The Numerical Simulation Of LNG Leakage And Dispersion

As a kind of clean and efficient energy, liquefied natural gas (LNG) is widely used in industry and daily life. Its security has aroused much concern for its property of low temperature, flammability and explosibility. The results in the literatures show that when LNG leaks to the environment, it will form a liquid pool and evaporate which may cause serious damage to the facilities and workers. Furthermore, it will cause inestimable loss when ignited, and external environmental condition will have effects on the damage degree. Therefore, it’s very necessary to do some research on the process of LNG leakage and dispersion and its influencing factors to predict the hazardous areas, in order to give guidance to establishing contingency plan and minimise harm. In view of this, the main research of this paper is as followed:Firstly, a non-point source Mixed Gaussian Plume Model is built to simulate the dynamic gas dispersion process by means of MATLAB. The model has the striking advantage of simulating the initial stage of dispersion and describing the process of LNG dispersion visually while Gaussian Plume Model only could simulate the steady state and it can be utilized to simulate the dispersion process of non-point source such as pool and big hole. A hazard assessment programme is developed to simulate the dynamic dispersion process of nature gas and classify hazardous areas. The assessment process can be finished in a few seconds, so it can give guidance to emergency rescue immediately.Secondly, from the point of fluid dynamics, Realizable k -ε model, Species Transport model and DPM model are adopted to simulate fluid flow, species dispersion and evaporation problems involved in LNG leakage and dispersion process utilizing FLUENT software. The model is validated with the experimental data from Burro tests. The results show that the model can describe vapor dispersion very well and the concentration distribution coincides better with the measured value.Thirdly, the influence factors on vapor dispersion are discussed by method of numerical experiment. The main results show that leakage source intensity has significant effect on vapor dispersion. The stronger leakage source will lead to larger liquid pool and vapor cloud, and as a result the hazardous area will be larger and have a longer duration time. The main influence of wind speed on vapor dispersion is at downwind direction. When the wind speed is faster, its ability to transport and dilute cloud is stronger and it will lead to the cloud move and disperse faster. The barrier enhances the atmospheric turbulence intensity near itself and accelerates the mixing between vapor and air, but it impedes vapor dispersion and as a result the hazardous area is reduced at downwind direction. Up slope terrain has a similar character with barrier, it enhances the ability of diluting cloud, so it is beneficial to vapor dispersion. Down slope terrain is adverse to vapor dispersion for its low lying and that vapor is easy to accumulate under the action of gravity.Fourthly, vapor leakage and liquid leakage of large LNG tank are simulated respectively by coupling leakage source model to FLUENT model, and it shows that liquid leakage causes much greater hazards than vapor leakage.LNG leakage and dispersion models with different height of impounding are established to research the influence of impounding. The results show that the impounding impedes pool spreading and vapor dispersing leading to the reduction of risk outside the impounding, and the higher the impounding is, the more obvious the effect is. But at the same time it impedes the heat transfer among pool, atmosphere and ground, as a result the pool evaporates slowly and vapor cloud dissipates tardily.Finally, according to the actual scene of an LNG terminal, an actual LNG leakage and dispersion model is established by FLUNET software to forecast the hazardous areas and give some suggestion to drawing up emergency plans.