Hydrocarbon Processing - January 2022 - 38

Biofuels and Alternative/Renewable Fuels
LNG. LNG is leading the race as a substitute
green fuel. It has a relatively high energy
density of 22.2 MJ/L, a rapidly developing
infrastructure and is widely available.
However, it is viewed as a non-sustainable
transition fuel since it emits 2% more carbon
during its lifecycle. LNG has the potential
to be a bridge fuel to hydrogen due
to similar cryogenic storage requirements.
Hydrogen. Hydrogen is an energydense
fuel (FIG. 2) and can be produced
with no GHG emissions. With an energy
density of 8.5 MJ/L, liquid hydrogen can
be used in both internal combustion engines
(ICEs) and fuel cells. However, the
journey using hydrogen sustainably is
long winded. At present, gray hydrogen is
produced via methane reforming, which
emits GHGs comparable to HFOs. Zerocarbon-emissions
hydrogen is produced
from renewable-electricity-driven water
electrolysis, which is more expensive than
gray hydrogen production. Although hydrogen-energy
dense, it has a much lower
energy density vs. fossil fuels, which will
result in cargo capacity limitations.
Ammonia. With an energy density of
11.5 MJ/L, liquid ammonia is another viable
option that can be used in existing
engines and bunkering facilities. Used
either as a hydrogen carrier or as a fuel,
green ammonia can have zero emissions
within its lifecycle when produced with
green hydrogen or directly via electrochemical
cells. However, just like hydrogen,
ammonia is less energy dense than
conventional fossil fuels. It is also highly
toxic and requires strict guidelines.
Methanol. Methanol has a high energy
density of 16 MJ/L. It gained popularity
due its availability and easy storability.
Renewable methanol (i.e., bio-methanol
or e-methanol) has the potential of reducing
GHG emissions by 65%-95%. However,
it is less dense than traditional fuels,
and renewable methods are significantly
more expensive than conventional fossilfuel-derived
methanol.
Biofuels. Biofuels are the most researched
alternative fuel. Several marine
engines and fueling infrastructures are
compatible with biofuels, with minimum
modifications. Bio-derived fuels
(e.g., biodiesel) show potential. The major
challenge with the use of biofuels in
the marine industry is the significant increase
in production required to satisfy
demand, which will necessitate more land
reuse and the elimination of vegetation.
The sustainability of biofuels is put into
question when the lifecycle analysis and
carbon offset are considered. GHG emissions
reductions are hindered by land-use
changes and other upstream emissions.
These green fuels have the potential to
reduce carbon emissions. However, when
the exact quantities are presented alongside
the lifecycle analysis, their viability is
questioned. The primary challenges are
that green fuels have lower energy densities
vs. conventional fossil fuels. There are also
diverse issues regarding availability, port
and bunker infrastructure, engine development
challenges, cost, supply and safety.
The lifecycle emissions further highlight
the misconception that people have about
green fuels and their emissions reductions.
As a possible solution, a multistage
strategy must be developed. Since infrastructure
exists for LNG, biofuels and
conventional methanol, these fuels can be
viable as short-term solutions (5 yr-10 yr).
Corporations should start moving away
from LNG, gray methanol and biofuels in
the medium term (10 yr-15 yr) and begin
focusing on converting LNG engines/facilities
to use green hydrogen fuel and converting
biofuels/methanol to e-methanol.
As a long-term solution (15 yr-20 yr),
corporations should invest in advancing
green ammonia technology. Since ammonia
infrastructure already exists and can be
used in existing engines/bunking facilities,
green ammonia has the capability to be
used as a sustainable fuel for the marine
industry, while also ensuring zero GHG
emissions. It would also be beneficial for
diverse fuel alternatives to continue being
used to provide flexibility to the industry.
Therefore, in the long term, most ships
should be fueled by ammonia, while smaller
ships can be fueled by hydrogen and
existing methanol ships should continue
operations using e-methanol.
FIG. 2. Energy density of fuels per liter equivalent of fuel. Source: The Royal Society.
38 JANUARY 2022 | HydrocarbonProcessing.com
Statement of the problem. The questions
that the marine industry are battling
with is which green fuel is the most feasible
alternative for short-term and long-term
sustainability, and is it realistic? This article
provides a review analyzing the feasibility
and practicality of several green fuels. First,
it is important to consider the source/feedstock
and production mechanism used to
produce the fuel-the amount of energy
required to produce the fuel and the relative
cost of production. Then, the practicality
of each fuel is investigated based
on the port and bunker infrastructure required,
fuel engine development, projection
of the correlation between fossil fuels,
the fuel's suitability among long-range vessels,
supply issues and the associated risks
involved. The short-term and long-term
initiatives associated with each green fuel
are analyzed through an assessment of current
and projected technological projects,
research and development initiatives and
projects, and competing industries. Finally,
the overall feasibility outlining the benefits
of each fuel and the lifecycle analysis of
GHG reduction of each fuel are provided
as recommendations.
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