Thursday 21 July 2022

All-in-one solar tower produces jet fuel from CO2, water and sunlight!


Taking carbon dioxide, water and sunlight as its only inputs, this solar thermal tower in Spain produces carbon-neutral, sustainable versions of diesel and jet fuel. Built and tested by researchers at ETH Zurich, it's a promising clean fuel project.

Why do we need sustainable aviation fuel (SAF)?

Fossil fuels can be replaced with batteries or hydrogen in cars and trucks – but aircraft are trickier. With more than 25,000 commercial airliners in service today, and service lifetimes around 25 years, airlines are looking to carbon-neutral fuels to bring down their emissions. It's a transitional step, but an important one until clean aviation tech is ready and the entire global fleet can be converted to something else.

Carbon-neutral fuels are drop-in replacements for today's kerosene Jet-A fuel; they mix in with regular fuel and get burned in jet engines as per normal, producing the normal amount of carbon emissions. The difference is that rather than pulling that carbon straight out of the ground, carbon-neutral fuels grab CO2 from elsewhere; it'll still end up in the atmosphere, but at least it does some useful work before it gets there, and every gallon burned is a gallon of conventional fuel that wasn't burned.

How is SAF currently made?

There are a lot of ways to make carbon-neutral fuels – and not all of those are acceptable for other reasons. Biofuels grown from specially raised corn crops, for example, create their own emissions, from fertilizers and farm equipment, and they use land that could otherwise be producing food. Chopping down forests and using the wood as biomass is also out, for reasons that should be obvious, but the fact that there are rules in place around this suggests that even in the sustainability game, there are still bad-faith operators.

Landfill waste-to-jet-fuel plants are popping up here and there, taking municipal garbage or old cooking oil and using that as a feedstock to create syngas, which can be refined into synthetic fuels. But the pyrolysis process usually involved requires a lot of energy – either dirty energy or clean energy that could be used elsewhere – and the feedstock is so wildly random that the resulting fuels sometimes need an extra, energy-intensive cleaning step before they're ready to go save the planet in a Dreamliner.

Another way is to capture carbon directly from other emissions sources, and convert that into fuel. This can be done by using green electricity to power an electrolyzer, then mixing the resulting hydrogen with carbon monoxide to create syngas, which can then be refined into fuels – but there are energy losses at each of these steps.

Which brings us to this new, much simpler design out of ETH Zurich, which has been built and tested at the IMDEA Energy Institute in Spain.

The 50-kW pilot reactor, installed in Spain, uses heat from a concentrating solar tower to drive a thermochemical redox cycle

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