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Ash CharacteristicsThe Buyer's Guide features commercial uses of four specific classes of coal combustion byproducts (known collectively as CCBs). CCBs include fly ash, bottom ash, boiler slag, and flue gas desulfurization (FGD) material. Fly AshFly ash is the fine powder formed from the mineral matter in coal, consisting of the noncombustible matter in coal plus a small amount of carbon that remains from incomplete combustion. It is called "fly" ash because it is transported from the combustion chamber by exhaust gases. Fly ash is generally light tan in color and consists mostly of silt-sized and clay-sized glassy spheres (<0.0625mm). Properties of fly ash vary significantly with coal composition and plant operating conditions.Bottom Ash/Boiler SlagCoal bottom ash and boiler slag are the coarse, granular, incombustible byproducts that are collected from the bottom of furnaces that burn coal for the generation of steam, the production of electric power, or both. Both bottom ash and boiler slag are coarser than fly ash, with grain sizes spanning from fine sand to fine gravel (0.125 mm to 2 mm). The type of byproduct produced depends on the type of furnace used to burn the coal.FGD GypsumFGD gypsum is the byproduct of an air pollution control system that removes sulfur from the flue gas in calcium-based scrubbing systems. It is produced by employing forced oxidation in the scrubber and is composed mostly of calcium sulfate. | |||
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EERC • University of North Dakota • 15 N 23rd St • Grand Forks • North Dakota • USA • 58202-9018 • Phone (701) 777-5000 • Fax (701) 777-5181 |
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