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Title: Coal

Pictures collected from
ault.htm These pictures are taken in Wyoming.
  • Coal is a combustible mineral formed from the
    remains of trees, ferns and other plants that
    existed and died during the time of the dinosaurs
  • Coal generates more than half the electricity
    used in the United States
  • Coal is far more plentiful than domestic oil or
    natural gas, accounting for some 95 percent of
    the nation's fossil energy reserves
  • About 23 billion tonnes of minerals, including
    coal, are produced each year
  • The United States has nearly 275 billion tons of
    recoverable coal. That's more than 250 years of
    supply at today's usage rates
  • The mining industry is now recognized as one of
    the safest, with a lower rate of nonfatal
    injuries and illnesses per 100 employees than the
    agriculture, construction or retail trades.
    Mining accounted for 2.1 percent of U.S. fatal
    injuries in 2001
  • Worldwide, coal accounts for nearly 25 percent of
    total energy consumption

Pictures collected from http//
  • Coal is by far the cheapest source of power fuel
    per million Btu, averaging less than half the
    price of petroleum and natural gas
  • Nine of every 10 tons of coal used in the United
    States are for electricity generation
  • Of all fuel and non-fuel commodities mined, the
    quantity of coal currently produced ranks third
    behind crushed stone, sand gravel
  • The largest coal producing state is Wyoming, with
    369 million tons of production in 2001. In the
    past five years, the U.S. has produced more than
    one billion tons of coal each year
  • Approximately two-thirds of today's coal
    production results from surface rather than
    underground mining
  • While coal use for domestic electricity has more
    than tripled since 1970, government statistics
    show sulfur dioxide emissions have decreased more
    than 35 percent below 1970 levels
  • Productivity rates have reached an astonishing
    average of more than 6 tons per miner per hour,
    or 48 tons in single 8-hour day

Four Types of Coal
Anthracite The hard coal," formed from
bituminous coal when great pressures developed in
folded rock strata during the creation of
mountain ranges has the highest energy content
of all coals and is used for space heating and
generating electricity. Anthracite averages 25
million Btu per ton. Bituminous The "soft coal
formed when greater pressure was applied to
subbituminous coal most commonly used for
electric power generation in the U.S. has a
higher heating value than either lignite or
subbituminous, but less than that of anthracite.
Bituminous coal averages 24 million Btu per
ton. Subbituminous Formed from lignite when it
came under higher pressure a combustible mineral
formed from the remains of trees, ferns and other
plants that existed and died during the time of
the dinosaurs. A dull black coal with a higher
heating value than lignite that is used primarily
for generating electricity and for space heating.
Subbituminous coal averages 18 million Btu per
ton. Lignite Increased pressures and heat from
overlying strata caused buried peat to dry and
harden into lignite, a brownish-black coal with
generally high moisture and ash content and lower
heating value. However, it is an important form
of energy for generating electricity,
particularly in the American Southwest. Lignite
averages 14 million Btu per ton
How coal is obtained
ROOM AND PILLAR METHOD More than two-thirds of
the coal produced underground is extracted by
continuous mining machines in the room-and-pillar
method.  The continuous mining machine contains
tungsten bits on a revolving cylinder. The
continuous miner breaks the coal from the face
and then conveys it to a waiting shuttle car
which transports it to the conveyor belt to be
moved to the surface.  No blasting is needed. 
After advancing a specified distance, the
continuous miner is backed out and roof bolts are
put in place.  The process is repeated until the
coal seam is mined.
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How coal is obtained
LONG WALL LINING Another method, called longwall
mining, accounts for about 20 percent of
production.   This method involves pulling a
cutting machine across a 400 to 600 foot long
face (longwall) of the coal seam.  This machine
has a revolving cylinder with tungsten bits that
shear off the coal.  The coal falls into a
conveyor system which carries it out of the
mine.  The roof is supported by large steel
supports, attached to the longwall machine.  As
the machine moves forward, the roof supports are
advanced.  The roof behind the supports is
allowed to fall.  Nearly 80 percent of the coal
can be removed using this method.  The remaining
11 percent of underground production is produced
by conventional mining which uses explosives to
break up the coal for removal.
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How coal is obtained
SURFACE MINING Most surface mines follow the same
basic steps to produce coal.  First, bulldozers
clear and level the mining area.  The topsoil is
removed and stored for later use in the
reclamation process.  Many small holes are
drilled through the overburden (dirt and rock
above the coal seam) to the coal seam.  Each is
loaded with explosives which are discharged,
shattering the rock in the overburden.  Giant
power shovels or draglines clear away the
overburden until the coal is exposed.  Smaller
shovels then scoop up the coal and load it onto
trucks, which carry the coal to the preparation
plant. Once the coal is removed, the land is
returned to the desired contour and the topsoil
is replaced.  Native vegetation and/or trees are
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Crushing Coal
Ore goes in
Crushed ore comes out
JAW CRUSHER It is one of the main types of
primary crushers in a mine or ore processing
plant. Rocks or ore is crushed by the V shaped
jaw until it is small enough to exit through the
gap at the bottom.
Both images of jaw crusher were found at
This is another major type of crushers in a mine
or ore processing plant. The crushing action is
caused by the closing of the gap between the
mantle line (movable) mounted on the central
vertical spindle and the concave liners (fixed)
mounted on the main frame of the crusher. The gap
is opened and closed by an eccentric on the
bottom of the spindle that causes the central
vertical spindle to gyrate. The vertical spindle
is free to rotate around its own axis.
Both images of jaw crusher were found at
A Ball Mill grinds material by rotating a
cylinder with steel grinding balls, causing the
balls to fall back into the cylinder and onto the
material to be grounded. A rod mill is very
similar, except it uses a long rod to grind the
Images of ball and rod mill were found at
Images of hammer mill were found at
A hammer mill crushes material that is friable,
by impacting it against a rotating hammer
(typically traveling between 750 RPM and 1800
RPM). Then the material is forced against a
rugged solid plate called a "breaker plate" which
further degrades the particle size. Finally, the
material is forced over a discharge grate by the
hammers, where crushed finer particles drop
through the discharge grate and larger particles
travel around for another crushing cycle, until
they fall through the discharge grid.
The particles are drawn into the gap between the
rolls by their rotating motion and a friction
angle formed between the rolls and the particle,
called the nip angle. The two rolls force the
particle between their rotating surface into the
ever smaller gap area, and it fractures from the
compressive forces presented by the rotating
Images of roll crusher were found at
Coal Preparation Plants
At this prep plant, all feed coal (ROM) is
crushed to -2" before entering the plant
circuits. The 2" x 10 mesh coal is screened and
goes to the primary dense medium cyclone circuit.
The 2" x 10 mesh coking coal is recovered from
the refuse here. The middlings (-10 mesh x 60
mesh) are processed in the Secondary Dense Medium
Cyclone Circuit to recover the coal here, this
produces a higher ash coal and is used as steam
coal. The coking coal product conveyor has an
intermediate screen that enables material to be
diverted in varying proportions to steam coal if
necessary to enhance the coking properties.The
-10 mesh coal is deslimed at 100 mesh and then
sized at 10 mesh x 100 mesh is processed in the
spiral circuit to produce coking coal. The -100
mesh slimes and -60 mesh coal is then processed
in the flotation circuit to produce coking
coal.The cleaned coal is dried in centrifuges
and a belt filter press. Coarse rejects are
crushed and then recombined with the fine
tailings for disposal to the refuse fill. All ROM
coal production is beneficiated in the coal
preparation plant. Approximately 2,000,000 tonnes
of cleaned coal is produced annually, with the
plant processing about 3,000,000 tons of raw coal
A Coal preparation plant, nestled among the
Another photo of a coal prep plant. 
Coal Power Plants
How a coal-fired power plant worksElectricity is
produced at a coal-fired fossil plant by the
process of heating water in a boiler to produce
steam. The steam, under tremendous pressure,
flows into a turbine, which spins a generator to
produce electricity.
  • Conversion hydrocarbon feedstock (e.g. coal,
    biomass, petroleum, waste) into gaseous
    components by applying heat under pressure in the
    presence of steam.
  • The heat and pressure in the chemically break
    apart the feedstock and set into motion chemical
    reactions that produce syngas (primarily
    hydrogen, carbon monoxide and other gaseous
  • Syngas can be burned as a fuel in a combustion
    turbine to produce electricity.

Other Uses of Syngas
  • As chemical "building blocks" to produce a broad
    range of liquid or gaseous fuels and chemicals
    (using processes well established in today's
    chemical industry)
  • As a fuel producer for highly efficient fuel
    cells (which run off the hydrogen made in a
    gasifier) or perhaps in the future, fuel
    cell-turbine hybrid systems
  • As a source of hydrogen that can be separated
    from the gas stream and used as a fuel (for
    example, in President Bush's hydrogen-powered
    Freedom Car initiative) or as a feedstock for
    refineries (which use the hydrogen to upgrade
    petroleum products).

Integrated Gasification Combined Cycle(IGCC)
  • Combination of steam turbines and combustion
    turbines to generate electricity.
  • Can currently operate at 45 efficiency and in
    the future up to 60. (Conventional power plants
    employing only the steam turbines is capable of
    33-38 efficiencies)
  • Can reduce emission of greenhouse gases
  • (A 60 efficient gasification power plant can
    cut emissions by 40)

ication/howgasificationworks.shtml (10/20/03)
Combustion Turbine
Fluidized Bed Combustion
  • Fluidized beds suspend solid fuels on
    upward-blowing jets of air during the combustion
    process. The result is a turbulent mixing of gas
    and solids. The tumbling action, much like a
    bubbling fluid, provides more effective chemical
    reactions and heat transfer.
  • The popularity of fluidized bed combustion is due
    largely to the technology's fuel flexibility -
    almost any combustible material, from coal to
    municipal waste, can be burned - and the
    capability of meeting sulfur dioxide and nitrogen
    oxide emission standards without the need for
    expensive add-on controls.

Hybrid Systems
  • Combination of coal combustion and coal
  • Less expensive power plants because only a
    partial gasifier is needed instead of a full
  • Because of the lower capital costs and the
    capability to use relatively low cost fuels, a
    future "hybrid" power plant might be able to
    produce electricity at costs 25 percent or more
    lower than today's conventional pulverized
    coal-fired power plants.

The End