Hydrodynamic properties in an internally circulating fluidized bed coal gasifier (0.28 m I.D. × 2.6 m high) with a draft tube (0.1 m I.D. × 0.9 m high) have been determined. The effects of orifice diameter (15, 20, 25, 30 mm), particle size (300, 390, 460, 610 μm), inlet gas velocities to the draft tube (fluidized bed, 1.5-2.7 m/s) and the annulus (moving bed, 0.09-0.38 m/s), static bed height (0.8, 0.85, 0.88, 0.9, 0.95 m) on the solids circulation rate and gas bypassing factions between the annulus and draft tube regions have been determined. The solids circulation rate has been determined by using two thermistor probes. The solids circulation rate increases with increasing gas velocities to the draft tube and it is greatly enhanced by increasing gas velocities to the annulus. The gas bypassing fractions has been determined by using a tracer gas ($CO_2$). At a constant gas velocity to the annulus, the gas bypassing fraction from draft to annulus decreases but the fraction from annulus to draft increases with increasing gas velocity to the draft tube. The actual minimum fluidization condition of the annulus region can be attained at 1.4-1.5 $U_{mf}$ due to gas bypassing circulation rate increases with increasing particle size. The solids circulation rate increases with increasing orifice diameter. The gas bypassing fraction from draft to annulus decreases but the fraction from annulus to draft increases with increasing orifice diameter. The solids circulation rate and gas bypassing fractions decrease with increasing static bed height up to the separator bottom and then increase with increasing the static bed height above the separator bottom. The obtained solids circulation rate with an internally circulating fluidized bed with a draft tube has been correlated with the pertinent dimensionless groups as:
$\frac{W_a}{\rho_s(1-\varepsilon_{mf})U_{mf}}=2.63\times 10^{-5}(\frac{U_a\times U_d}{U^2_{mf}})^{1.19}(\frac{d_{or}}{d_p})^{1.29}(\frac{H}{H_s})^{0.873}$
The obtained gas flow per orifice and the orifice discharge coefficient with an internally circulating fluidized bed with draft tube has been correlated with the experimental variables as:
$\phi_{vo}=8.85\times10^{-6}(U_a)^{1.73}(U_d)^{0.77}(D_{or})^{0.24}(H_s)^{0.77} (d_p)^{-2.11}$
$C_d=0.229(D_{or})^{0.725}(d_P)^{-0.44}$
The solids circulation rate can be determined from the following equation with the information of $\phi_{vo}$ and $C_d$.
$W_a=\frac{-\rho^*_sC^2_d(b+\frac{2a\phi_{vo}}{\varepsilon_{mf}})+\rho^{\dot}_sC_d\sqrt{\frac{4a\phi^2_{vo}}{\varepsilon^2_{mf}}+\frac{4b\phi_{vo}}{\varepsilon_{mf}}+C^2_db^2}{2(1-aC^2_d)}$
