Strong brine resource utilization system

Abstract

The utility model relates to the technical field of water treatment, and discloses a strong brine resource utilization system. The strong brine resource utilization system comprises: a nanofiltration unit for separating monovalent ions and divalent ions in strong brine to realize salt separation and hardness removal; the concentration reduction unit is used for evaporating and concentrating the produced water separated by the nanofiltration unit; the evaporative crystallization unit is used for performing evaporative crystallization on the strong brine treated by the flash evaporation module; the freezing crystallization unit is used for freezing crystallization and centrifugation of the concentrated water separated by the nanofiltration unit; and the evaporation drying unit is used for evaporating and drying the solid phase separated by the freezing crystallization unit. According to the utility model, the solid salt can be produced while the overall treatment energy consumption and the operation cost of the system are reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of water treatment, in particular to a concentrated brine resource utilization system. Background Art

[0002] With water shortages becoming increasingly prominent, the development of seawater desalination has become a crucial means of increasing water supply and optimizing water supply structures. This development is crucial for alleviating water resource bottlenecks in my country's coastal areas and offshore islands, and for ensuring sustainable economic and social development. Currently, the brine produced by desalination is primarily discharged back into the sea. Some desalination projects use the brine for drying in salt pans. However, the land yield from salt pans is relatively low, and with the shrinking area of available salt pans, the development of new salt production routes is urgent. In the future, the discharge of brine into the sea will be further restricted to protect the marine ecosystem. Therefore, comprehensive resource utilization of desalinated brine is necessary. Building on existing salt production processes, new desalination brine production routes can be developed to optimize process flows, reduce operating costs, and ultimately lower both desalination costs and sea salt production costs.

[0003] Patent application CN107954528B discloses a method for producing concentrated brine from sea salt. This involves separating the concentrated reverse osmosis brine through nanofiltration. The separated nanofiltration water is then concentrated through high-pressure reverse osmosis to produce concentrated brine. However, the final product of this utility model is concentrated brine, which is less convenient to transport and store than solid brine. Furthermore, multi-stage high-pressure reverse osmosis produces high pressure and consumes a lot of electricity. Furthermore, no treatment method for the concentrated brine is proposed.

[0004] Therefore, there is an urgent need for a new concentrated brine resource utilization system that can achieve the output of solid salt while reducing the overall processing energy consumption and operating costs of the system. Utility Model Content

[0005] The purpose of the utility model is to overcome the problems of high energy consumption and operating costs in the process of treating brine in the prior art, high difficulty in salt production, and difficulty in realizing resource utilization of brine, and to provide a brine resource utilization system. The technical solution combines membrane water treatment and thermal water treatment technologies, and realizes effective separation of monovalent and divalent ions in brine through nanofiltration units, thereby improving the quality of subsequent monovalent and divalent salts and reducing the scaling risk of subsequent MED modules; and through the combination of reverse osmosis membrane, MED, flash evaporation and MVR, the power energy consumption and steam consumption are reduced; heat is provided by a low-grade heat source unit, which reduces the overall processing energy consumption and operating costs of the system and realizes the output of solid salt.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a concentrated brine resource utilization system, the concentrated brine resource utilization system comprising:

[0007] The nanofiltration unit is used to separate the monovalent ions and divalent ions in the concentrated brine to achieve salt separation and hardness removal; the concentration and reduction unit includes a reverse osmosis module, a MED module and a flash evaporation module, the reverse osmosis module is used to concentrate the produced water obtained by the nanofiltration unit, the MED module is used to evaporate and condense the concentrated water obtained by the reverse osmosis module, and the flash evaporation module is used to flash the concentrated brine treated by the MED module; the evaporation crystallization unit is used to evaporate and crystallize the concentrated brine treated by the flash evaporation module; the freeze crystallization unit is used to freeze crystallize and centrifuge the concentrated water obtained by the nanofiltration unit; the evaporation and drying unit is used to evaporate and dry the solid phase obtained by the freeze crystallization unit.

[0008] Preferably, the reverse osmosis module includes a first reverse osmosis device and a second reverse osmosis device, the first reverse osmosis device is used to concentrate the produced water obtained by separation by the nanofiltration unit, and the second reverse osmosis device is used to perform reverse osmosis treatment on the produced water obtained by separation by the first reverse osmosis device, and the concentrated water obtained by separation by the second reverse osmosis device is returned to the first reverse osmosis device for concentration.

[0009] Preferably, the reverse osmosis module further includes an energy recovery device, and the energy recovery device is used to recover the pressure energy in the concentrated water separated by the first reverse osmosis device and the second reverse osmosis device.

[0010] Preferably, the MED module includes an evaporator and a condenser, the evaporator is used to evaporate and condense the concentrated water obtained by separation by the reverse osmosis module, and the condenser is used to condense the steam generated by the evaporator.

[0011] Preferably, the evaporator is a low-temperature multiple-effect evaporator, and the evaporation temperature of the low-temperature multiple-effect evaporator is below 70°C, preferably 60-70°C.

[0012] Preferably, the steam obtained from the flash module is returned to the MED module to provide a steam heat source.

[0013] Preferably, the evaporation crystallization unit comprises a heater, a separator and a steam compressor.

[0014] Preferably, the freeze crystallization unit comprises a freeze crystallizer and a centrifuge, the freeze crystallizer is used to freeze crystallize the concentrated water obtained by separation by the nanofiltration unit, and the centrifuge is used to centrifuge the product obtained by treatment by the freeze crystallizer.

[0015] Preferably, the mother liquor obtained by centrifugation is passed into the first reverse osmosis device for concentration.

[0016] Preferably, the concentrated brine resource utilization system further comprises a product water tank, which is used to collect product water separated by the second reverse osmosis device, the MED module and the evaporation crystallization unit.

[0017] Preferably, the concentrated brine resource utilization system further comprises a low-grade heat source, and the low-grade heat source is used to provide heat to the MED module and the evaporation crystallization unit.

[0018] The second aspect of the present invention provides a method for resource utilization of concentrated brine, the method comprising the following steps:

[0019] (1) passing concentrated brine into a nanofiltration unit, separating monovalent ions and divalent ions in the concentrated brine in the nanofiltration unit to achieve salt separation and hardness removal, passing the concentrated water separated by the nanofiltration unit into a freezing crystallizer for freeze crystallization, passing the product obtained by the freeze crystallization into a centrifuge for centrifugation, passing the solid phase obtained by the centrifugation into an evaporation and drying unit for evaporation and drying, and recovering the obtained sodium sulfate;

[0020] (2) The produced water separated by the nanofiltration unit and the mother liquor obtained by the centrifugation are passed into a first reverse osmosis device for concentration, the concentrated water separated by the first reverse osmosis device is passed into a MED module for evaporation and condensation, the concentrated brine treated by the MED module is passed into a flash evaporation module for flash evaporation, the concentrated brine treated by the flash evaporation module is passed into an evaporation crystallization unit for evaporation and crystallization, and the obtained sodium chloride is recovered;

[0021] (3) The produced water separated by the first reverse osmosis device is passed into the second reverse osmosis device for reverse osmosis treatment, the concentrated water separated by the second reverse osmosis device is returned to the first reverse osmosis device, and the product water separated by the second reverse osmosis device, the MED module and the evaporation crystallization unit is passed into the product water tank.

[0022] Preferably, the TDS of the concentrated brine is 30,000-70,000 mg / L, the calcium ion concentration of the concentrated brine is 300-1,000 mg / L, and the magnesium ion concentration is 500-3,000 mg / L.

[0023] Preferably, the pH value of the concentrated brine in the nanofiltration unit (1) is 6.5-9.0.

[0024] Preferably, the concentrated brine in the nanofiltration unit (1) contains a scale inhibitor, and the scale inhibitor includes at least one of sodium hexametaphosphate, organic phosphate and polyacrylate.

[0025] Compared with the prior art, the technical solution of the utility model has the following advantages:

[0026] (1) The nanofiltration system is used to separate the salt and remove the hardness of the concentrated brine, avoiding the need to add a large amount of reagents to remove calcium and magnesium ions. At the same time, the monovalent ions and divalent ions are separated, which improves the purity of the subsequent industrial salt. In addition, the concentration of calcium and magnesium ions in the produced water separated by the nanofiltration system is low, which reduces the scaling tendency of the subsequent reverse osmosis module and MED module. During operation, the scaling tendency can be further reduced by adjusting the pH and adding appropriate scale inhibitors to ensure the safe operation of the equipment.

[0027] (2) Combining available low-grade waste heat as the heat source for the MED module and evaporation crystallization unit reduces the energy consumption of thermal water treatment and reduces the operating cost of the treatment;

[0028] (3) By combining reverse osmosis, MED and flash evaporation, the high power consumption caused by high pressure when using reverse osmosis technology alone and the large steam consumption when using MED technology alone are avoided. The concentration and reduction unit can achieve full concentration and reduction of brine at lower pressure and energy consumption, thereby improving heat utilization efficiency, simplifying the process flow, reducing energy consumption, and reducing processing costs. Finally, solid salt is produced, realizing the comprehensive resource utilization of brine and opening up a new salt production process route.

[0029] The concentrated brine resource utilization system described in the present invention is applicable to concentrated brine including concentrated brine produced by reverse osmosis seawater desalination and concentrated brine produced by pretreated MED seawater desalination. This technical solution can also be applied to the field of water treatment, for example, concentrated brine produced by membrane treatment of industrial wastewater, mine water, etc. Since pretreatment has been carried out in the previous process, impurities such as suspended matter, colloids, microorganisms, and organic matter have been removed, the treatment process is shortened, the pretreatment cost is reduced, and it also has broad application prospects in the fields of deep wastewater treatment and zero emission. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the process flow of the concentrated brine resource utilization system described in the utility model.

[0031] Description of Reference Numerals

[0032] 1. Nanofiltration unit; 2. Concentration and reduction unit; 3. Evaporation and crystallization unit; 4. Freeze crystallization unit; 5. Evaporation and drying unit; 6. Product water tank; 7. Low-grade heat source; 21. Reverse osmosis module; 22. MED module; 23. Flash evaporation module. DETAILED DESCRIPTION

[0033] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0034] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0035] The concentrated brine resource utilization system described in the utility model is shown in FIG Figure 1 The concentrated brine resource utilization system includes:

[0036] The nanofiltration unit 1 is used to separate the monovalent ions and divalent ions in the concentrated brine to achieve salt separation and hardness removal; the concentration and reduction unit 2 includes a reverse osmosis module 21, a MED module 22 and a flash evaporation module 23, wherein the reverse osmosis module 21 is used to concentrate the produced water obtained by the nanofiltration unit 1, the MED module 22 is used to evaporate and condense the concentrated water obtained by the reverse osmosis module 21, and the flash evaporation module 23 is used to flash the concentrated brine treated by the MED module 22; the evaporation crystallization unit 3 is used to evaporate and crystallize the concentrated brine treated by the flash evaporation module 23; the freeze crystallization unit 4 is used to freeze crystallize and centrifuge the concentrated water obtained by the nanofiltration unit 1; the evaporation and drying unit 5 is used to evaporate and dry the solid phase obtained by the freeze crystallization unit 4.

[0037] The brine resource utilization system of the present invention utilizes the Donann effect of the nanofiltration membrane in the nanofiltration system 1 to intercept divalent ions and pass monovalent ions, effectively separating monovalent and divalent ions in the brine, achieving salt separation and hardness removal. Furthermore, the reverse osmosis module 21 concentrates the brine to a certain salinity when the salinity is low. At this point, the required pressure is relatively low, reducing the energy consumption of the reverse osmosis module 21. The MED module 22 and the flash evaporation module 23 then further concentrate and reduce the salinity. Finally, the evaporation and crystallization unit 3 produces qualified product salt. This system leverages the advantages of each process, shortens the overall process flow, reduces system operating energy consumption and costs, and ensures stable and reliable equipment. The MED module 22 comprises a low-temperature multi-effect evaporator, which is a series of horizontal tube falling-film heat exchangers. Steam heat source condenses within the heat exchange tubes, releasing heat. The brine is sprayed onto the outside of the heat exchange tubes, absorbing heat and evaporating into steam. The steam evaporated from the previous effect serves as the steam heat source for the next effect. At lower temperatures and pressures, the low-temperature multi-effect evaporator can reuse input heat multiple times by connecting multiple evaporators in series. The low-temperature multi-effect evaporator is preferably a six-effect evaporator with independent intellectual property rights developed by the New Energy Research Institute. The specific number of effects can be determined based on conventional parameters in the field and the actual processing capacity.

[0038] In the brine resource utilization system described in the present invention, the nanofiltration unit 1 may include a nanofiltration membrane assembly. The nanofiltration membrane assembly may be a single-stage nanofiltration membrane assembly or a multi-stage, multi-segment nanofiltration membrane assembly. The nanofiltration membrane assembly includes a membrane element, a support structure, a sealing port, and a connection port. The nanofiltration unit 1 can retain divalent ions such as calcium, magnesium, and sulfate ions in the separated brine, while allowing monovalent ions such as sodium, potassium, and chloride ions to pass through the nanofiltration membrane into the separated product water. To ensure salt separation and hardness removal of the brine, the nanofiltration membrane element preferably uses a nanofiltration membrane with good retention and anti-scaling properties. Specific examples include nanofiltration membranes manufactured by mainstream membrane manufacturers such as DuPont, Wharton, Veolia, or OriginWater. In some specific embodiments, the nanofiltration membrane may be DK8040F30 nanofiltration membrane manufactured by Suez. The nanofiltration membrane element has a salt rejection rate of 98% or higher. The nanofiltration membrane element has a retention rate of 98% or higher for sulfate, calcium, and magnesium ions.

[0039] In the brine resource utilization system described in the present invention, the reverse osmosis module 21 may include a first reverse osmosis device and a second reverse osmosis device, the first reverse osmosis device is used to concentrate the produced water obtained by separation of the nanofiltration unit 1, and the second reverse osmosis device is used to perform reverse osmosis treatment on the produced water obtained by separation of the first reverse osmosis device, and the concentrated water obtained by separation of the second reverse osmosis device is returned to the first reverse osmosis device for concentration. The brands of the reverse osmosis membranes in the first reverse osmosis device and the second reverse osmosis device can be DuPont, Veolia, Wharton or OriginWater. In some specific embodiments, the reverse osmosis membrane can be SW30XLE-400 reverse osmosis membrane produced by Dow Chemical.

[0040] In the concentrated brine resource utilization system described in the present invention, the reverse osmosis module 21 further includes an energy recovery device, which is used to recover the pressure energy in the concentrated water separated by the first reverse osmosis device and the second reverse osmosis device.

[0041] In the brine resource utilization system described in the present invention, the MED module 22 includes an evaporator and a condenser. The evaporator is used to evaporate and condense the brine separated by the reverse osmosis module 21, and the condenser is used to condense the steam generated by the evaporator.

[0042] In the brine resource utilization system described in the present invention, the evaporator is a low-temperature multi-effect evaporator. The specific device can refer to the content disclosed in patent application CN211688498U. The low-temperature multi-effect evaporator can be a 3-10 effect evaporator. The evaporation temperature of the low-temperature multi-effect evaporator is below 70°C, preferably 60-70°C. In the low-temperature multi-effect evaporator, the steam heat source heats the brine outside the heat exchange tubes in the heat exchange tubes. Part of the brine is evaporated into secondary steam. The secondary steam enters the heat exchange tubes of the next effect as the heat source, and then heats the brine outside the heat exchange tubes while being condensed. This is repeated until the last effect. The temperature of the brine between each effect is higher, and partial steam can be flashed and generated while flowing between different effects, thereby improving the thermal efficiency of the entire system. The concentrated water separated by the reverse osmosis module 21 is concentrated to near saturation in the MED module 22. The condenser is used to condense the steam generated in the last effect.

[0043] In the brine resource utilization system described in the present invention, in order to reduce the energy consumption of thermal water treatment and reduce the operating cost of the treatment, the steam obtained by the flash evaporation module 23 is preferably returned to the MED module 22 to provide a steam heat source.

[0044] In the brine resource utilization system of the present invention, the evaporation crystallization unit 3 may include a heater, a separator, and a steam compressor. The steam compressor compresses the secondary steam generated during the evaporation process, increases the pressure and temperature of the secondary steam, and then uses the steam as a steam heat source, thereby achieving the purpose of energy recycling.

[0045] In the brine resource utilization system described in the present invention, the freezing crystallization unit 4 may include a freezing crystallizer and a centrifuge. The freezing crystallizer can be used to freeze crystallize the brine obtained by separation of the nanofiltration unit 1, and the centrifuge can be used to centrifuge the product obtained by treatment of the freezing crystallizer.

[0046] In the brine resource utilization system of the present invention, in order to improve the resource utilization rate of brine, the mother liquor obtained by centrifugation is preferably passed into the first reverse osmosis device for concentration.

[0047] In the concentrated brine resource utilization system described in the present invention, the concentrated brine resource utilization system can also include a product water tank 6, which is used to collect the product water separated by the second reverse osmosis device, the MED module 22 and the evaporation crystallization unit 3.

[0048] In the concentrated brine resource utilization system of the present invention, the concentrated brine resource utilization system may further include a low-grade heat source 7, which may be used to provide heat to the MED module 22 and the evaporation crystallization unit 3. The low-grade heat source 7 includes steam, exhaust gas, and hot water, which may directly enter the MED module 22 and the evaporation crystallization unit 3, or enter the MED module 22 and the evaporation crystallization unit 3 after heat exchange.

[0049] In some embodiments, when the steam heat source of the MED module 22 is a high-grade heat source, the MED module 22 can use steam energy through a steam jet thermal compressor (TVC) to increase its water production ratio, which can be 8-15.

[0050] In other embodiments, when the steam heat source of the MED module 22 is a low-grade heat source, the MED module 22 can directly transport the steam heat source to the first effect, and the steam heat source heats the concentrated brine outside the heat exchange tube in the heat exchange tube. Part of the concentrated brine is evaporated into secondary steam, and the secondary steam enters the heat exchange tube of the next effect as the heat source of the next effect, and then heats the concentrated brine outside the heat exchange tube while being condensed, and so on to the last effect.

[0051] In some embodiments, the brine resource utilization system described in the present invention includes: a nanofiltration unit 1, which is used to separate and remove monovalent ions and divalent ions in brine; a concentration and reduction unit 2, which includes a reverse osmosis module 21, a MED module 22 and a flash evaporation module 23, the reverse osmosis module 21 includes a first reverse osmosis device, a second reverse osmosis device and an energy recovery device, the first reverse osmosis device is used to concentrate the produced water obtained by separation by the nanofiltration unit 1, the second reverse osmosis device is used to perform reverse osmosis treatment on the produced water obtained by separation by the first reverse osmosis device, and the concentrated water separated by the second reverse osmosis device is returned to the first reverse osmosis device for concentration, and the energy recovery device is used to recover the pressure energy in the concentrated water separated by the first reverse osmosis device and the second reverse osmosis device; the MED module 22 includes a low-temperature multi-effect evaporator and a condenser, the low-temperature multi-effect evaporator is a 3-10 effect evaporator, in the low-temperature multi-effect evaporator, the steam heat source heats the concentrated brine outside the heat exchange tube in the heat exchange tube, and part of the concentrated brine is evaporated into secondary steam, and the secondary steam enters the next effect as the heat source of the next effect. The concentrated brine outside the heat exchange tube is then heated while being condensed, and so on to the final effect; the condenser is used to condense the steam generated in the final effect of the evaporator; the flash evaporation module 23 is used to flash the concentrated brine treated by the MED module 22; the evaporation crystallization unit 3 includes a heater, a separator and a steam compressor, the steam compressor compresses the secondary steam generated during the evaporation process, and the evaporation crystallization unit 3 is used to evaporate and crystallize the concentrated brine treated by the flash evaporation module 23; the freezing crystallization unit 4 includes a freezing crystallizer and a centrifuge, the freezing crystallizer is used to freeze and crystallize the concentrated water separated by the nanofiltration unit 1, and the centrifuge is used to centrifuge the product obtained by the freezing crystallizer; the evaporation drying unit 5 is used to evaporate and dry the solid phase separated by the freezing crystallization unit 4; the product water tank 6 is used to collect the produced water separated by the second reverse osmosis device, the MED module 22 and the evaporation crystallization unit 3; the low-grade heat source 7 is used to provide a heat source for the MED module 22 and the evaporation crystallization unit 3.

[0052] The utility model also provides a method for resource utilization of concentrated brine, which is carried out in the above-mentioned system and comprises the following steps:

[0053] (1) passing concentrated brine into a nanofiltration unit 1, separating monovalent ions and divalent ions in the concentrated brine in the nanofiltration unit 1 to achieve salt separation and hardness removal, passing the concentrated water separated by the nanofiltration unit 1 into a freezing crystallizer for freeze crystallization, passing the product obtained by the freeze crystallization into a centrifuge for centrifugation, passing the solid phase obtained by the centrifugation into an evaporation and drying unit 5 for evaporation and drying, and recovering the obtained sodium sulfate;

[0054] (2) The produced water separated by the nanofiltration unit 1 and the mother liquor obtained by the centrifugation are passed into a first reverse osmosis device for concentration, the concentrated water separated by the first reverse osmosis device is passed into the MED module 22 for evaporation and condensation, the concentrated brine treated by the MED module 22 is passed into the flash evaporation module 23 for flash evaporation, the concentrated brine treated by the flash evaporation module 23 is passed into the evaporation crystallization unit 3 for evaporation and crystallization, and the obtained sodium chloride is recovered;

[0055] (3) The produced water separated by the first reverse osmosis device is passed into the second reverse osmosis device for reverse osmosis treatment, the concentrated water separated by the second reverse osmosis device is returned to the first reverse osmosis device, and the product water separated by the second reverse osmosis device, the MED module 22 and the evaporation crystallization unit 3 is passed into the product water tank 6.

[0056] According to the method described in the present invention, the nanofiltration unit 1 is used to effectively separate monovalent and divalent ions in the concentrated brine, thereby improving the quality of subsequent monovalent and divalent salts and reducing the scaling risk of the subsequent MED module. In addition, the reverse osmosis membrane method, low-temperature multi-effect thermal method and flash evaporation are combined through the concentration and reduction unit 2. When the salinity is low, the concentrated brine is concentrated to a certain salinity through the reverse osmosis module 21. At this time, the required pressure is low, which reduces the energy consumption of the reverse osmosis module. Subsequently, the MED module 22 and the flash evaporation module 23 are used for further and sufficient concentration and reduction. The advantages of each treatment method are utilized for treatment, the heat utilization efficiency is improved, and the output of solid salt is achieved.

[0057] In the method described in the present invention, when the concentrated brine is concentrated brine produced by reverse osmosis seawater desalination, the TDS of the concentrated brine can be 30,000-70,000 mg / L, preferably 45,000-65,000 mg / L; the calcium ion concentration of the concentrated brine can be 300-1000 mg / L, preferably 600-800 mg / L; the magnesium ion concentration can be 500-3000 mg / L, preferably 1000-2500 mg / L.

[0058] In the method of the present invention, the pH value of the concentrated brine in the nanofiltration unit 1 can be 6.5-9.0, preferably 7.4-8.4. The concentrated brine in the nanofiltration unit 1 can contain a scale inhibitor, which can be at least one of sodium hexametaphosphate (SHMP), an organic phosphate, and a polyacrylate.

[0059] The water inlet flow rate of the nanofiltration unit 1 can be determined according to the processing scale, and the water inlet pressure can be 1.5-3MPa, preferably 1.5-2.5MPa. The recovery rate of the nanofiltration unit 1 can be 35-45%, preferably 38-42%. The membrane flux of the nanofiltration membrane can be 15-25L / m 2 h, preferably 18-22 L / m 2 ·h. In this article, pressure is gauge pressure.

[0060] In the method described herein, the TDS of the influent to the first reverse osmosis device can be 36,000-68,000 mg / L, preferably 46,000-64,000 mg / L. The influent flow rate to the first reverse osmosis device is determined based on the water output of the nanofiltration unit; the influent pressure can be 6-10 MPa, preferably 7-9 MPa. The recovery rate of the first reverse osmosis device can be 35-45%, preferably 38-42%.

[0061] In the method described herein, the water inlet flow rate of the second reverse osmosis unit is determined based on the water output of the first reverse osmosis unit. The water inlet pressure can be 0.5-2 MPa, preferably 1-1.5 MPa. The recovery rate of the second reverse osmosis unit can be 80-95%, preferably 85-95%. The TDS of the water produced by the second reverse osmosis unit can be 5-50 mg / L, preferably 10-20 mg / L. The water produced by the second reverse osmosis unit meets drinking water standards (National Standard for Drinking Water Quality (GB5749-2022)).

[0062] In the method described in the present invention, the brine separated by the first reverse osmosis device is passed into the MED module 22 via parallel feeding or grouped countercurrent feeding. The MED module 22 can concentrate the brine separated by the reverse osmosis device by more than 2 times. The TDS of the brine after treatment by the MED module 22 can be 200,000-220,000 mg / L, preferably 210,000-215,000 mg / L. The temperature of the brine after treatment by the MED module 22 can be 40-55°C, preferably 45-50°C.

[0063] In the method described in the present invention, the MED module 22 includes a low-temperature multi-effect evaporator. The evaporation conditions include: the first-effect inlet steam temperature of the low-temperature multi-effect evaporator can be 65-70° C. To ensure heat utilization efficiency and cost, the low-temperature multi-effect evaporator is preferably a four-effect evaporator.

[0064] In the method described in the present invention, in order to improve the heat utilization efficiency of the concentration reduction unit 2, the concentrated brine treated by the MED module 22 is flash evaporated in the flash evaporation module 23 to generate steam.

[0065] In the method described in the present invention, in the flash evaporation module 23, the flash evaporation chamber may be set to a pressure of 7.5-12 kPa, preferably 8-10 kPa.

[0066] In the method described in the present invention, the method for resource utilization of concentrated brine described in the present invention may further include: discharging the mother liquor obtained by the treatment and separation of the evaporation crystallization unit 3 .

[0067] In the method described in the present invention, the conditions for the freezing crystallization include: the temperature can be from -6 to 0°C, preferably from -4 to -2°C.

[0068] In the method described in the present invention, the evaporative drying is negative pressure evaporation, and the conditions of the evaporative drying include: the temperature can be 65-95°C, preferably 70-80°C; the pressure can be 25-84.6kPa, preferably 31.2-47.4kPa.

[0069] In the method described in the present invention, the low-grade heat source can be hot water at 90-99° C., or steam with a pressure not less than 25 kPa.

[0070] In some embodiments, the method for resource utilization of concentrated brine described in the present invention is carried out in the above-mentioned system and includes the following steps:

[0071] (1) Brine with a TDS of 35,000-70,000 mg / L is introduced with a recovery rate of 35-45% and a membrane flux of 15-25 L / m 2h nanofiltration unit 1, wherein the pH value of the concentrated brine in the nanofiltration unit 1 is 6.5-9.0, and the concentrated brine contains a scale inhibitor, which is at least one of sodium hexametaphosphate (SHMP), an organic phosphate, and a polyacrylate; in the nanofiltration unit 1, monovalent ions and divalent ions in the concentrated brine are separated, the concentrated water separated by the nanofiltration unit 1 is passed into a freezing crystallizer, and frozen crystallized at a temperature of -6 to 0°C, the product obtained by the freezing crystallization is passed into a centrifuge for centrifugation, and the solid phase obtained by the centrifugation is passed into an evaporation drying unit 5, and the evaporation temperature is controlled to be 65-95°C for negative pressure evaporation to produce sodium sulfate salt;

[0072] (2) The produced water separated by the nanofiltration unit 1 and the mother liquor obtained by centrifugation are mixed to obtain a mixed concentrated brine, the TDS of the mixed concentrated brine is 36000-68000 mg / L, the mixed fluid is passed into a first reverse osmosis device with a recovery rate of 35-45% for concentration, and the concentrated water separated by the first reverse osmosis device is passed into the MED module 22, the MED module 22 includes a 4-effect evaporator, the first-effect steam temperature is 68°C, the concentrated water is evaporated in the MED module, and passes through the MED module After treatment at 22, concentrated water with a TDS of 200,000-220,000 mg / L and a temperature of 40-55°C is obtained. The concentrated brine is passed into the flash evaporation module 23. The flash evaporation chamber is set at a pressure of 6-10 kPa. The steam after flash evaporation enters the fourth effect of the MED module as an evaporation heat source. The concentrated brine treated by the flash evaporation module 23 is passed into the evaporation crystallization unit 3 for evaporation and crystallization to produce solid sodium chloride salt; the steam heat source of the MED module 22 and the evaporation crystallization unit 3 adopts low-grade steam with a pressure of not less than 25 kPa;

[0073] (3) The produced water separated by the first reverse osmosis device is passed into a second reverse osmosis device with a recovery rate of 80-95% for reverse osmosis treatment, and the pressure is set to 1-1.5 MPa. The concentrated water separated by the second reverse osmosis device is returned to the first reverse osmosis device, and the produced water separated by the second reverse osmosis device, the MED module 22 and the evaporation crystallization unit 3 is passed into the product water tank 6. The produced water with a TDS of 5-50 mg / L is obtained by separation by the second reverse osmosis device.

[0074] The following examples further illustrate the concentrated brine resource utilization system of the present invention. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following examples.

[0075] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0076] The process of resource utilization of concentrated brine in the following examples is as follows Figure 1 The system shown is implemented, specifically, the system includes:

[0077] The nanofiltration unit 1 is used to separate the monovalent ions and divalent ions in the concentrated brine; the concentration and reduction unit 2 includes a reverse osmosis module 21, a MED module 22 and a flash evaporation module 23. The reverse osmosis module 21 includes a first reverse osmosis device, a second reverse osmosis device and an energy recovery device. The first reverse osmosis device is used to concentrate the produced water obtained by the nanofiltration unit 1, and the second reverse osmosis device is used to perform reverse osmosis treatment on the produced water obtained by the first reverse osmosis device. The concentrated water separated by the second reverse osmosis device is returned to the first reverse osmosis device for concentration. The energy recovery device is used to recover the pressure energy in the concentrated water separated by the first reverse osmosis device and the second reverse osmosis device; the MED module 22 includes a low-temperature multi-effect evaporator and a condenser. The low-temperature multi-effect evaporator is a four-effect evaporator. In the low-temperature multi-effect evaporator, the steam heat source heats the concentrated brine outside the heat exchange tube in the heat exchange tube, and part of the concentrated brine is evaporated into secondary steam. The secondary steam enters the heat exchange tube of the next effect as the heat source of the next effect, and then heats the exchange tube while being condensed. The concentrated brine outside the heat pipe is analogous to the last effect; the condenser is used to condense the steam from the last effect of the evaporator; the flash evaporation module 23 is used to flash the concentrated brine treated by the MED module 22; the evaporation crystallization unit 3 includes a heater, a separator and a steam compressor, the steam compressor compresses the secondary steam generated during the evaporation process, and the evaporation crystallization unit 3 is used to evaporate and crystallize the concentrated brine treated by the flash evaporation module 23; the freezing crystallization unit 4 includes a freezing crystallizer and a centrifuge, the freezing crystallizer is used to freeze and crystallize the concentrated water separated by the nanofiltration unit 1, and the centrifuge is used to centrifuge the product obtained by the freezing crystallizer; the evaporation and drying unit 5 is used to evaporate and dry the solid phase separated by the freezing crystallization unit 4; the product water tank 6 is used to collect the produced water separated by the second reverse osmosis device, the MED module 22 and the evaporation and crystallization unit 3; the low-grade heat source 7 is used to provide a heat source for the MED module 22 and the evaporation and crystallization unit 3.

[0078] Example 1

[0079] (1) Brine with a TDS of 62135 mg / L, a calcium ion concentration of 698 mg / L, and a magnesium ion concentration of 2289 mg / L was added to the water at an inlet flow rate of 205 m3 / h and the inlet pressure is 2.1MPa, the recovery rate is 40% and the membrane flux is 20L / m 2 h of nanofiltration unit 1, the pH value of the concentrated brine in the nanofiltration unit 1 is 8.2, and it contains sodium hexametaphosphate scale inhibitor. The monovalent ions and divalent ions in the concentrated brine are separated in the nanofiltration unit 1, and the TDS of the concentrated water separated by the nanofiltration unit 1 is 72910 mg / L; the TDS of the produced water separated by the nanofiltration unit 1 is 60514 mg / L, the calcium ion concentration is 69 mg / L, and the magnesium ion concentration is 229 mg / L; the concentrated water separated by the nanofiltration unit 1 is passed into a freezing crystallizer for freeze crystallization at a temperature of -3°C, the product obtained by the freeze crystallization is passed into a centrifuge for centrifugation, and the solid phase obtained by centrifugation is passed into an evaporation and drying unit 5 for evaporation and drying at a temperature of 70°C and a pressure of 31.2 kPa, to obtain 4.6 t / h of sodium sulfate;

[0080] (2) The produced water separated by the nanofiltration unit 1 and the mother liquor obtained by centrifugation were mixed to obtain a mixed fluid. The TDS of the mixed fluid was 60905 mg / L. The mixed fluid was filtered at an inlet flow rate of 85.2 m 3 / h and an inlet pressure of 8.9 MPa were passed into the first reverse osmosis device with a recovery rate of 37% for concentration. The concentrated water obtained by the first reverse osmosis device was concentrated at an inlet flow rate of 47.9 m 3 / h is passed into the MED module 22, the first-effect steam temperature of the MED module 22 is 68℃, and the concentrated water is evaporated and concentrated in the MED module 22. The TDS of the concentrated water after being treated by the MED module 22 is 210457mg / L and the temperature is 47℃. The concentrated brine is passed into the flash evaporation module 23 at a flow rate of 22.8t / h for flash evaporation, and 0.8m 3 / h steam returns to the end effect of MED module 22 as steam heat source, and the brine TDS after treatment by flash module 23 is 21780mg / L. 3 / h flow rate into the evaporation crystallization unit 3 for evaporation crystallization, and the obtained 5.1t / h sodium chloride is recovered; the low-grade heat source uses 35kPa steam as the heat source for the MED module 22 and the evaporation crystallization unit 3;

[0081] (3) The produced water separated by the first reverse osmosis device is separated by a flow rate of 34m 3 / h and the water inlet pressure is 0.9MPa, and the water is passed into the second reverse osmosis device with a recovery rate of 90% for reverse osmosis treatment. The concentrated water separated by the second reverse osmosis device is returned to the first reverse osmosis device, and the product water separated by the second reverse osmosis device, the MED module 22 and the evaporation crystallization unit 3 is passed into the product water tank 6, of which 30.6m3 of water is produced by the second reverse osmosis device. 3 / h, 25.1m3 of water is produced through MED module 22 3 / h, and 15.7m3 of water is produced through evaporation and crystallization unit 3 3 / h, total water production 71.4m 3 / h enters the product water tank 6; the TDS of the produced water obtained by separation of the second reverse osmosis device is 21mg / L, the TDS of the produced water after the MED module 22 is 7mg / L, and the TDS of the produced water after the evaporation crystallization unit 3 is 85mg / L.

[0082] Example 2

[0083] (1) Brine with a TDS of 29879 mg / L, a calcium ion concentration of 385 mg / L, and a magnesium ion concentration of 565 mg / L is introduced into the water at an inlet flow rate of 200 m 3 / h and the inlet pressure is 1.8MPa, the recovery rate is 45% and the membrane flux is 22L / m 2 h nanofiltration unit 1, the pH value of the concentrated brine in the nanofiltration unit 1 is 7.4, and it contains sodium hexametaphosphate scale inhibitor. The monovalent ions and divalent ions in the concentrated brine are separated in the nanofiltration unit 1, and the TDS of the concentrated water separated by the nanofiltration unit 1 is 31207 mg / L; the TDS of the produced water separated by the nanofiltration unit 1 is 28764 mg / L, the calcium ion concentration is 32 mg / L, and the magnesium ion concentration is 59 mg / L; the concentrated water separated by the nanofiltration unit 1 is passed into a freezing crystallizer for freeze crystallization at a temperature of -4°C, the product obtained by the freeze crystallization is passed into a centrifuge for centrifugation, and the solid phase obtained by centrifugation is passed into the evaporation and drying unit 5 for negative pressure evaporation and drying at a temperature of 65°C and a pressure of 25 kPa to obtain 2.5 t / h of sodium sulfate;

[0084] (2) The produced water separated by the nanofiltration unit 1 and the mother liquor obtained by centrifugation were mixed to obtain a mixed fluid. The TDS of the mixed fluid was 28955 mg / L. The mixed fluid was filtered at an inlet flow rate of 93.75 m 3 / h and an inlet pressure of 8.4 MPa were passed into the first reverse osmosis device with a recovery rate of 40% for concentration, and the concentrated water obtained by the first reverse osmosis device was concentrated at an inlet flow rate of 52.5 m 3 / h into the MED module 22, the first-effect steam temperature of the MED module 22 is 65℃, the concentrated water is evaporated and concentrated in the MED module 22, the TDS of the concentrated water after being treated by the MED module 22 is 199673mg / L, the temperature is 45℃, and the concentrated brine is transported at a flow rate of 25m 3 / h is passed into the flash evaporation module 23 for flash evaporation, and 0.8m 3 / h steam returns to the end effect of MED module 22 as steam heat source, and the TDS of the concentrated brine after being treated by flash module 23 is 201957 mg / L. 3 / h flow rate into the evaporation crystallization unit 3 for evaporation crystallization, and the obtained 3.1t / h sodium chloride is recovered; the low-grade heat source uses 98℃ hot water flash evaporation to generate 70℃ steam as the heat source for the MED module 22 and the evaporation crystallization unit 3;

[0085] (3) The produced water separated by the first reverse osmosis device is separated by an inlet flow rate of 37.5m 3 / h and the water inlet pressure is 0.8MPa, and the water is passed into the second reverse osmosis device with a recovery rate of 90% for reverse osmosis treatment. The concentrated water separated by the second reverse osmosis device is returned to the first reverse osmosis device, and the product water separated by the second reverse osmosis device, the MED module 22 and the evaporation crystallization unit 3 is passed into the product water tank 6, of which 33.75m3 of water is produced by the second reverse osmosis device. 3 / h, 27.5m3 of water is produced through MED module 22 3 / h, 18.6m3 of water is produced through evaporation and crystallization unit 3 3 / h, total water production 79.85m 3 / h enters the product water tank 6; the TDS of the produced water obtained by separation of the second reverse osmosis device is 15mg / L, the TDS of the produced water after the MED module 22 is 7mg / L, and the TDS of the produced water after the evaporation crystallization unit 3 is 76mg / L.

[0086] Example 3

[0087] (1) Brine with a TDS of 70131 mg / L, a calcium ion concentration of 854 mg / L, and a magnesium ion concentration of 2776 mg / L is introduced into the water at an inlet flow rate of 200 m 3 / h and the inlet pressure is 2.2MPa, the recovery rate is 40% and the membrane flux is 20L / m 2 h nanofiltration unit 1, the pH value of the concentrated brine in the nanofiltration unit 1 is 8.4, and it contains sodium hexametaphosphate scale inhibitor. The monovalent ions and divalent ions in the concentrated brine are separated in the nanofiltration unit 1, and the TDS of the concentrated water separated by the nanofiltration unit 1 is 72437 mg / L; the TDS of the produced water separated by the nanofiltration unit 1 is 68459 mg / L, the calcium ion concentration is 79 mg / L, and the magnesium ion concentration is 278 mg / L; the concentrated water separated by the nanofiltration unit 1 is passed into a freezing crystallizer for freeze crystallization at a temperature of -2°C, the product obtained by the freeze crystallization is passed into a centrifuge for centrifugation, and the solid phase obtained by centrifugation is passed into an evaporation and drying unit 5 for negative pressure evaporation and drying at a temperature of 80°C and a pressure of 47.4 kPa, to obtain 4.7 t / h of sodium sulfate;

[0088] (2) The produced water obtained by the nanofiltration unit 1 and the mother liquor obtained by centrifugation were mixed to obtain a mixed fluid. The TDS of the mixed fluid was 69813 mg / L. The mixed fluid was filtered at an inlet flow rate of 83.3 m 3 / h and an inlet pressure of 9MPa were passed into the first reverse osmosis device with a recovery rate of 40% for concentration. The concentrated water obtained by the first reverse osmosis device was concentrated at an inlet flow rate of 46.7m 3 / h is passed into the MED module 22. The first-effect steam temperature of the MED module 22 is 70℃. The concentrated water is evaporated and concentrated in the MED module 22. The TDS of the concentrated water after being treated by the MED module 22 is 219438mg / L and the temperature is 48℃. The concentrated brine is transported at a flow rate of 22.2m 3 / h is passed into the flash evaporation module 23 for flash evaporation, and 0.9m 3 / h steam returns to the end effect of MED module 22 as steam heat source, and the brine TDS after treatment by flash module 23 is 220846 mg / L. 3 / h flow into the evaporation crystallization unit 3 for evaporation crystallization, and the obtained 5.3t / h sodium chloride is recovered; the low-grade heat source uses 95 degrees generated by flash evaporation of 130-degree hot water as the heat source of the steam evaporation crystallization unit 3, and the 95-degree hot water is further flashed to generate 70-degree steam as the heat source of the MED module 22;

[0089] (3) The product water separated by the first reverse osmosis device is separated by an inlet flow rate of 33.3m 3 / h and the water inlet pressure is 0.8MPa, and the water is passed into the second reverse osmosis device with a recovery rate of 90% for reverse osmosis treatment. The concentrated water separated by the second reverse osmosis device is returned to the first reverse osmosis device, and the product water separated by the second reverse osmosis device, the MED module 22 and the evaporation crystallization unit 3 is passed into the product water tank 6, of which 30m3 of the water produced by the second reverse osmosis device is 0.8MPa. 3 / h, 24.5m3 of water is produced through MED module 22 3 / h, 15m3 of water is produced through evaporation and crystallization unit 3 3 / h, total water production 69.5m 3 / h enters the product water tank 6; the TDS of the produced water obtained by separation of the second reverse osmosis device is 26mg / L, the TDS of the produced water after the MED module 22 is 9.1mg / L, and the TDS of the produced water after the evaporation crystallization unit 3 is 57mg / L.

[0090] Comparative Example 1

[0091] The system used in this comparative example is the same as that of Example 1, except that the mixed fluid is not passed into the reverse osmosis module 21. Specifically, in step (2), the produced water separated by the nanofiltration unit 1 and the mother liquor obtained by centrifugation are mixed to obtain a mixed fluid. The mixed fluid is then fed to the reverse osmosis module 21 at an inlet flow rate of 85.2 m 3 / h is passed into the MED module 22. The first-effect steam temperature of the MED module 22 is 68°C. The concentrated water is evaporated and concentrated in the MED module 22. The concentrated brine treated by the MED module 22 is discharged at a flow rate of 60.1m 3 / h is passed into the flash evaporation module 23 for flash evaporation, and 1.2m 3 / h of steam returns to the end effect of MED module 22 as a steam heat source. The TDS of the brine after being treated by the flash module 23 is 13374 mg / L. It is passed into the evaporation crystallization unit 3 at a flow rate of 39.4 t / h for evaporation crystallization. Due to the certain processing capacity of the equipment and the heat source provided, the brine is not fully concentrated and reduced in the MED module. The MED module has a large amount of concentrated water and a relatively low TDS. Therefore, the heat of the evaporation crystallization unit is used for further evaporation and concentration. The solid salt that cannot be produced is also less. In step (3), the product water tank 6 only collects the water separated by the MED module 22 and the evaporation crystallization unit 3; among them, the 1.5 t / h of sodium chloride obtained is recycled, and 25.1m of water is produced after passing through the MED module 22. 3 / h, 2.8m3 of water is produced through evaporation and crystallization unit 3 3 / h, total water production 27.9m 3 / h enters the product water tank 6. The TDS of the water produced after the MED module 22 is 7 mg / L, and the TDS of the water produced after the evaporation crystallization unit 3 is 97 mg / L.

[0092] Comparative Example 2

[0093] The system used in this comparative example is the same as that of Example 1, except that the mixed fluid is not passed into the MED module 22 and the flash evaporation module 23. Specifically, in step (2), the produced water separated by the nanofiltration unit 1 and the mother liquor obtained by centrifugation are mixed to obtain a mixed fluid. The mixed fluid is then fed to the MED module 22 and the flash evaporation module 23 at an inlet flow rate of 85.2 m 3 / h and the water inlet pressure is 8.9MPa, and the water is concentrated into the first reverse osmosis device with a recovery rate of 37%. The TDS of the concentrated water separated by the first reverse osmosis device is 101554mg / L. 3 / h is passed into the evaporation crystallization unit 3. Due to the limited processing capacity of the equipment, the concentrated brine is not fully concentrated and reduced in the reverse osmosis module. The concentrated water volume of the reverse osmosis module is large, and the TDS is relatively low. Therefore, the heat of the evaporation crystallization unit is used for further evaporation and concentration, and no solid salt is produced. Among them, 30.6m3 of water is produced after the second reverse osmosis device. 3 / h, and the TDS of the water produced by the second reverse osmosis device is 21 mg / L.

[0094] Comparative Example 3

[0095] The system used in this comparative example is the same as that of Example 1, except that the mixed fluid is not passed into the MED module 22, the flash module 23 and the evaporation crystallization unit 3. Specifically, in step (2), the produced water separated by the nanofiltration unit 1 and the mother liquor obtained by centrifugation are mixed to obtain a mixed fluid, and the mixed fluid is evaporating at an inlet flow rate of 85.2 m 3 / h and the water inlet pressure is 8.9MPa, and the first reverse osmosis device with a recovery rate of 37% is used for concentration. The TDS of the concentrated water obtained by the first reverse osmosis device is 101554mg / L, of which 30.6m3 of water is produced by the second reverse osmosis device. 3 / h; the TDS of the water produced after the second reverse osmosis device is 21mg / L.

[0096] By comparing the embodiment and the comparative example, it can be seen that by combining the reverse osmosis module 21, the MED module 22 and the flash evaporation module 23, the brine is fully concentrated and reduced at a lower pressure and energy consumption, thereby improving the heat utilization efficiency, reducing energy consumption, and achieving the output of solid salt.

[0097] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be considered as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A concentrated brine resource utilization system, characterized in that: The concentrated brine resource utilization system includes: The nanofiltration unit (1) is used to separate monovalent ions and divalent ions in the concentrated brine to achieve salt separation and hardness removal; A concentration and reduction unit (2) comprises a reverse osmosis module (21), a MED module (22) and a flash evaporation module (23), wherein the reverse osmosis module (21) is used to concentrate the produced water separated by the nanofiltration unit (1), the MED module (22) is used to evaporate and concentrate the concentrated water separated by the reverse osmosis module (21), and the flash evaporation module (23) is used to flash the concentrated brine treated by the MED module (22); an evaporation crystallization unit (3), used for evaporating and crystallizing the concentrated brine after being treated by the flash evaporation module (23); A freezing crystallization unit (4) is used to perform freezing crystallization and centrifugation on the concentrated water separated by the nanofiltration unit (1); The evaporation and drying unit (5) is used to evaporate and dry the solid phase separated by the freezing and crystallization unit (4).

2. The concentrated brine resource utilization system according to claim 1, characterized in that: The reverse osmosis module (21) comprises a first reverse osmosis device and a second reverse osmosis device, wherein the first reverse osmosis device is used to concentrate the produced water obtained by separation by the nanofiltration unit (1), and the second reverse osmosis device is used to perform reverse osmosis treatment on the produced water obtained by separation by the first reverse osmosis device, and the concentrated water obtained by separation by the second reverse osmosis device is returned to the first reverse osmosis device for concentration.

3. The concentrated brine resource utilization system according to claim 2, characterized in that: The reverse osmosis module (21) further comprises an energy recovery device, wherein the energy recovery device is used to recover the pressure energy in the concentrated water separated by the first reverse osmosis device and the second reverse osmosis device.

4. The concentrated brine resource utilization system according to claim 1 or 2, characterized in that: The MED module (22) comprises an evaporator and a condenser. The evaporator is used to evaporate and condense concentrated water obtained by separation in the reverse osmosis module (21), and the condenser is used to condense steam generated by the evaporator.

5. The concentrated brine resource utilization system according to claim 4, characterized in that: The evaporator is a low-temperature multi-effect evaporator, and the evaporation temperature of the low-temperature multi-effect evaporator is below 70°C.

6. The concentrated brine resource utilization system according to any one of claims 1 to 3, characterized in that: The steam obtained by the flash module (23) is returned to the MED module (22) to provide a steam heat source.

7. The concentrated brine resource utilization system according to any one of claims 1 to 3, characterized in that: The evaporation crystallization unit (3) comprises a heater, a separator and a steam compressor.

8. The concentrated brine resource utilization system according to any one of claims 1 to 3, characterized in that: The freeze crystallization unit (4) comprises a freeze crystallizer and a centrifuge, wherein the freeze crystallizer is used to freeze crystallize the concentrated water obtained by separation by the nanofiltration unit (1), and the centrifuge is used to centrifuge the product obtained by treatment by the freeze crystallizer.

9. The concentrated brine resource utilization system according to claim 2 or 3, characterized in that: The mother liquor obtained by centrifugation is transported to the first reverse osmosis device for concentration.

10. The concentrated brine resource utilization system according to claim 2 or 3, characterized in that: The concentrated brine resource utilization system further comprises a product water tank (6), wherein the product water tank (6) is used to collect product water separated by the second reverse osmosis device, the MED module (22) and the evaporation crystallization unit (3).

11. The concentrated brine resource utilization system according to any one of claims 1 to 3, characterized in that: The concentrated brine resource utilization system further comprises a low-grade heat source (7), and the low-grade heat source (7) is used to provide a heat source for the MED module (22) and the evaporation crystallization unit (3).

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