Experimental And Simulation Study On The Diffusion Of Leaking Natural Gas In Drainage Pipeline

With the continuous advancement of modern urban construction in China,more and more underground space resources have attracted people’s attention,and a large number of urban pipelines have been introduced underground.Due to the flammable and explosive characteristics of natural gas,when the gas pipeline is damaged and leaked,it is easy to spread to other underground adjacent Spaces and cause explosions and fire accidents,especially when it enters the drainage pipeline,causing heavy casualties and property losses.In addition,the interference of biogas in the drainage pipeline often leads to the problem of misidentification of natural gas leakage,so it is urgent to identify and analyze the diffusion of natural gas leakage in the drainage pipeline.Firstly,based on the characteristics of combustible gas in the drainage pipeline,the gas in the drainage inspection well is detected on the spot,and the combustible gas in the drainage pipeline is identified and analyzed by gas chromatography.Secondly,the experiment of natural gas diffusion in the drainage pipeline is carried out under the condition of no water in the drainage pipeline.The results show that the methane volume fraction of each monitoring point increases with the increase of natural gas leakage,and the increase of methane content of each monitoring point remains unchanged when the increase of natural gas leakage remains unchanged.Then,the mathematical model and two-dimensional physical model of the leakage natural gas diffusion in the drainage pipeline are established by using FLUENT software to study the diffusion law of the leakage natural gas in the drainage pipeline and the influence of different factors on the diffusion.The results show that when the leakage rate of natural gas increases proportionally,the diffusion area of natural gas corresponding to10 s leakage increases proportionally,and the diffusion area of natural gas corresponding to 120 s leakage increases exponentially.The flow of water at the bottom of the drainage pipe plays a positive role in promoting the diffusion of natural gas.When the leakage time is 73 s,the diffusion area of natural gas is 2.46 times of that when the water velocity is0.2m/s,which is 1.5 times of that when the water velocity is 0.1m/s.The positive ventilation can promote the diffusion of natural gas,while the reverse ventilation can hinder it,so the pipeline ventilation should be strengthened.Finally,the risk of leakage of natural gas diffusion in the drainage pipeline is studied.The warning concentration level of natural gas is established,and the influence of different factors on the dangerous area and warning time in the drainage pipeline is studied.The results show that: at the same time,the dangerous area in the drainage pipeline increases with the increase of natural gas leakage rate,water flow rate,positive wind speed in the pipeline and the number of vent holes;It decreases with the increase of water level.According to the layout scheme in this paper,monitoring point 5 is the point at the edge of the manhole cover of the drainage inspection well,so it is easier to obtain the natural gas concentration at this position in life,so the analysis of monitoring point 5 is focused on.When the leakage rate of natural gas increases from 0.17m/s to 0.64m/s,the three-level warning time at 5 monitoring points is shortened from 85s to 37s.When the water level increases from 0.16m to 0.32m,the three-level warning time at 5 monitoring points is shortened from 45s to 35s.When the number of ventilation holes increased from one to two,the second level warning time at 5 monitoring points was shortened from 45s to 37s.The water flow rate has little effect on the alarm time.