Methane fermentation apparatus and methane fermentation treatment method

Abstract

To provide a methane fermentation apparatus including an agitation mechanism that is suitable for large-sizing of a methane fermentation tank even when viscosity of a fermentation sludge is large.SOLUTION: A methane fermentation apparatus includes: a methane fermentation tank for methane fermentation treatment of a raw material supplied to the tank by using fermentation sludge retained in the tank; a biogas discharge mechanism for discharging a biogas from two or more biogas discharge parts installed at a lower peripheral edge of the methane fermentation tank and stirring the fermentation sludge in the methane fermentation tank; and a first push-in mechanism comprising stir blades arranged at a liquid level height vicinity at the center part of a liquid level of the fermentation sludge in the methane fermentation tank and pushing a floater of the liquid level into under the liquid level.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a methane fermentation apparatus and a methane fermentation treatment method.

Background Art

[0002] There has been attention paid to a methane fermentation apparatus and a methane fermentation treatment method that use anaerobic microorganisms to produce biogas mainly composed of methane that can be used as an energy source, using organic waste such as paper waste and food waste contained in general waste, and agricultural waste generated after harvesting grains harvested in fields represented by rice straw and wheat straw as raw materials.

[0003] Patent Document 1 proposes a resource circulation method that utilizes methane fermentation treatment using agricultural waste as a raw material. Further, Patent Document 2 proposes a methane fermentation apparatus (digestion apparatus) including a first circulation means for causing an upward flow in the liquid in the tank and a downward flow that descends outside the upward flow to circulate the liquid, and a second circulation means for causing a horizontal swirling flow centered on the portion of the upward flow in the liquid in the tank to circulate the liquid.

[0004] In order to efficiently proceed with the methane fermentation treatment, it is necessary to efficiently perform the methane fermentation treatment by promoting the stirring and mixing of the raw material and the fermentation sludge without retaining the methane fermentation sludge, which is sludge containing bacteria, in the methane fermentation tank.

[0005] Therefore, methods such as mechanically stirring the fermentation liquid in the tank using a stirring blade, supplying biogas into the tank and using the upward flow of the gas to stir the fermentation liquid, and circulating the fermentation liquid in the tank using a pump to stir it have been proposed so far.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, the method of mechanically stirring using a stirring blade not only makes the power excessive and difficult to cope with the enlargement of the fermentation tank, but also has a limited stirring pattern for the fermentation sludge, so there is a risk of forming a dead water area in the tank. Once a dead water area is formed, the object to be treated as a raw material accumulates and sufficient fermentation treatment is inhibited, and there is a problem that the dead water area needs to be cleaned during maintenance.

[0008] In addition, the method using a pump requires setting a circulation route to draw out the fermentation sludge from the fermentation tank and return the drawn fermentation sludge to the tank in order to circulate the fermentation sludge in the tank. However, when the fermentation tank is enlarged, it is difficult to set an effective circulation route for uniformly stirring the fermentation sludge in the tank.

[0009] As an example of the method of stirring the fermentation sludge using biogas, a method of supplying biogas to a draft tube and stirring by the circulation flow generated inside and outside the draft tube along with the movement of the biogas rising in the draft tube can be exemplified. However, when the fermentation tank is enlarged, the stirring range is limited, so it is necessary to increase the number of installed draft tubes. In addition, since the behavior of the circulation flow varies depending on the properties of the fermentation sludge, it is difficult to determine its arrangement. There is also a problem that the degree of enlargement is limited by the discharge pressure of the blower used for supplying biogas.

[0010] An object of the present invention is to provide a methane fermentation apparatus and a methane fermentation treatment method equipped with a stirring mechanism suitable for enlarging a methane fermentation tank even when the viscosity of the fermentation sludge is high.

Means for Solving the Problems

[0011] To achieve the above object, the first characteristic configuration of the methane fermentation apparatus according to the present invention is a methane fermentation tank that performs methane fermentation treatment on the raw materials supplied into the tank with the fermented sludge stored in the tank, and a biogas release mechanism that releases biogas from two or more biogas release parts installed at the lower peripheral edge in the methane fermentation tank to stir the fermented sludge in the methane fermentation tank, and a first pushing mechanism that includes stirring blades arranged near the liquid level height at the center of the liquid surface of the fermented sludge in the methane fermentation tank and pushes the floating matter on the liquid surface downward below the liquid surface.

[0012] When the biogas generated in the methane fermentation tank is released into the fermented sludge from the biogas release part installed at the lower peripheral edge in the methane fermentation tank, the biogas rises in the fermented sludge toward the liquid surface. In the process, the fermented sludge is pushed up by the biogas to generate an upward flow of the fermented sludge. When the fermented sludge reaches the liquid surface, a horizontal flow toward the surroundings is generated, and further a downward flow that descends downward is generated, thereby forming a circulating flow that repeats upward and downward movements. The raw materials are stirred into the fermented sludge along with the flow of the circulating flow, and the methane fermentation proceeds efficiently.

[0013] By installing a plurality of biogas release parts at the lower peripheral edge in the methane fermentation tank, raw materials that are likely to float in the central part of the liquid surface of the fermented sludge, which is the boundary of the circulating flow formation region generated by the biogas released from each biogas release part, tend to stay. By providing the first pushing mechanism in such a raw material retention region, even a small stirring blade can effectively push the raw materials into the fermented sludge and ensure sufficient contact opportunities between the fermented sludge and the raw materials. In addition, the larger the ratio of the vertical size to the horizontal size, that is, the more vertically long the circulating flow formation region formed by one system of biogas release parts, the more the stirring efficiency can be improved. Therefore, by adjusting the number of biogas release parts according to the size of the methane fermentation tank, it becomes possible to stir efficiently regardless of the size of the methane fermentation tank.

[0014] The second characteristic configuration is that, in addition to the first characteristic configuration described above, the biogas discharge mechanism is provided with an adjustment mechanism for adjusting the biogas discharge amount or discharge ratio from the biogas discharge section.

[0015] By adjusting the biogas discharge amount or discharge ratio from the biogas discharge section, the position and size of the formation region of the circulation flow can be variably adjusted, avoiding the generation of a dead water area where the fermented sludge continuously stays in the methane fermentation tank and enabling efficient stirring treatment to proceed.

[0016] The third characteristic configuration is that, in addition to the first or second characteristic configuration described above, it consists of stirring blades arranged near the liquid level height at the peripheral edge of the liquid surface of the fermented sludge in the methane fermentation tank, and is provided with a second pushing mechanism for pushing the floating matter on the liquid surface below the liquid surface.

[0017] When the raw materials floating on the liquid surface of the fermented sludge are located at the periphery of the liquid surface of the fermented sludge and are difficult to handle with the first pushing mechanism, by providing the second pushing mechanism, a sufficient contact opportunity between the fermented sludge and the raw materials can be ensured. Also, when the second characteristic configuration is provided, by adjusting the biogas discharge amount or discharge ratio from the biogas discharge section, it is also possible to move the position of the raw materials floating on the fermented sludge toward the second pushing mechanism.

[0018] The fourth characteristic configuration is that, in addition to the first characteristic configuration described above, the methane fermentation tank is configured in a cylindrical shape along the vertical axis, and the biogas discharge section is arranged at equal intervals on the lower peripheral edge of the methane fermentation tank.

[0019] For a methane fermentation tank configured in a cylindrical shape along the vertical axis, by arranging the biogas discharge section at equal intervals on the lower peripheral edge of the methane fermentation tank, the methane fermented sludge and the raw materials can be evenly mixed.

[0020] The first characteristic configuration of the methane fermentation treatment method according to the present invention is a methane fermentation treatment method in which the raw materials supplied into the methane fermentation tank are subjected to methane fermentation treatment by the fermentation sludge stored in the methane fermentation tank, and biogas is released from two or more biogas release parts installed at the lower peripheral edge in the methane fermentation tank to stir the fermentation sludge in the methane fermentation tank, and a gas stirring treatment step, and a first pushing treatment step of pushing the floating matter on the liquid surface below the liquid surface by a stirring blade arranged near the liquid surface height at the central part of the liquid surface of the fermentation sludge in the methane fermentation tank.

[0021] The second characteristic configuration is that, in addition to the first characteristic configuration described above, the gas stirring treatment step includes an adjustment step of adjusting the biogas release amount or release ratio from the biogas release part.

[0022] The third characteristic configuration is that, in addition to the first or second characteristic configuration described above, a second pushing treatment step of pushing the floating matter on the liquid surface below the liquid surface by a stirring blade arranged near the liquid surface height at the peripheral edge of the liquid surface of the fermentation sludge in the methane fermentation tank is provided.

[0023] The fourth characteristic configuration is that, in addition to the first characteristic configuration described above, the methane fermentation tank is configured in a cylindrical shape along the vertical axis, and the gas stirring treatment step releases biogas from the biogas release parts arranged at equal intervals at the lower peripheral edge in the methane fermentation tank.

Effect of the Invention

[0024] As described above, according to the present invention, it has become possible to provide a methane fermentation apparatus and a methane fermentation treatment method equipped with a stirring mechanism suitable for increasing the size of a methane fermentation tank even when the viscosity of the fermentation sludge is high.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0026] Hereinafter, the methane fermentation apparatus and the methane fermentation treatment method of the present invention will be described when rice straw, which is a rice harvest residue generated in the field, is used as a raw material.

[0027] FIG. 1(a) and (b) illustrate a methane fermentation apparatus 1 according to the present invention. FIG. 1(a) is a perspective explanatory view showing the internal configuration of the methane fermentation tank 2 in a perspective view, and FIG. 1(b) is a plan view explanatory view seen from above the liquid surface of the fermented sludge. The methane fermentation apparatus 1 includes a cylindrical methane fermentation tank 2 in which fermented sludge is stored, a raw material input mechanism 3 for inputting raw materials into the methane fermentation tank 2, a storage tank 4 for storing the biogas generated in the methane fermentation tank 2, and a biogas release mechanism 5 for releasing the biogas stored in the storage tank 4 from two biogas release parts 5A and 5B oppositely installed at the lower peripheral edge inside the methane fermentation tank 2 via a blower B. A heat medium flow-through heat preservation jacket is provided on the peripheral wall of the methane fermentation tank 2, and the inside of the tank is maintained at a predetermined temperature suitable for fermentation.

[0028] In the present embodiment, the biogas release parts 5A and 5B are oppositely arranged at the lower peripheral edge inside the methane fermentation tank 2 so as to be 180° in a plan view. However, the number of biogas release parts is not limited to two, and a plurality of three or more biogas release parts may be installed at equal intervals at the lower peripheral edge inside the methane fermentation tank 2.

[0029] In addition, it is equipped with a first pushing mechanism 6 that pushes the floating matter including rice straw on the liquid surface downward by the stirring blade 6A disposed near the liquid surface height at the central part of the liquid surface of the fermented sludge. The first pushing mechanism 6 is composed of an electric motor 6B installed on the ceiling lid 2A that seals the methane fermentation tank 2, a rotating shaft 6C that is rotationally driven by the electric motor 6B, and a stirring blade 6A attached to the tip of the rotating shaft 6C.

[0030] The raw material input mechanism 3 includes a supply cylinder 3A installed so as to hang down from the ceiling lid 2A, and a screw-type transport mechanism is built into the supply cylinder 3A. Although not shown, a hopper for inputting raw materials is provided at the upper end of the supply cylinder 3A, and the lower end is immersed in the fermented sludge. The raw materials input into the hopper are transported into the fermented sludge by the transport mechanism. As raw materials, in addition to rice straw, organic wastes such as paper waste and food waste, and agricultural wastes generated after harvesting grains harvested in the field represented by wheat straw are preferably used. In this embodiment, the rice straw used is cut short. The raw materials are digested by the fermented sludge under anaerobic conditions to generate biogas containing methane gas, carbon dioxide, etc. The generated biogas is reused as fuel for power generation equipment and heat generation equipment.

[0031] The bottom 2B of the methane fermentation tank 2 is formed in an inverted conical shape with the central part protruding downward, and the fermentation-inappropriate substances deposited on the bottom 2B are drawn out by a pump P from the discharge part 2C formed in the central part.

[0032] As shown in Fig. 2(a), when the biogas generated in the methane fermentation tank 2 is released into the interior of the methane fermentation tank 2 from the biogas discharge parts 5A and 5B installed at the lower periphery in the methane fermentation tank 2, bubbles of biogas rise through the fermentation sludge along the vicinity of the inner wall of the methane fermentation tank 2 toward the liquid surface. In the process, the fermentation sludge is pushed up by the biogas to generate an upward flow of the fermentation sludge. As shown in Fig. 2(b), when the fermentation sludge reaches the liquid surface, it diffuses horizontally around the rising position as a base point, and then descends downward, thereby forming a circulating flow that repeats the upward and downward movements as indicated by the dashed-dotted line in Fig. 2(a). Note that in Figs. 2(a) and 2(b), some of the configurations shown in Figs. 1(a) and 1(b) are omitted for easier understanding of the explanation.

[0033] The formation region of the circulating flow formed by the biogas discharged from the biogas discharge parts 5A and 5B gradually expands to the periphery, and as shown by the arrow in Fig. 2(b), the raw materials are diffused around along the circulating flow. And at the boundary part 8 where the formation regions of the circulating flows with the respective biogas discharge parts 5A and 5B as the base points are in contact, a stagnation occurs where the flow of the fermentation sludge becomes weak.

[0034] At the liquid surface of the fermentation sludge, the floating raw materials and the raw materials containing biogas stay in the central part of the liquid surface that becomes the boundary of the formation region of the circulating flow. By providing the first pushing mechanism in such a stagnation region, even a small stirring blade can effectively push the raw materials into the fermentation sludge, and a sufficient contact opportunity between the fermentation sludge and the raw materials can be ensured.

[0035] The larger the ratio of the vertical size to the horizontal size, that is, the more vertically long the formation region of the circulating flow formed by one system of biogas discharge parts becomes, the more the stirring efficiency using the rising of the bubbles can be improved. Therefore, by adjusting the number of biogas discharge parts according to the size of the methane fermentation tank 2, it becomes possible to stir efficiently regardless of the size of the methane fermentation tank.

[0036] For example, as the diameter of the methane fermentation tank increases, by increasing the number of biogas discharge parts, the number of formation regions of vertically long circulation flows adjacent to each other along the circumferential direction inside the methane fermentation tank increases, and the stirring efficiency of the raw materials with respect to the fermentation sludge becomes higher.

[0037] Figs. 3(a) and (b) show an example in which three biogas discharge parts 5A, 5B, and 5C are formed at equal intervals on the lower peripheral edge of the side wall of the fermentation tank 2, and three systems of circulation flow formation regions are formed.

[0038] The raw materials floating in the central part of the liquid surface, which is the upper end of the boundary of the formation region of the circulation flow generated by the biogas discharged from the biogas discharge part installed on the lower peripheral edge in the methane fermentation tank 2, will stay. By providing the first pushing mechanism 6 in such a staying region, even a small stirring blade 6A can effectively push the raw materials 7 into the fermentation sludge, and a sufficient contact opportunity between the fermentation sludge and the raw materials 7 can be ensured.

[0039] The biogas discharge mechanism 5 preferably includes an adjustment mechanism for adjusting the biogas discharge amount or discharge ratio from the biogas discharge parts 5A, 5B, and 5C. By adjusting the biogas discharge amount or discharge ratio from each biogas discharge part 5A, 5B, and 5C by the adjustment mechanism, the position and size of the circulation flow formation region can be variably adjusted, and the generation of a dead water region where the fermentation sludge continuously stays in the fermentation tank 2 can be avoided, and the stirring process can be efficiently advanced.

[0040] For example, when the biogas discharge amount from the biogas discharge parts 5A, 5B, and 5C is decreased, the formation region of the circulation flow becomes smaller, and when the biogas discharge amount is increased, the formation region of the circulation flow becomes larger. Therefore, the stirring efficiency can be adjusted by adjusting the biogas discharge amount. Further, by adjusting the biogas discharge ratio from the biogas discharge parts 5A, 5B, and 5C, the position and size of each circulation flow formation region fluctuate. By using this fluctuation to change the region where the sedimentation of the fermentation sludge occurs, the generation of a dead water region can be avoided.

[0041] In the above examples, the examples of supplying biogas from the storage tank 4 to each of the biogas discharge parts 5A, 5B, 5C by individual blowers B have been described. However, by adjusting the gas supply amount by each blower B, the biogas discharge amount or the discharge ratio can be adjusted. As an adjustment mechanism, a control panel for adjusting the power supply amount to each blower B can be configured.

[0042] Also, a single blower B for sending biogas from the storage tank 4 may be provided, and a valve may be provided in the air supply pipe provided between the blower B and each of the biogas discharge parts 5A, 5B, 5C so as to adjust the biogas discharge amount or the discharge ratio. In this case, as an adjustment mechanism, a control panel for adjusting the opening degree of each valve may be configured.

[0043] Also, as shown in FIG. 4, when the floating position of the raw material 7 floating on the liquid surface of the fermented sludge is biased in the circumferential direction from the central part of the liquid surface as a result of adjusting the biogas discharge amount or the discharge ratio by the adjustment mechanism, it is preferable to provide a second pushing mechanism 9 in which the stirring blades 9A are positioned in the vicinity of the liquid surface height at the peripheral edge of the liquid surface of the fermented sludge.

[0044] When the raw material floating on the liquid surface of the fermented sludge is located at the peripheral edge of the liquid surface of the fermented sludge and it becomes difficult to handle with the first pushing mechanism, by providing the second pushing mechanism, a sufficient contact opportunity between the fermented sludge and the raw material can be ensured.

[0045] In other words, by adjusting the biogas discharge amount or the discharge ratio from the biogas discharge parts 5A, 5B, 5C via the adjustment mechanism, the floating position of the raw material floating on the liquid surface of the fermented sludge can be biased to the position where the stirring blades of the first pushing mechanism or the second pushing mechanism are installed.

[0046] The methane fermentation tank only needs to be configured in a cylindrical shape along the longitudinal axis. It may be formed into a cylinder with an elliptical or oval cross-section in addition to a true cylinder with a circular cross-section. The biogas discharge parts only need to be arranged at equal intervals on the lower peripheral edge inside the methane fermentation tank, and the number thereof is not particularly limited as long as it is plural. For example, the lower peripheral edge of the side wall of the methane fermentation tank is provided with 12 biogas discharge parts so that the central angle is 30°, and biogas may be supplied by selecting any plurality of the 12 biogas discharge parts. The biogas discharge parts can be selected so as to effectively stir according to the diameter of the fermentation tank 2, the viscosity of the fermentation sludge, etc.

[0047] As described above, the methane fermentation treatment method according to the present invention is a methane fermentation treatment method for subjecting the raw material supplied into the methane fermentation tank to methane fermentation treatment with the fermentation sludge stored in the tank, and discharging biogas from two or more biogas discharge parts installed at the lower peripheral edge inside the methane fermentation tank to stir the fermentation sludge inside the methane fermentation tank, and a gas stirring treatment step, and a first pushing treatment step of pushing the floating matter on the liquid surface downward by the stirring blades arranged in the vicinity of the liquid surface height at the central part of the liquid surface of the fermentation sludge in the methane fermentation tank.

[0048] Further, it is preferable that the gas stirring treatment step includes an adjustment step of adjusting the biogas discharge amount or discharge ratio from the biogas discharge part.

[0049] It is preferable to include a second pushing treatment step of pushing the floating matter on the liquid surface downward by the stirring blades arranged in the vicinity of the liquid surface height at the peripheral part of the liquid surface of the fermentation sludge in the methane fermentation tank.

[0050] The methane fermentation tank is configured in a cylindrical shape along the longitudinal axis, and in the gas stirring treatment step, it is preferable to discharge biogas from the biogas discharge parts arranged at equal intervals on the lower peripheral edge of the methane fermentation tank.

[0051] The various embodiments described above are examples of the present invention, and the scope of the present invention is not limited by the description. Needless to say, it can be appropriately modified and designed within the range where the functions and effects of each aspect of the present invention are achieved.

Explanation of Reference Numerals

[0052] 1: Methanogenic apparatus 2: Fermentation tank 3: Raw material feeding mechanism 4: Storage tank 5: Biogas discharge mechanism 5A, 5B: Biogas discharge part 6: First pushing mechanism 6A: Stirring blade 6B: Electric motor 6C: Rotating shaft 7: Raw material (rice straw) 8: Boundary part

Claims

1. A methane fermentation tank that performs methane fermentation treatment on the raw material supplied into the tank with the fermented sludge stored in the tank, A biogas release mechanism that releases biogas from two or more biogas release parts installed at the lower peripheral edge in the methane fermentation tank to stir the fermented sludge in the methane fermentation tank, It consists of stirring blades arranged near the liquid level height at the central part of the liquid level of the fermented sludge in the methane fermentation tank, and a first pushing mechanism that pushes the floating matter on the liquid surface below the liquid surface, A methane fermentation device comprising the above.

2. The methane fermentation device according to claim 1, wherein the biogas release mechanism is provided with an adjustment mechanism for adjusting the biogas release amount or release ratio from the biogas release part.

3. The methane fermentation device according to claim 1 or 2, comprising a second pushing mechanism that consists of stirring blades arranged near the liquid level height at the peripheral edge of the liquid level of the fermented sludge in the methane fermentation tank and pushes the floating matter on the liquid surface below the liquid surface.

4. The methane fermentation device according to claim 1, wherein the methane fermentation tank is configured in a cylindrical shape along the vertical axis, and the biogas release parts are arranged at equal intervals on the lower peripheral edge of the methane fermentation tank.

5. A methane fermentation treatment method for performing methane fermentation treatment on the raw material supplied into the methane fermentation tank with the fermented sludge stored in the methane fermentation tank, A gas stirring treatment step of releasing biogas from two or more biogas release parts installed at the lower peripheral edge in the methane fermentation tank to stir the fermented sludge in the methane fermentation tank, A first pushing treatment step of pushing the floating matter on the liquid surface below the liquid surface by stirring blades arranged near the liquid level height at the central part of the liquid level of the fermented sludge in the methane fermentation tank, A methane fermentation treatment method comprising the above.

6. The methane fermentation treatment method according to claim 5, wherein the gas stirring treatment step includes an adjustment step of adjusting the amount or ratio of biogas released from the biogas release part.

7. The methane fermentation treatment method according to claim 5 or 6, further comprising a second pushing step of pushing the floating matter on the liquid surface downward by a stirring blade disposed near the liquid surface height at the peripheral edge of the liquid surface of the fermentation sludge in the methane fermentation tank.

8. The methane fermentation treatment method according to claim 5, wherein the methane fermentation tank is configured in a cylindrical shape along a vertical axis, and in the gas stirring treatment step, biogas is released from the biogas release parts arranged at equal intervals on the lower periphery in the methane fermentation tank.

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