The Engineer

Direct air capture 'unlikely' to address CO2 concerns

News

According to a report issued by the American Physical Society, direct air capture (DAC) technologies for removing carbon dioxide (CO2) from the atmosphere are unlikely to offer an economically feasible way to slow human-driven climate change.

‘We humans should not kid ourselves that we can pour all the CO2 we wish into the atmosphere right now and pull it out later at little cost,’ said Robert Socolow, a professor of mechanical and aerospace engineering at Princeton University.

The report — Direct Air Capture of CO2 with Chemicals — was issued by a committee of 13 experts co-chaired by Socolow and Michael Desmond, a chemist at BP.

The group looked at technologies, known as DAC, in which ambient air flows over a chemical sorbent that selectively removes the CO2. The CO2 is then released as a concentrated stream for disposal or reuse, while the sorbent is regenerated and the CO2-depleted air is returned to the atmosphere.

In essence, the committee found that such technologies would be far more expensive than simply preventing the emission of the CO2 in the first place.

Making optimistic assumptions about initial DAC technologies, the committee concluded that, from the evidence it had seen, building and operating a system today would cost at least $600 (£367) for each metric ton of CO2 removed from the atmosphere. In comparison, removing CO2 from the flue gas of a coal-fired power plant would cost about $80 per ton.

As a result, the group concluded, DAC is not likely to become worthwhile until nearly all the significant concentrated sources of CO2 — emissions from power plants or other industrial operations — are eliminated.

‘We ought to be developing plans to bring to an end the CO2 emissions at every coal and natural gas power plant on the planet. We don’t have to do this job overnight. But the technologies we studied in this report, capable of removing CO2 from the air, are not a substitute for addressing [emissions from] power plants directly,’ Socolow said.

The possibility of using DAC has arisen in policy discussions that contemplate a so-called ’overshoot’ strategy in which the target level of CO2 in the atmosphere is exceeded and then reduced later through the use of some air capture technology.

In its report, the group noted that no demonstration or pilot-scale DAC system has yet been deployed anywhere on Earth, and it is entirely possible that no DAC concept under discussion today or yet to be invented will actually succeed in practice.

Interested readers can view the report here.