CFD analysis on leakage and diffusion of hydrogen-blended natural gas pipeline in soil-brick gutter coupling space

With the increasing number and scale of buried natural gas pipelines, accidents resulting from gas leaks into adjacent underground spaces, which can lead to gas explosions, have become increasingly prevalent. Currently, the transportation of hydrogen blended with natural gas is emerging as the most economical method for longdistance hydrogen delivery. However, blending hydrogen with natural gas significantly increases the explosion hazard of the resulting mixture. In this paper, a computational fluid dynamics (CFD) numerical simulation method is used to establish the leakage and diffusion model of hydrogen-blended natural gas (HBNG) pipeline in soil-brick gutter coupling space. The concentration diffusion trends of HBNG within this coupling space are examined, alongside the effects of the hydrogen blending ratio (HBR), leakage aperture, pipeline pressure, leakage location and leakage direction on the leakage and diffusion processes. The results indicate that an increased HBR prolongs the hazardous presence of HBNG in the brick gutter. A larger leakage aperture and higher pipeline pressure lead to a higher leakage rate and faster diffusion of HBNG. Conversely, small leakage aperture and lower pressure conditions extend the duration for which the gas concentration remains within the flammability limit. When the leakage points are located inside the brick gutter, the HBNG rapidly fills the gutter upon leakage. The direction of the leakage affects the distance the HBNG will spray, after which it will diffuse into the ground and deeper soil under the influence of buoyancy and gravity. Finally, a regression-based formula for calculating the leakage rate of buried HBNG pipeline is derived by fitting the simulation data, providing valuable references for pipeline operation and maintenance.