This paper presents an experimental study on the fluid dynamics of a circulating fluidized bed with secondary air injection. The experiments were run in a 4 m high, 100 mm internal diameter riser system. The solid material was 200-920 μm diameter sand. The gas temperature at the beginning of the riser was around 200°C and the superficial gas velocity varied in the 2.5-9.5 m/s range. The data obtained made possible to suggest correlations for the pressure drop in a cyclone and in a recirculating L-valve, which are necessary to study the system pressure balance. The pressure profiles in the loop of the circulating fluidized system show the secondary air injection influence.334 287292Cho, Y.J., Namkung, W., Kim, S.D., Park, S., Effect of Secondary Air Injection on Axial Solid Holdup Distribution in a Circulating Fluidized Bed (1994) Journal of Chemical Engineering of Japan, 27 (2), pp. 158-164Geldart, D., Jones, P., The Behaviour of L-Valves with Granular Powders (1991) Powder Technology, 67, pp. 163-174Knowlton, T.M., Hirsan, I., L-Valves Characterized for Solids Flow (1978) Hydrocarbon Processing, pp. 19-156. , MarchMori, S., Yan, Y., Kato, K., Matubara, K., Liu, D., Hydrodynamics of Circulating Fluidized Bed (1990) Proceedings of the 3rd International Conference on Circulating Fluidized Beds, pp. 4.5.1-4.5.6. , Oct. 15-18, Nagoya, JapanPécora, A.A.B., (1995) Estudo da Fluidodinâmica de Leitos Fluidizados Circulantes com Injeção de Ar Secundário, 254p. , PhD Thesis, Unicamp, BrazilYerushalmi, J., Turner, D.H., Squires, A.M., The Fast Fluidized Bed (1976) Ind. Eng. Chem. Process Des. Dev., 15 (1), pp. 47-53Wang, X.S., Gibbs, B.M., Hydrodynamics of a Circulating Fluidized Bed with Secondary Air Injection (1990) Proceedings of the 3rd International Conference on Circulating Fluidized Beds, pp. 4.6.1-4.6.6. , Oct. 15-18, Nagoya, Japan