【Weekly Question】Describe the wear of metal components in circulating fluidized bed boilers?

In circulating fluidized bed boilers, large particles, due to mechanical forces or in combination with chemical or electrical effects, cause the material on the surface of the working components to be gradually worn away as a result of relative motion; this phenomenon is known as wear. The wear of the heating surfaces and refractory materials in circulating fluidized bed boilers is primarily the result of a combination of erosion wear and impact wear. Scouring wear occurs when the impact angle of the particles on the solid surface is small, or even nearly parallel; the velocity at which the particles touch the solid surface enables them to exert a certain cutting effect on the solid. With such repeated actions over a large scale, wear occurs on the solid surface. Impact wear occurs when particles strike a solid surface at a large angle relative to the surface, sometimes even nearly vertically, and impact it at a certain speed, causing very slight plastic deformation or cracks in the solid surface. Under the long-term, repeated impact of particles on various solid surfaces, the plastic deformation layer gradually detaches in its entirety, resulting in wear. Wear is closely related to factors such as the depth of the solid material, velocity, properties of the particles, and the geometry of the channel. In particular, the wear in circulating fluidized bed boilers is dozens to hundreds of times that in coal powder boilers.

Wear of metal parts: External wall wear occurs when soot particles in the flue gas strike the solid surface at a large angle relative to the surface, sometimes even nearly vertically; they impact the solid surface at a certain speed, causing minor plastic deformation or cracks in it. Under the long-term and repeated impact of particles on various solid surfaces (especially the side facing the smoke flow), the plastic deformation layer gradually detaches in its entirety, resulting in wear; the degree of wear is closely related to the velocity of the smoke flow.

I. Main parts prone to wear in boilers: In circulating fluidized bed boilers, since the concentration of solid materials inside the furnace and their particle size are much higher than those in coal-fired boilers, the wear on the heating surfaces of fluidized bed boilers is significantly greater. However, the wear is not uniform throughout the furnace; the areas most affected by wear include the following: (1) Wear on the air nozzles, with the most severe wear occurring near the material return port； (2) Wear of the water wall occurs most severely at the junction between the lower part of the water wall and the refractory castable in the furnace chamber, in the four corners of the furnace chamber, as well as on some irregular pipe walls; these irregular pipe walls include pipes passing through the wall, bends at openings in the furnace wall, and welds on the pipe walls ； (3) At the secondary air nozzle and at the location where the thermocouple is inserted ； (4) The inlet flue and upper area of the high-temperature cyclone separator, as well as the central cylinder ； (5) Certain parts of the heated surfaces in the convective flue, such as certain sections of the superheater, economizer, and air preheater. II. Main hazards of wear: Circulating fluidized bed boilers are primarily affected by wear on the heat-exchanging surfaces and wear on the refractory materials. In the wear of the heated surfaces, whether it is the wear of water tubes, steam tubes, flue tubes, or air tubes, mild cases result in changes in thermal stress, leading to uneven heating; severe cases cause tube rupture or leakage at the heated surfaces, and in extreme situations, this can lead to the shutdown of the boiler ； Wear of refractory materials can cause the refractory layer to peel off, lead to air leakage in the boiler, or exacerbate wear on the heated surfaces ； Wear of the wind cap leads to uneven air distribution; in severe cases, it can cause coking in the boiler, all of which will affect the normal, safe, and economical operation of the boiler to varying degrees. III. Treatment of wear: For areas that may be worn or are already worn, thorough inspection should be carried out during maintenance, and appropriate action taken promptly. This can be achieved by replacing worn wind caps, water wall tubes, and anti-wear plates, repairing damaged refractory materials, or using more suitable refractory materials or adding protective components; for example: (1) selecting anti-wear materials suitable for circulating fluidized bed boilers ； (2) Employ metal surface spraying technology and other surface treatment methods ； (3) “Blue Clay” anti-wear technology ； (4) Install anti-wear components on the heated surfaces, such as anti-wear plates ； (5) The geometric shape of certain specific areas should be altered; the tubes on the inner surface of the furnace must be \"flat\", \"straight\" and \"smooth\", with no protruding parts. For certain areas that are severely worn and are detected during operation, such as tube ruptures or leaks in the heat-exposed surfaces, particularly in the pressure-bearing components, the boiler should be shut down promptly for maintenance in order to prevent the accident from worsening.

The answer on the 4th floor was very professional. To add more details: 1. When a circulating fluidized bed boiler is in operation, it is crucial to control the operating wind speed, especially the primary air speed. While ensuring normal fluidization of the material bed and maintaining an appropriate bed temperature, efforts should be made to reduce the amount of primary air used; the boiler should not be operated beyond its capacity limits； 2. During normal operation, it is necessary to ensure that the coal supply volume from each coal feeder is consistent; no individual feeder should supply too much or too little coal, in order to prevent excessive local speeds.

The flow rate in the furnace chamber must be strictly controlled within a certain range