Methane fermentation treatment device and methane fermentation treatment method

Abstract

To provide a methane fermentation treatment device that can easily discharge a material unsuitable for fermentation from a methane fermentation tank and can keep a height of the methane fermentation tank low.SOLUTION: A methane fermentation treatment device includes a methane fermentation tank 4 and a sludge agitation device 6 that agitates a sludge 2 in the methane fermentation tank 4, the sludge agitation device 6 having a circulation path 15 for circulating the sludge 2 in the methane fermentation tank 4, and a flow generating device 16 for generating a flow of the sludge 2 in the circulation path 15, the circulation path 15 having an upward path 21 through which the sludge 2 flows upward, the upward path 21 having a settling path portion 22, in which a flow path cross-sectional area of the settling path portion 22 is larger than a flow path cross-sectional area of a circulation path 19 connected upstream of the settling path portion 22, and a discharge portion 37 is provided to discharge a sedimentable matter 34 that has settled in the settling path portion 22 to outside.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a methane fermentation treatment apparatus and a methane fermentation treatment method for subjecting organic substances to be treated to methane fermentation treatment.

Background Art

[0002] Conventionally, as this type of methane fermentation treatment apparatus, for example, as shown in FIG. 10, there is one including a methane fermentation tank 101 and an external circulation path 102 connected to the outside of the methane fermentation tank 101. The external circulation path 102 is a path for withdrawing the fermented sludge 103 in the methane fermentation tank 101 outside the methane fermentation tank 101 and then returning it into the methane fermentation tank 101.

[0003] Both ends of the external circulation path 102 are connected to the side wall 104 of the methane fermentation tank 101. The inlet 105 and the outlet 106 of the external circulation path 102 are each open to the side wall 104 of the methane fermentation tank 101.

[0004] The external circulation path 102 has an upward path 107 through which the fermented sludge 103 flows upward. A membrane separation device 108 and an air diffuser 109 are provided in the upward path 107. The membrane separation device 108 has a plurality of flat plate-shaped membrane cartridges arranged in parallel, and a vertical flow path is formed between these membrane cartridges. An operating gas supply system 110 for supplying the biogas in the methane fermentation tank 101 to the air diffuser 109 is provided. At the bottom of the methane fermentation tank 101, a pit 111 and an inclined surface 112 having a downward gradient toward the pit 111 are formed.

[0005] According to this, the biogas in the methane fermentation tank 101 is ejected as bubbles from the air diffuser 109 through the operating gas supply system 110. As a result, the fermented sludge 103 flows upward through the upward path 107, and the fermented sludge 103 in the methane fermentation tank 101 flows into the external circulation path 102 from the inlet 105 and is drawn out of the methane fermentation tank 101. After flowing upward through the upward path 107, it flows out from the outlet 106 and is returned to the methane fermentation tank 101. At this time, the fermented sludge 103 is solid-liquid separated by the membrane separation device 108 while flowing through the upward path 107.

[0006] In addition, the flow cross-sectional area of the upward path 107 is reduced due to the presence of the membrane cartridges of the membrane separation device 108. Therefore, the flow velocity of the fermented sludge 103 flowing upward through the upward path 107 increases.

[0007] Also, the sedimentable substances contained in the fermented sludge 103 in the methane fermentation tank 101 settle in the methane fermentation tank 101, slide down along the inclined surface 112, and are stored in the pit 111. Then, by opening the valve 113, the sedimentable substances in the pit 111 are discharged. In addition, examples of the sedimentable substances include granular substances such as sand, shells, and glass pieces, and these substances are called fermentation-inappropriate substances that are not suitable for methane fermentation. The methane fermentation treatment device 100 as described above is described in, for example, Patent Document 1 below.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, in the above conventional form, in order to discharge the sedimentable substances in the methane fermentation tank 101, an inclined surface 112 and a pit 111 are provided at the bottom of the methane fermentation tank 101. Therefore, in order to secure the capacity inside the methane fermentation tank 101, there is a problem that the height H of the methane fermentation tank 101 increases.

[0010] An object of the present invention is to provide a methane fermentation treatment apparatus and a methane fermentation treatment method capable of easily discharging sedimentable substances in a methane fermentation tank and suppressing the height of the methane fermentation tank to be low.

Means for Solving the Problems

[0011] In order to achieve the above object, the first invention is a methane fermentation treatment apparatus for subjecting an organic object to be treated to methane fermentation treatment, a methane fermentation tank that generates biogas by subjecting the object to be treated to methane fermentation with the stored fermentation sludge, and a sludge stirring device that stirs the fermentation sludge in the methane fermentation tank. The sludge stirring device has a circulation path for circulating the fermentation sludge in the methane fermentation tank and a flow generation device for generating a flow of the fermentation sludge in the circulation path. The circulation path has an upward path through which the fermentation sludge flows upward. The upward path has a sedimentation path section. The flow cross-sectional area of the sedimentation path section is larger than the flow cross-sectional area of the circulation path connected upstream of the sedimentation path section. A discharge section for discharging the sedimentable substances sedimented in the sedimentation path section to the outside is provided.

[0012] According to this, a flow of the fermentation sludge is generated in the circulation path by the flow generation device, and the fermentation sludge in the methane fermentation tank circulates by flowing through the circulation path. Thereby, the fermentation sludge in the methane fermentation tank is stirred.

[0013] When the fermented sludge flows upward in the upward path of the circulation path, the flow velocity of the fermented sludge decreases in the sedimentation path section. Therefore, the sedimentable substances contained in the fermented sludge settle and accumulate at the lower part of the sedimentation path section. By discharging the sedimentable substances accumulated at the lower part of the sedimentation path section to the outside from the discharge section, the sedimentable substances in the methane fermentation tank can be easily removed in the circulation path. As a result, it is not necessary to form pits or inclined surfaces at the bottom of the methane fermentation tank, and the height of the methane fermentation tank can be kept low.

[0014] In the methane fermentation treatment apparatus according to the second invention, the upstream end of the circulation path opens at the bottom inside the methane fermentation tank, and the downstream end of the circulation path opens inside the methane fermentation tank above the upstream end of the circulation path.

[0015] According to this, the fermented sludge in the methane fermentation tank flows into the circulation path from the upstream end of the circulation path, and after flowing through the circulation path, it flows out into the methane fermentation tank from the downstream end of the circulation path. As a result, a downward flow from the downstream end to the upstream end of the circulation path is generated inside the methane fermentation tank, and the fermented sludge in the methane fermentation tank is agitated.

[0016] In the methane fermentation treatment apparatus according to the third invention, the flow generating device is a gas lift pump, and the gas lift pump has an air supply device for supplying biogas to the sedimentation path section.

[0017] According to this, the biogas generated in the methane fermentation tank is supplied to the sedimentation path section by the air supply device. The biogas supplied to the sedimentation path section rises as bubbles in the upward path, generating a driving flow of a gas-liquid mixed phase by utilizing the gas lift effect, and the fermented sludge flows upward in the upward path. At this time, since the flow velocity of the fermented sludge decreases in the sedimentation path section, the sedimentable substances contained in the fermented sludge settle and accumulate at the lower part of the sedimentation path section. In this way, in order to generate a driving flow of a gas-liquid mixed phase in the external circulation path by utilizing the gas lift effect, the consumption amount of power such as electricity can be reduced.

[0018] In the methane fermentation treatment apparatus of the fourth invention, the flow generating device is a mechanically driven pump, and the pump is provided in the circulation path on the downstream side of the sedimentation path section.

[0019] According to this, by driving the mechanically driven pump, the fermented sludge in the circulation path is forcibly sent, and an upward flow of the fermented sludge is generated in the upward path. At this time, since the flow velocity of the fermented sludge decreases in the sedimentation path section, the sedimentable substances contained in the fermented sludge settle and accumulate at the lower part of the sedimentation path section.

[0020] Since the pump is provided on the downstream side of the sedimentation path section, the fermented sludge with less sedimentable substances after the sedimentable substances have settled in the sedimentation path section passes through the pump. Thereby, deterioration of the pump can be suppressed and the service life of the pump can be extended.

[0021] In the methane fermentation treatment apparatus of the fifth invention, the circulation path has a drawing path for drawing out the fermented sludge in the methane fermentation tank to the outside of the tank and a return path for returning the drawn fermented sludge into the tank, the downstream end of the drawing path is connected to the sedimentation path section, the upstream end of the return path is connected to the upward path, the sedimentation path section has a storage section at the bottom for storing the sedimented sedimentable substances, the storage section is formed below the connection point between the drawing path and the sedimentation path section, and the discharge section discharges the sedimentable substances accumulated in the storage section to the outside.

[0022] According to this, the fermented sludge in the methane fermentation tank flows through the drawing path and is drawn out of the methane fermentation tank. After flowing upward through the upward path from the drawing path, it flows through the return path and is returned into the methane fermentation tank. Thereby, the fermented sludge in the methane fermentation tank is agitated. When the fermented sludge flows through the upward path, the flow velocity of the fermented sludge decreases in the sedimentation path section, so the sedimentable substances contained in the fermented sludge settle and accumulate in the storage section. By discharging the sedimentable substances from the storage section by the discharge section, the sedimentable substances in the methane fermentation tank can be easily and surely removed.

[0023] In the methane fermentation treatment apparatus according to the sixth aspect of the present invention, a plurality of sludge stirring devices are arranged at different positions in the circumferential direction of the methane fermentation tank. The upstream end of the circulation path of each sludge stirring device opens at the bottom inside the methane fermentation tank. The downstream end of the circulation path of each sludge stirring device opens inside the methane fermentation tank above the upstream end of the circulation path and facing the center of the methane fermentation tank in plan view.

[0024] According to this, the fermented sludge in the methane fermentation tank flows into the circulation path from the upstream end of the circulation path of each sludge stirring device, and after flowing through the circulation path, it flows out into the methane fermentation tank from the downstream end of the circulation path. At this time, the fermented sludge flowing out into the methane fermentation tank from the downstream end of the circulation path of each sludge stirring device flows toward the center of the methane fermentation tank, and the flow of the fermented sludge collides at the center of the methane fermentation tank to generate a downward flow (downflow).

[0025] When such a downward flow occurs at the center in the methane fermentation tank and hits the bottom of the methane fermentation tank, the fermented sludge in the methane fermentation tank flows horizontally along the bottom of the methane fermentation tank and flows upward along the side wall surface of the methane fermentation tank to circulate in the vertical direction, so it is sufficiently stirred.

[0026] In the methane fermentation treatment apparatus according to the seventh aspect of the present invention, a plurality of sludge stirring devices are arranged at different positions in the circumferential direction of the methane fermentation tank. The upstream end of the circulation path of each sludge stirring device opens at the bottom inside the methane fermentation tank. The downstream end of the circulation path of each sludge stirring device opens inside the methane fermentation tank above the upstream end of the circulation path and facing either one of the circumferential directions along the side wall surface of the methane fermentation tank in plan view.

[0027] According to this, the fermented sludge in the methane fermentation tank flows into the circulation path from the upstream end of the circulation path of each sludge stirring device, and after flowing through the circulation path, it flows out into the methane fermentation tank from the downstream end of the circulation path. At this time, since the fermented sludge flowing out into the methane fermentation tank from the downstream end of the circulation path of each sludge stirring device flows in one of the circumferential directions along the side wall surface, a swirling flow of the fermented sludge swirling in one direction is generated in the methane fermentation tank. Thereby, the fermented sludge in the methane fermentation tank is sufficiently stirred, and the sedimentation substances contained in the fermented sludge are collected near the center of the bottom of the methane fermentation tank and are likely to settle.

[0028] In the methane fermentation treatment apparatus according to the eighth aspect of the present invention, the circulation path has a drawing path for drawing out the fermented sludge in the methane fermentation tank to the outside of the tank and a return path for returning the drawn fermented sludge into the tank. The downstream end portion of the drawing path is connected to the lower part of the upward path. The upstream end portion of the return path is connected to the upper part of the upward path. The upstream end of the drawing path is located at a position closer to the center of the bottom in the methane fermentation tank than the downstream end of the return path.

[0029] According to this, the sedimentation substances deposited at the bottom and the center of the methane fermentation tank flow into the circulation path from the upstream end of the drawing path, and after flowing through the circulation path, they flow out into the methane fermentation tank from the downstream end of the circulation path. Thereby, the sedimentation substances can be effectively drawn out of the methane fermentation tank by the drawing path.

[0030] In the methane fermentation treatment apparatus according to the ninth aspect of the present invention, the bottom of the methane fermentation tank is flat.

[0031] According to this, compared with the case where the bottom of the methane fermentation tank is formed in a conical shape in order to facilitate discharging the sedimentation substances in the methane fermentation tank to the outside, the height of the methane fermentation tank can be kept low.

[0032] The tenth aspect of the present invention is a methane fermentation treatment method for subjecting an organic object to be treated to methane fermentation treatment, A biogas generation step of subjecting a material to be treated to methane fermentation with fermented sludge stored in a methane fermentation tank to generate biogas, and a stirring step of stirring the fermented sludge in the methane fermentation tank, In the stirring step, the fermented sludge in the methane fermentation tank flows through a circulation path connected to the methane fermentation tank, is drawn out of the methane fermentation tank, and then returned to the methane fermentation tank. When the fermented sludge flows upward through a sedimentation path portion formed in the circulation path, the flow velocity of the fermented sludge decreases by expanding the flow cross-sectional area of the sedimentation path portion to be larger than the flow cross-sectional area of the circulation path connected to the upstream side of the sedimentation path portion, and the sedimentable substances contained in the fermented sludge settle to the bottom of the sedimentation path portion.

[0033] According to this, since the sedimentable substances in the methane fermentation tank can be easily removed, it is not necessary to form pits or inclined surfaces at the bottom of the methane fermentation tank, and the height of the methane fermentation tank can be kept low.

Advantages of the Invention

[0034] As described above, according to the present invention, the sedimentable substances in the methane fermentation tank can be easily discharged, and the height of the methane fermentation tank can be kept low.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0036] Hereinafter, embodiments of the present invention will be described with reference to the drawings. (First Embodiment)

[0037] In the first embodiment, as shown in FIGS. 1 to 3, reference numeral 1 denotes a methane fermentation treatment apparatus for subjecting organic substances to be treated (for example, food waste, livestock manure, food processing residues, etc.) to methane fermentation. The methane fermentation treatment apparatus 1 includes a methane fermentation tank 4 that ferments the substances to be treated with the stored fermentation sludge 2 to generate biogas 3, and a plurality of sludge stirring devices 6 that are installed outside the methane fermentation tank 4 and stir the fermentation sludge 2 in the methane fermentation tank 4.

[0038] The methane fermentation tank 4 has a cylindrical side wall 9, a ceiling wall 10 provided at the upper part of the side wall 9, and a flat bottom wall 11 provided at the lower part of the side wall 9. Fermentation sludge 2 is stored inside the methane fermentation tank 4, and biogas 3 generated in the methane fermentation tank 4 is stored above the liquid surface 13 of the fermentation sludge 2.

[0039] The plurality of sludge stirring devices 6 are arranged at different positions in the circumferential direction 14 of the methane fermentation tank 4. For example, in FIG. 2, four sludge stirring devices 6 are arranged at intervals of 90° in the circumferential direction 14 of the methane fermentation tank 4, but the number and angle of the sludge stirring devices 6 are not limited to four and intervals of 90°.

[0040] Each of the sludge agitation devices 6 has an external circulation path 15 (an example of a circulation path) that draws the fermented sludge 2 in the methane fermentation tank 4 out of the methane fermentation tank 4 and then returns it to the inside of the methane fermentation tank 4 for circulation, and a gas lift pump 16 (an example of a flow generation device) that generates a flow of the fermented sludge 2 in the external circulation path 15.

[0041] The external circulation path 15 has a withdrawal pipe 19 (an example of a withdrawal path) that draws the fermented sludge 2 in the methane fermentation tank 4 out of the methane fermentation tank 4, a return pipe 20 (an example of a return path) that returns the drawn fermented sludge 2 to the inside of the methane fermentation tank 4, and an upward pipe 21 (an example of an upward path) through which the drawn fermented sludge 2 flows upward. The upward pipe 21 is provided outside the methane fermentation tank 4 and has a sedimentation chamber 22 (an example of a sedimentation path section) with an enlarged flow path cross-sectional area and a connecting pipe 23. The sedimentation chamber 22 has a cylindrical body 26, a bottom plate 27 provided at the lower end of the body 26, and a tapered upper plate 28 provided at the upper end of the body 26.

[0042] The downstream end of the withdrawal pipe 19 is connected to the lower part of the body 26 of the sedimentation chamber 22. A connecting pipe 23, which is part of the upward pipe 21, is connected between the upstream end of the return pipe 20 and the upper plate 28 of the sedimentation chamber 22, whereby the upstream end of the return pipe 20 is connected to the upper end of the upward pipe 21.

[0043] The withdrawal pipe 19, the return pipe 20, and the connecting pipe 23 have the same inner diameter, and thus, the withdrawal pipe 19, the return pipe 20, and the connecting pipe 23 have the same flow path cross-sectional area. The flow path cross-sectional area of the sedimentation chamber 22 is set to be larger than the flow path cross-sectional area of each of the withdrawal pipe 19 (corresponding to the circulation path 15 connected upstream of the sedimentation chamber 22), the return pipe 20, and the connecting pipe 23.

[0044] The extraction pipeline 19 and the return pipeline 20 extend horizontally and penetrate from the outside to the inside of the methane fermentation tank 4. The extraction pipeline 19 is provided at the bottom inside the methane fermentation tank 4. In FIG. 1, the extraction pipeline 19 is slightly spaced above the bottom wall 11 inside the methane fermentation tank 4, but it may also be in contact with the bottom wall 11.

[0045] The return pipeline 20 is located above the extraction pipeline 19. The inlet 30, which is the upstream end of the external circulation path 15, opens at the bottom inside the methane fermentation tank 4. The outlet 31, which is the downstream end of the external circulation path 15, opens above the inlet 30 (see FIG. 1) and towards the central part 32 of the methane fermentation tank 4 in a plan view (see FIG. 2) inside the methane fermentation tank 4. The inlet 30 is located closer to the central part 32 of the methane fermentation tank 4 than the outlet 31. The outlet 31 is submerged below the liquid level 13 of the fermented sludge 2 inside the methane fermentation tank 4. A valve 24 is provided in the extraction pipeline 19, and a valve 25 is provided in the connecting pipe 23.

[0046] The sedimentation chamber 22 has a storage part 35 at the bottom for storing the sedimented sedimentable substances 34. The storage part 35 is formed below the connection point 36 between the extraction pipeline 19 and the body part 26 of the sedimentation chamber 22. The sedimentation chamber 22 is provided with a discharge part 37 for discharging the sedimentable substances 34 accumulated in the storage part 35 from inside the sedimentation chamber 22 to the outside. The discharge part 37 has a discharge pipeline 38 connected to the lower part of the body part 26, and a discharge pump 39 and a discharge valve 40 provided in the discharge pipeline 38.

[0047] The gas lift pump 16 has an air supply device 41 for supplying the biogas 3 inside the methane fermentation tank 4 into the sedimentation chamber 22. The air supply device 41 has a biogas supply pipeline 42 connected between the ceiling wall 10 of the methane fermentation tank 4 and the body part 26 of the sedimentation chamber 22, and a blower 43 (a blower) for forcibly sending the biogas 3 from the biogas supply pipeline 42 into the sedimentation chamber 22. Hereinafter, the operation in the above configuration will be described.

[0048] A treatment method for subjecting an organic material to methane fermentation using a methane fermentation treatment apparatus 1 includes a biogas generation step of subjecting the material to be treated to methane fermentation with the fermented sludge 2 in the methane fermentation tank 4 to generate biogas 3, and a stirring step of stirring the fermented sludge 2 in the methane fermentation tank 4. Usually, the stirring step is performed while the biogas generation step is being carried out.

[0049] In the stirring step, with the discharge pump 39 stopped and the discharge valve 40 closed, the blower 43 is driven, so that the biogas 3 in the methane fermentation tank 4 flows through the biogas supply pipeline 42 by the blower 43 and is supplied into the sedimentation chamber 22. The biogas 3 supplied into the sedimentation chamber 22 forms bubbles 47 and rises through the connecting pipe 23 of the upward pipe 21, thereby generating a driving flow of a gas-liquid mixed phase by utilizing the gas-lift effect, and the fermented sludge 2 flows upward through the upward pipe 21.

[0050] As a result, the fermented sludge 2 in the methane fermentation tank 4 flows into the external circulation path 15 from the inlet 30 (the upstream end of the external circulation path 15) of each sludge stirring device 6, and after being drawn out of the methane fermentation tank 4 by flowing through the external circulation path 15, it flows out of the methane fermentation tank 4 from the outlet 31 (the downstream end of the external circulation path 15) and is returned. At this time, as shown in FIG. 1, the fermented sludge 2 flowing out of the methane fermentation tank 4 from the outlet 31 of each sludge stirring device 6 flows toward the central portion 32 of the methane fermentation tank 4, and at the central portion 32 of the methane fermentation tank 4, the flow of the fermented sludge 2 collides to generate a downward flow 48.

[0051] When such a downward flow 48 is generated at the central portion 32 in the methane fermentation tank 4 and hits the bottom wall 11, the fermented sludge 2 in the methane fermentation tank 4 flows radially laterally along the bottom wall 11 and upward along the inner surface of the side wall 9 to circulate in the vertical direction, so that it is sufficiently stirred.

[0052] When the fermented sludge 2 drawn from the inside of the methane fermentation tank 4 to the outside of the methane fermentation tank 4 flows upward through the upward pipeline 21 as described above, the flow velocity of the fermented sludge 2 decreases in the sedimentation chamber 22. Therefore, as shown in FIG. 3, the sedimentable substances 34 contained in the fermented sludge 2 settle in the sedimentation chamber 22 and accumulate in the storage section 35.

[0053] Thereafter, by driving the discharge pump 39 and opening the discharge valve 40, the sedimentable substances 34 are discharged from the storage section 35 to the outside through the discharge pipeline 38. Thereby, the sedimentable substances 34 in the methane fermentation tank 4 can be easily and surely removed, and the fermentation-inhibiting substances contained in the sedimentable substances 34 can be removed.

[0054] Therefore, it is not necessary to form pits or inclined surfaces (for example, refer to the pits 111 and inclined surfaces 112 in FIG. 10) at the bottom of the methane fermentation tank 4, and the height of the methane fermentation tank 4 can be kept low. Further, even if the bottom wall 11 of the methane fermentation tank 4 is made flat, the sedimentable substances 34 in the methane fermentation tank 4 can be easily and surely removed as described above. Therefore, compared with the case where the bottom wall 11 of the methane fermentation tank 4 is formed in a conical shape to facilitate the discharge of the sedimentable substances 34 in the methane fermentation tank 4 to the outside, it is also possible to keep the height of the methane fermentation tank 4 low.

[0055] In addition, the gas lift pump 16 is connected to the external circulation path 15, and by using the gas lift effect to generate a driving flow of a gas-liquid mixed phase in the external circulation path 15, the fermented sludge 2 flows in one direction through the external circulation path 15. Therefore, compared with the case of using an electric pump, the power consumption can be reduced. In the first embodiment described above, the biogas 3 in the methane fermentation tank 10 is supplied to the gas lift pump 16. However, a gas holder for storing the biogas 3 may be provided separately, and the biogas 3 in the gas holder may be supplied to the gas lift pump 16. In the first embodiment described above, one blower 43 is provided for one gas lift pump 16. However, one blower 43 may supply the biogas 3 to a plurality of gas lift pumps 16. (Second Embodiment)

[0056] The second embodiment will be described below with reference to FIGS. 4 and 5. For the members that are the same as those of the methane fermentation treatment apparatus 1 of the first embodiment described above, the same reference numerals are given and detailed description thereof is omitted.

[0057] As shown in FIGS. 4 and 5, the return pipe 20 of the external circulation path 15 is bent inside the methane fermentation tank 4, and the outlet 31 opens toward one of the circumferential directions 14 along the inner peripheral surface of the side wall 9 of the methane fermentation tank 4 above the inlet 30 and in a plan view inside the methane fermentation tank 4. The operation of the above configuration will be described below.

[0058] In the stirring step, the fermented sludge 2 in the methane fermentation tank 4 flows into the external circulation path 15 from the inlet 30 of each sludge stirring device 6, and after being drawn out of the methane fermentation tank 4 by flowing through the external circulation path 15, it flows out of the methane fermentation tank 4 from the outlet 31 and is returned. At this time, since the fermented sludge 2 flowing out of the outlet 31 of each sludge stirring device 6 into the methane fermentation tank 4 flows toward one 55 along the inner peripheral surface of the side wall 9 of the methane fermentation tank 4, a swirling flow 56 of the fermented sludge 2 swirling in one 55 is generated in the methane fermentation tank 4. Thereby, the fermented sludge 2 in the methane fermentation tank 4 is sufficiently stirred, and the sedimentable substances 34 contained in the fermented sludge 2 are collected near the center of the bottom of the methane fermentation tank 4 and are likely to settle.

[0059] In the first and second embodiments described above, as shown in FIG. 1, the outlet 31 of the external circulation path 15 is located below the liquid level 13, but it may be located at the same height as the liquid level 13. (Third Embodiment)

[0060] The third embodiment will be described below with reference to FIG. 6. For the members that are the same as those of the methane fermentation treatment apparatus 1 of the first embodiment described above, the same reference numerals are given and detailed description thereof is omitted.

[0061] In the above-described first embodiment, as shown in FIG. 1, a gas lift pump 16 is used as an example of the flow generating device. However, the present invention is not limited to the gas lift pump 16. For example, in the third embodiment, as shown in FIG. 6, as another example of the flow generating device, a mechanically driven pump 60 is used. Examples of the mechanically driven pump 60 include an electric centrifugal pump, an axial flow pump, etc. driven by a motor or the like.

[0062] The pump 60 is provided in the external circulation path 15 outside the methane fermentation tank 4 and on the downstream side of the sedimentation chamber 22. Specifically, the pump 60 is provided in the connecting pipe 23 of the external circulation path 15. The operation of the above configuration will be described below.

[0063] In the stirring step, by driving the pump 60, the fermented sludge 2 in the external circulation path 15 is forcibly sent in one direction, and an upward flow of the fermented sludge 2 is generated in the upward pipe 21. As a result, the fermented sludge 2 in the methane fermentation tank 4 flows into the external circulation path 15 from the inlet 30 of each sludge stirring device 6, and after being drawn out of the methane fermentation tank 4 by flowing through the external circulation path 15, it flows out of the methane fermentation tank 4 from the outlet 31 and is returned. At this time, since the flow rate of the fermented sludge 2 decreases in the sedimentation chamber 22, the sedimentable substances 34 contained in the fermented sludge 2 settle and accumulate in the storage section 35.

[0064] Since the pump 60 is provided in the connecting pipe 23 on the downstream side of the sedimentation chamber 22, the fermented sludge 2 with less sedimentable substances 34 after the sedimentable substances 34 have settled in the sedimentation chamber 22 passes through the pump 60. Thereby, the deterioration of the pump 60 can be suppressed and the service life of the pump 60 can be extended.

[0065] In the above-described third embodiment, as shown in FIG. 6, the pump 60 is provided in the connecting pipe 23. However, it may be provided on the downstream side of the sedimentation chamber 22. For example, it may be provided in the return pipe 20.

[0066] In the above-described third embodiment, the outlet 31 of the external circulation path 15 is located below the liquid level 13, but it may be located at the same height as the liquid level 13 or above the liquid level 13. (Fourth Embodiment)

[0067] In the first embodiment described above, as shown in FIG. 3, the downstream end of the extraction pipe 19 is connected to the body 26 of the sedimentation chamber 22. However, in the fourth embodiment described below, as shown in FIGS. 7 and 8, the downstream end of the extraction pipe 19 is connected to the bottom of the sedimentation chamber 22 and penetrates the bottom plate 27 from below to above and enters the inside of the sedimentation chamber 22. Inside the sedimentation chamber 22 and above the downstream end of the extraction pipe 19, a baffle plate 63 is provided. The baffle plate 63 is supported by a plurality of support arms 64 provided on the body 26 and faces the downstream end of the extraction pipe 19 from above.

[0068] Hereinafter, the operation of the above configuration will be described. The fermented sludge 2 in the methane fermentation tank 4 flows into the extraction pipe 19 from the inlet 30 of the external circulation path 15, flows through the extraction pipe 19, flows into the sedimentation chamber 22 from the downstream end of the extraction pipe 19, and flows upward in the sedimentation chamber 22. At this time, since the flow velocity of the fermented sludge 2 decreases in the sedimentation chamber 22, the sedimentable substances 34 contained in the fermented sludge 2 settle in the sedimentation chamber 22 and accumulate in the storage section 35.

[0069] The fermented sludge 2 that has flowed into the sedimentation chamber 22 from the downstream end of the extraction pipe 19 first hits the baffle plate 63 and spreads radially in the lateral direction (the radial direction of the body 26) while flowing upward. For this reason, the flow velocity of the fermented sludge 2 sufficiently decreases in the sedimentation chamber 22.

[0070] If the baffle plate 63 is not provided, the fermented sludge 2 flowing into the sedimentation chamber 22 from the downstream end of the extraction pipeline 19 flows along the shortest path and into the upper connecting pipe 23. As a result, the upward flow (upflow) of the fermented sludge 2 may short-circuit, and there is a possibility that the flow velocity of the fermented sludge 2 does not sufficiently decrease within the sedimentation chamber 22. By providing the baffle plate 63, such problems can be solved. (The Fifth Embodiment)

[0071] In the first embodiment described above, as shown in FIGS. 1 and 3, as an example of the circulation path for circulating the fermented sludge 2 in the methane fermentation tank 4, the external circulation path 15 is connected outside the methane fermentation tank 4. However, in the fifth embodiment described below, as shown in FIG. 9, as another example of the circulation path, an internal circulation path 67 may be provided inside the methane fermentation tank 4.

[0072] The internal circulation path 67 includes an extraction pipeline 19 (an example of an extraction path) for extracting the fermented sludge 2 in the methane fermentation tank 4, a return pipeline 20 (an example of a return path) for returning the extracted fermented sludge 2 into the methane fermentation tank 4, and an upward pipeline 21 (an example of an upward path) through which the extracted fermented sludge 2 flows upward.

[0073] The upward pipeline 21 is formed by a partition or the like provided in the methane fermentation tank 4, and includes a sedimentation chamber 22 (an example of a sedimentation path portion) with an enlarged flow path cross-sectional area and a connecting flow path 69. A part of the upward pipeline 21, the connecting flow path 69, is connected between the upstream end of the return pipeline 20 and the upper part of the sedimentation chamber 22, whereby the upstream end of the return pipeline 20 is connected to the upper end of the upward pipeline 21.

[0074] The flow path cross-sectional area of the sedimentation chamber 22 is set to be larger than the flow path cross-sectional areas of the extraction pipeline 19 (corresponding to the circulation path 67 connected upstream of the sedimentation chamber 22), the return pipeline 20, and the connecting flow path 69, respectively.

[0075] The sedimentation chamber 22 has a storage section 35 at the bottom for storing the sedimented sedimentable substances 34. The sedimentation chamber 22 is provided with a discharge section 37 for discharging the sedimentable substances 34 accumulated in the storage section 35 from inside the sedimentation chamber 22 to the outside. According to this, the same operations and effects as those of the first embodiment can be obtained.

[0076] In each of the above embodiments, as shown in FIGS. 2 and 4, four sludge agitation devices 6 are evenly distributed around the methane fermentation tank 4 at predetermined angles, but a plurality of devices other than four may be arranged. Further, for example, when the methane fermentation tank 4 is small, only one sludge agitation device 6 may be installed. In each of the above embodiments, the discharge of the sedimentable substances 34 deposited in the storage section 35 to the outside is performed by driving the discharge pump 39 and opening the discharge valve 40. However, the discharge pump 39 may not be provided, and only the discharge valve 40 may be provided to discharge by its own weight. Furthermore, instead of the discharge pump 39, a dumper truck may be connected to the downstream side of the discharge valve 40 to suck and discharge the sedimentable substances 34.

Explanation of Reference Numerals

[0077] 1 Methane fermentation treatment apparatus 2 Fermentation sludge 3 Biogas 4 Methane fermentation tank 5 Sludge agitation device 9 Side wall 11 Bottom wall 14 Circumferential direction 15 External circulation path (circulation path) 16 Gas lift pump (flow generating device) 19 Extraction pipeline (extraction path) 20 Return pipeline (return path) 21 Upward pipeline (upward path) 22 Sedimentation chamber (sedimentation path section) 30 Inlet (upstream end of external circulation path) 31 Outlet (downstream end of external circulation path) 32 Central part 34 Sedimentable substance 35 Storage section 36 Connection point 37 Discharge section 41 Air supply device 55 One side 60 Mechanically driven pump 67 Internal circulation path (circulation path)

Claims

1. A methane fermentation treatment apparatus for subjecting an organic material to be treated to methane fermentation, comprising: a methane fermentation tank for subjecting the material to be treated to methane fermentation with the stored fermentation sludge to generate biogas; a sludge stirring device for stirring the fermentation sludge in the methane fermentation tank; the sludge stirring device having a circulation path for circulating the fermentation sludge in the methane fermentation tank and a flow generating device for generating a flow of the fermentation sludge in the circulation path; the circulation path having an upward path through which the fermentation sludge flows upward; the upward path having a sedimentation path section; the flow cross-sectional area of the sedimentation path section being larger than the flow cross-sectional area of the circulation path connected to the upstream side of the sedimentation path section; a methane fermentation treatment apparatus, characterized in that a discharge section for discharging the sedimented substances sedimented in the sedimentation path section to the outside is provided.

2. The upstream end of the circulation path opens at the bottom in the methane fermentation tank; The methane fermentation treatment apparatus according to claim 1, characterized in that the downstream end of the circulation path opens in the methane fermentation tank above the upstream end of the circulation path.

3. The flow generating device is a gas lift pump; The methane fermentation treatment apparatus according to claim 2, characterized in that the gas lift pump has an air supply device for supplying biogas to the sedimentation path section.

4. The flow generating device is a mechanically driven pump; The methane fermentation treatment apparatus according to claim 2, characterized in that the pump is provided in the circulation path on the downstream side of the sedimentation path section.

5. The circulation path has a drawing path for drawing out the fermentation sludge in the methane fermentation tank to the outside of the tank and a return path for returning the drawn-out fermentation sludge into the tank; the downstream end of the drawing path is connected to the sedimentation path section; the upstream end of the return path is connected to the upward path; the sedimentation path section has a storage section at the bottom for storing the sedimented substances; the storage section is formed below the connection point between the drawing path and the sedimentation path section; The methane fermentation treatment apparatus according to claim 1, characterized in that the discharge section discharges the sedimented substances accumulated in the storage section to the outside.

6. A plurality of sludge stirring devices are arranged at different locations in the circumferential direction of the methane fermentation tank; the upstream end of the circulation path of each sludge stirring device opens at the bottom in the methane fermentation tank; The methane fermentation treatment apparatus according to claim 1, characterized in that the downstream end of the circulation path of each sludge stirring device opens in the methane fermentation tank above the upstream end of the circulation path and faces the center of the methane fermentation tank in a plan view.

7. A plurality of sludge stirring devices are arranged at different locations in the circumferential direction of the methane fermentation tank; The upstream end of the circulation path of each sludge agitation device opens at the bottom inside the methane fermentation tank, The methane fermentation treatment apparatus according to claim 1, wherein the downstream end of the circulation path of each sludge agitation device opens inside the methane fermentation tank above the upstream end of the circulation path and facing any one of the circumferential directions along the side wall surface of the methane fermentation tank in plan view.

8. The circulation path has a drawing path for drawing out the fermented sludge inside the methane fermentation tank to the outside of the tank and a return path for returning the drawn-out fermented sludge to the inside of the tank. The downstream end portion of the drawing path is connected to the lower part of the upward path. The upstream end portion of the return path is connected to the upper part of the upward path. The methane fermentation treatment apparatus according to claim 6 or claim 7, wherein the upstream end of the drawing path is located at a position closer to the center and at the bottom inside the methane fermentation tank than the downstream end of the return path.

9. The methane fermentation treatment apparatus according to any one of claims 1 to 8, wherein the bottom of the methane fermentation tank is flat.

10. A methane fermentation treatment method for subjecting an organic object to be treated to methane fermentation, A biogas generation step of generating biogas by subjecting the object to be treated to methane fermentation with the fermented sludge stored in the methane fermentation tank, And a stirring step of stirring the fermented sludge inside the methane fermentation tank. In the stirring step, the fermented sludge inside the methane fermentation tank flows through a circulation path connected to the methane fermentation tank, is drawn out of the methane fermentation tank, and then returned to the inside of the methane fermentation tank. When the fermented sludge flows upward through the sedimentation path portion formed in the circulation path, the flow velocity of the fermented sludge decreases by the flow path cross-sectional area of the sedimentation path portion expanding more than the flow path cross-sectional area of the circulation path connected upstream of the sedimentation path portion, and the sedimentable substances contained in the fermented sludge settle to the bottom of the sedimentation path portion. The methane fermentation treatment method is characterized by this.

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