Returning Water to the Bosom of Nature Cleaning Urban Water Using Water as an Energy Source

Using Water as an Energy Source

	The ultimate clean energy source Our planet is awash in some 1.4 billion cubic kilometers of water; yet about 97.5% of that is seawater, with fresh water accounting for only 2.5%. Of that, the proportion which is useable is estimated at only 100,000 cubic kilometers. Imagine what would happen if seawater could be used as it is and, in the process, that use produced fresh water! The technology—on the face of it, the stuff of dreams—already exists. It involves generating electricity by exploiting the temperature differential of seawater at different depths as an energy source. When this technology is put to work, it also can produce potable fresh water—which makes it a focus of worldwide attention. The technology’s underlying principle involves a “working fluid.” The liquid-state working fluid is boiled and the resulting vapor used to drive a turbine, thus generating electricity. Warm surface seawater is used to heat the working fluid, while cold deep seawater is used to cool the vapor as it comes off the turbine, returning it to its liquid state. This repeated cycle of thermal (heat) transfer from seawater to working fluid and then back to seawater, is the origin of the name of the process: ocean thermal energy conversion, or OTEC for short. Associate Professor Yasuyuki Ikegami of the Institute of Ocean Energy at Saga University (IOES), the center of OTEC research in Japan, says: “Japan is at the forefront in this technology, and our know-how has been introduced in several countries. For example, Saga University supported the design of a 1,000-kW demonstration plant that began operating in India in September 2003. Japan’s OTEC research was started by Professor Haruo Uehara, currently at Saga University, who 30 years ago started work from a single miniature light bulb. Today, the world is looking to Saga University’s research as a source of environmentally friendly, clean energy.” Several different OTEC systems have been developed. The most promising variation is the Uehara Cycle, developed by Professor Uehara. It is characterized by use of an ammonia-water mixture high in ammonia content as its working fluid, which allows low-temperature vaporization, and the achievement of high heat-transfer efficiency in its heat exchangers. Thirty years ago, the power generated was completely consumed just by the operation of the pump bringing up deep seawater; but today, researchers look forward to netting 50 to 80% of the output.	Institute of Ocean Energy, Saga University (IOES)
	Variety of by-products
	Because OTEC uses seawater, its heat source is inexhaustible. Unlike fossil-fueled power, OTEC does not give off large amounts of carbon dioxide; unlike atomic power, OTEC does not generate radioactive waste; and, unlike wind, solar, and tidal power, OTEC does not fluctuate due to the vagaries of weather. This means that power generation using OTEC is cleaner than schemes using traditional energy sources, and more stable than those using alternative sources. Further, OTEC can produce myriad useful by-products, including mineral water, distilled water, lithium, and hydrogen. According to Kazuya Urata, a technician at the institute, “As long as there’s a temperature differential of 15°C or more between the surface and the deep seawater, OTEC can generate electricity. Calculating from this figure, we have energy reserves equivalent to 8.6 billion tons of crude oil in Japan’s maritime economic zone alone. And deep seawater is rich in minerals, so it can be exploited for marine culture. “India has plans to build 1,000 plants with generating capacities of 20,000–50,000 kW each, and the Republic of Palau also has plans to build a power plant. OTEC has the potential to provide solutions for a whole range of energy, environmental, water-resource, food, and population issues, and the technology is already heading into the practical application phase.” The Institute of Ocean Energy Research at Saga University is recipient of a 2002 Environmental Research Grant from the Sumitomo Foundation. The grant was applied to the building of a new facility on Imari Bay in Saga Prefecture, which is now the world’s largest OTEC research facility. Its R&D capability has been further enhanced through the introduction of an intelligent hybrid experimental power generation station that is combined with a 10 ton- per- day desalination plant. In March 2003, in conjunction with the 3rd World Water Forum, the leaders of ten South Pacific nations, including the president of the Republic of Palau and the prime minister of the Cook Islands, and water-resource officials from Saudi Arabia, convened an international forum to facilitate implementation of IOES technology, with forum participants even visiting the institute. From Imari Bay, a small corner of the world’s oceans, a new era is about to begin!	Experimental and demonstration works of OTEC technology are being carried out in this section. Also hybrid type OTEC technology combined with desalination system is another objective here. The output capacity of the pilot OTEC plant is 30 kW, while the desalination test plant has a production capacity of 10 tons per day.

(Data collected September 2003)