Study On Urban Gas Leakage And Diffusion Model And Its Risk Control

In recent years,urbanization in China is accelerating because of the rapid development of light industry and heavy industry,and city gas accidents have occurred.Gas poisoning,suffocation and explosion affect a wide range,so it is easy to cause mass death injuries and extensive property damage,and even affect social stability.Therefore,exploring the effective method of controlling gas accident is absolutely essential.To control the gas accident,we must know the law of gas leakage and diffusion and the spread range after the accident,also known as the danger zone.Only in this way can we guide the gas disaster and rescue scientifically.Based on the model of gas leakage and diffusion and jet theory,this paper establishes a gas leakage and diffusion physical model referring to the actual laying of city gas pipeline.On the basis of numerical simulation method,three conservation laws and k-e model,this paper establishes geometric model in GAMBIT software and then simulates gas leakage and diffusion in open spaces and obstruction in FLUENT software.The results show that gas spew from the leak and migrate in slender band.The level of gas concentration reaches the highest at the mouth of leak.Driven by concentration difference,gas diffusion continues after the jet flow.Horizontal wind changes the diffusion direction to downwind and near-earth side.As the leakage size becomes larger,the lever of the outermost edge concentration of natural gas becomes higher.The safety zone of H2 S is smaller than CH₄,so gas safety zone can refer to the H2 S security zone.The existence of obstacles will hinder the gas diffusion,changing the spread direction from downwind to upper air.The lever of concentration of windward is high,while leeward is low.As the height of obstacles increases,obstacles impede horizontal and vertical diffusion.And the width of obstacles has little impact on gas diffusion.If the distance between leak and the center of obstacle increase,the lever of gathering gas concentration as well as the diffusion height would decrease,and the lateral diffusion distance increase.Gas explosion zone mainly distribute in upper air and high level of gas concentration in windward of obstacles.Simulation results indicate that once there is a gas leakage accident,people around the leak and downwind should be evacuated immediately.Then the security cordon should be set up for gas emergency.When there are obstacles,the concentration is high in gas poisoning and suffocation region.An infusion of fresh air can change poisoning area into blast zone.Thus high-altitude gas should be enhanced ventilation and safety rescue should focus on the windward of the obstacles.