Low Leakage Turbine Shaft Seals for Advanced Combined Cycle Systems

摘要

Advanced combined-cycle (COGAS) steam turbine overall system complexity and reliability can profit dramatically from low-leakage seals. The most critical seal locations are the high speed mainshaft seals at the bearings. The optimum seal system was selected as utilizing the feedwater as a buffer fluid. It was further shown advantageous from at least seal performance, life and reliability standpoints to vent the turbine high pressure end also to condenser vacuum. Three candidate late state-of-the-art low/zero leakage face seal assemblies were selected for manufacture and experimental test in a specially-modified test rig. Testing demonstrated that leakage rates from zero to 11 liters/day (3 gal/day) at speeds up to 92 m/sec (310 ft/sec) could be achieved at practical values of buffer pressure. These rates therefore met both the program objective of less than 11 liters/day (3 gal/day). Higher than anticipated parasitic drag was measured. A seal design which overcomes this drag was proposed. Limited cyclic endurance testing was carried out. (Author)