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A New Twist for Wet Rock Dusting


A major rock dust supplier proposes a simple, yet effective system tailored for coal operators
A coal miner applies Wright Mix O2 Aerated Rock Dust to the rib underground.

 

On November 8, Wright Concrete received patent protection for its Wright Mix O2 Aerated Rock Dust (ARD). This is a major milestone for the company, which has been developing and testing it in the field for the last three years. If anyone knows rock dust, it’s Wright Concrete; after all, they deliver more than 20 truckloads of rock dust a day to coal mines throughout southern Appalachia. The next step is to gain approval for the product from the Mine Safety and Health Administration (MSHA) and the National Institute for Occupational Safety and Health (NIOSH).

Wright-Mix O2 ARD is a single-component, dustless, dry powder mixture that contains ordinary rock dust. It is preblended in 40-lb bags. Once activated by mixing with water, an operator sprays it on the rib and roof where it forms a “cellular structure,” think honeycomb, that dries quickly (12 hours or less). The product meets or exceeds the new caking standards found in 30 C.F.R. § 75.2.

One 40-lb bag of Wright-Mix O2 ARD will cover approximately 110 ft2 at a thickness of 0.25 inches (in.). The mixing process is much simpler than other wet rock dusting systems and the sprayed mixture has strong cohesive qualities, meaning that it sticks to the roof and rib and other hard to dust areas. Because it can be applied effectively and evenly, there is less waste. Moreover, the system is dustless, so inby working sections can remain active during wet rock dusting operations.

“We felt that the industry needed some better, safer rock dust practices, particularly with the respiration issues that will arise in the future,” said Steve Williamson, West Virginia plant manager, Wright Concrete. “We also felt that we needed to make dust that would disperse better after it received moisture.”

The primary focus, Williamson explained, was to make it as user-friendly as possible, by just adding a prescribed amount of water to a bagged product. “Most of the other comparable foaming rock dusts typically require large machinery to mix three or four components to make them work,” Williamson said. “That’s not exactly user-friendly, when you consider the working conditions underground. High-water demand was one of the reasons we believe these other systems didn’t work as well.”

Other companies, such as the Swiss chemical conglomerate BASF and the support experts at DSI Underground Systems, developed foam rock-dusting products that relied on surfactants and soap-foaming agents. The development period for these products was a little rushed as a large Appalachian coal operator wanted to implement these products over a large number of its mines. Ultimately, the products ended up being complicated to mix and the equipment was bulky, expensive and unique.

Wright’s approach was different. By actively participating in the former trials, as other companies tried to apply its rock dust as a wet formula, they could see firsthand what was working and what was not. They also knew their customers and their working environments well.

 
A New Approach to Foam

Wright-Mix O2 ARD uses ingredients to create the bubbles rather than solely relying on the mixing action and a lot of water to make the foam. “A surfactant-based product of any kind typically requires quite a bit of water to activate the process and some rigorous mixing and a mixing sequence as far as when the water is added to the process,” Williamson said.

This is an all-powder mix that is blended in one bag, explained Shannon Wright, president, Wright Concrete. “The foaming agent represents less than 3% of the total bag,” Wright said. “Most of the bag is normal rock dust. The chemical reaction creates O2 making the bubbles rather than generating a formaldehyde smell. No one has that or a single-component product.”

“The other groups were very excited to introduce these products eight or 10 years ago,” said Al Campoli, vice president of special projects, Jennmar. “NIOSH cleared them. They used so much water that when the product rehydrated it began to cake. Because of the caking, all the wet rock dusts are now restricted to three breaks from the face and the miners are required to re-dust the area with dry dust by law. This product could conceivably be used once and not require re-dusting.”

The product reportedly will not cake and offers high illumination.

 

Jennmar obtained the rights to the DSI foamed rock dust product when it acquired its U.S. subsidiary. The promising surfactant-based product was rejected by NIOSH and MSHA due to caking difficulties. Jennmar’s review of the product led to an investigation of the oxygen generating product developed by Wright Concrete.

Considering the new rock dust regulations that MSHA placed on the industry, and even the older regulations, no rock dust has ever fully complied with the regulations. All rock dust cakes when it gets wet, meaning that it will not release under the concussion of an explosion and it never dries. Once it cakes, it’s like concrete. “The definition of caking is vague at best and certainly open to interpretation,” Williamson said. “This product performs 10 times better than any rock dust that gets wet and dries.”

The new Wright ARD product has a cellular structure like a honeycomb. Less material is applied to the rib, but it will expand to a 0.5-in. layer. “The mixture stays wet along the rib-roof contact zone,” Wright said. “The surface area and the rest dries. Even if it gets wet, it dries again in minutes. When it dries, it returns to the cellular structure; it doesn’t cake. The top layer or front portion will release from the rib or top during a concussion even if the contact zone is still moist.”

Wright believes this is the only products that has been developed that meets all the MSHA regulations regarding rock dust, including the more stringent rules imposed recently.

Once activated by mixing with water, the Wright Mix O2 ARD creates a cellular structure.
 
Application & Development

One of Wright-Mix O2 ARD’s biggest benefits is that it does not create a dust cloud as it’s applied. The mixture is 28% water, compared to conventional foaming rock dusts that are composed of a slurry that contains 50% to 60% water to properly activate the foam-making surfactant. “If the miners do not add enough water, they don’t get the foaming action,” Williamson said. “Our product uses less water, which significantly improves the drying time.”

A miner dumps a single bag into a standard mixture-pumping machine that exists within the industry. “We can use any machine,” Wright said. “You can literally apply this product to a wet surface and it will react to the water on the wet surface.” A reducing-cavity pump works best.

“A lot of the surfactant-based products, after they dry and a combustible test is performed, they usually contain 4%-7% combustible content in the product before any coal dust ever hits that protective layer,” Williamson said. “When a mine is limited to 20% by law, that other percentage loss becomes much more important. Our product has a combustible content
of 1% to 1.5%.”

From an environmental perspective, the mixture breaks down into biodegradable components. “After the chemical reaction, the structure transforms, but nothing remains that is hazardous to the environment,” Williamson said. “None of the chemistry has combustible content so the only combustible component is what is normally found in ordinary rock dust.” The only environmental concern might be the pH level and the rock dust itself would influence pH much more than any additive in the product.

The patent process was lengthy, Wright lamented with a chuckle. “We started developing this product four years ago,” Wright said. “We applied for the patent about a year after we decided what we wanted. It took about 2.5 years to get the patent approved. It’s so uniquely different and we didn’t want to release it to the market until we had a full patent.”

For miners to apply wet rock dust correctly, the process must be simple. “If they are underground and they need to add exactly three gallons of water with exactly one gallon of surfactant and mix it rigorously within 30 seconds, it’s not going to work consistently, if it all,” Wright said. He and his team understand this because they witnessed the trials with the other products.

The mixing system for Wright Mix O2 ARD is relatively compact. It uses a reducing cavity pump similar to gunite systems.
 
Testing the ARD Product Underground

Wright Concrete tested its new product at several Blackhawk mines to see how it dispersed and how it dried underground. “We applied the Wright ARD product in a couple of crosscuts,” said Eric Coleman, superintendent at Blackhawk Mining’s Mine No. 89. “The illumination was very good. The system uses water and hydraulics rather than water and compressed air. It’s really simple to mix — very similar principle to the old gunite machines — you just add the water to the dust.”

Coleman said he had worked with the other cumbersome systems. “We would drag those bulky machines around behind the scoop and it took two or three miners to operate the system,” Coleman said. “This system can be operated with only two miners and the machine is much more portable. You must flush it out when you are finished. If you were on the section or outby, you could go to any water source and wash out the machine.”

As far as adherence and caking, Coleman agreed with the developers at Wright Concrete. “We used it on a high entry with a high volume of air moving through it and it has performed well,” Coleman said. “As far as application and illumination, it worked great and it would be a good fit for the industry. As opposed to regular dry dust, this stays on the rib and top once its applied.”

Williamson has also provided NIOSH with dry material and they are testing it independently at the Pittsburgh Research Laboratory. Jennmar also recently organized a trial at the Cumberland mine in southwest Pennsylvania. “We wanted to see how it would work in the Pittsburgh No. 8 seam and this mine is also located near NIOSH and MSHA researchers,” Campoli said.

The initial response from MSHA and NIOSH has been favorable, Campoli explained. “There is no reason this product could not be used right now as a wet rock dust with the limitations currently placed on wet rock dust, but we want to go one step further,” Campoli said. “We want it to be a one-use-only product without the dry dusting behind it.”

“We want MSHA to help us move it along,” Williamson said. “We believe this is the product they envisioned when they introduced the first regulations on non-caking dust. We think we have got it and we want to prove it.

“We have been working with the coal industry for 20 years and we sell rock to dust a lot of mines throughout southern Appalachia,” Wright said. “We realized that the miners needed a better wet rock-dusting method. Everything in this bag was designed and made at our facility in Logan County, West Virginia.”

Today, mines with idle capacity can get by with rock dusting on the off shift. Once demand picks up, and the mines begin to run three shifts per day, that will not be possible. This product could allow them to dust on shift and comply with dust regulations.