A multiscale heterarchical streamline model for comminution in rotary mills

Abstract

This dissertation presents a new approach to modelling comminution in rotary mills based on heterarchical concepts. The work is structured around four main chapters. The first three are built upon published papers, each prefaced with an explanation of the motivation for the study, while the fourth is presented as a standard chapter. These chapters progressively build upon one another to advance our understanding of comminution within rotary mills.

In the first paper, we develop the new comminution model by integrating the heterarchical physics of particle crushing along the streamlines. Applied to an idealised ball mill and an autogenous grinding mill, this model can predict the particle size distribution at any point in space and time within the mill.

In the second paper, we extend the model to include segregation and mixing by tessellating the equal mass material points along the streamlines. We explore the coupled effect of particle crushing, segregation, and mixing on the comminution, showing that segregation significantly enhances crushing within the mill, and thus cannot be ignored.

In the third paper, we further include the dynamics of the grinding media consisting of steel balls and study comminution within a semi-autogenous grinding mill. Additionally, we analyse how mill operating parameters affect comminution.

Finally, in Chapter 6, we demonstrate that the heterarchical model can predict the energy dissipation at any point in space and time within the mill, allowing the measurement of its grinding energy efficiency. We also explore how operational parameters impact this efficiency.

Together, these contributions provide a new framework for understanding the granular dynamics and comminution within rotary mills.