Effect of staged air on heat transfer in circulating fluidized beds

The purpose of this work is to develop a model for bed-to-surface heat transfer in circulating fluidized bed (CFB) risers with secondary air (SA) injection. The heat transfer coefficient is correlated to cross-sectionally averaged solids hold-up. The average solids hold-up is correlated with the operating and design parameters of CFB risers with SA injection. The data used in developing the correlations cover a range of 2.0–8.6 m/s for superficial gas velocity, 5–100 kg/m2s for solids circulation rate, 0–0.6 for secondary to primary air ratio, and 60–300 μm for particle diameter (groups A and B). The predictions obtained with the correlations show good agreement with the experimental data. Furthermore, an experimental correlation, developed in our previous work for prediction of wall-to-bed heat transfer coefficient was used in a parametric study to investigate the effects of design and operating parameters on heat transfer.