We will be presenting at the 12th Conference on Geostatistics for Environmental Applications – Geoenv 2018, in Belfast,

Integrating uncertainty in rock hardness and solar irradiation in the optimization of a SAG mill energy system

Julian M. Ortiz – Robert M. Buchan Department of Mining, Queen’s University

Willy Kracht – Department of Mining Engineering / AMTC, Universidad de Chile

Giovanni Pamparana – Department of Mining Engineering / AMTC, Universidad de Chile

Jannik Haas – Energy Center, U. de Chile / D. of Stochastic Sim. and Safety Research, University of Stuttgart



In mining, one of the most energy-intensive activities is the grinding of the rock, prior to the concentration processing. Peaks in energy consumption are severely penalized in electrical contracts, hence the use of alternative energy sources can help optimizing the energy cost.

In this paper, we use geostatistical simulations to characterize the in situ variability of rock hardness, to build a geometallurgical model of realistic feed to the Semi Autogenous (SAG) mill. The hardness is linked to the SAG’s energy consumption, which is optimized by means of the use of an integrated photovoltaic-battery energy storage system (PV-BESS) with backup from the power grid. We show a sizing methodology to determine the optimum size of the PV-BESS system, which combined with the power grid minimizes the total energy cost. Furthermore, several sensitivities over the mill’s feed are performed. To account for the variability in the energy available from the PV-BESS system, solar irradiation is simulated from historical data using a Markov chain approach.

Results show that the PV-BESS system can help reducing the energy consumption from the grid, and have a significant impact in avoiding peak requirements that are costly. Furthermore, we propose a demand side management (DSM) option, where the SAG feed is optimized by drawing from two stockpiles of rock with different hardness. In all scenarios tested, the PV-BESS option proves convenient, reducing the overall energy costs in over 30%. The uncertainty in rock hardness and the variability in solar irradiation have a direct effect on the sizing decisions.