Below is a summary of the award-winning paper “Quantifying the additional energy consumed by ancillary equipment and embodied in grinding media in comminution circuits” by Grant Ballantyne, presented at SAG 2019.
The impact of the embodied energy of grinding media and ancillary equipment power on comminution energy consumption
Energy reduction in comminution typically focusses on reducing the mill motor power draw. This paper looked at the additional energy consumption associated with transporting the rock and slurry (conveyors and pumps) and the energy embodied in the steel grinding media.
Conveyors and slurry pumps use electrical energy to move ore between comminution and classification equipment in mineral processing circuits. On average, conveyors were found to consume 0.44 kWh/t.km and pumps consumed 1.6 kWh/t.
Steel balls and rods are regularly used as grinding media in tumbling mills to assist with ore breakage. The energy consumed in mining, smelting, casting, and shipping of media which is then consumed in a mill is defined as “embodied” energy. The embodied energy in steel grinding media was found to add 15% to 40% on top of the electrical energy consumed by the mill.
Together, the embodied energy of the grinding media and ancillary power added 45% (average) to the electrical power of the mills and crushers. By calculating these values, they can be visualised using the Comminution Energy Curve methodology.
The paper presents two case studies that explore the effect of circuit type on electrical comminution energy as well as embodied and ancillary energy consumption:
1. Progression from AG to SAG to BAG milling
The first case study looked 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 embodied energy and the ancillary equipment power.
2. Trade-off between HPGR and SAG mills
The second case study re-visited the trade-off between SAG and high-pressure grinding rolls (HPGR) at the Tropicana mine by including conveyor power. The below chart shows that the energy efficiency of the HPGR circuit was reduced when the conveying power was included.
These case studies show the importance of including ancillary equipment power and the embodied energy of the grinding media wear in the assessment of comminution energy efficiency.
Hear Grant talk about how this study can contribute to the improvement of comminution eco-efficiency.
Contact Grant Ballantyne to learn more about how to optimise energy efficiency of your comminution circuits.
This paper was achieved through a collaboration between organisations - Ausenco, the University of Queensland, and the CEEC. Special mention to the following individuals - Chris Greet, Evert Lessing, Malcolm Powell, and Greg Lane.