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Direct Air Capture: The most ideal, non-ideal solution
You can't always get what you want...
I want to start this week by giving a shout-out to all of the impressive, mission-driven direct-air carbon capture start-ups that I’ve had the pleasure to interact with over the past months. In a strictly alphabetical order: Carbon Engineering, Carbyon, Heirloom, Mission Zero, Mosaic Materials, and Verdox — keep building the future!
and shout-out to ExxonMobil for buying the Google Ad word “carbonengineering”
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Now for this week’s Musing…
Let’s be honest…
Nothing about this whole climate crisis thing is ideal.
Humans are a rather near-sighted, least path of resistance type of species.
⌛ We like to believe we think-long term… but anything beyond a 5-year plan might as well be abstract art
💵 We like to spend as little money as possible to build our infrastructure… and once it’s going, we don’t like to spend more money keeping it running
🏛️ And… we definitely don’t like letting the government tell us what to do
Almost nothing about global warming lends itself to this philosophy on life.
Managing the changes that climate change will bring is going to take long-term planning and cost considerations, complete overhauls of the existing infrastructure base, and lots & lots of government intervention.
In short: we’re dealing with a lot of non-ideal options.
Here we are — an existential crisis in waiting. Current behaviors put us on a pathway for ~5 degrees Celsius of warming by the end of the century.
Fun fact? The Earth was ~6 degrees Celsius colder than the 20th century during the last Ice Age. I don’t know about you, but I don’t want to find out what 5 degrees in the other direction looks like…
So… we’re swimming in a pool of non-ideal solutions… which is the least non-ideal of all? I pick direct-air carbon capture. The most ideal, non-ideal solution of the bunch!
Direct air carbon capture (DAC): 35K foot view ✈️
To keep it short-and-sweet for the 101 section this week…
DAC is the process of capturing CO2 that is floating around us in the air directly. Then storing that CO2 somewhere not in the atmosphere (likely underground wells).
There’s multiple approaches to direct-air capture, but they all involve 3 components:
Moving air: as I’ll describe below, the low concentrations of CO2 in the air and slow reaction rates mean you need to move a lot of air in these systems.
Capturing carbon: to capture CO2, you need a chemical reaction to take place. This could come from a solvent solution like KOH, a solid sorbent covered in amines, dead-simple rocks like MgO or CaO, or electrochemical quinone reactions. Lots of options!
Releasing carbon: the reason you can capture carbon is thermodynamics — said simply, DAC systems are set up so the CO2 wants to react. But once you react, you have to fight nature and inject energy into the system so you can release the carbon again for permanent storage out of the atmosphere.
Check out this rendering of a Carbon Engineering DAC system to get the idea…
DAC: Why so non-ideal? ❌
I won’t deny it — there’s a fair amount of DAC skepticism out there in the world. For every DAC believer, it feels like there are two non-believers.
So why all the non-believers? What makes DAC so non-ideal? A few things…
CO2 concentration 💨
First and foremost… there just isn’t a lot of carbon dioxide in the air. I know, I know… global warming crisis and everything, how can that be?
As opposed to capturing carbon from smoke stacks (flue gas), the CO2 concentration in air is extremely dilute. How much so? There’s about 120,000ppm CO2 in coal flu gasvs. ~420ppm CO2 in air. That’s a ~300x difference.
For reference: Air is ~78% N2 and ~21% O2 (by volume), CO2 pales in comparison.
Reaction requirements 🧪
Once you find that carbon… the chemical reaction of capturing carbon takes some work. Without getting too technical, a few factors are at play: the capture materials don’t have a high capacity to capture CO2, the reaction takes a long time, once it happens… you have to dump energy into it to release the CO2 for storage, and that process degrades the capture materials over time.
This means a lot of capture materials, replaced frequently, with a lot of fans to speed up the reaction, and a lot of energy to facilitate the reaction… 💰💰💰
Energy requirements ⚡
Largely due to the energy required to regenerate or “restart” the reaction, DAC is energy expensive. For reference, existing liquid-solvent DAC solutions call for ~10-12GJ of energy per ton of CO2 captured.
Advanced solid sorbents are targeting ~8-9GJ of energy per ton, and best-in-class solutions are targeting 3-5GJ per ton. Slice it any way you want, that’s a lot of energy.
For scale: 10Gt-CO2 of DAC per year at 5GJ per ton is equivalent to 14,000 TWh of energy demand. The globe consumes ~22,000 TWh of electricity annually.
Take the above three factors and you end up with a pretty expensive solution unless it’s done at scale and the technology & process efficiencies are improved. To make matters worse, the people paying for the solution don’t get a physical product, like electricity, in returns - making the price tag even harder to swallow.
Order of magnitude: DAC today costs >$600/t-CO2. By 2024, the target is ~$300/t-CO2, and long-term, the target is less than $100/t-CO2.
The above complaints are all completely fair… and the start-ups I named at the beginning are vigorously working to address these challenges. But science & engineering takes time.
At least the concentration of CO2 in the atmosphere is going up… 😓
DAC: Why so ideal? ✔️
Even with the above challenges, I remain a strong ‘bull’ on DAC due to the inherent characteristics that make it shine in a world of non-ideal solutions. Specifically:
Going negative ➖
Almost all of the 1.5C pathways call for large quantities of negative emissions. This means reducing emissions with electric vehicles, solar power, or even point-source carbon capture isn’t enough. We need negative emissions (full stop).
And not small quantities of negative emissions either — a lot — on the order of 50% of today’s CO2 footprint alone. DAC is primed to meet the call of negative emissions.
Anywhere, anytime 🌎⌚
Meeting the call of billions of tons of captured carbon annually means a lot of new infrastructure, where site location & operations will only increase in importance.
Atmospheric carbon is everywhere, all the time — offering DAC the luxury of flexible siting (anywhere) and operations (anytime), which are serious technical and economic advantages. This translates to two primary optimization opportunities:
Energy optimization: siting DAC in the vicinity of ultra-low cost renewables and heat sources provides cheap energy to power the process and lower net capture costs. Additionally, the ability to ramp up / down alongside these resources (e.g., duck curve) is important for optimizing system-wide energy costs.
Site optimization: once you capture the carbon, you have to store or use it somewhere! Placing a DAC facility next to underground storage wells or large sources of customer demand improves the overall carbon ecosystem and removes the requirement to build miles-and-miles of CO2 pipelines.
Stack these factors alongside alternatives (e.g., point-source)… they’re hard to beat!
Turning the knob 🖨️
Now for the human nature argument. Humans are sadly… a bit lazy.
As mentioned, we tend to focus on near-term, acute consequences and often brush the long-term, chronic risks under the rug. Moreover, the distributed nature of carbon emissions and climate risk across countries makes attribution difficult. This means, as we’ve seen over the past decades, that the world is unlikely to make the changes required on the timeline required.
As sad as that may be, when we wake up in 10-20 years and finally see the physical consequences, we’ll be looking for a solution where we can simply ‘turn the knob’ and crank up as high as we want — maximizing negative emissions. DAC fits that mold.
Crystal ball time 🔮
DISCLAIMER: I’m not saying that all of the challenges with DAC will be resolved. And I’m not sponsoring a DAC investment for every investor out there.
What I am saying is that I’m a pragmatically optimistic believer in a 1.5-2C world, and DAC is one of our more reliable bets to get there.
It plays right into human nature, is the closest thing to a silver bullet that we’ve got, and with any luck, #science will make it even less non-ideal than it is today.
If I was a betting man… I’d put my money on DAC for the long haul. Fingers crossed 🤞
Until next time…
PPM = Parts per Million; 120,000ppm ~ 12%
Energy input requirements: For the climate-geeks out there, DAC isn’t all electricity. Today, it’s about 50% heat and 50% electricity to run the processes. And for many processes, that heat can be so “high quality” that it isn’t efficient to generate it through electrical methods. I’m using electricity and TWh as a reference point as it’s a bit easier to understand for most than primary energy demand.
Flexibly operated… to an extent: Similar to green hydrogen, the trade-off of flexible operations (or only running part of the time) is the economics hit you take. Essentially, you can’t lower your operating capacity (% of the day you are running) too much, or your upfront costs (CAPEX) start to become overwhelming in the grand scheme of things.
Point source capture: some of the challenges for point-source systems include dealing with humidity, heat, and harsh chemicals that are often present in flue gas from power plants… along with retrofitting existing facilities and designing around infrastructure rather than building an optimized system from scratch.