Design and Operability Challenges for Supercritical CO2 Plants: The sCO2-Flex Centrifugal Compressor Test Experience

Abstract

Interest in supercritical carbon dioxide (sCO2) cycles has grown significantly in recent years. The peculiar properties of the fluid open unique opportunities but also poses several challenges. Here we aim at narrowing the knowledge gap in operating such plants, leveraging the test experience of a full-scale 5 MW Centrifugal Compressor prototype designed for the sCO2-flex project (H2020 funded program, grant agreement #764690). The test rig replicated a complete recycle loop for the compressor. In addition to validating the compressor’s performances in its design condition, a larger envelope of operation and transients was explored. The paper describes engineering groundwork and design choices regarding: i) transient operation such as pressurized startups and emergency shutdowns; ii) safety relief valves and discharge lines, with possible CO2 solidification; and iii) vibrations due to extremely high density. For all these topics, specific challenges brought by the sCO2 are described. We show the most meaningful results, in excellent agreement with predictions, and discuss key learnings from the test experience. We highlight how important it was to anticipate risks during the design phase and we give recommendations for future installations. We conclude with hints on testing severe off-design conditions, with two-phase flow at compressor suction.