KR100616081B1 - The bottom tube of coal fired boiler on which thermal spray coated with aluminum alloy reinforced by ceramic powder - Google Patents

Abstract

It is related to the boiler bottom water pipe of coal fired power plant, which has the effect of suppressing corrosion and erosion by coating the reinforced aluminum film mixed and reinforced with ceramic particles such as alumina. It is characterized by making a coal-fired bottom water pipe which simultaneously forms corrosion protection and erosion resistance by forming a protective film layer on the outside of the water pipe by spraying the wire made by adding 5 to 15% by weight of particles and dispersing melting.

Coal Boiler Lower Water Pipe, Alumina, Aluminum, Arc Spray, Flame Spray

Description

The bottom tube of coal fired boiler on which thermal spray coated with aluminum alloy reinforced by ceramic powder}

1 is a cross-sectional view of the aluminum wire mixed with alumina particles

Figure 2: Flame spray organization chart

Figure 3: Arc spray organization chart

The combustion chambers of coal-fired power plants such as pulverized coal power plants are large structures, but the expansion and contraction are severe due to the low temperature during non-operation and the high temperature during operation. And the upper combustion chamber expands and descends due to the temperature rise during operation. Therefore, a space is provided between the lower part of the combustion chamber and the upper part of the hopper to prevent collision, so that air other than the air that is metered for combustion can be sucked into the upper combustion chamber. Therefore, a large amount of water is filled in the space, and when the thermal expansion, the lower end of the upper structure descends into the water to be sealed and sealed, and the seawater is supplied to facilitate the mass supply. However, because the water used is seawater, the adjacent lower water pipes are corroded. In addition, the lower water pipe is severely eroded by falling collisions of combustion solids left in the combustion chamber. Therefore, the eroded part is coated with a hard film and the corroded part is coated with an aluminum film. However, the boundary part does not have a proper film because erosion and corrosion occur at the same time.

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There may be a number of ways to solve the above problem. For example, the water pipe itself may be solved by making a rare metal such as titanium, molybdenum, tantalum, or an alloy thereof. However, they are not considered because they are expensive. Therefore, there are technical challenges to be solved at economic cost.

In the present invention, in order to suppress corrosion and erosion relatively inexpensively, corrosion and erosion are simultaneously performed using an arc spray or flame spray (aka flame spray) method for a composite wire obtained by mixing and melting a low-cost ceramic powder such as alumina in an inexpensive aluminum alloy. The purpose can be achieved by coating the surface of the water pipes generated. Corrosion resistance has sacrificial anode function and passivation function, and aluminum alloy with excellent seawater resistance responds. Wear resistance and corrosion resistance function with ceramic particles such as alumina, which has high hardness and excellent corrosion resistance.

The mixing ratio of the ceramic particles is preferably set to 5 to 15% by weight, which does not interfere with aluminum spraying. Less than 5% of the wear resistance effect is insufficient, more than 15% of the ceramic content is too high difficult to melt because workability worsens. The ceramic particle size is suitable for 8 ~ 10㎛ for the maintenance of thermal spraying and uniform distribution. The ceramic material can be selected according to the use.

For example, alumina is advantageous for price competition, and silicon carbide is advantageous for erosion resistance. However, considering the ductility of the aluminum base material, it is not necessary to use expensive ceramics, and most of them select alumina, and sometimes other ceramic powders may be used. When the cross section of the wire made by mixing aluminum and alumina of the above configuration is enlarged 20 times as shown in FIG.

The coating sequence of the thermal spray coating using the above material is as follows. Prior to coating, sand spray is applied to the surface of the water pipe to enhance the adhesion. Then, the mixed wire is sprayed onto the surface of the boiler water pipe roughened by pretreatment through a flame spraying or arc spraying process and coated. All parameters should be matched to the normal aluminum wire spraying parameters and the spraying distance should be about 130mm to 180mm. In order to ensure that there is no lack of thickness, spray two or more times. As for thickness, 250 micrometers or less are suitable as 175 micrometers or more which is the limit of the connection type pore length used as the passage | route of a base material corrosion. As a result, it is shown in FIG. 2 that the flame spraying has been enlarged 200 times, and FIG. The flame-sprayed figure shows that aluminum is sufficiently melted but alumina is less melted and more angular, and arc sprayed is less melted aluminum but more alumina melted to partially round the particles. Also, in the flame spraying, aluminum is partially oxidized to alumina, but in the arc spraying, the oxidized portion is hardly visible. As a result, the flame-sprayed layer additionally produces alumina by oxidation by oxygen used in the process, so that the hardness of the sacrificial anode consumes less than that of aluminum because of its higher hardness. On the contrary, the arc-sprayed layer has less hardness due to less addition of alumina, but has a longer aluminum residue, resulting in a longer corrosion resistance. However, since both are more resistant to corrosion than aluminum alloys, they do not need to be applied separately except for special places.

In the spray spray coating, the corrosion resistance was the same as that of aluminum, but the wear resistance was greatly increased. The durability was increased 10 to 12 times in the rub wear test according to ASTM D-3702 and 35 to 45% in the rubber plate / sand wear test according to ASTM G-65B. Therefore, if the material is applied to the water pipe at the same time erosion and wear of the coal-fired boiler, it becomes a water pipe having corrosion and corrosion resistance at the same time

Claims (3)

Coal-fired boiler bottom water pipe with spray coating of ceramic powder mixed with aluminum by 5-15% by weight on the outer surface of the pipe Coal-fired boiler bottom water pipe with a thermal spray coating containing 5 to 15% by weight of alumina powder in aluminum attached to the outer surface of the pipe Making a material in which 5 to 15% by weight of alumina powder with a particle size of 6 to 12 µm is mixed and melted in aluminum, and spraying it on the lower water pipe of the boiler using this material to make a spraying distance of 130 to 180 mm, overlapping two or more times. Coal-fired boiler bottom water pipe manufacturing method consisting of a step of making a film having a thickness of 175 ~ 250㎛

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