Multistage eutectic freezing crystallization salt extraction system and method

Abstract

The invention belongs to the technical field of salt extraction and separation, and particularly relates to a multistage eutectic freezing crystallization salt extraction system and method. According to the multi-stage eutectic freezing crystallization salt extraction system provided by the invention, the characteristic that solutions of different soluble salts have different eutectic temperatures is ingeniously utilized, the temperature of saline water is gradually reduced, the temperature of each stage of crystallization process section is accurately controlled, a single salt component is separated from a solution containing multiple salts, and high-purity single salt crystals are obtained; the purpose of selective separation is achieved. In the low-temperature crystallization process, water can be separated from the solution in an ice crystal form at the same time, and high-purity ice crystals are obtained while salt crystals are separated and can be converted into high-purity water. Compared with a solarization method and a vacuum boiling method, the method has the advantages of high selectivity, complete separation, small occupied area, continuous production, zero wastewater discharge and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of salt extraction and separation, and in particular relates to a multi-stage eutectic freezing crystallization salt extraction system and method. Background Art

[0002] Seawater and brine from various sources contain a variety of useful salts, such as sodium chloride, potassium salts, calcium salts, magnesium salts, and sulfates. Sodium chloride and potassium salts are of particular economic value and strategic significance. Sodium chloride is not only an essential mineral for the human body but also a crucial raw material in the salt chemical industry, being indispensable for the production of soda ash and caustic soda. Potash salts are essential fertilizers in agricultural production. Other salts also have diverse uses. For example, magnesium salts can be used as a raw material for magnesium metal extraction, while calcium salts and sulfates can be used as thermal insulation fillers.

[0003] Methods for extracting salt from seawater and other brine include solar evaporation, vacuum cooking, and ion exchange. Currently, solar evaporation and vacuum cooking are the most popular processes. Solar evaporation is simple, but it relies heavily on hot, sunny weather and requires large, flat areas of land for salt drying. Vacuum cooking uses heat and vacuum to accelerate water evaporation, enabling continuous and rapid extraction of salt from concentrated brine. However, this method consumes significant energy, and the high-temperature brine is severely corrosive to machinery, requiring expensive, corrosion-resistant alloys to construct heat exchangers. Furthermore, solar evaporation and vacuum cooking lack selectivity for salt separation; they can only extract salts closest to saturation concentration in the brine by seeding the evaporation process, preventing further separation of other valuable salts. Furthermore, solar evaporation and vacuum cooking also discharge highly concentrated brine, making them difficult to meet sustainable development requirements. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a multi-stage eutectic freeze crystallization salt extraction system and method.

[0005] The technical solution adopted by the present invention is as follows: a multi-stage eutectic freeze crystallization salt extraction system, comprising: A carbonate precipitation unit is used to input water-soluble carbonate to react with calcium and magnesium ions in the brine solution to produce carbonate precipitate, and separate the carbonate precipitate and the first mother liquor; The second cooling crystallization unit includes a crystallization device and a separation device, which is used to cool the first mother liquor to 0°C to -9°C, produce ice crystals and salt crystals with a eutectic temperature higher than -9°C, and separate the ice crystals, second salt crystals and second mother liquor; A third cooling crystallization unit, comprising a crystallization device and a separation device, is used to cool the second mother liquor to -9°C to -20°C, produce ice crystals and salt crystals of salt with a eutectic temperature of -9°C to -20°C, and separate the ice crystals, third salt crystals and third mother liquor; The fourth cooling crystallization unit includes a crystallization device and a separation device, which is used to cool the third mother liquor to below -20°C, produce ice crystals and salt crystals with a eutectic temperature of ice crystals and a eutectic temperature of salt below -20°C, and separate to obtain ice crystals, fourth salt crystals and a fourth mother liquor.

[0006] The carbonate precipitation unit includes a first cooling crystallization unit, which includes a crystallization device and a separation device. After the brine solution is mixed with the water-soluble carbonate, it is cooled to a minimum of 0°C by the first cooling crystallization unit to separate ice crystals, carbonate salt crystals and a first mother liquor.

[0007] The fourth cooling crystallization unit cools the third mother liquor to -20°C to -25°C, and the fourth salt crystals are salt crystals of a salt having a eutectic temperature lower than -20°C but higher than -25°C.

[0008] The method further comprises an evaporation module, which is used to evaporate the fourth mother liquor so that the water in the aqueous solution is completely evaporated to separate the salt.

[0009] The crystallization device includes a crystallizer and a heat exchange pipeline. The crystallizer includes a tank body, an air inlet, an air outlet, a feed port, and a discharge port arranged on the tank body. The air inlet and the air outlet are connected through the tank body cavity to form a gas flow path from the air inlet to the air outlet in the tank body cavity. The feed port and the discharge port are connected through the tank body cavity to form a liquid flow path from the feed port to the discharge port in the tank body cavity. The flow direction of the gas flow path is opposite to the flow direction of the liquid flow path; the heat exchange pipeline is provided with a heat exchange device and a pressurizing device, the heat exchange device is connected to a cold source, and the two ends of the heat exchange pipeline are respectively connected to the air inlet and the air outlet, and under the action of the pressurizing device, a gas pressurized delivery path from the air outlet to the air inlet is formed.

[0010] The air inlet is arranged at the bottom of the tank body or near the bottom of the tank body, the air outlet is arranged at the top of the tank body or near the top of the tank body, the feed port is arranged at the top of the tank body or near the top of the tank body, and the discharge port is arranged at the bottom of the tank body or near the bottom of the tank body.

[0011] The heat exchange device includes a pre-cooling heat exchanger and a main heat exchanger, which are arranged successively along the conveying direction of the gas pressurized conveying path. The pre-cooling heat exchanger is connected to the first cold source, and the main heat exchanger is connected to the second cold source. The pre-cooling heat exchanger includes a condensate outlet and a gas outlet. The tank body is provided with a condensate reflux port, and the condensate outlet is connected to the condensate reflux port.

[0012] The pressurizing device is a gas compressor arranged between the pre-cooling heat exchanger and the main heat exchanger.

[0013] A check valve is provided on the heat exchange pipeline, and the check valve is arranged between the heat exchange device and the pressurizing device and the air inlet.

[0014] A multi-stage eutectic freeze crystallization salt extraction method based on the multi-stage eutectic freeze crystallization salt extraction system as described above.

[0015] The multi-stage eutectic freeze crystallization salt extraction system provided by the present invention cleverly utilizes the characteristics that solutions of different soluble salts have different eutectic temperatures, gradually lowers the temperature of the brine, accurately controls the temperature of each crystallization process section, separates a single salt component from a solution containing multiple salts, and obtains a high-purity single type of salt crystals, thereby achieving the purpose of selective separation. During the low-temperature crystallization process, water will simultaneously separate from the solution in the form of ice crystals. While separating the salt crystals, high-purity ice crystals are obtained, which can be converted into high-purity water. Compared with the sun-drying method and the vacuum boiling method, the present invention has the advantages of high selectivity, complete separation, small footprint, continuous production and zero wastewater discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0017] Figure 1 This is a schematic diagram of the multi-stage eutectic freeze crystallization salt extraction system provided by the present invention; Figure 2 This is a schematic structural diagram of the freeze crystallization device used in the present invention; Figure 3 This is an operation flow chart of the freeze crystallization device used in the present invention; In the figure, Crystallizer-100, air inlet-110, air outlet-120, feed inlet-130, discharge outlet-140, condensate reflux outlet-150; Heat exchange pipeline-200, pre-cooling heat exchanger-210, main heat exchanger-220, gas compressor-230, check valve-240; The first cold source is 310 and the second cold source is 320. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0019] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. Subsequent embodiments will not explain this one by one.

[0020] The terms used herein, such as "up," "down," "front," "back," "left," "right," "inside," "outside," "top," "bottom," and "side," are intended solely to refer to the accompanying drawings. These terms are intended to illustrate and facilitate understanding of the present invention and are not intended to limit its scope.

[0021] Different salt solutions have different eutectic temperatures. Below this temperature, the water and salt in the brine solution crystallize and precipitate, forming ice crystals and salt crystals. These crystallized ice crystals and salt crystals are of high purity. If a brine solution contains multiple salts, when the solution temperature drops to freezing, the solution begins to freeze, and ice crystals begin to form first. As ice crystals form, the water content of the solution decreases, the salt concentration increases, and the freezing point of the brine solution decreases with the increasing salt concentration. As the brine solution cools, the different soluble salt components in the solution crystallize into solid crystals when the solution temperature reaches their respective eutectic temperatures. For example, the eutectic temperature of sodium chloride is -21.2°C, and that of potassium chloride is -10.7°C. If a brine solution contains both sodium chloride and potassium chloride, the potassium chloride will crystallize into solid potassium chloride monohydrate crystals when the brine temperature drops to -10.7°C, allowing the potassium chloride to separate from the aqueous solution. At this temperature, sodium chloride in the solution does not form crystals and will not separate from the brine solution. If the brine temperature drops to -21.2°C, the sodium chloride in the solution will begin to form dihydrate sodium chloride crystals, and the water will freeze to form ice crystals. After separating the ice crystals and sodium chloride salt crystals, high-purity ice and sodium chloride salt crystals are obtained. Based on the above principle, the present invention designs Figure 1 The multi-stage eutectic freeze crystallization salt extraction system shown includes a carbonate precipitation unit, a second cooling crystallization unit, a third cooling crystallization unit, a fourth cooling crystallization unit and an evaporation module.

[0022] The carbonate precipitation unit consists of a mixing tank, a crystallization unit, and a separation device, all connected by pipelines. The carbonate precipitation unit introduces water-soluble carbonate, which reacts with calcium and magnesium ions in the brine solution to produce carbonate precipitates. Specifically, in the mixing tank, the brine feed is mixed with a saturated sodium carbonate solution. The sodium carbonate solution addition ratio per liter of brine feed is calculated as (calcium ion concentration + magnesium ion concentration) ÷ sodium carbonate solution concentration, with all variables expressed in mol / L. The calcium and magnesium ions in the aqueous solution react with the carbonate ions to form insoluble calcium carbonate and magnesium carbonate, thereby separating the calcium and magnesium ions from the brine. Ideally, the calcium and magnesium carbonates are completely precipitated, removing all calcium and magnesium ions from the brine. However, trace amounts of calcium and magnesium carbonate still dissolve in water. At 25°C, the solubility of calcium carbonate is approximately 0.0014 g / 100 g, and the solubility of magnesium carbonate is approximately 0.01 g / 100 g. These trace amounts of calcium and magnesium can affect the purity of subsequent salt crystals. Therefore, a crystallizer is further installed to further cool the mixed solution to a minimum of 0°C. At 0°C, the solubility of calcium carbonate in water is approximately 0.0013g / 100g water, and the solubility of magnesium carbonate in water is approximately 0.0095g / 100g water. This further reduces the impact of residual calcium and magnesium ions on the purity of subsequent salt crystals. If the crystallizer is equipped with a stirring device, the crystallizer can be used directly as a mixing tank, where the saturated sodium carbonate solution and brine are mixed and cooled to crystallize directly.

[0023] Among them, the second cooling crystallization unit includes a crystallization device and a separation device, which is used to cool the first mother liquor to 0℃~-9℃, produce ice crystals and salt crystals with a eutectic temperature higher than -9℃, and separate them to obtain ice crystals, second salt crystals and second mother liquor; the second salt crystals precipitated in this process section are mainly sulfate hydrate crystals, and the cooling temperature is preferably set to -9℃ to effectively reduce the influence of residual sulfate ions on the purity of subsequent salt crystals.

[0024] Among them, the third cooling crystallization unit includes a crystallization device and a separation device, which is used to cool the second mother liquor to -9°C ~ -20°C, produce ice crystals and salt crystals with a eutectic temperature of -9°C ~ -20°C, and separate them into ice crystals, third salt crystals and third mother liquor; the salt crystals separated in this process section are mainly salt crystals of potassium chloride hydrate, and the cooling temperature is preferably set to -20°C to effectively reduce the impact of residual potassium ions on the purity of subsequent salt crystals.

[0025] Among them, the fourth cooling crystallization unit includes a crystallization device and a separation device, which is used to cool the third mother liquor to -20°C~-25°C, produce ice crystals and salt crystals with a eutectic temperature of -20°C~-25°C, and separate them into ice crystals, fourth salt crystals and fourth mother liquor; the salt crystals separated in this process section are mainly salt crystals of sodium chloride hydrate, and the cooling temperature is preferably set to -25°C to allow sodium chloride to be extracted more fully and effectively.

[0026] After the fourth cooling crystallization unit, the brine solution has essentially completed salt separation. After solid-liquid separation, a very small amount of brine solution with a freezing temperature below -25°C may remain. This residual brine solution undergoes evaporation to completely evaporate the water in the solution, separating the salt from the brine solution and achieving zero liquid discharge. Evaporation methods include, but are not limited to, spray drying and vacuum evaporation. The vapor generated by evaporation is condensed and distilled water is recovered.

[0027] One of the most important goals of the multi-stage process proposed in this invention is to reduce energy consumption during the freeze-crystallization salt extraction process. According to the principles of thermodynamics, if a compressor is used for refrigeration, assuming the ambient temperature remains constant, the lower the temperature of the cooling source and the greater the difference from the ambient temperature, the more electrical or mechanical energy is required per unit of cooling capacity, while the lower the temperature, the less electrical or mechanical energy is required.

[0028] For example, the eutectic temperature of sodium chloride aqueous solution is -21.2°C. If a cold source below -21.2°C is used throughout the freezing process to cool the solution, the energy consumption per unit of sodium chloride crystal produced will be very high. However, if a cold source at -10°C is first used to cool the sodium chloride aqueous solution to around -10°C, and then a cold source below -21.2°C is used to cool the sodium chloride aqueous solution to the eutectic temperature, the energy consumption of the cooling process can be effectively reduced. The present invention proposes to set up four crystallization units with different temperatures, match cold sources of different temperatures to different crystallization units, and each crystallization unit can extract different types of target salt crystals while reducing the temperature of the brine solution, thereby realizing the cascade utilization of the cold source temperature. Magnesium chloride and calcium chloride are widely present in brine solutions from various sources. The eutectic temperature of magnesium chloride aqueous solution is -33.6°C, and the eutectic temperature of calcium chloride aqueous solution is -49.8°C. The eutectic temperatures of the above two salts are both far below -25°C, requiring extremely low-temperature cold sources for cooling. To reduce energy consumption and improve efficiency, the present invention proposes pre-adding soluble carbonates to separate calcium and magnesium ions from the aqueous solution in the first carbonate precipitation crystallization unit, thus avoiding the use of a low-temperature cooling source with low cooling efficiency. In the proposed process flow, these two process designs work together to significantly improve energy efficiency and overall production efficiency.

[0029] Among them, the crystallization devices used in the carbonate precipitation unit, the second cooling crystallization unit, the third cooling crystallization unit, and the fourth cooling crystallization unit are all for cooling and crystallizing the liquid part, including a crystallizer 100 and a heat exchange pipeline 200. The heat exchange pipeline 200 is provided with a heat exchange device, and the heat exchange device is connected to a low-temperature refrigeration device. The low-temperature refrigeration device provides a cold source, and the heat exchange device transfers the heat of the brine to the cold source, thereby reducing the temperature of the brine.

[0030] Since the cooling temperatures of the second cooling crystallization unit, the third cooling crystallization unit, and the fourth cooling crystallization unit are all lower than 0°C, in order to avoid the water freezing and icing in the heat exchange device, which leads to a decrease in heat exchange efficiency and affects production efficiency, the crystallization device used in the present invention is as follows: Figure 2 As shown, the crystallizer 100 includes a tank body, an air inlet 110, an air outlet 120, a feed port 130, a discharge port 140, and a condensate reflux port 150 arranged on the tank body, wherein the air inlet 110 is arranged at the bottom of the tank body or near the bottom of the tank body, the air outlet 120 is arranged at the top of the tank body or near the top of the tank body, the feed port 130 is arranged at the top of the tank body or near the top of the tank body, the discharge port 140 is arranged at the bottom of the tank body or near the bottom of the tank body, and the condensate reflux port 150 is arranged at the top of the tank body or near the top of the tank body, as shown in FIG. Figure 3 As shown, the air inlet 110 and the air outlet 120 cooperate within the tank cavity to form a bottom-up flow path for the gas within the tank, while the feed inlet 130 and the feed outlet 140 cooperate within the tank cavity to form a top-down flow path for the liquid within the tank. The heat exchange pipeline 200 connects the air inlet 110 and the air outlet 120 at both ends, and is equipped with a pre-cooling heat exchanger 210, a gas compressor 230, a main heat exchanger 220, and a check valve 240 in the direction from the air outlet 120 to the air inlet 110.

[0031] The pre-cooling heat exchanger 210 is connected to the first cold source 310. Under the heat exchange effect of the first cold source 310, the pre-cooling heat exchanger 210 cools the medium to a temperature below the condensation temperature of the solvent in the feed liquid and above the freezing temperature of the solvent in the feed liquid. After the gas passes through the liquid in the tank, it inevitably entrains a small amount of vaporized solvent. The present invention provides a pre-cooling heat exchanger 210 to pre-cool the gas discharged through the gas outlet 120, condensing and liquefying the entrained solvent vapor in the gas. The solvent vapor is then returned to the tank of the crystallizer 100 through the condensate return port 150 of the ventilation pipe. The main heat exchanger 220 is connected to the second cold source 320. Under the heat exchange effect of the second cold source 320, the main heat exchanger 220 cools the medium to a temperature no higher than the preset eutectic temperature of the feed liquid, ensuring that the gas is fully cooled within the main heat exchanger. Under the pressure of the gas compressor 230, the gas in the tank is discharged through the gas outlet 120, transported under pressure in the heat exchange pipeline 200, and after flowing through the pre-cooling heat exchanger 210 and the main heat exchanger 220, it enters the tank through the gas inlet 110, forming a cycle. The gas in the tank flowing from bottom to top forms a countercurrent heat flow with the liquid in the tank flowing from top to bottom. The feed liquid enters the tank through the feed inlet 130 at the top of the tank, fully exchanges heat with the gas, and then cools and crystallizes. The solid-liquid mixture containing crystals is then discharged from the discharge port 140 at the bottom. When the low-temperature high-pressure gas passes through the solution, as the pressure decreases and the volume increases, it can also produce an additional throttling effect, further reducing the temperature of the gas flow, which can improve the heat transfer efficiency and crystallization efficiency.

[0032] The present invention cleverly utilizes high-pressure gas as a heat transfer carrier, and utilizes the flowing high-pressure, low-temperature gas to conduct heat between the heat exchanger and the solution. The airflow and the solution are in direct contact for heat transfer, thus avoiding direct contact between the solution and the wall of the heat exchanger. The problems of corrosion and surface crystallization of the heat exchanger can be basically solved, thus improving efficiency and reducing the manufacturing cost of the heat exchanger. Furthermore, the present invention can further effectively avoid the freezing and formation of ice in the main heat exchanger 220 of the solvent vapor entrained in the discharged high-pressure gas after sufficient heat exchange between the crystallizer and the solution by setting the pre-cooling heat exchanger 210. The check valve 240 is provided to prevent liquid from flowing back into the main heat exchanger 220 and the gas compressor 230.

[0033] In the present invention, the heat transfer carrier gas is preferably a non-flammable gas that does not chemically react with any components in the solution. The gas selected can be based on the type of feed solution and the desired crystallization temperature. Commonly used gases include, but are not limited to, air, nitrogen, inert gases, and gaseous carbon dioxide. When air is not selected as the heat transfer carrier gas, the crystallizer should be kept in the same gas atmosphere as the heat transfer carrier gas.

[0034] In the present invention, the first cold source 310 and the second cold source 320 include, but are not limited to, low-temperature atmosphere, compression refrigeration equipment, absorption refrigeration equipment, and low-temperature liquids or gases generated in other industrial processes.

[0035] In the present invention, if the feed liquid contains combustible components, the gas compressor should be a gas compressor that meets the corresponding explosion-proof standards.

[0036] In the present invention, the air pressure generated by the gas compressor should be equal to or slightly greater than the liquid pressure at the gas inlet 110 within the tank, allowing air to flow smoothly through the gas inlet 110 and into the liquid. Since the gas inlet 110 is located at the bottom of the tank, the gas compressor outlet pressure should be calculated as follows: liquid density × liquid level in the tank × local acceleration of gravity. All variables are calculated using international standard units.

[0037] In the present invention, the crystallizer can be various types of chemical crystallizers, including but not limited to stirring crystallizers, pipeline crystallizers and ultrasonic assisted crystallizers.

[0038] In the present invention, in the solid-liquid mixture produced in the crystallization devices of the carbonate precipitation unit, the second cooling crystallization unit, the third cooling crystallization unit, and the fourth cooling crystallization unit, the density of ice is less than that of brine, and the density of brine is less than that of salt crystals. Therefore, a process including but not limited to gravity sedimentation, a centrifugal separation process or a combination of multiple separation processes can be used to separate ice crystals, brine and salt crystals from the solid-liquid mixture.

[0039] The brine of the present invention can be natural brine such as seawater, salt lake brine, underground brine, or brine treated by processes such as solarization, vacuum boiling, or ion exchange. After treatment by this process, the various salts and water in the brine solution will be separated, and various high-purity salt crystals and pure water will be produced. If the process of the present invention is used to treat seawater, high-purity sodium chloride crystals and potassium chloride crystals, pure water, sulfate crystals, calcium salt crystals, and magnesium salt crystals can be extracted from the seawater. Compared with solarization and vacuum boiling methods, the present invention has the advantages of high selectivity, complete separation, small footprint, continuous production, and zero wastewater discharge.

[0040] The above disclosure is merely a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A multi-stage eutectic freeze crystallization salt extraction system, characterized in that: include: A carbonate precipitation unit is used to input water-soluble carbonate to react with calcium and magnesium ions in the brine solution to produce carbonate precipitate, and separate the carbonate precipitate and the first mother liquor; The second cooling crystallization unit includes a crystallization device and a separation device, which is used to cool the first mother liquor to 0°C to -9°C, produce ice crystals and salt crystals with a eutectic temperature higher than -9°C, and separate the ice crystals, second salt crystals and second mother liquor; A third cooling crystallization unit, comprising a crystallization device and a separation device, is used to cool the second mother liquor to -9°C to -20°C, produce ice crystals and salt crystals of salt with a eutectic temperature of -9°C to -20°C, and separate the ice crystals, third salt crystals and third mother liquor; The fourth cooling crystallization unit includes a crystallization device and a separation device, which is used to cool the third mother liquor to below -20°C, produce ice crystals and salt crystals with a eutectic temperature of ice crystals and a eutectic temperature of salt below -20°C, and separate to obtain ice crystals, fourth salt crystals and a fourth mother liquor.

2. The multi-stage eutectic freeze crystallization salt extraction system according to claim 1, characterized in that: The carbonate precipitation unit includes a first cooling crystallization unit, which includes a crystallization device and a separation device. After the brine solution is mixed with the water-soluble carbonate, it is cooled to a minimum of 0°C by the first cooling crystallization unit to separate ice crystals, carbonate salt crystals and a first mother liquor.

3. The multi-stage eutectic freeze crystallization salt extraction system according to claim 1, characterized in that: The fourth cooling crystallization unit cools the third mother liquor to -20°C to -25°C, and the fourth salt crystals are salt crystals of a salt having a eutectic temperature lower than -20°C but higher than -25°C.

4. The multi-stage eutectic freeze crystallization salt extraction system according to claim 3, characterized in that: The method further comprises an evaporation module, which is used to evaporate the fourth mother liquor so that the water in the aqueous solution is completely evaporated to separate the salt.

5. The multi-stage eutectic freeze crystallization salt extraction system according to claim 1, characterized in that: The crystallization device includes a crystallizer and a heat exchange pipeline. The crystallizer includes a tank body, an air inlet, an air outlet, a feed port, and a discharge port arranged on the tank body. The air inlet and the air outlet are connected through the tank body cavity to form a gas flow path from the air inlet to the air outlet in the tank body cavity. The feed port and the discharge port are connected through the tank body cavity to form a liquid flow path from the feed port to the discharge port in the tank body cavity. The flow direction of the gas flow path is opposite to the flow direction of the liquid flow path; the heat exchange pipeline is provided with a heat exchange device and a pressurizing device, the heat exchange device is connected to a cold source, and the two ends of the heat exchange pipeline are respectively connected to the air inlet and the air outlet, and under the action of the pressurizing device, a gas pressurized delivery path from the air outlet to the air inlet is formed.

6. The multi-stage eutectic freeze crystallization salt extraction system according to claim 5, characterized in that: The air inlet is arranged at the bottom of the tank body or near the bottom of the tank body, the air outlet is arranged at the top of the tank body or near the top of the tank body, the feed port is arranged at the top of the tank body or near the top of the tank body, and the discharge port is arranged at the bottom of the tank body or near the bottom of the tank body.

7. The multi-stage eutectic freeze crystallization salt extraction system according to claim 5, characterized in that: The heat exchange device includes a pre-cooling heat exchanger and a main heat exchanger, which are arranged successively along the conveying direction of the gas pressurized conveying path. The pre-cooling heat exchanger is connected to the first cold source, and the main heat exchanger is connected to the second cold source. The pre-cooling heat exchanger includes a condensate outlet and a gas outlet. The tank body is provided with a condensate reflux port, and the condensate outlet is connected to the condensate reflux port.

8. The multi-stage eutectic freeze crystallization salt extraction system according to claim 7, characterized in that: The pressurizing device is a gas compressor arranged between the pre-cooling heat exchanger and the main heat exchanger.

9. The multi-stage eutectic freeze crystallization salt extraction system according to claim 5, characterized in that: A check valve is provided on the heat exchange pipeline, and the check valve is arranged between the heat exchange device and the pressurizing device and the air inlet.

10. A multi-stage eutectic freeze crystallization salt extraction method based on the multi-stage eutectic freeze crystallization salt extraction system according to any one of claims 1 to 9.

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