Benchmarking: Fimiston Ball Mills

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Benchmarking: Ball Mill Power Draw - Fimiston

  • Nelson, M; Valery, W; Morrell, S, Performance Characteristics and Optimisation of the Fimiston (KCGM) SAG Mill Circuit, Page 233 - 248, SAG 1996 Conference, Vancouver, Canada.
    • Diameter inside shell = 5.49 m (18 ft)
    • Diameter inside liners = 5.35 m (17.5 ft, 70 mm effective liner thickness)
    • Belly length inside liners (EGL) = 7.60 m (25 ft)
    • Centre-line length = 8.76 m
    • Top ball size = 80 mm
    • Ore density 2.93 t/m3

Table 5 presents results of a single ball mill survey. The survey measured motor input power. Drives are assumed to have an efficiency of 0.96 and gearbox+pinion efficiency of 0.970, so the model shell power draw is converted to motor input power by dividing by 0.9312. The predicted power draw of Example project circuit number 7 (Fimiston) using sample MLE, based on the KCGM paper published by Campbell, J. et al; 1998 AusIMM Annual Conference.

Survey Survey Power,
kW at input
Mill speed,
Total load,
Pulp %solids,
Morrell SAG Model,
kW at input / shell
Nordberg Model,
no density correction
kW at input / shell
Nordberg Model,
density correction
kW at input / shell
Survey 1 3,864 66.7 68.4 38.7 72.0 3,798 / 3,798 3,619 / 3,370 3,894 / 3,626

The appendix of the paper lists the mill speed as 12.5 RPM. The mill is fixed speed, so the %critical speed is only a function of mill effective diameter (as liners wear). Doing the math (neglecting the balls) gives a 68.4% critical speed.

The ball mill belly length can be achieved with a 18 degree head angle and 1.9 m trunnion diameter.