Adaptation of Air Centrifugal Compressor Stages for Hydrogen-Based Economy: Impact on the Design Point and its Corresponding Flow Coefficient

One approach to saving time and R&D capacity in providing a compressor stage portfolio for a hydrogen-based economy is to adapt established air centrifugal compressor stages for operation with hydrogen. However, this shift from air to hydrogen operation in air-ready centrifugal compressor stages results in notable changes in the design point and its corresponding flow coefficient. These alterations arise due to distinct gas properties, differences in pressure ratio, and outlet temperature. The design point flow coefficients for the analyzed air-driven centrifugal compressor stages spanned from 0.04 to 0.1. To predict the hydrogen operation of these stages there is an urge to predict the flow coefficient range for the new gas. Therefore, this paper aims to comprehensively investigate the impact of shifting from air to hydrogen mode on the design point and its corresponding flow coefficient. The transition has been analyzed by developing a comprehensive methodology that integrates a prediction method, 1D mean line calculation, computational fluid dynamics (CFD) analysis, and a corrector method. The investigation has been conducted on five different centrifugal compressor stages at a wide range of flow coefficients. The maximum speed of the individual stages has not been exceeded to ensure that the machines remain structurally feasible. The findings derived from the simulation results suggest that air-ready centrifugal compressor stages, when operated with hydrogen, experience a shift in the peak efficiency point flow coefficient. This mode shift leads to a reduction in the peak efficiency flow coefficient; hence the hydrogen design point flow coefficient of air-designed stages is in the range of 0.02-0.08. An investigation to analyze the flow coefficient dependency on gas molecular mass and other factors is carried out to explain the findings. Then, the hydrogen peak efficiency flow coefficient can be used for the 1D mean line calculation of air-ready centrifugal compressor stages for hydrogen mode.