COAL

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COAL
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What is it?
Woody substances buried in an oxygen-deprived
heat and pressureconvert wood to carbon process
may give off water and methane Most coal comes
from the Carboniferous period of geologic
time(180-360 mya)
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Usage
Most of the coal used in the U.S. (90) is used
to generateelectricityAlmost all of the
remainder is used to make heat and coke for
industrial processesVery small amounts (less
than 1) go toward home and building heatWe
use about 1,000 million short tons of coal a
year we haveWe have an estimated 500,000
million short tons of reserves
Source DOE, http//www.eia.doe.gov/cneaf/coal/res
erves/appendixa_taba1.html
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Coal Types
Anthracite - the hardest variety of coal 86-98
carbon When burned, produces very little ash
extremely high heat value of 15,000 BTUs per
poundAlmost complete conversion means that it
had to be buried verydeep at some point, if not
stillIn the U.S., anthracite is found primarily
in 13 counties in Pennsylvania
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Bituminous
Second hardest variety of coal large range of
carbon content (45-86 carbon) still has
extremely high heat value (10,500-14,000 BTUs
per pound)Most bituminous coal was formed in
swamps near ocean influxof ocean water into
swamp brought a lot of sulfur into thedeposits ?
a lot of sulfur dioxide formed when
burnedBituminous is our largest single variety
of coal in the U.S.
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Subbituminous
Carbon content getting fairly low (35-45)
heating value fairlyvariable (8,300-11,500 BTUs
per pound)Coal has not undergone a lot of
conversion, which means it cannever have been
buried deep ? stripminingMost of it is found in
the western U.S.
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Lignite
Carbon content very low (25-35) heating values
also low(4,000-8,300 BTUs per pound)As with
subbituminous, never has been buried
deeplyFound chiefly in South and West
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Coal mining
Found in seams underground that often run
parallel to the surface
UNDERGROUND MINING Dig out coal seam from
underground
STRIP MINING Get to coal seam by removing soil
on top of it
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UNDERGROUND MINING
Dig shaft to depth of seam, then follow seam and
mine it out
DANGERS Cave-ins Inhalation of coal dust
particles (black lung)
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STRIP MINING
Use large machinery to remove overburden covering
shallow seamMust remediate land after coal
removed Cheaper, safer, not much else you can do
with shallow coal
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Strip mining Impacts
ACIDIC MINE DRAINAGE
After mining, bedrock and soil replaced on site
Rainwater flows through disturbed rock and soil
and accumulates pollutants
Runoff with low pH and high metal content
pollutes streams and lakes
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Coal reserves
The United States has the largest reserve of coal
in the world. Current usage is about 1 billion
short tons per year
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Coal States
Top Coal-Producing States (2001) (Thousand
Short Tons) State Amount Wyoming 368,749 West
Virginia 162,416 Kentucky 133,834 Pennsylvania
74,146 Texas 45,042
Almost 1,500 mines in the U.S.About 50/50 on
strip mines vs.traditional subsurface mines
About 70 of the coal comes from stripmining,
some quite hugeAll of Wyomings contribution
comes from 17 mines
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Coal Uses
Used primarily in developed world for electricity
production
GLOBAL ENERGY PRODUCTION 25
U.S. ENERGY PRODUCTION 57
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Combustion Pollution
As with all fossil fuels, burning coal produces
CO2High sulfur coals (bituminous) produce SO2,
which turnsinto sulfuric acidCoal burns most
efficiently if burned at high temperatures High
temperatures produce a lot of NOx, as nitrogen in
aircombines with oxygen
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Removing Sulfur
Sulfur attached to other chemicals (iron pyrite)
can be removedby crushing and washingOrganic
sulfur (sulfur attached to coal molecules) could
be removed before burning chemically, but
expensiveScrubbers - pass flue gas through
crushed limestone and watersolution SO2
combines with calcium in water to form calcium
sulfate (gypsum)
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Clean Burning Coal
Removing NOx from flue gas not that easy better
not to produce itCan be removed with chemical
scrubber, but expensiveStaged combustion -
initially burn coal at low temperaturesuntil
nitrogen has been bled from coal then move to
high temperature burner once nitrogen
reducedFluidized bed - finely crushed coal
mixed with limestone to burnwhile floating in
air limestone removes sulfur while coal burnsat
cooler temperature efficiency increased by using
coal as if a gas (turbine plus steam turbine)
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Coal Gasification and Liquefaction
Coal is the most abundant fossil fuel, but its
solid nature makes ithard to use in many
applications
Gasification and liquefaction convert coal to
gaseous and liquid fuels, respectively, by
heating coal in the presence of oxygen and/or
steam.
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Coal Plusses and Minuses
WHY USING COAL IS GOOD 90 of FF in U.S. is
coal Abundant domestic supplies Reduces reliance
on imports
WHY USING COAL IS BAD Burning coal releases
lots of CO2 Coal burning causes acid rain Coal
mining can damage waterways