Geographic information systems Category: Scientific disciplines Geographic information systems GIS originated pri-marily from efforts to manage natural resources and analyze environment
Trang 1hydration of the gel and subsequent crystallization
oc-cur, along with shrinkage and cracking of the geode
wall, allowing mineral-bearing waters to percolate
into the geode and deposit crystals on the cavity wall
Subsequent periods of water circulation and
crystalli-zation may follow, forming the characteristic layers of
crystals
Geodes are found in many parts of the world One
well-known type found in Uruguay is called hydrolite,
or water stone, because it contains quartz crystals left
when water containing silica in solution evaporated
Many highly prized geodes that are filled with
beauti-ful crystals and curved-banded colors of agate can be
found at various collecting sites in the United States,
such as near Dugway, Utah, and Keokuk, Iowa
Alvin K Benson
See also: Groundwater; Hydrothermal solutions and
mineralization; Limestone; Quartz; Sedimentary
pro-cesses, rocks, and mineral deposits; Silicates
Geographic information systems
Category: Scientific disciplines
Geographic information systems (GIS) originated
pri-marily from efforts to manage natural resources and
analyze environmental issues In recent years,
ad-vances in computing technology and the development
of large digital databases have made GIS a powerful
tool for analyzing the natural environment GIS is
particularly suited to support multidisciplinary
anal-yses of natural systems at a variety of scales.
Background
Although geographic information systems (GIS)
sci-entists and practitioners may define GIS in broader
terms, the initials are commonly used to refer to the
computer software and peripheral technologies that
are used to collect, manipulate, analyze, and visualize
geographic information While many of the concepts
that underpin GIS have a long history in academic
dis-ciplines such as cartography, geography, and
plan-ning, GIS computer software largely originated in the
1960’s with academic and government initiatives to
study how computers could be used to make maps
and manage geographic data In academia, this
in-cluded work by cartographers to develop computer
programs that replicated manual procedures for cre-ating maps It also included research by geographers, planners, and computer scientists to develop meth-ods for conducting spatial analysis with computers The pioneering work of researchers at the Harvard Laboratory for Computer Graphics and Spatial Analy-sis from the 1960’s to the 1980’s was an important fac-tor in the development of early GIS
The origins of GIS software also lie in government efforts to develop spatial information systems for mili-tary applications and to manage large demographic and environmental datasets The U.S military, for in-stance, was active in developing highly accurate digi-tal maps and information systems to manage large databases of remotely sensed imagery Starting in the 1970’s the Department of Defense also developed the Global Positioning System (GPS), a satellite navi-gation system used for a number of applications— including in-car navigation systems and mobile de-vices—to determine location In the late 1960’s, the U.S Census Bureau developed GIS resources to facili-tate the collection, analysis, and dissemination of data collected in the census Similar efforts were under-taken by environmental resource managers and orga-nizations like the United States Geological Survey and the National Park Service to manage natural resources One of the first GIS programs to be devel-oped and used on a large scale was the Canada Geo-graphic Information System (CGIS) CGIS was devel-oped by the Canadian government to inventory natural resources, manage how resources were used, and structure decisions regarding the development and conservation of natural resources
The widespread use of GIS by private companies and nonprofit organizations and at multiple levels of government began in the late 1980’s with the develop-ment of the personal computer and “off-the-shelf” GIS software These developments were significant to the field of natural resource management because they fostered broader efforts to develop and share en-vironmental datasets They also facilitated efforts by researchers from different disciplines to collaborate
on environmental issues Today, most GIS software is developed by private companies Common packages include ArcGIS, Manifold Systems, MapInfo, Inter-graph, and IDRISI While most GIS programs are de-veloped for a broad range of applications, some pro-grams like IDRISI are designed specifically for natural resource management and planning and environ-mental modeling Organizations such as Google,
Trang 2Microsoft, and the National Aeronautics and Space
Administration have also made significant investments
in Web-based GIS resources, which have numerous
applications in the environmental sciences
GIS Design
Three fundamental concepts that underlie the design
of modern software are map overlay, vector and raster
data models, and the relationship between spatial and
attribute information Map overlay refers to the
man-ner in which different types of spatial data (for
exam-ple, the locations of wells, rivers, and lakes or changes
in elevation) are stored as individual thematic layers
in the GIS The GIS allows the user to superimpose
the layers on top of one another to explore the
rela-tionships between them In the GIS community, this
technique is commonly attributed to landscape
archi-tect Ian McHarg, who, in the 1960’s, used overlays
of maps drawn on Mylar transparencies in
environ-mental planning
The data stored in the thematic layers are typically
structured according to two data models, known as
vector and raster The vector data model represents
entities as one of three simple geometric features: a
point, line, or polygon It is best suited to represent
discrete entities as exemplified by a point layer,
de-picting the locations of water wells; a line layer,
depict-ing the layout of a stream network; or a polygon layer,
depicting the boundaries of large water bodies The
raster data model, in contrast, is better suited to
repre-sent phenomena that vary continuously across space,
such as temperature or elevation The raster data
model partitions a data layer according to a uniform
grid mesh This is similar to the manner in which a
digital photograph partitions space into uniform
pix-els that each store information on light
characteris-tics In this manner, the raster data model is
particu-larly well suited to represent natural resource imagery
collected from satellites and other forms of remote
sensing
Additionally, the vector and raster data models not
only store information on where an entity is located
but also store information on the characteristics of
en-tities Thus, a user can click on a map layer in a GIS
and receive additional information about a feature or
location This is an important design characteristic
because it enables GIS users to analyze the spatial
characteristics of attributes that do not necessarily
have a spatial component For example, a natural
re-source manager could use GIS to analyze how water
characteristics, such as pH or dissolved oxygen, vary along a stream network based on point samples col-lected at various locations throughout a watershed
GIS Applications GIS can be applied to almost any task that has been traditionally evaluated using maps In the social sci-ences, for example, GIS is used to map crimes, modify election districts, and model population migration Business analysts use GIS to identify potential sites for businesses, identify consumer markets, and distribute products The medical community uses GIS technol-ogy to track diseases and study environmental impacts
on health GIS software is used in schools to teach ge-ography and promote spatial literacy There are also numerous applications of GIS in the natural sciences For one, GIS is used to observe and study natural sys-tems This includes efforts to monitor agricultural production, track endangered species, or study bird migration patterns GIS is used to explore the rela-tionships between different environmental systems
to delineate wildlife habitats or study the impact of climate change on local ecosystems It is also used to manage the use of natural resources, such as forests, water, and fossil fuels It can also be used to model human-environment interactions, develop predic-tions, and structure debates regarding the conserva-tion or development of natural resources Finally, and perhaps most routinely, GIS can be used to visualize spatial data and disseminate information regarding environmental systems
An example of how GIS is used to analyze environ-mental systems is illustrated in the following scenario
of identifying an acceptable location for a wind farm
To begin, a power company could use a GIS to analyze wind-speed data to identify locations where the aver-age wind speed is strong enough to generate wind power Next, the company might compare the loca-tions to a digital layer that shows high-power transmis-sion lines to determine which sites will be easiest to connect to the existing energy grid The company could then use GIS to explore the land-cover charac-teristics and the cost of developing access roads to pre-pare acceptable building sites for construction GIS could also be used to identify property owners that would be impacted by the project or determine which municipalities the company will have to contact for le-gal and tax purposes In a similar manner, GIS may be used to empower opponents of the wind farm For ex-ample, opponents could use GIS to evaluate and
Trang 3de-bate the aesthetics of the proposed wind farm or the
impacts it would have on culturally sensitive
land-scapes or wildlife
Future of GIS
GIS software and related technologies have become
increasingly common in research, education, and
people’s daily lives The development of Web-based
GIS, mobile GPS devices, off-the-shelf software, and
advances in remote sensing have fostered a broad
in-terest in developing GIS data and resources in many
different domains For the natural sciences, these
developments have resulted in greater access to
high-quality digital datasets and improved ability to
con-sider a broad range of factors in environmental
analy-ses The developments have also highlighted many of
the limitations of existing GIS software packages
re-garding the analysis of environmental systems The
most noteworthy limitations draw on the fact that GIS
is designed to represent space based on static,
two-dimensional maps and is therefore poorly suited to
represent three-dimensional, dynamic
environmen-tal entities such as weather phenomena or ocean
circulation patterns In recent years an academic
dis-cipline called GIScience has evolved to address
re-search issues regarding the design and use of GIS
Jeffrey C Brunskill
Further Reading
Bolstad, Paul GIS Fundamentals: A First Text on
Geo-graphic Information Systems 3d ed White Bear Lake,
Minn.: Eider Press, 2008
Lang, Laura Managing Natural Resources with GIS.
Redlands, Calif.: Environmental Systems Research
Institute Press, 1998
Longley, Paul, et al Geographic Information Systems and
Science 2d ed New York: Wiley, 2005.
Randolph, John Environmental Land Use Planning and
Management Washington, D.C.: Island Press, 2004.
Scally, Robert GIS for Environmental Management.
Redlands, Calif.: Environmental Systems Research
Institute Press, 2006
Web Sites
Clark Labs IDRISI Homepage
http://www.clarklabs.org/
Environmental Systems Research Institute
http://www.esri.com
See also: Aerial photography; Environmental engi-neering; Forest management; Land-use planning; Landsat satellites and satellite technologies; Ocean-ography; Remote sensing
Geology
Category: Scientific disciplines
The study of Earth and its geological processes is essen-tial to the discovery, extraction, and management of natural resources, from minerals to energy resources.
Background Geology is the study of the planet Earth: its composi-tion, origin, and history, and the environmental, bio-logical, chemical, and physical forces outside and within it As a science, geology grew from the nine-teenth century study of natural features, stratigraphy, and fossils in rock outcroppings to a wide variety of sci-entific subspecialties covering myriad aspects of the planet Since the early nineteenth century, geology has involved accurate mapping of the Earth’s topogra-phy and discovery, study, and exploitation of major mineral deposits around the world
A guiding principle in geology has been unifor-mitarianism: geological processes that are observed today are the same as those that occurred in the past and those that will occur in the future Application
of this concept on a planetary scale allows scientists
to prospect for minerals using remote-sensing tech-niques
Catastrophic events, including meteor impacts, have been deduced from geological deposits and have been credited with causing widespread mass ex-tinctions observed in the fossil record Identification
of the large meteor impact responsible for forming Chesapeake Bay has provided an explanation for re-cent earthquakes in the region and for the presence
of saltwater aquifers in Virginia Some economic geol-ogists have postulated that the platinum deposit at Sudbury, Ontario, is a meteor impact site from bil-lions of years ago
The United States Geological Survey (part of the Department of the Interior) is the governmental agency responsible for producing official maps and reports Most other nations have similar agencies, in-cluding the Geological Survey of Canada, Servicio
Trang 4Geológico Mexicano, the British
Geological Survey, Geoscience
Aus-tralia, the Geological Survey of
Ja-pan, and the South Africa Council
for Geoscience, which all host
infor-mational Web sites
Knowledge of geology is
funda-mental to the understanding of all
inanimate resources on Earth
Geo-thermal energy can provide an
in-expensive alternative to fossil and
nuclear sources for generating
elec-tricity Discovery of necessary
min-eral resources is a prerequisite to
exploitation, while the mechanics of
exploiting those resources also
re-quires geological expertise
Environ-mental geologists are involved in
mapping and investigating toxic
con-tamination areas for possible
mitiga-tion Search for permanent
geologi-cal sites for radioactive materials is
going on in countries around the
world Potential natural hazards—
including unstable topography,
earth-quake fault lines, and volcanic
activ-ity—require geological monitoring to
warn people of impending disasters
Exploration Geology
Exploration geologists focus on the
discovery and exploitation of
min-eral and ore deposits and fossil fuels
Stone Age humans found
outcrop-pings of flint and chert with which to
make arrowheads and other tools Eventually,
hu-mans moved on to easily worked metals such as
cop-per, tin, silver, gold, and iron Precious gems have
been highly valued for millennia, and new sources for
these ores and minerals continue to be found
Modern industrialized society requires metals for
basic construction and manufacturing The increasing
technological demand has moved geological
explora-tion from the California gold rush era of the American
West to the worldwide search for uranium for nuclear
weapons to the search for rare earth elements for
high-tech electronics and lithium deposits for batteries
Geologists in the twenty-first century rarely engage in
time-consuming initial field exploration and
prospect-ing, relying on remote sensing from aircraft and
satel-lites to determine where new mineral deposits might
be found Confirmation of mineral deposits and plans for exploitation require geological expertise The exploitation of coal, oil, and gas deposits around the world provides vital sources of energy to the billions of people on Earth Most geologists are employed, usually by governments and private indus-try, in this aspect of geology
Coal remains the most important fuel for electric power production worldwide, with reserves of anthra-cite (“hard”) and bituminous (“soft”) coal widespread
in North America, Europe, and Asia Large-scale un-derground coal mining is labor intensive and expen-sive Many American coal companies have opted to use cheaper methods of obtaining coal, such as strip
Primary Rocks and Minerals in Earth’s Crust
Rocks
% Volume
of Crust Minerals
% Volume
of Crust
Clays and shales 4.2 Plagioclase 39
salt-bearing deposits) 2.0 Amphiboles 5
Granites 10.4 Clay minerals (and Granodiorites, diorites 11.2 chlorites) 4.6 Syenites 0.4 Calcite (and aragonite) 1.5
amphibolites, eclogites 42.5 Magnetite (and Dunites, peridotites 0.2 titanomagnetite) 1.5
Others (garnets, kyanite,
Metamorphic andalusite, sillimanite,
Quartz and feldspars 63
Totals Pyroxene and olivine 14 Sedimentary 7.9 Hydrated silicates 14.6
Source: Michael H Carr et al., The Geology of the Terrestrial Planets, NASA SP-469,
1984 Data are from A B Ronov and A A Yaroshevsky, “Chemical Composition of the Earth’s Crust,” American Geophysical Union Monograph 13.
Trang 5mining and mountaintop removal mining (MTR), in
which coal deposits are located at or near surface
level MTR in areas like West Virginia and Kentucky is
unpopular with the general public because of the
widespread environmental degradation that occurs
when entire mountains are leveled and overburden
(soil and non-coal rock) materials are placed in
ad-jacent valleys Land use after MTR may be
deter-mined by geological studies; the areas are usually left
unvegetated after mining activities end Coal slurry
impoundments are used to hold huge amounts of
MTR coal waste, and if the impoundment fails, aquatic
wildlife in the area’s streams and rivers is eradicated
In March, 2009, the U.S Environmental Protection
Agency announced that permits for MTR of coal
would be carefully scrutinized
Oil deposits occur around the world, and
geologi-cal exploration teams continue to find major
discov-eries Exploration and development of new oil fields
are often complicated by politics, on both national
and international scales Opening up the Alaskan
Na-tional Wildlife Reserve (ANWR) to oil exploration
and drilling is an example of such complications
Even though President George W Bush and Vice
President Dick Cheney both strongly favored drilling,
Congress was unwilling to authorize oil leases in the
eight years (2001-2009) of the Bush presidency In the
2008 U.S presidential election, ANWR became a
ma-jor campaign issue when Alaskan governor Sarah
Palin, who was the Republican vice presidential
candi-date, strongly endorsed drilling
Discovery and commercial exploitation of heavy
bitumen oil sands, which cannot be pumped out of
the ground like petroleum deposits, have become
ma-jor political issues because this fossil fuel leaves a large
carbon footprint Oil sands are strip-mined or hauled
from massive open-pit mines An estimated 780,000
barrels of oil are produced per day from Canadian oil
sands in Alberta, and about 60 percent of this is
ex-ported to the United States Oil sands in Alberta are
estimated to contain more than one trillion barrels of
oil, 80 percent of which is not accessible through
pres-ent surface mining methods Oil sand deposits also
occur in Utah, Venezuela, and Russia
Geological Monitoring of Volcanoes and
Earthquakes
The devastating Boxing Day tsunami of December 26,
2004, which engulfed Indian Ocean shorelines from
Indonesia to East Africa and killed more than 225,000
people, followed an undersea event known as the Great Sumatra-Andaman earthquake The countries most affected by the tsunami lacked geological moni-toring stations Such a seismological monimoni-toring net-work could have provided many areas with several hours warning of the impending tsunami and less-ened the death toll The U.S National Oceanic and Atmospheric Administration operates the Pacific Tsu-nami Warning System, which warns of potential prob-lems for Hawaii, Alaska, and the Pacific coast of North America
Volcano monitoring is necessary to warn people
of impending eruptions Erupting volcanoes emit clouds of ash that can be sucked into jet aircraft en-gines, where the ash liquefies and then deposits a solid glass coating to the rear of the jet turbine This glass coating interferes with the jet enough to cause the aircraft to crash Ash problems necessitate closure
of airports within the reach of the erupting volcano, and aircraft must be diverted from routes that pass through the ash clouds
Environmental Geology Environmental geologists use a variety of geological, geochemical, microbiological, and hydrological tech-niques to identify and mitigate hazards resulting from urban sprawl, industrialization, and mining activities The most common environmental problems include surface water and groundwater contamination, dump-ing of hazardous wastes in unprotected ground, and air pollution related to improper waste handling
A permanent geological storage site for reactor waste in the United States has been a limiting factor in public support for the nuclear power industry (Nu-clear weapons waste is stored in Carlsbad, New Mex-ico.) Requirements for geological storage include the absence of groundwater and total lack of seismic activ-ity in a solid bedrock formation Many locations have been proposed In 1987, Yucca Flat, Nevada, was se-lected, but the selection met with almost immediate opposition because of unanswered geological ques-tions In March, 2009, President Barack Obama an-nounced that plans to use Yucca Flat had been aban-doned Stephen Chu, the secretary of energy for the Obama administration, indicated that the United States might build nuclear power reactors that could utilize nuclear waste, thus dramatically lessening (but not eliminating) the amount of radioactive waste requiring permanent storage Other countries, in-cluding Sweden, have conducted rigorous
Trang 6wide geological surveys to identify potential nuclear
waste storage sites and are moving closer to final site
selection Some nuclear industry experts believe that
the United States will not select a site until 2030
Commercial Power Production from
Geothermal Energy
Harnessing hot springs and geysers to produce
elec-tricity has been going on at Larderello, Italy, for more
than a century and is well established in Iceland
and the Philippines; the latter two countries produce
about 20 percent of their electricity from
geother-mal energy Iceland has a geothergeother-mal capacity of 1.3
terawatt-hours per year There are twenty-seven
elec-tricity plants at The Geysers, in Northern California,
producing 750 megawatts Important geological
con-cerns arise when harnessing geothermal sources The
major problem at generating locations like Wairakei,
New Zealand, and The Geysers is local depletion of
heat sources; heated zones are tapped too intensively
for too long of a period to allow recharge of heat from
deep within the Earth Other problems include the
need for drilling deep wells and for fracturing rock
around the deep wells at geothermal locations
Al-though the technology for drilling deep wells exists, it
is a costly process
Anita Baker-Blocker
See also: Department of Energy, U.S.; Earth’s crust;
Ecology; Igneous processes, rocks, and mineral
de-posits; Metamorphic processes, rocks, and mineral
deposits; Minerals, structure and physical properties
of; Oceanography; Sedimentary processes, rocks, and
mineral deposits
Geothermal and hydrothermal
energy
Categories: Geological processes and formations;
energy resources; obtaining and using resources
Geothermal energy is the energy associated with the
heat in the interior of the Earth The common usage of
the term refers to the thermal energy relatively near the
surface of the Earth that can be utilized by humans.
Hydrothermal energy is the energy associated with hot
water, whereas geothermal is a more general term
Geo-thermal energy has been exploited since early history It
is a source of energy with a low pollution potential that can be used for producing electricity as well as for heat-ing and coolheat-ing and helpheat-ing with a number of other needs.
Background
A geothermal system is made up of three elements: a heat source, a reservoir, and a fluid that transfers the heat The heat source can be a magmatic intrusion
or the Earth’s normal temperature, which increases with depth The reservoir is a volume of hot perme-able rock from which circulating fluids extract heat Fluid convection transports the heat from the higher-temperature low regions to the upper regions, where
it can be accessed and used
Causes of Geothermal Phenomena While individuals in early mining operations may have noted the general increase in temperature with depth, not until the eighteenth centur y were subsurface temperature measurements performed The results often showed an increase in temperature with depth The rate of increase varied from site to site An average value that is often used today is a 2.5°
to 3° Celsius increase per 100 meters increase in depth from the surface The geothermal gradient suggested that the source of the Earth’s heat was be-low the surface, but the exact cause of the heat was open to discussion for many years It was not until the early part of the twentieth century that the decay of ra-dioactive materials was identified as the primary cause
of this heat The thermal energy of the Earth is very large; however, only a small portion is available for capture and utilization The available thermal energy
is primarily limited to areas where water or steam car-ries heat from the deep hot regions to, or near, the surface The water or steam is then available for cap-ture and may be put to such uses as electricity genera-tion and heating
The interior of the Earth is often considered to be divided into three major sections, called the crust, mantle, and core The crust extends from the surface down to about 35 kilometers beneath the land and about 6 kilometers beneath the ocean Below the crust, the mantle extends to a depth of roughly 2,900 kilometers Below, or inside, the mantle is the Earth’s core The crust is rich in radioactive materials, with a much lower density in the mantle and essentially none in the core The radioactive decay of these mate-rials produces heat The Earth is also cooling down,
Trang 7however The volume of the mantle is roughly forty
times that of the crust The combination of the heat
generated from the decay of radioactive materials and
the cooling of the Earth results in the flow of heat to
the Earth’s surface The origin of the total heat
flow-ing to the surface is roughly 20 percent from the crust
and 80 percent from the mantle and core
The outermost shell of the Earth, made up of the
crust and upper mantle, is known as the lithosphere
According to the concept of plate tectonics, the
sur-face of the Earth is composed of six large and several
smaller lithospheric regions or plates On some of the
edges of these plates, hot molten material extends to
the surface and causes the plates to spread apart On
other edges, one plate is driven beneath another
There are densely fractured zones in the crust around
the plate edges A great amount of seismic activity
oc-curs in these regions, and they are where large
num-bers of volcanoes, geysers, and hot springs are
lo-cated High terrestrial heat flows occur near the edges
of the plates, so the Earth’s most important
geother-mal regions are found around the plate margins A
concentration of geothermal resources is often found
in regions with a normal or elevated geothermal
gra-dient as well as around the plate margins
History of Development
The ancient Romans used the water from hot springs
for baths and for heating homes China and Japan
also used geothermal waters for bathing and washing
Similar uses are still found in various geothermal
re-gions of the world Other uses of thermal waters were
not developed until the early part of the nineteenth
century An early example occurred in the Larderello
area of Italy In 1827, Francesco Larderel developed
an evaporation process that used the heat from
geo-thermal waters to evaporate the geo-thermal waters found
in the area, leaving boric acid Heating the water by
burning wood had been required in the past
Also in the early nineteenth century, inventors
be-gan attempting to utilize the energy associated with
geothermal steam for driving pumps and winches
Beginning in the early twentieth century,
geother-mal steam was used to generate electricity in the
Larderello region Several other countries tried to
uti-lize their own geothermal resources Geothermal wells
were drilled in Beppu, Japan, in 1919, and at The
Gey-sers, California, in 1921 In the late 1920’s, Iceland
began using geothermal waters for heating Various
locations in the western United States have used
geo-thermal waters for heating homes and buildings in the twentieth century Among these are Klamath Falls, Oregon, and Boise, Idaho
After World War II, many countries became inter-ested in geothermal energy; geothermal resources of some type exist in most countries Geothermal energy was viewed as an energy source that did not have to be imported and that could be competitive with other sources of electricity generation In 1958, New Zea-land began using geothermal energy for electric power production One of the first power plants in the United States began operation at The Geysers, Cali-fornia, in 1960 Mexico began operating its first geo-thermal power plant at Cerro Prieto, near the Califor-nia border, in 1973
By 2007, the United States was a leading country
in electric power production from geothermal re-sources with 2,700 megawatts of installed electrical capacity By 2004, Costa Rica, El Salvador, Iceland, Kenya, and the Philippines had significant geother-mal energy outputs that accounted for at least 15 per-cent of each countries’ energy production Nonelec-tric uses of geothermal energy occur in most countries
In 2000, the leading nonelectric users of geothermal energy in terms of total usage were, in descending or-der, China, Japan, the United States, Iceland, Turkey, New Zealand, the Republic of Georgia, and Russia
Classification of Geothermal Resources Geothermal resources are classified by the tempera-ture of the water or steam that carries the heat from the depths to, or near, the surface Geothermal re-sources are often divided into low temperature (less than 90° Celsius), moderate temperature (90° to 150° Celsius), and high temperature (greater than 150° Celsius) There are still various worldwide opinions
on how best to divide and describe geothermal re-sources The class or grouping characterizing the geo-thermal resource often dictates the use or uses that can be made of the resource
A distinction that is often made in describing geo-thermal resources is whether there is wet or dry steam present Wet steam has liquid water associated with it Steam turbine electric generators can often use steam directly from dry steam wells, but separation is neces-sary for the use of steam from wet steam wells In vari-ous applications the water needs to be removed from wet steam This is achieved through the use of a sepa-rator, which separates the steam gas from liquid hot water The hot water is then re-injected into the
Trang 8voir; used as input to other systems to recover some
of its heat; or, if there are not appreciable levels of
environmentally threatening chemicals present,
dis-charged into the environment after suitable cooling
Exploration
The search for geothermal resources has become
eas-ier in the twenty-first century than it was in the past
be-cause of the considerable amount of information and
maps that have been assembled for many locations
around the world and because of the availability of
new instrumentation, techniques, and systems The
primary objectives in geothermal exploration are to
identify geothermal phenomena, determine the size
and type of the field, and identify the location of the
productive zone Further, researchers need to
deter-mine the heat content of the fluids that are to be
dis-charged from the wells, the potential lifetime of the
site, problems that may occur during operation of the
site, and the environmental consequences of
develop-ing and operatdevelop-ing the site Geological and
hydrologi-cal studies help to define the geothermal resource
Geochemical surveys help to determine if the re-source is vapor- or water-dominated as well as to esti-mate the minimum temperature expected at the re-source’s depth Potential problems later in pipe scaling, corrosion, and environmental impact are also determined by this type of survey Geophysical surveys help to define the shape, size, and depth of the re-source The drilling of exploration wells is the true test of the nature of the resource Because drilling can
be costly, use of previous surveys in selecting or siting each drill site is important
Electricity Generation The generation of electrical energy from geothermal energy primarily occurs through the use of conven-tional steam turbines and through the use of binary plants Conventional steam turbines operate on fluid temperatures of at least 150° Celsius An atmospheric exhaust turbine is one from which the steam, after passing through the turbine, is exhausted to the atmo-sphere Another form of turbine is one in which the exhaust steam is condensed The steam consumption
Geothermal steam is funneled through the pipes in the foreground from the geyser drilling station in the background at this Northern Califor-nia location (Manny Crisostomo/MCT/Landov)
Trang 9per kilowatt-hour produced for an atmospheric
ex-haust unit is about twice that for a condensing unit,
but atmospheric exhaust units are simpler and
cheaper
The Geysers has one of the largest dry-steam
geo-thermal fields in the world Steam rises from more
than forty wells Pipes feed steam to the
turbogen-erators at a temperature of 175° Celsius Some of the
wells are drilled to depths as great as 2,700 meters
The geothermal field at Wairakei on North Island of
New Zealand has been a source of electric power for
several decades The hot water (near 300° Celsius)
rises from more than sixty deep wells As the pressure
falls, the hot water converts to steam The flashing of
hot water to steam is the major source of geothermal
energy for electric power production
Binary plants allow electricity to be generated from
low- to medium-temperature geothermal resources as
well as from the waste hot water coming from steam/
water separators Binary plants use a secondary
work-ing fluid The geothermal fluid heats the secondary
fluid, which is in a closed system The working fluid is
heated, vaporizes, drives a turbine, is cooled,
con-denses, and is ready to repeat the cycle Binary plant
technology is becoming the most cost-effective means
to generate electricity from geothermal resources
be-low 175° Celsius
In cascaded systems, the output water from one
sys-tem is used as the input heat source to another syssys-tem
Such systems allow some of the heat in waste water
from higher temperature systems to be recovered and
used They are often used in conjunction with electric
generation facilities to help recover some of the heat
in the wastewater or steam from a turbine
Space Heating
Space heating by geothermal waters is one of the most
common uses of geothermal resources In some
coun-tries, such as Iceland, entire districts are heated using
the resource The nature of the geothermal water
dic-tates whether that water is circulated directly in pipes
to homes and other structures or (if the water is too
corrosive) a heat exchanger is used to transfer the
heat to a better fluid for circulation Hot water in the
range from 60° to 125° Celsius has been used for space
heating with hot-water radiators Water with as low a
temperature as 35° to 40° Celsius has been used
effec-tively for heating by means of radiant heating, in
which pipes are embedded in the floor or ceiling
An-other way of using geAn-othermal energy for heating is
through the circulation of heated air from water-to-air heat exchangers Heat pumps are also used with geo-thermal waters for both heating and cooling
In district heating, the water to the customer is of-ten in the 60° to 90° Celsius range and is returned at 35° to 50° Celsius The distance of the customers from the geothermal resource is important Transmission lines of up to 60 kilometers have been used, but shorter distances are more common and desirable When designing a district heating system, the selec-tion of the area to be supplied, building density, char-acteristics of the heat source, the transmission system, heat loss in transmission, and heat consumption by customers are all important factors
There are more than 550 geothermal wells serving
a variety of uses in Klamath Falls, Oregon Utiliza-tion includes heating homes, schools, businesses, and swimming pools as well as snow-melting systems for sidewalks and a section of highway pavement Most of the eastern side of the city is heated by geothermal energy The principal heat extraction system is the closed-loop downhole heat exchanger utilizing city water in the heat exchangers Hot water is delivered
at approximately 82° Celsius and returns at 60° Cel-sius
Hot water from springs is delivered through pipes
to heat homes in Reykjavík, Iceland, and several outly-ing communities This is the source of heatoutly-ing for 95 percent of the buildings in Reykjavík Hot water is de-livered to homes at 88° Celsius The geothermal water
is also used for heating schools, swimming pools, and greenhouses and is used for aquaculture
Greenhouse Heating Using geothermal resources to heat greenhouses is similar to using it to heat homes and other buildings The objective in this case is to provide a thermal envi-ronment in the greenhouse so that vegetables, flow-ers, and fruits can be grown out of season The green-house is supplied with heated water, and through the use of radiators, embedded pipes, aerial pipes, or sur-face pipes, the heat is transferred to the greenhouse environment Forced air through heat exchangers is also used The United States, Hungary, Italy, and France all have considerable numbers of geothermal greenhouses
Aquaculture One of the major areas for the direct use of geother-mal resources is in aquaculture The main idea is to
Trang 10adjust the temperature of the water environment in
a production pond so that freshwater or marine fish,
shrimp, and plants have greater growth rates and
thus reach harvest age more quickly There are many
schemes to regulate the temperature of the pond
water For supply wells where the geothermal water is
near the required temperature, the water is
intro-duced directly into the pond For locations having a
well-water temperature too high, the water is spread
in a holding pool where evaporative cooling,
radia-tion, and conductive heat loss to the ground can all be
used to reduce the temperature to a level in which it
can be added to the main production pond
Industrial Applications
The Tasman Pulp and Paper Company, located in
Kawerau, New Zealand, is one of the largest industrial
developments to utilize geothermal energy
Geother-mal exploration started there in 1952; it was directed
toward locating and developing a geothermal resource
for a pulp and paper mill In 1985, the company was
using four wells to supply steam to the operations
The steam is used to operate log kickers directly,
to dry timber, to generate clean steam, and to drive
an electricity generator Geothermal energy supplies
about 30 percent of the total process steam and 4
per-cent of the electricity for the plant Geothermal
en-ergy in the form of steam is used to dry diatomaceous
earth in Námafjall, Iceland The diatomaceous earth
is dredged from the bottom of a lake and pumped 3
ki-lometers by pipeline to a plant where it is dried
Numerous other industrial applications of
geo-thermal resources exist in the world These range
from timber drying in Japan to salt production from
evaporating seawater in the Philippines, vegetable
drying in Nevada, alfalfa drying in New Zealand, and
mushroom growing in Oregon
Environmental Impact
The environmental impacts associated with the use
or conversion of geothermal resources are typically
much less than those associated with the use or
con-version of other energy sources The resource is often
promoted as a clean technology without the potential
radiation problems associated with nuclear energy
fa-cilities or the atmospheric emissions problems often
associated with oil and coal electric plants
Nonethe-less, although associated environmental problems are
low, there are some present In the exploration and
development phases of large-scale geothermal
devel-opments, access roads and platforms for drill rigs must be built The drilling of a well can result in possi-ble mixing of drilling fluids with the aquifers inter-sected by the well if the well is not well-cased Blowouts can also pollute the groundwater The drilling fluids need to be stored and handled as wastes
Geothermal fluids often contain dissolved gases such as carbon dioxide, hydrogen sulfide, and meth-ane Other chemicals, such as sodium chloride, bo-ron, arsenic, and mercury, may also be associated with the geothermal water The presence of these gases and chemicals must be determined, and appropriate means must be selected to prevent their release into the environment In some cases this problem is re-duced by the re-injection of wastewater into the geo-thermal reservoir
The release of thermal water into a surface water body such as a stream, pond, or lake can cause severe ecosystem damage by changing the ambient water temperature, even if only by a few degrees Any dis-charge of hot water from the geothermal site needs to involve a means of cooling the water to an acceptable level—one that will not cause environmental damage This result is often achieved through the use of hold-ing ponds or evaporative coolhold-ing The removal of large volumes of geothermal fluid from the subsur-face can cause land subsidence This is irreversible and can cause major structural damage Subsidence can be prevented by the re-injection of a volume of fluid equal to that removed
Noise pollution is one of the potential problems with geothermal sites where electricity generation is conducted Noise reduction can require costly mea-sures Because many geothermal electric generation sites are rural, however, this is often not a problem The noise generated in direct heat applications is typi-cally low
Economics The initial cost of a geothermal plant is usually higher than the initial cost of a similar plant run on conven-tional fuel On the other hand, the cost of the energy for operating a geothermal plant is much lower than the cost of conventional fuels In order to be economi-cally superior, the geothermal plant needs to operate long enough to at least make up for the difference in initial cost
Cascaded systems can be used to optimize the re-covery of heat from the geothermal water and steam and therefore to decrease the overall costs Systems