A comprehensive study of particle velocity and solids flux is conducted in a high density circulating fluidized bed with extremely high solids circulation rate up to 1000 kg/m(2) s, for the first time in the lab-scale settings. Results show that the axial distribution of particle velocity becomes more uniform in such extremely high solids flux conditions than cases with lower solids flux. Radial profiles of particle velocity and solids flux become increasingly steep with increasing solids circulation rate. No net downward flow near the wall is detected, which is considered an important advantage of the high density riser leading to reduced solids backmixing. Correlations of particle velocity against solids holdup are stronger for low density conditions than for high density cases, suggesting that gas-particle interaction dominates in low density risers, while particle-particle interaction plays a key role for the motion of particles in the extremely high density ones. (C) 2014 Elsevier Ltd. All rights reserved.