Experimental and Theoretical Study on Stability of High Expansion Foam Used for LNG Vapor Risk Mitigation

Abstract

Liquefaction of natural gas is an effective way to easily store and transport natural gas. A spill of liquefied natural gas (LNG) can result in the formation of a vapor cloud, which can migrate downwind near the ground because of a density greater than air. This cloud has the potential to ignite, and presents an asphyxiation hazard as well. The National Fire Protection Association (NFPA) recommends the use of high expansion (HEX) foam to mitigate the vapor risk due to cryogenic LNG. This dissertation studies the effects of forced convection and thermal radiation on HEX foam breakage. A lab-scale foam generator was used to produce HEX 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 in the foam. In addition, zirconium phosphate (ZrP) nanoplates were utilized to improve the stability of HEX foam. A heat transfer model was also developed to estimate HEX foam height that should be applied. The results indicated that forced convection and thermal radiation can significantly affect foam breakage rates. Therefore, accounting for these effects provides a better estimate for the amount of foam that needs to be applied for effective vapor risk mitigation. Nanoplates could be used to improve HEX foam stability and showed lower foam breakage rates. The heat transfer model predicted the height of the HEX foam that needs to be applied for outgoing vapors to be naturally buoyant.