Composite coating for water-cooled wall

Abstract

The invention provides a composite coating for a water cooling wall, and relates to the technical field of anticorrosive paints.The composite coating comprises a bottom coating, a middle coating and a face coating; for the middle coating, the ratio of the number of particles with the size larger than 0.5 mm to the total number of particles is larger than or equal to 80%; part of particles of the face coating are embedded into particle gaps of the middle coating to form a fusion structure, and the face coating is tightly connected with the middle coating through the fusion structure. According to the invention, the large-particle middle coating is added into the composite coating to provide skeleton support for the face coating, and after the thickness of the face coating is reduced, the face coating in the particle gaps of the middle coating still exerts the anti-coking performance of the coating, so that the corrosion resistance of the composite coating is greatly improved, and the service life of the composite coating is prolonged. The comprehensive performance and the service life of the composite coating are prolonged.

Description

Technical Field

[0001] The present application relates to the technical field of anti-corrosion coatings, and in particular to a composite coating for water-cooled walls. Background Art

[0002] The water-cooled walls of coal-fired boilers face high-temperature corrosion and coking problems, which may be caused by changes in coal types or ultra-low emission requirements, posing hidden dangers to the safe operation of the boiler. In order to deal with these problems, the measures usually taken include adjusting the combustion angle, optimizing the air-fuel ratio, and changing the coal type, but these methods cannot completely solve the problem. In addition to these solutions, another commonly used solution is to spray a coating on the heating surface to solve the corrosion and coking problems of the heating surface.

[0003] In coating technology, the construction process has an important influence on the performance of the coating. Common spraying methods are: Thermal spraying: usually uses arc spraying technology, suitable for high temperature environments. Cold spraying: using high temperature paint, spraying at a lower temperature. Composite coating: combining the advantages of thermal spraying and cold spraying, first perform thermal spraying as the base layer, and then spray the cold spray surface layer to form a composite coating. There are still many defects in the spraying process of composite coatings in the prior art, resulting in low comprehensive performance of the coating after spraying, which needs to be improved to solve the problems of boiler corrosion and coking. Summary of the invention

[0004] In view of the above problems, the present application provides a composite coating for a water-cooled wall, which is used to solve the technical problem of low comprehensive performance of the composite coating in the prior art.

[0005] To achieve the purpose of this application, this application provides the following technical solutions:

[0006] The present invention provides a composite coating for spraying a water-cooled wall, wherein the composite coating comprises a bottom coating, an intermediate coating and a surface coating; for the intermediate coating, the number of particles with a size greater than 0.5 mm accounts for greater than or equal to 80% of the total number of particles in the intermediate coating; the bottom coating, the intermediate coating and the surface coating are sequentially applied on a substrate of the water-cooled wall, some particles of the surface coating are embedded in the particle gaps of the intermediate coating to form a fusion structure, and the surface coating is tightly connected to the intermediate coating through the fusion structure.

[0007] Preferably, the coating thickness of the intermediate coating is greater than or equal to 0.5 mm.

[0008] Preferably, the spraying material of the intermediate coating includes a nickel-based alloy metal material, and the spraying method is arc spraying.

[0009] Preferably, the voltage during arc spraying of the intermediate coating is 32-40V, the current is 180-240A; the spraying distance is 50-80cm, and the moving speed of the arc spray gun head during spraying is 80-120cm per second.

[0010] Preferably, the spraying material of the bottom coating includes a nickel-based alloy metal material, and the spraying method is arc spraying.

[0011] Preferably, the voltage during arc spraying of the bottom coating is 32-50V, the current is 150-160A; the spraying distance is 25-45cm, and the moving speed of the arc spray gun head during spraying is 30-50cm per second.

[0012] Preferably, among the particles of the bottom coating, the number of particles with a size less than 30 μm accounts for greater than or equal to 80%, and the number of particles with a size of 40 μm accounts for 15%; the particle porosity of the bottom coating is less than 3%; and the coating thickness of the bottom coating is greater than or equal to 60 μm.

[0013] Preferably, the coating thickness of the facial coating is greater than or equal to 60 μm; the spraying material of the facial coating includes one or more of silicate-based coating, phosphate-based coating, silica sol-based coating and organosilicon high-temperature resistant coating.

[0014] The composite coating for water-cooled wall provided by the present application provides skeleton support for the surface coating by adding a large-particle intermediate coating, so that the bottom coating and the surface coating are more closely connected. When the thickness of the surface coating is reduced, the surface coating in the gap between the intermediate coating particles still exerts the anti-coking performance of the coating, thereby greatly improving the corrosion resistance of the composite coating, thereby extending the comprehensive performance and service life of the composite coating, and further solving the problems of water-cooled wall corrosion and coking. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation to the present application.

[0016] Figure 1 A schematic diagram of a composite coating structure for a water-cooled wall provided in an embodiment of the present application;

[0017] Figure 2 A schematic diagram of the water-cooled wall spraying area provided in an embodiment of the present application;

[0018] Reference numerals:

[0019] 1. Four-corner tangential boiler burner; 2. Water-cooled wall; 3. First area; 4. Second area; 5. Third area. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of this application, unless otherwise specified, "plurality" means two or more.

[0022] Coking of boiler water-cooled walls will aggravate boiler corrosion in actual operation, and boiler corrosion will further lead to coking; spraying composite coating is an important solution to boiler coking and corrosion. This embodiment provides a composite coating for water-cooled walls, which provides skeleton support for the surface coating by adding a large-particle intermediate coating, so that the bottom coating and the surface coating are more closely connected, which can greatly improve the corrosion resistance of the composite coating, thereby extending the comprehensive performance and service life of the composite coating.

[0023] according to Figure 1 As shown, the embodiment of the present application provides a composite coating for spraying water-cooled walls, and the composite coating includes a bottom coating, an intermediate coating, and a surface coating. The composite coating is sprayed on the heating surface of the boiler water-cooled wall, and the intermediate coating and the bottom coating are the same spraying material. In this embodiment, the bottom coating is a dense layer for corrosion resistance, the intermediate coating is a large particle layer for corrosion resistance, and the surface coating is a ceramic coating.

[0024] Optionally, the spraying material of the intermediate coating includes a nickel-based alloy metal material or other amorphous alloy material; the spraying material of the bottom coating includes a nickel-based alloy metal material or other amorphous alloy material; the spraying material of the surface coating includes one or more of silicate-based coating, phosphate-based coating, silica sol-based coating and organic silicon high-temperature resistant coating. In this embodiment, preferably, the bottom coating and the intermediate coating are made of 45CT alloy material; the surface coating is made of ceramic material.

[0025] Specifically, boiler anti-corrosion thermal spraying generally uses 45CT alloy material (a high-density Cr2O3 oxide film can be formed on the coating surface at high temperature. This metal material has super high resistance to high-temperature corrosion, including resistance to fuel dust or atmosphere corrosion containing sulfur, sodium or chlorine). The main components of 45CT alloy material are nickel (≥52%), chromium (42.0-46.0%) and titanium (0.3-1.0%).

[0026] Preferably, the intermediate coating is sprayed by arc spraying. The specific spraying method is as follows: the voltage during spraying is 32-40V, the current is 180-240A; the spraying distance is 50-80cm, and the moving speed of the arc spray gun head during spraying is 80-120cm per second. For the intermediate coating, the number of particles with a particle size greater than 0.5mm accounts for greater than or equal to 80% of the total number of particles, and the coating thickness is greater than or equal to 0.5mm. Among them, when the number of particles with a size greater than 1mm accounts for 10%, the coating thickness is greater than or equal to 1mm. The bottom coating, the intermediate coating and the face coating are sequentially applied to the substrate of the water-cooled wall, and the intermediate coating provides a skeleton support for the face coating; and the intermediate coating and the bottom coating are obtained by different processing methods of the same metal material, so that some particles of the face coating form a fusion structure by embedding the particle gaps of the intermediate coating, and the face coating is tightly connected to the intermediate coating through the fusion structure, thereby achieving a closer connection with the bottom coating. When the thickness of the surface coating is reduced, the surface coating in the gaps between the middle coating particles still exerts the anti-coking performance of the coating, thereby improving the corrosion resistance of the composite coating and further extending the comprehensive performance and service life of the composite coating.

[0027] Furthermore, the basic principle of thermal spraying is to heat the spraying material by high temperature (electricity or fuel high temperature) to make the spraying material produce a micro-molten state, and then atomize the micro-molten particles by high-speed airflow, so as to form a coating on the surface of the substrate and then modify the substrate surface to make the substrate surface more wear-resistant and corrosion-resistant. The spraying methods of the intermediate coating and the bottom coating are all sprayed by an arc sprayer in thermal spraying (a technology that uses an arc between two continuously fed metal wires connecting the positive and negative electrodes to melt the metal, atomizes the molten metal with a high-speed airflow, and accelerates the atomized metal particles to spray them onto the workpiece to form a coating); or other thermal spraying methods include but are not limited to flame spraying, oxyacetylene flame powder spraying, oxyacetylene flame wire spraying, oxyacetylene flame welding, supersonic flame spraying (HVOF), plasma spraying, atmospheric plasma spraying, and low-pressure plasma spraying. One or more.

[0028] Commonly used spraying materials for thermal spraying include: single component spraying materials: such as aluminum, copper, etc.; these materials can be made into powder, wire, and rod for use. This category includes metals such as tungsten, molybdenum, tantalum, niobium, zinc, aluminum, copper, tin, lead, nickel, iron, titanium, zirconium, and some metal oxygen, carbon, nitrogen, boron, and silicide. Commonly used ones include: molybdenum as a bonding layer material, zinc and aluminum as protective materials against seawater and atmospheric corrosion, Al 2 O 3 and ZrO 2 Alloy spraying materials: Alloy spraying materials include stainless steel materials with comprehensive wear and corrosion resistance, wear-resistant and machined carbon steel materials, and non-ferrous metal alloy series, such as Ni-Cr, Ni-Cr-W, Fe-Cr-Al, Co-Cr-Al-Y, Zn-Al, Ti-Ni, Al-Si, etc. Composite spraying materials: including composite powders and composite wires; such as Ni / Al, Co / WC, NiAl 2 O 3 、Ni / Cr 2 O 3 、Ni / graphite、(Ni-Cr) / Cr 2 O 3 , Ni / Cr, (Ni-Cr-Al) / diatomaceous earth, etc. Mixed spraying materials: mainly mixed powders, such as Cr 3 C 2 +(Ni-Cr), (Co / WC)+self-fluxing alloy+(Ni / Al), BN+Al+(Ni-Cr), Ni+graphite, etc.

[0029] Preferably, the bottom coating is 45CT metal material, and the spraying method is arc spraying. The specific spraying method is as follows: the voltage during spraying of the bottom coating is 32-50V, and the current is 150-160A; the spraying distance is 25-45cm, and the moving speed during spraying is 30-50cm per second. Among the particles of the bottom coating, the number of particles with a size less than 30μm accounts for greater than or equal to 80%, and the number of particles with a size of 40μm accounts for 15%; the particle porosity of the bottom coating is less than 3%; the coating thickness of the bottom coating is greater than or equal to 60μm. The bottom coating provides the basic conditions for the comprehensive performance of the composite coating.

[0030] Preferably, the coating thickness of the facial coating is greater than or equal to 60 μm.

[0031] Optionally, the spraying material of the face coating includes one or more of silicate-based coating, phosphate-based coating, silica sol-based coating and organic silicon high temperature resistant coating. The face coating relies on the middle large particle coating to exert its anti-coking function.

[0032] Specifically, when spraying the composite coating provided by this specific embodiment on the water-cooled wall, the spraying speed is about 5-10min / square meter; the hardening time of each coating includes: the bottom coating and the middle coating are naturally cooled for 30 minutes after spraying, and the surface coating requires 24h of surface drying time; the order of spraying materials: first, the surface of the water-cooled wall is sandblasted for pretreatment to achieve the cleanliness standard of Sa3.0; after the surface pretreatment is completed, the bottom coating is sprayed according to the bottom coating spraying method as described above; after the bottom coating is hardened, the middle coating (large particle layer) is sprayed according to the middle coating spraying method as described above, and after the middle coating is hardened, the surface coating is sprayed. The spraying of each layer of coating should be carried out after the hardening time of the previous layer of coating meets the above requirements to ensure good bonding and performance between the coatings.

[0033] As shown in Table 1 below, the performance comparison data of the water-cooled wall after spraying with 45CT single coating, single ceramic coating, dense 45CT + ceramic coating and the composite coating (dense layer 45CT + large particle layer 45CT + ceramic coating) provided in the above embodiments of this application are shown. As described in Table 1 below, the composite coating provided in the embodiment of this application has obvious advantages, the number of tube replacements is significantly reduced, the number of slag crusher tripping times is significantly reduced, the anti-corrosion and explosion-proof performance is better, and the dust accumulation on the surface of the water-cooled wall is reduced. Therefore, the composite coating provided in this application has great advantages in the anti-coking performance and performance life of the water-cooled wall.

[0034] Table 1: Comparison of performance of different coatings

[0035]

[0036] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0037] Embodiment 1

[0038] according to Figure 2 As shown, the spraying area of ​​the main combustion zone water-cooled wall 2 is divided based on the height of the square-tangential boiler burner 1, including the first area 3, the second area 4 and the third area 5. The first area 3 is located in the upper half of the water-cooled wall 2, above the second area 4 and the third area 5, and its height is half of the height of the square-tangential boiler burner 1; the second area 4 has the same height as the third area 5, which is half of the height of the square-tangential boiler burner 1, and is located in the lower half of the water-cooled wall 2, wherein the second area 4 occupies an area of ​​2 / 3 of the length of the water-cooled wall 2, and the third area occupies an area of ​​1 / 3 of the length of the water-cooled wall 2.

[0039] In this embodiment, the coating sprayed in the first area 3 includes: bottom coating: stainless steel + 45CT dense layer; middle coating: stainless steel large particle layer; face coating: phosphate-based ceramic coating; the metal material of the bottom coating is 304 stainless steel + 45CT, and the metal material of the middle coating is 304 stainless steel. This area has slight corrosion and not serious coking. In order to extend the life of the surface coating and improve the heat exchange efficiency of the equipment (reduce the flue gas temperature at the furnace outlet), cost-effective stainless steel is used as the metal material for the bottom coating and the middle coating. The material 3001 of the face coating mainly includes 30-40% aluminum dihydrogen phosphate, 1-3% chromium trioxide, 15-20% copper chrome black, 1-5% mica, and the others are additives and solvent materials to improve the film-forming performance of the surface layer. The copper chrome black has high blackness and excellent high temperature resistance, and is suitable for high temperature radiation heat exchange.

[0040] In the second area 4, the bottom coating is made of 45CT metal material; the middle coating is a large particle layer, and the large particle layer of 45CT metal material is selected; the surface coating is phosphate-based ceramic coating. The second area is seriously corroded and coked, so the spray material for the surface coating mainly includes 30-40% aluminum dihydrogen phosphate, 15-25% chromium trioxide, 3-4% boron nitride, 0.5-2% graphite, 1-5% mica and 1-3% barium sulfate, and the others are additives and solvent materials to improve the film-forming performance of the surface layer. Lubricating materials reduce coking, and chromium trioxide has a good protective effect on corrosion.

[0041] In the third area 5, the bottom coating is made of amorphous alloy + 304 stainless steel; the middle coating is a large particle layer, and an amorphous alloy large particle layer is selected; the surface coating is a silicate-based ceramic coating. The third area is mainly subject to wear and tear. The main components of the surface coating material include 15-20% sodium silicate, 15-20% potassium silicate, 15-25% kaolin, 1-2% boron nitride, 0.5-1% graphite, 1-3% mica and 1-3% silicon dioxide. The others are additives and solvent materials to improve the film-forming properties of the surface layer. The solid content of the coating is increased to improve the wear resistance of this area.

[0042] The beneficial effects of the embodiments of the present application are as follows:

[0043] This application provides skeleton support for the surface coating by adding a large-particle intermediate coating, so that the bottom coating and the surface coating are more tightly connected. When the thickness of the surface coating is reduced, the surface coating in the gap between the intermediate coating particles still exerts the anti-coking performance of the coating, thereby increasing the service life of the ceramic coating and greatly improving the corrosion resistance of the composite coating, thereby extending the comprehensive performance and service life of the composite coating, and further solving the problems of water-cooled wall corrosion and coking.

[0044] The above embodiments are only used to illustrate the technical solution of the present application, but not to limit it. The present application is not limited to the exact structure described above and illustrated in the accompanying drawings, and it cannot be determined that the specific implementation of the present application is limited to these descriptions. For ordinary technicians in the technical field to which the present application belongs, various changes and modifications made without departing from the concept of the present application should be deemed to belong to the protection scope of the present application.

Claims

1. A composite coating for a water-cooled wall, wherein the composite coating is used for spraying a water-cooled wall, characterized in that: The composite coating includes a bottom coating, an intermediate coating and a surface coating; for the intermediate coating, the number of particles with a size greater than 0.5 mm accounts for greater than or equal to 80% of the total number of particles in the intermediate coating; the bottom coating, the intermediate coating and the surface coating are sequentially applied on the substrate of the water-cooled wall, and some particles of the surface coating form a fusion structure by embedding in the particle gaps of the intermediate coating, and the surface coating is tightly connected to the intermediate coating through the fusion structure.

2. The composite coating for water-cooled wall according to claim 1, characterized in that: The coating thickness of the intermediate coating is greater than or equal to 0.5 mm.

3. The composite coating for water-cooled wall according to claim 1, characterized in that: The spraying material of the intermediate coating includes a nickel-based alloy metal material, and the spraying method is arc spraying.

4. The composite coating for water-cooled wall according to claim 3, characterized in that: The voltage of the intermediate coating during arc spraying is 32-40V, the current is 180-240A, the spraying distance is 50-80cm, and the moving speed of the arc spray gun head during spraying is 80-120cm per second.

5. The composite coating for water-cooled wall according to claim 1, characterized in that: The spraying material of the bottom coating includes a nickel-based alloy metal material, and the spraying method is arc spraying.

6. The composite coating for water-cooled wall according to claim 5, characterized in that: The voltage during arc spraying of the bottom coating is 32-50V, the current is 150-160A, the spraying distance is 25-45cm, and the moving speed of the arc spray gun head during spraying is 30-50cm per second.

7. The composite coating for water-cooled wall according to claim 6, characterized in that: Among the particles of the bottom coating, the number of particles with a size less than 30 μm accounts for greater than or equal to 80%, and the number of particles with a size of 40 μm accounts for 15%; the porosity of the particles of the bottom coating is less than 3%.

8. The composite coating for water-cooled wall according to claim 7, characterized in that: The bottom coating has a coating thickness greater than or equal to 60 μm.

9. The composite coating for water-cooled wall according to claim 1, characterized in that: The coating thickness of the face coating is greater than or equal to 60 μm.

10. The composite coating for water-cooled wall according to claim 9, characterized in that: The spraying material of the face coating includes one or more of silicate-based coating, phosphate-based coating, silica sol-based coating and organic silicon high-temperature resistant coating.

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