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> They also claim that they will be net-zero Carbon due to advances in sustainable aviation fuels, with processes like CO2-fuel direct air capture. This fig le

> They also claim that they will be net-zero Carbon due to advances in sustainable aviation fuels, with processes like CO2-fuel direct air capture. This fig leaf is transparent.

Maxion 3y ago
If I burn 10^21 gallons of sustainable, carbon neutral, aviation fuel every year, what would happen? Somehow I think the CO2 sensor on Mauna Loa would need to be dug out from a piece of percipitated carbon.
- regularfry 3y ago
  Mostly what would happen is a lot of questions about where you are hiding that Dyson sphere you need to power the carbon capture.
zmgsabst 3y ago
How so? If the fuel is made from captured CO2, then there isn’t any net CO2 from burning it after.
- ajuc 3y ago
  You could capture the CO2 and take a train. No matter how you get your clean fuel - burning more of it is worse for environment than burning less of it.
  - zmgsabst 3y ago
    Okay — but there’s no harm to the environment. You’re just not improving it. The grandparent claimed this was a “fig leaf”: instead, you made an ideological post about how we need to not do even environmentally neutral things — that doesn’t make carbon neutral air travel a “fig leaf”.
    - ajuc 3y ago
      You can say anything is carbon neutral if you use synthetic fuel. It's meaningless at best, and manipulative at worst. Producing synthetic fuel requires energy.
      - zmgsabst 3y ago
        Okay — like solar? …or nuclear? …or hydroelectric? …maybe geothermal? And yes, that’s correct: Synthetic fuels mean that it’s carbon neutral — that’s a fact, not a fig leaf.
        ajuc 3y ago
        Like oil, natural gas and coal which is top 3 of our energy sources worldwide. Together in 2021 they amounted to 130 000 out of 160 000 TWh of energy produced. Wasting energy is bad. Even if we actually used synthetic fuel. Even if we actually moved to 100% renewable energy sources - we'd still have limited amount of energy. And before we do - it's just PR. Source: https://i.imgur.com/vZkz3sf.png https://i.imgur.com/vZkz3sf.png https://ourworldindata.org/energy-mix https://ourworldindata.org/energy-mix
        regularfry 3y ago
        What's missing from all this is how stunningly impractical the route from atmospheric CO2 to aviation fuel actually is. It's multiple GJ/tonne just to reverse atmospheric entropy and get the CO2 where you want it, and that's before you have to climb backwards up combustion's enthalpy cliff to turn it back into usable fuel. But the capture cost is a rounding error, even at 1GJ/tonne. People often have the wrong mental model of how energy dense aviation fuel actually is. A 747 burns 4 litres of fuel per second. Do the maths on aviation fuel energy content, and that comes out in the order of 120MW. Megawatts. With an M. 10^6. Those small modular reactors everyone's excited about? One of those. That's the thermodynamic range anything proposed has to operate in. Ok, so divide that by the number of passengers (say 400 to make the maths easy) and it's 300KW per passenger. Multiply by 9 for our fancy new supersonic plane: 2.7MW per passenger. Concorde had 128 seats; let's say ours has 100. 270MW for the whole thing. Now, a transatlantic flight might be 10 hours. Assume a spherical cow in a vacuum and 270MW x 10h = 2.7GWh. Say two flights per day doubles it, but they're only 5 hours each supersonic, so halve back down and that cancels out. Round to 3GWh to make the maths easy. In joules: 11TJ. With a T. 10^12. Now, we need to fuel this thing. Which means we need to convert enough energy into enough fuel. If we completely ignore the energy cost of actually capturing the carbon, 11TJ is the absolute lower bound. It will take more than that, but in the interests of generosity let's put that to one side. 86400 seconds per day gives us 127MW. So the good news is that the total energy requirements for this one aircraft to run on fuel made of already captured carbon are within the bounds of what we know how to build. You can, if you are a government, choose to buy these things. The bad news is that you need one per aircraft, for the eventual ability to fling 100 meatsacks across the Atlantic a bit faster. I would suspect, looking at the costs (in terms of energy, money, space) that this is not a choice a rational actor would make.
- Maxion 3y ago
  Capturing Co2 requires energy, laws of thermodynamics say there is no way to get free energy. Any Co2 capture system will undoubtedly be responsible for some small amount of Co2 emissions.

> They also claim that they will be net-zero Carbon due to advances in sustainable aviation fuels, with processes like CO2-fuel direct air capture. This fig leaf is transparent.

Maxion 3y ago

If I burn 10^21 gallons of sustainable, carbon neutral, aviation fuel every year, what would happen? Somehow I think the CO2 sensor on Mauna Loa would need to be dug out from a piece of percipitated carbon.

regularfry 3y ago
Mostly what would happen is a lot of questions about where you are hiding that Dyson sphere you need to power the carbon capture.

zmgsabst 3y ago

How so? If the fuel is made from captured CO2, then there isn’t any net CO2 from burning it after.

ajuc 3y ago
You could capture the CO2 and take a train. No matter how you get your clean fuel - burning more of it is worse for environment than burning less of it.
- zmgsabst 3y ago
  Okay — but there’s no harm to the environment. You’re just not improving it. The grandparent claimed this was a “fig leaf”: instead, you made an ideological post about how we need to not do even environmentally neutral things — that doesn’t make carbon neutral air travel a “fig leaf”.
  - ajuc 3y ago
    You can say anything is carbon neutral if you use synthetic fuel. It's meaningless at best, and manipulative at worst. Producing synthetic fuel requires energy.
    - zmgsabst 3y ago
      Okay — like solar? …or nuclear? …or hydroelectric? …maybe geothermal? And yes, that’s correct: Synthetic fuels mean that it’s carbon neutral — that’s a fact, not a fig leaf.
      - ajuc 3y ago
        Like oil, natural gas and coal which is top 3 of our energy sources worldwide. Together in 2021 they amounted to 130 000 out of 160 000 TWh of energy produced. Wasting energy is bad. Even if we actually used synthetic fuel. Even if we actually moved to 100% renewable energy sources - we'd still have limited amount of energy. And before we do - it's just PR. Source: https://i.imgur.com/vZkz3sf.png https://i.imgur.com/vZkz3sf.png https://ourworldindata.org/energy-mix https://ourworldindata.org/energy-mix
        regularfry 3y ago
        What's missing from all this is how stunningly impractical the route from atmospheric CO2 to aviation fuel actually is. It's multiple GJ/tonne just to reverse atmospheric entropy and get the CO2 where you want it, and that's before you have to climb backwards up combustion's enthalpy cliff to turn it back into usable fuel. But the capture cost is a rounding error, even at 1GJ/tonne. People often have the wrong mental model of how energy dense aviation fuel actually is. A 747 burns 4 litres of fuel per second. Do the maths on aviation fuel energy content, and that comes out in the order of 120MW. Megawatts. With an M. 10^6. Those small modular reactors everyone's excited about? One of those. That's the thermodynamic range anything proposed has to operate in. Ok, so divide that by the number of passengers (say 400 to make the maths easy) and it's 300KW per passenger. Multiply by 9 for our fancy new supersonic plane: 2.7MW per passenger. Concorde had 128 seats; let's say ours has 100. 270MW for the whole thing. Now, a transatlantic flight might be 10 hours. Assume a spherical cow in a vacuum and 270MW x 10h = 2.7GWh. Say two flights per day doubles it, but they're only 5 hours each supersonic, so halve back down and that cancels out. Round to 3GWh to make the maths easy. In joules: 11TJ. With a T. 10^12. Now, we need to fuel this thing. Which means we need to convert enough energy into enough fuel. If we completely ignore the energy cost of actually capturing the carbon, 11TJ is the absolute lower bound. It will take more than that, but in the interests of generosity let's put that to one side. 86400 seconds per day gives us 127MW. So the good news is that the total energy requirements for this one aircraft to run on fuel made of already captured carbon are within the bounds of what we know how to build. You can, if you are a government, choose to buy these things. The bad news is that you need one per aircraft, for the eventual ability to fling 100 meatsacks across the Atlantic a bit faster. I would suspect, looking at the costs (in terms of energy, money, space) that this is not a choice a rational actor would make.
Maxion 3y ago
Capturing Co2 requires energy, laws of thermodynamics say there is no way to get free energy. Any Co2 capture system will undoubtedly be responsible for some small amount of Co2 emissions.