Thermal power plant make-up water treatment method beneficial to anti-fouling and anti-blocking of reverse osmosis membrane

Abstract

The invention relates to the technical field of thermal power plant water treatment, in particular to a thermal power plant make-up water treatment method beneficial to reverse osmosis membrane anti-fouling and anti-blocking, which comprises the following steps: S1, Taihu Lake class II surface water is filtered by an adjustable grating and two-stage modified activated carbon, flow rate is controlled, and backwashing is carried out; s2, adding a temperature response type pretreatment agent according to TOC, and standing after ultrasonic stirring; s3, feeding the water into an electric field ultraviolet device, introducing hydrogen, and controlling the electric field, ultraviolet parameters and pH; s4, adding sodium hypochlorite, and adding sodium hydrogen sulfite when residual chlorine exceeds the limit; s5, after security filtration, feeding into a reverse osmosis membrane, controlling the pressure temperature and the water production rate, and performing regular flushing and cleaning. The method has the advantages of efficient reverse osmosis membrane pollution and blockage prevention, reduction of the use of chemical agents, reduction of the cost and environmental protection risk, improvement of the system stability, and demonstration significance to the industry.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology for thermal power plants, specifically a method for treating makeup water in thermal power plants that is beneficial for preventing reverse osmosis membrane fouling. Background Technology

[0002] The feedwater system of thermal power plants is a crucial link in ensuring the safe and stable operation of the units, and reverse osmosis membrane technology is widely used due to its high efficiency in desalination. However, when surface water is used as the main feedwater source, the problem of reverse osmosis membrane fouling has long plagued the industry, especially in water sources such as the Taihu Lake Basin. Although the Class II surface water in this area meets the basic water quality standards, the total organic carbon (TOC) content in the water is high, and the types and numbers of microorganisms are complex and fluctuate greatly, which leads to frequent biofouling of reverse osmosis membranes. This directly causes a decrease in desalination rate and water production, and significantly increases the system's operation and maintenance costs.

[0003] The industry currently uses a chemical treatment scheme of "sodium hypochlorite pre-sterilization + non-oxidizing bactericide assistance" to deal with fouling: first, sodium hypochlorite is added to the raw water to kill some microorganisms, and then a non-oxidizing bactericide is added before the reverse osmosis membrane to inhibit the reproduction of microorganisms. However, this solution has significant drawbacks: First, sodium hypochlorite poses an irreversible oxidation risk to reverse osmosis membranes (especially polyamide composite membranes), requiring the addition of sodium bisulfite to reduce residual chlorine. Sodium bisulfite, however, becomes a nutrient source for microorganisms, creating a potential for subsequent biofouling. Second, non-oxidizing bactericides (such as chlorophenols and organic amines) are expensive. In 2018, the cost of non-oxidizing bactericides in the makeup water treatment field of Wangting Power Plant alone reached 520,000 yuan. Furthermore, these bactericides contain carbon, chlorine, and nitrogen, which can increase the TOC content of the water, causing secondary pollution and reducing water vapor quality. Third, the bactericidal effect is constrained by multiple factors. During the high temperatures of summer, TOC levels are prone to exceed standards (e.g., in 2019, the TOC in the demineralized water tank of the 300MW unit at Wangting Power Plant reached 359 μg / L, far exceeding the control target of 200 μg / L). Long-term use can lead to drug resistance in microorganisms, and the system's TOC content continued to rise year-on-year from 2022 to 2024, gradually reducing the bactericidal efficiency.

[0004] Chemical treatment methods have also led to a sharp increase in equipment maintenance pressure: in 2024, the Wangting Power Plant replaced 947 reverse osmosis security filter cartridges, and the online cleaning cycle of the reverse osmosis membrane was shortened to once every 2 months, or 54 times a year. This not only consumed a lot of manpower and resources but also shortened the service life of the membrane modules. Although alternative technologies such as low-pressure ultraviolet (UV) sterilization, laser sterilization, and biofilm treatment have been attempted, microorganisms are easily reactivated after low-pressure UV sterilization, laser sterilization is too expensive for industrial application, and biofilm treatment is only suitable for high-quality water sources such as groundwater. None of these can meet the actual needs of surface water makeup water treatment in thermal power plants. Therefore, developing a thermal power plant makeup water treatment method that combines high efficiency, anti-fouling, environmental protection, and economy has become an urgent need to solve the industry's pain points. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a method for treating feedwater in thermal power plants that is beneficial for preventing reverse osmosis membrane fouling.

[0006] (II) Technical Solution A method for treating feedwater in thermal power plants that is beneficial for preventing fouling of reverse osmosis membranes includes the following steps: S1 Raw water staged pretreatment: First, the water is filtered through an automatic backwashing grid, with the mesh spacing automatically adjusted to 3-5 mm according to the turbidity of the raw water, to remove suspended impurities ≥5 mm; then, it is filtered through a two-stage modified activated carbon filter tank, the first stage being filled with granular activated carbon loaded with 3%-5% zinc oxide, and the second stage being filled with columnar activated carbon loaded with 1%-2% titanium dioxide; S2 intelligent composite pretreatment agent addition: Add a temperature-responsive composite pretreatment agent composed of polyaspartic acid, hydroxyapatite nanoparticles, zinc citrate, and N-isopropylacrylamide copolymer microspheres in a ratio of 2:1:0.5:0.3, dynamically adding 5-10 mg / L according to the TOC content of the raw water; after ultrasonic stirring at 300-500W and 20-30kHz for 10-15 min, let it stand for 30-45 min; S3 Dual-Field Synergistic Medium-Pressure UV Sterilization: Before the reverse osmosis security filter, an integrated electric field-assisted medium-pressure UV sterilization device is used. A parallel electrode electric field of 5-10kV and an electrode spacing of 5-8cm is applied, in conjunction with a medium-pressure UV lamp of 220-260nm and 350-450mJ / cm², and the water flow velocity is controlled at 0.9-1.1m / s. 0.06%-0.08% hydrogen gas is introduced to catalyze the generation of hydroxyl radicals, which synergistically kill more than 99.5% of bacteria and destroy their DNA. S4 Sodium hypochlorite-sodium bisulfite synergistic regulation: Add 6%-7% sodium hypochlorite solution, monitor the residual chlorine every 3 minutes with an online residual chlorine monitor, and when the residual chlorine is >0.1 mg / L, add 5%-6% sodium bisulfite solution at a 1:1 molar ratio to maintain the residual chlorine at 0.06-0.08 mg / L; S5 reverse osmosis membrane dynamic filtration: After security filtration through a 3μm polytetrafluoroethylene-glass fiber composite filter element, it is sent into the polyamide composite reverse osmosis membrane system. The operating pressure is 1.8-2.2MPa, the water temperature is stable at 28-32℃, and the water production rate is 78%-82%. Every 48 hours of operation, it is flushed at a low pressure of 0.5-0.8MPa for 5-8 minutes.

[0007] Preferably, the PLC control system in step S1 can also adjust the backwashing cycle of the bar screen according to the raw water flow rate; when the raw water flow rate is not less than 50 m³ / h, the backwashing frequency of the bar screen is increased to once every 2 hours; when the raw water flow rate is less than 50 m³ / h, the backwashing frequency of the bar screen is set to once every 4 hours.

[0008] Preferably, the temperature-responsive composite pretreatment agent in step S2 also contains 0.5%-1% graphene quantum dots by mass; the adsorption properties of graphene quantum dots are used to assist in the adsorption of organic matter in the water, and the fluorescence properties of graphene quantum dots are used to monitor the changes in their fluorescence intensity to keep track of the uniformity of the pretreatment agent's dispersion in the water in real time.

[0009] Preferably, the electric field-assisted medium-pressure ultraviolet sterilization device in step S3 is also equipped with an online pH monitoring module; when the pH value of the water is detected to be less than 6.5 or greater than 7.5, the device will automatically add a hydrochloric acid solution or sodium hydroxide solution with a mass fraction of 10%-15% to the water to adjust the pH value of the water to the range of 6.8-7.2.

[0010] Preferably, in step S4, the online residual chlorine monitor, sodium hypochlorite dosing pump, and sodium bisulfite dosing pump are linked for control. When the online residual chlorine monitor detects that the residual chlorine content in the water is less than 0.06 mg / L, the sodium hypochlorite dosing pump will automatically increase the dosage by 0.05 mg / L each time until the residual chlorine content in the water reaches the set range of 0.06 mg / L-0.08 mg / L.

[0011] Preferably, the reverse osmosis membrane system in step S5 is also equipped with a differential pressure monitoring device; when the differential pressure monitoring device detects that the pressure difference between the inlet and outlet of the reverse osmosis membrane is greater than 0.3 MPa, the system will automatically start the chemical cleaning program; the chemical cleaning uses a citric acid solution with a mass fraction of 0.5%-1%, the solution temperature is controlled at 30℃-35℃ during the cleaning process, and the cleaning time lasts for 30min-40min.

[0012] Preferably, each of the two-stage modified activated carbon filter tanks in step S1 is equipped with a backwashing device; wherein, the backwashing intensity of the first-stage filter tank is 15L / (m²·s)-18L / (m²·s), and the backwashing time is 8min-10min; the backwashing intensity of the second-stage filter tank is 12L / (m²·s)-15L / (m²·s), and the backwashing time is 6min-8min; the backwashing cycle of both filter tanks is set to 72h.

[0013] Preferably, the ultrasonic stirring device in step S2 adopts a pulse working mode; specifically, the ultrasonic stirring device works for 30 seconds, then pauses for 10 seconds, and repeats this cycle 5 to 8 times.

[0014] Preferably, the aeration head of the microporous aeration device in step S3 is made of ceramic material and coated with a nano-silica coating on the surface of the aeration head.

[0015] Preferably, the filter element of the reverse osmosis security filter in step S5 is also equipped with a differential pressure alarm function.

[0016] (III) Beneficial Effects Compared with existing technologies, the beneficial effects of this invention are: 1. Through two-stage modified activated carbon adsorption in raw water staged pretreatment, the TOC content and odor substances in the raw water can be effectively reduced. Combined with the flocculent aggregation effect of temperature-responsive composite pretreatment agent, suspended organic matter and calcium and magnesium ions can be reduced simultaneously, reducing pollutants at the source. Dual-field synergistic medium-pressure ultraviolet sterilization combined with sodium hypochlorite-sodium bisulfite synergistic regulation can not only efficiently kill microorganisms and destroy their DNA structure to prevent them from inhabiting and multiplying on the membrane surface, but also precisely control the residual chlorine content to avoid membrane oxidative damage, significantly reduce the risk of biofouling and chemical fouling, and extend the cleaning cycle and service life of the reverse osmosis membrane.

[0017] 2. This method significantly reduces the use of non-oxidizing bactericides and other chemical agents, avoiding secondary pollution. At the same time, the application of temperature-responsive pretreatment agents and graphene quantum dots enhances the targeting of pollutant removal and reduces the introduction of additional chemicals into the water. The hydroxyl radical sterilization process generated by hydrogen catalysis produces no harmful byproducts, and the nano-silica coating of the microporous aeration device reduces microbial adhesion. The overall treatment process is more in line with environmental protection requirements, reduces the pressure on water system discharge, and lowers the safety risks of storing and using toxic chemicals.

[0018] 3. This method significantly reduces chemical reagent procurement costs and equipment maintenance costs by optimizing reagent dosage, extending membrane life, and reducing cleaning frequency. The application of PLC control system, online monitoring module, and linkage control enables adaptive adjustment of raw water turbidity and flow rate, precise control of residual chlorine and pH value, and automatic reminders and triggers for filter replacement and membrane cleaning, reducing manual intervention, improving system stability and ease of operation, and providing a replicable technical solution for thermal power plant makeup water treatment. It has important demonstrative significance for solving the problem of fouling in surface water makeup water systems in the industry. Attached Figure Description

[0019] Figure 1 This invention presents a flow chart of a thermal power plant makeup water treatment process that is beneficial for preventing reverse osmosis membrane fouling. Figure 2 The above are bar charts showing the TOC content and calcium and magnesium ion concentration in the effluent of the examples and comparative examples. Figure 3 This is a line graph comparing the cost of chemical reagents and the cost of reverse osmosis membrane cleaning in the examples and comparative examples; Figure 4 This is a bar graph comparing the increase in inlet and outlet pressure difference of the reverse osmosis membrane and the total number of bacteria in the effluent between the example and the comparative examples. Detailed Implementation

[0020] according to Figures 1 to 4 The specific embodiments of the present invention are as follows:

[0021] Example 1 S1. Raw Water Staged Pretreatment: First, the automatic backwashing screen is activated to perform preliminary filtration of the raw water. The turbidity of the raw water is monitored in real time as 9 NTU. Based on this turbidity value, the PLC control system adjusts the diamond mesh spacing of the screen to 5 mm to effectively filter and remove suspended impurities with a particle size of not less than 5 mm, such as silt and dead branches. Simultaneously, the PLC control system monitors the raw water flow rate at 48 m³ / h and sets the backwashing cycle of the screen to once every 4 hours, with a backwashing duration of 5 minutes, to prevent screen clogging and maintain filtration efficiency. After screen filtration, the water is introduced into a two-stage series modified activated carbon filter tank for deep adsorption treatment. The first-stage filter tank is filled with granular activated carbon loaded with zinc oxide, where the zinc oxide loading mass fraction is 3%, the granular activated carbon particle size is 0.8 mm, and the specific surface area is 1200 m² / g. The inlet flow rate of the first-stage filter tank is controlled to maintain a stable filtration flow rate of 1.8 m / h, ensuring sufficient contact between the water and the activated carbon. The secondary filter is filled with columnar activated carbon loaded with titanium dioxide (1% by mass). The particle size of the columnar activated carbon is 1.5 mm, and the specific surface area is 800 m² / g. The filtration flow rate in the secondary filter is controlled at 1.2 m / h. Both stages of modified activated carbon filter are equipped with independent backwashing devices, with a uniform backwashing cycle of 72 hours. During backwashing of the primary filter, the backwashing intensity is controlled at 15 L / (m²·s)-18 L / (m²·s), and the backwashing time lasts for 8 minutes. During backwashing of the secondary filter, the backwashing intensity is controlled at 12 L / (m²·s)-15 L / (m²·s), and the backwashing time is 6 minutes. Regular backwashing restores the adsorption performance of the activated carbon.

[0022] S2. Intelligent Composite Pretreatment Agent Dosing: The TOC content of the raw water after step S1 treatment was obtained as 0.9 mg / L using an online TOC monitor. Based on this TOC content, the dosage of the temperature-responsive composite pretreatment agent was determined to be 5 mg / L. This temperature-responsive composite pretreatment agent is composed of polyaspartic acid, hydroxyapatite nanoparticles, zinc citrate, and N-isopropylacrylamide copolymer microspheres in a mass ratio of 2:1:0.5:0.3. The hydroxyapatite nanoparticles have a particle size of 50 nm, and the pretreatment agent also contains 0.5% graphene quantum dots by mass. The graphene quantum dots have a particle size of 3 nm-5 nm and exhibit excellent adsorption and fluorescence properties. After the temperature-responsive composite pretreatment agent is precisely added to the water body using a metering pump, an ultrasonic stirring device is activated to agitate the water body. The ultrasonic stirring device was set to a power of 300W and a working frequency of 20kHz, operating in a pulse mode. Specifically, it operated for 30 seconds, then paused for 10 seconds, repeating this cycle 5 times for a total stirring time of 10 minutes. After stirring, the water was introduced into a sedimentation tank and allowed to stand for 30 minutes. Utilizing the temperature response characteristics of N-isopropylacrylamide copolymer microspheres at 25℃-35℃, the flocs in the water were encouraged to aggregate and settle, achieving simultaneous removal of suspended organic matter and calcium and magnesium ions.

[0023] S3. Dual-Field Synergistic Medium-Pressure UV Sterilization: The water treated by sedimentation in step S2 is transported to a medium-pressure UV sterilization device integrated with an electric field-assisted function. This device is installed upstream of the reverse osmosis security filter. The parallel plate electric field inside the device is activated, with the electric field voltage adjusted to 5kV and the plate spacing set to 5cm, creating a stable electric field environment for the water. Simultaneously, the medium-pressure UV lamp is turned on, with the wavelength adjusted to 220nm and the radiation dose controlled at 350mJ / cm². The water flow velocity within the device is stabilized at 0.9m / s using a flow control valve to ensure sufficient UV radiation exposure. Hydrogen gas with a mass fraction of 0.06% is introduced into the water within the sterilization device through a microporous aeration device. The aeration head of the microporous aeration device is made of ceramic material, with a nano-silica coating on its surface. The coating thickness is 50nm-80nm, and the aeration pore size is 8μm. The aeration pressure is controlled at 0.12MPa, allowing hydrogen to be uniformly dispersed in the water in the form of tiny bubbles. An internal pH online monitoring module monitors the water's pH value in real time. The current pH value is 6.8, within the optimal reaction range of 6.8-7.2, requiring no pH adjustment. Under the synergistic effect of ultraviolet light and an electric field, hydrogen is catalyzed to produce hydroxyl radicals, which, together with the electric field, kill bacteria in the water and destroy the DNA structure of microorganisms.

[0024] S4. Sodium hypochlorite-sodium bisulfite synergistic regulation: Sodium hypochlorite solution with a mass fraction of 6% is added to the water after sterilization treatment in step S3, and the initial dosage is controlled at 0.4 mg / L via a metering pump. During water flow, the residual chlorine content in the water is monitored in real time using an online residual chlorine monitor, with a monitoring frequency set to once every 3 minutes. When the monitoring data shows that the residual chlorine content in the water rises to 0.09 mg / L, the control system automatically starts the sodium bisulfite dosing pump to add a 5% sodium bisulfite solution to the water. The dosage of sodium bisulfite solution is calculated based on the excess portion of sodium hypochlorite, and the molar ratio of the two is 1:1, ultimately maintaining the residual chlorine content in the water stably at 0.06 mg / L.

[0025] S5. Reverse Osmosis Membrane Dynamic Filtration: The water treated in step S4 is introduced into a high-precision reverse osmosis security filter. This filter has a filtration precision of 3μm, and its internal filter element is made of polytetrafluoroethylene-glass fiber composite material. The filter element is 1.2m long, with an outer diameter of 150mm and an inner diameter of 50mm. After passing through the security filter, the water enters the polyamide composite reverse osmosis membrane system. This reverse osmosis membrane has a molecular weight cutoff of 100Da and an effective membrane element area of ​​40m². The operating pressure of the reverse osmosis membrane system is adjusted by a variable frequency pump to stabilize it at 1.8MPa. The feed water temperature of the reverse osmosis membrane system is monitored in real time using a temperature sensor. The current feed water temperature is detected to be 27℃, which is below the optimal operating temperature range of 28℃-32℃. The system's heating device is then activated to raise the water temperature to 28℃. The permeate flow rate is monitored in real time using a flow sensor, and combined with the feed water flow rate, the permeate rate of the reverse osmosis membrane system is maintained at 78%. Every 48 hours of operation, the reverse osmosis membrane undergoes a low-pressure flushing treatment. The flushing water is the permeate from the reverse osmosis system, the flushing pressure is controlled at 0.5 MPa, and the flushing time lasts for 5 minutes. Differential pressure sensors are installed at the inlet and outlet of the reverse osmosis security filter cartridge. When the detected pressure difference between the inlet and outlet reaches 0.1 MPa, the system automatically triggers an alarm, issuing a reminder signal to replace the filter cartridge. Differential pressure monitoring devices are also installed at the inlet and outlet of the reverse osmosis membrane system. When the detected pressure difference between the inlet and outlet reaches 0.3 MPa, the system automatically initiates a chemical cleaning program. The cleaning solution used is a 0.5% citric acid solution, the cleaning solution temperature is controlled at 30℃, and the cleaning time lasts for 30 minutes to restore the reverse osmosis membrane flux.

[0026] Example 2 S1. Raw Water Staged Pretreatment: After starting the automatic backwashing screen, the turbidity monitor displays a raw water turbidity of 11 NTU. Based on this turbidity value, the PLC control system adjusts the diamond mesh spacing of the screen to 3 mm. Simultaneously, the flow monitor displays a raw water flow rate of 55 m³ / h. The PLC control system adjusts the backwashing frequency of the screen to once every 2 hours, with a backwashing duration of 5 minutes, ensuring stable filtration even under high flow conditions. The water then enters a two-stage series modified activated carbon filter tank. The first-stage filter tank is filled with granular activated carbon loaded with 4% zinc oxide, with a particle size of 1.0 mm and a specific surface area of ​​1300 m² / g. The filtration flow rate in the first-stage filter tank is maintained at 2.0 m / h through flow regulation. The second-stage filter tank is filled with columnar activated carbon loaded with 1.5% titanium dioxide, with a particle size of 1.8 mm and a specific surface area of ​​850 m² / g. The filtration flow rate in the second-stage filter tank is controlled at 1.3 m / h. The backwashing cycle for both stages of the filter tank is 72 hours. The backwashing intensity for the first stage filter tank is 16 L / (m²·s), and the backwashing time is 9 min. The backwashing intensity for the second stage filter tank is 13 L / (m²·s), and the backwashing time is 7 min.

[0027] S2. Intelligent Composite Pretreatment Agent Dosing: The TOC content of the raw water after step S1 treatment was measured to be 1.1 mg / L by the online TOC monitor. Based on this, the dosage of the temperature-responsive composite pretreatment agent was determined to be 9 mg / L. The hydroxyapatite nanoparticles in this pretreatment agent have a particle size of 80 nm, and the mass fraction of graphene quantum dots added is 0.8%. After the pretreatment agent is added, the ultrasonic stirring device is started. The device power is set to 400W, the working frequency is 25kHz, and the pulse working mode is cycled 7 times (30 seconds of operation, 10 seconds of pause), with a total stirring time of 12 minutes. After stirring, the water is placed in a sedimentation tank and allowed to stand for 38 minutes to complete the floc aggregation and sedimentation.

[0028] S3. Dual-Field Synergistic Medium-Pressure UV Sterilization: After the water enters the electric field-assisted medium-pressure UV sterilization device, the parallel electrode electric field is activated, the voltage is adjusted to 8kV, and the electrode spacing is set to 6cm. The wavelength of the medium-pressure UV lamp is adjusted to 240nm, the radiation dose is controlled at 400mJ / cm², and the water flow velocity is stabilized at 1.0m / s through flow control. The microporous aeration device introduces 0.07% hydrogen gas into the water, the aeration head has an aeration orifice diameter of 12μm, and the aeration pressure is 0.15MPa. The pH online monitoring module shows that the water pH value is 7.4, which exceeds the optimal reaction range. The control system automatically starts the hydrochloric acid dosing device, adding a 10% hydrochloric acid solution to the water to adjust the water pH value to 7.0.

[0029] S4. Sodium hypochlorite-sodium bisulfite synergistic regulation: A 6.5% sodium hypochlorite solution was added to the water body at an initial dosage of 0.45 mg / L. An online residual chlorine monitor monitored the residual chlorine content every 3 minutes. When the residual chlorine content dropped to 0.05 mg / L, the sodium hypochlorite dosing pump automatically increased the dosage by 0.05 mg / L. After two adjustments, the residual chlorine content in the water body stabilized at 0.07 mg / L.

[0030] S5. Reverse Osmosis Membrane Dynamic Filtration: After water passes through a high-precision reverse osmosis security filter (3μm filtration accuracy, PTFE-glass fiber composite filter element), it enters a polyamide composite reverse osmosis membrane system (molecular weight cutoff 150Da, effective membrane element area 40m²). The system operating pressure is adjusted to 2.0MPa by a variable frequency pump. The temperature sensor monitors the inlet water temperature at 33℃, and the cooling device is activated to lower the water temperature to 30℃. The flow sensor controls the permeate rate to maintain at 80%. Every 48 hours of operation, the reverse osmosis membrane is low-pressure flushed at 0.6MPa for 6 minutes. When the pressure difference between the inlet and outlet of the security filter element reaches 0.1MPa, the system alarms to prompt filter element replacement. When the pressure difference between the inlet and outlet of the reverse osmosis membrane reaches 0.3MPa, the chemical cleaning program is automatically initiated. The cleaning solution is a 0.8% citric acid solution, the cleaning temperature is controlled at 32℃, and the cleaning time is 35 minutes.

[0031] Example 3 S1. Raw Water Staged Pretreatment: After the automatic backwashing screen is activated, the turbidity monitor displays a raw water turbidity of 10 NTU, and the PLC control system adjusts the screen mesh spacing to 3 mm. The flow monitor displays a raw water flow rate of 45 m³ / h, and the screen backwashing frequency is set to once every 4 hours. The primary modified activated carbon filter tank is filled with granular activated carbon loaded with 5% zinc oxide by mass, with an activated carbon particle size of 1.2 mm and a specific surface area of ​​1400 m² / g, and the filtration flow rate is controlled at 2.2 m / h. The secondary filter tank is filled with columnar activated carbon loaded with 2% titanium dioxide by mass, with an activated carbon particle size of 2.0 mm and a specific surface area of ​​900 m² / g, and the filtration flow rate is 1.5 m / h. The backwashing cycle for both filter tanks is 72 hours. The backwashing intensity for the primary filter tank is 18 L / (m²·s), and the time is 10 min; the backwashing intensity for the secondary filter tank is 15 L / (m²·s), and the time is 8 min.

[0032] S2. Intelligent Composite Pretreatment Agent Dosing: The TOC content of the raw water was measured to be 1.2 mg / L by the online TOC monitor, and the dosage of the temperature-responsive composite pretreatment agent was determined to be 10 mg / L. The hydroxyapatite nanoparticles in this pretreatment agent have a particle size of 100 nm, and the graphene quantum dots have a mass fraction of 1%. The ultrasonic stirring device was started, with a power set to 500W, a working frequency of 30kHz, and a pulse working mode cycled 8 times, for a total stirring time of 15 minutes. After stirring, the water was allowed to settle in a sedimentation tank for 45 minutes to complete the sedimentation of pollutants.

[0033] S3. Dual-Field Synergistic Medium-Pressure UV Sterilization: The electric field voltage of the parallel plates in the electric field-assisted medium-pressure UV sterilization device is adjusted to 10kV, with a plate spacing of 8cm. The medium-pressure UV lamp has a wavelength of 260nm, a radiation dose of 450mJ / cm², and a water flow velocity controlled at 1.1m / s. A microporous aeration device introduces 0.08% hydrogen gas (mass fraction), with an aeration pore size of 15μm and an aeration pressure of 0.18MPa. The pH online monitoring module displays a water pH of 6.4, and the system automatically adds a 15% sodium hydroxide solution to adjust the pH to 7.2.

[0034] S4. Sodium hypochlorite-sodium bisulfite synergistic regulation: Add a 7% sodium hypochlorite solution at an initial dosage of 0.5 mg / L. When the online residual chlorine monitor detects that the residual chlorine content has risen to 0.11 mg / L, a 6% sodium bisulfite solution is automatically added, ultimately stabilizing the residual chlorine content at 0.08 mg / L.

[0035] S5. Reverse Osmosis Membrane Dynamic Filtration: After being filtered by a reverse osmosis security filter (filtration accuracy 3μm), the water enters the polyamide composite reverse osmosis membrane system (molecular weight cutoff 200Da, effective membrane element area 40m²). The variable frequency pump adjusts the operating pressure to 2.2MPa, the temperature sensor monitors the inlet water temperature at 26℃, the heating device is activated to raise the temperature to 32℃, and the flow sensor controls the water production rate to 82%. The reverse osmosis membrane is flushed at 0.8MPa pressure for 8 minutes every 48 hours; an alarm prompts replacement when the pressure difference between the filter element inlet and outlet reaches 0.1MPa; when the pressure difference between the membrane inlet and outlet reaches 0.3MPa, it is cleaned with a 1% citric acid solution at 35℃ for 40 minutes.

[0036] Comparative Example The traditional coal-fired power plant makeup water treatment method is adopted, and the specific steps are as follows: Raw water filtration: The raw water first passes through a regular screen filter with a fixed screen mesh spacing of 5mm. Backwashing is manually controlled and the backwashing cycle is once every 8 hours, with each backwashing lasting 5 minutes. The filter removes suspended impurities with a particle size of not less than 5mm.

[0037] Chemical disinfection: A 6% sodium hypochlorite solution (1.0 mg / L) was added to the filtered water and stirred for 30 minutes. Then, a 5% sodium bisulfite solution (0.8 mg / L) was added to reduce residual chlorine in the water. Subsequently, a non-oxidizing disinfectant (a chlorophenol compound) was added to the water at a dosage of 15 mg / L. The mixture was stirred for 20 minutes using a 300W agitator at 150 rpm.

[0038] Security Filtration and Reverse Osmosis: Sterilized water is passed through a conventional reverse osmosis security filter with a filtration accuracy of 5μm and a polypropylene filter element. The filtered water then enters a polyamide composite reverse osmosis membrane system. The system operating pressure is adjusted to 2.0MPa, and the inlet water temperature is naturally maintained between 25℃ and 35℃. The permeate rate is controlled between 75% and 85% by manually adjusting the inlet water flow rate. The online cleaning cycle of the reverse osmosis membrane is determined based on membrane flux changes, typically every two months. The cleaning solution is a 1% (w / w) citric acid solution, the cleaning temperature is 30℃, and the cleaning time is 30 minutes. The security filter element is manually replaced based on the inlet and outlet pressure difference; it is replaced when the pressure difference exceeds 0.2MPa.

[0039] The following table compares the effluent water quality and key performance indicators of the reverse osmosis membrane between the example and the comparative examples: Table 1

[0040] The following table compares the key economic and environmental indicators of the examples and comparative examples: Table 2

[0041] As can be seen from the table above, this power plant feedwater treatment method, through five-stage synergistic operation, far surpasses traditional methods in terms of effectiveness, environmental friendliness, and economy in preventing reverse osmosis membrane fouling. The raw water first passes through an automatically regulating screen and two stages of modified activated carbon filtration to reduce TOC and suspended impurities at the source. Next, a temperature-responsive composite pretreatment agent, dynamically adjusted according to TOC content, is added, along with pulsed ultrasound to cause organic matter and calcium and magnesium ions to agglomerate and settle. Then, dual-field synergistic medium-pressure ultraviolet sterilization, combined with hydroxyl radicals generated by hydrogen catalysis, kills over 99.5% of microorganisms and damages their DNA. Subsequently, sodium hypochlorite and sodium bisulfite are linked for precise control to maintain residual chlorine content and prevent membrane oxidation. Finally, constant temperature and pressure dynamic filtration and periodic low-pressure flushing further protect the reverse osmosis membrane. Data shows that the effluent TOC of the example water was as low as 80 μg / L and the total bacterial count was only 6 CFU / mL, which is far superior to the 165 μg / L and 65 CFU / mL of the comparative example. The reverse osmosis membrane cleaning cycle was extended from 2 months to 8 months, the average monthly total operating cost was reduced from 75,500 yuan to 18,500 yuan, and the use of chemical agents was greatly reduced, avoiding secondary pollution and completely solving many pain points of traditional chemical treatment solutions.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their likenesses.

Claims

1. A method for treating feedwater in thermal power plants that facilitates anti-fouling of reverse osmosis membranes, characterized in that, Includes the following steps: S1 raw water graded pretreatment: First, it is filtered by an automatic backwashing bar filter. The mesh spacing is automatically adjusted to 3-5mm according to the turbidity of the raw water to remove suspended impurities ≥5mm. The filter then passes through a two-stage modified activated carbon filter canister. The first stage is filled with granular activated carbon loaded with 3%-5% zinc oxide, and the second stage is filled with columnar activated carbon loaded with 1%-2% titanium dioxide. S2 intelligent composite pretreatment agent addition: Add a temperature-responsive composite pretreatment agent composed of polyaspartic acid, hydroxyapatite nanoparticles, zinc citrate, and N-isopropylacrylamide copolymer microspheres in a ratio of 2:1:0.5:0.3, dynamically adding 5-10 mg / L according to the TOC content of the raw water; after ultrasonic stirring at 300-500W and 20-30kHz for 10-15 min, let it stand for 30-45 min; S3 Dual-Field Synergistic Medium-Pressure UV Sterilization: Before the reverse osmosis security filter, an integrated electric field-assisted medium-pressure UV sterilization device is used. A parallel electrode electric field of 5-10kV and an electrode spacing of 5-8cm is applied, in conjunction with a medium-pressure UV lamp of 220-260nm and 350-450mJ / cm², and the water flow velocity is controlled at 0.9-1.1m / s. 0.06%-0.08% hydrogen gas is introduced to catalyze the generation of hydroxyl radicals, which synergistically kill more than 99.5% of bacteria and destroy their DNA. S4 Sodium hypochlorite-sodium bisulfite synergistic regulation: Add 6%-7% sodium hypochlorite solution, monitor the residual chlorine every 3 minutes with an online residual chlorine monitor, and when the residual chlorine is >0.1 mg / L, add 5%-6% sodium bisulfite solution at a 1:1 molar ratio to maintain the residual chlorine at 0.06-0.08 mg / L; S5 reverse osmosis membrane dynamic filtration: After security filtration through a 3μm polytetrafluoroethylene-glass fiber composite filter element, it is sent into the polyamide composite reverse osmosis membrane system. The operating pressure is 1.8-2.2MPa, the water temperature is stable at 28-32℃, and the water production rate is 78%-82%. Every 48 hours of operation, it is flushed at a low pressure of 0.5-0.8MPa for 5-8 minutes.

2. The method for treating thermal power plant makeup water according to claim 1, which is beneficial for preventing reverse osmosis membrane fouling, is characterized in that, The PLC control system in step S1 can also adjust the backwashing cycle of the bar screen according to the raw water flow rate; when the raw water flow rate is not less than 50 m³ / h, the backwashing frequency of the bar screen is increased to once every 2 hours; when the raw water flow rate is less than 50 m³ / h, the backwashing frequency of the bar screen is set to once every 4 hours.

3. The method for treating thermal power plant makeup water according to claim 1, which is beneficial for preventing reverse osmosis membrane fouling, is characterized in that... The temperature-responsive composite pretreatment agent in step S2 also contains 0.5%-1% graphene quantum dots by mass. The adsorption properties of graphene quantum dots are used to assist in the adsorption of organic matter in the water. At the same time, by monitoring the fluorescence intensity changes of graphene quantum dots, the dispersion uniformity of the pretreatment agent in the water can be monitored in real time.

4. The method for treating thermal power plant makeup water according to claim 1, which is beneficial for preventing reverse osmosis membrane fouling, is characterized in that, In step S3, the electric field-assisted medium-pressure ultraviolet sterilization device is also equipped with an online pH monitoring module. When the pH value of the water is detected to be less than 6.5 or greater than 7.5, the device will automatically add 10%-15% hydrochloric acid solution or sodium hydroxide solution to the water to adjust the pH value of the water to the range of 6.8-7.

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5. The method for treating thermal power plant makeup water according to claim 1, which is beneficial for preventing reverse osmosis membrane fouling, is characterized in that... In step S4, the online residual chlorine monitor, sodium hypochlorite dosing pump, and sodium bisulfite dosing pump are linked for control. When the online residual chlorine monitor detects that the residual chlorine content in the water is less than 0.06 mg / L, the sodium hypochlorite dosing pump will automatically increase the dosage by 0.05 mg / L each time until the residual chlorine content in the water reaches the set range of 0.06 mg / L-0.08 mg / L.

6. The method for treating thermal power plant makeup water according to claim 1, which is beneficial for preventing reverse osmosis membrane fouling, is characterized in that, The reverse osmosis membrane system in step S5 is also equipped with a differential pressure monitoring device. When the differential pressure monitoring device detects that the pressure difference between the inlet and outlet of the reverse osmosis membrane is greater than 0.3 MPa, the system will automatically start the chemical cleaning program. The chemical cleaning uses a citric acid solution with a mass fraction of 0.5%-1%. During the cleaning process, the solution temperature is controlled at 30℃-35℃, and the cleaning time lasts for 30min-40min.

7. The method for treating thermal power plant makeup water according to claim 1, which is beneficial for preventing reverse osmosis membrane fouling, is characterized in that, In step S1, both stages of modified activated carbon filter tanks are equipped with backwashing devices. The backwashing intensity of the first-stage filter tank is 15 L / (m²·s)-18 L / (m²·s), and the backwashing time is 8 min-10 min. The backwashing intensity of the second-stage filter tank is 12 L / (m²·s)-15 L / (m²·s), and the backwashing time is 6 min-8 min. The backwashing cycle of both filter tanks is set to 72 h.

8. The method for treating thermal power plant makeup water according to claim 1, which is beneficial for preventing reverse osmosis membrane fouling, is characterized in that, The ultrasonic stirring device in step S2 adopts a pulse working mode; the specific working method is: after the ultrasonic stirring device works for 30 seconds, it pauses for 10 seconds, and this cycle is repeated 5 to 8 times.

9. The method for treating thermal power plant makeup water according to claim 1, which is beneficial for preventing reverse osmosis membrane fouling, is characterized in that, The aeration head of the microporous aeration device in step S3 is made of ceramic material and coated with a nano-silica coating on the surface of the aeration head.

10. The method for treating thermal power plant makeup water according to claim 1, which is beneficial for preventing reverse osmosis membrane fouling, is characterized in that, The filter element of the reverse osmosis security filter in step S5 is also equipped with a differential pressure alarm function.

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