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Wait a sec. Coal produces about 24 MJ/kg and this only takes 1.29 MJ/kg of CO2, or 4.73/kg of carbon. Even if coal were pure carbon this means we could burn co

Wait a sec. Coal produces about 24 MJ/kg and this only takes 1.29 MJ/kg of CO2, or 4.73/kg of carbon. Even if coal were pure carbon this means we could burn coal to capture ~5x as much carbon as it generates. That’s amazing! I’m assuming there are significant energy costs in scaling production of these materials up to any scale at which it could have an environmental impact though.

arethuza 6y ago
The efficiency of coal fired power plants is ~40% and there might be further inefficiencies in running this process at industrial scales.
DennisP 6y ago
With global CO2 emissions of 36 gigatonnes annually, it would take 1.4 terawatts or about 7% of total annual energy consumption (i.e. not just electricity) to absorb all our emissions. That's a lot but fixing a problem for just 7% of the energy we used to make the problem strikes me as pretty good. A gallon of gasoline produces 9 kg CO2, requiring 3 kWh to absorb, at a cost of 30 cents. There'd also be capital cost. Avoiding emissions will often be cheaper, but for many sectors that's not so easy, so direct air capture could end up being an important part of the solution. We've also got a lot of excess CO2 right now that we'd be better off removing. Sequestering CO2 seems to be a solved problem by injecting into basalt formations, where it turns into rock in about a year.
- Scarblac 6y ago
  Is the problem of injecting CO2 solved to the point where we can do it at a rate of 36 gigaton per year, indefinitely? And how much energy does that cost?
  - DennisP 6y ago
    I'm not advocating we do that much, just that we use it for the amount of emissions that's less practical to avoid. There's enough basalt for a very large amount, and energy to pump gas underground wouldn't be a major factor. Another option though is to turn the CO2 into liquid fuels. That wouldn't reduce ambient CO2 but to whatever extent we keep using liquid fuels (e.g. for airliners), it'd be nice if they were carbon neutral.

arethuza 6y ago

The efficiency of coal fired power plants is ~40% and there might be further inefficiencies in running this process at industrial scales.

DennisP 6y ago

With global CO2 emissions of 36 gigatonnes annually, it would take 1.4 terawatts or about 7% of total annual energy consumption (i.e. not just electricity) to absorb all our emissions. That's a lot but fixing a problem for just 7% of the energy we used to make the problem strikes me as pretty good. A gallon of gasoline produces 9 kg CO2, requiring 3 kWh to absorb, at a cost of 30 cents. There'd also be capital cost. Avoiding emissions will often be cheaper, but for many sectors that's not so easy, so direct air capture could end up being an important part of the solution. We've also got a lot of excess CO2 right now that we'd be better off removing. Sequestering CO2 seems to be a solved problem by injecting into basalt formations, where it turns into rock in about a year.

Scarblac 6y ago
Is the problem of injecting CO2 solved to the point where we can do it at a rate of 36 gigaton per year, indefinitely? And how much energy does that cost?
- DennisP 6y ago
  I'm not advocating we do that much, just that we use it for the amount of emissions that's less practical to avoid. There's enough basalt for a very large amount, and energy to pump gas underground wouldn't be a major factor. Another option though is to turn the CO2 into liquid fuels. That wouldn't reduce ambient CO2 but to whatever extent we keep using liquid fuels (e.g. for airliners), it'd be nice if they were carbon neutral.