An Assessment of Carbon Removal Technologies

Carbon dioxide reduction (CDR) technologies have made great strides in the last ten years and there is support for the view that they are necessary and will play a major role in efforts to decarbonize our world. CDR includes direct air capture and sequestration (DACCS), carbon capture and utilization (CCU), and carbon capture and sequestration (CCS). This view is buoyed by pilot projects that have been deployed around the world, however, there is some disagreement about the cost and speed at which they can scale.

It is likely that no one technology will dominate, and we will need to co-deploy a wide range of approaches.  Whatever the exact configuration may be, CDR technologies can help countries achieve the emissions reduction goals laid out in the Paris Climate Agreement. The reality is that extracting carbon from the atmosphere is now as important as eliminating source emissions.  To keep temperatures below the upper threshold limits we must deploy large-scale negative emission technologies (Ross, 2018).

Direct Air Capture and Sequestration (DACCS)

DACCS may be in the early stages of its development, but it has immense CDR potential. A wide range of DACCS technologies are being field-tested (Andrews, 2018) and as of 2018, there were already 18 commercial-scale CDR projects around the world.  The most common working DACs technology employs solid amine sorbents (Realmonte et al, 2019).

Pacala and others think DACCS can fill the gaps as we decarbonize our economy (Welch, 2018). Other researchers think DACCS will be a critical part of our long-term carbon removal plan. DACCS could remove and sequester 16 to 30 GtCO2/year over the period 2070–2100 (Realmonte et al, 2019). Other estimates suggest that DACCS could suck up 0.5 to 5 GtCO2/year by 2050 with possibly of as much as 40 GtCO2/year by 2100 (Cho, 2018).

However, not everyone is convinced. More cautious assessments say that DACCS has a high technology risk and is not ready for deployment. “The thing about direct-air capture is that it’s one of the less technologically developed solutions out there,” says Matt Lucas, associate director of the Oakland, California-based nonprofit Carbon180 (Siegel, 2018).  The Worcester Polytechnic Institute’s Wilcox is also skeptical about DACCS’ feasibility citing the difficult chemical engineering separations process and concern that physicists and not engineers are at the forefront of the field.  As explained by Wilcox, challenges associated with DACCS must be confronted by engineers who build it, while others like Friedmann think DACCS will provide half of our CO2 capture needs (Kramer, 2020).

The economic reality of carbon capture is challenging. The universal applicability of DAC makes it a critically important CDR technology, but it is also relatively more expensive. “Air capture costs money, so anything we can do which is cheaper than air capture, we should do it, definitely,” says Wurzbacher. “But we’ll need this on top of that” (Peters, 2017). Although it is not easy to anticipate the commercialized costs of running a DAC plant, a 2011 American Physical Society study suggests the cost of DAC technology is around $600 per metric ton (Socolow et al 2011). Another study put the cost at $60 per ton of CO2 for capture, and up to $1,000 per ton of CO2 for both capture and reuse (National Research Council, 2015).  According to Welch, the cost of DACCS has fallen by more than half in the last 12 years (Welch, 2018). The most recent estimates for the cost of DACCS go as low as $50 per ton of CO2 (Bipartisan Policy Center, 2019).

Realmonte et al (Realmonte et al, 2019) believe that DACCS can help us to achieve the goals laid out in the Paris agreement by more-than-halving carbon prices in 2030.  According to this research, DACCS can reduce the marginal abatement costs to achieve the climate target by between 60% and more than 90%. DAC is not currently considered to be an economically viable approach to mitigating climate change (Socolow et al., 2011). Although the current slate of DACCS technologies are too expensive, we have seen numerous examples of declining costs as technological innovations scale. Solar panels are a good illustration. They now cost around one percent of what they did in the 1960s (Andrews, 2018). Friedmann agrees that high costs can be overcome through mass production (Kramer, 2020).  Costs will decline to as little as $50/t CO2 as the technology scales (Keith, Holmes, St. Angelo & Heidel, 2018).  It is also important to understand that as climate impacts increase so will the perceived value of DACCS.

The high cost of DAC is due to energy consumption because DAC machines need to push vast amounts of air. According to some estimates, this technology will require as much as a quarter of the world’s total energy demands by 2100 (Realmonte, 2019).  Using DAC it takes six weeks’ worth of an average UK household’s gas and electricity use to strip every tonne of CO2 from the atmosphere (Keith, Holmes, St. Angelo & Heidel, 2018).

That is because the cost of removing a pollutant is inversely proportional to its concentration (Watson, 1998). Consequently, it’s far easier to filter out CO2 from flue gases than it is to do so from the air. The ratio of carbon in a coal power-plant exhaust flue is about 10% while CO2 concentrations in the ambient air are about 0.04%. This amounts to one CO2 molecule for every 2,500 molecules in the air.  That is why DAC is much more energy-intensive than CCS. DAC machines must push more than 300 liters of air to capture the same amount of carbon as one liter of coal plant flue gas (Haszeldine, Flude, Johnson, & Scott, 2018). That is why CCS is one-tenth of the cost of DAC. However, renewable energy and waste heat from industrial processes could help to make DAC a winning CDR technology.

DACCS fares well in comparative assessments and its flexibility makes it the best technology to draw down atmospheric carbon. Some prominent researchers have suggested that DACCS may be better suited to help us meet the goals laid out in the Paris Agreement (Realmonte et al, 2019). There are several advantages to DAC that make it a centrally important part of CDR. DAC is far more efficient than Natural Climate Solutions (NCS). According to some estimates, DAC is as much as a thousand times more efficient than photosynthesis. (Lant, 2017).  DACCS has a negligible environmental impact. An individual CO2 collector has the same footprint as a tree and can remove 50 tons of CO2 out of the air every year while a tree removes 50 kilograms in the

same time frame. A tree takes up 1,000 times more space and unlike a tree, DACCS does not require soil or water and thus can be deployed in places that are not suitable for agriculture. Unlike NCS solutions DACCS will not interfere with food production (Peters, 2017). Researchers recommend accelerated development and deployment of DACCS (Realmonte et al, 2019) and Lackner suspects that as soon as one major player adopts DACCS, others will fall into line (Andrews, 2018).

There are almost no limits to where DACCS can be set up and almost no limits to how big it can scale. They are superior to CCS technologies in that they are highly adaptable and modular, they can be small or large and placed almost anywhere. Together these reasons have led many researchers to conclude that DACCS may be the most promising CDR technology in the long term (Roberts, 2019).

Models demonstrate that the maximum scale-up rate of DACCS is about twice that of Bioenergy with Carbon Capture and Storage (BECCS) (Nemet et al, 2018). However, there is evidence to suggest that BECCS and DAC can complement each other and as such both strategies should be developed in tandem to avoid excessive specialization and reduce both risks and costs (Realmonte et al, 2019). In fact, DACCS is easily co-deployed with other CDR approaches and as such it complements rather than substitutes other NETs.

Overall DACCS has very few external constraints limiting deployment. Although DACs may be the most important CDR technology. Like any technology that successfully draws down atmospheric carbon, widespread implementation of DACCS would cause oceans to release carbon through a process known as carbon cycle feedback.  Past studies using Earth System Models estimate that removing 491 GtCO2 from the atmosphere over a period of 30 years (16 GtCO2/year GtCO2/year) or 10 years (49 GtCO2/year) would result in 51 or 95 GtCO2 outgas emissions from the oceans respectively (Vichi et al, 2013). According to the Realmonte et al study, between 10% and 19% of the carbon removed by DACCS would be released back into the atmosphere from the oceans, requiring an additional removal of 1.7 to 9.5 GtCO2/year to meet the same carbon budget (Realmonte et al, 2019).

The most significant drawback associated with DACCS is the fact that the widespread deployment will require vast amounts of energy to power fans, provide heat, and then compress and transport the captured carbon to storage sites.  It is estimated that scaling up DACCS could consume between 50 EJ/and 300 EJ/yr of energy input by the year 2100 (Realmonte et al, 2019).

In addition to cost, there are concerns about the rate at which DACCS can be scaled. To achieve the goals of the Paris Agreement 30,000 plants would need to capture 30 GtCO2/year (Realmonte et al, 2019). The ability to build out DACCS to the required scale is limited by how quickly they can be constructed (Realmonte et al, 2019). Models suggest that the DACCS maximum scale-up rate is an average of 1.5 GtCO2/year (Realmonte et al, 2019).

Scaling up DACCS would also require massive increases in sorbent production which is required to collect CO2. This could contribute to chemical pollutants associated with sorbent manufacture at vast scales.  There are also concerns about the environmental impacts associated with the extraction, refining, transport, and waste disposal of the minerals that capture CO2.

Although we must address these concerns, the flexibility and scalability potential of DACCS make it an essential part of CDR. DACCS affords what has been described as a “high-premium insurance policy against what would surely be a much more expensive disaster” (Rathi, 2017). If we do not deploy DACCS at the required scale, there is virtually no hope of keeping temperatures within the upper thresholds limits. Succinctly stated, failure to deploy and scale DACCS will surely lead to an overshoot of the Paris objectives (Realmonte et al, 2019).

Carbon capture and utilization (CCU)

A wide range of products can be made through a process called carbon capture and utilization or CCU. This is another way of sequestering captured carbon. Interest in the chemical conversion of carbon into plastics and other materials has been ongoing for around 170 years. Estimates of CO2 utilization for the manufacture of chemicals place an upper limit of 650–700 Mt CO2 per year on total global utilization (Mac Dowell, Fennell, Shah, and Maitland, 2017).

Although fuel production and EOR is the most common application of CCU, for the reasons laid out in the methodology section this is not the focus of this paper. A quick review of the costs of making fuel with captured carbon suggests that this approach is expensive. Pearl GTL, in Ras Laffan Industrial City, 80km north of Doha, is the world’s largest source of gas-to-liquids (GTL) products and it took 7 years and over $18 billion to build a plant that produces less than 1% of US consumption of liquid fuels from natural gas (Shell, n.d.).

Many other products can be made from CCU including plastics and soft drinks although the latter releases CO2 when consumed and therefore it cannot be considered as a technology that draws down carbon.  One of the most effective CCU approaches involves incorporating CO2 into durable building materials. Cement production contributes about 8% of global CO2 emissions, however, a New Jersey company by the name of Solidia Technologies has developed a process that both sequesters carbon and reduces emissions. They use CO2 to cure cement instead of water and this reduces the carbon footprint of cement and concrete production by 60%. Solidia’s process forms calcium carbonate and silica to harden the concrete. Their proprietary product sequesters about 300 kg of CO2 per ton and the company claims about 0.5 Gt of CO2 could be captured per year if the company’s technologies were adopted by the entire precast concrete industry. Solidia’s cement also produces 30% less CO2 than conventional Portland cement (Kramer, 2020). However, this does not draw down carbon levels and as such, it is not a NET. One of the more promising applications for captured CO2 is carbon fiber (see promising research at the end of this paper).

If CCU is “successfully implemented at scale, it could transform how humanity thinks about the problem of climate change…It could give people a decisive new tool in the race against a warming planet” (Meyer, 2018).  According to the most optimistic assessments, CCU could reduce up to 10% of total global emissions by 2030 (Dimitriou, García-Gutiérrez, Elder, Cuéllar-Franca, Azapagic, & Allen, 2015). Estimates of the potential of CCU to scale optimistically project a growth rate of 3% per year over 40 years to achieve a cumulative total of 15.42 GtCO2.  However, only about 25% of CCU products sequester CO2 for any significant duration which translates to 3.86 GtCO2, or slightly less than 0.5% of the carbon mitigation challenge of 800 Gt CO2 (Mac Dowell, Fennell, Shah, and Maitland, 2017).  The High-Level Group of Scientific Advisors to the European Commission reported an estimated long-term utilization potential of 1-2 GtCO2/year.

As demonstrated above CCU’s contribution to climate mitigation is likely to be negligible. Others have offered assessments that are even less optimistic.  A 2017 study concludes that CCU will account for no more than 1% of the mitigation challenge causing these researchers to discourage reliance on CCU as a means of drawing down atmospheric carbon emissions. These authors argue that CCU should only be considered as a feedstock or when it can offer the same service at the same price without increasing CO2 emissions (Mac Dowell, Fennell, Shah, and Maitland, 2017).

CCU can at best supplement more effective climate mitigation efforts, but it is not a realistic alternative to geologic sequestration (Mac Dowell, Fennell, Shah, and Maitland, 2017). Although CCU could make a small contribution to decarbonization it is not a viable replacement for other CDR technologies. CCU will not be able to achieve anywhere near the drawdown in atmospheric emissions of DACCS or CCS. Conversely, CCU could drive demand for CO2 and help to both scale carbon capture technology and reduce costs (Dimitriou, García-Gutiérrez, Elder, Cuéllar-Franca, Azapagic, & Allen, 2015). However, other researchers have suggested that we may want to exclude CCU as it could prove to be a destructive distraction (Mac Dowell, Fennell, Shah, and Maitland, 2017).

Carbon Capture and Storage (CCS)

CCS is the dominant CDR technology in the world today and the advances is CCS over the last ten years are part of what Pacala describes as a decade of “spectacular technological achievements” and “unrelenting progress” (Welch, 2018).  As of 2019, there were 19 large-scale CCS facilities in operation around the world. (Jones, 2020). There are currently at least 22 such plants operating or under construction (Quest, n.d.).

Researchers describe CCS as an important part of efforts to decarbonize the global economy (Matter, 2016). Some have concluded that CCS is a “well-understood, mature technology that is deployable at commercial scale today.” (Mac Dowell, Fennell, Shah, and Maitland, 2017). However, CCS has yet to prove itself at scale. The total global capacity of all CCS facilities that were either operating or under construction was 40 million metric tons of CO2, while worldwide emissions are around 42 GtCO2/year. If we add up all the CDR technologies (comprised mostly of CCS) in the world they removed less than 0.1% of global emissions in 2019 (Jones, 2020).

The need for CCS has been apparent for well over a decade. In 2009 the IEA estimated that globally, over 200 power plants need CCS technology by 2030 in order to prevent temperature rises of over 3°C (IEA, 2009) and a more recent IPCC report stated that all power plants must be fitted with CCS technology (IPCC, 2018).  Despite research from MIT that suggested CCS can reduce human-generated CO2 to 80% of 1990 levels by 2050 (Paltsev, et al, 2007), we are still nowhere near being close to deployment that makes a meaningful impact. While the Global CCS Institute believes that CCS technology can and must be widely deployed (Global CCS Institute, 2018), there are many who doubt we will ever be able to scale CCS to the needed size (Jones, 2020).

A serious problem with most CCS applications is the ratio of emitted CO2 compared to the amount of carbon that they capture (Ross, 2018). According to researchers from the Sustainable Gas Institute at Imperial College London, CCS technologies must improve so that they capture at least 95% of CO2 emissions. Currently, CCS technology captures about 85 to 90% of these emissions and the remaining 10 to 15% are released back into the atmosphere (Smith, 2016; Budinis et al, 2016).

Although CCS technology is well understood high costs have prevented widespread deployment (Mac Dowell, Fennell, Shah, and Maitland, 2017). The problem is financing these projects and operating costs. CCS operating costs are high because plants fitted with the technology require 25% more power (Spath & Mann, 2002).

There is broad agreement that costs for CCS would need to decrease before the technologies could be deployed commercially (Folger, 2018). However, there are indications that the costs of CCS will decline. European research indicates that CCS projects in the power sector are likely to go down to as little as €35 per tonne ($38 U.S.) in the early 2020s (Carbon Capture and Storage Association, n.d.). Many agree that the primary way to decrease costs is by deploying these technologies at scale and some have argued that EOR may be the key to lowering the cost of CCS (Mac Dowell, Fennell, Shah, and Maitland, 2017).

However, as we will review in the next section CCS pilot projects have failed all around the world. They failed in the EU despite massive European government subsidies (IEEFA Europe, 2017). In 2009 nine European countries (Norway, Germany, France, Switzerland, the Netherlands, Hungary. Poland, Croatia, and Denmark) invested €81 million ($105 million U.S.) to build fifteen research laboratories for CCS. The US has invested $3.4 billion in the technology (PlanetWatch, 2009). Yet after more than a decade, CCS is still not able to secure interest from investors who seem to have concluded that the technology is not economically viable (Jones, 2020).

Failed Carbon Capture and Storage Technologies

A review of failed carbon capture projects reveals some of the issues and obstacles that have prevented these technologies from taking off.  Most carbon capture plants have failed due to cost overruns and/or failure to meet sequestration targets. This includes the Schwarze Pumpe power station in Spremberg Germany, the Engie Uniper plants in the Netherlands, and the DOE’s CCS projects in Texas, Illinois, USA, and Mississippi.

In 2014 Vattenfall abandoned its research on CO2 storage at the Schwarze Pumpe power station in Spremberg Germany because its costs and the energy requirements made the technology unviable (AFP, 2014). In 2016 the US Department of Energy withdrew from five CCS projects (Hardcastle, 2016) and the Carbon Capture and Sequestration Technologies program at MIT was closed. By 2017 it was apparent that carbon capture was dead in Europe (Wynn, 2017).

One of the longest-running and best-known CCS projects is the Boundary Dam in Saskatchewan Canada. The cost of the project is currently $1.5 billion. The original cost was $1.3 billion with $800 million for the CCS process and the remaining $500 million for retrofit costs. This is the first commercial-scale power plant to use CCS and it was the industry’s biggest success story. However, it has been partially closed due to a decline in economic activity and the Canadian government’s decision to phase out coal-fired electricity by 2030 (CJME News, 2020).  In recent years the company has had to pay tens of millions of dollars in penalties due to lower-than-expected capture rates and their failure to deliver promised CO2 to Cenovus Energy (Carbon Capture and Sequestration Technologies program at MIT., n.d.).

Significant cost overruns have plagued CCS technologies from their inception.  In 2009 the Dakota Gasification Company plant in Beulah, North Dakota saw construction costs balloon to $2.35 billion which is almost twice the original estimate (PlanetWatch, 2009). The operating costs of many CCS plants have also exceeded projections.

Some of these plants were shuttered because the information came to light that suggested owners were being dishonest about their performance and cost data. This appears to be the case at the Kemper project in Mississippi. An employee leaked documents revealing that the plant’s owner concealed technical difficulties and cost overruns (Silverstein, 2016).

Carbon Capture and Storage and fossil fuels

A lot of the interest in CCS technologies is being driven by the fossil fuel industry which sees CCS, CCU, and DAC technologies as a way of extending the life of oil and gas extraction. However, the fact is we are not going to achieve large-scale drawdowns of atmospheric CO2 with technologies that make burnable fuel out of captured CO2 (McGrath, 2017). The need to radically reduce CO2 levels has led some to say that using captured carbon for fuel is putting the cart before the horse (Andrews, 2018). Despite the massive pent-up demand (Mac Dowell, Fennell, Shah, and Maitland, 2017) and the fact that CO2 for EOR can sequester vast amounts of carbon, extracting more combustible fuels will add to the carbon load and exacerbate climate change.

The fossil fuel industry is pouring billions of dollars into carbon sequestration plants that store carbon and without this support geologic sequestration of CO2 is often considered non-viable (Nace, 2019).  However, others argue that these investments are delaying efforts to wean ourselves off fossil fuels (Welch, 2018). Even a scaled-up EOR-CCS industry will likely only account for a 4–8% drawdown in atmospheric carbon emissions. Therefore, whilst CO2-EOR may be an important economic incentive for some early CCS projects, CCU may prove to be a costly distraction from the real task of mitigation (Mac Dowell, Fennell, Shah, and Maitland, 2017).

Lili Fuhr says that approaches to capturing carbon are all part of a self-preservation strategy by the fossil fuel industry. “For many decades the fossil fuel industry has funded climate skeptics and, in that way, tried to prevent climate action. But they’ve seen that this is not working, so instead of denying, they are beginning to come up with these magical techno-fixes that would help prolong the lifespan of their industry” (McGrath, 2017).

For references and more information go to CDR Resources. See also Glossary of Terminology Related to CDR.

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