Transcript Coal vs Diamonds

Coal vs Diamonds
• Diamonds need high temperature and pressure,
which is found at large depths in the Earth,
usually between 140-190 km deep.
• Coal mines reach depths of 2000 ft (0.6 km)
• Don’t form from coal, dating of diamonds shows
them to be older than the oldest known plants
that existed on the planet and it is unlikely to find
coal that deep.
• Confusion stems from both being high in carbon
content
US Coal resources
World distribution of coal
World coal production
Problems with coal
• Like oil and natural gas it will not last forever
– Best estimates are 100-200 years
– Be skeptical of large estimates, based on new discoveries, new technologies
• It is not a clean fuel source, lots of environmental impact from using coal
–
–
–
–
Environmental effects of surface (strip) mining
CO2 (carbon dioxide) emissions impact environment (green house effect)
SO2 (sulfur dioxide) emissions pose health risks
Mining risks (mine accidents, black lung disease)
• Is it really cheap?
– From an NRC report on the hidden costs of energy production:
• “In 2005 the total annual external damages from sulfur dioxide, nitrogen oxides, and
particulate matter created by burning coal at 406 coal-fired power plants, which produce
95 percent of the nation's coal-generated electricity, were about $62 billion;”
• This is twice as high as the cost of the coal itself
Coal Liquefaction
• Process of producing synthetic fuel from coal
• Direct and indirect process to achieve this
• Direct:
– Carbonization- produces coal tar, oil, water vapor, synthetic gas
and char (a solid residue). Produces fluids that are of low quality
for fuel.
– Hydrogenation –add H2 to coal mixed with solvents and
catalysts. No proven commercial value to the process
• Indirect: Fischer-Tropsch process (Coal gasification)
– Coal is gasified into syngas, which is converted to gasoline ad
diesel.
• Produces more CO2 than the crude oil refinement-needs
carbon sequestering technologies.
Coal gasification
• Process of producing coal gas, which can be
converted into gasoline and diesel fuel and
Hydrogen.
• Coal is heated and blown with oxygen and steam.
Produces syngas, which can then be turned into
gasoline as described on the previous slide.
• Or syngas is fed into another reaction which
produces H
• Produces by-products which are environmentally
damaging and need mitigation techniques
Shale oil and tar sands:
Nonconventional fossil fuels
• Shale oil: largest deposit
is found in the Green
River Formation
• 50 million years ago, this
area was covered by 2
large tropical lakes.
Organic material at the
bottom of the lakes
combined with sediment
and formed a carbon
containing mudstone,
called marlstone.
Green River Formation
Recovery methods
• Getting the oil is not easy, nor is it cheap, thus as long
as there is abundant, cheaper coal, this resources will
remain untapped
• Same amount of coal produces much more energy
• Traditional removal process require heating (a process
called retorting) of the shale to remove the
hydrocarbons which expands the remaining shale by
35%. Need a deposit site to handle the waste
• This process also requires lots of water, Green River
formation is in a very dry part of the country.
• In situ (on site) recovery methods are being developed
to overcome these difficulties
Recovery methods
Recovery methods
Recovery methods
Tar Sands
• Deposits of sand mixed
with a thick
hydrocarbon substance
called bitumen
• Bitumen is so thick
(viscous) that it does
not flow. So sands must
be transported to a
processing plant.
Locations
• Primarily in Canada
• Tar sands form where
petroleum migrates
upward into deposits of
sand or consolidated
sandstone. When the
petroleum is exposed to
water and bacteria
present in the sandstone,
the hydrocarbons often
degrade over time into
heavier, asphaltlike
bitumen.
Tar sands processing
• Tar sand is placed in rotating
drums along with water and
caustic soda that separates the
water,
soda and bitumen.
• Bitumen is placed in a centrifuge and cracked
into naptha, kerosene and heavy fuel oil
• Similar energy density to shale oil, much less
than coal
In situ processing
•
•
•
Two parallel horizontal oil wells are
drilled in the formation. The upper
well injects steam and the lower one
collects the water that results from
the condensation of the injected
steam and the crude oil or bitumen.
The injected steam heats the
bitumen and lowers its viscosity,
which allows it to flow down into the
lower wellbore.
The water and bitumen is recovered
to the surface by several methods
including a natural steam lift or by
pumps that work well for moving
high-viscosity fluids with suspended
solids.
Fossil fuels-going the way of the
dinosaur?
• Total resource vs proved reserve
– Total resource is the amount of a resource that is known to exist
– Proven resource is the amount that is recoverable under current
economic and technical conditions
– They are not equal!
• Barriers to untapped resources
– Restrictions on offshore oil drilling
– Strip mining of coal-environmentally a bad idea
– Tar sands mining has been referred to as the “most destructive
project on Earth”
• No mater how you look at it, fossil fuels follow a Hubbert
type curve, they will run out! It is a question of when, not if.
Heat Engines
• How do we get the heat energy of the fuel and
turn it into mechanical energy?
• Simply put we combine the carbon and
hydrogen in the fuel with oxygen.
• 2 reactions that occur are
– C + O2  CO2 + heat energy
– H2 + O  H2O + heat energy
• This process is just the reverse of
photosynthesis.