Environmental Science & Engineering - www.esemag.com - September 2002
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Aquaculture and energy-generation benefit from pipeline deep under the sea


Installers make a flange connection in the 55-inch diameter HDPE pipe in Kawaihae Harbor. The pipe was painted white to keep it cool and provide better visibility when floating at sea.
Photo: Tom Daniel

A Canadian company supplied the piping for an application to pump ashore 38° F seawater from deep below the surface for use in aquaculture and energy-generation in Hawaii. The 9,000-foot long, cold water pipeline was successfully deployed last October by the contractor, Healy Tibbitts Builders, Inc. of Honolulu. KWH Pipe of Mississauga, Ontario, a member of the Plastics Pipe Institute (PPI), produced the pipe.

Makai Ocean Engineering, consultants to the Natural Energy Laboratory of Hawaii Authority (NELHA), near Keahole Point on the western-most point of the Big Island of Hawaii, chose about 10,000 feet of HDPE pipe in 55- inch and 63-inch diameters. NELHA operates the Hawaii Ocean Science and Technology Park that provides the resources, support, and facilities for many innovative ocean-related businesses.

As the world’s tropical oceans are a huge collector of heat energy, NELHA engineers are taking advantage of a process that uses that energy for various scientific and practical endeavours. That process is called Ocean Thermal Energy Conversion (OTEC). NELHA has hosted a series of OTEC experiments since its founding in 1974.

OTEC utilizes the difference in temperature between warm surface seawater and cold deep seawater to produce energy. The cold deep seawater can also be used to air-condition buildings, desalinate water, grow lobsters and fish, produce algae and shellfish, grow cold-climate fruit and vegetables and much more. To do that, NELHA must get the cold water from deep in the ocean to the surface.

Tom Daniel, one of the project scientists with NELHA explained that the pipe is filled with air, which supports it and its anchors during towing to the site where it is flooded for sinking. The intrinsic buoyancy of the HDPE pipe allows designs using pendant-weighted buoyant sections to avoid rough areas on the bottom of the ocean.

The pipe was fused into nine sections, each approximately 1,000 feet in length on shore at Kawaihae Harbor on the northwest corner of the Big Island. In a three day assembly and deployment operation, the flanged sections were joined into one 9,000-foot long pipe segment, towed 27 miles to the site and deployed using a controlled submergence process.

A separate warm water intake structure was also installed near the 80-foot-deep end of one shore-crossing tunnel, and spool pieces connect that structure and the offshore HDPE pipe to the two tunnels constructed earlier. The tunnels extend about 500 feet onshore to the pump station which is now under construction. The system was expected to begin pumping ashore deep cold (38°F) and surface (76°F - 81°F) seawater by the end of July 2002. Daniel says OTEC has tremendous potential for large-scale energy generation in the future.

There is growing interest in smaller diameter suction pipelines for bringing ashore deep seawater for aquaculture and cooling applications, like the one at Keahole Point. The only existing example outside of NELHA is Cornell University’s Lake Source Cooling Project, which cools the University campus by pumping cold water from 250 feet deep in Cayuga Lake through a two mile long, 63-inch HDPE pipeline, also designed by Makai Ocean Engineering.

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