Numerical Investigation of Instationary Stress and Temperature Effects in a Steam Turbine during Start-Up

Steam turbines supplied from heat recovering boilers behind gas turbines in combined cycle plant are subjected to very fast increase in load. The rapid heating of the casing especially the inlet parts and the first blade rows in the rotor may lead to high stressing and even distortion of casings. In this project we were asked to investigate the casing stresses and to secure the tightness of the casing. Instationary calculations of the internal heat transfer in the casing had been performed. On the basis of these results recommendations for the improvements resulted leading to more uniform temperature distributions and a saver operation of the turbine in the whole load range