Hydrodynamics of High-Density Particles in a Multistage Fluidized Bed With Downcomers

Abstract Fluidized bed reactor is commonly used in uranium recycling processes of nuclear industry, particles used in these reactors usually have very high densities, which are usually several times higher than those of catalyst particles in chemical industry or fuel particles in fluidized bed boiler in power plants. Multistage fluidized bed reactor has advantages of better residence time distribution and higher gas-solids contact efficiency. However, less literature has involved the operation of multistage fluidized beds with high-density particles. In this study, we used a super-high-density powder of wolfram carbide (WC) powder, which had a true density of 15630 kg/m3 and a typical light powder of similar size, FCC particles, to investigate systematically the different hydrodynamics in a cold-model counter-current three-stage fluidized bed with downcomers. The column diameter, stage height, and downcomer diameter were 186mm, 400mm and 30mm, respectively. The ranges of superficial gas velocity and volumetric solids feeding rate were 0–0.2 m/s and 4–8 ml/s. Pressure drop, pressure fluctuation and solids flow rate at the bottom outlet were measured during stable operation status to evaluate the operating stability. The stable operating ranges were also determined in experiment. The experimental results indicated that this high-density WC powder could be fluidized and circulated continuously in this multistage fluidized bed, but lower fluidization quality was observed using WC than FCC. The minimum operating gas velocities of WC were higher than those of FCC particles, which was determined by the change of transient pressure signals. Different flow phenomena were observed at the minimum operating velocities using the two powders of different densities. The experimental results demonstrated the feasibility of operating uranium compound powders in multistage fluidized beds.