JP2009066559A - Biogas system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biogas system in which an ammonia component in a digested liquid is oxidized at a low cost without using a catalyst. <P>SOLUTION: The biogas system is provided with: a methane fermentation tank 1 for methane-fermenting biomass at ≥50°C; an ammonia diffusion column 4 into which the digested liquid discharged from the methane fermentation tank 1 is introduced and from which ammonia contained in the digested liquid is diffused; and an ammonia treatment apparatus 5 for oxidizing the ammonia, which is diffused from the ammonia diffusion column 4, by using a combustion improver. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a biogas system, and more particularly to a biogas system that effectively treats ammonia in digestive juice by oxidizing the digestive juice discharged from a methane fermentation tank and then oxidizing it.

  Biogas obtained by methane fermentation of organic waste such as biomass is used for power generation and boilers using combustion heat, and is attracting attention as a recycled bioenergy resource.

  Since biomass contains proteins and the like, a large amount of ammonia is generated as they are decomposed. Therefore, a large amount of ammonia is contained in the digestive juice generated along with methane fermentation, and when these digestive fluids are reduced to farmland, the amount of nitrogen is excessive. In the case of plants, if there is too much nitrogen, the crops will become weak, and there will be a problem that illnesses and chiefs will frequently occur. This mechanism is that nitrogen is absorbed, turns into amino acids, and a lot of protein is produced, which is preferred by fungi and insects (harm), so it is easy to attach, and the carbohydrates ingested by the plant are used for reaction with ammonia. It is estimated that the cell walls (mainly polysaccharides such as cellulose) become thin and weak against external stimuli. Also, when released into the ocean or river, it causes eutrophication problems.

  For this reason, some process for removing ammonia in the digestive juice is required. Conventionally, a biological nitrification denitrification method is generally known as a method for removing ammonia in digestive juice. This method is an excellent method for decomposing organic substances and removing nitrogen components as nitrogen gas. However, since organic matter is a necessary nutrient source in the methane fermenter, it is a component that is desired to be reused.

  On the other hand, membrane treatment using an electrodialysis membrane (Patent Document 1), ammonia stripping (Patent Document 2), and the like are known as methods for selectively removing only ammonia in the digestive fluid.

Ammonia usually undergoes catalytic oxidation at 150 ° C. or higher under a catalyst and decomposes at about 600 ° C. in the gas phase. Therefore, the catalytic oxidation method is easy to operate in terms of process. Patent Document 3 discloses a method for selectively and efficiently decomposing nitrogen and water at a relatively low temperature using an ammonia decomposition catalyst. Patent Document 4 discloses an ammonia decomposition tank, which is an ammonia desorption tank. A method of heating the supplied ammonia gas, converting it to nitrogen oxide with a catalyst at 300 to 450 ° C. as a first step, and reducing it to nitrogen gas with a titanium-based catalyst at 600 to 700 ° C. as a second step and releasing it to the atmosphere Is disclosed.
JP 2007-44579 A JP 2003-088833 A JP 2001-9281 A JP 2004-160406 A

  However, in the ammonia decomposition method using a catalyst as in Patent Documents 3 and 4, although decomposition is excellent, there is a problem of high cost.

  Then, this invention makes it a subject to provide the biogas system which can oxidize the ammonia component in digestive liquid without a catalyst, and can process it at low cost.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

(Claim 1)
A methane fermentation tank for methane fermentation of biomass at a temperature of 50 ° C. or more, an ammonia diffusion tower for releasing ammonia contained by introducing a digested liquid discharged from the methane fermentation tank, and ammonia released from the ammonia diffusion tower A biogas system comprising: an ammonia treatment device that oxidizes the gas using an auxiliary combustor.

(Claim 2)
The biogas system according to claim 1, wherein the auxiliary combustor is biogas.

(Claim 3)
The biogas system according to claim 1 or 2, wherein the temperature in the methane fermentation tank is 60 ° C or higher.

(Claim 4)
The biogas system according to claim 1, 2 or 3, wherein the product of the ammonia treatment apparatus is nitrogen gas.

(Claim 5)
An ammonia treatment apparatus includes an apparatus main body, a filler filled in the apparatus main body, an ammonia supply pipe for supplying ammonia gas from the lower part of the apparatus main body, an auxiliary combustion material supply pipe for supplying an auxiliary combustion material, and an auxiliary combustion material. An ignition device that burns,
5. The biogas system according to claim 1, wherein ammonia gas is oxidized at a temperature of 150 ° C. or higher and 800 ° C. or lower in the apparatus main body.

(Claim 6)
The biogas system according to claim 5, wherein the filling material filled in the apparatus main body is configured in two stages.

(Claim 7)
The biogas system according to claim 5 or 6, wherein the filler filled in the apparatus main body is at least one selected from a metal wire mesh, a granular material, and a magnetic granular material. An ammonia treatment apparatus includes an apparatus main body, a filler filled in the apparatus main body, an ammonia supply pipe for supplying ammonia gas from the lower part of the apparatus main body, an auxiliary combustion material supply pipe for supplying an auxiliary combustion material, and an auxiliary combustion material. An ignition device that burns,

(Claim 8)
The biodeposition according to any one of claims 1 to 7, further comprising a decarboxylation tank that decarboxylates the digested liquid discharged from the methane fermentation tank between the methane fermentation tank and the ammonia diffusion tower. Gas system.

  ADVANTAGE OF THE INVENTION According to this invention, the biogas system which can oxidize the ammonia component in digestive liquid without a catalyst, and can process it at low cost can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a flowchart showing an example of the biogas system of the present invention. In FIG. 1, reference numeral 1 denotes a methane fermenter that performs methane fermentation of biomass at a temperature of 50 ° C. or higher.

  Biomass that is fermented with methane (organic waste) includes, for example, livestock waste (eg, livestock manure such as cattle, pigs, sheep, goats, and chickens), green farm waste, food waste, agricultural and fishery industry waste, food processing Examples thereof include waste materials and wastewater treatment sludge (for example, sewage treatment sludge and human waste treatment sludge).

  The methane fermentation of the present invention is a wet treatment, and specifically, the treatment is performed under a condition where the solid content concentration in the methane fermentation tank 1 is preferably 20% or less, more preferably 15% or less.

  The inside of the methane fermentation tank 1 is preferably fermented in a high temperature environment of 55 ° C. or more and 85 ° C. or less, more preferably 60 ° C. or more and 80 ° C. or less, and further preferably 65 ° C. or more and 80 ° C. or less. When the inside of the fermenter 1 is heated as described above, it can be expected that chemical hydrolysis is likely to occur in addition to microbiological degradation by the thermophilic methane fermentation sludge.

  The methanogen in the methane fermenter 1 coexists with various organisms and receives a substrate for the growth of the methanogen from other organisms. Biomass contains protein, starch, fat, fiber (cellulose), etc., but these substrates are reduced in molecular weight by hydrolyzing bacteria, acid-fermenting bacteria, etc., and become substrates of methanogenic bacteria, causing methane fermentation reaction .

  The means for heating the inside of the methane fermenter 1 is not particularly limited, but electricity, hot water, steam and the like obtained by the combustion energy of the purified biogas can be used. It is also preferable that the biomass is heated in the process of introducing it into the methane fermentation tank 1. In the illustrated example, preheating is performed by the heat exchanger 2.

The digested liquid discharged | emitted from the methane fermenter 1 is the range of pH 7-9, and contains a nitrogen component and a carbon dioxide gas. The total nitrogen concentration is, for example, 1500-15000 mg / L, the ammoniacal nitrogen concentration is in the range of 1000-10000 mg / L, and NO ₃ -N is in the range of 0.5-100 mg / L, and NO ₂ -N Is in the range of 2 to 5 mg / L (analysis method: Kjeldahl method, ion gas chromatograph method). Further, the carbon dioxide gas concentration is generally in the range of 5 to 10 L / L-digested liquid as total carbonic acid (analysis method: volumetric method by acid emission).

The digested liquid is sent to the decarboxylation tank 3 through the pipe 10 and decarboxylated. The decarboxylation tank 3 only needs to provide a place where the digested liquid comes into contact with air, and if there is such an environment, it is dissipated until it is at least equilibrated with carbon dioxide (CO ₂ ) concentration in the air. The pH of digestive juice gradually increases due to the release of carbon dioxide. The pH of the digestive juice after carbon dioxide gas emission rises by about 1. In order to promote the separation of carbon dioxide gas in the decarbonation treatment tank 3, the tank may be formed in a tower shape and a filler is provided inside, and the digestive juice may be sprinkled from above the filler. In this case, since carbon dioxide has a molecular weight greater than that of air, carbon dioxide cannot be naturally diffused from above the decarbonation tank 3, so that air is sent from the suction means (not shown) or below the decarbonation tank 3 to be diffused upward. It can also be.

  Next, the decarboxylated digested liquid is sent to the ammonia diffusion tower 4 where the contained ammonia is diffused. The ammonia stripping tower 4 can use an ammonia stripping device. The ammonia stripping apparatus adopts a tower system, and can introduce and release air from below, sprinkle the digested liquid from the top and counter-flow the ammonia to separate and release it. Further, a packing material may be provided inside the tower to increase the gas-liquid contact efficiency. Furthermore, if the alkali is mixed with the digested liquid, the efficiency of ammonia gas emission is further increased. According to the experiments by the present inventor, it has been found that the ammonia stripping device is superior in ammonia separation efficiency to the selective separation of ammonia by an electrodialysis membrane.

  The digested liquid from which ammonia has been separated warms the biomass in the heat exchanger 2. For example, if the fermentation temperature in the methane fermenter 1 is 55 ° C. or more and 85 ° C. or less, the temperature of the digested liquid after ammonia stripping is 45 ° C. or more and 75 ° C. or less when the outside air is used as it is, and there is sufficient residual heat. Therefore, it can be used for heating biomass. Accordingly, the cost performance in the biogas system is excellent.

  The released ammonia gas is sent to the ammonia treatment device 5 and is oxidized using a combustion aid. Since ammonia stripping is performed in the ammonia diffusion tower 4 by introducing air, the ammonia gas introduced into the ammonia treatment apparatus 5 contains about 1 to 10% by weight of air.

  On the other hand, the biogas generated from the methane fermentation tank 1 is sent to the biological desulfurization tank 6 where the hydrogen sulfide is oxidized by sulfur-oxidizing bacteria to obtain a purified biogas. The washing water (circulated water) used in the biological desulfurization tank 6 may be external water, but a part or all of the digested liquid generated from the methane fermentation tank 1 can be used.

  Next, as shown in FIG. 2, the ammonia treatment apparatus 5 includes an apparatus main body 500, a filler 501 filled in the apparatus main body 500, and an ammonia supply pipe 502 for supplying ammonia gas from the lower portion of the apparatus main body 500. And an auxiliary combustion material supply pipe 503 for supplying the auxiliary combustion material, and an ignition device (not shown) for burning the auxiliary combustion material.

  The apparatus main body 500 is preferably configured in a tower shape, and in the illustrated example, two-stage fillers 501A and 501B are arranged. As the filler, only a metal wire mesh may be used, and a punching metal may be used. Further, a Raschig ring or the like may be placed on a metal wire mesh or punching metal. As the metal wire mesh or punching metal, stainless steel wire mesh or punching metal is preferable.

  As the auxiliary combustor, it is preferable to use biogas, particularly purified biogas, especially purified methane gas, in order to improve the energy efficiency (cost performance) of the biogas system of the present invention.

  When oxidizing ammonia gas in the apparatus main body 500, it is preferable to perform non-catalytic oxidation at a temperature of 150 ° C. or higher and 800 ° C. or lower.

  When the temperature is lower than 150 ° C., the oxidation reaction of ammonia does not occur sufficiently. When the temperature exceeds 800 ° C., the amount of NOx produced increases remarkably. The most preferred temperature range is 200-350 ° C.

Combusting the auxiliary combustion material in the apparatus body 500, setting the combustion temperature in the above range,
4NH ₃ + 3O ₂ = 2N ₂ + 6H ₂ O
By this reaction, nitrogen gas (N ₂ ) is obtained. In this reaction, the production of NOx has not been confirmed experimentally.

In this reaction, temperature management is important. In the example of FIG. 2, a temperature sensor 504 is provided at the site of the first stage filler 501A, and a temperature sensor 505 is provided at the site of the second stage filler 501B, and control is performed from each sensor. Temperature data is sent to the units 506 and 507, and according to the measured temperature, the control valve 509 provided in the auxiliary combustion material supply pipe 503 and the control valve 511 provided in the pipe 510 for introducing diffused CO ₂ or air are used. Controls opening and closing. In this control, for example, the control valve 509 and the control valve 511 are set to open and close by proportional control based on the detected temperature.

  The example in FIG. 2 is an example in which the filler has two stages, but may have one stage as shown in FIG. In the example of FIG. 3, the temperature sensor includes a temperature sensor 512 that measures the temperature in the upper part of the tower and a temperature sensor 513 that measures the temperature in the lower part. Each temperature sensor is connected to temperature data transmission / reception units 514 and 515. The temperature data transmission / reception units 514 and 515 are connected to the control unit 516, and adjust the opening / closing of the control valve 517 that adjusts the supply amount of biogas from the upper and lower temperature data.

  Hereinafter, the effects of the present invention will be illustrated by examples.

Example 1
Using the ammonia treatment apparatus shown in FIG. 3, the ammonia gas released from the digested liquid was oxidized. Stainless steel wire mesh was used as the filler. Biogas was used as a support material.

  When ammonia gas was supplied and oxidation treatment was performed so that the average temperature of the upper and lower parts was 250 ° C., 90% of the ammonia component could be removed.

Further, when the exhaust gas was analyzed (NOx: detector tube, N ₂ O: gas chromatograph having an electron capture detector), NOx and N ₂ O were not detected, and nitrogen gas could be almost completely obtained.

Flow chart showing an example of the biogas system of the present invention Diagram showing an example of an ammonia treatment device The figure which shows another example of an ammonia processing apparatus

Explanation of symbols

1: Methane fermenter 2: Heat exchanger 3: Decarbonation treatment 4: Ammonia stripping tower 5: Ammonia treatment device 500: Main body of the device 501: Filler 502: Ammonia supply pipe 503: Auxiliary material supply pipe 504, 505: Temperature Sensors 506, 507: Control unit 509: Control valve 510: Piping 511: Control valve 512, 513: Temperature sensor 514, 515: Temperature data transmission / reception unit 516: Control unit 517: Control valve 6: Biological desulfurization tank

Claims (8)

  A methane fermentation tank for methane fermentation of biomass at a temperature of 50 ° C. or more, an ammonia diffusion tower for releasing the ammonia contained by introducing the digested liquid discharged from the methane fermentation tank, and ammonia released from the ammonia diffusion tower A biogas system comprising: an ammonia treatment device that oxidizes the gas using an auxiliary combustor.   The biogas system according to claim 1, wherein the auxiliary combustor is biogas.   The biogas system according to claim 1 or 2, wherein the temperature in the methane fermentation tank is 60 ° C or higher.   The biogas system according to claim 1, 2 or 3, wherein the product of the ammonia treatment apparatus is nitrogen gas. An ammonia treatment apparatus includes an apparatus main body, a filler filled in the apparatus main body, an ammonia supply pipe for supplying ammonia gas from the lower part of the apparatus main body, an auxiliary combustion material supply pipe for supplying an auxiliary combustion material, and an auxiliary combustion material. An ignition device that burns,
5. The biogas system according to claim 1, wherein ammonia gas is oxidized at a temperature of 150 ° C. or higher and 800 ° C. or lower in the apparatus main body.   The biogas system according to claim 5, wherein the filling material filled in the apparatus main body is configured in two stages.   The biogas system according to claim 5 or 6, wherein the filling material filled in the apparatus main body is at least one selected from a metal wire mesh, a granular material, and a magnetic granular material.   The biodeposition according to any one of claims 1 to 7, further comprising a decarboxylation tank that decarboxylates the digested liquid discharged from the methane fermentation tank between the methane fermentation tank and the ammonia diffusion tower. Gas system.

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