Mining in focus
Diesel-driven equipment contributes to the amount of diesel particulate matter( DPM) circulating the underground environment. A good ventilation system is required to prevent the DPM from becoming a potential hazard.
underground mines is a result of the geothermal gradient, where the temperature normally increases from about 25˚C to 30 ° C per kilometre. The conduction of heat by different rock types is determined by the mineral composition and density of the rock. Dense rock, like the igneous rocks of the Bushveld Complex in South Africa, conduct heat more effectively than the clastic sediments such as the quartzite and shale of the country’ s coalfields.“ A secondary source of heat, especially in trackless mining operations, stems from the engines of underground vehicles and equipment,” says Steenkamp.
The rock type will also determine the hazards associated with mining it and the ventilation remedial measures. In coal mines, the dust has to be suppressed and safely ventilated, along with methane, to prevent explosions.
In gold mines, the silica dust needs to be suppressed and sufficient fresh air supplied to the working face. Silicosis and other lung diseases can directly be ascribed to the dust generated in underground mining operations.
According to Steenkamp, the layout of a mine needs to take the ventilation and cooling requirements into consideration. In bord-and-pillar operations, for example, the layout of the mine advance resembles a Christmas tree, as this is the most effective layout for mining advances, ventilation, and cooling flow.
Ventilation regimes
In underground mining operations, there are two main ventilation regimes— an upcast and a downcast— where air is either‘ sucked’ out of the mine or forced down into the operations.
Booster fans will also be installed, and ventilation walls built to aid effective ventilation and cooling. The placement of the ventilation shaft, the diameter of the shaft, and the specifications of the extraction fans need to be done with great care, as it will usually need to last the entire production life of the mine. Sinking secondary ventilation shafts or replacing / upgrading / refurbishing is expensive and almost always results in a period of operations being halted or severely limited.
Steenkamp says that the introduction of prototype platinum cell electric vehicles, instead of traditional machines in underground mines, will affect the ventilation requirements significantly. Traditional mining methods make use of diesel-driven equipment that not only increases the temperatures but generates a range of noxious gases that
[ 22 ] MINING MIRROR JULY 2018