Quantifying the heat load effects of micro-hydropowered stope environments

Abstract

Handheld rock drills powered by compressed air are conventionally used in underground mining operations in South Africa. Compressed air is generated using large compressors on surface, with extensive and inefficient compressed-air networks that supply underground working areas. This leads to reduced compressed-air pressure in the stopes and lower drill penetration rates. Alternative drilling technologies have been developed to combat the energy inefficiencies of compressed-air supply networks, including hydropower, electro-hydraulic and electric-powered drilling equipment. However, these new technologies add heat to the stope environment. Additional heat can lead to increased heat injuries and reduced labourer efficiency in the workplace. Of the identified alternatives, micro-hydropower has the highest electrical heat load per drill and thus the highest probability of adding heat to the stope environment. Therefore, there is a need to quantify the heat load of micro-hydropower technologies in stope environments as the additional heat added through the introduction of micro-hydropower is largely undetermined in literature. The stope heat load was quantified through ventilation simulation modelling, which enabled the prediction of thermal changes when micro-hydropower technologies were introduced into the stope environment. A method was developed from literature to achieve the study objectives. In this dissertation, the heat load characteristics of a stope environment were simulated to predict the thermal changes when introducing micro-hydropower technologies. The heat load was quantified by first determining the nett amount of heat added to/removed from the stope environment, determining the effect on the stope environment conditions, and analysing the effect that the conversion may have on multiple stopes in series. A hydropowered stope conversion case study was observed and thermal-hydraulic solver simulation software was used and calibrated with empirical data captured from a real-world stope environment. The hydropowered drills were seen to add heat to the stope environment compared with a conventional stope environment equipped with compressed-air drills. The first stope's reject wet-bulb temperature increased by 0.6 °C. Thereafter, the simulation was extended to predict the thermal changes along a micro-hydropower converted raise line. By the third stope environment, the wet-bulb temperature of the micro-hydropowered environment was 1.8 °C hotter than the compressed-air raise line environment. This implies that the hydropower raise line will be at a greater risk of heat injuries and will experience a reduction of labourer efficiency because of the higher temperatures.