Highly efficient combined-cycle plants maximize the electricity-producing potential of their fuel source by combining natural gas and steam generation technologies. This process uses the extremely hot exhaust from natural-gas combustion turbines (see the description of the simple-cycle process) to create steam and generate additional electricity.
Heat recovery steam generators (HRSGs) contain boiler tubes filled with ultrapure water. Hot exhaust flows past these tubes, turning the water into steam. The steam is routed to steam turbines, which are connected to their own generators. HRSGs are so efficient that exhaust leaving turbines at more than 1,000 degrees Fahrenheit is reduced in temperature to about 200 degrees by the time the heat recovery process is completed.
The spent steam then flows into a condenser. The condenser converts the steam back into water, which is returned to the HRSG in a closed-loop cycle to be reused. In most cases, a cooling tower adjacent to the plant provides a constant flow of cool water to the condenser.
Click here to watch a video describing the combined-cycle power production process at our Russell City Energy Center.