Segregation in circulating turbulent fluidized beds with a broad particle size distribution: A Froude number-based model approach

Iron production based on direct reduction processes in fluidized beds facilitates the direct processing of iron ore fines, thereby bypassing energy-intensive agglomeration steps. The inherent broad particle size distribution (PSD) of iron ore fines introduces substantial hydrodynamic complexity due to factors such as elutriation. To date, research on particle entrainment has relied predominantly on empirical correlations, leaving a notable void in comprehensive theoretical and dimensionless investigations. This study addresses this critical gap by providing a fundamentally novel modeling approach that specifically incorporates the Froude number to characterize the PSD and entrainment above the bed surface, instead of employing an empirically determined elutriation rate constant. The analysis of the experimental data, recorded with bronze and air, confirms that the Froude number serves as a reliable dimensionless parameter to correlate fluidization velocity with height. On this basis, a Froude number based model is elaborated for the progression of the PSD with height above the dense bed. The model is validated and shows hydrodynamic consistency and good agreement with the two experimentally investigated bed materials (bronze, d 50 = 75 μm and d 50 = 143 μm). The study further introduces a simple method to estimate the total entrainment flux based on the proposed Froude model. The outcome is successfully compared with experimental data presented in this work.