| The hydrocyclone has been widely used as a classification and separation device in grinding-classification operations.However,the "fish-hook" caused by constant velocity settlement of multi-component particles in a swirl field can cause ore over-grinding,which leads to further problems,such as reductions in the metal recovery and the ball mill throughput.Based on the point of view of loose classification,a new W-shaped hydrocyclone was proposed.In this hydrocyclone,the conventional column-cone combination was changed to a full-column structure,and the apex was inserted back into the hydrocyclone to form a W-shaped inner cavity.It was supposed to achieve the looseness and mass transfer of high concentration particles through the regulation of flow field so as to reduce the entrainment of fine particles in the underflow.In this paper,the distribution of flow field,special flow form,particle movement and distribution were studied with the help of theoretical modeling,numerical simulation,experimental verification and industrial application,aiming to clarify the multiphase flow characteristics and classification mechanism of W-shaped hydrocyclone.The research results have important theoretical and practical significance.Firstly,considering that the fluid inside the W-shaped hydrocyclone included three phases,that is,gas,liquid and solid,the RSM model was applied to the simulation of high-speed rotating flow,and the VOF model was adopted to obtain the dynamic development of the air core.The DPM model was adopted to obtain particle trajectory,meanwhile the Euler model was used to simulate the separation performance.The high concentration of particles at the bottom of the W-shaped hydrocyclone was noticed.According to the theory of fluid dynamics and particle dynamics,the particle phase properties of Euler model were modified to fully consider the interaction between particles,so as to make it more suitable for the study of particle motion in a W-shaped hydrocyclone.The accuracy of the mathematical model was further verified by PIV flow field test and separation performance test.Secondly,the influence of boundary structure on the flow field and separation performance of hydrocyclone was studied.It was proved that compared with the column-cone structure,the axial velocity of the fluid in the W-shaped hydrocyclone decreases and the residence time of particles is prolonged,which is conducive to the full separation of particles.At the same time,a high concentration suspended fluidized layer is formed near the apex,which plays a role of elutriation on the particles,allowing the fine particles mixed in the underflow to precipitate out and be trapped again by the inner swirl,thus reducing the fine particles in the underflow.The optimization of W-shaped structure was studied,the results show that reducing the width of the W structure can increase the density of the suspended fluidized layer at the bottom of the column,and increasing the height of the W structure can increase the thickness of the suspended layer.After comparing the separation granularity,the total separation efficiency and the separation precision,the optimal W structure parameters in this study were obtained:the height ratio is 0.064 and the width ratio is 0.333.Thirdly,the gas-liquid two-phase flow field in the W-shaped hydrocyclone was simulated,and the influence of the parameters such as the diameter of apex,the diameter and the insertion depth of the vortex finder,the height of the column section and the inlet velocity on the development of the flow field,pressure drop,shunt ratio,pressure field and velocity field in the hydrocyclone was investigated.The results show that,the pressure drop of the hydrocyclone decreases slightly with the increase of the diameter of apex,while the shunt ratio increases gradually with an obvious trend.The diameter change of apex has less influence on the tangential velocity and axial velocity of the external swirl,but it has more influence on the axial velocity of the internal swirl.The diameter change of the vortex finder has a great influence on the air core.As the diameter of vortex finder increases,the air core gradually stabilizes and the diameter increases.Meanwhile,the pressure drop and the shunt ratio decrease significantly.In the outer swirl region,the axial velocity decreases with the increase of the insertion depth,while in the inner swirl region,it increases with the increase of the insertion depth.As the height of the column increases,the total pressure drop decreases gradually.For the hydrocyclone design,appropriately increasing the height of the column can reduce the energy loss and increase the processing capacity.Although increasing the inlet velocity can increase the strength of centrifugal force field,it will cause more energy loss.Meanwhile,if the velocity is too fast,it will shorten the residence time of particles,which is not conducive to the complete separation of particles.Then,the motion characteristics of particles in a W-shaped hydrocyclone were studied.The results show that the radial centrifugal inertial acceleration and pressure gradient are several hundred times higher than gravity,and the radial drag force level is up to 106,which is the main driving force of radial motion.The radial drag force decreases exponentially with the increase of particle size.In the main separation region,the radial centrifugal force gradually increases with the increase of particle density,while the pressure gradient force is unaffected.At the bottom region inside the hydrocyclone,the change of particle density has no obvious effect on the radial centrifugal force.In contrast,the pressure gradient force gradually decreases and the radial drag force on the particle increases with the increase of particle density.When the feed concentration increases,the radial centrifugal inertia force and radial drag force of the particles are greatly reduced,but the pressure gradient force is not significantly affected.Finally,the influence of the diameter and insertion depth of vortex finder,diameter of apex,particle concentration and inlet pressure on product concentration,yield,particle size and fractional efficiency of W-shaped hydrocyclone was studied by laboratory test.At the same time,based on the response surface method,a prediction model was established with the fine particles content in underflow,quality efficiency and quantity efficiency as performance indicators.The multi-parameter optimization was carried out to obtain the optimal parameter combination of this study.Aiming at the problem of serious anti-enrichment of the hydrocyclone in an iron ore dressing plant,a ?660mm W-shaped hydrocyclone was designed on the basis of the research results and then applied to industrial sites.Through the verification of industrial operation,the content of-200 mesh particles in the underflow was reduced by 1.46 percentage points,the quantity efficiency was increased by 8.32 percentage points,and the sand return load was reduced by 33.38%,effectively solving the problem of low refined mineral yield brought by ball mill overgrinding. |
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