| The hydrocyclone is an effective device to perform the multiphase separation by taking advantage of the centrifugal force field. Although a hydrocyclone appears a simple structure, the internal flow field is very complicated. It is well known that there is a close relationship between the separation mechanism and the multiphase fluid flow in a hydrocyclone, thus, a in-depth investigation about this relationship is meaningful to regulate the hydrocyclone separation and optimize the hydrocyclone structure. In this work, by numerical simulation and experimental test, the study focused on the motion rule of gas-liquid-solid multiphase, the separation characteristic and the motion behavior of the particle phase, and the influence mechanism of high sharpness particle classification.The mathematical models to precisely describe the multiphase flow in a hydrocyclone were established by the computational fluid dynamics (CFD) method. Based on the RANS equations, the anisotropic turbulent flow of the liquid phase was predicted by the Reynolds Stress Model (RSM). The transient variation characteristic of the gas phase was captured by the Volume of Fluid Model (VOF). The motion behavior of the particle phase was described by the Discrete Phase Model (DPM). The mathematical models were proved to be accurate and reliable by comparing the velocity distributions of the liquid phase, the radium of air core and the separation efficiency of the particle phase with the experimental data.According to the established mathematical models, the separation mechanism of the particle phase was completely explored from three views of the separation efficiency, the force analysis and the motion trajectory. The results showed that the particle motion was jointly controlled by the drag force, the pressure gradient force and the centrifugal force. For particles of different sizes, the drag force played a decisive role in the radial direction, the centrifugal force and the pressure gradient force remained about the same. While with the increasing of particle size, the drag force decreased exponentially. As a result, the influence of the centrifugal force and the pressure gradient force was strengthened, manifested as the increasing of the separation efficiency. Among the overflow particles, most particles moved rapidly to the bottom of the vortex finder, entering the inner vortex. Among the underflow particles, with the increasing of particle size, particles entered the outer vortex in a faster rotation speed with a clearer motion trajectory. Besides, it also investigated the influence mechanism of particle density, fluid viscosity, inlet flow rate, particulate arrangement and split ratio on the separation characteristic and the motion behavior of the particle phase.Aiming at a sharpness classification of the particle phase, the hydrocyclone structure was optimized and evaluated by the systematic indexes of classification sharpness. The results showed that the dimensionless inlet diameter (Di/Dc), the dimensionless diameter of vortex finder (Do/Dc), the dimensionless conic section length (Lz/Dc) and the dimensionless diameter of spigot (Du/Dc) were the key parameters to the classification sharpness. With the increasing of the dimensionless inlet diameter, the classification sharpness increased. However, when the dimensionless inlet diameter exceeded its critical value (as D/Dc=0.35 in the work), the classification sharpness decreased significantly, because of a decreasing of the underflow recovery efficiency of the coarse particles, due to the aggravation of short-circuit flow. With the increasing of the dimensionless diameter of vortex finder, the classification sharpness increased and then decreased. The decreasing of split ratio led to the increasing of the overflow separation efficiency of the fine particles, while the decreasing of tangential velocity led to the decreasing of the underflow recovery efficiency of the coarse particles. With the increasing of the dimensionless conic section length, the classification sharpness increased and then decreased, too. The increasing of split ratio led to the decreasing of the overflow separation efficiency of the fine particles, while the extending of retention time led to the increasing of the underflow recovery efficiency of the coarse particles. With the increasing of the dimensionless diameter of spigot, the classification sharpness decreased. The significant increasing of split ratio led to a significant decreasing of the overflow separation efficiency of the fine particles. In conclusion, the optimization range is Di/Dc=0.20-0.30, Do/Dc=0.35-0.60, Lz/Dc=1.25?2.00 and Du/Dc=0.05-0.15.The high sharpness hydrocyclone is designed by the response surface methodology. The results showed the dimensionless diameter of vortex finder is the most significant factor, followed by the dimensionless conic section length, and the dimensionless inlet diameter and the dimensionless diameter of spigot is the least significant factors. The optimal hydrocyclone structure is Di/Dc=0.20, Do/Dc=0.35, Lz/Dc=1.67 and Du/Dc=0.10. The simulation results of the overflow separation efficiency of the fine particles and the underflow recovery efficiency of the coarse particles were 89.9% and 96.7%, respectively. The test results of this designed high sharpness hydrocyclone showed that, for the system of acidolysis tailings, the overflow separation efficiency of the fine particles could reach to 96.0%, meanwhile, the underflow recovery efficiency of the coarse particles was 69.7%. The operation data indicated that the recovered underflow particles just contained a few of fine particle impurities, without any necessity to a secondary overflow washing. Moreover, it reduced the ilmenite loss, making the TiO2 recovery efficiency as 51.0%. |
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