Page 105 - ΝΑΥΤΙΚΑ ΧΡΟΝΙΚΑ - ΜΑΙΟΣ 2023

fuels. It may be suitable for small vessels on relatively short distances. But for
large ships, the “hydrogen carriers” methanol and ammonia are easier to handle
and have a higher energy density.
Ammonia: It is produced from hydrogen by adding nitrogen but needs only -34° C to remain
liquid, so it is easier than hydrogen to store. It does not emit any carbon when
burnt but releases a lot of NOx. In engines, it requires pilot fuel, whereas such
engines are still in development. Among its negatives is that the infrastructure
for using ammonia as marine fuel does not exist. However, its biggest deterrent is
its toxicity. Only a 0.5% air concentration kills a human instantly, whereas a tank
spill at sea will decimate a few cubic kilometres of any sea life.
Methanol: Among its negatives is the fact that it is hard to make green methanol since CO₂
must be added to green hydrogen. The sourcing of CO₂ and the cost of the
process is a challenge. Other than that, the positives outweigh the negatives. It
is easy to use even on existing ships using the existing bunkering infrastructure
since it is liquid at ambient conditions and is harmless to the marine environment.
Biofuels: They can easily be used as drop-in fuels to conventional marine fuels. Thus, they
will be the first and easiest method to reduce emissions in the near future and
to comply with some upcoming regulations, like Fuel-EU, which require a gradual
reduction of the carbon content of ships’ fuel. A challenge will be their proper
certification and ensuring their production does not compete with food sources.
So, we see that the members’ choices have properly ranked each fuel primarily
based on its practicality and technological readiness.

Considering that we are talking about green fuels, how is the issue complicated by the need
for green hydrogen to produce green ammonia and
green methanol?
98% of current hydrogen production is
from natural gas or even coal! Only 2%
is from water electrolysis, and even a
smaller amount, perhaps 1%, is really
green, where the electricity used is
from renewable sources (wind or solar).
Indeed, for ammonia and methanol to
be green, they need to be produced
from green hydrogen. And here lies
the challenge. The current and future
projected renewable electricity is insuf-
ficient to produce the enormous quan-
tities of green hydrogen required by
shipping. Not only that, but a recent
study submitted to IMO shows that
even if, theoretically, those quantities
were produced, the CO₂ reduction by
supplying them to other industries
(such as land transportation and facto-
ries) would be 8 times larger than sup-
plying them to ships. So, the question
is, even if green hydrogen was avail-
able, would any be left for ships? Here
nuclear energy could help to produce
the green hydrogen required. But in the
end, we need new technology, such as
better batteries and cheaper and faster
methods to produce green fuels.
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