Capture CO2 from fumes?

Burning fossil fuels releases a mixture of CO2, water vapor, and other waste products [1]. Usually about 15% of these fumes (or “flue gas”) is CO2 [2]. Can we filter the CO2 out?

Yes! Using an approach known as carbon capture and storage (CCS), CO2 can be filtered out by many different methods based on specially designed chemical and physical reactions [3,6,7]. A common method used to extract CO2 from exhaust gas is “absorption” [6].

Here is the step-by-step process of absorption of CO2 [3] (and swipe for a diagram!):

Step 1: Burning fuel produces flue gas which is really hot, so the first step is to cool the flue gas down [3].

Step 2: The flue gas flows over a liquid called the “solvent” [5]. CO2 moves from the flue gas into the solvent – it is “absorbed” [3].

Step 3: The rest of the flue gas (without CO2) is released as exhaust [3].

Step 4: The liquid solvent (now containing CO2) is heated up, which causes it to release the CO2 [3].

Step 5: The solvent is now CO2-free and can be reused to clean up the next load of flue gas [3].

Step 6: The CO2 can be stored or turned into fuel or other products [4]. CO2 can be stored in different ways, including pumping it into old oil fields [6].

This process is not yet done on a large scale: in 2018 there were 18 commercial CCS plants globally, which together captured 40 million tons of CO2 that year [8]. That’s just 0.1% of total global emissions in 2018 [9]. However, as CCS becomes more efficient, it will likely become more popular in the future [6].

A major advantage of capturing CO2 from fumes rather than directly from the air is that the concentration of CO2 in fumes is 100-300x higher than in air [6] – it’s like trying to find a needle in a haystack, rather than a needle in a forest! Therefore, it is easier to make this process cost effective than capturing CO2 directly from the air [6].

References

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