Publication Date: 2005-Jan-24
The IP.com Prior Art Database
A system for removal of condensed water from turbine vanes comprises a set of grooves on the surface of the vanes. They are first oriented in the direction of the steam flow and then are curved in the radial outward direction of the vane. The water removed from the vane by means of the grooves is accumulated on the casing where it may be removed via extraction slits and a casing drainage system. The system avoids the use of hollow vanes and extracts the water without entraining any steam. The power output of the turbine thus remains unchanged.
In the last stages of steam turbines water typically condenses into small droplets. In steam turbines for nuclear applications condensations can occur even upstream from the last stages. While the droplets are small and light weight they are transported with the main steam flow. However, with increasing size and weight they impinge on the pressure sides of the downstream rotating blades, where water collects to form a water film. At the trailing edges of the blades even larger droplets can develop. The water film and water droplets can cause additional skin friction and heat extraction resulting in efficiency losses. Furthermore, mechanical damages on the blades can result due to droplet impact and erosion.
The condensation itself and the associated efficiency loss are unavoidable. Hence, passive and/or active measures for damage and wear prevention are required in order to ensure an acceptable lifetime of the blades.
Possible passive measure are the use of hard materials, the reduction of trailing edge sizes, the decrease in blade counts, which would reduce the generation of droplets, or an increase in meridional blade-to-blade distance.
A possible active measure is the water removal by means of slits arranged on the blade surfaces or on the casings such as extraction slits on the vanes arranged along the longitudinal direction of the vane (figure 1). The slits lead the water on the vane surface into hollow spaces within the vane, from where it is drawn out of the vane into a drainage system. By this measure, the number and size of large water droplets on the trailing edge is reduced.
An additional active measure that is independent of the extractions slits on the hollow vanes comprises extraction slits may be arranged on the casing (figure 2), which are in fluid connection with a drainage system. However, a considerable amount of steam is sucked away through the extraction slits along with the extracted water, which results in reduced power output of the turbine.
Further known measures comprise the addition of chemicals to the steam or the application of surface coatings. These affect the water droplet surface tension such that water droplet sizes are reduced and thus...