Hazard analysis and control measures for hydrogen-blended natural gas leakage in utility tunnels

Abstract

Hydrogen-blended natural gas (HBNG) can utilize existing natural gas pipelines and infrastructure for hydrogen transportation. However, the introduction of HBNG pipelines into utility tunnel gas chambers leads to an increased risk of pipeline leakage and diffusion. Consequently, a numerical model for the gas chamber in the utility tunnel is constructed in this study, and the risks of HBNG leakage incidents under different scenarios are analyzed by using detector alarm times, hazardous areas, and combustible cloud volumes as indicators. Targeted hazard control measures for HBNG leakage incidents are proposed from two aspects: optimizing the detector alarm system and enhancing the ventilation system. The results show that under different hydrogen blending ratios (HBRs), leak hole diameters, ventilation speeds, and operating pressures, detectors located directly above the leak hole can rapidly detect leaking gas. However, when gas leaks from the bottom of the pipe (at 6 o′clock) or the leak hole is positioned in the middle downwind, the detector directly above the leak hole may not give an immediate alarm. The alarm time of the furthest detector from the leak hole is inversely correlated with the HBR, leak hole diameter, ventilation speed, and pipeline operating pressure, while the leakage direction has no significant impact on the alarm time for this detector. The diameter of the leak hole, its location, and the ventilation speed are the main factors influencing the extent of hazardous areas and the volume of combustible clouds after natural gas and HBNG leaks within the gas chamber. Additionally, the leak pressure is a key factor affecting the volume of the combustible cloud after the leakage of natural gas and HBNG in the chamber. When the wind speed in the chamber is 4 m/s and the pipeline operating pressure is 0.8 MPa, compared to other leakage scenarios, the hazardous area and the volume of the combustible cloud formed by the gas leakage are largest when the leak hole is located near the inlet. For HBRs of 10 % and 20 %, setting the installation spacing of methane detectors in the chamber to be less than or equal to 13.5 m and 9.5 m respectively, along with adjusting the positions of the vents, can effectively mitigate the impact of accidents.