CN114702185A

CN114702185A - Zero-discharge treatment system and method for wastewater of synthetic ammonia and glycol

Info

Publication number: CN114702185A
Application number: CN202210377689.4A
Authority: CN
Inventors: 权秋红; 张建飞; 元西方; 李争光; 丁哲
Original assignee: Bestter Group Co ltd
Current assignee: Bestter Group Co ltd
Priority date: 2022-04-11
Filing date: 2022-04-11
Publication date: 2022-07-05

Abstract

The invention relates to a zero discharge treatment system for wastewater of synthetic ammonia and glycol. The pretreatment unit is used for removing heavy metal ions, silicon dioxide and hardness ions in the wastewater; the nanofiltration unit carries out nanofiltration to separate salt. The invention designs a treatment system for evaporative crystallization of wastewater based on multiple design concepts of step treatment, discharge of pollutants out of the system as much as possible and no return of high-salt-content concentrated water, extracts sodium chloride by a mode of two-stage membrane concentration and sodium chloride thermal crystallization of second produced water, extracts sodium sulfate by a mode of cooling concentration crystallization and melting crystallization of second concentrated water, and further extracts sodium chloride by cooling concentration crystallization, so that the physicochemical indexes of the prepared sodium chloride and sodium sulfate meet the coal chemical industry byproduct industrial standard, the water quality of produced water reaches the index, and the zero discharge effect of synthetic ammonia and ethylene glycol wastewater is achieved.

Description

Zero-discharge treatment system and method for wastewater of synthetic ammonia and glycol

Technical Field

The invention relates to the technical field of zero-discharge treatment, in particular to a system and a method for zero-discharge treatment of wastewater of synthetic ammonia and ethylene glycol.

Background

With the continuous development of the current society, the whole process field of water treatment needs to further improve efficiency and reduce cost. The zero-discharge system is different from the conventional standardized chemical desalting water system and the non-zero-discharge reuse water system, the design concept of the zero-discharge system is not mainly appealing based on water production indexes, but wholly appeals to zero discharge, and the subsequent treatment device permanently treats the concentrated water of the previous stage, so that the design initiation and the whole consideration are required. The requirements and difficulties of the high-salinity wastewater zero-emission salt separation crystallization and the traditional salt and nitrate preparation industry are greatly different and different, and a treatment system and a method integrating pretreatment, reduction and concentration and zero-emission salt separation are urgently needed. The invention is designed by various design concepts of step treatment, discharge of pollutants out of the system as far as possible and no return of high-salinity concentrated water.

Chinese patent CN111320318A discloses a zero-emission deep treatment process for RO (reverse osmosis) concentrated water, which comprises the steps of coagulating and precipitating the RO concentrated water, adsorbing organic pollutants in the RO concentrated water by means of activated carbon with a catalytic structure, and then performing evaporative crystallization treatment in an evaporative crystallization process, wherein the miscellaneous salt solid obtained by evaporation can be continuously subjected to salt separation and reused in industrial production. Meanwhile, the activated carbon with the catalytic function can realize regeneration in the process of removing adsorbed organic matters. The whole RO concentrated water zero-discharge advanced treatment process can simply and efficiently remove organic matters and improve the subsequent evaporation, evaporation and crystallization efficiency, thereby realizing the zero discharge of the RO concentrated water. The defect of the patent is that, regarding the treatment before the evaporation crystallization, the zero emission effect of the RO concentrated water is achieved only by adding a simple step, namely adding activated carbon with a catalytic structure, the technical scheme is not strict, and the existence of carbon and silicon in the RO concentrated water is not considered, so that the impurities of sodium sulfate and sodium chloride are excessive. In addition, the removal effect of COD by adopting ozone catalytic oxidation is better, and the activated carbon with a catalytic structure cannot achieve the corresponding technical effect.

Chinese patent CN107381886B discloses a reverse osmosis concentrated water near-zero emission method, which comprises the following steps: reverse osmosis concentration separation, nanofiltration separation, chemical softening, sodium resin softening and bipolar membrane electrodialysis are performed to produce acid and alkali. The method for realizing near-zero emission of reverse osmosis concentrated water provided by the invention has the advantages that low-concentration inlet brine is concentrated through a reverse osmosis concentration separation system, the concentrated brine enters a nanofiltration membrane treatment system to achieve the aim of further concentration, nanofiltration effluent flows back to raw water which does not enter the reverse osmosis concentration separation system, the nanofiltration concentrated water enters a sodium resin softening device to carry out ion exchange, and the exchanged effluent enters a bipolar membrane electrodialysis device to produce acid and alkali. The reverse osmosis concentrated water is finally used for producing acid and alkali through the mutual matching of the devices, and the aim of near zero emission of the reverse osmosis concentrated water is fulfilled. The method for realizing zero discharge of reverse osmosis concentrated water provided by the patent is simple and easy to implement, simple in visible process and strong in operability, and realizes maximized concentrated water recycling with lower energy consumption. The patent has a drawback in that no zero discharge effect is achieved because the concentrated water fed to the reverse osmosis membrane is high in hardness and contains much carbon without a pretreatment device, and the reverse osmosis membrane is contaminated by untreated water, resulting in a reduction in service life and performance. And also does not take into account the effect of the silicon oxide inside the concentrate.

The invention designs a treatment system for evaporative crystallization of wastewater based on multiple design concepts of step treatment, discharge of pollutants out of the system as much as possible and no return of high-salt-content concentrated water, extracts sodium chloride by a mode of two-stage membrane concentration and sodium chloride thermal crystallization of second produced water, extracts sodium sulfate by a mode of cooling concentration crystallization and melting crystallization of second concentrated water, and further extracts sodium chloride by cooling concentration crystallization, so that the physicochemical indexes of the prepared sodium chloride and sodium sulfate meet the coal chemical industry byproduct industrial standard, the water quality of produced water reaches the index, and the zero discharge effect of synthetic ammonia and ethylene glycol wastewater is achieved.

Furthermore, on the one hand, due to the differences in understanding to the person skilled in the art; on the other hand, since the inventor has studied a lot of documents and patents when making the present invention, but the space is not limited to the details and contents listed in the above, however, the present invention is by no means free of the features of the prior art, but the present invention has been provided with all the features of the prior art, and the applicant reserves the right to increase the related prior art in the background.

Disclosure of Invention

Aiming at the defects of the prior art, the technical scheme of the invention is to provide a wastewater zero-discharge treatment system for synthetic ammonia and ethylene glycol, the system comprises a pretreatment unit, a nanofiltration unit and a crystallization unit, the pretreatment unit is used for removing heavy metal ions, silicon dioxide and hardness ions in wastewater and sending the wastewater to a first reverse osmosis membrane module to obtain first produced water and first concentrated water, the nanofiltration unit carries out nanofiltration salt separation on the first concentrated water obtained by the treatment of the first reverse osmosis membrane module through a nanofiltration membrane element and obtains second produced water and second concentrated water after the treatment of the nanofiltration unit, the crystallization unit is used for carrying out crystallization treatment on the second produced water and the second concentrated water after the treatment of the nanofiltration unit, the first produced water enters the crystallization unit as fresh water and/or circulating water and forms mixed condensate water with the condensate water of the crystallization unit to be used as a heat exchange source and/or the condensate water of the crystallization unit Level controlled water supply to provide reuse water support for the extraction of sodium chloride and sodium sulfate from the second product water and second concentrate water. And after the wastewater is treated by the pretreatment unit, sodium chloride and sodium sulfate crystals in the synthetic ammonia and glycol wastewater are recovered by the nanofiltration unit and the crystallization unit, so that zero discharge of the wastewater is realized. The invention designs a treatment system for evaporative crystallization of wastewater based on multiple design concepts of step treatment, discharge of pollutants out of the system as much as possible and no return of high-salt-content concentrated water, extracts sodium chloride by a mode of two-stage membrane concentration and sodium chloride thermal crystallization of second produced water, extracts sodium sulfate by a mode of cooling concentration crystallization and melting crystallization of second concentrated water, and further extracts sodium chloride by cooling concentration crystallization, so that the physicochemical indexes of the prepared sodium chloride and sodium sulfate meet the coal chemical industry byproduct industrial standard, the water quality of produced water reaches the index, and the zero discharge effect of synthetic ammonia and ethylene glycol wastewater is achieved.

According to a preferred embodiment, the crystallization unit comprises a first sodium chloride evaporative crystallization module, a second sodium chloride evaporative crystallization module and a sodium sulfate crystallization module, the second produced water treated by the nanofiltration unit enters the first sodium chloride evaporative crystallization module through a second reverse osmosis membrane module for evaporative crystallization, and the second concentrated water treated by the nanofiltration unit enters the second sodium chloride evaporative crystallization module and the sodium sulfate crystallization module through a freezing module for crystallization.

According to a preferred embodiment, the second produced water passes through the second reverse osmosis membrane module to obtain third produced water and third concentrated water, the third concentrated water enters the ultrahigh pressure membrane module to obtain fourth produced water and fourth concentrated water, the fourth concentrated water enters the first sodium chloride evaporation and crystallization module, and the first sodium chloride evaporation and crystallization module processes the fourth concentrated water in a triple effect evaporation and crystallization manner to obtain sodium chloride, wherein the triple effect evaporation and crystallization means that the boiling points of high-salt water in each evaporation chamber are sequentially reduced, secondary steam is separated based on the difference of the boiling point temperatures, and heat energy in the generated steam is utilized step by step for multiple times. The first sodium chloride evaporative crystallization module adopts a triple effect evaporative crystallization treatment mode, the pressure of each evaporation chamber is changed through a vacuum system, so that the boiling point of high-salt water in the evaporation chambers is changed, the separation of secondary steam is realized, the heat energy in raw steam is utilized step by step for many times, the power consumption of the system is saved, and the evaporation rate of the system is improved.

According to a preferred embodiment, the system further comprises a pre-concentration module and a defoaming module, wherein before the second concentrated water enters the freezing module, the pre-concentration module compresses the secondary steam so that the temperature of the secondary steam is increased and the secondary steam is used for a system evaporation heat source, and the defoaming module is used for the first sodium chloride evaporation crystallization module and the second sodium chloride evaporation crystallization module and is used for removing liquid drops and/or foams in the secondary steam generated in the evaporation process. The defoaming module intercepts liquid drops, foams and the like carried by secondary steam, can ensure the quality of condensed water, and avoids the problems that a compressor, an evaporator heating chamber or a condenser works under adverse conditions of corrosion, scaling, reduction of heat transfer coefficient and the like and causes serious pollution.

According to a preferred embodiment, the freezing module comprises a primary precooler and a secondary precooler, the primary precooler carries out countercurrent heat exchange on the circulating cooling water and the second concentrated water for cooling, the precooled second concentrated water enters the secondary precooler, the supernatant in the freezing module and the second concentrated water are subjected to countercurrent heat exchange for cooling, and the supernatant after heat exchange enters the second sodium chloride evaporation crystallization module. Firstly, optimizing the extraction quality of subsequent sodium sulfate, and further removing sodium chloride contained in second concentrated water, secondly, the invention aims to extract high-quality sodium chloride and sodium sulfate, wherein the sodium chloride extracted from supernate meets the high-quality requirement, and the efficiency of the system for extracting sodium chloride is improved.

According to a preferred embodiment, the second sodium chloride evaporative crystallization module processes the supernatant after heat exchange in a double-effect evaporative crystallization manner to obtain sodium chloride, wherein the double-effect evaporative crystallization means that the boiling points of the high-salt water in each evaporation chamber are sequentially reduced, secondary steam is separated based on the difference of the boiling point temperatures, and the heat energy in the raw steam is utilized step by step for multiple times. The second sodium chloride evaporation crystallization module adopts a two-effect evaporation crystallization treatment mode so as to save construction cost and operation cost.

According to a preferable embodiment, the system further comprises a mixed salt unit, and the fourth concentrated water enters the mixed salt unit through the triple-effect evaporative crystallization mother liquor of the first sodium chloride evaporative crystallization module and the supernatant after heat exchange through the double-effect evaporative crystallization mother liquor of the second sodium chloride evaporative crystallization module for drying treatment. The mixed salt unit treats the residual mother liquor after the sodium chloride is extracted, and the produced water and the concentrated water after the treatment of each unit are fully utilized, so that the zero discharge of the synthetic ammonia and the glycol wastewater is realized.

According to a preferred embodiment, the sodium sulfate crystallization module comprises a melt crystallizer and a centrifuge, the second concentrated water is treated by the freezing module and then enters the melt crystallizer for evaporation crystallization to obtain sodium sulfate crystallized salt, and the sodium sulfate crystallized salt enters the centrifuge to obtain sodium sulfate. The second concentrated water sent to the sodium sulfate crystallization module from the components has higher sodium sulfate content, and other impurities are also removed, so that the construction cost and the operation cost are saved by adopting a melt crystallizer, and the investment and the occupied area are further saved by adopting forced circulation single-effect evaporation crystallization in the melt crystallizer.

According to a preferred embodiment, the first, third and fourth produced waters enter a product water basin for storing the first, third and fourth produced waters during treatment and for providing the pre-treatment unit with recycled water. The water is recycled for a plurality of times, the use efficiency of the produced water is improved on the basis that the concentrated water is not refluxed, and the concentrated water is concentrated in a product water tank and can enter a circulation again, so that the water quantity entering an evaporative crystallization salt production system is further reduced, and the investment, the occupied area and the operation energy consumption are saved.

The invention also comprises a zero discharge treatment method of the wastewater of the synthetic ammonia and the glycol, which comprises the following steps: removing heavy metal ions, silicon dioxide and hardness ions in the wastewater to obtain first produced water and first concentrated water; carrying out nanofiltration salt separation on the obtained first concentrated water, and obtaining treated second produced water and second concentrated water; and carrying out crystallization treatment on the second produced water and the second concentrated water. The wastewater is subjected to removal of heavy metal ions, silicon dioxide and hardness ions, and then subjected to nanofiltration salt separation and crystallization treatment to recover sodium chloride and sodium sulfate crystals in the synthetic ammonia and glycol wastewater, so that zero discharge of the wastewater is realized.

The invention has the beneficial technical effects that:

(1) the invention designs a treatment system for evaporative crystallization of wastewater based on multiple design concepts of step treatment, discharge of pollutants out of the system as far as possible and no return of high-salt-content concentrated water, wherein sodium chloride extraction is carried out on second produced water in a two-stage membrane concentration and sodium chloride thermal crystallization mode, sodium sulfate extraction is carried out on second concentrated water in a cooling concentration crystallization and melting crystallization mode, and sodium chloride is further extracted through cooling concentration crystallization, so that the physicochemical indexes of the produced sodium chloride and sodium sulfate meet the coal chemical industry byproduct industrial standard, the water quality of produced water reaches the index, and the zero discharge effect of synthetic ammonia and glycol wastewater is achieved;

(2) the first produced water, the third produced water and the fourth produced water all enter a product water pool to be used as fresh water of each part or recycled water supplement for multiple utilization of each produced water, the water production use efficiency is improved on the basis of no backflow of the concentrated water, and the concentrated product water pool can enter the circulation again, so that the water quantity entering an evaporation crystallization salt production system is further reduced, the investment, the occupied land and the operation energy consumption are saved, and simultaneously, the concentrated product water and the condensed water of each effect steam tank in a crystallization unit form mixed condensed water to be used as a heat exchange heat source and/or a liquid level control water supply source of the crystallization unit;

(3) softening the synthetic ammonia and glycol wastewater and removing Ca by a high-density clarification tank, a high-strength membrane, a two-stage cation bed and a carbon remover process in a pretreatment unit²⁺、Mg²⁺、SiO₂. Meanwhile, coagulation and flocculation effects are realized, and substances such as suspended matters, organic matters, colloids and the like in raw water can be coagulated into larger flocculates so as to be convenient for effective precipitation removal, effectively reduce the organic matters, suspended matters and turbidity of the incoming water, and create good conditions for stable operation of a subsequent high-strength membrane;

(4) the high-strength membrane is different from the multi-medium and ultrafiltration schemes in the prior art, a large amount of fine suspended matters are successfully intercepted in a suction mode, the problems of high brine density, poor sedimentation effect, easy blockage and yarn breakage of a common ultrafiltration membrane and the like are solved, the high-strength membrane has high water recovery rate, and the drainage of backwashing is still in a high-strength membrane pool;

(5) the first sodium chloride evaporation crystallization module adopts a triple effect evaporation crystallization processing mode, the pressure of each evaporation chamber is changed through a vacuum system, the boiling point of high-salt water in the evaporation chambers is changed, secondary steam separation is realized, heat energy in raw steam is utilized step by step for many times, the power consumption of the system is saved, the evaporation rate of the system is improved (namely, the amount of the raw steam in the heating chamber is adjusted by the temperature and pressure reduction opening degree), and the second sodium chloride evaporation crystallization module adopts a double effect evaporation crystallization processing mode so as to save the construction cost and the operation cost. The second concentrated water is treated by the second sodium chloride evaporation and crystallization module and mainly contains sodium sulfate, and the purpose of extracting sodium chloride from the second concentrated water is firstly to optimize the subsequent extraction of the sodium sulfate and further remove the sodium chloride contained in the second concentrated water;

(6) obtaining second produced water and second concentrated water through a nanofiltration unit, further ensuring the safety and corrosion probability of each device by different extraction means of sodium chloride and sodium sulfate and by a mode of producing water backflow and concentrated water non-backflow, and simultaneously considering the extraction of high-quality sodium chloride and sodium sulfate, so as to extract sodium chloride from the second produced water and extract sodium chloride from the supernatant of the second concentrated water, thereby improving the preparation efficiency of sodium chloride and the preparation quality of sodium sulfate, and the residual mother liquor enters a mixed salt unit to obtain mixed salt with poor quality, thereby realizing zero discharge of the synthetic ammonia and the ethylene glycol wastewater;

(7) the upper ends of the first sodium chloride evaporation crystallization module and the second sodium chloride evaporation crystallization module are respectively provided with a defoaming module, liquid drops and foams carried by secondary steam are intercepted, the quality of condensate water can be guaranteed, the problems that a compressor, an evaporator heating chamber or a condenser works under adverse conditions such as corrosion, scaling and heat transfer coefficient reduction and serious pollution is caused are avoided, and in addition, the lower ends of the first sodium chloride evaporation crystallization module and the second sodium chloride evaporation crystallization module are provided with crystallization chambers, so that salt particles grow up and are concentrated, concentrated and the quality of salt is improved.

Drawings

FIG. 1 is a schematic structural diagram of a preferred embodiment of a zero-discharge treatment system for wastewater from ammonia synthesis and ethylene glycol production according to the present invention;

FIG. 2 is a water quality data chart of the synthetic ammonia and ethylene glycol wastewater of the present invention;

FIG. 3 is a graph of the production data 22 days before one month operation of a zero-emission treatment system for synthetic ammonia and ethylene glycol wastewater in accordance with the present invention;

FIG. 4 is a graph of the production data 9 days after one month of operation of a zero-emission treatment system for ammonia synthesis and ethylene glycol wastewater in accordance with the present invention.

List of reference numerals

1: a regulating tank; 2: a high density pond; 3: a sludge concentration tank; 4; a filter press; 5: a high-strength membrane tank; 6: a two-stage male bed; 7: a carbon remover; 8: a first reverse osmosis membrane module; 9: a product water pool; 10: removing silicon; 11: a nanofiltration unit; 12: a second reverse osmosis membrane module; 13: an ultra-high pressure membrane module; 14: a first sodium chloride evaporative crystallization module; 15: a thickener; 16: a centrifuge; 17: drying the bed; 18: a pre-concentration module; 19: a freezing module; 20: a second sodium chloride evaporative crystallization module; 21: a miscellaneous salt unit; 22: a hot melting tank; 23: a melt crystallizer; a1: first producing water; a2: producing water for the second time; a3: thirdly, producing water; a4: fourthly, producing water; b1: first producing water; b2: second concentrated water; b3: third concentrated water; b4: fourth concentrated water; a: sodium chloride; b: sodium sulfate; c: miscellaneous salt; d: and (4) sludge.

Detailed Description

First, each standard will be explained.

The synthetic ammonia and glycol wastewater is secondary RO concentrated water for sewage treatment and reclaimed water reuse, and the chemical oxygen demand and the PH value of each heavy metal ion and hardness ion are shown in figure 2. RO produces water and secondary steam condensate and is regarded as recirculated cooling water moisturizing, divides salt output sodium chloride and accords with industry dry salt quality and recovery rate requirement, combines the crystallized salt market demand of planned resource utilization to go to in order to satisfy the highest control index requirement. Wherein, the sodium chloride is required to be white, yellowish or bluish white crystal without obvious foreign matters. The sodium sulfate sensory requirement is white crystalline particles, with no apparent foreign matter.

The following detailed description is made with reference to the accompanying drawings.

Examples

The application relates to a zero discharge treatment system for wastewater of synthetic ammonia and glycol, which comprises a pretreatment unit, a nanofiltration unit and a crystallization unit. The pretreatment unit is used for removing heavy metal ions, silicon dioxide and hardness ions in the wastewater and sending the heavy metal ions, silicon dioxide and hardness ions to the first reverse osmosis membrane module to obtain first produced water and first concentrated water. And the nanofiltration unit carries out nanofiltration salt separation on the first concentrated water obtained by the treatment of the first reverse osmosis membrane module through a nanofiltration membrane element, and obtains second produced water and second concentrated water which are treated by the nanofiltration unit. And the crystallization unit is used for carrying out crystallization treatment on the second produced water and the second concentrated water after the nanofiltration unit is treated. And the first produced water enters the crystallization unit as fresh water and/or recycled water for supplementing water and forms mixed condensed water with the condensed water of the crystallization unit to serve as a heat exchange heat source and/or a liquid level control water supply source of the crystallization unit so as to provide recycled water support for extraction of sodium chloride and sodium sulfate of the second produced water and the second concentrated water. After the wastewater is treated by the pretreatment unit, sodium chloride and sodium sulfate crystals in the synthetic ammonia and glycol wastewater are recovered by the nanofiltration unit and the crystallization unit, so that zero discharge of the wastewater is realized. And as the steam process continues, the water in the crystallization unit starts to vaporize, the liquid level drops, and the mixed condensate water formed by the first produced water and the condensate water is added to keep the liquid level at the optimal working height of the steam tank, so that the system achieves dynamic balance. Since the solution to be evaporated must be preheated before entering the evaporator, the mixed condensate thereof can also be used as a heat source for the heat exchanger.

Because the water quality components of the common water contain high contents of calcium, magnesium hardness and SiO₂And alkalinity, and temporary hardness in water, and calcium in waterMagnesium does not scale in the subsequent concentration section and crystallization section, so that dirt blockage is generated, and hardness and SiO need to be treated in a pretreatment unit₂Removing indexes, and meanwhile, arranging a filtering module; in order to use the carbonate and bicarbonate in the water, the heat exchange effect of the heat exchanger is not influenced in the subsequent evaporation and crystallization section, and the equipment operation and the equipment load are not influenced.

According to a preferred embodiment, the pretreatment unit comprises a high density clarifier, a high strength membrane, a two stage cation bed, and a carbon remover. Softening treatment is carried out by adopting a high-density clarification tank to remove most of the hardness of calcium and magnesium. Adding PAC, lime, NaOH, PAM and magnesium agents into the tank to remove Ca in the water²⁺、Mg²⁺、SiO₂The insoluble compound is converted into the insoluble compound and passes through a sedimentation tank to be precipitated out, so that the water quality is softened. Meanwhile, coagulation and flocculation effects are realized, and substances such as suspended matters, organic matters, colloids and the like in raw water can be coagulated into larger flocculates, so that effective precipitates can be removed, the organic matters, suspended matters and turbidity of the coming water are effectively reduced, and good conditions are created for stable operation of a subsequent high-strength membrane filtering device.

According to a preferred embodiment, the high-density clarifier includes a conditioning tank and a high-density tank. The regulating reservoir is configured with on-line and on-site instruments. The inlet pipe of the adjusting tank enters from the designed highest water level. The bottom of the adjusting tank is provided with a sump. The design of equalizing basin has the concrete top cap. The high-density tank is a hard high-density tank and comprises coagulation, clarification, neutralization and other systems besides on-line and on-site meters. The complete design of the hardness-removing high-density tank comprises the process design of the system, related measuring instruments, dosing, sludge discharge, stirring, backflow and the like. The hard removing high-density tank has the following performance requirements: different agents are arranged in different stirring areas, the HRT from water inlet to flocculation end is not less than 40min, and the HRT of the clarification area is not less than 2 hours. The total hardness of the produced water is less than 100mg/L (calculated by calcium carbonate), SiO₂Less than 40 mg/L.

According to a preferred embodiment, the sludge dewatering module is connected to a high-density tank, which has an effective volume of 60m³The sludge storage pool adopts a plate and frame filter press. The filtrate of the filter press flows back to the high-density tank to prevent sludge deposition in the regulating tank. After the sludge is dehydrated,the water content is 65% or more. The filter press is provided with an automatic cloth washing facility and an automatic pulling plate unloading facility, and after the filter press is subjected to dehydration treatment, the automatic pulling plate unloading facility conveys mud cakes out of a battery compartment. Other performance indexes of the filter press are implemented according to HJ/T283 'environmental protection product technical requirement box filter press and plate-and-frame filter press'.

According to the characteristics of the high enriched brine of the coal chemical industry, because the system contains the salt content height, the characteristics that a large amount of tiny suspended solids are difficult for subsiding, to the product water in high-density pond, optimize the original multimedium of prior art and the scheme of ultrafiltration for high strength membrane filtration, membrane product water passes through the suction mode, successfully intercepts a large amount of tiny suspended solids. As a novel filtering device, the high-strength membrane filter solves the problems of high brine density, poor settling effect, easy blockage, yarn breakage and the like of a common ultrafiltration membrane. It has the following characteristics: (1) can intercept partial COD; (2) high resistance to suspended matter; (3) high sludge concentration resistance; (4) the colloid is well removed; (5) the water recovery rate is up to more than 95%, and the drainage of backwashing is still in the high-strength membrane pool; (6) strong impact resistance and convenient operation and management. And a high-strength membrane filtering tank is matched with a chemical feeding, maintainable cleaning and restorative cleaning facility. And discharging sludge generated by the high-density pond into a sludge dewatering module, and conveying sludge cakes out of the battery limits after dewatering treatment by a filter press.

According to a preferred embodiment, the high-strength membrane is a long-life PVDF (polyvinylidene fluoride) high-strength membrane, the quality guarantee period is not less than 5 years, the net output of the high-strength membrane device and the quality of effluent are not changed, and the designed water flux of the membrane element is selected according to the low value of the water flux specified in the design guide of the membrane element manufacturer. The average running flux of the water inlet of the high-strength membrane is not more than 25 LMH. The pH operation range of the high-strength film is 2-11, the pH range of chemical cleaning is 2-12, and the operation pressure is less than-0.07 MPa. The SDI index of the high-strength membrane effluent is less than or equal to 3 (after running for three years), the turbidity is less than or equal to 0.2NTU (after running for three years), and the recovery rate is more than or equal to 95 percent. The high-strength membrane filtration cycle is more than or equal to 35 minutes (after running for three years), and the chemical cleaning cycle is more than or equal to 30 days. A sampling interface is arranged on a water outlet pipe of each high-strength membrane pool, the number and the position of sampling points can effectively diagnose and determine the running condition of the system, and the sampling interface is provided with a sampling valve. The inlet and outlet of each high-strength membrane device are provided with manual isolation valves.

According to a preferred embodiment, the two-stage cation bed (i.e. the two-stage weak acid bed) is a resin exchanger, made of carbon steel lined with rubber, and the two stages are operated in series, operating in the ABBA mode (possibly in alternating sequence). The total hardness of the resin inlet water is designed according to 200mg/L, macroporous hydrogen type weak acid cation exchange resin which is not easy to block by organic matters is adopted, and the regeneration period is not less than 24 hours. The hardness of the water treated by the resin exchanger (as CaCO 3) was not detected. When the exchanger works under the condition of rated water yield, the consumption of the regenerant is not more than 80g/mol of resin (1/2 Ca); the water consumption rate is not more than 5%. Resin exchanger design operating flow rate

The regeneration mode is countercurrent regeneration, and the regeneration flow rate is 4-6 m/h. The resin annual loss rate is not more than 5 percent.

According to a preferred embodiment, the carbon remover is filled with a filler with a gas resistance of < 490Pa/m per height of filler. The air source for blowing-off of the carbon remover is 0.3-O.4MPa, the low-pressure nitrogen (or a set of matched fans) at the temperature of less than or equal to 40 ℃ is used for designing the carbon remover with the water spraying density of 50-60 m3/m 2. h and the air-water ratio of 20-30 m3/m 3.

According to a preferred embodiment, the first and second reverse osmosis membrane modules comprise cartridge filters, high pressure pumps, reverse osmosis modules, associated instrumentation, on-site control and dosing, cleaning systems, etc. Wherein, the cartridge filter and the cleaning cartridge filter adopt a large-flux filter element, the filtering precision is at least 5 μm, and the material of PP is adopted. According to the water quality characteristics of the inlet water of the unit, a polyamide membrane with good pollution resistance, high mechanical strength, good chemical stability and long service life is selected, the quality guarantee period is not less than 3 years, and the desalination rate of the system is required to reach 98 percent (after one year of operation) and 95 percent (after three years of operation). The designed water flux of the membrane element is selected according to the low value of the water flux of the membrane element, the average flux of the reverse osmosis membrane is less than or equal to 16LMH, the system recovery rate is more than or equal to 70 percent, and reasonable arrangement and combination are selected to ensure the normal operation and the reasonable cleaning period of the membrane element. Each set of reverse osmosis can be operated independently or simultaneously. The pH operation range of the reverse osmosis membrane is 4-11, and the pH cleaning range is 2-12. When the chemical adding point of the reverse osmosis reducing agent is designed, the reducing agent can be fully mixed and has sufficient reaction time with the oxidizing agent, so that the reverse osmosis membrane is not oxidized. The first reverse osmosis membrane module obtains first product water and first dense water through handling the waste water through preliminary treatment, because the enrichment that has silicon in the first dense water after handling, carries out the desiliconization through removing silicon system, second high strength membrane pond and ozone catalytic oxidation, gets into the unit of receiving filtration afterwards.

According to a preferred embodiment, the zero discharge device employs a nanofiltration unit, i.e., a nanofiltration membrane element, having a primary and a divalent salt separation function. The type selection selects a nanofiltration membrane separated by a process with large water permeability, high selectivity of primary and secondary ions, good chemical stability, good mechanical strength, strong pollution resistance and low energy consumption according to the water quality characteristics of the inlet membrane, the surface of the membrane is electrically neutral, and the material is a composite membrane. The flow channel of the nanofiltration membrane is more than 30mil, and the normal service life is more than or equal to 3 years. According to the basic performance of the nanofiltration membrane, the nanofiltration salt separation effect is achieved through optimized design, and the specific requirements are as follows: the nanofiltration unit comprises a security filter, a high-pressure pump, an intersegmental booster pump, a nanofiltration component, a matched instrument, an on-site control, dosing and cleaning system and the like. The design water flux of the membrane element is selected according to the low value of the water flux specified in the design guide of the membrane element manufacturer, the average flux of the nanofiltration membrane is 16.9LMH at the first section and 12.7LMH at the second section, and reasonable arrangement and combination are selected to ensure the normal operation and reasonable cleaning period of the membrane element. The cartridge filter and the cleaning cartridge filter adopt a large-flux filter element, the filtering precision is at least 5 mu m, and PP material is adopted. The nanofiltration membrane with the highest tolerance pressure of less than or equal to 42bar is adopted, the pH operation range is required to be 3-10, the pH cleaning range is required to be 1-11, the chemical cleaning period is more than or equal to 30 days, and the highest temperature is tolerated to be 50 ℃.

According to a preferred embodiment, the second produced water passes through the second reverse osmosis membrane module to obtain third produced water and third concentrated water, the third concentrated water enters the ultrahigh pressure membrane module to obtain fourth produced water and fourth concentrated water, the fourth concentrated water enters the first sodium chloride evaporation crystallization module, and the first sodium chloride evaporation crystallization module processes the fourth concentrated water in a triple effect evaporation crystallization mode to obtain sodium chloride, wherein triple effect evaporation crystallization is to sequentially reduce the boiling points of high-salt water in each evaporation chamber, secondary steam is separated based on the difference of the boiling point temperatures, and heat energy in generated steam is repeatedly utilized step by step.

Specifically, the second produced water enters a first sodium chloride evaporation crystallization module after being concentrated by a two-stage membrane. To increase the yield of salt, reduce SO4^2-The invention adopts a stable and reliable downstream triple effect evaporation crystallization form for the influence on salt. In the evaporation crystallization unit, in order to realize multi-effect evaporation, the boiling points of high-salt water in the subsequent evaporation chambers are sequentially reduced, different pressures (vacuum) can be formed in each evaporation chamber through a vacuum system, and when the solution exceeds the boiling point temperature under the corresponding pressure, secondary steam is boiled and separated. The heat energy in the raw steam is utilized step by step for many times. The second produced water is sent to a preheater, a mixed condenser (the circulating water is directly contacted with the last-effect secondary steam) is adopted in the last effect, the heated circulating water is used as a primary preheater, the secondary steam condensate water generated in the first effect is used as the heat source of a secondary preheater, and the generated steam condensate water is used as the heat source of a tertiary preheater. The evaporative crystallizers (I, II and III) all adopt externally heated forced circulation evaporation tanks. The raw steam is 0.5MPa, is subjected to temperature reduction and pressure reduction to be about 0.103MPa saturated steam, is driven by the whole system, enters an I-effect heating chamber to exchange heat with the feed liquid, the temperature of the feed liquid rises to be close to the boiling point, the feed liquid circularly reaches an evaporation chamber through a circulating pump, the pressure of the evaporation crystallization chamber is reduced, second produced water reaches the boiling point to be subjected to rapid flash evaporation concentration, the concentrated feed liquid sequentially enters II-effect and III-effect evaporation chambersA hair-sending device. Crystallizing and separating out in an effect III evaporation crystallization chamber, and precipitating in the evaporation crystallization chamber to enter a salting-out leg for aggregation, concentration and discharge; the evaporation rate of the system is adjusted by adjusting the temperature-reducing and pressure-reducing opening degree of the I effect to adjust the consumption of the steam generated by the heating chamber. The upper end of the evaporation crystallizer is provided with a defoaming module which intercepts liquid drops, foams and the like carried by secondary steam and can ensure the quality of the generated condensed water; the lower part is provided with a crystallization chamber for growing the salt particles, collecting the salt, concentrating and improving the salt quality. The salt slurry is discharged from the crystallizer to a salt slurry tank and is conveyed to the cyclone through the discharge pump, the cyclone separator mainly has a concentration function, after the separation of the cyclone separator, solid and liquid contained in the cyclone discharged liquid enters the thickener to further improve the concentration of the salt slurry, further grow salt crystals, eliminate the supersaturation degree of the discharged salt water and stably enter the centrifugal dehydrator to obtain the concentration of the salt slurry. At the moment, the elutriation brine (inlet water) and the salt slurry reversely run to carry out heat exchange, the salt discharge temperature is reduced, the heat loss is reduced, the energy consumption is reduced, and the centrifuge is protected. The top flow of the cyclone has pressure and directly enters the III-effect evaporation chamber, and the salt slurry tank overflow mother liquor, the thickener overflow mother liquor and the centrifuge thrown liquor enter the salt mother liquor tank and are sent to the III-effect evaporation chamber by the salt mother liquor pump to be evaporated continuously. And finally, centrifugally dewatering the salt slurry by using a centrifugal dewatering machine, conveying the dewatered wet salt into a screw conveyor, drying the salt in a salt fluidized bed, and then conveying the salt into a ton bag packaging system for ton bag packaging.

Condensed water from a heating chamber of the I-effect evaporator is generated by raw steam condensed water, is discharged from the I-effect heating chamber and enters an I-effect condensed water balance barrel, is sent to a first-stage plate by a salt-first-effect condensed water pump to exchange heat with heating feed liquid, is mixed with other raw steam condensed water in a condensed water tank, and is sent to a nitrate melting tank by a condensed water pump to further recover heat; and the rest secondary air condensed water enters a washing tank for mixing after heat exchange, one part of the condensed water is used as hot water washing water for system pipeline equipment and the like when the system is blocked, and the other part of the condensed water is sent out of a product water tank of the pretreatment unit.

The secondary steam generated by the III-effect evaporative crystallizer enters the mixing condenser to be condensed through circulating water, the system needs to be provided with the circulating water to directly exchange heat for the secondary steam in the heat exchanger, the heat is taken away by the circulating water, and the secondary steam is separated from non-condensable gas by condensed water. The non-condensable gas carried in the secondary steam is extracted by a vacuum system and discharged into the atmosphere.

According to a preferred embodiment, the system further comprises a pre-concentration module and a defoaming module, wherein before the second concentrated water enters the freezing module, the pre-concentration module compresses the secondary steam so that the temperature of the secondary steam is increased and the secondary steam is used for a system evaporation heat source, and the defoaming module is used for the first sodium chloride evaporation crystallization module and the second sodium chloride evaporation crystallization module and is used for removing liquid drops and/or foams in the secondary steam generated in the evaporation process.

Specifically, the pre-concentration module is used for compressing secondary steam by adopting a centrifugal steam compressor by MVR to increase the temperature of the secondary steam by more than 10-18 ℃ and using the secondary steam as a system evaporation heat source. In order to remove the superheat of the vapor generated by the compression, water is injected at the compressor inlet or outlet. MVR allows the secondary steam heat source to be reused. The evaporation energy source only consumes the electric energy consumed by the heat energy cycle. Compared with the common steam heat source evaporator, the energy consumption is greatly reduced. The pre-concentration module comprises a heat exchanger, a separation chamber and an automatic control system. The heat exchanger adopts a tube type heat exchanger, and materials in the falling film type heat exchanger uniformly flow down from top to bottom in the heat exchange tube through a specially designed distribution plate. The heat exchanger has the technical characteristics of high material flow rate, uniform heat transfer and high efficiency. The crystallization separation chamber adopts a spray type film-forming separator, so that the gas and the liquid can be quickly and fully separated, and the crystallization separation chamber is particularly used for separating materials with high viscosity, effectively damaging the surface tension of the liquid level and ensuring that the gas can overflow more quickly; the high-efficiency demister effectively prevents material fogging foam from being carried along with secondary steam, reduces products from not losing so as to avoid bringing extra economic loss or causing secondary pollution to users, effectively solves the problems that separation efficiency is reduced due to the easily foamed material and the like, and further optimizes the whole separation process technology. The automatic control system is the key for the stable operation of the whole set of equipment, consists of a PLC control system, has high automation degree, and can realize the functions of automatic operation of the equipment, monitoring of the whole flow, shutdown and startup operation of the equipment, automatic shutdown of the existing conditions and the like through a human-computer interface.

Since the liquid may contain a small amount of surfactant or an organic matter and a solution which is easy to foam, a small amount of foam and droplets may be generated during the evaporation. The secondary steam generated by evaporation often carries droplets or bubbles of varying sizes. The defoaming device is adopted, so that on one hand, the loss of products is avoided, and on the other hand, the problems that the compressor, the heating chamber of the evaporator or the condenser works under the adverse conditions of corrosion, scaling, reduction of heat transfer coefficient and the like and serious pollution is caused are solved.

According to a preferred embodiment, the freezing module comprises a primary precooler and a secondary precooler, the primary precooler carries out countercurrent heat exchange cooling on the circulating cooling water and the second concentrated water, the precooled second concentrated water enters the secondary precooler, the supernatant in the freezing module and the second concentrated water are subjected to countercurrent heat exchange cooling, and the supernatant after heat exchange enters the second sodium chloride evaporative crystallization module. Specifically, after the concentration is finished, precooling and cooling are carried out through a primary precooler and a secondary precooler. The first-stage precooler adopts a plate heat exchanger form, uses circulating cooling water and second concentrated water to perform countercurrent heat exchange for cooling, the precooled second concentrated water enters the second-stage precooler, the second-stage precooler adopts a fixed tube plate heat exchanger, and uses the supernatant of a freezing crystallization system and feed liquid to perform countercurrent heat exchange for cooling. The freezing crystallization system is the remaining component of the freezing module. Due to the possibility of crystallization of the second concentrated water and the possibility of fine crystals entrained in the supernatant, the tube-plate heat exchanger has better plugging capacity than the plate heat exchanger. And the supernatant after heat exchange enters a second sodium chloride evaporation crystallization module. And the residual precooled second concentrated water enters a freezing crystallization system, a forced circulation crystallizer in the freezing crystallization system is adopted and is conveyed to a nitrate precipitation tank through a pump, the supernatant of the nitrate precipitation tank enters a mother liquor tank, the slurry enters a centrifugal machine for dehydration, and the dehydrated nitrate decahydrate enters a nitrate melting tank. In the nitrate melting tank, appropriate amount of condensed water is added and heated to melt the sodium nitrate decahydrate into supersaturated sodium sulfate solution, and the sodium sulfate solution is preheated by two-stage plate exchange and enters into a nitrate melting crystallizer. The nitrate melting crystallizer adopts a single-effect evaporator and adopts a double-effect evaporation crystallization mode for crystallization, the principle of triple-effect evaporation crystallization of the nitrate melting crystallizer is the same as that of the first sodium chloride evaporation crystallization module, one effect is reduced, and the details are not repeated.

According to a preferred embodiment, the second sodium chloride evaporative crystallization module processes the supernatant after heat exchange in a double-effect evaporative crystallization manner to obtain sodium chloride, wherein the double-effect evaporative crystallization means that the boiling points of the high-salt water in each evaporation chamber are sequentially reduced, secondary steam is separated based on the difference of the boiling point temperatures, and the heat energy in the raw steam is utilized step by step for multiple times. The two-effect evaporative crystallization has the same principle as the three-effect evaporative crystallization of the first sodium chloride evaporative crystallization module, and one effect is reduced, which is not described herein again.

The first sodium chloride evaporation crystallization module and the second sodium chloride evaporation crystallization module both select forced circulation evaporation crystallizers, and a steam buffer zone is arranged at the inlet of the heating chamber to prevent the impact on the heat exchange tube. And set up and remove the foam module, remove the foam module mounted position and be convenient for wash, remove the foam efficiency and should be not less than 99.5%. The vertical distance between the operating liquid level of the evaporator and the demister is more than or equal to 3 m. The working temperature of the evaporation system does not deviate from the original design value, and sudden temperature deviation can be corrected in actual operation. The temperature monitoring is reasonably set by an operator so as to judge whether the inside of the temperature difference is scaled or not according to the temperature difference. The end sockets (pipe boxes) at two ends of the heat exchanger adopt an openable flange type packaging form so as to clean insoluble scaling substances. The concentrated water after the evaporation crystallization by the first sodium chloride evaporation crystallization module and the second sodium chloride evaporation crystallization module also needs to be dehydrated and dried. Wherein, the dehydration treatment adopts a domestic two-stage pusher centrifuge, and the centrifuge adopts a totally enclosed type. The centrifuge can continuously run 24 hours a day after feeding, separating and discharging filtrate and crystallized salt, and can also intermittently run. The centrifuge is matched with a vibration detection device, and the solid content of the mother liquor sent into the centrifuge is not more than 4%. The centrifuge is further provided with a cleaning system. The water content of the crystallized salt after centrifugation is less than or equal to 4 percent. And drying by adopting a fluidized bed, and packaging by a ton bag after drying.

It should be noted that the system should fully utilize the waste heat of the steam condensate, distilled water or non-condensable gas to preheat the stock solution, so as to reduce the energy consumption of the system; the structure should satisfy certain negative pressure intensity, or set up negative pressure protection device, reduce the separator and be inhaled the possibility of shriveling.

According to a preferable embodiment, the system further comprises a mixed salt unit, and the fourth concentrated water enters the mixed salt unit through the triple-effect evaporative crystallization mother liquor of the first sodium chloride evaporative crystallization module and the supernatant after heat exchange through the double-effect evaporative crystallization mother liquor of the second sodium chloride evaporative crystallization module for drying treatment. Specifically, salt triple-effect and double-effect evaporation crystallization mother liquor and mixed salt mother liquor enter a rotary drum drying system through a separation device on a salt circulating pipe. The drum dryer is a continuous operation device for drying liquid-phase materials or strip-shaped materials attached to the outer wall of a cylinder body in a heat transfer mode through a rotating cylinder. The feed liquid to be dried flows into the receiving groove in the roller dryer from the elevated groove. The drying drum is driven by the transmission device to rotate at a specified rotating speed. The material is formed into a material film on the wall surface of the roller by a film distribution device. The cylinder is continuously filled with a heat supply medium to heat the cylinder body, the cylinder wall transfers heat to gasify the moisture of the material film, the material meeting the drying requirement is scraped by a scraper, and the material is discharged out of a finished product through a discharging auger under the action of a scraper with an inclination and hot air flow in an adjustable way. Spray drying is the most widely used process in the liquid process shaping and drying industries. Most suitable for the production of powdery, granular or lumpy solid products from solution, emulsion, suspoemulsion and pumpable pasty liquid raw materials.

According to a preferred embodiment, the sodium sulfate crystallization module comprises a melt crystallizer and a centrifuge, the second concentrated water is treated by the freezing module and then enters the melt crystallizer for evaporation crystallization to obtain sodium sulfate crystallized salt, and the sodium sulfate crystallized salt enters the centrifuge to obtain sodium sulfate. The melting crystallizer is similar to the first sodium chloride evaporative crystallization module and the second sodium chloride evaporative crystallization module in structure, and is different from the melting crystallizer in that a forced circulation single-effect evaporative crystallizer is adopted. The centrifugal machine is the same as that adopted by the first sodium chloride evaporative crystallization module and the second sodium chloride evaporative crystallization module.

According to a preferred embodiment, the first, third and fourth produced waters enter a product water basin for storing the first, third and fourth produced waters during treatment and for providing the pre-treatment unit with recycled water.

Throughout this document, the features referred to as "preferably" are only an optional feature and should not be understood as necessarily requiring that such applicant reserves the right to disclaim or delete the associated preferred feature at any time.

It should be noted that the above-mentioned embodiments are exemplary, and that those skilled in the art, having benefit of the present disclosure, may devise various arrangements that are within the scope of the present disclosure and that fall within the scope of the invention. It should be understood by those skilled in the art that the present specification and figures are illustrative only and are not limiting upon the claims. The scope of the invention is defined by the claims and their equivalents.

Claims

1. A zero discharge treatment system for wastewater of synthetic ammonia and glycol is characterized in that the system comprises a pretreatment unit, a nanofiltration unit and a crystallization unit,

the pretreatment unit is used for removing heavy metal ions, silicon dioxide and hardness ions in the wastewater and sending the heavy metal ions, the silicon dioxide and the hardness ions to the first reverse osmosis membrane module to obtain first produced water and first concentrated water,

the nanofiltration unit carries out nanofiltration salt separation on the first concentrated water obtained by the treatment of the first reverse osmosis membrane module through a nanofiltration membrane element to obtain second produced water and second concentrated water which are treated by the nanofiltration unit,

the crystallization unit is used for extracting sodium chloride from the second produced water treated by the nanofiltration unit based on a two-stage membrane concentration and sodium chloride thermal crystallization mode and extracting sodium sulfate from the second concentrated water based on a cooling concentration crystallization and a melting crystallization mode, the first produced water enters the crystallization unit as fresh water and/or recycled water replenishing water and forms mixed condensed water with the condensed water of the crystallization unit as a heat exchange heat source and/or a liquid level control water supply source of the crystallization unit so as to provide recycled water support for the extraction of sodium chloride and sodium sulfate from the second produced water and the second concentrated water,

and after the wastewater is treated by the pretreatment unit, sodium chloride and sodium sulfate crystals in the synthetic ammonia and glycol wastewater are recovered by the nanofiltration unit and the crystallization unit, so that zero discharge of the wastewater is realized.

2. The zero discharge treatment system for wastewater generated in ammonia synthesis and ethylene glycol production as claimed in claim 1, wherein the crystallization unit comprises a first sodium chloride evaporative crystallization module, a second sodium chloride evaporative crystallization module and a sodium sulfate crystallization module,

and the second produced water treated by the nanofiltration unit enters the first sodium chloride evaporative crystallization module through a second reverse osmosis membrane module for evaporative crystallization, and the second concentrated water treated by the nanofiltration unit enters the second sodium chloride evaporative crystallization module and the sodium sulfate crystallization module through a freezing module for crystallization.

3. The zero-discharge treatment system for wastewater from ammonia synthesis and ethylene glycol production as claimed in claim 2, wherein the second produced water passes through the second reverse osmosis membrane module to obtain a third produced water and a third concentrated water, the third concentrated water enters an ultra high pressure membrane module to obtain a fourth produced water and a fourth concentrated water, the fourth concentrated water enters the first sodium chloride evaporative crystallization module, and the first sodium chloride evaporative crystallization module treats the fourth concentrated water in a triple effect evaporative crystallization manner to obtain sodium chloride, wherein,

the triple-effect evaporative crystallization is to sequentially reduce the boiling points of the high-salt water in each evaporation chamber, separate secondary steam based on the difference of the boiling point temperatures, and utilize the heat energy in the raw steam step by step for multiple times.

4. The zero emission treatment system for wastewater from synthesis ammonia and ethylene glycol production as claimed in claim 3, further comprising a pre-concentration module and a defoaming module, wherein before the second concentrated water enters the freezing module, the pre-concentration module compresses the secondary steam to increase the temperature of the secondary steam and is used for the system to evaporate the heat source, and the defoaming module is used for the first sodium chloride evaporation crystallization module and the second sodium chloride evaporation crystallization module and is used for removing liquid drops and/or foams in the secondary steam generated in the evaporation process.

5. The zero-emission treatment system for wastewater generated in synthesis of ammonia and ethylene glycol according to claim 4, wherein the freezing module comprises a primary precooler and a secondary precooler, the primary precooler performs counter-current heat exchange to cool the circulating cooling water and the second concentrated water, the pre-cooled second concentrated water enters the secondary precooler, the counter-current heat exchange to cool the supernatant in the freezing module and the second concentrated water is performed, and the supernatant after heat exchange enters the second sodium chloride evaporation crystallization module.

6. The zero discharge treatment system for wastewater of synthesis ammonia and glycol as set forth in claim 5, wherein the second sodium chloride evaporation crystallization module processes the supernatant after heat exchange in a two-effect evaporation crystallization manner to obtain sodium chloride, wherein,

the double-effect evaporation crystallization is that the boiling points of high-salt water in each evaporation chamber are sequentially reduced, secondary steam is separated based on the difference of the boiling point temperatures, and heat energy in the raw steam is utilized step by step for multiple times.

7. The zero-emission treatment system for wastewater from synthesis ammonia and ethylene glycol production as claimed in claim 6, wherein the system further comprises a miscellaneous salt unit, and the fourth concentrated water is dried by passing through the triple effect evaporation crystallization mother liquor of the first sodium chloride evaporation crystallization module and the heat exchanged supernatant through the double effect evaporation crystallization mother liquor of the second sodium chloride evaporation crystallization module.

8. The zero-discharge treatment system for wastewater from synthesis ammonia and ethylene glycol production as claimed in claim 7, wherein the sodium sulfate crystallization module comprises a melt crystallizer and a centrifuge, the second concentrated water is treated by the freezing module and then enters the melt crystallizer for evaporation crystallization to obtain sodium sulfate crystal salt, and the sodium sulfate crystal salt enters the centrifuge to obtain sodium sulfate.

9. The zero discharge treatment system for wastewater from synthesis ammonia and ethylene glycol production as claimed in claim 8, wherein the first, third and fourth produced waters are fed into a product water tank for storing the first, third and fourth produced waters during treatment and for providing recycled water to the pretreatment unit.

10. A zero-emission treatment method for wastewater generated in ammonia synthesis and ethylene glycol synthesis is characterized by comprising the following steps:

removing heavy metal ions, silicon dioxide and hardness ions in the wastewater to obtain first produced water and first concentrated water;

carrying out nanofiltration salt separation on the obtained first concentrated water, and obtaining treated second produced water and second concentrated water;

crystallizing the second produced water and the second concentrated water,

the wastewater is subjected to removal of heavy metal ions, silicon dioxide and hardness ions, and then subjected to nanofiltration salt separation and crystallization treatment to recover sodium chloride and sodium sulfate crystals in the synthetic ammonia and glycol wastewater, so that zero discharge of the wastewater is realized.