Heat transfer in the downer and the riser of a circulating fluidized bed - a comparative study

The characteristics of heat transfer were studied in both a gas-solids concurrent downflow fluidized bed (downer) and a gas-solids concurrent upflow fluidized bed (riser) with FCC particles. The radial and axial distribution profiles of the heat transfer coefficient between a suspended surface and the gas-solids flow suspension were obtained using a miniature heat transfer probe, under different operating conditions. Comprising the results of the heat transfer in the downer and the riser shows that there exists some significant distinction between the heat transfer processes in the two reactors. The characteristics of heat transfer in both cases are closely related to their hydrodynamics and the distinct flow structures determinate the different heat transfer behaviors. The results also indicate that the operating conditions present some different effects in the two beds.