Carbon Removal 8

[Carbodynamics]

thread730-443054
CO2 can be removed from the atmosphere and separated into solid carbon and oxygen gas. Essentially unburning carbon.
Switching to renewable energy sources will reduce CO2 emissions however it won't remove excess CO2 in the atmosphere as a result of the combustion of fossil fuels.
2Mg + CO2 ⇌ 2MgO + C
Solid carbon submerged is relatively inert and compact.
Electrolytically recovering the Mg and collecting CO2 will require energy from renewable sources. This is the mechanism that I propose. Does anyone have any arguments against using it to sequester atmospheric CO2?

 

[3DDave]

Do you have the ability to process about 0.4 trillion tons of carbon this way?

One estimate is that 441.5 Pg C (petagrams of carbon)/441.5 Gigatons of Carbon (metric tons) has been added by clearing trees and burning fossil fuels.

https://cdiac.ess-dive.lbl.gov/pns/faq.html

Have you developed a rough estimate on energy and facilities required for the processing a gigaton of carbon?

 

[Carbodynamics]

At this point everything is theoretical. I'm here to invite you to challenge the concept.

I've calculated 9110 kWh per tonne C.
This is at 100% efficiency.
I propose that calcination of MgCO3 be used to collect and concentrate CO2.
It's difficult think of the scale but the problem is approaching incomprehensiblity. The solutions may have to approach impossibility.

 

[miningman]

The production of mettalic magnesium is incredibly energy intensive. Have you factored this into your thinking??? Somehow I think not

 

[Carbodynamics]

Do I have the ability to process 2400 Gt of CO2? The answer is no. It's going to require about $5 a person per day for 30 years to do the job. Unfortunately we are going to have to pay up or suffer the consequences.

 

[Carbodynamics]

The problem isn't the mechanism. The problem is the capital investment to build the infrastructure and a design to maximize efficiency. Energy recovery at each step. Energy infrastructure development over the next 30 years could be exponential. Renewable energy cost for survival might be placed in a unique cost category. The cost may be inversely exponentially lower even without subsidies.

 

[Carbodynamics]

If we can built multiple reactors executing this mechanism using clean energy all the excess atmospheric CO2 can be processed.

 

[Carbodynamics]

 

[3DDave]

That's 9.1 GW-hr per ton, onto 441.5 Gigatons of carbon - lessee, carry the 1, and ...

The Earth intercepts about 173,000 teraWatts (trillions of Watts) of solar power, or 173*10^15 Watts. That comes to 4*10^18 Watt-hours per day.

Your proposal takes 4*10^21 Watt-hours of energy, so the entire intercepted solar radiation on Earth for 1*10^3 days, about 3 years that not one photon from the sun is allowed to land on Earth; complete blackout.

Seems reasonable. Moving it to 30 years means only 1/10th of the solar radiation needs to be converted, but the conversion is still only 30% efficient, so 1/3rd of the cross-section area of the Earth needs to be used to intercept the sunlight, but that needs to be from every angle as the Earth turns, so a cylinder maybe 3000 miles wide (1500 miles on each side of the equator) completely encircling the planet should do the trick. It will, of course, produce 100% shadow for those 30 years under that belt, but all should be good afterwards.

So 3000 miles * pi*8000 miles = .08 billion square miles of solar cells.

Figure 10*10^9 people, that's roughly 21,000 square feet per person. $5*365*30 = $55,000 per person, so the solar cell price, installed (crossing the oceans is extra) can be no more than about $2 per square foot.

Altogether it looks entirely realistic. I wonder why no one is working on it.

(edit because it's 2*pi*R, and pi*D, for the circumference. Long day for a megaproject. )

 

[GregLocock]

$5 per person per day for 30 years= $438 trillion dollars, or per year, roughly the GDP of the USA. Looney tunes.





Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[3DDave]

By the way, where does the magnesium come from?

 

[dik]

I'm afraid, the world is in for some serious heartburn...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[cranky108]

I think I can afford $5 a day, but can people in other places afford that?

Would it not be cheaper to grow trees and burry them when they die?

 

[DrZoidberWoop]

Spend the money terraforming Mars.

 

[btrueblood]

Agree, cranky. But you don't have to bury the trees right away, just don't burn them, and bury the waste once the wood products have reached the end of their usefulness.

 

[3DDave]

I have a 30 foot tree - the local dumps/tree services are seem set to want $500 to bury what is about 200 pounds of carbon in that tree. It's insane.

 

[cranky108]

Maybe I do differently. I burn wood for heat, but I find some amount of charcoal in with the ashes, which both go to the landfill.
So I get to heat my home, from trees that are dead, problem trees, and from what someone else cut. The ash and charcoal go to the landfill.

I tried collecting charcoal, but after problems storing it, and having enough, I have had enough of it.

We also send pine needles to the landfill, again because we have enough of them.
But I do add cheap fert back to the area, so I don't completly depleat the soil.

 

[MintJulep]

There seems to be at least one company that has progressed beyond the cartoon CAD model.

https://www.cnbc.com/2021/07/23/these-companies-are-sucking-carbon-from-the-atmosphere.html

 

[Carbodynamics]

@3ddave. Thanks for the math.
2Mg+CO2⇌2MgO+C
441.5 x 48.61/12 = 1800 GT Mg
I'm using tons here.
I need about 570000 tons of Mg assuming that a lb of Mg takes 5 min to convert to MgO on pure CO2.
About.04 grams of Mg per person.
Or 950000 tons of MgO.
About .06 grams MgO per person.
The Mg is just a buffer atom. It's convenient due to its oxidation state.
The Mg⇌MgO equilibrium will be maintained by the electrolysis of MgO. Super heated CO2 injected into the molten cathode of the cell. O2 being released at a carbon anode.
Carbon should float up through the molten MgO and collected anaerobically to avoid C+O2 back reaction.
I need a million tons of MgO.

 

[Carbodynamics]

@cranky108 80 20 rule. We may have to find $20 per day.