Transcript Option F : Fuels and Energy

Option F :Fuels and Energy
• The developments of human society has
been directly related to the ability to use and
manipulate fuels for energy production.
This option considers the chemical
principles and environmental issues
associated with the use of fossil fuels, and
nuclear and solar energy.
Desirable characteristics of
energy sources.
• These include energy released at
reasonable rates (neither too fast nor
too slow) and minimal pollution.
Current and potential energy sources.
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fossil fuels,
nuclear (fission and fusion),
electrochemical cells,
solar energy
alternative sources (eg wind, tidal,
geothermal).
Fossil Fuels
• Fossil fuels originated from the decay of living
organisms millions of years ago, and account for
about 80% of the energy generated in the U.S.
• The fossil fuels used in energy generation are:
– Natural gas, which is 70 - 80% methane (CH4).
– Liquid hydrocarbons obtained from the distillation
of petroleum.
– Coal - a solid mixture of large molecules with a H/C
ratio of about 1.
Coal: Supply and Demand
• Coal exists in many forms therefore a
chemical formula cannot be written for it.
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Peat- Low carbon content, heat High Moisture
Lignite- 40% moisture low energy value
Sub-bituminous- 30% moisture used for heat
Bituminous-86% Carbon industrial/domestic use
Anthracite- 98% Carbon, burns with blue flame
Sources of Coal
World Coal Reserves
Latin America
25%
29%
North America
Africa
Western Europe
2%
6%
29%
9%
Asia and Australia
Central Europe
Problems with Fossil Fuels
• Fossil fuels are nonrenewable resources.
– At projected consumption rates, natural gas and
petroleum will be depleted before the end of the
21st century.
• Impurities in fossil fuels are a major source of
pollution.
• Burning fossil fuels produce large amounts of
CO2, which contributes to global warming.
Describe how the burning of fossil fuels produces
pollutants.
• The primary pollutants are CO, CO2, SO2,
NOx, particulates (fly ash) and
hydrocarbons.
Coal Cleaning
• Gasification - Coal is converted to synthetic gas.
It is carried out in 4 steps: devolatilization, steamcarbon reaction, CO-shift reaction, and catalytic
methanation.
• Devolatilization - Coal is exposed to high
temperatures and the volatile matter is released
and decomposes to methane and char.
• Steam-Carbon Reaction - Addition of hydrogen in
the form of water (steam) reacts with the char.
• C + H2O  CO + H2
Coal Cleaning
• CO-Shift Reaction - Some of the carbon monoxide
is reacted with more steam, to form more
hydrogen.
• CO + H2O  CO2 + H2
• Catalytic Methanation - The additional hydrogen
is then caused to react with the remaining carbon
monoxide.
• CO + 3 H2  H2O + CH4
Coal Cleaning
• Claus Process - During gasification sulfur
is leaves the system as H2S gas. It is
converted to free sulfur, S, which can be
sold as a by-product.
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(1)
(2)
H2S + FeO  FeS + H2O
2 FeS + 3 O2  2 FeO + 2
SO2
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(3) 2 H2S + SO2  2 H2O + 3 S
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Net: 2 H2S + O2  2 H2O + 2 S
Coal Cleaning
• Liquefaction - The products from gasification, CO
and H2, are further reacted to form the liquid
compounds, formaldehyde (H2C=O) and methanol
(CH3OH).
• Scrubbers - flue-gas desulfurization devices.
These devices remove SO2 from combustion gases.
One important scrubber is limestone (CaCO3).
• CaCO3 + SO2  CaSO3 + CO2
Products of Oil Distillation
Petroleum Fractions
Fraction
Gas
Pet ether
Petrol
Kerosene
LG Oil
HG Oil
Lubricant
Solids
BP (oC)
0–20
20-70
70-180
180-230
230-305
305-405
405-515
Composition
CH4-C4H10
C5H12,C6H14
C6H14-C10H22
C11H24,C12H36
C13H28-C17
C18 – C25
Higher C
Use
Fuel
Solvent
Fuel
Jet fuel
Diesel
Powerplant
Grease
Pitch
Octane Rating
• Petrol fraction consists of straight-chain
alkanes
• Fuel burns before ignition by the spark plug
– knock – loss of power, damage to engine
• 2,2,4-trimethylpentane: Octane =100
• N-heptane: Octane = 0
Octane Rating
• Can increase octane rating for petrol
fraction from 50 to 90 by 3 methods:
– Cracking
– Catalytic reforming
– Addition of octane enhancers like TEL,
methanol, ethanol and MTBE
Nuclear Energy
Electricity - Nuclear Fusion ?
Distinguish between nuclear reactions and chemical reactions.
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Emphasize that in nuclear reactions nuclei are converted to other nuclei, while in chemical reactions
only valence electrons are involved and atoms do not change into other atoms.
Write balanced nuclear equations.
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Both the atomic number and mass number must be balanced.
Describe the nature of a , b and g radiation.
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Compare the charge, mass, penetrating power and behaviour in an electric field.
Types of Radiation
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alpha, beta or gamma
Alpha
a = 42He2+ or 42He or 42a
least penetrating
can be stopped by aluminum foil > 10-3 cm, paper,
skin
• least harmful
• most massive
Types of Radiation
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Beta
b = 0-1ehigh energy electrons (e-) or positrons (e+)
more penetrating
stopped by 0.05 - 0.1 cm of aluminum
travel 10 ft through air
commonly emitted by TV sets
electron: 0-1b- or 0-1e- or epositron: 0+1b- or 0+1e+ or e+
Types of Radiation
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Gamma
g = energy with no mass or charge
Most penetrating radiation
Stopped by 5 - 11 cm of aluminum or thick layer
of concrete or lead
• Lead is commonly used to enclose radioactive
materials because radiation does not penetrate
readily
• In the 1950s, it was common to build thick
concrete bomb shelters
Types of Radiation
• Other particles:
– proton (p+ or 11p or 11H)
– neutron (n or 10n)
– neutrino (00n) and antineutrino (00n),
which have no mass or charge and
accompany emission of beta particles;
these are generally ignored by chemists
F.3.4
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State the concept of half-life.
Half-life is independent of the amount of a radioactive sample.
F.3.5
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Apply the concept of half-life in calculations.
Restrict this to whole number of half-lives.
F.3.6
Compare nuclear fission and nuclear fusion.
F.3.7
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Explain the functions of the main components of a nuclear power
plant.
Include the fuel, moderator, control rods, coolant and shielding. The materials used for the different
components should be considered.
Reactor core
• We use B or Cd control rods.
• 105B + 10n --> 73Li + 42He
Diagram of Nuclear Reactor
Discuss the differences between conventional power generation and
nuclear reactors.
Discuss the concerns about safety in nuclear power plants.
Solar Energy:
The Ultimate Renewable Resource
What is Solar Energy?
• Originates with the
thermonuclear fusion
reactions occurring
in the sun.
• Represents the entire
electromagnetic
radiation (visible
light, infrared,
ultraviolet, x-rays,
and radio waves).
Advantages and Disadvantages
• Advantages
• All chemical and radioactive polluting byproducts of the
thermonuclear reactions remain behind on the sun, while
only pure radiant energy reaches the Earth.
• Energy reaching the earth is incredible. By one
calculation, 30 days of sunshine striking the Earth have
the energy equivalent of the total of all the planet’s fossil
fuels, both used and unused!
• Disadvantages
• Sun does not shine consistently.
• Solar energy is a diffuse source. To harness it, we must
concentrate it into an amount and form that we can use,
such as heat and electricity.
• Addressed by approaching the problem through:
1) collection, 2) conversion, 3) storage.
Electricity - Solar Cells
How much solar energy?
The surface receives about 47% of the total solar
energy that reaches the Earth. Only this amount
is usable.
Putting Solar Energy to Use: Heating
Water
• Two methods of heating
water: passive (no moving
parts) and active (pumps).
• In both, a flat-plate collector
is used to absorb the sun’s
energy to heat the water.
• The water circulates
throughout the closed system
due to convection currents.
• Tanks of hot water are used
as storage.
Heating Water: Active System
Active System uses antifreeze so that the liquid does not
freeze if outside temp. drops below freezing.
Heating Living Spaces
Passive Solar
Trombe Wall
Passively heated home
in Colorado
Heating Living Spaces
• A passively heated home uses about 60-75% of
the solar energy that hits its walls and windows.
• The Center for Renewable Resources estimates
that in almost any climate, a well-designed
passive solar home can reduce energy bills by
75% with an added construction cost of only 510%.
• About 25% of energy is used for water and
space heating.
• Major factor discouraging solar heating is low
energy prices.
Power Towers
Power tower in Barstow, California.
Parabolic Dishes and Troughs
Collectors in southern CA.
Because they work best under direct sunlight, parabolic
dishes and troughs must be steered throughout the day in
the direction of the sun.
Direct Conversion into Electricity
• Photovoltaic cells are capable of
directly converting sunlight into
electricity.
• A simple wafer of silicon with wires
attached to the layers. Current is
produced based on types of silicon
(n- and p-types) used for the layers.
Each cell=0.5 volts.
• Battery needed as storage
• No moving partsdo no wear out,
but because they are exposed to the
weather, their lifespan is about 20
years.
State how solar energy can be converted to other forms of energy.
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Include chemical energy (biomass), thermal energy (passive and active methods) and electricity
generation (direct and indirect methods).
Describe the role of photosynthesis in converting solar energy to other
forms of energy.
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Products of photosynthesis are used for food, primary fuels and conversion to other fuels, eg. ethanol.
The equation for photosynthesis is required.
Outline the principles of using solar energy for space heating.
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Example should include storage of heat by water and rocks.
F.4.5
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Discuss the methods for converting solar energy into electricity.
Include parabolic mirrors and photovoltaic cells. Consider the advantages and disadvantages of each
method.
Discuss how biomass can be converted to energy.
Include :
Electrochemical Energy
Explain the workings of lead-acid storage batteries and dry cell (zinccarbon and alkaline) batteries. Include the relevant half-equations.
Electrochemical Cell
The Alkaline Dry Cell
“Dry” Cell Battery
• Leclanche cell:
• anode: Zn(s) + 2e-  Zn2+(aq) + 2e• cathode: 2NH4+(aq) + 2MnO2(s) + 2e- 
Mn2O3(s) + 2NH3(aq) + H2O(l)
• overall: Zn(s) + 2NH4+ (aq) +MnO2(s) 
Zn2+(aq) + Mn2O3(s) + 2NH3(aq) + H2O(l)
• supplies 1.5V new; not rechargeable;
voltage decreases on use (why?)
• Advantages and disadvantages?
Dry Cell
Why?
Mercury Battery
•Zn(Hg)+ HgO(s)  ZnO(s) + Hg(l)
Fuel Cells
• Fuel cells :“Non-polluting” energy source
(vs fossil fuels as CH4, gasoline)
• CH4 + 2O2(g)  CO2(g) + 2H2O(l) +energy
(40% of chem energy converted into
electricity)
Explain how a hydrogen-oxygen fuel cell works.
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Include the relevant half-equations.
Hydrogen-Oxygen Fuel Cell
Cathodic Protection
Identify the factors that affect the voltage and power available from a
battery.
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Voltage depends primarily on the nature of the materials used while power depends on their quantity.
Storage of Energy and Limits of Efficiency
Advantages and disadvantages of energy storage schemes.
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Include both pumped storage and conversion to hydrogen.
Electricity
• Main way to produce electricity now is coal.
• Alternative ways to produce electricity:
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Hydroelectric power - (falling water) - it is a
renewable resource and nonpolluting however, dams are
expensive, environmental and political problems.
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Geothermal energy - (heat energy) - it is a
renewable resource however, it is a very limited source,
only used in Ca, and it releases some polluting
chemicals.
Electricity
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3.
Wind Power - It is a primary renewable
resource, however it is unreliable and intermittent.
Can be used as a supplemental energy source for
example to pump water up a hill into a reservoir. Then
use hydroelectric power to produce electricity.
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4.
Tidal Power - (changing tides) - uses
variations in water levels. One in France, 40 feet tides,
twice a day, 5 hours each.
Solar Energy
• Ultimate energy resource is the sun. Problems
include the intermittency of sunlight, available at
high intensity for only 6 to 8 hours a day and only
on sunny days.
• Solar Thermal Energy - collect the rays of the sun
on a solar collector, a black absorbing surface,
where it is transformed into heat energy or
infrared radiation.
Solar Energy
• Photovoltaic Energy Conversion - convert solar energy
directly into electricity without intermediate
conversion to heat. Chief components of the cells are
semiconductors, wafers of silicon with gallium or
arsenic.
• Passive Solar Heating - space heating using solar
collectors is called active solar heating. South facing
windows and skylights fall under passive solar heating.
Natural convection in the home circulates the heat.
Na2SO4•10 H2O; CaCl2•6 H2O - melt and absorbs heat
then gives off heat as it cools.
Solar Energy
• Ocean Thermal Energy Conversion - sun causes
water near the surface of a body of water to be
warmer, it may be possible to take advantage of the
temperature difference to generate electricity. A fluid
(liquid ammonia or propane) circulating in a
conversion system could be alternately vaporized
(absorb) and condensed (give off).
• Solar Power Satellite - a satellite in space that would
collect solar energy. The collecting would be
continuous and at higher intensity.
Energy Storage
• Pumped storage - Uses off-peak electric power for
pumping water uphill to a reservoir so it can be used to
generate hydroelectric power.
• Batteries - electrochemical cells - dry cells -batteries
are used to power flashlights, etc..
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Alkaline battery - zinc-alkaline-manganese dioxide
battery. Major competitor of dry cell.
• Storage Batteries - can be recharged - lead-acid battery.
The Hydrologic Cycle:
Water constantly moves
through a vast global
cycle, in which it
evaporates from lakes and
oceans, forms clouds,
precipitates as rain or
snow, then flows back to
the ocean. The energy of
this water cycle, which is
driven by the sun, it
tapped most efficiently
with hydropower.
The End