Advanced Compliant Foil Bearings and Seals for Supercritical CO2 (Final Report)
- MOHAWK INNOVATIVE TECHNOLOGY, INC.
The objective for this Phase II SBIR project is to demonstrate the feasibility of using MITI’s 4th and 5th generation compliant foil bearings and seals to support the related turbomachinery for sCO₂ power cycles under relevant pressure and temperature conditions in turbomachinery from 1 MW to 100s of MW. For this effort, the following tasks are planned: Design of the dynamic test system, foil bearings, and foil seals Fabricate the dynamic test system, bearings, and seals Conduct dynamic tests to measure and demonstrate the performance of the foil bearings and seals Examine the bearings and seals to assess condition after testing Compare the measured bearing and seal performance to analytic design predictions The project builds upon the results of a prior effort SBIR Phase II program “Advanced Design for Scalable S-CO2 Turbomachinery Systems” (contract DE-SC0015811). The project also leverages hardware elements of that effort. A significant portion of the project was dedicated to the design of the test system, since it had to balance complex interactions between rotordynamics, fluid dynamic imbalances arising from the extremely dissimilar pressures affecting the rotor (air atmospheric conditions vs. sCO2 conditions), and their combined effects on bearing and seal behavior. Experiments were conducted to determine if the transition from supercritical CO2 to subcritical conditions had an effect on the performance of the test journal bearing, and to determine the level of pressure drop performance of the foil seal elements. The results of this study can be qualified as generally successful but with mixed levels of maturity. The first critical element for deployment of compliant foil bearings and seals is the survivability of it coatings. This study has demonstrated that MiTi’s proprietary Korolon™ coatings are as capable of performing and surviving in the harsh conditions of s-CO₂ as they are with air and other reactive gases. The study also showed that the bearing presented a normal rotordynamic behavior under all sets of conditions, and particularly during transitions from CO₂ to s-CO₂ operating regimes, with no discernible effect of such transition on rotor operation. Foil seal technology viability has also been demonstrated, achieving a performance that compares favorably to other sealing technologies, like labyrinth seals or more rudimentary compliant technologies like brush seals, since they increase their pressure drop capability as a function of increasing flow and remain essentially unaffected by fluctuations in rotor operating speed. The foil seals are clearly superior to afore mentioned technologies when one takes into account that they operate in an essentially contactless manner, with no discernible wear against the rotor (unlike brush seals and other friction-based seals), and since they are based on compliant foil bearing technology, they are tolerant of incidental rotor contact, unlike labyrinth and other rigid seals. However, with regard to foil seal pressure drop capability, there is room for further improvement. The lessons learned during the development iterations of the seal elements have provided invaluable information with respect to geometric and assembly modifications that could result in significant sealing capability gains, allowing to run the seals at narrower gaps, and better control of secondary and tertiary leakage paths, all while reducing the size of the foil seal stack. Addressing these improvements will benefit from further development funding in the near future.
- Research Organization:
- MOHAWK INNOVATIVE TECHNOLOGY, INC.
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0017830
- OSTI ID:
- 1864800
- Type / Phase:
- SBIR (Phase II)
- Report Number(s):
- DOE-MITI-SC0017830; 18SC503419
- Country of Publication:
- United States
- Language:
- English
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