Quantitative Spontaneous Combustion Risk Assessment of a Hydrogen-Blended Natural Gas Pipeline Safety Venting System

In response to the demand for green energy transition, the transportation of hydrogen-blend natural gas through pipelines has become a significant means for large-scale, long-distance, low-cost hydrogen transfer. However, during emergency venting in pipelines, there are high spontaneous combustion risks due to hydrogen’s low ignition energy (0.02 mJ, about 1/10 that of methane) and a high diffusion coefficient (about 3.8 times that of air). A transient finite-element model was established, combined with kinetic analysis of free radical chain reactions, using the evolution of the temperature field and the concentration of hydroxyl radicals (OH−) as key criteria to investigate the effects of venting pressure, valve opening, and hydrogen blending ratio on spontaneous combustion tendencies. The results indicate the sensitivity ranking of parameters affecting the tendency for spontaneous combustion during pipeline venting: pressure → hydrogen blending ratio → valve opening. Under the same hydrogen blending ratio conditions, an increase in pressure by 1 MPa can lead to a maximum temperature rise of 1.8%, accompanied by a 13.9% increase in OH− concentration. The quantitative assessment model established in the research provides theoretical support for the design of safe venting systems for hydrogen-blended natural gas (HBNG) pipelines.