ADVANCED COMPLIANT FOIL BEARINGS AND SEALS FOR SCALABLE SUPERCRITICAL CO2 TURBOMACHINERY
- Mohawk Innovative Technology, Inc.
The general objective of the Phase I research program was to demonstrate the feasibility of practical supercritical carbon dioxide (sCO2) turbomachinery systems utilizing oil-free, compliant foil bearings. Given the high temperatures and pressures involved with sCO2 turbomachinery, MiTi’s bearing and seal technology is superior when contrasted with traditional off-the-shelf alternatives. For example, while rolling element bearings have very high load capacity they are limited to less than 1.5 Million DN (i.e., D=diameter in mm * N = rpm). Oil-lubricated fluid film bearing load capacity is about 300 psi with oil and possibly 500 psi in SCO2 but they are limited to PV values (i.e., Pressure times Velocity in MPa m/s) of less than 220 MPa-m/s and material compatibility issues between bearing Babbitt (i.e., bearing liner material) and sCO2 exist. Active Magnetic Bearings (AMB) can support up to 75 psi loading (i.e., applied load divided by bearing projected area) but are limited to less than 250 m/s surface velocity and they are susceptible to failure during transient vibration events (i.e, surge or shock, etc.). Each of the aforementioned bearings are also limited in temperature to less than approximately 200°C. Both rolling element and fluid film bearings require special lubricant and seals to prevent contamination both of the sCO2 and the lubricant. AMBs require backup bearings in the event of a failure to sensors, controls, power supply or the bearing elements. Conversely, MITI 5th and 6th Generation compliant foil bearings operate at temperatures above 815°C, are compatible with sCO2, use the process fluid as the lubricant, have load capacities comparable to rigid sCO2 hydrodynamic bearings, can operate under two-phase flow conditions, have been operated in excess of 6.5 Million DN being limited only by the structural integrity of the shaft. The research conducted under Phase I demonstrates the feasibility of designing, fabricating and testing of turbogenerators using compliant foil journal bearings with sCO2 as a working fluid. To this effect, MITI conducted parametric analyses and tests concerning the effects of high-temperature sCO2 exposure on Korolon coated bearing elements through both delamination/bend and tribological wear testing. The parametric analyses showed that foil bearings have the ability to support rotors to 3000 lbs or greater depending upon size and clearance and that they can accommodate variations in viscosity expected from start up to full operating temperatures and pressures. Experimentally, Korolon™ high temperature coated thrust foil pads were exposed to sCO2 at temperatures to 650°C to replicate conditions the bearings would experience once implemented in a sCO2 turbine. Following exposure, the foils underwent bending and tribological wear testing to compare their performance. The study found that for the conditions examined, that low and high temperature sCO2 exposure does not affect the Korolon coating or its adhesion to the foil substrate material nor does it adversely affect the foil bearings’ ability to perform its intended function. Specifically, the tested foils completed the standard 500 cycles for tribological testing, which entailed lifting off from a spinning disc to replicate performance as a thrust bearing. Moreover, extreme 90° bend testing following exposure did not result in cracking or delamination of the Korolon™ coating along the bend site. Finally, a foil observed under scanning electron microscopy determined that the coating remained adhered to the substrate following exposure and full tribological testing. Finally, MITI established a preliminary rotor simulator test rig design that can accommodate testing of journal bearings in sCO2 at relevant speeds. The design effort produced preliminary CAD models and finite-element analysis for the rotating assembly. This effort demonstrated the feasibility of foil bearings for oil-free sCO2 turbomachinery through parametric analyses and experiments in sCO2.
- Research Organization:
- Mohawk Innovative Technology, Inc.
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0017830
- OSTI ID:
- 1430532
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- MiTi-TR2018-DE61307
- Country of Publication:
- United States
- Language:
- English
Similar Records
Advanced Compliant Foil Bearings and Seals for Supercritical CO2 (Final Report)
Additively Manufactured Compliant Hybrid Gas Thrust Bearing for Supercritical Carbon Dioxide Turbomachinery: Experimental Evaluation and Fluid–Structure Model Predictions