CN108203197B

CN108203197B - Processing system who contains salt waste water

Info

Publication number: CN108203197B
Application number: CN201810004577.8A
Authority: CN
Inventors: 权秋红; 张建飞; 元西方; 石维平
Original assignee: Bestter Group Co ltd
Current assignee: Bestter Group Co ltd
Priority date: 2015-12-23
Filing date: 2015-12-23
Publication date: 2020-07-31
Anticipated expiration: 2035-12-23
Also published as: CN105540972A; CN108203197A; CN108558099B; CN108558099A; CN105540972B

Abstract

The invention relates to a salt-containing wastewater treatment system, which comprises a circulating pretreatment unit, a circulating reduction unit and a zero discharge unit, it is characterized in that the circulating pretreatment unit is used for filtering the produced water after the high-salinity wastewater reacts with the pretreatment agent through a tubular microfilter and then discharging the filtered produced water to the circulating reduction unit, the circulating reduction unit carries out preliminary reduction treatment on the produced water treated by the circulating pretreatment unit through a reverse osmosis device, and the multistage electrically driven ionic membrane device consisting of at least one electrically driven ionic membrane device is used for carrying out deep concentration treatment so as to further reduce and separate water in the wastewater with high salt content to a fresh water tank for recycling, the concentrated mixed salt solution obtained by deep concentration is discharged to a zero emission unit, and the zero emission unit is used for recovering nitrate and sodium salt in the concentrated mixed salt solution by heating, evaporating and crystallizing the concentrated mixed salt solution. The final mixed salt separated by the method accounts for less than 5% of the total salt content, and the produced water is completely recycled, so that zero discharge of wastewater is achieved.

Description

Processing system who contains salt waste water

The invention has the original application number of 201510981321.9, the application date of 2015 is 12 and 23, and the original invention name is as follows: a divisional application of a zero-discharge treatment system for high-salt wastewater.

Technical Field

The invention relates to the field of zero-emission treatment of high-salt-content wastewater, in particular to a zero-emission treatment system of high-salt-content wastewater.

Background

In recent years, with the rapid development of industries such as petrochemical industry, electric power industry, metallurgy industry, coal chemical industry and the like, the amount of sewage with complex components such as reverse osmosis concentrated water, industrial sewage, circulating sewage, part of process drainage and the like generated in the industrial production process is increased year by year, and how to finally dispose and utilize the sewage with complex components is widely regarded.

At present, the treatment method for high-salt complex wastewater containing refractory organic matters mainly comprises the following schemes:

firstly, performing catalytic oxidation on refractory organic substances in the wastewater by adopting strong oxidizing substances (mainly comprising ozone, hydrogen peroxide and the like) to effectively degrade the refractory organic substances in the wastewater, removing the organic substances in the wastewater by the wastewater after oxidation treatment in a biochemical unit, and directly discharging the wastewater after precipitation and filtration;

secondly, softening the calcium and magnesium containing hard wastewater, performing decrement treatment by a secondary reverse osmosis device to further recover partial water, and directly discharging concentrated water generated after decrement;

thirdly, the high-salinity concentrated water after reduction is subjected to zero-discharge treatment, and the high-salinity concentrated water is treated by a multi-evaporation and crystallization unit to form mixed salts, so that zero discharge of water is realized.

The first scheme only aims at the organic matters in the wastewater to carry out effective treatment and digestion, the general sewage treatment is carried out through a longer biochemical treatment process, and the biodegradability of the rest organic matters in the wastewater is extremely poor and even can not be biochemical, so that the removal effect of the rest organic matters by chemical catalytic oxidation is limited, and most importantly, the rest organic matters have no removal effect on inorganic salt components of the wastewater; although the raw water is subjected to certain decrement treatment from the aspect of process, reverse osmosis concentrated water is high-salinity wastewater obtained by concentrating the raw water by at least 4 times, and the concentrations of pollutants such as calcium ions, magnesium ions, heavy metal ions, silicon ions and the like and non-biochemical organic matters and the like are high, so that the recovery rate of the wastewater is not high by a common reverse osmosis membrane, even a seawater desalination membrane can only achieve about 50%, the produced concentrated water is reduced but has a relatively large water quantity, and stronger concentrated water accounting for more than 10% of the total treated water still has great influence on the environment; according to the third scheme, the concentrated high-salinity wastewater is treated more thoroughly, the technology is mature relatively, only the treatment cost is too high, a large amount of steam is consumed in the process, the treatment cost of general water is more than 50 yuan/ton according to the salt concentration of final concentrated water, only one salt is separated or mixed salt is directly formed, the mixed salt is used as dangerous waste and needs to be specially treated, the cost is very high, the investment cost and the operation cost of the method for treating the high-salinity water with large water content are very high, and enterprises can not accept the method.

Chinese patent (CN 103482810B) provides a novel zero-discharge treatment system for heavy metal wastewater with high salt content, which comprises a wastewater adjusting and oxidizing tank, a wastewater lifting pump, a filter and a spray cooler, wherein the wastewater adjusting and oxidizing tank is provided with a wastewater inlet, an air inlet and a wastewater outlet, the spray cooler is provided with a high-temperature flue gas inlet, a low-temperature flue gas outlet and a wastewater inlet, the wastewater outlet on the wastewater adjusting and oxidizing tank is connected with the inlet of the wastewater lifting pump, the inlet of the filter is connected with the outlet of the wastewater lifting pump, the outlet of the filter is connected with the wastewater inlet of the spray cooler, and the spray cooler is internally provided with an atomizing nozzle. Although the patent technology realizes zero discharge treatment of heavy metal wastewater with high salt content, the patent adopts a third scheme, the treatment cost is high, a large amount of steam is consumed in the treatment process, and only one kind of salt is separated or mixed salt is directly formed. The mixed salt as a hazardous waste needs special treatment, further increasing the cost. The patent technology has very high investment cost and operation cost for treating the high-volume brine with large water content, and is difficult to be accepted and used by enterprises.

Therefore, there is an urgent need in the market for a low-cost zero-emission treatment system, which can classify the treated salt and generate economic value, thereby protecting the environment and creating economic value for enterprises at low cost.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a zero-emission treatment system for high-salt-content wastewater, which comprises a circulating pretreatment unit, a circulating reduction unit and a zero-emission unit and is characterized in that,

the circulating pretreatment unit is used for filtering the produced water after the high-salinity wastewater reacts with the pretreatment agent through a tubular micro-filter and then discharging the filtered water to the circulating reduction unit,

the circulation reduction unit carries out preliminary reduction treatment on the produced water treated by the circulation pretreatment unit through a reverse osmosis device, and carries out deep concentration treatment through a multi-stage electric drive ionic membrane device consisting of at least one electric drive ionic membrane device so as to further reduce and separate the water in the high-salt-content wastewater to a fresh water tank for recycling, and concentrated mixed salt solution obtained by deep concentration is discharged to the zero discharge unit,

and the zero-emission unit is used for recovering nitrate and sodium salt in the concentrated mixed salt solution by heating, evaporating and crystallizing the concentrated mixed salt solution.

According to a preferred embodiment, the recycling pre-treatment unit comprises at least a conditioning tank, a dense tank, a tubular micro-filter and a sludge tank,

the high-density tank discharges sludge generated by mixing the saline wastewater homogenized and uniformly regulated by the regulating tank and the pretreatment agent to the sludge tank at the lower part of the high-density tank under the action of gravity, and the produced water treated by the pretreatment agent in the high-density tank enters a circulating reduction unit for treatment after being subjected to microfiltration treatment by the tubular microfilter;

and sludge and water in the sludge tank are separated in a sludge dewatering and drying device in a filter pressing mode, and separated water is discharged back to the adjusting tank or the high-density tank for recycling pretreatment.

According to a preferred embodiment, the circulation reduction unit comprises at least one electrically driven ionic membrane device, a medium pressure reverse osmosis device, a high pressure reverse osmosis device, an activated carbon filter, a second tubular microfilter, a two-stage reverse osmosis device and a fresh water tank,

the high-pressure reverse osmosis device is used for concentrating the produced water discharged by the circulating pretreatment unit in a medium-pressure reverse osmosis filtration mode by the medium-pressure reverse osmosis device to obtain concentrated water which is subjected to high-pressure reverse osmosis filtration concentration, so that the produced water is subjected to preliminary reduction treatment;

fresh water generated by the medium-pressure reverse osmosis device and the high-pressure reverse osmosis device is purified by the secondary reverse osmosis device in a reverse osmosis and ultraviolet sterilization mode and then is recycled to the fresh water tank;

the activated carbon filter and the second tubular micro-filter sequentially filter and soften calcium and magnesium ions of the reverse osmosis concentrated solution and then discharge the solution to the multistage electrically driven ionic membrane device for deep reduction treatment;

the multistage electrically-driven ionic membrane device comprises a first electrically-driven ionic membrane device and a second electrically-driven ionic membrane device, wherein the TDS of the second electrically-driven ionic membrane device for concentrating and filtering the first electrically-driven ionic membrane device is 1.2 × 10⁵Carrying out secondary concentration and filtration on mg/l concentrated water to obtain TDS of 2 × 10⁵mg/l of a concentrated mixed salt solution, wherein,

and the desalted water separated by the second electrically-driven ionic membrane device is discharged back to the medium-pressure reverse osmosis device to be subjected to circulating reduction treatment of primary reduction and deep concentration.

According to a preferred embodiment, the zero-emission unit comprises at least a raw material feed preheater, a nitrate evaporative crystallization device, a nitrate thickener, a nitrate circulating pump, a first steam compressor, at least one drying device, a cooling water system, a salt evaporative crystallization device,

the nitrate evaporative crystallization device is used for circularly heating the concentrated mixed salt solution discharged by the circular reduction unit preheated by the raw material feed preheater to the nitrate evaporative crystallization device for evaporative crystallization, concentration and separation to obtain nitrate and feed liquid after the concentrated mixed salt solution passes through a nitrate circulating pump and a first heater in sequence,

the feed liquid enters a centrifugal separator through the nitrate thickener to package the centrifugally separated nitrate salt into commercial nitrate salt after being dried by first drying equipment,

freezing the nitre mother liquor separated by the centrifugal separator to-5 ℃, then feeding the nitre mother liquor into a frozen nitre crystallizing tank, returning the separated nitre decahydrate obtained by the frozen nitre centrifugal separator to the raw material feeding preheater for carrying out circulating crystallization separation of nitrate,

and discharging supersaturated feed liquid separated by the frozen nitre centrifugal separator to the salt evaporation crystallization device to obtain commercial salt through centrifugal separation.

According to a preferred embodiment, the saltpeter evaporation crystallizer compresses low-temperature secondary dead steam generated by evaporation through a first steam compressor in a negative pressure/slight positive pressure state to increase the temperature of the dead steam, so that a circulating heating device formed by the saltpeter circulating pump, the first heater and the saltpeter evaporation crystallizer has continuous and stable heat energy,

the nitrate evaporation crystallization device utilizes a first vapor compressor to connect a cooling water system through the first vapor compressor according to the temperature required by frozen nitrate crystallization under the condition of extracting and compressing secondary vapor, and utilizes a cooler and/or a freezing station to maintain the temperature required in the frozen nitrate crystallization device.

According to a preferred embodiment, the nitrate mother liquor separated by the centrifugal separator enters a nitrate mother liquor tank, and enters the frozen nitrate crystallization device through a nitrate mother liquor pump for cooling and crystallization, the nitrate mother liquor is crystallized in the frozen nitrate crystallization device and then is discharged to a first thickener for adjustment, the frozen nitrate crystallization device is connected with a cooler, the frozen nitrate crystallization device is kept at-6 to-5 ℃ through a cold nitrate circulating pump, the frozen nitrate mother liquor enters a preheater for heating through the frozen nitrate mother liquor pump, then enters the salt evaporation crystallization device for evaporation and crystallization under negative pressure;

the salt evaporation crystallization device is connected with a second heater through a circulating pump to heat the salt evaporation crystallization device, secondary steam generated by the salt evaporation crystallization device is extracted through a second steam compressor and used for heating liquid in the preheater after the temperature of the secondary steam is increased through the second heater,

and (3) the product after salt evaporation and crystallization enters a salt centrifugal separator through a second thickener for separation, and then the crystals are dried through second drying equipment to obtain the sodium salt of the commodity.

According to a preferred embodiment, a spiral-flow type electrocoagulation device is connected between the adjusting tank and the high-density tank, and comprises a cathode, an anode, a water inlet, a water outlet, a reaction chamber formed between the cathode and the anode, an insulating fixed sealing cover and an insulating sealing support plate, wherein the insulating fixed sealing cover is arranged at the upper part of the cathode, the anode formed by a cylindrical rod is fixed by the insulating fixed sealing cover by taking the center of the cathode as an axis, the insulating sealing support plate is arranged at the lower part of the cathode, the water inlet is arranged at the lower end of a shell at one side of the cathode, the water outlet is arranged at the upper end of a shell at the other side of the cathode, and the water inlet and the;

the electrocoagulation device enables the salt-containing wastewater which is homogenized and uniformly regulated in the regulating tank to enter the reaction chamber from the water inlet in a tangent shape and flow in the reaction chamber in a spiral-flow manner, and the salt-containing wastewater generates electrochemical reaction under the action of direct current applied to the electrodes, so that impurity particles contained in the salt-containing wastewater generate flocculation.

According to a preferred embodiment, the first and second electrically-driven ionic membrane devices each comprise an anode and a cathode arranged at intervals, at least one membrane pair composed of an anode membrane, a cathode membrane and a partition plate is arranged between the anode and the cathode at regular intervals, the anode membrane and the cathode membrane are homogeneous membranes with low membrane resistance and high performance, the partition plate with uniform flow state is arranged between the anode membrane and the cathode membrane, the power supply is a high-frequency direct-current power supply with positive and negative polarities capable of being automatically switched, the module controls the power supply by using a digital program, high-frequency reverse polarity direct current is output by adopting adjustable gap high-frequency oscillation to disturb an easily formed polarization layer on the membrane surface, calcium and magnesium cations with high concentration times in the polarization layer formed on the membrane surface are damaged, the molecular disproportionation of the polarization layer is caused by the crystallization process, physical scale inhibition is exerted, hydrodynamic force conditions are optimized, and the power consumption is effectively reduced by 30-50%,

the pretreatment unit discharges salt-containing solution to enter a compartment of a deep concentration electric-driven ionic membrane device, the electric-driven ionic membrane causes anions and cations in the salt-containing solution flowing through the compartment to directionally move under the action of an external direct current electric field, the anions move towards the direction of an anode, and the cations move towards the direction of a cathode, so that ions in the solution of a fresh water compartment are transferred to a concentrated water compartment, the ions in the salt-containing solution are separated from the salt-containing solution, and concentrated water and desalted fresh water are obtained.

According to a preferred embodiment, the electrically driven ionic membrane device at least comprises a membrane stack, a locking frame, a feeding frame, an anionic membrane, a cationic membrane, a partition plate, a water distribution groove, a partition net, an electrode, a polar chamber and a press, wherein the membrane stack is composed of at least one membrane pair formed by combining a positive membrane, a negative membrane and a partition plate which form a concentration chamber and/or a desalination chamber, and a fixed exchange group of a cation exchange membrane with selective permeability is negatively charged so as to allow cations in water to pass through and block anions; the stationary exchange groups of the permselective anion exchange membrane are positively charged, thereby allowing anions in the water to pass through and blocking cations, resulting in migration of ions in the fresh water compartment into the concentrated water compartment, the thickness of the membrane being in the range of 0.5-2.0 mm.

According to a preferred embodiment, the recycling pre-treatment unit comprises a conditioning tank, a dense tank, a tubular micro-filter, at least one intermediate basin and a sludge tank,

the adjusting tank is connected with the high-density tank connected with at least one dosing device through a lifting pump so as to enable the uniform salt-containing wastewater to be coagulated, softened and precipitated after reaction with a medicine, the high-density tank is connected with the tubular micro-filter through a first booster pump so as to discharge the treated produced water to the first intermediate water tank, the high-density tank is connected with the sludge tank so as to dehydrate the precipitated sludge, and the sludge tank is connected with the adjusting tank so as to discharge the dehydrated produced water to the adjusting tank for cyclic pretreatment;

the circulating pretreatment unit also comprises a filter element filter, the filter element filter is connected between the tubular micro filter and the first intermediate water tank, and the sludge tank is connected with a sludge dewatering and drying device for dewatering and drying sludge;

the circulation reduction unit comprises at least one middle water tank, at least one electrically-driven ionic membrane device, a medium-pressure reverse osmosis device, a high-pressure reverse osmosis device, an activated carbon filter, a second tubular micro-filter, a secondary reverse osmosis device and/or a fresh water tank,

the first intermediate water tank is connected with the high-pressure reverse osmosis device through a medium-pressure reverse osmosis device, the high-pressure reverse osmosis device discharges the treated produced water to a hardness removal reactor, an activated carbon filter and a tubular microfiltration filter which are connected with the high-pressure reverse osmosis device through a reverse osmosis concentrated water tank, the activated carbon filter is connected with a first electrically-driven ionic membrane device through a second tubular microfiltration filter, the first electrically-driven ionic membrane device is connected with a second electrically-driven ionic membrane device so that the produced water is circularly desalted and then discharged to a second concentrated brine tank, the first electrically-driven ionic membrane device and the second concentrated brine tank are connected with the second-stage reverse osmosis device together, and the second-stage reverse osmosis device is connected with the first intermediate water tank and the fresh water tank;

the zero-discharge unit comprises a raw material feeding preheater, a nitrate evaporation and crystallization device, a nitrate thickener, a nitrate circulating pump, a steam compressor, at least one drying device, a cooling water system and a salt evaporation and crystallization device,

the second strong brine tank pass through the fifth booster pump with the raw materials feeding pre-heater is connected, the raw materials feeding pre-heater loops through nitre evaporation crystallization device nitre thickener, centrifugal separator, nitre mother liquor groove, nitre mother liquor pump is connected with freezing nitre crystallizer, freezing nitre crystallizer loop through first thickener, freezing nitre centrifugal separator, freezing nitre mother liquor groove, freezing nitre mother liquor pump, pre-heater and the salt evaporation crystallization device is connected, the salt evaporation crystallization device is connected with circulating pump, second heater and second thickener respectively, the second heater is connected with second vapor compressor and new vapor device respectively, the second thickener loops through salt centrifugal separator, second drying equipment and is connected with second measurement packing plant, the nitre evaporation crystallization device is connected respectively with vacuum system, nitre circulating pump, first heater and first vapor compressor respectively, the first heater is respectively connected with the saltpeter circulating pump, the new steam device and the first steam compressor, the first steam compressor is connected with the cooler sequentially through a cooling water system and a freezing station, and the cold saltpeter circulating pump is connected between the cooler and the frozen saltpeter crystallizing tank;

a first drying device is connected between the centrifugal separator and the first metering and packaging device, the frozen nitrate centrifugal separator is connected with the nitrate thickener, the preheater is respectively connected with a second heater and a recycling device, and the nitrate evaporative crystallization device and the salt evaporative crystallization device are jointly connected with a defoaming agent feeding system;

the first middle water tank is connected with the medium-pressure reverse osmosis device through a filtering device consisting of a booster pump and a cartridge filter in sequence, the medium-pressure reverse osmosis device is connected with the high-pressure reverse osmosis device through a second middle water tank and a filtering device consisting of the booster pump and the cartridge filter, and the first electrically-driven ionic membrane device is connected with the second electrically-driven ionic membrane device through a first concentrated brine tank and a fourth booster pump.

The invention has the beneficial technical effects that:

the process has the characteristics of mature technology, low engineering investment, low operation cost, simple operation management, stable and reliable system operation, small occupied area and the like. The quality of the recovered product water and the condensed water is excellent, and the method can be used for circulating water replenishing water or desalted water station replenishing water. The separated simple substance salt sodium sulfate is more than 96 percent, the sodium chloride is more than 98 percent, and the final mixed salt accounts for less than 5 percent of the total salt. The produced water is completely recycled, no wastewater is discharged, and zero discharge of the wastewater is achieved.

Drawings

FIG. 1 is a simplified schematic of the process flow of the present invention;

FIG. 2 is a schematic process flow diagram of the present invention;

FIG. 3 is a schematic diagram of the construction of the cyclonic electrocoagulation apparatus of the present invention; and

FIG. 4 is a schematic top view of the cyclonic electrocoagulation apparatus of the present invention.

List of reference numerals

1: salt-containing wastewater 2: and (3) adjusting the pool: lift pump

4: high density pond 5: the first booster pump 6: tubular micro-filter

7: a cartridge filter 8: first intermediate pool 9: second booster pump

10: first security filter 11: medium-pressure reverse osmosis device 12: second intermediate pool

13: the third booster pump 14: second canister filter 15: high-pressure reverse osmosis device

16: reverse osmosis concentrated water tank 17: the booster water pump 18: activated carbon filter

19: second tube type microfilter 20: the intermediate water tank 21: pressure water pump

22: third cartridge filter 23: first electrically-driven ionic membrane device 24: first strong brine tank

25: the fourth booster pump 26: second electrically-driven ionic membrane device 27: second strong brine tank

28: the fifth booster pump 29: raw material feed preheater 30: nitre evaporation crystallization device

31: first heater 32: the fresh steam device 33: nitre circulating pump

34: the vacuum system 35: first vapor compressor 36: saltpeter thickener

37: the centrifugal separator 38: the first drying apparatus 39: nitre mother liquid tank

40: first metering and packaging device 41: nitre mother liquor pump 42: freezing nitre crystallizer

43: cooling water system 44: the freezing station 45: cooling device

46: frozen saltpeter circulating pump 47: first thickener 48: centrifugal separator for frozen nitre

49: frozen nitre mother liquor tank 50: frozen nitre mother liquor pump 51: preheater

52: salt evaporative crystallization apparatus 53: the circulating pump 54: second heater

55: second vapor compressor 56: second thickener 57: salt centrifugal separator

58: the second drying apparatus 59: second metering and packaging device 60: sludge tank

61: sludge dewatering and drying device 62: the secondary reverse osmosis device 63: fresh water tank

64: the recycling device 65: first dosing device 66: second medicine adding device

67: defoaming agent dosing system

Detailed Description

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

The high-salinity wastewater refers to oil refining wastewater, coal chemical wastewater, circulating system sewage, reverse osmosis concentrated water, wastewater containing complex components in a sewage treatment plant and the like, the TDS of the high-salinity wastewater is 5000-10000 mg/L, namely the total soluble solid content in the 1L high-salinity wastewater is 5000-10000 mg.

FIG. 1 is a simplified schematic of the process flow of the present invention. As shown in figure 1, the invention provides a zero-emission treatment system for high-salinity wastewater, which comprises a circulating pretreatment unit, a circulating reduction unit and a zero-emission unit. The circulating pretreatment unit is used for filtering the produced water after coagulation and softening reaction of the waste saline and the medicament through a tubular microfilter and then discharging the filtered water to the circulating reduction unit. The circulation reduction unit is used for carrying out deep reduction treatment on the produced water treated by the circulation pretreatment unit through a security filter and at least one electrically-driven ionic membrane device so as to discharge the obtained condensed water to a fresh water tank for recycling, and discharging the obtained concentrated mixed salt solution to the zero discharge unit. And the zero-discharge unit is used for circularly heating, evaporating and crystallizing the concentrated mixed salt solution to obtain the nitrate and the commercial salt which can be packaged and sold.

As shown in fig. 2, the circulation pretreatment unit includes a conditioning tank 2, a high-density tank 4, a tubular micro filter 6, at least one intermediate water tank, and a sludge tank 60. The adjusting tank 2 is connected with a high-density tank 4 connected with at least one dosing device through a lifting pump 3 so as to enable the salt-containing wastewater to be coagulated, softened and precipitated after the salt-containing wastewater and the drugs react. The high density tank 4 is connected to a tubular micro-filter 6 by a first booster pump 5 to discharge the treated produced water to a first intermediate water tank 8. And the high-density tank 4 is connected to a sludge tank 60 to subject the precipitated sludge to a dehydration treatment. The sludge tank 60 is connected with the adjusting tank 2 to discharge the produced water after the dehydration treatment to the adjusting tank 2 for the cyclic pretreatment.

According to a preferred embodiment, the recycling pre-treatment unit further comprises a cartridge filter 7, the cartridge filter 7 being connected between the tubular micro-filter 6 and the first intermediate basin 8.

According to a preferred embodiment, the sludge tank 60 is connected with a sludge dewatering and drying device 61 for dewatering and drying sludge.

The circulating pretreatment unit effectively removes heavy metal ions, calcium, magnesium and other hardness ions before the hardness ions enter the concentrated water for reverse osmosis by adopting a chemical method, and simultaneously removes most COD, silicon ions and organic colloidal substances. The concentration of COD and silicon ions is reduced through the coagulation and adsorption effects, and the PH value of reverse osmosis inlet water is kept between 8.0 and 9.5. The treated brine inhibits the tendency of silicon scaling and organic pollution on the surface of the membrane under the alkaline condition, so that the reverse osmosis membrane surface of the reverse osmosis system avoids the problems of organic pollution and calcium-magnesium scaling. The method is characterized in that precipitates, coagulated colloid substances and the like generated by chemical reaction are further removed through a tubular micro-filter with the aperture of 1-5 microns, so that pretreatment meets the SDI index of subsequent reverse osmosis inflow, organic pollution and inorganic pollution blockage caused by subsequent reverse osmosis are reduced, the whole system wastewater treatment process is more reasonable, and the long-term, stable and reliable operation of the system is ensured.

According to a preferred embodiment, the circulation reduction unit comprises at least one booster pump, at least one cartridge filter, at least one intermediate water basin, at least one electrically driven ionic membrane device, a high pressure reverse osmosis device 15, an activated carbon filter 18, a second tubular micro filter 19, a secondary reverse osmosis device 62 and/or a fresh water tank 63,

the first intermediate water tank 8 discharges filtered produced water to a high-pressure reverse osmosis device 15 through at least one filtering device consisting of a booster pump and a cartridge filter, the high-pressure reverse osmosis device 15 discharges the treated produced water to an activated carbon filter 18 connected with the high-pressure reverse osmosis device through a reverse osmosis concentrated water tank 16, the activated carbon filter 18 is connected with a first electrically-driven ionic membrane device 23 through a second tubular micro-filter 19, the first electrically-driven ionic membrane device 23 is connected with a second electrically-driven ionic membrane device 26 so that the produced water is discharged to a second concentrated brine tank 27 after cyclic desalination, the first electrically-driven ionic membrane device 23 and the second concentrated brine tank 27 are jointly connected with a second-stage reverse osmosis device 62, and the second-stage reverse osmosis device 62 is connected with the first intermediate water tank 8 and a fresh water tank 63.

According to a preferred embodiment, the first intermediate water tank 8 is connected to the medium-pressure reverse osmosis device 11 through a filtering device composed of a booster pump and a cartridge filter in sequence, the medium-pressure reverse osmosis device 11 is connected to the high-pressure reverse osmosis device 15 through the second intermediate water tank 12 and the filtering device composed of the booster pump and the cartridge filter, and the first electrically-driven ionic membrane device 23 and the second electrically-driven ionic membrane device 26 are connected through the first concentrated brine tank 24 and the fourth booster pump 25.

The saline complex wastewater aimed by the invention is generally from reverse osmosis concentrated water concentrated by 4 times or other production wastewater with high salinity, the TDS of the saline complex wastewater is generally between 5000-10000 mg/L, and the recovery rate of the system can reach about 85% by carrying out primary reduction treatment on the concentrated solution to reach about 50000mg/l of TDS through a medium-pressure reverse osmosis device and a high-pressure reverse osmosis device.

The first and second electrically driven ion membrane devices 23 and 26 further concentrate the high brine with a TDS of 50000 mg/l. The first electrically driven ionic membrane device 23 increased the TDS to 120000 mg/l. The second electrically driven ionic membrane device 26 increases the TDS to 200000 mg/l. The electrically driven ionic membrane device replaces the conventional multiple-effect evaporation to reduce the evaporation water amount with lower concentration, greatly reduces the evaporation water amount and saves energy consumption. The reduction of the whole process flow reaches more than 95 percent of the recovered water, and the concentrated brine with TDS about 200000mg/l is used as the raw material water of the evaporation crystallization unit. According to a preferred embodiment, the zero-emission unit comprises a raw material feed preheater 29, a nitrate evaporative crystallization device 30, a nitrate thickener 36, a nitrate circulating pump 33, a steam compressor 35, at least one drying device, a cooling water system 43, a salt evaporative crystallization device 52,

the second concentrated brine tank 27 is connected with a raw material feeding preheater 29 through a fifth booster pump 28, the raw material feeding preheater 29 sequentially passes through a nitre evaporation crystallization device 30, a nitre thickener 36, a centrifugal separator 37 and a nitre mother liquor tank 39, a nitre mother liquor pump 41 is connected with a frozen nitre crystallization tank 42,

the frozen saltpeter crystallizing tank 42 is connected with a salt evaporation crystallizing device 52 sequentially through a first thickener 47, a frozen saltpeter centrifugal separator 48, a frozen saltpeter mother liquor tank 49, a frozen saltpeter mother liquor pump 50 and a preheater 51,

the salt evaporation crystallization device 52 is respectively connected with a circulating pump 53, a second heater 54 and a second thickener 56, the second heater 54 is respectively connected with a second steam compressor 55 and the new steam device 32, and the second thickener 56 is connected with a second metering and packaging device 59 through a salt centrifugal separator 57 and a second drying device 58 in sequence.

According to a preferred embodiment, the nitre evaporative crystallization device 30 is respectively connected with a vacuum system 34, a nitre circulating pump 33, a first heater 31 and a first steam compressor 35, the first heater 31 is respectively connected with the nitre circulating pump 33, a new steam device 32 and the first steam compressor 35, the first steam compressor 35 is sequentially connected with a cooler 45 through a cooling water system 43 and a freezing station 44, and a cold nitre circulating pump 46 is connected between the cooler 45 and the frozen nitre crystallization tank 42.

According to a preferred embodiment, a first drying device 38 is connected between the centrifugal separator 37 and the first metering and packaging device 40, and a frozen saltpeter centrifugal separator 48 is connected to the saltpeter thickener 36.

According to a preferred embodiment, the preheater 51 is respectively connected with the second heater 54 and the recycling device 64, and the saltpeter evaporative crystallization device 30 and the salt evaporative crystallization device are jointly connected with the defoaming agent feeding system 67.

Through the two-stage reduction process of the first electrically-driven ionic membrane device and the second electrically-driven ionic membrane device, the formed high-concentration salt solution enters a preheater for evaporative crystallization, is solidified and fixed in nitre crystallization, and is heated by circulating through a heater. Under negative pressure, the salt solution is heated to boiling by the primary heat provided by the steam, and the salt solution is evaporatedThe raw low-temperature secondary exhaust steam is compressed by a steam compressor to improve the temperature of the exhaust steam, so that the continuous evaporation heat energy of the salt solution in the saltpeter tank is realized. By using water-salt system N_a ⁺//Cl^-，SO₄ ^2--H₂Phase O diagram, separation by crystallization of nitrate and sodium chloride is carried out according to the liquid phase composition/%, of sodium sulfate and sodium chloride of the solution at 100 ℃. Further, the nitrate decahydrate is further separated by a low-temperature freezing method according to a phase diagram according to the residual dissolution amount of the nitrate mother liquor at about 75 ℃. And (3) dissolving the sodium nitrate decahydrate back into the feed liquid to be separated discharged from the crystallizing tank, and performing hot melting together to separate out the sodium nitrate, thereby finally performing mass separation on the sodium nitrate and the sodium chloride.

Example one

As shown in the process flow diagram of FIG. 2, the integrated process is applied to treat industrial saline wastewater with complex components, wherein the wastewater comes from reclaimed water drainage, circulating water system sewage drainage, production process drainage and desalted water station, secondary reverse osmosis concentrated water, reverse washing water and the like in industrial sewage treatment and reuse.

Firstly, homogenizing and uniformly regulating the wastewater 1 sent from each path through a regulating tank 2, sending raw water to a high-density tank 4 through a lift pump 3, sequentially adding lime or sodium hydroxide, sodium carbonate, PAC, PAM and sodium hydroxide into a first dosing device 65 and a second dosing device 66 to prepare a 20% concentration solution, wherein the dosage is 1.5 g/L to prepare a 15% concentration sodium carbonate solution, the dosage is 3 g/L of the raw water concentration to soften the water, the PAC is prepared into a 20% concentration solution according to the 30 mg/L of the raw water concentration, the PAM is added to prepare a 0.3% concentration solution according to the 3 mg/L of the raw water concentration, the dosage is required to be regulated according to the actual water inlet ion concentration change conditions, and otherwise, membrane pollution is easily caused, and the service life of a membrane is influenced.

The mixed liquid enters a tubular micro-filter 6 or an immersed micro-filter 6, the total hydraulic retention time of the filter is 2.5h, under the action of natural sedimentation, supernatant liquid enters a filter element filter 7 or bag filtration effluent enters a first intermediate water tank 8 through the tubular micro-filter 6, chemical sludge is discharged into a sludge tank 60 from the bottom through gravity sedimentation, sludge is adjusted and then enters a sludge dewatering device for sludge-water separation, dry sludge which is formed into a sludge cake after sludge dewatering is finally dewatered and dried in a sludge dewatering and drying device 61, the intermediate pressure reverse osmosis device 11 adopts an aromatic polyamide composite material as a membrane material, the operation pressure is 2.0-3.5 MPa, the recovery rate is more than 70%, 97.5% of salt substances can be intercepted, raw water with the average TDS of 6500 mg/L can be concentrated to a TDS which is more than 21600 mg/L, concentrated water with the total treatment capacity of 30% of the total treatment capacity is treated by a reverse osmosis device 11, the intermediate pressure reverse osmosis membrane device 11, the raw water enters a high pressure reverse osmosis device 15 for further concentration, the high pressure reverse osmosis membrane material of the high pressure reverse osmosis membrane of the high pressure desalination device 15, the high pressure desalination of the aromatic polyamide composite desalination membrane material, the raw water is 3.5 mg/L, the concentrated fresh water enters a second stage reverse osmosis membrane of a second stage reverse osmosis membrane, the first stage reverse osmosis membrane, the second stage reverse osmosis membrane is more than 50020% of the concentration desalination concentrate desalination device, the concentrate desalination of the concentrate desalination water, the concentrate desalination device, the concentrate desalination of the concentrate fresh water, the concentrate desalination of the.

The raw water is concentrated and primarily reduced through reverse osmosis of the circulating pretreatment unit and the circulating reduction unit, and the generated high-salt-content concentrated water is subjected to heat exchange with high-temperature condensate water through the raw material reduction preheater 29. The heated material enters a nitrate evaporation crystallization device 30, and the feed liquid and a first heater 31 are circularly heated by a nitrate circulating pump 33. When the MVR device is started, raw steam is firstly introduced, and after the feed liquid is boiled, the secondary exhaust steam generated by the evaporating pot is compressed and heated by the first steam compressor 35 to replace the raw steam to circularly heat the feed liquid. The compressed secondary high-temperature steam is converted into high-temperature condensed water after heat exchange by a heat exchanger. The condensed water enters the preheater 51 to exchange heat with the feed liquid and then is condensed into low-temperature condensed water and sent to the recycling device 64 for recycling the production process. According to the water-salt system Na⁺//Cl^-，SO₄ ^2--H₂The content of main components in the O phase diagram ensures that the supersaturated nitrate is discharged from the evaporation crystallization device 30 and enters a nitrate thickener 36. The nitrate is mixed with decahydrate which is separated from the subsequent frozen nitrate for hot melting, and the simple substance salt is obtained through a centrifugal separator 37. The monomeric salt is dried using a first drying apparatus 38. And packaging the dried elemental salt by a first metering and packaging device 40 for export sale.

The nitrate separation mother liquor is pumped from the nitrate mother liquor tank 39 to the frozen nitrate crystallization tank 42 by the nitrate mother liquor pump 41. Freezing the nitre mother liquor to-5 ℃, and separating to obtain the nitre decahydrate. The sodium sulfate decahydrate returns to the sodium sulfate thickener 36 to be thermally melted with the sodium sulfate solution, and the sodium sulfate is separated from the sodium sulfate-containing solution together with the temperature reduction.

Mother liquor generated by freezing the saltpeter enters a salt evaporation crystallization device 52 through a frozen saltpeter mother liquor tank 49 and a frozen saltpeter mother liquor pump 50. The salt-containing concentrated water is subjected to heat exchange with high-temperature condensed water through a heat exchanger 51, and enters a salt evaporation crystallization device 52 after being heated by the heat exchanger. The salt-containing feed liquid and the second heater 54 are circularly heated by the circulating pump 53. When the MVR device is started, raw steam is firstly introduced, after the feed liquid is boiled, secondary exhaust steam generated by the evaporating pot is compressed and heated by the second steam compressor 55, the feed liquid is circularly heated by replacing the raw steam, and the compressed secondary high-temperature steam is changed into high-temperature condensed water after heat exchange by the heat exchanger and enters the preheater 51. After the heat exchange between the high-temperature condensed water and the salt solution, the high-temperature condensed water is condensed into low-temperature condensed water and sent to a recycling device 64 for recycling the production process. According to the water-salt system Na⁺//Cl^-，SO₄ ^2--H₂The content of the main component in the O-phase diagram allows the salt that has reached supersaturation to be discharged from the salt evaporative crystallization device 52 into the second thickener 56. The salt is separated in a salt centrifugal separator 57 to obtain the salt. The salt is dried by the second drying device 58 and then packaged and sold by the second metering and packaging device 59. And the defoaming agent adding system 67 adds defoaming agent to the nitrate evaporation crystallization device 30 and the salt evaporation crystallization device 52. A small amount of mixed salt finally formed in the invention is evaporated into salt mud. Stockpiling place after dewatering salt mudAnd (6) processing.

The water inlet index of the salt-containing wastewater and the salt index of the treatment process are shown in table 1.

The separated simple substance salt sodium sulfate reaches more than 96 percent, the sodium chloride reaches more than 98 percent, and finally the mixed salt accounts for less than 5 percent of the total salt. Wherein, the produced water is completely recycled, no waste water is discharged, and zero discharge of waste water is achieved. The quality of the condensed water in the treatment process is excellent, and the condensed water can be used for circulating water replenishing water or desalting station replenishing water. Therefore, the invention realizes the recovery of various simple substance salts besides the recovery of high-quality water, greatly reduces the amount of final mixed salt and saves a large amount of solid waste disposal cost. The treatment cost of the treatment process is effectively reduced after the produced commercial salt is sold. Realizes the treatment process with low cost and zero emission.

Example two

The present embodiment is a modified example of the first embodiment, and is a preferred implementation manner of the present invention. In this embodiment, only the system part different from the first embodiment is described, and the same system part is not described again.

An electrocoagulation device is connected between the conditioning tank 2 and the high density tank 4, consisting of a cylindrical acrylic resin housing and metal electrodes, 6 medium carbon steel electrodes of size 110mm × 90mm × 2mm are used as anodes and 6 stainless steel (SS 316) electrodes of size 110mm × 90mm × 1mm are used as cathodes in the electrocoagulation device, the anode and cathode electrodes are assembled in an alternating sequence with a 6mm gap remaining between the electrodes, a DC power supply is used to apply a DC current to the electrocoagulation device, the DC current varies between 1.5 and 3.5 amperes, the residence time is 30 minutes, the saline wastewater forms two types of sludge, a light sludge containing organic impurities floats on the surface of water, which is removed by a skimming method, a heavy sludge containing inorganic impurities is removed by adding polyelectrolyte, 1ppm AT-7594 (XTECH) is used as polyelectrolyte to rapidly settle the inorganic sludge.

According to a preferred embodiment, the electrocoagulation device is a cyclonic electrocoagulation device. As shown in FIG. 3, the cyclonic electrocoagulation apparatus 700 comprises a cathode 702, an anode 703, a water inlet 701, a water outlet 705, a reaction chamber, an insulating fixed sealing cover 704 and an insulating sealed support plate 706. Wherein the cathode 702 is an inverted conical frustum stainless steel cathode casing. The anode 703 is a cylindrical rod anode. The anode 703 is an aluminum or iron rod. An insulating fixing sealing cap 704 is provided on the upper portion of the cathode 702. The cylindrical rod anode is fixed by an insulating fixing seal cap 704 with the center of the cathode 702 as an axis. An insulating sealing support plate 706 is disposed at a lower portion of the cathode 702. The water inlet 701 is provided at the lower end of the casing at one side of the cathode 702. The water outlet 705 is arranged at the upper end of the shell at the other side of the cathode 702. The water inlet 701 and the water outlet 705 are arranged on the cathode 703 in the same direction, and are arranged in the tangential direction of the shell section of the cathode 703. The reaction chamber is the region formed between the cathode 702 and the cylindrical rod anode. As shown in fig. 4, an insulating flow guide 707 or an insulating flow guide channel for forced flow guide is disposed between the cathode 702 and the anode 703. An insulating deflector 707 or insulating deflector channel increases the hydraulic retention time of the water to be treated the deflector 707 is disposed on the inner wall of the cathode 702 by an adhesive. The flow guide plates 707 are alternately arranged on the inner wall of the cathode 702 and the anode cylindrical rod by an adhesive. The alternatively arranged guide plates 707 are connected with the anode cylindrical rod in a socket joint mode through adhesive. The anode cylindrical rod is provided with a slot 708 matching with the flow guide plate 707. The guide plate is an insulating plate made of PVC materials. The adhesive is a silicone rubber material.

The saline wastewater to be treated is homogenized and uniformly treated in the regulating tank 2 and then enters the reaction chamber from the water inlet 701 in a tangent shape. The fluid flowing between the two poles flows in a cyclone type in the reaction chamber, so that the hydraulic retention time of the fluid is increased. Meanwhile, applying direct current on the electrode to perform electrochemical reaction in the saline wastewater to be treated to generate Al (OH)₃Or Fe (OH)₃Further promoting the flocculation of impurity particles contained in the water to be treated. The eddy flow makes the turbulent effect of the fluid aggravated, and can effectively wash away impurities deposited on the surface of the electrode, so that the electrochemical reaction of the electrode is not influenced, and a good flocculation effect is ensured. Finally, the treated water enters the high-density tank 4 from the water outlet 705 for subsequent treatment. The steps of the subsequent processing are the same as in the first embodiment.

EXAMPLE III

The invention is an embodiment improved on the basis of the first embodiment and/or the third embodiment. In this embodiment, only the system parts different from those in the first and second embodiments are described, and the description of the same system parts is omitted.

The first and second electrically-driven ionic membrane devices 23 and 26 of the present invention each include an anode and a cathode disposed at a distance. A fill chamber is provided between the anode and the cathode. The filling chamber is insulated from the anode and the cathode by a diaphragm, respectively. The anode and cathode are made of activated carbon fiber. The diaphragm is an ion exchange membrane or an insulating porous diaphragm. The filling cavity is filled with a plurality of activated carbon particles with the particle size of 0.1-5.0 mm, carbon fibers or carbon nanotubes. Preferably, the filling chamber is filled with a plurality of activated carbon particles with the particle size of 0.1-5.0 mm.

And (3) the pretreated salt-containing solution enters a cavity of the electrically-driven ionic membrane device and is filled in the filler layer or the filler layer is immersed in the salt-containing solution. The power supply system provides a direct-current constant-voltage electric field for the electrically-driven ionic membrane device, so that anions and cations move towards the two electrodes under the action of the direct-current electric field and are adsorbed on the surfaces of the two electrodes, and ions in the salt-containing solution are separated from the salt-containing solution, thereby realizing desalination. In this example, the thickness of the middle filler layer was 2cm, and the dc voltage was 1.2V. The surface of the filler is provided with the double electric layers, so that the charge density is higher, the resistance of ion migration is reduced, the migration of ions is accelerated, and the desalting speed of electro-adsorption desalting is improved.

The first electrically driven ionic membrane device 23 carries out electrically driven ionic membrane separation on the passing moderately concentrated water, and the separated desalted water enters the secondary reverse osmosis device 62. The filtrate from the first electrically driven membrane device 23 enters the second electrically driven membrane device 26. The second-stage electrically-driven membrane device 26 is used for carrying out electrically-driven ionic membrane separation on the filtrate again, and the separated desalted water enters the zero-emission unit.

According to a preferred embodiment, the inventive circulation reduction unit comprises at least two electrically driven ionic membrane devices. Namely, in the circulation reduction unit, at least one electrically-driven ionic membrane device is added between a first electrically-driven ionic membrane device and a second electrically-driven ionic membrane device so as to form a multi-stage electrically-driven ionic membrane device, and the saline wastewater is deeply concentrated.

According to a preferred embodiment, the electrically-driven ionic membrane device comprises a membrane stack, an electrode device, an ion exchange membrane, a positive electrode chamber and a negative electrode chamber. The inner side of the positive electrode cavity is provided with a cation exchange membrane, a positive electrode protection chamber, an anion exchange membrane and a first membrane stack concentration chamber towards the negative electrode direction. The inner side of the negative electrode cavity is provided with a cation exchange membrane, a negative electrode protection chamber, an anion exchange membrane and a membrane stack tail end concentration chamber towards the positive electrode direction. The water flow is divided into a first-stage two-section or a first-stage multi-section from the inlet to the outlet by the cation exchange membrane. Two adjacent concentrating chambers are arranged successively after the cation exchange membrane is reversed according to the direction of water flow from the inlet to the outlet. And a cation exchange membrane is arranged between two adjacent concentrating chambers. The first concentrating chamber after the water flow is reversed is filled with macroporous mixed bed resin. The macroporous mixed bed resin contains 50-100% of anion resin by volume ratio. The electrically-driven ion exchange membrane can synchronously realize concentration and purification of salt-containing wastewater.

According to a preferred embodiment, the electrically-driven ionic membrane device of the invention comprises a membrane stack, an electrode device, an ion exchange membrane, a positive plate and a negative plate. The inner side of the positive plate is provided with a cation exchange membrane, a positive electrode protection chamber, an anion exchange membrane and a membrane stack first concentration chamber towards the negative electrode direction. The inner side of the negative electrode cavity is provided with a cation exchange membrane, a negative electrode protection chamber, an anion exchange membrane and a membrane stack tail end concentration chamber towards the positive electrode direction. The water flow is divided into a first-stage two-section or a first-stage multi-section from the inlet to the outlet by the cation exchange membrane. Two adjacent concentrating chambers are arranged successively after the cation exchange membrane is reversed according to the direction of water flow from the inlet to the outlet. And a cation exchange membrane is arranged between two adjacent concentrating chambers. The first concentrating chamber after the water flow is reversed is filled with macroporous mixed bed resin. The macroporous mixed bed resin contains 50-100% of anion resin by volume ratio. The electrically-driven ion exchange membrane can synchronously realize concentration and purification of salt-containing wastewater.

A plurality of membrane pairs, which are a combination of an anode membrane, a cathode membrane and a separator, are arranged regularly between the anode and the cathode. The positive film and the negative film are homogeneous films with low film resistance and high performance and clapboards for effectively improving the flow state of water flow. The membrane can still keep higher ion dynamic exchange capacity, lower membrane surface resistance and lower water migration and permeability in the process of concentrating high-concentration brine. The power supply adopts a high-frequency direct current power supply with positive and negative polarities automatically switched, the module utilizes a digital program to control the power supply, and the adjustable-gap high-frequency oscillation is adopted to output high-frequency reverse polarity direct current to disturb a polarizing layer which is easy to form on the surface of the membrane, so that calcium and magnesium cations with high concentration times in the polarizing layer formed on the surface of the membrane are damaged, the molecular disproportionation of the polarizing layer caused by the crystallization process is damaged, the formation of compact salt scale is effectively prevented, the hydrodynamic condition is optimized, and the power consumption is effectively reduced by 30-50%.

The circulating pretreatment unit discharges salt-containing solution to enter a compartment of a deep concentration electric-driven ionic membrane device, an electric-driven ionic membrane causes anions and cations in the salt-containing solution flowing through the compartment to directionally move under the action of an external direct current electric field, the anions move towards the direction of an anode, and the cations move towards the direction of a cathode, so that ions in the solution of a fresh water compartment are transferred into a concentrated water compartment, the ions in the salt-containing solution are separated from the salt-containing solution, and concentrated water and desalted fresh water are obtained.

After the salt-containing wastewater to be treated is treated by the circulating pretreatment unit, the obtained salt-containing wastewater respectively enters the desalting chamber and the concentrating chamber in the first electrically-driven ionic membrane device 23 according to different flow ratios, and under the driving of a direct current electric field, the separation action of an anion-cation exchange membrane and the promotion and transmission action of filled resin, heavy metal ions and anions in the water flow of the desalting chamber migrate to enter the concentrating chamber, so that fresh water flow is obtained. The water flow in the concentration chamber is subjected to partial circulation or closed circulation, the concentration of the water flow is continuously increased, and the concentrated solution of the waste metal is obtained. The fresh water is transmitted to a fresh water recovery system, and the concentrated water enters a second electrically-driven ionic membrane device for concentration again. And finally, enabling the obtained concentrated solution to enter a zero-emission system, and evaporating and crystallizing to obtain nitrate and sodium salt. Thereby realizing zero discharge of the salt-containing wastewater and realizing continuous, clean and environment-friendly treatment of the salt-containing wastewater.

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 treatment system for salt-containing wastewater comprises a circulation pretreatment unit, a circulation reduction unit and a zero discharge unit which are arranged in sequence,

the zero-emission unit recovers nitrate and sodium salt in the concentrated mixed salt solution by heating, evaporating and crystallizing the concentrated mixed salt solution, wherein the zero-emission unit at least comprises a raw material feeding preheater (29), a nitrate evaporation and crystallization device (30), a nitrate thickener (36), a nitrate circulating pump (33), a first steam compressor (35), at least one drying device, a cooling water system (43) and a salt evaporation and crystallization device (52),

the nitrate evaporative crystallization device (30) sequentially passes through a nitrate circulating pump (33) and a first heater (31) and then discharges the concentrated mixed salt solution discharged by the circulation reduction unit preheated by the raw material feed preheater (29) back to the nitrate evaporative crystallization device (30) for circulation heating so as to carry out evaporative crystallization, concentration and separation to obtain nitrate and feed liquid,

the feed liquid enters a centrifugal separator (37) through the nitrate thickener (36) to package the centrifugally separated nitrate salt into commercial nitrate salt after being dried by a first drying device (38),

freezing the nitre mother liquor separated by the centrifugal separator (37) to-5 ℃, then feeding the nitre mother liquor into a frozen nitre crystallization device (42), returning the separated nitre decahydrate to the raw material feed preheater (29) by a frozen nitre centrifugal separator (48) for carrying out cyclic crystallization separation of nitrate,

the supersaturated feed liquid separated by the frozen nitre centrifugal separator (48) is discharged to the salt evaporation crystallization device (52) to be centrifugally separated to obtain commercial salt;

the circulating pretreatment unit is used for filtering the produced water after the high-salinity wastewater reacts with the pretreatment agent through a tubular micro-filter (6) and then discharging the filtered produced water to the circulating reduction unit, wherein the circulating pretreatment unit at least comprises a regulating tank (2), a high-density tank (4), the tubular micro-filter (6) and a sludge tank (60),

the high-density pond (4) discharges sludge generated by mixing the saline wastewater homogenized and uniformly regulated by the regulating pond (2) with the pretreatment agent to the sludge pond (60) at the lower part of the high-density pond under the action of gravity, and the produced water treated by the pretreatment agent in the high-density pond (4) enters a circulating reduction unit for treatment after being subjected to microfiltration treatment by the tubular microfilter (6);

sludge in the sludge tank (60) is subjected to sludge-water separation in a pressure filtration mode by a sludge dewatering and drying device (61), and water obtained after separation is discharged back to the adjusting tank (2) or the high-density tank (4) for recycling pretreatment again;

the circulation reduction unit carries out preliminary reduction treatment on the produced water treated by the circulation pretreatment unit through a reverse osmosis device, carries out deep concentration treatment through a multi-stage electric drive ionic membrane device consisting of at least one electric drive ionic membrane device so as to further reduce and separate the water in the high-salt-content wastewater to a fresh water tank (63) for recycling, and discharges the concentrated mixed salt solution obtained by deep concentration to the zero emission unit, wherein the circulation reduction unit at least comprises at least one electric drive ionic membrane device, a medium-pressure reverse osmosis device (11), a high-pressure reverse osmosis device (15), an activated carbon filter (18), a second tubular micro-filter (19), a second-stage reverse osmosis device (62) and a fresh water tank (63),

the high-pressure reverse osmosis device (15) is used for concentrating the concentrated water obtained by concentrating the produced water discharged by the circulating pretreatment unit in a medium-pressure reverse osmosis filtration mode by the medium-pressure reverse osmosis device (11) so as to perform primary reduction treatment on the produced water;

fresh water generated by the medium-pressure reverse osmosis device (11) and the high-pressure reverse osmosis device (15) is purified in a reverse osmosis and ultraviolet sterilization mode through the secondary reverse osmosis device (62) and then is recycled to the fresh water tank (63);

the activated carbon filter (18) and the second tubular micro-filter (19) sequentially filter reverse osmosis concentrated solution and soften calcium and magnesium ions, and then the reverse osmosis concentrated solution is discharged to the multistage electrically-driven ionic membrane device for deep reduction treatment;

the multistage electrically-driven ionic membrane device comprises a first electrically-driven ionic membrane device (23) and a second electrically-driven ionic membrane device (26), wherein the TDS of the first electrically-driven ionic membrane device (23) concentrated and filtered by the second electrically-driven ionic membrane device (26) is 1.2 × 10⁵Carrying out secondary concentration and filtration on mg/l concentrated water to obtain TDS of 2 × 10⁵mg/l of a concentrated mixed salt solution, wherein,

the desalted water separated by the second electrically-driven ionic membrane device (26) is discharged back to the medium-pressure reverse osmosis device (11) to be subjected to circulating reduction treatment of primary reduction and deep concentration, wherein,

raw water is subjected to reverse osmosis concentration and preliminary reduction through a circulation pretreatment unit and a circulation reduction unit, the generated high-salt-content concentrated water is subjected to heat exchange with high-temperature condensate water through a raw material reduction preheater (29), the high-salt-content concentrated water is heated by a heat exchanger and then enters a nitrate evaporation crystallization device (30), and feed liquid and a first heater (31) are subjected to circulating heating through a nitrate circulating pump (33).

2. The salt-containing wastewater treatment system according to claim 1, wherein the saltpeter evaporation crystallization device (30) compresses the low-temperature secondary exhaust steam generated by evaporation through a first steam compressor (35) under the condition of negative pressure or slight positive pressure to increase the temperature of the exhaust steam, so that the circulating heating device formed by the saltpeter circulating pump (33), the first heater (31) and the saltpeter evaporation crystallization device (30) has continuous and stable heat energy,

the nitrate evaporative crystallization device (30) utilizes a first vapor compressor (35) to draw and compress secondary vapor, and is connected with a cooling water system (43) through the first vapor compressor (35) according to the temperature required by frozen nitrate crystallization, and utilizes a cooler (45) and/or a freezing station (44) to maintain the temperature required in the frozen nitrate crystallization device (42).

3. The salt-containing wastewater treatment system according to claim 2, wherein the nitrate mother liquor separated by the centrifugal separator (37) enters a nitrate mother liquor tank (39) and enters the frozen nitrate crystallization device (42) through a nitrate mother liquor pump (41) for cooling and crystallization, the nitrate mother liquor is crystallized in the frozen nitrate crystallization device (42) and then is discharged to a first thickener (47) for adjustment, the frozen nitrate crystallization device (42) is connected with a cooler (45) and enables the frozen nitrate crystallization device (42) to be kept at-6 to-5 ℃ through a cold nitrate circulating pump (46), and the frozen nitrate mother liquor enters a preheater (51) through a frozen nitrate mother liquor pump (50) for heating and then enters the salt evaporation crystallization device (52) for evaporation and crystallization under negative pressure;

the salt evaporation crystallization device (52) is connected with a second heater (54) through a circulating pump (53) to heat the salt evaporation crystallization device (52), secondary steam generated by the salt evaporation crystallization device (52) is extracted through a second steam compressor (55) and used for heating liquid in the preheater (51) after the temperature of the secondary steam is increased through the second heater (54),

and (3) feeding the product after salt evaporation crystallization into a salt centrifugal separator (57) through a second thickener (56) for separation, and drying the crystals through second drying equipment (58) to obtain the sodium salt of the commodity.

4. The saline wastewater treatment system according to claim 1, wherein a spiral-flow type electrocoagulation device (700) is connected between the conditioning tank (2) and the high-density tank (4), the spiral-flow type electrocoagulation device (700) comprises a first cathode (702), a first anode (703), a water inlet (701), a water outlet (705), a reaction chamber formed by the first cathode (702) and the first anode (703), an insulating fixing sealing cover (704) and an insulating sealing support plate (706), the insulating fixing sealing cover (704) is arranged on the upper portion of the first cathode (702), the first anode (703) formed by a cylindrical rod is fixed by the insulating fixing sealing cover (704) by taking the center of the first cathode (702) as an axis, the insulating sealing support plate (706) is arranged on the lower portion of the first cathode (702), the water inlet (701) is arranged on the lower end of the housing on one side of the first cathode (702), the water outlet (705) is arranged at the upper end of the shell at the other side of the first cathode (702), and the water inlet (701) and the water outlet (705) are arranged in the tangential direction of the section of the shell of the first cathode (702) in the same direction;

the electrocoagulation device (700) enables the salt-containing wastewater homogenized and uniformly regulated by the regulating tank (2) to enter the reaction chamber from the water inlet (701) in a tangent shape and flow in a spiral-flow manner in the reaction chamber, and the salt-containing wastewater is subjected to electrochemical reaction under the action of direct current applied to the electrodes, so that impurity particles contained in the salt-containing wastewater are subjected to flocculation.

5. The saline wastewater treatment system according to claim 1, wherein the first electrically-driven ionic membrane device (23) and the second electrically-driven ionic membrane device (26) each comprise a second anode and a second cathode which are arranged at intervals, at least one membrane pair composed of a positive membrane, a negative membrane and a partition plate is arranged between the second anode and the first cathode in a regular arrangement, the positive membrane and the negative membrane are homogeneous membranes with low membrane resistance and high performance, the partition plate with uniform flow state is arranged between the positive membrane and the negative membrane, the power supply is a positive polarity and automatic switching high-frequency direct current power supply, the module controls the power supply by using a digital program, high-frequency oscillation with adjustable gaps is adopted to output high-frequency reversed polarity direct current to disturb easily formed polarized layers on the membrane surfaces, calcium and magnesium cations under high concentration times in the polarized layers formed on the membrane surfaces are destroyed, and the crystallization process is destroyed to cause molecular disproportionation, physical scale inhibition is exerted, hydrodynamic conditions are optimized, the power consumption is effectively reduced by 30-50%,

the circulating pretreatment unit discharges salt-containing solution to enter a compartment of a deep concentration electric-driven ionic membrane device, the electric-driven ionic membrane causes anions and cations in the salt-containing solution flowing through the compartment to directionally move under the action of an external direct current electric field, the anions move towards the direction of a second anode, and the cations move towards the direction of a second cathode, so that ions in the solution of the fresh water compartment are transferred into a concentrated water compartment, the ions in the salt-containing solution are separated from the salt-containing solution, and concentrated water and desalted fresh water are obtained.

6. The saline wastewater treatment system according to claim 5, wherein said cyclic pretreatment unit further comprises at least one intermediate water tank,

the adjusting tank (2) is connected with the high-density tank (4) which is connected with at least one dosing device through a lifting pump so as to enable the salt-containing wastewater to be coagulated and softened and precipitated after reaction with medicines, the high-density tank (4) is connected with the tubular micro-filter (6) through a first booster pump so as to discharge the treated produced water to the first intermediate water tank, the high-density tank (4) is connected with the sludge tank (60) so as to dehydrate the precipitated sludge, and the sludge tank (60) is connected with the adjusting tank (2) so as to discharge the dehydrated produced water to the adjusting tank (2) for cyclic pretreatment;

the circulation pretreatment unit still includes the filter core filter, the filter core filter is connected tubular micro filter (6) with between the pond in the middle of the first, sludge impoundment (60) are connected with and are used for carrying out dehydration mummification's sludge dewatering mummification device (61) to mud.