Meeting gold production targets may be Gold Fields’ core business focus. But reducing its energy consumption and carbon footprint is rapidly moving to the top of its priority list, writes Laura Cornish.

Because energy costs keep rising, and already constitute more than 20% of Gold Fields’ total cost base (which has more than doubled in the last two years), the company is taking serious steps to ensure its operations remain sustainable for their remaining lifespans.

“In March this year we launched our integrated energy and carbon strategy – a global project that sets out to understand how we can transform our management of energy and carbon through direct interventions and by changing our operating behaviour,” says Gold Fields‘ CEO, Nick Holland.

Vice president and group head of energy, carbon and waste management, Jan du Plessis, says the strategy, which was developed for use across all of Gold Fields regions, was developed in three and a half months to ensure that the first stages of the strategy roll-out could be included in the company’s 2013 business cycle. It will be run from the group’s head office in South Africa.

The strategy aims to achieve specific targets, in particular reducing group energy consumption by up to 10% by 2016, depending on the investment required. This will enable the company to cut its carbon emissions by 13% on the same basis, because energy, particularly in South Africa where 90% of electricity is derived from coal, is a proxy for carbon emissions.

Du Plessis adds that in addition to this target, at least 20% of energy use at new operations must come from alternative/renewable energy.

Holland explains: “The strategy provides a framework to guide the way we source energy, the way we consume energy and the way we manage our core business activities that drive energy efficiency. It also looks at the linkage between energy consumptions and carbon emissions, and how we can mitigate these emissions. We have found significant scope for saving energy in all our operating regions across both fuels and electricity.”

Ghana:Tarkwa and Damang

Energy in Ghana comprises 35% of total operating costs in the region, meaning that reducing energy as well as fuel costs is critical.

“We are currently investigating the feasibility of a 30 MW biomass plant at our Tarkwa operation and negotiating a power purchase agreement (PPA) alongside this. Once we have final sign-off on the PPA, this project will move into execution. We are aiming for a completion timeframe of late 2014,” Du Plessis says.

This is the most advanced of Gold Fields’ renewable energy projects and will provide Tarkwa with a long-term energy solution. “We could even consider building a power line to the Damang mine, 60 km away, should the mine expand its operations,” he adds.

South Africa:KDC, South Deep and Beatrix (500 MW)

Thanks to the incorporation of Eskom’s DemandSide Management initiatives, Gold FieldsSouth African mines are already well advanced in terms of energy saving ventures. The plan is to introduce renewable energy projects into the mix as well.

Renewable energy initiatives

“I am confident that renewable power will be cheaper than Eskom power by 2018, meaning that the time to start investing in and building renewable energy projects is now,” Du Plessis comments.

Gold Fields has completed a feasibility study for a 3 to 5 MW biomass plant at KDC’s Driefontein site, using alien vegetation as a feedstock. The project is currently in review.

“We are also providing space at our Beatrix site for the development of an 80 MW solar plant, whose output would mostly be fed directly back into the national grid,” Du Plessis explains.

Due to the high levels of methane gas at Beatrix, the company is also looking at a methane extraction project on site, which will generate about 4 MW of power while reducing carbon emissions by approximately 250 000 t of CO2 per annum.

 

Energy recovery and efficiency

In addition to renewable projects, Gold Fields continues to implement a number of operational initiatives aimed at reducing electricity consumption. According to Du Plessis, one of the company’s most exciting projects to date is the investment in energy efficient fans.

“Former Counsil of Scientific and Industrial Research employees founded a company in 2007 called MechCaL and have designed a high-efficient 33.5 kW fan that provides the same airflow as a 45 kW fan. The company is rolling the fans out to the mining industry. Gold Fields alone is purchasing hundreds of fans every month.”

About 600 fans will be installed over the next 12 months and should save about 7 MW of power resulting in R30 million in annual savings (in 2012 terms).

Another initiative is the three-chamber pump system or 3CPS (also known as a three-chamber pipe feeder system), which recovers energy from incoming water and uses it to pump water out of the mine. The system has been implemented at Driefontein 3 Shaft, Kloof 4 Shaft and will be commissioned at Driefontein 1 Shaft in 2013.

“We have also installed Sulzer hydraulic power recovery turbines (HPRTs) at Kloof 3 and 4 Shafts and Driefontein 5 Shaft,” Du Plessis continues.

HPRTs convert excess pressure into mechanical shaft energy and increase the overall process efficiency. Sulzer Pumps has years of experience in using reverse running pumps as turbines as an economical solution to recover energy. “This project alone will provide in the region of 15 MW of energy recovery.”

Gold Fields has further optimised ventilation across all of its operations thanks to the incorporation of inlet guide vanes, which lower ampere consumption by an average of 3 to 7% compared to a butterfly valve.

Other power generation activities to achieve energy savings include:

  • fixing leaks
  • monitoring Demand Side Management valves on a daily basis in order to increase effectiveness and uptime
  • investigating the compressor control system in order to identify improvements and reduce compressed air set points where possible
  • gold plant agitation air flow reduction and instrument air isolation.

“We also recently launched a programme aimed at optimising the efficiency of our comminution circuits, which will run over the next 18 months to three years. This could improve our energy consumption by a further 3 to 5%.

With up to 83% of processing plant energy usage derived from comminution energy, which can in turn account for up to 51% of total site power usage, the optimisation of the blasting/crushing/comminution/classification circuits (mine-to-mill) forms a key component of Gold Fields’ energy efficiency programmes. Similarly, comminution can account for around 28% of a sites total greenhouse gas emissions as measured in tonnes of CO2 equivalent.

The Gold Fields comminution efficiency project is aimed at the following key deliverables:

  • decrease power consumption per tonne of ore treated by 5% to reduce unit CO2 emissions
  • optimise throughput for each operation based on current design
  • introduce group standards with regard to modelling and evaluation of comminution circuits
  • develop group standards with regard to comminution practice, in particular the use of on-line control, measurement and logic systems
  • develop group standards for engineering and maintenance of comminution circuits
  • reduce grinding media consumption by 5%
  • standardise group grinding media testing by establishing a group testing facility in Ghana
  • facilitate the establishment of comminution skills in each region sourced from within regional metallurgical teams.