Coarse-grained CFD-DEM simulation to determine the multiscale characteristics of the air dense medium fluidized bed

Abstract Coal beneficiation via the air dense medium fluidized bed (ADMFB) has increased its popularity in recent decades. However, due to the coexistence of bubbles and the emulsion phases, obtaining a uniform and stable bed density for coal separation in ADMFB remains challenging. In this work, a coarse-grained CFD-DEM method with high accuracy in capturing the macroscale behaviors of the bed expansion rates and the axial solid concentration, was tested and validated. Besides, the microscale and mesoscale behaviors of the ADMFB were also analyzed via power spectrum density and wavelet decomposition. The findings show that the pressure fluctuation mainly results from bubbles motion of mesoscale rather than from particles motion of microscale and global bed expansion of macroscale. Furthermore, the apparent densities at different scales were calculated and a stable and uniform separation density was obtained within appropriate domains where the coal separation efficiency could be ensured.