Ocean thermal energy conversion
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Ocean thermal energy conversion (OTEC) is a method for generating electricity which uses the temperature difference that exists between deep and shallow waters to run a heat engine. As with any heat engine, the greatest efficiency and power is produced with the largest temperature difference. This temperature difference generally increases with decreasing latitude, i.e. near the equator, in the tropics. Historically, the main technical challenge of OTEC was to generate significant amounts of power, efficiently, from this very small temperature ratio. Changes in efficiency of heat exchange in modern designs allow performance approaching the theoretical maximum efficiency.

The Earth's oceans are continually heated by the sun and cover nearly 70% of the Earth's surface; this temperature difference contains a vast amount of solar energy which can potentially be harnessed for human use. If this extraction could be made cost effective on a large scale, it could provide a source of renewable energy needed to deal with energy shortages, and other energy problems. The total energy available is one or two orders of magnitude higher than other ocean energy options such as wave power, but the small magnitude of the temperature difference makes energy extraction comparatively difficult and expensive, due to low thermal efficiency. Earlier OTEC systems had an overall efficiency of only 1 to 3% (the theoretical maximum efficiency lies between 6 and 7%[1]). Current designs under review will operate closer to the theoretical maximum efficiency. The energy carrier, seawater, is free, although it has an access cost associated with the pumping materials and pump energy costs. Although an OTEC plant operates at a low overall efficiency, it can be configured to operate continuously as a Base load power generation system. Any thorough Cost-benefit analysis should include these factors to provide an accurate assessment of performance, efficiency, operational and construction costs and returns on investment.

The concept of a heat engine is very common in thermodynamics engineering, and much of the energy used by humans passes through a heat engine. A heat engine is a thermodynamic device placed between a high temperature reservoir and a low temperature reservoir. As heat flows from one to the other, the engine converts some of the heat energy to work energy. This principle is used in steam turbines and internal combustion engines, while refrigerators reverse the direction of flow of both the heat and work energy. Rather than using heat energy from the burning of fuel, OTEC power draws on temperature differences caused by the sun's warming of the ocean surface.

The only heat cycle suitable for OTEC, is the Rankine cycle, using a low-pressure turbine. Systems may be either closed-cycle or open-cycle. Closed-cycle engines use working fluids that are typically thought of as refrigerants such as ammonia or R-134a. Open-cycle engines use the water heat source as the working fluid


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OCEAN THERMAL ENERGY CONVERSION
A seminar report

PRESENTED BY:
A.Swathi P.Srivalli Sneha

PRASAD.V. POTLURI SIDDHARTHA INSTITUTE OF TECHNOLOGY
Affiliated to JNTU, Hyderabad


ABSTRACT
Ocean Thermal Energy Conversion (OTEC) is an energy technology that converts solar radiation to electric power. OTEC systems use the ocean's natural thermal gradient”the fact that the ocean's layers of water have different temperatures to drive a power-producing cycle. As long as the temperature between the warm surface water and the cold deep water differs by about 20°C (36°F), an OTEC system can produce a significant amount of power, with little impact on the surrounding environment.
The distinctive feature of OTEC energy systems is that the end products include not only energy in the form of electricity, but several other synergistic products. The principle design objective was to minimize plan cost by minimizing plant mass, and taking maximum advantage of minimal warm and cold water flows. Power is converted to high voltage DC, and is cabled to shore for conversion to AC and integration into the local power distribution network.
The oceans are thus a vast renewable energy resource, with the potential to help us produce billions of watts of electric power.
OCEAN THERMAL ENERGY CONVERSION
Oceans cover more than 70% of Earth's surface, making them the world's largest solar collectors. The sun's heat warms the surface water a lot more than the deep ocean water, and this temperature difference creates thermal energy. Just a small portion of the heat trapped in the ocean could power the world.
I. INTRODUCTION TO OCEAN ENERGY:
Most people have been witness to the awesome power of the world's oceans. For least a thousand years, scientists and inventors have watched ocean waves explode against coastal shores, felt the pull of ocean tides, and dreamed of harnessing these forces. But it's only been in the last century that scientists and engineers have begun to look at capturing ocean energy to make electricity.
The ocean can produce two types of energy: thermal energy from the sun's heat, and mechanical energy from the tides and waves. Ocean thermal energy is used for many applications, including electricity generation. Ocean mechanical energy is quite different from ocean thermal energy. Even though the sun affects all ocean activity, tides are driven primarily by the gravitational pull of the moon, and waves are driven primarily by the winds. As a result, tides and waves are sporadic sources of energy, while ocean thermal energy is fairly constant. Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices.
II. OCEAN THERMAL ENERGY CONVERSION:
OTEC is a process which utilizes the heat energy stored in the tropical ocean. The world's oceans serve as a huge collector of heat energy. OTEC plants utilize the difference in temperature between warm surface sea water and cold deep sea water to produce electricity.
Intensive Energy
The energy associated with OTEC derives from the difference in temperature between two thermal reservoirs. The top layer of the ocean is warmed by the sun to temperatures up to 20 K greater than the seawater near the bottom of the ocean. OTEC energy is different from geothermal energy in that one cannot assume the cold reservoir is infinite. The physical energy of two large reservoirs of fluid at different temperatures is
in J/kg where r is the mass of warm water divided by the mass of cold water entering the plant(1). For optimal performance, r is approximately 0.5. It is assumed in this analysis that the specific heat of the two fluid reservoirs is an average value over the often small temperature difference, but varying with salinity in the case of seawater.
Thermal energy conversion is an energy technology that converts solar radiation to electric power. OTEC systems use the ocean's natural thermal gradient”the fact that the ocean's layers of water have different temperatures”to drive a power-producing cycle. As long as the temperature between the warm surface water and the cold deep water differs by about 20°C, an OTEC system can produce a significant amount of power. The oceans are thus a vast renewable resource, with the potential to help us produce billions of watts of electric power. This potential is estimated to be about 1013 watts of base load power generation, according to some experts. The cold, deep seawater used in the OTEC process is also rich in nutrients, and it can be used to culture both marine organisms and plant life near the shore or on land. OTEC produce steady, base-load electricity, fresh water, and air-conditioning options.
OTEC requires a temperature difference of about 36 deg F (20 deg C). This temperature difference exists between the surface and deep seawater year round throughout the tropical regions of the world. To produce electricity, we either use a working fluid with a low boiling point (e.g. ammonia) or warm surface sea water, or turn it to vapor by heating it up with warm sea water (ammonia) or de-pressurizing warm seawater. The pressure of the expanding vapor turns a turbine and produces electricity.
Plant Design and Location
Commercial OTEC facilities can be built on
¢ Land or near the shore
¢ Platforms attached to the shelf
¢ Moorings or free-floating facilities in deep ocean water
Land-based and near-shore are more advantageous than the other two. OTEC plants can be mounted to the continental shelf at depths up to 100 meters, however may make shelf-mounted facilities less desirable and more expensive than their land-based counterparts. Floating OTEC facilities with a large power capacity, but has the difficulty of stabilizing and of mooring it in very deep water may create problems with power delivery.
Commercial ocean thermal energy conversion (OTEC) plants must be located in an environment that is stable enough for efficient system operation. The temperature of the warm surface seawater must differ about 20°C (36°F) from that of the cold deep water that is no more than about 1000 meters (3280 feet) below the surface. The natural ocean thermal gradient necessary for OTEC operation is generally found between latitudes 20 deg N and 20 deg S.
III. TYPES OF ELECTRICITY CONVERSION SYSTEMS
There are three types of electricity conversion systems: closed-cycle, open-cycle, and hybrid. Closed-cycle systems use the ocean's warm surface water to vaporize a working fluid, which has a low-boiling point, such as ammonia. The vapor expands and turns a turbine. The turbine then activates a generator to produce electricity. Open-cycle systems actually boil the seawater by operating at low pressures. This produces steam that passes through a turbine/generator. And hybrid systems combine both closed-cycle and open-cycle systems.
Closed-Cycle OTEC
In the closed-cycle OTEC system, warm sea water vaporizes a working fluid, such as ammonia, flowing through a heat exchanger (evaporator). The vapor expands at moderate pressures and turns a turbine coupled to a generator that produces electricity. The vapor is then condensed in heat exchanger (condenser) using cold seawater pumped from the ocean's depths through a cold-water pipe. The condensed working fluid is pumped back to the evaporator to repeat the cycle. The working fluid remains in a closed system and circulates continuously.
The heat exchangers (evaporator and condenser) are a large and crucial component of the closed-cycle power plant, both in terms of actual size and capital cost. Much of the work has been performed on alternative materials for OTEC heat exchangers, leading to the recent conclusion that inexpensive aluminum alloys may work as well as much more expensive titanium for this purpose.
Required condensate pump work, wC. The major additional parasitic energy requirements in the OTEC plant are the cold water pump work, wCT, and the warm water pump work, wHT. Denoting all other parasitic energy requirements by wA, the net work from the OTEC plant, wNP is
wNP = wT + wC + wCT + wHT + wA
The thermodynamic cycle undergone by the working fluid can be analyzed without detailed consideration of the parasitic energy requirements. From the first law of thermodynamics, the energy balance for the working fluid as the system is
wN = QH + QC
Where wN = wT + wC is the net work for the thermodynamic cycle. For the special idealized case in which there is no working fluid pressure drop in the heat exchangers,
QH = THds
H
and
QC = TCds
C
so that the net thermodynamic cycle work becomes
wN = THds + TCds
H C
Subcooled liquid enters the evaporator. Due to the heat exchange with warm sea water, evaporation takes place and usually superheated vapor leaves the evaporator. This vapor drives the turbine and 2-phase mixture enters the condenser. Usually, the subcooled liquid leaves the condenser and finally, this liquid is pumped to the evaporator completing a cycle.
Open-Cycle OTEC
The open cycle consists of the following steps: (i) flash evaporation of a fraction of the warm seawater by reduction of pressure below the saturation value corresponding to its temperature (ii) expansion of the vapor through a turbine to generate power; (iii) heat transfer to the cold seawater thermal sink resulting in condensation of the working fluid; and (iv) compression of the non-condensable gases (air released from the seawater streams at the low operating pressure) to pressures required to discharge them from the system.
This process being iso-enthalpic,
h2 = h1 = hf + x2hfg
Here, x2 is the fraction of water by mass that has vaporized. The warm water mass flow rate per unit turbine mass flow rate is 1/x2.
The low pressure in the evaporator is maintained by a vacuum pump that also removes the dissolved non condensable gases from the evaporator. The evaporator now contains a mixture of water and steam of very low quality. The steam is separated from the water as saturated vapour. The remaining water is saturated and is discharged back to the ocean in the open cycle. The steam we have extracted in the process is a very low pressure, very high specific volume working fluid. It expands in a special low pressure turbine.
h3 = hg
Here, hg corresponds to T2. For an ideal adiabatic reversible turbine,
s5,s = s3 = sf + x5,ssfg
The above equation corresponds to the temperature at the exhaust of the turbine, T5. x5,s is the mass fraction of vapour at point 5.
The enthalpy at T5 is,
h5,s = hf + x5,shfg
This enthalpy is lower. The adiabatic reversible turbine work = h3-h5,s.
Actual turbine work wT = (h3-h5,s) × polytropic efficiency
The condenser temperature and pressure are lower. Since the turbine exhaust will be discharged back into the ocean anyway, a direct contact condenser is used. Thus the exhaust is mixed with cold water from the deep cold water pipe which results in a near saturated water.That water is now discharged back to the ocean.
h6=hf, at T5. T7 is the temperature of the exhaust mixed with cold sea water, as the vapour content now is negligible,
There are the temperature differences between stages. One between warm surface water and working steam, one between exhaust steam and cooling water and one between cooling water reaching the condenser and deep water. These represent external irreversibilities that reduce the overall temperature difference.
The cold water flow rate per unit turbine mass flow rate,
Turbine mass flow rate,
Warm water mass flow rate,
Cold water mass flow rate
Hybrid OTEC System
Another option is to combine the two processes together into an open-cycle/closed-cycle hybrid, which might produce both electricity and desalinated water more efficiently. In a hybrid OTEC system, warm seawater might enter a vacuum where it would be flash-evaporated into steam, in a similar fashion to the open-cycle evaporation process.
The steam or the warm water might then pass through an evaporator to vaporize the working fluid of a closed-cycle loop. The vaporized fluid would then drive a turbine to produce electricity, while the steam would be condensed within the condenser to produced desalinated water
IV. OTHER TECHNOLOGIES
OTEC offers one of the most benign power production technologies, since the handling of hazardous substances is limited to the working fluid (e.g., ammonia), and no noxious by-products are generated. OTEC requires drawing sea water from the mixed layer and the deep ocean and returning it to the mixed layer, close to the thermo cline, which could be accomplished with minimal environmental impact. Aquaculture is perhaps the most well-known byproduct of OTEC. Cold-water delicacies, such as salmon and lobster, thrive in the nutrient-rich, deep, seawater from the OTEC process. Micro algae such as Spirulina, a health food supplement, also can be cultivated in the deep-ocean water.
Wave energy systems also cannot compete economically with traditional power sources. However, the costs to produce wave energy are coming down, Once built, however, wave energy systems (and other ocean energy plants) should have low operation and maintenance costs because the fuel they use sea water is free. Like tidal power plants, OTEC power plants require substantial capital investment upfront. Another factor hindering the commercialization of OTEC is that there are only a few hundred land-based sites in the tropics where deep-ocean water is close enough to shore to make OTEC plants feasible.
V. BENEFITS OF OTEC
We can measure the value of an ocean thermal energy conversion (OTEC) plant and continued OTEC development by both its economic and no economic benefits. OTECâ„¢s economic benefits include the:
¢ Helps produce fuels such as hydrogen, ammonia, and methanol
¢ Produces base load electrical energy
¢ Produces desalinated water for industrial, agricultural, and residential uses
¢ Is a resource for on-shore and near-shore Mari culture operations
¢ Provides air-conditioning for buildings
¢ Provides moderate-temperature refrigeration
¢ Has significant potential to provide clean, cost-effective electricity for the future.
¢ Fresh Water-- up to 5 liters for every 1000 liters of cold seawater.
¢ Food--Aquaculture products can be cultivated in discharge water.
OTECâ„¢s no economic benefits, which help us achieve global environmental goals, include these:
¢ Promotes competitiveness and international trade
¢ Enhances energy independence and energy security
¢ Promotes international sociopolitical stability
¢ Has potential to mitigate greenhouse gas emissions resulting from burning fossil fuels.
In small island nations, the benefits of OTEC include self-sufficiency, minimal environmental impacts, and improved sanitation and nutrition, which result from the greater availability of desalinated water and Mari culture products
VI. DISADVANTAGES
¢ OTEC-produced electricity at present would cost more than electricity generated from fossil fuels at their current costs. The electricity cost could be reduced significantly if the plant operated without major overhaul for 30 years or more, but there are no data on possible plant life cycles.
¢ OTEC plants must be located where a difference of about 40° Fahrenheit (F) occurs year round. Ocean depths must be available fairly close to shore-based facilities for economic operation. Floating plant ships could provide more flexibility.
VII. APPLICATIONS
Ocean thermal energy conversion (OTEC) systems have many applications or uses. OTEC can be used to generate electricity, desalinate water, support deep-water Mari culture, and provide refrigeration and air-conditioning as well as aid in crop growth and mineral extraction. These complementary products make OTEC systems attractive to industry and island communities even if the price of oil remains low.
The electricity produced by the system can be delivered to a utility grid or used to manufacture methanol, hydrogen, refined metals, ammonia, and similar products. The cold [5°C (41ºF)] seawater made available by an OTEC system creates an opportunity to provide large amounts of cooling to operations that are related to or close to the plant. Likewise, the low-cost refrigeration provided by the cold seawater can be used to upgrade or maintain the quality of indigenous fish, which tend to deteriorate quickly in warm tropical regions. The developments in other technologies (especially materials sciences) were improving the viability of mineral extraction processes that employ ocean energy.
VIII. CASE STUDY: (INDIA)
Conceptual studies on OTEC plants for Kavaratti (Lakshadweep islands), in the Andaman-Nicobar Islands and off the Tamil Nadu coast at Kulasekharapatnam were initiated in 1980. In 1984 a preliminary design for a 1 MW (gross) closed Rankine Cycle floating plant was prepared by the Indian Institute of Technology in Madras at the request of the Ministry of Non-Conventional Energy Resources. The National Institute of Ocean Technology (NIOT) was formed by the governmental Department of Ocean Development in 1993 and in 1997 the Government proposed the establishment of the 1 MW plant of earlier studies. NIOT signed a memorandum of understanding with Saga University in Japan for the joint development of the plant near the port of Tuticorin (Tamil Nadu).
It has been reported that following detailed specifications, global tenders were placed at end-1998 for the design, manufacture, supply and commissioning of various sub-systems. The objective is to demonstrate the OTEC plant for one year, after which it could be moved to the Andaman & Nicobar Islands for power generation. NIOTâ„¢s plan is to build 10-25 MW shore-mounted power plants in due course by scaling-up the 1 MW test plant, and possibly a 100 MW range of commercial plants thereafter.
IX. CONCLUSION
OTEC has tremendous potential to supply the worldâ„¢s energy. It is estimated that, in an annual basis, the amount solar energy absorbed by the oceans is equivalent to atleast 4000 times the amount presently consumed by humans. For an OTEC efficiency of 3 percent, in converting ocean thermal energy to electricity, we would need less than 1 percent of this renewable energy to satisfy all of our desires for energy.
OTEC offers one of the most compassionate power production technologies, since the handling of hazardous substances is limited to the working fluid (e.g., ammonia), and no noxious by-products are generated. Through adequate planning and coordination with the local community, recreational assets near an OTEC site may be enhanced. OTEC is capital-intensive, and the very first plants will most probably be small requiring a substantial capital investment. Given the relatively low cost of crude oil and of fossil fuels in general, the development of OTEC technologies is likely to be promoted by government agencies. Conventional power plants pollute the environment more than an OTEC plant would and, as long as the sun heats the oceans, the fuel for OTEC is unlimited and free.
X. REFERENCE
1. D. H. Johnson, Energy, Vol. 8, No. 20, pp. 927-946 (1983).
2. Claude G. (1930), "Power from the Tropical Seas" in Mechanical Engineering, Vol. 52, No.12, 19, pp. 1039-1044.
3. Nihous G.C. and. Vega L.A (1991), "A Review of Some Semi-empirical OTEC Effluent Discharge Models", in Oceans ˜91, Honolulu, Hawaii. [The OTEC effluent models are summarized]
4. Ocean Thermal Corporation. (1984a). Ocean Thermal Energy Conversion (OTEC) Preliminary Design Engineering Report. Prepared for U.S. Department of Energy, Washington, D.C.
5. Ocean Data Systems Inc. (1977). OTEC Thermal Resource Report for Hawaii Monterey, CA: Ocean Data Systems, Inc.
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#3
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Ocean Thermal Energy Conversion (OTEC)

Covering over 70% of the planet’s area, the Earth’s oceans could potentially be utilized as a source of virtually inexhaustible renewable energy. Ocean Thermal Energy Conversion (OTEC) is a method that employs naturally occurring temperature differences between warm surface water and colder deep seawater. To be effective a minimum temperature difference between the ocean surface layers is 20°C . These temperature gradients exist primarily in specific tropical regions near the equator originally proposed by French Engineer Jacques Arsene d’Arsonval in 1881, OTEC is not a new technology. Since then many advancements have been made in the development of this technology. The three most common OTEC systems are: open-cycle, closed-cycle and hybrid cycle, all requiring a working fluid, condenser and evaporator within the system. These three systems all employ the thermodynamics of a working heat exchanger and use the temperature differences naturally occurring in the ocean as the driving force. Concerns with efficiency losses due to befouling, system power requirements and heat exchanging systems have lead to exploration through case studies and analysis. While OTEC systems have been studied since 1881 there have been few full-scale implementations. There are still, however, a number of studies being conducted, especially in Japan, regarding the implementation of this renewable large scale technology
History

The first known Ocean Thermal Energy Conversion (OTEC) system was proposed by a French Engineer Jacques Arsened’Arsonval, in 1881 (Takahashi and Trenka, 1996). Recognizing the tropical oceans as a potential source of energy, through the natural temperature differences between the ocean’s surface water and deep water, D’Arsonval built a closed-cycle OTEC system, with ammonia as the working fluid that powered an engine (Takahashi and Trenka, 1996). Ammonia was chosen as the best fluid available to accommodate the pressure differences between the two temperatures of water assuming that the temperature of the boiler was 30°C and the condenser was 15°C (Avery and Wu, 1994). The pressure differences in the OTEC system design was one of the challenges D’Arsonval had to overcome. Ammonia was selected because it had such a low boiling point allowing it to become vaporized by the small temperature gradients when by the pumps in the system. In similar cycles where the Rankine cycle is followed there is usually a higher pressure gradient in which to generate energy i.e. combustion driven engines. In the case of OTEC the temperature gradients are maximum 22°C therefore a working fluid that was able to change phases with such as small gradient was chosen. This proposed technology was never tested by d’Arsonval himself.A student of d’Arsonval named George Claude soon took on the challenge of properly designing and building a working OTEC system. Claude, however, took a different approach to the design. He stated that corrosion and bio fouling of the heat exchanger in an OTEC system would be a problem in the closed-cycle design. Claude suggested using the warm seawater itself as the working fluid in an open-cycle, now better known as the Claude cycle (Aver Ougree-Marhaye in Belgium by creating an engine fueled by water temperature differences.
Using the 30°C cooling water from a steel plant as the source for warm water for the boiler (evaporator) and 10°C water from the Meuse River as the condensing fluid, Claude successfully demonstrated the feasibility of the open-cycle concept (Avery and WU, 1994). This water from the steel plant was the cooling water sprayed on the steel during fabrication in order to prevent flaws in the steel when still malleable. In 1930 George Claude designed and built a fully operational closed loop system OTEC power station in Matanzas Bay in Northern Cuba (Takahashi and Trenka, 1996). This power station generated 22 kilowatts (kW), but had a negative energy balance, consuming more power then it produced.
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Submitted By:
Patel Bhavik
Thakar Harsh

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Ocean Thermal Energy Conversion
The more we use renewable energy, the more we benefit the environment, strengthen our energy security, create jobs locally, and help improve our economy
Types of energy resources
• Non-renewabe
– Cannot be replenished or renewable
• Fossil fuels
• Nuclear energy
• Renewable
– Can be replenished or renewed
• Geothermal
• Hydropower
• Ocean energy
• Solar energy
• Wind energy
• Biomass energy
Renewable: ocean energy
• Still in experimental stage, not common
• Three types:
– Waves energy
– Tidal energy
– Ocean thermal energy
Ocean energy: waves
When the air flows, turbine is turned and it would drive the generator.
Electricity is produced.
Ocean energy: tidal and thermal

• Tidal energy
– similar to hydropower plant
• dam traps the sea water when high tide
• when tide drops, water flow turns the turbine and drives the production of electricity of generator
• Ocean thermal energy
– application of the temperature difference of sea water
OTEC Description
• Oceanic Thermal Energy Conversion
• OTEC utilizes the ocean’s 20ºC natural thermal gradient between the warm surface water and the cold deep sea water to drive a Rankine Cycle
• OTEC utilizes the world’s largest solar radiation collector - the ocean. The ocean contains enough energy power all of the world’s electrical needs.
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#5
PRESENTED BY
KUSHAGRA KHAMESRA

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OTEC
 Ocean thermal energy conversion, or OTEC, is a way to generate electricity using the temperature difference of seawater at different depths.
 The method involves pumping cold water from the ocean depths (as deep as 1 km) to the surface and extracting energy from the flow of heat between the cold water and warm surface water.
INTRODUCTION
 The oceans are continually heated by the sun and cover nearly 70% of the Earth's surface, this temperature difference contains a vast amount of solar energy which could potentially be tapped for human use.
 If this extraction could be done profitably on a large scale, it could be a solution to some of the human population's energy problems.
REQUIRMENT
 OTEC requires a temperature difference of about 36 deg F (20 deg C).
 This temperature difference exists between the surface and deep seawater.
 The cold seawater is an integral part of OTEC.
TYPES OF CYCLES
 On the basis of cycles it can be divided into three:-
 OPEN CYCLE
 CLOSED CYCLE
 HYBRID CYCLE
 Open-Cycle OTEC Flow Diagram
OPEN CYCLE
 Open-cycle OTEC uses the tropical oceans' warm surface water to make electricity.
 When warm seawater is placed in a low-pressure container, it boils.
 The expanding steam drives a low-pressure turbine attached to an electrical generator.
 The steam, which has left its salt behind in the low-pressure container, is almost pure fresh water.
 It is condensed back into a liquid by exposure to cold temperatures from deep-ocean water
RANKINE CYCLE (CLOSED CYCLE)
CLOSED CYCLE

 Closed-cycle systems use fluid with a low boiling point, such as ammonia, to rotate a turbine to generate electricity.
 Warm surface seawater is pumped through a heat exchanger where the low-boiling-point fluid is vaporized.
 The expanding vapour turns the turbo-generator.
 Then, cold, deep seawater—pumped through a second heat exchanger—condenses the vapor back into a liquid, which is then recycled through the system.
HYBRID CYCLE
 Hybrid systems combine the features of both the closed-cycle and open-cycle systems.
 In a hybrid system, warm seawater enters a vacuum chamber where it is flash-evaporated into steam, similar to the open-cycle evaporation process.
 The steam vaporizes a low-boiling-point fluid (in a closed-cycle loop) that drives a turbine to produce electricity.
 OTEC DESCRIPTION
OCEAN THERMAL ENERGY CONVERSION
 Ocean Thermal Energy Conversion (OTEC) is a means of converting into useful energy the temperature difference between surface water of the oceans in tropical and sub-tropical areas, and water at a depth of approximately 1000 metres which comes from the polar regions. For OTEC a temperature difference of 20oC is adequate, which embraces very large ocean areas, and favours islands and many developing countries.
SCHEMATIC DAIGRAM OF OTEC
FUTURE BENEFITS

 It is suitabale for base-loads.
 It can readily be provided–
food (aquaculture and agriculture);potable water;air conditioning; etc.
 Some floating OTEC plants would actually result in net CO2absorption.
APPLICATIONS
 ELECTRICITY
 DRINKING
 IRRIGATION
 COLD WATER REFRIGERATION
 AIR-CONDITIONING
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#6
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Ocean thermal energy conversion
Abstract
Ocean thermal energy conversion, or OTEC, is a way to generate electricity using the temperature difference of seawater at different depths. The method involves pumping cold water from the ocean depths (as deep as 1 km) to the surface and extracting energy from the flow of heat between the cold water and warm surfacewater.
OTEC utilizes the temperature difference that exists between deep and shallow waters within 20° of the equator in the tropics — to run a heat engine. Because the oceans are continually heated by the sun and cover nearly 70% of the Earth's surface, this temperature difference contains a vast amount of solar energy which could potentially be tapped for human use. If this extraction could be done profitably on a large scale, it could be a solution to some of the human population's energy problems. The total energy available is one or two orders of magnitude higher than other ocean energy options such as wave power, but the small size of the temperature difference makes energy extraction difficult and expensive. Hence, existing OTEC systems have an overall efficiency of only 1 to 3%. The concept of a heat engine is very common in engineering, and nearly all energy utilized by humans uses it in some form. A heat engine involves a device placed between a high temperature reservoir (such as a container) and a low temperature reservoir. As heat flows from one to the other, the engine extracts some of the heat in the form of work. This same general principle is used in steam turbines and internal combustion engines, while refrigerators reverse the natural flow of heat by "spending" energy. Rather than using heat energy from the burning of fuel, OTEC power draws on temperature differences caused by the sun's warming of the ocean surface.
INTRODUCTION
Ocean Thermal Energy conversion:-

Ocean Thermal Energy Conversion (OTEC) is a process which utilizes the heat energy stored in the tropical ocean. The world's oceans serve as a huge collector of heat energy. OTEC utilizes the difference in temperature between warm, surface seawater and cold, deep seawater to produce electricity. OTEC requires a temperature difference of about 36 deg F (20 deg C). This temperature difference exists between the surface and deep seawater year round throughout the tropical regions of the world.
In one, simple form of OTEC a fluid with a low boiling point (e.g. ammonia) is used and turned into vapor by heating it up with warm seawater. The pressure of the expanding vapor turns a turbine and produces electricity. Cold sea water is then used to reliquify the fluid. Other forms of OTEC also exist as explained in the sites listed below. One important bi-product of many of these techniques is fresh water.
This is also an indirect method of utilizing solar energy. A large amount of solar energy is collected and stored in tropical oceans. The surface of the water acts as the collector for solar heat, while the upper layer of the sea constitutes infinite heat storage reservoir. Thus the heat contained in the oceans, could be converted into electricity by utilizing the fact that the temperature difference between the warm surface waters of the tropical oceans and the colder waters in the depths is about 20 – 25o k. Utilization of this energy, with its associated temperature difference and its conversion into work, forms the basis of ocean thermal energy conversion (OTEC) systems.
The surface water which is t higher temperature could be used to heat some low boiling organic fluid, the vapours of which would run a heat engine. The exit vapours would be condensed by pumping cold water from the deeper regions. The amount of energy available for ocean thermal power generation is enormous, and is replenished continuously.
Several such plants are built in France after World War II (the largest of which has a capacity of 7.5 MW) with a 22oK temperature difference between surface and depths, such as exists in warmer ocean areas than the north sea, the carnot efficiency is around 7%. This is obviously very low.
OCEAN THERMAL ENERGY CONVERSION:OTEC: -
RANKINE CYCLE OTEC PLANT: -

The warm surface water is used for supplying the heat input in boiler, while the cold water brought up from the ocean depths is used for extracting the heat in the condenser. In India, Department of Non – conventional energy sources (DNES) has proposed to install a 1 MW OTEC plant in Lakshadweep Island at Kavaratti and Minicoy. Preliminary oceanographic studies the eastern side of Lakshadweep Island suggest the possibility of the establishment of shore based OTEC plant at the Island with a cold water pipe line running down the slope to a depth of 800-1000m. Both he Islands have large lagoons on the western side. The lagoons are very shallow with hardly any nutrient in the sea water. The proposed OTEC plant will bring up the water from 1000m depth which has high nutrient value. After providing the cooling effect in the condenser, a part of sea waster is proposed to be diverted to the lagoons for the development of aqua culture.
Rankine Cycle Description: -
1-2: Liquid water pumped to a higher pressure adiabatically: -

T1<T2, P1<P2
Work is added to run the pump Win= (-)
No heat is transferred Q = 0
2-3: Heat is added by boiling the water: -
T2<T3, P2=P3
No work is added W = 0
Heat is added QH= 0
3-4: High pressure steam drives the turbine adiabatically: -
T3>T4, P3>P4
Work is generated by the turbine Wout= (+)
No heat is transferred Q = 0
4-1: Steam is condensed to liquid water: -
T4=T1, P4=P1
No work is added W = 0
Heat is removed QL= (-)
Rankine Cycle PV diagram: -
•Water is the working fluid in the Rankine Cycle
•The water exists in two phases: liquid and steam
•The heat (QH) added to the boiler comes from burning coal, burning liquid fuels, or from a nuclear reactor
•The steam exiting the turbine is converted to a liquid in the condenser because it is more efficient to pump a liquid.
Background and History of OTEC Technology
In 1881, Jacques Arsene d'Arsonval, a French physicist, was the first to propose tapping the thermal energy of the ocean. Georges Claude, a student of d'Arsonval's, built an experimental open-cycle OTEC system at Matanzas Bay, Cuba, in 1930. The system produced 22 kilowatts (kW) of electricity by using a low-pressure turbine. In 1935, Claude constructed another open-cycle plant, this time aboard a 10,000-ton cargo vessel moored off the coast of Brazil. But both plants were destroyed by weather and waves, and Claude never achieved his goal of producing net power (the remainder after subtracting power needed to run the system) from an open-cycle OTEC system.
Then in 1956, French researchers designed a 3-megawatt (electric) (MWe) open-cycle plant for Abidjan on Africa's west coast. But the plant was never completed because of competition with inexpensive hydroelectric power. In 1974 the Natural Energy
Laboratory of Hawaii (NELHA, formerly NELH), at Keahole Point on the Kona coast of the island of Hawaii, was established. It has become the world's foremost laboratory and test facility for OTEC technologies.
In 1979, the first 50-kilowatt (electric) (kWe) closed-cycle OTEC demonstration plant went up at NELHA. Known as "Mini-OTEC," the plant was mounted on a converted U.S. Navy barge moored approximately 2 kilometers off Keahole Point. The plant used a cold-water pipe to produce 52 kWe of gross power and 15 kWe net power.
In 1980, the U.S. Department of Energy (DOE) built OTEC-1, a test site for closed- cycle OTEC heat exchangers installed on board a converted U.S. Navy tanker. Test results identified methods for designing commercial-scale heat exchangers and demonstrated that OTEC systems can operate from slowly moving ships with little effect on the marine environment. A new design for suspended cold-water pipes was validated at that test site. Also in 1980, two laws were enacted to promote the commercial development of OTEC technology: the Ocean Thermal Energy Conversion Act, Public Law (PL) 96-320, later modified by PL 98-623, and the Ocean Thermal Energy Conversion Research, Development, and Demonstration Act, PL 96-310. At Hawaii's Seacoast Test Facility, which was established as a joint project of the State of Hawaii and DOE, desalinated water was produced by using the open-cycle process. And a 1-meter-diameter col seawater/0.7-meter-diameter warm-seawater supply system was deployed at the Seacoast Test Facility to demonstrate how large polyethylene cold-water pipes can be used in an OTEC system.
In 1981, Japan demonstrated a shore-based, 100-kWe closed-cycle plant in the Republic of Nauru in the Pacific Ocean. This plant employed cold-water pipe laid on the sea bed to a depth of 580 meters. Freon was the working fluid, and a titanium shell-and-tube heat exchanger was used. The plant surpassed engineering expectations by producing 31.5 kWe of net power during continuous operating tests. Later, tests by the U.S. DOE determined that aluminum alloy can be used in place of more expensive titanium to make large heat exchangers for OTEC systems. And at- sea tests by DOE demonstrated that biofouling and corrosion of heat exchangers can be controlled. Biofouling does not appear to be a problem in cold seawater systems. In warm seawater systems, it can be controlled with a small amount of intermittent chlorination (70 parts per billion per hour per day). In 1984, scientists at a DOE national laboratory, the Solar Energy Research Institute (SERI, now the National Renewable Energy Laboratory), developed a vertical-spout evaporator to convert warm seawater into low-pressure steam for open-cycle plants. Energy conversion efficiencies as high as 97% were achieved. Direct-contact condensers using advanced packings were also shown to be an efficient way to dispose of steam. Using freshwater, SERI staff developed and tested direct-contact condensers for open-cycle OTEC plants. British researchers, meanwhile, have designed and tested aluminum heat exchangers that could reduce heat exchanger costs to $1500 per installed kilowatt capacity. And the concept for a low-cost soft seawater pipe was developed and patented. Such a pipe could make size limitations unnecessary, as well as improve the economics of OTEC systems. In May 1993, an open-cycle OTEC plant at Keahole Point, Hawaii, produced 50,000 watts of electricity during a net power-producing experiment. This broke the record of 40,000 watts set by a Japanese system in 1982. Today, scientists are developing new, cost-effective, state-of-the-art turbines for open cycle OTEC systems.
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#7
Presented by:
JIJO JAMES

[attachment=14603]
OCEAN THERMAL ENERGY CONVERSION (OTEC)
INTRODUCTION
Generating electricity by utilizing temperature difference between shallow and deep water.
The temperature difference can be as high as 25-30 ok in the tropical oceans
2nd law of thermodynamics.
Proposed in 1881 by Jacques Arsene d'Arsonval, a French physicist.
Lambert's law of absorption.
CLASSIFICATION
Depending on the location
Land based plant
Shelf based plant
Floating plant
Depending on the cycle used
Open cycle
Closed cycle
Hybrid cycle
Land-based power plant
This is done so that the outflow does not re enter the plant, which would lower the available temperature difference.
Shelf-based plant
This plant could be towed to the site and affixed to avoid the turbulent surf zone as well as to move closer to the cold-water resource.
Floating power plant
Floating OTEC facilities could be designed to operate off-shore.
OPEN CYCLE
CLOSED CYCLE
HYBRID CYCLE
ADVANTAGES
Eco- friendly.
Uses clean, renewable, natural resources.
Cold water replaces fossil fuels to produce electricity.
Will not produce little or no carbon dioxide or other polluting chemicals.
Minimal maintenance costs compared to other power production plants.
DISADVANTAGES
Low efficiency
High capital costs for initial construction
Potential ecological consequences
Must operate in a corrosive marine environment
Harms marine environment
OTHER APPLICATIONS
Air conditioning
Chilled-soil agriculture
Aquaculture
Desalination
Hydrogen production
Mineral extraction
TECHINICAL DIFFICULTIES
Dissolved gases
Bio fouling
Sealing
COST
$ 40000000 for 10 MW
$ 10000000 Profit pet year
Return of 25%
$ 215000000 for 100MW
$ 100000000 profit per year
Will make profit within 5 years
AVILABLE ENERGY SOURCES
AREA WHERE OTEC WILL WORK
OTEC SITES

Kehole point in the island of Hawaii
Providence Island in the Bahamas
St. Croix in the Virgin Islands
Caribbean islands
Bahamas
Japan
Atlantic costs
Colombia
India
OTEC IN INDIA
1MW OTEC plant in Lakshadweep island at Minicoy
OTEC Ship Sagar Shakti
Kulasekharapatnam in Tamilnadu
Tuticorin
Aluva
Azikkal
SOME PROPOSED PROJECTS
FOR US navy base in the island of Diego Garcia in the Indian ocean
A private U.S. company has proposed a 10-MW OTEC plant on Guam
Alternative Energy Development team with Makai Ocean Engineering  to built 10-MW closed cycle OTEC plant in Hawaii in 2013 .
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