H2Tech - Q3 2022 - 19

SPECIAL FOCUS: PATHWAYS FOR SUSTAINABLE H2
The future of aviation fuel:
Are we on the right track?
T. REINERTSEN, REINERTSEN New Energy AS, Trondheim, Norway
There is no doubt that the aviation
industry has revolutionized travel by significantly
reducing travel times between
destinations. However, with increased air
travel comes additional climate effects. For
example, the global aviation sector emits
about 1 Btpy of carbon dioxide (CO2
). In
addition, studies on condensation trails-
those line-shaped clouds produced by aircraft
engine exhaust-show that they are
contributing to global warming.
The emissions from aviation represent
about 3%-4% of the negative climate
changes from human activities and are
equivalent to the emissions from 500 MM
fossil-fuel-powered cars.
The Clean Sky Joint Undertaking
(CSJU) program (a public-private partnership
between the European Commission
and the European aeronautics
industry) and other programs focus on efficiency
improvements and the blending
of new fuels such as biofuels, sustainable
air fuel (SAF) and synthetic fuel. However,
these fuels are expensive, and the
implementation and utilization of these
new fuels has been slow, as the availability
of sustainable sources are limited-e.g.,
biofuels represent only approximately 1%
of total air fuel. There seems to be a weak
sense of urgency in the aviation industry
for solving emissions challenges.
H2 as aviation fuel. In the future, global
H2 production will increase, and H2
is
expected to be available in sufficient volumes
for the decarbonization of multiple
sectors. H2
can be produced emissionsfree
in centralized natural gas plants, with
carbon capture and storage (CCS) or in
decentralized electrolyzer plants from water
and renewable power.
Airbus and other aviation companies
have started to develop large airplanes
with liquid H2
as fuel. The plan is to store
liquid H2 in the aircraft as fuel for modified
jet engines. Other concepts are based
on electric motors using batteries or fuel
cells, but these are not technically feasible
for large airplanes.
For a large airplane that needs more
than 50,000 horsepower for liftoff, turbines
fueled with H2
and/or ammonia
and amseem
to be the logical choice. The development
of turbines that use H2
monia as feedstock is ongoing in other
sectors, as well, and these turbines are
likely to be available in 3 yr-5 yr.
Numerous studies and projects performed
by the author's company and
others demonstrate that H2
storage of compressed H2
. The transportation and
in tanks at 300
can be transported
efficiently as compressed gas in
pipelines, but not in tanks as liquefied or
compressed H2
bars-700 bars are very inefficient and
costly, while transportation and storage
of liquid hydrogen at -253°C is very complex
and is probably unrealistic for distribution
to the world's airports.
Is clean ammonia more realistic? H2
can be efficiently transported as compressed
gas in pipelines or as ammonia by
ships or trucks. The expanding pipeline
infrastructure for H2
will facilitate the decarbonization
of many sectors, but will not
be sufficient to reach the world's airports.
However, ammonia is a traded commodity,
and the global ammonia infrastructure
is well developed. Ammonia is
far less explosive than H2
, but it is toxic
and must be handled safely by professionals.
It is easy to transport in large
quantities, and it exists in a liquid phase at
atmospheric pressure and at -33°C or at
room temperature and 10 barg pressure.
A fleet of marine vessels already exists
in global ammonia trading, transporting
approximately 20 MMtpy of ammonia
around the world, with many ports having
installed ammonia receiving and storage
facilities. The ammonia can then be
shipped by trucks, pipelines or marine
vessels to demand centers.
An alternative path for low-carbon
aviation? Global ammonia distribution
and storage infrastructure will be expanded,
partly due to the demand for clean fuel
from marine shipping. Presently, there is
a strong trend for redesigning and modifying
marine vessel engines to accommodate
ammonia as fuel. Several companies
are actively researching and developing
technologies for this transition. Emissions
from the shipping sector produce approximately
1 Btpy of CO2
, about the same as
from the aviation sector. To reduce the
marine sector's emissions to zero will require
about 500 MMtpy of ammonia.
In 2021, a group led by Reaction Engines
Ltd. presented a concept for ammonia-fueled
jet engines (FIG. 1). Recently,
NASA, Boeing and the University of
Central Florida presented a program for
the development of similar technologies.
These concepts for the use of ammonia
are based on loading ammonia into aircraft
fuel tanks, cracking some of the ammonia
into H2
and feeding the mixture to modified
jet engines. The heat from the comFIG.
1. Concept of how ammonia could fuel
jet engines.
H2Tech | Q3 2022 19
H2Tech - Q3 2022

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