Annular Downflow Layer in a Recirculating Fluidized Bed

The effect of various operational and design parameters on the annular downflow layer thickness is studied experimentally in a recirculating fluidized bed. Inventory of solids, superficial gas velocity in the riser, particle size, axial height, and spacing between the riser bottom and the distribution plate are the various operational and design parameters considered in this study. A correlation between the annular layer thickness and the operating parameters is developed based on the experimental results. The correlation developed can be useful in the better understanding of the hydrodynamics of the recirculating fluidized beds. The results indicate that the annular layer thickness decreases with an increase in superficial gas velocity as well as with the axial position in the riser. The annular layer thickness increases with the increase in the spacing between riser bottom and distribution plate. The fine sand has a relatively stable annular downflow layer as compared to the coarse sand.