While electric cooperatives are actively diversifying the portfolio of fuels to meet their members’ energy needs, coal remains a lynchpin in providing reliable power generation. The industry is continually developing new ways to reduce the environmental impact of coal-fired power generation and one of the most important technologies is the reuse of waste by-products from coal-fired generation.
Reusing coal-combustion residuals (CCRs) can reduce greenhouse gas emissions, energy consumption and water use. In addition, residuals that are reused will not go into a landfill.
Manufacturers have figured out how to incorporate CCRs into concrete, roof shingles, wallboard, asphalt and bricks.
The environmental benefits are significant. Each ton of fly ash that replaces cement in the production of concrete reduces greenhouse gases emissions by about a ton of CO2 equivalents. According to a 2010 study by the Electric Power Research Institute, the beneficial reuse of fly ash in concrete production in 2007:
- reduced U.S. greenhouse gas emissions by 10 million tons (9 million metric tonnes) CO2e
- reduced energy consumption by 63 trillion BTUs
- reduced water consumption by 5.9 billion gallons
Army engineers have used the product to repair combat related damage to runways at the airfield in Kandahar. U.S. Army combat engineers in Afghanistan have used “SwiftCrete, an all-purpose concrete and asphalt repair and anchor cement that combines fly ash from Great River Energy’s Coal Creek Power Station in North Dakota with another type of fly ash from Iowa and portland cement, to make quick repairs to damaged runways and concrete structures.
Great River Energy in Minnesota markets a significant amount of the fly ash that it generates at its Coal Creek Station and Stanton Station for beneficial uses. In 2010, more than 400,000 tons of fly ash were sold from Great River Energy power plants. Fly ash has chemical and physical properties that improve the characteristics of concrete, improving its strength and making it more resistant to water infiltration and extreme temperatures. Nearly 12,000 tons of Coal Creek Station fly ash were used in the biggest road project in Minnesota’s state history — the Crosstown construction project just south of downtown Minneapolis.
Concrete using CCRs from cooperative power plants can be found in the I-35 bridge that replaced the collapsed bridge in St. Paul, Minnesota, and in two Mississippi bridges rebuilt after being destroyed by Hurricane Katrina.
The majority of Seminole Electric Cooperative’s CCRs are sold and used to make concrete, concrete block and wallboard. The Florida-based G&T invested over $25 million to modify its generating station in order to produce synthetic gypsum for wall board manufacturing. In 1999, Lafarge North America constructed a wallboard manufacturing facility adjacent to the Florida Seminole generating station. The Lafarge facility cost over $100 million to construct and currently employs more than one hundred people.
The volume of CCRs being recycled and put to beneficial use has increased steadily through time and now constitutes about 45 percent of all CCRs produced, displacing the use of raw materials.
Southern Mississippi Electric Power Association’s reuse of CCRs from its Morrow generation facility illustrates the benefits. Using a new technique, the fly ash is collected from the co-op plant’s boiler exhaust gases by electrostatic precipitators, which use electric charges to attract the very light, very small ash particles. A vacuum system collects the ash and a pressure system transfers the ash to a storage silo.
Positive and negative charges separate the ash into two streams, one high in carbon content and one low in carbon. The high‐carbon stream is returned to the plant to be burned with the coal, saving approximately $80,000‐$100,000 monthly in fuel that would otherwise be lost—equivalent to a trainload of coal each year. The low‐carbon fly ash stream goes to a storage silo, where the material is kept until being shipped via tanker trucks to customers.
In 2007 and 2008, more than 85 percent of the fly ash produced by the plant was sold. Customers include numerous Mississippi Department of Transportation contractors who are rebuilding roads and bridges, including those destroyed by Hurricane Katrina.
Although the funds generated from the sales are a new source of revenue, and can help keep costs down for the cooperative’s member owners, an even greater benefit comes from the savings of not having to handle and landfill the ash. Current costs average about $7 per ton to develop, fill and maintain the landfill. By avoiding landfill costs, reclaiming the unburned carbon and selling 85,000 tons of treated fly ash per year, the ash handling program creates a total annual savings of more than $1 million.
The recycling is also helping to reduce the amount of solid TRI (Toxic Release Inventory) elements—including mercury and compounds of lead, manganese, and antimony—going to the landfill.