Review on the Safe Use of Ammonia Fuel Cells in the Maritime Industry

Abstract

In April 2018, the International Maritime Organisation adopted an ambitious plan to contribute to the global efforts to reduce the Greenhouse Gas emissions, as set by the Paris Agreement, by targeting a 50% reduction in shipping’s Green House Gas emissions by 2050, benchmarked to 2008 levels. To meet these challenging goals, the maritime industry must introduce environmentally friendly fuels with negligible, or low SOX, NOX and CO2 emissions. Ammonia use in maritime applications is considered promising, due to its high energy density, low flammability, easy storage and low production cost. Moreover, ammonia can be used as fuel in a variety of propulsors such as fuel cells and can be produced from renewable sources. As a result, ammonia can be used as a versatile marine fuel, exploiting the existing infrastructure, and having zero SOX and CO2 emissions. However, there are several challenges to overcome for ammonia to become a compelling fuel towards the decarbonisation of shipping. Such factors include the selection of the appropriate ammonia-fuelled power generator, the selection of the appropriate system safety assessment tool, and mitigating measures to address the hazards of ammonia. This paper discusses the state-of-the-art of ammonia fuelled fuel cells for marine applications and presents their potential, and challenges.

A Review of the Latest Trends in the Use of Green Ammonia as an Energy Carrier in Maritime Industry

“…Hydrogen is far more expensive to store than ammonia, despite the fact that both fuels have similar energy densities [18]. There are numerous barriers to ammonia becoming a competitive fuel in shipping's transition to decarbonisation, namely (1) an "appropriate ammonia-fuelled power generator, (2) appropriate system safety assessment tool, and (3) mitigating measures to address the hazards of ammonia" [23]. Hydrogen handling and safety are important issues to address.…”

“…Hydrogen handling and safety are important issues to address. Ammonia storage is generally simpler than that of hydrogen [23]. Another limitation of hydrogen, as shown in Table 1, is that it has a low energy density (4.7 GJ/m 3 ) in gaseous form compared to liquefied hydrogen (8.5 GJ/m 3 ); however, liquefying hydrogen is an energy-intensive process [24].…”

“…Table 1 shows that ethanol and methanol are competitive alternative fuels due to their relatively high volumetric energy density (21.1 GJ/m 3 and 15.8 GJ/m 3 , respectively). Note that ethanol methanol and liquid ammonia, compared to liquid methane, have almost half the energy density, which means that, to achieve the same power output, twice the amount of fuel is required [23], which implies higher storage costs and less space on vessels to transport goods. The situation is even worse for liquefied or compressed hydrogen, despite having the largest energy density on a LHV basis.…”

“…The situation is even worse for liquefied or compressed hydrogen, despite having the largest energy density on a LHV basis. It is worth mentioning that ethanol and methanol can be produced from renewable energy sources, whereas natural gas is extracted from fossil fuels [23]. In the short term, transition fuels such as LNG and LPG are necessary due to the low availability of green fuels such as ammonia and hydrogen, which are expected to be dominant in the longer term.…”

“…Ammonia can be used as a drop-in fuel in diesel in internal combustion engines and gas turbines and as a primary fuel in fuel cells, making it a very appealing and competitive alternative [6,18,23]. However, as Imhoff et al suggest in their study, "naval vessels are less likely to adopt ammonia powertrains without significant redesigns" [29].…”