Leakage Diffusion Simulation And Risk Assessment Of Tunnel Gas Pipelines

The long distance natural gas pipelines which across the tunnels are not supposed to be maintained as usually as the normal ones because of its’ enclosed space.The construction cost of tunnel pipelines is much higher than the regular ones.When the leakage or explosion accidents happen,because of the above two reasons,the rescue crews can’t get to the spot in time,and the economic loss is uncountable,the environment damage is extensive.However,few researches on tunnel gas pipelines have been done both in China and abroad,therefore,study on the operation state and the accident risk of tunnel section of gas pipeline is definitely necessary.The research object of this paper is the pipeline which is buttressed in the tunnels with doors sealed.The system vulnerability,mountain tunnels and construction of the pipelines are studied in the paper.Based on the principle of system division,the pipeline construction is divided to tunnel system,gas pipeline system and monitoring system.And then,the formation mechanism of the vulnerability of the whole system has been analyzed,and notation of vulnerability has been defined.In order to further situation after the gas leakage,FLUENT is applied to establish the gas leakage and diffusion module with appropriate solver and calculating parameters.The progress of gas diffusion and the analysis on the maximum range of the explosion are stimulated,which makes it possible to analyze the sensitive factors on gas diffusion progress.In order to figure out how these factors impact on the stimulation,in another word,how to assort these factors,the degree of influence on diffusion progress is analyzed by the single factor method.At last,the influential factors which include air speed,leakage aperture,operational pressure,etc,are arranged by their own importance.Based on the definition of the vulnerability on tunnel gas pipeline system,combining with the computer simulation,the gas pipeline risk assessment index system for tunnel areas are established,which contains risk factors’ vulnerability,object’s vulnerability and response ability’s vulnerability.Besides,according to the results of FLUENT simulation,the influence factor is determined.The AGA-AHP method is adopted to fit the formula of the subjective weight value of indexes.According to the vulnerability analyses and the interactional matrixes the combination weights are decided.The risk degrees of tunnel gas pipelines are defined by set pair analysis method.At the end of the thesis,a risk assessment is applied on a gas pipeline located at the west of Hubei province of the Sichuan to East Gas Transmission which passes through the tunnel.Correspondingly,combining with the computer simulation,the mitigation measures are proposed from two aspects of accident prevention and accident control.