View
234
Download
0
Category
Preview:
Citation preview
8/8/2019 otec sd mem
1/18
OceanThermalEnergyConversion
84914 ,84915
84916, 84917
84917, 84918
84919, 84920
8/8/2019 otec sd mem
2/18
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.
8/8/2019 otec sd mem
3/18
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%
8/8/2019 otec sd mem
4/18
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.
8/8/2019 otec sd mem
5/18
8/8/2019 otec sd mem
6/18
Open-Cycle
8/8/2019 otec sd mem
7/18
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.
8/8/2019 otec sd mem
8/18
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.
8/8/2019 otec sd mem
9/18
Closed-Cycle (Rankine)
8/8/2019 otec sd mem
10/18
8/8/2019 otec sd mem
11/18
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.
8/8/2019 otec sd mem
12/18
Closed Loop
8/8/2019 otec sd mem
13/18
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.
8/8/2019 otec sd mem
14/18
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
8/8/2019 otec sd mem
15/18
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.
8/8/2019 otec sd mem
16/18
8/8/2019 otec sd mem
17/18
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.
8/8/2019 otec sd mem
18/18
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
Recommended