In this study, a three-fluid Eulerian model coupled with the kinetic theory of granular flow was developed to investigate the mixing/segregation behaviors of binary-mixture particles in a pilot-scale fluidized bed reactor. The proposed model was validated by comparing predictions with the classical calculated data and the experimental data. A new mixing index was defined by counting the mixing information in each mesh, and then it was applied to evaluate quantitatively the effects of the key model parameters (i.e., restitution coefficient, friction coefficient) and operating conditions (i.e., inlet gas velocity, particle size ratio) on the mixing characteristics of binarymixture particles. The hydrodynamic characteristics of binary-mixture particles in semi-continuous feed mode were also obtained. Numerical results demonstrate that the size segregation of particles can be easily realized under the conditions of high air velocity and large particle size ratio when the binary-mixture particles differ only in size. (C) 2020 Published by Elsevier B.V.