There’s a lot of industry talk about whether applying counter carbon technologies and techniques like carbon storage, carbon capture, carbon conversion, and carbon sequestration could have a sizable impact on removing carbon dioxide, the most abundant greenhouse gas emitted today. Here’s a debrief on what these terms mean, the current state of technology, and what they would look like in practice.
Carbon capture most commonly refers to the process of removing carbon dioxide from various sources like the smokestacks of power plants running on fossil fuels like coal, oil, or gas, as well as manufacturing and production facilities. Capture also refers to removing carbon dioxide directly from the atmosphere, called Carbon Dioxide Removal (CDR), or Direct Air Capture (DAC).
However, the flue gas coming out of a smokestack from a power plant or industrial facility's chimney contains a much higher concentration of carbon, ranging from 10 to 15% carbon dioxide.Meanwhile, the concentration of carbon dioxide in the general atmosphere is around 400 to 450 ppm (parts per million), or about 0.04 percent.
In the atmosphere, we have carbon dioxide that we’re worried about. That’s significant from the point of view of affecting radiative forcing and climate warming. But it’s very dilute from the point of view of capture, "says Harry Atwater, professor of applied physics and materials science at the California Institute of Technology. "So, people have to develop ingenious methods for capturing and then concentrating the carbon dioxide as a pure stream."
The Swiss company Clime Works, for example, is one of the leading companies in the carbon capture space. Across Europe, there are more than a dozen direct air capture facilities that use fan-like machines to filter out carbon dioxide from the air and then heat up the captured molecules to pump them underground.
Another company, like Carbon Engineering, mists a basic chemical like potassium hydroxide to bind and draw down the carbon dioxide (which is acidic) from the air.
"There are multiple technologies for doing direct air capture that are being pursued. There’s also capture of carbon dioxide from the oceans, "like the ARPA-E project he’s working on, which received funding from the Department of Energy. Several National Academies reports indicate that technologies that actively remove carbon dioxide from the atmosphere need to be seriously considered as one of the many climate change combating solutions.
From Kelemen’s perspective, storage and sequestration are "pretty much synonymous," except sequestration is used when the storage of carbon dioxide is "essentially permanent" through methods like geological storage. The Norwegian Sleipner Project in the North Sea, for example, stores dense carbon dioxide fluid under pressure in a pore space under the seabed, Kelemen says. Carbon sequestration underground has one major flaw, however—the major market for the technology is in enhanced recovery of fossil fuel, Atwater notes, where companies want to pump pressurised carbon dioxide into existing oil and gas reservoirs to get more product out.
Atwater says simply putting extra carbon underground makes less sense than sequestering carbon dioxide into a marketable product that has economic value. Luckily, multiple companies and scientists have turned down this path. Many researchers have considered embedding solid forms of carbon in building materials like steel and cement, an already emissions-heavy industry, says Atwater. "What if we could actually take the carbon dioxide emitted through all the past synthesis of construction materials and then turn it back into materials that we could use like carbon fibre composites and other forms of more benignly stored carbon?" he adds. "That would be an indefinite form of storage. In contrast with solid carbon storage, there’s another type of less indefinite form of carbon storage: as fuel.
Fossil fuels, like gasoline (a type of liquid hydrocarbon), combine with oxygen to undergo a combustion reaction in our cars to make carbon dioxide and water. Many scientists have been tinkering with ways of running that reaction backwards, taking carbon dioxide and water and turning it back into fuel and oxygen.
Meanwhile, a huge issue for carbon capture and sequestration technology is the price tag. "If you’re simply going to sequester carbon, it requires citizens and leaders of advanced industrial societies to agree to basically tax themselves to underwrite the cost of storing that carbon," says Atwater. "There’s no worldwide agreed-upon price of carbon per tonne at the moment, which is one of the problems."
While carbon credit markets are emerging across the corporate sector, right now, there’s a gap between demand and capacity for storage methodologies. "We simply don’t have enough technologies to meet the demand. We’re in a weird moment, "he says . "There’s literally gigatons of demand for carbon credits, and there’s only kilotons of capacity."
Most anti-carbon technologies are in their infancy. There’s also no large-scale infrastructure supporting their growth and expansion. "Carbon negative technologies, unless you’re going to just pump that carbon dioxide underground that you’ve captured, they’re going to have to create new products like fuels, specialty chemicals, and materials," He says . "The big markets are for things like fuel, cement, and steel. Those are the things that we make at the gigawatt scale. "
These techniques are sometimes shrouded in controversy—namely because many argue that capture and storage let fossil fuel companies off the hook for their giant carbon footprints. Atwater says, "To reach our condition of sustainable level of carbon in the atmosphere below our current levels and back towards pre-industrial levels, we’re going to need to decarbonize and electrify everything that we can." But for industries that are "almost impossible to decarbonize," storage opens up an opportunity to put those emissions to good use.
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