DACCS, Direct Air Capture and Storage, is a carbon dioxide removal technology that extracts CO2 from the atmosphere through chemical processes, which is then stored in geological formations or in materials.
The CO2 capturing process:
Today’s leading approaches capture CO2 by passing ambient air over either solid sorbent materials such as zeolites or metal-organic frameworks (substances or materials that can absorb or take in other substances, such as liquids or gases) or liquid solvents (substances that are in a liquid state and are used to dissolve other substances) such as aqueous amine solutions, which react selectively with the CO2. These materials have a strong attraction to the carbon, so, put simply, they pull it out of the air and hold onto it. After the CO2 is captured from the atmosphere it is removed from the solvent or sorbent, typically by heating, enabling it to be re-used. The next step is to concentrate the CO2, making it easier to separate and store. This procedure also helps reduce the energy required for subsequent processes. In addition to removing CO2, models have shown that DACCS may be able to remove some quantity of other air pollutants like particulate matter (PM), nitrogen oxides (NOx) and sulphur oxides (SOx).
The CO2 storing process:
To realize carbon removal, a direct air capture facility must be paired with CO2 storage, such as injection deep underground into specific geological formations, or into products with storage opportunities that prevent the CO2 from re-entering the atmosphere, thereby resulting in net negative emissions.
Most CO2 desorption processes (the general term for the release or removal of a substance) require high temperatures and hence heat sources. The type of thermal energy used for the process has a large impact on the electricity requirements of a given DACC application. So far, DAC companies have been using a variety of sources such as geothermal energy, natural gas, or photovoltaic electricity to cover their energy needs. Most direct air capture techniques are energy-intensive and expensive, although costs are expected to fall with increasing carbon removal volumes.
Potential and scalability:
DACCS is a novel technology that was developed in the last 15 years specifically for the purpose of removing carbon dioxide from the atmosphere. Investment in R&D and early deployments have been robust. There are currently more than a dozen direct air capture plants in worldwide. DACCS has a potential for broad deployment given that there are no specific geographical conditions required for its installation. This flexibility allows for strategic placement to optimize CO₂ capture and reduce transportation costs. Additionally, direct air capture does not rely on local natural resources and hence doesn’t add any pressure to local ecosystems. On the other hand, DACCS doesn’t have the co-benefits that some other approaches do, such as producing soil amendments that improve soil health and crop yields.
DACCS is projected to capture more than 93 million tonnes of CO2 a year by 2030 and 1.08 gigatonnes (Gt) of CO2 annually by 2050. The challenge for DACCS deployment currently remains the high energy requirements and high deployment costs. Projections based on current technology assumptions estimate an energy requirement for DAC processes, equivalent to around one-fifth of a U.S. household’s annual natural gas consumption, which would add significant demand to our current energy system.
This is a real-world problem: To make the technology work on a larger scale while continuing to use renewable sources to power it, a large amount of energy would need to be made available. It is estimated that with the currently available DACCS technologies, gigatonne CDR deployment would require 50 EJ/year (over 10,000 Terrawatt hour) of electricity by 2100, equivalent to 10-15% of the projected global energy production for 2100.
However, we are currently not even producing enough renewable energy to meet existing demands. New research and development and continued advancements in materials, energy requirements, and engineering will be key to unlocking the scaling potential of DACCS.