Blade cooling improvement for heavy duty gas turbine: the air coolant temperature reduction and the introduction of steam and mixed steam/air cooling

This paper proposes a theoretical study of some alternative solutions to im prove the blade cooling in the heavy-duty gas turbine. The study moves to t he evaluations of the air coolant reduction temperature effects, considerin g two different methods: a water surface exchanger (WSE) and a cold water i njection (CWI). A logical development of these possible cooling system impr ovements is the steam cooling application, particularly suitable for mixed or combined gas-steam cycles; the steam cooling is evaluated using open and closed loop configurations; the possible interaction of steam and air cool ing is also studied. All the simulation is realized with a family of modula r codes developed by authors and the study is conducted with the analysis o f the characteristic cooling parameters (efficiency, effectiveness) and by the evaluation of blade temperature distribution. The study is related to a typical configuration of heavy-duty rotor blade with a standard air coolin g scheme and the possible variations are related to coolant characteristics only. The results show the interesting possibility due to air coolant temp erature reductions, particularly for the CWI method, but the steam cooling turns out to be more incisive. All of the considered techniques show the po ssibility of a mass coolant reduction and/or the possibility of a maximum c ycle temperature increase in comparison to the standard air-cooling. The be st results are obtained for an innovative closed-open/steam-air cooling sys tem. (C) 2000 Editions scientifiques et medicales Elsevier SAS.