The fluidization characteristics of bell-type air nozzles used in several domestic large scale circulating fluidized bed(CFB) boilers were studied in cold and hot states. Based on the actual operating conditions of power station boilers

the gas-solid flow characteristics of the material layer near the air nozzle were measured by resistance method

and the motion characteristics of large particles in the material layer around the air nozzle at different fluidized wind temperatures were observed with high-speed photography. The results show that

the inner tube orifice area has a greater effect on the resistance characteristics and fluidization characteristics. Increasing the fluidizing air volume and the fluidizing air temperature could enlarge the disturbance range of the bell-type air nozzle

decrease the large particle parking height around the air nozzle

and improve the disturbance characteristics of the material layer. The research work can provide references for optimization design of bell-type air nozzle in large scale CFB boilers and the analysis and corresponding solution of operational problems

such as nozzle wear and boiler slagging with load changing.