Coal is a fossil fuel - a
sedimentary organic rock that contains more than 50 percent carbonaceous
material by weight and is composed largely of carbon, hydrogen, oxygen,
nitrogen, and sulfur, with small amounts of other materials ranging from
aluminum to zirconium. Its beginning was in the form of ancient plants that
grew in swamps millions of years ago. Geological processes working over
vast spans of time compressed and altered the plant remains, increasing
the percentage of carbon present and thereby producing various ranks of
coal.
Coal Ranking
The four recognized
ranks of coal in the U.S. classification scheme are: anthracite, bituminous
coal, sub-bituminous coal, and lignite. In the United States coal
rank is classified according to its heating value, its fixed carbon and
volatile matter content and, to some extent, its caking characteristics
during combustion.
Anthracite: Used primarily for residential and commercial space heating,
anthracite is the highest rank of coal. Its hard, brittle, lustrous
black texture contains a high percentage of fixed carbon and low
percentage of volatile matter. It is often called "hard coal."
Freshly-mined anthracite usually contains less than 15 percent moisture
content. Its typical heat content is 15 million Btu per short ton or
less.
Bituminous:Dense coal of black or dark brown color and usually has
well-defined bands of contrasting bright and dull material. It is used
primarily to generate steam electric power. Substantial quantities are
used for power and heat applications in manufacturing as well as to make
coke. In active U.S. mining regions, bituminous coal is the most
abundant coal. It has a a moisture content of less than 20 percent and a
heat content range between 21 to 30 million Btu per ton in a moist,
mineral-matter-free basis. Of the four ranks, bituminous coal accounts
for over half (51 percent) of the demonstrated reserve base. Bituminous
coal is concentrated primarily east of the Mississippi River, with the
greatest amounts in Illinois, Kentucky, and West Virginia.
Sub-bituminous: This coal can be dull, dark brown to black in color and soft and
crumbly as one quality, to bright, jet black, hard and strong. Used
primarily as fuel for steam-electric power generation, subbituminous
coal has properties ranging from the properties of lignite or bituminous
coal. The heat content of sub-bituminous coal consumed in the U.S.
ranges from 17 to 18 million Btu per ton on a moist, mineral-matter-free
basis. All sub-bituminous coal (38 percent of the demonstrated reserve
base) is west of the Mississippi, with most of it in Montana and
Wyoming.
Lignite: This coal's brownish-black color has a high moisture content and is the
lowest rank coal. It is often called "brown coal" and is used almost
entirely as fuel for steam-electric power generation. It accounts for
slightly less than 10 percent of the demonstrated reserve base and is
found mostly in Montana, Texas, and North Dakota.
Coal Deposits
The United States
contains vast deposits of coal more extensive than those of natural gas
and petroleum, the other major fossil fuels. If total estimated recoverable
reserves of the major fossil fuels are compared on the basis of heat content,
about three percent of reserves are crude oil, about four percent are
natural gas, and over 90 percent are coal.
Total U.S. coal resources
in the ground are estimated to be four trillion tons, of which 1.7 trillion
tons are identified resources. Identified resources include the demonstrated
reserve base, which comprises coal resources that have been mapped within
specified levels of reliability and accuracy. They occur in coal beds
meeting minimum criteria of thickness and depth from the surface generally
required for economic mining under current technologies. The U.S. demonstrated
reserve base contains an estimated 470 billion short tons. Because of
property rights, land use conflicts, and physical and environmental restrictions,
some coal in the demonstrated reserve base may not be available and accessible
for mining.
The actual proportion
of mineable coal resources that can be recovered from undisturbed deposits
varies from less than 40 percent in some underground mines to more than
90 percent at some surface mines. In some underground mines, much of the
coal may be left untouched as pillars needed to prevent surface collapse.
Geologic features, such as folding, faulting, and interlayered rock strata,
can mean a reduction in the amount of coal that can be recovered at both
underground and surface mines.
New Uses for Coal
Continuing research
is underway to develop and increase the beneficial uses and products of
coal. Efforts to develop efficient conversion of coal-derived synthesis
gas to clean-burning alcohol fuels and fuel extenders are underway at
the National
Research Center for Coal and Energy (NRCCE) at West Virginia
University.
The "energy
park" study to produce a magnitude of fuels and chemical feed stocks
in order to minimize production costs is another focus of the Center.
Producing coal-derived fuels with the enormous abundance of domestic coal
may be helpful in reducing our nation's dependence on foreign petroleum.
Clean Coal Technology
In 1985, when the
U.S. and Canada saw that their rivers, lakes, forests, and buildings were
being damaged by "acid rain," both countries agreed to a partnership
program for their governments, several U.S. states, and private companies
to develop new, cleaner coal-burning technologies. This "Clean Coal
Technology Program" develops methods to clean coal, to clean the
sulfur from coal's combustion gases (called "scrubbers"), to
find better ways to remove nitrogen oxides ("NOx") from the
flue gases of coal burners, as well as to develop other coal-burning technologies
such as coal gasification.
Additional Information
The U.S. Department
of Energy: Coal
The U.S. Energy Information
Administration: Coal overview
The Maryland Department of the Environment: Coal Mining in Maryland
