A seminar report On GEO THERMAL ENERGY
Submitted to Jawaharlal Nehru Technological University, Kakinada In Partial Fulfillment of the Requirements for the Award of the Degree Of Bachelor of Technology In Mechanical Engineering
By C.MADHURI LATHA
(07481A0317)
Under the esteemed guidance of Dr. A. Jawahar Babu , Ph.D
Professor and Head of ME
Department of Mechanical Engineering GUDLAVALLERU ENGINEERING COLLEGE SESHADRIRAO KNOWLEDE VILLAGE GUDLAVALLERU – 521356 2010 – 2011
GUDLAVALLERU ENGINEERING COLLEGE: GUDLAVALLERU SESHADRI RAO KNOWLEDGE VILLAGE DEPARTMENT OF MECHANICAL ENGINEERING
CERTIFICATE
This is to certify that this seminar work entitled “GEO THERMAL ENERGY”
Is a bonafide record of work done By C.MADHURI LATHA
(07481A0317)
Under my guidance and supervision and submitted in partial fulfillment of the requ requir irem ement entss for for the the award award of Degr Degree ee of Bachelo achelorr of Technology nology in Mechanical Engineering during the Year 2010–2011 by Jawaharlal Nehru Technological University, K akinada. akinada.
Dr. A. JAWAHAR BABU,
Seminar Guide.
Dr. A. JAWAHAR BABU,
Head of Department, Mechanical Engineering.
ABSTRACT
In present day scenario, people are very much worried about POLLUTION (mainly caused by non-renewable sources such as petroleum, diesel, coal etc), which is increasing rapidly day by day. So, as to breathe easy, pollution should be avoided or reduced to some extent in one way or the other. Besides pollution, the cost of non-renewable sources is being cumulated. So, it is our turn to find alternative for these non-renewable energy sources. This is an attempt to create an awareness regarding GEO-THERMAL ENERGY and its applications in various fields, which is one among the alternative energy resources. The Earth’s crust is a bountiful source of energy and fossil fuels are only part of the story. Heat or thermal energy is by far the more abundant resource. To put it in perspective, the thermal energy in the uppermost six miles of the Earth’s crust amounts to 50,000 times the energy of all oil and gas resources in the world! The word “geothermal” literally means “Earth” plus “heat.” The geothermal resource is the world’s largest energy resource and has been used by people for centuries. In addition, it is environmentally friendly. It is a renewable resource and can be used in ways that respect rather than upset our planet’s delicate environmental balance. Geothermal power plants operating around the world are proof that the Earth’s thermal energy is readily converted to electricity in geologically active areas. This also deals the things concerning about geo-thermal power plant advantages and environmental aspects.
INTRODUCTION Geothermal energy comes from the heat within the earth. The word "geothermal" is derived from the Greek words geo, meaning earth," and thermal, meaning "heat." People around the world use geothermal energy to produce electricity, to heat buildings and for other purposes. The earth's core lies almost 4,000 miles beneath the earth's surface. The doublelayered core is made up of very hot molten iron surrounding a solid iron center. Estimates of the temperature of the core range from 5,000 to 11,000 degrees Fahrenheit (F). Heat is continuously produced within the earth by the slow decay of radioactive particles that is natural in all rocks. Surrounding the earth's core is the mantle, thought to be partly rock and partly magma. The mantle is about 1,800 miles thick. The crust is the outermost layer of the earth, the land that forms the continents and ocean floors. It can be three to five miles thick under the oceans and 15 to 35 miles thick on the continents.
Earth’s Interior
The earth's crust is broken into pieces called plates. Magma comes close to the earth's surface near the edges of these plates. This is where volcanoes occur. The lava that erupts from volcanoes is partly magma. Deep underground, the rocks and water absorb the heat from this magma. The temperature of the rocks and water get hotter and hotter as the depth increases underground. People around the world use geothermal energy to heat their homes and to produce electricity by digging deep wells and pumping the heated underground water or steam to the surface. Or, one can make use of the stable temperatures near the surface of the earth to heat and cool buildings.
First Geothermal Power Plant In The World
In 1904 emerging steam was used to turn a small turbine which in turn powered five light bulbs - the first ever demonstration of geothermal electricity generation. In 19 11 the Valle del Diavolo (Devil's Valley) was chosen as the site of what would remain the world's only geothermal power station for almost half a century. By 19 13 a 250kW power station had been built which provided power for the Italian electric railway system.
Prince Piero Ginori Conti invented the first geothermal power plant in 1904, at the Larderello dry steam field in Italy How does geothermal energy come to the surface?
Flow of magma up into volcanoes, which discharge it as lava.
Flow of underground water, or steam, naturally heated deep in the Earth.
Flow of water or steam, injected and retrieved by human effort.
Because the geologic processes known as plate tectonics, the Earth’s crust has been broken into 12 huge plates that move apart or push together at a rate of millimeters per year. Where two plates collide, one plate can thrust below the other, producing extraordinary phenomena such as ocean trenches or strong earthquakes. At great depth, just above the down going plate, temperatures become high enough to melt rock, forming magma. Because magma is less dense than surrounding rocks, it moves up toward the earth’s crust and carries heat from below. Sometimes magma rises to the surface through thin or fractured crust as lava. However, most magma remains below earth’s crust and heats the surrounding rocks and subterranean water.
Schematic representation of an ideal geothermal system.
So, how does water get there then, deep in the Earth? It usually gets there through rain water trickling down rock fissures. Where a lot of it collects in underground aquifers, and is heated by the Earth, it expands and may rise to the surface as water or steam. Hot water in such geothermal reservoirs can reach temperatures of 700F (or 370C). Now this source of heating energy has been used by people for many centuries.
The third way of getting at this energy is facilitated by humans. It involves injecting water at high pressures deep into porous heated rock formations and retrieving it as hot water.
The Three Main Applications Of Geothermal Energy Are:
1) Direct Use and District Heating Systems which use hot water from springs or reservoirs near the surface. 2) Electricity generation in a power plant requires water or steam at very high temperature (300 to 700 degrees Fahrenheit). Geothermal power plants are generally built where geothermal reservoirs are located within a mile or two of the surface. 3) Geothermal heat pumps use stable ground or water temperatures near the earth's surface to control building temperatures above ground.
1) DIRECT USE AND DISTRICT HEATING SYSTEMS The direct use of hot water as an energy source has been happening since ancient times. The Romans, Chinese, and Native Americans used hot mineral springs for bathing, cooking and heating. Hot water near the earth's surface can be piped directly into buildings and industries for heat. A district heating system provides heat for 95 percent of the buildings in Reykjavik, Iceland.
2. GEOTHERMAL POWER PLANTS: There are three geothermal power plant technologies being used to convert hydrothermal fluids to electricity. The conversion technologies are
Dry steam
Flash Steam and
Binary Cycle
The type of conversion used depends on the state of the fluid (whether steam or water) and its temperature.
Dry Steam Power Plants:
Steam plants use hydrothermal fluids that are primarily steam. The steam goes directly to a turbine, which drives a generator that produces electricity. The steam eliminates the need to burn fossil fuels to run the turbine. (Also eliminating the need to transport and store fuels!) This is the oldest type of geothermal power plant. It was first used at Lardarello in Italy in 1904, and is still very effective. Steam technology is used today at The Geysers in northern California, the world's largest single source of geothermal power. These plants emit only excess steam and very minor amounts of gases.
Dry steam power plant Types of dry steam power plants:
Atmospheric exhaust geo-thermal power plants.
Condensing geo-thermal power plants.
Atmospheric exhaust geo-thermal power plants:
Atmospheric exhaust turbines are simpler and cheaper. The steam, direct from dry steam wells or, after separation, from wet wells, is passed through a turbine and exhausted to the Atmosphere. With this type of unit, steam consumption (from the same inlet pressure) per Kilowatt-hour produced is almost double that of a condensing unit. However, the Atmospheric exhaust turbines are extremely useful as pilot plants, stand-by plants, in the Case of small supplies from isolated wells, and for generating electricity from test wells during field development. They are also used when the steam has a high
non condensable Gas content (>12% in weight). The atmospheric exhaust units can be Constructed and installed very quickly and put into operation. This type of machine is usually available in small sizes (2.5 - 5 MW).
Atmospheric exhaust geo thermal power plant
Condensing geo-thermal power plants:
The condensing units, having more auxiliary equipment, are more complex than the atmospheric exhaust units and the bigger sizes can take twice as long to construct and install. The specific steam consumption of the condensing units is, however, about half that of the atmospheric exhaust units. Condensing plants of 55 - 60 MW capacity are very common.
Condensing geo thermal power plant
Flash Steam Power Plants:
Hydrothermal fluids above 360°F (182°C) can be used in flash plants to make electricity. Fluid is sprayed into a tank held at a much lower pressure than the fluid, causing some of the fluid to rapidly vaporize, or "flash." The vapor then drives a turbine, which drives a generator. If any liquid remains in the tank, it can be flashed again in a second tank to extract even more energy. Both dry steam and flash steam power plants emit small amounts of carbon dioxide, nitric oxide, and sulfur, but generally 50 times less than traditional fossil-fuel power plants.
Flash steam power plant
Binary-Cycle Power Plants:
Generating electricity from low-to-medium temperature geothermal fluids and from the waste hot waters coming from the separators in water - dominated geothermal fields has made considerable progress since improvements were made in binary fluid technology. The binary plants utilize a secondary working fluid, usually an organic fluid (typically n-pentane), that has a low boiling point and high vapour pressure at low temperatures when compared to steam. The secondary fluid is operated through a conventional Rankine cycle (RC): the geothermal fluid yields heat to the secondary fluid through heat exchangers, in which this fluid is heated and vaporizes; the vapour produced drives a normal axial flow turbine, is then cooled and condensed, and the cycle begins again.
Binary cycle power plant
By selecting suitable secondary fluids, binary systems can be designed to utilize geothermal fluids in the temperature range 85-170 °C. The upper limit depends on the thermal stability of the organic binary fluid, and the lower limit on technical-economic factors: below this temperature the size of the heat exchangers required would render the project uneconomical. Apart from low-to-medium temperature geothermal fluids and waste fluids, binary systems can also be utilized where flashing of the geothermal fluids should preferably be avoided (for example, to prevent well sealing). In this case, down hole pumps can be used to keep the fluids in a pressurized liquid state, and the energy can be extracted from the circulating fluid by means of binary units. Binary plants are usually constructed in small modular units of a few hundred kW to a few MW capacities. These units can then be linked up to create power-plants of a few tens of megawatts. Their cost depends on a number of factors, but particularly on the temperature of the geothermal fluid produced, which influences the size of the turbine, heat exchangers and cooling system. The total size of the plant has little effect on the specific cost, as a series of standard modular units is joined together to obtain larger capacities. Binary plant technology is a very cost-effective and reliable means of converting into Electricity the energy available from water-dominated geothermal fields (below 170 °C). A new binary system, the Kalina cycle, which utilizes a water-ammonia mixture as Working fluid was developed in the 1990s. The working fluid is expanded, in superheated Conditions, through the high-pressure turbine and then re-heated before entering the low-pressure turbine. After the second expansion the saturated vapour moves through a recuperative boiler before being condensed in a water-cooled condenser. The Kalinaf cycle is more efficient than existing geothermal RC binary power plants, but is of more complex design. Electricity could facilitate many apparently banal, but extremely important operations, such as pumping water for irrigation, freezing fruit and vegetables for longer conservation.
3. GEOTHERMAL HEAT PUMPS
Geothermal (ground water/ground source) technology utilizes a type of heat pump known as a geothermal heat pump. This type of geothermal heat pump device extracts its heat from water rather than from air. In this water is pumped through a special type of heat exchanger and is either "chilled" by the evaporating refrigerant (in the heating mode) or heated by the condensing refrigerant (in the cooling mode). Types of Geothermal heat pumps
Open –Loop systems
Closed-Loop systems
Open –Loop systems:
An open loop is a loop established between a water source and a discharge area in which the water is collected and pumped to a GWHP then discharged to its original source or to another location. The piping for such configuration is open at both ends and the water is utilized only once.
Open loop system
Examples of such loops are: systems operating off wells wherein water is pumped from a supply well, through the unit and discharged to a return well; open systems operating from such surface water sources as ponds, lakes, streams, etc, where the source water is pumped to the unit and returned to the source. Open loops have the advantage of higher equipment performance since the source water is used only once and then discharged, but have two significant disadvantages: 1. water quality needs to be carefully analyzed and treated if such corrosives as sulphur, iron, or manganese are present , if pH is low, or if there are abrasives in it 2. the costs of pumping water through an open loop are usually somewhat higher than those associated with circulating water through a closed loop Closed –Loop systems:
A closed loop is one in which both ends of the loop's piping are closed. The water or other fluid is re-circulated over and over and no new water is introduced to the loop. The heat is transferred through the walls of the piping to or from the source, which could be ground, ground water, or surface water. As heat is extracted from the water in the loop the temperature of the loop falls and the heat from the source flows toward the loop.
Closed loop system
In closed loop operation water quality is not an issue because corrosives become rapidly "spent" or used up and corrosion caused by poor water quality is quickly curtailed The wire-to-water efficiencies of circulators used in closed loop operation are very high and the costs of pumping the water are lower as compared to open loops. System efficiencies are somewhat lower in closed loop operation, but given the lower pumping costs associated with this method, economics sometimes, but not always favor this approach. Installed costs, however, are higher and need to be considered if the consumer already has a well or other water source. OTHER APPLICATIONS OF GEOTHERMAL ENERGY
Agriculture:
Thermal water can be used in open-field agriculture to irrigate and/or heat the soil and also to sterilize soil. Geothermal heat can also be used for crop and timber drying. The main advantages of temperature control in open-field agriculture are: o
The prevention of plant damage from low air temperatures;
o
Extension of the growing season;
o
Increased plant growth and production; and
o
Soil sterilization that controls pests and diseases.
Greenhouses:
Greenhouse heating is a common use of geothermal energy. Glass or plastic film is used to trap solar radiation and heat, which provides a controlled environment for plants to grow and increase yields. Many commercially grown vegetables, flowers, house plants and tree seedlings are suitable for greenhouse culture.
Aquaculture:
Aquaculture is the farming of aquatic organisms including fish, and aquatic plants. Farming implies some sort of intervention in the rearing process to enhance production, such as regular stocking, feeding, and protection from predators. In geothermal aquaculture the objective is to heat the water to the optimum temperature for
fish growth. An emerging aqua cultural industry is the cultivation of vegetable species that can be adapted for human and animal foods. Crops adaptable to geothermal enhanced growth include duckweed, numerous algae species and kelp.
Industrial applications:
Geothermal energy can be cost effective and reliable in industrial applications. Some of these uses include drying fish, fruits, vegetables and timber products, washing wool, dying cloth, manufacturing paper and pasteurizing milk. The largest industrial applications are in pulp, paper and wood processing.
Electricity Generation from Geothermal Energy In U.S.
2700 MW of power
0.4% of all electrical generation
Iceland is one of the more countries successful in using geothermal energy:
86% of their space heating uses geothermal energy.
16% of their electricity generation uses geothermal energy.
Potential Geothermal Provinces of India Province
Surface To C
Himalaya Cam bay West coast SONATA Godavari
>90 40-90 46-72 60-95 50-60
Reservoir C
260 150-175 102-137 105-217 175-215
To
Heat Flow
mW/m2
468 80-93 75-129 120-290 93-104
Thermal gradient
C/km 100 70 47-59 60-90 60
o
Geothermal Energy And The Environment The environmental impact of geothermal energy depends on how it is being used. Direct use and heating applications have almost no negative impact on the environment. Geothermal power plants do not burn fuel to generate electricity, so their emission levels are very low. They release about 1 to 3 percent of the carbon dioxide emissions of a fossil fuel plant. Geothermal plants use scrubber systems to clean the air of hydrogen sulfide that is naturally found in the steam and hot water. Geothermal plants emit 97 percent less acid rain - causing sulfur compounds than are emitted by fossil fuel plants. After the steam and water from a geothermal reservoir have been used, they are injected back into the earth. Well-designed binary cycle power plants have no emissions at all.
ADVANTAGES OF GEOTHERMAL ENERGY
Geothermal is a reliable renewable energy source.
By using geothermal energy, millions of tones of fossil fuels are being saved worldwide. The land area required for geothermal power plants is smaller per megawatt than
for almost every other type of power plant.
It is resistant to interruptions of power generation due to weather, natural disasters or political rifts that can interrupt transportation of fuels.
No fuel is needed
Once we've built a geothermal power station, the energy is almost free. It may need a little energy to run a pump, but this can be taken from the energy being generated. So it is an economic benefit.
Geothermal energy does not produce any pollution, and does not contribute to the greenhouse effect. So it is eco-friendly in nature.
DISADVANTAGES OF GEOTHERMAL ENERGY
The big problem is that there are not many places where you can build a geothermal power station. You need hot rocks of a suitable type, at a depth where we can drill down to them. The type of rock above is also important, it must be of a type that we can easily drill through.
Brine can salinate soil if the water is not injected back into the reserve after the heat is extracted.
Extracting large amounts of water can cause land subsidence, and this can lead to an increase in seismic activity. To prevent this the cooled water must be injected back into the reserve in order to keep the water pressure constant underground.
Drilling operation is noisy.
The steam and hot water gushing out of the earth may contain H2S, CO2, NH3 and radon gas etc. If these gases are vented into the air, air pollution will be a real hazard. These gases are to be removed by chemical action, before they are discharged.
Overall efficiency for power production is low, about 15%, as compared to (35 to 40) % for fossil fuel plants.
CONCLUSION:
The demand for electricity is growing exponentially year by year in India. Much of this electricity is made by burning fossil fuels that are dirty and irreplaceable. Fortunately, there are alternatives. From the first power plant in Larderello, Italy, to the state-of-the-art facilities found all over the world today, geothermal plants use natural hot water and steam from the earth to run turbine generators. If geothermal energy continues to be used at the present rate, it is estimated that the available resources could last for five million years. Technological advances are making this a cost-effective resource. Expect to see its increased use in the near future, especially in the geothermally active western United States, India, Indonesia, and other "hot spots" around the Pacific.
REFERENCES
1. www.energy.gov/energysources/geothermal.htm 2. www.trimodalgesthermal.com 3. www.geothermal.org/index.htm 4. www.geothermal.marin.org 5. Non-Conventional Energy Resources by G.D.RAI
