Direct Air Carbon Capture and Storage (“DACCS”)

Direct Air Capture (“DAC”) is an approach to carbon removal in which mechanical systems capture Carbon Dioxide directly from the atmosphere and was first proposed by Lackner, Et al. in 1999. [1]

There are a variety of technologies for Direct Air Capture. Some use liquid chemicals that bind with CO₂ in the air and release the CO₂ when heated. Others use solid filter-type media that chemically adsorbs the CO₂ when contact is made and then use changes in pressure or humidity to release CO₂ when desired. Another type uses an electrical charge to capture the CO₂ and then releases it when the charge is reversed in polarity. Opportunities exist for new materials that can capture CO₂ from ultra-dilute gas streams and operate under all humidity levels to play a role in emerging DAC technologies.[2]

DAC is related to the more common “site-specific” carbon removal that has been in industrial use for many years – namely in industries such as power generation, cement processing, chemical production, etc. This Point Source Capture (PSC) is a well-proven technology that has gone far in drastically reducing or eliminating carbon emissions from some of the most notorious historic emitters.

Direct Air Carbon Capture produces a stream of pure CO₂ that can be then compressed and injected into geological storage like certain spent deep-shaft oil wells or used to make long-lasting products such as cement. Other uses include using the captured CO₂ in greenhouses to enhance plant growth or as a primary component in the manufacture of synthetic fuels. Synthetic fuels made with Direct Air Carbon Capture (“Air-to-Fuels”) contribute to mitigating climate change by displacing an equal amount of fossil fuels. These, however, are a form of “Carbon Capture and Use” or “Carbon Recycling” because the CO₂ returns to the atmosphere quickly after the products are consumed.[3]

This captured Carbon Dioxide can be used in other ways as well. For instance, it can be used to produce more oil and, surprisingly, it may actually reduce the total amount of CO₂ released into the atmosphere from burning crude oil. Called “Carbon Dioxide Enhanced Oil Recovery”, the process involves capturing CO₂ emissions then transporting it to nearly spent oil fields where production has peaked. By injecting this captured CO₂ into these existing oil wells, hard-to-get crude oil can become pressurized and/or thinned by the CO₂ and production can be revived. As counterintuitive as it may seem, this may actually be beneficial for the climate because more Carbon Dioxide is often needed to be pumped into the wells and thereby sequestered than is emitted from the oil’s later use.[4]

CO2 Removal

Apart from being targeted to a specific emission source, DAC aims to remove excess anthropogenic Carbon Dioxide from our atmosphere wherever it might have originated. Moreover, since Carbon Dioxide concentrations are nearly equal at every point on the globe, DAC infrastructure can be widely deployed and remain similarly effective. This uniform disbursement comes at a cost, however, in that atmospheric Carbon Dioxide is quite dilute and has an average atmospheric concentration of only .04%. With this level of concentration, it has, historically, been a significant challenge to economically remove CO₂ at scale or even that approaching scale.

[1] (Lackner, Ziock, & Grimes, 1999)
[2] (Chemical Reviews, 2016)
[3] (The American University, Institute for Carbon Removal Law and Policy, 2021)
[4] (The American University, Institute for Carbon Removal Law and Policy, 2021)