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Fossil Fuels
Photosynthesis: Plants take in:energy from sunlight
matter from the soil and air
simplest form:
CO2(g)+ H2O(g,l) + energy Carbohydrate + O2(g) .
eg
6 CO2(g)+ 6 H2O(g,l) + energy C6H12O6+ 6 O2(g)
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Fossil Fuels
When plants decay in air:aerobic
decay:Rapid recycling of the carbon, hydrogen andoxygen in the biosphere via the action of aerobicbacteria
When plants decay in the absence of air: anaerobicdecay:
Slow decay via anaerobic bacteria
Sedimentation
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Fossil Fuels
Anaerobic decay (no oxygen) and sedimentation(high pressure and temperature):
The oxygen is slowly expelled from thecompounds, leaving behind hydrocarbons
Carbohydrates (C, H, O) Hydrocarbons (C, H)
CxHyremain: x = 1100s
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Fossil FuelsExtraction: Coal
Coal is simply Carbon, Cand the contaminantsfound with it.
Two types of extraction categories:
Surface extraction: Strip mining (< ~30m deep)
Subsurface extraction: Closed mining (> ~30mdeep)
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Fossil FuelsExtraction: Coal
Surface extraction: Strip mining (< ~30m deep)
cheaper
safer for workers
greater environmental impact
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Fossil FuelsExtraction: Coal
Surface extraction: Strip mining (< ~30m deep)
Strip off surface soil
Dig up overlying rock scoop up coal
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Fossil FuelsExtraction: Coal
Surface extraction: Strip mining (< ~30m deep)
Strip off surface soil
No topsoil, no ecology! Living material isunlikely to survive the process.
Post-mining reclamation can restore this,but often doesnt restore the full diversity.
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Fossil FuelsExtraction: Coal
Surface extraction: Strip mining (< ~30m deep)
Dig up overlying rock
Acid Leachates: Natural iron sulfide minerals in the
rock are exposed to air and water by the process:
eg.4 FeS(s)+ 4 H2O(l) + 9 02(g) 4 H2SO4(aq)+ 2 Fe2O3(s)
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Fossil FuelsExtraction: Coal
Surface extraction: Strip mining (< ~30m deep)4 FeS(s)+ 4 H2O(l) + 9 02(g) 4 H2SO4(aq)+ 2 Fe2O3(s)
H2SO4 is sulfuric acidso mine run-off is generallyhighly acidic.
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Fossil FuelsExtraction: Coal
Surface extraction: Strip mining (< ~30m deep)
This acid helps to dissolve other metals in the rock, and
can contribute to mercury, lead and other toxic metals
being carried into natural waters from mine run-off.
The metals (and the starting materials for the sulfuric
acid) were naturally present in the rock, but theexposure to the air is what makes them available in the
environment rather than staying bound in the rocks.
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Fossil FuelsExtraction: Coal
Subsurface mining: Generally if the coal is more thanabout 30 metres deep.
A network of tunnels is used.
There is lessdisruption to topsoil
There is lessexposure of rock to air
There is much greater danger to mine workers!(accidents and deaths are both about 4X greater)
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Fossil FuelsUses: Coal
As a fuel:
Coal contains:
sulfur, S:which can produce sulfur dioxide, SO2,when the coal is burned. This can then form
sulfuric acid, H2SO4(g)when exposed to humid air.
mercury, Hg: combustion of coal is responsible for
about 1/3 of all mercury emissions world-wide.
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Fossil FuelsUses: Coal
As a fuel:
Soot: Combustion is often incomplete, and
particles of soot (C) are produced. These are
serious respiratory irritants.
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Fossil FuelsUses: Coal
Treatments:
I: Remove S and Hg before burning:
Wash the crushed coal before burning; coalfloats, while sulfur and mercury containing
minerals sink.
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Fossil FuelsUses: Coal
Treatments:
I I : Remove S after burning:
Pass the product gas stream through limestone,
CaCO3(s) .
2 SO2(g)+ 2 CaCO3(s) + O2(g) 2 CaSO4(s) + 2 CO2(g)
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Fossil FuelsUses: Coal
Resource reclamation:
Finding an economic use for the by-product of anindustrial process
CaSO4(s)is gypsum, used to manufacture wallboard andas a soil amendment
A major coal-fired power plant will produce enough inone year to cover 1 square mile 1 foot deep.
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Fossil FuelsUses: Coal
Newer burning technique: Fluidized Bed
Crushed coal and limestone are mixed prior to
burning
O2(g) is passed over the combustion
Calcium carbonate forms, so the sulfur is dealt with.Lower burning temperatures can be used (less NOX)
More heat is released per kilogram of coal
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Fossil Fuels: Oil and Gas
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porous
rock
non-porous rock
Gas deposit
Oil deposit
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Fossil Fuels: Oil and Gas
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porous
rock
non-porous rock
Gas deposit
Oil deposit
Extractiongenerallyby geologic pressure
Extraction
pumping plusother
techniques
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Fossil Fuels: Oil and Gas
Extraction techniques:
Gas: the naturally occurring pressure is enough
Oil: 1:Mechanical pumping.
2:pump water (liquid or steam down to displaceand warm the oil (reduce viscosity)
3:pump detergent down to disrupt surfacetension, or heat by burning on-site to reduceviscosity.
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Fossil Fuels: Oil refining
Gas separates out spontaneously:
Oil: separated based on mass (proportional to the
number of carbon atoms in the molecule)
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400 C
heat to 400 C
tar
Natural gas 1-5 C
Solvents 57 C
Gasoline 5 - 12 C
Kerosene 12 - 16 C
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Fossil Fuels: Burning oil/gas
Carbon dioxide: All of the carbon atoms in the fuelare converted to CO2during combustion.
You can see the relative amounts (in moles)directly from the formula of the fossil fuel:
C8H18(octane) will give 8 CO2
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Fossil Fuels: Burning oil/gas - smog
Smog:
Another case of what is present naturally in the
environment coming back to bite you
The combustion of fossil fuels
is generally carried out in metal containers
liberates heat
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Fossil Fuels: Burning oil/gassmog
Hot metal and air: The nitrogen and oxygen in theair interact in the presence of hot metal: Above
1100 C, the airburns!
combustion of nitrogen gas:
N2(g) + O2(g) 2 NO(g)
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ozone depleter
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Fossil Fuels: Burning oil/gas - smog
N2(g) + O2(g) 2 NO(g)
then:
2 NO(g) + O2(g) 2 NO2 (g)
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ozone depleter
when unburned hydrocarbonsare present as catalysts
reddish-brown gasyou seeit as the orange haze of smog
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Fossil Fuels: Burning oil/gas - smog
2 NO(g) + O2(g) 2 NO2 (g)
NO2 (g) + O2(g) NO(g) + O3 (g)
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sunlight as catalyst
Ozone: very welcome in thestratosphere, but NOT a good
thing to have at ground level.
Severe lung irritant
Damaging to rubber and plastics
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Fossil Fuels: Burning oil/gas - smog
N2(g) + O2(g) 2 NO(g)
2 NO(g) + O2(g) 2 NO2 (g)
NO2 (g) + O2(g) NO(g) + O3 (g)
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hot metal as catalyst
unburned hydrocarbons as catalyst
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Fossil Fuels: Burning oil/gas
Catalytic converters in cars:
1. Help the hydrocarbon burn more fully
minimizing unburned hydrocarbon
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Fossil Fuels: Burning oil/gas
N2(g) + O2(g) 2 NO(g)
2 NO(g) + O2(g) 2 NO2 (g)
NO2 (g) NO(g) + O(g)
O(g) + O2(g) O3 (g)
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Fossil Fuels: Burning oil/gas
Catalytic converters in cars:
2. Reduction catalysts (less common) convert
the nitric oxide back to nitrogen gas andoxygen gas (i.e. air)
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F il F l B i il/
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Fossil Fuels: Burning oil/gas
Photochemical smog
NOx (g) + CnHy PAN
PAN stands for peroxyacyl nitrates, the name of afamily of compounds containing C, H, O, and N.
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sunlightas catalyst
powerful eye irritants
persistent : do not break down
easily
O
RCO ONO2
R stands for some
hydrocarbon attachedhere