Internally circulating fluidized beds(ICFBs)enable effective control of the reactions and heat distribu-tion in reactors.The ICFB contains two or more connected fluidized regions with different gas velocities to promote controlled solid circulation.The control of solid circulation rate(Go)is a critical factor.We recorded single particle trajectories by tracing a fluorescent particle,based on which particle flow behav-iors were analyzed in different regions.Go was obtained for a wide range of operating parameters.An increase in gas velocity in the down-and upflow beds shortened the particle circulation time in both beds and Go increased significantly.As the static bed height increased,the differential pressure on both sides of the circulation port increased,which resulted in an increase in the solid circulation rate.As the orifice area increased,the flow resistance through the orifice decreased and thus the solid circulation rate increased.Go increased with the decrease in particle size.The gas velocity in the upflowing bed and orifice area was the most important parameter to control the solid circulation rate.Go was compared with the experimental measurements in literature and predictions using the correlation based on Bernoulli's equation,and they agreed well.