Discrete Element Modeling (DEM) for mixing of cohesive solids in rotating cylinders

Abstract

Granular solids mixing is a pivotal unit operation in manufacturing processes for numerous industries such as pharmaceuticals, food, and petroleum refining, wherein mixture homogeneity is critical to ensure for product quality and control. In this work, Discrete Element Modeling (DEM) was used to study mixing of cohesive granular solids using a rotary kiln. This work's goal was to develop a quantitative relationship between particle properties and their simulated mixing behavior. Particle properties evaluated in this work were surface energy, particle density, and particle diameter given their relationship to particle cohesion, often quantitatively measured using the granular Bond number. For the simulations, the rotary kiln's fill level, cylinder dimensions, and angular velocity remained constant while the particle properties changed. The DEM simulated mixing results were used to regress the dispersion coefficient for the closed-closed boundary axial dispersion to quantify mixing rates. The results indicated that both surface energy and true density were negatively correlated with axial dispersion, while particle size was positively correlated. From these results and analysis, an empirical correlation was developed between the evaluated particle properties and the regressed axial dispersion constant. The empirical correlation was employed to evaluate the rates of mixing inside the rotary kiln using relative standard deviation as a mixing metric.