JP4758932B2 - Biogas system - Google Patents

Description

  The present invention relates to a biogas system, and more particularly to a biogas system capable of increasing the calorie of biogas obtained by methane fermentation and treating or using digestive juice.

  Biogas systems that produce livestock and urine from organic waste such as urine to obtain methane gas and recover electricity and heat are attracting attention as bioenergy technologies, but are not as widespread as in the West.

  The reason for this is that there are many small-scale facilities in Japan, and when recovering power from methane gas generated by methane fermentation, the amount of power generated is at most several hundred kW, resulting in a small amount of energy and economical advantages. There are few.

  Another reason is that it is difficult to treat digestive juice after methane fermentation.

  Digested liquid after methane fermentation can be reduced to farmland as fertilizer, but conventionally, the method of performing methane fermentation temperature at 37 ° C or 55 ° C is the mainstream (Patent Document 3), and various bacteria contained in the digested liquid There was a problem with hygiene because it was not killed. In order to solve this problem, it is necessary to heat and kill germs in the digestive fluid, and energy is required for heating, which increases costs.

Furthermore, the digestive fluid of methane fermentation contains a large amount of nitrogen components. If it is directly returned to farmland as fertilizer, it may cause groundwater contamination or health damage to livestock due to excessive nitrogen in the grass. Or need to add additives.
No. 2006-224090 (Methane fermentation temperature 55 ° C.) 2004-358400 gazette (methane fermentation temperature 50-60 ° C.) Hei 11-290828 Publication (Methane fermentation temperature 37 ° C, 55 ° C)

  The present inventors consider that it is indispensable to increase the amount of energy obtained from biogas and to construct a system that can treat or use digestive juice at a low cost for the spread of methane fermentation. As a result, the present invention was reached.

  Accordingly, an object of the present invention is to provide a biogas system capable of increasing the calorie of biogas obtained by methane fermentation and treating or using digestive juice.

  The other subject of this invention becomes clear by the following description.

  The above problems are solved by the following inventions.

(Claim 1)
Methane fermentation means for introducing methane into a methane fermentation tank and performing methane fermentation at a high temperature of 60 ° C. or higher and under a pressure of 0.2 to 5 MPa by natural fermentation pressure generated by fermentation;
Carbon dioxide removal means for removing the carbon dioxide by depressurizing the digested liquid extracted from the methane fermentation tank;
A biogas system comprising ammonia stripping means for introducing the digested liquid from which carbon dioxide has been removed by the carbon dioxide removing means into an ammonia stripping apparatus to dissipate ammonia.

(Claim 2)
The biogas system according to claim 1, wherein the biomass to be administered into the methane fermenter is placed in an environment of 60 ° C to 70 ° C for 1 hour or longer, or in an environment exceeding 70 ° C for 10 minutes or longer. .

(Claim 3)
The biogas system according to claim 2, wherein the environment of 60 ° C to 70 ° C or the environment exceeding 70 ° C is formed in a methane fermentation tank.

(Claim 4)
The biogas system according to claim 2, wherein the environment of 60 ° C. to 70 ° C. or the environment exceeding 70 ° C. is formed before biomass is introduced into the methane fermentation tank.

(Claim 5)
The biogas system according to any one of claims 1 to 4, further comprising ammonia recovery means for recovering the ammonia stripped by the ammonia stripping means.

(Claim 6)
6. The biogas system according to claim 5, further comprising a processing unit that introduces ammonia recovered by the ammonia recovery unit to perform nitritation and denitrification.

(Claim 7)
The biogas according to claim 6, wherein the treatment means for performing nitritation and denitrification introduces ammonia recovered by the ammonia recovery means and co-denitrifies by reaction of nitrous acid and ammonia. system.

(Claim 8)
The biogas system according to claim 7, further comprising an input unit that administers the ammonia recovered by the ammonia recovery unit into a plant cultivation facility that is blocked from outside air.

(Claim 9)
The carbon dioxide removed and diffused by the carbon dioxide removing means is collected, and the collected carbon dioxide is fed into a plant cultivation facility that is shielded from the outside air. The biogas system according to crab.

  ADVANTAGE OF THE INVENTION According to this invention, the biogas system which can make the biogas obtained by methane fermentation high calorie, and can also process or utilize a digestive liquid can be provided.

  Embodiments of the present invention will be described below.

  Examples of biomass (organic waste) to be introduced into the methane fermentation system of the present invention include livestock waste (eg, livestock manure such as cattle, sheep, goats and chickens) and green agricultural waste (eg, garbage, agriculture and fisheries industry waste). Wastewater treatment sludge (such as sewage treatment sludge and human waste treatment sludge), etc., and co-fermentation using two or more types of these biomass as a raw material for methane fermentation You can also.

  FIG. 1 is a flow diagram illustrating a preferred embodiment for implementing the biogas system of the present invention.

  In FIG. 1, 1 is a methane fermentation means. The methane fermentation means 1 includes a screw pump 101, a heat exchanger 102, a transport pipe 103, a methane fermentation tank 104, one or more agitators 105, a digestive juice discharge pipe 106, and a biogas holder 107. Yes.

  The biomass is quantitatively conveyed to the transport pipe 103 by the screw pump 101 and sent to the methane fermentation tank 104. Further, in the process of reaching the methane fermentation tank 104, it is heated by the heat exchanger 102. In addition to the stirrer 105, the methane fermentation tank 104 is provided with a heating heater, a pressure sensor, a temperature sensor, a pressure regulating valve (for example, releasing pressure when pressurized to 5 MPa or more), and the like. It is preferable.

  In the methane fermentation tank 104, the pressure in the tank is in the range of 0.2 MPa to 5 MPa, preferably 0 by the natural fermentation pressure generated by fermentation without forced pressurization at a high temperature of 60 ° C. or higher, preferably 65 ° C. to 75 ° C. The methane fermentation is carried out by raising the pressure to 3 to 2 MPa, more preferably 0.5 to 1 MPa.

  Note that “without forcibly pressurizing” means that a technique for artificially increasing the pressure in the fermentor using a pressurizing device such as a compressor is not adopted.

  In addition, “natural fermentation pressure generated by fermentation” means that the pressure in the methane fermentation tank becomes high due to the formation of gaseous components such as methane by biological reactions such as methane fermentation in a closed fermentation tank. Means.

  In the present invention, the biomass to be administered into the methane fermentation tank 104 is placed in an environment of 60 ° C. to 70 ° C. for 1 hour or more and 1 day or less, or in an environment exceeding 70 ° C. for 10 minutes or more and 30 minutes or less. The environment of 60 ° C. to 70 ° C. or the environment of over 70 ° C. may be formed in the methane fermenter, or the environment of 60 ° C. to 70 ° C. or the environment of over 70 ° C. It may be formed before biomass is introduced into the methane fermenter.

  In order to form the environment before the biomass is introduced into the methane fermenter, the raw material biomass is heat-exchanged with the digested liquid discharged from the discharge pipe 106 in the heat exchanger 102, and the biomass is heated. . Since the digestion liquid has a high fermentation temperature of 60 ° C. or higher in the fermenter, the temperature (heat content) can be used.

  In the present invention, when the biomass to be introduced into the methane fermentation tank by heat exchange is not sufficiently heated, a heating heater including a heat exchanger (not shown) is separately provided for heating, and an environment of 60 ° C. to 70 ° C. Alternatively, an environment above 70 ° C. is formed before biomass is introduced into the methane fermenter.

  Pathogens in biomass are sterilized by being placed in a high temperature environment of 1 hour or more and 1 day or less in an environment of 60 ° C to 70 ° C, or 10 minutes or more and 30 minutes or less in an environment exceeding 70 ° C, Can solve hygiene problems. Note that there is no upper limit necessary for the effect of this temperature holding time.

  Thereby, the process of disinfecting digestive juice and inactivating seeds of weeds can be omitted.

  In normal pressure medium temperature fermentation, the methane concentration in the biogas is about 40%, and in addition, carbon dioxide and hydrogen sulfide are contained. By doing so, since carbon dioxide and hydrogen sulfide having water-soluble properties in the product gas are absorbed by the digestive fluid, the methane concentration in the biogas can be increased to 70% or more. Further, since there is almost no hydrogen sulfide in the biogas, it is not necessary to provide a desulfurization apparatus.

  It is preferable to use a spherical or lorry-type methane fermentation tank having a pressure-resistant structure for the methane fermentation tank for performing such pressurized methane fermentation.

  Methane gas obtained by methane fermentation is stored in the biogas holder 107. The obtained biogas can store a large volume of methane, for example, in a gas holder that dissolves methane in liquid butane or propane.

  2 is a carbon dioxide removing means. The carbon dioxide removing means 2 includes a deaeration device 201.

  Carbon dioxide can be recovered by providing a container or the like for recovering carbon dioxide released from the digested liquid after heat exchange.

  Since carbon dioxide is dissolved in the digested liquid in a pressurized state, 50% or more of the dissolved carbon dioxide is released simply by reducing the pressure in the deaerator 201 and returning to normal pressure.

  The deaeration device 201 may be simply a tank having a valve capable of depressurizing the digestion liquid, or a gas-liquid contact tower provided with a shelf, etc., and introducing digestion from the lower part of the gas-liquid contact tower The liquid can be sprayed from the spraying section provided in the upper part of the gas-liquid contact tower, and carbon dioxide can be further recovered, or an aeration pipe is provided in the tank for storing the digestive liquid, and external air is taken in. The carbon dioxide can be recovered by aeration.

  3 is an ammonia stripping means. The ammonia stripping means 3 includes a liquid feed pump 301 and an ammonia stripping device 302.

  A configuration example of the ammonia stripping apparatus 302 is shown in FIG.

  Reference numeral 303 denotes a circulation tank for introducing a digested liquid from which carbon dioxide has been removed. The circulation tank 303 is installed on a gantry 304, and an ammonia-dispersing tower 305 is provided above the circulation tank 303 so that it can be configured in a tower form. In order to prevent clogging of the filler 307, it is preferable to provide a screen before introducing the digested liquid into the circulation tank to remove coarse solids.

  As an example of the ammonia diffusion tower 305, a porous plate 306 is provided inside, and the porous plate 306 is filled with various fillers 307 formed of resin, metal, and ceramic. A spray nozzle 308 is provided above the filler 307 so that the digestive juice can be sprayed onto the filler 307. The spray nozzle 308 is connected to the circulation pump 310 via a pipe 309. In FIG. 2, the digestive fluid sprayed on the filler 307 is stored in the circulation tank 303 via the connection pipe 311 and is sent to the spray nozzle 308 by the circulation pump 310 to circulate. In some cases, it is discharged without going through the tank. Reference numeral 312 denotes a compressor or blower for introducing air into the ammonia diffusion tower.

  The digested liquid from which the ammonia component has been removed by the ammonia stripping apparatus is discharged as a denitrifying digested liquid.

  In FIG. 2, the water is discharged from a drain valve 313 provided in the circulation tank 303.

  Since the nitrogen component is removed from the denitrification digestion liquid, it is in a state that it can be easily treated as organic wastewater, and can be treated in an organic wastewater treatment facility. In addition, it can be easily returned to farmland as liquid fertilizer.

  Moreover, since the pathogen etc. are sterilized in the methane fermenter 104 under the high temperature conditions of 60 to 70 ° C. for 1 hour or more and 1 day or less, or 70 ° C. or more and 10 minutes or more and 30 minutes or less, sanitary fertilizer Can also be returned to farmland.

  Ammonia in the digested liquid is discharged from above the ammonia diffusion tower 305 through the discharge pipe 314 in the form of gas or mist.

  FIG. 1 shows an example of co-denitrification as an example of an ammonia treatment means after ammonia stripping.

  Co-denitrification uses an autotrophic ammonia-oxidizing bacterium that oxidizes ammonia nitrogen to nitrite nitrogen and a fiber treatment material carrying anammox bacteria that produces nitrogen by the reaction of nitrite nitrogen and ammonia. At the same time, denitrification is performed.

  The condenser 4 introduces water, and the ammonia stripping device 302 absorbs the ammonia that has become gaseous or mist into the water to form ammonia water.

  Ammonia can be recovered as ammonia water relatively easily by a packed tower or a wet wall type gas-liquid contact device.

  Ammonia water is introduced into the co-denitrification reactor 5 from the aggregator 4 to perform co-denitrification. A part of the water denitrified in the reactor 5 to remove the nitrogen content is returned to the aggregator 4 and absorbs ammonia again.

  FIG. 3 is a diagram showing an example of a co-denitrification reactor. In the figure, the co-denitrification reactor 5 includes an autotrophic ammonia-oxidizing bacterium and a microbial carrier 501 carrying anammox bacteria, and the microbial carrier 501. Are supported by support rods 502 and 503 at the top and bottom. The microbial carrier 501 may be an embodiment in which a plurality of plate-shaped ones are arranged side by side, or one formed in a cylindrical shape may be arranged in an annular shape. Moreover, although not shown, the microorganism carrier 501 may be formed in a spiral shape.

  Reference numeral 504 denotes a liquid to be processed introduction section for introducing ammonia water (hereinafter referred to as a liquid to be processed) from the aggregator 4, and reference numeral 505 denotes a processing liquid discharge section. Reference numeral 506 denotes an air introduction unit, and 507 denotes an air transfer pipe. A nitrogen gas discharge unit (not shown) is provided in the upper part of the reaction tank 5.

  Reference numeral 508 denotes a pH control unit, and 509 denotes a temperature control unit.

  In the co-denitrification reactor 5, nitrite is generated from ammoniacal nitrogen by adjusting at least one of the temperature in the co-denitrification reactor 5, the pH of the liquid to be treated, DO, and the oxidation-reduction potential (ORP). Then, reaction kinetic control is performed so that nitrogen is generated by the reaction of the generated nitrous acid and ammonia to perform co-denitrification.

  As the microorganism carrier 501, a carrier in which ammonia-oxidizing bacteria and anammox bacteria (ammonia-nitrite co-denitrifying bacteria) are supported on a nonwoven fabric (polyacrylonitrile fiber or the like) having a thickness of 5 mm or more is used.

  In this embodiment, the microbial carrier 501 in the co-denitrification reactor 5 may have a structure in which the liquid to be processed flows along the surface, or a structure in which the liquid to be processed flows in the microbial carrier 501. Alternatively, a structure in which both are combined may be used.

  Next, another example of the co-denitrification reactor employed in the present invention will be described.

  In this embodiment, a conductive microorganism-carrying electrode carrying bacteria is provided, a counter electrode using a carbon plate or the like is installed on the conductive microorganism-carrying electrode, and the ammonia-containing water is adjusted by adjusting the potential of the microbial electrode. Co-denitrification can be performed.

  FIG. 4 is a schematic cross-sectional view showing a potential control type co-denitrification reactor, and the co-denitrification reactor 5 basically includes a reaction tank 50C composed of a main body 50A and a lid 50B.

  The reaction tank 50 </ b> C includes a processing liquid introducing unit 50 for introducing a liquid containing ammonia nitrogen, a processing liquid discharging unit 51, a nitrogen gas discharging unit 52, and an air introducing unit 53.

  The reaction tank 50C is provided with a pair of electrodes including a conductive microorganism-carrying electrode 54 that performs ammonia oxidation and denitrification, and a counter electrode 55 through a diaphragm (ion exchange membrane). Reference numeral 56 denotes a lead wire.

  For example, the conductive microorganism-carrying electrode 54 is formed in a cylindrical shape by winding a conductive carbon fiber felt or cloth, for example, in a spiral shape.

  As the conductive microorganism-carrying electrode 54, for example, other than the conductive carbon fiber felt (nonwoven fabric) or cloth (cloth), it is preferably fired at 1200 ° C. or higher, more preferably 1500 ° C. or higher, and the air is cut off and fired. And various carbides, and those having sufficient conductivity are preferable. Further, a material in which the hydrogen overvoltage is improved with almost no loss of surface conductivity by surface treatment can be preferably used.

  The conductive microorganism-carrying electrode 54 carries ammonia-oxidizing bacteria that generate nitrite nitrogen from ammonia nitrogen and co-denitrifying bacteria (anammox bacteria) that generate nitrogen from nitrite nitrogen and ammonia nitrogen.

  Ammonia-oxidizing bacteria and co-denitrifying bacteria are directly supported on the surface of the conductive fiber constituting the conductive microorganism-supporting electrode 54, so that their metabolic activity is regulated by the electrode potential.

  In the conductive carbon fiber felt or cloth, it is preferable that a region where ammonia-oxidizing bacteria are inhabited and a region where co-denitrifying bacteria are inhabited are divided into zones.

  For example, when carrying ammonia-oxidizing bacteria or co-denitrifying bacteria on a conductive microorganism-carrying electrode 54 formed in a cylindrical shape by winding a conductive carbon fiber felt or cloth in a spiral shape, When the tip of the air supply pipe is arranged on the center side, it is supported so that ammonia-oxidizing bacteria inhabit the vicinity, and co-denitrifying bacteria inhabit in the cylindrical outer peripheral area where air is not supplied. It is preferable to be supported on the surface.

  The reason why the ammonia-oxidizing bacteria-carrying part and the co-denitrifying bacteria-carrying part are in contact with the conductive microorganism-carrying electrode is because the equilibrium potential for nitrous acid production and the equilibrium potential region where nitrogen stably exists are common. is there.

  A diaphragm or partition wall 57 is provided between the conductive microorganism-carrying electrode 54 and the counter electrode 55 to prevent an electrical short circuit therebetween. Reference numeral 58 denotes a reference electrode. As the reference electrode 58, a silver-silver chloride (Ag / AgCl) electrode can be used.

  In this co-denitrification reactor 5, a reaction for generating nitrite nitrogen from ammonia nitrogen occurs and proceeds on a pair of electrodes composed of a microorganism-carrying electrode 54 and a counter electrode 55, but a reaction for generating nitrate nitrogen is performed. Apply a potential that does not occur.

  In controlling the applied potential, it is necessary to consider the influence of pH. Therefore, in order to more reliably control the applied potential, the pH value of the liquid to be treated is measured and the value is used to control the applied potential. Reflecting is a preferred mode.

59 is a pH measurement unit for measuring the pH of the digestive juice, and the measurement data is input to the potential control unit 510. The potential control unit 510 outputs a pH adjustment signal and a potential application signal to the potential application unit 511 based on the data from the pH measurement unit 59, and outputs nitrous acid by a reaction of 4NH ₃ + 3O ₂ → 2HNO ₂ + 2NH ₃ + 2H ₂ O. Then, co-denitrification is performed by controlling to generate nitrogen gas by a reaction of HNO ₂ + NH ₃ → N ₂ + 2H ₂ O.

  By performing the potential control by the potential control unit 510, it is possible to eliminate the risk of an undesirable side reaction such as the generation of dinitrogen monoxide, for example, and to convert ammonia into nitrogen gas and discharge it.

  In the biogas system of the present invention, means for utilizing carbon dioxide recovered by the carbon dioxide removing means 2 and ammonia recovered by the ammonia stripping means 3 as resources in the industry can be provided.

  FIG. 5 shows an example in which carbon dioxide and ammonia are used as resources.

  Gas separated from the digestive juice by the carbon dioxide recovery means 2 and mostly composed of carbon dioxide is conveyed through the line 202 to the plant cultivation facility 6 that is blocked from the outside air.

  Plant cultivation facilities that are blocked from outside air include a plastic house, a glass room, and a plant cultivation facility called a plant factory.

  In such plant cultivation facilities, carbon dioxide is supplied in order to promote photosynthesis and promote growth and quality improvement of cultivated plants, and mainly supplies gas obtained by burning kerosene and propane gas.

  By supplying the carbon dioxide recovered by the carbon dioxide removing means 2 into the facility, carbon dioxide generated by methane fermentation can be used effectively, and consumption of fossil fuels can be reduced.

  Similarly, the ammonia recovered by the ammonia stripping means 3 is also converted to ammonia nitrogen-containing water by the condenser 4 and then supplied as liquid fertilizer, so that the nitrogen of the plants cultivated in the plant cultivation facility 6 that is blocked from the outside air. Can be used as a source.

The flowchart which shows the preferable aspect which implements the methane fermentation system of this invention The figure which shows the example of the ammonia stripping apparatus used for this invention The figure which shows the example of the co-denitrification reactor used for this invention The figure which shows another example of the co-denitrification reactor used for this invention Flow diagram showing an aspect of using recovered carbon dioxide and ammonia

Explanation of symbols

1: Methane fermentation means 101: Screw pump 102: Heat exchanger 103: Transport pipe 104: Methane fermentation tank 105: Stirrer 106: Digestion liquid discharge pipe 107: Biogas holder 2: Carbon dioxide removal means 201: Deaeration device 202: Line 3: Ammonia stripping means 301: Liquid feed pump 302: Ammonia stripping device 303: Circulation tank 304: Mount 305: Ammonia diffusion tower 306: Perforated plate 307: Filler 308: Spray nozzle 309: Piping 310: Circulation pump 311 : Connection pipe 312: Compressor or blower 313: Drain valve 314: Discharge pipe 4: Ammonia recovery condenser 5: Co-denitrification reactor 50: Liquid to be treated 50A: Main body 50B: Lid 50C: Reaction tank 51: Treatment liquid Discharge part 52: Nitrogen gas discharge part 5 3: Air introduction part 54: Conductive microorganism supporting electrode 54A: Area 54B: Area 55: Counter electrode 56: Lead wire 57: Partition wall 58: Reference electrode 59: pH measuring part 501: Microorganism carrier 502, 503 support rod 504: Processed Liquid introduction part 505: Treatment liquid discharge part 506: Air introduction part 507: Air transfer pipe 508: pH control part 509: Temperature control part 510: Potential control part 511: Potential application part 6: Plant cultivation facility

Claims (9)

Methane fermentation means for introducing methane into a methane fermentation tank and performing methane fermentation at a high temperature of 60 ° C. or higher and under a pressure of 0.2 to 5 MPa by natural fermentation pressure generated by fermentation;
Carbon dioxide removal means for removing the carbon dioxide by depressurizing the digested liquid extracted from the methane fermentation tank;
A biogas system comprising ammonia stripping means for introducing the digested liquid from which carbon dioxide has been removed by the carbon dioxide removing means into an ammonia stripping apparatus to dissipate ammonia.   The biogas system according to claim 1, wherein the biomass to be administered into the methane fermenter is placed in an environment of 60 ° C to 70 ° C for 1 hour or longer, or in an environment exceeding 70 ° C for 10 minutes or longer. .   The biogas system according to claim 2, wherein the environment of 60 ° C to 70 ° C or the environment exceeding 70 ° C is formed in a methane fermentation tank.   The biogas system according to claim 2, wherein the environment of 60 ° C. to 70 ° C. or the environment exceeding 70 ° C. is formed before biomass is introduced into the methane fermentation tank.   The biogas system according to any one of claims 1 to 4, further comprising ammonia recovery means for recovering the ammonia stripped by the ammonia stripping means.   6. The biogas system according to claim 5, further comprising a processing unit that introduces ammonia recovered by the ammonia recovery unit to perform nitritation and denitrification. The biogas according to claim 6, wherein the treatment means for performing nitritation and denitrification introduces ammonia recovered by the ammonia recovery means and co-denitrifies by reaction of nitrous acid and ammonia. system.   The biogas system according to claim 7, further comprising an input unit that administers the ammonia recovered by the ammonia recovery unit into a plant cultivation facility that is blocked from outside air.   The carbon dioxide removed and diffused by the carbon dioxide removing means is collected, and the collected carbon dioxide is fed into a plant cultivation facility that is shielded from the outside air. The biogas system according to crab.

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