The hydrodynamic characteristics in the bottom region of circulating fluidized bed (CFB) risers with fluid catalytic cracking (FCC) particles were studied over a wide range of operating conditions. The results included radial solids concentration and corresponding radial profiles of standard deviation, particle velocity profiles, and probability density distributions. Comparisons were made between the flow structures in the riser bottom region and those in bubbling and turbulent fluidized beds. (C) 2008 Elsevier B.V. All rights reserved.