Real-time Estimation of SAG Mill Charge Characteristics for Process Optimization

Abstract

Control of both the total charge and the ball charge volume is vital to the optimum performance of SAG mills to maximise throughput and energy efficiency. However, neither of these parameters can be directly measured online. At best, load cells, where they are installed, measure the total mass of the mill and the charge. Where load cells are not installed the total mass can be inferred from bearing pressure. The charge mass is then estimated by subtracting the mass of the mill shell plus lifters and liners, but the mass of the liners change with wear and mill relines. However, when combined with an accurate SAG mill power draw model, both total charge volume and ball load can be estimated with reasonable accuracy.

The Morrell C-model is generally regarded as one of the most accurate tumbling mill power draw models and is ideally suited for this application. This paper presents three methods using the Morrell C-model to estimate total and ball charge volumes for SAG mills depending on the data and measurements available. These methodologies all allow analysis of real time data and large sets of data spanning months and years of operation. Thus, facilitating identification of optimum operating conditions and can also aid in early detection, trouble shooting, and rectification of poor mill performance. Several case studies are provided to demonstrate the application and accuracy of the results.