Gas-Liquid Dispersion Characteristics In A Stirred Tank With Medium Viscosity Fluid

In many process industries, mechanical agitation is widely used for mass transfer in gas-liquid mixing processes. Nowadays, gas is not only distributed in water but also some liquid with high viscosity. The existing empirical correlations for water are no longer applicable.Considering the properties of glycerol and xanthan gum, several kinds of impellers were selected in this research and gas dispersion characteristics in those mediums was thoroughly studied. More specifically, power consumption and gas holdup were analyzed qualitatively and quantitatively. The conclusions drawn from the experiments can used to optimize the impeller type, so as to provide reference for design optimization in large scale mixing equipment.Several factors which Influence gas distribution were studied. In aqueous glycerol, the variables include combined impeller types, distance between two impeller players, number of impeller players and gas distributors; while in aqueous xanthan gum, the impeller types and the types of bottom impellers (InterMIG impeller and PDT impeller) were taken into consideration.The results show that in aqueous glycerol, with the same power input:(1)3interMIGUD impeller can obtain the highest gas holdup (2)when the space between two impeller is145mm(C/T=0.305), gas holdup is higher than other data (3) mixing tank with3p layers is better than2or4layer ones (4) The gas hold up increases with increasing diameter of gas distributor and decreasing distributor hole diameter.In gased aqueous Xanthan, though the gas holdup of axial flow impellers combination is the lowest in the3kinds of impellers, the RPD is highest. That is to say, bubble dispersion by this kind of impeller combination is better. The highest gas holdup is obtained with the bottom impeller PDT and upper impeller InterMIG, while its power consumption decreased dramatically with RPD lower than0.5. This can be attributed to the huge cavitation at the back of impeller blades, which is detrimental for gas-liquid dispersion. From the research result, it is recommended to use slotted axial flow impellers for dispersing gas in high viscosity liquid such as xanthan gum solution.At the main time, this essay preliminarily analyzed gas distribution in CMC solution with3different kinds of impellers.