Coal fly ash is one type of product form of Coal Combustion Products (CCPs) produced by the burning of coal in a boiler. Other product forms include bottom ash, boiler slag, and flue gas desulfurization materials. CCPs have a myriad of uses that allow the substitution of CCPs for natural or manufactured materials in many processes and applications.
In other words, these products, including the coal fly ash, are waste products from coal-fired power plants. Fly ash consists of inorganic, incombustible matter present in the coal . It is often landfilled. In places where air quality isn't regulated, it can just get blown out smokestakes into the air, fly around with its heavy metal content to become particulate pollution (smog) and settle on the ground to contaminate soil and groundwater. But, fly ash is a material that can easily be recycled into many other materials, including:
Portland cement and grout;
Embankments and structural fill;
Waste stabilization and solidifaction;
Raw feed for cement clinkers;
Soft soil stabilization;
Mineral filler in asphaltic concrete;
And: cellular concrete, roofing tiles, paints, metal castings, and filler in wood and plastic products.
According to the ACAA, increased energy use and a corresponding increase in the use of coal to generate electricity have resulted in the production of increased quantities of fly ash and other CCPs. Coal reserves are by far the largest volume of fossil energy reserves. Thus, coal is expected to be a major source of energy far into the next century, and CCPs will continue to be produced in substantial volumes.
CCPs are the fourth largest volume mineral resource produced in the United States. Their use provides many environmental and financial benefits. It reduces the volume of natural materials needed to be mined or otherwise obtained for construction purposes as indicated by the list above. Utilization helps reduce greenhouse gas emissions and reduces the need for landfill. Recycling the CCPs further reduces the cost of electricity.
According to the ACAA, in 2003, over 121 million tons of CCPs were generated. Approximate quantities produced were:
fly ash 70 million tons
bottom ash 18.1 million tons
boiler slag 1.8 million tons
FGD material and other by-products 31.6 million tons
Approximately 46.3 million tons of these CCPs were recycled into useful applications through utilization programs. CCP use has increased as utilities, marketers, and others have worked to identify and promote opportunities for reuse. Currently, 38% of CCPs are recycled through utilization programs.