Using energy to scrub the atmosphere of greenhouse gases

[dbaezner]

I was wondering if someone could help me with the current and foreseeable technology to use Earth's energy (nuclear, hydro, etc.) to actually scrub the atmosphere of CO2 and other gases. I'm curious if this is even possible and how it might be done. I've been trolling the internet for this without much success.

Thanks,
Dirk

 

[Drakkith]

Hmmm. An interesting question. While I don't know offhand how to scrub CO2, I can guarantee you that there is simply far too much in the atmosphere for any manmade scrubbing method to be feasible. At 397 ppm, the total amount of CO2 is simply staggering. (Something like 3x10¹² tons)

 

[SteamKing]

And you don't want to scrub ALL of the CO2, otherwise plants would starve, and eventually us.

 

[mrspeedybob]

And you don't want to scrub ALL of the CO2, otherwise plants would starve, and eventually us.

Which raises the question of what the ideal atmospheric CO2 concentration is and for whom. Even if it were possible to accurately simulate the effects of various concentrations (which I doubt), I would be surprised if there was any kind of agreement on which effects were preferable.

 

[CWatters]

In 2012 this company demonstrated c02 capture from the air and conversion to fuel for motor sports. I suspect there might be a better use for the renewable energy you need to fun the plant...

http://www.airfuelsynthesis.com/investment-opportunity/projects/demonstrator-unit.html

Google found a paper on c02 capture from the air. Includes a surprising statement that appears to suggest it might be more efficient (in what terms?) to capture c02 than to avoid emitting it by building wind turbines..

http://www.netl.doe.gov/publications/proceedings/01/carbon_seq/7b1.pdf

Results of our dimensional analysis suggest that the collection of CO2 directly from air is
feasible. Collecting CO2 from air is far more efficient than collecting wind energy. We
emphasize that we can make this statement without having determined an optimal collection
system or having settled on an optimal choice of sorbents. Even looking at the most simple
implementations suggests that the cost of the effort is tolerable. Our simple analysis suggests,
that filter systems using alkaline solutions of Ca(OH)2, or sodium or potassium hydroxide could
easily capture CO2 from air. The major cost of any such process is in the recovery of the sorbent.
A preliminary analysis assuming Ca(OH)2 as a possible sorbent suggests, that the cost will be on
the order of $10 to $15 per ton of CO2 and that the additional CO2 generated in the process of
collection is substantially less than the amount of CO2 captured.

I think carbon credits are currently around $13 a ton ?

 

[Chestermiller]

Which raises the question of what the ideal atmospheric CO2 concentration is and for whom. Even if it were possible to accurately simulate the effects of various concentrations (which I doubt), I would be surprised if there was any kind of agreement on which effects were preferable.

Prior to the industrial age, the concentration of CO2 in the atmosphere was about 290 ppm.

 

[Buckleymanor]

Prior to the industrial age, the concentration of CO2 in the atmosphere was about 290 ppm.

Prior is a long time.In the past there were periods when the concentrations were higher than today.
A very large proportion of ancient CO2 is locked away in rocks etc.

 

[mfb]

Results of our dimensional analysis suggest that the collection of CO2 directly from air is
feasible.

Is that a joke?
A dimensional analysis does not give any relevant numerical results.

CO2 capture in the exhaust of coal power plants is still expensive, and there you have a concentration of ~20%. Why bothering with the atmosphere with 0.04%, if you have CO2 in a much higher concentration to start such a project?

Capturing CO2 is not sufficient - you have to store it somewhere, or use it in some way.

 

[Chestermiller]

Prior is a long time.In the past there were periods when the concentrations were higher than today.
A very large proportion of ancient CO2 is locked away in rocks etc.

Maybe I should have been more precise. For the few thousand years of man's existence before the industrial age, the concentration was less than 300 ppm.

 

[SteamKing]

If only someone could come up with a process to manufacture limestone.

 

[UltrafastPED]

If only someone could come up with a process to manufacture limestone.

Grow lots of clams!

 

[Vanadium 50]

I don't think it makes much difference whether one plans to reduce the CO2 concentration by 10% (going back to 1950's levels) or 20% (going back to 1850's levels) - it's a factor of 2 in removal: if you can remove three trillion tons, you can probably remove six trillion tons.

If you want to do chemical sequestration, you're limited to the availability of calcium that's not already locked in carbonates.

If you want to do biological sequestration, we can do that today by seeding oceans with small amounts of iron. This is not a popular solution, since we don't know what other effects there would be.

If you want a closed-cycle sequestration, for every joule you produce with fossils, you need to spend half a joule for sequestration. That assumes 100% efficiency.

 

[mrspeedybob]

Prior to the industrial age, the concentration of CO2 in the atmosphere was about 290 ppm.

So?

The fact that 290 ppm is the equilibrium level in the absence of man made emissions does not necessarily mean that 290 ppm is the ideal concentration of CO2 in the atmosphere.

 

[Vanadium 50]

the ideal concentration of CO2 in the atmosphere.

...is not the subject of this thread, and is treading mighty close to a banned topic. Let's all stay on topic, please.

 

[OmCheeto]

Hmmm. An interesting question. While I don't know offhand how to scrub CO2, I can guarantee you that there is simply far too much in the atmosphere for any manmade scrubbing method to be feasible. At 397 ppm, the total amount of CO2 is simply staggering. (Something like 3x10¹² tons)

Interesting indeed. I've been watching a field of plants around where I've worked for the last 10 years. They seem to get taller every year. It might just me my imagination though. But one day, someone asked; "What the hell are those"? I had not a clue and spent some time googling.

They turned out to be Equisetum, a "living fossil".

Some Equisetopsida were large trees reaching to 30 meters tall. The genus Calamites of the family Calamitaceae, for example, is abundant in coal deposits from the Carboniferous period.

Given that they now only grow to 3 feet, I thought maybe they were stunted by the lack of CO₂ in the atmosphere. Then I thought that they might have some recessive gene, that when reactivated, might make them grow really big again, if there was as much CO₂ in the atmosphere today, as there was 100,000,000 years ago, and that they might be a simple biological solution to our "scubber" problem.

But then I decided that I knew nothing about biology, so I didn't say anything, to anyone.

 

[mheslep]

This CO2 into snow approach in Antarctica using some chillers powered by wind turbines seems feasible. Winter temperatures in the interior already fall close to the CO2 freezing point at 1 bar. Intermittent nature of the wind resource would be irrelevant. The proposed 1 billion tons of carbon removal per year using 20 GW (average) should have a notional onshore wind turbine capital cost of $200 billion.

Agee, Ernest, Andrea Orton, John Rogers, 2013: CO2 Snow Deposition in Antarctica [...] J. Appl. Meteor. Climatol., 52, 281–288.
doi: http://dx.doi.org/10.1175/JAMC-D-12-0110.1

Abstract:

A scientific plan is presented that proposes the construction of carbon dioxide (CO2) deposition plants in the Antarctic for removing CO2 gas from Earth’s atmosphere. The Antarctic continent offers the best environment on Earth for CO2 deposition at 1 bar of pressure and temperatures closest to that required for terrestrial air CO2 “snow” deposition—133 K. This plan consists of several components, including 1) air chemistry and CO2 snow deposition, 2) the deposition plant and a closed-loop liquid nitrogen refrigeration cycle, 3) the mass storage landfill, 4) power plant requirements, 5) prevention of dry ice sublimation, and 6) disposal (or use) of thermal waste. Calculations demonstrate that this project is worthy of consideration, whereby 446 deposition plants supported by sixteen 1200-MW wind farms can remove 1 billion tons (1012 kg) of carbon (1 GtC) annually (a reduction of 0.5 ppmv), which can be stored in an equivalent “landfill” volume of 2 km × 2 km × 160 m (insulated to prevent dry ice sublimation). The individual deposition plant, with a 100 m × 100 m × 100 m refrigeration chamber, would produce approximately 0.4 m of CO2 snow per day. The solid CO2 would be excavated into a 380 m × 380 m × 10 m insulated landfill, which would allow 1 yr of storage amounting to 2.24 × 10−3 GtC. Demonstrated success of a prototype system in the Antarctic would be followed by a complete installation of all 446 plants for CO2 snow deposition and storage (amounting to 1 billion tons annually), with wind farms positioned in favorable coastal regions with katabatic wind currents.

 

[mheslep]

...
If you want a closed-cycle sequestration, for every joule you produce with fossils, you need to spend half a joule for sequestration. That assumes 100% efficiency.

Does that energy calculation assume some endothermic chemical reaction in sequestration to fix the CO2? I'm curious since the Antarctica CO2-freezing scheme above claims to do considerably better. Combustion of, say, methane releases 55 kJ/g or 20 kJ/g of the CO2 product. The authors claim deposition of solid CO2 at 136 K in Antarctica requires 0.6kJ/g-CO2 (appendix D), or 33:1

 

[SteamKing]

Oh yeah, that Antarctic plan is going to fly. Turning the Southern Continent into an industrial park to freeze CO2. Won't be any environmental opposition there! Dead penguins? I see no dead penguins!

Assume you built a plant at the pole which did remove atmospheric CO2. Does atmospheric CO2 migrate from the northern hemisphere to the southern hemisphere? How much CO2 migrates? How long does it take?

 

[mheslep]

Oh yeah, that Antarctic plan is going to fly. Turning the Southern Continent into an industrial park to freeze CO2. Won't be any environmental opposition there!

I don't consider placing wind turbines on a *continent* of five million square miles as turning it into an industrial park.

There's also objection by some to the manned mission equipment still on the moon's surface because people placed it there. I don't give that misanthropy any credence either.

 

[SteamKing]

Yeah, that's why we're drilling for oil in the Alaska National Wildlife Refuge right now.

 

[anorlunda]

The proposed 1 billion tons of carbon removal per year using 20 GW (average) should have a notional onshore wind turbine capital cost of $200 billion.

Very clever. Please help me put it in perspective. How much is 1 billion tons of CO2 compared to the global emissions of CO2?

 

[SteamKing]

IDK the proportion of CO2 cleaned up to CO2 produced, but I know you aren't going to find $200 billion under your couch cushions.

Even if everyone was on board with this idea, building and operating an industrial plant in arctic conditions is not going to be cheap or easy. Whatever design you have for a wind farm will have to be carefully engineered to operate in very cold temperatures. There are only small scientific stations on Antarctica now, and the logistics of supplying and maintaining this industrial plant will be daunting and expensive.

http://en.wikipedia.org/wiki/Antarctica

All but 2% of the area of the continent is covered by ice sheets. There are also several international treaties which govern what activities are permitted and what may be brought to and removed from the continent.

 

[mheslep]

Very clever. Please help me put it in perspective. How much is 1 billion tons of CO2 compared to the global emissions of CO2?

One billion tons of carbon per year or about four billion tons of CO2. That's 1/4 to 1/5 of annual global CO2 from human sourced emissions. Also, the price might be significantly lower than the cost of other CO2 emissions reduction schemes, which run up to 3.5% of global GDP ($71 trillion 2012)

 

[mheslep]

...

...

All but 2% of the area of the continent is covered by ice sheets. ...

Apparently the plan depends on the ice sheets for deposition. Do you have anything on topic and specifically relevant to this scheme as detailed in the paper?

 

[NascentOxygen]

Quite a bit of CO2 is sent into the atmosphere by the production of concrete (an increasingly feverish activity in countries that are modernising). Someone invented a concrete that as it sets it absorbs CO2 from the atmosphere. It does not have the full strength of the conventional stuff, but for many uses that is not so important. It was proposed as a way to extract and lock away CO2 from the air, making the concreting process nearer to carbon neutral. The ingredients cost a bit more, though.

 

[Vanadium 50]

Does that energy calculation assume some endothermic chemical reaction in sequestration to fix the CO2?

I am assuming that the net effect is that the hydrogen in the hydrocarbons burns, but (after a complete cycle) the carbon does not: i.e. I am replacing net reactions like CH₄ + 3O₂ --> CO₂ + 2H₂O with ones like CH₄ + 2O₂ --> C + 2H₂O That costs about half the energy; i.e. if you get 2 joules in the initial combustion, it will cost you 1 joule to convert the CO₂ back to carbon.

 

[SteamKing]

Apparently the plan depends on the ice sheets for deposition. Do you have anything on topic and specifically relevant to this scheme as detailed in the paper?

You won't be erecting the wind turbine farm directly on an ice sheet. These machines require proper foundations for installation.

 

[mheslep]

Apparently the Antarctic frozen CO2 sequestration scheme requires far less energy per unit mass of CO2 than the capture-at-time-of-combustion concepts.

However, unlike some kind of calcium chemical capture of carbon, the disadvantage of frozen CO2 is that the storage areas would have to be maintained at temperature-pressure ... forever. The energy requirement to maintain the insulated land-fills would likely not be large nor would intermittent, short term, power outages matter. But if the site was abandoned over time the CO2 must slowly sublimate.

The Purdue paper only briefly touches on the point:

Figure 7 is an illustration of the landfills (per deposition
plant), and they will be insulated with polyisocyanurate
(effective down to 93 K). Snowcat-type excavators will
operate in groups of five to compact the dry ice into the
insulated landfills. A partial vacuum or even refrigeration
could be some alternative considerations for maintaining
solid CO2.