Energy production and utilization Chapters 15

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Energy productionand utilization Chapters 1-5

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Outline 1. What is energy? 2. Energy flows on
Earth 3. Fossil fuels 4. Nuclear energy 5.
Renewable energy
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1. What is energy?
Energy can take many forms, which can be grouped
into potential energy (ability to do work or
bring about changes), kinetic energy (ongoing
transfer of mass) and radiation (ongoing transfer
of photons). Driven by the increasing entropy,
energy changes its forms and eventually turns
into heat and IR-radiation. Consumption of
energy is making these energy fluxes do
something useful for us. Due to the law of
conservation of energy, the energy itself can not
be consumed. We must eventually return into space
all the energy taken from there.
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2. Energy flows on Earth
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Where does the energy come from?

• Solar source
• Direct
• Solar energy (Earth intercepts 500 parts per
  trillion of the energy emitted by the Sun)
• Indirect
• Food
• Wind
• hydropower
• Fossil fuel
• Nonsolar sources
• Tidal energy
• Geothermal heat
• Nuclear energy

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Human Energy Use vs. Natural Energy Flows
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We are overwhelmingly dependent on the fossil
fuels
3. Fossil fuels
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Forms of fossil fuels

• Fossil fuels are the remains of plants, animals,
  and microorganisms that lived millions of years
  ago and over time, were buried and subjected to
  high temperatures and pressures in Earths crust.
• Fossil fuels are classified into three types
  based on the chemical composition and origin.
• Coal
• Petroleum (oil)
• Natural gas

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Carbon cycle
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How oil fields are formed?

• Marine microscopic organisms once lived in great
  numbers in shallow coastal waters.
• When the organisms died, a minute fraction
  settled to the ocean bottom, where supply of O2
  was insufficient to oxidize all the organic
  materials.
• Over millions of years, the biological debris was
  covered by clay and sand particles and formed a
  compacted organic layer.
• In some locations, the sea dried up, leaving
  behind a new landmass.
• As the organic debris became more deeply buried,
  the temperature and pressure rose.
• High temperature and pressure converted some of
  the organics to liquid hydrocarbon (crude oil or
  petroleum) and gaseous hydrocarbons (natural
  gas).

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Composition of petroleum

• Crude petroleum is a complex mixture of thousands
  of organic compounds.
• The majority of these compounds are hydrocarbons,
  including alkanes, cycloalkanes, alkenes, and
  aromatic hydrocarbons (10).
• Small amounts of sulfur- (lt10), nitrogen- (lt1),
  and oxygen- (lt5) containing compounds are also
  present.

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Some example of organic sulfur compounds in fuels.
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Octane Rating

• Some components of gasoline begin to burn before
  they are ignited by the spark plug.
• This premature ignition produces a knocking sound
  and leads to loss of engine power and excess wear
  to the engine.
• The tendency of gasoline to cause knocking is
  rated according to an arbitrary scale known as
  the octane rating.
• Isooctane (2,2,4-trimethylpentane) is
  particularly resistant to premature ignition. It
  burns without causing knocking, therefore it is
  assigned an octane rating of 100.
• The straight-chain alkane n-heptane, in contrast,
  causes serious knocking and was given an octane
  rating of 0.

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• An octane rating of a particular gasoline is
  determined by burning the gasoline in a standard
  engine and comparing its knocking properties with
  those of standard mixtures of isooctane and
  n-heptane.
• The gasoline fraction from the distillation
  tower, known as straight-run gasoline, has an
  octane rating of 50-55, much too low for todays
  automobiles, which requires a rating between 87
  and 90.

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What octane number a car engine requires to run
knock-free?

• The required octane number to run knock free
  depends on both design factors (car models) and
  environmental conditions.
• BMW R models requires 87 pump octane
• BMW K100 K1100 requires 89 pump octane
• Increase in barometric pressure and temperature
  requires higher octane number gasoline to run
  smoothly Increase in humidity or altitude
  lessens the required octane number.

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Pump Octane

• Pump octane numbers are what you see on the
  yellow decal on the pumps at the gas stations.
• Pump octane number is the average of the Research
  Octane Number (RON) and the Motor Octane Number
  (MON)
• Pump Octane (RON MON)/2
• MON82, RON 91 ? Pump octane 87
• MON is a measure of the gasolines ability to
  resist knock under severe operating conditions.
• RON is a measure of the gasolines ability to
  resist knock under less severe operating
  conditions.

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Octane numbers of selected hydrocarbons
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Chemistry affecting octane rating

• Combustion is a radical chain process. Pre-mature
  ignition is caused by secondary radicals,
  generated from fuel components at the relatively
  lower temperature before ignition.
• The methylene groups (-CH2-) in straight chain
  hydrocarbons are more susceptible to attack by
  thermally activated oxygen molecules to produce
  hydrocarbon radicals.
• In contrast, branched-chain hydrocarbons are more
  resistant to formation of secondary radicals
  because branching increases the fraction of the H
  atoms that are on methyl groups, CH3. Tertiary
  radicals are much less reactive, than secondary.
  Primary radicals are to unstable to be formed.
• C-H in CH3 has a bond energy of 423 kJ/mol
• C-H in CH2- has a bond energy of 410 kJ/mol

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How to increase the octane rating?

• Cracking
• catalytic reforming
• addition of octane enhancers

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Octane enhancers

• Before 1975, the most widely used octane enhancer
  was tetraethyl lead (TEL). Adding as little as
  0.1 of TEL per gallon of gasoline can increase
  the octane rating by 10 to 15 points
• Other octane enhancers
• Organometallic compounds methyllcyclopentadienyl
  manganese tricarbonyl (MMT)
• Alcohols methanol, ethanol
• Ethers MTBE (methyl-t-butyl ether), and
  ethyl-t-butyl ether (ETBE).

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Why we have abandoned leaded gasoline?

• Pb is toxic to humans.
• Cumulative exposure of concentrated TEL by
  refinery workers made them suddenly insane.
• Pb poisons Rh and Pt catalysts in catalytic
  converters (The catalytic converters are used to
  reduce NOx and VOC emissions from tailpipes.)

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MTBE (methyl-t-butyl ether)

• The addition of MTBE to gasoline has two
  benefits
• Reduce CO emission (The extra O in MTBE helps
  combustion) during winter months.
• Boost octane rating (MTBE has an octane rating of
  116)

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MTBE Controversy

• MTBE is readily available from petroleum
  refining.
• MTBE could contaminate drinking waters
• get into ground water through underground
  gasoline tank leakage.
• MTBE has a strong unpleasant taste and smell,
  noticeable at 15 ppm, although no significant
  health effects to humans

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Processing of petroleum fractions
1. Cracking (with or without a catalyst)
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2. Alkylation and reforming
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Atoms, Nuclei, and isotopes
4. Nuclear energy

• An element is characterized by the number of
  protons, i.e. atomic number.
• Nuclei are composed of protons and neutrons the
  nucleons.
• An atom is made of a nucleus and electrons
• Isotopes are atoms of a same element but having
  different numbers of neutrons in their nuclei.

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Simple Atomic Particles
In atomic mass unit (amu), where 1 amu 1/12
of the atomic mass of 12 C isotope.
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Symbols for isotopes
Mass number
Element symbol
Atomic number
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Nuclear decay

• Not all combinations of protons and neutrons are
  stable.
• Neutrons act as glue for repulsing protons.
  However, nuclei containing too many neutrons, may
  fall apart.

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• Unstable nuclei undergo nuclear decay to form
  stable nuclei.
• Nuclear decay processes release a large amount of
  energy.
• This release of energy during nuclear decay is
  called radioactivity.
• Radioisotopes are isotopes of an element that are
  unstable and undergo nuclear decay.

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Nuclear Equations
- Nucleons need to be balanced - The
atomic numbers of products and starting materials
need to be balanced - The mass numbers of
products and starting materials need to be
balanced.
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Forms of nuclear decay

• Alpha decay
• Beta decay
• Positron (anti-electron) emission
• Electron capture
• Gamma-ray (high energy photons) emission

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Naturally Occurring radioisotopes

• Most unstable isotopes have disappeared from the
  Earth since its formation (4.5 billions years
  ago).
• A few isotopes decay slowly. ? They still exist
  in detectable abundance.
• 238U (half-life 4.5 billion years)
• 235U (half-life 0.7 billion years)
• 232Th (half-life 14 billion years)
• 87Rb (half-life 49 billion years)
• 40K (half-life 1.3 billion years)

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Half-lives and Isotope Dating

• The rate of nuclear decay vary from one
  radioisotope to another. The decay process is
  always exponential.
• Half-life characterize the decay rate. (t1/2
  ln2/k)
• The amount of an radioisotope decays to half
  after each half-life, no matter how much to start
  with.
• The half-life is a characteristic property of an
  radioisotope. It does change for a given
  radioisotope.
• The constant nature of half-life makes it useful
  for dating various natural processes.

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Carbon-14 dating

• Carbon-14 is formed in the upper atmosphere by
  the bombardment of ordinary nitrogen by neutrons
  from cosmic rays.
• This process leads to a steady-state
  concentration of carbon-14 in Earths CO2.
• Living plants and animals incorporate this
  isotope into their own cells.
• When they die, the incorporation of C-14 ceases,
  and the C-14 in the organism decays to N-14, with
  a half-life of 5730 years. ? A 5730-year-old
  sample contains half the C-14 content of living
  tissue.
• Useful for dating objects 500-50,000 years old.

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Naturally occurring radioisotopes The Radon
Problem
Rn is a noble gas. It escapes from where it is
formed and becomes airborne.
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Penetrating Power of Radiation
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Background radiation
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Nuclear stability is greatest near iron. Fission
of very large atoms or fusion of very small ones
results in greater nuclear stability.
fission
fusion
Fusion of two hydrogen nuclei to form a He
nucleus also release a large amount of energy.
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Nuclear Fission
The splitting of a mole of U-235 produces 5.3
million kWh of energy. (One gram of U-235 is
equivalent to 2.5 tons of high-grade coal.
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Fission of 235U
The combination of intensely radioactive fission
products and long-lived actinides produces the
uniquely complicated potential for environmental
impact that characterizes the nuclear energy.
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How to make fission take place and sustain?

• Fission is an extremely rare event, even among
  uranium atoms.
• Fission of 235U is induced by thermal neutrons.
• Not all neutron collisions with uranium nuclei
  lead to fission.
• A critical mass of 4.4 kg of pure 235U is needed
  to sustain the chain reaction.
• Natural uranium isotope composition 99 238U,
  0.7 235U. ? Isotope separation necessary to
  achieve gt93 235U.
• Enrich 235U through UF6 by gaseous diffusion
  235UF6 diffuses faster than 238UF6.
• Gas diffusion has now largely been replaced by
  gas centrifuge.
• Separation of uranium isotopes is extremely
  difficult and so expensive, that can be afforded
  only by wealthy nations.

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The Manhattan Project Nuclear Bombs

• The Manhattan project had four teams to work on
  four projects
• How to sustain the nuclear fission chain reaction
• How to enrich U-235
• How to make plutonium-239
• How to build a bomb based on nuclear fission.
• Two atomic bombs dropped on Japanese cities in
  August 1945 (The only case in human history)
• Little Boy (a uranium bomb) on Hiroshima
• Fat Man (a plutonium bomb) on Nagasaki

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Example nuclear power reactor
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Breeder reactor
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Hazards of nuclear power

• Reactor failures
• Highly radioactive materials released to the
  environments.
• 1979, Three Mile Island, USA
• 1986, Chernobyl, Ukraine, thousands died and many
  more made ill.
• 1999, Tokaimura, Japan, 49 workers gravely
  overexposed.

Taken as a whole, the human toll of the nuclear
industry is not worse than in a number of
non-nuclear large-scale industrial accidents.
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• Weapons proliferation
• 235U is not a concern. (A bomb requires gt93 235U
  whereas conventional fuel rods are only slightly
  enriched. Enrichment of 235U to achieve
  weapons-grade requires a major commitment of
  resources.)
• 239Pu is a concern. (239Pu is created in a
  uranium reactor. No isotope enrichment is needed
  to produce weapons-grade fuel.)
• 239Pu can be relatively easily recovered from
  reprocessed reactor fuel.

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Nuclear water disposal
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• Nuclear waste disposal
• The waste must be isolated from the environment
  for exceedingly long periods. (10 half-lives of
  the radioisotopes in the waste Pu has a
  half-life in the order of 10,000 yr.)
• Temporary storage
• Transportation is a potential hazard

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Is Nuclear Power Part of the Future?

• Advantages
• No CO2 emission
• Minimal air pollution
• Disadvantages
• Potential for disastrous accidents
• Nuclear weapons proliferation
• Disposal of nuclear waste

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Fusion
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Is Fusion the Energy Source of the Future?

• Advantages
• Safer than fission technologies (No runaway
  reactions)
• Simpler post-shutdown or emergency cooling
  systems
• Radioisotopes created in the process are much
  shorter-lived.
• Disadvantages
• Substantial technical challenges remain.
• Economic competitiveness of fusion is unknown at
  present.

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Sustainability and Renewable Energy
5. Renewable energy

• Human activity is using up natures resources at
  rates beyond the capacity of nature to restore
  them.? Unsustainable Development
• Sustainability implies that using the natural
  resources in ways that allow regeneration for
  future use.
• Deriving energy from fossil fuels is an
  unsustainable practice.
• Utilization of renewable energy is core to
  sustainable development.

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Major forms of renewable energy

• Solar energy
• Solar heating
• Solar thermal electricity
• Photovoltaic electricity
• Biomass
• Ethanol from biomass
• Methane from biomass
• Biodiesel
• Hydroelectricity
• Wind power
• Ocean energy
• Geothermal energy

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Major feature of renewable energy sources

• Dispersed in space and time
• Available everywhere ? potential to bypass the
  necessity of installing expensive electricity
  supply grids or fuel transportation systems.
• Analogy Wireless versus wired communication
• The availability not necessarily matching needs
  for energy.
• Attractiveness of renewable energy sources
  changes with technology advance and environmental
  policies and regulations.