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Mobile nitrogen plant for underground fires

The collieries committee of the Chamber of Mines has commissioned the world’s largest mobile Floxal membrane nitrogen plant, its purpose being to put out underground fires, some of which can potentially burn for decades.

The plant, which cost R22 million to develop, was built by industrial and medical gas company Air Liquide, and will be used primarily in the inertisation of combustible environments during underground coal fires.

“We looked at other underground fire fighting systems available internationally, but the deployment and running costs are extremely prohibitive,” Christo de Klerk, general manager of Mines Rescue Services, says.

The system comprises a Floxal membrane plant that separates nitrogen from ambient air that can then be pumped into the underground fire area. “Inertisation is a method of controlling underground fires,” de Klerk says. “And the plant is entirely mobile making transportation and rapid deployment easy.”

Air Liquide marketing director, Jonathan Madden says, “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 tonnes a day.”

“The Floxal inertisation system allows for a safe process conducted from the surface,” de Klerk adds. “This means fire fighters do not have to put their lives at risk by having to go underground during the inertisation process once the burn-area is sealed-off.”

Underground fires can have a huge financial impact on the industry. In a well-documented case in 2005, it cost a mine well over R500 million to bring a fire under control.

The portable nitrogen plant was modelled from Air Liquide’s sister company in Australia which has developed similar, but 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,” Madden says.

“We were able to deliver the completed system within nine months of agreement, including detailed design, procurement and construction. While the Floxal membrane skid was constructed in USA, the trailers and the integration of the mechanical and electrical systems were completed locally.”