Fossil fuels or mineral fuels are
fossil source fuels, that is, hydrocarbons found within the top layer of the
earth’s crust.
It is generally accepted that they
formed from the fossilized remains of dead plants and animals by exposure to
heat and pressure in the Earth's crust over hundreds of millions of years. This
is known as the biogenic theory and was first introduced by Mikhail Lomonosov
in 1757.
Mikhail Lomonosov
Russian writer, chemist, and
astronomer, who made important contributions to both literature and science
Fossil fuels are non-renewable
resources because they take millions of years to form, and reserves are being
depleted much faster than new ones are being formed.
When coal, natural
gas or oil are burned, they release gases into the atmosphere:
Carbon dioxide
(CO2) is a "greenhouse gas," trapping heat in the lowest part of the earth's
atmosphere. This contributes to "global warming" - the average temperature
of the earth slowly increases, affecting ecosystems across the globe.
Sulfur dioxide
(SO2) is a key contributor to acid rain, primarily in the northeast U.S.
Nitrogen oxide
(NOx) contributes to acid rain and smog, as well as health issues such as
lung inflammation, immune system changes and eye irritation.
There are three major forms of
fossil fuels:
coal
Coal is an abundant fossil resource that consists mostly of
carbon. Energy content (Btu/pound) ranges from 5,000 to 15,000
depending on the type of coal. Coal reserves are located all over
the world. Electric utilities consume about 87 percent of the
total coal produced. In the United States, coal is used to
generate more than half of all the electricity produced. It is
also used as a basic energy source in many industries, and as a
heating fuel. The U.S. is one of the top exporters of coal in the
world. Most exported U.S. coal goes to Western Europe, Canada, and
Japan. Coal is recovered from the earth by surface mining or deep
mining. Surface mining, or strip mining, is less expensive and
usually occurs on flat land. Deep mining requires digging shafts
and tunnels to get to the coal seam. Automation of deep mining has
helped to counter its safety and health hazards. Coal can be
gasified to form a synthetic fuel similar to natural gas. It can
also be liquefied to make a synthetic crude oil. To date, it has
not been economical to make synthetic fuels from coal on a large
scale. As processes become more efficient, the use of synthetic
fuels may become more economical.
oil
Oil comes from
crude oil, which is a mix of hydrocarbons with some oxygen,
nitrogen, and sulfur impurities. One barrel of oil (42 U.S.
gallons) can provide about 6 million Btu. Crude oil reserves are
found all over the world, but the Middle East alone has about 63
percent of the known reserves. Of the oil consumed in the United
States, most is used in transportation, and much of the rest goes
to industrial, commercial, and residential uses. Crude oil is used
to produce not only a range of fuels, but also petrochemical
ingredients for plastics, inks, tires, pharmaceuticals, and a host
of other products.
High-tech oil
exploration technology and practices have led to the discovery of
as many new reserves as have already been used. To make the most
of this valuable resource, energy producers are developing more
efficient refining methods, product makers are finding more
efficient ways to use petrochemicals, and manufacturers are
developing more efficient cars. New techniques of locating and
extracting oil from the earth are also making it possible to
recover oil that was once too expensive to produce.
Oil is usually
recovered by drilling wells through the non-porous rock barrier
that traps the oil. In general, about 30 percent of the oil
trapped can be economically recovered by pumping. "Secondary"
recovery can remove another 10 percent, by flooding the well with
high-pressure water or gas. Another 10 percent can sometimes be
recovered with "tertiary" methods that heat the oil to scrub it
out. About half of the oil is left trapped in the rock. Oil
producers are continually seeking economical ways to recover more
of this oil.
The oil refining
process separates crude oil into different hydrocarbons and
removes impurities such as sulfur, nitrogen, and heavy metals. The
first step is fractional distillation, a process that takes
advantage of the fact that different hydrocarbons boil at
different temperatures. In a tall tower called a fractionating
column, crude oil is heated until it boils. Horizontal trays
divide the column at intervals. As the oil boils, it vaporizes.
Each hydrocarbon rises to a tray at a temperature just below its
own boiling point. There, it cools and turns back into a liquid.
The lightest
fractions are liquefied petroleum gases (propane and butane) and
the petrochemicals used to make plastics, fabrics, and a wide
array of consumer products. Next come gasoline, kerosene, and
diesel fuel. Heavier fractions make home heating oil and fuel for
ships and factories. Still heavier fractions are made into
lubricants and waxes. The remains include asphalt.
The refining
process then continues, with heavy fractions converted into
lighter fractions. In most cases, "cracking" processes are used to
transform large (heavy) hydrocarbon molecules and make the
smaller, lighter molecules such as gasoline and jet fuel. Better
refining technologies have made it possible to produce over 21
gallons of gasoline from a 42-gallon barrel of crude oil�a
remarkable advance over the industry�s early days, when a barrel
of oil yielded just 11 gallons of gasoline.
Oil shale was never
buried deeply enough or heated enough to form crude oil. Its
hydrogen content is between that of coal and crude oil.
Concentrations of oil are low, so that, at most, one barrel of oil
can be recovered from 2.4 tons of sand or 1.5 tons of rock. Huge
amounts of oil shale are found all over the world. In fact, the
total global resource is 1,000 times greater than crude oil
reserves. But extracting the energy value of oil shale is not
practical today. Scientists and engineers continue working on ways
to recover oil shale for a reasonable cost.
natural gas
Natural gas is the
gas component of coal and oil formation. It is used in industrial
and commercial heating and cooking, and, increasingly, to fuel
electricity generation. In a compressed form, natural gas can also
be used as a transportation fuel. Natural gas is either found
mixed in oil or is released from coal. Energy in 6,000 cubic feet
of natural gas is equivalent to one barrel of oil. World reserves
of natural gas are greatest in Russian, Iran, Qatar, Saudi Arabia,
United Arab Emirates, and the U.S. The U.S. consumed 19.7 million
cubic feet of natural gas in 1999, nearly all of which came from
domestic production. Five states�Texas, Louisiana, Alaska, New
Mexico, and Oklahoma�hold more than 85 percent of U.S. natural gas
reserves.
Wells for natural
gas are drilled in underground reservoirs of porous rock. When it
is removed from a reservoir, natural gas can either be pumped to
the processing station for removal of liquid hydrocarbons, sulfur,
carbon dioxide, and other components, or stored in large caverns
underground until it is needed. Pipelines are the main method of
transporting natural gas. Natural gas can also be liquefied and
shipped overseas, but this process is complex and expensive.
Electrical
generation by natural gas has been improved by the development of
combined-cycle systems. These systems put together a
natural-gas-fueled combustion turbine with a heat-recovery steam
generator and steam turbine, to produce electricity in two ways
rather than just one. The result: roughly 60 percent of the heat
from the natural gas is harnessed to make electricity, creating a
more energy-efficient system.
All three were formed many
hundreds of millions of years ago before the time of the dinosaurs - hence the
name fossil fuels. The age they were formed is called the Carboniferous Period.
It was part of the Paleozoic Era. "Carboniferous" gets its name from carbon,
the basic element in coal and other fossil fuels. The Carboniferous Period
occurred from about 360 to 286 million years ago. At the time, the land was
covered with swamps filled with huge trees, ferns and other large leafy plants.
The water and seas were filled with algae - the green stuff that forms on a
stagnant pool of water. Algae is actually millions of very small plants.
All fossil fuels, whether solid,
liquid, or gas, are the result of organic material being covered by successive
layers of sediment over the course of millions of years. Some deposits of coal
can be found during the time of the dinosaurs. For example, thin carbon layers
can be found during the late Cretaceous Period (65 million years ago) - the
time of Tyrannosaurus Rex. But the main deposits of fossil fuels are from the
Carboniferous Period. Fossil fuels supply over 80% of the world’s energy
needs.
Coal is derived from the
accumulation of partially decayed land plants. As the sediment solidifies into
rock, the organic material decomposes under the influence of great pressure and
high temperature.
