Environmental Engineering Reference
In-Depth Information
Ocean thermal energy conversion projects would be sources of waterborne noise,
arising from operation of ammonia turbines, seawater pumps, support systems asso-
ciated with the energy-producing cycle, and in some cases propulsion machinery for
dynamic positioning of the OTEC platform. Janota and Thompson (1983) measured
noise from OTEC-1, a 1-MWe test facility that was moored near Keahole Point, Hawaii.
The most significant sources of noise from the small project resulted from the interac-
tion of inflow turbulence with the seawater pumps and from thrusters used for dynamic
positioning. Based on their measurements, Janota and Thompson (1983) predicted that
a 160-MWe OTEC plant would radiate less than 0.05 acoustic W of broadband sound
in the frequency range of 10 to 1000 Hz, which is at least an order of magnitude less
than that which is produced by a typical ocean-going freighter. Similarly, Rucker and
Friedl (1985) predicted that pump noise (at 10 Hz) from a 40-MWe OTEC plant would
be reduced from 136 dB to 78 dB at about 0.8 km; this is less than ambient noise at a
sea state of 1 (very gentle sea with waves less than 0.3 m in height).
Large marine organisms may be impinged on the screens that protect the OTEC
intakes, and smaller organisms (e.g., zooplankton, fish eggs, larvae) will pass through
the screens and be entrained in the heat-exchanger system (Abbasi and Abbasi, 2000).
The number of organisms entrained in the water will depend on their concentrations
in the intake areas; more aquatic organisms are likely to be impinged and entrained
at the surface water intake than from the deep water intake. Due to the large flow
rates of water at the warm water intake, impingement and entrainment will especially
need to be monitored there. As with steam electric power plants, the heat exchanger-
entrained organisms will be susceptible to mechanical damage in the piping and to
rapid changes in temperature, pressure, salinity, and dissolved gases that may cause
mortality. For example, the temperature of cold, deep water is expected to increase by
about 2 to 3°C after passing through the heat exchangers; likewise, the temperature of
shallow, warm water is expected to decrease by the same amount. Myers et al. (1986)
noted that there is insufficient information to judge the impacts of a 2 to 3°C tempera-
ture shock but assumed that most organisms will probably not be directly impacted
by this amount of temperature change. However, secondary entrainment into the dis-
charge plume will also expose marine organisms to chemical, physical, and tempera-
ture stresses. A mixed discharge of warm and cold water could subject organisms
entrained from the warm surface waters to a drop of 10°C, which would likely cause
lethal cold shock for some species. Few organisms are expected to be entrained in the
deep, cold water flow, but those that do will be subjected to potentially lethal pressure
decreases of 70 to 100 atmospheres (7100 to 10,100 kilopascals) (Myers et al., 1986).
ENVIRONMENTAL IMPACTS OF HYDROKINETIC ENERGY
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In the previous section, we provided a general discussion of potential environmental
impacts of hydrokinetic energy technology. In this section, we provide a discussion
of many of the specific impacts related to site evaluation, construction, and opera-
tions and maintenance (O&M) activities.
*
Adapted from Tribal Energy and Environmental Information Clearinghouse,
http://teeic.indianaffairs.
