Mammoth Undertaking

As Climeworks starts up the world’s largest direct air capture plant, Adam Duckett looks at the engineering challenges involved

DIRECT AIR CAPTURE (DAC) crossed a new engineering threshold in May as the world’s largest plant – Mammoth – started operations in Iceland where it will draw 36,000 t/y of CO2 from the atmosphere.

Built by Climeworks, the new plant has begun operating 12 carbon collecting units which have a capacity to remove up to 6,000 t/y of CO2 from the air. It will reach full capacity later this year when all 72 of its collectors are installed and in operation. At this point it will be capturing nine times more CO2 than the previous iteration – Orca – which started on a neighbouring site in 2021.

How does the direct air capture plant work?

Climeworks says the core “know how” it has developed is the system used to capture the CO2. Collectors are housed in V-shaped structures located around the edge of the process plant and fans are used to draw air into the collectors and pass it over a solid highly porous sorbent material that binds the CO2.

To release this captured CO2, the doors on the collectors are closed and steam produced from an onsite geothermal power plant heats up the sorbent material to around 100°C. This frees a concentrated stream of CO2 mixed with steam that is piped to a process hall for further purification. From here on in, Climeworks is making use of established processing technologies.

The CO2 passes into a process hall containing a maze of pipework, pumps, and heat exchangers. The steam is condensed out, providing a pure stream of CO2 that is then collected in a giant low-pressure balloon. From here, the CO2 heads to a compressor that ramps up its pressure from ambient to 20 bar, ready for the final stage of separation – an absorption tower.

“It’s essentially a SodaStream on steroids,” says Douglas Chan, COO of Climeworks. Absorption water is injected at the top of the tower and trickles down through packing that fills the column. The water dissolves the CO2 coming up through the bottom of the tower producing a pressurised mix that is ready for injection underground through two onsite wells operated by project partner Carbfix.

Deep under the earth it reacts with the rock, becoming mineralised and locking up the emissions for long-term storage, as Jan Wurzbacher, Climeworks CEO, explains: “Within two years, the CO2 has become solid carbonate rock, 800m underground where it will stay for the next couple of millions of years for sure.”

A step up from the Orca plant

Climeworks has come a long way since it was established in the labs of ETH Zurich in 2009. There, company founders Wurzbacher and Christoph Gebald were capturing just milligrams of CO2. A kilogram-scale prototype followed in 2012. By 2014 the company’s first modular CO2 collector began capturing tonnes of CO2. The first commercial facility – Capricorn – opened in Switzerland in 2017 capturing hundreds of tonnes. The technology was then stepped up to the thousands of tonnes scale in 2021 when the Orca plant started operation in Iceland. Just a year later, Climeworks broke ground on Mammoth.

Asked by TCE to explain the process engineering differences between Orca and Mammoth, Chan touches on the changes made to how the CO2 is purified.

“There are a few different ways that industry has to purify CO2, and we can actually compare the two between Orca and Mammoth. In Orca, what we’re doing is a traditional liquefaction process which involves dehydration, refrigeration, and liquefaction of CO2 which gets rid of all the unwanted gases…and leaves you with pure CO2 in its liquid form.

“And then finally we have to evaporate that CO2 to send it over to Carbfix for injection into the well.

“So up until that point, you’re probably wondering ‘hey, where is the water?’ So, we actually are injecting CO2 into the well in the Orca process, and then the water is mixed with the CO2 [using] an injected stream underground.”

Mammoth uses an absorption tower to combine all of that.

“Everything I just described there, from the purification through to the injection and mixing with water is simplified into one step in Mammoth, which is much more elegant from a design and an operation perspective. We simply have the column with the water and the CO2 and air mixture contacting at 20 bar.”

The simplification has also increased the capture efficiency. By reducing the number of purification steps, Chan says they’ve reduced the CO2 losses at each stage.

“The more steps there are, the more losses there are. What we did at Mammoth relative to Orca is that we cut down the number of steps and, specifically, some really high energy and some really high complexity steps, which now helps us ensure that more of the carbon that we capture actually goes into the earth. So, we’re looking at over 90% recovery rates that gives us our 15% percentage point increase in recovery [compared to Orca].”

What’s the cost of capturing carbon?

Chan says that simplifying process steps and site design during scaleup from Orca to Mammoth has achieved a 10–20% reduction in capex per tonne of CO2 captured and halved the operations and maintenance costs. This includes arranging the collectors in a V-shaped configuration, which has reduced the length of piping needed to transport the captured CO2.

Asked how much the plant cost to build, Chan admitted he wasn’t allowed to disclose the exact figure. He would only say that “It’s in the order of low triple-digit millions”.

As for the cost of capturing the carbon, Wurzbacher says: “Today we are closer to the US$1,000 per tonne mark than we are to the US$100 per tonne mark.”

That cost will reduce as the scale of plants are increased. By 2030, he expects the costs to come down to around US$300/t. The UN’s Intergovernmental Panel on Climate Change (IPCC) says that the deployment of CO2 removal schemes, including DAC, are unavoidable if we are to counterbalance emissions from hard-to-abate sectors and achieve net zero.

Almost all current global CO2 removal (2bn t/y) is carried out by natural methods including plants absorbing it from the air. Novel methods including DAC are responsible for just 2m t/y according to data from Oxford University’s Smith School of Enterprise and the Environment. These novel methods could need to grow to as much as 10bn t/y by 2050 to meet international climate targets.

Analysis by Boston Consulting Group found that for DAC to become widely adopted and help meet these targets, the cost will have to fall to US$100/t.

Wurzbacher says Climeworks aims to achieve gigaton capture capacity between 2030 and 2050.

“If we apply learning rates, which are known from other industries such as solar PV and the wind industry, and if we compare them to our predicted technological learning, we’ll end up at a cost level at the order of US$100 per tonne, going towards 2050.”

How a carbon removal agreement works

Clients have already purchased a third of the plant’s 25-year lifetime capture capacity. Wurzbacher expects the entire capacity will be sold within two years. A client buys a volume of stored carbon over a set period.

“So, we would have, for example, a ten-year agreement with a certain number of tonnage of CO2 to be removed every year,” he says. Like the purchase power agreements for solar and wind farms, Climeworks wants to reach a point where the full capacity of the plant is purchased before the final investment decision on the capture facility is made. This helps secure third-party financing to build the plant.

“That is a stage we are working towards for direct air capture as well. We are not fully there yet. So, for the Mammoth plant, that has been mainly financed by Climeworks on equity. But, going forward, project financing will be vital to accelerate the scaleup.”

As for who is buying the carbon removal, the types of companies are broadening. The earliest buyers were finance, consulting, and insurance firms who want to make their services CO2 neutral. The company is now seeing a much broader interest, including from manufacturers and airlines.

The credibility of the carbon credits market is under question, however. Earlier his month, Shell came under fire for selling millions of carbon credits for CO2 that was never removed, according to an investigation by Greenpeace. In 2022, the UK’s Climate Change Committee urged the government to put in place stronger guidance, regulation, and standards.

Chan says Climeworks is working with third parties including an auditor to validate the process and certify their removals.

If we look back at the history of what we have achieved as humans that the engineered solutions will have to play a major, and I would say even THE major, part of this task of capturing 10bn tonnes of CO2 from the air by 2050

What next? Pushing for gigaton scale

Climeworks has plans to scale out its technology across the world. In March, the US Department of Energy awarded a consortium including Climeworks funding to develop a plant in Louisiana capable of capturing 1m t/y by 2030. If the project goes ahead, it could receive as much as US$600m in matched funding from the US government. Climeworks is also involved in plans for plants at megaton scale in Canada, Norway, and Kenya.

“About 200 out of 500 people at Climeworks are constantly working on developing the next generation of direct air capture technology,” says Wurzbacher. This includes chemists and engineers developing more effective sorbent materials and new processes to save energy.

Looking ahead, he says nature-based solutions have a key role to play but given that deforestation is not slowing, he thinks relying on afforestation to scale up carbon removal is a “tricky bet”.

“My strong personal belief is if we look back at the history of what we have achieved as humans that the engineered solutions will have to play a major, and I would say even the major, part of this task of capturing 10bn tonnes of CO2 from the air by 2050.”