Numerical Simulation Of Gas-liquid Mixing Processes For Pseudoplastic Fluid With High Viscosity In Industrial Scale Stirred Tank

Xanthan gum is a kind of widely used natural biopolymer, it’s aqueous solution is a kind of typical high viscosity pseudo-plastic, but in the process of fermentation, the property of high viscosity pseudo-plastic fluid hinders the mass transfer process in the late fermentation. This is essentially a mixing problem of high viscous pseudo-plastic fluid.This paper used 1.0wt% Xanthan gum solution as research system, focusing on industrial scale(10m3) stirred tank whose ratio of height to diameter is three, agitated by three different impellers. The three impellers include Maxblend(MB) 、 Full-zone(FZ)and three layers of six straight blade disc turbine impeller which is often used in industrial production. The aim is to perform numerical simulation for their single phase and gasliquid mass transfer mixing behaviors.The results showed that :(1) Single phase numerical simulation: The flow pattern of MB is typical double circulation; when stirred speed is low, FZ performs upper and lower two large cycle, with the increase of rotational speed, there is a obvious small cycle in the leaf blade junction;TT performs independent flow pattern. Under the high speed, the power consumption of the unit volume of FZ is higher than MB and TT. Under the same power consumption, FZ used the shortest time to fulfill the requirements of hybrid, the second is MB, the longest is TT. The high shear rate and pumping of the three impellers are all concentrate nearby blades.(2) The gas-liquid two phase numerical simulation: After the gas is piped in, liquid phase flow field and gas phase flow field present the same flow pattern structure. When the velocity-inlet is same, with the increase of rotational speed, gas holdup increases, the average bubble diameter becomes smaller, but the distribution range of bubble size becomes wider. The gas-liquid mass transfer coefficient of MB is higher than FZ, FZ is higher than TT.When the rotational speed is same, with the increase of velocity-inlet, gas holdup increases, the probability of big bubble increases. Under the lowest velocity-inlet, the gas-liquid mass transfer coefficient of FZ is highest, but with the increase of velocity-inlet,MB is highest.This paper is simulated by computational fluid dynamics(CFD) method, directly previews local characteristic parameters of the high viscosity pseudo-plastic in industrial scale stirred tank. The aim is to provide basic information for industrial optimization of industrial scale stirred tank.