Gravitational discharge of packed particles through side orifices with different lengths for continuous dry beneficiation of raw coal in fluidized beds

For coal dry beneficiation in air-fluidized beds, the sorted gangue particles can be discharged continuously from a side orifice underneath the gas distributor. The mass discharge rate (q_m) was found to decrease with l_o (orifice length) increasing from 0.003 to 0.010 m. The Beverloo equation worked well in correlating q_m and d_o (orifice diameter) at all levels of l_o. The independence of C and k on d_o was demonstrated by good linearity between $q_m^{0.25}$and d_o. C was fitted as ∼0.20, irrelevant to l_o or particle type. k was derived as >10, differing significantly from <2 for bottom orifices. The greater k was revealed to arise from a thick region with retarded particle flow at bottom of side orifices. Such a stagnant zone also explained why k increased with increasing l_o and ρ_b (bulk density) or decreasing d_p (particle size). l_o is promising for adjusting q_m and exploring the clogging/jamming phenomenon.