Research On The Mitigating Mechanism Of Leakage And Diffusion Of LNG Based On High Expansion Foam

In recent years,with liquefied natural gas projects of production,transportation and storage continuous applied,the industry of LNG has been developed rapidly.The rapid development of LNG industry partly filled the gaps of energy demand,and improved the status of energy shortage and environmental pollution in our country,but the rapid increase of LNG stations also brought a lot of hazards and risks.Numerous studies have shown that: because of its properties of low temperature,flammability and explosibility,the leakage of liquid and steam of LNG will damage facilities and workers.Specifically,when the LNG vapor comes in contact with an ignition source,it may result in serious fire and/or explosion.Therefore,it's very necessary to do some research on the process and the mitigating mechanism of LNG leakage and dispersion and,so that to select appropriate mitigating measure to minimize the hazardous areas and avoid the occurrence of catastrophic accidents.High expansion foam is an effective method for mitigating LNG diffusion,but its mitigating mechanism is not clear,especially,some key parameters of application need to be determined by further research.In view of this,the main research of this paper is as followed:Firstly,it's shown that the main factors of the evaporation and diffusion of LNG are heat input and flow momentum by analyzing the balances of heat,momentum and mass in the evaporation process of liquid pool,and the diffusion mechanism of the vapor cloud in the atmosphere.And the mitigating mechanism of diffusion and evaporation of LNG based on high expansion foam was proposed: lots of heat will be brought to the cryogenic LNG while high expansion foam was released on an LNG liquid pool,which will warm the gas vapor cloud,decrease vapor density,increase the buoyancy of LNG vapor,decrease concentration and volume of flammable vapor cloud near ground,thus to reduce the occurrence of fire and/or explosion.Secondly,from the point of fluid dynamics,CFD-based KFX software was used to simulate a large-scale abroad experiments of leakage and diffusion of LNG.The results show that: the KFX software is an effective method to simulate the evaporation and diffusion process of LNG liquid pool.The simulation results which consist of the concentration change of methane,the temperature change of liquid,the gas cloud range and the mitigating impact of high expansion foam are similar to those of experimental results.And the previous mitigating mechanism of expansion foam has been well validated with the simulation results.Thirdly,some experimental scenes have been simulated before the experiment.The simulation results showed that the most decrease of temperature is about 22? around the LNG leakage field,which will not damage facilities and workers.The simulation determined the regions of gas vapor cloud under the function of wind and the concentration of methane on the key position,and provided a reference for arranging the monitoring points of LNG field experiment.Finally,according to the simulation results,the experiment of leakage and diffusion of LNG was carried,the results which consist of the methane concentrations in the downwind direction,temperature change and the mitigating effect of high expansion foam were similar to abroad experiments.The change rate of temperature of liquid,vapor cloud and mass evaporation rate were given,which validated the effectiveness and mitigating mechanism of diffusion and evaporation of LNG based on high expansion foam.