Effects of forced convection and thermal radiation on high expansion foam used for LNG vapor risk mitigation

Liquefaction of natural gas is an effective way of easily storing and transporting natural gas because of its high ratio of liquid to vapor densities. Any spill of liquefied natural gas (LNG) can result in the formation of a vapor cloud, which cannot only cause asphyxiation but can also migrate downwind near ground level because of a density greater than air and has the potential to ignite. The NFPA recommends the use of high expansion foam to mitigate the vapor risk due to cryogenic LNG. This paper studies the effects of heat transfer mechanisms, such as forced convection and thermal radiation on high expansion foam breakage, with and without a cryogenic liquid. A lab scale foam generator was used to produce high expansion foam and carry out experiments to evaluate the rate of foam breakage, the amount of liquid drained from foam, the vaporization rate of the cryogenic liquid, and the temperature profile through the foam. High expansion foam breakage was found to depend on the amount of wind induced forced convection and thermal radiation. At the highest wind speed (2.5 m/s) and thermal radiation intensity (270 W/m2) measured, foam breakage was found to be nearly 3 and 5 times the value without any wind or thermal radiation, respectively. Liquid drainage from the foam was found to affect the vaporization rate of the cryogenic liquid, especially immediately after foam application. Accounting for external factors such as forced convection and thermal radiation can help provide a better estimate for the amount of foam that needs to be applied for effective vapor risk mitigation.