Reducing carbon dioxide in the atmosphere is one of the most pressing concerns facing the world today. Cutting back the amount of CO2 that's newly pumped into the air is vital, but it might not be enough – we need to suck out some that's already up there. Direct air capture (DAC) systems have been discussed as a possibility for decades but it was, until recently, deemed too expensive to be practical. After running a pilot plant for three years, Canadian company Carbon Engineering (CE) has broken down the costs of a DAC system and shown it can be done much more cost-effectively than previously thought.

As the team notes, DAC technology itself is not particularly new. Last year, Swiss company Climeworks opened one of the first commercial DAC plants near Zurich, which is made up of a roof-mounted facility that captures CO2 from the air and pipes it into a nearby greenhouse. A few months later, Climeworks partnered with a geothermal plant to lock the CO2 in stone, but the purified carbon could also be used to make methanol, carbon nanofibers, or diesel fuel.

But the cost of setting up these kinds of systems has traditionally been thought of as too high to be economical. Previous estimates have put the cost at between US$500 to $1,000 per metric ton, but in a new research paper based on three years of data from a pilot plant, the CE team shows how it could be done for between $94 and $232 per metric ton.

"Until now, research suggested it would cost $600USD per ton to remove CO2 from the atmosphere using DAC technology, making it too expensive to be a feasible solution to removing legacy carbon at scale," says David Keith, lead researcher on the project. "At CE, we've been working on direct air capture since 2009, running our pilot plant since 2015, and we now have the data and engineering to prove that DAC can achieve costs below $100USD per ton. No prior research in the peer-reviewed literature provides a design and engineering cost for a complete DAC system – and this paper fills that gap."

Carbon Engineering's direct air capture equipment. Shown are the calciner (left) and air contactor (right) Carbon Engineering

The pilot plant is made up of an industrial cooling tower, remodeled to pull CO2 from the air before converting it from a gas to a solid and back to a purified gas. To start with, the facility uses a liquid hydroxide solution to capture the CO2, and convert it into a carbonate. That is then formed into pellets, which are in turn heated in an industrial kiln to produce a pure carbon dioxide gas.

That gas can then form the basis of a synthetic fuel. The company has developed a process it calls Air To Fuels, which uses water electrolysis and fuels synthesis techniques to turn that pure CO2 into liquid hydrocarbon fuels. CE says these fuels are compatible with existing transportation infrastructure.

"Our clean fuel is fully compatible with existing engines, so it provides the transportation sector with a solution for significantly reducing emissions, either through blending or direct use," says Steve Oldham, CEO of CE. "Our technology is scalable, flexible and demonstrated."

The research was published in the journal Joule.

Sources: Carbon Engineering, Harvard