Methanation apparatus and methanation method

Abstract

To provide a methanation apparatus and a methanation method each of which enables conditions related to the progress of anaerobic treatment to be maintained, and furthermore enables increase of contact efficiency between hydrogen and carbon dioxide, which are the starting materials for methane production using methanogens, and methanogens treatment, thereby enabling improvement of the methane yield.SOLUTION: A methanation apparatus is provided, which includes: an anaerobic treatment tank; a circulation unit which circulates liquid including methanogens within the anaerobic treatment tank; a carbon dioxide supply unit; and a hydrogen supply unit, and which collects the liquid including methanogens from the bottom of the anaerobic treatment tank and supplies the collected liquid from the top of the anaerobic treatment tank to thereby circulate the supplied collected liquid within the anaerobic treatment tank. A method for producing methane using the methanation apparatus is also provided. The above apparatus and the method enable the increase of the contact efficiency between the starting materials (hydrogen and carbon dioxide) and the methanogens regardless of the solubility of hydrogen in water, thereby enabling improvement of the methane yield without changing the conditions related to the progress of anaerobic treatment.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a methane generation device and a methane generation method. More specifically, the present invention relates to a methane generation device and a methane generation method that utilize anaerobic treatment.

Background Art

[0002] As one of the methods for treating water to be treated such as wastewater, it is known to perform biological treatment (hereinafter referred to as "anaerobic treatment") in an anaerobic environment using sludge containing various microorganisms. This anaerobic treatment has high merits in terms of not requiring aeration power and hardly generating excess sludge.

[0003] Among anaerobic treatments, methane fermentation by microorganisms that generate methane in an anaerobic environment (hereinafter referred to as "methanogens") is widely used from the viewpoint of the high utility of the generated gas, biogas (methane). Also, it is known that some methanogens generate methane by oxidizing hydrogen and reducing carbon dioxide. By supplying hydrogen to carbon dioxide in the biogas generated by anaerobic treatment, methane generation is further promoted, and the methane yield in the biogas generated as a whole of the anaerobic treatment is increased.

[0004] For example, Patent Document 1 describes that methane is generated by separating hydrogen from the generated gas generated in the acid generation tank before the methane fermentation tank and introducing the separated hydrogen into the methane fermentation tank.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Here, the technology of producing methane from carbon dioxide and hydrogen using methanogens is called biomethanation. Since it produces methane, which is useful as an energy source by consuming carbon dioxide, it is expected not only to improve the methane yield in biogas but also to contribute to decarbonization efforts to suppress carbon dioxide emissions into the environment. In particular, the technology related to biomethanation using an anaerobic treatment tank with carbon dioxide and hydrogen as starting materials is a technology worthy of attention because it can utilize existing anaerobic treatment facilities and reduce initial costs.

[0007] On the other hand, one of the chemical properties of hydrogen is its low solubility in water at normal temperature and pressure (1.6 mg / L). Generally, to increase the solubility of a gas in water, it is known to lower the temperature or operate under high-pressure conditions. However, to maintain the progress conditions of anaerobic treatment by methanogens, the temperature in the anaerobic treatment tank is not set below normal temperature, and it is also difficult to operate under high-pressure conditions. Considering these factors, as in Patent Document 1, simply introducing hydrogen into an anaerobic treatment tank (methane fermentation tank) for anaerobic treatment by methanogens results in low contact efficiency of hydrogen with methanogens in the anaerobic treatment tank, and consequently, does not lead to an improvement in methane yield.

[0008] Therefore, an object of the present invention is to provide a methane production apparatus and a methane production method that can enhance the contact efficiency between hydrogen and carbon dioxide, which are starting materials for methane production, and methanogens while maintaining the progress conditions of anaerobic treatment in methane production (biomethanation) using methanogens, thereby improving the methane yield.

Means for Solving the Problems

[0009] As a result of intensive studies on the above problems, the present inventor has found that in methane production (biomethanation) using methane-producing bacteria, a circulation path is formed in which a liquid containing methane-producing bacteria is recovered from the lower part of an anaerobic treatment tank and supplied from the upper part of the anaerobic treatment tank. By bringing this liquid into contact with hydrogen and carbon dioxide, the contact efficiency between the starting materials (hydrogen and carbon dioxide) and the methane-producing bacteria can be increased, and the methane yield can be improved. Based on this finding, the present invention has been completed.

[0010] The methane production apparatus of the present invention for solving the above problems includes an anaerobic treatment tank, a circulation unit for circulating a liquid containing methane-producing bacteria in the anaerobic treatment tank, a carbon dioxide supply unit, and a hydrogen supply unit. The liquid containing methane-producing bacteria is recovered from the lower part of the anaerobic treatment tank and supplied from the upper part of the anaerobic treatment tank, thereby circulating the inside of the anaerobic treatment tank. According to the methane production apparatus of the present invention, by recovering the liquid containing methane-producing bacteria at the lower part of the tank, supplying it from the upper part of the tank, and circulating it, gas-solid contact and gas-liquid contact proceed efficiently inside the anaerobic treatment tank. As a result, regardless of the solubility of hydrogen in water, the contact efficiency between the gaseous starting materials (hydrogen and carbon dioxide) and the solid methane-producing bacteria, or the contact efficiency between the gaseous starting materials and the liquid in which the methane-producing bacteria are dispersed can be increased. As a result, without changing the conditions related to the progress of anaerobic treatment, the reaction efficiency related to methane production by methane-producing bacteria is improved, and the methane yield can be improved.

[0011] Furthermore, as an embodiment of the methane production apparatus of the present invention, the anaerobic treatment tank is characterized in that a filler is accommodated therein. According to this methane production apparatus, in addition to the circulation of the liquid containing methane-producing bacteria, the effect of improving the gas-solid contact efficiency or the gas-liquid contact efficiency by the filler can be obtained. Furthermore, by forming a biofilm on the surface of the filler, it is also possible to increase the concentration of methane-producing bacteria in the anaerobic treatment tank. As a result, the reaction efficiency related to methane production by methane-producing bacteria is further improved, and a further improvement in the methane yield can be achieved.

[0012] Furthermore, as an embodiment of the methane generation device of the present invention, the carbon dioxide supply unit and the hydrogen supply unit are connected to the lower part of the anaerobic treatment tank, and a methane recovery unit for recovering the generated methane is provided at the upper part of the anaerobic treatment tank. According to this methane generation device, the supply positions of carbon dioxide and hydrogen to the anaerobic treatment tank can be made close to or the same, facilitating the design and manufacture of the entire methane generation device. Also, it has the effect of easily allowing the reuse of existing anaerobic treatment facilities.

[0013] Furthermore, as an embodiment of the methane generation device of the present invention, the hydrogen supply unit is connected to the upper part of the anaerobic treatment tank, the carbon dioxide supply unit is connected to the lower part of the anaerobic treatment tank, and a methane recovery unit for recovering the generated methane is provided at the central part of the anaerobic treatment tank. According to this methane generation device, by utilizing the different densities of the starting substances (hydrogen and carbon dioxide) and the product substance (methane), it is possible to improve the contact efficiency between the starting substances and the methane-producing bacteria and the recovery efficiency of the product substance. More specifically, by introducing carbon dioxide, which has a high density and high solubility in water, from the lower part of the anaerobic treatment tank, the contact efficiency with the liquid containing methane-producing bacteria inside the anaerobic treatment tank is increased. On the other hand, by introducing hydrogen, which has a low density and low solubility in water, from the upper part of the anaerobic treatment tank, the contact efficiency with the liquid containing methane-producing bacteria supplied from the upper part of the tank can be increased. Furthermore, by recovering methane, which is a product substance with a density between hydrogen and carbon dioxide, from the central part of the anaerobic treatment tank, the mixing of the starting substances (hydrogen and carbon dioxide) is suppressed, enabling the recovery of methane with high purity and concentration.

[0014] The methane generation method of the present invention for solving the above problems is a methane generation method using an anaerobic treatment tank, comprising a circulation step of circulating a liquid containing methane-producing bacteria in the anaerobic treatment tank, a carbon dioxide supply step, and a hydrogen supply step. The circulation step is characterized by recovering the liquid containing methane-producing bacteria from the lower part of the anaerobic treatment tank and supplying it from the upper part of the anaerobic treatment tank to circulate inside the anaerobic treatment tank. According to the methane production method of the present invention, when using an anaerobic treatment tank to produce methane by methane-producing bacteria, the liquid containing methane-producing bacteria is collected at the lower part of the tank, supplied from the upper part of the tank, and circulated. Inside the anaerobic treatment tank, gas-solid contact and gas-liquid contact proceed with high efficiency. As a result, regardless of the solubility of hydrogen in water, the contact efficiency between gaseous starting materials (hydrogen and carbon dioxide) and solid methane-producing bacteria, or the contact efficiency between gaseous starting materials and the liquid in which methane-producing bacteria are dispersed can be increased. As a result, without changing the conditions related to the progress of anaerobic treatment, the reaction efficiency related to methane production by methane-producing bacteria is improved, and the methane yield can be increased.

Advantages of the Invention

[0015] According to the present invention, in methane production (biomethanation) using methane-producing bacteria, it is possible to provide a methane production apparatus and a methane production method capable of increasing the contact efficiency between hydrogen and carbon dioxide, which are starting materials for methane production, and methane-producing bacteria, and improving the methane yield while maintaining the progress conditions of anaerobic treatment.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0017] Hereinafter, embodiments of a methane production apparatus and a methane production method according to the present invention will be described in detail with reference to the drawings. Note that the methane generation device described in the embodiment is merely an example for explaining the methane generation device according to the present invention, and is not limited thereto. Further, the methane generation method of the present embodiment shall be substituted for the following description of the configuration and operation of the methane generation device.

[0018] The methane generation device and the methane generation method of the present invention are what is called so-called biomethanation, and perform methane generation using an anaerobic treatment tank. In other words, the methane generation device and the methane generation method of the present invention do not perform anaerobic treatment of treated water such as industrial wastewater and domestic wastewater, but perform methane generation using carbon dioxide and hydrogen as starting materials.

[0019] [First Embodiment] FIG. 1 is a schematic explanatory diagram of the methane generation device according to the first embodiment of the present invention. As shown in FIG. 1, the methane generation device 1A in the present embodiment includes an anaerobic treatment tank 2 in which a liquid S containing methane-producing bacteria (hereinafter also simply referred to as "liquid S") is housed, a circulation unit 3 for circulating the liquid S in the anaerobic treatment tank 2, a carbon dioxide supply unit 4, a hydrogen supply unit 5, and a methane recovery unit 6. The arrow in the anaerobic treatment tank 2 indicates the moving (transferring) direction of the liquid S.

[0020] Then, the methane generation device 1A in the present embodiment uses the anaerobic treatment tank 2, introduces carbon dioxide and hydrogen as starting materials into the anaerobic treatment tank 2, and brings them into contact with the liquid S inside the anaerobic treatment tank 2, thereby performing methane generation by methane-producing bacteria. Hereinafter, each configuration of the methane generation device 1A in the present embodiment will be described.

[0021] The anaerobic treatment tank 2 is a reaction tank for performing anaerobic treatment by methane-producing bacteria on the starting materials (hydrogen and carbon dioxide) introduced into the tank. As shown in FIG. 1, the anaerobic treatment tank 2 houses a liquid S containing methane-producing bacteria inside, and the circulation unit 3, hydrogen supply unit 4, carbon dioxide supply unit 5, and methane recovery unit 6 described later are connected thereto.

[0022] The anaerobic treatment tank 2 in this embodiment can have the structure of a reaction tank used for general anaerobic treatment. For example, the anaerobic treatment tank 2 is preferably a closed system to maintain an anaerobic environment. Here, the anaerobic treatment that proceeds 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.

[0023] Also, the liquid S containing methanogens accommodated in the anaerobic treatment tank 2 of this embodiment may be any substance that contains methanogens and a certain amount of moisture. For example, it may mainly consist of a solution (water) with methanogens dispersed in the water, or a liquid containing a large amount of solids called sludge. And as the liquid S, a liquid containing isolated methanogens may be used, or seed sludge from other wastewater treatment facilities etc. may be used. Also, the reaction tank after anaerobic treatment of the water to be treated may be diverted as the anaerobic treatment tank 2 in this embodiment, and the sludge (including granules etc.) present in the tank may be utilized.

[0024] Note that the anaerobic treatment tank 2 in this embodiment can be further provided with various additional facilities. For example, the anaerobic treatment tank 2 may be equipped with means for adjusting the internal water temperature, means for injecting a pH adjuster, and means for adding metals such as nitrogen, phosphorus, cobalt, and nickel which are nutrient sources required by microorganisms. This makes it easier to adjust and maintain the conditions for the smooth progress of anaerobic treatment in the anaerobic treatment tank 2.

[0025] Also, as shown in FIG. 1, it is preferable to accommodate the filler P in the anaerobic treatment tank 2 of this embodiment. By accommodating the filler P in the anaerobic treatment tank 2, the area (volume) related to the contactable region between the liquid S supplied from the upper part of the tank via the circulation section 3 described later and the hydrogen and carbon dioxide introduced from the hydrogen supply section 4 and the carbon dioxide supply section 5 is expanded, and the gas-solid contact efficiency or the gas-liquid contact efficiency is improved. In addition, anaerobic microorganisms (methanogens in this embodiment) involved in anaerobic treatment adhere to the surface of the filler P, and a biofilm is formed, enabling the methanogens to be retained in the treatment tank 2. As a result, the concentration of anaerobic microorganisms in the treatment tank 2 can be increased, and the anaerobic treatment efficiency can be improved.

[0026] The filler P in this embodiment may be any substance that can expand the region involved in gas-solid contact or gas-liquid contact, and is not particularly limited as long as it is a solid material having a certain degree of strength. As the filler P, a solid material to which anaerobic microorganisms involved in anaerobic treatment adhere, that is, a so-called carrier (microbial carrier), may be used.

[0027] Specific examples of the material of the filler P include, for example, silica sand, ceramics, activated carbon, polymers, resins, clay, incineration ash, blast furnace granulated slag, and the like. Specific examples of the shape of the filler P include, for example, spherical, pellet-shaped, honeycomb-shaped, sponge-shaped, small cylindrical, tube-shaped, cubic-shaped, and the like. Note that, as the filler P of this embodiment, the presence or absence of pores is not particularly limited. However, from the viewpoint of being able to adsorb components that inhibit anaerobic treatment by anaerobic microorganisms in addition to expanding the region involved in gas-solid contact or gas-liquid contact and retaining anaerobic microorganisms, it is preferable to have pores, and it is preferable to use a material having a structure with a high porosity (such as a porous carrier).

[0028] The circulation unit 3 is for circulating the liquid S in the anaerobic treatment tank 2. More specifically, the circulation unit 3 is for circulating the inside of the anaerobic treatment tank 2 by collecting the liquid S from the lower part of the anaerobic treatment tank 2 and supplying it from the upper part of the anaerobic treatment tank 2. As the circulation unit 3 in this embodiment, as shown in FIG. 1, it includes a liquid recovery unit 31 provided at the lower part of the anaerobic treatment tank 2, a transfer pipe 32 for transferring the recovered liquid S, a pump 33 for promoting the transfer of the liquid S, and a liquid supply unit 34 provided at the upper part of the anaerobic treatment tank 2.

[0029] The liquid recovery section 31 only needs to be able to supply the liquid S contained in the anaerobic treatment tank 2 to the transfer pipe 32 side, and the specific structure is not particularly limited. For example, as shown in FIG. 1, it may include a discharge port 31a that is a connection point between the inside and outside of the anaerobic treatment tank 2 below the side wall of the anaerobic treatment tank 2, and a recovery pipe 31b that enters the liquid S contained at the bottom of the anaerobic treatment tank 2. The discharge port 31a is connected to the transfer pipe 32 and is for discharging the liquid S in the anaerobic treatment tank 2 to the outside of the anaerobic treatment tank 2. Note that the discharge port 31a may be provided with a structure or mechanism for removing foreign substances other than the liquid S and crushing the methane-producing bacteria aggregates (lumps) in the liquid S in order to prevent blockage of the transfer pipe 32 and the pump 33. As shown in FIG. 1, the recovery pipe 31b may be a pipe having a plurality of holes and connected to the transfer pipe 32 and the pump 33 via the discharge port 31a. At this time, the shape of the recovery pipe 31b may be one that extends along the diameter of the anaerobic treatment tank 2 or one that extends along the circumference of the anaerobic treatment tank 2. Also, a plurality of recovery pipes 31b may be provided. This makes it possible to recover the liquid S evenly from the anaerobic treatment tank 2 even when the liquid S is sludge with a large amount of solid content. Note that the recovery pipe 31b can be omitted, and only the discharge port 31a may be used as the liquid recovery section 31.

[0030] The transfer pipe 32 and the pump 33 are for transferring the liquid S recovered by the liquid recovery section 31 to the upper part of the anaerobic treatment tank 2. Note that as the pump 33, those that can facilitate the transfer of a fluid containing solid content are preferable, and specifically, a vortex pump, a single-screw pump, a diaphragm pump, etc. can be mentioned.

[0031] The liquid supply section 34 only needs to be able to supply the liquid S transferred through the transfer pipe 32 and the pump 33 into the anaerobic treatment tank 2 from the upper part of the tank, and the specific structure is not particularly limited. As the liquid supply unit 34 in the present embodiment, for example, as shown in FIG. 1, it is connected to the transfer pipe 32 and includes a pipe having a plurality of holes, and the liquid S is dropped from these holes. At this time, when the liquid S is sludge with a large amount of solid content, etc., the holes provided in the pipe are preferably in a shape and size that are less likely to be blocked.

[0032] As another example of the liquid supply unit 34, instead of a pipe, an overflow weir is used. FIG. 2 is a schematic explanatory diagram showing an example of the structure of each component constituting the liquid supply unit 34, which is a partial structure of the circulation unit 3 in the present embodiment. As shown in FIG. 2, as another aspect of the liquid supply unit 34, there is an example including a plate-shaped overflow weir 341, a liquid receiving tank 342 composed of a rectangular container with an open front surface, and a liquid supply pipe 343 for supplying the liquid S into the liquid receiving tank 342. By using the overflow weir 341 as the liquid supply unit 34, when supplying the liquid S such as sludge with a large amount of solid content, blockage on the liquid supply unit 34 is suppressed, and the liquid S can be circulated smoothly. Note that FIG. 2A is a front view showing an example of the structure related to the overflow weir 341 among the liquid supply unit 34. FIG. 2B is a front view showing an example of the structure related to the liquid receiving tank 342 and the liquid supply pipe 343 among the liquid supply unit 34. And FIG. 2C is a side view showing an example of the structure when the overflow weir 341, the liquid receiving tank 342, and the liquid supply pipe 343 are assembled. Hereinafter, each component of the liquid supply unit 34 will be described based on FIG. 2.

[0033] As the overflow weir 341 in the present embodiment, as shown in FIG. 2A, an overflow portion 341a formed by a triangular notch formed at the upper end of the overflow weir 341, a water channel 341b formed so as to hang down from the overflow portion 341a, and a triangular convex portion 341c protruding from the bottom at the position of the water channel 341b are formed on a plate-shaped member.

[0034] The overflow section 341a indicates the portion where the liquid S overflows at the overflow weir 341. As shown in Fig. 2A, the overflow section 341a may be formed by forming a plurality of notches at the upper end of the overflow weir 7 and may be composed of a plurality of overflow sections, or may be composed of one overflow section having a substantially horizontal plane without providing a notch. When the overflow section 341a is composed of one overflow section having a substantially horizontal plane, the overflow rate per unit width length of the overflow section 341a becomes small, so it cannot be evenly distributed within the range of the overflow section 341a, and there is a risk that the liquid S is supplied unevenly. Therefore, it is preferable to provide a plurality of overflow sections composed of a plurality of notches to increase the overflow rate per unit width length of the overflow section 341a.

[0035] Note that the shape of the overflow section 341a divided into a plurality is not particularly limited, and in addition to the triangular shape shown in Fig. 2A, for example, a rectangular shape, an arc shape, etc. may be used. Further, in addition to providing a plurality of notches at the upper end of the overflow weir 341 (plate-like member), a plurality of overflow holes may be provided in the overflow weir 341 (plate-like member). From the viewpoint of easy processing, it is preferable that the plurality of overflow sections 341a are formed by a plurality of cutout portions.

[0036] Here, although the overflow weir 341 shown in Fig. 2 is formed of a plate-like member, any shape may be used as long as it can be widely distributed in the width direction. For example, a structure such as a prism or a cylinder may be laid down and fixed to the front opening of the liquid receiving tank 342.

[0037] Further, it is preferable to form an inclined surface in the thickness direction of the overflow section 341a. When an inclined surface is formed so as to descend toward the downstream side of the overflow weir 341, the overflowed liquid S flows down the inclined surface and quickly passes through the overflow section 341a, so that drying of the liquid S (adhesion of solid components in the liquid S) in the overflow section 341a can be prevented. On the other hand, even when an inclined surface is formed so as to descend toward the upstream side of the overflow weir 341, since the substantial thickness of the overflow section 341a becomes small, drying of the liquid S (adhesion of solid components in the liquid S) can be prevented.

[0038] The water channel 341b is formed on the downstream surface of the overflow weir 341 and is configured for the liquid S to flow down. As the water channel 341b, as shown in Fig. 2A, there is an example constituted by a recess (groove) formed on the downstream surface of the overflow weir 341. When the liquid S that has overflowed from the overflow portion 341a flows down the downstream surface of the overflow weir 341, it may not flow evenly on the surface of the overflow weir 341 because it diffuses on the surface due to wetting with the surface of the overflow weir 341. On the other hand, by providing the water channel 341b, since the liquid S flows down along the water channel 341b, diffusion of the liquid S can be prevented and uniform distribution becomes possible.

[0039] The water channel 341b only needs to be able to guide the liquid S to the bottom of the overflow weir 341 so that the liquid S does not diffuse, and is not particularly limited. For example, as shown in Fig. 2A, in addition to forming a recess (groove) on the surface of the overflow weir 341, there are examples such as providing a plurality of water channel walls protruding on the surface of the overflow weir 341, or coating the surface of the overflow weir 341 with a water-repellent film.

[0040] The direction of the water channel 341b is not particularly limited, and as shown in Fig. 2A, it may be formed vertically from the overflow portion 341a, or may be formed inclined. From the viewpoint of more surely flowing down inside the water channel 341b, it is preferable to form it in the vertical direction.

[0041] The convex portion 341c is provided at the bottom of the overflow weir 341 and is configured to let the liquid S that has overflowed from the overflow portion 341a drip down. When the liquid S that has overflowed from the overflow portion 341a drips down from the bottom of the overflow weir 341, if it diffuses in the width direction of the overflow weir 341, there is a possibility that the liquid S may not be dripped evenly from the liquid supply portion 34. On the other hand, by forming the convex portion 341c at the bottom of the overflow weir 341, when the liquid S that has overflowed the overflow weir 341 flows down, the diffusion of the liquid S in the width direction of the overflow weir 341 is limited to the length of the width at the lower end of the convex portion 341c, so that the liquid S can be dripped more evenly.

[0042] The shape of the convex portion 341c is not particularly limited. For example, in addition to the triangular shape shown in Fig. 2A, it may also be a rectangular shape, an arc shape, etc. Note that the narrower the width of the lower end of the convex portion 341c, the more the diffusion can be restricted. Therefore, the triangular shape shown in Fig. 2A is preferable.

[0043] As shown in Figs. 2B and 2C, the liquid receiving tank 342 in this embodiment includes a container in which an overflow weir 341 is fixed so as to close the lower part of the front opening, and a certain amount of liquid S can be stored inside. The shape of the liquid receiving tank 342 may be any shape as long as it can form a space for storing a certain amount of liquid S in combination with the overflow weir 341. For example, in addition to the rectangular container shown in Fig. 2C, a cylindrical container or the like may also be used. Note that as a fixing means in the combination of the overflow weir 341 and the liquid receiving tank 342, for example, using fixing members such as bolts can be mentioned.

[0044] Also, as shown in Figs. 2B and 2C, the liquid supply pipe 343 in this embodiment includes a pipe installed so as to penetrate the top plate of the liquid receiving tank 342. Thereby, the liquid S is supplied into the space formed by the liquid receiving tank 342 and the overflow weir 341. Note that this liquid supply pipe 343 is connected to the transfer pipe 32 or is used in place of the transfer pipe 32.

[0045] The liquid S supplied from the liquid supply pipe 343 is stored inside the liquid receiving tank 342. When the water level of the liquid S exceeds the height of the overflow weir 341, it will overflow the overflow weir 341 and drip from the liquid supply part 34. At this time, since the liquid S is widely distributed in the width direction of the overflow weir 341, the liquid S can be evenly supplied (dropped) over a wide range from the upper part of the anaerobic treatment tank 2.

[0046] Note that although Fig. 2 shows the overflow weir 341 and the liquid receiving tank 342 configured as separate bodies, the overflow weir 341 and the liquid receiving tank 342 may be of an integral type. Furthermore, as shown in Fig. 2, it is not limited to the structure in which the overflow weir 341 is fixed only to the front surface of the liquid receiving tank 342, and the overflow weir 341 may be provided around the entire circumference of the liquid receiving tank 342.

[0047] The carbon dioxide supply unit 4 is for supplying carbon dioxide as a starting material into the anaerobic treatment tank 2. As the carbon dioxide supply unit 4 in the present embodiment, any device that can introduce carbon dioxide into the anaerobic treatment tank 2 may be used. For example, as shown in FIG. 1, a device including a pipe 41 connected to a carbon dioxide source (not shown) may be mentioned. It is preferable to provide a flow rate adjustment mechanism (such as an on-off valve, a valve, etc.) for adjusting the supply amount of carbon dioxide on the pipe 41.

[0048] Here, the carbon dioxide supplied into the anaerobic treatment tank 2 via the carbon dioxide supply unit 4 of the present embodiment may be any gas whose main component is carbon dioxide (CO2) gas, or a mixed gas containing components other than carbon dioxide. However, in view of the methane production rate, it is preferable that the carbon dioxide to be supplied has a higher CO2 purity. For example, the content ratio as CO2 is preferably greater than 50%, and more preferably 70% or more.

[0049] The hydrogen supply unit 5 is for supplying hydrogen as a starting material into the anaerobic treatment tank 2. As the hydrogen supply unit 5 in the present embodiment, any device that can introduce hydrogen into the anaerobic treatment tank 2 may be used. For example, as shown in FIG. 1, a device including a pipe 51 connected to a hydrogen source (not shown) may be mentioned. It is preferable to provide a flow rate adjustment mechanism (such as an on-off valve, a valve, etc.) for adjusting the supply amount of hydrogen on the pipe 51.

[0050] Here, the hydrogen supplied into the anaerobic treatment tank 2 via the hydrogen supply unit 5 of the present embodiment may be any gas whose main component is hydrogen (H2) gas, or a mixed gas containing components other than hydrogen. However, in view of the methane production rate, it is preferable that the hydrogen to be supplied has a higher H2 purity. For example, the content ratio as H2 is preferably greater than 50%, and more preferably 70% or more. In addition, as the hydrogen to be supplied, hydrogen generated by electrolysis of water using renewable energy (green hydrogen) or hydrogen obtained by a technique for recovering hydrogen from fossil resources without discharging carbon dioxide into the atmosphere (blue hydrogen) may be used. This enables decarbonization in relation to the procurement of the hydrogen source.

[0051] Note that the carbon dioxide supply unit 4 and the hydrogen supply unit 5 in the present embodiment are not limited to being composed of separate pipes (pipe 41 and pipe 51) and supplying carbon dioxide and hydrogen from their respective pipes as shown in FIG. 1. For example, the pipe 41 of the carbon dioxide supply unit 4 and the pipe 51 of the hydrogen supply unit 5 may be connected in front of the anaerobic treatment tank 2, and the mixture gas of carbon dioxide and hydrogen may be supplied to the anaerobic treatment tank 2.

[0052] The methane recovery unit 6 is for recovering methane as a product substance generated in the anaerobic treatment tank 2. As the methane recovery unit 6 in the present embodiment, any unit may be used as long as it can recover methane generated in the anaerobic treatment tank 2 and discharge it outside the system. For example, as shown in FIG. 1, a unit including a pipe 61 connected to the anaerobic treatment tank 2 may be mentioned. Further, the methane recovery unit 6 preferably includes means for utilizing methane as an energy source. For example, it may be connected to means for purifying and storing methane gas via the pipe 61.

[0053] In the methane generation device 1A in the present embodiment, regarding the arrangement of the carbon dioxide supply unit 4, the hydrogen supply unit 5, and the methane recovery unit 6, as shown in FIG. 1, the carbon dioxide supply unit 4 and the hydrogen supply unit 5 are connected to the lower part of the anaerobic treatment tank 2, and the methane recovery unit 6 is provided above the anaerobic treatment tank 2. Thereby, the supply positions of carbon dioxide and hydrogen to the anaerobic treatment tank 2 can be made close to or the same, facilitating the design and manufacture of the entire methane generation device 1A. In addition, there is an effect that it is easy to divert an existing anaerobic treatment facility as the methane generation device 1A.

[0054] Referring to FIG. 1, the operation of the methane generation device 1A related to methane generation will be described below. In the methane generation device 1A in this embodiment, for the anaerobic treatment tank 2 containing the liquid S containing methane-producing bacteria, the supply of starting materials (carbon dioxide and hydrogen) (carbon dioxide supply step and hydrogen supply step) is performed via the carbon dioxide supply unit 4 and the hydrogen supply unit 5. At the same time, the liquid S is recovered from below the anaerobic treatment tank 2 via the liquid recovery unit 31 of the circulation unit 3 and supplied (dropped) from above the anaerobic treatment tank 2 via the liquid supply unit 34 of the circulation unit 3, so that the liquid S circulates in the anaerobic treatment tank 2 (circulation step).

[0055] At this time, since the carbon dioxide supply unit 4 and the hydrogen supply unit 5 are connected to the lower part of the anaerobic treatment tank 2, carbon dioxide and hydrogen are supplied to the liquid S contained at the bottom of the anaerobic treatment tank 2. The carbon dioxide (CO2) supplied from the carbon dioxide supply unit 4 dissolves in the liquid S and circulates in the anaerobic treatment tank 2 together with the liquid S via the circulation unit 3. On the other hand, since the hydrogen (H2) supplied from the hydrogen supply unit 5 does not dissolve much in the liquid S, it moves upward in the anaerobic treatment tank 2 in a gaseous state.

[0056] Then, the liquid S (carbon dioxide-containing state) circulating in the anaerobic treatment tank 2 via the circulation unit 3 is dropped from above the anaerobic treatment tank 2 via the liquid supply unit 34, so that it comes into contact with the hydrogen moving upward in the anaerobic treatment tank 2. In particular, as shown in FIG. 1, when the filler 34 is accommodated in the anaerobic treatment tank 2, on the surface of the filler 34, the gas-liquid contact between the liquid S and hydrogen proceeds efficiently, and at the same time, the gas-solid contact between the methane-producing bacteria (solid) in the liquid S and hydrogen also proceeds efficiently. At this time, since carbon dioxide is present (dissolved) in the liquid S from the liquid supply unit 34 together with the methane-producing bacteria, methane generation by the methane-producing bacteria using carbon dioxide and hydrogen as starting materials proceeds due to this gas-solid (gas-liquid) contact. That is, without changing the conditions related to the progress of anaerobic treatment such as the temperature and pressure in the anaerobic treatment tank 2, it is possible to improve the reaction efficiency related to methane generation by methane-producing bacteria and improve the methane yield.

[0057] The generated methane is recovered via the methane recovery unit 6 provided at the upper part of the anaerobic treatment tank 2 and discharged to the outside.

[0058] As described above, the methane generation device 1A in the present embodiment collects the liquid S containing methane-producing bacteria at the lower part of the anaerobic treatment tank 2, supplies it from the upper part of the anaerobic treatment tank 2, and circulates it, thereby enabling the gas-solid contact and gas-liquid contact inside the anaerobic treatment tank 2 to proceed with high efficiency. As a result, regardless of the solubility of hydrogen in water, the contact efficiency between the gaseous starting materials (hydrogen and carbon dioxide) and the solid methane-producing bacteria, or the contact efficiency between the gaseous starting materials and the liquid in which the methane-producing bacteria are dispersed can be increased. As a result, without changing the conditions related to the progress of the anaerobic treatment, the reaction efficiency related to methane generation by methane-producing bacteria is improved, and the methane yield can be improved.

[0059] [Second Embodiment] FIG. 3 is a schematic explanatory view of the methane generation device 1B according to the second embodiment of the present invention. The methane generation device 1B in the present embodiment is different in the arrangement of the hydrogen supply unit 5 and the methane recovery unit 6 in the methane generation device 1A shown in the first embodiment. Among the configurations of the methane generation device 1B in the present embodiment, the description of the configurations that are the same as those of the methane generation device 1A in the first embodiment will be omitted.

[0060] As shown in FIG. 3, in the methane generation device 1B in the present embodiment, the carbon dioxide supply unit 4 is connected to the lower part of the anaerobic treatment tank 2 in the same manner as the methane generation device 1A, while the hydrogen supply unit 5 is connected to the upper part of the anaerobic treatment tank 2, and the methane recovery unit 6 is provided in the central part of the anaerobic treatment tank 2.

[0061] As one of the chemical properties of hydrogen, it has a very low density (about 0.09 g / cm 3 , 1 atm·0 °C). On the other hand, the density of carbon dioxide is about 1.98 g / cm 3 (1 atm·0 °C), and the density of methane is about 0.72 g / cm 3 (1 atm·0 °C) is known. The methane generation device 1B in this embodiment utilizes the fact that the densities of the gaseous starting materials (hydrogen and carbon dioxide) and the product gas (methane) are different to improve the gas-solid contact (or gas-liquid contact between the starting materials and liquid S) efficiency between the starting materials and the methane-producing bacteria, and to improve the recovery efficiency of the product gas.

[0062] Referring to FIG. 3, the operation of the methane generation device 1B related to methane generation will be described below. Also in the methane generation device 1B in this embodiment, similar to the above-described methane generation device 1A, a carbon dioxide supply step, a hydrogen supply step, and a circulation step are performed. That is, the starting materials (carbon dioxide and hydrogen) are supplied to the anaerobic treatment tank 2 containing the liquid S containing methane-producing bacteria via the carbon dioxide supply unit 4 and the hydrogen supply unit 5, and the liquid S is recovered from below the anaerobic treatment tank 2 via the liquid recovery unit 31 of the circulation unit 3 and supplied (dropped) from above the anaerobic treatment tank 2 via the liquid supply unit 34 of the circulation unit 3. Then, the liquid S in which carbon dioxide is present (dissolved) together with the methane-producing bacteria is dropped from above the anaerobic treatment tank 2 via the liquid supply unit 34 of the circulation unit 3 and comes into contact with the hydrogen introduced into the anaerobic treatment tank 2. The point that methane generation by the methane-producing bacteria using carbon dioxide and hydrogen as starting materials proceeds due to this gas-solid (gas-liquid) contact is the same as the operation in the above-described methane generation device 1A.

[0063] At this time, in the methane generation device 1B in this embodiment, the carbon dioxide supply unit 4 is connected to the lower part of the anaerobic treatment tank 2. As a result, carbon dioxide (CO2), which has a high density and high solubility in water, is introduced from the lower part of the anaerobic treatment tank 2, so that the contact efficiency with the liquid S stored at the bottom of the anaerobic treatment tank 2 can be increased. On the other hand, the hydrogen supply unit 5 is connected to the upper part of the anaerobic treatment tank 2. As a result, hydrogen (H2), which has a low density and low solubility in water, is introduced from the upper part of the anaerobic treatment tank 2. Therefore, hydrogen does not move through the entire anaerobic treatment tank 2 but remains in the upper part of the anaerobic treatment tank 2, and the abundance of hydrogen becomes relatively large in the upper part of the anaerobic treatment tank 2. Accordingly, in the upper part of the anaerobic treatment tank 2, the contact efficiency between the liquid S supplied (dropped) from the upper part of the anaerobic treatment tank 2 via the liquid supply unit 34 and hydrogen can be increased.

[0064] Furthermore, methane, which is a product substance with a density between that of hydrogen and carbon dioxide, is recovered from the methane recovery unit 6 provided in the central part of the anaerobic treatment tank 2. In the methane generation device 1B in the present embodiment, since hydrogen gas with a low density and carbon dioxide gas with a high density mainly exist in the upper and lower parts of the anaerobic treatment tank 2, respectively, the mixing of the starting substances, hydrogen gas and carbon dioxide gas, is suppressed in the methane recovery unit 6 provided in the central part of the anaerobic treatment tank 2, and methane with high purity and concentration can be recovered. Note that the position where the methane recovery unit 6 of the present embodiment is provided is not limited to the central part of the anaerobic treatment tank 2 as shown in FIG. 3. The methane recovery unit 6 of the present embodiment may be provided at a position where the mixing of hydrogen gas and carbon dioxide gas is suppressed. More specifically, the methane recovery unit 6 can be arranged at any position between the arrangement position (carbon dioxide supply position) of the carbon dioxide supply unit 4 and the arrangement position (hydrogen supply position) of the hydrogen supply unit 5 with respect to the anaerobic treatment tank 2.

[0065] As described above, the methane generation device 1B in the present embodiment can improve the contact efficiency between the starting substances and the methane-producing bacteria by taking advantage of the fact that the densities of the gases of the starting substances (hydrogen and carbon dioxide) and the product substance (methane) are different, in addition to improving the methane yield by circulating the liquid S containing methane-producing bacteria in the anaerobic treatment tank 2. Furthermore, high-purity and high-concentration methane can be recovered.

[0066] Note that the above-described embodiments show examples of the methane generation device and the methane generation method. The methane generation device and the methane generation method according to the present invention are not limited to the above-described embodiments, and the methane generation device and the methane generation method according to the above-described embodiments may be modified without changing the gist described in the claims.

Industrial Applicability

[0067] The methane generation device and the methane generation method of the present invention are suitably used as technologies related to methane generation useful as an energy source. In particular, as a technology for generating methane while consuming carbon dioxide, it is suitably used for efforts towards decarbonization.

Explanation of Signs

[0068] 1A, 1B Methane generation device, 2 Anaerobic treatment tank, 3 Circulation unit, 31 Liquid recovery unit, 31a Discharge port, 31b Recovery pipe, 32 Transfer pipe, 33 Pump, 34 Liquid supply unit, 341 Overflow weir, 341a Overflow part, 341b Waterway, 341c Protrusion, 342 Liquid receiving tank, 343 Liquid supply pipe, 4 Carbon dioxide supply unit, 41 Pipe, 5 Hydrogen supply unit, 51 Pipe, 6 Methane recovery unit, 61 Pipe, P Filling material, S Liquid containing methane-producing bacteria

Claims

1. An anaerobic treatment tank, a circulation section for circulating a liquid containing methane-producing bacteria in the anaerobic treatment tank, a carbon dioxide supply section, and a hydrogen supply section, and in the circulation section, the liquid containing methane-producing bacteria is recovered from the lower part of the anaerobic treatment tank and supplied from the upper part of the anaerobic treatment tank to circulate the inside of the anaerobic treatment tank. A methane generation device characterized by this.

2. The anaerobic treatment tank is characterized in that a filler is accommodated. The methane generation device according to Claim 1.

3. The carbon dioxide supply section and the hydrogen supply section are connected to the lower part of the anaerobic treatment tank, and a methane recovery section for recovering the generated methane is provided in the upper part of the anaerobic treatment tank. The methane generation device according to Claim 1 or 2, characterized by this.

4. The hydrogen supply section is connected to the upper part of the anaerobic treatment tank, the carbon dioxide supply section is connected to the lower part of the anaerobic treatment tank, and a methane recovery section for recovering the generated methane is provided in the central part of the anaerobic treatment tank. The methane generation device according to Claim 1 or 2, characterized by this.

5. A methane generation method using an anaerobic treatment tank, comprising: a circulation step of circulating a liquid containing methane-producing bacteria in the anaerobic treatment tank, a carbon dioxide supply step, and a hydrogen supply step, and in the circulation step, the liquid containing methane-producing bacteria is recovered from the lower part of the anaerobic treatment tank and supplied from the upper part of the anaerobic treatment tank to circulate the inside of the anaerobic treatment tank. A methane generation method characterized by this.

Images