After combustion some flue gases are produced having temperature about 5000C which exits through the chimney. This will be great loss if the flue gases are not used properly. For this a combine cycle plant is introduced which use the flue gas as working fluid. Here damper is used to recover the waste heat.
Figure: Flow diagram of Waste Heat Recovery Unit (WHRU)
Damper blocks the chimney and passes the flue gas to boiler and produce steam. This steam is used to generate electricity at steam turbine. Since both of steam and gas turbines are used it is called combine cycle power plant (CCPP).