Numerical investigation of particle segregation in millstone systems: An enhanced quantification approach

Abstract

As the core equipment in powder grinding, the vertical mill's material uniformity on the millstone directly affects grinding efficiency and product quality. Particle segregation critically affects this uniformity. However, the underlying mechanism of particle segregation within the millstone remains unclear, and existing quantification methods lack accuracy. To address these issues, this study proposes an enhanced quantification approach and investigates the segregation mechanism through a Discrete Element Method (DEM). Additionally, this study performs simulations utilizing both spherical and tetrahedral particles. Specifically, the trajectories of spherical particles were analyzed to explore the axial segregation mechanism, whereas the position probability method was applied to tetrahedral particles for investigating the axial segregation mechanism at the edge of the millstone. Finally, the proposed weighted mass segregation index was compared with traditional indices to evaluate its performance. Results reveal significant axial segregation on the millstone, primarily driven by size effects and upward migration of coarse particles. However, at the edge of the millstone, the axial mobility of particles decreases due to compressive forces, suppressing the size effects and resulting in a slower segregation rate compared to the inner regions. The weighted mass segregation index effectively mitigates grid-induced biases, providing a precise tool for quantifying particle segregation.