Carbon Dioxide Removal (CDR) vs Carbon Capture and Storage (CCS)
Topic: CDR vs. CCS
What is it?
Carbon capture and storage (CCS) is the capture of carbon dioxide (CO₂). This can be applied to CO₂ emitters, or point-sources, specifically electricity generation from natural gas and industrial operations such as cement production, as well as to the ambient atmosphere. Carbon dioxide removal (CDR) is a specific subset of CCS that results in the net-removal of CO₂ from the atmosphere.. There are many pathways to achieve CDR, such as planting trees and engineered direct air capture (DAC).
How does it work?
CCS can be used to separate the CO₂ from other gases that are emitted from point-sources. For example, flue gas that comes from a natural gas power plant will also have gases such as nitrogen (N₂), oxygen (O₂), and water vapor (H₂O). The CO₂ often makes up 4-30% of the gas mixture in flue gases. To isolate the CO₂ from these other gases, the flue gas is bubbled through special chemicals called amines that are dissolved in water. The CO₂ binds to the amines and the other gases pass through unaffected and are vented to the atmosphere. Once the CO₂ has bound to the amines dissolved in water, the solution is heated up so the CO₂ can be captured in a pure stream and the amine solution can be used again. This method allows for N₂, O₂, and H₂O to enter the atmosphere and for CO₂ to be separated so it can be compressed and sent to storage or to be utilized.
CDR can be used to separate CO₂ from other gases in the atmosphere. Similar to flue gas, other gases in the atmosphere are N₂, O₂, and H₂O. However, the CO₂ in the atmosphere only makes up 0.04% of the gas mixture! This makes the capture of CO₂ much more difficult. The primary way to capture CO₂ from the atmosphere is by use of chemical reactions. These chemical reactions come in many different forms, from photosynthesis to rock weathering to engineered DAC. Some promising CDR methods include:
- Afforestation/Reforestation: Afforestation is the planting of trees where there were none previously. Reforestation is the planting of trees where there were before.
- Mineral Carbonation: Binding of CO₂ with alkaline rocks or industrial materials to form new, stable, carbon-containing minerals. Mineral carbonation can act as a form of CO₂ storage and has the potential to be part of a CDR system when the CO₂ derives from the atmosphere. Mineral carbonation also forms the basis of some emerging DAC approaches.
- Direct Air Capture (DAC): Capture of CO₂ from the atmosphere using special chemicals. Two primary methods to achieve this are the use of liquid solvents and solid sorbents.
- Bioenergy for Carbon Removal and Storage (BiCRS): Using biomass, which captures CO₂ during its lifetime to create energy and use CCS to capture CO₂ from the flue gas produced.
- Coastal Blue Carbon: Protection and restoration of coastal wetlands to increase their uptake of CO₂ from the atmosphere.
- Soil Carbon Sequestration: Land management practices that result in soil uptake of CO₂ out of the atmosphere and storing it deep in the soil ecosystem.
Why is it important and what are the major barriers?
CCS and CDR are both important to achieve climate goals because they both reduce the amount of CO₂ that is pooled into the atmosphere. CCS can be used specifically to reduce CO₂ emissions in cases where they are difficult to reduce otherwise. An example of easier to reduce emissions would be replacing a natural gas power plant with renewable energy, but in some cases, such as cement production, the reduction of CO₂ emissions is much more difficult. This is where CCS would be well applied. Further research is needed to optimize CCS systems where the power needed to run these systems impact the economic viability of deploying them. Additionally, further research needs to be done to determine where the most difficult to decarbonize facilities are located and the policy instruments could be used to promote their deployment.
CDR is important because it allows for CO₂ emissions already in the atmosphere to be reduced. This is going to be helpful when we aim to bring the CO₂ concentration down closer to 350 ppm, as opposed to the current 410 ppm. Additionally, since CCS is expensive to deploy, CDR can assist in capturing emissions from smaller CO₂ emitters, such as long-haul trucks or airplanes, until there are ways to achieve this transportation without emissions. Further research is needed in optimizing the many approaches for CDR, measuring and verifying the carbon removal and/or storage for most nature-based solutions, and in determining the geo-bio-spatial constraints in deploying these solutions at large scale. Research is also needed to better understand and design policy instruments to further promote the development and deployment of these solutions.
What we do
In the Clean Energy Conversions Lab (CECL), we do research to determine how CCS can assist in the energy transition without justifying the continued use of fossil fuels for sectors that are easier to abate. Additionally, our research focuses on two main CDR approaches, DAC and mineral carbonation. We have furthered the field by completing techno-economic assessments for various DAC approaches powered by multiple different energy sources and using mapping strategies to illustrate places where DAC may be best deployed for access to low-carbon energy and CO₂ storage. Finally, we also have worked in the mineral carbonation space by conducting techno-economic assessments and experimental work focused on determining the best pathways and conditions for carbonating various mineral feedstocks.
- CDR Primer (2021)
- Direct Air Capture: Resource Considerations and Costs for Carbon Removal (2021)
- A Review of Direct Air Capture (DAC): Scaling Up Commercial Technologies and Innovating for the Future (2021)
- Natural Gas vs. Electricity for Solvent-Based Direct Air Capture (2021)
- The Royal Society of Chemistry - Carbon Capture and Storage (2020)
- Carbon Capture and Storage (CCS): The Way Forward (2018)
- Current State of Industrial Heating and Decarbonization Opportunities (2022)