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

The invention relates to a method for operating a combined gas and steam turbine system comprising a gas turbine (GT), a waste heat steam generator which is located downstream of the gas turbine (GT) in the direction of flow of the exhaust gas or fuel gas and includes at least one evaporator heating area (6) through which a moving fluid can flow, and a steam turbine (DT) which is located downstream of the waste heat steam generator in the direction of flow of the moving fluid. The moving fluid is fed to the waste heat steam generator in the form of feed water, a primary control loop being provided for predictively controlling the feed water flow rate. Taking into account the heat stored in the components in the evaporator heating area, a primary desired value for the feed water flow rate is determined on the basis of a desired overheating value that is characteristic of the temperature by which the moving fluid exceeds its boiling point as the moving fluid exits the evaporator heating area (6) and on the basis of a heat flow parameter that is characteristic of the heat flow transferred from the fuel gas to the moving fluid via the evaporator heating area (6), and the feed water flow rate is adjusted accordingly. The proposed method is characterized in that the desired overheating value is lowered from a normal value defined for the stationary operation of the gas and steam turbine system at a comparatively high efficiency to a smaller activation value in order to activate a temporarily available instantaneous power reserve.