The primary air is mainly used for ensuring normal fluidizing of boiler, stabilizing temperature of bed of materials and differential pressure of bed of materials. The secondary air is used for controlling the total air amount. When the load is about 18t/h, the secondary air is put into use, On the precondition that the primary air meets the requirement of fluidizing, temperature of bed of materials and differential pressure of bed of materials, when the total air amount is insufficient( the oxygen after the over heater shall prevail, in normal operation the oxygen content shall be 3-5% approximately), gradually open the damper of the secondary air. With the increasing of the load, the secondary air will be increased gradually. When it reaches the rated evaporation, the proportion of primary air and secondary air is about 60% and 40% approximately, for the coal with high volatile matter and easy to burn, the primary air can be less, and vice versa.