Benchmarking: Bond - Macraes
Contents
Benchmarking: Bond/Barratt Circuit Specific Energy Consumption - Macraes
Barns, K., Lane, G., Osten, K. & Scagliotta, N., Benchmarking Energy Efficiency - A Case Study at Macraes Gold Mine, Proceedings of the AusIMM MetPlant conference, Perth, Australia, September 2004.
Raw data from paper
The paper describes overall plant unit operation efficiency rather that specific grinding mill surveys, but does reference five surveys that are useful for benchmarking.
| Survey 5 | Survey 4 | Survey 3 | Survey 2 | Survey 1 | ||
|---|---|---|---|---|---|---|
| throughput | dry t/h | 536 | 454 | 493 | 514 | 527 |
| SAG feed F80 | mm | 82.9 | 106.8 | 72.7 | 56.8 | 51.4 |
| SAG specific power | kW at DCS | 3.84 | 5.04 | 4.32 | 4.02 | 3.76 |
| ball mill specific power | kW at DCS | 8.60 | 8.76 | 7.78 | 7.86 | 7.63 |
| transfer size, T80 | µm | 795 | 3318 | 804 | 2215 | 2043 |
| cyclone overflow size, P80 | µm | 100 | 100 | 100 | 117 | 116 |
| grindability, SPI | minutes | 40.7 | 46.3 | 43.2 | 34.7 | 40.5 |
| grindability, WiBM | kWh/t | 10.3 | 11.6 | 11.3 | 11.9 | 11.4 |
Interpretation and Interpolation
Assume that the power provided at the motor input is converted to shell power using 0.96 motor efficiency and 0.985 gear efficiency for an overall conversion of 0.9456.
The paper gives interpolated values for the rod mill work index, but those do not appear to be calibrated to a "Bond" style rod mill with wave liners. Use the WiRM calibration to SGI from the Example database, these are the interpolated rod mill work index numbers that can be used for the Bond/Barratt method. No crushing work index values are given; assume that WiC = WiRM for modelling.
| Survey 5 | Survey 4 | Survey 3 | Survey 2 | Survey 1 | ||
|---|---|---|---|---|---|---|
| SAG specific energy | kWh/t at shell | 3.6 | 4.8 | 4.1 | 3.8 | 3.6 |
| ball mill specific energy | kWh/t at shell | 8.1 | 8.3 | 7.4 | 7.4 | 7.2 |
| total specific energy | kWh/t at shell | 11.8 | 13.0 | 11.4 | 11.2 | 10.8 |
| grindability, WiRM | kWh/t | 9.5 | 10.1 | 9.8 | 8.8 | 9.5 |
The transfer sizes are assumed to be "as-measured" and have not been subjected to a 'phantom cyclone' fine removal. The transfer size in the Bond/Barratt model (because it excludes 'additional' fines) will be iterated to give the ESAG/Eball ratio reported. The different between the iterated T80 and the measured T80 will be assumed to be the "phantom cyclone effect".
Because full mill surveys aren't given, abbreviated model runs are used in this benchmarking rather than full models (there is no saved data to view).
Use Bond/Barratt SABC model with 10% SSBM contingency.
Model Results
| Survey 5 | Survey 4 | Survey 3 | Survey 2 | Survey 1 | ||
|---|---|---|---|---|---|---|
| SAG specific energy | kWh/t at shell | 3.41 | 4.56 | 4.36 | 3.82 | 3.68 |
| ball mill specific energy | kWh/t at shell | 7.59 | 7.91 | 7.67 | 7.54 | 7.43 |
| total specific energy | kWh/t at shell | 11.00 | 12.5 | 12.02 | 11.36 | 11.11 |
| transfer size, T80 to achieve ESAG/Eball ratio |
µm | 4200 | 2000 | 2000 | 2700 | 3250 |
It is important to remember that the Bond/Barratt equation for total circuit specific energy (Etotal) is independent of transfer size. The transfer size is only used to split total circuit power between the SAG and ball mills. The difference between measured and predicted transfer sizes only affects the split of power between the milling stages and not the overall circuit power.
Comparison
Difference between model results and plant surveys:
| Survey 5 | Survey 4 | Survey 3 | Survey 2 | Survey 1 | Overall Average | ||
|---|---|---|---|---|---|---|---|
| SAG specific energy | -5.3% | -5.0% | 6.3% | 0.5% | 2.2% | -0.2% | |
| ball mill specific energy | -6.3% | -4.7% | 3.6% | 1.9% | 3.2% | -0.5% | |
| total specific energy | -6.8% | -3.8% | 5.4% | 1.4% | 2.9% | -0.2% | |
| transfer size, T80 | 428.3% | -39.7% | 148.8% | 21.9% | 59.1% | 123.7% |
