Development of Brush Seal Technology for Steam Turbine Retrofit Applications

Increased cylinder efficiency is one of the main drivers in the steam turbine retrofit market, particularly for HP and IP modules. To-date most retrofit turbine suppliers have concentrated their efforts on improving the aerodynamic efficiency of blades and other steampath components, optimizing stage numbers and reducing leakage losses. Developments in all of these areas rely heavily on improved design and analysis tools to refine existing designs and evaluate new concepts. The opportunity exists to further reduce leakage losses by replacing conventional labyrinth seal designs by more advanced turbomachinery sealing technology. Brush seals, which have now been used successfully in some gas turbine (mainly aero-engines) applications for several years, are a natural candidate for steam turbine retrofits. Careful thought is needed when applying brush seals as the mechanical integrity of the cylinder needs to be maintained at all times. Attempts to increase performance should never be at the expense of availability and reliability. This paper describes the development work undertaken by the authors’ company and covers research in the areas of brush seal design, performance improvement, operational issues, and life assessment.