(The) retention time of powdered active carbon in inert fluidized bed

Abstract

Both qualitative and quantitative studies on the retention time of powdered active carbon in an inert fluidized bed were made for thermal regeneration. Carbon flow rate, gas velocity, and the size and the density of powdered active carbon, and of inert particles were chosen as variables and the effects of these variables on the retention time of carbon particles were examined. The experimental results showed that the retention time of carbon particles was considerably affected by the variables such as gas velocity, the size and the density of powdered carbon, and of inert particles, while carbon flow rate seemed to have no effects on the retention time of powdered carbon when inert fluidized beds were those of dilute phases of carbon powder. The results also showed that the retention time of carbon particles varied sensitively, as gas velocity was decreased, and the same effects were observed when either the size or the density of inert particles was decreased. The sensitivity of the retention time of powdered carbon in inert fluidized beds was compared with that in empty beds. From the result, the inert fluidized beds were likely to have an advantage over the empty beds for the convenience of controls on the retention time. Semi-empirical correlations were obtained for estimating the average velocity of carbon particles in inert fluidized beds. These were expressed as; $$U_{sc} = 0.014 (1-\delta-\alpha \delta) \varepsilon_{mf}^{1.74} \Bigg( \frac{d_{pi}}{d_{pc}} \Bigg)^{2.75} (U_e-U_{tc}) + (\delta + \alpha \delta \varepsilon_{mf}) (U_b-U_{tc})$$ when $$U_e \geq U_{tc}$$ and $$U_{sc} = (1-\delta-\alpha \delta) \varepsilon_{mf} (-U_s) + (\delta+\alpha \delta \varepsilon_{mf}) (U_b-U_{tc})$$ when $$|U_e| < U_{tc}$$