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The horizontal flue of a circulating fluidized bed boiler is usually lined with refractory castables to resist high temperatures, corrosion, and erosion by combustion products in the flue. Suitable castables can provide good fire resistance and stability.
In the horizontal flue of circulating fluidized bed boilers, high-aluminum refractory castables are usually used. These castables have the characteristics of high-temperature resistance, corrosion resistance, and wear resistance, and are suitable for the flue lining of circulating fluidized bed boilers.
The horizontal flue is the channel through which flue gas enters the cyclone separator from the furnace. The structure is generally made of high-temperature and wear-resistant bricks on the bottom and both sides of the wall, and high-temperature and wear-resistant castables on the top. For the water-cooled wall around the entrance of the horizontal flue, pins are welded to the fire surface and high-temperature-resistant and wear-resistant castables are laid. The high-speed flue gas carries unburned coal particles and fly ash that are more than ten times the amount of coal input, rotates 90 degrees into the horizontal flue, and impacts the water-cooled wall at the entrance. Therefore, the water-cooled wall at the entrance must be laid toward the fire surface. 400mm wide castable. The horizontal flue flow area is small, and the flow rate of flue gas increases after entering the horizontal flue from the furnace. At the same time, the cross-section of the horizontal flue is in the shape of a tapered nozzle, and the flue gas flow rate gradually increases in the horizontal flue. The wind speed at the inlet of the cyclone separator reaches 12-18 m/s, which causes great wear on the four walls and may also cause a vibration of the four walls.
The material selection and construction requirements for high-temperature and wear-resistant castables here are the same as those in the combustion zone. There are also material selection issues for high-temperature and wear-resistant bricks and refractory mud for bricklaying. Materials with high wear resistance in the 800 to 1000°C temperature zone must be selected. Mistakes in material selection by castable manufacturers will cause serious consequences and seriously affect the economic operation of the boiler. The side wall of the horizontal flue cannot be built as a single wall, and adding additional bricks cannot solve the fundamental problem. Long-term erosion and vibration will cause the wall to collapse. Heat-resistant steel bars should be used to connect the side walls and the sheathing, at least once every 500mm in the height direction. Walls without sheathing should connect two adjacent walls into a whole, and they should also be connected at least once every 500mm in the height direction.
The specific castable type and composition may vary depending on the boiler design and operating conditions, so it is recommended that suitable refractory castables be selected based on the boiler manufacturer’s recommendations or specific engineering requirements. This ensures that the flue lining can operate stably for a long time in high temperature, high pressure, and corrosive environments.
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