Fluidization and Sedimentation of Carrier Material in a Pilot-Scale Airlift Internal-Loop Reactor

Balsalt (ρ=2760 kg.m⁻³, d=0.245 mm) was used as the solid carrier in a pilot-scale airlift internal-loop reactor for wastewater treatment (AILRW), which was filled with tap water in this study, to investigate the regimes of fluidization and sedimentation. Solid sediment was observed even when the liquid velocity in the riser was much higher than the terminal settling velocity of the particles. Circulation cannot be maintained if the superficial liquid velocity in the downcomer u_d. is below a definite value (blocking velocity u_b) . In a dimensionless model, u_b is related to the bulk volume of carrier solids added (V_t), the available space at the bottom (V_a) and the gap size at the bottom (a₀) according to u_b²/(a₀.g) = 0.04(V_t/V_a) −0.036.