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Liquefied Natural Gas (LNG) Vapor Dispersion Modeling with Computational Fluid Dynamics CodesQi, Ruifeng 2011 August 1900 (has links)
Federal regulation 49 CFR 193 and standard NFPA 59A require the use of validated consequence models to determine the vapor cloud dispersion exclusion zones for accidental liquefied natural gas (LNG) releases. For modeling purposes, the physical process of dispersion of LNG release can be simply divided into two stages: source term and atmospheric dispersion. The former stage occurs immediately following the release where the behavior of fluids (LNG and its vapor) is mainly controlled by release conditions. After this initial stage, the atmosphere would increasingly dominate the vapor dispersion behavior until it completely dissipates. In this work, these two stages are modeled separately by a source term model and a dispersion model due to the different parameters used to describe the physical process at each stage.
The principal focus of the source term study was on LNG underwater release, since there has been far less research conducted in developing and testing models for the source of LNG release underwater compared to that for LNG release onto land or water. An underwater LNG release test was carried out to understand the phenomena that occur when LNG is released underwater and to determine the characteristics of pool formation and the vapor cloud generated by the vaporization of LNG underwater. A mathematical model was used and validated against test data to calculate the temperature of the vapor emanating from the water surface.
This work used the ANSYS CFX, a general-purpose computational fluid dynamics (CFD) package, to model LNG vapor dispersion in the atmosphere. The main advantages of CFD codes are that they have the capability of defining flow physics and allowing for the representation of complex geometry and its effects on vapor dispersion. Discussed are important parameters that are essential inputs to the ANSYS CFX simulations, including the mesh size and shape, atmospheric conditions, turbulence from the source term, ground surface roughness height, and effects of obstacles. A sensitivity analysis was conducted to illustrate the impact of key parameters on the accuracy of simulation results.
In addition, a series of medium-scale LNG spill tests have been performed at the Brayton Fire Training Field (BFTF), College Station, TX. The objectives of these tests were to study key parameters of modeling the physical process of LNG vapor dispersion and collect data for validating the ANSYS CFX prediction results. A comparison of test data with simulation results demonstrated that CFX described the physical behavior of LNG vapor dispersion well, and its prediction results of distances to the half lower flammable limit were in good agreement with the test data.
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The application of expansion foam on liquefied natural gas (LNG) to suppress LNG vapor and LNG pool fire thermal radiationSuardin, Jaffee Arizon 15 May 2009 (has links)
Liquefied Natural Gas (LNG) hazards include LNG flammable vapor dispersion and
LNG pool fire thermal radiation. A large LNG pool fire emits high thermal radiation
thus preventing fire fighters from approaching and extinguishing the fire. One of the
strategies used in the LNG industry and recommended by federal regulation National
Fire Protection Association (NFPA) 59A is to use expansion foam to suppress LNG
vapors and to control LNG fire by reducing the fire size.
In its application, expansion foam effectiveness heavily depends on application rate,
generator location, and LNG containment pit design. Complicated phenomena involved
and previous studies have not completely filled the gaps increases the needs for LNG
field experiments involving expansion foam. In addition, alternative LNG vapor
dispersion and pool fire suppression methodology, Foamglas® pool fire suppression
(PFS), is investigated as well.
This dissertation details the research and experiment development. Results regarding
important phenomena are presented and discussed. Foamglas® PFS effectiveness is
described. Recommendations for advancing current guidelines in LNG vapor dispersion
and pool fire suppression methods are developed. The gaps are presented as the future
work and recommendation on how to do the experiment better in the future. This will
benefit LNG industries to enhance its safety system and to make LNG facilities safer.
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Control of Vapor Dispersion and Pool Fire of Liquefied Natural Gas (LNG) with Expansion FoamYun, Geun Woong 2010 August 1900 (has links)
Liquefied Natural Gas (LNG) is flammable when it forms a 5 – 15 percent volumetric
concentration mixture with air at atmospheric conditions. When the LNG vapor comes in
contact with an ignition source, it may result in fire and/or explosion. Because of
flammable characteristics and dense gas behaviors, expansion foam has been
recommended as one of the safety provisions for mitigating accidental LNG releases.
However, the effectiveness of foam in achieving this objective has not been sufficiently
reported in outdoor field tests. Thus, this research focused on experimental
determination of the effect of expansion foam application on LNG vapor dispersion and
pool fire.
Specifically, for evaluating the use of foam to control the vapor hazard from
spilled LNG, this study aimed to obtain key parameters, such as the temperature changes
of methane and foam and the extent reduction of vapor concentration. This study also
focused on identifying the effectiveness of foam and thermal exclusion zone by investigating temperature changes of foam and fire, profiles of radiant heat flux, and fire
height changes by foam. Additionally, a schematic model of LNG-foam system for
theoretical modeling and better understanding of underlying mechanism of foam was
developed.
Results showed that expansion foam was effective in increasing the buoyancy of
LNG vapor by raising the temperature of the vapor permeated through the foam layer
and ultimately decreasing the methane concentrations in the downwind direction. It was
also found that expansion foam has positive effects on reducing fire height and radiant
heat fluxes by decreasing fire heat feedback to the LNG pool, thus resulting in reduction
in the safe separation distance. Through the extensive data analysis, several key
parameters, such as minimum effective foam depth and mass evaporation rate of LNG
with foam, were identified. However, caution must be taken to ensure that foam
application can result in initial adverse effects on vapor and fire control. Finally, based
on these findings, several recommendations were made for improving foam delivery
methods which can be used for controlling the hazard of spilled LNG.
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