Transcript Document

TERRESTRIAL HEAT –
energy from the inside of
the Earth
What does “geothermal“ mean?
 The term geothermal comes from the
Greek geo meaning earth and therine
meaning heat thus geothermal energy
is energy derived from the natural heat
of the earth.
 The heat inside the Earth core is
continually generated by the decay of
the long lived radioactive isotopes of
uranium, thorium and potassium,
which are present in the Earth.
 The heat that flows from the Earth's
hot interior due to plate movements,
zones of high heat flow, may be
located close to the surface where
convective circulation plays a
significant role in bringing the heat
close to the surface
What happens with the heat?
 Without utilization, the terrestrial
heat flow is lost to the
atmosphere. In this case, the
isotherms run parallel to the
earth’s surface and the heat flow
lines are perpendicular to them. If,
instead, the heat flow can be
captured, the isotherms are
deformed and the heat flow lines
can be diverted towards heat
sinks.
 Due to variations of the earth’s
crust thickness there will be
different temperature profiles from
place to place. Some areas are
known to have hot springs and the
like and volcanic activities, such
areas will also be well suited for
geothermal utilization.
How does geothermal heat get up to the
surface?
 Sometimes the hot magma
reaches all the way to the surface,
where we know it as lava. But
most often the magma remains
below earth's crust, heating
nearby rock and water (rainwater
that has seeped deep into the
earth) - sometimes as hot as 700
degrees F. Some of this hot
geothermal water travels back up
through faults and cracks and
reaches the earth's surface as hot
springs or geysers, but most of it
stays deep underground, trapped
in cracks and porous rock. This
natural collection of hot water is
called a geothermal reservoir.
Best locations
 Geothermal systems can be found in
regions with a normal or slightly
above normal geothermal gradient.
 The margins of the plates correspond
to weak, densely fractured zones of
the crust, characterized by an intense
seismic activity, by a large number of
volcanoes and, because of the ascent
of very hot materials towards the
surface, by a high terrestrial heat flow.
The most important geothermal areas
are located around plate margins.
 World pattern of plates, oceanic
ridges, oceanic trenches, subduction
zones, and geothermal fields.
Accessing geothermal energy
 If geothermal reservoirs are close
enough to the surface, we can reach
them by drilling wells, sometimes over
two miles deep. Scientists and
engineers use geological, electrical,
magnetic, geochemical and seismic
surveys to help locate the reservoirs.
Then, after an exploration well
confirms a reservoir discovery,
production wells are drilled.
 Geothermal system can be described
schematically as "convecting water in
the upper crust of the Earth, which, in
a confined space,transfers heat from a
heat source to a heat sink, usually the
free surface". A geothermal system is
made up of three main elements: a
heat source, a reservoir and a fluid,
which is the carrier that transfers the
heat.
Generating electricity :
Geothermal power plants
 In geothermal power plants,
we use the natural hot water
and steam from the earth to
turn turbine generators to
produce electricity. Unlike
fossil fuel power plants, no
fuel is burned. Geothermal
power plants give off water
vapour, but have no smoky
emissions.
 There are several different
types of plants: flashed steam
plants, dry steam plants and
binary power plants
Flashed Steam Plants
 Most geothermal power plants
operating today are "flashed
steam" power plants. Hot
water from production wells is
passed through one or two
separators where, released
from the pressure of the deep
reservoir, part of it flashes
(explosively boils) to steam.
The force of the steam is used
to spin the turbine generator.
To conserve the water and
maintain reservoir pressure,
the geothermal water and
condensed steam are directed
down an injection well back
into the periphery of the
reservoir, to be reheated and
recycled.
 Flash steam power plants use
hot water reservoirs. In flash
plants, as hot water is
released from the pressure of
the deep reservoir in a flash
tank, some if it flashes to
steam.
Dry Steam Plants
 A few geothermal reservoirs
produce mostly steam and very
little water. Here, the steam
shoots directly through a rockcatcher and into the turbine. The
first geothermal power plant was
a dry steam plant, built at
Larderello in Tuscany, Italy in
1904. The power plants at the
Larderello dry steam field were
destroyed during World War II,
but have since been rebuilt and
expanded. That field is still
producing electricity today. The
Geysers dry steam reservoir in
northern California has been
producing electricity since 1960.
It is the largest known dry steam
field in the world and, after 40
years, still produces enough
electricity to supply a city the size
of San Francisco.
Binary Power Plants
 In a binary power plant, the geothermal
water is passed through one side of a
heat exchanger, where it's heat is
transferred to a second (binary) liquid,
called a working fluid, in an adjacent
separate pipe loop. The working fluid
boils to vapour which, like steam,
powers the turbine generator. It is then
condensed back to a liquid and used
over and over again. The geothermal
water passes only through the heat
exchanger and is immediately recycled
back into the reservoir. In some power
plants, flash and binary processes are
combined.
Direct (non-electrical) uses of
geothermal water
 Shallower reservoirs of lower
temperature -- 21-149°C (70300°F) are used directly in health
spas, greenhouses, fish farms,
and industry and in space heating
systems for homes, schools and
offices.
 It is only during the last century
that we have used geothermal
energy to produce electricity. But
using geothermal water to make
our lives more comfortable is not
new: people have used it since
the dawn of mankind. Wherever
geothermal water is available,
people find creative ways to use
its heat.
Agriculture and aquaculture
Geothermal energy is used directly in
agriculture and aquaculture:
 to help grow flowers, vegetables,
and other crops in greenhouses
while snow-drifts pile up outside
 to shorten the time needed for
growing fish, shrimp, abalone and
alligators to maturity
Industry
 The heat from geothermal water is
used worldwide for industrial
purposes. Some of these uses
include drying fish, fruits,
vegetables and timber products,
washing wool, dying cloth,
manufacturing paper and
pasteurizing milk.
 Geothermally heated water can be
piped under sidewalks and roads
to keep them from icing over in
freezing weather. Thermal waters
are also used to help extract gold
and silver from ore and even for
refrigeration and ice-making.
Hot Spring Bathing and Spas
(Balneology)
 For centuries, peoples of China, Iceland,
Japan, New Zealand, North America and
other areas have used hot springs for cooking
and bathing. The Romans used geothermal
water to treat eye and skin disease and, at
Pompeii, to heat buildings. Medieval wars
were even fought over lands with hot springs.
 In Europe, natural hot springs have been very
popular health attractions. The first known
"health spa" was established in 1326 in
Belgium. (One resort was named "Espa"
which means "fountain." The English word
"spa" came from this name.) All over Eurasia
today, health spas are still very popular.
Russia, for example, has 3,500 spas.
 Japan is considered the world’s leader in
balneology. The Japanese tradition of social
bathing dates back to ancient Buddhist rituals.
Beppu, Japan, has 4,000 hot springs and
bathing facilities that attract 12 million tourists
a year. Other countries with major spas and
hot springs include New Zealand, Mexico and
the United States.
District heating
 The oldest and most common use of
geothermal water, apart from hot spring
bathing, is to heat individual buildings, and
sometimes entire commercial and residential
districts.
 A geothermal district heating system supplies
heat by pumping geothermal water -usually 60°
C (140°F) or hotter- from one or more wells
drilled into a geothermal reservoir. The
geothermal water is passed through a heat
exchanger which transfers the heat to water in
separate pipes that is pumped to the buildings.
After passing through the heat exchanger, the
geothermal water is injected back into the
reservoir where it can reheat and be used
again.
 Because it is a clean, economical method of
heating buildings, geothermal district heating is
becoming more popular in many places. The
world's largest geothermal district heating
system is in Reykjavik, Iceland, where almost
all the buildings use geothermal heat. The air
around Reykjavik was once very polluted by
emissions from reliance on fossil fuels. Since it
started using geothermal energy, Reykjavik
has become one of the cleanest cities in the
world.
Geothermal heat pumps
 The heat pumps are machines that move
heat in a direction opposite to that in which
it would tend to go naturally, i.e. from a cold
space or body to a warmer one. A heat
pump is effectively nothing more than a
refrigeration unit. Any refrigeration device
(window air conditioner, refrigerator, freezer,
etc.) moves heat from a space (to keep it
cool) and discharges that heat at higher
temperatures. The only difference between
a heat pump and a refrigeration unit is the
desired effect, cooling for the refrigeration
unit and heating for the heat pump. A
second distinguishing factor of many heat
pumps is that they are reversible and can
provide either heating or cooling in the
space.
 Geothermal heat pumps reduce electricity
use 30-60% compared with traditional
heating and cooling systems, because the
electricity which powers them is used only
to move heat, not to produce it. The U.S.
Environmental Protection Agency rates
geothermal heat pumps among the most
efficient of heating and cooling
technologies.
Advantages of geothermal energy
 RENEWABILITY AND SUSTAINABILITY :Earth’s heat is continuously radiated from within,
and each year rainfall and snowmelt supply new water to geothermal reservoirs. Production
from individual geothermal fields can be sustained for decades and perhaps centuries. The
U.S. Department of Energy classifies geothermal energy as renewable.
 CONSERVATION OF RESOURCES : When we use renewable geothermal energy for direct
use or for producing electricity, we conserve exhaustible and more polluting resources like
fossil fuels and uranium. Installed geothermal electricity generation capacity around the
world is equivalent to the output of about 10 nuclear plants.
 PROTECTION OF THE ENVIRONMENT: Geothermal direct use facilities have minimal or
no negative impacts on the environment. Geothermal power plants are relatively easy on
the environment.
 Protection of the Air and Atmosphere. Hydrogen sulphide gas (H2S) sometimes occurs in
geothermal reservoirs. It is subject to regulatory controls for worker safety because it can be
toxic at high concentrations. Equipment for scrubbing H2S from geothermal steam removes
99% of this gas. Carbon dioxide CO2 occurs naturally in geothermal steam but the
geothermal plants release amounts less than 4% of that released by fossil fuel plants. And
there are no emissions at all when closed-cycle (binary) technology is used.
 Visual Protection. A geothermal plant sits right on top of its fuel source: no additional land is
needed such as for mining coal or for transporting oil or gas. When geothermal power plants
and drill rigs are located in scenic areas, mitigation measures are implemented to reduce
intrusion on the visual landscape.
 LOW COSTS: the price of geothermal power decreased with about 25 % in the last 2
decades due to the development of the technology used and the involvement of the
government in the research regarding this domain.
Future of geothermal energy
The outlook for geothermal energy use depends on at least three factors:
 The Demand for energy will continue to grow. Economies are expanding, populations are
increasing (over 2 billion people still do not have electricity), and energy-intensive
technologies are spreading. All mean greater demand for energy.
 The Inventory of accessible geothermal energy is sizable. Using current technology
geothermal energy from already-identified reservoirs can contribute as much as 10% of
the United States energy supply. And with more exploration, the inventory can become
larger. The entire world resource base of geothermal energy has been calculated in
government surveys to be larger than the resource bases of coal, oil, gas and uranium
combined
 The Competitive Position depends primarily on cost:
 Costs: Shorter and Longer Term. Production of fossil fuels (oil, natural gas and coal) are
a relative bargain in the short term. Like many renewable resources, geothermal
resources need relatively high initial investments to access the heat, hot water and
steam. But the geothermal "fuel" cost is predictable and stable. Renewable geothermal
energy is a better long term investment.
 Costs: Direct and Indirect. The monetary price we pay to our natural gas and electricity
suppliers, and at the gas pump, is our direct cost for the energy we use. Geothermal
energy is a clean, indigenous, renewable resource without hidden external costs.
 Costs: Domestic and Importing. Investment in the use of domestic, indigenous,
renewable energy resources like geothermal energy provides jobs, expands the regional
and national economies, and avoids the export of money to import fuels.
Conclusion:
 Energy demand is
increasing rapidly
worldwide. Some energy
and environmental
experts predict that the
growth of electricity
production and direct
uses of geothermal
energy will be revitalized
by international
commitments to reduce
carbon dioxide emissions
to avert global climate
change and by the
opening of markets to
competition.
Made by :
Diana Giurghita
&
Anca Muntean