The Theoretical And Experimental Research On The Leakage And Diffusion Of Gas Pipelines In The Integrated Pipeline Gallery

The construction of utility tunnel is conducive to the rational planning and development of urban underground space,and is conducive to the management and maintenance of urban pipelines.It is a modern urban construction project supported by the state,and trunk gas pipelines within the utility tunnel construction area must enter.Gas pipelines belong to high-risk pipelines and have serious consequences when leaks occur in integrated pipeline corridors.When gas pipelines are accidentally leaked,the diffusion rules within the utility tunnel can be studied.This can improve the gas tanks of the Technical Code for Urban Utility Tunnel Enegineering（GB50838-2015）.Ventilation strategies and ventilation,as well as correction of alarm decisions,provide a theoretical basis.Based on the possible leakage pattern of gas pipelines in the utility tunnel,the physical model and mathematical model of gas leakage have been established in actual gas cabins with a length of 200m.There are two major types of leaks,one of which is a circular leak caused by pipe sand holes,and the other is a crack formed by a weld fracture.It mainly studies the time for the concentration of 20%,40%,50%,80%,and 100%of the lower explosion limit directly above the leakage port and its radius of 7.5m under various conditions.Numerical simulation uses FLUENT software to study the diffusion law of gas pipeline leakage,and compares 74 gas conditions in different conditions such as different pressures in the gas pipeline,various leak apertures and shapes,different leak location and orientation,and different ventilation changes.The diffusion characteristics of gas in the utility tunnel under 74operating conditions such as the number of gas.According to the similarity principle,an experimental platform for the leakage diffusion and emergency response of underground pipeline corridor gas pipelines was developed.The leakage of methane gas in air was simulated using N₂ leakage in CO₂ gas.The experimental data were basically consistent with the numerical simulation results under experimental conditions.The feasibility of FLUENT simulation was verified.Studies have shown that gas leaks from the circular leak and spreads in the form of peaks and valleys on both sides of the chamber.After the crack leaks,the crack leaks first to the top of the chamber and then spreads along the sides of the wall in the form of wave troughs.Both meet the characteristics of a limited space jet.Gas pipeline pressure mainly affects gas concentration,and has little effect on diffusion rate and diffusion radius;The diameter of the circular leakage hole is positively correlated with the gas concentration and diffusion radius;And the crack leakage hole is more likely to reach the explosion limit range than the circular leakage hole.The larger air change rate,the greater the diffusion distance downstream of the leak and the smaller the upstream diffusion range.When the accident ventilation is used 12times/h,the concentration of gas concentration may occur at the downstream position of the leakage outlet.It is recommended that,when the accident is ventilated,low-velocity ventilation and high-speed ventilation can be performed first to avoid the concentration of the downstream gas to the lower explosion limit.The study on gas leakage law of leakage port shows that when the round leakage leaks,when the gas concentration reaches 40%and the accident ventilation is started 6 times/h or 12times/h,the gas concentration in the tank is always lower than the lower explosion limit.40%,It is recommended not to cut off the gas pipelines urgently,and to use the decompression online repair pipeline technology to repair the pipelines;crack leakage,when the gas concentration value reaches 40%,initiate accident ventilation 12 times/h,when the concentration reaches 45%of the lower explosion limit,cut off the gas urgently.The gas concentration in the tank is always below 30%of the lower limit of the explosion.Therefore,it is suggested that the alarm concentration after gas leakage can be set to 40%of the explosion threshold concentration,and the concentration of the emergency shutdown gas pipeline can be set to the 45%explosion lower limit concentration value.