When summer heat settles in, just like it did repeatedly in Texas over the last several years, the combination of a high demand for electricity and dwindling water supply can start a vicious circle.
That’s because power plants use water for cooling equipment and a lack of water can lead to plant outages. “The state of Texas is still experiencing severe drought and power plants typically need a lot of water,” says Bill Harris, a spokesman for Exelon Corp., one of the largest U.S. utilities. “We’ve got to keep that in mind.”
Top: The Brazos River north of Lake Granbury in Texas in 2012. Image credit:Leaflet Above and below: GE’s air-cooled HA “Harriet” turbine is the largest and most efficient gas turbine in the world. Image credits: GE Power and Water
Last year, Exelon did just that. The company’s two huge 1,000 MW power plants, which are under construction near Fort Worth, will use the latest GE power generation technology that needs just one tenth of the water amount typically required to cool such large installations, and save “millions of gallons” every day, according to Harris.
The savings should help local fishing and boating destinations like Lake Granbury. “This reduction in water consumption is important to us, but it’s also important to the people living around the plants,” Harris says. “Obviously, they use water for many other purposes than just generating electricity. ”
Instead of water, each of the two plants will use two powerful air-cooled“Harriet” gas turbines and one air-cooled steam turbine developed by GE. “The technology uses the same cooling principle as the radiator in your car,” Harris says. “You blow in the air and it cools the medium flowing in closed loops around the turbines.”
The power plants, which are expected to open next year, will be using a so-called combined cycle design (see image below) and produce power in two steps. First, the two gas turbines (in the center with exhaust stacks) extract energy from burning natural gas and use it to spin electricity generators. But they also produce waste heat.
The system sends the waste heat to a boiler filled with water, which produces steam that drives a steam turbine to extract more energy and generate more power (blue and gray building center left).
But that’s easier said than done. The steam inside the steamturbine moves in a closed loop and needs to be cooled down back to water so itcould be heated up again in the boiler. “Normally, we cool this steam with water, which evaporates and cools down in huge mechanical cooling towers,” says GE engineer Thomas Dreisbach. “A lot of the cooling water escapes in those huge white clouds you sometimes see rising from towers next to power plants.” The Exelon design is using a row of powerful fans and air condesers (rear right) to do the trick and save water.
Similar to the steam turbines, GE’s Harriet gas turbines also use air to chill a closed loop filled with the coolant glycol and reduce the temperature inside the turbine. The combined efficiency of the plant will approach 61 percent, which in the power-generation industry is like running a sub 4-minute mile.
Texans who will be living next to the plants seem energized, too. “It’s exciting to see [Exelon] providing several hundred jobs to the community and using air cooled gas turbines to reduce the effects on Lake Granbury,” Joe Williams, the founder of Save Lake Granbury, wrote to a local newspaper. “Thanks Exelon for being such good neighbor to Granbury and Hood County.”
A cross section of a GE air-cooled steam turbine