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NELHA Seawater Supply System
The NELHA seawater supply system is the only one of its size
and capacity in the world, and its cold seawater supply pipes,
in particular, are the deepest large diameter pipelines in the
world's oceans. Over the last 21 years, NELHA has compiled an
excellent record of continuous seawater delivery to its tenants,
and continues to incorporate redundancy and other supportive
measures as the seawater system expands to service the whole
technical park.
Main Seawater System
Pristine cold deep seawater from a consistent 6ºC (43ºF) source
is brought to shore from 2,000-foot depths off Keahole Point
through a 6,284 foot long, 40-inch (1 meter) diameter pipeline
made of high density polyethylene (HDPE). The durability, strength,
flexibility, buoyancy and inert properties of HDPE make it the
preferred material for coldwater pipelines (CWP) in the deep
ocean.
Waters offshore of Keahole Point that supply NELHA's seawater
systems are rated as Class AA by the Hawaii State Department
of Health, essentially unaffected by human influences and representative
of clean open ocean tropical surface seawater. The intake for
NELHA's main surface seawater supply pipe is located 69 feet
under the ocean surface over a 90-foot bottom depth. A 28-inch
HDPE pipeline carries the pristine water to a sump in the Main
Pump Station onshore. Surface seawater temperatures remain in
the narrow range of 24º to 28.5ºC (75 to 83ºF) year 'round.
Multiple submersible pumps push the seawater from the Main Pump
Station through the distribution system in the park. Warm seawater
is delivered throughout the NELH section of the park via a 28-inch
HDPE distribution pipeline while cold seawater is delivered
through a 24-inch distribution pipeline. The system is capable
of delivering up to 13,400 (~0.84m3/s) gpm of cold seawater
and 9,700 gpm (~0.61m3/s) of warm. Variable frequency drive
control devices maintain the water pressure between 10 and 12
psig, precisely controlling water flow in both distribution
lines.
The 24-inch cold seawater distribution line continues beyond
the NELH section of property to also service the HOST Park.
The Booster Pump Station, built in 1998, provides the additional
pressures needed to pump deep cold seawater to elevations up
to 80 feet above sea level in HOST Park. At present, up to 6,500
gpm (~0.41m3/s) of cold seawater can be delivered to this section
of the park.
An interim distribution pipeline and pump station was completed
in January 2001 and is currently supplying small volumes of
warm surface seawater to the HOST Park. The interim system will
remain operational until NELHA's new 55-inch pipeline system
is completed in the fall of 2002 (see SEAWATER SYSTEM EXPANSION
below).
Seawater System Redundancy
An 18-inch pipeline for cold seawater and a 24-inch pipeline
for warm seawater provide the reassurance of redundant supplies
for the main 40-inch and 28-inch seawater supply lines. When
needed, seawater from these pipelines at NELHA's Ka'u Pump Station
can be added to the main supply lines. The 24-inch pipeline
provides up to 5,400 gpm (~0.34m3/s) of warm surface seawater
while the 18-inch pipeline has a capacity of up to 3,000 gpm
(~0.19m3/s) deep seawater.
Regular operations of the NELHA seawater supply system are further
enhanced by the following:
1) An automated alarm system
2) Operations personnel on call 24 hours a day
3) A 1-megawatt generator to provide complete electrical redundancy
for the NELHA Main Pump Station and facilities controlled from
within the Research Compound.
4) A mobile 200-kilowatt generator to provide electrical redundancy
to any location within the NELHA properties
5) A 125-kilowatt generator to provide electrical redundancy
for the 24-inch warm seawater supply pipeline
Seawater System Expansion
NELHA and its tenants look forward to the completion of a major
expansion to the existing NELHA Seawater Supply System in the
HOST Park by the end of year 2002. This system expansion consists
of two 55-inch diameter supply pipelines with pumping capacities
up to 40,500 gpm (2.56m3/s) of surface seawater and 27,000 gpm
(1.80m3/s) of deep seawater. The surface seawater intake will
be located at a depth of approximately 80-feet below the ocean
surface. The 10,247 foot long CWP has an intake at 3,000 feet
below the ocean surface to access 4ºC (39ºF) source seawater.
It is the deepest cold seawater pipeline ever built in the world's
oceans. The CWP was installed according to plan in late 2001
and the shore-based distribution system is currently under construction.
The NELHA seawater system expansion has been designed to accommodate
a wide range of potential water uses, including ocean thermal
energy conversion power production, air conditioning, industrial
cooling, aquaculture, coldwater agriculture and many others.
NELHA Seawater Supply System
Deep Seawater (DSW)
Pipe Inner Diameter: 40-inch (100 cm)
Status: Fully operational
Date Installed: Aug. 1987
Intake Depth*: 2,210 ft. (674 m)
Offshore Pipe Length: 6,284 ft. (1,916 m)
Pumping Capacity: 13,400 gpm (0.84 m3/s)
Pipe Inner Diameter: 18-inch (45 cm)
Status: Fully operational
Date Installed: Oct. 1987
Intake Depth*: 2,060 ft. (628 m)
Offshore Pipe Length: 6,180 ft. (1,884 m)
Pumping Capacity: 3,000 gpm (0.19 m3/s)
Pipe Inner Diameter: 55-inch (140 cm)
Status: Under construction
Date Installed: Dec. 2001
Intake Depth*: 3,000 ft. (915 m)
Offshore Pipe Length: 10,247 ft. (3,124 m)
Pumping Capacity: 27,000 gpm (1.80 m3/s) |
Surface Seawater (SSW)
Pipe Inner Diameter: 28-inch (71 cm)
Status: Fully operational
Date Installed: Aug. 1987
Intake Depth*: 69 ft. (21 m)
Offshore Pipe Length: 535 ft. (163 m)
Pumping Capacity: 9,700 gpm (0.61 m3/s)
Pipe Inner Diameter: 24-inch (61 cm)
Status: Fully operational
Date Installed: June 1993
Intake Depth*: 33 ft. (10 m)
Offshore Pipe Length: 266 ft. (81 m)
Pumping Capacity: 5,400 gpm (0.34 m3/s)
Pipe Inner Diameter: 55-inch (140 cm)
Status: Under construction
Date Installed: Dec. 2001
Intake Depth*: 79 ft. (24 m)
Offshore Pipe Length: 540 ft. (165 m)
Pumping Capacity: 40,500 gpm (2.56 m3/s) |
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*
Actual intake depths may vary by several meters as the pipeline
moves slightly during each semi-diurnal tidal current cycle.
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