CN111170516A - Treatment process and treatment system for desulfurization wastewater - Google Patents
Treatment process and treatment system for desulfurization wastewater Download PDFInfo
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- C02F1/00—Treatment of water, waste water, or sewage
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- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
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- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
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- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/469—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
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- C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
- C02F5/02—Softening water by precipitation of the hardness
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- C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
- C02F5/08—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents
Abstract
The invention relates to the field of desulfurization wastewater treatment, and discloses a desulfurization wastewater treatment method and a desulfurization wastewater treatment system. The method comprises the following steps: (1) in the presence of sodium hydroxide, carrying out softening and clarifying treatment on the desulfurization wastewater to obtain softened and clarified effluent and magnesium hydroxide, and then adding acid into the softened and clarified effluent to obtain neutral softened and clarified effluent; (2) adding sodium carbonate into the neutral softened clear effluent to obtain softened water effluent and calcium carbonate; (3) performing nanofiltration separation treatment on the softened water to obtain nanofiltration produced water and nanofiltration concentrated water; (4) carrying out membrane concentration treatment on the nanofiltration produced water to obtain membrane concentrated produced water and membrane concentrated water; (5) and carrying out diaphragm electrolysis on the membrane concentrated water to obtain chlorine and a sodium hydroxide aqueous solution. The wastewater removal treatment method can realize the reduction of the whole operation cost by effectively matching each treatment stage, ensure the stable operation of the system and obtain products with high added values.
Description
Technical Field
The invention relates to the field of desulfurization wastewater treatment, in particular to a desulfurization wastewater treatment method and a desulfurization wastewater treatment system.
Background
A plurality of flue gas desulfurization systems adopted at home and abroad are limestone-gypsum wet flue gas desulfurization processes, which are large-scale commercialized desulfurization methods in the world, and have the advantages of mature technology, relatively reliable operation, high desulfurization efficiency and good adaptability to coal types. In the desulfurization process, a certain amount of wastewater must be discharged regularly, so as to maintain the balance of the materials of a slurry circulating system of a desulfurization device, prevent the concentration of chlorine in flue gas from exceeding a specified value and ensure the quality of gypsum. The wastewater mainly comes from a flushing water system, gypsum dehydration and the like, and the desulfurization wastewater is generally acidic and has the characteristics of high salt content, high suspended matter content, heavy metal content and large water quality fluctuation. Such as direct discharge, will severely affect the surrounding environment.
The zero discharge of the waste water of the power plant is a water using mode with high water saving level of the power plant, and has good social and environmental benefits. With the rapid development of economy and electric power in China, in areas with more coal and less water in the north of China, the available amount of water resources is reduced day by day, and the water price and the pollution discharge cost are increased continuously, so that zero discharge of waste water of a power plant is necessary and inevitable.
CN205653287U discloses a device of desulfurization waste water zero release processing includes: a remove magnesium and remove the heavy pond group, the intercommunication remove magnesium and remove a calcium sedimentation pond group of heavy pond group, the intercommunication remove a nanofiltration system (it includes a sulfate dense water export and a chlorine salt fresh water export, the sulfate dense water export through a dense water return line with remove calcium sedimentation pond group intercommunication), with the chlorine salt fresh water export through the multistage reverse osmosis system of a concentrated conveying pipeline intercommunication, with an evaporative crystallizer of multistage reverse osmosis system's a dense water export intercommunication. The device can carry out the preliminary treatment to desulfurization waste water, makes desulfurization waste water accord with membrane separation technical requirement to reduce operation and treatment cost by a wide margin.
CN104355473A discloses a method for carrying out desalination zero-emission treatment on power plant desulfurization wastewater by using an electrodialysis technology, wherein the power plant desulfurization wastewater is subjected to pretreatment such as neutralization, precipitation, coagulation, filtration and the like to remove COD (chemical oxygen demand), heavy metals, fluoride ions and the like in the wastewater; then, separating monovalent salt and divalent salt in the wastewater by using nanofiltration; and then desalting and concentrating nanofiltration produced water by utilizing multi-stage countercurrent reverse-flow electrodialysis, and evaporating and concentrating the electrodialysis concentrated water to obtain NaCl salt.
CN103979729A discloses a system and a method for recycling and zero discharge of desulfurization waste water, wherein the desulfurization waste water enters a nanofiltration system after being filtered, concentrated water of the nanofiltration system returns to a desulfurization tower, nanofiltration fresh water is concentrated by a brine concentration device and then is evaporated and crystallized, the obtained fresh water can be recycled, salt is separated out and dried into a crystal salt product, and therefore the zero discharge of the desulfurization waste water is realized, the quality of the recovered fresh water is high, and the whole process saves chemical reagents and operating cost.
CN104478141A discloses a power plant flue gas desulfurization wastewater treatment process, wherein desulfurization wastewater is firstly filtered by a plate-and-frame filter and is filtered by a micropore to obtain clear filtrate without suspended matters; secondly, concentrating the clear filtrate by using an electrodialysis membrane module with pH adjustment, and recycling the concentrated fresh water; and thirdly, performing microporous filtration on the mixture in the concentration chamber, recovering filter residues, and allowing filtrate to enter a calcium sulfate crystallization device for crystallization to separate out calcium sulfate crystals.
CN105174580A discloses a desulfurization waste water zero release processing system, and waste water gets into full-automatic softening filter, ultrafiltration, one-level RO and second grade RO system after neutralization equalizing basin, coagulating sedimentation tank in proper order, and the product water is as the clean water retrieval and utilization, and dense water gets into the salt manufacturing in the evaporation crystallizer. And the zero emission treatment of the desulfurization wastewater is realized through the combination of the membrane system.
CN105110538A discloses a desulfurization wastewater zero-discharge treatment method, wherein desulfurization wastewater is pretreated and then directly treated by an electrodialysis system, concentrated water is directly subjected to furnace-spraying incineration or evaporation, fresh water is treated by a reverse osmosis system, reverse osmosis produced water is directly recycled, and concentrated water is returned to the electrodialysis system for treatment. The invention adopts the 'pretreatment + membrane integration technology' to treat the desulfurization wastewater, so that most of water resources are recycled, and the environmental pollution is reduced.
CN105254104A discloses a low-cost power plant desulfurization wastewater zero-discharge treatment process, which mainly comprises a pretreatment process and an evaporative crystallization process. In the pretreatment process, lime and sodium sulfate are used for reaction in the first-stage reaction, sodium carbonate is used for complete softening in the second-stage reaction, the obtained wastewater enters a plate heat exchanger for temperature rise after pH adjustment, then enters an evaporator for evaporation and crystallization, and crystal slurry is subjected to crystallization and separation.
Aiming at the water quality characteristics of the desulfurization wastewater, the zero-emission treatment technology generally adopts two or more technologies of pretreatment, salt separation, membrane concentration, evaporative crystallization and the like to be integrated and combined, and the patent documents relate to the technologies. Through comparison, the subsequent treatment by utilizing the membrane technology is involved, the hardness in the wastewater is completely removed by adopting softening modes such as sodium carbonate, carbon dioxide flue gas or ion resin and the like in the pretreatment process, the running cost of sodium hydroxide, sodium carbonate, resin and the like used in the softening process is very high, and the development of the zero-emission technology is limited. The concentration degree and the reduction degree are different in the subsequent membrane treatment process, and the zero emission treatment is limited to be popularized.
The desulfurization wastewater not only has the characteristics of high suspended matters and heavy metals and is acidic, but also contains high-concentration chloride ions, calcium ions and sulfate ions. Therefore, after the conventional triple-box process is only utilized to adjust the pH value and remove suspended matters and heavy metals, the high-concentration salt-containing wastewater cannot meet the discharge requirement, and a zero-discharge process for recycling and reducing the wastewater is realized. As mentioned above, the recycling and reduction processes are mostly performed by using membrane technology, and in the using process of the membrane technology, the concentration and supersaturation of scaling factors such as calcium ions, magnesium ions and silicon which are easy to cause pollution to membrane elements are rapidly increased after membrane concentration, so that scaling is easily caused on the surface of a membrane concentration system to block the membrane elements, and further, the operation and maintenance costs of the process system are increased. Therefore, the removal of pollution factors such as calcium, magnesium, silicon and the like is important in the reduction and recycling process by using the membrane method. And the power plant desulfurization wastewater contains high-concentration calcium ions and magnesium ions, and scaling influence exists on a membrane system, a water path system and the like in the treatment process. In the conventional treatment process, calcium ions, magnesium ions, silicon and the like are mainly treated by the technologies of chemical precipitation, flue gas precipitation, electrochemical adsorption, resin softening and the like, so that the influence of the existence of the pollution factors on the system is reduced. However, the process flow is long, the operation is complicated, and the medicament cost is high in the operation process.
Therefore, the development of a low-cost and high-resource-recycling desulfurization wastewater treatment method and system has important practical significance and market application value.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a method and a system for treating desulfurization wastewater.
According to a first aspect of the present invention, there is provided a method for treating desulfurization waste water, comprising:
(1) in the presence of sodium hydroxide, carrying out softening and clarifying treatment on the desulfurization wastewater to obtain softened and clarified effluent and magnesium hydroxide, and then adding acid into the softened and clarified effluent to obtain neutral softened and clarified effluent;
(2) adding sodium carbonate into the neutral softened clarified effluent to obtain softened water effluent and calcium carbonate, wherein the addition amount of the sodium carbonate enables the concentration of calcium ions in the softened water effluent to be below 0.5 mmol/L;
(3) performing nanofiltration separation treatment on the softened water to obtain nanofiltration produced water and nanofiltration concentrated water;
(4) carrying out membrane concentration treatment on the nanofiltration produced water to obtain membrane concentrated produced water and membrane concentrated water;
(5) and (3) carrying out diaphragm electrolysis on the membrane concentrated water to obtain chlorine and a sodium hydroxide aqueous solution, and returning the sodium hydroxide aqueous solution to the step (1).
According to a second aspect of the present invention, there is provided a system for treating desulfurization waste water, comprising: the device comprises a softening and clarifying treatment unit, a sodium carbonate reaction and clarification unit, a nanofiltration separation unit, a membrane concentration unit and a diaphragm electrolysis unit;
the softening and clarifying treatment unit is used for softening and clarifying the desulfurization wastewater to obtain magnesium hydroxide and softened and clarified effluent;
the sodium carbonate reaction clarification unit is used for adding sodium carbonate into neutral softened clarified effluent obtained after the softened clarified effluent is subjected to acid pH adjustment to react to obtain softened effluent and calcium carbonate;
the nanofiltration separation unit is used for carrying out nanofiltration separation treatment on the softened water outlet water to obtain nanofiltration product water and nanofiltration concentrated water;
the membrane concentration unit is used for carrying out membrane concentration treatment on the nanofiltration water to obtain membrane concentration water and membrane concentration water;
and the diaphragm electrolysis unit is used for diaphragm electrolysis of the membrane concentrated water to obtain chlorine and a sodium hydroxide aqueous solution, and returning the obtained sodium hydroxide aqueous solution to the softening and clarifying treatment unit.
The treatment method provided by the invention realizes the recovery of different products: firstly, adding sodium hydroxide to recover a magnesium hydroxide byproduct in the pretreatment process, and then adding sodium carbonate to recover a calcium carbonate byproduct (the calcium carbonate can return to a desulfurizing tower to continue reacting, so that the calcium is fully recycled and utilized, and finally, the calcium in the wastewater from the desulfurizing tower to the desulfurizing tower is completely used for obtaining calcium sulfate); the combination of salt separation and membrane concentration can yield a high purity chlorine by-product and sodium hydroxide by-product. The sodium hydroxide returns to the pretreatment reaction to recover the magnesium hydroxide, so that on one hand, the addition of calcium hydroxide in the prior art can be reduced, and the introduced calcium ions are greatly reduced, thereby the subsequent addition of sodium carbonate is reduced; on the other hand, powerful guarantee is provided for the operation of the nanofiltration system, so that the pollution degree of the subsequent membrane concentration and diaphragm electrolysis system is greatly reduced, and no pollutant is discharged. According to a preferred embodiment, when the membrane concentration treatment adopts electrodialysis-reverse osmosis coupling treatment, membrane concentration concentrated water with higher salt concentration can be obtained, and the concentrated water can be electrolyzed in diaphragm electrolysis to obtain a sodium hydroxide aqueous solution with higher concentration, and the energy consumption of the diaphragm electrolysis is reduced.
The wastewater removal treatment method can realize the reduction of the whole operation cost by effectively matching each treatment stage, ensure the stable operation of the system and obtain products with high added values.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
FIG. 1 is a schematic diagram of one embodiment of a treatment process according to the present invention.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
According to a first aspect of the present invention, there is provided a method for treating desulfurization waste water, comprising:
(1) in the presence of sodium hydroxide, carrying out softening and clarifying treatment on the desulfurization wastewater to obtain softened and clarified effluent and magnesium hydroxide, and then adding acid into the softened and clarified effluent to obtain neutral softened and clarified effluent;
(2) adding sodium carbonate into the neutral softened clarified effluent to obtain softened water effluent and calcium carbonate, wherein the addition amount of the sodium carbonate enables the concentration of calcium ions in the softened water effluent to be below 0.5 mmol/L;
(3) performing nanofiltration separation treatment on the softened water to obtain nanofiltration produced water and nanofiltration concentrated water;
(4) carrying out membrane concentration treatment on the nanofiltration produced water to obtain membrane concentrated produced water and membrane concentrated water;
(5) and (3) carrying out diaphragm electrolysis on the membrane concentrated water to obtain chlorine and a sodium hydroxide aqueous solution, and returning the sodium hydroxide aqueous solution to the step (1).
The desulfurization waste water treated by the present invention is not particularly limited, and it is well known in the art that the desulfurization waste water may be waste water from a limestone-gypsum wet desulfurization system in which suspended substances, heavy metal ions, chloride ions, calcium ions, magnesium ions, sulfate ions, silicon, and other impurities are main components, and the waste water is acidic.
According to one embodiment, the desulfurization waste water has a pH of 4-6.5, a TDS value of 20000-40000mg/L, a conductivity of 20-35mS/cm, a calcium ion content of 400-6000mg/L, a magnesium ion content of 500-5000mg/L, a sodium ion content of 200-5000mg/L, a chloride ion content of 5000-20000mg/L, a sulfate ion content of 500-15000mg/L, a turbidity of 4000-15000NTU, a basicity of 0.2-50mg/L, and an ammonia nitrogen content of 10-200 mg/L.
In the treatment method of the present invention, according to a preferred embodiment, in the step (1), the softening and clarifying treatment is performed in stages, and specifically includes:
1-1: adjusting the pH value of the desulfurization wastewater to 7-8 by using a sodium hydroxide aqueous solution, reacting for 45-80min, and then settling for 80-150min to obtain first-stage clarified effluent;
1-2: and adjusting the pH value of the primary clarified effluent to 11-12 by using an aqueous solution of sodium hydroxide, reacting for 45-80min, and then settling for 80-150min to obtain magnesium hydroxide and the softened clarified effluent (namely, secondary clarified effluent).
More preferably, step 1-1 further comprises: while adding sodium hydroxide to the desulfurized wastewater, an organic sulfur, a coagulant aid and optionally a flocculant are added thereto. The dosage of the organic sulfur can be 5-150mg/L, preferably 5-80 mg/L; the dosage of the flocculating agent can be 0-30mg/L, and the dosage of the coagulant aid can be 3-10 mg/L.
In the step 1-1, pollutants such as heavy metal ions, silicon and the like in water can be removed by firstly adjusting the pH to 7-8 and carrying out reaction and sedimentation.
More preferably, step 1-2 further comprises: while adding sodium hydroxide to the desulfurization waste water, a coagulant aid was added thereto. The coagulant aid can be used in an amount of 3-10 mg/L.
In the step 1-2, the pH is adjusted to 11-12, reaction and sedimentation are carried out, and high-purity magnesium hydroxide (the purity is more than or equal to 98%) can be obtained through separation, so that the concentration of magnesium ions can be reduced to below 10mg/L through the step.
The organic sulfur, the flocculant and the coagulant aid of the present invention are not particularly limited, and may be various organic sulfur, flocculant and coagulant aid, respectively, which are commonly used in the art. Preferably, the organic sulfur is at least one of TMT-15, TMT-55 and DTC; the flocculating agent is at least one of polyaluminium sulfate, polyferric chloride, ferric chloride and aluminium sulfate; the coagulant aid is polyacrylamide.
In the treatment method of the present invention, in the step (1), the acid may be selected from sulfuric acid and/or hydrochloric acid, preferably hydrochloric acid.
In the step (1), the pH value of the neutral softened clear effluent is 6-8 due to the addition of the acid.
In the treatment method, in the step (2), softened water effluent and calcium carbonate are obtained by adding sodium carbonate. The obtained calcium carbonate can be further returned to a desulfurizing tower for treatment, and the full utilization of calcium is realized.
In the treatment method of the present invention, in the step (3), preferably, the nanofiltration separation treatment is performed in the presence of a scale inhibitor, and the operating pressure of the nanofiltration separation treatment is 0.5 to 2 MPa. The pressures mentioned in the present invention are gauge pressures.
The type and amount of the scale inhibitor are not particularly limited, and can be selected by referring to the prior art. Preferably, the scale inhibitor is selected from an organic phosphine type scale inhibitor, an organic phosphonate type scale inhibitor, a polycarboxylic acid type scale inhibitor and a composite type scale inhibitor. The composite scale inhibitor is a scale inhibitor containing more than two effective components, for example, two or three of organic phosphine, organic phosphonate and polycarboxylic acid can be combined to be used as the scale inhibitor. In the composite scale inhibitor, the content of each effective component can be selected according to the type of the effective component, and is not particularly limited. The addition amount of the scale inhibitor can be 0.5-3 mg/L.
In the step (3), the nanofiltration membrane element used in the nanofiltration separation process is required to have a lower rejection rate of monovalent salt and a higher rejection rate of divalent salt, so as to better realize the high-efficiency separation of monovalent salt and divalent salt and obtain a higher water recovery rate, preferably, the nanofiltration membrane element used in the nanofiltration separation process is a nanofiltration membrane element having a rejection rate of sulfate ions in the nanofiltration influent water of more than 98% and a rejection rate of calcium ions in the nanofiltration influent water of more than 95%, and may be, for example, a GE DL series nanofiltration membrane element, a GE SWSR series nanofiltration membrane element, a GE DK series nanofiltration membrane element, or a NE8040-40 nanofiltration membrane element of the korean TCK company.
In addition, before the nanofiltration treatment and separation are carried out, the method of the invention can also comprise the step of carrying out sand filtration and ultrafiltration treatment on the softened water effluent, wherein the sand filtration and ultrafiltration methods are well known in the art and are not described herein again.
In the treatment method of the invention, in the step (4), the membrane concentration treatment can be selected from the existing reverse osmosis or electrodialysis treatment, preferably electrodialysis-reverse osmosis coupling concentration,
when the salt content of the nanofiltration produced water (TDS) is more than or equal to 10g/L, the step (4) comprises the following steps:
4-1: carrying out electrodialysis treatment on the nanofiltration water to obtain electrodialysis water and electrodialysis concentrated water serving as membrane concentrated water;
4-2: performing reverse osmosis treatment on the obtained electrodialysis produced water to obtain reverse osmosis concentrated water and reverse osmosis produced water serving as the membrane concentration produced water, and returning the reverse osmosis concentrated water to perform the electrodialysis treatment; or
When the salt content of the nanofiltration produced water is less than 10g/L, the step (4) comprises the following steps:
4-1: performing reverse osmosis treatment on the nanofiltration produced water to obtain reverse osmosis produced water and reverse osmosis concentrated water which are used as the membrane concentration produced water;
4-2: and performing electrodialysis treatment on the obtained reverse osmosis concentrated water to obtain electrodialysis concentrated water and electrodialysis produced water which are used as the membrane concentrated water, and returning the electrodialysis produced water to perform reverse osmosis treatment.
In the treatment method, the salt in the nanofiltration produced water is mainly sodium chloride. As will be understood by those skilled in the art, the nanofiltration effluent is mainly chloride ions and sodium ions, so that the salt content in the nanofiltration effluent is related to the quality of the desulfurization wastewater, the desulfurization wastewater is discharged by controlling the chloride ion index in the desulfurization tower, and when the desulfurization wastewater with the above composition is treated, the treatment method is generally such that the salt content of the nanofiltration effluent is more than or equal to 10 g/L. Although the salt content of the nanofiltration product water is usually more than or equal to 10g/L, the invention is not limited to the method, and when the treated desulfurization wastewater of the invention enables the salt content of the nanofiltration product water to be less than 10g/L, the invention firstly concentrates the salt content of the product water to be more than 10g/L through reverse osmosis, and then carries out electrodialysis treatment.
Preferably, the operating pressure of the reverse osmosis treatment is 2-5 MPa. Further preferably, the reverse osmosis treatment is carried out so that the recovery rate of the obtained reverse osmosis produced water is 50-75%, and the salt content of the obtained reverse osmosis concentrated water is 20-50 g/L.
Preferably, the current density of the electrodialysis treatment is 30-35mA/cm2The current is 120-150A, and the voltage is 100-120V.
In the preferred embodiment, the electrodialysis can concentrate nanofiltration water production to over 180g/L and desalinate electrodialysis water production to only certain concentration (< 10 g/L); the reverse osmosis concentrates the brine with certain concentration (less than 10g/L) and controls certain recovery rate, so that the brine and the brine both operate under optimized conditions, and the operating pressure and the energy consumption are optimized. Wherein, the outlet water of the electrodialysis fresh water chamber (namely electrodialysis produced water) is used as reverse osmosis inlet water, the reverse osmosis concentrated water can be concentrated to 30-55g/L through reverse osmosis treatment, and the concentrated water is continuously subjected to electrodialysis treatment; and the reverse osmosis produced water can reach the standard of recycled water (the salt concentration is less than or equal to 1g/L), and is preferably returned to a factory for recycling. The water produced by nanofiltration is deeply concentrated by electrodialysis-reverse osmosis coupling, so that the problem of high energy consumption caused by separate electrodialysis or reverse osmosis deep concentration can be effectively solved.
In the treatment method of the present invention, in the step (5), the operating conditions of the membrane electrolysis include: the current density is 2-4kA/m2The current is 2000-5000A, and the voltage is 30-100V, preferably 30-50V.
It will be understood by those skilled in the art that the diaphragm electrolysis, in addition to producing chlorine and aqueous sodium hydroxide, will produce a low concentration brine solution (sodium chloride solution) after electrolysis, which is the solution after dechlorination of the anode region during diaphragm electrolysis, preferably with a salt content of 100-120 g/L. When the membrane concentration treatment employs the electrodialysis-reverse osmosis coupled concentration, the method of the present invention may further include: returning the low-concentration brine solution to continue the electrodialysis treatment.
According to a second aspect of the present invention, there is provided a system for treating desulfurization waste water, comprising: the device comprises a softening and clarifying treatment unit, a sodium carbonate reaction and clarification unit, a nanofiltration separation unit, a membrane concentration unit and a diaphragm electrolysis unit;
the softening and clarifying treatment unit is used for softening and clarifying the desulfurization wastewater to obtain magnesium hydroxide and softened and clarified effluent;
the sodium carbonate reaction clarification unit is used for adding sodium carbonate into neutral softened clarified effluent obtained after the softened clarified effluent is subjected to acid pH adjustment to react to obtain softened effluent and calcium carbonate;
the nanofiltration separation unit is used for carrying out nanofiltration separation treatment on the softened water outlet water to obtain nanofiltration product water and nanofiltration concentrated water;
the membrane concentration unit is used for carrying out membrane concentration treatment on the nanofiltration water to obtain membrane concentration water and membrane concentration water;
and the diaphragm electrolysis unit is used for diaphragm electrolysis of the membrane concentrated water to obtain chlorine and a sodium hydroxide aqueous solution, and returning the obtained sodium hydroxide aqueous solution to the softening and clarifying treatment unit.
In the treatment system of the present invention, according to a preferred embodiment, the softening and clarifying treatment unit includes a primary neutralization reaction tank, a primary clarifying tank, a secondary neutralization reaction tank, and a secondary clarifying tank;
the primary neutralization reaction tank is used for adding sodium hydroxide into the desulfurization wastewater to adjust the pH value to 7-8, and simultaneously carrying out reaction to obtain a first reaction product, and the primary clarification tank is used for settling the first reaction product to obtain primary clarified effluent;
and the secondary neutralization reaction tank is used for adding sodium hydroxide into the primary clarified effluent to adjust the pH value to 11-12, and simultaneously carrying out reaction to obtain a second reaction product, and the secondary clarification tank is used for settling the second reaction product to obtain magnesium hydroxide and softened clarified effluent.
In the treatment system, the sodium carbonate reaction and clarification unit comprises a sodium carbonate reaction tank and a clarification tank, wherein the sodium carbonate reaction tank is used for adding sodium carbonate into neutral softened and clarified effluent obtained by adjusting the pH value of the softened and clarified effluent by acid for reaction, and the clarification tank is used for settling reaction products to obtain softened effluent and calcium carbonate product salt. The sodium carbonate reaction tank is usually provided with stirring equipment.
In the treatment system, the nanofiltration separation unit comprises at least one nanofiltration membrane element, and the nanofiltration membrane element has a retention rate of more than 98% for sulfate ions in the hardness-regulated outlet water and a retention rate of more than 95% for calcium ions in the nanofiltration inlet water, and can be, for example, a GE DL series nanofiltration membrane element, a GE SWSR series nanofiltration membrane element, a GEDK series nanofiltration membrane element or a NE8040-40 nanofiltration membrane element of Korea TCK company. Further preferably, the nanofiltration separation unit comprises at least two nanofiltration membrane elements used in series.
In addition, in order to further remove suspended matters in the softened water effluent, the treatment systems of the present invention may further comprise a sand filtration-ultrafiltration treatment unit, respectively, through which the suspended matters in the softened water effluent are further removed and then enter the nanofiltration separation unit, and the arrangement of the sand filtration-ultrafiltration treatment unit is well known in the art and will not be described herein.
In the treatment system of the present invention, according to a preferred embodiment, the membrane concentration treatment unit is an electrodialysis-reverse osmosis coupled concentration unit, and the electrodialysis-reverse osmosis coupled concentration unit includes an electrodialysis unit and a reverse osmosis unit; the electrodialysis-reverse osmosis coupling concentration unit comprises an electrodialysis unit and a reverse osmosis unit;
when the salt content of the nanofiltration produced water is more than or equal to 10g/L,
the electrodialysis unit is used for carrying out electrodialysis treatment on the nanofiltration water to obtain electrodialysis water and electrodialysis concentrated water serving as membrane concentrated water; the reverse osmosis unit is used for performing reverse osmosis treatment on the obtained electrodialysis produced water to obtain reverse osmosis concentrated water and reverse osmosis produced water serving as the membrane concentration produced water, and returning the obtained reverse osmosis concentrated water to the electrodialysis unit; or
When the salt content of the nanofiltration produced water is less than 10g/L,
the reverse osmosis unit is used for performing reverse osmosis treatment on the nanofiltration produced water to obtain reverse osmosis produced water and reverse osmosis concentrated water which are used as the membrane concentration produced water; and the electrodialysis unit is used for carrying out electrodialysis treatment on the obtained reverse osmosis concentrated water to obtain electrodialysis concentrated water and electrodialysis water production which are used as the membrane concentrated water, and returning the obtained electrodialysis water production to the reverse osmosis unit.
The reverse osmosis unit and the electrodialysis unit are not particularly limited in the present invention, and may be selected from those commonly used in the art. Generally, the reverse osmosis unit may comprise at least one reverse osmosis membrane element, preferably at least two reverse osmosis membrane elements used in series, the electrodialysis unit may comprise a three-stage hydraulic series electrodialysis membrane stack and corresponding auxiliary systems, and the evaporation unit may be an ambient temperature crystallization reactor, which are well known to those skilled in the art and will not be described herein.
In the treatment system of the present invention, the membrane electrolysis unit may be selected from membrane electrolysis cells commonly used in the salt membrane electrolysis soda production technology, and the membrane electrolysis cell generally comprises: a direct current stabilized voltage supply, a cation selective ion membrane, a chlorine gas recovery device and the like. Wherein the cation selective membrane can be cation selective ion membrane such as Asahi glass, Asahi chemical, and Home-made Dongye.
And electrolyzing to obtain a chlorine product at the anode of the diaphragm electrolysis unit and obtain a sodium hydroxide solution at the cathode.
The processing method of the first aspect of the invention may be implemented on a processing system of the invention.
The present invention will be described in detail below by way of examples, but the scope of the present invention is not limited thereby.
The following examples will explain the method of treating desulfurization waste water of the present invention with reference to FIG. 1.
The softening and clarifying treatment unit comprises a volume of 15m3And 20m3The first-stage neutralization reaction tank and the second-stage neutralization reaction tank respectively have the volume of 40m3And 50m3The first-stage clarification tank and the second-stage clarification tank;
the sodium carbonate reaction clarification unit comprises a volume of 10m3Sodium carbonate reaction tank and volume of 30m3The reaction tank is internally provided with a stirrer;
the nanofiltration separation unit comprises a first-stage two-stage nanofiltration system consisting of 7 membrane shells and 4 series-connected GE DK8040F30 nanofiltration membrane elements arranged in the nanofiltration separation unit;
the electrodialysis unit comprises a total membrane area of 1500m2The three-stage hydraulic series electrodialysis membrane stack and the corresponding auxiliary system;
the reverse osmosis unit is a first-stage two-stage reverse osmosis system consisting of 7 pressure containers and 4 series-connected seawater desalination reverse osmosis membrane elements assembled in the pressure containers;
the diaphragm electrolysis unit is a diaphragm electrolysis cell, wherein the cation selective ion membrane adopts an Asahi glass ion exchange membrane;
the flocculant is polyaluminium sulfate, which is purchased from Chengsheng water purification material factory in Chengsheng, Chengshen 05-11;
the coagulant aid is polyacrylamide, purchased from Nalcidae under the trademark 8103 PLUS;
the effective component of the scale inhibitor is organic phosphonate which is purchased from Nalco company and has the brand number of OSMOTREATOSM 1035;
the power plant desulfurization wastewater comprises the following components: the pH value is 6.15, the TDS value is 27643mg/L, the conductivity is 29.6mS/cm, the calcium ion content is 1013.81mg/L, the magnesium ion content is 4722.03mg/L, the sodium ion content is 200.19mg/L, the chloride ion content is 6880.71mg/L, the sulfate ion content is 13093.41mg/L, the turbidity is 7269NTU, the alkalinity is 18mg/L, and the ammonia nitrogen content is 17.3 mg/L.
Example 1
(1) Adding the sodium hydroxide aqueous solution obtained in the step (5) into the power plant desulfurization wastewater at 20t/h in a primary neutralization reaction tank for reaction, adjusting the pH of the wastewater to 7.8, adding 30mg/L organic sulfur TMT-15, 10mg/L flocculating agent and 5mg/L coagulant aid, reacting for 45min, conveying the obtained first reaction product into a primary clarifying tank, staying for 120min, and settling to obtain primary clarified effluent;
sending the first-stage clarified effluent to a second-stage neutralization reaction tank, continuously adding the sodium hydroxide aqueous solution obtained in the step (5), adjusting the pH of the effluent to 11.4, adding 3mg/L coagulant aid, reacting for 60min, conveying the obtained reaction product to the second-stage clarification tank, staying for 150min, and settling to obtain a magnesium hydroxide product (with the purity of 98.0%) and softened clarified effluent, wherein the concentration of magnesium ions in the effluent is reduced to 8.2 mg/L;
adding hydrochloric acid into the softened and clarified water at the speed of 20t/h, and adjusting the pH to 7.3 to obtain neutral softened and clarified water;
(2) feeding neutral softened and clarified effluent of 20t/h into a sodium carbonate reaction tank, adding a sodium carbonate solution with the mass concentration of 20%, reacting for 30min under the condition of stirring, then feeding a reaction product into the clarification tank, settling for 90min, separating to obtain softened water effluent (the concentration of calcium ions is 0.36mmol/L) and calcium carbonate, and returning the calcium carbonate to a desulfurization tower for reacting again;
(3) supplying 20t/h of softened water effluent to a nanofiltration separation unit, carrying out nanofiltration separation treatment in the presence of 1.5mg/L of scale inhibitor, wherein the operating pressure is 1.87MPa, so as to obtain nanofiltration concentrated water and nanofiltration produced water (the salt content is 12.6g/L), and returning the nanofiltration concentrated water to a desulfurization tower for continuous reaction at 5 t/h;
(4) performing electrodialysis treatment on nanofiltration produced water for 15t/h to obtain electrodialysis produced water and electrodialysis concentrated water, performing reverse osmosis treatment on the obtained electrodialysis produced water to obtain reverse osmosis concentrated water (the salt content is 42g/L) and reverse osmosis produced water, and returning the obtained reverse osmosis concentrated water to continue the electrodialysis treatment;
wherein the current density of the electrodialysis operation is 30mA/cm2Current 120A, voltage 110V;
the operating pressure of reverse osmosis is 3.9MPa, and the water recovery rate is 74.9%;
the coupling treatment is carried out to obtain 1t/h electrodialysis concentrated water (the salt content is 198g/L) and 14t/h reverse osmosis produced water (the salt concentration is less than 0.5g/L), and the produced water is reused as recycled water;
(5) feeding the electrodialysis concentrated water at 1t/h into a diaphragm electrolytic cell, electrolyzing to obtain 106kg of chlorine (with the purity of 99.6%), 0.4t/h of sodium hydroxide aqueous solution (with the mass concentration of 33%) and 0.6t/h of low-concentration brine (with the salt content of 109g/L), returning the sodium hydroxide aqueous solution to the step (1), and returning the rest low-concentration brine to electrodialysis for concentration treatment;
wherein, the diaphragm electrolysis conditions are as follows: the current density is controlled to be 3.2kA/m2The voltage was 36V.
The results prove that the method can realize the reduction treatment of the desulfurization wastewater, and simultaneously can recover and obtain magnesium hydroxide, calcium sulfate, sodium hydroxide and a high-purity chlorine product. The electrodialysis concentrated water entering the diaphragm electrolysis unit accounts for 5% of the consumption of the desulfurization wastewater, 70% of the reuse water is recovered, and in addition, 25% of the water is circulated in the system to optimize the system operation. Compared with the method for adjusting the pH value of the calcium hydroxide aqueous solution to the same value, the recycling of the sodium hydroxide can reduce the adding amount of calcium hydroxide into 14.6 kg/ton of water and further reduce the adding amount of sodium carbonate into 10.6 kg/ton of water. The energy consumption for the electrodialysis operation was 6.1kWh/t and for the membrane electrolysis 4.1 kWh/t.
Example 2
(1) Adding the sodium hydroxide aqueous solution obtained in the step (5) into the power plant desulfurization wastewater at 20t/h in a primary neutralization reaction tank for reaction, adjusting the pH of the wastewater to 8.0, adding 30mg/L organic sulfur TMT-15, 10mg/L flocculating agent and 5mg/L coagulant aid, reacting for 60min, conveying the obtained reaction product to a primary clarifying tank, and standing for 100min for settling to obtain primary clarified effluent;
sending the first-stage clarified effluent to a second-stage neutralization reaction tank, continuously adding the sodium hydroxide aqueous solution obtained in the step (5), adjusting the pH of the effluent to 11.8, adding 5mg/L coagulant aid, reacting for 60min, conveying the obtained reaction product to the second-stage clarification tank, staying for 100min, and settling to obtain a magnesium hydroxide product (with the purity of 98.2%) and softened clarified effluent, wherein the concentration of magnesium ions in the effluent is reduced to 6.5 mg/L;
adding hydrochloric acid into the softened and clarified water at the speed of 20t/h, and adjusting the pH to 7.5 to obtain neutral softened and clarified water;
(2) feeding the softened and clarified effluent of 20t/h into a sodium carbonate reaction tank, adding 20% by mass of sodium carbonate, reacting for 30min under stirring, then feeding the reaction product into a clarification tank, settling for 90min, separating to obtain softened water effluent (the concentration of calcium ions is 0.20mmol/L) and calcium carbonate, and returning the calcium carbonate to a desulfurization tower for retreatment;
(3) supplying the softened water of 20t/h to a nanofiltration separation unit, carrying out nanofiltration separation treatment in the presence of 2.4mg/L of scale inhibitor, wherein the operating pressure is 1.55MPa, so as to obtain nanofiltration concentrated water and nanofiltration produced water (the salt content is 12.5g/L), and returning the nanofiltration concentrated water of 7t/h to a desulfurization tower for continuous reaction;
(4) performing electrodialysis treatment on nanofiltration produced water for 13t/h to obtain electrodialysis produced water and electrodialysis concentrated water, performing reverse osmosis treatment on the obtained electrodialysis produced water to obtain reverse osmosis concentrated water (the salt content is 52g/L) and reverse osmosis produced water, and returning the obtained reverse osmosis concentrated water to continue the electrodialysis treatment;
wherein the current density of the electrodialysis operation is 30mA/cm2Current 120A, voltage 110V;
the reverse osmosis operating pressure is 4.0MPa, and the water recovery rate is 70.1%;
the coupling treatment is carried out to obtain 1.1t/h electrodialysis concentrated water (the salt content is 201g/L) and 11.9t/h reverse osmosis produced water (the salt concentration is less than 0.5g/L), and the produced water is reused as recycled water;
(5) feeding the electrodialysis concentrated water at 1.1t/h into a diaphragm electrolytic cell, electrolyzing to obtain 108kg of chlorine (with the purity of 99.3%), 0.5t/h of sodium hydroxide aqueous solution (with the mass concentration of 31%) and 0.6t/h of low-concentration brine (with the salt content of 112g/L), returning the sodium hydroxide aqueous solution to the step (1), and returning the rest low-concentration brine to the electrodialysis for concentration treatment;
wherein, the diaphragm electrolysis conditions are as follows: the current density is controlled to be 3.2kA/m2The voltage was 38V.
The results prove that the method can realize the reduction treatment of the desulfurization wastewater, and simultaneously can recover and obtain magnesium hydroxide, calcium sulfate, sodium hydroxide and high-purity chlorine products; the electrodialysis concentrated water entering the diaphragm electrolysis unit accounts for 5.5% of the consumption of the desulfurization wastewater, 59.5% of reuse water is recovered, and in addition, 35% of water is circulated in the system to optimize the system operation. Compared with the method for adjusting the pH value of the calcium hydroxide aqueous solution to the same pH value, the recycling of the sodium hydroxide can reduce the adding amount of calcium hydroxide into 14.8 kg/ton of water and further reduce the adding amount of sodium carbonate into 10.9 kg/ton of water. And (3) treating nanofiltration produced water in an electrodialysis-reverse osmosis coupling concentration unit, wherein the operation energy consumption of electrodialysis is 6.4kWh/t, and the energy consumption of diaphragm electrolysis is 4.5 kWh/t.
Example 3
(1) Adding the sodium hydroxide aqueous solution obtained in the step (5) into the power plant desulfurization wastewater of 20t/h in a primary neutralization reaction tank for reaction, adjusting the pH value of the wastewater to 11.5, adding 30mg/L organic sulfur TMT-15, 5mg/L flocculating agent and 15mg/L coagulant aid, reacting for 90min, conveying the obtained reaction product into a primary clarifying tank for 100min for settlement, obtaining a magnesium hydroxide product (the purity is 70%) and softened and clarified effluent, and reducing the concentration of magnesium ions in the effluent to 6.5 mg/L;
adding sulfuric acid into the softened and clarified effluent of 20t/h, and adjusting the pH to 7.5 to obtain neutral softened and clarified effluent;
(2) feeding the softened and clarified effluent of 20t/h into a sodium carbonate reaction tank, adding 20% by mass of sodium carbonate, reacting for 30min under stirring, then feeding the reaction product into a clarification tank, settling for 90min, separating to obtain softened water effluent (the concentration of calcium ions is 0.4mmol/L) and calcium carbonate, and returning the calcium carbonate to a desulfurization tower;
(3) supplying 20t/h of softened water effluent to a nanofiltration separation unit, carrying out nanofiltration separation treatment in the presence of 1.5mg/L of scale inhibitor, wherein the operating pressure is 1.92MPa, so as to obtain nanofiltration concentrated water and nanofiltration produced water (the salt content is 12.3g/L), and returning the nanofiltration concentrated water to a desulfurization tower for continuous reaction at 5 t/h;
(4) performing electrodialysis treatment on nanofiltration produced water for 15t/h to obtain electrodialysis produced water and electrodialysis concentrated water, performing reverse osmosis treatment on the obtained electrodialysis produced water to obtain reverse osmosis concentrated water (the salt content is 40.7g/L) and reverse osmosis produced water, and returning the obtained reverse osmosis concentrated water to continue the electrodialysis treatment;
wherein the current density of the electrodialysis operation is 33mA/cm2Current 132A, voltage 116V;
the reverse osmosis operating pressure is 4.2MPa, and the water recovery rate is 73.6 percent;
the coupling treatment obtains 1.2t/h electrodialysis concentrated water (the salt content is 193g/L) and 13.8t/h reverse osmosis produced water (the salt concentration is less than 0.5g/L), and the produced water is reused as recycled water;
(5) feeding the electrodialysis concentrated water at 1.2t/h into a diaphragm electrolytic cell, electrolyzing to obtain 107kg of chlorine (with the purity of 99.6%), 0.4t/h of sodium hydroxide aqueous solution (with the mass concentration of 32%) and 0.8t/h of low-concentration brine (with the salt content of 100g/L), returning the sodium hydroxide aqueous solution to the step (1), and returning the rest low-concentration brine to the electrodialysis for concentration treatment;
wherein, the diaphragm electrolysis conditions are as follows: the current density is controlled to be 3.2kA/m2And a voltage of 39V.
The results prove that the method can realize the reduction treatment of the desulfurization wastewater, and simultaneously can recover and obtain calcium sulfate, sodium hydroxide and high-purity chlorine products; the electrodialysis concentrated water entering the diaphragm electrolysis unit accounts for 6% of the consumption of the desulfurization wastewater, 69% of the reuse water is recovered, and in addition, 25% of the water is circulated in the system to optimize the system operation. Compared with the method for adjusting the pH value of the calcium hydroxide aqueous solution to the same pH value, the recycling of the sodium hydroxide can reduce the adding amount of calcium hydroxide into water by 14.7 kg/ton and further reduce the adding amount of sodium carbonate by 10.6 kg/ton. And (3) treating nanofiltration produced water in an electrodialysis-reverse osmosis coupling concentration unit, wherein the operation energy consumption of electrodialysis is 6.6kWh/t, and the energy consumption of diaphragm electrolysis is 4.6 kWh/t. The magnesium hydroxide obtained is less pure than in example 1.
Example 4
Treating the desulfurization wastewater according to the steps (1) to (3) of the embodiment 1 to obtain nanofiltration concentrated water and nanofiltration produced water, and returning the nanofiltration concentrated water to the desulfurization tower for continuous treatment;
(4) carrying out primary reverse osmosis treatment on nanofiltration produced water for 15t/h to obtain primary reverse osmosis produced water and primary reverse osmosis concentrated water (the salt content is 41g/L), carrying out high-pressure reverse osmosis treatment on the primary reverse osmosis concentrated water to obtain high-pressure reverse osmosis concentrated water and high-pressure reverse osmosis produced water, and returning the high-pressure reverse osmosis produced water to continue the primary reverse osmosis treatment; the treatment can obtain 1.8t/h high-pressure reverse osmosis concentrated water (the salt content is 106g/L) and 13.2t/h first-level reverse osmosis produced water (the salt content is less than 0.5 g/L);
wherein, the operating pressure of the first-stage reverse osmosis is 3.8MPa, and the water recovery rate is 69.3 percent;
the operating pressure of the high-pressure reverse osmosis is 9.0MPa, and the water recovery rate is 60 percent;
(5) the obtained high-pressure reverse osmosis concentrated water is sent to a diaphragm electrolytic cell at 1.8t/h, and 116kg of chlorine (the purity is 99.0 percent), 0.4t/h of sodium hydroxide aqueous solution (the mass concentration is 32 percent) and 1.4t/h of low-concentration brine (the salt content is 78g/L) are obtained through electrolysis.
Wherein, the diaphragm electrolysis conditions are as follows: the current density is controlled to be 3.2kA/m2And a voltage of 78V.
The results prove that the method can realize the reduction treatment of the desulfurization wastewater, and simultaneously can recover and obtain calcium sulfate products, sodium hydroxide and high-purity chlorine products; in addition, the electrodialysis concentrated water entering the diaphragm electrolysis unit accounts for 9% of the consumption of the desulfurization wastewater, 66% of reuse water is recovered, and in addition, 25% of water is circulated in the system to optimize the system operation. Compared with the embodiment 1, in order to obtain high-concentration brine for electrolysis, high-pressure reverse osmosis treatment is required, and the high-pressure reverse osmosis has higher requirements on equipment and high operating cost; in addition, the energy consumption of the diaphragm electrolysis is high, and is as high as 8.5kWh/t, in order to obtain the by-product with higher purity or concentration.
Comparative example 1
(1) Adding the sodium hydroxide aqueous solution obtained in the step (3) into the power plant desulfurization wastewater of 20t/h in a neutralization reaction tank for reaction, adjusting the pH value of the wastewater to 11.7, adding 10mg/L organic sulfur TMT-15 and 9mg/L coagulant aid, reacting for 60min, sending the obtained reaction product into a clarification tank for standing for 120min for sedimentation to obtain softened and clarified effluent, wherein the concentration of magnesium ions is reduced to 6.8 mg/L;
adding sulfuric acid into the softened and clarified effluent of 20t/h, and adjusting the pH to 7.4 to obtain neutral softened and clarified effluent;
(2) feeding the softened and clarified effluent of 20t/h into a sodium carbonate reaction tank, adding 20% by mass of sodium carbonate, reacting for 30min under stirring, then feeding the reaction product into a clarification tank, settling for 90min, separating to obtain softened water effluent (the concentration of calcium ions is 0.4mmol/L) and calcium carbonate, and returning the calcium carbonate to a desulfurization tower;
(3) performing reverse osmosis treatment on the softened clarified effluent at 20t/h to obtain reverse osmosis produced water and reverse osmosis concentrated water (the salt content is 52.9g/L), and reusing the reverse osmosis produced water as reuse water;
the reverse osmosis operating pressure is 4.1MPa, and the water recovery rate is 72 percent;
(3) 5.6t/h of the reverse osmosis concentrated water is sent into a diaphragm electrolytic cell, 126kg of chlorine (with the purity of 86.3 percent), 2.5t/h of sodium hydroxide aqueous solution (with the mass concentration of 8 percent) and 3.1t/h of low-concentration brine (with the salt content of 26g/L) are obtained through electrolysis, the sodium hydroxide aqueous solution returns to the step (1), and the residual low-concentration brine returns to the reverse osmosis for continuous concentration treatment;
wherein, the diaphragm electrolysis conditions are as follows: the current density is 4kA/m2And a voltage of 86V.
The results prove that in the operation process of the system of the comparative example, the diaphragm electrolysis not only has chemical scaling, but also has low chlorine purity and obvious reduction of current efficiency, so that the system can not be stably operated and needs to be shut down and cleaned frequently. The concentration of sodium hydroxide in the cathode chamber of the diaphragm electrolysis is low, and the energy consumption is 22 kWh/t.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (11)
1. A method for treating desulfurization wastewater is characterized by comprising the following steps:
(1) in the presence of sodium hydroxide, carrying out softening and clarifying treatment on the desulfurization wastewater to obtain softened and clarified effluent and magnesium hydroxide, and then adding acid into the softened and clarified effluent to obtain neutral softened and clarified effluent;
(2) adding sodium carbonate into the neutral softened clarified effluent to obtain softened water effluent and calcium carbonate, wherein the addition amount of the sodium carbonate enables the concentration of calcium ions in the softened water effluent to be below 0.5 mmol/L;
(3) performing nanofiltration separation treatment on the softened water to obtain nanofiltration produced water and nanofiltration concentrated water;
(4) carrying out membrane concentration treatment on the nanofiltration produced water to obtain membrane concentrated produced water and membrane concentrated water;
(5) and (3) carrying out diaphragm electrolysis on the membrane concentrated water to obtain chlorine and a sodium hydroxide aqueous solution, and returning the sodium hydroxide aqueous solution to the step (1).
2. The treatment method according to claim 1, wherein in the step (1), the softening and clarifying treatment method comprises the following steps:
1-1: adjusting the pH value of the desulfurization wastewater to 7-8 by using a sodium hydroxide aqueous solution, reacting for 45-80min, and then settling for 80-150min to obtain first-stage clarified effluent;
1-2: and adjusting the pH value of the first-stage clarified effluent to 11-12 by using an aqueous solution of sodium hydroxide, reacting for 45-80min, and then settling for 80-150min to obtain magnesium hydroxide and the softened clarified effluent.
3. The treatment method according to claim 1 or 2, wherein in the step (1), the acid is hydrochloric acid, and the pH of the neutral softened clear effluent is 6-8.
4. The treatment method according to claim 1, wherein in the step (3), the nanofiltration separation treatment is carried out in the presence of a scale inhibitor, and the operating pressure of the nanofiltration separation treatment is 0.5 to 2 MPa;
preferably, the flow of nanofiltration water production is controlled to be 65-90% of the nanofiltration water inlet flow.
5. The treatment method according to claim 1 or 4, wherein, in the step (4), the membrane concentration treatment employs electrodialysis-reverse osmosis coupling concentration,
when the salt content of the nanofiltration produced water is more than or equal to 10g/L, the step (4) comprises the following steps:
4-1: carrying out electrodialysis treatment on the nanofiltration water to obtain electrodialysis water and electrodialysis concentrated water serving as membrane concentrated water;
4-2: performing reverse osmosis treatment on the obtained electrodialysis produced water to obtain reverse osmosis concentrated water and reverse osmosis produced water serving as the membrane concentration produced water, and returning the reverse osmosis concentrated water to perform the electrodialysis treatment; or
When the salt content of the nanofiltration produced water is less than 10g/L, the step (4) comprises the following steps:
4-1: performing reverse osmosis treatment on the nanofiltration produced water to obtain reverse osmosis produced water and reverse osmosis concentrated water which are used as the membrane concentration produced water;
4-2: and performing electrodialysis treatment on the obtained reverse osmosis concentrated water to obtain electrodialysis concentrated water and electrodialysis produced water which are used as the membrane concentrated water, and returning the electrodialysis produced water to perform reverse osmosis treatment.
6. The process of claim 5 wherein the reverse osmosis process is operated at a pressure of 2 to 5 MPa;
preferably, the reverse osmosis treatment ensures that the recovery rate of the obtained reverse osmosis produced water is 50-75%, and the salt content of the obtained reverse osmosis concentrated water is 30-55 g/L.
7. The method of claim 5Wherein the current density of the electrodialysis treatment is 30 to 35mA/cm2The current is 120-150A, and the voltage is 100-120V.
8. The treatment method according to claim 1, wherein in step (5), the conditions of the membrane electrolysis include: the current density is 2-4kA/m2The voltage is 30-100V, preferably 30-50V.
9. A system for treating desulfurization waste water, comprising: the device comprises a softening and clarifying treatment unit, a sodium carbonate reaction and clarification unit, a nanofiltration separation unit, a membrane concentration unit and a diaphragm electrolysis unit;
the softening and clarifying treatment unit is used for softening and clarifying the desulfurization wastewater to obtain magnesium hydroxide and softened and clarified effluent;
the sodium carbonate reaction clarification unit is used for adding sodium carbonate into neutral softened clarified effluent obtained after the softened clarified effluent is subjected to acid pH adjustment to react to obtain softened effluent and calcium carbonate;
the nanofiltration separation unit is used for carrying out nanofiltration separation treatment on the softened water outlet water to obtain nanofiltration product water and nanofiltration concentrated water;
the membrane concentration unit is used for carrying out membrane concentration treatment on the nanofiltration water to obtain membrane concentration water and membrane concentration water;
and the diaphragm electrolysis unit is used for diaphragm electrolysis of the membrane concentrated water to obtain chlorine and a sodium hydroxide aqueous solution, and returning the obtained sodium hydroxide aqueous solution to the softening and clarifying treatment unit.
10. The treatment system of claim 9, wherein the membrane concentration treatment unit is an electrodialysis-reverse osmosis coupled concentration unit comprising an electrodialysis unit and a reverse osmosis unit;
when the salt content of the nanofiltration produced water is more than or equal to 10g/L,
the electrodialysis unit is used for carrying out electrodialysis treatment on the nanofiltration water to obtain electrodialysis water and electrodialysis concentrated water serving as membrane concentrated water; the reverse osmosis unit is used for performing reverse osmosis treatment on the obtained electrodialysis produced water to obtain reverse osmosis concentrated water and reverse osmosis produced water serving as the membrane concentration produced water, and returning the obtained reverse osmosis concentrated water to the electrodialysis unit; or
When the salt content of the nanofiltration produced water is less than 10g/L,
the reverse osmosis unit is used for performing reverse osmosis treatment on the nanofiltration produced water to obtain reverse osmosis produced water and reverse osmosis concentrated water which are used as the membrane concentration produced water; and the electrodialysis unit is used for carrying out electrodialysis treatment on the obtained reverse osmosis concentrated water to obtain electrodialysis concentrated water and electrodialysis water production which are used as the membrane concentrated water, and returning the obtained electrodialysis water production to the reverse osmosis unit.
11. The treatment system of claim 9, wherein the softening and clarifying treatment unit comprises a primary neutralization reaction tank, a primary clarifier, a secondary neutralization reaction tank, and a secondary clarifier;
the primary neutralization reaction tank is used for adding sodium hydroxide into the desulfurization wastewater to adjust the pH value to 7-8, and simultaneously carrying out reaction to obtain a first reaction product, and the primary clarification tank is used for settling the first reaction product to obtain primary clarified effluent;
and the secondary neutralization reaction tank is used for adding sodium hydroxide into the primary clarified effluent to adjust the pH value to 11-12, and simultaneously carrying out reaction to obtain a second reaction product, and the secondary clarification tank is used for settling the second reaction product to obtain magnesium hydroxide and softened clarified effluent.
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| CN113582410A (en) * | 2021-06-28 | 2021-11-02 | 国家能源投资集团有限责任公司 | Method for treating coal chemical industry wastewater |
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| CN113666556A (en) * | 2021-06-30 | 2021-11-19 | 国能朗新明环保科技有限公司 | Coal-electricity integrated wastewater recycling cooperative treatment method and system |
| CN114230055A (en) * | 2021-12-24 | 2022-03-25 | 华能山东发电有限公司 | Method for reducing membrane method concentration scaling rate and flux recovery promotion of desulfurization wastewater |
| CN116655056A (en) * | 2023-07-04 | 2023-08-29 | 粤海水资源工程研究中心(广东)有限公司 | Two-stage concentrated water treatment few-medicine self-regulating nanofiltration coupling system and use method |
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