The Diffusion Simulation And Risk Analysis Of The Gas Leakage In The Urban Utility Tunnel

The urban underground utility tunnel,which can effectively utilize underground space and provide fully operation and maintenance,completely impede the development of road zipper.Natural gas pipeline is a highly dangerous pipeline for potential safety hazard at operation.At present,research on security protection technology of pipelines in the urban underground complex is still in debated.And the corresponding standard also need improvement.Therefore,research on drain diffusion and danger of natural gas pipeline is urgent for safe operation of into-pipeline.In this context,the drain diffusion at into-pipeline is mainly researched.Firstly,based on the norm and actual investigate result,the feature of natural gas pipeline and independent tank at urban underground complex is analyzed.And the structure of tank,ventilate and anti-explosion design in tank is also analyzed.According to the working condition in this context,mathematic model is proposed,containing three mainly elementary equation and natural gas diffusion equation set which composed of many component transportation equation.Equation set is processed by finite volume method and turbulence model is a k-ε model with correction of buoyancy.By using FULENT software with a pretreatment-ICEM,the drain-diffusion model at different terminal condition is proposed.And the drain-diffusion model at micropore and macropore leakage is respectively simulated.The simulation result is analyzed by Tecplot software.The natural gas diffusion rule at micropore and macropore of independent tank is revealed by qualitatively analyzing diffusion contour band,velocity change and streamline placement.When the hole leaks,the concentration of natural gas in the cabin is stratified,and the diffusion rate of natural gas is also distributed.The concentration and velocity are high and lower in the upper layer.The diffusion of the macroporous is stronger and the concentration is not obvious.The greater the rate of leakage,the more intense the spread of natural gas in the cabin,the greater the scope of diffusion,the same location in the same place the higher the concentration of natural gas.When there is no ventilation,the natural gas is symmetrical after the leakage in the independent compartment.When there is ventilation,the natural gas is obviously shifted,and the wind speed is higher,the lower the concentration of the natural gas is,the better the ventilation effect.Based on natural gas diffusion at micropore leakage,the natural gas dispersion,where the drain initial velocity,the diameter of pore and ventilate have been considered,is obtained.Monitoring point to monitor natural gas concentration is chosen according to the diffusion model,to monitor the time where the concentration of natural gas achieves alarm concentration and explosion limits.When the leakage aperture increases from 5 mm to 40 mm,the alarm time is reduced from 13 s to 3.5 s.When the leakage rate increases from 50 m / s to 150 m / s,The alarm time is reduced from 18 s to 4.8 s.When the wind speed increases from 1 m / s to 4 m / s,the alarm time is within 5 s,indicating that the wind speed has little effect on the alarm time of the remote measuring point.Since explosive factor exists in the urban underground complex,the consequence of natural gas explosion at special condition is discussed.The theoretical basis for design of ventilate at tank and safety operation is provided by using TNT equivalent method to evaluate explosive result and analyze the destruction of construction.