(54ce) Understanding the Stability of High Expansion Foam Used for LNG Vapor Risk Mitigation

Natural gas consumption has increased as it is a clean source of energy, and advances in technology which have enabled its extraction from sources previously considered to be economically infeasible. Natural gas occupies a large volume in its vapor form and its liquefaction allows both ease of storage and transportation. Despite these advantages, a leak of Liquefied Natural Gas (LNG) can result in the formation of a cryogenic vapor cloud that has the potential to ignite, which also presents an asphyxiation hazard. NFPA 11 recommends the use of high expansion foam to mitigate the vapor risk of LNG spills. High expansion foam can not only help reduce the heat transfer to LNG through convection and radiation for reduced vaporization, but also heats up LNG vapor that passes through the foam layers, enabling ease of dispersal for risk mitigation. However, foam drains liquid over time which can increase the vaporization of LNG. Therefore, it is important to understand and model these mechanisms, so that the amount of foam required can be accurately quantified. A lab scale foam generator was used to produce the high expansion foam. The effects of several factors like convection, radiation, coalescence, coarsening, evaporation and liquid drainage on foam stability were studied. The factors that are crucial in determining the rate of foam breakage and the amount of liquid drained were identified, which helps determine the amount of foam that needs to be applied for effective vapor risk mitigation.

Keywords: Liquefied Natural Gas (LNG); vapor cloud; high expansion foam; mitigation; foam stability