Treatment method and treatment system for tail gas of lithium iron phosphate battery pole piece leftover material recycling production line

Abstract

The invention discloses a treatment method and a treatment system for tail gas of a lithium iron phosphate battery pole piece leftover material recycling production line, and belongs to the technical field of tail gas treatment. The method comprises the following steps: pretreating tail gas; performing high-temperature oxidation treatment; primary cooling: controlling the temperature of the cooled tail gas to be not lower than 500 DEG C; cooling for the second time; and alkali absorption: introducing the cooled tail gas into an alkali absorption tower, and removing hydrogen fluoride to obtain the treated tail gas. The temperature of the cooled tail gas is controlled to be not lower than 500 DEG C; the tail gas is prevented from condensing to form liquid drops, acid liquor is separated out, and equipment corrosion is avoided; and calcium hydroxide is utilized to regenerate an alkali absorbent sodium hydroxide, the absorption efficiency of hydrofluoric acid is improved, generated sodium fluoride is easily dissolved in water, precipitates cannot be generated to block a pipeline, the actually consumed absorbent is calcium hydroxide, and the cost is low.

Description

Technical Field

[0001] This invention belongs to the field of exhaust gas treatment technology, and more specifically, relates to a method and system for treating exhaust gas from a lithium iron phosphate battery electrode scrap recycling production line. Background Technology

[0002] In recent years, with the rapid development of new energy vehicles and energy storage batteries, the demand for lithium iron phosphate batteries has increased rapidly, resulting in a sharp increase in waste materials. The recycling of waste materials generated during the production of lithium iron phosphate battery cathodes is conducive to promoting the development of a circular economy and a low-carbon economy.

[0003] Currently, the recycling process for lithium iron phosphate battery cathode scraps generates exhaust gas, especially during high-temperature drying. This exhaust gas mainly contains particulate matter, nitrogen, VOCs (volatile organic compounds), tar, and hydrogen fluoride, and cannot be directly released into the air. Existing exhaust gas treatment typically involves pre-treating and dust removal, followed by a process using an incinerator + plate cooler + venturi cooler + alkali absorption tower. However, in actual operation, this process often suffers from severe corrosion of the plate cooler, venturi cooler, and connecting pipes. This is because acid is released during the exhaust gas cooling process, corroding the equipment. This results in frequent equipment replacement and maintenance, high maintenance costs, and simultaneous production shutdowns during maintenance, severely impacting the company's economic benefits and work efficiency. Summary of the Invention

[0004] 1. The problem to be solved To address the problem of acid precipitation corroding equipment during the cooling step in existing processes for treating exhaust gas from lithium iron phosphate battery electrode scrap recycling production lines, the primary objective of this invention is to provide a method for treating exhaust gas from lithium iron phosphate battery electrode scrap recycling production lines. The second objective of this invention is to provide a system for treating exhaust gas from a production line for recycling scrap materials from lithium iron phosphate battery electrode sheets.

[0005] 2. Technical Solution To solve the above problems, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for treating exhaust gas from a lithium iron phosphate battery electrode scrap recycling production line, particularly suitable for treating exhaust gas from a battery positive electrode scrap recycling production line, wherein the exhaust gas contains particulate matter, nitrogen, VOCs, hydrogen fluoride and tar-like substances.

[0006] The method includes the following steps: S1. Exhaust gas pretreatment: Removes particulate matter; S2. High-temperature oxidation treatment to remove VOCs and tar substances; S3, Primary Cooling: Control the temperature of the exhaust gas after cooling to be no lower than 500℃; S4. Secondary cooling: air cooling, controlling the temperature of the exhaust gas after cooling to not exceed 180℃; S5. Alkali absorption: The tail gas obtained from step S4 is passed into an alkali absorption tower to remove hydrogen fluoride and obtain the treated tail gas.

[0007] According to any embodiment of the first aspect of the present invention, in step S1, the initial temperature of the exhaust gas is 150-230°C.

[0008] According to any embodiment of the first aspect of the present invention, in step S1, the exhaust gas pretreatment preferably employs a high-temperature bag filter to remove particulate matter from the exhaust gas. High-temperature bag filters are highly efficient, and considering that the small amount of hydrogen fluoride gas contained in the exhaust gas can easily corrode the equipment, using a bag filter reduces the risk of corrosion, effectively extending the service life of the equipment.

[0009] According to any embodiment of the first aspect of the present invention, the high-temperature bag filter is further provided with a heating device at the front end for heating the exhaust gas in the exhaust gas pretreatment step, so as to prevent the organic waste gas in the exhaust gas from cooling down and condensing into viscous tar. These viscous substances will adhere and clog the filter bag. Preferably, the temperature of the exhaust gas is maintained at 180-230°C.

[0010] According to any embodiment of the first aspect of the present invention, in step S2, the high-temperature oxidation treatment is carried out by incineration, the incineration temperature is 800~900°C, the incineration atmosphere is air, and the incineration time is not less than 3s, preferably 3-5s. In this step, VOCs and tar substances are oxidized and decomposed into H2O, CO2 and hydrogen fluoride in the air at high temperature. The hydrogen fluoride produced by the incineration of tar substances in this step has a higher content than the hydrogen fluoride in the untreated tail gas introduced in step S1, and is more difficult to treat.

[0011] According to any embodiment of the first aspect of the present invention, the cooling methods used in steps S3 and S4 are methods that do not directly contact water, such as surface coolers or plate coolers, the purpose of which is to prevent hydrogen fluoride from dissolving in water and to avoid the formation of acid that corrodes the equipment.

[0012] According to any embodiment of the first aspect of the present invention, in step S3, cooling can be achieved using a surface cooler, or alternatively, a plate cooler can be used to control the temperature of the exhaust gas after cooling to be no lower than 500°C; to prevent the exhaust gas from condensing into droplets upon contact with the cold, releasing acid, and causing equipment corrosion, wherein the main component of the acid is hydrogen fluoride.

[0013] According to any embodiment of the first aspect of the present invention, in step S4, cooling is performed by air cooling: the exhaust gas obtained in step S3 is introduced into a cooling mixing box, and low-temperature dry air is introduced to mix with the exhaust gas for cooling. The cooling is performed by low-temperature dry air to prevent hydrogen fluoride from dissolving in water and forming acid that corrodes the equipment, while also preparing for the next step of entering the alkali absorption tower.

[0014] According to any embodiment of the first aspect of the present invention, the low-temperature dry air is dry air with a temperature of 30~40°C, and the volumetric flow rate ratio of the low-temperature dry air to the exhaust gas is (8-10):1.

[0015] According to any embodiment of the first aspect of the present invention, the mass flow rate M3 of the low-temperature dry air can be calculated based on the heat transfer Q, wherein the heat transfer Q satisfies: Q = C3M3ΔT2 + C4M4ΔT2 In the formula, C3 is the specific heat capacity of low-temperature dry air, kJ / (kg). K); C4 is the specific heat capacity of water vapor in low-temperature dry air, kJ / (kg). K); M3 is the mass flow rate of the low-temperature dry air, kg / h; M4 is the mass flow rate of water vapor in the low-temperature dry air, kg / h; ΔT2 is the temperature difference of the low-temperature dry air before and after cooling in step S4, K; The formula for calculating heat transfer Q satisfies: Q = C1M1ΔT1 + C2M2ΔT1, Where C1 is the specific heat capacity of the exhaust gas, kJ / (kg) K); C2 is the specific heat capacity of water vapor in the exhaust gas, kJ / (kg). K); M1 is the mass flow rate of the exhaust gas, kg / h; M2 is the mass flow rate of water vapor in the exhaust gas, kg / h; ΔT1 is the temperature difference of the exhaust gas before and after cooling in step S4, K.

[0016] According to any embodiment of the first aspect of the present invention, in step S5, the tail gas obtained in step S4 is passed into an alkali absorption tower, wherein the absorbent in the alkali absorption tower is sodium hydroxide.

[0017] According to any embodiment of the first aspect of the present invention, in step S5, the alkali absorption tower includes a primary alkali absorption tower and a secondary alkali absorption tower. The alkali absorption liquid in the primary alkali absorption tower is a sodium hydroxide solution. The initial pH of the alkali absorption liquid is 12-14. As hydrogen fluoride is absorbed, the pH gradually decreases. The temperature of the tail gas introduced into the primary alkali absorption tower does not exceed 180°C. The alkali absorption liquid in the secondary alkali absorption tower is a sodium hydroxide solution. The initial pH of the alkali absorption liquid is 12-14. As hydrogen fluoride is absorbed, the pH gradually decreases. The temperature of the tail gas introduced into the secondary alkali absorption tower does not exceed 50°C.

[0018] According to any embodiment of the first aspect of the present invention, the sodium hydroxide solution is a regenerated sodium hydroxide solution using quicklime, wherein the molar ratio of quicklime to sodium fluoride is (1-1.2):2. When the pH value of the alkali absorption solution decreases to 7-8, the absorption solution is pumped into the defluorination reactor, and quicklime is added to regenerate the sodium hydroxide.

[0019] According to any embodiment of the first aspect of the present invention, the external cooler of the primary alkali absorption tower can cool the absorbent liquid, and the tail gas is treated by the secondary alkali absorption tower and then sent into the exhaust stack by the exhaust fan, and then discharged into the atmospheric environment.

[0020] A second aspect of the present invention provides a treatment system for exhaust gas from a lithium iron phosphate battery electrode scrap recycling production line, the system comprising: Pretreatment unit: used to remove particulate matter from exhaust gas; Heat treatment unit: used for high-temperature oxidation treatment of exhaust gas after pretreatment and dust removal; Cooling unit: includes cooler A and cooler B connected in sequence, wherein cooler B is a cooling air mixing box used to cool exhaust gas; Alkali absorption unit: includes at least one alkali absorption tower for absorbing hydrogen fluoride in the exhaust gas.

[0021] The exhaust gas passes through a pretreatment unit, a heat treatment unit, a cooling unit, and an alkali absorption unit in sequence. The treated exhaust gas is then sent into the exhaust stack by an exhaust fan and then discharged into the atmosphere.

[0022] According to any embodiment of the second aspect of the present invention, in step S1, the pretreatment unit includes a high-temperature bag filter to remove particulate matter from the exhaust gas. High-temperature bag filters are highly efficient, and considering the small amount of hydrogen fluoride gas contained in the exhaust gas, which can easily corrode the equipment, using a bag filter reduces the risk of corrosion and extends the equipment's service life.

[0023] According to any embodiment of the second aspect of the present invention, the high-temperature bag filter is further provided with a heating device at the front end for heating the exhaust gas in the exhaust gas pretreatment step, so as to prevent the organic waste gas in the exhaust gas from cooling down and condensing into viscous tar. These viscous substances will adhere and clog the filter bag. Preferably, the temperature of the exhaust gas is maintained at 180-230°C.

[0024] According to any embodiment of the second aspect of the present invention, the heat treatment unit includes: an incinerator and a burner system and an oxygen supplement fan connected to the incinerator, the burner system being used to provide fuel and the oxygen supplement fan being used to supplement the oxygen required for combustion.

[0025] According to any embodiment of the second aspect of the present invention, the cooling unit includes a cooler A and a cooler B, wherein the cooler A is connected to the incinerator and the cooler B is connected to the cooler A.

[0026] According to any embodiment of the second aspect of the present invention, the cooler A is selected as a surface cooler or a plate cooler, and during the cooling process, the exhaust gas and water do not come into direct contact.

[0027] According to any embodiment of the second aspect of the present invention, the alkali absorption tower includes a spray layer, and the alkali absorption liquid contacts the tail gas through spray heads provided in the spray layer to achieve the absorption of hydrogen fluoride in the tail gas.

[0028] According to any embodiment of the second aspect of the present invention, the lower end of the alkali absorption tower is provided with a circulation pipe, and the alkali absorption liquid is recycled by a circulation pump.

[0029] According to any embodiment of the second aspect of the present invention, a cooler is provided outside the alkali absorption tower for cooling the temperature of the alkali absorption liquid in the alkali absorption tower.

[0030] According to any embodiment of the second aspect of the present invention, the alkali absorption tower is connected to an alkali absorption liquid regeneration unit, which includes a defluorination reactor, a filter press, and a water tank. The bottom of the alkali absorption tower is connected to the defluorination reactor via a pipe, and the other end of the defluorination reactor is connected to the filter press and the water tank. The water tank is connected to the alkali absorption tower via a pipe, thereby realizing the circulation of the alkali absorption liquid. A sewage pump is installed on the pipe connecting the bottom of the alkali absorption tower to the defluorination reactor, and a sewage pump is installed on the pipe connecting the defluorination reactor to the filter press. A regeneration pump is installed between the water tank and the alkali absorption tower.

[0031] According to any embodiment of the second aspect of the present invention, the rear end of the alkali absorption unit is connected to an exhaust fan, which sends the treated exhaust gas into an exhaust stack and then discharges it into the atmospheric environment.

[0032] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention controls the temperature of the exhaust gas after cooling to not be lower than 500℃; thus avoiding the exhaust gas from condensing into droplets upon cooling, releasing acid, and causing equipment corrosion. (2) The present invention cools the exhaust gas by means of a method that does not directly contact water. During the cooling process, the exhaust gas does not introduce water vapor, thus avoiding hydrogen fluoride dissolving in water and corroding the equipment. (3) This application replaces the alkali absorbent with sodium hydroxide, and the OH- produced by the complete ionization of NaOH... - With hydrofluoric acid H +The combined generation of H2O continuously disrupts the ionization equilibrium of hydrofluoric acid, causing it to almost completely ionize and participate in the reaction, thus improving the absorption efficiency of hydrofluoric acid. Furthermore, the generated sodium fluoride is readily soluble in water and will not produce precipitates that clog pipes. Ultimately, the absorption rate of hydrogen fluoride in the exhaust gas is over 99%. (4) This application regenerates sodium hydroxide in the alkali absorption liquid by adding quicklime to the reactor to generate calcium fluoride precipitate and sodium hydroxide, and finally pumps it into the primary alkali absorption tower or the secondary alkali absorption tower for recycling. Attached Figure Description

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that these drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless specifically indicated, these drawings are intended only to conceptually illustrate the structural construction described herein and are not necessarily drawn to scale.

[0034] Figure 1 This is a schematic diagram of the exhaust gas treatment system for the lithium iron phosphate battery electrode scrap recycling production line of the present invention: Heat treatment unit: 1. Combustion system; 11. Aeration fan; 12. Incinerator; Cooling units: 21. Cooler A; 22. Cooler B; Alkali absorption unit: 31. Primary alkali absorption tower; 311. Circulation pump A; 312. Circulation pump B; 313. Cooler C; 32. Secondary alkali absorption tower; 321. Circulation pump C; 322. Circulation pump D; Alkali absorption liquid regeneration unit: 41. Sewage pump; 42. Defluoridation reactor; 43. Sludge pump; 44. Filter press; 45. Water tank; 46. Regeneration pump; 5. Exhaust fan; 6. Exhaust pipe. Detailed Implementation

[0035] The following detailed description of exemplary embodiments of the invention is taken with reference to the accompanying drawings, which form part of the description and illustrate exemplary embodiments in which the invention may be practiced. While these exemplary embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and various changes may be made to the invention without departing from the spirit and scope thereof. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and not restrictive of the description of the features and characteristics of the invention, to suggest the best mode for carrying out the invention, and is sufficient to enable those skilled in the art to practice the invention. Therefore, the scope of the invention is defined only by the appended claims.

[0036] Example 1 This embodiment discloses a method for treating exhaust gas from a lithium iron phosphate battery electrode scrap recycling production line. The initial temperature of the exhaust gas is 150-230℃. This exhaust gas is generated in the lithium iron phosphate battery electrode scrap recycling production line and includes particulate matter, nitrogen, VOCs, hydrogen fluoride, and tar-like substances. The hydrogen fluoride in the exhaust gas leaches acid upon cooling, which can corrode the equipment. Furthermore, the tar-like substances are PVDF powder binders added during the preparation of the battery positive electrode. This binder decomposes and volatilizes at high temperatures in the exhaust gas, and also enters the exhaust gas along with the generated tar-like substances. During exhaust gas treatment, this also causes some corrosion to the equipment. Therefore, the method of this application includes the following steps: S1. Exhaust gas pretreatment to remove particulate matter; In this step, a high-temperature bag filter is used to remove particulate matter from the exhaust gas. High-temperature bag filters are highly efficient, and considering the small amount of hydrogen fluoride gas in the exhaust gas, which can easily corrode the equipment, using a bag filter minimizes corrosion and extends its service life. The high-temperature bag filter is also equipped with a heating device at its front end to heat the exhaust gas. Preferably, the temperature of the exhaust gas is maintained at 180-230℃ to prevent condensation of the exhaust gas during the pretreatment step. Hydrogen fluoride, along with the condensed water vapor, can adhere to the equipment and cause corrosion. Furthermore, it prevents the organic waste gas in the exhaust gas from condensing into viscous tar upon cooling, which can then adhere to and clog the filter bags.

[0037] S2. High-temperature oxidation treatment to remove VOCs and tar-like substances; the high-temperature oxidation treatment adopts incineration treatment, with an incineration temperature of 800~900℃, an incineration atmosphere of air, and an incineration time of not less than 3s.

[0038] In this step, VOCs and tar-like substances are oxidized and decomposed into H2O, CO2 and hydrogen fluoride in the air at high temperature. Among them, the hydrogen fluoride produced by the combustion of tar-like substances in this step has a higher content than the hydrogen fluoride in the untreated exhaust gas introduced in step S1, and is the main component of hydrogen fluoride in the exhaust gas, making it more difficult to treat.

[0039] S3, Primary cooling: A surface cooler is used to control the temperature of the exhaust gas after cooling to be no lower than 500℃; In this step, a surface cooler is used. The heat exchange medium flows through the inner cavity of the surface cooler's metal pipes, while the exhaust gas flows through the outer wall and fins of the metal pipes for heat exchange, achieving the effect of cooling the exhaust gas. In this step, the exhaust gas does not directly contact external water vapor to prevent hydrogen fluoride from dissolving in water and forming acid that corrodes the equipment. According to the applicant's actual tests, the temperature of the exhaust gas after cooling is not lower than 500℃, and the exhaust gas will not condense into droplets and precipitate acid. If the exhaust gas cooling temperature is too low, hydrogen fluoride will precipitate acid along with the condensed droplets, causing equipment corrosion.

[0040] S4. Secondary cooling: The exhaust gas obtained in step S3 is introduced into a cooling mixing box, and low-temperature dry air at 30~40℃ is introduced to mix with the exhaust gas for cooling. The temperature of the exhaust gas after cooling is controlled to be no higher than 180℃. The reason for hydrofluoric acid precipitation in existing technologies is that high-temperature exhaust gas condenses upon cooling, causing gaseous hydrogen fluoride to dissolve in the condensate droplets, thus forming droplets containing hydrofluoric acid, which corrodes the equipment. Exhaust gas from lithium iron phosphate battery cathode scrap recycling lines is typically incinerated at high temperatures to remove VOCs and tar-like substances. The resulting exhaust gas temperature is usually between 800 and 900°C. This high-temperature exhaust gas cannot be directly fed into the alkali absorption tower, so it needs to be cooled. To improve the cooling effect, a two-stage cooling process is generally used. Current processes employ an "incinerator + plate cooler + Venturi cooler + alkali absorption tower" process at the back end. The plate cooler performs the first cooling, and the Venturi cooler performs the second. This is because the Venturi cooler uses water cooling; to reduce water consumption, the exhaust gas temperature needs to be reduced to a relatively low level before the Venturi cooler. However, this leads to acid precipitation and equipment corrosion.

[0041] This application controls the temperature of the exhaust gas after cooling to be no lower than 500℃ to prevent hydrofluoric acid precipitation and to maintain a relatively high temperature when the exhaust gas enters the next stage cooler. In order to cool the relatively high-temperature exhaust gas, low-temperature dry air is selected for mixed cooling, which reduces the temperature of the exhaust gas without producing hydrofluoric acid liquid, avoiding equipment corrosion, and ensuring that the temperature entering the alkali absorption tower is no higher than 180℃.

[0042] The cooling mixing box cools the high-temperature exhaust gas by introducing low-temperature dry exhaust gas. During this process, the entire system remains dry and no new water vapor is introduced. The cooling mechanism of the existing Venturi cooler is to spray water into fine droplets, forming a high-speed airflow in the contraction section of the Venturi tube, so that the water droplets are fully mixed with the air and evaporated quickly, thus cooling the exhaust gas. However, this method introduces a large amount of water vapor into the exhaust gas. Hydrogen fluoride dissolves in the water, precipitating acid and corroding the equipment. This application uses air cooling, which does not introduce water vapor and reduces the acid produced by hydrogen fluoride dissolving in water.

[0043] The control of the tail gas temperature after cooling to not exceed 180℃ is based on considerations for the alkali absorption step. On the one hand, it reduces the temperature of the tail gas entering the alkali absorption tower to avoid the evaporation of moisture in the alkali absorbent due to high temperature. On the other hand, the tail gas in this application contains hydrogen fluoride. In the alkali absorption step, the tail gas containing hydrogen fluoride entering the alkali absorption tower will corrode the alkali absorption tower. Therefore, the material selected for the alkali absorption tower is corrosion-resistant fiberglass, which can prevent acid corrosion. However, if the temperature exceeds 180℃, the fiberglass will soften, affecting the service life of the alkali absorption tower.

[0044] The volumetric flow rate ratio of low-temperature dry air to exhaust gas is (8-10):1. Optionally, in this embodiment, the ratio of low-temperature dry air to exhaust gas is 9:1.

[0045] Among them, the volumetric flow rate V of low-temperature dry air satisfies: mass flow rate M = volumetric flow rate V × density ρ.

[0046] In the formula, M is the mass flow rate (kg / h); V is the volumetric flow rate (m³). 3 / h; ρ is density, kg / m³ 3 .

[0047] The mass flow rate (M3) of low-temperature dry air satisfies the formula: Q = C3M3ΔT2 + C4M4ΔT2 In the formula, Q represents the heat transfer, and C3 represents the specific heat capacity of low-temperature dry air, in kJ / (kg). K); C4 is the specific heat capacity of water vapor in low-temperature dry air, kJ / (kg). K); M3 is the mass flow rate of the low-temperature dry air, kg / h; M4 is the mass flow rate of water vapor in the low-temperature dry air, kg / h; ΔT2 is the temperature difference of the low-temperature dry air before and after cooling in step S4, K; The formula for calculating the heat transfer Q is: Q = C1M1ΔT1 + C2M2ΔT1, In the formula, C1 is the specific heat capacity of the exhaust gas, kJ / (kg). K); C2 is the specific heat capacity of water vapor in the exhaust gas, kJ / (kg). K); M1 is the mass flow rate of the exhaust gas, kg / h; M2 is the mass flow rate of water vapor in the exhaust gas, kg / h; ΔT1 is the temperature difference of the exhaust gas before and after cooling in step S4, K.

[0048] S5. Alkali absorption: The tail gas obtained from step S4 is sequentially passed into the primary alkali absorption tower 31 and the secondary alkali absorption tower 32. The temperature of the tail gas passing into the primary alkali absorption tower 31 does not exceed 180°C to prevent the moisture in the alkali absorbent from evaporating at excessively high temperatures. The alkali absorbent in the alkali absorption tower is sodium hydroxide, which is used to remove hydrogen fluoride to obtain the treated tail gas.

[0049] Among them, the alkali absorption liquid in the primary alkali absorption tower 31 is a regenerated sodium hydroxide solution, and the initial pH of the alkali absorption liquid is 12-14. The alkali absorption liquid in the secondary alkali absorption tower 32 is a regenerated sodium hydroxide solution. The initial pH of the alkali absorption liquid is 12-14. The temperature of the tail gas that is introduced into the secondary alkali absorption tower 32 after being treated by the primary alkali absorption tower 31 generally does not exceed 50℃. Sodium hydroxide is used as the alkaline absorbent to absorb hydrogen fluoride in the tail gas. Sodium hydroxide reacts with hydrogen fluoride to produce sodium fluoride, which is easily soluble in water and will not produce precipitates that clog the pipes.

[0050] In existing technologies, slaked lime is generally used as the absorbent. However, its reaction with hydrogen fluoride in the exhaust gas produces calcium fluoride precipitate inside the tower, leading to blockages in pipes and equipment. This necessitates frequent cleaning of the tower and requires simultaneous production shutdowns during equipment maintenance, thus impacting the company's economic efficiency. This application uses sodium hydroxide instead of slaked lime as the absorbent to react with hydrogen fluoride. This not only efficiently absorbs hydrogen fluoride gas but also avoids precipitation within the tower. Furthermore, a sodium hydroxide regeneration system is designed, utilizing slaked lime to regenerate sodium hydroxide. During operation, slaked lime is still the actual material consumed.

[0051] Sodium hydroxide reacts with hydrogen fluoride to produce sodium fluoride.

[0052] The existing alkali absorbent uses slaked lime, whose main component is calcium hydroxide. Its reaction product with hydrogen fluoride is calcium fluoride. Calcium fluoride is a sparingly soluble salt and precipitates out as a white precipitate during the reaction. On the one hand, the white precipitate can cause pipe blockage. On the other hand, the degree of reaction between slaked lime and hydrogen fluoride depends on the solubility of calcium hydroxide. During the reaction, high-temperature exhaust gas is introduced, water vapor evaporates and is lost with the exhaust gas, and the aqueous solution of slaked lime becomes supersaturated, producing slightly soluble substances. The calcium hydroxide content in the absorbent is reduced, resulting in a decrease in the amount of hydrofluoric acid absorbed.

[0053] The alkali absorbent used in this application is sodium hydroxide, which is the OH- ions produced by the complete ionization of NaOH. - With hydrofluoric acid H + The formation of H₂O continuously disrupts the ionization equilibrium of hydrofluoric acid, causing it to almost completely ionize and participate in the reaction, thus improving its absorption efficiency. Furthermore, the generated sodium fluoride is readily soluble in water and will not precipitate or clog pipes.

[0054] The sodium hydroxide alkali absorbent solution used in step S5 can be regenerated using quicklime. The molar ratio of quicklime to sodium fluoride is (1-1.2):1. As the tail gas is continuously absorbed, sodium hydroxide is continuously consumed. When the pH value of the alkali absorbent solution is 7-8, the absorbent solution is regenerated with quicklime to produce sodium hydroxide.

[0055] First, the regenerated sodium hydroxide solution has a low mass concentration, generally 0.1-5 wt%, but it can still achieve high absorption efficiency. Second, the sodium hydroxide solution is regenerated using quicklime, and its components after regeneration contain some calcium hydroxide, which can also be used as an alkaline absorbent for hydrogen fluoride.

[0056] When the absorbent in the primary alkali absorption tower 31 or the secondary alkali absorption tower 32 is saturated and the pH value drops to 7-8, it can be sent to the defluorination reactor 42 through the sewage pump 41. Quicklime is added to the defluorination reactor 42 to generate calcium fluoride precipitate and sodium hydroxide, thereby regenerating sodium hydroxide. The calcium fluoride precipitate is transported to the filter press 44 through the sludge pump 43 for filter pressing. The supernatant enters the water tank 45 and is then fed back into the primary alkali absorption tower 31 or the secondary alkali absorption tower 32 through the regeneration pump 46 for recycling. The recycled sodium hydroxide solution is the regenerated sodium hydroxide solution.

[0057] In this invention, the temperature is controlled to be no lower than 500℃ after the first cooling. Secondary cooling uses low-temperature dry air mixed with the exhaust gas in a cooling mixing box for further cooling, preventing acid precipitation and corrosion of equipment and pipelines. The Venturi cooler is replaced with a cooling mixing box, which further cools the exhaust gas without introducing moisture that could lead to acid precipitation and corrosion. Furthermore, the absorbent in the alkali absorption tower is changed from calcium hydroxide to sodium hydroxide, improving the alkali absorption effect and preventing pipeline blockage caused by calcium fluoride precipitation within the tower. In addition, the sodium hydroxide absorbent can be regenerated using quicklime, and the generated calcium fluoride precipitate is removed by pressure filtration; the actual consumption is still quicklime, without increasing reagent costs.

[0058] In an implementable method, the parameters of the processing method are specifically: S1. Exhaust gas pretreatment to remove particulate matter; the exhaust gas introduced in this step contains particulate matter, nitrogen, VOCs, hydrogen fluoride, and tar-like substances. The temperature of the exhaust gas is maintained at 200℃, and the volumetric flow rate of the introduced exhaust gas is 300-400 m³ / h. 3 / h; S2. High-temperature oxidation treatment to remove VOCs and tar-like substances; the high-temperature oxidation treatment adopts incineration treatment, with an incineration temperature of 820±20℃, an incineration atmosphere of air, and an incineration time of 3s.

[0059] S3, Primary cooling: A surface cooler is used to control the temperature of the exhaust gas after cooling to 500℃; S4. Secondary cooling: Low-temperature dry air at 30℃ is mixed with exhaust gas for cooling, and the temperature of the exhaust gas after cooling is controlled to be 180℃; the mass flow ratio of low-temperature dry air to exhaust gas is 9:1, and the mass flow rate M3 of low-temperature dry air is 4100 kg / h. S5, Alkali Absorption: The residence time in the primary alkali absorption tower 31 is 8s, and the outlet temperature is 50℃. The residence time in the secondary alkali absorption tower 32 is 8 seconds, resulting in tail gas with a hydrogen fluoride removal rate of 99%, and the final tail gas meets the discharge standards.

[0060] Example 2 This embodiment describes a system for treating exhaust gas from a lithium iron phosphate battery electrode scrap recycling production line. The workshop pipeline outlet is connected to the inlet of this system. The system is as follows: Figure 1 As shown, it includes: Pretreatment unit: used to remove particulate matter from exhaust gas; Heat treatment unit: used for high-temperature oxidation treatment of exhaust gas after pretreatment and dust removal; Cooling unit: used to cool exhaust gas; Alkali absorption unit: includes at least one alkali absorption tower for absorbing hydrogen fluoride from the tail gas; The exhaust gas passes through a pretreatment unit, a heat treatment unit, a cooling unit, and an alkali absorption unit in sequence. The treated exhaust gas is then sent into the exhaust stack 6 by the exhaust fan 5 and then discharged into the atmosphere.

[0061] The heat treatment unit includes an incinerator 12 and a burner system 1 and an oxygen supply fan 11 connected to the incinerator 12. The burner system 1 is used to provide fuel, and the oxygen supply fan 11 is used to supplement the oxygen required for combustion.

[0062] The cooling unit includes cooler A 21 and cooler B 22. The outlet of the incinerator 12 is connected to the inlet of cooler A 21 via a pipe, the outlet of cooler A 21 is connected to the inlet of cooler B 22 via a pipe, and the outlet of cooler B 22 is connected to the inlet of the primary alkali absorption tower 31. Optionally, in this embodiment, cooler A 21 is a surface cooler, and cooler B 22 is a cooling mixing box. Specifically, the surface cooler A can be a finned cooler, which includes a bare tube with fins on its surface to increase the overall heat exchange area. Specifically, cooler B 22 is a cooling mixing box, which includes a cavity with an exhaust gas inlet, a low-temperature dry air inlet, and a mixing outlet. The exhaust gas and the low-temperature dry air are fully mixed in the cavity to achieve cooling of the exhaust gas.

[0063] The alkali absorption tower includes a primary alkali absorption tower 31 and a secondary alkali absorption tower 32.

[0064] The primary alkali absorption tower 31 includes a spray layer with spray heads for spraying alkali absorption liquid to contact the exhaust gas and absorb hydrogen fluoride in it. A cooler C 313 is installed outside the primary alkali absorption tower 31 to cool the absorption liquid. In one optional configuration, the primary alkali absorption tower 31 consists of, from bottom to top, a water tank, an air inlet, a primary spray layer, a secondary spray layer, a top demisting layer, and an air outlet. The exhaust gas enters through the air inlet and exits through the air outlet, achieving the first cooling and absorption of the exhaust gas.

[0065] The secondary alkali absorption tower 32 includes a spray layer with spray heads for spraying alkali absorption liquid into contact with the exhaust gas, thereby absorbing hydrogen fluoride from the exhaust gas. In one optional configuration, the secondary alkali absorption tower 32, from bottom to top, comprises a water tank, an air inlet, a primary spray layer, a secondary spray layer, a top demister layer, and an air outlet. The exhaust gas enters through the air inlet and exits through the air outlet, achieving a second cooling and absorption process for the exhaust gas.

[0066] The exhaust fan 5 is connected to the rear end of the secondary alkali absorption tower 32. The exhaust fan 5 sends the treated exhaust gas into the exhaust stack 6 and then discharges it into the atmosphere.

[0067] The primary alkali absorption tower 31 and the secondary alkali absorption tower 32 are respectively connected to the alkali absorption liquid regeneration unit, which includes a defluorination reactor 42, a filter press 44, and a water tank 45.

[0068] The primary alkali absorption tower 31 and the secondary alkali absorption tower 32 are connected to the defluorination reactor 42 via pipelines at their bottoms. A sewage pump 41 is installed on the pipeline between the alkali absorption tower and the defluorination reactor 42. Specifically, the inlet of the sewage pump 41 is connected to both the primary alkali absorption tower 31 and the secondary alkali absorption tower 32, and the outlet of the sewage pump 41 is connected to the inlet of the defluorination reactor 42 via a pipeline. Circulation pumps A 311 and B 312 are installed on the circulation absorbent pipeline of the primary alkali absorption tower 31 to circulate the absorbent of the primary alkali absorption tower 31. Circulation pumps C 321 and D 322 are installed on the circulation absorbent pipeline of the secondary alkali absorption tower 32 to circulate the absorbent of the secondary alkali absorption tower 32. A cooler C313 is installed on the circulation absorbent pipeline to cool the circulation absorbent.

[0069] The other end of the defluorination reactor 42 is connected to the filter press 44 and the water tank 45 in sequence through pipes. A sludge pump 44 is installed on the pipe between the defluorination reactor 42 and the filter press 44. Specifically, the sludge outlet at the bottom of the defluorination reactor 42 is connected to the inlet of the sludge pump 44 through a pipe, the outlet of the sludge pump 44 is connected to the inlet of the filter press 44 through a pipe, and the supernatant outlet of the defluorination reactor 42 is connected to the inlet of the water tank 45 through a pipe.

[0070] Water tank 45 is connected to alkali absorption tower via a pipeline. A regeneration pump 46 is installed between water tank 45 and alkali absorption tower. Specifically, the outlet of water tank 45 is connected to the inlet of regeneration pump 46 via a pipeline. The outlet of regeneration pump 46 is connected to the return liquid ports of primary alkali absorption tower 31 and secondary alkali absorption tower 32, respectively, thereby forming a circulation of alkali absorption liquid.

[0071] Quicklime is introduced into the defluorination reactor 16. When the alkali absorption liquid in the primary alkali absorption tower 31 or the secondary alkali absorption tower 32 is saturated, it can be sent to the defluorination reactor 42 through the sewage pump 41. Quicklime is added into the defluorination reactor 42 to generate calcium fluoride precipitate and sodium hydroxide, thereby regenerating sodium hydroxide. The downstream end of the defluorination reactor 42 is connected to the filter press 44 and the water tank 45. The calcium fluoride precipitate is sent to the filter press 44 for filtration through the sludge pump 44. The supernatant enters the water tank 45 and is finally pumped into the primary alkali absorption tower 31 or the secondary alkali absorption tower 32 for recycling through the regeneration pump 46.

[0072] The outlet of the primary alkali absorption tower 31 is connected to the inlet of the secondary alkali absorption tower 32 via a pipeline. The outlet of the secondary alkali absorption tower 32 is connected to the inlet of the exhaust fan 5 via a pipeline. The outlet of the exhaust fan 5 is connected to the inlet of the exhaust stack 6 via a pipeline. The outlet of the exhaust stack 6 is directly connected to the atmospheric environment.

[0073] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0074] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A method for treating exhaust gas from a lithium iron phosphate battery electrode scrap recycling production line, characterized in that, Including the following steps: S1. Exhaust gas pretreatment to remove particulate matter, wherein the exhaust gas contains particulate matter, nitrogen, VOCs, hydrogen fluoride and tar-like substances; S2. High-temperature oxidation treatment to remove VOCs and tar substances; S3, First Cooling: Control the temperature of the exhaust gas after cooling to be no lower than 500℃; S4. Secondary cooling: air cooling, controlling the temperature of the exhaust gas after cooling to not exceed 180℃; S5. Alkali absorption: The tail gas obtained from step S4 is passed into an alkali absorption tower to remove hydrogen fluoride and obtain the treated tail gas.

2. The processing method according to claim 1, characterized in that, In step S2, the high-temperature oxidation treatment is carried out by incineration, with an incineration temperature of 800~900℃, an air atmosphere, and an incineration time of not less than 3 seconds.

3. The processing method according to claim 1, characterized in that, In step S4, the exhaust gas obtained in step S3 is introduced into a cooling mixing box, where low-temperature dry air is introduced to mix with the exhaust gas for cooling; and / or, The low-temperature dry air is dry air with a temperature of 30~40℃, and the volumetric flow rate ratio of the low-temperature dry air to the exhaust gas is (8-10):

1.

4. The processing method according to claim 1, characterized in that, In step S5, the alkali absorption tower includes a primary alkali absorption tower (31) and a secondary alkali absorption tower (32). The alkali absorption liquid in the primary alkali absorption tower (31) is a sodium hydroxide solution, and the initial pH of the alkali absorption liquid is 12-14; and / or, The alkali absorption liquid in the secondary alkali absorption tower (32) is a sodium hydroxide solution, and the initial pH of the alkali absorption liquid is 12-14.

5. The processing method according to claim 4, characterized in that, The sodium hydroxide solution is a regenerated sodium hydroxide solution.

6. The processing method according to claim 5, characterized in that, The sodium hydroxide absorbent solution used in step S5 is regenerated with quicklime. When the pH value of the alkali absorbent solution drops to 7-8, quicklime is used to regenerate the sodium hydroxide. The molar ratio of quicklime to sodium fluoride is (1-1.2):

2.

7. A system for treating exhaust gas from a lithium iron phosphate battery electrode scrap recycling production line, used to implement the treatment method described in any one of claims 1-6, characterized in that, include: Pretreatment unit: used to remove particulate matter from exhaust gas; Heat treatment unit: used for high-temperature oxidation treatment of pretreated exhaust gas; Cooling unit: includes cooler A (21) and cooler B (22) connected in sequence, wherein cooler B (22) is a cooling mixing box used to cool exhaust gas; Alkali absorption unit: includes at least one alkali absorption tower for absorbing hydrogen fluoride from the tail gas; The exhaust gas passes through a pretreatment unit, a heat treatment unit, a cooling unit, and an alkali absorption unit in sequence, and the treated exhaust gas is then discharged into the atmosphere.

8. The processing system according to claim 7, characterized in that, The pretreatment unit includes a high-temperature bag filter; and / or, The cooler A (21) is selected as a surface cooler or a plate cooler.

9. The processing system according to claim 8, characterized in that, The alkali absorption unit includes: a primary alkali absorption tower (31) and a secondary alkali absorption tower (32): The primary alkali absorption tower (31) includes a spray layer through which the alkali absorption liquid contacts the tail gas; and / or, The secondary alkali absorption tower (32) includes a spray layer, through which the alkali absorption liquid comes into contact with the tail gas.

10. The processing system according to claim 9, characterized in that, The alkali absorption tower is connected to the alkali absorption liquid regeneration unit, which includes a defluorination reactor (42), a filter press (44), and a water tank (45). The bottom of the alkali absorption tower is connected to the defluorination reactor (42), and the other end of the defluorination reactor (42) is connected to the filter press (44) and the water tank (45). The water tank (45) is connected to the alkali absorption tower through a pipeline.

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