Post by engineerpoet on Mar 21, 2020 0:34:13 GMT 9.5
Sooner or later (and probably sooner) it's going to be undeniable that we have passed a climate "tipping point" causing positive feedbacks in the system. The only way to offset the effects will be aggressive measures to block heating, remove GHGs or both in order to push the system back toward stability. Since even CO2 removal is deemed to be geoengineering, it's definitely going to be in our future.
Assuming all cost is for electric power @ $0.05/kWh (very rough estimate): 300 kWh/ton dunite, 1.2e14 kWh total energy required
Spread over 20 years, that's 684.5 GW average power.
This number could be high by a factor of 2; if energy at the reference mine costs $0.10/kWh instead of $0.05, the power requirement would fall to 342 GW average. Or there could be other costs which increase it somewhat. I'd bank on the number being within a factor of 2.
Another thing: A 60% efficient combined cycle plant burns 6 MJ of gas per kWh. At 50 MJ/kg LHV, that's 0.12 kg of gas which burns to 0.330 kg of CO2. Producing 300 kWh in such a plant generates 99 kgCO2 (call it 100).
If it takes 300 kWh to mine and crush 1 ton dunite and it removes 1.25 tCO2 from the atmosphere, we can burn fossil fuel to power our CO2 removal systems and barely dent the positive effect.
This would be a big job, requiring the mining of literally cubic kilometers of ultramafic rock and distributing it as fine particles so they would weather quickly. But it's doable. We CAN save the planet from our fossil fuel habit.