Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Robotic 'trees' can turn CO2 into concrete

engadget.com

Post reply on HN
Print view View original

81–90 of 125 posts

Re: Robotic 'trees' can turn CO2 into concrete

#81

Post by daveFNbuck »

throwaway5752 wrote: post #64

Seriously, everyone suggestions a crackpot idea for sequestering carbon should do the basic arithmetic for how much annual human emissions are (40 billion metric tons). I like https://blogs.scientificamerican.com/life-unbounded/the-craz... for the perspective it offers: current human CO2 emissions are equivalent to the entire continent of Africa being covered in coniferous forest and burning to the ground in forest f…

Concrete production accounts for about 5% of CO2 emissions, so this does reduce emissions.

Re: Robotic 'trees' can turn CO2 into concrete

#82

Post by 08-15 »

village-idiot wrote: post #25
ValleyOfTheMtns wrote: post #23

Earlier quoted context omitted.

I think all these comments about wood eventually releasing the carbon back into the atmosphere are missing the point. We don't need to capture it forever, we just need to get the ratio between carbon output and input under control in the next couple of decades. That should give us enough time to come up with longer term and sustainable ways of our planet... until we encounter the next problem, and so on. "Solutions"…

You could also just bury it. That’s effectively putting coal back into the ground.

I have a better idea. Leave the coal in the ground. You get the same result with literally no work!

Re: Robotic 'trees' can turn CO2 into concrete

#83

Post by atomic77 »

ksdale wrote: post #80
OscarCunningham wrote: post #76

Earlier quoted context omitted.

How is that possible? Surely the volume of fossil fuels being burnt isn't remotely comprable to the volume of that forest.

I don't know if the math is correct, but oil and coal are far more energy dense than wood which may account for the discrepancy.

This would have been my explanation too, but to my surprise, wood is only about 1/3 of the energy density of diesel fuel. I'm not sure why i expected it to be an order of magnitude difference.

https://en.wikipedia.org/wiki/Energy_density#Energy_densitie...

Re: Robotic 'trees' can turn CO2 into concrete

#84

Post by logfromblammo »

throwaway5752 wrote: post #64

Seriously, everyone suggestions a crackpot idea for sequestering carbon should do the basic arithmetic for how much annual human emissions are (40 billion metric tons). I like https://blogs.scientificamerican.com/life-unbounded/the-craz... for the perspective it offers: current human CO2 emissions are equivalent to the entire continent of Africa being covered in coniferous forest and burning to the ground in forest f…

How about this?

Create an Africa-sized algae bloom with iron and urea fertilization, in the middle of the waste-plastic zone in the north Pacific gyre.

Krill eat the algae. Baleen whales eat the krill and the plastic. Then we train/drug the older whales, so they swim far away from the continental shelf, dive deep, and commit suicide on the bottom. We solve two problems with one stroke. (Then the gorillas just freeze to death when winter comes.) ~

I think the only workable schemes for active carbon sequestration involve artificially weathering calcium and magnesium containing oxide rocks to expose more surface area, and turn them into carbonates. That has to be done on a scale that far exceeds the entire global demand for concrete. Like building a 1:1 scale replica of the white cliffs of Dover, every year, for no economically exploitable reason. Grind up olivines, pyroxenes, calcium-rich plagioclases, periclases, perovskites, spinels, etc. into sand, eventually get chalk.

Re: Robotic 'trees' can turn CO2 into concrete

#85

Post by ksdale »

atomic77 wrote: post #83
ksdale wrote: post #80

Earlier quoted context omitted.

I don't know if the math is correct, but oil and coal are far more energy dense than wood which may account for the discrepancy.

This would have been my explanation too, but to my surprise, wood is only about 1/3 of the energy density of diesel fuel. I'm not sure why i expected it to be an order of magnitude difference. https://en.wikipedia.org/wiki/Energy_density#Energy_densitie...

Interesting! I too, would have expected a much larger difference.

Re: Robotic 'trees' can turn CO2 into concrete

#86

Post by 08-15 »

throwaway5752 wrote: post #62
6nf wrote: post #2

Every time one of these articles come up I wonder about the price per tonne of CO2 removed by simply growing wood and not burning it. I'm not really sure what that price is, but it seems to be around $20-$40 per tonne? Does anyone have a more accurate number?

If only they had a soft cap and let people trade credits to try to keep emissions under that cap to incentivize sequestration and efficiency innovations.

You know what's the problem with that idea? There are no "sequestration and efficiency innovations".

Sequestration doesn't work and takes too much energy, and efficiency cannot be improved much thanks to thermodynamics.

Besides, if the IPCC is correct about how bad CO2 is, the only sensible cap for emissions is zero. You don't get there with tiny improvements in efficiency.

Re: Robotic 'trees' can turn CO2 into concrete

#87

Post by 08-15 »

Symmetry wrote: post #24
6nf wrote: post #2

Every time one of these articles come up I wonder about the price per tonne of CO2 removed by simply growing wood and not burning it. I'm not really sure what that price is, but it seems to be around $20-$40 per tonne? Does anyone have a more accurate number?

Well, according to Energy and Civilization forest stores an average of 1 watt per square meter in burnable wood. Wood burning is pretty carbon intensive as energy goes so I imagine that each square meter of forest, if the fallen trees are buried deep underground, could offset several watts of internal combustion engine use.

Nope. The energy density of gasoline and wood per carbon atom is about the same. So a watt is a watt, and forest are inefficient (about 0.4%) at converting sunlight into chemical energy.

Re: Robotic 'trees' can turn CO2 into concrete

#88

Post by milcron »

thinkcontext wrote: post #28
village-idiot wrote: post #25

Earlier quoted context omitted.

You could also just bury it. That’s effectively putting coal back into the ground.

Wood is not dense enough for this to be cost effective.

If a woodpile isn't dense enough, then surely building homes and furniture out of wood isn't dense enough either.

Can you think of a better way to store carbon!

Re: Robotic 'trees' can turn CO2 into concrete

#89

Post by [deleted] »

Cthulhu_ wrote: post #39
chii wrote: post #15

Earlier quoted context omitted.

but wood burns so much more dirtier than coal, and leaves much more uncombusted remains that then have to clean. The problem is energy (or lack thereof) - and so why not solve it directly by adding ever larger sources of renewables, which eventually will becomes enough that there's no need to burn any fossil fuels!

Is that so? Even when ground fine and with enough oxygen? For local heating, I heard good things about the efficiency and cleanliness of wood pellet heaters.

[deleted]

Re: Robotic 'trees' can turn CO2 into concrete

#90

Post by logfromblammo »

adwn wrote: post #72
sudhirj wrote: post #71

Earlier quoted context omitted.

Don’t know if this is sarcasm, but burning the wood releases most of the carbon dioxide back into the air. The ash is just the unburnt carbon residue and other leftovers.

Yes, it was a joke. Sorry for that.

Jokes aside, you could partially burn it, into charcoal, then grind down the charcoal, soak it in urea, and mix it with soil. The charcoal bits remain stable in soil for quite a long time, and helps retain plant nutrients.
Post reply on HN