The output of any induced draft fan is affected when the operating conditions are changed. If dust or ash is accumulated in the flue and dust collector and the preheater, the output of the induced draft fan can be reduced. Due to the corresponding reduction of the flue gas channel due to the ash deposition or ash blockage, and the air flow resistance is increased. Similarly, air leakage on the pipe will also affect the operation of the fan. Since the leaked air has no effect on the combustion, it is transported by the induced draft fan. In this case, the fan must have greater output to ensure the normal operation of the boiler.
The wear of fan passage is also the factor to reduce the output of fan. For any fan, its running performance should be unchanged because its speed, size and blade geometry are fixed. However, after running for a period of time, due to the action of ash particles in flue gas, the air seal device at the junction of inlet and impeller is worn out, which will affect the performance of fan. Under the same pipe resistance characteristic curve, the flow rate of fan affected by wear may be reduced, which may lead to insufficient output. Similarly, the blade of the induced draft fan is dusty in operation, which changes the channel shape of the air flow between the blades and changes the inlet and outlet angle of the blade. This change will also reduce the pressure of the fan, thus reducing the output of the induced draft fan.