Method and device for lithium extraction by roasting of lepidolite triple combination furnace and waste heat recovery

Abstract

This invention discloses a method and apparatus for lithium extraction and waste heat recovery from lepidolite using a three-stage furnace, relating to the field of lithium extraction from ore. The method includes the following steps: S1, mixing: Low-grade lepidolite with an initial water content of 12-20% and a Li₂O content ≤2.5% is mixed with sodium-potassium salt and calcium salt at a mass ratio of (65-80):(3-15):(5-32) in a mixer; S2, drying: The mixture obtained in S1 is fed into a cylindrical dryer, while hot flue gas from the roasting kiln at 300-480°C is introduced into the cylindrical dryer; S3, roasting and in-situ denitrification; S4, clinker cooling and waste heat recovery; S5, grate cooler intake control. This invention effectively reduces equipment operating load and flue gas emission power consumption, further improves flue gas waste heat utilization efficiency, increases the heat exchange efficiency of the air system, maximizes energy utilization, and simultaneously reduces flue gas emissions and pollutant content.

Description

Technical Field

[0001] This invention relates to the field of lithium extraction technology from ores, specifically to a method and apparatus for lithium extraction by roasting lithium mica using a triple furnace and recovering waste heat. Background Technology

[0002] Lepidolite is an important mineral raw material for lithium extraction. It often contains elements such as rubidium and cesium and occurs as fine scaly aggregates. It is mainly produced in pegmatites, greisen, and high-temperature hydrothermal veins. The sulfate roasting method is widely used in its lithium extraction process. The pyrometallurgical stage of this process requires preheating, high-temperature roasting, and cooling. The lepidolite concentrate is preheated in a preheating kiln and then enters a roasting kiln, where it is calcined at 900–1000°C. After that, it is cooled in a cooling kiln to form lithium-containing clinker. During this process, both the high-temperature flue gas in the roasting kiln and the clinker in the cooling kiln are maintained within this high-temperature range. Currently, waste heat recovery in the pyrometallurgical process for lithium extraction from lepidolite has several shortcomings: existing technologies mostly only recover waste heat from the flue gas in the roasting kiln or the clinker in the cooling kiln, failing to achieve synergistic recovery of both. A significant amount of high-temperature waste heat is lost through radiation, resulting in serious energy waste. Furthermore, in traditional processes, lepidolite has a high moisture content (approximately 15%), requiring it to be dried to about 5% before being cooled to room temperature for mixing, followed by roasting and cooling. These key processes often involve independent equipment and flue gas treatment systems, meaning the heat from the flue gas cannot be fully utilized during material transfer and processing, further reducing waste heat recovery efficiency. Summary of the Invention

[0003] The purpose of this invention is to provide a method and apparatus for lithium extraction and waste heat recovery from lithium mica using a triple furnace, in order to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for lithium extraction and waste heat recovery from lithium mica by roasting in a triple-furnace system, comprising the following steps: S1, Mixing: Low-grade lithium mica with an initial water content of 12-20% and a Li2O content of ≤2.5% is mixed with sodium-potassium salt and calcium salt in a mass ratio of (65-80):(3-15):(5-32) and mixed for 10-20 minutes. The sodium-potassium salt is a mixture of sodium sulfate and potassium sulfate in a mass ratio of (3-4):1, and the calcium salt is a mixture of calcium sulfate and calcium carbonate in a mass ratio of (1.8-3.5):1. S2, Drying: The mixture obtained in S1 is fed into the cylindrical dryer. At the same time, the hot flue gas discharged from the calcining kiln at 300~480℃ is introduced into the cylindrical dryer to preheat and dry the mixture for 30~90 minutes. The moisture content of the mixture after drying is controlled to be 3%~8% and the temperature of the drying tail gas is 120~180℃. After the drying tail gas is collected by cyclone dust collector and bag dust collector, it is then desulfurized and defluorinated by lime milk and wet electrostatic precipitator to meet the emission standards. The dust from the dust collection process is returned to the feed inlet of the cylindrical dryer. S3, Calcination and In-situ Denitrification: The dried mixture is fed into the calcination kiln, and the calcination transition temperature is controlled at 850~1000℃, the calcination time is 0.5~2.0h, and the kiln head is charged at 40~65Nm per ton of mixture. 3 Natural gas is added as fuel, and flue gas returned from the grate cooler is mixed in as combustion air; The combustion air is divided into primary roasting air and secondary roasting air. Primary roasting air accounts for 15% to 20% of the fresh air volume of the grate cooler. After being pressurized by the fan, it is introduced into the burner of the roasting kiln as auxiliary gas for natural gas combustion, which helps to ignite the natural gas and raise the temperature of the material. Secondary roasting air accounts for 80% to 85% of the fresh air volume of the grate cooler. It is directly diffused into the roasting kiln from the grate cooler and participates in the combustion reaction as combustion air. In the in-situ high-temperature section of the kiln, ammonia water with a mass concentration of 20%~25% is atomized with compressed air and sprayed into the ammonia water inlet. The amount of ammonia water added is 0.2~0.4 kg per ton of mixed material, so that the nitrogen oxides in the flue gas are reduced to nitrogen gas at high temperature. S4, Clinker Cooling and Waste Heat Recovery: The roasted clinker is fed into a grate cooler, and 750~950 Nm of heat is introduced into the grate cooler. 3 / ton of clinker fresh air and 350~600Nm 3 The independent circulating gas per ton of clinker cools the clinker to 50~100℃ before discharge; The independent circulating gas is recycled through cyclone dust collector, waste heat boiler, and bag dust collector to recover waste heat and dust. The dust and clinker are combined and sent to the subsequent lithium extraction process. The flue gas with a temperature of 120~145℃ after dust collection is returned to the front end of the grate cooler as a circulating cooling medium. S5, Grate Cooler Air Inlet Control: The grate cooler is equipped with 8 sets of gas inlets along the clinker travel direction. The 1st to 4th sets of inlets are supplied with the independent circulating air as the circulating cooling medium, and the 5th to 8th sets of inlets are supplied with the fresh air as fresh cold air, so as to realize the staged cooling of clinker and maximize the recovery of waste heat.

[0005] Furthermore, the discharge port of the cylindrical dryer in S2 is directly connected to the feed port of the roasting kiln in S3, and the discharge port of the roasting kiln in S3 is directly and sealed to the feed port of the grate cooler in S4. After the mixed material is dried, it directly enters the roasting process, and after roasting, the conveyed material directly enters the cooling process. The entire process has no intermediate transfer or open-air cooling steps.

[0006] Furthermore, the cylindrical dryer, calcining kiln, grate cooler, and connecting pipelines constitute a closed flue gas system. The self-generated flue gas generated by the grate cooler and the self-generated flue gas generated by the calcining kiln both participate in internal circulation through the flue gas conveying pipeline and induced draft fan inside the system, and no exhaust port leading to the outside of the system is provided.

[0007] Furthermore, in S5, the temperature of the circulating cooling medium introduced into the inlets of the first to fourth groups of the grate cooler decreases sequentially along the clinker travel direction, and the temperature of the fresh air introduced into the inlets of the fifth to eighth groups of the grate cooler decreases sequentially along the clinker travel direction, thus reducing the clinker temperature gradient.

[0008] An apparatus for lithium extraction and waste heat recovery from lithium mica using a triple furnace, for implementing the above method, comprising: The main body of the triple-fuel furnace, the mixing and feeding unit, the flue gas circulation unit, and the parameter control unit; The main body of the triple furnace is composed of a cylindrical dryer, a calcining kiln, and a grate cooler connected in series. The discharge port of the cylindrical dryer is directly connected to the feed port of the calcining kiln, and the discharge port of the calcining kiln is directly connected to the feed port of the grate cooler. The mixing and feeding unit includes, in sequence along the conveying direction, a batching silo, a first belt conveyor, a buffer silo, a mixer, and a second belt conveyor. The discharge port of the buffer silo is connected to the inlet of the mixer, and the discharge port of the mixer is connected to the inlet of the cylindrical dryer through the second belt conveyor. The flue gas circulation unit includes an induced draft fan, a flue gas conveying pipeline, and a waste heat boiler. The induced draft fans are respectively installed at the flue gas connection between the roasting kiln and the cylindrical dryer, at the flue gas connection between the grate cooler and the roasting kiln, and on the conveying path of the grate cooler's independent circulating flue gas. The parameter control unit is installed on the main body of the triple-burning furnace and the flue gas circulation unit.

[0009] Furthermore, the flue gas conveying pipeline includes a roasting flue gas conveying pipe, a grate cooler primary air conveying pipe, a grate cooler secondary air conveying pipe, and a grate cooler circulating flue gas conveying pipe. The roasting flue gas conveying pipe connects the kiln tail of the roasting kiln to the kiln head of the cylindrical dryer. The grate cooler primary air conveying pipe connects the grate cooler to the burner of the roasting kiln. The grate cooler secondary air conveying pipe directly connects the grate cooler to the interior of the roasting kiln. A second cyclone dust collector and a second bag dust collector are installed on the grate cooler circulating flue gas conveying pipe. The waste heat boiler is installed on the grate cooler circulating flue gas conveying pipe and is located between the second cyclone dust collector and the second bag dust collector. The independent circulating gas of the grate cooler flows back to the front end of the grate cooler through the grate cooler circulating flue gas conveying pipe. The discharge port of the second bag filter dust collector on the circulating flue gas conveying pipe of the grate cooler is equipped with a powder conveying device, which is connected to the clinker discharge port of the grate cooler to realize the combined conveying of recycled dust and clinker.

[0010] Furthermore, the exhaust port of the cylindrical dryer is connected in series with a first cyclone dust collector, a first bag dust collector, a lime slurry desulfurization and defluorination device, and a wet electrostatic precipitator via a pipeline; The calcining kiln is connected to an ammonia water addition device, which includes an ammonia water storage tank, a metering pump, a compressed air atomizing device, and an ammonia water spray gun. The metering pump is a variable frequency metering pump, and the ammonia water spray gun is a dual-fluid spray gun. The ammonia water spray gun is located in the in-situ high-temperature section of the calcining kiln and is connected to the inside of the calcining kiln and the compressed air atomizing device. The metering pump is connected to the ammonia water storage tank and the compressed air atomizing device, and can accurately meter and deliver ammonia water with a concentration of 20% to 25%, achieving ammonia water addition amount control of 0.2 to 0.4 kg per ton of mixed material.

[0011] Furthermore, the grate cooler is equipped with 8 sets of gas inlets, of which the first 4 to 5 gas inlets are circulating cooling medium inlet groups. These circulating cooling medium inlet groups are connected to the circulating flue gas conveying pipe of the grate cooler and can introduce 350 to 600 Nm of gas. 3 The circulating cooling medium per ton of clinker includes 3-4 gas inlets that form a fresh cold air inlet group. This group is connected to the fresh air supply pipe on the grate cooler and can supply 750-950 Nm³ of air. 3 / ton of clinker fresh cold air.

[0012] Furthermore, the parameter control unit includes a temperature sensor, a flow sensor, and a metering controller; The temperature sensors are respectively installed in the cylindrical dryer, the roasting kiln, the grate cooler, and each flue gas conveying pipeline, and can detect the temperature of roasting flue gas at 300~480℃, roasting kiln at 850~1000℃, clinker at 50~100℃, drying tail gas at 120~180℃, and circulating flue gas at 120~145℃ in real time. The flow sensor is installed in the natural gas delivery pipe, ammonia water addition pipe, fresh air delivery pipe, and flue gas delivery pipe, and can detect flow rates of 40~65 Nm in real time. 3 / ton of mixed natural gas, 0.2~0.4kg / ton of mixed ammonia, 750~950Nm 3 Fresh air per ton of clinker, 350~600 Nm 3 The flow rate of independent circulating gas per ton of clinker; The metering controller is electrically connected to the temperature sensor, flow sensor, natural gas valve, ammonia metering pump, fan, and grate cooler inlet valve to achieve dynamic control of temperature, flow rate, and intake ratio.

[0013] Furthermore, the cylindrical dryer, calcining kiln, and grate cooler are arranged in a stepped manner, with the cylindrical dryer installed at a higher height than the calcining kiln, and the calcining kiln installed at a higher height than the grate cooler, allowing the material to flow sequentially by gravity.

[0014] The technical effects and advantages provided by the present invention in the above technical solution are as follows: 1. This invention adopts a process scheme of direct mixing and simultaneous drying of lepidolite, completely eliminating the redundant steps of "separate drying of lepidolite → cooling and temperature reduction → re-mixing and batching" in the traditional process. This not only reduces heat loss and equipment occupancy during material transfer and avoids the risk of secondary contamination of materials caused by multiple process conversions, but also shortens the raw material pretreatment cycle and significantly improves the feeding stability and overall production efficiency of the subsequent roasting process; 2. This innovative method utilizes the waste heat from the roasting process as the core heat source for the drying process. A waste heat recovery system precisely controls the drying temperature and time, ensuring that the moisture content of the dried material is reduced to the minimum standard required for subsequent roasting processes. This method avoids additional fuel consumption, minimizes hydrogen fluoride formation at the source, reduces the cost of treating fluorine-containing waste gas, extends the service life of drying and roasting equipment, and significantly improves waste heat utilization efficiency. 3. This invention uses a grate cooler as a cooling device for roasted clinker. Combined with flue gas self-circulation and adaptive adjustment technology for fresh cold air, it can rapidly cool the roasted clinker to 50~100℃, meeting the requirements for direct discharge and eliminating the need for subsequent secondary cooling processes. Simultaneously, the self-generated flue gas within the roasting kiln and grate cooler does not require additional exhaust vents, effectively reducing equipment operating load and flue gas emission power consumption, further improving flue gas waste heat recovery efficiency, increasing the heat exchange efficiency of the air system, enhancing material cooling effect, and maximizing energy utilization. 4. Atomized ammonia water is directly injected into the roasting furnace for in-situ denitrification, eliminating the need for a separate denitrification unit and significantly simplifying the tail gas treatment system structure. Subsequent drying of the tail gas involves desulfurization, defluorination, and particulate matter treatment, achieving emission standards. This reduces equipment investment, operating costs, and floor space required for tail gas treatment, thereby improving the stability of the production system. 5. By precisely controlling the material ratio during the mixing process, combined with dynamic adjustment of the fuel consumption in the calcining kiln and the replenishment of fresh cold air, the system can control process parameters such as temperature, time, and atmosphere. This solves the problem of kiln clogging in engineering projects, while achieving efficient conversion of lithium and in-situ fixation of fluorine, reducing the migration of fluorine into flue gas, and reducing the difficulty of flue gas treatment and environmental impact from the source. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0016] Figure 1 This is a flow chart illustrating the flue gas path and process principle of the lithium mica triple-fuel furnace of the present invention; Figure 2 This is a schematic diagram of the connection of the lithium mica triple furnace device of the present invention.

[0017] Explanation of reference numerals in the attached figures: 1. Cylindrical dryer; 2. Calcination kiln; 3. Grate cooler; 4. Batching silo; 5. Buffer silo; 6. Mixer; 7. First belt conveyor; 8. Second belt conveyor; 9. Waste heat boiler; 10. First cyclone dust collector; 11. First bag dust collector; 12. Second cyclone dust collector; 13. Second bag dust collector; 14. Lime slurry desulfurization and defluorination device; 15. Wet electrostatic precipitator. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0019] This invention provides, for example Figure 1 The method for lithium extraction and waste heat recovery from lithium mica using a triple furnace includes the following steps: S1, Mixing: Low-grade lithium mica with an initial water content of 12~20% and Li2O content of ≤2.5% is mixed with sodium-potassium salt and calcium salt in a mass ratio of (65~80):(3~15):(5~32) and mixed for 10~20 min. Sodium-potassium mixed salt is a mixture of sodium sulfate and potassium sulfate in a mass ratio of (3~4):1. The synergistic effect of sodium sulfate and potassium sulfate can reduce the roasting temperature, increase the lithium conversion rate, and inhibit the sintering of materials. The calcium salt is a mixture of calcium sulfate and calcium carbonate in a mass ratio of (1.8~3.5):1. Calcium sulfate provides sulfate ions to participate in the reaction, while calcium carbonate provides an alkaline environment. The ratio of the two is optimized to avoid the generation of harmful gases, while adjusting the alkalinity of the reaction system to help lithium leach out better. S2, Drying: The mixture obtained in S1 is fed into the cylindrical dryer 1. At the same time, the hot flue gas of 300~480℃ discharged from the calcining kiln 2 is introduced into the cylindrical dryer 1 by an induced draft fan as a drying heat source to preheat and dry the mixture. The preheating and drying time is 30~90min. The moisture content of the dried mixture is controlled to be 3%~8% and the temperature of the drying tail gas is 120~180℃. After the drying exhaust gas is treated by cyclone dust collector and bag dust collector to remove particulate matter, it is then treated by lime milk desulfurization and defluorination and wet electrostatic precipitator to meet emission standards. The dust from the dust collection process is returned to the feed inlet of the cylindrical dryer 1 to realize the recycling of flue gas. The high-temperature flue gas from the calcining kiln 2 is used to directly dry the mixed materials, eliminating the redundant steps of "separate drying, cooling, and mixing of lithium mica" in the traditional process, thus realizing integrated batching and drying.

[0020] S3, Calcination and In-situ Denitrification: The dried mixture is fed into calcination kiln 2, with the calcination transition temperature controlled at 850~1000℃ and the calcination time at 0.5~2.0h. The kiln head is charged at 40~65 Nm per ton of mixture. 3 Natural gas is added as fuel, and flue gas returned from grate cooler 3 is mixed in as combustion air; Combustion air is divided into primary roasting air and secondary roasting air. Primary roasting air accounts for 15% to 20% of the fresh air volume of the grate cooler. After being pressurized by the fan, it is introduced into the burner of roasting kiln 2 as auxiliary gas for natural gas combustion, which helps to ignite natural gas and heat up the material. Secondary roasting air accounts for 80% to 85% of the fresh air volume of the grate cooler. It is directly diffused into the roasting kiln from the grate cooler and participates in the combustion reaction as combustion air. In the in-situ high-temperature section of the calcining kiln 2, ammonia water with a mass concentration of 20%~25% is atomized with compressed air and sprayed into the ammonia water inlet. The amount of ammonia water added is 0.2~0.4 kg per ton of mixed material. At high temperature, ammonia and nitrogen oxides undergo a selective non-catalytic reduction reaction: 4NH3+4NO+O2→4N2+6H2O, thereby achieving in-situ denitrification of flue gas.

[0021] The discharge port of the cylindrical dryer 1 is directly connected to the feed port of the roasting kiln 2. After drying, the mixed material directly enters the roasting process without intermediate transfer and cooling steps. S4, Clinker Cooling and Waste Heat Recovery: The roasted clinker is fed into the grate cooler 3, and 750~950 Nm of heat is introduced into the grate cooler 3. 3 / ton of clinker fresh air and 350~600Nm 3 The independent circulating air per ton of clinker is cooled to 50~100℃ before being discharged through the coordinated cooling of fresh air and circulating air. The discharge port of the roasting kiln 2 is directly and sealed to the inlet of the grate cooler 3. The roasted material is directly fed into the cooling process, and there are no intermediate transfer or open-air cooling steps in the whole process. Independent circulating gas passes through cyclone dust collector, waste heat boiler 9, and bag dust collector to realize waste heat recovery and collection of roasted clinker dust. The dust and clinker are combined and sent to the subsequent lithium extraction process. The flue gas with a temperature of 120~145℃ after dust collection is returned to the front end of grate cooler 3 as the circulating cooling medium for roasted clinker. The cylindrical dryer 1, the calcining kiln 2, the grate cooler 3, and the connecting pipelines constitute a closed flue gas system. The self-generated flue gas generated by the grate cooler 3 and the self-generated flue gas generated by the calcining kiln 2 both participate in the internal circulation through the flue gas conveying pipeline and the induced draft fan inside the system. No exhaust port leading to the outside of the system is provided.

[0022] In traditional technologies, cooling flue gas is difficult to utilize directly due to its low temperature and poor quality, and is often discharged for treatment. This invention circulates the cooling flue gas independently, recovering heat through the waste heat boiler 9 before returning it to the front end of the grate cooler 3, thus recovering waste heat and reducing flue gas emissions.

[0023] S5, Grate Cooler Air Inlet Control: The grate cooler 3 is equipped with 8 sets of gas inlets along the clinker travel direction. The first to fourth sets of inlets are supplied with independent circulating air as circulating cooling medium, and the fifth to eighth sets of inlets are supplied with fresh air as fresh cold air. The temperature of the circulating cooling medium supplied to the first to fourth sets of inlets of the grate cooler 3 decreases sequentially along the clinker travel direction, and the temperature of the fresh air supplied to the fifth to eighth sets of inlets of the grate cooler 3 decreases sequentially along the clinker travel direction, thus reducing the clinker temperature gradient. The clinker reaches its highest temperature when it enters the front end of the grate cooler 3. It is initially cooled by circulating air at a relatively high temperature of 120℃~145℃ to prevent rapid cooling that could cause clinker pulverization. Subsequently, it undergoes deep cooling by fresh air at a lower temperature, ultimately reducing the discharge temperature to 50℃~100℃. This temperature gradient control not only protects the quality of the clinker but also maximizes the recovery of waste heat.

[0024] like Figure 1 and Figure 2 As shown, an apparatus for lithium extraction and waste heat recovery from lithium mica using a triple furnace is provided to achieve the above-mentioned method, comprising: The main body of the triple-fuel furnace, the mixing and feeding unit, the flue gas circulation unit, and the parameter control unit; The main body of the triple furnace consists of a cylindrical dryer 1, a roasting kiln 2, and a grate cooler 3 connected in series. The discharge port of the cylindrical dryer 1 is directly connected to the feed port of the roasting kiln 2, and the discharge port of the roasting kiln 2 is directly connected to the feed port of the grate cooler 3, realizing continuous processing of materials from drying to roasting to cooling without transfer, reducing heat and material loss. The cylindrical dryer 1, the calcining kiln 2, and the grate cooler 3 are arranged in a stepped manner. The installation height of the cylindrical dryer 1 is higher than that of the calcining kiln 2, and the installation height of the calcining kiln 2 is higher than that of the grate cooler 3. The materials flow sequentially by gravity.

[0025] The mixing and feeding unit includes, in sequence along the conveying direction, a batching silo 4, a first belt conveyor 7, a buffer silo 5, a mixer 6, and a second belt conveyor 8. The discharge port of the batching silo 4 is connected to the inlet of the buffer silo 5 through the first belt conveyor 7. The discharge port of the buffer silo 5 is connected to the inlet of the mixer 6. The discharge port of the mixer 6 is connected to the inlet of the cylindrical dryer 1 through the second belt conveyor 8. The batching silo 4 specifically includes a lithium mica raw material silo, a sodium-potassium mixed salt raw material silo, and a calcium salt raw material silo. The raw materials are originally quantitatively transported to the buffer silo 5 by the first belt conveyor 7 to achieve temporary storage of the raw materials. The raw materials in the buffer silo 5 are directly transported to the mixer 6 for mixing. The mixed material is then fed into the cylindrical dryer 1 by the second belt conveyor 8.

[0026] The flue gas recirculation unit includes an induced draft fan, a flue gas conveying pipeline, and a waste heat boiler 9. The induced draft fans are respectively installed at the flue gas connection between the calcining kiln 2 and the cylindrical dryer 1, at the flue gas connection between the grate cooler 3 and the calcining kiln 2, and on the independent circulating flue gas conveying path of the grate cooler 3, to provide power for the flue gas flow. The flue gas conveying pipeline includes a roasting flue gas conveying pipe, a grate cooler primary air conveying pipe, a grate cooler secondary air conveying pipe, and a grate cooler circulating flue gas conveying pipe. The roasting flue gas conveying pipe connects the kiln tail of the roasting kiln 2 with the kiln head of the cylindrical dryer 1, and is used to introduce the roasting flue gas into the dryer as a drying heat source. The grate cooler primary air conveying pipe connects the grate cooler 3 with the burner of the roasting kiln 2. The grate cooler secondary air conveying pipe directly connects the grate cooler 3 with the interior of the roasting kiln 2. The grate cooler circulating flue gas conveying pipe is equipped with a second cyclone dust collector 12 and a second bag dust collector 13. The waste heat boiler 9 is installed on the grate cooler circulating flue gas conveying pipe and is connected in series between the second cyclone dust collector 12 and the second bag dust collector 13. The independent circulating gas of the grate cooler 3 flows back to the front end of the grate cooler 3 through the grate cooler circulating flue gas conveying pipe to realize the waste heat recovery and recycling of the circulating flue gas. The discharge port of the second bag dust collector 13 on the circulating flue gas conveying pipe of the grate cooler is equipped with a powder conveying device. The powder conveying device is connected to the clinker discharge port of the grate cooler 3 to realize the combined conveying of recycled dust and clinker, avoid powder loss and improve the utilization rate of raw materials for subsequent lithium extraction.

[0027] The parameter control unit is installed on the main body of the triple boiler and the flue gas circulation unit. The parameter control unit includes a temperature sensor, a flow sensor and a metering controller. Temperature sensors are installed in the cylindrical dryer 1, the calcining kiln 2, the grate cooler 3, and each flue gas conveying pipeline. They can detect the temperature of calcining flue gas at 300~480℃, calcining kiln at 850~1000℃, clinker at 50~100℃, drying tail gas at 120~180℃, and circulating flue gas at 120~145℃ in real time. Flow sensors are installed in natural gas delivery pipes, ammonia water addition pipes, fresh air delivery pipes, and flue gas delivery pipes, and can detect flow rates of 40~65 Nm in real time. 3 / ton of mixed natural gas, 0.2~0.4kg / ton of mixed ammonia, 750~950Nm 3 Fresh air per ton of clinker, 350~600 Nm 3 The flow rate of independent circulating gas per ton of clinker; The metering controller is electrically connected to the temperature sensor, flow sensor, natural gas valve, ammonia metering pump, fan, and grate cooler inlet valve to achieve dynamic control of temperature, flow rate, and inlet ratio, thereby preventing kiln caking and improving lithium conversion rate.

[0028] The exhaust port of the cylindrical dryer 1 is connected in series via a pipeline to a first cyclone dust collector 10, a first bag dust collector 11, a lime slurry desulfurization and defluorination device 14, and a wet electrostatic precipitator 15. The first cyclone dust collector 10 and the first bag dust collector 11 are used to remove particulate matter from the flue gas, while the lime slurry desulfurization and defluorination device 14 and the wet electrostatic precipitator 15 are used to desulfurize, defluorinate, and deeply remove dust from the drying exhaust gas. The calcining kiln 2 is connected to an ammonia water addition device, which includes an ammonia water storage tank, a metering pump, a compressed air atomizing device, and an ammonia water spray gun. The metering pump is a variable frequency metering pump, and the ammonia water spray gun is a dual-fluid spray gun. The ammonia water spray gun is located in the in-situ high-temperature section of the calcining kiln 2 and is connected to the interior of the calcining kiln 2 and the compressed air atomizing device. The metering pump is connected to the ammonia water storage tank and the compressed air atomizing device, which can accurately meter and deliver ammonia water with a concentration of 20% to 25%, and achieve the control of the ammonia water addition amount of 0.2 to 0.4 kg per ton of mixed material.

[0029] The grate cooler 3 is equipped with 8 sets of gas inlets, of which the first 4 to 5 gas inlets are the circulating cooling medium inlet group. The circulating cooling medium inlet group is connected to the circulating flue gas conveying pipe of the grate cooler, and can introduce 350~600Nm. 3 The circulating cooling medium per ton of clinker includes 3-4 gas inlets that are connected to a fresh air inlet group. This fresh air inlet group is linked to the fresh air delivery pipe on the grate cooler 3, allowing for the introduction of 750-950 Nm³ of air. 3 / ton of clinker fresh cold air.

[0030] Example 1: S1, Mixing process: Raw materials and proportions: Low-grade lepidolite: 157.60 t / h, water content 18.00%, Li₂O content 1.83%; In the sodium-potassium mixed salt, potassium sulfate (K2SO4): 5.60 t / h; sodium sulfate (Na2SO4): 19.40 t / h; In the calcium salts, calcium sulfate (CaSO4): 35.40 t / h; calcium carbonate (CaCO3): 18.80 t / h; Mixing ratio: Lithium mica: sodium-potassium mixed salt: calcium salt = 65:15:20, wherein in the sodium-potassium mixed salt, sodium sulfate: potassium sulfate = 3.46:1, and in the calcium salt, calcium sulfate: calcium carbonate = 1.88:1. Mixing time: 15 min.

[0031] S2, Drying process: Temperature of flue gas entering the kiln for roasting: 400℃; Drying time: 60min; Moisture content of the dried mixture: 3.27%; Drying exhaust gas temperature: 150℃; Drying flue gas flow rate: 250,000 Nm³ 3 / h.

[0032] S3, roasting and in-situ denitrification: Calcination process: Calcination temperature: 950℃; High-temperature period time: 1.0h; Natural gas addition: 10532 Nm 3 / h (approximately 66.8 Nm) 3 / ton of mixed feed); Mixing rate after drying: 216.00 t / h.

[0033] In-situ denitrification: Ammonia concentration: 23%; Ammonia dosage: 63.50 kg / h (approximately 0.294 kg / ton of mixed material).

[0034] S4, grate cooler cooling: Fresh air volume of the grate cooler: 192600 Nm 3 / h primary air of rotary kiln: 31600 Nm 3 / h (16.4%); Rotary kiln secondary air: balance (83.6%) Independent circulating gas volume: 80900 Nm 3 / h Clinker temperature at the grate cooler: 100℃.

[0035] Technical Specifications: NOx content after flue gas treatment: 32 mg / m³ 3 Lithium conversion rate: 82.3%; Overall energy consumption: 63.6 kgce / ton clinker.

[0036] Example 2: S1, Mixing process: Raw materials and proportions: Low-grade lepidolite: 58.00 t / h, water content 15.00%, Li2O content 2.10%; In the sodium-potassium mixed salt, potassium sulfate (K2SO4): 0.55 t / h, sodium sulfate (Na2SO4): 2.20 t / h; In the calcium salts, calcium sulfate (CaSO4): 10.50 t / h, calcium carbonate (CaCO3): 3.20 t / h; Mixing ratio: Lithium mica: sodium-potassium mixed salt: calcium salt = 80:5:15, wherein in the sodium-potassium mixed salt, sodium sulfate: potassium sulfate = 4:1, and in the calcium salt, calcium sulfate: calcium carbonate = 3.28:1. Mixing time: 10 min.

[0037] S2, Drying process: Rotary kiln flue gas temperature: 380℃; drying time: 30min; Moisture content of the dried mixture: 7.00%; Temperature of the drying exhaust gas: 180℃; Drying flue gas flow rate: 80500 Nm 3 / h.

[0038] S3, roasting and in-situ denitrification: Calcination process: Firing temperature: 1000℃; High-temperature period time: 0.5h; Natural gas addition: 3167 Nm 3 / h (approximately 54.6 Nm) 3 / ton of mixed feed); Mixing rate after drying: 72.50 t / h.

[0039] In-situ denitrification: Ammonia concentration: 20%; Ammonia water usage: 28.42 kg / h (approximately 0.392 kg / ton of mixed material).

[0040] S4, grate cooler cooling: Fresh air volume of the grate cooler: 57300 Nm 3 / h; primary air of rotary kiln: 9500 Nm ³ / h (16.6%); Rotary kiln secondary air: balance (83.4%). Independent recirculation volume: 41500 Nm 3 / h; Clinker temperature at the grate cooler: 80℃.

[0041] Technical Specifications: NOx content after flue gas treatment: 35 mg / m³ 3 Lithium conversion rate: 86.2%; Overall energy consumption: 56.4 kgce / ton clinker (optimal).

[0042] Example 3: S1, Mixing process: Raw materials and proportions: Low-grade lepidolite: 65.00 t / h, water content 15.00%, Li2O content 2.40%; In the sodium-potassium mixed salt, potassium sulfate (K2SO4): 9.00 t / h, sodium sulfate (Na2SO4): 13.00 t / h; In the calcium salts, calcium sulfate (CaSO4): 6.00 t / h, calcium carbonate (CaCO3): 7.00 t / h.

[0043] Mixing ratio: Lithium mica: sodium-potassium mixed salt: calcium salt = 70:20:10, wherein in the sodium-potassium mixed salt, sodium sulfate: potassium sulfate = 1.44:1, and in the calcium salt, calcium sulfate: calcium carbonate = 0.86:1. Mixing time: 20 min.

[0044] S2, Drying process: Drying process: Rotary kiln flue gas temperature: 480℃; drying time: 90min; Moisture content of the dried mixture: 8.00%; Temperature of the drying exhaust gas: 120℃; Drying flue gas flow rate: 125000 Nm 3 / h.

[0045] S3, roasting and in-situ denitrification: Calcination process: Calcination temperature: 850℃; High-temperature period time: 1.5h; Natural gas addition: 3845.43 Nm 3 / h (approximately 59.2 Nm) 3 / ton of mixed feed); Mixing rate after drying: 98.10 t / h.

[0046] In-situ denitrification: Ammonia concentration: 25%; Ammonia dosage: 19.23 kg / h (approximately 0.196 kg / ton of mixed material).

[0047] S4, grate cooler cooling: Fresh air volume of the grate cooler: 81715.49 Nm 3 / h; primary air of rotary kiln: 16343.10 Nm 3 / h (20.0%); Rotary kiln secondary air: balance (80.0%); Independent recirculation volume: 68600 Nm 3 / h; Clinker temperature at the grate cooler: 50℃.

[0048] Technical Specifications: NOx content after flue gas treatment: 28 mg / m³ 3 Lithium conversion rate: 88.6% (highest) Overall energy consumption: 58.8 kgce / ton clinker.

[0049] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for lithium extraction and waste heat recovery from lepidolite by roasting in a triple furnace, characterized in that, Includes the following steps: S1, Mixing: Low-grade lithium mica with an initial water content of 12-20% and a Li2O content of ≤2.5% is mixed with sodium-potassium salt and calcium salt in a mass ratio of (65-80):(3-15):(5-32) and mixed for 10-20 minutes. The sodium-potassium salt is a mixture of sodium sulfate and potassium sulfate in a mass ratio of (3-4):1, and the calcium salt is a mixture of calcium sulfate and calcium carbonate in a mass ratio of (1.8-3.5):

1. S2, Drying: The mixture obtained in S1 is fed into the cylindrical dryer (1), and the hot flue gas of 300~480℃ discharged from the calcining kiln (2) is introduced into the cylindrical dryer (1) to preheat and dry the mixture for 30~90 minutes. The water content of the mixture after drying is controlled to be 3%~8% and the temperature of the drying tail gas is 120~180℃. After the drying tail gas is collected by cyclone dust collector and bag dust collector, it is then desulfurized and defluorinated by lime milk and wet electrostatic precipitator to meet the emission standards. The dust from the dust collection process is returned to the feed port of the cylindrical dryer (1). S3, Calcination and In-situ Denitrification: The dried mixture is fed into the calcination kiln (2), and the calcination transition temperature is controlled at 850~1000℃ and the calcination time is 0.5~2.0h. The calcination kiln head is fed with 40~65Nm of material per ton of mixture. 3 Natural gas is added as fuel, and flue gas returned from the grate cooler (3) is mixed in as combustion air; the combustion air is divided into primary roasting air and secondary roasting air. Primary roasting air accounts for 15% to 20% of the fresh air volume of the grate cooler. After being pressurized by the fan, it is introduced into the burner of the roasting kiln. Secondary roasting air accounts for 80% to 85% of the fresh air volume of the grate cooler. It is directly dispersed into the roasting kiln from the grate cooler. In the in-situ high-temperature section of the roasting kiln (2), ammonia water with a mass concentration of 20% to 25% is atomized with compressed air and sprayed into the ammonia water inlet. The amount of ammonia water added is 0.2 to 0.4 kg per ton of mixed material, so that the nitrogen oxides in the flue gas are reduced to nitrogen at high temperature. S4, Clinker Cooling and Waste Heat Recovery: The roasted clinker is fed into a grate cooler (3), and 750~950 Nm of heat is introduced into the grate cooler (3). 3 / ton of clinker fresh air and 350~600Nm 3 / ton of clinker independent circulating gas cools the clinker to 50~100℃ before discharge; the independent circulating gas recovers waste heat and dust through the second cyclone dust collector (12), waste heat boiler (9), and second bag dust collector (13). The dust and clinker are combined and sent to the subsequent lithium extraction process. The flue gas with a temperature of 120~145℃ after dust collection is returned to the front end of the grate cooler (3) as a circulating cooling medium. S5, Grate cooler air intake control: The grate cooler (3) is equipped with 8 sets of gas inlets along the clinker travel direction, of which the independent circulating gas is introduced into the 1st to 4th sets of inlets as circulating cooling medium, and the fresh air is introduced into the 5th to 8th sets of inlets as fresh cold air.

2. The method for lithium extraction and waste heat recovery from lithium mica using a triple furnace according to claim 1, characterized in that: The discharge port of the cylindrical dryer (1) in S2 is directly connected to the feed port of the roasting kiln (2) in S3. The discharge port of the roasting kiln (2) in S3 is directly sealed and connected to the feed port of the grate cooler (3) in S4. After the mixed material is dried, it directly enters the roasting process. After roasting, the conveyed material directly enters the cooling process. There are no intermediate transfer and open-air cooling steps in the whole process.

3. The method for lithium extraction and waste heat recovery from lithium mica using a triple furnace according to claim 1, characterized in that: The cylindrical dryer (1), the calcining kiln (2), the grate cooler (3) and the connecting pipeline constitute a closed flue gas system. The self-generated flue gas generated by the grate cooler (3) and the self-generated flue gas generated by the calcining kiln (2) both participate in the internal circulation through the flue gas conveying pipeline and the induced draft fan inside the system, and no exhaust port leading to the outside of the system is provided.

4. The method for lithium extraction and waste heat recovery from lithium mica using a triple furnace according to claim 1, characterized in that: In S5, the temperature of the circulating cooling medium introduced into the first to fourth groups of the grate cooler (3) decreases sequentially along the clinker travel direction, and the temperature of the fresh air introduced into the fifth to eighth groups of the grate cooler (3) decreases sequentially along the clinker travel direction, thus reducing the clinker temperature gradient.

5. An apparatus for lithium extraction and waste heat recovery from lithium mica using a triple furnace for roasting in any one of claims 1-4, characterized in that, include: The main body of the triple-fuel furnace, the mixing and feeding unit, the flue gas circulation unit, and the parameter control unit; The main body of the three-unit furnace is composed of a cylindrical dryer (1), a roasting kiln (2) and a grate cooler (3) connected in series. The discharge port of the cylindrical dryer (1) is directly connected to the feed port of the roasting kiln (2), and the discharge port of the roasting kiln (2) is directly connected to the feed port of the grate cooler (3). The mixing and feeding unit includes, in sequence along the conveying direction, a batching silo (4), a first belt conveyor (7), a buffer silo (5), a mixer (6), and a second belt conveyor (8). The discharge port of the mixer (6) is connected to the inlet of the cylindrical dryer (1) through the second belt conveyor (8). The flue gas circulation unit includes an induced draft fan, a flue gas conveying pipeline and a waste heat boiler (9). The induced draft fans are respectively installed at the flue gas connection between the roasting kiln (2) and the cylindrical dryer (1), at the flue gas connection between the grate cooler (3) and the roasting kiln (2), and on the independent circulating flue gas conveying path of the grate cooler (3). The parameter control unit is installed on the main body of the triple-burning furnace and the flue gas circulation unit.

6. The apparatus for lithium extraction and waste heat recovery from lithium mica using a triple furnace as described in claim 5, characterized in that: The flue gas conveying pipeline includes a roasting flue gas conveying pipeline, a grate cooler primary air conveying pipeline, a grate cooler secondary air conveying pipeline, and a grate cooler circulating flue gas conveying pipeline. The roasting flue gas conveying pipeline connects the kiln tail of the roasting kiln (2) to the kiln head of the cylindrical dryer (1). The grate cooler primary air conveying pipeline connects the grate cooler (3) to the burner of the roasting kiln (2). The grate cooler secondary air conveying pipeline directly connects the grate cooler (3) to the roasting kiln (2). Inside, a second cyclone dust collector (12) and a second bag dust collector (13) are provided on the circulating flue gas conveying pipe of the grate cooler. The waste heat boiler (9) is installed on the circulating flue gas conveying pipe of the grate cooler. The waste heat boiler (9) is connected between the second cyclone dust collector (12) and the second bag dust collector (13). The independent circulating gas of the grate cooler (3) flows back to the front end of the grate cooler (3) through the circulating flue gas conveying pipe of the grate cooler. The discharge port of the second bag dust collector (13) on the circulating flue gas conveying pipe of the grate cooler is equipped with a powder conveying device, which is connected to the clinker discharge port of the grate cooler (3).

7. The apparatus for lithium extraction and waste heat recovery from lithium mica using a triple furnace as described in claim 6, characterized in that: The exhaust port of the cylindrical dryer (1) is connected in series with a first cyclone dust collector (10), a first bag dust collector (11), a lime milk desulfurization and defluorination device (14), and a wet electrostatic precipitator (15) via a pipeline. The calcining kiln (2) is connected to an ammonia water addition device, which includes an ammonia water storage tank, a metering pump, a compressed air atomizing device, and an ammonia water spray gun. The ammonia water spray gun is located in the in-situ high-temperature section of the calcining kiln (2) and is connected to the interior of the calcining kiln (2) and the compressed air atomizing device. The metering pump is connected to the ammonia water storage tank and the compressed air atomizing device.

8. The apparatus for lithium extraction and waste heat recovery from lithium mica using a triple furnace as described in claim 7, characterized in that: The grate cooler (3) is provided with 8 sets of gas inlets, of which the first 4 to 5 gas inlets are circulating cooling medium inlet groups, which are connected to the circulating flue gas conveying pipe of the grate cooler, and the last 3 to 4 gas inlets are fresh cold air inlet groups, which are connected to the fresh air conveying pipe on the grate cooler (3).

9. The apparatus for lithium extraction and waste heat recovery from lithium mica using a triple furnace as described in claim 8, characterized in that: The parameter control unit includes a temperature sensor, a flow sensor, and a metering controller. The temperature sensor is installed in the cylindrical dryer (1), the calcining kiln (2), the grate cooler (3), and each flue gas conveying pipeline. The flow sensor is installed in the natural gas conveying pipeline, the ammonia water adding pipeline, the fresh air conveying pipeline, and the flue gas conveying pipeline. The metering controller is electrically connected to the temperature sensor, the flow sensor, the natural gas valve, the ammonia water metering pump, the fan, and the grate cooler inlet valve.

10. The apparatus for lithium extraction and waste heat recovery from lithium mica using a triple furnace as described in claim 5, characterized in that: The cylindrical dryer (1), the calcining kiln (2), and the grate cooler (3) are arranged in a stepped manner. The installation height of the cylindrical dryer (1) is higher than that of the calcining kiln (2), and the installation height of the calcining kiln (2) is higher than that of the grate cooler (3).

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