A Review of Hydrogen Production from Onboard Ammonia Decomposition: Maritime Applications of Concentrated Solar Energy and Boil-Off Gas Recovery

The growing interest in the potential role of hydrogen in reducing CO2 emissions as an energy carrier has significant implications in the natural gas industry. Hydrogen will eventually replace natural gas as the most widely used cleaner energy carrier. However, due to the challenges of transporting pure hydrogen and its technological immaturity, transporting ammonia would be a practical alternative. Furthermore, unlike hydrogen, ammonia's distribution and transportation system has already been developed widely and is adaptable to several novel and promising purposes. Additionally, it is noted that ammonia commonly acts as a hydrogen carrier, meaning that the end product is likely to be hydrogen. Hence, there is a need to convert ammonia into hydrogen at the destination port or onboard. To date, existing literature primarily focuses on hydrogen production in general. There is a lack of intensive research on hydrogen production from ammonia decomposition, especially considering the boil-off gas recovery on board. Furthermore, there are limited studies on solar integration infrastructure for energy carrier ships due to the conventional utilization on land, in factories, or onshore plants. Therefore, this paper aims to comprehensively review various ammonia decomposition techniques to produce clean hydrogen by recovering the boil-off ammonia while integrating solar energy infrastructures onboard the energy carrier ship for electricity and heat requirements. Four techniques of ammonia decomposition were investigated: thermal decomposition, catalytic membrane reactor, electrochemical decomposition, and ammonia cracker integrated Solid Oxide Fuel Cell. Moreover, parabolic through collectors, linear Fresnel reflectors, solar dishes, and solar towers were examined as potential solar energy technologies for onboard applications. The selection of natural refrigerants and reliquefication methods was also studied based on their limiting and determining factors to define the suitable options for the reliquefication of boil-off gas onboard.