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.