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by semi-extrinsic 3615 days ago
Flue gases with a high CO2 content are better than cheap; people will actually pay you to get rid of them. And we have a lot of them (this is kind of the problem in the first place). If you look at something like the exhaust from an oxyfuel turbine, you can get 70/30 N2/CO2 with relatively high purity.

For this reason, I'm always skeptical of atmospheric capture projects. It's just got to be more efficient to capture from a mixture with 20% (or more) CO2 than from a mixture with 0.04%.
2 comments
danieltillett 3615 days ago
Actually if the CO2 absorbent is efficient it is not much harder to capture CO2 from the atmosphere than from flue gas. The key really is the CO2 flux rate which wind provides.

The real advantage of atmosphere capture is you can do the capture where the cost is lowest, not where the CO2 is emitted.

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semi-extrinsic 3615 days ago
> The key really is the CO2 flux rate which wind provides.

Indeed. This brings us to the issue of volumes. A useful carbon capture plant needs to capture at least 100 000 tons of CO2 per year (then we need "just" ~ 10 000 such plants). This means each of these minimal plants has to process an air volume of 250 billion cubic meters of air per year. At an air speed of 1 m/s (you can't flow too fast or there is no time for reaction), and assuming a wildly optimistic 50% capture from the filtered air, you need a reaction area of over 15 000 square meters.

Mind you, that's the area of the membrane which processes air. Add the auxiliary stuff around it, you can add at least another factor of 100 to the area, so each of your 10 000 plants have to be 1.5x the maximum planned size of the Tesla Gigafactory. And we're being optimistic.

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ytpete 3615 days ago
Couldn't the membrane be folded or stacked so you achieve that amount of surface area in a far smaller floorplan footprint?
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semi-extrinsic 3615 days ago
If I understand it correctly, all the membrane area has to be exposed to direct sunlight.
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ckcortright 3615 days ago
Cool idea to go straight to the source. I wonder if the same type of technology would be applicable. Likely not based on rate of reaction.
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semi-extrinsic 3615 days ago
My guess is that existing CCS technologies (such as amine-based separation) are much more efficient at high CO2 concentrations.
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