AAU researchers develop climate-friendly aircraft fuel



Aviation accounts for approx. 3% of Europe’s total greenhouse gas emissions.

But emissions are increasing, and flying to and from one of the world’s great destinations even once can represent up to half of the annual footprint of an average European.

Therefore, doing something about CO2 emissions from aircraft and other heavy machinery will not be insignificant for the future climate.

Aalborg University, in collaboration with Steeper Energy ApS among others, are now taking steps to build a new plant to convert sewage sludge, wood residue and organic household waste into crude oil.

- “The difference between the fuel used today and the one we make is simply that it is sustainable. It can go straight into the aeroplane, truck or ship”, says Lasse Rosendahl, Professor of Thermal Energy Technology at Aalborg University and a researcher in advanced biofuels.

Technology takes time

The system works by exposing the wet organic material to heat and pressure and thus mimicking the processes known from the formation of oil in nature. Nature takes millions of years, but under artificial conditions, oil can be made in half an hour and then refined into diesel, petrol or jet fuel at a refinery.

The technology is called HTL – hydrothermal liquefaction – and it has already been used at a test centre at Aalborg University for several years. However, it takes a long time to bring technology from the laboratory into reality, which is why it will only be ready for larger scale operations in coming years.

Biomass is used inappropriately today

The new HTL plant is expected to be ready in 2024, and depending on the material received, it will be able to deliver a CO2 reduction of 80% compared to fossil fuels.

The artificial crude oil is particularly interesting in relation to heavy transport such as planes, trucks or ships because there is currently no other alternative.

- “It is possible to mix organic materials into fossil fuels, but they only represent a small proportion and they have a number of adverse effects”, Torben Chrintz, scientific adviser at the green think tank Concito, explains.

We use a lot of biomass in our energy sector today, but we’re really using it in the wrong way. We need to use the biomass where there are no other alternatives.

Electric planes are not an alternative in the short term

He mentions a requirement within the EU that a certain amount – around 5% – of the diesel must be plant oil.

- “Unfortunately, this has had the effect that plant oil production has skyrocketed, and thus huge areas of forest are being cut down in Malaysia and Indonesia. If you could replace that 5% with sustainable bio oil, you could prevent this. That would be huge”, Torben Chrintz says.

Electric planes are not an alternative in the short term either, Lasse Rosendahl says.

- “A lot of work has been done on electric planes, but if we have a time frame in which a transition must move relatively quickly, then to the best of my knowledge, electric planes will not be delivering on that front”, he says.

There is huge potential

Exactly how great the potential of HTL plants will be is difficult to answer. Much depends on how organic matter will be sorted in the future, and how large the food chain becomes. But Lasse Rosendahl believes it can make a difference.

- “It isn’t limited to the approx. 3,000 barrels you might produce from sludge and waste. In principle, residual fractions from agriculture, industry and all sorts of other things can be used in the process. So, there is great potential”, he says.

Furthermore, the technology can also be exported to other countries.

- “We are on the absolute front line internationally, but it is also happening all around us”, Lasse Rosendahl says.

The project also involves the energy company OK and a number of local partners such as Aalborg Municipality and Aalborg Forsyning.

Foto: Henrik Egholm, Steeper Energy

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