Energy Resources

From GeoClasses

Energy Resources

US energy flow diagram, 2004

• 90% energy used in US comes from fossil fuels (coal, natural gas, petroleum, oil)
  • coal is still widely available, but very dirty; the rest are diminishing

• 10% remaining energy almost all hydropower or nuclear
  • hydropower is exhausted, no more room on rivers; nuclear is undersirable

• other options - solar, wind

Some energy concepts:

chart showing GDP versus energy consumption per capita

• 1. conservation = use less by changing habits
• 2. efficiency = better equipment that uses less energy
• 3. cogeneration = reuse wasted heat from energy plants

• Case Study: energy in the UK

• Which nations look like they are utilizing these techniques? Are they really?

Japan's energy consumption versus GDP growth since 1958

Fossil Fuels

Where do they come from?

1. coal

sources and types of coal in the US

legend for US coal map

• altered remains of plants that grew in freshwater or swamps (coastal regions)
  • buried without being oxidized, first makes peat, then is covered and squeezed by pressure of rock on top to make rock called coal

• classified by S content and C content
  • lignite - subbituminous - bituminous - anthracite
  • listed from lowest C to highest C (thus heat content and quality)
  • but lowest S content (least polluting) - subbituminous found W of Mississippi River

bituminous coal

anthracite coal

• coal acquired by strip mining (open pit)
  • commonly mined today in Appalachian Mountains - by mountain top removal
    • mined from the top and waste deposited in valleys in coal-waste sludge dams

mountaintop removal at Kayford Mountain, WV

open pit mining in Wyoming

strip mining lignite coal in Germany

coal sludge

• coal reserves are relatively abundant but nonrenewable
• US production of coal = 1 billion metric tons/year
  • global production = 5 billion metric tons/year

impact of coal mining:

acid mine drainage in the Tinto River

• if humid/wet climate, acid mine drainage is major problem
  • water reacts with sulfide minerals in mine waste to make H2SO4 that runs into streams and lakes
  • can be mininized by being careful with waste treatment - but cannot remove the problem
• if arid or semiarid, problem is in land sensitivity
  • road scars, poor soils make reclaiming land over mines very difficult

• reclaiming land:
  • before mining, topsoil is removed and saved, then replaced after mining
  • drainage should be improved and vegetation regrown on top

environmental impact:

• unlike oil and gas, coal leaves ash (5-20% of original volume), which is disposed of in landfills
• every step from mining to processing to disposing of waste creates pollution (air and water)
• burning coal produces large amounts of CO2 (greenhouse gas)

2. hydrocarbons (oil and gas)

Jupiter's atmosphere is almost entirely methane and ethane

• made of H, C, O
• natural gas = CH4 mostly (also ethane, propane, butane, hydrogen)
• usually extracted by wells driven into the right rock layers

• hydrocarbons formed when organic material is buried in oceans or freshwater lakes without being oxidized
  • burial creates high T, P conditions (compression) that converts chemicals in source rocks (fine grained, organic rich)
  • oil and gas then migrate through pore spaces into reservoir rock (sandstone or fractured limestone)
  • if pathway goes all the way to surface, then hydrocarbons leak out
  • but if layer of reservoir rock is capped by impermeable layer (clay) called cap rock and if the shape is right to trap hydrocarbons (such as a dome), then it can be extracted by wells

• oil and gas extracted 2 ways:
  • 1. primary recovery - using natural overpressure in pore space of reservoir to push oil and gas into well to be pumped up
  • 2. enhanced recovery - pumping chemicals (gas, water, steam or other chemicals) into reservoir to artificially raise pore pressure

oil well in Texas, used for primary recovery

offshore drilling rig in the Gulf of Mexico

• • • always pumps up dirty water as well, which has to be removed and disposed (either injection back to subsurface in or out of reservoir, or evaporated in lined pits)

• limitations of oil reservoirs
  • only found in sedimentary rocks younger than 500 my
  • most oil fields do not produce very much (85% of oil comes from 5% of fields)
  • reservoirs are usually located near plate junctions that were active within last 70 my

• supply and demand
• US imports most of its oil from Venezuela, Canada, and Mexico
  • Middle East supplies mainly Europe, Japan, SE Asia

natural gas is cleaner than oil or coal

• types of natural gas:
  • coal bed CH4
    • found on surfaces of organic matter in the coal
    • accessed by shallow wells
    • disadvantages: salty water is produced with the CH4 and must be disposed
    • must also also mine groundwater for CH4 extraction
    • migrating CH4 away from well is hazardous (flammable)

"flaring" - the burning of waste natural gas at an oil refinery

CH4 hydrates

methane clathrate (or methane hydrate): methane trapped in frozen water can be burned off from the ice

• exist at 1000m below sealevel
• hydrate is white, ice-like compound made of CH4 bubbles surrounded by frozen water that are formed by microbial digestion of organic matter in seafloor sediments
• also formed on land in permafrost in Siberia and N America - called marsh gas

map showing distribution of gas hydrates globally

• disadvantages: how do you catch it?
• hydrates can exist down into ocean sediment >1 km deep
• when lifted to 500 m they decompose and bubble away
• CH4 is strong greenhouse gas so an accident releasing lots of CH4 would be impossible to clean

greenhouse gas emissions and sources

Hubbert peak production curve estimates for nations

• the question is not "how long will oil reserves last", but "when will we reach peak production"
  • because after that, production decreases and experience shortages/price shocks
  • will likely reach peak production within our lifetime

pollution issues:

dissolution of a 100 year old limestone gravestone by acid rain

• acid rain - created by burning fossil fuels - includes both wet and dry
  • wet = SO2, No2 that react with water vapor in atmosphere and make H2SO4 or HNO3 acids
  • dry = particles fall to surface then react with water to make acids
• acid rain pH < 5.6

Nuclear Energy

cartoon showing nuclear fission

• fission - splitting nucleus of atom by neutron bombardment
  • creates more neutrons and heat and waste (smaller molecules)
  • if uncontrolled fission = nuclear weapons
    • if stable or sustained = nuclear reactor to make heat to make electricity
  • 1 kg uranium releases equal energy to 16 metric tons of coal

the bombing of Nagasaki, Japan on Aug. 9, 1945 - the mushroom cloud rose 11 miles into the atmosphere

cartoon of a chain reaction during fission

• 235U (only 0.7% of all U on Earth) is only fissionable form of U
  • can process other isotopes of U to make up to 3% 235U - called enriched U
• 238U can be bombarded to make 239Plutonium - which is fissionable

• U comes from magma but must be found in 400-2500X the natural concentration to be mined for profit
  • uranium mining in the US
  • lately found in U rich sandstones, veins in fractured rocks, and very old (2.2 by) placer deposits = coarse grained sedimentary rocks

Reactors to make energy

The Susquehanna Steam Electric Station. The nuclear reactors are contained inside the rectangular containment buildings towards the front of the cooling towers. The towers in the background vent water vapor

• most reactors are burner reactors = burn more than produced
  • they heat steam to run turbines to produce electricity
• core of reactor where chain reaction occurs (heavy stainless steel) inside a reinforced concrete building
• stable reaction maintained by controlling fuel concentration and the number of neutrons
  • neutrons controlled by control rods that capture neutrons to prevent uncontrolled explosion (put them in to slow down reaction, take them out to speed up reaction)

nuclear fuel pellets

control rods used to control neutron bombardment in nuclear power plant

looking down into the reactor at Pulstar Nuclear Reactor, North Carolina

• coolant water is pumped through reactor to extract heat produced (if not removed then meltdown)
  • hot coolant then used to make steam for turbines

pros:

• nuclear power could be used to produce H for fuel from H2O or CH4

cons:

• 235U supply is very limited
• current reactors only use 1% of U - rest is waste
• (need a different kind of reactor called breeder reactor that takes 99% waste to make new nuclear fuel (239Pl)
• accidents - 3 miles Island (Harrisburg, PA), Chernobyl

high level radioactive waste being transported to disposal site in reinforced containers

Three Mile Island Nuclear Power Station: reactor TMI-2 (in the background) suffered a partial meltdown in 1979

Pripyat, Ukraine - an abandoned city near the Chernobyl nuclear power plant

Must also talk about radioactive waste management (safe disposal):

Removal of 1500 cubic yards of soil contaminated with extremely low levels of nuclear waste from the former Fort Greely Nuclear Power Plant. Fort Greely, Alaska.

• 1. low level radioactive waste - only small amount of radioactivity
  • includes solutions from chemical processing, sludge, acids, contaminated equipment
  • to dispose - liquids must be solidified with material that will absorb 2X volume of liquid
  • radioactive decay of this waste does not produce much heat - so must be isolated for 500 yrs from environment (usually is buried)

permanent storage of transuranic waste in the US

• 2. transuranic waste - made of manmade elements heavier than U
  • includes contaminated industrial waste (equipment) mostly from nuclear weapons or cleanup operations (ex: Oak Ridge, TN)
  • Plutonium has long 1/2 life (decay time)
  • needs to be isolated 250,000 years
  • stored currently in Carlsbad NM in salt deposits
    • old, very stable region, easy to mine salt to make space for waste, then salt slowly flows back in to seal waste after 100-200 yrs

Yucca Mountain, site of high level nuclear waste disposal site in US

entering the north portal of the Yucca Mountain Nuclear Waste Disposal site

• 3. high level radioactive waste - equipment from power plants that clogs with large amounts of waste
  • equipment must be removed and reused or disposed of (but reuse is expensive and not done)
  • waste includes Krypton-85, Strontium-90, Cesium-137
    • each element has different 1/2 life, and at least 10 1/2 lives must pass before waste is considered safe for environment
    • if mixed waste, then takes 100s of yrs
    • compare to Plutonium-239 - 1/2 life 24,000 yrs - how do you safely contain for 1/4 million yrs?
  • Yucca Mountain is current new disposal site
    • rock is tuff (compacted volcanic ash), very dry climate, water table is very deep
    • but no knowing what might happen geologically 1000s of yrs in future

map of nuclear waste disposal sites in the US

Geothermal Energy

Krafla Geothermal Station in Iceland

• natural heat surfacing from Earth's interior
• ex: Hawaii, Yellowstone, Hot Springs
• vast resource but relatively untapped

• heat sources usually near convergent/divergent margins associated with volcanism
  • 1. hydrothermal convection - hot water circulates naturally through rocks
    • if tapped then hot water and steam piped into turbines to make electricity (but water must be separated from steam, only steam useful)
  • 2. groundwater system - in use in eastern US and midwest
    • where groundwater temp. 13 degrees C - it is hotter than winter air temp. and colder than summer air temp.
    • can transfer heat from air in building to/from groundwater

pros:

• less pollution
• on-site so no need to transport

cons:

• noisy
• initially expensive
• leaves scars on land and makes thermal pollution in waste water
• can create subsidence by cooling when remove the hot water
• if re-injecting waste water may reactivate old faults so cannot be used near National Parks because it destroys geysers

renewable energy: including solar and wind power

• does not create any greenhouse gases
• no pollution and renewable (obviously)
• no fuel burned in process
• faster to develop than building new power plants

1. solar power:

• passive system - involves changing architecture to prevent heating in summer and enhance heating in winter
• active system - requires mechanical system (pumps) to circulate air or water from solar collector to heat sink where it can be used
  • collectors - glass plate over black background with water circulating through tubes in black part (water is heated) - can be used on individual houses/buildings
  • photovoltaics - uses semiconductors to directly convert sunlight to energy (ex: solar cars)
    • no mechanics, just electricity, so can plug in directly
    • ex: currently done by Luz International in Mojave Desert
    • but to make large amount of energy must have large area of land for solar cells

photovoltaic cell used to convert the sun's energy to power

experimental solar power plant in the Mojave Desert

2. fuel cells:

diagram of how a fuel cell works

• similar to battery but produces electricity from H
• combustion product is H2O - no pollution

3. hydroelectric power:

Hoover Dam, one of the most famous hydroelectric dams

• running water turns turbines
• always associated with dams because you can control flow rate of water through dam
• capacity in US maxed out - no more areas to build new dams
• no fuel burned
• but environmental risks - kills fish in river (elevate N2 in water, prevents fish from reaching spawning grounds upriver)

4. wind power:

From Wikipedia: "Danish wind turbines near Copenhagen. Wind often flows briskly and smoothly over water since there are no obstructions. The large and slow turning turbines of this offshore wind farm near Copenhagen take advantage of the moderate yet constant breezes at this location. While the wind at this location is not strong it is very consistant, with the turbines generating substantial power over 97 percent of the time."

potential wind power in the US (darker blue colors indicate greater power available)

• wind farms = groups of windmills
• can only build in places where climate is right (lots of wind)
• no pollution
• estimated that TX, SD, ND have enough wind combined if harvested to supply entire US

5. biomass fuel:

sugar cane can be used as a biomass fuel

• organic matter that can be burned
• ex: CH4 from manure