CN112408568A - Method for treating high-salinity wastewater containing sodium chloride - Google Patents
Method for treating high-salinity wastewater containing sodium chloride Download PDFInfo
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- CN112408568A CN112408568A CN202011368969.6A CN202011368969A CN112408568A CN 112408568 A CN112408568 A CN 112408568A CN 202011368969 A CN202011368969 A CN 202011368969A CN 112408568 A CN112408568 A CN 112408568A
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- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 title claims abstract description 106
- 239000002351 wastewater Substances 0.000 title claims abstract description 78
- 239000011780 sodium chloride Substances 0.000 title claims abstract description 53
- 238000000034 method Methods 0.000 title claims abstract description 46
- 238000007710 freezing Methods 0.000 claims abstract description 84
- 230000008014 freezing Effects 0.000 claims abstract description 84
- 238000002425 crystallisation Methods 0.000 claims abstract description 71
- 230000008025 crystallization Effects 0.000 claims abstract description 69
- 239000013078 crystal Substances 0.000 claims abstract description 62
- 239000007787 solid Substances 0.000 claims abstract description 33
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 29
- 238000001816 cooling Methods 0.000 claims abstract description 21
- 238000000926 separation method Methods 0.000 claims abstract description 21
- 230000006835 compression Effects 0.000 claims abstract description 15
- 238000007906 compression Methods 0.000 claims abstract description 15
- 239000007788 liquid Substances 0.000 claims abstract description 14
- 239000000463 material Substances 0.000 claims abstract description 14
- 238000004065 wastewater treatment Methods 0.000 claims abstract description 14
- 238000005086 pumping Methods 0.000 claims abstract description 4
- 150000003839 salts Chemical class 0.000 claims description 32
- 238000005057 refrigeration Methods 0.000 claims description 10
- WECDUOXQLAIPQW-UHFFFAOYSA-N 4,4'-Methylene bis(2-methylaniline) Chemical compound C1=C(N)C(C)=CC(CC=2C=C(C)C(N)=CC=2)=C1 WECDUOXQLAIPQW-UHFFFAOYSA-N 0.000 claims description 8
- 238000007599 discharging Methods 0.000 claims description 8
- 238000000151 deposition Methods 0.000 claims description 2
- 238000007790 scraping Methods 0.000 claims description 2
- 238000005516 engineering process Methods 0.000 description 15
- 230000008569 process Effects 0.000 description 13
- 238000001704 evaporation Methods 0.000 description 10
- 239000012452 mother liquor Substances 0.000 description 10
- 230000008020 evaporation Effects 0.000 description 9
- 238000004519 manufacturing process Methods 0.000 description 9
- 230000005496 eutectics Effects 0.000 description 8
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 8
- 238000001223 reverse osmosis Methods 0.000 description 7
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 6
- 239000012267 brine Substances 0.000 description 6
- 238000001514 detection method Methods 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- 230000008901 benefit Effects 0.000 description 5
- 239000012528 membrane Substances 0.000 description 5
- 238000001728 nano-filtration Methods 0.000 description 5
- 238000005070 sampling Methods 0.000 description 5
- 229910052938 sodium sulfate Inorganic materials 0.000 description 5
- 235000011152 sodium sulphate Nutrition 0.000 description 5
- 238000006477 desulfuration reaction Methods 0.000 description 4
- 230000023556 desulfurization Effects 0.000 description 4
- 238000005265 energy consumption Methods 0.000 description 4
- 239000011521 glass Substances 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 238000004458 analytical method Methods 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 239000005457 ice water Substances 0.000 description 3
- 238000005342 ion exchange Methods 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 239000011550 stock solution Substances 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 238000000108 ultra-filtration Methods 0.000 description 3
- 239000002699 waste material Substances 0.000 description 3
- PAYRUJLWNCNPSJ-UHFFFAOYSA-N Aniline Chemical compound NC1=CC=CC=C1 PAYRUJLWNCNPSJ-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 2
- 238000005119 centrifugation Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000012065 filter cake Substances 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 239000012847 fine chemical Substances 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 239000005416 organic matter Substances 0.000 description 2
- 238000010587 phase diagram Methods 0.000 description 2
- 238000006116 polymerization reaction Methods 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 description 2
- 241000894006 Bacteria Species 0.000 description 1
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical group [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010612 desalination reaction Methods 0.000 description 1
- 238000011033 desalting Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- SOCTUWSJJQCPFX-UHFFFAOYSA-N dichromate(2-) Chemical compound [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O SOCTUWSJJQCPFX-UHFFFAOYSA-N 0.000 description 1
- 238000004821 distillation Methods 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000003344 environmental pollutant Substances 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 238000007667 floating Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- XLYOFNOQVPJJNP-ZSJDYOACSA-N heavy water Substances [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 description 1
- 239000012943 hotmelt Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 238000001471 micro-filtration Methods 0.000 description 1
- 239000010446 mirabilite Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 231100000719 pollutant Toxicity 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 239000003507 refrigerant Substances 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000004062 sedimentation Methods 0.000 description 1
- 229910001961 silver nitrate Inorganic materials 0.000 description 1
- 229910001415 sodium ion Inorganic materials 0.000 description 1
- RSIJVJUOQBWMIM-UHFFFAOYSA-L sodium sulfate decahydrate Chemical compound O.O.O.O.O.O.O.O.O.O.[Na+].[Na+].[O-]S([O-])(=O)=O RSIJVJUOQBWMIM-UHFFFAOYSA-L 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000004448 titration Methods 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
- 230000008016 vaporization Effects 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
- C02F2001/5218—Crystallization
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/12—Halogens or halogen-containing compounds
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Materials Engineering (AREA)
- Inorganic Chemistry (AREA)
- Physical Water Treatments (AREA)
- Removal Of Specific Substances (AREA)
Abstract
The invention provides a high-salinity wastewater treatment method containing sodium chloride, which comprises the steps of using a high-salinity wastewater treatment system, wherein the high-salinity wastewater treatment system comprises a freezing crystallization tower, a feeding pipe and a high-salinity wastewater feeding pump, wherein the feeding pipe and the high-salinity wastewater feeding pump are connected with the freezing crystallization tower; and a circulating cooling device used for cooling the materials in the freezing and crystallizing tower is arranged on the side of the tower, and comprises a circulating water outlet pipeline, a circulating pump, a compression refrigerator and a circulating water inlet pipeline, wherein the circulating water outlet pipeline is arranged at the middle lower part of the tower, and the circulating water inlet pipeline is arranged at the middle upper part of the tower. The method comprises the steps of pumping the high-salinity wastewater into a freezing and crystallizing tower through a feed pump, and circularly cooling materials in the freezing and crystallizing tower; collecting the top ice crystals into an ice crystal receiving groove by a scraper device; and (4) conveying the solid at the bottom of the tower into a centrifugal machine for solid-liquid separation. The treatment method can smoothly separate sodium chloride from the high-salinity wastewater. The wastewater obtained after separation can be directly subjected to biochemical treatment.
Description
Technical Field
The invention relates to the field of water treatment in the fine chemical industry, in particular to a method for treating high-salinity wastewater containing sodium chloride.
Background
In the production process of products of enterprises in the fine chemical industry, the pharmaceutical industry and the like, a large amount of high-salinity wastewater is generated, the components of the high-salinity wastewater are complex, organic matters and inorganic matters in the wastewater can not be effectively separated sometimes, and some organic matters are difficult to be completely treated by physicochemical, biochemical and other methods, so that the wastewater is difficult to achieve standard discharge. In the prior art, the traditional method for separating sodium chloride in wastewater from wastewater is evaporation concentration crystallization, such as multi-effect evaporation technology, gas-phase membrane separation and mechanical vapor recompression technology. The method has the advantages that the brine is completely separated, and the distilled fraction can directly enter the terminal biochemical treatment. However, the technology has the disadvantages that the energy consumption in the distillation process is high, and the separated sodium chloride contains a large amount of organic matters and is difficult to effectively treat.
For example, patent ZL201410796518.0 discloses a method for treating wastewater with high salt content, which comprises the following steps: high salt-containing wastewater → adjusting tank modulation → sedimentation tank chemical pretreatment → V type filter tank filtration → first stage ion exchange softening treatment → ultrafiltration system ultrafiltration → first stage reverse osmosis system reverse osmosis treatment → second stage ion exchange softening treatment → high pressure nanofiltration system nanofiltration → nanofiltration water production → second stage reverse osmosis system reverse osmosis treatment → first stage high pressure flat sheet membrane system concentration → MVR evaporative crystallization → industrial grade sodium chloride; nano-filtration concentrated water → concentration of a second section of high-pressure flat membrane system → freeze crystallization → industrial grade mirabilite; the invention reasonably couples ultrafiltration, nanofiltration, reverse osmosis and high-pressure flat membrane methods and combines the MVR crystallization and freezing crystallization technologies to treat the high-salt wastewater, overcomes the defects of a single technology, exerts the combination advantages, can treat and recover the high-salt wastewater efficiently and economically, and has remarkable economic and social benefits.
Patent ZL201510275955.2 discloses a desulfurization waste water zero release technology, including chemical medicine softening process and microfiltration membrane treatment process, and the water that comes adopts receiving and filtering and reverse osmosis separation after the two-stage softening, adopts freezing crystallization to separate out the purity of sodium sulfate decahydrate more than 99%, utilizes reverse osmosis dense water regeneration sodium ion exchange device, utilizes the evaporation crystallization to separate out the solid comprehensive utilization no liquid discharge more than 98% of sodium chloride purity. The invention can separate and reuse water in the desulfurization waste water to become usable water for life and industry, separates other impurities in the desulfurization waste water in a solid form, does not generate pollutants harmful to the natural environment, and can thoroughly solve the problem of environmental pollution caused by the desulfurization waste water.
Patent application CN201910356387.7 discloses a salt separation crystallization system for high-salinity wastewater containing organic matters, which comprises a sodium sulfate evaporation crystallization unit, a freezing crystallization unit, an organic concentration unit, a sodium chloride evaporation crystallization unit, a concentrated solution collecting tank and a miscellaneous salt drying crystallizer; also discloses a salt separation and crystallization system of the high-salinity wastewater containing organic matters, which comprises the following working procedures: evaporating and crystallizing sodium sulfate in the step (1), freezing and crystallizing in the step (2), organically concentrating in the step (3), crystallizing sodium chloride in the step (4), and drying mixed salt in the step (5). The system and the process can be used for pertinently treating the high-salinity wastewater containing the organic matters and having relatively high sulfate radical concentration, the treatment process is short, the treatment period is short, and the economic benefit of an enterprise can be ensured; in addition, the invention not only can realize the recovery of salt resources, but also can effectively ensure the purity of the recovered salt.
Patent application CN201910015558.X discloses a heat pump low temperature divides waste water treatment facilities of salt, uses the heat source heating evaporation concentration waste water of heat pump, uses the cold source freezing cooling waste water of heat pump, utilizes the characteristic that sodium sulfate solubility changes along with the temperature change, makes sodium sulfate precipitate to use the steam of secondary to carry out the evaporative crystallization of sodium chloride, the hot melt purification crystallization of sodium sulfate. The invention adopts the heat source and the cold source of the heat pump to carry out waste water desalination treatment respectively, and the energy consumption is extremely low; because of low-pressure and low-temperature evaporation, the requirement on equipment is low, a large amount of non-metallic materials can be used, and the investment is less; and has the advantages of low vibration and low noise.
In the above prior art, the methods for treating high-salinity wastewater containing sodium chloride are evaporative crystallization methods without exception. Therefore, there is a need in the art for a new method for treating high salinity wastewater containing sodium chloride.
Disclosure of Invention
The invention provides a high-salinity wastewater treatment method containing sodium chloride, which comprises the steps of using a high-salinity wastewater treatment system, wherein the high-salinity wastewater treatment system comprises a freezing crystallization tower (1), a feeding pipe and a high-salinity wastewater feeding pump (4), wherein the feeding pipe and the high-salinity wastewater feeding pump are connected with the freezing crystallization tower, and the freezing crystallization tower is an empty tower with a scraper device (11) at the top; and a circulating cooling device (2) for cooling the materials in the freezing and crystallizing tower is arranged on the side of the tower, and comprises a circulating water outlet pipeline (21) arranged at the middle lower part of the tower, a circulating pump (22), a compression refrigerator (23) and a circulating water inlet pipeline (24) arranged at the middle upper part of the tower; a solid outlet (12) is arranged at the bottom of the freezing crystallization tower, the solid outlet is communicated with the centrifugal machine (3), an ice crystal outlet (13) is arranged at the top or the middle upper part of the freezing crystallization tower and is used for timely sending the ice crystals scraped by the scraper device out of the freezing crystallization tower; the method comprises the steps of pumping the high-salinity wastewater into a freezing crystallization tower through a feed pump, starting a circulating pump and a compression refrigerating machine to perform heat exchange refrigeration circulation, and circularly cooling materials in the freezing crystallization tower; after ice crystals are separated out from the tower top, the ice crystals at the top are collected into an ice crystal receiving groove by a scraper device; and (4) conveying the solid at the bottom of the tower into a centrifugal machine for solid-liquid separation.
By using the treatment method, the sodium chloride can be successfully separated from the high-salinity wastewater. The wastewater obtained after separation can be directly subjected to biochemical treatment.
In a specific embodiment, when there is a large amount of solids at the bottom of the column before feeding the bottom solids to the centrifuge, the circulation pump and the refrigeration cycle of the compression refrigerator are stopped, the solids are discharged from the bottom of the column to the centrifuge, and the salt is centrifuged; when the bottom of the tower has no solid or has little solid, stopping discharging the solid into a centrifuge; starting a circulating pump and a compression refrigerating machine to perform heat exchange and refrigeration circulation, and circularly cooling the materials in the freezing and crystallizing tower; when the liquid level in the freezing and crystallizing tower is lowered to the lowest level of the scraper device at the top of the tower for scraping ice, the system is stopped.
In a specific embodiment, the feeding pipe is connected with a feeding port (14) of a freezing and crystallizing tower (1), the feeding port is positioned in the middle or middle lower part of the freezing and crystallizing tower (1), the circulating water outlet pipeline (21) is positioned below the feeding port (14), and the circulating water inlet pipeline (24) is positioned above the feeding port (14).
In a specific embodiment, the bottom of the freezing and crystallizing tower (1) is provided with a conical bottom (15) for depositing solid sodium chloride crystals.
In a specific embodiment, the sodium chloride-containing high-salt wastewater contains 3,3 '-dimethyl-4, 4' -diaminodiphenylmethane.
In a specific embodiment, the concentration of 3,3 '-dimethyl-4, 4' -diaminodiphenylmethane in the sodium chloride-containing high-salinity wastewater is 0.1 to 5 wt%, preferably 0.2 to 3 wt%.
In a specific embodiment, the concentration of sodium chloride in the high-salinity wastewater containing sodium chloride is 0-26.5 wt%, preferably 5-26.5 wt%.
In a specific embodiment, the feed pump and the circulation pump are both centrifugal pumps.
In a specific embodiment, the feeding pipe is arranged to exchange heat with the ice crystals in the ice crystal receiving groove (6), so that the high-salinity wastewater in the feeding pipe is precooled, and meanwhile, the ice crystals in the ice crystal receiving groove (6) absorb heat and melt.
The invention also provides a continuous treatment method of high-salinity wastewater containing sodium chloride, which comprises the steps of using a high-salinity wastewater treatment system, wherein the high-salinity wastewater treatment system comprises a freezing crystallization tower (1), a feeding pipe and a high-salinity wastewater feeding pump (4), wherein the feeding pipe and the high-salinity wastewater feeding pump are connected with the freezing crystallization tower, and the freezing crystallization tower is an empty tower with a scraper device (11) at the top; and a circulating cooling device (2) for cooling the materials in the freezing and crystallizing tower is arranged on the side of the tower, and comprises a circulating water outlet pipeline (21) arranged at the middle lower part of the tower, a circulating pump (22), a compression refrigerator (23) and a circulating water inlet pipeline (24) arranged at the middle upper part of the tower; a solid outlet (12) is arranged at the bottom of the freezing crystallization tower, the solid outlet is communicated with a centrifugal machine (3), centrifugal mother liquor separated by the centrifugal machine is directly or indirectly injected into the freezing crystallization tower in a circulating manner, an ice crystal outlet (13) is arranged at the top or the middle upper part of the freezing crystallization tower and is used for timely sending ice crystals scraped by a scraper device (11) out of the freezing crystallization tower; the method comprises the steps of continuously pumping the high-salinity wastewater into a freezing crystallization tower, collecting ice crystals at the top of the tower by a scraper device and discharging the ice crystals out of the tower; discharging the solid at the bottom of the tower into a centrifugal machine, and centrifuging to obtain salt; the centrifugal mother liquor obtained by centrifugation is directly or indirectly conveyed to a freezing crystallization tower through a pipeline.
The system can be operated continuously, and the brine separation efficiency after continuous operation can reach more than 99 percent. The waste water after the salinity separation can directly enter a biochemical treatment system for advanced treatment, so that the treatment target of the salt water separation is realized, and new three wastes are not generated in the treatment process.
The invention has at least the following beneficial effects: the invention uses the freezing crystallization technology, and because of no vaporization phase change process, the method has less energy consumption than the traditional evaporation concentration salt precipitation, and because of concentration under low temperature, the invention can avoid the organic matters in the high-salinity wastewater from polymerization and deterioration under high temperature, and can realize material recovery to a certain extent, thereby achieving the purpose of resource utilization. Therefore, the freezing crystallization technology has better development prospect when being applied to the treatment of wastewater containing sodium chloride.
Drawings
FIG. 1 shows NaCl-H2O system phase diagram.
FIG. 2 is a system diagram of a freezing crystallization treatment of high-salinity wastewater containing sodium chloride.
Detailed Description
The invention explores a novel treatment method, namely a freezing crystallization method is used for treating high-salt wastewater containing sodium chloride, and particularly the high-salt wastewater contains a certain amount of 3,3 '-dimethyl-4, 4' -diaminodiphenylmethane.
The main principle of separation in the present invention is as follows:
according to NaCl-H2O system phase diagram, the phase change of 25 wt% sodium chloride solution in the cooling process is shown in figure 1.
As can be seen from fig. 1, the first stage: 25 ℃ and → 2 ℃, the system is unchanged, and NaCl is saturated in the system when the temperature of the solution reaches-2 ℃. And a second stage: 2 ℃ below zero → 21.1 ℃, the solubility of NaCl is reduced along with the reduction of the system temperature, and a small amount of NaCl 2H2Separating out O, and when the temperature is reduced to-21.1 ℃, the system reaches the eutectic point temperature. And a third stage: the system is maintained at a eutectic point temperature of-21.1 ℃, the solution concentration is 23.3 wt%, NaCl & 2H2Continuously separating out O and ice crystals according to the mass ratio of 37.6: 62.4; all the systems are made of NaCl.2H2The temperature continues to drop when both O crystals and ice crystals are present. After the NaCl aqueous solution reaches the eutectic point temperature. Soluble salt and ice crystal are separated out simultaneously, NaCl density (2.2 g/cm)3) Large, deposited at the bottom, from which the salt was centrifuged after enrichment; ice crystal density (0.9 g/cm)3) Small, the ice crystals floating on the surface of the solution are separated by a scraper, and the ice crystals are melted into water and then enter a biochemical system for treatment; thereby achieving separation of brine.
In the invention, a compression type refrigerator (compression refrigerator) is used for cooling materials in a freezing crystallization tower, and the compression type refrigerator relies on a compressor to increase the pressure of a refrigerant so as to realize a refrigeration cycle. The refrigerating machine consists of a compressor, a condenser, a refrigerating heat exchanger (evaporator), an expander or a throttling mechanism and some auxiliary equipment.
Example 1
In order to effectively evaluate the application of the freezing crystallization technology to the treatment of high-salinity wastewater containing sodium chloride in practical production, a set of pilot plant was designed, and table 1 shows a list of devices and detection devices used in a corresponding high-salinity wastewater treatment system.
TABLE 1 equipment List
The high-salinity wastewater quality and analysis method comprises the following steps: the wastewater is produced from chemical plant production wastewater, wherein the main organic matters of the wastewater are 3,3 '-dimethyl-4, 4' -diaminodiphenylmethane and trace aniline, the COD range is 3000-4000 mg/L, the pH value is 8.0-9.0, and the sodium chloride content is about 25 wt%. The COD detection method is a dichromate method (GB11914-89), the salt content is converted according to the measured chloride ion content, the chloride ion content detection method is a silver nitrate titration method (GB/T15453-1995), the moisture detection method is a Karl Fischer method (GB6283-86), the organic matter content is obtained by calculating according to the difference value of ash and moisture, and the ash detection method refers to GB 5009.4.
The experimental process comprises the following steps: FIG. 2 is a schematic view of a high-salinity wastewater treatment system according to the present invention. The test is carried out in the system according to a batch method and a continuous freezing method in sequence, and the specific process is as follows.
Firstly, intermittently treating high-salinity wastewater:
(1) firstly, injecting 900kg of high-salinity wastewater into a freezing crystallization tower, starting a circulating pump and a compression refrigerator to perform heat exchange and refrigeration circulation, circularly cooling materials in the freezing crystallization tower, and cooling the high-salinity wastewater by a heat exchanger of the compression refrigerator;
(2) when ice crystals are separated out from the top of the freezing crystallization tower, indicating that the system reaches the eutectic point temperature, and recording the temperatures of the tower bottom and the tower top; and continuously circulating and cooling to separate out a large amount of sodium chloride crystals at the bottom of the freezing crystallization tower and ice crystals at the top. The top ice crystals are intermittently collected by a scraper into an ice crystal collecting tank, and the ice crystal generation amount in unit time is recorded. After ice crystals in the ice water collecting tank are completely melted into a water phase, detecting COD and salt content;
(3) when a large amount of solids are observed at the bottom of the freezing crystallization tower through a sight glass at the lower end of the tower, and the temperature at the bottom of the freezing crystallization tower is close to-21.5 ℃, the refrigeration cycle is stopped, the bottom solids are discharged into a centrifuge for centrifuging to remove salt, and when no solids appear in the sight glass, the discharge is stopped, namely, the discharge of the solids at the bottom of the tower into the centrifuge is stopped. Continuously starting a circulating pump, and repeating the steps for cooling and freezing crystallization circularly;
(4) and when the liquid level of the freezing and crystallizing tower is lowered to the deicing lowest position at the upper end, stopping operating the system. And discharging residual liquid in the tower, sampling, and taking the mother liquid in the centrifugal mother liquid tank and the liquid melted in the ice crystal collecting tank to respectively detect COD (chemical oxygen demand) and salt content.
Secondly, continuously freezing and crystallizing to treat high-salinity wastewater:
(1) injecting 900kg of high-salinity wastewater into a freezing crystallization tower, starting a refrigeration cycle, and circularly cooling;
(2) when ice crystals are separated out from the top of the freezing and crystallizing tower, high-salinity wastewater is continuously pumped into the freezing and crystallizing tower by a feed pump at 180 kg/h; continuously collecting ice crystals on the top of the freezing crystallization tower into an ice crystal collecting tank by a scraper, and sampling from an ice crystal outlet pipeline every 2 hours to detect COD and salt;
(3) discharging salt from the bottom of the freezing crystallization tower to a centrifuge every 2h for centrifugal desalting, wherein the salt discharging end point is based on the fact that the amount of solids in a tower bottom sight glass and a pipeline sight glass is small; mother liquor obtained by centrifugation is sent into a mother liquor tank 5, the centrifugal mother liquor in the mother liquor tank is mixed with high-salinity wastewater stock solution, and the mixture is transferred into a freezing crystallization tower by a feed pump to continue freezing crystallization treatment;
(4) the system treats 2.7t of high-salinity wastewater in total, and stops running the system after the ice crystal liquid level at the tower top is lower than the lowest position of the scraped crystal. Respectively weighing the discharged materials: materials in an ice crystal receiving tank at the top of the tower, centrifugal waste salt and residual liquid in the tower. And sampling the above samples to detect COD, salt content and the like.
The experimental results are as follows: from the intermittent operation experimental phenomenon and the recorded result, when the temperature of the bottom of the freezing and crystallizing tower reaches-21.5 ℃, a large amount of solids are separated out from the bottom of the freezing and crystallizing tower, and more ice crystals appear on the top of the tower. In this case, the crystal ice and NaCl 2H2O is simultaneously precipitated, and the temperature of minus 21.5 ℃ is the eutectic point temperature of the system. Summary the experimental test data for the batch runs are shown in table 2 below:
TABLE 2 pilot plant experimental results of batch freezing crystallization
As seen from the experimental results of table 2:
(1) the content of ice crystal salt and COD separated out from the top of the freezing crystallization tower are obviously reduced, the content of 0.23 percent of sodium chloride can not influence the activity of bacteria in a biochemical pool, and a water sample after ice crystal melting can enter a biochemical system for deep treatment to realize standard discharge.
(2) The COD of the centrifugal mother liquor after freezing and crystallizing treatment is reduced to a certain extent, and the analysis reason is probably that the solubility of organic matters in the wastewater is obviously reduced due to the reduction of the system temperature in the concentration process, and then the organic matters are accumulated in a centrifugal filter cake.
(3) The organic content in the centrifuge cake increased significantly (from about 0.32 wt% to 0.95 wt%) from the stock solution, consistent with the reasons for the COD reduction analysis of the centrifuge mother liquor as described previously.
Intermittent experiments show that after the wastewater reaches the eutectic point temperature, the ice crystal generation speed is about 100kg/h, the insoluble solid generation speed is 99kg/h, and the feed liquid temperature cannot reach the eutectic point temperature once during continuous feeding, so the high-salinity wastewater feeding flow in the continuous treatment process is set to be 180 kg/h. After a total of 10h of continuous operation, the main experimental results obtained are shown in tables 3 and 4 below:
TABLE 3 controlled sampling results in continuous freezing crystallization
TABLE 4 Pilot plant test results for continuous freeze crystallization
From the results in tables 3 and 4:
(1) the sodium chloride content in the ice crystals separated by continuous freezing crystallization is only 0.21-0.24 wt%, the COD is about 500-600 mg/L, the separated ice water meets the water inlet requirement of a biochemical system, and the treatment target of salt water separation is realized to a certain extent.
(2) The content of organic matters in the centrifugal filter cake is lower than that of the intermittent method, the organic matters are mainly products in the production process, namely 3,3 '-dimethyl-4, 4' -diaminodiphenylmethane, and the separated NaCl & 2H2The O crystal can be applied to the production process to realize the cyclic utilization of resources.
(3) From the intermediate process sampling detection result, the ice crystal melting water sample and the centrifugal mother liquor have little fluctuation of COD and salt content, and are relatively stable as a whole, and the centrifugal mother liquor is continuously applied to the high-salt wastewater stock solution, so that the problem of concentration efficiency reduction caused by organic matter enrichment is avoided;
according to the result of 10H of continuous freezing crystallization operation, the whole system operates stably, and the waste water entering the freezing crystallization system is finally treated by ice water and NaCl & 2H2The separation is realized in the form of O crystals, the separation efficiency of brine is more than 99 percent (the system continuously operates), and no new three wastes are generated in the treatment process.
In general, the invention adopts the freezing crystallization technology to treat the industrial high-salinity wastewater containing sodium chloride, and the main principle is that NaCl & 2H when the sodium chloride solution reaches the eutectic point temperature2The O crystal and the ice crystal are simultaneously separated out, and the ice and the salt are separated by utilizing the density difference between the O crystal and the ice crystal and the water, so that the aim of separating the salt and the salt from the high-salinity wastewater containing the sodium chloride is finally fulfilled. The research experiment shows that after the high-salinity wastewater is treated by the freezing crystallization technology, the content of sodium chloride in the separated ice crystals is only 0.21-0.24 wt%, the COD is about 500-600 mg/L, the separation efficiency of the brine is more than 99%, and the wastewater after direct separation can enter biochemical treatment. The content of organic matters in the separated sodium chloride is low, and the organic matters are mainly products required by production, such as 3,3 '-dimethyl-4, 4' -diaminodiphenylmethane, and can be applied to the production process.
Compared with the traditional evaporation concentration technology, the freezing crystallization technology can realize water-salt separation by using less energy consumption, and can avoid the problems of reduced concentration efficiency, poor salt production quality and the like caused by the polymerization reaction of organic matters at high temperature. Therefore, the freezing crystallization technology can be used as a new brine separation technology in the treatment of industrial high-salinity wastewater.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions and substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.
Claims (9)
1. A high-salinity wastewater treatment method containing sodium chloride comprises the steps of using a high-salinity wastewater treatment system, wherein the high-salinity wastewater treatment system comprises a freezing crystallization tower (1), a feeding pipe and a high-salinity wastewater feeding pump (4) which are connected with the freezing crystallization tower, and the freezing crystallization tower is an empty tower with a scraper device (11) at the top of the tower; and a circulating cooling device (2) for cooling the materials in the freezing and crystallizing tower is arranged on the side of the tower, and comprises a circulating water outlet pipeline (21) arranged at the middle lower part of the tower, a circulating pump (22), a compression refrigerator (23) and a circulating water inlet pipeline (24) arranged at the middle upper part of the tower; a solid outlet (12) is arranged at the bottom of the freezing crystallization tower, the solid outlet is communicated with the centrifugal machine (3), an ice crystal outlet (13) is arranged at the top or the middle upper part of the freezing crystallization tower and is used for timely sending the ice crystals scraped by the scraper device out of the freezing crystallization tower; the method comprises the steps of pumping the high-salinity wastewater into a freezing crystallization tower through a feed pump, starting a circulating pump and a compression refrigerating machine to perform heat exchange refrigeration circulation, and circularly cooling materials in the freezing crystallization tower; after ice crystals are separated out from the tower top, the ice crystals at the top are collected into an ice crystal receiving groove by a scraper device; and (4) conveying the solid at the bottom of the tower into a centrifugal machine for solid-liquid separation.
2. The method of claim 1 wherein the circulation pump and the refrigeration cycle of the compression chiller are stopped when there is a substantial amount of solids in the bottoms prior to feeding the bottoms solids to the centrifuge, discharging the solids from the bottoms to the centrifuge, and centrifuging the salt; when the bottom of the tower has no solid or has little solid, stopping discharging the solid into a centrifuge; starting a circulating pump and a compression refrigerating machine to perform heat exchange and refrigeration circulation, and circularly cooling the materials in the freezing and crystallizing tower; when the liquid level in the freezing and crystallizing tower is lowered to the lowest level of the scraper device at the top of the tower for scraping ice, the system is stopped.
3. The method according to claim 1, characterized in that the feed pipe is connected to a feed inlet (14) of the freezing and crystallizing tower (1), the feed inlet is located in the middle or middle-lower part of the freezing and crystallizing tower (1), the circulating water outlet pipe (21) is located below the feed inlet (14), and the circulating water inlet pipe (24) is located above the feed inlet (14).
4. The method according to claim 1, characterized in that the bottom of the freezing and crystallizing tower (1) is provided with a conical bottom (15) for depositing solid sodium chloride crystals.
5. The method of claim 1, wherein the high salinity wastewater containing sodium chloride contains 3,3 '-dimethyl-4, 4' -diaminodiphenylmethane.
6. The method according to claim 5, wherein the concentration of 3,3 '-dimethyl-4, 4' -diaminodiphenylmethane in the sodium chloride-containing high-salinity wastewater is 0.1 to 5 wt.%, preferably 0.2 to 3 wt.%.
7. The method according to claim 1, wherein the concentration of sodium chloride in the high-salinity wastewater containing sodium chloride is 0-26.5 wt%, preferably 5-26.5 wt%.
8. The method of claim 1, wherein the feed pump and the circulation pump are both centrifugal pumps.
9. The method according to any one of claims 1 to 8, wherein the feeding pipe is arranged to exchange heat with the ice crystals in the ice crystal receiving groove (6), so that the high-salt wastewater in the feeding pipe is precooled, and meanwhile, the ice crystals in the ice crystal receiving groove (6) absorb heat and melt.
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