Acoustic emissions monitoring of SAG mill performance

Abstract

Particle grinding is a final stage in the comminution process used to liberate minerals from gangue in mineral processing plants. Semi-autogenous grinding (SAG) occurs in tumbling mills which use both large ore particles and steel balls for grinding. Grinding is the most energy intensive mineral processing unit operation and hence its optimisation is of considerable interest to industry. Surface vibration (acoustic emissions) monitoring is a noninvasive low-cost means of monitoring normally inaccessible attributes of processes or equipment operation. The current investigation monitors vibrations in a SAG mill by an accelerometer attached to the outside of the rotating shell. Vibrations are interpreted in terms of the internal state of the SAG mill for a conditional experimental program over a wide range of operating conditions. Results support the view that higher feed rate dynamic steady states correspond to an increased charge mass, with enhanced cushioning of grinding media impacts on the liner due to an increase in the intervening charge volume. An increase in rotation speed results in grinding media being lifted higher and more often directly impacting on the liner, increasing acoustic emissions. Increased pulp density aids in damping collisions that generate acoustic emissions by increasing resistance to transport of media through the charge. Addition of grinding balls results in more high energy impact events between balls and liner. The relationships derived show promise for process control and condition monitoring.