Desulfurization wastewater treatment method and system

Abstract

The invention discloses a desulfurization wastewater treatment method and system, and relates to the technical field of wastewater treatment of thermal power enterprises, and the method comprises the following steps: S1, triple box treatment: sequentially introducing desulfurization wastewater into a neutralization box, a settling box and a flocculation box, adding Ca (OH) 2 into the neutralization box, and precipitating to remove fluoride and heavy metal ions; organic sulfur is added into the settling box, and residual heavy metal is removed; pAM is added into the flocculation box, and floc sedimentation is enhanced; and supernate is output after settling separation. According to the desulfurization wastewater treatment method and system, a triple box treatment technology is utilized, the pH value is accurately adjusted, and pollutants such as fluoride and heavy metal ions are removed; then the wastewater is concentrated through a disc tube type reverse osmosis device, the volume of the wastewater is greatly reduced, produced water can be directly recycled, the consumption of water resources is reduced, and after the sludge is subjected to plate-frame pressure filtration and low-temperature flue gas flash evaporation drying, the water content is remarkably reduced, the heat value is increased, and the sludge can be used as fuel for blending combustion adjustment.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment in thermal power enterprises, and in particular to a desulfurization wastewater treatment method and system. Background Art

[0002] In the thermal power generation sector, the limestone-gypsum wet flue gas desulfurization process is widely used due to its high efficiency in removing sulfur dioxide. However, the desulfurization wastewater produced by this process is complex, containing high concentrations of suspended solids, soluble salts, heavy metal ions, and other pollutants. As environmental standards continue to rise, the direct discharge of this wastewater without proper treatment poses a serious threat to the ecological environment. Therefore, the effective treatment and resource utilization of desulfurization wastewater has become a key issue in the environmental management of thermal power companies.

[0003] Currently, traditional desulfurization wastewater treatment technologies face numerous challenges in practical application. While the three-tank process (neutralization-sedimentation-flocculation) can remove some pollutants, its effectiveness in removing dissolved salts is limited. Among evaporation technologies, MVR (Mortar-Vehicle-Removal) consumes high energy and is uneconomical, making it difficult to scale up. Regarding solid waste disposal, the moisture content of sludge after conventional centrifugal dewatering exceeds 60%, increasing transportation and handling costs while also posing the risk of secondary contamination. These technical bottlenecks make it difficult for existing treatment processes to simultaneously meet the requirements of efficient purification, cost-effective operation, and resource recovery, hindering the achievement of zero desulfurization wastewater discharge. To address this, we have proposed a desulfurization wastewater treatment method and system. Summary of the Invention

[0004] In order to solve the above technical problems, a desulfurization wastewater treatment method and system are provided. This technical solution solves the problems of difficulty in removing soluble salts in the above-mentioned three-tank process, high energy consumption and poor economic efficiency of MVR evaporation, sludge moisture content exceeding 60% after conventional centrifugal dewatering, high disposal cost, and difficulty in simultaneously meeting the requirements of efficient purification, low-cost operation and resource recovery, which restricts the realization of the goal of zero discharge of desulfurization wastewater.

[0005] In order to achieve the above objects, the technical solution adopted by the present invention is: A method for treating desulfurization wastewater comprises the following steps: S1. Triple-tank treatment: Desulfurization wastewater is introduced into a neutralization tank, a sedimentation tank, and a flocculation tank in sequence. Ca(OH)2 is added to the neutralization tank to adjust the pH value and precipitate to remove fluoride and heavy metal ions. Organic sulfur is added to the sedimentation tank to remove residual heavy metals. PAM is added to the flocculation tank to enhance floc sedimentation. After sedimentation and separation, the supernatant is output. S2. Wastewater concentration treatment: The supernatant obtained in step S1 is introduced into a disc-tube reverse osmosis device for concentration, the produced water is reused as desulfurization process water, and the concentrated water is sent to subsequent treatment; S3, sludge dehydration: the sludge produced by the triple box treatment is transported to the plate and frame filter press for dehydration to form a mud cake; S4, flue spray evaporation: After premixing the concentrated water from step S2 with the fly ash, spray it into the flue through an atomizing nozzle, controlling the residence time of the droplets to achieve concentrated water evaporation; S5. Dry ash collection and resource utilization: Evaporation residues are collected through the separation and dust removal system downstream of the flue, transported to the ash storage bin, mixed with process water, and used as building materials or soil conditioners.

[0006] Preferably, after adding Ca(OH)2 to the neutralization tank in step S1, a turbine stirrer driven by a variable frequency motor is used for mixing and reacting at a stirring speed of 120-150 r / min, with a residence time of ≥15 minutes, so that the pH of the wastewater is stabilized at 9.5±0.2; Ca(OH)2 was added twice: 70–80% of the total amount was added first to raise the pH to 8.5–9.0, and the remaining amount was added after 10 minutes of reaction to reach the target pH. This segmented control strategy prioritized precipitation of F. - Form CaF2 crystal nuclei and then co-precipitate Zn 2+ , Pb 2+ Heavy metal hydroxides.

[0007] Preferably, the sludge cake after the plate and frame filtration in step S3 enters a low-temperature flue gas flash drying tower, and is countercurrently contacted with the 120-150°C flue gas after the air preheater for ≥10 minutes to reduce the sludge moisture content from 45% to ≤15%; The top of the drying tower is equipped with a cyclone air distribution device, and the bottom is equipped with a scraper type slag discharger. The flue gas inlet temperature fluctuation is controlled within ±5°C, and the outlet temperature is ≥70°C to prevent acid gas condensation. The calorific value of the dried sludge is greater than 2500kcal / kg, and it is added to the coal-fired boiler at a ratio of 3% of the dry mass for incineration.

[0008] Preferably, the atomizing nozzle in step S4 is a dual-fluid rotary mechanical atomizer, the volume ratio of compressed air to concentrated water is 1:3-1:5, and the atomized particle size is 30-50 μm; A flue gas deflector group is installed in the front section of the spray zone, and a baffle wall is installed in the rear section to extend the turbulent flow path, so that the droplets are retained in the temperature range of 120-150℃ for ≥2 seconds; The atomizer uses a silicon carbide ceramic nozzle core and uses an online pressure sensor to adjust the compressed air flow in real time to maintain atomization.

[0009] Preferably, when the wet ash material is used as a cement admixture in step S5, the admixture amount accounts for ≤8% of the dry basis weight of the cement; When used as raw material for brick making, the mixture of ash and clay is 1:3–1:4 and sintered, and the compressive strength of the brick is ≥15MPa; When used as a soil conditioner, its heavy metal indicators must meet the following requirements: As≤30mg / kg, Cd≤3mg / kg, Hg≤0.1mg / kg, and the total amount of water-soluble salts <1.5%; During the mixing process, humic acid is added in an amount of 0.5-1.0% of the ash mass.

[0010] A desulfurization wastewater treatment system, comprising: Triple tank optimization unit: a neutralization tank, a sedimentation tank, a flocculation tank and a solid-liquid separation device connected in sequence. The neutralization tank is provided with a Ca(OH)2 dosing device, the sedimentation tank is provided with an organic sulfur TMT-15 dosing device, and the flocculation tank is provided with a PAM dosing device; Wastewater concentration unit: a disc-tube reverse osmosis (DTRO) device connected to a flocculation tank, with an operating pressure of 5–8 MPa. The produced water end is connected to the desulfurization process water system, and the concentrated water end is connected to the flue spray evaporation unit. Plate and frame filter press strengthening unit: a plate and frame filter press connected to the neutralization tank and sedimentation tank; Flue spray evaporation unit: including the flue after the air preheater, atomizing nozzle and turbulent mixer. The flue length must be ≥16m, the atomizing nozzle atomizes particles with a diameter of 30-50μm, and the turbulent mixer is located upstream of the spraying area. Dry ash collection and resource recovery unit: includes a high-efficiency cyclone separator and bag dust collector composite system, a pneumatic ash conveying system, and a twin-shaft mixer. The composite system has a collection efficiency of >99.9%, and the pneumatic ash conveying system has a conveying pressure of 0.3–0.5 MPa.

[0011] Preferably, the turbulent mixer cylinder is provided with a stainless steel spiral guide vane with a spiral angle of 30°-45° and a rotation speed of 200-300 rpm; A fly ash quantitative feeder is installed at the mixer inlet, and fly ash is added according to 8-12wt% of the concentrated water volume, and the mixing time is ≥5 minutes; The surface of the spiral guide vane is sprayed with Al2O3-TiO2 wear-resistant coating (thickness 200-300μm), and the guide gap is 3-5mm, so that SO4 2- It reacts with fly ash CaO to form a CaSO4 coating, which covers the surface of Na2SO4 crystals and reduces the flue fouling rate by 40-60%. An online conductivity meter is configured at the mixer outlet, and the cleaning program is triggered when the conductivity changes by more than 15%.

[0012] Preferably, the high-efficiency cyclone separator adopts a multi-tube parallel structure, with a single tube diameter of Φ300mm, an inlet flow rate of 18-22m / s, and is equipped with a PTFE-coated filter bag with a pore size of ≤1μm for the bag filter; The pneumatic ash conveying system adopts variable pressure conveying, and the inner wall of the pipeline is inlaid with ultra-high molecular weight polyethylene lining, with a flow rate of 12-15m / s; The fluidized air system at the bottom of the ash storage bin (air pressure 0.05-0.08MPa) is linked to the twin-shaft mixer, the mixer speed is 15-20r / min, process water is added through the ultrasonic atomizing nozzle, and the wet ash is measured by the belt scale and output, with the moisture content control accuracy of ±0.5%.

[0013] Preferably, the filter plates of the plate and frame filter press are embedded with a heat transfer oil circulation pipeline, and the temperature is maintained at 60±2°C by a PID temperature control valve; The feeding system uses a plunger pump linked to a diaphragm pressure sensor, and the backflush program is automatically started when the filtration resistance rises to 1.0MPa; The filter cloth uses a double-layer monofilament structure with an upper pore size of 50 μm and a lower pore size of 100 μm. Periodic citric acid cleaning is used to restore the flux. The citric acid cleaning conditions are: concentration 2–3% and temperature 40°C. The mud cake after filtration is transferred to a closed drying bin via a belt conveyor. An ammonia sensor is installed in the bin with an alarm value of 20ppm.

[0014] Preferably, the membrane components of the DTRO device use anti-pollution polyamide composite membranes, which are arranged in a one-stage two-stage manner: The first stage operating pressure is 5-6 MPa, and the concentration ratio is 3-4 times; The second stage pressure is 7–8 MPa, and the concentration ratio is ≥5 times; The membrane system is equipped with a cross-flow flushing device and an online turbidity meter. When the TDS of the produced water is greater than 500 mg / L or the transmembrane pressure difference increases by more than 15%, the alkaline solution chemical cleaning program is automatically started. The cleaning cycle is greater than 72 hours. The alkaline solution has a pH value of 10-11 and contains 0.1-0.2wt% disodium ethylenediaminetetraacetic acid.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The desulfurization wastewater treatment method and system proposed in the present invention utilize triple-box treatment technology to accurately adjust the pH value and remove pollutants such as fluoride and heavy metal ions; the wastewater is then concentrated through a disc-tube reverse osmosis device, which greatly reduces the wastewater volume. The produced water can be directly reused, reducing water resource consumption. After the sludge is dried by plate and frame filter pressing and low-temperature flue gas flash evaporation, the moisture content is significantly reduced and the calorific value is increased. It can be used as a fuel blend to achieve waste reduction and resource utilization. The concentrated water is treated by flue spray evaporation technology, combined with fly ash premixing and turbulence control, which effectively prevents flue scaling. The evaporation residue is further processed into building materials or soil conditioners. The overall process flow is compact, the operating cost is low, and it is environmentally friendly, providing a feasible solution for zero wastewater discharge of thermal power companies. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a flow chart of the method of the present invention; Figure 2This is a system framework diagram of the present invention. DETAILED DESCRIPTION

[0017] The following description is intended to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are merely examples, and those skilled in the art may conceive of other obvious variations.

[0018] Reference Figure 1 As shown, a desulfurization wastewater treatment method includes:

[0019] First, desulfurization wastewater undergoes a three-tank treatment process, sequentially introducing a neutralization tank, a settling tank, and a flocculation tank. In the neutralization tank, Ca(OH)2 is added to adjust the wastewater's pH. This process is achieved by thoroughly mixing the wastewater at 120 to 150 rpm using a turbine agitator driven by a variable-frequency motor. The reaction time is ensured to be at least 15 minutes, ultimately stabilizing the wastewater's pH within a range of 9.5 plus or minus 0.2. Ca(OH)2 is added in a staged manner, initially adding 70% to 80% of the total amount to raise the pH to between 8.5 and 9.0. After a 10-minute reaction, the remaining amount is added to reach the target pH. This staged approach prioritizes the precipitation of fluoride ions to form CaF2 crystal nuclei, followed by the co-precipitation of heavy metal hydroxides such as zinc and lead ions. In the settling tank, organic sulfur is added to further remove residual heavy metal ions. In the flocculation tank, polyacrylamide (PAM) is added to enhance floc formation and settling. After settling and separation, the supernatant is collected and discharged.

[0020] The supernatant then enters the wastewater concentration stage, where it is introduced into a disc-tube reverse osmosis unit for concentration. This unit operates at an operating pressure of 5 to 8 MPa. The produced water is reused in the desulfurization process water system, while the concentrated water enters subsequent treatment units. The sludge generated during the triple-tank treatment process is conveyed to a plate and frame filter press for dehydration. The filter plates of the filter press are embedded with thermal oil circulation lines, and the temperature is precisely maintained at 60°C plus or minus 2°C by a proportional-integral-differential (PID) temperature control valve. The feed system utilizes a plunger pump linked to a diaphragm pressure sensor. When the filtration resistance rises to 1.0 MPa, the system automatically initiates a backflush to maintain efficiency. The filter cloth utilizes a monofilament, double-layer design with an upper layer pore size of 50 microns and a lower layer pore size of 100 microns. Periodic citric acid cleaning is performed to restore filtration flux at a citric acid concentration of 2% to 3% and a temperature of 40°C. The dehydrated sludge cake is transferred to a sealed drying bin via a belt conveyor.

[0021] The sludge cake undergoes low-temperature flue gas flash drying in the drying bin, using countercurrent contact with flue gas from the air preheater at a temperature of 120 to 150 degrees Celsius for at least 10 minutes, reducing the sludge moisture content from 45% to no more than 15%. A swirl air distribution device is installed at the top of the drying tower to ensure uniform gas distribution, and a scraper-type slag discharger is installed at the bottom for continuous slag discharge. Flue gas inlet temperature fluctuations are strictly controlled to no more than ±5 degrees Celsius, and the outlet temperature is maintained above 70 degrees Celsius to prevent acid gas condensation. The calorific value of the dried sludge exceeds 2500 kcal / kg and can be added to coal-fired boilers for incineration at a ratio of 3% of the dry mass.

[0022] The concentrated brine enters the flue for spray evaporation. The brine is first premixed with fly ash in a turbulent mixer. The mixer cylinder is equipped with stainless steel spiral guide vanes with a helix angle of 30 to 45 degrees and a rotation speed maintained at 200 to 300 rpm. A fly ash metering feeder is installed at the mixer inlet, adding fly ash at a mass ratio of 8% to 12% of the brine volume, for a mixing time of at least 5 minutes. The spiral guide vanes are spray-coated with a wear-resistant aluminum oxide-titanium dioxide coating with a thickness of 200 to 300 microns, and the guide gap is designed to be 3 to 5 mm. This promotes the reaction of sulfate ions in the brine with calcium oxide in the fly ash to form a calcium sulfate coating, which covers the surface of the sodium sulfate crystals and effectively reduces the flue fouling rate by 40% to 60%. An online conductivity meter is installed at the mixer outlet for monitoring. If the conductivity changes by more than 15%, the system automatically triggers a cleaning procedure. The premixed slurry is sprayed into the flue following the air preheater via a dual-fluid rotary mechanical atomizer, controlling the volume ratio of compressed air to concentrated water to 1:3 to 1:5, producing atomized droplets of 30 to 50 microns. A flue gas deflector group is installed at the front of the spray zone to guide the airflow, and a baffle wall is installed at the rear to extend the turbulent flow path, ensuring that the droplets remain in the flue gas temperature range of 120 to 150 degrees Celsius for at least 2 seconds, achieving complete evaporation. The atomizer uses a silicon carbide ceramic nozzle core to improve corrosion and wear resistance, and an online pressure sensor monitors and adjusts the compressed air flow in real time to maintain a stable atomization effect.

[0023] The residual evaporation residue is collected downstream of the flue by a combined system consisting of a high-efficiency cyclone separator and a bag filter, achieving a collection efficiency exceeding 99.9%. The high-efficiency cyclone separator utilizes a multi-tube parallel structure, with a single tube diameter of 300 mm and an inlet flow rate controlled at 18 to 22 meters per second. The bag filter utilizes polytetrafluoroethylene-coated filter bags with a pore size no larger than 1 micron. The collected dry ash is transported to the ash storage silo via a pneumatic ash conveying system. This system utilizes variable-pressure conveying, with the inner walls of the pipe lined with ultra-high molecular weight polyethylene (UHMWPE) panels. The flow rate is controlled at 12 to 15 meters per second, and the conveying pressure ranges from 0.3 to 0.5 MPa. In the ash storage silo, the dry ash enters the resource utilization stage. A fluidizing air system with a pressure of 0.05 to 0.08 MPa is installed at the bottom of the silo, operating in conjunction with a twin-shaft mixer. Process water is introduced into the mixer via ultrasonic atomizers, along with humic acid at a concentration equivalent to 0.5% to 1.0% of the dry ash mass. The twin-shaft mixer operates at a speed of 15 to 20 revolutions per minute. The wetted ash is precisely metered and output via a belt scale, with a moisture content control accuracy of ±0.5%. The wetted ash can be used as a building material or soil conditioner. When used as a cement admixture, the addition amount should not exceed 8% of the dry cement mass. When used as a raw material for brickmaking, the ash is mixed and sintered in a ratio of 1:3 to 1:4 by mass to clay, and the resulting bricks must have a compressive strength of no less than 15 MPa. When used as a soil conditioner, the heavy metal content must meet the requirements of no more than 30 mg / kg of arsenic, no more than 3 mg / kg of cadmium, no more than 0.1 mg / kg of mercury, and the total amount of water-soluble salts must be less than 1.5%.

[0024] The entire treatment system also includes a disc-tube reverse osmosis unit, whose membrane components utilize a contamination-resistant polyamide composite membrane, arranged in a two-stage design. The first stage operates at a pressure of 5 to 6 MPa, achieving a concentration ratio of 3 to 4 times; the second stage, operating at a pressure of 7 to 8 MPa, achieves a concentration ratio of at least 5 times. The membrane system is equipped with a cross-flow flushing device and an online turbidity meter for monitoring. If the total dissolved solids (TDS) in the produced water exceeds 500 mg / L or the transmembrane pressure differential increases by more than 15%, the system automatically initiates an alkaline chemical cleaning procedure. The cleaning cycle is designed to last longer than 72 hours, using an alkaline solution with a pH between 10 and 11 and containing 0.1% to 0.2% disodium EDTA as an additive.

[0025] refer to Figure 2 As shown, a desulfurization wastewater treatment system includes: Triple tank optimization unit: a neutralization tank, a sedimentation tank, a flocculation tank and a solid-liquid separation device connected in sequence. The neutralization tank is provided with a Ca(OH)2 dosing device, the sedimentation tank is provided with an organic sulfur TMT-15 dosing device, and the flocculation tank is provided with a PAM dosing device; Wastewater concentration unit: a disc-tube reverse osmosis (DTRO) device connected to a flocculation tank, with an operating pressure of 5–8 MPa and a concentration ratio of ≥5 times; the produced water end is connected to the desulfurization process water system, and the concentrated water end is connected to the flue spray evaporation unit; Plate and frame filter press strengthening unit: a plate and frame filter press connected to the neutralization tank and sedimentation tank; Flue spray evaporation unit: including the flue after the air preheater, atomizing nozzle and turbulent mixer. The flue length must be ≥16m, the atomizing nozzle atomizes particles with a diameter of 30-50μm, and the turbulent mixer is located upstream of the spraying area. Dry ash collection and resource recovery unit: includes a high-efficiency cyclone separator and bag dust collector composite system, a pneumatic ash conveying system, and a twin-shaft mixer. The composite system has a collection efficiency of >99.9%, and the pneumatic ash conveying system has a conveying pressure of 0.3–0.5 MPa.

[0026] It achieves refined process control in pollutant removal. The phased Ca(OH)2 dosing strategy employed in the triple-tank treatment prioritizes the precipitation and crystallization of fluoride by precisely controlling pH and reaction timing, effectively promoting the coordinated precipitation and removal of multiple heavy metal ions, and significantly improving the removal efficiency and selectivity of key pollutants. The variable frequency stirring system in the neutralization tank ensures thorough and uniform mixing of the reagent and wastewater, creating a stable reaction environment and laying a good foundation for subsequent treatment.

[0027] This technology achieves efficient concentration and reduction of wastewater and solid waste. The disc-tube reverse osmosis (DTRO) unit, with its high operating pressure and anti-fouling design, deeply concentrates the pretreated supernatant, significantly reducing the volume of brine requiring final disposal. The resulting high-quality product water can be directly reused in the desulfurization process, significantly reducing fresh process water consumption. For the resulting sludge, a plate and frame filter press with built-in temperature control and optimized filter cloth design improves dehydration efficiency. Subsequent flash drying utilizes waste heat from low-temperature flue gas, fully utilizing low-grade thermal energy while reducing the sludge moisture content to an extremely low level, significantly reducing sludge volume and the burden of subsequent disposal.

[0028] This technology offers unique anti-scaling and resource-recycling capabilities in the zero-discharge process for concentrated water. The key innovation is the premixing of concentrated water and fly ash in a specialized turbulent mixer. By enhancing the contact reaction, sulfates and calcium components in the fly ash form a stable calcium sulfate coating, effectively suppressing the sodium sulfate scaling common in subsequent flue evaporation of high-salinity concentrated water, ensuring the continuous and stable operation of the evaporation system. Precise control of the atomizing nozzle and optimized flue flow field design ensure sufficient retention time of the tiny droplets within the desired temperature range, enabling efficient concentrated water evaporation.

[0029] This technology establishes a closed-loop chain for waste resource utilization. Dried sludge, due to its low moisture content and increased calorific value, can be used as an auxiliary fuel for combustion, achieving energy recovery from solid waste. The fly ash remaining after evaporation is almost completely captured by a highly efficient collection system (high-efficiency cyclones and coated bag filters). The addition of a specific additive (humic acid) during the subsequent wet mixing process not only improves the ash's physical properties but also ensures that it meets the stringent quality standards (such as heavy metal limits, strength requirements, and salt control) for various uses, such as cement admixtures, brickmaking raw materials, or soil conditioners. This achieves high-value, diversified resource utilization of ash.

[0030] The entire system features a compact design, incorporating automated monitoring and feedback mechanisms into each unit operation (such as membrane cleaning, filter press backflushing, mixer cleaning, and ash-mixing control), enhancing operational stability and reliability. By deeply integrating wastewater treatment, sludge disposal, concentrated water evaporation, and ash utilization, this technology provides a highly efficient, stable, and resource-recovery-rich comprehensive treatment approach for desulfurization wastewater.

[0031] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions merely illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for treating desulfurization wastewater, characterized in that: The following steps are involved: S1. Triple-tank treatment: Desulfurization wastewater is introduced into a neutralization tank, a sedimentation tank, and a flocculation tank in sequence. Ca(OH)2 is added to the neutralization tank to adjust the pH value and precipitate to remove fluoride and heavy metal ions. Organic sulfur is added to the sedimentation tank to remove residual heavy metals. PAM is added to the flocculation tank to enhance floc sedimentation. After sedimentation and separation, the supernatant is output. S2. Wastewater concentration treatment: The supernatant obtained in step S1 is introduced into a disc-tube reverse osmosis device for concentration, the produced water is reused as desulfurization process water, and the concentrated water is sent to subsequent treatment; S3, sludge dehydration: the sludge produced by the triple box treatment is transported to the plate and frame filter press for dehydration to form a mud cake; S4, flue spray evaporation: After premixing the concentrated water from step S2 with the fly ash, spray it into the flue through an atomizing nozzle, controlling the residence time of the droplets to achieve concentrated water evaporation; S5. Dry ash collection and resource utilization: Evaporation residues are collected through the separation and dust removal system downstream of the flue, transported to the ash storage bin, and mixed with process water to make wet ash, which is used as a building material raw material or soil conditioner.

2. A desulfurization wastewater treatment method according to claim 1, characterized in that: After adding Ca(OH)2 to the neutralization tank in step S1, the mixture is mixed and reacted at a stirring speed of 120–150 r / min using a turbine agitator driven by a variable frequency motor for a residence time of ≥15 minutes, so that the pH of the wastewater is stabilized at 9.5±0.2; Ca(OH)2 was added twice: 70–80% of the total amount was added in the first dose to raise the pH to 8.5–9.0, and the remaining amount was added in the second dose after 10 minutes to reach the target pH. The first dose preferentially precipitated F - CaF2 crystal nuclei are formed, and Zn is co-precipitated by adding for the second time. 2+ , Pb 2+ Heavy metal hydroxides.

3. A desulfurization wastewater treatment method and system according to claim 1, characterized in that: The sludge cake after the plate and frame filtration in step S3 enters the low-temperature flue gas flash drying tower, and is countercurrently contacted with the 120-150°C flue gas after the air preheater for ≥10 minutes to reduce the sludge moisture content from 45% to ≤15%; The top of the drying tower is equipped with a cyclone air distribution device, and the bottom is equipped with a scraper type slag discharger. The flue gas inlet temperature fluctuation is controlled within ±5°C, and the outlet temperature is ≥70°C to prevent acid gas condensation. The calorific value of the dried sludge is greater than 2500kcal / kg, and it is added to the coal-fired boiler at a ratio of 3% of the dry mass for incineration.

4. A desulfurization wastewater treatment method according to claim 1, characterized in that: The atomizing nozzle in step S4 is a two-fluid rotary mechanical atomizer, the volume ratio of compressed air to concentrated water is 1:3-1:5, and the atomized particle size is 30-50 μm; A flue gas deflector group is installed in the front section of the spray zone, and a baffle wall is installed in the rear section to extend the turbulent flow path, so that the droplets are retained in the temperature range of 120-150℃ for ≥2 seconds; The atomizer uses a silicon carbide ceramic nozzle core and uses an online pressure sensor to adjust the compressed air flow in real time to maintain atomization.

5. A desulfurization wastewater treatment method according to claim 1, characterized in that: The wet ash material in step S5, when used as a cement admixture, has an admixture amount of ≤8% of the dry mass of the cement; When used as raw material for brick making, the mixture of ash and clay is 1:3–1:4 and sintered, and the compressive strength of the brick is ≥15MPa; When used as a soil conditioner, its heavy metal indicators must meet the following requirements: As≤30mg / kg, Cd≤3mg / kg, Hg≤0.1mg / kg, and the total amount of water-soluble salts <1.5%; During the mixing process, humic acid is added in an amount of 0.5-1.0% of the ash mass.

6. A desulfurization wastewater treatment system, characterized in that: include: Triple tank optimization unit: a neutralization tank, a sedimentation tank, a flocculation tank and a solid-liquid separation device connected in sequence. The neutralization tank is provided with a Ca(OH)2 dosing device, the sedimentation tank is provided with an organic sulfur TMT-15 dosing device, and the flocculation tank is provided with a PAM dosing device; Wastewater concentration unit: a disc-tube reverse osmosis (DTRO) device connected to the flocculation tank, with an operating pressure of 5–8 MPa. The produced water end is connected to the desulfurization process water system, and the concentrated water end is connected to the flue spray evaporation unit; Plate and frame filter press strengthening unit: a plate and frame filter press connected to the neutralization tank and sedimentation tank; Flue spray evaporation unit: including the flue after the air preheater, atomizing nozzle and turbulent mixer. The flue length must be ≥16m, the atomizing nozzle atomizes particles with a diameter of 30-50μm, and the turbulent mixer is located upstream of the spraying area. Dry ash collection and resource recovery unit: includes a high-efficiency cyclone separator and bag dust collector composite system, a pneumatic ash conveying system, and a twin-shaft mixer. The composite system has a collection efficiency of >99.9%, and the pneumatic ash conveying system has a conveying pressure of 0.3–0.5 MPa.

7. A desulfurization wastewater treatment system according to claim 6, characterized in that: The turbulent mixer cylinder is provided with a stainless steel spiral guide vane with a spiral angle of 30°–45° and a rotation speed of 200–300 rpm; A fly ash quantitative feeder is installed at the mixer inlet, and fly ash is added according to 8-12wt% of the concentrated water volume, and the mixing time is ≥5 minutes; The surface of the spiral guide vane is sprayed with Al2O3-TiO2 wear-resistant coating (thickness 200-300μm), and the guide gap is 3-5mm, so that SO4 2- It reacts with fly ash CaO to form a CaSO4 coating, which covers the surface of Na2SO4 crystals and reduces the flue fouling rate by 40-60%. An online conductivity meter is configured at the mixer outlet, and the cleaning program is triggered when the conductivity changes by more than 15%.

8. A desulfurization wastewater treatment system according to claim 6, characterized in that: The high-efficiency cyclone separator adopts a multi-tube parallel structure, with a single tube diameter of Φ300mm and an inlet flow rate of 18-22m / s, and is equipped with a PTFE-coated filter bag with a pore size of ≤1μm for the bag filter; The pneumatic ash conveying system adopts variable pressure conveying, and the inner wall of the pipeline is inlaid with ultra-high molecular weight polyethylene lining, with a flow rate of 12-15m / s; The fluidized air system at the bottom of the ash storage bin (air pressure 0.05-0.08MPa) is linked to the twin-shaft mixer, the mixer speed is 15-20r / min, process water is added through the ultrasonic atomizing nozzle, and the wet ash is measured by the belt scale and output, with the moisture content control accuracy of ±0.5%.

9. A desulfurization wastewater treatment system according to claim 6, characterized in that: The filter plates of the plate and frame filter press are embedded with a heat transfer oil circulation pipeline, and the temperature is maintained at 60±2°C through a PID temperature control valve; The feeding system uses a plunger pump linked to a diaphragm pressure sensor, and the backflush program is automatically started when the filtration resistance rises to 1.0MPa; The filter cloth uses a double-layer monofilament structure with an upper pore size of 50 μm and a lower pore size of 100 μm. Periodic citric acid cleaning is used to restore the flux. The citric acid cleaning conditions are: concentration 2–3% and temperature 40°C. The mud cake after filtration is transferred to a closed drying bin via a belt conveyor. An ammonia sensor is installed in the bin with an alarm value of 20ppm.

10. A desulfurization wastewater treatment system according to claim 6, characterized in that: The membrane components of the DTRO device use anti-pollution polyamide composite membranes, and are arranged in a one-stage two-stage configuration: The first stage operating pressure is 5-6 MPa, and the concentration ratio is 3-4 times; The second stage pressure is 7–8 MPa, and the concentration ratio is ≥5 times; The membrane system is equipped with a cross-flow flushing device and an online turbidity meter. When the TDS of the produced water is greater than 500 mg / L or the transmembrane pressure difference increases by more than 15%, the alkaline solution chemical cleaning program is automatically started. The cleaning cycle is greater than 72 hours. The alkaline solution has a pH value of 10-11 and contains 0.1-0.2wt% disodium ethylenediaminetetraacetic acid.

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