Study On Early Warning And Response Of Leakage Of Gas Pipeline In Underground Utility Tunnel

Unility tunnel is an important infrastructure to ensure the safe operation of the city,the construction of which is conducive to the comprehensive utilization of underground space resources.It is one of the symbols of the level of urban development modernization.However,there is a lack of scientific and reliable basis for the management norms of utility tunnel in China,and the analysis of gas entrance into utility tunnel is inadequate.The study on diffusion law of gas leakage dangerous zone,gas early warning and response measures in utility tunnel can provide theoretical basis for the revision of utility tunnel norms in China.In this paper,experimental and numerical simulation methods are used to study the gas leakage of small holes in gas pipelines.Based on the similarity theory,an experimental platform for gas leakage warning and response in a utility tunnel is built.For safety’s sake,experimental platform using neon gas leakage instead of gas leakage in the air,and the feasibility of it is verified.The reliability of the simulation is verified by experimental data.Experiments were carried out to study the diffusion law of gas in static diffusion,diffusion with low wind speed and diffusion with high wind speed.And whether gas accumulation occurs in the interlayer is also studied by experiment.FLUENT simulation studies the gas leakage diffusion radius and its influencing factors.And the simumlation researches the appropriate installation distance of the gas alarm,the online repair pressure and emergency cut-off concentration after gas alarm response.The results show that the leakage area and pipeline pressure have the largest influence on the gas leakage and diffusion in utility tunnel,and the correlation coefficient is above 0.9.When the leakage area is small and gas diffuses without ventilation,the gas jet to the top of the utility tunnel,then settles down to the middle of the utility tunnel and diffuses back to both sides;when the leakage area is large,the leakage gas is injected back to the top of the utility tunnel and diffuses to both sides.When the pipeline pressure is below 0.8 MPa,the relationship between diffusion radius and the leakage time are approximately linear after 60 seconds of gas leakage diffusion.The shape of the leakage outlet mainly affects the diffusion radius of leakage gas with low concentration at the initial time.The simulation result of leakage by small holes occurs in utility tunnel shows that installation spacing of gas detector in utility tunnel should not exceed 15 meters.When the diameter of leakage outlet is less than 10 mm,it is feasible to set the on-line repair pressure to 0.08 MPa and the emergency cut-off concentration to 45% of the lower explosion limit.When the detector concentration reaches 20% of the lower explosion limit,it is suggested to start the accident ventilation and pressure reduction measures(down to 0.4 MPa).After 150 seconds,if the alarm concentration is lower than the cut-off concentration,the pipeline pressure should be reduced to 0.08 MPa.And then,after 150 seconds of continuous ventilation,the largest gas concentration in the utility tunnel will be less than 1%,which meets the on-line repair conditions.If the detector concentration reaches 45% of the lower explosion limit,start the emergency shut-off valve.After 310 s,the largest gas concentration at all points in the utility tunnel will be less than 1%,.When the gas pipeline in utility tunnel leaks,accident ventilation will be started,and gas accumulation will not occur in the interlayer and exhaust well.