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Straw essential part of project SkyClean

New technology can halve agriculture's climate impact and introduce climate neutral air travel

It sounds almost too good to be true, but experts from Technical University of Denmark and Aarhus University estimate that agriculture can reduce its greenhouse gas emissions by 50 per cent using the new SkyClean technology. At the same time, we can introduce climate neutral aviation fuel. It only requires straw, slurry, offshore wind power and a 400 million DKK investment from the Danish politicians to initiate the necessary research steps to complete the technology and use it.

Air travel and agriculture are often highlighted in the climate debate as some of the greatest culprits. But the demand for food increases as the world’s population grows, and although climate shame has become a concept of our time, air transport is probably here to stay.
- If we want to fight the climate crisis and ensure that the global warming does not exceed 1.5 °C, we must find completely new solutions. One of the important solutions to which agriculture can contribute is to transform straw and slurry into climate neutral aviation fuel and at the same time halve agriculture’s climate impact. The Danish politicians’ actions must match their climate ambitions, and we need them to find the funds for research and development of the project now, says Thor Gunnar Kofoed, Deputy Chairman of the Danish Agriculture & Food Council. 

The SkyClean technology is developed by Henrik Stiesdal, CEO of Stiesdal A/S. The technology uses straw and slurry from agriculture to produce climate neutral aviation fuel and to bind carbon in the soil. 
- In the agricultural sector we already produce green energy. Soon we can also help the transport sector. We are talking about lifting the positive climate effects to unprecedented levels when we deal with circular bioeconomy in the food sector. This can be huge if the politicians will join in, says Thor Gunnar Kofoed.

Plants consist largely of carbon that they absorb in the form of CO2 from the atmosphere. As the plants grow in the spring, the CO2 content of the atmosphere decreases because part of the carbon is fixed in the plants. When the plants shed their leaves or die in the autumn, the plant material decomposes and the carbon is returned to the atmosphere as CO2. The same happens in agriculture when the straw is plowed down, and when biogas extracted from slurry is burned in engines or in gas furnaces.

With the new SkyClean technology, we can avoid that the total amount of carbon from agricultural surplus straw and residual fibers from biogas plants return to the atmosphere as CO2. Instead, part of the carbon is converted to aviation fuel while the rest is permanently bound in the form of bio coal which contributes to the carbon content in the agricultural soil instead of decomposing.
- The straw and residual fibers are converted in a pyrolysis process where oil and gas are produced from about 50 per cent of the carbon. We have already come a long way with the development of the pyrolysis process and trials with bio coal production at Technical University of Denmark’s campus at Risø, says Jesper Ahrenfeldt from the Department of Chemical Engineering.

To obtain the correct chemical composition for aviation fuel, the oil and gas from the pyrolysis process need a supplement of hydrogen from green offshore wind power.

The residual product from the pyrolysis becomes a so-called bio coal that can be spread on the farmers' fields. Bio coal can be used to fertilize and improve the agricultural soil while carbon is stored in the soil, thus reducing the agricultural climate impact.

- If the straw is simply plowed down as we do today, most of the carbon in the straw is converted to CO2 within a few years. Bio coal on the other hand is very stable and is only scantly converted into CO2 over many, many years, says Anne Winding from the Department of Environmental Science at Aarhus University.

The 50 per cent of the plants' carbon that becomes aviation fuel is returned to the atmosphere as CO2 when the fuel is burned in the aircraft engine. But the other 50 per cent of the carbon is permanently bound in the bio coal and is not returned to the atmosphere. The net result is that the more SkyClean fuel we produce, the more CO2 we absorb from the atmosphere.

According to Technical University of Denmark, this process enables the agricultural sector to halve its own climate impact and to provide enough climate neutral aviation fuel to supply the entire domestic air traffic in Denmark.
- Besides doing something good for the climate, I also hope that with SkyClean we can create a new position of strength for Denmark. There is no doubt that if there is a political will to provide the necessary funds, it could potentially become a new, important business venture for Danish industry, says Henrik Stiesdal.