3 ms·

I'm not sure what this is? You might be thinking of solar radiation management or other "geoengineering" techniques to try to make the earth shiner and reflect

by orbuch 7y ago

I'm not sure what this is? You might be thinking of solar radiation management or other "geoengineering" techniques to try to make the earth shiner and reflect more sunlight, making us cooler at a constant CO2 concentration. Theres a ton of interesting topics within that to write about, I mention it briefly as "things I didn't include"

foxhill 7y ago
having not read the article (yet), i the OP is referring to “cooling down air until it liquifies then using fractional distillation to pull out the CO2”?
- avmich 7y ago
  You don't want to do unnecessary transformations, to preserve as much energy as possible (so the turbine, which is needed for cooling, should work on small pressure difference). So, no air liquification - just let CO2 separate and send cleaned air back to the heat exchanger.
  - peteretep 7y ago
    > to preserve as much energy as possible Aren't there plenty of places where energy is so plentiful that you don't need to care that much?
    - adrianN 7y ago
      Not really?
avmich 7y ago
No, the idea is something similar to this - https://sesinnovation.com/ https://sesinnovation.com/ . You carefully compress incoming air. Separate water vapors (and liquids, and hopefully not solids) from it. Cool this air in thermal exchanger - at this point CO2 falls off. Then you pass that air through turbo detander, which returns you some energy, and get a pre-liquified air, which pass to the thermal exchanger. Clean air of normal temperature is released to atmosphere. You have to compress the air - but you also cool air, so compression is easier, and you also get some energy from the turbine where you decrease the pressure. Subject to optimizations. How much energy will you need?
- orbuch 7y ago
  Ah, thanks! I haven't seen this before. Will look into it.
- rckoepke 7y ago
  > How much energy will you need? A lot. Air compression is not cheap, energetically. Chilling is also energetically expensive. You'll need to do both. This would be pretty much the "brute force" method, like O(n!) in software engineering. The concept would be to bring half the planet's atmosphere down to near its liquid temperature. Currently in most US homes, Air Conditioning (air cooling) contributes the majority of each home's energy use. This would be much greater than that, it requires chilling air to -140 °C to get CO2 to "drop out". In contrast, seeding the ocean with iron would be fairly close to O(1). However, potential side effects of this process concern some scientists greatly. Googling 'Russ George' may provide more insight. Side note: The press material for sesinnovation also says the outlet stream is nearly 100% nitrogen...that means they're using a stream which already has oxygen removed from it (likely because the air was just used for combusting fuels). Air is roughly 21% oxygen so you can't take air, only remove CO2, and get 100% nitrogen out. Generally these "Carbon Capture" technologies only work on feed streams with high CO2. So hey're placed at industrial outlets, where fuel/coal is being burned. These streams can be > 10% CO2. Often they don't work as well, or at all, on diffuse streams like 0.04% atmospheric CO2. The technical reasons why this is the case deal with "partial pressures" as well as general entropy.
  - avmich 7y ago
    > Air compression is not cheap, energetically. Chilling is also energetically expensive. You'll need to do both. Not exactly. The idea is that you don't just compress air - and let the heated compressed air cool to the atmosphere in order to then expand it so it would cool some more, and then just release whatever's left back to the atmosphere. No, you use those leftovers to cool the incoming air - so you need to compress air spending less energy - and you also get the expanding air to help you to compress incoming air. The principal point where you have non-reversibility is that extra cooling - making compressed cold air to do the work - which you need to reach necessary temperature. And you only need that temperature to separate gases; after that you can use the cold products to help with compression. So - without colorful metaphors - I'd like to figure out how much energy will you need. I see the approach of SES with flue gases. I'm not sure how it will look like with regular air.

by orbuch 7y ago

foxhill 7y ago

having not read the article (yet), i the OP is referring to “cooling down air until it liquifies then using fractional distillation to pull out the CO2”?

avmich 7y ago
You don't want to do unnecessary transformations, to preserve as much energy as possible (so the turbine, which is needed for cooling, should work on small pressure difference). So, no air liquification - just let CO2 separate and send cleaned air back to the heat exchanger.
- peteretep 7y ago
  > to preserve as much energy as possible Aren't there plenty of places where energy is so plentiful that you don't need to care that much?
  - adrianN 7y ago
    Not really?

avmich 7y ago

No, the idea is something similar to this - https://sesinnovation.com/ https://sesinnovation.com/ . You carefully compress incoming air. Separate water vapors (and liquids, and hopefully not solids) from it. Cool this air in thermal exchanger - at this point CO2 falls off. Then you pass that air through turbo detander, which returns you some energy, and get a pre-liquified air, which pass to the thermal exchanger. Clean air of normal temperature is released to atmosphere. You have to compress the air - but you also cool air, so compression is easier, and you also get some energy from the turbine where you decrease the pressure. Subject to optimizations. How much energy will you need?

orbuch 7y ago
Ah, thanks! I haven't seen this before. Will look into it.
rckoepke 7y ago
> How much energy will you need? A lot. Air compression is not cheap, energetically. Chilling is also energetically expensive. You'll need to do both. This would be pretty much the "brute force" method, like O(n!) in software engineering. The concept would be to bring half the planet's atmosphere down to near its liquid temperature. Currently in most US homes, Air Conditioning (air cooling) contributes the majority of each home's energy use. This would be much greater than that, it requires chilling air to -140 °C to get CO2 to "drop out". In contrast, seeding the ocean with iron would be fairly close to O(1). However, potential side effects of this process concern some scientists greatly. Googling 'Russ George' may provide more insight. Side note: The press material for sesinnovation also says the outlet stream is nearly 100% nitrogen...that means they're using a stream which already has oxygen removed from it (likely because the air was just used for combusting fuels). Air is roughly 21% oxygen so you can't take air, only remove CO2, and get 100% nitrogen out. Generally these "Carbon Capture" technologies only work on feed streams with high CO2. So hey're placed at industrial outlets, where fuel/coal is being burned. These streams can be > 10% CO2. Often they don't work as well, or at all, on diffuse streams like 0.04% atmospheric CO2. The technical reasons why this is the case deal with "partial pressures" as well as general entropy.
- avmich 7y ago
  > Air compression is not cheap, energetically. Chilling is also energetically expensive. You'll need to do both. Not exactly. The idea is that you don't just compress air - and let the heated compressed air cool to the atmosphere in order to then expand it so it would cool some more, and then just release whatever's left back to the atmosphere. No, you use those leftovers to cool the incoming air - so you need to compress air spending less energy - and you also get the expanding air to help you to compress incoming air. The principal point where you have non-reversibility is that extra cooling - making compressed cold air to do the work - which you need to reach necessary temperature. And you only need that temperature to separate gases; after that you can use the cold products to help with compression. So - without colorful metaphors - I'd like to figure out how much energy will you need. I see the approach of SES with flue gases. I'm not sure how it will look like with regular air.