Optimization Of DTB Crystallizer Structure And Its Internal Flow Field Simulation Based On CFD

The crystallization technology has been widely used and the value of application is high due to its advantages of high separation efficiency,low energy consumption,and low environmental pollution.The DTB crystallizers that appeared in the late 1950 s have been widely used due to their simple structure and high production strength.In recent years,CFD has been widely used to simulate the crystallization process.Most scholars pay attention to crystallization parameters such as nucleation and growth of crystals.Less scholars pay attention to the flow field distribution and crystal suspension in industrial and double cylinder DTB crystallizers.The mixing effect,which has a great influence on the crystallization effect.In this paper,the Fluent commercial software is used to simulate the mixing effect of the flow field in the industrial DTB crystallizer.The structure and operation mode of the stirring paddle are optimized,and the numerical values of the single-phase flow and the two-phase flow field in the crystallizer are carried out.The simulation lays a theoretical foundation for studying the crystallization process and provides a reference for the application design of industrial crystallizers.The solution algorithm is verified.Different solving algorithms are selected for single-phase flow and solid-liquid two-phase flow,and the simulated values of the power quantity are compared with the experimental values and the simulated values of the critical suspension speed and the empirical values.The results show that the relative error between the simulated value and the experimental value obtained by the steady state solver,the standard k-? turbulence model,the multiple reference system(MRF)and the SIMPLE algorithm is 2.5%;the transient solver,the standard k-? The relative error between the simulated and empirical values obtained by the turbulence model,the multiple reference system(MRF),the Phase Coupled SIMPLE algorithm,and the syamlal-obrien drag model is 2.5%.The configuration of the paddle is different,and the flow pattern generated in the crystallizer will also be different.Based on the speed,shear rate,power consumption and medium mass flow rate,the mixing paddle was optimized for the paddle type,paddle mounting height,paddle spacing,number of paddles,etc.The simulation results showed that the single layer PBT was stirred.The paddle performs better at a mounting height of 1/4H.On the basis of single-phase flow,the flow field distribution,power consumption,cycle performance,and turbulent kinetic energy in the mold were compared and analyzed from the macroscopic flow field,the rotation direction of the stirring paddle,the medium density and the stirring speed.The influence of the crystallizer structure on the flow field shows that the effect of the counterclockwise rotation of the stirring paddle is better than that of the clockwise rotation;the density of the medium has no significant effect on the flow field in the crystallizer,and the media flux and power consumption are respectively related to the media density.A linear relationship is exhibited;the increase in the stirring speed does not affect the flow pattern,and there is a linear relationship between the speed and the flow rate.The multiphase flow model was used to analyze the suspension effect of the crystal.The effects of crystal volume fraction,crystal size and crystal density on the suspension effect were studied.The results show that the larger the crystal volume fraction,the better the overall suspension effect of the crystal in the crystallizer.When the crystal diameter is 0.1mm and 0.3mm,it can be completely and uniformly suspended in the crystallizer;the influence on the crystal density is analyzed,and it is found that the better the suspension effect and the smaller the power consumption when the density is small.The feeding position commonly used in the industry was selected.With the mixing time as the index,it was found that the effect of the lower part of the crystallizer was better;the transfer rate of the tracer below the blade was significantly higher than that of the free liquid surface.