17 DAC -Direct Air Capture
If direct air removal costs $500 per tonne, removing just US emissions would cost ~$3 trillion annually (that’s ~4x US military spending). It would also require twice the total power generation capacity of the US today (and it has to be carbon-free). Ho toot
House
Separating carbon dioxide from air, while technically straightforward, is outrageously expensive.
House (2023) Direct air capture: An expensive, dangerous distraction from real climate solutions
Room
DACCS - a costly distraction
DACCS systems generally use enormous fans to push large volumes of air over either a liquid solvent or solid sorbent that absorbs CO2. Then a large amount of energy is needed to release the CO2 and regenerate the sorbents. The overall efficiency of this process is very low (5% to 10%) and the price very high because CO2 in the air is so diluted—it’s 300 times more diffuse than the CO2 in a coal plant’s flue gas, and the entire Houston Astrodome contains only about 1 ton of CO2.
Per ton of CO2 captured and stored, current DACCS costs range from several hundreds of dollars to $1000 or more. A 2018 “techno-economic assessment” of DAC concluded, “CO2 separation from air is unable to economically compete with CCS.”
At more than 50 times the cost per metric ton of most natural climate solutions, long-term solutions [like DACCS] today are both limited in availability and practically cost prohibitive. These prices for carbon removal assume DACCS is powered entirely by carbon-free power such as solar and wind. Powering DACCS system by natural gas, increases costs for the negative emissions by 250%.
DAC is an expensive and inefficient way to use vast amounts of renewables (or nuclear power). That carbon-free power could have been used to directly replace the CO2 emissions from fossil fuel plants and cars cheaply and efficiently.
Only when the region’s electricity system is nearly completely decarbonized, do the opportunity costs of dedicating a low- carbon electricity source to DAC disappear.
DACC is unfortunately an energetically and financially costly distraction in effective mitigation of climate changes at a meaningful scale.
The affordability, scalability, and wisdom of running DACCS on carbon–free power are likely to remain problematic for decades. Yet, tree planting also has limited scalability, and scaling up BECCS increases CO2 in the air for several decades.
Since CDR will very likely be a bit player for decades, “net zero” is a dangerous myth.
The idea we can overshoot a temperature target by mid-century and then turn global emissions massively negative to quickly cool back down is magical thinking.
(Reference contains usefull introduction to DACCS in the appendix):
Gallucci
The startup Heirloom says it’s capturing CO2 from the sky and locking away the planet-warming gas, making it the first and only commercial U.S. plant to do so. On Thursday, the startup Heirloom unveiled its “direct air capture” facility in Tracy, California, which the company says has so far clocked nearly 1,000 hours of operations. Heirloom’s technology uses limestone to absorb CO2 from the atmosphere. Through a novel process, the captured carbon is then injected into concrete, where it ostensibly stays trapped forever.
To be sure, Heirloom’s plant is hardly capable of reversing the damage caused by decades of rampant fossil fuel consumption. The open-air warehouse, located some 70 miles east of San Francisco, can absorb a maximum of 1,000 metric tons of CO2 per year — less than 0.1 percent of the annual emissions from a single gas-fired power plant.
In 2017, the Swiss company Climeworks opened the world’s first DAC facility near Zurich, which used large fans to suck air into containers and filter out CO2 molecules. Although that facility stopped operating last year, Climeworks now runs a 4,000-metric-ton plant in Iceland.
Heirloom’s own process begins with an industrial kiln, which the company says is powered by renewable electricity from a local provider. Inside the kiln, limestone is heated to 1,650 degrees Fahrenheit, which breaks down the mineral into its constituent parts of calcium oxide and CO2. The same reaction occurs in cement-making, which is why cement is one of the world’s top-emitting industries.
But instead of releasing CO2 like cement kilns do, Heirloom’s kiln pumps the gas into a storage tank. The remaining calcium oxide is then spread onto hundreds of flat silver trays that are stacked vertically on 40-foot-tall racks, resembling a bakery of comically large proportions. The racks are exposed to open air for several days, during which time the white powder soaks up CO2 from the air like a sponge. Once saturated, the material heads back into the kiln, and the process starts again.
According to Heirloom, the captured CO2 gas could eventually be permanently stored “safely underground.” For now, however, the company is working with the startup CarbonCure to turn the CO2 into a dry-ice-like material and mix it with concrete, where the CO2 mineralizes and gets trapped.
By some estimates, DAC currently costs around $600 to $1,000 per metric ton of CO2.
Direct air capture allows polluting industries to live on, when we should be focusing on a just transition to renewables.
Gallucci (2023) America’s first commercial direct air capture plant just got going