JP7596587B1 - Methane fermentation system and methane fermentation method - Google Patents

Abstract

The present invention provides a methane fermentation system and a methane fermentation method that improve the ease of removing high-water content solid biomass and the ease of cleaning the fermentation chamber.
[Solution] The methane fermentation system comprises a fermentation chamber 1, a second storage section 32 that is provided below the floor surface 12 of the fermentation chamber 1 and that stores a first fermentation raw material 7 having a TS (solids concentration) of less than 15%, and a box section 2 that is installed within the fermentation chamber 1 and stores a second fermentation raw material 8 having a TS of 15% or more. When the first fermentation raw material 7 stored in the second storage section 32 is supplied and comes into contact with the second fermentation raw material 8, the box section 2 separates it from the second fermentation raw material 8 by causing at least a portion of the first fermentation raw material 7 to fall through a separation hole 23 drilled in the bottom plate 21.
[Selected figure] Figure 6

Description

This invention relates to a methane fermentation system and a methane fermentation method used to ferment biomass resources such as agricultural waste and livestock manure.

Traditionally, methane fermentation technology, which efficiently ferments stored biomass resources, has been researched as a method for effectively utilizing biomass resources as an energy resource.

One method for efficiently fermenting biomass resources is to repeatedly contact the solid biomass with digestive fluid, which acts as a seed culture liquid, by circulating it through a fermentation chamber storing solid biomass. In this method, the solid biomass after fermentation absorbs water from the digestive fluid and becomes high-moisture solid biomass, which is prone to collapse and presents a problem in terms of ease of removal from the fermentation chamber. In addition, high-moisture solid biomass tends to stick to the walls and floor of the fermentation chamber, which presents a problem in that cleaning workability cannot be improved even by spraying water. Therefore, when implementing this methane fermentation method, it is necessary to improve the ease of transporting and cleaning the high-moisture solid biomass.

Patent Document 1 discloses a fermenter that has a liquid groove formed on the floor of the fermenter to accommodate liquid raw materials, and is installed inside the fermenter to accommodate solid raw materials, to which the fermentation liquid contained in the liquid groove is supplied, and the fermentation liquid and solid biomass are separated by a rice husk layer on the surface of the liquid groove.

JP 2007-744 A

The fermentation tank disclosed in Patent Document 1 allows for smooth replacement of biomass. However, the fermentation tank disclosed in Patent Document 1 has problems in that it is not possible to improve the ease of unloading from the perspective of preventing the collapse of high-water content biomass, and the liquid groove is filled with rice husks, making it difficult to improve the ease of cleaning the inside of the fermentation tank.

The present invention was devised in consideration of the above-mentioned problems, and its purpose is to provide a methane fermentation system and a methane fermentation method that improve the ease of transporting high-moisture solid biomass and the ease of cleaning the fermentation chamber.

The methane fermentation system of the first invention comprises a fermentation chamber, a storage section that is provided below the floor surface of the fermentation chamber and stores a first fermentation raw material having a TS (solids concentration) of less than 15%, and a box section that is installed in the fermentation chamber and stores a second fermentation raw material having a TS of 15% or more. The box section is characterized in that when the first fermentation raw material stored in the storage section is supplied and comes into contact with the second fermentation raw material, at least a portion of the first fermentation raw material is separated from the second fermentation raw material by dropping it through a separation hole drilled in a bottom plate.

The methane fermentation system of the second invention is characterized in that, in the first invention, the box section includes an upper box section and a lower box section each for storing the second fermentation raw material, and when the first fermentation raw material stored in the storage section is supplied and comes into contact with the second fermentation raw material, the upper box section separates at least a portion of the first fermentation raw material from the second fermentation raw material by dropping it through an upper separation hole drilled in the bottom plate of the upper box section, and when the first fermentation raw material dropped from the upper box section is supplied and comes into contact with the second fermentation raw material, the lower box section separates at least a portion of the first fermentation raw material from the second fermentation raw material by dropping it through a lower separation hole drilled in the bottom plate of the lower box section.

The methane fermentation system of the third invention is the same as that of the first or second invention, characterized in that the box section is supplied with the first fermentation raw material to generate biogas, and the storage section is supplied with the biogas generated by the box section.

The methane fermentation method according to the fourth invention is characterized by having a raw material supplying step of supplying a first fermentation raw material contained in a storage section that is provided below the floor surface of the fermentation chamber and that stores a first fermentation raw material having a TS of less than 15% to a box section that is installed in the fermentation chamber and that stores a second fermentation raw material having a TS of 15% or more, and a separation step of separating at least a portion of the first fermentation raw material that has been supplied to the box section by the raw material supplying step and that has come into contact with the second fermentation raw material from the second fermentation raw material by dropping it through a separation hole drilled in the bottom plate of the box section.

According to the first and second inventions, the methane fermentation system is provided with a box section that separates the first fermentation raw material from the second fermentation raw material by allowing it to fall through a separation hole when the first fermentation raw material is supplied from the storage section that is located below the floor of the fermentation chamber. This makes it possible to prevent the second fermentation raw material, which has a high moisture content, from collapsing and sticking to the inside of the fermentation chamber. This makes it possible to improve the ease of transporting high moisture solid biomass and the ease of cleaning the fermentation chamber in the methane fermentation system.

In particular, according to the second invention, an upper box section is provided that, when the first fermentation raw material contained in the storage section is supplied, causes it to fall through an upper separation hole to separate it from the stored second fermentation raw material, and a lower box section is provided that, when the first fermentation raw material that has fallen from the upper box section is supplied, causes it to fall through a lower separation hole to separate it from the stored second fermentation raw material. This makes it possible to efficiently ferment a large amount of fermentation raw material regardless of the volume of the box section. This makes it possible to improve the productivity of biogas in the methane fermentation system.

In particular, according to the third invention, the storage section is supplied with biogas produced by the box section. That is, the biogas produced by the box section comes into contact with the first fermentation raw material and the product of fermentation of the first fermentation raw material contained in the storage section, and hydrogen sulfide and ammonia in the biogas may be eluted. For this reason, it is not necessary to provide equipment for desulfurization and ammonia removal of the generated biogas. This allows the methane fermentation device to be made smaller. In addition, carbon dioxide in the generated biogas is also eluted in the same manner, so that a biogas with a purified methane concentration and high calorific value can be produced. This allows the usefulness of the biogas to be improved, such as by reducing the costs required for gas transportation and storage.

According to the fourth invention, the methane fermentation method includes a raw material supplying step of supplying the first fermentation raw material contained in a storage section provided below the floor surface of the fermentation chamber to a box section containing the second fermentation raw material, and a separation step of separating the supplied first fermentation raw material from the second fermentation raw material by allowing it to pass through a separation hole and fall. This makes it possible to prevent the second fermentation raw material, which has a high water content, from collapsing and sticking to the inside of the fermentation chamber. This makes it possible to improve the ease of transporting high water content solid biomass and the ease of cleaning the fermentation chamber in the methane fermentation system.

FIG. 1 is a schematic perspective view showing an example of a methane fermentation system according to the present embodiment. FIG. 2 is a schematic perspective view showing an example of a fermentation chamber constituting the methane fermentation system in this embodiment. FIG. 3 is a schematic cross-sectional view showing an example of a fermentation chamber corresponding to the cross section AA in FIG. FIG. 4 is a schematic plan view showing an example of a box body that constitutes the methane fermentation system in this embodiment. FIG. 5 is a schematic cross-sectional view showing an example of the case part corresponding to the cross section BB in FIG. FIG. 6 is a schematic cross-sectional view showing an example of a process included in the operation of the methane fermentation system in this embodiment. FIG. 7 is a schematic cross-sectional view showing an example of a process included in the operation of the methane fermentation system in this embodiment. FIG. 8 is a schematic cross-sectional view showing an example of a process included in the operation of the methane fermentation system in this embodiment. FIG. 9 is a schematic cross-sectional view showing a first modified example of the steps included in the operation of the methane fermentation system in this embodiment. FIG. 10 is a schematic perspective view showing a second modified example of the fermentation chamber constituting the methane fermentation system in this embodiment. FIG. 11 is a schematic cross-sectional view showing an example of a process included in the operation of the methane fermentation system, which corresponds to the cross-section BB of FIG. FIG. 12 is a schematic cross-sectional view showing an example of a process included in the operation of the methane fermentation system, which corresponds to the cross-section BB of FIG. FIG. 13 is a schematic cross-sectional view showing an example of a process included in the operation of the methane fermentation system corresponding to the cross-section BB of FIG. FIG. 14 is a schematic cross-sectional view showing an example of a process included in the operation of the methane fermentation system corresponding to the cross-section BB of FIG.

Below, with reference to the drawings, a detailed description will be given of an example of a methane fermentation system 100 and a methane fermentation method according to an embodiment of the present invention. In each drawing, a first horizontal direction X is defined, a direction perpendicular to the first horizontal direction X is defined as a second horizontal direction Y, and a direction perpendicular to each of the first horizontal direction X and the second horizontal direction Y is defined as a height direction Z. The configurations in each drawing are shown diagrammatically for the purpose of explanation, and for example, the size of each component and the size comparison between the components may differ from those shown in the drawing.

(Methane fermentation system 100)
An example of a methane fermentation system 100 according to the present embodiment will be described with reference to the drawings.

The methane fermentation system 100 is a system that promotes methane fermentation and produces biogas by contacting a fermentation raw material (first fermentation raw material) having a TS (solids concentration) of less than 15%, which may include seed culture liquid, livestock manure, digestive fluids, etc., with a fermentation raw material (second fermentation raw material) having a TS of 15% or more, which may include solid biomass such as rice husks and waste materials. Note that the unit "%" for TS refers to % by mass.

As shown in FIG. 1, the methane fermentation system 100 includes one or more fermentation chambers 1 having an opening/closing section 11, and a box section 2. The methane fermentation system 100 may include a biogas collection tank T for storing biogas generated in the fermentation chamber 1, for example. In addition, the methane fermentation system 100 includes a box section 2 containing the second fermentation raw material being carried into the fermentation chamber 1 by an operator U, and after the opening/closing section 11 is closed and methane fermentation is completed, the opening/closing section 11 is opened and the box section 2 is carried out of the fermentation chamber 1.

As shown in Figs. 2 and 3, the methane fermentation system 100 is provided with a storage section 3 that is provided below the floor surface 12 (the inner surface of the floor plate material of the fermentation chamber 1) of the fermentation chamber 1 and stores a first fermentation raw material with a TS of less than 15%. Here, the storage section 3 below the floor surface 12 means that the height of the bottom of the storage section 3 in the height direction Z (vertical direction) is lower than the height of the inner surface (floor surface 12) of the floor plate material of the fermentation chamber 1. Specifically, the storage section 3 below the floor surface 12 includes a case where the storage section 3 is integral with the floor surface 12 and inseparable from the fermentation chamber 1, such as a groove portion cut into the floor surface 12, and a case where the storage section 3 is separate from the floor surface 12 and separated from the fermentation chamber 1, such as a storage space provided vertically (see Fig. 10) or diagonally below the floor surface 12.

As shown in Figures 4 and 5, the methane fermentation system 100 is a box having an opening O at the top, with the box section 2 made of a bottom plate 21 and a side plate 22, and a separation hole 23 that allows the first fermentation raw material to pass through but does not allow the second fermentation raw material to pass through. As a result, when the first fermentation raw material stored in the storage section 3 is supplied to the box section 2 and comes into contact with the second fermentation raw material, the methane fermentation system 100 allows at least a portion of the first fermentation raw material to pass through the separation hole 23 and fall, thereby separating it from the second fermentation raw material.

Here, in the conventional technology, when the first fermentation raw material and the second fermentation raw material are repeatedly brought into contact with each other, the moisture content of the second fermentation raw material increases, and as a result, the high moisture content of the second fermentation raw material collapses in the fermentation chamber 1 or sticks to the floor or walls of the fermentation chamber 1, and there are problems with the workability of carrying it out and cleaning it. On the other hand, according to the methane fermentation system 100 of the present invention, the high moisture content of the second fermentation raw material does not leak from the box body part 2, and the first fermentation raw material can be discharged from the separation hole 23 of the box body part 2. In this case, the collapse of the high moisture content of the second fermentation raw material and sticking to the fermentation chamber 1 can be suppressed. This makes it possible to improve the workability of carrying out the high moisture content solid biomass and the workability of cleaning the fermentation chamber 1 for the methane fermentation system 100. In addition, since the storage part 3 is provided below the floor surface 12, the fermentation raw material in the fermentation chamber 1 can be efficiently replaced by running a vehicle such as a forklift on the floor surface 12. This can improve the ease of transporting high-moisture solid biomass from the methane fermentation system 100.

As shown in FIG. 2, the methane fermentation system 100 may further include a drainage pipe 4, a water pump 5, and a sprinkler pipe 6. The methane fermentation system 100 repeats the process of draining the first fermentation raw material stored in the storage section 3 from the storage section 3 via the drainage pipe 4, supplying the first fermentation raw material from above the box section 2 via the water pump 5 and the sprinkler pipe 6, and then recovering the first fermentation raw material in the storage section 3. In this case, the promotion of methane fermentation can be sustained without adding the first fermentation raw material. This can improve the workability and economy of the methane fermentation system 100.

<Fermentation chamber 1>
The fermentation chamber 1 is a closed space that can be opened and closed to accommodate fermentation raw materials and perform methane fermentation. When the methane fermentation system 100 includes a plurality of fermentation chambers 1, each fermentation chamber 1 is an independent closed space. The material of the fermentation chamber 1 may be any material that can seal the inside of the fermentation chamber 1 and has a strength sufficient to allow vehicles such as a forklift to travel inside the chamber, and may be made of, for example, concrete or steel.

The shape and dimensions of the fermentation chamber 1 can be any shape and size as long as it can accommodate one or more box sections 2 and has sufficient floor space to form the accommodation section 3, but for example, it is a roughly rectangular parallelepiped with a width of 1m to 10m, a height of 1m to 10m, and a depth of 1m to 50m.

As shown in Figures 2 and 3, for example, the fermentation chamber 1 is a closed space surrounded by an opening/closing section 11, a floor surface 12, side surfaces 13, and a ceiling 14. The fermentation chamber 1 is formed by cutting out one or more storage sections 3 into the floor surface 12.

The fermentation chamber 1 has a substantially horizontal floor surface 12, for example, in consideration of the ease of installation of the box body 2. The fermentation chamber 1 may be formed such that the floor surface 12 slopes downward from the opening/closing section 11 toward the depth direction of the fermentation chamber 1 on the drain pipe 4 side (first horizontal direction X in FIG. 2). In this case, it is possible to prevent the first fermentation raw material from passing through the opening/closing section 11 and leaking out of the fermentation chamber 1. This can improve the economic efficiency of the methane fermentation system 100.

<Box body part 2>
The box body 2 contains the second fermentation raw material having a TS of 15% or more. The box body 2 is made of a material, for example, steel, and has rigidity.

The shape and dimensions of the box body 2 are arbitrary as long as it can be installed independently within the fermentation chamber 1, but for example, it is a roughly rectangular parallelepiped with a width of 0.5m to 2.5m x height of 0.5m to 2.5m x depth of 0.5m to 2.5m. The box body 2 is preferably a columnar body extended in the height direction Z, such as a polygonal column or a cylindrical body. In this case, multiple box body parts 2 can be stacked in the height direction Z, and the amount of the second fermentation raw material used for methane fermentation can be flexibly adjusted regardless of the dimensions of the box body parts 2. This improves the manufacturability of the methane fermentation system 100. It is also easy to design the dimensions so that the operator U can easily carry it in and out. This improves the workability of the methane fermentation system 100.

As shown in Figures 4 and 5, for example, the box body 2 has a bottom plate 21, side plates 22, separation holes 23, and an opening O. The box body 2 stores the second fermentation raw material inside, or discharges the stored second fermentation raw material through the opening O. The box body 2 is composed of side plates 22 made of, for example, one or more known steel plates, and a bottom plate 21 made of a lattice-shaped steel plate and a punched metal layered on top of each other, where the gap between the lattice and the punched holes corresponds to the separation hole 23. The thickness of the bottom plate 21 and the side plates 22 is, for example, 0.1 mm to 50 mm.

<<Separation hole 23>>
One or more separation holes 23 are pre-drilled in the bottom plate 21 of the box body 2. The width of the separation hole 23 (width in the first horizontal direction X in FIG. 5 ) is, for example, 0.05 mm to 10 mm. For example, when a plurality of separation holes 23 are drilled, they are drilled at predetermined intervals from each other. The separation holes 23 can separate a plurality of different fermentation raw materials that are in contact with or mixed with each other by dropping solid bodies or fluid bodies that are smaller than the width of the separation hole 23, among the fermentation raw materials contained in the box body 2, into the second storage section 32.

When the first fermentation raw material is supplied to the box section 2, which already contains the second fermentation raw material, and comes into contact with the second fermentation raw material, the separation hole 23 allows at least a portion of the first fermentation raw material to pass through and fall, thereby separating it from the second fermentation raw material. Here, some of the components contained in the second fermentation raw material that are dissolved in association with methane fermentation caused by contact between the first fermentation raw material and the second fermentation raw material are considered to be the first fermentation raw material that passes through the separation hole 23 and falls. In other words, as methane fermentation progresses, the volume of the first fermentation raw material increases, and the volume of the second fermentation raw material may decrease.

<Storage section 3>
The accommodation section 3 accommodates the first fermentation raw material having a TS of less than 15%. The accommodation section 3 is, for example, as shown in Figures 2 and 3, in the shape of a groove formed by cutting out the floor surface 12 of the fermentation chamber 1. That is, the groove-shaped accommodation section 3 is provided below the floor surface 12, which is the inner surface of the floor plate material of the fermentation chamber 1.

The storage section 3 may be formed by cutting out any shape into the floor surface 12 as long as it is separated from the opening/closing section 11, and may be a shape that combines one or more rectangles, trapezoids, triangles, etc. in a plan view. For example, one part (one end) of the storage section 3 is formed on the floor surface 12 on the opening/closing section 11 side, and the other part (the other end) is formed on the floor surface 12 on the side surface 13 side. For example, the other end of the storage section 3 is connected to the drain pipe 4. At this time, the first fermentation raw material stored in the storage section 3 flows from one end to the other end within the storage section 3, and is drained from the storage section 3 via the drain pipe 4.

The width of the storage section 3 (width in the second horizontal direction Y in FIG. 2) is arbitrary, but is, for example, 100 mm to 500 mm.

As shown in FIG. 2, the storage section 3 may include a first storage section 31, a second storage section 32, and a third storage section 33. The storage sections 31, 32, and 33 are separated from each other, for example, at one end and merge at the other end. In this case, the first fermentation raw material is less likely to remain at one end than when the first fermentation raw material merges at one end and the other end, and can be efficiently caused to flow toward the drain pipe 4 and drained from the storage section 3. This can improve the manufacturability of the methane fermentation system 100.

As shown in FIG. 3, for example, the bottom surface of the storage section 3 is formed to be approximately horizontal. In this case, it is easier to expand the space for storing the first fermentation raw material than when the bottom surface of the storage section 3 is formed to be inclined downward toward the depth direction of the fermentation chamber 1, and more first fermentation raw material can be stored and used for methane fermentation in one methane fermentation run. This improves the manufacturability of the methane fermentation system 100.

The storage section 3 may be formed, for example, so as to slope downward from one end to the other end. In this case, the first fermentation raw material is less likely to remain in the storage section 3, and can be efficiently drained from the storage section 3. This can improve the manufacturability of the methane fermentation system 100.

<Drainage pipe 4>
One end of the drain pipe 4 is connected to the storage unit 3, and the other end is connected to the water pump 5. The drain pipe 4 drains the first fermentation raw material stored in the storage unit 3. The drain pipe 4 is made of a material, for example, resin.

In the example shown in Figures 2 and 3, the drain pipe 4 is provided to communicate between the inside and outside of the fermentation chamber 1 so as to connect to a water pump 5 installed outside the fermentation chamber 1, but this is not limited thereto, and the drain pipe 4 may also be connected to a water pump 5 installed inside the fermentation chamber 1.

<Water Pump 5>
One end of the water supply pump 5 is connected to the drain pipe 4, and the other end is connected to the sprinkling pipe 6. The water supply pump 5 supplies the first fermentation raw material drained from the storage section 3 to the drain pipe 4 to the sprinkling pipe 6. As the water supply pump 5, for example, a known water supply pump is used.

<Watering pipe 6>
One end of the water sprinkler pipe 6 is connected to the water pump 5, and the other end is disposed inside the fermentation chamber 1. The water sprinkler pipe 6 is made of a material, for example, resin.

The other end of the water sprinkler pipe 6 is provided near the ceiling 14 of the fermentation chamber 1, as shown in Figures 2 and 3. When the water sprinkler pipe 6 is rigid, it penetrates the side surface 13 and is fixed to the ceiling 14, and when the water sprinkler pipe 6 is flexible, it penetrates the side surface 13 and is fixed to the ceiling 14.

The water sprinkler pipe 6 has water sprinkler holes (not shown) drilled in advance on the side of the pipe on the other end side placed inside the fermentation chamber 1, and the first fermentation raw material pumped from one end side by the water supply pump 5 is sprinkled through the water sprinkler holes. In other words, the water sprinkler pipe 6 can supply the first fermentation raw material stored in the storage section 3 to the box section 2 installed inside the fermentation chamber 1 by sprinkling and dropping the first fermentation raw material stored in the storage section 3 from above inside the fermentation chamber 1.

The sprinkler pipes 6 may include a first sprinkler pipe 61, a second sprinkler pipe 62, and a third sprinkler pipe 63, as shown in FIG. 2, for example. Each sprinkler pipe 61, 62, 63 branches off from one pipe at one end side within the fermentation chamber 1, for example, and is separated from each other at the other end side. In this case, compared to the case where the first fermentation raw material is sprinkled from a single pipe that does not branch off, the first fermentation raw material can be evenly spread over a wide area, and the promotion of methane fermentation can be sustained for a larger amount of the fermentation raw material. This can improve the manufacturability of the methane fermentation system 100.

<Biogas collection tank T>
The biogas collection tank T is a tank for collecting the biogas generated in the fermentation chamber 1. The biogas collection tank T is directly connected to the fermentation chamber 1, for example.

The biogas collection tank T only collects and discharges the biogas generated in the fermentation chamber 1, and does not generate biogas within the biogas collection tank T. The material of the biogas collection tank T is, for example, the same steel material as known gas holders, or a resin material such as polyvinyl chloride.

(Methane fermentation method)
Next, as a methane fermentation method in this embodiment, an example of the operation of the methane fermentation system 100 will be described with reference to the drawings. The methane fermentation method includes, for example, a raw material supplying step and a separation step.

For ease of explanation, this embodiment uses an example in which the second storage section 32 of the storage section 3 and the second sprinkler pipe 62 of the sprinkler pipe 6 are used, but this is not limited thereto, and the first storage section 31 and the third storage section 33 or the first sprinkler pipe 61 and the third sprinkler pipe 63 may be used.

In addition, in this embodiment, the methane fermentation system 100 may control each component and execute each process based on a program or the like installed in a publicly known computer (not shown) included in the methane fermentation system 100, or the worker U may take the lead in operating each component of the methane fermentation system 100 to execute each process of the methane fermentation method.

First, the first fermentation raw material A and the second fermentation raw material B will be described as fermentation raw materials used in the methane fermentation method of this embodiment. Note that the first fermentation raw material A corresponds to the first fermentation raw material described above, and the second fermentation raw material B corresponds to the second fermentation raw material described above.

<First fermentation raw material A>
The first fermentation raw material A is stored in the second storage section 32 in advance, and is circulated by repeatedly draining the water from the storage section 32 and spraying water into the fermentation chamber 1 using the water pump 5 as power. The first fermentation raw material A undergoes wet methane fermentation in the fermentation chamber 1. For example, the first fermentation raw material A is a fluid biomass resource with a TS of 2% to 5% or more and less than 15%, and includes seed culture liquid, livestock manure, digestive fluid, etc. By using the first fermentation raw material A that satisfies the above-mentioned TS, it is expected that the liquid first fermentation raw material A will circulate in the fermentation chamber 1 while maintaining sufficient fluidity, and the activity of the microorganisms required for methane fermentation will be actively carried out.

<Second fermentation raw material B>
The second fermentation raw material B is accommodated in the box body 2 in advance. The second fermentation raw material B is subjected to dry methane fermentation in the box body 2. For example, the second fermentation raw material B is a solid material having a TS of 15% or more and less than 30% to 40% among biomass resources, and includes solid biomass such as rice husks and waste materials. In a typical single dry methane fermentation, a raw material having a moisture content of about 60% to 80% is used, which corresponds to a TS of about 20% to 40%. Therefore, 40% is generally considered to be a guideline for the upper limit of the TS of the second fermentation raw material B to be subjected to dry methane fermentation. By using the second fermentation raw material B that satisfies the above-mentioned TS, it is expected that the fermentation of the second fermentation raw material B, which is a solid biomass, will proceed while appropriately retaining moisture, and methane will be efficiently produced.

Next, the methane fermentation method of this embodiment will be described in detail. Note that the solid arrows in the figure indicate the flow direction of the first fermentation raw material A.

<Advance preparations>
6, for example, the first fermentation raw material A is stored in advance in the second storage section 32, and the second fermentation raw material B is stored in advance in the box body section 2. Methane-producing bacteria are already present in the first fermentation raw material A or the second fermentation raw material B. Here, the first fermentation raw material A stored in the second storage section 32 is referred to as the first fermentation raw material Aa.

In order to create an anaerobic environment in the fermentation chamber 1 that promotes methane fermentation, the worker U places the first fermentation raw material A and the second fermentation raw material B in the fermentation chamber 1 with the opening/closing section 11 open, closes the opening/closing section 11 to seal the fermentation chamber 1, and degass (deoxygenate) the fermentation chamber 1 as necessary.

<Raw material supply process>
In the raw material supply step, the methane fermentation system 100 drains the first fermentation raw material A by flowing it from the second storage section 32 to the drain pipe 4 via the water supply pump 5, as shown in Fig. 6 for example. Thereafter, the methane fermentation system 100 sends the first fermentation raw material Aa drained into the drain pipe 4 to a second sprinkler pipe 62 installed above the fermentation chamber 1, as shown in Fig. 7 for example. Here, the first fermentation raw material A sent to the second sprinkler pipe 62 is referred to as the first fermentation raw material Ab.

Next, as shown in FIG. 7, the methane fermentation system 100 sprays water from above the fermentation chamber 1 through a spray hole (not shown) drilled in the second spray pipe 62 on the first fermentation raw material Ab. Here, the first fermentation raw material A sprayed from above the fermentation chamber 1 is referred to as the first fermentation raw material Ac.

Next, as shown in FIG. 8, the methane fermentation system 100 supplies at least a portion of the first fermentation raw material Ac, which has been sprayed from above the fermentation chamber 1 via the water pump 5 and the second water spray pipe 62, to the inside of the box body 2 in which the second fermentation raw material B is previously stored. Here, the first fermentation raw material A supplied to the box body 2 is referred to as the first fermentation raw material Ad.

At this time, the second fermentation raw material B that has come into contact with the first fermentation raw material Ad undergoes methane fermentation due to the action of the methanogens. As a result, the second fermentation raw material B undergoes dry methane fermentation, and biogas and digestive liquid are produced in the box body 2. The biogas generated from the second fermentation raw material B in the box body 2 moves upward within the fermentation chamber 1 and is collected in the gas collection tank T installed above the fermentation chamber 1.

<Separation step>
8, the methane fermentation system 100 passes the first fermentation raw material Ad through a separation hole 23 pre-drilled in the bottom plate 21 of the box body 2 and drops it into the second storage section 32 below the box body 2. Here, the first fermentation raw material A passing through the separation hole 23 is referred to as the first fermentation raw material Ae, and the first fermentation raw material A passing through the separation hole 23 and dropping into the second storage section 32 is referred to as the first fermentation raw material Af.

That is, the methane fermentation method of this embodiment has a raw material supplying process in which the first fermentation raw material A contained in the second storage section 32 is supplied to the box section 2 in which the second fermentation raw material B is contained, and a separation process in which the supplied first fermentation raw material A is passed through the separation hole 23 and dropped to separate it from the second fermentation raw material B. In this case, it is possible to prevent the high moisture content second fermentation raw material B from collapsing and sticking to the inside of the fermentation chamber 1. This can improve the ease of transporting high moisture content solid biomass and the ease of cleaning the fermentation chamber 1 in the methane fermentation system 100.

The digestive liquid generated from the second fermentation raw material B that has undergone dry methane fermentation inside the box body 2 flows down through the separation hole 23 into the second storage section 32, similar to the first fermentation raw material Ae. The digestive liquid that flows down into the second storage section 32 is discharged from the second storage section 32 together with the first fermentation raw material Af or instead of the first fermentation raw material Af, and is sprayed from above the fermentation chamber 1 via the drain pipe 4, the water pump 5, and the second sprinkling pipe 62, and is supplied to the box body 2.

At this time, in the second storage section 32, the first fermentation raw material A and the digestive liquid are repeatedly flowed down from the box section 2, stirring the first fermentation raw material A, which promotes wet methane fermentation of the first fermentation raw material A and produces biogas and digestive liquid in the second storage section 32. The biogas produced from the first fermentation raw material A in the second storage section 32 moves upward in the fermentation chamber 1 and is collected in a gas collection tank T provided above the fermentation chamber 1.

The digestive liquid produced in the second storage section 32 is supplied to the box section 2 above the second storage section 32, and then flows down into the second storage section 32. In this case, there is no need to provide an agitator for stirring the fermentation raw materials, etc., to promote methane fermentation. This allows the methane fermentation system 100 to be made more compact. In addition, the digestive liquid produced in the second storage section 32 may contain more dissolved NPK components due to contact with the second fermentation raw material B contained in the box section 2 and the products of fermentation of the second fermentation raw material B. This increases the content of NPK components and allows the liquid to be used as a better bio-liquid fertilizer. This reduces the labor required for applying the liquid fertilizer, and improves the usefulness of the liquid fertilizer.

After carrying out each of the above-mentioned steps, the operation of the methane fermentation system 100 in this embodiment is completed. Note that in the methane fermentation system 100, for example, each of the above-mentioned steps may be carried out repeatedly.

(First Modification of Methane Fermentation System 100)
In the methane fermentation system 100, for example, as shown in FIG. 9, the box portion 2 may include an upper box portion 2' and a lower box portion 2'' that respectively accommodate the second fermentation raw materials B' and B''.

In addition, for the upper box portion 2' and the lower box portion 2'', the bottom plates 21', 21'', the side plates 22', 22'', and the separation holes 23', 23'' have the same shapes and functions as the bottom plate 21, the side plate 22, and the separation hole 23, respectively. In addition, the second fermentation raw materials B', B'' are fermentation raw materials similar to the second fermentation raw material B.

That is, the methane fermentation system 100 includes an upper box section 2' that separates the first fermentation raw material A contained in the second storage section 32 from the contained second fermentation raw material B' by dropping it through the upper separation hole 23' when supplied, and a lower box section 2'' that separates the first fermentation raw material A contained in the second storage section 32 from the contained second fermentation raw material B'' by dropping it through the lower separation hole 23'' when supplied. In this case, a large amount of fermentation raw material can be fermented efficiently regardless of the volume of the box section 2. This can improve the productivity of biogas in the methane fermentation system 100.

In addition, in FIG. 9, the upper box part 2' and the lower box part 2'' are illustrated as two adjacent box parts 2 stacked in the height direction Z, but this is not limited thereto. The upper box part 2' and the lower box part 2'' may be, for example, any two adjacent box parts 2 out of three or more box parts 2 stacked in the height direction Z, or any two spaced apart box parts 2. In addition, the upper box part 2' and the lower box part 2'' may be two box parts 2 that are spaced apart from each other in a plan view and have different heights, as long as the separation hole 23' of the upper box part 2' and the opening O of the lower box part 2'' are capable of supplying the first fermentation raw material A through a known resin pipe or the like.

Next, we will explain the details of this modified methane fermentation method.

<Raw material supply process>
In the raw material supply step, the methane fermentation system 100 supplies at least a part of the first fermentation raw material Ac, which is sprayed from above the fermentation chamber 1 via the water pump 5 and the second sprinkling pipe 62, to the inside of the upper box portion 2' in which the second fermentation raw material B' has been accommodated in advance, as shown in Fig. 9. Here, the first fermentation raw material A supplied to the upper box portion 2' is referred to as the first fermentation raw material Ag.

At this time, the second fermentation raw material B' that has come into contact with the first fermentation raw material Ag undergoes methane fermentation due to the action of methanogens. As a result, the second fermentation raw material B' undergoes dry methane fermentation, and biogas and digestive liquid are produced in the upper box section 2'. The biogas generated from the second fermentation raw material B' in the upper box section 2' moves upward within the fermentation chamber 1 and is collected in the gas collection tank T installed above the fermentation chamber 1.

<Separation step>
In the separation process, the methane fermentation system 100 passes, for example, the first fermentation raw material Ag through a separation hole 23' drilled in advance in the bottom plate 21' of the upper box section 2' and drops it into the lower box section 2'' below the upper box section 2'. Here, the first fermentation raw material A that passes through the separation hole 23' and drops into the lower box section 2'' is referred to as the first fermentation raw material Ah.

Then, the methane fermentation system 100 supplies at least a portion of the first fermentation raw material Ah that has fallen from the upper box section 2', for example by passing through the upper separation hole 23', to the inside of the lower box section 2'' in which the second fermentation raw material B'' is already contained. Here, the first fermentation raw material A supplied to the lower box section 2'' is referred to as the first fermentation raw material Ai.

At this time, the second fermentation raw material B" that has come into contact with the first fermentation raw material Ai undergoes methane fermentation due to the action of methanogens. As a result, the second fermentation raw material B" undergoes dry methane fermentation, and biogas and digestive liquid are produced in the lower box section 2". The biogas generated from the second fermentation raw material B" in the lower box section 2" moves upward within the fermentation chamber 1 and is collected in the gas collection tank T installed above the fermentation chamber 1.

Then, the methane fermentation system 100 passes, for example, the first fermentation raw material Ai through a separation hole 23'' pre-drilled in the bottom plate 21'' of the lower box section 2'' and drops it into the second storage section 32 below the lower box section 2''. Here, the first fermentation raw material A passing through the separation hole 23'' is referred to as the first fermentation raw material Aj, and the first fermentation raw material A passing through the separation hole 23 and dropping into the second storage section 32 is referred to as the first fermentation raw material Ak.

That is, in the methane fermentation method of this modified example, in the raw material supplying process, the first fermentation raw material A stored in the second storage section 32 is supplied to the upper box section 2' in which the second fermentation raw material B' is stored. In the separation process, the first fermentation raw material A supplied in the raw material supplying process is passed through the separation hole 23' and dropped to be separated from the second fermentation raw material B', and the first fermentation raw material A supplied to the lower box section 2'' in which the second fermentation raw material B'' is stored is passed through the separation hole 23'' and dropped to be separated from the second fermentation raw material B''. In this case, a large amount of fermentation raw material can be fermented efficiently regardless of the volume of the box section 2. This can improve the productivity of biogas in the methane fermentation system 100.

(Second modified example of methane fermentation system 100)
10 , the methane fermentation system 100 may be provided such that the accommodation section 3 (underfloor accommodation section 34) is separated from the fermentation chamber 1 and below the floor surface 12 of the fermentation chamber 1. The methane fermentation system 100 may further include, for example, a gas recovery pipe 7, a gas pump 8, and a gas blowing pipe 9.

The sprinkler pipe 6 may further include, for example, a first sprinkler pipe 61 that branches off from a base extending in the first horizontal direction X and extends in the second horizontal direction Y, and a second sprinkler pipe 62 that branches off from the first sprinkler pipe 61 and extends in the first horizontal direction X.

<Underfloor storage section 34>
The underfloor accommodation section 34 is provided, for example, below the floor surface 12 of the fermentation chamber 1. The underfloor accommodation section 34 accommodates the first fermentation raw material having a TS of less than 15%. The underfloor accommodation section 34 is connected (communicates) with the fermentation chamber 1, and the first fermentation raw material, etc. in the fermentation chamber 1 drop into the underfloor accommodation section 34.

As shown in FIG. 10, for example, the underfloor storage section 34 is provided vertically below the floor surface 12 and is connected to the fermentation chamber 1 via one or more perforations 121 drilled through a portion of the floor surface 12. That is, when cleaning the inside of the fermentation chamber 1, cleaning water falls into the underfloor storage section 34 via the perforations 121 and fills the inside of the underfloor storage section 34, so that the inside of the fermentation chamber 1 and the inside of the underfloor storage section 34 can be cleaned at the same time by simultaneously cleaning the inside of the fermentation chamber 1 and the inside of the underfloor storage section 34 and pumping the cleaning water out of the underfloor storage section 34. In this case, the time required for cleaning the methane fermentation system 100 can be shortened. This can improve the cleaning workability of the methane fermentation system 100.

The shape and dimensions of the underfloor storage section 34 can be any shape and size as long as it provides sufficient space to store the first fermentation raw material, but for example, it is a roughly rectangular parallelepiped with a width of 1 to 10 m, a height of 1 to 10 m, and a depth of 1 to 50 m.

<Gas recovery pipe 7>
One end of the gas recovery pipe 7 is disposed inside the fermentation chamber 1, and the other end is connected to a gas pump 8. The gas recovery pipe 7 recovers, for example, biogas produced by fermentation of the second fermentation raw material contained in the box portion 2 inside the fermentation chamber 1. The gas recovery pipe 7 is made of, for example, resin.

The gas recovery pipe 7 may further include a first gas recovery pipe 71 and a second gas recovery pipe 72 branching off from a base extending in the first horizontal direction X, for example.

<Gas pump 8>
One end of the gas pump 8 is connected to the gas recovery pipe 7, and the other end is connected to the gas inlet pipe 9. The gas pump 8 sends the biogas discharged from the fermentation chamber 1 to the gas recovery pipe 7 to the gas inlet pipe 9. As the gas pump 8, for example, a known gas pump is used.

<Gas injection pipe 9>
One end of the gas blowing pipe 9 is connected to the gas pump 8, and the other end is disposed inside the underfloor storage section 34. The gas blowing pipe 9 blows the biogas discharged from the fermentation chamber 1 into the first fermentation raw material stored in the underfloor storage section 34. The gas blowing pipe 9 is made of a material, for example, resin.

The gas injection pipe 9 may further include a first gas injection pipe 91 and a second gas injection pipe 92 branching off from a base extending in the first horizontal direction X, for example.

In other words, in the methane fermentation system 100, the storage section 3 (underfloor storage section 34) is supplied with gas generated by the box section 2. That is, the biogas generated by the box section 2 comes into contact with the first fermentation raw material and the product of fermentation of the first fermentation raw material stored in the storage section 3, and hydrogen sulfide and ammonia in the biogas may be eluted. In this case, there is no need to provide equipment for desulfurization and ammonia removal of the generated biogas. This allows the methane fermentation device to be made smaller. In addition, carbon dioxide in the generated biogas is also eluted in the same way, so that a biogas with a purified methane concentration and high calorific value can be generated. This allows the usefulness of the biogas to be improved, such as reducing the costs required for gas transportation and storage.

Next, the details of the methane fermentation method of this modified example will be described. Figures 11 to 14 are schematic cross-sectional views showing an example of the operation of a methane fermentation system corresponding to the cross section B-B in Figure 10.

<Advance preparations>
11, for example, the first fermentation raw material A is stored in advance in the underfloor storage section 34, and the second fermentation raw material B is stored in advance in the box body section 2. Methane-producing bacteria are already present in the first fermentation raw material A or the second fermentation raw material B. Here, the first fermentation raw material A stored in the underfloor storage section 34 is referred to as the first fermentation raw material Al.

Here, the box body 2 may be installed on the floor surface 12 via the legs 24, for example, by attaching the legs 24 to the bottom plate 21 in advance. In this case, a space is formed between the bottom plate 21 and the floor surface 12, so that the supplied first fermentation raw material A can pass through the separation hole 23 even if the box body 2 is not placed in the fermentation chamber 1 so that the separation hole 23 and the perforation 121 overlap in a plan view.

In order to create an anaerobic environment in the fermentation chamber 1 that promotes methane fermentation, the worker U places the first fermentation raw material A and the second fermentation raw material B in the fermentation chamber 1 with the opening/closing section 11 open, closes the opening/closing section 11 to seal the fermentation chamber 1, and degass (deoxygenate) the fermentation chamber 1 as necessary.

<Raw material supply process>
In the raw material supply step, the methane fermentation system 100 drains the first fermentation raw material A by flowing it from the underfloor storage section 34 to the drain pipe 4 via the water supply pump 5, as shown in Fig. 12. Thereafter, the methane fermentation system 100, for example, sends the first fermentation raw material Am drained into the drain pipe 4 to a second sprinkler pipe 62 installed above the fermentation chamber 1. Here, the first fermentation raw material A sent to the second sprinkler pipe 62 is referred to as the first fermentation raw material An.

Next, the methane fermentation system 100 sprays water, for example, on the first fermentation raw material An from above in the fermentation chamber 1 through a spray hole (not shown) drilled in the second spray pipe 62. Here, the first fermentation raw material A sprayed from above in the fermentation chamber 1 is referred to as the first fermentation raw material Ao.

Next, as shown in FIG. 13, the methane fermentation system 100 supplies at least a portion of the first fermentation raw material Ao, which has been sprayed from above the fermentation chamber 1 via the water pump 5 and the second water spray pipe 62, to the inside of the box body 2 in which the second fermentation raw material B is previously stored. Here, the first fermentation raw material A supplied to the box body 2 is referred to as the first fermentation raw material Ap.

At this time, the second fermentation raw material B that has come into contact with the first fermentation raw material Ap undergoes methane fermentation due to the action of the methanogens. As a result, the second fermentation raw material B undergoes dry methane fermentation, and biogas Ga (G) and digestive liquid are produced in the box body 2. The biogas Ga generated from the second fermentation raw material B in the box body 2 moves upward in the fermentation chamber 1 and is collected in the gas recovery pipe 7 installed above the fermentation chamber 1. Here, the biogas G collected in the gas recovery pipe 7 is referred to as biogas Gb.

Then, the gas pump 8 blows the biogas Gb recovered in the gas recovery pipe 7 into the first fermentation raw material Al stored in the underfloor storage section 34 via the gas blowing pipe 9. Here, the biogas G sent to the underfloor storage section 34 is referred to as biogas Gc, and the biogas G blown into the first fermentation raw material Al in the underfloor storage section 34 is referred to as biogas Gd. After some components of the biogas Gd come into contact with the first fermentation raw material Al and are dissolved, the biogas Gd passes through the perforations 121 and flows into the fermentation chamber 1, and is then recovered in the gas recovery pipe 7 together with the biogas Ga or instead of the biogas Ga.

<Separation step>
14, the methane fermentation system 100 passes the first fermentation raw material Ap through a separation hole 23 pre-drilled in the bottom plate 21 of the box body 2 and drops it into the underfloor storage section 34 below the box body 2. Here, the first fermentation raw material A passing through the separation hole 23 is referred to as the first fermentation raw material Aq, the first fermentation raw material A passing through the separation hole 23 and flowing on the floor surface 12 is referred to as the first fermentation raw material Ar, and the first fermentation raw material A passing through the perforation 121 from the floor surface 12 and dropping into the underfloor storage section 34 is referred to as the first fermentation raw material As.

The digestive liquid generated from the second fermentation raw material B that has undergone dry methane fermentation inside the box body 2 flows over the floor surface 12 through the separation hole 23, similar to the first fermentation raw material Aq, and passes through the perforations 121 to flow down into the underfloor storage section 34. The digestive liquid that has flowed down into the underfloor storage section 34 is discharged from the underfloor storage section 34 together with the first fermentation raw material As or instead of the first fermentation raw material As, and is sprayed from above the fermentation chamber 1 via the drain pipe 4, the water pump 5, and the second sprinkling pipe 62, and is supplied to the box body 2.

At this time, in the underfloor storage section 34, the first fermentation raw material A and the digestive liquid are repeatedly flowed down from the box section 2, stirring the first fermentation raw material A, which promotes wet methane fermentation of the first fermentation raw material A and produces biogas and digestive liquid in the underfloor storage section 34. The biogas generated from the first fermentation raw material A in the underfloor storage section 34 moves upward in the fermentation chamber 1 and is collected in the gas collection pipe 7 provided above the fermentation chamber 1.

The digestive fluid generated in the underfloor storage section 34 is supplied to the box section 2 above the underfloor storage section 34, and then flows down into the underfloor storage section 34. In this case, there is no need to provide an agitator for stirring the fermentation raw materials, etc., to promote methane fermentation. This allows the methane fermentation system 100 to be made more compact. In addition, the digestive fluid generated in the underfloor storage section 34 may contain more dissolved NPK components due to contact with the second fermentation raw material B stored in the box section 2 and the products of fermentation of the second fermentation raw material B. This increases the content of NPK components and allows the liquid to be used as a better bio-liquid fertilizer. This reduces the labor required for liquid fertilizer application, and improves the usefulness of the liquid fertilizer.

According to this embodiment, the methane fermentation system 100 is provided with a box section 2 that separates the first fermentation raw material 7 from the second fermentation raw material 8 by dropping it through a separation hole 23 when the first fermentation raw material 7 stored in the storage section 3 provided below the floor surface 12 of the fermentation chamber 1 is supplied. This makes it possible to prevent the second fermentation raw material 8, which has a high moisture content, from collapsing and sticking to the inside of the fermentation chamber 1. This makes it possible to improve the ease of transporting high moisture solid biomass and the ease of cleaning the fermentation chamber 1 in the methane fermentation system 100.

In addition, according to this embodiment, the upper box section 2' separates the first fermentation raw material 7 contained in the storage section 3 from the contained second fermentation raw material 8' by dropping it through the upper separation hole 23' when supplied, and the lower box section 2'' separates the first fermentation raw material 7 contained in the storage section 3 from the contained second fermentation raw material 8'' by dropping it through the lower separation hole 23'' when supplied. Therefore, a large amount of fermentation raw material can be fermented efficiently regardless of the volume of the box section 2. This improves the productivity of biogas in the methane fermentation system 100.

According to this embodiment, the storage section 3 is supplied with the biogas G produced by the box section 2. That is, the biogas G produced by the box section 2 comes into contact with the first fermentation raw material A and the product of fermentation of the first fermentation raw material A contained in the storage section 3, and hydrogen sulfide and ammonia in the biogas G may be dissolved. For this reason, it is not necessary to provide equipment for desulfurization and ammonia removal of the generated biogas G. This allows the methane fermentation device to be made smaller. In addition, carbon dioxide in the generated biogas G is also dissolved in the same manner, so that biogas G with a purified methane concentration and high calorific value can be produced. This reduces the costs required for gas transportation, storage, etc., and improves the usefulness of the biogas G.

According to this embodiment, the methane fermentation method includes a raw material supplying process in which the first fermentation raw material 7 stored in the storage section 3 provided below the floor surface 12 of the fermentation chamber 1 is supplied to the box section 2 in which the second fermentation raw material 8 is stored, and a separation process in which the supplied first fermentation raw material 7 is separated from the second fermentation raw material 8 by dropping it through the separation hole 23. This makes it possible to prevent the high moisture content second fermentation raw material 8 from collapsing and sticking to the inside of the fermentation chamber. This makes it possible to improve the ease of transporting high moisture content solid biomass and the ease of cleaning the fermentation chamber 1 in the methane fermentation system 100.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

100 Methane fermentation system 1 Fermentation chamber 11 Opening/closing section 12 Floor surface 121 Perforation 13 Wall surface 14 Ceiling 2 Box section 2' Upper box section 2'' Lower box section 21, 21', 21'' Bottom plate 22, 22', 22'' Side plate 23, 23', 23'' Separation hole 24 Leg section 3 Storage section 31, 32, 33 Storage section 34 Underfloor storage section 4 Drain pipe 5 Water pump 6 Sprinkler pipe 61, 62, 63, 64, 65 Sprinkler pipe 7, 71, 72 Gas recovery pipe 8 Gas pump 9, 91, 92 Gas blowing pipe A, Aa to As First fermentation raw material B, B', B'' Second fermentation raw material G, Ga to Gd Biogas T Gas collection tank O Opening U Operator

Claims (4)

The fermentation room and
A storage section that is provided below the floor surface of the fermentation chamber and stores a first fermentation raw material having a TS (solid concentration) of less than 15%;
A box portion installed in the fermentation chamber and accommodating a second fermentation raw material having a TS of 15% or more;
Equipped with
The methane fermentation system is characterized in that, when the first fermentation raw material contained in the storage section is supplied and comes into contact with the second fermentation raw material, the box section separates at least a portion of the first fermentation raw material from the second fermentation raw material by dropping it through a separation hole formed in a bottom plate. The case includes an upper case and a lower case, each of which accommodates the second fermentation raw material;
When the first fermentation raw material contained in the storage section is supplied and comes into contact with the second fermentation raw material, the upper case portion separates at least a portion of the first fermentation raw material from the second fermentation raw material by dropping the first fermentation raw material through an upper separation hole formed in a bottom plate of the upper case portion,
The methane fermentation system of claim 1, characterized in that when the first fermentation raw material dropped from the upper box section is supplied and comes into contact with the second fermentation raw material, the lower box section separates at least a portion of the first fermentation raw material from the second fermentation raw material by dropping it through a lower separation hole drilled in a bottom plate of the lower box section. The housing portion is supplied with the first fermentation raw material to generate biogas,
The methane fermentation system according to claim 1 or 2, wherein the storage section is supplied with the biogas produced by the box section. A raw material supplying step of supplying the first fermentation raw material accommodated in an accommodation section that is provided below the floor surface of the fermentation chamber and accommodates a first fermentation raw material having a TS of less than 15% to a box section that is provided in the fermentation chamber and accommodates a second fermentation raw material having a TS of 15% or more;
A separation process in which at least a portion of the first fermentation raw material that has been supplied to the box section by the raw material supply process and contacted with the second fermentation raw material is dropped through a separation hole formed in a bottom plate of the box section to separate it from the second fermentation raw material;
The methane fermentation method according to claim 1,

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