Mechanism of Full Cone Angle Effects on Fluidization Behavior in High-density Particle Fluidized Beds

Gas-solid fluidized beds are employed in multiple procedures of the natural uranium conversion process, and all particles involved are high-density ones. Previous studies using orthogonal experimental design have confirmed that the full cone angle exerts a significant influence on the fluidization behavior of the fluidized bed. On the basis, a series of fluidized models with the full cone angle (α) as the sole variable were established using the dense discrete phase model (DDPM) fluidization model. The instantaneous solid-phase concentration distribution and flow field characteristics in the reaction section under different full cone angles at various moments were obtained. Time series analysis and spectral analysis were adopted to investigate pressure fluctuations, and the fluidization quality of each bed was quantitatively evaluated based on the standard deviation of pressure drop and spatial deviation analysis. The results show that when α=3°, channeling is the dominant flow phenomenon. When 3°＜α＜13°, as the full cone angle increases, the gas phase tends to pass through the bed along the wall surface, and slugging becomes the primary flow pattern. When 13°≤α≤15°, channeling re-emerges as the main pattern due to the further enlargement of the radial flow area. At α=16° and 18°, the gas flow concentrates toward the central axis of the bed, resulting in poor gas-solid contact. Among small full cone angles, the bed pressure drop is relatively stable at α=9°, with small fluctuation range and degree, indicating favorable fluidization quality. As the full cone angle continues to increase, the radial flow cross-sectional area further expands and the gas flow tends to concentrate in the central axis region. Although the pressure drop appears relatively stable, its fluidization quality cannot be effectively evaluated. No single peak appears in the mean square amplitude (MSA) for any full cone angle, indicating the absence of periodic bubbles. Obvious structural band peaks are observed at α=9° and α=10°, demonstrating that bubbles penetrate through the bed. For other full cone angles, the interface of the continuous coherent structural bands in the reaction section is indistinct, accompanied by significant disturbances in gas-solid flow. At α=9°, both the standard deviation (σ) and the spatial deviation number (S) reach their minimum values, with weak pressure drop fluctuations and stable gas uniformity, representing optimal fluidization performance. It is recommended that the full cone angle be set to 9° in engineering design. As the full cone angle increases, the overall bed expansion ratio decreases. At α=9°, the axial solid holdup fluctuates slightly and the bed remains stable. The findings of this study provide a theoretical foundation for the iteration of the uranium conversion process and the optimization of related equipment.