Fluidized-bed reactors are widely used in chemical and biochemical processes, including polymerization (Kunii, D. G.; Levenspiel, O. Fluidization Engineering; Wiley: New York, 1969). To enhance the efficiency of the fluidized-bed reactors, more flexibility in controlling the residence time of particles of different sizes, particularly very fine particles, is needed. To achieve this goal, we studied gas and particle flow patterns in a vertical rotating fluidized bed (RFB). We limited our study to the quasi-three-dimensional simulation of an isothermal RFB with constant particle size and no chemical reaction to examine the predictability of a computational fluid dynamics approach to the analysis of RFB systems. We used 200-mum particles (with properties similar to polyethylene) as the particulate phase and air as the gas phase in our simulation. The instantaneous velocity, volume fraction, and pressure drop profiles for the gas and particulate phases were calculated. Simulation results showed that the particle residence time distribution could be controlled by the manipulation of rotational speed and inlet gas velocity. Also our simulation results detected the beginning of fluidization at the inner surface of the bed. The pressure drop curve of Geldart group A particles showed that under higher "g" they fluidized like group B particles.