Biogenic CO2 sequestration: Bioenergy with carbon capture and storage

By now, we are all well aware of the impacts of carbon dioxide emissions. While great effort is made to reduce emissions globally, the question remains: What can be done about carbon already in the atmosphere? After all, turning off the tap doesn’t make much difference to a flooded bathroom.

This is where carbon capture and storage (CCS) comes in. The idea is that carbon is captured and permanently stored, where it can’t add to the greenhouse gas effect. This differs from carbon capture and utilisation (CCU), which would involve capturing CO2 and then using it somewhere it will be emitted shortly after, like in fizzy drinks or greenhouses (although there are some cases where CCU can provide permanent storage, such as in cement or concrete).

How can CO2 be captured?

CO2 can be captured from emitters using technologies such as membranes or amine solutions, extracted from the air with direct air capture (DAC), or during photosynthesis in plants and other organisms. After all, nature has spent the last few million years perfecting these carbon-capturing machines.

Adding CCS to bioenergy

Bioenergy takes biological material with all the carbon it has absorbed and uses it to create energy through combustion or by making biofuels. However, this process releases the carbon that was stored in the biological material. An answer is to add CCS to the bioenergy process (BECCS).

BECCS captures the carbon released during the production of energy and stores it, either permanently in geological stores or by returning it to the soil as biochar (which has the added benefit of improved soil health), meaning there is a net reduction of CO2 over the course of the whole process.

BECCS as it stands

In theory, zero-emission bioenergy can be produced while also preventing the emissions that would have been released by the biomass at the end of its lifetime. This incredibly exciting ’carbon negative’ process utilises technology that is already mature. DAC on the other hand, requires energy to drive the process and is a developing technology.

However, currently there are very few BECCS facilities globally, with a total capacity of 2 million tonnes per year and most being North American bio-ethanol producers which use carbon capture to trap the CO2 produced in the fermentation process. One of these plants has a capacity of 1,000,000 tonnes of CO2 a year, permanently storing the captured gas in a geological site below the plant. That alone is 20 times more than global DAC capacity.[1] Even though 1,000,000 tonnes per year can be captured and stored, there are still emissions associated with the production and use of the bioethanol which are greater than the amount captured in this facility.

There are two ways to look at the previous statement. One is that more CO2 is released by the process than captured. The other is that a significant portion of the CO2 released by the ethanol product was mitigated through CCS. The latter viewpoint shows the power of BECCS to mitigate hard-to-decarbonise industries, such as heavy transport. The former viewpoint highlights the need for whole-system thinking when considering carbon capture, something that lifecycle analysis (LCA) can help address.

From a purely carbon reduction point of view, direct combustion of biomass and subsequent capture of the CO2 released would be the preferred option for BECCS compared to biofuel production. This is because CO2 capture from large point sources, such as power plants, is much more cost-effective than for diffuse sources, such as vehicles. But if combustion engines hang around, they need fueling, and it’s better to have some of the emissions mitigated than none at all.

BECCS deployment

BECCS clearly has huge potential for carbon reduction and perhaps the best potential as a carbon-negative technology, but as we’ve seen, there are very few operational facilities, the largest of which would barely put a dent in the UK’s emissions, let alone the US. So why aren’t there more BECCS facilities?

The reality is that the drivers to encourage their development have only really been around very recently. The push for net zero and, eventually, negative emissions has only been in vogue for the last decade or so, with the Paris Climate Agreement being signed in 2015 and the UK becoming the first major economy to enshrine its net zero target into law as recently as 2019.

Similarly, the existence of significant carbon markets is a very recent phenomenon. Figures show that the demand for carbon offsetting [2] and the price of carbon [3] was low before 2018 but has, in recent years, skyrocketed. These historical market conditions go some way to explaining the nascent stage of BECCS projects. The current and forecast financial landscape surrounding CCS will likely lead to significant future investment, which BECCS will surely benefit from, though it will have to compete with other carbon removal techniques, such as afforestation.

Another factor impacting BECCS deployment is the extensive and costly infrastructure required to transport and store the captured CO2. Suitable geological storage sites need to be identified, and kilometres of pipes, as well as pressurisation and injection equipment, are required to actually store the CO2.

There are also concerns about land use, with some estimating as much as 700 million hectares is needed to meet CO2 emission reduction targets,[4] which is as much land as the entire Amazon basin. This also raises the concern of whether the value of energy crops may lead to a reduction in the amount of food grown, which could lead to potential food shortages, water shortages, and price hikes. The term used to describe this notion is the food-water-energy nexus.[5]

Similarly, the carbon removal potential of BECCS is directly tied to biomass sourcing. If the source is not sustainable, then any benefit may be lost. The sustainability of the source is affected by many factors, such as transport and processing requirements, speed of re-growth, and disturbance of soil stores. This point is the cause of much of the historical controversy surrounding biomass energy. To address this issue, emphasis should be placed on using sustainably sourced biomass, such as waste biomass, rather than virgin sources.

Additionally, the storage of CO2 needs to be approaching geological timescales, and humanity has never attempted to achieve that longevity before. Some sites have already reported leaks in their carbon storage, raising concerns about groundwater and soil contamination, not to mention the potential emission of CO2.

Furthermore, there is the ever-present spectre of greenwashing and fears that any carbon-negative technology will be used to offset other emissions with no overall reduction in the amount of CO2 we pump into the atmosphere.

The future of CCS

But it’s not all doom and gloom, and progress is being made in the area. In the UK alone, there are several significant projects, such as Acorn and HyNet. Should its planned projects all reach their scheduled capacities, the UK could be capturing and storing up to 30 million tonnes of CO2 per year by 2030, which is about 11% of current emissions.

Globally, projects in the early and advanced stages of deployment have a planned capacity of around 60 million tonnes of CO2 per year by 2030 [6], comparedto the existing capacity of roughly 2 million tonnes a year and the huge rate of growth is self-evident. It still falls short of the predicted CO2 removal requirement of 8 billion tonnes a year [7], but the momentum in the sector is huge and as technology, skills, and commercial incentives develop, BECCS deployment is sure to increase.

If the world is going to get serious about its climate targets, it needs carbon-negative technologies, and the best one we have at our disposal for now is BECCS. It’s not without its drawbacks, but it needs to be part of the broad mix of our solutions to meet net zero. It takes advantage of effective nature-based carbon capture, combined with human ingenuity, to produce a carbon-negative solution that meanwhile generates clean electricity, heat or both. All things must come with effective legislation, commercial drivers, ethical implementation, and consideration of the system as a whole. If not, a vast potential won’t be realised.

How can SLR help?

Carbon capture utilisation and storage (CCUS) is a complex topic, especially considering evolving legislation, government support schemes, and technological advancements. SLR has a wealth of experience across multiple CCUS projects. For example:

• A technical peer review for Peterhead Power Station
• Development of a commercialisation plan on behalf of Premier Oil
• Owner’s Engineer and Technical Due Diligence for Crofthead Anaerobic Digestion (AD)

As such, SLR is well equipped to provide a full suite of support for CCUS projects, such as:

• Technical feasibility studies and optioneering
• Technical due diligence
• Support with civil and structural aspects such as construction and pipeline requirements
• Geotechnical support for identification of suitable storage locations
• Economic advice for carbon credits and financial modelling
• Permitting and regulatory support from planning through to ESG reporting
• Contract management for the lifecycle of the project
• Ecological and environmental impact studies for construction and operation of projects

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References

1. The Chemical Engineer, (June 2024).Direct Air Capture: The State of Play and What’s to Come. Issue 996, p.26. https://www.thechemicalengineer.com/magazine/issues/issue-996/
2. https://www.forest-trends.org/publications/state-of-the-voluntary-carbon-markets-2021
3. https://bluebellindex.com/what-is-the-impact-of-high-carbon-credit-prices
4. https://www.globalccsinstitute.com/wp-content/uploads/2019/03/BECCS-Perspective_FINAL_18-March.pdf
5. https://www.fao.org/land-water/water/watergovernance/waterfoodenergynexus/en
6. https://www.iea.org/energy-system/carbon-capture-utilisation-and-storage/bioenergy-with-carbon-capture-and-storage
7. Genden, Oliver, et al., The State of Carbon Dioxide Removal (2024), 2nd Edition. https://www.stateofcdr.org/