On the Regimes of Fluidized Beds for Solid Fuel Conversion

Much work has been presented on the regimes of fluidization of Group A particles in chemical reactors, and this area is rather well known. However, the description of the fluidization behaviour of Group B particles at high fluidization velocities in wide vessels is more ambiguous. Bubbling, turbulent, and fast fluidization regimes are analysed here, especially related to boilers. It is found that the bottom bed of boilers is operated in a bubbling regime even at high gas velocities, accompanied by a tall splash zone, as long as there is sufficient bed material in the system. It is shown that conventional circulating fluidized bed boilers operate in a dilute suspension mode. Also for denser flows, a comparison between transport velocity and terminal velocity indicates that clustering flow is much stronger for Group A particles than for Group B. The bottom bed and its mode of fluidization have implications for the modelling of a furnace.