Numerical and experimental study on hydrogen permeation law of hydrogen-blended natural gas in urban gas polyethylene pipelines

Mixing a proportion of hydrogen into existing urban gas pipelines is an important approach to achieve efficient hydrogen transportation and reduce carbon emissions in natural gas industry. However, due to the smaller volume of hydrogen molecule compared to that of methane molecule, hydrogen is more likely to permeate through polyethylene pipelines and leaks to the external environment, causing safety issues. To reveal the hydrogen permeation law of hydrogen-blended natural gas in urban gas polyethylene pipelines, the molecular dynamics simulation is used in this study to explore the influence of hydrogen blending ratio, temperature, and pressure on the hydrogen permeation process. In addition, permeation experiments of hydrogen-blended natural gas are conducted on polyethylene pipelines to validate the accuracy of molecular dynamic simulation. Results show that the higher the hydrogen blending ratio and temperature, the stronger the solution capability of hydrogen molecules in polyethylene pipelines. The diffusion ability of hydrogen molecules is positively correlated with the temperature and pressure, and negatively correlated with the hydrogen blending ratio. Overall, the hydrogen permeability coefficient of hydrogen-blended natural gas in polyethylene pipelines increases with the rise of temperature, pressure, and hydrogen blending ratio. The relationship between the hydrogen solubility coefficient, diffusion coefficient, permeability coefficient of hydrogen-blended natural gas and temperature can be described by the Arrhenius law. Besides, the diffusion path of hydrogen molecules reveals that the diffusion of hydrogen-blended natural gas in polyethylene pipelines conforms to the "skipping" principle. This study can provide beneficial guidance for the anti-permeation of hydrogen-blended natural gas in urban polyethylene pipeline transportation.