Week 14: Taking jet engine technology underground

By Donna Caudill. Courtesy American Longwall Magazine, see www.longwalls.com

WHEN a fire breaks out underground, operations cannot take chances with fire suppression. European manufacturer Liberty Gasturbine Holland couldn’t agree more, and has introduced its Steamexfire jet engine technology to help kill underground fires quickly by “blanketing” them.

Ironic, really – a technology that has helped man take to the skies, the jet engine, is being brought to ground to inertize underground mine fires. 
Since the company launched its technology this year it has been involved in the successful dousing of several coal mine fires around the world. A fire at the Anglo Coal Goedehoop colliery was put out in eight days in April, and in September GSIS put out a fire that had broken out in the Svea Nord longwall mine in Norway.
GSIS (Global Steamexfire Inertisation Services) director Michel Kooij explains that the use of the jet engine suppresses what is vital to a fire’s life and force: oxygen.
“An important factor often overlooked when dealing with coal mine fires is that underground coal mine fires change dynamics with time,” Kooij said.
“In addition to generated heat and flammable products, fire becomes self-propelled with the production of hydrogen and higher hydrocarbons such as ethane; the energy produced in an underground fire is much stronger than similar fires on the surface.”
The way the GSIS technology works is very straightforward. According to Kooij, it can be a cost-efficient alternative to nitrogen alone because the latter is “very, very expensive and, from my own experience, I can assure you it’s not necessarily the right gas to use in mine fires.”  The GSIS technology, in contrast, uses steam and water blown into an area underground, where they cover the fire “like a blanket,” Kooij said, adding that the process is continued until the fire dies.

Kooij said that inherent challenges with underground mining include the distance to the fire, the explosive atmospheres that can prevent rescue personnel from fighting the fire, fire-damaged roof supports and damaged ventilation devices that therefore change the air flow throughout the mine, often causing instability.
The Steamexfire technology process occurs in three parts.
The first step is rapid response to move the energy of the fire. 
“We need to remove that energy so that we can stop the fire from self-propagation and from doing any [further] damage,” Kooij explained.
The second part is to keep the fire’s energy low, which is done through the continuing displacing of the fire’s oxygen and lowering its ambient temperature. 
“This will kill the flames completely,” Kooij said.  “Once the oxygen is displaced, there’s no flame and combustion processes [are] seized when oxygen levels fall below 1%.”
Third and final is the monitoring stage, where the site is watched carefully to ensure that the fire is out.

What makes the Steamexfire jet engine system work, Kooij said, is the mixture of what’s being forced into the site of a fire.  The system output, at a rate of 20-30 cubic meters per second, comprises carbon dioxide (10-15%), small amounts of carbon monoxide, less than 1% oxygen, and the remaining percentage in nitrogen. 
“In addition, the system produces a steam-to-water vapor in the ratio of 3:7,” Kooij said.

One liter of water produces 1700 liters of steam to blanket the fire. To put that into perspective: “The system uses 23,000 liters per hour, pulling out energy equal to 14MW – enough to power 14,000 houses.” 
With fires underground that can reach temperatures above 3632F (2000C), the technique of blanketing may be the most efficient alternative.
The advantages of the GSIS system, in addition to a reduced dependence on nitrogen, are threefold, according to Kooij.  They include the ability to provide large quantities of inert product in very short time, the mobility of the system (it is movable from location to location as needed) and an output that is controlled by a computer program.
“The [entire] process is conducted from surface,” said Kooij. “This eliminates underground deployment of rescue services.”

Kooij said the company was always working on offering more advanced technology. One of their upcoming releases will be a software inertization program that he said would allow mines to run experimental exercises in real time, such as deciding the best possible inert site for a mine fire, goaf inertization during longwall changeouts and experiments showing contaminate distribution underground and Steamexfire’s affects on it.

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