The effect of the operating parameters on the system hydrodynamics and mixing inside two circulating fluidized bed reactor (CFBR) risers with different ring baffle configurations were investigated using computational fluid dynamics simulations and a 2(4) factorial experimental design analysis. The operating parameters varied were the gas inlet velocity, and the mass flux, diameter and density of the solid particles, while the response variables were the standard deviation of the solid volume fraction (SVF) in the radial direction (SDSVF-RD) and the average SVF (ASVF). The results from the two CFBR risers with different ring baffle configurations showed a similar trend. The operating parameters that significantly affected the ASVF in both modified CFBR risers were the inlet gas velocity and solid particle mass flux, while those that significantly affected the SDSVF-RD were the inlet gas velocity and the inlet gas velocity-solid particle diameter-solid particle density interaction. For these systems, the lowest and highest ASVF was approximately 0.07 and 0.20, respectively, while the lowest and highest SDSVF-RD was 0.01 and 0.04, respectively. The low variability of the solid particle distribution and the high solid particle concentration will be suitable for chemical reactions. All the obtained results could be explained in terms of the system hydrodynamics. Finally, regression models to predict the mean solid particle concentration and variability of solid particle distribution in the system were obtained. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.