Effects of sound fields on hydrodynamic and dry beneficiation of fine coal in a fluidized bed

Abstract

The difficulty of forming a stable fluidized bed for fine coal (<1 mm) reduces the effectiveness of the density-segregation process and subsequent dry beneficiation of fine coal. Sound fields provide a new method of improving the bed stability of fine coal. In this study, the hydrodynamic and dry beneficiation of fine coal under a sound field was investigated by a numerical simulation and an experiment. The results indicate that when the sound frequency f (or sound pressure level SPL) is increased, the fluidization characteristics of the bed significantly improve, although the increased sound absorption coefficient weakens the positive effects of the sound field on the fluidization characteristics under high frequencies (f > 120 Hz). Moreover, the simulation results indicate that the introduction of the sound field eliminates large bubbles at a high gas velocity, resulting in an expansion of the gas velocity range for the efficient density segregation process of fine coal. Finally, under appropriate operating conditions (f = 120 Hz, SPL = 120 dB, u = Umf), fine coal was separated in a sound-assisted fluidized bed, with probable error E values as low as 0.11 g/cm3, where the clean coal yield was 52.20% with an ash content of 23.28%; the yield of gangue products was 47.80% with an ash content of 47.80%, demonstrating the efficient beneficiation of fine coal in a sound-assisted fluidized bed.