Coal

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Coal
Pictures collected from www.mine-engineers.com/Def
ault.htm These pictures are taken in Wyoming.
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Background

• 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//www.ilo.org/public/
english/dialogue/sector/sectors/mining.htm
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Background

• 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

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http//www.eia.doe.gov/oiaf/aeo/figure_4.html
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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
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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
planted.
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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.
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Both images of jaw crusher were found at
http//66.113.204.26/mining/jaw_crusher.htm
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CONE CRUSHER
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.
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Both images of jaw crusher were found at
http//66.113.204.26/mining/cone_crusher.htm
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BALL MILL and ROD MILL
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
material.
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Images of ball and rod mill were found at
http//66.113.204.26/mining/ballmill.htm
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HAMMER MILL
Images of hammer mill were found at
http//66.113.204.26/mining/hammil.htm
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.
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ROLL CRUSHER
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
rolls.
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Images of roll crusher were found at
http//66.113.204.26/mining/rollcrush.htm
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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
annually.
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http//66.113.204.26/mining/coal/coalprep.htm
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A Coal preparation plant, nestled among the
mountains.
http//66.113.204.26/mining/coal/coalprep.htm
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Another photo of a coal prep plant. 
http//66.113.204.26/mining/coal/coalprep.htm
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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.
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http//www.tva.gov/power/coalart.htm
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Gasification

• 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
  constituents).
• Syngas can be burned as a fuel in a combustion
  turbine to produce electricity.

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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).

http//www.fe.doe.gov/programs/powersystems/gasifi
cation/howgasificationworks.shtml
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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
  significantly.
• (A 60 efficient gasification power plant can
  cut emissions by 40)

http//www.fe.doe.gov/programs/powersystems/gasif
ication/howgasificationworks.shtml (10/20/03)
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http//www.fe.doe.gov/programs/powersystems/gasifi
cation/howgasificationworks.shtml
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Combustion Turbine
http//www.fe.doe.gov/programs/powersystems/turbin
es/turbines_howitworks.shtml
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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.

http//www.fe.doe.gov/programs/powersystems/combus
tion/fluidizedbed_overview.shtml
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Hybrid Systems

• Combination of coal combustion and coal
  gasification.
• Less expensive power plants because only a
  partial gasifier is needed instead of a full
  gasifier.
• 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.

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http//www.fe.doe.gov/programs/powersystems/combus
tion/
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The End