Steam turbines create electricity in four key steps. First, a fuel is combusted to create heat energy. The heat is used to convert water or other liquids to high-pressure steam in a boiler. The steam is then piped into the steam turbine that spins the turbine blades, thus spinning the generator and creating electricity. The steam expands as it drives the blades, lowering the steam pressure and temperature. The lower energy steam exiting the turbine is cooled using either water from a lake, ocean, or river, or evaporative cooling in a cooling tower. This returns the feedwater to a liquid state so it can be pumped back to the boiler and the cycle can be repeated.
Flue gases resulting from the fuel combustion are directed up an exhaust stack where products of the fuel combustion are emitted into the air. Depending on the type of fuel, various emissions control devices may be attached to the exhaust stack to capture pollutants before they are emitted. There are several fuel sources used to operate a steam turbine including coal, nuclear fuel, natural gas, biofuel, and oil.