Direct Air Capture

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In this report

Direct air capture is a technology to capture CO2 from the atmosphere. The CO2 can be permanently stored in deep geological formations or used in the production of fuels, chemicals, building materials and other products containing CO2. When CO2 is geologically stored, it is permanently removed from the atmosphere, resulting in negative emissions. There are currently 15 direct air capture plants operating worldwide, capturing more than 9 000 tCO2/year, with a 1 MtCO2/year capture plant in advanced development in the United States. In the SDS, direct air capture is scaled up to capture almost 10 MtCO2/year by 2030. This is within reach but will require several more large-scale demonstrations to refine the technology and reduce capture costs.

CO2 capture by direct air capture in the Sustainable Development Scenario, 2010-2030

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Tracking progress

Direct air capture technologies extract CO2 directly from the atmosphere. The CO2 can be permanently stored in deep geological formations (thereby achieving negative emissions), or it can be used in food processing, for example, or combined with hydrogen to produce synthetic fuels.

Today, two technology approaches are being used to capture CO2 from the air. Liquid systems pass air through chemical solutions (e.g. a hydroxide solution), which removes the CO2 while returning the rest of the air to the environment.

Solid direct air capture technology makes use of solid sorbent filters that chemically bind with CO2. When the filters are heated, they release the concentrated CO2, which can be captured for storage or use.

Most large-scale opportunities to use the captured CO2 would result in its re-release into the atmosphere, such as when the synthetic fuel is burned. This would not create negative emissions but could still generate climate benefits, for example if synthetic fuels replace conventional fossil fuels.

In a transition to net-zero emissions, the CO2 used to produce synthetic fuels would increasingly need to be captured from bioenergy sources or from the atmosphere to avoid delayed emissions from fossil-based CO2 when the fuel is combusted.

Direct air capture is one of few technology options available to remove CO2 from the atmosphere. Carbon removal is expected to play a key role in the transition to a net-zero energy system in which the amount of CO2 released into the atmosphere is equivalent to the amount being removed. Because certain sectors such as aviation and heavy industry are difficult to decarbonise, carbon removal technologies can offset these emissions and support a faster transition.

Other carbon removal options include nature-based solutions (e.g. afforestation, reforestation, restoration of costal and marine habitats), measures to enhance naturally occurring processes (e.g. land management approaches to increase the carbon content in soil, biochar) and other technology-based solutions such as bioenergy with carbon capture and storage (BECCS).

Some benefits of direct air capture as a carbon removal option include its limited land and water footprint and the possibility of locating plants close to suitable storage or utilisation sites, eliminating the need for long-distance CO2 transport.

The choice of location also needs to be based on the energy source needed to run the plant, which would help determine whether the system is carbon-negative, as well as the cost of the energy. For instance, both solid and liquid capture technologies could be fuelled by renewable energy sources (such as geothermal, solar PV and wind), while solid direct air capture could be powered by recovering waste heat, which would reduce lifecycle emissions considerably.

The CO2 in the atmosphere is much more dilute than, for example, the flue gas from a power station or a cement plant. This contributes to the higher energy needs and costs for direct air capture relative to other CO2 capture technologies and applications.

Costs and energy needs vary according to the type of technology (solid or liquid) and whether the captured CO2 is going to be geologically stored or used immediately at low pressure. In fact, CO2 needs to be compressed at a very high pressure in order to be injected into geological formations. This step increases both the capital cost of the plant (due to the requirement for additional equipment such as a compressor) and the operating costs (to run the compressor). 

Energy needs for DAC technologies for CO2 use and storage

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As the technology has yet to be demonstrated at large scale, the future cost of direct air capture is uncertain. Capture cost estimates reported in the literature are wide, typically ranging anywhere from USD 100/t to USD 1 000/t.1

Carbon Engineering recently claimed that capture costs of USD 94/t to USD 232/t were achievable depending on financial assumptions, energy costs and specific plant configuration.2

Fifteen direct air capture plants are currently operational in Europe, the United States and Canada. Most of these plants are small and sell the captured CO2 for use – for carbonating drinks, for example.

However, the first large-scale direct air capture plant is now being developed in the United States by a Carbon Engineering and Occidental Petroleum partnership. The plant will capture up to 1 MtCO2 each year for use in enhanced oil recovery and could become operational as early as 2023.

A plant of this size would be eligible for the 45Q tax credit (providing USD 35 per tonne of CO2 used in enhanced oil recovery and USD 50 per tonne for CO2 storage). Moreover, it could also be eligible for the California Low Carbon Fuel credit if the CO2 is used to produce low-carbon transportation fuels. These credits traded at around USD 180/tCO2 in 2019.

In Iceland, the CarbFix project is currently capturing CO2 from the atmosphere and blending it with CO2 captured from geothermal fluids for injection and underground storage in basalt rock formations. This is the first operating application of this type, turning CO2 into rocks within a couple of years through mineralisation.

Carbon removal technologies such as direct air capture are not an alternative to cutting emissions or an excuse for delayed action, but they can be an important part of the suite of technology options used to achieve climate goals.

For this reason, direct air capture needs to be demonstrated at scale, sooner rather than later, to reduce uncertainties regarding future deployment potential and costs, and to ensure that these technologies can be available to support the transition to net-zero emissions and beyond.

In the near term, large-scale demonstration of direct air capture technologies will require targeted government support, including through grants, tax credits and public procurement of CO2 offsets.

Technology deployment may also benefit from corporate sector initiatives and pledges to become carbon-negative, such as Microsoft’s announcement of a USD 1‑billion climate innovation fund for carbon reduction, capture and removal technologies.

Longer-term deployment opportunities will be closely linked to robust CO2 pricing mechanisms and accounting frameworks that recognise and value the negative emissions associated with storing CO2 captured from the atmosphere.

Resources
Acknowledgements

Christoph Beuttler, Climeworks

Geoff Holmes, Carbon Engineering 

References
  1. Realmonte, G. et al. (2019), An inter-model assessment of the role of direct air capture in deep mitigation pathways, Nature Communications, Vol. 10, No. 1, p. 3277, doi: 10.1038/s41467-019-10842-5.

  2. Keith, D.W. et al. (2018), A process for capturing CO2 from the atmosphere, Joule, Vol. 2, No. 8, Cell Press, Cambridge, MA, pp. 1573–1594, doi: 10.1016/J.JOULE.2018.05.006.