Negative Emissions Technologies (NETs): Comparing Different CO₂ Removal Strategies

A Breakdown of DAC vs. BECCS vs. Ocean-based CO₂ Removal

Direct Air Capture (DAC)

DAC technology directly removes CO₂ from the atmosphere, providing an engineered solution to mitigate climate change [1]. When paired with geological carbon sequestration, this process is known as Direct Air Carbon Capture and Storage (DACCS). The DAC.SI project in Brazil represents South America’s first foray into this technology, with three units at varying technological readiness levels:

• The DAC Test Bench (operational since September 2023)
• The DAC 15TA (operational since April 2024) with a 15 tons/year removal capacity
• The DAC 300TA plant (operational since November 2024) with a 300 tons/year capacity [1]

Currently, there are 27 operational DAC plants worldwide capturing nearly 0.01 Mt CO₂ per year, with plans for approximately 130 additional facilities in various stages of development [3].

Bioenergy with Carbon Capture and Storage (BECCS)

BECCS combines biomass energy production with carbon capture technology. Unlike DAC, which captures CO₂ directly from the air, BECCS captures emissions from biomass combustion. Plants naturally absorb CO₂ during growth, and when this biomass is used for energy, the resulting emissions are captured and stored underground [4].

Ocean-based CO₂ Removal

Ocean-based approaches include ocean alkalinization, seaweed cultivation, and artificial upwelling. These methods leverage the ocean’s natural carbon absorption capabilities but face challenges related to ecosystem impacts and verification of carbon sequestration [5].

Evaluating the Energy Requirements and Environmental Impact of Different NETs

Energy Efficiency

The DAC.SI project reports that their DAC 300TA system requires approximately 1,289 kWh per ton of CO₂ captured, with 398 kWh for electrical components and 891 kWh for thermal energy [1]. These are targets, set at the start of the project, that are not being met today.
This presents opportunities for integration with waste heat sources in industrial areas.
BECCS, by comparison, can potentially generate net energy while capturing carbon, though actual performance depends heavily on biomass source, transportation, and processing efficiency [6].

Water Usage

Water consumption is another critical factor. The DAC 300TA system consumes approximately 2 tons of water per ton of CO₂ captured [1]. Other NETs vary significantly in their water requirements, with some BECCS implementations requiring substantial water inputs for biomass production [7].

Land Requirements

DAC systems have relatively small physical footprints compared to BECCS, which requires substantial land for biomass cultivation. Ocean-based methods have minimal land requirements but raise other environmental considerations [8].

How NETs Can Complement Other Decarbonization Efforts Like Emissions Reduction

Addressing Different Emission Sources

NETs are particularly valuable for addressing historical CO₂ production and Scope 3 emissions that are difficult to eliminate directly [1]. They complement traditional emission reduction strategies like renewable energy adoption, energy efficiency improvements, and electrification.

Regional Implementation Strategies

As the DAC.SI project demonstrates, NETs can be tailored to regional conditions. Brazil’s vast clean energy resources, geological potential for underground CO₂ storage (such as mineral carbonation in basaltic rocks), and unique environmental conditions make it particularly well-suited for certain NET approaches [1].

Integration with Energy Systems

The DAC.SI project explores opportunities to reduce energy demand by sharing infrastructure and utilizing waste heat, further enhancing DAC’s decarbonization potential [1]. This approach of system integration represents how NETs can be incorporated into existing energy and industrial infrastructures.

The Future of NETs in Global Climate Strategy

The development of NETs, particularly in regions like Brazil, is essential for fostering a comprehensive and equitable global response to climate change. Currently, CDR policy initiatives are predominantly centered in developed nations [9], but expanding these technologies to the Global South is crucial given increasing population growth, rising CO₂ emissions, and the expanding economic influence of these regions.

Brazil’s updated Nationally Determined Contribution (NDC) establishes goals to reduce net GHG emissions by 48.4% by 2025 and 53.1% by 2030, relative to 2005 levels, with a commitment to achieving net-zero GHG emissions by 2050 [1]. NETs will play a critical role in meeting these ambitious targets.

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Want to dive deeper into the technical details of Brazil’s pioneering Direct Air Capture initiatives? Download the comprehensive whitepaper about our project “Leading the way: Brazil’s pioneering steps toward Direct Air Capture (DAC) deployment in South America” to access:

• Detailed technical specifications of the DAC Test Bench, DAC 15TA, and DAC 300TA systems
• Complete performance metrics and experimental results
• In-depth analysis of implementation challenges and solutions
• Strategic roadmap for scaling DAC technology in the Global South

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References:

[1] Dalla Vecchia, F., et al. (2024). Leading the way: Brazil’s pioneering steps toward Direct Air Capture (DAC) deployment in South America. 17th International Conference on Greenhouse Gas Control Technologies, GHGT-17.

[2] IPCC. (2023). Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.

[3] International Energy Agency (IEA). (2023). Direct Air Capture. www.iea.org/reports/direct-air-capture.

[4] Fajardy, M., & Mac Dowell, N. (2017). Can BECCS deliver sustainable and resource efficient negative emissions? Energy & Environmental Science, 10(6), 1389-1426.

[5] National Academies of Sciences, Engineering, and Medicine. (2022). A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. The National Academies Press.

[6] Smith, P., et al. (2016). Biophysical and economic limits to negative CO₂ emissions. Nature Climate Change, 6(1), 42-50.

[7] Fuss, S., et al. (2018). Negative emissions—Part 2: Costs, potentials and side effects. Environmental Research Letters, 13(6), 063002.

[8] Minx, J.C., et al. (2018). Negative emissions—Part 1: Research landscape and synthesis. Environmental Research Letters, 13(6), 063001.

[9] Sovacool, B.K. (2023). Expanding carbon removal to the Global South: Thematic concerns on systems, justice, and climate governance. Energy and Climate Change, 4, 100103.