Supercritical CO2 compressor operation near stall and surge conditions

Abstract

Instabilities such as stall and surge have been widely studied in open loop gas turbine system for several decades. However, researches on instabilities in a closed loop are limited. Especially, no experimental investigation in a supercritical CO2 compressor has been performed thoroughly before. An integral test loop equipped with a turbo-alternator-compressor using active magnetic bearing was utilized to study the instabilities in a supercritical CO2 compressor. The compressor performance testing was conducted including near stall and surge operating conditions. The mass flow rate of compressor was greatly reduced even beyond surge limit and pressure was measured with high frequency transducer to observe the characteristics. It was observed that as the inertia of the system was changed by altering the compressor inlet conditions, the characteristics of the supercritical CO2 compressor in unstable operating conditions also vary. This can be qualitatively explained by using the theory Greitzer proposed previously.

Keywords

• Supercritical CO2
• Centrifugal compressor
• Instability
• Surge
• Stall
• Magnetic bearing