Analysis Of Leakage Factors And Diffusion Characteristics Of Natural Gas Pipeline Network In Mountain Cities

As one of the cleanest energy sources in the world,natural gas has a broad demand prospect.Due to its flammable and explosive chemical characteristics,the use of natural gas has potential safety hazards.The municipal roads,viaducts and buildings in mountainous cities constitute a unique three-dimensional intersecting semi-closed terrain space,which poses new challenges to the planning,layout and operation and maintenance management of natural gas pipeline network.Therefore,in this article,through mathematical analysis method of gas pipeline network dynamic risk factors,to assess the dangers of semi-closed terrain mountain city gas use,numerical simulation under different working conditions,combined with gas leakage,and targeted mountain city gas pipeline network safety protection measures are put forward,promote the standardization of the structure and layout of mountain city gas pipeline network planning level.Firstly,this paper studies the terrain characteristics of the mountainous city represented by Guiyang,and analyzes the causes of the three-dimensional intersecting semi-closed terrain space composed of municipal roads,viaducts and buildings.Secondly,based on the polystate fuzzy Bayesian theory,the potential hazard sources existed in the operation of the pipeline network were identified,and the critical importance degree,prior probability and posterior probability were verified each other.The results show that the weakest link of the natural gas pipeline network comes from the large hole leakage caused by the third party's destruction and utilization.Combined with previous research and analysis,USES the software FLUNENT respectively in the flat slope and gentle slope and slope in mountain city gas pipeline macroporous leakage model is set up three kinds of terrain and to carry out the numerical simulation of the gas explosion limit the quality score is located in the range of 3.5% ? 10.5% for the standard,divided into natural gas leakage danger zone,study the influence of different factors on the hazardous area change.The results show that :(1)Because the density of natural gas is less than the density of air,the vertical diffusion speed of the leaked natural gas is greater than the horizontal direction.Due to the adverse impact of the shielding of the viaduct,the leaked gas quickly converges under the viaduct and reaches the explosion limit,and there is a risk of great accident damage.(2)Influenced by the wind speed,the flow rate increases,the natural gas leakage and diffusion effect is strengthened,the gas cloud is migrated and diffused downwind,the flow rate distribution is turbulent,and the local scope of the dangerous area is expanded;(3)In a space with relatively flat terrain and less shielding,the area of contact between the leaked natural gas and the surrounding atmosphere expands,so that the concentration of the mixed gas diffused to the ground at the same distance height is lower,which is conducive to the dilution of the mixed gas,the reduction of the dangerous area in a large range and the improvement of the safety of the overall space;(4)Influenced by the slope,the slope size directly determines the vertical diffusion distance.The natural gas leakage diffusion in the middle slope is obviously slower than that in the gentle slope and the gentle slope,and the range of the dangerous area is larger.(5)Through the simulated control study of LNG tank car leakage,it is found that the impact force of LNG tank car leakage is more severe than that of pipeline leakage,and the space volume within the explosion concentration range is also larger;In the semi-closed space of mountainous city,the leakage natural gas will rise and spread along the facade of the building,and reach the explosion limit within the height range of 23m-46 m vertical against the wall.There is a risk of damage caused by the reaction with the indoor space.(6)The danger area caused by the leakage of large holes in general pipelines is in the range of 10 m to 20 m,while the maximum danger area caused by the leakage of liquefied LNG tank car is in the range of30 m.Therefore,more stringent conditions should be given to the driving route of liquefied LNG tank car.Based on the conclusions of the maximum distance and maximum width of the above dangerous areas,some references are given to the actual warning line and rescue emergency area.Combined with the influencing factors and diffusion characteristics of natural gas leakage,relevant effective prevention and control measures are proposed,providing theoretical basis for the safe planning and use of natural gas in mountainous cities.