JP7298842B2 - Methane fermentation device and methane fermentation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a methane fermentation apparatus and a methane fermentation method for introducing solid waste such as waste paper into a methane fermentation tank.

In a wet methane fermentation system, for example, separated garbage is stored in a solubilization tank. In the solubilization tank, hydrolysis and acid fermentation (that is, solubilization) of garbage proceed to obtain a slurry containing organic acids. After that, the slurry is sent to a methane fermentation tank and decomposed by anaerobic microorganisms in the methane fermentation tank (see Patent Document 1). The biogas produced at this time generally contains about 60 vol% methane and about 40 vol% carbon dioxide, and is useful as an energy source.

From the viewpoint of reducing the volume of waste and increasing the amount of biogas produced, it is desirable to use not only food waste but also solid waste containing organic matter such as paper waste as raw materials. For example, Patent Literature 2 proposes solubilizing organic solid waste while immersing it in a fermentation liquid in a tank and decomposing it into biogas.

JP-A-2008-246461 JP 2012-86157 A

Solid waste tends to contain air and contains materials of various properties, shapes and specific gravities. Therefore, it is desired to construct a system capable of degassing the air from the material suitable for fermentation and appropriately removing the material unsuitable for fermentation before the material is put into the methane fermentation tank.

A first characteristic configuration of the methane fermentation apparatus according to the present invention includes a fermenter containing a fermentation liquid for generating biogas, the fermentation liquid taken out from the fermenter, and waste containing fermentation materials. A mixing unit that is charged and mixed to obtain a fluid and separates at least a part of unsuitable substances for fermentation derived from the waste, an input route that sends the fluid from the mixing unit to the fermenter, and the fermented liquid a separation device for removing solids contained in the fermenter, a filtrate route for sending the fermented liquid from which solids have been removed by the separation device to the mixing unit, and the a withdrawal route for sending the fermented liquid to the mixing section without passing through the separation device, and the supply route of the fermented liquid sent to the mixing section is switched between the filtrate route and the withdrawal route. The point is that it is configured to be possible.

The second characteristic configuration includes, in addition to the first characteristic configuration described above, a circulation route for returning the fermented liquid extracted from the fermenter to the fermenter, and a branch route branching from the circulation route. The point is that the device is provided.

The first characteristic configuration of the methane fermentation method according to the present invention includes (i) a step of taking out the fermented liquid from a fermenter containing the fermented liquid and sending it to a mixing section; (iii) mixing the extracted fermentation liquid with waste containing fermentation-suitable substances to obtain a fluid and separating at least a part of fermentation-unsuitable substances derived from the waste; (iv) hydrolysis, acid fermentation, and methane fermentation of the fermentable material in the fermenter to generate biogas; (v) the fermentation; taking out the fermentation liquid from the tank, removing solids using a separation device, and sending it to the mixing unit, wherein the solids concentration (M) of the fermentation liquid contained in the fermentation tank The point is that the step (i) and the step (v) are switched based on the above.

In the second characteristic configuration, in addition to the first characteristic configuration described above, when the solid matter concentration (M) of the fermentation liquid contained in the fermenter is lower than a predetermined concentration, the step (i ) The point is to execute

The third characteristic configuration is, in addition to the first or second characteristic configuration described above, when the solid matter concentration (M) of the fermentation liquid contained in the fermenter is higher than a predetermined concentration, the step It lies in executing (v).

The fourth characteristic configuration is, in addition to the second or third characteristic configuration described above, the solid concentration (M) is the amount of fermentation liquid (A) sent to the separation device and the fermentation liquid filtered by the separation device. The point is that the liquid volume (B) is measured and calculated by M=(AB)/A.

According to the methane fermentation apparatus and the methane fermentation method according to the present invention, solubilization of solid waste such as waste paper and methane fermentation can be stably progressed in the fermentation tank.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows the structure of an example of the methane fermentation system which concerns on embodiment of this invention. FIG. 2 is a schematic diagram of an example of a mixing unit that mixes a fermentation liquid and a raw material waste to obtain a fluid and separates substances unsuitable for fermentation. FIG. 2 is a schematic diagram of an example of a separation device that removes substances unsuitable for fermentation floating in a fermented liquid. FIG. 3 is a schematic diagram of another example of a separation device that removes substances unsuitable for fermentation floating in the fermented liquid. 1 is a block diagram showing the configuration of an example of a pretreatment device for sorting raw material waste; FIG.

In the methane fermentation apparatus according to the present invention, solid waste is introduced into the fermenter as a raw material. In the fermenter, hydrolysis, acid fermentation and methane fermentation of fermentable substances in the solid waste proceed to produce biogas. That is, the methane fermentation apparatus is equipped with a fermenter that accommodates a fermentation liquor that generates biogas and that advances hydrolysis, acid fermentation, and methane fermentation of a fermentation-suitable substance.

The methane fermentation apparatus according to the present embodiment can enable construction of a methane fermentation system that does not include a solubilization tank for promoting acid fermentation of a fermentable substance. In the wet methane fermentation system, a solubilization tank is usually installed to store the sorted garbage and to promote hydrolysis and acid fermentation of the garbage. On the other hand, in the methane fermentation apparatus according to the present invention, solid waste is introduced into the fermentation tank as a raw material. Solid waste is supplied as raw material waste from which a portion of unfermentable substances have been removed in advance. The raw material waste is mixed with the fermented liquor partially withdrawn from the fermenter. The fluid containing raw material waste thus obtained is introduced into the methane fermenter.

Solid waste contains fermentables and may contain some unfermentables. Solid waste may be, for example, general waste generated by a household. Materials unsuitable for fermentation contained in general waste are sufficiently sorted in advance.
Hereinafter, solid wastes used as raw materials for methane fermentation are referred to as raw material wastes.

A fermented liquid is a liquid obtained through hydrolysis and acid fermentation of a fermentable material, followed by digestive decomposition by fungal cells that promote methane fermentation.

Fermentable matter refers to organic matter that can be decomposed by methane fermentation via hydrolysis and acid fermentation (ie, solubilization). Materials suitable for fermentation include, but are not particularly limited to, raw garbage, waste paper, and biodegradable plastics.

Substances unsuitable for fermentation are materials unsuitable for solubilization, and examples thereof include metals, plastics, minerals, and shellfish. Inappropriate substances for fermentation may be mixed in raw material waste even if they are sufficiently separated in advance. Such substances unsuitable for fermentation are appropriately removed from the apparatus system by separation.

A methane fermentation apparatus according to the present invention mixes a fermenter containing a fermented liquid for generating biogas, the fermented liquid taken out from the fermenter, and a waste containing a fermentation suitable material to produce a fluid material. a mixing unit for separating at least a portion of unsuitable substances for fermentation derived from the waste, an input route for sending the fluid from the mixing unit to the fermenter, and removing solids contained in the fermentation liquid and a filtrate route for sending the fermented liquid, which has been taken out from the fermenter and from which solid matter has been removed by the separation device, to the mixing section.

Equipped with a circulation route that returns the fermented liquid drawn from the fermenter to the fermenter, and a separation device is installed in the branch route that branches off from the circulation route. The fermented liquid contained in the fermenter is maintained in an appropriate state by sending the mixed fermented liquid to the mixing section.

Since at least part of the substances unsuitable for fermentation are removed by the separator, clogging of the piping to the dehydrator and the body of the dehydrator can be prevented when dehydrating the fermented liquid with the dehydrator. In addition, when the removal of floating unfermentable substances and unfermentable substances, which are solid substances, is insufficient, the solid substances are further removed by a separation device. In addition to the floating unsuitable materials, which are solids, the separation device also removes fermentation unsuitable materials that remain without being fermented.

A withdrawal route is further provided for sending the fermented liquid taken out from the fermenter to the mixing section without passing through the separator.

Further, the methane fermentation method according to the present invention includes: (i) a step of partially or intermittently taking out the fermented liquid from a fermenter containing the fermented liquid and sending it to a mixing section; and (ii) in the mixing section, (iii) a step of mixing the fermentation liquid taken out from the fermenter with waste containing fermentation-suitable substances to obtain a fluid and separating at least a part of fermentation-unsuitable substances derived from the waste; and (iv) hydrolysis, acid fermentation, and methane fermentation of the fermentable material in the fermenter to generate biogas. .

When the solid matter concentration of the fermented liquid contained in the fermenter is lower than a predetermined concentration, the waste is introduced into the mixing unit, and the fermented liquid taken out of the fermenter is removed through the extraction route. and sent to the mixing section.

When the solid matter concentration of the fermentation liquid contained in the fermentation tank is higher than a predetermined concentration, the fermentation liquid from which the solid matter has been removed is supplied to the fermentation tank through a filtrate route .

The solids concentration (M) is calculated by measuring the amount of fermented liquid (A) sent to the separation device and the amount of fermented liquid (B) filtered by the separation device, and calculated by M = (A - B) / A. be.

In step (i), when the solids concentration of the fermentation liquid contained in the fermenter is lower than the predetermined concentration, the fermentation liquid taken out of the fermenter is directly sent to the mixing section, and the solids concentration reaches the predetermined concentration. When the fermentation liquid is removed from the fermenter, the solid matter is removed through the separation device and sent to the mixing unit to shorten the time required for initial start-up, and the fermenter is stored in the fermenter. The state of the fermented liquid can be maintained in a state suitable for fermentation, and the fermentation treatment can be efficiently performed.

A storage tank for storing the fermented liquid from which the solid matter has been removed by the separation device, and a storage tank for storing the fermented liquid in which the concentration of solids in the fermented liquid contained in the fermenter tank is higher than a predetermined concentration and there is a risk that the fermentation efficiency will decrease. By providing a recovery route for supplying the stored fermentation liquid to the fermenter, the solid concentration of the fermentation liquid can be quickly adjusted to an appropriate concentration.

In addition, since the mixing section is not a solubilization tank for the purpose of solubilizing the fermentable material, the volume of the mixing section is, for example, 20% or less of the volume of the fermenter. Moreover, in the mixing section, the retention time of the fluid or raw material waste is, for example, within 0.5 days.

The retention time of the fluid in the mixing section is the amount of the fermentation-suitable material introduced into the mixing section per day, and the number of divisions (for example, 1 to 6 times) when dividing the fermentation-suitable material for one day into the mixing section. , are variables determined by the mixing ratio of the fermented liquid and the fermented material. In general, when the residence time of the fluid in the mixing section is X days (or hours) or less, for example, the flow in the mixture is within X days (or hours) after the raw material waste is introduced into the mixing section. It refers to the case where animals are sent to the fermenter.

The mixing section may have a dead space in which the separated fermentation unsuitable materials settle. At this time, the mixing section has a discharge port that discharges the fluid above the dead space. The dead space may be provided with a scraping and discharging mechanism for discharging the separated unsuitable substances for fermentation. The removal of unsuitable substances for fermentation is preferably performed after stopping the supply of raw material waste to the mixing section. As a result, it is possible to suppress the amount of the fermentation-suitable substances in the raw material waste supplied to the mixing section that are removed together with the fermentation-unsuitable substances.

The methane fermentation apparatus may further have a circulation route for circulating the fermentation liquid in the fermenter. For example, the fermentation liquid L can be circulated by withdrawing the fermentation liquid from the bottom of the fermenter and returning it to the top. By circulating the fermented liquid, hydrolysis, acidolysis and methane fermentation of the fermentable material are promoted. Circulation of fermentation liquid also suppresses retention of biogas generated by methane fermentation, so gas recovery is facilitated. The liquid flow generated by the circulation of the fermentation broth agitates the substances unsuitable for fermentation, which have a high specific gravity, and deposits them at the bottom of the fermenter, thus facilitating the separation and recovery of such substances unsuitable for fermentation.

When the methane fermentation apparatus has a circulation route, the extraction route may be branched from the circulation route at the first branch. That is, the withdrawal route may be branched from the circulation route so that at least a portion of the fermentation liquid withdrawn from the fermenter for circulating the fermentation liquid is sent to the mixing section. In this case, part of the circulation route is used as part of the withdrawal route for sending the fermentation liquid from the fermenter to the mixing section. A pump that provides a driving force for circulating the fermentation broth through the circulation route may be used as a pump that sends the fermentation broth through the withdrawal route to the mixing section.

The input route may be merged with the second branching portion on the downstream side of the first branching portion of the circulation route. This promotes mixing of the fluid with the fermentation broth, since the fluid is sent to the fermenter together with the circulating fermentation broth. In addition, it is difficult for the fluid to flow back into the extraction route. In this case, part of the circulation route is used as part of the input route. Also, the pump that provides the driving force for sending the fluid to the fermenter via the input route may be provided separately from the pump that sends the fermentation liquid to the fermenter via the circulation route.

Each route, such as a withdrawal route and an injection route, may be composed of a pipe or the like through which a fluid can pass.

Hereinafter, embodiments of the present invention will be further described with reference to the drawings. However, the following embodiments do not limit the present invention.

FIG. 1 shows an example configuration of a methane fermentation system 10 including a methane fermentation apparatus 100 according to the present invention. The methane fermentation apparatus 100 includes a fermenter 110 containing a fermented liquid L, a mixing section 120 for mixing the fermented liquid L extracted from the fermenter 110 and raw material waste C to obtain a fluid S, and a fermenter 110. A first withdrawal route R11 for sending the fermentation liquid L taken out from the fermenter 120 to the mixing unit 120, and an input route R2 for sending the fluid S from the mixing unit 120 to the fermenter 110.

The methane fermentation apparatus 100 has a circulation route R3 for withdrawing the fermented liquid L from the bottom of the fermenter 110 and then returning it upward. A first discharge port 114 for extracting the fermentation liquid L is provided below the fermentation tank 110 . The fermented liquid L is pulled out from the first discharge port 114 by the driving force of the first pump (Hydrostar) P1 provided on the circulation route R3 and sent upward. By circulating the fermentation liquid L, the fermentation of the fermentable substances in the fermenter 110 is promoted, and the separation and recovery of the unfermentable substances are facilitated.

The downstream end of the circulation route R3 is bifurcated, and each of the two branches has an upper outlet 111 and a submerged outlet 112 for discharging the fermentation liquid L that has passed through the circulation route R3 into the fermentation tank 110. . Valves V1 and V2 are provided upstream of the upper outlet 111 and upstream of the submerged outlet 112, respectively.

The fermenter 110 is a vertical cylindrical container, and has airtightness so that the inside is maintained in an anaerobic atmosphere. The fermenter 110 may have dead space for unfermentables to settle. High specific gravity substances that settle in the dead space are appropriately discharged to the outside from the first bottom outlet 113 and removed. The first bottom outlet 113 preferably has, for example, a scraper and discharge mechanism.

In FIG. 1, the upstream side of the first withdrawal route R11 and the second withdrawal route R12 and the upstream side of the circulation route R3 are configured by common piping. The fermented liquid L is drawn from below the fermenter 110 by the driving force of the first pump P1 provided on the circulation route R3. The first withdrawal route R11 and the second withdrawal route R12 branch from the circulation route R3 at the first branch point T1.

By opening the valve V3 provided downstream of the first branch point T1 and the valve V10 provided on the first extraction route R11 and closing the valve 11 provided on the second extraction route R12, the fermentation liquid L is It can be configured to be sent to the mixing section 120 through the 1 withdrawal route R11. The circulation of the fermentation liquid L in the fermentation tank 110 and the supply of the fermentation liquid L to the mixing section 120 may be performed in parallel with the valves V3 and V10 kept open. Such parallel operations may occur continuously over a period of time.

In addition, the valve V3 provided downstream of the first branch point T1 and the valve V11 provided on the second withdrawal route R12 are opened, and the valve V5 provided on the filtrate route R4 is opened to move to the first withdrawal route R11. By closing the provided valve V10, the fermented liquid L can be sent to the mixing section 120 through the filtrate route R4.

The mixing unit 120 mixes the raw material waste C and the fermentation liquid L to give fluidity to the raw material waste C, improve the dispersibility of the raw material waste C in the fermentation tank 110, and mix the fluid S It has the significance of degassing air from. The residence time of the fluid in the mixing section 120 may be less than 0.5 days, such as 3 hours or less, or 2 hours or less, or even 0.5 hours or less. The raw material waste C is mixed and stirred with the fermentation broth L in the mixing unit 120, dispersed in a liquid state or a slurry state, and then introduced or transferred to the fermenter 110 where airtightness is maintained.

By visually observing the liquid surface of the mixing section 120, the state of the fermentation liquid can be grasped, and the supply route of the fermentation liquid L to the mixing section 120 can be switched based on the state. In other words, in the case where the fermentation liquid contains a large amount of floating unsuitable substances that are solids, the fermentation liquid (separated liquid) taken out from the fermentation tank 110 and having the solids removed by the separation device 300 described later is used. When the solid concentration of the fermentation liquid is low, the fermentation liquid taken out from the fermenter 110 can be switched to the route R11 so that it is directly fed into the mixing section 120. .

Although not shown in FIG. 1, instead of the filtrate route R4, a fermentation liquid (separated liquid) from which solid matter has been removed by the separation device 300 and stored in the storage tank 170 (separated liquid) liquid) can also be introduced into the mixing section 120 .

The fluid S sent from the mixing section 120 to the fermenter may undergo acid fermentation to some extent, but at least not significantly. Hydrolysis and acid fermentation of fermentables in the stream proceed in a fermenter where methane fermentation takes place.

The fluid S in the mixing section 120 is pulled out by the driving force of the second pump P2. Fluid S passes through input route R2 and is supplied to fermentor 110 via valve V4. The input route R2 may be branched on the upstream side of the valve V4, and the branched route may be merged with the circulation route R3 at the second branch portion T2. By opening the valve V6 on the upstream side of the second branch T2, the fluid S joins the circulation route R3 and is discharged from the upper outlet 111 and/or the submerged outlet 112 into the fermentation tank 110. At this time, the circulation of the fermentation liquid L within the fermenter 110 and the supply of the fluid S to the fermenter 110 may be performed in parallel. Such parallel operations may occur continuously over a period of time. The second branch portion T2 may be provided on the downstream side of the circulation route R3 from the first branch portion T1. As a result, the fluid S obtained in the mixing section 120 can be prevented from flowing back to the second withdrawal route R12. Therefore, even when a separation device 300 as described later is provided, removal of the fermentable material in the fluid S is prevented. The second pump P2 may also be used as a crushing pump.

When the methane fermentation is performed in batch mode, after the fluid S is introduced into the fermentation tank 110, the valve V3 may be closed until the fermentation is completed.

Methane fermentation system 100 may have a steam inlet that introduces steam into fermentor 110 . Steam is introduced into the fermenter 110 as a heat source for maintaining the interior of the fermenter 110 within an appropriate temperature range of, for example, 50-60°C. Steam also functions as dilution water for controlling the ammonia concentration or organic acid concentration of the fermentation broth L. When solid waste such as waste paper is used, the ammonia concentration in the fermentation liquid is less likely to increase. Therefore, there is no need to add diluent water from the outside, and the amount of fermented liquid in the fermenter is maintained within a proper range for a relatively long period of time. As a method for maintaining the inside of the fermenter 110 within the proper temperature range, a method other than heating with steam may be used.

Fermentable material sent to the fermenter 110 is sequentially hydrolyzed in the limited space within the fermenter 110 . Apart from the fermenter 110, it is not necessary to install a solubilization tank for proceeding with hydrolysis and acid fermentation of the fermentable material. In the methane fermentation apparatus 100, the space required for solubilizing the fermentable material is greatly reduced. Along with this, the number of required equipment and energy consumption are also reduced. As described above, the cost required for constructing and operating the methane fermentation system 10 is reduced.

The amount of fermentation suitable material introduced into the fermenter 110 affects the amount of organic acid in the fermenter 110 . The amount of fermentation suitable material in the fermenter 110 can be adjusted by controlling the amount of the fluid S sent from the mixing section 120 to the fermenter 110 . The organic acid concentration of the fermented liquid L in the fermenter 110 is maintained within an appropriate range by appropriately controlling the amount of the fluid S sent from the mixing section 120 to the fermenter 110 .

Since solid waste containing organic matter containing air is introduced into the mixing section 120, it is difficult to maintain the inside of the mixing section 120 in a good anaerobic atmosphere. However, if the volume of the mixing section 120 is much smaller than the volume of the fermenter 110, the amount of fermented liquid sent to the mixing section 120 and coming into contact with air is limited. If the volume of the mixing section 120 is set to 20% or less of the volume of the fermenter 110, excess fermented liquid L will not be extracted from the fermenter 110, and changes in the amount of fermented liquid will be reduced. The volume of the mixing section 120 is preferably 20% or less, more preferably 10% or less, of the volume of the fermentation tank 110, for example.

When the fluid S is obtained in the mixing unit 120, the amount of the raw material waste C mixed with 100 parts by mass of the fermentation liquid is preferably 10 to 50 parts by mass, more preferably 10 to 30 parts by mass. Depending on the properties, physical properties, and moisture content of the raw material waste C, it is not necessary to add water from the outside for the purpose of increasing fluidity. By obtaining the fluid S having sufficient fluidity, the rate of occurrence of various problems such as clogging of pipes is reduced. In order to further suppress the clogging of the piping, it is preferable to take measures to increase the flow velocity and to set the piping gradient in the horizontal direction to -45° to +45°. In addition, it is preferable to provide an optional pipe (trap pipe section) for retaining deposits in the pipe.

The fermenter 110 basically has a structure in which the interior is blocked from contact with the atmosphere. Sunlight irradiation to the fermented liquid L also needs to be suppressed. On the other hand, it is also necessary to grasp the internal conditions of the fermenter 110, that is, the generation of scum (SCUM) in the fermenter 110, the concentration of contaminants in the fermentation liquid L, the pH value of the fermentation liquid L, and the like. The mixing unit 120 also functions as a monitoring unit for the fermentation liquid L for grasping the situation. In this case, even if a separation device 300 as described later is provided, the fermented liquid L is sent to the mixing section 120 from the first branch section T1 bypassing the separation device 300 .

FIG. 2 shows a schematic diagram of an example of the mixing section. The mixing section 120 is configured to mix the raw material waste C and the fermentation liquid L introduced from the outside. The mixing section 120 includes a mixing vessel 121 sufficiently smaller than the fermenter 110 , a stirring blade 122 , and a second pump P<b>2 for moving the generated fluid S to the fermenter 110 . The driving force of the second pump P2 discharges the fluid S from the mixing section 120 through the second discharge port 124 to the input route R2 toward the fermenter 110 . As the second pump P2, it is preferable to use a crushing pump capable of crushing the solid waste containing the organic matter contained in the fluid S.

The mixing container 121 has a first input port 125 for inputting the raw material waste C and a second input port 126 for inputting the fermented liquid L thereinto. Since the volume of the mixing vessel 121 is small, even if air enters the inside of the mixing vessel 121 and the anaerobic property is impaired, the influence on the inside of the fermenter 110 can be ignored.

When the raw material waste C and the fermentation liquid L are mixed in the mixing section 120, high specific gravity materials (e.g., metals, gravel, shells) and light specific gravity materials (e.g., expanded polystyrene) are separated by the specific gravity separation action in the mixing section 120. be done. Therefore, in the mixing section 120, the high specific gravity sediment (SED) and the low specific gravity floating matter can be easily taken out and removed. Specifically, the material with high specific gravity accumulates in the dead space 121 d at the bottom of the mixing container 121 . The dead space 121 d is a region vertically below the second discharge port 124 of the fluid S obtained in the mixing section 120 . On the other hand, in the mixing space 121u vertically above the second discharge port 124, the material with a low specific gravity floats on the liquid surface of the fluid as floating matter. As a result, high specific gravity substances and light specific gravity substances are less likely to be discharged from the second discharge port 124, and adverse effects caused by substances unsuitable for fermentation can be reduced.

High specific gravity objects (SED) that settle in the dead space are appropriately discharged to the outside from the second bottom outlet 123 . The second bottom outlet 123 preferably has a scraper discharge mechanism 127, for example. Suspended matter with a low specific gravity may be removed from the liquid surface by a predetermined suction device. In this way, by previously removing substances unsuitable for fermentation in the mixing section, the occurrence rate of problems during operation of the methane fermentation apparatus is greatly reduced. In other words, by reducing the low specific gravity substances, gas escape in the fermentation tank is less likely to be inhibited by the low specific gravity substances, and by reducing the high specific gravity substances, the amount of sediment that settles in the dead space of the fermentation tank is reduced. reduced, and the discharge of sediment from the first bottom outlet 113 is less likely to be obstructed. Furthermore, clogging of piping is reduced when circulating the fermented liquid.

The removal of fermentation unsuitable substances (high specific gravity substances and light specific gravity substances) from the mixing section 120 may be performed after stopping the supply of the raw material waste C to the mixing section 120 . As a result, it is possible to prevent the fermentation-suitable substances contained in the raw material waste C newly supplied to the mixing section 120 from being removed together with the fermentation-unsuitable substances.

In the fermentation tank 110, in addition to high specific gravity substances that settle in the tank as fermentation unsuitable substances and light specific gravity substances that float on the liquid surface, fermentation unsuitable substances floating in the fermentation liquid L (hereinafter referred to as floating unsuitable substances) ) exists. While it is difficult to separate suspended solids in the fermenter 110, the use of raw material waste containing organic solids tends to increase the amount of suspended solids in the fermentation broth. Floating unsuitable matter causes problems such as clogging of pipes.

Such floating unsuitable matter may be removed by filtering the fermented liquid L partially or intermittently taken out of the fermenter 110 by the separator 300 . In the methane fermentation system of FIG. 1, the second withdrawal route R12 is configured to pass through the separation device 300, and the fermentation liquid (separation liquid FL) after the floating matter in the liquid is separated by the separation device 300 is mixed. sent to section 120. In addition, when the purpose is to remove floating unsuitable substances, as a general rule, no flocculant or the like is added to the fermentation liquid sent to the separator.
Hereinafter, the route from the separation device 300 to the mixing section 120 of the second withdrawal route R12 is referred to as a filtrate route R4.

FIG. 3 shows the configuration of a rotary disc type concentrator, which is an example of the separation device 300 . FIG. 3A schematically shows a bird's-eye view of the relationship between the filtering unit 310 and the clearance self-cleaning unit 320 provided in the separation device 300. As shown in FIG. The gap self-cleaning unit 320 includes a plurality of rotating shafts 323 and a plurality of disk-shaped rotating bodies 321 fixed to the rotating shafts 323 and arranged at intervals along the axial direction thereof. FIG. 3B schematically shows the relationship between the filtering section 310 and the clearance self-cleaning section 320 as a cross-sectional view along the rotating shaft 323. As shown in FIG.

Filtration section 310 is formed of a plurality of band-shaped portions 315 extending along the conveying direction of unfermented substances, and slit-shaped gaps 312G are formed between adjacent band-shaped portions 315 . The upper end surfaces of the plurality of band-shaped portions 315 form a filtering surface 311S together with the slit-shaped gaps 312G. In FIG. 3(b), the level of the filtering surface 311S is indicated by a dashed line. The plurality of rotating shafts 323 are pivotally supported below the plurality of belt-shaped portions 315 so as to intersect the longitudinal direction of the belt-shaped portions 315 . A plurality of disc-shaped rotating bodies 321 move up and down in accordance with the rotation of the rotating shaft 323 within the slit-shaped gap 312G.

The disk-shaped rotating body 321 is fixed to the rotating shaft 323 at its eccentric position. The disc-shaped rotors 321 adjacent to each other in the axial direction differ in phase by 180 degrees for each disc 321 in vertical motion accompanying rotation of the rotating shaft 323 . Between the adjacent rotating shafts 323, the vertical motion phases of the adjacent disk-shaped rotating bodies 321 are the same. Since all the rotating shafts 323 rotate synchronously in the same direction at the same speed, the states shown on the left and right in the schematic diagram are alternately realized each time the rotating shaft 323 rotates half a turn.

It is generally difficult to separate floating unsuitable substances from fermentation suitable substances in the process of decomposition, but according to the separation device 300, undissolved unsuitable substances that maintain a relatively large size are selected. can be removed. Fermented liquid L is poured from above the filtering section 310 of the separating device 300 toward the inlet side end of the filtering surface 311S. The inlet side end is the rear end in the rotation direction of the gap self-cleaning section 320 . Floating unsuitable matter having a relatively large size does not pass through the gap between the filtering section 310 and the gap self-cleaning section 320 and is trapped on the filtering surface 311S. The trapped unsuitable matter moves forward in the rotational direction on the filtering surface 311S due to the rotation of the gap self-cleaning section 320, and is conveyed toward a predetermined outlet. The separated unsuitable matter is collected as residual sludge RC.

In the separation device 300, since the gap self-cleaning section 320 is constantly moving up and down, the gap between the filtering section 310 and the gap self-cleaning section 320 is less likely to be blocked. On the other hand, if a mesh type screen is used, for example, the mesh is easily clogged.

The fermented liquid L containing small-sized fermentable substances in the middle of decomposition passes through the gap between the gap self-cleaning section 320 and the filtering section 310 and is collected in the storage tank 170 or the mixing section 120 as the separated liquid FL.

FIG. 4 shows an example configuration of another separation device 300A.
Filtration unit 310A included in separation device 300A has substantially the same configuration as separation device 300 in FIG. A slit-like gap 312AG is formed between the portions 315A. The upper end surfaces of the plurality of band-shaped portions 315A form a filtration surface 311AS together with the slit-shaped gaps 312AG.

The gap self-cleaning part 320A provided in the separation device 300A has a substantially comb-like shape instead of a rotating body. The gap self-cleaning part 320A includes a plurality of claws 321A that are inserted into the respective slit-shaped gaps 312AG from one direction, and a strut 322A that supports the claws 321A. The strut part 322A is pivotally supported so as to intersect the conveying direction of the unfermentable substances, and moves along the conveying direction as shown in order from FIG. 4(a) to FIG. 4(b). After that, as shown in FIG. 4(c), it has a mechanism to move in the reverse direction under the filtering section 310A and return to the original position. By repeating this revolving motion, unfermented substances deposited on the filtration surface are scraped off by the plurality of claw portions 321A and collected as residual sludge RC behind the filtration portion 310A.

That is, the separation device has a filtration surface for filtering the fermented liquid, a filtration unit having a plurality of slit-shaped gaps that open to the filtration surface, and unfermented substances that move in the slit-shaped clearances and accumulate on the filtration surface. and a gap self-cleaning section for conveying. The filtering section has a plurality of band-shaped portions arranged to extend along the conveying direction of the unfermentable substances, and slit-shaped gaps are formed between the adjacent band-shaped portions.

Further, the gap self-cleaning part is fixed to a plurality of rotating shafts arranged below the filtering part, and a plurality of disk-shaped rotating shafts arranged at intervals along the axial direction of the rotating shafts. A plurality of disk-shaped rotating bodies each having a plurality of rotating shafts supported so as to intersect the conveying direction of the unfermentable substances and arranged at intervals along the conveying direction of the unfermentable substances. move up and down with the rotation of the rotary shaft within the slit-shaped gap.

A step of introducing a fermented liquid into a filtration surface having a plurality of slit-shaped gaps, draining the fermentation liquid through the plurality of slit-shaped gaps, depositing substances unsuitable for fermentation on the filtration surface, and a step of self-cleaning the slit-shaped gaps. A step of removing fermentation-improper substances deposited on the filtration surface by the self-cleaning part is provided.

The separated liquid FL may be collected in the storage tank 170 without being sent to the filtrate route R4. At this time, the valve V5 provided in the filtrate route R4 between the separation device 300 and the mixing section 120 is closed, and the valve V7 provided between the storage tank 170 and the separation device 300 is opened. The separated liquid FL recovered in the storage tank 170 is passed through the recovery route R5 and the valve V8 by the driving force of the third pump P3 and returned to the fermenter 110, or is discarded in order to properly maintain the state of the fermenter 110. You may Fermentation inhibitors such as ammonia are accumulated in the separated liquid FL, so it is desirable to sequentially and partially discharge the separated liquid FL to the outside of the methane fermentation system.

When discarding the separated liquid FL, a flocculant is mixed with the separated liquid FL in the storage tank 170, and the fermentation liquid L containing the flocculant is sent to the dehydrator 180 through the dehydration route R6 and the valve V9, The residual sludge and the dehydrated filtrate can be separated and then discarded.

The separation device 300 can be used not only for removing floating substances in the liquid, but also for confirming the state of decomposition of fermentable substances in the fermenter 110 . It is difficult to visually check the inside of the fermenter 110 at the time of start-up of fermentation, steady operation, etc., but according to the separation device 300, the state of digestion and decomposition of the appropriate substances in the fermented liquid can be detected on the filtration surface 311S. Since the unsuitable floating matter remaining in the waste material C can be visually observed and clearly grasped, the supply amount of the raw material waste material C can be easily controlled. Furthermore, the route of the fermented liquid to be introduced into the mixing unit 120 can be selected as described above based on the state of digestion and decomposition of the appropriate substances in the fermented liquid.

FIG. 5 shows the configuration of an example of a pretreatment device for sorting raw material waste C. As shown in FIG. The pretreatment device 200 includes a first conveying device 210 for transferring the waste C1 introduced from the outside, a crusher 220 for crushing the waste C1 supplied from the first conveying device 210, and crushed by the crusher 220. A second conveying device 230 for transferring crushed waste C2 and a separator 240 are provided.

The first conveying device 210 is, for example, a belt conveyor, and supplies the crusher 220 with equalizing the amount of the waste C1 continuously introduced into the system within a certain period of time. The crusher 220 is, for example, a twin-screw crusher, which crushes large-sized solid waste containing organic matter into small pieces and performs pre-shredding treatment so that the waste has a size suitable for processing in the sorting machine 240 . The second conveying device 230 is, for example, a belt conveyor, and supplies the crushed waste C2 including crushed solid waste to the sorting machine 240 after equalizing the amount of crushed waste C2 supplied within a certain period of time.

The sorting machine 240 may have any configuration, but has a cylindrical drum made of a perforated sheet such as a mesh having a plurality of holes or punching metal, and a rotary crushing blade provided in the drum. Shredded waste C2 is introduced into the drum. Among the crushed waste C2, solids smaller than the pore size of the perforated sheet are discharged outside the drum due to the wind force and centrifugal force flowing through the drum. The discharged solids are collected as raw material waste C containing the correct content of fermentable material. Low specific gravity materials such as cloth and plastic sheets and high specific gravity materials such as metals are recovered from the drum as unfermentable materials NC.

As described above, the methane fermentation apparatus according to the present invention mixes a fermenter containing a fermented liquid for generating biogas, a fermented liquid taken out of the fermenter, and a waste material containing fermentable substances. A mixing unit for obtaining a fluid material and separating at least a part of unsuitable substances derived from waste, an input route for sending the fluid material from the mixing unit to the fermenter, and removing solids contained in the fermentation broth. and a filtrate route for feeding the waste into the mixing section, and sending the fermentation liquid taken out of the fermentation tank and having solids removed by the separation device to the mixing section, wherein the waste is removed in the mixing section and the fermented liquid from which the floating unsuitable matter has been removed to obtain a fluid.

A circulation route for returning the fermented liquid extracted from the fermenter to the fermenter is provided, and a separation device is provided in a branch route branching from the circulation route.

In addition, the fermented liquid taken out from the fermenter is further provided with a withdrawal route to the mixing section without passing through the separation device, and when the solid concentration of the fermented liquid contained in the fermenter is lower than a predetermined concentration, the mixing section and the fermentation liquid taken out from the fermentation tank is sent to the mixing section through the extraction route.

Further, a storage tank for storing the fermentation liquid from which the floating unsuitable matter has been removed by the separation device, and the fermentation liquid stored in the storage tank when the solid matter concentration of the fermentation liquid stored in the fermentation tank is higher than a predetermined concentration. and a recovery route for supplying the fermenter.

The methane fermentation method according to the present invention includes (i) a step of removing the fermentation liquid from the fermentation tank containing the fermentation liquid and sending it to the mixing section; (iii) a step of sending the fluid from the mixing section to the fermenter; (iv ) a step of hydrolyzing, acid fermentation, and methane fermentation of a fermentation suitable material in a fermenter to generate biogas, and in step (i), solids are removed from the fermentation liquid taken out of the fermenter. It is configured to send the removed fermented liquid to the mixing section.

In addition, when the solid concentration of the fermented liquid contained in the fermenter is lower than the predetermined concentration, the fermented liquid taken out from the fermenter is directly sent to the mixing unit, and when the solids concentration reaches the predetermined concentration, The fermentation liquid taken out from the fermenter may be configured to be sent to the mixing section after removing the solids through the separation device.

The concentration of solids in the fermented liquid can be indirectly determined by visually confirming the liquid surface of the mixing unit 120 and visually confirming the state of the solids separated by the separation device 300. A portion of the fermentation liquor circulated via route R3 may be sampled and determined for solids concentration using a predetermined test method.

The solids concentration (M) can be calculated by measuring the amount of fermented liquid (A) sent to the separator and the amount of fermented liquid (B) filtered by the separator, and calculated by M = (A - B) / A. Alternatively, the fermentation broth can be filtered through a mesh and the dry weight of the residue left on the mesh can be measured relative to the weight of the original specimen.

The above-described embodiment is one aspect of the present invention, and the present invention is not limited by the description, and the specific configuration and control mode of each part can be appropriately changed and designed within the scope of the effects of the present invention. It goes without saying that

10: Methane fermentation system 100: Methane fermentation device 110: Fermentation tank 111: Upper outlet 112: Submerged outlet 113: First bottom outlet 114: First outlet 120: Mixing section 121: Mixing container 121d: Dead space 121u : Mixing space 122: Stirring blade 123: Second bottom outlet 124: Second discharge port 125: First inlet 126: Second inlet 127: Scraping discharge mechanism 170: Storage tank 180: Dehydrator 200: Pretreatment device 210: First Conveying Device 220: Crusher 230: Second Conveying Device 240: Separating Machine 300: Separating Device 310: Filtration Part 311S: Filtration Surface 312G: Slit-shaped Gap 315: Band-shaped Part 320: Gap Self-cleaning Part 321: Disc-shaped Rotating body C1: Waste C2: Crushing waste C: Raw material waste NC: Unsuitable for fermentation L: Fermentation liquid FL: Fermentation liquid (filtrate)
S: fluid RC: residual sludge P1-P3: 1st-3rd pumps R11: 1st withdrawal route R12: 2nd withdrawal route R2: Input route R3: Circulation route R4: Filtrate route R5: Recovery route V1-V9 : valve T1: first branch T2: second branch

Claims (6)

a fermenter containing a fermented liquid for generating biogas;
The fermented liquid taken out from the fermenter and the waste containing the fermentation suitable material are put in and mixed to obtain a fluid material, and a mixing unit that separates at least a part of the fermentation unsuitable material derived from the waste. and,
an input route for sending the fluid from the mixing unit to the fermenter;
a separation device for removing solids contained in the fermentation liquid;
a filtrate route for sending the fermented liquid taken out from the fermenter and from which solid matter has been removed by the separation device to the mixing section;
a withdrawal route for sending the fermented liquid taken out from the fermenter to the mixing unit without passing through the separation device;
with
A methane fermentation apparatus , wherein a supply route of the fermented liquid sent to the mixing section is switchable between the filtrate route and the extraction route. Equipped with a circulation route that returns the fermented liquid extracted from the fermenter to the fermenter,
The methane fermentation apparatus according to claim 1, wherein the separation device is provided in a branch route branching from the circulation route. (i) removing the fermented liquid from a fermenter containing the fermented liquid and sending it to a mixing section;
(ii) in the mixing unit, the fermentation liquid taken out from the fermenter and waste containing fermentation-suitable substances are mixed to obtain a fluid, and at least part of fermentation-unsuitable substances derived from the waste is removed; a step of separating;
(iii) sending the flow from the mixing section to the fermenter;
(iv) hydrolysis of the fermentable material, acid fermentation and methane fermentation in the fermenter to generate biogas;
(v) removing the fermented liquid from the fermenter, removing solids using a separation device, and then sending it to the mixing section;
A method of methane fermentation, wherein the step (i) and the step (v) are switched based on the solid matter concentration (M) of the fermentation liquid stored in the fermenter. 4. The methane fermentation method according to claim 3 , wherein said step ( i ) is carried out when said solid matter concentration (M) of said fermentation liquor contained in said fermenter is lower than a predetermined concentration. 5. The methane fermentation method according to claim 3 or 4 , wherein the step (v) is performed when the solid matter concentration (M) of the fermentation liquor contained in the fermenter is higher than a predetermined concentration. The solids concentration (M) is calculated by measuring the amount of fermented liquid (A) sent to the separation device and the amount of fermented liquid (B) filtered by the separation device, and calculated by M = (A - B) / A. The methane fermentation method according to claim 4 or 5 .

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