A device and method for improving biogas yield through micro-aeration and reflux of biogas slurry.

Abstract

This application proposes a device and method for improving biogas production through micro-aeration and reflux of biogas slurry, relating to the field of organic solid waste energy technology. The device includes a high-solids-content anaerobic reactor and a biogas slurry reflux aeration tank. A biogas slurry outlet is located at the upper end of the reactor, connected to the upper end of the reflux aeration tank via a biogas slurry outlet pipe. The lower end of the reflux aeration tank is connected to the lower end of the reactor via a biogas slurry reflux pipe. Aeration heads are located at the bottom of the reflux aeration tank. This application utilizes micro-aeration and reflux of biogas slurry to carry air into the reactor, with reflux occurring 4–12 times daily. The total daily biogas slurry reflux volume is 1.0–8.0% of the reactor volume. The dissolved oxygen in the refluxed biogas slurry is 0.3–1.5 mg / L, resulting in a 20% increase in biogas production. This demonstrates that micro-aeration and reflux of biogas slurry carrying air can significantly improve biogas production. Furthermore, this application fundamentally avoids the safety hazards caused by excessive O2 in the biogas due to the injection of air into the reactor.

Description

Technical Field

[0001] This application relates to the field of organic solid waste energy technology, and more specifically, to a device and method for improving biogas production through micro-aeration and reflux of biogas slurry. Background Technology

[0002] Anaerobic digestion refers to the process by which microorganisms convert organic matter into biogas (mainly containing CH4 and CO2) under anaerobic conditions. It can convert organic matter in waste into clean energy CH4 and organic fertilizer, thereby reducing, rendering harmless, and recycling waste. It provides an important technical path for solving problems such as environmental pollution, green energy, green agriculture, and greenhouse gas emissions.

[0003] The total solids (TS) content of livestock and poultry manure, kitchen waste, and municipal sludge is 10-30%, of which the volatile solids (VS) content is 70-95%, rich in non-water-soluble substances such as cellulose (14-20%), hemicellulose (17-27%), lignin (4-15%), and humic matter (5-20%) (Ma et al., 2019; Lou et al., 2020). Extensive production practice has demonstrated that for organic waste with high solids content (TS ≥ 10%, rich in non-water-soluble organic matter), anaerobic digestion technology faces a technical bottleneck of low CH4 yield, severely restricting its role in production (Hu et al., 2019; Zhou et al., 2020). Therefore, improving the CH4 yield of anaerobic digestion is of great significance for realizing the energy conversion and organic fertilizer production of pig manure.

[0004] Most current research focuses on how in-situ O2 supply affects CH4 production under low solids conditions. For example, Nguyenet et al. (2019) studied the effect of O2 on organic loading using elephant grass as raw material and the CSTR process with a solids content of approximately 4.5%, when the organic loading was 5 g (VS) L. -1 d -1 When O2 supply increased the ORP value from -495mV to -470mV, the acidification of fermentation was alleviated compared to no O2 supply, thus significantly improving the stability of CH4 production. This indicates that O2 enhances the stability of the reactor under high organic loading rates. The above study shows that under low solids content (TS≤5%) anaerobic digestion conditions, moderate O2 supply does not decrease the CH4 yield, but excessive O2 supply decreases the CH4 yield. This suggests that under low solids content, trace amounts of O2 supply do not increase the CH4 yield of anaerobic digestion.

[0005] The problem addressed in the patented method and apparatus for increasing CH4 yield from high-solids-content organic waste (CN 115466751B) is that continuous input of trace amounts of air in a high-solids-content total mixed fermentation reactor (CSTR) significantly promotes CH4 production from organic waste (increasing by 21%), without increasing O2 in the biogas. The CH4 content is no different from the control group without air, ensuring the safety and quality of the biogas. Mechanistic studies have found that the degradation rates of cellulose, lignin, and humic substances are higher with trace amounts of air than without, indicating that the increased CH4 yield comes not only from increased cellulose hydrolysis but may also be related to the decomposition of lignin and humic substances. However, this invention, which continuously supplies air directly into the fermentation device, poses a safety risk of air transfer into the biogas, leading to excessive oxygen levels in the biogas. Summary of the Invention

[0006] The purpose of this application is to provide a device and method for improving biogas production through micro-aeration and reflux of biogas slurry, which has the advantages of reducing costs, increasing biogas production, and ensuring safety.

[0007] To solve the above-mentioned technical problems, the technical solution adopted in this application is as follows:

[0008] On one hand, this application provides a device for improving biogas production through micro-aeration and reflux of biogas slurry, including a high-solids-content anaerobic reactor (CSTR) and a biogas slurry reflux aeration tank. The high-solids-content anaerobic reactor is provided with a biogas slurry outlet at its upper end, which is connected to the upper end of the biogas slurry reflux aeration tank through a biogas slurry outlet pipe. The lower end of the biogas slurry reflux aeration tank is connected to the lower end of the high-solids-content anaerobic reactor through a biogas slurry reflux pipe. An aeration head is provided at the bottom of the biogas slurry reflux aeration tank.

[0009] On the other hand, this application provides a method for improving biogas yield by using the above-mentioned device for micro-aeration and reflux of biogas slurry, comprising the following steps:

[0010] S1. The upper layer of biogas slurry in the high solids content anaerobic reactor is sent into the biogas return aeration tank.

[0011] S2. Air is periodically introduced through the aeration heads located at the bottom of the biogas return aeration tank to aerate the biogas slurry;

[0012] S3. The biogas slurry after aeration is periodically returned to the high-content anaerobic reactor through the biogas slurry return pipe.

[0013] S4. Mechanical stirring mixes the returned biogas slurry with the fermentation material in the reactor evenly, and biogas is discharged from the top of the high solids anaerobic reactor.

[0014] Compared with the prior art, the embodiments of this application have at least the following advantages or beneficial effects:

[0015] 1. This application introduces micro-aeration of biogas slurry and recirculation of air into a high-solids-content anaerobic reactor (air is readily available and can be introduced into the reactor at low cost), which significantly promotes the production of CH4 from organic waste (livestock and poultry manure, kitchen waste, municipal sludge, distiller's grains, etc.) (increasing by 19-25%), improves the high-solids-content anaerobic reactor's ability to withstand high organic loads, and the CH4 content is no different from the control group without air.

[0016] 2. This application's device includes an external biogas return aeration tank. A portion of the biogas slurry from the high-solids-content anaerobic reactor is returned to the reactor carrying air in the biogas return aeration tank. This method fundamentally avoids the safety hazard of excessive O2 in the biogas caused by injecting air into the high-solids-content anaerobic reactor, ensuring the safety and quality of the biogas. Furthermore, both air injection and return are intermittent in this application, with a daily total biogas slurry return flow rate of 1.0%–8.0%. Compared to traditional continuous systems, this application has a lower biogas slurry return flow rate, saving energy and reducing costs.

[0017] 3. This application can be used for existing large and super-large biogas projects using livestock and poultry manure, kitchen waste, municipal sludge, and distiller's grains. When applied, only minor modifications are needed to the existing facilities and equipment (the modification cost is only 3-5% of the total construction cost of the project) to significantly improve the energy conversion efficiency of the biogas project and its ability to withstand high solids content and high organic load. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a structural diagram of the device in Embodiment 1 of this application;

[0020] Figure 2 This is a comparative graph showing the effect of biogas slurry micro-aeration reflux on the average CH4 yield of anaerobic fermentation of pig manure (TS=10%) in Example 2 of this application;

[0021] Figure 3 This is a comparative graph showing the effect of micro-aeration reflux of biogas slurry on the daily CH4 production of anaerobic fermentation of pig manure (TS=10%) in Example 2 of this application.

[0022] Figure 1Indicators: 1-High solids anaerobic reactor; 2-Aeration head; 3-Biogas return aeration tank; 4-Biogas slurry return pipe; 5-Dissolved oxygen monitoring controller; 6-Biogas slurry discharge pipe; 7-Agitator; 8-Biogas meter; 9-Feed pipe; 10-Sludge and sand discharge port; 11-Timed micro-aeration equipment; 12-Timed biogas slurry return pump; 13-Discharge tank. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to specific embodiments.

[0025] A device for improving biogas production through micro-aeration and reflux of biogas slurry includes a high-solids-content anaerobic reactor 1 and a biogas slurry reflux aeration tank 3. The high-solids-content anaerobic reactor 1 is provided with a biogas slurry outlet at its upper end, which is connected to the upper end of the biogas slurry reflux aeration tank 3 through a biogas slurry outlet pipe 6. The lower end of the biogas slurry reflux aeration tank 3 is connected to the lower end of the high-solids-content anaerobic reactor 1 through a biogas slurry reflux pipe 4. An aeration head 2 is provided at the bottom of the biogas slurry reflux aeration tank 3.

[0026] In some embodiments of this application, the aeration head 2 is a microporous aeration head with a pore diameter of 5-30 μm, a spacing of 1-50 mm between aeration holes, and a spacing of 5-50 cm between adjacent microporous aeration heads; the end of the microporous aeration head is connected to a timed micro-aeration device 11.

[0027] In some embodiments of this application, a dissolved oxygen monitoring controller 5 is also provided at the bottom of the above-mentioned biogas slurry return aeration tank 3.

[0028] In some embodiments of this application, the high solids content anaerobic reactor 1 is provided with a stirrer 7, the bottom of the high solids content anaerobic reactor 1 is provided with a sludge and sand discharge port 10, the lower side wall of the high solids content anaerobic reactor 1 is connected to a feeding tank 9, the top of the high solids content anaerobic reactor 1 is connected to a biogas outlet pipe, and the biogas outlet pipe is connected to a biogas meter 8.

[0029] In some embodiments of this application, a timed biogas slurry return pump 12 is installed on the biogas slurry return tank 4.

[0030] A method for increasing biogas yield using the above-mentioned device with micro-aeration and reflux of biogas slurry includes the following steps:

[0031] S1. Part of the upper layer of biogas slurry in the high solids anaerobic reactor 1 is sent to the discharge tank, and part of it is sent to the biogas return aeration tank 3.

[0032] S2. Air is periodically introduced through the aeration head 2 located at the bottom of the biogas return aeration tank 3 to aerate the biogas slurry;

[0033] S3. The biogas slurry after aeration is periodically returned to the high solids anaerobic reactor 1 through the biogas slurry return pipe 4.

[0034] S4. Mechanical stirring mixes the returned biogas slurry with the fermentation material in the high solids anaerobic reactor 1 evenly, and biogas is discharged from the top of the high solids anaerobic reactor 1.

[0035] In some embodiments of this application, in step S3 above, the frequency of returning biogas slurry from the biogas return aeration tank 3 to the high-solids anaerobic reactor 1 is 8-12 times / day, 50-500 seconds / time; the TS content of the returned biogas slurry is 0.3-1.0%; and 100-500 mL of air is supplied to the biogas slurry half an hour before the return. -1 h -1 When the dissolved oxygen in the biogas slurry reaches 0.3–1.5 mg / L, reflux begins.

[0036] In some embodiments of this application, the mechanical stirring frequency in step S4 is 12 times / day, 2 minutes / time, and the rotation speed is 60-80 rpm.

[0037] In some embodiments of this application, the fermentation product in step S4 above is fed using a semi-continuous fermentation process, with feeding and discharging once a day, discharging first and then feeding, and the TS concentration in the feed being 10-30%; the organic loading rate is 6 g (TS) L. -1 d -1 The fermentation temperature in the high-solids-content anaerobic reactor 1 is 30-40℃.

[0038] In some embodiments of this application, the fermented product is a non-degradable organic matter rich in lignocellulose, specifically including one or more of pig manure, cow manure, chicken manure, straw, and municipal sludge.

[0039] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0040] Example 1

[0041] A device for improving biogas production through micro-aeration and reflux of biogas slurry, such as... Figure 1As shown, it includes a high-solids-content anaerobic reactor 1, which is used for the fermentation and degradation of refractory organic matter rich in lignocellulose. The high-solids-content anaerobic reactor 1 is equipped with a stirrer 7 to agitate the fermentation material in the reactor. The bottom of the high-solids-content anaerobic reactor 1 is equipped with a sludge and sand discharge port 10. The lower side wall of the high-solids-content anaerobic reactor 1 is connected to a feeding tank 9. The top of the high-solids-content anaerobic reactor 1 is connected to a biogas outlet pipe, which is connected to a biogas meter 8 to collect the gas produced after anaerobic fermentation.

[0042] The high-solids-content anaerobic reactor 1 is equipped with a biogas slurry outlet at its upper end, which is connected to the upper end of the biogas slurry return aeration tank 3 via a biogas slurry outlet pipe 6. The lower end of the biogas slurry return aeration tank 3 is connected to the lower end of the high-solids-content anaerobic reactor 1 via a biogas slurry return pipe 4, forming a biogas slurry return path. A timed biogas slurry return pump 12 is installed on the biogas slurry return pipe 4 to periodically return the micro-aerated biogas slurry to the high-solids-content anaerobic reactor 1. An aeration head 2 is installed at the bottom of the biogas slurry return aeration tank 3. This aeration head 2 is a microporous aeration head with a pore diameter of 50μm, a spacing of 5mm between aeration holes, and a spacing of 10cm between adjacent microporous aeration heads. A timed micro-aeration device 11 is connected to the end of the microporous aeration head to precisely and quantitatively introduce air into the aeration tank. A dissolved oxygen monitoring controller 5 is also installed at the bottom of the biogas slurry return aeration tank 3 to monitor the oxygen content.

[0043] The usage steps include:

[0044] S1. Feed the high solids anaerobic reactor 1. The fermentation reaction of the fermentation product is carried out in the high solids anaerobic reactor 1. Then, the upper layer of biogas liquid in the high solids anaerobic reactor 1 is sent into the biogas return aeration tank 3.

[0045] S2. Air is periodically introduced through the aeration head 2 located at the bottom of the biogas return aeration tank 3 to aerate the biogas slurry;

[0046] S3. The biogas slurry after aeration is periodically returned to the high-solids-content anaerobic reactor 1 through the biogas slurry return pipe 4; the frequency of biogas slurry return is 12 times / day, 20 seconds / time; the TS content of the returned biogas slurry is 0.3-1.0%; half an hour before the biogas slurry return, 100-500 ml of air is supplied into the biogas slurry. -1 h -1 When the dissolved oxygen in the biogas slurry reaches 0.3–1.5 mg / L, reflux begins.

[0047] S4. Mechanical stirring: The returned biogas slurry is uniformly mixed with the fermentation material in the reactor. The stirring frequency is 12 times / day, 2 minutes / time, and the rotation speed is 60-80 rpm. The biogas produced after the reaction is discharged from the top of the reactor.

[0048] After the system has been running continuously, the fermentation material is fed using a semi-continuous fermentation process, with one feeding and one discharge per day, discharging first and then feeding. The TS concentration in the feed is 10-30%; the organic loading rate is 6 g (VS) L. -1 d -1 The fermentation temperature in the high-solids-content anaerobic reactor 1 is 30-40℃.

[0049] Example 2

[0050] This embodiment uses pig manure with a solid content of 10% for the experiment.

[0051] This experiment used pig manure from a pig farm in Xiuwen County, Guizhou Province as raw material and designed two experimental groups. An 11L CSTR fermenter was used, corresponding to a hydraulic retention time (HRT) of 15 days and an organic loading rate of 6 g (TS) / L. -1 d -1 Fermentation temperature was maintained at 35℃, with stirring frequency of 12 times / day, 2 minutes / time. The biogas slurry was refluxed 12 times / day, 20 seconds / time; the total saturation (TS) content of the refluxed biogas slurry was 0.3-1%; 300 ml of air was supplied to the biogas slurry half an hour before reflux. -1 h -1 When the dissolved oxygen in the biogas slurry reaches 0.3–1.5 mg / L, reflux begins. Feeding and discharging occur once daily (semi-continuous), with each feeding and discharging volume being 0.6 L.

[0052] Two air supply gradients were set up: a control group with 0 mL / L (biogas slurry) and an experimental group with (200±50) mL / L. -1 h -1 Each fermentation gradient lasted 20 days, for a total of 40 days. The results are as follows: Figure 2 and Figure 3 As shown in the figure, compared with the un-air-supply group, the biogas yield of the experimental group increased by 20.35%. The above experiment indicates that in CSTR fermentation with a solids content of 10%, when the air supply intensity is (200±50) mL... - 1 h -1 The average biogas production rate increased by 20.35%.

[0053] Example 3

[0054] This application also designed a control experiment using the lees of a winery in Bozhou District, Guizhou Province as raw material. The experimental process was basically the same as in Example 2. In the end, compared with the unsupplied air, the biogas production rate of the experimental group could be increased by 19.0±1.6%.

[0055] In summary, the method and apparatus for improving biogas yield through micro-aeration and reflux of biogas slurry according to embodiments of this application have the following advantages:

[0056] 1. This application significantly promotes the production of CH4 from organic waste (livestock and poultry manure, kitchen waste, municipal sludge, distiller's grains, etc.) by introducing air into a high-solids-content anaerobic reactor through micro-aeration of biogas slurry (air is readily available and can be introduced into the reactor at low cost) by increasing it by 19-25%, thereby improving the reactor's ability to withstand high organic loads. The CH4 content is no different from that of the control without air.

[0057] 2. This application's device includes an external biogas return aeration tank. A portion of the biogas slurry from the high-solids-content anaerobic reactor is returned to the reactor carrying air in the biogas return aeration tank. This method fundamentally avoids the safety hazard of excessive O2 in the biogas caused by injecting air into the high-solids-content anaerobic reactor, ensuring the safety and quality of the biogas. Furthermore, this application uses intermittent air injection and return methods, which saves energy and reduces costs compared to traditional continuous methods.

[0058] 3. This application can be used for existing large and super-large biogas projects using livestock and poultry manure, kitchen waste, municipal sludge, and distiller's grains. When applied, only minor modifications are needed to the existing facilities and equipment (the modification cost is only 3-5% of the total construction cost of the project) to significantly improve the energy conversion efficiency of the biogas project and its ability to withstand high solids content and high organic load.

[0059] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A device for improving biogas yield through micro-aeration and reflux of biogas slurry, comprising a high-solids-content anaerobic reactor (1), characterized in that, It also includes a biogas slurry return aeration tank (3), the upper end of the high solids content anaerobic reactor (1) is provided with a biogas slurry outlet, the biogas slurry outlet is connected to a biogas slurry outlet pipe (6), the biogas slurry outlet pipe (6) is connected to the upper end of the biogas slurry return aeration tank (3); the lower end of the biogas slurry return aeration tank (3) is connected to the lower end of the high solids content anaerobic reactor (1) through a biogas slurry return pipe (4); the bottom of the biogas slurry return aeration tank (3) is provided with an aeration head (2).

2. The device for improving biogas yield through micro-aeration and reflux of biogas slurry according to claim 1, characterized in that, The aeration head (2) is a microporous aeration head with a pore diameter of 5-30 μm, a spacing of 1-50 mm between aeration holes, and a spacing of 5-50 cm between adjacent microporous aeration heads; the end of the microporous aeration head is connected to a timed micro-aeration device (11).

3. The device for improving biogas yield through micro-aeration and reflux of biogas slurry according to claim 1, characterized in that, The bottom of the biogas slurry return aeration tank (3) is also equipped with a dissolved oxygen monitoring controller (5).

4. The device for improving biogas yield through micro-aeration and reflux of biogas slurry according to claim 1, characterized in that, The high solids anaerobic reactor (1) is equipped with a stirrer (7), a sludge and sand discharge port (10) is provided at the bottom of the high solids anaerobic reactor (1), a feeding tank (9) is connected to the lower side wall of the high solids anaerobic reactor (1), and a biogas outlet pipe is connected to the top of the high solids anaerobic reactor (1), which is connected to a biogas meter (8).

5. The device for improving biogas yield through micro-aeration and reflux of biogas slurry according to claim 1, characterized in that, The biogas slurry return tank (4) is equipped with a timed biogas slurry return pump (12).

6. A method for increasing biogas yield by using the device described in any one of claims 1-5 with micro-aeration and reflux of biogas slurry, characterized in that, Includes the following steps: S1. Send a portion of the upper layer of biogas slurry in the high solids anaerobic reactor (1) to the discharge tank and a portion to the biogas return aeration tank (3). S2. Air is periodically introduced through the aeration head (2) located at the bottom of the biogas return aeration tank (3) to aerate the biogas slurry; S3. The biogas slurry after aeration is periodically returned to the high solids anaerobic reactor (1) through the biogas slurry return pipe (4); S4. Mechanical stirring mixes the returned biogas slurry with the fermentation material in the high solids anaerobic reactor (1) evenly, and biogas is discharged from the top of the high solids anaerobic reactor (1).

7. The method for improving biogas yield through micro-aeration and reflux of biogas slurry according to claim 6, characterized in that, In step S3, the frequency of returning biogas slurry from the biogas return aeration tank (3) to the high-solids anaerobic reactor (1) is 8-12 times / day, 50-500 seconds / time; the TS content of the returned biogas slurry is 0.3-1.0%; 100-500 mL of air is supplied to the biogas slurry half an hour before the return. -1 h -1 When the dissolved oxygen in the biogas slurry reaches 0.3–1.5 mg / L, reflux begins.

8. The method for improving biogas yield through micro-aeration and reflux of biogas slurry according to claim 6, characterized in that, In step S4, the mechanical stirring frequency is 12 times / day, 2 minutes / time, and the rotation speed is 60-80 revolutions / min.

9. The method for improving biogas yield through micro-aeration and reflux of biogas slurry according to claim 6, characterized in that, In step S4, the fermentation product is fed using a semi-continuous fermentation process, with feeding and discharging once a day. The TS concentration in the feed is 10-30%, and the organic loading rate is 6 g (TS) / L. -1 d -1 The fermentation temperature in the high solids anaerobic reactor (1) is 30-40℃.

10. The method for improving biogas yield through micro-aeration and reflux of biogas slurry according to claim 9, characterized in that, The fermented product is rich in lignocellulose and difficult-to-degrade organic matter, specifically including one or more of pig manure, cow manure, chicken manure, straw, municipal sludge, kitchen waste, and distiller's grains.

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