Managing coal combustion residues

1. Managing coal combustion residues Information from: Managing Coal Combustion Residues in Mines Committee on Mine Placement of Coal Combustion Wastes, National Research Council, 2006

3. Coal fired utilities are the largest electricity provider in the United States Burning coal results in the formation of coal combustion residues (CCRs), such as fly ash, bottom ash, boiler slag, etc. “The amount of CCRs produced annually would fill about one million standard rail- road coal cars, which, if hitched together, would create a train about 9,600 miles long (Conrail Cyclopedia, 2005) that would span the United States from New York City, New York, to Los Angeles, California, 3.5 times.” Managing Coal Combustion Residues in Mines http://www.nap.edu/catalog/11592.html

4. Coal Lime injection (CaO or CaCO3) Limestone Gases (mainly CO2, H2O, SO2, NOx) Boiler furnace SO2 scrubber Air Gases and fly ash Particulate matter control device Water Flue gas desulfurization (FGD) material Bottom ash Boiler slag Fly ash Coal Combustion Residues (CCRs)

5. Factors Influencing the Characteristics of Coal Combustion Residues • Chemical characteristics of the source coal • Chemical characteristics of any co-fired materials • Combustion technology, • Pollution control technology used by the CCR producing facility, and • Residue handling technology used by the CCR producing facility.

6. Chemical characteristics of the source coal When coal is burned, the non-volatile trace elements (Lead, Cadmium, Uranium, Thorium etc.) tend to concentrate within the CCR Form and concentration of trace elements depend on coal type (Lignite, bituminous, anthracite) and region The extent of concentration depend on the ash content of the coal “For example, with an ash content of 12.5 percent, nonvolatile metals should be found at eightfold higher concentrations in bulk CCRs than in the source coal.”

7. Soils Anthracite Bituminous Sub-bituminous Lignite FBC Fly Ash FBC Fly Ash Bottom Ash FBC Bed Ash Bottom Slag FGD Arsenic Selenium Lead

8. Soils Anthracite Bituminous Sub-bituminous Lignite FBC Fly Ash FBC Fly Ash Bottom Ash FBC Bed Ash Bottom Slag FGD Boron Cadmium Mercury

9. Viable options for CCR disposal • Surface impoundments Theseare natural depressions, excavated ponds, or dikedbasins usually containing a mixture of liquids and solids CCRsmanaged in surface impoundments typically are sluiced with water from the point of generation to the impoundment. The solid CCRs gradually settle out of this slurry, accumulating at the bottom of the impoundment Solids that accumulate at the bottom of a surface impoundment may be left in place, or later removed for disposal elsewhere, such as a landfill Tennessee Coal Sludge Disaster, 12/25/08 Bluff collapse at Oak Creek Power Plant, WI, 10/31/2011

10. Viable options for CCR disposal • Landfills Landfills are usually natural depressions or excavations that are gradually filled with residue Coal combustion residues managed in landfills may be transported dry from the point of generation, or they may be placed after dredging from a surface impoundment Residues are placed in the active cell and compacted until the predetermined cell area is filled Completed cells are covered with soil or other material, and then the next cell is opened

11. Viable options for CCR disposal • Minefills (CCR can neutralize AMD to some extent, but can leach trace elements) This involves placing the CCRs in surface or underground mines When used in surface mines, the CCRs are incorporated into the mine reclamation plan and generally are deposited in the mine as backfill combined with the overburden CCRscan also be used to form a grout to fill underground mines in order to prevent subsidence Because the transportation of CCRs to the disposal site can be costly, disposal in mines is commonly done when the utility and the mine are located near one another

12. Alternative uses for CCR • Cement and concrete • Road base materials, manufactured aggregates, structural fills, and embankments, other civil engineering applications • Used as synthetic gypsum for making wallboards • Roofing tiles and shingles • Abrasives, traction on snow and ice • Paints, coatings, adhesives • Micronutrients in soils (boron, selenium etc.)