The domino effect of poor sealing: A SMALL INCREASE IN INNER-STAGE SEAL CLEARANCES COULD IMPACT GAS TURBINE PERFORMANCE

摘要

Inner-stage seal clearances have a significant impact on overall gas turbine performance. Larger seal clearances require additional sealing air, which automatically leads to higher cooling air flows that bypass the combustion system and the Row 1 blades. The effects are reduced output, greater firing temperature, and higher NO{sub}X values. Since gas turbine hot path or major inspections are typically performed at 24,000-hour intervals, users are advised to restore the turbine inner-stage seals to design values at every opportunity to maintain optimal thermal performance and to protect the rotor body and blade roots. The cost to address excessive clearance after an outage can be significant. Users of advanced frame gas turbines may wish to upgrade to combination labyrinth and brush seal configurations to provide additional margin. The economic impact of excessive seal clearances (capacity and heat rate) exceeds (in many cases substantially) the cost of restoring or replacing the inner stage seals during hot gas path inspections. Users may have experienced lower disc cavity (DC) temperatures due to increase in cooling air flows. To solve this problem in cooling systems that employ fixed orifices, the orifices can be resized after an outage to improve output, efficiency, and increase exhaust energy.