Discrete analysis and numerical simulation for separation process of dense medium cyclone

The dense medium cyclone is widely used in coal separation process. The experimental study on internal flow field and particle motion characteristics of dense medium cyclone is difficult and time-consuming with high cost, due to the complicated separation process. With the development of numerical calculation technology,the numerical simulation method was widely used to study the multiphase flow field inside the cyclone. In this paper,the computa- tional fluid dynamics (CFD) and discrete analysis (DEM) coupling techniques were used to numerically simulate the separation process of dense medium cyclones,which provided a new way to optimize the structural parameters and op- erating parameters of dense medium cyclones. The Fluent software was used to study the velocity field,density field, pressure gradient field and viscosity field of the internal suspension of the cyclone. The EDEM software was used to study the coal particle movement behavior and the evaluation of separation efficiency during the cyclone separation process. The results showed that the pressure distribution and the pressure gradient of suspension were basically sym- metrical,and the pressures at the overflow and underflow outlet were the lowest. The pressure gradient was formed along the radial direction,the difference gradually increased,and the largest pressure gradient was at the boundary of the air column. The coal particles in different sizes had different residence time inside the cyclone. For the coal parti- cles of same density,the smaller the particle size,the longer the residence time. The residence time of the discharged coal particles in the overflow in the cyclone was significantly longer than that from the underflow outlet. For coal parti- cles discharged from the overflow outlet,the higher the density,the longer the residence time. While for coal particles discharged from the underflow outlet,the higher the density,the shorter the residence time. The structural parameters of different cyclones had different effects on separation process,and the influence of the diameter of the overflow pipe was the most significant. When the diameter of the overflow pipe exceeded 500 mm,a complete air column cannot be formed,resulting in failure to separation. When the diameter of the overflow pipe was 300 mm,the separation efficiency was better. In addition,the insertion depth of the over-flow pipe significantly affected the separation efficiency. When the insertion depth was 160 mm,the separation density increased,and the fine high-density coal particles would mis- place into the overflow. When the insertion depth of the overflow was 320-800 mm,the separation density was close to the suspension density,Ep value was 0. 084-0. 100,and the separation efficiency was better. The diameter of the un- derflow outlet had a great influence on the separation precision of the cyclone. When the diameter was 272 mm and 306 mm,the separation density was close to the density of the suspension,and the Ep value was less than 0. 1,which had a better separation efficiency. The length of the cylindrical section had little effect on the separation density.