Study Of Affecting Factors On Over-pressure Of Premixed Explosion In Gas Pipeline Gallery Of Utility Tunnel

As an important type of infrastructures to ensure the normal operation of the city,utility tunnels can effectively enhance the city’s comprehensive carrying capacity and standardize the layout of urban pipelines.However,due to the complex internal structure and numerous pipelines,an underground utility tunnel is likely to encounter interlocking and coupling disasters in the event of an explosion.The deflagration caused by gas leakage often leads to heavy losses and casualties.Therefore,many uncertain factors must be considered in the initial planning and design of the utility tunnel,for which whether and how to introduce a gas pipeline into a tunnel is a focal issue.Under normal circumstances,a separate compartment is adopted to separate the gas pipeline from other pipelines.On the one hand,this method reduces the risk of gas explosion accidents;and on the other hand,it avoids the occurrence of accidents caused by the coupling disasters in a utility tunnel.This thesis clarified the influencing factors of over-pressure in the premixed gas explosion accident of gas compartment by determining the worst condition,aiming to assess the over-pressure hazard to the compartment structure.The feasibility of introducing a gas pipeline into a tunnel was analyzed and the safety protection measures of underground utility tunnels were discussed,so as to further improve the level of sciencetization and standardization of the gas pipeline compartment structure layout.In this thesis,a combination of experimental research and numerical simulation was used to study the flame propagation front morphology,influencing factors and propagation mechanism of the premixed combustible gas in a narrow and long limited space after ignition.A simulation experiment platform for a reduced-scale model of a gas pipeline compartment was built to carry out the explosion experiment of methane-air premixed gas.It was found that the vents on both sides of the pipe compartment have the function of pressure relief,which can effectively reduce the safety risk of the pipe compartment structure.At the same time,through numerical computation of 2D/3D models and comparative analysis of experimental data and numerical results,it was found that the 3D numerical model including more comprehensive factors was more compatible with the actual physical model,though the computation process was more complicated to solve the nonlinear model,.Hence,the3D-simulation results were even closer to the experimental data.This study took an existed underground utility tunnel as an example.The influences of pipelines,supports,fire extinguishers and other auxiliary facilities on the over-pressure of the methane-air premixed gas explosion were considered.A 3D numerical model was established according to the typical structural characteristics of the separate ventilation zone of the gas compartment based on the standard design conditions.It was found that obstacles such as pipeline holders hindered the propagation of the premixed gas explosion shock wave,result in the enhancement of turbulence around the obstacles and the surge of local pressure.And the pipeline supports caused the continuous fluctuation of the peak over-pressure and over-temperature on the wall surface during the stable development period,which would affect the structural loads of the utility tunnel.By analyzing the effects of different methane-air premix concentrations and ignition positions,the over-pressure and over-temperature on the wall surface of the gas compartment in a methane-air premixed gas explosion experienced four periods: I rapid burning period,Ⅱ stable combustion period,Ⅲ combustion zooming period,and Ⅳoscillating retracement period.Both the peak over-pressure and the peak over-temperature on the wall surface appeared during the combustion zooming period.The worst working condition of methane-air premixed gas explosion in the gas compartment was determined to be 9% for the methane-air premixed concentration and the middle of the tunnel for the ignition source location.It was found that under this working condition,the maximum peak over-pressure and the maximum peak over-temperature produced by the explosion of premixed gas were higher than those under other working conditions.Based on the over-pressure analysis of the shock wave on the wall surface under the worst condition,combined with the structural strength check of the gas pipeline compartment,it was concluded that the bending of the edge and the middle part of the structure would be the main failure mode.According to the binding clauses of current national standards,this thesis conducted an extending research.The anti-explosive performance of the gas pipeline compartment structure was further discussed by varying the pipeline layout and the length of the ventilation zone.The author studied the impact of propagation characteristics of methane-air premixed gas explosion shock waves under different working conditions,and analyzed the variation rules of the maximum peak over-pressure and the peak over-temperature of the premixed combustible gas explosion shock wave acting on the gas pipeline gallery.CFD simulation results showed that therisk of combustible gas explosion over-pressure in the compartment would not increase if water supply pipes were introduced to coexist with gas pipes,or the length of each independent ventilation zones of the compartment was increased.Therefore,just from the perspective of the anti-explosion of the gas pipeline compartment structure,the author tried to explore the reasonable layout of pipelines in a utility tunnel to enhance the capacity of the utility tunnel to house pipelines;and also to determine the reasonable range of the length of each independent ventilation zone of a utility tunnel to reduce key nodes setting(such as isolation doors).For the design of utility tunnels,especially the optimization of pipelines ’ layout in the gas pipeline compartment and the determination of the length of each ventilation zone,more attention should be paid to the comprehensive decision-making optimization analysis of multi-factors such as personnel escape,pipe compartment ventilation,and cost-effectiveness.The thesis revealed the propagation mechanism of premixed gas explosion shock wave in the gas pipeline compartment of an underground utility tunnel and ascertained the influencing factors of over-temperature and over-pressure of the methane-air premixed gas explosion.The results of this study could provide some reference for risk assessment of introducing gas pipelines into a utility tunnel,for perfecting the safety design concept of the gas pipeline compartment,and for improving the scientific rationality of the gas pipeline compartment safety protection.