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

High performance supercritical carbon dioxide (sCO2) turbo-expanders/power turbines will provide significant increases in efficiency and compactness, while reducing greenhouse gases and water usage. However, the needed operation in a 900°C environment is a challenge for this type of turbomachinery. While magnetic bearings have many advantages over foil bearings, including no wear during startups, low drag loss, higher load capacity, controllable and adaptive stiffness and damping, health monitoring, and fault tolerance, the typical magnetic bearing cannot survive at ultra-high temperatures. This Small Business Technology Transfer project will develop a permanent magnet based magnetic bearing system actively cooled to the 550°C maximum operating temperature limit of permanent magnets, while meeting the load, speed and high temperature 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 compared to Nd-Fe-B material. 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. Phase I will proceed with: (1) the development of optimized and air cooled ultra-high temperature permanent magnet assembly, (2) development of low cost ultra-high temperature shaft position sensors for the feedback control, (3) a small prototype of radial magnetic bearing, (4) the design of the test rig including 2 radial and 1 thrust permanent magnet assemblies, and (5) the detailed, high fidelity design of the magnet bearing system, auxiliary bearings and position sensors to be used in the Phase II test rig. Phase II will develop a low cost, low loss, ultra-high temperature permanent magnet bearing system with redundant, fail safe coil/power amplifier/sensor failure compensation. 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 ultra-high temperature 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.