Unwanted releases of liquids from storage tanks, railroad trucks and transportation vehicles will spread on the ground, evaporate and form a potentially hazardous gas cloud. The size, shape and density of the gas cloud depend on the magnitude of the spill, along with the geometry and evaporation rate of the pool. To adequately predict the resulting gas cloud, it is necessary to realistically model the direction of the spill and its evaporation rate. The source of the spill, terrain, vegetation and buildings will influence the flow field. FLACS incorporates liquid releases on solid ground and on water. The spread of the pool in FLACS is governed by the terrain elevation, the presence of obstructions and obstacles, and the pool will extract heat from the surface on which is spreads (ground or water). Evaporation is locally driven by the heat transfer to the pool, the wind and flow over the pool, the temperature of the flow above the pool, and the vapor pressure of the evaporating species. The FLACS LNG-spill model has been validated against Burro and Coyote large scale LNG spill experiments.
A real world application of the LNG pool spill model can be seen above. The lower plot shows the pool spread (pool depth >0.2m is red) from a massive spill from an LNG tanker. The upper plot shows the contour of the resulting flammable vapor cloud due to the pool evaporation and a 7 m/s wind originating from the lower right corner. Below is an example of liquid pool spread (left) and flammable vapor cloud (right) from an LNG spill between 4 tanks. The dense flammable vapor is lifted in the turbulent wakes behind the tanks. The predicted hazards for both these examples would be very different if using a simpler consequence model that ignores the geometry (ship and tanks in this case).
You can read more about the pool spill models and functionality in the following papers.
Gavelli, F., Davis, S.G., and Hansen, O.R., CFD Simulation of Vapor Dispersion from LNG Jetting and Flashing Releases, Paper presented at AIChE Spring meeting, Natural Gas Utilization Topical Sessioin, San Antonio, USA, March 22-24, 2010.
Gavelli, F., Davis, S.G., and Hansen, O.R., A Unified Model for LNG Pool Spread and Vapor Dispersion: Is Wind Scooping Really A Factor?, Paper presented at AIChE Spring meeting, Natural Gas Utilization Topical Sessioin, San Antonio, USA, March 22-24, 2010.
Hansen, O.R., Hinze, P., Engel, D., and Davis S.G., Validation of FLACS for Vapor Dispersion from LNG Spills: Model Evaluation Protocol, Presented at the Mary Kay O'Connor Process Safety Symposium, College Station, USA, Oct. 27-28, 2009.
Hansen, O.R., Melheim, J.A. and Storvik, I.E., CFD-Modeling of LNG Dispersion Experiments. Paper presented at AIChE Spring Meeting, Natural Gas Utilization Topical Session, Houston, USA, April 22-26, 2007.
In version 9, new pool spread and evaporation models were introduced in FLACS. These new models were developed to predict the hazards of LNG-spills. The models can also be used for spills of other liquified gases (e.g. LPG, butane, ammonia) and liquids (e.g. heptane, hexane).
