Geothermal Energy

1
Geothermal Energy

• Based on the heat that naturally occurs in the
  Earths interior
• Sine the Earths interior is hotter than the
  surface, this heat flows form the interior
  towards the surface.
• Heat is the result of decay of radioactive nuclei
  inside the Earth, heat left over from the
  formation of the Earth and heat from the friction
  of heavier material sinking towards the center.
• Earths core temperature is 7200 F, which is
  close to the temperature on the Suns surface.

2
Radioactive Decay

• the process in which an unstable atomic nucleus
  loses energy by emitting ionizing particles and
  radiation.
• Most important source of heat inside the earth
• loss of energy results in an atom of one type
  (parent nuclide) transforming to an atom of a
  different type, (daughter nuclide).
• Eg a carbon-14 atom (the "parent") emits
  radiation and transforms to a nitrogen-14 atom
  (the "daughter").
• This is a random process on the atomic level, in
  that it is impossible to predict when a given
  atom will decay, but given a large number of
  similar atoms the decay rate, on average, is
  predictable.

3
Geothermal

• Not a new idea
• Used the heat from inside the Earth for thousands
  of years for bathing (hot springs) and space
  heating.
• First electric power use was by Prince Piero
  Ginori Conti tested the first geothermal power
  generator on 4 July 1904 in Larderello, Italy.
• In 1958 New Zealand built a plant of its own.
• First geothermal power plant in the United States
  was made in 1922 by John D. Grant at The Geysers
  Resort Hotel.
• In 1960, Pacific Gas and Electric began operation
  of the first successful geothermal power plant in
  the United States at The Geysers. The original
  turbine installed lasted for more than 30 years
  and produced 11 MW net power.

4
The Geysers

• The Geysers is a geothermal power field located
  72 miles (116 km) north of San Francisco,
  California.
• It is the largest geothermal development in the
  world.
• It is currently outputting over 750 MW. It
  consists of 22 separate power plants that utilize
  steam from more than 350 producing wells.

5
Harnessing Geothermal Resources

• Hot Water Reservoirs
• Natural Steam reservoirs
• Geopressured Reservoirs
• Normal Geothermal Gradient
• Hot Dry Rock
• Molten Magma

6
Hot Water reservoirs

• Heated underground reservoirs
• Used for heating buildings, raising plants in
  greenhouses, drying crops, heating water for fish
  farms, or for industrial processes.
• Example of a direct use system
• a well is drilled into a geothermal reservoir to
  provide a steady stream of hot water.
• The water is brought up through the well, piping,
  a heat exchanger, and controls delivers the heat
  directly for its intended use.
• A disposal system then either injects the cooled
  water underground or disposes of it in a surface
  storage pond.

7
Natural Steam Reservoirs

• Sources of natural steam, like the geysers
  previously discussed, used to drive a turbine.
• Hydrothermal reservoirs consist of a heat source
  covered by a permeable formation through which
  water circulates.
• Steam is produced when hot water boils
  underground and some of the steam escapes to the
  surface under pressure.
• Once at the surface, impurities and tiny rock
  particles are removed, and the steam is piped
  directly to the electrical generating station

8
Geopressurized reservoirs

• Geopressurized reservoirs are sedimentary
  formations containing hot water (brine-water
  saturated with salt) and methane gas.
• Could be a source of both power and natural gas

9
Normal geothermal gradient/Hot Dry Rock

• Natural geothermal gradient of about 30/km
  exists.
• A geothermal heat pump system consists of pipes
  buried in the shallow ground near a building, a
  heat exchanger, and ductwork into the building.
• In winter, heat from the relatively warmer ground
  goes through the heat exchanger into the house.
• In summer, hot air from the house is pulled
  through the heat exchanger into the relatively
  cooler ground. Heat removed can be used as
  no-cost energy to heat water.
• Variation Direct exchange geothermal heat pump
  A heat pump without a heat exchanger, which
  circulates the working fluid through pipes in the
  ground.
• Hot Dry rock is the same idea, but in certain
  locations the gradient is much higher

10
US Geothermal Resources
11
Advantages

• Geothermal power requires no fuel and is
  emissions free and is not susceptible to
  fluctuations in fuel cost.
• geothermal power station dont rely on transient
  sources of energy (wind, sun)
• It is considered to be sustainable because the
  heat extraction is small compared to the size of
  the heat reservoir.
• individual wells may need to recover, geothermal
  heat is inexhaustible and is replenished from
  greater depths. The long-term sustainability of
  geothermal energy production has been
  demonstrated at the Lardarello field in Italy
  since 1913, at the Wairakei field in New Zealand
  since 1958, and at The Geysers field in
  California since 1960.
• However, there has been a decrease in output
  noted at The Geysers
• Geothermal has minimal land use requirements

12
Disadvantages

• The geothermal fluid is corrosive and, worse, is
  at a low temperature compared to steam from
  boilers, this limits the efficiency of heat
  engines in extracting useful energy during the
  generation of electricity. Much of the heat
  energy is lost, but could be used for
  co-generation purposes
• Construction of the power plants can adversely
  affect land stability in the surrounding region.
  This is mainly a concern with Enhanced Geothermal
  Systems, where water is injected into hot dry
  rock where no water was before.
• Dry steam and flash steam power plants also emit
  low levels of carbon dioxide, nitric oxide, and
  sulphur, although at roughly 5 of the levels
  emitted by fossil fuel power plants. However,
  geothermal plants can be built with
  emissions-controlling systems that can inject
  these substances back into the earth, thereby
  reducing carbon emissions to less than 0.1 of
  those from fossil fuel power plants.
• Hot water from geothermal sources will contain
  trace amounts of dangerous elements such as
  mercury, arsenic, and antimony which, if disposed
  of into rivers, can render their water unsafe to
  drink.
• Locations may eventually cool down

13
Biomass

• Plant matter grown to generate electricity or
  produce biofuel
• Examples trash such as dead trees and branches,
  yard clippings and wood chips, plant or animal
  matter used for production of fibers, chemicals
  or heat.
• Biomass may also include biodegradable wastes
  that can be burnt as fuel.
• It excludes organic material which has been
  transformed by geological processes into
  substances such as coal or petroleum.

14
Energy from Biomass

• Comes initially from the sun
• Solar energy is stored as chemical energy in the
  plants
• This chemical energy is released when the biomass
  is burned or converted to another fuel that is
  burned.
• Process starts with the conversion of sunlight to
  chemical energy in the plant we call this
  photosynthesis

15
Review of Photosynthesis

• Plant takes in water and carbon dioxide. The
  energy in visible light excites atoms in the
  water and carbon dioxide which allows bonding to
  take place. As a result, compounds with hydrogen,
  carbon and oxygen are formed (called
  carbohydrates), along with oxygen and water.
• The simplest carbohydrate formed is sugar, and
  these compounds are the plants fuel.

16
Biomass

• About 30 of the energy in the incident sunlight
  is stored in biomass.
• Not a new idea, remember way back in the semester
  when we looked at sources of energy production in
  the US? Wood was a primary source of energy until
  1880.
• If you look at the average crop yield for all the
  harvested land in the US, you find that nearly
  all our energy needs could be furnished from
  biomass.

17
Municipal Waste

• Our solid waste (garbage) needs a home-we
  normally put it in a landfill (polite name for a
  dump!)
• Landfill sites are diminishing for a variety of
  reasons, but our waste production is increasing.
• Unfriendly to the environment
• Can contaminate groundwater
• Nasty smell
• Harbor diseases and disease carrying rodents
• Can contain toxic chemicals
• Emit methane (produced in the decay of organic
  materials and is not only toxic, but a greenhouse
  gas)

18
Municipal waste

• This waste has energy stored in it, which can be
  released of the waste is burned.
• Energy produced is modest, but this solves
  another environmental problem.
• Plants are expensive to construct and maintain,
  most cities do not have the money to get one
  started. Rely on private investors or companies

19
Creating Fuel from Biomass

• Ethanol common form of alcohol, it is an
  oxygenated hydrocarbon (a hydrocarbon with oxygen
  added).
• Also known as ethyl alcohol, pure alcohol, grain
  alcohol, or drinking alcohol,
• volatile, flammable, colorless liquid.
• type of alcohol found in alcoholic beverages and
  in modern thermometers.
• Fermentation of sugar to ethanol is one of the
  earliest organic reactions employed by humanity

20
Ethanol

• Usually produced from corn, though other grains
  can be used. (Brazil is a major user of Ethanol,
  and uses sugar cane to produce their ethanol)
• Entire plant is ground up and mixed with water.
• Cooked to convert starch to sugars via enzymatic
  action.
• Sugars are converted to alcohol via fermentation.
• Distillation removes the rest of the material
  from the alcohol.

21
Ethanol as a Fuel additive

• Ethanol increases the oxygen content of gasoline,
  and leads to more complete combustion and reduces
  CO2 emissions.
• Mixtures are defined by E, where is the
  percent of ethanol in the fuel.
• So E100 is 100 ethanol
• E10 (10 ethanol) is a particular type of mixture
  called gashol.
• Current gasoline engines cannot run on pure
  ethanol since to maximize its energy conversion
  efficiency, higher compression ratios are needed,
  which wont work for gasoline engines.

22
Debate rages

• Will it really solve all our problems?
• Is it cheaper?
• Is it cost effective?
• What about the issue of using a food source
  (corn) for fuel?

23
Methane from Biomass

• Methane makes up 85 of the natural gas extracted
  from the ground.
• In the presence of water and absence of oxygen,
  organic material will ferment naturally.
• Such organic materials include
• Crops
• Agricultural waste (animal or vegetable)
• Waste from lumber mills
• waste from breweries
• Algae
• Sludge from sewage treatment plants
• Municipal waste
• Fermentation by bacteria in the absence of oxygen
  is called anaerobic fermentation

24
Methane from Biomass

• Same heating value as natural gas
• High conversion efficiency(50-70 of the useful
  energy is converted)
• High cost
• Useful in systems that can generate their own
  power - for example sewage plants

25
Biodiesel

• Diesel fuel made from vegetable oil, recycled
  cooking grease or oil and animal fat
• Used as a fuel additive, designate the same way
  we designate ethanol fuels-i.e B where is the
  amount of biodiesel in the diesel fuel.
• B20 widely used in trucks and school buses