A multi-fluid Eulerian modeling approach is employed to simulate coal combustion and desulfurization in a CFB riser reactor. The unsteady processes of gas solid two phase flow, heat and mass transfer incorporating the devolatilization, heterogeneous and homogeneous reactions, and sorbent model are considered in the simulation. The dispersed solid phase within the CFB riser reactor is modeled as two continuous phases with different diameters and densities. The constitutive properties of the dispersed solid phases are predicted by the kinetic theory of granular mixture (KTGM) with unequal granular temperature. By numerical simulations, the distributions of volume fraction, velocity, temperature and concentrations of gas species are studied. Two-dimensional simulation results for a CFB riser reactor are compared with experimental data for gas species concentration and temperature. The impact of the inlet region on coal combustion and limestone calcination is observed. This model has demonstrated its capability to predict the main fluid mechanic/fluidization and chemical reactions during coal combustion and desulfurization in CFB riser reactors. (C) 2014 Elsevier B.V. All rights reserved.