Download 1. Introduction - Geothermal Communities

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GEOTHERMAL SYSTEMS AND
TECHNOLOGIES
1. INTRODUCTION
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1. INTRODUCTION
The word "geothermal" comes from the combination of the Greek words:
gê
⇒ meaning Earth, and
thérm
⇒ meaning heat
It is considered as renewable resource because the
heat emanating from the interior of the Earth is
essentially limitless.
The heat of the earth is available everywhere, and
we are learning to use it in a broader diversity of
circumstances.
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1.INTRODUCTION
Spatial variations of the thermal energy within the deep
crust
and mantle of the Earth give rise to concentrations of thermal energy
near the surface of the Earth that can be used as an energy resource.
Heat is transferred from the deeper portions of the Earth by
conduction through rocks, by the movement from hot, deep rocks
toward the surface, and by deep circulation of water.
Most high-temperature geothermal resources are associated with
concentrations of heat caused by the movement of magma (melted
rock) to near-surface positions where the heat is stored.
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1.INTRODUCTION
The Earth is consisted of crust, mantle and core.
The physical and chemical characteristics
of the crust, mantle and core vary from
surface of the Earth to its center.
Inner structure of the Earth
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1.INTRODUCTION
Lithosphere, is made up of the
crust and the upper layer of the
mantle and it is behaves as a rigid
body. (80-200 km)
Cross section
of the Earth
Below the lithosphere is the
asthenosphere, 200-300 km in
thickness.
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1.INTRODUCTION
According to Stacey and Loper (1988), the total flow of heat from the
Earth is estimated at 42 x 1012 W of which:
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8 x 10 W comes from the crust
32.3 x 1012 W comes from the mantle and
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1.7 x 10 W comes from the core.
Since the radiogenic heat of the mantle is estimated at 22 x 1012 W,
the cooling rate of this part of the Earth is 10.3 x 1012 W.
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With increasing depth through crust, from the
surface to the Earth interior, temperature increases for 17 - 30oC/km.
This temperature increase is called the temperature gradient and it
varies based on factors such as:
the porosity of the rock,
the degree of liquid saturation of the rock and sediments,
their thermal conductivity,
their heat storage capacity, and
the vicinity of magma chambers or heated underground reservoirs
of liquid.
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1.INTRODUCTION
Temperature gradient is different in different
parts of the Earth ranging from 10 to over
80oC/km.
Average temperature gradient is ∼ 30oC/km.
The mean terrestrial heat flow of continents
and oceans is 65 and 101 W/m2, respectively,
which, when really weighted, yield a global
mean of 87 W/m2.
Temperature profile of the Earth’s crust
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1.INTRODUCTION
Average geothermal heat flow through the crust to the Earth surface,
with a temperature gradient of 30oC/km is 0.06 W/m2.
For regions with higher temperature
gradient, geothermal heat flow is 10-20
W/m2.
The estimated total thermal energy
above mean surface temp. to a depth of
10 km is 1.3 x 1027 J, equivalent to
burning 4.8 x 1019 liters of oil.
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1.INTRODUCTION
Since the global energy consumption for all types of energy, is
equivalent to use of about 16 billion liters of oil per day, the
Earth’s energy to a depth of 10 km could theoretically supply
all of mankind’s energy needs for six million years.
Earth's mantle is composed of highly viscous, partially molten
rock, with temperature of 600÷1250oC at a depth of about
80÷100 km.
Earth's core is composed of outer liquid and inner solid core,
with temperature from 4000÷7000oC.
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In the foreseeable future geothermal energy will not
meet more than a very few percent of the total energy
consumption of the world, but it is of great importance
for many of the individual countries to harness it.
Geothermal research is now under way in about 60
countries. Most of these are developing countries.
All existing applications of GE use a circulating fluid to carry the heat from depth
to its use at the surface. Otherwise, enhanced techniques are available.
Fluids produced at lower temperatures (below ∼ 80oC) are used for space heating,
food drying, or industrial processes. Geothermal fluids with higher temperature
and sufficient flow rate can be used to generate electricity.
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1.INTRODUCTION
Main characteristics of geothermal energy which
makes it a very important future energy source
are:
Extensive global distribution,
Environmentally friendly,
Sustainable resource,
Independent of season and day time,
Immune from weather effects,
Contributes to development of
diversified power sources, and
Effective for distributed application.