Direct Air Carbon Capture versus Bioenergy Carbon Capture and Storage

The 2021 Intergovernmental Panel on Climate Change (IPCC) report discusses the impact of human activities on the state of the climate and different solutions that can be implemented to reduce further warming of the planet. Here, the technologies addressing global warming, Direct Air Carbon Capture (DACCS) and Bioenergy Carbon Capture and Storage (BECCS), are discussed.

Since around 1750, there has been a rise in well-mixed greenhouse gas (GHG) concentrations unequivocally linked to human activities. Moreover, since 2011, these levels have continued to rise within the atmosphere at an annual average of 410 parts per million (ppm) for carbon dioxide (CO2), 1,866 parts per billion (ppb) for methane (CH4), and 332 ppb for nitrous oxide (N2O) as of 2019.

Over the past four decades, there has been a consistent increase in global surface temperatures, with each decade getting successively warmer than the previous one. For example, between 2001 and 2020, the global surface temperature was 0.99 °C warmer than recordings between 1850 and 1900.

Current climate models predict that between 2030 and 2052, global surface temperatures will likely rise by 1.5 °C if human activities continue at their current pace. This projected increase in global warming will inevitably impact the health and livelihoods of people around the world. Food security, water supplies, and economic growth are also predicted to suffer significantly.

Effective Approaches to CO2 Removal

GHG emissions, especially CO2, are the main contributors to climate change and, as a result, rising global temperatures. Some of the primary causes of CO2 emissions include human activities like the pre-and post-combustion of fuels, agricultural practices, the transportation sector, as well as industrial operations.

Several CO2 removal technologies have been developed to overcome the potentially disastrous effects of continued CO2 release into the environment. Adsorption technologies, for example, are a promising approach involving the use of solid adsorbents that can remove CO2 from gas mixtures. Biochar, enhanced weathering (EQ), ocean fertilization (OF), BECCS, and DACCs have also been explored as potential solutions. Each of these CO2 removal methods differs widely in their costs, risks, co-benefits, and trade-offs, as well as the duration of which they have been available for public use.

What is Direct Air Carbon Capture and Storage?

The primary goal of DACCS systems is to remove CO2 from ambient air and subsequently store the extracted CO2 in a geological storage medium. One of the key advantages associated with DACCS includes its ability to effectively capture GHG emissions that have already been released into the environment. In doing so, DACCS can assist in international goals aiming to achieve net-negative global GHG emissions in the future.

One of the fundamental limitations of other CO2 removal technologies is that they often focus on cleaning emissions from the source. However, such an approach is often impractical, particularly when dealing with the small and numerous sources of CO2 emissions worldwide. Comparatively, DACCS offers a large-scale CO2 removal strategy that could potentially remove several billions of tons of CO2 each year.

Carbon Capture Technology Explained | Seachange

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Several thousands of DACCS plants have already been, or are in the process of being, developed around the world. For example, in Squamish, British Columbia, a barn-sized DACCS device will become operational by September 2021. This system, which Carbon Engineering has developed, will scrub out at least one ton of CO2 from the air each year. As well as this, Carbon Engineering is currently in the process of preparing for the development of an even larger DACCS plant in Texas, expected to remove 1 million tons of CO2 from the atmosphere regularly.

Although several different technologies can be employed within a given DACCS system, Carbon Engineering has instead focused on a system comprised of fans that draw in air containing 0.04% CO2 - the current concentration of CO2 in the atmosphere. Then, the air is brought across a filter soaked in potassium hydroxide solution, otherwise known as potash. The potash absorbs CO2 from the air, after which the liquid is transported into a second chamber and mixed with calcium hydroxide. This dissolved COand calcium hydroxide combination produces small limestone flakes that are ultimately stored until their decomposition.

What is Bioenergy Carbon Capture and Storage?

BECCS is another type of CO2 removal technology that involves the conversion of biomass into heat, electricity, or liquid, all of which can be referred to as bioenergy. CO2 emissions produced from the production of bioenergy are then captured and stored in geological formations or embedded into various products.  

To date, several major companies, including Chevron Corporation, Microsoft, CleanEnergy Systems, and Schlumberger New Energy, have collaborated to begin working on a large-scale BECCS project located in Mendota, California. These companies aim to convert agricultural waste biomass like almond trees into renewable synthesis gas that will be mixed with oxygen to generate electricity. Since more than 200,000 tons of agricultural waste are produced each year in this Central Valley area of California, this project will also assist in improving the local air quality.

Subsequently, over 99% of the carbon generated from this plant will be captured and stored underground into deep geologic formations. Once completed, this plant is expected to remove about 300,000 tons of CO2 annually, equivalent to the electricity use of more than 65,000 houses within the United States.

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DACCS vs. BECCS

Although these technologies are promising solutions for achieving an emission-free future, limitations exist for both. BECCS, for example, is associated with an increased fertilizer use that could further stress nitrogen-saturated ecosystems. Also, the land required for growing the biomass could alter existing habitats and further threaten biodiversity in these areas. Still, when compared to DACCS, it is the only removal technology that produces energy.

DACCS is also associated with high energy requirements. Furthermore, the transportation and injection of CO2 into geological reservoirs raises concerns about potential leakage and pollution of waterways from these sources.

Research has found that DACCS outperforms BECCS in terms of the primary energy required for each ton of carbon captured from the environment despite these challenges. More specifically, DACCS is linked with a 75-100% sequestration efficiency, while BECCS is between 50 and 90%.

Future of DACCS and BECCS

Notably, Direct Air Carbon Capture and Storage and Bioenergy Carbon Capture and Storage technologies should be used to complement decarbonization strategies. Although these approaches can assist in reducing the impacts of climate change, these forms of CO2 removal should not be used to replace climate mitigation strategies, such as transitions to renewable energy sources.

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Industrial Response to Climate Change 

This article is a part of the IPCC Editorial Series: Industrial Response to Climate Change, a collection of content exploring how different sectors are responding to issues highlighted within the IPCC 2018 and 2021 reports. Here, Cleantech showcases the research institutions, industrial organizations, and innovative technologies driving adaptive solutions to mitigate climate change. 

References and Further Reading

IPCC. (2018) Summary for Policymakers. Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. Available at: https://www.ipcc.ch/site/assets/uploads/sites/2/2019/05/SR15_SPM_version_report_LR.pdf

IPCC. (2021) Summary for Policymakers. Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate. Available at: https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf

Swain, F., (2021) The device that reverses CO2 emissions. [online] Bbc.com. Available at: https://www.bbc.com/future/article/20210310-the-trillion-dollar-plan-to-capture-co2 

Carbon Engineering. (2021) Direct Air Capture Technology | Carbon Engineering. [online] Available at: https://carbonengineering.com/our-technology/ 

Bioenergy Insight. (2021) Chevron, Microsoft among firms to develop US BECCS project. [online] Available at: https://www.bioenergy-news.com/news/chevron-microsoft-among-firms-to-develop-us-beccs-project/

American University. (2020) What is BECCS?. [online] Available at: https://www.american.edu/sis/centers/carbon-removal/fact-sheet-bioenergy-with-carbon-capture-and-storage-beccs.cfm 

Creutzig, F., Breyer, C., Hilaire, J., Minx, J., Peters, G. and Socolow, R., (2019) The mutual dependence of negative emission technologies and energy systems. Energy & Environmental Science, 12(6), pp.1805-1817. Available at: https://doi.org/10.1039/C8EE03682A

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Benedette Cuffari

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Benedette Cuffari

After completing her Bachelor of Science in Toxicology with two minors in Spanish and Chemistry in 2016, Benedette continued her studies to complete her Master of Science in Toxicology in May of 2018. During graduate school, Benedette investigated the dermatotoxicity of mechlorethamine and bendamustine; two nitrogen mustard alkylating agents that are used in anticancer therapy.

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