Direct Air Capture - assessing Energy, Cost and Kinetic constraints based on outlined boundary conditions

Direct Air Capture (DAC) is a carbon dioxide (CO₂) removal (CDR) technology focusing on removal from ambient air in response to mitigating climate change. Our previous research has compared DAC technologies with other CO₂extraction technologies and shown that DAC systems are heavily dependent on factors such as the type of sorbent material used, cost of separation equipment and local weather/geographical conditions. The size and porosity of resin particles has an important role in determining the kinetics of DAC. Humidity swing sorbents can reduce energy costs, but introduce additional location constraints. Passive designs eliminate the capital cost and energy cost of pushing air through sorbent beds, but require innovative designs for air contactors. The kinetics of DAC is also influenced by ambient conditions, including wind speeds, temperature and humidity. These parameters affect mass transfer coefficients in the adsorption process. An energy-based, comparative study for CO₂separation from air versus flue gas from natural gas combined cycle and pulverized coal combustion plants can point to early applications for DAC. In this paper, we try to delineate the possibilities of using DAC systems for applications requiring varying CO₂purity streams based on energy, cost and kinetic considerations. In general higher CO₂concentrations in the input stream result in lower energy costs for separation. However, the ability to locate CO₂capture from air at the point of use, makes it possible to lower the purity and pressure of the captured CO₂. Under those conditions it is possible to reach parity in energy consumption between capture and a remote point source and local capture from air. Several technologies can be explored for coupling CO₂utilization and DAC systems operating on feedstock with dilute CO₂streams. Our analysis suggests technologies such as enhanced oil recovery and microalgae cultivation seem to be most beneficial near-term applications for utilizing CO₂ from direct air capture.