Chemical Engineering Research & Design, Vol.154, 60-69, 2020
Investigation of gas-liquid dispersion and mass transfer performance of wide-viscosity-range impellers in water solutions of xanthan gum
Wide-viscosity-range impellers have extensive demands and applications in process industry. The gas-liquid dispersion and mass transfer characteristics of wide-viscosity-range impellers including Large-double-blade (LDB) impeller, Fullzone (FZ) impeller and Maxblend (MB) impeller in water solutions of xanthan gum were investigated experimentally and compared. The influences of gas flow rate, impeller speed and polymer concentration of liquid on the power consumption, overall gas holdup epsilon(g) and mass transfer coefficient K(L)a were also analyzed. On this basis, the appropriate operating parameters and impeller type were determined. The results indicate that with rising flow rate, the higher epsilon(g) and K(L)a can be achieved with a drop in power consumption, and a relatively high flow rate is recommended on the premise of guaranteeing the complete dispersal condition in aerated vessel. Higher impeller speed provides better gas-liquid dispersion and mass transfer performance, but results in more power consumption simultaneously. The appropriate impeller speed should be just enough to meet the requirements of epsilon(g) and K(L)a. It also is found that the increasing concentration of water solution of xanthan gum adds to the complexity of gas dispersion and mass transfer in aerated vessel. Under the same specific power consumption P-V, the epsilon(g) and K(L)a are positive and negative correlation with the polymer concentration of liquid, respectively. Specially, when the concentration of water solution of xanthan gum is relatively low, the FZ impeller exhibits the best gas dispersion and mass transfer performance under the same specific power consumption. Nevertheless, the mass transfer performance of FZ impeller deteriorates significant when the concentration of water solution of xanthan gum increases to 1.00 wt%, and the MB impeller becomes the most appropriate impeller type in this condition. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.