Leakage and diffusion characteristics of hydrogen enriched natural gas in utility tunnel

In order to investigate the diffusion characteristics of hydrogen enriched natural gas after its leakage from pipelines in the utility tunnel, the numerical model of aperture leakage of pipelines in the utility tunnel was established by CFD Fluent transient simulation.Meanwhile, the effects of leakage aperture direction, hydrogen blending ratio, pressure and leakage aperture diameter on the temporal and spatial distribution of combustible gas volume fraction in the utility tunnel were analyzed. The results show that different leakage aperture directions have a great influence on the shape of the distribution curve of the combustible gas volume fraction in the utility tunnel, but different curves are in a similar trend, with the maximum value of the combustible gas volume fraction reached the coordinates of the leakage aperture. When the combustible gas diffuses to the opposite direction of the ventilation, two stepwise declines occur in the curve. But when the combustible gas diffuses to the same direction of the ventilation, the curve has a second peak value. The factors, such as hydrogen blending ratio, pressure and leakage aperture diameter, only affect the value range of the combustible gas volume fraction curve but not the trend. For natural gas with a hydrogen content not more than 20%, 12 times/h of emergency ventilation can ensure that the volume fraction of combustible gas in the tunnel is below the explosion limit after an aperture leakage with a hole diameter less than 12 mm occurs in the 0.4 MPa pipeline or an aperture leakage with the hole diameter less than 7 mm in the 1.6 MPa pipeline. The research results could provide theoretical guidance for the safe operation of hydrogen enriched natural gas pipelines in the utility tunnel.