Hydrodynamic properties(solid circulation rate, gas bypassing) in a cold model internal circulating fluidized bed(0.3m I.D. × 0.6m height) with a draft tube(0.1m I.D. × 0.3m height) have been determined. The effect of gas velocities(0.12~1.05m/s) to the draft tube and to the downward moving bed(0.12~0.18m/s), gap height(0.065~0.2m), static bed height(0.365~0.465m) of solids on solids circulation rate and gas bypassing from the draft tube to the moving bed have been determined. The solids circulation rate has been determined by using two thermistors probes. The solids circulation rate increases with increasing gas velocities to the draft tube and to the downward moving bed and consequent increase in pressure drop across the gap opening. When the static bed height of solids is identical to the height of draft tube, a maximum solids circulation rate can be attained. At a constant gas velocity to the annulus, the gas bypassing from the annulus to the draft tube increases with increasing gas velocity to the draft tube and gap height. It has been found that the gas bypassing from the draft tube to the annulus occurs up to the gas velocity to the annulus reaches 0.6 times of minimum fluidizing velocity($U_{mf}$). However, the gas bypassing reverses from the annulus to the draft tube when the gas velocity to annulus reaches above 0.6$U_{mf}$.
Combustion characteristics of CWM(coal-water mixture) in an internal circulating fluidized bed combustor as the same dimension of the cold model bed have been determined. The total entrainment rate increase with an increases in gas velocity in the draft tube, but it decrease with an increase in bed temperature. The unburned carbon loss in flyash increases with an increase in gas velocity in the draft tube. The overall combustion efficiency increases with increasing bed temperature, but decrease with increasing gas velocity in the draft tube. The heat transfer coefficient in the annulus(moving bed) increases with increasing gas velocity and bed temperature.
