EARTH SCIENCES - Notable Research and Discoveries Part 6 ppt

Most power companies use steam turbines, in which steam funneled at high pressure through the turbine presses against Iceland has abundant geysers and hot springs, such as those at Namas

tivate a search for clean, renewable sources of energy The problem thus

seeps into the ground, producing geysers and hot springs Ancient

people, Romans took advantage of hot springs where they were avail-able Some of the Romans in the city of Pompeii, for example, used

water from geothermal sources to heat their houses Archaeologists

made this discovery when they excavated Pompeii, which, as described

in chapter 3, was buried by a volcanic eruption in 79 c.e A portion of

the city’s buildings remain intact and have features such as plumbing to

circulate hot water, allowing the heat to warm the interior

of physics as a dynamo—a conductor spinning in a magnetic field pro-duces electricity A turbine is an engine consisting of a rotating shaft on

United States Most power companies use steam turbines, in which

steam funneled at high pressure through the turbine presses against

Iceland has abundant geysers and hot springs, such as those at Namaskard,

near Lake Myvatn (Steve Allen/Getty)

Electricity

Electric generators are devices to convert energy in one form

or another into electrical energy Heat is a common form of

en-ergy that is transformed into electricity, as in turbines that are

driven by a hot gas such as steam The heat to create this hot

gas can come from burning oil, coal, or natural gas, but it can

also come from the Earth Geothermal power stations use heat

coming from beneath the surface to rotate the turbines.

There are three main types of geothermal power station, differing in the nature of the geothermal supply that they tap

(A) In a dry steam power plant, the steam rises, turns turbine,

then returns, in a cooler state, to the reservoir.

A “dry” steam geothermal power station taps into a reservoir that is mostly vapor—steam—with little or no liquid (water), which is what gives it its name Figure A on page 104 illus- trates the basic operation Pipes sunk into the underground reservoir bring steam into the turbine, where it rotates the shaft and drives the electric generator The steam expends some of its energy in the turbine, which lowers its tempera- ture Pipes on the other side of the turbine return the fl uid

to the reservoir, so that it can be reheated and reused Dry steam power stations are simple and were the fi rst type

of geothermal power station developed—the early

genera-(B) In a fl ash steam power plant, hot water abruptly changes to steam in the fl ash tank due to the decreased pressure, then turns

a turbine and returns to the reservoir.

(continues)

the United States, such as California and Nevada, geothermal reservoirs

are within reach or in some cases rise all the way to the surface Other

parts of the country are not so fortunate

tor of Italian inventor Conti was a rudimentary dry steam

generator The world’s largest geothermal power station, 30

square miles (77 km 2 ) along the Sonoma and Lake Count

border, about 100 miles (160 km) north of San Francisco,

California, is known as The Geysers This dry steam power

station harnesses naturally occurring steam field reservoirs

below the Earth’s surface.

Some of the reservoirs hold hot water instead of steam

These reservoirs can be used in a type of geothermal power

station called a flash station or a flash steam station Water

deep below the surface can have a temperature in excess of

the boiling point at sea level—212°F (100°C)—because the

boiling point depends on pressure, and the high pressure

beneath the surface means that water can exist at much

higher temperatures without boiling When this extremely

hot water is brought to the surface and placed in an

environ-ment that does not exert as much pressure, the water

rap-idly boils or “flashes” into steam As illustrated in figure (B),

flash steam power stations employ this process to generate

the steam needed to drive the turbine.

The third type of geothermal power station is called a binary station This type of power station uses a geother-

mal reservoir containing water that is hot but not quite hot

enough to operate a flash station Instead, a piece of

equip-ment called a heat exchanger transfers heat from the hot

water to another fluid, which flashes at a lower temperature

This second fluid boils, producing the vapor that rotates

the turbine The term binary, referring to two components,

comes from the use of two fluids.

(continued)

Geothermal opportunities are clustered in certain spots in other parts of the world Volcanic activity coincides with a lot of geothermal

fluctuate, depending on demand Oil prices also depend on political

while goal In recognition of this goal, the DOE has established the

amount of power generated from each station and the reliability and

lifetime of these stations But at these temperatures, which approach

the melting point of substances such as aluminum and magnesium,

geothermal engineers must learn how to protect sensitive equipment

before applications can be developed

ing geothermal energy Iceland, which is located along the boundary of

because they use fluids circulating in the system that alternately expand,

capturing heat from the house, and then condense in pipes outside,

which transfers the heat The expenditure of energy comes from the

spas—the presence of minerals in the water Silica, the sandy

mate-rial that is used for glassmaking and other applications, is a common

constituent of geothermal reservoirs Hot water carries a substantial

Is geothermal energy renewable? A geologist could argue that geo-amount of heat As heat flows out of an object, its temperature drops

Excessive use of geothermal energy could possibly cool the planet’s ac-cessible depths to an unusable temperature

heat fl owing from the surrounding areas Heat does not conduct very

Interdisciplinary Science—Many

Specialties, one Goal

Most scientists spend part of their time directly on science—

making observations in the fi eld, doing experiments, or

devel-oping theories—and the rest of their time fulfi lling other

obliga-tions, such as writing reports in their area of expertise,

evalu-ating the reports of other scientists that have been submitted

to scientifi c journals (so that the journal editors can decide

whether the report is worthy of publishing), and participating in

conferences Scientists contribute their expertise in the writing

and evaluation of reports to increase knowledge in their own

disciplines, but scientists with different specialties often attend

the same conferences Such meetings provide opportunities to

exchange ideas and to learn different points of view.

An interdisciplinary panel, such as that organized by MIT

to study geothermal energy, is a means of exchanging

in-formation and pooling expertise in the pursuit of a common

goal No one can possibly have a deep knowledge of all fi elds

of science and engineering; more than half a million scientifi c

papers are published each year, and keeping up to date on

just a single branch or discipline is demanding enough.

quickly through rock, so in the absence of significant convection cur-rents, it may take decades for a cooled reservoir to reheat

sible reservoirs at certain geothermal sites are factors that limit geother-

sachusetts Institute of Technology (MIT), recently addressed these is-sues and issued a report, The Future of Geothermal Energy, in 2006.

Heading the MIT panel was Jefferson W Tester, an MIT professor of chemical engineering (the study of chemical reactions and conversions that produce industrially useful substances) The panel also included chemists, geophysi- cists (geologists who specialize in applying the principles of physics to the study of Earth), engineers who specialize in petroleum products, geothermal experts, economists who specialize in the study of energy production and manage- ment, and experts in the conversion of energy into electrical power All these specialties were important in analyzing the problem of developing geothermal energy into the most use- ful products in the most efficient way.

Organizing the MIT panel, bringing the panel members together, and providing the essential data and materials to study costs money The Office of the Geothermal Technology Program, established by DOE, donated these funds Panel members met and reviewed past and current research proj- ects from the United States, Europe, Japan, and Australia

The panel’s findings were detailed in a 372-page report, The Future of Geothermal Energy, issued in 2006 This project

serves as an example of the need to call on the skills of many different people in order to tackle a complicated scientific or technical problem.

The report was the product of a team of 18 scientists, engineers, geothermal specialists, and drilling experts As described in the side-

Colorado, on May 16, 2006 The report, Geothermal—the Energy

un-der Our Feet, authored by Bruce D Green and R Gerald Nix of NREL,

therefore has a lot of heat available at a shallow depth—it is somewhat

like a hot spot without the volcanic activity (see chapter 3)

In this geothermal system, water circulates in pipes, which extend

through the relatively cool sedimentary rocks to reach the hot granite

rocks below After heating, the water enters the heat exchanger and

releases some of its energy, which drives the electricity generators in

the power plant.

As illustrated in the figure opposite, Geodynamics plans to pump cool water through the top-level sedimentary rocks and into the hot, frac-

As the world’s supply of fossil fuel comes to an end, alternative en-

ergy sources must be found To the extent that these sources are re-newable, people will not face expensive and disruptive energy crises

in the future Energy production and consumption that emit little

pollution or otherwise entail minimal damage to the environment

ish studying the exact cause of the tremors The results of these studies

will be used in a thorough analysis of the risks of the project, which is

1

Surveyors led by John C Fremont (1813–90) dis-cover The Geysers, an area of California rich with steam and hot springs rising from the surface