Entrainment behavior of iron ore particles in a fluidized bed under varying gas properties

This study investigates the entrainment characteristics of iron ore particles under varying gas properties, considering the low-density gas conditions of reducing agents in a fluidized bed for hydrogen-based iron reduction. Experiments were conducted in a fluidized bed (0.05 m I.D × 3.05 m high) using iron ore particles (125–2800 μm) and gases of different densities. Iron ore particles were characterized by a high fraction of fines smaller than 45 μm (F₄₅), which adhered to the surfaces of primary coarse particles. The laser diffraction method effectively evaluated the particle size distribution of iron ore. The total entrainment rate (G_s) increased with gas velocity (U_g) and gas density (ρ_g), with the increase being more pronounced at higher F₄₅. The entrainment of coarse particles with terminal velocities (U_t) higher than a given U_g was affected by the entrained flow of fine particles. G_s consistently exhibited an exponential increase with increasing U_g/U_t across varying U_g and gas properties. The size ratio of critical to coarse particles (d_crit/d_p,coarse) was identified as a physical factor to interpret the entrainment of adhered fines from coarse particles. A correlation was proposed to predict G_s by incorporating U_g/U_t, Archimedes number, and particle characteristics such as F₄₅ and d_crit/d_p,coarse.