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Air Capture

Filed under: — group @ 30 March 2008 - (Español)

Guest Commentary by Frank Zeman

[This is one of an occasional series on the science of mitigation/adaptation/geo-engineering that we hope to continue. Since this isn’t our core expertise, we’d especially appreciate balanced contributions from other scientists.]

One of the central challenges of controlling anthropogenic climate change is developing technologies that deal with emissions from small, dispersed sources such as automobiles and residential houses. Capturing these emissions is more difficult as they are too small to support infrastructure, such as pipelines, and may be mobile, as with cars. For these reasons, proposed solutions, such as switching to using hydrogen or electricity as a fuel, rely on the carbon-free generation of electricity or hydrogen. That implies that the fuel must be made either by renewable generation (wind, solar, geothermal etc.), nuclear or by facilities that capture the carbon dioxide and store it (CCS).

There is however an alternative that gets some occasional attention: Air Capture (for instance, here or here). The idea would be to let people emit the carbon dioxide at the source but then capture it directly from the atmosphere at a separate facility.

The removal of carbon dioxide directly from the atmosphere is a natural phenomenon that occurs in the surface ocean or during photosynthesis. Ocean absorption is a result of both the higher concentration of CO2 in the atmosphere and the alkaline nature of seawater (Note that this absorption that is leading to the “other” CO2 problem, ocean acidification – which may prove detrimental to coral reefs and other organisms that use carbonate). Land-based air capture is an effort to enhance this mechanism at an industrial scale so that CO2 can be removed from the atmosphere under controlled conditions. Given that it is performed under controlled conditions, we can use more alkaline solutions to improve the rate of capture without adversely affecting the biosphere.

Industrial air capture is based on the absorption of CO2 using alkali earth metals such as sodium or potassium. The process is a variant of the Kraft Process used in most pulp and paper mills and as such, benefits from a long industrial history. The CO2 is absorbed into solution, transferred to lime via a process called causticization and released in a kiln. With some modifications to the existing processes, mainly an oxygen-fired kiln, the end result is a concentrated stream of CO2 ready for storage or use in fuels. An alternative to this thermo-chemical process is an electrical one in which an electrical voltage is applied across the carbonate solution to release the CO2. While simpler, the electrical process consumes more energy as it splits water at the same time. It also depends on electricity and so unless the electricity is renewable or nuclear, will result in the storage of more CO2 than the chemical process.

If the technology is well established and, aside from the oxygen combustion of lime, dates back over 50 years, what stops it from being used and what might change in the future?

The main barrier is the efficiency of the energy requirements during the reducing process. Air capture requires energy to move the air, manufacture the absorbing solutions and solids as well as to produce the oxygen, fuel and make up chemicals. All of these items will result in additional CO2 emissions, which reduce the efficiency and therefore the benefits. The second important consideration, and maybe the dominant one, is cost. Air capture has to be more economical than the proposed alternatives (hydrogen, electricity, renewables, greater efficiency etc.). It should be stated clearly that air capture is not a viable alternative to capture at large, point source emitters such as power plants since it will always be more efficient to capture and store carbon dioxide from more concentrated streams. So while there are any non-CCS fossil fuel plants, Air Capture is a non-starter.

But recent suugestions have re-thought air capture as a thermal process. The early incarnations of air capture used electricity as the energy source and therefore depended on carbon-free sources. A thermal Air Capture system uses heat that can be generated on-site, reducing the inefficiencies associated with producing electricity, but of course it still needs a source of (carbon-free) heat. Notably, this implies that air capture could reduce greenhouse gas emissions independently of developments in the power generation or transportation sector. Preliminary experimentation has shown that causticization can occur at ambient temperatures and that conventional vacuum filtration is sufficient to avoid large evaporation penalties. These developments reduce the total energy required for the process by about half compared to the conventional method and thereby reduce the amount of CO2 that would need to be sent to storage.

However, the cost of air capture is still basically unknown. Estimates have varied wildly and real numbers will only come from pilot projects over the next few years. In some sense, that puts this technology on par with the hydrogen economy with expansion potentially starting sometime after 2015. For now there are far easier (efficiency) and cheaper (power plants) ways of reducing emissions of CO2 and so air capture is not a replacement for other efforts to reduce emissions. But in the long run, all carbon sources will require mitigation – including the transportation sector – and at that time air capture could be the most cost effective option for some sources. It is not any kind of panacea though.

238 Responses to “Air Capture”

  1. 1
    Danny Bloom says:

    I promised a few months ago that I would post only once in a blue moon about
    the ongoing polar cities adaptation strategy project, and since this topic is about adaptation strategies, just a note to say the New York Times posted a brief introduction today to the polar cities idea here:

  2. 2
    Nigel Williams says:

    …and we need to add to the equation the issue of the transport of the captured CO2. Since we are aiming to reduce CO2 faster than we are emitting it we will need to be transporting three to four times the volume of oil used at the time (plus coal cartage, of course) so it appears we are looking at a CO2-free transport system approaching five times the capacity of the global oil transport system to cart the CO2 to its eventual sequestration destination. What does that do to the economics? Not much, I suspect!

  3. 3
    dreamin says:

    Fascinating. Now what about the ARGO measurements?

  4. 4
    C. W. Magee says:

    What is the point of turning the CO2 back into a gas? You then need to store CO2 gas somewhere safe for hundreds of years, which we don’t yet know how to do.

    If you are going to go down the path of air capture, serpentine mineral carbonation (a la the UBC group) seems like a much more sensible alternative. There is no net energy cost, the only waste products are silica and water, and the CO2 is stuck in a mineral phase that should be stable on the timescale of civilization.

  5. 5

    A fascinating post. Thank you to the RC guys for opening up this area of discussion.

    Is there any hope for this: in effect the acceleration of natural CO2 exothermic weathering of rocks, to sequester CO2 or even generate power?

    I didn’t understand the reference to an oxygen-fired kiln. How does that work?

  6. 6
    Steve Horstmeyer says:

    As a person who has tried to be as green as possible for decades, (my wife takes public transportation, I ride my bike about half of my commute milage, in winter our thermostat is rarely set above 57°F, 14°C) I am always suspicious of what I call “life goes on as normal” (LGOAN) solutions to environmental problems.

    Carbon sequestration/removal in the various proposed forms (air removal, underground storage, using iron filings to seed the ocean, etc.)all only make sense as short-term, emergency measures.
    If all the world put forth maximum effort is there enough time and potentially enough carbon removal to make a difference?

    I suspect that as governments allocated funds for massive projects politician would sell the project by stressing this is a painless solution and, “yes my constitutents you can now drive you gas gussler guilt free and LGOAN.”

    Electric cars are not carbon free, but the source of emissions is centralized making carbon removal of emissions less daunting. Solar panels on all new homes and incentives for installing them on existing homes, along with universal net electrical metering would go a long way to reduce emissions, especially if some the the captured insolation was used to heat water and the home when needed in lieu of fuel oil or natural gas.

    Both those solutions have a “corporate” problem. GM killed a fully functional electric commuter car because, I suspect, there was little if any maintainance neededand therefore less money to be made. How much carbon could be eliminated if an electric car targeted at the urban commuter was affordable?

    Solar panels on homes have to buck the electric power industry after all they want to sell power not buy it. I live in Ohio and even this state has net metering.

    What is needed is a well coordinated attack using all viable means of removing carbon emissions, reducing the emissions of current technologies and switching to new carbon-free technologies.

    As the price of gasoline in the U.S. approaches what Europeans have been paying for years the sales of low gas milage SUVs have plunged while, turn on your TV, auto manufacturers spend millions in advertising to convince the buyer they need a 7000 pound (15,400 kg.)vehicle with all the comforts of home.

  7. 7
    James Annan says:

    “It should be stated clearly that air capture is not a viable alternative to capture at large, point source emitters such as power plants since it will always be more efficient to capture and store carbon dioxide from more concentrated streams. So while there are any non-CCS fossil fuel plants, Air Capture is a non-starter.”

    This seems rather simplistic, even in an article intended for popular consumption rather than scientific rigour. It only takes a few seconds thought to realise that there are (at least?) two ways in which air capture can have an advantage over CCS at power plants: first, if cheap/renewable energy is available at a site remote from the fossil fuel plants (eg solar-powered air capture could in principle be viable in some sunny but otherwise low-amenity desert region), and second, it could in principle be better to capture at a suitable storage site rather than capture at the emissions site and then transport to a storage site (effectively, we can use the atmospheric circulation to do the transport for free). And maybe both of these advantages could be combined, eg via my patented maintenance-free floating rafts of coconut trees which directly sink their genetically-engineered carbon-heavy fruit to the ocean floor for long-term sequestration (you read it here first, folks).

    I’m not suggesting that these possibilities are necessarily so advantageous as to make free air capture a strong contender at this time or even in the near future (in fact I’ve argued against it on Roger Pielke Jnr’s blog), but surely any comparison must be made on the basis of a quantitative accounting for the various costs, not just a dismissive hand-wave.

  8. 8
    Meltwater says:

    Are there processes that could sequester air-captured CO2 in durable and economically useful bulk material goods, perhaps in railway cross-ties or something similar, without energy-intensive requirements like prior concentration of the CO2?

  9. 9
    Bernie says:

    This is an extremely disappointing post. How large are these facilities? Exactly where and how will the CO2 be sequestered? Wouldn’t reforesting the Sahara be easier and cheaper?

  10. 10

    “One of the central challenges of controlling anthropogenic climate change is developing technologies that deal with emissions from small, dispersed sources such as automobiles and residential houses.”

    This is certainly true as far as it goes, but don’t forget that technologies are not the only way of addressing this problem. Social innovations like David Fleming’s TEQs scheme play a major and necessary part in reducing these dispersed emissions, thus reducing the direct technical challenge of atmospheric removal.

  11. 11

    Two things:

    First, it seems rather likely to me that air capture will be needed by the second half of this century. Assuming we actually seriously try to keep emissions below 450 ppm (currently, a doubtful proposition), we’ll probably need to go back to below 400 by 2100 and 350 by 2150, if I can put an optimistic spin on Hansen’s latest paper:

    Second, the world has a LOT of zero carbon waste heat not currently being used for anything. Indeed, U.S. thermal power plants alone throw away in waste heat as much energy as Japan uses for every purpose! That’s more than 20 quads. And that doesn’t even count the heat thrown away in industrial processes. Now the smartest thing to do with that heat for the next few decades is obviously either generate electricity with it or use it for heating buildings or industrial processes.

    But we should surely do a fair amount of research on air capture, since, by not later than the 2020s, we’re going to get desperate for emissions reductions, and by the 2030s, we’re going to be very desperate and willing to pursue expensive options we that aren’t yet politically realistic.

  12. 12
    pete best says:

    If there is no full scale prototype of the technology (one of the broadsheets or sky TV in the UK has mentioned this technology) then it either needs talking up(as do other geoengineering -ve feedbacks such as eliminating 1% of sunlight etc) in order to be demontrated to be viable for when we do not listen to James Hansen and build the non CCS coal fired power stations hat he is trying to eliminate.

  13. 13
    Jim Bullis says:

    Six+ things from me: (see Joe Romm above)

    Thing 1:
    The cogeneration possibilities mentioned by Joe Romm are a way to make the cost of electricity generated by by burning natural gas much closer to the cost of electricity generated by burning coal.

    And natural gas can much more easily be distributed to locations where heat can be put to good use. In fact, it already is distributed to a sizable number of US households. Try that MR.Coal.

    Thing 2:
    Then we need a cogeneration power plant sized to fit the typical household. This has not yet been seen as a viable application by Solar Turbines of Caterpillar (last I checked) But it looks like it would be a lot easier to develop such equipment than it would be to squeeze CO2 out of the air. And CO2 capture? I remain skeptical when I see the size and rate of flow out of the power plant smokestacks. But maybe, ok.

    Thing 3:
    There is a real possibility that such a development is within reach using engines on automobiles that are tied to electric generators. Example:Prius. Well, not too good an example since this would be oversized for heat usage of most households. Maybe time bursts of operation would work.

    Thing 4:
    We already understand the physics subject of aerodynamics sufficiently to know how to greatly reduce energy required to push cars down the road at high speeds. Prandtl and Fuhrman figured out how to make airships with very low drag a hundred years ago. Perish the thought, they might have been engineers rather than physicists, though I don’t think they cared about this too much. Anyway, there are old fluid dynamics texts that show the ideal airship having a drag coefficient of about .06, which is about a fourth that of the best cars we now build. If you can talk people into riding with their rarely present companion behind them, it is possible to make cars half as wide. “Wait a minute,” you might say. “This means that a car could use 1/8 the energy pushing air.” You might even go on to say, “So the engines could be a lot smaller, maybe about an eighth the size of the engine in the Prius.”

    Thing 5:
    So why not make this new kind of car using hybrid methodology? Now you cut the energy needed for personal tranportation by a lot (not quite down to an eighth due to rolling resistance and such), compared to a Prius, and a whole lot more compared to a Hummer. And all people have to do is learn to ride in tandem. (And ride in a wierd looking car.)

    Thing 6:
    Oops, the car I talked about in thing 5 has a very small engine already tied to a generator. Now it fits with the heat requirements of many households, and by hooking up to the existing natural gas plumbing when parked, and connecting coolant and exhaust systems to the household, we can get the cogeneration that Joe Romm suggested. Now, it is on a massive scale.

    The capital cost of this is next to nothing, or less. Wouldn’t the fuel cost savings when driving the car and the electricity cost savings when the car is parked make this into a formula that could greatly reduce CO2?

  14. 14
    David B. Benson says:

    As but a discussion item, I point a method of capturing the carbon which surely works and is safe:

    Ending Global Warming by Burying Biocoal

    Hansen et al., March 2008,”Target CO2: Where Should Humanity
    Aim?” found here:

    states that we need to soon reduce atmospheric CO2 from the
    current 385 ppm to an initially desired 350 ppm for compelling
    reasons. Here is a sketch of a plan for doing so.

    The world economy is about 67 trillion dollars (GDP) per year.
    Imposing a VAT of 1% raises 670 billion dollars per year.
    This sum is used to grow biomass, convert it to biocoal, and
    sequester the biocoal in carbon landfills, every year until
    the goal of 350 ppm is met.

    Using Powder River Basin style earth movement, it would cost
    about $16.50 per tonne to sequester the biocoal. In addition,
    the biomass must be harvested, moved to the hydrothermal
    carbonization facility, converted to biocoal (while generating
    some process heat for electricity generation), and then the
    biocoal moved to the landfill site. I assume these steps can
    be done, averaging over time and location, for only $33.50 per
    tonne, under half the currently required amount in the so-
    called developed world. So the carbon capture and
    sequestration net costs are assumed to be $50 per tonne of

    I will assume, for simplicity, that the biocoal is 85% carbon.
    Humans are currently adding about 8.5 gigatonnes of carbon
    (GtC) to the active carbon cycle per year, mostly by burning
    fossil carbon. Just to maintain the current 385 ppm of
    atmospheric CO2 then requires producing and sequestering
    10 gigatonnes of biocoal per year. This costs $500 billion
    per year, leaving a net of $170 billion available for
    producing and sequestering additional biocoal to reduce the
    concentration of CO2 in the atmosphere.

    To reduce the concentration to 350 ppm requires removing
    about 185 GtC from the active carbon cycle. At the rate
    of an additional 3.4 gigatonnes of biocoal per year, using
    the net funds available, we would remove 2.89 GtC from the
    active carbon cycle each year. Assuming this is done at
    a steady rate, it will require 64 years to bring about the
    initially desired atmospheric CO2 concentration of 350 ppm.

    About Biocoal

    Popular accounts:,2144,2071791,00.html

    A demonstration plant is described in the following link.

    Technical article:

    M.-M. Titrisci, et al.,
    Back in the Black: hydrothermal carbonization of plant
    material as an efficient chemical process to treat the CO_2
    New Journal of Chemistry, 207, 31, 787–798 (25 references). (Linked below)

    or as a .pdf file

  15. 15

    The UBC group C.W. Magee mentions has a website at .

    It seems to me that pulverizing silicate minerals and strewing them in out-of-the-way places is a way of reducing net CO2 emissions that has already demonstrated itself and will be innocuous if scaled up enough that those net emissions are negative.

    The CO2 will come to the strewn grains. Once they have become SiO2 and MgCO3 they can lie where they are. Transport issues therefore don’t seem to arise.

  16. 16
    Martin Vermeer says:

    Re #7 James Annan: another situation where this technology might become attractive is when we overshoot and realize too late that we need to get atmospheric CO2 back down in order to prevent bad things happening. I see that’s Joe Romm’s argument as well (#11).

    Also, imagine the situation where some (large) country just refuses to bring its emissions down, perhaps arguing that if the West did it, then they have the right to do it too. Still, in that case bribing and bullying in various mixing ratios are things to try first.

  17. 17
    Jim Galasyn says:

    I’ve been following Klaus Lackner’s efforts in this area for a few years. Thoughts?

    First Successful Demonstration of Carbon Dioxide Air Capture Technology Achieved

    Global Research Technologies, LLC (GRT), a technology research and development company, and Klaus Lackner from Columbia University have achieved the successful demonstration of a bold new technology to capture carbon from the air. The “air extraction” prototype has successfully demonstrated that indeed carbon dioxide (CO2) can be captured from the atmosphere. This is GRT’s first step toward a commercially viable air capture device.

    The carbon capture technology was developed by GRT and Klaus S. Lackner, a professor at Columbia University’s Earth Institute and the School of Engineering and Applied Sciences. The Tucson-based technology company began development of the device in 2004 and has recently successfully demonstrated its efficacy. The air extraction device, in which sorbents capture carbon dioxide molecules from free-flowing air and release those molecules as a pure stream of carbon dioxide for sequestration, has met a wide range of performance standards in the GRT research facility.

    “This is an exciting step toward making carbon capture and sequestration a viable technology,” said Lackner. “I have long believed science and industry have the technological capability to design systems that will capture greenhouse gases and allow us to transition to energies of the future over the long term.”

    The GRT’s demonstration could have far-reaching consequences for the battle to reduce greenhouse gas levels. Unlike other techniques, such as carbon capture and storage from power plants, air extraction would allow reductions to take place irrespective of where carbon emissions occur, enabling active management of global atmospheric carbon dioxide levels. The technology shows, for the first time, that carbon dioxide emissions from vehicles on the streets of Bangkok could be removed from the atmosphere by devices located in Iceland. This could present a solution to three problems that until now have posed intractable obstacles for advocates of greenhouse gas reduction: how to deal with the millions of vehicles that together represent over 20 percent of global CO2 emissions, how to manage the emissions from existing infrastructure, and how to connect the sources of carbon to the sites of carbon disposal.

    “This significant achievement holds incredible promise in the fight against climate change,” said Jeffrey D. Sachs, director of The Earth Institute, “and thanks to the ingenuity of GRT and Klaus Lackner, the world may, sooner rather than later, have an important tool in this fight.”

    A device with an opening of one square meter can extract about 10 tons of carbon dioxide from the atmosphere each year. If a single device were to measure 10 meters by 10 meters it could extract 1,000 tons each year. On this scale, one million devices would be required to remove one billion tons of carbon dioxide from the atmosphere. According to the U.K. Treasury’s Stern Review on climate change, the world will need to reduce carbon emissions by 11 billion tons by 2025 in order to maintain a concentration of carbon dioxide at twice pre-industrial levels.

  18. 18
    Steve Albers says:

    I would give consideration to “biochar” or “terra preta”. This would be a somewhat more natural way to capture CO2 using pyrolysis of agricultural waste and sequestering the resulting carbon in the soil. This improves the fertility of the soil at the same time. It actually can make biofuels carbon negative if this is done right.

    Here are two “must read” links to help understand the enormous potential here:

  19. 19
    John Mashey says:

    R&D portfolio management, as learned at a place that was OK at this, Bell Labs (in its height in the 1970s):

    1) Fund a lot of little R efforts, including relatively crazy stuff, like research on weird things on transistors in the 1940s. Modest $, spread around many research efforts, most of which won’t get far.

    2) Pick a few of the more promising ones and do further R. Modest $, but bigger per project.

    3) Pick a few of those for some actual development D. $$

    4) Then see if you have some solutions that can be scaled up, which usually means trying them out in fair-sized installations. big D $$$

    5) Deploy $$$$$$$$ which means, don’t do it until you know what you’re doing.

    All of this often takes decades.

    The most expensive things are to try to jump from an idea to 5) directly; this is usually a good way to waste a lot of money.

    The problem of course, is that Bell Labs, in the days, could afford to do this, because AT&T had very long-term thinking for an industrial corporation. People actually worried about building things like “no more than 2 hours down-time in 40 years”, because some infrastructure actually lasted that long. Monopoly money helped :-) People (at Murray Hill especially) were often working on research that *might* lead to something in 20 years. On the other hand, most of us were building things for the next 1-5 years, with technology more-or-less in-hand, not waiting for the wonders that might happen in 20 years.

    Venture Capitalists do not fund steps 1 & 2, at least not on purpose.

    At this point, most real R pretty much has to be funded by government, which means it needs a coherent long-term plan for how to manage such, not in evidence of late. Some big companies do some funding of this, often via university programs, like Stanford’s GCEP, and that’s an encouraging trend, i.e., bulkier, longer-term funding for multidisciplinary teams.

    Anyway, as Joe knows, good long-term R&D portfolio management is really needed, both to encourage the right sorts of research, encourage rapid deployment of existing technology, and discourage premature leaps into deployment.

  20. 20
    Edward says:

    In the same way that lap-top computers use less energy than the mainframe prototypes of several decades ago the only result was a huge proliferation of electronic devices from the cell phone to the I-Pod. Necessitating things like the California Electronic Waste Recycling Act. If hydrogen fuel-cell cars ever becomes widespread the only result will be a huge depletion of more non-renewable resources as industry promotes “non-polluting” cars. A hydrogen nuclear reactor which would also have to be used to power the factories building these cars has a reaction temperature of 3 billion degrees. The hydrogen bomb is more powerful than a conventional nuclear fission bomb. There is no known substance that can withstand such sustained temperatures, so the reactors would have to be continually disassembled and buried at a toxic waste sight somewhere, probably where millions of people live. Then new reactors would have to be built consuming more non-renewable resources. Many of the mineral properties needed would be of an exotic nature and scarce so hydrogen reactors can only exist as long as these rare metals remain. They will be used up very quickly for the reasons given above. I’m not a geo-engineer but it doesn’t make much sense to destroy the world in the name of stopping green house gas emmissons.

  21. 21
    David Beach says:

    CO2 sequestration in massive quantities may be the ONLY salvation for mankind. Everything else that we are doing or thinking of doing is trivial compared to the anticipated global population increase from 6.7 billion at present to 9 or 10 billion by 2050-2070. And every one of those 9 or 10 billion want water, food, warmth, transport and social contacts just like the “West” enjoys right now.
    That’s 40% more consumers of energy in the next 40 years. How do we deal with that except by CO2 (and CH4) sequestration? Birth control for 3 billion women?
    We have to accept that Nature will do the job for us. Drought, famine, disease and resource wars – starting soon in the fight for oil.

  22. 22
    DougO says:

    Efficient and economical air capture seems to be highly improbable from a thermodynamic perspective. Think of it this way, “air capture” is occurring on a massive scale all over the planet via photosynthesis, or natural carbon fixation. Can we possibly invent a process that can compete with natural photosynthesis which uses “free energy” from the sun and produces things of value such as food and fiber? Any artificial capture system will require energy investment (which costs money) and produce a carbon stream that needs to be disposed of (another cost).

    Let continue to research this area, but lets not put too much hope in a thermodynamic sink hole. Instead, let’s nurture and restore the biosphere to do what it does best, fix carbon.

  23. 23
    per says:

    Once had this idea that windmills could be used to counter the effect of soot and acidic sulfur haze downwind of coal power plants. The idea was simply to use the wings of the windturbine to spray a dilute magnesium carbonate/bicarbone solution into the air.( just like the wings of agricultural spray planes does)

    Assume that the alkaline solution have to be dilute, 0.5 – 1 %, to make most of the magnesium carbonate small enough to get airborne and prevent unwanted fallout close to the windmill. In an CO2 capture project the opposite might be true, less dilute solution and big droplets in order to prevent a big reflective cloud downwind of the CO2 wash out windmill plant.

  24. 24
    Pierre Allemand says:

    As suggested at the beginning of this post, I take advantage of it to introduce some practical and personnal ideas on the subject.
    My paper can be read at the following web address :
    Unfortunately, it is in French… (nobody’s perfect…)

  25. 25

    1. Danny Bloom: Forget polar cities because we will all be dead from the H2S bubbling out of the ocean before then. See:

    11. Joe Romm: Thermodynamics prohibits converting most of that waste heat into electricity. It is waste heat because it couldn’t be converted. It can only be used to heat houses in the winter.

    0. Frank Zeman: Taking CO2 back out of the air has to require more energy that you got by putting the CO2 into the air in the first place. Basic thermodynamics says so. Using sodium or potassium to take CO2 out of the air seems to me like a good idea for terraforming Venus, if you find an enormous supply of reduced sodium or potassium in the Oort cloud. If you do it on earth, it is bound to require a self-defeating quantity of energy. May I suggest joining Lifeboat [] instead? We scientists move to Mars, allow the coal burning part of humanity to extinct itself, and repopulate earth in a few thousand years. We need to get more women into science.

  26. 26
    Kiashu says:

    I wonder where we’re going to store all this CO2 once we’ve captured it.

    CO2 at room temperature and normal atmospheric pressure has a density of 1.98g/lt. 1 tonne (a million grams) of it will take 1,000,000/1.9 = 526,315lt of volume, which is 526.315 cubic metres. A million tonnes will take up 526.315 million cubic metres, which is 0.526315 cubic kilomtres. A billion tonnes – which is half the mass of CO2 put out by US coal-fired electricity generation annually – will take up 526km3.

    According to the most recent IPCC report, the world in 2004 produced 49Gt CO2equivalent, of which 56.6% or 27.7Gt were CO2 from the combustion of fossil fuels.

    Thus, to absorb all our CO2 from fossil fuel combustion would require 14,597km3 of volume annually, and we would of course still be left with 22.3Gt CO2e annually from other sources, more than enough to take us past 450ppm by 2100.

    But let us not ask so much from CCS, asking it to absorb only 1% of all CO2 from emissions; we must still find 146km3 annually. Let’s imagine that we remove all 1,300Gbbl or so of oil and put the CO2 in its place. The oil gives us 207km3, enough for a year and a bit.

    Of course we might also compress the carbon dioxide, down to liquid form at 60 atmospheres or so. This will then require only 243km3 for all the combustion of our fossil fuels, or a mere 2.4km3 for 1% of it. Of course, keeping CO2 liquid is far from a simple task, and preventing these billions of tonnes from leaking out seems difficult.

    Again, I wonder where this great volume is to be found. Perhaps HG Wells’ molochs could be summoned to excavate the vast caverns required.

    It’s a crock. Burn less stuff.

  27. 27
    Phil Scadden says:

    Recent comments – in line responses has been blank again for a week. Its so much easier to read this when this has been fixed.

    [Response: Agreed, but I’ve had to take it down for performance reasons – when I get a chance I will install a new plugin that doesn’t cause such problems. – gavin]

  28. 28
    Stephen Gloor says:

    Or you could use it to make methane from hydrogen in a Solar Tower. This could keep the co-gen plants going for a while. While this does not make the CO2 go away it at least takes back out what is released.

  29. 29
    Jim Bullis says:

    Re 11 Edward Greisch

    The payoff of heating houses with waste heat is that the natural gas that would otherwise be used is no longer required. Ideally, this could mean an system efficiency of 100% instead of the 34% thermal efficiency of the present US power grid fossil fuel plants. This alone is a lot.

    I have looked at this quite a lot. Hot water is also needed. Clothes dryers use a lot of heat. But much more interesting is the possibility of using absorption chiller technology for air conditioners and refrigerators. This comes in various efficiencies, the better ones being more expensive. But the gas burning refrigerator was used in the US for many years, and industrial airconditioners use this technology.

    In the scheme I discussed, there would be a car parked next to a household when an adult was present to need the air conditioning. Not always of course, but enough to make this an important large scale possibility, even in hot climates.

    Re 26 Kiashu
    I am also a little underwhelmed by the air scrubbing potential for real gains. We are going to pump the entire world’s atmosphere through this machine? Or would it be half of it to cut the CO2 count in half?

  30. 30
    Gene Hawkridge says:

    Rising sea level and warming sea water will result in an increase in organisms that convert CO2 and various other minerals into carbonates. Carbonates represent a stable way to store carbon – no industrial process required. However, how much mitigation will this provide in a world where governments are already trying to figure out how to build more dikes to keep out the sea? I don’t expect that carbonate-producing organisms, alone, are a solution, but what can we do to encourage this natural carbon sequestration process, instead of squandering the opportunity in a futile attempt to hold back the rising seas?

  31. 31

    20. Edward: There is no such thing as nuclear waste. It is fuel that needs to be recycled. Where in the world did you get a 3 billion degree temperature in the core of a reactor? “Hydrogen reactor” has nothing whatsoever to do with hydrogen bombs, and neither do fusion reactors. Nuclear reactors likewise have nothing to do with fission bombs. What was meant by “Hydrogen reactor”, I think, is an ordinary fission reactor used to generate electricity with which to electrolyze water, making H2 and O2.

    We don’t recycle nuclear fuel because spent fuel is valuable and people steal it. The place it went that it wasn’t supposed to go to is Israel. This happened in a small town near Pittsburgh, PA circa 1970. A company called Numec was in the business of reprocessing nuclear fuel. I almost took a job there, designing a nuclear battery for a heart pacemaker. [A nuclear battery would have the advantage of lasting many times as long as any other battery, eliminating many surgeries to replace batteries.] Numec did NOT have a reactor. Numec “lost” half a ton of enriched uranium. It wound up in Israel. The Israelis have fueled both their nuclear power plants and their nuclear weapons by stealing nuclear “waste.” It could work for any other country, such as Iran or the United States. It is only when you don’t have access to nuclear “waste” that you have to do the difficult process of enriching uranium, unless you have a Canadian “Candu” reactor that runs on unenriched uranium.
    Numec is no longer in business. The reprocessing of nuclear fuel in the US stopped. That was the only politically possible solution at that time, given that private corporations did the reprocessing. My solution would be to reprocess the fuel at a Government Owned Government Operated [GOGO] facility. At a GOGO plant, bureaucracy and the multiplicity of ethnicity and religion would disable the transportation of uranium to Israel or to any unauthorized place. Nothing heavier than a secret would get out.
    Nobody is paying me to post this.

  32. 32
    Chris Dudley says:

    I have to agree with Kaishu (#26) that the problem is not capturing the CO2 per se but doing something with it. The annual respiration of the planet is still four or five times larger than the annual increase in CO2. Plenty of CO2 is captured and even transformed into a solid form, it just doesn’t stay captured.

    The biochar suggestions look scalable, and we may even get into a competition about who gets the last bits of carbon for soil improvement as we approach 300 ppm. But, it is not yet clear that biochar remains as stable as coal in the ground in all soil ecologies so a portion of our sequestration activities should also be aimed at reconnecting carbon to the geological cycle through formation of calcium carbonate. It seems to me that protecting existing reefs, establishing new ones where they will flourish in a changing water temperature environment, and generally promoting healthy estuaries where mollusks can reestablish their historic abundance should be major priorities. Biochar may have a role in buffering nitrogen to help with this.

    So far as I can tell, the only place where we actually need liquid hydrocarbon fuels is in aviation. My estimate of how it might be produced competitively using air capture of CO2 is here. Christopher Graves, a student of Lackner’s, feels that a larger scale system that still makes use of the process heat might make a better first start and there are a number of existing university co-generation plants where a heat distribution system is already in place that might make good demonstration project sites. During the period of time when natural gas generators are still in use, it may make sense to use the Sabatier reaction in cogeneration plants to produce methane when the wind blows and then use the the methane in the turbine when the wind does not blow. Because the heat from the electrolysis of water and the formation of methane can be used just as the waste heat from the turbine is used, the conversion of wind power into methane is essentially one-to-one. Again, air capture of the CO2 feedstock can make sense if there is no nitrogen free source nearby. Of course, the turbine, when it is used, might be fed the coproduced oxygen from the electrolyis so that the turbine exhuast is nitrogen free, making a nice closed system.

    I think that air capture is good for making fuel, and much more efficient than attempting to make fuel using plants, but storing carbon as CO2 seems like an endeavour fraught with perils whereas storing (nearly) elemental carbon or mineral carbonates is just how the Earth manages carbon balance. Coal left in the ground is the best form of sequestration there is. It is here, rather than in making fuel, that biological assistance can be most fruitful. Reforestation, rebuilding soils with biochar and reviving the oceans, because they turn carbon into a solid, are the way forward for sequestration rather than foolhardy attempts to contain a water soluble gas.

  33. 33

    We should not ignore NO2 levels.

    “It only makes up 9% of total greenhouse gas emissions, but it’s got 300 times more global warming potential than carbon dioxide”, says Prof Richardson. “It can survive in the atmosphere for 150 years, and it’s recognised in the Kyoto protocol as one of the key gases we need to limit”.

  34. 34

    Re: Kiashu #26,

    The IPCC estimate from the Special Report on Carbon Capture and Storage is that the geological formations (principally deep saline aquifers) can store 2000 to 10000 GtCO2, which is of course much, much larger than the ~30 GtCO2 emitted per year.

    You are right that the volume numbers are large, but the Earth’s surface is enormous (~150 million km^2 of land). Depths upto 3 km are easily accessible, and even deeper areas are reachable but probably less interesting. You only need a small fraction of that to be able to accept CO2 at 70-100 bar to come up with a large hypothetical storage area.

    Most CO2 injection would be into pore spaces in sedimentary formations currently occupied with water. You don’t need “caves”, merely porous rocks, which are relatively abundant in sedimentary formations. (Also the fraction of rocks that qualify as porous improves considerably when you drive CO2 in at an overpressure of 100 bar.)

    There are plenty of technical challenges with CCS, but most analysts currently think there is more than enough capacity for the needs during this century.

  35. 35
    Kiashu says:

    I was inspired to research is a little bit and write an article on it. To be honest it’s really unpromising – in their remarkably few tests it’s leaked out.

  36. 36
    Jerry Toman says:

    I’ve commented on ideas similar to this before and I am surprised they keep coming up time and time again as if none of us here has never had a College P. Chem. or Chemical Engineering course emphasizing thermodynamics as the basis for chemical equilibrium.

    J. Willard Gibbs, one of the most revered icons of American Science, spent a lifetime of careful analysis to establish the validity of the “new” science of Thermodynamics. His purpose was to provide the tools to make sure ideas like this would be nipped in the bud before they gained too much “political traction”.

    One of the main tenents of the science is the Second Law which states that in every process that occurs at a finite rate, there are irreversibilities, which result in increases in entropy.

    Far less entropy is created if CO2 is captured directly from flue gas at concentrations of up to 100,000 ppm, than if it is first allowed to mix irreversibly with air, diluting its concentration down to 400 ppm.

    As a practical example from the discussions, it is suggested that CO2 be captured using strong bases such as sodium hydroxide or potassium carbonate. Of course we know this is possible as anyone who has left open a container containing these substances to the air has realized.

    The problem is that the heat of reaction required to absorb the CO2 must be very high to overcome the high entropy of CO2 in air. This “heat of reaction” is dissipated and put to no good use. When the CO2 is regenerated, however, (if even possible) the heat must be put back in.

    One the other hand, when treating flue gases containing much higher amounts of CO2, a much weaker base, such as a (promoted) monoethanolamine solution can be used to absorb the CO2. The CO2 is regerated from the solution at slightly above atmospheric pressure by applying heat (to a reboiler) at about 250 F. The system makes effective use of a “cross-exchanger” to transfer heat and minimize “irreversibilities”. This is one of the “preferred” ways the DOE is funding the clean coal initiative. Even this (plus compression of CO2) causes a loss of about a one-third of the electrical output from the plant.

    Of course, because it is a relatively “weak base” MEA would be useless in absorbing CO2 directly from air.

    The bottom line is that there is a dilution factor beyond which a point of economic “no-return” is surpassed for which it doesn’t make sense (e.g., low-grade uranium ore, uranium in sea water, low-grade iron ore, or in this case, CO2 in air), to expend energy to recover it. This is without even mentioning the embodied energy in the equipment used to carry out the process.

    Suggestion: If we are getting off on a geo-engineering tangent, may I suggest you invite Louis M. Michaud of AVEtec to discuss some ideas on how a fleet of stationary vortices might be deployed in the atmospshere to cool an area, perhaps a very large one (Great Lakes region) and return it to its historical temperature levels, or to discuss any topic he may wish to address with regard to about how the Atmospheric Vortex Engine can be used to mitigate climate change.

    At least he knows Thermo…

  37. 37
    JeandeBegles says:

    I am very skeptic about the feasability of CO2 removal in the atmosphere; the natural mechanisms performing it (photosynthesis and sea absortion) work very slowly and are efficient because spread all over the earth. More, the CO2 concentration is rising, and this is a problem, but the number remains very low (0,04%).
    So I would be very surprised if a real solution come out of this path.
    What is a fact is that some of theses studies are founded (linked) to the oil industry. Then the purpose is more obvious. No need to care about our CO2 emission, no need to tax carbon or even cap and trade, there will be an easy way to remove this CO2 pollution!
    So these studies about CO2 removal, that look like fancy thinking, may be more about global warming fight removal.

  38. 38

    Interesting. I agree with Kiashu (#26). Where are you going to put it? Even if you can convert the CO_2 to a solid form chemically, you end up with at least as much volume as the original coal.

    I don’t buy the concept of compressing the gas and storing it deep underground. Sooner or later if that is done often enough, a mistake will be made and it will force its way out somewhere unexpected. Examine the costing in CCS schemes of this sort of failure, and you see a big finger pointing at “government” (i.e., us) as the insurer of last resort because the cost of a catastrophic failure is so high.

    Meanwhile, a little OT, but I thought some here may appreciate this (posted a day early to allow time to get through moderation):

    Exxon-Mobil to abandon climate change obfuscation

  39. 39
    Nigel Williams says:

    Kaishu – you’ve got it in one! Of course IF as from yesterday we sequester all we emit and the same again the problem will go away. Of course IF we stop demanding more energy we will stop building fossil-fuelled power generation and we will stop the rot. Of course IF we turn off all our lights, cook on solar stoves, bin our PCs, insulate our houses, beds and quilted jackets with straw, wool and down and we walk everywhere behind cart horses and beat our fast food fat fryers and TIG welders into ploughshares, then our energy needs will drop and things may be better.

    But let’s get real folks. We wont. Someone somewhere is going to keep on doing the bad things for our planet, in fact everybody is going to keep on doing it until the lights go out at their place, or until their carpet is wet with salt water, or until they have nothing to drink and/or nothing to eat.

    Because deep down it is our fervent hope that this is all a bad dream. That Mother Nature will kiss the Earth and make it all better. But this time we have run out of favours. Our nine lives are cut.

    We know enough to foretell our end with out persisting with the endless examination of the minutiae of political, social or of climate science. We know there is enough climate change in the pipeline to pretty well end life as we know it – even if we turned off all the motors today. We know that as our present society expires it will go like the end of a small star; in a final stuttering surge of conspicuous, indeed of desperate consumption of the remaining resources. Emissions will peak, as a final gesture of our defiance at all-avenging Gia. From then on it will be all down hill.

    The astute among us will try and make other arrangements; to adapt – as the technical optimists euphemistically put it – but even so I don’t like our; I dont like my chances.

  40. 40

    Re #14 David B. Benson:

    So the carbon capture and
    sequestration net costs are assumed to be $50 per tonne of

    …and there’s the rub. Politics. Once we get to spend $50 to keep a tonne of coal out of the atmosphere, there are lots of technologies that suddenly become interesting. And the portfolio approach of John Mashey #19 the only sensible way.

    Re #20 Edward:

    There is no known substance that can withstand such sustained temperatures, so the reactors would have to be continually disassembled and buried at a toxic waste sight somewhere, probably where millions of people live. Then new reactors would have to be built consuming more non-renewable resources.

    I get the impression you are mixing up the “hydrogen economy” with nuclear fusion. But apart from that, the above is not true: there are two techniques for containing a hot fusion plasma, magnetic containment and inertial containment.

    The problem isn’t heat but neutron activation: the fusion energy is carried off as fast neutrons, which can be captured in a lithium blanket for breeding new fuel. They will however also be absorbed in structural elements of the reactor, which thus will become radiactive and, after a while, structurally compromised. So yes, “used-up” reactors will have to be disposed of, just like with fission reactors. But the difference is that the process itself doesn’t produce any high active waste, just helium.

    Re #25 Edward Greisch:

    Taking CO2 back out of the air has to require more energy that you got by putting the CO2 into the air in the first place. Basic thermodynamics says so.

    Yes, but only if you convert the CO2 back to C. Otherwise it is a lot less (but still much).

    Re #26 Kiashu:

    CO2 at room temperature and normal atmospheric pressure has a density of 1.98g/lt

    But it won’t be at normal atmospheric pressure… already at a depth of 300 m you will have 100 atmospheres, and it will become/remain liquid ( ).

    Of course we might also compress the carbon dioxide, down to liquid form at 60 atmospheres or so. This will then require only 243km3 for all the combustion of our fossil fuels, or a mere 2.4km3 for 1% of it. Of course, keeping CO2 liquid is far from a simple task, and preventing these billions of tonnes from leaking out seems difficult.

    The density of liquid CO2 is 1600 g/liter ( for solid, but I expect liquid to be similar). So you would only need to store 18 km3, or 0.18 km3 for 1%. If you store this under a 100×100 km area, it would rise by 18 mm/year.

    These same layers have safely contained oil and gas for millions of years. The oil industry is already using CO2 injection into wells for recovery of oil, and leakage doesn’t seem a major problem. And even if some leakage were to occur, remember current leakage is 100% :-)

    Burn less stuff.


  41. 41
    Johnno says:

    I suspect that when biochar is studied more carefully the effective carbon capture won’t be so great. So far most of the bio-carbon comes from outside the test farm field into which it is plowed; example forestry waste. However left alone it may (depending on humidity and fire) remain as near-inert carbon in forms such as bark, fallen trees, leaf litter and humus. By harvesting and partially burning that biomass we accelerate atmospheric CO2 addition. The difference is that we accurately measure that leftover charcoal in grams added per square of farm soil. In contrast we only guess at the unburnt yet semi-stable litter back in the forest, perhaps also downplaying the liquid fuel requirement for harvesting machinery. I think burn less carbon period whatever the source.

  42. 42
    Jim Cripwell says:

    I find it interesting that no-one seems to have mentioned Craig Ventner (? spelling). If Craig is successful, his micro-organisms which “eat” CO2 and produce methane or other hydrocarbons, will require an atmosphere of almost pure CO2 to live in. These organisms may be only 18 months away. This is certainly as long as it will take to build carbon dioxide sequestration hardware.

  43. 43
    Francois Marchand says:

    Re N° 40 – I thought that even the carbon sequestering enthusiasts had never imagined liquefying CO2, cooling it down a bit (say down to a couple dozen degrees K), and pumping it down in some old mine shaft, for it to stay there for an eternity (until we die, that is). The amount of energy needed… There are laws against that : thermodynamics.

  44. 44
    pete best says:

    It is as had been stated already. The worlds energy comsumption is growing by 2 – 3 % per year. Therefore all new energy requirements/demands should be met with non fossil fuel technology wherever possible but that still leaves the existing infrastructure pumping out some 7+ billion tonnes of CO2 per annum which has to be dealt with.

    Heating your home via is the most energy intensive practise even though it usually burns gas locally you get through a lot of KWh of it in a cold country. Here in the UK its around 20,000 KWh.

    Electricity use is quite low, around 5000 KWh per average house. A UK (4.5 litres relative to the US 3.9) gallon of Petrol produces some 43 KWh of energy so the anount used depends on mileage done and fuel conumption per annum. The average in the UK is 9000 miles and 32 MPG. The average in the USA is 12000 miles are 20 MPG. Petrol produces some 2.3 Kg/Litres of fuel used whilst diesel 2.6 Kg/litre used. Diesels also produce black carbon recent articles have stated.

    Therefore cost effictive measures to curb carbon use or increase efficiency range from lagging your loft and cavity wall insulation, double glazing, wearing a fleece and slippers in the winter – effective measures for staying warm to driving a more economic car (20 to 40 mpg makes a big difference tonnage wise) to using the new CF lightbulbs and AAA rated applicances (lowest gain). The average american produces some 6.5 EU tonnes of Co2 per annum. There is massive scope for efficiency gains here.

    On solar power for example. A typical system here in the UK costs around £5K with the grant and will produce some 800 – 1200 KWh of electricity per annum (20 to 25%) saving but it will never pay for itself at the present time and solar is seasonal and hence a lot of it is sold back to the grid. Relative to overall energy usage solar is poor value for money compared to getting a new fuel efficient car (when you next buy a car) or insulating your home and wearing more clothes inside the house.

  45. 45
    JCH says:

    ” And maybe both of these advantages could be combined, eg via my patented maintenance-free floating rafts of coconut trees which directly sink their genetically-engineered carbon-heavy fruit to the ocean floor for long-term sequestration (you read it here first, folks). …” – James Annan

    I’ve suggested this same thing. In Wisconsin they are salvaging massive old-growth logs that sank during logging operations done in the 19th Century. They’re still in excellent condition. It’s some of the most valuable timber on the market.

  46. 46

    Edward Greisch posts:

    [[Taking CO2 back out of the air has to require more energy that you got by putting the CO2 into the air in the first place. Basic thermodynamics says so]]

    No, it doesn’t.

  47. 47

    Edward Greisch posts:

    [[There is no such thing as nuclear waste. It is fuel that needs to be recycled. ]]

    Super! We’re going to store some in your bedroom.

  48. 48

    Re #43: François Marchand: No couple dozen Kelvins. Room temperature! Look up the phase diagram in my Wikipedia link. And no “old mine”, but drill holes. Oil/gas technology in reverse.

    I see it as a possible transitional solution buying us time. Which we’d better use wisely.

  49. 49
    Ray Ladbury says:

    There appears to be a lot of misinformation among posters about what is involved in carbon sequestration. It does not involve turning the CO2 into carbon, so you don’t give up all the energy you got from burning the carbon in the first place. Rather, it involves causing the CO2 to react or bind with a material and then either storing the reaction product or freeing the pure CO2 and storing it in liquid or solid form. CO2 liquifies under pressure, so this is not prohibitive energy-wise.
    And yes, the normal processes that take up CO2 are slow, but it is quite possible they can be sped up via catalysis or using nanoparticles. So bottom line: There is nothing in the laws of thermodynamics that precludes carbon sequestration. Whether it can be made economically viable is entirely another question. The problem Frank is addressing here is especially problematic, since 1)CO2 emissions from a point source are concentrated, so much of the work is already done for you; 2)distributed sources preclude an efficient centralized plant; 3)No one has even shown that carbon capture and storage could be made to work even for a point source.
    The non-point source problem seems to become more urgent as development progresses. Early in development, there is a migration to cities, as increased agricultural efficiency causes people to migrate there looking for work. Later on as people become more affluent, the migration is away from the cities, and distributed emissions increase. The problem is in some ways very similar to that of pollution of the watershed. Cities can solve their problems by improving sewage treatment, while emissions from suburbs are much more difficult to control.

  50. 50
    Frank Zeman says:

    Wow! Really interesting comments for the most part. I was originally thinking of trying to respond to most of them but that seems like a full time job. Having scanned a few of them I thought I would make a few comments.

    1) Air Capture is not expected to be cheaper or easier than capture from power plants. This technology is aimed at vehicles and other small sources of CO2. Recall the IPCC threshold for capture was 0.1 MtCO2 per year, which I think is a 100 MW coal plant (don’t remember exactly).

    2) Air Capture is essentially a CO2 concentrator meaning the CO2 would have to be stored or converted back to fuel through CO2 hydrogenation. The latter idea is not as crazy as it sounds and the carbon essentially becomes a hydrogen storage device. The tradeoff is the cost of capturing and converting the CO2 to fuel versus transporting and storing H2 along with new re-fueling stations and vehicles.

    3) The best estimates for the energy consumption of AIr Capture is 350 kJ/mol CO2. I think we can get that down to 250. The heat released from coal is 400 kJ/mol CO2 with all other fuels higher owing to the hydrogen present. While not super efficient, we regularly accept only 35% conversion of coal to electricity.

    4) If the CO2 is to be stored the Air Capture allows capture at the storage site, thereby avoiding large transportation networks and opening isolated storage sites to operation.

    Just some thoughts.