ClassNK has awarded an approval in principle (AiP) for the design of a prismatic ammonia fuel tank (IMO Type B independent tank) for container Ships developed by Planning and Design Center for Greener Ships (GSC).
Ammonia could be used as a marine fuel for shipping decarbonization as it does not emit CO2 when combusted. However, its utilization presents challenges, such as the risk of leakage and relatively low volumetric efficiency. Ammonia combustion also produces copious amounts of nitrous dioxide, itself a major greenhouse gas, and it is very toxic.
While Type B tanks require a refined fatigue analysis, it is possible to use ordinary steel as the material for the structure of fuel storage hold space, except for the bottom part which is intended to be a partial secondary barrier, Class NK reports, and this results in a reduction in the amount of steel for low temperature service. Additionally, prismatic tanks offer superior volume efficiency compared to cylindrical tanks as they can be designed to fit the ship’s hold.
The Type B tank developed by GSC has been designed to ensure safe storage of ammonia and to minimize the reduction in the number of cargo containers due to the placement of fuel tanks in consideration of operational needs. Furthermore, the shape of the storage space for the tank has been simplified from the typical bench corners for container carriers, improving constructability and increasing the fuel volume.
ClassNK carried out the design review of the tank based on Part GF of its “Rules and Guidance for the Survey and Construction of Steel Ships” incorporating theIGF Code and “Guidelines for Ships Using Alternative Fuels (Edition 2.1)”. Upon confirming it complies with the prescribed requirements, ClassNK awarded the AiP.
ClassNK will continue to make contributions to advanced initiatives toward decarbonization, including safety assessments.
