Spring Creek Coal Mine Solves Dust Control Problems
Domestic mine by Harold Hough

            Although Wyoming’s Powder River Coal is prized for its low sulfur content, it does offer another sort of environmental problems - dust.  “It’s a dusty animal,” complains one coal expert.
            Powder River Coal (PRC) is a sub-bituminous coal with lignite characteristics.  When federal sulfur emission regulations became tighter, this PRC became the coal of choice for many Midwestern and Eastern coal fired utilities.  Not only that, it was cheaper because the Powder River coalmines were surface operations and known as some of the most efficient mines in the world.  Soon power plants as far away as New Jersey substituted PRC for the high sulfur content sub-bituminous coal from mines in places like Illinois.
            However, both mines and utility companies learned that they had merely traded one set of environmental problems for others.  Not only did it have more mercury in it than “Eastern” coal, it was considerably dustier.
            PRC has very little surface moisture according to coal mine experts and during the mining and processing processes, it releases a lot of dust into the air.  Not only is this dust a health hazard for mineworkers, coal dust is extremely explosive and can ignite with the power of dynamite if a spark comes into contact with the airborne dust.
            The traditional method for controlling coal dust has been large bag houses that collect the coal dust and store it.  These facilities however weren’t as effective as hoped.  “If you looked up at the light inside, you could see the dust, when we used bag houses,” noted a Plant Coordinator.  “It was everywhere.”
            This was a problem at the Spring Creek Mine which is northwest of Decker, Montana in the northwest section of the Powder River Basin. The mine was acquired by Rio Tinto Energy America in 1993.   The Spring Creek Mine mines the Anderson-Dietz seam in four pits. The site is 6,700 acres and the average thickness of the seam is 80 feet. The seam ranges from approximately 50-220 feet below the surface.
            Spring Creek has a reputation for good environmental practices.  In 2009 it won the National Excellence in Surface Mining and Reclamation from the Office of Surface Mining for achievements in establishing and maintaining a rare plant species, the woolly twinpod.  Three years earlier it won the same award for establishing excellent topographic and vegetative diversity of the South Fork reclamation

BETTER DUST CONTROL

            Although bag houses were the conventional coal dust control answer, there were other solutions like water and chemicals.  However, with 18 million tons of coal being produced by Spring Creek annually, conventional water or chemical systems were not practical. 
            Using water to suppress the dust may seem practical and cheap, but there are problems like clogged nozzles and high water usage.  Typical water spray systems have limited success in suppressing dust because the water droplet size is too large to effectively control dust.  Some companies have tried to make smaller nozzles to solve the water particle size problem, but the tiny orifices were more likely to plug. 
            The answer for Spring Creek was fog based.  The nozzle technology used today in fog based technology is the sonic type air assist “fog” nozzle that uses less water, while controlling droplet size.  This fogging system uses a nozzle that fogs water droplets by passing water through high frequency sound waves.  This shock wave, which is created as the air stream is accelerated beyond the speed of sound, explodes the water droplets into thousands of microscopic water particles or fog. 
            Although The Powder River Basin can get quite cold during the winter, the fog systems are very effective at low temperatures thanks to cloud physics.  According to physicists, small water droplets have suppressed freezing points because their surface tension inhibits expansion.  If water can’t expand, it can’t freeze.  Consequently, systems that are well maintained can operate at temperatures as low as -31 F.
            Although the fog system has solved part of the coal dust problem, there remain several other issues like mercury in the coal and the anti coal mining attitude by the current administration.  In the meantime, Spring Creek continues to provide nearly half of Montana’s coal production and fuel for electrical production in Wyoming, Montana, Washington, Arizona, North Dakota, South Dakota, Kansas, Minnesota, Wisconsin, Michigan, Illinois, New Hampshire and various Canadian provinces.