Treatment method and treatment unit for foam generated in methane fermentation

Abstract

To provide a method for treating sponge-like foam (scum) formed on a liquid surface when methane gas is generated from an organic fermentation liquid.SOLUTION: A treatment method for foam can: rotate, in a horizontal plane, a foam breaking agitation blade 5 arranged facing a liquid surface 11 of an organic fermentation liquid 3; tear and divide large sponge-like foam (scum) into small lumps by rotation of respective blades of the foam breaking agitation blade 5; and discharge lumps of the divided foam from a discharge port.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and treatment device for treating foam generated during methane fermentation of organic waste such as livestock manure and food waste, which is constructed with a small-scale structure, and to a methane fermentation method and device equipped with said treatment device. [Background technology]

[0002] Organic waste such as food waste, livestock waste, food processing residues, and sludge can be fermented to produce methane, which is an environmentally friendly renewable energy source that can replace fossil fuels. Methane gas is produced during the fermentation of organic matter and is a colorless, odorless, flammable gas. There has been growing interest in using methane fermentation technology to treat the large amounts of waste that are produced. Methane fermentation technology uses almost no fossil fuels and utilizes carbon-neutral organic waste as an energy source, making it a system that contributes to reducing greenhouse gas emissions from the perspective of preventing global warming.

[0003] There are various known devices that ferment organic waste such as food waste, livestock waste, and food processing residues into methane. However, conventional methane fermentation devices are large in scale, and when methane is fermented, scum (sponge-like foam) is generated on the upper part of the liquid surface in the fermentation tank, and this foam is a major obstacle when recovering methane gas. For this reason, devices for removing this foam are also known.

[0004] The "methane fermentation treatment method and treatment device" of Patent No. 6184041 has a waste input tank for inputting waste, a fermentation tank which generates methane gas, a generator which runs on the methane gas, and a heater which circulates hot water heated using waste heat generated when the generator is operating and heats the organic waste liquid flowing through the circulation path to a predetermined temperature. The circulation path has an outlet at the bottom of the fermentation tank and has an inlet above the liquid level of the organic waste liquid in the fermentation tank. Therefore, the organic waste liquid flowing down from the inlet falls onto the foam, causing the sponge-like foam to disappear.

[0005] The "foaming drain device and methane fermentation tank" disclosed in JP 2022-109016 A has a simple structure and can prevent bubbles from getting into biogas recovery pipes, etc., even when there is intense foaming. The foaming drain device includes a foaming drain pipe having an inlet that is located at a position higher than the liquid level in the methane fermentation tank and communicates with the interior of the methane fermentation tank, and a gas seal device (liquid seal tank) that is provided on the outlet side of the foaming drain pipe and prevents gas from leaking from the outlet of the foaming drain pipe.

[0006] The "methane fermentation treatment device" disclosed in JP 2015-51390 A is a methane fermentation treatment device capable of sufficiently stirring highly viscous, high-concentration sludge. That is, the methane fermentation treatment apparatus comprises a digestion tank for storing sludge, a digestion gas transfer mechanism for collecting digestion gas generated from the sludge in the digestion tank and returning the collected digestion gas to the digestion tank, a gas dispersion device connected to the digestion gas transfer mechanism for dispersing the digestion gas in the digestion tank as gas bubbles, and an agitator blade located above the gas dispersion device for agitating the sludge containing the digestion gas bubbles, and the gas dispersion device is located at the bottom of the digestion tank.

[0007] The "method and apparatus for concentrating methane gas" disclosed in JP 2008-255209 A can effectively increase the concentration of methane gas in biogas, which is composed mainly of methane gas and carbon dioxide, without requiring any large-scale equipment. Therefore, when concentrating methane gas from biogas generated by anaerobic fermentation of organic waste and composed mainly of methane and carbon dioxide, the biogas is turned into bubbles and passed through a liquid, mainly carbon dioxide in the biogas is dissolved in the liquid, and the biogas containing the methane gas that passed through the liquid without being dissolved is recovered.The concentrating device is equipped with a fine bubble generating device that turns the biogas into fine bubbles and diffuses them, a liquid tank (storage tank) that stores a liquid that diffuses the fine bubbles, and recovery means that recovers methane gas from the biogas that has passed through the liquid.

[0008] [Patent Document 1] "Methane fermentation processing method and processing device" related to Patent No. 6184041 [Patent Document 2] "Foaming drain device and methane fermentation tank" according to JP 2022-109016 A [Patent Document 3] "Methane fermentation treatment device" according to JP 2015-51390 A [Patent Document 4] "Method and apparatus for concentrating methane gas" in JP 2008-255209 A DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0009] Thus, various methane fermentation treatment devices are known that have a function for treating bubbles that are generated when methane gas is produced from organic waste. The problem that the present invention aims to solve is to provide a foam treatment device that functions to efficiently treat sponge-like foam and efficiently recover methane gas from organic waste, which is different from conventional foam treatment methods, and a methane fermentation treatment device equipped with said foam treatment device. [Means for solving the problem]

[0010] The methane fermentation treatment device according to the present invention has a methane fermentation tank in which an organic fermentation liquid is stored and which ferments methane, and the methane fermentation tank is equipped with a circulation means for circulating the stored organic fermentation liquid. Although the specific method of the circulation means is not limited, a circulation pump is provided so that the organic fermentation liquid flows out from the bottom of the methane fermentation tank and falls and flows in from above the liquid level of the stored organic fermentation liquid. The methane fermentation treatment apparatus of the present invention is also provided with a heater for heating the circulating organic fermentation liquid to a predetermined temperature.

[0011] A sponge-like layer of foam forms on the surface of the organic fermentation liquid in the methane fermentation tank. In the present invention, however, stirring blades are provided that can cut through the layer of foam that forms on the liquid surface so that the foam layer can be processed and methane gas can be efficiently recovered. A plurality of blades are attached to arms extending radially from the rotation axis so that the stirring blades rotate in a horizontal plane parallel to the liquid surface, and these blades are inclined in an oblique direction.

[0012] As the stirring blade rotates around the axis, the inclined blade cuts through the sponge-like layer of foam, and the layer of foam that has been cut into smaller pieces is discharged outside the fermentation tank. The side of the fermentation tank is equipped with a discharge port through which the foam mass that has been cut into smaller pieces is discharged. Methane gas is produced from the organic fermentation liquid, and this methane gas is recovered from the recovery port of the fermentation tank. Effect of the Invention

[0013] In the methane fermentation treatment device according to the present invention, organic waste fed into a waste feed tank is liquefied and sent to a fermentation tank, where the organic waste flows out of an outlet at the bottom of the fermentation tank, circulates through a circulation path, and falls from above the liquid level at the top of the fermentation tank. Thus, the organic waste liquid circulates between the upper and lower layers inside the fermentation tank, and is heated to an appropriate temperature by a heater provided in the middle of the circulation path, making it possible to efficiently generate methane gas from the organic waste liquid.

[0014] A sponge-like layer of foam forms on the top of the fermentation liquid, but as the stirring blade rotates facing the surface of the fermentation liquid, the layer of foam is cut by the rotating blade and separated into small foam clumps. These small foam clumps are discharged from the outlet, and the large amount of foam that is generated is removed, allowing methane gas to be efficiently recovered. In addition, malfunctions of various measuring instruments arranged in the upper space of the fermenter caused by bubbles can be prevented. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a front view showing a schematic diagram of a methane fermentation treatment apparatus according to the present invention. [Diagram 2] FIG. 1 is a plan view showing a schematic diagram of a methane fermentation treatment apparatus according to the present invention. [Diagram 3] FIG. 2 is a left side view showing a schematic diagram of a methane fermentation treatment apparatus according to the present invention. [Figure 4] FIG. 2 is a right side view showing a schematic diagram of a methane fermentation treatment apparatus according to the present invention. [Diagram 5] A specific example showing a foam-removing stirring blade attached to the upper end of a rotating shaft and a fermentation liquid stirring blade attached to the lower end. [Figure 6] Enlarged view of arrow AA in Figure 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The general process by which methane gas is produced from organic waste is as follows: (1) Raw material input The raw organic waste is fed into the crusher. (2) Adjustment tank transfer The crushed raw material (organic waste) is transported to the adjustment tank by a transfer pump. In the adjustment tank, water is added to adjust the solids concentration (the solids concentration varies depending on the raw material, but is around 15-20%). (3) Fermentation tank transfer The raw material, after adding water to adjust the solids concentration, is transferred to the fermentation tank using a transfer pump. Methane bacteria have been added to the fermentation tank beforehand, creating an anaerobic (oxygen-free) environment inside the tank. After the raw materials are transferred to the fermentation tank, they are stirred with a stirrer or the like, and in order to promote fermentation, they are heated by circulating them with a circulation pump through a heat exchanger such as a double pipe. There are no specific limitations on the temperature of the raw materials to be heated, but in high-temperature fermentation, they are heated to about 55°C. Then, fermentation begins in the fermenter, producing methane gas. The ingredients will not spoil during this process, and if they did, fermentation would no longer be possible.

[0017] The present invention is directed to the fermentation tank that constitutes the methane fermentation treatment device, and does not limit the specific structures of the input tank into which the raw organic waste is input and crushed, and the adjustment tank into which the crushed raw material (organic waste) is transferred to adjust the solid concentration. 1 to 4 show an embodiment of a fermentation tank constituting a methane fermentation treatment device according to the present invention, with FIG. 1 being a front view, FIG. 2 being a plan view, FIG. 3 being a left side view, and FIG. 4 being a right side view, respectively.

[0018] In the figure, reference numeral 1 denotes a fermentation tank, which is a rectangular parallelepiped having a large space, and an organic fermentation liquid 3 is contained in the internal space 2. A waste input tank (not shown) is installed near the fermenter 1, and organic waste such as food waste, livestock waste, food processing residues, and sludge, which are raw materials that generate methane gas, are input into the waste input tank. The mixed solid matter is then crushed into small pieces by a pump equipped with a crushing function and sent to the adjustment tank. In the adjustment tank, water is added to adjust the solid content concentration to about 15 to 20%.

[0019] The raw material, after adding water to adjust the solids concentration, is transferred to fermentation tank 1 by a transfer pump. Methane bacteria have been added to fermentation tank 1 in advance, and the inside of the fermentation tank is anaerobic (oxygen-free). The organic waste sent to the fermentation tank 1 passes through a pump equipped with a crushing function. The waste input tank is also equipped with an agitator, which mixes the various types of waste input and agitates the organic waste so that it is uniform. Water is added to the adjustment tank, and the organic waste becomes an organic fermentation liquid. The organic fermentation liquid is then pushed out by the pump and sent to the fermentation tank 1 through the transport pipe.

[0020] In the fermenter 1, the organic fermentation liquid 3 sent from the adjustment tank is heated to a predetermined temperature and stirred so that methane gas is efficiently produced by fermentation. The fermenter 1 is composed of a tank having a large internal space 2, and an organic fermentation liquid 3 is circulated within the fermenter. There are various methods for circulating the organic fermentation liquid 3 within the fermenter 1, and the present invention is not limited to a specific method. For example, an outlet is provided at the bottom of the fermenter 1, and the organic fermentation liquid 3 is sucked in by a pump equipped with a crushing function, and the organic fermentation liquid 3 flows through a circulation path and circulates, and can flow down from an inlet provided at the top of the fermenter 1. Here, the inlet is disposed above the liquid surface, so that the organic fermentation liquid 3 can flow down onto the liquid surface.

[0021] A heater is installed in a part of the circulation path, and the liquid organic fermentation liquid 3 flowing through the circulation path can be heated by this heater. As the liquid flows out from the bottom of the fermentation tank 1 and falls from above the liquid surface, the weight of the falling flow creates a vertical circulating flow within the fermentation tank. Also, by installing two paired agitators diagonally on either side of the fermentation tank, a circulating flow can be created in the horizontal plane, allowing the liquid to mix evenly.

[0022] Incidentally, the upper space 4 of the fermenter 1 is filled with methane gas generated by fermenting the organic fermentation liquid 3, and this methane gas can be introduced and stored in a container (tank) provided separately from the fermenter 1, and the methane gas can be used separately. However, the specific use is free and the present invention is not limited thereto. The power for the agitators attached to the waste input tank and fermenter 1 and for driving the pumps can be supplied from a generator driven by methane gas. In other words, the methane fermentation treatment device of the present invention can be configured to operate independently without requiring an external energy supply.

[0023] However, when methane gas is fermented, sponge-like foam (scum) is generated on the upper part of the liquid surface in the fermentation tank, and this foam is a major obstacle to the recovery of methane gas. The present invention is equipped with a foam treatment device to efficiently remove this sponge-like foam (scum) and enable efficient recovery of methane gas. Therefore, in the present invention, a foam-removing agitator blade 5 is provided which rotates in a horizontal plane facing the liquid surface 11 of the organic fermentation liquid. The foam-removing agitator blade 5 is shaped like a comb having multiple blades on an arm extending radially outward, and each blade is inclined obliquely with respect to the rotation axis.

[0024] 5 shows the foam-removing impeller 5 and the fermentation liquid agitator 6. The foam-removing impeller 5 and the fermentation liquid agitator 6 are attached to a rotating shaft 7, which is rotated by a motor 10 attached above the fermenter 1, so that the foam-removing impeller 5 and the fermentation liquid agitator 6 can rotate together with the rotating shaft 7. As shown in the figure, the foam-removing stirring blade 5 has an arm 8 extending radially outward from a rotating shaft 7, and is shaped like a comb with a plurality of blades 9, 9 . . . formed on the arm 8.

[0025] Fig. 6 is an enlarged view taken along the line AA in Fig. 5, in which the foam-removing agitator blade 5 is inclined obliquely with respect to the rotation shaft 7. When the foam-removing agitator blade 5 rotates in the direction of the arrow on a horizontal plane, it can press down on the sponge-like foam (scum) formed on the surface of the organic fermentation liquid from diagonally above and cut it up. The foam lumps that have been cut up and become smaller are discharged from a discharge port provided slightly above the liquid surface 11. In other words, the multiple blades 9, 9... extending at predetermined intervals can cut and divide the sponge-like foam (scum) that covers the entire liquid surface 11 into small lumps.

[0026] Although the inclination angle θ of each of the blades 9, 9... is not limited, as the blades 9, 9... rotate about their axes, the sponge-like foam (scum) is pressed down from diagonally above and cut up. In FIG. 5, the number of foam-removal stirring blades 5 extending outward from the rotating shaft 7 is two, but it may be three or four.

[0027] Four fermentation liquid stirring blades 6, 6... are attached to the lower end of the same rotating shaft 7, extending radially outward. The fermentation liquid stirring blades 6, 6... do not have multiple blades 9, 9... like the foam-removing stirring blade 5, but are inclined at a specified angle. The foam-removal stirring blade 5 is positioned near the liquid surface of the organic fermentation liquid 3 where sponge-like foam (scum) is formed, but its mounting height relative to the rotating shaft 7 is adjustable so that its position can be changed.

[0028] The fermentation tank 1 shown in FIG. 1 has two rotating shafts 7, 7, and the fermentation liquid stirring blades 6, 6 are attached to the lower ends of both rotating shafts 7, 7, but the foam-removing stirring blade 5 is attached to the upper part of one of the rotating shafts 7, which is the discharge outlet side from which small foam clumps are discharged. The fermentation liquid stirring blades 6, 6... serve to stir the organic fermentation liquid 3 contained in the fermenter 1, and their shape is not limited to that shown in FIG. It is also possible to circulate the organic fermentation liquid 3 by attaching stirring blades to the diagonally opposite sides of the fermentation tank 1. [Explanation of symbols]

[0029] 1 Fermentation tank 2. Interior space 3. Organic fermentation liquid 4 Upper space 5. Foam-removing stirring blade 6 Fermentation liquid stirring blade 7 Rotation Axis 8 Arm 9. Feather 10 Motor 11 Liquid level

Claims

1. A foam treatment method capable of discharging large sponge-like foam (scum) formed on the liquid surface of the organic fermentation liquid in the upper space of the fermentation tank when an organic fermentation liquid made by finely crushing organic waste is contained in the fermentation tank and methane gas is generated from the organic fermentation liquid, the foam treatment method being characterized in that a foam-removing agitator blade arranged facing the liquid surface of the organic fermentation liquid is rotated in a horizontal plane, the large sponge-like foam (scum) is cut and divided into small lumps by the rotation of each blade of the foam-removing agitator blade, and the divided foam lumps are discharged from a discharge port provided in the fermentation tank.

2. A method for treating foam as described in claim 1, wherein the blades of the foam-removing agitator are provided at predetermined intervals on an arm extending radially outward from the rotating shaft, and each blade is inclined in a direction to cut through the sponge-like foam (scum) while pressing it down from diagonally above as the foam-removing agitator rotates.

3. This foam treatment device has a fermentation tank that contains an organic fermentation liquid made by finely crushing organic waste, and is capable of discharging large sponge-like foam (scum) that forms on the surface of the organic fermentation liquid in the upper space of the fermentation tank when methane gas is generated from the organic fermentation liquid.The foam treatment device is characterized in that a foam-removing agitator blade that rotates in a horizontal plane facing the surface of the organic fermentation liquid is attached to a rotating shaft, and the foam-removing agitator blade has a plurality of blades at predetermined intervals on an arm that extends radially outward from the rotating shaft, and each blade is inclined in a direction that allows the foam-removing agitator blade to rotate so as to press down on the large sponge-like foam (scum) from diagonally above and cut it up to divide it into small chunks.

4. 4. A foam processing device according to claim 3, wherein the foam removing stirring blade attached to the rotating shaft can be moved vertically to adjust the height.

5. 5. A foam treatment device as claimed in claim 3 or claim 4, wherein a fermentation liquid stirring blade for stirring the organic fermentation liquid contained in a fermentation tank is attached to the lower end of a rotating shaft about which the foam removing stirring blade rotates in a horizontal plane.

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