Mass transfer in gas-liquid stirred reactor with various triple-impeller combinations

The gassed power demand and volumetric mass transfer coefficient (k(L)a) were investigated in a fully baffled, dished-base stirred vessel with a diameter of 0.30 m agitated by five triple-impeller combinations. Six types of impellers (six-half-elliptical-blade disk turbine (HEDT), four-wide-blade hydrofoil impeller (WH) pumping down (D) and pumping up (U), parabolic-blade disk turbine (PDT), and CBY narrow blade (N) and wide blade (W)) were used to form five combinations identified by PDT + 2CBY(N), PDT + 2CBY(W), PDT + 2WH(D), HEDT + 2WH(D) and HEDT + 2WH(U), respectively. The results show that the relative power demand of HEDT + 2WH(U) is higher than that of other four impeller combinations under all operating conditions. At low superficial gas velocity (u(G)), k(L)a differences among impeller combinations are not obvious. However, when u(G) is high, PDT + 2WH(D) shows the best mass transfer performance and HEDT + 2WH(U) shows the worst mass transfer performance under all operating conditions. At high u(G) and a given power input, the impeller combinations with high agitation speed and big projection cross-sectional area lead to relatively high values of k(L)a. Based on the experimental data, the regressed correlations of gassed power number with Froude number and gas flow number, and k(L)a with power consumption and superficial gas velocity are obtained for five different impeller combinations, which could be used as guidance for industrial design. (C) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.