Gas Dispersion Modeling
Dispersion of gas/vapor from release of gas, gas flashed over liquid release, will form cloud that is initially momentum driven and eventually with time buoyancy takes over. The model should be chosen depending on the density of the gas/vapor. The significance of calculating the dispersed cloud footprint are:
Determining if the toxic gas will reach concentrations that could cause fatalities.
Determining if the flammable gas/vapor cloud will ignite (downwind distance concentrations are significant for fire and ignition hazards, hazardous area zoning, strategic position of detectors, alarm, shutdown, blowdown, deluge as required).
In modeling dispersion of releases in enclosed or semi-enclosed spaces, care should be taken to model obstacles and ventilation rates as well as the vent positions. Dispersion in open areas, especially of pressurized release, will initially be momentum driven unless obstructions are present. At large distances Gaussian dispersion may take over. Factors like changes in density and thermodynamic properties of the fluid should be understood during modeling such scenarios.
In case of large LNG release, the evolution of LNG vapor cloud will be influenced by the characteristics of pool that forms from spill. The heavy and cold LNG vapor (white cloud) that is formed rapidly after the release is driven by gravity. The obstacles and heat transfer mechanism may dilute the vapor faster and hence it also is possible that buoyancy will take over the dispersion phenomenon faster.
We employ both empirical models and computational fluid dynamic models for dispersion studies. We also carry out fire and explosion risk assessments.