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Advances in stonedusting. I will talk about and show footage relating to the basics about Stonedust methane and coal dust explosions why previous wet dusting attempts failed ACARP project C16014 - Advances in wet slurry dusting how the slurry additive process works
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I will talk about and show footage relating to the basics about Stonedust methane and coal dust explosions why previous wet dusting attempts failed ACARP project C16014 - Advances in wet slurry dusting how the slurry additive process works and look at the equipment involved in the process Some information within this presentation is well known by the coal industry. It has been included to provide a summary of how various elements interact.
Stone dust Stone dust or calcium carbonate is used in underground coal mines as a primary inerting agent, in the prevention of coal dust explosions. The application of dry stone dust creates large quantities of airborne dust along the ventilation circuit, requiring the extraction of inbye personnel. In a methane explosion, a pressure pulse travels through the immediate area of the mine. This wave raises any dust into suspension, both coal and stonedust. Areas treated with adequate quantities of stone dust, will render the dust cloud inert and a coal dust explosion will not occur.
Methane The ignition of methane in an underground mine is not common but does occur. Friction sparks from continuous miner and shearer drum picks have provided ignition sources for methane gas. Other potential sources are cable flashes, belt friction, heating and open fires. Given the right conditions a methane explosion itself is most explosive at 9% general body and has deadly consequences. The following footage is a weaker explosion that compares to a typical 10 metre overdrive allowed to accumulate a methane concentration of only 7.5%. If an ignition source is present………….
Coal dust Minimising the make of coal dust and reducing float dust is an ongoing challenge for all coal operations. Areas that were stone dusted once, if left unmaintained, accumulate coal dust deposits providing fuel for an explosion to propagate. Only 4-5mm of dry dust will be lifted in a weak methane explosion. The more float dust accumulated, the less of the underlying stone dust will be lifted. We saw that a methane explosion creates a fire ball that travels behind the shock wave and hits the dust cloud. Insufficient quantities of stonedust in suspension will allow the coal dust to ignite will obvious catastrophic consequences.
Wet stone dusting Wet dusting was always viewed as an opportunity to help overcome reductions in cutting times due to stoppages caused by stone dusting. The onset of 7 day operations compounded the problem and attempts were made to apply stone dust as a slurry. This allowed crews to continue production while wet dusting was carried out in the ventilation intakes of the panels. Wet dusting is a process of creating a stone dust / water slurry and pumping it onto the mines walls. The intent was to replicate the conventional dry dusting without the need to withdraw inbye personnel.
Why wet dusting does not work The application of wet dusting was proven however the final product failed to provide adequate inerting qualities. When stone dust comes in contact with water the particles partly dissolve. As the slurry dries, the dissolved solution moves between the stonedust particles forming a bonding bridge that locks the particles together. This is referred to as “The Caking Effect”. This caking reduces the amount of stone dust raised into suspension, creating enough doubt on its effectiveness as an inerting agent. Inspectors in NSW and Qld rightfully issued directives restricting the use of slurry dusting
ACARP project C16014 Australian Coal Association Research Program (ACARP) contracted Mining Attachments to research and develop a wet slurry treatment process that could overcome the caking effect. Applied Australia were requested to engineer an additive that would work but had to be end user friendly. In 2006 the additive was ready to be trialled and tested on large scale. The 3 stage project spanned over two years. Surface full scale spray trials Underground spraying trials Full scale explosion testing Industry monitors were required to assess each stage objectives were achieved, before advancing onto the next.
Airo-Dust™ Additive Airo-Dust™Additive has been designed with the primary focus of providing a safe product for use in the underground mining environment The MSDS outlines all the health and safety requirements. Non-combustible Operators wear standard PPE Classified Non-dangerous goods Warnings in regards to skin, eyes, inhalation and ingestion are similar to those of concentrated household dishwashing detergent pH of the additive is between 6-8 (water 7.0 neutral) The required dosage of 10 litres of additive is required to treat one tonne of stone dust. Airo-Dust™ Additive is a trademark of Illinois Tool Works Inc.
Surface full scale trials Samples were taken during the surface spraying trials and sent for particle size distribution. Results showed little change to the original particle sizes, supporting the anti caking ability of the process. A simulated explosion demonstrated that the treated wet dust could be put into suspension. The project moved to Cook Colliery, one of many operations that supported the project. Mining Attachments fit for purpose equipment was mobilised onsite and the first underground trials began.
Underground Trials The experience gathered from the 6 months of trials allowed the necessary time to refine the process with dedicated personnel allowed to focus on achieving the projects aims. Industry monitors evaluated the underground trials, operating the equipment and viewing other areas of the mine previously dusted using the new slurry additive process. The project then moved into the final stages of conducting full scale explosion testing by third parties. The new slurry additive process was named Airo-Dust. The CSIR explosion testing facility in Kloppersbos South Africa, hosted comparative Dry v’s Airo-Dust testing, facilitated by Skillpro Services.
Explosion Testing The testing facility comprises of a 200m steel pipe tunnel that has a methane mixing station and ignition centre one end and the other end is open.
Explosion Testing Trays were prepared prior to testing. Prior to each test explosion, trays were weighed and secured into the tunnel. After the blast the loss of stone dust from each tray was recorded. High and low speed video footage captured each blast.
Explosion Testing On average 40% more stonedust was lifted from the Airo-Dust trays compared to the stonedust lifted from the Dry dust trays.
Explosion Testing On average the depth of dust lifted by the explosions also varied. 4-5mm in the case of the Dry dust trays in most cases the Airo-Dust trays were empty (30mm)
Explosion Testing Full details of this project including all the results from the explosion and underground testing can be obtained on line by visiting www.acarp.com.au Project number C16014
How the Airo-Dusting process works Stonedust slurry is made by mixing two parts stonedust with 1 part water. The Airo-Dust additive is dosed into the pump out line which provides a protection barrier around the stone dust particles, minimising the caking effect. Air is entrained into the line to create a foam. The product is highly vesicular, trapping millions of tiny air pockets or voids in the product as it dries. From the explosion testing it was evident that a methane pressure wave is able to penetrate these voids, smashing through the surface and raising the stonedust into suspension.
How the Airo-Dusting process works The equipment consists of a mixing tank and paddle, slurry pumps, additive pumps and the foam generation equipment. The system is non adjustable making the process less complicated and simple to use. The additive is accurately dosed into the pump out line and delivers a steady stream of shaving cream like slurry to either a hand held nossel or machine spray bars. Existing equipment can be modified or new custom made Airo-Dusters can be supplied. The Airo-Dust additive is supplied and serviced Australia wide by ITW’s Applied Australia or nominated overseas agent.
Getting started A copy of the final ACARP report has been sent to both NSW and Queensland inspectors for review. The NSW DPI have assembled a review committee to firstly review the ACARP report and secondly participate in the initial underground trials in NSW. This will allow the Airo-Dusting process to be viewed from both a technical and practical perspective. Operations can now make application to the NSW DPI to use the Airo-Dusting process underground.
Current participating sites Grasstree Mine 1 x existing wet duster modified into an Airo-Duster 2 x new Airo-dusters Greenside Colliery (South Africa) 1 x new Airo-Duster North Goonyella 1 x Hire Airo-Duster Centennial Coal (Mandalong, Clarence, Springvale) DPI application pending Vale (Integra Coal) DPI application pending
