Benchmarking: SGI - Macraes
Contents
Benchmarking: Amelunxen SGI 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 power draw | kW, motor input | 2057 | 2288 | 2129 | 2066 | 1984 |
| SAG specific power | kW at DCS | 3.84 | 5.04 | 4.32 | 4.02 | 3.76 |
| combined ball mill power | kW, motor input | 4612 | 3977 | 3833 | 4038 | 4023 |
| 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
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.
Other published information on Macraes state that there is a pebble crusher in the circuit, but no crusher size or power draws are published. Assume a 400 HP crusher for the purposes of modelling.
| Survey 5 | Survey 4 | Survey 3 | Survey 2 | Survey 1 | ||
|---|---|---|---|---|---|---|
| SAG power draw | kW at shell | 1945 | 2164 | 2013 | 1954 | 1876 |
| ball mill specific power | kW at shell | 4361 | 3761 | 3424 | 3818 | 3804 |
| SAG specific power | kW at shell | 3.6 | 4.8 | 4.1 | 3.8 | 3.6 |
| ball mill specific power | kW at shell | 8.1 | 8.3 | 7.4 | 7.4 | 7.2 |
| total specific power* | kW at shell | 11.8 | 13.0 | 11.4 | 11.2 | 10.8 |
| Ball mill Operating work index, WiO | kWh/t | 12.6 | 10.0 | 11.4 | 10.4 | 10.2 |
| CFball values | actual | 1.22 | 0.86 | 1.01 | 0.88 | 0.90 |
* includes allowance for pebble crushing
The calculated operating work index values permit CFball values to be determined for each of the surveys. This factor includes any phantom cyclone effect and any accumulated Rowland efficiency factors. For the purposes of modelling, the CFball values are predicted using Amelunxen's method and will be compared to the actual measurements.
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 Amelunxen SGI model with pebble crushing, fine feed (where appropriate) and predicted CF factors.
Model Results
| Survey 5 | Survey 4 | Survey 3 | Survey 2 | Survey 1 | ||
|---|---|---|---|---|---|---|
| SAG specific power | kW at shell | 3.79 | 4.98 | 4.71 | 3.83 | 3.77 |
| ball mill specific power | kW at shell | 8.5 | 8.64 | 8.49 | 7.55 | 7.68 |
| total specific power* | kW at shell | 12.64 | 14.03 | 13.62 | 11.73 | 11.81 |
| transfer size, T80 to achieve ESAG/Eball ratio |
µm | 2864 | 1419 | 1485 | 1374 | 1429 |
| Ball mill operating Wo | kWh/t | 10.45 | 11.77 | 11.46 | 11.53 | 11.56 |
| CFball | predicted | 1.01 | 1.01 | 1.01 | 0.97 | 0.97 |
* includes allowance for pebble crushing
Comparison
Difference between model results and plant surveys:
| Survey 5 | Survey 4 | Survey 3 | Survey 2 | Survey 1 | Overall Average | ||
|---|---|---|---|---|---|---|---|
| SAG specific power | 4.4% | 4.5% | 15.3% | 0.8% | 6.0% | 6.2% | |
| ball mill specific power | 4.5% | 4.3% | 15.5% | 1.6% | 6.4% | 6.5% | |
| total specific power | 4.5% | 4.4% | 15.4% | 1.3% | 6.3% | 6.4% | |
| CFball | -17.5% | 16.9% | 0.5% | 10.6% | 8.3% | 3.8% |
The overall specific energy consumption predictions of the model are conservative by about 6%. The CFball predictions are within 4% overall, but can be wildly different on any particular sample.
