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.

主权项

1. A method for operating a combined gas and steam turbine system, comprising a gas turbine, a waste heat steam generator which is located downstream of the gas turbine in direction of flow of exhaust gas of the gas turbine and includes at least one evaporator through which a moving fluid flows, and a steam turbine which is located downstream of the waste heat steam generator in direction of flow of the moving fluid, the moving fluid is fed to the waste heat steam generator in the form of feed water, the method comprising:
providing a primary control loop for a predictive control of a feed water flow rate, determining, taking into account heat stored in components of the at least one evaporator, a primary desired value for the feed water flow rate based upon a desired overheating value that is characteristic of a temperature by which the moving fluid exceeds a boiling point as the moving fluid outlets the evaporator and based upon a heat flow parameter that is characteristic of a heat flow transferred from the exhaust gas to the moving fluid via the at least one evaporator, adjusting the feed water flow rate according to the primary desired value, and lowering the desired overheating value from a normal value defined for a stationary operation of the combined 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, wherein the comparatively high efficiency is at least an increased power output of 5% of the combined gas and steam turbine system, and wherein the smaller activation value is less than the normal value after the lowering.