What it will take to achieve affordable carbon removal

A pair of companies have begun designing what could become Europe&#;s largest direct-air-capture plant, capable of capturing as much as a million metric tons of carbon dioxide per year and burying it deep beneath the floor of the North Sea.

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The sequestered climate pollution will be sold as carbon credits, reflecting the rising demand for carbon removal as a drove of nations and corporations lay out net-zero emissions plans that rely heavily, whether directly or indirectly, on using trees, machines, or other means to pull carbon dioxide out of the air.

Climate researchers say the world may need billions of tons of carbon dioxide removal annually by midcentury to address the &#;residual emissions&#; from things like aviation and agriculture that we can&#;t affordably clean up by then&#;and to pull the climate back from extremely dangerous levels of warming.

The critical and unanswered question, however, is how much direct air capture will cost&#;and whether companies and nations will decide they can afford it.

The facility proposed by the two companies, Carbon Engineering and Storegga Geotechnologies, will likely be located in North East Scotland, enabling it to draw on plentiful renewable energy and funnel captured carbon dioxide to nearby sites offshore, the companies said. It&#;s expected to come online by .

&#;We can&#;t stop every [source of] emissions,&#; says Steve Oldham, chief executive of Carbon Engineering, which is based in British Columbia. &#;It&#;s too difficult, too expensive, and too disruptive. That&#;s where carbon removal comes in. We&#;re seeing an increasing realization that it&#;s going to be essential.&#;

Getting to $100 a ton

Oldham declines to say how much the companies plan to charge for carbon removal, and he says they don&#;t yet know the per-ton costs they&#;ll achieve with the European plant.

But he is confident the company will eventually reach the target cost levels for direct air capture identified in a analysis in Joule, led by Carbon Engineering founder and Harvard professor David Keith. It put the range at between $94 and $232 per ton once the technology reaches commercial scale.

Getting to $100 per ton is essentially the point of economic viability, as large US customers generally pay $65 to $110 for carbon dioxide used for commercial purposes, according to a little-noticed May paper by Habib Azarabadi and direct-air-capture pioneer Klaus Lackner, both at Arizona State University&#;s Center for Negative Carbon Emissions. (The $100 doesn&#;t include the separate but considerably smaller cost of carbon sequestration.)

At that point, direct air capture could become a reasonably cost-effective way of addressing the 10% to 20% of emissions that will remain too difficult or expensive to eliminate&#;and may even compete with the cost of capturing carbon dioxide before it leaves power plants and factories, the authors state.

But the best guess is that the sector is nowhere near that level today. In , the Swiss direct-air-capture company Climeworks said its costs were around $500 to $600 per ton.

What it will take to get to that $100 threshold is building a whole bunch of plants, Azarabadi and Lackner found.

Specifically, the study estimates that the direct-air-capture industry will need to grow by a factor of a little more than 300 in order to achieve costs of $100 a ton. That's based on the "learning rates&#; of successful technologies, or how rapidly costs declined as their manufacturing capacity grew. Getting direct-air capture to that point may require total federal subsidies of $50 million to $2 billion, to cover the difference between the actual costs and market rates for commodity carbon dioxide.

Lackner says the key question is whether their study applied the right learning curves from successful technologies like solar&#;where costs dropped by roughly a factor of 10 as scale increased 1,000-fold&#;or if direct air capture falls into a rarer category of technologies where greater learning doesn&#;t rapidly drive down costs.

&#;A few hundred million invested in buying down the cost could tell whether this is a good or bad assumption,&#; he said in an .

Dreamcatcher

The United Kingdom has set a plan to zero out its emissions by that will require millions of tons of carbon dioxide removal to balance out the emissions sources likely to still be producing pollution. The government has begun providing millions of dollars to develop a variety of technical approaches to help it hit those targets, including about $350,000 to the Carbon Engineering and Storegga effort, dubbed Project Dreamcatcher.

The plant will likely be located near the so-called Acorn project developed by Scotland-based Storegga&#;s subsidiary, Pale Blue Dot Energy. The plan is to produce hydrogen from natural gas extracted from the North Sea, while capturing the emissions released in the process. The project would also repurpose existing oil and gas infrastructure on the northeast tip of Scotland to transport the carbon dioxide, which would be injected into sites below the seabed.

The proposed direct-air-capture plant could leverage the same infrastructure for its carbon dioxide storage, Oldham says.

The companies initially expect to build a facility capable of capturing 500,000 tons annually but could eventually double the scale given market demand. Even the low end would far exceed the otherwise largest European facility under way, Climeworks&#; Orca facility in Iceland, slated to remove 4,000 tons annually. Only a handful of other small-scale plants have been built around the world.

The expected capacity of the Scotland plant is essentially the same as that of Carbon Engineering&#;s other full-sized facility, planned for Texas. It will also begin as a half-million-ton-a-year plant with the potential to reach a million. Construction is likely to start on that plant early next year, and it&#;s expected to begin operation in .

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Much of the carbon dioxide captured at that facility, however, will be used for what&#;s known as enhanced oil recovery: the gas will be injected underground to free up additional oil from petroleum wells in the Permian Basin. If done carefully, that process could potentially produce &#;carbon neutral&#; fuels, which at least don&#;t add more emissions to the atmosphere than were removed.

Oldham agrees that building more plants will be the key to driving costs, noting that Carbon Engineering will see huge declines just from its first plant to its second. How sharply the curve bends from there will depend on how rapidly governments adopt carbon prices or other climate policies that create more demand for carbon removal, he adds. Such policies will essentially force &#;hard-to-solve&#; sectors like aviation, cement, and steel to start paying someone to clean up their pollution.

RICHLAND, Wash.&#;As part of a marathon research effort to lower the cost of carbon capture, chemists have now demonstrated a method to seize carbon dioxide (CO2) that reduces costs by 19 percent compared to current commercial technology. The new technology requires 17 percent less energy to accomplish the same task as its commercial counterparts, surpassing barriers that have kept other forms of carbon capture from widespread industrial use. And it can be easily applied in existing capture systems.

In a study published in the March edition of International Journal of Greenhouse Gas Control, researchers from the U.S. Department of Energy&#;s Pacific Northwest National Laboratory&#;along with collaborators from Fluor Corp. and the Electric Power Research Institute&#;describe properties of the solvent, known as EEMPA, that allow it to sidestep the energetically expensive demands incurred by traditional solvents.

&#;EEMPA has some promising qualities,&#; said chemical engineer Yuan Jiang, lead author of the study. &#;It can capture carbon dioxide without high water content, so it&#;s water-lean, and it&#;s much less viscous than other water-lean solvents.&#;

Carbon capture methods are diverse. They range from aqueous amines&#;the water-rich solvents that run through today&#;s commercially available capture units, which Jiang used as an industrial comparison&#;to energy-efficient membranes that filter CO2 from flue gas emitted by power plants.

Current atmospheric CO2 levels have soared higher in recent years than at any point within the last 800,000 years, as a new record high of 409.8 parts per million was struck in . CO2 is primarily released through human activities like fossil fuel combustion, and today&#;s atmospheric concentrations exceed pre-industrial levels by 47 percent.

At a cost of $400&#;$500 million per unit, commercial technology can capture carbon at roughly $58.30 per metric ton of CO2, according to a DOE analysis. EEMPA, according to Jiang&#;s study, can absorb CO2 from power plant flue gas and later release it as pure CO2 for as little as $47.10 per metric ton, offering an additional technology option for power plant operators to capture their CO2.

Jiang&#;s study described seven processes that power plants can adopt when using EEMPA, ranging from simple setups similar to those described in s technology, to multi-stage configurations of greater complexity. Jiang modeled the energy and material costs to run such processes in a 550-megawatt coal power plant, finding that each method coalesces near the $47.10 per metric ton mark.

Solving a solvent&#;s problems

One of the first known patents for solvent-based carbon capture technology cropped up in , filed by Robert Bottoms.

&#;I kid you not,&#; said green chemist David Heldebrant, coauthor of the new study. &#;Ninety-one years ago, Bottoms used almost the same process design and chemistry to address what we now know as a 21st century problem.&#;

The chemical process for extracting CO2 from post-combustion gas remains largely unchanged: water-rich amines mix with flue gas, absorb CO2 and are later stripped of the gas, which is then compressed and stored. But aqueous amines have limitations. Because they&#;re water-rich, they must be boiled at high temperatures to remove CO2 and then cooled before they can be reused, driving costs upward.

&#;We wanted to hit it from the other side and ask, why are we not using 21st century chemistry for this?&#; Heldebrant said. So, in , he and his colleagues began designing water-lean solvents as an alternative. The first few solvents were too viscous to be usable.

&#;&#;Look,&#;&#; he recalled industry partners saying, &#;&#;your solvent is freezing and turning into glass. We can&#;t work with this.&#; So, we said, OK. Challenge accepted.&#;

Over the next decade, the PNNL team refined the solvent&#;s chemistry with the explicit aim to overcome the &#;viscosity barrier.&#; The key, it turned out, was to use molecules that aligned in a way that promoted internal hydrogen bonding, leaving fewer hydrogen atoms to interact with neighboring molecules.

Heldebrant draws a comparison to children running through a ball pit: if two kids hold each other&#;s hands while passing through, they move slowly. But if they hold their own hands instead, they pass as two smaller, faster-moving objects. Internal hydrogen bonding also leaves fewer hydrogen atoms to interact with overall, akin to removing balls from the pit.

Pivoting to plastic

Where the team&#;s solvent was once viscous like honey, it now flowed like water from the kettle. EEMPA is 99 percent less viscous than PNNL's previous water-lean formulations, now nearly on par with commercial solvents, allowing them to be utilized in existing infrastructure, which is largely built from steel. Pivoting to plastic in place of steel, the team found, can further reduce equipment costs.

Steel is expensive to produce, costly to ship and tends to corrode over time in contact with solvents. At one tenth the weight, substituting plastic for steel can drive the overall cost down another $5 per metric ton, according to a study led by Jiang in .   

Pairing with plastic offers another advantage to EEMPA, whose reactive surface area is boosted in plastic systems. Because traditional aqueous amines can&#;t &#;wet&#; plastic as well (think of water beading on Teflon), this advantage is unique to the new solvent.

The PNNL team plans to produce 4,000 gallons of EEMPA in to analyze at a 0.5-megawatt scale inside testing facilities at the National Carbon Capture Center in Shelby County, Alabama, in a project led by the Electric Power Research Institute in partnership with Research Triangle Institute International. They will continue testing at increasing scales and further refine the solvent&#;s chemistry, with the aim to reach the U.S. Department of Energy&#;s goal of deploying commercially available technology that can capture CO2 at a cost of $30 per metric ton by .  

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