Heat Transfer Intensification at Particle Scale for Fast Formation of α-Al2O3 in Transport Bed

Conventional kiln-based calcination of aluminum hydroxide for α-Al 2 O 3 production is inherently limited by inefficient heat transfer within bulk materials, resulting in high energy consumption, prolonged processing times, and non-uniform product quality. To address this fundamental limitation, a rapid calcination method based on a transport bed reactor is proposed. A multi-stage research program integrating single particle heat transfer simulations, controlled calcination experiments on pellets and fine powders, flash calcination tests, and pilot-scale transport-bed validation was conducted to elucidate the relationship between particle size, heating uniformity, and phase-transformation behavior. The results reveal that particle size governs the heat-transfer mode and, consequently, the α-Al 2 O 3 transformation pathway: coarse pellets (φ20 mm × 20 mm) develop pronounced radial temperature gradients that induce sequential surface-to-core conversion, whereas fine powders (D90≈150 µm) experience nearly uniform internal heating, enabling homogeneous phase transformation throughout the particle. Under transport bed conditions at 1400°C, aluminum hydroxide powder was converted to α-Al 2 O 3 within approximately 20 s, achieving a conversion rate of 96.4%, which represents a substantial reduction compared with the several hours typically required in conventional bulk calcination. These findings demonstrate that enhancing heating uniformity through particle downsizing combined with transport bed operation fundamentally shortens the α-Al 2 O 3 formation process from hours to seconds, thereby establishing a technically feasible and scalable route for fast, high purity alumina production.