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Evolution of SAG Mill Process Control at the Xstrata Nickel Raglan Operation

E. Bartsch, G. Comeau and C. Hardie

June 10,2009

The Xstrata Nickel Raglan Concentrator, located at the northern limit of Quebec’s Nunavik Region has been in operation since 1997. Originally designed to process 800,000 tonnes per year of high grade nickel ore, plant capacity is currently approaching 1.2 million tonnes per year due to an Optimization Project (Fully Autogenous Grinding to SAG conversion) in 2005 and many recent process improvements.

In 2006, the Raglan Metallurgical Group with assistance from the Xstrata Process Support group decided to make SAG control one of its priorities in order to further increase throughput and improve stability. The original primary mill control logic delivered by the Optimisation Project in 2005 consisted of a simple PID loop controlling the mill charge (bearing pressure) through feed rate changes. Due to the nonlinear and disturbance dominated nature of the SAG circuit it was quickly found that this traditional PID control strategy was not able to adequately control the mill; resulting in poor stability, frequent operator interventions and less than optimum performance.

This paper describes the successful integration of advanced fields systems such as mill feed image analysis (Wipfrag) and crusher gap controller (ASRi), into a multi-variable fuzzy logic SAG mill controller. The process of how a strategy for control was developed and implemented directly in the existing control system (exploiting standard system capabilities) is discussed. It is also shown how this approach has provided mill automation which is simple, robust (despite erratic feed characteristics), and delivers both an increase in throughput and a reduction of variability.