Vapor Cloud Diffusion And Explosion Risk Assessment Of LNG Terminal Transmission Pipeline

In order to comply with the transformation trend of the world’s energy structure,China’s LNG industry has developed rapidly in recent years.As one of the important links in the LNG storage and transportation industry chain,the LNG terminal is also constantly developing and improving.At present,compared with the mature LNG terminal system in foreign countries,China’s emerging LNG terminal industry lacks a perfect LNG terminal safety assessment system and effective emergency management measures.Once LNG leakage and diffusion accident occurs,the consequences will be unimaginable.Based on this,this paper takes the LNG terminal as the research object,in order to explore the risk safety assessment of the explosion accident caused by the LNG transmission pipeline leakage and its diffused gas cloud,uses FLACS to simulate and analyze the diffusion behavior of the gas cloud and the expansion of the liquid pool after the pipeline leakage in the LNG terminal,and conducts numerical simulation of the ignition of the diffused steam cloud to study the damage level of the thermal radiation to the LNG terminal and its surroundings after the explosion accident.The main contents are as follows:（1）A large-scale LNG terminal and pipeline model in the station are established to simulate the gas cloud diffusion after LNG leakage at the important dangerous pipelines in the process area and storage tank area,and to study the diffusion behavior of LNG leakage gas cloud and the change trend of the regional influence range in the LNG terminal under the influence of different wind speeds and different leakage diameters:（1）The increase of wind speed will accelerate the dilution rate of LNG gas cloud,and the greater the wind speed within a certain wind speed range,the larger the area affected by LNG leakage vapor cloud diffusion,however,when the wind speed exceeds the critical value,the affected area will continue to shrink with the increase of the wind speed;（2）The leakage diameter affects the upper limit of the LNG leakage vapor cloud diffusion area.With the increase of the leakage diameter,the greater the LNG leakage,the more obvious the gas cloud sedimentation,and the influence of wind speed on LNG leakage vapor cloud diffusion is gradually weakened.（2）The expansion of the liquid pool,the trend of the evaporation rate of the liquid pool,the temperature distribution of the gas cloud diffusion and its diffusion behavior were studied:（1）The area of the liquid pool will increase with the increase of leakage,and its thickness will decrease with the increase of the distance from the leakage center,and the higher the wind speed,the greater the evaporation rate of the liquid pool;The temperature distribution of the gas cloud is basically opposite to the gas cloud concentration,the area with high concentration is cold,while the area with low concentration is relatively high;（2）The pumps,valves,condensers and pipelines around the high-pressure pump input pipeline in the process area and the tall storage tanks near the low-temperature export pipeline at the bottom of the storage tanks in the storage tank area will inhibit the diffusion behavior of the LNG leaking gas cloud and reduce the influence range of LNG leakage gas cloud diffusion;the LNG leaked gas cloud around the tank will also produce a Karman vortex street phenomenon,resulting in a gas cloud swirl,which is not conducive to the diffusion and dilution of the gas cloud,and measures should be taken to avoid the occurrence of this phenomenon.（3）The numerical simulation results of LNG leakage vapor cloud diffusion are analyzed and the safety range of low-temperature asphyxiation of vapor cloud diffusion is divided,so as to obtain the safety radius of low asphyxiation range of process and tank area leakage vapor cloud;Taking the leakage and diffusion simulation results of the storage tank area as the basic working condition,carry out numerical simulation of ignition and explosion in the initial,middle and end stages of gas cloud diffusion,divide the safety assessment scope with flame heat radiation as the main hazard,and summarize the maximum death radius and the safe radius distance of accidental leakage in the storage tank area;The explosion numerical simulation and leakage failure and ignition probability calculated that the personal risk value in the LNG terminal is between 10^-4-10^-6 every year,which is within the acceptable area of the risk acceptance standard.