Advancing Oil-Free Reciprocating Compressor Technology For Hydrogen Service: Experimental Investigation Of Seal Performance

Abstract

High-pressure hydrogen storage requires up to 700 bar to achieve sufficient volumetric energy density, with reciprocating compressors preferred for their high flow capacity and oil-free operation. Meeting purity requirements while handling hydrogen's low molecular weight, high pressures, and dry seals presents major challenges for sealing elements. As a result, non-lubricated compressor technology must extend beyond conventional API 618 applications. Predicting leakage, piston ring wear, and seal performance under non-lubricated conditions is therefore essential to ensure the reliability, efficiency, and safety of hydrogen compression systems. To address these challenges, a dedicated test campaign was developed to evaluate sealing performance under representative operating conditions using a unique setup. The setup features a special single-acting, non-lubricated cylinder mounted on a vertical compressor operating with helium at pressures above 200 bar. Extensive instrumentation was implemented, including 45 dynamic pressure probes positioned along the cylinder liner to capture instantaneous pressure profiles in the gaps between seals, piston, and liner, as well as 6 dynamic pressure probes positioned along the pressure packing. Since fixed sensors measure within a moving volume, a tailored procedure was established to reconstruct pressure signals inside the moving gaps. The results reveal how pressure drop is distributed among sealing elements throughout the compression cycle, depending on the operating conditions, and highlight the distinct operating principles of different seal typologies.