Hydrogen Compression in Hydraulically Driven Piston Systems: Analysis of Technical Data and Selection of the Electric Motor

The hydraulically driven piston compressor is a state-of-the-art solution for compressing hydrogen to pressure levels up to 100 MPa and even beyond, especially for use in hydrogen refueling stations. Based on the technical data of a few commercial hydraulically driven piston systems for hydrogen compression, thermodynamic calculations are developed in this paper, and a preliminary indicator, the compression-to-electric power ratio (CEPR), is assessed. In order to justify calculated CEPR values no greater than 0.42 for the analyzed compression units, attention is paid to the hydrogen compression duty, and the instantaneous power is drawn based on a simple but effective procedure. In detail, the instantaneous power profile has a peak value approximately double that of the average power, and this peak is maintained for almost half of the working period. According to this result, the electric motor must be sized correctly. Thus, it might seem over-configured if compared to the average compression power, hence the relatively low CEPR values. Finally, in order to support the current assessment of the instantaneous power, considerations about the control system for piston movement inversion are reported.