Flow of Hydrogen from Buried Leaks

The substitution of hydrogen for natural gas within a gas network has implications for the potential rate of leakage from pipes and the distribution of gas flow driven by such leaks. This paper presents theoretical analyses of low-pressure flow through porous ground in a range of circumstances and practical experimental work at a realistic scale, using natural gas, hydrogen or nitrogen for selected cases. This study considers flow and distribution of 100% hydrogen. A series of eight generic flow regimes have been analysed theoretically e.g. (i) a crack in uncovered ground (ii) a crack under a semi-permeable cover in a high porosity channel (along a service line or road). In all cases the analyses yield both the change in flow rate when hydrogen leaks and the change in distance to which hydrogen gas can travel at a dangerous rate compared to natural gas. In some scenarios, a change to hydrogen gas from natural gas makes minimal difference to the range (i.e. distance from the leak) at which significant gas flows will occur. However, in cases where the leak is covered by an impermeable membrane, a change to hydrogen from natural gas may extend the range of significant gas flow by tens or even hundreds of metres above that of natural gas. Experimental work has been undertaken in specific cases to investigate the following: (i) Flow rate vs pressure curves for leaks into media with different permeability, (ii) Effects of the water content of the ground on gas flow, (iii) Distribution of surface gas flux near a buried leak,