Biomass treatment device

Abstract

To provide a biomass treatment device that facilitates enhancement of methane concentration in biogas, which in turn enables utilization of the biogas for diverse purposes.SOLUTION: A biomass treatment device 1A configured to produce a biogas BG through fermentation of biomass, the device including: a two-stage fermentation tank 2 that stores a fermentation liquid in which the biomass is fermented; and a gas supply part 7 that supplies a hydrogen-containing gas to the fermentation tank 2. The two-stage fermentation tank 2 comprises an acid fermentation tank 11 into which the biomass is introduced, and a methane fermentation tank 12 provided downstream of the acid fermentation tank 11. The gas supply part 7 supplies the hydrogen-containing gas to the methane fermentation tank 12.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a biomass treatment apparatus for fermenting biomass to produce biogas. [Background technology]

[0002] The use of biogas has been attracting attention from the viewpoints of preventing environmental pollution and regenerating energy.

[0003] Anaerobic fermentation of organic resources (biomass) derived from living organisms ultimately produces combustible biogas, primarily composed of methane and carbon dioxide. Anaerobic fermentation of biomass can be broadly divided into two biochemical reactions: a solubilization process using hydrolytic and acidogenic bacteria, and a methane fermentation process using methanogenic bacteria. High molecular weight organic compounds such as proteins, carbohydrates, and fats are broken down into smaller molecules by hydrolytic bacteria and other bacteria, resulting in higher fatty acids, amino acids, and sugars. The smaller organic compounds are then broken down by acidogenic bacteria into hydrogen, CO2, and organic acids (acetic acid, butyric acid, propionic acid, pyruvic acid, formic acid, lactic acid, succinic acid, etc.). The organic acids are then subjected to methane fermentation by methanogenic bacteria, producing methane.

[0004] As a biomass treatment device that generates biogas containing methane and the like through anaerobic fermentation as described above, a device is known that has an acid fermentation tank in the upstream stage to perform a solubilization step, and a methane fermentation tank in the downstream stage to perform a methane fermentation step (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-289946 Summary of the Invention [Problem to be solved by the invention]

[0006] In the biomass treatment device of Patent Document 1, the biogas contains CO2, which is inevitably produced by the decomposition of low-molecular-weight organic matter by acid-producing bacteria. This means that the methane concentration in the generated biogas is low, at approximately 50 to 60%, and there is a problem that the biogas can only be used for limited purposes.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a biomass treatment device that can increase the methane concentration in biogas, thereby enabling the biogas to be used for a variety of purposes. [Means for solving the problem]

[0008] The characteristic configuration of the biomass processing device according to the present invention for solving the above problems is as follows: A biomass treatment device that ferments biomass to produce biogas, a two-stage fermenter for storing a fermentation liquid obtained by fermenting the biomass; a gas supply unit that supplies a hydrogen-containing gas to the fermenter; The purpose is to provide the following.

[0009] In the biomass treatment device of this configuration, in the two-stage fermenter where biomass is fermented, methane is ultimately produced by methanogens from acetic acid, hydrogen, and CO2. The reaction that produces methane using acetic acid as a substrate is the acetic acid decomposition methanogenesis reaction, which is catalyzed by acetic acid decomposition methanogens. On the other hand, the reaction that produces methane using hydrogen and CO2 as substrates is the CO2 reduction methanogenesis reaction, which is catalyzed by hydrogen-assimilating methanogens. In this biomass treatment device, a hydrogen-containing gas is supplied to the fermentation liquor in the two-stage fermenter by the gas supply unit. Therefore, in addition to the hydrogen produced by the decomposition of low-molecular-weight organic matter by the acid-producing bacteria, hydrogen derived from the hydrogen-containing gas supplied by the gas supply unit is also contained in the fermentation liquor. Then, methane is produced by the CO2 reduction methanogenesis reaction by the hydrogen-assimilating methanogens using as substrates the hydrogen derived from the decomposition of low-molecular-weight organic matter by the acid-producing bacteria, the hydrogen derived from the hydrogen-containing gas supplied by the gas supply unit, and the CO2 produced by the decomposition of low-molecular-weight organic matter by the acid-producing bacteria. In this way, by reducing CO2 in a hydrogen-rich state, the methane concentration in the biogas can be increased, which allows the biogas to be used for a variety of purposes.

[0010] In the biomass treatment device according to the present invention, The two-stage fermenter comprises an acid fermenter into which the biomass is introduced and a methane fermenter provided downstream of the acid fermenter, The gas supply unit preferably supplies the hydrogen-containing gas to the methane fermentation tank.

[0011] In this biomass treatment device, the two-stage fermenter is composed of an acid fermenter into which biomass is introduced and a methane fermenter located downstream of the acid fermenter. In the acid fermenter, acid-producing bacteria decompose organic matter into lower organic acids such as butyric acid, propionic acid, and acetic acid. Meanwhile, in the methane fermenter, methanogens produce methane from acetic acid, hydrogen, and CO2. However, if hydrogen-containing gas from a gas supply unit is supplied to the acid fermenter, hydrogen from the hydrogen-containing gas supplied by the gas supply unit accumulates in addition to the hydrogen by-product of the acid production reaction in the acid fermenter, resulting in an increase in hydrogen partial pressure. This can result in product inhibition, preventing the acetic acid production reaction from proceeding, and ultimately reducing the methane production rate in the downstream methane fermenter. Therefore, in this biomass treatment device, hydrogen-containing gas from the gas supply unit is supplied to the methane fermenter located downstream of the acid fermenter. This avoids product inhibition in the acid fermenter. As a result, in the methane fermentation tank, methane is produced by an acetic acid decomposition methanogenesis reaction using acetic acid as a substrate, and methane is also produced by a CO2 reduction methanogenesis reaction using hydrogen and CO2 as substrates, thereby improving the efficiency of methane production.

[0012] In the biomass treatment device according to the present invention, The methane fermenter preferably has a hydrogen supply area to which the hydrogen-containing gas is supplied.

[0013] According to the biomass treatment apparatus of this configuration, the hydrogen supply area can be set according to the progress of the methane production reaction in the methane fermentation tank, thereby making it possible to appropriately adjust the supply of hydrogen-containing gas.

[0014] In the biomass treatment device according to the present invention, It is preferable that a circulation circuit be provided for returning a portion of the biogas produced in the methane fermentation tank to the gas supply unit and circulating it.

[0015] According to the biomass treatment device of this configuration, a portion of the biogas produced in the methane fermentation tank is returned to the gas supply section and circulated, thereby converting the CO2 remaining in the biogas into methane, thereby further increasing the methane concentration in the biogas.

[0016] In the biomass treatment device according to the present invention, The methane fermenter is a plug flow type fermenter in which the biomass is fermented while being flowed, It is preferable that a plurality of compartments for storing biogas produced in the methane fermentation tank are formed in a state of communication along the flow direction of the biomass.

[0017] In the biomass treatment device of this configuration, biogas is sequentially introduced into multiple compartments in a plug flow type methane fermentation tank from the upstream side to the downstream side in the direction of biomass flow, and a portion of the biogas in each compartment is supplied to the gas supply section by a circulation circuit and circulated, thereby gradually increasing the methane concentration in the biogas.

[0018] In the biomass treatment device according to the present invention, It is preferable to provide a recycling device that filters the fermented liquid from the methane fermentation tank, discharges the filtrate, and returns the filtered matter to the methane fermentation tank.

[0019] According to the biomass treatment device of this configuration, the filtrate (digestion liquid) discharged after filtering the fermentation liquid from the methane fermentation tank can be effectively used, for example, as liquid fertilizer. Furthermore, the filtered matter, which contains a large amount of methane bacteria, is returned to the methane fermentation tank for reuse. This maintains a high concentration of methane bacteria in the methane fermentation tank, enabling efficient methane fermentation. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a biomass treatment apparatus according to a first embodiment. [Figure 2]FIG. 2 is a schematic diagram showing a schematic configuration of a biomass treatment apparatus according to the second embodiment. [Figure 3] FIG. 3 is a schematic diagram showing a schematic configuration of a biomass treatment apparatus according to the third embodiment. [Figure 4] FIG. 4 is a schematic diagram showing a schematic configuration of a biomass treatment apparatus according to the fourth embodiment. [Figure 5] FIG. 5 is a schematic diagram showing a schematic configuration of a biomass treatment apparatus according to the fifth embodiment. [Figure 6] FIG. 6 is a schematic diagram showing a schematic configuration of a biomass treatment apparatus according to the sixth embodiment. [Figure 7] FIG. 7 is a diagram showing another example of the state of diffusion of the hydrogen-containing gas. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described below with reference to the drawings. In this specification, biomass refers to organic resources derived from living organisms. Examples of biomass include organic waste, resource crops, and their waste. Examples of organic waste include food waste, manure, sludge, food processing residues, livestock waste, waste oil, animal fats and oils, agricultural crop residues, and organic wastewater from the food industry, paper industry, or livestock industry. Examples of sludge include sewage treatment sludge, human waste treatment sludge, septic tank sludge, and treated industrial wastewater from food factories. Examples of resource crops include potatoes, sugar beets, rapeseed, sunflowers, wheat, chlorella, water hyacinth, corn, sugarcane, and waste generated during the processing of these crops. In this specification, biogas refers to gas generated by anaerobic fermentation of biomass. Examples of biogas components include hydrogen gas, methane gas, and carbon dioxide gas. In the following embodiments, a biomass treatment device equipped with a two-stage fermenter that ferments organic waste to produce biogas will be described as an example. However, the present invention is not intended to be limited to the embodiments described below or the configurations shown in the drawings. The present invention can be applied to both dry and wet biomass treatment devices.

[0022] First Embodiment <Overall structure> FIG. 1 is a schematic diagram showing the overall configuration of a biomass processing device 1A according to a first embodiment. As shown in FIG. 1, the biomass processing device 1A is a fermentation device equipped with a two-stage fermenter 2, a biomass supply unit 3, a fermentation liquid supply unit 4, a first agitator 5, a second agitator 6, a gas supply unit 7, a biogas recovery unit 8, and a recycling device 9 of any configuration. When the fermentation device is a wet type, the solid matter concentration in the fermenter 2 is adjusted to approximately 10% by weight or less, and organic waste is fermented in a medium-temperature environment (30-45°C) or a high-temperature environment (45-65°C) to produce biogas. When the fermentation device is a dry type, the solid matter concentration in the fermenter 2 is adjusted to approximately 8-40% by weight, and organic waste is fermented by methane fermentation in a high-temperature environment (45-65°C) to produce biogas. Dry fermentation devices include vertical dry fermentation devices and horizontal dry fermentation devices. Dry vertical fermentation equipment can process high-concentration waste with a solids concentration of about 15 to 40% by weight.Like the dry vertical type, dry horizontal fermentation equipment can also process high-concentration waste with a solids concentration of about 15 to 40% by weight.

[0023] <Two-stage fermentation tank> The two-stage fermenter 2 stores a fermentation liquid obtained by fermenting organic waste, and is composed of an acid fermenter 11 into which the organic waste is introduced, and a methane fermenter 12 provided downstream of the acid fermenter 11. The acid fermenter 11 is a vertical single tank having a cylindrical body 11a with its axis (not shown) oriented in the vertical direction, with the upper and lower sides of the body 11a closed, and stores a fermentation liquid FL1 obtained by acid fermentation of organic waste. Similar to the acid fermenter 11, the methane fermenter 12 has a cylindrical body 12a with its axis (not shown) oriented in the vertical direction, and is a vertical single tank having its upper and lower sides closed. Compared to the acid fermenter 11, the methane fermenter 12 has a larger overall capacity and is formed in a vertically elongated shape. The methane fermentation tank 12 is configured to store the fermentation liquid FL2 obtained by introducing the fermentation liquid FL1 from the acid fermentation tank 11 and fermenting it into methane, and to fill the space above the liquid level of the fermentation liquid FL2 with biogas BG containing methane, etc.

[0024] <Biomass Supply Department> The biomass supply unit 3 includes a pressure-feeding unit 15 and a biomass supply pipe 16. The pressure-feeding unit 15 includes, for example, a pump and a control valve for controlling the feed rate and pressure, although detailed illustrations are omitted. The biomass supply pipe 16 connects the pressure-feeding unit 15 to a biomass supply port 17 provided on one side of the acid fermentation tank 11. Before the biomass supply unit 3, the organic waste used as raw material is subjected to pretreatment equipment (not shown) to homogenize the raw material by removing foreign matter and adjust the moisture content to a level suitable for methane fermentation. The pretreated organic waste is introduced into the acid fermentation tank 11 through the biomass supply port 17 by the biomass supply unit 3. The introduced organic waste undergoes acid fermentation in the acid fermentation tank 11. The fermented liquor FL1 is then discharged from a fermentation liquor outlet 18 provided on the other side of the acid fermentation tank 11.

[0025] <Fermentation liquid supply unit> The fermentation liquid supply unit 4 includes a pressure-feeding unit 19 similar to the above-described pressure-feeding unit 15, and a fermentation liquid supply pipe 20. The fermentation liquid supply pipe 20 connects the fermentation liquid outlet 18 of the acid fermentation tank 11 with a fermentation liquid supply port 21 provided on one side of the methane fermentation tank 12.

[0026] <Stirring device> The first agitator 5 is disposed for the purposes of homogenizing the fermentation liquor FL1 in the acid fermentation tank 11 and preventing the formation of scum. The second agitator 6 is disposed similarly for the purposes of homogenizing the fermentation liquor FL2 in the methane fermentation tank 12 and preventing the formation of scum. Examples of agitators 5 and 6 include mechanical agitation types, gas agitation types, and circulation agitation types, and are not particularly limited, but in this example, a mechanical agitation type is employed. The mechanical agitation type agitators 5 and 6 employed in this example are configured to agitate the fermentation liquors FL1 and FL2 by transmitting rotational power from a drive unit to a rotor via a rotating shaft to rotate the rotor.

[0027] <Gas supply section> The gas supply unit 7 supplies a hydrogen-containing gas to the fermentation liquid FL2 in the methane fermenter 12. The hydrogen-containing gas refers to a gas containing at least 10% hydrogen by volume relative to the total hydrogen-containing gas. The hydrogen gas content in the hydrogen-containing gas is preferably 80% or more, more preferably 90% or more, and most preferably 95% or more. There is no particular upper limit to the hydrogen gas content in the hydrogen-containing gas, and it may be 100%.

[0028] The gas supply unit 7 includes a gas supply source 22 and a gas supply pipe 23. Although not shown in detail, the gas supply source 22 includes a hydrogen storage unit that stores hydrogen gas under high pressure and a pressure reducing valve that reduces the pressure of the high-pressure hydrogen gas from the hydrogen storage unit. Examples of the hydrogen used here include hydrogen obtained by electrolyzing water using electricity generated by renewable energy sources such as solar, wind, and geothermal energy, and surplus hydrogen from a nearby petrochemical plant. The upstream end of the gas supply pipe 23 is connected to the gas supply source 22, and the downstream end is configured to allow a hydrogen-containing gas to be injected into the fermentation liquid FL2 in the methane fermentation tank 12. The gas introduced into the fermentation liquid FL2 in the methane fermentation tank 12 is not limited to the hydrogen-containing gas from the gas supply unit 7. For example, if CO2 gas is generated in the acid fermentation tank 11, the CO2 gas may be introduced into the methane fermentation tank 12.

[0029] <Biogas Recovery Section> The biogas recovery section 8 includes a gas discharge pipe 25 and a gas extraction section 26. The upstream end of the gas discharge pipe 25 is connected to a gas vent port 27 provided on the top surface of the methane fermentation tank 12 so that the biogas BG can be discharged outside the tank, and the downstream end of the gas flow is connected to a gas holder 28. The gas extraction section 26 is disposed midway along the gas discharge pipe 25. The biogas BG extracted by the gas extraction section 26 through the gas discharge pipe 25 from the methane fermentation tank 12 is temporarily stored in the gas holder 28 and then effectively utilized. A gas purification device may be connected to the downstream gas flow side of the gas holder 28. Examples of gas purification devices include a device that removes hydrogen sulfide from the biogas BG, a moisture removal device, a device that further reduces CO2 from the biogas BG by pressure swing adsorption (PSA), membrane separation, high-pressure water absorption, chemical absorption, physical absorption, or the like, and a siloxane removal device.

[0030] <Reuse equipment> The recycling apparatus 9 includes a reflux pipe 31, a pressure pump 32, and a solid-liquid separator 33. The reflux pipe 31 is disposed in a manner that connects an outlet 34 provided on the other side of the methane fermentation tank 12 with an inlet 35 provided at the bottom of the methane fermentation tank 12. The pressure pump 32 is disposed in the reflux pipe 31 at a position close to the outlet 34. The solid-liquid separator 33 is disposed in the reflux pipe 31 so as to be located between the pressure pump 32 and the inlet 35. The solid-liquid separator 33 can use a filtration membrane such as a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane), and examples of the membrane shape include a flat membrane and a hollow fiber membrane. In the recycling apparatus 9, the pressure pump 32 is operated to send the fermentation liquid (methane fermentation digested liquid) remaining after biogas is removed from the upper part of the methane fermentation tank 12 to the solid-liquid separator 33. The solid-liquid separator 33 filters the methane fermentation digested liquid fed from the pressure pump 32 to separate it into a filtrate and a filtrate residue. The filtrate residue is returned to the bottom of the methane fermentation tank 12 via the reflux pipe 31 and reused. On the other hand, the filtrate (filtered digested liquid) is discharged via a filtrate discharge pipe 36 connected to a filtrate discharge port of the solid-liquid separator 33. The discharged filtered digested liquid is recovered in a digested liquid recovery section 37 and is effectively utilized, for example, as liquid fertilizer. In this embodiment, an example has been shown in which a device that separates solids and liquids using a filtration membrane such as an MF membrane or an UF membrane is used as the solid-liquid separator 33, but the present invention is not limited to this, and devices such as a rotary drum, a drum screen, a belt press, a screw press, a belt thickener, a flotation separator, and a sedimentation separator can also be used. In this example, the entire amount of the fermentation liquid (methane fermentation digested liquid) remaining after the biogas BG is removed is sent to the solid-liquid separator 33, but the present invention is not limited to this, and a portion of the methane fermentation digested liquid may be returned to the fermenter 2 via the fermentation liquid supply pipe 20. In another embodiment, the filtered digested liquid recovered in the digested liquid recovery section 37 is incinerated to recover heat.

[0031] In the biomass treatment apparatus 1A configured as described above, organic waste is supplied to the acid fermentation tank 11 by the biomass supply unit 3. The supplied organic waste undergoes acid fermentation in the acid fermentation tank 11. The fermentation liquid FL1 in the acid fermentation tank 11 is stirred by the first stirrer 5. The fermentation liquid FL1 discharged from the fermentation liquid outlet 18 of the acid fermentation tank 11 is supplied to the methane fermentation tank 12 by the fermentation liquid supply unit 4. The supplied fermentation liquid FL1 undergoes methane fermentation in the methane fermentation tank 12. The fermentation liquid FL2 in the methane fermentation tank 12 is stirred by the second stirrer 6. A hydrogen-containing gas is blown into the fermentation liquid FL2 in the methane fermentation tank 12 from the gas supply unit 7.

[0032] In the acid fermenter 11, a solubilization process is carried out using hydrolytic bacteria and acid-producing bacteria with organic waste as a substrate. That is, high molecular weight organic compounds such as proteins, carbohydrates, and fats are first broken down into lower molecular weight compounds by the hydrolytic bacteria, etc., into higher fatty acids, amino acids, and sugars. Next, these low molecular weight organic compounds are decomposed by the acid-producing bacteria into hydrogen, CO2, and organic acids (acetic acid, butyric acid, propionic acid, pyruvic acid, formic acid, lactic acid, succinic acid, etc.).

[0033] In the methane fermentation tank 12, a methanogenesis reaction is carried out by methanogens to produce methane from acetic acid, hydrogen, and CO2. The reaction to produce methane using acetic acid as a substrate is an acetolytic methanogenesis reaction, and this reaction is carried out by acetolytic methanogens. On the other hand, the reaction to produce methane using hydrogen and CO2 as substrates is a CO2-reducing methanogenesis reaction, and this reaction is carried out by hydrogen-utilizing methanogens.

[0034] In the biomass treatment apparatus 1A of the first embodiment, the gas supply unit 7 supplies hydrogen-containing gas to the fermentation liquor FL2 in the methane fermentation tank 12. Therefore, in addition to hydrogen produced by the decomposition of low-molecular-weight organic matter by the acid-producing bacteria, hydrogen derived from the hydrogen-containing gas supplied by the gas supply unit 7 is also contained in the fermentation liquor FL2. Then, using the hydrogen derived from the decomposition of low-molecular-weight organic matter by the acid-producing bacteria, hydrogen derived from the hydrogen-containing gas supplied by the gas supply unit 7, and CO produced by the decomposition of low-molecular-weight organic matter by the acid-producing bacteria as substrates, methane is produced by a CO2-reducing methane production reaction carried out by hydrogen-assimilating methanogens. By reducing CO2 in this hydrogen-rich state, the methane concentration in the biogas can be increased. The biogas BG produced by methane fermentation accumulates above the liquid level of the fermentation liquor FL2 stored in the methane fermentation tank 12 and is recovered by the biogas recovery unit 8 for effective utilization.

[0035] The fermentation liquid (methane fermentation digested liquid) FL2 remaining after the biogas BG is removed from the top of the methane fermentation tank 12 is sent to the solid-liquid separator 33 by the pressure pump 32 and separated into a filtrate and a filtrate. The filtrate is returned to the methane fermentation tank 12. The filtrate contains a large amount of methane bacteria, and is reused by returning it to the methane fermentation tank 12, thereby maintaining a high concentration of methane bacteria and allowing fermentation to proceed efficiently. Meanwhile, the filtrate (filtered digested liquid) is recovered in the digested liquid recovery section 37 and is effectively used, for example, as liquid fertilizer. As mentioned above, the recycling device 9 has an optional configuration, and therefore devices such as the pressure pump 32 and the solid-liquid separator 33 may be omitted in some cases.

[0036] Second Embodiment Figure 2 is a schematic diagram showing the overall configuration of a biomass processing device 1B of a second embodiment. In the second embodiment, components that are the same as or similar to those in the first embodiment are simply given the same reference numerals in the figure, and detailed descriptions thereof will be omitted. The following description will focus on parts unique to the second embodiment. As shown in Figure 2, in the biomass processing device 1B of the second embodiment, a return pipe 41, which is arranged in a form branching from a portion of the gas exhaust pipe 25 between the gas extraction section 26 and the gas holder 28, is connected to the gas supply pipe 23. A circulation circuit 40 is formed by the methane fermentation tank 12, the gas exhaust pipe 25, the return pipe 41, and the gas supply pipe 23. The rest of the configuration is the same as that of the biomass processing device 1A of the first embodiment. In this example, the return pipe 41 is connected to the gas supply pipe 23, thereby circulating a portion of the biogas BG by merging it with the hydrogen-containing gas flowing through the gas supply pipe 23. However, this is not limited to this. For example, the return pipe 41 may be connected to the lower part of the methane fermentation tank 12 in a manner that branches off from the gas exhaust pipe 25, thereby forming a circulation circuit 40 by the methane fermentation tank 12, the gas exhaust pipe 25, and the return pipe 41, and a portion of the biogas BG may be circulated through an independent circulation circuit 40 separate from the supply route of the hydrogen-containing gas by the gas supply unit 7.

[0037] It goes without saying that the biomass processing device 1B of the second embodiment can achieve the same effects as the biomass processing device 1A of the first embodiment. Furthermore, in the biomass processing device 1B of the second embodiment, a portion of the biogas BG extracted by the gas extraction unit 26 through the gas exhaust pipe 25 from the inside of the methane fermentation tank 12 is returned to the gas supply pipe 23 of the gas supply unit 7 through the return pipe 41 and circulated by the circulation circuit 40. This converts CO2 remaining in the biogas BG to methane, thereby further increasing the methane concentration in the biogas BG.

[0038] Third Embodiment Fig. 3 is a schematic diagram showing the overall configuration of a biomass processing apparatus 1C of the third embodiment. As shown in Fig. 3, the biomass processing apparatus 1C of the third embodiment employs a horizontal plug-flow type methane fermenter 42 instead of the vertical single-tank methane fermenter 12 of the first embodiment.

[0039] <Methane fermentation tank> The methane fermentation tank 42 has a horizontally elongated cylindrical body 50 with its axis (not shown) oriented horizontally, a first end 51 closing one end of the body 50, and an opposite end 52 closing the other end of the body 50. A fermentation liquid supply port 53 is provided in the first end 51, and the fermentation liquid supply port 53 is connected to the fermentation liquid discharge port 18 by a fermentation liquid supply pipe 20. The methane fermentation tank 42 stores (contains) a fermentation liquid FL2 obtained by fermenting fermentation liquid FL1 supplied from the acid fermentation tank 11 through the fermentation liquid supply pipe 20 while allowing it to flow from the first end 51 to the opposite end 52, and is configured so that the space above the liquid level of the fermentation liquid FL2 is filled with biogas BG. A stirring paddle (not shown) is provided inside the fermentation tank 2 to gently stir the fermentation liquid FL2 in order to promote degassing from the fermentation liquid FL2.

[0040] <Gas supply section> In the gas supply unit 7, an aeration unit 60 is provided downstream of the gas flow of the gas supply pipe 23. The aeration unit 60 is disposed at the bottom of the body portion 50 so as to be able to diffuse the hydrogen-containing gas into the methane fermentation tank 42. In this example, the aeration unit 60 is disposed so as to extend in the longitudinal direction (the direction in which the one-side end surface portion 51 and the other-side end surface portion 52 are disposed) and the circumferential direction of the body portion 50 so as to be able to diffuse the hydrogen-containing gas throughout the entire interior of the methane fermentation tank 42. Here, the aeration unit 60 is not particularly limited as long as it can diffuse the hydrogen-containing gas supplied from the gas supply source 22 via the gas supply pipe 23 into the fermentation liquid FL2. For example, an aeration pipe with required holes, a membrane-type aeration pipe, or a porous so-called air stone can be used.

[0041] <Biogas Recovery Section> The upstream end of the gas flow in the gas discharge pipe 25 in the biogas recovery section 8 is connected to a gas vent 54 provided at the top of the body 50 of the methane fermentation tank 42 so that the biogas BG can be discharged outside the tank.

[0042] <Reuse equipment> In the recycling device 9, the reflux pipe 31 is disposed in a form that connects the digestion liquid discharge port 55 provided on the other end surface portion 52 of the methane fermentation tank 42 to the fermentation liquid supply pipe 20. In the recycling device 9, the pressure pump 32 is operated to send the fermentation liquid (methane fermentation digestion liquid) remaining after the biogas BG is removed to the solid-liquid separator 33. The solid-liquid separator 33 filters the methane fermentation digestion liquid sent from the pressure pump 32 to separate it into filtrate and a residue. The residue is returned to the inside of the methane fermentation tank 42 via the reflux pipe 31, the fermentation liquid supply pipe 20, and the fermentation liquid supply port 53 and is reused.

[0043] In the biomass treatment apparatus 1C configured as described above, the fermentation liquid FL1 discharged from the fermentation liquid outlet 18 of the acid fermentation tank 11 is supplied to the methane fermentation tank 42 by the fermentation liquid supply unit 4 and forced into the methane fermentation tank 42 through the fermentation liquid supply port 53. Furthermore, a hydrogen-containing gas is blown into the fermentation liquid FL2 in the methane fermentation tank 42 from the gas supply unit 7. Furthermore, to promote degassing from the fermentation liquid FL2, the fermentation liquid FL2 is gently stirred by a stirring paddle (not shown).

[0044] In the methane fermentation tank 42, the fermentation liquid FL2 is forced to flow toward the digestion liquid discharge port 55. As the fermentation liquid FL2 gradually moves from the fermentation liquid supply port 53 toward the digestion liquid discharge port 55, it undergoes a methane production reaction and is converted into biogas BG, and the fermentation liquid (methane fermentation digestion liquid) remaining after the biogas BG is removed is discharged from the digestion liquid discharge port 55.

[0045] In the methane fermenter 42, the reaction to produce methane using acetic acid as a substrate is an acetic acid decomposition methanogenesis reaction, which is catalyzed by acetic acid decomposing methanogens. On the other hand, the reaction to produce methane using hydrogen and CO2 as substrates is a CO2 reduction methanogenesis reaction, which is catalyzed by hydrogen-utilizing methanogens.

[0046] In the biomass treatment apparatus 1C of the third embodiment, the gas supply unit 7 supplies hydrogen-containing gas to the fermentation liquor FL2 in the methane fermentation tank 42. Therefore, in addition to the hydrogen produced by the acid-producing bacteria through decomposition of low-molecular-weight organic matter, the fermentation liquor FL2 also contains hydrogen derived from the hydrogen-containing gas supplied by the gas supply unit 7. Then, methane is produced by a CO2-reducing methanogenesis reaction using the hydrogen-assimilating methanogens as substrates: the hydrogen derived from the decomposition of low-molecular-weight organic matter by the acid-producing bacteria, the hydrogen derived from the hydrogen-containing gas supplied by the gas supply unit 7, and CO2 produced through decomposition of low-molecular-weight organic matter by the acid-producing bacteria. By reducing CO2 in this hydrogen-rich state, the methane concentration in the biogas can be increased. The biogas BG produced by methane fermentation accumulates above the liquid surface of the fermentation liquor FL2 stored in the methane fermentation tank 42 and is recovered by the biogas recovery unit 8 for effective utilization.

[0047] The fermentation liquid (methane fermentation digested liquid) FL2 discharged from the inside of the methane fermentation tank 42 through the digested liquid outlet 55 is sent to the solid-liquid separator 33 by the pressure pump 32 and separated into a filtrate and a filtrate. The filtrate is returned to the methane fermentation tank 42. The filtrate contains a large amount of methane bacteria, and is reused by returning it to the methane fermentation tank 42, thereby maintaining a high concentration of methane bacteria and allowing methane fermentation to proceed efficiently. Meanwhile, the filtrate (filtered digested liquid) is recovered in the digested liquid recovery unit 37 and is effectively utilized, for example, as liquid fertilizer.

[0048] Fourth Embodiment 4 is a schematic diagram showing the overall configuration of a biomass processing apparatus 1D of the fourth embodiment. In the biomass processing apparatus 1D of the fourth embodiment, a return pipe 66 branching off from the gas exhaust pipe 25 is connected to an aeration unit 60. A circulation circuit 65 is formed by the methane fermentation tank 42, the gas exhaust pipe 25, the return pipe 66, and the aeration unit 60. The remaining configuration is the same as that of the biomass processing apparatus 1C of the third embodiment.

[0049] It goes without saying that the biomass processing apparatus 1D of the fourth embodiment can achieve the same effects as the biomass processing apparatus 1C of the third embodiment. Furthermore, in the biomass processing apparatus 1D of the fourth embodiment, a portion of the biogas BG extracted by the gas extraction unit 26 from the inside of the methane fermentation tank 42 via the gas discharge pipe 25 is returned to the inside of the methane fermentation tank 42 via the return pipe 66 and the aeration unit 60 and circulated by the circulation circuit 65. As a result, CO2 remaining in the biogas BG is converted to methane, and the methane concentration in the biogas BG can be further increased.

[0050] Fifth Embodiment FIG. 5 is a schematic diagram showing the overall configuration of a biomass processing apparatus 1E of a fifth embodiment. The biomass processing apparatus 1E of the fifth embodiment is based on the biomass processing apparatus 1C of the third embodiment (see FIG. 3). In the biomass processing apparatus 1E of the fifth embodiment, a plurality of (three in this example) compartments 71-73 are formed in the space filled with biogas BG above the liquid level of the fermentation liquid FL2 in the methane fermentation tank 42, and are arranged in a communicating state along the flow direction of the biomass (hereinafter referred to as the "biomass flow direction"). That is, in the methane fermentation tank 42, a plurality of (two in this example) partition plates (a first partition plate 75 and a second partition plate 76) are attached to the inner circumferential surface of the trunk portion 50 at predetermined intervals in the longitudinal direction of the trunk portion 50 (the biomass flow direction) between the one end surface 51 and the other end surface 52 so as to partition the space between the inner circumferential surface of the upper region of the trunk portion 50 and the liquid level of the fermentation liquid FL2. A first compartment 71 is formed by the inner circumferential surface in the upper region of the trunk 50, the one side end surface 51, and the first partition plate 75, a second compartment 72 is formed by the inner circumferential surface in the upper region of the trunk 50, the first partition plate 75, and the second partition plate 76, and a third compartment 73 is formed by the inner circumferential surface in the upper region of the trunk 50, the second partition plate 76, and the other side end surface 52. The first compartment 71, the second compartment 72, and the third compartment 73 are arranged in a communicated state so that the biogas BG flows in a direction from the first compartment 71 to the third compartment 73, or in a direction from the third compartment 73 to the first compartment 71, or in both directions.

[0051] Here, the method for communicating the first compartment chamber 71, the second compartment chamber 72, and the third compartment chamber 73 is not particularly limited, but examples thereof include providing vent holes in the first partition plate 75 and the second partition plate 76, or disposing a communication pipe that connects the compartment chambers 71 to 73 in a communication state inside or outside the body 50. In this example, the first compartment chamber 71, the second compartment chamber 72, and the third compartment chamber 73 are communicated by providing vent holes in the first partition plate 75 and the second partition plate 76.

[0052] The relative sizes of the first compartment chamber 71, the second compartment chamber 72, and the third compartment chamber 73 are not particularly limited, but for example, as shown in Fig. 5, the size of each compartment chamber 71 to 73 can be made smaller toward the downstream side in the biomass flow direction. By doing so, even when methane fermentation progresses from the upstream side to the downstream side in the biomass flow direction in the methane fermenter 42 and the amount of biogas BG generated gradually increases, it is possible to uniformize the amount of biogas BG stored in each compartment chamber 71 to 73. Furthermore, in this embodiment, an example has been shown in which the number of compartment chambers (first compartment chamber 71 to third compartment chamber 73) is three, but the number of compartment chambers is not limited, and the number of compartment chambers may be two or four or more.

[0053] In the upper region of the body of the methane fermentation tank 42, a first gas outlet 77 is provided to allow biogas BG to be extracted from the first compartment 71 to the outside of the tank, a second gas outlet 78 is provided to allow biogas BG to be extracted from the second compartment 72 to the outside of the tank, and a third gas outlet 79 is provided separately from the gas vent port 54 to allow biogas BG to be extracted from the third compartment 73 to the outside of the tank.

[0054] In the methane fermentation tank 42, the area between the first compartment chamber 71 and the second compartment chamber 72 and the aeration unit 60 is a hydrogen supply area 81 to which hydrogen-containing gas is supplied. In addition, in the methane fermentation tank 42, the area between the third compartment chamber 73 and the aeration unit 60 is a hydrogen non-supply area 82 to which hydrogen-containing gas is not supplied.

[0055] The gas supply unit 4 supplies hydrogen-containing gas to the hydrogen supply area 81 while not supplying hydrogen-containing gas to the hydrogen non-supply area 82. For example, in the aeration unit 60, a diffusion pipe or the like is arranged, and the aeration pipe or the like is connected by piping, and control valves or the like are arranged at key points in the piping.

[0056] The first gas outlet 77 and the aeration unit 60 are connected by a first return pipe 91a. The second gas outlet 78 and the aeration unit 60 are connected by a second return pipe 91b. The third gas outlet 79 and the aeration unit 60 are connected by a third return pipe 91c. A first circulation circuit 90a is formed by the methane fermentation tank 42, the first return pipe 91a, and the aeration unit 60, a second circulation circuit 90b is formed by the methane fermentation tank 42, the second return pipe 91b, and the aeration unit 60, and a third circulation circuit 90c is formed by the methane fermentation tank 42, the third return pipe 91c, and the aeration unit 60.

[0057] A portion of the biogas BG accumulated in the first compartment chamber 71, which is located upstream in the direction of biomass flow among the multiple compartment chambers (first compartment chamber 71 to third compartment chamber 73), is supplied to the aeration unit 60 via the first return pipe 91a. In this way, a portion of the biogas BG in the first compartment chamber 71 is circulated by the first circulation circuit 90a from the first compartment chamber 71 through the first return pipe 91a, the aeration unit 60, and the hydrogen supply area 81 back into the first compartment chamber 71. As a result, CO2 remaining in the biogas BG in the first compartment chamber 71 is converted to methane, and the methane concentration in the biogas BG is increased.

[0058] The biogas BG in the first compartment chamber 71, which has an increased methane concentration due to circulation through the first circulation circuit 90a, passes through the vent hole in the first partition plate 75 and is introduced into the second compartment chamber 72, which is located downstream in the biomass flow direction. Similar to the circulation and concentration operation of the biogas BG in the first compartment chamber 71, a portion of the biogas BG in the second compartment chamber 72 is supplied to the aeration unit 60 via the second return pipe 91b. In this way, a portion of the biogas BG in the second compartment chamber 72 is circulated by the second circulation circuit 90b from the second compartment chamber 72 through the second return pipe 91b, the aeration unit 60, and the hydrogen supply area 81 back into the second compartment chamber 72. As a result, CO2 remaining in the biogas BG in the second compartment chamber 72 is converted to methane, increasing the methane concentration in the biogas BG. The biogas BG in the second compartment 72, in which the methane concentration has been increased, passes through the vent hole in the second partition plate 76 and is introduced into the third compartment 73, which is located downstream in the direction of biomass flow.

[0059] Then, a portion of the biogas BG introduced into the third compartment 73 with its methane concentration gradually increased is supplied to the aeration unit 60 via the third return pipe 91c. In this way, a portion of the biogas BG in the third compartment 73 is circulated by the third circulation circuit 90c from the third compartment 73 through the third return pipe 91c, the aeration unit 60, and the hydrogen non-supply area 82 back into the third compartment 73. By circulating the biogas BG through the hydrogen non-supply area 82 to which hydrogen is not supplied from the aeration unit 60 in this way, the hydrogen in the biogas BG is consumed by hydrogen-assimilating methanogens, and the methane concentration in the biogas BG is further increased.

[0060] In the first circulation circuit 90a, the entire amount of biogas BG returned from the first return pipe 91a through the aeration unit 60 to the methane fermentation tank 42 may be returned to the first compartment chamber 71, but it is also possible for only a portion of the biogas BG to be returned to the first compartment chamber 71, and not necessarily all of it. In this case, the remaining biogas BG that has not been returned to the first compartment chamber 71 is introduced into the second compartment chamber 72 and / or the third compartment chamber 73.

[0061] In the second circulation circuit 90b, the entire amount of biogas BG returned from the second return pipe 91b through the aeration unit 60 to the methane fermentation tank 42 may be returned to the second compartment chamber 72, but it is also possible for the entire amount to be partially returned to the second compartment chamber 72. In this case, the remaining biogas BG that has not returned to the second compartment chamber 72 is introduced into the first compartment chamber 71 and / or the third compartment chamber 73.

[0062] In the third circulation circuit 90c, the entire amount of biogas BG returned from the third return pipe 91c through the aeration unit 60 to the methane fermentation tank 42 may be returned to the third compartment chamber 73, but it is not necessary that the entire amount is returned to the third compartment chamber 73; instead, only a portion of the biogas BG may be returned. In this case, the remaining biogas BG that has not returned to the third compartment chamber 73 is introduced into the first compartment chamber 71 and / or the second compartment chamber 72.

[0063] The biogas BG in the methane fermentation tank 42 is recovered by the biogas recovery unit 8 through the gas vent port 54 from the third compartment 73, for example, as shown by the solid line in Fig. 5, and is then effectively utilized. Note that the mode of recovery of the biogas BG by the biogas recovery unit 8 is not limited to the example shown by the solid line in Fig. 5, and may be recovered by the biogas recovery unit 8 from the first compartment 71 or the second compartment 72 through the gas vent port 54, as shown by the two-dot chain line in Fig. 5.

[0064] In this way, biogas BG is sequentially introduced into multiple compartments (first compartment 71 to third compartment 73) from the upstream side to the downstream side in the biomass flow direction, and a portion of the biogas BG in each compartment 71 to 73 is returned to and circulated into the methane fermentation tank 42 via the circulation circuits 90a, 90b, 90c and the aeration section 60, thereby ultimately enabling the methane concentration in the biogas BG to be gradually increased.

[0065] Sixth Embodiment Figure 6 is a schematic diagram showing the overall configuration of a biomass treatment apparatus 1F of a sixth embodiment. Figure 6(a) is a diagram showing a state in which a hydrogen-containing gas is diffused into a position between the upstream and downstream portions of the biomass flow direction inside the methane fermentation tank 42. Figure 6(b) is a diagram showing a state in which a hydrogen-containing gas is diffused so that a hydrogen-supply area 81 and a hydrogen-non-supply area 82 are alternately formed in the biomass flow direction inside the methane fermentation tank 42. Figure 6(c) is a diagram showing a state in which a hydrogen-containing gas is diffused so that a hydrogen-non-supply area 82 and a hydrogen-supply area 81 are alternately formed in the biomass flow direction inside the methane fermentation tank 42.

[0066] 6(a) to 6(c), in the biomass processing apparatus 1F of the sixth embodiment, the aeration unit 60 is disposed so as to extend in the longitudinal direction (biomass flow direction) and circumferential direction of the trunk portion 50 so as to be able to diffuse a gas to any part throughout the interior of the methane fermentation tank 42. In the gas supply unit 7, for example, aeration pipes and the like are disposed in the aeration unit 60, and the aeration pipes and the like are connected by piping, and control valves and the like are disposed at key points in the piping so that the position at which the hydrogen-containing gas is diffused within the methane fermentation tank 42 can be freely changed.

[0067] In the biomass processing apparatus 1F of the sixth embodiment, the position at which the hydrogen-containing gas is diffused by the gas supply unit 7 into the methane fermentation tank 42 can be freely changed. As a result, for example, as shown in Fig. 6(a), the hydrogen-containing gas can be diffused into a position between the upstream and downstream portions of the methane fermentation tank 42 in the direction of biomass flow, forming a hydrogen supply area 81; as shown in Fig. 6(b), the hydrogen-containing gas can be diffused so that the hydrogen supply area 81 and the hydrogen non-supply area 82 are alternately formed in the direction of biomass flow inside the methane fermentation tank 42; or as shown in Fig. 6(c), the hydrogen-containing gas can be diffused so that the hydrogen non-supply area 82 and the hydrogen supply area 81 are alternately formed in the direction of biomass flow inside the methane fermentation tank 42. This makes it possible to appropriately adjust the supply of hydrogen-containing gas depending on the progress of the methane production reaction.

[0068] The above describes the biomass processing device of the present invention based on several embodiments, but the present invention is not limited to the configurations described in the above embodiments, and the configuration can be changed as appropriate within the scope of the spirit of the invention, such as by appropriately combining the configurations described in each embodiment.

[0069] (Another embodiment 1) 7A and 7B are diagrams showing other examples of the diffusion state of the hydrogen-containing gas. Fig. 7A is a diagram showing a state in which a relatively large amount of the hydrogen-containing gas is diffused in an intermediate area between the upstream and downstream portions in the biomass flow direction. Fig. 7B is a diagram showing a state in which the amount of the hydrogen-containing gas diffused is gradually reduced from the upstream portion to the downstream portion in the biomass flow direction.

[0070] In the gas supply unit 7 shown in Figures 7(a) and (b), for example, a diffuser pipe or the like is arranged in the aeration unit 60, and the aeration pipe or the like is connected by piping, and control valves or the like are provided at key points in the piping so that the position and amount of diffusion of the hydrogen-containing gas into the fermentation liquid FL2 can be freely changed.

[0071] 7(a) and 7(b), the position and amount of hydrogen-containing gas diffused into the fermentation liquid FL2 can be freely changed. This makes it possible, for example, to diffuse a relatively large amount of hydrogen-containing gas into the area between the upstream and downstream portions in the biomass flow direction as shown in Fig. 7(a), or to gradually decrease the amount of hydrogen-containing gas diffused from the upstream portion toward the downstream portion in the biomass flow direction as shown in Fig. 7(b).

[0072] (Alternative embodiment 2) In the biomass processing apparatus 1E of the fifth embodiment shown in FIG. 5, the biogas BG in the first compartment chamber 71, the second compartment chamber 72, and the third compartment chamber 73 is returned to essentially the same compartment chamber (the first compartment chamber 71, the second compartment chamber 72, and the third compartment chamber 73) via the first circulation circuit 90a, the second circulation circuit 90b, and the third circulation circuit 90c. However, the present invention is not limited to this. For example, by changing the return position of the biogas BG to the aeration unit 60 via the first return pipe 91a in the first circulation circuit 90a, the biogas BG may be introduced from the first compartment chamber 71 to the second compartment chamber 72 or the third compartment chamber 73 via the first return pipe 91a, the aeration unit 60, and the fermentation liquid FL2. Furthermore, by changing the return position of the biogas BG to the aeration unit 60 via the second return pipe 91b in the second circulation circuit 90b, the biogas BG may be introduced from the second compartment chamber 72 to the first compartment chamber 71 or the third compartment chamber 73 via the second return pipe 91b, the aeration unit 60, and the fermentation liquid FL2. Furthermore, by changing the return position of the biogas BG to the aeration section 60 by the third return pipe 91c in the third circulation circuit 90c, the biogas BG may be introduced from the third compartment 73 through the third return pipe 91c, the aeration section 60, and the fermentation liquid FL2 into the first compartment 71 or the second compartment 72.

[0073] (Alternative embodiment 3) In the third to sixth embodiments, the present invention is applied to horizontal plug-flow biomass treatment devices 1C to 1F. However, the present invention is not limited to this, and can also be applied to vertical plug-flow biomass treatment devices. In this case, the methane fermentation tank has, for example, a vertically elongated cylindrical body with a vertical axis, an upper end face that closes the upper end of the body, and a lower end face that closes the lower end of the body. The biomass is fermented while flowing from a biomass supply port provided in the upper end face toward a digestion liquid discharge port provided in the lower end face. Note that if the organic waste introduced into the methane fermentation tank is pushed out of the digestion liquid discharge port by gravity, a power source for pumping the biomass into the tank can be omitted. [Industrial Applicability]

[0074] The biomass treatment device of the present invention can be used, for example, to produce fuel for city gas, gas engines, and the like. [Explanation of symbols]

[0075] 1A~1F Biomass processing equipment 2 Two-stage fermenter 7 Gas supply section 9 Reuse equipment 11 Acid Fermenter 12,42 Methane fermentation tank 40,65 circulation circuit 71~73 compartments 81 Hydrogen Supply Area 82 Hydrogen non-supply area 90a~90c circulation circuit

Claims

1. A biomass treatment device that ferments biomass to produce biogas, A two-stage fermenter that stores a fermentation liquid obtained by fermenting the biomass; a gas supply unit that supplies a hydrogen-containing gas to the fermenter; A biomass treatment device comprising:

2. The two-stage fermenter comprises an acid fermenter into which the biomass is introduced and a methane fermenter provided downstream of the acid fermenter, The biomass treatment apparatus according to claim 1 , wherein the gas supply unit supplies the hydrogen-containing gas to the methane fermentation tank.

3. The biomass treatment apparatus according to claim 2 , wherein the methane fermentation tank has a hydrogen supply area to which the hydrogen-containing gas is supplied.

4. The biomass treatment apparatus according to claim 2, further comprising a circulation circuit for returning a part of the biogas produced in the methane fermentation tank to the gas supply unit.

5. The methane fermenter is a plug flow type fermenter in which the biomass is fermented while being flowed, The biomass treatment apparatus according to claim 4, wherein a plurality of compartments for storing the biogas produced in the methane fermentation tank are formed in a state of being in communication with each other along the direction of flow of the biomass.

6. The biomass treatment device according to any one of claims 2 to 5, further comprising a recycling device that filters the fermented liquid from the methane fermentation tank, discharges the filtrate, and returns the filtered material to the methane fermentation tank.

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