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Delegation in Japan: Ocean Thermal Energy Conversion (OTEC) on the island Kumejima

Gepubliceerd op
5 juni 2014

On 13-15 May 2014, a Dutch/Colombian delegation travelled to Kumejima to visit the deep sea water research and industry park at the island. Goal of the mission was to evaluate whether the Kumejima approach could serve as a model for the island of San Andres, Columbia. San Andres considers to develop a similar deep seawater program in collaboration with Dutch company Bluerise and Wageningen UR.

Kumejima: a model island in Japan

Kumejima is a small (46 km2) tropical island in Japan. It is part of the Okinawa prefecture and has 8300 inhabitants. The prefecture of Okinawa wants Kume Island to be 100% sustainable in the year 2020. This was the incentive to install a deep seawater pipeline in 2003.

Every day, 13.000 m3 of cold (10°C) seawater is pumped from a depth of 612 m to the island. The water is used for several purposes such as cooling, energy generation, aquaculture and the production of drinking water, salts and cosmetics. The deep water facility includes a research station and a deep water tower, from where the water is further distributed. Around the institute is a 10 ha industrial park. Companies located here are directly connected to the deep water supply. Companies located at a further distance can obtain deep seawater at the “fuel” station for tank wagons.

Water generates electricity

In addition to direct cooling, the deep water is also used to generate electricity through the process of Ocean Thermal Energy Conversion (OTEC). Kumejima currently has the world’s only operating OTEC installation, a 50 KW demonstration plant. OTEC takes advantage of the difference in temperature between surface water and deep sea water. Warm surface water is used to evaporate a low-boiling point liquid such as ammonia to create steam. The steam drives a turbine that generates electricity. The steam is condensated back to liquid using cold deep seawater.

Used seawater further used for aquaculture

Deep seawater that has been used for OTEC or cooling can be further used for other purposes such as aquaculture. This 6 ha shrimp farm uses the clean, virus-free deep seawater for its hatchery. The farm produces 250 tonnes of tiger prawn per year and is currently the largest deep water based industry on the island.

Deep seawater is rich in inorganic nutrients and as such very suitable for the aquaculture of seaweeds. This farm produces 180 tonnes per year of seagrapes, a local variety of Caulerpa.

Deep seawater can also be used for human consumption. In a water factory, deep seawater is converted into drinking water and salt through reversed osmosis.

The Dutch delegates conclude the following:

  • Kumejima’s deep water park is an inspiring Small Tropical Island Solution, generating energy, enabling seafood production, creating employment and increasing sustainability.
  • Currently, the deep water-based industries at Kumejima generate an annual turnover of 20 million USD, which is 25% of the islands Gross National Product.
  • Deepwater pipelines at tropical islands should first serve energy generating devices such as OTEC and SWAC. The “waste” water can then be applied for aquaculture and other industries, providing solutions for tropical challenges related to energy, food security and water.
  • Bluerise and Wageningen UR should cooperate in advocating and developing and designing deep water solutions for other tropical islands around the world such as San Andres.