What is the primary air of a circulating fluidized bed boiler?

　　The primary air of the circulating fluidized bed boiler refers to the air that is sent into the furnace from below the air distribution plate to fully fluidize the material layer, control the bed temperature and ensure the initial fluidized combustion. The primary air needs to overcome the resistance of the combustion chamber and the air distribution plate, and needs to be supplied by a special high-pressure primary air fan.