Assessment of comminution energy intensity has traditionally been confined to the crusher and mill motor power consumption. However, a measure of ancillary equipment power and the embodied energy consumed through media wear is required to compare disparate equipment types and circuit configurations fairly, as they can contribute a significant (average 45% increase) proportion of energy to the comminution circuit. Conveyors and slurry pumps use electrical energy to move ore between comminution and classification equipment in mineral processing circuits. Steel balls and rods are regularly used as grinding media in tumbling mills to assist with ore breakage. The consumption of this media through wear processes can be viewed as a form of embodied energy consumption, as the mining, smelting, casting, and shipping of media consumes a substantial quantity of “embodied” energy.
The comminution energy curve database has been developed at the Julius Kruttschnitt Mineral Research Centre over recent years to capture comprehensive energy data for comminution circuits. The database also contains limited data for both ancillary equipment power and embodied energy of grinding media. However, as the database does not contain ancillary and embodied energy data for all the circuits, simplified models were required to populate circuits where these figures were not known. In the comminution circuits studied from the database, the average additional specific power attributable to pumps, conveyors, and media was 1.6, 0.6, and 3.4 kWh/t, respectively. These figures were highly dependent on the type of comminution circuit. New energy curves were generated that included the ancillary equipment power and embodied energy in the grinding media. The resulting energy curves allow mines to be benchmarked on specific comminution energy as well as media wear and ancillary equipment power draw.
In this paper, the authors will present two case studies that explore the effect of circuit type on electrical comminution energy as well as embodied and ancillary energy consumption. The first case study looks at the transition of a circuit from autogenous (AG) through semi-autogenous (SAG) and pre-crushed barely-autogenous (BAG) milling. Each circuit change achieved an increase in throughput, but the result of this decision also increased the specific comminution energy, the embodied energy, and the ancillary equipment power. The second case study explores the change in the trade-off between SAG and high pressure grinding rolls (HPGR) circuits when the increase in conveying requirement and change in media wear are considered when comparing comminution circuit options. These two case studies demonstrate the importance of including ancillary equipment power and the embodied energy of the grinding media wear in the assessment of comminution energy efficiency.
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Comminution energy, conveyors, pumps, media wear
1. Ausenco 144 Montague Road, South Brisbane, Queensland, 4101
2. University of Queensland, Sustainable Minerals Institute, Julius Kruttschnitt Mineral Research Centre