Steam injection impact on the performances of nozzle grid in wet-vapor stream

Abstract

Results of experimental study of the efficiency of intra-channel steam injection on the surface of nozzle grids of steam turbines operating in the wet steam flow are presented. The main objective of this study was to determine the basic mechanisms of the steam injection impact on the kinematic characteristics of the liquid phase outside an isolated nozzle grid. The kinetic energy loss distributions of the liquid phase and sliding coefficients of droplets along the grid spacing depending on the injected steam pressure at different theoretical values of the Mach number and the initial wetness are presented. The efficiency index was determined taking into account the kinetic energy loss distribution for the liquid phase along the grid spacing, depending on the pressure reduction on the slot. The investigation was conducted using the total pressure probe placed behind the object under study. The average diameters of large droplets of erosion-hazardous liquid phase at a certain distance from the grid were determined. In measuring the characteristics of the liquid phase particles, a laser diagnostics system of streams was used, based on the “POLIS” complex. The main advantage of this complex is the fact that it is contactless, which allows one to measure characteristics of the liquid phase particles without any distortion of the results and aerodynamic influence on the main stream. It is established that an intra-channel steam injection promotes the destruction of liquid film that formed as a result of the condensation of liquid droplets on the surfaces of nozzle blades, as well as the alignment of the velocity field and the average size reduction of droplets behind the grid. The experimental results have shown that the efficiency of injection (relative to the reduction of the amount of erosion-hazardous droplets) of hot steam substantially depends on the flowing regime of wet steam.