CN111170518A

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Info

Publication number: CN111170518A
Application number: CN201811340941.4A
Authority: CN
Inventors: 钟振成; 程子洪; 陈权; 佟振伟; 李永龙; 熊日华; 卫昶
Original assignee: China Energy Investment Corp Ltd; National Institute of Clean and Low Carbon Energy
Current assignee: China Energy Investment Corp Ltd; National Institute of Clean and Low Carbon Energy
Priority date: 2018-11-12
Filing date: 2018-11-12
Publication date: 2020-05-19

Abstract

Translated fromChinese

本发明涉及脱硫废水处理领域，公开了一种脱硫废水的处理方法和处理系统。该方法包括：(1)在氢氧化钠存在下，将脱硫废水进行软化澄清处理，得到软化澄清出水，再向软化澄清出水中加入酸，得到中性软化澄清出水；(2)向所述中性软化澄清出水中加入硫酸钠并进行常温结晶，得到常温结晶出水等；(3)向常温结晶出水中加入碳酸钠，得到硬度调控出水等；(4)将硬度调控出水进行纳滤分离处理，得到纳滤产水和纳滤浓水；(5)将所述纳滤产水进行膜浓缩处理，得到膜浓缩产水和膜浓缩浓水；(6)将膜浓缩浓水进行隔膜电解，得到氯气和氢氧化钠水溶液。本发明的方法能同时得到具有高附加值的多种副产品，总体投资成本降低。

The invention relates to the field of desulfurization wastewater treatment, and discloses a desulfurization wastewater treatment method and a treatment system. The method comprises: (1) softening and clarifying desulfurization wastewater in the presence of sodium hydroxide to obtain softened and clarifying effluent, then adding acid to the softening and clarifying effluent to obtain neutral softening and clarifying effluent; (3) adding sodium carbonate to the normal temperature crystallization effluent to obtain hardness control effluent, etc.; (4) carrying out nanofiltration separation treatment of the hardness control effluent, Obtaining nanofiltration product water and nanofiltration concentrated water; (5) subjecting the nanofiltration product water to membrane concentration treatment to obtain membrane concentrated product water and membrane concentrated concentrated water; (6) carrying out membrane electrolysis on the membrane concentrated concentrated water to obtain Chlorine gas and aqueous sodium hydroxide solution. The method of the invention can simultaneously obtain a variety of by-products with high added value, and the overall investment cost is reduced.

Description

Treatment process and treatment system for desulfurization wastewater

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 adding acid into the softened and clarified effluent to obtain neutral softened and clarified effluent;

(2) adding sodium sulfate into the neutral softened clarified effluent and crystallizing at normal temperature to obtain normal-temperature crystallized effluent and calcium sulfate product salt;

(3) adding sodium carbonate into the normal-temperature crystallization effluent to obtain hardness-controlled effluent and calcium carbonate; the addition of sodium carbonate ensures that the concentration of calcium ions in the hardness regulated and controlled effluent is 3-5 mmol/L;

(4) performing nanofiltration separation treatment on the hardness-regulated effluent to obtain nanofiltration product water and nanofiltration concentrated water, and returning the nanofiltration concentrated water to the step (2);

(5) carrying out membrane concentration treatment on the nanofiltration produced water to obtain membrane concentrated produced water and membrane concentrated water;

(6) 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 another 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;

(2) adding sodium sulfate into the softened and clarified effluent and crystallizing at normal temperature to obtain normal-temperature crystallized effluent and calcium sulfate product salt;

(3) introducing carbon dioxide into the normal-temperature crystallized effluent to obtain hardness-regulated effluent and calcium carbonate, wherein the addition amount of the carbon dioxide enables the concentration of calcium ions in the hardness-regulated effluent to be 3-5 mmol/L;

According to a third 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 normal-temperature crystallization 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 softened and clarified effluent;

the normal-temperature crystallization unit is used for adding sodium sulfate into neutral softened and clarified effluent obtained after the softened and clarified effluent is subjected to acid pH adjustment and carrying out normal-temperature crystallization treatment to obtain normal-temperature crystallized effluent and calcium sulfate product salt;

the sodium carbonate reaction clarification unit is used for adding sodium carbonate into the normal-temperature crystallization effluent for reaction to obtain hardness-regulated effluent and calcium carbonate;

the nanofiltration separation unit is used for carrying out nanofiltration separation treatment on the hardness-regulated effluent to obtain nanofiltration product water and nanofiltration concentrated water, and returning the nanofiltration concentrated water to the normal-temperature crystallization unit;

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.

According to a fourth aspect of the present invention, there is provided another desulfurization wastewater treatment system, comprising: the device comprises a softening and clarifying treatment unit, a normal-temperature crystallization unit, a carbon dioxide reaction and clarification unit, a nanofiltration separation unit, a membrane concentration unit and a diaphragm electrolysis unit;

the normal-temperature crystallization unit is used for adding sodium sulfate into the softened and clarified effluent and performing normal-temperature crystallization treatment to obtain normal-temperature crystallized effluent and calcium sulfate product salt;

the carbon dioxide reaction and clarification unit is used for introducing carbon dioxide into the normal-temperature crystallized effluent for reaction to obtain hardness-regulated effluent and calcium carbonate;

The two treatment methods provided by the invention both adopt a normal temperature crystallization-nanofiltration technology, firstly, low-cost sodium sulfate is adopted to replace sodium carbonate to preliminarily regulate and control the hardness and crystallize at normal temperature; the balance of sulfate radicals and calcium ions in water can be destroyed by adding a small amount of sodium carbonate and carbon dioxide, so that the supersaturation degree of calcium sulfate in wastewater is rapidly reduced, the operation of a subsequent membrane system is fully protected, and the problem of membrane scaling is avoided. The nanofiltration water production is further subjected to reduction concentration by membrane concentration treatment, the salt concentration of the concentrated water can recover high-purity chlorine and sodium hydroxide aqueous solution through diaphragm electrolysis, the concentration of the sodium hydroxide aqueous solution is higher (more than 20 wt%), the sodium hydroxide aqueous solution is returned to pretreatment for cyclic utilization, so that the addition of an additional alkaline medicament (such as calcium hydroxide) can be avoided, the self-sufficiency in a system can be realized, the dosage of sodium carbonate or carbon dioxide for softening corresponding to the sodium hydroxide or carbon dioxide is reduced, and the effective coupling of the whole treatment process is realized. Moreover, the treatment method of the invention can simultaneously obtain a plurality of byproducts (chlorine, calcium sulfate, magnesium hydroxide, calcium carbonate and the like) with high added values.

In particular, the advantages of the present invention compared to existing methods are:

(1) in view of the operation cost, the sodium sulfate with lower cost is utilized to replace high-cost sodium carbonate to regulate and control calcium ions during normal-temperature crystallization treatment instead of completely removing the calcium ions, so that the operation cost can be greatly reduced; a small amount of sodium carbonate or carbon dioxide is added to regulate the supersaturation degree of calcium sulfate, so that the pollution of a membrane system is avoided, the service life of the membrane is prolonged, and the consumption cost of the membrane is reduced;

in addition, in the two treatment methods, compared with the method of adding a small amount of sodium carbonate, the addition of a small amount of carbon dioxide gas can not only quickly reduce the supersaturation degree of calcium sulfate, but also play a role in reducing pH, can avoid the additional addition of acid to regulate and control softening and clarifying effluent, and has lower medicament cost;

(2) considering from the whole process flow, the incomplete softening is carried out through the hardness regulation treatment, and further the treatment is combined with the nanofiltration system treatment and the membrane concentration treatment, so that the scale, the investment and the energy consumption required by the diaphragm electrolysis are saved;

(3) in view of equipment investment, the sodium carbonate reaction tank and the carbon dioxide reaction tank are respectively combined with the normal-temperature crystallization unit in the two treatment systems provided by the invention, and compared with the conventional reaction tank and a clarification tank, the reaction time and the retention time are greatly shortened, so that the occupied area of the system is saved, and the operation is simple and convenient; in addition, compared with the method of adding sodium carbonate, carbon dioxide gas can be introduced into the reaction tank in a micro-aeration mode, and the reaction efficiency is improved by stirring in the process, so that the occupied area is relatively smaller, and no additional stirring equipment is needed in the reaction tank.

Therefore, in the overall process, the overall investment cost, the occupied area of the device and the like are greatly reduced compared with the conventional treatment process.

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 first aspect of the present invention.

FIG. 2 is a schematic diagram of one embodiment of a treatment process according to the second aspect of 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.

(3) adding sodium carbonate into the normal-temperature crystallization effluent to obtain hardness-controlled effluent and calcium carbonate, wherein the addition amount of the sodium carbonate enables the concentration of calcium ions in the hardness-controlled effluent to be 3-5 mmol/L;

(3) adding carbon dioxide into the normal-temperature crystallization effluent to obtain hardness-regulated effluent and calcium carbonate, wherein the addition amount of the carbon dioxide enables the concentration of calcium ions in the hardness-regulated effluent to be 3-5 mmol/L;

For convenience of description, the processing method according to the first aspect of the present invention will be hereinafter referred to as a first processing method, and the processing method according to the second aspect of the present invention will be hereinafter referred to as a second processing method.

In the two treatment methods of the present invention, the desulfurization waste water 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 matter, 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 first treatment method of the present invention, in the step (1), preferably, the acid is sulfuric acid, and the pH of the neutral softened clear effluent is 6 to 8, more preferably 7 to 8. In the step, sulfuric acid is added into the softened and clarified effluent to adjust the pH value to be neutral, and the added sulfate ions react with calcium ions in water to generate a small amount of calcium sulfate crystals, so that the reaction in a subsequent normal-temperature crystallization reactor is facilitated.

In the two treatment methods of the present invention, preferably, the softening and clarifying treatment is performed in stages in step (1), 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 30-60min, 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 step 1-2, the magnesium hydroxide with high purity can be isolated by adjusting the pH to 11-12 and carrying out the reaction and precipitation, and the magnesium ion concentration can be reduced to 10mg/L or less by this 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 two treatment methods of the present invention, preferably, the amount of the organic sulfur is 5 to 150mg/L, more preferably 5 to 80 mg/L; the dosage of the flocculating agent is 0-30mg/L, and the dosage of the coagulant aid is 3-10 mg/L.

In the two treatment methods, in the step (2), sodium sulfate is added into the softened and clarified effluent and the returned nanofiltration concentrated water, and normal-temperature crystallization treatment is carried out, the added sulfate radicals react with calcium ions to generate calcium sulfate, the solubility of the calcium sulfate in the wastewater is low, and the calcium sulfate can be crystallized and separated out under the normal-temperature condition to obtain calcium sulfate product salt.

In the step (2), the addition amount of the sodium sulfate ensures that the concentration of calcium ions in the normal-temperature crystallization water is preferably 8-12 mmol/L. Through the treatment of the step (2), the supersaturation degree of the calcium sulfate in the obtained normal-temperature crystallized effluent is usually 100-120%.

In the two treatment methods, in the step (3), the normal-temperature crystallized effluent reacts with sodium carbonate or carbon dioxide, carbonate in the normal-temperature crystallized effluent reacts with calcium ions quickly to generate calcium carbonate precipitates, so that the balance of sulfate radicals and calcium ions in water is broken quickly, and the supersaturation degree of calcium sulfate is reduced. In the process, calcium ions in the wastewater do not need to be completely removed. Wherein, the addition amount of sodium carbonate or carbon dioxide is preferably selected to ensure that the calcium ion concentration in the hardness regulated water is 3-5 mmol/L. When the concentration of calcium ions is too high, the supersaturation degree of calcium sulfate is higher, so that the nanofiltration system is easy to block and the operation pressure is too high. Preferably, the step may further include: returning the obtained calcium carbonate to a desulfurizing tower for desulfurization reaction.

The added carbon dioxide is not particularly limited, and industrial carbon dioxide can be directly used or flue gas of a thermal power plant containing carbon dioxide can be directly used for regulating and controlling the hardness of normal-temperature crystallized effluent.

In the two treatment methods of the invention, in the step (4), preferably, the nanofiltration separation treatment is carried out in the presence of a scale inhibitor, and the operating pressure of the nanofiltration separation treatment is 0.5-2 MPa. The pressures mentioned in the present invention are gauge pressures.

In the two treatment methods, the flow of nanofiltration water production is preferably controlled to be 40-60 wt% of the nanofiltration water inlet flow. In the nanofiltration concentrated water, the supersaturation degree of calcium sulfate is more than 200%.

In the two treatment methods, the step (2) of returning the nanofiltration concentrated water is to mix the nanofiltration concentrated water with clear effluent (softened clear effluent or neutral softened clear effluent), add sodium sulfate and crystallize at normal temperature; or sodium sulfate is added into the two streams respectively to carry out normal temperature crystallization, and the former is preferably adopted.

In the two treatment methods of the present invention, the nanofiltration membrane element used in the nanofiltration separation treatment is required to have a lower rejection rate of monovalent salt and a higher rejection rate of divalent salt, so as to better achieve 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 treatment is a nanofiltration membrane element having a rejection rate of more than 98% for sulfate ions in the nanofiltration influent water and a rejection rate of more than 95% for calcium ions in the nanofiltration influent water, and the membrane element can be, for example, a GEDL series nanofiltration membrane element, a GE SWSR series nanofiltration membrane, a GE DK series nanofiltration membrane element or a NE8040-40 nanofiltration membrane element of the korean TCK company.

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 2-20mg/L, and preferably 3-10 mg/L.

In the two treatment methods, 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.

In addition, in order to further remove suspended matters in the desulfurization wastewater, the method of the present invention may further include subjecting the hardness-controlled effluent to sand filtration and ultrafiltration before the nanofiltration separation, and the methods of sand filtration and ultrafiltration are well known in the art and will not be described herein again.

In the two treatment methods of the present invention, preferably, the step (5) comprises subjecting the nanofiltration product water to high pressure reverse osmosis treatment to obtain reverse osmosis product water (i.e. the membrane concentrated product water) and reverse osmosis concentrate water (i.e. the membrane concentrated concentrate water); wherein the operating pressure of the high-pressure reverse osmosis is 10-12 MPa.

More preferably, the salt content of the obtained reverse osmosis concentrated water is more than 100g/L, and further more preferably more than 120g/L, so that the investment cost of membrane concentration equipment is reduced, and the energy consumption of subsequent membrane electrolysis is reduced. Optionally, the nanofiltration product water is subjected to a conventional reverse osmosis treatment, typically at a pressure of 3-5MPa, prior to the high pressure reverse osmosis.

In the step (6), the operation conditions of the membrane electrolysis include: 2-4kA/m²The voltage is 30-100V, preferably 40-50V.

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, also called diaphragm electrolyzed fresh water) after electrolysis, which is the solution after dechlorination of the anode region during diaphragm electrolysis, preferably with a salt content of 35-70 g/L. When the membrane concentration treatment employs the high-pressure reverse osmosis treatment, the method of the present invention may further comprise: returning the low-concentration brine solution to continue the high-pressure reverse osmosis treatment.

According to a fourth aspect of the present invention, there is provided another desulfurization wastewater treatment system, comprising: the device comprises a softening and clarifying treatment unit, a normal-temperature crystallization unit, a carbon dioxide reaction and clarification unit, a nanofiltration separation unit, a membrane concentration unit and a diaphragm electrolysis unit; wherein,

the carbon dioxide reaction and clarification unit is used for adding carbon dioxide into the normal-temperature crystallized effluent for reaction to obtain hardness-regulated effluent and calcium carbonate;

For convenience of description, the processing system according to the third aspect of the present invention will be hereinafter referred to as a first processing system, and the processing system according to the fourth aspect of the present invention will be hereinafter referred to as a second processing system. In addition, the first treatment method of the present invention may be performed using a first treatment system, and the second treatment method may be performed using a second treatment system.

In both treatment systems of the present invention, according to a preferred embodiment, the softening and clarifying treatment unit comprises 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 first 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 the normal-temperature crystallized effluent for reaction, and the clarification tank is used for settling reaction products to obtain hardness-regulated effluent and calcium carbonate product salt. The sodium carbonate reaction tank is usually provided with stirring equipment.

In the second treatment system, the carbon dioxide reaction and clarification unit comprises a carbon dioxide reaction tank (also called an acidification reaction tank) and a clarification tank, wherein the carbon dioxide reaction tank is used for introducing carbon dioxide into the normal-temperature crystallized effluent for reaction, and the clarification tank is used for settling reaction products to obtain hardness-regulated effluent and calcium carbonate product salt.

In the two treatment systems, the nanofiltration separation unit comprises at least one nanofiltration membrane element, the nanofiltration membrane element has a retention rate of sulfate ions in the hardness-regulated outlet water of more than 98% and a retention rate of calcium ions in the nanofiltration inlet water of more than 95%, and the nanofiltration membrane element can 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 Korean TCK NE8040-40 nanofiltration membrane element. 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 hardness-controlled effluent, the two treatment systems of the present invention may further comprise a sand filtration-ultrafiltration treatment unit, respectively, through which the suspended matters in the hardness-controlled 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 again.

In the two treatment systems of the present invention, preferably, the membrane concentration unit includes a high-pressure reverse osmosis unit for performing a high-pressure reverse osmosis treatment on the nanofiltration product water to obtain a reverse osmosis concentrated water as the membrane concentrated water and a reverse osmosis effluent as the membrane concentrated effluent.

The high pressure reverse osmosis unit is not particularly limited in the present invention and may be selected commonly used in the art. As is well known in the art, the high pressure reverse osmosis unit may include components such as a booster pump, a high pressure pump, a pressure vessel, and an anti-fouling reverse osmosis membrane module.

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 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 according to the present invention with reference to FIGS. 1 and 2.

In both of the two types of treatment systems,

softeningThe clarifying unit comprises a volume of 15m³And 20m³The first-stage neutralization reaction tank and the second-stage neutralization reaction tank respectively have the volume of 30m³And 60m³A first-stage clarification tank and a 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 carbon dioxide reaction clarification unit comprises a volume of 15m³And the volume of the reaction tank is 30m³The carbon dioxide is introduced into the reaction tank through the microporous aeration pipe;

the nanofiltration separation unit comprises a first-stage two-stage nanofiltration system consisting of 6 membrane shells and 4 series-connected GE DK 8040F30 nanofiltration membrane elements arranged in the nanofiltration separation unit;

the normal temperature crystallization unit comprises a stirring device with a volume of 40m³The stainless steel container of (1);

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 trade name of OSMOTREAT OSM 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

This example will explain a first method of treating desulfurization waste water with reference to FIG. 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 7.2, 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 to a primary clarifying tank, staying for 90min, 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 11.0, adding 5mg/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 98.7%) and softened clarified effluent, wherein the concentration of magnesium ions in the effluent is reduced to 9.2 mg/L;

adding sulfuric acid into the softened and clarified effluent of 20t/h, and adjusting the pH to 6.7 to obtain neutral softened and clarified effluent;

(2) mixing 20t/h neutral softened clarified effluent with nanofiltration concentrated water, feeding the mixture into a normal-temperature crystallization reactor at a flow rate of 40t/h, adding a sodium sulfate solution with the mass concentration of 20%, reacting for 60min under a stirring condition, feeding the obtained reaction product into a clarification tank, and settling for 80min to obtain normal-temperature crystallized effluent (the concentration of calcium ions is 11.3mmol/L) and a calcium sulfate product;

(3) enabling 40t/h of normal-temperature crystallized effluent to enter a sodium carbonate reaction tank, adding a sodium carbonate solution with the mass concentration of 20%, reacting for 30min under a stirring condition, then enabling a reaction product to enter a clarification tank for settling for 90min, separating to obtain hardness-regulated effluent (the calcium ion concentration is 3.6mmol/L) and calcium carbonate, and returning the calcium carbonate to a desulfurization tower;

(4) supplying the water with the hardness of 40t/h regulated to a nanofiltration separation unit, and carrying out nanofiltration separation treatment in the presence of 4mg/L scale inhibitor, wherein the operating pressure is 1.56MPa, so as to obtain nanofiltration concentrated water and nanofiltration produced water (the salt content is 13.1 g/L); the nanofiltration concentrated water and the neutral softened clear effluent enter a normal-temperature crystallization reactor together for reaction;

(5) carrying out high-pressure reverse osmosis treatment on nanofiltration produced water at 20t/h, wherein the operating pressure is 10.6MPa, so as to obtain 16t/h reverse osmosis produced water (the salt content is 0.8g/L) and 4t/h reverse osmosis concentrated water (the salt content is 129g/L), and reusing the reverse osmosis produced water as reuse water;

(6) 4t/h of the reverse osmosis concentrated water is sent into a diaphragm electrolytic cell, 107kg of chlorine (with the purity of 99.6 percent), 1t/h of sodium hydroxide aqueous solution (with the mass concentration of 36 percent) and 3t/h of low-concentration brine (with the salt content of 53g/L) are obtained through electrolysis, the sodium hydroxide aqueous solution returns to the step (1), and the rest low-concentration brine returns to a high-pressure reverse osmosis system for concentration treatment;

wherein, the diaphragm electrolysis conditions are as follows: the current density is controlled to be 3.0kA/m²And a voltage of 48V.

The results prove that the method of the embodiment can recover calcium sulfate products, calcium carbonate products, sodium hydroxide and high-purity chlorine products at the same time through hardness control treatment and membrane concentration treatment. The reverse osmosis concentrated water entering the diaphragm electrolysis unit accounts for 20% of the consumption of the desulfurization wastewater, and 80% of the reuse water is recovered. And compared with the condition that the pH value of the calcium hydroxide aqueous solution is adjusted to be the same, the recycling of the sodium hydroxide can reduce the addition of 11.2 kg/ton of water into the calcium hydroxide, finally reduce the addition of 8.5 kg/ton of water into the sodium carbonate, and the energy consumption of diaphragm electrolysis is 7.3 kWh/t.

Example 2

(1) Adding the sodium hydroxide aqueous solution obtained in the step (5) into the 20t/h power plant desulfurization wastewater 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 flocculant and 5mg/L coagulant aid, reacting for 50min, conveying the obtained first reaction product into a first clarification tank, and standing for 90min for sedimentation 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 5mg/L coagulant aid, reacting for 60min, conveying the obtained reaction product to a second clarification tank, staying for 150min, and settling to obtain a magnesium hydroxide product (with the purity of 98.3%) and softened clarified effluent, wherein the concentration of magnesium ions in the effluent is reduced to 7.9 mg/L;

adding sulfuric acid into the softened and clarified effluent of 20t/h, and adjusting the pH to 6.8 to obtain neutral softened and clarified effluent;

(2) mixing 20t/h neutral softened clarified effluent with nanofiltration concentrated water, feeding the mixture into a normal-temperature crystallization reactor at a flow rate of 40t/h, adding a sodium sulfate solution with the mass concentration of 20%, reacting for 90min under a stirring condition, feeding the obtained reaction product into a clarification tank, and settling for 120min to obtain normal-temperature crystallized effluent (the concentration of calcium ions is 8.5mmol/L) and a calcium sulfate product;

(3) enabling 40t/h of normal-temperature crystallized effluent to enter a sodium carbonate reaction tank, adding a sodium carbonate solution with the mass concentration of 20%, reacting for 30min under a stirring condition, then enabling a reaction product to enter a clarification tank for settling for 90min, separating to obtain hardness-regulated effluent (the calcium ion concentration is 3.4mmol/L) and calcium carbonate, and returning the calcium carbonate to a desulfurization tower;

(4) supplying the water with the hardness of 40t/h regulated to a nanofiltration separation unit, and carrying out nanofiltration separation treatment in the presence of 4mg/L scale inhibitor, wherein the operating pressure is 1.62MPa, so as to obtain nanofiltration concentrated water and nanofiltration produced water (the salt content is 11.6 g/L); the nanofiltration concentrated water and the neutral softened clear effluent enter a normal-temperature crystallization reactor together for reaction;

(5) carrying out reverse osmosis treatment on nanofiltration produced water at 20t/h, wherein the operating pressure is 3.8MPa, so as to obtain 12t/h reverse osmosis produced water (the salt content is 0.5g/L) and 8/h reverse osmosis concentrated water (the salt content is 57g/L), and reusing the reverse osmosis produced water as reuse water;

carrying out high-pressure reverse osmosis treatment on the reverse osmosis concentrated water continuously, wherein the operating pressure is 11MPa, and obtaining 5.5t/h reverse osmosis produced water (the salt content is 0.9g/L) and 2.5t/h reverse osmosis concentrated water (the salt content is 132g/L), wherein the reverse osmosis produced water is reused as reuse water;

(6) feeding the reverse osmosis concentrated water at 2.5t/h into a diaphragm electrolytic cell, electrolyzing to obtain 106kg of chlorine (with the purity of 99.3%), 1.2t/h of sodium hydroxide aqueous solution (with the mass concentration of 30%) and 1.3t/h of low-concentration brine (with the salt content of 57g/L), returning the sodium hydroxide aqueous solution to the step (1), and returning the rest low-concentration brine to a high-pressure reverse osmosis system for concentration treatment;

wherein, the diaphragm electrolysis conditions are as follows: the current density is controlled to be 3.0kA/m²And a voltage of 42V.

The results prove that the method can realize the reduction treatment of the desulfurization wastewater through the hardness regulation treatment and the membrane concentration treatment, and simultaneously can recover and obtain calcium sulfate products, calcium carbonate products, sodium hydroxide and high-purity chlorine products; the reverse osmosis concentrated water entering the diaphragm electrolysis unit accounts for 12.5 percent of the consumption of the desulfurization wastewater, and 87.5 percent of reuse water is recovered. And compared with the condition that the pH value of the calcium hydroxide aqueous solution is adjusted to be the same, the recycling of the sodium hydroxide can reduce the addition of 11.8 kg/ton water into the calcium hydroxide, finally reduce the addition of 8.9 kg/ton water into the sodium carbonate, and the energy consumption of diaphragm electrolysis is 7.4 kWh/t.

Example 3

Treating the desulfurization wastewater according to the steps (1) to (4) 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;

(5) carrying out reverse osmosis treatment on nanofiltration produced water at 20t/h, wherein the operating pressure is 3.7MPa, and obtaining 14t/h reverse osmosis produced water (the salt content is 0.7g/L) and 6t/h reverse osmosis concentrated water (the salt content is 52 g/L);

(6) the obtained reverse osmosis concentrated water is sent into a diaphragm electrolytic cell at 6t/h, and 87kg of chlorine (the purity is 99.1 percent), 2t/h of sodium hydroxide aqueous solution (the mass concentration is 20 percent) and 4t/h of low-concentration brine (the salt content is 38g/L) are obtained through electrolysis.

Wherein, the diaphragm electrolysis conditions are as follows: the current density is controlled to be 3.0kA/m²And a voltage of 102V.

The results prove that the method of the embodiment can recover calcium sulfate products, calcium carbonate products, sodium hydroxide and chlorine products through hardness regulation and control treatment and conventional reverse osmosis concentration treatment; the reverse osmosis concentrated water entering the diaphragm electrolysis unit accounts for 30% of the consumption of the desulfurization wastewater, and 70% of the reuse water is recovered. The energy consumption for membrane electrolysis was 26.8 kWh/t.

Example 4

This example will explain a second method of treating desulfurization waste water with reference to FIG. 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 7.4, 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 to a primary clarifying tank, staying for 90min, 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 value of the effluent to be 11.2, adding 5mg/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 98.6%) and softened clarified effluent, wherein the concentration of magnesium ions in the effluent is reduced to 8.7 mg/L;

(2) mixing the softened and clarified effluent of 20t/h with nanofiltration concentrated water, feeding the mixture into a normal-temperature crystallization reactor at a flow rate of 40t/h, adding a sodium sulfate solution with a mass concentration of 20%, reacting for 60min under a stirring condition, feeding the obtained reaction product into a clarification tank, and settling for 90min to obtain normal-temperature crystallized effluent (the concentration of calcium ions is 12.0mmol/L) and a calcium sulfate product;

(3) allowing 40t/h of normal-temperature crystallized effluent to enter a carbon dioxide reaction tank, introducing carbon dioxide to react for 45min, allowing reaction products to enter a clarification tank to settle for 90min, separating to obtain hardness-regulated effluent (the concentration of calcium ions is 3.5mmol/L, and the pH value is 7.6) and calcium carbonate, and returning the calcium carbonate to a desulfurization tower;

(4) supplying the water with the hardness of 40t/h regulated to a nanofiltration separation unit, and carrying out nanofiltration separation treatment in the presence of 5mg/L scale inhibitor, wherein the operating pressure is 1.57MPa, so as to obtain nanofiltration concentrated water and nanofiltration produced water (the salt content is 12.3 g/L); the nanofiltration concentrated water and the neutral softened clear effluent enter a normal-temperature crystallization reactor together for reaction;

(5) carrying out high-pressure reverse osmosis treatment on nanofiltration produced water at 20t/h, wherein the operating pressure is 11.0MPa, so as to obtain 16.5t/h reverse osmosis produced water (the salt content is 0.8g/L) and 3.5t/h reverse osmosis concentrated water (the salt content is 136g/L), and reusing the reverse osmosis produced water as reuse water;

(6) 3.5t/h of the reverse osmosis concentrated water is sent into a diaphragm electrolytic cell, 102kg of chlorine (with the purity of 99.6 percent), 1.5t/h of sodium hydroxide aqueous solution (with the mass concentration of 32 percent) and 2t/h of low-concentration brine (with the salt content of 61g/L) are obtained through electrolysis, the sodium hydroxide aqueous solution returns to the step (1), and the rest low-concentration brine returns to a high-pressure reverse osmosis system for concentration treatment;

wherein, the diaphragm electrolysis conditions are as follows: the current density is controlled to be 3.0kA/m²And a voltage of 49V.

The results prove that the method can realize the reduction treatment of the desulfurization wastewater through the hardness regulation treatment and the membrane concentration treatment, and simultaneously can recover and obtain calcium sulfate products, calcium carbonate products, sodium hydroxide and high-purity chlorine products; the reverse osmosis concentrated water entering the diaphragm electrolysis unit accounts for 17.5 percent of the consumption of the desulfurization wastewater, and 82.5 percent of reuse water is recovered. And compared with the condition that the pH value of the calcium hydroxide aqueous solution is adjusted to be the same, the recycling of the sodium hydroxide can reduce the addition of 12.1 kg/ton of water into the calcium hydroxide, finally replace the addition of 10.6 kg/ton of water into the sodium carbonate, and the energy consumption of diaphragm electrolysis is 7.2 kWh/t.

Example 5

(1) Adding the sodium hydroxide aqueous solution obtained in the step (5) into the 20t/h power plant desulfurization wastewater in a primary neutralization reaction tank for reaction, adjusting the pH value of the wastewater to 11.3, adding 30mg/L organic sulfur TMT-15, 10mg/L flocculating agent and 5mg/L coagulant aid, reacting for 45min, conveying the obtained reaction product to a primary clarifying tank for standing for 90min for settling to obtain a magnesium hydroxide product (with the purity of 68.4%) and softened and clarified effluent, and reducing the concentration of magnesium ions in the effluent to 9.1 mg/L;

(2) mixing the softened and clarified effluent of 20t/h with nanofiltration concentrated water, feeding the mixture into a normal-temperature crystallization reactor at a flow rate of 40t/h, adding a sodium sulfate solution with a mass concentration of 20%, reacting for 60min under a stirring condition, feeding the obtained reaction product into a clarification tank, and settling for 90min to obtain normal-temperature crystallized effluent (the concentration of calcium ions is 18.8mmol/L) and a calcium sulfate product;

(3) allowing 40t/h of normal-temperature crystallized effluent to enter a carbon dioxide reaction tank, introducing carbon dioxide to react for 30min, allowing reaction products to enter a clarification tank to settle for 90min, separating to obtain hardness-regulated effluent (the concentration of calcium ions is 3.7mmol/L, the pH value is 7.1) and calcium carbonate, and returning the calcium carbonate to a desulfurization tower;

(4) supplying the water with the hardness regulated at 40t/h to a nanofiltration separation unit, and carrying out nanofiltration separation treatment in the presence of 4.1mg/L scale inhibitor, wherein the operating pressure is 1.87MPa, so as to obtain nanofiltration concentrated water and nanofiltration water (the salt content is 12.6 g/L); the nanofiltration concentrated water and the neutral softened clear effluent enter a normal-temperature crystallization reactor together for reaction;

(5) carrying out reverse osmosis treatment on nanofiltration produced water at 20t/h, wherein the operating pressure is 4.2MPa, so as to obtain 15t/h reverse osmosis produced water (the salt content is 0.5g/L) and 5/h reverse osmosis concentrated water (the salt content is 89g/L), and reusing the reverse osmosis produced water as reuse water;

(6) feeding the reverse osmosis concentrated water at 5t/h into a diaphragm electrolytic cell, electrolyzing to obtain 86kg of chlorine (with the purity of 99.5%), 1.5t/h of sodium hydroxide aqueous solution (with the mass concentration of 21%) and 3.5t/h of low-concentration brine (with the salt content of 35g/L), returning the sodium hydroxide aqueous solution to the step (1), and returning the rest low-concentration brine to a high-pressure reverse osmosis system for concentration treatment;

wherein, the diaphragm electrolysis conditions are as follows: the current density is controlled to be 3.0kA/m²And a voltage of 120V.

The results prove that the method of the embodiment can realize the reduction treatment of the desulfurization wastewater through the hardness regulation treatment and the membrane concentration treatment, and simultaneously can recover and obtain calcium sulfate products, calcium carbonate products, sodium hydroxide and chlorine products; the reverse osmosis concentrated water entering the diaphragm electrolysis unit accounts for 25% of the consumption of the desulfurization wastewater, and 75% of the reuse water is recovered. 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 addition of 8.5 kg/ton of water into the calcium hydroxide, and finally replace sodium carbonate to add 10.8 kg/ton of water into the calcium hydroxide. The energy consumption for membrane electrolysis was 29.6 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

1. A method for treating desulfurization wastewater is characterized by comprising the following steps:

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: 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;

preferably, the acid is sulfuric acid, and the pH of the neutral softened clear effluent is 6-8.

3. The treatment method according to claim 1, wherein in the step (2), the sodium sulfate is added in an amount such that the concentration of calcium ions in the normal-temperature crystallization effluent is 8 to 12 mmol/L.

4. The treatment method according to claim 1, wherein in the step (4), 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 40-60% of the nanofiltration water inlet flow.

5. The processing method according to claim 1, wherein the step (5) comprises: performing high-pressure reverse osmosis treatment on the nanofiltration produced water to obtain reverse osmosis produced water serving as the membrane concentrated produced water and reverse osmosis concentrated water serving as the membrane concentrated water, wherein the operating pressure of the high-pressure reverse osmosis is 10-12 MPa;

preferably, the salt content of the reverse osmosis concentrated water is more than 100g/L, and more preferably more than 120 g/L.

6. The treatment method according to claim 1, wherein in step (6), the conditions of the membrane electrolysis include: the current density is 2-4kA/m²The voltage is 30-100V, preferably 40-50V.

7. A method for treating desulfurization wastewater is characterized by comprising the following steps:

8. The treatment method according to claim 7, wherein in the step (1), the softening and clarifying treatment method comprises the following steps:

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.

9. The treatment method according to claim 7, wherein in the step (2), the sodium sulfate is added in an amount such that the calcium ion concentration in the normal-temperature crystallization effluent is 8-12 mmol/L;

preferably, in the step (3), the hardness is adjusted to control the pH of the effluent to be 7-8.

10. The treatment method according to claim 7, wherein in the step (4), 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 the nanofiltration concentrated water is controlled to be 40-60% of the nanofiltration inlet water flow.

11. The processing method according to claim 7, wherein the step (5) comprises: performing high-pressure reverse osmosis treatment on the nanofiltration produced water to obtain reverse osmosis produced water serving as the membrane concentrated produced water and reverse osmosis concentrated water serving as the membrane concentrated water, wherein the operating pressure of the high-pressure reverse osmosis is 10-12 MPa;

12. The treatment method according to claim 7, wherein in the step (6), the conditions of the membrane electrolysis include: the current density is 2-4kA/m²The voltage is 30-100V, preferably 40-50V.

13. A system for treating desulfurization waste water, comprising: the device comprises a softening and clarifying treatment unit, a normal-temperature crystallization unit, a sodium carbonate reaction and clarification unit, a nanofiltration separation unit, a membrane concentration unit and a diaphragm electrolysis unit;

14. The treatment system of claim 13, 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 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; and/or

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 the normal-temperature crystallized effluent for reaction, and the clarification tank is used for settling reaction products to obtain hardness-regulated effluent and calcium carbonate product salt.

15. The treatment system of claim 13, wherein the membrane concentration unit comprises a high pressure reverse osmosis system.

16. A system for treating desulfurization waste water, comprising: the device comprises a softening and clarifying treatment unit, a normal-temperature crystallization unit, a carbon dioxide reaction and clarification unit, a nanofiltration separation unit, a membrane concentration unit and a diaphragm electrolysis unit;

17. The treatment system of claim 16, 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 carbon dioxide reaction and clarification unit comprises a carbon dioxide reaction tank and a clarification tank, wherein the carbon dioxide reaction tank is used for introducing carbon dioxide into the normal-temperature crystallized effluent for reaction, and the clarification tank is used for settling reaction products to obtain hardness-regulated effluent and calcium carbonate product salt.

18. The treatment system of claim 16, wherein the membrane concentration unit comprises a high pressure reverse osmosis system.