4 ms·

I came here to say essentially this. To your point about how low (in percentage terms) the concentration of CO2 is, direct carbon capture from the atmosphere st

I came here to say essentially this. To your point about how low (in percentage terms) the concentration of CO2 is, direct carbon capture from the atmosphere still seems a fool's errand to me. The only way I see carbon capture being at all viable for this purpose in the short term is to scrub the waste gasses from industrial processes where carbon-containing compounds are extremely concentrated.

tim333 7y ago
The green beaches thing seemed quite promising https://news.ycombinator.com/item?id=20403570 https://news.ycombinator.com/item?id=20403570
- rotexo 7y ago
  right, but that's for sequestering the carbon, not turning it into a valuable product like a fuel, unless I'm mistaken
  - tempestn 7y ago
    Yes, but the main benefit of turning it into a valuable product is to make the process of sequestration cost effective. If sequestration could instead be made cost effective by just being really cheap (relative to other techniques), as will hopefully be the case with the olivine beaches, that could work too.
Robotbeat 7y ago
Cement (of certain types) relies on direct carbon capture from the atmosphere to complete curing (although conventional cement only carbonizes through a finite depth during its expected lifetime), so it's definitely possible. It just takes a lot of energy. About 2 MWh (thermal, or ~7GJ) per tonne of CO2 captured (not counting storing that CO2) to regenerate the chemical CO2 capturing agent. Here's a review: https://www.sciencedirect.com/science/article/pii/S0959652619307772 https://www.sciencedirect.com/science/article/pii/S095965261... (As an aside, a gallon of gasoline emits about 10kg of CO2, so to capture that CO2 from a gallon of gasoline would require about 20kWh worth of electricity.... Typically, a gallon of gasoline gives you about as much range as 10 kWh in an electric car, so you can go 2 times as far in an electric car just using the energy it'd take to capture the CO2 from a gasoline car. And that doesn't count the electricity required to refine/crack the gasoline from crude.) And also, on board the International Space Station, CO2 is captured from the atmosphere regeneratively. Capturing CO2 in this way takes less energy at the higher concentrations on board ISS, but is still possible. As an aside: Much of the ISS's CO2 is converted into a hydrocarbon (methane) using hydrogen (from water and solar electricity) and, amusingly, vented to space as a waste product. The point is to recover the oxygen (again, in the form of water) from the CO2.
- Zanni 7y ago
  In case someone else is wondering about the math on the aside about how a gallon of gas (3.8kg) can emit 10kg of CO2: https://www.fueleconomy.gov/feg/contentIncludes/co2_inc.htm https://www.fueleconomy.gov/feg/contentIncludes/co2_inc.htm
- pcl 7y ago
  > And that doesn't count the electricity required to refine/crack the gasoline from crude. If we can figure out how to extract atmospheric CO2 and convert it into hydrocarbons efficiently, crude oil won’t be bart of the equation any longer — our atmospheric carbon supply will be part of a closed loop. As a lay person, that’s an awfully appealing prospect. I wonder how many kWh it takes to pump, transport and process a gallon of gasoline when sources from crude.
vondur 7y ago
It’s doable, it just requires energy. You are really working against thermodynamics with CO2 sequestration.
pilsetnieks 7y ago
If it's an unmoving device fixed in place, I could see that capture from air wouldn't be particularly efficient. But what if it's a device that already exists that moves through air with great speed, filtering through huge amounts of air? Like, say, a jet engine?
- mrfredward 7y ago
  Okay, but producing fuel requires a lot of energy, so how are you going to power that? With a different engine onboard your jet? The point of this device is to take energy available on the ground and store it for use in the air, and use a storage method with a tremendous amount of energy per unit weight (hydrocarbons).
adrianN 7y ago
Planting forests and turning the trees into biochar seems like a cost effective way of carbon capture. You even get some energy out of it.
- captainredbeard 7y ago
  The biochar can then be used to plant more forests, for more biochar. It’s a virtuous cycle.

tim333 7y ago

The green beaches thing seemed quite promising https://news.ycombinator.com/item?id=20403570 https://news.ycombinator.com/item?id=20403570

rotexo 7y ago
right, but that's for sequestering the carbon, not turning it into a valuable product like a fuel, unless I'm mistaken
- tempestn 7y ago
  Yes, but the main benefit of turning it into a valuable product is to make the process of sequestration cost effective. If sequestration could instead be made cost effective by just being really cheap (relative to other techniques), as will hopefully be the case with the olivine beaches, that could work too.

Robotbeat 7y ago

Cement (of certain types) relies on direct carbon capture from the atmosphere to complete curing (although conventional cement only carbonizes through a finite depth during its expected lifetime), so it's definitely possible. It just takes a lot of energy. About 2 MWh (thermal, or ~7GJ) per tonne of CO2 captured (not counting storing that CO2) to regenerate the chemical CO2 capturing agent. Here's a review: https://www.sciencedirect.com/science/article/pii/S0959652619307772 https://www.sciencedirect.com/science/article/pii/S095965261... (As an aside, a gallon of gasoline emits about 10kg of CO2, so to capture that CO2 from a gallon of gasoline would require about 20kWh worth of electricity.... Typically, a gallon of gasoline gives you about as much range as 10 kWh in an electric car, so you can go 2 times as far in an electric car just using the energy it'd take to capture the CO2 from a gasoline car. And that doesn't count the electricity required to refine/crack the gasoline from crude.) And also, on board the International Space Station, CO2 is captured from the atmosphere regeneratively. Capturing CO2 in this way takes less energy at the higher concentrations on board ISS, but is still possible. As an aside: Much of the ISS's CO2 is converted into a hydrocarbon (methane) using hydrogen (from water and solar electricity) and, amusingly, vented to space as a waste product. The point is to recover the oxygen (again, in the form of water) from the CO2.

Zanni 7y ago
In case someone else is wondering about the math on the aside about how a gallon of gas (3.8kg) can emit 10kg of CO2: https://www.fueleconomy.gov/feg/contentIncludes/co2_inc.htm https://www.fueleconomy.gov/feg/contentIncludes/co2_inc.htm
pcl 7y ago
> And that doesn't count the electricity required to refine/crack the gasoline from crude. If we can figure out how to extract atmospheric CO2 and convert it into hydrocarbons efficiently, crude oil won’t be bart of the equation any longer — our atmospheric carbon supply will be part of a closed loop. As a lay person, that’s an awfully appealing prospect. I wonder how many kWh it takes to pump, transport and process a gallon of gasoline when sources from crude.

vondur 7y ago

It’s doable, it just requires energy. You are really working against thermodynamics with CO2 sequestration.

pilsetnieks 7y ago

If it's an unmoving device fixed in place, I could see that capture from air wouldn't be particularly efficient. But what if it's a device that already exists that moves through air with great speed, filtering through huge amounts of air? Like, say, a jet engine?

mrfredward 7y ago
Okay, but producing fuel requires a lot of energy, so how are you going to power that? With a different engine onboard your jet? The point of this device is to take energy available on the ground and store it for use in the air, and use a storage method with a tremendous amount of energy per unit weight (hydrocarbons).

adrianN 7y ago

Planting forests and turning the trees into biochar seems like a cost effective way of carbon capture. You even get some energy out of it.

captainredbeard 7y ago
The biochar can then be used to plant more forests, for more biochar. It’s a virtuous cycle.