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
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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 • 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 • 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 • Peat: peat bogs still exist throughout the world • Burned for fuel • Sedimentary rock • Lignite: softest coal, lots of moisture, woody texture, western US • Bituminous coal is the most common, high sulfur • Greater heat capacity than lignite • Appalachians, Mississippi, Central Texas, Great Lakes • Anthracite: greatest heat capacity • 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 • U.S. • Russia • China • India • Australia • Uncommon in Africa, Middle East, Central and South America
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 • 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 • Three isotopes • 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 100-200 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. Photovoltaicsare 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.