SAG Mill Stability and Control Improvements at the Nova Nickel-Copper Operation
G Gomes-Sebastiaõ1 and P Hudson2
1. Executive Director, Improve IO Pty Ltd, 5/74 Kent Way, Malaga, WA, This email address is being protected from spambots. You need JavaScript enabled to view it.
2. Senior Metallurgist, IGO Nova Pty Ltd, 85 South Perth Esplanade, WA, This email address is being protected from spambots. You need JavaScript enabled to view it.
*This paper was presented at MetPlant 2023 held 6-8 November 2023 in Adelaide, Australia. To view the full paper select download file below.
ABSTRACT
Strategies introduced at IGO’s Nova operation have improved stability and control in the SAG milling circuit. These strategies relate to the development of a prediction model for SAG mill media volume (ball charge), and improvements to the SAG mill charge weight (total load) controller.
Prior to these improvements, poor control over SAG media charge volume and charge weight had resulted in process instability, downtime and overall reduced throughput. Media overcharging and lack of control was tackled by development of a power-based model and a media consumption rate model of the SAG mill. These models are used to control media addition rates on a day-to-day basis to target the desired media charge.
Control of the SAG mill charge weight was improved by incorporating modelled disturbance inputs into the existing PID loop. The disturbances included were derived from an online mill feed particle size distribution measurement and a proxy for ore density/hardness, both of which were determined to be significant predictors of future mill weight changes. The issue of reducing mill weight resulting from liner wear over the reline cycle, rather than changes in actual charge weight, has also been compensated for using an adjustment to the mill weight setpoint based on measured liner
consumption rates.
Following the introduction of these improvements, the issues resulting from overcharging and unstable weight control have greatly diminished resulting in improved overall throughput, reduced average SAG specific energy (kWh/t) and greater downstream stability within the flotation circuit. These models and controllers require occasional re-calibration but have proved robust over time.