Fossil fuels-going the way of the dinosaur?

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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!
• Remember technically recoverable includes both!
• 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
• Risks associated with fracking
• How much does any one (or combination of
  )solution contribute to global climate change?
• 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.
• Understanding and managing the potential risks

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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.

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Just a little chemistry

• For example, the the equation for burning heptane
  looks like
• C7H16 11O2 ? 7CO2 8 H2O 1.15 X 106 calories
  per 100g of Heptane
• 1.15 x106 is called the heat of combustion for
  heptane. Every hydrocarbon has such a number
• It is the maximum amount of energy for a certain
  amount of mass of a substance you can extract.
• It represents the energy from the sun stored in
  the fuel since ancient times

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So what is a heat engine?

• A heat engine is any device that can take energy
  from a warm source and convert it to mechanical
  energy
• Efficiency not all of the energy from the
  burning of the fuel goes into the production of
  energy. Heat is lost as waste heat and needs to
  be disposed of.
• For example, most energy generating plants are
  located near bodies of water or have cooling
  towers which are used to carry off waste heat.

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Diagram of a heat engine
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How well does one work?

• Your car often carries off waste heat via its
  cooling system. But your car recycles some of
  that heathow?
• No heat engine will perfectly convert all the
  heat energy to mechanical energy.
• We need to quantify the efficiency and designers
  of heat engines work to maximize this efficiency.

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Carnot and his cycle

• Sadi Carnot created an efficiencey
  measure for a heat engine, now
  named after him (Carnot Efficiency).
• Always less than 100
• Simply put it is the percentage of the energy
  taken from the heat source which is actually
  converted to mechanical work.

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Carnot Efficciency

• Efficiency work done/energy put into the system
• In terms of the flow of heat (Q) energy this
  becomes (Qhot - Qcold)/Qhot X 100
• Now energy is not easy to quantify, but
  temperature is, and since we know the Kelvin T
  scale is true measure of energy, we can express
  the efficiency in terms of temperature.

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Carnot Efficciency

• So our efficiency, in terms of T becomes
• Carnot Efficiency (Thot - Tcold)/Thot X 100
  
• Or with some algebraic wizardry we get
• Carnot efficiency 1- (Tcold/Thot) X 100
• Example for a coal fired electric power plant,
  the boiler temperature 825K and the cooling
  tower temperature is 300k. So 1-(300/825) X
  100 64

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Carnot Cycle

• From an initial state A, the gas is placed in
  contact with the hot temperature reservoir (Th)
  and expands isothermally (keeping T Th
  constant) to some state B. During this isothermal
  expansion heat Qh flows into the gas from the hot
  temperature Th.
• From state B, the gas undergoes an adiabatic
  expansion to state C. No heat is exchanged during
  this expansion. Expanding an insulated gas means
  work is done at the "expense" of the internal
  energy. That means the gas will have a lower
  temperature. This is the cold temperature Tc.
• At state C, we place the gas in contact with the
  cold temperature heat reservoir (like a large
  tank of water) and do an isothermal compression
  to state D. In compressing the gas, work is done
  on the gas by the outside. But the temperature
  remains constant -- meaning the internal energy U
  of the gas remains constant. For this to happen,
  heat Qc is given out to the cold temperature heat
  reservoir.
• From state D we do an adiabatic compression back
  to state A. Remember, "adiabatic" means insulated
  so there is no heat exchange.

Figure 1
Adiabatic constant pressure Isothermal-constant
temperature
Figure 2
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So how can we make this work for usThe Steam
Engine

• Concept of a heat engine was revolutionary-if the
  heat energy could be turned into mechanical
  energy, human and labor could be replaced cheaply
  and more efficiently.

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Simple steam engine

• Water is heated in the boiler and steam forces
  piston up
• At the valve, steam escapes into the cooling
  tower, where it cools and condenses.
• Cool water is pumped back into boiler, T drops
  and piston drops, until sufficient steam is
  created to cause the process to repeat.

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A little history

• First writings on the power of steam are from
  Hero of Alexandria (10-70 CE).
• The aeolipile (known as Hero's engine)
  was a rocket-like reaction engine
  and the first recorded
  steam engine.
• He also created an engine that used air from a
  closed chamber heated by an altar fire to
  displace water from a sealed vessel the water
  was collected and its weight, pulling on a rope,
  opened temple doors.
• Taqi al-Din in 1551 and Giovanni Branca in 1629
  both created experimental steam engines.

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More History

• Thomas Savery (1650-1715), in 1698, patented the
  first crude steam engine.
• Based on Denis Papin's Digester or pressure
  cooker of 1679. Papins device was for extracting
  fats from bones in a high-pressure steam
  environment, which also renders them brittle
  enough to be easily ground into bone meal.
• Savery had been working on solving the problem of
  pumping water out of coal mines
• Thomas Newcomen created the atmospheric engine,
  which was relatively inefficient, and in most
  cases was only used for pumping water out of deep
  mines

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Newcomens atmospheric engine
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Watts Steam Engine

• Improvement upon Newcomens
• Used 75 less coal than Newcomen's, and was hence
  much cheaper to run.
• Watt developed his engine further, modifying it
  to provide a rotary motion suitable for driving
  factory machinery.
• This enabled factories to be sited away from
  rivers, and further accelerated the pace of the
  Industrial Revolution.