Environmental Engineering Reference
In-Depth Information
T
ypes
oF
oTeC T
eChnologies
The types of OTEC systems include the following:
•
Closed-cycle
systems use fluid with a low-boiling point, such as ammo-
nia, to rotate a turbine to generate electricity. Warm surface seawater is
pumped through a heat exchanger where the lower boiling point fluid is
vaporized. The expanding vapor turns the turbogenerator. Deep, cold sea-
water pumped through a second heat exchanger condenses the vapor back
into a liquid, which is then recycled through the system.
•
Open-cycle
systems use the warm surface water of tropical oceans to make
electricity. When warm seawater is placed in a low-pressure container, it
boils. The expanding steam drives a low-pressure turbine attached to an
electrical generator. The steam, which has left its salt behind in the lower
pressure container, is almost pure fresh water. It is condensed back into a
liquid by exposure to cold temperatures from deep ocean water.
•
Hybrid
systems combine the features of both the closed-cycle and open-
cycle systems. In a hybrid system, warm seawater enters a vacuum chamber
where it is flash-evaporated into steam, similar to the open-cycle evapora-
tion process. The steam vaporizes a lower boiling point fluid (in a closed-
cycle loop) that drives a turbine to produce electricity.
OCEAN ENERGY AND HYDROKINETIC TECHNOLOGY IMPACTS
*
This section summarizes the potential (generalized) environmental impacts of new
ocean energy and hydrokinetic technologies. Environmental issues that apply to all
technologies include the following:
•
Alteration of river or ocean currents or waves
•
Alteration of substrates and sediment transport and deposition
•
Impacts of habitat alterations on benthic organisms
•
Impacts of noise
•
Effects of electromagnetic fields
•
Toxic effects of chemicals
•
Interference with migratory animals
•
Potential for injury to aquatic organisms from strike or impingement due to
designs that incorporate moving rotors or blades (see
Fig u r e 7.9
)
•
Impacts of ocean thermal energy conversion
*
Adapted from USEPA,
Report to Congress on the Potential Environmental Effects of Marine and
Hydrokinetic Energy Technologies
, U.S. Environmental Protection Agency, Washington, DC, 2009
(http://www1.eere.energy.gov/water/pdfs/doe_eisa_633b.pdf).
