Taking carbon out of the air and putting it into concrete

Under a new partnership, Heirloom Carbon Technologies captures carbon dioxide from the air, then passes it to CarbonCure Technologies, which permanently sequesters it in concrete. In this episode, CEOs Shashank Samala of Heirloom and Robert Niven of CarbonCure give the lowdown on this pioneering carbon removal project.

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David Roberts

Last month saw the announcement of a pioneering project: a company called Heirloom Carbon Technologies will capture carbon dioxide from the ambient air and then hand it off to a company called CarbonCure Technologies, which will inject the CO2 into concrete made by a company called Central Concrete. It will mark the first time ever that carbon from the air is permanently sequestered in concrete.

Heirloom, with runs the US’s only operating direct air capture (DAC) facility, does not use the familiar capture technique that involves giant fans. Instead, it binds carbon to exposed rock and then cooks it out using electric kilns — and then binds more carbon to the rock, in a circular process. It claims the capture is cheaper and more efficient than previous methods.

CarbonCure injects the CO2 into a concrete mixer, where it mineralizes, becoming permanently captured even if the building using the concrete is demolished. In the process, it strengthens the mix, requiring less cement and cutting costs.

Direct air capture (DAC) has faced a great deal of skepticism, and concrete has the reputation as one of the worst carbon offenders, so this project — one of the first that can fairly be called carbon removal — could go a long way toward convincing investors that the former can help the latter change its ways, with a technology that is, at least some day, commercializable.

I talked with Heirloom CEO Shashank Samala and CarbonCure CEO Robert Niven about their respective processes, how they work together, and what the project says about the future of carbon removal.

All right, Shashank Samala, CEO of Heirloom Carbon Technologies, and Robert Niven, CEO of CarbonCure. Welcome to Volts. Thank you guys for coming.

Robert Niven

Thanks very much for having us.

David Roberts

This is really a nifty project you guys are working on together. It's two separate pieces that normally I would probably do a pod on each. So we're going to have to, or at least I'm going to have to be less wordy than normal to squeeze it all in in 1 hour. I want to talk about both halves of it. So let's start with Shashank. The first half of this process is Heirloom’s process of removing carbon from the air. Can you just explain quickly how that process works, what it looks like?

Shashank Samala

Sure. So, Heirloom, if you're not aware of who we are, our goal is to basically remove a billion tons of CO2 from the atmosphere annually by 2035. And our whole goal is to help reverse climate change. And the way we do that is through a process called limestone looping. Essentially what that means is we use a rock that is very abundant in nature, limestone, that has a natural propensity to pull carbon from the air. What we do is we basically give superpowers to limestone to pull a lot more carbon than it otherwise would naturally.

So how it works is we start with limestone, we put that into a kiln, we heat it up, and we pull out the CO2 that's already sequestered in the limestone, which makes the leftover lime highly thirsty for CO2. So we take advantage of that natural property by laying it out on trays. Think about baking trays. I lay them out on trays, and then we vertically stack those trays, very tall, and the air brings in the CO2. And the the lime sitting on the tray acts as a sponge, pulls up the CO2 molecules. From there, it becomes limestone again after it pulls it up. And we do that in about three days.

Naturally, it would take many months to pull carbon from the air. We did that in three days using our well treated algorithms and technology.

David Roberts

So in three days means the lime is full, absorbed as much CO2 as it can.

Shashank Samala

Exactly. We don't go all the way up to 100%. We go up to about 85%, which is sort of the optimal point, we realized. And then, yeah, it becomes limestone again, which is great, because that's what you started with. So we can recycle limestone by putting it back into the kiln, pull out the CO2 we captured, and then store it underground or store it into concrete, which you're doing with Carbon here.

David Roberts

Right. So one of the questions I had is you crush up this lime and spread it out on, well, calcium carbonate is limestone. Calcium carbonate ...

The chemical formula. Exactly right, the calcium carbonate.

And then after you bake it, take CO2 out. Then what is the chemical remainder?

Shashank Samala

Calcium oxide.

David Roberts

Calcium oxide. Right. So you have calcium oxide laid out on trays, becoming calcium carbonate. Then you take the calcium carbonate, cook it, get the CO2 out of it, and then do the whole thing over again.

Shashank Samala

Exactly. We just keep doing that. It's a super simple chemical process to pull carbon from the air.

David Roberts

You have this calcium oxide, and it's absorbing CO2 from the air. That just sounds like an ambient chemical process. How can it be accelerated? What does it even mean to accelerate that?

Shashank Samala

So, technically, calcium oxide, we hydrate it, it becomes calcium hydroxide. Basically, there's a water molecule binding onto the calcium oxide. But essentially what we realized is that there's a specific parameter space where particle size, particle size distribution, thickness of the bed, humidity, temperature, airflow, there's all these different variables that dictate how fast calcium hydroxide likes to bind on to CO2 molecules. So it just so happens that in nature, there's a specific parameter space where this happens, and in nature, it doesn't see that parameter space as often. What we do is essentially make it see that all the time.

And how we specifically do that is really the IP. But we've collected millions and millions of data points over the last few years, doing lots of small experiments, adjusting thickness, adjusting particle size, surface area, all of these things. And we found that parameter space. And as the weather changes throughout the day, we have to change that parameter space. So essentially, we babysit these trays. If you look at, essentially, what this technology looks like is you have these tall stacks of trays, and in the middle, you have a little robot that goes up and down, and every few hours, it's babysitting these trays so that they can be carbonating as fast as they possibly could.

David Roberts

So is this all in a big climate