Desulfurization wastewater resourceful zero-emission treatment system and method thereof

Abstract

The present application relates to wastewater purification treatment technical field, disclose a kind of desulfurization wastewater resource zero discharge treatment system and method thereof.The system includes: dynamic nanometer fine filtration unit, ion directional dialysis concentration unit and recrystallization unit, wherein the dynamic nanometer fine filtration unit is used to filter particulate matter in desulfurization wastewater;The ion directional dialysis concentration unit is used to separate anion and cation in desulfurization wastewater treated by the dynamic nanometer fine filtration unit, obtain the mixed solution of calcium chloride, magnesium chloride and calcium sulfate;The recrystallization unit is used to separate the mixed solution of calcium chloride, magnesium chloride and calcium sulfate to obtain six water magnesium chloride and six water calcium chloride mixed inorganic salt.The technical scheme shortens process flow, solves the problem of large amount of softening agent used in existing concentration reduction technology, insufficient running stability and high investment operation cost, realizes zero discharge technology green short process breakthrough iteration.

Description

Technical Field

[0001] This invention relates to the field of wastewater purification and treatment technology, specifically to a zero-discharge treatment system and method for desulfurization wastewater resource utilization. Background Technology

[0002] Currently, the main technology for zero-discharge resource utilization of high-salinity wastewater adopts a combination process of "softening pretreatment + multi-stage membrane concentration + thermal crystallization". However, based on the construction and operation of current zero-discharge resource utilization projects, there are still problems such as long process, high investment cost, and insufficient operational stability. As a result, in actual operation, the water quality after the pretreatment process is unstable and the system stability is poor. Membrane fouling is serious. Due to the severe decline in membrane retention rate, the membrane generally needs to be replaced every six months, resulting in high investment costs. At the same time, the purity of salt after conventional evaporation and crystallization processes after membrane separation is limited, resulting in low market value and difficulty in selling.

[0003] From a pretreatment process perspective, traditional pretreatment processes typically employ coagulation sedimentation followed by multi-stage filtration to remove major suspended solids in water. This approach is land-intensive, requires large amounts of chemicals, is difficult to operate, and results in unstable effluent quality. Furthermore, residual pollutants and incomplete solid-liquid separation after coagulation can still lead to subsequent membrane fouling, significantly increasing backwashing frequency. The rapid increase in transmembrane pressure, frequent backwashing, and chemical cleaning of commonly used tubular membranes and ultrafiltration membranes significantly increase operating costs. Additionally, some membrane fouling is irreversible and cannot be eliminated by simple backwashing. In such cases, higher energy consumption is required to overcome the increased transmembrane pressure, or membrane flux must be reduced, sacrificing membrane productivity, ultimately necessitating membrane module replacement.

[0004] From the perspective of membrane separation concentration and reduction processes, the commonly used multi-stage reverse osmosis (RO) membrane separation concentration and reduction technology is widely used in the water treatment field. However, it is greatly affected by membrane fouling, which mainly refers to phenomena such as decreased membrane flux, reduced rejection rate, and increased operating pressure during membrane filtration. Membrane fouling not only causes scaling and reduces membrane flux but is also extremely difficult to clean, greatly increasing the difficulty of membrane separation and concentration. Due to the characteristics of high-salinity wastewater, especially high-salinity desulfurization wastewater with high suspended solids and fine coal slime, membrane fouling is even more severe. When using nanofiltration membranes to separate monovalent and divalent salts from high-salinity wastewater, severe decline in nanofiltration membrane rejection rate and serious membrane clogging problems often occur, requiring nanofiltration membrane replacement, leading to increased operating and maintenance costs. At the same time, to obtain high-purity by-product crystalline salts, nanofiltration is often required for the separation of monovalent and divalent salts. However, nanofiltration is poorly adaptable to fluctuations in the ratio of chloride and sulfate ions in the influent. Once the chloride and sulfate ion ratios in the influent fluctuate, the flow rates of the nanofiltration permeate and concentrate change, making it difficult to match the treatment loads of the associated sodium chloride and sodium sulfate evaporation systems. This necessitates increasing the design margin and construction costs. Furthermore, because nanofiltration does not retain monovalent ions during the salt separation process, the amount of mother liquor discharged from the nanofiltration permeate side is large, resulting in a significant overall amount of mixed salts and low resource utilization. During the evaporation and crystallization process, as the quality of the influent from the front-end treatment system changes significantly, the existing concentration process cannot accurately control the chloride and sulfate ion concentrations (i.e., the salt-to-nitrate ratio) in the effluent. This causes the chloride and sulfate ion concentrations to gradually deviate significantly from the design values, impacting the quality of the sodium sulfate crystals.

[0005] Therefore, there is an urgent need to develop a zero-discharge treatment system and method for desulfurization wastewater resource utilization to solve problems such as long process, high investment cost and operational stability, and to achieve innovative iteration of resource utilization zero-discharge technology. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of long process, high investment cost and poor operational stability in the existing technology of zero-discharge treatment of desulfurization wastewater resource utilization. It provides a zero-discharge treatment system and method for desulfurization wastewater resource utilization. The technical solution forms a short-process concentration technology for high-salt wastewater based on "dynamic nano-fine filtration + non-softening ion directional dialysis concentration". It solves the problems of large amount of softening agent used, insufficient operational stability and high investment and operating cost of existing concentration and reduction technologies, and realizes a breakthrough iteration of green short-process zero-discharge technology.

[0007] To achieve the above objectives, the first aspect of the present invention provides a zero-discharge treatment system for desulfurization wastewater resource recovery, the system comprising: Nanofiltration unit, ion-directed dialysis concentration unit, and recrystallization unit. The nanofiltration unit is used to filter particulate matter in desulfurization wastewater. The ion-directed dialysis concentration unit is used to separate the anions and cations in the desulfurization wastewater treated by the nanofiltration unit to obtain a mixed solution of calcium chloride, magnesium chloride and calcium sulfate. The recrystallization unit includes an evaporation crystallization device and a crystallization device. The evaporation crystallization device is used to separate a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate from the mixed solution of calcium chloride, magnesium chloride and calcium sulfate. The crystallization device is used to further purify the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0008] Preferably, the filter bed filtration accuracy of the nanofiltration unit is 0.01-1 NTU.

[0009] Preferably, the system further includes a reverse osmosis unit, which is used to concentrate the desulfurization wastewater treated by the nanofiltration unit, and the desulfurization wastewater treated by the reverse osmosis unit enters the ion-directed dialysis concentration unit.

[0010] A second aspect of this invention provides a method for zero-discharge treatment of desulfurization wastewater for resource recovery, the method comprising the following steps: (1) The desulfurization wastewater is filtered through a nanofiltration unit to remove particulate matter from the desulfurization wastewater; (2) The desulfurization wastewater treated by the nanofiltration unit is passed into the ion-directed dialysis concentration unit for anion and cation separation to obtain a mixed solution of calcium chloride, magnesium chloride and calcium sulfate; (3) The mixed solution of calcium chloride, magnesium chloride and calcium sulfate enters the evaporation crystallization device for separation to obtain a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate; the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate enters the crystallization device for separation to obtain magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0011] Preferably, the method further includes: passing the desulfurization wastewater treated by the nanofiltration unit into a reverse osmosis device for concentration, and then passing the desulfurization wastewater treated by the reverse osmosis device into the ion-directed dialysis concentration unit.

[0012] Preferably, in step (1), the suspended solids concentration of the desulfurization wastewater is 50-500 mg / L.

[0013] Preferably, the turbidity of the desulfurization wastewater treated by the nanofiltration unit is 0.01-1 NTU.

[0014] Preferably, in step (2), the water processing capacity of the ion-directed dialysis concentration unit can be 7-10 m³. 3 / h.

[0015] Preferably, in the evaporation crystallization apparatus, the mixed solution of calcium chloride, magnesium chloride and calcium sulfate is first heated to 95-105°C to precipitate calcium sulfate, and then evaporation continues. Next, magnesium chloride hexahydrate is precipitated, and evaporation continues until calcium chloride is supersaturated. Then, a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is precipitated by cooling.

[0016] Preferably, in the crystallization apparatus, the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is dissolved in water, and the resulting solution is kept at a temperature of 0-30°C to precipitate the mixed inorganic salt of magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0017] Compared with the prior art, the technical solution of the present invention has the following advantages: (1) In the system described in this invention, a short-process concentration technology for high-salt wastewater based on "dynamic nano-fine filtration + non-softening ion directional dialysis concentration" is formed, which solves the problems of large amount of softening agent used, insufficient operational stability and high investment and operating costs of existing concentration and reduction technologies, and realizes a breakthrough iteration of green short-process zero-emission technology. (2) In the nanofiltration unit, based on the dynamic fine filtration of nano-oxides to remove particulate matter in desulfurization wastewater, the mechanism of novel coating process, scale-causing factor reduction and adsorption filtration was explored, and the effluent turbidity was stabilized at less than 1 NTU, and preferably reached less than 0.1 NTU. (3) In the ion-directed dialysis concentration unit and recrystallization unit, the chloride ions in the wastewater are accurately separated and concentrated at a high rate through multi-stage sieve separation. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process flow of the desulfurization wastewater resource utilization zero-discharge treatment system described in this invention; Figure 2 This is a schematic diagram of the process flow of the ion-directed dialysis concentration unit.

[0019] Explanation of reference numerals in the attached figures 1. Nanofiltration unit; 2. Ion-directed dialysis concentration unit; 21. First flow channel; 22. Second flow channel; 23. Third flow channel; 24. Fourth flow channel; 3. Recrystallization unit; 31. Evaporation crystallization device; 32. Crystallization device; 4. Reverse osmosis device. Detailed Implementation

[0020] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] like Figure 1 As shown, the desulfurization wastewater resource utilization zero-discharge treatment system of the present invention includes: The system comprises a nanofiltration unit 1, an ion-directed dialysis concentration unit 2, and a recrystallization unit 3. The nanofiltration unit 1 is used to filter particulate matter from desulfurization wastewater. The ion-directed dialysis concentration unit 2 is used to separate cations and anions from the desulfurization wastewater treated by the nanofiltration unit 1, obtaining a mixed solution of calcium chloride, magnesium chloride, and calcium sulfate. The recrystallization unit 3 includes an evaporation crystallization device 31 and a crystallization device 32. The evaporation crystallization device 31 is used to separate a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate from the mixed solution of calcium chloride, magnesium chloride, and calcium sulfate. The crystallization device 32 is used to further purify the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0023] The zero-discharge treatment system for desulfurization wastewater according to the present invention solves the problems of long process, large scale, high energy consumption, large amount of softening agent used in existing concentration and reduction technologies, high investment cost and poor operation stability by combining dynamic nanofiltration, ion-directed dialysis concentration and terminal crystallization. It achieves green, low-cost, short-process efficient and intensive utilization of desulfurization wastewater resources and zero discharge of terminal concentrate.

[0024] In the desulfurization wastewater resource utilization zero-discharge treatment system of the present invention, the filter bed filtration accuracy of the nanofiltration unit 1 can be 0.01-1 NTU, preferably 0.01-0.1 NTU. In the nanofiltration unit 1, a nanoscale sand filter bed is formed through a filter screen coating process, thereby improving the filtration effect. The filtration accuracy is further improved by adjusting the thickness of the filter bed and the size of the fine filter material. The nanofiltration unit 1 is formed from modified alumina particles and can filter pollutants in water with a size of 24-26 nm. The nanofiltration unit 1 has the characteristics of adsorption effect, nano-effect, large specific surface area, and wide pH tolerance threshold. The modified alumina particles can quickly reach adsorption equilibrium with dissolved pollutants in the water. The nanofiltration unit 1 can be described with reference to the content disclosed in patent application CN117776323A.

[0025] In the desulfurization wastewater resource utilization zero-discharge treatment system of the present invention, the system may further include a reverse osmosis unit 4. The reverse osmosis unit 4 is used to concentrate the desulfurization wastewater treated by the nanofiltration unit 1, and the desulfurization wastewater treated by the reverse osmosis unit 4 enters the ion-directed dialysis concentration unit 2. When the concentration of the desulfurization wastewater treated by the nanofiltration unit 1 is higher than a predetermined value, the desulfurization wastewater treated by the nanofiltration unit 1 is passed into the ion-directed dialysis concentration unit 2. When the concentration of the desulfurization wastewater treated by the nanofiltration unit 1 is lower than a predetermined value, the desulfurization wastewater treated by the nanofiltration unit 1 is passed into the reverse osmosis unit 4. The predetermined value is that the total dissolved solids of the concentrated water is 10,000-100,000 mg / L.

[0026] In the zero-discharge treatment system for desulfurization wastewater resource utilization described in this invention, the ion-directed dialysis concentration unit 2 employs a multi-stage sieve separation ion replacement process. This multi-stage sieve replacement process overcomes the problems of large dosage, high operating costs, and difficult control associated with existing high-salt, high-hardness wastewater desalination, concentration and volume reduction treatment, and softening pretreatment. In the zero-discharge treatment system for desulfurization wastewater resource utilization described in this invention, such as... Figure 2 As shown, in the ion-directed dialysis concentration unit 2, wastewater first enters the first channel 21. Under the action of direct current, the anions in the wastewater migrate to the third channel 23. The sieving action of the monovalent and divalent anion selective membrane completes the primary monovalent and divalent anion separation, increasing the concentration ratio of monovalent and divalent anions in the primary chloride (desalted) water. The primary chloride (concentrated) water in the effluent of the third channel 23 then enters the second channel 22 to complete the second separation of monovalent and divalent anions. The concentration of divalent ions such as sulfate and carbonate in the concentrated water of the fourth channel 24 is controlled to be kept in an extremely low range. During the concentration process of high-salt and high-hardness wastewater, scaling is caused by the combination of divalent anions and divalent cations to form sparingly soluble salts such as calcium sulfate, calcium carbonate, and magnesium carbonate. In the concentrated water of the fourth channel 24, since the concentration of sulfate and carbonate ions is extremely low, calcium sulfate, calcium carbonate, and magnesium carbonate have not reached saturation. Therefore, the concentration process completely eliminates the risk of scaling, thus ultimately achieving high-rate concentration of high-salt and high-hardness wastewater without softening.

[0027] In the desulfurization wastewater resource utilization zero-discharge treatment system of the present invention, the ion-directed dialysis concentration unit 2 is used to separate the anions and cations in the desulfurization wastewater treated by the nanofiltration unit 1 and the desulfurization wastewater treated by the reverse osmosis device 4, to obtain a mixed solution of calcium chloride, magnesium chloride, and calcium sulfate. In some embodiments, harmful ions such as chloride ions and fluoride ions in the concentrate are selectively and precisely separated, realizing the dialysis separation and high-rate concentration of harmful ions in the slurry. Since there is no risk of scaling in the separation and concentration process, no softening pretreatment is required, and the consumption of reagents is low. At the same time, the concentration process does not involve phase change and has low operating energy consumption. This will play a leading technological role in solving the dual operational and environmental pressures faced by the deep desalination and zero-discharge system for high-salinity desulfurization wastewater.

[0028] In some implementations, such as Figure 1 As shown, the desulfurization wastewater resource utilization zero-discharge treatment system of the present invention includes: The system comprises a nanofiltration unit 1, an ion-directed dialysis concentration unit 2, and a recrystallization unit 3. The nanofiltration unit 1 is used to filter particulate matter in desulfurization wastewater, and its filtration accuracy is 0.01-1 NTU. The ion-directed dialysis concentration unit 2 is used to separate anions and cations in the desulfurization wastewater treated by the nanofiltration unit 1 to obtain a mixed solution of calcium chloride, magnesium chloride, and calcium sulfate. The recrystallization unit 3 includes an evaporation crystallization device 31 and a crystallization device 32. The evaporation crystallization device 31 is used to separate a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate from the mixed solution of calcium chloride, magnesium chloride, and calcium sulfate. The crystallization device 32 is used to further purify the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0029] In other implementations, such as Figure 1 As shown, the desulfurization wastewater resource utilization zero-discharge treatment system of the present invention includes: The system comprises a nanofiltration unit 1, an ion-directed dialysis concentration unit 2, a recrystallization unit 3, and a reverse osmosis unit 4. The nanofiltration unit 1 filters particulate matter from desulfurization wastewater with a filtration accuracy of 0.01-1 NTU. The reverse osmosis unit 4 concentrates the desulfurization wastewater treated by the nanofiltration unit 1. When the concentration of the wastewater treated by the nanofiltration unit 1 exceeds a predetermined value, the wastewater is passed into the ion-directed dialysis concentration unit 2. When the concentration of the wastewater treated by the nanofiltration unit 1 falls below a predetermined value, the wastewater is passed into the reverse osmosis unit 4. The predetermined value is that the total dissolved solids in the concentrated water is 10,000-100,000 mg / L. The ion-directed dialysis concentration unit 2 is used to separate the anions and cations in the desulfurization wastewater treated by the nanofiltration unit 1 and the desulfurization wastewater treated by the reverse osmosis device 4 to obtain a mixed solution of calcium chloride, magnesium chloride and calcium sulfate; the recrystallization unit 3 includes an evaporation crystallization device 31 and a crystallization device 32. The evaporation crystallization device 31 is used to separate a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate from the mixed solution of calcium chloride, magnesium chloride and calcium sulfate; the crystallization device 32 is used to further purify the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0030] This invention also provides a method for zero-discharge treatment of desulfurization wastewater, the method comprising the following steps: (1) The desulfurization wastewater is passed into the nanofiltration unit 1 for filtration to remove particulate matter from the desulfurization wastewater; (2) The desulfurization wastewater treated by the nanofiltration unit 1 is passed into the ion-directed dialysis concentration unit 2 for anion and cation separation to obtain a mixed solution of calcium chloride, magnesium chloride and calcium sulfate; (3) The mixed solution of calcium chloride, magnesium chloride and calcium sulfate enters the evaporation crystallization device 31 for separation to obtain a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate; the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate enters the crystallization device 32 for separation to obtain magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0031] According to the method described in this invention, the combination of nanofiltration unit 1 and ion-directed dialysis concentration unit 2 achieves short-process concentration of high-salt wastewater, solving the problems of large amount of softening agent used, insufficient operational stability and high investment and operating costs in existing concentration and reduction technologies; in addition, the combination of ion-directed dialysis concentration unit 2 and recrystallization unit 3 achieves precise separation and high-rate concentration of chloride ions in wastewater.

[0032] In the method described in this invention, the method may further include: passing the desulfurization wastewater treated by the nanofiltration unit 1 into a reverse osmosis unit 4 for concentration, and then passing the desulfurization wastewater treated by the reverse osmosis unit 4 into the ion-directed dialysis concentration unit 2. The recovery rate of the reverse osmosis unit 4 can be 87-92%. When the concentration of the desulfurization wastewater treated by the nanofiltration unit 1 is higher than a predetermined value, the desulfurization wastewater treated by the nanofiltration unit 1 is passed into the ion-directed dialysis concentration unit 2. When the concentration of the desulfurization wastewater treated by the nanofiltration unit 1 is lower than a predetermined value, the desulfurization wastewater treated by the nanofiltration unit 1 is passed into the reverse osmosis unit 4. The predetermined value is that the total dissolved solids of the concentrated water is 10,000-100,000 mg / L.

[0033] In the method described in this invention, in step (1), the suspended solids concentration of the desulfurization wastewater is 50-500 mg / L. The desulfurization wastewater conforms to the national standard DL / T 997-2006 "Water Quality Control Indicators for Limestone-Gypsum Wet Desulfurization Wastewater from Thermal Power Plants".

[0034] In the method described in this invention, to ensure filtration effectiveness, the turbidity of the desulfurization wastewater treated by the nanofiltration unit 1 is preferably 0.01-1 NTU, more preferably 0.01-0.1 NTU. The energy consumption per ton of desulfurization wastewater treated by the nanofiltration unit 1 is less than 0.5 kWh. In the nanofiltration unit 1, the effective contact time can be 1 second. The nanofiltration unit 1 can be equipped with two ultrafiltration devices, with one in operation and one on standby. The processing capacity of the ultrafiltration device can be 15-18 m³ / h. 3 / h, preferably 15-16m 3 / h.

[0035] In the method described in this invention, in step (2), the water volume processed by the ion-directed dialysis concentration unit 2 can be 7-10 m³. 3 / h, preferably 7-8m 3 / h.

[0036] In the method described in this invention, the mass percentage of calcium chloride and magnesium chloride in the mixed solution of calcium chloride, magnesium chloride and calcium sulfate obtained in step (2) can be 90-95%, preferably 92-95%.

[0037] In the method described in this invention, in the evaporation crystallization apparatus 31, the mixed solution of calcium chloride, magnesium chloride and calcium sulfate is first heated to 95-105°C to precipitate calcium sulfate, and then evaporation continues. Next, magnesium chloride hexahydrate is precipitated, and evaporation continues until calcium chloride is supersaturated. Then, a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is precipitated by cooling.

[0038] In the method described in this invention, the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is dissolved in water in the crystallization apparatus 32, and the temperature of the resulting solution is controlled at 0-30°C to precipitate the mixed inorganic salt of magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0039] In some embodiments, the zero-discharge treatment method for desulfurization wastewater resource utilization according to the present invention includes the following steps: (1) The desulfurization wastewater with a suspended solids concentration of 50-500 mg / L is passed into the nanofiltration unit 1 for filtration to remove particulate matter from the desulfurization wastewater. The desulfurization wastewater complies with the national standard DL / T 997-2006 "Water quality control indicators for limestone-gypsum wet desulfurization wastewater from thermal power plants". (2) The desulfurization wastewater treated by the nanofiltration unit 1 is passed into the ion-directed dialysis concentration unit 2 for anion and cation separation to obtain a mixed solution of calcium chloride, magnesium chloride and calcium sulfate. In the mixed solution of calcium chloride, magnesium chloride and calcium sulfate, the mass ratio of calcium chloride and magnesium chloride is 90-95%. (3) The mixed solution of calcium chloride, magnesium chloride and calcium sulfate enters the evaporation crystallization device 31 for separation. First, the mixed solution of calcium chloride, magnesium chloride and calcium sulfate is heated to 95-105℃ to precipitate calcium sulfate. Evaporation continues, followed by the precipitation of magnesium chloride hexahydrate. Evaporation continues until calcium chloride is supersaturated. Then, a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is precipitated by cooling. The mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate enters the crystallization device 32 for separation. The mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is dissolved in water. The temperature of the resulting solution is controlled at 0-30℃ to precipitate a mixed inorganic salt of magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0040] In other embodiments, the desulfurization wastewater resource utilization and zero-discharge treatment method of the present invention includes the following steps: (1) The desulfurization wastewater with a suspended solids concentration of 50-500 mg / L is passed into the nanofiltration unit 1 for filtration to remove particulate matter from the desulfurization wastewater. The desulfurization wastewater meets the national standard DL / T 997-2006 "Water Quality Control Indicators for Limestone-Gypsum Wet Desulfurization Wastewater from Thermal Power Plants". The desulfurization wastewater treated by the nanofiltration unit 1 is passed into the reverse osmosis device 4 for concentration. The desulfurization wastewater treated by the reverse osmosis device 4 enters the ion-directed dialysis concentration unit 2. When the concentration of the desulfurization wastewater treated by the nanofiltration unit 1 is higher than a predetermined value, the desulfurization wastewater treated by the nanofiltration unit 1 is passed into the ion-directed dialysis concentration unit 2. When the concentration of the desulfurization wastewater treated by the nanofiltration unit 1 is lower than a predetermined value, the desulfurization wastewater treated by the nanofiltration unit 1 is passed into the reverse osmosis device 4. The predetermined value is that the total dissolved solids of the concentrated water is 10,000-100,000 mg / L. (2) The desulfurization wastewater treated by the nanofiltration unit 1 and the desulfurization wastewater treated by the reverse osmosis device 4 are passed into the ion-directed dialysis concentration unit 2 for anion and cation separation to obtain a mixed solution of calcium chloride, magnesium chloride and calcium sulfate. In the mixed solution of calcium chloride, magnesium chloride and calcium sulfate, the mass ratio of calcium chloride and magnesium chloride is 90-95%. (3) The mixed solution of calcium chloride, magnesium chloride and calcium sulfate enters the evaporation crystallization device 31 for separation. First, the mixed solution of calcium chloride, magnesium chloride and calcium sulfate is heated to 95-105℃ to precipitate calcium sulfate. Evaporation continues, followed by the precipitation of magnesium chloride hexahydrate. Evaporation continues until calcium chloride is supersaturated. Then, a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is precipitated by cooling. The mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate enters the crystallization device 32 for separation. The mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is dissolved in water. The temperature of the resulting solution is controlled at 0-30℃ to precipitate a mixed inorganic salt of magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0041] The following examples further illustrate the zero-discharge treatment system and method for desulfurization wastewater resource utilization according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0042] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0043] The zero-discharge treatment process for desulfurization wastewater resource utilization in Example 1 is implemented in the zero-discharge treatment system for desulfurization wastewater resource utilization described in this invention, such as... Figure 1 As shown, the system includes: The system comprises a nanofiltration unit 1, an ion-directed dialysis concentration unit 2, and a recrystallization unit 3. The nanofiltration unit 1 is used to filter particulate matter in desulfurization wastewater; the filtration accuracy of the nanofiltration unit 1 is 0.01 NTU; the nanofiltration unit 1 is equipped with two ultrafiltration devices; the ion-directed dialysis concentration unit 2 is used to separate anions and cations in the desulfurization wastewater treated by the nanofiltration unit 1 to obtain a mixed solution of calcium chloride, magnesium chloride, and calcium sulfate; the recrystallization unit 3 includes an evaporation crystallization device 31 and a crystallization device 32. The evaporation crystallization device 31 is used to separate a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate from the mixed solution of calcium chloride, magnesium chloride, and calcium sulfate; the crystallization device 32 is used to further purify the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0044] Example 1 (1) The desulfurization wastewater with a suspended solids concentration of 498 mg / L is passed into the nanofiltration unit 1 for filtration to remove particulate matter from the desulfurization wastewater. The processing capacity of the ultrafiltration device is 16 m³ / L. 3 / h, the water quality of the desulfurization wastewater is recorded in Table 1, and the desulfurization wastewater complies with the national standard DL / T 997-2006 "Water Quality Control Indicators for Limestone-Gypsum Wet Desulfurization Wastewater from Thermal Power Plants"; (2) The desulfurization wastewater treated by the nanofiltration unit 1 is passed into the ion-directed dialysis concentration unit 2 for anion and cation separation to obtain a mixed solution of calcium chloride, magnesium chloride and calcium sulfate. The treatment capacity of the ion-directed dialysis concentration unit 2 is 8 m³ / s. 3 / h, in the mixed solution of calcium chloride, magnesium chloride and calcium sulfate, the concentration of chloride ions is 90362 mg / L, the concentration of sulfate ions is 3518 mg / L, the concentration of magnesium ions is 20965 mg / L, the concentration of calcium ions is 25143 mg / L, and the concentration of sodium ions is 4237 mg / L. (3) The mixed solution of calcium chloride, magnesium chloride and calcium sulfate enters the evaporation crystallization device 31 for separation. First, the mixed solution of calcium chloride, magnesium chloride and calcium sulfate is heated to 100°C to precipitate calcium sulfate. Evaporation continues, followed by the precipitation of magnesium chloride hexahydrate. Evaporation continues until calcium chloride is supersaturated. Then, a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is precipitated by cooling. The mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate enters the crystallization device 32 for separation. The mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is dissolved in water. The temperature of the resulting solution is controlled at 0°C to precipitate the mixed inorganic salt of magnesium chloride hexahydrate and calcium chloride hexahydrate and recover it.

[0045] The zero-discharge treatment process for desulfurization wastewater resource utilization in Example 2 is implemented in the zero-discharge treatment system for desulfurization wastewater resource utilization described in this invention, such as... Figure 1 As shown, the system includes: The system comprises a nanofiltration unit 1, an ion-directed dialysis concentration unit 2, a recrystallization unit 3, and a reverse osmosis unit 4. The nanofiltration unit 1 filters particulate matter from the desulfurization wastewater, with a filtration accuracy of 0.1 NTU. The nanofiltration unit 1 includes two ultrafiltration devices. The reverse osmosis unit 4 concentrates the desulfurization wastewater treated by the nanofiltration unit 1. When the concentration of the desulfurization wastewater treated by the nanofiltration unit 1 exceeds a predetermined value, the wastewater is passed into the ion-directed dialysis concentration unit 2. When the concentration of the desulfurization wastewater treated by the nanofiltration unit 1 falls below a predetermined value, the wastewater is passed into the reverse osmosis unit 4. The predetermined value is a total dissolved solids concentration of 61,000 mg / L in the concentrated water. The ion-directed dialysis concentration unit 2 is used to separate the anions and cations in the desulfurization wastewater treated by the nanofiltration unit 1 and the desulfurization wastewater treated by the reverse osmosis device 4 to obtain a mixed solution of calcium chloride, magnesium chloride and calcium sulfate; the recrystallization unit 3 includes an evaporation crystallization device 31 and a crystallization device 32. The evaporation crystallization device 31 is used to separate a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate from the mixed solution of calcium chloride, magnesium chloride and calcium sulfate; the crystallization device 32 is used to further purify the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate.

[0046] Example 2 (1) The desulfurization wastewater with a suspended solids concentration of 151 mg / L is passed into the nanofiltration unit 1 for filtration to remove particulate matter from the desulfurization wastewater. The ultrafiltration device has a processing capacity of 15 m³ / L. 3 The water quality of the desulfurization wastewater is recorded in Table 2. The desulfurization wastewater meets the national standard DL / T 997-2006 "Water Quality Control Indicators for Limestone-Gypsum Wet Desulfurization Wastewater from Thermal Power Plants". The desulfurization wastewater treated by the nanofiltration unit 1 is passed into the reverse osmosis unit 4 for concentration. The desulfurization wastewater treated by the reverse osmosis unit 4 then enters the ion-directed dialysis concentration unit 2. When the concentration of the desulfurization wastewater treated by the nanofiltration unit 1 is higher than a predetermined value, the desulfurization wastewater treated by the nanofiltration unit 1 is passed into the ion-directed dialysis concentration unit 2. When the concentration of the desulfurization wastewater treated by the nanofiltration unit 1 is lower than a predetermined value, the desulfurization wastewater treated by the nanofiltration unit 1 is passed into the reverse osmosis unit 4. The predetermined value is that the total dissolved solids of the concentrated water is 63000 mg / L. (2) The desulfurization wastewater treated by the nanofiltration unit 1 and the desulfurization wastewater treated by the reverse osmosis device 4 are passed into the ion-directed dialysis concentration unit 2 for anion and cation separation to obtain a mixed solution of calcium chloride, magnesium chloride and calcium sulfate. The processing capacity of the ion-directed dialysis concentration unit 2 is 7m³. 3 / h, in the mixed solution of calcium chloride, magnesium chloride and calcium sulfate, the mass percentage of calcium chloride and magnesium chloride is 95%, the concentration of chloride ions is 91361 mg / L, the concentration of sulfate ions is 3501 mg / L, the concentration of magnesium ions is 21324 mg / L, the concentration of calcium ions is 25261 mg / L, and the concentration of sodium ions is 4156 mg / L. (3) The mixed solution of calcium chloride, magnesium chloride and calcium sulfate enters the evaporation crystallization device 31 for separation. First, the mixed solution of calcium chloride, magnesium chloride and calcium sulfate is heated to 105°C to precipitate calcium sulfate. Evaporation continues, followed by the precipitation of magnesium chloride hexahydrate. Evaporation continues until calcium chloride is supersaturated. Then, a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is precipitated by cooling. The mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate enters the crystallization device 32 for separation. The mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is dissolved in water. The temperature of the resulting solution is controlled at 30°C to precipitate the mixed inorganic salt of magnesium chloride hexahydrate and calcium chloride hexahydrate, which is then recovered.

[0047] Table 1

[0048] Table 2

[0049] The embodiments of the desulfurization wastewater resource utilization zero-discharge treatment system and method described in this invention better achieve precise ion separation and high-rate concentration, solving the problems of large amount of softening agent used, insufficient operational stability and high investment and operating costs of existing concentration and reduction technologies.

[0050] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for zero-discharge treatment of desulfurization wastewater for resource recovery, characterized in that, The method includes the following steps: (1) The desulfurization wastewater is passed into the nanofiltration unit (1) for filtration to remove particulate matter from the desulfurization wastewater; wherein the turbidity of the desulfurization wastewater treated by the nanofiltration unit (1) is 0.01-1 NTU. (2) The desulfurization wastewater treated by the nanofiltration unit (1) is passed into the ion-directed dialysis concentration unit (2), which includes an anode, a primary bipolar membrane, a primary monovalent anion selective membrane, a cation membrane, a secondary monovalent anion selective membrane, a secondary bipolar membrane and a cathode arranged in sequence. Specifically, a first flow channel is formed between the primary monovalent anion-selective membrane and the cation membrane; a third flow channel is formed between the primary bipolar membrane and the primary monovalent anion-selective membrane; a fourth flow channel is formed between the cation membrane and the secondary monovalent anion-selective membrane; and a second flow channel is formed between the secondary monovalent anion-selective membrane and the secondary bipolar membrane. In the ion-directed dialysis concentration unit (2), wastewater first enters the first flow channel, and the anions in the wastewater migrate to the third flow channel under the action of direct current. The separation of monovalent and divalent anions is completed by the sieving action of the first-stage monovalent anion selective membrane. The effluent from the third flow channel then enters the second flow channel and the separation of monovalent and divalent anions is completed by the sieving action of the second-stage monovalent anion selective membrane. The concentration of sulfate and carbonate divalent ions in the concentrate in the fourth flow channel is controlled to be kept in an extremely low range. A mixed solution of calcium chloride, magnesium chloride and calcium sulfate is obtained in the fourth flow channel. (3) The mixed solution of calcium chloride, magnesium chloride and calcium sulfate enters the evaporation crystallization device (31) for separation to obtain a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate; the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate enters the crystallization device (32) for separation; In the mixed solution of calcium chloride, magnesium chloride, and calcium sulfate, the mass percentage of calcium chloride and magnesium chloride is 90-95%. In the evaporation crystallization apparatus (31), the mixed solution of calcium chloride, magnesium chloride and calcium sulfate is first heated to 95-105°C to precipitate calcium sulfate. Evaporation continues, followed by the precipitation of magnesium chloride hexahydrate. Evaporation continues until calcium chloride is supersaturated. Then, a mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is precipitated by cooling. In the crystallization apparatus (32), the mixed salt of magnesium chloride hexahydrate and calcium chloride hexahydrate is dissolved in water, and the resulting solution is controlled at 0-30°C to precipitate the mixed inorganic salt of magnesium chloride hexahydrate and calcium chloride hexahydrate. The method further includes: passing the desulfurization wastewater treated by the nanofiltration unit (1) into the reverse osmosis device (4) for concentration, and then passing the desulfurization wastewater treated by the reverse osmosis device (4) into the ion-directed dialysis concentration unit (2).

2. The method according to claim 1, characterized in that, In step (1), the suspended solids concentration of the desulfurization wastewater is 50-500 mg / L.

3. The method according to claim 1 or 2, characterized in that, In step (2), the water treatment capacity of the ion-directed dialysis concentration unit (2) is 7-10 m³. 3 / h.

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