Near-zero discharge system and method for high-salt and high-concentration organic matter industrial wastewater

Abstract

The present invention discloses a near-zero discharge system and method for high-salt and high-concentration organic industrial wastewater, which includes a freezing crystallization system, a fine crystal clarification and separation system, a nanofiltration salt separation system, a sodium chloride evaporation crystallization system, a sodium sulfate evaporation crystallization system, a mixed salt crystallization system, a hot melt system, and a miscellaneous salt drying system. Through the process of the present invention, most of the sulfate in the water is first precipitated in the form of thenardite decahydrate. As the temperature rises or the fine crystals are reversely dissolved, the sulfate content in the lean nitrate solution is increased, which increases the difficulty of operating the sodium chloride evaporation crystallization system. By rotary immersion ultrafiltration, the thenardite decahydrate can be effectively separated, and a large amount of pre-ultrafiltration pretreatment can be omitted; the water produced by the rotary immersion ultrafiltration enters the nanofiltration system, which can increase the mass ratio of sodium chloride: sodium sulfate in the lean nitrate solution to more than 100; the mixed salt after crystallization is re-salted by hot melting, which greatly reduces the output of miscellaneous salts.

Description

Technical Field

[0001] The present invention belongs to the technical field of zero discharge of industrial wastewater, and specifically relates to a near-zero discharge system for high-salt and high-concentration organic industrial wastewater, and also relates to a near-zero discharge method for high-salt and high-concentration organic industrial wastewater. Background Art

[0002] After chemical softening, resin softening, decarbonization, silicon removal, COD degradation, activated carbon adsorption, and multiple concentrations, industrial wastewater contains primarily chloride, sulfate, and sodium ions, with minor amounts of calcium, magnesium, carbonate, bicarbonate, silicon, and other impurities, as well as some organic matter. Two common treatment processes are used for this concentrated wastewater, once its TDS exceeds 250 g / L. One involves using nanofiltration membranes for salt separation and subsequent quality separation crystallization. This process offers the advantage of stable separation of monovalent and divalent salts. Depending on system requirements, the mass ratio of sodium chloride to sodium sulfate after separation can reach >100:1, resulting in stable system operation and mature technology. However, its disadvantages include the need for lengthy nanofiltration pretreatment, the addition of desalted water to dilute the high-salinity wastewater to below 60 g / L, the need for re-evaporation of the dilution water, high energy consumption, and a high total investment. The nanofiltration membrane is significantly affected by the stability of the pretreatment stage, and generally has a short operating life. Another method is to use freeze crystallization to separate sodium sulfate and sodium chloride. The process involves freezing the lean nitrate solution and then evaporating and crystallizing it to obtain sodium chloride crystals. This process has the advantages of relatively high purity of the crystallized sodium sulfate and a simple process flow. However, its disadvantages are that the frozen lean nitrate solution contains high levels of impurities and fine sodium sulfate decahydrate crystals, making it difficult to achieve a sodium chloride:sodium sulfate mass ratio greater than 25:1, and making it difficult to guarantee the purity of the subsequent sodium chloride.

[0003] Patents CN108275815A and CN105523676A disclose a zero-discharge evaporation and crystallization salt separation system and method for high-salt wastewater. The treatment process for TDS > 250g / L involves the nitrate evaporation and crystallization mother liquor entering a freezing crystallization system, the frozen crystallized lean nitrate solution entering a settler, and the supernatant after settling undergoes salt evaporation and crystallization. However, the settler described in this patent only separates the solid decahydrate sodium sulfate crystals from the lean nitrate solution, without further reducing the sulfate content in the lean nitrate solution. Based on actual field operation, the sulfate content in the lean nitrate solution exceeds 6000mg / L at -5°C, making it difficult for the subsequent salt evaporation and crystallization system to meet the standards set forth in GB / T 5462-2015.

[0004] Patents CN107352727A, CN107777815A, and CN107777803A disclose a high-concentration brine zero-discharge system. These invention patents use nanofiltration membranes to separate monovalent and divalent anions when the TDS (total saturation density) reaches less than 200 g / L. Subsequently, the monovalent and divalent salts are evaporated and crystallized separately to recover salt and nitrate. However, these invention patents use nanofiltration to separate salt at relatively low TDS concentrations, resulting in high investment and operating costs. The salt mother liquor contains a certain amount of nitrate, and the nitrate mother liquor also contains a certain amount of salt. This leads to the problem of large amounts of mother liquor discharged from the evaporation and crystallization of salt and nitrate, as well as a high concentration of impurities. Summary of the Invention

[0005] The purpose of the present invention is to provide a near-zero emission system for high-salt and high-concentration organic industrial wastewater, which solves the problems of high treatment cost, poor freezing crystallization salt separation effect, and high amount of impurities in existing processes.

[0006] The present invention also aims to provide a method for near-zero discharge of industrial wastewater with high salt content and high organic concentration.

[0007] The first technical solution adopted by the present invention is a near-zero emission system for high-salt and high-concentration organic industrial wastewater, which includes a freezing crystallization system, a fine crystal clarification separation system, a nanofiltration salt separation system, a sodium chloride evaporation crystallization system, a sodium sulfate evaporation crystallization system, a mixed salt crystallization system, a hot melt system, and a mixed salt drying system; the outlet of the freezing crystallization system is connected to the inlet of the fine crystal clarification separation system; the fine crystal clarification separation system is provided with three outlets, which are respectively connected to the inlets of the nanofiltration salt separation system, the sodium sulfate evaporation crystallization system and the mixed salt crystallization system; the nanofiltration salt separation outlet is provided with two outlets, which are respectively connected to the inlets of the sodium chloride evaporation crystallization system and the mixed salt crystallization system; the outlet of the sodium sulfate evaporation crystallization system is connected to the inlet of the mixed salt crystallization system; the mixed salt crystallization system is provided with two outlets, which are respectively connected to the hot melt system and the mixed salt drying system; the mixed salt output by the mixed salt crystallization system is reversely dissolved in the hot melt system to maximize the recovery of inorganic salt resources in the water; the outlet of the mixed salt drying system is connected to the mixed salt discharge system.

[0008] The present invention is also characterized in that:

[0009] Preferably, the pore size of the rotary immersion ultrafiltration is set between 50 and 200 nm, and ultrafiltration membranes with pore sizes in other ranges are also within the scope of protection of this patent.

[0010] Preferably, the nanofiltration system includes a refrigerated nanofiltration water inlet tank, a nanofiltration water inlet pump, a nanofiltration feed pump, a nanofiltration membrane, a nanofiltration water production tank, a nanofiltration concentrated water tank, a nanofiltration water production pump, and a nanofiltration concentrated water pump;

[0011] Preferably, the pore size of the nanofiltration system is selected between 0.6 and 1.2 nm, and nanofiltration membranes with pore sizes in other ranges are also within the scope of protection of this patent. The rotary immersion ultrafiltration and nanofiltration system are coupled into a rotary immersion nanofiltration, and the remaining immersion filters are coupled with ultrafiltration and nanofiltration systems, which are also within the scope of protection of this patent.

[0012] Preferably, the hot melt system includes a hot melt tank and a saturated solution delivery pump.

[0013] The second technical solution adopted by the present invention is a near-zero discharge method for high-salt and high-concentration organic industrial wastewater. The high-salt and high-concentration organic industrial wastewater with a TDS greater than 250g / L and a COD greater than or equal to 1000mg / L in a frozen raw material tank is fed through a frozen feed pump and heat exchanged in a precooler into a circulation pipeline of a frozen crystallizer. The decahydrated sodium sulfate in the lower section of the frozen crystallizer is fed through a frozen thickening feed pump and sequentially into a frozen thickener and a refrigerated centrifuge to obtain decahydrated sodium sulfate with a moisture content of ≤5%. This portion of sodium sulfate enters a sodium sulfate evaporation and crystallization system. The liquid separated by the frozen thickener and the refrigerated centrifuge enters a frozen mother liquor tank and then returns to the frozen raw material tank through the frozen mother liquor pump. The supernatant of the frozen crystallizer overflows and enters a fine crystal clarification separation system. The material in the frozen crystallizer is continuously heat-exchanged and cooled in a refrigerated heat exchanger through a frozen circulation pump and its pipeline.

[0014] The raw water of the fine crystal clarification separation system comes from the supernatant of the freezing crystallization system, and the overflow to the inlet pipeline of the fine crystal clarification separation tank is passed into the bottom of the fine crystal clarification separation tank. The residence time in the fine crystal clarification separation tank is greater than 1 hour. The fine crystal clarification separation tank is provided with three sewage outlets, which are respectively located above, below and below the rotary immersion ultrafiltration tank, and the sewage outlet is connected to the mixed salt crystallization system; the rotary immersion ultrafiltration is placed in the fine crystal clarification separation tank, and the water is mechanically extracted during the ultrafiltration backwash and placed in the raw material tank in the sodium sulfate evaporation crystallization system. After all the fine crystals of decahydrate sodium sulfate intercepted on the surface of the rotary immersion ultrafiltration are dissolved, they are placed back into the fine crystal clarification separation tank, and the water produced by the rotary immersion ultrafiltration is connected to the nanofiltration system; a solid-liquid discharge outlet is provided at the bottom of the fine crystal clarification separation tank, and the solid-liquid discharge outlet is connected to the sodium sulfate evaporation crystallization system;

[0015] Preferably, the rotary submerged ultrafiltration is configured to rotate to prevent the crystallized salt from forming a dense layer of crystallized salt on the surface of the rotary submerged ultrafiltration membrane in a short period of time.

[0016] Preferably, the rotation speed of the rotary immersion ultrafiltration is 50 to 200 rpm;

[0017] Nanofiltration produced water enters the sodium chloride evaporation crystallization system, and nanofiltration concentrated water enters the mixed salt crystallization system. The sodium sulfate evaporation crystallization system has two inlets, one for frozen crystallized thenardite decahydrate, and the other for the solid-liquid in the fine crystal clarification separation system. The raw material tank of the sodium sulfate evaporation crystallization system is used to dissolve the fine crystals of thenardite decahydrate on the surface of the rotary immersion ultrafiltration, and the mother liquor of sodium sulfate evaporation crystallization is sent to the mixed salt crystallization inlet.

[0018] The inlet water for sodium chloride evaporation crystallization comes from nanofiltration produced water, and the mother liquor of sodium chloride evaporation crystallization is sent to the mixed salt crystallization inlet; there are four mixed salt crystallization inlets, one is the wastewater from the fine crystal clarification separation system, one is the nanofiltration concentrated water, one is the sodium sulfate evaporation crystallization mother liquor, and one is the sodium chloride evaporation crystallization mother liquor; the mixed salt produced by the mixed salt crystallization is sent to the hot melt system, and the mixed salt crystallization mother liquor is sent to the miscellaneous salt drying system; the hot melt system performs hot melt treatment on the mixed salt produced by the mixed salt crystallization and then returns it to the frozen crystallization system, the inlet water for the miscellaneous salt drying system comes from the mother liquor of the mixed salt crystallization system, and the COD in the mixed salt crystallization system is controlled within 2000 mg / L.

[0019] The present invention's zero-discharge evaporation and crystallization salt separation method for high-salt wastewater utilizes sodium sulfate and commercial salt separated as industrially recyclable raw materials, reusing water resources and achieving low-cost zero-discharge of industrial wastewater, thereby preventing the adverse environmental impacts of wastewater discharge. The patented process produces sodium sulfate that consistently meets the requirements of Class I, Grade I, for industrial anhydrous sodium sulfate according to GB / T6009-2014, and sodium chloride that consistently meets the requirements of Class I, Grade I, for industrial dry salt according to GB / T5462-2015. The amount of impurities is reduced by 2% compared to the prior process system.

[0020] Therefore, the present invention combines the advantages of nanofiltration salt separation and freeze crystallization salt separation, and proposes that high-salt (TDS>250g / L) and high-concentration organic matter industrial wastewater first passes through a freeze crystallization system to freeze and crystallize the decahydrate sodium sulfate, and the lean saltpeter liquid enters a fine crystal clarification separation tank. The rotary submerged ultrafiltration in the fine crystal clarification separation tank intercepts the sodium sulfate decahydrate fine crystals and COD, and the rotary submerged ultrafiltration water is fed into the nanofiltration system. The nanofiltration water is sent to a sodium chloride evaporation crystallization system to obtain a qualified sodium chloride solution.

[0021] The beneficial effects of the present invention are:

[0022] The rotary immersion ultrafiltration in the fine crystal clarification separation tank used in the process of the present invention has the functions of anti-pollution, stable operation at low temperatures, and separation of fine crystals of thenardite decahydrate. Through the process of the present invention, most of the sulfate in the water is first precipitated in the form of thenardite decahydrate. In a low-temperature environment, especially between -5 and 0°C, freezing crystallization will inevitably produce a certain amount of fine crystals. The diameter of this part of fine crystals is usually less than 50um, which is difficult to separate by solid-liquid separation equipment such as cyclones, thickeners and centrifuges, and it is also difficult to directly enter ordinary ultrafiltration membranes / nanofiltration membranes. As the temperature rises or these fine crystals dissolve, the sulfate content in the lean nitrate solution increases, making the operation of the sodium chloride evaporation crystallization system more difficult. The unique rotary immersion ultrafiltration of the present invention can effectively separate the decahydrate sodium sulfate, slow down the speed of the crystallized salt forming a dense layer on the surface of the rotary immersion ultrafiltration, and save a lot of pre-ultrafiltration pretreatment; the water produced by the rotary immersion ultrafiltration enters the nanofiltration system, which can increase the mass ratio of sodium chloride:sodium sulfate in the lean nitrate solution to more than 100, ensuring that the by-product salt of the sodium chloride evaporation crystallization system meets the standards described in GB / T 5462-2015; after the mixed salt is crystallized, the mixed salt is re-salted by hot melting, which greatly reduces the output of miscellaneous salts. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the overall structure of the near-zero discharge system for high-salt and high-concentration organic wastewater of the present invention;

[0024] Figure 2 It is a structural schematic diagram of the fine crystal clarification separation tank of the present invention. DETAILED DESCRIPTION

[0025] The following describes the implementation of the present invention in detail with reference to the accompanying drawings. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiments.

[0026] The structure of the near-zero discharge system for high-salt and high-concentration organic wastewater of the present invention is as follows: Figure 1 As shown, it includes freezing crystallization system, fine crystal clarification and separation system, nanofiltration salt separation system, sodium chloride evaporation crystallization system, sodium sulfate evaporation crystallization system, mixed salt crystallization system, hot melt system, and miscellaneous salt drying system.

[0027] (1) The freezing crystallization system includes: a freezing raw material tank, a freezing feed pump, a freezing crystallizer, a freezing circulation pump, a freezing thickener, a freezing centrifuge, a freezing heat exchanger, a precooler, a freezing thickening feed pump, a freezing mother liquor tank, and a freezing mother liquor pump.

[0028] like Figure 1As shown, the industrial wastewater with high salt content (TDS>250g / L) and high concentration of organic matter (COD≥1000mg / L) in the frozen raw material tank passes through the frozen feed pump and enters the circulation pipeline of the frozen crystallizer through the heat exchange of the precooler. The decahydrated sodium sulfate in the lower section of the frozen crystallization passes through the frozen thickening feed pump and enters the frozen thickener and the frozen centrifuge in sequence to obtain decahydrated sodium sulfate with a moisture content of ≤5%. This part of the sodium sulfate enters the sodium sulfate evaporation crystallization system; the liquid separated by the frozen thickener and the frozen centrifuge enters the frozen mother liquor tank and then returns to the frozen raw material tank through the frozen mother liquor pump; the supernatant of the frozen crystallizer enters the fine crystal clarification separation system through overflow; the material in the frozen crystallizer is continuously heat-exchanged and cooled in the frozen heat exchanger through the frozen circulation pump and its pipeline; the temperature of the frozen crystallizer is controlled at -5~5℃.

[0029] (2) The fine crystal clarification and separation system mainly includes: fine crystal clarification and separation tank, rotary immersion ultrafiltration, thenardite delivery pump, sewage pump, and vacuum pump.

[0030] The raw water of the fine crystal clarification separation system comes from the supernatant overflow of the freezing crystallization system, including the fine crystal clarification separation tank. Figure 2 As shown, the inlet pipeline of the fine crystal clarification separation tank is connected to the bottom of the fine crystal clarification separation tank. The residence time of the fine crystal clarification separation tank is greater than 1 hour. The fine crystal clarification separation tank is provided with three sewage outlets, which are respectively located above, below and below the rotary immersion ultrafiltration. The sewage outlets are connected to the mixed salt crystallization system. The rotary immersion ultrafiltration is placed in the fine crystal clarification separation tank. During the backwash of the ultrafiltration, it is mechanically extracted and placed in the raw material tank in the sodium sulfate evaporation crystallization system. After all the fine crystals of decahydrate sodium sulfate intercepted on the surface of the rotary immersion ultrafiltration are dissolved, they are placed back into the fine crystal clarification separation tank. The water produced by the rotary immersion ultrafiltration is connected to the nanofiltration system. A solid-liquid discharge outlet is provided at the bottom of the fine crystal clarification separation tank, and the solid-liquid discharge outlet is connected to the sodium sulfate evaporation crystallization system.

[0031] The temperature in the fine crystal clarification separation tank is controlled between -5°C and 5°C. The pore size of the rotary immersion ultrafiltration membrane is set between 50 and 200 nm, and ultrafiltration membranes with pore sizes in other ranges are also within the scope of protection of this patent. The rotation speed of the rotary immersion ultrafiltration is set between 50 and 200 rpm, and other speeds are also within the scope of protection of this patent.

[0032] (3) The water produced by the rotary immersion ultrafiltration enters the nanofiltration system. Preferably, the nanofiltration system adopts a one-stage process, and the other nanofiltration components are also within the scope of protection of this patent. The nanofiltration water enters the sodium chloride evaporation crystallization system, and the nanofiltration concentrated water enters the sodium sulfate evaporation crystallization system. Preferably, the pore size of the nanofiltration system is selected between 0.6 and 1.2 nm, and the nanofiltration membranes with pore sizes in other ranges are also within the scope of protection of this patent. The rotary immersion ultrafiltration and the nanofiltration system are coupled to form a rotary immersion nanofiltration, and the other immersion filters are coupled to ultrafiltration and the nanofiltration system is also within the scope of protection of this patent.

[0033] (4) The sodium sulfate evaporation crystallization system has two inlets, one is the frozen crystallized Glauber's salt decahydrate, and the other is the solid-liquid containing fine crystal clarification separation system. The sodium sulfate evaporation crystallization system can adopt a conventional system. The raw material tank of the sodium sulfate evaporation crystallization system takes into account the dissolution of the fine crystals of Glauber's salt decahydrate on the surface of the rotary immersion ultrafiltration structure. The sodium sulfate evaporation crystallization mother liquor is sent to the mixed salt crystallization inlet.

[0034] (5) The inlet water for sodium chloride evaporation and crystallization comes from nanofiltration water. The sodium chloride evaporation and crystallization system can adopt a conventional system. The mother liquor of sodium chloride evaporation and crystallization is sent to the mixed salt crystallization inlet.

[0035] (6) There are four inlets for mixed salt crystallization: one for the wastewater from the fine crystal clarification separation system, one for the concentrated water from the nanofiltration, one for the mother liquor from the evaporation crystallization of sodium sulfate, and one for the mother liquor from the evaporation crystallization of sodium chloride. The mixed salt produced by the mixed salt crystallization is sent to the hot melt system, and the mother liquor from the mixed salt crystallization is sent to the mixed salt drying system. Preferably, the COD in the mixed salt crystallization system is controlled within 2000 mg / L.

[0036] (7) The hot melt system can be equipped with a COD degradation device, a decarbonization device, a softening device and a silicon removal device according to demand. The hot melt system melts the mixed salt produced by the mixed salt crystallization and returns it to the frozen crystallization system in combination with appropriate treatment.

[0037] (8) The water inlet of the mixed salt drying system comes from the mother liquor of the mixed salt crystallization system. The mixed salt drying system selects a suitable dryer according to the system requirements. Preferably, a vacuum drum dryer is used.

[0038] Example 1:

[0039] Refrigeration system water inlet 2m 3 / h, TDS is 300g / L, COD is 3000mg / L, chloride ion content is 120g / L, sulfate content is 70g / L, the temperature in the freezing crystallizer is controlled at 0℃, the pore size of the rotary immersion ultrafiltration is selected to be 100nm, the rotation speed is selected to be 80rpm, and the pore size of the nanofiltration membrane is selected to be 1nm. The TDS of the water produced by the refrigeration system is 200g / L, COD is 3000mg / L, chloride ion content is 120g / L, sulfate content is 8g / L, and turbidity is 60NTU. The lean nitrate solution is raised to room temperature (25℃), and the sulfate content in the lean nitrate solution is 15g / L. The TDS of the water produced by the rotary immersion ultrafiltration is 200g / L, COD is 500mg / L, chloride ion content is 120g / L, sulfate content is 8g / L, and turbidity is 2NTU. While intercepting COD by the rotary immersion ultrafiltration, most of the fine crystals of the decahydrate sodium sulfate are also intercepted. After running for 50 minutes, the rotary immersion ultrafiltration needs to be placed in the feed tank of the sodium sulfate evaporation crystallization system to dissolve the fine crystals. The water produced by the nanofiltration T The DS is 200g / L, the COD is 100mg / L, the chloride ion content is 125g / L, and the sulfate content is 0.16g / L. The nanofiltration system effectively controls the mass ratio of sodium chloride and sodium sulfate in the lean nitrate solution to more than 100 times. The sodium sulfate evaporation and crystallization system produces sodium sulfate crystals with a purity of 99.3%, and the sodium chloride evaporation and crystallization system produces sodium chloride with a purity of 99.1%, respectively meeting the requirements of Class I first-class industrial anhydrous sodium sulfate of GB / T6009-2014 and the first-class industrial dry salt of GB / T5462-2015. The mixed salt crystallization system produces 20kg / h of mixed salt, which is completely dissolved, reducing the amount of miscellaneous salt by 20kg / h.

[0040] Example 2:

[0041] Refrigeration system water inlet 2m 3 / h, TDS is 300g / L, COD is 3000mg / L, chloride ion content is 120g / L, sulfate content is 70g / L, the temperature in the freezing crystallizer is controlled at -5℃, the pore size of the rotary immersion ultrafiltration is selected to be 100nm, the rotation speed is selected to be 80rpm, and the pore size of the nanofiltration membrane is selected to be 1nm. The TDS of the water produced by the refrigeration system is 185g / L, the COD is 3000mg / L, the chloride ion content is 120g / L, the sulfate content is 0.6g / L, and the turbidity is 140NTU. The lean nitrate solution is raised to room temperature (25°C), and the sulfate content in the lean nitrate solution is 17g / L; the TDS of the water produced by the rotary immersion ultrafiltration is 185g / L, the COD is 500mg / L, the chloride ion content is 120g / L, the sulfate content is 0.6g / L, and the turbidity is 2.3NTU. While intercepting the COD by the rotary immersion ultrafiltration, most of the fine crystals of the decahydrate sodium sulfate are also intercepted. After running for 45 minutes, the rotary immersion ultrafiltration needs to be placed in the feed tank of the sodium sulfate evaporation crystallization system to dissolve the fine crystals; the nanofiltration product The water TDS is 200g / L, COD is 100mg / L, chloride ion content is 125g / L, and sulfate content is 0.012g / L. The nanofiltration system effectively controls the mass ratio of sodium chloride to sodium sulfate in the lean nitrate solution to more than 100 times. The sodium sulfate evaporation and crystallization system produces sodium sulfate crystals with a purity of 99.6%, and the sodium chloride evaporation and crystallization system produces sodium chloride with a purity of 99.4%, respectively meeting the requirements of Class I first-class industrial anhydrous sodium sulfate of GB / T6009-2014 and the first-class industrial dry salt of GB / T5462-2015. The mixed salt crystallization system produces about 16kg / h of mixed salt, which is completely dissolved, reducing the amount of miscellaneous salt by 16kg / h.

[0042] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. The near-zero discharge system for high-salt and high-concentration organic industrial wastewater is characterized by: It includes a freezing crystallization system, a fine crystal clarification separation system, a nanofiltration salt separation system, a sodium chloride evaporation crystallization system, a sodium sulfate evaporation crystallization system, a mixed salt crystallization system, a hot melt system, and a miscellaneous salt drying system; the outlet of the freezing crystallization system is connected to the inlet of the fine crystal clarification separation system; The fine crystal clarification and separation system is provided with three outlets, which are respectively connected to the nanofiltration salt separation system, the sodium sulfate evaporation crystallization system and the mixed salt crystallization system inlet; the nanofiltration salt separation outlet is provided with two outlets, which are respectively connected to the sodium chloride evaporation crystallization system and the mixed salt crystallization system inlet; the sodium sulfate evaporation crystallization system outlet is connected to the mixed salt crystallization system inlet; the mixed salt crystallization system is provided with two outlets, which are respectively connected to the hot melt system and the mixed salt drying system; the mixed salt produced by the mixed salt crystallization system is reversely dissolved in the hot melt system to maximize the recovery of inorganic salt resources in the water; the mixed salt drying system outlet is connected to the mixed salt discharge system; The fine crystal clarification and separation system includes a fine crystal clarification and separation tank, which has a conical bottom. A rotary submerged ultrafiltration structure is built into the upper part of the fine crystal clarification and separation tank. A sodium sulfate outlet is provided at the conical bottom of the fine crystal clarification and separation tank. Three sewage outlets are provided at the upper, middle and lower parts of the fine crystal clarification and separation tank. The temperature inside the fine crystal clarification and separation tank is controlled at -5 to 5°C. The pore size of the rotary immersion ultrafiltration is set between 50 and 200 nm, and the rotation speed is set between 50 and 200 rpm; The nanofiltration salt separation system includes a refrigerated nanofiltration water inlet tank, a nanofiltration water inlet pump, a nanofiltration feed pump, a nanofiltration membrane, a nanofiltration water production tank, a nanofiltration concentrated water tank, a nanofiltration water production pump, and a nanofiltration concentrated water pump; the pore size of the nanofiltration salt separation system is selected between 0.6 and 1.2 nm.

2. The near-zero discharge system for high-salt and high-concentration organic industrial wastewater according to claim 1 is characterized in that: The temperature in the freezing crystallizer of the freezing crystallization system is controlled at -5~5°C.

3. The near-zero discharge system for high-salt and high-concentration organic wastewater according to claim 1 is characterized in that: The hot melt system includes a hot melt tank and a saturated solution delivery pump.

4. A method for near-zero discharge of high-salt and high-concentration organic industrial wastewater, characterized in that: The near-zero discharge system for high-salt and high-concentration organic wastewater according to any one of claims 1 to 3 is used, and the specific operating steps are as follows: The high-salt and high-concentration organic wastewater with TDS>250g / L and COD≥1000mg / L in the frozen raw material tank is passed through a frozen feed pump and heat exchanged in a precooler into the circulation pipeline of the frozen crystallizer. The decahydrated sodium sulfate in the lower section of the frozen crystallizer is sequentially fed into a frozen thickener and a refrigerated centrifuge through a frozen thickening feed pump to obtain decahydrated sodium sulfate with a moisture content of ≤5%. This part of the sodium sulfate enters the sodium sulfate evaporation crystallization system; the liquid separated by the frozen thickener and refrigerated centrifuge enters the frozen mother liquor tank and then returns to the frozen raw material tank through the frozen mother liquor pump; the supernatant of the frozen crystallizer overflows and enters the fine crystal clarification separation system; the material in the frozen crystallizer is continuously heat-exchanged and cooled in the refrigerated heat exchanger through a frozen circulation pump and its pipeline. The raw water of the fine crystal clarification separation system comes from the supernatant overflow of the freezing crystallization system. The inlet pipeline of the fine crystal clarification separation tank is led to the bottom of the fine crystal clarification separation tank. The residence time in the fine crystal clarification separation tank is more than 1 hour. The fine crystal clarification separation tank is provided with three sewage outlets, which are respectively located above and below the rotary immersion ultrafiltration and below the fine crystal clarification separation tank. The sewage outlets are connected to the mixed salt crystallization system. A rotary immersion ultrafiltration is placed in the fine crystal clarification separation tank. The water is mechanically extracted during ultrafiltration backwashing and placed in a raw material tank in a sodium sulfate evaporation and crystallization system. After all the fine crystals of mirabilite intercepted on the surface of the rotary immersion ultrafiltration are dissolved, they are placed back into the fine crystal clarification separation tank. The water produced by the rotary immersion ultrafiltration is connected to a nanofiltration system. A solid-liquid discharge port is provided at the bottom of the fine crystal clarification separation tank, and the solid-liquid discharge port is connected to the sodium sulfate evaporation and crystallization system. Nanofiltration produced water enters the sodium chloride evaporation crystallization system, and nanofiltration concentrated water enters the mixed salt crystallization system. The sodium sulfate evaporation crystallization system has two inlets, one for frozen crystallized thenardite decahydrate, and the other for the solid-liquid in the fine crystal clarification separation system. The raw material tank of the sodium sulfate evaporation crystallization system is used to dissolve the fine crystals of thenardite decahydrate on the surface of the rotary immersion ultrafiltration, and the mother liquor of sodium sulfate evaporation crystallization is sent to the mixed salt crystallization inlet. The inlet water for sodium chloride evaporation crystallization comes from nanofiltration produced water, and the mother liquor of sodium chloride evaporation crystallization is sent to the mixed salt crystallization inlet; there are four mixed salt crystallization inlets, one is the wastewater from the fine crystal clarification separation system, one is the nanofiltration concentrated water, one is the sodium sulfate evaporation crystallization mother liquor, and one is the sodium chloride evaporation crystallization mother liquor; the mixed salt produced by the mixed salt crystallization is sent to the hot melt system, and the mixed salt crystallization mother liquor is sent to the miscellaneous salt drying system; the hot melt system performs hot melt treatment on the mixed salt produced by the mixed salt crystallization and then returns it to the frozen crystallization system, the inlet water for the miscellaneous salt drying system comes from the mother liquor of the mixed salt crystallization system, and the COD in the mixed salt crystallization system is controlled within 2000 mg / L.

5. The method for near-zero discharge of high-salt and high-concentration organic industrial wastewater according to claim 4, characterized in that: The mixed salt drying system uses a vacuum drum dryer.

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