A power plant boiler cleaning device and a cleaning commissioning method

Abstract

The application discloses a power plant boiler cleaning device and a cleaning and debugging method, wherein the boiler cleaning device comprises a dosing tank body, a supporting leg and a drain pipe are arranged at the bottom of the dosing tank body, a valve is arranged at the outer end of the drain pipe, a filter tank capable of being hung is arranged in the tank body, and an acid-resistant filter screen is arranged at the bottom of the filter tank; a second supporting plate is arranged on the outer wall of the two ends of the dosing tank body, a supporting plate is arranged above the second supporting block, a U-shaped bracket is penetrated through the supporting plate, and the U-shaped bracket is fixed through a nut. The application clamps and fixes the return flow corrugated pipe through the U-shaped bracket, restrains the movement of the pipeline, matches the filter tank and the filter screen to intercept impurities, and can clean the filter residue on line; in combination with the front small corrosion test, the complete citric acid cleaning process and the waste liquid treatment process, the construction cost and the corrosion risk are reduced, the cleaning quality is stable, the waste liquid can be treated as a resource, and the standardization implementation of the boiler chemical cleaning site is facilitated.

Description

Technical Field

[0001] This invention relates to a chemical mixing tank and a citric acid cleaning method, and particularly to a boiler cleaning device and cleaning and commissioning method for power plants, belonging to the field of boiler cleaning technology. Background Technology

[0002] After long-term operation, the heating surface tubes of power plant boilers will be covered with oxide scale, rust products and various deposits. During the unit maintenance phase, chemical cleaning is required to remove the deposits from the tube walls, ensure the boiler heat exchange efficiency, prevent the deposits from causing local overheating and tube rupture, and ensure the safe and stable operation of the generator unit.

[0003] Currently, during the citric acid chemical cleaning of boilers, the return pipeline of the cleaning circulation loop discharges directly into the chemical mixing tank. The return medium carries a large amount of solid impurities such as oxide scale and welding slag directly into the mixing tank. These impurities can easily enter the cleaning pump, causing wear and jamming of the pump impeller and affecting the stable operation of the circulation system. At the same time, the return pipeline is subjected to the impact of the liquid flow, causing the pipeline to move back and forth and shake. The return outlet position may shift, and the dirty liquid may splash outside the tank, resulting in poor safety at the work site. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a power plant boiler cleaning device and cleaning and commissioning method to suppress the surging and shaking caused by fluid impact in the return pipeline, intercept oxide scale and welding slag impurities in the circulating medium, and improve the construction quality and operation safety of boiler chemical cleaning.

[0005] The technical solution adopted by this invention to solve the technical problem is as follows: A power plant boiler cleaning device includes a dosing tank body with an open top and four support legs at the four corners of the bottom. A drain pipe is located at the center of the bottom of the dosing tank body, and a valve is located at the outer end of the drain pipe. A filter tank is located inside the dosing tank body, and a filter screen is installed at the bottom of the filter tank. Insert brackets are installed at both ends of the top surface of the filter tank and are attached to both ends of the dosing tank body. First support blocks are provided on the outer walls of both sides of the dosing tank body. Support plates are provided on the first support blocks, and U-shaped frames are passed through the support plates. Limit nuts are threadedly connected to the bottom ends of the U-shaped frames.

[0006] The overall height of the filter tank is two-thirds of the height of the inner cavity of the drug preparation tank.

[0007] The outer walls at both ends of the dispensing tank are provided with second support blocks, and the outer end of the insert penetrates through the second support blocks.

[0008] A screw is vertically installed at the bottom center of the support plate. The screw passes through the first support block and is fixed by a matching nut.

[0009] The filter screen is made of 316L stainless steel that is resistant to citric acid.

[0010] The drain pipe is an L-shaped pipe. The outer end of the drain pipe is connected to a cleaning pump through a first corrugated pipe. The output end of the cleaning pump is connected to the boiler inlet pipe through a pipe to transport the filtered cleaning solution into the boiler heating surface. A return pipe is set at the bottom of the boiler heating surface. A second corrugated pipe is connected to the outlet of the return pipe. The second corrugated pipe is fixed to the support plate by a U-shaped frame so that all the boiler return sewage falls into the filter screen to complete the circulation filtration.

[0011] The cleaning and commissioning method of a power plant boiler cleaning device includes the following steps: S1. Construction Preparation: ① Determine the scope of boiler cleaning, calculate the water volume of the cleaning system, and prepare the required amount of cleaning agent and supporting consumables based on the calculation results; ② Conduct on-site verification of the formal system and temporary cleaning system, complete system isolation, test point debugging, temporary pipeline layout, and install monitoring pipes and corrosion indicator plates; ③ Complete the assembly and debugging of the dosing tank body: Place the filter tank bracket on the upper end of the second support block at the opening of the dosing tank body; connect the dosing tank body to the boiler cleaning closed circulation loop, so that the drain pipe of the dosing tank is connected to the boiler liquid inlet pipe through the cleaning pump, and the boiler return pipe outlet is correspondingly arranged on the support plate, and is clamped and fixed by U-shaped bracket and matching thread. ④ After all pipelines are connected, open the drain valve and check that there are no leaks at each connection point; conduct a small-scale pre-pickling test to simulate the on-site cleaning conditions, determine the corrosion rate, and determine the on-site cleaning process control parameters. S2. Specific cleaning procedures ① System water flushing: Use demineralized water at room temperature to flush for 24-48 hours, using twice the water volume, until the flushing water is clear, transparent and free of impurities; ② Alkaline washing: Prepare an alkaline washing solution containing 0.05-0.1% hydrogen peroxide, circulate for 3 hours at room temperature and soak for 8 hours, using water equal to the volume of water. ③ Rinse with water after alkaline washing: Rinse with deionized water at room temperature for 6-8 hours, using 1 volume of water, until the hydrogen peroxide content is 0. ④ Superheater protection fluid: Prepare a protection fluid with a hydrazine concentration of 200-300 ppm and a pH of 9.5-10, fill it into the superheater and complete the 1MPa pressure increase sealing test; ⑤ Simulated circulating heating test: Establish circulation of demineralized water, raise the temperature to 90℃, and end the test after checking that there are no leaks in the system. The water consumption is 1 times the water volume. ⑥ Prepare a pickling solution with 2%-4% citric acid, 0.3%-0.4% corrosion inhibitor, and 0.05%-0.1% hydrazine. Adjust the pH to 3.5-4.0 with ammonia water. Control the cleaning temperature at 85-95℃ and circulate the solution for 6-8 hours. Throughout the process, control the Fe³⁺ content to be less than 300 mg / L. During the pickling process, the wastewater carrying oxide scale and welding slag from the boiler return flows into the filter tank of the mixing tank. Solid impurities are intercepted by the filter screen, and the filtered clean solution is returned to the bottom of the mixing tank for reuse. If the Fe³⁺ content exceeds the limit, add a reducing agent to adjust it. ⑦ Water-top acid flushing: Use 50-80℃ demineralized water for water-top acid flushing for 4-6 hours, with a water volume of 1.5 times the system water volume, and control the pH of the drain outlet to be >4.0 and the total iron content to be <50mg / L; ⑧ Rinsing: Prepare a rinsing solution with citric acid (0.1%-0.3% by mass) and corrosion inhibitor (0.05%-0.1% by mass). Adjust the pH to 3.5-4.0 with ammonia. Rinse for 2-3 hours at 50-80℃. Control the total iron content of the system to be less than 300ppm. The rinsing return wastewater is also filtered through the chemical preparation tank to remove impurities. ⑨ Passivation: After rinsing, adjust the pH of the system to 9.5-10.0 with ammonia water, add hydrogen peroxide to make its concentration reach 0.3%-0.5%, and passivate by circulation at 45-55℃ for 4-6 hours; S3. Quality inspection after cleaning Remove deposits and debris from inside the boiler and cut the monitoring tube for inspection; control the acceptance indicators: corrosion rate < 8g / m²·h, total corrosion < 80g / m²; the metal substrate surface is clean, without pitting or secondary rust, and the passivation film is continuous and dense; if the boiler cannot be put into operation within 20 days after cleaning, use ammonia-hydrazine protective solution or nitrogen pressure to implement shutdown protection. S4. Waste liquid disposal Collect the cleaning waste liquid generated in each process, add strong oxidant and aerate and stir for no less than 2 hours to degrade COD; add solid caustic soda or lime slurry to adjust pH to 6-9; add 10mg / L coagulant and 5mg / L coagulant aid in sequence to complete coagulation and sedimentation; use a screw press dewatering machine for solid-liquid separation, the separated water is recycled and reused, and the generated mud cake is sent to the coal yard for incineration or transported away for disposal in compliance with regulations. S5, Online maintenance of the dosing tank During the cleaning operation, when there is a lot of residue on the surface of the filter screen, loosen the clamping limit of the U-shaped frame on the insert frame, use the hoisting rope to hook the insert frame to lift the filter tank as a whole away from the dosing tank body, and clean the solid impurities trapped by the filter screen; after the impurities are cleaned, lift the filter tank back into place, re-lock the U-shaped frame, and restore the system circulation.

[0012] The small-scale experiment before pickling in step S1 includes the following operations: selecting boiler water-cooled wall tubes, processing them into tube samples and indicator plates, weighing and calculating the surface area; preparing 3% citric acid solutions (pH 3.5-4.0) containing 0.3% corrosion inhibitor and without corrosion inhibitor; immersing the tube samples and indicator plates into the two solutions respectively, maintaining a constant temperature of 90℃ for 4 hours; removing them, drying and weighing them, calculating the total corrosion and corrosion rate, and determining the appropriate parameters for the corrosion inhibitor.

[0013] The positive and beneficial effects of this invention are: 1. This invention uses a U-shaped frame on the support plate to clamp and fix the return corrugated pipe, which can counteract the impact force of the liquid flow, prevent the return pipeline from moving back and forth and shaking during operation, stabilize the falling position of the sewage, prevent the cleaning sewage from splashing out, and thus improve the safety of on-site operation.

[0014] 2. This invention uses a suspended filter tank to intercept oxide scale and welding slag solid impurities in the circulating cleaning solution, reducing the entry of hard impurities into the cleaning pump and thus protecting the cleaning pump. Through the assembly structure of the bracket suspension, the filter residue can be directly lifted out of the filter tank for cleaning after accumulation, without the need to empty the solution in the tank, reducing downtime and improving the efficiency of chemical cleaning.

[0015] 3. This invention determines suitable process parameters by conducting a small-scale corrosion test before acid washing, and then combines it with a complete and coherent cleaning process, quality inspection and waste liquid disposal process, which reduces the reliance on personal experience of construction personnel, stabilizes the quality of boiler chemical cleaning, and meets the cleaning technical requirements for unit maintenance.

[0016] 4. This invention uses citric acid as the main cleaning agent. Citric acid is an organic acid, which is less harmful to personnel and equipment and is suitable for various boilers and metal materials. Compared with hydrochloric acid, EDTA and other agents, it can avoid excessive corrosion and toxic waste liquid problems, and can also significantly reduce the cost of agents and overall construction. Through precise control of process parameters, it can effectively remove rust and oxide scale inside the boiler, form a dense passivation film on the metal surface, improve boiler thermal efficiency, and reduce the probability of boiler tube rupture failure. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the dispensing tank body of the present invention; Figure 2 This is a schematic diagram of the filter tank structure of the present invention; Figure 3 This is a connection diagram of the support plate and U-shaped frame of the present invention; The components are: 1-dosage tank body, 2-support leg, 3-drain pipe, 4-valve, 5-first support block, 6-support plate, 7-support rod, 8-U-shaped frame, 9-filter tank, 10-filter screen, 11-second support block, 12-insertion frame. Detailed Implementation

[0018] The invention will be further explained and described below with reference to the accompanying drawings: Example 1, see Figures 1-3 A power plant boiler cleaning device includes a dosing tank body 1, the top of which is an open structure; four sets of support legs 2 are welded and fixed at the four corners of the bottom of the dosing tank body 1, and the dosing tank body 1 is lifted off the ground by the support legs 2, so as to reserve installation and maintenance space for the bottom drain pipe 3 and the external pipeline; an L-shaped drain pipe 3 is installed at the center of the bottom of the dosing tank body 1, and a valve 4 is installed at the outer end of the drain pipe 3. The output end of the drain pipe 3 is connected to the inlet of the cleaning pump through a first corrugated pipe.

[0019] A second support block 11 is welded to the outer wall at both ends of the dosing tank body 1. The brackets 12 set at both ends of the top surface of the filter tank 9 are placed on the second support block 11, so that the filter tank 9 is suspended in the inner cavity of the dosing tank body 1. The overall height of the filter tank 9 is set to two-thirds of the height of the inner cavity of the dosing tank body 1. The bottom of the filter tank 9 is equipped with a filter screen 10. The filter screen 10 is made of 316L stainless steel that is resistant to citric acid, which can withstand the corrosion of acidic liquid during the cleaning process and intercept and filter solid impurities such as oxide scale and welding slag in the return sewage.

[0020] The first support block 5 is welded to the outer walls of both sides of the main body 1 of the dosing tank. A screw is vertically welded to the bottom of the support plate 6. The screw passes through the first support block 5 downward and is locked and fixed by a matching nut, so that the support plate 6 can be detached and assembled. A through hole is opened on the plate body of the support plate 6. A U-shaped frame 8 is vertically inserted through the support plate 6. A limit nut is threaded on the lower end of the U-shaped frame 8. The U-shaped frame 8 serves as a pipe clamp component to hold and fix the second corrugated pipe on the boiler return side. During operation, the second corrugated pipe is inserted into the inside of the U-shaped frame 8 and the bottom limit nut is tightened to clamp the corrugated pipe, thereby offsetting the impact force brought by the return fluid, preventing the return pipeline from reciprocating, jumping and shaking during operation, and ensuring that the outlet of the return pipeline is always aligned with the top of the filter tank 9, and the sewage falls stably into the range of the filter screen 10.

[0021] The cleaning and commissioning method for the power plant boiler cleaning device described above includes the following steps: S1. Construction preparation stage: First, determine the scope of boiler cleaning and calculate the overall water volume of the cleaning system. Based on the calculated water volume, prepare the required amount of cleaning agent and supporting consumables. Then, conduct on-site verification of the formal system and temporary cleaning system, complete system isolation, test point debugging, temporary pipeline layout, and install monitoring pipes and corrosion indicator plates on the circulation loop.

[0022] Assemble and debug the dosing tank body 1: Place the brackets 12 at both ends of the filter tank 9 onto the upper surface of the second support block 11 at the opening of the dosing tank body 1 to complete the hanging and positioning of the filter tank 9; insert the second corrugated pipe of the boiler return pipeline into the U-shaped bracket 8 on the support plate 6, and tighten the limit nut to clamp and fix the return pipeline; connect the drain pipe 3 of the dosing tank body 1 to the boiler inlet pipeline through the cleaning pump to complete the connection of the entire closed-loop circulation circuit. After all pipelines are connected, open the valve 4 of the drain pipe 3 and check each pipeline joint for leakage. Then, a small-scale pre-pickling test was conducted: boiler water-cooled wall tubes were selected and processed into tube samples and indicator plates, which were weighed and their surface areas were calculated; solutions containing 0.3% corrosion inhibitor and 3% citric acid without corrosion inhibitor were prepared, with the pH controlled between 3.5 and 4.0; the tube samples and indicator plates were immersed in the two solutions respectively and kept at a constant temperature of 90°C for 4 hours; after drying, they were weighed, the total corrosion amount and corrosion rate were calculated, and the corrosion inhibitor parameters and cleaning process control parameters suitable for the on-site working conditions were determined.

[0023] S2. Specific cleaning procedures: ① System water flushing: Pass demineralized water through the system at room temperature for 24-48 hours, using twice the system water volume, and continue flushing until the flushing water is clear and transparent, with no visible solid impurities. ②Alkaline washing: Prepare an alkaline washing solution with a mass fraction of 0.05-0.1% hydrogen peroxide, using water equal to the system water volume, and circulate for 3 hours at room temperature, followed by soaking for 8 hours; ③ Water rinsing after alkaline washing: Rinse with demineralized water at room temperature for 6-8 hours, using water volume equal to 1 times the system water volume, and test the effluent until the hydrogen peroxide content is zero; ④ Fill the superheater with protective fluid: Prepare a protective fluid with a concentration of hydrazine of 200-300 ppm and a pH of 9.5-10, fill the superheater with the protective fluid, and complete the 1MPa pressure increase sealing test; ⑤ Simulated circulating heating test: introduce demineralized water to establish a closed-loop system, raise the temperature to 90℃, and thoroughly check all joints and welds in the system to eliminate potential leakage risks; ⑥ Citric acid pickling: Prepare a pickling solution with 2%-4% citric acid, 0.3%-0.4% corrosion inhibitor, and 0.05%-0.1% hydrazine. Adjust the pH to 3.5-4.0 using ammonia. Control the system temperature to 85-95℃ and circulate the solution for 6-8 hours. Maintain the Fe³⁺ content in the solution below 300 mg / L throughout the process. During the pickling operation, the boiler return liquid carrying oxide scale and welding slag falls into the filter tank 9. Solid impurities are trapped by the filter screen 10. After filtration, the clean solution falls back to the bottom of the mixing tank 1 and is then transported to the cleaning pump via the drain pipe 3, where it is recycled back to the boiler heating surface. When the Fe³⁺ content exceeds the limit, a reducing agent is added promptly for adjustment. ⑦ Water-top acid flushing: Use 50-80℃ demineralized water for water-top acid flushing for 4-6 hours, with a water volume of 1.5 times the system water volume, and control the pH of the drain outlet to be >4.0 and the total iron content to be <50mg / L; ⑧ Rinsing: Prepare a rinsing solution with citric acid mass fraction of 0.1%-0.3% and corrosion inhibitor mass fraction of 0.05%-0.1%. Adjust the pH to 3.5-4.0 with ammonia water. Circulate and rinse for 2-3 hours at 50-80℃. Control the total iron content of the system to be less than 300ppm. The refluxed wastewater generated during rinsing also falls into filter tank 9 to complete filtration and impurity removal. ⑨ Passivation: After rinsing, adjust the pH of the system to 9.5-10.0 with ammonia water, add hydrogen peroxide to make the system concentration reach 0.3%-0.5%, and passivate by circulation at 45-55℃ for 4-6 hours.

[0024] S3. Post-cleaning quality inspection: After all cleaning processes are completed, remove any deposits and debris from inside the boiler, and inspect the pre-installed monitoring pipes by cutting them open. Acceptance control indicators are: corrosion rate < 8 g / m²·h, total corrosion < 80 g / m²; the metal substrate surface is clean, free from pitting and secondary corrosion, and the passivation film is continuous and dense. If the boiler cannot be put into operation within 20 days after cleaning, shutdown protection will be carried out using ammonia-hydrazine protective solution or nitrogen pressure maintenance.

[0025] S4. Wastewater Treatment: Collect the cleaning wastewater generated from each cleaning process, add a strong oxidant to the wastewater, and aerate and stir for no less than 2 hours to achieve COD degradation; add solid caustic soda or lime slurry to adjust the pH of the wastewater to 6-9; add 10 mg / L coagulant and 5 mg / L coagulant aid in sequence to carry out coagulation and sedimentation; then send it to a screw press dewatering machine to complete solid-liquid separation; the separated clean water is recycled and reused, and the generated mud cake is sent to the coal yard for incineration or transported off-site for disposal in accordance with the specifications.

[0026] S5. Online maintenance of the dosing tank: During the continuous cleaning operation, when there is a lot of residue accumulation on the surface of the filter screen 10, which affects the flow of the medicine, loosen the limiting nut of the U-shaped frame 8 to release the clamp on the return bellows; use the hanging rope to hook the bracket 12 to lift the filter tank 9 off the dosing tank body 1 as a whole, and clean the solid impurities trapped by the filter screen 10; after the impurities are cleaned, lift the filter tank 9 back into place, re-lock the U-shaped frame 8, and restore the system circulation.

[0027] This invention utilizes a U-shaped frame on the support plate to clamp and position the return corrugated pipe, effectively counteracting pipe movement caused by liquid flow impact and stabilizing the falling position of the waste liquid. By incorporating a hanging filter tank 9 and filter screen 10 within the chemical preparation tank, it intercepts oxide scale and welding slag impurities in the circulating chemical solution, protecting the cleaning pump. Furthermore, the filter tank 9 can be lifted out to clean the filter residue without emptying the chemical solution, shortening downtime. Simultaneously, by determining suitable process parameters through small-scale corrosion tests before construction, and in conjunction with a complete citric acid cleaning process, quality inspection, and waste liquid disposal procedure, this invention reduces overall chemical costs, minimizes the risk of toxic waste liquid and excessive corrosion, efficiently removes deposits from the boiler inner wall and forms a good passivation film, improving boiler operating safety and thermal efficiency. It also reduces reliance on personnel experience, simplifies waste liquid treatment, and enables resource-based disposal. The overall solution is highly feasible on-site and conducive to the standardized promotion and application of chemical cleaning work for power plant boilers.

Claims

1. A boiler cleaning device for power plants, comprising a dosing tank body (1), wherein the top of the dosing tank body (1) is open, characterized in that: The medicine dispensing tank body (1) is provided with support legs (2) at the four corners of the bottom. The medicine dispensing tank body (1) is provided with a drain pipe (3) at the center of the bottom. The drain pipe (3) is provided with a valve (4) at the outer end. The medicine dispensing tank body (1) is provided with a filter tank (9). The filter screen (10) is provided at the bottom of the filter tank (9). The top surface of the filter tank (9) is provided with a bracket (12) at both ends. The bracket (12) is hung on both ends of the medicine dispensing tank body (1). The outer walls on both sides of the medicine dispensing tank body (1) are provided with a first support block (5). The first support block (5) is provided with a support plate (6). A U-shaped frame (8) runs through the support plate (6). A limit nut is connected to the bottom of the U-shaped frame (8) by a thread.

2. The power plant boiler cleaning device according to claim 1, characterized in that: The overall height of the filter tank (9) is two-thirds of the height of the inner cavity of the drug preparation tank.

3. The power plant boiler cleaning device according to claim 1, characterized in that: The outer walls at both ends of the dispensing tank body (1) are provided with second support blocks (11), and the outer end of the insert (12) passes through the second support block (11).

4. The power plant boiler cleaning device according to claim 1, characterized in that: The bottom center of the support plate (6) is provided with a screw rod, which passes through the first support block (5) and is fixed by a matching nut.

5. The power plant boiler cleaning device according to claim 1, characterized in that: The filter screen (10) is made of 316L stainless steel that is resistant to citric acid.

6. The power plant boiler cleaning device according to claim 1, characterized in that: The drain pipe (3) is an L-shaped pipe. The outer end of the drain pipe (3) is connected to a cleaning pump through a first corrugated pipe. The output end of the cleaning pump is connected to the boiler inlet pipe through a pipe to transport the filtered cleaning solution into the boiler heating surface. A return pipe is set at the bottom of the boiler heating surface. A second corrugated pipe is connected at the outlet of the return pipe. The second corrugated pipe is fixed on the support plate (6) by a U-shaped frame (8) so that all the boiler return sewage falls into the filter screen (10) to complete the circulation filtration.

7. A cleaning and commissioning method for a power plant boiler cleaning device according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Construction Preparation: ① Determine the scope of boiler cleaning, calculate the water volume of the cleaning system, and prepare the required amount of cleaning agent and supporting consumables based on the calculation results; ② Conduct on-site verification of the formal system and temporary cleaning system, complete system isolation, test point debugging, temporary pipeline layout, and install monitoring pipes and corrosion indicator plates; ③ Complete the assembly and debugging of the dosing tank body (1): Place the bracket (12) of the filter tank (9) on the upper end face of the second support block (11) at the opening of the dosing tank body (1); connect the dosing tank body (1) to the boiler cleaning closed circulation loop, so that the drain pipe of the dosing tank is connected to the boiler liquid inlet pipe through the cleaning pump, and the boiler return pipe outlet is arranged on the support plate (6) and clamped and fixed by the U-shaped bracket (8) and the matching thread; ④ After all pipelines are connected, open the drain valve and check that there are no leaks at each connection point; conduct a small-scale pre-pickling test to simulate the on-site cleaning conditions, determine the corrosion rate, and determine the on-site cleaning process control parameters. S2. Specific cleaning procedures ① System water flushing: Use demineralized water at room temperature to flush for 24-48 hours, using twice the water volume, until the flushing water is clear, transparent and free of impurities; ② Alkaline washing: Prepare an alkaline washing solution containing 0.05-0.1% hydrogen peroxide, circulate for 3 hours at room temperature and soak for 8 hours, using water equal to the volume of water. ③ Rinse with water after alkaline washing: Rinse with deionized water at room temperature for 6-8 hours, using 1 volume of water, until the hydrogen peroxide content is 0. ④ Superheater protection fluid: Prepare a protection fluid with a hydrazine concentration of 200-300 ppm and a pH of 9.5-10, fill it into the superheater and complete the 1MPa pressure increase sealing test; ⑤ Simulated circulating heating test: Establish circulation of demineralized water, raise the temperature to 90℃, and end the test after checking that there are no leaks in the system. The water consumption is 1 times the water volume. ⑥ Prepare a pickling solution with 2%-4% citric acid, 0.3%-0.4% corrosion inhibitor, and 0.05%-0.1% hydrazine. Adjust the pH to 3.5-4.0 with ammonia water. Control the cleaning temperature at 85-95℃ and circulate the solution for 6-8 hours. Throughout the process, control the Fe³⁺ content to be less than 300 mg / L. During the pickling process, the wastewater carrying oxide scale and welding slag from the boiler return flows into the filter tank of the mixing tank. Solid impurities are intercepted by the filter screen, and the filtered clean solution is returned to the bottom of the mixing tank for reuse. If the Fe³⁺ content exceeds the limit, add a reducing agent to adjust it. ⑦ Water-top acid flushing: Use 50-80℃ demineralized water for water-top acid flushing for 4-6 hours, with a water volume of 1.5 times the system water volume, and control the pH of the drain outlet to be >4.0 and the total iron content to be <50mg / L; ⑧ Rinsing: Prepare a rinsing solution with citric acid (0.1%-0.3% by mass) and corrosion inhibitor (0.05%-0.1% by mass). Adjust the pH to 3.5-4.0 with ammonia. Rinse for 2-3 hours at 50-80℃. Control the total iron content of the system to be less than 300ppm. The rinsing return wastewater is also filtered through the chemical preparation tank to remove impurities. ⑨ Passivation: After rinsing, adjust the pH of the system to 9.5-10.0 with ammonia water, add hydrogen peroxide to make its concentration reach 0.3%-0.5%, and passivate by circulation at 45-55℃ for 4-6 hours; S3. Quality inspection after cleaning Remove deposits and debris from inside the boiler and cut the monitoring tube for inspection; control the acceptance indicators: corrosion rate < 8g / m²·h, total corrosion < 80g / m²; the metal substrate surface is clean, without pitting or secondary rust, and the passivation film is continuous and dense; if the boiler cannot be put into operation within 20 days after cleaning, use ammonia-hydrazine protective solution or nitrogen pressure to implement shutdown protection. S4. Waste liquid disposal Collect the cleaning wastewater generated in each process, add a strong oxidant and aerate and stir for no less than 2 hours to degrade COD; add solid caustic soda or lime slurry to adjust the pH to 6-9; add 10 mg / L coagulant and 5 mg / L coagulant aid in sequence to complete coagulation and sedimentation. After solid-liquid separation by a screw press dewatering machine, the separated clean water is recycled and reused, while the resulting mud cake is sent to the coal yard for incineration or transported away for disposal in accordance with regulations. S5, Online maintenance of the dosing tank During the cleaning operation, when there is a lot of residue on the surface of the filter screen, loosen the clamping limit of the U-shaped frame on the insert frame, use the hoisting rope to hook the insert frame to lift the filter tank as a whole away from the dosing tank body, and clean the solid impurities trapped by the filter screen; after the impurities are cleaned, lift the filter tank back into place, re-lock the U-shaped frame, and restore the system circulation.

8. The cleaning and commissioning method of a power plant boiler cleaning device according to claim 7, characterized in that, The small-scale experiment before pickling in step S1 includes the following operations: selecting boiler water-cooled wall tubes, processing them into tube samples and indicator plates, weighing and calculating the surface area; preparing 3% citric acid solutions (pH 3.5-4.0) containing 0.3% corrosion inhibitor and without corrosion inhibitor; immersing the tube samples and indicator plates into the two solutions respectively, maintaining a constant temperature of 90℃ for 4 hours; removing them, drying and weighing them, calculating the total corrosion and corrosion rate, and determining the appropriate parameters for the corrosion inhibitor.

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