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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)
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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
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.
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
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.
