unit 4 in this embodiment may be any unit capable of introducing carbon dioxide into the anaerobic treatment tank 2, and may include, for example, a unit equipped with a pipe 41 connected to a biogas source, as shown in Fig. 1. It is preferable to provide a flow rate adjustment mechanism 85 (such as an on-off valve or a valve) on the pipe 41 to adjust the amount of biogas supplied.

[0029] Although not shown, an example of a biogas source is an anaerobic treatment tank in which methane fermentation can proceed. The specific structure is not particularly limited. For example, it can be selected appropriately depending on the properties of the water to be treated W that is the treatment target. For example, an appropriate structure of the anaerobic treatment tank can be selected depending on whether the water to be treated W contains a large amount of liquid components or a large amount of solid components. Specific examples of water to be treated include industrial wastewater discharged from various factories such as food factories, chemical factories, and pulp and paper factories, and domestic wastewater such as sewage.

[0030] The anaerobic treatment tank is a sealed container equipped with an agitation mechanism to maintain anaerobic conditions. The water to be treated W introduced into the anaerobic treatment tank through an inlet pipe reacts with anaerobic bacteria, generating biogas primarily composed of methane and carbon dioxide in the anaerobic treatment tank. The biogas generated in the anaerobic treatment tank is supplied to the reaction section 90 via pipe 41.

[0031] Note that the biogas supply unit 4 and the hydrogen supply unit 5 in this embodiment are not limited to being configured with separate pipes (pipe 41 and pipe 51) and supplying carbon dioxide and hydrogen from the respective pipes, as shown in Figure 1. For example, the pipe 41 of the biogas supply unit 4 and the pipe 51 of the hydrogen supply unit 5 may be connected upstream of the anaerobic treatment tank 2, and a mixed gas of carbon dioxide and hydrogen may be supplied to the anaerobic treatment tank 2.

[0032] [Control means] The control means 80 is for suppressing the efficiency of the methanation reaction in the reaction section 90 to obtain methane gas with a desired methane concentration. The control means 80 in this embodiment is not particularly limited as long as it can suppress the methanation reaction in the reaction section 90, and may, for example, control the supply of raw materials (hydrogen gas, biogas) involved in the methanation reaction to the reaction section 90. More specifically, the control means 80 may control the amount of hydrogen gas supplied by the hydrogen supply section 5 and / or the amount of biogas supplied by the biogas supply section 4.

[0033] As an example of the control means 80, the control of the supply amount of hydrogen gas by the hydrogen supply unit 5 will be described. The control unit 80 uses a detection unit (not shown) to detect the methane concentration of the methane gas discharged from the pipe 61. If the detected methane concentration exceeds the appropriate methane concentration at the point of use, the control unit 80 controls the flow rate adjustment mechanism 85 to reduce the amount of hydrogen supplied to the reaction unit 90 via the pipe 51. This reduces the efficiency of the methanation reaction in the reaction unit 90.

[0034] Furthermore, the control of the hydrogen gas supply amount by the control means 80 can be suppressed to an extent that allows the methane bacteria to be maintained within the reaction section 90. This allows biomethanation to continue in a resource-saving state even if the hydrogen supply amount decreases, and allows for a rapid return to normal operation when the hydrogen supply amount recovers.

[0035] Furthermore, as another example of the control means 80, control of the amount of biogas supplied by the biogas supply unit 4 will be described. The control unit 80 uses a detection unit (not shown) to detect the methane concentration of the methane gas discharged from the pipe 61. If the detected methane concentration exceeds the appropriate methane concentration at the point of use, the control unit 80 controls the flow rate adjustment mechanism 84 to increase the amount of biogas supplied to the reaction unit 90 via the pipe 41. This results in a relative shortage of hydrogen supply, and the efficiency of the methanation reaction in the reaction unit 90 is reduced.

[0036] [About the operation of the methane generator] The process flow and operation of the methane generator 1 will be described with reference to FIG.

[0037] First, the control unit 80 controls the flow rate adjustment mechanism 84 to supply biogas containing carbon dioxide from the biogas source to the reaction unit 90 via the piping 41. This process is referred to as a step of supplying biogas to the reaction unit 90. Next, the control unit 80 controls the flow rate adjustment mechanism 85 to supply hydrogen gas from the biogas source to the reaction unit 90 via the pipe 51. This process is referred to as a step of supplying hydrogen gas to the reaction unit 90.

[0038] Then, a methanation reaction occurs inside the reaction section 90, and methane fermentation occurs between the hydrogen and the carbon dioxide in the biogas, producing methane gas, which is then supplied to the point of use through the pipe 61. This process is called the methane fermentation step.

[0039] The control unit 80 then monitors the methane concentration of the methane gas supplied to the point of use through the piping 61, and performs adaptive control to increase or decrease the amount of hydrogen gas and / or biogas supplied so that the concentration falls within a predetermined range. The above steps complete the operation of the methane generator of the present invention. In conventional technology, biogas is produced by methane fermentation, but the methane concentration in the biogas is low at 60%, with carbon dioxide accounting for 40%. In the first embodiment, methane gas is further produced by biomethanation using the carbon dioxide contained in the biogas and hydrogen obtained by electrolysis, etc., making it possible to increase the methane concentration to around 80%, while also making it possible to control the reaction efficiency of biomethanation to suit the location where the methane gas is used.

[0040] As described above, the methane generator 1 in this embodiment can supply methane gas at an appropriate concentration depending on the location where the methane gas is used. The methane generator 1 in this embodiment is particularly suitable for use in devices and facilities related to power generation using methane gas as fuel. Hereinafter, a power generation system using the methane generator 1 will be described as one application example of the methane generator 1 in this embodiment.

[0041] [Power generation system using methane generation equipment] FIG. 2 shows a schematic diagram of a power generation system according to an embodiment of the present invention. The power generation system 100 according to this embodiment will be described with reference to FIG. As shown in Fig. 2, the power generation system 100 in this embodiment includes the methane generator 1 described above and a power generation unit 110 connected to the methane generator 1. As also shown in Fig. 2, the methane generator 1 and the power generation unit 110 are connected by a pipe 61, and biogas (methane gas) is introduced into the power generation unit 110 via the pipe 61.

[0042] The power generation unit 110 is not particularly limited to a specific device or facility as long as it uses methane gas as fuel and generates electricity. For example, it may be a cogeneration system equipped with a gas combustion boiler or a gas engine. In particular, it is preferable to use a commercially available gas generator, which is widely used as a device that runs on methane gas as fuel and generates electricity, as the power generation unit 110 in this embodiment. This makes it possible to effectively utilize existing gas generators, thereby reducing initial costs.

[0043] Here, biogas produced by conventional anaerobic treatment has a methane concentration of 70%, and commonly used gas generators are sometimes designed with an upper limit of 75% methane concentration for normal operation. In contrast, biogas produced by general biomethanation is known to produce methane gas more efficiently than conventional anaerobic treatment, and can sometimes have a methane concentration of over 80%. However, biogas with a methane concentration of 80% cannot be supplied to commonly used gas generators. On the other hand, in the methane generation apparatus 1 of this embodiment, as described above, the control means 80 can reduce the amount of hydrogen supplied to the methane fermentation tank 5 or increase the amount of biogas supplied, thereby reducing the carbon dioxide methane conversion rate and controlling it to, for example, 75%. In other words, by forming a power generation system 100 in which biogas (methane gas) with reduced methanation reaction efficiency is generated by the methane generation device 1 and supplied to the power generation unit 110, it becomes possible to use a commonly used gas generator as the power generation unit 110 and operate it as the power generation system 100.

[0044] [Modification of methane generation device] FIG. 4 shows a schematic explanatory diagram of a methane generator 10 which is a modified example of the methane generator 1 according to the embodiment of the present invention. The methane generator 10 according to this modification will be described with reference to FIG. As shown in Fig. 4, in the methane generation apparatus 10, instead of biogas being supplied to the reaction section 90 from the biogas supply section 4 through the pipe 41, carbon dioxide is supplied from the carbon dioxide supply section 7 through the pipe 71. Then, the biogas from the biogas supply section 4 is supplied through the pipe 41 to the pipe 61, which is the methane recovery section 6 of the reaction section 90, where the methane gas produced in the methanation reaction and the biogas are mixed and supplied to the location where the methane gas is used. The other configurations are the same as those of the methane generator 1 according to the embodiment of the present invention. According to this modification, the carbon dioxide required for the methanation reaction is supplied from the carbon dioxide source, so that methane gas can be supplied through a stable methanation reaction.

[0045] The above-described embodiments are examples of a methane generation apparatus, a methane generation method, and a power generation system. The methane generation apparatus, the methane generation method, and the power generation system according to the present invention are not limited to the above-described embodiments, and the methane generation apparatus, the methane generation method, and the power generation system according to the above-described embodiments may be modified within the scope of the gist of the claims. [Industrial Applicability]

[0046] The methane generation apparatus and method of the present invention are suitable for use in methane generation by biomethanation, and in particular can facilitate the utilization of the generated methane gas. Furthermore, the power generation system of the present invention is suitable for use in gas power generation using methane gas as fuel, and enables power generation that combines the benefits of methane production through biomethanation with the effective use of the produced methane gas. [Explanation of symbols]

[0047] 1, 10 methane generation device, 2 anaerobic treatment tank, 4 biogas supply unit, 5 hydrogen supply unit, 7 carbon dioxide supply unit, 41, 51, 61, 71 piping, 80 control unit, 84, 85, 87 flow rate adjustment mechanism, 90 reaction unit, 100 power generation system, 110 power generation unit

Claims

1. A methane generator that generates methane based on biomethanation, a reaction section to which hydrogen gas and biogas are supplied and which performs a methanation reaction; A methane generation device characterized by comprising a control means for suppressing methanation reaction efficiency in order to obtain methane gas of a desired methane concentration.

2. 2. The methane generator according to claim 1, wherein the control means controls the amount of hydrogen gas supplied to the reaction section.

3. 3. The methane generator according to claim 2, wherein the control means continues to supply hydrogen gas to an extent that methane bacteria can be maintained in the reaction section.

4. The methane generator according to claim 1 , wherein the control means controls the amount of biogas supplied to the reaction section.

5. A method for producing methane based on biomethanation, comprising: a reaction step in which hydrogen gas and biogas are supplied and a methanation reaction is carried out; A methane generation method comprising a control step of suppressing methanation reaction efficiency in order to obtain methane gas of a desired methane concentration.

6. A power generation system that utilizes methane gas obtained from the methane generator according to claim 1.

7. A method for producing methane based on biomethanation, comprising: a reaction step in which a gas containing hydrogen gas and carbon dioxide is supplied and a methanation reaction is carried out; a control step of suppressing methanation reaction efficiency in order to obtain methane gas of a desired methane concentration; A method for producing methane, further comprising a step of mixing the produced methane gas with biogas.

Images