A treatment system and a recovery method for high-concentration phosphine waste gas incineration and recovery of phosphoric acid

Abstract

The application discloses a treatment system and a recovery method for high-concentration phosphine waste gas incineration and recovery of phosphoric acid, and the system comprises an incineration tower and an absorption tower, wherein the first spraying mechanism is arranged in the incineration tower, and the second spraying mechanism is arranged in the absorption tower. The second circulating water tank of the second spraying mechanism is communicated with the first circulating water tank of the first spraying mechanism through a first liquid transferring pipeline, which is used for sending dilute phosphoric acid generated by absorbing P2O5 in the second circulating water tank into the first circulating water tank, and evaporating and concentrating the dilute phosphoric acid in the incineration tower through the first spraying mechanism; the first circulating water tank is connected with a second liquid transferring pipeline, which is used for discharging and recovering the concentrated phosphoric acid. The dilute phosphoric acid generated by the absorption tower is evaporated and concentrated by using the heat of the incineration tower, and an independent concentration device is not needed, so that the cascade concentration and efficient recovery of the phosphoric acid are realized, the problem of high-concentration phosphine waste gas treatment is effectively solved, and the environmental protection benefit and the economic benefit are combined.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically a treatment system and method for recovering phosphoric acid by incinerating high-concentration phosphine waste gas. Background Technology

[0002] Phosphine (PH3) is an important specialty gas in semiconductor doping, the electronics industry, and phosphate chemical production. Its production, filling, and use generate high-concentration phosphine-containing process waste gas, with phosphine volume concentrations reaching over 1% and instantaneous emissions reaching tens of kilograms per hour. Phosphine is a highly toxic gas, and its emission concentration must be strictly controlled at 0.3 mg / m³. 3 Furthermore, phosphorus is an important resource with extremely high recycling value. Therefore, the safe treatment and resource recovery of high-concentration phosphine waste gas has become a key technical problem that the industry urgently needs to solve.

[0003] Among existing treatment technologies, adsorption and oxidation absorption methods suffer from insufficient treatment capacity, high consumption of adsorbents or oxidants, intense exothermic reactions, and significant safety hazards for high-concentration phosphine waste gas, making it difficult to achieve stable compliance treatment. While combustion methods can effectively treat high-concentration phosphine, current combustion processes generally only focus on waste gas destruction. Either the phosphorus pentoxide generated during combustion is simply sprayed and then directly discharged, resulting in a waste of phosphorus resources and secondary water pollution; or although an absorption and recovery stage is included, it uses a single-stage circulating absorption method, which limits the increase in absorbent concentration and fails to obtain economically valuable high-concentration phosphoric acid products. Furthermore, it requires additional independent evaporation and concentration equipment, leading to high energy consumption and operating costs.

[0004] Therefore, how to fully utilize the heat of the incineration system itself to achieve graded concentration and efficient recovery of phosphoric acid during the incineration treatment of high-concentration phosphine waste gas, avoid additional energy consumption and equipment investment, and ensure the safety and controllability of the entire treatment process, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention provides a treatment system and method for recovering phosphoric acid by incinerating high-concentration phosphine waste gas. By connecting the second circulating water tank and the first circulating water tank 25 in series through the first liquid transfer pipeline, the dilute phosphoric acid generated in the absorption tower is transferred into the incineration tower. The heat of the incineration tower itself is used for spray evaporation and concentration, thereby realizing the step-by-step concentration and efficient recovery of phosphoric acid. No external independent concentration equipment is required, which has the dual benefits of low energy consumption operation and high value-added phosphoric acid product output.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention discloses a treatment system for recovering phosphoric acid by incinerating high-concentration phosphine waste gas, comprising an incineration tower and an absorption tower; the incineration tower is provided with a first spraying mechanism, and the absorption tower is provided with a second spraying mechanism; the second circulating water tank of the second spraying mechanism is connected to the first circulating water tank of the first spraying mechanism through a first liquid transfer pipeline, for sending the absorbent liquid in the second circulating water tank for absorbing P2O5 to generate phosphoric acid into the first circulating water tank, and evaporating and concentrating it in the incineration tower through the first spraying mechanism; the first circulating water tank is connected to a second liquid transfer pipeline for discharging and recovering the concentrated phosphoric acid.

[0007] As a further aspect of the present invention: the outlet of the incineration tower is connected to the inlet of the absorption tower, the incineration tower is used to oxidize and burn phosphine waste gas to generate flue gas containing P2O5, and the absorption tower is used to absorb the P2O5 in the flue gas to generate phosphoric acid.

[0008] As a further aspect of the present invention: the first spraying mechanism further includes a first spraying component and a first circulating pump connecting the first spraying component and the first circulating water tank; the second spraying mechanism further includes a second spraying component.

[0009] As a further aspect of the present invention: the absorption tower is a packed tower or a plate tower, and the P2O5-containing flue gas flowing upward from the bottom of the absorption tower is countercurrently contacted and absorbed by the absorbent liquid sprayed downward from the second spraying mechanism.

[0010] As a further aspect of the present invention: the first spray assembly is located at the top of the incineration tower, and the absorbent is evaporated and concentrated at a temperature of 120-200°C inside the incineration tower.

[0011] As a further aspect of the present invention, it also includes a multi-stage demister, a fan, a tail gas buffer tower, and an electrostatic demister arranged sequentially downstream of the absorption tower along the exhaust gas flow direction, wherein the outlet of the electrostatic demister is connected to an exhaust stack.

[0012] As a further aspect of the present invention, it also includes a water seal tank arranged sequentially upstream of the incineration tower (2) along the direction of exhaust gas flow.

[0013] As a further aspect of the present invention: the incineration tower is equipped with a temperature monitor and a flame monitor. The temperature monitor is used to monitor the temperature inside the incineration tower in real time and adjust the amount of combustion air in a chain. The flame monitor is used to detect the flame status and, when the flame is extinguished, to cut off the phosphine gas intake and start nitrogen purging in a chain.

[0014] As a further aspect of the present invention: the air inlet end of the exhaust pipe is equipped with an online phosphine concentration detector.

[0015] As a further aspect of the present invention: the system is equipped with a DCS / PLC automatic control system, which can realize full-process automatic control and safety interlocking, thereby improving the system's automation level and operational stability.

[0016] Secondly, this invention discloses a method for treating high-concentration phosphine waste gas by incineration to recover phosphoric acid, employing the aforementioned treatment system and including the following steps: S1: Phosphine waste gas is passed into an incineration tower for oxidation and combustion to generate flue gas containing P2O5; S2: The flue gas is passed into the absorption tower and the absorption liquid is sprayed through the second spraying mechanism to absorb P2O5 in the flue gas to generate phosphoric acid. The absorption liquid gradually forms dilute phosphoric acid in the second circulating water tank. S3: When the absorbent in the second circulating water tank reaches the preset concentration, the absorbent is sent into the first circulating water tank through the first transfer pipeline. S4: The absorbent in the first circulating water tank is sprayed into the incineration tower through the first spraying mechanism, and the waste heat of the incineration tower is used to evaporate and concentrate it to obtain concentrated phosphoric acid. S5: When the concentrated phosphoric acid in the first circulating water tank reaches the preset product concentration, it is discharged and recycled through the second transfer pipeline.

[0017] Compared with the prior art, the beneficial effects of the present invention are: The high-concentration phosphine waste gas incineration and phosphoric acid recovery system provided by this invention features a dual-spray circulation loop consisting of an incineration tower and an absorption tower. The circulating water tanks of the two towers are connected in series via a first transfer pipeline. The dilute phosphoric acid generated from the absorption of P2O5 in the absorption tower is transferred to the first circulating water tank, and then concentrated by spraying and evaporating it in the high-temperature zone (120~200℃) of the first spray assembly at the top of the incineration tower. The heat released during the incineration process raises the phosphoric acid concentration to a commercially viable product level before it is discharged and recovered via a second transfer pipeline. This tiered concentration process fully utilizes the system's waste heat, eliminating the need for separate evaporation and concentration equipment, and significantly reducing energy consumption and operating costs.

[0018] Simultaneously, the system can be further configured with purification units such as water seal tanks, double-layer demisters, exhaust gas buffer towers, and wet electrostatic precipitators, as well as safety protection systems such as nitrogen protection and DCS / PLC automatic interlock control, ensuring that the incineration process is safe and controllable and that exhaust gas emissions meet standards. This invention deeply couples the high-temperature incineration treatment of highly toxic phosphine waste gas with the resource recovery of phosphoric acid, achieving both harmless treatment of waste gas and turning waste into treasure, possessing significant environmental and economic benefits, and providing a safe, efficient, and energy-saving systematic solution for the treatment of phosphorus-containing special waste gases. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the incineration tower in this invention; Figure 3 This is a schematic diagram of the absorption tower in this invention; In the picture: 1-Water seal tank; 2-Incineration tower; 21-Burner; 22-Combustion air inlet; 23-Temperature monitor; 24-Flame monitor; 25-First circulating water tank; 26-First circulating pump; 27-First spray assembly; 28-Second liquid transfer pipeline; 3-Absorption tower; 31-Second circulating water tank; 32-Second circulating pump; 33-Second spray assembly; 34-First liquid transfer pipeline; 4-Multi-stage demister; 5-Fan; 6-Tail gas buffer tower; 7-Electrostatic demister; 8-Exhaust stack; 9-External acid recovery tank; 10-DCS / PLC automatic control system. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0022] Please see Figure 1-3 The present invention provides a treatment system for recovering phosphoric acid from high-concentration phosphine waste gas by incineration, comprising a water seal tank 1, an incineration tower 2, an absorption tower 3, a multi-stage demister 4, a fan 5, a tail gas buffer tower 6, and an electrostatic demister 7 connected in sequence along the waste gas flow direction; and also includes a DCS / PLC automatic control system 10 that is interlocked with each treatment unit.

[0023] The high-concentration process waste gas generated in the phosphine workshop first enters the water seal tank 1. The water seal tank is equipped with a water seal layer with a certain liquid level. Its function is to isolate the flame with water and prevent backfire that may occur in the incinerator 2 from propagating backward through the pipeline to the upstream workshop, thus ensuring system safety. The waste gas after passing through the water seal enters the incinerator 2.

[0024] The incineration tower 2 is a vertical cylindrical structure with a refractory lining on its inner wall. A burner 21 and a combustion air inlet 22 are located at the bottom of the tower. High-concentration phosphine waste gas mixes and combusts with combustion air inside the incineration tower, with the combustion temperature controlled between 900 and 1100°C. Phosphine reacts with oxygen to produce P2O5. A temperature monitor 23 is installed inside the incineration tower to detect the temperature in real time and feeds it back to the DCS / PLC automatic control system 10. The system automatically adjusts the supply of combustion air based on the temperature signal to ensure complete combustion and stable temperature. A flame monitor 24 is used to detect the combustion flame status in real time. When the flame is detected to be extinguished, the system automatically interlocks and shuts off the phosphine inlet valve and starts nitrogen purging to prevent unburned phosphine from accumulating and forming an explosive mixture.

[0025] The incineration tower 2 is connected to a first circulating water tank 25, which is connected to a first spray assembly 27 at the top of the incineration tower via a first circulating pump 26, forming a circulating spray circuit for the incineration tower. The absorbent in the first circulating water tank 25 is dilute phosphoric acid, which is pumped to the top of the tower for spraying. Under the relatively high temperature of 120~200℃ inside the incineration tower, it comes into contact with the flue gas containing P2O5, further absorbing P2O5. At the same time, some water is removed by high-temperature evaporation, thereby concentrating the phosphoric acid.

[0026] The high-temperature P2O5-containing flue gas generated from incineration is discharged from the top of incineration tower 2 and enters the lower inlet of absorption tower 3. Absorption tower 3 is a packed tower structure, filled with corrosion-resistant packing. Absorption tower 3 is connected to a second circulating water tank 31, which is connected to the first spray assembly 33 at the top of the absorption tower via a second circulating pump 32, forming a circulating spray loop for the absorption tower. Dilute phosphoric acid is sprayed evenly from top to bottom, and comes into countercurrent contact with the P2O5-containing flue gas flowing upwards on the surface of the packing. The P2O5 is absorbed by the dilute phosphoric acid to form phosphoric acid. The operating temperature of the absorption tower is controlled at 60~80℃ to balance absorption efficiency and equipment corrosion control.

[0027] As the absorption process continues, the phosphoric acid concentration in the second circulating water tank 31 gradually increases. When the concentration reaches the first preset concentration (e.g., 30%~40%), a portion of the absorbent is transferred to the first circulating water tank 25 via the first transfer pipeline 34, serving as the absorbent for the circulating spray in the incinerator. The phosphoric acid in the first circulating water tank 25 continues to absorb P2O5 and evaporate and concentrate under the higher temperature conditions of the incinerator. When the concentration reaches the second preset concentration (e.g., above 65%), the phosphoric acid product is discharged into the external acid recovery tank 9 via the second transfer pipeline 28. This cascade concentration process utilizes the synergistic effect of low-temperature absorption in the absorption tower and high-temperature concentration in the incinerator to achieve efficient recovery and energy-saving concentration of phosphoric acid.

[0028] The exhaust gas from absorber 3 still carries a certain amount of phosphoric acid droplets, which enter the secondary demister 4 through a pipeline. The secondary demister 4 is a baffle-type demister, which utilizes the inertia of the phosphoric acid droplets as the airflow changes direction multiple times in the tortuous channel to impact the surface of the baffles and be captured, effectively removing larger phosphoric acid droplets (typically >5μm). The captured phosphoric acid droplets converge and flow back to the second circulating water tank.

[0029] After initial demisting by the secondary demister 4, the gas is pressurized and transported by the fan 5. The fan 5 is a corrosion-resistant centrifugal fan that provides the power for gas transport in the system, overcoming the pipeline resistance of the subsequent tail gas buffer tower 6, electrostatic demister 7, and exhaust stack 8. The pressurized gas enters the tail gas buffer tower 6, which buffers and balances the airflow at the fan outlet, stabilizing the gas flow and pressure, and providing stable intake conditions for the subsequent electrostatic demister.

[0030] After being pressurized by the exhaust gas buffer tower 6, the gas enters the electrostatic precipitator 7. The electrostatic precipitator 7 is a wet electrostatic precipitator, whose core components include a corona electrode and an anode collecting tube. By applying high-voltage direct current, a high-voltage electrostatic field is formed between the corona electrode and the anode. Fine phosphoric acid droplets in the gas become charged in the electric field and move towards the anode collecting tube with opposite polarity. After being captured by the anode, they converge into a liquid film and flow down by gravity for collection. The electrostatic precipitator can efficiently remove submicron-sized phosphoric acid droplets, with a demisting efficiency of over 99%. The clean gas after two stages of demisting is discharged through the exhaust stack 8 in compliance with standards. An online phosphine concentration detector is installed at the inlet of the exhaust stack, interlocked with the DCS / PLC automatic control system 10. When an abnormally high phosphine concentration is detected, an emergency response procedure is automatically triggered.

[0031] Nitrogen protection is implemented throughout the entire treatment system. Before system startup, pipelines and equipment are purged with nitrogen to remove air and prevent the formation of an explosive mixture with phosphine. After system shutdown, nitrogen purging is performed to remove residual phosphine. Nitrogen purging is automatically initiated when the flame monitor 24 detects an abnormal flameout. Incineration tower 2, absorption tower 3, and related electrical equipment are all designed and selected according to IICT4 or higher explosion-proof standards.

[0032] As a preferred embodiment, the nitrogen protection system is a distribution network with a multi-branch structure, which can deliver nitrogen to any equipment and pipeline in the system that needs to be replaced or purged as needed.

[0033] The entire system adopts a skid-mounted modular design, with each unit integrated on a steel structure frame, which facilitates transportation, installation and on-site layout. The fully enclosed operation ensures no exhaust gas leakage.

[0034] When the system of this invention is running, the high-concentration waste gas generated in the phosphine workshop first enters the incineration tower 2 after passing through the water seal tank 1 to prevent backfire. There, it mixes with combustion air and burns to generate high-temperature flue gas containing P2O5. After entering the absorption tower 3, the second spraying mechanism sprays absorbent liquid from top to bottom, counter-currently absorbing the P2O5 in the flue gas to generate phosphoric acid. The absorbent liquid gradually forms dilute phosphoric acid in the second circulating water tank 31. When the dilute phosphoric acid reaches a preset concentration, it is transferred to the first circulating water tank 25 through the first transfer pipeline 34, and then transported by the first circulating pump 26 to the first spraying mechanism 27 at the top of the incineration tower 2 for spraying. At a high temperature of 120~200℃, it is evaporated and concentrated using the residual heat of incineration, finally forming commercial-grade concentrated phosphoric acid, which is then transferred through the second transfer pipeline 28. The exhaust gas is discharged into the external recovery tank 9; after incineration and absorption, the exhaust gas passes through the secondary demister 4 to capture large-diameter phosphoric acid droplets, is boosted and transported by the fan 5, and is stabilized by the exhaust gas buffer tower 6 before entering the electrostatic demister 7 to remove fine phosphoric acid droplets, and is finally discharged through the exhaust stack 8 in compliance with standards.

[0035] It should be particularly noted that during system operation, operators can read the liquid level and concentration data of each water tank through field instruments, and manually open and close the corresponding valves and pumps to complete the liquid transfer and acid discharge operations. As a preferred embodiment of the present invention, the above-mentioned valves and pumps can be connected to the DCS / PLC automatic control system 10. The system automatically performs liquid transfer, water replenishment, and acid discharge operations according to preset liquid level and concentration thresholds, and realizes the interlocking regulation and safety protection of temperature, flame monitoring, and combustion air and phosphine intake, further improving the automation level and operational safety of the system.

[0036] On the other hand, the present invention also discloses a method for recovering phosphoric acid using the above-described processing system, comprising the following steps: S1: Incineration Oxidation. High-concentration phosphine waste gas is introduced into incineration tower 2 and mixed with combustion air for combustion. Phosphine (PH3) reacts with oxygen to produce phosphorus pentoxide (P2O5). The reaction formula is: 4PH3 + 8O2 = 2P2O5 + 6H2O. The incineration temperature is controlled at 900~1100℃ to ensure complete conversion of phosphine.

[0037] S2: Spray absorption. The high-temperature P2O5-containing flue gas generated in S1 is introduced into the absorption tower 3. At the same time, the second spray mechanism pumps the absorbent liquid water or dilute phosphoric acid from the second circulating water tank 31 to the top of the absorption tower and sprays it from top to bottom, making countercurrent contact with the flue gas flowing from bottom to top. P2O5 is absorbed by the absorbent liquid to form phosphoric acid P2O5 + 3H2O = 2H3PO4. The operating temperature of the absorption tower is controlled at 60~80℃. At this temperature, both high absorption efficiency is ensured and excessive corrosion of the equipment due to high temperature is avoided.

[0038] S3: Dilute acid to liquid transfer. As the absorption process of S2 continues, the phosphoric acid concentration in the second circulating water tank 31 continues to rise. When it reaches the preset concentration (e.g., 30%~40%), the dilute phosphoric acid in the second circulating water tank 31 is transferred to the first circulating water tank 25 through the first liquid transfer pipeline 34, realizing the intermediate-stage recovery and transfer of dilute phosphoric acid.

[0039] S4: High-temperature concentration. The first circulating pump 26 pumps the dilute phosphoric acid in the first circulating water tank 25 to the first spray mechanism 27 at the top of the incineration tower 2 for spraying. The dilute phosphoric acid continues to contact and absorb P2O5 in the high-temperature flue gas environment of 120~200℃ in the incineration tower 2, while the water evaporates continuously, and the phosphoric acid concentration gradually increases. This step uses the waste heat generated by the incineration tower itself as a heat source for evaporation and concentration, without the need for an external heat source.

[0040] S5: Concentrated acid recovery. When the phosphoric acid concentration in the first circulating water tank 25 reaches the preset product concentration (e.g., above 65%), the concentrated phosphoric acid is discharged into the external acid recovery tank 9 for storage through the second transfer pipeline 28.

[0041] S2~S5 constitute a phosphoric acid cascade concentration cycle: the absorption tower completes the initial capture of P2O5 and the generation of dilute phosphoric acid at a lower temperature, and the incineration tower completes the deep absorption and water evaporation using its own waste heat at a higher temperature. The circulating water tanks of the two towers are connected in series through the first liquid transfer pipeline, and the concentration is progressively increased from low to high, realizing the natural concentration and efficient recovery of phosphoric acid.

[0042] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0043] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A treatment system for recovering phosphoric acid by incinerating high-concentration phosphine waste gas, characterized in that, It includes an incineration tower (2) and an absorption tower (3); the incineration tower (2) is provided with a first spraying mechanism, and the absorption tower (3) is provided with a second spraying mechanism; the second circulating water tank (31) of the second spraying mechanism is connected to the first circulating water tank (25) of the first spraying mechanism through a first transfer pipeline (34), which is used to send the absorbent liquid in the second circulating water tank (31) for absorbing P2O5 to generate phosphoric acid into the first circulating water tank (25), and evaporate and concentrate it in the incineration tower (2) through the first spraying mechanism; the first circulating water tank (25) is connected to a second transfer pipeline (28) for discharging and recovering the concentrated phosphoric acid.

2. The processing system according to claim 1, characterized in that, The outlet of the incineration tower (2) is connected to the inlet of the absorption tower (3). The incineration tower (2) is used to oxidize and burn phosphine waste gas to generate flue gas containing P2O5. The absorption tower (3) is used to absorb P2O5 in the flue gas to generate phosphoric acid.

3. The processing system according to claim 1, characterized in that, The first spraying mechanism further includes a first spraying component (27) and a first circulating pump (26) connecting the first spraying component (27) and the first circulating water tank (25); the second spraying mechanism further includes a second spray (32).

4. The processing system according to claim 1, characterized in that, The absorption tower (3) is a packed tower or a plate tower. The P2O5-containing flue gas inside the absorption tower (3) is absorbed by the absorbent liquid sprayed from top to bottom by the second spraying mechanism.

5. The processing system according to claim 3, characterized in that, The first spray assembly (27) is located at the top of the incineration tower (2), and the absorbent is evaporated and concentrated at a temperature of 120-200°C inside the incineration tower (2).

6. The processing system according to claim 1, characterized in that, It also includes a multi-stage demister (4), a fan (5), a tail gas buffer tower (6) and an electrostatic demister (7) arranged sequentially downstream of the absorption tower (3) along the direction of exhaust gas flow. The outlet of the electrostatic demister (7) is connected to the exhaust stack (8).

7. The processing system according to claim 6, characterized in that, It also includes a water seal tank (1) arranged sequentially upstream of the incineration tower (2) along the direction of exhaust gas flow.

8. The processing system according to claim 1, characterized in that, The incineration tower (2) is equipped with a temperature monitor (23) and a flame monitor (24). The temperature monitor (23) is used to monitor the temperature inside the incineration tower in real time and adjust the amount of combustion air in a chain. The flame monitor (24) is used to detect the flame status and, when the flame is extinguished, to cut off the phosphine gas intake and start nitrogen purging in a chain.

9. The processing system according to claim 6, characterized in that, The exhaust pipe (8) is equipped with an online phosphine concentration detector at its inlet end.

10. A method for treating high-concentration phosphine waste gas by incineration to recover phosphoric acid, employing the treatment system described in any one of claims 1-9, characterized in that, Includes the following steps: S1: Phosphine waste gas is fed into the incineration tower (2) for oxidation and combustion to generate flue gas containing P2O5; S2: The flue gas is introduced into the absorption tower (3), and the absorption liquid is sprayed through the second spraying mechanism to absorb P2O5 in the flue gas to generate phosphoric acid. The absorption liquid gradually forms dilute phosphoric acid in the second circulating water tank (31). S3: When the absorbent in the second circulating water tank (31) reaches the preset concentration, the absorbent is sent into the first circulating water tank (25) through the first transfer pipeline (34). S4: The absorbent in the first circulating water tank (25) is sprayed into the incineration tower (2) through the first spraying mechanism, and concentrated by evaporation using the residual heat of the incineration tower to obtain concentrated phosphoric acid; S5: When the concentrated phosphoric acid in the first circulating water tank (25) reaches the preset product concentration, it is discharged and recycled through the second liquid transfer pipeline (28).

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