CN115465995A

CN115465995A - Membrane separation salt and nitrate-based salt-containing wastewater recycling treatment system and method

Info

Publication number: CN115465995A
Application number: CN202211161777.7A
Authority: CN
Inventors: 权秋红; 郭以果; 元西方; 鲁喜平
Original assignee: Bestter Group Co ltd
Current assignee: Bestter Group Co ltd
Priority date: 2022-09-22
Filing date: 2022-09-22
Publication date: 2022-12-13

Abstract

The invention relates to a membrane separation salt nitrate-based salt-containing wastewater circulating treatment system and method, which comprises a pretreatment unit and an NF membrane separation device, wherein the pretreatment unit is used for separating sodium chloride and sodium sulfate from salt-containing wastewater at least once according to the water inlet requirement of the NF membrane separation device with impurity concentration; the NF membrane separation device discharges the nitrate-poor sodium chloride-rich water to a sodium chloride production unit in a mode that the generated nitrate-poor sodium chloride-rich water can meet the concentration of sodium chloride required by a sodium chloride production unit, and conveys the nitrate-rich high-impurity concentrated water to a sodium sulfate production unit in a mode of refluxing to a pretreatment unit; the NF membrane separation device comprises at least two mutually-nanofiltration devices which can be communicated based on the concentration of sulfate ions in the water produced by the sodium chloride rich in nitrate, and the at least two mutually-nanofiltration devices can be communicated to different treatment parts of the pretreatment unit based on the nitrate content in the concentrated water rich in nitrate and high impurities.

Description

Membrane separation salt and nitrate-based salt-containing wastewater recycling treatment system and method

Technical Field

The invention relates to the technical field of salt-containing wastewater purification, in particular to a membrane separation salt and nitrate-based salt-containing wastewater circulating treatment system, equipment and a method.

Background

High salt waste water, desulfurization waste water, hydrophobic water and the like generated in industries such as the coal chemical industry, the stone chemical industry, electric power, cogeneration, coal mine hydrophobic water, metallurgy, nonferrous materials, pharmacy, papermaking, natural gas purification, comprehensive park industrial waste water and the like generally have high salt content, high hardness, complex components such as silicon, fluorine, organic matters and the like, are not treated, are stored and placed, and tend to cause pollution factors to the surrounding environment, and serious regional environmental pollution is caused after long-term accumulation. In view of the requirements of tail water treatment in the industries, the tail water cannot meet the environmental protection requirements through simple treatment, and serious pollution is caused to the received water and underground water after discharge, so that near zero discharge of high-salinity wastewater gradually becomes a final treatment trend and approach of the high-salinity wastewater in order to protect ecological environment for people to live and meet self requirements of resource utilization. In the design of the comprehensive high-salt-content wastewater treatment zero-emission process, the final solid product can be separated out at higher purity, about 90% of sodium sulfate and sodium chloride in high-salt water can be sold as a zero-emission byproduct as industrial raw materials, the impurity salt amount in the zero-emission treatment process is greatly reduced, a large amount of sodium sulfate and sodium chloride are not treated as solid hazardous waste, the environment-friendly benefit and the resource recycling value are very high, about 10% of the impurity salt in the near place is treated as the hazardous waste, and the cost and the resource are saved remarkably.

Comprehensive high-salinity concentrated water (the TDS is more than 5000mg/l generally) discharged by enterprises and accepted by gardens at present, high-salinity wastewater contains a large amount of organic matters and complex impurities and is generally not suitable for removing the organic matters by adopting the traditional biological treatment degradation, and the pretreatment adopted more frequently is' hardness removal double-alkali softening pretreatment → reduction → high-salinity water deep treatment for hardness removal, silicon removal, fluorine removal and the like → NF → sodium nitrate-poor chloride water production → concentration → evaporative crystallization → sodium chloride; NF → rich nitrate high-impurity concentrated water → organic matter removal (measures such as advanced oxidation, resin adsorption and high-temperature treatment) → evaporative crystallization → sodium sulfate; the 'near zero emission' process technical route has the advantages that the purity of the finally produced sodium sulfate and sodium chloride crystal salt is not high, the impurity content is higher, the quality of the sodium sulfate and the sodium chloride obtained by the process route is unstable and poor, and the aim of comprehensively utilizing the saltpeter as an industrial raw material is difficult to achieve; the process route has the advantages that the amount of the generated miscellaneous salt is large, the miscellaneous salt contains a large amount of organic matters and complex components, the generated miscellaneous salt is solid dangerous waste and needs to be treated by qualified professional companies, the cost for treating the solid dangerous waste in China is basically more than 3000-4000 yuan/ton, the treatment cost is very high, the treatment bottleneck of a large amount of zero-discharge crystalline salt is formed, the small-scale treatment capacity of the professional companies is very limited at present, and the treatment requirement of the large amount of miscellaneous salt generated by the zero-discharge treatment of the waste water of a plurality of industrial enterprises cannot be met.

For example, chinese patent publication No. CN209188174U discloses a device for crystallizing a salt, which comprises at least a pre-separation unit, a first crystallization unit, a second crystallization unit and a heating unit. The pre-separation unit at least comprises a nanofiltration unit; the first crystallization unit comprises at least a first heat exchanger and a first crystallizer. The second crystallization unit comprises at least a second heat exchanger and a second crystallizer. Wherein the nanofiltration unit is connected with the first crystallizer through the first heat exchanger. The heating unit is connected with the first crystallizer through the first heat exchanger. The nanofiltration unit is connected with the second crystallizer through a second heat exchanger. The heating unit is connected with the second crystallizer through a second heat exchanger. Ions in the incoming water are separated in advance through a nanofiltration unit, and the separated solution is concentrated, heated and crystallized respectively, so that the obtained crystals have higher purity.

Furthermore, on the one hand, due to the differences in understanding to the person skilled in the art; on the other hand, as the inventor studies a lot of documents and patents while making the present invention, but the space is not detailed to list all the details and contents, however, this invention doesn't have these prior art features, but this invention has all the features of the prior art, and the applicant reserves the right to add related prior art in the background art.

Disclosure of Invention

Aiming at the defects of the prior art: the most main components in the comprehensive high-salt wastewater are sodium chloride and sodium sulfate, the ratio of the two salts to the total salt is relatively high, usually more than 90%, so the current mainstream technical route is as follows: pretreatment → reduction → retreatment → NF → high nitrate-rich high-impurity concentrated water is reduced respectively → retreatment → salt separation evaporation crystallization and low sodium chloride water production → concentration (optional) → salt separation evaporation crystallization; pretreatment → NF → respectively reducing the rich nitrate and high-impurity concentrated water → retreatment → salt separation evaporation crystallization and the poor nitrate and sodium chloride water production → concentration → salt separation evaporation crystallization; in the process, NF is contacted with a large amount of organic impurities, the frequent chemical cleaning of the NF membrane is considered, and the permeation of small molecular organic matters enters an evaporative crystallization system, so that the stable operation of salt separation through the process route and the frequent use cost of replacement of the NF membrane are caused to be high, the evaporative crystallization of sodium chloride and sodium sulfate is influenced by the adverse effect of low impurities on the purity, or a large amount of miscellaneous salts is generated, particularly the content of sodium nitrate in high-salt water is high, and the quantity of miscellaneous salts is increased more.

The invention provides a membrane separation salt nitrate-based salt-containing wastewater circulating treatment system, which comprises a pretreatment unit and an NF membrane separation device, wherein the pretreatment unit is used for separating sodium chloride and sodium sulfate from salt-containing wastewater at least once according to the water inlet requirement of the NF membrane separation device with impurity concentration; the NF membrane separation device discharges the nitrate-poor and sodium-rich water to the sodium chloride production unit and conveys nitrate-rich high-impurity concentrated water to the sodium sulfate production unit in a manner of refluxing the nitrate-rich high-impurity concentrated water to the pretreatment unit according to the manner that the generated nitrate-poor and sodium-rich water can meet the sodium chloride concentration required by the sodium chloride production unit; the NF membrane separation device comprises at least two mutual nanofiltration devices which can be communicated based on the sulfate ion concentration in the water produced by the sodium chloride rich in nitrate and the at least two mutual nanofiltration devices can be communicated to different treatment parts of the pretreatment unit based on the nitrate content in the rich-nitrate high-impurity concentrated water.

According to a preferred embodiment, the pretreatment unit comprises at least a primary purification part and a secondary purification part, wherein the primary purification part is used for separating out sodium sulfate and sodium chloride in the salt-containing wastewater in a mixed salt manner under the condition of certain impurity concentration; the second-stage purification part freezes the rich-nitrate mother liquor prepared based on the mixed salt so as to separate out sodium sulfate in a decahydrate mode, so that frozen lean-nitrate mother liquor is generated and discharged to the NF membrane separation device, the NF membrane separation device discharges the rich-nitrate high-impurity concentrated water to different processing equipment of the second-stage purification part based on the nitrate content in the rich-nitrate high-impurity concentrated water, and the different processing equipment at least comprises a freezing crystallizer.

According to a preferred embodiment, the NF membrane separation device has a sodium sulfate rejection rate of 95-98% and a sodium chloride rejection rate of-10%.

According to a preferred embodiment, the primary and secondary purification sections are provided with separation units for controlling the water content of the mixed salt, which is 4% to 5%.

According to a preferred embodiment, the secondary purification part uses a coolant to separate out sodium sulfate in a supersaturated state in a cooling process in a decahydrate manner under the condition that a near-saturated sodium sulfate and sodium chloride solution which are hot-melted and matched based on the mixed salt are precooled to obtain a precooled feed liquid, and the coolant can reduce the temperature of the precooled feed liquid to minus 5-0 ℃ to obtain a frozen feed liquid.

According to a preferred embodiment, after the sodium sulfate decahydrate is at least subjected to hot melting and condensed water hot melting in a sodium sulfate production unit to prepare a near-saturated sodium sulfate solution, the sodium sulfate solution and the condensed water are subjected to heat exchange and heating, and the sodium sulfate solution is concentrated through multi-effect countercurrent evaporation crystallization, so that sodium sulfate in the solution is continuously concentrated to be supersaturated and separated out and gradually grows and deposits in sodium sulfate foot.

According to a preferred embodiment, the pretreatment unit is communicated with the NF membrane separation device through a filtering device, the filtering device is used for further removing impurities from the frozen nitrate-depleted mother liquor in a manner according with the impurity concentration requirement of the NF membrane separation device to obtain an impurity liquid, and an impurity liquid outlet of the filtering device is communicated with the primary purification part, so that the primary purification part can purify a mixed salt containing sodium sulfate crystals and sodium chloride crystals in a manner of approximately equalizing the impurity concentration in the saline wastewater.

According to a preferred embodiment, concentrated brine waste is concentrated at least once before entering the primary purification section, so that the TDS value of the concentrated brine waste is 6 to 20 ten thousand ppm.

According to a preferred embodiment, the invention also discloses a method for circularly treating the salt-containing wastewater based on membrane separation of saltpeter, which comprises the following steps: the pretreatment unit is used for separating sodium chloride and sodium sulfate from the salt-containing wastewater at least once according to the water inlet requirement of the impurity concentration NF membrane separation device; the NF membrane separation device discharges the nitrate-poor sodium chloride-rich water to a sodium chloride production unit in a mode that the generated nitrate-poor sodium chloride-rich water can meet the sodium chloride concentration required by a sodium chloride production unit, and transmits nitrate-rich high-impurity concentrated water to a sodium sulfate production unit in a mode of refluxing to the pretreatment unit; wherein the NF membrane separation device is configured to comprise at least two mutual nanofiltration devices capable of communicating based on the sulfate ion concentration in the nitrate-rich sodium chloride producing water, the at least two mutual nanofiltration devices being capable of communicating to different treatment sections of the pretreatment unit based on the nitrate content in the nitrate-rich high-impurity concentrated water.

According to a preferred embodiment, the pretreatment unit is configured to at least comprise a primary purification part and a secondary purification part, wherein the primary purification part is used for separating out sodium sulfate and sodium chloride in the salt-containing wastewater under the condition of certain impurity concentration in a mixed salt manner; the second-stage purification part freezes the rich-nitrate mother liquor prepared based on the mixed salt so as to separate out sodium sulfate in a decahydrate mode, so that frozen lean-nitrate mother liquor is generated and discharged to the NF membrane separation device, the NF membrane separation device discharges the rich-nitrate high-impurity concentrated water to different processing equipment of the second-stage purification part based on the nitrate content in the rich-nitrate high-impurity concentrated water, and the different processing equipment at least comprises a crystallizer.

Drawings

FIG. 1 is a block diagram of a processing system provided by the present invention;

FIG. 2 is a schematic view of a crystallizer according to the present invention;

FIG. 3 is a schematic view of the structure of a draft tube provided by the present invention;

FIG. 4 is an enlarged schematic structural view of a preferred counterflow section of the present invention;

FIG. 5 is a schematic block diagram of a portion of a preferred cyclic processing system of the present invention.

List of reference numerals

100: a primary purification section; 400: a sodium sulfate production unit; 200: a secondary purification section; 500: a sodium chloride production unit; 300: a third purification part; 201: a crystallizer; 202: a mixing zone; 203: a flow guide pipe; 204: a flow dividing section; 205: settling holes; 206: a baffle plate; 207: a settling zone; 208: an outlet port; 209: a bottom; 210: a first expansion section; 211: a second expansion segment; 212: a housing; 213: a baffling cylinder; 214: an overflow port; 215: a first vortex section; 216: a second vortex section; 401: a first counterflow section; 402: a second counterflow section; 403: a first substream segment; 404: a second substream section.

Detailed Description

This is described in detail below with reference to fig. 1-4.

In the invention, english abbreviations and corresponding Chinese paraphrases are as follows:

TDS: total dissolved solids, total amount of all solutes in water, i.e.: total amount of soluble solids. Generally, organic matter and inorganic matter in molecular form contained in natural water are not considered, and therefore the salt content is referred to as TDS.

NF: and (4) a nanofiltration device. Nanofiltraction, nanofiltration, is used to separate out relatively small molecular mass materials, such as sodium chloride, from the solvent.

MVR: the vapor mechanically recompresses the evaporator.

TVR: a vapor thermal recompression evaporator.

DTRO: dish tubular reverse osmosis unit.

ED: an electrodialysis device.

And (3) RO: a reverse osmosis device.

Example 1

The embodiment discloses a salt-containing wastewater recycling treatment system based on membrane separation of salt and nitrate. The system includes a pretreatment unit and an NF membrane separation unit 300b. The pre-treatment unit includes at least a primary purification section 100 and a secondary purification section 200. The pretreatment unit performs at least one sodium chloride and sodium sulfate separation on the salt-containing wastewater according to the water inlet requirement of the impurity concentration NF membrane separation device 300b. Specifically, the method comprises the following steps:

first-stage purification section 100: the high-salt-content wastewater enters a thermal method (MVR/multiple-effect/TVR) evaporation crystallization system after passing through a pretreatment device, the generated magma is thickened, concentrated, separated and dehydrated to produce sodium sulfate and sodium chloride (mixed salt), the sodium chloride and sodium sulfate mixed salt with low impurity content is obtained preliminarily, the sodium sulfate and sodium chloride separated out by main crystallization are isolated from high-content organic matters in the enriched mother liquor and impurities such as sodium nitrate, fluorine ions, silicon and the like, and the process is a primary salt nitrate purification process. The separated impurities do not enter the secondary purification part 200 and the tertiary purification part 300, and especially do not block the membrane pores in the tertiary purification part 300, so that the tertiary purification part 300 can be continuous. Part of the mixed salt mother liquor discharged from the primary purification part 100 enters a mixed salt production unit (adopting a thermal method for drying) to produce the mixed salt mainly containing organic substances, sodium nitrate, salt nitrate and impurities.

Second-stage purification section 200: sodium chloride and sodium sulfate produced by purification, evaporation, crystallization and separation enter a dissolving and stirring tank or a groove, condensed water is added and stirred for dissolution, saturated concentration sodium sulfate and sodium chloride solution are prepared, salt and nitrate solution enters a liquid storage barrel and is pumped into a freezing and crystallizing system, the temperature of the liquid is controlled by a crystallizer of the freezing and crystallizing system, decahydrate is crystallized and separated, the produced decahydrate is redissolved and then enters a sodium sulfate production unit 400 (a multi-effect nitrate evaporation and crystallization device is adopted), finally, sodium sulfate liquid is evaporated and concentrated by steam heating to achieve the supersaturated production of sodium sulfate crystals, and high-purity sodium sulfate (commonly called as glauber salt) is obtained by thickening, separation and drying.

Preferably, the NF membrane separation apparatus 300b discharges the nitrate-depleted and sodium chloride-enriched produced water to the sodium chloride production unit 500 and returns the nitrate-enriched and high-impurity concentrated water to the pretreatment unit in such a manner that the produced nitrate-depleted and sodium chloride-enriched produced water can meet the required sodium chloride concentration of the sodium chloride production unit 500. Preferably, the NF membrane separation apparatus 300b comprises at least two mutual nanofiltration devices that can be communicated based on the sulfate ion concentration in the nitrate-rich sodium chloride production water, the at least two mutual nanofiltration devices being capable of being communicated to different treatment sections of the pretreatment unit based on the nitrate content in the nitrate-rich high-impurity concentrated water. As shown in fig. 5, the NF membrane separation apparatus 300a may be provided as a part of the three-stage purification section 300, which is capable of communicating with a water outlet of the filtration apparatus 300 a. The water inlet of the filtering means 300a is communicated with the secondary purification section 200. The filter device 300a may be a tube filter, a cartridge filter. The filtering device 300a is arranged between the secondary purification part 200 and the NF membrane separation device 300b, and is used for filtering the frozen lean nitre mother liquor so as to further reduce the impurity concentration of the NF membrane separation device 300b, and meet the liquid inlet requirement of the NF membrane separation device 300b. On one hand: the aperture of the nanofiltration membrane of the NF membrane separation device 300b is small, and the blockage of the NF membrane separation device 300b is easily caused by the overlarge particle size of impurities, so that the arrangement of the filtration device 300a can reduce the probability of the blockage of the nanofiltration membrane, effectively improve the separation efficiency of the NF membrane separation device 300b, and improve the purity of the obtained sodium chloride; on the other hand, the impurity liquid of the filtering device 300a can be used as the quenching and tempering liquid of the wastewater with high salt content, and when the impurity concentration in the wastewater with high salt content is too high or too low, the impurity liquid and the wastewater with high salt content can be mixed to control the impurity concentration in the range of the required impurity concentration of the first-stage purification part 100, so that the mixed salt can be more easily separated out.

Preferably, the NF membrane separation apparatus 300b includes at least one nanofiltration device. As shown in fig. 5, when the number of the nanofiltration devices is greater than or equal to 2, the former stage of nanofiltration device is connected in series and communicated in a way that the water produced by the poor sodium nitrate and chloride can be discharged to the next nanofiltration device, the content of sodium sulfate in the water produced by the poor sodium nitrate and chloride is reduced in a multistage way, and the interception rate of sodium sulfate is controlled between 95% and 98%; and the rich nitrate high-impurity concentrated water generated by each stage of nanofiltration device is discharged to the second-stage purification part 200, and is further used for nitrate extraction. Preferably, as shown in fig. 5, the NF membrane separation apparatus 300b includes a primary nanofiltration apparatus 300b-1, a secondary nanofiltration apparatus 300b-2, and an N-stage nanofiltration apparatus 300b-N (N is greater than or equal to 3). Through a pilot test, the interception rate of sodium sulfate is controlled to gradually increase according to the flow direction of produced water, and when the interception rate of sodium sulfate reaches 95-98%, the NF membrane separation device 300b discharges the nitrate-poor sodium chloride produced water to the sodium chloride production unit 500; and if the interception rate of the sodium sulfate does not reach 95-98%, the upper-stage nanofiltration device discharges the sodium chloride and nitrate-poor water to the lower-stage nanofiltration device. Preferably, the NF membrane separation apparatus 300b comprises a primary, secondary or tertiary nanofiltration apparatus, which is preferred, i.e. the purity of the produced sodium chloride is increased at the best cost. Because the interception rate of sodium sulfate is gradually controlled to be increased according to the flowing direction of produced water, the content of sodium sulfate in concentrated water rich in nitrate and high impurities discharged by an n-grade nanofiltration device is gradually reduced, and therefore, the concentrated water rich in nitrate and high impurities discharged by the first-grade nanofiltration device can be directly discharged to a crystallizer 201 for direct crystallization after being cooled; and concentrated water rich in nitrate and high in impurity discharged from the second-stage 8230; and concentrated water rich in nitrate and high in impurity discharged from the n-stage nanofiltration device needs to be further concentrated.

Preferably, the NF membrane separation device is at least a portion of three-stage purification section 300. Third purification unit 300: the nitre-poor mother liquor generated by freezing crystallization enters a three-stage purification part 300 (provided with an NF membrane separation device) to further re-separate sodium chloride and sodium sulfate. Concentrating the sodium chloride water (sodium chloride water) or directly feeding the sodium chloride water into a sodium chloride evaporative crystallization system, heating the sodium chloride feed liquid by steam, circularly evaporating to reach supersaturation, separating out a large amount of sodium chloride crystals from the feed liquid, thickening, concentrating, separating and drying to obtain high-purity sodium chloride; and returning the high-impurity concentrated water rich in the nitrate generated by the NF membrane separation device to the freezing crystallizer, and extracting the nitrate from the sodium sulfate in the high-impurity concentrated water rich in the nitrate. The invention can ensure the stability and high-efficiency operation of the salt separation crystallization system when the water quantity and the water quality of the system fluctuate, realize the thorough separation of sodium chloride and sodium sulfate, is not influenced by organic matters, nitrate and impurities, particularly has the advantages of obviously prolonged one-time use time and high stability of a membrane structure in the three-stage purification part 300, and has high purity of the produced sodium chloride and sodium sulfate and high recovery rate of product salt after multi-stage purification, can reduce the amount of miscellaneous salt in the system to the maximum extent and has low miscellaneous salt yield.

Preferably, the NF membrane separation device is configured to further separate sodium chloride and sodium sulfate in the frozen lean sodium chloride mother liquor discharged from the secondary purification unit, and the NF membrane separation device enters the sodium chloride production unit with the generated lean sodium chloride rich water according to a manner that can meet the sodium chloride concentration required by the sodium chloride production unit, so as to reflux the rich-nitrate high-impurity concentrated water to the secondary purification unit; the NF membrane separation device can be communicated with a filtering device, the filtering device can be communicated with the secondary purification part, the filtering device is used for further removing impurities of the frozen poor saltpeter mother liquor in a mode meeting the impurity concentration requirement of the NF membrane separation device to obtain impurity liquid, and an impurity liquid outlet of the filtering device is communicated with the primary purification part, so that the primary purification part can purify mixed salt containing sodium sulfate crystals and sodium chloride crystals in a mode of roughly balancing the impurity concentration in salt-containing wastewater. The NF membrane separation device has a sodium sulfate rejection rate of 95-98% and a sodium chloride rejection rate of-10%.

The processing system of the invention is concretely as follows:

1) A pretreatment device: a membrane concentration system is used for obtaining high-salinity concentrated water containing a large amount of organic matters, sodium nitrate and other impurities, and the produced water is recycled;

2) The concentrated high-salt water is subjected to mixed salt purification I, and sodium sulfate and sodium chloride are separated through evaporative crystallization to obtain relatively pure mixed salt of sodium sulfate and sodium chloride;

3) The first-stage purification part is used for purifying and purifying the high-salinity concentrated water by using salt and nitre; isolating the concentrated organic matter, sodium nitrate, silicon, fluorine and other impurity substances in the feed liquid to obtain relatively pure salt and nitrate mixed salt with the water content of about 5%;

4) Heating and supplementing a small amount of condensed water to dissolve salt and nitrate generated in the first-stage purification part to obtain pure sodium sulfate and sodium chloride solution saturated in crystallization; the mixed solution of nearly saturated sodium sulfate and sodium chloride enters a purification unit II;

5) A second-stage purification part, which is used for cooling the nearly saturated feed liquid of sodium sulfate and sodium chloride to separate out a low-temperature saturated sodium sulfate solution from sodium sulfate by decahydrate crystals to obtain pure sodium sulfate decahydrate crystals containing 10 crystal waters, so as to realize the purification treatment of the sodium chloride solution in the feed liquid;

6) The secondary purification part is used for heating and hot melting (or supplementing condensed water for hot melting) the generated sodium sulfate decahydrate, then feeding the sodium sulfate decahydrate into a sodium sulfate evaporation crystallization system for sodium sulfate recrystallization to separate out high-purity sodium sulfate, feeding a small amount of mother liquor discharged by sodium sulfate evaporation crystallization back to the primary purification part to recover sodium sulfate in the mother liquor and a small amount of impurities in balanced enrichment, feeding the mother liquor into a mixed salt crystallizer, and removing the impurities in a balanced manner through the mother liquor of the removed salts;

the purified feed liquid of the purification unit II is filtered, the filtered discharge liquid returns to a feed tank before the purification unit II, the filtered clear liquid enters an adjusting tank for blending, and then enters a purification unit III, and the blended sodium sulfate solution which mainly contains sodium chloride and is in small quantity is purified again;

7) The third purification part generates a nitrate-rich solution and returns the nitrate-rich solution to the second purification part; the purification unit III is used for generating a poor nitrate solution, and the poor nitrate solution enters a sodium chloride evaporation crystallizer to be evaporated and crystallized to separate out high-purity sodium chloride salt; the condensed water produced by the sodium chloride evaporative crystallizer after evaporative crystallization is completely recycled through heat exchange;

sodium chloride is evaporated and crystallized to generate a small amount of mother liquor, the mother liquor returns to the purification unit I, and sodium chloride is further recovered; a small amount of mother liquor discharged by salt evaporation crystallization returns to the primary purification part to recover sodium chloride and a small amount of impurities which are balanced and enriched in the mother liquor, the mother liquor enters a mixed salt crystallizer, and the impurities are removed through the balance of the mother liquor after the impurities are discharged;

8) And (3) enabling the mixed salt mother liquor discharged from the purification unit I to enter a mixed salt treatment system, separating out the mixed salt through evaporation and crystallization, and removing the mother liquor from the mixed salt mother liquor discharged from a mixed salt evaporation crystallizer to perform solidification treatment to obtain the mixed salt, wherein the impurity content of the system is mainly balanced.

Preferably, the multistage purification impurity separation salt separation crystallization system comprises a mixed salt evaporation crystallization treatment system, a mixed salt hot-melt sodium sulfate and sodium chloride saturated solution freezing crystallization treatment system, a sodium nitrate hot-melt (hot-melt) sodium sulfate evaporation crystallization system, a freezing mother liquor NF separation treatment system and a sodium chloride salt evaporation crystallization separation system.

Preferably, the pretreatment system comprises an AOP unit such as hardness-removing softening sedimentation clarification, a filter or membrane filtration, resin softening, advanced oxidation unit activated carbon and the like, so as to remove most of hardness, alkalinity, heavy metals, suspended substances, part of silicon, part of fluorine, alkali liquor for reaction, part of organic matters and other impurities in the wastewater.

Preferably, the purification, evaporation and crystallization processing system I comprises a crystallization process device such as multi-effect forced circulation evaporation crystallization, TVR evaporation crystallization, MVR falling film evaporation + forced circulation evaporation crystallization, flash evaporation and the like, wherein sodium sulfate and sodium chloride are separated out from the evaporation and concentration feed liquid when the evaporation and concentration feed liquid is salt nitrate in an oversaturated state, and mixed salt solids, CODcr, silicon, fluoride, suspended matters, alkali liquor obtained by reaction of pretreatment residues, scale inhibitors added by pretreatment, impurities of corrosion inhibitors remaining in the system and the like are thoroughly isolated, so that subsequent recrystallization and purification units ii and iii are carried out in a relatively alcoholic solution to respectively obtain pure sodium sulfate and sodium chloride solids; CODCr, silicon, fluoride, suspended solids, the alkali liquor which is the reaction residue after pretreatment, the scale inhibitor which is added after pretreatment, impurities of the corrosion inhibitor which is remained in the system and the like which are enriched in the feed liquid enter a mixed salt system through mother liquor discharge, the mother liquor is discharged through mixed salt evaporation crystallization and mixed salt evaporation crystallization for solidification, and the balance system is enriched with higher CODCr, silicon, fluoride, suspended solids, the alkali liquor which is the reaction residue after pretreatment, the scale inhibitor which is added after pretreatment, the impurities of the corrosion inhibitor which is remained in the system and the like.

In this example, purification I corresponds to the first-stage purification section 100, purification II corresponds to the second-stage purification section 200, and purification III corresponds to the third-stage purification section 300.

Example 2

This embodiment may be a further improvement and/or a supplement to embodiment 1, and repeated contents are not described again. The preferred embodiments of the present invention are described in whole and/or in part in the context of other embodiments, which can supplement the present embodiment, without resulting in conflict or inconsistency.

Preferably, the pretreatment unit includes at least the primary purification section 100 and the secondary purification section 200 of embodiment 1. The pretreatment unit also comprises a pretreatment device, and is mainly characterized in that the comprehensive high-salinity wastewater is subjected to mixing regulation, softening, hardness removal and suspended matter removal, filtering, resin hardness removal, membrane reduction concentration, concentrated high-salinity wastewater retreatment and silicon and fluorine removal, organic matter removal by advanced oxidation, activated carbon adsorption (advanced oxidation and activated carbon are arranged at a position before or after reduction according to the impurity content or between two-stage membranes, the reduced produced water is recycled, and the reduced produced concentrated water enters the concentration unit.

Preferably, the reduced concentrated water enters a concentration process (ED, DTRO, MVR falling film evaporation concentration or multiple effect evaporation) and is concentrated to about 6 to 20 ppm (preferably 10 to 20 ppm), and then enters the first-stage purification part 100: the multi-effect evaporative crystallization and the steam circularly exchange heat in the heating chamber, the feed liquid reaches the boiling point and is subjected to flash evaporation in the evaporation chamber, the circularly-performed feed liquid is concentrated, each effect feed liquid is gradually concentrated, the concentration of sodium sulfate and sodium chloride in the last effect feed liquid is continuously increased until reaching supersaturation and being separated out and gradually grown up and deposited on salt feet, the salt slurry liquid is discharged, wet salt sodium sulfate and sodium chloride are obtained through a thickening and centrifugal separation channel, and the water produced by the evaporator is completely recycled after heat exchange with the feed liquid. The content of impurities such as organic matters, silicon, fluorine and the like in the evaporative crystallization feed liquid is continuously enriched and increased through cyclic concentration of the evaporative crystallization feed liquid, a certain amount of mother liquid needs to be discharged, the total impurity content of an evaporation system is balanced by the impurity content of the discharged mother liquid, and the impurities of the evaporative crystallization system are approximately kept in a certain balance range, so that the purity of precipitated sodium sulfate and sodium chloride can be ensured by the ion content in the primary purification part 100.

Preferably, the system further comprises a miscellaneous salt production unit: the mixed salt mother liquor which is discharged from a mixed salt crystallizer in the primary purification part 100 and balances the impurities in the feed liquid enters a mixed salt mother liquor adjusting tank, the mixed salt mother liquor is continuously evaporated and crystallized through a mixed salt evaporation crystallizer to obtain mixed salt slurry, the mixed salt slurry is subjected to cyclone separation, the underflow mixed salt slurry enters a centrifugal machine for separation to obtain mixed salt, and the water content of the mixed salt is about 10-20 percent and then the mixed salt is treated; and (3) evaporating and crystallizing the miscellaneous salt, discharging the mother liquor, allowing the mother liquor to enter a miscellaneous salt mother liquor storage tank, and allowing the mother liquor to enter a miscellaneous salt mother liquor curing system for drying treatment to obtain the miscellaneous salt.

Preferably, there is a separation unit between the primary and

secondary purifier sections

100 and 200. The separation unit adopts a centrifugal separation mode to control the water content of the mixed salt of the crystalline sodium sulfate and the sodium chloride to be between about 4 and 5 percent. And carrying out hot melting on the mixed salt of the sodium sulfate crystal and the sodium chloride in a stirring tank by utilizing condensed water generated by the system to prepare a nearly saturated solution of the sodium sulfate and the sodium chloride. And the sodium sulfate and sodium chloride solution overflows to a mixed solution storage barrel, and then is sent to a precooler for precooling and cooling. And (3) when the precooled feed liquid reaches a precooling design temperature (generally between 22 and 27 degrees, preferably 25 degrees), the feed liquid enters a freezing crystallizer. The precooled feed liquid is circulated and exchanges heat with a secondary refrigerant (ethylene glycol solution or calcium chloride solution is selected, the preparation concentration is 15-25 percent, and the optimal selection is 20 percent) to reduce the temperature under the action of a crystallization chamber of a freezing crystallization system and a heat exchanger recirculation pump, sodium sulfate in the solution is separated out in the form of sodium sulfate decahydrate, and the final feed liquid operation temperature is controlled to be in the range of-5 ℃ to 0 ℃. The feed liquid separates out sodium nitrate decahydrate crystals, the sodium nitrate decahydrate crystals are settled and the supersaturation degree is eliminated, then sodium nitrate decahydrate solid is separated out through a centrifugal machine, and the sodium nitrate decahydrate enters a unit 500 for producing sodium sulfate (mainly comprising sodium nitrate sell-effect evaporation crystallization) after hot melting and condensed water hot melting to obtain the sodium sulfate.

Preferably, secondary purification section 200 includes a cryogenic crystallizer 201, as shown in fig. 2.

The crystallizer 201 comprises at least a shell 212. The housing 212 is roughly divided into a mixing zone 202, a flow guiding zone, and a settling zone 207 from top to bottom.

A baffling cylinder 213 is provided in the center of the mixing zone 202. An overflow 214 is provided in the housing 212 corresponding to the mixing zone. The overflow port 214 is provided in such a manner that the opening is inclined downward.

The bottom 209 of the housing 212 is approximately conical. A flow guide tube 203 is provided in the contact area between the bottom 209 and the baffle cylinder 213.

Draft tube 203 is arranged in a vertical flow direction and draft tube 203 is arranged above baffle 206 of settling zone 207. The baffle 206 is curved in a curved arc toward the direction of the draft tube 203. The curvature of the baffle 206 ranges from 0.8 to 2.4. The conical tip of the bottom 209 is provided with a discharge port 208 for discharging crystallized crystals.

In the prior art, the flow guide pipe 209 is arranged in a straight cylinder shape, so that the speed of the feed liquid does not have gradient change when the feed liquid passes through the flow guide pipe 29, and the problems of mixing strengthening of the material and control of the crystal particle size cannot be completely solved.

Based on the defect, the invention improves the guide pipe 203 in the crystallizer 201, and enhances the shearing and mixing effect in the guide pipe by improving the flow field distribution in the guide pipe. The invention realizes the grading control of crystal particles according to the particle sedimentation theory and simultaneously improves the crystallization rate of the crystals. The baffle 206 and the bottom enclose a settling zone 207. The baffle 206 is provided at the center thereof with a settling hole 205 at a position corresponding to the outlet of the draft tube 203. The crystals in the draft tube 203 settle down on their own weight and fall into the settling hole 205, and finally are discharged from the discharge port 208.

In the prior art, a propeller is arranged in a flow guide pipe for promoting the stirring of fluid to generate vortex, thereby realizing the crystallization of crystals. The presence of the propeller reduces the space inside the guide tube, generating transverse vortices, and not being able to significantly modify the speed of the fluid. Therefore, the effect of fluid vortex and crystallization which can be realized by the guide pipe and the propeller in the prior art is not good, and the crystallization rate is low.

The invention aims to eliminate the structure of the propeller and strengthen the strength of the vortex in the guide pipe, so that how to realize the core effect is an important problem to be solved by the invention.

As shown in fig. 2, the inside of the draft tube 203 of the present invention is not straight cylindrical. The flow path inside the flow guide tube 203 comprises at least one expanding section and at least one swirling section. The vortex section is arranged at the downstream of the expansion section, namely the feed liquid in the expansion section flows into the vortex section.

For example, when there is one expanding section and one swirling section, the swirling section is disposed downstream of the expanding section. When there are two expansion sections and one swirl section, the swirl section is disposed between the two expansion sections; alternatively, two expansion sections are provided in series, with the swirl section being provided downstream of the two expansion sections.

When two expansion sections and two vortex sections exist, the expansion sections and the vortex sections can be arranged in a staggered mode; alternatively, two expansion sections are arranged in series, two swirl sections are arranged in series, and two swirl sections are arranged at the outlet of two successive expansion sections.

As indicated above, regardless of the ordering of the diverging section and the swirling section, at least one swirling section is located downstream of the diverging section. That is, the liquid inlet of the flow guide pipe 203 is an expanding section, and the liquid outlet of the flow guide pipe 203 is an expanding section or a swirling section. The reason for this is that the expanding section is used to make the feed liquid form a velocity shear in the flow direction, and the vortex section can strengthen the mixing of the feed liquid in a vortex-generating manner so as to grow crystal particles.

As shown in fig. 3, the present invention is illustrated with one of the nozzle structures as an example.

The flow path inside the draft tube 203 comprises a first expanding section 210, a first swirling section 215, a second expanding section 211 and a second swirling section 216 connected in sequence. Namely, the expansion section and the vortex section are arranged in a staggered mode, and the vortex section is arranged at the outlet of the expansion section.

The inner side surface of the expansion section of the invention is in an arc shape expanding outwards, so that the width of the channel at the inner side of the expansion section is larger than the width of the inlet of the expansion section and the outlet of the expansion section. The feed liquid enters from the inlet of the expansion section, the flow speed is reduced due to the rapid expansion of the flow channel, and the flow speed is increased due to the outlet of the reduced expansion section, so that the first speed change of the feed liquid is realized.

Preferably, the arc of the arc-shaped side surface of the expanding section is 0.8 to 2.0.

The flow channel of the swirl section is provided as a straight flow channel, but the side surface is provided with a flow dividing part 204 in such a manner that the forward feed liquid is transmitted at an accelerated speed and the reverse feed liquid is prevented from being generated during the transmission.

As shown in fig. 2 to 4, the flow dividing section 204 includes a plurality of counterflow sections. In the present invention, at least one first counterflow unit 401, at least one second counterflow unit 402, and branch flow paths corresponding to the contour of the counterflow unit are provided in the flow guide tube. The first counter flow part 401 and the second counter flow part 402 are arranged in a staggered manner and opposite to each other. For example, the first counterflow unit 401 and the second counterflow unit 402 are identical in shape and are arranged in mirror image. The first counterflow unit 401 and the second counterflow unit 402 are vertically offset from each other.

The branch flow channel formed by the counter-flow part and the main flow channel wall at least comprises two sections of flow sections. As shown in fig. 3, the branch flow path of the counterflow section includes a first branch flow section 403 and a second branch flow section 404. The first branch flow section 403 is a direct flow section, and the flow channel direction and the vertical direction have an inclined downward angle, so that the feed liquid can rapidly enter the first branch flow section 403. Preferably, the angle formed by the first branched flow section 403 and the vertical direction is in the range of 15 ° to 45 °. Too large or too small angle of the included angle may cause the liquid material to generate different hydraulic pressure difference at the inlet and outlet when entering the first branch flow section 403, and may cause the liquid material not to flow stably.

The second flow branch section 404 is a flow passage continuous and curved with the first flow branch section 403. Second branch flow segments 404 are arranged in a curved orientation with the feed liquid direction approximately opposite to the feed liquid direction of first branch flow segments 403 such that feed liquid flowing out of second branch flow segments 404 conflicts with the feed liquid direction of the main channel. First substream section 403 and second substream section 404 cause the feed liquid path to be sealed into multiple pressure zones, generate thrust by changes in pressure differential and cause the flow rate of the feed liquid to increase. The separation of the multiple pressure zones allows for increased flow of the feed liquid in the branch flow channels during flow, thereby creating greater turbulence at the intersection with the feed liquid in the primary flow channel.

Preferably, the branch flow channel in the countercurrent part is blocked by the flow guide block. The profile of the flow guide block corresponds to the profile of the branch flow channel, and the profile portion of the flow guide block not adjacent to the second branch flow section 404 has an arc-shaped structure. In the cross section shown in fig. 3, one end of the flow guiding block is arc-shaped in the longitudinal section and the curvature is identical to the curvature of the second branch flow section 404. The arc-shaped end of the flow guide block gradually converges towards the non-arc-shaped end, and the contact profile of the flow guide block and the first branch flow section 403 is a linear inclined profile. The profile of the flow guide block contacting the main flow channel is arc-shaped and makes the outlet of the second branch flow section 404 a grouting expansion outlet. In a simple manner, the diversion block is shaped like a teardrop, and the arc end of the teardrop is disposed at the bending position of the second branch 404 to form a flow channel for allowing the liquid to flow. The tear drop-shaped tip is contacted with the feed liquid of the main flow passage. Preferably, the shape of the deflector block can also be arranged to be egg-shaped. The tear drop shape has an optimal shape, a plurality of pressure areas are uniformly distributed, the flow velocity can be reduced to the maximum extent, and natural vortex can be generated without auxiliary equipment. And the oval or elliptical or spherical shape has smooth surfaces and causes minimal obstruction to the flow of the feed liquid. The oval or elliptical or spherical shape has longer service life, no cleaning dead angle, and can effectively remove micro crystals and the like generated by the convection action of the feed liquid.

When the feed liquid flowing out of the expansion section enters the swirl section, most of the feed liquid flows from the main flow channel, and a small part of the feed liquid enters the first counter-flow part 401 and the second counter-flow part 402 respectively. Obviously, the inlet of first branch flow section 403 is smaller than the outlet of second branch flow section 404, and this is because the feed liquid is easily crystallized during the flow, and minute crystals are inevitably generated although the flow rate of the feed liquid in the counter flow portion is fast and not easily crystallized. To avoid small crystals blocking the branch flow section, the smaller inlet of the first branch flow section 403 can avoid large crystals entering the branch flow section. Faster flow rates in the branch flow section also reduce the risk of crystal plugging. The outlet of second branch flow section 404 is larger, which is beneficial to the rapid outflow of tiny crystal bodies. Preferably, the channel width of the first branched section 403 is smaller than that of the second branched section 404, so as to further avoid the blockage of the second branched section 404 by the micro-crystals.

Because the second branch flow section 404 makes the feed liquid flow out fast and reversely, the reverse feed liquid collides with the forward feed liquid of the main flow channel and generates a vortex, so that the flow velocity of the feed liquid of the main flow channel in the vortex section can be obviously reduced, and the feed liquid can be fully mixed and crystals can be precipitated.

As shown in fig. 3 and 4, inside the draft tube, a first expanding section 210, a first swirling section 215, a second expanding section 211, and a second swirling section 216 are sequentially arranged in a vertical direction. The feed liquid generates primary speed shearing in the first expansion section 210, the feed liquid flowing out of the first expansion section enters the first vortex section 215 to generate a vortex, the vortex also has the speed shearing effect of the feed liquid and increases the mixing range of the feed liquid, so that the feed liquid generates secondary speed shearing, and the separation of crystals is facilitated. The feed liquid and the crystals thereof flowing out of the first vortex section 215 enter the second expansion section 211, and third-time speed shearing is realized based on the circular-arc-shaped flow channel expansion. The feed liquid exiting second expansion section 211 enters second vortex section 216 to generate a vortex that imparts a fourth velocity shear to the feed liquid. The staggered arrangement of the first expansion section 210, the first vortex section 215, the second expansion section 211 and the second vortex section 216 enables the feed liquid to realize step change of flow velocity for at least four times when passing through the draft tube 203, thereby improving the extraction rate of the feed liquid. Meanwhile, the larger crystallized particles do not enter first branch flow section 403 and do not get stuck all the way to the inlet of first branch flow section 403 due to the impact of the feed liquid of the main flow channel.

Preferably, the height difference between the first backflow part 401 and the second backflow part 402 is H. The smaller the height difference H, the more symmetrical the first counterflow unit 401 and the second counterflow unit 402 have. When the height difference H is zero, the first counterflow unit 401 and the second counterflow unit 402 form a symmetrical structure. The height difference H is maximum one half of the length of the guide pipe, and the guide pipe has the longest service life and has the flow speed reduction function.

The height difference H can also be found out by dimensional analysis to its optimum value. The scale relationship of the height difference H further includes other parameters, such as the length L of the flow guide pipe, the width D of the flow channel, the density ρ of the feed liquid, the flow velocity V, the reynolds number Re, the number N of vortex sections, and the like. Specifically, in the case where the height difference H is zero, the pressure drop formula of the draft tube is: (the power of N of the correction parameter α) × (feed liquid density ρ × (the square of the flow velocity V) × (draft tube length lx (the negative power of the flow channel width D) × (the negative quarter power of the reynolds number Re)).

And fitting the formula to obtain the pressure drop. Wherein the correction parameter α is replaced by the number of swirl segments N and the reynolds number Re after fitting.

In summary, the numerical value of the height difference H affects the pressure drop ratio of the entire feed liquid in the draft tube 203, and the higher the symmetry, the larger the pressure drop. With the introduction of service life and costs, a suitable height difference H can be selected for use in the draft tube 203 according to the above formula.

Preferably, there is also a height difference between the outlet of the second counter-flow section 402 and the inlet of the first counter-flow section 401, so as to avoid the crystals condensed in the vortex generated by the second counter-flow section 402 at a higher position from being stuck to the inlet of the first counter-flow section 401 at a lower position. After the height difference is set, the inlet of the first countercurrent portion 401 is mainly divided from the liquid flowing into the main flow channel vertically downward, and the gravity of the crystal is larger and is easier to fall, so that the crystal cannot be influenced by the division flow to enter the branch flow channel. Even if the liquid is stuck to the inlet of the first backflow portion 401, the liquid is easily washed and moved by the liquid in the main flow passage, and further, the liquid is reduced again to enter the branch flow passage.

In the present invention, as shown in fig. 3, the crystals separated by four times of speed shearing have larger volume and larger weight, so that the crystals can be more easily separated from the impact force of the feed liquid, fall into the settling zone 207 from the settling pores 205, and finally are discharged from the discharge port 208.

Preferably, the sodium sulfate production unit 400: preparing a nearly saturated sodium sulfate solution from sodium sulfate decahydrate through hot melting and condensate water hot melting, performing heat exchange heating on the sodium sulfate decahydrate and the condensate water, then entering a sodium sulfate evaporation crystallization system, concentrating a sodium sulfate solution through multi-effect countercurrent evaporation crystallization, continuously concentrating sodium sulfate in the solution to be supersaturated and separated out, gradually growing up and depositing on sodium sulfate foot, discharging a sodium sulfate slurry liquid, obtaining wet sodium sulfate through thickening and centrifugal separation channels, drying through a sodium sulfate drying bed, and packaging to obtain a sodium sulfate product; a small amount of mother liquor discharged from the last effect of sodium sulfate evaporative crystallization returns to a pre-freezing or mixed salt crystallizer unit, and condensed water produced by an evaporative crystallization system exchanges heat with the feeding material of the system and is recycled;

preferably, the three-stage purification section 300: the mother liquor of the frozen supernatant obtained after sedimentation of the sodium chloride-poor nitrate solution produced by the secondary purification part 200 is discharged and enters a membrane filtration single device for treatment, partial impurities are removed to prevent the impurities from damaging the structure of the nanofiltration membrane, and the filtered concentrated water returns to the mixed salt evaporative crystallization feeding tank of the primary purification part 100. The frozen material liquid is filtered to produce water and then enters a subsequent NF device to purify the poor sodium nitrate and sodium chloride material liquid, the NF treatment mainly uses sodium chloride as a small amount of sodium sulfate solution, the rich sodium nitrate high-impurity concentrated water returns to the crystallizer of the secondary purification part 200, sodium sulfate is continuously recovered, and the poor sodium nitrate and sodium chloride produced water directly enters a sodium chloride production unit 500: sodium chloride evaporative crystallizer or produced water enters a sodium chloride evaporative crystallization system after concentration (the water with large quantity and low concentration is matched (RO or ED or DTRO or MVR);

sodium chloride production unit 400: the sodium chloride solution is concentrated through multi-effect countercurrent evaporation crystallization, sodium chloride in the solution is continuously concentrated to be supersaturated and separated out, and gradually grows up and deposits on salt feet, salt slurry liquid is discharged, wet sodium chloride is obtained through a thickening and centrifugal separation channel, and then the wet sodium chloride is dried and packaged through a salt drying bed to obtain a sodium chloride product; a small amount of mother liquor discharged at the end of sodium chloride evaporative crystallization returns to a NF front or mixed salt crystallizer unit, and condensed water produced by an evaporative crystallization system is recycled after heat exchange with the feeding material of the system.

Example 3

This embodiment may be a further improvement and/or a supplement to

embodiments

1, 2 or a combination thereof, and repeated contents are not described again. This example discloses that, without causing conflict or contradiction, the whole and/or partial contents of the preferred embodiments of other examples can be supplemented by this example.

The embodiment discloses a membrane type purification method for salt-containing wastewater, in particular to a multistage purification balance salt and nitrate separation process method for high-salt-containing wastewater, which comprises the following process steps:

(1) Carrying out pretreatment of removing impurities such as hardness, silicon, fluorine and part of organic matters on the high-salinity wastewater after homogenizing the incoming water of the wastewater, and enabling the pretreated high-salinity wastewater to enter a concentration system to obtain high-salinity concentrated water containing saltpeter;

(2) The concentrated high-salinity concentrated water obtained in the step (1) generally has a TDS of about 6-20 ten thousand ppm, is subjected to MVR and multi-effect forced circulation evaporation crystallization to enable saltpeter to reach a supersaturated state, sodium sulfate and sodium chloride mixed salt crystals are separated out, sodium sulfate and sodium chloride crystal slurry discharged from an evaporation crystallizer is subjected to thickening separation to obtain sodium sulfate and sodium chloride mixed salt with the water content of 4-5%, meanwhile, part of miscellaneous salt mother liquor discharged from the evaporation crystallization system is subjected to impurity removal and drying, organic matters, sodium nitrate and other impurities of saturated concentrated feed liquid enter an evaporation crystallization tank are mainly balanced, and produced water in the process is subjected to heat exchange and then is sent to a produced water recycling system;

(3) Sodium sulfate and sodium chloride which are subjected to concentration, salt precipitation and purification in the step (2) and are subjected to moisture removal enter a hot-melt treatment unit to prepare nearly saturated sodium sulfate and sodium chloride solution;

(4) The high-concentration saltpeter feed liquid prepared by carrying out the secondary purification II treatment in the step (3) and carrying out hot melting on saltpeter is firstly fed into a purification unit II to purify sodium chloride and recover sodium sulfate;

(5) Sodium sulfate is supersaturated in a crystal water form through the secondary purification of the step (4), sodium sulfate decahydrate crystals (sodium nitrate decahydrate) are crystallized and separated out, the sodium sulfate decahydrate crystals enter a sodium nitrate decahydrate hot-melting or hot-melting system through thickening, concentration and crystallization, and sodium sulfate is separated out through evaporation, concentration and crystallization of the sodium nitrate evaporation and crystallization system; the produced water after the thermal dissolution and the evaporation crystallization after the melting is sent to a produced water recycling system through heat exchange;

(6) The mother liquor after salt purification in the step (5) enters a filtering system for three-stage purification;

(7) The solution filtered in the step (6) enters three-stage purification;

(8) Feeding the high-salinity concentrated water obtained after the purification III concentration in the step (7) into a feeding tank before secondary purification;

(9) Carrying out evaporative crystallization on the purified product water (sodium chloride solution) obtained in the step (8), concentrating, and then carrying out evaporative crystallization to separate out sodium chloride;

(10) And (3) purifying and discharging a small amount of mother liquor in the step (2), introducing the mother liquor into a mixed salt mother liquor curing system, mainly balancing the impurities enriched in organic matters, sodium nitrate, soluble silicon and the like in the system, controlling the concentration of the impurities enriched in organic matters, sodium nitrate and the like, and treating the mixed salt produced by drying and curing the mixed salt mother liquor separately or uniformly mixing the small amount of mixed salt mother liquor and sewage for biochemical treatment and the like.

Preferably, the process steps are more refined as follows: sodium sulfate and sodium chloride generated by I-stage purification are subjected to hot melting and then sent into a purification II to reduce nitrate content so as to purify the sodium chloride, and crystal nitrate containing water generated by the purification II is subjected to hot melting and hot melting, wherein feed liquid after hot melting is filtered in the step (6) and subjected to water inlet heat exchange with condensed water generated by a system so as to improve the temperature of circulating liquid, meet the water inlet requirement of entering the purification III, the temperature is about 25-35 ℃, the produced water of the purification III system mainly contains sodium chloride and is sent to the step (9) to be concentrated and crystallized so as to recover high-purity sodium chloride; and (4) returning purified III concentrated water which mainly contains sodium sulfate to the step (8) for further recovering the sodium sulfate.

Preferably, in the purification II system, the temperature of the purification II is controlled to be-5-0 ℃, and the refrigerant adopts ethylene glycol solution or calcium chloride solution, and the preparation concentration is 20%.

Preferably, in the purification III system, the retention rate of sodium sulfate is controlled to be 95-98%, and the retention rate of sodium chloride is controlled to be-10%. The reason why negative rejection occurs is that: because the salt content is high, the transmittance of sodium ions is increased, and the transmittance of chloride ions is greater than that of sulfate ions, more chloride ions are needed to permeate the nanofiltration membrane in order to balance the electrical property of the two sides of the nanofiltration membrane, and therefore, the rejection rate of chloride ions is negative.

Preferably, the control concentration of each pollutant in the effluent of the purification treatment system is controlled as follows: CODCr is less than or equal to 2000mg/l (TDS 20 ten thousand ppm is upper limit), TDS low and TDS high are respectively low value and high value, total hardness (calculated by CaCO 3) is less than 5mg/l, total alkalinity (calculated by CaCO 3) is 10-30 mg/l; the control concentration of each pollutant of effluent water of the first-stage purification part 100 (mixed salt crystallization system I) is controlled as follows: CODCr is less than or equal to 50000mg/l, and silicon is less than 1000mg/l.

Preferably, the temperature of the frozen feed liquid is controlled to be within the range of-5-0 ℃, separated nitre decahydrate solid is produced and dehydrated through centrifugal separation, the solid is subjected to hot melting by using condensed water, a saturated sodium sulfate solution is prepared, a nitre evaporation crystallization system is removed, high-temperature production is carried out, a high-purity sodium sulfate product is prepared, a small amount of enriched impurities are returned to a mixed salt evaporation system, sodium sulfate is continuously recovered, and meanwhile, a small amount of enriched impurities in the nitre evaporation crystallization system are balanced through reflux;

preferably, the rejection rate of the NF system to sodium sulfate is more than or equal to 98 percent, and the rejection rate to sodium chloride is negative. Negative entrapment refers to: the sodium chloride solution was allowed to pass completely.

Example 4

A method for circularly treating salt-containing wastewater based on membrane separation of salt and nitrate comprises the following steps:

the pretreatment unit is used for separating the salt-containing wastewater at least once by sodium chloride and sodium sulfate according to the water inlet requirement of the impurity concentration NF membrane separation device 300 b;

the NF membrane separation apparatus 300b will discharge the nitrate-poor and sodium-rich produced water to the sodium chloride production unit 500 and return the nitrate-rich high-impurity concentrated water to the pretreatment unit in such a manner that the produced nitrate-poor and sodium-rich produced water can meet the sodium chloride concentration required by the sodium chloride production unit 500;

wherein the NF membrane separation apparatus 300b is configured to include at least two mutual nanofiltration devices that can be communicated based on the sulfate ion concentration in the nitrate-rich sodium chloride production water, the at least two mutual nanofiltration devices being capable of being communicated to different treatment sections of the pretreatment unit based on the nitrate content in the nitrate-rich high-impurity concentrated water.

Preferably, the pre-treatment unit is configured to include at least a primary purifier section 100 and a secondary purifier section 200,

the first-stage purification part 100 is used for separating out sodium sulfate and sodium chloride in the salt-containing wastewater under the condition of certain impurity concentration in a mixed salt mode;

the second purification unit 200 freezes the rich-saltpeter mother liquor prepared from the mixed salt to precipitate sodium sulfate as decahydrate, thereby generating frozen lean-saltpeter mother liquor and discharging the frozen lean-saltpeter mother liquor to the NF membrane separation device 300b,

the NF membrane separation apparatus 300b discharges the rich saltpeter high impurity concentrated water to different treatment facilities of the secondary purification section 200 based on the saltpeter content in the rich saltpeter high impurity concentrated water,

the different treatment apparatuses comprise at least a crystallizer.

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 intended to be limiting on the claims. The scope of the invention is defined by the claims and their equivalents.

Claims

1. The salt-containing wastewater recycling treatment system based on membrane separation of salt and nitrate comprises a pretreatment unit and an NF membrane separation device (300 b), wherein the pretreatment unit is used for carrying out at least one time of sodium chloride and sodium sulfate separation on the salt-containing wastewater according to the water inlet requirement of the impurity concentration NF membrane separation device (300 b); it is characterized in that the preparation method is characterized in that,

the NF membrane separation device (300 b) discharges the nitrate-poor and sodium-rich water to the sodium chloride production unit (500) in a way that the generated nitrate-poor and sodium-rich water can meet the sodium chloride concentration required by the sodium chloride production unit (500), and conveys nitrate-rich and high-impurity concentrated water to the sodium sulfate production unit (400) in a way of refluxing to the pretreatment unit;

the NF membrane separation device (300 b) comprises at least two mutual nanofiltration devices which can be communicated based on the sulfate ion concentration in the nitrate-depleted and sodium chloride-enriched water, and the at least two mutual nanofiltration devices can be communicated to different treatment parts of the pretreatment unit based on the nitrate content in the nitrate-enriched and high-impurity concentrated water.

2. The processing system of claim 1, wherein the pre-processing unit comprises at least a primary purifier section (100) and a secondary purifier section (200),

the primary purification part (100) is used for separating out sodium sulfate and sodium chloride in the salt-containing wastewater under the condition of certain impurity concentration in a mixed salt mode;

the secondary purification unit (200) freezes the rich saltpeter mother liquor prepared from the mixed salt to precipitate sodium sulfate in the form of decahydrate, thereby generating frozen lean saltpeter mother liquor which is discharged to the NF membrane separation device (300 b),

the NF membrane separation device (300 b) discharges the nitrate-rich high-impurity concentrated water to different treatment equipment of the secondary purification part (200) based on the nitrate content in the nitrate-rich high-impurity concentrated water,

the different treatment equipment comprises at least a crystallizer.

3. The treatment system of claim 2, wherein the NF membrane separation unit has a rejection rate of 95 to 98% for sodium sulfate and a rejection rate of-10% to 10% for sodium chloride.

4. A treatment system according to claim 2 or 3, characterized in that the primary purification section (100) and the secondary purification section (200) are provided with separation units for controlling the water content of the mixed salt, which is 4-5%.

5. The treatment system according to claim 4, wherein the secondary purification section (200) uses a coolant to separate out sodium sulfate in a supersaturated state in a cooling process in the form of sodium nitrate decahydrate under the condition of precooling the sodium sulfate and sodium chloride solution in a nearly saturated state based on the mixed salt hot melt blending to obtain a precooled feed liquid, and the coolant can reduce the temperature of the precooled feed liquid to minus 5-0 ℃ to obtain a frozen feed liquid.

6. The treatment system according to claim 5, wherein the sodium sulfate decahydrate is subjected to at least hot melting and condensate water hot melting in a sodium sulfate production unit (400) to prepare a nearly saturated sodium sulfate solution, the sodium sulfate solution is subjected to heat exchange heating with condensate water, and then is subjected to multi-effect countercurrent evaporation crystallization to concentrate the sodium sulfate solution, so that sodium sulfate in the solution is continuously concentrated to supersaturation and separated out and gradually grows and deposits in sodium sulfate foot.

7. The treatment system according to any one of claims 1 to 6, wherein the pretreatment unit is communicated with the NF membrane separation device through a filtering device (300 a) which is used for further removing impurities of the frozen Mirabilitum-depleted mother liquor according to the impurity concentration requirement of the NF membrane separation device to obtain an impurity liquid, and an impurity liquid outlet of the filtering device is communicated with the primary purification part (100) so that the primary purification part (100) can purify mixed salt containing sodium sulfate crystals and sodium chloride crystals in a manner of approximately equalizing the impurity concentration in the saline wastewater.

8. A treatment system according to any one of claims 1 to 6, wherein said concentrated brine effluent is concentrated at least once to a TDS value of between 6 and 20 ppm before entering said primary purification section (100).

9. A method for circularly treating salt-containing wastewater based on membrane separation of salt and nitrate comprises the following steps:

the pretreatment unit is used for separating the salt-containing wastewater at least once by sodium chloride and sodium sulfate according to the water inlet requirement of the impurity concentration NF membrane separation device (300 b); it is characterized in that the preparation method is characterized in that,

the NF membrane separation device (300 b) discharges the nitrate-poor sodium chloride-rich water to a sodium chloride production unit (500) in a mode that the generated nitrate-poor sodium chloride-rich water can meet the sodium chloride concentration required by the sodium chloride production unit (500), and transmits nitrate-rich high-impurity concentrated water to a sodium sulfate production unit (400) in a mode of refluxing to the pretreatment unit;

wherein the NF membrane separation device (300 b) is configured to comprise at least two mutual nanofiltration devices connectable to different treatment sections of the pretreatment unit based on nitrate content in the nitrate-rich high-impurity concentrated water, based on nitrate ion concentration in the nitrate-depleted sodium chloride-rich produced water.

10. The processing system of claim 9, wherein the pre-processing unit is configured to include at least a primary purifier section (100) and a secondary purifier section (200),

the different processing equipment comprises at least a cryocrystallizer.