Geothermal Enegy

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Energy Technology Assignment By Khalil Raza Bhatti (07ME40)

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GEOTHERMAL ENERGY

The heat of the Earth makes up what is known as geothermal energy. When dust and gasses from

Earth mixed together 4 billion years ago, geothermal energy resulted.

Inside the Earth at its core, some 4, 000 miles deep, the temperature is estimated at about 9,000

degrees Fahrenheit. Geothermal energy has been used throughout history for bathing, relaxing,

cooking and heating. It was thought by some to have healing effects and was used to treat eye and

skin diseases. The first geothermal generator that produced energy was built in Lardarello, Italy in

1904. The United States followed with their first attempt at geothermal power in 1912 at The

Geysers in California. Today it is produced in twenty-one countries around the world.

Geothermal energy is located deep in the ground. The heat at the core of the Earth has an outward

flow. As it moves, it is transferred to surrounding rock layers called the mantle. As temperatures and

pressure increase, the rock melts and becomes magma. The magma moves toward the surface of

the earth carrying the heat with it. If the magma reaches the Earths surface, it becomes lava.

However, most of it stays below the Earths crust and heats rocks and water that surround it. These

temperatures can reach up to 700 degrees Fahrenheit. When the water travels to the Earthssurface, it becomes hot springs or geysers. Mostly it stays trapped in fractured, porous rocks called

geothermal reservoirs. This heat near the Earths surface becomes a form of energy.

Hot water or steam from the reservoir exerts a force that can spin a turbine connected to a

generator and produces electricity. The cooled water is then returned to the reservoir in order for it

to reheat. Much exploration and testing needs to be done to determine where the geothermal

underground waters are. When ideal spots are located, drilling is done to create production wells

that bring the water to the Earths surface for power generation in geothermal power plants.

Although the costs to construct geothermal plants and geothermal wells are high, the cost of

producing electricity is lower over time. The fuel is reliable, stable and does not need to be

transported. The white smoke you will see over geothermal power plants is not smoke but rather

steam. During the process of operations it may, however, bring some hazardous gases from

underground.

The United States stands as the biggest producer of geothermal energy. Unfortunately, interest in it

is low and it only accounts for about 1% of this countrys energy supply. Through research and

experience new methods and technologies for accessing geothermal energy will improve. Tapping

into the heat under the Earths surface can produce much more of the nations energy. We are at a

point where renewable energy sources must make their way to the forefront of the energy picture.

Not only are fossil fuels being depleted, but also they are ruining our air quality. In time, geothermal

energy may become an appealing alternative. Competitive pricing and minimal environmental

impact could produce a hot future for this renewable energy source.


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SOU RCES OF GEOTHERMAL ENERGY

Geothermal energy is an unlimited resource. The lot surrounding a home contains a vast reservoir of

low temperature thermal energy, typically 10 times that required over an entire heating season. This

resource is constantly resupplied by the sun, the surrounding earth, and heat rejected while cooling

during the summer. The universal definition of geothermal is "...pertaining to the heat of the earth."

By using the earth to provide up to 50% of a building's total heating and cooling needs, thesesystems are truly geothermal energy made practical.

Four basic types of geothermal energy resources:

Horizontal loops areoften considered when

adequate land surface

is available. Pipes are

placed in trenches, in

lengths that range

from 100 to 400 feet.

Pond (lake) loops arevery economical to

install when a body of

water is available.

Excavation costs are

virtually eliminated.

Coils of pipe are simply

placed on the bottom

of the pond or lake.

Vertical loops are theideal choice when

available land surface

is limited. Drilling

equipment is used to

bore small-diameter

holes from 75 to 300

feet deep.

Open loop systems arethe fourth type and

utilize ground water as

a direct energy source.

In ideal conditions, an

open loop application

can be the most

economical type of

geothermal system

Four times the efficiency:

A geothermal system uses the Earth's thermal properties in conjunction with electricity to provide

unprecedented efficiency. For every unit of electricity the system uses, it provides four units of

heating energy, giving a geothermal system a 400% efficiency rating on average. These numbers

translate into real savings on your utility bills year-round.


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GEOTHERMAL SYSTEMS

The word geothermal comes from the Greek words geo (earth) and therme (heat), and means the

heat of the earth.

Geothermal energy is ultimately derived from the heat contained in the core of the earth and fromradioactive decay within its mantle. At high temperatures and pressures within the mantle, melting

of mantle rock forms magma which rises towards the surface

carrying the heat from below.

In some regions where the earth's crust is thin or fractured, or

where magma bodies are close to the surface, there are high

temperature gradients. Deep faults, rock fractures and pores

allow groundwater to percolate towards the heat source and

become heated to high temperatures. Some of this hot

geothermal water travels back to the surface through buoyancy

effects to appear as hot springs, mud pools, geysers, or

fumaroles. If the ascending hot water meets an extensively

fractured or permeable rock zone, the heated water will fill pores and fractures and form a

geothermal reservoir. These reservoirs are much hotter than surface hot springs, reaching

temperatures of more than 350C, and are potentially an accessible source of energy.

These high temperatures can be achieved in liquid-dominated reservoirs because increasing

hydrostatic pressure with depth allows elevated temperatures without boiling. Many undisturbed

geothermal reservoirs in New Zealand have temperature and pressure profiles such that the fluid is

close to boiling point to depths of more than 1 km.

Geothermal areas are commonly close to the edges of continental plates, and New Zealand'slocation on an active plate boundary (between the Indo-Australian and Pacific Plates) has resulted in

the development of numerous geothermal systems and a world-class geothermal energy resource.

The characteristics of geothermal systems vary widely, but three components are essential:

a subsurface heat source that may be igneous magma bodies or heat stored in other rocks fluid to transport the heat Faults, fractures or permeability within sub-surface rocks that allow the heated fluid to flow

from the heat source to the surface or near-surface.

Geothermal resources can be classified into three categories:

High temperature, usually magmatic-related resources. These have temperatures of 200-350C at economically-drillable depth. They are of limited occurrence, and form individual

convective geothermal systems of up to 50 sq km in area. Technologies may be developed in

the future to exploit even deeper, hotter resources.

Moderate to low temperature resources, of non-magmatic origin, usually associated withdeep faults. Maximum temperatures at drillable depth do not exceed 140C, and are often


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less. These are more widespread than the high temperature resources, but the individual

systems are no larger. The distinction between these and the first kind is not entirely clear-

cut, as cooled outflows from hotter resources can also fall into the same temperature range.

Very low temperature resources, which are widespread but close to ambient temperature.


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EFFECTS OF GEOTHERMAL ENERGY ON

THE ENVIRONMENT

Fluids drawn from the deep earth carry a mixture of gases, notably carbon dioxide (CO2), hydrogen

sulfide (H2S), methane (CH4) and ammonia (NH3). These pollutants contribute to globalwarming, acid rain, and noxious smells if released. Existing geothermal electric plants emit an

average of 122 kg of CO2 per megawatt-hour (MWh) of electricity, a small fraction of the emission

intensity of conventional fossil fuel plants. Plants that experience high levels of acids and volatile

chemicals are usually equipped with emission-control systems to reduce the exhaust. Geothermal

plants could theoretically inject these gases back into the earth, as a form of carbon capture and

storage.

In addition to dissolved gases, hot water from geothermal sources may hold in solution trace

amounts of toxic chemicals such as mercury, arsenic, boron, antimony, and salt. These chemicals

come out of solution as the water cools, and can cause environmental damage if released. The

modern practice of injecting spent geothermal fluids back into the Earth to stimulate production has

the side benefit of reducing this environmental risk.

Direct geothermal heating systems will contain pumps and compressors, and the electricity they

consume may come from a polluting source. This parasitic load is normally a fraction of the heat

output, so it is always less polluting than electric heating. However, if the electricity is produced by

burning fuels, then the net pollution of geothermal heating may be comparable to directly burning

the fuel for heat. For example, a geothermal heat pump powered by electricity from a combined

cycle natural gas plant would produce about as much pollution as a natural gas condensing

furnace of the same size. Therefore the environmental value of direct geothermal heating

applications is highly dependent on the emissions intensity of the neighboring electric grid.

Plant construction can adversely affect land stability. Subsidence has occurred in the Wairakei

field in New Zealand and in Staufen in Breisgau, Germany. Enhanced geothermal systems can

trigger earthquakes as part of hydraulic fracturing. The project in Basel, Switzerland was suspended

because more than 10,000 seismic events measuring up to 3.4 on the Richter scale occurred over the

first 6 days of water injection.

Geothermal has minimal land and freshwater requirements. Geothermal plants use

3.5 square kilometers per gigawatt of electrical production (not capacity) versus 32 and

12 square kilometers for coal facilities and wind farms respectively. They use 20 litres of freshwater

per MWh versus over 1000 litres per MWh for nuclear, coal, or oil.

Geothermal fluids contain dissolved gases which are released into the atmosphere. The main toxic

gases are carbon dioxide (CO2) and hydrogen sulfide (H2S). Both are denser than air and can collect in

pits, depressions or confined spaces. These gases are a recognised hazard for people working at

geothermal stations or bore fields, and can also be a problem in urban areas. In Rotorua a number of

deaths have been attributed to hydrogen sulfide poisoning, often in motel rooms or hot-pool


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enclosures. Carbon dioxide is also a greenhouse gas, contributing to potential climate change.

However, geothermal extraction releases far fewer greenhouse gases per unit of electricity

generated than burning fossil fuels such as coal or gas to produce electricity.

Geothermal fluids contain elevated levels of arsenic, mercury, lithium and boron because of the

underground contact between hot fluids and rocks. If waste is released into rivers or lakes instead of

being injected into the geothermal field, these pollutants can damage aquatic life and make the

water unsafe for drinking or irrigation.

A serious environmental effect of the geothermal industry is arsenic pollution. Levels of arsenic in

the Waikato River almost always exceed the World Health Organisation standard for drinking water

of 0.01 parts per million. Most of the arsenic comes from geothermal waste water discharged from

the Wairkei power station. Natural features such as hot springs are also a source of arsenic, but it

tends to be removed from the water as colourful mineral precipitates like bright red realgar and

yellowy green orpiment.

The process of extracting geothermal fluids (which include gases, steam and water) for power

generation typically removes heat from natural reservoirs at over 10 times their rate of

replenishment. This imbalance may be partially improved by injecting waste fluids back into the

geothermal system.


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SUGGESTIONS ABOUT COURSE

DEF IC IENCIES AND IMPROVEMENTS

DEFICIENCIES

The course is set by higher education commission therefore it is well arranged. As for teaching way

can be commented. To best thing was that very student in Energy Technology lecture was very

interested, as class discussion was always there. Also, questions and answers also contributed a lot.

Overall, it was great to have such a lecture of one subject, opening more ideas, so to me teaching

way was very good, but few things may be rechecked, like thered always be a introductory and

concluding briefing by the teacher on the topic and in between the class discussion, in which no one

should be allowed interrupt. Rest theres nothing which I can think of.

Geothermal Enegy

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