How does carbon capture work?

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Carbon dioxide capture is not a new concept. In the 1920s, some drillers were already venting gas through liquid-filled chambers to separate CO2 from the more lucrative methane. The fundamentals of carbon capture – bringing carbon molecules close to something they stick to – haven’t changed much since then.

Today, the Intergovernmental Panel on Climate Change tells us that to maintain a livable climate, we must not only stop carbon dioxide from entering the atmosphere, but also remove billions of tons of the substance each year by the middle of the century. Plants, our ancient allies, can only absorb a limited amount. Wacky ideas like “ocean fertilization” risk destroying entire ecosystems just to store carbon. Carbon capture cannot reverse all of our past emissions, but it could help. Here’s a look at cutting-edge technologies – promising, hopeful, but also troublesome.

WAYS TO CAPTURE CARBON


Carbon capture at source

HOW IT WORKS
Collecting CO2 from a point source such as a chimney or gas well is the most efficient form of carbon capture as well as the oldest. Point-source carbon capture costs about $70 per metric ton of carbon, or about one-fifth the price of capturing the gas once it is dispersed in the open air.

WHY IT’S PROBLEMATIC
This type of carbon capture has a long history. For most, it’s a long history of failure. Capturing carbon at the point source consumes a lot of energy, so factories and fossil-fuel power plants that use it run less efficiently, use more water, and are more expensive to operate. For this reason, the point source is better suited to industries like steel that are difficult to decarbonize by simply switching to renewables.

Direct Aerial Capture (DAC)

HOW IT WORKS
Carbon scrubbers have been making the air on space shuttles and submarines breathable for decades – a fan draws air through a filter coated in a chemical to which CO2 molecules adhere. Amines, a smelly derivative of ammonia, are a common choice, as are soda lime and lithium hydroxide. Heating the filter releases the CO2, which can be stored or sold (although space shuttles and submarines simply vent it outside).

WHY IT’S PROBLEMATIC
Catching CO2 in the open air is difficult because the carbon is so dilute – 0.04% compared to around 15% in a steel mill chimney. But if we want a reasonably livable planet, we need to bring that CO2 in the open air closer to 0.035%, which would require hundreds of thousands of DAC plants and a huge amount of energy. Scaling this technology is not easy. For one thing, it needs renewable energy or the entire facility will generate more CO2 than it can capture.

DAC is also expensive. The Orca plant in Iceland, which is run by global carbon capture firm Climeworks, draws abundant energy from a nearby geothermal power plant, but its captured carbon still costs well-heeled buyers $600 to $1,200 per metric ton.

Bioenergy with Carbon Capture and Storage (BECCS)

HOW IT WORKS
With this method, plants (from agricultural remnants like sugarcane stalks to fast-growing crops like poplars) do the job of sequestering carbon. The process of burning these plants, capturing carbon, using energy, and establishing a new crop is, at least in theory, carbon negative. If you’re familiar with ethanol production, you have some idea of ​​how BECCS works. Many ethanol and other bioenergy plants already exist in the United States. The difference is that BECCS factories store or reuse any CO2 emitted in the production process.

WHY IT’S PROBLEMATIC
The process by which vegetation captures CO2 from the atmosphere is carbon negative. The transport of these plants and the refining, capture and storage of CO2 are not. For BECCS to be carbon negative, all of the above would have to be done with renewable energy.

The illustration shows carbon capture technologies, pipelines, electricity pylons and crops being incorporated.

WHAT TO DO WITH CARBON AFTER IT IS CAPTURED

Use it to do something

HOW IT WORKS
Once the CO2 is captured, it can be used for a variety of things. It can be pumped into greenhouses to boost growth rates, or turned into synthetic fuels that can replace diesel, gasoline, and jet fuel, or used to create chemicals and plastics. It can also be used to make sparkling water (most of the CO2 used to fizzle soda is a fossil fuel by-product).

WHY IT’S PROBLEMATIC
Carbon Engineering, a Canadian energy start-up, succeeded in converting carbon captured from the atmosphere into synthetic fuel for the first time in 2017 (it calls this technology “air to fuels”). But to be carbon neutral, this synthetic fuel must be created with renewable energy. Plus, it would cost several times more than a gallon of gas.

Store it deep underground

HOW IT WORKS
After Norway passed a $50 per ton tax on vented CO2 in the 1990s, state oil company Statoil began pumping excess CO2 back into the Sleipner underwater gas field. It was relatively inexpensive to do, at $17 a ton, and Statoil (now called Equinor) has been sequestering about a million tons of CO2 per year since 1996. (Sounds like a lot, but remember that in the second half this century, we may need to capture billions of tons per year.) However, if done correctly, underground storage can be an effective way to sequester CO2 indefinitely.

WHY IT’S PROBLEMATIC
The Sleipner project is only a small part of a much larger operation “bringing gas to the surface of the earth and burning it, thereby worsening climate change”. This is why underwater carbon sequestration is so popular with oil and gas companies, which already have the offshore infrastructure and expertise to carry out projects like this.

Without this pre-existing infrastructure and an oil and gas company to help subsidize the cost, underground CO2 piping costs much more than $17 a ton. There are also questions about how much CO2 injected into the earth (or under the seabed) will stay there – a massive crack was recently discovered near Sleipner’s field, where gas could be escaping.

Store it in a suitable rock formation

HOW IT WORKS
In Iceland, Carbfix pumps CO2-laden water (captured by the Orca project) into basalt rock formations, where it solidifies into carbonate. This currently sequesters around 4,000 tonnes of CO2 per year, equivalent to the annual emissions of around 800 cars.

WHY IT’S PROBLEMATIC
If you’re trying to sequester carbon for good, that’s the gold standard. But it takes a carbon capture setup to have access to an ideal rock formation.

Use it for better oil recovery

HOW IT WORKS
“Enhanced oil recovery” has been used in the United States since the 1970s and is almost always what oil and gas companies talk about when touting their carbon capture projects. A significant percentage of the captured CO2 that is bought and sold around the world ends up being injected into oil fields to expel more oil. Even cutting-edge carbon projects like SaskPower’s Boundary Dam, the first DAC plant to open in North America, sell all the CO2 they capture to local oil and gas companies.

WHY IT’S PROBLEMATIC
Most of the CO2 remains trapped underground in this process. But because enhanced oil recovery brings even more oil and gas to market, it partially, if not completely, negates the benefit of CO2 sequestration in the first place.

THE RESULT

For high-tech carbon capture to work, a lot of other things have to work first and keep working. Public money must be directed towards producing the clean energy needed to eliminate the carbon capture pencil. Financial incentives need to be reworked so that capturing and storing carbon is more lucrative than releasing it. Corruption and outright carbon fraud must be relentlessly monitored.

The sheer cost of carbon capture reminds us that investing in emissions reduction right now is a bargain. If financing carbon capture is worth it, so is spending money on not releasing it in the first place.

This article originally appeared in the Summer 2022 quarterly edition under the title “Carbon Captured.

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