Power consumption and mass transfer in a gas-liquid-solid stirred tank reactor with various triple-impeller combinations

Abstract

Five triple-impeller combinations were used to study the effects of impeller combination on gassed power consumption and volumetric mass transfer coefficient kLa in a baffled gas-liquid-solid stirred tank reactor with air, water, and 12vol% of glass beads. The bottom impeller was chosen from two radial flow type impellers of half-elliptical-blade disk turbine (HEDT) and parabolic-blade disk turbine (PDT), and the upper two impellers were chosen from four axial flow type impellers with different blade widths and pumping modes, forming five different triple-impeller combinations: HEDT+2WHU, HEDT+2WHD, PDT+2WHD, PDT+2CBYW, and PDT+2CBYN. The experimental results show that the addition of solid particles has little effect on the relative power demand (RPD), but significant effect on kLa. kLa in a three-phase system is smaller than that in a two-phase system, and HEDT+2WHU with two up-pumping upper impellers shows the best mass transfer performance in these five triple-impeller combinations at various superficial gas velocities uG, much different from what HEDT+2WHU behaves in two-phase systems. The bottom impeller mainly influences the absolute power consumption, but the two upper impellers play a more important role on the change of RPD than the bottom impeller. The impeller combinations with a higher power number and larger projection cross-sectional area can lead to a higher kLa. The effect of operating conditions (e.g., power consumption and superficial gas velocity), the bottom impeller, the blade width and pumping mode of the two upper impellers, and solid particles were investigated and discussed in detail. To better explain the difference of mass transfer performance between impeller combinations HEDT+2WHD/U, the Eulerian-Eulerian formulation of the k-ε turbulence model with the population balance model (PBM) was used to simulate the flow field in gas-liquid systems.