two centuries of the burning of fossil fuels has released more carbon dioxide, a potent greenhouse gas, into the atmosphere than nature can remove.
As this CO2 accumulates, it traps excess heat near the Earth’s surface, causing global warming. There is so much CO2 in the atmosphere now that most scenarios show end emissions alone enough to stabilize the climate — humanity will also have to remove CO2 from the air.
The US Department of Energy has a new goal to scale direct aerial capture, a technology that uses chemical reactions to capture CO2 from the air. While federal funding for carbon capture often draws criticism because some people see it as an excuse to continue using fossil fuels, removing carbon in one form or another still be needed, IPCC reports show.
Mechanical carbon removal technology is under development and operates at a very small scale, in part because current methods are extremely expensive and energy-intensive. Corn new technics are being tested this year that could help reduce energy demand and cost.
We asked the Arizona State University professor Klaus Lackner, a pioneer in direct air capture and carbon storage, on the state of the technology and its future.
What is direct carbon removal and why is it considered necessary?
When I became interested in carbon management in the early 1990s, what pushed me was the realization that carbon accumulates in the environment. It takes nature thousands of years to eliminate this CO2, and we are on a trajectory towards much higher CO2 concentrations, far beyond anything humans have known.
Humanity cannot afford to have increasing amounts of excess carbon floating around in the environment, so we must recover it.
Not all emissions come from major sources, such as power plants or factories, where we can capture the CO2 as it exits. So we have to deal with the other half of the emissions – from cars, planes, taking a hot shower while your gas furnace is emitting CO2. This means extracting CO2 from the air.
How direct air capture works.
Since CO2 mixes rapidly in the air, it doesn’t matter where in the world the CO2 is removed — the removal has the same impact. So we can place direct air capture technology where we plan to use or store the CO2.
The method of storage is also important. Storing CO2 for only 60 or 100 years is not enough. If in 100 years all that carbon is back in the environment, we’ve just taken care of ourselves, and our grandchildren have to figure it out again. Meanwhile, global energy consumption is increasing by approximately two percent per year.
One of the complaints about direct air capture, in addition to the cost, is that it is energy-intensive. Can this energy consumption be reduced?
Two important uses of energy in direct air capture are running fans to draw in air and then heating to extract the CO2. There are ways to reduce the energy demand for both.
For example, we came across a material that attracts CO2 when dry and releases it when wet. We realized that we could expose this material to the wind and it would pick up CO2. Then we could make it wet, and it would be release CO2 in a way that requires much less energy than other systems. Adding heat created from renewable energy further increases the CO2 pressure, so we have a CO2 gas mixed with water vapor from which we can collect pure CO2.
We can save even more energy if the capture is passive — there’s no need for fans blowing air; air moves on its own.
My lab is creating a method to do this, called mechanical shafts. They are tall, vertical columns of disks coated with a chemical resin, about five feet in diameter, with the disks about two inches apart, like a stack of disks.
As the air blows, the surfaces of the discs absorb CO2. After about 20 minutes the discs are full and they sink into a barrel below. We send water and steam to release the CO2 in an enclosed environment, and now we have a low pressure mixture of water vapor and CO2.
We can recover most of the heat that went into heating the box, so the amount of energy needed for heating is quite low.
By using humidity, we can avoid about half of the energy consumption and use renewable energy for the rest. This requires water and dry air, so it won’t be ideal everywhere, but there are other methods as well.
Can CO2 be stored safely long term, and is there enough of this type of storage?
I started working on the concept of mineral sequestration in the 1990s, leading a group in Los Alamos. The world can actually store CO2 permanently by taking advantage of the fact that it is an acid and some rocks are basic.
For example, there is a lot of basalt — volcanic rock — in Iceland reacting with CO2 and transforms it into solid carbonates in a few months. Iceland could sell carbon sequestration certificates to the rest of the world because it stores CO2 for the rest of the world.
There are also huge underground reservoirs of oil production in the Permian Basin in Texas. There are large saline aquifers. In the North Sea, one kilometer below the ocean floor, the energy company Equinor captures CO2 from a gas processing plant and stores it one million tons of CO2 per year since 1996, saving Norway tax on CO2 emissions. The amount of underground storage where we can perform mineral sequestration is far greater than we will ever need for CO2. The question is how much can be converted into a proven reserve.
We can also use direct air capture to close the carbon loop – which means that the CO2 is reused, captured and reused again to avoid producing more.
Right now, people are using carbon from fossil fuels to extract energy. You can convert CO2 into synthetic fuels – gasoline, diesel or kerosene – which do not contain carbon by mixing CO2 with green hydrogen created with renewable energy.
This fuel can easily be shipped through existing pipelines and stored for years, so you can generate heat and power in Boston on a winter night using energy that has been collected as sunshine in West Texas last summer. A full tank of “synfuel” is not expensive, and it’s more profitable than a battery.
The Department of Energy has set a new target to reduce carbon dioxide disposal costs to $100 per ton and rapidly increase them within a decade. What must happen for this to become reality?
The DOE scares me because they give the impression that the technology is already ready. After neglecting technology for 30 years, we can’t just say there are companies that know how to do it and all we have to do is push it. We have to assume that this is a nascent technology.
Climeworks is the largest commercial direct capture company, and it sells CO2 at around $500 at $1,000 per ton. It’s too expensive. On the other hand, at $50 a ton, the world could do it. I think we can do it.
The United States consumes approximately seven million tons of CO2 per year in Merchant CO2 – think carbonated drinks, fire extinguishers, grain silos use it to control grain powder, which is a risk of explosion. The average price is $60 to $150. So below $100 you have a market.
What you really need is a regulatory framework that says we require CO2 to be stored, and then the market will go from capturing kilotonnes of CO2 today to capturing gigatonnes of CO2.
Where do you see this technology going in 10 years?
I see a world moving away from fossil fuels, probably gradually but with a mandate to capture and store all CO2 in the long term.
Our recommendation is that when the carbon comes out of the ground, it should come with equal removal. If you produce a ton of carbon associated with coal, oil, or gas, you must set aside a ton. It doesn’t have to be the same ton, but there must be a escrow certificate this guarantees that it has been put away and should last more than 100 years. If all the carbon is certified as it comes out of the ground, it’s harder to fool the system.
A big unknown is how much pressure industry and society will push to become carbon neutral. It’s encouraging to see companies like Microsoft and stripes buy carbon credits and certificates to eliminate CO2 and willing to pay quite high prices.
New technologies may take a decade or two to penetrate, but if the economic pull is there, things can move quickly. The first commercial jet was available in 1951. By 1965 they were ubiquitous.