Not all dust control solutions are the same. Dave McMillan, Air Division Manager at Marc Technologies explains how different technologies can provide effective solutions, as a holistic approach to mine site dust control.
Respirable dust under 10 micron in size poses a health hazard to workers exposed to it and is the main contributor to lung disease in the industry
Legislation is being implemented around occupational exposure limits for crystalline silica, which can be found in many ore bodies, following Safe Work Australia’s extensive review into safe exposure levels.
Dust is generated wherever the product is disturbed, such as at truck dumps and hoppers, crushers, screens, conveyor transfers, stackers and reclaimers, train loaders and unloaders, and shiploaders, as well as in stockpiles where wind has the potential to lift dust off the piles.
Where material is being handled, it is important to limit fugitive dust and tackle the dust problem at the source. Engineering controls such as covers, well-sealed conveyor skirts and extraction systems can assist, but additional controls need to compliment these controls and provide effective prevention of emissions where they occur.
Dave McMillan, Air Division Manager at Marc Technologies, says the droplet size from traditional low pressure water sprays will dwarf the dust particles the sprays are trying to control, and as a result the dust will migrate round the water droplets, and escape the area.
“Most water sprays are designed to wet the material surface, but unless these are applied in the right way, they will also cause problems with overwet product such as carryback, avalanching and blockages,” McMillan says.
“Once the material is disturbed again, either at conveyor transfers or into secondary or tertiary crushers for example, more exposed dry surfaces appear and are likely to cause fugitive dust. Add to that, the increasing cost of the precious water resource, and it becomes an expensive way of not dealing with a common problem.
“Engineered solutions incorporating a few different technologies in a holistic approach can make a huge difference to controlling the fugitive dust in various parts of the mining process.”
In operations such as crushing and stockpiling, careful water addition in a controlled fashion, with targeted moisture addition using properly selected spray types and positions, can ensure minimal dust emissions further down the process at the stackers and transfer points, as well as controlling the dust at source.
Material being stockpiled can become susceptible to dust lift-off, where wind causes dust particles to escape the pile. Using a windfence positioned upwind of the pile helps to minimise this issue.
Where there is no opportunity to condition the material as it enters the handling process, such as at a load hopper or a dump truck, fugitive dust can be controlled with microscopic Dry Fog, that produces water droplets that bind with the dust particles in the air, preventing it from leaving the area.
Dust Solutions Inc has developed systems that can be used in combination to offer a complete dust control solution. The Dry Fog system uses an ultra-sonic nozzle with low pressure air and water to produce water particles less than 10 microns. These scrub out fugitive dust by agglomeration of like-sized particles, effectively binding with the dust particles and drop it them out of suspension.
McMillan says Dry Fog uses less than one fifth of the water used in a traditional water spray, producing a fog that is dry to touch and helps avoid associated issues with carry back and belt wear.
“This also reduces decreases thermal penalty in coal power applications,” he says. “Blockages are rare as the venturi design within the nozzle means that the water and air orifices are relatively large, though these systems also have dual filtration as standard to factor out poor water supply.”
“Dry Fog is not a new technology, and it is widely used in the US and many other countries, with a proven track record of well over 500 installations with the major miners.
“The US Environmental Protection Agency lists it as a best demonstrated technology for suppression of sub-bituminous and lignite coal dust and is listed as a control technology for new CCR Rules in the USA in relation to fly ash and coal residuals handling.”
DustTamer Windfences are also an effective dust control method for larger areas such as stockpiles and tailings piles. Controlling the top surface of the pile with water cannons offers limited protection but must be constantly applied and excess water can cause detrimental and unwanted effects.
DustTamer Windfence Systems are designed to drastically reduce wind velocity and particle movement for a potentially large area such as a stockpile, minimising fugitive dust emissions with consistent reliable results.
The windfence is a permanent structure, and uses a hard wearing, ultraviolet light stable kitted polyester material that is strong enough to be used in cyclonic regions. This material exerts a drag force on oncoming wind velocities and allows a portion of the wind volume to penetrate through the screen as well as deflect the remainder of the wind to the surrounding sheltered area.
McMillan says MARC technologies has been delivering dust control solutions to the mining and industrial sectors since 1995.
“MARC Technologies is a wholly owned subsidiary of the Brisbane based ALS, providing a global presence,” he says.
“MARC is also a licensed electrical contractor in Western Australia. This means our products are shipped out to our clients with safe electrical systems and we we can offer the supply and installation of distribution boards and control systems with our products.”