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Bituminous Coal

Common hard coal with thermal and metallurgical uses


Coal Mountain
Graham Turner/Hulton Archive/Getty Images

Bituminous coal is the most common coal. Bituminous and sub-bituminous coal together represent more than 90 percent of all the coal consumed in the U.S. When burned, bituminous coal produces a high, white flame. Bituminous coal includes two subtypes: thermal and metallurgical.

Thermal coal is sometimes called steaming coal because it is used to fire power plants that produce steam for electricity and industrial uses. Locomotive trains that run on steam may also be fueled with "bit coal" (a nickname for bituminous coal).

Metallurgical coal is sometimes referred to as coking coal, because it is used in the process of creating coke necessary for iron and steel-making. Coke is a porous, hard black rock of concentrated carbon that is created by heating bituminous coal without air to extremely high temperatures. This process of melting the coal in the absence of oxygen to remove impurities is called pyrolysis.

Heating value: Bituminous coal provides approximately 10,500 to 15,000 Btu per pound as mined.

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Characteristics: Bituminous coal contains moisture up to about 17 percent. Its fixed carbon content can range up to about 85 percent, with ash content up to 12 percent by weight. Bituminous coal can be categorized further by the level of volatile matter it contains: high-volatile A, B, and C, medium-volatile, and low-volatile. About 0.5 to 2 percent of the weight of bituminous coal is nitrogen.

Bituminous coal lights on fire easily and can produce excessive smoke and soot (particulate matter) if improperly burned. Its high sulfur content contributes to acid rain.

Bituminous coal commonly contains the mineral pyrite, which can serve as a host for impurities such as arsenic and mercury. Burning of bituminous coal releases trace mineral impurities into the air as pollution. During combustion, about 95 percent of the sulfur content of bituminous coal gets oxidized and released as gaseous sulfur oxides.

Hazardous emissions from bituminous coal combustion include particulate matter (PM), sulfur oxides (SOx), nitrogen oxides (NOx), trace metals such as lead (Pb) and mercury (Hg), vapor-phase hydrocarbons (such as methane, alkanes, alkenes, benzenes, etc.) and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (known popularly as dioxins and furans). When burned, bituminous coal can also release hazardous gases such as hydrogen chloride (HCl), hydrogen fluoride (HF), and polycyclic aromatic hydrocarbons (PAHs).

Incomplete combustion leads to higher levels of PAHs, which are carcinogenic. Burning bituminous coal at higher temperatures reduces its carbon monoxide emissions. Therefore, large combustion units and well-maintained ones generally have lower pollution output. Bituminous coal has slagging and agglomerating characteristics.

Availability: Abundant. More than half of all available coal resources are bituminous.

Location: Illinois, Kentucky, West Virginia, Arkansas (Johnson, Sebastian, Logan, Franklin, Pope, and Scott counties), and locations east of the Mississippi river.

Additional notes: Bituminous coal combustion releases more pollution into the air than sub-bituminous coal combustion, but due to its greater heat content, less of the fuel is required to produce a given output of electricity. Therefore, bituminous and sub-bituminous coals produce approximately the same amount of pollution per kilowatt of electricity generated.

In the early twentieth century, bituminous coal mining was an exceptionally dangerous job, taking an average of 1,700 coal miners lives per year. During that same time frame, approximately 2,500 men each year were left permanently disabled as a result of coal mining accidents.

Tiny particles of waste bituminous coal that are left over after preparation of commercial grade coal are called "coal fines." Fines are light, dusty, and difficult to handle, and traditionally were stored with water in slurry impoundments to keep them from blowing away.

New technologies have been developed to reclaim fines that were formerly considered waste. One approach is to use a centrifuge to separate the coal particles from slurry water. Other approaches have been developed to bind the fines together into briquettes that have low moisture content, making them suitable for fuel use.

Ranking: Bituminous coal ranks 2nd in heat and carbon content compared with other types of coal, according to ASTM D388 - 05 Standard Classification of Coals by Rank.

Learn about other types of coal

#1 Ranked Coal - Anthracite

#2 Ranked Coal - Bituminous

#3 Ranked Coal - Sub-bituminous

#4 Ranked Coal - Lignite, or brown coal

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