These machines scrub greenhouse gases from the air – an inventor of direct air capture technology shows how it works

Fossil fuels have put more carbon dioxide into the atmosphere than nature can remove. CO2 traps excess heat near Earth's surface, which causes global warming. Humans will have to remove CO2 from the air in order to keep the climate stable.

The Conversation is illustrated by Arizona State University.

Direct air capture is a technology that uses chemical reactions to capture CO2 from air. Some people see federal funding for carbon capture as an excuse for fossil fuel use to continue, so carbon removal in some form will likely still be necessary, according to the reports. Current methods of removing carbon are too expensive and energy intensive, which is why technology to remove carbon mechanically is in development. New techniques are being tested to see if they can lower the cost and energy demand.

We asked Klaus Lackner, a pioneer in direct air capture and carbon storage, about the state of the technology and where it is headed.

Why is direct carbon removal necessary?

The observation that carbon piles up in the environment drove me when I was interested in carbon management. It takes nature thousands of years to remove CO2, and we are on a trajectory toward much higher concentrations.

We have to get carbon out of the environment because we can't afford it.

We can capture CO2 when it comes out of power plants or factories. We need to deal with the other half of emissions from cars, planes, taking a hot shower, and so on. Pulling CO2 out of the air is what that means.

Direct air capture works.

Since CO2 mixes quickly in the air, it doesn't matter where the CO2 is removed, it has the same impact. Direct air capture technology can be placed right where we plan to use or store the CO2.

The method of storage is important. CO2 can be stored for 60 years or 100 years. If all that carbon is back in the environment, we have to figure it out again, because we didn't take care of ourselves. The world is consuming 2% more energy per year.

Direct air capture is energy intensive and one of the complaints about it. Can the energy use be reduced?

Two large energy uses in direct air capture are running fans to draw in air and then heating to extract the CO2. There are ways to reduce energy demand.

We found a material that attracts CO2 when it is dry and releases it when wet. We realized we could expose that material to the wind. We could make it wet and it would release the CO2 in a way that requires less energy than other systems. Adding heat from renewable energy raises the CO2 pressure even higher because we have a CO2 gas mixed with water vapor.

Climeworks has plants that remove carbon dioxide from the air. Climeworks.

If the capture is passive, we can save more energy because the air moves on its own.

My lab is working on a way to do this. The discs are about 5 feet in diameter and 2 inches apart, and they are tall vertical columns. The discs absorb CO2 when the air blows through. The discs sink into a barrel after 20 minutes. We use water and steam to release the CO2 into a closed environment, and now we have a low-pressure mixture of water vapor and CO2. The amount of energy needed for heating is small because we can recover most of the heat that went into heating up the box.

We can use renewable energy for the majority of the energy we use. It will not be ideal everywhere, but there are other methods.

Is there enough of the type of storage for CO2?

I started working on the concept of mineral sequestration in the 1990s. The world can permanently remove CO2 by taking advantage of the fact that it is an acid and certain rocks are base. Solid carbonates are formed when CO2 reacts with calcium-rich minerals. By mineralizing the CO2 like this, we can store a lot of carbon permanently.

There is a lot of basalt in Iceland that reacts with CO2 and becomes solid carbonates within a few months. The rest of the world could buy certificates of carbon sequestration from Iceland.

There are huge underground oil production areas in Texas. There are large underground sources of water. Equinor has been capturing CO2 from a gas processing plant and storing a million tons of CO2 a year in the North Sea, avoiding a tax on CO2 releases. The amount of underground storage we can do is larger than we will ever need. How much can be converted into proven reserve?

Klaus Lackner is testing air capture technologies. Arizona State University.

Direct air capture can be used to close the carbon loop because CO2 is captured and reused again to avoid producing more. Carbon from fossil fuels is being used to extract energy. If you mix the captured CO2 with green hydrogen created with renewable energy, you can convert CO2 to synthetic fuels. It is possible to produce heat and electricity in Boston on a winter night using energy that was collected in West Texas last summer. A tankful of synfuel is more cost-effective than a battery.

The Department of Energy wants to cut the cost of carbon dioxide removal to US0 per ton within a decade. What can be done to make that a reality?

The DOE makes it sound like the technology is ready. We have to push the technology along after neglecting it for 30 years. This is a new technology.

Climeworks is the largest company doing direct capture, and it sells CO2 at a rate of between 0 and,000 per ton. That is too expensive. The world could do it at a per ton rate. I think we can get there.

The U.S. consumes 7 million tons of CO2 a year in merchant CO2, which is used to control grain powder, which is an explosion hazard. The average price over the course of the year. You have a market.

You need a regulatory framework that says we demand CO2 is put away, and then the market will move from capturing kiloton of CO2 today to gigatons of CO2.

Where do you think this technology will go in 10 years?

A world that abandons fossil fuels probably gradually, but has a mandate to capture and store all the CO2 long term.

When carbon comes out of the ground, it should be matched with an equal removal. 1 ton of carbon is associated with coal, oil or gas. It doesn't have to be the same ton, but there has to be a certificate of sequestration that assures it has been put away, and it has to last more than 100 years. It is harder to cheat the system if all carbon is certified.

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It's not known how hard industry and society will push to become carbon neutral. It is encouraging to see companies like Microsoft buying carbon credits and certificates to remove CO2 and willing to pay high prices.

If the economic pull is there, new technology can go fast. In 1951, the first commercial jet was available. By 1965, they were ubiquitous.

The Conversation is a news site that shares ideas from academic experts. Klaus Lackner was the author.

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Klaus Lackner is a Scientific advisor to Carbon Collect and holds shares in the company that is working with Arizona State University. Aircela is developing a household-scale system to convert carbon dioxide into synthetic fuel. Lackner's work in carbon management has been supported by research grants from private companies, foundations, universities and the U.S. Department of Energy.