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Harnessing Geothermal Resources

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Harnessing Geothermal Resources Hot Water Reservoirs Natural Steam reservoirs Geopressured Reservoirs Normal Geothermal Gradient Hot Dry Rock Molten Magma – PowerPoint PPT presentation

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Title: Harnessing Geothermal Resources


1
Harnessing Geothermal Resources
  • Hot Water Reservoirs
  • Natural Steam reservoirs
  • Geopressured Reservoirs
  • Normal Geothermal Gradient
  • Hot Dry Rock
  • Molten Magma

2
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.

3
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

4
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

5
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

6
US Geothermal Resources
7
Advantages
  • Geothermal power requires no fuel, is emissions
    free and is not susceptible to fluctuations in
    fuel cost.
  • geothermal power stations 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

8
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

9
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.

10
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

11
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.

12
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.

13
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)

14
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

15
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

16
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.

17
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.

18
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?

19
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

20
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

21
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
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