POWER CONSUMPTION, GAS HOLDUP, AND MASS-TRANSFER COEFFICIENT OF TRIPLE-IMPELLER CONFIGURATIONS IN A STIRRED VESSEL WITH VERTICAL TUBULAR COILS

Three kinds of impellercombinations (3 x 4WHd, HB + 2 x 4WHd, 2 x HB + 4WHd) were used to investigate the effects of coil baffles on systempower consumption, gas holdup, and mass transfer coefficient. The experiments were performed in a dish-bottomed vessel with a diameter of 0.29 m. Results of the power consumption experiments show that at the same rotation speed and an increasing rate of gas flow, the power consumptions of 3 x 4WHd and 2 x HB + 4WHd with coil baffles are almost the same as that of a system with four planar baffles, but there is a clear power draw for the HB + 2 x 4WHd combination. At rotational speeds of 250-350rpm, the largest power draws for the 2 x HB + 4WHd, HB + 2 x 4WHd, and 3 x 4WHd impeller combinations equipped with coil baffles are 27, 25, and 15%, respectively. The gas holdup experiment shows that with installation of coil baffles in the vessel, axial and radial impeller combinations can achieve gas dispersion identical to that attained with planar baffles. At the same power inputand superficial gas rate over a wide range of gas velocities, the k(L)a values of the coil baffles for the 3 x 4WHd and 2 x HB + 4WHd combinations are almost identical to those of a conventional system with four baffles. However, in the HB + 2 x 4WHd system, k(L)a values of the coilbaffles are 15% higher than for planar baffles at low gas velocities and 30% higher at high superficial gas rates. Finally, all data from the experiments on gas holdup and k(L)a values may be correlated through the equations epsilon = alpha(P-g/V)(beta) (Vs)(gamma) and K-L a = K1 (P-G/V)(K2) (V-S)(K3).