Numerical Simulation Of Leakage Diffusion Of Buried Gas Pipeline

Nowadays, buried gas pipeline becomes the most convenient and economic form of gas transportation. When the natural gas released through the leakage hole by corrosion of soil, pipe ageing, man-made damage from third parties, and so on, it may increase the rescue time for the difficult detection and positioning. Thus, it is necessary to understand the diffusion regular of natural gas caused by leakage of buried gas pipeline in order to locate the position of pipe leakage quickly.The main purpose of this work is to establish three-dimensional computational fluid dynamics (CFD) models for studying the leakage and diffusion process of buried natural gas. Based on the established models, the effects of the key factors on the leakage and diffusion of natural gas are also obtained. The main results are listed as follow.(1) The concentration distribution of methane in the soil with the leakage time was calculated. The results show that the spread form of natural gas is penetration diffusion mainly and its concentrate clouds are similar to spherical because of the soil resistance. Both leakage rate and leakage distance increase with an increasing pipe pressure, soil porosity and leakage hole diameter. The effects of the leakage hole shape and pipeline buried depth buried are very weak. When the pipe pressure is prescribed as 0.156MPa, pipe inner diameter 20mm with the diameter of circular leakage hole 2mm and soil porosity 0.48, the leakage rate is 2.25 ×10-4 kg·s-1. Compared with experimental data in public literature, the calculated leakage rate shows higher reliability with relative error 10.78%,26.67%, respectively.(2) The correlation is put forward for the leakage rate of buried gas pipeline which fit well with the effects of soil porosity, pipe inlet pressure and leakage hole diameter. The results lie within ±15% error of the values simulated by the model. Q=2.76×10-5 (Pin/P0)0.703(dL/d0)1.31(3) On the basis of the above results, the models of buried nature gas diffusion in atmosphere are established. The simulation results indicate that the vertical diffusion distance increases firstly, then decreases with the increase of wind velocity, and the horizontal diffusion distance also has a trend of increase. When the wind velocity is faster than 1.5 m·s-1, the higher concentration area of natural gas focuses near the surface. Buildings can increase the vertical diffusion distance of natural gas in the atmosphere and its effect is promoted when the buildings are close to the leakage hole. With the increase of building height, the vertical diffusion distance of natural gas increases at first and then decreases, and the gas raises obviously when the building height is about 20 m.(4) The model of buried gas diffusion in a community is established. The natural gas easily spreads toward an open space and the diffusion area with methane concentration range from 0.1% to 1% is close to stable after 2 min. The methane area with higher concentration becomes smaller and smaller when wind velocity increases and its vertical diffusion distance will also decrease.