Device and process for realizing methane carbon sequestration through comprehensive utilization of pig farm methane ammonia nitrogen and ardealite

Abstract

The invention discloses a device and a process for realizing methane carbon sequestration by comprehensive utilization of ammonia nitrogen and ardealite in biogas digester in a pig farm, the device comprises a methane supply unit, an ammonia water preparation unit and a reaction crystallization unit, the ammonia water preparation unit comprises a wastewater treatment tank, an ammonium online detector and an ammonia gas absorption tank; phosphate and magnesium salt are added into the wastewater treatment tank to treat pig farm biogas slurry, generated struvite precipitates are filtered and then heated to release NH3, and the NH3 is introduced into the ammonia gas absorption tank to prepare ammonia water. The reaction crystallization unit comprises a carbon sequestration tower and a crystallization tank, ammonia water and CO2-containing biogas supplied by the biogas supply unit are conveyed into the carbon sequestration tower to react to generate (NH4) 2CO3, and after reaction, a mixed solution is conveyed into the crystallization tank to react with phosphogypsum for crystallization to generate CaCO3 and (NH4) 2SO4. According to the method, pig farm biogas slurry wastewater and ardealite are ingeniously and cooperatively treated, CO2 in biogas is successfully captured, and a high-value calcium carbonate product and a nitrogen fertilizer are generated in the process.

Description

Technical Field

[0001] The present invention relates to the field of resource utilization of livestock and poultry breeding waste, and particularly relates to a device and process for comprehensively utilizing biogas slurry ammonia nitrogen and phosphogypsum in a pig farm to realize biogas carbon fixation. Background Art

[0002] According to the characteristics of high-concentration organic matter and ammonia nitrogen in the raw water, the traditional pig farm wastewater treatment process usually adopts a combined process of anaerobic digestion-aerobic nitrification-anaerobic denitrification for carbon removal and nitrogen removal. The anaerobic digestion process can achieve the conversion of organic matter into CH4. After the pig farm manure is treated by anaerobic technology, 40%-90% of the organic matter in the influent is degraded, and this part of the organic matter is relatively easy to degrade. Most of the remaining pollutants in the biogas slurry are organic matter, ammonia nitrogen, heavy metals and minerals that are difficult for microorganisms to utilize. The ratio of BOD to COD in the biogas slurry is about 0.3, and some are even lower, which is not suitable for biochemical treatment. The anaerobic digestion process will also release more ammonia nitrogen due to the degradation of proteins by organisms, further increasing the ammonia nitrogen concentration in the biogas slurry (NH4 + -N > 1000mg / L). If the biogas slurry is directly discharged into the surrounding water system, the enrichment of a large amount of nitrogen and phosphorus elements in the biogas slurry in the water body will accelerate the reproduction of algae, resulting in a decrease in the dissolved oxygen content in the water, threatening aquatic animals and plants. In addition, nitrite nitrogen and nitrate nitrogen converted from ammonia nitrogen will also have triple carcinogenic effects on the human body, namely causing diseases, cancer and teratogenesis. On the other hand, biogas, as a combustible gas produced by the fermentation of organic substances under anaerobic conditions, its main components include CH4, CO2, etc. The development and utilization of biogas is of great significance for promoting the adjustment of China's energy structure. However, due to the high CO2 concentration in biogas, its wide application in the energy field is limited.

[0003] China is also facing an increasingly severe solid waste treatment problem, and the treatment problem of phosphogypsum, as one of the main industrial waste materials, is particularly prominent. Phosphogypsum is a by-product produced in the process of wet smelting of phosphoric acid, and its main component is calcium sulfate dihydrate (CaSO4·2H2O). If not properly treated, phosphogypsum will cause serious harm to the environment and human health, and then threaten the health and balance of the earth's ecological system. The conventional method for treating phosphogypsum is the ammonia method of phosphogypsum, which effectively captures CO2 by reacting phosphogypsum with ammonia water and generates CaCO3 and (NH4)2SO4. However, this method requires a large amount of ammonia water and has a high treatment cost, which limits its large-scale application.

[0004] If the ammonia nitrogen in the biogas slurry wastewater from pig farms can be recovered and prepared into ammonia water through struvite crystallization method and applied to capture CO2 in biogas by ammonia method with phosphogypsum, it can not only realize the resource utilization of biogas slurry wastewater and phosphogypsum from pig farms, but also upgrade biogas, thus promoting the wide application of biogas in the energy field and providing a new way for optimizing China's energy structure and improving the ecological environment. Summary of the Invention

[0005] Aiming at problems such as "excessive CO2 in biogas", "high cost of traditional treatment of phosphogypsum", and "poor effect of biological nitrogen removal in pig farm wastewater", the purpose of the present invention is to provide a device and process for comprehensively utilizing ammonia nitrogen in biogas slurry from pig farms and phosphogypsum to realize carbon fixation in biogas, so as to reduce the amount of CO2 in biogas and promote the clean utilization of biogas. At the same time, explore harmless treatment methods for phosphogypsum to reduce the emission of solid waste. Through innovative process design, using the ammonia method with phosphogypsum and the magnesium ammonium phosphate method, the biogas slurry wastewater from pig farms and phosphogypsum are co-treated to realize carbon fixation in biogas, opening up a new way of treating waste with waste and providing scientific basis and technical support for environmental protection and resource recycling.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A device for comprehensively utilizing ammonia nitrogen in biogas slurry from pig farms and phosphogypsum to realize carbon fixation in biogas, comprising a biogas supply unit, an ammonia water preparation unit, and a reaction crystallization unit;

[0008] The ammonia water preparation unit includes an ammonium online detector, a wastewater treatment tank for treating biogas slurry from pig farms, and an ammonia gas absorption tank; a first stirring device, a water inlet pipe for introducing biogas slurry from pig farms, a first powder feeding device, and a first electromagnetic flowmeter are arranged on the wastewater treatment tank; a steam heating layer is arranged on the outer wall of the wastewater treatment tank, a first filtering component is arranged at the bottom inside, a drain valve is arranged on the drain pipe at the bottom liquid outlet of the wastewater treatment tank, and phosphate and magnesium salts are added into the wastewater treatment tank through the first powder feeding device; the ammonia gas absorption tank is filled with water, and an aeration disc is immersed in the water, and the air inlet of the aeration disc is connected to the top air outlet of the wastewater treatment tank through a pipe;

[0009] The reaction crystallization unit includes a carbon fixation tower and a crystallization tank. The ammonia water prepared inside the ammonia gas absorption tank is transported to the upper part of the carbon fixation tower for spraying, and the CO2-containing biogas supplied by the biogas supply unit is transported to the lower air inlet of the carbon fixation tower, so that the ammonia water and the CO2-containing biogas react in countercurrent contact to form (NH4)2CO3 solution at the bottom of the carbon fixation tower;

[0010] The bottom liquid outlet of the carbon fixation tower is connected to the crystallization tank by a pipeline, and the aqueous solution at the bottom of the tower is transported to the crystallization tank for crystallization. A second powder feeding device for adding phosphogypsum is also arranged on the crystallization tank.

[0011] Further, a first gas-phase NH3 sensor and a first gas ultrasonic flowmeter are provided on the pipeline between the top gas outlet of the wastewater treatment tank and the aeration disk, and a first electromagnetic flowmeter is provided on the inlet pipeline to quantitatively control the dosage of the pig farm biogas slurry transported to the wastewater treatment tank through the first electromagnetic flowmeter; a second electromagnetic flowmeter is provided on the drainage pipeline at the bottom liquid outlet of the wastewater treatment tank;

[0012] Among them, the air holes of the aeration disk are micro-hole structures with a pore diameter of less than 0.5 mm;

[0013] The biogas supply unit includes a biogas raw material tank and a buffer tank. The biogas raw material tank and the buffer tank are connected by a pipeline with a pressure gauge. The air outlet of the buffer tank is connected to the lower air inlet of the carbon sequestration tower by a pipeline through a third gas ultrasonic flowmeter.

[0014] Further, the ammonium on-line detector is used to monitor the NH4 concentration in the wastewater treatment tank and the ammonia water concentration in the ammonia gas absorption tank respectively; an exhaust pipeline is provided at the upper end of the ammonia gas absorption tank, and a second gas-phase NH3 sensor and a second gas ultrasonic flowmeter are provided on the exhaust pipeline. The exhaust pipeline is connected to a secondary ammonia gas absorption tank and a final ammonia gas leakage protection unit through pipelines in sequence. The final ammonia gas leakage protection unit sprays and absorbs the residual NH3 with an NH3 absorbent. + Further, the reaction crystallization unit further includes a water storage tank and a water pump. The liquid inlet of the water storage tank is connected to the liquid outlet of the ammonia gas absorption tank by a pipeline through a third electromagnetic flowmeter; an air outlet pipeline, a liquid sprayer, a packing layer, an air inlet and a liquid outlet are respectively arranged on the carbon sequestration tower from top to bottom, and a CO2 sensor is provided on the air outlet pipeline;

[0015] The liquid outlet of the water storage tank is connected to the inlet of the liquid sprayer by a water pump through a pipeline, and the liquid outlet at the bottom of the carbon sequestration tower is connected to the crystallization tank by a pipeline through a fourth electromagnetic flowmeter;

[0016] A maintenance port and an observation window are also provided on the carbon sequestration tower, and the observation window is arranged below the packing layer; a second stirring device and a second powder feeding device are provided on the crystallization tank, a second filtering component is arranged inside the bottom of the crystallization tank, and the liquid outlet at the bottom of the crystallization tank is connected to a nitrogen fertilizer collector through a pipeline in sequence through a fifth electromagnetic flowmeter. A drain valve is provided on the drainage pipeline at the liquid outlet at the bottom of the crystallization tank.

[0017] A pig farm biogas slurry ammonia nitrogen recovery and biogas-phosphogypsum comprehensive utilization process based on struvite crystallization method includes the following steps:

[0018]

[0019] ​Step S1: Pour the pig farm biogas slurry wastewater into the wastewater treatment tank, add phosphate and magnesium salt in sequence, start stirring, add NaOH solution to maintain the pH of the reaction system alkaline, react under stirring to promote the formation of struvite MgNH4PO4·6H2O precipitate. When the ammonia nitrogen concentration in the reaction system monitored by the ammonium on-line detector is less than the threshold, terminate the reaction, filter out the water in the reaction system, and the remaining struvite precipitate is left. Then heat the wastewater treatment tank to make the struvite precipitate decompose and volatilize NH3;

[0020] Step S2: The NH3 volatilized in Step S1 enters the aeration plate in the ammonia absorption tank through the pipeline. NH3 is released into the water through the microporous structure of the aeration plate. The formed microbubbles are inhaled into the water by absorption to form ammonia water, and the ammonia water concentration is detected by the ammonium on-line detector until the required concentration is reached;

[0021] Step S3: The ammonia water obtained in Step S2 is transported to the upper part of the carbon sequestration tower for spraying. At the same time, the biogas supply unit transports the CO2-containing biogas to the lower air inlet of the carbon sequestration tower, so that the ammonia water and the CO2-containing biogas react in a countercurrent contact in the packing layer of the carbon sequestration tower. The ammonia water absorbs CO2 in the biogas to form (NH4)2CO3 solution and flows to the bottom of the carbon sequestration tower;

[0022] Step S4: The (NH4)2CO3 solution at the bottom of the carbon sequestration tower is transported to the crystallization tank, and then phosphogypsum is added to the crystallization tank. Start stirring to make the CaSO4 component of (NH4)2CO3 and phosphogypsum in the mixed liquid react to form CaCO3 precipitate and (NH4)2SO4. Then stop stirring and let it stand for more than 1 h to complete the crystallization and sedimentation process. Filter the liquid nitrogen fertilizer containing (NH4)2SO4 solution into the nitrogen fertilizer collector, and then take out the remaining CaCO3 precipitate.

[0023] The reactions involved in the present invention are as follows:

[0024] The reaction formula of the struvite crystallization method is:

[0025] Mg 2+ +PO4 3- +NH4 + →MgNH4PO4

[0026] The reaction formula of the low-temperature volatilization of struvite is:

[0027] MgNH4PO4→MgHPO4↓+3NH3↑

[0028] The reaction formula of the aeration process is:

[0029] NH3+H2O→NH3·H2O

[0030] The reaction formula of the phosphogypsum ammonia method is:

[0031] 2NH₃·H₂O + CO₂ + H₂O → (NH₄)₂CO₃ + 2H₂O

[0032] CaSO₄ + (NH₄)₂CO₃ → (NH₄)₂SO₄ + CaCO₃↓

[0033] Further, in step S1, the ammonia nitrogen content in the pig farm biogas slurry wastewater is 1000 - 3000 mg / L. By monitoring the content of NH₄ + and PO₄ 3- concentration in the pig farm biogas slurry wastewater, and then determining the feeding amounts of phosphate and magnesium salt, so that the molar ratio of each substance in the reaction system Mg 2+ : PO₄ 3- : NH₄ + = 1.15 - 1.25: 1 - 1.05: 1, the stirring speed is 200 - 300 rpm, adding NaOH solution to maintain the pH of the reaction system at 8.0 - 9.0, the reaction temperature is normal temperature; when the ammonia concentration in the reaction system monitored by the ammonium on - line detector is less than 30 mg / L, the reaction is terminated; the temperature for heating the wastewater treatment tank is 100 - 105 °C to make struvite release NH₃, and stop heating the wastewater treatment tank until the concentration of the volatilized NH₃ < 30 ppm.

[0034] Further, in step S2, adjust the NH₃ absorption time until the ammonia water reaches a target concentration of more than 4%.

[0035] In step S2 of the present invention, it also includes a treatment process for preventing NH₃ leakage, specifically as follows:

[0036] 1) Cascade absorption protection: Connect two ammonia absorption tanks in series. The first - stage ammonia absorption tank absorbs NH₃ so that the discharged NH₃ concentration < 30 ppm. When the NH₃ concentration at the exhaust pipe outlet of the first - stage ammonia absorption tank > 30 ppm, start the second - stage ammonia absorption tank for supplementary absorption of NH₃;

[0037] 2) Emergency treatment protection: If the NH₃ concentration is still > 30 ppm after secondary absorption, start the final ammonia leakage prevention protection unit to spray - absorb the residual NH₃ with an NH₃ absorbent. The NH₃ absorbent is a citric acid aqueous solution with a mass concentration of 5 - 8%, ensuring that the NH₃ concentration in the tail gas ≤ 30 ppm.

[0038] Further, in step S3, the CO₂ concentration in the biogas is 20 - 40%. Control the residence time of ammonia water in the packing layer of the carbon sequestration tower to be ≥ 60 s, the absorption temperature is normal temperature, and control the CO₂ concentration at the gas outlet of the carbon sequestration tower to be ≤ 1.5%; if the CO₂ concentration in the exhaust gas > 1.5% or the H₂S concentration > 4 mg / m 3, an alkaline absorbent is used to absorb it to remove the remaining CO2; in the (NH4)2CO3 solution formed at the bottom of the carbon sequestration tower, the mass concentration of (NH4)2CO3 is 5-20%.

[0039] Furthermore, in step S4, the molar ratio of the CaSO4 component of phosphogypsum to (NH4)2CO3 in the mixed liquid is 1.3-1.8:1, the reaction temperature is room temperature, the reaction time is 1-1.5 h, the stirring speed of the reaction is 100-200 rpm, and the mass concentration of (NH4)2SO4 in the liquid nitrogen fertilizer obtained by filtration after the reaction is 10-15%.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] 1. Realize the reduction of CO2 in biogas, significantly improve the utilization value of biogas as a clean energy source. By efficiently removing impurities such as CO2 in biogas, the quality of the treated biogas is significantly improved, meeting the requirements for energy utilization or the preparation of high-purity gas.

[0042] 2. Treat waste with waste and recycle resources. The present invention cleverly co-treats the biogas slurry wastewater from pig farms and phosphogypsum, not only successfully capturing and sequestering CO2 in biogas, realizing the environmental protection concept of "treating waste with waste", but also generating high-value calcium carbonate products and nitrogen fertilizers in this process, creating significant economic benefits. Description of the Drawings

[0043] Figure 1 is the overall structural schematic diagram of the device of the present invention;

[0044] Figure 2 is the structural schematic diagram of the biogas supply unit of the present invention;

[0045] Figure 3 is the structural schematic diagram of the ammonia water preparation unit of the present invention;

[0046] Figure 4 is the structural schematic diagram of the reaction crystallization unit of the present invention;

[0047] The reference numerals are:

[0048] 1. Biogas raw material tank, 2. Pressure gauge, 3. Buffer tank, 4. Third gas ultrasonic flowmeter, 5. First electromagnetic flowmeter, 6. First powder feeding device, 7. Steam heating layer, 8. First filtering component, 9. Second electromagnetic flowmeter, 10. First stirring device, 11. Ammonium on-line detector, 12. First gas-phase NH3 sensor, 13. First gas ultrasonic flowmeter, 14. Aeration disc, 15. Second gas-phase NH3 sensor, 16. Second gas ultrasonic flowmeter, 17. Third electromagnetic flowmeter, 18. Water storage tank, 19. Water pump, 20. Observation window, 21. Packing layer, 22. Liquid sprayer, 23. Maintenance port, 24. Exhaust gas pipeline, 25. CO2 sensor, 26. Fourth electromagnetic flowmeter, 27. Second powder feeding device, 28. Second stirring device, 29. Second filtering component, 30. Fifth electromagnetic flowmeter, 31. Nitrogen fertilizer collector. Detailed implementation manners

[0049] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0050] Example: Control Figures 1-4

[0051] A device for comprehensively utilizing ammonia nitrogen and phosphogypsum in pig farm biogas slurry to realize biogas carbon sequestration, comprising a biogas supply unit, an ammonia water preparation unit and a reaction crystallization unit.

[0052] The ammonia water preparation unit includes an ammonium on-line detector 11, a wastewater treatment tank for treating pig farm biogas slurry, and an ammonia gas absorption tank; a first stirring device 10, a water inlet pipe for introducing pig farm biogas slurry, a first powder feeding device 6 and a first electromagnetic flowmeter 5 are arranged on the wastewater treatment tank, a steam heating layer 7 is arranged on the outer wall of the wastewater treatment tank, a first filtering component 8 is arranged at the bottom inside, a drain valve is arranged on the drain pipe at the bottom liquid outlet of the wastewater treatment tank, and phosphates and magnesium salts are added into the wastewater treatment tank through the first powder feeding device 6; the ammonia gas absorption tank is filled with water, and an aeration disc 14 is immersed in the water, and the air inlet of the aeration disc 14 is connected to the top air outlet of the wastewater treatment tank through a pipeline.

[0053] The reaction crystallization unit includes a carbon sequestration tower and a crystallization tank. The ammonia water prepared inside the ammonia gas absorption tank is transported to the upper part of the carbon sequestration tower for spraying, and the CO2-containing biogas supplied by the biogas supply unit is transported into the lower air inlet of the carbon sequestration tower, so that the ammonia water and the CO2-containing biogas react in countercurrent contact to form an (NH4)2CO3 aqueous solution at the bottom of the carbon sequestration tower; the bottom liquid outlet of the carbon sequestration tower is connected to the crystallization tank by a pipeline, and the aqueous solution at the bottom of the tower is transported to the crystallization tank for crystallization, and a second powder feeding device 27 for adding phosphogypsum is also arranged on the crystallization tank.

[0054] A first gas-phase NH₃ sensor 12 and a first gas ultrasonic flowmeter 13 are provided on the pipeline between the top gas outlet of the wastewater treatment tank and the aeration disk 14. A first electromagnetic flowmeter is provided on the inlet pipeline to quantitatively control the dosage of the pig farm biogas slurry transported to the wastewater treatment tank through the first electromagnetic flowmeter; a second electromagnetic flowmeter 9 is provided on the drainage pipeline at the bottom liquid outlet of the wastewater treatment tank; the air holes of the aeration disk 14 are micro-hole structures with a pore diameter of less than 0.5 mm.

[0055] The biogas supply unit includes a biogas raw material tank 1 and a buffer tank 3. The biogas raw material tank 1 and the buffer tank 3 are connected by a pipeline with a pressure gauge 2. The gas outlet of the buffer tank 3 is connected to the lower inlet of the carbon fixation tower by a pipeline through a third gas ultrasonic flowmeter 4.

[0056] The ammonium on-line detector 11 is used to monitor the NH₄ + concentration in the wastewater treatment tank and the ammonia water concentration in the ammonia absorption tank respectively; an exhaust pipeline is provided at the upper end of the ammonia absorption tank. A second gas-phase NH₃ sensor 15 and a second gas ultrasonic flowmeter 16 are provided on this exhaust pipeline. The exhaust pipeline is connected to a secondary ammonia absorption tank and a final ammonia leakage protection unit in sequence through pipelines. The final ammonia leakage protection unit uses an NH₃ absorbent to spray and absorb the residual NH₃.

[0057] The reaction crystallization unit further includes a water storage tank 18 and a water pump 19. The liquid inlet of the water storage tank 18 is connected to the liquid outlet of the ammonia absorption tank by a pipeline through a third electromagnetic flowmeter 17; on the carbon fixation tower, an air outlet pipeline 24, a liquid sprayer 22, a packing layer 21, an air inlet and a liquid outlet are respectively arranged from top to bottom. A CO₂ sensor 25 is provided on the air outlet pipeline 24.

[0058] The liquid outlet of the water storage tank 18 is connected to the inlet of the liquid sprayer 22 by a pipeline through the water pump 19. The liquid outlet at the bottom of the carbon fixation tower is connected to the crystallization tank by a pipeline through a fourth electromagnetic flowmeter 26.

[0059] The carbon fixation tower is also provided with a maintenance port 23 and an observation window 20. The observation window 20 is arranged below the packing layer 21; a second stirring device 28 and a second powder feeding device 27 are arranged on the crystallization tank. A second filtering component 29 is arranged inside the bottom of the crystallization tank. The liquid outlet at the bottom of the crystallization tank is connected to a fifth electromagnetic flowmeter 30 and a nitrogen fertilizer collector 31 in sequence through pipelines. A drain valve is provided on the drainage pipeline of the liquid outlet at the bottom of the crystallization tank.

[0060] Example 1:

[0061] The ammonia nitrogen content of the pig farm biogas slurry wastewater from a certain factory in Zhejiang Province is 1100 mg / L; in the CO₂-containing biogas, the CO₂ concentration is about 30% ± 2%, and the rest is mainly methane.

[0062] For the above-mentioned comprehensive utilization process of ammonia nitrogen recovery from pig farm biogas slurry and biogas-phosphogypsum, it includes the following steps:

[0063] Step S1: Put pig farm biogas slurry wastewater into the wastewater treatment tank, and sequentially add sodium phosphate and magnesium chloride to make the molar ratio of each substance in the reaction system Mg 2+ :NH4 + :PO4 3- =1.2:1:1. Start stirring, and the stirring speed is 200 rpm. Add NaOH solution to maintain the pH of the reaction system at 8.0 - 9.0, and stir and react at room temperature to promote the formation of struvite MgNH4PO4·6H2O precipitation. When the ammonia nitrogen concentration in the reaction system monitored by the ammonium on-line detector 11 is less than 30 mg / L, terminate the reaction, filter out the water in the reaction system, and leave the struvite precipitate. The ammonia nitrogen content of the treated wastewater is < 30 mg / L.

[0064] Then input high-temperature steam into the steam heating layer on the outer wall of the wastewater treatment tank to make the heating temperature 100 - 105 °C. The struvite precipitate in the wastewater treatment tank is thermally decomposed to release volatile NH3 until the concentration of the volatilized NH3 is < 30 ppm, and then stop heating the wastewater treatment tank.

[0065] The precipitate remaining after the decomposition of struvite in the wastewater treatment tank is magnesium hydrogen phosphate, which can be re-added to the pig farm biogas slurry wastewater and stirred to regenerate into magnesium ammonium phosphate precipitation for recycling. Magnesium hydrogen phosphate can be recycled well because the precipitation degree of magnesium ammonium phosphate is greater than that of magnesium hydrogen phosphate. Pig farm biogas slurry wastewater can be re-added to magnesium hydrogen phosphate to provide ammonium to form magnesium ammonium phosphate. At the same time, stirring can increase the reaction contact area to make magnesium hydrogen phosphate recycled well. In addition, phosphoric acid agents or magnesium salts can be added to promote the formation of magnesium ammonium phosphate, ensuring that magnesium ions and phosphate ions are in excess in the wastewater treatment tank, so that ammonium in the wastewater can be recovered. When the magnesium hydrogen phosphate precipitate is recycled, the recovery rate of waste ammonium in the pig farm biogas slurry wastewater is > 92%.

[0066] Step S2: The ammonia absorption tank is filled with water, and the aeration disk 14 is immersed in the water. The NH3 volatilized in Step S1 enters the aeration disk 14 of the ammonia absorption tank through the pipeline, and NH3 is released into the water through the microporous structure of the aeration disk 14. The formed microbubbles are inhaled into the water by absorption to form ammonia water. The absorption temperature is room temperature, and the concentration of ammonia water is detected by the ammonium on-line detector 11 until it reaches a mass concentration of 4%. When performing absorption treatment, if the NH3 concentration detected by the second gas phase NH3 sensor 15 after absorption is > 30 ppm, a secondary ammonia absorption tank is used for supplementary absorption.

[0067] Step S3: The ammonia water obtained in step S2 is transported to the upper part of the carbon sequestration tower for spraying. Meanwhile, the biogas supply unit transports the CO2-containing biogas to the lower air inlet of the carbon sequestration tower. The flow rate of the CO2-containing biogas introduced into the carbon sequestration tower is 10000 m 3 / d, and the flow rate of the ammonia water obtained in step S2 introduced into the carbon sequestration tower is 100 - 110 m 3 / d. The ammonia water and the CO2-containing biogas undergo countercurrent contact reaction in the packing layer 21 of the carbon sequestration tower. The absorption temperature is at normal temperature. The residence time of the ammonia water absorbed in the packing layer 21 of the carbon sequestration tower is controlled to be ≥60 s. The ammonia water absorbs CO2 in the biogas to form (NH4)2CO3 solution, which flows into the bottom of the carbon sequestration tower. The mass concentration of (NH4)2CO3 in the mixed aqueous solution at the bottom of the carbon sequestration tower is 10 - 12%. In the tail gas discharged from the top of the carbon sequestration tower, the CO2 concentration is 0.5 - 1.5%.

[0068] Step S4: The (NH4)2CO3 solution at the bottom of the carbon sequestration tower is transported to the crystallization tank. Then, 87% phosphogypsum (the mass fraction of the effective component CaSO4·2H2O in the phosphogypsum is 87%) is put into the crystallization tank. The molar ratio of the CaSO4 component of the phosphogypsum to (NH4)2CO3 in the mixed liquid is controlled to be 1.5:1. Stirring is started, and the stirring speed is 100 rpm. The reaction temperature is at normal temperature, and the reaction time is 1.5 h. The (NH4)2CO3 in the mixed liquid reacts with the CaSO4 component of the phosphogypsum to form CaCO3 precipitate and (NH4)2SO4. Then, stirring is stopped, and it is left standing for more than 1 h to complete the crystallization and sedimentation process. The liquid nitrogen fertilizer containing (NH4)2SO4 solution is filtered into the nitrogen fertilizer collector 31, and then the remaining CaCO3 precipitate is taken out. The concentration of (NH4)2SO4 in the liquid nitrogen fertilizer can reach 13 - 15% respectively. The purity of the remaining CaCO3 precipitate can reach 82% after drying.

[0069] The content described in this specification is only an enumeration of the implementation forms of the inventive concept. The protection scope of the present invention should not be regarded as limited to the specific forms stated in the embodiments.

Claims

1. A device for realizing biogas carbon fixation by comprehensive utilization of ammonia nitrogen and phosphogypsum in piggery biogas, characterized in that: It includes a biogas supply unit, an ammonia water preparation unit and a reaction crystallization unit; The ammonia water preparation unit comprises an ammonium online detector (11), a wastewater treatment tank for treating pig farm biogas slurry, and an ammonia absorption tank; the wastewater treatment tank is provided with a first stirring device (10), a water inlet pipe for introducing pig farm biogas slurry, a first powder feeding device (6), and a first electromagnetic flowmeter (5); a steam heating layer (7) is provided on the outer wall of the wastewater treatment tank, a first filtering component (8) is provided in the bottom, a liquid discharge valve is provided on the liquid discharge pipe at the bottom liquid outlet of the wastewater treatment tank, and phosphate and magnesium salt are added into the wastewater treatment tank through the first powder feeding device (6); the ammonia absorption tank is filled with water, and an aeration plate (14) is immersed in the water, and the air inlet of the aeration plate (14) is connected to the top air outlet of the wastewater treatment tank through a pipe; The reaction crystallization unit includes a carbon fixation tower and a crystallization tank. The ammonia water prepared in the ammonia absorption tank is transported to the upper part of the carbon fixation tower for spraying, and the CO2-containing biogas supplied by the biogas supply unit is transported to the lower air inlet of the carbon fixation tower, so that the ammonia water and the CO2-containing biogas are contacted and reacted in countercurrent to form (NH4)2CO3 liquid at the bottom of the carbon fixation tower; The bottom liquid outlet of the carbon fixation tower is connected to the crystallization tank by a pipeline, and the aqueous solution at the bottom of the tower is transported to the crystallization tank for crystallization. The crystallization tank is also provided with a second powder feeding device (27) for adding phosphogypsum.

2. The device for realizing biogas carbon fixation by comprehensive utilization of ammonia nitrogen and phosphogypsum in piggery biogas as claimed in claim 1, characterized in that: A first gas-phase NH3 sensor (12) and a first gas ultrasonic flowmeter (13) are arranged on the pipeline between the top gas outlet of the wastewater treatment tank and the aeration plate (14); a first electromagnetic flowmeter is arranged on the water inlet pipeline, and the amount of pig farm biogas slurry transported to the wastewater treatment tank is quantitatively controlled by the first electromagnetic flowmeter; a second electromagnetic flowmeter (9) is arranged on the discharge pipeline of the bottom liquid outlet of the wastewater treatment tank; The aeration holes of the aeration plate (14) are microporous structures with a pore diameter of less than 0.5 mm; The biogas supply unit comprises a biogas raw material tank (1) and a buffer tank (3); the biogas raw material tank (1) and the buffer tank (3) are connected by a pipeline with a pressure gauge (2); the gas outlet of the buffer tank (3) is connected to the lower gas inlet of the carbon fixation tower by a pipeline via a third gas ultrasonic flow meter (4).

3. The device for realizing biogas carbon fixation by comprehensive utilization of ammonia nitrogen and phosphogypsum in piggery biogas as claimed in claim 1, characterized in that: The ammonium online detector (11) is used to detect NH4 + The concentration of the ammonia gas and the ammonia water concentration in the ammonia absorption tank are monitored respectively; an exhaust pipe is arranged at the upper end of the ammonia absorption tank, and a second gas phase NH3 sensor (15) and a second gas ultrasonic flow meter (16) are arranged on the exhaust pipe; the exhaust pipe is connected to the secondary ammonia absorption tank and the final ammonia leakage protection unit in sequence through a pipeline; the final ammonia leakage protection unit adopts NH3 absorbent to spray and absorb the residual NH3.

4. The device for realizing biogas carbon fixation by comprehensive utilization of ammonia nitrogen and phosphogypsum in piggery biogas as claimed in claim 1, characterized in that: The reaction crystallization unit further comprises a water storage tank (18) and a water pump (19); the liquid inlet of the water storage tank (18) is connected to the liquid outlet of the ammonia absorption tank by a pipeline through a third electromagnetic flowmeter (17); the carbon fixation tower is provided with an air outlet pipeline (24), a liquid sprayer (22), a packing layer (21), an air inlet and a liquid outlet from top to bottom, and a CO2 sensor (25) is provided on the air outlet pipeline (24); The liquid outlet of the water storage tank (18) is connected to the inlet of the liquid sprayer (22) by a pipeline through a water pump (19), and the liquid outlet at the bottom of the carbon fixation tower is connected to the crystallization tank by a pipeline through a fourth electromagnetic flowmeter (26); The carbon fixation tower is also provided with a maintenance port (23) and an observation window (20), and the observation window (20) is arranged below the packing layer (21); the crystallization tank is provided with a second stirring device (28) and a second powder feeding device (27), and a second filtering component (29) is arranged in the bottom of the crystallization tank. The liquid outlet at the bottom of the crystallization tank is connected to the fifth electromagnetic flowmeter (30) and the nitrogen fertilizer collector (31) in sequence through pipelines, and a liquid discharge valve is arranged on the discharge pipe of the liquid outlet at the bottom of the crystallization tank.

5. A process for recovering ammonia nitrogen from biogas slurry in pig farms and comprehensive utilization of biogas and phosphogypsum based on the struvite crystallization method, comprising the following steps: Step S1: adding pig farm biogas wastewater into a wastewater treatment tank, adding phosphate and magnesium salt in sequence, starting stirring, adding NaOH solution to maintain the pH of the reaction system at an alkaline level, reacting under stirring to promote the precipitation of struvite MgNH4PO4·6H2O, terminating the reaction when the ammonia nitrogen concentration in the reaction system monitored by an ammonium online detector (11) is less than a threshold value, filtering out the water in the reaction system to leave struvite precipitates, and then heating the wastewater treatment tank to decompose the struvite precipitates under heat to volatilize NH3; Step S2: the NH3 volatilized in step S1 enters the aeration plate (14) of the ammonia absorption tank through a pipeline, releases NH3 in the water through the microporous structure of the aeration plate (14), and the formed microbubbles are absorbed into the water to form ammonia water, and the concentration of the ammonia water is detected by the ammonium online detector (11) until the required concentration is reached; Step S3: The ammonia water obtained in step S2 is transported to the upper part of the carbon fixation tower for spraying, and at the same time, the biogas supply unit transports the CO2-containing biogas to the lower air inlet of the carbon fixation tower, so that the ammonia water and the CO2-containing biogas are in countercurrent contact reaction in the packing layer (21) in the carbon fixation tower, and the ammonia water absorbs the CO2 in the biogas to form a (NH4)2CO3 solution that flows into the bottom of the carbon fixation tower; Step S4: The (NH4)2CO3 solution at the bottom of the carbon fixation tower is transported to a crystallization tank, and then phosphogypsum is added to the crystallization tank, and stirring is started to allow the (NH4)2CO3 in the mixed liquid to react with the CaSO4 component of the phosphogypsum to form CaCO3 precipitate and (NH4)2SO4. Then, stirring is stopped and the mixture is allowed to stand for more than 1 hour to complete the crystallization and sedimentation process, and the liquid nitrogen fertilizer containing (NH4)2SO4 is filtered into a nitrogen fertilizer collector (31), and the remaining CaCO3 precipitate is taken out.

6. The process according to claim 5, characterized in that In step S1, the ammonia nitrogen content of the pig farm biogas wastewater is 1000-3000 mg / L. By monitoring the NH4 + and PO4 3- concentration, and then determine the amount of phosphate and magnesium salt to make the molar ratio of each substance in the reaction system Mg 2+ :PO4 3- :NH4 + =1.15-1.25:1-1.05:1, the stirring speed is 200-300rpm, NaOH solution is added to maintain the pH of the reaction system at 8.0-9.0, and the reaction temperature is room temperature; the reaction is terminated when the ammonia nitrogen concentration in the reaction system is less than 30 mg / L monitored by an ammonium online detector (11); the temperature for heating the wastewater treatment tank is 100-105°C to allow the struvite to release NH3, and the heating of the wastewater treatment tank is stopped when the concentration of volatilized NH3 is less than 30 ppm.

7. The process according to claim 5, characterized in that In step S2, the NH3 absorption time is adjusted until the ammonia water reaches a target concentration of more than 4%.

8. The process according to claim 5, characterized in that Step S2 also includes a process for preventing NH3 from leaking, which is specifically as follows: 1) Cascade absorption protection: two ammonia absorption tanks are connected in series, and the first-stage ammonia absorption tank absorbs NH3 so that the discharged NH3 concentration is less than 30ppm. When the NH3 concentration at the exhaust pipe outlet of the first-stage ammonia absorption tank is greater than 30ppm, the second-stage ammonia absorption tank is opened to supplement the absorption of NH3; 2) Emergency treatment protection: If the NH3 concentration is still greater than 30ppm after the secondary absorption, the final NH3 leakage protection unit is started to use NH3 absorbent to spray and absorb the residual NH3. The NH3 absorbent is a citric acid aqueous solution with a mass concentration of 5-8%, ensuring that the tail gas NH3 concentration is ≤30ppm.

9. The process according to claim 5, characterized in that In step S3, the CO2 concentration in the biogas is 20-40%, the residence time of ammonia water absorbed in the packing layer (21) in the carbon fixation tower is controlled to be ≥60s, the absorption temperature is room temperature, and the CO2 concentration of the exhaust gas at the gas outlet of the carbon fixation tower is controlled to be ≤1.5%; if the CO2 concentration in the exhaust gas is greater than 1.5%, an alkaline absorbent is used to absorb it to remove the remaining CO2; in the (NH4)2CO3 solution formed at the bottom of the carbon fixation tower, the mass concentration of (NH4)2CO3 is 5-15%.

10. The process according to claim 5, characterized in that In step S4, the molar ratio of the CaSO4 component of phosphogypsum to the (NH4)2CO3 in the mixed liquid is 1.3-1.8:1, the reaction temperature is room temperature, the reaction time is 1-1.5h, the stirring speed of the reaction is 100-200rpm, and the mass concentration of (NH4)2SO4 in the liquid nitrogen fertilizer obtained by filtration after the reaction is 10-15%.

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