Energy loss analysis in two-stage turbine of compressed air energy storage system: Effect of varying partial admission ratio and inlet pressure

Abstract

The compressed air energy storage (CAES) system experiences decreasing air storage pressure during energy release process. To ensure system stability, maintaining a specific pressure difference between air storage and turbine inlet is necessary. Hence, adopting a judicious air distribution scheme for the turbine is crucial. Partial admission, based on reasoned nozzle governing methods, enhances system performance. This investigation explores the impact of varying partial admission ratio (PAR) and inlet pressure on flow dynamics and loss characteristics under rated output power. Full circumferential numerical simulations of a two-stage axial turbine within CAES system elucidates insights. First-stage efficiency declines linearly with decreasing PAR, while second-stage displays escalating reductions. Principally, turbine energy losses primarily stem from the entropy production rate (EPR) by turbulent dissipation and EPR arising from heat transfer with fluctuating temperature gradients. Partial admission significantly affects losses within the rotor, especially within the second stage. Leaving velocity loss for 50 % PAR is about 3 times that of 100 % PAR. The percentage of losses within R2 for 50 % PAR increases by 6.7 % compared with that for 100 % PAR. This research provides theoretical insights for designing, regulating, and optimizing nozzle governing and partial admission turbines in CAES systems.