>” […] 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.
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 it could 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 condensers (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. […]”<