> One thing I learned is that these experiments are generally done with a pure CO2 stream.

According to this comment three months ago [1] "they used 6%-20% CO2 mixtures with balance nitrogen and some water to try and approximate different exhausts including flue gas".

[1] https://news.ycombinator.com/item?id=28873458

I.e. no oxygen. It would probably not be suitable for direct air capture.

If you burn carbon, you can just decrease your air input to furnace. It is not done today because it causes lots of CO, which is very poisonous. If you don't care about CO like in this process, you an put O2 sensor (lambda sensor, used in all new cars to alter how much air is used) and almost eliminate oxygen from your output.

I wonder if it might be possible to add a separations stage (centrifugal gas separator perhaps) and redirect any remaining oxygen back to the furnace?

Technically yes, but practically no. It's much easier to just let in less air, you just set your blower to slightly less power, controlled by sensor.

It works fine for any degree of oxygen blend too, it just requires proportionally more Gallium. 400 times more or so for atmospheric blend. The problem is the energy required to then reduce the gallium.

But perhaps it will be possible to filter out oxygen by a different process and let the remainder gas be filtered.

It's quite simple: burn excess incoming O2 with a bit more carbon.

I wish it were this simple... but given that there's ~5250 O2 molecules for each CO2 molecule in the air, this will result in the production of 5250x additional CO2 molecules. Our CO2 capture process would then have to be 99.9999% efficient for this to pencil out.

One could mix the incoming air with hydrogen. Igniting that would capture the oxygen in the resultant water. This would allow precipitating it out prior to the mix hitting the gallium. Hydrogen could then be recaptured by using electrolysis on the byproduct water, exhausting the oxygen.

I don't imagine this would be particularly efficient, however.

We don't want to deplete oxygen in the atmosphere. Plants are much better suited to capturing CO2, IMHO, as they also produce oxygen.

CO2 is 0.04% of the atmosphere. Oxygen is 21%. We're not going to run out of oxygen.

I don't understand the downvotes. The idea of turning excess oxigen into CO2 which I replied to is plainly stupid just because of this proportion. How much coal (and oxygen) would we use up to bring down CO2 levels to 0.03?

I don't understand your question.

GP proposed to filter out O2 by burning carbon. This will create a CO2-rich gas, perhaps at about 30% (depends of the density of CO2 compared to O2).

GP didn't mean that we deplete oxygen in the athmosphere, but that this is an intermediate step inside the CO2 scrubbing apparatus. Perhaps that's why you got downvotes.

The burnt carbon will be gained back by the Gallium process, however this might not work out anyway because the process needs to be very efficient in filtering out CO2, as someone else already pointed out.

In my opinion the idea of burning hydrogen seems a lot better: https://news.ycombinator.com/item?id=29994000

>Plants are much better suited to capturing CO2

I do wonder if it would be much cheaper to capture CO2 by investing technology and capital into 'building' forests. What if we can irrigate Sahara and cultivate some fast-growing plants like bamboos there? Maybe that has ecological consequences but it doesn't seem to be much different than the agricultural land expansion that has happened in rainforests in the first place.

The sahara seems like a bit of a hassle compared to the taiga (russia to canada). The real problem with growing forests is that they do not store significant amounts of carbon after they reach maturity. They did during the carboniferous, but after fungi figured out how to decompose cellulose they haven't, and wont. Fast growing plants only capture carbon faster, but the total storage would be less per area.

However, we do know of how the deposits of fossil fuels formed in the first place, and most places newer than the carboniferous, formed at the bottom of deep lakes and especially oceans. They form from the anoxic compaction of marine snow. Either during massive algae booms, or more slowly from slightly larger corpses. This process is slow for several reasons, but a significant, in particular for the latter category, one is the lack of surfaces for attachment on the open ocean. The creation of large floating artificial coral reefs could provide this, and with it a highly productive rich ecosystem. We could further fertilize these, with iron in particular being rare, but also regular fertilizer.

Focusing scrubbing smokestacks (where large amounts of new CO2 is concentrated) should be exactly where the focus should be. Direct open air capture really only makes sense once we've learnt to deal with the low hanging fruit.

> One thing I learned is that these experiments are generally done with a pure CO2 stream.

That's probably why these kinds of things will likely only be super effective if taking the immediate exhaust of carbon fuel burning.

So...

1. Legally require all fossil fuel plants capture the carbon from their exhaust, which will have the knock on effect of increasing the economic cost of burning fuel, which means economic forces will naturally start to more strongly prefer carbon free sources, because they're cheaper.

2. Keep pushing for the migration to full BEVs and possibly have a similar requirement of carbon capture devices added to industrial vehicles that can't reasonably be EVs. I could see things like mining and construction vehicles go out with a tank full of fuel and return with a tank full of captured carbon to leave at a dump.

> it probably means that future breakthroughs will occur in private labs, protected by patents and trade secret laws.

This does well to incentivize the inventors; perhaps they could be purchased rather than nationalizing the successful innovation models.

I would almost suggest that gov't should be funding this, but it is primarily private corps doing the polluting. Maybe have gov't fund it, then force polluters to pay gov't back from actual carbon tax?

Have government fund it, then limit or tax net emissions and now there is tech on the market to capture carbon to reduce your net emissions.

Ah.. independant invention without significant capital/money based support is very rare in the modern day world. So I'm sure it will support only inventors at an organizational level and at that level, there are lots of skewed incentives for the CXO level peeps to do more marketing that inventing and ensuring most value is captured for the organization than passed on.