An experimental study on the gas dispersion behavior of cocurrent downflow gas-solid suspension in a 140 mm i. d. circulating fluidized beds (CDCFB) using the steady-state tracer method is presented. The influence of gas velocity

solids circulating rate and particle density on radial gas dispersion has been examined. Gas dispersion can well be described by eddy diffusion mechanics and a proposed two dimensional dispersed plug- flow model fits the experimental data very well. The correlation Per = 4. 35× 10-3Re0.95ε-73.4(while 1>ε>0. 99) for radial diffusion coefficient is obtained. It is found that the obtained axial diffusion coefficient in the CDCFB is much lower than that in a circulating fluidized bed.