CN111099773A

CN111099773A - Desulfurization wastewater treatment method and system

Info

Publication number: CN111099773A
Application number: CN201811271561.XA
Authority: CN
Inventors: 佟振伟; 程子洪; 钟振成; 段亚威; 陈权; 霍卫东; 熊日华; 李永龙; 李晓峰; 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: 2018-10-29
Filing date: 2018-10-29
Publication date: 2020-05-05

Abstract

The invention discloses a desulfurization wastewater treatment method and a desulfurization wastewater treatment system, relates to the technical field of desulfurization, and aims to reduce the difficulty in recovering useful substances in desulfurization wastewater. This desulfurization wastewater treatment system includes: the salt separating device comprises a primary treatment unit, a secondary treatment unit connected with a water outlet of the primary treatment unit, and a salt separating unit connected with a water outlet of the secondary treatment unit, wherein a first water outlet of the salt separating unit is connected with a first recovery unit, and a second water outlet of the salt separating unit is connected with a second recovery unit. The desulfurization wastewater treatment method comprises the application of the desulfurization wastewater treatment system. The desulfurization wastewater treatment system and the method provided by the invention are used for desulfurization wastewater treatment.

Description

Desulfurization wastewater treatment method and system

Technical Field

The invention relates to the technical field of desulfurization, in particular to a desulfurization wastewater treatment method and a desulfurization wastewater treatment system.

Background

The limestone-gypsum wet flue gas desulfurization process is a flue gas desulfurization method with mature technology and relatively reliable operation, the raw material source is wide, and the generated by-products can be fully utilized. The existing limestone-gypsum wet flue gas desulfurization equipment needs to regularly discharge a certain amount of desulfurization wastewater in the operation process so as to ensure the normal operation of flue gas desulfurization.

However, the desulfurization wastewater discharged by the limestone-gypsum wet flue gas desulfurization equipment is acidic, high in salt content, high in suspended matter content, heavy in metal content and large in water quality fluctuation. If directly discharged, the surrounding environment will be severely affected. At present, the zero-discharge treatment technology is adopted to treat the desulfurization wastewater so as to basically realize the zero discharge of the desulfurization wastewater. The zero-emission treatment technology generally realizes zero emission of the desulfurization wastewater by combining two or more of the processes of pretreatment, salt separation, membrane concentration, evaporative crystallization and the like. Magnesium ions contained in the desulfurization wastewater are finally removed in the form of slag sludge, so that magnesium ion precipitates are difficult to recover, and the difficulty in recovering other useful substances in the desulfurization wastewater is increased.

Disclosure of Invention

The invention aims to provide a desulfurization wastewater treatment method and a desulfurization wastewater treatment system, which are used for reducing the difficulty in recovering useful substances in desulfurization wastewater.

In order to achieve the above purpose, the invention provides the following technical scheme:

a desulfurization wastewater treatment method, comprising:

removing suspended matters, non-metallic ions and heavy metal ions contained in the desulfurization wastewater to obtain primary treatment wastewater;

precipitating magnesium ions contained in the primary treatment wastewater to obtain magnesium ion precipitate and secondary treatment wastewater;

treating the secondary treatment wastewater to obtain monovalent salt wastewater and divalent salt wastewater;

recovering monovalent salt contained in the monovalent salt wastewater to obtain monovalent salt recovered matter and first recovered water;

and (3) recovering divalent salt contained in the divalent salt wastewater to obtain a divalent salt recovery material and second recovered effluent.

Compared with the prior art, in the desulfurization wastewater treatment method provided by the invention, before magnesium ions contained in the primary treatment wastewater are precipitated, suspended matters, non-metal ions and heavy metal ions contained in the desulfurization wastewater are removed to obtain the primary treatment wastewater, so that substances used for forming sludge in the desulfurization wastewater are effectively removed, and thus, when the magnesium ions contained in the primary treatment wastewater are precipitated, almost no sludge is formed, and the obtained magnesium ion precipitate has high purity, so that the purity of the magnesium ion precipitate is improved, and the formation amount of the sludge is reduced. Moreover, in the desulfurization wastewater treatment method provided by the invention, the secondary treatment wastewater is treated, so that the monovalent salt and the divalent salt originally dissolved in the secondary treatment wastewater are separated, and monovalent salt wastewater and divalent salt wastewater are obtained; and the monovalent salt contained in the monovalent salt wastewater and the divalent salt contained in the divalent salt wastewater are recovered, so that the desulfurization wastewater treatment method provided by the invention not only can reduce the difficulty in recovering magnesium, but also can recover the monovalent salt and the divalent salt contained in the desulfurization wastewater, thereby fully recovering useful substances in the desulfurization wastewater.

The present invention also provides a desulfurization wastewater treatment system, including:

the primary treatment unit is used for removing suspended matters, non-metallic ions and heavy metal ions contained in the desulfurization wastewater to obtain primary treatment wastewater;

a secondary treatment unit connected with the water outlet of the primary treatment unit and used for precipitating magnesium ions contained in the primary treatment wastewater to obtain magnesium ion precipitate and secondary treatment wastewater

The salt separating unit is connected with a water outlet of the secondary treatment unit and is used for treating the secondary treatment wastewater to obtain monovalent salt wastewater and divalent salt wastewater;

the first recovery unit is connected with the first water outlet of the salt separation unit and is used for recovering monovalent salt contained in the monovalent salt wastewater;

and the second recovery unit is connected with the second water outlet of the salt separation unit and is used for recovering divalent salt contained in the divalent salt wastewater.

Compared with the prior art, in the desulfurization wastewater treatment system provided by the invention, the water outlet of the primary treatment unit is connected with the secondary treatment unit, and the primary treatment unit can remove suspended matters, non-metal ions and heavy metal ions contained in the desulfurization wastewater to obtain the primary treatment wastewater so as to effectively remove substances used for forming sludge in the desulfurization wastewater, so that when the secondary treatment unit precipitates the magnesium ions contained in the primary treatment wastewater, almost no sludge is formed, and the obtained magnesium ion precipitate has high purity, thereby not only improving the magnesium ion precipitation purity, but also reducing the formation amount of sludge. Moreover, the water outlet of the secondary treatment unit is connected with the salt separation unit, and the salt separation unit can treat the secondary treatment wastewater to separate monovalent salt and divalent salt originally dissolved in the secondary treatment wastewater, so that monovalent salt wastewater and divalent salt wastewater are obtained; the first water outlet of the salt separating unit and the first recovery unit are used for recovering monovalent salt contained in the monovalent salt wastewater, the second water outlet of the salt separating unit and the second recovery unit are used for recovering divalent salt contained in the divalent salt wastewater, and therefore the desulfurization wastewater treatment method provided by the invention not only can reduce the difficulty in recovering magnesium, but also can recover monovalent salt and divalent salt contained in the desulfurization wastewater, and therefore useful substances in the desulfurization wastewater can be fully recovered.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is a first schematic structural diagram of a desulfurization wastewater treatment system provided by an embodiment of the present invention;

FIG. 2 is a schematic structural diagram II of a desulfurization wastewater treatment system provided in an embodiment of the present invention;

FIG. 3 is a first flow chart of a desulfurization wastewater treatment method provided by an embodiment of the invention;

FIG. 4 is a second flow chart of the desulfurization waste water treatment method provided by the embodiment of the invention;

FIG. 5 is a flow chart of a desulfurization wastewater treatment method provided in the embodiment of the present invention;

FIG. 6 is a fourth flow chart of the desulfurization waste water treatment method provided by the embodiment of the invention;

FIG. 7 is a fifth flow chart of the desulfurization wastewater treatment method provided by the embodiment of the invention;

FIG. 8 is a sixth flow chart of the desulfurization wastewater treatment method according to the embodiment of the present invention.

Reference numerals:

100-a primary treatment unit, 110-a primary regulation pool;

120-primary clarifier, 130-first collection unit;

200-a secondary treatment unit; 210-a secondary regulating reservoir;

220-secondary clarifier, 230-second collection unit;

300-a sand filtration device, 400-an ultrafiltration device;

500-neutralization unit, 600-salt separation unit;

610-nanofiltration device, 700-first recovery unit;

710-reverse osmosis unit, 720-bipolar membrane electrodialysis unit;

730-lye tank, 740-acid tank;

800-a second recovery unit, 810-a normal temperature crystallization reactor;

900-water pipe network for power plant.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the prior art, in order to maintain the material balance of a slurry circulating system included in limestone-gypsum wet flue gas desulfurization equipment and prevent the corrosion problem of a desulfurization tower caused by over-standard chlorine concentration of slurry, a certain amount of wastewater generated by desulfurization of the limestone-gypsum wet flue gas desulfurization equipment on flue gas needs to be discharged periodically, the wastewater is defined as desulfurization wastewater, and the desulfurization wastewater is acidic, high in salt content, high in suspended matter content, heavy in metal content, large in water quality fluctuation and directly discharged, so that the surrounding environment is seriously influenced. When desulfurization waste water is treated by a conventional triple box process, suspended matters and heavy metal ions contained in the desulfurization waste water are removed and discharged outwards mainly by adjusting the pH value of the desulfurization waste water, so that a large amount of salt substances enter the environment along with the discharged desulfurization waste water, and adverse effects are caused on the ecological environment. Therefore, how to realize zero discharge of the desulfurization wastewater is an urgent technical problem to be solved.

In order to solve the above problems, two or more technologies such as pretreatment, salt separation, membrane concentration, evaporative crystallization and the like are usually combined to treat the desulfurization wastewater, so that the desulfurization wastewater is completely recovered and treated as much as possible, and zero discharge of the desulfurization wastewater is achieved. However, when the desulfurization wastewater is pretreated, the desulfurization wastewater is mostly softened by sodium hydroxide, sodium carbonate, carbon dioxide flue gas or ion resin, etc. to reduce the hardness of the desulfurization wastewater, so that the hardness of the desulfurization wastewater meets the standard, but the running costs of sodium hydroxide, sodium carbonate, resin, etc. are high, which limits the development of the desulfurization wastewater treatment technology. And the concentration and reduction degree in the subsequent membrane treatment process is uncontrollable, thereby further limiting the popularization of the desulfurization wastewater treatment process.

For example: the prior art provides a process for performing zero discharge treatment on desulfurization wastewater of a power plant by utilizing a bipolar membrane electrodialysis technology, which is to subject desulfurization wastewater generated by the power plant to NaOH and Ca (OH)₂Carrying out three-stage reaction treatment on the carbon dioxide flue gas to sequentially reduce the heavy metal content, the hardness, the sulfate radical content and the like in the wastewater; and then the treated wastewater is subjected to salt separation by a nanofiltration device, nanofiltration concentrated water is subjected to reflux circulation treatment, nanofiltration produced water enters bipolar membrane electrodialysis electrolysis to generate alkali liquor and hydrochloric acid, part of the alkali liquor is recycled to a pretreatment unit, and no wastewater is discharged out of the system.

However, in the pretreatment section, a large amount of calcium and sodium ions are additionally introduced for removing magnesium and calcium ions, and the subsequent desalting load of the system is increased. Furthermore, magnesium and calcium resources contained in the desulfurization waste water, particularly magnesium resources, are treated in the form of sludge in the above-mentioned treatment techniques, and it is necessary to consider treatment and storage costs. High purity Mg (OH)₂、CaSO₄As an inorganic chemical raw material, the recovery process is continuously appeared along with the shortage of natural resources. When the carbon dioxide flue gas is used for softening the desulfurization wastewater so as to remove calcium ions contained in the desulfurization wastewater, the introduction of additional impurity components cannot be guaranteed, and CO in the carbon dioxide flue gas₂The content is low, so that the removal rate of calcium ions is difficult to control. When the nanofiltration system is used for nanofiltration treatment of the treated wastewater, nanofiltration produced water directly enters the bipolar membrane electrodialysis system without being concentrated, the treatment capacity is large, the salt content of the electrodialysis produced water is more than 5000mg/L, and the quality of reuse water is low.

For the above reasons, referring to fig. 1 and 3, the desulfurization wastewater treatment system provided by the embodiment of the present invention includes:

the primary treatment unit 100 is used for removing suspended matters, non-metallic ions and heavy metal ions contained in the desulfurization wastewater to obtain primary treatment wastewater, wherein the non-metallic ions mainly comprise silicon ions and/or fluorine ions;

the secondary treatment unit 200 is connected with the water outlet of the primary treatment unit 100 and is used for precipitating magnesium ions contained in the primary treatment wastewater to obtain magnesium ion precipitates and secondary treatment wastewater;

the salt separating unit 600 is connected with a water outlet of the secondary treatment unit 200 and is used for treating the secondary treatment wastewater to obtain monovalent salt wastewater and divalent salt wastewater;

the first recovery unit 700 is connected to the first water outlet of the salt separating unit 600 and is used for recovering monovalent salt contained in the monovalent salt wastewater;

and the second recovery unit 800 is connected with the second water outlet of the salt separating unit 600 and is used for recovering the divalent salt contained in the divalent salt wastewater.

The wastewater treatment process of the desulfurization wastewater treatment system according to the embodiment of the present invention will be described in detail with reference to fig. 1 and 3.

Step S100: the primary treatment unit 100 removes suspended matter, non-metallic ions and heavy metal ions contained in the desulfurization wastewater to obtain primary treatment wastewater;

step S200: the secondary treatment unit 200 precipitates magnesium ions contained in the primary treatment wastewater to obtain magnesium ion precipitates and secondary treatment wastewater, wherein the magnesium ion precipitates are magnesium hydroxide with the purity of more than 95%; the concentration of magnesium ions contained in the secondary treatment wastewater is less than or equal to 10 mg/L;

step S400, the secondary treatment wastewater is treated by a salt separation unit 600 to obtain monovalent salt wastewater and divalent salt wastewater;

step S500: the first recovery unit 700 recovers monovalent salt contained in the monovalent salt wastewater to obtain a monovalent salt recovery product and first recovered water; the second recovery unit 800 recovers divalent salt contained in the divalent salt wastewater to obtain divalent salt and second recovered effluent.

Known by above-mentioned desulfurization wastewater treatment system's structure and desulfurization wastewater treatment process, the delivery port and the secondary treatment unit 200 of primary treatment unit 100 are connected, and suspended solid, non-metallic ion and heavy metal ion that desulfurization wastewater contained can be got rid of to primary treatment unit 100, obtain primary treatment wastewater, be used for forming the material of sediment mud in effectively getting rid of desulfurization wastewater, this makes secondary treatment unit 200 when deposiing the magnesium ion that primary treatment wastewater contains, almost no sediment mud forms, the magnesium ion sediment that obtains has higher purity, so not only improved the purity that the magnesium ion deposits, the formation volume of sediment mud has still been reduced. Furthermore, the water outlet of the secondary treatment unit 200 is connected with the salt separating unit 600, and the salt separating unit can treat the secondary treatment wastewater, so that the monovalent salt and the divalent salt originally dissolved in the secondary treatment wastewater are separated, and the monovalent salt wastewater and the divalent salt wastewater are obtained; the first water outlet of the salt separating unit 600 and the first recovery unit 700 are provided, the first recovery unit 700 is used for recovering monovalent salt contained in the monovalent salt wastewater, the second water outlet of the salt separating unit 600 and the second recovery unit 800 are provided, and the second recovery unit 800 is used for recovering divalent salt contained in the divalent salt wastewater, so that the desulfurization wastewater treatment method provided by the embodiment of the invention can not only reduce the difficulty in recovering magnesium, but also recover monovalent salt and divalent salt contained in the desulfurization wastewater, and thus can fully recover useful substances in the desulfurization wastewater.

In some embodiments, as shown in fig. 1, 2 and 6, the salt separation unit 600 is a nanofiltration device 610, a water inlet of the nanofiltration device 610 is connected to a water outlet of the secondary treatment unit 200, a water outlet of the nanofiltration device 610 is connected to a water inlet of the first recovery unit 700, and a concentrated water outlet of the nanofiltration device 610 is connected to a water outlet of the second recovery unit 800. At this time, after the secondary treatment wastewater is treated by the nanofiltration device 610, monovalent salt wastewater flows out from the water outlet of the nanofiltration device 610, and divalent salt wastewater flows out from the concentrated water outlet of the nanofiltration device 610.

Considering the recovery of calcium resources and magnesium resources contained in the desulfurization wastewater, the retention rate of the nanofiltration device 610 on sulfate ions is greater than 98%, the retention rate of the nanofiltration device 610 on calcium ions is greater than 95%, and the water yield of the nanofiltration device 610 is 50%.

As shown in fig. 1, in order to ensure that the secondary wastewater entering the salt separating unit 600 contains small particles, the desulfurization wastewater treatment system further comprises a sand filtration device 300 and/or an ultrafiltration device 400, and the sand filtration device 300 and/or the ultrafiltration device 400 are connected in series between the outlet of the secondary treatment unit 200 and the inlet of the salt separating unit 600. When the desulfurization wastewater is treated by the desulfurization wastewater treatment system, the method further comprises the following steps between step S200 and step S400:

step S300: the secondary treatment wastewater is filtered by the sand filtering device 300 and/or the ultrafiltration device 400 to avoid the influence on the subsequent salt separating unit 600.

For example: as shown in fig. 2, when the salt separation unit 600 is the nanofiltration device 610, the secondary treated wastewater is filtered by the sand filtration device 300 and/or the ultrafiltration device 400, so that fine particles contained in the secondary treated wastewater can be prevented from blocking the nanofiltration membrane included in the nanofiltration device 610, thereby prolonging the service life of the nanofiltration device 610.

It can be understood that, when the desulfurization wastewater treatment system includes the sand filtration device 300 and the ultrafiltration device 400, the sand filtration device 300 and the ultrafiltration device 400 are sequentially disposed between the water outlet of the secondary treatment unit and the water inlet of the salt separation unit, so that the particulate matters contained in the secondary treatment wastewater are filtered in a graded manner in order of large to small, thereby further completely removing the particulate matters contained in the secondary treatment wastewater.

In some embodiments, as shown in fig. 1, fig. 2 and fig. 6, the first recovery unit 700 is further configured to recover the monovalent salt contained in the monovalent salt wastewater to obtain an alkali solution, an acid solution and a product water, send the product water into an electric power plant water pipe network, send the alkali solution into the primary treatment unit 100 and/or the secondary treatment unit 200, make the primary treatment unit 100 specifically configured to adjust the pH of the desulfurization wastewater to 9-10 by using the alkali solution, and add an organic sulfur, a flocculant and a coagulant aid to the desulfurization wastewater to make suspended matters, non-metal ions and heavy metal ions contained in the desulfurization wastewater precipitate in the form of sludge, so as to obtain a magnesium ion precipitate and a secondary treatment wastewater; and/or the secondary treatment unit 200 is specifically used for adjusting the pH value of the primary treatment wastewater from which the sludge is removed to 11-13 by using alkali liquor.

The desulfurization wastewater treatment system further comprises a neutralization unit 500 which is respectively connected with the water outlet of the secondary treatment unit 200 and the water inlet of the salt separation unit 600, and is used for adjusting the pH value of the secondary treatment wastewater to be neutral before the secondary treatment wastewater is treated so as to ensure that monovalent salt and divalent salt are fully separated. The first recovery unit is also used for adjusting the pH value of the secondary treatment wastewater to be neutral by utilizing acid liquor before the secondary treatment wastewater is treated.

Specifically, as shown in fig. 1 and fig. 2, the first recovery unit 700 includes a reverse osmosis device 710 and a bipolar membrane electrodialysis device 720; the water inlet of the reverse osmosis device 710 is connected with the first outlet of the salt separating unit 600, the produced water outlet of the reverse osmosis device 710 is connected with the water pipe network 900 for the power plant, the concentrated water outlet of the reverse osmosis device 710 is connected with the water inlet of the bipolar membrane electrodialysis device 720, and the produced water outlet of the bipolar membrane electrodialysis device 720 is connected with the water inlet of the reverse osmosis device 710.

Further, the above-mentioned process of removing the suspended matters, the non-metal ions and the heavy metal ions contained in the desulfurization wastewater by the primary treatment unit 100 can substantially precipitate the suspended matters, the non-metal ions and the heavy metal ions contained in the desulfurization wastewater by adjusting the pH value of the desulfurization wastewater, and discharge the precipitated matters as sludge. The secondary treatment unit 200 may substantially adjust the pH of the primary treatment wastewater to precipitate magnesium ions in the form of magnesium hydroxide. Based on this, the acid liquid outlet of the bipolar membrane electrodialysis device 720 is connected with the acid liquid inlet of the neutralization unit 500, and the alkali liquid outlet of the bipolar membrane electrodialysis device 720 is respectively connected with the alkali liquid inlet of the primary treatment unit 100 and the alkali liquid inlet of the secondary treatment unit 200.

The following describes a specific process of recovering monovalent salt contained in monovalent salt wastewater by the salt separating unit 600 with reference to fig. 1, fig. 2 and fig. 7.

Adopting a reverse osmosis device 710 to perform reverse osmosis concentration on the monovalent salt wastewater to obtain monovalent salt concentrated water and reverse osmosis produced water; the monovalent salt wastewater mainly contains sodium chloride, the concentration of the sodium chloride contained in the monovalent salt wastewater is 10g/L-20g/L, and the concentration of the sodium chloride contained in the monovalent salt concentrated water is 100g/L-150 g/L; the reverse osmosis device 710 may be a reverse osmosis device such as a disk reverse osmosis device.

Electrolyzing the monovalent salt concentrated water by adopting a bipolar membrane electrodialysis device 720 to obtain monovalent salt recovery and electrodialysis water; the reverse osmosis produced water and the electrodialysis produced water form first recovered water. Wherein the Total Dissolved Solids (TDS) of the reverse osmosis produced water is less than 1000mg/L, and at least 80L of reverse osmosis produced water is recovered per 100L of the desulfurization waste water. At this time, the reverse osmosis produced water meets the standards of water (such as cooling water, cleaning water and the like) for power plants, and can be directly provided for the water pipe network 900 for power plants for desulfurization treatment. The electrodialysis product water may be passed to a reverse osmosis unit 710 for further purification. The monovalent salt recovery comprises hydrochloric acid and a sodium hydroxide solution (a sodium hydroxide aqueous solution), the concentration of the generated hydrochloric acid and the mass concentration of the sodium hydroxide solution are 8-15%, and the concentration of the generated hydrochloric acid and the concentration of the sodium hydroxide solution can be in other ranges according to different processes.

As described above, when the first recovery unit 700 recovers monovalent salts contained in monovalent salt wastewater, sodium chloride contained in monovalent salt wastewater can be electrolyzed into a sodium hydroxide solution and hydrochloric acid, the sodium hydroxide can be used for the first treatment unit 100 to treat desulfurization wastewater and the second treatment unit 200 to treat first treatment wastewater, and the hydrochloric acid can be used for the neutralization unit 500 to neutralize second treatment wastewater. Meanwhile, when the first recovery unit 700 recovers the monovalent salt contained in the monovalent salt wastewater, the obtained reverse osmosis produced water meets the water quality standard of the process water of the power plant, and can be directly recycled as the process water (cooling water, cleaning water and the like) of the power plant. Therefore, the first recovery unit 700 can be used for treating the monovalent salt wastewater, so that the obtained sodium hydroxide solution, hydrochloric acid and reverse osmosis produced water are completely recycled, and no pollution is caused to the environment; in addition, the sodium hydroxide solution and the hydrochloric acid are used as the desulfurization wastewater treatment chemicals, so that the desulfurization wastewater treatment cost is reduced.

In consideration of the control of the usage amount of the sodium hydroxide solution used for adjusting the pH value of the desulfurization wastewater and the pH value of the primary treatment wastewater, as shown in fig. 1 and 2, the above desulfurization wastewater treatment system further includes an alkali liquid tank 730, an alkali liquid outlet of the bipolar membrane electrodialysis device 720 is connected to an alkali liquid inlet of the primary treatment unit 100 and an alkali liquid inlet of the secondary treatment unit 200 through the alkali liquid tank 730, respectively, so that the sodium hydroxide solution obtained by the bipolar membrane electrodialysis device 720 is stored in the alkali liquid tank 730, and when the sodium hydroxide solution needs to be added to the primary treatment unit 100 and/or the secondary treatment unit 200, the sodium hydroxide solution is supplied to the primary treatment unit 100 and/or the secondary treatment unit 200 through an alkali-resistant pipe. The addition of the sodium hydroxide solution can be controlled by an alkali liquor valve according to the adjustment condition of the pH value.

In consideration of the need for controlled use of acid solution when neutralizing secondary treatment wastewater, as shown in fig. 2, the desulfurization wastewater treatment system further includes an acid solution tank 740, wherein an acid solution outlet of the bipolar membrane electrodialysis device 720 is connected to an acid solution inlet of the neutralization unit 500 through the acid solution tank 740, so that hydrochloric acid obtained by the bipolar membrane electrodialysis device 720 is stored in the acid solution tank 740, and when the neutralization unit 500 needs to add hydrochloric acid, the hydrochloric acid is supplied to the neutralization unit 500 through an acid-resistant pipe. The addition amount of hydrochloric acid can be adjusted by an acid valve according to the neutralization degree.

In some embodiments, the produced water outlet of the second recycling unit 800 is connected to the water inlet of the salt separating unit 600, so as to recycle the second recycled water by the salt separating unit 600.

Illustratively, as shown in fig. 1 and 2, the second recovery unit 800 is an ambient temperature crystallization reactor 810, and the ambient temperature in the ambient temperature crystallization reactor 810 is the ambient temperature. The produced water outlet of the normal temperature crystallization reactor 810 is connected with the water inlet of the salt separating unit 600, so that the salt separating unit 600 is further utilized to carry out salt separating concentration treatment on the second recovered water generated by the normal temperature crystallization reactor 810 again. The process of recovering the divalent salt contained in the divalent salt wastewater by the second recovery unit 800 will be described below with reference to fig. 8. Wherein, the divalent salt wastewater mainly contains sulfate ions and calcium sulfate consisting of calcium ions.

Introducing the divalent salt wastewater into a normal-temperature crystallization reactor 810, adding seed crystals into the divalent salt wastewater, and uniformly stirring to obtain a crystallization solution; the time required for uniform stirring is 60min, and the stirring time can be shortened or prolonged according to actual conditions.

And settling the crystallization solution in a settling zone of the normal-temperature crystallization reactor 810 to obtain gypsum and second recovered effluent.

In the process of sedimentation, high-concentration sulfate radicals and calcium ions spontaneously react in a supersaturated solution to generate calcium sulfate dihydrate serving as a divalent salt recovery product, and the calcium sulfate dihydrate is precipitated in the form of crystals. The precipitated calcium sulfate dihydrate is called gypsum, and the purity of the precipitated gypsum is more than 95 percent. . When the seed crystal added is sodium sulfate, the second recovered effluent obtained contains not only calcium ions but also sodium ions, and at this time, the second recovered effluent is sent to the salt separation unit 600, so that calcium ions and sodium ions in the second recovered effluent can be separated.

Therefore, in the embodiment of the present invention, the normal temperature crystallization reactor 810 is used to recover calcium sulfate dihydrate, and the calcium ion concentration in the second recovered effluent generated by the normal temperature crystallization reactor 810 can be effectively controlled by adjusting the dosage of sodium sulfate as the seed crystal. For example: the calcium ion concentration of the second recovered effluent can be controlled between 15mmmol/L and 18mmol/L by adjusting the addition amount of the sodium sulfate. Therefore, the desulfurization wastewater treatment system provided by the embodiment of the invention can adopt low-cost sodium sulfate to replace sodium carbonate to regulate and control the calcium ion hardness of the second recovered effluent so as to reduce the medicament cost, and can recover high-added-value calcium sulfate dihydrate. Therefore, after the divalent salt wastewater is recycled by using the conventional crystallizer, the calcium sulfate dihydrate with high added value can be recycled, and the second recycled effluent is not discharged outside, but is sent to the salt separation unit 600 for cyclic salt separation treatment. Therefore, the recycling of the divalent salt wastewater using the conventional crystallizer does not cause any environmental pollution, and the introduced sodium ions can also enter the monovalent salt wastewater in the salt separating unit 600 and be recycled through the first recycling unit 700.

In some embodiments, as shown in fig. 1 and 2, the primary treatment unit 100 includes a primary conditioning tank 110 and a primary clarifier 120; the secondary treatment unit 200 includes a secondary conditioning tank 210 and a secondary clarifier 220; the water inlet of the primary regulating reservoir 110 is connected with a desulfurization wastewater pipeline, the water outlet of the primary regulating reservoir 110 is connected with the water inlet of the primary clarifier 120, the solid outlet of the primary clarifier 120 is connected with the first collecting unit 130, the water outlet of the primary clarifier 120 is connected with the water inlet of the secondary regulating reservoir 210, the water outlet of the secondary regulating reservoir 210 is connected with the water inlet of the secondary clarifier 220, the solid outlet of the secondary clarifier 220 is connected with the second collecting unit 230, and the water outlet of the secondary clarifier 220 is connected with the water inlet of the salt separating unit 600. The first collection unit 130 and the second collection unit 230 may be implemented in various forms, such as a solid container, such as a tank, a box, or the like.

When the first recovery unit 700 comprises the reverse osmosis device 710 and the bipolar membrane electrodialysis device 720, the alkali liquor inlet of the primary regulation tank 110 is connected with the alkali liquor outlet of the bipolar membrane electrodialysis device 720, the alkali liquor inlet of the secondary regulation tank 210 is connected with the alkali liquor outlet of the bipolar membrane electrodialysis device 720,

in specific implementation, as shown in fig. 4 and 5, the desulfurization wastewater pipeline supplies desulfurization wastewater to the primary regulation tank 110 through the water inlet of the primary regulation tank 110, the bipolar membrane electrodialysis device 720 supplies sodium hydroxide solution to the desulfurization wastewater entering the primary regulation tank 110 through the alkali liquor inlet of the primary regulation tank 110 until suspended matters, non-metal ions and heavy metal ions contained in the desulfurization wastewater in the primary regulation tank 110 precipitate, the desulfurization wastewater is fed into the primary clarifier 120, the precipitates are discharged from the solid outlet of the primary clarifier 120 in the form of sludge, the obtained primary treatment wastewater is discharged from the water outlet of the primary clarifier 120 and enters the secondary regulation tank 210 through the water inlet of the secondary regulation tank 210, the bipolar membrane electrodialysis device 720 supplies sodium hydroxide solution to the primary treatment wastewater in the secondary regulation tank 210 through the alkali liquor inlet of the secondary regulation tank 210, at the moment, magnesium ions contained in the primary treatment wastewater are combined with hydroxide radicals to form magnesium ion precipitate, then the primary treatment wastewater is sent into a secondary clarification tank 220, the magnesium ion precipitate is settled in the secondary clarification tank 220, and the concentration of the magnesium ions contained in the obtained secondary treatment wastewater is less than or equal to 10 mg/L.

In summary, sodium hydroxide and hydrochloric acid are required to be added at the initial operation stage of the desulfurization wastewater treatment system provided by the embodiment of the invention, no chemical is required to be used except for adding sodium sulfate in the operation process of the normal-temperature crystallization reactor 810, and the sodium hydroxide and hydrochloric acid required by the subsequent operation of the desulfurization wastewater are both from the products of the desulfurization wastewater treatment system after the desulfurization wastewater treatment; and only a small amount of sludge is discharged after the desulfurization wastewater is treated, the generated sodium hydroxide solution and hydrochloric acid can be collected and used for treating the desulfurization wastewater, and the generated effluent can be used for power plant process water. Therefore, the desulfurization wastewater treatment system provided by the embodiment of the invention has the advantages of smaller desalination load and medicament cost, shorter wastewater treatment process, capability of realizing recovery of calcium resources, magnesium resources and water resources in desulfurization wastewater, and reduction of the overall operation cost of the system. Specifically, the desulfurization wastewater treatment system provided by the embodiment of the invention has the following beneficial effects:

firstly, the primary treatment unit 100 removes most heavy metal ions, suspended matters and heavy metal ions contained in the desulfurization wastewater in a pH value adjusting manner in advance, and then the secondary treatment unit 200 precipitates magnesium ions contained in the primary treatment wastewater in a pH value adjusting manner to form Mg (OH) with the purity of more than 95%₂Precipitating to recover high purity magnesium resource for reuse while reducing the amount of sludge produced by the primary treatment unit 100.

Secondly, a mode of combining a nanofiltration system and a normal-temperature crystallization reactor 810 is adopted, so that divalent salt wastewater mainly containing calcium sulfate is separated from secondary treatment wastewater by the nanofiltration system, and then calcium sulfate contained in the divalent salt wastewater is crystallized by the normal-temperature crystallization reactor 810, so that calcium sulfate is prevented from being recovered by an evaporative crystallization mode, the purity of the calcium sulfate is improved, and the energy consumption and the investment cost are reduced. Moreover, when calcium sulfate is crystallized by the normal-temperature crystallization reactor 810, low-cost sodium sulfate can be used to replace sodium carbonate as a softening agent (namely, seed crystal), so that the calcium sulfate is crystallized at normal temperature in the form of gypsum with the purity of more than 95%, thereby reducing the hardness of the divalent salt wastewater and recovering the high-added-value calcium sulfate dihydrate solid salt; meanwhile, the obtained second recovered effluent contains calcium ions and sodium ions introduced by the added sodium sulfate, but the second recovered effluent is sent to the water inlet of the nanofiltration device 610, so that the nanofiltration device 610 can further circularly treat the second recovered effluent, and therefore, the combination of the nanofiltration system and the normal-temperature crystallization reactor 810 not only can controllably realize the recovery of divalent salt, but also can circularly treat the second recovered effluent, thereby realizing zero emission in the recovery process of divalent salt.

Thirdly, reducing and concentrating the monovalent salt wastewater of the nanofiltration device 610 in a coupling mode of a reverse osmosis device 710 and a bipolar membrane electrodialysis device 720, so that sodium chloride contained in the monovalent salt wastewater is electrolyzed into NaOH and HCl, the formed sodium hydroxide solution is sent to the primary treatment unit 100 and the secondary treatment unit 200 for use, the formed hydrochloric acid is sent to the neutralization unit 500 for use, and reverse osmosis produced water obtained by the reverse osmosis device 710 meets the requirements of process water of a power plant and can be sent to a water network 900 for the power plant for use. Moreover, the bipolar membrane electrodialysis device 720 can control the sodium chloride contained in the monovalent salt concentrated water generated by the electrolysis reverse osmosis device 710, so that the sodium chloride contained in the monovalent salt waste water can be electrolyzed controllably.

Fourthly, the desulfurization wastewater treatment system provided by the embodiment of the invention has a simpler structure, and can simplify the desulfurization wastewater treatment process, so that the desulfurization wastewater treatment process is simple and convenient to operate; moreover, no evaporation unit is provided in the desulfurization wastewater treatment system, so that the operation energy consumption and the investment cost can be reduced, the primary treatment unit 100 and the secondary treatment unit 200 only need to be started for the first time, and the sodium hydroxide required by the subsequent operation is all from the high-purity sodium hydroxide solution generated by the bipolar membrane electrodialysis device 720. Therefore, compared with the prior art, the desulfurization wastewater treatment system provided by the embodiment of the invention has the advantages that the additional desalination load and the medicament cost are lower, the recovery processes of calcium resources, magnesium resources and water resources are simpler, and the overall operation cost can be reduced.

As shown in fig. 3, an embodiment of the present invention further provides a desulfurization wastewater treatment method, including the following steps:

step S100: removing suspended matters, non-metallic ions and heavy metal ions contained in the desulfurization wastewater to obtain primary treatment wastewater;

step S200: precipitating magnesium ions contained in the primary treatment wastewater to obtain magnesium ion precipitate and secondary treatment wastewater;

step S400: treating the secondary treatment wastewater to obtain monovalent salt wastewater and divalent salt wastewater;

step S500: recovering monovalent salt contained in the monovalent salt wastewater to obtain monovalent salt recovered materials and first recovered water; and (3) recovering divalent salt contained in the divalent salt wastewater to obtain a divalent salt recovery material and second recovered effluent.

As can be seen from the above, in the desulfurization wastewater treatment method provided by the embodiment of the present invention, before magnesium ions contained in primary treatment wastewater are precipitated, suspended matters, non-metal ions, and heavy metal ions contained in the desulfurization wastewater are removed to obtain the primary treatment wastewater, so as to effectively remove substances used for forming sludge in the desulfurization wastewater, so that when magnesium ions contained in the primary treatment wastewater are precipitated, almost no sludge is formed, and the obtained magnesium ion precipitate has high purity, thereby not only improving the purity of the magnesium ion precipitate, but also reducing the formation amount of sludge. Furthermore, in the desulfurization wastewater treatment method provided by the embodiment of the present invention, the secondary treatment wastewater is treated, so that the monovalent salt and the divalent salt originally dissolved in the secondary treatment wastewater are separated, thereby obtaining monovalent salt wastewater and divalent salt wastewater; and the monovalent salt contained in the monovalent salt wastewater and the divalent salt contained in the divalent salt wastewater are recovered, so that the desulfurization wastewater treatment method provided by the embodiment of the invention not only can reduce the difficulty in recovering magnesium, but also can recover the monovalent salt and the divalent salt contained in the desulfurization wastewater, thereby fully recovering useful substances in the desulfurization wastewater.

In some embodiments, as shown in fig. 4, the above-mentioned removal of suspended matters, non-metal ions and heavy metal ions contained in the desulfurization waste water; obtaining primary treatment wastewater comprises:

step S110: adjusting the pH value of the desulfurization wastewater to be 9-10, so that suspended matters, non-metallic ions and heavy metal ions contained in the desulfurization wastewater are precipitated in a slag mud form, and obtaining primary treatment wastewater containing slag mud;

step S120: removing slag and mud contained in the primary treatment wastewater to obtain clarified primary treatment wastewater.

In order to better enable suspended matters, non-metal ions and heavy metal ions contained in the desulfurization wastewater to be precipitated in a slag mud form, organic sulfur, a flocculating agent and a coagulant aid can be added into the desulfurization wastewater on the basis except that the pH value of the desulfurization wastewater is adjusted to be 9-10, so that the suspended matters, the non-metal ions and the heavy metal ions in the desulfurization wastewater are precipitated in the slag mud form as much as possible. The organic sulfur can be a TMT-15 heavy metal ion remover produced by Hengsheng chemical Co., Ltd. The flocculating agent can be inorganic flocculating agent, organic polymer flocculating agent or natural organic polymer flocculating agent, and the specific type can be selected according to actual conditions. The coagulant aid can be one or more of polyacrylamide and activated silicic acid.

Wherein, after organic sulfur, flocculating agent and coagulant aid are added into the desulfurization waste water, the concentration of the organic sulfur contained in the desulfurization waste water is 5ppm to 50ppm, the concentration of the flocculating agent contained in the desulfurization waste water is 10ppm to 20ppm, and the concentration of the coagulant aid contained in the desulfurization waste water is 10ppm to 20 ppm.

In some embodiments, as shown in fig. 5, the precipitating magnesium ions contained in the primary treated wastewater to obtain magnesium ion precipitate and the secondary treated wastewater comprises:

step S210: adjusting the pH value of the primary treatment wastewater without the slag sludge to 11-13 to obtain secondary treatment wastewater containing magnesium hydroxide precipitate;

step S220: collecting magnesium hydroxide precipitate contained in the secondary treatment wastewater, wherein the purity of the collected magnesium hydroxide precipitate is more than 95%, and the concentration of magnesium ions contained in the secondary treatment wastewater is less than or equal to 10 mg/L.

In order to better precipitate magnesium ions contained in the primary treatment wastewater, after the pH value of the primary treatment wastewater from which the sludge is removed is adjusted to 11-13, a coagulant aid can be added. The coagulant aid can be one or more of polyacrylamide and activated silicic acid. The concentration of the coagulant aid in the primary treatment wastewater can be 10ppm to 20 ppm.

In some embodiments, as shown in fig. 2 and 6, the treating the secondary treatment wastewater to obtain monovalent salt wastewater and divalent salt wastewater comprises:

step S410: neutralizing the secondary treatment wastewater by using hydrochloric acid;

step S420: carrying out nanofiltration treatment on the neutralized secondary treatment wastewater to obtain nanofiltration product water serving as monovalent salt wastewater and nanofiltration concentrated water serving as divalent salt wastewater;

in order to prevent fine particles contained in the secondary treated wastewater from clogging the nanofiltration membrane inside the nanofiltration device 610, in some embodiments, after the magnesium ion precipitate is obtained and the secondary treated wastewater is treated, as shown in fig. 1 and 3, the desulfurization wastewater treatment method further includes:

step S300: and filtering the secondary treatment wastewater by adopting a sand filtration and/or ultrafiltration mode to avoid the damage of fine particles contained in the secondary treatment wastewater to subsequent wastewater treatment equipment.

In some embodiments, as shown in fig. 7, the recovering monovalent salt contained in the monovalent salt wastewater to obtain a monovalent salt recovering material and a first recovered water comprises:

step S510A: and (3) concentrating the monovalent salt wastewater to obtain monovalent salt concentrated water and concentrated produced water, wherein a reverse osmosis concentration mode or other concentration modes can be adopted when concentrating the monovalent salt wastewater. When reverse osmosis concentration is adopted, the concentrated produced water is defined as that the monovalent salt concentrated water produced by reverse osmosis contains 10g/L-20g/L of sodium chloride, and at least 80L of concentrated produced water is recovered per 100L of desulfurization waste water, namely, the water yield of the concentrated produced water which can be obtained per hour is 80% of the raw water yield of the desulfurization waste water.

Step S520A: feeding the concentrated produced water into a water network 900 for power plant use; and electrolyzing the monovalent salt concentrated water by adopting a bipolar membrane electrodialysis mode to obtain monovalent salt recovery and electrodialysis water. For example: when the monovalent salt wastewater mainly contains sodium chloride, the concentration of the sodium chloride contained in the monovalent salt wastewater is 100g/L-150 g/L; the monovalent salt recovery comprises hydrochloric acid and sodium hydroxide solution; the mass concentration of hydrogen sulfide contained in the hydrochloric acid is 8-15%, and the mass concentration of sodium hydroxide contained in the sodium hydroxide solution is 8-15%. Wherein, at least 80L of concentrated produced water can be obtained per 100L of desulfurization waste water, the total soluble solid content of the concentrated produced water is less than 1000mg/L, and 20L of monovalent salt recovery can be obtained per hour by bipolar membrane electrodialysis.

Step S530A: mixing electrodialysis water production with monovalent salt wastewater to concentrate the electrodialysis water production and the monovalent salt wastewater together; regulating the pH value of the desulfurization wastewater and the primary treatment wastewater by using a sodium hydroxide solution contained in the monovalent salt recovery; the secondary treatment wastewater is adjusted to be neutral by utilizing the hydrochloric acid contained in the monovalent salt recovery substances, so that the dosing cost is saved, and the desalting load of the whole system is reduced.

In some embodiments, as shown in fig. 8, the recovering divalent salt contained in the divalent salt wastewater to obtain a divalent salt recovered material and a second recovered effluent includes:

step S510B: sodium sulfate is added to the divalent salt wastewater, and the sodium sulfate reacts with calcium ions contained in the divalent salt wastewater. Sodium sulfate is added into the divalent salt wastewater in the form of sodium sulfate solution, and the concentration of the sodium sulfate solution is 15-30%.

Step S520B: reacting sodium sulfate with calcium ions contained in the divalent salt wastewater and crystallizing to obtain a divalent salt recovery product and second recovery water, wherein the divalent salt recovery product is calcium sulfate dihydrate (also called gypsum) with the purity of more than 95%, and the second recovery water is crystallization water; the concentration of calcium ions contained in the second recovered water is 15 mmol/L-18 mmol/L.

Step S530B: and mixing the crystallized effluent with secondary treatment wastewater to further separate monovalent salt and divalent salt contained in the crystallized effluent by adopting a nanofiltration mode.

The following describes, with reference to fig. 1 to 8, a treatment process of desulfurization wastewater discharged from a power plant, in which the desulfurization wastewater treatment method provided by the embodiment of the present invention is applied to the desulfurization treatment system.

Example one

Step S100: introducing 15t/h of desulfurization wastewater into a primary regulating tank 110, adding a sodium hydroxide solution with the mass concentration of 10% into the desulfurization wastewater to enable the pH value of the desulfurization wastewater to be 9.5, simultaneously adding a TMT-15 heavy metal ion remover, aluminum sulfate and polyacrylamide into the desulfurization wastewater, stirring for reaction for 30min, introducing the desulfurization wastewater into a primary clarifying tank 120, clarifying for 60min, settling suspended matters, non-metal ions and heavy metal ions contained in the desulfurization wastewater in a slag mud mode, collecting settled slag mud through a first collecting unit 130, and conveying primary treatment wastewater into a secondary regulating tank 210; the concentration of a TMT-15 heavy metal ion remover contained in the desulfurization wastewater is 25ppm, the concentration of aluminum sulfate contained in the desulfurization wastewater is 14ppm, and the concentration of polyacrylamide contained in the desulfurization wastewater is 18 ppm. In Table 1, the water quality of the desulfurization waste water used in example one is shown.

TABLE 1 Water quality of desulfurized waste Water used in example one

Step S200: adding a sodium hydroxide solution with the mass concentration of 10% into the secondary regulating tank 210 to regulate the pH value to 11.5, adding polyacrylamide, stirring and reacting for 30min, sending the primary treatment wastewater into a secondary clarifying tank 220, standing for 30min for settling to obtain magnesium hydroxide precipitate and secondary treatment wastewater, collecting the magnesium hydroxide precipitate through a second collecting unit 230, and enabling the concentration of magnesium ions contained in the secondary treatment wastewater to be 10.0 mg/L; the concentration of polyacrylamide in the primary wastewater was 15 ppm.

Step S300: and sequentially carrying out sand filtration and ultrafiltration on the primary treatment wastewater.

Step S400: adding hydrochloric acid with the mass concentration of 8% into the primary treatment wastewater to adjust the pH value to 7.4, and then carrying out salt separation treatment on the primary treatment wastewater by adopting a nanofiltration device 610 to obtain monovalent salt wastewater and divalent salt wastewater, wherein the rejection rate of the nanofiltration device 610 on sulfate ions is more than 98%, the rejection rate of calcium ions is more than 95%, and the water yield of the nanofiltration device 610 is 50%; wherein the monovalent salt wastewater is nanofiltration product water of the nanofiltration device 610, which mainly contains sodium chloride with the concentration of 18g/L, and the divalent salt wastewater is nanofiltration concentrated water formed by the nanofiltration device 610, which mainly contains calcium sulfate.

Step S500: and (3) concentrating the monovalent salt wastewater by using a disc tube reverse osmosis device, delivering the obtained reverse osmosis produced water to a water pipe network 900 for a power plant for reuse, and obtaining monovalent salt concentrated water with the concentration of 120 g/L. Feeding the monovalent salt concentrated water into a bipolar membrane electrodialysis device 720 for electrolysis to obtain hydrochloric acid with the mass concentration of 8% and a sodium hydroxide solution with the mass concentration of 10%, recycling 85L of reverse osmosis water per 100L of desulfurization wastewater, wherein the total soluble solid of the reverse osmosis water is less than 1000 mg/L. 12.7t of reverse osmosis water can be obtained every hour; the hydrochloric acid and sodium hydroxide solution obtained each hour was 20L.

And (3) feeding the divalent salt wastewater into a normal-temperature crystallization reactor 810, adding a sodium sulfate solution with the mass percent of 20%, stirring and reacting for 60min in the presence of seed crystals, and allowing the mixture to enter a settling zone for settling for 60min to obtain gypsum with the purity of more than 95%. The calcium ion concentration of the effluent from the normal temperature crystallization reactor 810 is 17.0mmol/L, and the effluent directly flows back to the water inlet of the nanofiltration device 610 for circulation treatment.

Example two

Step S100: introducing 15t/h of desulfurization wastewater into a primary regulating tank 110, adding a sodium hydroxide solution with the mass concentration of 15% into the desulfurization wastewater to enable the pH value of the desulfurization wastewater to be 9, simultaneously adding a TMT-15 heavy metal ion remover, aluminum sulfate and polyacrylamide into the desulfurization wastewater, stirring for reaction for 30min, introducing the desulfurization wastewater into a primary clarifying tank 120, clarifying for 60min, settling suspended matters, non-metal ions and heavy metal ions contained in the desulfurization wastewater in a slag mud mode, collecting settled slag mud through a first collecting unit 130, and sending primary treatment wastewater into a secondary regulating tank 210; the concentration of a TMT-15 heavy metal ion remover contained in the desulfurization wastewater is 5ppm, the concentration of aluminum sulfate contained in the desulfurization wastewater is 10ppm, and the concentration of polyacrylamide contained in the desulfurization wastewater is 20 ppm. Table 2 shows the water quality of the desulfurization waste water used in example two.

TABLE 2 Water quality of desulfurized waste Water used in example two

Step S200: adding a sodium hydroxide solution with the mass concentration of 15% into the secondary regulating tank 210 to regulate the pH value to 11, adding polyacrylamide, stirring and reacting for 30min, sending the primary treatment wastewater into a secondary clarifying tank 220, staying for 30min, and settling to obtain magnesium hydroxide precipitate and secondary treatment wastewater, wherein the magnesium hydroxide precipitate is collected by a second collecting unit 230, and the concentration of magnesium ions contained in the secondary treatment wastewater is 8.5 mg/L; the concentration of polyacrylamide in the primary wastewater was 10 ppm.

Step S400: adding hydrochloric acid with the mass concentration of 10% into the primary treatment wastewater to adjust the pH value to 7.0, and then carrying out salt separation treatment on the primary treatment wastewater by using a nanofiltration device 610 to obtain monovalent salt wastewater and divalent salt wastewater, wherein the rejection rate of the nanofiltration device 610 on sulfate ions is more than 98%, the rejection rate of calcium ions is more than 95%, and the water yield of the nanofiltration device 610 is 50%; wherein the monovalent salt wastewater is nanofiltration product water of the nanofiltration device 610, which mainly contains sodium chloride with the concentration of 10g/L, and the divalent salt wastewater is nanofiltration concentrated water formed by the nanofiltration device 610, which mainly contains calcium sulfate.

Step S500: and (3) concentrating the monovalent salt wastewater by using a disc tube reverse osmosis device, and delivering the obtained reverse osmosis produced water to a water pipe network 900 for a power plant for reuse, wherein the concentration of the obtained monovalent salt concentrated water is 100 g/L. Feeding the monovalent salt concentrated water into a bipolar membrane electrodialysis device 720 for electrolysis to obtain hydrochloric acid with the mass concentration of 8% and a sodium hydroxide solution with the mass concentration of 15%, and recovering 80L of reverse osmosis water per 100L of desulfurization wastewater, wherein the total soluble solid content of the reverse osmosis water is less than 1000 mg/L. 12t of reverse osmosis water can be obtained every hour; the hydrochloric acid and sodium hydroxide solution obtained per hour was 25L.

And (3) feeding the divalent salt wastewater into a normal-temperature crystallization reactor 810, adding a sodium sulfate solution with the mass percent of 15%, stirring and reacting for 60min in the presence of seed crystals, and allowing the mixture to enter a settling zone for settling for 60min to obtain gypsum with the purity of more than 95%. The calcium ion concentration of the effluent from the normal temperature crystallization reactor 810 is 18.0mmol/L, and the effluent directly flows back to the water inlet of the nanofiltration device 610 for circulation treatment.

EXAMPLE III

Step S100: introducing 15t/h of desulfurization wastewater into a primary regulating tank 110, adding a sodium hydroxide solution with the mass concentration of 8% into the desulfurization wastewater to enable the pH value of the desulfurization wastewater to be 9.5, simultaneously adding a TMT-15 heavy metal ion remover, poly-dimethyl diallyl ammonium chloride and activated silicic acid into the desulfurization wastewater, stirring for reaction for 30min, introducing the desulfurization wastewater into a primary clarifying tank 120, clarifying for 60min, and settling suspended matters, non-metal ions and heavy metal ions contained in the desulfurization wastewater in the form of sludge, wherein the settled sludge is collected by a first collecting unit 130, and the primary treatment wastewater is sent into a secondary regulating tank 210; the concentration of the TMT-15 heavy metal ion remover contained in the desulfurization wastewater is 50ppm, the concentration of the poly dimethyl diallyl ammonium chloride contained in the desulfurization wastewater is 20ppm, and the concentration of the activated silicic acid contained in the desulfurization wastewater is 10 ppm. Table 3 shows the water quality of the desulfurization waste water used in example three.

TABLE 3 Water quality of desulfurized waste Water used in example III

Step S200: adding a sodium hydroxide solution with the mass concentration of 8% into the secondary regulating tank 210 to regulate the pH value to 13, adding activated silicic acid, stirring and reacting for 30min, sending the primary treatment wastewater into a secondary clarifying tank 220, staying for 30min, and settling to obtain magnesium hydroxide precipitate and secondary treatment wastewater, wherein the magnesium hydroxide precipitate is collected by a second collecting unit 230, and the concentration of magnesium ions contained in the secondary treatment wastewater is 8 mg/L; the concentration of the activated silicic acid in the primary treatment wastewater is 15 ppm.

Step S400: adding hydrochloric acid with the mass concentration of 15% into the primary treatment wastewater to adjust the pH value to 7.2, and then carrying out salt separation treatment on the primary treatment wastewater by using a nanofiltration device 610 to obtain monovalent salt wastewater and divalent salt wastewater, wherein the rejection rate of the nanofiltration device 610 on sulfate ions is more than 98%, the rejection rate of calcium ions is more than 95%, and the water yield of the nanofiltration device 610 is 50%; wherein the monovalent salt wastewater is nanofiltration product water of the nanofiltration device 610, which mainly contains sodium chloride with the concentration of 20g/L, and the divalent salt wastewater is nanofiltration concentrated water formed by the nanofiltration device 610, which mainly contains calcium sulfate.

Step S500: and (3) concentrating the monovalent salt wastewater by using a disc tube reverse osmosis device, delivering the obtained reverse osmosis produced water to a water pipe of a power plant for recycling, and obtaining monovalent salt concentrated water with the concentration of 150 g/L. Feeding the monovalent salt concentrated water into a bipolar membrane electrodialysis device 720 for electrolysis to obtain hydrochloric acid with the mass concentration of 15% and a sodium hydroxide solution with the mass concentration of 8%, recycling 85L first recycled water system per 100L monovalent salt wastewater, wherein the total soluble solid content of the first recycled water is less than 1000 mg/L. 12.7t of reverse osmosis water can be obtained every hour; the hydrochloric acid and sodium hydroxide solution obtained each hour was 20L.

And (3) feeding the divalent salt wastewater into a normal-temperature crystallization reactor 810, adding a sodium sulfate solution with the mass percent of 30%, stirring and reacting for 60min in the presence of seed crystals, and allowing the mixture to enter a settling zone for settling for 60min to obtain gypsum with the purity of more than 95%. The calcium ion concentration of the effluent from the normal temperature crystallization reactor 810 is 15.0mmol/L, and the effluent directly flows back to the water inlet of the nanofiltration device 610 for circulation treatment.

Experimental results prove that the desulfurization wastewater treatment method provided by the embodiment of the invention can remove suspended matters, non-metallic ions and heavy metal ions contained in desulfurization wastewater in a gradient manner and obtain magnesium ion precipitate with the purity of more than 95%. And a normal-temperature crystallization-nanofiltration coupling system (a nanofiltration device 610 is combined with a normal-temperature crystallization reactor 810) is adopted, and sodium sulfate is used as a softening agent during normal-temperature crystallization, so that calcium ions are crystallized in the form of gypsum, and the purity of the crystallized gypsum is higher. Meanwhile, the desulfurization wastewater can be reduced by utilizing a reverse osmosis-bipolar membrane electrodialysis coupling system (coupling the reverse osmosis device 710 and the bipolar membrane electrodialysis device 720), so that more than 85% of reverse osmosis produced water can be recovered from every 100L of desulfurization wastewater, a sodium hydroxide solution with higher concentration and hydrochloric acid are generated by electrolysis, the sodium hydroxide solution is recycled to the primary treatment unit 100 and the secondary treatment unit 200 to form sludge and magnesium ion precipitation, and the hydrochloric acid is recycled to the neutralization unit 500 to assist in the separation of monovalent salt and divalent salt. Therefore, the desulfurization wastewater treatment system and the method provided by the embodiment of the invention can achieve the purpose of gradient wastewater treatment, magnesium ion precipitate and gypsum with higher added values can be generated in the wastewater treatment process except for sludge, byproducts such as hydrochloric acid can be recycled in the early treatment process of desulfurization wastewater, and reverse osmosis water can meet the requirement of power plant reuse water and directly enters a corresponding pipe network. Therefore, the desulfurization wastewater treatment system and method provided by the embodiment of the invention can basically realize zero emission of desulfurization wastewater and reduce the system operation cost and desalination load.

In the foregoing description of embodiments, the particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

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

2. The desulfurization wastewater treatment method according to claim 1, wherein the removing suspended matter, non-metal ions, and heavy metal ions contained in the desulfurization wastewater to obtain a primary treatment wastewater comprises:

adjusting the pH value of the desulfurization wastewater to be 9-10, and adding organic sulfur, a flocculating agent and a coagulant aid into the desulfurization wastewater to precipitate suspended matters, non-metallic ions and heavy metal ions contained in the desulfurization wastewater in a slag mud form, so as to obtain primary treatment wastewater containing slag mud;

removing sludge contained in the primary treatment wastewater;

the step of precipitating magnesium ions contained in the primary treatment wastewater to obtain magnesium ion precipitates and secondary treatment wastewater comprises the following steps:

adjusting the pH value of the primary treatment wastewater without the slag sludge to 11-13 to obtain secondary treatment wastewater containing magnesium hydroxide precipitate;

and collecting magnesium hydroxide precipitate contained in the secondary treatment wastewater.

3. The desulfurization waste water treatment method according to claim 2, wherein the desulfurization waste water contains organic sulfur in a concentration of 5ppm to 50ppm, the flocculant in a concentration of 10ppm to 20ppm, and the coagulant aid in a concentration of 10ppm to 20ppm, after the organic sulfur, the flocculant and the coagulant aid are added to the desulfurization waste water.

4. The desulfurization waste water treatment method according to claim 2,

after the magnesium ion precipitate and the secondary treatment wastewater are obtained and before the secondary treatment wastewater is treated, the desulfurization wastewater treatment method further comprises the following steps:

filtering the secondary treatment wastewater by adopting a sand filtration and/or ultrafiltration mode.

5. The desulfurization wastewater treatment method according to claim 1, wherein said treating the secondary treatment wastewater to obtain monovalent salt wastewater and divalent salt wastewater comprises:

adjusting the secondary treatment wastewater to be neutral;

and (3) carrying out nanofiltration treatment on the secondary treatment wastewater adjusted to be neutral to obtain nanofiltration product water serving as monovalent salt wastewater and nanofiltration concentrated water serving as divalent salt wastewater.

6. The desulfurization wastewater treatment method according to claim 5, wherein the recovering monovalent salt contained in the monovalent salt wastewater to obtain a monovalent salt-recovered material and first recovered water comprises:

concentrating the monovalent salt wastewater to obtain monovalent salt concentrated water and concentrated produced water;

feeding the concentrated produced water into a water pipe network for power plants, and electrolyzing the monovalent salt concentrated water in a bipolar membrane electrodialysis manner to obtain monovalent salt recycled materials and electrodialysis produced water; the monovalent salt recovery comprises hydrochloric acid and sodium hydroxide solution;

mixing the electrodialysis produced water with monovalent salt wastewater, removing suspended matters, non-metal ions and heavy metal ions contained in the desulfurization wastewater by using a sodium hydroxide solution contained in the monovalent salt recovery material, precipitating magnesium ions contained in the primary treatment wastewater, and adjusting the secondary treatment wastewater to be neutral by using hydrochloric acid contained in the monovalent salt recovery material.

7. The desulfurization wastewater treatment method of claim 6, wherein the concentrated product water has a total soluble solids content of less than 1000mg/L, at least 80L of the concentrated product water is recovered per 100L of the desulfurization wastewater, and the monovalent salt concentrated water has a sodium chloride concentration of 100g/L to 150 g/L.

8. The desulfurization wastewater treatment method according to any one of claims 1 to 7,

when the divalent salt wastewater contains calcium sulfate, the step of recovering divalent salt contained in the divalent salt wastewater to obtain a divalent salt recovery product and second recovered effluent comprises the following steps:

adding sodium sulfate into the divalent salt wastewater;

reacting the sodium sulfate with calcium ions contained in the divalent salt wastewater and crystallizing to obtain a divalent salt recovery product and second recovered water; the divalent salt recovered matter is calcium sulfate dihydrate, and the second recovered effluent is crystallized effluent;

and mixing the crystallized effluent with secondary treatment wastewater.

9. The desulfurization wastewater treatment method according to any one of claims 1 to 7,

the concentration of magnesium ions contained in the secondary treatment wastewater is less than or equal to 10mg/L, and the purity of the magnesium hydroxide precipitate is more than 95%; and/or the presence of a gas in the gas,

the monovalent salt wastewater contains sodium chloride, and the concentration of the sodium chloride contained in the monovalent salt wastewater is 10g/L-20 g/L; and/or the presence of a gas in the gas,

the monovalent salt recovery product comprises hydrochloric acid and a sodium hydroxide solution, wherein the mass concentration of hydrogen chloride contained in the hydrochloric acid is 8-15%, and the mass concentration of sodium hydroxide contained in the sodium hydroxide solution is 8-15%; and/or the presence of a gas in the gas,

the divalent salt wastewater contains calcium sulfate, and the concentration of calcium ions contained in the second recovery water is 15 mmol/L-18 mmol/L.

10. A desulfurization wastewater treatment system, comprising:

the secondary treatment unit is connected with a water outlet of the primary treatment unit and is used for precipitating magnesium ions contained in the primary treatment wastewater to obtain magnesium ion precipitate and secondary treatment wastewater;

11. The desulfurization wastewater treatment system of claim 10, further comprising a sand filtration device and/or an ultrafiltration device connected in series between an outlet of the secondary treatment unit and an inlet of the salt separation unit.

12. The desulfurization wastewater treatment system according to claim 10, wherein the salt separation unit is a nanofiltration device, a water inlet of the nanofiltration device is connected to a water outlet of the secondary treatment unit, a produced water outlet of the nanofiltration device is connected to a water inlet of the first recovery unit, and a concentrated water outlet of the nanofiltration device is connected to a water inlet of the second recovery unit.

13. The desulfurization wastewater treatment system of claim 12, wherein the nanofiltration device has a rejection rate of more than 98% for sulfate ions, a rejection rate of more than 95% for calcium ions, and a water production rate of 50% for the nanofiltration device.

14. The desulfurization wastewater treatment system according to claim 10, wherein the first recovery unit is further configured to recover monovalent salt contained in the monovalent salt wastewater to obtain an alkali solution, an acid solution and a produced water, the produced water is sent to a water supply network for power plant, and the alkali solution is sent to the primary treatment unit and/or the secondary treatment unit;

the primary treatment unit is specifically used for adjusting the pH value of the desulfurization wastewater to be 9-10 by using alkali liquor, and adding organic sulfur, a flocculating agent and a coagulant aid into the desulfurization wastewater, so that suspended matters, non-metal ions and heavy metal ions contained in the desulfurization wastewater are precipitated in the form of slag mud, and magnesium ion precipitation and secondary treatment wastewater are obtained; and/or the secondary treatment unit is specifically used for adjusting the pH value of the primary treatment wastewater from which the slag mud is removed to 11-13 by using alkali liquor;

the desulfurization wastewater treatment system further comprises a neutralization unit which is respectively connected with a water outlet of the secondary treatment unit and a water inlet of the salt separation unit, an acid liquor outlet of the first recovery unit is connected with an acid liquor inlet of the neutralization unit, and the first recovery unit is further used for adjusting the pH value of the secondary treatment wastewater to be neutral by using acid liquor before the secondary treatment wastewater is treated.

15. The desulfurization wastewater treatment system of claim 14, wherein the first recovery unit comprises a reverse osmosis device and a bipolar membrane electrodialysis device; the water inlet of the reverse osmosis device is connected with the first water outlet of the salt separation unit, the produced water outlet of the reverse osmosis device is connected with a water pipe network for a power plant, the concentrated water outlet of the reverse osmosis device is connected with the water inlet of the bipolar membrane electrodialysis device, the produced water outlet of the bipolar membrane electrodialysis device is connected with the water inlet of the reverse osmosis device, and the alkali liquor outlet of the bipolar membrane electrodialysis device is respectively connected with the alkali liquor inlet of the primary treatment unit and the alkali liquor inlet of the secondary treatment unit.

16. The desulfurization wastewater treatment system of claim 10, wherein the second recovery unit is an ambient temperature crystallization reactor, and a water outlet of the second recovery unit is connected with a water inlet of the salt separation unit.

17. The desulfurization wastewater treatment system of any one of claims 10-16, wherein the primary treatment unit comprises a primary conditioning tank and a primary clarifier; the secondary treatment unit comprises a secondary adjusting tank and a secondary clarification tank; the water inlet of the primary equalizing basin is connected with a desulfurization wastewater pipeline, the water outlet of the primary equalizing basin is connected with the water inlet of the primary clarifying basin, the solid outlet of the primary clarifying basin is connected with the first collecting unit, the water outlet of the primary clarifying basin is connected with the water inlet of the secondary equalizing basin, the water outlet of the secondary equalizing basin is connected with the water inlet of the secondary clarifying basin, the solid outlet of the secondary clarifying basin is connected with the second collecting unit, and the water outlet of the secondary clarifying basin is connected with the water inlet of the salt separating unit.