Hydrogen (H2) can be used in engines or fuel cells, emitting nothing more than heat and water. The trouble is storing it. With a density of just 71 kg/m3, storage is a challenge.. It must also be kept at -252.87°C, not far from absolute zero. Maintaining this temperature entails constant energy usage. No wonder the shipping industry is looking for a more sensible approach.
Ammonia (NH3) contains more hydrogen than a single hydrogen molecule. This is useful in itself; but more so is the fact that, with its boiling point of −33.34°C, ammonia can be stored as a liquid at much more manageable temperatures. Its energy density is lower than conventional bunker fuel, but ten times higher than the best lithium-ion batteries.
Let’s get started
Recently, the Korean Register granted an Approval in Principle (AIP) for an 8,000m3 ammonia bunkering vessel concept developed by Korea’s KMS EMEC and Singapore shipping company Navig8. The design would run using a portion of its own cargo, fired in dual-fuel configuration with a small feed of marine gas oil (MGO).
For smaller vessels, fuel cells—which can use hydrogen once it is extracted from ammonia—could be an option. They can double the energy efficiency of an internal combustion engine (ICE), making them an ideal substitute for a four-stroke engine in diesel-electric configuration. The problem, at present, is making a fuel cell large enough to do the job.
Nevertheless, Eidesvik Offshore, in January 2020, committed to installing a full ammonia-fuel-cell propulsion system on its vessel Viking Energy, by 2024. “The goal is to install fuel cell modules with a total power of 2 MW on board Viking Energy in 2024,” said Jan Fredrik Meling, CEO of Eidesvik Offshore. “This will make the vessel the world’s first emission-free supply vessel.”
The biggest potential of ammonia, though, arises from the ability to use the fuel to run ultra-large ships. To this end, MAN Energy Solutions is already working on a two-stroke NH3-fired engine, to be commercially available by 2024; and a conversion kit for existing two-stroke engines shortly after that, in 2025.
“…we’re currently focusing R&D in the creation of a complete system from fuel tank to engine, making trials with double walls, using different materials solutions, developing smart software, and finding the optimal process solutions,” said Østergaard Sørensen, MAN head of Two-Stroke Research and Development.
The benefit would be twofold. Not only would this allow a switch to be made, in the longer-term, to a zero-carbon fuel (provided that fuel can be generated through renewable means) without downsizing the fleet. But the ability to convert existing vessels would enable this shift without new tonnage having to be constructed.
Indeed, once the initial hurdle of establishing an NH3-powered fleet is overcome, it is possible that individual vessels will benefit from far longer service lives—no longer having to compete with themselves to reduce carbon emissions.
Temper your enthusiasm
There are problems to overcome, however; NH3 is corrosive, and toxic. Exposure to high concentrations can cause blindness, lung damage, even death, making it far more hazardous to handle than conventional fuels. Introduction into the marine environment, via spillage, could have severe ramifications for the local wildlife.
Furthermore, ammonia, like other hydrogen-based fuels, comes with the caveat that it will only provide a CO2 reduction with ‘green’ (renewable) hydrogen. The ability to generate hydrogen using renewable energy sources could enormously improve the latter’s business case, if done correctly, it could perform a vital ‘load-leveling’ function, allowing us to harness power that would otherwise be wasted.
Unfortunately, almost all H2, at the time of writing, is generated using fossil fuels. All enthusiasm for ammonia is conditional, therefore, on whether it uses ‘green’ hydrogen, rather than ‘brown’ as a feedstock. If a renewable alternative cannot be found, implementing an NH3-based shipping economy will achieve nothing for the climate.