■ BURNING PULVERIZED COAL AT LOWER TEMPERATURES: coal is crushed into
a very fine powder and injected into a firebox. Burning pulverized coal
provides about 50% of the world’s electric supply.
■ COAL GASIFICATION: a process that turns coal and other carbon-based fuels
into gas known as “syngas.” Impurities are removed from the syngas
before it is combusted, which results in lower emissions of sulfur dioxide,
particulates, and mercury.
■ CYCLONE SEPARATOR: a method of removing particulates through
rotational (spinning) effects and gravity.
■ ELECTROSTATIC PRECIPITATORS: a filtration device that removes fine
particles, like dust and smoke, from a flowing gas using an electrostatic
charge.
■ FLUIDIZED-BED COMBUSTION: a method of burning coal in which the
amount of air required for combustion far exceeds that found in
conventional burners. This process can be used to reduce the amount of
NOx, SOx, and particulates.
■ SCRUBBERS: systems that inject chemical(s) into a dirty exhaust stream to
“wash out” acidic gases. Scrubbers can also be used to reduce SOx and
particulates from burning coal.
■ SORBENTS: activated charcoal, calcium compounds, or silicates can
convert gaseous pollutants in the smokestacks, such as mercury, into
compounds that can then be collected with baghouse filters, electrostatic
precipitation, or scrubbers.“Clean coal” is a term for technology that mitigates emissions of carbon
dioxide and other greenhouse gases that arise from the burning of coal for
electrical power. Typically the term “clean coal” is used by coal companies in
reference to carbon capture and storage, which pumps and stores CO 2 emissions
underground. Historically, this term has also been used to refer to technologies
for reducing emissions of ash, sulfur, and heavy metals from coal combustion.
This process includes washing the coal to remove minerals and impurities and
capturing the sulfur dioxide and carbon dioxide from the flue gases.