Cluster and Bed-to-wall Heat Transfer Characteristics in a Dual Circulating Fluidized Bed

Abstract

The cluster and bed-to-wall heat transfer characteristics in a dual circulating fluidized bed have been determined by a particle velocity and a heat flux meters, respectively. The mean cluster length, mean cluster velocity, cluster fraction, and heat transfer coefficients increase with increasing solid circulation rate and decreasing gas velocity in the riser. The heat transfer coefficient with a solid circulation in the bubbling fluidized bed is found to be lower than that without solid circulation. With the distinct solid flow pattern, a correlation to predict convective heat transfer coefficient as a function of the operating variables is proposed. To verify the heat–transfer mechanism in a dual circulating fluidized bed, it is found that the cluster-renewal model can be utilized with high accuracy. The obtained bed hydrodynamics and the heat transfer coefficients in the dual circulating fluidized bed can be used to determine the optimum operating conditions in the gasification and combustion operations.