Separation and purification system for mixed solution of sodium chloride and potassium chloride

Abstract

The utility model discloses a sodium chloride and potassium chloride mixed solution separation and purification system which is characterized in that an outlet of a stock solution feeding pipe is connected with a first-effect circulating pipe through a cold side of a condensate water plate heat exchanger, a first-effect material transfer pipe is connected with a second-effect circulating pipe, and the second-effect material transfer pipe is connected with a feeding hole of an FC crystallizer; a bottom outlet of the FC crystallizer is connected with a circulating inlet of the FC crystallizer through a forced evaporation circulating pump and a forced evaporator; a secondary steam outlet of the secondary-effect gas-liquid separator and a secondary steam outlet of the FC crystallizer are connected with an inlet of a steam compressor through a scrubber tower; an outlet of the steam compressor is connected with a shell pass inlet of a first-effect and forced evaporator; a secondary steam outlet of the first-effect gas-liquid separator is connected with a shell pass inlet of the second-effect falling film evaporator; a crystal mush outlet of the FC crystallizer is connected with an inlet of the first settling tank through a discharging pump, a bottom outlet of the first settling tank is connected with an inlet of the first centrifugal machine, and a solid phase outlet of the first centrifugal machine is connected with a sodium chloride salt articulated chute. The system is good in salt separation effect, economic benefit and environmental protection benefit.

Description

Technical Field

[0001] This utility model relates to waste liquid treatment, and more particularly to a system for separating and purifying a mixed solution of sodium chloride and potassium chloride, belonging to the field of comprehensive resource utilization technology. Background Technology

[0002] In recent years, the commercial application of lithium batteries has developed rapidly. To meet the ever-increasing demands of end-use markets such as new energy vehicles, the demand for lithium batteries has been continuously increasing, leading to a rapid growth in the demand for lithium battery raw materials. Currently, most domestic lithium resources come from lepidolite ores and salt lake brines. Methods for extracting lithium from salt lake brines include precipitation, solvent extraction, adsorption, and calcination leaching. Many of these methods generate large amounts of potassium chloride and sodium chloride wastewater during production. This wastewater mainly contains potassium chloride, sodium chloride, magnesium ions, and small amounts of boron and calcium ions, making it difficult to treat. Direct discharge of this wastewater would cause serious pollution to the surrounding environment. Although some simple evaporation and crystallization techniques can remove most of the wastewater and produce crystals, the purity of the crystals is low, making complete separation of potassium chloride and sodium chloride impossible, resulting in low utilization value. Furthermore, it is ultimately impossible to treat the small amount of residual wastewater. Therefore, recovering potassium resources from this type of wastewater has significant economic benefits.

[0003] Chinese utility model patent CN 221981581U discloses a potassium chloride and sodium chloride solution evaporation crystallization and salt separation device, including a material flow process, a heating steam flow process, a condensate flow process, and a vacuum system flow process. The condensate flow process includes a steam condensate flow process and an evaporation condensate flow process. This technology employs a multi-effect evaporation + crystallization and salt separation device. Although this technical solution has advantages such as good continuity and low auxiliary material usage, and simultaneously increases the concentration of chloride crystals and sodium chloride through evaporation and concentration, and when sodium chloride reaches saturation while potassium chloride has not yet reached saturation, thus requiring a separation device to separate the sodium chloride crystals, the following problems exist:

[0004] 1. By continuing to heat and evaporate a solution of sodium chloride saturated and potassium chloride unsaturated, a mixture of potassium chloride and sodium chloride salts will precipitate. This method can yield relatively pure sodium chloride crystals, which have a lower market price. However, it cannot yield relatively pure potassium chloride crystals, which have a higher market price.

[0005] 2. The large amount of mixed salts results in a large amount of solid waste particles; a small amount of residual waste liquid will be discharged, which will also cause some pollution to the environment.

[0006] 3. The forced circulation evaporation heat exchange process is not only inefficient, but also requires a large heat exchange area and floor space, resulting in high initial investment in production.

[0007] 4. The system consumes a large amount of steam, resulting in high production and operating costs and poor production efficiency. Utility Model Content

[0008] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, and such simplifications or omissions should not be construed as limiting the scope of the present invention.

[0009] In view of the problems existing in the above and / or prior art, this utility model is proposed.

[0010] The purpose of this invention is to overcome the problems existing in the prior art and provide a separation and purification system for a mixed solution of sodium chloride and potassium chloride. This system has good salt separation effect and economic benefits, produces less mixed salt solid waste, and has no residual waste liquid discharge, resulting in good environmental benefits.

[0011] To solve the above technical problems, this utility model provides a separation and purification system for a mixed solution of sodium chloride and potassium chloride. The system includes a raw liquid feed pipe, the outlet of which is connected to the middle of a first-effect circulation pipe via the cold side of a condensate plate heat exchanger. A first-effect gas-liquid separator is connected to the lower part of a first-effect falling film evaporator. The bottom outlets of both the first-effect falling film evaporator and the first-effect gas-liquid separator are connected to the top tube-side inlet of the first-effect falling film evaporator via a first-effect falling film circulation pump and a first-effect circulation pipe. The first-effect circulation pipe is also connected to the middle of a second-effect circulation pipe via a first-effect transfer pipe. A second-effect gas-liquid separator is connected to the lower part of a second-effect falling film evaporator. The lower outlets of both the second-effect falling film evaporator and the second-effect gas-liquid separator are connected to the upper tube-side inlet of the second-effect falling film evaporator via a second-effect falling film circulation pump and a second-effect circulation pipe. The middle of the second-effect circulation pipe is also connected to a second-effect transfer pipe. The feed pipe is connected to the feed inlet of the FC crystallizer. The bottom outlet of the FC crystallizer is connected to the tube-side inlet of the forced evaporator via a forced evaporation circulation pump. The upper tube-side outlet of the forced evaporator is connected to the circulation inlet of the FC crystallizer. The secondary steam outlets at the top of the second-effect gas-liquid separator and the FC crystallizer are both connected to the inlet of the gas scrubbing tower. The outlet of the gas scrubbing tower is connected to the inlet of the steam compressor. The outlet of the steam compressor is connected to the shell-side inlet of the first-effect falling film evaporator and the forced evaporator via a compressed steam pipe. The top secondary steam outlet of the first-effect gas-liquid separator is connected to the shell-side inlet of the second-effect falling film evaporator. The bottom crystal slurry outlet of the FC crystallizer is connected to the inlet of the first settling tank via a discharge pump. The bottom outlet of the first settling tank is connected to the inlet of the first centrifuge. The solid phase outlet of the first centrifuge is connected to a sodium chloride salt chute.

[0012] As an improvement of this utility model, the liquid phase outlet of the centrifuge is connected to the centrifugal mother liquor tank, the bottom outlet of the centrifugal mother liquor tank is connected to the inlet of the mother liquor pump, and the outlet of the mother liquor pump is connected to the inlet pipe of the forced evaporation circulation pump through the mother liquor return pipe.

[0013] As a further improvement of this utility model, the outlet of the mother liquor pump is also connected to the middle of the flash circulation pipe, the upper end of the flash circulation pipe is connected to the circulation liquid inlet of the FC crystallizer, and the circulation liquid outlet of the FC crystallizer is connected to the lower end of the flash circulation pipe through the flash circulation pump.

[0014] As a further improvement of this utility model, the FC crystallizer is provided with a salt leg below the cone hopper. The salt leg outlet is connected to the inlet of the second settling tank through a flash discharge pump. The bottom outlet of the second settling tank is connected to the inlet of the second centrifuge. The solid phase outlet of the second centrifuge is connected to the inlet of the washing tank through a conveyor. The bottom outlet of the washing tank is connected to the inlet of the third centrifuge. The solid phase outlet of the third centrifuge is connected to the potassium chloride salt chute.

[0015] As a further improvement of this utility model, the liquid phase outlet of the centrifuge three is connected to the inlet of the washing mother liquor tank, the outlet of the washing mother liquor tank is connected to the inlet of the washing mother liquor circulation pump, and one outlet of the washing mother liquor circulation pump is connected to the return port of the washing tank, and the other outlet is connected to the inlet of the centrifuge mother liquor tank two.

[0016] As a further improvement of this utility model, the liquid phase outlet of the centrifuge II is also connected to the inlet of the centrifuge mother liquor tank II, the outlet of the centrifuge mother liquor tank II is connected to the inlet of the mother liquor pump II, and the outlet of the mother liquor pump II is connected to the inlet pipe of the forced evaporation circulation pump through the mother liquor return pipe II.

[0017] As a further improvement of this utility model, the outlet of the mother liquor pump II is also connected to the feed inlet of the drum dryer, the liquid phase outlet of the drum dryer is connected to the reflux port of the centrifugal mother liquor tank II, and the solid phase outlet of the drum dryer is connected to the mixed salt chute.

[0018] As a further improvement of this utility model, the condensate outlets at the bottom of the shell side of the first-effect falling film evaporator, the second-effect evaporator, and the forced evaporator are all connected to the inlet of the condensate tank. The outlet of the condensate tank is connected to the heat-side inlet of the condensate plate heat exchanger via a condensate pump, and the heat-side outlet of the condensate plate heat exchanger is connected to the condensate recycling system.

[0019] As a further improvement of this utility model, the cold side outlet of the condensate heat exchanger is also connected to the inlet of the centrifugal mother liquor tank through a raw liquid return pipe.

[0020] As a further improvement of this utility model, the non-condensable gas suction ports of the first-effect falling film evaporator, the second-effect falling film evaporator, and the forced evaporator are all connected to the shell-side inlet of the evaporator tube condenser, and the shell-side outlet of the evaporator tube condenser is connected to the evaporation vacuum device; the top exhaust port of the FC crystallizer is connected to the shell-side inlet of the flash tube condenser, and the shell-side outlet of the flash tube condenser is connected to the suction port of the flash vacuum device.

[0021] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. The concentration stage uses a double-effect falling film evaporator + MVR forced circulation evaporation system. The entire process requires almost no additional external steam. Only a small amount of heat is needed to start the equipment. After the secondary steam is washed by the steam scrubbing tower, the gas without any impurities is returned to the system for recycling after the steam compressor increases the pressure, temperature and enthalpy value. This greatly reduces the system energy consumption. Secondly, the use of falling film evaporator improves the heat transfer efficiency and reduces the heat exchange area and floor space.

[0022] 2. After the concentration is increased by double-effect falling film evaporation, MVR forced circulation evaporation is used. The material circulation flow rate is fast, scale is reduced, heat transfer efficiency is improved, and clogging is reduced. The concentration is further increased until sodium chloride is supersaturated, and pure sodium chloride crystals are precipitated. The system is simple to operate, has a low risk of clogging, stable performance, and long service life, and is more economical in terms of overall performance.

[0023] 3. Based on the different solubilities of potassium chloride and sodium chloride at different temperatures, with potassium chloride solubility significantly affected by temperature while sodium chloride solubility is less affected, this system uses a flash vacuum device to precisely control the negative pressure evaporation of the FC crystallizer. The system also adjusts the concentration endpoint and temperature of the FC crystallizer to ensure that the solution is supersaturated with potassium chloride and unsaturated with sodium chloride during the flash cooling stage. This prevents sodium chloride crystals from precipitating during this stage due to improper operation or other impurities, thus avoiding impure potassium chloride crystals. The salt is then sent to a washing tank to remove surface sodium chloride for further purification. Finally, it is separated into pure potassium chloride crystals using a centrifuge. The purity meets the Class II, Grade I standard of potassium chloride in the national standard GB6549-2011, providing a sales channel for process waste salt. Furthermore, the high value of potassium salt recovery can offset some of the wastewater treatment costs, resulting in significant economic benefits, reduced operating costs, and improved environmental benefits.

[0024] 4. After the system has been running continuously for a certain period of time, the TDS (Total Dissolved Solids) value inside the system will continue to increase, which will have a significant impact on the operation of the system. Therefore, this part of the solution is sent to a drum dryer to dry most of the impurity ions in the system into solid salt particles, thereby further ensuring the stable operation of the system. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The drawings are provided for reference and illustration only and are not intended to limit this utility model. Wherein:

[0026] Figure 1 This is a flowchart of the sodium chloride and potassium chloride mixed solution separation and purification system of this utility model;

[0027] In the diagram: 1. Single-effect falling film evaporator; 2. Single-effect gas-liquid separator; 3. Double-effect falling film evaporator; 4. Double-effect gas-liquid separator; 5. Forced evaporator; 6. FC crystallizer; 7. Condensate tank; 8. Condensate plate heat exchanger; 9. Gas scrubbing tower; 10. Steam compressor; 11. Evaporator tube condenser; 12. Evaporation vacuum device; 13. Evaporation collection water tank; 14. Settling tank one; 15. Centrifuge one; 16. Centrifuge mother liquor tank one; 17. FC crystallizer; 18. Settling tank two; 19. Centrifuge two; 20. Centrifuge mother liquor tank two; 21. Flash evaporator tube condenser; 22. Flash evaporation vacuum device; 23. Flash collection water tank; 24. Conveyor; 25. Brine washing tank; 26. Centrifuge three; 27. Drum dryer; 28. Brine washing mother liquor tank;

[0028] B1. Single-effect falling film circulation pump; B2. Double-effect falling film circulation pump; B3. Forced evaporation circulation pump; B4. Discharge pump; B5. Mother liquor pump one; B6. Flash evaporation circulation pump; B7. Flash evaporation discharge pump; B8. Mother liquor pump two; B9. Condensate pump; B10. Evaporation collection water pump; B11. Flash evaporation collection water pump; B12. Washing brine mother liquor circulation pump;

[0029] G1. Raw material feed pipe; G2. First-effect circulation pipe; G3. First-effect transfer pipe; G4. Second-effect circulation pipe; G5. Second-effect transfer pipe; G6. Forced evaporation circulation pipe; G7. Sodium chloride chute; G8. Raw material return pipe; G9. Flash evaporation circulation pipe; G10. Mother liquor reflux pipe one; G11. Mother liquor reflux pipe two; G12. Mixed salt chute; G13. Potassium chloride chute; G14. Compressed steam pipe; G15. Live steam pipe. Detailed Implementation

[0030] In the following description of this utility model, the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and do not mean that the device must have a specific orientation.

[0031] To make the technical means, creative features, achieved objectives and effects of this utility model easier to understand, the present utility model will be further described below with reference to specific illustrations. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0033] like Figure 1 As shown, the sodium chloride and potassium chloride mixed solution separation and purification system of this utility model includes a first-effect falling film evaporator 1, a first-effect gas-liquid separator 2, a second-effect falling film evaporator 3, a second-effect gas-liquid separator 4, a forced evaporator 5, an FC crystallizer 6, a condensate tank 7, a condensate plate heat exchanger 8, a gas scrubbing tower 9, and a steam compressor 10. The outlet of the raw liquid feed pipe G1 is connected to the cold side inlet of the condensate plate heat exchanger 8, and the cold side outlet of the condensate plate heat exchanger 8 is connected to the middle of the first-effect circulation pipe G2. The lower part of the first-effect falling film evaporator 1 is connected to the first-effect gas-liquid separator 2 through a connecting pipe. The bottom outlets of the first-effect falling film evaporator 1 and the first-effect gas-liquid separator 2 are connected to the inlet of the first-effect falling film circulation pump B1. The outlet of the first-effect falling film circulation pump B1 is connected to the lower end of the first-effect circulation pipe G2, and the upper end of the first-effect circulation pipe G2 is connected to the top tube inlet of the first-effect falling film evaporator 1.

[0034] The first-effect circulation pipe G2 is also connected to the middle of the second-effect circulation pipe G4 through the first-effect transfer pipe G3. The upper end of the second-effect circulation pipe G4 is connected to the upper tube inlet of the second-effect falling film evaporator 3. The top secondary steam outlet of the first-effect gas-liquid separator 2 is connected to the shell inlet of the second-effect falling film evaporator 3. The lower part of the second-effect falling film evaporator 3 is connected to the second-effect gas-liquid separator 4 through a connecting pipe. The lower outlets of the second-effect falling film evaporator 3 and the second-effect gas-liquid separator 4 are both connected to the inlet of the second-effect falling film circulation pump B2. The outlet of the second-effect falling film circulation pump B2 is connected to the lower end of the second-effect circulation pipe G4.

[0035] The middle part of the double-effect circulation pipe G4 is also connected to the feed inlet of the FC crystallizer 6 through the double-effect transfer pipe G5. The bottom outlet of the FC crystallizer 6 is connected to the inlet of the forced evaporation circulation pump B3. The outlet of the forced evaporation circulation pump B3 is connected to the lower inlet of the tube side of the forced evaporator 5. The upper outlet of the tube side of the forced evaporator 5 is connected to the side wall circulation inlet of the FC crystallizer 6 through the forced evaporation circulation pipe G6.

[0036] The secondary steam outlets at the top of the double-effect gas-liquid separator 4 and the FC crystallizer 6 are both connected to the inlet of the gas scrubbing tower 9. The outlet of the gas scrubbing tower 9 is connected to the inlet of the steam compressor 10. The outlet of the steam compressor 10 is connected to the shell-side inlet of the first-effect falling film evaporator 1 and the forced evaporator 5 through the compressed steam pipe G14. The outlet of the live steam pipe G15 is also connected to the compressed steam pipe G14, providing a heat source for production startup or serving as a supplementary heat source.

[0037] The bottom condensate outlets of the shell side of the first-effect falling film evaporator 1, the second-effect evaporator 3, and the forced evaporator 5 are all connected to the inlet of the condensate tank 7. The outlet of the condensate tank 7 is connected to the inlet of the condensate pump B9. The top vapor phase outlet of the condensate tank 7 is connected to the vapor phase space of the first-effect gas-liquid separator 2. The bottom outlet of the condensate pump B9 is connected to the hot side inlet of the condensate plate heat exchanger 8. The hot side outlet of the condensate plate heat exchanger 8 is connected to the condensate recycling system.

[0038] The non-condensable gas suction ports of the single-effect falling film evaporator 1, the double-effect falling film evaporator 3, and the forced evaporator 5 are all connected to the shell-side inlet of the evaporator tube condenser 11, and the shell-side outlet of the evaporator tube condenser 11 is connected to the evaporation vacuum device 12. The shell-side drain port of the evaporator tube condenser 11 is connected to the evaporation water collection tank 13, and the outlet of the evaporation water collection tank 13 is connected to the inlet of the evaporation water collection pump B10.

[0039] The bottom slurry outlet of FC crystallizer 6 is connected to the inlet of discharge pump B4. The outlet of discharge pump B4 is connected to the inlet of settling tank 14. The bottom outlet of settling tank 14 is connected to the inlet of centrifuge 15. The solid phase outlet of centrifuge 15 is connected to sodium chloride salt chute G7. The liquid phase outlet of centrifuge 15 is connected to the inlet of centrifugal mother liquor tank 16. The bottom outlet of centrifugal mother liquor tank 16 is connected to the inlet of mother liquor pump B5. One outlet of mother liquor pump B5 is connected to the inlet pipe of forced evaporation circulation pump B3 through mother liquor reflux pipe G10, and the other outlet is connected to the middle of flash evaporation circulation pipe G9.

[0040] The upper end of the flash circulation pipe G9 is connected to the circulating liquid inlet of the FC crystallizer 17, which is also known as a forced circulation evaporation crystallizer. The circulating liquid outlet on the cone of the FC crystallizer 17 is connected to the inlet of the flash circulation pump B6, and the outlet of the flash circulation pump B6 is connected to the lower end of the flash circulation pipe G9.

[0041] The top exhaust port of the FC crystallizer 17 is connected to the shell-side inlet of the flash tube condenser 21, and the shell-side outlet of the flash tube condenser 21 is connected to the suction port of the flash vacuum device 22; the shell-side condensate outlet of the flash tube condenser 21 is connected to the inlet of the flash collection water tank 23, the outlet of the flash collection water tank 23 is connected to the inlet of the flash collection water pump B11, and the outlet of the flash collection water pump B11 is connected to the condensate recycling system.

[0042] The FC crystallizer 17 has a salt leg below the cone hopper. The salt leg outlet is connected to the inlet of the flash discharge pump B7. The outlet of the flash discharge pump B7 is connected to the inlet of the settling tank 18. The bottom outlet of the settling tank 18 is connected to the inlet of the centrifuge 19. The liquid phase outlet of the centrifuge 19 is connected to the inlet of the centrifuge mother liquor tank 20. The solid phase outlet of the centrifuge 19 is connected to the lower inlet of the conveyor 24. The upper outlet of the conveyor 24 is connected to the inlet of the salt washing tank 25. The bottom outlet of the salt washing tank 25 is connected to the inlet of the centrifuge 26. The solid phase outlet of the centrifuge 26 is connected to the potassium chloride salt chute G13.

[0043] The liquid phase outlet of centrifuge 3 26 is connected to the inlet of the washing mother liquor tank 28. The outlet of the washing mother liquor tank 28 is connected to the inlet of the washing mother liquor circulation pump B12. One outlet of the washing mother liquor circulation pump B12 is connected to the reflux port of the washing tank 25, and the other outlet is connected to the inlet of the centrifuge mother liquor tank 20. The outlet of the centrifuge mother liquor tank 20 is connected to the inlet of the mother liquor pump 2 B8. One outlet of the mother liquor pump 2 B8 is connected to the inlet pipe of the forced evaporation circulation pump B3 through the mother liquor reflux pipe 2 G11. The second outlet of the mother liquor pump 2 B8 is connected to the feed port of the drum dryer 27. The liquid phase outlet of the drum dryer 27 is connected to the reflux port of the centrifuge mother liquor tank 20. The solid phase outlet of the drum dryer 27 is connected to the mixed salt chute G12.

[0044] The cold side outlet of the condensate plate heat exchanger 8 is also connected to the inlet of the centrifugal mother liquor tank 16 through the raw liquid return pipe G8. The preheated raw liquid is returned to the centrifugal mother liquor tank 16, which can change the sodium chloride solution in the centrifugal mother liquor tank 16 from a saturated state to an unsaturated state, preventing sodium chloride salt from precipitating in the flash evaporation stage and affecting the purity of potassium chloride salt.

[0045] A mixed solution of potassium chloride and sodium chloride from the feed pipe G1 enters the cold side of the condensate plate heat exchanger 8, raising the temperature of the feed solution by approximately 30°C. This solution mixes with the circulating liquid from the first-effect falling film evaporator B1 and the first-effect circulating pipe G2, and then enters the tube side of the first-effect falling film evaporator 1 for evaporation. The solution reaching the lower end of the tube side of the first-effect falling film evaporator 1 enters the first-effect gas-liquid separator 2 for separation. The first-effect flash vapor discharged from the top of the first-effect gas-liquid separator 2 serves as the heat source for the second-effect falling film evaporator 3. The feed liquid at the bottom of the first-effect falling film evaporator 1 and the first-effect gas-liquid separator 2 is returned to the top of the first-effect falling film evaporator 1 by the first-effect falling film circulating pump B1 for circulation.

[0046] After evaporation in the first-effect falling film evaporator 1, the concentration is increased to 1150 kg / m³, and the temperature is 90℃. The concentrated liquid from the first effect is sent out through the first-effect transfer pipe G3. After mixing with the circulating liquid from the second effect, which is sent out by the second-effect falling film circulation pump B2 and the second-effect circulation pipe G4, they enter the tube side of the second-effect falling film evaporator 3 for evaporation. The solution reaching the lower end of the tube side of the second-effect falling film evaporator 3 enters the second-effect gas-liquid separator 4 for separation. The flash vapor discharged from the top of the second-effect gas-liquid separator 4 enters the scrubbing tower 9 for washing. The liquid at the bottom of the second-effect falling film evaporator 3 and the second-effect gas-liquid separator 4 is sent back to the top of the second-effect falling film evaporator 3 for circulation by the second-effect falling film circulation pump B2.

[0047] After evaporation in the double-effect falling film evaporator 3, the concentration is increased to 1250 kg / m³. It is then fed into the FC crystallizer 6 for further evaporation and crystallization via the double-effect transfer pipe G5. The crystal slurry discharged from the bottom of the FC crystallizer 6 is sent to the tube side of the forced evaporator 5 via the forced evaporation circulation pump B3 for evaporation, and then returns to the FC crystallizer 6 via the forced evaporation circulation pipe G6. The forced evaporator 5 continuously provides heat to the system, further concentrating the original liquid density to 1300 kg / m³.

[0048] Part of the crystal slurry discharged from the bottom of FC crystallizer 6 is sent to settling tank 14 through discharge pump B4. After a certain residence time, the large particles gradually settle to the bottom of settling tank 14 and then enter centrifuge 15 to separate sodium chloride salt and centrifugal mother liquor. Sodium chloride salt is discharged from sodium chloride salt chute G7.

[0049] The centrifugal mother liquor separated by centrifuge 15 is collected by centrifugal mother liquor tank 16. Part of the centrifugal mother liquor is sent to FC crystallizer 17 through flash evaporation circulation pipe G9 via mother liquor pump B5 for flash evaporation. The other part of the centrifugal mother liquor is sent back to FC crystallizer 6 through mother liquor return pipe G10.

[0050] Based on the different solubility characteristics of potassium chloride and sodium chloride at different temperatures, the FC crystallizer 17 is evacuated to an absolute pressure of 10 kPa and a temperature of 45°C by the flash vacuum device 22. The secondary steam after heat exchange is condensed by the flash tube condenser 21 and collected by the flash collection water tank 23, and then discharged from the system by the flash collection water pump B11.

[0051] The crystal slurry discharged from the bottom of FC crystallizer 17 is sent into settling tank 18 via flash discharge pump B7. After a certain residence time, the large particles gradually settle to the bottom of settling tank 18 and then enter centrifuge 19 to separate the mother liquor and crude potassium chloride salt. The mother liquor is collected in centrifuge mother liquor tank 20 and sent out via mother liquor pump B8. Part of it is sent back to FC crystallizer 6 through mother liquor return pipe G11; the other part is sent to drum dryer 27 for drying, using live steam as a heat source. The dried impurities are discharged from impurity salt chute G12.

[0052] The crude potassium chloride salt separated by centrifuge 219 is conveyed by conveyor 24 to washing tank 25 to remove surface sodium chloride. After a certain period of settling, the crystal slurry at the bottom of washing tank 25 is sent to centrifuge 326 for solid-liquid separation. The separated pure potassium chloride salt is discharged from potassium chloride chute G13. The separated mother liquor is collected in washing mother liquor tank 28 and then returned to washing tank 25 and centrifuge mother liquor tank 20 for circulation via washing mother liquor circulation pump B12.

[0053] The heat source for the second-effect evaporator 3 is the secondary steam separated by the first-effect separator 2. The 90°C secondary steam discharged from the top of the second-effect gas-liquid separator 4 and the FC crystallizer 6 enters the gas scrubbing tower 9 for washing. The clean steam enters the steam compressor 10 for compression. The compressed steam, after its enthalpy is increased and its temperature is increased to 110°C, enters the shell side of the first-effect falling film evaporator 1 and the forced evaporator 5 as a heat source. During startup, live steam is used as the heat source.

[0054] The condensate discharged from the bottom of the shell side of the first-effect falling film evaporator 1, the second-effect evaporator 3, and the forced evaporator 5 all enter the condensate tank 7 for collection. The condensate is then pumped by the condensate pump B9 to the heat side of the condensate plate heat exchanger 8 as a heat source. The condensate after heat exchange is discharged from the system and collected for reuse.

[0055] The non-condensable gases in the first-effect falling film evaporator 1, the second-effect falling film evaporator 3, and the forced evaporator 5 are drawn into the shell side of the evaporator tube condenser 11 by the evaporation vacuum device 12, condensed, and discharged outside the system. The non-condensable gas valve draws the interior of the second-effect falling film evaporator 3 and the forced evaporator 5 to an absolute pressure of 70 kPa. The first-effect falling film evaporator 1 evaporates at room temperature, and the tube side of the evaporator tube condenser 11 uses circulating cooling water for heat exchange.

[0056] The above description is merely a preferred embodiment of the present utility model, showing and describing the basic principles, main features, and advantages of the present utility model. It is not intended to limit the scope of patent protection of the present utility model. Those skilled in the art should understand that the present utility model is not limited to the above embodiments. In addition to the above embodiments, the present utility model may have other implementations without departing from the spirit and scope of the present utility model. Various changes and improvements to the present utility model are also possible. All technical solutions formed by equivalent substitutions or equivalent transformations fall within the scope of protection claimed by the present utility model. The scope of protection claimed by the present utility model is defined by the appended claims and their equivalents. Technical features not described in the present utility model can be implemented by or using existing technology, and will not be elaborated here.

Claims

1. A system for separating and purifying a mixed solution of sodium chloride and potassium chloride, comprising a raw solution feed pipe, characterized in that, The outlet of the raw liquid feed pipe is connected to the middle of the first-effect circulation pipe via the cold side of the condensate plate heat exchanger. The lower part of the first-effect falling film evaporator is connected to the first-effect gas-liquid separator. The bottom outlets of the first-effect falling film evaporator and the first-effect gas-liquid separator are both connected to the top tube inlet of the first-effect falling film evaporator via the first-effect falling film circulation pump and the first-effect circulation pipe. The first-effect circulation pipe is also connected to the middle of the second-effect circulation pipe through the first-effect transfer pipe. The lower part of the second-effect falling film evaporator is connected to the second-effect gas-liquid separator. The lower outlets of the second-effect falling film evaporator and the second-effect gas-liquid separator are both connected to the upper tube inlet of the second-effect falling film evaporator through the second-effect falling film circulation pump and the second-effect circulation pipe. The middle part of the double-effect circulation pipe is also connected to the feed inlet of the FC crystallizer through the double-effect transfer pipe. The bottom outlet of the FC crystallizer is connected to the tube-side inlet of the forced evaporator through the forced evaporation circulation pump. The upper tube-side outlet of the forced evaporator is connected to the circulation inlet of the FC crystallizer. The secondary steam outlets at the top of the double-effect gas-liquid separator and the FC crystallizer are both connected to the inlet of the gas scrubbing tower. The outlet of the gas scrubbing tower is connected to the inlet of the steam compressor. The outlet of the steam compressor is connected to the shell-side inlet of the first-effect falling film evaporator and the forced evaporator through a compressed steam pipe. The secondary steam outlet at the top of the first-effect gas-liquid separator is connected to the shell-side inlet of the double-effect falling film evaporator. The bottom slurry outlet of the FC crystallizer is connected to the inlet of settling tank 1 via a discharge pump. The bottom outlet of settling tank 1 is connected to the inlet of centrifuge 1. The solid phase outlet of centrifuge 1 is connected to a sodium chloride salt chute.

2. The sodium chloride and potassium chloride mixed solution separation and purification system according to claim 1, characterized in that: The liquid phase outlet of centrifuge one is connected to centrifugal mother liquor tank one, the bottom outlet of centrifugal mother liquor tank one is connected to the inlet of mother liquor pump one, and the outlet of mother liquor pump one is connected to the inlet pipe of forced evaporation circulation pump through mother liquor return pipe one.

3. The sodium chloride and potassium chloride mixed solution separation and purification system according to claim 2, characterized in that: The outlet of the mother liquor pump is also connected to the middle of the flash circulation pipe. The upper end of the flash circulation pipe is connected to the circulation liquid inlet of the FC crystallizer. The circulation liquid outlet of the FC crystallizer is connected to the lower end of the flash circulation pipe through the flash circulation pump.

4. The sodium chloride and potassium chloride mixed solution separation and purification system according to claim 3, characterized in that: The FC crystallizer has a salt leg below the cone hopper. The salt leg outlet is connected to the inlet of settling tank two via a flash discharge pump. The bottom outlet of settling tank two is connected to the inlet of centrifuge two. The solid phase outlet of centrifuge two is connected to the inlet of washing tank via a conveyor. The bottom outlet of washing tank is connected to the inlet of centrifuge three. The solid phase outlet of centrifuge three is connected to potassium chloride salt chute.

5. The sodium chloride and potassium chloride mixed solution separation and purification system according to claim 4, characterized in that: The liquid phase outlet of centrifuge three is connected to the inlet of the washing mother liquor tank, the outlet of the washing mother liquor tank is connected to the inlet of the washing mother liquor circulation pump, and one outlet of the washing mother liquor circulation pump is connected to the return port of the washing tank, and the other outlet is connected to the inlet of centrifuge mother liquor tank two.

6. The sodium chloride and potassium chloride mixed solution separation and purification system according to claim 5, characterized in that: The liquid phase outlet of centrifuge two is also connected to the inlet of centrifugal mother liquor tank two, the outlet of centrifugal mother liquor tank two is connected to the inlet of mother liquor pump two, and the outlet of mother liquor pump two is connected to the inlet pipe of forced evaporation circulation pump through mother liquor return pipe two.

7. The sodium chloride and potassium chloride mixed solution separation and purification system according to claim 6, characterized in that: The outlet of the second mother liquor pump is also connected to the inlet of the drum dryer, the liquid phase outlet of the drum dryer is connected to the reflux port of the second centrifugal mother liquor tank, and the solid phase outlet of the drum dryer is connected to the mixed salt chute.

8. The sodium chloride and potassium chloride mixed solution separation and purification system according to claim 1, characterized in that: The condensate outlets at the bottom of the shell side of the first-effect falling film evaporator, the second-effect evaporator, and the forced evaporator are all connected to the inlet of the condensate tank. The outlet of the condensate tank is connected to the heat-side inlet of the condensate plate heat exchanger via a condensate pump. The heat-side outlet of the condensate plate heat exchanger is connected to the condensate recycling system.

9. The sodium chloride and potassium chloride mixed solution separation and purification system according to claim 2, characterized in that: The cold-side outlet of the condensate heat exchanger is also connected to the inlet of the centrifugal mother liquor tank through a raw liquid return pipe.

10. The system for separating and purifying a mixed solution of sodium chloride and potassium chloride according to any one of claims 3 to 7, characterized in that: The non-condensable gas suction ports of the first-effect falling film evaporator, the second-effect falling film evaporator, and the forced evaporator are all connected to the shell-side inlet of the evaporator tube condenser, and the shell-side outlet of the evaporator tube condenser is connected to the evaporation vacuum device; the top exhaust port of the FC crystallizer is connected to the shell-side inlet of the flash tube condenser, and the shell-side outlet of the flash tube condenser is connected to the suction port of the flash vacuum device.

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