7 ms·

Always flue gas, never atmospheric concentrations. We have loads of good ideas for scrubbing flue. We have no good ideas for atmospheric CO2. 420/1000000 isn'

by Mizza 4y ago

Always flue gas, never atmospheric concentrations. We have loads of good ideas for scrubbing flue. We have no good ideas for atmospheric CO2. 420/1000000 isn't a lot of particles per million. Moving and concentrating those particles and grabbing them is going to require an _incredible amount of energy_ no matter how you swing it. People have not comprehended the scale of this challenge yet.

ealexhudson 4y ago
If the source of the flue gas is ~renewable (e.g. wood) and the energy generated is used usefully, this isn't a bad idea for carbon capture. It's much easier to capture the carbon technologically like this, and rely on broader capture (e.g. trees) to pull it out of the atmosphere. What really counts is what happens to the concentrated carbon being extracted - it needs to not go back into the atmosphere.
amelius 4y ago
How do trees do it, then?
- bjornsing 4y ago
  Sunshine. Lots of it.
- pjc50 4y ago
  At about 3% efficiency, but compensating by being spread over a large fraction of the land surface.
- Mizza 4y ago
  One adult tree captures 25kg per year. One transatlantic flight releases 500kg per passenger. Twenty trees, per person, per flight. Get serious. IPCC projections for a "good" scenario still depend on magical BECCS processes that don't yet exist., not flue scrubbing, which I think if anything will be away to keep coal plants online for _longer_. It's still valuable science, but don't get excited until there are major, major advancements in non-flue DAC/CCS.
  - PaulHoule 4y ago
    There is nothing magical about BECCS. At the power plant it is a matter of putting together technology that already exists. All of the elements such as amine strippers, pyrolysis, oxy-fuel combustion, etc. have been around since the 1970s. The literature has a "stopped clock" appearance in that people have talked about these things in the context of "clean coal" and biofuels for a long time without anything being built. There are two problems with it. One of them is that any kind of carbon capture is expensive and competes directly with a power plant (maybe the same power plant) without the CCS equipment. To win that competition, the operator of the power plant either needs to be fined for emitting CO₂ or has to be paid for capturing it, to the tune of $50-$100 per tonne. Another is that the ecological accounting for biofuels is frequently not favorable. When you consider water consumption, effects of land use, and the effects of inputs, many biofuel schemes (such as Ethanol from corn in the US) seem to be a net negative. The cheapest BECCS scheme is to capture CO₂ from the alcohol fermentation process, this has been implemented with great success https://bioenergyinternational.com/adm-starts-commercial-scale-ccs-decatur-ethanol-plant/ https://bioenergyinternational.com/adm-starts-commercial-sca... Ethanol from sugarcane in Brazil is much better from an ecological and economic perspective and it would cost something like $30 a tonne to capture CO₂ and inject it into a saline aquifer but politically it seems impossible given that most international bodies think that the real problem in Brazil is deforestation and that somehow promoting agriculture in Brazil is going to cause deforestation despite the fact that the Ethanol industry is mostly around São Paulo and nowhere near the rainforest. In principle there might be some agreement that Brazil gets credits for BECCS and also gets credits for protecting the rainforest but the latter is somewhat nonsensical in that there is a mismatch in time between processes that emit CO₂ (say you spend 5 hours on a plane) and the need to protect a forest forever to sequester a finite amount of CO₂.
    - Mizza 4y ago
      Why is sugarcane in Brazil any better than corn in the US? If they use petrochemical fertilizer, the problem is the same. You cannot sequester a ton of CO2 for $30/tn anywhere in the world right now. You can't even do it for five times that. If what you say were true, I'd be able to clean up after my own existence right now, which I can't do. I can only buy scammy "credits" and "offsets".
kragen 4y ago
direct air capture has been demonstrated by a variety of methods, including the literally oldest human industrial chemical process, lime burning. i've done the calculations, it's not such a bfd, even with lime yes, it requires an incredible amount of energy guess what solar panels give you
- Mizza 4y ago
  I would be very curious to see that math that you solved the problem with, given that all of the scientists in the world working on this missed your solution.
  - kragen 4y ago
    no they didn't, you did, because that's what happens when you don't read any of the existing research quoting my comment at https://news.ycombinator.com/item?id=32198793 https://news.ycombinator.com/item?id=32198793 about the theoretical thermodynamic minimum for direct air capture, as https://en.wikipedia.org/wiki/Direct_air_capture#Environment https://en.wikipedia.org/wiki/Direct_air_capture#Environment... explains, it is only 250 kWh/tonne CO₂, or 900 kJ/kg in SI units. To remove the ≈60 Gt/year of anthropogenic CO₂ currently being emitted and get us to carbon-neutral with direct air capture would consequently require a theoretical minimum of 1.7 terawatts, which is only about 10% of current world marketed energy consumption, and presumably about 5% of world marketed energy consumption 10 years from now. Kicking climate change into reverse would require a bit more than that, maybe double. Depending on the sorbent system, this energy can be solar thermal; it does not have to be electrical. Existing direct air capture systems like Climeworks's do not closely approach the theoretical minimum. ... Point source capture is of course much cheaper but it cannot get us to net negative CO₂ emissions. (note https://news.ycombinator.com/item?id=33504318 https://news.ycombinator.com/item?id=33504318 points out a way that point source capture could conceivably get us to net negative emissions) https://news.ycombinator.com/item?id=29327736 https://news.ycombinator.com/item?id=29327736 describes the lime approach. it uses a huge amount of energy, 1600 kWh/tonne CO2 (5700 kJ/kg CO2), much larger than the theoretical minimum above and much more than Climeworks, so the purpose of explaining it is only to demonstrate that there's no practical scalability limit to direct air capture. you don't have to ramp up your production of triethanolamine or aluminum formate or whatever the fuck. those are just a matter of optimizing the energy efficiency
lemming 4y ago
We have no good ideas for atmospheric CO2 https://www.projectvesta.org https://www.projectvesta.org is the best-looking option I have seen for this.
- Mizza 4y ago
  The one I am most interested in is https://verdox.com/ https://verdox.com/
namibj 4y ago
Yes we do, they don't work in all climates, but we do have a quite well-working approach: Step 1: base-resistand swamp cooler structured packing. Step 2: NaOH or KOH solution in water, at equilibrium with air (temperature& humidity). Step 3: blow air sideways while running liquid down via gravity. Step 4: regenerate liquid via salt metathesis reaction on column packed with Ca(OH)2. Step 5: dry-distill the CO2 out of the CaCO3 in a lime kiln (carbon capture for those is easier than for a gas turbine, as they exhaust like around iirc 3~5x as much C02 for each oxygen you feed in, assuming you fuel both with the usual methane). Step 6: inject the captured CO2 into old gas/oil formations. Of course this would be better if you combine it with already-needed air handling, for example in central forced air HVAC installations where adjusting the concentration of the lye in step 2 through adding water or vacuum-distilling allows it to humidify/dehumidify the air and where the liquid/air contact can also easily do the heat exchanger task (that strongly basic water shouldn't support growth of any harmful micrograms, I think (for KOH it would typically be half the molarity of a saturated solution, for NaOH more like 80~90%)). They use similar scrubbing but in dry columns (Ca(OH)2 beads soaked with NaOH solution, then left to drip and packed into canisters) for anesthesia rebreathers to scrub a patient's exhaled CO2, and similar lime/lye cycling in paper Mills (Kraft process; green liquor (sodium carbonate + sodium sulfite) to white liquor (sodium hydroxide+ sodium sulfite) recausticizing). Assuming negligible cost of the initial wet air scrubbing (via fusing the air handling with HVAC and in the process even providing extra-low-CO2 air), assuming a methane-fired lime kiln, this overall prices should be able to compensates for around 2~4x as much fossil fuel burn in, say, vehicles, than the burn/consumption of the DAC plant. And much of the process is quite amenable to using solar electricity (with about a day's worth of storage, but part might be able to use thermal storage in rock piles for pre-heating the kiln gas feed), especially as nothing really requires the lime kiln to work in the winter.

by Mizza 4y ago

ealexhudson 4y ago

If the source of the flue gas is ~renewable (e.g. wood) and the energy generated is used usefully, this isn't a bad idea for carbon capture. It's much easier to capture the carbon technologically like this, and rely on broader capture (e.g. trees) to pull it out of the atmosphere. What really counts is what happens to the concentrated carbon being extracted - it needs to not go back into the atmosphere.

amelius 4y ago

How do trees do it, then?

bjornsing 4y ago
Sunshine. Lots of it.
pjc50 4y ago
At about 3% efficiency, but compensating by being spread over a large fraction of the land surface.
Mizza 4y ago
One adult tree captures 25kg per year. One transatlantic flight releases 500kg per passenger. Twenty trees, per person, per flight. Get serious. IPCC projections for a "good" scenario still depend on magical BECCS processes that don't yet exist., not flue scrubbing, which I think if anything will be away to keep coal plants online for _longer_. It's still valuable science, but don't get excited until there are major, major advancements in non-flue DAC/CCS.
- PaulHoule 4y ago
  There is nothing magical about BECCS. At the power plant it is a matter of putting together technology that already exists. All of the elements such as amine strippers, pyrolysis, oxy-fuel combustion, etc. have been around since the 1970s. The literature has a "stopped clock" appearance in that people have talked about these things in the context of "clean coal" and biofuels for a long time without anything being built. There are two problems with it. One of them is that any kind of carbon capture is expensive and competes directly with a power plant (maybe the same power plant) without the CCS equipment. To win that competition, the operator of the power plant either needs to be fined for emitting CO₂ or has to be paid for capturing it, to the tune of $50-$100 per tonne. Another is that the ecological accounting for biofuels is frequently not favorable. When you consider water consumption, effects of land use, and the effects of inputs, many biofuel schemes (such as Ethanol from corn in the US) seem to be a net negative. The cheapest BECCS scheme is to capture CO₂ from the alcohol fermentation process, this has been implemented with great success https://bioenergyinternational.com/adm-starts-commercial-scale-ccs-decatur-ethanol-plant/ https://bioenergyinternational.com/adm-starts-commercial-sca... Ethanol from sugarcane in Brazil is much better from an ecological and economic perspective and it would cost something like $30 a tonne to capture CO₂ and inject it into a saline aquifer but politically it seems impossible given that most international bodies think that the real problem in Brazil is deforestation and that somehow promoting agriculture in Brazil is going to cause deforestation despite the fact that the Ethanol industry is mostly around São Paulo and nowhere near the rainforest. In principle there might be some agreement that Brazil gets credits for BECCS and also gets credits for protecting the rainforest but the latter is somewhat nonsensical in that there is a mismatch in time between processes that emit CO₂ (say you spend 5 hours on a plane) and the need to protect a forest forever to sequester a finite amount of CO₂.
  - Mizza 4y ago
    Why is sugarcane in Brazil any better than corn in the US? If they use petrochemical fertilizer, the problem is the same. You cannot sequester a ton of CO2 for $30/tn anywhere in the world right now. You can't even do it for five times that. If what you say were true, I'd be able to clean up after my own existence right now, which I can't do. I can only buy scammy "credits" and "offsets".

kragen 4y ago

direct air capture has been demonstrated by a variety of methods, including the literally oldest human industrial chemical process, lime burning. i've done the calculations, it's not such a bfd, even with lime yes, it requires an incredible amount of energy guess what solar panels give you

Mizza 4y ago
I would be very curious to see that math that you solved the problem with, given that all of the scientists in the world working on this missed your solution.
- kragen 4y ago
  no they didn't, you did, because that's what happens when you don't read any of the existing research quoting my comment at https://news.ycombinator.com/item?id=32198793 https://news.ycombinator.com/item?id=32198793 about the theoretical thermodynamic minimum for direct air capture, as https://en.wikipedia.org/wiki/Direct_air_capture#Environment https://en.wikipedia.org/wiki/Direct_air_capture#Environment... explains, it is only 250 kWh/tonne CO₂, or 900 kJ/kg in SI units. To remove the ≈60 Gt/year of anthropogenic CO₂ currently being emitted and get us to carbon-neutral with direct air capture would consequently require a theoretical minimum of 1.7 terawatts, which is only about 10% of current world marketed energy consumption, and presumably about 5% of world marketed energy consumption 10 years from now. Kicking climate change into reverse would require a bit more than that, maybe double. Depending on the sorbent system, this energy can be solar thermal; it does not have to be electrical. Existing direct air capture systems like Climeworks's do not closely approach the theoretical minimum. ... Point source capture is of course much cheaper but it cannot get us to net negative CO₂ emissions. (note https://news.ycombinator.com/item?id=33504318 https://news.ycombinator.com/item?id=33504318 points out a way that point source capture could conceivably get us to net negative emissions) https://news.ycombinator.com/item?id=29327736 https://news.ycombinator.com/item?id=29327736 describes the lime approach. it uses a huge amount of energy, 1600 kWh/tonne CO2 (5700 kJ/kg CO2), much larger than the theoretical minimum above and much more than Climeworks, so the purpose of explaining it is only to demonstrate that there's no practical scalability limit to direct air capture. you don't have to ramp up your production of triethanolamine or aluminum formate or whatever the fuck. those are just a matter of optimizing the energy efficiency

lemming 4y ago

We have no good ideas for atmospheric CO2 https://www.projectvesta.org https://www.projectvesta.org is the best-looking option I have seen for this.

Mizza 4y ago
The one I am most interested in is https://verdox.com/ https://verdox.com/

namibj 4y ago

Yes we do, they don't work in all climates, but we do have a quite well-working approach: Step 1: base-resistand swamp cooler structured packing. Step 2: NaOH or KOH solution in water, at equilibrium with air (temperature& humidity). Step 3: blow air sideways while running liquid down via gravity. Step 4: regenerate liquid via salt metathesis reaction on column packed with Ca(OH)2. Step 5: dry-distill the CO2 out of the CaCO3 in a lime kiln (carbon capture for those is easier than for a gas turbine, as they exhaust like around iirc 3~5x as much C02 for each oxygen you feed in, assuming you fuel both with the usual methane). Step 6: inject the captured CO2 into old gas/oil formations. Of course this would be better if you combine it with already-needed air handling, for example in central forced air HVAC installations where adjusting the concentration of the lye in step 2 through adding water or vacuum-distilling allows it to humidify/dehumidify the air and where the liquid/air contact can also easily do the heat exchanger task (that strongly basic water shouldn't support growth of any harmful micrograms, I think (for KOH it would typically be half the molarity of a saturated solution, for NaOH more like 80~90%)). They use similar scrubbing but in dry columns (Ca(OH)2 beads soaked with NaOH solution, then left to drip and packed into canisters) for anesthesia rebreathers to scrub a patient's exhaled CO2, and similar lime/lye cycling in paper Mills (Kraft process; green liquor (sodium carbonate + sodium sulfite) to white liquor (sodium hydroxide+ sodium sulfite) recausticizing). Assuming negligible cost of the initial wet air scrubbing (via fusing the air handling with HVAC and in the process even providing extra-low-CO2 air), assuming a methane-fired lime kiln, this overall prices should be able to compensates for around 2~4x as much fossil fuel burn in, say, vehicles, than the burn/consumption of the DAC plant. And much of the process is quite amenable to using solar electricity (with about a day's worth of storage, but part might be able to use thermal storage in rock piles for pre-heating the kiln gas feed), especially as nothing really requires the lime kiln to work in the winter.