Benchmarking: Bond - Macraes

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 Wi_RM 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 Wi_C = Wi_RM for modelling.

		Survey 5	Survey 4	Survey 3	Survey 2	Survey 1
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
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 E_SAG/E_ball 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

Model results:

		Survey 5	Survey 4	Survey 3	Survey 2	Survey 1
SAG specific power	kW at shell	3.41	4.56	4.36	3.82	3.68
ball mill specific power	kW at shell	7.59	7.91	7.67	7.54	7.43
total specific power	kW 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 power (E_total) 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 power		-5.3%	-5.0%	6.3%	0.5%	2.2%	-0.2%
ball mill specific power		-6.3%	-4.7%	3.6%	1.9%	3.2%	-0.5%
total specific power		-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%