Together with the Centre for Solar Energy and Hydrogen Research Baden Württemberg (ZSW) and ela Industriegas GmbH, atmosfair is developing a DAC system that captures up to 800 tonnes of CO2 per year. The project is called Air2Fuel and is subsidised by the German government. The partners have joined forces to show that a technology developed by ZSW also works beyond the research scale. The research plant for scaling up with amine-based scrubbing processes has already been in continuous operation at ZSW in Stuttgart for several years. The large plant, in which 100kg of CO2 are captured per hour, is being built in Werlte in Lower Saxony. We want to produce methane from the captured CO2 and green hydrogen and feed it into the natural gas grid, where it will replace fossil natural gas. In addition to the technical potential, we will also demonstrate the market potential of this technology and prepare for further scaling.

We are involved as a partner in further research projects with various universities and institutes. In addition to the development of further DAC processes, these projects also focus on the issue of long-term storage and the regulatory framework required for this. We are also cooperating with start-ups that are currently developing further DAC processes based on various approaches and implementing them for the first time in terms of process technology. We want to drive forward the technical solutions so that they are available in sufficient quantities at a later date and CO2 storage can become less dependent on biomass.

Backgroundinformation DAC

In the Direct Air Capture process (DAC), air is passed over a CO2-absorbing material called a sorbent. The sorbent becomes saturated and separates the CO2 from the air. The challenge here lies in the low concentration of CO2 (400ppm = 0.04 vol%) in the air. Accordingly, large quantities of air have to be channelled through the absorbent material to capture the CO2. The pumping power required for this is a driver of the high electrical energy requirement of the DAC technology. In a second step, the CO2 bound to the sorbent is dissolved again. Depending on the process, separation takes place either by changing the temperature, electrical charge or pressure. Due to the strong bond between the sorbent and CO2, this regeneration step is also very energy-intensive. A look at the state of the art of DAC processes also shows that currently only heat and thermal pressure swing-based processes have the necessary technical maturity. A distinction is made between high-temperature and low-temperature processes. In high-temperature processes, the sorbent is a highly concentrated alkaline solution that is regenerated by the formation of lime. At high temperatures (900°C), the CO2 is then released from the lime and can be separated. Low-temperature processes use a solid absorber material with amino groups or an aqueous amine solution to bind the CO2 from the air. These release the CO2 at lower temperatures (80-480°C). The total energy requirement of DAC processes is around 2.5 MWh per tonne of CO2. That is a lot. To put it in perspective: If you burn oil to generate energy (e.g. electricity), this electricity is not enough to capture the CO2 produced during oil combustion by DAC, not to mention the electricity that should remain for actual use. Avoidance therefore remains the ideal solution, DAC capture is sensible and necessary for emissions that are unavoidable or difficult to avoid, as long as the energy for this comes from renewables. New processes based on charge exchange cycles could enable significantly lower-energy CO2 capture in the future. Here, the CO2 binds to an absorber electrode depending on its electrical charge state and is released again at a later point in time by changing its polarisation.

Adeline Schreiner
Project Analyst
Environmental Scientist