JP2012086157A - Fermentation liquid circulating methane fermentation method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably keeping high efficient methane fermentation treatment for a long period of time.SOLUTION: Organic solid waste C containing lightweight foreign matter M is supplied into an anaerobic raw material tank 10 provided with a movable rake 60 and a screw conveyer 70 penetrating a peripheral wall at predetermined heights on the inside. The liquid level is kept at a predetermined height by feeding a fermentation solution S to the raw material tank 10, drawing out the fermentation solution S from a lower part and returning it to an upper side. The waste C supplied into the raw material tank 10 is dipped in the fermentation solution S for solubilization and circulated with the fermentation solution S and decomposed into biogas G. The lightweight foreign matter M floating on the surface of the liquid of the raw material tank 10 is collected to the screw conveyer 70 by the movement of the rake 60 and discharged. Preferably, the fermentation solution S stored in a fermentation tank 30 is continuously fed to the raw material tank 10, the fermentation solution S of the raw material tank 10 is continuously drawn out to be separated into solid and liquid. The separated filtrate D is transferred to the fermentation tank 30, and the solid content E is returned to the raw material tank 10 for circulation.

Description

  The present invention relates to a fermentation liquid circulation type methane fermentation method and apparatus, and more particularly, to a method and apparatus for storing organic solid waste in a raw material tank and performing a methane fermentation treatment while circulating the fermentation liquid.

  In order to realize a resource recycling society, biogas (approximately 60% methane gas, approximately 40% carbon dioxide gas, small amount) that can be used as an energy source by organic solid waste such as garbage and paper waste by anaerobic microorganisms The methane fermentation process is being put to practical use. An example of conventional methane fermentation treatment is, for example, as disclosed in Patent Document 1, after separating organic solid waste from mixed foreign substances and finely pulverizing it into a slurry, and in a methane fermentation tank (anaerobic fermentation tank) This is a wet method in which methane fermentation is performed by contacting with anaerobic microorganisms. However, the wet methane fermentation method requires time and labor for slurrying, and the amount of fermentation waste liquid generated after fermentation treatment increases because it is necessary to add at least 1 to 2 times dilution water to the waste for slurrying. There is a problem that the burden of wastewater treatment increases.

  On the other hand, as disclosed in Patent Documents 2 to 4, the present inventors have developed a fermented liquid circulation type methane fermentation method capable of treating organic solid waste without adding water to a slurry. FIG. 6 shows an example of the methane fermentation apparatus 1 disclosed in Patent Document 4. The methane fermentation apparatus 1 in the illustrated example has a raw material tank 10 for storing organic solid waste C in an airtight manner and a 767A fermentation liquid (digestion solution) S containing anaerobic microorganisms for decomposing the waste C in an airtight manner. The tank 30, the supply device 40 that continuously supplies the fermented liquid S from the fermenter 30 to the raw material tank 10, the fermented liquid S from the raw material tank 10 is continuously withdrawn and separated into solid E and filtrate D, and The separated filtrate D is sent to the fermenter 30 and has a solid-liquid separation device 20 that returns the solid content E to the raw material tank 10, and wastes are circulated while circulating the fermented liquid S between the raw material tank 10 and the fermenter 30. C is methane-fermented. The raw material tank 10 and the fermenter 30 are anaerobic tanks capable of storing the waste C and the fermented liquid S in an airtight manner, and the gas phase portions are communicated with each other by a gas recovery path 44.

  At the inlet 8 of the raw material tank 10, for example, organic solid waste C such as so-called combustible waste discharged from ordinary households, restaurants, food factories, etc. is roughly pulverized to an appropriate size by the crushing device 2. A fixed amount is continuously added. Fermentation liquid S is supplied from the fermenter 30 to the raw material tank 10, and waste C is immersed in the fermentation liquid S. The waste C in the raw material tank 10 is gradually solubilized by anaerobic microorganisms while being immersed and mixed in the fermentation broth S. The mixed liquid (C + S) of the waste C and the fermented liquid S is extracted by the pulling device 14 to the raw material tank 10. And is introduced into the solid-liquid separator 20 and separated into a solid content E and a filtrate D. Waste C that has been sufficiently solubilized in the raw material tank 10 to have a small particle size is sent from the separation device 20 together with the fermentation liquid S to the fermenter 30 via the transport path 28 as a filtrate D. It is further decomposed into biogas G by anaerobic microorganisms while circulating between the tank 10. On the other hand, the waste C having a large particle size that has not yet been sufficiently solubilized in the raw material tank 10 is returned to the raw material tank 10 from the separation device 20 via the return path 27 as a solid content E, and is further allowed in the raw material tank 10. After being solubilized to a small particle size, it is reintroduced into the solid-liquid separator 20.

  In the fermentation liquid circulation type methane fermentation method shown in FIG. 6, the organic solid waste C is first solubilized in the raw material tank 10 while being immersed in the fermentation liquid S, and only the solubilized waste C is fermented with the fermentation liquid S. This is a method of circulating to 30 to decompose into biogas G, in which the microbial decomposition rate in the waste C is relatively fast (for example, garbage) and the relatively slow degradable organic material (for example, paper waste) ) And the residence time remaining in the raw material tank 10 is separated, and the entire waste C including both can be subjected to methane fermentation treatment with high efficiency without slurrying. Moreover, since the waste C is processed without water addition, the amount of the fermentation waste liquid N drawn out from the fermenter 30 as appropriate can be kept small. An organic acid is generated in the raw material tank 10 by the decomposition reaction (acid fermentation) of the solid waste C. However, the circulation of the fermentation liquor S can prevent the pH drop (acid loss) of the raw material tank 10 due to the accumulation of the organic acid. 10 promotes efficient solubilization of the solid waste C, and methane-producing bacteria in the fermentation broth S supplied also in the raw material tank 10 decomposes the product of acid fermentation to produce biogas G. be able to.

  In addition, the fermented liquid circulation type methane fermentation apparatus 1 is not limited to the two-tank type using the raw material tank 10 and the fermenter 30 as shown in FIG. 6, for example, one tank using only the raw material tank 10 as shown in FIG. 8. It is also possible to use a formula (see Non-Patent Document 3). The raw material tank 10 in FIG. 8 has a perforated partition wall 21 that divides the inside up and down, an organic solid waste C intake 8 provided above the partition wall, and a supply path for supplying the fermentation broth S into the raw material tank 10. 41 and circulation paths 15 and 27 with a pump 16 for extracting the fermentation liquid S in the raw material tank 10 from below the partition wall and returning it to the partition wall and circulating it. For example, organic solid waste C such as combustible waste is introduced above the partition wall of the raw material tank 10 and the fermentation liquid S is supplied, solubilized while the waste C is immersed in the fermentation liquid S, and solubilized waste C Is circulated through the circulation paths 15 and 27 together with the fermentation liquid S to perform methane fermentation. The single tank type fermented liquid circulation type methane fermentation apparatus as shown in FIG. 8 also holds the waste C before solubilization in the raw material tank 10 by the solid-liquid separation action of the perforated partition wall 21 and only the solubilized waste C. Is circulated together with the fermentation liquor S to be decomposed into biogas G, so that the entire waste C including both easily decomposable organic matter and hardly decomposable organic matter can be subjected to methane fermentation treatment with high efficiency.

Japanese Patent No. 3064272 JP 2007-044588 A JP 2007-216135 A JP 2010-142735 A

  In the conventional fermentation liquid circulation type methane fermentation apparatus 1 shown in FIG. 6 and FIG. 8, a sorting device 3 is provided at the intake 8 of the raw material tank 10 for methane fermentation contained in organic solid waste C such as combustible waste. Inappropriate foreign matter K (such as polystyrene foam or wood chips) is separated and separated, and an organic solid organic substance C suitable for biogasification is put into the raw material tank 10. However, it is difficult to completely sort out the foreign matter K by the sorting device 3, and the foreign matter K that could not be sorted gradually accumulates in the raw material tank 10. In order to maintain the fermented liquid circulation type methane fermentation apparatus 1 stably, the foreign matter K accumulated in the raw material tank 10 must be discharged and removed as appropriate. However, when the raw material tank 10 is opened, air (oxygen) flows in. This causes inactivation of anaerobic microorganisms (decrease in fermentation efficiency), and there is a possibility that biogas G containing explosive methane and harmful hydrogen sulfide may diffuse to the surroundings. A mechanism for discharging K to the outside is required.

  The raw material tank 10 of FIGS. 6 and 8 discharges foreign matter while keeping the inside in a sealed state (anaerobic state), and therefore has a discharge port with an opening / closing valve 19a at the bottom of the internal space (in FIG. 8, the bottom of the space above the partition wall). 19 is provided, and a drawing path 17 with an on-off valve 17a is provided at the liquid level above the space. Heavy foreign matter G (wood pieces such as chopsticks, sand, shells, etc.) having a specific gravity greater than the water settled on the bottom is discharged from the discharge port 19 by opening the on-off valve 19a. Further, the lightweight foreign matter M (foamed polystyrene, vinyl, plastic, etc.) having a specific gravity smaller than the water floating on the liquid surface of the raw material tank 10 is collected in the overflow weir 18 by the water flow by opening the on-off valve 17a, and the residue treatment from the draw-out path 17 Discharge to device 52. For example, as shown in FIG. 6, the foreign matter M discharged to the residue processing device 52 is dehydrated by a dehydrating device 53 and disposed, and the filtrate (dehydrated separation liquid) is passed through a liquid receiving tank 54 and a return device (pump or the like) 55. It can return to the fermenter 30 or the raw material tank 10. If necessary, the foreign matter L floating in the fermentation broth S of the raw material tank 10 can be discharged to the residue treatment device 52 through a drawing path 56 with an on-off valve 56 a provided in the solid-liquid separation device 20.

However, when the organic solid waste C such as combustible waste is actually processed in the fermentation liquid circulation type methane fermentation apparatus 1 of FIG. 6 or FIG. There has been a problem that accumulated foreign matter, particularly lightweight foreign matter M, cannot be discharged sufficiently. That is, lightweight foreign matter M such as expanded polystyrene mixed in combustible waste, when moisture adheres in the raw material tank 10, adheres to each other due to the surface tension of water as shown in FIG. It has been found that the overflow weir 18 does not easily overflow. FIG. 7 (A) shows the results of a levitation experiment conducted by collecting the lightweight foreign matter M contained in the actual combustible waste, and the light foreign matter M adheres and gathers and a large lump with an apparent specific gravity of about 0.95 g / cm ³ is obtained. However, when the raw material tank 10 was actually opened and confirmed, a lump of lightweight foreign matter M protruded above the surface of the water more than the apparent specific gravity as shown in FIG. 7B. It also turned out to be accumulated in a (floating) state. The mass of the lightweight foreign matter M in FIG. 7B includes a part of the heavy foreign matter G that should originally sink to the bottom, and the reason why the lightweight foreign matter M is accumulated in a state different from the apparent specific gravity as shown in FIG. It is presumed that the biogas G generated in the raw material tank 10 adheres to the lightweight foreign matter M and gives buoyancy.

  The light-weight foreign matter M accumulated in a lump shape as shown in FIG. 7B is removed by a mechanism that discharges scum (float) or the like floating on the liquid surface with a water flow like the drawing-out path 17 in FIGS. Can not stay in the raw material tank 10 for a long period of time, greatly reducing the effective volume and lowering the efficiency of methane fermentation. In order to efficiently and stably treat organic solid waste C such as combustible waste for a long period of time by the fermentation liquid circulation method, the sealed state (anaerobic state) of the raw material tank 10 is maintained, as shown in FIG. A mechanism capable of removing foreign substances accumulated in the raw material tank 10 as shown in FIG.

  Therefore, an object of the present invention is to provide a fermentation liquid circulation type methane fermentation method and apparatus capable of stably maintaining a highly efficient methane fermentation treatment for a long period of time.

  Referring to the embodiment of FIG. 1, the fermented liquid circulation type methane fermentation method according to the present invention moves the organic solid waste C mixed with the light foreign matter M to a predetermined height on the inner side and a movable rake 60 and a screw passing through the peripheral wall. The liquid level is maintained at a predetermined level by circulation into the raw material tank 10 provided with the conveyor 70, supplying the fermentation liquid S to the raw material tank 10, and drawing the fermentation liquid S of the raw material tank 10 from below and returning it upward. Then, the waste C introduced into the raw material tank 10 is solubilized while being immersed in the fermentation broth S, and is decomposed into the biogas G while being circulated together with the fermented liquid S, and the lightweight foreign matter M floating on the liquid surface of the raw material tank 10 The rake 60 moves and is collected on the screw conveyor 70 and discharged.

  Further, referring to the block diagram of FIG. 1, the fermented liquid circulation type methane fermentation apparatus according to the present invention includes a raw material tank 10 provided with a movable rake 60 and a screw conveyor 70 penetrating a peripheral wall at a predetermined height inside, a raw material. The inlet 8 for introducing the organic solid waste C mixed with the light foreign matter M into the tank 10, the supply path 41 for supplying the fermentation liquid S to the raw material tank 10, and the fermentation liquid S in the raw material tank 10 are pulled out from below. Circulation paths 15 and 27 to return to the waste water C, solubilized waste C introduced into the raw material tank 10 while being soaked in the fermentation liquid S and circulated with the fermentation liquid S, decomposed into biogas G, Lightweight foreign matter M floating on the liquid surface is collected on the screw conveyor 70 by the movement of the rake 60 and discharged.

  Preferably, as shown in FIG. 1, a methane fermentation tank 30 for storing the fermentation liquor S is provided, and a supply device 40 for continuously supplying the fermentation liquor S of the fermentation tank 30 to the raw material tank 10 is supplied to the supply path 41. The paths 15 and 27 include a solid-liquid separator 20 that continuously pulls out the fermentation liquid S from the raw material tank 10 for solid-liquid separation and sends the separated filtrate D to the fermentation tank 30 and returns the solid content E to the raw material tank 10. .

  Preferably, as shown in FIG. 2, the movable rake 60 includes a horizontal arm member 62 and a scraping blade 63 hinged to the arm member 62. A plurality of mountain-shaped irregularities can be provided on the protruding edge of the scraping blade 63. More desirably, a discharge port 19 with an opening / closing valve 19a is provided at the bottom of the raw material tank 10, and the mobile rake 60 includes a lower rake 67 that slides on the bottom surface of the raw material tank 10, and sinks under the fermentation liquid in the raw material tank 10. The foreign matter G is collected at the discharge port 19 by the lower rake 67 and can be discharged by opening the on-off valve 19a.

  More preferably, as shown in FIG. 2, the horizontal section of the raw material tank 10 is circular, and the movable rake 60 has an intermediate arm member 62 in which an intermediate portion rotating around the vertical central axis of the raw material tank 10 is bent forward in the rotation direction. And a scraping blade 63 that is hinged to the inward portion 62a on the tip side of the bent portion of the arm member 62. Further, the screw conveyor 70 is extended in the radial direction of the raw material tank 10, and the inner part of the raw material tank is surrounded by a foreign material intake member 71 with a trapezoidal upper end intake groove 72. In 73, the scraping feather 63 of the rake 60 can be lifted up. As shown in FIG. 1, the screw conveyor 70 can include a water tank 75 that seals its outlet end.

  The fermented liquid circulation type methane fermentation method and apparatus according to the present invention includes a mobile rake 60 and a screw conveyor 70 that penetrates a peripheral wall to a predetermined height inside a raw material tank 10 into which an organic solid waste C mixed with a lightweight foreign matter M is introduced. And supplying the fermentation liquid S to the raw material tank 10 and maintaining the liquid level at a predetermined height by circulating the fermentation liquid S in the raw material tank 10 from below and returning it to the information. The waste C is solubilized while being immersed in the fermentation broth S, is circulated with the fermentation broth S, decomposes into biogas G, and the foreign matter M floating on the fermentation broth surface of the raw material tank 10 is transferred to the screw conveyor 70 by the movement of the rake 60. Since it is collected and discharged, the following advantageous effects are obtained.

(A) Lightweight foreign matter M mixed in the organic solid waste C adheres to each other inside the raw material tank 10 and floats as a large lump on the liquid surface. M can be scraped off from the lump and collected on the screw conveyor 70.
(B) Although the scraped light foreign matter M adheres again in a lump in the discharge process and may cause blockage, the light foreign matter M is sent out of the raw material tank 10 while avoiding blockage by using the screw conveyor 70. Can do.
(C) The light-weight foreign matter M that has become agglomerated may be in a state in which the biogas G is embraced inside the raw material tank 10 and protrudes high from the liquid surface, but the horizontal arm member 62 and the hinge are coupled to the movable rake 60. By including the vertically movable scraping blades 63, it is possible to efficiently collect lightweight foreign substances having different flying heights on the liquid level together with lightweight foreign substances below the liquid level.

(D) In addition, by including the scraper blades 63 provided with a plurality of mountain-shaped irregularities on the protruding edge in the movable rake 60, various kinds of light-weight foreign matters M including string-like light-weight foreign matters M can be efficiently removed. Can be scraped.
(E) When the cross section of the raw material tank 10 is circular, the movable rake 60 includes a light-weighted foreign substance M that floats on the liquid surface by including a rotary middle bent arm member 62 whose middle portion is bent forward in the rotational direction. It can be efficiently recovered while scraping inwardly.
(F) Reduction of the effective volume of the raw material tank 10 due to accumulation of the lightweight foreign matter M by methane fermentation of the organic solid waste C while discharging the lightweight foreign matter M from the raw material tank 10 by the mobile rake 60 and the screw conveyor 70 The methane fermentation efficiency of the waste C can be stably maintained for a long time.
(G) Further, by sealing the outlet end of the screw conveyor 79 with the water tank 75, the lightweight foreign matter M can be discharged to the outside while the raw material tank 10 is kept sealed.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments and examples for carrying out the present invention will be described with reference to the accompanying drawings.
These are explanatory drawings of one Example of the fermented liquid circulation type methane fermentation apparatus of this invention. These are horizontal sectional views of the raw material tank 10 including the mobile rake 60 and the screw conveyor 70 of FIG. These are explanatory drawings of other Examples of the mobile rake 60 of this invention. These are the graphs which show the experimental result which confirmed the foreign material discharge | emission capability by the fermented liquid circulation type methane fermentation apparatus of FIG. These are explanatory drawings of other Examples of the fermented liquid circulation type methane fermentation apparatus of the present invention. These are explanatory drawings of an example of the conventional fermentation liquid circulation type methane fermentation apparatus. These are explanatory drawings which show the state of the lightweight foreign material accumulate | stored in the methane fermentation apparatus of FIG. These are explanatory drawings of other examples of the conventional fermentation liquid circulation type methane fermentation apparatus.

  FIG. 1 shows an embodiment of a fermentation liquid circulation type methane fermentation apparatus 1 of the present invention. The illustrated methane fermentation apparatus 1 includes a raw material tank 10 for storing organic solid waste C in an airtight manner. A mobile rake 60 and a screw conveyor 70 penetrating a peripheral wall are provided at a predetermined height inside the raw material tank 10. Is provided. In addition, the raw material tank 10 is provided with an intake 8 into which the organic solid waste C mixed with the lightweight foreign matter M, a supply path 41 for supplying the fermentation broth S, and an internal fermentation broth S is drawn from below to move upward. Circulation paths 15 and 27 with a return pump 16 are provided. The organic solid waste C is introduced into the raw material tank 10 from the inlet 8 and the fermentation liquid S is supplied from the supply path 41. The fermentation liquid S in the raw material tank 10 is extracted from below by the circulation paths 15 and 27. The liquid level of the fermentation broth S is maintained at a predetermined height while being returned and circulated, solubilized while immersing the input waste C in the fermentation broth S, and the solubilized waste C is further added to the fermentation broth S. It decomposes into biogas G while circulating with it. An example of the fermentation broth S is sludge containing anaerobic microorganisms (for example, seed sludge acclimatized by other methane fermentation treatments). If necessary, decomposition treatment additives such as neutralizing agents and micronutrients are added. May be added.

  The methane fermentation apparatus 1 in the illustrated example is of the same type as that in FIG. 6, includes a methane fermentation tank 30 that stores the fermentation liquid S in an airtight manner, and uses the fermentation liquid S in the fermentation tank 30 as a raw material on a supply path 41. Including the supply device 40 (for example, a pump) that continuously supplies the tank 10, the fermentation liquor S mixed with the waste C in the raw material tank 10 is continuously drawn on the circulation paths 15 and 27, and the solid content E The filtrate D includes a solid-liquid separation device 20 that performs solid-liquid separation. The solid-liquid separation device 20 in the illustrated example includes a drawing device 14 (drawing path 15 with a pump 16 in the illustrated example) that pulls out the mixed solution (C + S) of the waste C and the fermentation liquid S from the raw material tank 10, and a filtrate D after separation. Are transported to the fermenter 30 and a return path 27 for returning the separated solid content E to the raw material tank 10. The organic solid fermentation broth S charged into the raw material tank 10 is solubilized while being immersed in the fermented liquid S circulating between the raw material tank 10, the solid-liquid separator 20 and the fermenter 30, and solubilized waste C. Is further decomposed into biogas G while being circulated between the raw material tank 10, the solid-liquid separator 20, and the fermenter 30 together with the fermentation liquid S. The biogas G generated in the fermenter 30 and the raw material tank 10 is recovered in the gas holder 45 via the recovery path 44.

  The solid-liquid separation device 20 used in the present invention is not particularly limited in the separation method and the like, for example, a sedimentation separation method and a screen (filter ) Method, vibration shaking method, membrane separation method, or separation device 20 as shown in FIG. Moreover, it is desirable to maintain the fermented liquid S to be circulated at the activation temperature of anaerobic microorganisms (for example, 20 to 65 ° C., preferably 30 to 60 ° C.). In the illustrated example, a stirring device 31 (external circulation path 32 with a circulation pump 33) is provided in the methane fermentation tank 30 to stir the internal fermentation solution S, and a heating device (heat exchanger) is provided on the circulation path 32. 34 is provided to heat the fermentation broth S to the required temperature. For example, a hot water boiler 47 (see FIG. 6) using the biogas G in the gas holder 45 as fuel can be provided, and the hot water of the hot water boiler 47 can be supplied to the heating device 34 via the supply path 48. As shown in FIG. 5, the raw material tank 10 can be provided with a stirring device 11 (for example, an external circulation path 12 with a circulation pump 13) as required.

  Hereinafter, although the operation of the mobile rake 60 and the screw conveyor 70 provided in the raw material tank 10 will be described with reference to FIG. 1, the application target of the present invention is limited to the two-tank fermentation liquid circulation type methane fermentation process. For example, as shown in FIG. 8, the present invention can be applied to a one-tank methane fermentation process. That is, for example, by including a perforated partition wall 21 as shown in FIG. 8 in the raw material tank 10 of FIG. 1, it can be diverted to the one tank type fermented liquid circulation type methane fermentation apparatus 1. Even in the case of using the raw material tank 10, the mobile rake 60 and the screw conveyor 70 described below are provided to prevent the effective volume from decreasing, thereby stabilizing the single tank type fermented liquid circulation type methane fermentation process for a long period of time. Can be maintained.

  In the raw material tank 10 in the illustrated example, it is assumed that combustible waste containing organic solid waste C discharged from the surrounding area is collected and processed at a cleaning center, etc., and packaging (plastic bags, etc.) is crushed and discarded. A crushing device 2 for roughly pulverizing the material C to an appropriate size and a sorting device 3 such as a trommel for sorting (sieving) the waste C having a predetermined particle size (for example, 50 mm) or less are provided. The waste C sorted by the sorting device 3 is temporarily stored in the raw material hopper 7 and continuously fed into the raw material tank 10 by a fixed amount through the intake port 8. As described above with reference to FIG. 6, the fermented liquid circulation type methane fermentation treatment is performed by separating the waste C containing the hardly-decomposable organic substance and the easily-decomposable organic substance according to the decomposition rate of each organic substance while separating the treatment time. It is suitable for the case where waste C such as combustible waste containing various solid organic substances having different decomposition rates can be continuously treated without separation. However, the organic solid waste C to be treated according to the present invention is not limited to combustible waste.

  The inlet 8 of the raw material tank 10 has a structure in which the waste C of the raw material hopper 7 is pushed below the surface of the fermentation liquid S in the raw material tank 10 by a screw conveyor, and the backflow of the biogas G in the raw material tank 10 (Outflow) is suppressed by water sealing of the fermentation broth S. However, the charging method is not limited to the illustrated example as long as the waste C can be charged without destroying the sealed state (anaerobic state) of the raw material tank 10. The foreign matter K having a large particle diameter mixed in the organic solid waste C is partially removed by the sorting device 3, but the foreign matter K (including the lightweight foreign matter M and the heavy foreign matter G) that cannot be sorted is discarded. The material C is put together with the material C into the raw material tank 10. As described above, in the fermentation liquid circulation type methane fermentation process, the lightweight foreign matter M introduced into the raw material tank 10 stays in the raw material tank 10 together with the waste C before solubilization, and becomes a large lump as shown in FIG. And accumulates on the liquid surface of the raw material tank 10. The movable rake 60 and the screw conveyor 70 penetrating the peripheral wall provided at the liquid surface position of the raw material tank 10 are for discharging the light weight foreign matter M on the liquid surface accumulated in a lump shape as shown in FIG. Is.

  For example, the lightweight foreign matter M mixed in the organic solid waste C such as combustible waste is mainly made of foamed polystyrene, vinyl, plastic or the like that does not swell even if it contains water. It is conceivable to discharge such a lightweight foreign matter M together with the fermented liquid S by a pump (such as a Mono pump) that can transfer the solid content, but according to the experiments of the present inventors, a liquid containing foamed polystyrene having a low water content is used. If it is continuously discharged with a MONO pump or the like, there is a possibility of frequent blockages. The screw conveyor 70 is suitable for the case where the lightweight foreign matter M having a low moisture content is continuously discharged without being blocked. Further, in order to maintain the raw material tank 10 in an anaerobic state, it is desirable to seal the outlet end of the discharge path with water, but in the discharge path of the mechanism swept by the water flow of the pump, the lightweight foreign matter M cannot be pushed out at the water seal part, There exists a possibility that the lightweight foreign material M may stay in a discharge channel. According to the screw conveyor type discharge path, the lightweight foreign matter M can be pushed out to the water sealing part (below the liquid level of the water tank 75 in the illustrated example) by pressing the screw. In the illustrated example, the raw material tank 10 is sealed with a structure in which the three-stage screw conveyor 70 is combined and the outlet end of the outer third-stage conveyor is inserted into the water tank 75 to push in the lightweight foreign matter M. Yes.

  The mobile rake 60 scrapes off and collects the light-weight foreign matter M on the liquid surface that has become a lump as shown in FIG. According to the experiment of the present inventor, it is possible to discharge the lightweight foreign matter M at the insertion position only by inserting the screw conveyor 70 into the massive lightweight foreign matter M, but they adhere to each other due to the surface tension of water. It is difficult to discharge the lightweight foreign matter M around the insertion position that is in a wall-like state. The rake 60 moving along the liquid level of the raw material tank 10 scrapes the lump-shaped lightweight foreign matter M and gathers it on the screw conveyor 70, thereby discharging the lump-like lightweight foreign matter M floating on the entire liquid level to the outside. can do.

  The mobile rake 60 in the illustrated example includes a rotary shaft 61 arranged along the vertical center of the cylindrical raw material tank 10, a horizontal arm member 62 provided at the liquid level of the rotary shaft 61, and the arm member 62. It has scraping feathers 63 joined together. Further, the screw conveyor 70 is extended in the radial direction of the raw material tank 10, and the lump-shaped lightweight foreign matter M floating on the liquid surface is scraped little by little by rotating the scraping blade 63 around the rotating shaft 61. 70. However, the rotation of the mobile rake 60 is not an indispensable condition for the present invention. For example, when the raw material tank 10 is a rectangular tank, the screw conveyor 70 is extended along one side of the rectangular cross section, and in a direction perpendicular thereto. It is also possible to move the movable rake 60 (the horizontal arm member 62 and the scraping blade 63) and collect the lump-like lightweight foreign matter M that floats on the liquid surface on the screw conveyor 70.

  Preferably, as shown in FIG. 2, the scraping blade 63 of the movable rake 60 is coupled to the horizontal arm member 62 by a hinge 64 so as to be movable up and down. As described with reference to FIG. 7 (B), the lump-shaped lightweight foreign matter M can be brought into a state in which the biogas G is embraced inside the raw material tank 10 and protrudes high from the liquid surface. When fixed to the member 62, the scraping feathers 63 are lifted upward by the buoyancy of the lightweight foreign matter M, and an excessive load may be applied to the arm member 62. By making the scraping blade 63 movable up and down, the lightweight foreign matter M that floats on the liquid surface at different heights can be efficiently collected together with the lightweight foreign matter M below the water surface. Further, by providing a mounting portion for the weight 65 on the vertically movable scraping blade 63, the scraping force of the scraping blade 63 can be adjusted by the weight 65.

  More preferably, as shown in FIG. 2, the movable rake 60 includes an intermediate bent arm member 62 whose intermediate portion is bent forward in the rotational direction, and the inward portion 62 a on the tip side from the middle bent portion of the arm member 62. The scraping blade 63 is hinged. According to the experiment of the present inventor, when the scraping blade 63 is rotated around the vertical center axis of the raw material tank 10, the lightweight foreign matter M on the liquid surface is pushed outward by the centrifugal force of the rotation, and the scraping blade. A phenomenon in which the load on the outside of 63 increased was observed. By making the scraping blade 63 inward by the folded arm member 62 and scraping the lightweight foreign matter M inward, the load of the scraping blade 63 can be made uniform and efficient recovery can be achieved.

  The scraping wing 63 may be a flat wing 63b having a flat protruding edge as shown in FIG. 3A or a comb wing 63c having a plurality of comb-shaped irregularities on the protruding edge. As shown in FIG. 6, it is desirable to use a mountain-shaped wing 63a having a plurality of mountain-shaped irregularities on the protruding edge. The flat wing 63b has a low rotational load and can efficiently scrape the lightweight foreign matter M such as foamed polystyrene, but is not suitable for efficiently scraping the vinyl or string-like lightweight foreign matter M. Although the comb-shaped wing 63c has a relatively high rotational load, it can also efficiently scrape the vinyl or string-like lightweight foreign matter M. However, when used for a long period of time, the lightweight foreign matter M tends to be entangled with the comb-shaped irregularities. The mountain-shaped wings 63a have a relatively small rotational load and are suitable for efficiently scraping various shapes of foamed polystyrene, vinyl, and string-like lightweight foreign matter M over a long period of time. If necessary, the mobile rake 60 may include a plurality of scraping blades 63 of different types.

  More preferably, as shown in FIG. 2, the inner part of the raw material tank of the screw conveyor 70 extended in the radial direction of the raw material tank 10 is surrounded by a foreign material intake member 71 having a trapezoidal upper end intake groove 72. The scraping blade 63 of the movable rake 60 can be flipped up by the inclined surface 73 having a trapezoidal cross section of the member 71. In the illustrated example, a trapezoidal cross-section foreign material intake member 71 having a trough-shaped intake groove 72 formed at the upper end is provided to project radially from the inner surface of the raw material tank 10, and a through-hole communicating with the intake groove 72 is provided. Is drilled in the peripheral wall of the raw material tank 10, and the screw conveyor 70 is disposed inside the intake groove 72 of the intake member 71 through the through hole. Further, the intake groove 72 of the intake member 71 is provided at a position higher than the liquid level of the raw material tank 10, and the scraping blade 63 is flipped up by the inclined surface 73 having a trapezoidal cross section as shown by the arrow in FIG. In other words, the lightweight foreign matter M on the liquid surface is dropped into the inlet groove 72 by deformation or rotation of the scraping blade 63 with the inclined surface 73 as a “profile surface”. Thus, by adopting a structure in which the scraping blade 63 is flipped up above the intake groove 72, it can be expected that the lightweight foreign matter M on the liquid level is surely dropped into the intake groove 72.

  By discharging the lightweight foreign matter M floating on the liquid surface of the raw material tank 10 by the mobile rake 60 and the screw conveyor 70 described above, reduction of the effective volume of the raw material tank 10 is prevented, and organic solid waste mixed with foreign matters is prevented. C can be stably subjected to methane fermentation for a long period of time by a fermentation liquid circulation system. The mobile rake 60 may be constantly driven at an appropriate speed, but can also be driven at a predetermined time interval in which the lightweight foreign matter M accumulates or appropriately. The lightweight foreign matter M discharged from the raw material tank 10 floats on the water surface of the water tank 75 connected to the outlet end of the screw conveyor 70, for example, and can be recovered from the water tank 75 and disposed.

  Thus, the provision of “fermentation liquid circulation type methane fermentation method and apparatus capable of stably maintaining a highly efficient methane fermentation treatment for a long period of time”, which is an object of the present invention, can be achieved.

  In addition, the rotating shaft 61 of the raw material tank 10 in the illustrated example includes not only the mobile rake 60 but also the stirring rod 66 for loosening the lightweight foreign matter M staying in the fermentation liquid S of the raw material tank 10, and the raw material tank. 10 and a lower rake 67 which slides on the bottom surface. As shown in FIG. 7, the light foreign matter M is loosened by the stirring rod 66 before becoming a large lump as shown in FIG. 7, whereby the mobile rake 60 can easily collect the light foreign matter M from the liquid surface. Further, in the conventional method of FIG. 6, the heavy foreign matter G that has settled at the bottom may be incompletely discharged and accumulated, but for example, as shown in FIG. The heavy foreign matter G settled on the bottom portion of the raw material tank 10 is collected and discharged to the discharge port 19 in the center of the bottom portion, including the arm member 68 protruding to the bottom and the scraping member 69 attached to the arm member 68 so as to be inclined in the rotational direction. Therefore, it is possible to reliably prevent a reduction in the effective volume of the raw material tank 10 due to accumulation of heavy foreign matter M. The shape of the lower rake 67 is not limited to the illustrated example, and when the raw material tank 10 is a rectangular tank, the heavy foreign matter G that has settled at the bottom by moving the lower rake 67 along one side of the rectangular cross section is discharged 19 It is also possible to gather together.

  FIG. 5 shows another embodiment of the fermentation liquid circulation type methane fermentation apparatus 1 according to the present invention. The raw material tank 1 in the illustrated example is provided with a reduced diameter portion 77 having a thick peripheral wall 78 at a predetermined height, and the movable rake 60 and the screw conveyor 70 described above are disposed inside the reduced diameter portion 77, and the reduced diameter portion 77. The intake 8 is provided through the thick peripheral wall 78 in the vertical direction. For example, the organic solid waste C stored in the raw material hopper 7 is thrown in while being continuously pushed into the liquid level of the fermentation liquid S in the raw material tank 10 by a certain amount by a screw conveyor provided at the intake port 8. The mobile rake 60 and the screw conveyor 70 have the same structure as described above with reference to FIG.

  In addition, the solid-liquid separation device 20 of FIG. 5 swivels facing the introduction chamber 22 and the separation chamber 23 partitioned by a perforated partition wall (for example, a partition wall with a screen) 21 and the surface of the partition wall 21 on the introduction chamber 22 side. And a rotating blade 24. The mixed liquid (C + S) in the raw material tank 10 is introduced into the introduction chamber 22 through the drawing path 15 and is solid-liquid separated by the screen of the partition wall 21. By rotating 24, the introduced mixed liquid (C + S) can be loosened and the screen of the partition wall 21 can be prevented from being clogged. Further, the introduction chamber 22 of the solid-liquid separation device 20 in FIG. 5 is connected to the residue treatment device 52 via a lead-out path 56 with an on-off valve 56a, and floats in the fermentation broth S of the raw material tank 10 as necessary. The remaining foreign matter L can be removed by the residue processing device 52. The method for circulating the fermentation broth S by the solid-liquid separator 20 and the method for removing foreign matter by the residue treatment device 52 are the same as those in FIGS. 1 and 6 described above.

  When this inventor makes the fermentation liquid circulation type methane fermentation apparatus 1 shown in FIG. 5 as a prototype and combusts 1 ton / day of combustible waste as the organic solid waste C, it accumulates in the raw material tank 10. An experiment was conducted to confirm the amount of foreign matter. Combustible waste is broken by the crushing device 2 and the contents are crushed to a particle size of 150 mm or less, and the foreign material K having a particle size of 50 mm or more is separated by a sorting device (such as Trommel) 3 to produce waste having a particle size of 50 mm or less. C was selected and put into the raw material tank 10. When the composition of the sorted waste C is confirmed, solid organic matter (garbage and paper waste) C suitable for biogasification is about 75%, and foreign matter (lightweight foreign matter M and heavy foreign matter G) unsuitable for biogasification. Was about 25%. While continuously measuring the amount of waste C input to the raw material tank 10, the discharge amount of the lightweight foreign matter M and heavy foreign matter G discharged from the screw conveyor 70 and the discharge port 19 of the raw material tank 10 is continuously measured. From these measured amounts, the accumulated amounts of foreign matters M and G (including undecomposed organic matter of methane fermentation) remaining in the raw material tank 10 were estimated based on the composition of the sorted waste C.

  FIG. 4 shows the transition of the estimation result of the amount of accumulated foreign matter in the raw material tank 10. As can be seen from the figure, the estimated accumulated amount of foreign matter M and G in the raw material tank 10 (the amount in the tank) gradually increased with an increase in the cumulative amount of waste C introduced. It was estimated that the accumulated amount became almost constant when it reached 900 to 1000 kg, and that the accumulated amount did not increase further even if the input integrated amount further increased. After the experiment was completed, the raw material tank 10 was opened and the amount of accumulated foreign matter M and G was confirmed. As a result, 922 kg of foreign matter was accumulated in dry weight. From this, it can be judged that the estimation result of the amount of accumulated foreign matter in FIG. 4 is appropriate. In addition, the solid organic matter (garbage and paper waste) C is hardly seen in the lightweight foreign matter M and heavy foreign matter G discharged from the raw material tank 10, and the biogasification rate of the solid organic matter C is maintained at about 90%. It was confirmed that From this experimental result, the foreign matter discharge mechanism of the present invention using the mobile rake 60 and the screw conveyor 70 suppresses the amount of foreign matter accumulated without adversely affecting the methane fermentation efficiency (anaerobic state) of the raw material tank 10, and fermentation. It was confirmed that it is effective for stably maintaining a high-efficiency methane fermentation treatment of organic solid waste C by liquid circulation for a long period of time.

DESCRIPTION OF SYMBOLS 1 ... Fermentation liquid circulation type methane fermentation apparatus 2 ... Crushing apparatus 3 ... Sorting apparatus 7 ... Raw material hopper 8 ... (with screw conveyor) Intake 10 ... Raw material tank 11 ... Stirring device 12 ... External circulation path 13 ... Circulation pump 14 ... Pull-out device 15 ... Pull-out path 16 ... Pull-out pump 17 ... Pull-out path 18 ... Overflow weir 19 ... Discharge port 20 ... Solid-liquid separator 21 ... Perforated partition (partition with screen)
DESCRIPTION OF SYMBOLS 22 ... Introduction chamber 23 ... Separation chamber 24 ... Rotor blade 25 ... Drive device 26 ... Rotating shaft 27 ... Return path 28 ... Transport route 29 ... Flow meter 30 ... Methane fermentation tank 31 ... Stirrer 32 ... External circulation path 33 ... Circulation Pump 34 ... Warming device (heat exchanger) 35 ... Waste liquid passage 35a ... Overflow port 40 ... Supply device 41 ... Supply passage 42 ... Supply pump 44 ... Gas recovery passage 45 ... Gas holder 46 ... Desulfurization device 47 ... Hot water boiler 48 ... Hot water supply path 50 ... control device 52 ... residue removal device 53 ... dehydration device 54 ... filtrate receiving tank 55 ... return device (return pump)
56 ... Pull-out path 57 ... Return path 60 ... Mobile rake (rotary rake) 61 ... Rotating shaft 62 ... (Folded) horizontal arm member 62a ... Inward portion 63 ... Scraping feather 63a ... Mountain-shaped feather 63b ... Flat feather 63c ... comb-shaped wing 64 ... hinge 65 ... weight 66 ... stirring rod 67 ... lower rake 68 ... overhang arm member 69 ... scraping member 70 ... screw conveyor 71 ... foreign material intake member 72 ... intake groove 73 ... inclined surface )
75 ... Water tank 76 ... Container 77 ... Reduced diameter part 78 ... Thick peripheral wall C ... Organic solid waste D ... Filtrate E ... Solid matter F ... Separate G ... Heavy foreign matter H ... Heat medium K ... Selected foreign matter L ... Floating foreign matter M ... Light foreign matter N ... Waste liquid S ... Fermentation liquid G ... Biogas (decomposition product gas)

Claims (16)

The organic solid waste mixed with light foreign matters is put into a raw material tank provided with a movable rake and a screw conveyor penetrating the peripheral wall at a predetermined height inside, and fermented liquid is supplied to the raw material tank and the raw material tank By circulating the fermentation broth from the bottom and returning it upward, the liquid level is maintained at the predetermined height, and the waste introduced into the raw material tank is solubilized while immersed in the fermentation broth and circulated along with the fermentation broth. A fermented liquid circulation type methane fermentation method in which lightweight foreign substances that decompose into gas and float on the liquid surface of the raw material tank are collected on a screw conveyor by a rake movement and discharged. In the method of Claim 1, the methane fermentation tank which stores the said fermented liquid is provided, fermented liquid is continuously supplied from the fermenter to a raw material tank, and the fermented liquid of a raw material tank is extracted continuously, and it passes through a solid-liquid separator. A fermented liquid circulation type methane fermentation method in which the separated solids are sent back to the fermentor and circulated back to the raw material tank. The method of claim 1 or 2, wherein the mobile rake includes a horizontal arm member and a scraper blade hinged to the arm member. 4. The fermentation liquid circulation type methane fermentation method according to any one of claims 1 to 3, wherein the mobile rake includes a scraping blade provided with a plurality of mountain-shaped irregularities on a protruding edge. 5. The method according to claim 1, wherein a horizontal section of the raw material tank is circular, and an intermediate portion of the movable rake that rotates around a vertical central axis of the raw material tank is bent forward in the rotation direction. A fermented liquid circulation type methane fermentation method comprising an arm member and a scraping blade hinged to the inward portion on the tip side from the folded portion of the arm member. 6. The method according to claim 5, wherein the screw conveyor is extended in the radial direction of the raw material tank, and the inner part of the raw material tank is surrounded by a foreign substance intake member having a trapezoidal cross-section with an upper-end intake groove. Fermentation liquid circulation type methane fermentation method that enables rake scraping feathers to be lifted on an inclined surface. The method according to any one of claims 1 to 6, wherein an outlet with an on-off valve is provided at the bottom of the raw material tank, and the mobile rake includes a lower rake that slides on the bottom surface of the raw material tank. A fermentation liquid circulation type methane fermentation method in which foreign matter that sinks under the liquid is collected at a discharge port by a lower rake and discharged by opening an on-off valve. 8. The fermentation liquid circulation type methane fermentation method according to any one of claims 1 to 7, wherein the screw conveyor includes a water tank that seals its outlet end. A raw material tank provided with a mobile rake and a screw conveyor penetrating a peripheral wall at a predetermined height inside, an inlet for introducing organic solid waste mixed with lightweight foreign substances into the raw material tank, and fermented liquid in the raw material tank A supply path for supplying and a circulation path for extracting the fermentation broth of the raw material tank from below and returning it upward, solubilized waste immersed in the fermentation liquid and circulated together with the fermentation liquid A fermented liquid circulation type methane fermentation apparatus that decomposes into biogas and collects and discharges light-weight foreign substances floating on the liquid surface of the raw material tank to a screw conveyor by movement of the rake. 10. The apparatus according to claim 9, wherein a methane fermentation tank for storing the fermentation broth is provided, and a supply device for continuously supplying the fermentation broth from the fermentation tank to the raw material tank is provided in the supply path, and the fermented liquid in the raw material tank is provided in the circulation path. A fermentation liquid circulation type methane fermentation apparatus including a solid-liquid separation apparatus that continuously pulls out the solid and separates the liquid and sends the separated filtrate to the fermenter and returns the solid content to the raw material tank. 11. The apparatus according to claim 9 or 10, wherein the mobile rake includes a horizontal arm member and a scraper blade hinged to the arm member. The fermenter circulation type methane fermentation apparatus according to any one of claims 9 to 11, wherein the movable rake includes a scraping blade provided with a plurality of mountain-shaped irregularities on a protruding edge. The apparatus according to any one of claims 9 to 12, wherein a horizontal section of the raw material tank has a circular shape, and an intermediate portion that rotates around the vertical central axis of the raw material tank is bent forward in the rotation direction in the movable rake. A fermented liquid circulation type methane fermentation apparatus including an arm member and a scraping blade hinged to an inward portion on the tip side from a folded portion of the arm member. 14. The apparatus according to claim 13, wherein the screw conveyor extends in the radial direction of the raw material tank, and the inner portion of the raw material tank is surrounded by a foreign substance intake member having a trapezoidal upper cross-sectional shape, and the trapezoidal cross section of the intake member is formed. Fermentation liquid circulation type methane fermentation device that makes it possible to lift rake scraping feathers on an inclined surface. The apparatus according to any one of claims 9 to 14, wherein an outlet with an on-off valve is provided at the bottom of the raw material tank, and the mobile rake includes a lower rake that slides on the bottom surface of the raw material tank. A fermented liquid circulation type methane fermentation apparatus in which foreign matter that sinks under the liquid is collected at a discharge port by a lower rake and discharged by opening an on-off valve. 16. The fermentation liquid circulation type methane fermentation apparatus according to claim 9, wherein the screw conveyor includes a water tank that seals its outlet end.