Some features of a novel gas dispersion impeller in a dual-impeller configuration

The performance of the concave blade BT-6 impeller was evaluated in a dual-impeller agitated tank (T = 0.48 m, H / T = 2). Power draw was measured and almost constant Pg/Pu ratio with aeration was found in agreement with what had been reported previously. Gas hold-up exhibited the same dependence on power per unit volume and superficial velocity as shown by other types of impellers. The same holds true for the volumetric mass transfer coefficients. Mixing time was measured at several vertical positions in the tank, after a pulse of an electrolytic tracer or a dye was introduced. No significant compartmentalization was apparent. Mixing time at a given specific power input under ungassed and gassed conditions is in between that of standard radial turbines and hydrofoil axial impellers, very close to the latter. Mixing time dependence on power consumption per unit volume exhibits -1/3 law, i.e. the same as reported in the literature for other impeller types. The experimental curves from which mixing time was determined were also analysed in terms of the axial dispersion model, that proved satisfactory to interpret the behaviour of dual BT-6 impellers under both ungassed and gassed conditions.