Direct Air Carbon Capture Is Scaling Up, With Mineralization

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The carbon capture field is sprawling out in all directions, including the challenging area of direct air capture. Here in the US, though, federal support for carbon capture is waning. Earlier this month the Department of Energy abruptly cancelled a $3.7 billion suite of new decarbonization technology demonstrations, including carbon capture. However, it’s a big world out there and other solutions are working their way into the global economy.

Carbon Capture: How Much, And For How Long?

Scalability is one way to measure the effectiveness of carbon capture solutions, but let’s start with duration because that is fairly straightforward.

The biofuel industry, for example, can help keep virgin fossil fuels sequestered in the Earth by deploying natural carbon recycling systems to produce bio-based liquid fuels. Biofuel stakeholders are also beginning to use carbon-reducing alternative energy crops including trees and other perennials. However, the ability of biofuels to reduce the amount of fossil fuel circulating through the global economy also depends on the force of public policy.

Similarly, electrofuels also re-circulate carbon. They are produced by combining hydrogen (ideally, green hydrogen) with captured carbon from waste gasses, or carbon extracted from biomass.

Longer periods of removal are possible when airborne carbon is captured by reforestation and other long term bio-based systems instead of recirculated as fuel. Regenerative agriculture and biochar can fall into this category. The US Department of Agriculture notes that biochar, for example, can retain carbon in soil for decades.

Reforming captured carbon into solid, durable products is another means of longer-term sequestration. Energy storage is the latest area to emerge in a growing list of new applications. The use of carbon nanofibers in cement is another example.

Carbon Capture And The Mineralization Solution

Sequestering carbon underground offers the potential for much longer periods of duration, and the scale is attractive. Back in 2014, for example, the US Geological Survey assessed that the nation could sequester up to 3,000 metric gigatons of carbon dioxide underground.

However, the economic case for simple sequestration has been a difficult one to make. The US tried — and failed spectacularly — to showcase carbon capture and sequestration (CCS) with the $1 billion “FutureGen” project of the early 2000s. Other stumbling blocks involve community opposition to new carbon pipelines. Additionally, fossil energy stakeholders in the US have begun leveraging captured carbon to reinvigorate their wells, which pretty much defeats the whole purpose.

In that context, mineralization represents a step up in the sustainable sequestration ladder. Mineralization can lock carbon away for decades, while keeping it out of the hands of fossil energy producers, too.

Natural mineralization is a common feature of the global ecosphere, involving rainwater that contains dissolved carbon dioxide. When the water hits reactive rocks, it draws out other elements that combine with carbon dioxide, forming new, solid carbonate minerals.

“Most of the rocks that have the potential for carbon mineralization are igneous or metamorphic, as opposed to porous sedimentary reservoirs,” USGS explains. The difference is important because carbon dioxide simply dissolves in the groundwater trapped in sedimentary rock, leaving the door open to escape. Reactive rock is a more permanent solution.

The Climeworks Solution

Some innovators in the mineralization field are exploring ways to stimulate surface rocks to capture more airborne carbon, a field called enhanced rock weatherization. Another approach that involves ambient air is to deploy human-made DAC systems to provide the input for underground mineralization systems.

The Swiss startup Climeworks is among the DAC firms that have begun working with stakeholders in the underground mineralization field, with the aim of achieving both scale and permanency. Climeworks has been surfacing on the CleanTechnica radar since 2017, when it revved up a small scale DAC demonstration facility at the Hellisheiði Geothermal Park in Iceland, site of the Hellisheiði geothermal power plant. Both the plant and the Geothermal Park are under the umbrella of the energy firm ON Power, a subsidiary of Reykjavik Energy.

Along with the availability of geothermal energy to run the carbon capture system, the opportunity for scalable, onsite carbon sequestration was part of the attraction. Reykjavik Energy had been running a carbon sequestration project at the site 2007, deploying the reactive property of basalt rock at the site to mineralize carbon emissions from the geothermal plant.

Next Steps For Climeworks

Climeworks has followed up on the pilot project with the new “Mammoth” DAC facility, also located in the Geothermal Park. I toured the site earlier this month on a technology tour supported by the public-private initiative Green by Iceland, which included visits with more than a dozen clean tech firms and facilities.

The scalability potential is clearly in evidence at the Mammoth facility, and so are the advantage of on-site sequestration. The injection well for the mineralization step comes under the umbrella of Climeworks’s partner, the Iceland-based firm Carbfix. The wellhead is only a few feet high, small enough to hide inside a prefabricated igloo the size of a tool shed. It sits adjacent to Mammoth, eliminating the need for long pipelines. The small size of the igloo also makes it easy to disguise, should aesthetic concerns arise. During the tour we ducked into the igloo on the tour to get a closeup look at the injection well, but there was practically nothing to see aside from some pipes.

Mammoth also represents lessons learned from the pilot-scale operation, including placement of the capturing elements to take better advantage of the wind — of which there is plenty in Iceland. Climeworks is also incorporating recent improvements in the capturing adsorbents into the new facility.

As for who’s going to pay for all this, that requires public policies that treat carbon pollution like, well, pollution. Our Climeworks tour guide framed the issue in terms of other familiar pollution control systems. Businesses routinely pay for garbage disposal as a cost of doing business. They don’t simply shovel their waste out the back door. For that matter, businesses routinely pay for air scrubbers and wastewater treatment systems at the point of emission. Similarly, those who dump excess carbon into the atmosphere should pay for removal.

Next Steps For Direct Air Carbon Capture

Ideally, of course, carbon emitters should reduce or eliminate excess carbon at the point of emission. If you have any thoughts about that, drop a note in the comment thread. Meanwhile, Climeworks emphasizes that direct air carbon capture is a complement to, not a replacement for, other climate management technologies, a position affirmed by the Intergovernmental Panel on Climate Change in 2018.

That report came out before the business case for direct air carbon capture began to materialize. It still hasn’t materialized, at least not to the extent that it is fully reflected in public policy. However, momentum has been building in the voluntary market for carbon capture.

Morgan Stanley, Tik Tok, and the leading Japanese shipping firm Mitsui OSK are among the additions to the Climeworks portfolio in recent months.

Stay tuned for more details about Carbfix, including a first-of-its-kind visit to the company’s pilot facility in Iceland.

Photo: Climeworks’s “Mammoth” direct air carbon capture plant demonstrates how Iceland’s reactive rock and geothermal resources can support the emerging carbon mineralization industry (original photo by Tina Casey).