¹Ship Planning & Development Dept., Shipbuilding & Defense Hq. Hitachi Zosen Corporation, Osaka, JAPAN

kobayashi_hi@hitachizosen.co.jp

　

²Energy Division, Xenesys Inc. Tokyo, JAPAN

　

³Institute of Ocean Energy, Saga University Saga, JAPAN

　

A new era in the technology of Ocean Thermal Energy Conversion (OTEC), which is a system of converting thermal energy in ocean into electricity, has come now. The concept of OTEC was first proposed in 1881. Since then, although many scientists have made earnest effort to materialization, OTEC has never commercialized yet. However an IMW pilot OTEC plant has been constructed in India being supported by Saga University in the matter of thermal engineering. In fact the Indian plant was pushed technical break through of innovative thermal cycle, which is called 'UEHARA CYCLE', and its associated heat exchanger technology. The Indian plant has created a great sensation in the world, and at the same time many countries have started to investigate the feasibility of OTEC.

　

OTEC provides not only power generation but also some solutions to the three greatest global issues we are facing in 21^st century, i.e., 'Energy', 'Water' and 'Food' associated with the fundamental problems of environment destruction and population explosion.

　

In collaboration among Saga University, Xenesys Inc and Hitachi Zosen Corporation, they are promoting several projects concerning the technologies including seawater desalination utilizing natural energy combined with OTEC. As the ocean thermal energy is perfectly clean and renewable, and the potential is very huge, a bright future for the new OTEC technology and the wide application is prospected. This paper describes an outlook and a trend of the new OTEC technologies spreading rapidly now in the world.

　

　

¹National Institute of Ocean Energy Chennai, INDIA

mravi@niot.res.in

　

²Saga University Saga, JAPAN

　

³Institute of Ocean Energy, Saga University Saga, JAPAN

　

The bathymetry of the coast around India, where cold water at a depth of 1000m is available at about 40 km from the shore necessitates the use of a floating platform to house the OTEC plant. NIOT proposes to build a 1 MW floating OTEC plant working on a closed cycle off the coast of Tamilnadu. The aim of the demonstration plant is the design, manufacture, and erection commissioning and performance evaluation of a floating OTEC plant rating 1 MW gross. In addition to the power module operating on closed loop ammonia and associated turbine generator, control system technologies, this will imply the need to develop and assimilate some technologies. For example, (1) Design, Manufacture and Performance evaluation of high quality, compact heat exchangers with phase change under marine conditions, (2) Measurements and development of methods for control of bio fouling in heat exchangers, (3) Structural analysis under marine environment of 1.0 diameter, 1,000 m long HDPE pipe coupled to a floating barge, etc.

　

In this paper, it is presented the concept proposed by NIOT and the detailed engineering and technology is shown.

　

　

¹Steel Structure & Ocean Laboratory, Technical Research Institute Hitachi Zosen Corporation, Osaka, JAPAN

niizato@hitachizosen.co.jp

　

²Ship & Offshore Design Department, Shipbuilding & Defense Hq. Hitachi Zosen Corporation, Osaka, JAPAN

　

³Energy Division, Xenesys Inc. Tokyo, JAPAN

　

⁴Institute of Ocean Energy, Saga University Saga, JAPAN

　

In the paper is presented computations of motions of an offshore floating OTEC plant unit. Plant for OTEC (Ocean Thermal Energy Conversion), which is now in the spotlight as a renewable energy technology, is characterized by involving large diameter riser pipe(s) for pumping up cold deep ocean water from 1,000 m depth.

　

Two types of the OTEC plant have been known generally, one is onshore type, and the other is offshore floating type. The offshore floating type has been considered to be more economical when plant size becomes large. On the other hand, the offshore floating type, especially that for the sea near Japan, is having some difficulties because of the severe environment such as the typhoons in summer and the monsoons in winter.

　

The authors basically designed an offshore floating unit for a small size 1 MW OTEC plant, and computed its motions by use of a sequential analysis method. Then the dynamic response of its riser pipe was also computed. The East China Sea of 1,000 m depth is assumed as an example of environmental conditions for the computation. The designed unit has octagon column shape of 24 m diameter and 19 m draft, and is moored by 4 points with hybrid mooring system of steel chains and wires.

　

The results indicated the good characteristics of motions, and confirmed that the offshore floating unit for a small OTEC plant has enough realizability.

　

　

The Pacific Society JAPAN

　

Wave power generator Kaimei was tested at 20 years ago in Japan, Good generation was confirmed, but efficiency was not enough. Backward Bent Duct Buoy (BBDB) was proposed. Air chamber bent to backward, and opens to stern, and air output per the same air chamber increased 10 times than Kaimei.

　

One sea test (B2D2 200KW) of single float BBDB started from 2002 in Ireland. Wave power in Ireland is 60KW/m , very high,. Wave power cost in such high wave area is estimated to 6-10 yen/KWh. Other isolated island such as Hawaii is 20KW/m. Japanese coast is 10 KW/m. In order to open practical use in low wave power area, terminator BBDB with cylinder duct is proposed.

　

Terminator BBDB with box duct (29.5m long, 38.25m wide) and terminator BBDB with 6 cylinder duct (29.5m long 38.25m wide) were compared, Later was higher output with smaller steel weight. Wave data was compared in North Atlantic and Japan Sea, and average wave is distributed in 1/40 line of HS/LS (Wave height. / wave length) in both areas.

　

Model test was conducted, and high efficiency (100% In peak) and terminator was 30% higher efficiency than attenuator was observed. 2 Valve box and 4 valve box were used in Kaimei, Since 2 valve box with impulse turbine is the best efficiency (60%), and it can decrease number of turbine. and 2 valve with impulse turbine. With Hellers generator will be adopted.

　

Economy of Terminator BBDB was estimated, 3 floats terminator with box duct in Ireland is estimated 6.7 yen/KWh, Terminator BBDB with cylinder duct in Japanese coast is estimated 7.8 yen/KWh, and it has a possibility to be economical in low wave density area.