4 ms·

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.

by ajuc 3y ago

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.
        credit_guy 3y ago
        I checked your numbers, and they check out. It is sobering. Now, leaving aside the hypothetical supersonic jet planes, we still have this problem with the existing airplanes. If we want to decarbonize aviation, then how do we go about this? On one hand, maybe 747 is an old plane and not that fuel optimized. I checked for 787-9, and it burns only 1.5 liters per second, which translates into 55 MW. It can only carry about 300 passengers vs 520 for a 747, so overall there is an improvement by about 33%. It's not nothing, but it's not that impressive either. Anyway, with whatever fleet of commercial airplanes the world has now, some old, some new, we consume about 100 billion gallons of fuel per year. That's about 300 million tons. Let's say we switch to hydrogen somehow. Which has more than double the energy density of jet fuel. We would need about 150 million tons H2 per year. According to the DOE [1], a 1GW nuclear power plant can produce about 150 kT of H2 per year, so we'd need 1000 of them. The whole world produces about 400 GW from nuclear reactors, we'd need to multiply the current fleet by a factor of 2.5, just to decarbonize air travel. [1] https://www.energy.gov/ne/articles/could-hydrogen-open-new-markets-nuclear https://www.energy.gov/ne/articles/could-hydrogen-open-new-m...

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.

by 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.
      - credit_guy 3y ago
        I checked your numbers, and they check out. It is sobering. Now, leaving aside the hypothetical supersonic jet planes, we still have this problem with the existing airplanes. If we want to decarbonize aviation, then how do we go about this? On one hand, maybe 747 is an old plane and not that fuel optimized. I checked for 787-9, and it burns only 1.5 liters per second, which translates into 55 MW. It can only carry about 300 passengers vs 520 for a 747, so overall there is an improvement by about 33%. It's not nothing, but it's not that impressive either. Anyway, with whatever fleet of commercial airplanes the world has now, some old, some new, we consume about 100 billion gallons of fuel per year. That's about 300 million tons. Let's say we switch to hydrogen somehow. Which has more than double the energy density of jet fuel. We would need about 150 million tons H2 per year. According to the DOE [1], a 1GW nuclear power plant can produce about 150 kT of H2 per year, so we'd need 1000 of them. The whole world produces about 400 GW from nuclear reactors, we'd need to multiply the current fleet by a factor of 2.5, just to decarbonize air travel. [1] https://www.energy.gov/ne/articles/could-hydrogen-open-new-markets-nuclear https://www.energy.gov/ne/articles/could-hydrogen-open-new-m...