1. Field of the Invention
The invention relates to a combined power station installation with a gas turbine and a steam turbine, in which the exhaust gases from the gas turbine give up their residual heat to the steam turbine via the working medium flowing in a waste heat boiler, whereby the waste heat boiler consists essentially of an economizer, an evaporator and a superheater and whereby at least one cooling air cooler is provided which is designed as a forced circulation steam generator and is connected on the water side to the economizer of the waste heat boiler.
2. Discussion of Background
Gas turbines of the modern generation and the higher power class operate with very high turbine inlet temperatures, which makes cooling of the combustion chambers, the rotors and the blading unavoidable. For this purpose, highly compressed air is generally extracted at the compressor outlet and, if appropriate, from a lower pressure stage. Because a very high proportion of the compressed air is consumed for the currently conventional premixed combustion, there remains--on the one hand--only a minimum of cooling air for cooling purposes. On the other hand, this air intended for cooling is already very hot because of the compression so that it is desirable that it should be previously cooled. Cooling by means of water injection ("gas quenching") is known for this purpose; in this method, however, the high-quality heat of the cooling air, whose proportion can amount to as much as 20 MW in current machines, is only partially utilized. In consequence, the use of forced circulation steam generators as coolers for recooling seems appropriate, particularly if the gas turbine operates in a combined gas/steam turbine process with waste heat steam generation.
Such a once-through steam generator for cooling highly compressed air of the type mentioned at the beginning is known, in association with a combined gas/steam turbine process, from EP-A-709 561. In this specification, a partial flow of the boiler feed water is extracted either upstream or downstream of the economizer and, after further preheating, evaporation and superheating in the cooler, is fed back into the high pressure superheater of the waste heat boiler. This boiler is designed as a circulating system boiler with drums. In order to avoid the penetration of moisture or water into the steam turbine when the cooler is run wet, the heated water or wet steam is fed into a blow-down tank until the cooler is dry or until defined conditions are stably present at the cooler outlet, for example hot steam with a few degrees Kelvin superheat or wet steam with a humidity of a few percent. In addition to the water losses, this has the consequent disadvantage of a corresponding monitoring and control system.