Combating of the Solid Particle Erosion in a Steam Turbines

Abstract

The causes and possible solutions of solid particles erosion of the steam path components to reducing it substantially are presented. Applying numerical CFD simulations excessive solid particle erosion damage of the blades tenons, wheel filets, rotor labyrinth seals and main stop valves were studied and steam/solid particles flow conditions which play a main role in the erosion process determined. Afterwards, the flow was simulated introducing specific changes to the geometry of components in order to modify the flow pattern favourably. In each case analyzed, the results confirmed that is possible to reduce the erosion process significantly due to reduction of the volumetric flow rate and velocity of vapour (case of blade tenons), velocity reduction and to modify the angle of particle flow incidence on the surface by increasing the distance from the labyrinth seal to the rotor wheel (case of wheel filets) and flow velocity reduction due to incorporating a steam flow deflector to the diaphragm, which changing flow direction in the inlet zone to the rotor labyrinth seal channel (case of rotor labyrinth seal). In the case of the main steam valve, introducing profile off-set on the valve spherical surface, the steam/particle flow was separated from the valve critical zone, changing the particles trajectories and angle of impact on the surface, resulting in erosion rate reduction. Also, a passive methods of combating solid particle erosion of tenons in the form of weld deposits around them as a protective barrier and wheel filets, rotor labyrinth seals and blades and shrouds coating are presented. All analyzed design modifications and other improvements were implemented and its performance monitored.