Experimental and Numerical Research of Hydrogen-Blended Natural Gas Leakage and Diffusion in Utility Tunnels

Abstract

Incorporating hydrogen-blended natural gas (HCNG) pipelines into urban utility tunnels can enhance the safety and management levels of urban pipeline systems. However, the semi-enclosed working environment of these utility tunnels may lead to severe consequences in the event of a combustible gas leak. In this paper, the leakage and diffusion law of HCNG in utility tunnels was studied through experiments and numerical simulation. A leakage and diffusion experiment platform in the utility tunnel was built to examine the effects of ventilation methods, leak direction, leakage flow rate, and ventilation velocity on leakage and diffusion. A three-dimensional pipeline leakage numerical model was developed to analyze the impact of the hydrogen blend ratio (HBR) on concentration distribution and alarm time. The results indicate that mechanical ventilation plays a significant role in ensuring the safe operation of the utility tunnel, with a more pronounced effect on the diffusion of hydrogen components. During vertical downward leakage, the ventilation effect on hydrogen components is poorer than vertical upward leakage, with the opposite being true for methane. Increased HBR leads to a greater lateral dispersion distance of the combustible gas cloud, significantly increasing safety risks in the utility tunnel when the HBR exceeds 30%. The alarm time shows a linear relationship with the horizontal distance from the leak source on the downwind side. Within the first 30 meters, the gas jet has a significant impact, while beyond 30 meters, the influence is mainly governed by the HBR. The shorter the HBR, the shorter the alarm time. A fitting relationship is obtained between the alarm time and the horizontal distance from the leak source on the downwind side for different HBRs. By rationally placing alarm devices, it is possible to ensure detection effectiveness while reducing economic costs.

Keywords: Experiment, Numerical simulation, Hydrogen-blended natural gas, Hydrogen blend ratio, Leakage diffusion, Utility tunnel