Study On Multiphase Fluid Dynamics In Stirred Tank Bio-oxidation Reactor

In order to reveal the basic law of gas-liquid-solid three-phase flow of biological oxidation reactor for refractory gold ore containing arsenic,A stirred tank reactor was designed and manufactured to be used in cold model experiments.Arsenic bearing refractory gold ore-water as the experimental materials,solid suspension and gas dispersion characteristics were studied by electrical conductivity probe,and the corresponding computational fluid dynamics model was established.The details are as follow.1.The influences of paddle type,impeller diameter,stirring speed,the distance from the reactor bottom and the solid holdup on the axial solid concentration distribution were discussed.The results indicated that under the same conditions,the solid distribution of 6PBT(45°)is better,but the critical speed Njs of Rushton turbine is lower;with the increase of the impeller clearance,the values of Njs is increased.while C/D is in 1/5-1/3,the difference of distribution quality is negligible.Though the a value is small,C/D=0.4,the Njs have relatively large increase;when the solid holdup increased from 15%to 25%,the critical speed went up;In Njs,the invariant of distribution quality illustrates that the solid particles are strongly influenced by the liquid entrainment;the empirical correlation of Zwietering can be used to predict the critical speed of the liquid-solid system.2.According to the industrial design practice of gas distributor and related literature,three types of gas distributor were designed.Conductivity probe was introduced to study the effect of gas distributor on the gas dispersion.In the impeller region,for disc and annular distributor,the tendency of the local gas holdup developed is opposite;the stirring speed have the opposite effect on the uniformity of the local gas holdup distribution which increases with the increasing of air flow rate;the local gas holdup of the upper circulation area of disc distributor is higher and the uniformity of the annular distributor is preferable.3.CFD simulations have been carried out to study gas-liquid-solid three-phase using Eulerian-Eulerian multifluid approach along with standard k-s turbulence model and multiple frame of reference(MFR).And the values predicted by CFD simulation and experimental data are analyzed.The results indicates that the prediction and experimental data of three-phase off bottom suspension is consistent,in Njsg,Rushton and HEDT have maintained a better particle suspension quality in the stirred tank;for HEDT,compared with the Rushton turbine,the local gas holdup distribution is better and the region of high turbulent flow energy and dissipation rate is smaller,resulting lower shear rate;the increase of aeration rate can improve the gas-liquid dispersion quality and reduce the shear rate,but the effect is decreased with the increase of gas flow rate.This paper provides experimental foundation and theoretical basis for the study of mass transfer,heat transfer and industrial application in the biological oxidation reactor of refractory gold ore containing arsenic.