COAL
What is coal?
Coal is a fossil fuel created from the remains of plants
that lived and died about 100 to 400 million years ago
when parts of the earth were covered with huge swampy
forests. Coal is classified as a nonrenewable energy
source because it takes millions of years to form.
The energy we get from coal today comes from the energy
that plants absorbed from the sun millions of years ago.
All living plants store energy from the sun through a
process known as photosynthesis. When plants die, this
energy is usually released as the plants decay. Under
conditions favorable to coal formation, however, the
decay process is interrupted, preventing the release of
the stored solar energy. The energy is locked into the
coal. Millions of years ago, dead plant matter fell into
the swampy water and over the years, a thick layer of
dead plants lay decaying at the bottom of the swamps.
Over time, the surface and climate of the earth changed,
and more water and dirt washed in, halting the decay
process. The weight of the top layers of water and dirt
packed down the lower layers of plant matter. Under heat
and pressure, this plant matter underwent chemical and
physical changes, pushing out the oxygen and leaving rich
hydrocarbon deposits. What once had been plants gradually
turned into coal. Seams of coal--ranging in thickness
from a fraction of an inch to hundreds of feet--may
represent hundreds or thousands of years of plant growth.
One seam, the seven foot thick Pittsburgh seam, may
represent 2,000 years of rapid plant growth. One acre of
this seam contains about 14,000 tons of coal.
Coal Mining
There are two ways to remove coal from the ground:
surface mining and underground mining. Surface mining is
used when a coal seam is relatively close to the surface,
usually within 200 feet. The first step in surface mining
is to remove and store the soil and rock covering the
coal, called the overburden. Workers use a variety of
equipment--draglines, power shovels, bulldozers, and
front-end loaders--to expose the coal seam for mining.
After surface mining, workers replace the overburden,
grade it, cover it with topsoil, and fertilize and seed
the area. These steps help restore the biological balance
of the area and prevent erosion. Although only about 32
percent of the nation’s coal can be extracted by
surface mining, almost two-thirds of all U.S. coal is
mined using this method today. Why? Because surface
mining is typically much cheaper than underground mining.
With new technologies, productivity has more than tripled
since 1973. Underground mining is used when the coal seam
is buried several hundred feet below the surface. In
underground mining, workers and machinery go down a
vertical shaft or a slanted tunnel called a slope to
remove the coal. Mine shafts may sink as much as 1,000
feet deep. One underground mining method is called
room-and-pillar mining. With this method, much of the
coal must be left behind to support the mine’s roofs
and walls. Sometimes as much as half the coal is left
behind in large column formations to keep the mine from
collapsing.
A more efficient and safer underground mining method,
called longwall mining, uses a specially shielded machine
which allows a minesd-out area to collapse in a
controlled manner. This method is called longwall mining
because huge blocks of coal up to several hundred feet
wide can be removed.
Coal Reserves
When scientists estimate how much coal, petroleum,
natural gas, or other energy sources there are in the
United States, they use the term reserves. Reserves are
coal deposits that can be mined using today’s mining
methods and technology. Experts estimate that the United
States has about 274 billion tons of recoverable coal
reserves. If we continue to use coal at the same rate as
we do today, we will have enough coal to last almost 300
years. This vast amount of coal makes the United States
the world leader in known coal reserves. Where is all
this coal located? Coal deposits can be found in 38
states. Montana has the most coal--about 75 billion
minable tons. Other top coal states in order of known
reserves are: Illinois, Wyoming, Kentucky, West Virginia,
Pennsylvania, Ohio, Colorado, Texas, and New Mexico. Some
coal produced in the United States is exported to other
countries. In 1998, foreign countries bought ten percent
of all the coal produced in the U.S. The five biggest
foreign markets for U.S. coal are Canada, Japan, United
Kingdom, Italy, and Brazil.
How Coal is Used
What do we use coal for? Electricity is the main use. In
1998, 90 percent of all the coal used in the United
States was for electricity production. Coal generated
more than half (51.7%) of the electricity in the U.S.
(Other energy sources used to generate
electricity include nuclear power, hydropower, and
natural gas.). Another major use of coal is in iron and
steelmaking. The iron industry uses coke ovens to melt
iron ore. Coke, an almost pure carbon residue of coal, is
used as a fuel in smelting metals. The United States has
the finest coking coals in the world. These coals are
shipped around the world for use in coke ovens. Coal is
also used by other industries. The paper, brick,
limestone, and cement industries all use coal to make
products. Contrary to what many people think, coal is no
longer a major energy source for heating American homes
or other buildings. Less than one percent of the coal
produced in the U.S. today is used for heating. Coal
furnaces, which were popular years ago, have largely been
replaced by oil or gas furnaces, or by electric hear
pumps.
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This is how coal looks
immediately following its extraction from beneath earth's
surface.
Coal is extremely heavy. Miners must use these gigantic
cranes to lift the tons of coal out of the ground that
they mine each day.
Coal is burnt in order to
generate power. Pictured here is a very old coal power
plant located on the Savannah River. Unfortunately,
burning the coal gives off a lot of smoke that is harmful
to the ozone and our breathing. |
