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Geothermal Energy

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Geothermal plants do not require a lot of land, 400m2 can produce a gigawatt of energy over 30 years. Availability of Geothermal Energy On average, ... – PowerPoint PPT presentation

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Title: Geothermal Energy


1
Geothermal Energy
2
What is Geothermal Energy?
  • Geo (Greek) earth

Thermal - relating to, using, producing, or
caused by heat.
3
Sources of Earths Internal Energy
  • 70 comes from the decay of radioactive nuclei
    with long half lives that are embedded within the
    Earth
  • Some energy is from residual heat left over from
    Earths formation.
  • Friction of tectonic plates
  • The rest of the energy comes from meteorite
    impacts.

4
The Earth
  • Heat can be ejected as steam or hot water.
  • Hydrothermal reservoirs, water and hot porous
    rock. (aquifer)

It is around 4000-6000oCelsius at centre of the
Earth In general, the temperature rises one
degree Celsius for every 36 metres you go down.
5
Where is Geothermal Energy?
  • Heat generated by natural processes occurring
    within the earth
  • Hot springs, geysers and mud pots are natural
    phenomena that result from geothermal activity

6
Different Geothermal Energy Sources
  • Hot Water Reservoirs As the name implies these
    are reservoirs of hot underground water. There
    is a large amount of them in the US, but they are
    more suited for space heating than for
    electricity production.
  • Natural Steam Reservoirs In this case the
    underground water changes to steam.
  • Hot Dry Rock This type of condition exists in
    5 of the US. It is similar to Normal Geothermal
    Gradient, but the gradient is 400C/km dug
    underground.
  • Molten Magma No technology exists to tap into
    the heat reserves stored in magma. The best
    sources for this in the US are in Alaska and
    Hawaii.

7
Where Can Geothermal Energy be Harnessed?
  • Technology today allows for small scale
    harnessing everywhere
  • Heat pumps (for shallow geothermal energy)
  • Different areas have different thermal gradients
    and thus different utilization potentials
  • Higher thermal gradients correspond to areas
    containing more geothermal energy

8
High Temperature Systems
  • These areas are associated with the Ring of
    Fire volcanic activities around the Pacific Rim
    Basin

9
High Temperature Surface Geothermal Systems
  • There are three different types of surface
    geothermal system designs
  • 1. Dry-steam Power Plant
  • 2. Flash-steam Power Plant
  • 3. Binary-cycle Power Plant

10
Direct Use of Steam
  • Conventional geothermal plants capture hot water
    from geysers or steam from vents to spin turbines.

11
Dry-steam Geothermal Power Plant
  • Steam passes through turbine
  • 1050 -1220 degrees F

12
Dry-steam Geothermal Power Plant
  • These were the first type of plants created.
    They use underground steam to directly turn the
    turbines. Generation of Electricity is
    appropriate for sources gt150oC .
  • Vapor dominated resources where steam production
    is not contaminated
  • Steam is 1050F - 1220 F
  • Steam passes through turbine
  • Steam expands
  • Blades and shaft rotate and generate power
  • Cooling towers generate waste heat
  • Most common and most commercially attractive
    (Godfrey Boyle)
  • Used in areas where geysers do not exist
  • Need water to inject down into rock
  • Well is deep
  • Takes more time to inject water in well

13
Flash-steam Geothermal Power Plant
  • Hot, High pressure water
  • Turbines generate electricity
  • Costs 4-6 cents per Kwh.

14
Flash-steam Geothermal Power Plant
These are the most common plants. These systems
pull deep, high pressured hot water that reaches
temperatures of 3600F or more to the surface.
This water is transported to low pressure
chambers, and the resulting steam drives the
turbines. The remaining water and steam are then
injected back into the source from which they
were taken. Use very hot (more than 300 F)
steam and hot water resources Steam either comes
directly from the resource, or the very hot,
high-pressure water is depressurized ("flashed")
to produce steam. Steam then turns turbines,
which drive generators that generate electricity.
Only significant emission from these plants is
steam (water vapor). Minute amounts of carbon
dioxide, nitric oxide, and sulfur are emitted,
but almost 50 times less than at traditional,
fossil-fuel power plants. The flash steam power
plant uses hot water reservoirs as a source of
power. When the hot water comes up from the earth
into the flash tank, there is a drop in pressure
which causes some of the water to turn into
steam. This steam is then used to spin the
turbine much like in the Dry Steam power plant.
The water is then returned to the earth to be
used again later. This is the most used type of
geothermic power plant since there are a lot of
hot water reservoirs.
15
Binary-cycle Geothermal Power Plant
  • Hot water (100 300 deg F)
  • Heat Exchanger
  • Binary liquid lower specific heat (vaporizes)

16
Binary-cycle Geothermal Power Plant
This system passes moderately hot geothermal
water past a liquid, usually an organic fluid,
that has a lower boiling point. The resulting
steam from the organic liquid drives the
turbines. This process does not produce any
emissions and the water temperature needed for
the water is lower than that needed in the Flash
Steam Plants (2500F 3600F). Uses
lower-temperatures, but much more common, hot
water resources (100 F 300 F). Hot water is
passed through a heat exchanger in conjunction
with a secondary (hence, "binary plant") fluid
with a lower boiling point (usually a hydrocarbon
such as isobutane or isopentane). Secondary
fluid vaporizes, which turns the turbines, which
drive the generators. Remaining secondary fluid
is simply recycled through the heat exchanger.
Geothermal fluid is condensed and returned to
the reservoir. Binary plants use a
self-contained cycle, nothing is emitted. Energy
produced by binary plants currently costs about 5
to 8 cents per kWh. Lower-temperature reservoirs
are far more common, which makes binary plants
more prevalent.
17
Limitations of Surface Geothermal Power Plant
  • Dependent on location.
  • Most viable sites have been tapped.
  • Not as efficient as coal fired power plant.

18
Geothermal Power from Hot Dry Rocks
The simplest models have one injection well and
two production wells. Pressurized cold water is
sent down the injection well where the hot rocks
heat the water up. Then pressurized water of
temperatures greater than 2000F is brought to the
surface and passed near a liquid with a lower
boiling temperature, such as an organic liquid
like butane. The ensuing steam turns the
turbines. Then, the cool water is again injected
to be heated. This system does not produce any
emissions. US geothermal industries are making
plans to commercialize this new technology.
19
How Energy is extracted from Hot Dry Rocks
  • Direct Sources function by sending water down a
    well to be heated by the Earths warmth.
  • Then a heat pump is used to take the heat from
    the underground water to the substance
  • Then after the water it is cooled is injected
    back into the Earth.

20
Overview of Geothermal systems
1960s
1980s
1900s
Flash Systems 1) Single-Flash vs. Dual-Flash
Systems 2) Combined Cycle Systems 180 C
Binary Systems 1) Organic Rankine cycle
technology 2) Kalina Cycle technology 87 C
Dry Steam Systems 200 C
  • Other Technology Directions
  • like direct use
  • Hot Dry Rock/Enhanced Geothermal Systems

The Kalina cycle uses water and ammonia at
various ratios and a registered thermodynamics
facility to reduce  thermodynamic irreversibility
and therefore increase overall thermodynamic
efficiency. There are multiple variants of the
Kalina cycle systems available specifically
applicable to increase the efficiencies of
different types of heat source that would have
previously been lost as waste thermal energy.
21
Low Temperature Heat Extraction/Rejection
  • The classic use of earth/water is as a heat sink
    or source for air conditioning or heating
  • Pipes embedded in the earth carry refrigerant or
    water and conduct heat from the hotter to cooler
    substance
  • Since the earth (or water) has a high specific
    heat in comparison with air, there is good
    thermal transfer
  • In winter, heat is extracted from the earth by
    the chilled refrigerant, while in the summer, the
    hot refrigerant conducts heat to the earth
  • Houses have been built partially underground to
    moderate the winter and summer temperatures

22
  • Geothermal Heat Pumps
  • - produces 4 times the energy that they consume.
  • -initially costs more to install, but its
    maintenance cost is 1/3 of the cost for a
    typical conventional heating system and it
    decreases electric bill. This means that
    geothermal space heating will save the consumer
    money.
  • -can be installed with the help of special
    programs that offer low interest rate loans.

Heat pumps (for shallow geothermal energy), At a
lower thermal level, an air conditioner can
extract heat from the ground for winter heating
or insert energy into the ground to gain a more
efficient cooling sink
23
Geothermals Positive Attributes
  • Geothermal production of energy is 3rd highest
    among renewable energies. It is behind hydro and
    biomass, but before solar and wind.
  • Useful minerals, such as zinc and silica, can be
    extracted from underground water.
  • Geothermal energy is homegrown. This will
    create jobs, a better global trading position and
    less reliance on oil producing countries.
  • In large plants the cost is 4-8 cents per
    kilowatt hour. This cost is almost competitive
    with conventional energy sources.
  • Geothermal plants can be online 100-90 of the
    time. Coal plants can only be online 75 of the
    time and nuclear plants can only be online 65 of
    the time.
  • Flash and Dry Steam Power Plants emit 1000x to
    2000x less carbon dioxide than fossil fuel
    plants, no nitrogen oxides and little SO2.
  • Geothermal electric plants production in 13.380 g
    of Carbon dioxide per kWh, whereas the CO2
    emissions are 453 g/kWh for natural gas, 906g
    g/kWh for oil and 1042 g/kWh for coal.
  • Binary and Hot Dry Rock plants have no gaseous
    emission at all.
  • Geothermal plants do not require a lot of land,
    400m2 can produce a gigawatt of energy over 30
    years.

24
(No Transcript)
25
Availability of Geothermal Energy
  • On average, the Earth emits 1/16 W/m2. However,
    this number can be much higher in areas such as
    regions near volcanoes, hot springs and
    fumaroles.
  • As a rough rule, 1 km3 of hot rock cooled by
    1000C will yield 30 MW of electricity over thirty
    years.
  • It is estimated that the world could produce
    600,000 EJ over 5 million years.
  • There is believed to be enough heat radiating
    from the center of the Earth to fulfill human
    energy demands for the remainder of the
    biospheres lifetime.

26
Geothermals Harmful Effects
  • Brine can salinate soil if the water is not
    injected back into the reserve after the heat is
    extracted.
  • Extracting large amounts of water can cause land
    subsidence, and this can lead to an increase in
    seismic activity. To prevented this the cooled
    water must be injected back into the reserve in
    order to keep the water pressure constant
    underground.
  • Power plants that do not inject the cooled water
    back into the ground can release H2S, the
    rotten eggs gas. This gas can cause problems if
    large quantities escape because inhaling too much
    is fatal.
  • One well blew its top 10 years after it was
    built, and this threw hundreds of tons of rock,
    mud and steam into the atmosphere.
  • There is the fear of noise pollution during the
    drilling of wells.
  • Geyser-temperature steam is contaminated with
    salts that cause corrosion of turbines or engines
  • Geophysical/geological data availability
  • Access to finances
  • Technologies drilling (for EGS)

27
Direct uses of geothermal energy is appropriate
for sources below 1500C
  • space heating
  • air conditioning
  • industrial processes
  • drying
  • Greenhouses
  • Aguaculture
  • hot water
  • resorts and pools
  • melting snow

28
Geothermal technologies
  • EXPLORATION

ENERGY SYSTEMS
  • Drilling
  • mud-pumping technology
  • better drill bits for hard rocks and higher
    temperatures
  • Enhanced geothermal systems
  • demo facility
  • system operation

Geothermal heat pumps
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