Ultra High-Temperature Magnetic Bearing System for S-CO2 Turbines/Expanders

High performance supercritical carbon dioxide (S-CO2) turbo-expanders/power turbines will provide significant increases in efficiency and compactness, while reducing greenhouse gases and water usage. This project will develop a permanent magnet biased magnetic bearing system, that is actively cooled to the 550°C maximum operating temperature limit of permanent magnets. The magnetic bearing test environment will include 700°C, 40krpm and 4,000 psi requirements to advance the sCO2 and other types of Brayton power cycle systems. The proposed novel magnetic bearings combine permanent magnets for supplying the bias field and electromagnets for supplying the control field, both in ultra-high temperature conditions. The choice of material is the ultra-high temperature Sm-Co permanent magnets (US patent 6,451,132) due to their significantly better thermal stability. The 6-pole homopolar design permits uninterrupted force delivery via a redundant control capability (US patent 7,429,811) even if 3 poles were to fail. In Phase I, as of April 1, 2019, Electron Energy Corporation working with Texas A&M University completed over 70% of all Phase I Tasks; (1) the development of air cooled ultra-high temperature radial magnetic bearing for feasibility test, (2) permanent magnet development, (3) test rig design, (4) design of 2 radial and 1 thrust magnetic bearings, and (5) development of low cost, high temperature shaft position sensors. In Phase II, the goal is to develop 1) a low cost, low loss, ultra-high temperature permanent magnet bearing system with redundant, fail safe coil/power amplifier/sensor failure compensation and 2) a high temperature magnetic coupler for use in seal-free, rotating shaft power transmission. Notably, on March 12, 2019, per the program manager’s recommendation, the proposers visited the Sandia National Laboratory and discussed the opportunity in utilizing the state-of-the-art facilities for Phase II testing and system validation in S-CO2 environment. In Phase III, we will team with an industry partner to develop a full size S-CO2 turbine or turbo expander utilizing the magnetic bearing technology developed in Phase II. We will also produce and distribute design and manufacturing guidelines and software for further development. Once successfully completed, this project will significantly extend the operating environment capability for turbomachinery applications such as nuclear power, concentrated solar thermal, fossil fuel, geothermal, and shipboard propulsion. The further advancement of ultra-high temperature permanent magnet bearings will also strengthen the US position in permanent magnet technology, which is presently heavily dominated by China. The Sm-Co magnet material that will be utilized in the proposed work has been developed exclusively by the project proposer. Many actuators, motors, generators and other magnetic bearing applications will greatly benefit from the proposed work.