Refrigeration of mines in central Queensland started with the Anglo Coal Moranbah longwall operation in 2001. Every year since then, a hired bulk-air cooling unit has been based on site for around four months during mid-summer to reduce underground temperatures to statutorily acceptable levels. This is normally about two to four degrees cooler than summer temperatures underground - about the same temperature as in winter.
Anglo’s nearby Central mine is also being refrigerated, using a range of techniques which includes cooling roadway development sections. The main supplier of the equipment is Aggreko, a major global service provider of rental energy solutions. The UK-listed company has the largest refrigeration capacity available in the world, with over 150MW cooling capacity in Australia.
Cooling a mine is not cheap (ranging anywhere from around 40c per tonne of longwall coal to $3/t), particularly in development sections. As such, mine owners will typically hold off on refrigeration until forced to introduce it by statutory requirements. Refrigeration is increasingly used, though, as part of a risk management approach, with growing recognition of the effect heat has on a workforce’s morale and productivity.
Aggreko national sales and marketing manager George Whyte has observed a significant impact on the morale of the workforce in such industries.
“Traditional heat management methods, such as men working in pairs and in ten minute intervals to cool off, not only affected productivity but also caused frustration and stress due to constant hot to cold changes,” he said.
Rio Tinto’s Kestrel mine recently embarked on its first project to cool the mine this summer using bulk-air cooling, the most common approach used to date. Kestrel’s senior compliance engineer and ventilation officer Chris Rogers said the need for cooling at the mine had been recognised for some years but was driven by a requirement to comply with safety legislation. The health effects on employees working 12-hour shifts, along with productivity impacts, were other factors.
Rogers said there had been a marked improvement in comfort levels in the mine. “The biggest effect has been psychologically with the blokes. When they go into the mine and pass a cut-through with cool air, they can see we are doing things. They can see Rio Tinto is investing in their comfort.”
Kestrel is also experimenting with other approaches, such as introducing cooling at the back of a longwall, previously done at Central. This can be done through a 300mm vent that can be drilled or may pre-exist for exhausting gas. This downcast shaft can take 10 cubic metres per second of cooled air, delivering efficient localised cooling.
The mine is currently investigating cooling options for roadway development, including spot cooling along the development panel by means of chilled water in pipes, as well as delivering cooled water to continuous miners. At the moment, water servicing CMs gets to the machines at temperatures nearing 40C, making this equipment a major source of ambient temperature.
“The CMs are a big radiator of heat. In particular, blokes using bolting rigs on the side of the machine are subject to high temperatures,” Rogers said.
The long-term strategy is to have two plants delivering cooled water, one on primary development, and the other on secondary development. One of these would then go on to serve the longwall once development was complete. Another plan is to chill the surface water before delivery to the miner at cooler temperatures.
Down the track, Kestrel plans to investigate running cooled water onto the longwall into services such as the pantechnicon, beam stage loader and armoured face conveyor motors. Cooling the longwall face itself is still proving something of a challenge for most mines.
“If you can reduce the overall effective temperature on the longwall by two degrees, you’ll be doing well,” Rogers said.
Refrigeration equipment is best hired, offering a more flexible and better financial solution than owning the quite complex, labour-intensive equipment, Whyte said.
“Customers benefit from the hiring arrangement because operating costs include engineering support, maintenance, exposure-to-risk, back-up support, and full turnkey management. What governs the benefits of rental for us is if it doesn’t work they’ll never rent again,” he said.
Other companies have tried unsuccessfully to break into the market, but none have outlasted Aggreko. Whyte believes the success of the company is attributable to its commitment to advanced technology and to providing the best possible service. He sees the service more as a partnership with mine management and ventilation engineers
“We’re a global company that comes with a reliable international reputation and not just a dry rental company. We’re a very advanced engineering support company utilising the best equipment.”