Biogas direct desulfurization device

Abstract

To provide a biogas direct desulfurization device which not only efficiently inhibits activity of a sulfate-reducing bacterium while reducing adhesion of a precipitation onto an upper wall surface of a methane fermentation tank and preventing an influence on a methane bacterium but also attains reduction in hydrogen sulfide concentration in biogas by chemical reaction between oxygen dissolved into liquid and hydrogen sulfide.SOLUTION: A biogas direct desulfurization device 1 according to the present invention is composed of a fermentation tank 2 (methane fermentation tank) including: a resource introduction part 4 for introducing a biomass resource from a pretreatment device F into which the biomass resource is charged; an air introduction part 6 for introducing air (a); a digestive liquid derivation part 12 for deriving digestive liquid (d); and a gas derivation part 15 for deriving biogas (b). The fermentation tank 2 has a headspace (h) not charged with fermentation liquid (c) at an upper part. The air introduction part 6 is configured so that the air (a) is introduced into the liquid in the vicinity of a liquid surface not exceeding a liquid surface (w) of the fermentation liquid (c) in the fermentation tank 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a biogas direct desulfurization device that efficiently removes hydrogen sulfide contained in biogas generated in a methane fermentation process. [Background technology]

[0002] Organic waste (also called waste biomass) is primarily processed through methane fermentation to produce biogas, whose main component is methane. Biogas contains 55% to 85% methane, 15% to 45% carbon dioxide, and 400 ppm to 6,000 ppm hydrogen sulfide as its main components, although the concentration varies depending on the type of waste biomass being fermented and the method of methane fermentation.

[0003] The biogas produced can be used as fuel for boilers and gas engines, and when methane is converted into carbon dioxide through use as fuel, the global warming potential (GWP) is said to be reduced to 1 / 25.

[0004] The hydrogen sulfide contained in biogas is highly corrosive to metals and toxic, so it must be removed (desulfurized). There are three types of desulfurization equipment: dry, wet, and biological.

[0005] Generally, dry desulfurization uses an iron oxide-based desulfurization agent that selectively reacts with hydrogen sulfide. The desulfurization agent is shaped to have a large contact surface with the gas, and biogas is desulfurized by passing it through a reactor filled with this agent. However, it is costly to replace the desulfurization agent periodically and to regenerate any that have passed through.

[0006] In addition, wet desulfurization involves directing biogas to the bottom of a gas-liquid contact tower, where it comes into countercurrent contact with NaOH liquid and hydrogen sulfide is absorbed by the NaOH liquid as Na2S, making it necessary to replace or replenish the NaOH solution.

[0007] Furthermore, biological desulfurization involves supplying water, hydrogen sulfide, and oxygen to sulfur-oxidizing bacteria, which convert the hydrogen sulfide primarily into sulfate ions. Conventional technology involves biologically oxidizing hydrogen sulfide using sulfur-oxidizing bacteria activated by blowing in air, which can be used to recover sulfate ions. However, it is generally difficult to remove hydrogen sulfide to low concentrations, and so depending on how the biogas is used, it may be necessary to install a dry desulfurization device in a downstream stage.

[0008] In addition, the amount of air required for biological desulfurization is large, at 5 to 10% of the biogas volume, which can cause problems such as a decrease in the apparent calorific value of the biogas and misfires in the boiler. Furthermore, if a fixed-bed system is used in the biological desulfurization method, a filler material or the like is required to fix the participating bacterial group.

[0009] As such, while various desulfurization methods are currently in use, Germany is a leading country in greenhouse gas countermeasures. For example, in 1982 it was discovered that sulfur-oxidizing bacteria live in the digestive sludge liquid from methane fermentation and that these bacteria convert hydrogen sulfide into sulfur or sulfides. One example of prior art implementation around 2000 was the direct gas engine power generation using biogas produced in a methane fermentation device.

[0010] To reduce the hydrogen sulfide in the biogas, a desulfurization method was used in which 3-5% of the biogas volume of air was supplied to the top of the methane fermentation tank, reducing the hydrogen sulfide concentration to 200-100 ppm.

[0011] Thus, although biological desulfurization has been proven to be effective, there is a limit to how much hydrogen sulfide can be removed to low concentrations. Furthermore, because a large amount of sulfur, the main component, precipitates as crystals on the upper walls of the methane fermentation tank, it was necessary to shut down the equipment and carry out extensive cleaning work to remove the precipitates on the upper walls in order to avoid the risk of clogging the piping.

[0012] In response to this, for example, Patent Document 1 discloses a method of suppressing hydrogen sulfide production while maintaining methane fermentation by intentionally supplying a small amount of oxygen into a methane fermentation tank inhabited by both obligate anaerobic methanogens and sulfate-reducing bacteria, thereby suppressing the sulfate-reducing bacteria that do not form flocs, while maintaining an environment in which the floc-forming methanogens can remain. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] JP 2003-136089 A Summary of the Invention [Problem to be solved by the invention]

[0014] It is true that the technology disclosed in Patent Document 1 is excellent in that it can suppress the production of hydrogen sulfide while maintaining methane fermentation. However, oxygen, which is toxic to obligate anaerobic bacteria, is supplied from the bottom side of the methane fermentation tank. Although the technology aims to kill sulfate-reducing bacteria, which are the cause of hydrogen sulfide by-production at the methane fermentation stage and which do not form flocs, the exteriors of many methanogens that form flocs as the oxygen rises in the form of bubbles are also sterilized, resulting in a problem in that not only is the amount of biogas produced reduced, but the recovery and proliferation of the remaining bacteria is also significantly affected.

[0015] The present invention has been made in consideration of the above circumstances, and has an object to provide a biogas direct desulfurization device that not only reduces the adhesion of precipitates to the upper wall surface of a methane fermentation tank and efficiently suppresses the activity of sulfate-reducing bacteria while suppressing the effects on methane bacteria, but also reduces the concentration of hydrogen sulfide in the biogas through a chemical reaction between oxygen dissolved in the liquid and hydrogen sulfide. [Means for solving the problem]

[0016] In order to achieve the above object, the present invention provides the following:

[0017] The invention of claim 1 provides a biogas direct desulfurization device comprising a fermentation tank equipped with a resource introduction section for introducing the biomass resource from a pretreatment device into which the biomass resource is filled, an air introduction section for introducing air, a digestive liquid discharge section for discharging digestive liquid, and a gas discharge section for discharging biogas, wherein the fermentation tank has a head space at the top that is not filled with fermentation liquid, and the air introduction section is configured to introduce air into the liquid in the fermentation tank near the liquid level but not exceeding the liquid level of the fermentation liquid.

[0018] The invention according to claim 2 aims to provide a biogas direct desulfurization device as described in claim 1, characterized in that it is provided with a circulation section that circulates a portion of the biogas discharged from the fermentation tank back to the fermentation tank.

[0019] The invention according to claim 3 aims to provide the biogas direct desulfurization apparatus described in claim 2, characterized in that the air inlet section in the liquid has a tubular inlet pipe, and the inlet pipe has an air outlet arranged approximately horizontally and / or approximately vertically.

[0020] The invention according to claim 4 provides the biogas direct desulfurization apparatus according to claim 3, characterized in that the inlet pipe has the air outlet formed on a peripheral side surface thereof.

[0021] The invention according to claim 5 provides the biogas direct desulfurization apparatus according to claim 4, characterized in that the inlet pipe is formed in a substantially circular ring shape and is disposed with its axial direction vertical inside the fermenter. Effect of the Invention

[0022] According to the invention of claim 1, the fermentation tank includes a resource introduction section for introducing biomass resources from a pretreatment device filled with biomass resources, an air introduction section for introducing air, a digestive liquid discharge section for discharging digestive liquid, and a gas discharge section for discharging biogas. The fermentation tank has a head space at the top that is not filled with fermentation liquid, and the air introduction section is configured to introduce air into the liquid near the liquid level that does not exceed the liquid level of the fermentation liquid in the fermentation tank. This reduces adhesion of precipitates to the upper wall surface of the methane fermentation tank and efficiently kills sulfate-reducing bacteria while suppressing the effect on methane bacteria, thereby reducing the hydrogen sulfide concentration in the biogas.

[0023] According to the invention described in claim 2, by providing a circulation section that circulates a portion of the biogas discharged from the fermenter back to the fermenter, the hydrogen sulfide concentration in the biogas can be efficiently reduced to an even lower concentration.

[0024] According to the invention described in claim 3, the air introduction section in the liquid has a tubular introduction pipe, and the introduction pipe has an air exhaust port arranged approximately horizontally and / or approximately vertically, making it possible to easily introduce air into the liquid near the liquid level but not exceeding the liquid level of the fermentation liquid.

[0025] According to the invention described in claim 4, the introduction pipe has an air exhaust port formed on the peripheral side, which makes it possible to easily suppress the impact on methane bacteria when air is introduced into the liquid near the liquid level but not above the liquid level of the fermentation liquid.

[0026] According to the invention described in claim 5, the introduction pipe is formed in an approximately circular ring shape and is arranged with its axial direction vertically inside the fermentation tank, so that the effect on the methane bacteria can be efficiently and easily suppressed when air is introduced into the liquid near the liquid level but not above the liquid level of the fermentation liquid. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic diagram of a first embodiment of a biogas direct desulfurization apparatus according to the present embodiment. [Diagram 2]14(a), (b), and (c) are explanatory diagrams of an introduction pipe that delivers air horizontally. [Diagram 3] 14(a), (b), and (c) are explanatory diagrams of an introduction pipe that delivers air in a vertical direction. [Figure 4] FIG. 2 is a top perspective view of the first annular inlet pipe; [Diagram 5] (a) is a plan view of the first annular inlet pipe, and (b) is a front perspective view. [Figure 6] FIG. 13 is a top perspective view of a second annular inlet pipe disposed immediately below a first annular inlet pipe. [Figure 7] 7(a) is a plan view of FIG. 6, and (b) is a front perspective view thereof. [Figure 8] FIG. 4A is a schematic diagram of a second embodiment of a biogas direct desulfurization apparatus according to the present embodiment, and FIG. 4B is a conceptual diagram of a circulation section. [Figure 9] 1 is a graph showing the behavior of the generated gas amount, hydrogen sulfide concentration, and pH during a desulfurization test with an air introduction rate of 5%. [Figure 10] 1 is a graph showing the behavior of organic acids and TOC during a desulfurization test with an air introduction rate of 5%. [Figure 11] 1 is a graph showing the behavior of hydrogen sulfide concentration during an air oxidation test with different air introduction amounts. [Figure 12] 1 is a graph showing the behavior of hydrogen sulfide concentration during a long-term desulfurization test at an air introduction rate of 5%. [Figure 13] 1 is a graph showing the behavior of organic acids and TOC during a long-term desulfurization test with an air intake rate of 5%. [Figure 14] 1 is a graph showing the behavior of hydrogen sulfide concentration during a long-term desulfurization test at an air introduction rate of 3%. [Figure 15] 1 is a graph showing the behavior of hydrogen sulfide concentration during a gas circulation test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The gist of the biogas direct desulfurization apparatus according to the present invention is a fermentation tank equipped with a resource introduction section for introducing biomass resources from a pretreatment device filled with biomass resources, an air introduction section for introducing air, a digestive liquid outlet section for discharging digestive liquid, and a gas outlet section for discharging biogas, the fermentation tank having a head space at the top where the fermentation liquid is not filled, and the air introduction section configured to introduce air into the liquid near the liquid level that does not exceed the liquid level of the fermentation liquid in the fermentation tank. That is, the present invention aims to provide a biogas direct desulfurization apparatus that not only reduces adhesion of precipitates to the upper wall surface of the methane fermentation tank and efficiently suppresses the activity of sulfate-reducing bacteria while suppressing the effect on methane bacteria, but also reduces the concentration of hydrogen sulfide in the biogas by a chemical reaction between oxygen dissolved in the liquid and hydrogen sulfide.

[0029] Hereinafter, an embodiment of a biogas direct desulfurization apparatus 1,100 according to the present invention will be described with reference to the drawings. In addition, in this description, the same structures and parts are generally given the same reference numerals, and only one of them will be described, and the description of the other may be omitted as appropriate.

[0030] In addition, the "biogas direct desulfurization apparatus" of the present invention is a device in which the "fermenter" in this description functions as a biogas direct desulfurization apparatus as it is, and the two are substantially synonymous.

[0031] [First embodiment] As shown in FIG. 1 , a desulfurization apparatus 1 according to a first embodiment of the present invention comprises a fermenter 2 (methane fermenter) equipped with a resource introduction section 4 for introducing biomass resources from a pretreatment device F into which biomass resources are filled, an air introduction section 6 for introducing air a, a digestive liquid discharge section 12 for discharging digestive liquid d, and a gas discharge section 15 for discharging biogas b, and the fermenter 2 has a head space h at its upper portion which is not filled with fermentation liquid c, and the air introduction section 6 is configured so that air a is introduced into the liquid near the liquid level not exceeding the liquid level w of the fermentation liquid c in the fermenter 2.

[0032] The fermentation tank 2 is a device that processes organic waste, which is a biomass resource consisting of sludge, through methane fermentation to generate biogas whose main component is methane, and can be an anaerobic wastewater treatment device such as an IC (Internal Circulation) reactor.

[0033] Biomass resources include livestock manure, food waste, shochu lees, etc., which are treated as sludge using a pretreatment device F or the like to make them ready for methane fermentation, and then sent to the fermentation tank 2 via a resource introduction section 4 consisting of piping, valves, and pumps. The biogas b generated in the fermentation tank 2 is stored in an external gas recovery facility R or the like via a gas outlet section 15 consisting of piping.

[0034] The fermenter 2 is a so-called airtight container of a size according to the scale of the facility, and is generally of a substantially cylindrical shape, which is also the case with the fermenter 2 according to this embodiment.

[0035] The hydrogen sulfide concentration in the biogas generated by methane fermentation of sweet potato shochu lees or barley shochu lees, which are by-produced in the shochu production process, in the fermenter 2 is 2,200 to 2,400 ppm for sweet potato shochu lees and 2,600 to 2,800 ppm for barley shochu lees.

[0036] The fermentation tank 2 according to this embodiment used in the desulfurization test described below is a 10 L small-scale culture apparatus (MD-1000 model, capacity 10 L, effective tank height 32 cm, manufactured by Marubishi Bioengineering Co., Ltd.), and the test is carried out by filling it with 8 L of actual volume of fermentation liquid c to ensure a head space h.

[0037] The fermentation tank 2 also has an agitation section 30 equipped with fins connected to the rotating shaft of a motor 31, and is equipped with an air inlet section 6 consisting of an air cylinder 7, an air flow regulator 8 and piping that supplies air a to the inside of the fermentation tank 2, as well as a digestive liquid discharge section 12 consisting of piping that discharges the recovered sulfur-containing digestive liquid d to the outside.

[0038] The air introduction section 6 in the liquid near the liquid level not exceeding the liquid level w of the fermentation liquid c has a tubular introduction pipe 9, and the introduction pipe 9 forms an air exhaust port 10 in the liquid approximately horizontally as shown in Figures 2(a) and (b) and / or approximately vertically as shown in Figures 3(a) and (b).

[0039] The air exhaust port 10 of the introduction pipe 9 is formed so as to blow air substantially horizontally from the peripheral side surface as shown in FIG. 2(b), or so as to blow air a substantially vertically upward from the peripheral side surface as shown in FIG. 3(b). It is preferable that the air exhaust port 10 is positioned in the liquid near the liquid level not exceeding the liquid level w of the fermentation liquid c, particularly within 0 cm to 3 cm below the liquid level.

[0040] In other words, it is desirable to configure the device so that air a does not come into contact with the fermentation liquid c other than in the vicinity of the liquid surface as much as possible. Furthermore, if we generalize the range from 0 cm of the liquid surface to 3 cm below the liquid surface from this desulfurization test, it is desirable to position the air exhaust port 10 of the introduction pipe 9 within the range from the liquid surface w, which is 0% deep, to 11.7% of the depth of the fermentation liquid c filled in the fermenter 2.

[0041] The number of air exhaust ports 10 is not limited to that in this embodiment, and may be, for example, an introduction pipe 9 having two air exhaust ports 10 as shown in FIG. 2(c) or FIG. 3(c).

[0042] Alternatively, the introduction pipe 9 may be formed in a substantially circular ring shape as a first circular introduction pipe 9A as shown in Figures 4, 5(a) and (b), and four air exhaust ports 10 may be drilled in the peripheral side surface facing substantially vertically upward, so that the axis of the ring is arranged vertically inside the fermentation tank 2 so as to send air a toward the liquid surface directly above.

[0043] Furthermore, as shown in Figures 6, 7(a) and (b), the introduction pipe 9 may be configured so that a second circular ring introduction pipe 9B, which is approximately annular in shape and has a smaller diameter than the outer diameter of the first circular ring introduction pipe 9A and has four air exhaust ports 10 drilled approximately vertically upward on its circumferential side directly below the first circular ring introduction pipe 9A, and which sends out air a toward the liquid surface directly above, is concentrically arranged with the first circular ring introduction pipe 9A inside the fermenter 2 with the axis of the ring vertical.

[0044] In addition, the number of air exhaust ports 10 in the first annular inlet pipe 9A and the second annular inlet pipe 9B is not limited to that in this embodiment, and the air a sent to the first annular inlet pipe 9A and the second annular inlet pipe 9B may be separated immediately before being sent out from the same route, or may be sent out via a different route from the beginning.

[0045] These various introduction pipes 9 are fixed to the inner wall of the fermentation tank 2, or are formed so that they can slide vertically and be fixed at any position, so that the air exhaust port 10 is located in the liquid near the liquid level not exceeding the liquid level w of the fermentation liquid c.

[0046] Furthermore, when the introduction pipe 9 is formed to be freely slidable up and down, by forming a float so that the air exhaust port 10 of the introduction pipe 9 is positioned in the liquid near the liquid level but not exceeding the liquid level w of the fermentation liquid c, the air exhaust port 10 can be stably positioned relative to the liquid level w even if the height of the liquid level w changes, and by forming the weight of the introduction pipe 9 to be changeable with a weight or the like, it becomes possible to finely adjust the depth relative to the liquid level w.

[0047] Next, a biogas direct desulfurization apparatus 100 according to a second embodiment of the present invention will be described in detail with reference to the drawings.

[0048] [Second embodiment] As shown in FIG. 8(a), the biogas direct desulfurization apparatus 100 according to the second embodiment includes, in addition to the configuration of the biogas direct desulfurization apparatus 1 according to the first embodiment, a circulation section 120 that circulates a portion of the biogas b discharged from the fermenter 2 back to the fermenter 2.

[0049] Specifically, the biogas b discharged from the fermenter 2 via the gas discharge section 15 is stored in a gas recovery facility R or the like, but a portion of the biogas b is circulated to the fermenter 2 by the circulation section 120.

[0050] The circulation section 120 is composed of an air pump 121 connected to the gas recovery equipment R or the like via an air piping in order to guide a portion of the biogas b stored in the gas recovery equipment R or the like into the fermentation liquid c in the fermenter 2, a flow meter 122 having an adjustment valve for adjusting the flow rate of the portion of the biogas b discharged from the air pump 121 and discharging it, and a re-introduction pipe 123 which is a piping for supplying the biogas b into the fermentation liquid c in the fermenter 2.

[0051] The configuration of the circulation section 120 is not limited to this embodiment, and may be any configuration, including a configuration in which a portion of the biogas b generated in the fermenter 2 can be sent back into the fermentation liquid c in the fermenter 2, as conceptually shown in Figure 8(b).

[0052] Next, a desulfurization test using the biogas direct desulfurization apparatus 1 according to the first embodiment and the biogas direct desulfurization apparatus 100 according to the second embodiment will be described in detail with reference to the drawings.

[0053] In the desulfurization tests, first, an experimental facility was constructed that reproduced the configuration of the biogas direct desulfurization apparatus 1 according to the first embodiment in FIG. 1 , and methane fermentation was performed. Tests were then conducted to confirm the concentration of hydrogen sulfide contained in the generated biogas and the effect of introducing air.

[0054] In addition, before introducing air, the following preparatory operation was carried out to stabilize the amount of biogas and the hydrogen sulfide concentration in the gas.

[0055] Initially, 8 L of anaerobic sludge was added to the fermentation tank 2, and the biomass resource added was sweet potato shochu lees. This biomass resource was not introduced through the pretreatment device F, but through the resource introduction section 4 at the top of the fermentation tank 2 (not shown).

[0056] In addition, a certain amount of liquid in the tank was withdrawn once a day together with sludge through the upper inlet using the so-called draw and fill method, and the same amount of sweet potato shochu lees was added.

[0057] In addition, the fermentation tank 2 was operated at a temperature of 55°C and an agitation speed of the agitation unit 30 of 80 rpm, and the total organic carbon (hereinafter referred to as "TOC"), amount of acetic acid, and amount of propionic acid in the liquid withdrawn from the tank were measured as indicators of whether the fermentation was proceeding smoothly.

[0058] In the methane fermentation, in order to gradually increase the processing volume, i.e., the organic load, while increasing the number of microorganisms that process the organic matter, the amount of volatile solids (hereinafter referred to as "VTS") contained in the sweet potato shochu lees was measured, and the organic load was gradually increased to 2, 4, 6, and 8 g-VTS / L of the liquid volume in the tank.

[0059] In addition, since it is known that the addition of trace metals promotes methane fermentation, NiCl2 and CoCl2 were added to the soil so that the Ni and Co concentrations were 0.05 mg / g-VTS, respectively, depending on the organic matter load.

[0060] In addition, since high concentrations of hydrogen sulfide are known to inhibit methane fermentation, 90 mg / L of FeCl2 was added to the sweet potato shochu lees at the same time as adding them in order to reduce the amount of hydrogen sulfide in the tank liquid.

[0061] Furthermore, when the daily organic load reached 8g-VTS / L, the amount of biogas generated per day was 5,000-7,000mL relative to the liquid in the tank, the hydrogen sulfide concentration in the gas was 1,000-1,200ppm, the TOC was 1,500-2,500mg / L, and the amounts of acetic acid and propionic acid were each less than 100mg / L. The pH was stable at 7.5-8.5, so a desulfurization test was started by introducing air as follows.

[0062] For air introduction, in addition to the above-mentioned test configuration and conditions, an air introduction section 6 was provided in which an air introduction pipe 9 shown in FIG. 3(a) was led from an air cylinder 7 through an air flow regulator 8 from the top of the fermenter 2 and placed below the surface of the fermentation liquid c.

[0063] [Example 1] A ball filter with a pore size of 5 to 15 μm was attached to the tip of the inlet pipe 9 of the air inlet section 6, and this was placed 3 cm below the liquid surface. Air was passed through the filter at a rate of 3.5% of the amount of biogas generated per day for five consecutive days. The results are shown in Figures 9 and 10.

[0064] After the third day of aeration, the hydrogen sulfide concentration in the gas was reduced by approximately 70%, as shown in Figure 9. At the same time, however, the propionic acid concentration in the sludge increased, as shown in Figure 10. This indicates that the accumulation of organic acids such as acetic acid and propionic acid, which are intermediate decomposition products of organic matter in anaerobic fermentation, slows down methane fermentation, as it is known that excessive accumulation of organic acids inhibits the activity of methane bacteria.

[0065] These results show that when a ball filter is used to increase the efficiency of contact between sludge and air, the introduction of air can be confirmed to reduce hydrogen sulfide in the gas, but the presence of excessive air in anaerobic fermentation has a negative effect on microorganisms.

[0066] [Example 2] In order to significantly reduce the contact efficiency between the sludge and the air, the ball filter was changed to an inlet pipe 9 of a single-pipe air inlet section 6 shown in Figure 3(a) with an opening diameter at the tip of 0.7 mm (same below), as in Example 1, and this was placed 3 cm below the liquid surface. Air was aerated at levels of 0%, 3%, 4%, and 5% of the amount of biogas generated per day for 4 consecutive days. The results are shown in Figure 11.

[0067] In all test areas, the hydrogen sulfide concentration in the gas was reduced by approximately 80% after three days of air introduction, and no increase in the organic acid concentration was observed. In addition, although not shown in the figure, the amount of gas generated, pH, and TOC values ​​were stable during this period.

[0068] These results confirmed that it was possible to reduce the amount of hydrogen sulfide in the gas without affecting fermentation by introducing air using a single pipe below the surface of the fermentation liquid (above the sludge). Figures 12 and 13 show the results of aeration with 5% air relative to the amount of biogas generated each day for two consecutive weeks.

[0069] As shown in Figure 12, the hydrogen sulfide in the gas continued to be reduced by approximately 80%, and as shown in Figure 13, no increase in the organic acid concentration or decrease in the amount of gas generated was observed, confirming that good results can be maintained even with long-term air introduction.

[0070] [Example 3] Next, the single pipe used in Example 2 was installed at a liquid level of 0 cm, and at the head space of the fermenter. The results of aeration with 3% of the amount of air generated per day for five consecutive days are shown in FIG. 14.

[0071] Regardless of the conditions, the hydrogen sulfide concentration in the gas was reduced by approximately 80%. However, in the test of introducing air into the headspace, yellow deposits composed mainly of sulfur were observed on the walls of the headspace. Since this precipitated sulfur crystallized and could cause blockages in the piping, it was confirmed that air should be introduced from 0 cm to 3 cm below the liquid surface, rather than into the headspace.

[0072] Furthermore, based on the results of the multiple tests mentioned above, it can be said that the most suitable configuration for introducing air into sludge between the liquid level of 0 cm and 3 cm below the liquid level is one in which the air exhaust port is directed vertically upward toward the liquid level, rather than one in which the opening of the single pipe is directed downward.

[0073] [Example 4] Next, methane fermentation was carried out in an experimental facility reproduced according to the configuration of FIG. 8(a), which shows a biogas direct desulfurization apparatus 100 according to a second embodiment, in which a circulation section 120 for circulating biogas has been added to the above-mentioned test configuration, and a test was conducted to confirm the concentration of hydrogen sulfide contained in the generated biogas and the effect of introducing air.

[0074] The preparation operations up to the start of the air introduction test are similar to those described above using the biogas direct desulfurization apparatus 1 according to the first embodiment, and therefore a description thereof will be omitted.

[0075] In this test, 3% of the amount of biogas generated each day was aerated for 12 consecutive days, and 3% of the generated biogas was introduced back into the fermenter 15 cm below the liquid level through the circulation piping. Figure 15 shows the results of simultaneous air introduction and biogas circulation.

[0076] By simultaneously introducing air and circulating biogas, the hydrogen sulfide concentration in the gas was reduced by approximately 95%, as shown in Figure 15, confirming that biogas circulation can improve desulfurization efficiency.

[0077] As described above, the biogas direct desulfurization apparatus 1, (100) according to this embodiment includes the fermenter 2, which is equipped with the resource introduction section 4 that introduces biomass resources from the pretreatment device F that is filled with biomass resources, the air introduction section 6 that introduces air a, the digestive liquid discharge section 12 that discharges digestive liquid d, and the gas discharge section 15 that discharges biogas b. The fermenter 2 has a head space h at its upper portion that is not filled with fermentation liquid c, and the air introduction section 6 is configured so that air a is introduced into the liquid near the liquid level that does not exceed the liquid level w of the fermentation liquid c in the fermenter 2. As a result, adhesion of precipitates to the upper wall surface of the methane fermentation tank can be reduced, and the sulfate-reducing bacteria can be efficiently killed while suppressing the effect on methane bacteria, thereby reducing the hydrogen sulfide concentration in the biogas.

[0078] Furthermore, by providing the circulation unit 120 that circulates a portion of the biogas b discharged from the fermenter 2 to the fermenter 2, the hydrogen sulfide concentration in the biogas can be efficiently reduced to a lower concentration.

[0079] In addition, the air introduction section 6 in the liquid has a tubular introduction pipe 9, and the introduction pipe 9 has an air exhaust port 10 arranged approximately horizontally and / or approximately vertically, making it possible to easily introduce air into the liquid near the liquid level but not exceeding the liquid level w of the fermentation liquid c.

[0080] Furthermore, since the introduction pipe 9 has an air exhaust port 10 formed on the peripheral side, the effect on the methane bacteria can be easily suppressed when air is introduced into the liquid near the liquid level not exceeding the liquid level w of the fermentation liquid c.

[0081] Furthermore, since the introduction pipe 9 is formed in an approximately circular ring shape and is arranged with its axis directed vertically inside the fermentation tank 2, the effect on the methane bacteria can be efficiently and easily suppressed when air is introduced into the liquid near the liquid level but not exceeding the liquid level w of the fermentation liquid c.

[0082] Although a preferred embodiment of the biogas direct desulfurization apparatus 1,100 according to this embodiment of the present invention has been described above, the present invention is not limited to a specific embodiment, and various modifications and variations are possible. [Explanation of symbols]

[0083] Air b. Biogas c Fermentation liquid d Digestive fluid F Pretreatment device h Headspace R Gas recovery equipment w Liquid level 1 Biogas direct desulfurization device (first embodiment) 2 Fermentation tank 4 Resource Introduction Section 6 Air intake section 9 Introductory tube 10 Air exhaust port 12 Digestive fluid outlet 100 Biogas direct desulfurization device (second embodiment) 120 Circulation section

Claims

1. The fermentation tank includes a resource introduction section for introducing a biomass resource from a pretreatment device filled with the biomass resource, an air introduction section for introducing air, a digestive liquid discharge section for discharging a digestive liquid, and a gas discharge section for discharging a biogas, The fermenter has a head space at the top that is not filled with fermentation liquid, A biogas direct desulfurization apparatus, characterized in that the air introduction section is configured to introduce air into the liquid in the fermentation tank near the liquid level but not exceeding the liquid level.

2. The biogas direct desulfurization apparatus according to claim 1, further comprising a circulation unit that circulates a portion of the biogas discharged from the fermenter to the fermenter.

3. The biogas direct desulfurization apparatus according to claim 2, characterized in that the air inlet portion in the liquid has a tubular inlet pipe, and the inlet pipe has an air outlet disposed substantially horizontally and / or substantially vertically.

4. The biogas direct desulfurization apparatus according to claim 3 , wherein the inlet pipe has the air outlet formed on a peripheral side surface thereof.

5. 5. The biogas direct desulfurization apparatus according to claim 4, wherein the inlet pipe is formed in a substantially circular ring shape and is disposed inside the fermenter with its axis extending vertically.

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