Some questions remain over their capacity to really put a dent in the problem, but direct air capture (DAC) systems that collect carbon dioxide from the atmosphere are starting to take shape as new tools in the fight against climate change. A company at the cutting edge of this technology has outlined its vision to use Australia's vast, open spaces and abundant sunlight to power millions of modular DAC systems, which they say could collectively capture many hundreds of times the amount of carbon the country emits each year.
Quite separately from reducing carbon emissions in the first place, the potential of DAC systems lies in their ability to remove those already in the air. This could have an important impact in sectors that are difficult to decarbonize, such as aviation, but the idea doesn't come without controversy, with skeptics concerned it could detract from efforts to mitigate emissions, which must remain the primary focus. In any case, the IPCC has stated that the world will need to rely on technologies like DAC to avoid dangerous levels of global warming, and there are a growing number of outfits taking up the challenge.
Among those is Australian renewable energy company Southern Green Gas, which is in the business of developing carbon-neutral fuels, among other endeavors. Its DAC units use porous structures called metal organic frameworks to selectively soak up CO2 as ambient air is drawn into the system, which would then be stored underground to permanently lock away the carbon. The company's managing director, Rohan Gillespie, tells us this could be achieved in a few different ways.
"Underground CO2 storage could be via three options," he explains. "Into depleted oil or gas reservoirs where CO2 is stored in the pores in the rock and a sealing cap rock layer above holds it there permanently, into deep non-oil or gas bearing formations where CO2 is stored in the pores in the rock and a sealing cap rock layer above holds it there permanently, or into basalts where CO2 reacts with the salts to form carbonate rock."
This last approach is the one being employed rather successfully by the CarbFix project, which in 2016 made a big breakthrough with a new technique that turns CO2 into solid rock within two years, instead of centuries or even longer. This technology is now the basis of the world's largest DAC plant operated by startup Climeworks, which was switched on in Iceland earlier this month and is expected to harvest 4,000 tons of CO2 each year.
Where Climeworks' plant takes advantage of Iceland's abundant sources of sub-surface geothermal energy to power its DAC systems, Southern Green Gas is looking to the sky. Australia is among the sunniest continents on the planet and has much available land that is not used for agriculture, which the company hopes to leverage to establish a sprawling collection of solar-powered DAC plants around the country.
"This solution is hugely scalable with Australia’s vast area of non-arable land with high solar intensity and estimated underground storage of over 400 billion tonnes of CO2 – about 800 times Australia’s yearly emissions," says Gillespie.
Each of the company's solar-powered DAC modules can capture two tons of CO2 a year, according to Gillespie, but could be deployed in their millions. And such a feat would be necessary to tackle the more than 30 gigatons of CO2 per year the world emits each year.
As it stands, there are more than a dozen small DAC plants in operation around the world, all contending with prohibitively high operating costs. Climeworks was running at a cost of around US$600 per ton of CO2 captured once its first plant was up and running, but aims to drive that down towards $100 per ton as it scales up, also using a modular approach. This is in line with the ambitions of Canadian company Carbon Engineering, which is currently developing the first large-scale DAC plant to capture up to one million tons of CO2 each year, and expects to do so at a cost of $94 to $232 per ton. Gillespie anticipates Southern Green Gas will meet the same price point.
"Our unique DAC adsorbent is based on nanomaterial whose properties can be finely tuned and allow low cost," he says. "Several giga-scale manufacturing facilities are planned in regional areas throughout Australia, which will facilitate cost reduction below AU$100 (US$72) per ton for CO2."
The company plans to demonstrate its technology for the first time later this year.
Source: Southern Green Gas
