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8/8/2019 otec sd mem

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OceanThermalEnergyConversion

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What is OTEC

OTEC, or Ocean Thermal Energy

Conversion, is an energy technology

that converts solar radiation to electric

power.

OTEC systems use the ocean's natural

thermal gradientthe fact that the

ocean's layers of water have differenttemperaturesto drive a power-

producing cycle.


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How Does it Work

Carnot Efficiency (T1-T2)/T1: in transferringheat to do work, the greater the spread in

temperature between the heat source and

the heat sink, the greater the efficiency of

the energy conversion.

As long as the temperature between the

warm surface water and the cold deep

water differs by about 20C (36F), anOTEC system can produce a significant

amount of power with a maximum Carnot

Efficiency of about 6.7%


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History 1881: Jacques Arsene d'Arsonval, a French

physicist, was the first to propose tapping thethermal energy of the ocean. Georges Claude, astudent of d'Arsonval's, built an experimentalopen-cycle OTEC system at Matanzas Bay,

Cuba, in 1930. The system produced 22 kilowatts(kW) of electricity by using a low-pressureturbine. In 1935, Claude constructed anotheropen-cycle plant, this time aboard a 10,000-toncargo vessel moored off the coast of Brazil. But

both plants were destroyed by weather andwaves, and Claude never achieved his goal ofproducing net power (the remainder aftersubtracting power needed to run the system)from an open-cycle OTEC system.


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Open-Cycle


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

low-pressure turbine attached to anelectrical generator. The steam, whichhas left its salt behind in the low-pressure container, is almost pure

fresh water. It is condensed back into aliquid by exposure to coldtemperatures from deep-ocean water.


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Oceanic ThermalEnergy Conversion

OTEC utilizes theoceans 20C naturalthermal gradientbetween the warmsurface water and thecold deep sea waterto drive a RankineCycle

OTEC utilizes theworlds largest solar

radiation collector -the ocean. The oceancontains enoughenergy power all ofthe worlds electrical

needs.


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Closed-Cycle (Rankine)


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Closed-cycle systems use fluid with a

low-boiling point, such as ammonia, to

rotate a turbine to generate electricity.

Here's how it works.Warm surface

seawater is pumped 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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Closed Loop


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Hybrid System

Hybrid systems combine the features

of both the closed-cycle and open-

cycle systems. In a hybrid system,

warm seawater enters a vacuumchamber where it is flash-evaporated

into steam, similar to the open-cycle

evaporation process. The steamvaporizes a low-boiling-point fluid (in a

closed-cycle loop) that drives a turbine

to produces electricity.


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Advantages

Low Environmental Impact

The distinctive feature of OTEC energy systemsis that the end products include not only energyin the form of electricity, but several othersynergistic products.

FreshWater

The first by-product is fresh water. A small 1 MWOTEC is capable of producing some 4,500 cubicmeters of fresh water per day, enough to supplya population of 20,000 with fresh water.

EcoEco-- friendlyfriendly Minimal maintenance costs compared to otherMinimal maintenance costs compared to otherpower production plantspower production plants

Open cycle OTEC systems can produceOpen cycle OTEC systems can producedesalinated water which is very important indesalinated water which is very important in

thirdthird--world countriesworld countries


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Provide air conditioning to buildings withinProvide air conditioning to buildings withinthe OTEC plantthe OTEC plant

FoodA further by-product is nutrient rich coldwater from the deep ocean. The cold"waste" water from the OTEC is utilised in

two ways. Primarily the cold water isdischarged into large contained ponds,near shore or on land, where the watercan be used for multi-species mariculture(shellfish and shrimp) producing harvestyields which far surpass naturallyoccurring cold water upwelling zones, justlike agriculture on land.


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The Future

Records available from experimentalplants demonstrate technical viability andprovide invaluable data on the operationof OTEC plants. The economic evaluation

of OTEC plants indicates that theircommercial future lies in floating plants ofapproximately 100 MW capacity forindustrialized nations and smaller plantsfor small-island-developing-states

Small OC-OTEC plants can be sized toproduce from 1 MW to 10 MW ofelectricity, and at least 1700 m 3 to 3500 m3

of desalinated water per day.


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Consider 1000 MW plant

Assume 3% efficiency

Require 1000 cubic meters/sec flow rate

Pipe of radius of 10 m with flow rate of

3 m/s

Approximately the same flow rate as the

Tully River in moderate flood

Energy loss is relatively small aspumping head is equivalent about 6 m.

Perhaps 60 MW

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