What is Air Capture?
Direct Air Capture (DAC) is the extraction of carbon dioxide from atmospheric air in a closed-loop industrial process.
Capturing CO2 directly from the air allows emissions originating from any source to be managed with standardized scalable industrial facilities. Our full-scale design, for example, could absorb the emissions created by 300,000 typical cars.
Air capture is a tool for managing the buildup of CO2 in the atmosphere which drives climate change. Since much of the CO2 already emitted to the atmosphere will stay there for hundreds of years, air capture can serve as a complement to climate strategies that reduce emissions at their source. Air capture requires an energy source - such as natural gas, concentrated solar power, or nuclear – but typically energy is generated on-site so that any emissions incurred can be captured and delivered along with the CO2 from the air.
Direct air capture can remove far more CO2 per acre of land footprint than trees and plants (see FAQ for more details), and air capture produces a stream of pure CO2 as its principal output, for use in industrial applications or storage in geological formations deep underground.
Enabling Low-Carbon Fuels
Air Capture provides atmospheric CO2 for industrial use, where-as traditional point-source carbon capture (CCS) provides CO2 of geologic origin. When used in fuel production, air capture can produce fuels with much lower carbon-intensity than CCS, as we show below. This makes air capture an important complement, rather than a competitor, to CCS.
This material is also available as a PDF: CE - DAC and CCS Comparison for Low-Carbon Fuels.
CE’s chief commercialization strategy is to use air capture to enable low-carbon fuel production, and we are often asked how we can compete against CCS, which can usually provide CO2 more cheaply than DAC.
DAC does not compete with CCS in reducing emissions from large fixed sources such as electric power or by being cheaper on a $/ton basis. Rather, DAC competes by providing an atmospheric – rather than geological – CO2 source, which when used to produce fuels, can result in a lower life-cycle carbon intensity (CI) than fuels produced from CCS CO2. Low-carbon intensity alternatives to conventional fuels command a premium value in carbon-constrained transportation markets, such as in California where a Low Carbon Fuel Standard has already been implemented. Costs of decarbonizing transportation systems are generally higher than the costs of decarbonizing the electricity sector, and significant fuel premiums are becoming available for technologies and producers that can deliver low-carbon alternatives to conventional fuels. DAC aims to meet this demand. The business model for commercializing DAC is different than that for CCS, and there are sizable markets where it can succeed.
The origin of CO2 that is used to produce fuels – whether embodied in petroleum, mined for enhanced oil recovery (EOR), or captured from the air - is crucial to determining the net flow of CO2 from the sub-surface to the atmosphere, and thus in determining the life-cycle carbon intensity of the fuel. This is true for EOR, where CO2 is injected to stimulate production from oil reservoirs, but algal biofuels provide another illustrative example. Algal biofuels have a low carbon intensity because they capture CO2 from the atmospheric photosynthesis during their production, which compensates for the CO2 released when they are used. If one were to supply an algal pond with CO2 from a geologic reservoir – often the lowest cost CO2 – the resultant algal biofuel would have CI very similar to that of conventional oil because the net transfer of carbon from geologic reservoirs to the atmosphere would be the same. The following three scenarios illustrate the role of CO2 source in determining the carbon intensity of fuels produces from EOR.
Scenario A: Conventional EOR Fuel Production
A geologic CO2 reservoir supplies CO2 for EOR to produce petroleum, and ultimately fuel. The carbon intensity (CI) can vary depending upon the specifics of the EOR field and the petroleum in the reservoir, but a typical value is 95 g-CO2/MJ as represented by the bar to the right of the image below.
Scenario B: Power Plant CCS to EOR
In this scenario the source of CO2 is still geological. Coal or gas – which embody geologic carbon - is extracted and used in a power plant with CCS and the resulting CO2 is used to produce fuel as in the first scenario. A simple interpretation is that the fuel has the same 95 g-CO2/MJ CI as in the first scenario, although the system has produced low-carbon electricity. Under some regulatory regimes the emissions reductions in the electricity sector be partially allocated to the fuel, though one cannot claim both low carbon fuel and low carbon electricity. Assuming the low-carbon electricity displaces U.S. grid average carbon intensity, and all electric-sector emissions reductions are allocated to the fuel, the resulting fuel CI may be of order 40 g-CO2/MJ (as shown in the right hand bar of the figure). Note that as natural gas and renewables gain in the generation portfolio the grid average intensity decreases and so do the reductions obtained by replacing grid electricity with CCS electricity, so that in a fully de-carbonized grid CCS-EOR produces fuel with exactly the same CI as conventional oil.
Scenario C: Air Capture to EOR
DAC captures CO2 from the air, which compensates for the CO2 released in fuel use, and in effect recycles the emissions for reuse in fuel production. Fossil fuel is used to power DAC and both the combustion CO2 and atmospheric CO2 are captured and injected for EOR. The CO2 delivered to the oil reservoir is permanently sequestered, resulting in a low CI fuel, roughly 35g-CO2/MJ or lower (depending on the oil to CO2 “lift ratio”).
DAC enables the direct extraction of CO2 from the atmosphere, which cannot be accomplished by CCS, and thus enables revenue streams and associated business models distinct from those for CCS. Revenue streams from premium-value low-carbon fuels can be much larger per ton of CO2 than revenue streams available per ton of CO2 avoided in the electric sector. DAC is harder and more expensive than capture from power plants. Likewise cutting carbon in the transportation sector is harder and more expensive than cutting carbon in the electricity sector. One should therefore think of DAC as competing with biofuels and electric vehicles, not with power plant CCS and wind power. Finally, regulators have often chosen to impose higher effective carbon prices on the transportation sector than they have on electricity. DAC is more expensive than CCS but it competes in a different market with a different incentive structures CCS.
The per barrel cost of DAC-EOR fuel is about 20% higher than the cost of conventional oil and it has a carbon intensity that is lower than most biofuels. DAC thus provides a near-term scalable technology that can supply low-carbon transportation fuels at a lower cost (and a lower land use footprint) than most biofuels. DAC has near-term markets where it can compete, and successful commercialization of DAC will add to our ability to make deep reductions in economy-wide emissions, and meet critical long-term climate change goals.