The promise of scalable direct air capture - ScienceDirect
Greg Rau
infogeoeng
Carlos J. Jiménez Haertel
Climeworks AG
A mere handful of years ago, the concept of direct air capture (DAC) was known to a small specialist circle of inventors and entrepreneurs only. The challenges to overcome in those early days were still primarily of a technical nature. Front and center was the question of whether or not candidate technologies, which often showed great promise in the laboratory, could indeed be scaled up and made robust enough for deployment in the field.
Today, it’s clear that DAC is not only feasible in practice but has the long-term potential to make essential contributions to carbon removal from the atmosphere. Climeworks’ very first large DAC plant already has been in commercial operation for several years in Switzerland, and we recently completed and commissioned our much bigger installation “Orca” in Iceland. The latter has a nominal capacity to remove almost 4,000 tons of CO2 every year. While this figure is still modest in comparison to the enormity of the carbon-removal challenge we’re faced with, Orca clearly demonstrates that DAC is feasible at an industrial scale and ready for scale up. Technological solutions to carbon removal do have the potential to contribute several billion tons of negative emissions per year by about 2050, provided we put the right incentives in place without any further delay. To some, three decades may sound like a very long time in our fast-paced modern world; however, in light of the required industrial expansion, it’s basically tomorrow.
DAC slow, expensive to implement
Marcia McNutt
National Academy of Sciences
DAC should be retained in a portfolio of approaches to reducing atmospheric carbon, but as described in two recent reports from the National Academies of Sciences, Engineering, and Medicine (Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration [2015], Negative Emissions Technologies and Reliable Sequestration: A Research Agenda [2019]), it is slow to have impact (as compared with the rate at which we emit CO2 and the urgency of climate action) and very expensive to implement (as compared with other mitigation approaches). While additional research may result in improved approaches, the laws of thermodynamics fundamentally constrain the minimum amount of work that must be done to capture CO2 from dilute concentrations in ambient air. Capturing the CO2 in the emissions from coal gasification (1–4 kJ/mol of CO2) or from direct coal combustion (5–7 kJ/mol CO2) are four times more efficient than DAC (19–21 kJ/mol). Furthermore, there is a financial (and energy) cost of regenerating the solvent or sorbent for continued reuse in DAC applications.
DAC may be less expensive and less disruptive than reducing emissions in some limited scenarios, such as mitigating the emissions from soil carbon released after disrupting landscapes and some agricultural applications. However, deploying DAC to remove CO2 caused by burning fossil fuels is unlikely to be the preferred solution, as it is far more efficient and less costly to either use renewable energy sources or capture the CO2 in a waste stream before it is released to the atmosphere.
While this comment is based on official reports of the National Academies of Sciences, Engineering, and Medicine (NASEM), this opinion is the author’s alone, and not an official product of the NASEM.
Energy and materials requirements of DAC: Is it realistic?
Mihrimah Ozkan
University of California, Riverside
DAC can help with hard-to-avoid carbon emissions from distributed sources (transportation, wildfires) and from natural gas processing, the production of cement, iron, steel, ammonia, and urea, biofuel use, and more, helping to offset the nearly 1.9 billion tons of industrial CO2 emissions per year that cannot be feasibly avoided using production technologies.
The implementation of DAC faces two major technical challenges: (1) energy and (2) materials. Current CO2 emissions reach nearly 32.6 gigatons/year. With the assumption that only 25% of total CO2 emissions would be captured, implementing existing liquid and solid sorbent DAC systems would require 10%–20% and 30%–50% of the total global energy supply, respectively. This includes the energy needed to produce sorbent materials and sorbent regeneration. High energy demand could raise the final cost of carbon capture; therefore, inexpensive and low-carbon energy sources are vital. The current goal for DAC is to keep the cost at $100/tCO2.
Sorbent material production must also ramp up to meet the demand for DAC scaling. For example, to capture 25% of the total CO2 emissions per year, sorbents must be produced on the gigaton scale, requiring 20 to 30 times more NaOH, NH3, and ethanol than is currently produced. Similarly, steel and other construction materials have to scale up, too. The sustainability of DAC will depend on the use of affordable, low-carbon, and low-power capture technologies and stable and selective sorbents with a shortage-free supply chain.
DAC and safe, permanent storage are essential to climate action
Edda Sif Pind Aradóttir
Carbfix
Reaching net-zero greenhouse gas emissions is essential to managing the climate crisis. Even though decarbonization is the most important step toward net-zero, we still need to deploy DAC technologies on a large scale to reach these goals. Furthermore, these technologies are essential to create the negative emission pathways needed during the latter half of the century to limit global warming to 1.5°C (Rogelj, J. et al. “Mitigation Pathways Compatible with 1.5°C in the Context of Sustainable Development” in Global warming of 1.5°C, 950–163).
The most feasible way to capture CO2 is from concentrated sources. However, DAC technologies provide a pathway to offset hard-to-avoid emissions, accounting for roughly 1.5–3 gigatons/CO2 per year (Wilcox, J., Kolosz, B., and Freeman, J., eds., CDR Primer).
The primary limitation of large-scale implementation of DAC technologies at their current state of development is the system’s energy demand: DAC technologies are energy intensive and dependent on carbon neutral energy resources. Strategies that minimize energy consumption are a vital step for moving from the megaton to gigaton scale.
In addition, secure geological storage for captured CO2 is fundamental to the successful implementation of DAC facilities. Without safe and permanent storage, DAC technologies will only solve one part of the problem.
We need rapid development and deployment of DAC technologies parallel to the identification of safe and permanent storage locations for the large-scale removal of CO2. The strategic location of DAC facilities is key to maximize their efficiency in terms of CO2 removal, both regarding access to CO2-free energy and storage.
DAC of CO2 as a potential mitigation measure
Kalliat T. Valsaraj
Louisiana State University
Paul R. Sanberg
University of South Florida
It is an accepted scientific consensus that increased carbon dioxide results in a variety of issues that range from long-term variations in the earth’s climate as well as public health. The most recent Intergovernmental Panel on Climate Change assessment pointed to the need for methodologies to limit such changes via technological innovations. DAC is one among the many of such fixes that has been identified by a recent NASEM report. The National Academy of Inventors (NAI) membership has several patents on specific issues among our portfolio of technologies available for patenting.
It is the opinion of the present authors that DAC is a promising technology for carbon capture and sequestration for further use in other technologies. We feel that it has merits as a future promising technology. However, its feasibility on a large scale is yet to be determined. It can only be considered one of the possibilities among a potpourri of technologies in the area of carbon capture and sequestration (CCS). The future of the DAC technology depends primarily on the economics of adequate and promising materials that may be manufactured to allow carbon capture directly from air. We believe NAI members have a major role to play in making the technology a reality in the future.
The role of CDR in achieving net-zero carbon emissions
Shuchi Talati
U.S. Department of Energy
Jennifer Wilcox
U.S. Department of Energy
Carbon dioxide removal (CDR) has an important role to play in achieving global and national carbon emissions goals as a complement to deep decarbonization. DAC coupled to reliable storage (DACS) is an exciting, innovative CDR approach that we will need to deploy. However, the sustainability of DACS at scale is deeply dependent on a well-designed governance infrastructure: the policies and guardrails that governments put in place. Ensuring that DACS is coupled to low carbon energy utilizing robust carbon accounting is essential for true removal.
Additionally, we must recognize the resources that may be required for DACS, including land, low-carbon energy, and water, and be deeply cognizant of where we site it. Importantly, CDR, whether nature or technology based, should not be used as a strategy to offset emissions that can be avoided: it will always be easier to avoid emissions rather than take them back out of the atmosphere. Approaches like DACS are needed for net-zero targets, but only for addressing hard to avoid sectors today (e.g., agriculture, aviation, and shipping).
These are not only issues of technological innovation, but also of justice, equity, and responsibility. Meaningful public engagement must be a priority and decision-making must incorporate community and stakeholder input. Those in government are in a position to ensure the responsible build-out of DACS. We have the opportunity and responsibility to deploy the right way, in a manner that improves the quality of life of those who have been affected by the legacy of fossil fuels and the energy transition.
The sustainability of DACS is dependent on these choices we make today.
Bruce Melton -- Austin, Texas
These opinions, like most on DAC we see in the literature today,
are based on biased scenarios and disproven literature.
The concepts that DAC cannot be implemented at any reasonable scale until 2050 is scenario biased. Scenarios are almost all defined by market forces where captured CO2 is utilized and there are not enough markets for decades to utilize gigatons of CO2, and or they are defined by quantities needed to meet scenario criteria of 1.5 or 2.0 degrees C by some predetermined date. The difference between scenarios is how fast market forces grow, and how fast the scenario chooses to achieve the given temperature target. There are only very few scenarios that implement capture and storage as a function of the commons with goals that rapidly produce meaningful quantities -- at any temperature target.
Costs are biased high because of two pieces of literature in
2011: American Physical Society (Socolow) and MIT (House). Both of
these original sources of misinformation are reflected in the
often cited National Academies DAC works in both 2015 and 2019.
The reality is that APS and MIT were rebutted because they used
poor process choices and used enthalpy backwards (Van Norden 2011,
Holmes and Keith 2011, Realff and Eisenberger 2012.) National
Academies 2019 recognizes the rebuttals, but does not give them
much weight.
Further cost evaluation: The often cited $100 a ton is actually
Keith 2018 that reflects actual costs of the Carbon Engineering
pilot facility in Squamish BC of $94 to $232 per ton. Keith says
this range represent energy costs that use $0.03 to $0.06 kWh
natural gas energy with a 10 percent carbon penalty, 8 percent
profit, and 7.5 to 12.5 percent capitol recovery. Because 87
percent of costs are energy related, and the lowest cost renewable
energy today is $0.01 kWh, and undoubtedly these processes will
use on site utility scale renewable energy with batteries that
will be at parity in the next few years, costs from energy
reduction alone makes the $94 a ton with $0.03 kWh energy reduce
to $39 a ton with $0.01 kWh energy. This cost does not reflect
further reduction because of the natural gas penalty, or a
nonprofit model with actions for the commons, or any further
process refinements or scaling.
The high energy use arguments in these opinions and elsewhere are
likewise biased because of the APS and MIT use of enthalpy
backwards* where they suggested costs would be in the $600 to
$1,000 per ton range.
As per the technical challenges referred to, the recyclable lime/potash process (Carbon Engineering) was discovered in 1907 and among many other things, was used to keep our sailors safe in WWII from carbon dioxide poisoning in submarines; and amine processes (1930s) used by most of the rest of the DAC crowd, became widely used in the 1950s and are what are likely the most important group of industrial chemicals ever. To insinuate these processes are immature and isolated to the lab is widely misleading.
Realff and Eisenberger, Flawed analysis of the possibility of air capture, June 19, 2012.
http://sequestration.mit.edu/pdf/2012_PNAS_StorageCapacity_LetterToEditor.pdf
Director, Climate Change Now Initiative, 501c3
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