Direct air capture (DAC) is a technology for separating and concentrating carbon dioxide from ambient air. DAC in contrast to CO2 capture from point sources can compensate emissions from non-point sources such as transportation, aviation, shipping, land-use and many more. Separated CO2 from air can be stored or used for production of renewable fuels and chemicals independent of locations of point sources of CO2. Other applications of captured CO2 can be enrichment of air for algae or greenhouse cultivation only to mention a few of them.
While DAC technology has long been adopted in life support systems in submarines and spacecraft and for terrestrial safety rooms, it was in 1999 when Lackner et. al.[1] first proposed the separation of CO2 from the atmosphere as an approach to climate change mitigation. Nevertheless, the commercial application of DAC has remained limited so far. However, there are a few companies that are engaged in DAC design and development efforts. Most companies use reversible adsorption/desorption processes in their DAC technology as these processes are very selective for CO2 separation and comparably easy to operate.
The proposers of this research project are convinced that DAC is a necessary contribution to keep the CO2 level in such an area that the 1.5 °C target according to the Paris Agreement can be reached at all. Of course, besides DAC also CO2 separation from point sources as well as a drastic reduction of fossil fuel utilization in many areas of our life are necessary prerequisites for this ambitious goal.
Like any technology, DAC has its challenges too. Discussed in depth afterwards, they are broadly: humidity, changing weather conditions and high energy requirements. One major drawback of DAC is the relatively low concentration of CO2 in ambient air which reduces the separation efficiency compared to point source separation.
A specific part of the research project is dedicated to exploring the possibility of solving most of these problems by retrofitting DAC technology to commercial HVAC systems. HVAC systems could be the source of air that is less diluted in CO2 than ambient air, as on an average hundreds of occupants reside in commercial buildings and CO2 concentrations of up to 1000 ppm can be expected. Furthermore, in contrast to ambient air being affected changing weather conditions, air released by HVAC’s is mostly consistent in temperature and conditions. Finally, DAC blower energy requirements could be reduced by using the same air removed by the HVAC blower.
In the first part, the research project aims to develop and construct a test unit that[JF1] will be primarily designed for laboratory use. The installation adaptations/requirements as well as relevant performance indicators will be discussed in the first month of the project (M0). The overall aim is to prove the general feasibility of a combined HVAC system with integrated CO2 separation.
In the second part of the project which requires a project extension to 3 years, development and utilization of hydrophobic adsorbents as well as an optimized process set-up with advanced heat integration shall enable an optimized DAC unit that is 20% more efficient than current standards.
