Numerical Simulation Of Gas-Liquid Flow In Gold Leaching Reactors

Leaching reactors are used as key facilities for gold extraction in hydrometallurgy and pre-oxidation of refractory gold ore.They can be classified into two different styles:air-agitated tank and mechanical stirred tank.As the complicated gas-liquid-solid three phase flow in the gold leaching process,considerable uncertainties remain in reactor design and scale-up procedures.As the industrial reactor scales are much larger than before,calculations and extrapolations of results from laboratory reactors to industrial facilities cannot be justified quantitatively.Along with the development of computer technique and the computational fluid dynamics modeling method,CFD modelling has been a powerful tool since it may assist in investigating the detailed flow characteristics of leaching reactors,and give advices for scale-up methods and operation conditions.After testified by the experimental data,the CFD model can help to get quick estimation of new designs,tank hydrodynamics optimization and process optimization,and save resource and time in the meanwhile.In this paper,detailed two-fluid modeling methodology was discussed.The models for bubble distrubution in mechanical stirred tank and air-agitated tank were proposed.In the mean time the simulation results were reasonable.For gas dispersion in a liquid,the modelling method employed the Eulerian-Eulerian two-fluid equations,in conjunction with the k-? turbulence model.The equations of turbulence in gas-liquid two-phase flow were described,especially the turbulence modelling methods of considering the bubble induced turbulence.Different forms of the interfacial forces,such as drag force,virtual mass force,lit force,wall lubrication force and turbulent dispersion force,were introduced.The effects of these interfacial forces in Eulerian-Eulerian two-fluid simulation were discussed.For the prediction of bubble size and the circulation regime under high gas flow rates,the inhomogeneous MUSIG model was used to compute the complex flow regimes.The MUSIG model is a population balance method to predict the bubble sizes,taking break-up and coalescence into account.Simulation results show reasonable overall agreement in comparison with experimental data for bubble distribution,gas volume fraction,gas and liquid velocities.Finally,simulations of gas-liquid flow were carried out for a full-scale mechanical stirred tank for pre-oxidation of refractory gold ore designed by BGRIMM and a gas-agitated reactor equipped at a Shandong Gold Group leaching plant in Laizhou China.The CFD model enables the efficiency of the functions of several main design and operating parameters to be investigated.Under a wide range of reactor designs and process conditions,the circulation velocities,gas hold-up in the tank and bubble residence time distribution were simulated and compared.CFD simulations demonstrated a better performance than the original reactor design.In comparison to results based on previously published modelling methods,a significant improvement has been demonstrated.However,a number of limitations have been identified in the modelling method,which can be attributed either to the practical limitations on computer resources,or to a lack of understanding of the underlying physics.Recommendations have been made regarding investigations which could assist with further improvement of the CFD modelling method.