Reducing the use of fossil fuels in shipping requires new, alternative maritime fuels. Hydrogen carriers offer a safe and energy-dense solution for storing hydrogen, a zero-emission alternative fuel. This research focuses on ammonia borane, NaBH4, n-ethylcarbazole and dibenzyltoluene. Applying hydrogen carriers influences ship design significantly, as they require additional specialised equipment to remove hydrogen from the hydrogen carrier. This research estimates the size of the equipment. As this equipment will need to be stored and maintained on the ship, the exact sizing and sequence of the additional equipment will likely influence ship design. Results show that the reactor size is significant for all hydrogen carriers. The mixing tank is considerably sized for NaBH4 and ammonia borane, while the heat exchangers are large for dibenzyltoluene and n-ethylcarbazole.@en

Every now and then, every marine engineer dreams of a compact, lightweight and inexhaustible energy source to power large ships across the seven seas. Nuclear fusion of deuterium and tritium promises to be a safe, compact, carbon-free, and inexhaustible energy source. Even though it will take decades before conventional power plants may be replaced with nuclear fusion, the concept of nuclear fusion for marine propulsion has already been put on the table by commercial parties. This research investigates the potential of nuclear fusion onboard ships. The design investigates putting the smallest imaginable magnetic confinement reactor, ARC, on a ship. The only commercial ship requiring significant amounts of power is the Queen Mary 2. The large power output of ARC (200 MWe) is one of the major issues of putting a fusion reactor on a ship. Other issues may include intact stability, structural design and influences of vibrations on the fusion reactor. All in all, we found that a fusion reactor onboard a ship is unlikely to be feasible in the near future.@en

Hydrogen carriers are attractive alternative fuels for the shipping sectors. They are zero-emission, have high energy densities, and are safe, available, and easy to handle. Sodium borohydride, potassium borohydride, dibenzyltoluene, n-ethylcarbazole, and ammoniaborane are interesting hydrogen carriers, with high theoretical energy densities. The exact energy density of these hydrogen carriers depends on the integration of heat and mass with the energy converters. This combination defines the energy efficiency and, thus, the energy density of the system. Using a 0D model, we combined the five carriers with two types of fuel cells (PEM and SOFC), an internal combustion engine and a gas turbine. This resulted in 20 combinations. Despite the limitations of the 0D model and the occasional difficulty of validating input values, this model still produces exciting findings, which are valuable for further research. For the dehydrogenation of both dibenzyltoluene and n-ethylcarbazole, an external hydrogen burner is required if no waste heat resources from the integrated system are available. For the borohydrides, on the other hand, energy integration is essential for reducing cooling power. Dehydrogenation produces substantial energy, but only a fraction of this energy can be used for internal preheating. Dehydrogenation of ammoniaborane produces less energy. Among all hydrogen carriers, both ammoniaborane and sodium borohydride provide energy densities comparable to that of marine diesel oil. In particular, ammoniaborane possesses a remarkably high energy density. Thus, we conclude, that hydrogen carriers are attractive alternative fuels that deserve more attention, including their potential performance for hydrogen imports. @en

Green hydrogen combined with PEM fuel cell systems is a viable option to meet the demand for alternative maritime fuels. However, hydrogen storage faces challenges, including low volumetric density, fire and explosion risks and transport challenges. We assessed over fifteen hydrogen carriers based on their maritime performance characteristics to determine their suitability for shipboard use. Evaluation criteria included energy density, locally zero-emission, circularity of process, safety, dehydrogenation process, logistic availability and handling. Thus, excluding ammonia and methanol because of these constraints, we found that borohydrides, liquid organic hydrogen carriers and ammoniaborane are the most promising hydrogen carriers to use on ships with PEM fuel cells. Borohydrides, specifically sodium borohydride, have high energy densities but face regeneration issues. The liquid organic hydrogen carrier dibenzyltoluene has a lower energy density but exhibits easy hydrogenation and good handling. Given varying operational demands, we developed a framework to assess the suitability of hydrogen carriers for use in different ship categories. Evaluating the three types of hydrogen carriers, using our framework and considering current practices, shows that these are viable options for almost all ship types. Thus, we have identified three types of hydrogen carriers, which should be the focus of future research.

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It is essential to use alternative fuels if we are to reach the emission reduction targets set by the IMO. Hydrogen carriers are classified as zero-emission, while having a higher energy density (including packing factor) than pure hydrogen. They are often considered as safe alternative fuels. The exact definition of what safety entails is often lacking, both for hydrogen carriers as well as for ship safety. The aim of this study is to review the safety of hydrogen carriers from two perspectives, investigating potential connections between the chemical and maritime approaches to safety. This enables a reasoned consideration between safety aspects and other design drivers in ship design and operation. The hydrogen carriers AB, NaBH4, KBH4 and two LOHCs (NEC and DBT) are taken into consideration, together with a couple reference fuels (ammonia, methanol and MDO). After the evaluation of chemical properties related to safety and the scope of the current IMO safety framework, it can be concluded that safety remains a vague and non-explicit concept from both perspectives. Therefore, further research is required to prove the safe application of hydrogen carriers onboard ships.@en

Increasing pressure on the reduction or elimination of the use of fossil fuels in shipping requires the application of new maritime fuel alternatives. Green and circular produced hydrogen as a maritime fuel in fuel cell systems offers a great solution for these concerns. A fuel cell system has a zero emission performance, solid state silent process cycle, graceful degradation and no single point of failure. From a naval perspective, these characteristics very much support operational requirements like a silent propulsion and very low thermal and acoustic signatures as well as the possibility of an air independent system. Storage of hydrogen, however, is an issue. Traditional hydrogen storage in gas or liquefied aggregation has low volumetric density, low flame point, fire and explosion risks and transport challenges. The aim of this literature review is to investigate several hydrogen carriers and evaluate their characteristics on maritime and naval performance. This includes their volumetric and gravimetric density, dehydrogenation process, safety, logistic availability and handling. Over 15 different (types of) hydrogen carriers have been researched. Borohydrides, specifically sodium borohydride appeared to have several advantages, but still has issues with its hydrogenation process and handling due to it being a solid. The liquid organic hydrogen carrier dibenzyl toluene, on the other hand, does not meet the required energy density, but does have favourable additional properties, such as easy hydrogenation and good handling. Both of these are also subject of current research and development: For example, Hydrogenious LOHC Maritime AS, in combination with �stensj? Rederi, is working on a megawatt application for maritime, which should be finished in 2025. The Dutch government funds the SH2IPDRIVE project and the European Interreg North West Europe organization funds the H2SHIPS research project to analyse the shipboard use of these hydrogen carriers and to establish the design and engineering optimization opportunities.@en