Despite being at an early stage of development, direct air capture for carbon dioxide holds huge potential to decarbonise our atmosphere. Michael Nelson discovers the potential impact of this new technology, as well as the journey towards commercial viability.

According to the International Energy Agency (IEA), global carbon dioxide (CO2) emissions declined by 5.8 per cent in 2020, owing to the pandemic hitting demand for oil and coal harder than other energy sources while renewables increased. Despite the drop in emissions however, global energy-related CO2 emissions remained at 31.5 gigatons, which contributed to CO2 reaching its highest ever average annual concentration in the atmosphere of 412.5 parts per million in 2020 – around 50 per cent higher than when the industrial revolution began.

With projections estimating that CO2 emissions will rebound and grow by 4.8 per cent in 2021, the global community is growing increasingly concerned about whether climate targets will be achievable. In order to limit global warming to 1.5 degrees Celsius, humanity will need to remove billions of tons of CO2 from the atmosphere per year by mid-century.

In the face of this daunting challenge, promising solutions are being developed which could help reduce atmospheric CO2. Direct air capture (DAC) is a method of extracting and filtering CO2 from the air or other low-concentration sources such as building ventilation.

Compared to conventional carbon capture technologies, which focus primarily on extracting CO2 from concentrated point sources such as flue gases, effluents from biogas, or other industrial processes, the concentration of CO2 in ambient air and ventilation exhausts varies between 400 parts per million (PPM) and up to 2000 PPM.

While this may seem like a small amount considering that CO2 concentration in flue gases can be between ten and 15 per cent – and even higher in gases released from the purifying or upgrading steps used in biological processes – the fact that DAC is removing CO2 from the atmosphere directly, rather than preventing further pollution, could help to turn the tide in decelerating climate change.

How has DAC been developed?

Climeworks is one of the best-known companies in the world of direct air capture, and were among the first to develop the technology. Their machines consist of modular CO2 collectors that can be stacked to build machines to any scale, and are powered solely by renewable energy or energy-from-waste.

The CO2 collectors selectively capture CO2 in a two-step process. First, air is drawn into the collector with a fan, and CO2 is captured on the surface of a highly selective filter material that sits inside the collectors. This process is known as ‘adsorption’.

Second, after the filter material is full of CO2, the collector is closed and the temperature is increased to between 80 and 100 degrees Celsius. This releases the CO2 – ‘desorption’ – which is then collected in both high purity and concentration. The air-captured CO2 can either be upcycled into climate-friendly products such as carbon-neutral fuels and materials, or completely removed from the air by safely storing it in geological formations underground.

“The inspiration for Climeworks goes back almost a decade,” said a Climeworks spokesperson. “The company’s two co-founders, Jan Wurzbacher and Christoph Gebald, met on their first day of university at ETH Zurich in 2003. Besides their love of engineering, they both shared a passion for alpine sports and spent a lot of time in the Swiss Alps, where they experienced the effects of climate change first-hand.

“Shocked by the retreat of the glaciers, they vowed to do everything they could to tackle climate change – one of the biggest challenges humanity has ever faced.”

Founded in 2009, Climeworks has been commercially operational since 2017, with solutions already scaled to industrial size.

From capturing just a few milligrams of CO2 per day in small-scale laboratory experiments a decade ago, to capturing thousands of tons a year in the present day, the scale-up of their technology has been at a factor of one billion. The challenge now is to replicate a comparable scale-up over the next few years to ensure DAC remains a viable solution to help support decarbonisation efforts.

Orca – The world’s largest DAC plant

One of the biggest steps towards Climeworks’ target of mass production by 2025 was the launch of Orca in September of this year. Located in Iceland, the Orca carbon capture plant is being built close to ON Power’s Hellisheidi Geothermal Power Plant near Reykjavik, meaning that all the energy required to run the DAC process will come from purely renewable sources.

The carbon that is captured at the site will be stored underground in basaltic rock formations where a natural mineralisation process will turn it to stone. This is performed by Climeworks’ partners, Carbfix.

For now, while other carbon capture organisations scramble to catch up, Orca is the largest DAC plant in the world, with the capacity to capture 4000 tones of CO2 per year. Significantly, in comparison to carbon mitigation through planting trees, the facility can capture the same amount of carbon as a forest 400 times the size.

The plant is considered a first milestone in a journey to expand to megaton removal capacity by the second part of the decade.

Speaking in a press release announcing the launch, Wurzbacher said that: “Orca… Has provided a scalable, flexible and replicable blueprint for Climeworks’ future expansion. With this success, we are prepared to rapidly ramp up our capacity in the next years. Achieving global net-zero emissions is still a long way to go, but wih Orca, we believe that Climeworks has taken one significant step closer to achieving that goal.”

Solutions to enable DAC scale-up

While carbon capture technology holds promise, a recent report by the Coalition for Negative Emissions and conslutancy firm McKinsey estimates that the world needs to deliver one gigatonne of negative emissions globally by 2025 to keep global warming within the Paris Agreement target of 1.5 degrees Celsius. Clearly, more work needs to be done, and current carbon capture facilities need to be rapidly scaled-up so that they can play a role alongside increased renewable generation and energy efficiency strategies.

According to Petri Laakso, CEO at Finnish carbon capture company Soletair Power, one of the most efficient and promising ways to scale-up DAC technology is by converting carbon into food, fuel, or consumer products.

Soletair Power are also pioneering DAC applications to capture carbon from buildings. “We are combining two ideas – capturing CO2 and improving air quality in offices,” says Laakso. “ We aim to lower the cost of capturing by mass manufacturing our units and utilising better sorbents, the latter of which also lowers energy consumption. Our DAC units follow a modular design principle which enables our customers to install multiple units and assemble them on site. Customers can then choose to get a unit with a large production capacity, or a regular unit capable of supporting add-on units to increase production capacity at a later stage.”

“Around 40 per cent of global CO2 emissions come from buildings. By transforming buildings into carbon sinks, net-zero targets can become achievable. Only the combination of DAC technologies and renewable energy sources will enable businesses to become carbon neutral or negative.”

To prove the capabilities of their technology, Soletair Power are providing a demonstration unit for the Dubai Expo 2020. The unit, which has power-to-X incorporated into it, consists of a CO2 capturing device, an electrolyser, and a synthesis device, and will be used to power an espresso machine with the synthetic natural gas that is produced.

While the Dubai unit has a 1kW flame, Soletair’s technology can be scaled-up to 30 times the size of the machine exhibited at the Expo.

For Climeworks, scaling-up means reaching out to more private individuals and businesses, and generating greater demand for carbon dioxide removal. They say that their priority is to unite a strong network of different stakeholders that drive forward the direct air capture industry together, thus democratising the process.

There are four main areas that Climeworks have identified for improvement in order to facilitate the scale-up of carbon capture technology.

First, a market demand for carbon dioxide removal must be created to show there is a growing interest in these solutions. Pioneering customers, both individuals and organisations, are at the forefront of enabling this.

Second, investor support is a crucial part of being able to scale and pre-finance new facilities. This would mean DAC companies can increase their capacity and potimise the technology at a much faster rate.

Third, a political framework is required that gives security for such investments and reflects the true costs of CO2 emissions.

And finally, a structured supply chain needs to be developed to ensure an easier transition towards mass production.

Conclusion

Critics are quick to point out that, currently, carbon capture technology is not a cost-effective measure, concluding that it is merely a distraction from the real policy measures and systemic changes that are needed to fight climate change. Insight from an expert elicitation survey published by Frontiers In Climate estimates that CO2 removal costs will remain expensive heading towards mid-century, at around $200 per ton of CO2 removed.

Nevertheless, the publication expects the role of direct air capture in a two degrees Celsius policy scenario to be significant.

Meanwhile, a recent lifecycle assessment by the RWTH Aachen University confirmed that DAC can play a major role in reversing climate change, with the study stating that the environmental benefits of the technology far outweigh its environmental impact, and that both the resources and energy required for climate-relevant scales of DAC are available.

Given this evaluation, perhaps the next decade will see DAC take its place alongside other strategies as one of the pillars of our drive towards climate neutrality.

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