Research On The Vibrating Three-phase Evaporation Model Of LNG Rail Tank Container Transportation And Safety Assessment Technique

Liquefied Natural Gas (LNG) is obtained by natural gas at the atmosphere pressure and at the temperature of-162?, after a series of treatments such as purification, refrigeration, liquefaction and so on.It is a multi-component mixture, and the change of temperature will cause many problems, more and more LNG rail tank container run on the railway, the risk of LNG release from tanks greatly increased. In order to solve these problems during the storage and transportation processes, it is necessary to understand the distribution of temperature field and the evaporation rate in LNG tank during the transportation , study the modeling of LNG release from tank and vapor dispersion in air.According to the vibration characteristics of LNG tank during the transportation . Analyzed the heat transfer coefficient of cryogenic liquid is affected by the vibration amplitude and frequency under vibrating condition. Analyzed the boundary layer initial position of cryogenic liquid is affected by up and down, side to side, and front to back motion under vibrating condition. The rule of the lossless storage in the horizontal cryogenic tanks was studied. Based on the achievements of the layer theory, combined with mass conservation principle and energy conservation principle, the evaporation rate model of three-phase in the LNG rail tank container is established. Through example calculation, it can be indicated that this model can be used to predict the variation trend of pressure and evaporation rate in the LNG rail tank container.Due to the fact that a great deal of flammable, explosive and low temperature LNG Was stored in the LNG rail tank container, the accident of LNG release from the LNG rail tank container will pose a disastrous risk to people, structures and atmospheric environment in proximity to such release. The modeling of LNG release from tank and vapor dispersion in air can provide scientific guidelines for evaluation and claims of hazard suffered from accident. In order to choose an appropriate model or modeling tool among a wide range of vapor dispersion models, numerous previous research works were firstly referred to, the methodologies for quantitative assessing the validity of LNG dispersion models were set up. The suitability of PHAST for modeling LNG dispersion was quantitatively evaluated by means of the datasets from the large scale LNG release field trials. The results of evaluation indicated that the PHASTnumerical dispersion model was valid in predicting dispersion of LNG.Build a security assessment program of LNG rail container during the transportation. The vibrating three-phase evaporation model of LNG rail tank container is used to analyze various factors which affect evaporation rate of the LNG rail tank container. The results show that: there exists a critical initial fill rate within the range of the maximum pressure limited by the storage tank, and there exists an "optimum initial fill rate" in the LNG rail tank container. The safety storage time is longest with the optimum initial fill rate.The higher the environment temperature is, and the bigger the thermal conductivity of the LNG tank insulation is, the pressure of the LNG rail tank container will increase more quickly, and the safety storage time become shorter. The conclusion can provide theoretic criterion for the safety storage and transportation of LNG. PHAST software simulated the hazardous areas of leak gas of the LNG rail tank container, and studied the effects of pressure, leakage of pore size, wiind speed, atmospheric stability,leakage direction, ambient temperature. The results showed that the stronger of wind and the higher of ambient temperature, the more strength of gas diffusion; The more stable of the atmosphere, the bigger of aperture; The greater pressure of leaking and the larger of diffusion area, and also more dangerous. Make an accident consequence simulation analysis to the LNG rail tank container and the LPG (Liquefied Petroleum Gas) rail tank container. The result shows that LNG influences space smaller than LPG.