Every minute, our atmosphere gets clogged with more particles of carbon dioxide being spewed from factories and cars and more; the concentration of CO2 is currently at 408 parts per million, and it’s projected to continue growing. It’s a problem that has vexed scientists, who know the more carbon dioxide that gets into the atmosphere, the more global warming.
And just preventing fossil fuel emissions—driving less and using less energy at home—may not be enough. Engineers are instead looking into being proactive and directly taking carbon dioxide out of the atmosphere using conventional carbon capture and storage (CCS), and the newer method of direct air capture (DAC).
“Let’s imagine we have a chemical processing facility, and over time chemicals spill in the ground,” said Christopher Jones, professor of chemical and biomolecular engineering at Georgia Tech. “We remove the chemicals before we repurpose that site to build something else there. That’s exactly what direct air capture is. We can capture a large fraction of CO2 that we’ve emitted over hundreds of years.”
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CCS is currently feasible and can remove emissions from fossil fuel powered plants—in other words, keeping more CO2 from going into the atmosphere. On the other hand, DAC can actually remove existing CO2 from the atmosphere.
In CCS, CO2 is captured from a nearby power plant’s emissions, where the concentration of CO2 is much higher. CCS facilities must be built next to fossil fuel powered plants to capture the plants’ CO2 emissions, and it just prevents fossil fuel emissions from growing.
Unlike CCS, which removes CO2 from a nearby power plant’s emissions, DAC directly takes CO2 from the air, even removing CO2 that was in the air hundreds of years ago. However, the technology for DAC is still in development.
In CCS, the CO2 is more concentrated, so it’s easier to remove it, similar to removing all the green M&M’s from a holiday bag. But in DAC, CO2 is being removed from the atmospheric air. The concentration of CO2 is much more dilute, similar to how there is a lower concentration of green M&M’s in a regular bag.
The technology for CCS is feasible today, but much of DAC technology is still in development. This is because removing CO2 from the atmosphere is more difficult, as the concentration of CO2 in the atmosphere is much lower than the concentration of CO2 from power plant emissions. For example, the Petra Nova plant near Houston is already capturing CO2 using CCS methods. The technology for DAC will be very different due to CO2 concentration. Jones, who works with DAC company Global Thermostat, compares this to removing green M&M’s from a regular bag, vs. a holiday bag with red and green M&M’s.
“Even though the challenge is similar, you need a new approach and a new technology,” Jones said. “You can’t use technology for natural gas fired power plant and apply it to the air. The difference is big enough that the technology can’t be mapped to each other.”
Carbon Engineering, based in Canada, has been developing DAC technology since 2009, and it's ready to hit the market now. The firm uses chemical processing techniques, capturing CO2 through a scrubber. The scrubber is similar to a cooling tower, and as atmospheric air passes through it, a regeneration process separates CO2 from the air.
In carbon capture methods, once CO2 is caught and purified, it can be used for commercial purposes. For example, Carbon Engineering is looking into using CO2 for fuel synthesis—combining CO2 and hydrogen to make molecules to power cars. This has a lower carbon footprint than fossil fuels and can be used as a substitute. Other alternatives include feeding CO2 into a greenhouse, using it to make plastics and using it for carbonated drinks.
However, the most environmentally friendly way is to inject and store it underground. If a unit of carbon dioxide is stored underground, then that’s negative emission, since CO2 originally came from fossil fuels from beneath the Earth. In the past, there have been accidental deaths caused by natural CO2 seeps, but the risk of this is lower, said Jennifer Wilcox, chemical and biological engineering professor at the Colorado School of Mines, and more research needs to be conducted on this.
“In order for CO2 separation from air to be considered a negative emissions strategy, it needs to be put back underground, where it came from in the first place,” Wilcox said. “People get nervous about this. We need improved education and communication to the general public in addition to more demonstration-scale efforts, for instance, more monitoring, and more analysis so that people can feel good about this approach.”
However, carbon capture isn’t completely clean: It may release harmful chemicals from chemical processing, said Wilcox. Another is that separating CO2 from the air can take massive amounts of energy and water, so DAC companies must look into how to use heat efficiently.
At Carbon Engineering, CO2 is captured directly from the air, as well as the CO2 needed to generate the energy to do this, preventing more CO2 from being released. Another DAC company, Climeworks, uses geothermal energy to power their DAC systems.
Right now Carbon Engineering is in the final validation phase, which will take three to four years, before they can enter the mainstream market.
“We imagine individual facilities going to megaton scales—million tons of CO2 captured per year at individual facilities,” Geoff Holmes, who works in business development at Carbon Engineering, told The Daily Beast. “That’s capturing and purifying the quantity of emissions released by 250,000 cars […] If you ask yourself, which is more difficult, reducing 250,000 cars or building a facility? It’s probably harder to reduce 250,000 cars.”
Jones predicts that in the next five years, more companies will be launching large scale testing programs for DAC that will better help them evaluate what the economic and energy costs for operating direct air capture would be. Still, Jones says, right now there’s little focus on DAC methods from the government, and it needs more investment to continue developing.
DAC could potentially reverse the effects of climate change, but it’s not a band-aid, Rather, Wilcox says, it should be seen as a part of a whole portfolio of options (such as renewable energy sources, CCS and reducing waste) to solve the emissions problem.
“We have to be careful with this approach because it can tempt people to keep burning fossil fuels,” Wilcox said. “It can’t be seen as a silver bullet. It has to be one part of multiple options.”
