Solids concentration in the fully developed zone of CFB downers

In order to investigate the solid concentrations in the fully developed region of the circulating fluidized bed (CFB) downers, the actual solid concentration was measured by an optical solid concentration probe in a 9.5 m high downer with fluid catalytic cracking (FCC) particles. Based on the experimental data from this work and in the literature, the influences of operating conditions, particle diameter and downer diameter on the solid concentration in the fully developed zone of CFB downers were studied. The results show that, for a given superficial gas velocity, the solid concentration linearly increases with the solid circulation rate, and the effect of particle diameter on the solid concentration in the fully developed zone of the CFB downers reduces with increasing superficial gas velocity. The results also show that the solid concentration in fully developed zone of CFB downers changes little with the downer diameter. Based on these facts, an empirical correlation used to predict the solid concentration in the fully developed zone of CFB downers was proposed. The comparison of the experimental data with the predicted values confirms the validity of the proposed correlation.