This paper presents a computational study of the flow behavior in a cold-flow pilot-scale circulating fluidized bed. A multi-fluid Computational Fluid Dynamics (CFD) model has been developed and verified against experimental data reported in the literature. The flow model is based on an Eulerian description of the phases where the kinetic theory of granular flow forms the basis for the turbulence modelling in the solid phases. The model is generalized for one gas phase and N number of solid phases to enable a realistic description of the particle size distributions in gas/solids flow systems. Each solid phase is characterized by a diameter, density and restitution coefficient. The simulations are performed with different superficial gas velocities, initial solids concentrations and standard deviations of the particle size distribution. Most emphasis is given to study the effects of different particle size distributions and to study the fluctuating behavior of the dilute gas/solids flow system. Altogether, the simulation results are in very good agreement with experimental data. Both mean diameters, axial and radial mean and turbulent velocities, and mass fluxes are calculated successfully.