The Role of Different Fans in a Thermal Power Plant Boiler System

In a thermal power plant's boiler system, various fans play a crucial role in transporting gas, maintaining combustion, and controlling emissions. Different types of fans have unique structural and performance characteristics due to varying operating conditions.

The boiler induced draft fan is responsible for transporting the flue gas discharged from the furnace. The medium it handles is the high-temperature exhaust gas generated from coal or oil combustion. When the boiler burns ordinary pulverized coal, the fan blades and the inner wall of the casing require anti-wear treatment. If the fuel is heavy oil, certain components in the exhaust gas are prone to low-temperature corrosion, requiring the addition of an anti-corrosion protective layer to the blade surface. Induced draft fans generally adopt a centrifugal structure. Because the flue gas temperature often exceeds 150℃, the bearing housing needs to be equipped with a water-cooling device to control the temperature rise.

The boiler blower's function is to supply combustion air to the boiler. It can be divided into centrifugal and axial flow types. Centrifugal fans are preferably equipped with airfoil blades, and the airflow is adjusted through inlet guide vanes. For large units, axial flow fans with adjustable blades can be used to adapt to a wider range of operating conditions. Due to the high blower pressure, the noise level during operation is relatively high, usually requiring the installation of a silencer to reduce environmental impact.

Gas recirculation fans also handle high-temperature flue gas from boilers, demanding high heat resistance and structural rigidity. The blades must be wear-resistant, and the bearing housings must be water-cooled. To prevent thermal deformation due to temperature differences after shutdown, these fans are often equipped with a turning gear. Structurally, they are mostly centrifugal, with typical air volumes of approximately 4600~16000 m³/min and air pressures between 1700~4000 Pa.

Desulfurization fans also handle boiler flue gas, but their operating conditions differ depending on their location: fans installed before the desulfurization unit operate under conditions similar to induced draft fans; while fans operating after the desulfurization unit face gases containing corrosive components, therefore requiring the use of corrosion-resistant materials.

Pulverized coal fans are specifically designed to convey pulverized coal to boilers. Although the pulverized coal does not flow directly through the impeller, the particles entrained by the high-speed airflow can still cause wear on the blades. Therefore, the blades need to be reinforced for wear resistance, such as by using wear-resistant welding rods for overlay welding, spraying, or chemical treatment, or even by coating the surface with hard materials such as silicon carbide. The inner wall of the volute is also lined with removable protective plates for easy replacement after wear. Cooling water pipes are installed in the bearing housing to cool and protect the lubricating oil.