Hydrodynamics of particle segregation in fluidized beds

摘要

Research in multiple particulate phase hydrodynamics is important in many industrial applications that involve segregation or mixing processes, specifically in mineral classification, elutriation, sedimentation, crystallization and fluid bed leaching, just to name a few. There have been several investigations dealing with segregation and mixing of particles of different sizes and densities in fluidized bed reactors or classifiers (Chen et al., 2002). The studies show that particles will segregate into layers if a bed, consisting of two different size particles with the same density, is fluidized with a velocity that is in between the individual minimum fluidization (u_(mf)) velocities for each particle type. The binary system will not segregate if the fluidizing velocity is higher than the umf of the larger particles; rather the particles mix vigorously. The models reported in the literature are able to predict the segregation of the particles at an intermediate fluidization velocity (Goldschmidt et al., 2001). However, they predict particle segregation even at a low fluidization velocity, when segregation is not observed. In this study we modified the particle–particle drag term so that the model predicts no segregation at low velocities, segregation at intermediate velocities, and mixing at high velocities. Furthermore we show that the predicted rate of segregation at intermediate velocities agrees quantitatively with experimental data.