Multiscale assessment of gravity-induced stratification for hydrogen blending applications in gas networks

Hydrogen blending into the existing gas grid is increasingly viewed as a viable strategy for decarbonizing the natural gas sector. However, incomplete mixing may pose operational and safety risks due to the non-uniform distribution of hydrogen within the gas stream. Even when initial mixing is effective, specific scenarios, such as prolonged static conditions in vertical risers, have raised concerns about the potential for localized hydrogen accumulation. Despite its practical importance, research on stratification phenomena in hydrogen-natural gas mixtures remains limited and lacks a standardized framework. This study provides multiscale and independent insights from both Molecular Dynamics (MD) simulations and an industrial-scale field study to investigate the phenomenon directly. MD simulations with gravity effects were used to describe diffusion and gravity-driven stratification at the molecular scale, revealing that stratification occurs only under artificially amplified gravitational fields of 12 orders of magnitude. Concurrently, multi-point gas chromatography measurements conducted over daily and weekly intervals at a full-scale distribution facility with a vertical riser and a 10% vol hydrogen blend confirmed vertical homogeneity. Observed differences remained within the method uncertainty, with no statistically significant divergence on volume fraction measurements between upper and lower sampling points.