Understanding the gas flow behavior in rotary kilns is very important for predicting thermal conditions. This paper describes CFD simulation of the flowcharacteristics within an industrial rotary kiln containing a rolling bed of granules. The axis of the cylinder assumed to be horizontalwith no axial bulk of flow of particles. The velocity profile of the gas flowing through the cylinder is simulated by CFD. At first, model applied on a laboratory scale rotary cylinder and the results were compared with the available literature for validation. Themethod is applied to an industrial kiln producing granular lightweight aggregates. The results indicate that the velocity field is asymmetric with respect to a diameter perpendicular to the granular bed. The gas velocity profiles are crucial in determining heat transfer from gas to solid.