The effects of gas velocity (0.038~0.15 m/s), excess air ratio (1.0~1.3) and bed temperature in the fluidized bed (700~900°C) on the total entrainment rate, combustion efficiency and heat transfer coefficient in the combustor have been determined.
The solids circulation rate has been determined by particle velocity of heated particles which is measured by the time-lag of signals from two thermistor probes vertically located in the bed.
The solids circulation rate increases linearly with increasing gas velocity in the fluidized bed and pressure drop across an orifice opening.
The total entrainment rate increases with an increase in gas velocity in the fluidized bed, but it decreases with an increase in bed temperature. The unburned carbon loss in flyash decreases with an increase in bed temperature, but it increases with an increase in gas velocity in the fluidized bed.
The combustion efficiency increases with increasing bed temperature, excess air ratio and solids circulation rate.
The heat transfer coefficient in the fluidized bed combustor increases with an increase in gas velocity, through a maximum value, thereafter, it decreases with increasing gas velocity. The heat transfer coefficient in fluidized bed increases with increasing bed temperature. The heat transfer coefficients in the present study have been correlated in terms of the relevant dimensionless parameters as:
$Nu_t=\frac{h_oD_t}{k_g}=259.1(1-\epsilon)(Re_s/Ar_s)^{0.33}\Bigg[\frac{\rho _sC_{ps}D_t^{3/2}g^{1/2}}{k_g}\Bigg]^{0.06}Pr^{0.30}$
$Nu_p=\frac{h_od_p}{k_g}=1.108Re^{-0.36}Re_w^{0.34}[(Re_s/Ar_s)^{0.59}+0.6944Fr_w^{0.89}]Pr^{0.28}$
$Nu_p=\frac{h_od_p}{k_g}=0.648Re^{0.33}Re_m^{-0.91}Re_w^{-0.10}$
