Study On Dispersion Characteristics Of Leaked Natural Gas From Buried Pipelines

With the increase in natural gas consumption annually,the distribution of natural gas pipeline is increasingly intensive.Part of the city underground pipelines are old and in bad repair so that they are in the accident-prone stage,and a variety of factors have led to the frequent occurrence of natural gas pipeline leakage accidents.Among them,the buried natural gas pipeline leakage is hidden and difficult to detect.The leaked natural gas can explode through the soil to the nearby enclosed space in the case of sufficient time.Therefore,how to effectively prevent the threat of leaked natural gas spread through the soil to near confined spaces become an urgent problem.To this end,this paper explored the regular pattern of diffusion and migration of leaked natural gas in soil and its influence on nearby enclosed space,and compared the risk of leakage under different conditions.In this paper,three types of experiments were carried out,include the percolation experiments of natural gas in the soil column and the diffusion experiments of leaked natural gas in soil when there are other pipes nearby or not.Experimental soils were sand and clay,the influence of soil properties and seepage direction on the diffusion coefficient of natural gas in soil was analyzed.And the influence of various factors on regular pattern and dangerous range of natural gas diffusion in soil was compared.The main results are as follows:(1)The relationship between pressure drop and flow rate during natural gas seepage in soil column can be described by formula ofv=K(35)p L,and the seepage coefficient can be calculated using the fitting curve.The increase of water content leads to a decrease in soil porosity,which leads to a decrease in seepage coefficient.However,the effect of porosity reducing on seepage capacity is more pronounced when porosity is higher.The natural gas has stronger seepage capacity in the vertical direction in the case of the porosity does not change.In this experiment,the seepage coefficient of the clay in the vertical direction is 3% higher than that in the horizontal direction.(2)When the leaked gas diffuses in the soil without the adjacent pipeline,the response speed of each measuring point increases from 1 to 10 times as the leakage flow increases,and the concentration growth rate and the final cumulative concentration are significantly improved.When the leakage is about 0.6m3/h,the minimum cumulative concentration of clay is only 2.25%,but the sand is 75.41%.In the sand,changing the leakage direction will increase the influence of the diffusion and make the cumulative concentration of each measuring point higher,but the response time is relatively slow,and in the clay instead.When the leaked gas is hydrogen,the response time of each measuring point is shortened by 2-3 times,but the cumulative concentration decreases by 28.38%.(3)When the leaked gas diffuses in the soil with the adjacent pipeline,the response time in the diffusion tube nozzle reduces by about 2 times in the sand and 7 times in the clay as the leakage flow increases.Under the same medium,the ability of the leaked natural gas to diffuse into the adjacent pipeline decreases with the increase of the horizontal distance between the leak and the inlet of the diffusion tube.When the horizontal distance is 90 cm in the clay,the leaked gas has been unable to spread later from the inlet of the diffusion tube.The response time of each measuring points is shortened by nearly one time when the leak downwards in the sand and the response time of the inlet of the diffusion tube extended more than twice in the clay.The response time of each measuring points in the sand was shortened by 100-200 s,but extended by 1-5 times in the clay when the depth of the leak increased by 30 cm,and the accumulated concentration also decreased at the end of the diffusion tube.The above coverage will shorten the response time at each point in the sand,but increase in the clay.The cumulative concentration of each point in the sand reaches 100%,and the minimum concentration of clay in the clay is increased by about 28% after covering.