CFD Numerical Simulation In Stirred Tank Based On The Pressurized Acid Leaching Of Manganese Dust

As a mixing equipment,stirring kettle is widely used in food,sewage treatment,metallurgy,petrochemical and other fields.Its main function is to mix single-phase or multi-phase substances to achieve the purpose of heat and mass transfer.At present,most stirring cauldron on the market is airtight and opaque,which makes the stirring cauldron like a "black box" in the operation process,and it is impossible to know the motion state,speed,turbulent kinetic energy and other parameters in the cauldron,and these parameters are an important embodiment of understanding the information in the stirring cauldron and optimizing the structure of the stirring cauldron.Based on this situation,more and more devices are applied to measure these parameters,which in a sense provide guidance for studying the information in the stirring kettle.However,the use of these equipment has limitations and wastes a lot of manpower and material resources according to the previous half-experience half-theory method.In recent years,the emergence of computational fluid dynamics(CFD)provides effective means to solve this kind of problem.In addition,the development of computer hardware makes the application of CFD to practical problems become a reality,and its obvious advantages make CFD become the most powerful tool in solving fluid problems.This paper firstly using UG three-dimensional structure of asymmetric stirred tank,the whole 3 d model according to MRF model is divided into two parts modeling,and then import in Igs or Iges format to ICEM mesh,and compare the structured and unstructured mesh grid in common,selection model,boundary conditions and numerical strategy,through monitoring residual reached under 10-4 and specific point double ensure the convergence of calculation speed.As for the gas-liquid phase numerical simulation,the grid independence test is carried out firstly to exclude the influence of the grid on the simulation results,and the result is better when the number is 631507.Using euler-euler model,PBM model and standard k-model,numerical simulation of asymmetric stirred tank was carried out.With stirring speed,ventilation rate and liquid medium viscosity as variables,it is concluded that increasing stirring rate,ventilation rate and liquid viscosity can increase the gas holdup of the kettle.The increase of liquid viscosity causes obvious gas accumulation on the right side of the stirring shaft.The distribution area of large and small diameter bubbles is basically unchanged.The average bubble diameter in the kettle increases with the increase of aeration rate and liquid viscosity.The stirring rate decreased with the increase of the stirring rate,and the stirring rate had the largest change on the average bubble diameter,which was 17.9%.The viscosity effect was followed by the change amplitude of 5.5%.Aeration rate has the least effect.The change was 4.5%.As for the soild-liquid phase numerical simulation,Carletti et al.2014 experimental system was used to verify the applicability of the two-fluid model with particle dynamics theory(KTGF),k-turbulence model and Gidaspow traction model as closed models for liquid-solid two-phase simulation.Then taking the stirring speed,the viscosity of liquid medium and the volume fraction of solid as variables,the simulation shows that the liquid velocity increases with the increase of stirring speed and decreases with the increase of viscosity and volume fraction of solid.The solid volume fraction was 2.5%,7% and 13%,and the corresponding liquid velocity decreased by 8%,16.2% and 18.4%.Turbulent kinetic energy increases with the increase of stirring speed and viscosity,and decreases with the increase of solid volume fraction.The solid volume fraction was 2.5%,7% and 13%,and the corresponding turbulent kinetic energy decreased by 7.6%,13.2% and 20.6%.The method of red ink tracer was adopted to measure the mixing time of liquid in the kettle.It was found that the mixing time decreased with the increase of stirring speed,and the mixing time was more sensitive at low stirring speed.When the stirring speed increased from 350 rpm to 900 rpm,the mixing time decreased from 24.2s to 6s.Mixing time increased with the increase of viscosity and solid volume fraction.Solid volume fraction increased from 0 to 13%,and mixing time increased by 16 s.Then,the gas-liquid two-phase numerical simulation was carried out for three different structures of the stirred tank,and the results showed that the best dispersion effect was the double-layer oval type with baffle,with the gas holdup of 10.8% in the same time,the gas holdup of 5.2% in the single-layer oval type and 2.2% in the single-layer flat bottom type.For the distribution of axial turbulent kinetic energy,the region with the turbulent kinetic energy of 0 is the stirring blade.There is little difference in the turbulent kinetic energy of the single-layer flat bottom type and the single-layer oval type,and the turbulent kinetic energy of the single-layer flat bottom type and the single-layer oval type is much larger than that of the former two.The leaching kinetics of high calcium silicomanganese ore with different stirring speeds and ventilation rates as experimental variables was studied by using the numerical simulation and experiment of the double-layer agitator,and it was concluded that the speed of 500 rpm was more appropriate and the ventilation rate of 7m/s was more appropriate.