Study On Dynamic Model Of Mixer-Settlers Based On Droplet Mass Transfer In Uranium Purification Cycle Process

In uranium purification cycle process of PUREX process,the uranium(Ⅵ)and purified by mixer-settlers.However,there are many kinds of mixer-settlers.In the previous simulation of mixer-settlers,the differences in structure and process conditions are rarely taken into account,which may lead to the adaptability of the model to other working conditions.Therefore,this paper describes the extraction process in the mixer-settlers by using the droplet mass transfer method.Through the relationship between the droplet diameter,the droplet mass transfer formula,the structure of the mixer-settlers and the process conditions,the coupling degree between the dynamic model of the droplet mass transfer and the equipment and the process conditions is strengthened.The dynamic simulation of the extraction stage and the reverse extraction stage of the uranium purification cycle process is carried out.Firstly,the dynamic models of extraction and back extraction of neptunium based on liquid drop mass transfer and phase equilibrium in uranium purification cycle process are established.The relationship between the size,rotation speed and paddle shape of the mixing and settling tank was established by using the droplet diameter model and the mass transfer rate model.The model was verified by the experimental data in the literature,and it was found that the droplet type was stagnant under the process conditions of 0.1～0.5 retention fraction and 600～2000rotation speed.The relative error of the stagnant droplet mass transfer model is less than 5% in the simulation of uranium water phase.In the stationary droplet type mass transfer model,the stage efficiency is about 99%,and in the stationary droplet type mass transfer model,the stage efficiency is proportional to the number of revolutions.The time for the dynamic model based on droplet mass transfer to reach steady state is consistent with the experimental results,and the equilibrium is reached at the volume of 2～3 tanks.When the single-stage mixer-settlers reaches steady state,the distribution ratio is verified in the literature,and the maximum relative error of uranium(Ⅵ)is 15.90% under the same system.The maximum relative error of nitric acid is 13.04%.Finally,the process conditions under three different working conditions are simulated and compared with the experimental data in the literature.The simulated values are in good agreement with the experimental values.The recoveries of uranium and neptunium can reach more than 99%,and the relative error of outlet concentration in extraction section is basically less than 20%.The average recovery rate of all levels is about 60%,and the relative error of the outlet concentration of the reverse section is basically lower than 17.38%.The simulation of neptunium in the washing stage is consistent with the experimental data,and neptunium is basically extracted back water phase in the 7th stage.