Fractional freezing denitration device of lithium hydroxide production line

Abstract

This utility model discloses a staged cryogenic denitrification device for a lithium hydroxide production line, belonging to the field of lithium battery cathode material production technology. It includes a primary precooler, a secondary precooler, a primary cryogenic crystallization unit, an intermediate separation unit, a secondary cryogenic crystallization unit, and a fine separation unit connected in sequence. The primary cryogenic crystallization unit achieves initial separation through a primary cryogenic crystallizer, a cryogenic thickening tank, and a two-stage pusher centrifuge. The secondary cryogenic crystallization unit performs deep separation through a secondary cryogenic crystallizer connected to a three-phase horizontal screw discharge centrifuge. The solid phase from the three-phase centrifuge returns to the thickening tank, the turbid liquid flows back to the centrifugal mother liquor tank, and the clear liquid enters the cryogenic clear liquid tank to provide a cold source for the secondary precooler. This device adopts a staged freezing and material circulation method, significantly improving the separation efficiency of sodium sulfate, reducing the system's cold load, and minimizing lithium loss, offering advantages in low investment and operating costs.

Description

Technical Field

[0001] This utility model relates to a cryogenic denitrification device, and more particularly to a graded cryogenic denitrification device for a lithium hydroxide production line, belonging to the field of lithium battery cathode material production technology. Background Technology

[0002] Driven by the rapid development of the new energy electric vehicle and lithium-ion smart device industries in recent years, global demand for lithium resources has exploded. As a key lithium source for high-nickel ternary lithium battery cathode materials, lithium hydroxide can significantly improve the energy density and stability of batteries, making it an essential material for high-end electric vehicles. With the accelerating penetration rate of the global electric vehicle market, its demand continues to grow rigidly.

[0003] The main processes in a lithium hydroxide production line include: 1. Raw material preparation, 2. Acid leaching, 3. Alkali conversion, 4. Freezing, 5. Crude product evaporation, 6. Resolution, 7. Refined product evaporation, and 8. Separation, drying, crushing, and packaging. The lithium hydroxide solution produced in the alkali conversion process contains a large amount of sodium sulfate. To obtain a higher purity lithium hydroxide product, a freezing process is usually used to separate the sodium sulfate from the solution in the form of sodium sulfate (Glauber's salt).

[0004] Patent CN 208711098U discloses a continuous freezing crystallization device for lithium hydroxide sodium sulfate, comprising a first crystallizer, a second crystallizer, and multiple external coolers. The first and second crystallizers are respectively equipped with a material circulation port, a feed port, and a discharge port. The discharge port of the first crystallizer is connected to the feed port of the second crystallizer. The first and second crystallizers are also connected to two external coolers via material circulation ports. This technical solution has the following drawbacks: 1. Incomplete separation of sodium sulfate, resulting in a high solid content in the discharged clear liquid; 2. High lithium content in the sodium sulfate, leading to significant lithium loss and resource waste; 3. High cooling load, resulting in high investment costs for equipment such as the refrigeration unit; 4. High operating costs (electricity consumption).

[0005] Therefore, there is an urgent need for a cryogenic denitrification method that achieves thorough separation with low investment and operating costs. Utility Model Content

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, and such simplifications or omissions should not be construed as limiting the scope of the present invention.

[0007] In view of the problems existing in the above and / or prior art, this utility model is proposed.

[0008] The purpose of this invention is to overcome the problems existing in the prior art and provide a staged freezing denitrification device for a lithium hydroxide production line. Through two-stage precooling, two-stage freezing crystallization and the combination of different types of centrifuges, it achieves efficient and low-energy separation of sodium sulfate, with low investment and operating costs.

[0009] To solve the above technical problems, this utility model provides a staged freezing denitrification device for a lithium hydroxide production line, including a lithium hydroxide raw liquid pipe. The outlet of the lithium hydroxide raw liquid pipe is connected in sequence to the tube side of the primary precooler and the secondary precooler. The tube side outlet of the secondary precooler is connected to the top inlet of the primary freezing crystallizer. The circulating liquid outlet of the primary freezing crystallizer is connected to the circulating liquid inlet of the primary freezing crystallizer via the tube side of the primary feed liquid circulation pump and the primary freezing heat exchanger. The bottom crystal slurry outlet of the first-stage cryogenic crystallizer is connected to the inlet of the cryogenic thickening tank via the first-stage cryogenic crystal slurry pump. The bottom outlet of the cryogenic thickening tank is connected to the inlet of the two-stage pusher centrifuge. The solid phase outlet of the two-stage pusher centrifuge is connected to the sodium sulfate chute, and the liquid phase outlet is connected to the inlet of the centrifugal mother liquor tank. The bottom outlet of the centrifugal mother liquor tank is connected to the top inlet of the secondary cryogenic crystallizer via a centrifugal mother liquor pump. The circulating liquid outlet of the secondary cryogenic crystallizer is connected to the circulating liquid inlet of the secondary cryogenic crystallizer via a secondary feed liquid circulation pump and the tube side of the secondary cryogenic heat exchanger. The bottom crystal slurry outlet of the secondary cryogenic crystallizer is connected to the inlet of the three-phase horizontal screw discharge centrifuge via a secondary cryogenic crystal slurry pump. The solid phase outlet of the three-phase horizontal screw discharge centrifuge is connected to the cryogenic thickening tank; the turbid liquid outlet is connected to the centrifugal mother liquor tank; and the clear liquid outlet is connected to the cryogenic clear liquid tank. The bottom outlet of the cryogenic clear liquid tank is connected to the shell side of the secondary precooler via a cryogenic clear liquid pump.

[0010] Furthermore, the upper overflow port of the frozen thickening tank is also connected to the inlet of the centrifugal mother liquor tank through the frozen thickening tank overflow pipe.

[0011] Furthermore, the shell side of the primary precooler is connected to the circulating cooling water pipeline.

[0012] Compared with the prior art, the advantages or beneficial effects of this utility model include at least the following: 1. This device employs a two-stage precooling process using circulating cooling water and chilled liquid, significantly reducing the refrigeration load on the primary chiller unit. Simultaneously, it raises the discharge temperature, reducing steam preheating consumption during the downstream evaporation process. This reduces initial equipment investment, lowers the equipment footprint, improves the overall production system's operational efficiency and stability, and lowers operating costs.

[0013] 2. This device adopts a staged denitrification method. After the first-stage freezing crystallization, a two-stage pusher centrifuge is set up to separate most of the sodium sulfate before sending it to the second-stage freezing unit. This greatly reduces the refrigeration load of the second-stage freezing unit, reduces the initial equipment investment, reduces the equipment footprint, and improves the operating efficiency and stability of the entire production system, further reducing operating costs. Based on the on-site operation analysis of the staged freezing denitrification system with a capacity of 25 tph, the annual operating cost of this device can be reduced by 1.7 million yuan.

[0014] 3. This device uses a three-phase horizontal screw discharge centrifuge to separate the secondary frozen crystal slurry into solid sodium sulfate, turbid liquid containing fine crystals, and qualified clear liquid for discharge. This allows for more thorough separation of sodium sulfate from the lithium hydroxide solution, resulting in extremely low solid content in the discharge and greatly improving the quality of lithium hydroxide products in subsequent processes.

[0015] 4. This device sends the sodium sulfate solid separated by the three-phase horizontal screw discharge centrifuge to a frozen thickening tank and separates it together with the sodium sulfate through a two-stage pusher centrifuge. This reduces the free water in the sodium sulfate, thereby preventing lithium hydroxide from being carried out of the system with the free water, greatly reducing the lithium loss rate, and achieving the goal of cost reduction and efficiency improvement. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The drawings are provided for reference and illustration only and are not intended to limit this utility model. Wherein: Figure 1 This is a flowchart of the graded freezing denitrification device for the lithium hydroxide production line of this utility model; In the diagram: 1. Primary precooler, 2. Secondary precooler, 3. Primary cryogenic crystallizer, 4. Primary cryogenic heat exchanger, 5. Cryogenic thickening tank, 6. Two-stage pusher centrifuge, 7. Centrifugal mother liquor tank, 8. Secondary cryogenic crystallizer, 9. Secondary cryogenic heat exchanger, 10. Three-phase horizontal screw discharge centrifuge, 11. Cryogenic clear liquid tank; B1. Primary feed liquid circulation pump, B2. Primary refrigerant circulation pump, B3. Primary cryogenic crystallizer pump, B4. Centrifugal mother liquor pump, B5. Secondary feed liquid circulation pump, B6. Secondary refrigerant circulation pump, B7. Secondary cryogenic crystallizer pump, B8. Cryogenic clear liquid pump; G1. Lithium hydroxide raw material pipe; G2. Primary refrigeration circulation pipe; G3. Primary refrigerant circulation pipe; G4. Primary refrigeration crystal slurry discharge pipe; G5. Refrigeration thickening tank overflow pipe; G6. Double-push centrifuge separation mother liquor pipe; G7. Primary refrigeration mother liquor discharge pipe; G8. Secondary refrigeration circulation pipe; G9. Secondary refrigerant circulation pipe; G10. Secondary refrigeration crystal slurry discharge pipe; G11. Three-phase horizontal screw centrifuge turbid liquid pipe; G12. Three-phase horizontal screw centrifuge salt discharge pipe; G13. Three-phase horizontal screw centrifuge clear liquid pipe; G14. Refrigeration clear liquid discharge pipe; G15. Circulating cooling water pipe. Detailed Implementation

[0017] To make the technical means, creative features, achieved objectives and effects of this utility model easier to understand, the present utility model will be further described below with reference to specific illustrations. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0019] like Figure 1 As shown, the graded freezing denitrification device for the lithium hydroxide production line of this utility model includes a primary precooler 1, a secondary precooler 2, a primary freezing crystallizer 3, a primary freezing heat exchanger 4, a freezing thickening tank 5, a two-stage pushing centrifuge 6, a centrifugal mother liquor tank 7, a secondary freezing crystallizer 8, a secondary freezing heat exchanger 9, a three-phase horizontal screw discharge centrifuge 10, and a freezing clear liquid tank 11.

[0020] The outlet of lithium hydroxide feedstock pipe G1 is connected to the tube-side inlet of the first-stage precooler 1. The shell side of the first-stage precooler 1 is connected to the circulating cooling water pipe G15. The tube-side outlet of the first-stage precooler 1 is connected to the tube-side inlet of the second-stage precooler 2. The tube-side outlet of the second-stage precooler 2 is connected to the top inlet of the first-stage cryogenic crystallizer 3. The circulating liquid outlet on the upper side wall of the first-stage cryogenic crystallizer 3 is connected to the inlet of the first-stage feed liquid circulation pump B1 through the first-stage cryogenic circulation pipe G2. The outlet of the first-stage feed liquid circulation pump B1 is connected to the tube-side bottom inlet of the first-stage cryogenic heat exchanger 4. The tube-side upper outlet of the first-stage cryogenic heat exchanger 4 is connected to the circulating liquid inlet at the upper end of the central feed pipe of the first-stage cryogenic crystallizer 3. The lower end of the central feed pipe extends along the axis to the lower outlet of the inner cavity of the first-stage cryogenic crystallizer 3.

[0021] The outlet of the primary refrigerant circulation pipe G3 is connected to the shell-side inlet of the primary refrigeration heat exchanger 4. The shell-side outlet of the primary refrigeration heat exchanger 4 is connected to the inlet of the primary refrigerant circulation pump B2. The outlet of the primary refrigerant circulation pump B2 is connected to the inlet of the primary refrigerant circulation pipe G3. The primary refrigerant circulation pipe G3 is also connected to the refrigerant circulation main pipe.

[0022] The bottom crystal slurry outlet of the first-stage cryogenic crystallizer 3 is connected to the inlet of the first-stage cryogenic crystal slurry pump B3. The outlet of the first-stage cryogenic crystal slurry pump B3 is connected to the inlet of the cryogenic thickening tank 5 through the first-stage cryogenic crystal slurry discharge pipe G4. The bottom outlet of the cryogenic thickening tank 5 is connected to the inlet of the double-stage pusher centrifuge 6. The solid phase outlet of the double-stage pusher centrifuge 6 is connected to the sodium sulfate chute. The liquid phase outlet of the double-stage pusher centrifuge 6 is connected to the inlet of the centrifugal mother liquor tank 7 through the double-pusher centrifuge separation mother liquor pipe G6. The upper overflow port of the cryogenic thickening tank 5 is also connected to the inlet of the centrifugal mother liquor tank 7 through the cryogenic thickening tank overflow pipe G5.

[0023] The bottom outlet of the centrifugal mother liquor tank 7 is connected to the inlet of the centrifugal mother liquor pump B4. The outlet of the centrifugal mother liquor pump B4 is connected to the top inlet of the secondary cryogenic crystallizer 8 through the primary cryogenic mother liquor discharge pipe G7. The circulating liquid outlet of the upper side wall of the secondary cryogenic crystallizer 8 is connected to the inlet of the secondary feed liquid circulation pump B5 through the secondary cryogenic circulation pipe G8. The outlet of the secondary feed liquid circulation pump B5 is connected to the bottom inlet of the tube side of the secondary cryogenic heat exchanger 9. The upper outlet of the tube side of the secondary cryogenic heat exchanger 9 is connected to the circulating liquid inlet at the upper end of the central feed pipe of the secondary cryogenic crystallizer 8. The lower end of the central feed pipe extends along the axis to the lower outlet of the inner cavity of the secondary cryogenic crystallizer 8.

[0024] The outlet of the secondary refrigerant circulation pipe G9 is connected to the shell-side inlet of the secondary refrigeration heat exchanger 9. The shell-side outlet of the secondary refrigeration heat exchanger 9 is connected to the inlet of the secondary refrigerant circulation pump B6. The outlet of the secondary refrigerant circulation pump B6 is connected to the inlet of the secondary refrigerant circulation pipe G9. The secondary refrigerant circulation pipe G9 is also connected to the refrigerant circulation main pipe.

[0025] The bottom crystal slurry outlet of the secondary cryogenic crystallizer 8 is connected to the inlet of the secondary cryogenic crystal slurry pump B7. The outlet of the secondary cryogenic crystal slurry pump B7 is connected to the inlet of the three-phase horizontal screw discharge centrifuge 10 through the secondary cryogenic crystal slurry discharge pipe G10. The three-phase horizontal screw discharge centrifuge 10 has three-phase outlets. Its solid phase outlet is connected to the inlet of the cryogenic thickening tank 5 through the three-phase horizontal screw centrifuge salt outlet pipe G12. Its turbid liquid outlet is connected to the inlet of the centrifugal mother liquor tank 7 through the three-phase horizontal screw centrifuge turbid liquid pipe G11. Its clear liquid outlet is connected to the inlet of the cryogenic clear liquid tank 11 through the three-phase horizontal screw centrifuge clear liquid pipe G13. The bottom outlet of the cryogenic clear liquid tank 11 is connected to the inlet of the cryogenic clear liquid pump B8. The outlet of the cryogenic clear liquid pump B8 is connected to the shell side of the secondary precooler 2 through the cryogenic clear liquid discharge pipe G14.

[0026] The working process of the graded cryogenic denitrification unit in this lithium hydroxide production line is as follows: A lithium hydroxide solution containing sodium sulfate enters sequentially through the lithium hydroxide raw solution pipe G1 into the tube side of the primary precooler 1 and the tube side of the secondary precooler 2. The shell side of the primary precooler 1 uses circulating cooling water from the circulating cooling water pipe G15, while the shell side of the secondary precooler 2 uses secondary cryogenic liquid pumped by the cryogenic liquid pump B8 through the cryogenic liquid discharge pipe G14. After two stages of precooling, the lithium hydroxide solution containing sodium sulfate is cooled to 20°C. The precooled material enters the primary cryogenic crystallizer 3, where it circulates between the tube side of the primary cryogenic heat exchanger 4 and the primary cryogenic crystallizer 3 via the primary feed liquid circulation pump B1 and the primary cryogenic circulation pipe G2. The primary refrigerant circulation pump B2 circulates the refrigerant within the shell side of the primary cryogenic heat exchanger 4, cooling the circulating material in the tube side to 0°C. Most of the sodium sulfate in the solution precipitates as sodium sulfate. The sodium sulfate at the bottom of the primary cryogenic crystallizer 3 is sent to the cryogenic thickening tank 5 for settling via the primary cryogenic crystallizer pump B3 and the primary cryogenic crystallizer discharge pipe G4.

[0027] After settling, the high-solids slurry at the bottom of the frozen thickening tank 5 enters the double-stage pusher centrifuge 6 for solid-liquid separation. The separated sodium sulfate is discharged from the solid phase outlet of the double-stage pusher centrifuge 6 and sent outside the boundary area. The separated mother liquor is discharged from the liquid phase outlet of the double-stage pusher centrifuge 6 and enters the centrifugal mother liquor tank 7 through the double-pusher centrifuge mother liquor separation pipe G6. The overflow of the frozen thickening tank 5 also enters the centrifugal mother liquor tank 7 through the frozen thickening tank overflow pipe G5. The centrifugal mother liquor discharged from the bottom of the centrifugal mother liquor tank 7 is sent to the second-stage frozen crystallizer 8 for further cooling through the centrifugal mother liquor pump B4 and the first-stage frozen mother liquor discharge pipe G7. At this time, the sodium content in the centrifugal mother liquor is still 90g / L.

[0028] The material entering the cryogenic crystallizer 8 circulates between the tube side of the secondary cryogenic heat exchanger 9 and the secondary cryogenic crystallizer 8 through the secondary cryogenic circulation pipeline G8 and the secondary feed liquid circulation pump B5. The secondary refrigerant circulation pump B6 circulates the refrigerant in the shell side of the secondary cryogenic heat exchanger 9 through the secondary refrigerant circulation pipeline G9 to cool the tube side circulating material to -10℃. The remaining sodium sulfate in the solution precipitates out in the form of sodium sulfate and is sent to the three-phase horizontal screw discharge centrifuge 10 for solid-liquid separation through the secondary cryogenic crystallizer pump B7 and the secondary cryogenic crystallizer discharge pipeline G10.

[0029] Solid sodium sulfate is discharged from the solid phase outlet of the three-phase horizontal screw centrifuge 10, and enters the frozen thickening tank 5 through the salt outlet pipe G12 of the three-phase horizontal screw centrifuge to settle and separate together with the primary frozen crystal slurry.

[0030] The turbid liquid is discharged from the turbid liquid outlet of the three-phase horizontal screw centrifuge 10, enters the centrifugal mother liquor tank 7 through the turbid liquid pipeline G11 of the three-phase horizontal screw centrifuge, and is then sent to the secondary freezing crystallizer 8 by the centrifugal mother liquor pump B4 for re-crystallization.

[0031] The clarified liquid is discharged from the clarified liquid outlet of the three-phase horizontal screw centrifuge 10, and enters the cryogenic clarified liquid tank 11 through the clarified liquid pipeline G13 of the three-phase horizontal screw centrifuge. The clarified liquid discharged from the bottom of the cryogenic clarified liquid tank 11 is pumped into the shell side of the secondary precooler 2 by the cryogenic clarified liquid pump B8 for heat exchange with the feed before being sent to the subsequent process. At this time, the sodium content in the qualified clarified liquid has been reduced to below 25g / L, which can ensure that the sodium content of the downstream product does not exceed the standard. The above technical solution achieves low cost, high separation efficiency, and continuous and stable operation.

[0032] The above description is merely a preferred embodiment of the present utility model, showing and describing the basic principles, main features, and advantages of the present utility model. It is not intended to limit the scope of patent protection of the present utility model. Those skilled in the art should understand that the present utility model is not limited to the above embodiments. In addition to the above embodiments, the present utility model may have other implementations without departing from the spirit and scope of the present utility model. Various changes and improvements to the present utility model are also possible. All technical solutions formed by equivalent substitutions or equivalent transformations fall within the scope of protection claimed by the present utility model. The scope of protection claimed by the present utility model is defined by the appended claims and their equivalents. Technical features not described in the present utility model can be implemented by or using existing technology, and will not be elaborated here.

Claims

1. A staged cryogenic denitrification device for a lithium hydroxide production line, comprising a lithium hydroxide feedstock pipe (G1), characterized in that, The outlet of the lithium hydroxide raw liquid pipe (G1) is connected in sequence to the tube side of the first-stage precooler (1) and the second-stage precooler (2). The tube side outlet of the second-stage precooler (2) is connected to the top inlet of the first-stage cryogenic crystallizer (3). The circulating liquid outlet of the first-stage cryogenic crystallizer (3) is connected to the circulating liquid inlet of the first-stage cryogenic crystallizer (3) via the tube side of the first-stage feed liquid circulation pump (B1) and the first-stage cryogenic heat exchanger (4). The bottom crystal slurry outlet of the first-stage cryogenic crystallizer (3) is connected to the inlet of the cryogenic thickening tank (5) via the first-stage cryogenic crystal slurry pump (B3). The bottom outlet of the cryogenic thickening tank (5) is connected to the inlet of the two-stage pusher centrifuge (6). The solid phase outlet of the two-stage pusher centrifuge (6) is connected to the sodium sulfate chute, and the liquid phase outlet is connected to the inlet of the centrifugal mother liquor tank (7). The bottom outlet of the centrifugal mother liquor tank (7) is connected to the top inlet of the secondary cryogenic crystallizer (8) via the centrifugal mother liquor pump (B4). The circulating liquid outlet of the secondary cryogenic crystallizer (8) is connected to the circulating liquid inlet of the secondary cryogenic crystallizer (8) via the secondary feed liquid circulation pump (B5) and the tube side of the secondary cryogenic heat exchanger (9). The bottom crystal slurry outlet of the secondary cryogenic crystallizer (8) is connected to the inlet of the three-phase horizontal screw discharge centrifuge (10) via the secondary cryogenic crystal slurry pump (B7). The solid phase outlet of the three-phase horizontal screw discharge centrifuge (10) is connected to the cryogenic thickening tank (5). The turbid liquid outlet is connected to the centrifugal mother liquor tank (7). The clear liquid outlet is connected to the cryogenic clear liquid tank (11). The bottom outlet of the cryogenic clear liquid tank (11) is connected to the shell side of the secondary precooler (2) via the cryogenic clear liquid pump (B8).

2. The staged cryogenic denitrification device for a lithium hydroxide production line according to claim 1, characterized in that: The upper overflow port of the frozen thickening tank (5) is also connected to the inlet of the centrifugal mother liquor tank (7) through the frozen thickening tank overflow pipe (G5).

3. The lithium hydroxide production line's fractional freeze de-nitrating device according to claim 1, characterized in that: The shell side of the primary precooler (1) is connected to the circulating cooling water pipe (G15).

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