A continuous evaporation crystallization system and method for lithium dihydrogen phosphate

Abstract

The invention discloses a continuous evaporation and crystallization system and method for lithium dihydrogen phosphate. The system comprises: a two-effect countercurrent forced circulation evaporation and concentration device and a flash crystallization device; the two-effect forced circulation evaporation and concentration device comprises a raw material pump, a preheater, a two-effect forced circulation pump, a two-effect heater, a two-effect separator, a material transfer pump, a first-effect forced circulation pump, a first-effect heating chamber and a first-effect separator connected by pipelines; the top of the first-effect separator is connected to the second-effect heater, and the bottom of the first-effect separator is connected to the flash crystallization device; since the viscosity of the lithium dihydrogen phosphate solution is relatively large, compared with thermal crystallization, flash crystallization can avoid crystals blocking the heater tube array, reduce the number of shutdowns and cleaning times caused by tube blockage, thereby effectively improving production efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of preparing products by evaporation and crystallization, and in particular to a continuous evaporation and crystallization system and method for lithium dihydrogen phosphate. Background Art

[0002] Lithium iron phosphate batteries have become one of the important choices for electric vehicle power batteries and large-scale power storage due to their high safety, relatively low cost, and long cycle life. As market demand continues to expand, the demand for lithium iron phosphate will continue to increase. Lithium dihydrogen phosphate has good performance in both solid-phase and liquid-phase processes for preparing lithium iron phosphate due to its high reactivity, environmental friendliness, and high adaptability.

[0003] The process of preparing lithium dihydrogen phosphate generally involves an evaporation crystallization process. The existing technology generally adopts an evaporation concentration + cooling crystallization process, which first concentrates the solution by evaporation at normal pressure or reduced pressure, and then transfers the concentrated solution to a cooling device for cooling crystallization. This process can adjust the particle size and morphology of the crystals and improve the particle size of the product, but the disadvantage is that it is intermittent operation, the process flow is relatively complex, the control and operation are difficult, and the equipment investment and operating costs are high.

[0004] A Chinese patent with publication number CN117563249A discloses "a system for producing lithium dihydrogen phosphate by heat pump steam coupled low-temperature evaporation crystallization", which can realize continuous operation of lithium dihydrogen phosphate evaporation crystallization, but its essence is a thermal crystallization method. Lithium dihydrogen phosphate crystals are obtained by heating evaporation crystallization in a second-effect evaporator; since the second-effect evaporation temperature is lower, the concentration of lithium dihydrogen phosphate is higher, and lithium dihydrogen phosphate itself is a high-viscosity medium, and its viscosity will be greater under low temperature and high concentration conditions, so this method will lead to greater material flow losses, and the precipitated crystals are easy to block the heat exchange tubes when circulating in the heater, causing frequent shutdowns for maintenance, which is not conducive to long-term stable operation. Summary of the invention

[0005] The present invention provides a continuous evaporation crystallization system and method for lithium dihydrogen phosphate, which solves the problem that cooling crystallization cannot be continuously operated, and also solves the flow loss caused by the high viscosity of lithium dihydrogen phosphate and the shutdown problem caused by crystal pipe blockage in hot crystallization. The two-effect countercurrent evaporation concentration + flash crystallization process of the present invention is adopted to evaporate and concentrate the solution to saturation at high temperature, and then flash crystallize at low temperature in a vacuum crystallization tank to obtain lithium dihydrogen phosphate crystals.

[0006] In order to solve this technical problem, the present invention provides the following technical solution:

[0007] A continuous evaporation and crystallization system for lithium dihydrogen phosphate, comprising: a two-effect countercurrent forced circulation evaporation and concentration device and a flash crystallization device;

[0008] The two-effect countercurrent forced circulation evaporation and concentration device comprises a raw material pump, a preheater, a two-effect forced circulation pump, a two-effect heater, a two-effect separator, a material transfer pump, a first-effect forced circulation pump, a first-effect heating chamber and a first-effect separator connected by pipelines;

[0009] The top of the first-effect separator is connected to the second-effect heater, and the bottom of the first-effect separator is connected to the flash crystallization device.

[0010] The solubility of lithium dihydrogen phosphate increases with increasing temperature, while the viscosity decreases with increasing temperature and increases with increasing concentration. Based on the above characteristics, two-effect countercurrent evaporation concentration + flash crystallization is adopted. Since the temperature of the first effect is higher, the viscosity of lithium dihydrogen phosphate does not increase significantly. At the same time, lithium dihydrogen phosphate can enter the vacuum crystallizer for flash crystallization at a higher concentration, thereby improving production efficiency.

[0011] The lithium dihydrogen phosphate liquid is pumped to the preheater through the raw material pump to heat exchange with the condensed water and then enter the second-effect forced circulation evaporator. After being pumped to the second-effect heater through the second-effect forced circulation pump and heat exchanged with the secondary steam generated by the first effect, it enters the second-effect separator for vapor-liquid separation, and the liquid is concentrated.

[0012] The concentrated liquid is transferred to the first-effect forced circulation evaporator by the transfer pump, and then sent to the first-effect heating chamber by the first-effect forced circulation pump to exchange heat with the raw steam, and then enters the first-effect separator for vapor-liquid separation, and the liquid is further concentrated to the saturated concentration.

[0013] The saturated lithium dihydrogen phosphate liquid is sent to a flash crystallization device for flash crystallization by using a pressure difference; the precipitated crystals are centrifugally dehydrated, and the liquid after centrifugation returns to a first-effect forced circulation evaporator.

[0014] Preferably, the first-effect heating chamber is also connected to a first-effect condensation water tank, and the first-effect condensation water tank is connected to the preheater through a first-effect condensation water pump.

[0015] As the heat source of the system, the raw steam first enters the first-effect heating chamber to heat the liquid, and at the same time, the raw steam condenses, and the condensed water enters the first-effect condensed water tank. The first-effect condensed water is pumped to the preheater for preheating the raw materials.

[0016] Preferably, the second-effect heater is also connected to a second-effect condensed water tank, the second-effect separator is connected to a steam condenser I, and the steam condenser I is communicated with the second-effect condensed water tank.

[0017] After the water in the first effect liquid is evaporated, it enters the second effect heating chamber as secondary steam to heat the liquid, and the secondary steam is condensed and enters the second effect condensation water tank. After the water in the second effect liquid is evaporated, it enters the steam condenser I to condense into water, and the condensed water enters the second effect condensation water tank.

[0018] Preferably, the second-effect condensed water tank is connected to a second-effect condensed water pump.

[0019] Preferably, the steam condenser I is connected to a vacuum pump I.

[0020] The water in the second-effect condensed water tank is pumped to the boundary area for reuse by the second-effect condensed water pump. The vacuum pump I is used to evacuate and maintain the vacuum degree of the two-effect countercurrent evaporation concentration system.

[0021] Preferably, the flash crystallization device includes a vacuum crystallizer, a steam condenser II, a flash condensate water tank and a flash condensate water pump connected by pipelines.

[0022] After the gas-liquid separation in the first-effect separator, the saturated lithium dihydrogen phosphate liquid is sent to the vacuum crystallizer for flash crystallization by pressure difference. The water in the vacuum crystallizer evaporates and enters the steam condenser II for condensation. The condensed water enters the flash condensation water tank and is pumped to the boundary area for reuse through the flash condensation water pump.

[0023] Preferably, the vacuum crystallizer is also connected to a vacuum pump II and a flash circulation pump.

[0024] The vacuum pump II is used to evacuate and maintain the vacuum degree of the vacuum crystallization system; the flash circulation pump makes the vacuum crystallizer liquid maintain uniform fluidity and makes the high-temperature liquid flow to the liquid surface for flashing.

[0025] The present solution also provides a continuous evaporation and crystallization method for lithium dihydrogen phosphate, using the above-mentioned continuous evaporation and crystallization system for lithium dihydrogen phosphate, comprising the following steps:

[0026] The lithium dihydrogen phosphate liquid is pumped to the preheater through the raw material pump to heat up with the condensed water, and then pumped to the second-effect heating chamber through the second-effect forced circulation pump to heat with the secondary steam generated in the first effect, and then enters the second-effect separator for vapor-liquid separation to obtain concentrated liquid;

[0027] The concentrated liquid is pumped to the first-effect heating chamber through a transfer pump via a first-effect forced circulation pump, and after heat exchange with the raw steam, enters the first-effect separator for vapor-liquid separation. The liquid is further concentrated to a saturated concentration to obtain a saturated lithium dihydrogen phosphate liquid.

[0028] The saturated lithium dihydrogen phosphate liquid is sent to a flash crystallization device for flash crystallization by using a pressure difference to precipitate crystals.

[0029] Preferably, the mass concentration of the lithium dihydrogen phosphate solution is 38% to 45%, the mass concentration of the concentrated solution is 50% to 57%, and the mass concentration of the saturated lithium dihydrogen phosphate solution is 65%.

[0030] Preferably, the heat exchange temperature of the lithium dihydrogen phosphate liquid after being heated by heat exchange with condensed water is 55-60°C; the heating temperature of the second-effect heating chamber (9) is 60-70°C; the evaporation temperature of the gas-liquid separation of the second-effect separator (10) is 40-50°C;

[0031] The heating temperature of the first-effect heating chamber (6) is 90-100°C, the evaporation temperature of the first-effect separator (7) for vapor-liquid separation is 60-70°C, and the feed liquid is further concentrated to a saturated concentration;

[0032] The absolute pressure of the flash crystallization device is less than 10KPa.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] The two-effect countercurrent evaporation concentration + flash crystallization process of the present invention is used to evaporate and concentrate the solution to saturation at high temperature, and then flash crystallize at low temperature in a vacuum crystallization tank to obtain lithium dihydrogen phosphate crystals. Since the viscosity of the lithium dihydrogen phosphate solution is relatively large, compared with thermal crystallization, flash crystallization can avoid crystal clogging of the heater tubes, reduce the number of shutdowns and cleaning times caused by tube clogging, and effectively improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0036] Figure 1 The present invention is a schematic structural diagram of a continuous evaporation crystallization system for lithium dihydrogen phosphate.

[0037] Figure 2 The present invention is a process flow chart of the continuous evaporation and crystallization method of lithium dihydrogen phosphate;

[0038] Marks and corresponding parts names in the attached drawings:

[0039] 1. Raw material pump; 2. Preheater; 3. First-effect condensate pump; 4. First-effect condensate tank; 5. First-effect forced circulation pump; 6. First-effect heater; 7. First-effect separator; 8. Second-effect forced circulation pump; 9. Second-effect heater; 10. Second-effect separator; 11. Transfer pump; 12. Second-effect condensate tank; 13. Second-effect condensate pump; 14. Steam condenser I; 15. Vacuum pump I; 16. Vacuum crystallizer; 17. Steam condenser II; 18. Flash condensate tank; 19. Vacuum pump II; 20. Flash condensate pump; 21. Flash circulation pump. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0041] Example 1

[0042] like Figure 1As shown, a continuous evaporation crystallization system for lithium dihydrogen phosphate includes: a two-effect countercurrent forced circulation evaporation concentration device and a flash crystallization device;

[0043] The two-effect countercurrent forced circulation evaporation and concentration device comprises a raw material pump 1, a preheater 2, a second-effect forced circulation pump 8, a second-effect heater 9, a second-effect separator 10, a material transfer pump 11, a first-effect forced circulation pump 5, a first-effect heating chamber 6 and a first-effect separator 7 connected by pipelines; the top of the first-effect separator 7 is connected to the second-effect heater 9, and the bottom of the first-effect separator 7 is connected to the flash crystallization device.

[0044] The first-effect heating chamber 6 is also connected to a first-effect condensed water tank 4 , and the first-effect condensed water tank 4 is connected to the preheater 2 through a first-effect condensed water pump 3 .

[0045] The second-effect heater 9 is also connected to a second-effect condensed water tank 12, and the second-effect separator 10 is connected to a steam condenser 114, which is in communication with the second-effect condensed water tank 12. The second-effect condensed water tank 12 is connected to a second-effect condensed water pump 13, and the steam condenser 114 is connected to a vacuum pump 115.

[0046] The flash crystallization device includes a vacuum crystallizer 16, a steam condenser II17, a flash condensate water tank 18 and a flash condensate water pump 20 connected by pipelines; the vacuum crystallizer 16 is also connected to a vacuum pump II19 and a flash circulation pump 21.

[0047] When the above system is working, the lithium dihydrogen phosphate liquid is sent to the preheater 2 through the raw material pump 1 for heat exchange with condensed water to increase the temperature, and then sent to the second-effect heater 9 through the second-effect forced circulation pump 8 for heat exchange with the secondary steam generated by the first effect, and then enters the second-effect separator 10 for gas-liquid separation, and the liquid is concentrated.

[0048] The concentrated liquid is transferred by the transfer pump 11, and sent to the first-effect heating chamber 6 by the first-effect forced circulation pump 5 for heat exchange with the raw steam, and then enters the first-effect separator 7 for vapor-liquid separation, and the liquid is further concentrated to the saturated concentration.

[0049] The saturated lithium dihydrogen phosphate liquid is sent to the vacuum crystallizer 16 for flash crystallization by using the pressure difference; the precipitated crystals are centrifuged for dehydration, and the liquid after centrifugation returns to the first effect for forced circulation evaporation.

[0050] The raw steam is firstly sent to the first-effect heating chamber 6 as the system heat source to heat the liquid feed, and the raw steam is condensed at the same time, and the condensed water enters the first-effect condensed water tank 4. The first-effect condensed water is sent to the preheater 2 through the first-effect condensed water pump 3 for preheating the raw materials.

[0051] After the water in the first-effect liquid is evaporated, it enters the second-effect heater 9 as secondary steam to heat the liquid. After the secondary steam is condensed, it enters the second-effect condensation water tank 12. After the water in the second-effect liquid is evaporated, it enters the steam condenser I14 to condense into water. The condensed water enters the second-effect condensation water tank 12. The water in the second-effect condensation water tank 12 is sent to the boundary area for reuse through the second-effect condensation water pump 13. The vacuum pump I15 is used to evacuate and maintain the vacuum degree of the two-effect countercurrent evaporation concentration system.

[0052] After the water in the vacuum crystallizer 16 evaporates, it enters the steam condenser II17 for condensation. The condensed water enters the flash condensate tank 18 and is sent to the boundary area for reuse through the flash condensate pump 20. The vacuum pump II19 is used to evacuate the vacuum crystallization system to maintain the vacuum degree.

[0053] Example 2

[0054] like Figure 2 As shown, this embodiment provides a continuous evaporation crystallization method for lithium dihydrogen phosphate, using the continuous evaporation crystallization system for lithium dihydrogen phosphate of Example 1, comprising the following steps:

[0055] The lithium dihydrogen phosphate feed liquid with a mass concentration of 38% to 45% is sent to the preheater 2 through the raw material pump 1 to exchange heat with condensed water to preheat the feed liquid to 55 to 60° C., and then sent to the second-effect heating chamber 9 through the second-effect forced circulation pump 8 to exchange heat with the secondary steam generated by the first effect, with a heating temperature of 60 to 70° C. After heat exchange, it enters the second-effect separator 10 for vapor-liquid separation, with an evaporation temperature of 40 to 50° C., to obtain a concentrated feed liquid with a mass concentration of 50% to 57%;

[0056] The concentrated liquid is sent to the first-effect heating chamber 6 for heating through the transfer pump 11 and the first-effect forced circulation pump 5 at a heating temperature of 90-100°C. After heat exchange with the raw steam, it enters the first-effect separator 7 for vapor-liquid separation at an evaporation temperature of 60-70°C. The liquid is further concentrated to a saturated concentration to obtain a saturated lithium dihydrogen phosphate liquid with a mass concentration of 65%.

[0057] The saturated lithium dihydrogen phosphate liquid is sent to the vacuum crystallizer 16 for flash crystallization by using the pressure difference, and the absolute pressure of the vacuum crystallizer 16 is less than 10KPa; the precipitated crystals are centrifugally dehydrated, and the liquid after centrifugation returns to the first effect for forced circulation evaporation.

[0058] The raw steam is firstly sent to the first-effect heating chamber 6 as the system heat source to heat the liquid feed, and the raw steam is condensed at the same time, and the condensed water enters the first-effect condensed water tank 4. The first-effect condensed water is sent to the preheater 2 through the first-effect condensed water pump 3 for preheating the raw materials.

[0059] After the water in the first-effect liquid is evaporated, it enters the second-effect heater 9 as secondary steam to heat the liquid. After the secondary steam is condensed, it enters the second-effect condensation water tank 12. After the water in the second-effect liquid is evaporated, it enters the steam condenser I14 to condense into water. The condensed water enters the second-effect condensation water tank 12. The water in the second-effect condensation water tank 12 is sent to the boundary area for reuse through the second-effect condensation water pump 13. The vacuum pump I15 is used to evacuate and maintain the vacuum degree of the two-effect countercurrent evaporation concentration system.

[0060] After the water in the vacuum crystallizer 16 evaporates, it enters the steam condenser II17 for condensation. The condensed water enters the flash condensate tank 18 and is sent to the boundary area for reuse through the flash condensate pump 20. The vacuum pump II19 is used to evacuate the vacuum crystallization system to maintain the vacuum degree.

[0061] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A continuous evaporation crystallization system for lithium dihydrogen phosphate, characterized in that: include: Two-effect countercurrent forced circulation evaporation concentration device and flash crystallization device; The two-effect countercurrent forced circulation evaporation and concentration device comprises a raw material pump (1), a preheater (2), a second-effect forced circulation pump (8), a second-effect heater (9), a second-effect separator (10), a material transfer pump (11), a first-effect forced circulation pump (5), a first-effect heating chamber (6) and a first-effect separator (7) connected by pipelines; The top of the first-effect separator (7) is connected to the second-effect heater (9), and the bottom of the first-effect separator (7) is connected to the flash crystallization device.

2. The continuous evaporation and crystallization system for lithium dihydrogen phosphate according to claim 1, characterized in that: The first-effect heating chamber (6) is also connected to a first-effect condensing water tank (4), and the first-effect condensing water tank (4) is connected to the preheater (2) via a first-effect condensing water pump (3).

3. The continuous evaporation and crystallization system for lithium dihydrogen phosphate according to claim 1, characterized in that: The second-effect heater (9) is also connected to a second-effect condensed water tank (12), and the second-effect separator (10) is connected to a steam condenser I (14), and the steam condenser I (14) is in communication with the second-effect condensed water tank (12).

4. The continuous evaporation crystallization system for lithium dihydrogen phosphate according to claim 3, characterized in that: The second-effect condensed water tank (12) is connected to a second-effect condensed water pump (13).

5. The continuous evaporation and crystallization system for lithium dihydrogen phosphate according to claim 3, characterized in that: The steam condenser I (14) is connected to a vacuum pump I (15).

6. The continuous evaporation and crystallization system for lithium dihydrogen phosphate according to claim 1, characterized in that: The flash crystallization device comprises a vacuum crystallizer (16), a steam condenser II (17), a flash condensation water tank (18) and a flash condensation water pump (20) which are connected by pipelines.

7. The continuous evaporation and crystallization system for lithium dihydrogen phosphate according to claim 1, characterized in that: The vacuum crystallizer (16) is also connected to a vacuum pump II (19) and a flash circulation pump (21).

8. A continuous evaporation crystallization method for lithium dihydrogen phosphate, characterized in that: The continuous evaporation and crystallization system for lithium dihydrogen phosphate according to any one of claims 1 to 7 comprises the following steps: The lithium dihydrogen phosphate liquid is sent to the preheater (2) through the raw material pump (1) to heat exchange with condensed water to increase the temperature; then it is sent to the second-effect heating chamber (9) through the second-effect forced circulation pump (8) to heat exchange with the secondary steam generated by the first effect, and then enters the second-effect separator (10) for vapor-liquid separation to obtain concentrated liquid; The concentrated liquid feed is sent to the first-effect heating chamber (6) through the material transfer pump (11) and the first-effect forced circulation pump (5), and after heat exchange with the raw steam, enters the first-effect separator (7) for vapor-liquid separation, and the liquid feed is further concentrated to a saturated concentration to obtain a saturated lithium dihydrogen phosphate liquid feed; The saturated lithium dihydrogen phosphate liquid is sent to a flash crystallization device for flash crystallization by using a pressure difference to precipitate crystals.

9. The continuous evaporation and crystallization method of lithium dihydrogen phosphate according to claim 8, characterized in that: The mass concentration of the lithium dihydrogen phosphate solution is 38% to 45%, the mass concentration of the concentrated solution is 50% to 57%, and the mass concentration of the saturated lithium dihydrogen phosphate solution is 65%.

10. The continuous evaporation and crystallization method of lithium dihydrogen phosphate according to claim 8, characterized in that: The heat exchange temperature of the lithium dihydrogen phosphate liquid after being heated by heat exchange with condensed water is 55-60° C.; the heating temperature of the second-effect heating chamber (9) is 60-70° C.; the evaporation temperature of the gas-liquid separation of the second-effect separator (10) is 40-50° C.; The heating temperature of the first-effect heating chamber (6) is 90-100°C, the evaporation temperature of the first-effect separator (7) for vapor-liquid separation is 60-70°C, and the feed liquid is further concentrated to a saturated concentration; The absolute pressure of the flash crystallization device is less than 10KPa.

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