A device and method for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite

Abstract

The present invention relates to the technical field of sludge treatment, and discloses a device suitable for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite. The device includes an NH3 adsorption recovery unit and a struvite preparation unit. The NH3 adsorption recovery unit includes an anaerobic digestion tank, an adsorption separator, and a biogas storage tank connected in sequence through pipelines. The adsorption separator includes an adsorption separator A and an adsorption separator B arranged in parallel, and are respectively connected to the struvite preparation unit and a phosphoric acid storage tank through pipelines. The struvite preparation unit includes a struvite preparation unit and a phosphoric acid storage tank connected through pipelines. The present invention adsorbs and recovers high-concentration NH3 in biogas and prepares struvite, eliminates air pollution caused by high-concentration NH3 in biogas products, and realizes the resource utilization of waste NH3; by setting the adsorption separator A and the adsorption separator B connected in parallel, the system cycle adsorption and elution mode are guaranteed to operate continuously.

Description

Technical Field

[0001] The invention relates to the technical field of sludge treatment, and relates to a device and a method suitable for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite. Background Art

[0002] By the end of 2020, my country will produce 50 million tons of municipal sludge every year. Sludge contains a large amount of toxic and harmful substances, such as heavy metals, pathogenic microorganisms, organic pollutants, etc. If the sludge enters the environment directly without treatment, it will inevitably cause harm to the ecological environment and human health. In recent years, the combination of anaerobic digestion of sludge and land use disposal has been gradually promoted and applied in my country. Anaerobic digestion is an effective deep treatment method for sludge. It inactivates pathogens and viruses in sludge through microbial fermentation, and passivates the heavy metals contained in sludge to achieve harmlessness and stabilization of sludge; at the same time, the process can effectively reduce the volume of sludge, and improve the subsequent sludge dewatering efficiency, so as to achieve sludge reduction. A large amount of biogas will be produced during the anaerobic digestion of sludge, which can be used for power generation; in addition, the sludge after anaerobic digestion can be used as a soil conditioner or fertilizer after deep dehydration (water content <60%), realizing sludge resource utilization.

[0003] However, the mud quality in different regions of my country varies greatly, and the municipal sludge in most regions has a low content of organic components and a high proportion of difficult-to-degrade organic components, which often causes the anaerobic digestion process to operate unsatisfactorily. Before anaerobic digestion of sludge, thermal hydrolysis pretreatment can solve the above problems. During the thermal hydrolysis process, the sludge is subjected to high temperature (150~170℃) and high pressure (6~8bar), which decomposes large particles and difficult-to-degrade substances in the sludge into small molecules and easily degradable components, which can effectively increase the biogas production and improve the dewatering performance of the sludge. The sludge treatment points involved in this process usually include: mud inlet pump room, pre-dewatering workshop, sludge silo, thermal hydrolysis unit, heat exchange room, anaerobic digestion unit and plate and frame dewatering workshop.

[0004] The biogas produced during anaerobic digestion of sludge contains high concentrations of NH 3 During the biogas combustion process, it will be converted into nitrogen oxides and enter the ambient air, promoting PM 2.5 and O 3 The generation of NH 3 It is also an important raw material for inorganic nitrogen fertilizer and other resources. 3 , consumes 1-3% of the world’s energy each year and causes 1% of CO 2 If the NH in biogas can be 3 Adsorption and recovery to prepare nitrogen fertilizer products (such as struvite slow-release fertilizer), which is not only beneficial to environmental protection, but also reduces the production of NH 3The energy consumption and greenhouse gas emissions generated can also be achieved by waste NH 3 Resource utilization.

[0005] A Chinese patent with the authorization number CN 2500877 Y and the publication date of July 17, 2002 discloses a method and device for removing and recycling nitrogen and phosphorus in biogas slurry. This method adopts a combined process of struvite crystallization-ammonia stripping-SBBR treatment-BAF treatment to treat and recycle biogas slurry, converting phosphorus and nitrogen in biogas slurry into struvite and ammonium sulfate that can be used as fertilizers. While ensuring that the biogas slurry meets the pollutant emission standards of livestock and poultry breeding after treatment, it realizes the recovery of nitrogen and phosphorus, effectively reduces the operating costs of traditional biogas slurry treatment, and also has the characteristics of stable treatment effect. The device of the present invention is designed based on the above method, and each part of the device is optimized and improved, which can operate continuously and stably, and is easy to promote and use.

[0006] However, this patent only processes biogas slurry to recover nitrogen and phosphorus, but cannot process biogas containing high concentrations of NH 3 Effectively treat the biogas and realize the waste NH 3 Resource utilization. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a device and method for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite. By cyclically switching between adsorption separator A and adsorption separator B, high-concentration NH 3 Continuous adsorption is carried out, and phosphoric acid storage liquid is added to elute the adsorbent in the adsorption separator. The eluent and the water vapor after heating and drying the adsorbent enter the struvite preparation unit through pipelines respectively to obtain a high-purity struvite slow-release fertilizer product. In addition, the waste liquid in the struvite preparation unit flows back to the phosphoric acid storage tank and continues to be used as the phosphoric acid storage liquid after concentration adjustment.

[0008] The specific technical scheme of the present invention is: a device suitable for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite, comprising NH 3 Adsorption recovery unit and struvite preparation unit, the NH 3 The adsorption recovery unit comprises an anaerobic digester, an adsorption separator, and a biogas storage tank which are sequentially connected through pipelines, and the adsorption separator comprises an adsorption separator A and an adsorption separator B which are arranged in parallel; the struvite preparation unit comprises a struvite preparation unit and a phosphoric acid storage tank which are sequentially connected through pipelines, and the adsorption separator A and the adsorption separator B are arranged in parallel and are respectively connected to the struvite preparation unit and the phosphoric acid storage tank through pipelines.

[0009] Preferably, the main body of the adsorption separator A is a cylindrical structure, the top is a conical structure, and the bottom is an inverted conical structure. A water collecting plate A is provided at the connection between the internal main body and the top of the adsorption separator A, and a filter plate A is provided at the connection between the internal main body and the bottom. A water and air distribution plate A is provided below the filter plate A. A water vapor discharge pipeline A is provided on the outer wall of the adsorption separator A, one end of the water vapor discharge pipeline A is connected to the water collecting plate A, and the other end is connected to the struvite preparation unit.

[0010] The conical top structure of the adsorption separator A helps to accelerate the condensation and dripping of water vapor generated by the dry adsorbent. The water collecting plate A collects the water generated by the dry adsorbent. The water flows from the water collecting plate A into the struvite preparation unit through the water vapor discharge pipeline A. The filter plate A is used to place NH 3 The adsorbent is prevented from falling to the bottom of the adsorption separator A. There are many small holes on the water and air distribution plate A. The phosphoric acid storage liquid enters the adsorption separator A from bottom to top to backwash the adsorbent. After passing through the water and air distribution plate, it forms a spray, which increases the contact area with the adsorbent and can more fully absorb the adsorbed NH 3 reaction.

[0011] Preferably, an air inlet valve A is provided between the adsorption separator A and the anaerobic digester, an air outlet valve A is provided between the adsorption separator A and the biogas storage tank, a liquid outlet valve A is provided between the adsorption separator A and the struvite preparation unit, and a backwash valve A is provided between the adsorption separator A and the phosphate storage tank.

[0012] Through the backwash valve A, the phosphoric acid storage liquid enters the adsorption separator A from bottom to top and mixes with the adsorbed NH 3 reaction, and the adsorbent is eluted and regenerated through a backwashing process.

[0013] Preferably, the adsorption separator A is provided with a heating plate A, a temperature controller A and NH 4 + Online monitor A.

[0014] When NH 4 + Online monitor A detects NH 4 + When the concentration rises to less than 2 mg / L, close the backwash valve A, open the liquid outlet valve A, stop backwashing, and the eluent flows into the struvite preparation unit through the liquid outlet valve A.

[0015] Preferably, the struvite preparation unit is provided with a heating plate C, a temperature controller C, a pH meter and an agitator, a waste liquid outlet pump is provided between the struvite preparation unit and the phosphate storage tank, a feed metering pump is provided on one side of the struvite preparation unit, and a gas one-way valve is provided below the struvite preparation unit, which are respectively connected to the pipeline between the anaerobic digester and the adsorption separator A and the pipeline between the anaerobic digester and the adsorption separator B through air pipes.

[0016] Gas check valve controls NH 3 It can only enter the pipeline between the anaerobic digester and the adsorption separator from the struvite preparation unit and cannot flow back. The heating plate C adjusts the temperature at 25-35°C according to the measured value of the temperature controller C. The stirring frequency of the stirrer is 80-100r / min. NaOH and MgCl 2 The solution is added into the struvite preparation unit through a feed metering pump, and the pH is adjusted between 8.5 and 10 by controlling the amount of NaOH.

[0017] Preferably, the phosphate storage tank is provided with a PO 4 3- Online monitor: a phosphoric acid liquid lifting pump is arranged above the phosphoric acid storage tank.

[0018] When PO 4 3- The monitoring value of the online monitor is less than 10 mol / L. Phosphoric acid reagent is added to the phosphoric acid storage tank to adjust the concentration of the phosphoric acid storage solution, which enters the adsorption separator A through the phosphoric acid liquid lifting pump and backwash valve A.

[0019] As a preference, there is an NH 3 Online monitor.

[0020] When NH 3 When the monitoring value of the online monitor reaches the set value of 500ppm, stop introducing biogas into the adsorption separator A, open the backwash valve A, keep the liquid outlet valve A closed, and start introducing phosphoric acid storage solution into the adsorption separator A to backwash the adsorbent.

[0021] Preferably, the main body of the adsorption separator B is a cylindrical structure, the top is a conical structure, and the bottom is an inverted conical structure. A water collecting plate B is provided at the connection between the internal main body and the top of the adsorption separator B, and a filter plate B is provided at the connection between the internal main body and the bottom. A water and air distribution plate B is provided below the filter plate B. A water vapor discharge pipeline B is provided on the outer wall of the adsorption separator B, one end of the water vapor discharge pipeline B is connected to the water collecting plate B, and the other end is connected to the struvite preparation unit; an air inlet valve B is provided between the adsorption separator B and the anaerobic digester, an air outlet valve B is provided between the adsorption separator B and the biogas storage tank, a liquid outlet valve B is provided between the adsorption separator B and the struvite preparation unit, and a backwash valve B is provided between the adsorption separator B and the phosphoric acid storage tank; the adsorption separator B is provided with a heating plate B, a temperature controller B and NH 4 + Online monitor B.

[0022] While stopping the introduction of biogas into the adsorption separator A, open the air inlet valve B and the air outlet valve B, switch the biogas inlet to the adsorption separator B, and perform backwashing after adsorption.

[0023] A method for adsorbing and recovering ammonia from biogas produced by anaerobic digestion of sludge and preparing struvite by using the device comprises the following steps:

[0024] Step 1: pass the biogas into the adsorption separator A for NH 3 After the adsorption separator A is saturated, it switches to the adsorption separator B to adsorb NH 3 ;

[0025] Step 2: Adsorption separator B adsorbs NH 3 At the same time, the phosphoric acid storage solution enters the adsorption separator A to react with NH 3 The adsorbent is eluted and the adsorbent is dried by heating;

[0026] Step 3: The eluate enters the struvite preparation unit and NaOH and MgCl are added. 2 The solution generates struvite, and the waste liquid is pumped back to the phosphoric acid storage tank, and the generated gas continues to return to the adsorption separator for adsorption recovery.

[0027] Preferably, the energy required for heating and the power required for the pump are provided by burning biogas produced by anaerobic digestion of sludge in the plant to generate electricity.

[0028] The temperature for heating and drying the adsorbent is set at 100-110°C.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] (1) High concentration of NH in biogas 3Adsorption collection, elution with phosphoric acid to prepare struvite, eliminating the high concentration of NH in the biogas product 3 air pollution caused by waste NH 3 Resource utilization, the ammonia recovery rate reaches more than 90%;

[0031] (2) Through NH 3 Online monitoring to achieve the cyclic adsorption and elution operation mode of adsorption separator A and adsorption separator B to ensure the continuous operation of the system;

[0032] (3) The energy required for heating and the power required for pumps are provided by the biogas generated by anaerobic digestion of sludge in our plant through combustion and power generation, which reasonably solves the energy consumption in the system;

[0033] (4) The phosphoric acid eluate circulates between the adsorption separator and the phosphoric acid storage tank through the backwash process. The eluate and the water vapor after heating and drying the adsorbent enter the struvite preparation unit through pipelines respectively. During the reaction process, no reaction by-products are discharged outside the system, thereby reducing pollution to the surrounding environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the present invention.

[0035] The reference numerals are: adsorption separator A1, air inlet valve A1-1, air outlet valve A1-2, liquid outlet valve A1-3, backwash valve A1-4, water collecting plate A1-5, water vapor discharge pipeline A1-6, filter plate A1-7, water and air distribution plate A1-8, heating plate A1-9, temperature controller A1-10, NH 4 + Online monitor A1-11, adsorption separator B2, air inlet valve B2-1, air outlet valve B2-2, liquid outlet valve B2-3, backwash valve B2-4, water collecting plate B2-5, water vapor discharge pipeline B2-6, filter plate B2-7, water and air distribution plate B2-8, heating plate B2-9, temperature controller B2-10, NH 4 + Online monitor B 2-11, anaerobic digester 3, struvite preparation unit 4, waste liquid discharge pump 4-1, feed metering pump 4-2, heating plate C4-3, temperature controller C4-4, pH meter 4-5, stirrer 4-6, gas check valve 4-7, phosphoric acid storage tank 5, phosphoric acid liquid lifting pump 5-1, PO 4 3- Online monitor 5-2, biogas storage tank 6, NH 3 Online monitor 6-1. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and beneficial technical effect of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. The devices, connection structures and methods involved in the present invention are all devices, connection structures and methods known in the art unless otherwise specified.

[0037] Example 1

[0038] like Figure 1 As shown: A device suitable for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite, including NH 3 Adsorption recovery unit and struvite preparation unit, the NH 3 The adsorption recovery unit comprises an anaerobic digester, an adsorption separator, and a biogas storage tank which are sequentially connected through pipelines, and the adsorption separator comprises an adsorption separator A and an adsorption separator B which are arranged in parallel; the struvite preparation unit comprises a struvite preparation unit and a phosphoric acid storage tank which are sequentially connected through pipelines, and the adsorption separator A and the adsorption separator B are arranged in parallel and are respectively connected to the struvite preparation unit and the phosphoric acid storage tank through pipelines.

[0039] The operation mode of the adsorption separator A1 and the adsorption separator B2 is cyclic switching. A large amount of biogas is generated after the reaction in the anaerobic digester. The air inlet valve A1-1 and the air outlet valve A1-2 are opened, and the liquid outlet valve A1-3 and the backwash valve A1-4 are kept closed. The biogas enters the adsorption separator A1 from bottom to top through the pipeline. The main body of the adsorption separator A1 is a cylindrical structure, the top is a conical structure, and the bottom is an inverted conical structure. A water collecting plate A1-5 is provided at the connection between the internal main body and the top of the adsorption separator A1, and a filter plate A1-7 is provided at the connection between the internal main body and the bottom. A water and air distribution plate A1-8 is provided below the filter plate A1-7. A water vapor discharge pipeline A1-6 is provided on the outer wall of the adsorption separator A. One end of the water vapor discharge pipeline A1-6 is connected to the water collecting plate A1-5, and the other end is connected to the struvite preparation unit. NH 3 Adsorbent to prevent NH 3 The adsorbent falls to the bottom of the adsorption separator, and the NH 3 NH 3 The adsorbent absorbs and retains the biogas, and the purified biogas passes through NH 3 Online monitor 6-1 enters into biogas storage tank 6. When NH 3After the monitoring value of the online monitor 6-1 reaches the set value of 500ppm, close the air inlet valve A1-1 and the air outlet valve A1-2, keep the liquid outlet valve A1-3 closed, open the backwash valve A1-4, and the phosphoric acid storage liquid enters the adsorption separator A1 from the phosphoric acid storage tank 5 through the phosphoric acid liquid lifting pump 5-1 and the backwash valve A1-4. At the same time, open the air inlet valve B2-1 and the air outlet valve B2-2, keep the liquid outlet valve B2-3 and the backwash valve B2-4 closed, and switch to the adsorption separator B2 to adsorb NH 3 The biogas inlet is switched from the adsorption separator A1 to the adsorption separator B2 of the same configuration. The main body of the adsorption separator B2 is a cylindrical structure, the top is a conical structure, and the bottom is an inverted conical structure. A water collecting plate B2-5 is provided at the connection between the internal main body and the top of the adsorption separator B2, and a filter plate B2-7 is provided at the connection between the internal main body and the bottom. A water and air distribution plate B2-8 is provided below the filter plate B2-7. A water vapor discharge pipeline B2-6 is provided on the outer wall of the adsorption separator B2. One end of the water vapor discharge pipeline B2-6 is connected to the water collecting plate B2-5, and the other end is connected to the struvite preparation unit. NH 3 Adsorbent, NH in biogas 3 NH 3 The adsorbent absorbs and retains the biogas, and the purified biogas passes through NH 3 The online monitor 6-1 then enters the biogas storage tank 6. Adsorption separator B 2 adsorbs NH 3 At the same time, the phosphoric acid storage liquid enters the adsorption separator A1, and the phosphoric acid storage liquid diffuses from bottom to top through the water and air distribution plate A1-8 and the filter plate A1-7 to backwash the adsorbent. The phosphoric acid storage liquid forms a spray after passing through the water and air distribution plate A1-8, which increases the contact with NH 3 The adsorbent is regenerated by backwashing and the eluent (NH 4 ) 3 PO 4 Solution), there is NH below the backwash liquid level of adsorption separator A1 4 + Online monitor A 1-11, when NH 4 + The online monitor A 1-11 detected NH 4 +If the concentration rises to less than 2 mg / L, the backwash is stopped, the elution is completed, the backwash valve A1-4 is closed, the outlet valve A1-3 is opened, and the eluate flows into the struvite preparation unit 4 through the outlet valve A1-3. At the same time, the adsorption separator A1 is provided with a heating plate A1-9 and a temperature controller A1-10. By setting the temperature parameter of the heating plate A1-9 to 100°C, the temperature in the adsorption separator A1 is controlled to accelerate the drying of the adsorbent after elution regeneration. The water vapor generated during the drying process condenses into water droplets on the top inner wall of the adsorption separator A1, flows into the water collecting plate A1-5, and then flows into the struvite preparation unit 4 through the water vapor discharge pipeline A1-6. When the eluate is emptied, the outlet valve A1-3 is closed, the backwash valve A1-4 is kept closed, the air inlet valve A1-1 and the air outlet valve A1-2 are opened, and the adsorption separator A1 continues to adsorb NH in the biogas. 3 The struvite preparation unit 4 is provided with a heating plate C 4-3, a temperature controller C 4-4, a pH meter 4-5 and a stirrer 4-6. A feed metering pump 4-2 is provided on one side of the struvite preparation unit 4. A gas one-way valve 4-7 is provided below the struvite preparation unit 4, which is connected to the pipeline between the anaerobic digester 3 and the adsorption separator A1 and the pipeline between the anaerobic digester 3 and the adsorption separator B2 through the air pipe. The temperature parameter of the heating plate C 4-3 is set to 30°C to control the temperature in the struvite preparation unit 4. The stirrer 4-6 is set to have a stirring frequency of 90r / min. NaOH and MgCl are added to the struvite preparation unit 4 through the feed metering pump 4-2. 2 The solution was added with NaOH to adjust the pH. The pH value of the pH meter was 9 at 4-5. After the reaction, the precipitate struvite was obtained. After heating and drying, the struvite slow-release fertilizer product was obtained. The by-product NH 3 The gas enters the pipeline between the anaerobic digester 3 and the adsorption separator A1 and the pipeline between the anaerobic digester 3 and the adsorption separator B2 through the gas check valve 4-7, and enters the adsorption separator again together with the biogas for adsorption recovery. A waste liquid outlet pump 4-1 is provided between the struvite preparation unit 4 and the phosphoric acid storage tank 5. The phosphoric acid storage tank 5 is provided with a PO 4 3- Online monitor 5-2, the struvite preparation unit 4 produces NH 4 + The waste liquid enters the phosphoric acid storage tank 5 through the waste liquid outlet pump 4-1, and is 4 3- The monitoring value of the online monitor 5-2 drops to 5 mol / L to replenish the phosphoric acid reagent and adjust the concentration of the phosphoric acid storage solution in the phosphoric acid storage tank 5 to contain NH 4 + The phosphoric acid storage solution will elute the adsorbent again, making the NH 4 +The reaction byproducts are not discharged outside the system during the reaction process, thus reducing the pollution to the surrounding environment.

[0040] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A device suitable for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite, characterized by: It comprises an NH3 adsorption recovery unit and a struvite preparation unit, wherein the NH3 adsorption recovery unit comprises an anaerobic digestion tank, an adsorption separator, and a biogas storage tank which are sequentially connected through pipelines, and the adsorption separator comprises an adsorption separator A and an adsorption separator B which are arranged in parallel; the struvite preparation unit comprises a struvite preparation unit and a phosphoric acid storage tank which are sequentially connected through pipelines, and the adsorption separator A and the adsorption separator B are arranged in parallel and are respectively connected to the struvite preparation unit and the phosphoric acid storage tank through pipelines; A water collecting plate A is provided at the connection between the internal body and the top of the adsorption separator A, a filter plate A is provided at the connection between the internal body and the bottom, and a water and air distribution plate A is provided below the filter plate A; An air inlet valve A is provided between the adsorption separator A and the anaerobic digester, an air outlet valve A is provided between the adsorption separator A and the biogas storage tank, a liquid outlet valve A is provided between the adsorption separator A and the struvite preparation unit, and a backwash valve A is provided between the adsorption separator A and the phosphate storage tank.

2. A device for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite as claimed in claim 1, characterized in that: The main body of the adsorption separator A is a cylindrical structure, the top is a conical structure, and the bottom is an inverted conical structure. The outer wall of the adsorption separator A is provided with a water vapor exhaust pipeline A, one end of the water vapor exhaust pipeline A is connected to the water collecting plate A, and the other end is connected to the struvite preparation unit.

3. A device for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite as claimed in claim 2, characterized in that: The adsorption separator A is provided with a heating plate A, a temperature controller A and NH4 + Online monitor A.

4. A device for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite as claimed in claim 1, characterized in that: The struvite preparation unit is provided with a heating plate C, a temperature controller C, a pH meter and an agitator. A waste liquid outlet pump is provided between the struvite preparation unit and the phosphate storage tank. A feed metering pump is provided on one side of the struvite preparation unit. A gas one-way valve is provided below the struvite preparation unit, which is respectively connected to the pipeline between the anaerobic digester and the adsorption separator A and the pipeline between the anaerobic digester and the adsorption separator B through an air pipe.

5. A device for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite as claimed in claim 1, characterized in that: The phosphoric acid storage tank is provided with PO4 3- Online monitor: a phosphoric acid liquid lifting pump is arranged above the phosphoric acid storage tank.

6. A device for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite as claimed in claim 1, characterized in that: An NH3 online monitor is provided below the biogas storage tank.

7. A device for adsorbing and recovering ammonia in biogas from anaerobic digestion of sludge and preparing struvite as claimed in claim 1, characterized in that: The main body of the adsorption separator B is a cylindrical structure, the top is a conical structure, and the bottom is an inverted conical structure. A water collecting plate B is provided at the connection between the internal main body and the top of the adsorption separator B, and a filter plate B is provided at the connection between the internal main body and the bottom. A water and air distribution plate B is provided below the filter plate B. A water vapor discharge pipeline B is provided on the outer wall of the adsorption separator B, one end of the water vapor discharge pipeline B is connected to the water collecting plate B, and the other end is connected to the struvite preparation unit; an air inlet valve B is provided between the adsorption separator B and the anaerobic digester, an air outlet valve B is provided between the adsorption separator B and the biogas storage tank, a liquid outlet valve B is provided between the adsorption separator B and the struvite preparation unit, and a backwash valve B is provided between the adsorption separator B and the phosphoric acid storage tank; the adsorption separator B is provided with a heating plate B, a temperature controller B and NH4 + Online monitor B.

8. A method for preparing struvite by adsorbing and recovering ammonia from biogas produced by anaerobic digestion of sludge using the device according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: passing the biogas into the adsorption separator A to adsorb NH3, and after the adsorption separator A is saturated, switching to the adsorption separator B to adsorb NH3; Step 2: While the adsorption separator B adsorbs NH3, the phosphoric acid storage solution enters the adsorption separator A to elute the NH3 adsorbent and heat and dry the adsorbent; Step three, the eluate enters the struvite preparation unit, and NaOH and MgCl2 solutions are added to generate struvite. The waste liquid generated flows back to the phosphoric acid storage tank through a pump, and the generated gas continues to return to the adsorption separator for adsorption recovery.

9. The method for recovering ammonia from biogas produced by anaerobic digestion of sludge and preparing struvite according to claim 8, characterized in that: The energy required for heating and the power required for the pump are provided by burning biogas produced by anaerobic digestion of sludge in this plant to generate electricity.

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