Each year, the U.S. electric utility industry generates about 100 million tons of coal combustion byproducts. Just over half of this amount is fly ash (a talcum-like solid in the flue gas from a coal-fired boiler), approximately one-fourth is sludge from wet flue gas scrubbers, another 16 percent is boiler ash (a heavier, coarser solid removed from the bottom of a boiler), and about 7 percent is boiler slag (a hard, glassy material made from boiler ash that has been melted by the heat of the combustor).

Currently only about a third of this coal ash and just over one fourth of the scrubber waste is recycled in commercially beneficial uses. The largest amount is fly ash that is typically used as a Portland cement replacement in concrete and concrete products. The remainder, more than 70 million tons a year, is disposed of in impoundments and landfills.

IF DOE IS SUCCESSFUL If the DOE research program can help increase the use of coal utilization byproducts by 50% by 2010, the annual economic benefits could range from $500 million to $1 billion.

Many experts believe the coal combustion byproducts represent a vastly underused resource. Combustion byproducts can strengthen construction materials and reduce overall product costs. The gypsum-rich byproducts of flue gas scrubbers can provide plants with nutrients and enhance depleted soils in various agricultural applications. Coal combustion byproducts can be used to immobilize hazardous wastes for safer disposal.

Greater use of coal combustion byproducts can also help reduce concerns over greenhouse gases. Using fly ash for cement making, for example, reduces the need for limestone calcination, a process that requires a large amount of heat typically provided by burning fossil fuels. For every ton of fly ash used in concrete, approximately 0.8 tons of carbon dioxide would be prevented from being released into the atmosphere.

Industry has used coal combustion byproducts since the 1950s. For example, the 31-story Columbus, Ohio, headquarters of American Electric Power, one of the nation's largest utilities, is built from materials containing coal combustion byproducts. The runways at the Brownsville/South Padre Island, Texas, International Airport are made from concrete enhanced by coal combustion byproducts. In Galveston Bay, off the Texas coastline, coal combustion byproducts have been used to stabilize reefs and promote oyster breeding.

Today, however, there are new challenges confronting the commercial use of coal combustion byproducts, and the Department of Energy's Office of Fossil Energy has set a goal of increasing the use of coal utilization byproducts from 30 percent to 50 percent by 2010.

Some of the key technical challenges being addressed by the Energy Department are the changing chemical and physical characteristics of coal combustion byproducts as more utilities adopt advanced clean coal technologies.

MORE INFO DOE-EPA Report: Coal Combustion Waste Management at Landfills and Surface Impoundments, 1994-2004 [3.3MB PDF]

For example, as more power plant owners install low-NOx burners, the unburned carbon content is raised. Carbon in fly ash can absorb reagents added to concrete mixtures and affect the concrete's quality. Also to meet new air quality requirements, some utilities are installing ammonia-based selective catalytic and non-catalytic reduction systems that can increase the level of ammonia in fly ash. Capturing other air emissions - in particular, mercury that would be regulated for the first time under President Bush's Clear Skies Initiative - could also change the characteristics of coal combustion byproducts. The Energy Department's objective is to ensure that as the electric power industry continues to adopt cleaner and more advanced coal technologies, the recycling of coal combustion byproducts in beneficial applications can continue and expand.