An Experimental Investigation into Nozzle Vane Heating to Prevent Erosion in the Last Stages of Steam Turbines

Resumo

The paper is devoted to an experimental investigation of nozzle vane heating in the last stage of a wet steam turbine. The investigation was performed at a steam-dynamic test facility whose circuit was connected to an operating cogeneration power station (TETs). The working fluid was steam from a heat extraction assembly of a steam turbine. To prepare a polydisperse wet steam flow specific for the last stages of steam turbines, a three-stage wetting system based on feedwater injection into the flow was used. The object of investigation is a flat vane cascade consisting of hollow vanes. The vane cavities are fed with superheated steam to provide heating. Experimental data are presented demonstrating that it is advisable to heat nozzle vanes: first, the economic characteristics are improved, and, second, erosion of the blades in the last stages decreases. This method can be used as an alternative to the internal moisture separation from the steam path. The experimental investigation yielded the effect of the temperature difference between the main flow and the heating steam on the amount of heat transferred to the main flow and on the steam conditions at the outlet from the heating chamber. It was found that condensation in the heating chamber decreased its outlet pressure. This should be considered in designing a similar active system to control erosion of rotor blades. The measured profile losses of kinetic energy downstream of the vane cascade for different temperature difference values are presented. The kinematic characteristics of the liquid phase downstream of the vane trailing edge are determined. Large temperature differences are found to have a negative effect on droplets and can reduce the erosion resistance of the blades as compared with profiles without any active erosion control methods.