Methane fermentation treatment method and methane fermentation treatment apparatus

Abstract

This invention provides a methane fermentation treatment method that can reduce the risk of clogging while improving the removal performance of unsuitable substances for fermentation, even when using a small supply of dilution hot water and a small-capacity mixing and adjusting tank. [Solution] A methane fermentation treatment method for treating organic waste containing unsuitable materials for fermentation with methane fermentation, comprising: a sedimentation separation step of separating the organic waste into a light component and a heavy component using a liquid cyclone; a solid-liquid separation step of separating the light component after the sedimentation separation step into solid and liquid components; a methane fermentation treatment step of supplying the liquid component after the solid-liquid separation step to a methane fermentation tank for methane fermentation treatment; and a fermentation sludge circulation step of extracting the fermentation sludge from the methane fermentation tank, supplying it together with the organic waste to the liquid cyclone performing the sedimentation separation step, and returning it to the methane fermentation tank as the light component after the sedimentation separation step.

Description

Technical Field

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

Background Art

[0002] In order to realize a resource recycling society, a methane fermentation treatment apparatus that converts organic waste such as food waste and paper waste into biogas (containing about 60% methane gas, about 40% carbon dioxide gas, a small amount of hydrogen sulfide, etc.) that can be used as an energy source by anaerobic microorganisms has attracted attention.

[0003] Patent Document 1 discloses such a methane fermentation treatment apparatus. The methane fermentation treatment apparatus includes a solubilization tank that premixes crushed organic waste as a raw material and a fermentation liquid drawn from a methane fermentation tank to promote hydrolysis and acid fermentation, and a methane fermentation tank to which the liquid component separated from the slurry-like organic waste treated in the solubilization tank through a solid-liquid separation device is supplied.

[0004] For example, as shown in FIG. 4, organic waste including food waste such as kitchen waste generated in ordinary households and paper waste is crushed by a crushing and separating device and roughly separated into fermentation-inappropriate substances and fermentation-appropriate substances, and the separated fermentation-appropriate substances are put into a mixing adjustment tank that functions as a solubilization tank. In the mixing adjustment tank, diluted warm water is introduced, and the fermentation-appropriate substances are stirred and mixed by a stirrer, so that the paper waste is crushed into fibrous form and slurried, and fine heavy particles such as sand and shells, which are fermentation-inappropriate substances mixed in the fermentation-appropriate substances, precipitate to the bottom and are drawn out from the mixing adjustment tank by sequentially opening and closing a plurality of gate valves provided at the bottom.

[0005] Lightweight substances such as plastics mixed in the slurry-like organic waste are drawn out by a withdrawal pump and put into a dehydrator. In the dehydrator, the heavy substances and the slurry-like organic waste put in are subjected to solid-liquid separation to remove fermentation-inappropriate substances, and the dehydrated filtrate is stored in a filtrate receiving tank and supplied to a methane fermentation tank by a filtrate input pump.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2012-86157 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The aforementioned crushing and sorting equipment could not accurately separate fermentable and unfermentable materials. Therefore, it was necessary to separate the unfermentable materials contained in the separated fermentable materials by sedimentation in a mixing and adjustment tank. Furthermore, as the amount of organic waste to be processed increased, the amount of dilution hot water added also increased, leading to a larger mixing and adjustment tank, which in turn increased equipment costs. Additionally, the power required for the agitator also increased, resulting in higher operating costs.

[0008] Furthermore, sediment could adhere to the bottom of the mixing and adjustment tank or the gate valve, causing blockages or malfunctions in opening and closing the valve, which presented the challenge of requiring frequent and time-consuming maintenance.

[0009] In view of the above-mentioned prior art, the object of the present invention is to provide a methane fermentation treatment method and a methane fermentation treatment apparatus that can reduce the risk of clogging while improving the removal performance of unsuitable substances for fermentation, even when the supply amount of dilution hot water is small and the mixing and adjusting tank has a small capacity. [Means for solving the problem]

[0010] To achieve the above objective, the first characteristic configuration of the methane fermentation treatment method according to the present invention is a methane fermentation treatment method for methane fermentation treatment of organic waste containing unsuitable materials for fermentation, comprising: a sedimentation separation step of separating the organic waste into a light component and a heavy component using a liquid cyclone; a solid-liquid separation step of separating the light component after the sedimentation separation step into solid and liquid components; a methane fermentation treatment step of supplying the liquid component after the solid-liquid separation step to a methane fermentation tank for methane fermentation treatment; and a fermentation sludge circulation step of extracting the fermentation sludge from the methane fermentation tank, supplying it together with the organic waste to the liquid cyclone performing the sedimentation separation step, and returning it to the methane fermentation tank as the light component after the sedimentation separation step.

[0011] In the sedimentation separation process, organic waste is fed into a liquid cyclone, where it is separated into lightweight and heavy components. The lightweight component is then separated into solid and liquid components in the solid-liquid separation process, and the resulting liquid component is supplied to a methane fermentation tank for methane fermentation treatment. In the sedimentation separation process, fermentation sludge extracted from the methane fermentation tank is supplied to the liquid cyclone along with the organic waste. After the sedimentation separation process, the lightweight component, i.e., the liquid components of the fermentation sludge and organic waste, is returned to the methane fermentation tank in a fermentation sludge circulation process. By performing a sedimentation separation process using a liquid cyclone in this way, there is no need to remove unsuitable materials from the organic waste in a mixing and adjustment tank; it is sufficient to simply dilute the organic waste, shortening the residence time in the tank and eliminating the need for a large mixing and adjustment tank.

[0012] The second characteristic configuration is that, in addition to the first characteristic configuration described above, it further includes a crushing and separation process prior to the sedimentation and separation process, in which the organic waste is crushed using a crushing and separation device while removing materials unsuitable for fermentation.

[0013] In order to separate unsuitable materials for fermentation by sedimentation using a liquid cyclone, a crushing and sorting process using a crushing and sorting device can be performed to crush the organic waste and remove coarse unsuitable materials for fermentation in advance.

[0014] The third characteristic configuration is that, in addition to the second characteristic configuration described above, it further includes a bag-breaking step prior to the crushing and sorting step, in which the organic waste contained in the storage bags is broken open using a bag-breaking device and removed.

[0015] By using a bag-breaking device to break open the bags containing organic waste and removing the contents, the crushing and sorting process can be carried out quickly.

[0016] The fourth characteristic configuration is that, in addition to the first characteristic configuration described above, in the fermentation sludge circulation process, the flow rate of the fermentation sludge supplied to the liquid cyclone is set to 10 times or more the flow rate of the organic waste.

[0017] In a liquid cyclone, heavy materials unsuitable for fermentation, contained in a slurry of organic waste and fermented sludge, are separated by centrifugal force. If the flow rate of the fermented sludge supplied to the liquid cyclone is set to 10 times or more the flow rate of the organic waste, the fluidity of the heavy materials within the slurry can be ensured, thereby guaranteeing the separation performance of these heavy materials.

[0018] The fifth characteristic configuration is that, in addition to the fourth characteristic configuration described above, in the fermentation sludge circulation process, the fermentation sludge and the organic waste are supplied to the liquid cyclone from separate supply ports.

[0019] By supplying highly fluid fermented sludge and less fluid organic waste to the liquid cyclone from separate inlets, the organic waste is efficiently broken down inside the cyclone by the flow of fermented sludge, thereby promoting centrifugal separation.

[0020] The first characteristic configuration of the methane fermentation treatment apparatus according to the present invention is a methane fermentation treatment apparatus for subjecting organic waste containing fermentation-inappropriate substances to methane fermentation, comprising a liquid cyclone for separating the input organic waste into a light fraction and a heavy fraction, a solid-liquid separation device for solid-liquid separating the light fraction separated by the liquid cyclone, and a methane fermentation tank for supplying the liquid fraction solid-liquid separated by the solid-liquid separation device as a fermentation-appropriate substance. A fermentation sludge circulation flow path is provided for supplying the fermentation sludge withdrawn from the methane fermentation tank to the liquid cyclone and returning the light fraction containing the fermentation sludge separated by the liquid cyclone to the methane fermentation tank.

[0021] The second characteristic configuration is that, in addition to the first characteristic configuration described above, a mixing and adjustment tank is provided which is arranged in the front stage of the liquid cyclone and kneads the organic waste containing kitchen waste and paper waste into a slurry state.

Effects of the Invention

[0022] As described above, according to the present invention, it has become possible to provide a methane fermentation treatment method and a methane fermentation treatment apparatus that can reduce the clogging risk while improving the removal performance of fermentation-inappropriate substances even in a mixing and adjustment tank with a small supply amount of diluted warm water and a small capacity.

Brief Description of the Drawings

[0023] [Figure 1] Explanatory drawing of the methane fermentation treatment apparatus according to the present invention [Figure 2] (a) to (d) show the liquid cyclone used in the present invention, the upper part of each being an explanatory drawing in plan view and the lower part being an explanatory drawing in front view [Figure 3] Explanatory drawing of the pretreatment apparatus of the methane fermentation treatment apparatus according to the present invention [Figure 4] Explanatory drawing of a conventional methane fermentation treatment apparatus

Embodiments for Carrying Out the Invention

[0024] The methane fermentation treatment method and methane fermentation treatment apparatus according to the present invention will be described below with reference to the drawings. [Description of methane fermentation equipment] Figure 1 illustrates the main components of the methane fermentation treatment apparatus 1 according to the present invention. The methane fermentation treatment apparatus 1 is a device that performs methane fermentation treatment on organic waste containing unsuitable materials for fermentation. The main components of the methane fermentation treatment apparatus 1 include a crushing and separating device 4, a mixing and adjusting tank 6, a liquid cyclone 7, a dewatering machine 8, a multi-disc type separator (MD separator) 9, a filtrate receiving tank 10, and a methane fermentation tank 11.

[0025] The crushing and separating device 4 includes a hopper 40 into which the material to be fed, a crushing mechanism that crushes the material fed into the hopper 40 by striking it with a rotating blade, a sieving and sorting mechanism that selects materials suitable for fermentation from the material crushed by the crushing mechanism, and an air-powered sorting mechanism that removes lightweight resin sheet pieces and the like from the material.

[0026] Food waste (kitchen waste) and paper waste, which have been pre-sorted from the collected combustible waste as suitable for fermentation, are fed into the crushing and sorting device 4. The crushing mechanism finely crushes the waste, and the sieving mechanism and air separation mechanism separate it into materials suitable for fermentation and materials unsuitable for fermentation. The separated materials suitable for fermentation are then fed into the mixing and adjustment tank 6.

[0027] The mixing and adjusting tank 6 comprises a casing 60 with a circular cross-section and a tapered bottom, a motor-driven agitator 61, and a dilution hot water injection section. The fermentation material is mixed and stirred (kneaded) with dilution hot water in the mixing and adjusting tank 6, and the paper waste is broken down into fibers and homogenized into a slurry together with the food waste.

[0028] The slurry-like fermentation-suitable material, which is drawn out from the bottom of the mixing and adjusting tank 6 by an extraction pump, contains fine, heavy particles such as sand and seashells, as well as lightweight materials with a low specific gravity such as plastic, which are considered unsuitable for fermentation.

[0029] As shown in Figure 2(a), the liquid cyclone 7 has a double-cylinder structure consisting of an outer cylinder 70 and an inner cylinder 71 with a circular cross-section and a tapered lower end. A pair of input sections 72 and 73 are positioned opposite each other so that the material to be separated flows in the same rotational direction in the space formed between the outer cylinder 70 and the inner cylinder 71, separating the input organic waste into light and heavy components.

[0030] From one input section 72, a slurry-like fermentation material homogenized in the mixing and adjusting tank 6 is injected under pressure, and from the other input section 73, fermentation sludge extracted from the methane fermentation tank 11 by a methane circulation pump is injected under pressure. The slurry-like fermentation material injected from input section 72 and the fermentation sludge injected from input section 73 are injected into the space between the outer cylinder 70 and the inner cylinder 71, and are mixed by the difference in flow velocity to form a mixed slurry, which increases in fluidity and descends while rotating at high speed along the wall. Solid particles with a high specific gravity and particle size contained in the mixed slurry are subjected to centrifugal force and are arranged towards the periphery wall, while solid particles with a low specific gravity and particle size are arranged towards the center at the bottom of the inner cylinder 71.

[0031] Finally, heavy, fine-grained materials such as sand and seashells are discharged from the lower outlet 74, while lighter materials with a lower specific gravity, such as plastics, are discharged together with the mixed slurry from the upper outlet 75.

[0032] The lightweight components separated by the liquid cyclone 7 are separated into solid and liquid components using a solid-liquid separation device such as a multi-disc type separator (MD separator). The solid components are transported to the dewatering machine 8 via a conveyor mechanism, and the liquid components are introduced into the methane fermentation tank 11 as a material suitable for fermentation.

[0033] The weight portion separated by the liquid cyclone 7 is fed into a dewatering machine 8, such as a screw press dewatering machine, where it undergoes solid-liquid separation. The solid portion is removed as unsuitable for fermentation, and the liquid portion is stored in a filtrate receiving tank 10 and fed into the methane fermentation tank 11 by a filtrate input pump. The fermentation sludge circulation channel 14 is composed of an extraction channel 12 that supplies the fermentation sludge extracted from the methane fermentation tank 11 to the liquid cyclone 7, and a return channel 13 that returns the lighter portion, including the fermentation sludge separated by the liquid cyclone 7, back to the methane fermentation tank.

[0034] In the mixing and adjusting tank 6, organic waste, including food waste and paper waste, is kneaded into a slurry. However, there is no need to separate unsuitable materials for fermentation by sedimentation, as they are separated in the subsequent liquid cyclone 7. This allows for a smaller size and reduces the amount of hot water used for dilution.

[0035] The pair of inlet sections 72 and 73 provided in the liquid cyclone 7 are not limited to the configuration shown in Figure 2(a), but may be arranged as shown in Figure 2(b) so that a counterflow is formed in the space between the outer cylinder 70 and the inner cylinder 71. The low-fluidity slurry-like fermentation material is dispersed by the high-fluidity fermentation sludge flowing as a counterflow and flows along the flow of the fermentation sludge, and is centrifuged in the process.

[0036] Furthermore, as shown in Figure 2(c), the input section 72 into which a low-fluidity slurry-like fermentation material is introduced may be configured to be positioned perpendicular to the outer cylinder 70. The low-fluidity slurry-like fermentation material, which is injected from the perpendicular direction into the space formed between the outer cylinder 70 and the inner cylinder 71, is dispersed by the highly fluid fermentation sludge injected tangentially from the input section 73, and flows along the flow of the fermentation sludge, and is centrifuged in the process.

[0037] Furthermore, as shown in Figure 2(d), the piping constituting the input section 72 may be connected to the piping constituting the input section 73 in an orthogonal or inclined position so that a slurry-like fermentation material with low fluidity is injected into the piping constituting the input section 73 into which highly fluid fermentation sludge is injected.

[0038] Figure 3 illustrates other processing devices that make up the methane fermentation processing device 1, which are installed upstream of the crushing and separating device 4. The processing device includes a bag collection conveyor C1, a bag breaking device 2, a post-bag removal conveyor C2, a ballistic sorter 3, a flight conveyor C3, and the like.

[0039] The waste is separated at each household as combustible waste and collected in storage bags by collection trucks and gathered in the receiving pit of the processing plant. The storage bags are fed from the receiving pit into the receiving hopper of the bag breaker 2, where they are broken open by the bag breaker mechanism of the bag breaker 2. After the contents are removed, they are transported by conveyor C2 to the ballistic sorter 3. The storage bags broken open by the bag breaker mechanism are then transported by bag collection conveyor C1 to the receiving pit as combustible waste.

[0040] The ballistic sorting machine 3 is a device for sorting different materials and consists of an inclined screen equipped with a vibration device. Heavy materials roll down along the inclined surface and are transported to the receiving pit by the heavy material conveyor C4, while lighter materials rise along the inclined surface without rebound and fall from the edge of the screen, and are dropped into the hopper of the crushing and separating device 4 by the flight conveyor C3.

[0041] The unsuitable materials for fermentation, sorted by the crushing and sorting device 4, are transported to the receiving pit by the unsuitable material conveyor C5.

[0042] [Explanation of the methane fermentation process] A methane fermentation treatment method for treating organic waste containing unsuitable materials for fermentation includes: a sedimentation separation step in which the organic waste is separated into light and heavy components using a liquid cyclone 7; a solid-liquid separation step in which the light component after the sedimentation separation step is separated into solid and liquid components; a methane fermentation treatment step in which the liquid component after the solid-liquid separation step is supplied to a methane fermentation tank 11 for methane fermentation treatment; and a fermentation sludge circulation step in which the fermentation sludge in the methane fermentation tank 11 is extracted and supplied together with the organic waste to the liquid cyclone 7 which is performing the sedimentation separation step, and returned to the methane fermentation tank 11 as the light component after the sedimentation separation step.

[0043] In the sedimentation separation process, organic waste is fed into the liquid cyclone 7, where it is separated into lightweight and heavy components. The lightweight component undergoes a solid-liquid separation process, after which the liquid component is supplied to the methane fermentation tank for methane fermentation treatment. In the sedimentation separation process, fermentation sludge extracted from the methane fermentation tank is supplied to the liquid cyclone 7 along with the organic waste. After the sedimentation separation process, the lightweight component undergoes a solid-liquid separation process to separate the solid components, meaning that the fermentation sludge and the liquid components of the organic waste are returned to the methane fermentation tank in a fermentation sludge circulation process. This sedimentation separation process using the liquid cyclone 7 eliminates the need to remove unsuitable materials from the organic waste in a mixing and adjustment tank. It is simply necessary to dilute the organic waste with fermentation sludge from which the solid components have already been removed, thus eliminating the need for a large mixing and adjustment tank.

[0044] Prior to the sedimentation separation process, the process further includes a crushing and separation process in which organic waste is crushed by a crushing and separation device 4 while removing unsuitable materials for fermentation. By performing the crushing and separation process using the crushing and separation device 4 in order to separate unsuitable materials for fermentation by sedimentation with the liquid cyclone 7, the organic waste can be crushed and large unsuitable materials for fermentation can be removed in advance.

[0045] The process further includes a bag-breaking step preceding the crushing and sorting step, in which the organic waste contained in the storage bags is broken open using a bag-breaking device and removed. By breaking open the storage bags containing the organic waste with a bag-breaking device and removing the contents, the crushing and sorting step can be carried out quickly.

[0046] In the fermentation sludge circulation process, it is preferable that the flow rate of fermentation sludge supplied to the liquid cyclone 7 is set to 10 times or more the flow rate of the slurry-like fermentation-compatible material as organic waste. The liquid cyclone 7 centrifugally separates heavy materials that are unsuitable for fermentation, which are contained in the mixed slurry formed by mixing the slurry-like fermentation-compatible material and the fermentation sludge. When the flow rate of fermentation sludge supplied to the liquid cyclone 7 is set to 10 times or more the flow rate of the slurry-like fermentation-compatible material, the fluidity of heavy materials within the fermentation sludge can be ensured, and the separation performance of heavy materials can be ensured.

[0047] In the fermentation sludge circulation process, it is preferable that the fermentation sludge and organic waste are supplied to the liquid cyclone 7 from separate inlets. By supplying the highly fluid fermentation sludge and the less fluid, slurry-like fermentation material (organic waste) to the liquid cyclone 7 from separate inlets, the organic waste is efficiently broken down inside the cyclone by the flow of the fermentation sludge, thereby promoting centrifugal separation.

[0048] The embodiments described above represent only one aspect of the present invention, and the present invention is not limited by this description. It goes without saying that the specific configuration of each part can be appropriately modified and designed within the scope that the effects of the present invention are achieved. [Explanation of Symbols]

[0049] 1: Methane fermentation apparatus 4: Crushing and separating device 6: Mixing adjustment tank 7: Liquid Cyclone 8: Dehydrator 11: Methane fermentation tank 12: Extraction route 13: Return route 14: Fermentation sludge circulation channel

Claims

1. A methane fermentation treatment method for treating organic waste containing unsuitable materials for fermentation, A sedimentation separation process in which organic waste is separated into light and heavy components using a liquid cyclone, A solid-liquid separation step is performed to separate the lightweight portion after the aforementioned sedimentation separation step, A methane fermentation process in which the liquid remaining after the solid-liquid separation process is supplied to a methane fermentation tank for methane fermentation treatment, A fermentation sludge circulation process is performed in which the fermentation sludge in the methane fermentation tank is extracted and supplied together with organic waste to the liquid cyclone that is performing the sedimentation separation process, and the sludge is returned to the methane fermentation tank as the lighter portion after the sedimentation separation process. A methane fermentation treatment method that includes this process.

2. The methane fermentation treatment method according to claim 1, further comprising, prior to the sedimentation separation step, a crushing and separation step in which the organic waste is crushed by a crushing and separation device while removing materials unsuitable for fermentation.

3. The methane fermentation treatment method according to claim 2, further comprising, prior to the crushing and sorting step, a bag-breaking step of breaking open a bag containing the organic waste using a bag-breaking device to remove it.

4. The methane fermentation treatment method according to claim 1, wherein in the fermentation sludge circulation step, the flow rate of the fermentation sludge supplied to the liquid cyclone is set to 10 times or more the flow rate of organic waste.

5. The methane fermentation treatment method according to claim 4, wherein in the fermentation sludge circulation step, the fermentation sludge and the organic waste are supplied to the liquid cyclone from separate supply ports.

6. A methane fermentation treatment apparatus for treating organic waste containing unsuitable materials for fermentation with methane fermentation, A liquid cyclone separates the organic waste that is put in into light and heavy components, A solid-liquid separation device for separating the lightweight component separated by the liquid cyclone, A methane fermentation tank that supplies the liquid separated by the solid-liquid separation device as a fermentation material, Equipped with, A fermentation sludge circulation channel supplies the fermentation sludge extracted from the methane fermentation tank to the liquid cyclone, and returns the lightweight portion containing the fermentation sludge separated by the liquid cyclone to the methane fermentation tank, A methane fermentation treatment apparatus equipped with the following features.

7. The methane fermentation apparatus according to claim 6, comprising a mixing and adjusting tank positioned upstream of the liquid cyclone for kneading the organic waste, including kitchen waste and paper waste, into a slurry.

Images