Comment by Robotbeat | Hacker News Reader

Comment by Robotbeat | Hacker News Reader

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Not objectively true, as plants and even rocks grab CO2 out of the air pretty efficiently. From a thermodynamics standpoint, you can burn fossil fuels at 50-70% efficient (50% is not uncommon), and the actual theoretical lower bound of CO2 direct air capture is ~20 kJ/mol,[0] or about 1.7MJ/kg of elemental carbon, compared to 33MJ/kg for burning elemental carbon (same as high grade coal).

(Burning methane is even better as it releases much more energy per unit CO2 i.e. ~860kJ-per-mole-of-CO2 vs anthracite's ~400kJ.)

And as others have said, rocks actually are able to exothermally absorb CO2 permanently. It's possible to speed this up by grinding rocks to a powder, placing in water with a catalyst.

...none of this is to say I support relying on direct air capture and just go ahead and burn fossil fuels. We need to keep that in the ground and transfer the whole civilization to non-fossil fuels, otherwise if some populist jerks wer elected, they could just order the expensive direct air capture program to stop (can't do that if you're already transitioned to clean energy and all your wellheads and drills and coal mining equipment are rusted or melted down for scrap).

Source: [0] https://www.researchgate.net/publication/257177020_The_therm...

With solar prices hitting negative rates for some periods in a day capturing carbon and converting into burnable fuel will probably start making sense in the next few years.

Think we could frack with corn syrup? Inject that carbon back into the ground?

Not corn syrup. That takes way too much CO2 and water to produce. Not even corn itself I suspect.

It's partly the problem alleged marshland and forest sequestration schemes face, alongside the assumption they're going to grow well in the changed climate.

(Limited experimental data suggests this works up to some 500 ppm as long as there's excess water and minerals. If the conditions are bad you lose capture potential. And what do you do with the methane releases from these systems? It's much more diffuse than from landfills.)

As long as there's still fossil fuel powered transportation, it would make more sense to use that excess power to charge batteries, since that converts electricity into motion more efficiently than taking the detour through synthetic burnable fuel.

Destroying fossil fuel powered transportation then replacing them with electric would actually produce more carbon. All new transportation should be electric but the already running transportation if can be run on captured carbon would result net carbon decrease.

> Burning methane is even better

Actually, burning is probably the best way to deal with any excess methane. Methane has a significantly higher warming potential than CO2 does. So if there's any methane we're venting into the atmosphere, we should burn it to convert it into CO2. Bonus points if you can use the generated energy to capture the CO2 as well.

From what I can recall, landfills produce more methane than any other process. How about we build a carbon capture next to every landfill, divert the methane and burn it to run the DAC?

Landfills do collect and burn methane. Those pipe like structures you see sticking out of a completed landfill are part of the process.

https://archive.epa.gov/climatechange/kids/solutions/technol...

TIL. Now we just need to execute the second part of his plan to capture the carbon from the energy produced

Or capture the methane, upgrade it and run generators/cars/busses of it. It's existing tech

https://en.wikipedia.org/wiki/Biogas

This scheme is used in real life in Czech Republic

Why bother for landfills?

If the landfill can generate electricity that would otherwise be generated, it will convert the CH4 more efficiently than a bus and you don't expand energy upgrading it.

You can power the bus with the already high quality CH4 you extracted from the ground that you would have otherwise burned in to generate the electricity.

Buses have different power requirements than cars; they need a lot more range because they run throughout the day.

I was reading somewhere that in buses in cold climates, heating is actually what eats up all the energy in an electric bus. ICE buses just use the waste heat from a combustion engine.

Or you just burn the trash directly.

This.

Releasing CO2 and NOx.

From what I can see, yes, methane is abstractly a worse greenhouse gas. However its absorption band is within that of water vapor. Since water vapor is plentiful around the blue marble, methane doesn’t really cause any problems.

This is incorrect, it’s well established that methane is a more potent GHG. See the reply here: https://news.ycombinator.com/item?id=21485738

What’s not taken into conservation with that comment is that methane at those altitudes does not impact much because the energy is radiate back to space.

You have doubled down on a casual assertion ("methane is not a significant greenhouse gas") because you don't understand radiative transfer in the upper atmosphere. It's OK, radiative transfer is complex. Your options are to accept this consensus, or do a lot more study than you have.

'Populist jerks' meaning people who are democratic?

Reply on news.ycombinator.com