(25d) Study of Dry Beneficiation of Coal Particles in Air Dense Medium Fluidized Bed using CFD-DEM Method
Dry beneficiation of coal particles is an effective method of removing the ash, sulfide minerals and other harmful substances from raw coal. In this study, CFD-DEM method was adopted to study the dry beneficiation of coal particles in dense bubbling fluidized bed, where coarse-grained model is employed to simulate the motion of large amount of Geldart B magnetite powders and DEM is employed to model the motion of coal particles. In the CFD-DEM model, the weight function method and the center-count method are used to calculate the solid fraction and velocity of coal particles and coarse-grained magnetite powders, respectively. It was shown that (1) the simulated separation process of coal particles is in a good agreement with the experimental data under both of the superficial gas velocities of 1.5Umf and 1.75Umf; (2) The light particles with densities of 1400kg/m3 and 1700kg/m3 are easily floated to the bed surface while the dense particles with densities of 2300kg/m3 and 2500kg/m3 settle down slowly to the bed bottom at the superficial gas velocity of 1.5Umf. But for the higher velocity of 1.75Umf, the particles with middle densities of 1700kg/m3, 2000kg/m3 and 2300kg/m3 cannot be separated well due to the entrainment of large bubbles; (3) The force analysis indicates that the dense particles of 2300kg/m3 and2500kg/m3 have a greater resistance force from dense medium particles in separation process. In summary, the CFD-DEM method is an effective method for studying dry beneficiation of coal particles.