Power generation from
the meeting of river water and seawater.
Where the river meets the sea, there is the
potential to harness a significant amount of renewable energy. The evaluation
of an emerging method of power generation called pressure retarded osmosis
(PRO), in which two streams of different salinity are mixed to produce energy.
In principle, a PRO system would take in river water and seawater on either
side of a semi-permeable membrane. Through osmosis, water from the less-salty
stream would cross the membrane to a pre-pressurized saltier side, creating a
flow that can be sent through a turbine to recover power.
The model on a
simplified PRO system in which a large semi-permeable membrane divides a long
rectangular tank. One side of the tank takes in pressurized salty seawater,
while the other side takes in river water or waste water. Through osmosis, the
membrane lets through water, but not salt. As a result, freshwater is drawn
through the membrane to balance the saltier side. As the freshwater enters the
saltier side, it becomes pressurized while increasing the flow rate of the
stream on the salty side of the membrane. This pressurized mixture exits the
tank, and a turbine recovers energy from this flow.
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