Numerical investigation on leakage and diffusion characteristics of buried hydrogen-blended natural gas pipelines

Currently, mixing hydrogen into natural gas networks is the most cost-effective method for transporting significant quantities of hydrogen over long distances. However, after mixing natural gas with hydrogen, the properties of the mixed gas will change significantly, manifested as faster diffusion rate, increased combustion rate, and wider flammability limit. In this paper, a CFD numerical simulation method is used to establish a numerical model for the leakage and diffusion of buried hydrogen-blended natural gas (HBNG) pipelines, and the concentration diffusion trend and velocity flow field distribution of HBNG in soil under different leakage conditions are studied, as well as the alarm time when HBNG diffusion reaches the lower flammability limit (LFL) at the ground surface. At the same time, the effects of hydrogen blending ratio (HBR), pipeline operating pressure, soil porosity and leakage diameter on HBNG leakage and diffusion are investigated. The simulation results indicate that increasing the HBR will increase the diffusion rate of the mixed gas and reduce the LFL, resulting in a decrease of the alarm time. The increase of pipeline operating pressure and leakage diameter will increase the mass flow rate, and the increase of soil porosity will reduce the resistance when HBNG spreads in the soil. All three cases will significantly reduce the alarm time. The results of this study will provide some references for the emergency response work of buried pipeline leakage and the risk assessment of HBNG leakage and explosion.