Study On Small Hole Leakage Diffusion Law And Ventilation Strategy Of Gas Pipeline In Utility Tunnel

The utility tunnel is the "lifeline" to maintain the vitality of the city,and the leakage of the gas pipeline in the gallery is extremely harmful.In order to ensure the safety inside and outside the utility tunnel after gas leakage,the gas leakage and diffusion simulation of the utility tunnel was carried out,and the leakage and diffusion law of the small holes of the gas pipeline in the utility tunnel,the optimal ventilation strategy and the safety distance of the exhaust pavilion were studied.The main results are as follows:(1)Construct the geometric model of the gas tank with a fire compartment of 200 m,and study the gas diffusion characteristics of the natural ventilation benchmark leakage condition when the gas pipeline leaks,and the different leakage directions,leakage locations,leakage apertures and shapes,and leakage pressures during mechanical ventilation.According to the distribution law of gas diffusion in the corridor,the most unfavorable leakage situation of the integrated pipe corridor is summarized.The results show that the methane in the corridor is symmetrically distributed along the center of the leakage hole under the natural ventilation state,the methane diffusion distance is positively correlated with the leakage time,and the diffusion rate is negatively correlated with the leakage time.The Z+ leakage direction methane is mainly distributed at the top of the utility tunnel,and it is easier to accumulate at the upper wind of the leak;the Z-leakage direction becomes the lowest methane concentration in the bottom area after 30 s of leakage;Y+,Y-leakage direction The methane is more distributed at the bottom of the utility tunnel;The time of each leak reaching the alarm threshold and the total duration of explosion concentration are Z+<Z-<Y-<Y+ and Z+<Y-<Z-<Y+ respectively.There is a ventilation stagnation zone near the air inlet of the integrated utility tunnel.When the leakage position is within the range of the “stagnation zone”,gas is easy to accumulate in the “stagnation zone”;the coordinates of the leakage position are negatively correlated with the distribution range of methane in the gallery.The leak hole diameter and pressure are positively correlated with the gas leakage volume and diffusion range,and negatively correlated with the alarm time;the gas diffusion capacity of the slottype leak is weaker than that of the circular leak,and the average concentration of methane is higher upwind of the leak point.(2)Based on the most unfavorable leakage situation,study the control effect of different normal and accident ventilation times and ventilation sizes on the leakage gas concentration in the corridor,and summarize the best ventilation strategy for gas leakage in the pipe corridor.The results show that the accumulation state of leaked methane is related to the number of ventilations;the alarm time of the detector is positively related to the number of normal ventilation,and the detection points in the "stagnation zone" are more likely to reach the alarm concentration;when the normal ventilation reaches 4 times/h,the gas leaked from the small holes is Diffusion has a significant effect,which is the critical effective number of small hole leakage.The relative dilution rate of the accident ventilation to the gas concentration decreases with the increase of the number of times,and falls into a marginal effect,and 21times/h is the optimal accident ventilation frequency.The ventilation volume is unchanged,and the ventilation effect is nonlinear with the size of the vent,and the impact is small.Among them,the ventilation size of 1.2m × 1.2m has a better ventilation effect and is convenient for people to evacuate.(3)The geometric model of the exhaust pavilion was constructed,and the gas diffusion simulation was carried out based on the most unfavorable leakage situation and the optimal accident ventilation strategy.When there is no wind,the methane gas spreads and spreads in the shape of V toward the wind pavilion,and the distribution of methane is in a divergent state as it is farther away from the outside air outlet;when there is wind outside,the methane gas flows in the shape of a C shape toward the air outlet,and the methane will flow in the exhaust air.accumulation above the pavilion.The farthest boundaries of the safe methane concentration(18.8%LEL)outside the pavilion with or without natural wind are 8.47 m and12.32 m respectively.It is recommended to set a circular area with a radius of 9m outside the pavilion as a rapid warning area when there is no wind;When the wind blows,set a 4m ×13m rectangular area in the downwind direction with the upwind outlet of the exhaust pavilion as the starting boundary as a fast warning area.