Independent power supply small-sized methane fermentation treatment system

Abstract

To provide a methane fermentation treatment system that can be downsized, and can efficiently perform methane fermentation treatment, while saving energy during operation.SOLUTION: The methane fermentation treatment system according to one embodiment, which ferments organic waste in fermentation tanks 3 and 4, comprises a biogas hot-water supply device 9 that warms water using biogas generated by fermenting the organic waste, water flow stirring means that stirs fermentation liquid by water flow, a natural energy generator, and a power storage battery that stores electric power energy generated by the natural energy generator, and further comprises an independent power supply control unit that can supply all energy that is required in the methane fermentation treatment, from internal energy constituted of natural energy and the biogas.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a methane fermentation treatment system. More specifically, it relates to a methane fermentation treatment system that is small-sized and operable with an independent power source.

Background Art

[0002] Conventionally, organic waste including food waste from households and the like has been incinerated or landfilled. Incineration requires a large amount of energy, and carbon dioxide is generated during incineration. From the perspective of environmental problems, methods for effective utilization other than incineration are required.

[0003] One method for the effective utilization of organic waste is methane fermentation treatment. Methane fermentation treatment decomposes organic substances by various microorganisms including methane bacteria to produce biogas and methane fermentation digestate. Biogas contains a high concentration of methane gas and has attracted attention as a non-depletable renewable energy. In addition, since methane fermentation digestate has the characteristic of containing a large amount of fertilizer components, it is expected to be effectively utilized as a fertilizer substitute.

[0004] Generally, the popular methane fermentation treatment apparatus is a large-scale methane fermentation treatment facility. Although large-scale methane fermentation treatment facilities can treat a large amount of organic waste, in order to collect it from a wide area, CO 2 generated during collection is a problem. In addition, securing a use destination for a large amount of digestate is also a problem. When agricultural land use or the like is not possible, it is necessary to perform wastewater treatment. Then, it also incurs costs and has a large environmental load.

[0005] In recent years, there has been an increasing demand to process organic waste generated in a region locally and effectively utilize the generated energy and digested liquid locally, and the development of small-scale methane fermentation treatment facilities has been underway. Compared with large-scale devices, small-scale methane fermentation treatment facilities tend to have higher construction and operation costs per unit of processing capacity. In addition, since methane fermentation treatment facilities are equipped with crushers, pumps, agitators, heating devices, etc., energy is required for operation. Therefore, in order to promote the spread of small-scale methane fermentation treatment facilities, a more energy-saving methane fermentation treatment system is required, and research and development are underway.

[0006] For example, Patent Document 1 describes a method of stirring the inside of a fermentation tank by blowing the gas generated in the fermentation tank into the liquid based on the principle of a siphon. Patent Document 2 describes a method of generating a liquid level difference by utilizing the pressure of biogas in an upstream fermentation tank and a downstream fermentation tank and stirring and transferring the fermentation liquid through a communication pipe. Patent Document 3 describes a system for comprehensively utilizing renewable energy by improving the power generation efficiency of a solar power generation device, using the warm wastewater used for cooling the solar power generation device as a heating source for a methane fermentation tank, and anaerobically fermenting the biomass cultivated underground of the solar power generation device to generate methane.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, although Patent Document 1 performs stirring using the gas generated in the fermentation tank, it has a structure with a plurality of liquid suction pipes in the fermentation broth. Since it is necessary to suck up the fermentation broth without power from the bottom of the fermentation broth containing solids for stirring the fermentation broth, it is necessary to make the liquid suction pipes thin, resulting in poor stirring efficiency and not being suitable for small-scale methane fermentation treatment. Patent Document 2 also performs stirring using the generated gas, but a high fermentation tank is required to create a water level difference, necessitating an increase in the size of the apparatus. In addition, since a large pressure is applied, it is necessary to have a structure that can withstand that pressure, and there is also the problem of increased construction costs. Patent Document 3 is a system for the combined utilization of renewable energy, but there are restrictions on the installation location and a large area of land suitable for biomass cultivation is required, so it cannot be considered a small-scale system. Thus, although there is a method of stirring the fermentation broth using non-powered means, for example, the generated biogas, there is currently no system suitable for small-scale methane fermentation treatment.

[0009] In addition, if it is possible to minimize the energy during operation, including the stirring power, without requiring an external power source, it can be installed even in places where it is difficult to secure an external power source, and it is expected that the popularization of small-scale methane fermentation treatment devices will progress.

[0010] Therefore, an object of the present invention is to provide a methane fermentation treatment system that can efficiently perform methane fermentation treatment while reducing the energy during operation and can be miniaturized. Another object of the present invention is to provide a methane fermentation treatment system provided with stirring means useful for miniaturization while reducing the energy during operation.

Means for Solving the Problems

[0011] As a result of discretionary studies to achieve the above object, the inventors of the present invention have realized energy savings in operation by using a methane fermentation treatment facility equipped with a hot water supply facility that does not use a heater, such as stirring by gas dissolution, water flow stirring, and have found that methane fermentation treatment can be performed without external energy by using methane gas generated by methane fermentation treatment and natural energy. The present invention has been completed based on these findings.

[0012] One embodiment of the present invention is a methane fermentation treatment system for fermenting organic waste in a fermentation tank, a biogas hot water supply device that heats water using biogas generated by fermentation of organic waste, a water flow stirring means that stirs the fermentation broth by water flow, a natural energy power generation device, and a storage battery that stores electric energy generated by the natural energy power generation device, and provides a methane fermentation treatment system including an independent power supply control unit capable of supplying all the energy required for methane fermentation treatment from natural energy and internal energy from the biogas.

[0013] Hot water is used for heating the fermentation tank and the like. In the above-described embodiment, a biogas water heater that heats water using biogas generated by the fermentation of organic waste is provided, and the above-described hot water can be produced by the biogas water heater. Further, in the above-described embodiment, a natural energy power generation device and a storage battery that stores the electric energy generated by the natural energy power generation device are provided. Thereby, the electric energy generated by the natural energy power generation device or stored in the storage battery can be used as the power for the pump used for feeding the fermentation liquid and the like. Further, by providing a water flow stirring means, the fermentation liquid can be stirred with no power or minimal power. And by providing an independent power supply control unit capable of supplying all the energy required for the methane fermentation treatment from the natural energy and the internal energy by the above-described biogas, the above-described methane fermentation treatment system can be operated without using external power. According to such an embodiment of the present invention, it is possible to provide a methane fermentation treatment system that can efficiently perform methane fermentation treatment while reducing energy during operation and can be miniaturized.

[0014] Another embodiment of the present invention is a methane fermentation treatment system for fermenting organic waste in a fermentation tank, A gas dissolution stirring means is provided that increases the fluidity of the fermentation liquid by dissolving biogas generated by the fermentation of organic waste in the fermentation liquid by increasing the internal pressure in the fermentation tank, releasing the pressure when it reaches an arbitrary pressure or higher, vaporizing the biogas dissolved in the fermentation liquid, and allowing the vaporized biogas to diffuse and / or float in the fermentation liquid, thereby providing a methane fermentation treatment system.

[0015] In the above gas dissolution stirring means, biogas generated by the fermentation of organic waste is dissolved in the fermentation liquid by increasing the internal pressure in the fermentation tank, and when the pressure reaches a certain level or higher, the pressure is released. As a result, the biogas dissolved in the fermentation liquid is vaporized, and the vaporized biogas diffuses and / or rises in the fermentation liquid, thereby stirring the fermentation liquid. According to such gas dissolution stirring means, the stirring of the fermentation liquid can be carried out with no power or minimal power, and a methane fermentation treatment system equipped with a stirring means useful for miniaturization can be provided while reducing the energy during operation.

[0016] Still another embodiment of the present invention is a methane fermentation treatment system for introducing organic waste from an input tank into a fermentation tank and fermenting the organic waste in the fermentation tank, A methane fermentation treatment system is provided, which includes a water flow stirring means for stirring the fermentation liquid by water flow as described in the following (i) and / or (ii). In addition, it is preferable to include the above water flow stirring means also in embodiments other than this embodiment. (i) Means for returning the fermentation liquid from the fermentation tank to the input tank to stir the fermentation liquid by water flow (ii) Means for stirring the fermentation liquid in at least one fermentation tank by the water level difference between a plurality of fermentation tanks connected by a communication pipe

[0017] In the above water flow stirring means, the fermentation liquid can be stirred by utilizing the water flow generated by transferring liquid between the input tank and the fermentation tank, or between a plurality of fermentation tanks. According to such water flow stirring means, the stirring of the fermentation liquid can be carried out with no power or minimal power, and a methane fermentation treatment system equipped with a stirring means useful for miniaturization can be provided while reducing the energy during operation.

[0018] The above methane fermentation treatment system includes the water flow stirring means of (i) above, and connects the input tank and the fermentation tank with an input line and a return line via a return valve, It is preferable to introduce the above-mentioned organic waste into the above-mentioned input tank, and to generate the above-mentioned water flow and perform the water flow stirring by opening the above-mentioned return valve and returning the fermentation liquid in the above-mentioned fermentation tank to the above-mentioned input tank through the above-mentioned return line.

[0019] The above-mentioned methane fermentation treatment system may be provided with the above-mentioned (ii) water flow stirring means. In this case, the plurality of fermentation tanks include a first fermentation tank connected to the above-mentioned input tank by an input line, and a second fermentation tank located downstream of the above-mentioned first fermentation tank. Connect the above-mentioned input tank and the above-mentioned second fermentation tank with a return line via a return valve. When the above-mentioned return valve is opened and the fermentation liquid in the above-mentioned second fermentation tank is returned to the above-mentioned input tank through the above-mentioned return line, and when the volume of the fermentation liquid in the above-mentioned input tank reaches an arbitrary value due to the above-mentioned return, the above-mentioned organic waste is introduced from the above-mentioned input tank to the above-mentioned first fermentation tank through the above-mentioned input line, so that it is preferable to generate the above-mentioned water level difference among the above-mentioned input tank, the above-mentioned first fermentation tank, and the above-mentioned second fermentation tank and perform the above-mentioned water flow stirring.

[0020] It is preferable that the discharge port of the above-mentioned input line in the fermentation tank connected to the above-mentioned input tank via the above-mentioned input line is installed in the fermentation liquid in the above-mentioned fermentation tank.

[0021] The above-mentioned input line is provided with a siphon break function for preventing the siphon phenomenon, and it is preferable that the above-mentioned siphon break function uses the biogas generated by the fermentation of the above-mentioned organic waste.

[0022] The above-mentioned methane fermentation treatment system includes a gas holder for storing the biogas generated by the fermentation of the above-mentioned organic waste, and a gas line for transferring the above-mentioned biogas in the above-mentioned fermentation tank to the above-mentioned gas holder. It is preferable to provide an automatic on-off valve on the above-mentioned gas line.

[0023] Preferably, the methane fermentation treatment system is provided with an automatic control means such that the automatic on-off valve closes when the pressure in the fermentation tank is less than 10 kPa and opens when the pressure becomes 10 kPa or more.

[0024] Preferably, the methane fermentation treatment system includes an internal pressure increase period in which the biogas stored in the gas holder is transferred to the gas phase portion in the fermentation tank to increase the internal pressure of the fermentation tank.

[0025] Preferably, the methane fermentation treatment system is provided with a solar heat water heater that heats water by solar heat to produce hot water, and the hot water is supplied to a hot water pipe to heat the fermentation tank.

[0026] Preferably, the methane fermentation treatment system is provided with a foreign matter removal device for removing hardly decomposable solids.

[0027] Preferably, hot water heated by the biogas water heater is supplied to a hot water pipe to heat the fermentation tank.

[0028] Preferably, the methane fermentation treatment system includes a plurality of fermentation tanks connected by a communication pipe, and the water flow stirring means stirs the fermentation liquid in at least one fermentation tank by the water level difference between the plurality of fermentation tanks.

[0029] Preferably, the electric energy stored in the storage battery is used as the energy of one or more systems selected from the group consisting of a pump, a crusher, and an electronic control system of the methane fermentation treatment system.

Advantages of the Invention

[0030] According to the methane fermentation treatment system of the present invention, methane fermentation treatment can be efficiently performed while reducing energy during operation, and miniaturization is possible. Further, according to another methane fermentation treatment system of the present invention, energy during operation is reduced, which is useful for miniaturization.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0032] [Methane Fermentation Treatment System] Figure 1 is a diagram schematically showing the basic configuration of the methane fermentation treatment system according to an embodiment of the present invention. As shown in Figure 1, the methane fermentation treatment system according to an embodiment of the present invention includes a water tank 1, an input tank 2, a first fermentation tank 3, a second fermentation tank 4, a liquid fertilizer tank 5, a first gas holder 6, a second gas holder 7, a solar thermal water heater 8, a biogas water heater 9, a hot water tank 10, and a crusher 11. In addition, a foreign matter removal device, a gas purification device, a natural energy power generation device, a biogas power generation device, and a storage battery may be provided.

[0033] Conventionally, a large amount of energy was required to perform methane fermentation treatment with a small-sized device. However, according to the methane fermentation treatment system of the present invention, by using hot water made from biogas with a water heater or hot water produced by a solar hot water device for heating the fermentation tank, a heater is not required, and a stirrer is not required by gas dissolution stirring or water flow stirring with biogas. Thus, it is possible to perform methane fermentation treatment with energy savings. In addition, other power is supplied from natural energy, and since an external power source is not required, it is possible to minimize the running cost and the limitation of the installation location. For this reason, the methane fermentation treatment system of the present invention is preferably small-sized. In this specification, a small-sized methane fermentation treatment system means that the total volume of the fermentation tank is 5 m 3 refers to the following.

[0034] First, the organic waste 12 is put into the crusher 11. Here, the organic waste refers to things that can be easily decomposed by microorganisms, such as food waste from homes, food residues from schools and workplaces, food factory waste, manure waste, sewage sludge, biodegradable plastics, etc. The input organic waste is put into the input tank 2 through the crusher 11. The size of the crushed organic waste is not particularly limited, but is preferably 10 mm or less. From the viewpoint of being easily decomposed in the fermentation tank, it is more preferably 5 mm or less. The crusher 11 is preferably a hammer type. If it is a hammer type, there is an advantage that the risk of clogging with fibrous materials is low and it is difficult to bite.

[0035] The shredded organic waste is mixed with water pumped from the water tank 1 by a pump (feed water pump) P1 and sent through the pipe 13 to the input tank 2 for storage. When being shredded by the shredder 11, water from the water tank 1 is also fed into the shredder 11 to improve the transferability. The volume ratio of the organic waste to water is not particularly limited, but about 1:1 is preferred. The water supply may be directly fed into the shredding chamber of the shredder 11 or fed from the inlet. It can be automatic or manual. By supplying water simultaneously with shredding, the load on the shredder 11 can be reduced. After shredding, the inner diameter of the pipe 13 when sending to the input tank 2 is not particularly limited, but it is preferably 50 mm or more. If it is smaller than 50 mm, the shredded organic waste may get clogged. The shorter the pipe length, the better. If it is long, a large amount of water is required to transfer the organic waste. To absorb the vibration of the shredder, the material of the pipe is preferably a material that is easy to absorb vibration. To improve the transferability, it is preferable that there are no protrusions inside the pipe 13.

[0036] A liquid level sensor may be provided in the input tank 2. Examples of the liquid level sensor include ultrasonic type, electrode type, pressure type, etc. The ultrasonic type is desirable in that it is not affected by impurities.

[0037] The mixture of organic waste and water stored in the input tank 2 is fed into the first fermentation tank 3 through the input line 14 by the pump P2. Also, the above mixture may be fed into the second fermentation tank 4 located downstream of the first fermentation tank 3 through the input line 14 by the pump P2. For example, the above mixture may be basically fed from the input tank 2 into the first fermentation tank 3 by the pump P2, and periodically fed into the second fermentation tank 4. By doing so, when scum has formed in the upper layer of the second fermentation tank 4, the scum can be broken by the impact of the input of organic waste. If scum forms in the upper layer of the second fermentation tank 4, clogging of the pipes of the liquid fertilizer tank 5 may occur. For example, the path change valve 30 may be periodically switched by a time switch or the like, and the specification may be such that the transfer destination of the above mixture can be switched between the first fermentation tank and the second fermentation tank. The timing and frequency of feeding the above mixture into the second fermentation tank 4 are not particularly limited and can be appropriately set according to the situation.

[0038] The pump P2 is preferably a pump suitable for pumping a liquid with a high solid content. If the suction port is in contact with the bottom surface, the settled organic waste is likely to clog, so it is preferable that the suction port is 5 cm or more higher than the bottom surface. When the organic waste in the input tank 2 is fed into the fermentation tank by the pump P2, the height of the liquid level in the input tank 2 may be set to an arbitrary value such that the pump P2 does not suck in air. The input tank 2 is designed such that gas flows in together with the organic waste through the crusher 11, but by making the pump P2 not suck in air, all the fermentation tanks and the like after the input line 14 can be kept anaerobic, and efficient methane fermentation can be carried out. The organic waste transferred through the input line 14 is fed into the first fermentation tank 3.

[0039] The discharge port of the input line 14 is installed in the fermentation liquid (inside the fermentation liquid phase) in the transferred fermentation tank (for example, the first fermentation tank 3). If the discharge port is above the liquid level of the fermentation liquid, the organic waste transferred by the pump P2 will strike the liquid surface, the flow rate will weaken, and the effect of stirring the fermentation liquid by the water flow will be reduced. On the other hand, by installing the discharge port inside the fermentation liquid phase, the effect of water flow stirring can be further enhanced. Further, in order to enhance the effect of water flow stirring, it is preferable that the discharge port is near the center in the fermentation tank in terms of stirring the fermentation liquid.

[0040] The input line 14 is provided with a siphon break function (siphon break structure) for preventing the siphon phenomenon. The siphon break structure is, for example, one in which the input line 14 and the gas header 20 after desulfurization are connected via a check valve. The siphon break function can use the biogas generated by the fermentation of the organic waste. Due to the siphon break function, when the liquid feeding by the pump P2 is completed, the inside of the pipe changes from positive pressure to negative pressure, and the biogas is drawn in to break the siphon. By using biogas for siphon break, the anaerobic property of the methane fermentation treatment system can be maintained.

[0041] The fermentation tank may be provided with only one or a plurality (multi-tank fermentation tank). In FIG. 1, the fermentation tank is composed of a first fermentation tank 3 and a second fermentation tank 4. The fermentation tank preferably has a multi-tank type including a first tank (for example, the first fermentation tank 3) for decomposing coarse organic substances and a second tank or more (for example, the second fermentation tank 4) for decomposing the fine organic substances decomposed in the first tank. In the case of a multi-tank fermentation tank, the plurality of fermentation tanks may be arranged in series (for example, an arrangement in which the above mixture can be input from the input tank 2 to the first fermentation tank 3 and transferred from the first fermentation tank 3 to the second fermentation tank 4), or may be arranged in parallel (for example, an arrangement in which the above mixture can be input from the input tank 2 to both the first fermentation tank 3 and the second fermentation tank 4), or a combination of these.

[0042] In the case of a multi-tank fermentation tank, consecutive fermentation tanks, for example, the first fermentation tank and the second fermentation tank, are connected by a communication pipe. Specifically, for example, the first fermentation tank 3 and the second fermentation tank 4 are connected by communication pipes 16 and 17. The organic waste introduced through the input line 14 is transferred from the first fermentation tank 3 to the second fermentation tank 4 through the communication pipes 16 and 17. In order to more effectively exert the water flow stirring effect due to the water level difference, it is preferable that there is one such communication pipe, but two or more are also acceptable and are not particularly limited.

[0043] In the first fermentation tank 3 and the second fermentation tank 4, the organic waste is decomposed and biogas is generated. The biogas generated in fermentation tanks such as the first fermentation tank 3 and the second fermentation tank 4 is sent to the gas header 20 through the gas lines 18 and 19 and stored in the first gas holder 6 and the second gas holder 7. When the biogas passes between the gas lines 18 and 19 and the gas header 20, it may be passed through a condensation tower and a desulfurizing agent to remove water and sulfur components. There may be only one gas holder, or there may be a plurality of them, and they can be appropriately set according to the amount of biogas to be stored.

[0044] It is preferable that the input tank and the fermentation tank are provided with a return line for returning the fermentation liquid from the fermentation tank to the input tank. For example, when the crusher is operated, the return valve of the return line connecting the input tank and the fermentation tank opens, and the fermentation liquid in the fermentation tank is returned to the input tank. When the operation of the crusher is completed and the volume in the input tank reaches an arbitrary value, the pump installed in the input tank operates, and the organic waste is introduced from the input tank to the fermentation tank through the input line. In this example, an example is given in which the crusher 11 and the return valve 31 are interlocked to automatically open and close the return valve 31, but it is not limited to such a mode. For example, the weight of the input tank may be detected and interlocked with the return valve, or the water level of the input tank may be detected and interlocked with the return valve, or other sensing may be interlocked with the return valve. In this way, by returning from the fermentation tank to the input tank and introducing from the input tank to the fermentation tank, water flow stirring can be implemented, and the stirrer in the fermentation tank can be made unnecessary.

[0045] Also, for example, when the volume of the fermentation broth is large, or when it is necessary to further enhance the water flow stirring effect, the fermentation tank may be made into a multi-tank type with two or more tanks, and a plurality of fermentation tanks may be connected by a communication pipe. For example, when there are two fermentation tanks as shown in FIG. 1, the charging tank 2 and the second fermentation tank 4 are provided with a return line 15 for returning the fermentation broth from the second fermentation tank 4 to the charging tank 2. When the organic waste is charged and the crusher 11 is operated, the return valve 31 of the return line 15 connecting the charging tank 2 and the second fermentation tank 4 opens, and the fermentation broth in the second fermentation tank 4 is returned to the charging tank 2. When the operation of the crusher 11 is completed, the return valve 31 closes and the return ends. During the return, the water level difference between the first fermentation tank 3 and the second fermentation tank 4 occurs due to the decrease in the fermentation broth in the second fermentation tank 4. When the volume in the charging tank 2 reaches an arbitrary value due to the return from the second fermentation tank 4, the pump P2 in the charging tank 2 operates, and the organic waste is charged from the charging tank 2 to the first fermentation tank 3 through the charging line 14. When the organic waste is charged into the first fermentation tank 3, a further water level difference occurs between the first fermentation tank 3 and the second fermentation tank 4. Due to the water level difference, the fermentation broth in the first fermentation tank 3 is vigorously transferred to the second fermentation tank 4 through the communication pipes 16 and 17, and the fermentation broth is stirred. The connection position of at least one communication pipe (for example, the communication pipe 16) is preferably at the lower part of the first fermentation tank 3 and the second fermentation tank 4. By connecting to the lower part of the fermentation tank, the flow rate of the fermentation broth transferred from the first fermentation tank 3 to the second fermentation tank 4 increases, and the stirring effect can be enhanced. Also in this case, the example of interlocking the crusher 11 and the return valve 31 to automatically open and close the return valve 31 is not limited, and various sensings and the return valve may be interlocked.

[0046] In this way, due to the return from the second fermentation tank 4 to the charging tank 2 and the charging from the charging tank 2 to the first fermentation tank 3, the fermentation broth is transferred from the first fermentation tank 3 to the second fermentation tank 4 through the communication pipes 16 and 17, and in both the first fermentation tank 3 and the second fermentation tank 4, the fermentation broth inside the fermentation tank can be stirred by the water flow. Also, by performing the water flow stirring due to the above-mentioned water level difference, the stirring effect can be further enhanced, and the fermentation broth can be stirred without installing a stirrer in the fermentation tank. Therefore, a power-saving system that does not require a stirrer can be realized.

[0047] The methane treatment fermentation system according to an embodiment of the present invention includes a water flow stirring means for stirring the fermentation broth by water flow. As the above water flow stirring means, for example, as described above, (i) means for returning the fermentation broth from the fermentation tank to the input tank to stir the fermentation broth by water flow, (ii) a plurality of fermentation tanks connected by a communication pipe, and means for stirring the fermentation broth in at least one fermentation tank by the water level difference of the plurality of fermentation tanks.

[0048] When the above fermentation tank is a single tank, it is preferable to provide the water flow stirring means of (i) above. In the above (i), it is preferable that the input tank and the fermentation tank are connected by an input line and a return line via a return valve. By having such a structure, by returning the organic waste to the input tank, the return valve opens and the fermentation broth in the fermentation tank is returned to the input tank through the return line. Then, by the return of the fermentation broth and the input of the organic waste, a water flow can be generated to perform water flow stirring.

[0049] When the above fermentation tank is a multi-tank type including a plurality of fermentation tanks, it is preferable to provide the water flow stirring means of (ii) above, and it is more preferable to provide both the water flow stirring means of (i) and (ii). Referring to FIG. 1 for explanation, in the above (ii), the plurality of fermentation tanks include an input tank 2, a first fermentation tank 3 connected by an input line 14, and a second fermentation tank 4 which is a fermentation tank located downstream of the first fermentation tank 3. The input tank 2 and the second fermentation tank 4 are connected by a return line 15 via a return valve 31. Then, by sensing such as operating the crusher 11, the return valve 31 opens and the fermentation broth in the second fermentation tank 4 is returned to the input tank 2 through the return line 15. When the volume of the fermentation broth in the input tank 2 reaches an arbitrary value due to this return, the organic waste is input from the input tank 2 to the first fermentation tank 3 through the input line 14. Thereby, a water level difference can be generated among the input tank 2, the first fermentation tank 3, and the second fermentation tank 4 to perform water flow stirring.

[0050] The connection mode between the fermentation tank and the gas holder is not particularly limited, and it may be the mode shown in Fig. 1 or the mode shown in Fig. 2. Fig. 1 is a flow diagram of a methane fermentation treatment system including the connection form between the fermentation tank and the gas holder when the gas dissolution stirring means is not implemented, and Fig. 2 is a flow diagram of a methane fermentation treatment system including the connection form between the fermentation tank and the gas holder when the gas dissolution stirring means is implemented.

[0051] In the embodiment shown in Fig. 2, the first fermentation tank 3 and the second fermentation tank 4 are connected to the first gas holder 6 via the gas line G1. On the gas line G1, there are a pressure gauge and an automatic on-off valve 22. Also, the first fermentation tank 3 and the second fermentation tank 4 are connected to the second gas holder 7 via the gas line G2. On the gas line G2, there is an automatic on-off valve 21. Further, the first fermentation tank 3 and the second fermentation tank 4 are connected to the second gas holder 7 via the gas line G3 from a branch in front of the automatic on-off valve 21 on the gas line G2. On the gas line G3, there are an automatic on-off valve 24 and a pump P4. Also, the gas line G1 and the gas line G2 are connected via the gas line G4. The gas line G4 connects a branch point located between the automatic on-off valve 22 on the gas line G1 and the gas header 20 and a branch point located between the automatic on-off valve 21 on the gas line G2 and the point where it branches into the gas line G3. On the gas line G4, there are a pressure regulating valve 23 and an automatic on-off valve 29.

[0052] The gas line G1 is a gas line used when filling the first gas holder 6 with gas from the first fermentation tank 3 and the second fermentation tank 4 (for example, during the period of input of organic waste described later). The gas line G3 is a gas line used when transferring gas from the second gas holder 7 to the gas phase part of the first fermentation tank 3 and the second fermentation tank 4 (for example, the gas dissolution stirring means described later). The gas line G4 is a gas line for transferring surplus gas that has not been transferred to the gas phase part to the first gas holder 6 when transferring gas from the second gas holder 7 to the gas phase part of the first fermentation tank 3 and the second fermentation tank 4. The gas line G2 is a gas line used when filling the second gas holder 7 with gas dissolved in the gas phase gas and the fermentation liquid of the first fermentation tank 3 and the second fermentation tank 4.

[0053] The flow diagram of the gas line during the organic waste input period is shown in FIG. 3. As shown in FIG. 3, during the organic waste input period, the automatic on-off valve 21 and the automatic on-off valve 24 are closed, and the automatic on-off valve 22 and the automatic on-off valve 28 are open. Note that the organic waste input period refers to the period when the organic waste is pulverized as needed and input from the input tank 2 into the fermentation tank. The organic waste input period can be appropriately selected according to the management conditions where the methane fermentation treatment system is installed, such as from 9:00 to 18:00. During the organic waste input period, the gas dissolution stirring means is not implemented. The biogas generated at this time is filled into the first gas holder 6 from the first fermentation tank 3 and the second fermentation tank 4 through the gas line G1. Before being filled into the first gas holder 6, the biogas that has been desulfurized and had its moisture removed is filled into the first gas holder 6 through the desulfurization device and the dew condensation tower.

[0054] The methane treatment fermentation system according to an embodiment of the present invention includes gas dissolution stirring means for dissolving the biogas generated by the fermentation of organic waste into the fermentation liquid by increasing the internal pressure in the fermentation tank, releasing the pressure when it reaches a pressure equal to or higher than an arbitrary pressure, vaporizing the biogas dissolved in the fermentation liquid, and increasing the fluidity of the fermentation liquid by the diffusion and / or floating of the vaporized biogas in the fermentation liquid.

[0055] The gas dissolution stirring means is preferably carried out during time periods other than the organic waste input period, for example, at night, but can be appropriately selected according to the management conditions where the methane fermentation treatment system is installed. This is because the input of organic waste increases the internal pressure of the fermentation tank, making it difficult to dissolve biogas into the fermentation liquid.

[0056] The gas dissolution stirring means is composed of an "internal pressure increase period" in which the biogas stored in the gas holder is transferred to the gas phase part in the fermentation tank to increase the internal pressure of the fermentation tank, a "gas dissolution period" in which biogas is generated and the generated biogas is dissolved in the fermentation broth, and a "gas release stirring period" in which the pressure of the fermentation tank is released and the dissolved biogas is instantly gasified to stir the fermentation broth. The gas dissolution stirring means can be implemented, for example, by a configuration consisting of a gas line G2, a gas line G3, a gas line G4, a pressure gauge, an automatic on-off valve 21, an automatic on-off valve 24, an automatic on-off valve 29, a pressure regulating valve 23, a pump P4, and a second gas holder 7. Note that the above internal pressure increase period can be provided to increase the internal pressure in the fermentation tank to a state where gas is easily dissolved, perform gas dissolution, and implement more efficient gas dissolution stirring, and it may not be provided in the above gas dissolution stirring means.

[0057] The implementation flowchart of the gas dissolution stirring means is shown in FIG. 4. First, the "internal pressure rising period" will be described. During the period of inputting organic waste, the automatic on-off valves 21 and 24 are closed, and the automatic on-off valves 22 and 28 are open. However, when the operation of the gas dissolution stirring means is started, as shown in FIG. 4, the automatic on-off valve 22 is closed, the automatic on-off valve 29 is open, the automatic on-off valve 28 is closed, the path change valve 30 is closed, the automatic on-off valve 24 is open, the pump P4 is turned on, and the biogas filled in the second gas holder 7 is filled into the gas phase parts of the first fermentation tank 3 and the second fermentation tank 4 through the gas line G3. The set pressure of the pressure regulating valve 23 connected to the gas line G4 is not particularly limited, but it is preferably set to a value lower than the pressure at which the automatic on-off valve 21 opens. In this case, when the biogas is transferred to the first fermentation tank 3 and the second fermentation tank 4 and the internal pressure of the first fermentation tank 3 and the second fermentation tank 4 increases and the pressure becomes equal to or higher than the above set pressure, the pressure regulating valve 23 opens and the surplus gas is transferred to the first gas holder 6. When the transfer of the gas in the second gas holder 7 is completed, the pump P4 is stopped. The transfer time is estimated from the gas volume in the second gas holder 7 and the flow rate of the pump P4, and the pump P4 is stopped. It is preferable to provide an automatic control means in which the pressure regulating valve 23 is closed when the pressure in the first fermentation tank 3 and the second fermentation tank 4 is lower than the above set pressure and the automatic on-off valve 23 opens when the pressure becomes equal to or higher than the above set pressure. With such a configuration, the above internal pressure rising period can be automatically completed. Note that the set pressure of the pressure regulating valve 23 may be set in a timely manner according to the set pressure at which the automatic on-off valve 21 opens, the capacity of the fermentation liquid and the fermentation tank, the number of times of gas dissolution stirring, etc.

[0058] Next, the "gas dissolution period" will be described. After increasing the internal pressure of the first fermentation tank 3 and the second fermentation tank 4 and completing the transfer of the gas in the second gas holder 7, the automatic on-off valves 29 and 24 are closed. As a result, all the valves connected to the first fermentation tank 3 and the second fermentation tank 4 are closed, and the biogas newly generated from the fermentation liquid dissolves in the fermentation liquid simultaneously with the increase in the internal pressure.

[0059] Next, the "gas release stirring stage" will be described. During the gas dissolution stage, the pressure in the fermentation tank further increases due to the generation of biogas. When the value on the pressure gauge connected to the gas line G1 reaches 10 kPa or more, the automatic on-off valve 21 is opened. Simultaneously with the opening of the automatic on-off valve 21, the gas in the fermentation tank is instantly transferred to the second gas holder 7 via the gas line G2, and the pressure in the first fermentation tank 3 and the second fermentation tank 4 decreases. The biogas dissolved in the fermentation broth gasifies from the entire fermentation broth. Due to the impact of gasification and the rising of the gasified gas in the fermentation broth, the fluidity of the entire fermentation broth increases and stirring occurs. Also, the biogas generated during the gas release stirring stage adheres to the undigested organic matter precipitated at the bottom of the fermentation tank, thereby reducing the specific gravity of the undigested organic matter and causing it to float in the fermentation broth. After floating, when the gas migrates to the gas phase part, the undigested organic matter from which the gas has separated precipitates again at the bottom of the fermentation tank. In this way, by gasifying the dissolved gas through gas release, vertical stirring of the sediment in the fermentation broth occurs, and the stirring effect is further enhanced.

[0060] The pressure when opening the automatic on-off valve 21 is set to 10 - 100 kPa. The above pressure is preferably 20 - 100 kPa, more preferably 30 - 60 kPa. If it is 10 kPa or more, the fermentation broth can be stirred more sufficiently. If it is 30 kPa or more, the entire fermentation broth can be stirred even more sufficiently. Also, if the pressure is increased too much, such as exceeding 100 kPa, the load on the fermentation tank will increase, and there is also a risk that the gas and the fermentation broth will spout out together during gas release. Therefore, 10 - 100 kPa is preferred. It is advisable to select a tank that can withstand this pressure for the fermentation tank.

[0061] In addition, in the gas release stirring period, an example of transferring biogas to the second gas holder 7 through the gas line G2 was shown. Along with this, or instead of this, biogas may be transferred to the first gas holder 6 through the gas line G4 and the gas line G1. When using the gas line G4 and the gas line G1, the automatic on-off valve 29 may be opened. However, since a desulfurization device or the like exists on the gas line G1 connecting the first gas holder 6 and the fermentation tank, for example, when biogas is transferred using the gas line G1 during the gas release stirring period, the gas does not rush into the first gas holder 6 all at once due to the resistance of the desulfurization device or the like, leading to a decrease in the stirring ability due to gas release. Therefore, when using the first gas holder 6 during the gas release stirring period, it is preferable to use it together with the second gas holder 7. The pressure when the automatic on-off valve 29 opens may be the same as the pressure when the automatic on-off valve 21 opens, or may be higher. By using the first gas holder 6 together with the second gas holder 7, the surplus gas that could not fit into the gas holder 7 can be stored in the first gas holder 6.

[0062] After the gasification, floating, and diffusion stirring of biogas are completed by opening the automatic on-off valve 21, close the automatic on-off valve 21. The closing of the automatic on-off valve 21 due to the completion of the gasification, floating, and diffusion stirring of biogas may be performed by time control. The time required for the completion of the gasification, floating, and diffusion stirring of biogas depends on the size of the fermentation tank, the amount of fermentation broth, etc., so it is advisable to confirm in advance and set it to an arbitrary value.

[0063] Close the automatic on-off valve 21, open the automatic on-off valve 24, and shift back to the "internal pressure rising period" again, repeating a series of flows of the "internal pressure rising period", "gas dissolution period", and "gas release stirring period". As shown in FIG. 2, in the gas dissolution stirring means, the gas line connecting the first fermentation tank 3 and the second fermentation tank 4 to the second gas holder 7 is provided with a gas line G2 used in the gas release period and a gas line G3 used in the internal pressure rising period. In the gas release period, it is important to transfer the gas in the fermentation tank to the gas holder all at once to reduce the pressure. By doing so, the dissolved gas in the fermentation broth vigorously vaporizes and the stirring force increases. If the gas line G2 and the gas line G3 are aggregated into one gas line, the momentum of gasification will be weakened due to the resistance of the pump in the gas line, leading to a decrease in the stirring ability. Therefore, the gas line G2 and the gas line G3 are preferably installed separately.

[0064] When switching from the operating period of the gas dissolution stirring means to the organic waste input period, through the gas release stirring period, close the automatic on-off valve 21, close the automatic on-off valve 24, open the automatic on-off valve 22, open the automatic on-off valve 28, and open the path change valve 30. At this time, the gas remains stored in the second gas holder 7, and this gas is used again when increasing the internal pressure of the fermentation tank by the gas dissolution stirring means. Also, when operating the series of gas dissolution stirring means, close the automatic on-off valve 28 of the overflow pipe 25 connecting the fermentation tank and the liquid fertilizer tank 5. This is because if the gas dissolution stirring means is operated with the on-off valve 28 of the overflow pipe 25 open, the fermentation broth will flow out from the overflow pipe 25 as the pressure in the fermentation tank rises. Also, when operating the series of gas dissolution stirring means, close the path change valve (quadruple valve) 30 of the input line 14. This is because if the gas dissolution stirring means is operated with the path change valve 30 of the input line 14 open, the fermentation broth will flow back into the input tank 2 through the input line 14 as the pressure in the fermentation tank rises.

[0065] Incidentally, the biogas filled in the first gas holder 6 can be used in known or conventional utilization methods such as a biogas water heater 9 and a biogas power generation device, etc. from the gas header 20 via the gas line 26 through the gas purification device, as shown in FIGS. 1 and 2. It can also be sent to the siphon break device in the input line 14 via the gas line 27. Further, gas holders other than the first gas holder 6 such as the second gas holder 7, or the biogas filled in a plurality of gas holders may be utilized as described above through a desulfurization device and a dew condensation tower.

[0066] When both the above gas dissolution stirring means and the above water flow stirring means are provided, the fermentation broth can be stirred more sufficiently without installing a stirrer in the fermentation tank, and power saving of the methane fermentation treatment system can be realized.

[0067] The installation heights of the crusher 11, the input tank 2, the first fermentation tank 3, and the second fermentation tank 4 are not particularly limited. However, for leakage prevention, the inlet of the crusher 11 and the input tank 2 are preferably at a height above the liquid levels of the first fermentation tank 3 and the second fermentation tank 4. Small methane fermentation treatment systems often do not have a specific administrator resident like a plant, and it is desirable to have a structure with as little leakage risk as possible.

[0068] The fermentation broth in the fermentation tank is preferably heated to perform optimal methane fermentation. For example, in medium-temperature fermentation, it is desirable to reach 32 to 37°C. The heating can be performed using the circulating water (warm water) heated by the solar hot water device 8 or the biogas water heater 9. The solar hot water device 8 heats water by solar heat to produce warm water. The circulating water (warm water) heated by the solar hot water device 8 or the biogas water heater 9 is stored in the warm water tank 10 and undergoes heat exchange through the warm water pipe (the line indicated by the dotted line in FIGS. 1 and 2) circulated into the fermentation tank from the warm water tank 10. The circulating water after heat exchange returns to the solar hot water device 8 or the biogas water heater 9 again and is heated. The biogas water heater 9 burns the biogas generated by methane fermentation to heat the circulating water.

[0069] Biogas generally consists of approximately 60% methane and approximately 40% carbon dioxide. Methane gas burns, but carbon dioxide does not. Since biogas has a methane concentration of about 60%, it is difficult to burn with currently popular household gas stoves. If carbon dioxide in biogas is removed and the methane concentration is increased, a gas with better combustion efficiency can be obtained. For example, if it is purified to a methane concentration of about 90%, it can burn even with a household gas stove.

[0070] As a method for removing carbon dioxide in biogas, known or commonly used biogas purification methods can be mentioned. Examples of biogas purification methods include passing the gas through an alkaline solution, dissolving carbon dioxide in the alkaline solution, and recovering only the methane gas that did not dissolve. The alkaline solution is not particularly limited, but from the perspective of ease of handling, lime water may be used. When lime water reacts with carbon dioxide, calcium carbonate is produced. The lime water containing this calcium carbonate is preferably used for agricultural land in combination with liquid fertilizer. Other examples of alkaline solutions include potassium hydroxide solution. When potassium hydroxide solution reacts with carbon dioxide, potassium carbonate is produced. This is also preferably used for agricultural land as fertilizer. The percentage to which the methane concentration is purified can be appropriately selected in a timely manner depending on the use of the concentrated gas, such as combustion with a household gas stove, biogas power generation, etc., and the gas-using equipment.

[0071] The secondary fermentation tank 4 and the liquid fertilizer tank 5 are connected by an overflow pipe 25. The fermentation liquid after methane fermentation is stored in the liquid fertilizer tank 5 through the overflow pipe 25. Since this liquid fertilizer contains useful components as fertilizer, it is preferably applied to agricultural land. In recent years, the soaring prices of fertilizer components have also become a problem, and using fertilizers derived from these organic wastes has great advantages not only in terms of environmental issues and resource recycling but also economically.

[0072] A foreign matter removal device may be provided in the return line 15 connecting the second fermentation tank 4 and the charging tank 2. The foreign matters referred to here mean non-biodegradable plastic pieces, seals, and hardly decomposable solids such as seeds and fibrous materials that are not suitable for fermentation (requiring time for fermentation). In particular, fibrous materials, if contained in the fermentation broth, may cause the generation of a scum layer, so they should be removed regularly.

[0073] The foreign matter removal device is not particularly limited, but the return line 15 may be branched and a strainer may be installed on one side. During normal operation, the fermentation broth circulates through the return line 15 where the strainer is not installed. During maintenance, it may be switched so that the fermentation broth passes through the pipe with the strainer installed to remove foreign matters in the fermentation broth.

[0074] Also, an antifoaming agent may be added to the fermentation broth to suppress the generation of the scum layer. In this specification, scum refers to undigested organic matter floating up together with biogas and forming a thick film. By adding the antifoaming agent, the bubbles in the scum are destroyed, preventing the floating of undigested organic matter and promoting the fermentation of undigested organic matter.

[0075] The above methane fermentation treatment system may be equipped with a natural energy power generation device. The electric energy generated by the natural energy power generation device can be used as the power for various devices and means in the above methane fermentation treatment system. Those that consume electric energy in the above methane fermentation treatment system are the crusher 11 for crushing organic waste, the water supply pump P1 installed in the water tank 1, the pump P2 installed in the charging tank 2 for transferring the mixture from the charging tank 2 to the first fermentation tank 3, the pump P3 for transferring hot water from the solar hot water device 8 or the biogas water heating device 9 to the hot water pipe, the pump P4 in the gas dissolution stirring means as shown in Figure 2, and the electronic control system.

[0076] Examples of the natural energy power generation device include known or commonly used devices such as a solar power generation device, a wind power generation device, and a geothermal power generation device. Among them, a solar power generation device is preferable from the viewpoint of being small-sized and capable of generating sufficient electric energy. The solar power generation device may be installed, for example, on the upper part or the wall surface of the methane fermentation treatment system. The size and capacity of the solar power generation device may be appropriately selected by estimating the size of the methane fermentation treatment system and the power consumption amount, etc. When the power consumption amount of the methane fermentation treatment system is large, a large solar power generation device that cannot be installed in the methane fermentation treatment system is required. However, in this methane fermentation treatment system, since the power consumption amount is less than before, the power supply-demand balance can be achieved by power generation by a solar power generation device in the space that can be installed in a small-sized methane fermentation treatment system. Further, since the power generation amount of solar power generation depends on the weather, it is preferable to also provide a storage battery in order to stably supply power to the methane fermentation treatment system. The electric energy stored in the storage battery can be used as the energy of one or more systems selected from the group consisting of a pump, a crusher, and an electronic control system of the methane fermentation treatment system.

[0077] As described above, in this methane fermentation treatment system, the thermal energy for hot water by the solar hot water device 8, the thermal energy for hot water by the biogas water heater 9, the electric energy by the natural energy power generation device, the electric energy by the biogas power generation device, and the biogas generated during methane fermentation are generated as supply energies. All of the energies required for the methane fermentation treatment can be covered by these supply energies. Thus, this methane fermentation treatment system includes an independent power supply control unit capable of supplying all of the energies required for the methane fermentation treatment from the natural energy and the internal energy by the biogas.

Example

[0078] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples in any way.

[0079] Example 1 Fig. 5 shows a flowchart of the methane fermentation treatment system of Example 1. As shown in Fig. 5, the methane fermentation treatment system of Example 1 includes a water tank 1, a crusher 11, a charging tank 2, a first fermentation tank 3, a second fermentation tank 4, a liquid fertilizer tank 5, a first gas holder 6, a biogas water heater 9, a solar power generation device, and a storage battery. In Example 1, the case where food waste discharged from households is treated by a two-tank methane fermentation treatment system will be described.

[0080] The capacities of the first fermentation tank 3 and the second fermentation tank 4 are each 1 m 3 , the daily food waste input capacity is 35 kg / day, and the biogas generation amount when 35 kg of food waste is input per day is 3 m 3 / day. The first fermentation tank 3, the second fermentation tank 4, and the tank for inputting food waste are installed in series, the first gas holder 6 is installed above the fermentation tank, and the biogas water heater 9 is installed on the side of the fermentation tank. The methane fermentation treatment system at this time includes a water tank 1, a crusher 11, a charging tank 2, a first fermentation tank 3, a second fermentation tank 4, a first gas holder 6, a biogas water heater 9, a liquid fertilizer tank 5, a storage battery, pumps and pipes associated therewith, and an electronic control device. Its size is 4,500 mm in width, 2,400 mm in height, and 2,000 mm in depth. It can be said to be a relatively small methane fermentation treatment system among small-scale methane fermentation treatment systems in circulation. This small-scale methane fermentation treatment system was installed in an open space without power supply infrastructure, and food waste was input and subjected to methane fermentation. A stirrer was not installed inside the fermentation tank, and the fermentation liquid was dispersed by the water flow stirring caused by the water level difference by the water flow stirring means of (i) and (ii) above. In addition, the generated biogas was burned to heat water to produce warm water, which was used for heating the fermentation liquid. A solar power generation device was installed on the roof of the small-scale methane fermentation treatment system, and the obtained electric energy was used as energy for the crusher 11 and the like. The size of the solar power generation device is such that it can be placed on the roof of the small-scale methane fermentation treatment system, and the panel size is 3 m 2Those of a certain degree were selected. Since the water flow agitation by the water level difference is a process executed every time food waste is input, assuming the amount of food waste input at one time is about 500 g, it was carried out 70 times a day. By the above water flow agitation, the fermentation broth was sufficiently dispersed, there was no generation of scum or clogging of pipes, etc., and methane fermentation was also carried out without problems, and 3 m 3 of biogas could be produced in 24 hours. When the generated biogas was measured with a gas concentration meter, the methane concentration was 59.5%. The warm water produced by the combustion of biogas was used for heating the fermentation broth, and the temperature of the fermentation broth could be maintained at 35 - 37 °C throughout the day. The amount of electricity generated by solar power generation was 2 kWh, which was used as the energy to operate the crusher and pump, etc. of the methane fermentation treatment system. The daily power supply amount and consumption amount in Example 1 are shown in Table 1.

[0081]

Table 1

[0082] In the methane fermentation treatment system of Example 1, by introducing water flow agitation by the water level difference, the agitator became unnecessary, and by introducing the biogas water heater 9, the heating heater became unnecessary, realizing power saving of the system, and the stable operation of the small methane fermentation treatment system could be realized only with the biogas generated by methane fermentation and the electricity obtained by solar power generation (that is, an independent power source). Due to the power saving of the system, there is an advantage that the scale of the solar power generation panel, which is the power supply source, can be reduced by minimizing the required power consumption. As a result, the initial cost is reduced, and the solar panel can be placed on the roof area of the small methane fermentation treatment system and integrated, contributing to further miniaturization of the device.

[0083] Example 2 Fig. 6 shows a flow diagram of the methane fermentation treatment system of Example 2. As shown in Fig. 6, the methane fermentation treatment system of Example 1 includes a water tank 1, a crusher 11, a charging tank 2, a first fermentation tank 3, a liquid fertilizer tank 5, a first gas holder 6, a second gas holder 7, a biogas water heater 9, a solar power generation device, and a storage battery. In Example 2, the case where food waste discharged from households is treated with a one-tank methane fermentation treatment system will be described.

[0084] The capacity of the first fermentation tank 3 is 1 m 3 , the daily food waste input capacity is 17 kg / day, and the biogas generation amount when 17 kg of food waste is input per day is 1.5 m 3per day. The first fermentation tank 3 and the tank for feeding food waste were installed in series, and the first gas holder 6 was installed above the fermentation tank, and the biogas water heater 9 was installed on the side of the fermentation tank. The methane fermentation treatment system at this time included, in addition to the liquid fertilizer tank, the water tank 1, the crusher 11, the input tank 2, the first fermentation tank 3, the first gas holder 6, the second gas holder 7, the biogas water heater 9, the liquid fertilizer tank 5, the storage battery, the pumps and pipes associated therewith, and the electronic control device. Its size was 3,500 mm in width, 2,400 mm in height, and 1,700 mm in depth, and it could be said to be a considerably small methane fermentation treatment system among the small-scale methane fermentation treatment systems in circulation. This small methane fermentation treatment system was installed on an empty lot without power supply facilities, and food waste was fed in for methane fermentation. A stirrer was not installed inside the fermentation tank, and the fermentation liquid was dispersed by the water flow stirring by the organic waste input and the return line from the first fermentation tank 3 to the input tank 2 (the water flow stirring means in (i) above) and the gas dissolution stirring means. In addition, a solar water heater 8 was installed on the roof of the methane fermentation treatment system, and the produced hot water was used for heating the fermentation tank. Also, the generated biogas was burned to heat water to produce hot water, which was used for heating the fermentation liquid. In the state where the heating was stopped, the heat dissipation temperature of the fermentation liquid was 4°C, but by heating the fermentation liquid with the hot water of the solar water heater 8 and the hot water of the biogas water heater 9, the temperature of the fermentation liquid could be maintained at 35 to 37°C. In cold regions or in winter, since the heat dissipation temperature of the fermentation liquid increases, if the temperature of the fermentation liquid cannot be maintained only by heating by burning biogas, a solar water heater can be added to implement a methane fermentation treatment system that does not require electricity.

[0085] A solar power generation device was installed on the wall surface of the small methane fermentation treatment system, and the obtained electric energy was used as energy for the crusher 11 and the like. The size of the solar power generation device was selected as something that could be installed on the wall surface of the small methane fermentation treatment system, and the size of the panel was 1.5 m 2 or so.

[0086] The gas dissolution and agitation means was executed during the night (6:00 p.m. to 8:00 a.m.) without input of food waste. At 6:00 p.m., the automatic on-off valves 22, 28 and the path change valve 30 were closed, the automatic on-off valves 24, 29 were opened, and the biogas in the second gas holder 7 was transferred to the first fermentation tank 3 using the pump P4 through the gas line G3 connecting the second gas holder 7 and the first fermentation tank 3. When the value of the pressure gauge installed in the first fermentation tank 3 reached 25 kPa, the pump was stopped, the automatic on-off valve 29 was closed, the automatic on-off valve 24 of the gas line G3 connecting the second gas holder 7 and the first fermentation tank 3 was closed, and the transfer of biogas was stopped. In the first fermentation tank 3, methane fermentation proceeded and biogas was generated, but because the pressure in the first fermentation tank 3 was high, it could not be gasified and was dissolved in a part of the fermentation broth. When the value of the pressure gauge reached 35 kPa, the automatic on-off valve 21 was opened to return the pressure in the first fermentation tank 3 to normal pressure. At this time, the biogas dissolved in the fermentation broth was gasified all at once, and the fermentation broth was dispersed by the impact, and the gas moved from the lower part to the upper part of the fermentation broth and into the gas phase part, diffusing the entire fermentation broth. The gasified biogas was stored in the second gas holder 7 through the gas line G2. The gas dissolution and agitation means of transferring gas to the first fermentation tank 3 again with a pump to increase the internal pressure in the first fermentation tank 3 and performing agitation with the gas generated by methane fermentation was repeatedly implemented. During the period from 6:00 p.m. to 8:00 a.m., the gas dissolution system was implemented 10 times. By the gas dissolution and agitation means, the fermentation broth was agitated, there was no generation of scum or clogging of pipes, etc., and methane fermentation was also carried out without problems, and 1.5 m 3 of biogas could be produced in 24 hours. When the generated biogas was measured with a gas concentration meter, the methane concentration was 59.5%. As in Example 2, by further adding the gas dissolution and agitation means to the methane fermentation treatment system of Example 1, the agitation effect of the fermentation broth could be further enhanced, and stable methane fermentation was promoted. The daily power supply amount and consumption amount in Example 2 are shown in Table 2.

[0087]

Table 2

[0088] In the methane fermentation treatment system of Example 2, by introducing water flow stirring and gas dissolution stirring means by a return line, the stirrer becomes unnecessary, and by introducing a solar heat water heater 8 and a biogas water heater 9, the heating heater becomes unnecessary, realizing power saving of the system. The stable operation of a small methane fermentation treatment system can be realized only by the biogas generated by methane fermentation and the power obtained by solar power generation (i.e., an independent power source). By saving power of the system, there is an advantage that the scale of the solar power generation panel as a power supply source can be reduced by minimizing the required power amount. As a result, the initial cost is reduced, and the solar panels can be placed on the roof area of the small methane fermentation treatment system and integrated, contributing to further miniaturization of the device.

Explanation of Signs

[0089] 1 Water tank 2 Feed tank 3 First fermentation tank 4 Second fermentation tank 5 Liquid fertilizer tank 6 First gas holder 7 Second gas holder 8 Solar heat water heater 9 Biogas water heater 10 Hot water tank 11 Crusher 12 Organic waste 13 Pipe 14 Feed line 15 Return line 16,17 Communication pipe 18,19 Gas line 20 Gas header 21,22,24,28,29 Automatic on-off valve 23 Pressure regulating valve 25 Overflow pipe 26,27 Gas line 30 Route change valve 31 Return valve G1,G2,G3,G4 Gas line P1,P2,P3,P4 Pump

Claims

1. A methane fermentation treatment system for fermenting organic waste in a fermentation tank, comprising a biogas water heater that heats water using biogas generated by the fermentation of organic waste, a water flow stirring means for stirring the fermentation broth by the water flow, a natural energy power generation device, and a storage battery for storing the electric energy generated by the natural energy power generation device, and an independent power supply control unit capable of supplying all the energy required for the methane fermentation treatment from natural energy and internal energy from the biogas. A methane fermentation treatment system.

2. The methane fermentation treatment system according to claim 1, comprising the water flow stirring means of the following (i) and / or (ii) as the water flow stirring means. (i) Means for returning the fermentation broth from the fermentation tank to the input tank to stir the fermentation broth by the water flow (ii) A plurality of fermentation tanks connected by a communication pipe, and means for stirring the fermentation broth in at least one fermentation tank by the water level difference of the plurality of fermentation tanks

3. The methane fermentation treatment system according to claim 1, comprising a gas dissolution stirring means for increasing the internal pressure in the fermentation tank by the biogas generated by the fermentation of organic waste, dissolving the biogas in the fermentation broth, releasing the pressure when it reaches an arbitrary pressure or higher, vaporizing the biogas dissolved in the fermentation broth, and increasing the fluidity of the fermentation broth by the diffusion and / or floating of the vaporized biogas in the fermentation broth.

4. A methane fermentation treatment system for fermenting organic waste in a fermentation tank, comprising a gas dissolution stirring means for increasing the internal pressure in the fermentation tank by the biogas generated by the fermentation of organic waste, dissolving the biogas in the fermentation broth, releasing the pressure when it reaches an arbitrary pressure or higher, vaporizing the biogas dissolved in the fermentation broth, and increasing the fluidity of the fermentation broth by the diffusion and / or floating of the vaporized biogas in the fermentation broth. A methane fermentation treatment system.

5. A methane fermentation treatment system for introducing organic waste from an input tank into a fermentation tank and fermenting the organic waste in the fermentation tank, comprising the water flow stirring means of the following (i) and / or (ii) for stirring the fermentation broth by the water flow. A methane fermentation treatment system. (i) Means for returning the fermentation broth from the fermentation tank to the input tank to stir the fermentation broth by the water flow (ii) A plurality of fermentation tanks connected by a communication pipe, and means for stirring the fermentation broth in at least one fermentation tank by the water level difference of the plurality of fermentation tanks

6. Comprising the water flow stirring means of (i) above, the charging tank and the fermentation tank are connected by a charging line and a return line via a return valve, The methane fermentation treatment system according to claim 3 or 5, wherein the organic waste is charged into the charging tank, and the return valve is opened to return the fermentation liquid in the fermentation tank to the charging tank through the return line, thereby generating the water flow and performing the water flow stirring.

7. Comprising the water flow stirring means of (ii) above, the plurality of fermentation tanks include a first fermentation tank connected to the charging tank by a charging line, and a second fermentation tank located downstream of the first fermentation tank, The charging tank and the second fermentation tank are connected by a return line via a return valve, The return valve is opened to return the fermentation liquid in the second fermentation tank to the charging tank through the return line. When the volume of the fermentation liquid in the charging tank reaches an arbitrary value due to the return, the organic waste is charged from the charging tank to the first fermentation tank through the charging line, thereby generating a water level difference among the charging tank, the first fermentation tank, and the second fermentation tank and performing the water flow stirring. The methane fermentation treatment system according to claim 2 or 5.

8. The methane fermentation treatment system according to claim 6, wherein the discharge port of the charging line in the fermentation tank connected to the charging tank via the charging line is installed in the fermentation liquid in the fermentation tank.

9. The charging line has a siphon break function for preventing the siphon phenomenon, and the siphon break function uses the biogas generated by the fermentation of the organic waste. The methane fermentation treatment system according to claim 6.

10. Comprising a gas holder for storing the biogas generated by the fermentation of the organic waste, and a gas line for transferring the biogas in the fermentation tank to the gas holder, The methane fermentation treatment system according to claim 3 or 4, wherein an automatic on-off valve is provided on the gas line.

11. The methane fermentation treatment system according to claim 10, comprising an automatic control means, wherein the automatic on-off valve is closed when the pressure in the fermentation tank is less than 10 kPa, and the automatic on-off valve is opened when the pressure becomes 10 kPa or more.

12. The methane fermentation treatment system according to claim 11, comprising an internal pressure increase period in which the biogas stored in the gas holder is transferred to the gas phase part in the fermentation tank to increase the internal pressure of the fermentation tank.

13. A methane fermentation treatment system according to any one of claims 1 to 5, comprising a solar water heater that heats water by solar heat to produce hot water, and supplying the hot water to a hot water pipe to heat the fermentation tank.

14. A methane fermentation treatment system according to any one of claims 1 to 5, comprising a foreign matter removal device for removing hardly decomposable solids.

15. A methane fermentation treatment system according to claim 1 or 2, wherein hot water heated by the biogas water heater is supplied to a hot water pipe to heat the fermentation tank.

16. A methane fermentation treatment system according to any one of claims 1 to 3, comprising a plurality of fermentation tanks connected by a communication pipe, wherein the water flow stirring means stirs the fermentation liquid in at least one fermentation tank by the water level difference between the plurality of fermentation tanks.

17. A methane fermentation treatment system according to claim 1 or 2, wherein the electric energy stored in the storage battery is used as energy for one or more systems selected from the group consisting of a pump, a crusher, and an electronic control system of the methane fermentation treatment system.

Images