| Nowadays,with the urbanization construction and "coal to gas" policy in China,natural gas,a clean and efficient energy,gradually become the most widely used fuel in residents’ daily life.With the increase of the amount of natural gas users.the accidents of natural gas in cities rank the third of accident fatal disaster in China.We can clearly find from the "Technical code for urban utility tunnel engineering"GB5083 8-2015 that the natural gas and other engineering pipelines can be included in the utility tunnel.Moreover,in the current construction or under construction of the utility tunnel engineering,we choose a separated module set as the natural gas pipeline module set.There are more and more local utility tunnel projects coming out in succession because of the technique development of utility tunnel and the support of relevant national policies.In the process of transporting,storing and using natural gas,once a leak has occurred which has not been detected in time,gas and air will mix to the explosive limit after diffusion.At that time a smallest spark will lead to accidents such as fire or explosion,causing severe social influence and economic loss.The domestic research on gas explosion began in the 1980s,and the research on gas leakage and explosion was mainly carried out in small scale test and finite element simulation.The explosion limit and concentration of methane,initial pressure,initial temperature and ignition can be used to study the distribution of explosive pressure along the pipeline and flame propagation.Few scholars have studied the consequences of gas leakage and explosion in the utility tunnel,and it is urgent to study the hazards of natural gas leakage and explosion in the urban utility tunnel.In order to study the characteristics of gas explosion load in urban utility tunnel,a series of methane-air mixed gas explosion tests was carried out in a gas explosion pipeline with a cross section size of 0.11m×0.11m and 6m long in this paper,including closed tests and open tests of different mixture gas concentration and different ignition ways,then the experimental process of each working condition was numerically simulated with finite element software FLCAS.The simulation results show that FLACS can reflect the experimental laws well.Then,we select a typical urban utility tunnel structure of a city demonstration area,numerical simulation of gas leakage and explosion consequence in tube gallery was carried out by fem FLACS.The gas leakage under the pipe pressure of 0.2Mpa and the explosive effect of 8 different conditions were simulated respectively,with the results of simulation is analyzed.Finally according to the influence factors of methane-air mixed gas explosion,with the viscosity and heat conduction of the medium and the effect of ignition on the result are ignored,the parameterized dimension analysis of the peak overpressure AP in gas explosion and the overpressure impulse I is carried out.Then based on the numerical simulation results of a simplified urban utility tunnel model.The formula for calculating the peak overpressure AP in gas explosion and the overpressure impulse I was obtained.This formula provides a solid theoretical basis for the safety analysis of gas inlet the utility tunnel,which can improve the disaster prevention and disaster resistance of the urban utility tunnel. |
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