Development of Large-Diameter Hybrid Film-Riding Seals for Supercritical Carbon Dioxide Turbines

Compared to traditional labyrinth seals, large-diameter (about 24 in or 609.6 mm) film-riding face seals are worth 0.55–0.65% points efficiency for utility-scale supercritical carbon dioxide (sCO₂) turbines. Conventional dry gas seals (DGS) that rely on aerodynamic spiral grooves cannot be used at such large diameters due to manufacturability limitations and mechanical deformations. Hybrid film-riding face seals are excellent compromise candidates that can operate at large diameters with slightly increased albeit leakier films. This paper presents the development and test data for a hybrid face seal developed for the utility-scale sCO₂ turbine application. A high-level overview of the seal design considerations is presented followed by test data on three seals—a small-size seal (5.7 in or 144.8 mm diameter), an intermediate-size seal (14 in or 355.6 mm diameter), and two full-size seals (24 in or 609.6 mm diameter) tested over a range of pressures and temperatures with both air and CO₂ as the working fluid. This paper presents nondimensional seal film thickness and seal leakage (effective clearance) data as a function of the pressure ratios, speed, and temperature. The film thickness measurements presented in this paper agree well with the computational fluid dynamics (CFD)-based film thickness predictions. The measured seal effective clearance for the seals was around 0.001 in (0.0254 mm) effective clearance, which is better than published data on aerostatic face seals and less risky compared to conventional DGS. Rotating test data across all three length scales presented in this work show successful laboratory-scale seal operation for the newly design hybrid face seals.