Potassium chloride three-stage flash crystallization system and method for potassium chloride three-stage flash crystallization

Abstract

The application provides a potassium chloride three-stage flash crystallization system and a potassium chloride three-stage flash crystallization method. The three-stage flash crystallization system is composed of a feed pump, a first crystallization unit, a second crystallization unit, a third crystallization unit, a first discharge pump, a second discharge pump, a third discharge pump, a first water pump, a second water pump, a third water pump, a first water tank, a second water tank, a third water tank, a flash circulation pump and a centrifuge. The three-stage flash crystallization system and the potassium chloride three-stage flash crystallization method can effectively reduce energy consumption and equipment cost.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and relates to a system and method for crystallizing sodium chloride and flash-evaporating potassium chloride in industrial water treatment containing both sodium chloride and potassium chloride. Specifically, it relates to a three-stage flash crystallization system and a method for three-stage flash crystallization of potassium chloride. Background Technology

[0002] Potash is an important chemical raw material, widely used not only in industry but also playing a vital role in agricultural production. However, the separation and purification equipment used in salt lake (or salt well) mining is complex, costly, and energy-intensive, which reduces the overall efficiency of potash mining.

[0003] Furthermore, industrial production generates a large amount of industrial wastewater daily, especially high-salinity wastewater. Ideally, valuable potassium salts could be extracted from this wastewater for recycling and sale, turning waste into treasure. However, current technologies can remove impurities and heavy metals from high-salinity industrial wastewater through pretreatment, resulting in wastewater containing only sodium chloride and potassium chloride. Due to the solubility of sodium chloride and potassium chloride in water, they can be produced separately through high-temperature evaporation, low-temperature evaporation, or cooling and crystallization separation. However, traditional methods for extracting potassium chloride require vacuum flash evaporation crystallization, which not only necessitates the installation of specialized equipment, increasing costs, but also results in high energy consumption and poor economic efficiency.

[0004] Therefore, developing a system and process that can treat both salt lake (or salt well) water and high-salinity industrial wastewater is of great practical significance for reducing costs and energy consumption in industrial production and for waste recycling. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a three-stage flash crystallization system for potassium chloride. This system can achieve system vacuum without the need for specialized vacuum equipment, thereby reducing equipment costs and saving energy.

[0006] Another object of the present invention is to provide a method for three-stage flash crystallization of potassium chloride.

[0007] To achieve the above objectives, the present invention provides a three-stage flash crystallization system, comprising a feed pump, a first crystallization unit, a second crystallization unit, a third crystallization unit, a first discharge pump, a second discharge pump, a third discharge pump, a first water pump, a second water pump, a third water pump, a first water tank, a second water tank, a third water tank, a flash circulation pump, and a centrifuge.

[0008] The first crystallization unit consists of a first condenser and a first crystallizer. The first condenser is cylindrical, and the middle part of the first crystallizer is cylindrical. A coaxial first clarifier is installed inside the cylinder. The upper part of the first crystallizer is frustum-shaped, the lower part is an inverted frustum-shaped, and the bottom of the first crystallizer is arc-shaped. A cylindrical first steam riser pipe is provided at the top of the first crystallizer. The first condenser is fitted onto the upper part of the first crystallizer, such that the first steam riser pipe of the first crystallizer is located inside the first condenser. A first stirring shaft passes through the lower part of the first crystallizer. The first stirring shaft is located outside the first crystallizer and connected to a first motor. The first stirring shaft is located inside the first crystallizer and connected to a first stirring fan blade. The upper part of the first condenser is connected to a first condenser inlet pipe, and the lower part of the first condenser is connected to a first condenser outlet pipe. A first regulating discharge pipe with a valve is connected to the first condenser inlet pipe.

[0009] The second crystallization unit consists of a second condenser and a second crystallizer. The second condenser is cylindrical, with a cylindrical middle section and a coaxial second clarifier inside. The upper part of the second crystallizer is frustum-shaped, the lower part is an inverted frustum-shaped, and the bottom is arc-shaped. A cylindrical second steam riser is located at the top of the second crystallizer. The second condenser is fitted over the upper part of the second crystallizer, such that the second steam riser is located inside the second condenser. A second stirring shaft passes through the lower part of the second crystallizer. The second stirring shaft is located outside the second crystallizer and connected to a second motor, and inside the second crystallizer and connected to a second stirring fan blade. The upper part of the second condenser is connected to a second condenser inlet pipe, and the lower part is connected to a second condenser outlet pipe. A second regulating discharge pipe with a valve and a second regulating inlet pipe with a valve are connected to the second condenser inlet pipe.

[0010] The third crystallization unit consists of a third condenser and a third crystallizer. The third condenser is cylindrical, and the middle part of the third crystallizer is cylindrical. A coaxial third clarifier is installed inside the cylinder. The upper part of the third crystallizer is frustum-shaped, the lower part is an inverted frustum-shaped, and the bottom of the third crystallizer is arc-shaped. A cylindrical third steam riser is provided at the top of the third crystallizer. The third condenser is fitted onto the upper part of the third crystallizer, so that the third steam riser of the third crystallizer is located inside the third condenser. A washing salt leg is connected to the bottom of the third crystallizer. The upper part of the third condenser is connected to the third condenser inlet pipe, and the lower part of the third condenser is connected to the third condenser outlet pipe.

[0011] The bottom of the first crystallizer is connected to the feed pump via a first feed pipe, and one end of the first discharge pump is connected to the bottom of the first crystallizer at a position opposite to the feed pump. The other end of the first discharge pump is connected to the bottom of the second crystallizer, and one end of the second discharge pump is connected to the bottom of the second crystallizer at a position opposite to the connection of the first discharge pump. The other end of the second discharge pump and one end of the flash circulation pump are connected together via a pipe to the upper middle part of the third crystallizer. The other end of the flash circulation pump is connected to the middle part of the third crystallizer. The washing salt leg is connected to one end of the third discharge pump, and the other end of the third discharge pump is connected to the centrifuge.

[0012] The third condenser outlet pipe is connected to the third water tank, the third water tank is connected to one end of the third water pump, and the other end of the third water pump is connected to the second condenser inlet pipe; the second condenser outlet pipe is connected to the second water tank; the second water tank is connected to one end of the second water pump, and the other end of the second water pump is connected to the first condenser inlet pipe; the first condenser outlet pipe is connected to the first water tank; the first water tank is connected to the first water pump;

[0013] The washing salt leg is connected to the first feed pipe via a pipeline.

[0014] As described above, a plurality of baffles are horizontally arranged inside the first condenser, the second condenser, and the third condenser.

[0015] As described above, the baffle plate is provided with a plurality of holes.

[0016] As described above, the height difference between the top of the first crystallizer and the liquid level in the first water tank is calculated using the following formula: Where P0 is atmospheric pressure; P1 is the pressure of the closed container; ρ is density; g is gravitational acceleration; h is the height of the hydrostatic column; where P1 < P0, so that the first crystallizer is kept under negative pressure.

[0017] The present invention also provides a method for three-stage flash crystallization of potassium chloride using the above-described three-stage flash crystallization system, comprising the following steps:

[0018] 1) The mother liquor discharged after evaporating and crystallizing the original brine to obtain sodium chloride product salt has a temperature of 100℃ and contains a saturated solution of potassium chloride with a mass percentage concentration of 19% and sodium chloride of 15.5%.

[0019] 2) Add alkali to the discharged mother liquor to adjust the pH of the discharged mother liquor to 12±0.2 to remove impurities, then keep it warm and let it settle, and separate the supernatant and precipitate; the settling time is 1 hour;

[0020] The addition of alkali is mainly used to precipitate calcium and magnesium ions, thereby reducing equipment structural problems.

[0021] 3) Pass the supernatant through a security filter for heat preservation filtration, and neutralize the filtrate to neutral with hydrochloric acid;

[0022] 4) The neutralized filtrate is fed to the first crystallizer by a feed pump for flash evaporation and cooling concentration at a temperature of 75℃ and a vacuum degree of -0.06 to -0.080 MPa;

[0023] 5) The slurry I obtained by flash cooling and concentration in the first crystallizer is transported to the second crystallizer by the first discharge pump for the next step of flash cooling and concentration; the temperature is 50℃ and the vacuum degree is -0.092MPa;

[0024] 6) The slurry II obtained by flash cooling and concentration in the second crystallizer is transported to the third crystallizer by the second discharge pump for further flash cooling and concentration at a temperature of 30℃ and a vacuum degree of -0.098MPa.

[0025] 7) The slurry III obtained by flash evaporation and cooling concentration in the third crystallizer is fed into a centrifuge for separation to obtain potassium chloride wet product and potassium chloride mother liquor;

[0026] 8) Pack the wet potassium chloride to obtain fertilizer-grade potassium fertilizer; discharge the potassium chloride mother liquor to the sodium chloride evaporation and crystallization production line;

[0027] 9) While performing steps 4) to 8), low-temperature raw brine or low-temperature chilled water is introduced from the inlet pipe of the third condenser; the secondary raw brine or secondary feed water obtained after heat exchange between the low-temperature raw brine or low-temperature chilled water and slurry II entering the third crystallizer is discharged from the outlet pipe of the third condenser to the third water tank, and then enters the second condenser from the inlet pipe of the second condenser via the third water pump; the tertiary raw brine or tertiary feed water obtained after heat exchange between the secondary raw brine or tertiary feed water and slurry I entering the second condenser is discharged from the outlet pipe of the second condenser to the second water tank, and then enters the first condenser from the inlet pipe of the first condenser via the second water pump; the high-temperature raw brine or high-temperature feed water obtained after heat exchange between the tertiary raw brine or tertiary feed water and filtrate entering the first condenser is discharged from the outlet pipe of the first condenser to the first water tank, and then discharged via the first water pump.

[0028] As described above, the alkali in step 2) is potassium hydroxide.

[0029] As described above, the heat-insulating filter in step 3) uses a security filter with heat-insulating properties, made of titanium, with a pore size of 5 micrometers.

[0030] As described above, the first crystallizer, the second crystallizer, and the third crystallizer are all DTB-type crystallizers.

[0031] This invention connects the condenser directly to the top of the crystallizer, enabling direct heat exchange between the liquid in the condenser and the steam generated during crystallization in the crystallizer via countercurrent flow. This eliminates the need for conventional indirect heat exchange equipment, reducing equipment costs. Furthermore, the direct heat exchange provides excellent performance and reduces energy consumption. In addition, combining the crystallizer and condenser reduces the floor space required. The heated brine can also be used as raw material in a three-stage flash crystallization system, further reducing energy consumption for heating.

[0032] In this invention, the first and second crystallizers are equipped with stirring blades, which can reduce the crystallization and sedimentation rate of potassium chloride, increase the crystal particle size, reduce the amount of impurities such as lithium and sodium entrained, and greatly improve the quality of potassium chloride crystal salt.

[0033] In the third crystallizer, a washing salt leg is set at the bottom of the cone to wash the product with the original solution, thereby increasing the purity of the salt; the uniformity of the salt particles (large salt particles) also improves the purity of the product.

[0034] The beneficial effects of this invention are as follows:

[0035] This invention provides a three-stage flash crystallization system and method for potassium chloride. The system eliminates the vacuum pump required in conventional systems, achieving vacuum through secondary steam exchange cooling. This eliminates the need for a vacuum pump, reducing equipment costs. Simultaneously, it raises the temperature of the raw brine and heats the initial sodium chloride evaporation crystallization, reducing system energy consumption. The method provided by this invention is applicable to low-temperature plateau regions in my country, where a vacuum is created through direct contact condensation between the low-temperature raw brine and the secondary steam in the crystallizer. It can also be used in plains areas, where a vacuum is created through cooling with chilled water and flash secondary steam. This method saves on the cost of a vacuum pump, significantly reducing energy consumption and improving efficiency. Furthermore, the prepared potassium chloride meets national standards and can be used directly as potash fertilizer. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the three-stage flash crystallization system provided by the present invention.

[0037] Figure Labels

[0038] 1: Feed pump; 2: First crystallization unit; 21: First discharge pump; 22: First water pump; 23: First water tank; 24: First condenser; 241: First condenser inlet pipe; 2411: First regulating discharge pipe; 242: First condenser outlet pipe; 25: First crystallizer; 26: First clarifier; 27: First steam riser pipe; 281: First stirring shaft; 282: First motor; 283: First stirring blade; 29: First feed pipe; 3: Second crystallization unit; 31: Second discharge pump; 32: Second water pump; 33: Second water tank; 34: Second condenser; 341: Second condenser inlet pipe; 34 11; Second regulating discharge pipe; 3412; Second regulating inlet pipe; 342; Second condenser outlet pipe; 35; Second crystallizer; 36; Second clarifier; 37; Second steam riser pipe; 381; Second stirring shaft; 382; Second motor; 383; Second stirring blade; 4; Third crystallization unit; 41; Third discharge pump; 42; Third water pump; 43; Third water tank; 44; Third condenser; 441; Third condenser inlet pipe; 442; Third condenser outlet pipe; 45; Third crystallizer; 46; Third clarifier; 47; Third steam riser pipe; 48; Washing salt leg; 5; Flash evaporation circulation pump; 6; Centrifuge. Detailed Implementation

[0039] The embodiments of the present invention will now be described in detail and comprehensively so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0040] like Figure 1 The three-stage flash crystallization system provided by the present invention is shown, which consists of a feed pump 1, a first crystallization unit 2, a second crystallization unit 3, a third crystallization unit 4, a first discharge pump 21, a second discharge pump 31, a third discharge pump 41, a first water pump 22, a second water pump 32, a third water pump 42, a first water tank 23, a second water tank 33, a third water tank 43, a flash circulation pump 5, and a centrifuge 6.

[0041] The first crystallization unit 2 consists of a first condenser 24 and a first crystallizer 25. The first condenser 24 is cylindrical, and the middle part of the first crystallizer 25 is cylindrical. A coaxial first clarifier 26 is disposed inside the cylindrical part. The upper part of the first crystallizer 25 is frustum-shaped, the lower part of the first crystallizer 25 is inverted frustum-shaped, and the bottom of the first crystallizer 25 is arc-shaped. A cylindrical first steam riser 27 is disposed at the top of the first crystallizer 25. The first condenser 24 is sleeved on the upper part of the first crystallizer 25, such that the first condenser 25... A steam pipe 26 is located inside the first condenser 24; a first stirring shaft 281 passes through the lower part of the first crystallizer 25, the first stirring shaft 281 is located outside the first crystallizer 25 and connected to a first motor 282, the first stirring shaft 281 is located inside the first crystallizer 25 and connected to a first stirring fan blade 283; the upper part of the first condenser 24 is connected to a first condenser inlet pipe 241, the lower part of the first condenser 24 is connected to a first condenser outlet pipe 242; a first regulating discharge pipe 2411 with a valve is connected to the first condenser inlet pipe 241;

[0042] The second crystallization unit 3 consists of a second condenser 34 and a second crystallizer 35. The second condenser 34 is cylindrical, and the middle part of the second crystallizer 35 is cylindrical. A coaxial second clarifier 36 is disposed inside the cylindrical part. The upper part of the second crystallizer 35 is frustum-shaped, the lower part of the second crystallizer 35 is inverted frustum-shaped, and the bottom of the second crystallizer 35 is arc-shaped. A cylindrical second steam riser 37 is provided at the top of the second crystallizer 35. The second condenser 34 is sleeved on the upper part of the second crystallizer 35, such that the steam riser 37 of the second crystallizer 35 is located in the second crystallizer 35. The interior of the second condenser 34; the lower part of the second crystallizer 35 is provided with a second stirring shaft 381, the second stirring shaft 381 is located outside the second crystallizer 35 and connected to a second motor 382, ​​the second stirring shaft 381 is located inside the second crystallizer 35 and connected to a second stirring fan blade 383; the upper part of the second condenser 34 is connected to a second condenser inlet pipe 341, the lower part of the second condenser 34 is connected to a second condenser outlet pipe 342; the second condenser inlet pipe 341 is connected to a second regulating discharge pipe 3411 with a valve and a second regulating inlet pipe 3412 with a valve;

[0043] The third crystallization unit 4 consists of a third condenser 44 and a third crystallizer 45. The third condenser 44 is cylindrical, and the middle part of the third crystallizer 45 is cylindrical. A coaxial third clarifier 46 is installed inside the cylindrical part. The upper part of the third crystallizer 45 is frustum-shaped, the lower part of the third crystallizer 45 is inverted frustum-shaped, and the bottom of the third crystallizer 45 is arc-shaped. A cylindrical third steam riser pipe 47 is provided at the top of the third crystallizer 45. The third condenser 44 is fitted onto the upper part of the third crystallizer 45, so that the steam riser pipe of the third crystallizer 45 is located inside the third condenser 44. A washing salt leg 48 is connected to the bottom of the third crystallizer 45. The upper part of the third condenser 44 is connected to the third condenser inlet pipe 441, and the lower part of the third condenser 44 is connected to the third condenser outlet pipe 442.

[0044] The bottom of the first crystallizer 25 is connected to the feed pump 1 via the first feed pipe 29. One end of the first discharge pump 21 is connected to the bottom of the first crystallizer 25 at a position opposite to the feed pump 1. The other end of the first discharge pump 21 is connected to the bottom of the second crystallizer 35. One end of the second discharge pump 31 is connected to the bottom of the second crystallizer 35 at a position opposite to the connection of the first discharge pump 21. The other end of the second discharge pump 31 and one end of the flash circulation pump 5 are connected together via a pipe to the upper part of the middle of the third crystallizer 45. The other end of the flash circulation pump 5 is connected to the middle of the third crystallizer 45. The washing salt leg 48 is connected to one end of the third discharge pump 41, and the other end of the third discharge pump 41 is connected to the centrifuge 6.

[0045] The third condenser outlet pipe 442 is connected to the third water tank 43, the third water tank 43 is connected to one end of the third water pump 42, and the other end of the third water pump 42 is connected to the second condenser inlet pipe 341; the second condenser outlet pipe 342 is connected to the second water tank 33; the second water tank 33 is connected to one end of the second water pump 42, and the other end of the second water pump 42 is connected to the first condenser inlet pipe 241; the first condenser outlet pipe 242 is connected to the first water tank 23; the first water tank 23 is connected to the first water pump 22;

[0046] The washing salt leg 48 is connected to the first feed pipe 29 through a pipe, thereby sending part of the filtrate into the washing salt leg position as washing liquid to wash the crystallized salt and improve product purity.

[0047] Preferably, a plurality of baffles 7 are horizontally arranged inside the first condenser 24, the second condenser 34 and the third condenser 44, and the baffles 7 are provided with a plurality of holes.

[0048] The height difference between the top of the first crystallizer 25 and the liquid level in the first water tank 23 conforms to the following formula: Where P0 is atmospheric pressure; P1 is the pressure of the closed container; ρ is density; g is gravitational acceleration; h is the height of the hydrostatic column, where P1 < P0, so that the first crystallizer is kept under negative pressure.

[0049] It should be noted that, in combination Figure 1 In this invention, the connections between various devices are represented by unmarked lines, which indicate general pipes, and arrows indicate the direction of liquid flow within the system.

[0050] Example 1

[0051] In this embodiment, the raw brine used as the raw material comes from the salt lake water of a salt lake in Tibet.

[0052] The specific processing steps are as follows:

[0053] 1) The mother liquor discharged after evaporating and crystallizing the original brine to obtain sodium chloride product salt has a temperature of 100℃ and contains a saturated solution of potassium chloride (19%) and sodium chloride (15.5%) by mass percentage. The composition of the mother liquor is shown in Table 1 below:

[0054] Table 1 Chemical composition of discharged mother liquor

[0055] Components <![CDATA[Li + ]]> <![CDATA[Na + ]]> <![CDATA[K + ]]> Cl- <![CDATA[B 3+ ]]> <![CDATA[CO3 2- ]]> unit g / L g / L g / L g / L g / L g / L numerical values 2.29 80.1 126.2 249 0.1 26.83

[0056] 2) Add potassium hydroxide to the discharged mother liquor to adjust the pH of the discharged mother liquor to 12±0.2 to remove impurities, then keep it warm and let it settle, and separate the supernatant and precipitate; the settling time is 1 hour;

[0057] 3) The supernatant is filtered through a security filter under heat preservation, and the resulting filtrate is neutralized to neutral with hydrochloric acid; the security filter is made of titanium and has a pore size of 5 micrometers.

[0058] 4) The neutralized filtrate is fed to the first crystallizer by a feed pump for flash evaporation and cooling concentration at a temperature of 75℃ and a vacuum degree of -0.06 to -0.080 MPa;

[0059] 5) The slurry I obtained by flash cooling and concentration in the first crystallizer is transported to the second crystallizer by the first discharge pump for the next step of flash cooling and concentration; the temperature is 50℃ and the vacuum degree is -0.092MPa;

[0060] 6) The slurry II obtained by flash cooling and concentration in the second crystallizer is transported to the third crystallizer by the second discharge pump for further flash cooling and concentration at a temperature of 30℃ and a vacuum degree of -0.098MPa.

[0061] 7) The slurry III obtained by flash evaporation and cooling concentration in the third crystallizer is fed into a centrifuge for separation to obtain potassium chloride wet product and potassium chloride mother liquor;

[0062] 8) Pack the wet potassium chloride to obtain fertilizer-grade potassium fertilizer; discharge the potassium chloride mother liquor to the sodium chloride evaporation and crystallization production line;

[0063] 9) While performing steps 4) to 8), low-temperature raw brine or low-temperature chilled water is introduced from the inlet pipe of the third condenser; the secondary raw brine or secondary feed water obtained after heat exchange between the low-temperature raw brine or low-temperature chilled water and slurry II entering the third crystallizer is discharged from the outlet pipe of the third condenser to the third water tank, and then enters the second condenser from the inlet pipe of the second condenser via the third water pump; the tertiary raw brine or tertiary feed water obtained after heat exchange between the secondary raw brine or tertiary feed water and slurry I entering the second condenser is discharged from the outlet pipe of the second condenser to the second water tank, and then enters the first condenser from the inlet pipe of the first condenser via the second water pump; the high-temperature raw brine or high-temperature feed water obtained after heat exchange between the tertiary raw brine or tertiary feed water and filtrate entering the first condenser is discharged from the outlet pipe of the first condenser to the first water tank, and then discharged via the first water pump.

[0064] The first regulating discharge pipe connected to the liquid inlet pipe of the first condenser and the second regulating discharge pipe and the second regulating liquid inlet pipe connected to the liquid inlet pipe of the second condenser are used to regulate the liquid volume of raw brine or water at each stage of the condensation process, thereby adjusting the condensation effect in the condenser.

[0065] The fertilizer-grade potassium fertilizer prepared in this embodiment was tested using the method of the national standard "Potassium Chloride Standard (GB6549-2011)". Its quality meets the requirements of Class I industrial salt grade 1 (potassium oxide (K2O) mass fraction) in "Potassium Chloride Standard (GB6549-2011)" and can be used to prepare compound fertilizers or applied directly as fertilizer.

[0066] Example 2

[0067] In this embodiment, the raw brine used for processing comes from a salt well in Shandong Province, and its composition is shown in Table 2 below:

[0068] Table 2 Chemical composition of raw brine in salt wells

[0069]

[0070] Potassium chloride was prepared by three-stage flash crystallization using the same method as in Example 1, and fertilizer-grade potassium fertilizer was obtained, which also meets the requirements of Class I industrial salt grade 1 (potassium oxide (K2O) mass fraction) in the national standard "Potassium Chloride Standard (GB6549-2011)".

[0071] Example 3

[0072] This example uses chemical wastewater from a steel plant in Hebei Province as the raw brine. The specific components are shown in Table 3.

[0073] Table 3 Chemical composition of industrial wastewater

[0074]

[0075] Potassium chloride was prepared by three-stage flash crystallization using the same method as in Example 1, and fertilizer-grade potassium fertilizer was obtained, which also meets the requirements of Class I industrial salt grade 1 (potassium oxide (K2O) mass fraction) in the national standard "Potassium Chloride Standard (GB6549-2011)".

[0076] As can be seen from the above embodiments, the present invention provides a three-stage flash crystallization system for potassium chloride, which reduces equipment costs and energy consumption through countercurrent heat exchange, and the produced potassium salt meets national standards and can be used as potassium fertilizer in agricultural production.

[0077] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A three-stage flash crystallization system for potassium chloride, characterized in that, It consists of a feed pump, a first crystallization unit, a second crystallization unit, a third crystallization unit, a first discharge pump, a second discharge pump, a third discharge pump, a first water pump, a second water pump, a third water pump, a first water tank, a second water tank, a third water tank, a flash circulation pump, and a centrifuge; The first crystallization unit consists of a first condenser and a first crystallizer. The first condenser is cylindrical, and the middle part of the first crystallizer is cylindrical. A coaxial first clarifier is installed inside the cylinder. The upper part of the first crystallizer is frustum-shaped, the lower part is an inverted frustum-shaped, and the bottom of the first crystallizer is arc-shaped. A cylindrical first steam riser pipe is provided at the top of the first crystallizer. The first condenser is fitted onto the upper part of the first crystallizer, such that the first steam riser pipe of the first crystallizer is located inside the first condenser. A first stirring shaft passes through the lower part of the first crystallizer. The first stirring shaft is located outside the first crystallizer and connected to a first motor. The first stirring shaft is located inside the first crystallizer and connected to a first stirring fan blade. The upper part of the first condenser is connected to a first condenser inlet pipe, and the lower part of the first condenser is connected to a first condenser outlet pipe. A first regulating discharge pipe with a valve is connected to the first condenser inlet pipe. The second crystallization unit consists of a second condenser and a second crystallizer. The second condenser is cylindrical, with a cylindrical middle section and a coaxial second clarifier inside. The upper part of the second crystallizer is frustum-shaped, the lower part is an inverted frustum-shaped, and the bottom is arc-shaped. A cylindrical second steam riser is located at the top of the second crystallizer. The second condenser is fitted over the upper part of the second crystallizer, such that the second steam riser is located inside the second condenser. A second stirring shaft passes through the lower part of the second crystallizer. The second stirring shaft is located outside the second crystallizer and connected to a second motor, and inside the second crystallizer and connected to a second stirring fan blade. The upper part of the second condenser is connected to a second condenser inlet pipe, and the lower part is connected to a second condenser outlet pipe. A second regulating discharge pipe with a valve and a second regulating inlet pipe with a valve are connected to the second condenser inlet pipe. The third crystallization unit consists of a third condenser and a third crystallizer. The third condenser is cylindrical, and the middle part of the third crystallizer is cylindrical. A coaxial third clarifier is installed inside the cylinder. The upper part of the third crystallizer is frustum-shaped, the lower part is an inverted frustum-shaped, and the bottom of the third crystallizer is arc-shaped. A cylindrical third steam riser is provided at the top of the third crystallizer. The third condenser is fitted onto the upper part of the third crystallizer, so that the third steam riser of the third crystallizer is located inside the third condenser. A washing salt leg is connected to the bottom of the third crystallizer. The upper part of the third condenser is connected to the third condenser inlet pipe, and the lower part of the third condenser is connected to the third condenser outlet pipe. The bottom of the first crystallizer is connected to the feed pump via a first feed pipe, and one end of the first discharge pump is connected to the bottom of the first crystallizer at a position opposite to the feed pump. The other end of the first discharge pump is connected to the bottom of the second crystallizer, and one end of the second discharge pump is connected to the bottom of the second crystallizer at a position opposite to the connection of the first discharge pump. The other end of the second discharge pump and one end of the flash circulation pump are connected together via a pipe to the upper middle part of the third crystallizer. The other end of the flash circulation pump is connected to the middle part of the third crystallizer. The washing salt leg is connected to one end of the third discharge pump, and the other end of the third discharge pump is connected to the centrifuge. The third condenser outlet pipe is connected to the third water tank, the third water tank is connected to one end of the third water pump, and the other end of the third water pump is connected to the second condenser inlet pipe; the second condenser outlet pipe is connected to the second water tank; the second water tank is connected to one end of the second water pump, and the other end of the second water pump is connected to the first condenser inlet pipe; the first condenser outlet pipe is connected to the first water tank; the first water tank is connected to the first water pump; low-temperature raw brine or low-temperature chilled water is input from the third condenser inlet pipe of the third condenser; The washed salt leg is connected to the first feed pipe via a pipeline; The height difference between the top of the first crystallizer and the liquid level in the first water tank is calculated using the following formula: Where P0 is atmospheric pressure and P1 is the pressure of the sealed container; ρ is density; g is gravitational acceleration; h is the height of the hydrostatic column, where P1 < P0, so that the first crystallizer is kept under negative pressure.

2. The three-stage flash crystallization system as described in claim 1, characterized in that, The first condenser, the second condenser, and the third condenser each have a plurality of baffles horizontally arranged inside.

3. The three-stage flash crystallization system as described in claim 2, characterized in that, The baffle plate has a plurality of holes.

4. A method for three-stage flash crystallization of potassium chloride using the three-stage flash crystallization system as described in any one of claims 1 to 3, characterized in that, Includes the following steps: 1) The mother liquor discharged after evaporating and crystallizing the original brine to obtain sodium chloride product salt has a temperature of 100℃ and contains a saturated solution of potassium chloride with a mass percentage concentration of 19% and sodium chloride of 15.5%. 2) Add alkali to the discharged mother liquor to adjust the pH of the discharged mother liquor to 12±0.2 to remove impurities, then keep it warm and let it settle, and separate the supernatant and precipitate; The settling time at 100℃ is 1 hour; 3) The supernatant was kept warm and filtered, and the pH of the filtrate was adjusted to 7-8 with hydrochloric acid. 4) The neutralized filtrate is fed to the first crystallizer via a feed pump for flash evaporation and cooling concentration at a temperature of 75℃ and a vacuum of -0.06 ~ -0.080MPa; 5) The slurry I obtained by flash cooling and concentration in the first crystallizer is transported to the second crystallizer by the first discharge pump for the next step of flash cooling and concentration; The temperature is 50℃ and the vacuum degree is -0.092MPa; 6) The slurry II obtained by flash cooling and concentration in the second crystallizer is transported to the third crystallizer by the second discharge pump for further flash cooling and concentration at a temperature of 30℃ and a vacuum degree of -0.098MPa. 7) The slurry III obtained by flash evaporation and cooling concentration in the third crystallizer is fed into a centrifuge for separation to obtain potassium chloride wet product and potassium chloride mother liquor; 8) Packaging wet potassium chloride yields fertilizer-grade potassium fertilizer; Potassium chloride mother liquor is discharged to the sodium chloride evaporation and crystallization production line; 9) While performing steps 4) to 8), low-temperature raw brine or low-temperature chilled water is introduced from the inlet pipe of the third condenser; the secondary raw brine or secondary feed water obtained after heat exchange between the low-temperature raw brine or low-temperature chilled water and slurry II entering the third crystallizer is discharged from the outlet pipe of the third condenser to the third water tank, and then enters the second condenser from the inlet pipe of the second condenser via the third water pump; the tertiary raw brine or tertiary feed water obtained after heat exchange between the secondary raw brine or tertiary feed water and slurry I entering the second condenser is discharged from the outlet pipe of the second condenser to the second water tank, and then enters the first condenser from the inlet pipe of the first condenser via the second water pump; the high-temperature raw brine or high-temperature feed water obtained after heat exchange between the tertiary raw brine or tertiary feed water and the filtrate entering the first condenser is discharged from the outlet pipe of the first condenser to the first water tank, and then discharged via the first water pump.

5. The method for three-stage flash crystallization of potassium chloride as described in claim 4, characterized in that, The alkali mentioned in step 2) is potassium hydroxide.

6. The method for three-stage flash crystallization of potassium chloride as described in claim 4, characterized in that, Step 3) The heat preservation filter uses a security filter with heat preservation properties, made of titanium, with a pore size of 5 micrometers.

7. The method for three-stage flash crystallization of potassium chloride as described in claim 4, characterized in that, The first and second crystallizers are both DTB type crystallizers, and the third crystallizer is an OSL type crystallizer.

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