Molten droplet impact on particle layers for adhesion-free centrifugal slag granulation

Efficient recovery of the immense thermal energy contained in high-temperature molten slags is critical for decarbonizing the energy-intensive industries. Dry centrifugal granulation offers a promising solution, yet its practical implementation is hindered by severe adhesion of granulated slag particles caused by insufficient cooling. Here, we propose an adhesion-free dry centrifugal granulation strategy enabled by porous water-quenched slag powders, which promotes droplet fragmentation while facilitating the transport and cooling of embedded particles. To elucidate the underlying mechanisms governing droplet-particle interactions, we performed high-speed visualization experiments of low-melting-point paraffin droplets impacting a horizontal single-particle-layer surface as a surrogate system for molten slags, capturing the coupled effects of impact spreading, phase-change cooling and particle embedding. Results indicate that elevated droplet temperatures reduce viscosity, intensifying penetration into the particle layer and enlarging the bottom adhesion area. Increasing the impact velocity from 1.4 to 2.42 m s −1 enhances the maximum spreading factor from 2.30 to 2.59, shortens the retraction duration by approximately 51%, and substantially increases interfacial adhesion. Dimensionless correlations are established to predict droplet spreading and adhesion behavior across varying impact conditions. These findings provide mechanistic insights into molten droplet interactions with self-derived particle layers and establish a quantitative foundation for designing adhesion-resistant dry granulation technologies for sustainable slag heat recovery.