Investigation of stress conditions and energy efficiency in dry stirred media milling by DEM simulation

Dry operated stirred media mills are gaining increasing relevance in fine grinding applications due to their high energy densities and process flexibility. Nevertheless, the interrelation between operating parameters and stress conditions remains insufficiently understood compared to wet milling systems. In this work, the grinding media motion within a vertically oriented batch stirred media mill was investigated using Discrete Element Method (DEM) simulations, experimentally calibrated to incorporate the influence of powder flowability as a function of grinding aid formulation and applied to dry milling experiments of calcium carbonate. The results reveal that, analogous to wet operation, an optimum stress intensity exists at which the specific energy demand to achieve a target fineness is minimized. For dry milling, however, the stress intensity must be defined as the ratio of stress energy to the stressed product mass, since the captured product fraction which varies with powder properties is decisive for the stress intensity value. DEM analysis further indicates that the tip speed alone does not adequately represent the effective bead velocity distribution under dry conditions. The study demonstrates that both operating parameters and product formulation significantly affect the stress environment and comminution efficiency, implying that individual optimization strategies are required for each product system.