Study of Magnetic Bearing Instability Issues in Supercritical CO2 Turbomachinery

Abstract

With the increasing emphasis on reducing the CO2 emission while improving power generation efficiency, a new power cycle is investigated. One of promising power cycles is a supercritical CO2 (S-CO2) power cycle. To generate over 10MW electricity, a good choice for the bearing is a magnetic bearing for the S-CO2 power cycle. However, from several studies on the magnetic bearing, the instability issues under high pressure and high speed operating conditions were repeatedly mentioned. The instability in the magnetic bearing was observed to be related to the fluid conditions, mostly pressure and density. Because of this issue, the magnetic bearing sometimes cannot maintain enough clearance for the rotor. Thus, these instability issues should be carefully studied and be resolved for the successful and steady operation of the power system. To study the instability issues experimentally, an impeller of the operating S-CO2 compressor is removed and the discharge line is blocked. Therefore, main instability factor in this experiment would be the interaction between the rotor and the bearing only. The instability from the proposed experiment can be simply described by the Reynolds equation. This equation can estimate the pressure distribution for thin fluid film. Because the prediction of the experimental results is helpful to identify the actual factors affecting instability, the predicted values from theory are first reported for the future comparison with the experimental measurements.