Manufacturing carbon-neutralized jet fuel with integrated solar tower

Researchers have designed a fuel production system that uses water, carbon dioxide and sunlight to produce aviation fuel. They have implemented the system on site, and the design published in Joule magazine on July 20 can help the aviation industry achieve carbon neutrality.

"We are the first person to demonstrate the whole thermochemical process chain from water and carbon dioxide to kerosene in a fully integrated solar tower system," said Aldo Steinfeld, a professor at the Federal Institute of Technology in Zurich and the corresponding author of the paper. In the past, most attempts to use solar energy to produce aviation fuel were carried out in the laboratory.

The aviation industry accounts for about 5% of global anthropogenic emissions resulting in climate change. It relies heavily on kerosene or aviation fuel, which is a liquid hydrocarbon fuel usually extracted from crude oil. At present, there is no clean alternative energy to power long-distance commercial flights worldwide.

"With our solar technology, we have proved that we can produce synthetic kerosene from water and carbon dioxide, rather than extracting kerosene from fossil fuels. The amount of carbon dioxide emitted during the combustion of jet engine kerosene is equivalent to the amount of carbon dioxide consumed during the production of solar power plants," Stanfield said. "This makes fuel carbon neutral, especially if we capture carbon dioxide directly from the air as a component, we hope to achieve this in the near future."

As part of the EU's "from the sun to the liquid" project, Stanfield and his colleagues have developed a system to use solar energy to produce alternative fuels, which are synthetic substitutes for fossil fuels such as kerosene and diesel. Stanfield said that the kerosene produced by solar energy is fully compatible with the existing aviation infrastructure, which is used for fuel storage, distribution and ultimately use in jet engines. It can also be mixed with fossil kerosene, he added.

In 2017, the team began to expand the design scale and built a solar fuel production plant at IMDEA Energy Research Institute in Spain. The power station consists of 169 solar tracking reflectors, which redirect and concentrate solar radiation into the solar reactor installed on the top of the tower. Then the concentrated solar energy drives the redox (redox) reaction cycle in the solar reactor, which contains a porous structure made of cerium dioxide. Cerium will not be consumed, but can be reused. It converts water and carbon dioxide injected into the reactor into synthetic gas, which is a special mixture of hydrogen and carbon monoxide. Then, the syngas is sent to the gas-liquid converter, where it is finally processed into liquid hydrocarbon fuel, including kerosene and diesel.

Stanfield said, "The operation of the solar tower fuel plant is related to the industrial implementation, which has set a technical milestone for the production of sustainable aviation fuel."

During the nine-day operation of the plant reported in the paper, the energy efficiency of the solar reactor (the part of the energy content converted from solar energy input into syngas production) is about 4%. Stanfield said that his team is focusing on improving the design and increasing the efficiency to more than 15%. For example, they are exploring ways to optimize the structure of cerium dioxide to absorb solar radiation, and developing methods to recover the heat released during the redox cycle. This work has been supported by the Swiss National Secretariat for Education, Research and Innovation and the EU Horizon 2020 Research and Innovation Plan.

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