A method and system for exhaust gas purification and resource recovery of lithium battery recycling

Abstract

The application discloses a system for waste gas purification and resource recovery in lithium battery recycling, comprising a pyrolysis device, a second dust removal device, a gas mixer, a combustion chamber and a boiler which are sequentially connected, a splitting device, a first dust removal device and the gas mixer which are sequentially connected, a hydration tower, a primary phosphoric acid catcher, a mixed acid pool, a secondary phosphoric acid catcher, a hydrofluoric acid recovery tower and a purification tower which are sequentially connected, and a method for waste gas purification and resource recovery in lithium battery recycling. The application has the advantages that P2O5 and HF are separated and purified, the energy of carbonic acid ester combustion is utilized, by-product phosphoric acid, hydrofluoric acid or ammonium fluoride products are extracted in stages, the treatment difficulty of waste water and waste residue is greatly reduced, and the environment is friendly. In addition, since the by-products have high market value, the environmental protection project has good economic benefits and resources are saved.

Description

Technical Field

[0001] This invention relates to the field of waste gas treatment in lithium battery recycling, and particularly to a method and system for purifying waste gas and recovering resources from lithium battery recycling. Background Technology

[0002] In recent years, with the development of the electronics and electric vehicle industries, the production and consumption of lithium batteries have been continuously increasing. Reports indicate that in 2018, China's battery production increased by 26.17% year-on-year, reaching 102 GWh. In 2020, China's lithium-ion battery market output is projected to reach 205.33 GWh, meaning that China's lithium battery production in 2020 was approximately 680,000 tons per year. If lithium batteries are carelessly discarded at the end of their lifespan, they will cause very serious environmental pollution. The best solution now is to recycle used lithium batteries. Recycling methods include dry and wet processes, but regardless of the method, the batteries must be crushed and sorted. During this process, the electrolyte in the batteries will evaporate and enter the exhaust gas, causing environmental pollution. The main components of lithium battery electrolytes include solvents such as ethylene carbonate, methyl ethyl carbonate, propylene carbonate, and dimethyl carbonate, and solutes such as LiPF6. Carbonate substances entering the exhaust gas will cause VOCs to exceed standards, and LiPF6 will hydrolyze upon contact with water, producing hydrogen fluoride and phosphoric acid, which seriously pollute the environment. Therefore, how to remove carbonate organics and LiPF6 from the exhaust gas during the lithium battery recycling process is a concern, and much research has been conducted in this regard.

[0003] Chinese patent CN110508057A discloses "A method and system for purifying waste gas during lithium battery recycling." This method first removes particulate matter from the waste gas generated during lithium battery recycling using a dust removal device, then removes most of the fluorine-containing components from the waste gas using a two-stage circulating absorption tower, and finally removes volatile organic compounds through combustion. The absorbent in the two-stage absorption is an alkaline solution, which reacts to produce calcium fluoride and calcium phosphate. However, this method has significant drawbacks. During the two-stage absorption, carbonate organic compounds are soluble in water, with propylene carbonate reaching a solubility of 240 g / L, greatly increasing the difficulty of wastewater treatment. Furthermore, the resulting mixed salt of calcium fluoride and calcium phosphate is difficult to utilize comprehensively, increasing production costs for manufacturing enterprises.

[0004] Chinese patent CN08096977A discloses a "method and system for treating waste gas generated during the recycling process of lithium batteries." This method employs nitrogen protection, molecular sieve filtration for moisture absorption, and cryogenic separation. However, this method has high energy consumption. Furthermore, since LiPF6 is soluble in carbonate organic compounds, it is difficult to separate relatively pure monomers that can be recycled after cryogenic treatment.

[0005] Chinese patent CN10124432A discloses a "flue gas purification device in the recycling and treatment process of waste lithium batteries". This device first uses a bag filter to remove dust from the waste gas, then performs a two-stage rinsing, and finally uses a UV photolysis device to photolyze the organic matter. This method has the problem that the organic matter dissolves in water during the rinsing, which increases the difficulty of wastewater treatment. In addition, the UV photolysis method is difficult to meet the emission standards due to the high concentration of organic matter.

[0006] Chinese patent CN108128953A discloses "An apparatus and method for treating waste gas and wastewater from the recycling and pyrolysis of waste lithium batteries." This method directly incinerates the waste gas from lithium battery recycling in a pyrolysis furnace. The flue gas is then absorbed by alkaline spray and further treated by activated carbon adsorption before being discharged at high altitude. However, in this method, the flue gas after combustion is directly absorbed by sodium hydroxide solution, resulting in a mixture of sodium phosphate and sodium fluoride salts, which are difficult to utilize comprehensively.

[0007] Chinese patent CN108736091A discloses a "disassembly and recycling process for lithium batteries." This method first crushes the battery, then sieves the metal casing and contents. Next, it separates the metal foil from the electrode binder and volatile gases through pyrolysis. The metal foil is then sorted to obtain copper and aluminum foil. The volatile gases are treated with regenerative combustion and dust removal before being emitted as exhaust gas. This patent does not recycle the components in the exhaust gas, and the organic matter concentration in the exhaust gas is 10 mg / m³. 3 It pollutes the environment.

[0008] Based on the description and analysis of the existing technologies above, it is clear that in the process of lithium battery recycling, the focus is only on removing the gas components in the exhaust gas that will seriously pollute the environment, while the recycling and utilization of phosphorus and fluorine are not carried out. This results in resource waste and air pollution on the one hand, and increases the difficulty of treating wastewater and waste residue at the downstream end, placing a heavy economic burden on recycling companies on the other. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to solve the problems existing in the prior art and provide a method for purifying waste gas and recycling resources in lithium battery recycling, separating P2O5 and HF gas in the exhaust gas and recycling them.

[0010] This invention also provides a system for purifying waste gas and recycling resources from lithium battery recycling. By purifying waste gas and recycling it in stages, pollution is reduced, resource waste is avoided, and better economic benefits are achieved.

[0011] The technical solution adopted in this invention is:

[0012] A system for purifying waste gas and recovering resources from lithium battery recycling includes a pyrolysis device, a second dust removal device, a gas mixer, a combustion chamber, and a boiler connected in sequence. A splitting device, a first dust removal device, and the gas mixer are also connected in sequence. The outlet of the boiler is connected to the inlet of a hydration tower. The outlet of the hydration tower is connected to the inlet of a primary phosphoric acid trap. The outlet of the primary phosphoric acid trap is connected to a mixed acid tank. The mixed acid tank is connected to the inlet of a secondary phosphoric acid trap. The outlet of the secondary phosphoric acid trap is connected to the inlet of a hydrofluoric acid recovery tower. The outlet of the hydrofluoric acid recovery tower is connected to the inlet of a purification tower. The outlet of the mixed acid tank and the mixed acid pump are connected in sequence to the inlet of the hydration tower.

[0013] Preferably, in order to further utilize fluorine resources, the outlet of the purification tower is connected to the inlet of the ammonium fluoride reaction crystallizer, and the outlet of the hydrofluoric acid recovery tower, the hydrofluoric acid storage tank, the hydrofluoric acid transfer pump, and the inlet of the ammonium fluoride reaction crystallizer are connected in sequence.

[0014] Preferably, the outlet of the ammonium fluoride reaction crystallizer is sequentially connected to the inlet of the centrifuge and the ammonium fluoride mother liquor tank for separation and filtration, so as to obtain the finished ammonium fluoride product.

[0015] Preferably, in order to further utilize the filtrate, the outlet of the ammonium fluoride mother liquor tank is connected in sequence to the ammonium fluoride mother liquor transfer pump and the purification tower.

[0016] Preferably, the air outlet of the purification tower is connected in sequence to the main fan and the chimney. The concentration of hydrogen fluoride tail gas generated by this system is less than 3 mg / m³. 3 This is far below the processing standards of existing technologies.

[0017] Preferably, the hydrofluoric acid recovery tower includes a condenser and a packed tower, with the packed tower positioned above the condenser. HF and water in the flue gas are condensed together to form hydrofluoric acid, which is then recovered. Hydrofluoric acid entrained in the flue gas is captured and recovered by the packed tower above.

[0018] Preferably, the purification tower adopts an empty tower structure, and the absorbent is ammonia water. HF gas in the flue gas undergoes a neutralization reaction with ammonia and is rapidly absorbed, generating ammonium fluoride.

[0019] Preferably, both the first dust removal device and the second dust removal device are bag filters.

[0020] Preferably, the primary phosphoric acid trap is a Venturi or a packed tower, and the secondary phosphoric acid trap is a packed tower with a demister.

[0021] This invention also discloses a method for purifying waste gas and recovering resources from lithium battery recycling, comprising the following steps:

[0022] S1. Under the protection of inert gas, the lithium battery is disassembled in the disassembly device to separate the electrolyte. The generated exhaust gas passes through the first dust removal device and then into the gas mixer.

[0023] S2. Add the electrolyte from S1 to the pyrolysis device and pyrolyze it under the protection of inert gas to obtain pyrolysis gas, which includes LiF and PF5. After the pyrolysis gas is cooled, it passes through the second dust removal device and then into the gas mixer to obtain mixed gas one.

[0024] S3. The mixed gas is introduced into the combustion chamber and burned to obtain oxidizing gas, which includes P2O5 and HF. The oxidizing gas enters the boiler and is cooled to 400-600℃.

[0025] The oxidizing gas cooled in S4 and S3 is passed into the hydration tower. At the same time, dilute phosphoric acid or water is added to the hydration tower for spraying to obtain phosphoric acid and unreacted gas. The phosphoric acid is collected through the liquid outlet of the hydration tower, and the unreacted gas includes phosphoric acid mist and hydrogen fluoride gas.

[0026] S5. Unreacted gas is sequentially passed through a primary phosphoric acid trap, a mixed acid tank, and a secondary phosphoric acid trap for phosphoric acid collection, resulting in a phosphoric acid mixed solution and a mixed gas. The phosphoric acid mixed solution is then purified by spraying in a hydration tower.

[0027] S6. Mixed gas 2 enters the hydrofluoric acid recovery tower for condensation and absorption, yielding hydrofluoric acid and mixed gas 3. The hydrofluoric acid is collected at the outlet of the hydrofluoric acid recovery tower.

[0028] S7. The mixed gas enters the purification tower, and ammonia water is added for spraying, resulting in ammonium fluoride liquid and flue gas. The concentration of hydrogen fluoride in the flue gas is less than 3 mg / m³. 3 Discharge will be carried out at that time.

[0029] This invention involves pyrolyzing the electrolyte separately, followed by oxidative combustion to obtain P2O5 and HF. Dilute phosphoric acid or pure water is then sprayed in, and the water is rapidly evaporated to react with the P2O5, yielding phosphoric acid. The remaining uncondensed phosphoric acid mist is then purified through phosphoric acid collection and spray evaporation to obtain phosphoric acid, thus separating phosphoric acid and HF. The resulting phosphoric acid meets the required product purity. The finished phosphoric acid product has high economic value and conserves resources.

[0030] In S4, the flue gas is rapidly cooled by the evaporation of dilute phosphoric acid or pure water, thus preventing the formation of dioxins.

[0031] Preferably, the above method further includes the following steps:

[0032] S8. In the ammonium fluoride reaction crystallizer, liquid ammonium fluoride and hydrofluoric acid from S6 are added to react and crystallize, yielding ammonium fluoride crystals. After filtration and drying, the finished ammonium fluoride product and filtrate are obtained. The filtrate is sent to a purification tower for continued use. Phosphoric acid mist is further separated from HF, and subsequent HF recovery and utilization yield the finished ammonium fluoride product. The finished ammonium fluoride product has high economic value and conserves resources.

[0033] Preferably, the pyrolysis temperature in S2 is 300-500℃; the inert gas in S1 and S2 is dry nitrogen. More preferably, the pyrolysis temperature in S2 is 400-500℃.

[0034] Preferably, the combustion temperature in S3 is 850-1200℃, and the cooling temperature is 400-600℃. More preferably, the combustion temperature in S3 is 900-1100℃.

[0035] Preferably, the temperature of the second mixed gas in S5 is 90-130°C, utilizing the difference in boiling points between phosphoric acid and hydrogen fluoride to ensure complete capture of phosphoric acid. More preferably, the temperature of the second mixed gas in S5 is 110-130°C.

[0036] Existing technologies use a wet process to directly treat the battery dismantling mixture. LiPF6 reacts with water to produce hydrochloric acid and phosphoric acid, and battery powder remains mixed in the water, making the wastewater difficult to treat and increasing the difficulty of subsequent wastewater and residue treatment. This invention uses a dry process to pyrolyze and burn the electrolyte. The organic matter is directly pyrolyzed and burned, yielding only gas and water as products, which are easier to recover and reuse in subsequent processes.

[0037] To achieve the separation of P2O5 and HF and ensure that the products meet the requirements, this invention employs a combination of phosphoric acid spraying, secondary phosphoric acid collection, and secondary phosphoric acid spraying to separate phosphoric acid and HF, ensuring that the phosphoric acid meets the product requirements while maintaining the purity of HF, thus guaranteeing the subsequent separation and purification of HF.

[0038] The advantages of this invention are that it achieves the separation and purification of P2O5 and HF, utilizes the energy from the combustion of carbonate organic compounds, and extracts byproducts such as phosphoric acid, hydrofluoric acid, or ammonium fluoride in a staged manner, greatly reducing the difficulty of wastewater and waste residue treatment and making it environmentally friendly. Furthermore, since the byproducts currently have high market value, this environmental protection project has good economic benefits and conserves resources. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the system structure for lithium battery recycling, waste gas purification, and resource recovery as described in this invention. Detailed Implementation Plan

[0040] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0041] Example

[0042] like Figure 1 As shown, a system for purifying waste gas and recovering resources from lithium battery recycling includes a splitting device 1, a first bag filter 2, a pyrolysis device 3, a second bag filter 4, a gas mixer 5, a combustion chamber 6, a boiler 7, a hydration tower 8, a hydrofluoric acid recovery tower 9, a purification tower 10, an ammonium fluoride reaction crystallizer 11, a primary phosphoric acid trap 12, a secondary phosphoric acid trap 13, a mixed acid pump 14, a mixed acid tank 15, a hydrofluoric acid storage tank 16, a main fan 17, a chimney 18, a hydrofluoric acid transfer pump 19, a centrifuge 20, an ammonium fluoride mother liquor tank 21, and an ammonium fluoride mother liquor transfer pump 22.

[0043] The pyrolysis unit 3, the second bag filter 4, the gas mixer 5, the combustion chamber 6, and the boiler 7 are connected in sequence. The splitting unit 1, the first bag filter 2, and the gas mixer 5 are also connected in sequence. The outlet of the boiler 7 is connected to the inlet of the hydration tower 8, and the outlet of the product phosphoric acid is located below the hydration tower 8. The outlet of the hydration tower 8 is connected to the inlet of the primary phosphoric acid trap 12, the outlet of the primary phosphoric acid trap 12 is connected to the mixed acid tank 15, the mixed acid tank 15 is connected to the inlet of the secondary phosphoric acid trap 13, and the outlet of the secondary phosphoric acid trap 13 is connected to the inlet of the hydrofluoric acid recovery tower 9. The hydrofluoric acid recovery tower 9 includes a condenser and a packed tower, with the packed tower positioned above the condenser. The primary phosphoric acid trap 12 is a Venturi trap, and the secondary phosphoric acid trap 13 is a packed tower with a demister. The outlet of the hydrofluoric acid recovery tower 9 is connected to the inlet of the purification tower 10. The outlet of the mixed acid tank 15 and the inlet of the mixed acid pump 14 are sequentially connected to the inlet of the hydration tower 8. The purification tower 10 adopts an empty tower structure, and ammonia water is used as the absorbent. The outlet of the purification tower 10 is connected to the inlet of the ammonium fluoride reaction crystallizer 11. The outlet of the hydrofluoric acid recovery tower 9, the hydrofluoric acid storage tank 16, and the hydrofluoric acid transfer pump 19 are sequentially connected to the inlet of the ammonium fluoride reaction crystallizer 11. The outlet of the ammonium fluoride reaction crystallizer 11 is sequentially connected to the inlet of the centrifuge 20 and the ammonium fluoride mother liquor tank 21. The outlet of the ammonium fluoride mother liquor tank 21 is sequentially connected to the ammonium fluoride mother liquor transfer pump 22 and the purification tower 10. The outlet of the purification tower 10 is sequentially connected to the main fan 17 and the chimney 18.

[0044] The operation procedure of this system includes the following steps:

[0045] S1. The lithium battery is broken down using a splitting device and protected with dry nitrogen. The resulting exhaust gas passes through a bag filter and is then connected to a downstream gas mixer.

[0046] S2. The battery solution is pyrolyzed using a pyrolysis device, with dry nitrogen gas for protection. The temperature is raised to 300-500℃ to evaporate the electrolyte solvent, and LiPF6 decomposes into LiF and PF5. Then, the temperature is lowered, and the solution is cleaned by a bag filter before being connected to the downstream gas mixer.

[0047] S3. The two exhaust gases are mixed and introduced into the combustion chamber, where air is introduced for direct oxidation and combustion. The combustion temperature is 850-1200℃, controlled by the amount of air introduced. In the combustion chamber, carbonate organic compounds are oxidized into CO2 and H2O, and PF5 is decomposed and oxidized to P2O5 and HF. The high-temperature flue gas is then cooled to 400-600℃ by a waste heat boiler before entering a hydration tower for rapid cooling and phosphoric acid extraction.

[0048] S4. Dilute phosphoric acid is injected into the hydration tower. On one hand, the dilute phosphoric acid rapidly evaporates moisture in the high-temperature flue gas, thus concentrating it. On the other hand, the evaporated water reacts with P2O5 to form H3PO4, which condenses at the bottom of the tower and is recovered. Simultaneously, the evaporation of moisture rapidly cools the flue gas, preventing the formation of dioxins. Uncondensed phosphoric acid mist and hydrogen fluoride gas are carried by the flue gas into the primary phosphoric acid trap.

[0049] S5. The primary phosphoric acid trap is a Venturi trap, and the secondary phosphoric acid trap is a packed tower with a demister. The flue gas temperature after phosphoric acid trapping is controlled at 90-130℃. Due to the difference in boiling points between phosphoric acid and hydrogen fluoride, phosphoric acid is completely trapped. The phosphoric acid trapped in this part dissolves a certain amount of HF, which is then returned to the hydration tower for spray purification. Undissolved HF enters the hydrofluoric acid recovery tower together with the flue gas.

[0050] S6. The hydrofluoric acid recovery tower adopts a structure with a lower condenser and an upper packed tower. After the flue gas enters the condenser, the flue gas is cooled, and the HF and water in the flue gas are condensed together to generate hydrofluoric acid and are recovered. The hydrofluoric acid entrained in the flue gas is captured and recovered by the upper packed tower. A small amount of HF that is not condensed enters the purification tower together with the flue gas.

[0051] The fillers in S5 and S6 meet the requirements for corrosion resistance and high temperature resistance.

[0052] S7. The purification tower adopts an empty tower structure, and ammonia water is used as the absorbent. In the purification tower, HF gas in the flue gas undergoes a neutralization reaction with ammonia and is rapidly absorbed, generating ammonium fluoride. The concentration of hydrogen fluoride in the flue gas is less than 3 mg / m³. 3 The CO2 is sent to the chimney by the main exhaust fan, and the unreacted CO2 is also discharged through the chimney. When the ammonium fluoride generated in the purification tower reaches a certain concentration, the ammonium fluoride and unreacted ammonia are pumped together to the ammonium fluoride reaction crystallizer.

[0053] S8. In the ammonium fluoride reaction crystallizer, add hydrofluoric acid recovered from the hydrofluoric acid recovery tower, control the pH value to around 4, and produce the finished ammonium fluoride product. After filtration and drying, it is sold as a commercial product. The filtrate is returned to the purification tower for continued use.

Claims

1. A method for off-gas purification and resource recovery of lithium battery recycling, characterized in that, The system for waste gas purification and resource recovery in lithium battery recycling is carried out by the following steps: S1, under the protection of inert gas, the lithium battery is disassembled in a disassembly device, and the electrolyte is separated, and the generated waste gas passes through a first dust removal device and then enters a gas mixer; S2, the electrolyte in S1 is added into a pyrolysis device, and pyrolysis is carried out under the protection of inert gas to obtain pyrolysis gas, the pyrolysis gas includes LiF and PF5, after the pyrolysis gas is cooled, it passes through a second dust removal device and then enters the gas mixer to obtain mixed gas one; the temperature in S2 is 300-500 DEG C; the inert gas in S1 and S2 is dry nitrogen; S3, the mixed gas one and air are introduced into a combustion chamber, and after combustion, an oxidation gas is obtained, the oxidation gas includes P2O5 and HF, and the oxidation gas is cooled to 400-600 DEG C in a boiler; S4, the cooled oxidation gas in S3 is introduced into a hydration tower, and dilute phosphoric acid or water is sprayed in the hydration tower to obtain phosphoric acid and unreacted gas, the phosphoric acid is collected through the outlet of the hydration tower, and the unreacted gas includes phosphoric acid mist and hydrogen fluoride gas; S5, the unreacted gas passes through a primary phosphoric acid trap, a mixed acid pool and a secondary phosphoric acid trap in sequence to collect phosphoric acid, and a phosphoric acid mixed solution and mixed gas two are obtained, and the phosphoric acid mixed solution is sprayed into the hydration tower for purification; The primary phosphoric acid trap is a Venturi, and the secondary phosphoric acid trap is a packed tower with a mist eliminator; The temperature of the mixed gas two in S5 is 90-130 DEG C; S6, the mixed gas two enters a hydrofluoric acid recovery tower for condensation and absorption to obtain hydrofluoric acid and mixed gas three, and the hydrofluoric acid is collected through the outlet of the hydrofluoric acid recovery tower; S7, the mixed gas three enters the purification tower, and ammonia water is added for spraying to obtain ammonium fluoride liquid and flue gas, and the hydrogen fluoride concentration in the flue gas is less than 3 mg / m 3 time, emission is performed; S8, ammonium fluoride liquid and the hydrofluoric acid in S6 are added into an ammonium fluoride reaction crystallizer to react and crystallize to obtain ammonium fluoride crystals, and after filtration and drying, ammonium fluoride products and filtrate are obtained, and the filtrate is transported to a purification tower for continuous use; The system for waste gas purification and resource recovery in lithium battery recycling comprises a pyrolysis device (3), a second dust removal device (4), a gas mixer (5), a combustion chamber (6) and a boiler (7) which are sequentially communicated, a disassembly device (1), a first dust removal device (2) and the gas mixer (5) which are sequentially communicated, an air outlet of the boiler (7) and an air inlet of a hydration tower (8) are communicated, an air outlet of the hydration tower (8) and an air inlet of a primary phosphoric acid trap (12) are communicated, an outlet of the primary phosphoric acid trap (12) and a mixed acid pool (15) are communicated, the mixed acid pool (15) and an air inlet of a secondary phosphoric acid trap (13) are communicated, an air outlet of the secondary phosphoric acid trap (13) and an air inlet of a hydrofluoric acid recovery tower (9) are communicated, an air outlet of the hydrofluoric acid recovery tower (9) and an air inlet of a purification tower (10) are communicated, and an outlet of the mixed acid pool (15), a mixed acid pump (14) and an inlet of the hydration tower (8) are sequentially communicated.

2. The method of claim 1, wherein: The combustion temperature in S3 is 850-1200 DEG C.

3. The method of claim 1, wherein: The liquid outlet of the purification tower (10) is communicated with the liquid inlet of an ammonium fluoride reaction crystallizer (11), the liquid outlet of the hydrofluoric acid recovery tower (9), a hydrofluoric acid storage tank (16), a hydrofluoric acid delivery pump (19) and the liquid inlet of the ammonium fluoride reaction crystallizer (11) are sequentially communicated.

4. The method of claim 1, wherein: The liquid outlet of the ammonium fluoride reaction crystallizer (11) is sequentially communicated with the liquid inlet of a centrifugal machine (20) and an ammonium fluoride mother liquor tank (21).

5. The method of claim 4, wherein: The liquid outlet of the ammonium fluoride mother liquor tank (21) is sequentially communicated with an ammonium fluoride mother liquor delivery pump (22) and the purification tower (10).

6. The method according to any one of claims 1 to 5, characterized in that: The air outlet of the purification tower (10) is sequentially communicated with a main air blower (17) and a chimney (18).

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