A freeze crystallization separation system and method

Abstract

The application relates to the technical field of crystallization, and discloses a frozen crystallization separation system and method, which comprises a raw material system, a heat exchange system, a frozen crystallization system, a separation system, a salt impurity system, a heat source system, a cold source system and an accident system connected in sequence, in the method, high-salinity water is pressurized by a feeding pump, is exchanged with cold, is led into a frozen crystallization device from a lower circulating pipe, after being cooled by freezing, crystals are discharged from the crystallization device, and then are sequentially led into a settler and a centrifugal machine to obtain crystallized salt and centrifugal mother liquor. The frozen crystallization separation system and method have the advantages of high heat / cold utilization efficiency, stable product quality, long operation period, wide raw material adaptation range and the like, and can be popularized and applied in the field of high-salinity water zero discharge.

Description

Technical Field

[0001] This invention relates to the field of crystallization technology, and more specifically to a freeze crystallization separation system and method. Background Technology

[0002] Domestic and international technologies for treating high-salinity wastewater mainly include membrane methods and thermal methods. Membrane methods utilize the selective permeability of semi-permeable membranes to separate certain substances from wastewater. The most commonly used membrane technologies are reverse osmosis and electrodialysis. Membrane methods have advantages such as low energy consumption, simple operation, and strong adaptability, and can also recover resources from wastewater. However, when treating high-salinity wastewater such as waste alkaline solutions, the biggest challenge of membrane technology lies in membrane fouling. The accumulation of large amounts of COD on the membrane surface in the influent directly leads to reduced permeate flow and deterioration of permeate quality, thus shortening the membrane's lifespan. Therefore, membrane technology places high demands on COD pretreatment of the influent and is not suitable for wastewater containing large amounts of recalcitrant COD. Thermal methods separate water or salt from wastewater by changing the system pressure and temperature to induce a phase change. The most common thermal technologies include evaporation concentration and freeze crystallization. Thermal methods have broad application prospects due to their simple operation, good treatment effect, and ability to recover salt.

[0003] In contrast to thermal methods, there is freeze crystallization technology. This technology utilizes the characteristic that the solubility of soluble substances decreases significantly with decreasing temperature, allowing crystallization to precipitate and thus achieving solid-liquid separation. Freeze crystallization technology is widely used in petrochemical, salt chemical, wastewater treatment, and environmental remediation fields due to its relatively low energy consumption, simple operation, short process, wide applicability, and low equipment cost.

[0004] In comparison, freeze crystallization technology has irreplaceable advantages over thermal crystallization. Currently, freeze crystallization is classified into continuous and intermittent methods based on its operation. Intermittent methods, due to their batch production, suffer from high energy consumption, poor material discharge, and low production capacity. Continuous methods, on the other hand, suffer from long piping between the crystallizer and cooler, susceptibility to cooler blockage, and poor-quality crystallized products, leading to frequent shutdowns for maintenance and hindering large-scale, high-efficiency development, while increasing production costs and operational energy consumption.

[0005] Against this background, the present invention studies a freeze crystallization separation system and method. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a freeze-crystallization separation system and method. This system is particularly suitable for the resource-based treatment of waste alkaline solutions after oxidation and neutralization in refining and chemical enterprises, as well as high-salt wastewater from coal chemical plants.

[0007] To achieve the above objectives, a first aspect of the present invention provides a freeze crystallization separation system, comprising a raw material system, a heat exchange system, a freeze crystallization and separation system connected in sequence, as well as a mixed salt system, a heat source system, a cold source system, and an emergency system;

[0008] The freeze crystallization and separation system is at least one stage; each stage of the freeze crystallization and separation system includes a freeze crystallization system and a separation system connected in sequence.

[0009] Each stage of the separation system is equipped with a crystallized salt discharge pipeline and a centrifugal mother liquor discharge pipeline. The centrifugal mother liquor discharge pipeline is connected to the feed pipeline of the next stage of the freeze crystallization system, or it is connected to the refrigerant inlet of the heat exchange system and the feed pipeline of the freeze crystallization system of this stage, respectively.

[0010] The refrigerant outlet pipeline of the heat exchange system is connected to the cooling mother liquor inlet of the mixed salt system.

[0011] The heat source system is connected to the heat medium inlet and outlet of each stage of the freezing crystallization system and the mixed salt system, respectively.

[0012] The cold source system is connected to the refrigerant inlet and outlet of each stage of the freezing and crystallization system;

[0013] The accident system is connected to each stage of the cryo-crystallization system.

[0014] A second aspect of the present invention provides a method for cryo-crystallization separation, wherein the cryo-crystallization separation method is performed in the above-described cryo-crystallization separation system and includes the following steps:

[0015] Pre-cooling of feed liquid: The feed liquid in the raw material system is pumped to the heat exchange system and cooled down to obtain cooled feed liquid;

[0016] Freeze-separation: The cooled liquid is fed into a freeze crystallization and separation system to obtain crystalline salt and centrifugal mother liquor through at least one stage of freeze crystallization and separation;

[0017] Circulating cooling: The mother liquor of each stage of centrifugation is sent to the next stage of freezing crystallization and separation system for freezing crystallization and separation to obtain the next stage of crystallized salt and centrifugation mother liquor. Alternatively, the mother liquor of each stage of centrifugation is divided into two streams. One stream is cooled and heated with the feed liquid to obtain heated mother liquor, and the other stream is sent to the freezing crystallization and separation system of this stage for freezing crystallization and separation to obtain the current stage of crystallized salt and centrifugation mother liquor.

[0018] Preparation of mixed salts: The mother liquor is heated and then fed into a mixed salt system for dehydration to obtain mixed salts;

[0019] Circulating refrigeration: The cooling capacity required for each stage of freezing, crystallization, and separation is provided by the circulating refrigerant of the cold source system;

[0020] Circulating heating: The heating medium of the heat source system provides the heat required for the circulating refrigerant in each stage of freezing crystallization and separation, as well as the heat required for the dehydration of the mother liquor;

[0021] Accident Handling: When the freezing crystallization and separation system malfunctions, the liquid from the freezing crystallization system is discharged into the accident system for real-time processing.

[0022] The effects of this invention are:

[0023] (1) This invention proposes a cryogenic crystallization separation system. The system pre-cools the feed by using the cold energy of the centrifugal mother liquor generated by the cryogenic crystallization and separation system. It has advantages such as high energy utilization and low operating cost. The system is combined with a mixed salt system to treat the small amount of discharged mother liquor into mixed salt to achieve zero wastewater discharge and resource utilization. In addition, the system is equipped with an emergency system. After the system is operating normally, the emergency discharge liquid is returned to the crystallization system. Therefore, zero discharge is truly achieved.

[0024] (2) The freeze crystallization separation system and method proposed in this invention are equipped with a mother liquor separator on the circulation pipe. Through its special structural form, solid-liquid separation and low-density component accumulation can be achieved locally. The quality of the crystallized product can be adjusted by discharging a small amount of mother liquor.

[0025] (3) The freeze crystallization separation system and method proposed in this invention use a dual axial flow pump to force the adjacent cold and hot side media to flow in a countercurrent manner, which greatly reduces the heat transfer resistance on the cold and hot side, effectively improves the heat / cold energy utilization efficiency, and reduces the amount of heat / cold energy used. Under the same processing capacity, it has the advantages of small equipment size, saving investment and space.

[0026] (4) The freeze crystallization separation system and method proposed in this invention have a refrigerant heater with inlet and outlet for the heating medium. Combined with a refrigerant feed pump, this enables rapid reheating of the heat exchanger, resolving the blockage problem within the heat exchange tubes. Furthermore, a high-speed flushing port is installed at the bottom of the heat exchanger. By detecting the pressure difference between the inlet and outlet of the heat exchanger, a high-speed jet flush is performed online when a certain pressure difference is reached, thus resolving the blockage. Therefore, the crystallizer proposed in this invention has advantages such as high efficiency, low cost, low energy consumption, long operating cycle, and wide adaptability to raw materials.

[0027] (5) The freeze crystallization separation system and method proposed in this invention have a salt separator located at the bottom of the crystallizer and equipped with multiple low-speed flushing ports. The crystallized salt is discharged from the bottom of the salt separator, and the crystallized particles are uniform, of high quality and large in size.

[0028] (6) The freeze crystallization separation system proposed in this invention is equipped with a flow guide tube, which helps to achieve uniform crystallization in the crystallizer and can effectively alleviate the operation fluctuations caused by changes in operating load and feed composition.

[0029] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0030] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0031] Figure 1 This is a schematic diagram of the process of the freeze crystallization separation system provided by the present invention.

[0032] Figure 2 This is a flowchart illustrating the first specific embodiment of the freeze crystallization separation system provided by the present invention.

[0033] Figure 3 This is a flowchart illustrating a second specific embodiment of the freeze crystallization separation system provided by the present invention.

[0034] Figure 4 This is a flowchart illustrating the third specific embodiment of the freeze crystallization separation system provided by the present invention.

[0035] Figure 5 This is a flowchart illustrating the fourth specific embodiment of the freeze crystallization separation system provided by the present invention.

[0036] Figure 6 This is a schematic diagram of the structure of the first specific embodiment of the cryo-crystallizer provided by the present invention.

[0037] Figure 7 This is a schematic diagram of the structure of a second specific embodiment of the cryo-crystallizer provided by the present invention.

[0038] Figure 8 This is a schematic diagram of the third specific embodiment of the cryo-crystallizer provided by the present invention.

[0039] Figure 9 This is a schematic diagram of the fourth specific embodiment of the cryo-crystallizer provided by the present invention.

[0040] Explanation of reference numerals in the attached figures:

[0041] A101—Raw material system; A102—Heat exchange system; A103—Freezing and crystallization system; A104—Separation system; A105—Miscellaneous salt system; A106—Heat source system; A107—Cold source system; A108—Emergency system;

[0042] B1—Raw material tank; B2—Raw material feed pump; B3—No. 1 cooler; B4—Frozen crystallizer; B5—Settler; B6—Centrifuge; B7—Mother liquor dryer; B8—Refrigerant tank; B9—Refrigerant feed pump; B10—Emergency tank; B11—Emergency pump; B12—Refrigerant cooler;

[0043] S1—Pumped raw material; S2—Pre-cooled raw material; S3—Crystallized slurry; S4—Crystallized salt; S5—Centrifuged mother liquor; S6—Emergency discharge pipeline; S7—Return pipeline; S8—Cooling medium; S9—Heating medium; S10—Pumped refrigerant; S11—Returned refrigerant; S12—Miscellaneous salts; S13—Secondary refrigerant;

[0044] 101—Crystallizer; 102—Cooler; 103—1# Axial Flow Pump; 104—Refrigerant Heater; 105—2# Axial Flow Pump; 106—Mother Liquor Separator; 107—Salt Setter; 201—Upper Circulation Pipe of Crystallizing Liquid; 202—Lower Circulation Pipe of Crystallizing Liquid; 203—Upper Circulation Pipe of Refrigerant; 204—Lower Circulation Pipe of Refrigerant; 301—Guide Flow Tube;

[0045] 1—Inlet; 2—Outlet; 3—Refrigerant inlet; 4—Refrigerant outlet; 5—Heating medium inlet; 6—Heating medium outlet; 7—High-speed flushing port; 8—Drain port; 9—Low-speed flushing port; 10—Crystallizer temperature measuring port; 11—Circulation pipe temperature measuring port; 12—Circulation pipe pressure measuring port; 13—Drain port; 14—Cooler refrigerant inlet; 15—Cooler refrigerant outlet; 16—Cooler inlet pressure measuring port. Detailed Implementation

[0046] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0047] In this disclosure, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its normal operating state, for example, as shown in the reference. Figure 1 In the drawing orientation, "inner" and "outer" refer to their relative to the outline of the device. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0048] This invention provides a freeze-crystallization separation system, such as... Figure 1As shown, it includes a raw material system A101, a heat exchange system A102, a freeze crystallization and separation system, a mixed salt system A105, a heat source system A106, a cold source system A107, and an emergency system A108 connected in sequence.

[0049] The freeze crystallization and separation system is at least one stage; each stage of the freeze crystallization and separation system includes a freeze crystallization system A103 and a separation system A104 connected in sequence.

[0050] Each stage of separation system A104 is equipped with a crystallized salt discharge pipeline and a centrifugal mother liquor discharge pipeline. The centrifugal mother liquor discharge pipeline is connected to the feed pipeline of the next stage of freezing crystallization system A103, or to the refrigerant inlet of heat exchange system A102 and the feed pipeline of freezing crystallization system A103 of this stage, respectively.

[0051] The refrigerant outlet pipeline of heat exchange system A102 is connected to the cooling mother liquor inlet of mixed salt system A105;

[0052] The heat source system A106 is connected to the heat medium inlet and outlet of each stage of the freezing crystallization system A103 and the mixed salt system A105, respectively.

[0053] The cold source system A107 is connected to the refrigerant inlet and outlet of each stage of the refrigeration crystallization system A103;

[0054] The accident system A108 is connected to each stage of the cryo-crystallization system A103.

[0055] In this invention, the cryogenic crystallization separation system pre-cools the feed by using the cold energy of the centrifugal mother liquor generated by the cryogenic crystallization and separation system, which has advantages such as high energy utilization and low operating cost. In conjunction with the mixed salt system, the small amount of discharged mother liquor is treated into mixed salt to achieve zero wastewater discharge and resource utilization. In addition, with the set-up emergency system, the emergency discharge liquid is returned to the crystallization system after the system is operating normally, thus truly achieving zero discharge.

[0056] In this invention, in order to obtain a high crystallization yield, the freeze crystallization and separation system is at least one stage, preferably 1-5 stages in series, and more preferably 1-3 stages.

[0057] According to the present invention, the raw material system A101 includes a raw material tank B1 and a raw material feed pump B2 connected in sequence.

[0058] Heat exchange system A102 includes cooler B3 (No. 1);

[0059] The discharge pipeline of raw material feed pump B2 is connected to the raw material inlet of cooler B3 (No. 1); the raw material outlet of cooler B3 (No. 1) is connected to the feed pipeline of primary freezing crystallization system A103.

[0060] Each stage of the cryogenic crystallization system A103 includes a cryogenic crystallizer B4, which includes a crystallizer 101, a cooler 102, a refrigerant heater 104, a mother liquor separator 106, an optional salt separator 107, an upper circulation pipe 201 for the crystallizing liquid, a lower circulation pipe 202 for the crystallizing liquid, an upper circulation pipe 203 for the refrigerant, and a lower circulation pipe 204 for the refrigerant.

[0061] Each stage of the separation system A104 includes a settling tank B5 and a centrifuge B6 connected in sequence;

[0062] Each centrifuge B6 is equipped with a crystallized salt discharge pipeline and a centrifugal mother liquor discharge pipeline. The centrifugal mother liquor discharge pipeline is connected to the feed pipeline of the next stage refrigerated crystallizer B4, or it is connected to the refrigerant inlet of the 1# cooler B3 and the feed pipeline of the refrigerated crystallizer B4 of this stage, respectively.

[0063] Each stage of the crystallizing liquid circulation pipe 202 is equipped with an optional crystallizing slurry outlet;

[0064] Each salt separator 107 is located below and connected to the crystallizer 101 of its respective stage;

[0065] The outlet of each stage of crystallization slurry is connected to the inlet of the B5 settling tank of the same stage, or the outlet of each stage of salt separator 107 is connected to the inlet of the B5 settling tank of the same stage.

[0066] According to the present invention, each crystallizer 101 includes a cylindrical section and upper and lower conical sections located at both ends of the cylindrical section, and the axis of the cylindrical section coincides with the axis of the upper and lower conical sections;

[0067] Each crystallizer 101 is provided with a first outlet and a second outlet;

[0068] The first outlet of each stage is located on the side of the lower conical section of the crystallizer 101 of that stage, and the second outlet of each stage is located at the bottom of the lower conical section of the crystallizer 101 of that stage.

[0069] The hot-side medium outlet at the top of each stage cooler 102 is connected to the top inlet of the crystallizer 101 through the upper circulation pipe 201 of the crystallizer 101 of the stage, and the hot-side medium inlet at the bottom is connected to the first or second outlet of the crystallizer 101 through the lower circulation pipe 202 of the crystallizer 102 of the stage.

[0070] The second outlet of each stage is connected to the lower circulation pipe 202 of the crystallizing liquid of this stage or the inlet of the salt precipitator 107 of this stage.

[0071] The top refrigerant inlet 14 of each stage cooler 102 is connected to the top refrigerant outlet of the stage refrigerant heater 104 through the stage refrigerant upper circulation pipe 203, and the bottom refrigerant outlet 15 is connected to the bottom refrigerant inlet of the stage refrigerant heater 104 through the stage refrigerant lower circulation pipe 204.

[0072] Each stage of refrigerant heater 104 is provided with a heating medium inlet 5 at the top and a heating medium outlet 6 at the bottom;

[0073] The heat source system A106 includes a heating medium inlet pipeline and a heating medium outlet pipeline. The heating medium inlet pipeline is connected to the inlet 5 of each stage of heating medium, and the heating medium outlet pipeline is connected to the outlet 6 of each stage of heating medium.

[0074] The mixed salt system A105 includes a mother liquor dryer B7. A branch of the heating medium feed pipeline is connected to the heat medium inlet of the mother liquor dryer B7. The heat medium outlet of the mother liquor dryer B7 is connected to the heating medium discharge pipeline. The mother liquor inlet of the mother liquor dryer B7 is connected to the refrigerant outlet of the No. 1 cooler (B3). The mother liquor dryer (B7) is equipped with a mixed salt collection pipeline.

[0075] According to the present invention, each stage of the crystallizing liquid circulation pipe 202 includes a vertical section and a horizontal section, wherein the vertical section is close to the crystallizer 101 and a mother liquor separator 106 is provided on the vertical section;

[0076] Each mother liquor separator 106 includes a cylindrical section and upper and lower conical sections located at both ends of the cylindrical section, and the axis of the cylindrical section coincides with the axis of the upper and lower conical sections;

[0077] Each stage of the mother liquor separator 106 has a drain port 13 at the upper part of the cylindrical section or the upper conical section, an optional crystallization slurry outlet at the middle part of the cylindrical section, and a feed port 1 at the bottom of each stage of the mother liquor separator 106.

[0078] The axis of each mother liquor separator 106 coincides with the axis of the crystallizing liquid circulation pipe 202, and the inner diameter of the mother liquor separator 106 is 1.01-5 times the inner diameter of the crystallizing liquid circulation pipe 202, preferably 1.01-1.5 times.

[0079] The straight section of the circulation pipe 202 of each stage of crystallizer near the crystallizer is inserted into the mother liquor separator 106. The length of the straight section inserted into the mother liquor separator 106 is 5%-95% of the axial length of the mother liquor separator 106, preferably 25%-75%.

[0080] In this invention, a mother liquor separator 106 is installed on the circulation pipe. Through its special structural form, solid-liquid separation and low-density component accumulation are achieved locally. The quality of the crystallized product can be adjusted by discharging a small amount of mother liquor.

[0081] In this invention, to ensure the quality of the crystallized product and guarantee the product yield, a mother liquor separator 106 is installed on the vertical pipe of the crystallization liquid circulation pipe 202. The mother liquor separator 106 is provided with a drain port 13, preferably located at the upper part of the cylindrical section or the upper conical section of the mother liquor separator 106. To ensure smooth flow of crystallized materials, avoid dead zones and pipe blockages, facilitate equipment installation and subsequent maintenance, and reduce footprint, the mother liquor separator 106 is required to be coaxially arranged with the crystallization liquid circulation pipe 202, and the inner diameter of the mother liquor separator 106 is equal to the diameter of the crystallization liquid circulation pipe 202. The inner diameter of the loop pipe 202 is 1.01-5 times that of the mother liquor separator 106; preferably, the inner diameter of the mother liquor separator 106 is 1.01-1.5 times that of the inner diameter of the crystallizing liquid circulation pipe 202; in addition, in order to discharge as many impurity components in the mother liquor as possible, such as VOCs, the straight section of the crystallizing liquid circulation pipe 202 near the crystallizer side is required to be inserted into the mother liquor separator 106, and the length of the straight section inserted into the mother liquor separator 106 accounts for 5%-95% of the axial length of the mother liquor separator 106; preferably, the length of the straight section inserted into the mother liquor separator 106 accounts for 25%-75% of the axial length of the mother liquor separator 106.

[0082] According to the present invention, each stage of the cooler 102 is provided with a high-speed flushing port 7 and a cooler inlet pressure measuring port 16 at the bottom;

[0083] The axis of each salt separator 107 coincides with the axis of the crystallizer 101 of the same stage.

[0084] Each stage salt separator 107 is equipped with a discharge port 2 and at least one low-speed flushing port 9 at its bottom;

[0085] The angle between the axis of each low-speed flushing port and the axis of the salt separator 107 is 0-90°, preferably 30-90°;

[0086] The number of low-speed flushing ports 9 is 1-10, preferably 2-5;

[0087] Each stage of crystallizing liquid circulation pipe 202 is equipped with a drain port 8 and a No. 1 axial flow pump 103;

[0088] Each stage of crystallization liquid circulation pipe 201 is equipped with a circulation pipe temperature measuring port 11 and a circulation pipe pressure measuring port 12;

[0089] Each stage of refrigerant circulation pipe 203 is equipped with a refrigerant outlet 4;

[0090] Each stage of refrigerant circulation pipe 204 is equipped with refrigerant inlet 3 and 2# axial flow pump 105;

[0091] The cold source system A107 includes a refrigerant inlet pipeline, a refrigerant tank B8, a refrigerant inlet pump B9, an optional refrigerant heat exchanger B12, and a refrigerant outlet pipeline connected in sequence.

[0092] Each level of refrigerant outlet 4 is connected to the refrigerant inlet pipeline, and each level of refrigerant inlet 3 is connected to the refrigerant outlet pipeline;

[0093] The accident system A108 includes an accident tank B10 and an accident pump B11 connected in sequence. All levels of drain ports 8 are connected to the inlet of the accident tank B10, and the outlet of the accident pump B11 is connected to the drain ports 8 at all levels through the return pipeline S7.

[0094] In this invention, if the refrigerant in refrigerant tank B8 cannot meet the operating temperature requirements of the cryogenic crystallizer, a refrigerant exchanger B12 is also provided at the outlet of the pumped refrigerant. This exchanger uses an externally supplied medium with a lower temperature than the refrigerant in the tank to cool the refrigerant, thus meeting the temperature requirements for cryogenic crystallization. For example, methanol stored at 5°C in the refrigerant tank can be cooled to -15°C using external liquid propylene at -40°C. By incorporating the refrigerant exchanger B12, the operational flexibility of the device is improved.

[0095] In this invention, the refrigerant heater is equipped with an inlet and outlet for the heating medium. Combined with a refrigerant feed pump, it enables rapid reheating of the heat exchanger, resolving the blockage problem within the heat exchange tubes. Furthermore, a high-speed flushing port is located at the bottom of the heat exchanger. By detecting the pressure difference between the inlet and outlet of the heat exchanger, a high-speed jet flush is performed online when a certain pressure difference is reached, thus resolving the blockage. Therefore, the crystallizer proposed in this invention has advantages such as high efficiency, low cost, low energy consumption, long operating cycle, and wide adaptability to raw materials.

[0096] In this invention, to achieve long-term stable operation of the crystallizer, a high-speed flushing port 7 and a cooler inlet pressure measuring port 16 are provided at the bottom of the cooler 102, and a circulation pipe temperature measuring port 11 and a circulation pipe pressure measuring port 12 are provided on the upper circulation pipe 201. During normal operation, the operating status of the cooler 12 can be determined by reading the temperature of the circulation pipe temperature measuring port 11 or the pressure difference between the cooler inlet pressure measuring port 16 and the circulation pipe pressure measuring port 12. Under normal operating conditions on the refrigerant side, if the temperature of the circulation pipe temperature measuring port 11 is higher than normal, or the pressure difference between the cooler inlet pressure measuring port 16 and the circulation pipe pressure measuring port 12 is larger than the normal set value, it indicates that there may be blockage or scaling in the cooler 102's cooling pipes. In this case, the valve on the high-speed flushing port 7 is opened to flush the cooler 12's cooling pipes online until the pressure difference returns to normal. The feed liquid is preferred for flushing, followed by relatively clean fresh water, demineralized water, etc.

[0097] In this invention, the refrigerant heater 104 is equipped with an inlet and outlet for the heating medium. Combined with an axial flow pump, it can quickly reheat the heat exchanger, resolving the blockage problem inside the heat exchange tubes. Additionally, a high-speed flushing port is provided at the bottom of the heat exchanger. By detecting the pressure difference between the inlet and outlet of the heat exchanger, when a certain pressure difference is reached, the heat exchanger is flushed online with a high-speed jet to resolve blockages.

[0098] In this invention, a dual axial flow pump is used to force the adjacent hot and cold sides to flow in a counter-current manner, which greatly reduces the heat transfer resistance on the hot and cold sides, effectively improves the heat / cold energy utilization efficiency, and reduces the amount of heat / cold energy used. Under the same processing capacity, it has the advantages of small equipment size, saving investment and floor space.

[0099] In this invention, the salt separator is located at the bottom of the crystallizer and is provided with at least one low-speed flushing port. The crystallized salt is discharged from the bottom of the salt separator, resulting in uniform crystal particles, high quality, and large particle size.

[0100] In this invention, in order to empty the material in the crystallizer during accident conditions or shutdown, a drain port 8 is provided on the lower circulation pipe 202 of the crystallizing liquid.

[0101] According to a preferred embodiment of the present invention, the axes of each crystallizer 101, cooler 102, and mother liquor separator 106 are parallel to each other and perpendicular to the horizontal plane; or the axes of each crystallizer 101, cooler 102, refrigerant heater 104, and mother liquor separator 106 are parallel to each other and perpendicular to the horizontal plane.

[0102] Each crystallizer 101 may be equipped with a flow guide tube 301;

[0103] The axis of each stage guide tube 301 coincides with the axis of the crystallizer 101 of the same stage.

[0104] Each stage of the guide tube 301 is selected from either cylindrical or frustum-shaped, and neither cylindrical nor frustum-shaped tubes have an upper top surface or a lower bottom surface;

[0105] The axial length of each stage guide tube 301 is 0.05-0.85 times the axial length of the crystallizer 101 of the same stage.

[0106] Preferably, it is 0.05-0.5 times, more preferably 0.10-0.35 times;

[0107] The distance between the bottom of each stage guide tube 301 and the bottom of the crystallizer 101 is 0.05-0.5 times the axial length of the crystallizer 101, preferably 0.10-0.35 times.

[0108] In this invention, to reduce sedimentation and blockage caused by solid materials, the axes of the crystallizer 101, cooler 102, mother liquor separator 106, and salt separator 107 are required to be parallel to each other and perpendicular to the horizontal plane; or the axes of the crystallizer 101, cooler 102, refrigerant heater 104, mother liquor separator 106, and salt separator 107 are required to be parallel to each other and perpendicular to the horizontal plane. Vertical arrangement of the equipment facilitates equipment manufacturing, installation, and subsequent maintenance, while also reducing the footprint.

[0109] In this invention, in order to achieve uniform crystallization of materials within the crystallizer and avoid problems such as poor product quality and difficulty in control caused by unstable operation within the crystallizer, a guide tube 301 is provided inside the crystallizer 101. Figure 8 , Figure 9 As shown.

[0110] According to the present invention, the flushing fluid entering each high-speed flushing port and low-speed flushing port is independently selected from at least one of feed liquid, fresh water, circulating water, demineralized water, production water, deoxygenated water, secondary recycled water, steam condensate and process condensate, preferably selected from at least one of feed liquid, fresh water and demineralized water.

[0111] The mother liquor dryer B7 is selected from any one of the following: rake dryer, scraper dryer, drum dryer, spray dryer, and horizontal spiral dryer;

[0112] 1# Cooler B3 and refrigerant cooler B12 are each independently selected from any one of the following: shell and tube heat exchangers, fixed tube sheet heat exchangers, floating head heat exchangers, coaxial heat exchangers, and plate heat exchangers.

[0113] Each of the heat exchangers 102 is independently selected from any one of shell-and-tube heat exchangers, fixed tube sheet heat exchangers, floating head heat exchangers, coaxial heat exchangers, and plate heat exchangers. It is preferred to select any one of shell-and-tube heat exchangers and fixed tube sheet heat exchangers, and most preferably to select a fixed tube sheet heat exchanger.

[0114] Each refrigerant heater 104 is independently selected from any one of shell-and-tube heat exchangers, fixed tube sheet heat exchangers, floating head heat exchangers, coaxial heat exchangers, and plate heat exchangers, and preferably selected from any one of shell-and-tube heat exchangers, fixed tube sheet heat exchangers, plate heat exchangers, and coaxial heat exchangers.

[0115] In this invention, the refrigerant heater 104 can be arranged horizontally, such as... Figure 9 As shown. The refrigerant enters the bottom of the refrigerant heater 104 from the bottom of the tube box side, flows through the heat exchange tube bundle, and exits from the top of the tube box side into the refrigerant upper circulation pipe 203. The heating medium enters from the top of the refrigerant heater shell side, and after heat exchange, the medium exits the refrigerant heater 104 from the bottom of the shell side.

[0116] This invention provides a method for cryo-crystallization separation, such as... Figure 1 As shown, the freeze-crystallization separation method is carried out in the above-mentioned freeze-crystallization separation system and includes the following steps:

[0117] Pre-cooling of feed liquid: The feed liquid in the raw material system A101 is pumped to the heat exchange system A102, and the feed liquid is cooled down by heat exchange to obtain cooled feed liquid;

[0118] Freeze-separation: The cooled liquid is fed into a freeze crystallization and separation system to obtain crystalline salt and centrifugal mother liquor through at least one stage of freeze crystallization and separation;

[0119] Circulating cooling: The mother liquor of each stage of centrifugation is sent to the next stage of freezing crystallization and separation system for freezing crystallization and separation to obtain the next stage of crystallized salt and centrifugation mother liquor. Alternatively, the mother liquor of each stage of centrifugation is divided into two streams. One stream is cooled and heated with the feed liquid to obtain heated mother liquor, and the other stream is sent to the freezing crystallization and separation system of this stage for freezing crystallization and separation to obtain the current stage of crystallized salt and centrifugation mother liquor.

[0120] Preparation of mixed salts: The heated mother liquor is fed into the mixed salt system A105 for dehydration to obtain mixed salts;

[0121] Circulating refrigeration: The circulating refrigerant of the cold source system A107 provides the cooling capacity required for each stage of freezing, crystallization, and separation;

[0122] Circulating heating: The heating medium of heat source system A106 provides the heat required for the circulating refrigerant for each stage of freezing crystallization and separation, as well as the heat required for heating the mother liquor for dehydration;

[0123] Accident Handling: When the freezing crystallization and separation system malfunctions, the liquid in the freezing crystallization system A103 is discharged into the accident system A108 for real-time processing.

[0124] According to the present invention, in the circulating cooling step, the centrifugal mother liquor of each stage except the last stage is sent to the next stage of the freezing crystallization and separation system for freezing and cooling, crystallization separation, sedimentation and centrifugation separation in sequence to obtain the next stage of crystallized salt and centrifugal mother liquor. The centrifugal mother liquor of the last stage is divided into two streams. One stream is exchanged with the feed liquid for cooling and heating to obtain heated mother liquor. The other stream is sent to the freezing crystallization and separation system of this stage for freezing and cooling, crystallization separation, sedimentation and centrifugation separation in sequence to obtain the current stage of crystallized salt and centrifugal mother liquor.

[0125] In the cyclic refrigeration step, the circulating refrigerant output from the freezing crystallization and separation system is sequentially pressurized, optionally cooled by a cooling exchange, and returned to the freezing crystallization and separation system for reuse.

[0126] In the accident handling procedure, when an accident occurs in the freezing crystallization and separation system or when it needs to be shut down for maintenance, the liquid material of the freezing crystallization and separation system is discharged to the accident tank B10. After the freezing crystallization and separation system is running normally, the liquid material in the accident tank B10 is sent back to the crystallizer through the accident pump B11.

[0127] According to the present invention, the sulfate ion concentration in the feed solution is 5000-500000 ppmwt, preferably 30000-300000 ppmwt;

[0128] The circulating refrigerant is selected from at least one of low-temperature methanol, low-temperature ethanol, low-temperature ethylene glycol, liquid propylene, chilled water, chilled brine, and cryogenic liquid, with a temperature of -100°C to 0°C, preferably -40°C to 0°C;

[0129] The heating medium is selected from at least one of saturated steam, secondary steam, hot water, hot flue gas, and hot materials, preferably from at least one of saturated steam and hot water. ， The temperature range is 20℃-350℃, preferably 80-250℃.

[0130] The present invention will be described in more detail below through embodiments.

[0131] Example 1

[0132] This embodiment provides a freeze-crystallization separation system, such as Figure 1 , 2 As shown in Figure 6, it includes a raw material system A101, a heat exchange system A102, a freeze crystallization and separation system, a mixed salt system A105, a heat source system A106, a cold source system A107, and an emergency system A108 connected in sequence.

[0133] The freeze crystallization and separation system includes a freeze crystallization system A103 and a separation system A104 connected in sequence;

[0134] The separation system A104 is equipped with a crystallized salt discharge pipeline and a centrifugal mother liquor discharge pipeline. The centrifugal mother liquor discharge pipeline is connected to the refrigerant inlet of the heat exchange system A102 and the feed pipeline of the freezing crystallization system A103.

[0135] The refrigerant outlet pipeline of heat exchange system A102 is connected to the cooling mother liquor inlet of mixed salt system A105;

[0136] Heat source system A106 is connected to the heat medium inlet and outlet of freezing crystallization system A103 and mixed salt system A105, respectively;

[0137] The cold source system A107 is connected to the refrigerant inlet and outlet of the freezing crystallization system A103;

[0138] The accident system A108 is connected to the cryogenic crystallization system A103;

[0139] The raw material system A101 includes a raw material tank B1 and a raw material feed pump B2 connected in sequence;

[0140] Heat exchange system A102 includes cooler B3 (No. 1);

[0141] The discharge line of raw material feed pump B2 is connected to the raw material inlet of cooler B3 (No. 1); the raw material outlet of cooler B3 (No. 1) is connected to the feed line of the freezing crystallization system A103.

[0142] The cryogenic crystallization system A103 includes a cryogenic crystallizer B4, which includes a crystallizer 101, a cooler 102, a refrigerant heater 104, a mother liquor separator 106, a salt precipitator 107, an upper circulation pipe 201 for the crystallizing liquid, a lower circulation pipe 202 for the crystallizing liquid, an upper circulation pipe 203 for the refrigerant, and a lower circulation pipe 204 for the refrigerant.

[0143] The separation system A104 includes a settling tank B5 and a centrifuge B6 connected in sequence;

[0144] Centrifuge B6 is equipped with a crystallized salt discharge pipeline and a centrifugal mother liquor discharge pipeline. The centrifugal mother liquor discharge pipeline is connected to the refrigerant inlet of the No. 1 heat exchanger B3 and the feed pipeline of the frozen crystallizer B4.

[0145] Salt separator 107 is located below crystallizer (101) and communicates with crystallizer (101);

[0146] The outlet of the salt separator (107) is connected to the inlet of the settling tank (B5);

[0147] The crystallizer 101 includes a cylindrical section and upper and lower conical sections located at both ends of the cylindrical section, and the axis of the cylindrical section coincides with the axis of the upper and lower conical sections;

[0148] The crystallizer 101 is provided with a first outlet and a second outlet;

[0149] The first outlet is located on the side of the lower conical section of the crystallizer 101, and the second outlet is located at the bottom of the lower conical section of the crystallizer 101.

[0150] The hot-side medium outlet at the top of the cooler 102 is connected to the top inlet of the crystallizer 101 through the upper circulation pipe 201 of the crystallizer liquid, and the hot-side medium inlet at the bottom is connected to the first outlet of the crystallizer 101 through the lower circulation pipe 202 of the crystallizer liquid.

[0151] The second outlet salt separator 107 inlet connection is provided;

[0152] The top refrigerant inlet 14 of the cooler 102 is connected to the top refrigerant outlet of the refrigerant heater 104 through the upper refrigerant circulation pipe 203, and the bottom refrigerant outlet 15 is connected to the bottom refrigerant inlet of the refrigerant heater 104 through the lower refrigerant circulation pipe 204.

[0153] The refrigerant heater 104 is provided with a heating medium inlet 5 at the top and a heating medium outlet 6 at the bottom;

[0154] The heat source system A106 includes a heating medium inlet pipeline and a heating medium outlet pipeline. The heating medium inlet pipeline is connected to the inlet 5 of each stage of heating medium, and the heating medium outlet pipeline is connected to the outlet 6 of each stage of heating medium.

[0155] The mixed salt system A105 includes a mother liquor dryer B7. A branch of the heating medium feed pipeline is connected to the heat medium inlet of the mother liquor dryer B7. The heat medium outlet of the mother liquor dryer B7 is connected to the heating medium discharge pipeline. The mother liquor inlet of the mother liquor dryer B7 is connected to the refrigerant outlet of the No. 1 cooler (B3). The mother liquor dryer (B7) is equipped with a mixed salt collection pipeline.

[0156] The crystallizer circulation pipe 202 includes a vertical section and a horizontal section, wherein the vertical section is close to the crystallizer 101 and a mother liquor separator 106 is installed on the vertical section;

[0157] The mother liquor separator 106 includes a cylindrical section and upper and lower conical sections located at both ends of the cylindrical section, and the axis of the cylindrical section coincides with the axis of the upper and lower conical sections;

[0158] The upper part of the cylindrical section or the upper conical section of the mother liquor separator 106 is provided with a drain port 13, and the lower part of the mother liquor separator 106 is provided with a feed port 1.

[0159] The axis of the mother liquor separator 106 coincides with the axis of the crystallizing liquid circulation pipe 202, and the inner diameter of the mother liquor separator 106 is 1.5 times the inner diameter of the crystallizing liquid circulation pipe 202;

[0160] The straight section of the crystallizer circulation pipe 202 near the crystallizer is inserted into the mother liquor separator 106, and the length of the straight section inserted into the mother liquor separator 106 is 65% of the length of the axis of the mother liquor separator 106.

[0161] The bottom of the cooler 102 is equipped with a high-speed flushing port 7 and a cooler inlet pressure measuring port 16;

[0162] The axis of salt separator 107 coincides with the axis of crystallizer 101;

[0163] The bottom of the salt separator 107 is equipped with a discharge port 2 and two low-speed flushing ports 9;

[0164] The angle between the axis of each low-speed flushing port and the axis of the salt separator 107 is 90°;

[0165] The crystallizer circulation pipe 202 is equipped with a drain port 8 and a No. 1 axial flow pump 103;

[0166] The upper circulation pipe 201 of the crystallizing liquid is equipped with a circulation pipe temperature measuring port 11 and a circulation pipe pressure measuring port 12;

[0167] The refrigerant circulation pipe 203 is equipped with a refrigerant outlet 4;

[0168] The refrigerant circulation pipe 204 is equipped with refrigerant inlet 3 and axial flow pump 105.

[0169] The cold source system A107 includes a refrigerant inlet pipeline, a refrigerant tank B8, a refrigerant inlet pump B9, and a refrigerant outlet pipeline connected in sequence.

[0170] Refrigerant outlet 4 is connected to the refrigerant inlet pipeline, and refrigerant inlet 3 is connected to the refrigerant outlet pipeline.

[0171] The accident system A108 includes an accident tank B10 and an accident pump B11 connected in sequence. The drain port 8 is connected to the inlet of the accident tank B10, and the outlet of the accident pump B11 is connected to the drain port 8 through the return pipeline S7.

[0172] The axes of crystallizer 101, cooler 102, refrigerant heater 104, and mother liquor separator 106 are parallel to each other and perpendicular to the horizontal plane.

[0173] The flushing fluid entering the high-speed flushing port is the feed fluid;

[0174] The flushing fluid entering the low-speed flushing port is fresh water;

[0175] Mother liquor dryer B7 is a scraper dryer;

[0176] #1 heat exchanger B3 is a plate heat exchanger;

[0177] Cooler 102 is a fixed tube sheet type cooler;

[0178] The refrigerant heater 104 is a fixed tube sheet heat exchanger.

[0179] In this example, the feed is a pretreated liquid rich in sodium sulfate from a chemical plant, with a feed rate of 15 t / h and a sulfate ion concentration of 100,000 ppmwt. The circulating refrigerant used is a -20°C ethylene glycol solution. The heating medium used in the refrigerant heater 104 is 95°C hot water. Additionally, approximately 5% by weight of crystalline sulfate, mixed salt S12, is obtained in the mixed salt system A105.

[0180] In this embodiment, the flushing fluid used at the high-speed flushing port is the feed liquid, while the low-speed flushing port samples fresh water. By monitoring the pressure difference between the inlet and outlet of the cooler 102, when the pressure difference exceeds a certain set value, the valve at the high-speed flushing port is opened to flush the tube bundle of the cooler 102 online, resolving blockage and flow problems and extending the operating cycle. Additionally, by analyzing the composition of impurities within the crystallizer, especially the concentration of organic matter, when it exceeds a set value, the valve on the mother liquor separator drain port 13 is opened to discharge a small amount of mother liquor, thereby improving product quality.

[0181] This embodiment can be applied to zero-emission projects in fields such as ethylene waste alkali, oil refining waste alkali, coal chemical industry, chlor-alkali chemical industry, and sewage treatment, enabling the recycling of resources and meeting current energy conservation and environmental protection requirements.

[0182] Example 2

[0183] This embodiment has the same operating conditions as Embodiment 1, with the following differences: Figure 3 and Figure 7 As shown, the bottom of the cryogenic crystallizer B4 only has a crystallization liquid circulation pipe 202, without a salt separator 107. A mother liquor separator 106 is also installed on the crystallization liquid circulation pipe 202, with the outlet located in the middle of the cylindrical section of the mother liquor separator 106. This embodiment is suitable for cryogenic crystallization feeds with high TDS, such as 150,000 ppmwt.

[0184] Example 3

[0185] This embodiment has the same operating conditions as Embodiment 1, with the following differences: Figure 4 and Figure 7 As shown, the methanol stored in refrigerant tank B8 at 5°C cannot meet the requirements of the cryogenic crystallizer B4. Therefore, a refrigerant cooler B12 is installed at the outlet of the refrigerant feed pump B9 to cool it to -15°C using the outside liquid propylene at -40°C. The refrigerant cooler B12 improves the operational flexibility of the unit.

[0186] Example 4

[0187] This embodiment has the same operating conditions as Embodiment 1, with the following differences: Figure 5 and Figure 6 As shown in the diagram. This embodiment features a two-stage, series-connected cryogenic crystallizer B4. Both stages use identical crystallizers, refrigerants, heat sources, and separation systems. All the centrifugal mother liquor from the first-stage crystallizer is sent to the second-stage crystallizer. Part of the centrifugal mother liquor generated by the second-stage centrifuge is returned to the second-stage crystallizer, while the remainder is pre-cooled and fed into the mixed salt system. This embodiment is suitable for cryogenic crystallization feeds with relatively low TDS (total dissolved solids) and where a high yield of crystallized salt is desired. For example, a TDS of 50,000 ppmwt.

[0188] This embodiment can further improve the particle size and uniformity of the crystals. It can also achieve stable operation even with significant fluctuations in the feed composition, demonstrating good raw material adaptability and operational flexibility.

[0189] This embodiment allows for flexible configuration of the refrigerant heater type and installation status based on actual conditions.

[0190] The embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A freeze crystallization separation system, characterized in that, It includes a raw material system (A101), a heat exchange system (A102), a freeze crystallization and separation system, a mixed salt system (A105), a heat source system (A106), a cold source system (A107), and an emergency system (A108) connected in sequence. The freeze crystallization and separation system is at least one stage; each stage of the freeze crystallization and separation system includes a freeze crystallization system (A103) and a separation system (A104) connected in sequence. Each stage of the separation system (A104) is equipped with a crystallized salt discharge pipeline and a centrifugal mother liquor discharge pipeline. The centrifugal mother liquor discharge pipeline is connected to the feed pipeline of the next stage of the freeze crystallization system (A103), or it is connected to the refrigerant inlet of the heat exchange system (A102) and the feed pipeline of the freeze crystallization system (A103) of this stage, respectively. The refrigerant outlet pipeline of the heat exchange system (A102) is connected to the cooling mother liquor inlet of the mixed salt system (A105); The heat source system (A106) is connected to the heat medium inlet and outlet of each stage of the freeze crystallization system (A103) and the mixed salt system (A105); The cold source system (A107) is connected to the refrigerant inlet and outlet of each stage of the freeze-crystallization system (A103); The accident system (A108) is connected to each stage of the cryo-crystallization system (A103); The raw material system (A101) includes a raw material tank (B1) and a raw material feed pump (B2) connected in sequence. The heat exchange system (A102) includes a #1 cooler (B3). The discharge pipeline of the raw material feed pump (B2) is connected to the raw material inlet of the No. 1 cooler (B3); the raw material outlet of the No. 1 cooler (B3) is connected to the feed pipeline of the primary freezing crystallization system (A103); Each stage of the cryogenic crystallization system (A103) includes a cryogenic crystallizer (B4), which includes a crystallizer (101), a cooler (102), a refrigerant heater (104), a mother liquor separator (106), an optional salt separator (107), an upper circulation pipe (201) for the crystallizing liquid, a lower circulation pipe (202) for the crystallizing liquid, an upper circulation pipe (203) for the refrigerant, and a lower circulation pipe (204) for the refrigerant. Each stage of the separation system (A104) includes a settling tank (B5) and a centrifuge (B6) connected in sequence. Each centrifuge (B6) is equipped with the crystallized salt discharge pipeline and the centrifugal mother liquor discharge pipeline. The centrifugal mother liquor discharge pipeline is connected to the feed pipeline of the next stage freeze crystallizer (B4), or connected to the refrigerant inlet of the No. 1 cooler (B3) and the feed pipeline of the freeze crystallizer (B4) of this stage, respectively. Each stage of the crystallizing liquid circulation pipe (202) is equipped with an optional crystallizing slurry outlet; Each salt separator (107) is located below and connected to the crystallizer (101) of its respective stage; The outlet of each stage of crystallization slurry is connected to the inlet of the settling tank (B5) of the same stage, or the outlet of each stage of salt separator (107) is connected to the inlet of the settling tank (B5) of the same stage; Each stage of the crystallizer circulation pipe (202) includes a vertical section and a horizontal section, wherein the vertical section is close to the crystallizer (101) and a mother liquor separator (106) is provided on the vertical section. Each mother liquor separator (106) includes a cylindrical section and upper and lower conical sections located at both ends of the cylindrical section, and the axis of the cylindrical section coincides with the axis of the upper and lower conical sections; Each stage of the mother liquor separator (106) has a drain port (13) at the upper part of the cylindrical section or the upper conical section, an optional crystallization slurry outlet at the middle part of the cylindrical section, and a feed port (1) at the bottom of each stage of the mother liquor separator (106). The axis of each mother liquor separator (106) coincides with the axis of the crystallizing liquid circulation pipe (202), and the inner diameter of the mother liquor separator (106) is 1.01-5 times the inner diameter of the crystallizing liquid circulation pipe (202); The straight section of the circulation pipe (202) of each stage of crystallizer is inserted into the mother liquor separator (106) near the crystallizer. The length of the straight section inserted into the mother liquor separator (106) is 5%-95% of the length of the axis of the mother liquor separator (106). Each stage of the cooler (102) is equipped with a high-speed flushing port (7) and a cooler inlet pressure measuring port (16) at the bottom. The axis of each salt separator (107) coincides with the axis of the crystallizer (101) of the same stage; Each salt separator (107) is provided with a discharge port (2) and at least one low-speed flushing port (9) at the bottom. The angle between the axis of each low-speed flushing port and the axis of the salt separator (107) is 0-90°; The number of low-speed flushing ports (9) is 1-10; Each stage of the crystallizing liquid circulation pipe (202) is equipped with a drain port (8) and a No. 1 axial flow pump (103). Each stage of the crystallizing liquid circulation pipe (201) is equipped with a circulation pipe temperature measuring port (11) and a circulation pipe pressure measuring port (12). Each stage of refrigerant circulation pipe (203) is equipped with a refrigerant outlet (4); Each stage of refrigerant circulation pipe (204) is equipped with a refrigerant inlet (3) and a No. 2 axial flow pump (105). The cold source system (A107) includes a refrigerant inlet pipeline, a refrigerant tank (B8), a refrigerant inlet pump (B9), an optional refrigerant heat exchanger (B12), and a refrigerant outlet pipeline connected in sequence. The refrigerant outlets (4) at each level are connected to the refrigerant feed line, and the refrigerant inlets (3) at each level are connected to the refrigerant discharge line. The accident system (A108) includes an accident tank (B10) and an accident pump (B11) connected in sequence. All levels of drain ports (8) are connected to the inlet of the accident tank (B10), and the outlet of the accident pump (B11) is connected to the drain ports (8) through a return pipeline (S7).

2. The freeze-crystallization separation system according to claim 1, characterized in that, Each crystallizer (101) includes a cylindrical section and upper and lower conical sections located at both ends of the cylindrical section, and the axis of the cylindrical section coincides with the axis of the upper and lower conical sections; Each crystallizer (101) is provided with a first outlet and a second outlet; The first outlet of each stage is located on the side of the lower conical section of the crystallizer (101) of this stage, and the second outlet of each stage is located at the bottom of the lower conical section of the crystallizer (101) of this stage. The hot-side medium outlet at the top of each stage cooler (102) is connected to the top inlet of the crystallizer (101) through the upper circulation pipe (201) of the crystallizer of this stage, and the hot-side medium inlet at the bottom is connected to the first or second outlet of the crystallizer (101) through the lower circulation pipe (202) of the crystallizer of this stage. The second outlet of each stage is connected to the lower circulation pipe (202) of the crystallizing liquid of this stage or the inlet of the salt precipitator (107) of this stage; The top refrigerant inlet (14) of each stage cooler (102) is connected to the top refrigerant outlet of the refrigerant heater (104) of the stage through the upper refrigerant circulation pipe (203) of the stage, and the bottom refrigerant outlet (15) is connected to the bottom refrigerant inlet of the refrigerant heater (104) of the stage through the lower refrigerant circulation pipe (204) of the stage. Each stage of refrigerant heater (104) is provided with a heating medium inlet (5) at the top and a heating medium outlet (6) at the bottom. The heat source system (A106) includes a heating medium inlet pipeline and a heating medium outlet pipeline. The heating medium inlet pipeline is connected to the inlet of each stage of heating medium, and the heating medium outlet pipeline is connected to the outlet of each stage of heating medium. The mixed salt system (A105) includes a mother liquor dryer (B7). A branch of the heating medium feed line is connected to the heat medium inlet of the mother liquor dryer (B7). The heat medium outlet of the mother liquor dryer (B7) is connected to the heating medium discharge line. The mother liquor inlet of the mother liquor dryer (B7) is connected to the refrigerant outlet of the No. 1 cooler (B3). The mother liquor dryer (B7) is equipped with a mixed salt collection line.

3. The freeze-crystallization separation system according to claim 1, characterized in that, The inner diameter of the mother liquor separator (106) is 1.01-1.5 times the inner diameter of the crystallization liquid circulation pipe (202); The length of the straight pipe section inserted into the mother liquor separator (106) is 25%-75% of the length of the axis of the mother liquor separator (106).

4. The freeze-crystallization separation system according to claim 1, characterized in that, The angle between the axis of each low-speed flushing port and the axis of the salt separator (107) is 30-90°; The number of low-speed flushing ports (9) is 2-5.

5. The freeze-crystallization separation system according to claim 1, characterized in that, The axes of each crystallizer (101), cooler (102), and mother liquor separator (106) are parallel to each other and perpendicular to the horizontal plane; or the axes of each crystallizer (101), cooler (102), refrigerant heater (104), and mother liquor separator (106) are parallel to each other and perpendicular to the horizontal plane. Each crystallizer (101) may be equipped with a flow guide tube (301); The axis of each stage guide tube (301) coincides with the axis of the crystallizer (101) of the same stage; Each stage of the guide tube (301) is selected from either cylindrical or frustum-shaped, and neither cylindrical nor frustum-shaped tubes have an upper top surface or a lower bottom surface; The axial length of each stage of the guide tube (301) is 0.05-0.85 times the axial length of the crystallizer (101) of the same stage; The distance between the bottom of each stage guide tube (301) and the bottom of the crystallizer (101) is 0.05-0.5 times the axial length of the crystallizer (101).

6. The freeze-crystallization separation system according to claim 5, characterized in that, The axial length of each stage of the guide tube (301) is 0.05-0.5 times the axial length of the crystallizer (101) of the same stage; The distance between the bottom of each stage guide tube (301) and the bottom of the crystallizer (101) is 0.10-0.35 times the axial length of the crystallizer (101).

7. The freeze-crystallization separation system according to claim 5, characterized in that, The axial length of each stage of the guide tube (301) is 0.10-0.35 times the axial length of the crystallizer (101) of the same stage.

8. The freeze-crystallization separation system according to claim 2, characterized in that, The flushing fluid entering each high-speed flushing port and low-speed flushing port is independently selected from at least one of demineralized water, deoxygenated water and process condensate. The mother liquor dryer (B7) is selected from any one of the following: rake dryer, scraper dryer, drum dryer, spray dryer, and horizontal spiral dryer; The No. 1 heat exchanger (B3) and the refrigerant heat exchanger (B12) are each independently selected from any one of the fixed tube sheet heat exchanger, floating head heat exchanger, and shell and tube heat exchanger. Each of the heat exchangers (102) is independently selected from any one of the following: fixed tube sheet heat exchanger, floating head heat exchanger, and shell and tube heat exchanger; Each refrigerant heater (104) is independently selected from any one of the following: fixed tube sheet heat exchanger, floating head heat exchanger, and shell and tube heat exchanger.

9. The freeze-crystallization separation system according to claim 2, characterized in that, The flushing fluid entering each high-speed flushing port and low-speed flushing port is demineralized water; All coolers (102) are fixed tube sheet type coolers; Each refrigerant heater (104) is independently selected from either a fixed tube sheet heat exchanger or a shell-and-tube heat exchanger.

10. A method for freeze crystallization separation, characterized in that, The freeze-crystallization separation method is carried out in the freeze-crystallization separation system according to any one of claims 1-9, and includes the following steps: Pre-cooling of feed liquid: The feed liquid in the raw material system (A101) is pumped to the heat exchange system (A102) and cooled to obtain cooled feed liquid; Freeze-separation: The cooled liquid is fed into a freeze crystallization and separation system to obtain crystalline salt and centrifugal mother liquor through at least one stage of freeze crystallization and separation; Circulating cooling: The mother liquor of each stage of centrifugation is sent to the next stage of freezing crystallization and separation system for freezing crystallization and separation to obtain the next stage of crystallized salt and centrifugation mother liquor. Alternatively, the mother liquor of each stage of centrifugation is divided into two streams. One stream is cooled and heated with the feed liquid to obtain heated mother liquor, and the other stream is sent to the freezing crystallization and separation system of this stage for freezing crystallization and separation to obtain the current stage of crystallized salt and centrifugation mother liquor. Preparation of mixed salts: The mother liquor is heated and then fed into the mixed salt system (A105) for dehydration to obtain mixed salts; Circulating refrigeration: The circulating refrigerant of the cold source system (A107) provides the cooling capacity required for each stage of freezing, crystallization, and separation; Circulating heating: The heating medium of the heat source system (A106) provides the heat required for the circulating refrigerant for each stage of freezing crystallization and separation, as well as the heat required for heating the mother liquor for dehydration; Accident Handling: When the freezing crystallization and separation system malfunctions, the liquid in the freezing crystallization system (A103) is discharged into the accident system (A108) for real-time processing; In the circulating cooling step, the centrifugal mother liquor from each stage except the last stage is sent to the next stage of the freezing crystallization and separation system for freezing, crystallization, sedimentation, and centrifugation to obtain the next stage of crystallized salt and centrifugal mother liquor. The centrifugal mother liquor from the last stage is divided into two streams. One stream is exchanged with the feed liquid for cooling and heating to obtain heated mother liquor, and the other stream is sent to the freezing crystallization and separation system of this stage for freezing, crystallization, sedimentation, and centrifugation to obtain the current stage of crystallized salt and centrifugal mother liquor. In the cyclic refrigeration step, the circulating refrigerant output from the freezing crystallization and separation system is sequentially pressurized, optionally cooled by a cooling exchange, and returned to the freezing crystallization and separation system for reuse. In the accident handling procedure, when an accident occurs in the freezing crystallization and separation system or when it needs to be shut down for maintenance, the liquid material of the freezing crystallization and separation system is discharged to the accident tank (B10). After the freezing crystallization and separation system is running normally, the liquid material in the accident tank (B10) is sent back to the crystallizer through the accident pump (B11).

11. The freeze-crystallization separation method according to claim 10, characterized in that, The sulfate ion concentration in the feed solution is 5000-500000 ppmwt; The circulating refrigerant is selected from at least one of low-temperature methanol, low-temperature ethanol, low-temperature ethylene glycol, liquid propylene, chilled water, and chilled brine, with a temperature of -100°C to 0°C; The heating medium is selected from at least one of saturated steam, secondary steam, hot water, hot flue gas, and hot materials, and the temperature is 20℃-350℃.

12. The freeze-crystallization separation method according to claim 10, characterized in that, The sulfate ion concentration in the feed solution is 30,000-300,000 ppmwt; The temperature of the circulating refrigerant is -40°C to 0°C; The heating medium is selected from at least one of saturated steam and hot water, and the temperature is 80-250℃.

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