CN115403057A - Salt-nitrate separation wastewater treatment system and method based on condensate recovery - Google Patents
Salt-nitrate separation wastewater treatment system and method based on condensate recovery Download PDFInfo
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- CN115403057A CN115403057A CN202211161569.7A CN202211161569A CN115403057A CN 115403057 A CN115403057 A CN 115403057A CN 202211161569 A CN202211161569 A CN 202211161569A CN 115403057 A CN115403057 A CN 115403057A
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- 238000000926 separation method Methods 0.000 title claims abstract description 130
- 229910002651 NO3 Inorganic materials 0.000 title claims abstract description 112
- 238000000034 method Methods 0.000 title claims abstract description 44
- 238000011084 recovery Methods 0.000 title claims abstract description 23
- 238000004065 wastewater treatment Methods 0.000 title claims abstract description 9
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims abstract description 257
- 150000003839 salts Chemical class 0.000 claims abstract description 223
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- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims abstract description 138
- 229910052938 sodium sulfate Inorganic materials 0.000 claims abstract description 132
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- 230000008025 crystallization Effects 0.000 claims abstract description 129
- 239000011780 sodium chloride Substances 0.000 claims abstract description 129
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims abstract description 81
- 238000001704 evaporation Methods 0.000 claims abstract description 72
- 239000012452 mother liquor Substances 0.000 claims abstract description 69
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- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 claims abstract description 54
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- 150000004691 decahydrates Chemical class 0.000 abstract description 10
- 238000000746 purification Methods 0.000 description 39
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- 238000006243 chemical reaction Methods 0.000 description 4
- 238000007599 discharging Methods 0.000 description 4
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Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D3/00—Halides of sodium, potassium or alkali metals in general
- C01D3/04—Chlorides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D9/00—Crystallisation
- B01D9/0059—General arrangements of crystallisation plant, e.g. flow sheets
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D9/00—Crystallisation
- B01D9/0077—Screening for crystallisation conditions or for crystal forms
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D9/00—Crystallisation
- B01D9/02—Crystallisation from solutions
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D3/00—Halides of sodium, potassium or alkali metals in general
- C01D3/14—Purification
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
- C01D5/16—Purification
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D9/00—Crystallisation
- B01D2009/0086—Processes or apparatus therefor
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
Abstract
The invention relates to a salt and nitrate separation wastewater treatment system and method based on condensed water recovery, which comprises the following steps: first salt nitre separating element and comdenstion water recovery unit, first salt nitre separating element, the mixed salt preparation that can obtain sodium sulfate and sodium chloride with waste water evaporation crystallization is the rich nitre mother liquor of saturated state, and can freeze the sodium sulfate in the rich nitre mother liquor with the mode of decahydrate crystallization and separate out and discharge the poor nitre mother liquor to second salt nitre separating element, comdenstion water recovery unit can communicate through ration unit and first salt nitre separating element with the mode of referring to the required solvent volume of first salt nitre separating element preparation mixed salt under the circumstances that can retrieve the comdenstion water that obtains after the steam cooling that produces in the evaporation crystallization process at least, so that the mixed salt can dissolve in the comdenstion water after the softening and obtain the rich nitre mother liquor of saturated state.
Description
Technical Field
The invention relates to the technical field of purification of salt-containing wastewater, in particular to a salt-nitrate separation wastewater treatment system and method based on condensate recovery.
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 body 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 the ecological environment for people to live and meet the self requirements of resource utilization. In the design of the comprehensive high-salt-content wastewater treatment zero discharge process, a final solid product can be separated out at a high purity, about 90% of sodium sulfate and sodium chloride in high-salt water can be used as a zero discharge byproduct to be sold as industrial raw materials, the impurity salt amount in the zero discharge treatment process is greatly reduced, a large amount of sodium sulfate and sodium chloride are not used as solid hazardous waste to be treated, the environment-friendly benefit and the resource recycling value are very high, about 10% of impurity salt is arranged near the zero discharge treatment process to be treated as hazardous waste, and the cost and the resource are saved considerably.
Comprehensive high-salt concentrated water (generally TDS is more than 5000 mg/l) discharged by enterprises and accepted by gardens at present, high-salt wastewater contains a large amount of organic matters and complex impurities, and is generally not suitable for removing the organic matters by adopting traditional biological treatment degradation, and the more commonly adopted pretreatment comprises' hardness removal double-alkali softening pretreatment → reduction → high-salt water advanced treatment for hardness removal, silicon removal, fluorine removal and the like → NF → lean sodium nitrate and chloride production water → concentration → evaporative crystallization → sodium chloride; NF → concentrated water rich in sodium nitrate and low in sodium sulfate → organic matter removal (measures such as advanced oxidation, resin adsorption and high-temperature treatment) → evaporative crystallization → sodium sulfate; the purity of the finally generated sodium sulfate and sodium chloride crystal salt is not high, the impurity content is higher, the quality of the sodium sulfate and sodium chloride obtained by the process route is unstable and poor, and the aim of comprehensively utilizing the salt and the nitrate as industrial raw materials is difficult to achieve; the process route generates large amount of miscellaneous salt, the miscellaneous salt contains a large amount of organic matters and complex components, the generated large amount of 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 is the treatment bottleneck of a large amount of zero-discharge crystal salt at present, the small-scale treatment capacity of the professional companies is very limited at present, and the treatment requirement of a large amount of miscellaneous salt generated by zero-discharge treatment of wastewater of a plurality of industrial enterprises cannot be met.
For example, a system and a method for treating high-salt-content wastewater by fractional crystallization in publication No. CN111153456A, the system includes a regulating reservoir, a first sodium chloride evaporative crystallization system, a sodium chloride mother liquor buffer reservoir, a potassium nitrate freezing crystallization system, a second sodium chloride evaporative crystallization system, and a miscellaneous salt evaporative crystallization system; the method comprises the following steps: (1) homogenizing and uniformly treating the wastewater; (2) evaporating and crystallizing the first sodium chloride; (3) Adding potassium chloride into the sodium chloride mother liquor to obtain a mixed liquor; (4) freezing to precipitate potassium nitrate; and (5) evaporating and crystallizing the frozen potassium nitrate mother liquor. The method has the advantages of low wastewater treatment cost, various product types, small impurity salt amount, high purity of the produced sodium chloride more than 99%, high purity of the sodium sulfate more than 99%, high purity of the potassium nitrate more than 99% and high impurity salt yield less than or equal to 10%.
In the prior art, the salt separation process is a heat and mass transfer process, and proper heat exchange schemes are required to be selected according to the solubility of different solutes to gradually separate the salt in the wastewater. In the salt separation process, evaporation is a common physical process for separating solute and solvent, which generates a large amount of steam, however, the steam generated in the prior art contains latent heat and is obvious, so that the steam can be fully recycled, and the resource utilization rate is improved.
Furthermore, on the one hand, due to the differences in understanding to the person skilled in the art; on the other hand, since the inventor has studied a lot of documents and patents when making the present invention, but the space is not limited to the details and contents listed in the above, however, the present invention is by no means free of the features of the prior art, but the present invention has been provided with all the features of the prior art, and the applicant reserves the right to increase the related prior art in the background.
Disclosure of Invention
Aiming at the defects of the prior art: the invention provides a salt and nitrate separation wastewater treatment system based on condensate recovery, which comprises: the condensate water recovery unit can be communicated with the first salt-nitrate separation unit through a quantitative unit in a mode of referring to the amount of a solvent required by the first salt-nitrate separation unit to prepare the mixed salt so that the mixed salt can be dissolved in softened condensed water to obtain the nitrate-rich mother liquor in a saturated state.
According to a preferred embodiment, the condensed water of the condensed water recovery unit is derived from steam generated in the mixed salt crystallization unit, steam generated in the sodium sulfate production unit, and steam generated in the sodium chloride production unit.
According to a preferred embodiment, the mixed salt crystallization unit separates sodium sulfate and sodium chloride in the salt-containing wastewater under the condition of certain impurity concentration in a mixed salt manner to obtain steam.
According to a preferred embodiment, the mixed salt crystallization unit and the first salt and nitrate separation unit are provided with separation units for controlling the water content of the mixed salt, which can be used to determine the amount of condensed water discharged by the dosing unit.
According to a preferred embodiment, the first salt-nitrate separation unit uses a coolant to separate out sodium sulfate in a supersaturated state in a cooling process in a decahydrate mode under the condition that a pre-cooling feed liquid is obtained by pre-cooling a saturated sodium sulfate and sodium chloride solution which are hot-melt blended based on the mixed salt, and the coolant can reduce the temperature of the pre-cooling 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 the sodium sulfate production unit to prepare a nearly saturated sodium sulfate solution, the sodium sulfate solution is subjected to heat exchange heating with condensed water and then subjected to multi-effect concurrent evaporation crystallization to concentrate the sodium sulfate solution, and sodium sulfate in the solution is continuously concentrated to supersaturation and separated out and gradually grows and deposits in sodium sulfate foot.
According to a preferred embodiment, the first salt-nitrate separation unit is communicated with a filtering device in the second salt-nitrate separation unit, the filtering device is used for further removing impurities of the frozen nitrate-depleted mother liquor to obtain an impurity liquid according to the impurity concentration requirement of an NF membrane separation device in the second salt-nitrate separation unit, and an impurity liquid outlet of the filtering device is communicated with the mixed salt crystallization unit, so that the mixed salt crystallization unit can purify mixed salt containing sodium sulfate crystals and sodium chloride crystals in a manner of approximately equalizing the impurity concentration in the salt-containing wastewater.
According to a preferred embodiment, concentrated salt wastewater is concentrated at least once before entering the mixed salt crystallization unit, so that the TDS value of the concentrated salt wastewater is 6 ten thousand ppm to 20 ten thousand ppm.
According to a preferred embodiment, the invention relates to a method for treating salt and nitrate separation wastewater based on condensed water recovery, wherein a first salt and nitrate separation unit prepares a mixed salt of sodium sulfate and sodium chloride obtained by evaporation crystallization of wastewater into a nitrate-rich mother liquor in a saturated state, can freeze and separate out sodium sulfate in the nitrate-rich mother liquor in a decahydrate crystallization manner and discharge a nitrate-poor mother liquor to a second salt and nitrate separation unit, and the condensed water recovery unit can be communicated with the first salt and nitrate separation unit through a quantitative unit in a manner of referring to the amount of a solvent required by the first salt and nitrate separation unit to prepare the mixed salt under the condition that at least condensed water obtained by cooling steam generated in the evaporation crystallization process can be recovered, so that the mixed salt can be dissolved in softened condensed water to obtain the nitrate-rich mother liquor in the saturated state.
According to a preferred embodiment, the condensed water of the condensed water recovery unit is derived from steam generated in the mixed salt crystallization unit, steam generated in the sodium sulfate production unit, and steam generated in the sodium chloride production unit.
Drawings
FIG. 1 is a block diagram of a processing system provided by the present invention;
FIG. 2 is a schematic diagram of the structure of a draft tube in a settler;
FIG. 3 is a settler provided by the present invention;
FIG. 4 is an enlarged schematic view of the return portion of the present invention;
FIG. 5 is a schematic block diagram of a portion of a preferred recycling system of the present invention.
List of reference numerals
100: a mixed salt crystallization unit; 400: a sodium sulfate production unit; 200: a first salt and nitrate separation unit; 500: a sodium chloride production unit; 300: a second saltpeter separation unit; 201: a settler; 202: a housing; 203: a vortex tube; 204: a support; 205: bending the frame; 206: a mother liquor outlet; 207: a bottom; 208: an evacuation port; 209: a liquid level transmitter; 210: a feed liquid inlet; 211: a liquid storage device; 213: a first vortex section; 214: a second swirl section; 215: a first expanding section; 216: a second expanded section; 401: a first reflux unit; 402: a second reflux part; 403: a curved section; 404: a direct current section; 300a: a filtration device; 300b: an NF membrane separation unit; 300b-1: a first-stage nanofiltration device; 300b-2: a secondary nanofiltration device; 300b-n: an n-stage nanofiltration device.
Detailed Description
This is described in detail below with reference to fig. 1-5.
In the invention, english abbreviations and corresponding Chinese paraphrases are compared 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: and an electrodialysis device.
And (3) RO: a reverse osmosis device.
Example 1
The embodiment discloses a salt and nitrate separation wastewater treatment system based on condensate recovery. The system mainly comprises a first salt and nitrate separation unit 200 and a condensed water recovery unit 600.
First saltpeter separation unit 200: sodium chloride and sodium sulfate produced by purification, evaporation, crystallization and separation enter a dissolving and stirring tank or a tank, condensed water is added and stirred for dissolution, saturated concentration sodium sulfate and sodium chloride solution are prepared, salt and nitrate solution enter a liquid storage barrel and then are pumped into a freezing and crystallization system, the temperature of the feed liquid is controlled through a settler of the freezing and crystallization system, decahydrate is crystallized and separated, the produced decahydrate is redissolved and then enters a sodium sulfate production unit 400 (a multi-effect evaporation and crystallization device of nitrate is adopted), finally, sodium sulfate liquid is evaporated and concentrated through steam heating to achieve overfull production of sodium sulfate crystals, and high-purity sodium sulfate (named as glauber salt) is obtained through thickening, separation and drying.
The condensed water recovery unit 600: used for storing condensed water formed after the heat release of steam generated in the evaporative crystallization process. In the invention, the evaporative crystallization process mainly comprises a mixed salt evaporative crystallization process, a sodium sulfate evaporative crystallization process and a sodium chloride crystallization process. The condensate recovery unit 600 includes at least one storage tank having a condenser tube. The condenser pipe can with evaporation unit evaporation inlet tube contact heat transfer, and the water in the evaporation unit evaporation inlet tube is preheated with evaporation unit to steam, and the water in the evaporation unit evaporation inlet tube can be with steam cooling and form the comdenstion water gradually. The evaporation unit mainly comprises an MVR evaporator, a TVR evaporator and the like. The cold condensate water belongs to softened water, and salt concentration in the cold condensate water is low and impurity rate is very low, can be used for dissolving the mixed salt in first salt and sodium chloride separation element 100 for sodium sulfate and sodium chloride dissolve once more, are convenient for freeze out the ten water nitre, make the water resource can be at system cyclic utilization.
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 → reprocessing → NF → reduction of sodium nitrate-rich and low-sodium sulfate concentrated water respectively → reprocessing → salt separation evaporation crystallization and sodium chloride-poor water production → concentration (optional) → salt separation evaporation crystallization; pretreatment → NF → respectively reducing the amount of the rich sodium nitrate and the low sodium sulfate concentrated water → retreatment → salt separation evaporation crystallization and the water production of the poor sodium nitrate and the low sodium chloride → 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. Preferably, the system further includes a mixed salt crystallization unit 100, a second saltpeter separation unit 300, a sodium sulfate production unit 400, and a sodium chloride production unit 500.
Mixed salt crystallization unit 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 portion of the separated impurities does not enter the first salt-nitrate separation unit 200 and the second salt-nitrate separation unit 300, and particularly does not block membrane pores in the second salt-nitrate separation unit 300, so that the second salt-nitrate separation unit 300 can be continuous. Part of the mixed salt mother liquor discharged from the mixed salt crystallization unit 100 enters a mixed salt production unit (adopting a thermal method for drying) to produce the mixed salt mainly containing organic matters, sodium nitrate, salt nitrate and impurities.
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 sodium sulfate-enriched 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 device 300b comprises at least two mutual nanofiltration devices that can be communicated based on the nitrate ion concentration in the nitrate-depleted sodium chloride-enriched produced water, the at least two mutual nanofiltration devices being communicable to different treatment sections of the pretreatment unit based on the nitrate content in the nitrate-enriched sodium low sulfate concentrated water. As shown in fig. 5, the NF membrane separation apparatus 300a may be provided as a part of the second brine separation unit 300, which can communicate with the water outlet of the filtration apparatus 300 a. The water inlet of the filtering device 300a is communicated with the first salt and nitrate separating unit 200. The filter device 300a may be a tube filter, a cartridge filter. The filtering device 300a is arranged between the first salt-nitrate separation unit 200 and the NF membrane separation device 300b, and is used for filtering the frozen lean nitrate mother liquor to further reduce the impurity concentration of the NF membrane separation device 300b, so that the liquid inlet requirement of the NF membrane separation device 300b is met. 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 concentration of the impurities 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 concentration of the impurities within the range of the required concentration of the impurities of the mixed salt crystallization unit 100, so that the mixed salt can be more easily separated out.
Preferably, the NF membrane separation apparatus 300b comprises at least one nanofiltration apparatus. 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 and low sodium sulfate concentrated water generated by each stage of nanofiltration device is discharged to the first salt and nitrate separation unit 200, and the rich nitrate and low sodium sulfate concentrated water 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 the sodium sulfate is controlled to gradually increase according to the flow direction of the produced water, and when the interception rate of the sodium sulfate reaches 95-98%, the NF membrane separation device 300b discharges the sodium chloride produced water poor in nitrate 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 nitrate and chloride-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 controlled to gradually increase according to the flowing direction of produced water, the content of sodium sulfate in concentrated water rich in sodium sulfate and low in nitre and sodium sulfate discharged by an n-stage nanofiltration device is gradually reduced, and therefore, concentrated water rich in sodium sulfate and low in nitre and low in sodium sulfate discharged by the first-stage nanofiltration device can be directly discharged to a settler 201 for direct crystallization after being cooled; and concentrated water rich in nitrate and sodium sulfate and discharged by a secondary grade 8230, a grade n nanofiltration device needs to be further concentrated.
Preferably, the NF membrane separation apparatus is at least a part of the second saltpeter separation unit 300. Second saltpeter separation unit 300: the nitrate-depleted mother liquor produced by the freeze crystallization enters a second salt-nitrate separation unit 300 (with an NF membrane separation device) for further re-separation of sodium chloride and sodium sulfate. Concentrating the water (namely the water) produced by the poor sodium chloride and the poor sodium chloride, or directly entering a sodium chloride evaporative crystallization system, heating a 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 the NF membrane separation device produces the concentrated water rich in sodium nitrate and low in sodium sulfate and returns the concentrated water to the freezing settler, and the sodium sulfate in the concentrated water rich in sodium nitrate and low in sodium sulfate is extracted again. The invention can ensure the stability and high-efficiency operation of the salt separation and 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 high stability of obviously prolonging the one-time use time of the membrane structure in the second salt and sulfate separation unit 300, and can reduce the amount of miscellaneous salt in the system to the maximum extent and have low miscellaneous salt yield through multi-stage purification.
Preferably, the NF membrane separation device is configured to further separate sodium chloride and sodium sulfate in the frozen nitrate-depleted mother liquor discharged from the first salt-nitrate separation unit, and the NF membrane separation device enters the sodium chloride production unit with the generated nitrate-depleted sodium chloride-enriched water in a manner that the nitrate-enriched sodium chloride-enriched water can meet the sodium chloride concentration required by the sodium chloride production unit and returns the nitrate-enriched sodium sulfate-enriched concentrated water to the first salt-nitrate separation unit; NF membrane separation device and filter equipment can communicate, filter equipment can with first salt nitre separating element intercommunication, filter equipment is used for according to accord with NF membrane separation device impurity concentration requires the mode will the impurity of freezing poor nitre mother liquor is further got rid of and is obtained the impurity liquid, filter equipment's impurity liquid export with mix salt crystal unit intercommunication, so that mix salt crystal unit can contain the mixed salt that sodium sulfate crystal and sodium chloride crystal are contained in the mode purification of impurity concentration in the salt waste water according to roughly the equilibrium. 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 mixed salt crystallization unit is used for purifying and purifying high-salinity concentrated water by using salt and nitrate; 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) Salt and nitre generated by the mixed salt crystallization unit are heated and supplemented with a small amount of condensed water to be dissolved again to obtain pure sodium sulfate and sodium chloride solution saturated in crystallization; the nearly saturated mixed solution of sodium sulfate and sodium chloride enters a purification unit II;
5) The first salt-nitrate separation unit 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 through sodium sulfate decahydrate crystallization, so that pure sodium sulfate decahydrate crystals containing 10 crystal waters are obtained, and the purification treatment of the sodium chloride solution in the feed liquid is realized;
6) The method comprises the following steps that (1) generated sodium nitrate decahydrate is heated and melted (or condensed water is added for hot dissolution) in a first salt-nitrate separation unit, sodium sulfate recrystallization is carried out in a sodium nitrate evaporation crystallization system, high-purity sodium sulfate is separated out, a small amount of mother liquor discharged by sodium nitrate evaporation crystallization is returned to a mixed salt crystallization unit, sodium sulfate in the mother liquor and a small amount of impurities enriched in balance are recycled, the obtained product enters a mixed salt settler, and the impurities are removed through balance of the mother liquor discharged from the mixed salt settler;
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 second salt and nitrate separation unit generates a nitrate-rich solution and returns the nitrate-rich solution to the first salt and nitrate separation unit; the purification unit III is used for generating a poor nitrate solution, and the poor nitrate solution enters a sodium chloride evaporation settler to be evaporated and crystallized to separate out high-purity sodium chloride salt; the condensate water produced by the evaporation and crystallization of the sodium chloride evaporation settler is completely recycled through heat exchange;
sodium chloride is evaporated and crystallized to generate a small amount of mother liquor to return to the mixed salt crystallization unit 100, and sodium chloride is further recovered; a small amount of mother liquor discharged by salt evaporation crystallization is returned to the mixed salt crystallization unit, sodium chloride in the mother liquor and a small amount of impurities which are balanced and enriched are recovered, the sodium chloride and the small amount of impurities enter a mixed salt settler, and the impurities are removed through balance of the mixed salt mother liquor;
8) And (3) enabling the mixed salt mother liquor discharged from the mixed salt crystallization unit 100 to enter a mixed salt treatment system, separating out the mixed salt through evaporation and crystallization, and discharging the mixed salt mother liquor from a mixed salt evaporation settler to perform mother liquor solidification treatment to obtain the mixed salt, wherein the system mainly balances the impurity content of the system.
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 removal softening sedimentation clarification, filter or membrane filtration, resin softening, advanced oxidation unit activated carbon, etc. to remove most of hardness, alkalinity, heavy metals, suspended substances, part of silicon, part of fluorine, alkali liquor for reaction, and part of organic matters in wastewater.
Preferably, the purification, evaporation and crystallization treatment system I comprises crystallization process devices such as multiple-effect forced circulation evaporation crystallization, TVR evaporation crystallization, MVR falling film evaporation + forced circulation evaporation crystallization, flash evaporation and the like, sodium sulfate and sodium chloride are separated out by supersaturation of salt nitrate in evaporation and concentration feed liquid, mixed salt solid separated out by crystallization, CODCr, silicon, fluoride, suspended matters enriched in the feed liquid, alkali liquor obtained by reaction of pretreatment residues, scale inhibitor added by pretreatment, impurities of corrosion inhibitor remained in the system and the like are thoroughly isolated, and subsequent recrystallization purification units ii and iii are carried out in 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 mixed salt crystallization unit 100, purification II corresponds to the first salt and nitrate separation unit 200, and purification III corresponds to the second salt and nitrate separation unit 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 or in part with reference to the following examples, which are intended to supplement the present invention and are not intended to be limiting.
Preferably, the pretreatment unit comprises at least the mixed salt crystallization unit 100 and the first salt and nitrate separation unit 200 in example 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) to be concentrated to about 6 to 20 ppm (preferably 10 to 20 ppm), and then enters the mixed salt crystallization unit 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 evaporative 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 mixed salt crystallization unit 100.
Preferably, the system further comprises a miscellaneous salt production unit: the mixed salt mother liquor which is discharged from a mixed salt settler in the mixed salt crystallization unit 100 and is used for balancing feed liquid impurities enters a mixed salt mother liquor adjusting tank, the mixed salt mother liquor is subjected to evaporative crystallization continuously through a mixed salt evaporative settler to obtain mixed salt slurry, the mixed salt slurry is subjected to cyclone separation, the underflow mixed salt slurry enters a centrifuge for separation to obtain mixed salt, and the water content of the mixed salt is about 10-20 percent and is treated; and (3) evaporating and crystallizing the mixed salt, discharging the mother liquor, allowing the mother liquor to enter a mixed salt mother liquor storage tank, and allowing the mother liquor to enter a mixed salt mother liquor curing system for drying treatment to obtain the mixed salt.
Preferably, there is a separation unit between the mixed salt crystallization unit 100 and the first salt and nitrate separation unit 200. The separation unit controls the water content of the mixed salt of the crystalline sodium sulfate and the sodium chloride to be between about 4 and 5 percent by adopting a centrifugal separation mode. And carrying out hot melting on the mixed salt of the crystalline sodium sulfate and the sodium chloride in a stirring tank by utilizing condensed water generated by the system to prepare a nearly saturated or saturated sodium sulfate and sodium chloride solution. And overflowing the sodium sulfate and sodium chloride solution into a mixed solution storage barrel, and then sending into a precooler for precooling and cooling. And (3) when the precooled feed liquid reaches a precooling design temperature (generally between 22 and 27 ℃, preferably 25 ℃), feeding the feed liquid into a freezing settler. 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 decahydrate crystals are separated out from the feed liquid, and are settled and supersaturation eliminated, decahydrate solid is separated out through a centrifugal machine, and the decahydrate is subjected to hot melting and condensed water hot melting and then enters a unit 500 (mainly comprising a nitrate evaporation settler) for producing sodium sulfate to obtain the sodium sulfate.
Preferably, the water content of the mixed salt can be used to determine the amount of condensed water discharged by the dosing unit. The dosing unit is preferably a dosing pump. The water in the mixed salt is crystal water which can be used as a part of solvent after being dissolved, and the nitre decahydrate needs to be precipitated in a saturated solution, so that the amount of condensed water added into the mixed salt needs to be proper. Suitably means: after water is added, the solids in the mixed salt can be completely dissolved, and the solution needs to be in a saturated state. The amount of condensed water is equal to (1/saturation-1-water content) multiplied by the mass of mixed salt to be dissolved.
Preferably, the first salt and nitrate separation unit 200 comprises a settler 201, as shown in figure 2.
In the prior art, the diversion pipeline in the settler is arranged in a straight cylinder shape, so that the speed of the feed liquid does not have gradient change when passing through the diversion pipeline, and the problems of mixing reinforcement and crystal particle size control of the material can not be completely solved. In the prior art, a propeller is arranged in the diversion pipeline for promoting the stirring of the fluid to generate a vortex, thereby realizing the crystallization of the crystal. The presence of the propeller reduces the space inside the guide duct, while generating a single vortex that does not allow a complete and thorough mixing and crystallization of the fluid. Therefore, the guide pipeline and the propeller in the prior art can realize poor fluid vortex and crystallization effects and low crystallization rate.
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.
Based on the defect, the invention improves the diversion pipeline in the settler 201, and enhances the shearing and mixing effect in the diversion pipe by improving the flow field distribution in the diversion pipe and forming the vortex pipe 203. 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 crystals in vortex tube 203 settle under their own weight and fall to the bottom, where they are finally discharged from bottom 207.
Specifically, as shown in fig. 2 to 4, the settler 201 includes at least a shell 202. The surface of the housing 202 is provided with an insulating layer. A vortex tube 203 for guiding the input feed liquid is disposed in the housing 202. The vortex tube 203 is held in a central position in the housing 202 by a bracket 204. Preferably, the conduits of the vortex tube 203 are arranged vertically such that fluid passes through the vortex tube 203 in a vertical direction. Feed liquid inlet 210 feeds feed liquid from the bottom of vortex tube 203 through a conduit, such that feed liquid flows from bottom to top within the vortex tube and from the top to the outside of vortex tube 203 under the action of negative pressure. The bottom 207 of the housing 202 is provided with a thermometer for measuring the temperature inside the housing. A mother liquor outlet 206 is arranged at one side of the thermometer. The pipeline for inputting the feed liquid is connected with the liquid storage device 211 through a pipeline, and at least one valve is arranged on the pipeline. The inner wall of the settler housing 202 surrounding the periphery of the vortex tube 203 is provided with a number of bent shelves 205. As shown in fig. 3, the bent frame 205 is bent upward in a certain curvature. The bending arc of the bent frame 205 ranges from 0.8 to 2.4. One side of the bent frame 205 is disposed obliquely with respect to the inner wall of the settler shell 202 at an angle of 30-45 °. The curved ends of the bent frame 205 contact the outer wall of the vortex tube 203 to limit the movement of the vortex tube and avoid deflection of the vortex tube.
Preferably, the bent frame 205 includes a plurality of layers of sub-bent frames arranged at different heights. The bent radian ends on the sub bent frames on different layers are arranged in a spiral stepped mode, so that the material liquid flowing out of the vortex tube can be subjected to speed shearing based on the effect of the bent frames, and the crystallization efficiency of crystals is improved. When the feed liquid containing crystals falling from the upper part falls on the bent frame, the feed liquid more easily flows upwards along the radian of the bent frame to form a plurality of tiny vortexes. These vortices are less pronounced than those in vortex tubes, but are sufficient to again promote adequate mixing of the feed liquid, causing it to precipitate more crystals.
Preferably, the side wall of the bottom 207 can also be provided with a remote pressure transmitter and a plurality of level gauges. The junction of the level gauge and the settler shell 202 is provided with a level transmitter 209, which is convenient for detecting the liquid level inside the settler shell 202 in time. A drain 208 is provided on the top side of the exterior of the housing 202. The other end of the evacuation port 208 is connected to a negative pressure suction system. The negative pressure suction system mainly comprises a vacuum suction station, a suction pipeline and a gas terminal connector. The vent 208 communicates with a gas terminal connector to facilitate regulation of the gas phase pressure inside the housing 202. The feed liquid with high temperature and saturation temperature is sent into the vortex tube 203 from the storage device 211 through a pipeline of the feed liquid inlet 210, and a vortex is generated by the vortex tube 203 and is fully mixed. The settler controls the gas phase pressure in the settler through the drain 208 and the negative pressure suction system. Through negative pressure flash evaporation, the feed liquid is saturated and crystallized and precipitated to be settled at the bottom 207. The heat is taken away in the flash evaporation process to achieve the purpose of cooling the mother liquor, and a large amount of crystals are separated out. The larger the temperature difference between the mother liquor at the mother liquor outlet 206 and the feed liquor inlet 210 is, the higher the evaporation efficiency is, the larger the crystal precipitation amount is, and the more remarkable the energy-saving effect is. While the mother liquor is continuously flashed and crystals are precipitated, the mother liquor forms internal circulation in the shell 202 through the vortex tube 203, the flash liquid level is increased, the crystals are crystallized in the settler shell 202, and crystallized particles are continuously grown.
As shown in fig. 2, the interior of the vortex tube 203 of the present invention is not straight cylindrical. The flow path inside the vortex tube 203 comprises at least one diverging section and at least one vortex section. The vortex section is arranged below the expansion section, namely, the feed liquid in the expansion section flows into the vortex section. The expanding section is used for enabling the flow velocity of the feed liquid to change rapidly. The vortex section is used for enabling the feed liquid to flow upwards under the action of negative pressure and generating a vortex, and generation of crystals is promoted.
For example, when there is one diverging section and one swirling section, the swirling section is disposed downstream of the diverging section.
When there are two diverging sections and one swirl section, the swirl section is disposed between the two diverging sections; alternatively, two diverging sections are provided in series, with the swirl section being provided downstream of the two diverging sections.
When two expansion sections and two vortex sections exist, the expansion sections can be arranged in a staggered mode with the vortex sections; or the two expansion sections are continuously arranged, the two vortex sections are continuously arranged, and the two vortex sections are simultaneously arranged at the outlets of the two continuous expansion sections.
In the present invention, regardless of the sequence of the diverging section and the swirl section, at least one swirl section is located downstream of the diverging section. That is, the feed liquid inlet of vortex tube 203 is set as an expansion section, and the feed liquid outlet of vortex tube 203 is an expansion section or a vortex section. The reason for this is that the expanding section is used to make the feed liquid form velocity shear in the flow direction, and the vortex section can strengthen the feed liquid to mix in a way of generating a vortex, so that the crystal particles grow up.
As shown in fig. 2, the present invention is explained by taking a cross-sectional view of the structure of one of the vortex tubes as an example.
The flow passage inside the vortex tube 203 includes a first diverging section 215, a first vortex section 213, a second diverging section 216, and a second vortex section 214 connected in sequence. That is, the expanding section and the vortex section are arranged in a staggered manner, and the vortex section is arranged at the outlet of the expanding section.
The inner side surface of the expanding section of the invention is in an outwardly expanding arc shape, so that the width of the channel at the inner side of the expanding section is larger than the width of the inlet of the expanding section and the outlet of the expanding 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 channels of the vortex section are arranged as direct flow channels, but the side surfaces are provided with flow guide structures in a manner of accelerating the transmission of the inverse crystals and simultaneously reducing the generation of forward feed liquid in the transmission process.
As shown in fig. 2 to 4, the drainage structure includes a plurality of backflow parts. In the invention, at least one first backflow part 401 and at least one second backflow part 402 are arranged in the guide pipe, and branch flow channels for guiding fluid to flow reversely are arranged in the guide pipe. The first backflow part 401 and the second backflow part 402 are opposite in direction and are arranged in a staggered mode. For example, the first and second flow returns 401, 402 are identically shaped and mirror images. The first backflow part 401 and the second backflow part 402 are arranged in a staggered manner in the vertical direction.
The branch flow channel formed by the backflow part and the inner wall of the main flow channel in a protruding mode at least comprises two flow sections. As shown in fig. 3, the branch flow path of the backflow portion includes a curved section 403 and a straight section 404. The flow channel direction of the straight section 404 has an inclined included angle with the vertical direction, so that the feed liquid can rapidly enter the bent section 403. Preferably, the included angle formed by the straight flow section 404 and the vertical direction is in the range of 15 ° to 45 °. Too big or too little angle of contained angle can lead to the feed liquid when getting into crooked section 403, produces different access & exit hydraulic pressure differences, can lead to the unable stable flow of feed liquid on the contrary.
The curved section 403 is a flow channel continuous with and curved from the straight section 404. Curved section 403 is arranged in a curved direction with the feed liquid direction approximately opposite to that of straight section 404, so that the feed liquid flowing out of curved section 403 collides with the feed liquid direction of the main flow channel. The bent section 403 and the straight section 404 allow the feed liquid path to be sealed into a plurality of pressure zones, generate a thrust by a change in the pressure difference and allow the flow rate of the feed liquid to be increased. 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 backflow part is formed by separating a straight main flow channel and an outwardly protruding streamline inner wall by a separation structure connected with the main pipe part. The profile of the isolation structure matches the profile of the protruding inner wall of the branch flow passage and the portion of the isolation structure that is distal from the straight flow section 404 is arcuate in configuration. In the cross-section shown in fig. 4, one end of the isolation structure is curved and has a curvature that is the same as the curvature of the straight section 404 in the longitudinal cross-section. The curved end of the spacer structure converges towards the non-curved end and the contact profile of the spacer structure with the curved section 403 is a straight sloping profile. The profile of the isolation structure in contact with the primary flowpath is arcuate and provides the outlet of the straight flow section 404 as a slip-expanded outlet. Briefly, the shape of the isolation structure is similar to that of a tear drop, and the arc end of the tear drop is disposed at the bending position of the straight flow section 404 to form a flow passage for allowing the feed liquid to flow. The tear drop-shaped tip is contacted with the feed liquid of the main flow passage. Preferably, the shape of the isolation structure can also be provided as an egg. 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.
The vortex section of the invention can replace a propeller to generate vortex, and the mixing action of the feed liquid and the crystal precipitation effect are not reduced.
When the feed liquid flowing out of the expanding section enters the swirling section, most of the feed liquid flows from the main flow channel, and a small part of the feed liquid enters the first reflux portion 401 and the second reflux portion 402, respectively. Obviously, the inlet of straight flow section 404 is smaller than the outlet of curved section 403, and the reason for this is that the feed liquid is easily crystallized during the flow, and although the flow rate of the feed liquid in the reflux portion is fast and not easily crystallized, minute crystals are inevitably generated. To avoid the blockage of the branch flow channel by small crystals, the inlet of the dc section 404 is smaller to avoid large crystals from entering the branch flow channel. The faster flow rate in the branch flow channel also reduces the risk of crystal blockage. The outlet of the bent section 403 is larger, which is beneficial to the micro crystal to flow out quickly. Preferably, the flow channel width of the direct current section 404 is smaller than that of the bending section 403, so as to further avoid the blockage of the tiny crystals in the bending section 403.
Because bent section 403 makes the feed liquid flow out fast and in reverse direction, reverse feed liquid collides with the forward feed liquid of sprue and produces the swirl, can obviously reduce the velocity of flow of the feed liquid of sprue in the vortex section for the feed liquid can intensive mixing and the crystal of appearing.
As shown in fig. 3 and 4, inside the vortex tube, a first expanding section 215, a first vortex section 213, a second expanding section 216, and a second vortex section 214 are sequentially arranged in a vertical direction. The feed liquid generates first speed shearing at the first expansion section 215, the feed liquid flowing out from the first expansion section enters the first vortex section 213 to generate a vortex, the vortex also has the speed shearing function of the feed liquid and increases the mixing range of the feed liquid, so that the feed liquid generates second speed shearing, and the separation of crystals is facilitated. The feed liquid and its crystals flowing out of the first vortex section 213 enter the second expanding section 216, and the third time of speed shearing is realized based on the circular-arc-shaped flow channel expansion. Feed liquid exiting second expanding section 216 enters second vortex section 214 creating a vortex that induces a fourth velocity shear to the feed liquid. The staggered arrangement of the first expanding section 215, the first vortex section 213, the second expanding section 216 and the second vortex section 214 enables the feed liquid to realize at least four times of flow rate step change when passing through the vortex tube 203, thereby improving the extraction rate of the feed liquid. Meanwhile, the larger crystal particles do not enter the bent sections 403 of the branch flow channels and are not always caught at the inlets of the bent sections 403 due to the impact of the feed liquid of the main flow channel.
Preferably, the height difference between the first reflow part 401 and the second reflow part 402 is set to H. The smaller the height difference H, the more the first reflow part 401 and the second reflow part 402 tend to have a symmetrical structure. When the height difference H is zero, the first reflow part 401 and the second reflow part 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 the vortex sections, and the like. Specifically, under the condition that the height difference H is zero, the pressure drop formula of the draft tube is as follows: (the power N of the correction parameter α) × feed liquid density ρ × (the square of the flow velocity V) × draft tube length L × (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 of the vortex tube 203, and the higher the symmetry, the larger the pressure drop. With the introduction of service life and cost, a suitable height difference H can be selected according to the above formula for use in the vortex tube 203.
Preferably, there is also a height difference between the outlet of the second backflow part 402 and the inlet of the first backflow part 401, so as to avoid the condensed crystals in the vortex generated by the first backflow part 401 at the upstream position from being stuck at the inlet of the second backflow part 402 at a lower position. After the height difference is set, the inlet of the first backflow part 401 is mainly divided from the material liquid flowing into the main flow channel which is vertically upward, the gravity of the crystal is large and is easy to fall, and therefore the crystal cannot be influenced by the division flow and enters 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 channel, and even shrinks again and enters the branch flow channel.
In the present invention, as shown in FIG. 4, the crystals precipitated by four times of speed shearing have a larger volume and a larger weight.
Preferably, the sodium sulfate production unit 500: preparing a nearly saturated sodium sulfate solution by hot melting of sodium sulfate decahydrate, performing heat exchange heating with condensed water, feeding the sodium sulfate decahydrate and the condensed water into a sodium sulfate evaporation crystallization system, concentrating a sodium sulfate solution by multi-effect forward flow evaporation crystallization, continuously concentrating sodium sulfate in the solution to be supersaturated and separated out, gradually growing up and depositing on sodium sulfate feet, discharging a sodium sulfate slurry liquid, obtaining wet sodium sulfate by thickening and centrifugal separation, drying by 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 settler unit, and condensed water produced by an evaporative crystallization system exchanges heat with the feeding material of the system and is recycled;
preferably, the second saltpeter separation unit 300: the frozen supernatant mother liquor obtained after sedimentation of the sodium chloride solution poor in nitrate produced by the first salt-nitrate separation unit 200 is discharged and enters a membrane filtration unit for treatment, partial impurities are removed to prevent the impurities from damaging the structure of the nanofiltration membrane, and the filtered concentrated water is returned to the mixed salt evaporation crystallization feed tank of the mixed salt crystallization unit 100. The freezing feed liquid is filtered to produce water and then enters a subsequent NF device to purify the poor sodium nitrate and sodium chloride feed liquid, the NF treatment mainly uses sodium chloride as a small amount of sodium sulfate solution, the rich sodium nitrate and low sodium sulfate concentrated water returns to a freezing settler (and/or settler) of the first salt and nitrate separation unit 200 to continuously recover sodium sulfate, and the poor sodium nitrate and sodium chloride produced water directly enters a sodium chloride production unit 400: the sodium chloride evaporation settler or the produced water is concentrated (the water with large quantity and low concentration is matched (RO or ED or DTRO or MVR) and then enters a sodium chloride evaporation crystallization system (a sodium chloride production unit 400).
Sodium chloride production unit 400: the sodium chloride solution is concentrated through multi-effect concurrent flow evaporative 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 through a salt drying bed and packaged 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 settler 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 of salt-containing wastewater, in particular to a process method for separating salt and nitrate from high-salt-containing wastewater by adopting multi-stage purification balance, 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), with TDS generally about 6-20 ten thousand ppm, is subjected to MVR and multi-effect forced circulation evaporation crystallization to enable salt and nitrate to reach a supersaturated state, sodium sulfate and sodium chloride mixed salt crystals are separated out, sodium sulfate and sodium chloride crystal slurry discharged by an evaporation settler are subjected to thickening separation to obtain sodium sulfate and sodium sulfate mixed salt with the water content of the sodium sulfate and the sodium chloride of 4-5%, meanwhile, a part of miscellaneous salt mother liquor discharged by an evaporation crystallization system is subjected to impurity removal and drying system, and impurities such as organic matters and sodium nitrate entering an evaporation crystallization tank saturated concentrated feed liquid are mainly balanced, wherein the 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 further detailed 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 is 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, the transmittance of chloride ions is greater than that of sulfate ions, and 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, so that 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), low TDS and high TDS are respectively low value and high value, and total hardness is CaCO 3 Calculated) is less than 5mg/l, and the total alkalinity (calculated as CaCO) 3 Calculated) is 10-30 mg/l; the control concentration of each pollutant in the effluent of the mixed salt crystallization unit 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 ℃ to 0 ℃, decahydrate solid is produced and separated, centrifugal separation and dehydration treatment are carried out, the solid is subjected to hot melting by using condensed water, a saturated sodium sulfate solution is prepared, a nitrate evaporation crystallization system is removed, high-temperature production and marketing are carried out, a high-purity sodium sulfate product is prepared, a small amount of enriched impurities return to a mixed salt evaporation system, sodium sulfate is continuously recovered, and meanwhile, a small amount of impurity enriched matters in the nitrate 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 and low-sodium sulfate-rich concentrated water to the pretreatment unit in such a manner that the produced nitrate-poor and sodium chloride-rich produced water can meet the sodium chloride concentration required by the sodium chloride production unit 500;
the NF membrane separation device 300b is configured to comprise at least two mutual nanofiltration devices which can be communicated based on the sulfate ion concentration in the nitrate-rich and sodium chloride-rich produced 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-rich and sodium sulfate-rich concentrated water.
Preferably, the pretreatment unit is configured to include at least the mixed salt crystallization unit 100 and the first salt and nitrate separation unit 200,
the mixed salt crystallization unit 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 first salt-nitrate separation unit 200 freezes the rich-nitrate mother liquor prepared based on mixed salt to separate out sodium sulfate in the form of decahydrate, thereby generating frozen lean-nitrate mother liquor which is discharged to the NF membrane separation device 300b,
the NF membrane separation apparatus 300b discharges the rich sodium sulfate/rich water to different treatment facilities of the first salt and nitrate separation unit 200 based on the nitrate content in the rich sodium sulfate/rich water,
the different treatment equipment at least comprises a settler and a freezing settler.
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 (10)
1. A salt-nitrate separation wastewater treatment system based on condensate recovery comprises: a first salt-nitrate separation unit (200) and a condensed water recovery unit (600),
it is characterized in that the preparation method is characterized in that,
the first salt and nitrate separation unit (200) can prepare a mixed salt of sodium sulfate and sodium chloride obtained by evaporating and crystallizing the wastewater into a nitrate-rich mother liquor in a saturated state, can freeze and separate out the sodium sulfate in the nitrate-rich mother liquor in a nitrate-decahydrate crystallization mode to obtain a nitrate-poor mother liquor, and discharges the nitrate-poor mother liquor to the second salt and nitrate separation unit (300),
the condensed water recovery unit (600) can be communicated with the first saltpeter separation unit (200) through a quantitative unit in a mode of referring to the amount of the solvent required by the first saltpeter separation unit (200) for preparing the mixed salt under the condition that at least condensed water obtained by cooling steam generated in the evaporation crystallization process can be recovered, so that the mixed salt can be dissolved in the softened condensed water to obtain nitrate-rich mother liquor in a saturated state.
2. The processing system according to claim 1, wherein the condensed water of the condensed water recovery unit (600) originates from steam generated in a mixed salt crystallization unit (100), steam generated in a sodium sulfate production unit (400), and steam generated in a sodium chloride production unit (500).
3. The treatment system according to claim 2, wherein the mixed salt crystallization unit (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 manner to obtain steam.
4. A treatment system according to claim 2 or 3, characterized in that the mixed salt crystallization unit (100) and the first salt-nitrate separation unit (200) are provided with separation units for controlling the water content of the mixed salt, which can be used to determine the amount of condensed water discharged by the dosing unit.
5. The treatment system according to claim 4, wherein the first salt-nitrate separation unit (200) separates out sodium sulfate in a supersaturated state in a cooling process in the form of sodium sulfate decahydrate by using a coolant under the condition of pre-cooling a saturated sodium sulfate and sodium chloride solution based on the mixed salt hot melt blending to obtain a pre-cooled feed liquid, and the coolant can reduce the temperature of the pre-cooled feed liquid to minus 5-0 ℃ to obtain a frozen feed liquid.
6. The treatment system according to claim 5, wherein the sodium nitrate decahydrate is at least subjected to hot melting and condensed water hot melting in a sodium sulfate production unit (400) to prepare a near-saturated sodium nitrate solution, the sodium nitrate solution and the condensed water are subjected to heat exchange heating, and the sodium sulfate solution is concentrated through multi-effect concurrent evaporative crystallization, so that sodium sulfate in the solution is continuously concentrated to be supersaturated and precipitated and gradually grows and deposits to be larger than nitre foot.
7. The treatment system according to any one of claims 1 to 6, wherein the first saltpeter separation unit (200) is in communication with a filtering device (300 a) in the second saltpeter separation unit (300) for further removing impurities from the frozen saltpeter-depleted mother liquor to obtain an impurity liquid in a manner according to the impurity concentration requirement of an NF membrane separation device in the second saltpeter separation unit (300), and an impurity liquid outlet of the filtering device is in communication with the mixed salt crystallization unit (100) so that the mixed salt crystallization unit (100) can purify mixed salt containing sodium sulfate crystals and sodium chloride crystals in a manner of approximately equalizing the impurity concentration in the salt-containing wastewater.
8. A treatment system according to any one of claims 1 to 6, characterized in that concentrated salt waste water is concentrated at least once before entering the mixed salt crystallization unit (100) so that its TDS value is between 6 and 20 ten thousand ppm.
9. A method for treating salt and nitrate separation wastewater based on condensate recovery is characterized by comprising the following steps:
the first salt-nitrate separation unit (200) prepares the mixed salt of sodium sulfate and sodium chloride obtained by evaporating and crystallizing the wastewater into nitrate-rich mother liquor in a saturated state, can freeze and separate out the sodium sulfate in the nitrate-rich mother liquor in a nitrate-decahydrate crystallization manner and discharge the nitrate-poor mother liquor to the second salt-nitrate separation unit (300),
the condensed water recovery unit (600) can be communicated with the first salt and nitrate separation unit (200) through a quantitative unit in a mode of referring to the amount of the solvent required by the first salt and nitrate separation unit (200) to prepare the mixed salt under the condition that at least condensed water obtained by cooling steam generated in the evaporation and crystallization process can be recovered, so that the mixed salt can be dissolved in softened condensed water to obtain nitrate-enriched mother liquor in a saturated state.
10. The process according to claim 9, wherein the condensed water of the condensed water recovery unit (600) originates from steam generated in the mixed salt crystallization unit (100), steam generated in the sodium sulfate production unit (400), and steam generated in the sodium chloride production unit (500).
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| US20210347649A1 (en) * | 2019-11-15 | 2021-11-11 | Go Higher Environment Group Co., Ltd. | Industrial waste salt resourceful treatment method and device |
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