Published in September 2006 Australian Longwall Magazine
The world’s biggest industrial gas company, Air Liquide, has designed and built the Austar nitrogen unit, which is rated at 1934 cubic metres per hour of inert gas at 97% purity.
According to Air Liquide national product manager Sajimon Joseph, the unit was specifically designed to continuously produce more than 500 litres per second of inert gas in environments up to 45C ambient temperature whilst maintaining availability, purity and, above all, low specific energy consumption.
The basic design consists of two surface-based skids, 14.5m long by 3.5m wide. One skid holds three air-cooled compressors, while membranes with associated engineering components are fitted on the second skid.
Compressed air is passed through the hollow membrane fibres generating the nitrogen gas at consistent purity. All the coal mine units come with a SIL2 rated purity control system and with the ability to produce nitrogen up to 99.5% purity at a reduced flow rate.
The system is automated and tele-monitored, allowing flow rates, purity and pressure to be monitored remotely with an ability to reticulate gas supply up to a distance of 92km using 6-inch pipe or more than 12km using 4in pipe as the Floxal AMSA system produces inert gas at 9 bar pressure.
Air Liquide has also just secured a contract from Xstrata to supply a unit to its Oaky North and Oaky No. 1 mines. Xstrata will use the nitrogen gas for sealing activities.
The company has also previously supplied a nitrogen unit rated at 1934cu.m/h to Anglo coal.
Today’s units are four times bigger than previously supplied to coal mines.
Longwall mines have used Floxal nitrogen systems since 2000 but these early units, rated at 500cu.m/h were originally designed for highwall mining applications. However, the new units are suited to faster, proactive inertisation.
After small beginnings in highwall mining, Joseph said underground mines showed interest during the 1990s to utilise the technology for sealing activities.
Joseph said the system offered several advantages including being substantially more cost-effective than alternatives such as liquid nitrogen – which is also expensive to transport.
In addition, the only utility the system needs is power and has low specific energy consumption, enabling the unit to be centrally located at a place where power is available and the inert gas can be reticulated over a long distance.
“If proactive inertisation can avoid an accident or incident, why not? This is a safety solution to an operational risk. If the unit can avoid a mine disruption for half a day, then mines have already made their money back – it is as simple as that,” Joseph said.
He said while Australia was leading the way, there was also interest from South Africa and China. Meantime, other mines in Australia are seriously considering Air Liquide’s Floxal AMSA solution, Joseph said.
