Method for optimizing material selection and construction process of coal-fired boiler water-cooled wall coating

Abstract

The invention relates to a method for optimizing material selection and construction processes of a coal-fired boiler water-cooled wall coating, and belongs to the technical field of special coatings for coal-fired boiler water-cooled wall surfaces. According to the method, the corrosion type and the distribution area of the boiler are accurately identified through corrosion diagnosis analysis in the step S1, and an accurate basis is provided for coating material selection; through the multi-dimensional screening criterion and the composite structure design in the step S2, optimal matching of the coating material is achieved; through the optimized spraying process and laser remelting treatment in the step S3, it is ensured that the coating has excellent bonding strength and compactness; s4, establishing a correlation model of coating performance and environmental protection requirements through performance and environmental safety detection in the step S4; through engineering application verification in the step S5, the long-term reliability of the coating is inspected under the actual operation condition; and finally, forming a continuously improved technical closed loop through data feedback and iterative optimization in the step S5.

Description

Technical Field

[0001] This invention relates to the field of coatings for water-cooled walls of coal-fired boilers, and in particular to a method for optimizing the selection of materials and construction process for water-cooled wall coatings of coal-fired boilers. Background Technology

[0002] As coal-fired power generating units develop towards high-parameter, large-capacity ultra-supercritical systems, the high-temperature corrosion and slagging problems of boiler water-cooled walls are becoming increasingly prominent. Existing protection technologies face severe challenges: the application of low-NOx combustion technology leads to a strongly reducing atmosphere in the near-wall region of the furnace, significantly increasing the concentration of corrosive media such as H2S; the implementation of coal blending strategies has exacerbated fluctuations in the quality of coal entering the furnace, further worsening the corrosive environment. Traditional coating technologies have significant shortcomings: material selection relies heavily on experience, lacking specificity for complex corrosion mechanisms; construction processes are rigid and fail to effectively coordinate with material properties; performance evaluation systems are incomplete, with a serious disconnect between laboratory data and field performance; and environmental risks are completely lacking. Furthermore, the contradictions between corrosion protection and multiple objectives such as combustion efficiency and pollutant control are difficult to reconcile.

[0003] Chinese Patent Publication No. CN117801577A discloses a coating for water-cooled walls of coal-fired boilers, its preparation method, and its application. The coating comprises nano-tungsten powder, tungsten carbide, rare earth composites, sodium borate, potassium chromate, rock pitch, binder, modifier, dispersant, defoamer, curing agent, and solvent. When this coating is fused onto the water-cooled wall of a coal-fired boiler, the resulting coating exhibits good interfacial bonding with the water-cooled wall composite coating material, low porosity, and prevents the penetration of corrosive gases and liquids, thus solving the corrosion problem of the water-cooled wall and preventing a decrease in coating hardness and wear resistance. This coating is not easily worn or damaged during long-term use, improving the high-temperature resistance, hardness, corrosion resistance, and wear resistance of the boiler water-cooled wall, effectively extending its service life and ensuring the safe and stable operation of the coal-fired boiler. However, this solution still suffers from the problems of existing coal-fired boiler water-cooled wall protection technologies, which suffer from poor adaptability, short lifespan, and easy early failure of coatings in actual complex corrosive environments due to the lack of targeted material selection, rigid process parameters, imperfect performance evaluation system and lack of environmental risk consideration. Furthermore, it is difficult to balance the protective effect with environmental protection requirements. Summary of the Invention

[0004] Therefore, the present invention provides a method for optimizing the material selection and construction process of water-cooled wall coatings for coal-fired boilers, in order to overcome the problems of existing coal-fired boiler water-cooled wall protection technologies, which suffer from poor adaptability, short lifespan, easy early failure, and difficulty in balancing protective effect and environmental protection requirements due to the lack of targeted material selection, rigid process parameters, imperfect performance evaluation system and lack of environmental risk consideration.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for optimizing the selection of materials and construction process of water-cooled wall coatings for coal-fired boilers, comprising: Step S1: Conduct corrosion diagnosis and analysis: Collect relevant boiler data, identify the dominant corrosion types and areas, obtain corrosion samples and analyze them, and convert the diagnosis results into quantitative requirements for coating performance. Step S2: Screening of coating materials and structural design: Based on the quantitative requirements, establish multi-dimensional screening criteria, screen coating materials from the material library, and design composite coating structures to obtain composite coatings; Step S3: Implement the coating process: perform surface pretreatment on the composite coating, prepare the coating using supersonic flame spraying, and perform post-treatment by laser remelting to obtain the processed composite coating; Step S4: Conduct performance and environmental safety testing: Perform performance simulation testing and water pollution correlation analysis on the processed composite coating, obtain the performance simulation test results and water pollution correlation analysis results, and establish a performance-environment correlation model; Step S5: Conduct engineering application verification: Apply the coating at the boiler site and monitor the operating performance data and environmental emission data; Step S6: Perform data feedback and system iterative optimization: Compare and analyze the performance simulation test results and water pollution correlation analysis results with the operation performance monitoring data and environmental emission monitoring data to identify failure mechanisms, and optimize the coating material selection and coating processing technology through feedback loops.

[0006] Furthermore, step S1 specifically includes the following sub-steps: Step S11: Collect boiler design parameters, historical operating data and maintenance data to obtain macroscopic analysis data. Based on the macroscopic analysis data, preliminarily determine the dominant corrosion type of the boiler and the area corresponding to the dominant corrosion type of the boiler. Step S12: Cut out the area corresponding to the dominant corrosion type of the boiler, obtain corrosion samples, analyze the corrosion samples, and obtain corrosion diagnosis results; Step S13: Convert the corrosion diagnosis results into quantitative requirements for coating performance.

[0007] Furthermore, step S12 also includes: By analyzing the chemical composition at the bottom of the sediment layer, the H2S concentration in the reducing flue gas atmosphere at the water-cooled wall adhesion point was determined.

[0008] Furthermore, step S2 specifically includes the following sub-steps: Step S21: Based on the quantitative requirements of the coating performance obtained in step S13, establish a multi-dimensional screening criterion that includes corrosion resistance, thermal conductivity, thermal shock resistance, adhesion, and potential environmental impact. Step S22: Based on the multi-dimensional screening criteria, screen coating materials from the material library constructed by collecting existing patents and research results. The material library includes NiCrTi alloys, nano high-entropy ceramics, and RSI series functional coatings. Step S23: Design a composite structure for the selected coating materials to obtain a composite coating. Specifically, a composite structure of a metal substrate and an inorganic surface layer is adopted. The metal substrate is made of NiCrTi alloy to provide bonding force, and the inorganic surface layer is made of nano-high entropy ceramic to provide a high inert barrier.

[0009] Furthermore, the composite coating also includes a transition layer disposed between the metal substrate and the ceramic surface layer. The transition layer is a gradient composite layer of NiCrTi alloy and 20% Al2O3 with a thickness of 50 μm.

[0010] Further, step S3 includes: Step S31: Sandblast the composite coating with copper slag sand, control the air pressure to 0.6MPa, and process until the pipe wall exposes a metallic luster and the roughness Rz=65±5μm to obtain the sandblasted composite coating. Step S32: Apply a supersonic flame spraying process to the sandblasted composite coating to obtain the sprayed composite coating. The process parameters of the supersonic flame spraying process are: kerosene flow rate 22L / h, oxygen flow rate 750m³ / h, spraying distance 300mm, and powder feed rate 45g / min. Step S33: Perform laser remelting on the sprayed composite coating to obtain the processed composite coating. The laser remelting parameters are: laser power 2.5kW, scanning speed 8mm / s, and spot diameter 3mm.

[0011] Further, step S4 includes: Step S41: Perform performance simulation testing on the processed composite coating and obtain the performance simulation test results; Step S42: Perform water pollution correlation analysis based on the performance simulation test results to obtain the water pollution correlation analysis results; Step S43: Establish a performance-environment correlation model based on the performance simulation test results and the water pollution correlation analysis results.

[0012] Furthermore, the performance simulation test in step S41 includes an ash deposition corrosion test: a simulated ash slag with a specific composition is coated on the coating surface and tested at 650°C for 200 hours. The composition of the simulated ash slag is Fe2O3 30%, Al2O3 20%, SiO2 25%, CaO 15%, and Na2SO4 10% by mass percentage.

[0013] Further, step S5 includes: Step S51: Apply the processed coating to the burner area of ​​the 1,000 MW ultra-supercritical boiler and reserve an adjacent uncoated area for comparison. Step S52: During the operation of the 1,000 MW ultra-supercritical boiler, monitor the H2S concentration and tube wall temperature in the coated area and the comparison area to obtain the first monitoring data; during shutdown maintenance, check the macroscopic morphology and coking status of the coating and measure the tube wall thinning to obtain the second monitoring data. Output the first and second monitoring data as operating performance monitoring data. Step S53: During the boiler shutdown and cleaning of the 1,000 MW ultra-supercritical unit boiler, the discharged wastewater is sampled and tested to obtain the third monitoring data. The requirements are that the suspended solids concentration is <50 mg / L and the Ni and Cr heavy metal ion concentrations are both <1 mg / L. The third monitoring data is output as environmental emission monitoring data.

[0014] Furthermore, the data feedback and iterative optimization of the coating system in step S6 specifically includes: Step S61: Compare and analyze the operational performance monitoring data and environmental emission monitoring data with the performance simulation test results and water pollution correlation analysis results in step S4 to identify the dominant failure mechanism of the processed coating in actual service. Step S62: If it is found that the coating has insufficient resistance to slag erosion in a specific area, the feedback is sent to the material screening stage of step S2, requiring the addition of 5% SiC to the surface layer to improve the erosion resistance; if the coating adhesion is found to be insufficient, the feedback is sent to the process optimization stage of step S3, adjusting the spraying parameters or introducing post-treatment processes; until the coating life is expected to reach more than 4 years.

[0015] Compared with existing technologies, the method for optimizing the material selection and construction process of water-cooled wall coatings for coal-fired boilers described in this invention has the following beneficial effects: The method accurately identifies the corrosion type and distribution area of ​​the boiler through corrosion diagnosis analysis, providing a precise basis for coating material selection; it achieves optimal matching of coating materials through multi-dimensional screening criteria and composite structure design; it ensures excellent bonding strength and density of the coating through optimized spraying process and laser remelting treatment; it establishes a correlation model between coating performance and environmental protection requirements through performance and environmental safety testing; it verifies the long-term reliability of the coating under actual operating conditions through engineering application verification; and finally, it forms a continuous improvement technology closed loop through data feedback and iterative optimization. This method achieves full-process quality control from corrosion diagnosis, material selection, process optimization to engineering verification, significantly improving the protective effect, service life, and environmental compatibility of the coating, providing a reliable guarantee for the safe, economical, and environmentally friendly operation of coal-fired boilers. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the method for optimizing the material selection and construction process of water-cooled wall coatings in coal-fired boilers, as described in this embodiment. Detailed Implementation

[0017] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0018] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0019] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0020] Please see Figure 1 As shown, this is a flowchart illustrating the method for optimizing the material selection and construction process of water-cooled wall coatings in this embodiment of a coal-fired boiler. The method includes: Step S1: Conduct corrosion diagnosis and analysis: Collect relevant boiler data, identify the dominant corrosion types and areas, obtain corrosion samples and analyze them, and convert the diagnosis results into quantitative requirements for coating performance. Step S2: Screening of coating materials and structural design: Based on the quantitative requirements, establish multi-dimensional screening criteria, screen coating materials from the material library, and design composite coating structures to obtain composite coatings; Step S3: Implement the coating process: perform surface pretreatment on the composite coating, prepare the coating using supersonic flame spraying, and perform post-treatment by laser remelting to obtain the processed composite coating; Step S4: Conduct performance and environmental safety testing: Perform performance simulation testing and water pollution correlation analysis on the processed composite coating, obtain the performance simulation test results and water pollution correlation analysis results, and establish a performance-environment correlation model; Step S5: Conduct engineering application verification: Apply the coating at the boiler site and monitor the operating performance data and environmental emission data; Step S6: Perform data feedback and system iterative optimization: Compare and analyze the performance simulation test results and water pollution correlation analysis results with the operation performance monitoring data and environmental emission monitoring data to identify failure mechanisms, and optimize the coating material selection and coating processing technology through feedback loops.

[0021] Specifically, this method is applied to the high-temperature corrosion protection of water-cooled walls in coal-fired boilers in the thermal power generation field. It is particularly suitable for water-cooled wall protection in ultra-supercritical boilers under low-NOx combustion and coal co-firing conditions. The method accurately identifies the corrosion type and distribution area of ​​the boiler through corrosion diagnosis analysis, providing a precise basis for coating material selection. Through multi-dimensional screening criteria and composite structure design, it achieves optimal matching of coating materials. Through optimized spraying process and laser remelting treatment, it ensures that the coating has excellent bonding strength and density. Through performance and environmental safety testing, it establishes a correlation model between coating performance and environmental protection requirements. Through engineering application verification, it tests the long-term reliability of the coating under actual operating conditions. Finally, through data feedback and iterative optimization, it forms a continuous improvement technology closed loop. This method realizes full-process quality control from corrosion diagnosis, material selection, process optimization to engineering verification, significantly improving the protective effect, service life and environmental compatibility of the coating, and providing reliable protection for the safe, economical and environmentally friendly operation of coal-fired boilers.

[0022] Specifically, step S1 includes the following sub-steps: Step S11: Collect boiler design parameters, historical operating data and maintenance data to obtain macroscopic analysis data. Based on the macroscopic analysis data, preliminarily determine the dominant corrosion type of the boiler and the area corresponding to the dominant corrosion type of the boiler. Step S12: Cut out the area corresponding to the dominant corrosion type of the boiler, obtain corrosion samples, analyze the corrosion samples, and obtain corrosion diagnosis results; Step S13: Convert the corrosion diagnosis results into quantitative requirements for coating performance.

[0023] Specifically, the design parameters include boiler capacity, steam parameters, and burner arrangement; the historical operating data includes records of coal sulfur and chlorine content, load curves, and wall temperature monitoring records; the maintenance data includes annual pipe replacement records and corrosion pit depth measurement data; the dominant corrosion type is determined by analyzing the composition and distribution pattern of corrosion products, including sulfide corrosion, chloride corrosion, or a combination of both; the corrosion samples are taken from the most severely corroded area and are 20mm × 20mm in size; the analysis includes metallographic observation, scanning electron microscopy energy dispersive spectroscopy, and X-ray diffraction phase analysis; the corrosion diagnosis results include the layered structure of corrosion products, the distribution of major corrosion elements, and corrosion interface characteristics; the quantitative requirements include temperature resistance level, sulfide corrosion resistance rate, chlorine corrosion resistance rate, thermal expansion coefficient matching range, and minimum bonding strength value.

[0024] Specifically, step S12 further includes: By analyzing the chemical composition at the bottom of the sediment layer, the H2S concentration in the reducing flue gas atmosphere at the water-cooled wall adhesion point was determined.

[0025] Specifically, the bottom of the deposition layer refers to the corrosion product layer that is closely attached to the metal composite coating; the chemical composition analysis is achieved through electron probe microanalysis; and the H2S concentration inversion is based on FeS / FeS2 equilibrium thermodynamic calculations.

[0026] Specifically, step S2 includes the following sub-steps: Step S21: Based on the quantitative requirements of the coating performance obtained in step S13, establish a multi-dimensional screening criterion that includes corrosion resistance, thermal conductivity, thermal shock resistance, adhesion, and potential environmental impact. Step S22: Based on the multi-dimensional screening criteria, screen coating materials from the material library constructed by collecting existing patents and research results. The material library includes NiCrTi alloys, nano high-entropy ceramics, and RSI series functional coatings. Step S23: Design a composite structure for the selected coating materials to obtain a composite coating. Specifically, a composite structure of a metal substrate and an inorganic surface layer is adopted. The metal substrate is made of NiCrTi alloy to provide bonding force, and the inorganic surface layer is made of nano-high entropy ceramic to provide a high inert barrier.

[0027] Specifically, the corrosion resistance requirement is that the coating has a corrosion rate of <0.1 mm / year at 650℃ and in a 0.3% H2S atmosphere; the thermal conductivity requirement is that the coating has a thermal conductivity >15 W / (m·K); and the thermal shock resistance requirement is that the coating withstands 30 cycles at 650℃. No peeling or cracking after room temperature thermal cycling; the adhesion requirement is a coating bond strength ≥ 50 MPa; the potential environmental impact requirement is that the heavy metal content in the coating material complies with RoHS standards, and the leaching concentration in water meets the GB 8978-1996 Class I emission standard; the material library is constructed by systematically searching domestic and foreign patent databases and academic journals, and includes material composition, performance parameters, and application cases; the NiCrTi alloy refers to a nickel-based alloy with a chromium content of 25%–35% and a titanium content of 3%–8%; the nano high-entropy ceramic refers to a nanocrystalline ceramic material composed of five or more metal elements, with a grain size of 50–100 nm; the RSI series functional coating refers to a silicide-based protective coating prepared by reaction sintering, the metal underlayer thickness is 100–200 μm, and it is prepared by supersonic flame spraying; the inorganic surface layer thickness is 50–100 μm, and it is prepared by atmospheric plasma spraying.

[0028] Specifically, the composite coating also includes a transition layer disposed between the metal substrate and the ceramic surface layer. The transition layer is a gradient composite layer of NiCrTi alloy and 20% Al2O3 with a thickness of 50 μm.

[0029] Specifically, the gradient composite layer achieves a smooth transition in the coefficient of thermal expansion through a composition gradient design, with its Al2O3 content gradually changing from 5% in the bottom layer to 20% in the top layer.

[0030] Specifically, step S3 includes: Step S31: Sandblast the composite coating with copper slag sand, control the air pressure to 0.6MPa, and process until the pipe wall exposes a metallic luster and the roughness Rz=65±5μm to obtain the sandblasted composite coating. Step S32: Apply a supersonic flame spraying process to the sandblasted composite coating to obtain the sprayed composite coating. The process parameters of the supersonic flame spraying process are: kerosene flow rate 22L / h, oxygen flow rate 750m³ / h, spraying distance 300mm, and powder feed rate 45g / min. Step S33: Perform laser remelting on the sprayed composite coating to obtain the processed composite coating. The laser remelting parameters are: laser power 2.5kW, scanning speed 8mm / s, and spot diameter 3mm.

[0031] Specifically, the copper slag sand has a particle size range of 0.5–1.0 mm and a Mohs hardness ≥7; the roughness is measured using a stylus profilometer; the supersonic flame spraying uses a JP-5000 system with a powder particle size of 15–45 μm and nitrogen as the carrier gas; the laser remelting uses a fiber laser with argon as the protective atmosphere and an overlap rate of 50%.

[0032] Specifically, step S4 includes: Step S41: Perform performance simulation testing on the processed composite coating and obtain the performance simulation test results; Step S42: Perform water pollution correlation analysis based on the performance simulation test results to obtain the water pollution correlation analysis results; Step S43: Establish a performance-environment correlation model based on the performance simulation test results and the water pollution correlation analysis results. Specifically, the performance simulation testing includes analyzing the coating's microstructure and phase composition using scanning electron microscopy and X-ray diffraction; conducting a high-temperature vulcanization test under the conditions of 650℃ and 0.3% H2S atmosphere for 500 hours, requiring a coating weight gain of <2.0 mg / cm²; and conducting a thermal shock test, requiring the coating to withstand 30 cycles of 650℃ room temperature thermal cycling without peeling. The high-temperature vulcanization test uses a tube furnace with a gas composition of N2S. 2%～ 0.3%H2S-3%CO-2%H2; the heating rate of the thermal shock test was 50℃ / min, and forced air cooling was used for cooling. The water pollution correlation analysis was designed by Boao Kuo, and the coating samples were immersed in solutions with pH=4, 7, and 10 for 30 days. The Ni concentration <1.0mg / L and Cr concentration <1.0mg / L in the leachate were determined by inductively coupled plasma mass spectrometry. The liquid-solid ratio of the leaching experiment was 20:1, the temperature was maintained at 25±2℃, and the mixture was stirred once every 24 hours. The establishment of the performance-environment correlation model included correlating the leaching experiment results with the electrochemical performance of the coating, requiring the coating self-corrosion potential >0V (SCE). The electrochemical performance test used a three-electrode system, with a saturated calomel electrode as the reference electrode and a scan rate of 1mV / s.

[0033] Specifically, the performance simulation test in step S41 includes an ash deposition corrosion test: a simulated ash slag with a specific composition is coated on the coating surface and tested at 650°C for 200 hours. The composition of the simulated ash slag is Fe2O3 30%, Al2O3 20%, SiO2 25%, CaO 15%, and Na2SO4 10% by mass percentage.

[0034] Specifically, the ash coating amount in the ash deposition corrosion test was 20 mg / cm², and the test atmosphere was N₂. 2%～ 5%O 2%～ 0.1% SO2.

[0035] Specifically, step S5 includes: Step S51: Apply the processed coating to the burner area of ​​the 1,000 MW ultra-supercritical boiler and reserve an adjacent uncoated area for comparison. Step S52: During the operation of the 1,000 MW ultra-supercritical boiler, monitor the H2S concentration and tube wall temperature in the coated area and the comparison area to obtain the first monitoring data; during shutdown maintenance, check the macroscopic morphology and coking status of the coating and measure the tube wall thinning to obtain the second monitoring data. Output the first and second monitoring data as operating performance monitoring data. Step S53: During the boiler shutdown and cleaning of the 1,000 MW ultra-supercritical unit boiler, the discharged wastewater is sampled and tested to obtain the third monitoring data. The requirements are that the suspended solids concentration is <50 mg / L and the Ni and Cr heavy metal ion concentrations are both <1 mg / L. The third monitoring data is output as environmental emission monitoring data.

[0036] Specifically, the area of ​​the processed coating applied to the burner area of ​​the 1,000 kW ultra-supercritical boiler is ≥50 m², the monitoring cycle covers a complete overhaul cycle, the wall-mounted H2S concentration is monitored using an electrochemical sensor with a measurement accuracy of ±1 ppm, the pipe wall thinning is measured using an ultrasonic thickness gauge with an accuracy of ±0.1 mm, and the wastewater sampling is performed according to GB / T 8978 standard, with a detection frequency of once every 4 hours.

[0037] Specifically, the data feedback and coating system iterative optimization in step S6 includes: Step S61: Compare and analyze the operational performance monitoring data and environmental emission monitoring data with the performance simulation test results and water pollution correlation analysis results in step S4 to identify the dominant failure mechanism of the processed coating in actual service. Step S62: If it is found that the coating has insufficient resistance to slag erosion in a specific area, the feedback is sent to the material screening stage of step S2, requiring the addition of 5% SiC to the surface layer to improve the erosion resistance; if the coating adhesion is found to be insufficient, the feedback is sent to the process optimization stage of step S3, adjusting the spraying parameters or introducing post-treatment processes; until the coating life is expected to reach more than 4 years.

[0038] Specifically, the comparative and correlation analysis employs principal component analysis and multiple regression analysis to establish a quantitative mapping relationship between laboratory data and field data. The dominant failure mechanism is determined by analyzing the microstructure, composition distribution, and phase composition of the failure area, including mechanisms such as sulfide corrosion, slag erosion, and thermal fatigue cracking. The criterion for insufficient slag erosion resistance is: a coating thickness loss rate > 0.1 mm / 100 h in the ash deposition corrosion test. The addition of 5% SiC to the surface layer refers to adding 5% SiC by mass to the high-entropy ceramic coating, with a particle size of... The coating consists of 1-3 μm silicon carbide particles; the criterion for insufficient coating adhesion is tensile bond strength < 30 MPa; the adjustment of spraying parameters includes increasing the oxygen flow rate of supersonic flame spraying from 750 m³ / h to 800 m³ / h and decreasing the powder feed rate from 45 g / min to 40 g / min; the post-treatment process refers to adding a vacuum heat treatment at 800℃ for 2 hours after spraying; the coating life is expected to be calculated using a Weibull distribution model corrected based on field data, requiring a life of not less than 4 years when the reliability reaches 90%.

[0039] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for optimizing the material selection and construction process of water wall coating of coal-fired boilers, characterized by, The method comprises the following steps: Step S1, performing corrosion diagnosis analysis: collecting boiler-related data, identifying the dominant corrosion type and area, obtaining corrosion samples and analyzing them, and converting the diagnosis results into quantitative requirements for coating performance; Step S2, performing coating material screening and structure design: based on the quantitative requirements, a multi-dimensional screening criterion is established, coating materials are screened from a material library, and a composite coating structure is designed to obtain a composite coating; Step S3, implementing coating processing technology: the composite coating is subjected to surface pretreatment, and the coating is prepared by using a supersonic flame spraying process, and is subjected to post-treatment by laser remelting to obtain a processed composite coating; Step S4, performance and environmental safety detection: performance simulation detection and water pollution correlation analysis are performed on the processed composite coating to obtain performance simulation detection results and water pollution correlation analysis results, and a performance-environment correlation model is established; Step S5, engineering application verification: the coating is applied on the boiler site, and operation performance monitoring data and environmental emission monitoring data are monitored; Step S6, data feedback and system iterative optimization: the performance simulation detection results and water pollution correlation analysis results are compared with the operation performance monitoring data and environmental emission monitoring data, the failure mechanism is identified, and the coating material screening and coating processing technology are optimized through a feedback loop.

2. The method for optimizing the material selection and construction process of water wall coating of coal-fired boilers as claimed in claim 1, wherein, The step S1 specifically comprises the following sub-steps: Step S11, collecting the design parameters, historical operation data and maintenance data of the boiler to obtain macroscopic analysis data, and preliminarily judging the dominant corrosion type of the boiler and the area corresponding to the dominant corrosion type of the boiler based on the macroscopic analysis data; Step S12, cutting the area corresponding to the dominant corrosion type of the boiler to obtain corrosion samples, and analyzing the corrosion samples to obtain corrosion diagnosis results; Step S13, converting the corrosion diagnosis results into quantitative requirements for coating performance.

3. The method for optimizing the material selection and construction process of water wall coating of coal-fired boilers as claimed in claim 2, wherein, The step S12 further comprises: The H2S concentration in the reducing flue gas atmosphere at the water wall attachment is inversely calculated by analyzing the chemical composition at the bottom of the deposition layer.

4. The method for optimizing the material selection and construction process of water wall coating of coal-fired boilers as claimed in claim 1, wherein, The step S2 specifically comprises the following sub-steps: Step S21, based on the quantitative requirements for coating performance obtained in step S13, a multi-dimensional screening criterion including corrosion resistance, thermal conductivity, thermal shock resistance, adhesion and potential environmental impact is established; Step S22, according to the multi-dimensional screening criterion, coating materials are screened from a material library constructed by collecting existing patents and research results, and the material library includes NiCrTi alloy, nano high-entropy ceramic and RSI series functional coating; Step S23, the screened coating materials are designed for composite structure to obtain a composite coating, specifically a composite structure of a metal bottom layer and an inorganic surface layer, wherein the metal bottom layer is selected from NiCrTi alloy to provide bonding force, and the inorganic surface layer is selected from nano high-entropy ceramic to provide a high inert barrier.

5. The method for optimizing the material selection and construction process of water wall coating of coal-fired boilers as claimed in claim 4 wherein, The composite coating further comprises a transition layer arranged between the metal bottom layer and the ceramic surface layer, and the transition layer is a gradient composite layer of NiCrTi alloy and 20% Al2O3, with a thickness of 50μm.

6. The method for optimizing the material selection and application process of water wall coating for coal-fired boilers as claimed in claim 1, wherein, The step S3 comprises: Step S31, the composite coating is sandblasted with copper slag sand, the air pressure is controlled to be 0.6 MPa, and the treatment is performed until the metal luster of the pipe wall is exposed and the roughness Rz is 65±5 μm, so that the sandblasted composite coating is obtained; Step S32, the sandblasted composite coating is subjected to a high-velocity oxygen fuel spraying process, so that the sprayed composite coating is obtained. The process parameters of the high-velocity oxygen fuel spraying process are as follows: kerosene flow 22 L / h, oxygen flow 750 m³ / h, spraying distance 300 mm, and powder feeding rate 45 g / min; Step S33, the sprayed composite coating is subjected to laser remelting, so that the processed composite coating is obtained. The laser remelting parameters are as follows: laser power 2.5 kW, scanning speed 8 mm / s, and spot diameter 3 mm.

7. The method for optimizing the material selection and application process of water wall coating for coal-fired boilers as claimed in claim 1, wherein, The step S4 comprises: Step S41, the processed composite coating is subjected to performance simulation detection, so that performance simulation detection results are obtained; Step S42, water pollution correlation analysis is performed based on the performance simulation detection results, so that water pollution correlation analysis results are obtained; Step S43, a performance-environment correlation model is established according to the performance simulation detection results and the water pollution correlation analysis results.

8. The method for optimizing the material selection and construction process of water wall coating of coal-fired boilers as claimed in claim 7 wherein, The performance simulation detection in the step S41 comprises a soot deposition corrosion test: a simulated ash of a specific composition is coated on the surface of the coating, and the test is performed at 650 DEG C for 200 h. The composition of the simulated ash is as follows: Fe2O3 30%, Al2O3 20%, SiO2 25%, CaO 15%, and Na2SO4 10% in terms of mass percentage.

9. The method for optimizing the material selection and application process of water wall coating for coal-fired boilers as claimed in claim 1, wherein, The step S5 comprises: Step S51, the processed coating is applied to the burner area of a million-kilowatt ultra-supercritical unit boiler, and an adjacent non-coated area is reserved as a comparison; Step S52, during the operation of the million-kilowatt ultra-supercritical unit boiler, the wall H2S concentration and the pipe wall temperature of the coated area and the comparison area are monitored, so that first monitoring data are obtained; during the shutdown maintenance, the macroscopic morphology of the coating, the coking condition and the pipe wall thinning amount are checked, so that second monitoring data are obtained; the first monitoring data and the second monitoring data are taken as operation performance monitoring data and are outputted; Step S53, during the boiler shutdown cleaning of the million-kilowatt ultra-supercritical unit boiler, the discharged wastewater is sampled and detected, so that third monitoring data are obtained. The suspended matter concentration is required to be less than 50 mg / L, and the Ni and Cr heavy metal ion concentrations are required to be less than 1 mg / L. The third monitoring data are taken as environmental emission monitoring data and are outputted.

10. The method for optimizing the material selection and application process of water wall coating for coal-fired boilers as claimed in claim 1, wherein, The data feedback and coating system iterative optimization in the step S6 specifically comprise: Step S61, the operation performance monitoring data and the environmental emission monitoring data are compared and correlated with the performance simulation detection results and the water pollution correlation analysis results in the step S4, so that the dominant failure mechanism of the processed coating in actual service is identified; Step S62, if it is identified that the anti-slag erosion performance of the coating in a specific area is insufficient, the feedback is given to the material screening stage of the step S2, and 5% SiC is required to be added to the surface layer to improve the anti-erosion performance; if it is detected that the adhesion of the coating is insufficient, the feedback is given to the process optimization stage of the step S3, and the spraying parameters are adjusted or a post-treatment process is introduced; until the coating life is expected to be more than 4 years.

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