OTEC [Ocean Thermal

Energy Conversion]

PRESENTED BY:-

Raj Ranjan Gupta

What Is OTEC ?

e Ocean thermal energy conversion (OTEC) is a method for generating electricity which uses the temperature difference that exists between deep and shallow waters.

e Ocean Thermal Energy Conversion produces electricity from the natural thermal gradient of the ocean, using the heat stored in warm surface water to create steam to drive a turbine, while pumping cold, deep water to the surface to re-condense the steam

e Temperature difference between warm surface water and cold deep water must be >20°C (36°F) for OTEC system to produce significant power.

Background Information

e 60 million km2. (23 million miles2) of tropical seas absorb a tremendous amount of solar radiation.

e Heat content equal to about 250 billion barrels of oil.e If less than 1/10th of 1% of this stored solar energy. converted to electric power, it

would supply more than 20 times the total amount of electricity consumed in the U.S. on any given day.

Why OTEC ?e A clean energy source:- it delivers an environment friendly solution that produces

electricity without the expense and price volatility of fossil fuels.e Improved technology: - the qualitative analysis of technical readiness of OTEC by

experts of US national oceanic and atmospheric administration (NOAA) suggest that a<10MW floating, closed cycle OTEC facility is technically feasible using current design, manufacturing, deployment technics and materials.

e Need for possible water: - large OTEC power plant can be designed to coproduce 120 million litres of fresh water daily. The OTEC power cycle moves about four cubic kilometre of high nutrient deep water per year (1 sq. km 11.5 m deep each day. Enough to grow 70 tons of shellfish meat per day).

e Increased awareness of the effects of climate change;- OTEC is carbon neutral and does not contribute to climate change by burning fossil fuel such as coal, gas and oil.

HISTORY

Initial Projectse 1881- Jacques Arsene d’Arsonval, French physicist, proposed tapping the thermal

energy of the ocean.e 1930- Georges Claude, d’Arsonval’s student, built the 1st OTEC plant in Cuba.e 1935- Claude constructed another plant aboard a 10,000 ton cargo vessel off the

coast of Brazil.e Weather & waves destroyed both plants before they could become net power

generators.e 1956- French scientists designed another OTEC plant for Abidjan, Ivory Coast,

West Africa.e The plant was never completed due to reduced energy costs. Large amounts of

cheap oil became available in the 1950’s.

First OTEC In Operatione 1970- Tokyo Electric Power Company successfully built & deployed a 100 kW

closed-cycle OTEC plant on the island of Nauru.e 1981- Became operational .e Produced about 120 kW of electricity .e 90 kW was used to power the plant & the remaining electricity used to power a

school & several other places on Nauru.e Set a world record for power output from an OTEC system where the power was

sent to a real power grid.

Types Of Cycles Used

1. Open Cycle2. Close fCycle &3. Hybrid Cycle

Open Cycle

e In open-cycle OTEC, the sea water is itself used to generate heat without any kind of intermediate fluid.

e At the surface of the ocean, hot sea water is turned to steam by reducing its pressure .water that leaves the OTEC plant is pure and salt-free.

Close Cycle

e In closed-cycle OTEC, warm surface seawater heats a working fluid, such as ammonia, with a low boiling point, such as ammonia, which flows through a heat exchanger (evaporator).

e The ammonia vapor expands at moderate pressures turning a turbine, which drives a generator which produces energy.

Hybrid Cycle

A hybrid cycle combines the features of the closed- and open-cycle systems. In a hybrid, warm seawater enters a vacuum chamber and is flash-evaporated, similar to the open-cycle evaporation process. The steam vaporizes the ammonia working fluid of a closed-cycle loop on the other side of an ammonia vaporizer. The vaporized fluid then drives a turbine to produce electricity. The steam condenses within the heat exchanger and provides desalinated water.

Some Projects

e Hawaii :- 10-MW closed cycle OTEC pilot system which will become operational in Hawaii. This effort was cancelled when the Navy determined that the system was not viable.

e Hainan :- 10 megawatt plant off the coast of southern China to provide power for a planned resort on Hainan island.

e Japan :- The main aim is to examine the expected fluctuation of electricity supply caused by changes in weather, season, and sea temperature. The testing and research will be conducted with the support of Saga University until the end of 2014. The plant installation was finished in March and the first trial run was held on the 30th of March.

OTEC in Indiae About 1.5 x 106 square kilometeres of tropical water in the

Exclusive Economic Zone around India with a power density of 0.2 MW/km2. Apart from this, attractive OTEC plant locations are available around Lakshedweep, Andaman & Nicobar Islands. The total OTEC potential around India is estimated as 180,000 MW considering 40% of gross power for parasitic losses. This indicates the promise of OTEC for India and points out the urgent need to develop OTEC technology.

e The Indian OTEC programme started in 1980 with the proposal of General Electrical Co. of USA to install a 20 MW plant off the Tamil Nadu coast and subsequently in 1982.

e A preliminary design was also done in 1984 for a 1 MW closed Rankine Cycle floating plant with ammonia as working fluid.

e Early 1997, DOD, Government of India proposed to establish a 1 MW gross OTEC plant in India.

e In January 2008 trial production of 1MW project has been completed.

Image of 1 mw plant in Tamil Nadu

Floating Plantse They are not tied to a land base and therefore require

long and expensive cables that would get tangled and need repair.

e If the base was not kept stable, the cold water pipe might break, especially during high seas and storms.

e However, this problem could be solved by using flexible polyethylene to attach the pipe to the bottom of the plant along with joints and collars.

e Instead of using a warm water pipe, the floating OTEC plant could simply draw in the warm water from the surface. But, storms and high seas can interrupt the water flow and cause major damage to the plant.

Shelf-Based Plants

e OTEC plants can be placed on the continental shelf, down to depths of no more than 100 meters.

e The same kind of construction that is used to build offshore oil rigs would be used to build shelf-based plants.

e These plants would have problems with product delivery and the stressors of the open ocean.

e Working these plants in water 100 meters deep also presents problems and these plants are more expensive than the land-based plants.

Land Based Plantse Have both advantages and disadvantages over shelf based

and floating plantse Unlike those plants that are on the ocean shelf or floating in

the open ocean, land based plants do not require long cables or anchors that are very expensive

e They require less maintenance and can be installed in areas that are sheltered from storms which could possibly destroy the plant.

e In addition, land based plants can support mariculture using desalinated water.

e However, land based plants are subject to the extremes of the surf zone, heavy seas and storms. This causes stress on the water supply and discharge pipes.

e The problem could be helped if the pipes were buried in trenches, or if the plant were moved into water 10-30 meters deep, but this presents erosion problems as well.

OTEC Efficiencye The thermal gradient gives OTEC a typical energy conversion of 3 to 4%,

whereas conventional oil or coal fired steam plants, often have temperature differentials of 500oF, yielding thermal efficiencies of 30 to 35%.

e Remember, the greater the difference between hot and cold temperatures, the greater the efficiency of the energy conversion system.

e So to compensate for its low thermal efficiency, OTEC has to move a tremendous amount of water.

e It takes 20 to 40% of the power generated to pump the water through intake pipes in and around an OTEC system.

e This is why, almost 100 years after the idea was first conceive, OTEC researchers are still striving to develop plants that will consistently produce more energy than is needed to run the pumps, and that will operate in the corrosive marine climate, to justify the development and construction.

RELATED ACTIVITIES Desalination Air Conditioning Chilled Soil Agriculture Aquaculture Hydrogen Production Mineral Extrection

Technical Difficulties

Dissolved gases Microbial fouling Sealing Parasitic power consumption by exhaust

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