Ammonia suggested as a possible future “low carbon” jet fuel – but problematic

A British company is hoping to use ammonia, in order to create “low carbon” flight in future decades.  The hope is to produce ammonia (NH3) using the very energy intensive Haber Bosch process, which is how fertiliser is produced.  Unless it used genuinely low carbon electricity for the process, a lot of carbon would be produced. The aspiration is that liquid ammonia could be stored in tanks on aircraft, and then – using the heat from the engines – “cracked” to produce hydrogen, which would fuel the plane. However NOx gases is produced in the process, and N2O is a highly potent greenhouse gas. Engines would need to have a second process, to turn the NOx into just water and nitrogen gas. The company wanting to do this hopes existing planes could be modified, though this would mean installing the cracker/heat exchanger unit next to each engine pod on an aircraft wing, and changes to fuel tanks. It is likely that an airliner with these modifications would only be able to fly short trips, of under 2,000km.  Ammonia fuel would cost a great deal more than fossil kerosene – and it is a toxic and corrosive substance, that can damage many metals.  

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British firm to unveil technology for zero-carbon emission flights at Cop26

As yet unnamed company claims it could enable ‘clean’ flights running on liquid ammonia by 2030

By Transport correspondent (Guardian)

A British company being launched at the Cop26 summit on Friday will unveil technology it claims could enable zero-carbon emission flights running on liquid ammonia by 2030.

It aims to build lightweight reactors to “crack” the chemical to produce hydrogen to burn as fuel, a design it says could allow existing planes to be modified to store liquid ammonia rather than kerosene.

Hydrogen is currently seen as the only possible “clean” fuel for future long-haul aviation, but the difficulty of safely storing it in fuel tanks, either as a gas or highly cooled liquid, means aerospace manufacturers have argued that vastly different planes would be needed.

Small reactors could be retrofitted into passenger planes to allow the hydrogen to be obtained from ammonia, according to scientists on the UK’s state-funded Science and Technology Facilities Council, who have demonstrated that a mix of cracked ammonia can burn with similar properties as the kerosene normally used as jet fuel.

The new joint venture, as yet unnamed, will combine their findings with rocket engine technology from Reaction Engines, with seed funding from cleantech investor IP Group.

They believe the first sector likely to adopt their technology is shipping. Ammonia has already been seen as a cleaner fuel for the maritime sector, and could be a readily available fuel, as a product that is currently widely transported and stored globally.

However, most of the world’s ammonia is produced from fossil fuels in an energy-intensive process [the Haber Bosch process – very energy intensive – used to make fertiliser] that is responsible for 1-2% of global carbon emissions.

To be truly carbon-neutral, the new aircraft would have to run on “green ammonia”, produced from water and air using renewable energy.

Cracking the ammonia using the reactors on the plane produces hydrogen and nitrogen, and the emissions are water and nitrous oxides (NOx). NOx is an indirect greenhouse gas and can lead to the formation of health-damaging air pollutants such as particulate matter.

The cost of ammonia, or hydrogen, would far outstrip kerosene as a jet fuel, but the firms hope carbon taxes and legislation will alter the future economics.

Aviation and shipping currently account for 5% of worldwide CO2 emissions and their impact is expected to grow without significant technological or behavioural change.

The British government last year set up a jet zero council with the aim of decarbonising flight, with Boris Johnson suggesting that the UK could build an actual zero-emission transatlantic plane by 2050. [Which is, of course utter irresponsible Boris bollocks. AW comment]. 

The industry has signed up to a net zero pledge for 2050, which relies heavily on offsetting and sustainable fuels. Cracking ammonia onboard, if proved feasible, could give zero-carbon flight 20 years earlier, the new joint venture suggests, although large challenges would remain to decarbonise production of ammonia, reduce NOx, and tackle the effects of aircraft contrails that contribute to global warming. [The non-CO2 impacts probably at least double the global warming impact of aviation]. 

Bill David, STFC senior fellow and professor of energy materials chemistry at Oxford, said: “I am excited about the impact that our technology can have in enabling low-impact transitions in hard-to-abate energy sectors.

“Playing to the complementary strengths of ammonia and hydrogen, our cracker technology can rely on the global ammonia infrastructure to provide, at scale, blended ammonia-hydrogen fuels that mimic fossil fuel performance and offer affordable retrofitted energy solutions.”

David said that they were “on a journey” to show NOx emissions could be reduced with the right mix and temperatures. Ammonia itself is a large part of the AdBlue used to reduce NOx emissions from diesel combustion engines.

Robert Trezona, head of Cleantech, IP Group, said the combination of technologies was “a profound breakthrough” with “myriad applications”. He added: “This is a credible, amazing combination of science and engineering … it’s a possible thing.”

The firm will aim to raise tens of millions in funding from other investors next year to build larger scale demonstrations – initially very much on the ground, Trezona said: “This works – but we know we need to show hardware to get investment.”

https://www.theguardian.com/environment/2021/nov/05/british-firm-to-unveil-technology-for-zero-carbon-emission-flights-at-cop26

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Comment on use of ammonia by an jet engine expert

Liquid ammonia only has marginally better volume than hydrogen… it is more stable, but the volumetric energy density is hopeless.
Page 10 of this:
https://royalsociety.org/topics-policy/projects/low-carbon-energy-programme/sustainable-synthetic-carbon-based-fuels-for-transport/ shows energy density by mass and volume of various fuels vs. fossil fuel. Might happen on boats, but unlikely on a plane due to these challenges.
Most of the points from the Hydrogen fact sheet hold equally true for Ammonia. https://stay-grounded.org/greenwashing/
The main difference is just Ammonia is bonded to Nitrogen which improves the handling/transport issues of hydrogen as it is far more stable, and the energy density is a bit better… but then you get the issues of higher NOx emissions (also a GHG), hence the need for a cracker to generate pure hydrogen…. but that’s too much complexity, weight, failure modes for an aircraft… hence this being consigned to boats rather than planes.
The other small issue is that ammonia is highly explosive… look at the Beirut disaster.
But if you really want to “blow this out the water” (perhaps an insensitive pun) then look no further than the need to use ALL green ammonia for fertiliser production and decarbonising agriculture, above and beyond the need to travel long haul by aircraft.
All green ammonia produced using renewables should be used for agriculture and you need a damn good reason not to, as we are talking about increasing food prices – and rising global human population.
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Whereas liquid hydrogen has to be stored and transported at a temperature of –253 °C, ammonia can be stored and transported at the much higher temperature of –33 °C. Large scale and well understood supply chains and storage facilities for ammonia already exist, and ammonia has a higher volumetric energy density than hydrogen..

Reaction Engines’ heat exchanger will use waste heat from a jet engine to power a compact and lightweight ammonia catalyst reactor, or ‘cracker’, developed by STFC. Each cracker/heat exchanger unit would be installed next to each engine pod on an aircraft wing. Installation would require changes to (replacement of) the aircraft’s wings and fuel tanks, but not to its fuselage or empennage. The engines themselves would need only small adjustments. One drawback, identified in modelling by Reaction Engines (based on an Airbus A320), would be that an airliner subjected to these minimum modifications would suffer a reduction in range to 2 000 km, but that this would still cover 90% of the most popular routes. This lost range would be restored if greater changes were made to the aircraft’s design.

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Whereas liquid hydrogen has to be stored and transported at a temperature of –253 °C, ammonia can be stored and transported at the much higher temperature of –33 °C. Large scale and well understood supply chains and storage facilities for ammonia already exist, and ammonia has a higher volumetric energy density than hydrogen..

Reaction Engines’ heat exchanger will use waste heat from a jet engine to power a compact and lightweight ammonia catalyst reactor, or ‘cracker’, developed by STFC. Each cracker/heat exchanger unit would be installed next to each engine pod on an aircraft wing. Installation would require changes to (replacement of) the aircraft’s wings and fuel tanks, but not to its fuselage or empennage. The engines themselves would need only small adjustments. One drawback, identified in modelling by Reaction Engines (based on an Airbus A320), would be that an airliner subjected to these minimum modifications would suffer a reduction in range to 2 000 km, but that this would still cover 90% of the most popular routes. This lost range would be restored if greater changes were made to the aircraft’s design.

https://www.engineeringnews.co.za/article/new-uk-joint-venture-to-make-ammonia-credible-as-a-zero-carbon-aviation-fuel-2021-11-08

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.Ammonia can be used as a fuel but there are several challenges in ammonia combustion, such as low flammability, high NOx emission, and low radiation intensity.

https://www.sciencedirect.com/science/article/pii/S1540748918306345

[There is a process to turn the NOx produced by burning ammonia (NH3) into nitrogen and water by  selective catalytic reduction (SCR).  Unclear if that could be used in jet engines, or if NOx would be produced.]


Ammonia
Materials of construction for ammonia are dependent on the operating temperature. Whilst mild steel may be used at ambient temperature special steels are required at low temperatures to avoid embrittlement. Impurities in liquid ammonia such as air or carbon dioxide can cause stress corrosion cracking of mild steel. Ammonia is highly corrosive towards copper and zinc.

https://www.hse.gov.uk/comah/sragtech/techmeasmaterial.htm

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Ammonia is a toxic gas or liquid that, when concentrated, is corrosive to tissues upon contact. Exposure to ammonia in sufficient quantities can be fatal. One of the highest production-volume chemicals in the U.S., concentrated ammonia is used in manufacturing, refrigeration, and agriculture (as a fertilizer)..

https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750013.html


Below are some comments from a LinkedIn forum on the subject of ammonia

12th November 2021

Joe Steinke

Ammonia has about 1/2 of the energy density of fossil fuel. A 737 jet at takeoff has a 25% by weight fuel, 25% cargo/passenger, and the rest is dry weight. If one doesn’t mind flying without passengers or cargo, the plane could go the same distance. Let alone the problems with NOx, toxicity,…..

Ammonia as energy carrier is simply no option for aviation due to the following reasons. NH3 is extreemly toxic. They simply cannot be used in places for the general public. The safety measures in a laboratory are very strict in relation to NH3. Furthermore according Arief Dahoe (Explosion, Hydrogen Safety and Combustion Scientist) the contaminants allowed in hydrogen for making NH3 are extremely strict, which makes the conversion from hydrogen to NH3 and back very difficult and expensive.

Agree with the posts here saying ammonia as an aviation fuel is a bad idea. It really is. Aviation safety, maintenance and airworthiness are hard enough as it is without adding in to the mix a highly dangerous, reactive and toxic chemical as “fuel”. It’s very simple. Small aircraft can be battery only. Larger commuter category and small short haul aircraft can use battery / hydrogen fuel cell hybrid systems to get sufficient range, and anything bigger can use biofuel or synthetic fuel, and possibly a degree of hybrid propulsion, depending on size, range and payload. Absolutely no need whatsoever for ammonia, ever.


What a wonderful idea. We will no longer have to worry about planes exploding when they crash, fire or no fire the ammonia fumes will kill everyone and probably a fair number of the first responders to boot. No amount of carbon savings is worth the risk. Ammonia as a fuel will achieve the objective of some. No one with a clue will fly on those planes.

Oh no! Not ammonia! It is poisonous and corrosive, risks that aviation can do without.

https://www.linkedin.com/posts/paulperera_british-firm-to-unveil-technology-for-zero-carbon-activity-6864863720758112256-6d1W

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