Transcript AP EXAM REVIEW

ENERGY EXAM REVIEW
Energy
• Defined as the ability to do work
– Work is force acting across a distance
– Power is the rate at which work is done
– Food energy is measured in calories
• A calorie is the amount of energy that can raise the
temp of 1 gram of water 1°C
• A kilocalorie (Calorie) is 1000 calories
• A Newton is the force needed to accelerate 1kg of mass
1 m/s
Energy Units
• 1 joule (J)= the force exerted by a current of 1 amp per
second flowing through a resistance of 1 ohm
• 1 watt (W)= 1 joule per second
• 1 kilowatt-hour (kWh)= 1000 watts exerted for 1 hour
• 1 megawatt (MW)= 1 million watts 106
• 1 gigawatt (GW)= 1 billion watts 109
• 1 petajoule (PJ)= 947 billion BTU, or 0.278 billion kWh
• 1 British Thermal Unit (BTU)= energy to heat 1lb of
water 1°F
• 1 standard barrel (bbl) of oil= 42 gal (160L) or 5.8 BTU
• 1 metric ton of standard coal= 27.8 million BTU
A little history
• Humans began using domesticated animals more
than 10,000 years ago to assist us with our work
• Wind and water were used to grind grain, cut
timber, and provide other necessary energy
• Steam engine development reduced available
wood supplies and increased the use of caol
• Coal fell into decline when it was discovered that
petroleum could be used for many of the same
applications
• 86% of the world’s energy use is supplied by fossil
fuels
• In the past, developed countries have used far
more energy than developing countries
• With rapid industrialization and economic growth
in China and India, developing countries will
consume a greater proportion of energy that they
have in the past
• Political turmoil in the Middle East has impacted
fuel prices
– OPEC embargo 1973
– Iranian Revolution in 1979
– Plus hurricane Katrina effected prices
World Energy Use
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Oil 40%
Coal 23%
Natural Gas 23%
Nuclear 7%
Renewable 7%
American Energy Use
• Oil 43%
• Vast coal reserves, so we use more coal than
natural gas, even though it is more polluting
• Nuclear power 8%
• Renewable sources 6%
• U.S. is world’s largest oil importer
– We use foreign oil for 75% of our supply
• Canada and Saudi Arabia supply most
U.S. Energy Use
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Industry
Mining and smelting
Chemical energy
Residential and commercial building use ~20%
– Heating, lighting, cooling, and water heating
• Transport 27%
– 98% from petroleum
Net Energy Production
• It takes tremendous amounts of energy to mine
coal and transport the coal to a power plant
• 70% is lost in energy conversion at the power
plant and 10 % more during electrical
transmission
• 75% of the energy lost as petroleum is converted
into fuels, transported, and burned in vehicles
• Natural gas is the greatest efficiency
– Loses about 10% and produces less CO2 than coal or
oil
Coal
• Fossilized remains of ancient plant material
– Formed during the Carboniferous period
• Coal Formation
1. Peat: peat bogs still exist throughout the world
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Burned for fuel
Sedimentary rock
2. Lignite: softest coal, lots of moisture, woody texture,
western US
3. Bituminous coal is the most common, high sulfur
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Greater heat capacity than lignite
Appalachians, Mississippi, Central Texas, Great Lakes
4. Anthracite: greatest heat capacity
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95% carbon, little sulfur; so cleanest burning
metamorphic rock
Pennsylvania
Coal Reserves
• Most abundant fossil fuel
– Proven reserves for 200 years
– Not equal distribution of reserves
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U.S.
Russia
China
India
Australia
Uncommon in Africa, Middle East, Central and South
America
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Coal Mining and Environmental
Damage
TWO major types
– Surface (strip mines)
• Remove overburden, remove coal, overburden fills in new strip
• Mountain top removal in Appalachians
– Places overburden in nearby valleys
– Miners apply for a variance in Surface Mining Control and
Reclamation Act
– Subsurface
• Found primarily in Eastern U.S.
• Bituminous and anthracite coals
• One of most dangerous: toxic gases, explosions, cave-ins
– One mine in China has been burning for 400 years
– One in Pennsylvania has been burning for 40 years
– Mines now have exhaust fans, protective masks
• Mines can strike groundwater and contaminate w/ heavy
metals
Environmental Impact of Mining
• Destroys natural vistas
– Creates unsightly scars on the earth’s surface
• Disturbs habitat for countless species
• Increases erosion
• Contaminate groundwater with acids + heavy
metals
– Iron pyrite frequently found in coal mines in Eastern
US dissolves in water and migrates into streams,
acidifying those ecosystems
• Underground mining creates tailings (lots of solid
waste) with heavy metals present
Coal Combustion
• Emits more CO2 per unit of heat than any other fuel
• Releases SO2 and NOX
– Acid deposition
• Releases more nuclear radiation than any nuclear
power plant
• Fly ash contains heavy metals: arsenic, lead, cadmium,
mercury and zinc
• Responsible for 25% of the mercury released in the US
• Bottom ash must be disposed of in a landfill
• Thermal pollution associated with steam production
used in turbines
Methods to Remove SO2 From Coal
Emissions
• Sulfur dioxide may be reduced precombustion
– Using higher grade of coal (anthracite)
– Washing the coal to remove excess sulfur
– Convert coal to gas (coal gasification) or oil (coal liquefaction
• Sulfur dioxide may be reduced during combustion
– Using fluidized bed combustion by burning the crushed coal with
crushed limestone
• Sulfur combines with the calcium to form calcium sulfate or gypsum
• Post combustion methods include
– Using catalytic converters to oxidize the sulfur to yield sulfur
compounds
– Lime scrubber in a smokestack may also be used
– Wet scrubber: slurry of lime mixed with water is sprayed across the
exiting gases, sulfur mixes with the calcium forming the calcium
sulfate, which falls to the bottom of the smokestack as bottom ash
Methods to Remove Particulates from
Coal Emissions
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By burning coal with a low ash content
Most removal is post combustion
Resultant particle mixture is often hazardous waste
Bag filters are a series of bags, (like a vacuum) which catch
the particulates as they rise in the smoke
– Bags are periodically emptied of their ash
• Electrostatic precipitators remove 99%
– Pass coal emissions past a series of charged plate, charging the
particulates, which then bind to an oppositely charged plate
• Cyclone collectors create a vortex in a smokestack
– Causing the particles to collide and fall to the bottom of the
stack as bottom ash
Natural Gas and Natural Gas Reserves
• 90% of gas in natural gas is Methane
– Followed by propane, ethane, and butane
• Cleanest burning fuel
• Highest net energy value
• NG pipelines run throughout U.S.
– Abundant reserves
– NG is cooled and compressed until it becomes a liquid
(LNG) for transport
– LNG is used in rural U.S. areas
– Russia has more than 30% of known reserves
– Middle East has 36% of reserves
Hydrogen gas
Hydrogen is clean and can be burned like fossil fuels.
(a) Fuel cell works like battery to generate electricity by oxidizing H2
and capturing e− (electrons) in external circuit (redox). Increase
second-law efficiency.
(b) Most economical way to produce hydrogen: H2O+CH4 ! C+CO2+
H2.
(c) Can be burned to heat water into steam.
Unconventional Methane Stores
• Methane can be found frozen in ice as methane
hydrate
– Can be removed by dissolving the ice in methanol
– Methane in the ice sheets will be released with global
warming
• Methane found with coal deposits
– Close to surface, making extraction feasible
– Under groundwater which would need to be extracted
first.
– The water is contaminated with salts and minerals
– The withdrawal is drying local wells
– Livestock and wildlife are being killed by traffic and waste
left around the drill sites
Nuclear Power
• U.S. has never had an accident where
significant amount of radiation was released
• Twice as expensive as coal
• 103 reactors in 31 states produce 20% of
nations electricity
• Obama has renewed interest in nuclear
Nuclear Fuel Enrichment
• U.S. has 22% of known Uranium reserves
– Australia has 26%
• Uranium must be mined
– Normally from sedimentary rock
– Mine tailings are radioactive
– Workers are susceptible to lung cancer from radon
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238U
(99.28% of ore); 235U (0.71%); 234U (0.01%)
235U is the desired isotope; so it is concentrated to 3%
or greater
Nuclear
• Pellets shape of pencil and roughly one-inch
long
– Placed in thin metal closed pipes ~12-16 feet long
called fuel rods; then clustered in groups of 100200 called fuel assemblies; 250 assemblies in
small reactor and 3,000 in large reactor
• Equivalent of one ton of coal or four barrels of
crude oil
Nuclear Fission
• Is the splitting of an atom to release energy and
particles
• In a reactor, neutron hits atom, splits atom into two
smaller nonfissionable nuclei, releasing energy and
more neutrons, continuing the reaction
• Fuel rods are replaced when spent
– 1/3rd at a time
• Moderators needed with the rapidly moving neutrons
attracted by 238U, 235U are more likely to be struck by
slow moving neutrons; so graphite, beryllium, H2O
(light water), or D20 (heavy water) is needed
• Moderators slow rapidly moving electrons, which
makes it more likely they will strike the 235U
Nuclear Fission Waste
Radioactive wastes
(a) Low-level wastes in not hazardous if properly disposed. Residues, solutions, sludges, acids,
slightly contaminated equipment. 3/6 sites closed because they have polluted groundwater.
(b) Transuranic waste is human-made materials heavier than U. Mostly made from weapons.
(c) High-level wastes is spent fuel (for energy such as power plants), military reprocessing waste,
weapons materials.
• Currently stored, mostly at commercial reactors.
• Geological disposal controversial; some don't think it should be
• buried.
• Nuclear Waste Policy Act of 1982 initiate disposal program.
A. 1987 amendment and Energy Power Act of 1992 specify deep underground
repository:
• Yucca Mountain BUT this was stopped due to political controversy .
• Waste isolation pilot plant in Carlsbad, New Mexico:
 Rooms excavated in rock salt (easy to mine) store wastes.
 Slow-owing salt naturally seal in 75200 years.
 Sites that have been stable in past may not be stable in future.
 Nearby citizens are in favor of plant due to increased jobs and economical
benefit.
Forms of Solar Power
1. Passive solar energy uses architecture to adjust to seasonal changes.
(a) South-facing building and windows and overhangs shade summer sun but allow winter sun to
penetrate.
(b) Walls can absorb energy then radiate into rooms.
(c) Deciduous trees block sun during summer but allow sun during winter.
Forms of Solar Power
12. Active solar energy requires mechanical power to circulate a fluid from solar collection site to usage site.
(a) Solar collectors have a glass plate and black background with tubes in between. Water heated to 3898C.
(b) Evacuated tube collector has each tube pass through a larger tube to reduce heat loss.
Forms of Solar Power
3. Photovoltaics are the fastest-growing source of energy at 35% annually.
(a) Standardized modules; build the system you need.
(b) Different electronic properties of semiconductor layers cause electrons to flow into wires when hit by
photons.
(c) Developing countries: cheap, simple, off grid rural electricity.
Forms of Solar Power
4. Power tower concentrates sunlight to a central collector to boil water.
Biofuels
Biofuels are organic matter, burned or converted (gasify, distill), then
burned.
(a) 35% of developing countries usually wood.
(b) Digestion bacteria digest matter to produce methane.
(c) Landlls, wastewater treatment plant can produce biogas (mainly
methane).
China, produced in sewage treatment.
India, produced locally from cow manure.
(d) Waste incineration releases pollutants, as not all hazardous trash
can always be removed.
(e) Land unsuited for food crop can grow biomass crop (like trees).
(f) By 2030, biomass can produce 100,000 MW (12%), using 2/5 of
banked farmland.
Wind power
(a) Winds are produced by differential heating of Earth's surface,
resulting in air masses with different heat and density.
Wind concentrated on mountain top or mountain pass.
(b) Small mills (for farm) produce 1 kW. Modern windmills 6075
kW.
High-tech ones 100 m, 30 stories, 35 MW. One is in Germany.
(c) Wind power currently cheaper than natural gas, approaching
coal.
(d) World total 48,000 MW (34,000 MW in E.U.).
1 large fossil or nuclear = 1,000 MW.
1% of total electricity used in the world
(e) High potential - many countries have more potential than
current use.
Geothermal
Geothermal energy harnesses natural heat from earth's interior.
(a) 9,000 MW0.15%.
(b) Competitive with other sources.
(c) At plate boundaries, heat flow is unusually high.
(d) Hot geothermal system (> 80C) resource base > fossil +
nuclear. A lot of energy!
Hydrothermal convection:
(a) Geysers Geothermal Field produce 1,000; near San Francisco.
(b) Lower temperature systems can be used for heating.
Groundwater is geothermal: at 100 m, groundwater is 13C and
can heat/cool homes.
Environmental impact
Releases some CO2, SO2. Thermal pollution. Hot wastewater
can be corrosive and saline.