CN110937728A - Desulfurization wastewater treatment method and system - Google Patents

Desulfurization wastewater treatment method and system Download PDF

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Publication number
CN110937728A
CN110937728A CN201811117088.XA CN201811117088A CN110937728A CN 110937728 A CN110937728 A CN 110937728A CN 201811117088 A CN201811117088 A CN 201811117088A CN 110937728 A CN110937728 A CN 110937728A
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nanofiltration
treatment
desulfurization wastewater
water
calcium
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段亚威
钟振成
陈权
程子洪
佟振伟
熊日华
霍卫东
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China Energy Investment Corp Ltd
National Institute of Clean and Low Carbon Energy
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China Energy Investment Corp Ltd
National Institute of Clean and Low Carbon Energy
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    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00Multistage treatment of water, waste water or sewage
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/44Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/44Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/441Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/44Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/442Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
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    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/46Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C02F1/46104Devices therefor; Their operating or servicing
    • C02F1/46109Electrodes
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    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/46Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/469Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
    • C02F1/4693Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis electrodialysis
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/66Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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    • C02F2101/10Inorganic compounds
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    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/18Nature of the water, waste water, sewage or sludge to be treated from the purification of gaseous effluents
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00Controlling or monitoring parameters in water treatment
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    • C02F2209/055Hardness
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    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00Controlling or monitoring parameters in water treatment
    • C02F2209/10Solids, e.g. total solids [TS], total suspended solids [TSS] or volatile solids [VS]
    • C02F2209/105Particle number, particle size or particle characterisation
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    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00Specific treatment goals
    • C02F2303/22Eliminating or preventing deposits, scale removal, scale prevention
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F5/00Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
    • C02F5/02Softening water by precipitation of the hardness
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F5/00Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
    • C02F5/08Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents

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Abstract

The invention relates to the technical field of wastewater treatment, in particular to a treatment method and a treatment system for desulfurization wastewater. Can separate monovalent salt and divalent salt, realize the utilization of the resourceization of salt in the waste water, avoid secondary pollution, simultaneously, can also reduce the treatment cost of desulfurization waste water. A method for treating desulfurization wastewater comprises the following steps: pretreating desulfurization wastewater to remove magnesium ions, silicon, heavy metal ions and suspended matters in the desulfurization wastewater; adding sodium sulfate into the pretreated desulfurization wastewater, so that calcium ions in the desulfurization wastewater are combined with sulfate ions to generate calcium sulfate, and performing calcium removal treatment on the desulfurization wastewater; carrying out nanofiltration treatment on the desulfurization wastewater after the calcium removal treatment to obtain monovalent ion fresh water and divalent ion concentrated water; and respectively carrying out crystallization treatment on the monovalent ion fresh water and the divalent ion concentrated water to obtain monovalent salt, divalent salt and reuse water. The embodiment of the invention is used for treating the desulfurization wastewater.

Description

Desulfurization wastewater treatment method and system
Technical Field
The invention relates to the technical field of wastewater treatment, in particular to a treatment method and a treatment system for desulfurization wastewater.
Background
At present, most of flue gas desulfurization processes of coal-fired power plants at home and abroad adopt a limestone-gypsum wet flue gas desulfurization process, the process technology is mature, the operation is stable, the desulfurization efficiency is high, but desulfurization wastewater with more complex components and containing heavy metals and suspended matters is also generated in the operation process. The desulfurization wastewater is one of the most difficult water to treat in a power plant, the wastewater is treated by mainly adopting a triple box technology at present, but the treated water still contains a large amount of calcium, magnesium, sodium, sulfate radicals, chloride ions and the like, the salt content of the effluent is high, and secondary pollution to the environment can be caused after the effluent is directly discharged.
With the shortage of water resources and the stricter requirements of environmental protection departments on zero discharge of wastewater, the development of efficient, energy-saving and stable desulfurization wastewater zero discharge technology is urgent.
At present, aiming at the treatment of wastewater with high salt content, a patent with the application number of CN105481157A provides a zero-emission treatment method for desulfurization wastewater based on flue gas waste heat evaporation, and specifically discloses the following technical scheme: the desulfurization wastewater is firstly pretreated by a double alkali method to soften, flocculate and clarify the wastewater, then a membrane process is used for desalting, concentrating and reducing clarified liquid, the obtained desalted water can be recycled, the concentrated liquid is sent into a flue gas bypass evaporation tower, evaporation is carried out by using the waste heat of boiler flue gas, gaseous water vapor enters a desulfurization absorption tower along with the flue gas for condensation and recovery, and crystals are discharged along with fly ash.
In the desulfurization wastewater treatment process, lime and sodium carbonate are adopted to pretreat the desulfurization wastewater of the coal-fired power plant, wherein the calcium ion concentration in the desulfurization wastewater is sharply increased due to the addition of the lime, so that the dosage of the sodium carbonate is increased, and the market price of the sodium carbonate is very high, so that the zero emission cost of the process system is high, and the treatment cost of the desulfurization wastewater is one of the bottlenecks of the zero emission technology. In addition, the process system disclosed in the patent cannot realize effective separation of monovalent ions and high-valence ions in high-salinity wastewater, the adopted membrane filtration concentration decrement system directly concentrates ions with different valence states in the wastewater at the same time, the solid obtained after the high-salinity concentrated water concentrated by the system is treated by the flue gas bypass evaporation tower evaporation system is a mixture which is dangerous waste, and the treatment of the dangerous waste further increases the cost of desulfurization wastewater treatment.
Disclosure of Invention
The invention provides a treatment method and a treatment system for desulfurization wastewater, which can separate monovalent salt from divalent salt, realize resource utilization of salt in wastewater, avoid secondary pollution and reduce the treatment cost of desulfurization wastewater.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for treating desulfurization wastewater, comprising:
pretreating desulfurization wastewater to remove magnesium ions, silicon, heavy metal ions and suspended matters in the desulfurization wastewater; adding a sulfate solution into the pretreated desulfurization wastewater, so that calcium ions and sulfate ions in the desulfurization wastewater are combined to generate calcium sulfate, and performing calcium removal treatment on the desulfurization wastewater; carrying out nanofiltration treatment on the desulfurization wastewater after the calcium removal treatment to obtain monovalent ion fresh water and divalent ion concentrated water; and respectively carrying out crystallization treatment on the monovalent ion fresh water and the divalent ion concentrated water to obtain monovalent salt, divalent salt and reuse water.
Optionally, the molar concentration of calcium ions in the pretreated desulfurization wastewater is between 80 and 120 mmol/L.
Optionally, before adding sodium sulfate to the pretreated desulfurization wastewater, the treatment method further comprises: and adjusting the pH value of the pretreated desulfurization wastewater to 6.5-7.5.
Optionally, after adding sodium sulfate to the pretreated desulfurization wastewater, the treatment method further comprises: and adding calcium sulfate crystal seeds into the pretreated desulfurization wastewater.
Optionally, adding sodium sulfate into the pretreated desulfurization wastewater, specifically comprising: adding a sodium sulfate solution into the pretreated desulfurization wastewater, and adjusting the addition amount of the sodium sulfate solution to ensure that the molar ratio of calcium ions to sulfate ions in the desulfurization wastewater is 1:2-1: 4.
Optionally, before performing nanofiltration treatment on the desulfurized wastewater after the calcium removal treatment, the treatment method further comprises: adding a scale inhibitor into the desulfurized wastewater after the calcium removal treatment; and before the crystallization treatment of the divalent ion concentrated water, adding a scale inhibitor deactivator into the divalent ion concentrated water.
Optionally, the molar rejection rate of sulfate ions in the nanofiltration treatment process is greater than or equal to 95%, and the molar rejection rate of calcium ions is greater than or equal to 90%.
Optionally, the crystallizing treatment of the monovalent ion fresh water and the divalent ion concentrated water respectively specifically comprises: adding calcium sulfate seed crystals into the divalent ion concentrated water to crystallize the divalent ion concentrated water; and concentrating the monovalent ion fresh water, and performing crystallization treatment by evaporation.
Optionally, the monovalent ion fresh water is concentrated by a combination of electrodialysis and reverse osmosis.
Optionally, the concentration of the concentrated monovalent ions is greater than or equal to 180 g/L.
Optionally, when the desulfurization wastewater after the calcium removal treatment is subjected to nanofiltration treatment, the treatment method further comprises: recovering pressure energy of the divalent ion concentrated water in the nanofiltration treatment process, transmitting the recovered pressure energy to nanofiltration inlet water, and/or recovering pressure energy of part of divalent ion concentrated water in the nanofiltration treatment process, and simultaneously pressurizing the part of divalent ion concentrated water for nanofiltration circulation.
In a second aspect, an embodiment of the present invention provides a system for treating desulfurization wastewater, including: the device comprises a pretreatment device, a calcium removal device, a nanofiltration device and a crystallization device which are sequentially connected in series, wherein the pretreatment device is used for pretreating the desulfurization wastewater to remove magnesium ions, silicon, heavy metal ions and suspended matters in the desulfurization wastewater; the calcium removal device is used for removing calcium from the pretreated desulfurization wastewater; the nanofiltration device is used for carrying out nanofiltration treatment on the desulfurization wastewater after the calcium removal treatment to obtain monovalent ion fresh water and divalent ion concentrated water; the crystallization treatment device is used for respectively carrying out crystallization treatment on the monovalent ion fresh water and the divalent ion concentrated water to obtain monovalent salt, divalent salt and reuse water.
Optionally, the crystallization treatment device comprises a first crystallization treatment device and a second crystallization treatment device, wherein the first crystallization treatment device comprises a concentration device communicated with a monovalent ion fresh water outlet in the nanofiltration device and an evaporative crystallization device communicated with the concentration device; the second crystallization treatment device comprises the calcium removal device, and the calcium removal device is communicated with a divalent ion concentrated water outlet in the nanofiltration device.
Optionally, the concentration device comprises an electrodialysis assembly and a reverse osmosis assembly which are communicated with each other in series.
Optionally, the nanofiltration device comprises a high-pressure pump and a nanofiltration assembly, wherein the input end of the high-pressure pump is communicated with the water outlet of the calcium removal device, and the output end of the high-pressure pump is communicated with the nanofiltration raw water inlet.
Optionally, the nanofiltration device further comprises an energy recovery system, wherein the energy recovery system is used for recovering pressure energy of the divalent ion concentrated water in the nanofiltration treatment process and transmitting the recovered pressure energy to nanofiltration inlet water, and/or the energy recovery system is used for recovering pressure energy of the divalent ion concentrated water in the nanofiltration treatment process and simultaneously pressurizing part of the divalent ion concentrated water for nanofiltration circulation.
Optionally, the energy recovery system comprises at least one of a booster pump and an energy recovery device, wherein an input end of the booster pump is communicated with a nanofiltration concentrated water outlet of the nanofiltration assembly, and an output end of the booster pump is communicated with a nanofiltration raw water inlet of the nanofiltration assembly; the energy recovery device comprises a nanofiltration concentrated water inlet communicated with a nanofiltration concentrated water outlet in the nanofiltration component, a nanofiltration concentrated water outlet communicated with the crystallization treatment device, a nanofiltration raw water inlet communicated with a water outlet of the calcium removal device, and a nanofiltration raw water outlet communicated with the nanofiltration raw water inlet of the nanofiltration component.
Optionally, the energy recovery system comprises a booster pump and an energy recovery device, and the energy recovery device is communicated with a nanofiltration raw water inlet of the nanofiltration component through the booster pump.
The embodiment of the invention provides a treatment method and a treatment system of desulfurization wastewater, wherein recycled water can be obtained by sequentially removing magnesium ions, silicon, heavy metal ions, suspended matters, calcium ions, monovalent ions and divalent ions in the desulfurization wastewater, secondary pollution can be avoided, meanwhile, in the treatment process, the divalent ions and the monovalent ions can be separated, so that monovalent salt and divalent salt can be separated, and sodium sulfate is adopted to precipitate the calcium ions in the process.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic flow chart of a method for treating desulfurization waste water according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a system for treating desulfurization waste water according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of another desulfurization wastewater treatment system according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it is to be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention. In the description of the present invention, "a plurality" means two or more unless otherwise specified.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; may be a mechanical connection; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
In a first aspect, the present invention provides a method for treating desulfurized wastewater, referring to fig. 1, comprising:
s1, pretreating the desulfurization wastewater to remove magnesium ions, heavy metal ions, silicon and suspended matters in the desulfurization wastewater;
s2, adding sodium sulfate into the pretreated desulfurization wastewater to combine calcium ions and sulfate ions in the desulfurization wastewater to generate calcium sulfate so as to carry out calcium removal treatment on the desulfurization wastewater;
s3, carrying out nanofiltration treatment on the desulfurization wastewater after the calcium removal treatment to obtain monovalent ion fresh water and divalent ion concentrated water;
s4, respectively crystallizing the monovalent ion fresh water and the divalent ion concentrated water to obtain monovalent salt, divalent salt and reuse water.
Before desulfurization waste water is treated, the desulfurization waste water contains a large amount of calcium ions, magnesium ions, sodium ions, sulfate ions, chloride ions, a small amount of heavy metal ions, suspended matters, silicon and the like, the desulfurization waste water is pretreated to remove the magnesium ions, the silicon, the heavy metal ions and the suspended matters in the desulfurization waste water, and the pretreated desulfurization waste water also contains a large amount of calcium ions, sodium ions, chloride ions, sulfate ions and the like.
And then adding sodium sulfate into the pretreated desulfurization wastewater, wherein under the condition that the concentration of sulfate ions is high enough, calcium ions in the desulfurization wastewater are combined with the sulfate ions to generate calcium sulfate precipitate, most of calcium ions can be removed, and sulfate radicals in the desulfurization wastewater are combined with the calcium ions to generate calcium sulfate divalent salt, so that the phenomenon that when sodium carbonate is used for removing the calcium ions, the sulfate radicals and chloride ions in the desulfurization wastewater are combined with sodium ions in the nanofiltration treatment process to obtain mixed salt is avoided.
Then, performing nanofiltration treatment on the desulfurization wastewater after the calcium removal treatment, and separating monovalent ions from divalent ions according to the principle of nanofiltration treatment to obtain monovalent ion fresh water and divalent ion concentrated water;
and finally, respectively crystallizing the monovalent ion fresh water and the divalent ion concentrated water to obtain monovalent salt, divalent salt and reuse water, wherein the monovalent salt is sodium chloride, the divalent salt is calcium sulfate, the purity of the monovalent salt and the purity of the divalent salt can reach more than 99%, the salt is recycled, and the reuse water mainly refers to non-drinking water which can be reused in a certain range and reaches a certain water quality standard after municipal sewage or domestic sewage is treated. Thereby really realizing zero emission.
The embodiment of the invention provides a method for treating desulfurization wastewater, which can obtain reuse water by sequentially removing magnesium ions, silicon, heavy metal ions, suspended matters, calcium ions, monovalent ions and divalent ions in the desulfurization wastewater, can avoid secondary pollution, can separate divalent ions from monovalent ions in the treatment process, can separate monovalent salt from divalent salt, and can precipitate calcium ions by using sodium sulfate.
In one embodiment of the present invention, the desulfurization waste water may be treated by adding lime (including quicklime CaO and slaked lime Ca (OH))2) Organic sulfur, flocculating agent and coagulant aid, and the desulfurization wastewater is pretreated.
In the embodiment of the invention, lime is added into the desulfurization waste water, magnesium ions and most heavy metal ions are combined with hydroxide radicals in calcium hydroxide to form hydroxide precipitates to be removed, silicon can be removed by coprecipitation with magnesium hydroxide, mercury in the heavy metal ions is combined with organic sulfur to form mercury sulfide precipitates to be removed, so that magnesium ions and heavy metal ions such as lead, zinc, chromium and mercury in the desulfurization waste water are removed, and suspended matters can be removed by adding a flocculating agent and a coagulant aid.
Wherein, when lime is added into the desulfurization wastewater, the pH value of the desulfurization wastewater can be adjusted to 11-12, such as 11 or 12, by utilizing the alkalinity of calcium hydroxide, magnesium ions and most heavy metal ions in the desulfurization wastewater can be removed, and the concentration of the magnesium ions in the pretreated desulfurization wastewater is detected to be less than or equal to 8.0 mg/L.
In order to avoid the alkaline desulfurization wastewater after pretreatment, the equipment is highly corroded in the subsequent treatment process. In an alternative embodiment of the present invention, before adding sodium sulfate to the pretreated desulfurization wastewater, the treatment method further comprises: the pH value of the pretreated desulfurization wastewater is adjusted to 6.5-7.5, such as 6.5, 6.8, 7.0, 7.2 or 7.5.
Wherein, the pH value of the pretreated desulfurization wastewater can be adjusted to 6.5-7.5 by adopting concentrated hydrochloric acid, so that new ions can be prevented from being introduced, and pure sodium chloride can be obtained after subsequent nanofiltration treatment and crystallization treatment.
In one embodiment of the invention, the molar concentration of calcium ions in the pretreated desulfurization wastewater is between 80 and 120 mmol/L.
Because the concentration of calcium ions in the pretreated desulfurization wastewater is high, if the desulfurization wastewater is not subjected to calcium removal treatment, the nanofiltration membrane or the nanofiltration device is blocked in the subsequent nanofiltration treatment process.
In another embodiment of the present invention, before adding sodium sulfate to the pretreated desulfurization wastewater, the treatment method further comprises: and adding calcium sulfate crystal seeds into the pretreated desulfurization wastewater. Under the induction of the calcium sulfate crystal seeds, calcium sulfate can be deposited in a crystal form, and calcium sulfate salt with higher purity is obtained, so that the resource utilization of the calcium sulfate salt is facilitated.
In another embodiment of the present invention, the adding sodium sulfate into the pretreated desulfurization wastewater specifically comprises: and adding a sodium sulfate solution into the pretreated desulfurization wastewater, and adjusting the addition amount of the sodium sulfate solution to ensure that the molar ratio of calcium ions to sulfate ions in the desulfurization wastewater is 1:2-1:4, or ensure that the molar concentration of the calcium ions in the desulfurization wastewater after calcium removal treatment is between 15-25 mmol/L.
In the embodiment of the invention, the molar ratio of calcium ions to sulfate ions in the desulfurization wastewater is 1:2-1:4 by adjusting the addition amount of the sodium sulfate solution, or the molar concentration of the calcium ions in the desulfurization wastewater after calcium removal treatment is 15-25mmol/L, so that the phenomenon that the nanofiltration membrane is blocked due to scaling caused by overlarge calcium ion concentration in the subsequent nanofiltration treatment process can be prevented.
Preferably, the molar concentration of calcium ions in the desulfurization wastewater after the calcium removal treatment is between 18 and 20 mmol/L.
In another embodiment of the present invention, before the nano-filtration treatment of the desulfurization wastewater after the calcium removal treatment, the treatment method further comprises: adding a scale inhibitor into the desulfurized wastewater after the calcium removal treatment; and before the crystallization treatment of the divalent ion concentrated water, adding a scale inhibitor deactivator into the divalent ion concentrated water.
In the embodiment of the invention, the scale inhibitor is added into the desulfurization wastewater after the calcium removal treatment, so that the scale formation in the nanofiltration treatment process can be further prevented, and the scale inhibitor deactivator is added into the divalent ion concentrated water before the crystallization treatment of the divalent ion concentrated water, so that the divalent salt can be smoothly crystallized.
In one embodiment of the invention, the molar rejection rate of sulfate ions in the nanofiltration treatment process is greater than or equal to 95%, and the molar rejection rate of calcium ions is greater than or equal to 90%. Can obtain relatively pure calcium sulfate salt and monovalent sodium salt.
In another embodiment of the present invention, the crystallizing treatment of the monovalent ion fresh water and the divalent ion concentrated water respectively specifically comprises: adding calcium sulfate seed crystals into the divalent ion concentrated water to perform crystallization treatment on the divalent ion concentrated water; the monovalent ion fresh water is concentrated and crystallized by evaporation. Calcium sulfate seed crystals are added into the divalent ion concentrated water, and calcium sulfate crystals can be obtained under the induction action of the calcium sulfate seed crystals. The monovalent ion fresh water is concentrated to obtain monovalent ion concentrated water, and high-purity monovalent salt can be obtained through evaporation.
In an alternative embodiment of the invention, the monovalent ion fresh water is concentrated by combining electrodialysis and reverse osmosis. Electrodialysis is a membrane separation operation method which uses potential difference as driving force and utilizes the selective permeability of an ion exchange membrane to remove or enrich electrolyte from a solution. Reverse osmosis is a membrane separation process that uses pressure differential as a driving force to separate a solvent from a solution.
The monovalent ion fresh water is concentrated by adopting a mode of combining electrodialysis and reverse osmosis, so that the water quantity for evaporative crystallization can be reduced to about 10%, and the investment and running cost of subsequent evaporative crystallization can be reduced.
In still another embodiment of the present invention, the concentration of the concentrated monovalent ions is 180g/L or more. The obtained produced water can reach the standard of recycled water.
In some embodiments of the present invention, when the desulfurization wastewater after the calcium removal treatment is subjected to nanofiltration treatment, the treatment method further comprises: recovering pressure energy of the divalent ion concentrated water in the nanofiltration treatment process, and transferring the recovered pressure energy to nanofiltration inlet water.
In the embodiments, the pressure energy of the divalent ion concentrated water in the nanofiltration treatment process is recovered, and the recovered pressure energy is transferred to the nanofiltration inlet water, so that the flow of the high-pressure pump used in the nanofiltration treatment process can be reduced by about 50%, and the investment and the operation cost of the high-pressure pump are saved.
In other embodiments of the present invention, when the desulfurization wastewater after the calcium removal treatment is subjected to nanofiltration treatment, the treatment method further includes: recovering pressure energy of the divalent ion concentrated water in the nanofiltration treatment process, and simultaneously pressurizing part of the divalent ion concentrated water for nanofiltration circulation.
In the embodiments, the pressure energy of the divalent ion concentrated water is recovered, the nanofiltration circulation can be realized by adding the booster pump, the divalent ion concentrated water can be continuously refluxed without arranging the high-pressure pump, the investment and the operation cost of the high-pressure pump are saved, and the scaling can be prevented.
In some embodiments of the present invention, when the desulfurization wastewater after the calcium removal treatment is subjected to nanofiltration treatment, the treatment method further includes: the pressure energy of the divalent ion concentrated water in the nanofiltration treatment process is recovered, part of the pressure energy in the recovered pressure energy is transferred to nanofiltration inlet water, and the divalent ion concentrated water carrying the rest pressure energy is used for nanofiltration circulation through pressurization, so that the surface flow rate of the membrane is improved, and scaling on the membrane is prevented.
And introducing the decompressed nanofiltration concentrated water into a crystallization treatment device for crystallization treatment.
In the embodiments, on one hand, nanofiltration circulation can be realized by adding the booster pump, and part of divalent ion concentrated water can be continuously refluxed without additionally arranging the high-pressure pump, so that the investment and the operation cost of the high-pressure pump are saved, and scaling can be prevented; on the other hand, the recovered partial pressure energy is transferred to nanofiltration inlet water, so that the flow of a high-pressure pump used in the nanofiltration treatment process can be reduced by about 50 percent, and the investment and the operation cost of the high-pressure pump can be saved.
The monovalent salt and the divalent salt of calcium sulfate are obtained after the monovalent ion fresh water and the divalent ion concentrated water are crystallized respectively, so that the monovalent salt and the divalent salt have high purity, the subsequent purification treatment can be avoided, and the salt separation cost is further reduced.
In a second aspect, an embodiment of the present invention provides a system for treating desulfurized wastewater, referring to fig. 2, including: the pretreatment device 1, the calcium removal device 2, the nanofiltration device 3 and the crystallization device 4 are sequentially connected in series; the pretreatment device 1 is used for pretreating the desulfurization wastewater to remove magnesium ions, silicon, heavy metal ions and suspended matters in the desulfurization wastewater; the calcium removal device 2 is used for removing calcium from the pretreated desulfurization wastewater; the nanofiltration device 3 is used for carrying out nanofiltration treatment on the desulfurization wastewater after the calcium removal treatment to obtain monovalent ion fresh water and divalent ion concentrated water; the crystallization treatment device 4 is used for respectively carrying out crystallization treatment on the monovalent ion fresh water and the divalent ion concentrated water to obtain monovalent salt, divalent salt and reuse water.
The embodiment of the invention provides a desulfurization wastewater treatment system, which is characterized in that a pretreatment device 1, a calcium removal device 2, a nanofiltration device 3 and a crystallization treatment device 4 are sequentially communicated in series to sequentially remove magnesium ions, silicon, heavy metal ions, suspended matters, calcium ions, monovalent ions and divalent ions in desulfurization wastewater to obtain reuse water, so that secondary pollution can be avoided.
Further, in the embodiment of the invention, the pretreated desulfurization wastewater is subjected to calcium removal treatment by adding sodium sulfate, so that calcium and sulfate radicals are combined to generate calcium sulfate precipitate, and compared with the case of adding sodium carbonate, the phenomenon that the sulfate radicals and chloride ions in the desulfurization wastewater are combined with sodium ions to obtain mixed salt in the nanofiltration treatment process when the sodium carbonate is used for removing calcium ions is avoided.
In yet another embodiment of the present invention, with continued reference to fig. 2 and 3, the crystallization treatment apparatus 4 comprises a first crystallization treatment apparatus 41 and a second crystallization treatment apparatus 42; wherein, the first crystallization treatment device 41 comprises a concentration device 411 communicated with a fresh water outlet of monovalent ions in the nanofiltration device 3 and an evaporative crystallization device 412 communicated with the concentration device 411.
The second crystallization treatment device 42 and the calcium removal device 2 may be the same device or different devices.
Preferably, the second crystallization treatment device 42 is the calcium removal device 2, and the calcium removal device 2 is communicated with a divalent ion concentrated water outlet in the nanofiltration device 3.
Because the second crystallization treatment device and the calcium removal device 2 are the same device, in practical application, the divalent ion concentrated water is returned to the calcium removal device 2, and crystallization treatment is carried out in the calcium removal device 2, so that equipment investment can be saved, the whole treatment system is simple and convenient to operate, the occupied area is small, and the system operation cost is low.
In another embodiment of the present invention, the concentration device 411 includes an electrodialysis module and a reverse osmosis module connected in series.
The electrodialysis is a desalting technology, monovalent ion fresh water contains a certain amount of monovalent salt, and anions and cations forming the monovalent salt respectively move to electrodes in opposite directions under the action of a direct current electric field. If one anion-exchange membrane and one cation-exchange membrane are inserted into one electrodialyzer, the ion-exchange membranes have permselectivity, that is, the cation-exchange membranes only allow cations to pass freely, and the anion-exchange membranes only allow anions to pass, so that the salt concentration is reduced in the middle compartments of the two membranes due to the directional migration of ions, and the two compartments close to the electrodes are respectively anion-cation concentrating compartments, and finally the desalting purpose is achieved in the middle desalting compartment. Reverse osmosis modules typically include a permeable membrane on one side of which a pressure is applied that causes the solvent to reverse osmosis against the natural osmotic direction when the pressure exceeds its osmotic pressure. Thus obtaining a permeated solvent, i.e. permeate, on the low pressure side of the membrane and a concentrated solution, i.e. concentrate, on the high pressure side. Therefore, when the electrodialysis module is connected in series with the reverse osmosis module, there are two possible connection modes, in the first possible connection mode, the outlet of the concentration chamber of the electrodialysis module is connected with the high-pressure side in the reverse osmosis module, the concentration device 41 is connected with the fresh water outlet of the monovalent ions in the nanofiltration device 3 through the inlet of the middle compartment of the electrodialysis module, and is connected with the evaporative crystallization device 412 through the outlet of the concentrated solution in the reverse osmosis module. In a second possible connection mode, the concentrated solution outlet of the reverse osmosis module is communicated with the inlet of the middle compartment in the electrodialysis module, the concentration device 41 is communicated with the monovalent ion fresh water outlet in the nanofiltration device 3 through the high-pressure side of the reverse osmosis module, and is communicated with the evaporative crystallization device 412 through the concentration compartment outlet of the electrodialysis module.
In the embodiment of the invention, the monovalent ion fresh water is concentrated by adopting a mode of combining electrodialysis and reverse osmosis, so that the water quantity for evaporative crystallization can be reduced to about 10%.
In still another embodiment of the present invention, with continued reference to fig. 3, the nanofiltration device 3 comprises a high pressure pump 31 and a nanofiltration assembly 32, wherein an input end of the high pressure pump 31 is communicated with a water outlet of the calcium removal device 2, and an output end is communicated with the nanofiltration raw water inlet.
In the embodiment of the invention, the desulfurization wastewater after the calcium removal treatment is pressurized by the high-pressure pump 31, and under the osmotic pressure higher than that of the nanofiltration membrane, water molecules and part of electrolytes (monovalent ions) pass through the nanofiltration membrane and are discharged through the nanofiltration water production outlet, and other electrolytes are discharged through the nanofiltration concentrated water outlet.
Wherein, the input end of the high-pressure pump 31 and the water outlet of the calcium removal device 2 can be communicated through the water feeding pump 6.
In still another embodiment of the present invention, with continued reference to fig. 3, the treatment system further comprises an energy recovery system 5, the energy recovery system 5 is configured to recover pressure energy of the divalent ion concentrated water during the nanofiltration treatment and transfer the recovered pressure energy to the nanofiltration feed water, and/or the energy recovery system 5 is configured to recover pressure energy of a portion of the divalent ion concentrated water during the nanofiltration treatment and simultaneously pressurize the portion of the divalent ion concentrated water for nanofiltration circulation.
In the embodiment of the invention, the energy consumption can be reduced, the investment and the operation cost of the high-pressure pump can be saved, and when part of the divalent ion concentrated water is used for nanofiltration circulation through pressurization, reflux can be realized to avoid scaling, and the recovery rate of divalent ions is ensured.
In view of this, in the first case, the energy recovery system 5 may include a booster pump 51, wherein an input end of the booster pump 51 is communicated with the nanofiltration concentrated water outlet of the nanofiltration module 32, and an output end is communicated with the nanofiltration raw water inlet of the nanofiltration module 32.
In this case, the pressurizing pump 51 pressurizes part of the nanofiltration concentrated water (i.e., the divalent ion concentrated water), so that the nanofiltration cycle can be realized, and the scaling can be prevented, and at the same time, the additional arrangement of the high-pressure pump can be avoided, and the flow rate of the high-pressure pump 31 can be reduced, thereby saving energy.
In a second case, the energy recovery system 5 may include an energy recovery device 52, wherein the energy recovery device 52 includes a nanofiltration concentrated water inlet communicated with the nanofiltration concentrated water outlet of the nanofiltration assembly 32, a nanofiltration concentrated water outlet communicated with the crystallization treatment device 4, a nanofiltration raw water inlet communicated with the water outlet of the calcium removal device 2, and a nanofiltration raw water outlet communicated with the nanofiltration raw water inlet of the nanofiltration assembly 32.
In this case, the energy recovery device 52 recovers the pressure energy in the nanofiltration module 32, and the recovered pressure energy is pressurized and then transferred to the nanofiltration inlet water, so that the high-pressure pump 31 can be avoided from being additionally arranged, the flow rate of the used high-pressure pump 31 can be reduced, and the energy-saving effect can be achieved.
Specifically, in practical applications, the energy recovery device 52 generally includes a pressure transfer module, and the pressure energy of the nanofiltration concentrated water (divalent ion concentrated water) is converted into the pressure energy of the nanofiltration raw water through the pressure transfer module. Therefore, the nanofiltration concentrated water pressurizes the nanofiltration raw water, the pressurized nanofiltration raw water can enter the nanofiltration component only through pressurization (for example, a booster pump is additionally arranged), and the depressurized nanofiltration concentrated water is discharged through a nanofiltration concentrated water outlet of the energy recovery device 52.
The pressure transmission assembly can be a turbine assembly or a pressure transmission cylinder assembly.
In a third case, the energy recovery system 5 includes a booster pump 51 and an energy recovery device 52, wherein an input end of the booster pump 51 is communicated with a nanofiltration concentrated water outlet of the nanofiltration assembly 32, an output end of the booster pump is communicated with a nanofiltration raw water inlet of the nanofiltration assembly 32, and the energy recovery device 52 includes a nanofiltration concentrated water inlet communicated with the nanofiltration concentrated water outlet of the nanofiltration assembly 32, a nanofiltration concentrated water outlet communicated with the crystallization treatment device 4, a nanofiltration raw water inlet communicated with a water outlet of the calcium removal device 2, and a nanofiltration raw water outlet communicated with an input end of the booster pump 51.
In this case, a part of the raw nanofiltration water is directly pressurized by the high pressure pump 31 and then enters the nanofiltration component 32, the other part of the raw nanofiltration water is subjected to energy boost by the energy recovery device 52 and joins with the outlet water of the high pressure pump 31 under the pressurization of the booster pump 51 and then enters the nanofiltration component 32, while a part of the concentrated nanofiltration water is pressurized by the booster pump 51 and then is used for nanofiltration circulation, the other part of the concentrated nanofiltration water is subjected to energy supply for the raw nanofiltration water by the energy recovery device 52, the concentrated nanofiltration water decompressed by the energy recovery device 52 returns to the calcium removal device 2, in the calcium removal device 2, calcium ions and sulfate radicals in the concentrated nanofiltration water are reacted by adding a scale inhibitor deactivator, calcium sulfate crystals are generated under the induction of calcium sulfate seed crystals, and calcium sulfate divalent salt is obtained after dehydration and drying. The investment and the running cost of the high-pressure pump 31 are effectively reduced.
In the third situation, the pressure of the nanofiltration raw water pressurized by the energy recovery device 52 can be further increased by the used booster pump 51, and the investment cost is further saved without additionally arranging a booster pump.
Hereinafter, the present invention will be described in detail by way of specific embodiments. These schemes are merely examples provided to specifically illustrate the present invention, and those skilled in the art will appreciate that the scope of the present invention is not limited by these schemes.
Scheme 1
As shown in FIG. 3, Ca (OH) was added to the desulfurized wastewater at a concentration of 10% in the pretreatment apparatus 1 (raw water flow rate of 20t/h)2Adjusting the pH value of the solution to 12, standing for 60min after full reaction for clarification, wherein the concentration of magnesium ions in effluent is 7.7mg/L, and the molar concentration of calcium ions is 80 mmol/L;
adjusting the pH value of the effluent of the pretreatment device to 7 by adopting concentrated hydrochloric acid;
conveying the wastewater into a calcium removal device 2 at a flow rate of 20t/h, adding a sodium sulfate solution with the mass percentage of 20%, regulating the molar ratio of calcium ions to sulfate ions in the wastewater to be 1:3, so that the molar concentration of the calcium ions in the effluent is 20mmol/L, reacting in the calcium removal device 2 for 60min, and entering a settling zone for clarifying for 90min to obtain calcium sulfate precipitate;
conveying a first part of desulfurization wastewater into a nanofiltration component 32 through a high-pressure pump 31, wherein the flow rate is 20t/h, the operating pressure of the nanofiltration component 32 is 1.5MPa, meanwhile, conveying a second part of wastewater into an energy recovery device 52 through a water feed pump 6 at the flow rate of 10t/h, returning a part of nanofiltration concentrated water generated by the nanofiltration component 32 to a calcium removal device at the flow rate of 10t/h for crystallization, conveying the other part of nanofiltration concentrated water into the energy recovery device 52 through a nanofiltration concentrated water inlet of the energy recovery device 52 (the pressure is 1.45MPa), pressurizing the second part of desulfurization wastewater entering the energy recovery device 52, wherein the pressurized pressure is 1.40MPa, then pressurizing through a pressurizing pump 51, the pressurized pressure is 1.5MPa, and the outlet flow rate is 30t/h, and conveying the pressurized second part of desulfurization wastewater into the nanofiltration component 32; wherein, the nanofiltration component 32 has a molar retention rate of more than 95% for sulfate ions and a molar retention rate of more than 90% for calcium ions;
nanofiltration water produced by the nanofiltration component 32 enters a concentration device 4 at a flow rate of 10t/h, and monovalent salt sodium chloride produced in nanofiltration is concentrated to obtain monovalent salt concentrated water with a concentration of 198g/L in a mode of combining reverse osmosis and electrodialysis, and recycle water with a salt concentration of 0.6g/L is obtained for reuse; the monovalent salt concentrated water enters an evaporation crystallization device for evaporation, and monovalent salt sodium chloride crystals with the purity of 99.2 percent and reuse water are obtained after crystallization.
Scheme 2
As shown in FIG. 3, Ca (OH) was added to the desulfurized wastewater at a concentration of 10% in the pretreatment apparatus 1 (raw water flow rate of 20t/h)2Adjusting the pH value of the solution to 11, standing for 60min after full reaction for clarification, wherein the concentration of magnesium ions in effluent is 8.0mg/L, and the molar concentration of calcium ions is 120 mmol/L;
adjusting the pH value of the effluent of the pretreatment device 1 to 7.5 by adopting concentrated hydrochloric acid;
conveying the wastewater into a calcium removal device 2 at a flow rate of 20t/h, adding a sodium sulfate solution with the mass percentage of 20% and a calcium sulfate seed crystal, regulating and controlling the molar ratio of calcium ions to sulfate ions in the wastewater to be 1:2, so that the molar concentration of the calcium ions in the effluent is 25mmol/L, reacting in the calcium removal device 2 for 60min, entering a settling zone, and clarifying for 90min to obtain calcium sulfate crystals;
the first part of the desulfurization wastewater is conveyed into a nanofiltration component 32 through a high-pressure pump 31, the flow rate is 20t/h, the operating pressure of the nanofiltration component 32 is 1.5MPa, while simultaneously a second portion of the waste water is fed by the feed pump 6 into the energy recovery device 52 at a flow rate of 10t/h, a first part of nanofiltration concentrated water generated by the nanofiltration assembly 32 is pressurized by a booster pump 51 and then used for nanofiltration circulation, a second part of nanofiltration concentrated water generated by the nanofiltration assembly 32 enters an energy recovery device 52 through a nanofiltration concentrated water inlet of the energy recovery device 52 (the pressure is 1.45MPa), the first part of the desulfurization wastewater entering the energy recovery device 52 is pressurized, the pressure after pressurization is 1.40MPa, then pressurized by a booster pump 51, the pressure is 1.5Mpa after pressurization, the outlet flow is 30t/h and is conveyed into a nanofiltration component 32, the second part of nanofiltration concentrated water for providing energy enters the calcium removal device 2 for calcium sulfate crystallization; wherein, the nanofiltration component 32 has a molar retention rate of 95% for sulfate ions and 90% for calcium ions;
nanofiltration water produced by the nanofiltration component 32 enters a concentration device 4 at a flow rate of 10t/h, and monovalent salt sodium chloride produced in nanofiltration is concentrated to obtain monovalent salt concentrated water with a concentration of 197g/L and simultaneously obtain reuse water with a salt concentration of 0.5g/L for reuse in a mode of combining reverse osmosis and electrodialysis; the monovalent salt concentrated water enters an evaporation crystallization device 42 for evaporation, and monovalent salt sodium chloride crystals with the purity of 99.4 percent and reuse water are obtained after crystallization.
Scheme 3
As shown in FIG. 3, Ca (OH) was added to the desulfurized wastewater at a concentration of 10% in the pretreatment apparatus 1 (raw water flow rate of 20t/h)2Adjusting the pH value of the solution, organic sulfur, a flocculating agent and a coagulant aid to 11.5, fully reacting, and standing for 60min for clarification, wherein the concentration of magnesium ions in effluent is 7.5mg/L, and the molar concentration of calcium ions is 100 mmol/L;
adjusting the pH value of the effluent of the pretreatment device 1 to 6.5 by adopting concentrated hydrochloric acid;
conveying the wastewater into a calcium removal device 2 at a flow rate of 20t/h, adding a sodium sulfate solution with the mass percentage of 20% and a calcium sulfate seed crystal, regulating the ratio of calcium ions to sulfate ions in the wastewater to be 1:4, enabling the molar concentration of the calcium ions in the effluent to be 15mmol/L, reacting in the calcium removal device 2 for 60min, entering a settling zone, and clarifying for 90min to obtain calcium sulfate crystals;
the first part of the desulfurization wastewater is conveyed into a nanofiltration component 32 through a high-pressure pump 31, the flow rate is 20t/h, the operating pressure of the nanofiltration component 32 is 1.5MPa, while simultaneously a second portion of the waste water is fed by the feed pump 6 into the energy recovery device 52 at a flow rate of 10t/h, a first part of nanofiltration concentrated water generated by the nanofiltration assembly 32 is pressurized by a booster pump 51 and then used for nanofiltration circulation, a second part of nanofiltration concentrated water generated by the nanofiltration assembly 32 enters an energy recovery device 52 through a nanofiltration concentrated water inlet of the energy recovery device 52 (the pressure is 1.45MPa), the first part of the desulfurization wastewater entering the energy recovery device 52 is pressurized, the pressure after pressurization is 1.40MPa, then pressurized by a booster pump 51, the pressure is 1.5Mpa after pressurization, the outlet flow is 30t/h and is conveyed into a nanofiltration component 32, the second part of nanofiltration concentrated water for providing energy enters the calcium removal device 2 for calcium sulfate crystallization; wherein, the nanofiltration component 32 has a molar retention rate of more than 95% for sulfate ions and a molar retention rate of more than 90% for calcium ions;
nanofiltration water produced by the nanofiltration component 32 enters the concentration device 4 at a flow rate of 10t/h, and monovalent salt sodium chloride produced in nanofiltration is concentrated to obtain monovalent salt concentrated water with a concentration of 199g/L in a mode of combining reverse osmosis and electrodialysis, and recycle water with a salt concentration of 0.4g/L is obtained for reuse; the monovalent salt concentrated water enters an evaporation crystallization device 42 for evaporation, and monovalent salt sodium chloride crystals with the purity of 99.5 percent and reuse water are obtained after crystallization.
In summary, by combining the calcium removal treatment and the nanofiltration treatment, calcium ions in the desulfurization wastewater are precipitated in the form of calcium sulfate, and compared with the case that sodium carbonate is adopted for the calcium removal treatment, on one hand, the cost can be reduced, on the other hand, the situation that sulfate radicals in the desulfurization wastewater cannot be removed and mixed salt of sodium chloride and sodium sulfate is generated in the nanofiltration treatment process can be avoided, and the embodiment of the invention can obtain more than 99% of calcium sulfate divalent salt and sodium chloride monovalent salt by combining normal-temperature crystallization and nanofiltration treatment, so that the resource utilization of the salt is realized, and the secondary pollution can be avoided; meanwhile, the pressure energy in the nanofiltration concentrated water is recovered by combining the nanofiltration treatment and the energy recovery, so that the energy consumption of the system can be reduced; finally, the reduction of the desulfurization wastewater can be realized by combining electrodialysis and reverse osmosis, the wastewater is reduced to about 10%, and more than 90% of reuse water is recovered.
The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims (18)

1. A method for treating desulfurization wastewater is characterized by comprising the following steps:
pretreating desulfurization wastewater to remove magnesium ions, silicon, heavy metal ions and suspended matters in the desulfurization wastewater;
adding sodium sulfate into the pretreated desulfurization wastewater, so that calcium ions in the desulfurization wastewater are combined with sulfate ions to generate calcium sulfate, and performing calcium removal treatment on the desulfurization wastewater;
carrying out nanofiltration treatment on the desulfurization wastewater after the calcium removal treatment to obtain monovalent ion fresh water and divalent ion concentrated water;
and respectively carrying out crystallization treatment on the monovalent ion fresh water and the divalent ion concentrated water to obtain monovalent salt, divalent salt and reuse water.
2. The method for treating desulfurization waste water according to claim 1,
the molar concentration of calcium ions in the pretreated desulfurization wastewater is between 80 and 120 mmol/L.
3. The method for treating desulfurization waste water according to claim 1,
before adding sodium sulfate into the pretreated desulfurization wastewater, the treatment method further comprises the following steps:
and adjusting the pH value of the pretreated desulfurization wastewater to 6.5-7.5.
4. The method for treating desulfurization waste water according to claim 1,
after sodium sulfate is added into the pretreated desulfurization wastewater, the treatment method further comprises the following steps:
and adding calcium sulfate crystal seeds into the pretreated desulfurization wastewater.
5. The method for treating desulfurization waste water according to any one of claims 1 to 4,
adding sodium sulfate into the pretreated desulfurization wastewater, and specifically comprising the following steps:
adding a sodium sulfate solution into the pretreated desulfurization wastewater, and adjusting the addition amount of the sodium sulfate solution to enable the molar ratio of calcium ions to sulfate ions in the desulfurization wastewater to be 1:2-1:4, or enable the molar concentration of the calcium ions in the desulfurization wastewater after calcium removal treatment to be 15-25 mmol/L.
6. The method for treating desulfurization waste water according to claim 1,
before the desulfurization wastewater after the calcium removal treatment is subjected to nanofiltration treatment, the treatment method further comprises the following steps:
adding a scale inhibitor into the desulfurized wastewater after the calcium removal treatment;
and before the crystallization treatment of the divalent ion concentrated water, adding a scale inhibitor deactivator into the divalent ion concentrated water.
7. The method for treating desulfurization waste water according to claim 1,
the molar retention rate of sulfate ions in the nanofiltration treatment process is more than or equal to 95 percent, and the molar retention rate of calcium ions is more than or equal to 90 percent.
8. The method for treating desulfurization waste water according to claim 1,
the crystallization treatment of the monovalent ion fresh water and the divalent ion concentrated water respectively comprises the following specific steps:
adding calcium sulfate seed crystals into the divalent ion concentrated water to crystallize the divalent ion concentrated water;
and concentrating the monovalent ion fresh water, and performing crystallization treatment by evaporation.
9. The method for treating desulfurization waste water according to claim 8,
and concentrating the monovalent ion fresh water by adopting a mode of combining electrodialysis and reverse osmosis.
10. The method of treating desulfurization waste water according to claim 8 or 9,
the concentration of the concentrated monovalent ions is more than or equal to 180 g/L.
11. The method for treating desulfurization waste water according to claim 1,
when the desulfurization wastewater after the calcium removal treatment is subjected to nanofiltration treatment, the treatment method further comprises the following steps:
recovering pressure energy of divalent ion concentrated water in the nanofiltration treatment process, transferring the recovered pressure energy to nanofiltration inlet water, and/or
Recovering pressure energy of part of divalent ion concentrated water in the nanofiltration treatment process, and simultaneously pressurizing the part of divalent ion concentrated water for nanofiltration circulation.
12. A system for treating desulfurization waste water, comprising:
a pretreatment device, a calcium removal device, a nanofiltration device and a crystallization device which are sequentially connected in series, wherein
The pretreatment device is used for pretreating desulfurization wastewater to remove magnesium ions, silicon, heavy metal ions and suspended matters in the desulfurization wastewater;
the calcium removal device is used for removing calcium from the pretreated desulfurization wastewater;
the nanofiltration device is used for carrying out nanofiltration treatment on the desulfurization wastewater after the calcium removal treatment to obtain monovalent ion fresh water and divalent ion concentrated water;
the crystallization treatment device is used for respectively carrying out crystallization treatment on the monovalent ion fresh water and the divalent ion concentrated water to obtain monovalent salt, divalent salt and reuse water.
13. The system for treating desulfurization waste water according to claim 12,
the crystallization treatment device comprises a first crystallization treatment device and a second crystallization treatment device, wherein
The first crystallization treatment device comprises a concentration device communicated with a monovalent ion fresh water outlet in the nanofiltration device and an evaporative crystallization device communicated with the concentration device; the second crystallization treatment device comprises the calcium removal device, and the calcium removal device is communicated with a divalent ion concentrated water outlet in the nanofiltration device.
14. The system for treating desulfurization waste water according to claim 13,
the concentration device comprises an electrodialysis assembly and a reverse osmosis assembly which are mutually connected and communicated in series.
15. The system for treating desulfurization waste water according to claim 12,
the nanofiltration device comprises a high-pressure pump and a nanofiltration component, wherein
The input end of the high-pressure pump is communicated with the water outlet of the calcium removal device, and the output end of the high-pressure pump is communicated with the nanofiltration raw water inlet of the nanofiltration component.
16. The system for treating desulfurization waste water according to claim 15,
the nanofiltration device also comprises an energy recovery system, wherein the energy recovery system is used for recovering pressure energy of the divalent ion concentrated water in the nanofiltration treatment process and transmitting the recovered pressure energy to nanofiltration inlet water, and/or the energy recovery system is used for recovering pressure energy of part of the divalent ion concentrated water in the nanofiltration treatment process and simultaneously pressurizing the part of the divalent ion concentrated water for nanofiltration circulation.
17. The system for treating desulfurization waste water according to claim 16,
the energy recovery system comprises at least one of a booster pump and an energy recovery device, wherein
The input end of the booster pump is communicated with a nanofiltration concentrated water outlet in the nanofiltration component, and the output end of the booster pump is communicated with a nanofiltration raw water inlet in the nanofiltration component;
the energy recovery device comprises a nanofiltration concentrated water inlet communicated with a nanofiltration concentrated water outlet in the nanofiltration component, a nanofiltration concentrated water outlet communicated with the crystallization treatment device, a nanofiltration raw water inlet communicated with a water outlet of the calcium removal device, and a nanofiltration raw water outlet communicated with the nanofiltration raw water inlet of the nanofiltration component.
18. The system for treating desulfurization waste water according to claim 17,
the energy recovery system comprises a booster pump and an energy recovery device, and the energy recovery device is communicated with a nanofiltration raw water inlet of the nanofiltration component through the booster pump.
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