GEOTHERMAL POWER GENERATION
AN OVERVIEW
Rajesh M Holmukhe
Assistant Professor
Engineering Department,
University, College of Engineering
Pune, India
e-mail:[email protected]
Electrical
Bharati Vidyapeeth
ABSTRACTTHIS PAPER PRESENTS
THE DEVELOPMENT,
UTILISATION
AND APPLICATION
OF GEOTHERMAL
POWER.
THE FAST DEPLETING
CONVENTIONAL
RESOURCES
HAVE
COMPLETED US TO LOOK OUT FOR NEW AVENUES IN ENERGY
GENERATION.THIS
PAPER DISCUSSES IN GREATER DEPTHS
DIFFERENT WAYS OF HARNESSING THIS NON-CONVENTIONAL
ENERGY SOURCE. THE CLASSIFICATION
AND OPERATION OF
GEOTHERAMAL
POWER PLANT AN LOG WITH SCHEMATIC
DIAGRMS HAVE BEEN EXPLAINED
IN DETAIL.IT GIVES AN
OVERVIEW OF THE GEOTHERMAL
POWER GENERATION
IN
INDIA AND ABROD AND ITS ECONIMIC FESIBILITY.FURTHER
ACOMPARISION
BETWEEN GEOTHERMAL
POWER PLANT AND
THERMAL POWER PLANT HAS BEEN MADE .WE HAVE TRIED
OUR LEVEL
BEST TO COVER
ALL THE
ASPECTS
OF
GEOTHERMAL
POWER GENERATION IN THIS PAPER.
Earth is made up of 3 layers namely, crust, mantle
and metallic core. The crust, mainly composed of granites is
split into 6 main plates which move away from each other at
the rate of 2 to 20 cm per year. Relative motion of the plates
occasionally gives rise to areas where internal heat of the earth
reaches the surface and where most volcanoes and most of the
world's geothermal fields are found.
I) Water is the most important carrier of the energy in
geothermal wells as it has a high heat capacity and
latent heat of vaporization.
2) Impermeable
rocks cover permeable
layers which
contain reservoir of hot water thereby preventing heat
loss and maintaining water under pressure.
Keywords- geothermal powert ,. renewable energy
I.
INTRODUCTION
Non-Conventional
Energy Source (NECS) which comprise
both renewable and non renewable
source should play an
increasingly important role in the coming periods in view of
fast depleting fossil fuel reserves and growing concerns for
environment protection.
Perennial energy shortages
and resulting inflation
have adversely affected the balance of payment position in
energy scare economies of developing countries. Renewable
energy sources occur in nature in the form of energy flows of
indefinite duration as opposed to non-renewable
conventional
fuels of finite values.
Here we shall see about Geothermal Power Plants as
product of clean energy concept and geothermal
energy
resource which of 1 or 2 orders of magnitude larger than the
recoverable energy from uranium and thorium in same volume
of rocks.
II.
ORIGIN AND DISTRIBUTION
GEOTHERMAL ENERGY
OF
Geothermal energy is present over the entire extent of the
earth's surface. It varies only in its ease and cost of extraction.
The need for developing the least expensive resource first has
resulted in the exploration of geothermal resources primarily
in these areas which have associated
volcanic
activity.
However, by no means is the resource restricted only to
volcanic areas.
Geothermal fields such as geysers require a combination of 3
geological factors-I) a natural underground source of water. 2)
an impermeable
layer that traps the water and permits
formation of steam. 3) a mass of hot rock near the natural
water system.
Geothermal energy is derived from the hot interior of
the earth. Crustal rock up to 70 km thick insulates it from
earth's surface. Due to this insulation temperature at the
surface is relatively cool but increases rapidly with growing
depth inside the rock. A small portion of the rock is permeable
so that over a long period of time it acquires a store of natural
ground water which gets heated. In places where the heated
water finds its way to the surface naturally, the geothermal
energy can be extracted with relative ease. In other places it
may be mined using deep bore holes.
In Pacific Ocean lies the richest belt of geothermal
energy known as 'RIM OF FIRE' stretching from New
Zealand up through New Guinea, Philippines, Japan, Western
Siberia and then down through
Western United States,
Mexico, Central America.
Geothermal Gradient:- It is defined as the rate of increase of
temperature
with depth. In developing a program to use
geothermal energy following factors need to be analyzedI. Variation of temperature
with depths in different
parts of the world.
2. Identification of location at convenient depths from
which it is possible to approach water bearing rocks
having water temperature higher than 50C.
3.
Identification of rocks that are sufficiently hot and
impermeable which render extraction of heat and
economically viable proposition.
III. CLASSIFICAITON OF TYPES OF
GEOTHERMAL POWER PLANTS:
Geothermal Power Plants are of several types. They are
classified on basis of
•
Geothermal fluid used
•
Thermodynamic cycle adopted
I.
2.
3.
4.
5.
6.
STEAM GEOTHERMAL
POWER PLANT: It is
called vapour dominated geothermal power plant.
Geothermal fluid is steam.
PETRO THERMAL GEOTHERMAL
POWER
PLANT: It is also called Hot Dry Rock geothermal
power plant. Thermal energy in hot dry geological
rock is extracted by circulating water through
artificial fracture in hot dry rock. Steam turbine is
used as prime mover.
FLASHED STEAM GEOTHERMAL
POWER
PLANT:- It is a type of Liquid Dominated
geothermal power plant. Production well produces
mixture of water and steam at temperature more than
180 C and with low content of dissolved minerals.
Steam turbine is the prime mover. Geothermal fluid
is flashed to obtain steam.
BINARY
LIQUID
DOMINATED
GEOTHERMAL
POWER
PLANT:
The
geothermal fluid is mixture of water and steam at
temperature less than 150 C. The geothermal fluid
cycle is different from the working fluid cycle. The
geothermal heat is exchanged with the working fluid
of low boiling point in a heat exchanger gas turbine
drives the generator shaft.
BINARY
CYCLE
GEOTHERMAL
POWER
PLANT WITH HOT BRlNE: When geothermal fluid
is liquid with high mineral content, binary cycle
similar to (4) is preferred.
TOTAL FLOW GEOTHERMAL POWER PLANT"
The entire geothermal fluid is passed through the
special turbine. Such system is used when the
geothermal fluid has very high content of mud,
dissolved minerals etc.
Geothermal Power Plants are operated continuously as base
load power plants. Production wells require a few hours from
start to reach the rated level of delivery. Thermal equipment
are loaded gradually. In the beginning, the geothermal fluids
contain excessive particulate and dirt. After a few hours the
quality of production fluid is improved. Hence frequent
restarts must be avoided.
IV. VAPOUR DOMINATED (STEAM)
GEOTHERMAL ELECTRIC POWER PLANT:
The geothermal fluid for such plants is dry steam at
temperature between 180 C to 240 C with low content of
particulate impurities and dissolved solid impurities. Mass
flow rate per well is around 10 kg/see with power rating per
well at rate of 6 MWe.
SCHEMATIC
DIAGRAM: Figure (3) gives a typical
schematic of a vapour dominated geothermal power plant. Dry
steam from the geothermal reservoir I) flows upwards through
the production well (2) and is admitted in the centrifugal
separator (4)
The temperature and pressure of the steam at the bottom of the
well are 280 C and 35 bar. As steam flows towards the ground
surface, it expands and cools. Temperature and pressure at the
well head is about 250 C and 8 bar.
The centrifugal separator (4) removes particulate
matter (13) from the steam. The steam is admitted into the
steam turbine (5) The steam expands in the turbine buckets
producing rotary kinetic energy. The low pressure steam at the
exhaust of the turbine is condensed in condenser (8) the
condensated is reinjected into the earth via the reinjection
wall. (9)
Cooling water for condensing the steam is circulated
through the cooling tower (12) by means of cooling water
pump. (13) The synchronous generator (6) generate electrical
power at high voltage 50 Hz A.C. The turbine and generator
form one unit. Complete power plants has several units.
Geothermal energy in the form of dry steam (1) is converted
into mechanical energy by the turbine (5) The mechanical
energy is converted to electrical energy by the generator. The
electrical power is transmitted by electrical transmission
system and fed to 30 AC supply network. Steam geothermal
power plant are grid connected and operated continuously as
base load power plants.
PRODUCTION
WELL: Are located at a distance of
about05. km. Life of a steam power production well is 6 to 15
years. Thereafter new well should be used. Steam production
from a well declines by about 20% in about 6 years.
REINJECTION
WELLS: The reason for reinjection of
condensate into the earth are :1) To ensure supply of fresh water from production well
for several years. The earth acts as a steam generator.
2) To prevent environmental pollution. The condensate
contains certain pollutants for e.g. The steam at the
geysers contains Hydrogen Sulphide up to 200 ppm.
If condensate is let out on ground level, it causes
environmental hazard.
V.
COMPARISION BETWEEN GEOTHERMAL
POWER PLANT AND STEAM THERMAL POWER
PLANT:
The main difference between conventional steam thermal
power plant and geothermal power plant are:-
•
•
•
•
•
•
Geothermal power plants have smaller units sizes (S
MW, 10 MW, IS MW) whereas the thermal steam
power plants have large unit sizes (200MW, SOO
MW,800MW)
A Variety of systems are used in geothermal power
plant for extraction of steam from geothermal energy
source.
geothermal
power plants need a large flow of
geothermal
fluids (due to lesser temperature
and
pressure)
Geothermal
power plants need a large flow of
geothermal
fluids (due to lesser temperature
and
pressure)
Geothermal power plants are located on geothermal
field. it is not technically feasible to transport hot
geothermal fluid over long distance due to drop in
pressure and temperature.
the energy conversion sequence in vapour dominated
geothermal power cycle is as following:-
DRY STEAM
GENERATOR
SEPERA TOR
•
•
CENTRIFUGAL
CONSUMER
TURBINE
UNIT
SIZE
OF
TURBINE
GENERATOR
STEAM
TEMPERA TURE
STEAM
PRESSURE
STEAM PER kWh
(relative)
VOLUME
OF
STEAM ( relative)
•
SMW-IOMW
COAL
FIRED
STEAM
THERMAL
POWER
PLANT
IOOMW-600
MW
270C
SOOC
8 Bar
30 BAR
2.SX
X
SOY
Y
of moderate
and low temperature
that is <160 C. the
geothermal fields in India are in the form of hot water springs
(40 C to 98 C) and shallow water reservoir temperatures are
less than 160 C. The important hydro-geothermal
resource
locations are:-
FIELD
PUGAJ&K
STEAM
STEAM
Geothermal power plant requires much larger flow of
steam per kWh of electrical energy generated.
Power available per well is relatively small.
VAPOUR
DOMINATED
GEOTHERMAL
POWER PLANT
VI. SCOPE FOR GEOTHERMAL ENERGY SYSTEM
IN INDIA:
India has I SO known geothermal sites having geothermal fluid
The working fluid in conventional steam thermal coal
fired power plant is high temperature high pressure
steam produced
from lean water with very low
particulate and dissolved solid matter. Geothermal
steam has highest content of particulate and dissolved
impurities. Additional equipments
are necessary in
geothermal power plant for production of clean steam
suitable for admitting into the steam turbines. The
configuration
of power plant and equipment
is
influenced
by the temperature
pressure
solid
particulate and dissolved
impurities in geothermal
steam water produced by production well.
WEST
COAST
MAHARASHTRA
GUJARAT
FIELDS,
AND
FIELD
T ATT APANI FIELDS - MP
AND
PARTICULARS
LlKEL Y APPLICATIONS
-Geo-hydrothermal
-I IS springs SO to 80 C
- total discharge 18 kllh
- field area 3 sq. meter
-Appl ications
-green house cultivation
- space heating
- drying of wool
-binary cycle power plant
-geo-hydrothermal
- 18 springs 34 to 72 C
- locations with water at 120
C at 200 to SOO m depths
-Applications
-mushroom farming
-animal husbandry
-biogas production
-drvinz of sea fish
PARTICULARS
AND
LlKEL Y APPLICATIONS
-geo-hydrothermal
- 23 springs, SO to 98 C
- total discharge 3600llh
-Applications
-silver culture
-drying of timber
- drying of cotton
- drying of fruits
Due to moderate and low temperature of geothermal fluids,
the prospects of such plants in India are very low. However
geothermal energy is likely to have several applications in
temperature range of 30 C to 190 C.
VII. GEOTHERMAL ELECTRICAL POWER PLANTS
IN THE WORLD:
About 20 nations in the world have known geothermal
resources. total installed capacity of geothermal power plants
in the world is around 10,000 MW.
HISTORIC
PLANTS:-
REVIEW
OF
GEOTHERMAL
-
1904
LARDERDLLO,
IT AL Y
1914
LARDERDLLO,
IT AL Y
1944
LARDERDLLO,
ITALY
1958
JAPAN, MEXICO
1960
THE GEYSERS,
USA
1982
THE GEYSERS,
USA
1979
USA,
ITALY,
NEW
MEXICO,
ZEALAND,
USSR
USA
1987
POWER
electricity
from
generated
geothermal energy
for first time
- 8.5 MW power
plant with steam
turbine generators
- 127 MW steam
geothermal power
plant
geothermal energy
electric
power
plants
- II MW steam
turbine generator
- 109 steam
turbine generator
-total
installed
capacity 1900 MW
VIII.
ECONOMICS
FOR POWER GENERATION:
Factors affecting economic growth of geothermal energy
based power generation are the well head temperature, well
flow rate and the cost of wells. Optimum plant size is in 50 to
100MW range. Scope of cost reduction in large plants through
economics of scale is limited and hence geothermal power
plants are more appropriate for supplying power to public
buildings and commercial
establishments.
Total cost of
geothermal plant can be divided in 3 categories:
1. Power Plant capital costs
2. Operating cost
3. Energy supply cost
Power plant costs mainly cover the initial capital required to
build it with operating cost forming a small proportion. As the
proportion of operating costs in total costs is low, uncertainties
in operating costs would not have a significant impact on
power costs.
Geothermal power generation is thus capital intensive with
75% of generating costs as fixed costs pertaining to capital
investment.
CONCLUSION
- 70 MW binary
cycle power plant
-total
installed
capacity 3500 MW
-total
installed
capacity 8000 MW
Geothermal power can become a valuable source of energy if
properly harnessed. Continued energy shortages have created
added interest in geothermal energy for both power generation
2000
THE WORLD
and direct applications. The technology is expensive and it is
necessary that for real breakthrough the cost be reduced
,
substantially.
GEOTHERMAL
ELECTRIC POWER PLANTS IN THE
Development
of geothermal
energy has some
li tiIons on the environment. Environmental problems
WORLD
imouca
COUNTRY AND TOTAL
GEOTHERMAL
TEMPRATURlissociated g eothermal development are physical disturbance
LOCATION
INSTALLED
FLUID
°C
of site, noi e, brine, disposal, ground water contamination, by
CAPACITY
fluids and air pollution especially by hydrogen
v
USA,THE
IIOOMW
STEAM
285
sulphide.
GEYSERS
ITALY,
406MW
STEAM+
260
A ditional and often less manageable problems relate
LARDERELLO
WATER
to serious social, economic and institutional impacts that
ccompany large scale geothermal development.
o·
'J
NEWZEALAND,
290MW
STEAM+WATER 260
This could be compounded by the effects of new industrial
WEIRAKAI
wrucn roup ws as a result of low cost geothermal power
JAPAN
IIOMW
STEAM+WATER 280
CHILE,ELTATIO
15MW
STEAM+WATER 280
developmehi t plans should include careful ground work to
mitigate irrp act on areas with geothermal resources.
1988
THE WORLD
,......
"
ACKNOWLEDGMENT
MEXICO,CERRO
PRlETO
150MW
STEAM+
WATER
370
TURKEY,
KIZILDEE
10MW
STEAM+
WATER
210
FORMERUSSR
7MW
STEAM+
WATER
200
ICELAND
2.5 MW
STEAM+
WATER
280
Bharati Vidyapeeth
Pune-43.
University College of
Engineering,
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,
3.
4.
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ENERGY SYSTEMS -K.M. Mittal
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E ECTRICAL ENGINEERING HANDBOOK 2nd EDITION.
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STANDARDHANDBOOKFORELECTRICALENGINEERING
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