High Hopes claims stratospheric breakthrough in direct air CO2 capture

In the race to get humanity toward zero carbon emissions by 2050, the vast majority of efforts will rightly be focused on reducing emissions at their source. But there are areas where this simply won't be possible, and as carbon taxes gradually rise around the globe there will definitely be a market for direct air capture.

The trouble right now is the extremely high cost of pulling carbon directly out of the air. Switzerland's Climeworks operates at 14 locations presently, with large factories processing ambient air and separating out the carbon, but its costs are currently somewhere in the range of US$600-1000 per ton, and its own future projections graph doesn't show this price dropping much below US$250/ton by 2035.

With the problem well into the billions of tons, and demand expected to be driven by carbon taxes as they ramp up across the globe, price is critical. And price is where Israeli startup High Hopes believes it has a killer proposition: starting off at around US$100/ton, the company believes it can reach US$50-60 a ton with scale – by far the cheapest direct air capture solution on the market.

How? Using balloons and high altitudes.

Ground-based direct air capture is expensive chiefly because it's an energy-intensive process. Taking the Climeworks process as an example, large fans are used to draw in ambient air, and carbon dioxide is captured on the surface of a filter. Then the collector is closed, and heated to 80-100 °C (176-212 °F), releasing a concentrated stream of CO2. This stream is then compressed to around 70 atmospheres and sent underground for geosequestration – a separate company mixes it with water and pumps it deep underground, where it reacts with basalt rock and gradually turns into stone over a few years.

The fans, the heating and the compression are the major costs here, and this is where High Hopes Founder and Chief Scientist Eran Oren had what may become his world-changing idea, calling his friend and eventual High Hopes Chief Marketing Officer Nadav Mansdorf at 4am to deliver an impassioned three-hour sermon on phase diagrams.

"It's 4am. I'm cursing his mother. My wife is wondering what's the emergency. I hate him," Mansdorf tells us, "but when Eran has an idea, you listen. He said carbon dioxide freezes at around -80 °C (-112 °F), it turns into dry ice, which is very easy to capture. You don't need heat, you don't need compression, you can do this with minimal energy. And there's a place where you can find ambient temperatures very close to that, with lots of wind to move air through at useful rates, and carbon everywhere: in the atmosphere, 10-15 km (33,000-50,000 ft) above sea level."

So the idea is this: put low-energy carbon capture rigs in high-altitude balloons, send them up to heights where they can work most efficiently (just below the inversion layer, where atmospheric temperatures start to rise), fill up pressure tanks with dry ice, then bring them down to Earth. As the temperature rises, the dry ice will turn back into CO2 gas, pressurizing itself thanks to the restricted volume of the tanks, and it can be sent straight out for geosequestration.

The balloons are already commercially available – they're the same Google was using for its now-defunct Project Loon stratospheric broadband project. "According to the publications, the Google balloons can carry 150-200 kilos (330-400 lb) up to 20, 20-something kilometers (65,000-plus ft)," says Oren. "So in relevant altitudes to us, it can carry something like 300 kg (660 lb). This is a commercial product, Google buys these balloons from Raven Aerostar, an American company."

"So this serves as a good reference point for what is very achievable in our roadmap," he continues. "Looking ahead, we'll probably want to go to larger balloons. These do exist, but they're not yet commercially available. NASA and several other entities have developed and flown balloons up to around one and a half metric tons of payload. So this doesn't require major breakthroughs in technology, and we look at this as more or less the upper limit of what's reasonable for us."

The balloons will carry two-step carbon-capture systems. As air flows in, a simple absorption process will slightly enrich the levels of carbon dioxide. Then, using a small amount of energy, some aluminum plates are cooled down to the freezing point of CO2. Dry ice freezes out of the air and settles on these plates like snowflakes, and these snowflakes are collected into the pressure tank.

"None of this is new," says Oren, "this is a very basic process called cryodistillation. The only thing is that when you do it at high altitude, you really don't need a lot of energy to extract carbon dioxide."

The balloons will use hydrogen, both as their lighter-than-air lift gas and as the energy storage for the carbon capture and to run their on-board navigation systems, which leverage directional wind patterns. A balloon would need to stay aloft for between 12-24 hours in order to collect a full metric ton of CO2, at which point it would come down, land, top up its hydrogen, swap its full CO2 tank for an empty one, and go back up.

A state-of-the-art stratospheric balloon running for a full day on expensive hydrogen fuel, only to come down and bring home just one ton of CO2, representing US$50-100 worth of bacon? How does that make for good business?

"The capital expenses are definitely not low here," says Oren. "Namely, you need the balloons, the fuel cells, and a system to manufacture the hydrogen on-site. But these are only capital expenses, they should last many years and we can divide those over a number of loads across a period of time. As to the operational expenses, most of that is just hydrogen: you use some for energy, and when you run the numbers, even under severe assumptions, the amount of energy you need for cryodistillation comes to several tens of dollars per metric ton of CO2."

"Some hydrogen will also leak, due to the natural permeability of the balloon's Mylar/BoPET material. Using lift gases is always accompanied by some leakage, because the molecules are very small. But putting the numbers in the equations, a balloon of relevant size will leak several kilograms per day. At several dollars per kilogram, this is not negligible but it's not a deal-breaker."

"And yes," he continues, "there are extra operational expenses on the ground. But these prices scale up very, very well. The manpower you need for one balloon is quite high, but it's virtually the same as what you'd need for ten balloons, or even a hundred."

"Compare that to the ground-based factories," adds Mansdorf, "and the cost of a hundred balloons is a fraction of the cost of a factory. Even if we start with modest 50 kg (110 lb) balloons, within five balloons we're more attractive than the factories in Switzerland. And to scale up, the factories need a huge amount of land and facilities to make a significant impact. In terms of scale, ours is a brilliant solution."

For large-scale implementation, the team is looking at sub-Saharan Africa, close to the equator for the optimal air conditions, close to areas with abundant geosequestration potential, and somewhere with relatively clear flight paths overhead so there's minimal impact on air traffic. Location is irrelevant to the end goal; a ton of carbon pulled from one spot on the planet will have the same impact as a ton pulled from elsewhere, so the team is free to chase the ideal situation wherever on the globe it might arise.

As to the inherent safety considerations around working with hydrogen, which can blow up in spectacular fashion: "There are many," says Oren, "and as a general guideline, we're trying to use existing tech and knowledge. The bottom line is that people should not be in close proximity to large amounts of hydrogen. Lightning is quite unlikely at cruise altitude as it is far above the clouds. It's unlikely on the ground because we're aiming for areas near the equator, that have sunshine almost year-round. Tears can definitely happen and they are taken into account as part of our operational model, by trying to prevent them, detect them, and when needed, fix them."

High Hopes has built, flown and tested small-scale demonstrator-size balloons in the "several kilos" range. "We have proven all of our assumptions, engineering-wise," says Oren. "Not to say that we haven't learned and corrected things along the way, but I can't stress enough: cryodistillation is extremely simple. These are solved problems."

"The next step," says Mansdorf, "is starting to scale up, continuing development and hitting our next major milestone, which is getting to 50-100 kg (110-220 lb) per day, which we expect in around eight to ten months. The real challenge is getting to the 1 ton balloons – although that technology already exists in one form or another. We think we can hit that in two to three and a half years. And even if we fail to get there, and we stall at balloons carrying just 100 kg, we're still better than any other solution that currently exists. It's very exciting."

"Direct air capture now," Oren adds, "is at around 1,000 tons a year. Generally speaking, if it doesn't get to the millions to ten of millions of tons per year, then it's probably irrelevant in the scheme of things. So that's the minimum that we're aiming at, and in terms of energy, land use, materials, rare Earth metals and technical restraints, we can scale it up as much as needed. In terms of geosequestration, the known amount of carbon we can put in the ground, that will settle there as minerals, is enough to cover everything that's been emitted so far, and many years into the future."

"Without funding limitations, we could extract billions of tons of carbon from the air," says Mansdorf. "But the debate is over. The political and business worlds are burning to find solutions and support them, because if we don't solve this, Covid-19 will look like a walk in the park. We're aiming to get into the tens or hundreds of millions of tons – and even if we only make it to 100,000 tons a year, it'll be much better than all the factories and facilities in the world, I believe."

As a reality check, the numbers are as daunting here as they seem to be with any climate solution. To reach just one million tons of carbon captured per year, High Hopes would need to get 2,055 massive one-ton balloons into operation, each pulling down a full CO2 tank every 18 hours. And that's assuming year-round availability and no punctures or tears.

On the other hand, carbon taxes are popping up all over the world, and they're likely to rise over the coming decades as governments put pressure on industry to account for the future costs they're causing the public sector with every ton of CO2 they put in the air.

Sweden is already taxing certain emitters at a robust US$126 per ton, and that's already high enough to work economically with a solution like this. The rest of the world is a long way behind this figure, but everything is moving in the right direction.

In most cases, the economical choice for emitters will be to embrace new technologies and decarbonize their operations, or grab their CO2 and sequester it right from the source. But where that's impossible, or too expensive, direct air carbon capture will be there to bridge the gap to zero, and we're going to want it as cheap as we can possibly get it.

We wish the High Hopes team every success in their venture and will keep tabs on progress. Check out a short video below – skip to around 40 seconds in if you've heard enough about the problem and want to get to the solution.

Source: High Hopes