Abstract

Increasing load ramps and temperature gradients in steam turbines, especially during start-ups, have a high impact on the component lifetime. Calculation models are commonly used to predict the lifetime consumption during such start-up procedures. However, the changing energy landscape requires innovative solutions to increase the power plant flexibility. In order to accelerate the start-ups with a simultaneously reduced lifetime consumption, hot air can be used to keep the steam turbine warm during shut downs. The calculation of heat fluxes within the steam turbine is crucial for the accurate prediction of the thermal state and the resulting lifetime consumption. Improved models enable the determination of life cycles as exact as possible.

During warm-keeping and pre-warming operations, the steam turbine rotates slowly. Thus, low centrifugal forces lead to high thermal contact resistances (TCR) at the blade roots, which influence the temperature distribution at the lifetime limiting locations, e.g. blade grooves. The paper presents heat transfer correlations, which describe the TCR depending on the rotational speed of the rotor. For this purpose, an experimental setup is designed in order to investigate the influence of contact pressure, ambient pressure and surface properties. For the detailed investigation of the complex heat fluxes at the T-root, a 3D Finite-Elements (FE) model is developed. This model calculates the TCR and specific heat fluxes based on measurement data. On the basis of the detailed evaluation, different analytical heat transfer correlation approaches with respect to the application in an overall steam turbine model are developed. These heat transfer correlations are integrated into the FE model and validated with additional measurements.

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