Managing coal combustion residues

Information from: Managing Coal Combustion Residues in Mines

Committee on Mine Placement of Coal Combustion Wastes,

National Research Council, 2006

Coal fired utilities are the largest electricity provider in the United StatesBurning 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

Boiler furnaceBoiler

furnaceAirAir

WaterWater

CoalCoal LimestoneLimestone

Bottom ash

Boiler slag

Gases and fly ash

Gases (mainly CO2, H2O, SO2, NOx)

Particulate matter control

device

Fly ash

SO2 scrubber

Lime injection (CaO or CaCO3)Lime injection (CaO or CaCO3)

Flue gas desulfurization (FGD) material

Coal Combustion Residues (CCRs)

Factors Influencing the Characteristics of Coal Combustion Residues

1. Chemical characteristics of the source coal2. Chemical characteristics of any co-fired

materials 3. Combustion technology, 4. Pollution control technology used by the

CCR producing facility, and 5. Residue handling technology used by the

CCR producing facility.

1. Chemical characteristics of the source coalWhen 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.”

Arsenic Selenium Lead

Boron Cadmium Mercury

Viable options for CCR disposal• Surface impoundments These are natural depressions, excavated ponds, or diked

basins usually containing a mixture of liquids and solids CCRs managed 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, 12/25/08Bluff collapse at Oak Creek Power Plant, WI, 10/31/2011

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

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

CCRs can 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

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.)