Methane generation apparatus and methane generation method

Abstract

A methanation system is provided that exhibits good conversion efficiency from carbon dioxide to methane even when using a low-concentration carbon dioxide gas as the carbon dioxide supply source, and simplifies the apparatus and reduces the installation area. A methane generation apparatus includes: a dissolution tank for exposing carbon dioxide gas to an aqueous phase to generate a carbon dioxide solution; a culture tank for cultivating methanogenic bacteria to generate methane; a carbon dioxide gas supply path for introducing carbon dioxide gas into the dissolution tank; a solution transfer unit for transferring the carbon dioxide solution from the dissolution tank to the culture tank; a hydrogen supply path for supplying hydrogen; and a methane discharge path for discharging the generated methane from the culture tank.

Description

Technical Field

[0001] This disclosure relates to a methane generation apparatus and a methane generation method. Background Technology

[0002] Methanation is a technology that produces methane from carbon dioxide and hydrogen, and it is highly regarded as a technology that helps achieve carbon neutrality by reducing overall emissions of greenhouse gases such as carbon dioxide to zero. For example, patent documents 1-3 disclose technologies for producing methane from waste gas from thermal power plants or factories.

[0003] In these methanation technologies, to increase the methane concentration generated during methanation, it is necessary to increase the carbon dioxide concentration of the feed gas. Since the carbon dioxide concentration in the exhaust gas from thermal power plants or factories is low, around 10%, it is necessary to use carbon dioxide separation and recovery devices to concentrate the carbon dioxide to a high concentration of over 90%.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2021-151196

[0007] Patent Document 2: Japanese Patent Application Publication No. 2004-321857

[0008] Patent Document 3: Japanese Patent Application Publication No. 2014-148934 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] Using carbon dioxide separation and recovery devices to increase carbon dioxide concentration from low to high presents challenges such as high technical difficulty, the need for large-scale equipment, and high costs. Therefore, it is believed that there is a demand for methanation systems that can directly use low-concentration carbon dioxide gas as a carbon dioxide supply source without the need for carbon dioxide concentration concentration.

[0011] The purpose of this disclosure is to provide a methanation system that achieves good conversion efficiency from carbon dioxide to methane even when using a gas with a low carbon dioxide concentration as the carbon dioxide supply source, and which simplifies the apparatus and reduces the installation area.

[0012] Methods for solving problems

[0013] [1] A methane generating apparatus, comprising:

[0014] A dissolving tank, which exposes carbon dioxide-containing gas to an aqueous phase to generate a carbon dioxide-containing solution;

[0015] A culture tank in which methanogenic bacteria are cultured in a culture medium to produce methane;

[0016] A carbon dioxide gas supply path introduces carbon dioxide-containing gas into the dissolution tank;

[0017] A solution transfer unit for transferring the carbon dioxide-containing solution generated in the dissolving tank from the dissolving tank to the culture tank;

[0018] A hydrogen supply path that supplies hydrogen to the dissolution tank or the culture tank; and

[0019] A methane discharge path that discharges the generated methane from the culture tank.

[0020] [2] According to the methane generating apparatus described in [1] above, wherein,

[0021] The dissolution tank and the culture tank are independent tanks.

[0022] The solution transfer unit is a solution transfer flow path connecting the dissolving tank and the culture tank.

[0023] [3] According to the methane generating apparatus described in [2] above, wherein,

[0024] The solution transfer path is a flow path used to supply the carbon dioxide-containing solution in the dissolving tank to the culture tank without deoxygenation treatment.

[0025] [4] According to the methane generating apparatus described in [1] above, wherein,

[0026] The methane generation device has a single tank that serves as both the dissolution tank and the culture tank.

[0027] The methane generation device also includes a gas phase discharge path for discharging the remaining gas phase when the single tank functions as the culture tank.

[0028] The aqueous phase is a culture medium.

[0029] The solution transfer unit is a switching unit used to switch between the dissolution tank and the culture tank.

[0030] The switching unit includes valves for opening and closing the carbon dioxide gas supply path, the hydrogen supply path, the gas phase discharge path, and the methane discharge path; and a control unit for controlling the opening and closing of the valves.

[0031] The control unit controls the switching between the following modes:

[0032] (i) a dissolution tank mode, which allows the single tank to function as a dissolution tank by opening the carbon dioxide gas supply path and the gas phase discharge path, and closing the hydrogen supply path and the methane discharge path; and

[0033] (ii) A culture tank mode in which the single tank functions as a culture tank by closing the carbon dioxide gas supply path and the gas phase discharge path, and opening the hydrogen supply path and the methane discharge path.

[0034] [5] According to the methane generating apparatus described in [4] above,

[0035] It also has a reuse flow path for merging the remaining gas phase discharged from the gas phase discharge flow path into the carbon dioxide-containing gas inlet.

[0036] [6] According to the methane generating apparatus described in [1] above, wherein,

[0037] The methane generating apparatus comprises a single tank with a liquid-permeable baffle inside the tank.

[0038] The partitions within each tank, separated by the partition, function as the dissolution tank and the culture tank, respectively.

[0039] The solution transfer unit is the partition.

[0040] [7] According to the methane generating apparatus described in [6] above, wherein,

[0041] The partition has an openable and closable opening.

[0042] [8] According to the methane generating apparatus described in [6] above, wherein,

[0043] The partition is a membrane that allows liquid to pass through but not microorganisms.

[0044] [9] The methane generating apparatus according to any one of [1] to [3], [6] and [7] above, wherein,

[0045] The dissolving tank also has a gas phase discharge path, which is used to discharge the remaining gas phase in the dissolving tank.

[0046]

[10] According to the methane generating apparatus described in [9] above,

[0047] It also has a reuse flow path for merging the remaining gas phase discharged from the gas phase discharge flow path into the carbon dioxide-containing gas inlet.

[0048]

[11] The methane generating apparatus according to any one of [1] to

[10] above,

[0049] It also has:

[0050] A culture medium discharge path is provided for discharging the culture medium from the culture tank.

[0051] A microbial removal device for removing microorganisms or residual moisture, or both, from a culture medium discharged from a culture medium discharge path; and

[0052] A reuse culture medium supply path is used to supply culture medium from which microorganisms have been removed by a microbial removal device to the dissolving tank for reuse.

[0053]

[12] The methane generating apparatus according to any one of [1] to

[11] above, wherein,

[0054] The gas containing carbon dioxide is combustion exhaust gas.

[0055]

[13] According to the methane generating apparatus described in [2] or [3] above,

[0056] It includes an adjustment unit that adjusts the supply amount of carbon dioxide-containing solution from the carbon dioxide-containing solution supply path to the culture tank and the hydrogen supply amount from the hydrogen supply path based on the carbon dioxide concentration or outflow rate of the culture medium in the culture tank and the carbon dioxide concentration or inflow rate of the liquid phase in the dissolving tank.

[0057]

[14] A method for generating methane, comprising:

[0058] A process in which carbon dioxide-containing gas is exposed to an aqueous phase in a dissolving tank;

[0059] The solution transfer process of transferring the carbon dioxide-containing solution from the dissolving tank to the culture tank;

[0060] The process of supplying hydrogen to the culture tank;

[0061] The process of culturing methanogenic bacteria in a culture medium in the culture tank to produce methane; and

[0062] The process of discharging the generated methane from the culture tank.

[0063] The effects of the invention

[0064] According to this disclosure, a methanation system can be provided that exhibits good conversion efficiency from carbon dioxide to methane even when using a gas with a low carbon dioxide concentration as the carbon dioxide supply source, and can simplify the apparatus and reduce the installation area. Attached Figure Description

[0065] [ Figure 1The configuration of the methane generating apparatus of this disclosure in the first embodiment is shown.

[0066] [ Figure 2 The configuration of the methane generating apparatus of this disclosure in the second embodiment is shown.

[0067] [ Figure 3 The configuration of the methane generating apparatus of this disclosure in the third embodiment is shown.

[0068] [ Figure 4 The configuration of the methane generating apparatus of this disclosure in the fourth embodiment is shown.

[0069] [ Figure 5 The configuration of the methane generating apparatus of this disclosure in the fifth embodiment is shown. Detailed Implementation

[0070] The present invention will now be described in detail with reference to the accompanying drawings. However, the drawings are merely illustrative examples of the invention, and the technical scope of the invention is not limited to the examples in the drawings.

[0071] (Methane generation unit)

[0072] The methane generation apparatus disclosed herein includes:

[0073] A dissolving tank, which exposes carbon dioxide-containing gas to an aqueous phase to generate a carbon dioxide-containing solution;

[0074] A culture tank in which methanogenic bacteria are cultured in a culture medium to produce methane;

[0075] A carbon dioxide gas supply path introduces carbon dioxide-containing gas into the dissolution tank;

[0076] A solution transfer unit for transferring the carbon dioxide-containing solution from the dissolving tank to the culture tank;

[0077] A hydrogen supply path that supplies hydrogen to the dissolution tank or the culture tank; and

[0078] A methane discharge path that discharges the generated methane from the culture tank.

[0079] In the methane generation apparatus disclosed herein, the method for supplying carbon dioxide to the methanogenic bacteria culture medium is not to directly supply the carbon dioxide-containing gas to the culture medium in gaseous form, but rather to supply it in the form of a carbon dioxide-containing solution obtained by exposing the carbon dioxide-containing gas to an aqueous phase. By supplying carbon dioxide in the form of a carbon dioxide-containing solution, even if the carbon dioxide concentration in the carbon dioxide-containing gas serving as the carbon dioxide supply source is low, the carbon dioxide concentration in the carbon dioxide-containing solution can be increased, thereby improving the methane generation efficiency of the methanogenic bacteria (e.g., the methane conversion efficiency from carbon dioxide, etc.), and thus improving the methanation efficiency. In addition, the amount of gaseous components other than carbon dioxide (e.g., nitrogen, oxygen, and other gases that are poorly soluble in water) in the carbon dioxide-containing gas serving as the carbon dioxide supply source is extremely small in the carbon dioxide-containing solution. Therefore, there is no need to remove these gaseous components other than carbon dioxide, nor is there a need for equipment for removing these gaseous components other than carbon dioxide, thereby reducing the apparatus space.

[0080] <Composition of a methane generation unit>

[0081] Examples of the methane generation apparatus disclosed herein include: a two-tank type, a single-tank type, and a single-tank type with a partition. The two-tank type methane generation apparatus has a configuration where the dissolution tank and the culture tank are separate tanks. The single-tank type methane generation apparatus has a configuration where the dissolution tank and the culture tank are the same tank, allowing switching between a dissolution tank mode where the tank functions as a dissolution tank and a culture tank mode where the tank functions as a culture tank. The single-tank type methane generation apparatus with a partition has the following configuration: a single tank with a partition that allows liquid to flow through it, wherein each section of the tank separated by the partition functions as both the dissolution tank and the culture tank.

[0082] <Dissolving tank>

[0083] A dissolving tank is a tank used to generate a carbon dioxide-containing solution by exposing carbon dioxide-containing gas introduced from a carbon dioxide-containing gas inlet to an aqueous phase maintained within the dissolving tank, thereby dissolving carbon dioxide in the aqueous phase. The carbon dioxide-containing gas is typically introduced into the aqueous phase by bubbling. The carbon dioxide-containing solution is then supplied to a culture tank. In the methane generation apparatus of this disclosure, by employing a configuration where the dissolving tank and culture tank are independent tanks, carbon dioxide for methanation is supplied to the culture tank in the form of a carbon dioxide-containing solution. Therefore, even if the carbon dioxide concentration in the carbon dioxide-containing gas used as a carbon dioxide supply source is low, a sufficiently high concentration of carbon dioxide-containing solution can be supplied to the culture tank, thereby ensuring sufficient methanation. Thus, even gases with relatively low carbon dioxide concentrations can be used as a carbon dioxide supply source.

[0084] <<Carbon Dioxide>>

[0085] In methanation, a carbon dioxide-containing gas is typically used as the carbon dioxide supply source, preferably a gas with a relatively high carbon dioxide concentration. However, in the methane generation apparatus of this disclosure, as described above, not only can a gas with a relatively high carbon dioxide concentration be used, but even a gas with a relatively low carbon dioxide concentration can be used as the carbon dioxide supply source. For example, a low concentration of carbon dioxide in the carbon dioxide-containing gas, such as 15% Vol or less, 12% Vol or less, or 10% Vol or less, can be used. Industrial exhaust gases, such as combustion exhaust, can be examples of such gases. Alternatively, the carbon dioxide-containing gas inlet can be used as an inlet for taking in exhaust gas from methane combustion, using the exhaust gas from methane combustion as the carbon dioxide-containing gas.

[0086] <<Water Phase>>

[0087] The aqueous phase is not particularly limited, and examples include culture medium, nutrient-containing liquids, physiological saline, and water. From the viewpoint of suppressing stress on methanogens, the aqueous phase is preferably a culture medium or a nutrient-containing liquid; from the viewpoint of simplifying the apparatus, the aqueous phase is preferably a culture medium. Nutrients contained in the nutrient-containing liquid can include, for example, carbohydrates, nucleic acids, proteins, and protein breakdown products (e.g., amino acids, peptides, etc.). Indicators of nutrient concentration can include directly measured values ​​of these components' concentrations, and the total content of any one or more of the following atoms: carbon, nitrogen, sulfur, and phosphorus.

[0088] <<Solutions Containing Carbon Dioxide>>

[0089] The carbon dioxide-containing solution obtained in the dissolving tank becomes the carbon dioxide supply source for methane production during methanogenic bacteria cultivation. Since carbon dioxide is dissolved in the aqueous phase within the dissolving tank, the carbon dioxide concentration in the solution is increased. Due to the high carbon dioxide concentration in the solution, the methanogenic efficiency of the methanogens (e.g., the efficiency of methane conversion from carbon dioxide) is improved, thereby enhancing the methanation efficiency.

[0090] <Cultivation Tank>

[0091] A culture tank is used to cultivate methanogenic bacteria in a culture medium to produce methane from carbon dioxide and hydrogen. Carbon dioxide is supplied from a dissolving tank in the form of a carbon dioxide-containing solution. Hydrogen is supplied from a hydrogen supply path, usually in the form of hydrogen gas, for example, by introducing it into the culture medium through bubbling. The methane produced by the methanogenic bacteria is discharged from a gas generation vent.

[0092] <<Methanogens>>

[0093] Examples of methanogenic bacteria include: *Methanobacterium alcaliphilum*, *Methanobacterium bryantii*, *Methanobacterium congolense*, *Methanobacterium defluvii*, *Methanobacterium espanolae*, *Methanobacterium formicicum*, *Methanobacterium ivanovii*, *Methanobacterium palustre*, *Methanobacterium thermaggregans*, *Methanobacterium uliginosum*, *Methanobrevibacter acididurans*, and *Methanobrevibacter*. *Methanobrevibacter arboriphilicus*, *Methanobrevibacter gottschalkii*, *Methanobrevibacter olleyae*, *Methanobrevibacter ruminantium*, *Methanobrevibacter smithii*, *Methanobrevibacter woesei*, *Methanobrevibacter wolinii*, *Methanothermobacter marburgensis*, *Methanothermobacter thermoautotrophicus*, *Methanobacterium thermoautotrophicus*, *Methanothermobacter thermoflexus*, *Methanothermobacter thermophilics*, *Methanothermobacter wolfeii*, and *Methanothermus*.Methanogens include *Methanococcus sociabilis*, *Methanococcus bavaricum*, *Methanococcus parvum*, *Methanococcus chikuoensis*, *Methanococcus submarinus*, *Methanogenium frigidum*, *Methanogenium liminatans*, *Methanogenium marinum*, *Methannomicrobium mobile*, *Methanocaldococcus jannaschii*, *Methanococcus aeolicus*, *Methanococcus maripaludis*, *Methanococcus vannielii*, *Methanococcus voltaei*, and *Methanothermococcus thermolithotrophicus*.

[0094] <<Cultivation Medium>>

[0095] As a culture medium, for example, the culture medium commonly used in the cultivation of methanogens can be used. As components of the culture medium, examples include sugars, nucleic acids, proteins, protein breakdown products (e.g., amino acids, peptides, etc.), marine water, lacustrine water, marine sediments, lacustrine sediments, salts, pH adjusters, etc. These culture medium components may be contained, for example, in the form of milk or meat broth or their hydrolysates, yeast or yeast extracts.

[0096] <<Cultivation Temperature>>

[0097] The culture temperature can be, for example, 35°C or higher, preferably 40°C or higher, more preferably 45°C or higher, and for example, 65°C or lower, preferably 60°C or lower, more preferably 55°C or lower. However, the optimal culture temperature can vary depending on the type of methanogen.

[0098] <Solution Transfer Unit>

[0099] The methane generation apparatus disclosed herein includes the following solution transfer unit for transferring a carbon dioxide-containing solution from a dissolving tank to a culture tank:

[0100] (a) Solution transfer path connecting the dissolving tank and the culture tank;

[0101] (b) A switching unit for switching between the dissolution tank and the culture tank; or

[0102] (c) A liquid-permeable partition.

[0103] In the case of a two-tank methane generation apparatus as disclosed herein, the solution transfer unit is the solution transfer flow path described in (a) above. The solution transfer flow path is used to supply the aqueous phase (carbon dioxide-containing solution) exposed to carbon dioxide gas in the dissolving tank to the culture tank. Alternatively, a container or the like for temporarily holding the aqueous phase drawn from the dissolving tank and added to the culture tank may be used instead of the solution transfer flow path. Furthermore, from the viewpoint of simplifying the equipment and reducing equipment space, the solution transfer flow path is preferably a flow path that supplies the solution to the culture tank without deoxygenation treatment.

[0104] In the case of a single-tank methane generation apparatus as disclosed herein, the solution transfer unit is the switching unit described in (b) above. As a switching unit, an example is a unit comprising valves for opening and closing the carbon dioxide gas supply path, the hydrogen supply path, the gas phase discharge path, and the methane discharge path; and a control unit for controlling the opening and closing of the valves. Such a control unit can control the switching between the following modes:

[0105] (i) a dissolution tank mode, which allows the single tank to function as a dissolution tank by opening the carbon dioxide gas supply path and the gas phase discharge path, and closing the hydrogen supply path and the methane discharge path; and

[0106] (ii) A culture tank mode in which the single tank functions as a culture tank by closing the carbon dioxide gas supply path and the gas phase discharge path, and opening the hydrogen supply path and the methane discharge path.

[0107] In the case of the methane generation apparatus of this disclosure being a single-tank type with a partition, the solution transfer unit is (c) a partition that allows liquid to pass through. Examples of such partitions include partitions with openable and closable openings, and membranes that allow liquid to pass through but not microorganisms. When the partition is a partition with an openable and closable opening, the methane generation apparatus of this disclosure may further include a unit that applies pressure to the aqueous phase in the dissolution tank or a unit that applies negative pressure to the culture medium in the culture tank when the partition is open. Examples of membranes that allow liquid to pass through but not microorganisms include resin filter membranes with a pore size of approximately 0.1 to 1 μm.

[0108] <Gas phase discharge path, reuse path>

[0109] The methane generating apparatus of this disclosure may further include a gas phase discharge path for discharging the gas phase from the dissolution tank. Furthermore, when the methane generating apparatus includes a gas phase discharge path, the methane generating apparatus of this disclosure may further include a reuse path for merging the gas phase discharged from the gas phase discharge path into the carbon dioxide gas supply path. By including a reuse path in the methane generating apparatus of this disclosure, the solubility of carbon dioxide in the carbon dioxide-containing gas can be increased, the methane conversion efficiency can be improved by making the carbon dioxide concentration in the carbon dioxide-containing solution high, and the amount of undissolved carbon dioxide discharged from the methane generating apparatus can be suppressed, thereby achieving the purpose of methanation. It should be noted that when the methane generating apparatus of this disclosure is a single-tank type and includes a gas phase discharge path for discharging the gas phase from the dissolution tank, gas phase discharge from the gas phase discharge path is further performed in dissolution tank mode, and gas phase discharge from the gas phase discharge path is further stopped in culture tank mode.

[0110] <Culture Medium Reuse Unit>

[0111] The methane generation apparatus disclosed herein may further include the following culture medium reuse unit: a culture medium discharge path for discharging the culture medium from the culture tank; and a reused culture medium supply path connecting a branch of the culture medium discharge path to a confluence of the aqueous phase supply path. Furthermore, a microbial removal device may be further included in the reused culture medium supply path. Through these units, the culture medium used for culturing can be regenerated into a microbial-free culture medium, which can be used for carbon dioxide dissolution. Additionally, residual water generated as a byproduct of methane generation can be removed, ensuring a constant culture medium composition. Examples of microbial removal devices include membrane separation devices. Examples of membrane separation devices include devices for removing microorganisms or residual water, or both, through a resin filter membrane with a pore size of approximately 0.1 to 1 μm.

[0112] <Measuring device, adjustment unit>

[0113] The methane generation apparatus disclosed herein may further include measuring devices for measuring the following parameters:

[0114] (a) The carbon dioxide concentration or pH of the liquid phase in the dissolving tank;

[0115] (b) The inflow rate of the liquid phase in the dissolving tank;

[0116] (c) Flow rate of liquid phase from the dissolution tank to the culture tank;

[0117] (d) The carbon dioxide concentration or pH of the culture medium in the culture tank;

[0118] (e) The outflow rate of the culture medium from the culture tank; and / or

[0119] (f) The volume level of the culture medium in the culture tank.

[0120] Carbon dioxide concentration can also be measured using pH as an indicator. Furthermore, the methane generation apparatus of this disclosure can be further equipped with an adjustment unit for adjusting the following parameters:

[0121] (c) The flow rate of the liquid phase from the dissolution tank to the culture tank; and / or

[0122] (g) Hydrogen supply from the hydrogen supply unit to the culture tank.

[0123] The methane generation apparatus disclosed herein may include an adjustment unit that adjusts the supply rate of the carbon dioxide-containing solution from the carbon dioxide-containing solution supply unit to the culture tank and the supply rate of hydrogen from the hydrogen supply unit based on the carbon dioxide concentration or outflow rate of the culture medium in the culture tank and the carbon dioxide concentration or inflow rate of the liquid phase in the dissolution tank. These parameters can be controlled within the aforementioned preferred ranges.

[0124] <Example of a methane generation unit>

[0125] As a component of the methane generating apparatus (1) disclosed herein, the following embodiments can be listed, for example.

[0126] In the first embodiment ( Figure 1 In this disclosure, the methane generating apparatus (1) is a two-tank type methane generating apparatus (1). The two-tank type methane generating apparatus (1) includes: two independent tanks, namely a dissolution tank (100) and a culture tank (200); and a carbon dioxide gas supply section (carbon dioxide gas supply flow path (101), carbon dioxide gas supply port (102)), a solution transfer flow path (103), a hydrogen supply section (hydrogen supply flow path (301), hydrogen supply port (302)), and a methane discharge section (methane discharge port (201), methane discharge flow path (202)). In addition, Figure 1 The following configuration is shown as an arbitrary configuration: the 2-tank methane generating apparatus (1) further includes a gas phase discharge section (gas phase discharge outlet (104), gas phase discharge flow path (107)), an aqueous phase supply flow path (401), a culture medium discharge flow path (402), and a reuse culture medium supply flow path for transferring the used culture medium from the branch (404) of the culture medium discharge flow path (402) to the confluence section (403) of the aqueous phase supply flow path (401).

[0127] In the second embodiment ( Figure 2In this disclosure, the methane generating apparatus (1) is a single-tank type methane generating apparatus (1) and further includes a gas phase discharge section (gas phase discharge flow path (107)). The left figure shows the dissolution tank mode, and the right figure shows the culture tank mode. In both figures, the carbon dioxide gas supply flow path (101) and the hydrogen supply flow path (301) merge via a switching valve and are connected to the single tank (100'', 200'') at the gas supply port (102''). The flow path connected from the single tank (100'', 200'') at the gas phase discharge port (104'') branches via a switching valve into a gas phase discharge flow path (107) and a gas phase (methane) discharge flow path (202). In the dissolving tank mode (left figure), the carbon dioxide gas supply path (101) and the gas phase discharge path (107) are open, while the hydrogen supply path (301) and the gas phase (methane) discharge path (202) are closed. The single tank functions as a single tank (100'') in the dissolving tank mode. In the incubation tank mode (right figure), the hydrogen supply path (301) and the gas phase (methane) discharge path (202) are open, while the carbon dioxide gas supply path (101) and the gas phase discharge path (107) are closed. The single tank functions as a single tank (200'') in the incubation tank mode.

[0128] In the third embodiment ( Figure 3 In this disclosure, the methane generating apparatus (1) is a single-tank methane generating apparatus (1) with a partition, wherein the single tank (500) has a liquid-passing partition (501). The tank is divided by the partition (501) into a dissolution zone (100a) that functions as a dissolution tank and a culture zone (200a) that functions as a culture tank. The single-tank methane generating apparatus (1) with a partition further includes a gas phase discharge section (gas phase discharge outlet (104), gas phase discharge flow path (107)) and a reuse culture medium supply section (aqueous phase (culture medium) supply flow path (401), aqueous phase (culture medium) discharge flow path (402), branch section (403), and confluence section (404)).

[0129] In the fourth embodiment ( Figure 4 In the present disclosure, the methane generating apparatus (1) has the following configuration: In the two-tank type methane generating apparatus (1) of the first embodiment, a microbial removal device (membrane separation device (405)) is further provided in the reuse culture medium supply flow path.

[0130] In the 5th embodiment ( Figure 5In the present disclosure, the methane generating apparatus (1) has the following configuration: In the two-tank type methane generating apparatus (1) of the fourth embodiment, it further includes: a flow meter (406) for measuring the liquid flow rate of the aqueous phase (culture medium) supply flow path (401), the solution transfer flow path (103), and the culture medium discharge flow path (402); a pH meter (407) for measuring the pH of the aqueous phase (111) in the dissolving tank (100) and the culture medium (211) in the culture tank (200); and a level gauge (408) for measuring the liquid level of the aqueous phase (111) in the dissolving tank (100) and the culture medium (211) in the culture tank (200). For example, pH can be used as an indicator of the carbon dioxide concentration in the aqueous phase, the suitability of the culture medium for methanogenic bacteria cultivation, etc. Based on these measured values, the supply of carbon dioxide-containing gas, hydrogen, and aqueous phase, the amount of aqueous phase transferred in the solution transfer flow path (103), etc., can be controlled.

[0131] (Methods for generating methane)

[0132] The methane generation method disclosed herein includes:

[0133] A process in which carbon dioxide-containing gas is exposed to an aqueous phase in a dissolving tank;

[0134] The process of transferring the carbon dioxide-containing solution from the dissolving tank to the incubation tank;

[0135] The process of supplying hydrogen to the culture tank;

[0136] The process of culturing methanogenic bacteria in a culture medium in the culture tank to produce methane; and

[0137] The process of discharging methane from the culture tank.

[0138] The methane generation method disclosed herein can be carried out using the methane generation apparatus described above. Examples of apparatus configurations for implementing the methane generation method of this disclosure include, for example, a two-tank type, a single-tank type, and a single-tank type with a partition, as described above.

[0139] When using a two-tank methane generation apparatus as the device for implementing the methane generation method of this disclosure, the step of transferring the carbon dioxide-containing solution from the dissolving tank to the culture tank is performed by supplying the carbon dioxide-containing solution from the dissolving tank to the culture tank. This step is not particularly limited; for example, it can be performed by transferring the carbon dioxide-containing solution via an aqueous flow path connecting the dissolving tank and the culture tank, or by drawing the carbon dioxide-containing solution from the dissolving tank and adding it to the culture tank. Furthermore, this step can be performed by supplying the carbon dioxide-containing solution from the dissolving tank to the culture tank without deoxygenation treatment, or by directly supplying the carbon dioxide-containing solution from the dissolving tank to the culture tank.

[0140] When using a single tank with a partition as the apparatus for implementing the methane generation method of this disclosure, the step of transferring the carbon dioxide-containing solution from the dissolving tank to the culture tank can be performed by using, for example, a partition with an openable and closable opening, a membrane that allows liquid to pass through but not microorganisms, etc., as the partition and opening the partition. When the partition has an openable and closable opening, this step can be accompanied by applying pressure to the aqueous phase in the dissolving tank or applying negative pressure to the culture medium in the culture tank when the partition is open.

[0141] When using a single tank type as the apparatus for implementing the methane generation method of this disclosure, the process of transferring the carbon dioxide-containing solution from the dissolution tank to the incubation tank can be performed by controlling the switching between the following modes:

[0142] (i) A dissolution tank mode, wherein the tank functions as a dissolution tank by supplying carbon dioxide-containing gas to the tank from the carbon dioxide-containing gas inlet, stopping the supply of hydrogen from the hydrogen supply to the single tank, and discharging methane from the generated gas outlet; and

[0143] (ii) A culture tank mode in which the tank functions as a culture tank by stopping the supply of carbon dioxide-containing gas from the carbon dioxide-containing gas inlet to the tank, and supplying hydrogen from the hydrogen supply to the single tank and discharging methane from the generated gas outlet.

[0144] The methane generation method disclosed herein may further include: a step of discharging the gas phase from the dissolving tank; a step of merging the gas phase discharged from the gas phase discharge section into the carbon dioxide-containing gas inlet section; a step of discharging the culture medium from the culture tank; a step of removing microorganisms or residual water or both from the culture medium discharged from the discharge section; and a step of supplying the culture medium, from which microorganisms have been removed using a microorganism removal device, to the dissolving tank.

[0145] In addition, the methane generation method disclosed herein may further include a step of measuring the following parameters:

[0146] (a) The carbon dioxide concentration or pH of the liquid phase in the dissolving tank;

[0147] (b) The inflow rate of the liquid phase in the dissolving tank;

[0148] (c) Flow rate of liquid phase from the dissolution tank to the culture tank;

[0149] (d) The carbon dioxide concentration or pH of the culture medium in the culture tank;

[0150] (e) The outflow rate of the culture medium from the culture tank; and / or

[0151] (f) The volume level of the culture medium in the culture tank.

[0152] Carbon dioxide concentration can also be measured using pH as an indicator. Furthermore, the methane generation method disclosed herein may further include steps for adjusting the following parameters based on these measurements:

[0153] (c) The flow rate of the liquid phase from the dissolution tank to the culture tank; and / or

[0154] (g) Hydrogen supply from the hydrogen supply unit to the culture tank.

[0155] The various conditions in the methane generation method of this disclosure can be used with the conditions described in the methane generation apparatus of this disclosure.

[0156] Industrial applicability

[0157] According to this disclosure, a methanation system can be provided that exhibits good conversion efficiency from carbon dioxide to methane even when using a gas with a low carbon dioxide concentration as the carbon dioxide supply source, and can simplify the apparatus and reduce the installation area.

[0158] Explanation of symbols

[0159] 1. Methane production system

[0160] 100 Dissolving tank

[0161] A single tank in a 100'' dissolving tank configuration

[0162] 100a Dissolution Zone

[0163] 101 Carbon dioxide gas supply path

[0164] 102 Carbon dioxide gas supply port

[0165] 102'' Gas supply port

[0166] 103 Solution transfer channel

[0167] 104 Gas phase outlet

[0168] 104'' Gas phase outlet

[0169] 107 Gas phase discharge flow path

[0170] 111 Aqueous phase

[0171] 112 Gas Phase

[0172] 200 culture tank

[0173] A single tank in a 200'' culture tank configuration

[0174] 200a Culture Zone

[0175] 201 Gas phase (methane) effluent outlet

[0176] 202 Gas phase (methane) discharge path

[0177] 211 Aqueous phase (culture medium)

[0178] 212 Gas phase

[0179] 301 Hydrogen Supply Flow Path

[0180] 302 Hydrogen Supply Port

[0181] 401 Aqueous phase (culture medium) supply flow path

[0182] 402 Aqueous phase (culture medium) drain flow path

[0183] 403 Convergence Department

[0184] 404 Branch

[0185] 405 Membrane Separation Unit

[0186] 406 Flow Meter

[0187] 407 pH meter

[0188] 408 Level Gauge

[0189] 500 Single tank with partition

[0190] 501 partition

Claims

1. A methane generating apparatus, comprising: A dissolving tank, which exposes carbon dioxide-containing gas to an aqueous phase to generate a carbon dioxide-containing solution; A culture tank in which methanogenic bacteria are cultured in a culture medium to produce methane; A carbon dioxide gas supply path introduces carbon dioxide-containing gas into the dissolution tank; A solution transfer unit for transferring the carbon dioxide-containing solution generated in the dissolving tank from the dissolving tank to the culture tank; A hydrogen supply path that supplies hydrogen to the dissolution tank or the culture tank; and A methane discharge path that discharges the generated methane from the culture tank.

2. The methane generating apparatus according to claim 1, wherein, The dissolution tank and the culture tank are independent tanks. The solution transfer unit is a solution transfer flow path connecting the dissolving tank and the culture tank.

3. The methane generating apparatus according to claim 2, wherein, The solution transfer path is a flow path used to supply the carbon dioxide-containing solution in the dissolving tank to the culture tank without deoxygenation treatment.

4. The methane generating apparatus according to claim 1, wherein, The methane generation device has a single tank that serves as both the dissolution tank and the culture tank. The methane generation device also includes a gas phase discharge path for discharging the remaining gas phase when the single tank functions as the culture tank. The aqueous phase is a culture medium. The solution transfer unit is a switching unit used to switch between the dissolution tank and the culture tank. The switching unit includes valves for opening and closing the carbon dioxide gas supply path, the hydrogen supply path, the gas phase discharge path, and the methane discharge path; and a control unit for controlling the opening and closing of the valves. The control unit controls the switching between the following modes: (i) a dissolution tank mode, which allows the single tank to function as a dissolution tank by opening the carbon dioxide gas supply path and the gas phase discharge path, and closing the hydrogen supply path and the methane discharge path; and (ii) A culture tank mode in which the single tank functions as a culture tank by closing the carbon dioxide gas supply path and the gas phase discharge path, and opening the hydrogen supply path and the methane discharge path.

5. The methane generating apparatus according to claim 4, It also has a reuse flow path, which is used to merge the remaining gas phase discharged from the gas phase discharge flow path into the carbon dioxide-containing gas inlet.

6. The methane generating apparatus according to claim 1, wherein, The methane generating apparatus comprises a single tank with a liquid-permeable baffle inside the tank. The partitions within each tank, separated by the partition plate, function as the dissolution tank and the culture tank, respectively. The solution transfer unit is the partition.

7. The methane generating apparatus according to claim 6, wherein, The partition has an openable and closable opening.

8. The methane generating apparatus according to claim 6, wherein, The partition is a membrane that allows liquid to pass through but not microorganisms.

9. The methane generating apparatus according to any one of claims 1 to 3, 6 and 7, wherein, The dissolving tank also has a gas phase discharge path, which is used to discharge the remaining gas phase in the dissolving tank.

10. The methane generating apparatus according to claim 9, It also has a reuse flow path, which is used to merge the remaining gas phase discharged from the gas phase discharge flow path into the carbon dioxide-containing gas inlet.

11. The methane generating apparatus according to any one of claims 1 to 7, It also has: A culture medium discharge path is provided for discharging the culture medium from the culture tank. A microbial removal device for removing microorganisms or residual moisture, or both, from a culture medium discharged from a culture medium discharge path; and A reuse culture medium supply path is used to supply culture medium from which microorganisms have been removed by a microbial removal device to the dissolving tank for reuse.

12. The methane generating apparatus according to any one of claims 1 to 8, wherein, The gas containing carbon dioxide is combustion exhaust gas.

13. The methane generating apparatus according to claim 2 or 3, It includes an adjustment unit that adjusts the supply amount of carbon dioxide-containing solution from the carbon dioxide-containing solution supply path to the culture tank and the hydrogen supply amount from the hydrogen supply path based on the carbon dioxide concentration or outflow rate of the culture medium in the culture tank and the carbon dioxide concentration or inflow rate of the liquid phase in the dissolving tank.

14. A method for generating methane, comprising: A process in which carbon dioxide-containing gas is exposed to an aqueous phase in a dissolving tank; The solution transfer process of transferring the carbon dioxide-containing solution from the dissolving tank to the culture tank; The process of supplying hydrogen to the culture tank; The process of culturing methanogenic bacteria in a culture medium in the culture tank to produce methane; and The process of discharging the generated methane from the culture tank.

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