Energy Resources and Consumption - Environmental Science - page 118

To form coal, plant matter must first become peat. Peat is a low-energy fuel that is still used today in some
parts of the world, generally when coal is unavailable. Peat varies from compressed matter to semihard sub-
stances that still look vegetative. It is cut from open pits, usually still wet, and must be dried to be used. The
less compressed the peat, the higher the water content.
After millions of years under high pressure and temperatures, the peat turns into lignite, often called brown
coal. This coal is drier and has a higher energy content than peat. Brown coal can still contain up to 70 percent
moisture. Of the three types of coal, it has the lowest heat content. Lignite is used in power generators in loca-
tions where it is found in large quantities.
A denser, drier fuel with a higher energy content than lignite is formed with further compression and time. This
black coal, called bituminous coal, is valuable as a fuel source for generating electricity and to manufacture
coke for use in the steel industry. Rarer than lignite, bituminous coal is soft with a higher sulfur content and
represents approximately 50 percent of the U.S. coal reserves.
After more compression, time, and exposure to extreme heat, black coal can be transformed into anthracite.
Anthracite is a glossy, almost metallic-looking substance. With the highest energy content of the three types of
coal, it has a low sulfur content and makes up approximately 2 percent of the U.S. reserves. Anthracite is the
rarest of the three types of coal.
Graphite is the final stage of the carbon compression and heating process but is not considered a fossil fuel
since it is difficult to ignite. Graphite is commonly used as the "lead" in pencils and as a dry lubricant.
Extraction and Purification of Coal
Two primary methods of mining coal are underground mining and surface mining. Most coal seams are too
deep for surface mining, so underground mines must be dug. Approximately 60 percent of the world's coal pro-
duction is from underground mining. Seams of coal, are found in long strands. When the seams of coal are near
the Earth's surface, it may be more economical to extract the coal through open cuts in the surface of the
Earth's crust. This method recovers a greater proportion of the coal deposit compared to underground mining.
Globally, about 40 percent of coal production involves surface mining, but in the United States and Australia
the technique is more prevalent, with 67 percent in the United States and around 80 percent in Australia. Mined
coal may go through a variety of processes to remove sulfur and contaminants.
Oil
Oil Shale
Oil shale is a sedimentary rock that is rich in kerogen, an organic compound from which liquid hydrocarbons
are extracted when heated. For use as an energy source, kerogen requires more processing than crude oil. It is,
thus, more costly than oil, and the processing increases the negative environmental impacts, including damage
to the surrounding environment due to surface mining and the disposal of waste material. The net-energy yield
is considered moderate because energy is needed to mine the deposits, to heat the mined material, and to re-
store the mined area. There are major deposits of oil shale around the world, with several in the United States.
These large deposits are found in Colorado, Utah, and Wyoming, but the world's largest reserves are in Aus-
tralia, Estonia, Germany, Israel, and Jordan. China and Estonia have well-established oil-shale industries, while
Brazil, Germany, Israel, and Russia have smaller oil-shale industries.
Tar Sands