April 22, 2013
Power Plants Use Rivers For Cooling, But Cause Stress To The Environment
Michael Harper for redOrbit.com — Your Universe Online
When thermoelectric power plants convert water to steam to turn large turbines and create energy, they´re left with plenty of what´s known as “waste heat.” This waste heat has to go somewhere and either flows up into the atmosphere or back into the rivers or ponds where these factories source their fresh water.To better understand where this waste heat goes and how it affects the environment, scientists from the University of New Hampshire (UNH) and the City College of New York (CCNY) ran a pair of computer models which measured how power plants interact with the environment and different ecosystems. Their analysis discovered that much of the waste heat generated by these power plants is actually dissipated in the rivers, leading them to define these bodies of water as “horizontal cooling towers” which help keep these power plants running.
No change in an ecosystem goes unnoticed, however. The study found that these power plants can cause a “considerable” disruption to fish habitat and river temperatures; disruptions to river flow are minimal. This research has been published in the current edition of the online journal Environmental Research Letters.
It´s important to know the full extent of the impact these thermoelectric plants have on the environment. Over 90 percent of the power consumed by the US is generated by these types of plants. This number is larger in the Northeast region where there´s a larger concentration of thermoelectric power generated. Thermoelectric plants are also the nation´s largest consumer of freshwater, even beating out the agriculture sector in water usage.
Once water passes through these plants, it is either returned to the ecosystem via evaporation or back into the rivers, albeit at higher temperatures. A combination of attenuation, conveyance and dilution work together to bring the temperature of the river back down to normal temperatures once the waste heat is introduced. This behavior is what led authors Robert Stewart of the UNH Institute for the Study of Earth, Oceans, and Space (EOS) and Wilfred Wollheim of the department of natural resources and environment at EOS to describe the rivers as cooling towers.
“Our modeling shows that, of the waste heat produced during the production of electricity, roughly half is directed to vertical, evaporative cooling towers while the other half is transferred to rivers,” explained Stewart in a statement.
What isn´t given back to the rivers is distributed back into the environment as steam. The study found that very little is distributed back into the atmosphere, however; only about 11 percent of this waste heat is transferred through the stacks and into the air.
“We were surprised to find that relatively little of the heat to rivers is exchanged back to the atmosphere,” notes Wollheim. “Reliance on riverine ecosystem services to dispense waste heat alters temperature regimes, which impacts fish habitat and other aquatic ecosystem services.”
According to the study, there are some 4,700 miles of river in the US which are potentially impacted by thermoelectric power plants.
Though the rivers are able to dissipate the heat from these plants once the water reaches the coastal regions, temperatures near the plants are increased, causing a considerable impact on the surrounding aquatic environment.
Stewart and Wollheim note that this study is important because “it is essential to assess the capacity and associated environmental trade-offs of heat regulating ecosystem services that support the electricity sector.”
For instance, a warming climate has already affected a nuclear power plant in Waterford, Connecticut after the water normally used to cool operations became too warm to use. Another nuclear plant in Illinois had to obtain special permission to continue operations once their cooling lake rose to 102 degrees Fahrenheit following low rainfall and high air temperatures.