Performance Test of A 9MW-Class 3-Stage Axial CO2 Compressor

Performance testing of a 3-stage 9MW axial CO2 compressor has been successfully completed at the closed-loop CO2 compressor test facility at the University of Notre Dame. The design speed, inlet pressure, inlet temperature, and mass flowrate of the compressor was 19,800rpm, 2.77MPa, 98°C, and 125.9kg/s respectively. The compressor performance was evaluated from 60% to 100% of the design speed. Blade tip clearance and blade vibrations were measured during the compressor operation to ensure the safety of the compressor. Calibrated capacitance probes were used to establish average running tip clearances of 0.38mm (1.2% of span), 0.5mm (1.9% of span), and 0.5mm (2.4% of span) for stage 1, stage 2, and stage 3 respectively. Blade vibrations were measured using tip timing probes. A six engine-order synchronous blade vibration of the first bending mode was observed at the 1st stage rotor around 73%-82% speed. Stall testing at 60% speed revealed a single stall cell which extends from the 1st stage rotor to the 3rd stage rotor, and is rotating at 60.4% of the shaft speed. The measured peak isentropic efficiency of the compressor was 91.5%, 91.1%, 90.6%, 90.0%, 85.3% at 60%, 70%, 83%, 90%, and 100% speeds respectively. The measured performance successfully demonstrated the performance benefit and usefulness of the axial compressor for grid-scale energy systems such as pumped thermal energy storage (PTES).