Device and method for increasing biogas yield through biogas slurry micro-aeration backflow

Abstract

The invention provides a device and a method for increasing the biogas yield through biogas slurry micro-aeration backflow, and relates to the technical field of organic solid waste energy regeneration. The device comprises a high-solid-content anaerobic reactor and a biogas slurry backflow aeration tank, a biogas slurry outlet is formed in the upper end of the reactor, and the biogas slurry outlet is connected to the upper end of the biogas slurry backflow aeration tank through a biogas slurry outlet pipe; the lower end of the biogas slurry backflow aeration tank is connected with the lower end of the reactor through a biogas slurry backflow pipe; and an aeration head is arranged at the bottom of the biogas slurry backflow aeration tank. According to the method, air is carried into the reactor through biogas slurry micro-aeration backflow, backflow is carried out 4-12 times every day, and the daily total biogas slurry backflow amount is 1.0-8.0% of the volume of the reactor; the dissolved oxygen of the backflow biogas slurry is 0.3-1.5 mg / L, the biogas yield is improved by 20%, it is indicated that biogas slurry micro-aeration backflow carrying air can significantly improve the biogas yield, and the problem of potential safety hazards caused by the fact that O2 in biogas exceeds the standard due to the fact that air is injected into the reactor is fundamentally avoided.

Description

Technical Field

[0001] The present application relates to the technical field of organic solid waste energy conversion, and in particular to a device and method for improving biogas yield by micro-aeration and reflux of biogas slurry. Background Art

[0002] Anaerobic digestion refers to the process in 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, achieve waste reduction, harmlessness and resource utilization, and provide an important technical path for solving problems including environmental pollution, green energy, green agriculture, greenhouse gas emissions, etc.

[0003] The solid content (Total solids, TS) of livestock and poultry manure, kitchen waste, and municipal sludge is 10-30%, of which the organic content (volatile solids, VS) is 70-95%, and it is rich in non-water-soluble substances such as cellulose (14-20%), hemicellulose (17-27%), lignin (4-15%), and humus (5-20%) (Ma et al., 2019; Lou Menghan et al., 2020). A large number of production practices have proved that for organic waste with high solid content (TS ≥ 10%, rich in non-water-soluble organic matter), anaerobic digestion technology faces the technical bottleneck of low CH4 yield, which seriously restricts its role in production (Hu et al., 2019; Zhou Huimin et al., 2020). Therefore, improving the CH4 yield of anaerobic digestion is of great significance for realizing the energy and organic fertilizer of pig manure.

[0004] At present, most of the research focuses on how in-situ O2 supply affects CH4 production under low solid content conditions. For example, Nguyen et al. (2019) studied the effect of O2 on organic loading, using elephant grass as raw material, using CSTR process, and solid content of about 4.5%. When the organic loading was 5g (VS) L -1 d -1 When O2 is supplied to increase the ORP value from -495mV to -470mV, the fermentation acidification is alleviated compared with no O2 supply, thereby significantly improving the stability of CH4 production, indicating that O2 enhances the stability of the reactor under high organic loading rate. The above studies show that under low solid content (TS≤5%) anaerobic digestion conditions, the CH4 yield does not decrease when O2 is supplied moderately, but the CH4 yield decreases when O2 is supplied excessively, which suggests that trace O2 supply does not increase the CH4 yield of anaerobic digestion under low solid content.

[0005] The problem solved in the patent "A method and device for improving the CH4 yield of high-solid organic waste (CN 115466751B)" is as follows: under the conditions of a high-solid fully mixed fermentation reactor (CSTR), the continuous input of trace air significantly promotes the production of CH4 from organic waste (increased by 21%), and the input of air does not lead to an increase in O2 in the biogas, and the CH4 content is no different from the control without air, ensuring the safety and quality of the biogas. Mechanistic studies have found that the degradation rates of cellulose, lignin and humus are higher when a trace amount of air is supplied than when no air is supplied, indicating that the increase in CH4 yield not only comes from more cellulose hydrolysis, but may also be related to the decomposition of lignin and humus. However, the invention uses a continuous supply of air directly to the fermentation device, which poses a safety risk of air being transferred to the biogas, resulting in excessive oxygen in the biogas. Summary of the invention

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

[0007] In order to solve the above technical problems, the technical solution adopted in this application is:

[0008] On the one hand, the present application provides a device for improving biogas yield by micro-aeration and reflow of biogas slurry, comprising a high-solid anaerobic reactor (CSTR) and a biogas slurry reflow aeration tank, wherein the upper end of the high-solid anaerobic reactor is provided with a biogas slurry outlet, and the biogas slurry outlet is connected to the upper end of the biogas slurry reflow aeration tank through a biogas slurry outlet pipe; the lower end of the biogas slurry reflow aeration tank is connected to the lower end of the high-solid anaerobic reactor through a biogas slurry reflow pipe; and an aeration head is provided at the bottom of the biogas slurry reflow aeration tank.

[0009] On the other hand, the present 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, sending the upper layer of biogas slurry in the high solid content anaerobic reactor into the biogas return aeration tank;

[0011] S2, regularly inputting air through the aeration head located at the bottom of the biogas return aeration tank to aerate the biogas slurry;

[0012] S3, the aerated biogas slurry is regularly refluxed to the high-content anaerobic reactor through the biogas slurry reflux pipe;

[0013] S4. Mechanical stirring is used to evenly mix the returned biogas slurry with the fermented material in the reactor, and the biogas is discharged from the upper end of the high-solid content anaerobic reactor.

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

[0015] 1. In this application, the micro-aeration reflux of biogas slurry carries air into a high-solid content anaerobic reactor (air is easily available and can be input into the reactor at a low cost), which significantly promotes the production of CH4 (increased by 19-25%) from organic waste (livestock and poultry manure, kitchen waste, municipal sludge, distiller's grains, etc.), improves the ability of the high-solid content anaerobic reactor to tolerate high organic loads, and the CH4 content is no different from the control without adding air.

[0016] 2. The device of the present application is provided with an external biogas return aeration tank, and part of the biogas slurry after the reaction in the high-solid anaerobic reactor is returned to the reactor with air in the biogas return aeration tank. This method fundamentally avoids the potential safety hazard of excessive O2 in the biogas caused by injecting air into the high-solid anaerobic reactor, and ensures the safety and quality of biogas. In addition, the injection of air and the return flow of the present application are both intermittent, and the total biogas slurry return rate is 1.0-8.0% per day. Compared with the traditional continuous method, the biogas slurry return rate of the present application is small, which saves energy consumption and reduces costs.

[0017] 3. This application can be used for existing large and super-large biogas projects using livestock and poultry manure, food waste, municipal sludge, distiller's grains, etc. When applied, a slight modification of existing facilities and equipment (the modification cost is only 3-5% of the total construction cost of the project) can significantly improve the energy conversion efficiency of the biogas project and its ability to withstand high solid content and high organic load rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 This is a structural diagram of the device of Example 1 of the present application;

[0020] Figure 2 This is a comparison chart of the effect of micro-aeration and recirculation of biogas slurry on the average CH4 yield of anaerobic fermentation of pig manure (TS=10%) in Example 2 of the present application;

[0021] Figure 3 This is a comparison chart of the effect of micro-aeration recirculation of biogas slurry on the daily CH4 production of anaerobic fermentation TS of pig manure (TS=10%) in Example 2 of the present application.

[0022] Figure 1Chinese symbols: 1- high solid content 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- mud and sand discharge port; 11- timed micro aeration equipment; 12- timed biogas slurry return pump; 13- discharge tank. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0024] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to specific embodiments.

[0025] A device for improving biogas yield by micro-aeration and reflow of biogas slurry comprises a high-solid content anaerobic reactor 1 and a biogas slurry reflow aeration tank 3. The high-solid content anaerobic reactor 1 is provided with a biogas slurry outlet at the upper end, and the biogas slurry outlet is connected to the upper end of the biogas slurry reflow aeration tank 3 through a biogas slurry outlet pipe 6; the lower end of the biogas slurry reflow aeration tank 3 is connected to the lower end of the high-solid content anaerobic reactor 1 through a biogas slurry reflow pipe 4; and the bottom of the biogas slurry reflow aeration tank 3 is provided with an aeration head 2.

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

[0027] In some embodiments of the present application, a dissolved oxygen monitoring controller 5 is further provided at the bottom of the biogas slurry return aeration tank 3 .

[0028] In some embodiments of the present application, an agitator 7 is provided in the high-solid anaerobic reactor 1, a mud and sand discharge port 10 is provided at the bottom of the high-solid anaerobic reactor 1, a feeding tank 9 is connected to the lower side wall of the high-solid anaerobic reactor 1, and a biogas outlet pipe is connected to the top of the high-solid anaerobic reactor 1, and the biogas outlet pipe is connected to a biogas meter 8.

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

[0030] A method for improving biogas yield by using the above-mentioned device for micro-aeration and reflux of biogas slurry comprises the following steps:

[0031] S1, sending part of the upper layer of biogas slurry in the high-solid content anaerobic reactor 1 to the discharge tank, and sending part to the biogas return aeration tank 3;

[0032] S2, regularly inputting air through the aeration head 2 located at the bottom of the biogas return aeration tank 3 to aerate the biogas slurry;

[0033] S3, the aerated biogas slurry is regularly refluxed to the high solid content anaerobic reactor 1 through the biogas slurry reflux pipe 4;

[0034] S4, mechanically stirring to uniformly mix the returned biogas slurry with the fermented material in the high-solid content anaerobic reactor 1 for reaction, and the biogas is discharged from the upper end of the high-solid content anaerobic reactor 1.

[0035] In some embodiments of the present application, in the above step S3, the frequency of returning the biogas slurry in the biogas return aeration tank 3 to the high solid content anaerobic reactor 1 is 8 to 12 times / day, 50 to 500 seconds / time; the TS content of the returned biogas slurry is 0.3 to 1.0%; 100 to 500 mL of air is supplied to the biogas slurry half an hour before the biogas slurry is returned. -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 the present application, the stirring frequency of the mechanical stirring in the above step S4 is 12 times / day, 2 minutes / time, and the rotation speed is 60 to 80 revolutions / min.

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

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

[0039] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0040] Example 1

[0041] A device for improving biogas production by micro-aeration and reflux of biogas slurry, such as Figure 1As shown, it includes a high-solid anaerobic reactor 1, which is used for fermentation and degradation of lignocellulose-rich and difficult-to-degrade organic matter. A stirrer 7 is arranged in the high-solid anaerobic reactor 1 for stirring the fermentation in the reactor; a mud and sand discharge port 10 is arranged at the bottom of the high-solid anaerobic reactor 1, a feeding tank 9 is connected to the lower side wall of the high-solid anaerobic reactor 1, and a biogas outlet pipe is connected to the top of the high-solid anaerobic reactor 1, and the biogas outlet pipe is connected to a biogas meter 8 for collecting the gas produced after anaerobic fermentation.

[0042] The upper end of the high-solid anaerobic reactor 1 is also provided with a biogas slurry outlet, which is connected to the upper end of the biogas slurry return aeration tank 3 through 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-solid anaerobic reactor 1 through a biogas slurry return pipe 4 to form a biogas slurry return passage, and a timed biogas slurry return pump 12 is installed on the biogas slurry return pipe 4, which is used to return the micro-aerated biogas to the high-solid anaerobic reactor 1 at a fixed time. An aeration head 2 is provided at the bottom of the biogas slurry return aeration tank 3, and the aeration head 2 is a microporous aeration head, the aperture of the microporous aeration head is 50μm, the spacing between the aeration holes is 5mm, and the spacing between adjacent microporous aeration heads is 10cm; the end of the microporous aeration head is connected to a timed micro-aeration device 11, which is used to accurately and regularly and quantitatively introduce air into the aeration tank. A dissolved oxygen monitoring controller 5 is also provided at the bottom of the biogas slurry return aeration tank 3 to monitor the oxygen content.

[0043] The steps for use include:

[0044] S1, feeding into the high-solid anaerobic reactor 1, fermenting the fermented product in the high-solid anaerobic reactor 1, and then sending the upper layer of biogas slurry in the high-solid anaerobic reactor 1 into the biogas return aeration tank 3;

[0045] S2, regularly inputting air through the aeration head 2 located at the bottom of the biogas return aeration tank 3 to aerate the biogas slurry;

[0046] S3, the aerated biogas slurry is regularly refluxed to the high solid content anaerobic reactor 1 through the biogas slurry reflux pipe 4; the frequency of biogas slurry reflux is 12 times / day, 20s / time; the TS content of the refluxed biogas slurry is 0.3-1.0%; 100-500mL of air is supplied to the biogas slurry half an hour before the biogas slurry reflux -1 h -1 When the dissolved oxygen in the biogas slurry reaches 0.3-1.5 mg / L, reflux begins.

[0047] S4. Mechanical stirring is used to evenly mix the returned biogas slurry with the fermented material in the reactor. The stirring frequency of the mechanical stirring is 12 times / day, 2 minutes / time, and the speed is 60-80 revolutions / min. The biogas after the reaction is discharged from the upper end of the reactor.

[0048] After the system is running continuously, the fermentation product is fed by semi-continuous fermentation process, with feeding and discharging once a day, first discharging and then feeding, and the feed TS concentration is 10-30%; the organic loading rate is 6g (VS) L -1 d -1 ; The fermentation temperature in the high solid content anaerobic reactor 1 is 30-40°C.

[0049] Example 2

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

[0051] In this experiment, pig manure from a pig farm in Xiuwen County, Guizhou Province was used as raw material to design two groups of experiments. An 11L CSTR fermenter was used, corresponding to a hydraulic retention time (HRT) of 15d and an organic loading rate of 6g (TS) L -1 d -1 The fermentation temperature was maintained at 35°C, and the stirring frequency was 12 times / day, 2 minutes / time. The slurry was refluxed 12 times / day, 20 seconds / time. The TS content of the refluxed slurry was 0.3-1%. 300 mL of air was supplied to the slurry half an hour before the slurry was refluxed. -1 h -1 When the dissolved oxygen of the biogas slurry reaches 0.3-1.5 mg / L, reflux begins. The feed and discharge are done once a day (semi-continuously), and the volume of each feed and discharge is 0.6L.

[0052] Two air supply gradients were set, namely 0 mL / L (biogas slurry) for the control group and (200 ± 50) mL for the experimental group. -1 h -1 Each gradient fermentation lasted 20 days, and the total operation was 40 days. Figure 2 and Figure 3 Compared with the group without air supply, the biogas yield of the experimental group increased by 20.35%. The above experiment shows that in a CSTR fermentation with a solid content of 10%, when the air supply intensity is (200±50)mL - 1 h -1 The biogas production rate increased by an average of 20.35%.

[0053] Example 3

[0054] The present application also designed a control experiment using lees from a winery company in Bozhou District, Guizhou Province as raw material. The experimental process was basically the same as that of Example 2. Ultimately, compared with the group without air supply, the biogas yield of the experimental group was substantially increased by 19.0±1.6%.

[0055] In summary, the method and device for improving biogas yield by micro-aeration and reflux of biogas slurry in the embodiment of the present application have the following advantages:

[0056] 1. This application significantly promotes the production of CH4 (increased by 19-25%) from organic waste (livestock and poultry manure, kitchen waste, municipal sludge, distiller's grains, etc.) by carrying air into a high-solid content anaerobic reactor (air is easily available and can be input into the reactor at a low cost) through micro-aeration of the biogas slurry and reflux, thereby improving the reactor's ability to tolerate high organic loads, and the CH4 content is no different from the control without adding air.

[0057] 2. The device of the present application is provided with an external biogas return aeration tank, and part of the biogas slurry after the reaction in the high-solid anaerobic reactor is returned to the high-solid anaerobic reactor with air in the biogas return aeration tank. This method fundamentally avoids the potential safety hazard of excessive O2 in the biogas caused by injecting air into the high-solid anaerobic reactor, and ensures the safety and quality of the biogas. In addition, the injection of air and the return flow of the present application are both intermittent, which can save energy and reduce costs compared to the traditional continuous method.

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

[0059] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present application.

Claims

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

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

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

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

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

6. A method for improving biogas yield by using the biogas slurry micro-aeration reflux device according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, sending part of the upper layer of biogas slurry in the high-solid content anaerobic reactor (1) to the discharge tank, and sending part to the biogas return aeration tank (3); S2, regularly inputting air through an aeration head (2) located at the bottom of the biogas return aeration tank (3) to aerate the biogas slurry; S3, the aerated biogas slurry is regularly refluxed to the high solid content anaerobic reactor (1) through the biogas slurry reflux pipe (4); S4. Mechanical stirring is used to uniformly mix the returned biogas slurry with the fermented material in the high-solid content anaerobic reactor (1) to react, and biogas is discharged from the upper end of the high-solid content anaerobic reactor (1).

7. The method for improving biogas yield by micro-aeration and reflux of biogas slurry according to claim 6, characterized in that: In the step S3, the frequency of returning the biogas slurry in the biogas return aeration tank (3) to the high solid content anaerobic reactor (1) is 8 to 12 times per day, 50 to 500 seconds per time; the TS content of the returned biogas slurry is 0.3 to 1.0%; 100 to 500 mL of air is supplied to the biogas slurry half an hour before the biogas slurry is returned. -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 by micro-aeration and reflux of biogas slurry according to claim 6, characterized in that: The frequency of mechanical stirring in step S4 is 12 times / day, 2 minutes / time, and the rotation speed is 60-80 revolutions / min.

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

10. The method for improving biogas yield by micro-aeration and reflux of biogas slurry according to claim 9, characterized in that: 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, municipal sludge, restaurant kitchen waste, and distiller's grains.

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