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2. Geothermal Power Plants by ajizai


									           GEO-THERMAL ENERGY
                                 POWER FROM DEPTHS

T.N.V.KISHORE KUMAR                 M.SYAM
06761A0326                          06761A0324

        LakiReddy Bali Reddy College Of Engineering
                  Mechanical Department

In present day scenario, we are very much worried about POLLUTION (mainly caused
by non-renewable sources such as petroleum, diesel, coal etc), which is increasing rapidly
day by day. So, as to breathe easy we must avoid pollution or even we should reduce it to
some extent in one way or the other. Besides pollution, the cost of non-renewable sources
is being cumulated. And also recent national focus on the value of increasing our supply
of indigenous, renewable energy underscores the need for reevaluating all alternatives,
particularly those that are large and well distributed nationally. So, it is our turn to find
alternative for these non-renewable energy sources. So, this paper is an attempt to create
an awareness regarding GEO-THERMAL ENERGY and its applications in various
fields, which is one among the alternative energy resources. Geothermal power plants
operating around the world are proof that the Earth’s thermal energy is readily converted
to electricity in geologically active areas. This paper also deals the things concerning
about geo-thermal power plant, advantages, disadvantages and environmental aspects.

        Geothermal energy comes from the heat within the earth. The word "geothermal"
comes from the Greek words geo, meaning earth," and therme, meaning "heat." People
around the world use geothermal energy to produce electricity, to heat buildings and for
other purposes.The earth's core lies almost 4,000 miles beneath the earth's surface. The
double-layered core is made up of very hot molten iron surrounding a solid iron center.
Estimates of the temperature of the core range from 5,000 to 11,000 degrees Fahrenheit
(F). Heat is continuously produced within the earth by the slow decay of radioactive
particles that is natural in all rocks.
        Surrounding the earth's core is the mantle, thought to be partly rock and partly
magma. The mantle is about 1,800 miles thick. The crust is the outermost layer of the
earth, the land that forms the continents and ocean floors. It can be three to five miles
thick under the oceans and 15 to 35 miles thick on the continents.
       The earth's crust is broken into pieces called plates. Magma comes close to the
earth's surface near the edges of these plates. This is where volcanoes occur. The lava that
erupts from volcanoes is partly magma. Deep underground, the rocks and water absorb
the heat from this magma. The temperature of the rocks and water get hotter and hotter as
you go deeper underground.People around the world use geothermal energy to heat their
homes and to produce electricity by digging deep wells and pumping the heated
underground water or steam to the surface. Or, we can make use of the stable
temperatures near the surface of the earth to heat and cool buildings.

       From earliest times, people have used geothermal water that flowed freely from
the earth's surface as hot springs. The oldest and most common use was, of course, just
relaxing in the comforting warm waters. The Romans used geothermal water to heat
buildings in the city of Pompeii.
In North America geothermal energy was used as early as 10,000 years ago. Paleo-
Indians used hot springs for cooking and medicine. For centuries the Maoris of New
Zealand have cooked "geothermally," and, since the 1960s, France has been heating up to
200,000 homes using geothermal water. Prince Piero Ginori Conti.
In 1960, the country's first large-scale geothermal electricity-generating plant begins
operation. Pacific Gas and Electric operates the plant, located at The Geysers. The first
turbine produces 11 megawatts (MW) of net power and operates successfully for more
than 30 years.

How does geothermal energy come to the surface?
    Flow of magma up into volcanoes, which discharge it as lava.
    Flow of underground water, or steam, naturally heated deep in the Earth.
    Flow of water or steam, injected and retrieved by human effort.
   Because the geologic processes known as plate tectonics, the Earth’s crust has been
broken into 12 huge plates that move apart or push together at a rate of millimeters per
year. Where two plates collide, one plate can thrust below the other, producing
extraordinary phenomena such as ocean trenches or strong earthquakes. At great depth,
just above the down going plate, temperatures become high enough to melt rock, forming
magma. Because magma is less dense than surrounding rocks, it moves up toward the
earth’s crust and carries heat from below. Sometimes magma rises to the surface through
thin or fractured crust as lava. However, most magma remains below earth’s crust and
heats the surrounding rocks and subterranean water.
       So, how does water get there then, deep in the Earth? It usually gets there through
rain water trickling down rock fissures. Where a lot of it collects in underground aquifers,
and is heated by the Earth, it expands and may rise to the surface as water or steam. Hot
water in such geothermal reservoirs can reach temperatures of 700F (or 370C). Now this
source of heating energy has been used by people for many centuries.
       The third way of getting at this energy is facilitated by humans. It involves
injecting water at high pressures deep into porous heated rock formations and retrieving it
as hot water.
Methods of extracting Geo-thermal energy:
Modern human use of geothermal energy derives two types of power.

1. Using hot water directly

2 .Converting heat into electricity

       The direct use of hot water as an energy source has been happening since ancient
times. The Romans, Chinese, and Native Americans used hot mineral springs for bathing,
cooking and heating.After bathing, the most common direct use of geothermal energy is
for heating buildings through district heating systems. Hot water near the earth's surface
can be piped directly into buildings and industries for heat Examples of other direct uses
include: growing crops, and drying lumber, fruits, and vegetables.
Agriculture:Thermal water can be used in open-field agriculture to irrigate and/or heat
the soil and also to sterilize soil. Geothermal heat can also be used for crop and timber
drying. The main advantages of temperature control in open-field agriculture are:
                o The prevention of plant damage from low air temperatures;
                o Extension of the growing season;
               o Increased plant growth and production; and
               o   Soil sterilization that controls pests and diseases.
       Greenhouse heating is a common use of geothermal energy. Glass or plastic film
is used to trap solar radiation and heat, which provides a controlled environment for
plants to grow and increase yields. Many commercially grown vegetables, flowers, house
plants and tree seedlings are suitable for greenhouse culture.
       Aquaculture is the farming of aquatic organisms including fish, and aquatic
plants. Farming implies some sort of intervention in the rearing process to enhance
production, such as regular stocking, feeding, and protection from predators. In
geothermal aquaculture the objective is to heat the water to the optimum temperature for
fish growth. An emerging aqua cultural industry is the cultivation of vegetable species
that can be adapted for human and animal foods. Crops adaptable to geothermal enhanced
growth include duckweed, numerous algae species and kelp.
Industrial applications:
       Geothermal energy can be cost effective and reliable in industrial applications.
Some of these uses include drying fish, fruits, vegetables and timber products, washing
wool, dying cloth, manufacturing paper and pasteurizing milk. The largest industrial
applications are in pulp, paper and wood processing.
Heating and cooling:
       Geothermal heat pumps enable the resources to be used economically. Ground-
coupled heat pumps use earth-temperature soil for heating during winter, cooling during
summer, and supplying hot water year-round. Water-to-air heat pumps exchange heat
with groundwater, surface water or water passed through cooling towers for industrial
and commercial uses.

       There are three geothermal power plant technologies being used to convert
hydrothermal fluids to electricity. The conversion technologies are
            DRY STEAM,
             FLASH STEAM and
             BINARY CYCLE.
         The type of conversion used depends on the state of the fluid (whether steam or
water) and its temperature.
Dry Steam Power Plants:
         Steam plants use hydrothermal fluids that are primarily steam. The steam goes
directly to a turbine, which drives a generator that produces electricity. The steam
eliminates the need to burn fossil fuels to run the turbine. (Also eliminating the need to
transport and store fuels!) This is the oldest type of geothermal power plant. It was first
used at Lardarello in Italy in 1904, and is still very effective. Steam technology is used
today at The Geysers in northern California, the world's largest single source of
geothermal power. These plants emit only excess steam and very minor amounts of

Conventional steam turbines require fluids at temperatures of at least 150 °C.
            o Atmospheric exhaust geo-thermal power plants.
            o Condensing geo-thermal power plants.
Atmospheric exhaust geo-thermal power plants:
         Atmospheric exhaust turbines are simpler and cheaper. The steam, direct from dry
steam wells or, after separation, from wet wells, is passed through a turbine and
exhausted to the Atmosphere. With this type of unit, steam consumption (from the same
inlet pressure) per
Kilowatt-hour produced is almost double that of a condensing unit. However, the
Atmospheric exhaust turbines are extremely useful as pilot plants, stand-by plants, in the
Case of small supplies from isolated wells, and for generating electricity from test wells
during field development. They are also used when the steam has a high non condensable
Gas content (>12% in weight). The atmospheric exhaust units can be Constructed and
installed very quickly and put into operation. This type of machine is usually available in
small sizes(2.5 - 5 MW).

Condensing geo-thermal power plants:
       The condensing units, having more auxiliary equipment, are more complex than
the atmospheric exhaust units and the bigger sizes can take twice as long to construct and
install. The specific steam consumption of the condensing units is, however, about half
that of the atmospheric exhaust units. Condensing plants of 55 - 60 MW capacity are very
Flash Steam Power Plants:
       Hydrothermal fluids above 360°F (182°C) can be used in flash plants to make
electricity. Fluid is sprayed into a tank held at a much lower pressure than the fluid,
causing some of the fluid to rapidly vaporize, or "flash." The vapor then drives a turbine,
which drives a generator. If any liquid remains in the tank, it can be flashed again in a
second tank to extract even more energy. Both dry steam and flash steam power plants
emit small amounts of carbon dioxide, nitric oxide, and sulfur, but generally 50 times less
than traditional fossil-fuel power plants.

Binary-Cycle Power Plants:
       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.

Advantages of Geothermal Energy
        Geothermal energy is environmental and land friendly. It reduces the emissions
         that harm the atmosphere.
        The land area required for geothermal power plants is smaller per megawatt than
         for almost every other type of power plant.
        Geothermal is a reliable renewable energy source.
        It is resistant to interruptions of power generation due to weather, natural
         disasters or political rifts that can interrupt transportation of fuels.
        Geothermal energy is an economic benefit.

Disadvantages of Geothermal Energy

    Drilling operation is noisy.
    Overall efficiency for power production is low, about 15%, as compared to (35 to
       40) % for fossil fuel plants.
    The steam and hot water gushing out of the earth may contain H2S, CO2, NH3
       and radon gas etc. If these gases are vented into the air, air pollution will be a real
        hazard. These gases are to be removed by chemical action, before they are

        By using geothermal energy, millions of tonnes of fossil fuels are being saved
worldwide and polluting emissions are being greatly reduced. It is one of the few
technologies that significantly contribute to reducing greenhouse gas emissions. If
geothermal energy continues to be used at the present rate, it is estimated that the
available resources could last for five million years.
        Current geothermal technologies use only a tiny fraction of total geothermal
resources. Several miles beneath Earth's surface is hot, dry rock being heated by the
molten magma directly below. Technology is now being developed to drill into this rock,
inject cold water down a well, circulate it through the hot, fractured rock, and draw off
the heated water from a different well. This has the potential to supply the energy needs
of the entire world for centuries to come.

        In our country, we use lots of watts...of electricity. Much of this electricity is
made by burning fossil fuels that are dirty and irreplaceable. Fortunately, there are
        From the first power plant in Larderello, Italy, to the state-of-the-art facilities
found all over the world today, geothermal plants use natural hot water and steam from
the earth to run turbine generators. Technological advances are making this a cost-
effective resource. Expect to see its increased use in the near future, especially in the
geothermally active western United States, India, Indonesia, and other "hot spots" around
the Pacific. A country like India can only be developed when only it will use its resources

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