Advances in Stonedusting - AiroDust
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Transcript Advances in Stonedusting - AiroDust
Advances in stonedusting
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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.
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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.
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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………….
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7.5% Methane
Explosion
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7.5% Methane
Explosion
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7.5% Methane
Explosion
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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.
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Coal dust explosion
1 kg
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Coal dust explosion
75kg
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Coal dust explosion
75kg
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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.
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Wet stone dusting
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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
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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.
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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.
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Surface full scale
trials
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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.
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Underground Trials
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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.
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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.
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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.
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Explosion Testing
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Explosion Testing
On average 40% more stonedust was lifted from the Airo-Dust
trays compared to the stonedust lifted from the Dry dust trays.
4000
3000
0
1420
3315
1845
2300
1810
3035
820
500
1485
1000
1755
2855
1754
1500
3218
2000
2075
2500
3462
Loss of stone dust (g)
3500
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10
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Dry stone dust trays
3462
1754
1755
2075
1810
1845
820
Slurry additive process trays
3218
2855
1485
3035
2300
3315
1420
Explosion test number
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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)
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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
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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.
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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 AiroDusters can be supplied.
The Airo-Dust additive is supplied and serviced Australia wide
by ITW’s Applied Australia or nominated overseas agent.
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Equipment
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Equipment
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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.
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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
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Airo-Dusting
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