Study On Leakage Diffusion Of LNG Refueling Station And Its Vapor Cloud Explosion Hazard

In recent years,the natural gas industry has developed rapidly.Liquefied natural gas(LNG),as an emergency peak shaving gas source for large and medium-sized cities,can effectively solve the problem of uneven energy distribution and greatly improve the reliability of urban gas supply.However,LNG has the characteristics of low temperature and flammability.Once the LNG filling station leaks,the mixed vapor cloud will easily cause an explosion accident after encountering the ignition source,and the consequences will be disastrous.Therefore,it is particularly important to study the leakage and diffusion process of LNG filling station and its vapor cloud explosion hazards for predicting the accident risk range and reducing the consequences of the accident.This article mainly carries out the following work:(1)Using FLACS software and using the JET jet model to simulate the leakage and diffusion process of LNG filling stations,the simulation results are compared with the Falcon No.1 test results to verify the validity of the model.(2)Research on the influence of wind speed,leakage aperture,ambient temperature and cofferdam height on the leakage and diffusion process of LNG filling stations has been carried out.The results show that: at the initial stage of diffusion,the difference in the distance of gas cloud diffusion at each wind speed is small.In the late stage of diffusion,the farthest diffusion distance of 1/2LFL gas cloud in the downwind direction decreases with the increase of wind speed.Due to the obstruction of the storage tank in the downwind direction,part of the gas cloud climbed when it passed the obstacle storage tank,and the other part of the gas cloud bypassed the two sides of the storage tank and accumulated behind the obstacle storage tank;the leakage aperture affects the LNG gas.The diffusion of clouds has a greater impact.As the leakage aperture decreases,the diffusion of gas clouds is more likely to enter an equilibrium state.When the leakage aperture is small,the gas cloud is fully mixed with the air,resulting in 1/2LFL gas cloud gathering only on the leeward side of the storage tank;when the leakage aperture is large,the height of the gas cloud behind the storage tank decreases,and at the same time the low concentration gas cloud The wind direction diffusion distance increases;at the initial stage of the diffusion,the environmental temperature has less influence on the gas cloud diffusion;at the later stage of the diffusion,the farthest diffusion distance of the 1/2 LFL gas cloud down the wind direction increases with the increase of temperature.The presence or absence of a cofferdam has a great influence on the form and process of LNG gas cloud diffusion.At the beginning of the leakage,a large number of gas clouds accumulated in the cofferdam due to the existence of the cofferdam.The gas cloud over the cofferdam did not sink to the ground due to the obstructive effect of the cofferdam.Without the cofferdam,the gas cloud spreads along the ground in the downward wind direction.In the middle of the leak,"leaf bifurcation" appeared at the tail of the gas cloud.As the height of the cofferdam decreases,the phenomenon of "leaf bifurcation" of the downwind gas cloud becomes more obvious.Through orthogonal experiment range and variance analysis,the significance of the influencing factors is quantitatively compared,and it is found that wind speed and leakage aperture have significant influence on the farthest diffusion distance under the 1/2LFL gas cloud.The environmental temperature and the height of the cofferdam are proportional to 1/ The influence of the farthest spreading distance in the downwind direction of the 2LFL gas cloud is not significant.(3)According to the leakage and diffusion results of LNG refueling stations,FLACS software was used to simulate the real gas cloud explosion of LNG refueling stations.It was found that the maximum overpressure of gas cloud explosion after the leak was only 4.2k Pa,which did not cause any harm to personnel.Based on the rupture of the storage tank of LNG refueling station,the effects of ignition position,gas cloud size and gas cloud concentration on the explosion consequences of gas cloud at LNG refueling station are studied.The results show that when the ignition point is located near the refueling island at the edge of the gas cloud,the maximum overpressure of the explosion is 28 k Pa;and when the ignition point is located at the center of the gas cloud,the maximum overpressure of the explosion is only 14 k Pa.The maximum overpressure of the gas cloud explosion continues to increase with the increase of the size of the gas cloud.When the size of the gas cloud is 30m×30m×30m,the maximum explosion overpressure is 36 k Pa,and the radius of minor injuries in the gas filling station is 20 m.The explosion overpressure of the gas cloud increases first and then decreases with the change of the gas cloud concentration.When the gas cloud concentration is 9.5%,the explosion overpressure is the largest.The research results in this paper provide a theoretical basis for predicting the distribution of methane concentration and determining the safety distance after gas phase leakage and diffusion of LNG filling stations,and have guiding significance for the formulation of emergency plans and safety assessment of accident consequences after vapor cloud explosions at LNG filling stations.