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Is a carbon-free aviation industry really possible?

Biofuels, an alternative that is still too expensive

Analysis Cécile Michaut, Science journalist
On February 2nd, 2021 |
3 mins reading time
4
Biofuels, an alternative that is still too expensive
Samuel Saysset
Samuel Saysset
Lead techno advisor at ENGIE Research
Jean-Philippe Héraud
Jean-Philippe Héraud
Process engineer at IFP Energies nouvelles
Paul Mannes
Paul Mannes
director of Total Aviation, in charge of the worldwide business line
Jérôme Bonini
Jérôme Bonini
Research and Technology Director, Safran aircraft engines
Key takeaways
  • Biofuels provide an option to help the aviation industry reduce its carbon footprint.
  • Current aeroplane models can run on jet fuel that contains 30-50% biokerosene.
  • To avoid competing with food supplies, biomass composed of waste and residue is the focus of industrial processes to produce biofuels.
  • At prices that are 1.5-2 times higher than kerosene, the cost remains a hurdle if biofuels are to remain competitive in comparison to fossil fuels.

Avi­a­tion is count­ing on the use of bio­fu­els and petrol-free syn­thet­ic fuels to reduce car­bon emis­sions. Tech­ni­cal­ly, it is pos­si­ble: “bio­fu­el stan­dards allow the incor­po­ra­tion of 30–50% biokerosene into cur­rent air­plane mod­els with­out mod­i­fy­ing the engine,” says Jean-Philippe Héraud, BioT­fu­eL project man­ag­er at IFP Éner­gies nou­velles (the for­mer French Petro­le­um Institute). 

How­ev­er, so-called first-gen­er­a­tion bio­fu­els made from food crops (grains or sug­ar) are not rec­om­mend­ed for use in sus­tain­abil­i­ty projects. They com­pete with the food indus­try and can have a neg­a­tive envi­ron­men­tal over­all when tak­ing into account the life cycle. How­ev­er, there is a place for sec­ond-gen­er­a­tion bio­fu­els made from for­est residues, straw and biosourced waste. 

Jean-Philippe Héraud says that “because France is a very green coun­try, the resources for these bio­fu­els exist. A major dif­fi­cul­ty, how­ev­er, comes from the mix of where the resources are locat­ed – as opposed to oil that arrives in France in only three ports. Hence, we need to know how to col­lect these wide­spread deposits and regroup the bio­mass so we can bet­ter trans­port it, whilst adapt­ing to sea­son­al vari­a­tions, too.” 

Hence, IFPEN has car­ried out research into the indi­rect ther­mo­chem­i­cal con­ver­sion of bio­mass. The bio­mass is gasi­fied to obtain a syn­thet­ic gas; a mix­ture of car­bon monox­ide (CO) and hydro­gen (H2). After purifi­ca­tion, this gas is trans­formed into a syn­thet­ic paraf­fin using a process known as Fis­ch­er Trop­sch. “We have demon­strat­ed the fea­si­bil­i­ty of the BioT­fu­eL project, now we have to turn it into an indus­tri­al real­i­ty, » explains Jean-Philippe Héraud. 

The cost of this bio­fu­el is high­er than that of kerosone made from fos­sil fuels, “between 1.5 and 2 times high­er than equiv­a­lent fos­sil fuels before tax,” says Jean-Phillipe. “This extra cost varies accord­ing to the price of the raw mate­r­i­al, the loca­tion and inte­gra­tion with sites under­go­ing con­ver­sion.” And he says that this is their chal­lenge, “it seems dif­fi­cult to make air­line cus­tomers bear the bur­den with­out the risk of them turn­ing away from air transport.”

Fuel rep­re­sents about 25–30% of the price of a flight. “For a round trip from Paris to New York on an air­craft using 1% bio­fu­el, the price of the tick­et would increase by $5 per pas­sen­ger,” explains Paul Mannes, direc­tor of avi­a­tion at Total. “For a flight using 10% bio­fu­el, it’s ten times more, or about $50. So yes, the price could be a deterrent.”

It goes with­out say­ing that air­lines will not raise tick­et prices if they are not forced to do so. “The French gov­ern­ment is work­ing with the nation­al com­pa­nies con­cerned, such as Total, Air­bus and Safran, to see how the SAF (Sus­tain­able avi­a­tion fuel) indus­try could be devel­oped, and the nec­es­sary leg­is­la­tion,” he says. For the moment, the pro­jet des loi de finance includes an oblig­a­tion to use 1% bio­fu­els in 2022, 2% in 2025 and 5% by 2030, in order to keep pace with the increase in demand and the avail­abil­i­ty of SAF on the market.

Syn­thet­ic fuels

French Ener­gy com­pa­ny, Engie, has launched a bio­mass pyro­gasi­fi­ca­tion project called Gaya. Wood is heat­ed to high tem­per­a­tures with very lit­tle oxy­gen, con­vert­ing it into a mix­ture of gas­es: hydro­gen, CO2, methane, car­bon monox­ide, which are then reor­gan­ised to form fuel. But here again, the price is high.

The oth­er way to make fuel from non-oil-sourced sources are syn­thet­ic fuels derived from hydro­gen, which itself comes from elec­tric­i­ty. The prin­ci­ple: com­bine hydro­gen with CO2 to obtain syn­thet­ic methane, the pre­cur­sor of oth­er fuels, called ekerosene. “We know how to pro­duce this ekerosene,” says Samuel Says­set, chief tech­ni­cal advi­sor at Engie. “South Africa, in par­tic­u­lar, devel­oped this know-how dur­ing Apartheid when there was an embar­go on petro­le­um prod­ucts. The main con­cern now is the eco­nom­ics of the sec­tor: ekerosene is more expensive.”

Is there elec­tric­i­ty in the air ?

Apart from hydro­gen and bio­fu­els, “clean” ener­gy sources are not suit­ed to the dras­tic con­straints of avi­a­tion. While Bertrand Piccard’s solar pow­ered plane, Solar Impulse, did suc­ceed in going around the world in 2015–2016, his design is unsuit­ed to com­mer­cial air­craft. As for bat­tery-pow­ered elec­tric planes, this con­cept cur­rent­ly seems lim­it­ed to small air­craft trav­el­ling short dis­tances, such as the e‑Caravan 1, a retro­fit­ted elec­tric ver­sion of a Cess­na air­craft. Bat­ter­ies are still the main lim­it­ing fac­tor. “The ener­gy den­si­ty of a bat­tery is 200Wh/kg, ver­sus 12,000Wh/kg for kerosene,” Jérôme Boni­ni, research and tech­nol­o­gy direc­tor at Safran, states. “Instead, we are work­ing on hybrid designs, to give a boost to a com­bus­tion engine at cer­tain stages of flight.” But this boost would only rep­re­sent a small per­cent­age of the plane’s ener­gy, with the vast major­i­ty being pro­vid­ed by jet fuel.

1https://​www​.avi​a​tion​to​day​.com/​2​0​2​0​/​0​5​/​2​9​/​h​i​s​t​o​r​i​c​-​f​l​i​g​h​t​-​o​f​-​m​a​g​n​i​x​s​-​e​c​a​r​a​v​a​n​-​s​h​o​w​c​a​s​e​s​-​m​a​t​u​r​i​t​y​-​o​f​-​e​l​e​c​t​r​i​c​-​a​v​i​a​tion/