LNG - Leakage, spreading and fire
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This master s thesis continues the line of LNG related theses in cooperation withComputIT AS. The Phoenix series large-scale LNG pool fire experiments have beensimulated using the CFD software Kameleon FireEx (KFX) for validation purposesof the software to experimental data. A number of simulations were performed, and the main investigations of theexperiment thermal radiation, pool spreading and flame morphology have beencompared to results from KFX, using a range of different simulation scenarios. Scenariosincluded simulating the LNG as either a liquid release or as a gaseous releaseof methane from a circular equivalent of the quasi-steady LNG pool area obtainedon the experiment. Other variations included transient or constant release, wherethe transient release was based on an approximated flow rate from the experiment,and the constant release was based on the average flow rate over the duration of theexperiment. Due to limitations in the pool model in KFX, the liquid releases weresimulated on a flat ground instead of on a pool of water, with various heat transfercoefficients to account for the heat transfer between the water and the LNG. The radiative heat fluxes from the simulations compared to experimental valueswere initially low by factors between two and four, regardless of simulation scenario.The soot model was investigated, and found to give an excess of relatively coldsoot outside of the flame, acting as a radiation screen, thus reducing the thermalradiation from the fire to the surroundings. The soot model was modified, andsubsequent simulations produced very comparable values for the radiative heatfluxes for the majority of simulation scenarios. For all liquid, transient simulations, the LNG pool spread much faster thanin the experiment, and only the simulations with adiabatic conditions betweenthe LNG and ground reached the same maximum area as the experiment. Allsimulations with non-adiabatic conditions had a maximum pool area below thatof the experiment. As a result, it was concluded that the LNG vaporized tooquickly, and consequently the duration of the fire was about 250 s shorter in thesimulations than in the experiment. As a consequence of the high vaporization ratein the simulations, the flame grew to heights far above the experiment, and at someinstances the flame in the simulations exceeded the flame height in the experimentof over 100 m. A new, simple model for LNG spreading through water was introduced, andinitial computations in MATLAB produced highly promising results.