Experimental validation of a wide-range centrifugal compressor stage for supercritical CO2 power cycles

Abstract

Successful implementation of sCO2 power cycles requireshigh compressor efficiency at both the design-point and over awide operating range in order to maximize cycle power outputand maintain stable operation over a wide range of transient andpart-load operating conditions. This requirement is particularlytrue for air-cooled cycles where compressor inlet density is astrong function of inlet temperature that is subject to daily andseasonal variations as well as transient events. In order to meetthese requirements, a novel centrifugal compressor stage designwas developed that incorporates multiple novel range extensionfeatures, including a passive recirculating casing treatment andsemi-open impeller design. This design, presented and analyzedfor CO2 operation in a previous paper, was fabricated via directmetal laser sintering and tested in an open-loop test rig in orderto validate simulation results and the effectiveness of the casingtreatment configuration. Predicted performance curves in air andCO2 conditions are compared, resulting in a reduced diffuserwidth requirement for the air test in order to match designvelocities and demonstrate the casing treatment.Test results show that the casing treatment performancegenerally matched CFD predictions, demonstrating an operatingrange of 69% and efficiency above air predictions across theentire map. The casing treatment configuration demonstratedimprovements over the solid wall configuration in stageperformance and flow characteristics at low flows, resulting inan effective 14% increase in operating range with a 0.5-pointefficiency penalty. The test results are also compared to atraditional fully shrouded impeller with the same flow coefficientand similar head coefficient, showing a 42% range improvementover traditional designs.