Anti-oxidation and anti-corrosion multi-stage combined protection method for coal-fired boiler

Abstract

The invention belongs to the technical field of safe operation of equipment, and provides a multistage combined protection method for oxidation resistance and corrosion resistance of a coal-fired boiler, which comprises the following steps: carrying out supersonic electric arc spraying treatment on a water-cooled wall tube, carrying out scouring-resistant coating on flue gas and an ash conveying channel, and transforming a deslagging system; by performing supersonic electric arc spraying on the water cooling wall tube, non-stop of corrosion, thinning and tube explosion of the water cooling wall tube in a combustion area can be basically eradicated, support and wear parts of a coal pulverizing system and an air and smoke system are coated, the wear of a smoke and air support and the workload of maintenance, repair and reinforcement are prevented, the leakage phenomenon caused by long-term wear is eliminated, and the service life of the water cooling wall tube is prolonged. A powerful guarantee is provided for long-term stable and safe operation of the boiler, and wide popularization significance is achieved in the industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of safe operation of equipment, and relates to the protection of boiler equipment in coal-fired power plants. Specifically, it is a multi-stage combined protection method for anti-oxidation and anti-corrosion of coal-fired boilers. Background Art

[0002] In China, coal-fired power generation accounts for about 70% of the total national power generation, and the coal used for power generation accounts for 1 / 3 of the coal consumption. In recent years, with the shortage of coal resources, in order to save costs, the quality of power coal in coal-fired power plants has gradually deteriorated. For example, the quality of the coal entering the furnace of the boilers of our company's 2×300MW units has deviated far from the designed coal type. The ash content has increased from the original designed 25% to 40%, and the calorific value has decreased from the original 4,682 kcal to 3,200 kcal. The combustion conditions of the company have changed greatly, which not only intensifies the erosion and abrasion of the coal pulverizing, air and flue gas, and dry slag removal systems of the boiler, but also causes serious consequences such as high-temperature oxidation, hot corrosion, erosion and coking of the "four tubes" of the boiler heating surface, including water wall tubes, superheater tubes, reheater tubes, and economizer tubes, resulting in frequent boiler tube bursts, greatly affecting the safe and stable operation of the unit. Although a lot of work has been done in preventing and controlling high-temperature corrosion problems, including increasing the oxygen content in the flue gas of the boiler; optimizing the operation of the coal pulverizing system to reduce the fineness of pulverized coal; opening the secondary air volume adjustment baffle in the middle and lower parts; strengthening the coal blending work of fuel and reducing the sulfur content of coal. But the effect on reducing the high-temperature corrosion of the water wall tubes is not very obvious.

[0003] Specifically, when a coal-fired boiler burns in the furnace area, a large amount of ash particles, sulfates, and a small amount of hydrogen sulfide, chlorates, etc. will be generated. Among them, sulfates will be in a molten state above 550°C, attach to the ash particles and adhere to the water wall tubes, and corrode them; hydrogen sulfide belongs to a strong acid and reacts directly with the water wall tubes; chlorates will show obvious corrosion when the oxygen content in the furnace is above 0.6%, and above 300°C, for every 50°C increase, its corrosion intensity will double, and the corrosion rate of the water wall tubes will reach 0.7 - 1.0 mm / year; the particle flow velocity in the furnace and flue gas passage will reach 8 m / s, which will scour and cut the flue gas and ash conveying passage. Under such working conditions, the corrosion rate of the flue gas and ash conveying passage will reach 1.2 - 3.0 mm / year.

[0004] The dry slag removal system mainly consists of equipment such as a slag well, an extrusion head, a steel belt machine, a cleaning chain, a slag crusher, a buffer hopper, and a bucket elevator, and is responsible for the transmission, treatment, and storage of large slag blocks and a small amount of fine ash after the combustion of the coal-fired boiler. Under high load, ash accumulates and blocks under the cleaning chain, coking occurs, the scraper is burned out, and the slag crusher is severely worn, which seriously threatens the surrounding electrical equipment and the tooth plate of the slag crusher, and seriously affects the safe and stable operation of the coal-fired boiler. Summary of the Invention

[0005] The object of the present invention is to provide a multi - level combined protection method for anti - oxidation and anti - corrosion of coal - fired boilers, realizing anti - oxidation and anti - corrosion of the heating surface, coal pulverizing system and components of the air and flue gas system of coal - fired boilers, and solving the problems of tube explosion, coking and wear of coal - fired boiler equipment caused by deteriorated coal quality.

[0006] The technical solution adopted by the present invention to achieve the above object is as follows: A multi - level combined protection method for anti - oxidation and anti - corrosion of coal - fired boilers, comprising: S1. Carry out supersonic arc spraying treatment on the water - wall tubes; S11. Carry out two - stage sandblasting pretreatment on the water - wall tubes; First, use quartz sand to remove rust roughly, and then use emery to roughen the surface to Rz40 - 80um; S12. Carry out supersonic arc spraying treatment; Use the arc burning at the end of the wire to melt the uniformly fed wire, with the arc - zone temperature of 5000 - 6000 °C; through air cooling, the supersonic air flow accelerated by the Laval nozzle atomizes the melted wire into fine - grained and evenly - distributed particles, and sprays them onto the water - wall tubes for spraying.

[0007] S13. Carry out sealing treatment on the coating after spraying; Use silicone plus aluminum powder as the sealing agent to carry out sealing treatment on the sprayed water - wall tubes.

[0008] Furthermore, the wire adopts a high - chromium nickel alloy wire, with a Cr content of 40 - 45% and a Ni content greater than 45%, a bonding strength ≥ 60 MPa, and a thermal expansion coefficient of 6.8×10⁻ 6 / °C.

[0009] Furthermore, the spraying speed is stable and uniform, controlled at 100 - 150 mm / s, the spraying angle is 60 - 90 degrees in the direction of the perpendicular line to the surface of the water - wall tube by the spray gun, the spraying distance is 150 - 200 mm between the spray gun and the surface of the water - wall tube, the spraying area adopts circuitous lapping, and a special person is arranged to feed the wire during spraying to avoid wire breakage.

[0010] S2. Carry out erosion - resistant coating on the flue gas and ash - conveying channels; S21. High - temperature flue - gas area: Carry out anti - abrasion coating on the ammonia injection grid, air pre - heater housing, and supports of the tail flue. For the flue above the air pre - heater, high - temperature cast stone wear - resistant tiles are pasted on the windward side, and low - temperature cast stone tiles are pasted on the windward side in the low - temperature section at the rear of the air pre - heater.

[0011] S22. In the ash - conveying pipelines and elbows area, integrally welded wear - resistant ceramic parts are embedded; S23. Pulverizing pipeline and elbow area: For the large flat areas before and after the inlets of the coal feeding pipes on both sides of the ball mill, the outlets of the pulverized coal pipes, the inlets of the separators, the outlets of the pulverized coal pipes of the separators, and the volumetric air ducts, wear-resistant ceramic tiles are pasted; for the small-space corner parts, wear-resistant mortar is applied; for the inner part of the pulverized coal pipe elbows, ceramic tiles are pasted, and for the outer part, patching and grouting are used.

[0012] S3. Modify the slag discharge system; S31. Adopt a split slag dropping structure, and adjust the climbing angle of the cleaning chain of the slag crusher from 32° to 20°; S32. Change the material of the dry slag discharge tooth plate to high chromium cast iron.

[0013] The beneficial effects of the present invention are as follows: By performing supersonic arc spraying on the water-cooled wall tubes, it is basically possible to prevent the non-stop operation caused by corrosion and thinning of the water-cooled wall tubes in the combustion area and bursting of the tubes. For the supporting and worn parts of the pulverizing system and the flue gas and air system, patching and coating are carried out, which prevents the wear of the flue gas and air support and the workload of maintenance patching and reinforcement, eliminates the leakage phenomenon caused by long-term wear, provides a strong guarantee for the long-term stable and safe operation of the boiler, and has broad promotion significance in the industry. Description of the Drawings

[0014] Figure 1 It is a schematic diagram of the split slag dropping structure and the tooth plate modification structure in the present invention; Detailed Embodiments

[0015] The following further describes the present invention in conjunction with embodiments: A multi-stage combined protection method for anti-oxidation and anti-corrosion of a coal-fired boiler, including: S1. Perform supersonic arc spraying treatment on the water-cooled wall tubes; Since the current anti-corrosion measures are not very effective in reducing the high-temperature corrosion of the water-cooled wall tubes, the "anti-wear, anti-corrosion, and anti-coking" supersonic arc spraying composite coating technology in the boiler burner area is introduced to perform spraying treatment on the water-cooled wall tubes.

[0016] S11. First, perform sandblasting pretreatment on the water-cooled wall tubes twice; First, use 80# quartz sand to roughly remove rust and paint. The quality requirement for the abrasive used in sandblasting is to use first-grade quartz sand, with the sand grain size being 1 - 2 mm (10 - 20 mesh), and the cleanliness should reach Sa3.0 level. Then, use 16# emery for sandblasting to achieve surface roughening. When the sandblasting is completed, the surface should reach Rz40 - 80 um. After the two sandblasting pretreatments, spraying should be carried out as soon as possible. In sunny or non-humid weather, the interval time should not exceed 12 hours. In rainy, humid or salt fog atmospheres, the interval time should not exceed 2 hours. During sandblasting and spraying, shields (such as canvas) should be used around the workpieces in a timely manner to prevent the workpieces from being recontaminated (such as dust brought by sandblasting and spraying in nearby workstations). Sandblasting is generally selected at night when there is no other work in the furnace, and the dust removal facilities should be put into operation, and the induced draft fan should be started to cooperate to eliminate the dust in the furnace. There should be no oil, water and other contaminants in the compressed air, and the pressure should be maintained at 0.3 - 0.66 MPa.

[0017] S12. Supersonic arc spraying treatment; The wire fed evenly is melted by the arc burning at the end of the wire, and the temperature in the arc zone is 5000 - 6000 °C. Through air cooling, the supersonic air flow accelerated by the Laval nozzle atomizes the melted wire into fine and evenly distributed particles, which are sprayed onto the water-cooled wall tubes for spraying. The supersonic air flow can make the micro-melted particles fine, uniform and high-speed, improve the bonding strength and cohesion strength of the coating, and reduce the porosity of the coating. At the same time, it makes the residence time of the particles in the air shorter before deposition, resulting in a lower oxide content in the coating. The wire used is a high-chromium nickel alloy wire, with a Cr content of 40 - 45% and a Ni content of more than 45%, the bonding strength ≥ 60 MPa, and the thermal expansion coefficient 6.8×10⁻ 6 / °C. The high-nickel chromium alloy coating has a good anti-corrosion effect. In a sulfur-containing atmosphere, the corrosion resistance of nickel is more obvious, and chromium can produce an oxide film Cr2O3 on the surface of the coating to prevent nickel from dissolving into nickel sulfide. The expansion coefficient of the sprayed coating material is close to that of the 20G material of the water-cooled wall tube, so that the coating will not fall off under the action of alternating thermal stress. It has the characteristics of anti-corrosion, anti-oxidation, high temperature resistance, good ductility, strong erosion resistance and low price. After spraying, atomic diffusion occurs between the coating and the surface of the base metal to form a bond, and the coating forms a rough surface, which is convenient for connecting with the working layer and improves the bonding strength of the coating.

[0018] The coating should be evenly transitioned from thick to thin to the substrate, with a transition zone of 150 mm - 200 mm. The appearance of the coating should be complete, with a uniform and continuous surface, no cracks, peeling, delamination and edge warping and other defects. The thickness of the arc spraying coating is 0.3 mm - 0.8 mm, and the thickness of the supersonic flame spraying coating is 0.2 mm - 0.3 mm.

[0019] The hardness of the arc spraying coating is 50HRc - 55HRc, and the hardness of the high-velocity oxy-fuel spraying coating is 55HRc - 58HRc. The bonding strength of the arc spraying coating should be not less than 30MPa, and the bonding strength of the high-velocity oxy-fuel spraying coating should be not less than 50MPa.

[0020] The porosity of the arc spraying coating should be not more than 5%, and the porosity of the high-velocity oxy-fuel spraying coating should be not more than 1%. The wear resistance of the arc spraying coating should be 15 times that of Q235 steel, and the wear resistance of the high-velocity oxy-fuel spraying coating should be 30 times that of Q235 steel.

[0021] The spraying speed is stable and uniform, controlled at 100 - 150mm / s. The spraying angle is 60 - 90 degrees with respect to the perpendicular line of the surface of the water-cooled wall tube. The spraying distance is 150 - 200mm from the surface of the water-cooled wall tube. The spraying area adopts a circuitous overlap, and a special person is assigned to feed the wire during spraying to avoid wire breakage.

[0022] For anti-wear spraying, attention should be paid to the surface acceptance before spraying and the spraying environment, as well as the spraying speed, spraying angle, spraying distance, and selection of spraying materials. A trial spraying should be carried out outside the furnace before spraying. In addition, pay attention to the spraying thickness requirements, and it should be sprayed 3 - 5 times with a thickness maintained at 0.4 - 0.6mm.

[0023] S13. After spraying, perform a sealing treatment on the coating; After the surface spraying is completed, the sealing treatment must be carried out as soon as possible. During the sealing process, it should be evenly coated without any coating exposure, and the thickness should be not less than 0.5mm. Use silicone plus aluminum powder (FM99) as the sealing agent to seal the sprayed water-cooled wall tube.

[0024] S2. Apply erosion-resistant coating to the flue gas and ash conveying channels; Since the particle flow velocity in the furnace and flue gas channels can reach 8m / s, it will erode and cut the flue gas and ash conveying channels. Under this working condition, the corrosion rate of the flue gas and ash conveying channels will reach 1.2 - 3.0 mm / year. In addition, the pulverizing system also belongs to the area with severe particle wear. Different materials and methods of coating application are used for different worn parts: First, for the high-temperature flue gas duct area: Paste cast stone wear-resistant tiles on the support surface, and use modified ceramic patches in the low-temperature section; Check and analyze the internal support parts of the flue gas duct, and apply anti-wear coating to the supports of the ammonia injection grid, air preheater housing, and tail flue. Analyze according to the temperature and anti-wear degree. Paste high-temperature cast stone wear-resistant tiles on the windward side of the flue above the air preheater, and paste low-temperature cast stone tiles on the windward side of the low-temperature section behind the air preheater to ensure the safety of the flue gas duct support.

[0025] Second, for the ash conveying pipeline and its elbow area: Inlay integral welded wear-resistant ceramic parts; For the worn parts and reasons, wear-resistant ceramic parts are embedded in the key worn parts, effectively enhancing the wear resistance of the easily worn and eroded parts, greatly extending the service life of the key worn parts, improving the safety and reliability of the system operation, and achieving a double improvement in life and safety.

[0026] Third, for the pulverizing pipelines and their elbow areas: on the one hand, optimize the operation adjustment and regular cleaning and maintenance, and on the other hand, improve the wear resistance of the equipment itself. First, determine the inlet of the coal pipes on both sides of the ball mill, the outlet of the powder pipes, the inlet of the separator, the coal powder pipes at the outlet of the separator, and the front and back of the capacity air ducts as the key anti-wear parts, and then process these parts separately. For large-space flat parts, paste anti-wear ceramic sheets, and for small-space corner parts, apply wear-resistant cement; for the most severely worn elbow parts of the coal powder pipes, paste ceramic sheets inside and use a combination of patching and grouting outside to achieve the safe operation of the anti-wear of the pulverizing system.

[0027] S3. Transform the slag discharge system; The deterioration of coal quality and coking has an adverse impact on the dry slag discharge system. The climbing angle of the cleaning chain of the slag crusher in the traditional slag discharge system is 32°. The cleaning chain pressure plate and the traction motor are subjected to large forces, resulting in serious wear, a long conveying process, ash accumulation and blockage at the bottom, deformation and burning of the scraper, and serious coking of the slag, which seriously troubles the safe and stable operation of the boiler. In view of the current problems, transform the slag discharge system: First, adopt a split slag dropping structure, as Figure 1 shown, adjust the climbing angle of the cleaning chain 1 of the slag crusher from 32° to 20° as Figure 1 shown, reduce the force on the cleaning chain pressure plate and the lifting force of the motor, increase the output of the cleaning chain, and effectively solve the problem of frequent failures caused by ash accumulation at the bottom of the transition section and climbing section of the steel belt conveyor; Second, based on the actual situation of coal quality and coking, change the material of the dry slag discharge tooth plate to high-chromium cast iron Cr15Mo3, with a 70% improvement in wear resistance, improve the processing performance and redundancy settings of the slag crusher, and achieve a double improvement in performance and emergency response capabilities.

[0028] The above method is applied to the coal-fired boilers of the company's 2×300MW units. During each major overhaul (A repair), supersonic arc spraying is carried out on the water-cooled wall tubes of the units, and patching is applied to the supporting and worn parts of the coal pulverizing system and the flue gas and air system, achieving good results. After spraying the water-cooled wall tubes in the combustion area, the coating porosity is <1%, the bonding strength is increased by 50%, and the nano high-temperature coating FM99 can withstand temperatures up to 1800°C, basically eliminating the unscheduled shutdowns caused by corrosion and thinning of the water-cooled wall tubes in the combustion area. In the supporting parts of the flue gas duct system, it prevents the wear of the flue gas and air supports and reduces the workload of maintenance patching and reinforcement. The wear-resistant life of the flue duct supports is extended from 1 year to 5 years, and the life of the ash conveying elbows is extended by 20 times. The phenomenon of leakage caused by long-term wear at the coal inlet of the coal pulverizing system and the inlet of the separator is completely eliminated, and the comprehensive effect is excellent, providing a strong guarantee for the long-term stable and safe operation of the boiler.

[0029] 1. Coating performance: The corrosion rate of the water-cooled wall tubes is reduced to 0.3 mm / a, and the coating thickness of 0.5 mm remains without peeling for 3 years; there is no leakage phenomenon caused by wear in the flue gas and air system and the coal pulverizing system within 3 years. 2. Dry slag discharge: The failure rate of the slag crusher is reduced by 85%, and the single cleaning time is shortened by 60%. 3. Economic benefits: The comprehensive annual economic benefits are: 6.048 + 2.88 + 2.1 = 11.028 million yuan.

[0030] ① The power generation benefit of failure losses: The annual failure hours of a single boiler are calculated as 288h (based on 3 failures, each failure requires 96h of emergency repair). It is 60.48 million kWh per year. Calculated at a profit of 0.05 yuan per kWh, the annual power generation profit of a single unit can be increased by 6.048 million yuan.

[0031] ② The saved fuel cost: Each unscheduled shutdown and startup is calculated based on 60 tons of diesel, and each ton of diesel is calculated at 8000 yuan. The number of unscheduled shutdowns is calculated as 6 times, saving a total of 2.88 million yuan in fuel.

[0032] ③ The emergency repair and maintenance cost: Each emergency repair is calculated at 350,000 yuan, and the number of unscheduled shutdowns is 6 times, totaling 2.1 million yuan.

[0033] The total comprehensive annual economic benefits are: 6.048 + 2.88 + 2.1 = 11.028 million yuan.

[0034] The application of the method of the present invention can, on the one hand, greatly reduce the unscheduled shutdown loss cost by 11.028 million yuan, and on the other hand, greatly improve the safe operation level of the unit, reducing the maintenance risks of emergency repair and daily maintenance.

Claims

1. A multi-stage combined protection method for anti-oxidation and anti-corrosion of coal-fired boilers, characterized in that: Including: S1. Conduct supersonic arc spraying treatment on the water-cooled wall tubes; S11. Conduct two sandblasting pretreatment operations on the water-cooled wall tubes; First, use quartz sand to roughly remove rust, and then use emery to roughen the surface to Rz40 - 80um; S12. Conduct supersonic arc spraying treatment; Use the arc burning at the end of the wire to melt the evenly fed wire, with the arc zone temperature at 5000 - 6000°C; through air cooling, the supersonic airflow accelerated by the Laval nozzle atomizes the melted wire into fine and evenly distributed particles, which are sprayed onto the water-cooled wall tubes for spraying; S13. Conduct hole sealing treatment on the coating after spraying; Use silicone plus aluminum powder as the hole sealing agent to conduct hole sealing treatment on the sprayed water-cooled wall tubes; S2. Conduct erosion-resistant coating on the flue gas and ash conveying channels; S3. Modify the slag discharge system; S31. Adopt a split slag falling structure, and adjust the climbing angle of the cleaning chain of the slag crusher from 32° to 20°; S32. Change the material of the dry slag discharge tooth plate to high chromium cast iron.

2. The multi-stage combined protection method for anti-oxidation and anti-corrosion of a coal-fired boiler according to claim 1, wherein: The wire material is made of a high chromium-nickel alloy wire with a Cr content of 40-45% and a Ni content of more than 45%, a bonding strength of ≥60 MPa, and a thermal expansion coefficient of 6.8×10⁻ 6 / °C.

3. The multi - stage combined protection method for antioxidant and anti - corrosion of a coal - fired boiler according to claim 1, characterized in that: The spraying speed is stable and uniform, controlled at 100 - 150mm / s, the spraying angle is 60 - 90 degrees in the direction perpendicular to the surface of the water-cooled wall tube by the spray gun, the spraying distance is 150 - 200mm between the spray gun and the surface of the water-cooled wall tube, the spraying area adopts circuitous overlapping, and a special person is arranged to feed the wire during spraying to avoid wire breakage.

4. The multi - stage combined protection method for anti - oxidation and anti - corrosion of a coal - fired boiler according to claim 1, characterized in that: The specific content of S2 is as follows: S21. High-temperature flue gas area: Conduct anti-wear coating on the support of the ammonia injection grid, air preheater housing, and tail flue. The flue on the upper side of the air preheater is pasted with high-temperature cast stone wear-resistant tiles on the windward side, and the low-temperature section at the rear of the air preheater is pasted with low-temperature cast stone tiles on the windward side; S22. Embedded integral welded wear-resistant ceramic parts in the ash conveying pipeline and elbow area; S23. Pulverizing pipeline and elbow area: For the large-space flat parts before and after the inlet of the coal feeding pipe on both sides of the ball mill, the outlet of the powder discharging pipe, the inlet of the separator, the outlet of the separator coal powder pipe, and the capacity air duct, paste anti-wear ceramic sheets, and apply wear-resistant cement in the small-space corner parts; paste ceramic sheets inside the elbow part of the coal powder pipe and conduct patching and grouting outside.

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