[ aviation ]
to store liquid hydrogen . The containers can be rolled on and off the aircraft in the same way that luggage waggons are currently used to load and unload passengers ’ suitcases . The containers are moved by truck to a central filling location and then distributed to the aircraft .
The Universal Hydrogen concept avoids liquid hydrogen tankers moving around the airport to refuel fixed tanks on the aircraft . It also eliminates the need for static storage and refuelling equipment in multiple locations on the airport apron . Perhaps aspects of their vision will be adopted in the future , despite their recent bankruptcy .
Hurray for hydrogen derivatives
Given the challenges associated with storing gaseous hydrogen and the immaturity of the liquid hydrogen supply chain , alternatives to hydrogen are being considered for sustainable aviation .
Green ammonia is a zero-carbon fuel . It can readily be liquefied and stored as a liquid at low pressure in lightweight containers . Whilst it has a lower gravimetric energy density than hydrogen , liquid ammonia has a higher volumetric energy density than liquid hydrogen . Furthermore , when considering the gravimetric efficiency of the storage system , liquid ammonia can approach liquid hydrogen for the combined gravimetric energy density .
Ammonia can be partially cracked using hightemperature waste heat from a jet engine and then burned in that engine . It can be stored in the aircraft wing , in a similar way to kerosene today . Reaction Engines in the UK and Aviation H2 in Australia are developing specialist equipment components that may one day enable the use of ammonia as a fuel for jet aircraft .
Synthetic aviation fuel , or e-SAF is a sub-category of sustainable aviation fuel ( SAF ). It is produced when green hydrogen is combined with CO 2
.
E-SAF can be burned in conventional jet engines , avoiding the cost of new aircraft and eliminating the need to implement new infrastructure for hydrogen storage and refuelling at airports .
E-SAF is a hydrocarbon fuel that releases CO 2 when burned . However , since it consumes CO 2 during its production , this is a circular use of
CO 2 that neither increases nor decreases the amount of CO 2 in the atmosphere over the long term . Furthermore , the use of e-SAF avoids the use of petroleum-derived kerosene . This means it displaces fossil fuels and contributes to a reduction in anthropogenic CO 2 emissions .
E-methanol can also be produced as a green hydrogen derivative . Methanol can be reformed to syngas and then fed to a high-temperature PEM fuel cell to provide motive power for turboprop aviation . Methanol is less toxic than ammonia , which may make it attractive for passenger applications . As a liquid with a low vapour pressure , it can also be stored in the wing of the aircraft to enable long flight missions .
About the author
Stephen B . Harrison is the founder and managing director of sbh4 GmbH in Germany . He focuses on decarbonisation technologies and strategies . Hydrogen and Power-to-X are fundamental pillars of his consulting practice . With a background that includes 27 years at BOC Gases , BOC Group , and Linde Gas , Stephen possesses an intimate knowledge of hydrogen from commercial , technical , operational , and safety perspectives . His expertise extends across the full length of the value chain , from production , purification , distribution , and storage through to utilisation .
40 Hydrogen Tech World | Issue 17 | August 2024