Published in March 2008 Australian Longwall Magazine
Under an Australian Coal Association Research Program (ACARP) grant, Queensland-based Mining Attachments managing director Matt Ryan has been hard at work proving the effectiveness of adding a "crystal inhibitor" to stone dust slurry mix to stop caking, and, in turn, allowing the stone dust to make a mine's atmosphere inert during an explosion.
Ryan has proved his concept and completed trials at Caledon Resources' Cook Colliery in Queensland to show the idea’s practicality. His last step will be explosion testing and data gathering in a test facility in South Africa. Subject to these results the product will be available commercially late this year.
Stone dust, made up of limestone or calcium carbonate, is used in underground coal mine roadway floors and walls. Historically stone dust has been applied dry, however this means that people can't work inbye of the ventilation while it is being applied. Hence, many mines apply wet stone dust – stone dust mixed with water – so it can be sprayed on, allowing people to work inbye and hence mine production is not affected.
Stone dust acts as inerter in the event of a methane explosion. During an explosion a shock wave is generated followed by a flame front that is hot enough to ignite coal dust.
Using stone dust is an easy way to prevent the propagation of the coal dust explosion. Both the stone and coal dust is suspended in the air by the shock wave, but at the right percentage the mix is inert.
Australian mines are required to carry out regular sampling to ensure the incombustibles verses combustibles percentages are maintained in accordance with regulations.
However, ACARP-funded research three years ago by Queensland's government-run Safety In Mines Testing And Research Station (Simtars) cast doubt on the effectiveness of wet stone dust in preventing the propagation of an explosion.
Simtars research indicated there was an issue with coal dust sitting on the surface of caked stone dust. Then in an explosion only the coal dust would be suspended in the atmosphere, allowing the spread of a coal dust explosion.
Enter Matt Ryan. Following on from the Simtars' research he decided to look into how this was possible, and searched for a way to overcome the caking. In conjunction with Applied Chemicals Technical Manager Alan Brown, they examined the chemistry behind mixing calcium carbonate and water.
Together they found a way to stop the particles binding. A trial solution was manufactured and prepared for large scale trials. The new process set out to utilise existing wet dusting equipment with a modification engineered by Mining Attachments.
The Dysart Mines Rescue Station was used to simulate an underground environment and the trials were successful, with stonedust sampling analysed by SGS Australia for particle distribution.
The project gained momentum and Ryan organised trialing of the additive at Cook Colliery.
"Cook Colliery have provided their site and some operators and said 'go and turn it white'," Ryan said. And Ryan and his team turned the roadways white for the six months to the end of February 2008.
The project is in the final stages and Ryan is taking the new process to CSIR Miningtek's Kloppersbos testing facility in South Africa. There they will set off a methane explosion inside the facility and test the suppression effectiveness.
"At the end of the testing we will have sufficient technical evidence to determine the effectiveness this new process," Ryan said.
Ryan said he expects a positive result from the testing and by December the chemical would be available from Applied Chemicals. Mining Attachments will be able to supply to the industry the equipment modification that will enable a seamless introduction of the new wet dusting process.
