Project Status: Complete
Project Participants: University of Queensland
Project Leader: Nenad Djordjevic (University of Queensland)
This aim of this project was to investigate the accumulation of thermal energy in rock using an advanced thermal imaging camera, to quantify how much energy is lost as increased thermal energy of the rock rather than used for rock breakage. The project explored potential relationships between this heat accumulation, the physical and/or mineralogical characteristics of the rock, the produced fragment size distribution and operational parameters of the comminution process. Ultimately, having a better understanding of heat losses will generate options for modification of operational and equipment parameters of comminution devices.
It was found that the best application was to use High Pressure Grinding Roll (HPGR), where the ore product is immediately visible after crushing. The project therefore focussed on this technology. HPGRs offer a more direct ability to measure thermal losses associated with rock crushing. Results of infrared imaging of crushed rock show that a large fraction of net energy supplied to the rock is transformed into heat, raising the temperature of the rock – which indicates that more energy is delivered to the rock that what is required to crush the rock.
Using a laboratory-scale HPGR, it was established that there is a close correlation between the measured temperatures and the applied net energy for the two types of ore tested. Rock crushing within the compressed zone of the HPGR occurs principally on the side of the active, moveable roll. The efficiency of crushing can be significantly improved by removing fines from the feed and, beyond a certain pressure, improvements in fragmentation rapidly diminish (i.e. all additional energy input ends up as heat).
The team visited Newmont’s Boddington gold mine in Western Australia for in-situ testing of the procedure. The final report will highlight the possible ways forward, including industry transfer, and will define additional research targets within this highly important area. Further analysis of measurements and modelling indicates that thermal losses are even higher than previously considered. Due to the close proximity of the metal rolls and crushed rock, and the high thermal conductivity of steel, a substantial part of the heat generated during crushing becomes conducted through compressed rock layers and into the rolls. Hence, the efficiency of the HPGR is potentially lower than previously considered.