An assessment of cooled air cooling for combined cycle gas turbines

Paper in proceeding, 2013

A triple pressure combined gas turbine cycle reference plant is established targeting technology that is expected to enter service over the next decade. Through the means of exergy analysis major losses occurred in this cycle is discussed, for which exergy destruction due to cooling is singled out as one of the relatively large sources. Several concepts concentrating on the cooling of the cooling air are then evaluated, with the purpose increasing the net efficiency in comparison with the reference plant. The cooling of the cooling flow is only included for the first stage of the turbine. By allowing a full transfer of heat from the cooling flow to the fuel an efficiency improvement of 1.2% in net efficiency is estimated. This estimate is to be seen as a theoretical limit for the one-stage cooling concept, since the fuel temperature is above what can be viewed as feasible. For a concept with a combined intermediate pressure steam heating and heating to a conservatively chosen fuel temperature the benefit is estimated at 0.6%.