Experimental Verification of Vapor Insulation System And Its Application to LNG and LH2 Tank

For storage and transport of liquefied gas such as LNG or LH2 (liquefied hydrogen), it is of great importance to reduce the boil off gas to a minimum. The thermal insulation system is playing a significant roll here. Though the specification of tank insulation should be decided by the boil off figure of a desired total system from a view point of an economical and practical use of it, the reduction of evaporated quantity is being demanded stronger, and any achievements to enhance the reduction are appreciated. The authors have introduced a new concept for enhancement of insulation efficiency by indirectly using the cold boil off gas as a protective shield or a heat sink to limit transmission of heat to the tank/cargo. To verify this theory of “vapor insulation system”, an experiment based on cold gas flow was carried out in a small scale apparatus to analyze carefully the effect on the heat transmission with and without cold vapor flow. These results were implemented in a calculation model of a spherical tank for LNG and LH2, and combined with some parameters such as gas flow quantity, gas temperature and location of gas passage. Based on this work realistic examples of design were proposed for a new insulation system. The configuration takes into account the concept of the small leak protection system for MOSS spherical tank. The principle of this new insulation concept proposed is that cold nitrogen gas which is produced by heat-exchange with the boil off LNG or LH2 vapor flows through a small passage created in the insulation structure. The upward flow of cold gas through the annular space around the tank will absorb the heat from the hold space of the cargo tank before it reaches the valuable liquid cargo, and it will simultaneously work as a leak detection system of cargo.