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Comment by plerpin | Hacker News Reader

Am I reading this right? 1.29 megajoules for one kilo captured? Uh, this doesn't seem feasible at scale.

That comes to 1290 Mj per tonne and the theoretical lower bound for sequestering is something like 450 Mj per tonne. So this is a lot but I don’t think it’s shocking for what is still an early stage technology.

Can you share the source, or the derivation, of the figure for lower bound on extracting CO2? I've had trouble finding the relevant information before. I just searched again and found this:

https://keith.seas.harvard.edu/files/tkg/files/116.cherry.he...

1kw of solar panels could do 5 tonnes a year. That seems feasible. 1000kw * 3600 * 5hr/day / 1.29e6 * 365

1.29 MJ/kg * 1kWh/3.6MJ = 0.3612 kWh per kg, or 361kWh per metric ton?

For comparison, you get about 5 tons of CO2 produced driving 12,000 miles in an 22mpg vehicle.

361kWh * 5 = 1,805kWh, so maybe $100 of energy cost? Seems totally economical to offset the CO2 from a full year of driving.

Now what I am wondering is if there’s any reason we won’t see a typical logistics curve / cost reduction pattern like we see with most tech whether it be solar panels, battery cost, etc.

Is there a law of thermodynamics that puts a ceiling on how good this can get, and how close to the theoretical maximum are we currently?

How does this compare with just planting trees?

Trees will die, decompose and release the CO2 back into the atmosphere. "Keep it in the ground" will need to become "Put it back in the ground"

By the same token: Power generators (solar panels, wind turbines, coal/nuclear/ whatever) break down, and need replacement.

Trees have other benefits too - potentially very long lifetimes, self-repairing, self-replacing, improving water tables, improving/generating/retaining soil, and can be used for building and in other processes once they reach maturity.

You ever eat a pine tree?

https://www.youtube.com/watch?v=qGp7OzTaoe4

Pine nuts a delicious, especially in salads and it's one of the main ingredients in pesto.

If only there was a way to make more trees that wasn't so labor-intensive...

My reading of the article is that actual storage of the carbon is not part of this work either.

We should used the captured carbon to make the fabled nanotubes that we're all going to be using, wearing and living in.

Wouldn't this captured carbon be a burnable fuel? Surely if you put it back underground a mining company would just dig it up and burn it again.

No, this captures carbon dioxide. Turning carbon dioxide back into carbon is not part of the process. You still need a way to store the CO2 permanently.

One thing that rarely gets mentioned is that trees having a cooling effect. Just stand under a big leafy tree and you feel it directly. Thats one reason Beside co2 to plant at least a gazillion trees.

Wood is a fantastic construction material.

A single tree, yes, but what about a forest? Haven't done any research on this, but wouldn't a forest as a whole recapture any carbon released by dead trees? Minus the trees used for construction--negative carbon system?

We would need to replicate the Azolla Event to have any real impact:

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

Otherwise, to take the data of this invention:

1.29 megajoules to scrub 1 kilo of CO2 = 3.58 kWh.

7.7cents/kWh is a recent Chinese electricity price.

$0.2757 to scrub one kilo.

EU carbon price is about $23 per tonne.

1000 x $0.2757 = $275.7 in electricity costs alone, ignoring manufacturing the devices and other overheads.

So all up, we'd need a Carbon Price of roughly $400/tonne to justify this kind of technology.

Its much easier to just keep the fossil fuels in the ground!

>Its much easier to just keep the fossil fuels in the ground!

This is what I have seen every time carbon capture comes up. It takes an insane amount of energy to burn fuels and then unburn them. Its always better to just use the energy to not need to burn the fuel to begin with. Once we have replaced all fossil fuels then it would make sense to start unburning the stuff in the air.

To put it even more crudely, Coal is 78% carbon by weight. Its a very effective store of potential CO2, and its already deep and stable underground!

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