Feasibility study of LOHC-SOFC systems under dynamic behavior for cargo ships compared to ammonia alternatives

Maritime propulsion is recognized as a hard-to-abate sector and its decarbonization will therefore require transversal efforts, including the introduction of alternative fuels to reduce CO2 emissions. Both ammonia and hydrogen could provide clean power; however, forecasts hint that ammonia will be especially useful for longer routes, while hydrogen suffers from low volumetric energy density. This paper evaluates the feasibility of a cargo ship with a SOFC powertrain equipped with LOHC-based hydrogen storage and compares the sizing and heat management requirements of four LOHC systems, namely N-ethylcarbazole (NEC), dibenzyltoluene (DBT), methylcyclohexane (MCH), decaline (DEC), with an ammonia-based one. The size of the 8.4 MW SOFC system is similar for the five carriers as expected. The dynamic performance of the LOHC system shows that the hydrogen flow rate can be effectively controlled by acting on the LOHC flow rate, reactor temperature, and pressure. However, LOHC systems are heavier (by a factor of 1.6 to 2.1) and larger (by 1.6 to 2.3 times) than ammonia systems. The decalin system results in the lowest mass and volume, while NEC is the heavier, and MCH is the least dense of the evaluated LOHCs. Similarly, the utilization of SOFC waste heat to cover dehydrogenation heat ranges from 45.6 % (NEC) to 27.9 % (ammonia). Overall, even considering the lower reaction temperature, LOHCs do not appear to be competitive with ammonia as hydrogen storage systems in the maritime sector.