Process Intensification On Turbulence For Fine Particle Separation And The Optimization Design Of A Vortex Mineralization Tube

Flotation is the main method to separate the fine useful mineral particles from the impurity particles.The basic principle is that the mineral particles collide with bubbles and then float up to recover in the three-phase flow system of gas,liquid and solid.In the current situation of the continuous shortage of mineral resources,the flotation technology is facing a great challenge.The fine coal particle has very light weight,small inertia and is difficult to collide with bubbles,the recovery of fine particles is extremely inefficient.At present,most researchers related to the flotation are focusing on the flotation agents and selective flocculation,and paying less attention to the fluid environment,especially the micro flow closely related to bubbles and particles.Increasing turbulence is recognized as an effective method to strengthen the flotation of fine particles in the industry.The vortex mineralizing tube designed by our research group strengthens the flow field in the tube,which performs better than the light tube.However,until now,the researchers only studied the effect of triangular cone vortex generator on the flow field in the tube and mineral flotation.And the enhancement of the flow field in the tube is not suitable for different sizes of particles.In this thesis,through the combination of experimental and numerical simulation researches,with the research object of flotation turbulent environment of vortex mineralizing tube,the corresponding relationship between flotation turbulent parameters and particle size floatability index were studied.Then according to the study results,the vortex mineralizing tube structure which can produce integrated turbulent environment was designed,so as to further improve the flotation recovery effect.The main achievements include the following aspects:Firstly,the effects of single row and multiple rows of circular,triangular,trapezoidal and rectangular vortex generators(VG)on the turbulent flow field in the mineralization tube were compared.The numerical simulation results show that the distribution of pressure and velocity behind the rectangular VG has the largest gradient,which leads to the widest distribution of streamwise vorticity.The average vorticity is676.22 at 0.48)³/h,which is 0.71%,2.27%and 4.06%higher than that of circular,trapezoidal and triangular VG respectively.Under the same conditions,the rectangular VG can enhance the turbulence better.The results show that the rectangular VG has advantages in enhancing the collision and adhesion process of particles and bubbles.The flotation effects of VG mineralizing tubes with different structures were verified,and the pure mineral flotation experiments of chalcopyrite were carried out at the flow rate of 0.48)³/h.The results showed that the recoveries of rectangular VG mineralizing tube for 0-45?m,45-75?m,75-125?m and 125-180?m were 85.93%,86.89%,90.14%and 88.84%respectively,which were 5.34%,2.91%,3.56%and 3.58%higher than oval VG mineralizing tube,8.63%,6.2%,4.85%and 4.97%higher than trapezoidal VG mineralizing tube,and 19.81%,15.92%,13.34%and 7.81%higher than triangle VG mineralizing tube.In conclusion,the flotation recovery effect of rectangular VG mineralizing tube is better than that of oval,trapezoidal and triangular VG mineralizing tube,so rectangular VG mineralizing tube was selected for further research.Furthermore,based on the rectangular VG mineralized tube structure,the corresponding relationship between the geometric structure and the turbulence characteristic parameters was clarified by using the numerical simulation method.The numerical simulation results of different circulation flow rates(0.48)³/h?0.58)³/h?0.68)³/h?0.78)³/h)and different rectangular VG inclination angles(25°?35°?45°?55°)show that when the flow rate increases from 0.48)³/hto 0.78)³/h,the volume average dissipation rate and the volume average turbulent flow energy increase by248.60%and 129.03%,but the vortex scale decreases by 36.68%,which means the turbulence intensity would increase with the increase of flow rate.When the angle increases from 25°to 55°,the volume average dissipation rate increases by 539.47%,the volume average turbulent energy increases by 293.55%,and the vortex scale decreases by 59%,which means that the turbulence intensity increases with the increase of the inclination angle.Thirdly,the relationship between turbulence characteristic parameters and particle size floatability was obtained through flotation test.The flotation experiments of pure chalcopyrite minerals with different circulation flow rates(0.48)³/h?0.58)³/h?0.68)³/h?0.78)³/h)and different rectangular VG inclination angles(25°,35°,45°and 55°)show that with the increase of particle size from 0-45?m,45-75?m,75-125?m and 125-180?m,the volume average turbulent kinetic energy and volume average turbulent dissipation rate needed to obtain the best flotation effect decrease in turn,and the vortex scale increases in turn.With the increase of turbulent kinetic energy and turbulent dissipation rate,the flotation rate constant of each particle size fraction increases followed by a decrease.Moreover,with the increase of particle size,the required turbulent kinetic energy and turbulent dissipation rate are lower.The flotation rate constant increases with₆)/d,it first increases and then decreases.When₆)/d is between 0.1-0.15,a higher flotation rate constant can be obtained.Finally,according to the relationship among the structure,turbulence environment and particle size floatability,the structure of the vortex mineralizing tube was optimized and the cascade vortex mineralizing tube was designed.Numerical simulation and flotation experiments of pure chalcopyrite minerals in 0.78)³/hflow rate and 0-45?m,45-75?m,75-125?m and 125-180?m particle size fractions show that there are high turbulence environment regions and low turbulence environment regions with cascade distribution in the cascade tube(decreasing with the flow direction in turn).The flotation recovery of each particle size can reach more than 93%,and a higher flotation rate constant can be obtained,which indicates that the turbulent environment in the cascade vortex mineralizing tube has an adaptive effect on the flotation recovery of each particle size.