METHOD FOR OPERATING A COMBINED GAS AND STEAM TURBINE SYSTEM, GAS AND STEAM TURBINE SYSTEM FOR CARRYING OUT SAID METHOD, AND CORRESPONDING CONTROL DEVICE

摘要

A method of operating a combined gas and steam turbine system is provided. The system includes a gas turbine, a waste heat steam generator with an evaporator heating area, and a steam turbine. Fluid is fed to the waste heat steam generator as feed water. A primary control loop controls a feed water flow rate. Taking into account heat stored in the evaporator heating area, a primary desired value for the feed water flow rate is determined based upon a desired overheating value characteristic of a temperature by which the fluid exceeds a boiling point as the fluid exits the evaporator heating area and based upon a heat flow parameter characteristic of a heat flow transfer from fuel gas to the fluid via the evaporator heating area. The desired overheating value is lowered from a first value to a second value in order to activate an instantaneous power reserve.