Reduced-pressure membrane separation system for cooperatively recovering ammonia gas and water from biogas slurry

Abstract

The utility model provides a decompression membrane separation system for recovering ammonia gas and water by biogas slurry synergistically, which relates to the technical field of ammonia-rich biogas slurry treatment and comprises a biogas slurry storage tank, a biogas slurry feeding pump is mounted at the output end of the biogas slurry storage tank, a micro-nano bubble generator is mounted at the output end of the biogas slurry feeding pump, and a micro-nano bubble generator is mounted at the output end of the micro-nano bubble generator. A biogas slurry heater is mounted at the output end of the micro-nano bubble generator. Compared with the defects that a large-aperture membrane is prone to liquid leakage and a small-aperture membrane is low in mass transfer efficiency, the aperture range accurately balances the mass transfer rate and the separation effect, the recovery efficiency of ammonia gas and water and the product purity are further improved, high-temperature heating of a traditional process is not needed, gas-liquid separation is achieved only through moderate temperature rising and accurate condensation of an air gap condensation cavity, and the production cost is reduced. And the energy consumption can be reduced by micro-bubble and alkaline adjustment assisted mass transfer. Compared with the problem of high energy consumption in traditional technologies such as evaporation and concentration, the system has the advantages that the energy consumption is obviously reduced, the system is more suitable for large-scale biogas slurry treatment requirements, and the long-term operation cost is lower.

Description

Technical Field

[0001] This utility model relates to the field of ammonia-rich biogas slurry treatment technology, and in particular to a depressurized membrane separation system for the synergistic recovery of ammonia and water from biogas slurry. Background Technology

[0002] With the rapid promotion of large-scale biogas projects in the resource utilization of agricultural waste (such as livestock and poultry manure and straw), the output of its by-product, biogas slurry, has been increasing year by year. As a high-concentration organic biogas slurry produced after anaerobic fermentation, biogas slurry not only contains a large amount of ammonia nitrogen, but also contains soluble organic matter, salts, and trace pollutants. If it is directly discharged or arbitrarily returned to the field, it can easily cause soil salinization, excessive nitrogen in groundwater, and damage the ecological balance of farmland and water bodies. At the same time, the ammonia in biogas slurry is a high-quality nitrogen fertilizer raw material, and the water also has the potential for recycling and reuse. Direct disposal not only wastes valuable resources, but also increases the cost of environmental treatment. Therefore, the pollution reduction of biogas slurry and the synergistic recovery of ammonia and water have become key links in promoting the green and sustainable development of biogas projects.

[0003] Currently, the main technologies for biogas slurry treatment in the industry include returning the biogas slurry to the field, biological denitrification, conventional membrane separation, and evaporation concentration. While traditional returning the biogas slurry to the field is simple to operate and low in cost, it is limited by farmland load and transportation radius, making it only suitable for small-scale biogas projects. Large-scale application can easily lead to excessive accumulation of nitrogen in the soil. Biological denitrification technology degrades ammonia through microorganisms, but it has poor tolerance to high concentrations of salt and organic matter in biogas slurry, resulting in low denitrification efficiency and large land area requirements, making it difficult to meet high-load treatment needs. Conventional membrane separation technology (such as direct contact membrane absorption) can separate ammonia, but it requires direct contact between the biogas slurry and the absorbent, which easily leads to membrane fouling and absorbent dilution. Furthermore, it requires high-temperature heating to promote ammonia volatilization, resulting in high energy consumption. Evaporation concentration technology can recover ammonia and water, but it relies on high-temperature evaporation, with energy costs accounting for over 60%, and it is also prone to salt scaling, affecting the long-term stable operation of the system. None of these methods can achieve low-cost, high-efficiency synergistic recovery of ammonia and water. The current biogas slurry treatment field urgently needs an integrated technical solution that balances pollution reduction, resource recovery, and low energy consumption. This solution must address the problems of incomplete ammonia removal and low resource recovery rates in existing technologies, while avoiding the high energy consumption and system failure risks associated with high-temperature heating and membrane fouling. Simultaneously, it should achieve the synchronous recovery of ammonia and water, thereby increasing the added value of biogas slurry resource utilization. However, existing technologies struggle to meet these requirements simultaneously, leading to a dilemma in most biogas projects where both substandard biogas slurry treatment and resource waste coexist, hindering the overall improvement of the industry's environmental and economic benefits. Therefore, developing a treatment system and process that can synergistically recover ammonia and water from biogas slurry, while maintaining low energy consumption and stable operation, has become a core area for breakthrough in the industry. Utility Model Content

[0004] This utility model mainly provides a depressurized membrane separation system for the co-recovery of ammonia and water from biogas slurry, which is energy-efficient and operates stably.

[0005] To achieve the above objectives, this utility model adopts the following technical solution: a pressure-reducing membrane separation system for the synergistic recovery of ammonia and water from biogas slurry, comprising a biogas slurry storage tank, a biogas slurry feed pump installed at the output end of the biogas slurry storage tank, a micro-nano bubble generator installed at the output end of the biogas slurry feed pump, a biogas slurry heater installed at the output end of the micro-nano bubble generator, a feed chamber installed at the output end of the biogas slurry heater, a biogas slurry circulation tank installed at the output end of the feed chamber, an absorbent tank provided on one side of the biogas slurry circulation tank, an absorbent pump installed at the output end of the absorbent tank, an absorbent cooler installed at the output end of the absorbent pump, the output end of the absorbent cooler connected to the feed chamber, a cold water chamber installed at one end of the feed chamber, a condensate storage tank installed at the output end of the cold water chamber, a cold water tank provided on one side of the cold water chamber, a cold water pump installed at the output end of the cold water tank, and the output end of the cold water pump connected to the cold water chamber.

[0006] Preferably, both the feed chamber and the cold water chamber are equipped with hydrophobic horizontal plate membranes, and hydrophobic hollow fiber membranes are installed on opposite sides of the two hydrophobic horizontal plate membranes. Condensation plates are installed on opposite sides of the two hydrophobic hollow fiber membranes. The feed chamber is provided with a first air gap chamber, and the cold water chamber is provided with a second air gap chamber.

[0007] Preferably, the output end of the biogas slurry storage tank is connected to the feed chamber, the input end of the biogas slurry storage tank is provided with a second valve, and the output end of the biogas slurry heater is equipped with a first thermometer.

[0008] Preferably, the input end of the biogas slurry circulation tank is provided with a first valve.

[0009] Preferably, a pH sensor is installed on the absorbent tank, and a second thermometer is installed at the output end of the absorbent cooler.

[0010] Preferably, a third thermometer is installed at the output end of the cold water pump.

[0011] Compared with the prior art, the advantages and positive effects of this utility model are as follows:

[0012] In this invention, through continuous microbubble agitation on the biogas slurry side and adjustment with an alkaline solution, the microbubbles actively flush the membrane surface, reducing the adhesion of suspended solids and colloids to the hydrophobic membrane surface. The alkaline environment also inhibits the deposition of organic matter in the biogas slurry within the membrane pores. Compared to conventional membrane separation, which suffers from frequent membrane fouling due to impurity accumulation and requires frequent membrane replacement, this solution reduces the risk of membrane fouling at the source, extends membrane lifespan, and reduces maintenance costs and downtime. Water vapor after passing through the membrane is directly condensed into liquid water in the air gap condensation chamber for recovery, while ammonia penetrates the second hydrophobic membrane and is captured by the acid in the acid absorption chamber, forming a high-concentration ammonium salt product. Unlike traditional processes that only recover a single substance and require additional equipment for secondary separation, this system simultaneously recovers ammonia and water in the same process, reducing the biogas slurry pollution load and improving resource utilization. It uses a hydrophobic hollow fiber membrane with a pore size of 0.1-0.45μm, which ensures smooth passage of ammonia and water vapor through the membrane while effectively blocking tiny impurities in the biogas slurry. Compared to the drawbacks of large-pore membranes being prone to leakage and small-pore membranes having low mass transfer efficiency, this pore size range precisely balances mass transfer rate and separation effect, further improving the recovery efficiency of ammonia and water and the purity of the product. It eliminates the need for high-temperature heating in traditional processes, achieving gas-liquid separation only through moderate heating and precise condensation in the air gap condenser. Furthermore, microbubbles and alkaline regulation assist mass transfer, reducing energy consumption. Compared to the high energy consumption of traditional technologies such as evaporation and concentration, this system significantly reduces energy consumption, making it more suitable for large-scale biogas slurry treatment needs and resulting in lower long-term operating costs. It features an innovative three-chamber structure: biogas slurry treatment chamber - air gap condenser chamber - acid absorption chamber. The biogas slurry treatment chamber integrates microbubble generation and alkaline regulation units, while the air gap condenser chamber is equipped with an independent condensation module. All chambers are separated by hydrophobic microporous membranes. Compared to the limitations of traditional membrane separation devices, which only have a single membrane layer and lack dedicated functional units, this system integrates the entire process of "biogas slurry pretreatment - gas-liquid separation - water recovery - ammonia capture", breaking through the bottleneck of the single function of existing devices and better meeting the core requirement of synergistic recovery of ammonia and water in biogas slurry. Attached Figure Description

[0013] Figure 1 A schematic diagram of the pressure-reducing membrane separation system for the synergistic recovery of ammonia and water from biogas slurry proposed in this utility model;

[0014] Figure 2 A schematic diagram of the feed chamber of the pressure-reducing membrane separation system for the synergistic recovery of ammonia and water from biogas slurry, as proposed in this utility model;

[0015] Figure 3 The diagram shows the cold water chamber of the pressure-reducing membrane separation system for the synergistic recovery of ammonia and water from biogas slurry, as proposed in this utility model.

[0016] Legend: 1. Biogas slurry storage tank; 2. Biogas slurry feed pump; 3. Micro-nano bubble generator; 4. Biogas slurry heater; 5. First thermometer; 6. Biogas slurry circulation tank; 7. First valve; 8. Second valve; 9. Hydrophobic horizontal plate membrane; 10. Hydrophobic hollow fiber membrane; 11. Condensate plate; 12. Absorbent liquid tank; 13. pH sensor; 14. Absorbent liquid pump; 15. Absorbent liquid cooler; 16. Second thermometer; 17. Condensate storage tank; 18. Cold water tank; 19. Cold water pump; 20. Third thermometer; 21. Feed chamber; 22. First air gap chamber; 23. Second air gap chamber; 24. Cold water chamber. Detailed Implementation

[0017] To better understand the above-mentioned objectives, features, and advantages of this utility model, the present utility model will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0018] Many specific details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed in the following specification.

[0019] Example 1, such as Figure 1-3 As shown, this utility model provides a pressure-reducing membrane separation system for the synergistic recovery of ammonia and water from biogas slurry. It includes a biogas slurry storage tank 1, a biogas slurry feed pump 2 installed at the output end of the storage tank 1, a micro / nano bubble generator 3 installed at the output end of the feed pump 2, a biogas slurry heater 4 installed at the output end of the generator 3, a feed chamber 21 installed at the output end of the heater 4, a biogas slurry circulation tank 6 installed at the output end of the circulation tank 21, and an absorbent tank 12 located on one side of the circulation tank 6. An absorbent pump 14 is installed at the output end of the absorbent tank 12, and an absorbent cooler 15 is installed at the output end of the absorbent pump 14. The output end of the absorbent cooler 15 is connected to the feed chamber 21. A cold water chamber 24 is installed at one end of the feed chamber 21. A condensate storage tank 17 is installed at the output end of the cold water chamber 24. A cold water tank 18 is provided on one side of the cold water chamber 24. A cold water pump 19 is installed at the output end of the cold water tank 18. The output end of the cold water pump 19 is connected to the cold water chamber 24.

[0020] The overall effect of Embodiment 1 is as follows: the biogas slurry feed pump 2 is used to pump the biogas slurry in the biogas slurry circulation tank 6 into the biogas slurry heater 4 and the feed chamber 21 in sequence; the biogas slurry heater 4 is used to heat the biogas slurry to a first preset temperature; the pH sensor 13 is used to detect the pH value of the absorbent in the absorbent tank 12; when the pH value in the absorbent tank 12 is greater than 6, acid is added to the absorbent tank 12 to lower the pH value in the absorbent tank 12 to below 6; the absorbent cooler 15 is used to cool the absorbent to a second preset temperature; and the second thermometer 16 is used to detect the temperature of the absorbent output by the absorbent cooler 15.

[0021] Example 2, as Figure 1-3 As shown, both the feed chamber 21 and the cold water chamber 24 are equipped with hydrophobic horizontal plate membranes 9. Hydrophobic hollow fiber membranes 10 are installed on opposite sides of the two hydrophobic horizontal plate membranes 9. Condensing plates 11 are installed on opposite sides of the two hydrophobic hollow fiber membranes 10. The feed chamber 21 is provided with a first air gap chamber 22, and the cold water chamber 24 is provided with a second air gap chamber 23. The output end of the biogas slurry storage tank 1 is connected to the feed chamber 21. The input end of the biogas slurry storage tank 1 is provided with a second valve 8. The output end of the biogas slurry heater 4 is provided with a first thermometer 5. The input end of the biogas slurry circulation tank 6 is provided with a first valve 7. The absorbent tank 12 is equipped with a pH sensor 13. The output end of the absorbent cooler 15 is equipped with a second thermometer 16. The output end of the cold water pump 19 is equipped with a third thermometer 20.

[0022] The overall effect achieved in Example 2 is as follows: the hydrophobic flat sheet membrane 9 is made of polypropylene, polytetrafluoroethylene, or polyvinylidene fluoride, allowing only gas passage and possessing certain resistance to high temperatures, acids and alkalis, and pollution; the pore size of the hydrophobic hollow fiber membrane 10 ranges from sub-nanometer to micrometer, with a pore diameter of 0.1-0.45 μm; the first thermometer 5 is used to detect the temperature of the biogas slurry output from the biogas slurry heater 4; the second valve 8 is used to open or close the input end of the biogas slurry storage tank 1; the first valve 7 is used to open or close the input end of the biogas slurry circulation tank 6; and the absorbent is a near-saturated ammonium salt solution combined with acid to form a solution with a low pH value. For a mixture of pH 6, the concentration of the ammonium salt solution is determined by the solubility of the corresponding ammonium salt. The acid solution is generally concentrated acid to maintain the pH value of the mixture below 6 so that the mixture has the ability to absorb the ammonia nitrogen that has permeated through. Alternatively, a high-concentration acid solution can be used. Commonly used absorbent solutions include a mixture of ammonium sulfate and sulfuric acid, a mixture of ammonium dihydrogen phosphate and phosphoric acid, and a mixture of ammonium chloride and hydrochloric acid. The first thermometer 5 is used to detect the temperature of the biogas slurry output from the biogas slurry heater 4. The pH sensor 13 is used to detect the pH value of the absorbent solution in the absorbent solution tank 12. When the pH value in the absorbent solution tank 12 is greater than 6, acid solution is added to the absorbent solution tank 12 to lower the pH value in the absorbent solution tank 12 to below 6.

[0023] Working principle: When using this device, the temperature of the biogas slurry is detected. If the temperature of the biogas slurry is greater than or equal to 80℃, the biogas slurry and absorbent are fed into the heat exchanger for heat exchange until their temperatures are equal. Then, the biogas slurry and absorbent are fed into the biogas slurry circulation tank 6 and the absorbent tank 12, respectively. If the temperature of the biogas slurry is less than 80℃, the biogas slurry and absorbent are directly fed into the biogas slurry circulation tank 6 and the absorbent tank 12, respectively. The biogas slurry heater 4 and the absorbent cooler 15 are turned on. The temperature of the biogas slurry heater 4 is set to be 60-80℃ higher than that of the absorbent heater, and the cooling temperature must be higher than 0℃. The biogas slurry circulation pump pumps the biogas slurry in the biogas slurry circulation tank 6 into the biogas slurry cooler. After the biogas slurry is cooled to the first preset temperature in the biogas slurry cooler, it is fed into the feed chamber 21. The absorbent pump 14 absorbs the absorbent in the absorbent tank 12 into the absorbent cooler 15. Within 5, the absorbent is cooled to a second preset temperature in the absorbent cooler 15 and then fed into the absorption chamber. The second preset temperature is lower than the first preset temperature. The ammonia nitrogen in the biogas slurry, in the form of free ammonia, permeates sequentially through the hydrophobic horizontal plate membrane 9, the air gap chamber, and the hydrophobic hollow fiber membrane 10 before entering the absorption chamber, resulting in a high ammonia nitrogen absorbent. Some of the water in the biogas slurry, in the form of water vapor, passes sequentially through the hydrophobic hollow fiber membrane 10 and the air gap chamber. Upon encountering cold in the air gap chamber, it condenses into water droplets and enters the condensate storage tank 17 through the condensate outlet. If the biogas slurry is subjected to single-cycle absorption, the second valve 8 is opened and the first valve 7 is closed, and the low ammonia nitrogen biogas slurry in the feed chamber 21 is fed into the biogas slurry storage tank 1. If the biogas slurry is subjected to cyclic absorption, the second valve 8 is closed and the first valve 7 is opened, and the low ammonia nitrogen biogas slurry in the feed chamber 21 is fed into the biogas slurry circulation tank 6 for recycling.

[0024] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present utility model without departing from the technical solution of the present utility model shall still fall within the protection scope of the technical solution of the present utility model.

Claims

1. A pressure-reducing membrane separation system for the co-recovery of ammonia and water from biogas slurry, comprising a biogas slurry storage tank (1), characterized in that: The output end of the biogas slurry storage tank (1) is equipped with a biogas slurry feed pump (2), the output end of the biogas slurry feed pump (2) is equipped with a micro-nano bubble generator (3), the output end of the micro-nano bubble generator (3) is equipped with a biogas slurry heater (4), the output end of the biogas slurry heater (4) is equipped with a feed chamber (21), the output end of the feed chamber (21) is equipped with a biogas slurry circulation tank (6), an absorption liquid tank (12) is provided on one side of the biogas slurry circulation tank (6), and an absorption liquid pump (14) is installed at the output end of the absorption liquid tank (12). An absorbent cooler (15) is installed at the output end of the absorbent pump (14). The output end of the absorbent cooler (15) is connected to the feed chamber (21). A cold water chamber (24) is installed at one end of the feed chamber (21). A condensate storage tank (17) is installed at the output end of the cold water chamber (24). A cold water tank (18) is provided on one side of the cold water chamber (24). A cold water pump (19) is installed at the output end of the cold water tank (18). The output end of the cold water pump (19) is connected to the cold water chamber (24).

2. The pressure-reducing membrane separation system for co-recovering ammonia and water from biogas slurry according to claim 1, characterized in that: Both the feed chamber (21) and the cold water chamber (24) are equipped with hydrophobic horizontal plate membranes (9), and hydrophobic hollow fiber membranes (10) are installed on opposite sides of the two hydrophobic horizontal plate membranes (9). Condensation plates (11) are installed on opposite sides of the two hydrophobic hollow fiber membranes (10). The feed chamber (21) is provided with a first air gap chamber (22), and the cold water chamber (24) is provided with a second air gap chamber (23).

3. The pressure-reducing membrane separation system for co-recovering ammonia and water from biogas slurry according to claim 1, characterized in that: The output end of the biogas slurry storage tank (1) is connected to the feed chamber (21), the input end of the biogas slurry storage tank (1) is provided with a second valve (8), and the output end of the biogas slurry heater (4) is equipped with a first thermometer (5).

4. The pressure-reducing membrane separation system for co-recovering ammonia and water from biogas slurry according to claim 1, characterized in that: The biogas slurry circulation tank (6) is equipped with a first valve (7) at its input end.

5. The pressure-reducing membrane separation system for co-recovering ammonia and water from biogas slurry according to claim 1, characterized in that: A pH sensor (13) is installed on the absorbent tank (12), and a second thermometer (16) is installed at the output end of the absorbent cooler (15).

6. The depressurized membrane separation system for co-recovering ammonia and water from biogas slurry according to claim 1, characterized in that: A third thermometer (20) is installed at the output end of the cold water pump (19).

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