Biogas slurry treatment system and method without addition of alkali agent

Abstract

The invention relates to a biogas slurry treatment system and method without addition of an alkali agent, and the method comprises the following steps: on the basis of removing CO2 through air aeration stripping to improve the pH value of biogas slurry, dropping the biogas slurry from the top end of a convection ammonia stripping tower for ammonia stripping. The blown-off ammonia-rich gas enters an absorption tower and is subjected to sulfuric acid pickling, and ammonia nitrogen self-circulation absorption is completed. The deaminated biogas slurry is further subjected to biogas aeration stripping, and biogas CO2 is absorbed to be purified while pH callback is completed through deamination. According to the method, the single deamination rate of the biogas slurry reaches 70% or above under the condition that no alkali agent is added, the ammonia nitrogen recovery rate exceeds 98%, finally, the biogas slurry meets the irrigation water discharge standard, and nitrogen fertilizer and pure biogas are obtained.

Description

Technical Field

[0001] The invention relates to the technical field of agricultural waste treatment and utilization, and in particular to a biogas slurry treatment system and method without the addition of an alkali agent. Background Art

[0002] The low-carbon circular agricultural model that uses biogas projects as a link to harmlessly treat livestock and poultry manure has been widely used. Biogas slurry is a derivative product of biogas projects. Because it contains high concentrations of ammonia and nitrogen, direct discharge is bound to cause serious environmental pollution and is also a waste of recyclable resources. Therefore, the deammoniation and recycling of biogas slurry has become one of the biggest obstacles to the promotion and application of biogas engineering technology. At present, the deammoniation of chicken manure biogas slurry mainly includes struvite precipitation, membrane separation, ammonia stripping and other technologies. Chinese patent CN215756840U discloses a struvite electrochemical precipitation method for chicken manure biogas slurry treatment, using Mg 2+ , NH 4+ ,PO4 3- Ion coprecipitation to achieve NH 4+ PO4 3- Simultaneous removal. However, this method not only requires the addition of a large amount of chemical agents, but also a large amount of stones will accumulate on the treatment equipment, which undoubtedly increases the operation and maintenance costs. Chinese patent CN207435283U uses filter membranes to realize the resource recycling of chicken manure fermented biogas slurry, but because the filter membrane needs to be cleaned regularly and has limited stability, drug resistance, heat resistance, and solvent resistance, it is difficult to promote it on a large scale. In addition, because the processing capacity of biogas slurry by membrane separation technology alone is limited, it needs to be used in conjunction with other separation technologies. Therefore, it is not suitable for large-scale biogas slurry deammoniation.

[0003] In comparison, ammonia stripping technology is considered to be the best choice for deammoniation of biogas slurry with high ammonia nitrogen concentration. By alkalizing the biogas slurry, ammonium ions are converted into free ammonia, and under the action of the free ammonia concentration gradient difference between the gas and liquid phases, ammonia migration from wastewater to gas is achieved. Finally, the biogas slurry can be deammonified by acid washing. The tail liquid of the washing is rich in ammonium salts and can be used as a biological fertilizer, which can effectively balance the cost of biogas slurry treatment. However, the addition of alkali agents greatly increases the cost of biogas slurry treatment. Therefore, seeking a cheap pH adjustment method to replace the traditional addition of alkali agents has become the key to reducing the cost of biogas slurry ammonia stripping. Chinese patent CN117361597A discloses a method for increasing the pH of biogas slurry by aeration stripping with purified biogas, thereby realizing biogas slurry ammonia recovery and biogas purification without the addition of alkali agents, but the purification of biogas means the introduction of additional operating expenses or time costs. In addition, the ammonia nitrogen removal capacity is limited by only one convection stripping, and the biogas after stripping is still alkaline and does not meet the emission standards. Summary of the invention

[0004] The present invention provides a biogas slurry treatment system and method without the addition of alkali agent, optimizes the design of the stripping-recovery device to improve the deammoniation efficiency, and ensures that the pH value of the biogas slurry can be adjusted after the stripping without affecting the discharge, thereby solving the problems of high process cost of biogas slurry ammonia recovery and biogas purification, low deammoniation efficiency, and too high pH value of the biogas slurry after stripping.

[0005] The present invention solves the above technical problems by providing a method for treating biogas slurry without adding an alkali agent, comprising the following steps:

[0006] 1) The original biogas pool is heated, and air enters the bottom of the original biogas pool through an air pump to aerate and blow off the biogas in the original biogas pool, so that the carbon dioxide and ammonia in the biogas are input into the absorption liquid of the ammonia recovery tower from the top of the original biogas pool;

[0007] 2) The biogas slurry after aeration and stripping is dripped into the convection ammonia stripping tower through the biogas slurry water pump, and the air is aerated and stripped from the bottom of the convection ammonia stripping tower through the gas circulation pump, and the ammonia in the biogas slurry in the convection ammonia stripping tower is input from the convection ammonia stripping tower into the absorption liquid filled in the ammonia recovery tower, and the absorption liquid is self-circulated in the ammonia recovery tower through the liquid circulation pump, and the biogas stripped by the convection ammonia stripping tower flows into the deammoniation biogas slurry pool from the bottom of the convection ammonia stripping tower;

[0008] 3) The biogas enters the deammonification biogas slurry tank through a biogas pump to aerate and blow off the biogas in the biogas slurry in the deammonification biogas slurry.

[0009] Preferably, the method further comprises: the input end of the gas circulation pump is connected to the top of the ammonia recovery tower, so that the ammonia that is not absorbed in the ammonia recovery tower enters the convection ammonia stripping tower for re-stripping.

[0010] Preferably, the method further comprises: the biogas for separation and the biogas in the biogas separation of the deammonification biogas slurry pool enter the methane gas storage tank from the top of the deammonification biogas slurry pool.

[0011] The original biogas pool undergoes the first air stripping to remove carbon dioxide in the biogas and increase the pH value; it enters the convection ammonia stripping tower for the second stripping to remove ammonia in the biogas and be absorbed by the absorption liquid; it then enters the deammonification biogas pool for the third stripping through biogas, and the stripped biogas and the biogas as the gas source are input into the methane gas storage tank together, so as to achieve the purpose of purifying the biogas in the biogas and adjust the pH value of the biogas to 6.0-8.5, which meets the irrigation water discharge standard.

[0012] Preferably, in step 1), the biogas slurry in the original biogas slurry pool is heated to 35-45° C., the ratio of the air ventilation volume to the biogas slurry volume in the original biogas slurry pool is 300-400; and the aeration stripping is performed every 2-6 minutes for 4-8 minutes.

[0013] When the temperature is below 35℃, HCO3 in the biogas slurry 2-It is relatively stable and not easy to decompose into CO2 to increase the pH of the biogas slurry. When the temperature exceeds 45℃, most of the nitrogen in the biogas slurry is NH4 + The CO2 in the biogas slurry is present in the form of NH3, about 80% of which is converted into NH3, which is easy to cause N loss. When the gas-liquid ratio is lower than 300, the gas disturbance time and intensity are not enough to completely blow out the CO2 in the biogas slurry. When the gas-liquid ratio is 350, more than 80% has been blown out. When it exceeds 400, it will cause energy waste. When the aeration blow-off time is short, the CO2 removal rate is low. When the interval time is short, there is too much foam, which affects the transfer of CO2 from the liquid phase to the gas phase.

[0014] Preferably, in step 2), the pH of the biogas slurry after aeration stripping in step 1) is 9-10, the operating temperature of the convection ammonia stripping tower is 40-50°C, and the ratio of the air ventilation volume to the biogas slurry volume of the convection ammonia stripping tower is 3000-4000.

[0015] When the pH is less than 9, the percentage of ammonium ions converted to NH3 is usually very low, while at pH = 10, almost all ammonium ions will be converted to NH3, and exceeding the pH will not increase the NH3 content, so a pH exceeding 10 is not an economical choice. When the stripping temperature is 45°C, most of the N in the biogas slurry is in the form of NH4 + In the form of NH3, more than 80% of it is converted into NH3. Exceeding 50℃ will not significantly improve the ammonia removal efficiency and reduce its economic benefits. The gas-liquid ratio is the same as above.

[0016] Preferably, in step 2), the absorption liquid is concentrated sulfuric acid with a mass concentration of 30-50%, and the circulation flow rate of the absorption liquid in the ammonia recovery tower is 6-10m 3 / h.

[0017] When the sulfuric acid concentration is too low, the solution cannot provide enough SO4 2- Absorbing NH3, the absorption efficiency is low, and when the concentration is too high, there will be excess SO4 2- , making the reagent cost too high and the economic benefit low. When the absorption liquid circulation flow is too high, the retention time of NH3 in sulfuric acid is too short, which can easily lead to incomplete reaction and low absorption efficiency; when the flow is too low, the system will work too long and the energy consumption will be too high.

[0018] Preferably, in step 3), the biogas in the deammonification biogas pool is heated to 40-60°C, the ratio of the biogas ventilation volume to the biogas volume of the heated deammonification biogas pool is 400-500, and the aeration stripping is performed for 4-8 minutes every 2-6 minutes.

[0019] When the temperature is lower than 40℃, the biogas is not fully released, which affects the stripping effect. If the temperature is higher than 60℃, on the one hand, it increases energy consumption, and on the other hand, it avoids equipment damage caused by high temperature.

[0020] A biogas slurry treatment system without adding an alkali agent, comprising a raw biogas slurry tank, a convection ammonia stripping tower, an ammonia recovery tower, a deammoniation biogas slurry tank, and a methane gas storage tank;

[0021] The air inlet pipe of the raw biogas slurry pool is connected to an air pump, the air outlet pipe is connected to the bottom of the ammonia recovery tower, the liquid outlet pipe is connected to the convection ammonia stripping tower, and the liquid outlet pipe of the raw biogas slurry pool is provided with a biogas slurry water pump;

[0022] The outlet of the air inlet pipe of the convective ammonia stripping tower is arranged at the bottom of the tower, a gas circulation pump is arranged on the air inlet pipe and the inlet is connected to the top of the ammonia recovery tower, the air outlet pipe of the convective ammonia stripping tower is connected to the bottom of the ammonia recovery tower, and the drain pipe of the convective ammonia stripping tower is connected to the deammoniation slurry pool;

[0023] The bottom of the ammonia recovery tower is filled with absorption liquid, the outlet of the gas outlet pipe of the original biogas slurry pool and the outlet of the gas outlet pipe of the convection ammonia stripping tower are immersed in the absorption liquid, a liquid circulation pump is provided on the liquid outlet pipe of the ammonia recovery tower, and the outlet of the liquid outlet pipe of the ammonia recovery tower is arranged at the top of the ammonia recovery tower and is connected to a nozzle;

[0024] The air inlet pipe of the deammonification biogas pool is connected to a biogas pump, and the air outlet pipe is connected to a methane gas storage tank.

[0025] Preferably, the convective ammonia stripping tower is provided with a sludge overflow support, filler, filler pressure plate, filler support plate and aeration disk from top to bottom; the filler, filler pressure plate and filler support plate are connected to the inner wall of the convective ammonia stripping tower to form a filler area; the output end of the gas circulation pump is connected to the aeration disk.

[0026] Preferably, the biogas slurry overflow support comprises an upper overflow disk and a lower overflow disk, the upper overflow disk is annular, and is provided with a plurality of holes evenly spaced along the circumference of the disk; the lower overflow disk is circular, and the ratio of the diameter of the hollow circle to the diameter of the large circle is 1:2; the lower overflow disk is provided with a plurality of holes evenly spaced along the circumference of the disk; the upper overflow disk and the lower overflow disk are connected by a plurality of support frames, and the bottom end of the support frame penetrates the lower overflow disk and abuts against the filler support plate. The diameter of the holes provided in the upper overflow disk and the lower overflow disk is 5 mm.

[0027] The biogas slurry overflow bracket is divided into two layers, upper and lower. When the biogas slurry drops on the upper overflow plate, part of the biogas slurry flows around and flows to the lower overflow plate through the small holes around it, and part of the biogas slurry flows directly from the hollow of the ring to the lower overflow plate, so that the biogas slurry flows evenly and prevents the biogas slurry from clogging the nozzle during spraying.

[0028] Preferably, the filler in the filler zone is 25 mm multi-faceted polypropylene hollow balls, and the filler filling height is 65%-75% of the height of the countercurrent ammonia stripping tower.

[0029] Preferably, the ammonia recovery tower comprises an absorption liquid filling area 31 and an absorption liquid reflux area 32, the outer diameter of the absorption liquid filling area is larger than that of the absorption liquid reflux area, the bottom end of the absorption liquid reflux area is immersed in the absorption liquid in the absorption liquid filling area and is close to the bottom of the absorption liquid filling area, the air inlet pipe at the bottom of the absorption liquid reflux area is connected with the air outlet pipe of the original biogas slurry pool and the air outlet pipe of the flowing ammonia stripping tower, and the outlet of the liquid outlet pipe of the ammonia recovery tower is arranged at the top of the absorption liquid reflux area and is connected with a nozzle.

[0030] The bottom of the absorption liquid reflux zone contacts with the absorption liquid to form a liquid seal, thereby increasing the contact between ammonia and sulfuric acid.

[0031] The beneficial effects of the present invention are:

[0032] (1) Intermittent aeration is beneficial to eliminate the foam generated during the aeration of biogas slurry. Using air instead of purified biogas as the stripping carrier can save 25 yuan / t compared with the traditional alkaline agent NaOH to adjust the pH of biogas slurry, which has a high economic benefit.

[0033] (2) Using biogas to aerate the stripped biogas slurry not only effectively removes CO2 from the biogas and achieves the purpose of biogas purification, but also reduces the pH of the biogas slurry, so that the pH of the stripped biogas slurry is adjusted to 6.0-8.5, which meets the irrigation water discharge standard.

[0034] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. The specific implementation of the present invention is given in detail by the following embodiments and their accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0036] Figure 1 It is the process flow chart of Example 1;

[0037] Figure 2 It is a process device diagram of Example 2;

[0038] Figure 3 This is a structural diagram of the biogas slurry overflow support in Example 2;

[0039] Figure 4 This is a schematic diagram of the liquid seal formed between the gas outlet pipe and the absorption liquid in the ammonia recovery tower in Example 2.

[0040] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0041] 1. Original biogas slurry pool, 2. Convective ammonia stripping tower, 3. Ammonia recovery tower, 4. Air pump, 5. Biogas slurry pump, 6. Liquid circulation pump, 7. Gas circulation pump, 8. Biogas pump, 9. Deammoniation biogas slurry pool, 10. Methane gas storage tank, 21. Biogas slurry overflow support, 22. Filling area, 23. Aeration plate, 211. Upper overflow plate, 212. Lower overflow plate, 31. Absorption liquid filling area, 32. Absorption liquid reflux area. DETAILED DESCRIPTION

[0042] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0043] Example 1

[0044] like Figure 1 As shown, this embodiment provides a biogas slurry treatment method without adding an alkali agent, comprising the following steps:

[0045] 1) The original biogas slurry pool 1 is heated until the biogas slurry reaches 35-45° C. The ratio of air ventilation volume to the biogas slurry volume of the original biogas slurry pool 1 is set to 300-400. Air enters the bottom of the original biogas slurry pool 1 through the air pump 4 and is aerated and stripped for 4-8 minutes every 2-6 minutes, so that the carbon dioxide and ammonia in the biogas slurry are input from the top of the original biogas slurry pool 1 into the 30-50wt% concentrated sulfuric acid absorption liquid in the ammonia recovery tower 3.

[0046] 2) After the first aeration stripping, the pH value of the biogas slurry reaches 9-10, and it is dripped from the top of the convective ammonia stripping tower 2 through the biogas slurry water pump 5, and the working temperature of the convective ammonia stripping tower 2 is maintained at 40-50°C. The ratio of the air ventilation volume to the biogas slurry volume of the convective ammonia stripping tower 2 is set to 3000-4000, and the air is aerated and stripped from the bottom of the convective ammonia stripping tower 2 through the gas circulation pump 7. The input end of the gas circulation pump 7 is connected to the top of the ammonia recovery tower 3, so that the ammonia that is not absorbed in the ammonia recovery tower 3 enters the convective ammonia stripping tower 2 for re-stripping; the convective ammonia stripping tower 2 is filled with 25mm multi-faceted polypropylene hollow balls, and the filling height is set to 65-75% relative to the tower height.

[0047] Ammonia in the biogas slurry is fed from the top of the convection ammonia stripping tower 2 into the 30-50wt% concentrated sulfuric acid absorption liquid filled at the bottom of the ammonia recovery tower 3. The absorption liquid is pumped from bottom to top in the ammonia recovery tower 3 at a speed of 6-10m 3 / h for self-circulation, the biogas slurry flows into the deammonification biogas slurry pool 9 from the bottom of the convection ammonia stripping tower 2. After the second stripping, the ammonia nitrogen concentration of the biogas slurry drops from the initial 4864 mg / L to 1268 mg / L, the removal rate reaches 74.7%, and the ammonia absorption rate exceeds 98%.

[0048] 3) The biogas in the deammonification biogas pool 9 is heated to a stripping temperature of 40-60°C, and the ratio of the biogas aeration volume to the biogas volume of the deammonification biogas pool 9 is set to 400-500. The biogas is introduced into the deammonification biogas pool 9 through the biogas pump 8. The aeration stripping is performed every 2-6 minutes for 4-8 minutes to separate the biogas in the biogas. The separated biogas and the biogas used for stripping enter the methane gas storage tank 10 from the top of the deammonification biogas pool 9 for storage. After stripping, the pH of the biogas can be adjusted back to 6.0-8.5.

[0049] Example 2

[0050] like Figure 2 As shown, this embodiment provides a biogas slurry treatment system without adding an alkali agent, comprising a raw biogas slurry pool 1, a convection ammonia stripping tower 2, an ammonia recovery tower 3, a deammoniation biogas slurry pool 9, and a methane gas storage tank 10;

[0051] The air inlet pipe of the original biogas slurry pool 1 is connected to an air pump 4, the air outlet pipe is connected to the bottom end of the ammonia recovery tower 3 and is provided with a flow meter, the liquid outlet pipe is connected to the top of the convection ammonia stripping tower 2 and is connected to a nozzle, and the liquid outlet pipe of the original biogas slurry pool 1 is provided with a biogas slurry pump 5;

[0052] The outlet of the air inlet pipe of the convective ammonia stripping tower 2 is arranged at the bottom of the tower, a gas circulation pump 7 is provided on the air inlet pipe and the inlet is connected to the top of the ammonia recovery tower 3, the air outlet pipe of the convective ammonia stripping tower 2 is connected to the bottom of the ammonia recovery tower 3, and the discharge pipe of the convective ammonia stripping tower 2 is connected to the deammoniation sludge pool 9.

[0053] The convection ammonia stripping tower 2 is provided with a biogas slurry overflow support 21, a filler, a filler pressure plate, a filler support plate, and an aeration plate 23 from top to bottom; the filler, the filler pressure plate, the filler support plate and the inner wall of the convection ammonia stripping tower 2 are connected to form a filler area 22; the output end of the gas circulation pump 7 is connected to the aeration plate 23. Figure 3 As shown, the biogas slurry overflow support 21 includes an upper overflow disk 211 and a lower overflow disk 21. The upper overflow disk 211 is annular, and the upper overflow disk 211 is provided with a plurality of holes evenly spaced along the circumference of the disk; the lower overflow disk 21 is circular, and the ratio of the diameter of the hollow circle to the diameter of the large circle is 1:2; the lower overflow disk 21 is provided with a plurality of holes evenly spaced along the circumference of the disk; the upper overflow disk 211 and the lower overflow disk 21 are connected by a plurality of support frames, and the bottom end of the support frame penetrates the lower overflow disk 21 and abuts against the packing support plate. The diameter of the holes provided in the upper overflow disk 211 and the lower overflow disk 21 is 5 mm. The packing filled in the packing area 22 is a 25 mm multi-faceted polypropylene hollow ball, and the packing filling height is 65%-75% of the tower height of the convective ammonia stripping tower 2.

[0054] A liquid circulation pump 6 is provided on the liquid outlet pipe of the ammonia recovery tower 3; the ammonia recovery tower 3 includes an absorption liquid filling area 31 and an absorption liquid reflux area 32, such as Figure 4The absorption liquid filling area 31 shown is integrally formed with the bottom of the ammonia recovery tower 3 and is filled with absorption liquid. Its outer diameter is larger than the absorption liquid reflux area 32. The bottom end of the absorption liquid reflux area 32 is immersed in the absorption liquid in the absorption liquid filling area 31 and close to the bottom of the absorption liquid filling area 31. The air inlet pipe at the bottom of the absorption liquid reflux area 32 is connected with the air outlet pipe of the original biogas slurry pool 1 and the air outlet pipe of the flowing ammonia stripping tower. The inlet of the liquid outlet pipe of the ammonia recovery tower 3 is arranged at the absorption liquid filling area 31, and the outlet is arranged at the top of the absorption liquid reflux area 32 and is connected with a nozzle.

[0055] The air inlet pipe of the deammonification biogas pool 9 is connected to a biogas pump 8 , and the air outlet pipe is connected to a methane gas storage tank 10 .

[0056] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the drawings and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A biogas slurry treatment method without adding an alkali agent, characterized in that: The following steps are involved: 1) heating the original biogas slurry pool (1), and allowing air to enter the bottom of the original biogas slurry pool (1) through an air pump (4) to aerate and blow off the biogas slurry in the original biogas slurry pool (1), so that carbon dioxide and ammonia in the biogas slurry are input from the original biogas slurry pool (1) into the absorption liquid in the ammonia recovery tower (3); 2) the biogas slurry after aeration and stripping is dripped into the convective ammonia stripping tower (2) through the biogas slurry water pump (5), the air is aerated and stripped from the bottom of the convective ammonia stripping tower (2) through the gas circulation pump (7), the ammonia in the biogas slurry of the convective ammonia stripping tower (2) is input into the absorption liquid filled in the ammonia recovery tower (3), the absorption liquid is self-circulated in the ammonia recovery tower (3) through the liquid circulation pump (6), and the biogas slurry stripped by the convective ammonia stripping tower (2) flows into the deammoniation biogas slurry pool (9) from the bottom of the convective ammonia stripping tower (2); 3) The biogas enters the deammonification biogas slurry tank (9) through the biogas pump (8) to aerate and blow off the biogas slurry in the deammonification biogas slurry.

2. A biogas slurry treatment method without adding an alkali agent according to claim 1, characterized in that: The method further comprises: the input end of the gas circulation pump (7) is connected to the top of the ammonia recovery tower (3), so that the ammonia that is not absorbed in the ammonia recovery tower (3) enters the convection ammonia stripping tower (2) for re-stripping.

3. The biogas slurry treatment method without adding an alkali agent according to claim 1, characterized in that: In the step 1), the biogas slurry in the original biogas slurry pool (1) is heated to 35-45°C, the ratio of the air ventilation volume to the biogas slurry volume in the original biogas slurry pool (1) is 300-400; and the aeration stripping is performed every 2-6 minutes for 4-8 minutes.

4. The biogas slurry treatment method without adding an alkali agent according to claim 1, characterized in that: In the step 2), the pH of the biogas slurry after aeration stripping in step 1) is 9-10, the working temperature of the convection ammonia stripping tower (2) is 40-50° C., and the ratio of the air ventilation volume to the biogas slurry volume of the convection ammonia stripping tower (2) is 3000-4000.

5. The biogas slurry treatment method without adding an alkali agent according to claim 1, characterized in that: In the step 2), the absorption liquid is concentrated sulfuric acid with a mass concentration of 30-50%, and the circulation flow rate of the absorption liquid in the ammonia recovery tower (3) is 6-10m 3 / h.

6. The biogas slurry treatment method without adding an alkali agent according to claim 1, characterized in that: In the step 3), the biogas in the deammonification biogas pool (9) is heated to 40-60°C, the ratio of the biogas ventilation volume to the biogas volume in the deammonification biogas pool (9) is 400-500, and the aeration stripping is performed for 4-8 minutes every 2-6 minutes.

7. A biogas slurry treatment system without adding alkali agent, characterized in that: It comprises a raw biogas slurry pool (1), a countercurrent ammonia stripping tower (2), an ammonia recovery tower (3), a deammonification biogas slurry pool (9), and a methane gas storage tank (10); The air inlet pipe of the raw biogas slurry pool (1) is connected to an air pump (4), the air outlet pipe is connected to the bottom of the ammonia recovery tower (3), the liquid outlet pipe is connected to the convection ammonia stripping tower (2), and the liquid outlet pipe of the raw biogas slurry pool (1) is provided with a biogas slurry pump (5); The outlet of the air inlet pipe of the convective ammonia stripping tower (2) is arranged at the bottom of the tower, a gas circulation pump (7) is arranged on the air inlet pipe and the outlet is connected to the top of the ammonia recovery tower (3), the outlet pipe of the convective ammonia stripping tower (2) is connected to the bottom of the ammonia recovery tower (3), and the drain pipe of the convective ammonia stripping tower (2) is connected to the deammoniation slurry pool (9); The bottom of the ammonia recovery tower (3) is filled with absorption liquid, the outlet of the gas outlet pipe of the original biogas slurry pool (1) and the outlet of the gas outlet pipe of the countercurrent ammonia stripping tower (2) are immersed in the absorption liquid, the liquid outlet pipe of the ammonia recovery tower (3) is provided with a liquid circulation pump (6), and the outlet of the liquid outlet pipe of the ammonia recovery tower (3) is arranged at the top of the ammonia recovery tower (3); The air inlet pipe of the deammonification biogas pool (9) is connected to a biogas pump (8), and the air outlet pipe is connected to a methane gas storage tank (10).

8. A biogas slurry treatment system without adding alkali agent according to claim 7, characterized in that: The convection ammonia stripping tower (2) is provided with a biogas slurry overflow support (21), a packing pressure plate, a packing support plate, and an aeration disk (23) from top to bottom; the packing pressure plate, the packing support plate and the inner wall of the convection ammonia stripping tower (2) are connected to form a packing area (22); the output end of the gas circulation pump (7) is connected to the aeration disk (23).

9. A biogas slurry treatment system without adding alkali agent according to claim 8, characterized in that: The biogas slurry overflow support (21) comprises an upper overflow disc (211) and a lower overflow disc (212); the upper overflow disc (211) is annular, and is provided with a plurality of holes evenly spaced along the circumference of the disc; the lower overflow disc (212) is circular, and is provided with a plurality of holes evenly spaced along the circumference of the disc; the upper overflow disc (211) and the lower overflow disc (212) are connected via a plurality of support frames, and the bottom ends of the support frames penetrate the lower overflow disc (212) and abut against a filler support plate.

10. A biogas slurry treatment system without adding alkali agent according to claim 8, characterized in that: The filler filled in the filler area (22) is 25 mm multi-faceted polypropylene hollow balls, and the filler filling height is 65%-75% of the tower height of the countercurrent ammonia stripping tower (2).

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