Numerical Simulation Of Mixing Efficiency In Industrial Scale Stirred Tank With Large Height-diameter Ratio

Vertical mechanical mixing biological fermentation reactor is the most commonly used equipment for xanthan gum fermentation.In the fermentation process,the optimization of the impeller to improve the yield and quality of xanthan gum is of great significance.During fermentation process the viscosity range of the system changes greatly because of aerobic fermentation,which further increases the difficulty of the impeller selection.With the progress of computer technology,the use of computational fluid dynamics(CFD)method to study the fluid flow and mixing process has obvious advantages,more and more widely used.In this paper,FLUENT 15.0 was used to simulate the single phase and gas-liquid two phases of the xanthan gum solution with mass fraction of 1wt%.The standard k-? model is adapted for turbulence,Euler-Euler model is used for multiphase flow,the group balance model is applied with the bubble,the blade area is treated with multiple reference systems.In this paper,four kinds of impellers(MB1,MB2,KSX,TT)are used in the mixing process.The results are as followed:The liquid flow field and the gas phase flow field of the four kinds of impellers show the same flow regime.The two kinds of MB impellers present a typical "large cycle" flow pattern;the KSX and TT impellers are layered in the flow field,KSX shows the axial flow characteristics.The power consumption per unit volume,the shear rate and the amount of liquid discharge of the four kinds of impellers increase with the increase of speed.Under the same unit volume power consumption,MB2 shear rate is the highest.Under the same gas velocity-inlet,with the increase of stirring speed,the gas holdup increases,the average bubble diameter becomes smaller and the bubble size distribution range becomes wider Compared with the four kinds of stirrer,mass transfer coefficient of TT impeller is the largest.Under the same unit volume power consumption,with the increase of gas velocityinlet,the he gas holdup shows a weak increasing trend,and the probability of large bubbles in the reactor increases.Compared with the four kinds of stirrer,mass transfer coefficient of TT impeller is the largest.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.