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Vapor Dispersion from LNG Spills into Trenches and Troughs

Exponent performed a CFD simulation of the flammable vapor cloud dispersion from LNG spills into trenches and troughs. To address this issue, Exponent developed a hydraulic model for the flow of LNG spilled inside a trench or trough. Based on this model, Exponent quantified the rate of evaporation of LNG, and used it as the input into the CFD model to quantify the spill-out vapor dispersion. This work was submitted to, and approved by, the Federal Energy Regulatory Commission as part of the LNG hazard analysis required for the LNG terminal siting application.

 



 

 


The video shows the dispersion of a vapor cloud from an LNG spill into a downward-sloping pipe trench. The video shows the footprint of the ½ the lower flammable limit (LFL) gas concentration cloud, with color gradients indicating the cloud thickness. LNG flows downhill along the trench, and vapor is formed along the path due to heat transfer from the trench walls. The vapor cloud is carried by wind perpendicular to the trough toward the nearest property boundary. A 7-ft fence is located along the property boundary and prevents the ½ LFL-concentration cloud from leaving the property.

 



 

 

The video shows the dispersion of a vapor cloud from an LNG spill into a downward-sloping pipe trench. The video shows the footprint of the ½ LFL gas concentration cloud, with color gradients indicating the cloud thickness. LNG flows downhill along the trench, and vapor is formed along the path due to heat transfer from the trench walls. The vapor cloud is carried by wind parallel to the trough toward the nearest property boundary. The ignitable cloud disperses and does not leave the property.

 



 

 

The video shows the dispersion of a vapor cloud from an LNG spill into an elevated trough in 2-D simulation. The video shows the concentration isocontours of the gas cloud down to ½ LFL. Vapor is formed within the trough due to heat transfer from the trench walls, and is then dispersed by wind blowing perpendicular to the trough. The higher concentration portion of the plume (shown) separates at the crest of the downwind hill. The ignitable cloud then disperses and does not leave the property boundary (at the base of the hill on the right side of the image).