The challenge to the customer
The Granny Smith gold mine near Laverton, Western Australia, is operated by Gold Fields- a global leader in sustainable gold mining, and has produced more than 7.4 million ounces of gold. In July 2014, Gold Fields issued a tender for the provision of a 22 MW gas power station for the next 10 years.
The mine had been powered by a competitor's diesel power package, along with an 8MW standby power package provided by Aggreko. However, the other generators were nearing the end of their life cycle and were due for retirement.
At the same time, a gas line extension was being built by AngloGold Ashanti to service their mining operations at Sunrise Dam and Tropicana, which presented the opportunity to spur off high pressure gas to use as the fuel source. Gold Fields saw that it could both make significant cost savings and reduce its carbon footprint.
Gold Fields wanted reliability, but also engines that would work efficiently in the long term, where a difference of one or two percent can result in fuel cost savings of millions of dollars over the course of a project lifecycle.
Aggreko had been trialling larger gas engines over the previous 18 months and these were chosen in favour of the standard QSK60 generators.
We proposed using modified high-efficiency gas fuelled Osprey engines in 20 foot containers, which meant we were able to offer savings in fuel costs. The smaller containers also create a smaller environmental footprint compared to competitors, who tend to provide equipment in 40 feet containers, which are more expensive to transport.
Aggreko has more efficient Ospreys than anywhere else in the world, and incorporated further technology to improve reduction of gas pressure to offset the cooling down process. A heat recovery system replaces the electric heaters. Aggreko is taking the heat from the Osprey jackets and using it to heat the gas. This represents a large cost saving for Gold Fields.
Benefits to the customer
The project was initially constrained by the high pressure of the gas, which was at 90 Bars. Our ability to build a high pressure reduction facility meant we could reduce the construction time and get the new plant commissioned quickly, thereby reducing operational costs.
The new power station will also reduce the mine's carbon dioxide emissions by approximately 80,000 tonnes over six years, and enable Gold Fields to trade carbon credits with the Australian Government's Emission Reduction Fund.