Session: 30-11 Testing 2 and Systems 2

Submission Number: 179262

Design of a Pilot-Scale Four-Stage Centrifugal Compressor for sCO2-Based Pumped-Thermal Energy Storage 

With the increasing integration of intermittent renewable energy sources with conventional power systems, the role of energy storage has become essential. Among the various storage technologies proposed in the literature, pumped-thermal energy storage systems utilizing supercritical carbon dioxide (sCO₂) as working fluid are emerging as a promising solution for medium/large-term and medium/large-capacity applications, owing to their high energy density and potential for high round-trip efficiency. However, to validate the feasibility of such systems, their technology readiness level must first enhanced through experimental demonstration using lab-scale prototypes.

This study focuses on the design and computational analysis of a four-stage compressor conceived for the charging (i.e., reverse) cycle of a pumped-thermal energy storage system operating with high-temperature sCO₂. Due to the extremely low flow coefficient (~0.006) resulting from the small power capacity (~100 kW) of the lab-scale configuration, the compressor design presents unique challenges.

Mean-line analysis results obtained using an in-house code are first presented. Subsequently, detailed design considerations for each compressor component are discussed, emphasizing the tailored strategies required to accommodate low-flow conditions. Among the most critical aspects of the design and operation of such machines, the influence of secondary flow paths, namely the assessment of the leakage flows through the disc and cover-disc clearances and the associated seals, are investigated in detail . Computational fluid dynamics (CFD) simulations are conducted with and without secondary flow passages, revealing significant differences in overall performance and flow behaviour, both in nominal and off-design conditions.

Finally, the mean-line analysis code—originally developed for higher flow coefficients and conventional seal designs—is calibrated using the CFD results, resulting in improved predictive accuracy for compressors designed to operate for extremely low flow functions.

Presenting Author: Kiavash Kamali Politecnico di Milano

Presenting Author Biography: Kiavash Kamali graduated in Mechanical Engineering at Politecnico di Milano in 2023. He is presently PhD candidate at Politecnico di Milano. His research interests are focused on the design and CFD modeling of turbomachinery operating with CO2 in supercritical and trans-critical conditions.

Authors:

Kiavash Kamali Politecnico di Milano
Alessandro Romei Politecnico di Milano
Giacomo Persico Politecnico di Milano