| With the increase in the number and scale of gas pipelines,the accidents of gas explosions caused by gas leakage into adjacent underground spaces are increasingly prominent.Once a natural gas pipeline leaks,it is likely that the gas will diffuse through the soil and accumulate in nearby underground spaces,posing a huge safety hazard.Therefore,this article conducts research on the diffusion process and laws of gas in the soil and underground space after the leakage of natural gas pipelines.Firstly,obtain soil permeability parameters by designing a soil permeability measurement device to provide data support for simulation conditions,and then establish a small-scale experimental platform for buried gas pipelines.At the same time,establish a mathematical model for buried gas pipelines.By comparing experimental results with simulation results,verify the accuracy and reliability of the established model,ensuring the reliability of subsequent simulation results,Finally,the diffusion process and laws of methane in soil and underground space under different soil and leakage source influence factors and different underground space influence factors are studied respectively.In this paper,the above process is simulated and studied by using the calculation method of coupling the porous media dilute material transfer interface and the free and porous media flow interface in COMSOL software.Firstly,for different soil and leakage source influencing factors,three variables,namely pipeline pressure,soil porosity,and the distance between the leakage hole and the valve well,are studied respectively.It is clear that as the pipeline pressure and soil porosity increase,The diffusion range of methane from small leaks increases accordingly;The difference in the volume fraction of methane in soil tends to a constant value under different porosity;The time for methane concentration to reach the lower explosion limit in the valve well decreases significantly with the decrease in the distance between the leakage point and the valve well.When the leakage position is less than 12.5 meters from the underground space,the time for the mole fraction of methane in the valve well to reach the lower limit of explosion is less than 7 days.While it takes more than a week for that when the distance is more than 12.5meters.Secondly,for different influencing factors of underground space,the effects of boundary conditions,exhaust conditions,and geometric morphology of valve wells on methane diffusion in soil and valve wells were studied.The results showed that when methane cannot enter the valve well through the wellbore wall,it can effectively reduce methane concentration in the well,but there is still methane accumulation phenomenon.Whether methane can enter the valve well through the bottom of the well has little effect on methane concentration in the well;Compared with the double row air holes,the single row air holes on the valve well cover only show a slight impact near the exhaust holes.However,under the condition that methane cannot enter the valve well through the well wall,the impact caused by the change in the number of exhaust holes is significantly higher than that under the condition that methane can enter the valve well through the well wall;The maximum methane volume fraction in a single pipe valve well is significantly higher than that in a directly buried valve well,with a maximum value of3.96%.The time required to reach the lower explosive limit is also shorter,but the methane concentration distribution in the two types of valve wells is basically the same.Figure [48] table [10] reference [73]... |
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