The first process includes a combustion turbine that operates like a jet engine that draws in outside air and compresses it to a high pressure. The pressurized air mixes with natural gas and is then burned, creating hot exhaust gases. These gases power the combustion turbine, spin a generator and ultimately make energy.
The second process sends the hot exhaust gases from the combustion turbine to a heat recovery system. This system captures the heat from the hot exhaust gases to produce steam. This steam then goes to a steam turbine that rotates another generator and makes more energy.
Combined-cycle technology is highly efficient because of this heat recovery system. Without this system, all of the heat from the hot exhaust gases would be released to the atmosphere instead of being captured and used to generate steam and make more energy.