Study on the leakage and diffusion behavior of hydrogen-blended natural gas in utility tunnels

Incorporating the hydrogen-blended natural gas pipeline into utility tunnels increases the potential safety risk caused by gas leakage and diffusion. In this paper, a numerical model for the leakage and diffusion of hydrogen-blended natural gas in the tunnel was established to study the influences of ventilation mode, initial pipeline pressure, hydrogen blend ratio (HBR), and leak size on gas leakage and diffusion. The results indicate that gas accumulates at the tunnel's top under natural ventilation. When the HBR exceeds 20%, the safety risk in the tunnel increases significantly. Unlike natural ventilation, mechanical ventilation significantly reduces the high-concentration area's impact range. Under the dynamic adjustment of ventilation frequency, the leak size significantly impacts gas diffusion concentration, while the HBR has the slightest impact. When the HBR is no higher than 40%, the pipeline pressure is no higher than 0.4 MPa, and the leak size is no high than 5 mm, the accident ventilation frequency of 12 times/h could ensure the leaked gas concentration is lower than the alarm concentration. A leaked gas concentration prediction model was established to provide a basis for predicting the distribution of the leaked gas concentration in actual engineering.