By Russell Ray, Managing Editor
Where there is coal, there is coal dust, one of the biggest nuisances for coal-fired power plants.
The U.S. produces more than 1 billion tons of coal each year, and more than 90 percent is used to generate electricity at U.S. power plants. Altogether, the nation's 1,400 coal-fired units consume more than 900 million tons of coal each year, according to the Energy Information Administration, the statistical arm of the U.S. Department of Energy.
For power plants handling millions of tons of coal a year, minimizing coal dust is a high priority. A wide range of techniques are used to manage, control and prevent coal dust in and around coal-fired power plants.
Controlling coal dust is vital to worker safety because of the risk of coal dust explosions. In addition to creating safety and environmental hazards, coal dust increases the cost of maintaining material handling equipment.
Many coal-fired plants are turning to high-tech dust suppression systems to control fine airborne coal particles known as fugitive coal dust. From high-powered fans that emit a fine mist of water over large areas to programs that use a combination of anti-oxidants, binders and foaming agents, the technologies vary in scale and cost.
A gust of wind can create swirling black clouds of coal dust as coal shipments are loaded and unloaded. These "blow-outs" may not exceed air-quality standards, but they do create a nuisance for neighboring businesses and homeowners. The suppliers and operators of coal handling equipment are under pressure to provide technologies and develop best practices to reduce the nuisance of fugitive coal dust.
Coal sealants offer coal-fired plants a way to protect large stockpiles of coal against moisture, oxidation and other forms of deterioration. Left unsealed, coal piles will suffer a loss of Btu value and burn less efficiently. What's more, it will result in an actual loss of coal.
GE TECHNOLOGY FOR COAL DUST CONTROL
|For power plants handling millions of tons of coal a year, minimizing coal dust is a high priority. A wide range of techniques are used to manage, control and prevent coal dust in and around coal-fired power plants.|
General Electric has developed a new line of products designed to mitigate fuel degradation brought about by oxidation and prevent coal dust emissions. At POWER-GEN International 2012, the company unveiled a portfolio of products known as PowerTreat.
GE's PowerTreat technologies allow power plants to control fugitive coal dust without adding excessive amounts of water. In addition, PowerTreat products can help reduce dusting from unloading of coal, by barge or railcar, by up to 90 percent, the company said. PowerTreat also offers effective dust suppression with low moisture addition to the coal, which reduces calorific value penalties and decreases coal flow problems that result from wet coal conditions.
"As coal plants face challenges to meet or exceed environmental considerations, GE's PowerTreat program gives utilities more fuel consumption flexibility and the ability to burn challenging coal. This new line of products improves the quality of coal, while reducing dust and minimizing hazardous conditions such as spontaneous combustion and hot spots," said John Schumann, general manager of Chemical and Monitoring Solutions—Water and Process Technologies for GE Power & Water.
PowerTreat products, which are a part of GE's CoalPlus portfolio, include:
- Foaming agents used to provide high expansion ratio foam for suppressing dust at transfer points while minimizing moisture addition to the coal.
- Anti-oxidants and dust control binders applied to coal that is directed to short term storage piles to inhibit oxidation of coal while controlling dust through agglomeration of fines.
- Dust control binders applied to coal sent to short term or long-term storage.
GE's CoalPlus technology retards the oxidation and weathering of low rank coals, which reduces hot spots, smokers and spontaneous combustion at generating stations. In addition, less weathering reduces Btu losses during outside storage at coal yards and terminals.
"The CoalPlus portfolio of dust control binders and antioxidants enhances coal quality, reduces dust emissions and minimizes spontaneous combustion, addressing operator safety and environmental compliance, two of the main challenges faced by mines and utilities," said Homero Endara, chemical and monitoring solutions (CMS) senior global product manager—water and process technologies for GE Power & Water.
WATERLESS DUST CONTROL
Elgin provides coal-fired power plants a waterless dust control system designed to collect fine dust particles without the use of water. Elgin supplies two types of waterless sweepers - the Waterless Eagle and the Waterless Pelican.
The Pelican is a three-wheel sweeper. The patented dry dust control feature includes a dust skirting system, dust separator in the hopper, and a dust control fan with a maintenance-free filter, working together to control fugitive dust without the use of spray water. A powerful vacuum fan on the sweeper creates an air stream through the debris hopper, conveyor, and skirted areas. The inward rushing air carries the airborne dust into the debris hopper where it's allowed to settle out with the rest of the swept debris. A majority of the fugitive dust falls into the hopper with only a small amount of dust getting to the filter.
The Eagle is equipped with a patented system to pick up PM 10 and PM 2.5 particles. Dry sweeping provides a number of environmental benefits, including a reduction in your water footprint and less silt, a byproduct of water-based dust control sweepers.
REDUCING AIRBORNE DUST AT UNLOADING
Other coal dust control technologies mitigate dust the same way firefighters put out a fire. They use a powerful water spray to smother clouds of dust erupting from a pile of coal as it is unloaded in the coal yard.
|The DustBoss DB-60 is an oscillating, 25 horse-power fan that can cover 21,000 square feet with a blanket of fine mist. Photo courtesy of Dust Control Technology.|
The DustBoss DB-60 is an oscillating, 25 horse-power fan that can cover 21,000 square feet with a blanket of fine mist - atomized water droplets designed specifically for capturing and containing coal dust.
The DB-60 is developed by Illinois-based Dust Control Technology. "We atomize the water to 50-200 microns, which gives us the maximum attraction and avoids a slipstream effect," said DCT President Edwin Peterson. The DB-60 features 30 brass nozzles designed specifically to atomize droplets to the optimum size for dust capture.
The dust suppression system is used at a coal-fired plant in Oahu, Hawaii. The owner, AES Hawaii, was using sprinklers and hoses to control the dust and was looking for a more efficient system. The company rented a DB-60 unit and consequently purchased the machine from DCT, according to DCT's website.
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