MASS TRANSFER RELATIONSHIPS IN FLUIDIZED-BED COMBUSTORS

Abstract

Abstract It is proposed that the transfer of oxygen from the bulk phase to the surface of a burning carbon particle immersed in a fluidized bed of incombustible particles can be characterized by the transfer associated with the interparticulate gas flow enhanced by the fluctuations in the gaseous environment around the burning particle. The enhancement is attributed to the movement of bubbles in the vicinity of the carbon particle and is predicted by a semi-empirical function of the bubble frequency. The resulting expression is incorporated in a recently proposed unsteady-state model for mass transfer (La Nauze et al., Chem. Eng. Sci., 39, 1623-1633 (1984)rpar; The new formulation correctly predicts the order and trends for the mass transfer coefficient for petroleum coke burning in a bed of sand fluidized by air over a wide range of conditions. In order to test the validity of the model, experiments have been performed using a helium/oxygen gas mixture instead of air. The model successfully predicts the mass transfer coefficient for this situation.