April 6, 2020
Carbon Capture Versus Direct Air Capture
Carbon capture and direct air capture (DAC) have gained
capital-intensive and energy-intensive. Also, the demand
prominence in recent years as options to address climate
for CO2 is small compared to its availability, resulting in
change. The two technologies have similarities (beyond
low CO2 revenues. The low value of CO2 presents a hurdle
their names), but they also have differences. Key
to commercialization for both technologies.
differences include how the technologies work, where the
technology can be used, how the technology can address
Where Can They Be Used?
climate change, and levels of federal support.
CCUS can be used at stationary sources of CO2 such as
power plants, ethanol production plants, or other industrial
Several major energy proposals in the 116th Congress would
facilities. Existing facilities can be retrofitted to add CCUS
increase federal support for carbon capture and DAC.
equipment, or CCUS can be integrated into the design of
Examples include the Senate energy package debated on the
new facilities. The type of source can affect the cost of a
floor in March 2020 (S.Amdt. 1407 to S. 2657) and the
project because different sources emit CO2 in different
Climate Leadership and Environmental Action for our
concentrations (purities). All else being equal, carbon
Nation’s Future Act (CLEAN Future Act) discussion draft
capture can be completed at lower cost per ton CO2
released by leaders of the House Energy and Commerce
captured for sources with higher-purity CO2 emissions (e.g.,
Committee in January 2020.
ethanol production plants). Sources of captured CO2 are
often located far away from where CO2 may be used or
This analysis explains key differences between the two
stored, creating logistical and cost challenges related to the
technologies to inform congressional deliberations.
transport of CO2.
How Do They Work?
DAC can be used anywhere. Many proposals envision
Carbon capture technologies prevent the release of carbon
building DAC projects close to either inexpensive
dioxide (CO2) to the atmosphere. In the most commonly
electricity sources or locations where CO2 can be used or
used arrangement today, a chemical that can “grab” CO2 is
stored. Both options could serve to lower overall project
placed in or near the stream of CO2 at a source. The
captured CO2 is then released and compressed so that it can
be transferred by pipeline. The CO
How Can They Address Climate
2 can then be used, for
example, as a feedstock to an industrial process or
permanently stored (sequestered) underground. The
CCUS would reduce CO2 emissions released to the
chemical that does the capturing can be reused in the
atmosphere. The extent of reduction is dependent upon the
process many times. The full process is called carbon
end use of the CO2. Currently, the main use of captured
capture, utilization, and storage (CCUS), or sometimes
CO2 is for enhanced oil recovery (EOR). In EOR,
carbon capture and storage (CCS).
compressed CO2 is injected into aging oil wells. This
process increases oil production while also permanently
Direct air capture technologies remove CO2 from the
sequestering some CO2.
atmosphere, even if that CO2 was released many years ago.
In many technological approaches, air is forced over a
Many stakeholders see CCUS as a way to enable continued
chemical that can “grab” CO2. DAC and CCUS may use the
use of fossil fuels even if CO2 emissions were restricted in
same chemicals, but some chemicals are better suited for
the United States and abroad. Fossil fuels have operational
one application or the other. Regardless, the supporting
advantages over alternative fuels in many economic sectors.
equipment must be optimized for the different CO2
For example, cement, steel, and petrochemical
concentrations involved in DAC and CCUS. After capture,
manufacturing all require very high temperatures, currently
the process for DAC is very similar to that used for CCUS
provided almost exclusively by fossil fuel combustion.
and can use the same equipment for compression, transfer,
CCUS may allow continued use of fossil fuels in these and
and storage. The chemical that does the capturing can be
other sectors with lower CO2 emissions than today.
reused for DAC many times.
DAC would remove CO2 from the atmosphere. It is one
Both technologies are in early stages of development, with
example of carbon removal, sometimes called negative
a few examples of operating projects worldwide. Of the
emissions technologies. Proponents see DAC and other
two, CCUS is more mature, though researchers expect
carbon removal options as a way to reduce atmospheric
significant technology advancement can still be achieved.
CO2 concentrations to desired levels. Some studies estimate
DAC and other carbon removal options (e.g., afforestation)
Although the capture technologies are different for CCUS
would need to be deployed at large scales globally to
and DAC, they face similar challenges. Both are typically
achieve climate targets investigated in those studies.
link to page 2 link to page 2 Carbon Capture Versus Direct Air Capture
What Federal Support Exists?
Source: U.S. Department of Energy annual budget justifications for
Beginning in the late 2000s, the Department of Energy’s
FY2018 through FY2021.
(DOE’s) coal research shifted to CCUS, particularly capture
technologies and geological sequestration. These research,
Notes: CCUS = carbon capture, utilization, and storage; N/A = not
development, and deployment (RD&D) programs are
applicable. Figures are rounded to the nearest mil ion. Carbon
authorized primarily by the Energy Policy Act of 2005
capture and carbon storage are the two program areas specified in
(P.L. 109-58) and the Energy Independence and Security
appropriations documents most related to CCUS, though other
Act of 2007 (P.L. 110-140). DOE’s Office of Fossil Energy
program areas may fund related research.
Research administers these R&D programs, with a focus on
improving CCUS efficiencies and reducing costs. In the
a. The FY2019, FY2020, and FY2021 budget requests proposed
2005 law, Congress directed DOE to focus on technologies
merging the carbon capture and carbon storage accounts into a
to capture CO
single carbon capture, utilization, and storage account. For
2 from coal combustion, especially at power
comparison purposes, this table combines the requested
plants. In the 2007 law, Congress expanded the program
budgets for carbon utilization and carbon storage into the
direction to include sequestration research, testing, and
carbon storage line.
DAC has not been a focus area for DOE research to date,
Total appropriations since 2005 for CCUS-related RD&D
although Congress, in the explanatory statement for
exceed $6 billion. Of this amount, $3.4 billion came from
FY2020 appropriations, did direct DOE to use at least $10
the American Recovery and Reinvestment Act of 2009
million of its appropriation for DAC research. DOE
(ARRA; P.L. 111-5). Much of the ARRA appropriation was
research on systems shared by both technologies (e.g.,
to fund demonstration projects and had to be spent by
compression, underground storage) could benefit DAC
FY2015. Of the $3.4 billion from ARRA, approximately $1
projects moving forward.
billion went unspent.
CCUS and DAC projects are both eligible for federal tax
The Trump Administration has proposed cutting funding
credits proportional to the amount of CO2 they use or store.
for CCUS RD&D. The Administration has stated a
Congress established these tax credits in 2008 and
preference for focusing DOE resources on early-stage
expanded them in 2018. Under current law, eligible projects
research and relying on the private sector to fund later-stage
may receive tax credits up to $50 per metric ton CO2.
activities such as demonstration projects. Congress has
Projects must meet certain requirements such as minimum
rejected such proposals and instead funded CCUS RD&D at
capture amounts, monitoring procedures, and start-of-
or above historic levels with a continued focus on both
construction deadlines. Some Members of Congress have
early-stage and later-stage RD&D activities. Presidential
proposed changes to these requirements.
budget requests and annual appropriations for CCUS
RD&D for FY2018-FY2021 are shown in Table 1.
Bills have been introduced in the 116th Congress that would
Table 1. Funding for DOE CCUS Research,
increase direct federal support for CCUS and DAC.
Proposals include expanding DOE’s RD&D activities and
Development, and Demonstration, FY2018-FY2021
establishing technology prize competitions. Bills have also
been introduced in the 116th Congress that could indirectly
support CCUS and DAC. These proposals include carbon
taxes, clean energy standards, and low carbon fuel
Tax credits for which CCUS and DAC may be eligible are
discussed in CRS In Focus IF11455, The Tax Credit for
Carbon Sequestration (Section 45Q).
CCUS technology and existing U.S. projects are discussed
in CRS Report R44902, Carbon Capture and Sequestration
(CCS) in the United States.
Past appropriations for CCUS are discussed in CRS In
Focus IF10589, FY2019 Funding for CCS and Other DOE
Fossil Energy R&D.
Ashley J. Lawson, Analyst in Energy Policy
Carbon Capture Versus Direct Air Capture
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