Coal combustion products (CCP) are what remain after the direct combustion of coal in power plants to generate electricity. There are different types of CCP:
- Fly ash is a very fine powder-like particle, ranging in color from tan to black. It is collected by emission controls, such as electrostatic precipitators (ESP) and baghouses, which prevent it from being released through the stacks of the plant.
- Bottom ash is a brown sand-like material collected in the bottom of the boilers.
- Boiler slag is black, shiny and angular. It is coarser than bottom ash and also collected in the bottom of boilers.
CCPs are comprised of melted sand and lime with smaller amounts of oxides containing aluminum, iron, magnesium, sulfur and trace materials. These same ingredients are also found in mud, silt, and/or soil.
How is coal ash reused?
Each of the types of coal ash can be reused in different ways.
- Boiler slag can be used for sandblasting or as the grit on roofing shingles.
- Bottom ash can be a gravel substitute and may be used as fill or an ice traction control agent.
- Fly ash can be used as a substitute for cement in concrete.
In 2011, Alliant Energy utility companies were able to beneficially use over 400,000 tons of coal combustion products or about 60%, thereby diverting it from being placed in a landfill as a waste material. The utilization rate varies from year to year due to variation in local construction activity and changes in approved uses for CCP.
When we built our corporate headquarters building in Madison, Wisconsin, the concrete used included 244 tons of fly ash. The fly ash is incorporated in the building's footings, walls, columns and the parking garage.
Our headquarters isn't the only prominent building that includes coal ash. Others include:
- The Mall of America in Minneapolis;
- The Ronald Reagan Government Office Building, home to the EPA in Washington;
- Freedom Tower, the complex being built on the former site of the World Trade Center in New York;
- The University of Wisconsin's Kohl Center in Madison, and
- The Monona Terrace Community & Convention Center in Madison.
Storing coal ash
Alliant Energy inspects its own coal ash ponds annually. The EPA has been assessing the structural integrity of coal ash ponds across the country as part of its response to the December 2008 coal ash spill from a Tennessee Valley Authority facility in Kingston, Tennessee. Over the last two years, in addition to our own inspections, the EPA has inspected all but two of our facilities as well. We expect the EPA will inspect those facilities’ ponds too. The inspections did identify some minor issues (for example, vegetation management and animal burrows) which are being corrected, and our technical reports demonstrate that the ponds meet or exceed the minimum factors of safety for structural stability.
In addition to the EPA inspections, Alliant Energy continues to be proactive in our efforts surrounding the integrity of the coal ash ponds at our facilities. Those efforts include stability testing, annual 3rd party inspections and the development of both an overall Generation Fleet Operations and Maintenance plan as well as facility specific plans regarding the policies and procedures for long term operation, maintenance, monitoring and inspections of our coal ash ponds.