Biogas desulfurizer

Abstract

To provide a biogas desulfurizer that enables easy operation management, allows desulfurization treatment in a short period, has a simple and inexpensive structure, and achieves high-precision desulfurization.SOLUTION: A biogas desulfurizer according to the present invention comprises: a fermentation tank 2 for generating biogas; and a reaction tank 4 filled with a liquid catalyst, the reaction tank 4 being provided with an air introduction part 5 for introducing air, a gas introduction part 6 for introducing biogas from the fermentation tank 2, a purified gas derivation part 7 for deriving purified biogas, and a first pH control unit 8 for controlling pH of the liquid catalyst.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a biogas 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] In addition, in a methane fermentation tank equipped with a draft tube, air was supplied into the draft tube to oxidize hydrogen sulfide with air, but the hydrogen sulfide concentration was still reduced to around 200 to 100 ppm.

[0012] In contrast, the allowable concentration of hydrogen sulfide in gas engines and boilers in Japan is set at approximately 10 ppm, and therefore there is a demand for the development of technology that can remove hydrogen sulfide at even lower concentrations. For example, Patent Document 1 discloses a method in which a trace amount of oxygen is deliberately supplied to a methane fermentation tank inhabited by both methanogens and sulfate-reducing bacteria, which are obligate anaerobes, to suppress the sulfate-reducing bacteria that do not form flocs, while maintaining an environment in which the floc-forming methanogens can remain, thereby suppressing the production of hydrogen sulfide while maintaining methane fermentation.

[0013] Furthermore, the technology disclosed in Patent Document 2 involves supplying a trace amount of air to a methane digestion liquid and bringing the culture liquid in which photosynthetic bacteria have been cultivated into gas-liquid contact with biogas; when gas-liquid contact is brought between a methane digestion liquid and only a trace amount of air, hydrogen sulfide can only be reduced to 120 ppm on the 19th day of digestion, and to 70 ppm even on the 40th day. In contrast, this technology is disclosed as a method capable of desulfurizing hydrogen sulfide to a low concentration (0 ppm (decimal points unknown)) (however, this is an example of a batch-type methane fermentation).

[0014] Furthermore, the technology related to Patent Document 3 does not involve a method of adding trace amounts of air to biogas produced by methane fermentation, but rather a method of directly supplying the oxygen required for biological desulfurization to a liquid catalyst, so that the methane concentration in the biogas is not diluted even when air is used as the oxygen source, and the liquid catalyst that is brought into gas-liquid contact with the biogas is supplied with oxygen in advance by micro-bubbling in a separate tank, and the biogas comes into contact with the liquid catalyst that has absorbed oxygen in a packed tower that is the main body of the biological desulfurization, allowing continuous biological desulfurization on the carrier surface, and further discloses a desulfurization method in which carbon dioxide in the biogas can be absorbed as carbon dioxide by similar gas-liquid contact with water. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] JP 2003-136089 A [Patent Document 2] JP 2004-043555 A [Patent Document 3] JP 2010-024269 A Summary of the Invention [Problem to be solved by the invention]

[0016] 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, focusing on the fact that hydrogen sulfide is by-produced at the methane fermentation stage due to the action of coexisting sulfate-reducing bacteria and that these bacteria have the property of not forming flocs, this method kills the sulfate-reducing bacteria with oxygen, which is toxic to obligate anaerobes, while sterilizing the outer methanogens that form flocs, but leaving the inner methanogens to remain. This method has the problem that it requires difficult operational management to suppress the sulfate-reducing bacteria while checking the sterilization by oxygen and the recovery and proliferation of the remaining bacteria.

[0017] In addition, the technology disclosed in Patent Document 2 is a method that utilizes the digestive liquid from methane fermentation to remove hydrogen sulfide, and is excellent in that it can desulfurize the hydrogen sulfide to a low concentration. However, it has a problem in that the fermentation tank is a single-stage tank (the material to be treated is placed in the fermentation tank and fermentation is completed in about one to two months), and desulfurization is required for a long period of time.

[0018] Furthermore, the technology disclosed in Patent Document 3 is excellent in that the air supply does not cause a decrease in the methane concentration in the biogas, and moreover, the carbon dioxide contained in the biogas is absorbed as carbon dioxide, thereby increasing the methane gas concentration. However, it has the problem that it requires multiple packed towers that are the main components of desulfurization, a tank and air compressor that perform micro-bubbling to supply oxygen to the corresponding liquid catalyst, a liquid feeder to circulate the liquid catalyst through the packed towers, and a biogas pressurizer to aerate the biogas through the multiple packed towers in series, resulting in a large-scale and complicated structure.

[0019] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a biogas desulfurization device that is easy to operate and manage, can perform desulfurization treatment in a short period of time, has a simple structure, is inexpensive, and enables highly accurate desulfurization. [Means for solving the problem]

[0020] In order to achieve the above object, the present invention provides the following:

[0021] The invention according to claim 1 provides a biogas desulfurization device comprising: a fermentation tank that generates biogas; and a reaction tank filled with a liquid catalyst, the reaction tank having an air inlet section for introducing air, a gas inlet section for introducing the biogas from the fermentation tank, and a purified gas outlet section for discharging purified biogas, the reaction tank being characterized in that it is equipped with a first pH control section that controls the pH of the liquid catalyst.

[0022] The invention of claim 2 aims to provide a biogas desulfurization apparatus as described in claim 1, characterized in that the first pH control unit includes a first catalyst introduction unit for introducing the liquid catalyst, and a first catalyst discharge unit for discharging the treated liquid, which is the liquid catalyst containing the recovered sulfur, to the outside.

[0023] The invention according to claim 3 aims to provide a biogas desulfurization apparatus as described in claim 1 or 2, characterized in that it is provided with a circulation section that circulates a portion of the refined biogas discharged from the reaction tank to the reaction tank.

[0024] The invention of claim 4 aims to provide a biogas desulfurization apparatus as described in claim 1 or 2, characterized in that it comprises a re-reaction tank filled with the liquid catalyst, the re-reaction tank having a refined gas inlet for introducing the refined biogas discharged from the refined gas outlet of the reaction tank and a re-refined gas outlet for discharging re-refined biogas, the re-reaction tank being equipped with a second pH control unit for controlling the pH of the liquid catalyst in the re-reaction tank.

[0025] The invention of claim 5 aims to provide a biogas desulfurization apparatus as described in claim 4, characterized in that the second pH control unit is provided with a second catalyst introduction unit for introducing the liquid catalyst, and a second catalyst discharge unit for discharging the treated liquid, which is the liquid catalyst containing the recovered sulfur, to the outside.

[0026] The invention according to claim 6 provides the biogas desulfurization apparatus according to any one of claims 1 to 5, characterized in that the liquid catalyst is a methane fermentation digestate.

[0027] The invention according to claim 7 provides the biogas desulfurization apparatus according to any one of claims 1 to 5, characterized in that the liquid catalyst is a nitrification / denitrification liquid. Effect of the Invention

[0028] According to the invention of claim 1, the system comprises a fermentation tank that generates biogas, and a reaction tank filled with a liquid catalyst, the reaction tank having an air inlet section for introducing air, a gas inlet section for introducing biogas from the fermentation tank, and a purified gas outlet section for discharging purified biogas. Since the reaction tank is equipped with a first pH control section that controls the pH of the liquid catalyst, the hydrogen sulfide concentration of the biogas can be stably reduced by controlling the pH value of the liquid catalyst.

[0029] According to the invention described in claim 2, the first pH control unit is equipped with a first catalyst introduction unit that introduces a liquid catalyst, and a first catalyst discharge unit that discharges the treated liquid, which is a liquid catalyst containing recovered sulfur, to the outside. This makes it possible to use the digestive liquid in an IC reactor, such as a fermenter, as a liquid catalyst, and by controlling the flow of the liquid catalyst in the first catalyst introduction unit and the first catalyst discharge unit, it is possible to control the pH value of the liquid catalyst in the reaction tank and stably reduce the hydrogen sulfide concentration in the biogas.

[0030] According to the invention described in claim 3, by providing a circulation section that circulates a portion of the refined biogas discharged from the reaction tank back to the reaction tank, not only can the reaction tank be configured as a single tank, but also pH control can be easily performed, making it possible to stably reduce the hydrogen sulfide concentration in the biogas to a high level.

[0031] According to the invention described in claim 4, the re-reaction tank is filled with a liquid catalyst and is equipped with a refined gas inlet for introducing the refined biogas discharged from the refined gas outlet of the reaction tank, and a re-refined gas outlet for discharging re-refined biogas. The re-reaction tank is equipped with a second pH control unit for controlling the pH of the liquid catalyst in the re-reaction tank, and therefore the hydrogen sulfide concentration in the biogas can be stably reduced by controlling the pH values ​​of the liquid catalyst in the two tanks.

[0032] According to the invention described in claim 5, the second pH control unit is provided with a second catalyst introduction unit for introducing a liquid catalyst, and a second catalyst outlet unit for outletting the treated liquid, which is a liquid catalyst containing recovered sulfur, to the outside. This makes it possible to use the digestive liquid in an IC reactor such as a fermenter as a liquid catalyst, and by controlling the flow of the liquid catalyst in the first and second catalyst introduction units and the first and second catalyst outlet units, it is possible to control the pH value of the liquid catalyst in the reaction tank and the re-reaction tank, thereby enabling a stable reduction in the hydrogen sulfide concentration in the biogas.

[0033] According to the invention described in claim 6, since the liquid catalyst is a methane fermentation digestate, it is possible to easily configure a biogas desulfurization device by utilizing an existing IC reactor such as a fermenter.

[0034] According to the invention described in claim 7, since the liquid catalyst is a nitrification / denitrification liquid, it is possible to easily configure a biogas desulfurization device by utilizing a denitrification tank, which is a post-treatment stage of digestive liquid discharged from an IC reactor such as an existing fermenter. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 is a schematic diagram of a basic form of a biogas desulfurization device according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic diagram of a first embodiment of a biogas desulfurization apparatus according to the present embodiment. [Diagram 3] FIG. 2 is a conceptual diagram of a circulation section of the first embodiment. [Figure 4] FIG. 4 is a schematic diagram of a second embodiment of a biogas desulfurization apparatus according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The gist of the biogas desulfurization apparatus of the present invention is that it comprises a fermentation tank that generates biogas, and a reaction tank filled with a liquid catalyst that is equipped with an air inlet section for introducing air, a gas inlet section for introducing biogas from the fermentation tank, and a purified gas outlet section for discharging purified biogas, and is characterized in that the reaction tank is equipped with a first pH control section that controls the pH of the liquid catalyst.In other words, the object is to provide a biogas desulfurization apparatus that is easy to operate and manage, can perform desulfurization treatment in a short period of time, has a simple structure, is inexpensive, and yet enables highly accurate desulfurization.

[0037] Hereinafter, embodiments of the biogas desulfurization apparatuses 1, 100, and 200 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 designated by the same reference numerals, and only one of them will be described, and the description of the other may be omitted as appropriate.

[0038] Hydrogen sulfide is a weak acid and in water, it changes from H2S to H + +HS - " "H.S. - →H + +S 2- " is known to dissociate as follows.

[0039] In addition, most metal ions other than alkali metals and alkaline earth metals are S 2- It reacts with hydrogen sulfide to produce sulfide. The molar solubility of hydrogen sulfide in water is 0.1 mol / L at room temperature and pressure, so the S 2- The molar solubility of is expressed by the formula "[S 2- ]=1.2×10 -22 / [H+ ] 2 " and S 2- The effect of pH on the molar solubility of S is shown in Table 1 below, which shows that the higher the pH, the lower the molar solubility of S. 2- This shows that the molar solubility of

[0040] [Table 1]

[0041] The biogas desulfurization apparatuses 1, 100, and 200 according to the present embodiment are a biogas desulfurization apparatus 100 (first embodiment) consisting of a single tank with a basic configuration (biogas desulfurization apparatus 1) at its core, and a biogas desulfurization apparatus 200 (second embodiment) consisting of multiple tanks, and the former may be referred to as a single-tank type and the latter as a multiple-tank type.

[0042] [Embodiment of the basic configuration] As shown in FIG. 1, a biogas desulfurization apparatus 1 having a basic configuration according to an embodiment of the present invention comprises a fermenter 2 that generates biogas B, and a reaction tank 4 filled with a liquid catalyst C1, the reaction tank 4 having an air inlet 5 for introducing air A, a gas inlet 6 for introducing biogas B from the fermenter 2, and a purified gas outlet 7 for discharging purified biogas B1, and the reaction tank 4 is equipped with a first pH control unit 8 that controls the pH of the liquid catalyst C1.

[0043] The fermentation tank 2 (methane fermentation tank) is a device that processes organic waste (also called waste biomass) through methane fermentation to generate biogas whose main component is methane, and an anaerobic wastewater treatment device such as an IC (Internal Circulation) reactor can be used.

[0044] The organic waste used includes livestock manure, food waste, shochu lees, etc., which are processed into a state suitable for methane fermentation using a pretreatment device (not shown) and then sent to the fermentation tank 2. The biogas B generated in the fermentation tank 2 is led to the reaction tank 4 via the gas inlet 6.

[0045] The fermenter 2 is a so-called airtight container of a size according to the scale of the facility, and is generally cylindrical in shape. The fermenter 2 according to the present embodiment is also the same. The fermenter 2 is an IC reactor (volume 556 m) owned by the applicant. 3 , height 22m).

[0046] 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.

[0047] In addition, the dehydrated residue from the distillation of barley shochu using barley shochu lees contains a lot of protein-derived sulfur, so the hydrogen sulfide concentration in the biogas tends to be high.

[0048] The reaction tank 4 is the main body of the biogas desulfurization apparatus of the present invention, and consists of a sealed container having a substantially cylindrical shape. The reaction tank 4 is filled with the liquid catalyst C1 so that there is space at the top (hereinafter referred to as the "headspace h") of the reaction tank 4.

[0049] The reaction tank 4 (and the re-reaction tank 204) according to this embodiment used in the desulfurization test described later is a 10 L small-scale culture apparatus (manufactured by Marubishi Bioengineering Co., Ltd.: MD-1000 type, capacity 10 L, effective tank height 32 cm), and the test is carried out by securing a head space h by filling it with 7 L of liquid catalyst in actual volume.

[0050] The liquid catalyst C1 is a methane fermentation digestive liquid or a nitrification / denitrification liquid having a pH buffering effect.

[0051] The reaction tank 4 is also equipped with an air inlet section 5 consisting of piping and a pump for supplying air A to the inside, and a gas inlet section 6 consisting of piping and a pump for supplying biogas B generated in the fermenter 2 to the inside. The air inlet section 5 and the gas inlet section 6 are arranged so that the air A and biogas B are supplied into the liquid catalyst C1 filled in the reaction tank 4.

[0052] In addition, the reaction tank 4 has an agitator 30 equipped with fins connected to the rotating shaft of a motor 31, so that the biogas B comes into even contact with the air A and the liquid catalyst C1 within the liquid catalyst C1, thereby promoting the reaction.

[0053] In addition, the biogas B that has come into contact with the air A and the liquid catalyst C1 in the reaction tank 4 fills the head space h of the reaction tank 4 as purified biogas B1 with a reduced concentration of hydrogen sulfide, and is discharged to the outside via the purified gas discharge section 7 consisting of a piping that communicates with the head space h.

[0054] In other words, refined biogas B1 with a reduced hydrogen sulfide concentration is obtained by converting biogas B, which has come into contact with air A and liquid catalyst C1, into sulfides, sulfur, and sulfur compounds, and removing hydrogen sulfide.

[0055] The first pH control unit 8 controls the pH value of the liquid catalyst C1 in the reaction tank 4 so as to be maintained at a preset value.

[0056] To this end, the first pH control unit 8 has pH meters 10a, 10b (D-24 manufactured by Horiba, Ltd., equipment used in the desulfurization test), a first catalyst inlet unit 11 that introduces liquid catalyst C1 into the reaction tank 4, and a first catalyst outlet unit 12 that discharges treated liquid D1, which is a liquid catalyst containing recovered sulfur, to the outside of the reaction tank 4. The first pH control unit 8 is configured to freely replace the liquid catalyst C1 in the tank so that a preset pH value is maintained and biogas with a low hydrogen sulfide concentration is produced, following the relationship between the pH value of the liquid catalyst C1 and the hydrogen sulfide concentration of the biogas determined by desulfurization tests or the like described below.

[0057] Specifically, the first catalyst introduction section 11 and the first catalyst discharge section 12 are provided with on-off control valves 14a, 14b (including valves, etc.) and pumps for controlling the introduction and discharge of the liquid, and the pH value of the liquid catalyst (digestion liquid D1) discharged from the first catalyst discharge section 12 is measured by a pH meter 10b installed at that location, and a first control device 9 receives the output pH value signal, calculates the deviation from a set value, and outputs the signal to each of the control valves 14a, 14b, making it possible to manage and control the pH value in the reaction tank 4 by controlling the opening and closing of the control valves 14a, 14b.

[0058] The location of the pH meter 10b is not limited to the rear side of the control valve 14b. For example, the pH meter 10b1 may be installed in front of the control valve 14b, or the pH meter 10b2 may be installed in the reaction tank 4.

[0059] In addition, the pH values ​​of the liquid catalyst at the inlet and outlet of the reaction tank 4 are measured using a pH meter 10a provided in the first catalyst introduction section 11, and the output signals of these pH values ​​are received by the first control device 9, which calculates the deviation from the set value and outputs the results to each of the control valves 14a, 14b to control their opening and closing, thereby enabling more precise management and control of the pH.

[0060] The location of the pH meter 10a is not limited to the rear side of the control valve 14a, and the pH meter 10a1 may be disposed in front of the control valve 14a.

[0061] In addition, the opening and closing of the control valves 14a, 14b is preferably controlled continuously, but batch control is also acceptable. In the case of continuous control, it is preferable to operate the first control device 9 with a time (residence time) until all of the liquid catalyst is replaced being settable, and in the case of batch control, it is preferable to perform opening and closing control for a similarly set residence time to replace all of the liquid catalyst C1 in the reaction tank 4 at once.

[0062] Furthermore, as described above, if pH meters 10b1, 10b2 are installed in front of control valve 14b or in reaction tank 4, the pH values ​​measured by these meters can be easily understood as the pH value in reaction tank 4, regardless of whether continuous control or batch control is used. This improves the accuracy of the opening and closing control of control valves 14a, 14b, making it possible to manage and control the pH more precisely.

[0063] In addition, the first pH control unit 8 does not necessarily have to be automatically controlled, and may be configured as a manual valve that allows the control valves 14a, 14b of the first catalyst introduction unit 11 and the first catalyst discharge unit 12 to be opened and closed manually in accordance with the value of the pH meter 10b (10a, 10a1, 10b1, 10b2).

[0064] The purified biogas B1 purified in the reaction tank 4 is stored in a purified gas recovery facility 35 or the like installed outside via a purified gas outlet 7 made of air piping.

[0065] The above-described configuration is the basic configuration of the biogas desulfurization device 1 according to an embodiment of the present invention.

[0066] Below, a detailed description will be given of the configuration of a first embodiment (circulation type) of a single-tank type biogas desulfurization apparatus based on the basic configuration, and a desulfurization test will be performed for each embodiment (series type).

[0067] [First embodiment] As shown in Figure 2, the biogas desulfurization apparatus 100 according to the first embodiment includes, in addition to the biogas desulfurization apparatus 1 according to the basic configuration, a circulation section 120 that circulates a portion of the refined biogas B1 discharged from the reaction tank 4 to the reaction tank 4.

[0068] Specifically, the refined biogas B1 discharged from the reaction tank 4 via the refined gas discharge section 7 is stored in a refined gas recovery facility 35, etc., but a portion of the refined biogas B1 is circulated to the reaction tank 4 by the circulation section 120.

[0069] The circulation section 120 is composed of an air pump 121 connected to the purified gas recovery equipment 35 etc. via an air piping for directing a portion of the purified biogas B1 stored in the purified gas recovery equipment 35 etc. to the liquid catalyst C1 in the reaction tank 4, a flow meter 122 having an adjustment valve for regulating the flow rate of a portion of the purified biogas B1 discharged from the air pump 121 and discharging it, and a re-introduction pipe 123 which is a piping for supplying the purified biogas B1 into the liquid catalyst C1 in the reaction tank 4.

[0070] The configuration of the circulation section 120 is not limited to this embodiment, and may be any configuration, such as a configuration in which a portion of the purified biogas B1 purified in the reaction tank 4 can be sent back into the liquid catalyst C1 in the reaction tank 4, as conceptually shown in Figure 3.

[0071] The contents and results of a biogas desulfurization test using the single-tank biogas desulfurization apparatus 100 according to the first embodiment will be described in detail below with reference to FIG. 2 and Tables 2 to 6.

[0072] Unless otherwise specified, this test was conducted without replacing the liquid catalyst in reaction tank 4, and the relationship between the decrease in hydrogen sulfide concentration and the pH of the liquid catalyst was clarified by observing the changes in the pH value of the liquid catalyst and the trends in the hydrogen sulfide concentration of the biogas.

[0073] Therefore, based on the results of this test, it will be possible to establish supply and discharge of the liquid catalyst and pH control by the first pH control unit 8.

[0074] Here, the air supply ratio is expressed as the ratio of the amount of air injected to the amount of biogas supplied into the reaction tank 4, the gas circulation ratio is the amount of biogas circulated input into the reaction tank 4 divided by the amount of biogas in the reaction tank 4, and the gas residence time is the actual volume of the reaction tank 4 (7 L) divided by the amount of biogas supplied; if the gas residence time is 10 minutes, it means the time it takes for the biogas to reach the actual volume in 10 minutes and for all of the biogas in the reaction tank 4 to be replaced.

[0075] In the desulfurization test, the temperature inside the reaction tank 4 was approximately 30°C, the stirring speed of the stirring unit 30 was 200 rpm to 300 rpm, the liquid catalyst C1 supplied to the reaction tank 4 was the IC reactor digestate produced in the fermentation tank 2, the biogas was generated in the fermentation tank 2 and introduced into the reaction tank 4 via the gas inlet unit 6 and introduced 18 cm below the water surface of the liquid catalyst C1, and air was supplied to the reaction tank 4 via the air inlet unit 5.

[0076] In addition, the pH value of the liquid catalyst was measured by installing pH meters at a position corresponding to the first catalyst inlet section 11, which is the inlet side to the reaction tank 4, and at a position corresponding to the first catalyst outlet section 12, which is the outlet side from the reaction tank 4, and the value at the inlet side was taken as the initial pH value of the liquid catalyst, and the value at the outlet side was taken as the result of the pH of the liquid catalyst.

[0077] Furthermore, the hydrogen sulfide concentration of the biogas was measured by installing a concentration meter 140 (XOS-353-2 manufactured by New Cosmos Electric Co., Ltd.) near the base point of the circulation section 120 connected to a storage container such as the refined gas recovery facility 35, and measuring the desulfurization status while taking the measured value as the hydrogen sulfide concentration result. However, the location of the concentration meter 140 may be a location equivalent to the refined gas outlet section 7, etc., as long as it is possible to measure the hydrogen sulfide concentration of the biogas discharged from the reaction tank 4 to the outside.

[0078] Table 2 shows the pH of liquid catalyst C1 and the hydrogen sulfide concentration of purified biogas B1 when biogas with an initial hydrogen sulfide concentration of approximately 2,200 ppm was supplied to IC reactor digestive liquid with an initial pH of 6.67 as liquid catalyst C1 for a gas residence time of 10 minutes, and air was supplied 2 cm below the water surface of liquid catalyst C1 at an air supply rate of 3%, and the gas circulation rate was changed from 2 to 0.5.

[0079] [Table 2]

[0080] As shown in Test No. A-1, when the gas circulation ratio was 2, the hydrogen sulfide concentration of the biogas was 1 ppm, and as shown in Test No. A-2, when the gas circulation ratio was 1, the hydrogen sulfide concentration of the biogas was 1 to 0.5 ppm. In both cases, good biogas with extremely low hydrogen sulfide concentrations was produced.

[0081] However, as shown in Test No. A-3, when the gas circulation ratio was 0.5 times, the hydrogen sulfide concentration in the biogas increased to 160 to 140 ppm, indicating that lowering the circulation ratio too much has a negative effect on the reduction of the hydrogen sulfide concentration.

[0082] Table 3 shows the pH of liquid catalyst C1 and the hydrogen sulfide concentration of purified biogas B1 when biogas with an initial hydrogen sulfide concentration of approximately 2,200 ppm was supplied to IC reactor digestive liquid with an initial pH of 6.64 as liquid catalyst C1 for a gas residence time of 7 minutes, and air was supplied 2 cm below the water surface of liquid catalyst C1 at an air supply rate of 3%, and the gas circulation rate was set to 1x and 2x.

[0083] In other words, this test compares the results of tests related to test numbers A-1 and A-2 in Table 1, in which good biogas with a hydrogen sulfide concentration of about 1 ppm was produced when the gas retention time was 10 minutes and the gas circulation ratios were 1x and 2x, with a gas retention time of 7 minutes.

[0084] [Table 3]

[0085] As shown in Test No. B-1, when the gas circulation ratio was 1, the hydrogen sulfide concentration in the biogas was high at 400 to 350 ppm, and as shown in Test No. B-2, when the gas circulation ratio was 2:1, the hydrogen sulfide concentration in the biogas decreased to 2.5 ppm. It was found that a short gas residence time of 7 minutes had a negative effect on the decrease in the hydrogen sulfide concentration and that this effect could be suppressed by increasing the gas circulation ratio.

[0086] Table 4 shows the pH of liquid catalyst C1 and the hydrogen sulfide concentration of purified biogas B1 when biogas with an initial hydrogen sulfide concentration of approximately 2,200 ppm was supplied to IC reactor digestive liquid with an initial pH of 6.62 as liquid catalyst C1 for a gas residence time of 10 minutes, the air supply ratio was set to 0%, and the gas circulation ratio was doubled.

[0087] In other words, this test compares the results of the test related to test number A-1 in Table 1, in which an air supply ratio of 3% was used to refine good biogas with a hydrogen sulfide concentration of 1 ppm, with the results of an air supply ratio of 0%.

[0088] [Table 4]

[0089] As shown in test number C-1, when the air supply ratio was 0%, the hydrogen sulfide concentration in the biogas was extremely high at 1,700 ppm, indicating that air supply is necessary to reduce the hydrogen sulfide concentration.

[0090] Table 5 shows the pH of liquid catalyst C1 and the hydrogen sulfide concentration of purified biogas B1 when biogas with an initial hydrogen sulfide concentration of approximately 2,200 ppm was supplied to IC reactor digestive liquid with an initial pH of 6.62 as liquid catalyst C1 for a gas residence time of 10 minutes, and air was supplied to 3 cm above the water surface of liquid catalyst C1 (head space h) at an air supply rate of 3%, and the gas circulation rate was set to 2 times, 1 time, and 0.7 times.

[0091] In other words, this test was conducted to confirm the effects of each condition when air was introduced into the headspace in the test related to Test No. A-1 in Table 1, in which good biogas with an air supply ratio of 3% and a hydrogen sulfide concentration of 1 ppm was refined, and in the test related to Test No. C-1 in Table 3, in which the necessity of air for sulfide production was confirmed.

[0092] [Table 5]

[0093] As shown in Table 5, an overall decrease in the pH of the liquid catalyst was observed compared to Test Nos. A-1 and C-1. In particular, as shown in Test No. D-1c, when the pH dropped significantly from pH 5.9 in Test No. D-1a to pH 5.4 in Test No. D-1b and then to 4.3, there was a tendency for the hydrogen sulfide concentration in the biogas to increase significantly.

[0094] This is thought to be because sulfide production occurs at a pH of 4 or higher, and when air is introduced into the headspace, the molar solubility caused by the air oxidation performance due to the bursting of biogas bubbles generated on the water surface has a significant effect on the pH. It was also confirmed that the pH is affected by the position at which air is introduced into liquid catalyst C1, and that a decrease in the pH of the liquid catalyst is related to an increase in the hydrogen sulfide concentration in the biogas, indicating the importance of pH management.

[0095] In addition, as shown in Test Nos. D-2a and D-2b, a slight effect was observed on the hydrogen sulfide concentration of the biogas by reducing the gas circulation ratio from 2 to 1, but as shown in Test No. D-3, a decrease in the gas circulation ratio to 0.7 was confirmed to have a negative effect on the reduction of the hydrogen sulfide concentration, as confirmed in Test No. A-3.

[0096] Table 6 shows the pH of liquid catalyst C1 and the hydrogen sulfide concentration of purified biogas B1 when biogas with an initial hydrogen sulfide concentration of approximately 2,800 ppm was supplied to IC reactor digestive liquid with an initial pH of 6.73 as liquid catalyst C1 for a gas residence time of 7 minutes, and air was supplied 2 cm below the water surface of liquid catalyst C1 at an air supply rate of 3%, and the gas circulation rate was set to 2 times, 1 time, 0.7 times, and 0.5 times.

[0097] That is, this test is to confirm the relationship between the optimum gas circulation ratio and the pH of the liquid catalyst when the gas residence time is set to 7 minutes.

[0098] [Table 6]

[0099] As shown in Table 6, in test numbers E-1 to E-3b (gas circulation ratio 2 to 0.7 times) where the pH of the liquid catalyst was 6.1 or higher, the hydrogen sulfide concentration of the biogas was generally good, but in test numbers E-4a to E-4c where the gas circulation ratio was 0.5 times, there was a tendency for the hydrogen sulfide concentration of the biogas to deteriorate from 10 ppm to 200 ppm as the pH of the liquid catalyst decreased from 5.83 to 5.

[0100] As described above, from the biogas desulfurization test using the single-tank biogas desulfurization apparatus 100 according to the first embodiment, it is clear that by fixing the gas residence time, air ratio, and gas circulation ratio at optimal conditions and controlling the pH of the liquid catalyst by the first pH control unit 8, which is a basic component, it is possible to stably refine biogas with a low hydrogen sulfide concentration.

[0101] [Second embodiment] As shown in FIG. 4, the biogas desulfurization apparatus 200 according to the second embodiment comprises a re-reaction tank 204 filled with a liquid catalyst C2, and the re-reaction tank 204 is equipped with a refined gas inlet section 206 (in the second embodiment, the refined gas outlet section 7 and the refined gas inlet section 206 are synonymous) for introducing the refined biogas B1 discharged from the refined gas outlet section 7 of the reaction tank 4 of the biogas desulfurization apparatus 1 according to the basic configuration, and a re-refined gas outlet section 207 for discharging re-refined biogas B2, and the re-reaction tank 204 is equipped with a second pH control section 208 for controlling the pH of the liquid catalyst C2 in the re-reaction tank 204.

[0102] In addition, the second pH control unit 208 is equipped with a second catalyst introduction unit 211 for introducing the liquid catalyst C2, and a second catalyst discharge unit 212 for discharging the treated liquid D2, which is the liquid catalyst containing the recovered sulfur, to the outside.

[0103] The re-reaction tank 204 consists of a substantially cylindrical sealed container, similar to the reaction tank 4 in the biogas desulfurization apparatus 1 of the basic configuration described above, and is filled with the liquid catalyst C2 so as to have a head space h at the top of the re-reaction tank 204.

[0104] The re-reaction tank 204 is also equipped with a purified gas inlet 206 consisting of piping and a pump for supplying the purified biogas B1 purified in the reaction tank 4 into the liquid catalyst C2 filled in the re-reaction tank 204.

[0105] In addition, the re-reaction tank 204, like the reaction tank 4, has an agitation unit 230 equipped with fins connected to the rotating shaft of a motor 231, so that the refined biogas B1 comes into even contact with the liquid catalyst C2 in the liquid catalyst C2, thereby promoting the reaction.

[0106] In addition, the refined biogas B1 that has come into contact with the liquid catalyst C2 in the re-reaction tank 204 fills the head space h of the re-reaction tank 204 as re-refined biogas B2 with a reduced concentration of hydrogen sulfide, and is discharged to the outside via the re-refined gas discharge section 207 consisting of a piping that communicates with the head space h.

[0107] The re-reaction tank 204 may be provided therein with a separate air inlet section 5 consisting of a pipe for supplying air, as in the basic configuration or the biogas desulfurization apparatus 1 according to the first embodiment.

[0108] The second pH control unit 208 controls the pH value of the liquid catalyst C2 in the re-reaction tank 204 so as to be maintained at a preset value.

[0109] To this end, the second pH control unit 208 has pH meters 210a, 210b (D-24, manufactured by HORIBA, Ltd., equipment used in the desulfurization test), a second catalyst introduction unit 211 that introduces liquid catalyst C2 into the re-reaction tank 204, and a second catalyst discharge unit 212 that discharges treated liquid D2, which is a liquid catalyst containing recovered sulfur, to the outside of the re-reaction tank 204. The second pH control unit 208 is configured to be freely replaced so that the pH value is maintained at a preset value and biogas with a low concentration of hydrogen sulfide is produced, following the relationship between the pH value of the liquid catalyst C2 and the hydrogen sulfide concentration of the biogas ascertained by the desulfurization test described below, etc.

[0110] Specifically, the second catalyst introduction section 211 and the second catalyst discharge section 212 are provided with on-off control valves 214a, 214b (including valves, etc.) and a pump for controlling the introduction and discharge of the liquid, and the pH value of the liquid catalyst (digestion liquid D2) discharged from the second catalyst discharge section 212 is measured by a pH meter 210b installed at the relevant location, and the second control device 209 receives a signal of the output pH value, calculates the deviation from a set value, and outputs the signal to each of the control valves 214a, 214b, thereby making it possible to manage and control the pH in the re-reaction tank 204 by controlling the opening and closing of the control valves 214a, 214b.

[0111] The location of the pH meter 210b is not limited to the rear side of the control valve 214b. For example, the pH meter 210b1 may be installed in front of the control valve 214b, or the pH meter 210b2 may be installed in the re-reaction tank 204.

[0112] In addition, the pH values ​​of the liquid catalyst at the inlet and outlet of the re-reaction tank 204 are measured by a pH meter 210a provided in the second catalyst introduction section 211, and the output signals of these pH values ​​are received by the second control device 209, which calculates the deviation from the set value and outputs the results to each of the control valves 214a, 214b to control opening and closing, thereby enabling more precise management and control of the pH.

[0113] The location of the pH meter 210a is not limited to the rear side of the control valve 214a, and the pH meter 210a1 may be disposed in front of the control valve 214a.

[0114] In addition, the opening and closing of the control valves 214a, 214b is preferably controlled continuously, but may be controlled in batches. In the case of continuous control, it is preferable to operate the second control device 209 with a time (residence time) until all of the liquid catalyst is replaced settable, and in the case of batch control, it is preferable to perform opening and closing control for a similarly set residence time and replace all of the liquid catalyst C2 in the re-reaction tank 204 at once.

[0115] Furthermore, as described above, if pH meters 210b1, 210b2 are installed in front of control valve 214b or in re-reaction tank 204, the pH values ​​measured by these meters can be easily understood as the pH value in re-reaction tank 204 regardless of whether continuous control or batch control is used. This improves the accuracy of the opening and closing control of control valves 214a, 214b, making it possible to perform even more precise management and control of pH.

[0116] In addition, the second pH control unit 208 does not necessarily have to be automatically controlled, and may be configured as a manual valve that allows the control valves 214a, 214b of the second catalyst introduction unit 211 and the second catalyst discharge unit 212 to be opened and closed manually in accordance with the value of the pH meter 210b (210a, 210a1, 210b1, 210b2).

[0117] Furthermore, the first control device 9 of the reaction tank 4 and the second control device 209 of the re-reaction tank 204 may be integrated, and the first pH control unit 8 and the second pH control unit 208 may be linked to configure an overall control device 216 to control the control valves 14a, 14b, 214a, and 214b and perform overall pH management.

[0118] The re-refined biogas B2 refined in the re-reaction tank 204 is stored in an externally installed refined gas recovery facility 35 or the like via a re-refined gas outlet 207 consisting of an air pipe.

[0119] The contents and results of a biogas desulfurization test using the multi-tank biogas desulfurization apparatus 200 according to the second embodiment will be described in detail below with reference to FIG.

[0120] Unless otherwise specified, this test was conducted without replacing the liquid catalyst in the reaction tank 4 and the re-reaction tank 204, and the relationship between the decrease in hydrogen sulfide concentration and the pH of the liquid catalyst was clarified by observing the changes in the pH value of the liquid catalyst and the trends in the hydrogen sulfide concentration of the biogas.

[0121] Therefore, based on the results of this test, it will be possible to establish supply and discharge of liquid catalyst and pH control by the first and second pH control units 8,208.

[0122] Here, the air supply ratio is expressed as the ratio of the amount of air injected to the amount of biogas supplied into the reaction tank 4, and the gas retention time is the sum of the actual volume of the reaction tank 4 (7 L) and the actual volume of the re-reaction tank 204 (7 L) divided by the amount of biogas supplied. If the gas retention time is 24 minutes, it means that it takes 12 minutes for the biogas in the reaction tank 4 and the re-reaction tank 204 to reach their actual volumes, and the biogas in the reaction tank 4 and the re-reaction tank 204 to be completely replaced.

[0123] In the desulfurization tests, the internal temperatures of the reaction tank 4, which is the first tank, and the re-reaction tank 204, which is the second tank, were both approximately 30°C, the stirring speed of the stirring units 30, 230 was 200 rpm to 300 rpm, and the liquid catalysts C1, C2 supplied to the reaction tank 4 and the re-reaction tank 204 were based on the use of the IC reactor digestive liquid produced in the fermenter 2, but different liquid catalysts were used in each test. When the liquid catalysts were replaced, the liquid catalyst C1 was introduced into the reaction tank 4 via the first catalyst introduction unit 11 and discharged from the first catalyst discharge unit 12, and the liquid catalyst C2 was introduced into the re-reaction tank 204 via the second catalyst introduction unit 211 and discharged from the second catalyst discharge unit 212.

[0124] In addition, biogas B was generated in the fermentation tank 2 and introduced into the reaction tank 4 via the gas inlet 6 and placed 18 cm below the water surface of the liquid catalyst C1, and air A was supplied to the reaction tank 4 via the air inlet 5.

[0125] Furthermore, the purified biogas B purified in the reaction tank 4 was discharged to the re-reaction tank 204 via the purified gas discharge part 7 (purified gas inlet part 206) and introduced into the liquid catalyst C2 at a position 18 cm below the water surface.

[0126] Table 7 shows the pH of the liquid catalysts C1 and C2 in the first and second tanks and the hydrogen sulfide concentrations of the purified biogas B1 and B2 when biogas B, which has an initial hydrogen sulfide concentration of approximately 2,400 ppm, is supplied with a gas residence time of 20 minutes (10 minutes in the first tank, 10 minutes in the second tank) and 24 minutes (12 minutes in the first tank, 12 minutes in the second tank), with the stirring speed set to 200 rpm in the first tank and 300 rpm in the second tank, and air A is supplied at an air supply ratio in the range of 2% to 15%.

[0127] Air A was introduced 2 cm below the water surface of the liquid catalyst C1 in the first tank (Test Nos. F-1 and F-2), but a test was also conducted in which a ball filter (pore size 100 μm to 120 μm) was placed 10 cm below the water surface (Test No. F-3) in order to increase the oxygen transfer capacity coefficient.

[0128] In other words, this test mainly uses water as the liquid catalyst to clarify the relationship between the pH of the liquid catalyst and the hydrogen sulfide concentration of biogas.

[0129] [Table 7]

[0130] In test number F-1, when the air ratio was changed from 2% to 10%, the pH decreased and the hydrogen sulfide concentration of the biogas in the first and second tanks only decreased to 2,100 ppm.

[0131] In test number F-2, when the gas residence time was extended from 20 minutes to 24 minutes and the air ratio was increased to 15%, the hydrogen sulfide concentration decreased to 400 ppm in the first tank and to 20 ppm (pH 7.4) in the second tank.

[0132] In test number F-3, the gas retention time was kept at 24 minutes and the air ratio was 5%, and the behavior of the liquid catalyst pH and biogas hydrogen sulfide concentration was confirmed. It was found that the hydrogen sulfide concentration of the biogas decreased up to about pH 5 in both the first and second tanks, but below pH 5 the hydrogen sulfide concentration of the biogas rose sharply.

[0133] From the above, it was found that a pH of at least 5 or higher is necessary to reduce the hydrogen sulfide concentration in biogas.

[0134] Table 8 shows the pH of the liquid catalysts C1 and C2 in the first and second tanks and the hydrogen sulfide concentrations of the purified biogas B1 and B2 when biogas B having an initial hydrogen sulfide concentration of approximately 2,200 ppm was supplied to 0.5 M PBS buffer (0.5 mol / L phosphate buffered saline) having an initial pH of 7.4 and 0.1 M acetate buffer (0.1 mol / L acetate buffer) having an initial pH of 4.5 as liquid catalysts C1 and C2 for a gas residence time of 24 minutes (12 minutes in the first tank, 12 minutes in the second tank), the stirring speed was 300 rpm in both the first and second tanks, and air A was supplied 2 cm below the water surface of the liquid catalyst C1 in the first tank at an air supply ratio of 3%.

[0135] [Table 8]

[0136] As shown in Table 8, the decrease in hydrogen sulfide concentration in the biogas was greater in Test No. G-1, where the pH of the liquid catalyst in the second tank was 6.2, than in Test No. G-2, where the pH was 4.3. However, in the 0.1 M acetate buffer in Test No. G-2, where the initial value was 5 or less from the beginning, the S 2- This directly reflects the fact that the decrease in molar solubility of is dependent on low pH.

[0137] Table 9 shows the pH of the liquid catalysts C1 and C2 in the first and second tanks and the hydrogen sulfide concentrations of the purified biogas B1 and B2 when biogas B, having an initial hydrogen sulfide concentration of approximately 2,400 ppm, was supplied to the methane fermentation digestate treated in fermenter 2 as liquid catalysts C1 and C2 with a gas residence time of 24 minutes (12 minutes in the first tank and 12 minutes in the second tank), the stirring speed was set to 300 rpm in both the first and second tanks, and air A was supplied to 2 cm below the water surface of the liquid catalyst C1 in the first tank at air supply ratios of 3% and 5%.

[0138] [Table 9]

[0139] As shown in Table 9, the hydrogen sulfide concentration in the biogas decreased smoothly in test number H-1, where the air ratio was 3%, and the hydrogen sulfide concentration in the biogas decreased further in test number H-2, where the air ratio was 5%.

[0140] Table 10 shows the pH of the liquid catalysts C1 and C2 in the first and second tanks and the hydrogen sulfide concentration of the purified biogas B1 and B2 when biogas B, which has an initial hydrogen sulfide concentration of about 2,200 ppm to about 2,400 ppm, is supplied to the IC reactor digestive liquid used as the liquid catalysts C1 and C2 for a gas residence time of 24 minutes (12 minutes in the first tank, 12 minutes in the second tank), 20 minutes (10 minutes in the first tank, 10 minutes in the second tank), 14 minutes (7 minutes in the first tank, 7 minutes in the second tank), 10 minutes (5 minutes in the first tank, 5 minutes in the second tank), and 6 minutes (3 minutes in the first tank, 3 minutes in the second tank). The stirring speed is 300 rpm for both the first and second tanks, and air A is supplied 2 cm below the water surface of the liquid catalyst C1 in the first tank at an air supply ratio of 3% (partially 0%).

[0141] In other words, the purpose of this study is to confirm the effect of gas retention time on the hydrogen sulfide concentration of biogas and the pH of the liquid catalyst at that time.

[0142] [Table 10]

[0143] As shown in Table 10, the liquid catalyst had a pH of 6 or higher in all cases, and the hydrogen sulfide concentration of the biogas was generally reduced well up to a gas retention time of 24 minutes to 10 minutes (Test Nos. I-1 to I-4). However, when the gas retention time was shortened to 6 minutes (Test No. I-5), a tendency for the concentration to increase was observed, and it was found that a gas retention time of 10 minutes or more was necessary under these conditions.

[0144] As shown in Test No. I-6, when the gas retention time was set to 24 minutes (12 minutes in the first tank, 12 minutes in the second tank) and the air supply was stopped, the hydrogen sulfide concentration in the biogas increased rapidly, reaching 3,000 ppm in the first tank and 3,600 ppm in the second tank.

[0145] In this way, it was confirmed that cutting off the air not only prevents hydrogen sulfide from being removed, but also reproduces hydrogen sulfide from the fixed sulfur and sulfides, increasing the hydrogen sulfide concentration in the biogas, making it necessary to supply air even if the retention time is extended.

[0146] Table 11 shows the pH of the liquid catalysts C1 and C2 in the first and second tanks and the hydrogen sulfide concentration of the purified biogas B1 and B2 when biogas B, which had an initial hydrogen sulfide concentration of approximately 2,400 ppm, was supplied to the nitrification / denitrification liquid used as liquid catalysts C1 and C2 with a gas residence time of 24 minutes (12 minutes in the first tank and 12 minutes in the second tank), the stirring speed was set to 300 rpm in both the first and second tanks, and air A was supplied to 2 cm below the water surface of the liquid catalyst C1 in the first tank at an air supply ratio of 5%.

[0147] The nitrification and denitrification liquid is the digestive liquid discharged from IC reactors such as fermenters that contains NH4 + This refers to the digestive liquid from the treatment tank, which contains nitrogen that is converted into nitrate nitrogen and nitrite nitrogen in the aeration treatment tank installed downstream, and then undergoes biological nitrification and denitrification as gaseous nitrogen in an anaerobic environment.

[0148] This test was conducted to confirm the possibility of using aerated nitrification / denitrification liquid as liquid catalysts C1 and C2 in addition to IC reactor digestive liquid.

[0149] [Table 11]

[0150] As shown in Test No. J-1 in Table 11, the hydrogen sulfide concentration of the biogas in the second tank was reduced to 10 ppm (liquid catalyst pH 6.3) and then further reduced to 4 ppm. However, the pH of the liquid catalyst rapidly dropped to 5.2 as a result. Therefore, as shown in Test No. J-2, when the liquid catalyst in the second tank was replaced, the hydrogen sulfide concentration of the biogas was further reduced to 2 ppm, but the pH of the liquid catalyst immediately dropped to 5.8.

[0151] In addition, the alkalinity (HCO3 - ) is thought to be due to the fact that the buffering effect is reduced as nitrifying bacteria utilize the water as a carbon source during the nitrification reaction, making it easier for the pH to drop.

[0152] In such a case, it is effective to replace the liquid catalysts by managing the pH values ​​of the liquid catalysts C1 and C2, as in the biogas desulfurization apparatus 200 according to this embodiment.

[0153] Table 12 shows the pH of the liquid catalysts C1 and C2 in the first and second tanks and the hydrogen sulfide concentration of the purified biogas B1 and B2 when biogas B, which has an initial hydrogen sulfide concentration of approximately 2,200 ppm, is supplied to the digestive liquid produced by the anaerobic membrane separation method (hereinafter referred to as "AnMBR", an abbreviation for Anaerobic Membrane Bio Reactor) with an initial pH of 7.4 as liquid catalysts C1 and C2, with a gas retention time of 24 minutes (12 minutes in the first tank and 12 minutes in the second tank), and the stirring speed is 200 rpm in the first tank and 300 rpm in the second tank in test number J-1, and 300 rpm in both the first and second tanks in test number J-2, and air A is supplied 2 cm below the water surface of the liquid catalyst C1 in the first tank with an air supply ratio of 3%.

[0154] Since strong foaming occurred at a stirring speed of 300 rpm, the stirring speed of the first and second tanks was set to 200 rpm.

[0155] This test was conducted to confirm the possibility of using other methane fermentation digestive liquids, such as AnMBR, in addition to IC reactor digestive liquids, as liquid catalysts C1 and C2.

[0156] [Table 12]

[0157] As shown in Test No. K-1 in Table 12, the hydrogen sulfide concentration of the biogas in the first tank was reduced to 800 ppm, and the hydrogen sulfide concentration of the biogas in the second tank was reduced to 80 ppm, confirming that other methane fermentation digestate such as AnMBR can also be used as a liquid catalyst.

[0158] As described above, from the biogas desulfurization test using the multiple-tank biogas desulfurization apparatus 200 according to the second embodiment, it is clear that it is possible to stably refine biogas with a low concentration of hydrogen sulfide by fixing the gas residence time, air ratio, and gas circulation ratio at optimal conditions and controlling the pH of the liquid catalyst by the first pH control unit 8 and the second pH control unit 208.

[0159] Any or all of the conditions of the gas residence time, air ratio, and gas circulation ratio may be linked to the first pH control unit 8 and the second pH control unit 208 to control the pH of the liquid catalyst.

[0160] As described above, the basic configuration of the biogas desulfurization apparatus 1 according to this embodiment comprises the fermentation tank 2 that generates biogas B, and the reaction tank 4 filled with a liquid catalyst C1 that is equipped with an air inlet section 5 for introducing air A, a gas inlet section 6 for introducing biogas from the fermentation tank 2, and a purified gas outlet section 7 for discharging purified biogas. The reaction tank 4 is equipped with a first pH control section 8 that controls the pH of the liquid catalyst C1, and therefore the hydrogen sulfide concentration of the biogas can be stably reduced by controlling the pH value of the liquid catalyst C1.

[0161] In addition, the first pH control unit 8 is equipped with a first catalyst introduction unit 11 that introduces the liquid catalyst C1, and a first catalyst discharge unit 12 that discharges the treated liquid D1, which is a liquid catalyst containing recovered sulfur, to the outside, so that the digestive liquid in an IC reactor such as a fermenter can be used as the liquid catalyst C1. Moreover, by controlling the flow of the liquid catalyst C1 with the first catalyst introduction unit 11 and the first catalyst discharge unit 12, the pH value of the liquid catalyst C1 in the reaction tank 4 can be controlled, and the hydrogen sulfide concentration of the biogas can be stably reduced.

[0162] Furthermore, the biogas desulfurization apparatus 100 according to the first embodiment is equipped with a circulation section 120 that circulates a portion of the refined biogas B1 output from the reaction tank 4 to the reaction tank 4. This not only enables the reaction tank 4 to be configured as a single tank, but also facilitates pH control, making it possible to stably reduce the hydrogen sulfide concentration in the biogas to a high level.

[0163] Furthermore, the biogas desulfurization apparatus 200 according to the second embodiment comprises a re-reaction tank 204 filled with a liquid catalyst C2, which is equipped with a refined gas inlet section 206 for introducing the refined biogas B1 discharged from the refined gas outlet section 7 of the reaction tank 4, and a re-refined gas outlet section 207 for discharging the re-refined biogas. The re-reaction tank 204 is equipped with a second pH control section 208 for controlling the pH of the liquid catalyst C2 in the re-reaction tank 204. As a result, the hydrogen sulfide concentration of the biogas can be stably reduced by controlling the pH values ​​of the liquid catalysts C1, C2 in the two tanks 4, 204.

[0164] In addition, the second pH control unit 208 is equipped with a second catalyst introduction unit 211 that introduces the liquid catalyst C2, and a second catalyst discharge unit 212 that discharges the treated liquid D2, which is a liquid catalyst containing recovered sulfur, to the outside, so that the digestive liquid of an IC reactor such as the fermenter 2 can be used as the liquid catalyst C2. Moreover, by controlling the flow of the liquid catalysts C1, C2 with the first and second catalyst introduction units 11, 211 and the first and second catalyst discharge units 12, 212, the pH values ​​of the liquid catalysts C1, C2 in the reaction tank 4 and the re-reaction tank 204 can be controlled, and the hydrogen sulfide concentration of the biogas can be stably reduced.

[0165] Furthermore, since the liquid catalysts C1, C2 that can be used in the biogas desulfurization apparatus 1, 100, 200 of the present invention are methane fermentation digestate, it is possible to easily configure the biogas desulfurization apparatus 1, 100, 200 using an existing IC reactor such as a fermenter.

[0166] Furthermore, since the liquid catalysts C1, C2 that can be used in the biogas desulfurization apparatus 1, 100, 200 of the present invention are nitrification denitrification liquid, it is possible to easily configure the biogas desulfurization apparatus 1, 100, 200 by utilizing a denitrification tank, which is a downstream treatment stage for digestive liquid discharged from an IC reactor such as an existing fermenter.

[0167] Although the preferred embodiments of the biogas desulfurization apparatuses 1, 100, and 200 according to the present invention have been described above, the present invention is not limited to the specific embodiments, and various modifications and variations are possible. [Explanation of symbols]

[0168] A. Air B. Biogas B1 Refined biogas B2 Re-refined biogas C1 liquid catalyst C2 Liquid Catalyst D1 Processing solution D2 Processing solution 1. Biogas desulfurization equipment (basic configuration) 2 Fermentation tank 4. Reactor 5 Air intake section 6 Gas inlet 7. Purified gas outlet 8 First pH control section 11 First catalyst introduction section 12 First catalyst outlet 100 Biogas desulfurization device (first embodiment) 120 Circulation section 200 Biogas desulfurization device (second embodiment) 204 Reaction tank 206 Refined gas inlet 207 Re-refined gas outlet 208 Second pH control section 211 Second catalyst introduction section 212 Second catalyst outlet

Claims

1. The present invention comprises a fermentation tank for generating biogas, and a reaction tank filled with a liquid catalyst, the reaction tank having an air inlet for introducing air, a gas inlet for introducing the biogas from the fermentation tank, and a purified gas outlet for discharging purified biogas, The biogas desulfurization apparatus is characterized in that the reaction tank is equipped with a first pH control unit that controls the pH of the liquid catalyst.

2. The biogas desulfurization apparatus according to claim 1, characterized in that the first pH control unit comprises a first catalyst introduction unit for introducing the liquid catalyst, and a first catalyst discharge unit for discharging the treated liquid, which is the liquid catalyst containing the recovered sulfur, to the outside.

3. The biogas desulfurization apparatus according to claim 1 or 2, further comprising a circulation unit that circulates a portion of the refined biogas discharged from the reaction tank to the reaction tank.

4. 3. The biogas desulfurization apparatus according to claim 1 or 2, characterized in that the re-reaction tank is filled with the liquid catalyst and is equipped with a purified gas inlet for introducing the purified biogas discharged from the purified gas outlet of the reaction tank and a re-refined gas outlet for discharging re-refined biogas, wherein the re-reaction tank is equipped with a second pH control unit for controlling a pH of the liquid catalyst in the re-reaction tank.

5. The biogas desulfurization apparatus according to claim 4, characterized in that the second pH control unit comprises a second catalyst introduction unit for introducing the liquid catalyst, and a second catalyst discharge unit for discharging the treated liquid, which is the liquid catalyst containing the recovered sulfur, to the outside.

6. 6. The biogas desulfurization apparatus according to claim 1, wherein the liquid catalyst is a methane fermentation digestate.

7. 6. The biogas desulfurization apparatus according to claim 1, wherein the liquid catalyst is a nitrification / denitrification liquid.

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