South Africa, ranked as the seventh largest producer of coal in 2008, now has a revolutionary method of extinguishing fires in underground coal mines, courtesy of Air Liquide.

The new Colliery Inertisation System (CIS), or Floxal membrane nitrogen plant as it is also known, was unveiled in Secunda on 10th March 2010.

A world-first as it is completely mobile and operates with its own integral power generator, the plant cost R22m to develop and was commissioned by the Collieries Committee of the Chamber of Mines. It will be used primarily in the inertisation of combustible environments during underground coal fires.

The plant be stationed at the Colliery Training Centre in Witbank that is centrally located in the coal production region of Mpumalanga and can be deployed within hours, depending on the distance and accessibility to the site of the underground fire.

Long experience has proved that the only effective way to extinguish coal mine fires is to reduce the availability of oxygen that forms 21% of air, by flooding the fire to displace the oxygen until its concentration is below 5%. The cost and logistics of delivering large but uncertain quantities of liquid gas to remote coal mines for this application, from conventional industrial sources, are prohibitive however.

South Africa is not alone in facing these challenges; Australia, China, India and even the US have underground fires that have been burning for decades.

Air Liquide’s AMSA Floxal Nitrogen Generator, which extracts inert nitrogen gas from air using hollow fibre membrane permeation, was selected as the core element of the new system – which is trailer mounted and powered by a mobile, diesel-fuelled electric generator. The skid-based Floxal unit was delivered by Air Liquid in nine months and its output is rated at 1800 Nm3/hr, of >97% pure nitrogen.

The system comprises a Floxal membrane plant that separates nitrogen from ambient air, which can then be pumped into the underground fire area. Air Liquide Marketing Director Jonathan Madden says putting out fires underground is extremely difficult, costly and very dangerous.

“In a nutshell, what Mines Rescue Services does is to seal off the burn area underground, drill emergency access holes from the surface and flood the space with nitrogen, thus extinguishing it by starving it of oxygen. The new plant has an output of 54 tons per day,” he said.

The portable nitrogen plant was modelled from Air Liquide’s sister company in Australia, who has developed similar, fixed nitrogen plants for use in mining. “There were some challenges, because in effect, no one had ever created a mobile unit before. We also had to comply with South African specifications. The plant consists of three components, the power supply, the air compression unit and the nitrogen generator,” added Madden.

“We were able to deliver the completed system within nine months of agreement, including detailed design, procurement and construction. While the Floxal membrane skid is constructed in US, the trailers and the integration of the mechanical and electrical systems were completed locally. It is very rewarding for us to see a project like this – first of its kind and for such a cause – completed successfully and delivered on schedule after so much cooperation and development.”