If the air speed of the small hole is high, the impact of air flow to the particles at the bottom of the bed is bigger and the disturbance is stronger, which is advantageous to the  fluidization of coarse particle and to make them operate in low load, therefore the load adjusting range is large. But if the air speed of  small holes is too large, the resistance of air nozzles increases, so the pressure head of the fan required is big, thus making the power consumption of the fan to increase; On the contrary, if the air speed of small holes is too low,  the coarse particles are easily caused to deposit,  thus making the fluidization at bottom poor, especially when the load is lower, the stable operation often cannot be maintained, so the air speed of the small holes shall be fully considered according to the factors of the characteristics of fire coal, characteristics of particles, adjusting range of load and power consumption of fan etc.