Methane production apparatus and methane production method

Abstract

Provided is a methanation system that has good efficiency of conversion of carbon dioxide to methane even when a gas containing a low concentration of carbon dioxide is used as a carbon dioxide source, and enables simplification and footprint reduction of an apparatus. This methane production apparatus comprises: a dissolution tank for exposing carbon dioxide gas to an aqueous phase to produce a carbon dioxide solution; a culture tank for culturing methane-producing bacteria to produce methane; a carbon dioxide gas supply flow passage for feeding carbon dioxide gas into the dissolution tank; a solution transfer means for transferring the carbon dioxide solution from the dissolution tank to the culture tank; a hydrogen supply flow passage for supplying hydrogen; and a methane discharge flow passage for discharging the produced methane from the culture tank.

Description

Methane generation device and methane generation method

[0001] The present disclosure relates to a methane generator and a method for producing methane.

[0002] Methanation is a technology for producing methane from carbon dioxide and hydrogen, and is considered a promising technology that will contribute to achieving carbon neutrality, which means reducing greenhouse gas emissions such as carbon dioxide to zero overall. For example, Patent Documents 1 to 3 propose methanation technologies for producing methane from carbon dioxide in exhaust gases from thermal power plants, factories, etc.

[0003] These methanation technologies require an increased carbon dioxide concentration in the feed gas to increase the methane production concentration during methanation. Because the carbon dioxide concentration in exhaust gas from thermal power plants and factories is low at around 10%, it is necessary to concentrate the carbon dioxide to a high concentration of over 90% using a carbon dioxide separation and capture device.

[0004] JP 2021-151196 A JP 2004-321857 A JP 2014-148934 A

[0005] Changing the carbon dioxide concentration from low to high using a carbon dioxide capture device is technically difficult, and there are issues such as the need for a large equipment area and a large amount of cost. Therefore, there is thought to be demand for a methanation system that does not require carbon dioxide concentration and uses gas with low carbon dioxide concentration as a carbon dioxide supply source.

[0006] The present disclosure aims to provide a methanation system that has good conversion efficiency from carbon dioxide to methane even when a gas with a low concentration of carbon dioxide is used as a carbon dioxide supply source, and that allows for simplification of the device and a reduction in installation area.

[0007] [1] A methane generation apparatus comprising: a dissolution tank that exposes a carbon dioxide-containing gas to an aqueous phase to produce a carbon dioxide-containing solution; a culture tank that cultivates methanogens in a culture solution to produce methane; a carbon dioxide gas supply flow path that introduces the carbon dioxide-containing gas into the dissolution tank; a solution transfer means that transfers the carbon dioxide-containing solution produced in the dissolution tank from the dissolution tank to the culture tank; a hydrogen supply flow path that supplies hydrogen to the dissolution tank or the culture tank; and a methane discharge flow path that discharges the produced methane from the culture tank. [2] The methane generation apparatus according to [1] above, wherein the dissolution tank and the culture tank are separate tanks, and the solution transfer means is a solution transfer flow path that connects the dissolution tank and the culture tank. [3] The methane generation apparatus according to [2] above, wherein the solution transfer flow path is a flow path that supplies the carbon dioxide-containing solution in the dissolution tank to the culture tank without oxygen removal treatment. [4] The methane generator according to [1] above, wherein the methane generator comprises a single tank serving as both the dissolution tank and the culture tank, the methane generator further comprising a gas phase discharge flow path that discharges an excess gas phase when the single tank functions as the culture tank, the aqueous phase is a culture solution, the solution transfer means is a switching means for switching between the dissolution tank and the culture tank, the switching means comprising valves that open and close the carbon dioxide gas supply flow path, the hydrogen supply flow path, the gas phase discharge flow path, and the methane discharge flow path, and a control unit that controls the opening and closing of the valves, and the control unit controls switching between: (i) a dissolution tank mode in which the single tank functions as a dissolution tank by opening the carbon dioxide gas supply flow path and the gas phase discharge flow path and closing the hydrogen supply flow path and the methane discharge flow path; and (ii) a culture tank mode in which the single tank functions as a culture tank by closing the carbon dioxide gas supply flow path and the gas phase discharge flow path and opening the hydrogen supply flow path and the methane discharge flow path. [5] The methane generator according to [4] above, further comprising a reuse flow path for joining the excess gas phase discharged from the gas phase discharge flow path to the carbon dioxide-containing gas introduction section.[6] The methane generator according to [1] above, wherein the methane generator comprises a single tank having a partition therein through which liquid can pass, each of the compartments within the tank separated by the partition functions as the dissolution tank and the culture tank, and the partition serves as the solution transfer means. [7] The methane generator according to [6] above, wherein the partition has an opening that can be opened and closed. [8] The methane generator according to [6] above, wherein the partition is a membrane through which liquid passes but microorganisms do not. [9] The methane generator according to any of [1] to [3], [6] and [7] above, wherein the dissolution tank further comprises a gas phase discharge flow path for discharging excess gas phase in the dissolution tank.

[10] The methane generator according to [9] above, further comprising a recycling flow path for allowing excess gas phase discharged from the gas phase discharge flow path to join the carbon dioxide-containing gas introduction part.

[11] The methane generator according to any of [1] to

[10] above, further comprising: a culture solution discharge flow path for discharging the culture solution from the culture tank; a microorganism removal device for removing microorganisms, excess water, or both from the culture solution discharged from the culture solution discharge flow path; and a reused culture solution supply flow path for supplying the culture solution from which microorganisms have been removed by the microorganism removal device to the dissolution tank for reuse.

[12] The methane generator according to any of [1] to

[11] above, wherein the carbon dioxide-containing gas is combustion exhaust gas.

[13] The methane generator according to [2] or [3] above, further comprising an adjustment unit that adjusts the amount of carbon dioxide-containing solution in the dissolution tank supplied from the carbon dioxide-containing solution supply flow path to the culture tank and the amount of hydrogen supplied from the hydrogen supply flow path, based on the carbon dioxide concentration of the culture solution in the culture tank or the outflow amount of the culture solution, and the carbon dioxide concentration of the liquid phase in the dissolution tank or the inflow amount of the liquid phase.

[14] A method for generating methane, comprising: a step of exposing a carbon dioxide-containing gas to an aqueous phase in a dissolution tank; a solution transfer means for transferring the carbon dioxide-containing solution from the dissolution tank to a culture tank; a step of supplying hydrogen to the culture tank; a step of culturing methanogens in a culture solution in the culture tank to generate methane; and a step of discharging the generated methane from the culture tank.

[0008] According to the present disclosure, it is possible to provide a methanation system that has good conversion efficiency from carbon dioxide to methane even when a gas with a low concentration of carbon dioxide is used as a carbon dioxide supply source, and that allows for simplification of the device and a reduction in installation area.

[0009] 1 shows the configuration of a methane generation device according to a first embodiment of the present disclosure; 2 shows the configuration of a methane generation device according to a second embodiment of the present disclosure; 3 shows the configuration of a methane generation device according to a third embodiment of the present disclosure; 4 shows the configuration of a methane generation device according to a fourth embodiment of the present disclosure; 5 shows the configuration of a methane generation device according to a fifth embodiment of the present disclosure.

[0010] The present invention will be described in detail below, with reference to the drawings as necessary. However, the drawings are merely examples for explaining the present invention, and the technical scope of the present invention is not limited by the examples shown in the drawings.

[0011] (Methane generation apparatus) The methane generation apparatus of the present disclosure comprises a dissolution tank that exposes a carbon dioxide-containing gas to an aqueous phase to produce a carbon dioxide-containing solution, a culture tank that cultivates methanogens in a culture solution to produce methane, a carbon dioxide gas supply flow path that introduces the carbon dioxide-containing gas into the dissolution tank, a solution transfer means that transfers the carbon dioxide-containing solution from the dissolution tank to the culture tank, a hydrogen supply flow path that supplies hydrogen to the dissolution tank or the culture tank, and a methane discharge flow path that discharges the produced methane from the culture tank.

[0012] In the methane generation apparatus disclosed herein, carbon dioxide is supplied to a methanogen culture solution not by supplying the carbon dioxide-containing gas to the culture solution in gaseous form, but 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 of the carbon dioxide-containing gas serving as the carbon dioxide supply source is low, the carbon dioxide concentration of the carbon dioxide-containing solution can be increased, thereby improving the efficiency of methane production by methanogens (e.g., the efficiency of methane conversion from carbon dioxide, etc.) and improving methanation efficiency. Furthermore, since the amount of gas components other than carbon dioxide in the carbon dioxide-containing gas serving as the carbon dioxide supply source (e.g., poorly water-soluble gases such as nitrogen gas and oxygen gas) dissolved in the carbon dioxide-containing solution is extremely small, removing these gas components other than carbon dioxide is not necessary. This eliminates the need for equipment for removing these gas components, thereby reducing the space required for the apparatus.

[0013] <Configuration of Methane Generator> Examples of the configuration of the methane generator of the present disclosure include a two-tank type, a single-tank type, and a single-tank type with a partition. A two-tank type methane generator has a configuration in which the dissolution tank and the culture tank are separate tanks. A single-tank type methane generator has a configuration in which the dissolution tank and the culture tank are the same tank, and is used by switching between a dissolution tank mode in which the tank functions as a dissolution tank and a culture tank mode in which the tank functions as a culture tank. A single-tank type methane generator with a partition has a single tank with a partition within the tank through which liquid can pass, and each compartment within the tank separated by the partition functions as the dissolution tank and the culture tank, respectively.

[0014] <Dissolution Tank> The dissolution tank is a tank for dissolving carbon dioxide in the aqueous phase by exposing the carbon dioxide-containing gas introduced from the carbon dioxide-containing gas inlet to the aqueous phase held in the dissolution tank, thereby producing a carbon dioxide-containing solution. The carbon dioxide-containing gas is usually introduced into the aqueous phase by bubbling. The carbon dioxide-containing solution is supplied to the culture tank. In the methane generation apparatus disclosed herein, the dissolution tank and the culture tank are configured as separate tanks, so that the carbon dioxide used 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 serving as the carbon dioxide supply source is low, it can be supplied to the culture tank as a carbon dioxide-containing solution with a sufficiently high concentration, allowing methanation to proceed sufficiently. Therefore, even gases with a relatively low carbon dioxide gas concentration can be used as a carbon dioxide supply source.

[0015] <<Carbon Dioxide>> In methanation, it is usually preferable to use a gas with a relatively high carbon dioxide concentration as the carbon dioxide-containing gas that serves as the carbon dioxide supply source. However, in the methane generation apparatus disclosed herein, as described above, not only gases with a relatively high carbon dioxide concentration but also gases with a relatively low carbon dioxide concentration can be used as the carbon dioxide supply source. Carbon dioxide-containing gases with low carbon dioxide concentrations, such as those with a carbon dioxide concentration of 15% vol or less, 12% vol or less, or 10% vol or less, can also be used. Examples of such gases include industrial exhaust gases such as combustion exhaust. Furthermore, the carbon dioxide-containing gas inlet may serve as an intake for taking in exhaust gas after methane combustion, and the exhaust gas after methane combustion may be used as the carbon dioxide-containing gas.

[0016] <<Aqueous Phase>> The aqueous phase is not particularly limited, and examples thereof include a culture solution, a nutrient-containing solution, physiological saline, and water. From the viewpoint of suppressing stress on methanogens, the aqueous phase is preferably a culture solution or a nutrient-containing solution, and from the viewpoint of simplifying the apparatus, the aqueous phase is preferably a culture solution. Examples of nutritional components contained in the nutrient-containing solution include sugars, nucleic acids, proteins, and protein hydrolysates (e.g., amino acids, peptides, etc.). Indicators of the concentration of nutrient components include direct measurements of the concentrations of these components, and the total content of one or more atoms of carbon atoms, nitrogen atoms, sulfur atoms, and phosphorus atoms.

[0017] <<Carbon dioxide-containing solution>> The carbon dioxide-containing solution obtained in the dissolution tank serves as a carbon dioxide source for methane production by methanogen cultivation. Because carbon dioxide is dissolved in the aqueous phase in the dissolution tank, the carbon dioxide concentration in the carbon dioxide-containing solution can be increased. A high carbon dioxide concentration in the carbon dioxide-containing solution improves the efficiency of methane production by methanogens (e.g., the efficiency of converting carbon dioxide to methane, etc.), and can improve methanation efficiency.

[0018] <Culture Tank> The culture tank is a tank for culturing methanogens in a culture solution to produce methane from carbon dioxide and hydrogen. Carbon dioxide is supplied from a dissolution tank in the form of a carbon dioxide-containing solution. Hydrogen is supplied from a hydrogen supply channel, usually in the form of hydrogen gas, and is introduced into the culture solution by, for example, bubbling. Methane produced by the methanogens is discharged from a produced gas discharge section.

[0019] <<Methane-producing bacteria>> Methane-producing bacteria include Methanobacterium alcaliphilum, Methanobacterium bryantii, Methanobacterium congolense, Methanobacterium defluvii, Methanobacterium espanolae, Methanobacterium formicicum, Methanobacterium ivanovii, Methanobacterium palustre, Methanobacterium thermaggregans, and Methanobacterium uriginosum. uliginosum), Methanobrevibacter acididurans, Methanobrevibacter arboriphilicus, Methanobrevibacter gottschalkii, Methanobrevibacter olleyae, Methanobrevibacter ruminantium, Methanobrevibacter smithii, Methanobrevibacter woesei, Methanobrevibacter wolinii, Methanothermobacter marburgensis marburgensis, Methanothermobacter thermoautotrophicusMethanothermobacter thermoautotrophicus, Methanothermobacter thermoflexus, Methanothermobacter thermophilics, Methanothermobacter wolfeii, Methanothermus sociabilis, Methanocorpusculum bavaricum, Methanocorpusculum parvum, Methanoculleus chikuoensis, Methanoculleus submarinus, Methanogenium frigidum, Methanogenium liminatans Examples of the fungal pathogen include Methanogenium marinum, Methanomicrobium mobile, Methanocaldococcus jannaschii, Methanococcus aeolicus, Methanococcus maripaludis, Methanococcus vannielii, Methanococcus voltaei, Methanothermococcus thermolithotrophicus, and the like.

[0020] <<Culture Solution>> The culture solution may be, for example, a conventional medium used for culturing methanogens. Examples of medium components include sugars, nucleic acids, proteins, protein hydrolysates (e.g., amino acids, peptides, etc.), ocean water, lake water, marine sediments, lake sediments, salts, pH adjusters, etc. These medium components may be contained in the form of, for example, milk or meat juice, or hydrolysates thereof, yeast, or yeast extract.

[0021] <<Culture Temperature>> The culture temperature may be, for example, 35° C. or higher, preferably 40° C. or higher, and more preferably 45° C. or higher, or may be, for example, 65° C. or lower, preferably 60° C. or lower, and more preferably 55° C. or lower. However, the optimal culture temperature may vary depending on the type of methanogen.

[0022] <Solution Transfer Means> The methane generation apparatus of the present disclosure includes, as a solution transfer means for transferring a carbon dioxide-containing solution from the dissolution tank to the culture tank, (a) a solution transfer flow path connecting the dissolution tank and the culture tank, (b) a switching means for switching between the dissolution tank and the culture tank, or (c) a partition through which a liquid can pass.

[0023] When the methane generation apparatus of the present disclosure is a two-tank type, the solution transfer means is the above-mentioned (a) solution transfer flow path. The solution transfer flow path serves as a flow path for supplying the aqueous phase (carbon dioxide-containing solution) exposed to the carbon dioxide-containing gas in the dissolution tank to the culture tank. Alternatively, a container or the like may be used to temporarily hold the aqueous phase pumped from the dissolution tank and introduced into the culture tank. From the viewpoint of simplifying the equipment and reducing the equipment space, the solution transfer flow path is preferably a flow path that supplies the solution to the culture tank without oxygen removal treatment.

[0024] When the methane generation apparatus of the present disclosure is a single-tank type, the solution transfer means is the above-mentioned (b) switching means. Examples of the switching means include means including valves that open and close the carbon dioxide gas supply channel, the hydrogen supply channel, the gas-phase discharge channel, and the methane discharge channel, and a control unit that controls the opening and closing of the valves. Such a control unit may control switching between: (i) a dissolution tank mode in which the single tank functions as a dissolution tank by opening the carbon dioxide gas supply channel and the gas-phase discharge channel and closing the hydrogen supply channel and the methane discharge channel; and (ii) a fermentor mode in which the single tank functions as a fermentor by closing the carbon dioxide gas supply channel and the gas-phase discharge channel and opening the hydrogen supply channel and the methane discharge channel.

[0025] When the methane generation apparatus of the present disclosure is a single-tank type with a partition, the solution transfer means is (c) a partition that allows liquid to pass through. Examples of such a partition include a partition with an opening that can be opened and closed, and a membrane that allows liquid to pass through but not microorganisms. When the partition is a partition with an opening that can be opened and closed, the methane generation apparatus of the present disclosure may further include a means for applying pressure to the aqueous phase in the dissolution tank or a means for applying negative pressure to the culture solution in the culture tank when the partition is opened. Examples of membranes that allow liquid to pass through but not microorganisms include resin filtration membranes with pore sizes of approximately 0.1 to 1 μm.

[0026] <Gas Phase Discharge Flow Path, Recycle Flow Path> The methane generator of the present disclosure may further include a gas phase discharge flow path for discharging the gas phase from the dissolution tank. Furthermore, when the methane generator includes a gas phase discharge flow path, the methane generator of the present disclosure may further include a reuse flow path for merging the gas phase discharged from the gas phase discharge flow path into the carbon dioxide gas supply flow path. By including a reuse flow path in the methane generator of the present disclosure, the dissolution rate of carbon dioxide in the carbon dioxide-containing gas can be improved, and the carbon dioxide concentration in the carbon dioxide-containing solution can be increased, thereby improving the methane conversion efficiency and suppressing the emission of undissolved carbon dioxide from the methane generator, thereby achieving the purpose of methanation. Note that when the methane generator of the present disclosure is a single-tank type and includes a gas phase discharge flow path from the dissolution tank, the gas phase is further discharged from the gas phase discharge flow path in the dissolution tank mode, and the discharge of the gas phase from the gas phase discharge flow path is further stopped in the culture tank mode.

[0027] <Culture Solution Reuse Means> The methane generation apparatus of the present disclosure may further include, as a culture solution reuse means, a culture solution discharge flow path for discharging the culture solution from the culture tank, and a reused culture solution supply flow path connecting the branching portion of the culture solution discharge flow path to the confluence portion of the aqueous phase supply flow path. Furthermore, a microorganism removal device may be further provided in the reused culture solution supply flow path. By using these means, the culture solution used for cultivation can be recycled as a microorganism-free culture solution that can be used for carbon dioxide dissolution. Furthermore, excess water generated as a by-product of methane production can be removed to stabilize the culture solution composition. Examples of the microorganism removal device include a membrane separation device. Examples of the membrane separation device include a device for removing microorganisms, excess water, or both using a resin filtration membrane with a pore size of approximately 0.1 to 1 μm.

[0028] <Measuring device, adjusting unit> The methane generation apparatus of the present disclosure may further include a measuring device that measures: (a) the carbon dioxide concentration or pH of the liquid phase in the dissolution tank; (b) the inflow rate of the liquid phase in the dissolution tank; (c) the flow rate of the liquid phase from the dissolution tank to the culture tank; (d) the carbon dioxide concentration or pH of the culture solution in the culture tank; (e) the outflow rate of the culture solution in the culture tank; and / or (f) the liquid level of the culture solution in the culture tank. The carbon dioxide concentration may be measured using pH as an indicator. The methane generation apparatus of the present disclosure may further include an adjusting unit that adjusts: (c) the flow rate of the liquid phase from the dissolution tank to the culture tank; and / or (g) the amount of hydrogen supplied from the hydrogen supply unit to the culture tank. The methane generation apparatus of the present disclosure may include an adjustment unit that adjusts the amount of carbon dioxide-containing solution supplied to the culture tank from the carbon dioxide-containing solution supply unit and the amount of hydrogen supplied from the hydrogen supply unit based on the carbon dioxide concentration of the culture solution in the culture tank or the outflow rate of the culture solution, and the carbon dioxide concentration of the liquid phase in the dissolution tank or the inflow rate of the liquid phase. Each of the above parameters may be controlled within the above-mentioned preferred ranges.

[0029] <Configuration Example of Methane Generator> The configuration of the methane generator (1) of the present disclosure may be, for example, the following embodiments.

[0030] In the first embodiment ( FIG. 1 ), the methane generator (1) of the present disclosure is a two-chamber methane generator (1). The two-chamber methane generator (1) includes two separate chambers, a dissolution chamber (100) and a culture chamber (200), as well as a carbon dioxide gas supply unit (carbon dioxide gas supply flow path (101), carbon dioxide gas supply port (102)), a solution transfer flow path (103), a hydrogen supply unit (hydrogen supply flow path (301), hydrogen supply port (302)), and a methane discharge unit (methane discharge port (201), methane discharge flow path (202)). FIG. 1 also shows an optional configuration in which the two-chamber methane generator (1) further includes a gas phase discharge section (gas phase discharge port (104) and gas phase discharge flow path (107)), an aqueous phase supply flow path (401), a culture solution discharge flow path (402), and a reused culture solution supply flow path for transporting used culture solution from a branching point (404) of the culture solution discharge flow path (402) to a joining point (403) of the aqueous phase supply flow path (401).

[0031] In the second embodiment (FIG. 2), the methane generator (1) of the present disclosure is a single-tank type methane generator (1) and is further provided with 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) join 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 into the gas phase discharge flow path (107) and the gas phase (methane) discharge flow path (202) via a switching valve. In the dissolution tank mode (left diagram), the carbon dioxide gas supply channel (101) and the gas phase discharge channel (107) are open, and the hydrogen supply channel (301) and the gas phase (methane) discharge channel (202) are closed, so that the single tank functions as a single tank (100'') in the dissolution tank mode. In the culture tank mode (right diagram), the hydrogen supply channel (301) and the gas phase (methane) discharge channel (202) are open, and the carbon dioxide gas supply channel (101) and the gas phase discharge channel (107) are closed, so that the single tank functions as a single tank (200'') in the culture tank mode.

[0032] In a third embodiment ( FIG. 3 ), the methane generator (1) of the present disclosure is a partitioned single-tank methane generator (1) having a partition (501) through which a liquid can pass inside the single tank (500). The interior of the tank is divided by the partition (501) into a dissolution compartment (100a) functioning as a dissolution tank and a culture compartment (200a) functioning as a culture tank. The partitioned single-tank methane generator (1) further includes a gas phase discharge section (gas phase discharge port (104), a gas phase discharge flow path (107)) and a recycled culture solution supply section (aqueous phase (culture solution) supply flow path (401), aqueous phase (culture solution) discharge flow path (402), a branching section (403), and a confluence section (404)).

[0033] In the fourth embodiment ( FIG. 4 ), the methane generation apparatus (1) of the present disclosure has a configuration in which the two-tank methane generation apparatus (1) of the first embodiment further includes a microorganism removal device (membrane separation device (405)) in the reused culture solution supply flow path.

[0034] In a fifth embodiment ( FIG. 5 ), a methane generator (1) according to the present disclosure further comprises a flow meter (406) for measuring the liquid flow rate in the aqueous phase (culture solution) supply channel (401), the solution transfer channel (103), and the culture solution discharge channel (402) in addition to the two-chamber methane generator (1) of the fourth embodiment, a pH meter (407) for measuring the pH of the aqueous phase (111) in the dissolution tank (100) and the culture solution (211) in the culture tank (200), and a level meter (408) for measuring the liquid level of the aqueous phase (111) in the dissolution tank (100) and the culture solution (211) in the culture tank (200). For example, pH is an indicator of the carbon dioxide concentration in the aqueous phase and the suitability of the culture solution for methanogen cultivation, and the supply amounts of carbon dioxide-containing gas, hydrogen, and the aqueous phase, the amount of aqueous phase transferred through the solution transfer channel (103), and the like, may be controlled based on these measurements.

[0035] (Method for producing methane) The method for producing methane according to the present disclosure includes the steps of exposing a carbon dioxide-containing gas to an aqueous phase in a dissolution tank, transferring the carbon dioxide-containing solution from the dissolution tank to a culture tank, supplying hydrogen to the culture tank, culturing methanogens in a culture solution in the culture tank to produce methane, and discharging methane from the culture tank.

[0036] The methane generation method of the present disclosure can be carried out using the methane generation apparatus of the present disclosure described above. Examples of the form of the apparatus for carrying out the methane generation method of the present disclosure include the two-tank type, single-tank type, and partitioned single-tank type as described above.

[0037] When a two-tank methanogen is used as the apparatus for performing the methane generation method of the present disclosure, the step of transferring the carbon dioxide-containing solution from the dissolution tank to the culture tank is performed by supplying the carbon dioxide-containing solution in the dissolution tank to the culture tank. This step is not particularly limited, but may be performed, for example, by transferring the carbon dioxide-containing solution through an aqueous flow path connecting the dissolution tank and the culture tank, or by pumping the carbon dioxide-containing solution from the dissolution tank and introducing it into the culture tank. This step may also be performed by supplying the carbon dioxide-containing solution in the dissolution tank to the culture tank without oxygen removal treatment, or by directly supplying the carbon dioxide-containing solution in the dissolution tank to the culture tank.

[0038] When a partitioned single-tank type apparatus is used as the apparatus for performing the methane production method of the present disclosure, the step of transferring the carbon dioxide-containing solution from the dissolution tank to the culture tank may be performed by opening the partition, using, for example, a partition with an openable opening, a membrane that allows liquid to pass but not microorganisms to pass, etc. When the partition has an openable opening, the step may be performed by applying pressure to the aqueous phase in the dissolution tank or applying negative pressure to the culture solution in the culture tank when the partition is opened.

[0039] When a single-tank type apparatus is used as the apparatus for performing the methane production method of the present disclosure, the step of transferring the carbon dioxide-containing solution from the dissolution tank to the culture tank may be performed by controlling switching between: (i) a dissolution tank mode in which the tank functions as a dissolution tank by supplying carbon dioxide-containing gas from the carbon dioxide-containing gas inlet to the tank and stopping the supply of hydrogen from the hydrogen supply unit to the single tank and the discharge of methane from the product gas discharge unit; and (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 unit to the single tank and discharging methane from the product gas discharge unit.

[0040] The methane production method of the present disclosure may further include a step of discharging the gas phase in the dissolution tank, a step of merging the gas phase discharged from the gas phase discharge part with the carbon dioxide-containing gas introduction part, a step of discharging the culture solution from the culture tank, a step of removing microorganisms, excess water, or both from the culture solution discharged from the discharge part, and a step of supplying the culture solution from which microorganisms have been removed using a microorganism removal device to the dissolution tank.

[0041] The methane production method of the present disclosure may further include measuring: (a) the carbon dioxide concentration or pH of the liquid phase in the dissolution tank; (b) the amount of liquid phase inflow into the dissolution tank; (c) the flow rate of the liquid phase from the dissolution tank to the culture tank; (d) the carbon dioxide concentration or pH of the culture solution in the culture tank; (e) the amount of culture solution outflow from the culture tank; and / or (f) the liquid level of the culture solution in the culture tank. The carbon dioxide concentration may be measured using pH as an indicator. The methane production method of the present disclosure may further include adjusting, based on these measured values: (c) the flow rate of the liquid phase from the dissolution tank to the culture tank; and / or (g) the amount of hydrogen supplied from the hydrogen supply unit to the culture tank.

[0042] The conditions for the methane generation method of the present disclosure can be the same as those described for the methane generation apparatus of the present disclosure.

[0043] According to the present disclosure, it is possible to provide a methanation system that has good conversion efficiency from carbon dioxide to methane even when a gas with a low concentration of carbon dioxide is used as a carbon dioxide supply source, and that allows for simplification of the device and a reduction in installation area.

[0044] 1 Methane production system 100 Dissolution tank 100 ″ Single tank in dissolution tank mode 100 a Dissolution section 101 Carbon dioxide gas supply channel 102 Carbon dioxide gas supply port 102 ″ Gas supply port 103 Solution transfer channel 104 Gas phase outlet 104 ″ Gas phase outlet 107 Gas phase outlet channel 111 Aqueous phase 112 Gas phase 200 Culture tank 200 ″ Single tank in culture tank mode 200 a Culture section 201 Gas phase (methane) outlet 202 Gas phase (methane) outlet channel 211 Aqueous phase (culture solution) 212 Gas phase 301 Hydrogen supply channel 302 Hydrogen supply port 401 Aqueous phase (culture solution) supply channel 402 Aqueous phase (culture solution) outlet channel 403 Confluence section 404 Branch section 405 Membrane separation device 406 Flow meter 407 pH meter 408 Level meter 500 Single tank with partition 501 Partition

Claims

1. A methane generation apparatus comprising: a dissolution tank that exposes a carbon dioxide-containing gas to an aqueous phase to produce a carbon dioxide-containing solution; a culture tank that cultivates methanogens in a culture solution to produce methane; a carbon dioxide gas supply flow path that introduces the carbon dioxide-containing gas into the dissolution tank; a solution transfer means that transfers the carbon dioxide-containing solution produced in the dissolution tank from the dissolution tank to the culture tank; a hydrogen supply flow path that supplies hydrogen to the dissolution tank or the culture tank; and a methane discharge flow path that discharges the produced methane from the culture tank.

2. The methane generation apparatus according to claim 1, wherein the dissolution tank and the culture tank are separate tanks, and the solution transfer means is a solution transfer flow path connecting the dissolution tank and the culture tank.

3. The methane generation apparatus according to claim 2, wherein the solution transfer flow path is a flow path that supplies the carbon dioxide-containing solution in the dissolution tank to the culture tank without oxygen removal treatment.

4. The methane generation apparatus according to claim 1, wherein the methane generation apparatus comprises a single tank that serves as both the dissolution tank and the culture tank, the methane generation apparatus further comprising a gas phase discharge flow path that discharges excess gas phase when the single tank functions as the culture tank, the aqueous phase is a culture solution, the solution transfer means is switching means for switching between the dissolution tank and the culture tank, the switching means comprising valves that open and close the carbon dioxide gas supply flow path, the hydrogen supply flow path, the gas phase discharge flow path, and the methane discharge flow path, and a control unit that controls the opening and closing of the valves, and the control unit controls switching between: (i) a dissolution tank mode in which the single tank functions as a dissolution tank by opening the carbon dioxide gas supply flow path and the gas phase discharge flow path and closing the hydrogen supply flow path and the methane discharge flow path; and (ii) a culture tank mode in which the single tank functions as a culture tank by closing the carbon dioxide gas supply flow path and the gas phase discharge flow path and opening the hydrogen supply flow path and the methane discharge flow path.

5. The methane generation apparatus according to claim 4, further comprising a recycling flow path for allowing the excess gas phase discharged from the gas phase discharge flow path to join the carbon dioxide-containing gas introduction section.

6. The methane generation apparatus according to claim 1, wherein the methane generation apparatus comprises a single tank having a partition therein through which liquid can pass, each of the compartments within the tank separated by the partition functions as the dissolution tank and the culture tank, respectively, and the partition serves as the solution transfer means.

7. The methane generating apparatus according to claim 6, wherein the partition has an opening that can be opened and closed.

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

9. A methane generation apparatus according to any one of claims 1 to 3, 6 and 7, wherein the dissolution tank further comprises a gas phase discharge passage for discharging excess gas phase in the dissolution tank.

10. The methane generation apparatus according to claim 9, further comprising a recycling flow path for allowing the excess gas phase discharged from the gas phase discharge flow path to join the carbon dioxide-containing gas introduction section.

11. The methane generation apparatus according to any one of claims 1 to 7, further comprising: a culture medium discharge flow path for discharging the culture medium from the culture tank; a microorganism removal device for removing microorganisms, excess water, or both from the culture medium discharged from the culture medium discharge flow path; and a reused culture medium supply flow path for supplying the culture medium from which microorganisms have been removed by the microorganism removal device to the dissolution tank for reuse.

12. A methane generator according to any one of claims 1 to 8, wherein the carbon dioxide-containing gas is a combustion exhaust gas.

13. A methane generation apparatus as described in claim 2 or 3, comprising an adjustment unit that adjusts the amount of carbon dioxide-containing solution in the dissolution tank supplied from the carbon dioxide-containing solution supply flow path to the culture tank and the amount of hydrogen supplied from the hydrogen supply flow path based on the carbon dioxide concentration of the culture solution in the culture tank or the outflow rate of the culture solution, and the carbon dioxide concentration of the liquid phase in the dissolution tank or the inflow rate of the liquid phase.

14. A method for generating methane, comprising: a step of exposing a carbon dioxide-containing gas to an aqueous phase in a dissolution tank; a solution transfer means for transferring the carbon dioxide-containing solution from the dissolution tank to a culture tank; a step of supplying hydrogen to the culture tank; a step of culturing methanogens in a culture solution in the culture tank to generate methane; and a step of discharging the generated methane from the culture tank.

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