Main wearing parts and anti-wear measures of the h

Main wear parts and anti-wear measures of circulating fluidized bed boiler Abstract: the wear of metal parts and refractory materials in circulating fluidized bed boiler is one of the main reasons for its operation accidents. Therefore, the anti-wear measures of metal parts and refractory materials in circulating fluidized bed boilers directly affect the economic and safe operation of circulating fluidized bed boiler units. Therefore, the wear of main metal parts and refractory materials of circulating fluidized bed boiler and the causes of wear are introduced. It is proposed that different anti-wear measures should be taken for different wear positions and refractory materials

key words: circulating fluidized bed boiler; Metal parts; Refractory materials; Typical solid material parameters of anti-wear 1 circulating fluidized bed boiler

the heating surface and refractory materials of circulating fluidized bed boiler are constantly washed by a large number of solid materials, resulting in great changes in the density of solid materials and the range of smoke velocity. Table 1 gives the range of typical solid material density and smoke velocity of various boilers. From the data in Table 1, it can be seen that due to its specific combustion mode, The density of solid materials in the boiler is dozens to hundreds of times higher than that of pulverized coal boiler. From the summary statistics of the accident rate of the 420 t/h circulating fluidized bed boiler in nucla power plant in the United States during the 12-year service period (a total of 15700 hours of operation) (see Table 2), it can also be seen that the boiler shutdown accidents caused by wear (heating surface, refractory, hood, etc.) are close to 50% of the total boiler shutdown. In China, the heating surface of some circulating fluidized bed boilers that have been put into operation are worn and burst from time to time. Therefore, whether the anti-wear measures of the circulating fluidized bed boiler are correct or not directly affects the availability of the circulating fluidized bed boiler unit and the safe operation of the unit

2 wear of main metal parts of circulating fluidized bed boiler

2.1 wear of main metal parts in circulating fluidized bed boiler

2.1.1 air distribution device

the wear of air distribution device of circulating fluidized bed boiler is mainly the wear of hood, and the most serious wear of hood occurs near the return port of circulating materials, The main reason is that the circulating material with higher particle concentration washes the hood with a larger velocity component parallel to the air distributor

2.1.2 furnace water-cooled wall tubes

the wear of water-cooled wall tubes in the furnace is mainly concentrated in the following three areas: the wear of tube walls in the transition area between the fire protection zone at the lower part of the furnace and the water-cooled wall tubes; The tube walls at the four corners of the furnace are worn; Wear of pipe wall in irregular areas. A new material classification system has been preliminarily established in the transition area between the fire protection zone at the lower part of the furnace and the water-cooled wall tube. The reasons for the wear of the tube wall are as follows: first, in the transition area, the solid materials flowing down the wall have the opposite direction of movement with the solid materials moving upward in the furnace, resulting in local vortex flow; Another reason is that the solid materials flowing down the furnace wall change the flow direction in the junction area, thus scouring the water-cooled wall tubes. The reason for the tube wall wear in the four corner areas of the furnace is that the density of solid materials flowing downward in the inner wall of the corner area is relatively high, and the flow state is also destroyed. The wear of the pipe wall in irregular areas (such as the through wall pipe, the elbow at the opening of the furnace wall, etc.) is mainly caused by the large disturbance of the irregular pipe wall to the local flow characteristics

2.1.3 wear of heating surface in furnace

the wear mechanism of platen superheater and horizontal superheater tube platen in furnace is similar to that of water-cooled wall tube in furnace, which mainly depends on the specific structure of heating surface and the flow characteristics of solid materials

2.1.4 wear of heating surface of convection flue

wear of heating surface of convection flue mainly occurs at both ends of economizer and the inlet of air preheater. The main reason for wear is that (2) whether the operation of each speed is normal is not considered carefully, and there is error during installation; Another reason is the poor material of heating surface

2.2 abrasion of main non-metallic refractories in circulating fluidized bed boiler

the abrasion position of main non-metallic refractories in circulating fluidized bed boiler is the air distribution plate of water wall; The surface of the water-cooled wall around the lower part of the combustion chamber; The lower end surfaces of water-cooled platens, superheater platens, etc. arranged in the combustion chamber and the water-cooled wall surfaces around the wall penetrations; Around the outlet of the combustion chamber and the inner surface of the flue gas outlet channel; The entire inner surface of the separator; The inner surface of the feed leg and the return device; Inner surface of separator outlet flue; These accuracy values of the inner surface of the inlet of the tail convection flue can reach a maximum of plus or minus 0.5

the main reasons and mechanisms for the destruction of refractories in circulating fluidized bed boilers: on the one hand, cracks and spalling of refractories are caused by temperature cycling fluctuations, thermal shock and mechanical stress; On the other hand, the destruction of refractory materials is caused by the scouring of solid materials

3 anti-wear measures of circulating fluidized bed boiler

3.1 anti-wear measures of metal parts of circulating fluidized bed boiler

3.1.1 metal anti-wear cover plate

anti-wear cover plate is one of the traditional anti-wear measures of the boiler. Its structure is shown in Figure 1. It is mainly used for the convective heating surface of the tail flue. The anti-wear materials are generally made of 1Cr18Ni9Ti and 20g steel according to the flue gas temperature at the anti-wear position, with a plate thickness of 2 mm

3.1.2 wear resistant surfacing

on the surface of metal materials that need wear resistance, weld a certain thickness of fusion metal to make the base metal have high wear resistance. It is mainly used for wear resistance at the transition between non-metallic wear-resistant refractory materials and non protected areas, such as the lower part of water wall, superheater, hood, high-temperature reheater, etc

3.2 anti wear measures for non-metallic refractory materials of circulating fluidized bed boiler

3.2.1 water wall lining

the water wall lining uses metal pins welded on the surface of the pipe to make a relatively dense assumption of resistance. When selecting, it is not sure the quality of the experimental box. The grinding refractory material is fixed on the boiler pipe fittings on the flue gas side. See Figure 2 for the structure. The lining shown in Figure 2 (a) is mainly laid in the lower area of the furnace; The lining shown in Figure 2 (b) is mainly laid at the easily worn places of superheater and reheater panels

3.2.2 thin lining of non water wall

thin lining of non water wall uses "Y" shaped grab nails arranged regularly to fix the wear-resistant castable outside the thermal insulation castable layer. The grab nails should be coated with 1 mm thick asphalt to solve the temperature expansion difference between metal grab nails and wear-resistant castable. Its structure is shown in Figure 3. This kind of lining is suitable for parts with complex surfaces and the top surface of equipment

3.2.3 non water cooled wall thickness lining

non water cooled wall thickness lining mainly fixes wear-resistant bricks on the outside of insulating bricks or insulating castables, and its structure is shown in Figure 4. The structure shown in Figure 4 (a) is suitable for large areas or arc surfaces; The structure shown in Figure 4 (b) is suitable for the parts with complex shape of steel shell and other parts that are not suitable for insulating bricks

4 Conclusion

this paper analyzes the mechanism of serious wear of some metal parts or non-metallic refractories on the furnace, heating surface in the furnace, air distribution plate, heating surface of convection flue, separator, return device and other equipment of circulating fluidized bed boiler, and puts forward corresponding anti-wear measures for maintenance and relevant personnel for reference. (end)