Slide 1: Ocean Power
Dr Yogesh J Barde
Madurai Kamraj University OTEC : OTEC Ocean Thermal Energy Conversion – The technology that converts solar radiation into electric power. In detail - OTEC : In detail - OTEC Hydro energy conversion system which uses ocean's natural thermal gradient—the fact that the ocean's layers of water have different temperatures—to run a heat engine. In detail : 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 largest temperature differences.
3. Uses the vertical temperature gradient in the ocean as a heat sink/source
4. Temperature differences generally increases with decreasing latitude , in the tropics, thereby mainly used in
equatorial waters where temperature difference is greatest Process : Process Carnot Efficiency (T1-T2)/T1:
in transferring heat 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
T1- Temp at surface level
T2- Temp at bottom level
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 a maximum Carnot Efficiency of about 6.7% History : History 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.
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. History- Contd : History- Contd 1979: The first 50-kilowatt
(kWe) closed-cycle OTEC
demonstration plant went up
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. History- Contd : History- Contd 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, experimenting with anti corroding Titanium and plastics as rotor material.
The new designs for OTEC are still mostly experimental. Only small-scale versions have been made. The largest so far is near Japan, and it can create 100 kilowatts of electricity Slide 9: 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. Slide 11: Closed-cycle systems( Rankine ) 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-point fluid is vaporized. The expanding vapor 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 systems : Hybrid systems 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 produces electricity. Advantages : Advantages Eco- friendly
Minimal maintenance costs compared to other power production plants
Provide air conditioning to buildings within the OTEC plant
Fresh water - first by-product is fresh water. A small 1 MW OTEC is capable of producing some 4,500 cubic meters of fresh water per day, enough to supply a population of 20,000 with fresh water
Open cycle OTEC systems can produce desalinated water which is very important in third-world countries
Chilled soil agriculture- cold seawater flowing through underground pipes, chills the surrounding soil. Thereby allowing many plants evolved in temperate to be grown in subtropics due to temp. difference in the plant roots in cool soil and plant leaves in warm air Advantages- Continued : Advantages- Continued Mineral Extraction – OTEC helps in mining
ocean water for 57 trace elements. Most economic analyses have suggested that mining the ocean for trace elements 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 already pumping the water, the only remaining economic challenge is to minimize the cost of the extraction process. Floating Plant for OTEC : Floating Plant for OTEC Future : Future The economic evaluation of OTEC plants indicates that their commercial future lies in floating plants of approximately 100 MW capacity for industrialized nations and smaller plants for small-island-developing-states
Small OC-OTEC plants can be sized to produce from 1 MW to 10 MW of electricity, and at least 1700 m 3 to 3500 m3 of desalinated water per day. BIBLIOGRAPHY : BIBLIOGRAPHY http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion