Thermo-economic analysis on the impact of improving inter-stage packing seals in a 500 MW class supercritical steam turbine power plant

The use of brush seals in turbomachinery has increased steadily in recent years because they reduce leakage and improve operating stability. This study evaluates the performance enhancement of a 500 MW-class steam turbine plant that results from replacing conventional seals with brush add-up seals for the inter-stage packing seal locations. Leakage flow rates of all seal locations in high--and intermediate-pressure turbines were estimated, and the brush add-up seal was found to reduce leakage by 50-68%. The entire power plant was simulated using a stage-by-stage turbine model and stage efficiency correction. With the advanced seals in all inter-stage locations of the high-- and intermediate-pressure turbines, 0.44% and 0.33% increases in power output and efficiency were predicted. A larger performance benefit was observed with the installation in the high-pressure turbine. An economic analysis shows that the seal replacement is quite cost-effective. The predicted net present value was quite large compared to the initial cost, and the estimated payback period was less than a year. The replacement in all the high-pressure turbine stages and in the front stages of the intermediate-pressure turbine stages has the highest business value.