Study on numerical simulation of leakage and diffusion law of parallel buried gas pipelines in tunnels

Abstract

Parallel buried gas pipelines in tunnels are located in a confined space environment, where natural gas is vulnerable to accumulating to the minimum explosion limit concentration after a leakage accident. Therefore, to reduce the time for locating the leakage source after an accident and compensate for the loss of emergency response, an experimental model for scaling parallel gas transmission pipelines in tunnels was established and the dispersion characteristics and influencing factors of continuous leakage of natural gas within buried soil and in tunnel space were investigated numerically, and the correlation between the volume of the explosion range of natural gas within the tunnel space and each influencing factor was explored using gray correlation analysis. The research shows that the leakage dispersion process of parallel buried gas pipelines in tunnels includes seepage leakage in the soil region and diffusion transport in the tunnel air region. In the soil region, natural gas from the pipeline leak forms a circular shape and tends to percolate upward due to the combined effect of pressure and concentration gradients.In the tunnel air region, the spatial dispersion of natural gas concentration obeys a multivariate Gaussian distribution, and the temporal dimension is divided into three phases: the initial phase of leakage, the spreading phase and the stable phase of leakage. The diffusion speed of natural gas is positively correlated with the operating pressure of pipeline. The concentration peak value (ymax) at the leakage orifice position and the leakage aperture (dx) approximately meet the linear relationship: ymax= 7.62dx. The diffusion path of natural gas is greatly influenced by the orientation of the pipeline perforations, and the tunnel walls have a directional effect on the diffusion of natural gas. The main factors affecting the volume of the explosion range of natural gas within the tunnel space are parallel pipeline leakage pressure, pipeline leakage aperture, parallel pipeline leakage position, pipeline operating pressure, and pipeline leakage direction, with grey correlation coefficients of 0.76, 0.675, 0.662, 0.553, and 0.55. The proposed model was demonstrated be able to simulate and predict the diffusion of natural gas under the accidental leakage of buried gas pipelines in tunnels. And the results of this study can guide the installation of buried gas pipelines crossing mountain tunnels to prevent accidents.