Efficient desalination and impurity removal system for mine water wastewater

Abstract

The application provides a high-efficiency salt separation and impurity removal system for mine water waste water, which comprises a nanofiltration salt separation membrane unit, the nanofiltration salt separation membrane unit is connected with a brine reverse osmosis membrane unit and a nitrate water hardness removal unit respectively, the brine reverse osmosis membrane unit is connected with a concentrated brine crystallization unit and a miscellaneous salt drying crystallization unit in sequence, the nanofiltration salt separation membrane unit is connected with the nitrate water hardness removal unit, a nitrate water reverse osmosis membrane unit, a concentrated nitrate water crystallization unit and a nitrate water evaporation salt separation unit in sequence, and the nitrate water evaporation salt separation unit is connected with the concentrated brine crystallization unit. The brine and the nitrate water are circulated to two sets of evaporation crystallization units respectively, so that the yield of salt and nitrate is improved, and the yield of miscellaneous salt is greatly reduced. The purity of sodium chloride and sodium sulfate can reach the industrial first-grade product, the yield of sodium chloride and sodium sulfate is greatly improved, and the system has great popularization value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wastewater treatment, in particular to a high-efficiency salt separation and impurity removal system for mine water wastewater. BACKGROUND

[0002] The mine wastewater treatment process produces a high-salt wastewater, which, if directly discharged into the environment, will cause salt pollution, such as land salinization. If directly evaporated and crystallized into mixed impurities, the impurities will cause serious environmental problems. The brine mainly contains sodium chloride and sodium sulfate. If these two salts can be efficiently separated, industrial-grade sodium chloride and sodium sulfate can be produced, which will solve the problem of mixed impurities in high-salt mine wastewater.

[0003] Currently, there are two main processes. One is a thermal process, which requires high process control accuracy, especially the circulation and balance between the salt crystallizer and the nitrate crystallizer. Once the process control fluctuates or the water quality fluctuates, the purity of the salt and nitrate will not be high, which cannot meet the industrial requirements. The other is a membrane process, which improves the yield of sodium sulfate to a certain extent, but still needs to discharge a large amount of impurities from the system, thereby reducing the yield of sodium chloride and sodium sulfate (generally 80%-85%), and wasting energy because evaporation crystallization is a high-temperature operation and freezing crystallization is a low-temperature operation. Therefore, we propose a high-efficiency salt separation and impurity removal system for mine water wastewater to solve the above problems. SUMMARY

[0004] The present application provides a high-efficiency salt separation and impurity removal system for mine water wastewater, which solves the problem of high process control accuracy in the thermal process, which easily leads to low purity of salt and nitrate, which cannot meet the industrial requirements. The membrane process needs to discharge a large amount of impurities from the system, thereby reducing the yield of sodium chloride and sodium sulfate, and wasting energy.

[0005] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a high-efficiency salt separation and impurity removal system for mine water wastewater, comprising a nanofiltration salt separation membrane unit, the nanofiltration salt separation membrane unit is connected with a brine reverse osmosis membrane unit and a nitrate water hardness removal unit respectively, the brine reverse osmosis membrane unit is connected with a concentrated brine crystallization unit and a impurity salt drying crystallization unit in sequence, the nanofiltration salt separation membrane unit is connected with the nitrate water hardness removal unit, a nitrate water reverse osmosis membrane unit, a concentrated nitrate water crystallization unit and a nitrate water evaporation mother liquor nanofiltration salt separation unit in sequence, and the nitrate water evaporation mother liquor nanofiltration salt separation unit is connected with the concentrated brine crystallization unit.

[0006] In the preferred solution, the brine tank is arranged between the nanofiltration desalting membrane unit and the brine reverse osmosis membrane unit, the nanofiltration desalting membrane unit is communicated with the high-salinity wastewater at the inlet, and the nanofiltration desalting membrane unit comprises a high-salinity adjusting tank, a nanofiltration desalting membrane, and a nanofiltration desalting concentration valve, the high-salinity adjusting tank is sequentially communicated with the nanofiltration desalting membrane and the nanofiltration desalting concentration valve, the nanofiltration desalting concentration valve is communicated with the first intermediate tank, and the nanofiltration desalting membrane is communicated with the brine tank.

[0007] In the preferred solution, the brine reverse osmosis membrane unit comprises a concentrated reverse osmosis membrane and a brine concentration concentration valve, the brine concentration concentration valve is communicated with the concentrated brine crystallization unit, the concentrated reverse osmosis membrane is communicated with the water production discharge unit, and the nitrate water reverse osmosis membrane unit has the same structure as the brine reverse osmosis membrane unit.

[0008] In the preferred solution, the dry salt crystallization unit comprises a drying machine, the drying machine is sequentially communicated with a steam condenser and a condensate tank at one end, the condensate tank is communicated with the water production discharge unit, the drying machine discharges dry salt, and the drying machine is provided with a drying intermediate tank communicated at the other end, and the drying intermediate tank is communicated with the mother liquor intermediate tank of the concentrated brine crystallization unit at the other end.

[0009] In the preferred solution, the nitrate water hardness removal unit comprises a hardness removal reaction tank and an immersed ultrafiltration membrane, the hardness removal reaction tank is communicated with the first intermediate tank, the immersed ultrafiltration membrane is communicated with the nitrate water tank, and the nitrate water tank is communicated with the concentrated reverse osmosis membrane of the nitrate water reverse osmosis membrane unit.

[0010] In the preferred solution, the hardness removal reaction tank is sequentially communicated with a beam current precipitation tank and an immersed ultrafiltration membrane, the beam current precipitation tank and the immersed ultrafiltration membrane are both communicated with a hardness removal sludge discharge pump, the hardness removal sludge discharge pump is communicated with a filter press, and the hardness removal sludge discharge pump and the filter press are both communicated with the hardness removal reaction tank.

[0011] In the preferred solution, the concentrated nitrate water crystallization unit comprises a hardness removal intermediate tank, the hardness removal intermediate tank is sequentially connected with a first preheater, a second preheater, a main heater, an MVR flash tank, a centrifugal dehydrator, and a mother liquor intermediate tank, the first preheater is connected with the water production discharge unit, and the centrifugal dehydrator discharges sodium sulfate salt.

[0012] In the preferred solution, the concentrated brine crystallization unit has the same structure as the concentrated nitrate water crystallization unit, the concentrated brine crystallization unit discharges sodium chloride salt,

[0013] In the preferred solution, the concentrated nitrate water crystallization unit further comprises a non-condensable gas cooler, the main heater and the MVR flash tank form a circulating loop, the main heater is connected with the second preheater at the other end to form a circulating loop, the second preheater is connected with the non-condensable gas cooler, and the hardness removal intermediate tank is connected with the nitrate water evaporation mother liquor nanofiltration desalting unit.

[0014] In a preferred scheme, the nitrate water evaporation mother liquor nanofiltration desalination unit comprises a dilution tank, the dilution tank is in communication with the nitrate mother liquor nanofiltration membrane, the nitrate mother liquor nanofiltration membrane is in communication with the hardness removal intermediate tank of the concentrated salt water crystallization unit, the produced water discharge unit is in communication with the dilution tank, and the produced water discharge unit comprises a mixing tank.

[0015] The beneficial effects of the present application are: based on the basic principle of membrane separation, since the nitrate mother liquor is a nearly saturated salt solution, the membrane system cannot handle saturated salt solution, therefore, the present application adopts a dilution process, uses the clean water produced by other units in the system to dilute the nitrate mother liquor, after reaching the working concentration of the nanofiltration desalination membrane, the nitrate mother liquor is separated into divalent salt and monovalent salt through the nanofiltration desalination membrane. The produced water of the nitrate water evaporation mother liquor nanofiltration desalination membrane is mainly a salt solution of sodium chloride, and this part of the salt water can be directly used as the feed water of the concentrated salt water MVR evaporation crystallization; the concentrated water of the nitrate water evaporation mother liquor nanofiltration desalination membrane can be used as the feed water of the concentrated nitrate water crystallization unit. The nitrate mother liquor after being separated into divalent salt and monovalent salt can be circulated in the system, thereby improving the yield of salt and nitrate.

[0016] The advantages of the present application relative to the traditional membrane desalination process are: through the salt water reverse osmosis membrane unit and the nitrate water reverse osmosis membrane unit, the salt water and the nitrate water after being separated by the membrane are concentrated by high-pressure reverse osmosis membranes, thereby reducing the scale of the evaporation crystallization unit and reducing the energy consumption of the system.

[0017] Through the nitrate water hardness removal unit, the nitrate water reverse osmosis membrane unit before concentration is subjected to softening and hardness removal treatment, and the "beam type precipitation + immersed ultrafiltration" is adopted to improve the water quality, thereby ensuring better operation of the subsequent nitrate water reverse osmosis membrane unit and the concentrated nitrate water crystallization unit.

[0018] Through the concentrated nitrate water crystallization unit, the nitrate mother liquor after crystallization of the concentrated nitrate water crystallization unit is subjected to secondary nanofiltration desalination, so that the produced water (salt water) and the concentrated water (nitrate water) are circulated to two sets of evaporation crystallization units, respectively, thereby improving the yield of salt and nitrate, and greatly reducing the yield of miscellaneous salt. The purity of sodium chloride and sodium sulfate can reach the industrial first-class product, and the yield of sodium chloride and sodium sulfate is greatly improved, which has great popularization value. BRIEF DESCRIPTION OF DRAWINGS

[0019] The present application will be further described below in combination with the drawings and examples.

[0020] Figure 1 is the process principle diagram of the overall structure of the present application;

[0021] Figure 2 is the equipment flow diagram of the overall structure of the present application;

[0022] Figure 3 is the equipment flow diagram of the overall structure of the present application;

[0023] Figure 4is the flow chart of the nanofiltration salt separation membrane unit and the brine reverse osmosis membrane unit of the present application;

[0024] Figure 5 is the flow chart of the nitrate water hardness removal unit of the present application;

[0025] Figure 6 is the flow chart of the concentrated nitrate water crystallization unit of the present application;

[0026] Figure 7 is the flow chart of the nitrate water evaporation mother liquor nanofiltration salt separation unit of the present application;

[0027] Figure 8 is the flow chart of the miscellaneous salt drying crystallization unit of the present application;

[0028] Figure 9 is the principle diagram of the prior art thermal process;

[0029] Figure 10 is the principle diagram of the prior art membrane process;

[0030] In the figure: high-salinity wastewater 1; nanofiltration salt separation membrane unit 2; high-salinity conditioning tank 201; nanofiltration salt separation membrane 202; nanofiltration salt separation concentration discharge valve 203; brine reverse osmosis membrane unit 3; concentrated reverse osmosis membrane 301; brine concentration discharge concentration valve 302; concentrated brine crystallization unit 4; miscellaneous salt drying crystallization unit 5; drying machine 501; steam condenser 502; condensate tank 503; drying intermediate tank 504; nitrate water hardness removal unit 6; hardness removal reaction tank 601; beam precipitation tank 602; immersed ultrafiltration membrane 603; hardness removal sludge discharge pump 604; filter press 605; nitrate water reverse osmosis membrane unit 7; concentrated nitrate water crystallization unit 8; hardness removal intermediate tank 801; first preheater 802; second preheater 803; MVR condensate tank 804; main heater 805; MVR flash tank 806; centrifugal dehydrator 807; mother liquor intermediate tank 808; non-condensable gas cooler 809; nitrate water evaporation mother liquor nanofiltration salt separation unit 9; dilution tank 901; nitrate mother liquor nanofiltration membrane 902; produced water discharge unit 10; mixing tank 1001; brine tank 11; nitrate water tank 12; first intermediate tank 13. DETAILED DESCRIPTION

[0031] Example 1:

[0032] As Figures 1-10The application discloses a high-efficiency salt separation and impurity removal system for mine water and wastewater, which comprises a nanofiltration salt separation membrane unit 2, the nanofiltration salt separation membrane unit 2 is connected with a brine reverse osmosis membrane unit 3 and a nitrate water hardness removal unit 6 respectively, the brine reverse osmosis membrane unit 3 is sequentially connected with a concentrated brine crystallization unit 4 and a mixed salt drying crystallization unit 5, the nanofiltration salt separation membrane unit 2 is sequentially connected with the nitrate water hardness removal unit 6, a nitrate water reverse osmosis membrane unit 7, a concentrated nitrate water crystallization unit 8 and a nitrate water evaporation mother liquor nanofiltration salt separation unit 9, and the nitrate water evaporation mother liquor nanofiltration salt separation unit 9 is connected with the concentrated brine crystallization unit 4. Based on the basic principle of membrane separation, the nitrate mother liquor is a nearly saturated salt solution, and the membrane system cannot handle the saturated salt solution, therefore, the application adopts a dilution process, uses the clean water produced by other units in the system to dilute the nitrate mother liquor, and after the working concentration of the nanofiltration salt separation membrane is reached, the nitrate mother liquor is separated into divalent salt and monovalent salt through the nanofiltration salt separation membrane. The water produced by the nitrate water evaporation mother liquor nanofiltration salt separation membrane is mainly a sodium chloride salt solution, and the salt water can be directly used as the water inlet of the concentrated brine MVR evaporation crystallization; the concentrated water of the nitrate water evaporation mother liquor nanofiltration salt separation membrane can be used as the water inlet of the concentrated nitrate water crystallization unit 8. The nitrate mother liquor is separated into divalent salt and monovalent salt, and then circulated in the system, so that the yield of salt and nitrate is improved.

[0033] Compared with the traditional membrane separation process, the application has the advantages that the high-pressure reverse osmosis membranes are used to concentrate the salt water and the nitrate water after the membrane separation, the scale of the evaporation crystallization units is reduced, and the energy consumption of the system is reduced.

[0034] The nitrate water is subjected to the softening and hardness removal treatment before being concentrated by the nitrate water reverse osmosis membrane unit 7 through the nitrate water hardness removal unit 6, and the beam type precipitation and the immersed ultrafiltration are used to improve the water quality, so that the subsequent nitrate water reverse osmosis membrane unit 7 and the concentrated nitrate water crystallization unit 8 can operate better.

[0035] The nitrate mother liquor after crystallization of the concentrated nitrate water crystallization unit 8 is subjected to secondary nanofiltration salt separation, so that the water produced by the nanofiltration salt separation membrane and the concentrated water of the nitrate water are circulated to two sets of evaporation crystallization units, the yield of salt and nitrate is improved, and the yield of mixed salt is greatly reduced. The purity of sodium chloride and sodium sulfate can reach the industrial first-grade product, and the yield of sodium chloride and sodium sulfate is greatly improved.

[0036] In the preferred scheme, the nanofiltration salt separation membrane unit 2 and the salt water reverse osmosis membrane unit 3 are provided with a salt water tank 11, the nanofiltration salt separation membrane unit 2 is communicated with the high-salt wastewater 1 at the inlet, and the nanofiltration salt separation membrane unit 2 comprises a high-salt adjusting tank 201, a nanofiltration salt separation membrane 202 and a nanofiltration salt separation concentration valve 203, the high-salt adjusting tank 201 is communicated with the nanofiltration salt separation membrane 202 and the nanofiltration salt separation concentration valve 203 in sequence, the nanofiltration salt separation concentration valve 203 is communicated with the first intermediate tank 13, and the nanofiltration salt separation membrane 202 is communicated with the salt water tank 11. With the structure, the nanofiltration salt separation membrane unit 2 comprises the high-salt adjusting tank 201, the nanofiltration salt separation membrane 202, the nanofiltration salt separation concentration valve 203, a high-salt water booster pump and a nanofiltration salt separation membrane circulating pump, the high-salt water booster pump is arranged between the high-salt adjusting tank 201 and the nanofiltration salt separation membrane 202, and the nanofiltration salt separation membrane circulating pump is arranged between the nanofiltration salt separation membrane 202 and the nanofiltration salt separation concentration valve 203.

[0037] The high-salt water booster pump provides reverse osmosis pressure for the nanofiltration salt separation membrane 202, guarantees water production rate and separation efficiency; the nanofiltration salt separation membrane 202 plays a role in separating salt water and nitrate water; the nanofiltration salt separation membrane circulating pump maintains a high flushing flow rate on the surface of the nanofiltration salt separation membrane 202, and reduces pollution and blockage; and the nanofiltration salt separation concentration valve 203 is a key to control the salt water-nitrate water ratio, the opening degree of the valve is controlled to control the pressure on the concentrated water side, so as to control the yield of salt water and nitrate water.

[0038] To ensure good salt separation efficiency, the head of the high-salt water booster pump needs to be 18 bar to 50 bar. To reduce pollution and blockage of the nanofiltration salt separation membrane 202, the flow rate of the nanofiltration salt separation membrane circulating pump needs to be 0.2 to 2 times the flow rate of the high-salt water booster pump. To obtain better separation effect, the flux of the nanofiltration salt separation membrane 202 is controlled to be 10 to 30 L / m2·h. The salt water produced from the nanofiltration salt separation membrane unit 2 is concentrated by the salt water concentration reverse osmosis membrane, the produced water is discharged up to the standard, and the concentrated salt water is sent to the concentrated nitrate water crystallization unit 8 to evaporate and crystallize sodium chloride salt.

[0039] In the preferred scheme, the salt water reverse osmosis membrane unit 3 comprises a concentrated reverse osmosis membrane 301 and a salt water concentration concentration valve 302, the salt water concentration concentration valve 302 is communicated with the concentrated salt water crystallization unit 4, the concentrated reverse osmosis membrane 301 is communicated with the produced water discharge unit 10, and the nitrate water reverse osmosis membrane unit 7 has the same structure as the salt water reverse osmosis membrane unit 3. With the structure, the salt water reverse osmosis membrane unit 3 comprises a salt water booster pump and a salt water concentration reverse osmosis membrane circulating pump, the salt water tank 11 and the concentrated reverse osmosis membrane 301 are provided with the salt water booster pump, and the salt water booster pump and the salt water concentration concentration valve 302 are provided with the salt water concentration reverse osmosis membrane circulating pump.

[0040] The brine booster pump provides reverse osmosis pressure for the high-pressure concentrated reverse osmosis membrane 301, ensuring water production rate and desalination efficiency; the brine concentrated reverse osmosis membrane 301 plays a role in concentrating brine; the brine concentrated reverse osmosis membrane circulating pump ensures that the surface of the brine concentrated reverse osmosis membrane 301 maintains a high water flow flushing speed, thereby reducing pollution and blockage; the 1 brine concentrated concentrated valve 302 is the key to controlling brine concentration, and by controlling the opening of the valve, the concentrated water side pressure is controlled, thereby controlling the concentration multiple of the brine.

[0041] To ensure good concentration effect, the head of the brine booster pump needs to be 60bar~120bar. To reduce the pollution and blockage of the concentrated reverse osmosis membrane 301, the flow rate of the brine concentrated reverse osmosis membrane circulating pump needs to be 0.3~3 times the flow rate of the brine booster pump. To obtain better separation effect, the flux of the concentrated reverse osmosis membrane 301 is controlled at 5~25L / m2·h.

[0042] Because the wastewater contains other impurity ions, monovalent impurity ions will also be contained in the brine. With the concentration and crystallization of the concentrated brine crystallization unit 4, sodium chloride is precipitated, and the concentration of impurity ions also rises until it approaches its saturated crystallization concentration. To ensure the purity of the output sodium chloride, a certain amount of brine mother liquor needs to be quantitatively discharged to the impurity salt drying and crystallization unit to output impurity salt.

[0043] In the preferred scheme, the impurity salt drying and crystallization unit 5 includes a drying machine 501, one end of the drying machine 501 is sequentially connected with a steam condenser 502 and a condensate tank 503, the condensate tank 503 is connected with the produced water discharge unit 10, the drying machine 501 discharges impurity salt, the other end of the drying machine 501 is provided with a connected drying intermediate tank 504, and the other end of the drying intermediate tank 504 is connected with the mother liquor intermediate tank of the concentrated brine crystallization unit 4. With this structure, a vacuum pump is arranged on one side of the steam condenser 502,

[0044] The impurity salt drying and crystallization unit 5 adopts a vacuum rake drying process. The mixed impurity salt solution discharged from the concentrated brine crystallization unit 4 and the concentrated nitrate water crystallization unit 8 is subjected to a drying process in the drying machine 501. The entire system is controlled by a vacuum pump to be in a super-low negative pressure vacuum state, so that the moisture of the impurity salt solution can be evaporated at a relatively low temperature, preventing the easy scaling ions from scaling and blocking the system. The pressure in the drying machine 501 is controlled at 5~20kPa absolute pressure.

[0045] Because the raw water contains various impurity ions, divalent impurity ions will also be concentrated in the nitrate water, especially calcium and magnesium divalent cations, which are easy to combine with sulfate and carbonate divalent anions to form calcium sulfate, calcium carbonate, magnesium carbonate and other scale, thereby blocking the subsequent membrane concentration equipment and evaporation crystallization equipment. Therefore, the nitrate water needs to be softened and hardened before being concentrated. The nitrate water softening unit adopts a "double-alkali softening + beam precipitation + submerged ultrafiltration" process to ensure stable water output.

[0046] In the preferred scheme, the nitrate water softening unit 6 comprises a softening reaction tank 601 and an immersed ultrafiltration membrane 603, the softening reaction tank 601 is communicated with the first intermediate tank 13, the immersed ultrafiltration membrane 603 is communicated with the nitrate water tank 12, and the nitrate water tank 12 is communicated with the concentrated reverse osmosis membrane of the nitrate water reverse osmosis membrane unit 7. Thus, the structure,

[0047] The nitrate water from the nanofiltration salt separation membrane unit is reacted with the softening agent sodium hydroxide and sodium carbonate in the softening reaction tank 601, and the calcium and magnesium ions in the nitrate water become precipitates. The slurry mixture is first removed to the beam current precipitation tank 602 to remove most of the precipitated slurry, and then the supernatant is subjected to the immersed ultrafiltration membrane 603 to remove the suspended matter to less than 50 ppm, thereby solving the problem of calcium and magnesium scaling in the subsequent membrane concentration unit. The slurry retained in the beam current precipitation tank 602 and the immersed ultrafiltration membrane 603 is transported by the softening sludge pump 604 to two places. One is the filter press 605, which discharges the softening sludge from the system, and the other is the softening reaction tank 601, which serves as a seed crystal to promote the precipitation and growth of the softening reaction precipitate, facilitating the separation of the beam current precipitation. In order to ensure that the calcium and magnesium in the nitrate water is fully precipitated, the pH value in the softening reaction tank 601 is controlled between 10 and 12. In order to ensure good slurry separation effect in the beam current precipitation tank 602, the calcium and magnesium precipitates need to have a large enough particle size, and the slurry concentration from the softening sludge pump 604 to the softening reaction tank 601 is ensured to be 1-10 g / L to ensure that the suspended matter content in the softening reaction tank 601 is within the range of 1-10 g / L. In order to ensure that the immersed ultrafiltration membrane 603 is not easily blocked, the flux is controlled at 2-6 L / m2·h.

[0048] In the preferred scheme, the softening reaction tank 601 is sequentially communicated with the beam current precipitation tank 602 and the immersed ultrafiltration membrane 603, the beam current precipitation tank 602 and the immersed ultrafiltration membrane 603 are both communicated with the softening sludge pump 604, the softening sludge pump 604 is communicated with the filter press 605, and the softening sludge pump 604 and the filter press 605 are both communicated with the softening reaction tank 601. Thus, the nitrate water produced by the nanofiltration salt separation membrane is subjected to softening and then further concentrated by the nitrate water reverse osmosis membrane unit 7, the produced water is discharged up to the standard, and the concentrated nitrate water is sent to the concentrated nitrate water crystallization unit 8 to evaporate and crystallize sodium sulfate.

[0049] In the preferred scheme, the concentrated nitrate water crystallization unit 8 comprises a softening intermediate tank 801, the softening intermediate tank 801 is sequentially connected with a first preheater 802, a second preheater 803, a main heater 805, an MVR flash tank 806, a centrifugal dehydrator 807, and a mother liquor intermediate tank 808, the first preheater 802 is connected with the produced water discharge unit 10, and the centrifugal dehydrator 807 discharges sodium sulfate salt. Thus, the concentrated nitrate water crystallization unit 8 adopts a mechanical vapor recompression evaporation crystallization process. The first preheater 802 and the second preheater 803 recover the heat of the condensate and the non-condensable gas discharged from the system, respectively; a nitrate water MVR compressor is arranged between the main heater 805 and the MVR flash tank 806,

[0050] The nitrate water MVR compressor is used to compress the secondary steam generated by the MVR flash tank 806 to the latent heat in the main heater 805 to recover the steam, thereby improving the thermal efficiency. The MVR flash tank 806 is provided with a nitrate water MVR slurry discharge pump forming a loop communication. The outlet of the nitrate water MVR slurry discharge pump is provided with two paths, one of which is connected to the centrifugal dewatering machine 807 to separate the nitrate, and the other of which is used as a circulating guarantee pipeline to ensure that there is always flowing fluid in the pipeline to avoid the deposition and blockage of the nitrate slurry in the pipeline.

[0051] The mother liquor intermediate tank 808 is provided with a nitrate mother liquor lifting pump in communication.

[0052] The outlet of the nitrate mother liquor lifting pump is provided with three paths, one of which is connected to the inlet of the main heater 805 for recirculation to heat and evaporate the nitrate, one of which is connected to the dryness intermediate tank 504 to send the impure salt to the dryness, so that there is no accumulation of impure salt and impurities in the system to ensure the quality of the salt, and the third of which is connected to the nitrate water evaporation mother liquor nanofiltration salt separation unit 9 for secondary salt separation to improve the overall salt production of the system.

[0053] To ensure stable evaporation of sodium sulfate and control the scaling tendency of each device in the unit, the liquid phase temperature in the 3MVR flash tank 806 is controlled at 50-65℃. To ensure that the energy consumption of the evaporation process is at a relatively economical level and to ensure the salt yield, the pressure ratio of the nitrate water MVR compressor is controlled at 1.5-2.2. To ensure that the main heater 805 does not scale or accumulate salt, the main heater 805 uses a vertical single-tube pass type fixed tube sheet heat exchanger, with salt water in the tube and steam in the shell, and the salt water flow rate in the tube is 1.5-3m / s. With the concentration and crystallization of the concentrated nitrate water in the concentrated nitrate water crystallization unit 8, sodium sulfate and sodium chloride will reach the eutectic point. If further concentration is performed, a eutectic mixed salt of sodium sulfate and sodium chloride will be produced instead of pure sodium sulfate, so it is necessary to discharge an appropriate amount of concentrated nitrate water mother liquor.

[0054] A small amount of the discharged concentrated nitrate water mother liquor is determined according to the concentration of divalent impurity ions in the raw water to be discharged to the impure salt dryness crystallization unit 5 to produce impure salt, so as to ensure that there is no accumulation of impure salt in the system. Most of it is discharged to the nitrate water evaporation mother liquor nanofiltration salt separation unit 9 for secondary salt separation.

[0055] In the preferred scheme, the structure of the concentrated salt water crystallization unit 4 is the same as that of the concentrated nitrate water crystallization unit 8, and the concentrated salt water crystallization unit 4 discharges sodium chloride salt. From this structure, the structure of the concentrated salt water crystallization unit 4 is the same as that of the concentrated nitrate water crystallization unit 8.

[0056] The concentrated brine crystallization unit 4 adopts a mechanical vapor recompression evaporation crystallization process. The first and second preheaters of the concentrated brine crystallization unit 4 recover the heat of the condensate and non-condensable gas discharged by the system respectively; the centrifugal dehydrator is used to press the secondary steam generated by the MVR flash tank into the latent heat in the recovered steam of the main heater of the concentrated brine crystallization unit 4 after being heated and pressurized, so as to improve the thermal efficiency; in order to ensure stable evaporation and salt output, the liquid phase temperature in the MVR condensate tank of the concentrated brine crystallization unit 4 is controlled at 85-110°C. In order to ensure that the energy consumption of the evaporation process is at a relatively economic level, while ensuring the salt output rate. In order to ensure that the main heater of the concentrated brine crystallization unit 4 is not scaled or salted, the main heater adopts a vertical single-tube fixed tube sheet heat exchanger, the salt water flows in the tube, the steam flows in the shell, and the salt water flow rate in the tube is 1.5-3 m / s.

[0057] In the preferred scheme, the concentrated nitrate water crystallization unit 8 further comprises a non-condensable gas cooler 809, the main heater 805 and the MVR flash tank 806 form a circulating loop, the other end of the main heater 805 and the second preheater 803 form a circulating loop, the second preheater 803 is connected with the non-condensable gas cooler 809, and the intermediate tank 801 for removing hardness is connected with the nitrate water evaporation mother liquor nanofiltration desalination unit 9. Based on the basic principle of membrane separation, since the nitrate mother liquor is a nearly saturated salt solution, the membrane system cannot handle saturated salt solution, therefore, the invention adopts a dilution process, uses the clean water produced by other units in the system to dilute the nitrate mother liquor, after reaching the working concentration of the nanofiltration desalination membrane, the nitrate mother liquor is separated into divalent salt and monovalent salt by the nanofiltration desalination membrane. The water produced by the nitrate water evaporation mother liquor nanofiltration desalination membrane is mainly a salt solution of sodium chloride, which can be directly used as the feed water of the concentrated brine MVR evaporation crystallization; the concentrated water of the nitrate water evaporation mother liquor nanofiltration desalination membrane can be used as the feed water of the concentrated nitrate water crystallization unit 8. After the nitrate mother liquor is separated into divalent salt and monovalent salt, it can be circulated in the system, thereby improving the yield of salt and nitrate.

[0058] In the preferred scheme, the nitrate water evaporation mother liquor nanofiltration desalination unit 9 comprises a dilution tank 901, the dilution tank 901 is communicated with the nitrate mother liquor nanofiltration membrane 902, the nitrate mother liquor nanofiltration membrane 902 is communicated with the intermediate tank for removing hardness of the concentrated brine crystallization unit 4, the produced water discharge unit 10 is communicated with the dilution tank 901, and the produced water discharge unit 10 comprises a mixing tank 1001. According to the structure, the dilution tank 901 and the nitrate mother liquor nanofiltration membrane 902 are provided with a nitrate mother liquor nanofiltration desalination booster pump, one side of the nitrate mother liquor nanofiltration membrane 902 is provided with a nitrate mother liquor nanofiltration desalination concentrated discharge valve, and the nitrate mother liquor nanofiltration desalination concentrated discharge valve and the nitrate mother liquor nanofiltration desalination booster pump are provided with a nitrate mother liquor nanofiltration desalination circulating pump.

[0059] The dilution tank 901 is used to dilute the nitrate mother liquor to meet the salt concentration suitable for the nitrate mother liquor nanofiltration membrane 902;

[0060] The nitrate mother liquor nanofiltration desalination booster pump provides reverse osmosis pressure for the separation membrane, guarantees the water production rate and separation efficiency; the nitrate mother liquor nanofiltration membrane 902 plays a role in separating brine and nitrate water; the nitrate mother liquor nanofiltration desalination circulating pump maintains a high flushing flow rate on the surface of the nitrate mother liquor nanofiltration membrane 902, reducing pollution and blockage; the nitrate mother liquor nanofiltration desalination concentrate valve is the key to controlling the brine-nitrate water ratio, and by controlling the opening of the valve, the pressure on the concentrated water side is controlled, thereby controlling the yield of brine and nitrate water. The mixing ratio of nitrate mother liquor and clean water is between 1:4 and 1:10. To ensure good desalination efficiency, the head of the nitrate mother liquor nanofiltration desalination booster pump needs to be 60bar-120bar. To reduce the pollution and blockage of the nanofiltration separation membrane, the flow rate of the nitrate mother liquor nanofiltration desalination circulating pump needs to be 0.3-3 times the flow rate of the nitrate mother liquor nanofiltration desalination booster pump. To obtain better separation effect, the flux of the nitrate mother liquor nanofiltration membrane 902 is controlled at 5-15L / m2·h.

[0061] The main function of the water production and discharge unit 10 is to mix and discharge the qualified clean water produced by each unit.

[0062] The above embodiments are only preferred technical solutions of the present application, and should not be regarded as a limitation of the present application. The protection scope of the present application should be based on the technical solutions claimed in the claims, including equivalent replacement solutions of the technical features claimed in the claims. That is, within this range, equivalent replacement improvements are also within the protection scope of the present application.

Claims

1. A highly efficient salt separation and impurity removal system for mine wastewater, characterized in that: The system comprises a nanofiltration salt separation membrane unit (2), the nanofiltration salt separation membrane unit (2) is connected with a salt water reverse osmosis membrane unit (3) and a nitrate water hardness removal unit (6) respectively, the salt water reverse osmosis membrane unit (3) is sequentially connected with a concentrated salt water crystallization unit (4) and a miscellaneous salt drying crystallization unit (5), the nanofiltration salt separation membrane unit (2) is sequentially connected with the nitrate water hardness removal unit (6), a nitrate water reverse osmosis membrane unit (7), a concentrated nitrate water crystallization unit (8) and a nitrate water evaporation mother liquor nanofiltration salt separation unit (9), the nitrate water evaporation mother liquor nanofiltration salt separation unit (9) is connected with the concentrated salt water crystallization unit (4); The miscellaneous salt drying crystallization unit (5) comprises a drying machine (501), one end of the drying machine (501) is sequentially communicated with a steam condenser (502) and a condensate tank (503), the condensate tank (503) is communicated with a water production discharge unit (10), the drying machine (501) discharges miscellaneous salt, the other end of the drying machine (501) is provided with a drying intermediate tank (504) in communication, and the other end of the drying intermediate tank (504) is communicated with a mother liquor intermediate tank of the concentrated salt water crystallization unit (4). The nitrate water hardness removal unit (6) comprises a hardness removal reaction tank (601) and an immersed ultrafiltration membrane (603), the hardness removal reaction tank (601) is communicated with a first intermediate tank (13), and the immersed ultrafiltration membrane (603) is communicated with a nitrate water tank (12); the nitrate water tank (12) is communicated with a concentrated reverse osmosis membrane of the nitrate water reverse osmosis membrane unit (7). The nitrate water evaporation mother liquor nanofiltration salt separation unit (9) comprises a dilution tank (901), the dilution tank (901) is communicated with a nitrate mother liquor nanofiltration membrane (902), the nitrate mother liquor nanofiltration membrane (902) is communicated with a hardness removal intermediate tank of the concentrated salt water crystallization unit (4), a water production discharge unit (10) is communicated with the dilution tank (901), and the water production discharge unit (10) comprises a mixing tank (1001).

2. The efficient desalination and impurity removal system for mine water and wastewater according to claim 1, characterized in that: A salt water tank (11) is arranged between the nanofiltration salt separation membrane unit (2) and the salt water reverse osmosis membrane unit (3), the nanofiltration salt separation membrane unit (2) is communicated with high-salinity wastewater (1) at an inlet, and the nanofiltration salt separation membrane unit (2) comprises a high-salinity adjusting tank (201), a nanofiltration salt separation membrane (202) and a nanofiltration salt separation concentration discharge valve (203); the high-salinity adjusting tank (201) is sequentially communicated with the nanofiltration salt separation membrane (202) and the nanofiltration salt separation concentration discharge valve (203); the nanofiltration salt separation concentration discharge valve (203) is communicated with a first intermediate tank (13); and the nanofiltration salt separation membrane (202) is communicated with the salt water tank (11).

3. The efficient desalination and impurity removal system for mine water and wastewater according to claim 1, characterized in that: The salt water reverse osmosis membrane unit (3) comprises a concentrated reverse osmosis membrane (301) and a salt water concentration concentration discharge valve (302), the salt water concentration concentration discharge valve (302) is communicated with the concentrated salt water crystallization unit (4), the concentrated reverse osmosis membrane (301) is communicated with the water production discharge unit (10), and the nitrate water reverse osmosis membrane unit (7) has the same structure as the salt water reverse osmosis membrane unit (3).

4. The efficient desalination and impurity removal system of mine water and wastewater according to claim 1, characterized in that: The hardening removal reaction tank (601) is communicated with the beam current precipitation tank (602) and the submerged ultrafiltration membrane (603) in turn, the beam current precipitation tank (602) and the submerged ultrafiltration membrane (603) are communicated with the hardening removal sludge pump (604), the hardening removal sludge pump (604) is communicated with the filter press (605), and the hardening removal sludge pump (604) and the filter press (605) are communicated with the hardening removal reaction tank (601).

5. The efficient desalination and impurity removal system of mine water and wastewater according to claim 1, characterized in that: The concentrated nitric water crystallization unit (8) comprises a hardening removal intermediate tank (801), the hardening removal intermediate tank (801) is connected with a first-stage preheater (802), a second-stage preheater (803), a main heater (805), an MVR flash tank (806), a centrifugal dewatering machine (807) and a mother liquor intermediate tank (808) in turn, the first-stage preheater (802) is connected with the water production and discharge unit (10), and the centrifugal dewatering machine (807) discharges sodium sulfate salt.

6. The efficient desalination and impurity removal system for mine water and wastewater according to claim 5, characterized in that: The concentrated salt water crystallization unit (4) has the same structure as the concentrated nitric water crystallization unit (8), and the concentrated salt water crystallization unit (4) discharges sodium chloride salt.

7. The efficient desalination and impurity removal system of mine water and wastewater according to claim 5, characterized in that: The concentrated nitric water crystallization unit (8) further comprises a non-condensable gas cooler (809), the main heater (805) and the MVR flash tank (806) form a circulating loop, the other end of the main heater (805) and the second-stage preheater (803) form a circulating loop, the second-stage preheater (803) is connected with the non-condensable gas cooler (809), and the hardening removal intermediate tank (801) is connected with the nitric water evaporation mother liquor nanofiltration desalination unit (9).

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