JOHANNESBURG (miningweekly.com) – The Johannesburg- and New York-listed Sibanye Gold is turning methane gas into electricity at the Beatrix gold mine in the Free State.

The highly explosive gas, which killed 40 employees between 1983 and 2001, is instead serving as a completely free fuel for the generation of an additional 2 MW of electricity after being captured and brought to surface from depths of more than 800 m.

The methane is intersected during mining operations and was being flared on surface until power services company Aggreko and Sibanye worked together to deliver this alternative source of power at a time of acute South African power shortage.

“We knew that we wanted to generate electricity from the gas as it was a precious resource that was being completely unutilised through flaring and we now have an additional 2 MW of power that runs completely on free fuel, which is released naturally underground,” Sibanye Gold environmental engineering manager Dirk van Greuning is quoted as saying in a media release by Aggreko, which is said to have entered into a rental contract with the mine, which is located 40 km south of Welkom.

To address variations in flow, quality and quantity, a gas accumulator acts as a reservoir balancing out peaks and troughs in gas supply and a methane sensor alerts the system to changes in gas consistency to allow the generators to intuitively adapt to any changes in gas quality.

Aggreko Southern Africa GM Martin Foster described the Beatrix project as an example of value being achieved through close customer/supplier cooperation.

Mining Weekly Online reported in 2013 that the five-million-reserve-ounce Beatrix was targeting an initial 2.4% self-sourcing of its electricity requirements and planning to extend that to 4.8% over time at a cost well below the Eskom power tariff.

At the time, Beatrix was paying 57c/kWh for the 82 MW of Eskom power that it consumed and the expectation was that it would be receiving the methane-fired power at a 33%-lower 37.44c/kWh.

“We’ll do 2 MW now and, as our extraction rate increases and as we get more gas, we’ll do another 2 MW,” Greuning told Mining Weekly Online at that time, when it was also reported that Beatrix had been earning carbon credits for flaring and now stood to earn a 25% premium on that for generating electricity.

In 2010, Gold Fields, out of which Sibanye Gold was unbundled, became the world’s first gold-mining company to sell certified emissions reductions (CERs), the financial securities used to trade carbon emissions, at a time when CER projects in Africa made up less than 2% of the total number of projects that the Clean Development Mechanism (CDM) had registered.

Project development firm Promethium Carbon designed the project for implementation as a carbon credit project under the CDM of the Kyoto Protocol, which allowed industrialised countries with emission-reduction commitments to meet part of their commitments by investing in projects in developing countries that reduce greenhouse-gas emissions.

It is rare for a hard-rock mine to have such large volumes of methane, which is said to arise from the Karoo rock formations below the gold seam.

It is understood that 1 900 litres of methane a second are needed for every megawatt of power generated.

The building from 2011 of the flare infrastructure on surface required a capital investment of some R42-million, with gas transported over a 3.6 km distance.

The Journal of the Southern African Institute of Mining and Metallurgy in December 2011 cited as major benefits the removal of more than half of the total volume of methane gas and the reduction in the risk of methane-related incidents.

The journal said the methane was released into the mine atmosphere in the course of normal mining operations, during which it was diluted by ventilation air to below its explosion limits, before being released into the atmosphere through the mine’s ventilation shafts.

The system, it said, was equipped with flashback arrestors, which isolated the surface main flare installation and the underground system from the main shaft column.

Self-closing valves at monitoring positions, the journal added, slammed shut if any operating conditions were breached and preset alarm levels activated strategically placed shutoff valves in emergency situations.