Multi-stage cooling crystallization device for lithium hydroxide solution and working method of multi-stage cooling crystallization device

Abstract

The invention relates to the technical field of lithium compound purification and crystallization, in particular to a lithium hydroxide solution multi-stage cooling crystallization device and a working method thereof.The lithium hydroxide solution multi-stage cooling crystallization device comprises a raw material liquid storage tank, a concentrator, a filter, a first-stage crystallizer, a second-stage crystallizer, a third-stage crystallizer, a centrifugal separator and a drying machine; the first-stage crystallizer, the second-stage crystallizer and the third-stage crystallizer are connected in series through a delivery pump, the third-stage crystallizer comprises a kettle body, a jacket is arranged in the kettle body, a feeding hole is formed in the top of the kettle body, and a discharging hole is formed in the bottom of the kettle body; by means of the unique design of the sealing cover, the discharging inner cavity and the built-in discharging channel, fine crystals scraped on the inner wall are collected and guided out of the kettle at the moment of generation. The problem of secondary pollution caused by a traditional wall scraping mechanism is thoroughly solved, secondary nucleation induced by fine grains is avoided from the source, and the method is the key for obtaining products with narrow particle size distribution.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium compound purification and crystallization, and particularly relates to a multi-stage cooling crystallization device for lithium hydroxide solution and a working method thereof. BACKGROUND

[0002] Lithium hydroxide is a key lithium source for preparing positive electrode materials (such as lithium iron phosphate, lithium cobaltate, lithium nickel cobalt manganese oxide, etc.) of lithium batteries, and its purity and crystal morphology have an important influence on the performance of the final battery product. In the production of lithium hydroxide, lithium carbonate causticization or lithium sulfate causticization is usually used to obtain lithium hydroxide solution, and then single water lithium hydroxide crystals are obtained through evaporation, concentration, crystallization, separation and drying processes.

[0003] Crystallization is a key process that determines the particle size, morphology and purity of the product. At present, the method of multi-stage cooling crystallization is mainly used in industry, and by gradiently reducing the temperature, the nucleation and growth of the crystals are controlled in order to obtain larger and uniform crystals. However, the existing crystallization devices have the following common problems:

[0004] Severe scarring of the inner wall: during the crystallization process, due to the non-uniformity of the solution supersaturation and temperature distribution, crystals are prone to nucleate and grow on the cold surfaces such as the inner wall of the crystallization kettle and the stirring shaft, forming hard "crystal scars". These scars not only occupy the effective volume and reduce the heat transfer efficiency, but also become the source of irregular crystals, destroying the uniformity of the product particle size distribution;

[0005] Secondary contamination problem of scraped crystals: although some devices are equipped with a wall scraping mechanism, the small crystals scraped off directly fall into the kettle crystal slurry. These small crystals can act as crystal nuclei in the solution, inducing secondary nucleation, resulting in a large number of fine crystals in the product, making the crystal particle size distribution wider, and seriously affecting the uniformity of the product and the subsequent application performance;

[0006] Accumulation of materials at the bottom and difficulty in discharging: the crystals deposited at the bottom of the kettle are prone to harden, and the traditional stirrer cannot effectively lift them and push them to the discharge port, often causing poor discharge or even blockage, which requires manual cleaning, affecting the continuity of production;

[0007] Insufficient process control precision: the stirring intensity of the existing devices is usually fixed, and it is difficult to dynamically adjust the mixing intensity according to the needs of different stages (nucleation period, growth period, crystal growth period) of the crystallization process, which is not conducive to the accurate control of the supersaturation. SUMMARY

[0008] The problem solved by this invention is to provide a multi-stage cooling crystallization device for lithium hydroxide solution and its working method. The device achieves particle size optimization through three-stage series crystallization and innovatively integrates an integrated "wall scraping-collection-discharge" system in the final crystallizer. This system can automatically remove crystal scars on the inner wall online and remove the scraped fine crystals from the crystallization system in real time, thereby effectively preventing secondary nucleation and obtaining a high-quality product with uniform particle size.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A multi-stage cooling crystallization device for lithium hydroxide solution includes a raw material storage tank, a concentrator, a filter, a primary crystallizer, a secondary crystallizer, a tertiary crystallizer, a centrifuge, and a dryer. The primary, secondary, and tertiary crystallizers are connected in series via a transfer pump. The tertiary crystallizer includes a vessel body with a jacket. The vessel body has an inlet at the top and an outlet at the bottom. A polygonal shaft is rotatably mounted inside the vessel body, and a rotating shaft is slidably fitted onto the bottom of the polygonal shaft. Furthermore, the diameter of the rotating shaft is adapted to the inner diameter of the discharge port. Several stirring blades are provided on the outer side of the rotating shaft. Arm sleeves are installed at the top and bottom of the side wall of the rotating shaft. Telescopic arms are elastically installed inside the arm sleeves. A sealing cover is installed at the end of the telescopic arm. A scraper is installed inside the sealing cover. A discharge cavity is opened inside the sealing cover, and the discharge cavity is connected to the discharge port opened at the bottom of the rotating shaft. A bottom scraper is installed on the side wall of the rotating shaft, and the curvature of the bottom scraper is adapted to the curvature of the bottom wall inside the vessel. A rubber sleeve is installed on the bottom scraper.

[0011] Preferably, the bottom of the enclosure has a material hole, which is connected to the inner support tube. The bottom side wall of the rotating shaft is fitted with a sleeve that communicates with the discharge port, and the sleeve is slidably fitted on the outside of the inner support tube.

[0012] Preferably, a support frame is installed on the vessel body, a speed reducer is installed on the support frame, and the output end of the speed reducer is connected to a polygonal shaft, while the input end of the speed reducer is connected to the output end of a motor.

[0013] Preferably, a first support plate is mounted on the polygonal shaft, a second support plate is mounted on the rotating shaft, and a lifting frame is mounted on the bearing of the second support plate.

[0014] Preferably, pneumatic cylinders are symmetrically installed on the top of the vessel body, and the telescopic ends of the pneumatic cylinders are connected to the lifting frame.

[0015] Preferably, a lifting arm that penetrates the second support plate and the arm sleeve is installed on the first support plate, and the bottom end of the lifting arm is slidably connected to the guide sleeve on the sleeve.

[0016] Preferably, the lifting arm is provided with a triangular guide block, and the triangular guide block is provided with a first inclined surface.

[0017] Preferably, an inner groove is provided between the arm sleeve and the telescopic arm, and a spring is installed in the inner groove.

[0018] Preferably, the arm sleeve has a guide groove, and a second inclined surface is provided in the guide groove. The triangular guide block is located in the guide groove, and the first inclined surface and the second inclined surface slide in contact.

[0019] A method for operating a multi-stage cooling crystallization apparatus for lithium hydroxide solution, the specific operating steps of which are as follows:

[0020] Step 1: The lithium hydroxide solution from the upstream purification process is stored in the raw material storage tank. The dilute solution is concentrated to saturation through a concentrator. A filter removes tiny insoluble particles that may become impurity crystal nuclei from the concentrate. The filtered lithium hydroxide solution is added to the primary crystallizer. The temperature in the primary crystallizer is reduced from 90℃ to 70℃ to induce the growth of a large number of crystals on the seed surface. Then, the lithium hydroxide solution and crystals in the primary crystallizer are added to the secondary crystallizer, where the temperature is reduced from 70℃ to 45℃, which is the main stage of crystal volume increase. The lithium hydroxide solution and crystals in the secondary crystallizer are added to the tertiary crystallizer, where the temperature is reduced from 45℃ to 20-25℃ to increase the average particle size of the crystals and narrow the particle size distribution. A centrifuge collects the final crystal slurry from the tertiary crystallizer. Through the centrifugal force of high-speed rotation, the crystals are completely separated from the mother liquor. The washed wet crystals are dried by a dryer to obtain the lithium hydroxide monohydrate product.

[0021] Step Two: The motor operates, and the speed reducer drives the polygonal shaft and rotating shaft to rotate. The rotating stirring blades on the rotating shaft stir and mix the lithium hydroxide solution, accelerating its crystallization. During crystallization, the pneumatic cylinder lowers the lifting frame. At this time, the guide groove of the telescopic arm moves down along the first inclined surface of the triangular guide block until the guide groove reaches the lifting arm. The compressed spring in the inner groove drives the telescopic arm to extend from the arm sleeve until the scraper and the top and bottom of the sealing cover are in contact with the inner wall of the reactor. At this point, the bottom end of the rotating shaft is inserted into the discharge port, and the bottom scraper and rubber sleeve are not in contact with the bottom wall of the reactor. The discharge port and the bottom end of the rotating shaft are connected by a sealing ring. Opening the valve on the discharge port allows the scraper to scrape off the fine crystals adhering to the inner wall of the reactor as the rotating shaft rotates, allowing them to enter the discharge cavity. The material passes through the discharge port, sleeve, and inner support tube, and is discharged from the outlet. The outlet valve is closed, and the discharged lithium hydroxide solution is heated and dissolved again before being added to the primary crystallizer. When the scraper rotates 360° inside the vessel, the pneumatic cylinder contracts, causing the lifting frame and rotating shaft to move upward. The second inclined plane moves upward along the first inclined plane, retracting the lifting arm into the guide sleeve and compressing the spring. At this time, the scraper separates from the inner wall of the vessel and continues the crystallization process. When crystallization is complete, the rotating shaft moves downward again under the action of the pneumatic cylinder. This time, it moves downward until the rubber sleeve of the bottom scraper contacts the bottom wall of the vessel. As the rotating shaft rotates, the bottom scraper rotates 360° inside the vessel, scraping off the crystals inside the vessel. Then the rotating shaft moves upward, opening the outlet valve to discharge the remaining lithium hydroxide solution and crystals.

[0022] The beneficial effects of this invention are:

[0023] It achieves instant isolation and removal of scraped crystals: Through the unique design of the closed cover, discharge cavity and built-in discharge channel, the fine crystals scraped off the inner wall are collected and discharged out of the vessel at the moment of generation, which completely solves the problem of "secondary pollution" caused by traditional wall scraping mechanism and avoids secondary nucleation induced by fine crystals from the source, which is the key to obtaining products with narrow particle size distribution.

[0024] Online automatic cleaning ensures continuous operation: The retractable scraper mechanism can automatically perform wall scraping operations according to preset programs or sensor signals without stopping the machine. This achieves online and automatic cleaning of internal wall scale, maintains the cleanliness of the heat exchange surface and the stability of the effective volume, and improves production efficiency and continuity.

[0025] Preventing bottom caking and ensuring smooth discharge: The combination of flexible bottom scraper and rubber sleeve can effectively scrape up the crystals caking on the bottom of the vessel and push them toward the discharge port, solving the problem of difficult discharge and reducing manual cleaning;

[0026] Three-stage gradient crystallization optimizes product particle size: precise gradient cooling is implemented through a series of three-stage crystallizers, which effectively controls the release of supersaturation, promotes the orderly growth of crystals, and is conducive to producing lithium hydroxide crystals with larger particle size and uniform distribution.

[0027] Compact structure and high degree of automation: The functions of scraping, collecting and discharging are highly integrated into the stirring system, and intelligent control is achieved through pneumatic cylinders and mechanical linkage mechanisms, which improves the automation level and reliability of the whole set of equipment. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the three-stage crystallizer structure of the present invention;

[0029] Figure 2 This is a schematic diagram of the internal structure of the three-stage crystallizer of the present invention;

[0030] Figure 3 This is a cross-sectional view of the three-stage crystallizer of the present invention;

[0031] Figure 4 This is a cross-sectional view of the arm sleeve and telescopic arm of the present invention;

[0032] Figure 5 This is a magnified view of region A in the present invention 4.

[0033] Legend:

[0034] 1. Kettle body; 2. Jacket; 3. Inlet; 4. Outlet; 5. Polygonal shaft; 6. Rotating shaft; 7. Stirring blades; 8. Arm sleeve; 9. Telescopic arm; 10. Enclosed cover; 11. Scraper; 12. Discharge cavity; 13. Discharge port; 14. Sleeve; 15. Support inner tube; 16. Bottom scraper; 17. Rubber sleeve; 18. Support frame; 19. Reducer; 20. Motor; 21. First support plate; 22. Pneumatic cylinder; 23. Lifting frame; 24. Second support plate; 25. Lifting arm; 26. Guide sleeve; 27. Triangular guide block; 28. First inclined surface; 29. ​​Inner groove; 30. Spring; 31. Guide groove; 32. Second inclined surface. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Specific implementation examples are given below.

[0037] See Figures 1-5A multi-stage cooling crystallization device for lithium hydroxide solution includes a raw material storage tank, a concentrator, a filter, a primary crystallizer, a secondary crystallizer, a tertiary crystallizer, a centrifuge, and a dryer, wherein the primary crystallizer, the secondary crystallizer, and the tertiary crystallizer are connected in series via a transfer pump.

[0038] The three-stage crystallizer includes a vessel body 1, with a jacket 2 inside the vessel body 1 for introducing cooling medium to provide a controllable temperature environment for the crystallization process. A feed inlet 3 is located at the top of the vessel body 1, and a discharge outlet 4 is located at the bottom. A polygonal shaft 5 is rotatably mounted inside the vessel body 1, and a rotating shaft 6 is slidably fitted onto the bottom of the polygonal shaft 5. The diameter of the rotating shaft 6 is adapted to the inner diameter of the discharge outlet 4. A support frame 18 is mounted on the vessel body 1, and a reducer 19 is mounted on the support frame 18. The output end of the reducer 19 is connected to the polygonal shaft 5, and the input end of the reducer 19 is connected to the output end of a motor 20. Several [unclear - possibly referring to a specific type of device] are arranged on the outer side of the rotating shaft 6. The stirring blade 7, motor 20, and speed reducer 19 provide stable and adjustable rotational power to drive the stirring blade 7. Arm sleeves 8 are installed at the top and bottom of the side wall of the rotating shaft 6. Telescopic arms 9 are elastically installed inside the arm sleeves 8. A closed cover 10 is installed at the end of the telescopic arm 9. A scraper 11 is installed inside the closed cover 10. A discharge cavity 12 is opened inside the closed cover 10, and the discharge cavity 12 communicates with a discharge port 13 at the bottom of the rotating shaft 6. A material hole is opened at the bottom of the closed cover 10, and the material hole is connected to the supporting inner tube 15. A material port is installed on the bottom side wall of the rotating shaft 6. A connecting sleeve 14 is slidably fitted onto the outside of the supporting inner tube 15. A bottom scraper 16 is installed on the side wall of the rotating shaft 6, and the curvature of the bottom scraper 16 is adapted to the curvature of the inner bottom wall of the vessel body 1. A rubber sleeve 17 is installed on the bottom scraper 16. The arm sleeve 8, the sealing cover 10, and the scraper 11 constitute a telescopic wall scraping mechanism. The scraper 11 is used to scrape off crystal scars on the inner wall. The sealing cover 10 is an arc-shaped cover, and its inner wall is fixedly connected to the scraper 11. Its outer wall maintains a small gap of 0.5-2mm with the inner wall of the vessel body 1. The scraper 11 protrudes slightly from the outer wall of the sealing cover 10 to scrape off crystal scars. The scraped crystals are collected in the sealing cover. Guided by 10, the material falls into the discharge cavity 12. Through the connection of the material hole, the supporting inner tube 15, and the sleeve 14, the material is introduced into the discharge port 13 inside the rotating shaft 6. This realizes the immediate and closed collection and discharge of the scraped crystals, avoiding the scraped fine crystals from falling back into the main crystal slurry and causing secondary nucleation. This is a key innovation to ensure the uniformity of product particle size. The bottom scraper 16 and the rubber sleeve 17 are installed at the lower part of the rotating shaft 6. The curvature of the bottom scraper 16 matches the bottom of the vessel, and the rubber sleeve 17 provides flexible contact. When the rotating shaft 6 descends to a specific position, the bottom scraper 16 can scrape the crystals deposited at the bottom of the vessel to prevent caking and ensure smooth and thorough discharge.

[0039] A first support plate 21 is mounted on the polygonal shaft 5, and a second support plate 24 is mounted on the rotating shaft 6. A lifting frame 23 is mounted on the bearing of the second support plate 24. Pneumatic cylinders 22 are symmetrically mounted on the top of the vessel body 1, and the telescopic ends of the pneumatic cylinders 22 are connected to the lifting frame 23. The lifting frame 23 is connected to the second support plate 24 through bearings, allowing the second support plate 24 and the rotating shaft 6 to rotate freely relative to the lifting frame 23. The lifting frame 23 is driven by the pneumatic cylinders 22 to lift as a whole, thereby driving the second support plate 24, the rotating shaft 6, and the components mounted on it to lift synchronously. A lifting arm 25 is mounted on the first support plate 21, penetrating the second support plate 24 and the arm sleeve 8. The bottom end of the lifting arm 25 is slidably connected to the guide sleeve 26 on the sleeve 14. A triangular guide block 27 is provided on the lifting arm 25, and a first inclined surface 28 is provided on the triangular guide block 27. An inner groove 29 is opened between the arm sleeve 8 and the telescopic arm 9, and a spring 30 is installed in the inner groove 29. The arm sleeve 8 is provided with a guide groove 31, and a second inclined surface 32 is provided in the guide groove 31. The triangular guide block 27 is located in the guide groove 31, and the first inclined surface 28 and the second inclined surface 32 slide in contact. The rotating shaft 6 is in a high position, and the triangular guide block 27 is located in the upper position in the guide groove 31. By pressing the first inclined surface 28 and the second inclined surface 32 together, the elastic force of the spring 30 is overcome, and the telescopic arm 9 and the scraper 11 are retracted. The pneumatic cylinder 22 pushes the rotating shaft 6 to descend. Since the lifting arm 25 is fixed, the arm sleeve 8 moves down relative to it. The guide groove 31 slides along the triangular guide block 27. The spring 30 is released, pushing the telescopic arm 9 to extend radially, so that the scraper 11 is close to the vessel wall. This process realizes the mechanical automatic conversion from lifting motion to radial telescopic motion. The rotating shaft 6 rotates, the scraper 11 works, and the scraped material is discharged through the built-in channel. The pneumatic cylinder 22 lifts the rotating shaft 6, and the guide groove 31 moves in the opposite direction along the inclined surface of the triangular guide block 27, forcibly pulling the telescopic arm 9 back, and the scraper 11 is separated from the vessel wall.

[0040] Working principle:

[0041] The lithium hydroxide solution from the upstream purification process is stored in the raw material storage tank. The dilute solution is concentrated to saturation concentration by a concentrator. A filter removes small insoluble particles that may become impurity crystal nuclei from the concentrate. The filtered lithium hydroxide solution is added to the primary crystallizer, where the temperature is lowered from 90℃ to 70℃ to induce the growth of a large number of crystals on the seed surface. Then, the lithium hydroxide solution and crystals in the primary crystallizer are added to the secondary crystallizer, where the temperature is lowered from 70℃ to 45℃, which is the main stage of crystal volume increase. The lithium hydroxide solution and crystals in the secondary crystallizer are added to the tertiary crystallizer, where the temperature is lowered from 45℃ to 20-25℃ to increase the average particle size of the crystals and narrow the particle size distribution. A centrifuge collects the final crystal slurry from the tertiary crystallizer. Through the centrifugal force of high-speed rotation, the crystals are completely separated from the mother liquor. The washed wet crystals are dried by a dryer to obtain the lithium hydroxide monohydrate product.

[0042] The motor 20 operates, and the speed reducer 19 drives the polygonal shaft 5 and the rotating shaft 6 to rotate. The rotating stirring blades 7 on the rotating shaft 6 stir and mix the lithium hydroxide solution, accelerating the crystallization of the lithium hydroxide solution. During the crystallization process, the lifting frame 23 is lowered by the pneumatic cylinder 22. At this time, the guide groove 31 of the telescopic arm 9 moves down along the first inclined surface 28 of the triangular guide block 27 until the guide groove 31 moves to the lifting arm 25. The compressed spring 30 in the inner groove 29 drives the telescopic arm 9 to extend out of the arm sleeve 8 until the top and bottom of the scraper 11 and the sealing cover 10 are in contact with the inner wall of the vessel body 1. At this time, the bottom end of the rotating shaft 6 is inserted into the discharge port 4, and the bottom scraper 16 and the rubber sleeve 17 are not in contact with the bottom wall of the vessel body 1. The discharge port 4 and the bottom end of the rotating shaft 6 are connected by a sealing ring. The valve on the discharge port 4 is opened. As the rotating shaft 6 rotates, the scraper 11 scrapes off the fine crystals adhering to the inner wall of the vessel body 1 and enters the discharge cavity 12. The lithium hydroxide solution enters the discharge port 13 through the material hole, sleeve 14, and support inner tube 15, and is discharged from the outlet 4. The valve of the outlet 4 is closed. The discharged lithium hydroxide solution is heated and dissolved again before being added to the primary crystallizer. When the scraper 11 rotates 360° inside the vessel 1, the pneumatic cylinder 22 contracts, driving the lifting frame 23 and the rotating shaft 6 to move upward. The second inclined surface 32 moves upward along the first inclined surface 28, retracting the lifting arm 25 into the guide sleeve 26, while compressing the spring 30. At this time, the scraper 11 separates from the inner wall of the vessel 1, and the crystallization work continues. When the crystallization is completed, the rotating shaft 6 moves downward again under the action of the pneumatic cylinder 22. This time, it moves downward until the rubber sleeve 17 of the bottom scraper 16 contacts the bottom wall of the vessel 1. As the rotating shaft 6 rotates, the bottom scraper 16 rotates 360° inside the vessel 1, scraping off the crystals inside the vessel 1. Then the rotating shaft 6 moves upward, opening the valve of the outlet 4 to discharge the remaining lithium hydroxide solution and crystals.

[0043] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A multi-stage cooling crystallization apparatus for lithium hydroxide solution, characterized in that, The system includes a raw material storage tank, a concentrator, a filter, a primary crystallizer, a secondary crystallizer, a tertiary crystallizer, a centrifuge, and a dryer. The primary, secondary, and tertiary crystallizers are connected in series via a transfer pump. The tertiary crystallizer includes a vessel body (1), a jacket (2) inside the vessel body (1), a feed inlet (3) at the top of the vessel body (1), and a discharge outlet (4) at the bottom of the vessel body (1). A polygonal shaft (5) is rotatably installed inside the vessel body (1), and a rotating shaft (6) is slidably fitted at the bottom of the polygonal shaft (5). The diameter of the rotating shaft (6) is adapted to the inner diameter of the discharge outlet (4). Several... A stirring blade (7) is installed on the top and bottom of the side wall of the rotating shaft (6). A telescopic arm (9) is elastically installed inside the arm sleeve (8). A closed cover (10) is installed at the end of the telescopic arm (9). A scraper (11) is installed inside the closed cover (10). A discharge cavity (12) is opened inside the closed cover (10), and the discharge cavity (12) is connected to the discharge port (13) opened at the bottom of the rotating shaft (6). A bottom scraper (16) is installed on the side wall of the rotating shaft (6), and the curvature of the bottom scraper (16) is adapted to the curvature of the bottom wall inside the vessel body (1). A rubber sleeve (17) is installed on the bottom scraper (16).

2. The multi-stage cooling crystallization device for lithium hydroxide solution according to claim 1, characterized in that, The bottom of the enclosure (10) is provided with a material hole, which is connected to the inner support tube (15). The bottom side wall of the rotating shaft (6) is equipped with a sleeve (14) that communicates with the discharge port (13), and the sleeve (14) is slidably fitted on the outside of the inner support tube (15).

3. The multi-stage cooling crystallization device for lithium hydroxide solution according to claim 2, characterized in that, A support frame (18) is installed on the vessel body (1), and a speed reducer (19) is installed on the support frame (18). The output end of the speed reducer (19) is connected to the polygonal shaft (5), and the input end of the speed reducer (19) is connected to the output end of the motor (20).

4. The multi-stage cooling crystallization device for lithium hydroxide solution according to claim 3, characterized in that, A first support plate (21) is installed on the polygonal shaft (5), a second support plate (24) is installed on the rotating shaft (6), and a lifting frame (23) is installed on the bearing of the second support plate (24).

5. The multi-stage cooling crystallization device for lithium hydroxide solution according to claim 4, characterized in that, The top of the vessel body (1) is symmetrically equipped with pneumatic cylinders (22), and the telescopic end of the pneumatic cylinders (22) is connected to the lifting frame (23).

6. The multi-stage cooling crystallization device for lithium hydroxide solution according to claim 5, characterized in that, A lifting arm (25) that passes through the second support plate (24) and the arm sleeve (8) is installed on the first support plate (21), and the bottom end of the lifting arm (25) is slidably connected to the guide sleeve (26) on the sleeve (14).

7. The multi-stage cooling crystallization device for lithium hydroxide solution according to claim 6, characterized in that, The lifting arm (25) is provided with a triangular guide block (27), and the triangular guide block (27) is provided with a first inclined surface (28).

8. The multi-stage cooling crystallization apparatus for lithium hydroxide solution according to claim 7, characterized in that, An inner groove (29) is provided between the arm sleeve (8) and the telescopic arm (9), and a spring (30) is installed in the inner groove (29).

9. The multi-stage cooling crystallization device for lithium hydroxide solution according to claim 8, characterized in that, The arm sleeve (8) is provided with a guide groove (31) and a second inclined surface (32) is provided in the guide groove (31). The triangular guide block (27) is located in the guide groove (31) and the first inclined surface (28) and the second inclined surface (32) slide in contact.

10. The operating method of the multi-stage cooling crystallization device for lithium hydroxide solution according to claim 9, characterized in that, The specific operational steps of the described working method are as follows: Step 1: The lithium hydroxide solution from the upstream purification process is stored in the raw material storage tank. The dilute solution is concentrated to saturation through a concentrator. A filter removes tiny insoluble particles that may become impurity crystal nuclei from the concentrate. The filtered lithium hydroxide solution is added to the primary crystallizer. The temperature in the primary crystallizer is reduced from 90℃ to 70℃ to induce the growth of a large number of crystals on the seed surface. Then, the lithium hydroxide solution and crystals in the primary crystallizer are added to the secondary crystallizer, where the temperature is reduced from 70℃ to 45℃, which is the main stage of crystal volume increase. The lithium hydroxide solution and crystals in the secondary crystallizer are added to the tertiary crystallizer, where the temperature is reduced from 45℃ to 20-25℃ to increase the average particle size of the crystals and narrow the particle size distribution. A centrifuge collects the final crystal slurry from the tertiary crystallizer. Through the centrifugal force of high-speed rotation, the crystals are completely separated from the mother liquor. The washed wet crystals are dried by a dryer to obtain the lithium hydroxide monohydrate product. Step 2: The motor (20) operates, and the speed reducer (19) drives the polygonal shaft (5) and the rotating shaft (6) to rotate. The rotating stirring blades (7) on the rotating shaft (6) stir and mix the lithium hydroxide solution, accelerating the crystallization of the lithium hydroxide solution. During the crystallization process, the lifting frame (23) is lowered by the pneumatic cylinder (22). At this time, the first inclined surface (28) along the triangular guide block (27) on the guide groove (31) of the telescopic arm (9) moves down until the guide groove (31) moves to the lifting arm (25). The pressure inside the inner groove (29) is reduced. The retracting spring (30) drives the telescopic arm (9) to extend out of the arm sleeve (8) until the top and bottom of the scraper (11) and the sealing cover (10) are in contact with the inner wall of the vessel body (1). At this time, the bottom end of the rotating shaft (6) is inserted into the discharge port (4), and the bottom scraper (16) and the rubber sleeve (17) are not in contact with the bottom wall of the vessel body (1). The discharge port (4) and the bottom end of the rotating shaft (6) are connected by a sealing ring. When the valve on the discharge port (4) is opened, as the rotating shaft (6) rotates, the scraper (11) scrapes off the fine crystals adhering to the inner wall of the vessel body (1) and they enter the discharge port. Inside the cavity (12), the material passes through the material hole, sleeve (14), and support inner tube (15) into the discharge port (13), and is discharged from the outlet (4). The valve of the outlet (4) is closed, and the discharged lithium hydroxide solution is heated and dissolved again before being added to the primary crystallizer. When the scraper (11) rotates 360° inside the vessel (1), the pneumatic cylinder (22) contracts, driving the lifting frame (23) and the rotating shaft (6) to move upward. The second inclined plane (32) moves upward along the first inclined plane (28), retracting the lifting arm (25) into the guide sleeve (26), and simultaneously stimulating the spring. (30) Compression is performed. At this time, the scraper (11) separates from the inner wall of the vessel (1) and continues the crystallization process. After the crystallization is completed, the rotating shaft (6) moves down again under the action of the pneumatic cylinder (22). This time, it moves down until the rubber sleeve (17) of the bottom scraper (16) contacts the bottom wall of the vessel (1). As the rotating shaft (6) rotates, the bottom scraper (16) rotates 360° inside the vessel (1) and scrapes off the crystals inside the vessel (1). Then the rotating shaft (6) moves up and opens the valve of the discharge port (4) to discharge the remaining lithium hydroxide solution and crystals.

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