What is the primary mechanism by which perlite insulation reduces boil-off gas (BOG) in LNG storage tanks?

The primary mechanism by which perlite insulation reduces boil-off gas (BOG) in LNG storage tanks is by minimizing heat leak into the tank. Heat leak refers to the transfer of heat from the warmer ambient environment to the extremely cold LNG inside the tank. This heat causes some of the LNG to vaporize, creating boil-off gas. Perlite is a volcanic glass that has been expanded by heating, creating a lightweight material with numerous tiny air pockets. When used as insulation, perlite significantly reduces heat transfer through several mechanisms. Primarily, it reduces conductive heat transfer because the air pockets within the perlite disrupt the continuous pathway for heat to flow. Air is a poor conductor of heat, so the presence of these air pockets greatly inhibits heat conduction. Secondly, perlite reduces convective heat transfer by restricting air movement within the insulation layer. Convection involves heat transfer through the movement of fluids (in this case, air). The small, confined spaces within the perlite limit air circulation, thereby minimizing convective heat transfer. Finally, perlite also reduces radiative heat transfer to some extent, although this is less significant than its impact on conduction and convection. The insulation system in an LNG tank typically consists of a layer of perlite packed between the inner LNG tank and the outer tank. This layer of perlite acts as a thermal barrier, significantly reducing the amount of heat that can penetrate the tank and vaporize the LNG. By minimizing heat leak, perlite insulation effectively reduces the generation of boil-off gas, which in turn reduces LNG losses and improves the overall efficiency of the storage tank.