Lithium mica raw material preparation lithium carbonate roasting tail gas purification system

Abstract

This invention discloses a purification system for the roasting tail gas of lithium carbonate preparation from lepidolite raw materials. The system includes a high-efficiency dust collector, a medium-high temperature SCR denitrification device, a waste heat boiler, a bag filter, a primary deacidification tower, a secondary deacidification tower, an induced draft fan, and a chimney, all connected sequentially via a flue. A reducing agent ammonia injection grid is installed in the flue between the high-efficiency dust collector and the medium-high temperature SCR denitrification device. Compared with existing technologies, pre-deacidification significantly reduces the corrosion of the waste heat boiler and downstream flue by polluted tail gas, and significantly improves the operating conditions of the secondary bag filter, while also greatly reducing the load on subsequent thallium removal. The primary and secondary deacidification towers ensure the removal of acidic gases such as SO2, SO3, and HF, while the secondary acid washing removes residual elemental thallium and thallium from the flue gas. +1 Thallium and its compounds are washed into the desulfurization tower slurry tank to ensure that the thallium in the flue gas meets the emission standards; in addition, a separate wastewater treatment system is set up to ensure that the thallium in the wastewater meets the emission standards.

Description

Technical Field

[0001] This invention relates to the technical field of flue gas purification, and in particular to the technical field of a purification system for the roasting tail gas of lithium carbonate prepared from lithium mica raw material. Background Technology

[0002] Lithium is hailed as the "green energy metal" and "white oil" that will change the world in the 21st century. It is an indispensable key raw material for strategic industries such as new energy vehicles, energy storage, and electronic information. Lithium carbonate is the most important storage and basic product form in the lithium industry system. As a strategic lithium salt, its core role is mainly reflected in three aspects: 1. As the cornerstone of the new energy field: Battery-grade lithium carbonate is a key raw material for preparing lithium battery cathode materials, used in the production of lithium cobalt oxide, lithium manganese oxide, ternary materials and lithium iron phosphate, etc. 2. As an additive in traditional industries: In the glass and ceramics industries, adding lithium carbonate can lower the melting point and coefficient of expansion, and improve the strength and gloss of the products; in aluminum electrolysis, it can be used as an additive to improve conductivity and reduce energy consumption. 3. Can be used as a mood stabilizer in the medical field: Lithium carbonate is a first-line drug for the treatment of bipolar disorder, which can effectively stabilize mood and inhibit mania.

[0003] In China, lithium carbonate production is highly concentrated in the three provinces of Jiangxi, Qinghai, and Sichuan, which account for more than 75% of the country's total lithium carbonate production.

[0004] Lithium carbonate production mainly utilizes lithium resources from lithium mines and salt lake brines. Globally, about 60% of the supply comes from ore and 40% from salt lakes. China currently needs to import a large amount of lithium production raw materials, mainly from Australia and Zimbabwe.

[0005] Lithium mica, as a type of lithium ore, has always been an important source for the production of lithium carbonate.

[0006] Due to the complex composition of associated minerals in lepidolite ore, the flue gas generated and emitted during the high-temperature roasting process in lithium extraction technology has a very complex composition of pollutants, mainly including SO2, NOx, dust, SO3, HF, heavy metals (including thallium) and their compounds. Compared with other industrial flue gas, the flue gas generated during the lithium extraction process of lepidolite roasting has the following characteristics: 1) High SO2 concentration, which can reach 5000~8000 mg / Nm³. 3 2) The SO3 concentration is relatively high, typically between 100 and 250 mg / Nm³. 3 Even higher; 3) High levels of nitrogen oxides (NOx), reaching up to 200 mg / Nm³. 3The above; 4) Fluorine associated with lepidolite ore volatilizes during roasting, resulting in a certain concentration of HF in the flue gas, which can reach 30 mg / Nm³. 3 5) The flue gas also contains highly toxic thallium pollutants, with concentrations of thallium and its compounds reaching up to 15 mg / Nm³. 3 At high temperatures, most of the flue gas exists in a gaseous form.

[0007] According to national regulations, newly established enterprises must comply with GB31573-2015 "Emission Standard of Pollutants for Inorganic Chemical Industry" for both water and air pollutant emissions, effective from July 1, 2015, and existing enterprises must comply with GB31573-2015 "Emission Standard of Pollutants for Inorganic Chemical Industry".

[0008] Currently, the purification of this flue gas mainly employs the traditional SCR + wet process technology. The flue gas treatment process primarily involves "rotary kiln roasting flue gas → high-temperature integrated dust and nitrogen removal system → air preheater → wet deacidification system → chimney." However, due to the complex composition and high concentrations of various pollutants in the lithium mica roasting flue gas, traditional wet processes cannot effectively remove sulfides, thallium, and other pollutants. This results in excessive concentrations of acidic gases such as SO2 and SO3 in the emitted flue gas, severe system corrosion, and the requirement that the emission concentration limit for thallium and its compounds be ≤0.05 mg / Nm³. 3 It is very difficult, and many newly installed systems cannot meet its emission requirements.

[0009] Patent CN116603385A discloses a process for removing sulfur dioxide and thallium from lepidolite sintering flue gas. This process collects and pressurizes the lepidolite sintering flue gas, then introduces it into a desulfurization and thallium removal tower. The process relies on sprayed lime slurry to react with SO2 and thallium in the flue gas to achieve purification. The slurry mixture generated in the tower is then separated into waste residue and wastewater for secondary treatment. However, this type of wet process has the following shortcomings: 1) It relies entirely on the wet desulfurization and thallium removal tower to maintain an inlet concentration of 15 mg / Nm³. 3 Reduced to 0.05 mg / Nm 3 1. It is basically impossible to achieve; 2. The removal efficiency of SO3 by wet desulfurization and thallium removal tower is only 20%-30%, resulting in serious SO3 exceedance in the outlet emissions.

[0010] Patent CN116651174A describes a treatment system and method for flue gas from a rotary kiln in smelting. The system includes a solid-state denitrification device, a high-temperature filtration dust collection device, a waste heat recovery device, a semi-dry deacidification device, and a low-temperature liquid-phase denitrification device. The main problems with this patent are: the semi-dry deacidification technology has low SO2 removal efficiency and cannot meet the requirements for purifying high SO2 concentration flue gas; furthermore, the process of setting up a solid-state denitrification device at the kiln end and then separately configuring a low-temperature liquid-phase denitrification device after the deacidification device is complex, and there are currently no very successful low-temperature liquid-phase denitrification agents in industrial applications. According to the patent description, the reaction temperature is below 180℃, where nitrogen oxides are reduced to nitrogen gas, achieving a denitrification efficiency of ≥85%. This requires selecting a specific manufacturer's chelated denitrification activator, as described in the patent, and there is still a long way to go before commercialization; moreover, this patent cannot effectively remove other pollutants such as heavy metal thallium.

[0011] Patent No. CN 120313370 A describes a purification system and method for lithium mica roasting flue gas, including a pre-dust removal device, a primary moving bed reactor, a secondary fluidized bed reactor, a tertiary dust removal reactor, and an induced draft fan connected in sequence. However, this system has the following main shortcomings in terms of process: It uses a strong oxidant in a high-temperature gaseous state, which, considering the presence of high concentrations of SO2, will preferentially consume a large amount of oxidant. Furthermore, under gaseous conditions, Tl⁺ mainly exists as extremely stable halides such as TlCl and TlF aerosols, whose chemical bonds are very strong and difficult to break by gaseous oxidants. Additionally, the use of a conventional dry-lime + semi-dry desulfurization process is insufficient for inlet SO2 concentrations of 5000~8000 mg / Nm³. 3 Under these circumstances, it is very difficult to achieve emissions standards.

[0012] Patent No. CN116422125U describes a method for treating the tail gas of lithium carbonate preparation from lepidolite raw materials. This process uses low-temperature denitrification and adds a supplementary combustion heating device, resulting in high investment and operating costs. In addition, the patent does not describe in detail the specific processes of wet dust removal, defluorination, and desulfurization, nor does it involve the thallium removal process, so its application is not very meaningful.

[0013] Analysis of existing environmental protection equipment and related patented technologies reveals the following main deficiencies: 1. The lack of a pre-desulfurization process leads to severe corrosion of the waste heat boiler, flue, and dust collector after cooling; 2. Some desulfurization processes, including semi-dry desulfurization, cannot achieve emission standards under high SO2 concentration conditions; 3. Wet desulfurization has low SO3 removal efficiency, resulting in SO3 exceeding standards; 4. The thallium treatment process is simple, causing both flue gas and wastewater emissions to exceed standards; 5. Some denitrification processes are complex, resulting in excessive investment or operating costs, or even causing the system to fail to meet standards. Summary of the Invention

[0014] The purpose of this invention is to solve the problems in the prior art by proposing a purification system for the roasting tail gas of lithium carbonate preparation from lepidolite raw materials, which can solve at least one of the above problems.

[0015] To achieve the above objectives, this invention proposes a lithium carbonate roasting tail gas purification system for lithium mica raw material preparation, comprising a high-efficiency dust collector, a medium-high temperature SCR denitrification device, a waste heat boiler, a bag filter, a primary deacidification tower, a secondary deacidification tower, an induced draft fan, and a chimney, which are connected sequentially through a flue. The flue between the high-efficiency dust collector and the medium-high temperature SCR denitrification device is equipped with a reducing agent ammonia injection grid, and the inlet flue before the waste heat boiler is equipped with a dry deacidification agent nozzle.

[0016] Preferably, the high-efficiency dust collector is an electrostatic precipitator or a cyclone separator.

[0017] Preferably, the medium-high temperature SCR denitrification device uses high-temperature denitrification in the range of 260℃ to 400℃, uses a high-temperature catalyst in the range of 260℃ to 400℃, and uses ammonia water or urea solution as the denitrification reducing agent.

[0018] Preferably, a dry desulfurization agent nozzle is installed on the inlet flue of the waste heat boiler. The desulfurization agent injected into the flue is slaked lime with a Ca(OH)2 content ≥90% and a sieve rate of 325 mesh ≥90%.

[0019] Preferably, the pH value of the slurry inside the primary deacidification tower is 5.3 to 5.8; the spray layer is set with 2 to 4 layers, and the demister is set with 2 to 3 stages.

[0020] Preferably, the pH value of the slurry inside the secondary deacidification tower is 5.8 to 6.3; the spray layer is set with 2 to 4 layers, and the demister is set with 2 to 3 stages.

[0021] As a preferred option, the slurry added to each stage of the deacidification tower is fresh limestone slurry, and the quality of the limestone powder used for slurry preparation should meet the requirements of CaCO3 purity ≥90% and sieve pass rate ≥90% of 325 mesh.

[0022] Preferably, the primary and secondary desulfurization towers are also used to wash and remove residual thallium from the flue gas. +1 Thallium and its compounds, the washed thallium in the column is mainly in the form of soluble Tl. + The salt dissolves in the slurry.

[0023] Preferably, the system also includes a wastewater treatment system, wherein the wastewater outlets of the primary and secondary deacidification towers are connected to the wastewater treatment system, the sediment outlets of the primary and secondary deacidification towers are connected to the gypsum dewatering system, and the wastewater outlet of the gypsum dewatering system is connected to the wastewater treatment system.

[0024] Preferably, the wastewater treatment system is equipped with multi-stage reaction tanks, with alkali, oxidant and flocculant added to each stage of the reaction tank.

[0025] The beneficial effects of this invention are as follows: 1. By setting up dry deacidification agent nozzles to inject deacidification agent into the flue gas for pre-deacidification, most of the HF, SO3 and some SO2 acidic gases can be removed, increasing the acid dew point, reducing corrosion to the waste heat boiler and downstream flue, and greatly improving the operating conditions of the secondary bag filter; 2. By setting up a waste heat boiler to reduce the flue gas temperature, and filtering through the secondary bag filter, most of the solid / aerosol particles such as elemental thallium or thallium compounds condensed / adsorbed on the surface of particulate matter can be removed. Generally, this amount can account for more than 80% of the total thallium, greatly reducing the load on subsequent thallium removal; 3. By setting up a primary deacidification tower and a secondary deacidification tower, the removal effect of acidic gases such as SO2, SO3, and HF is guaranteed, while ensuring that elemental thallium and thallium in the flue gas are removed under the secondary acid washing conditions. +1 Thallium and its compounds are washed into the desulfurization tower slurry pool to ensure that the emission of thallium in the flue gas meets the standards; 4. The medium and high temperature SCR denitrification unit is economical and reliable, with low investment and operating costs.

[0026] The features and advantages of the present invention will be described in detail through embodiments and in conjunction with the accompanying drawings. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a lithium carbonate roasting tail gas purification system based on lithium mica raw material according to the present invention.

[0028] In the diagram: 1-High-efficiency dust collector, 2-Reducing agent ammonia spray grid, 3-Medium-high temperature SCR denitrification device, 4-Waste heat boiler, 5-Dry deacidification agent nozzle, 6-Bag dust collector, 7-Primary deacidification tower, 8-Secondary deacidification tower, 9-Wastewater treatment system, 10-Exhaust fan, 11-Chimney, 71-Slurry circulation pump, 72-Spray layer, 73-Demister. Detailed Implementation

[0029] See Figure 1 The present invention discloses a lithium carbonate roasting tail gas purification system for lithium mica raw material preparation, comprising a high-efficiency dust collector 1, a medium-high temperature SCR denitrification device 3, a waste heat boiler 4, a bag filter 6, a primary deacidification tower 7, a secondary deacidification tower 8, an induced draft fan 10, and a chimney 11 connected in sequence through a flue. The flue between the high-efficiency dust collector 1 and the medium-high temperature SCR denitrification device 3 is provided with a reducing agent ammonia injection grid 2, and the inlet flue before the waste heat boiler 4 is provided with a dry deacidification agent nozzle 5.

[0030] A high-efficiency dust collector 1 is added before the medium-high temperature SCR denitrification device 3. The dust removal efficiency can be 80% to 90%. The removed solid waste is reused as raw material. The high-efficiency dust collector 1 adopts an electrostatic precipitator or a cyclone separator, which greatly reduces the investment compared with high temperature filter dust collectors.

[0031] The medium-high temperature SCR denitrification device 3 adopts high temperature denitrification in the range of 260℃~400℃, uses a high temperature catalyst in the range of 260℃~400℃, and uses ammonia water or urea solution as the denitrification reducing agent.

[0032] A waste heat boiler 4 is installed after the medium-high temperature SCR denitrification device 3 to reduce the flue gas temperature from 260℃~400℃ to 130℃~150℃, making full use of waste heat. At low temperature, some acidic gases and thallium compounds are condensed / adsorbed on particulate matter, which is beneficial for subsequent dust removal and thallium removal on the surface of the filter bags of the bag filter 6.

[0033] A dry desulfurizing agent nozzle 5 is added before the waste heat boiler 4 for pre-desulfurization. Ca(OH)2 powder has a high desulfurization efficiency in this temperature range, which can remove most of the acidic gases such as hydrogen fluoride and SO3 and some SO2 gas, greatly reducing the corrosiveness of the flue gas to the waste heat boiler and flue after cooling, and improving the operating conditions of the subsequent bag filter 6. The desulfurizing agent injected into the flue by the dry desulfurizing agent nozzle 5 is selected as quicklime with a Ca(OH)2 content ≥90% and a sieve rate of 325 mesh ≥90%.

[0034] The bag filter 6 performs secondary dust removal on the flue gas after dust collection and denitrification, controlling the outlet dust concentration to less than 10 mg / Nm³. 3 It removes most of the solid / aerosol particles such as elemental thallium or thallium compounds that are condensed / adsorbed on the surface of particulate matter; the filter media can be acid-resistant and high-temperature resistant PTFE filter media; the solid waste removed by the bag filter 6 can be reused as raw materials or treated as solid waste according to its composition.

[0035] The flue gas, after being treated by the bag filter 6, enters the primary acid removal tower 7. Fresh alkaline solution is simultaneously added to the tower. After thorough stirring and mixing within the tower, the solution is pumped by the slurry circulation pump 71 to various spray layers 72 for spraying, removing the remaining HF, SO3, and most of the SO2 and other acidic gases, as well as fine particulate matter. The treated flue gas then undergoes further purification by a demister 73. The pH value of the slurry in the primary acid removal tower 7 is 5.3–5.8. The spray layers 72 have 2–4 layers, and the demister 73 has 2–3 stages. Simultaneously, acid washing removes residual elemental thallium and thallium from the flue gas. +1 The compounds and other substances are washed into the deacidification tower slurry tank.

[0036] The pH value of the slurry in the secondary acid removal tower 8 is 5.8–6.3; the spray layer 72 has 2–4 layers, and the demister 73 has 2–3 stages to ensure the removal effect of acidic gases such as SO2, SO3, and HF. At the same time, the remaining elemental thallium and thallium in the flue gas are removed through secondary acid washing. +1 Thallium and its compounds are washed into the desulfurization tower slurry pool to ensure that the emission of thallium in the flue gas meets the standards.

[0037] The slurry added to each stage of the deacidification tower is fresh limestone slurry. The quality of the limestone powder used for slurry preparation should meet the requirements of CaCO3 purity ≥ 90% and sieve pass rate ≥ 90% (325 mesh).

[0038] As mentioned above, the primary desulfurization tower 7 and the secondary desulfurization tower 8 are also used to wash and remove residual thallium from the flue gas. +1 Thallium and its compounds, the washed thallium in the column is mainly in the form of soluble Tl. + The salt dissolves in the slurry.

[0039] It also includes a wastewater treatment system 9, the wastewater outlets of the primary deacidification tower 7 and the secondary deacidification tower 8 are both connected to the wastewater treatment system 9, the precipitate outlets of the primary deacidification tower 7 and the secondary deacidification tower 8 are connected to the gypsum dewatering system, and the wastewater outlet of the gypsum dewatering system is connected to the wastewater treatment system 9.

[0040] Wastewater treatment system 9 is set up so that wastewater generated by the gypsum dewatering system is discharged into the system. At the same time, the thallium ion concentration in the primary deacidification tower 7 and the secondary deacidification tower 8 is monitored regularly. Because the thallium concentration in the circulating slurry will gradually accumulate, when the measured concentration exceeds a certain threshold, usually 5-10 mg / L, some of the water in the deacidification tower needs to be discharged into the wastewater treatment system 9 and new process water is added to avoid the re-release of gaseous thallium due to saturation.

[0041] The wastewater treatment system 9 is equipped with multi-stage reaction tanks. Each stage of the reaction tank contains an alkali, an oxidant, and a flocculant. The alkali is calcium hydroxide, the oxidant is KMnO4, hydrogen peroxide, or ozone, and the flocculant is iron. 3+ or aluminum 3+ ; Wastewater treatment system with 9 pairs of Ti 3+ It is used for efficient adsorption and co-precipitation of other heavy metals, and finally the precipitated sludge and supernatant are separated; the precipitated sludge is discharged as sediment, and the supernatant is reused as process water.

[0042] Working process of this invention: In the operation of the lithium carbonate roasting tail gas purification system for lithium mica raw material preparation of the present invention, the flue gas first passes through a high-efficiency dust collector 1 for dust removal, and then enters a medium-high temperature SCR denitrification device 3 for high-temperature denitrification. A reducing agent is injected into the reducing agent grid 2 before the medium-high temperature SCR denitrification device 3; and a desulfurizing agent is injected into the flue through a dry desulfurization agent nozzle 5 after SCR denitrification. After denitrification and desulfurization, the flue gas enters the waste heat boiler 4 to be cooled to 130℃~150℃, and then enters the bag filter dust collector 6 for secondary dust removal. The flue gas then enters the primary desulfurization tower 7 and the secondary desulfurization tower 8 in sequence for desulfurization, washing and demisting. Finally, the clean flue gas is discharged into the atmosphere through the induced draft fan 10 and the chimney 11.

[0043] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. A system for purifying the roasting tail gas from lithium carbonate preparation using lepidolite as raw material, characterized in that: The system includes a high-efficiency dust collector (1), a medium-high temperature SCR denitrification device (3), a waste heat boiler (4), a bag filter (6), a primary deacidification tower (7), a secondary deacidification tower (8), an induced draft fan (10), and a chimney (11) connected in sequence through a flue. The flue between the high-efficiency dust collector (1) and the medium-high temperature SCR denitrification device (3) is equipped with a reducing agent ammonia spray grid (2), and the inlet flue before the waste heat boiler (4) is equipped with a dry deacidification agent spray nozzle (5).

2. The lithium carbonate roasting tail gas purification system according to claim 1, characterized in that: The high-efficiency dust collector (1) adopts an electrostatic precipitator or a cyclone separator.

3. The lithium carbonate roasting tail gas purification system according to claim 1, characterized in that: The medium-high temperature SCR denitrification device (3) adopts high temperature denitrification in the range of 260℃~400℃, adopts high temperature catalyst in the range of 260℃~400℃, and uses ammonia water or urea solution as denitrification reducing agent.

4. The lithium carbonate roasting tail gas purification system according to claim 1, characterized in that: The desulfurizing agent sprayed into the flue through the dry desulfurization agent nozzle (5) is quicklime with a Ca(OH)2 content ≥90% and a sieve pass rate of 325 mesh ≥90%.

5. The lithium carbonate roasting tail gas purification system according to claim 1, characterized in that: The pH value of the slurry in the first-stage deacidification tower (7) is 5.3 to 5.8; the spray layer (72) is set with 2 to 4 layers, and the demister (73) is set with 2 to 3 stages.

6. The lithium carbonate roasting tail gas purification system according to claim 1, characterized in that: The pH value of the slurry in the secondary deacidification tower (8) is 5.8 to 6.3; the spray layer (72) is set with 2 to 4 layers, and the demister (73) is set with 2 to 3 stages.

7. The lithium carbonate roasting tail gas purification system according to claim 1, characterized in that: The slurry added to each stage of the deacidification tower is fresh limestone slurry. The quality of the limestone powder used for slurry preparation should meet the requirements of CaCO3 purity ≥ 90% and sieve pass rate ≥ 90% (325 mesh).

8. The lithium carbonate roasting tail gas purification system according to claim 1, characterized in that: The primary desulfurization tower (7) and the secondary desulfurization tower (8) are also used to wash and remove residual thallium from the flue gas. +1 Thallium and its compounds, the washed thallium in the column is mainly in the form of soluble Tl. + The salt dissolves in the slurry.

9. The lithium carbonate roasting tail gas purification system according to claim 1, characterized in that: It also includes a wastewater treatment system (9), the wastewater outlets of the primary deacidification tower (7) and the secondary deacidification tower (8) are connected to the wastewater treatment system (9), the sediment outlets of the primary deacidification tower (7) and the secondary deacidification tower (8) are connected to the gypsum dewatering system, and the wastewater outlet of the gypsum dewatering system is connected to the wastewater treatment system (9).

10. The lithium carbonate roasting tail gas purification system according to claim 9, characterized in that: The wastewater treatment system (9) is equipped with multi-stage reaction tanks, with alkali, oxidant and flocculant added to each stage of the reaction tank.

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