Benchmarking: Bond - Cadia East
Benchmarking: Bond/Barratt - Cadia
Engelhardt, D., Robertson, J., Lane, G., Powwel, M.S. and Griffin, P., Cadia Expansion - From open pit to block cave and beyond. Proceedings of MetSoc 2012.
Design criteria and plant trial of underground Cadia East ore
- blased underground ore, secondary crushed to 80 mm.
- WiC = 30 (metric)
- WiRM = 26.5 (metric)
- WiBM = 21.4 (metric)
- DWI = 9.9
- density = 2.7 t/m³
The ore was reported blasted undergrond (block caving had not yet started). Particle size distribution given as two points which confirm a Bond-compatible "root-2" PSD.
- 80% passing 80 mm
- 20% passing 5 mm
Details of the mill operating conditions are not given, but the power draw at the shell is given.
- 15.737 MW SAG mill power draw
- 19.509 MW ball mill power draw
Circuit operating conditions:
- F80 = 80 mm
- P80 = 140 µm
- instantaneous throughput = 1482 t/h
The mill load, ball charge and pulp density was tweaked to mimic these power draws, corresponding to:
- SAG operating 9% v/v balls, 25.5% v/v total filling and 78% of critical speed (Austin model has fixed %solids)
- ball mills operating 37% v/v total filling and 70% w/w solids (fixed speed mills, 72% of critical speed)
The ball load required to match the reported power draw is very high, and could only be achieved with a significant reduction in the trunnion diameter (using ball retaining rings). Moreover, the motors are predicted to be operating at 100.5% of their rated output power to achieve the indicated power draw.
|Model||12.31 kWh/t||14.94 kWh/t||27.7 kWh/t||1243 t/h|
|Measured||10.6 kWh/t||13.2 kWh/t||23.8 kWh/t||1482 t/h|
|Difference||1.71 kWh/t||1.74 kWh/t||3.9 kWh/t||-239 t/h|
The predicted transfer size needed to balance the power draw between primary & second mills is very coarse, 5 mm.
There is a substantial difference between the survey and the predictions. Some observations:
- The rod mill work index was determined on an apparatus with smooth liners. This can cause a difference of 2-3 kWh/t versus the wave-liner apparatus specified by Bond. Using a rod mill work index of 24.0 kWh/t gives Etotal = 26.8 kWh/t; still 13% high.
- The Essbm predicts the energy required for a "standard" secondary crushing & ball milling plant that is believed to be one of the most energy efficient types of grinding circuits. This ore has Essbm = 24.3 kWh/t which is still less than the survey Etotal. Very odd result that a SABC circuit is more efficient than an SSBM (ergo, HPGR) circuit on such a hard ore.