Investigation of the leakage and diffusion characteristics of hydrogen-addition natural gas from indoor pipelines

The hydrogen-addition natural gas pipeline is a promising technology for large-scale civilian use, revealing the indoor diffusion behaviors of flammable gas in a leakage accident is of great importance for formulating a safety warning. A three-dimensional unsteady model is established, the distribution characteristics of CH₄ and H₂ are studied and the dynamic flammable regions are investigated. Case studies are performed to evaluate the effects of hydrogen-addition ratios and floor levels on average concentrations and flammable volumes of CH₄ and H₂. The results show that the high-concentration region of H₂ is always near the leakage hole. The increase rate of flammable gas mixture volume is larger than that of the volume of high-concentration CH₄. Under a higher hydrogen-addition ratio, the high-concentration region of CH₄ and the flammable region of gas mixture both float up while the high-concentration region of H₂ keeps horizontal, the flammable volume of gas mixture increases faster but the final volume is smaller. When the room is ventilated, a bigger wind speed leads to a smaller flammable volume of gas mixture. The flammable volume can be constrained at a quite low value from the beginning as the wind speed surpasses 1.5 m/s. When the leakage of hydrogen-addition natural gas occurs, floor 1 takes the most serious ignition risk with the largest flammable volume of 9.87 m³, occupying 44% of the room space. By contrast, the upper floors have quite smaller flammable volumes of gas mixture (under 0.05 m³) and the flammable region is near the leakage hole. The high-concentration region of H₂ is affected slightly by the floor height.