Advanced Compliant Foil Bearings and Seals for Supercritical CO2

Supercritical CO2 power cycles offer the promise of high efficiency in a compact footprint with a potential to offer disruptive changes to the US energy infrastructure. Applications include bottom cycles for electric co-generation power plants, nuclear power production, concentrated solar and other renewables as well as propulsion engines for space propulsion. Aerodynamic design theory dictates that the turbomachinery components for such power cycles will operate at high rotation speed with high-power density. Given these high operating speeds and performance requirements such as operation to 700oC, traditional off-the-shelf bearing technology is not available. MiTi’s 5th and 6th generation foil bearings are ideal candidates for integration into the necessary turbomachinery components of these power cycles. Phase I established the viability of using compliant foil bearings in sCO2 turbomachinery through analysis and testing of coated foil elements exposed to sCO2 at >700°C and subsequently undergoing tribological testing. Results show that the foil and coating were unaffected by sCO2. The proposed program begins with detailed design of the hardware test rig, foil bearings and radial seals, followed by methodical testing of the test foil bearing and seals in air, CO2 and sCO2 environments. Testing will characterize both foil bearing/seal dynamic and tribological performance in the three environments in order to validate the design and design analysis capabilities. Testing in air will provide the baseline performance for subsequent comparison with measurements in CO2 and sCO2 environments. Measured performance parameters will include liftoff speed, foil temperatures, shaft displacement as a function speed and frequency content in order to identify system response and stability (i.e., functions of bearing stiffness and damping) and load carrying capacity. Posttest examination of the foil bearing/seal will allow for assessment of potential tribological interactions during operation due to the sliding wear encountered during startup and shut down as well as possible high-speed rub during load capacity testing conditions. The results of testing with sCO2 will provide the basis for using foil bearings/seals in sCO2 turbogenerator and other extreme environment systems. Commercial Applications and Other Benefits: The foil bearing is a key enabling technology paramount to the success of the supercritical CO2 power cycle. MiTi has demonstrated scalability of the bearing technology from 8 mm to 150 mm diameters. Such scalability will support the development of multi-megawatt supercritical CO2 cycles that will reduce the environmental impact of large scale centralized energy production. Beyond supercritical CO2 applications, advancements in compliant foil bearings will provide industry exposure and open avenues for the technology into other parallel energy solutions such as natural gas and pipeline compressors, hydrogen fuel cells, liquid refrigerant compressors, cryogenic turbopumps, ammonia compressors and turbogenerator systems including Closed Brayton Cycles for terrestrial and space power.