Transcript

9

Chapter 2

Ocean Water and Its Wonderful Potential

Gold from Ocean Water!

In the First World War (1914-18), Germany was defeated. The countrywas ruined, and on top of that, the victorious nations demanded hugereparations. It was soon recognized that the only way out of this state ofpoverty was recovery through technological progress. An Association wasfounded to promote this.

The Association took the initiative in many fields of research, butamong one that attracted the nation was an oceanic survey. Its purpose wasto extract the gold dissolved in sea-water, and use it to settle Germany’s warreparations. Using the warship Meteor, the project was to determine theconcentration of gold at various locations, and to study the structure andmechanisms of the ocean.

The Meteor carried out its survey, mostly in the South Atlantic, betweenMarch, 1925 and July, 1927 (Figure 4). The results showed that gold wasdissolved in a far lower concentration than had been expected: only 0.003micrograms (0.0000003 grams) per liter of sea-water. Extracting enough tomake a gold coin would cost far more than the value of the coin. This project,therefore, was not put into practice, but what is noteworthy about it is theepoch-making idea of extracting a metal from sea-water, which no one hadthought of before.

What is more, the results were obtained with the latest instruments andaccording to a meticulous plan, which made them extremely useful as datafor academic research. For example, the Meteor was the first to measure thedepth of the ocean with sonar waves, rather than the traditional method of aweighted rope lowered to the sea bottom. The depth sounder measures waterdepth by measuring the time taken for a sound it emits to echo back from thebottom of the sea. With this new equipment, continuous depth measurementbecame possible as the ship moved along, and the “terrain” of the sea bottomcould be studied in detail. Sounding techniques are now applied for a widevariety of purposes, including for instance tracing shoals of fish.

The Meteor’s oceanographic expedition aroused people’s interest inthe ocean, in much the same way as interest was aroused in the Apollo

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expeditions and the first man to step on to the moon.One after another, resources on land are being overmined to the extent

that the minerals we need have become hard to obtain on land. Table 1 showsthe concentrations of a selection of metals in the oceans, and compares totalresources on land and in the sea. As you will see, the amounts of somemetallic minerals are actually greater in the oceans than on land: they includenickel, zinc, gold and silver.

As more and more of the earth’s land resources are extracted, it goeswithout saying that the supply is going to run out; the oceans will be the

Figure 4. The Meteor made observations of water mass movement, water temperature, salinityand plankton at 310 observing stations, as well as obtaining 14 bottom profiles and making anumber of balloon observations.

Rio de Janeiro

Buenos Aires

Walvis Bay

Observing stationCurrent measurement

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Earth’s greatest reservoir of metals. The German attempt to extract goldfrom sea-water in the 1920s may have ended in failure, but we are now at astage where the whole world must reconsider the oceans as a storehouse notonly of gold, but of other minerals as well.

It is easy to pump up sea-water in coastal areas. In this sense, extractingmetals from sea-water might seem easier than mining deep down into theearth for ores whose refining process involves extremely high temperaturesand large amounts of polluting waste. No such problems would arise in theprocess of extracting metals from sea-water — as long as large quantities ofchemicals were not used. And so much sea-water is so easily available.

In that case, why not start right away? The problem is that we do not yethave the technology to extract such low concentrations of metals efficiently.Some chemists have claimed that, in their expert opinion, it would beimpossible, and have given up the attempt even before starting. But I can’thelp feeling that there must be a method that has not yet been discovered. Forexample, there are marine creatures that do effectively concentrate outmetals such as mercury, lead or vanadium (Figure 5). But this process is stillonly vaguely known, and has yet to be explained.

To solve this problem, an entire set of new principles, and the epoch-making technology to put them into practice, are required. Mankind hasnever tired in the search for new horizons, and surely one great dream for thefuture must be how to extract metals from the world’s oceans.

Unveiled Energy in the Ocean

The ocean is a reservoir not only of metals but also of energy. Dr. J. A.

Table 1. Concentrations of metals in sea-water, estimates of land reserves, and annualproduction

All amounts in megatons; concentration in micrograms per liter

Total amount Concentration Estimated land Annual production

Iron

Aluminum

Nickel

Tin

Copper

Zinc

Lead

Gold

Silver

Mercury

reserves

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d’Arsonval, a French physicist, was the first person to think of exploiting theocean’s energy.

It is well known that the waters in deep seas and lakes are warmed uponly near the surface in summer, while their deeper parts remain cool.Unfortunate accidents sometimes happen when someone dives into a lake inthe mountains: deceived by the temperature at the surface into believing thewater is warm, they are shocked by the cold deeper down, and die of a heartattack. Generally sea-waters in tropical zones also have a significanttemperature difference between their surface and their depths; there, it isconstant throughout the year because of the high atmospheric temperature allyear round.

In 1881, Dr. d’Arsonval proposed generating electricity using thetemperature difference between the sea surface and its lower depths which,in tropical zones, is about 30 degrees Celsius. This was a unique idea, andat first it drew some public attention; but 1881 happened to be the year thefirst thermal power plant started operation in the United States. No onebelieved that a temperature difference of only thirty degrees could generateelectricity like the high temperatures that were used, by burning coal, toproduce the steam to drive the turbines in a power station. No one evenattempted to experiment with this idea.

It would probably be best to explain here how electricity can begenerated by exploiting the ocean’s temperature difference. It is actuallyquite a simple principle.

Figure 5. Some marine organisms accumulate metals: tunicates concentrate out vanadium.

Tunicates

Metal Refinery

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Generally water boils at 100 degrees Celsius, but this happens onlywhen the atmospheric pressure is exactly 1, on land near sea level. At thesummit of a high mountain like Mt. Fuji (3,776m), the rarity of the atmospheremeans that the atmospheric pressure is only 0.62, and water boils at only 86degrees. Therefore, because the water temperature does not go high enough,rice cannot be cooked well at the top of Mt. Fuji.

This means that water could boil and turn to steam at, say, 30 degreesCelsius if atmospheric pressure was sufficiently low. Electricity would begenerated if that steam was sent to a turbine to turn a generator. On land nearsea level, the air in a chamber could be reduced to create low pressure, andthen water in the chamber would boil. But the steam made in this way wouldturn the turbine only once. The turbine would turn continuously only if sucha condition could be repeatedly produced.

For this purpose, the steam must be turned into water again after turningthe turbine, so that it can be boiled over again. It is easy turning steam intowater. In winter, the water vapor in a warm room is condensed by contactwith the cold glass of a window, and water drops drip down the window.This is the same principle: air containing water vapor should be cooleddown.

Dr. d’Arsonval thought that generation of electricity would be possibleby utilizing warm sea-water for boiling water, and cool deep ocean water(DOW) for cooling it down. In other words, the solar energy stored up in sea-water could be exploited in the form of electricity.

It is a common misconception that water boils at 100 degrees Celsiuseverywhere, since we live normally under conditions of one atmosphericpressure. The idea of generating electricity by temperature difference seemsstrange, because we often do not consider the effects of pressure differences.It is another misconception that every liquid boils at 100 degrees Celsius. Atone atmospheric pressure, ethyl-alcohol, for example, boils at 78 degrees

Figure 6. Dr. J.A. d’Arsonval

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Celsius, ammonia at 33.5 degrees Celsius below zero, and propane at 42.1degrees Celsius below zero.

Dr. d’Arsonval’s idea received attention again in the twentieth century.In one Italian journal a scientific paper entitled “Utilization of Solar Heat”appeared: it discussed the utilization of the temperature difference in lakewater. In a deep lake in northern Italy, there is a 16-degree temperaturedifference in summer, since its surface temperature rises to 24 degreesCelsius, while the temperature at the bottom remains at 8 degrees Celsius. Acost estimation was made for operating an electric generator of 14,000kilowatts, utilizing such a temperature difference. This would be the firstattempt to estimate the cost of thermal difference generation.

Another paper was published by an American engineer in the journalEngineering News. In this paper, he discussed the problem of the insufficientdensity of the steam produced by sea-water in order to turn a generator. Itis certainly true that steam produced under low pressure is poor, just like airat high altitudes. Thus, compared with steam produced at a pressure of oneatmosphere, such steam would require an enormous turbine for generatingthe same amount of power.

Therefore, in this paper he proposed using some other high vapordensity liquid rather than water in a low pressure chamber. Since high vapordensity liquid turns into a heavy gas, he proposed using propane or ammonia.Water turns into only 0.337 grams of vapor when it boils at 32 degreesCelsius under low pressure in a one-liter flask, while on the other hand, therespective figures for methane, ammonia, propane, and fluorine (i.e.,chlorofluorocarbon) are 0.64 grams, 0.69 grams, 1.81 grams, and 4.55 gramsunder the same conditions. Even air turns into 1.16 grams.

In other words, such liquids are boiled with warm sea-water to producevapors heavier than steam, and once these vapors have done their job ofturning a turbine, they are condensed back into liquid form by cold sea-water. This cycle of boiling, condensing and then boiling again uses sea-water indirectly on some other substance. It is known as a “closed cycle”,and has been successfully developed. A cycle that actually turns water intosteam is called an “open cycle”.

Professor Claude, the Pioneer and His Challenge

The proposals so far reviewed were no more than proposals, which werenot actually subjected to experiment at the time. It was two French professors:G. Claude and P. Boucherat, President of the French Electric Society, whofirst carried out experiments on electric power generation utilizing thermaldifference (Figure 7). Using the small apparatus shown in Figure 8, theyperformed a public experiment at the French Academy of Sciences onNovember 15, 1926. The experiment was reported in detail by a leading

Ocean Water and Its Wonderful Potential 15

French newspaper: Paris Presse. With the press in other countries takingup the story, the world’s attention was attracted.

The British journal The Engineer reported on November 20, 1926:“The wheel of an ordinary Laval turbine, 15cm. diameter, wasmounted with its spindle vertical inside a glass flask and arrangedto drive a tiny dynamo. The bottom of the glass contained lumpsof ice, and air could be exhausted from it by a vacuum pumpconnected to the upper portion. Another flask, containing 25 litresof water at a temperature of 28 degree Celsius, was provided withan outlet in the form of a pipe which entered the first flask andterminated in a nozzle just above the blading of the turbine wheel.When the system was exhausted of air the water in the second flaskboiled, its vapour passing away through the pipe and driving theturbine wheel. After leaving the wheel the vapour was condensedby the ice in the bottom of the flask. It is said that the turbine wheelwas driven by this means at a speed of 5000 revolutions per minute,and enough power was obtained from the dynamo to light threelittle electric lamps for eight to ten minutes, after which the waterhad been cooled to 20 degree Celsius or so by its evaporation andapparently refused to boil any longer.”This was the first successful experiment to produce electricity from a

small thermal difference. Although it was really a primitive one, it arousedpublic interest in thermal difference power generation, which came to becalled in English “Ocean Thermal Energy Conversion,” or OTEC. Generationceased soon after the experiment was stopped, but it could have continued if

Figure 7. Professor G. Claude, the pioneer

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the warm water had kept its temperature and cooling had been donecontinuously with cold water. This is the principle of the open-cycle model:supplying warm water continuously to produce steam (the vaporizer) andcold water to condense the steam back to water (the condenser) (Figure 9).

At a press conference after his experiment, Professor Claude providedthe following figures: The surface temperature of tropical seas is generally

Figure 8. Generating electricity by temperature difference

Vacuum pump

Generator Nozzle

Lamps Turbine

Steam

Ice

20l warm water(28˚C)

Figure 9. An open-cycle

Water vapor

Evaporator

Mist of surface water

Warm surface water

Discharge

Ocean Water and Its Wonderful Potential 17

between 26 and 30 degrees Celsius, varying within a range of 3 degreesCelsius throughout the year. On the other hand, at a depth of 1,000 metersit is 4 to 5 degrees Celsius all year round. If 1,000 tons each of surface sea-water and DOW were used per second for OTEC, even using a steam turbineof 75% efficiency (i.e. a turbine that converted 75% of the energy itconsumed into electricity), it would be possible to generate 100,000 kilowattsof electricity. Moreover, the cost of construction would be lower than forthe most economically constructed hydropower generation plant.

The American and British press criticized him as too optimistic, butProfessor Claude was not discouraged by such criticisms and attempted withhis own assets a large-scale experiment to collect the necessary data forputting his theory into practice. First, he experimented with a 60-kilowattturbine using warm waste water from a Belgian steel works and cold seasurface water. Through this experiment, he was convinced that his figureswere right.

Then he proceeded to a real experiment using sea surface water and deepwater.

After a thorough search in his own yacht and amassing as many data aspossible, Professor Claude selected his first experimental site at MatanzasBay, Cuba (Figure 10). In 1929, he sank a 2-kilometer-long pipe 1.6 meters

OTEC generating system

Turbogenerator

Cold deep water

Fresh water

Condenser

DischargeCondenser

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in diameter in Matanzas Bay, intending to pump up sea-water from a depthof 700 meters. But constant trouble with the pipe prevented water frombeing raised. As such, his first experiment failed.

The following year he tried to construct a 1.75-kilometer-long pipe outto sea from the land, but the pipe was washed away when a connection failed.He finally succeeded in laying a pipe at his third attempt, but the pipe wasbadly damaged in the process, and the water soon stopped flowing.

Nevertheless, Professor Claude did succeed in generating 22 kilowattsfor 10 days, utilizing an actual thermal difference of 14 degrees Celsius inthe sea-water. It was only a small amount of electricity, but it was enoughfor an emotional Professor Claude to announce that human beings wouldnever again need to suffer from a shortage of energy.

Gambling on the Abidjan Project

Professor Claude became convinced through a series of experimentsthat the design and maintenance of intake pipes were the key factor of OTEC.He also found that cold deep water would get warmer than expected duringthe pumping up process if the thermal insulation of the intake pipe was notsufficient. Moreover, he discovered that dissolved gases such as carbondioxide (CO2) were separated out in the vaporizer and hindered themaintenance of low pressure.

In order to solve the problems with the inlet pipe, Professor Claudeabandoned generation on land and changed to generation on the sea surface.For this purpose, in 1933 he converted the 10,000-ton cargo ship Tunisie forOTEC, and carried his experiment to Brazil. The ship was equipped with an800-kilowatt turbine generator and had an inlet pipe 2.5 meters in diameterand 650 meters long. He tried to pump up sea-water from a depth of 120meters off the coast of Rio de Janeiro, but rough seas made the intake pipehard to control, and in the end the ship sank.

Professor Claude was so depressed by all this that for several years he

Figure 10. Matanzas Bay is located about 23˚N.

Havana Matanzas Bay

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seems to have done nothing. However, he took up the challenge again in1940 with what came to be known as the Abidjan Project. Abidjan is nowthe capital city of the French West African nation of Côte d’Ivoire, which atthat time was a French colony (Figure 11). This is an area where forests havebeen cleared for agriculture, and coffee and cocoa are grown. The coastlinedrops away steeply into the sea — a favorable condition for pumping upDOW. What is more, the sea is calm and its surface temperature is 30 degreesCelsius. Abidjan seemed a most appropriate place for an experiment.

In the Abidjan Project, Professor Claude proposed at the beginning to

Figure 11. Abidjan, the capital of the West African nation of Côte d’Ivoire, is located about6˚N and 4˚W.

Liberia

Côte d’Ivoire

Ghana

Abidjan

Accra

Gulf of Guinea

To Abidjan

Warm water supply

Bank

Lagoon Warm water Service zone

OTEC power plant

Cold water return

Cold deep water intake pipe

Bank

return channel

channel

channel

lagoonWarm water

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pump up cold DOW through a tunnel, thereby avoiding the use of unstableintake pipes. But he was obliged to abandon this idea, brilliant though it was,for reasons of cost and the great risks involved in tunnel construction. Healso had to revise output from the originally planned 40,000 kilowatts to aless ambitious 15,000.

Cold water would be pumped up from 430 meters deep; for this, a pipefour kilometers (4,000 meters) long would be necessary (Figure 12). Heplanned to connect sections of metal pipe with durable rubber joints, andsuspend his pipeline in the sea with special floats. Forty-two tons of 30-degree Celsius surface water and 14 tons of 8-degree Celsius deep waterwould have to be pumped up every second to achieve the target of 15,000kilowatts. To meet this condition, it was estimated that 4,000 kilowattswould be required for pumping up the water, and 1,000 kilowatts forremoving gases from the air and sea-water.

The generator turbine was to be 14.25 meters in diameter and to operateat 332 revolutions per minute (Figure 13). Professor Claude also hoped tocondense 14,000 tons of water per day by cooling the steam that had turnedthe turbine, and by preventing it from mixing with sea-water, produce theadded bonus of usable fresh water. He also thought of extracting salt,magnesium and bromine from condensed warm water after evaporation, andto use the remaining cold water for cooling. The pumping system for coldwater would take up 55% of the construction cost.

The French government was interested in Professor Claude’s projectand offered it joint support and promotion: in 1948 an organization named“Energie des Mers” (Energy from the Seas) was set up. This organization

Figure 12. Abidjan Project, intake pipe. For scale, see a person standing at bottom right.

Ocean Water and Its Wonderful Potential 21

was to carry out research and development for implementation of theAbidjan Project. Research and development covered various fields, such asthe evaporator, condenser, gas drainage, intake pipe, total design, etc.

Even so, construction of an OTEC plant was never completed. In the1950s, large amounts of oil became cheaply available, and it was thought thatthermal difference electricity generation would cost much more than oil-fired generation. There were domestic political problems in France, too, andthe Abidjan Project was abandoned in 1955. In this way, the developmentof OTEC was completely halted. Professor Claude passed away in 1960 atthe age of 90 without seeing his 30 years of determined efforts reach fruition.

The name of Professor Claude will always be linked with ocean thermalenergy conversion. But he was a man of many other achievements. Bornin France in 1870, before he became interested in OTEC, he did muchimportant work on liquefaction of oxygen, air and nitrogen; production ofammonia; industrial uses of gases such as argon, neon and helium; productionand storage of acetylene. He was the inventor of the neon lamp and had alarge income from the patents he held. But from the time he becameabsorbed in OTEC in 1926 at the age of 56, he devoted all of his fortune toit.

On 22 October 1930, Professor Claude received a commemorativemedal from the American Society of Mechanical Engineering for his researchon OTEC. At that time he said that when he started on his work he had notknown about the research previously done by others, including his ownrespected professor d’Arsonval, the American engineer Campbell and the

Figure 13. Open-cycle OTEC system developed for the Abidjan Project

Turbine

Evaporator

Pump for colddeep water

Cold deep waterCondenser

Flow of watervapor Warm

surfacewater

Evaporator

Generator

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Italian engineers Dornig and Boggia. This ignorance, he claimed, had beenfortunate, for he might not have embarked on his attempts if he had knownsomeone else was already concerned. A well-trodden path, he said, is notattractive to an inventor.

There is an important message here for all scientists.

The 1960s: Efforts at National Level

After the Abidjan Project was abandoned, no more attention was paidto OTEC for several years. Then in the 1960s in the United States, Dr. J. H.Anderson turned his attention to Professor Claude’s work, re-examined itthoroughly and identified some of its problems (Figure 14). On 31 August1964, Dr. Anderson applied to the US Patent Office for a patent on a “Sea-water power plant”.

Dr. Anderson pointed out three problems in Professor Claude’s project:First, it was too costly. The reason was the low-pressure vapor used to

turn the generator turbine. The gas used for jobs such as turning a turbinecan be called a working fluid. As has already been explained, if we use weak,low-pressure vapor as a working fluid, large amounts will be needed to turnthe turbine blades. This requires a gigantic turbine with huge blades.

Second, warm sea-water raised at low pressure by Professor Claude’smethod releases the gases dissolved in it, and they are hard to eliminate.

Third, if a power plant is constructed on land as Professor Claudeoriginally planned, the long intake pipes lead to high construction costs andother troubles.

Dr. Anderson worked out how to solve these problems:The first problem would be solved by using high-density fluids which

boil easily under relatively low pressure. In other words, the system shouldbe changed from open cycle to closed cycle.

Figure 14. Dr. J.H. Anderson (second from right)

Ocean Water and Its Wonderful Potential 23

The second problem would be solved if both evaporator and condenserwere immersed in sea-water at the same pressure as the working fluid. Then,the dissolved gases could not be released, since the pressure of the surroundingsea-water and working fluid are the same.

The third problem would be solved to a great extent if the power plantwere located in the sea, near the coast.

Based on this plan, Dr. Anderson estimated the cost of OTEC and theunit cost of electricity produced by that method. The figure was $166 perkilowatt: for the first time, a clear idea of the cost had been gained. Fromthis point, more and more people began to show an interest in OTEC and todo further research in it. Until then, Professor Claude had been alone, but anumber of scientists in different countries now started their own research anddevelopment, with support from their own countries.

In Japan, OTEC was described in detail in the evening edition of theAsahi Shinbun newspaper on July 3 1959. An article entitled “Generationof Electricity from Limitless Sea Water” by Professor Tadayoshi Sasakiintroduced Professor Claude and the French project. Eleven years later, in1970, Dr. Kenzo Takano pointed out six advantages of OTEC in his book TheOcean and Energy: First, temperature difference is the most stable naturalenergy source compared with solar or wind power. Second, ocean energydoes not pollute the atmosphere or produce radioactive waste. Third, sinceit does not require the high temperatures of thermal power plants, it does notneed special materials for its facilities. Fourth, sea-water is a limitlessresource, so that there is no need to worry about supplies running out, or totransport it over long distances. Fifth, fresh water can be obtained as a side-product, and also the salt and other minerals in sea-water can be extracted.Sixth, pumped up water can be utilized for both cooling and warming.

Research and Development in Japan

A Committee for a Comprehensive Survey of New Electric PowerGeneration was set up in Japan in 1970. The committee surveyed variousalternative types of electric generation to thermal power generation, andOTEC was among them. The ideas of Professor Claude and Dr. Andersonwere examined in detail. At the same time the committee studied the sea-water temperature surrounding Japan and considered possible materials forthe working fluid. After the disbanding of the committee, a planned LeisureCenter took over part of the project to utilize ocean thermal energy. TheCenter examined a project to build an OTEC power plant on a South Pacificisland and develop a leisure land around it.

Universities and governmental research institutions also started basicresearch on OTEC around 1972. Private companies showed great interest,too. Among them Toden Sekkei (Tokyo Electric Power Services) in 1971

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set up a plan to build an OTEC plant in the Pacific island Republic of Nauru,and in 1973 surveyed the geographical features of the planned site, seaconditions and climate. The fact that the power generated was actually usedfor normal purposes means that this was the world’s first practical OTECpower plant. The story will be described later.

Japan was badly hit by the oil shock, or energy crisis, of 1973, in whichthe price of oil soared after concerted action by the oil-exporting countries.The following year the “Sunshine Project” was started up by the IndustrialTechnology Agency of the Ministry of International Trade and Industry(MITI) to develop new energy sources.

This project was initiated by the government to examine alternativeenergy sources to fuel and atomic energy and to exploit any viable ones. A

Dr. T. Kajikawa Prof. H. Uehara Prof. T. Honma

Figure 15

Figure 16. #2 experimental closed-cycle OTEC generator at the Institute for ComprehensiveElectronic Technology

Ocean Water and Its Wonderful Potential 25

decision was made to utilize solar energy, geothermal energy, coal energyand hydrogen energy, and to research and develop technology for exploitingthem. Other potential energy sources remained as subjects for“comprehensive study.” These were new energy sources whose immediatepracticality was not clear, but which appeared to have potential for thefuture.

OTEC was classified for “comprehensive study” at this early stage ofthe Sunshine Project since it was considered an unrealistic idea. However,serious research was started because it was included in the project. Many

Imari #3, completed in 1985, currently Saga University’s main experimental generator

Imari #3 turbine, using ammonia as its working fluid. The generator is at back right.

Figure 17

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experts from governmental institutes, universities and industries participatedin the research group and examined in detail the possibilities of OTEC from1974 till 1979. Their conclusion was that ocean thermal difference powergeneration was relatively economical compared with other energy sources,could generate large quantities of electricity, and would be an importantmeans of providing energy in the future.

When the Sunshine Project started, research on engineering systems forOTEC was initiated at the same time. Dr. Takenobu Kajikawa from theIndustrial Science and Technology Agency’s Institute for ComprehensiveElectronic Technology, Professor Haruo Uehara from Saga University, andProfessor Takuya Honma from the University of Tsukuba carried out thisstudy (Figure 15).

The Institute for Comprehensive Electronic Technology completed itsfirst model system for a basic experiment in September 1975, and succeededin generating 100 watts of electricity. The system, built at the Institute, wasa closed cycle with 500 grams of fluorine (chlorofluorocarbon) as theworking fluid and circulated a maximum 50 tons of temperature-controlledwarm and cold water per hour. Although it generated only 50 watts ofelectricity when the temperature difference was 19 degrees Celsius, this wasincreased to 600 watts when the difference was raised to 27 degrees Celsius.With this system, experiments were carried out for various conditions andbasic data were collected for designing the most efficient system. TheInstitute for Comprehensive Electronic Technology completed its secondmodel system in 1977 for further advanced studies (Figure 16).

Saga University was busy, too, and built experimental facilities Nos. 1to 5 on its campus. These models were called Shiranui, which is the Japaneseword for marine luminescence. Shiranui No. 1 was a small one made withflasks, and generated one watt of electricity. It was open cycle, similar toProfessor Claude’s first experimental model. All later ones were closed

Figure 18. Hawaii, the largest volcanic island of the Hawaiian Islands

Keahole Pt

Island of Hawaii

Ocean Water and Its Wonderful Potential 27

cycle, and Nos. 3 to 5 produced 1,000 to 1,200 watts. The university alsoconstructed experimental systems, Imari Nos. 1 and 2, on the coast in Imaricity. Imari No. 2, completed in 1980, is capable of generating 50 kilowattsand as an actual operating OTEC system has been used for variousexperiments. For Imari No. 3, see Figure 17.

American Attempts

While all previous experiments had been basic, elementary ones, theexperiment named “Mini-OTEC” carried out off Hawaii Island from Augustto November 1979 aimed to produce surplus electric power beyond just whatwas necessary to operate the pumps and other components of the systemitself (Figure 18). This experiment was implemented by the State Governmentof Hawaii in cooperation with enterprises including Lockheed and theDillingham Corporation. After preparations lasting 13 months andexpenditure of $3 million, a 268-ton raft 37 meters long and 10 meters widewas positioned off Keahole Point where the sea was 1300 meters deep(Figure19). A generator with ammonia as the working fluid was installed,and a 60-cm diameter polyethylene tube (57.5 cm in inner diameter) wasused as the cold water intake. The experiment succeeded in generating 53.6kilowatts of electricity by pumping up 50 liters per second of about 5-degreeCelsius cold water from a depth of 650 meters. The system used 35.1kilowatts to operate its own water pumps, so that its net output was 18.5kilowatts. This corresponds to 34.5% of the total output of the generator.

Governor Ariyoshi of the State of Hawaii was delighted with thesuccess of this experiment, comparing it to the first flight by the Wright

Figure 19. Mini-OTEC. The water intake pipe is located in the ship’s bottom, and cannotbe seen in this figure.

Ammonia pool

Condenser

Diesel generatorfor starter

Evaporator

Connection for waterdischarge pipe

Turbine generator

Warm water pump

Cold water pump

Control operation room

Ammonia storagetank

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brothers. Generally speaking, in OTEC the rate of surplus power generationincreases with the size of the system, and will approach 75-80% with a100,000-kilowatt system. For practical power generation, it is necessary toincrease this rate by enlarging the system, but a number of problems remainto be solved.

The biggest problem of OTEC is the capacity and durability of theevaporator and condenser which are the heart of the system. In the UnitedStates, the Energy Research and Development Administration (ERDA) ledattempts to make various types of evaporators and condensers, and gatheredthem all together for tests at the Argone National Institute. Still more, aseries of experiments to examine their performance at sea were carried outat the same location on Hawaii Island between April 1980 and November1981.

A converted oil-tanker was used for this experiment, which was calledOTEC-1 (Figure 20). Surface sea-water was taken into the vessel from thestem, and cold water was pumped up from 686 meters deep through threeintake pipes installed in midship. These pipes were made of polyethyleneand were 1.2 meters in diameter; the pipe walls were 5 cm thick. They wereclosed at both ends and towed by a ship to the site, where they were sunk withweights at the end.

However, a generator was not installed in this experimental system:studies concentrated on the capabilities of evaporators and condensers, waysof connecting intake pipes, means for removing marine creatures and otherunwanted materials that fouled up the system, and the effects of sea currents.

Furthermore, the United States instituted a long-range plan leading upto the year 2000, whereby practical OTEC is achieved by the power industry,nation-wide research and development is promoted for systems other than

Figure 20. Converted tanker for OTEC-1. No generator is installed.

Helicopter deck

Cold water pump Environmental laboratoryand control room

Warm water pump

Thruster

Mixed cold and warmwater discharge

Cold water pipeEvaporator

CondenserWarm water intake

Ocean Water and Its Wonderful Potential 29

closed cycle and those with ammonia as the working fluid, and othertechnology is improved.

OTEC Lights Up a School

The Mini-OTEC experiment in Hawaii was the first to generate moreelectricity than was needed for operating the system itself; but the amountwas only small. The following story is about the world’s first instance ofpractically useful power generated by OTEC. This happened over a periodof about one year in the Republic of Nauru. It was implemented by TokyoElectric Power Company and Toden Sekkei with the support of the JapaneseGovernment, and in cooperation with the Toshiba Corporation and theShimizu Corporation.

The Republic of Nauru is an island country on a coral reef in the SouthPacific, located about 5,000 kilometers southeast of Tokyo and not far southof the Equator (Figure 21). The country covers an area of 21 squarekilometers and has a population of 8,000. Australia, New Zealand and theUnited Kingdom governed the country in the past, but it gained itsindependence in January 1968 as the smallest country in the world. Four-fifths of the area of the islands are covered by guano, the solidified droppingsof sea birds. The country’s economy is maintained by exports of guano,from which high quality phosphorus can be extracted. For this reason,medical care, education and electricity are all free and life is prosperous.

Figure 21. The island Republic of Nauru is located just south of the Equator. The plantlocation is about 166˚55’E.

Japan

Taiwan

The Phirippines

Republic of Nauru

Plant location

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Figure 22. View of the Nauru OTEC plant. Three pipes extend into the sea: one each forDOW intake, surface water intake, and discharge.

However, it was estimated in 1983 that guano reserves had fallen to no morethan 38 million tons, which would be exhausted by the end of the twentiethcentury if extraction continued at the rate of 2 million tons per year.

The sea surrounding Nauru plunges at a steep angle of 40 degreestoward the open ocean, and what is more, water from a depth of only 500meters is an impressive 20 degrees Celsius cooler than water at the surface.These two factors alone provide the great advantage of the need for only ashort intake pipe. The islands are hardly ever hit by typhoons, winds arelight and the waves are not so high; the islanders are friendly toward Japan.All of this made the islands ideal for the experiment.

The photo shows an overview of the whole OTEC station (Figure 22).A generator was situated on land and was designed to generate 100 kilowattswith fluorine-22 as the working fluid. The intake pipe for cold water was70 cm in inner diameter. Twenty-two tons per minute of cold water werepumped up from a depth of about 580 meters, 1250 meters off-coast, and 24tons per minute of surface water were pumped every minute from 150 metersoff-coast. A maximum of 120 kilowatts of electricity was generated. Outof this power, about 90 kilowatts was used at the plant, and the rest wassupplied to a local elementary school and other places in Nauru. The firstday OTEC electricity was delivered to that school in Nauru was 14 October1981.


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