UK picks “expensive” liquid hydrogen for zero-carbon aviation project
The UK government this week announced a design for a hydrogen-fueled airplane, lining up with its plans to subsidize both zero-carbon flight and hydrogen production.
The proposed plane, which uses hydrogen from renewable energy rather than the fossil fuels from which 96% of hydrogen is currently sourced, was designed by the FlyZero project, part of the government-funded public-private £3.9 billion Aerospace Technology Institute Program.
The research program works with NATEP, an industry-led incubator on zero-carbon aviation, and H2GEAR, an industry project aiming to create liquid hydrogen fuel cells for planes. The government said the projects could bring a £114 billion boost to the UK economy by 2035.
Transport Secretary Grant Shapps tweeted that the hydrogen plane design could enable "guilt-free flying."
UK Prime Minister Boris Johnson flew back to London from the Glasgow COP26 climate summit last month, provoking tough questions from the media. At the summit, the UK had joined over 20 countries in making tentative plans to reduce aviation emissions.
The UK is eager to carve out a path to low-carbon aviation. The government-backed HyFlyer project completed the first hydrogen fuel cell passenger flight in September 2020, although the first liquid hydrogen aircraft, the Soviet Tu-155, flew in 1988.
The government followed this up with a goal to research zero-emission planes and ships in its green industrial strategy. Pursuing these aims, the UK Department for Transport launched a joint industry council aiming for zero-emission trans-Atlantic flight "within a generation." It launched a consultation on its "Jet Zero" strategy for net-zero aviation in July.
Meanwhile, the UK is also investigating other types of low-carbon aviation fuel, known as sustainable aviation fuel (SAF), created for example from waste cooking oil.
This year it held a separate consultation on potentially requiring jet fuel suppliers to blend an increasing proportion of SAF into aviation fuel in 2025 and awarded $19.81 million (£15 million) to eight companies to study SAF production projects. It is also working on international standards for SAF within the UN's International Civil Aviation Organization.
Liquid hydrogen preferred to ammonia
The plane proposed would have two engines that use liquid hydrogen, which emits no CO2 when burned. Liquid hydrogen propulsion emits only NOX, water, and leaked or evaporated hydrogen (boil-off).
Researchers on the FlyZero project say the hydrogen-fueled aircraft might be cheaper than conventional aircraft operating on a taxed blend of kerosene and SAF.
The researchers also contemplated zero-carbon planes running on ammonia or batteries in an October paper, but determined batteries were too large and ammonia didn't offer the energetic payload and flight range.
They preferred liquid hydrogen to gaseous hydrogen, which takes up too much space on a plane.
The compact nature of liquid hydrogen makes it an attractive future low-emissions fuel for several transportation markets. "When we're thinking about hydrogen fuel cell vehicles, like trucks and cars, you want to get the hydrogen out to the refueling station in a liquid form, because then you only have to drive out a 10th or 20th of the number of times in order to physically deliver the molecules on site," said IHS Markit Hydrogen and Renewable Gas Research Director Alex Klaessig.
Liquid hydrogen is currently contemplated as a potential fuel for inter-coastal shipping, and it is already used as fuel for fuel cells and as feedstock in certain refineries, he said.
But while liquid hydrogen and associated equipment is less expensive to transport than gaseous hydrogen, it is nonetheless still more expensive than traditional fuels because it has more mass per unit of energy than LNG, ammonia, or traditional jet fuel (kerosene), presenting a barrier to its use. "It doesn't really work for long distances," said Klaessig.
The heavy burden of transporting liquid hydrogen is an argument for the continued development of SAF, including SAF which uses hydrogen mixed with carbon, Klaessig said.
What's more, liquified hydrogen should only be consumed in large volumes (2,500 cubic meters per month) because of the cryogenic liquid hydrogen lost to evaporation, IHS Markit analysts wrote in this month's hydrogen cost tracker.
The development of greater quantities of hydrogen fuel is one of the aims of subsidies proposed in the UK's Hydrogen Strategy in August.
Airline and state net-zero targets
Aviation is a hard-to-decarbonize sector for countries. Aviation contributed 2.8% of global CO2 emissions in 2019, according to the International Energy Agency, and the International Council on Clean Transportation estimates that passenger flights caused 85% of commercial aviation CO2 emissions that year.
British low-cost airline EasyJet, which participates in the UK's Jet Zero Council, said it saw the proposed plane "playing an important role in its decarbonization pathway." In November, the company joined the UN's Race to Zero campaign, pledging to achieve net-zero carbon emissions by 2050.
British Airways, which is also pursuing net-zero by 2050, pledged to offset carbon emissions for all its UK domestic flights in 2020. This month it signed a multi-year supply agreement for UK-produced SAF, which the airline said was a first for UK-produced SAF.
The UK is looking to decrease aviation emissions as it targets net-zero by 2050. However, the UK's Jet Zero consultation noted that aviation is expected to be a source of emissions beyond this date because many of the required technologies were "in their infancy and will take time to develop." This included not only zero-emission aircraft, but also SAFs and GHG removal technologies.
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