Ocen Thermal

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History

1881: Jacques Arsene d'Arsonval, a French physicist, was the first topropose tapping the thermal energy of the ocean. Georges Claude, a

student of d'Arsonval's, built an experimental open-cycle OTECsystem at Matanzas Bay, Cuba, in 1930. The system produced 22kilowatts (kW) of electricity by using a low-pressure turbine. In 1935,

Claude constructed another open-cycle plant, this time aboard a10,000-ton cargo vessel moored off the coast of Brazil. But both plantswere destroyed by weather and waves, and Claude never achieved hisgoal of producing net power (the remainder after subtracting power

needed to run the system) from an open-cycle OTEC system.

1956: French researchers designed a 3-megawatt (electric) (MWe)open-cycle plant for Abidjan on Africa's west coast. But the plant wasnever completed because of competition with inexpensivehydroelectric power.


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History- Contd

1979: The first 50-kilowatt

(kWe) closed-cycle OTECdemonstration plant went up

at NELHA.

Known as Mini-OTEC the plant wasmounted 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.


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Ocean Power

Presented By-Rajesh Kumar RoyB.Tech 1st year


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OTECOcean Thermal EnergyConversion

The technology that convertssolar radiation into electric power.


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In detail - OTEC

Hydro energy conversion system

which uses sea's natural thermal

gradientthe fact that the

ocean's layers of water have

different temperatures

to run aheat engine.


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In detail-1. Based on Rankine cycle - Thermodynamic cycle

which converts heat into work through a heat

engine

2. As with any heat engine , the greatest efficiency

and power is produced with the largesttemperature differences.

3. Uses the vertical temperature gradient in the

ocean as a heat sink/source

4. Temperature differences generally increases withdecreasing latitude , in the tropics, thereby mainly

used in

equatorial waters where temperature difference is

greatest


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Process-

Carnot Efficiency (T1-T2)/T1:

in transferring heat to do work,

the greater the spread in

temperature between theheat source and the heat sink,

the greater the efficiency

of the energy conversion

T1- Temp at surface level

T2- Temp at bottom level

As long as the temperature between the warm surface waterand the cold deep water differs by about 20C (36F), an OTECsystem can produce a significant amount of power with amaximum Carnot Efficiency of about 6.7%


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Open-cycle low-pressure OTEC uses the tropicaloceans' warm surface water to make electricity.When warm seawater is placed in a container, itboils. The expanding steam drives a low-pressure

turbine attached to an electrical generator. Thesteam, which has left its salt behind in the low-pressure container, is almost pure fresh water. It iscondensed back into a liquid by exposure to coldtemperatures from deep-ocean water.


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Closed-cycle systems ( Rankine ) use fluid with a low-boiling

point, such as ammonia, to rotate a turbine to generateelectricity. Here's how it works. Warm surface seawater ispumped through a heat exchanger where the low-boiling-pointfluid is vaporized. The expanding vapor turns the turbo-generator. Then, cold, deep seawaterpumped through asecond heat exchangercondenses the vapor back into a

liquid, which is then recycled through the system.


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Hybrid systems-

Hybrid systems combine the features ofboth the closed-cycle and open-cycle

systems. In a hybrid system, warmseawater enters a vacuum chamber whereit is flash-evaporated into steam, similar tothe open-cycle evaporation process. The

steam vaporizes a low-boiling-point fluid(in a closed-cycle loop) that drives aturbine to produces electricity.


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Floating Plant for OTEC


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Advantages-

Eco- friendly

Minimum maintenance costs compared to other powerproduction plants

Provide air conditioning to buildings within theOTEC

plant

Fresh water - first by-product is fresh water. A small 1 MW

OTEC is capable of producing some 4,500 cubic meters offresh water per day, enough to supply a population of 20,000with fresh water

Open cycleOTEC

systems can produce desalinated waterwhich is very important in third-world countries

Chilled soil agriculture- cold seawater flowing throughunderground pipes, chills the surrounding soil. Therebyallowing many plants evolved in temperate to be grown insubtropics due to temp. difference in the plant roots in cool soil

and plant leaves in warm air


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Advantages- Continued

Mineral ExtractionOTEC helps in miningocean water for 57 trace elements. Most economic

analyses have suggested that mining the ocean for traceelements would be unprofitable as so much energy is

required to pump the large volume of water needed and

because of the expense involved in separating the

minerals from seawater. But in OTEC plants alreadypumping the water, the only remaining economic

challenge is to minimize the cost of the extraction

process.


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Future

The economic evaluation ofOTEC plantsindicates that their commercial future lies infloating plants of approximately 100 MWcapacity for industrialized nations and smallerplants for small-island-developing-states

Small OTEC plants can be sized to producefrom 1 MW to 10 MW of electricity, and at least1700 m 3 to 3500 m3 of desalinated water per

day.


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