(1) The amount of wet flue gas under the condition of excess air in the operation of waste incineration; (2) The amount of supplementary air used to control the flue gas temperature;(3) caused by the use of chemicals or humidification in the flue gas purification system Additional amount of flue gas; (4) The amount of air leaking into the system in front of the induced draft fan. Therefore, the air volume of the induced draft fan should be determined according to the maximum calculated air volume plus a margin of 15%~30%. Due to the following reasons, the induced draft fan should adopt a frequency conversion speed regulation device: