Generating Fuel from Air-Conditioning

Researchers propose using air-conditioning and ventilation systems for decentralized production of carbon-neutral synthetic fuels.

To prevent the disastrous effects of global climate change, man-made greenhouse gas emissions must be reduced to “zero” over the next three decades. This is clear from the current special report of the Intergovernmental Panel on Climate Change (IPCC). The necessary transformation poses a huge challenge to the global community: entire sectors such as power generation, mobility, and building management must be redesigned. In a future climate-friendly energy system, synthetic energy sources could represent an essential building block.

“If we use renewable wind and solar power as well as carbon dioxide directly from the ambient air to produce fuels, large amounts of greenhouse gas emissions can be avoided,” says Professor Roland Dittmeyer from the Karlsruhe Institute of Technology (KIT) in Germany.

Due to the low CO2 concentration in ambient air–today, the proportion is 0.038 %–large quantities of air have to be treated in large filter systems in order to produce significant quantities of synthetic energy sources. A research team led by Professor Dittmeyer and Professor Geoffrey Ozin from the University of Toronto (UoT) in Canada now proposes to decentralize the future production of synthetic energy sources and to link them to existing ventilation and air conditioning systems in buildings. According to Professor Dittmeyer, the necessary technologies are essentially available, and the thermal and material integration of the individual process stages is expected to enable a high level of carbon utilization and a high energy efficiency.

“We want to use the synergies between ventilation and air-conditioning technology on the one hand and energy and heating technology on the other, to reduce the costs and energy losses in synthesis. In addition, ‘crowd oil’ could mobilize many new actors for the energy transition,” says Dittmeyer. “Private photovoltaic systems have shown how well this can work. However, the conversion of CO2 would require large amounts of electrical power to produce hydrogen or synthesis gas. This electricity must be CO2-free, i.e. it must not come from fossil sources. An accelerated expansion of renewable power generation, including through building-integrated photovoltaics, is therefore necessary.”

The scientists use quantitative analyses of office buildings, supermarkets, and energy-saving houses to demonstrate the CO2 saving potential of their vision of decentralized conversion plants coupled to building infrastructure. They reckon that a significant proportion of the fossil fuels used for mobility in Germany could be replaced by “crowd oil”. For example, according to the team’s calculations the amount of CO2 that could potentially be captured in the ventilation systems of the approximately 25,000 supermarkets of Germany’s three largest food retailers alone would be sufficient to cover about 30 % of Germany’s kerosene demand or about 8 % of its diesel demand. In addition, the energy sources produced could be used in the chemical industry as universal synthesis building blocks.

The team expects an energy efficiency–the proportion of electrical energy used that can be converted into chemical energy– of around 50 to 60%. In addition, they expect carbon efficiency–the proportion of spent carbon atoms found in the fuel produced–to range from around 90 to almost 100%. In order to confirm these simulation results, the researchers and project partners are currently building up the fully integrated process at KIT, with a planned CO2 turnover of 1.25 kg/h.

At the same time, however, the scientists have found that the proposed plan would not be able to fully meet today’s demand for crude oil products. Reducing the demand for liquid fuels, for example, through new mobility concepts and the expansion of local public transport remains a necessity. Although the components of the proposed technology, such as the plants for CO2 capture and the synthesis of energy sources, are already commercially available in some cases, the researchers believe that major research and development efforts, as well as an adaptation of the legal and social framework conditions are still required in order to put this vision into practice.

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