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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. 151

    At http://www.netl.doe.gov/publications/proceedings/01/carbon_seq/6c4.pdf, “Geochemical Aspects of the Carbonation of Magnesium Silicates in an Aqueous Medium”. It refers to Seifritz, W. (1990) CO2 disposal by means of silicates, Nature 345:486, which isn’t on the web.

    At http://www.geology.yale.edu/~ajs/1999/07-09.1999.07Velbel.pdf, “Bond Strength And The Relative Weathering Rates of Simple Orthosilicates”. Olivine is quick.

    Figure 1 in 07-09.1999.07Velbel.pdf says Mg2SiO4 weathers at the rate of 10^(-12.1) moles per square-centimetre-second. Fe2SiO4, -10.5. Don’t know Mg2SiO4′s density, but if it’s 3 g/mL, there are 0.02 mol/mL and figure 1 says it takes 27 billion seconds to weather forsterite one centimetre. For fayalite of the same molar concentration, 0.67 billion seconds.

    Suppose we have got the forsterite to 80 percent pass through a 100-micron screen by spending 25 kWh(e) per tonne, 12.7 kJ/mol, crushing it. Now weathering has to eat 0.005 cm from both sides to get to the middle, and that takes 135 Ms. Four years.

    The above means that when I said,

    Serpentinite-containing mine tailings have in fact shown [that carbon capture and sequestration works], without the mine operators’ intending it.

    it was plausible. I have been chastised for gathering that it was fact from chitchat surrounding the paper that revealed it rather than the paper itself. Here is that paper’s abstract:

    We have documented active sequestration of atmospheric carbon dioxide (CO2) in chrysotile mine tailings at Clinton Creek, Yukon and Cassiar, British Columbia. Hydrated magnesium carbonate minerals develop in mine tailings as a natural consequence of the weathering process within the residues. Magnesium, leached from minerals, reacts with dissolved CO2 in rainwater, precipitating carbonates at the surface of tailings upon evaporation of pore fluids. Increased reaction rates are observed in the tailings environment due to fine grainsize resulting from mineral processing. Mine tailings may therefore represent the optimal environment in which to pursue mineral sequestration. X-ray powder-diffraction studies demonstrate that CO2 is crystallographically bound within the hydrated magnesium carbonate minerals nesquehonite, dypingite, hydromagnesite, and lansfordite. Quantitative phase analysis with X-ray powder-diffraction is used to determine the modal abundance of hydrated magnesium carbonates in mine tailings. An atmospheric source of CO2 is confirmed with stable and radiogenic carbon isotope techniques. Serpentine and olivine-rich tailings are produced by many types of mining, including nickel, diamond, platinum, and chrysotile. The global scale of these mining activities has a sequestration capacity on the order of 100 million tonnes of carbon per year. Widespread implementation of mineral sequestration in mine tailings has the potential to render large mining operations greenhouse gas-neutral and significantly reduce CO2 emissions on a global scale.

    So, Ray Ladbury

    … concentrating CO2 from a concentration of 380 ppmv in air to anything like the concentrations needed in solution to make this effective will not be an efficient process.

    and, I think, some others, you haven’t quite got it yet. No concentration is necessary, not as a separate step. The minerals do it themselves.

    They have been seen to do it themselves.

    We do not have to concentrate the CO2. The energy this would take is already in the mineral-CO2 system. They do it themselves.

    Pulverized magnesium silicate minerals sequester CO2 from plain air, without our adding any energy other than the ~6 kJ/mol pulverization requires. (12.7 kJ/(mol Mg2SiO4), i.e., per two moles CO2.)

    That’s three repetitions. Maybe one more, really short one: pulverized magnesium silicates sequester CO2 for free.

  2. 152
    Patrick says:

    The one source of energy that is done more to reduce emissions from power generation than any other source is … nuclear.

    Thousands of operation-years of experience in the US and other advanced countries have proven it to be reliable, safe, environmentally sound and economical. All those adjectives can be argued but in all cases the alternatives are worse. (To rebut the standard concerns; Chernobyl was Stalin-era technology, and abysmal USSR operating standards, different category; nuclear ‘waste’ is used fuel that can be safely stored and then eventually reused.)

    Carbon sequestration and “50 SIMPLE THINGS YOU CAN DO TO SAVE THE EARTH” are going to be indirect and inneffective. Direct and effective would be non-fossil fuel energy sources; we just need nuclear power to be our baseload power generation source. If nuclear became 75% of our electricity generation (baseload), and if wind, renewables etc. complimented it for another 20%, and if transportation energy was displaced partially by electricity via plug-in hybrids … then USA could cut CO2 emissions by almost 2/3rds. And do it without huge CO2 emission mitigation costs.

    We should stop pretending there is no solution or the solution would be hugely expensive. We could provide subsidies that cost less than our ethanol subsidies, and get to a France-level adoption of nuclear (70%) in the next 30 years. No big deal.

    The #1 impediment to solving the GHG emissions problem is the money we waste on non-economical solutions (hydrogen cars, carbon sequestration, ethanol, etc.).
    If FutureGen can be done economically, great, but we wasted $20 billion on SynFuels in the 1970s and 1980s, and this has the feel of another great engineering idea that is simply not economical.

  3. 153
    David B. Benson says:

    Phil Scadden (138)— Pleased to read of it. One possibility for additional CO2 sequestration is to use biomass to produce carbonaceous solids such as biochar or biocoal. Bury these materials in an abandoned mine or a carbon landfill. Then squirt in the CO2.

  4. 154
    Ray Ladbury says:

    G.R.L. Cowan, I wasn’t saying that weathering did not happen w/o concentration, but rather that it would be too slow to make a meaningful contribution. I think your calculations pretty much show that. It is all about exposing surface area to gas. That takes energy, no matter how you slice (or pulverize) it. There may also be competing reactions, particularly if the forsterite is not pure Mg end member. That weathering will happen is beyond doubt. That it will not happen on a timescale meaningful to human survival without significant intevention on our part is also pretty much certain.

  5. 155
    Ray Ladbury says:

    Patrick, I don’t think we can prejudge the outcome at this point. We may have to resort to all strategies available to us to circumvent this threat. To speak as if the nuclear waste storage problem would be completely solved by fuel recycling is disingenuous. Recycling leaves lots of nasty isotopes that still need to be dealt with. Proliferation is not a trivial concern either. Personally, I think these problems can be dealt with and think nuclear power may be part of the solution, but it isn’t a solved problem.
    And yes, our politicians tend to lavish money on solutions that garner votes rather than decrease carbon emissions, but that is an issue for an educated electorate. It may be that inefficiency in government expenditures is the price we need to pay so that real strategies are pursued in addition to the boondoggles.

  6. 156
    Kevin Leahy says:

    Re 149 & questions re CCS. It is genearally accepted in the industry that CCS is likely to work. If you talk to oil folks, they tend to see little risk given their experience with EOR. The individual who claims all previous experience shows these do not work is bucking the published lit and field experience. Re why it isn’t happening on a large scale — yes, it is the economics. Until there is a price on CO2 in excess of $30 to $40/ton, CCS off of an IGCC is not competitive with a conventional, emitting coal plant. CCS off a conventional plant is unlikely to be competitive except for a few very new facilities in particular electricity markets (most likely the US Midwest).

    The tech has not been demonstrated yet at large scale. Efforts are underway to try to gain govt support in partnership with industry to do the deomonstrations. The industry believes it will take 10 years to get a plant up and running and another few years to gain full understanding of how the large scale injection behaves at depth. Once we KNOW it works, we will need to build hundreds of these facilities — the MOST optimistic projection is that all existing coal in the US can be retired and replaced with this new tech by 2040 to 2050.

    Yes, it will be expensive, but it is the least expensive option, along with expansion of nuclear for hiting a target of 60 to 80% reductions by 2050. Check out EPRI.COM for presentations re their analysis.

    Those who claim otherwise lack an understanding of the scale of the energy system and amount of emissions involved.

    Re Futuregen. It was cancelled because of a change in thinking at DOE, moving from the idea of supporting a single large plant/test site, to providing the incremental funds to perform test at several smaller sites in partnership with single firms. It was felt you’d be able to learn more/conduct more specific research through the latter approach. The project was not cancelled because it doesn’t work or was deemed a failure.

    Re the original idea of removing CO2 from air, again, one of the least costly alternatives possibilities so far is algae used as feedstock in IGCC, generate power and capture and geologically store the CO2. The CO2, just as in the process using coal, is captured before combustion, is concentrated and already at very high pressure — the remaining H2 is then combusted.

  7. 157
    DBrown says:

    Phillip Shaw, you mention that
    ‘the tone of your comment seemed a bit cranky . . .’
    Very true and it wasn’t necessary nor polite – my apologies.

    That ‘perhaps you should consider switching to decaf.’
    Yes, I relapsed.

    and ‘ Second, this is not the forum for flame wars.’
    Correct – you are trying to address a serious issue and should get a professional response.

    I will not try and address all the issues you raised but one thing I want to say up front: The issue of ASU’s or for any process made here is not whether they work and I have not once stated that any process discussed here can not work – only that some are not good approaches in terms of money/energy relative to the idea of removing CO2 from the atmosphere. No matter how you approach that issue, entropy is working against you and calculating real energy costs is critical – especially when you make strong claims relative to the process; otherwise, you end up with the monster boondoggles like corn based ethanol that is driving world food prices up, not addressing real US energy issues in a wise manner and worse, may lead to terrible hardship (read: deaths) for many people who did nothing to deserve such a tragedy – so be careful about claims.

    The main issue is that many people here are making claims about approaches with little and in some cases, no proof. This is not appropriate even in a blog – if you claim something, back it up with facts; otherwise, it is just opinion and needs to be qualified as such.
    No matter the approach, every thing is about energy cost and any process that consumes available funding (very limited) must justify its methodology relative to payoff and efficiency or it is just more ‘waste CO2′ in the atmosphere.

  8. 158

    Ray Ladbury said,

    I wasn’t saying that weathering did not happen w/o concentration, but rather that it would be too slow to make a meaningful contribution. I think your calculations pretty much show that. It is all about exposing surface area to gas. That takes energy, no matter how you slice (or pulverize) it. There may also be competing reactions, particularly if the forsterite is not pure Mg end member. That weathering will happen is beyond doubt. That it will not happen on a timescale meaningful to human survival without significant intevention on our part is also pretty much certain.

    If the olivine is not pure forsterite, more of it must be comminuted, but we can get away with particles that are less minute, because if much of the iron member, fayalite, is present, it much speeds up weathering.

    Your paragraph changes directions halfway through. Too slow to make a meaningful contribution — bad news — or too slow to do so without significant intervention on our part — neutral-to-good news?

    I agree with the direction taken by the paragraph’s second half. I understated the pulverization energy aspect of the “significant intervention” we should do by calling it 6 kJ/(mol CO2) without reiterating that these are kilojoules of electricity. Of primary energy, ~20 kJ/(mol CO2).

    Still a good deal compared to the 350-ish numbers that were being claimed for some other processes that, if those numbers are true, are ridiculous.

  9. 159
    Count Iblis says:

    Why not switch to nuclear energy? The volume of nuclear waste you need to store per joule of produced energy is much smaller than the volume of CO2 that has to be stored.

  10. 160
    Ray Ladbury says:

    Count Iblis, As someone who favors greater use of nuclear power to limit future climate change I still have to protest–stored CO2 presents little risk for creating WMD, while nuclear waste does. We risk a backlash if we do not admit the difficulties nuclear power faces. They are not inconsiderable and they are not solved. I believe they can be solved, but not without considerable effort and probably some residual risk. Handwaving arguments should not carry the debate wrt something this important.

  11. 161

    Why not switch to nuclear energy? The volume of nuclear waste you need to store per joule of produced energy is much smaller than the volume of CO2 that has to be stored.

    A total switch tomorrow morning would still leave ~200 billion tonnes of legacy CO2 in the air. It will be pleasant to ease the [CO2] back to where it was, and as I’ve been saying, a few hundred gigatonnes doesn’t make much of a dust layer if it’s innocuous dust (as it would be) dispersed over large areas of the planet’s surface — including sea surface.

    I can’t fault nuclear energy on the harmlessness-in-practice its leavings have shown, but lots of people can; or anyway, fault it, not exactly on that, but on what they seem to believe is a likely lack of future harmlessness.

    This, I think, reflects the fact that when governments allow their citizens to switch to nuclear energy, governments lose money. The recent price of a uranium-tonne-equivalent in natural gas was $5.2 million, inclusive of royalties but not of special end-user taxes. A tonne of the real thing costs less than $0.2 million, and at that sort of price has been being prospected at ten times the rate of use.

    So if you want to make the tax man your friend by pretending to be irrational, there are several nuclear-energy-related options. You can pretend to believe nuclear powerplant waste will be very different, no longer entirely harmless to all its neighbours, in the future; or that nuclear weapon proliferators will start using materials from, or putatively destined for, power reactors, despite in all known history having always chosen easier, more effective ways. Other such routines will soon be on display.

    They all serve to help governments slow the switch to nuclear by diverting attention away from the lucrativeness to governments of such delay. That lucrativeness is why it takes such an amazingly long time to get permits to build a nuclear power plant. Nuclear developers aren’t going to completely roll over City Hall before this year is out. If they could, nuclear plants would still take time to build, and the very long paper chase will have institutional inertia.

    So a lot of legacy-CO2-to-be is still sitting underground as CH4, and a lot of innocents are going to be blown up by it, or poisoned by it when it has lost its hydrogens and gained only half its usual pair of oxygens. There are forms to fill out, and new, shorter forms can’t be brought on stream overnight. So we won’t be able to prevent that, nor to resurrect those people, but in due time we will be able, not too expensively, to take down the CO2.

  12. 162
    Jim Eaton says:

    It’s really hard to see what events are necessary to awaken Americans to realize that lifestyle changes are mandatory to reduce CO2 impacts. As I returned from the Bay Area to Davis last week, I drove a safe and sane 70 MPH, although (except for a few semi-trailer trucks) I was the slowest passenger car on the road. I watched SUV after SUV, one driver to a two-ton chunk of steel, blew by me at speeds up to 80 MPH or more.

    In the (relatively affluent) neighborhood I live, Village Homes, nearly a quarter of the residents have installed photovoltaic systems on their roofs. And although many of them do what they can to reduce energy consumption (walk or take the bus to work, buy local produce, and compost everything they can), their carbon footprint is still relatively high. I sincerely appreciate all their efforts, but it still is a far cry from being carbon neutral. And this is from a community that is able to afford to pay for green alternatives.

    But the nuclear option raised on this blog gives me serious concern. Although I greatly respect the contributions of Ray Ladbury, I just can’t accept the idea that to deal with anticipated energy demands we must embrace nuclear power. It reeks of robbing Peter to pay Paul. We take an energy alternative (not without the carbon emissions of building the facility and mining the fuel), use it for a few decades, then plow fossil fuels back into sequestering dangerous radioactive spent fuel and power plant materials for many thousands of years. Not to mention the weapons concerns of the dangerous waste.

    What do I propose? Well, along with a great reduction of human propagation, I guess I do vote for renewable energy sources. Not they they all are benign (wind energy systems have become bird Cuisinarts in too many locations). But here in sunny California, I would ask that every new building be outfitted with photovoltaics and that there be a subsidy to retrofit all other buildings with solar panels.

    But from my freeway experience, I think of the oil crises of the 1970s. Set the national speed limit at 55 mph. And enforce it. On my last trip to Australia, I was astounded to see that most folks obey the speed limit. When you enter towns, there often is a notice of the presence of speed cameras. Even in the countryside, mobile speed cameras may be present. And if you drive over the speed limit, the owner of the car receives a citation. So I did not see many folks exceeding the speed limit. If you exceed the limit and are captured by a camera, you will pay.

    I know it is an American tradition it ignore traffic laws (have you watched a young person at a stop sign recently?) But we are faced with a crises that demands desperate actions. Rather than trying to accommodate anticipated energy demands in the future, we should be preparing our folks for the reality of the future. Conservation and renewables are the way to start. Other measures may prove necessary in the future.

  13. 163
    pete best says:

    Re #156. Kevin, if what you say is true then I am afraid then CCS is not going to help us in our fight to combat 2C of warming which is looking less and less likely for eacy 7 to 8 billion tonnes we release per annum. It might help us in fighting >2C but the time scales you specify means retrofitting which seems even less likely politically and economically.

    CCS is a green wash by the looks of it and should not be listed as a means of combating AGW until it is ready to fit to both existing and new coal fired power plants. until that time coal should stay in the ground as James Hansen is stating.

  14. 164
    Nick Gotts says:

    Re #161 [G R L Cowan]

    What an amazing load of hooey. In Europe at least, governments have mostly been promoting nuclear energy in the teeth of public resistance. Why is it so many nuclear advocates come out with this sort of rubbish?

  15. 165
    Ray Ladbury says:

    Jim Eaton, I think my posts make it clear that I do not discount the difficulties of nuclear power. I just don’t think we can preclude or prejudge any option at this point if we want to acheive sustainability (economic, ecological and social), and sustainability is a prerequisite to the survival of civilization.

  16. 166
    Jerry Toman says:

    Here is an alternative “cryongenic” carbon capture approach. I’m not saying it would be economic, or that it wouldn’t need testing or developmnent to minimize “solvent losses”, but should be way more efficient than starting with air containing only 400 ppm CO2.

    Compress air in two stages to 10-15 bar. Use it to burn coal to CO2 in a “pressurized fluid-bed combustor” to generate steam, and during which process which some of the impurities can be adsorbed.

    Cool combustion gases, pre-heating boiler feedwater in the process, and remove any water that condenses.

    Next, pre-cool the high-pressure gases with offgas, after which they are expanded to about 1.5 bar. If this doesn’t produce temperatures cold enough to condense out solid CO2, wash the offgases with either a physical solvent or one that is combined with a chemical absorbent to increase capacity.

    Use the CO2 lean off-gases to pre-cool the combustion gases before releasing to the atmopshere. Regenerate physical solvent with waste heat from the combustion process.

    Of course, “partial combusion” variations of this theme are also possible.

  17. 167
    DBrown says:

    Those saying nuclear power is a good solution, I was wondering which type of nuclear fission plant?
    As for Europe, the French are using breeders and these can be terribly dangerous (see my post # 122; however, ignore the fool behind the curtain in post # 137).

    I do not believe that nuclear power, except in the Canadian approach, is either safe or desirable. The old mantra “Keep it simple, stupid” should be printed on all nuclear engineering textbooks.

  18. 168

    Nick Gotts said, with reference to this,

    What an amazing load of hooey. In Europe at least, governments have mostly been promoting nuclear energy in the teeth of public resistance. Why is it so many nuclear advocates come out with this sort of rubbish?

    To anyone who follows the money, it doesn’t look like hooey.

    In Gotts’ version, the motivation of governments is obscure: they work against toothed public resistance in order to lose fossil fuel income. Governments. Who can figger’em, eh.

    Well, perhaps this will help in figuring them: per Ghislenghien- or Piper-Alpha-style death, per similar death in the much more numerous small fossil fuel disasters, they get a few tens of millions of Euros in oil and gas revenue. If they work to create the appearance of public opposition to nuclear energy development, they can justify the continuation of those lucrative deaths as something the public is forcing them to accept.

  19. 169

    As regards “… and then we all die.”, I think it’s worth noting that as the youngsters who are going to be the victims of “… and then we all die” approach voting age, the odds that enough of them will want to NOT die, and therefore vote different, increases.

    China can’t keep doing what it’s doing — their cities are massively polluted and things ain’t getting better. Look for a Soviet-style collapse any year now.

  20. 170
    Frank Zeman says:

    A few more comments. Kudos to those posters who are calling for civility. In topics like this, it is easy to get passionate.

    There is the question of why should some money be invested in air capture at this stage. There are two real reasons. First money is being spent of hydrogen and electric vehicles when it is far from clear that they are the most cost effective solution. For starters the cost of the vehicles has to come down by at least one order of magnitude and they both require billion dollar infrastructure. Secondly, whatever the cost of air capture, and it is initially expected to be much higher than conventional CCS, the final cost sets an upper limit on the cost of climate risk mitigation. It removes some uncertainty about the cost of solving the climate problem. This information may prove to be useful.

    Another point is that when considering any technology it is important to view them all as transient. We do not know what technologies will be around in 2050. We research things that look promising and implement things that have an immediate effect. Like efficiency, CCS would have the immediate effect of reducing CO2 emissions to the atmosphere. This does not mean that CCS will be used in 50 years, the conventional lifetime of an industrial facility.

    Mineral sequestration has the challenges of cost and kinetics. The absorption does indeed occur naturally but at a very slow rate. This is improved by attrition grinding and heat treatment, which consume too much energy.

    The ASU question can only be answered with a detailed design as the operating temperature of the facility rises from -180oC to -60oC. We can get started by recalling that a conventional ASU (producing O2) consumes 20 kJe per mol O2 or 10.5 MJe per mol CO2, as O2 is 20% and CO2 is 0.04%. The remaining question is the relation between operating temperature and energy consumption. Assuming it’s linear would result in one third less or 3 MJe, if quadratic then 1 MJe. Then you need to consider the primary energy used to generate the electricity.

    Then a stab at the specific list of questions presented earlier (126):
    1) the energy required to produce liquid CO2 is expected to consume 21% (see IPCC SR CCS) maybe more but 33% would be an upper limit not minimum.
    2) very good question: if we only use CCS then we build more plants. A better solution would be to save that 20% using efficiency ideas proposed by Amory Lovins and others.
    3) CCS from a power plant has not been attempted. There are three large CCS projects (Weyburn, Sleipner and In Salah) that are based on pressure swing absorption (easier and cheaper than thermal swing necessary at power plants). Without market signals or regulations it is unlikely that any will start.
    4) You do not reference a specific operation. The midland Texas CO2 injection projects derive there CO2 from natural deposits in Colorado. The gas is pipelined down proving the transport technology.
    Weyburn uses gasification CO2, which is also pressure swing absorption. Thermal swing absorption is done at refineries, which is were soda plants get their CO2.
    5) Again, you do not reference sites. No leakage has been measured at the three projects mentioned above and they are really looking. The only leakage site I’m aware of is Mammoth California, a natural occurrence. Another famous case is Lake Nyos in Africa, again natural. It integrity of the storage site depends on the cap rock and a suitable one must be verified. Oil reservoirs have been held in place for millions of years so it should be possible.
    6) methane leakage from all coal recovery projects is serious. As mentioned in another post, the USGS expects more CO2 to stay down than methane come up. Also burning the methane results in less emissions than burning coal.
    7) Air Capture is aimed at vehicles and small sources, that is the point of the article. Some agricultural greenhouse gases can be reduce by altered irrigation etc but it’s hard. Emissions from meat production are even bigger to my knowledge.

    Thanks for all the good comments.

  21. 171

    Re 170: For starters the cost of the vehicles has to come down by at least one order of magnitude and they both require billion dollar infrastructure.

    For electric vehicles this is patently false. I have to get rid of my gas guzzling V8 sports car (but only for a few years — I’ll buy another after the teenager departs the nest ;) ) and will likely replace it with a two-seater electric commuter that I’m expecting to run me about $13,000. It will plug into my wall in the garage. I may have to run an extra outlet to the other side of the garage, but I know how to add outlets to walls for less than a billion dollars.

    Here’s the biggest problem — people are so brainwashed by the nay-sayers that they are incapable of action. That doesn’t cost a billion dollars to overcome.

  22. 172
    Steve Albers says:

    Here is the link with biochar interviews that should work better than in the earlier post #71.

    http://beyondzeroemissions.org/2008/03/30/lukas-van-zwieten-nsw-dpi-biochar-agrichar-terra-preta-soil-trials-zero-carbon

    As another wedge I’m also hopeful about fusion power – where perhaps funding should be increased.

  23. 173
    Nick Gotts says:

    Re # [G R L Cowan]

    “If they work to create the appearance of public opposition to nuclear energy development, they can justify the continuation of those lucrative deaths as something the public is forcing them to accept.”
    Repeated hooey is still hooey. How about some actual evidence of
    governments doing this – for example, funding anti-nuclear organisations? Or is it a huge secret conspiracy that only you have managed to penetrate?

  24. 174

    “If they work to create the appearance of public opposition to nuclear energy development, they can justify the continuation of those lucrative deaths as something the public is forcing them to accept.”
    Repeated hooey is still hooey. How about some actual evidence of governments doing this – for example, funding anti-nuclear organisations? Or is it a huge secret conspiracy that only you have managed to penetrate?

    If a secret were impenetrable to everyone but me, that would suggest but not prove that I was a nut and the secret was not real. However, the same commentator a day earlier said, “so many nuclear advocates come out with this sort of rubbish”, emphasis mine.

    A government that sought to create the appearance of public antinuclearism and was not confident that its public would play along might stage a referendum in which voters were not allowed to approve of nuclear energy, instead being given only various choices on how fast to phase it out. An instance of this behaviour –

    … Voters were asked to pick one of three ‘lines’. But by this time all three ‘lines’ had formulated policies calling for the eventual phase-out of nuclear power …

    –is detailed in Walter C. Patterson’s Nuclear Power, pp. 127-128.

    In the comments Frank Zeman says,

    Mineral sequestration has the challenges of cost and kinetics. The absorption does indeed occur naturally but at a very slow rate. This is improved by attrition grinding and heat treatment, which consume too much energy.

    The evidence I introduced might seem to indicate the energy consumed by grinding, aka pulverization, aka comminution, was, at ~20 kJ/(mol CO2), not excessive, and heat treatment unnecessary, but that is inconsistent with the axiom he ends his initial posting with:

    It is not any kind of panacea though.

  25. 175
    Jerry Toman says:

    What I don’t understand is the willingness of people to advocate the spending of tens, if not hundreds of billions of dollars to develop technologies that have little chance of succeeding, instead of going after the “low-hanging fruit”.

    Expressed in terms of the original intent of the posting, which suggests the use air capture to remove CO2 from the air in compensation for lingering CO2 emissions that would be difficult or impossible to control, such as those emitted from highly distributed or mobile sources, a lot of proven and likely much cheaper possibilities remain to be examined.

    Let’s take the CO2 emitted from consumption of home heating oil as a first example. This system has almost double the carbon footprint of natural gas for the amount of heating actually delivered. First, these homes should be preferentially targeted for increased insulation and weatherization. Next, the larger, newer ones should be required to switch to heat pumps, ground based or otherwise, in which case the CO2 emitted would be reduced by a factor of two or more if the fuel used in the power plant were heating oil, or even 1.4 if it were to be coal. In this case the heating oil could be diverted back into the diesel pool (after hydrotreating) enhancing what is otherwise a fuel in short supply. In this case, we would only be replacing what would disappear naturally via “Peak Oil”

    For new construction, in most places, most of the heating requirements could be supplied by solar energy (Google Drake, Albera, solar). In any event the CO2 would be emitted from a central location, where it could be captured more economically, should a location for its ultimate disposal be found.

    For large mobile sources, such as that produced by diesel locomotives, it might in fact be possible to use a couple of tank cars to carry amine solutions that would be loaded up with CO2 during the trip, and discharged for regeneration at central facilites, such as a coal mine where the CO2 could be injected into unminable seams. This might remove perhaps 50% of the CO2 emissions from these sources.

    But this is still small potatos. A cheap, plentiful, reliable, carbon-free source of electricity could solve practically all our CO2 emissions problems. While I contend the development of the AVE would be a “slam-dunk” in achieving this goal, I can understand why most of the readers, for whatever reason, might not (yet) see it that way. As opposed to most of the ideas put forth here, however, this uncertainty can be resolved by a mere $50 million (or less) investment to devlop a final design and build one at an ideal location. If it works, game over. If it doesn’t work, at least I will be shut-up once and forever on this subject and you can all go forward with your more exotic and capital-intensive solutions, which will take years if not decades to develop.

    I ask all of you, including Frank Zeman, what is wrong with this strategy?

    May the AVE-Force be with you!

  26. 176
    François Marchand says:

    According to the latest readings from the Mauna Loa Observatory, the increase in atmospheric CO2 appears to be slowing down. Two months do not constitute a trend, and -perhaps- so far, it might be only Mauna Loa, but does anyone have an idea about the carbon-capturing process at work? I know it can be dismissed as “weather”, but any trail?

  27. 177
    Chris Dudley says:

    Frank,

    (#103) Thanks for taking a look. I would suggests then that molecular sieves make the most sense from an energy use standpoint. Absorption is slightly exothermic and may drive convective flow if properly arranged, or air motion from wind may be used for collection. I suspect that we will capture CO2 from the air to make liquid fuel sooner than we will do it to sequester the stuff so the energy input would need to be as low as possible to make the fuel economic should we run out of ways to use the process heat from the Fischer-Tropsch or Sabatier processes. The trade-off would be in cost of materials I think, but long lasting sieve material would seem to pay for itself through the energy saved since this seems substantial. Once we are making fuel from air capture (all the concentrated sources having been exploited) scale should be set to move into sequestration if it is really needed. I note that making liquid fuels from CO2 using renewable energy is about the only method that can approach current liquid fuel use, the Agrawal et al. (2007 PNAS 104 4828) H2CAR proposal notwithstanding. So, delays in electrification of transportation would likely push this sort of thing.

    Again, thanks! I’ve been looking for energy estimates for other methods for a while now. I should note that the lowest energy method looks to me to be using the brightness temperature of the Antarctic night sky to freeze out CO2 using reflectors to isolate the air from the ground temperature, but this poses logisitcal difficulties. Klaus Lackner once mentioned to me that there has been a little work done on looking at stabilizing the bases of glaciers by freezing them colder though. There might be something there….

  28. 178
    Nick Gotts says:

    Re #174 [Cowan] ““so many nuclear advocates come out with this sort of rubbish””. When I said that, I was thinking of Edward Greisch and others who insist that all opposition to nuclear power is paranoid – not exactly the same as your position, I concede, but similar in that it avoids the need to actually argue the issues. I’ll follow up your Patterson ref. and get back to you on that.

  29. 179
    Nick Gotts says:

    Re #174 [Cowan] I’d agree that the Swedish 1980 referendum was flawed, but it’s hard to see that this could have anything to do with tax revenues from fossil fuels, since Sweden’s electricity is and was almost entirely produced either from nuclear or hydroelectric stations. More relevant is surely that the decision to hold a referendum was a reversal of a previous decision only the previous year; and that it followed closely the “Three Mile Island” accident – which temporarily made nuclear power far less popular in Sweden than it has generally been (Chernobyl had a similar effect). From what I can discover, the three alternatives in the referendum were each backed by one or more of the political parties represented in the Swedish Parliament; it appears that at that time, no such party was willing to take the political risk of being seen to be backing nuclear power. If you look at what has happened in Sweden since, few if any measures have been taken by any government to prepare for the phase-out of nuclear power, which is due by 2010. It clearly won’t happen. I conclude that if this is the best “evidence” you can come up with for the conspiracy you suggest, your belief in it is clearly not held on rational grounds.

  30. 180

    Patrick posts:

    [[The one source of energy that is done more to reduce emissions from power generation than any other source is … nuclear.]]

    Yes, because other sources aren’t massively on-line yet. Apples and oranges. The best way to reduce GHG emission is to create new renewable power sources, not new nuclear plants. Photovoltaic, solar thermal, wind, geothermal, ocean thermal, tidal and biomass energy would be more helpful than nuclear, and a lot less dangerous. No country ever achieved nuclear proliferation because it had windmills.

  31. 181
    Kevin Leahy says:

    Re 163 (pete), you are correct insofar as this plan, which is seen as the most optimistic so far, will likely only prevent >2 degree C change. Getting less than this is already in the rear view mirror unless people are convinced enough to make bigger changes which will need to include air capture (ah, back to the topic).

    It is not however a retrofit question — unless you consider scrapping nearly all coal and replacing with CCS equipped plants retrofitting.

    Re the assertion that this has to be done with all renewables and efficiency (R&E), I’ve yet to see a serious analysis that supports that that will provide enough energy unless you increase the cost of energy so much that people simply quit using it. The problem is made more complex by the fact that we have a couple billion people in developing countries that also will be trying to improve their standard of living from current levels of

  32. 182
    David B. Benson says:

    François Marchand (176) — That dip is just for the Mauna Loa site. Notice that it has happened before, in 2004. Look further into the NOAA web pages to discover the average of all CO2 monitoring sites continues in a steady, rodust uptrend.

  33. 183
    Kevin Leahy says:

    181 continued (my post was truncated)! Wanted to make sure the point is understood that the renewables/nuclear/CCS/energy efficiency is not in any case an “either/or” sort of issue as some would like to make it, rather the answer must be “all of the above.” This must be if we are to have any hope of getting emissions down enough to prevent the worst of GCC. To shrink the solution set is to invite an unraveling of support for an emissions reduction program because of escalating costs. And yes, I know all about the fact that “if we do nothing it will cost a lot more” but most people don’t see the bills that come due in 50 years, they see they bills they pay today. Wishful thinking to the contrary, it is in everyones’ interest for the policy to be cost effective.

  34. 184
    Frank Zeman says:

    more comments

    (171) Indeed commuter cars may cost as little as $13,000 (Smart fortwo) and I was referring to the Tesla Roadster currently at $90,000. The main reason is it gets 200 miles per charge as opposed to the 70 miles of the Smart, in rough numbers. The challenge is that hybrids get over 400 miles per gallon with a lot more interior volume. In addition, it takes 5 minutes at a gas station while Tesla gives it more than two hours. So while the single person commute might be handled by these cars, the whole range of services provided by gas vehicles is not. The question is what do we want cars for aside from commuting. I mentioned the infrastructure because the EV1 has special charging stations that cut the time down.

    Aside from those points the electricity is not currently carbon free so that leaves two options. Implement CCS which requires infrastructure to transport and store the CO2 as well as capture. Alternatively convert the electricity generation fleet to renewables and nuclear, which would cost a lot of money, raise the price of electricity (in short term at least) and require upgrading of the grid to handle the intermittency. These are all going to take time and cost money, as will air capture.

    (175) I agree, I think every idea in Amory Lovins “Factor 4″ should be implemented first if they make sense based on Lifecycle analysis. Some ideas, like increasing the gauge of copper wire I’m skeptical about. Needless to say, huge strides can be made using efficiency but even reducing electricity consumption by a factor 4 might be offset by global development and population growth.

    The train with MEA idea is interesting Some thoughts would be that the mass of the train would increase the farther it travels. The scrubbing would also add backpressure to the engine. Finally I don’t think that diesel locomotives are a big player in the transportation sector. Every idea is worth looking at for back of the envelope.

    What is AVE?

    (175) You’re welcome. I don’t know much about the molecular sieve thing at all. I’ve read the H2CAR process but at this time I’m not keen on biomass solutions as the first priority should be feeding people.

    (183) Couldn’t agree more. If you read Socolow’s Scientific American article about the wedges he mentions that air capture might be a wedge in the second half of the century. All solutions should be applied at this stage, including electric commuter cars. The lifetime of an industrial facility is 20-60 years so there’s time to change course and starting them all prevents lock-in.

    thanks, Frank

  35. 185

    Re 184: Aside from those points the electricity is not currently carbon free so that leaves two options.

    My entire life is carbon negative. Click on the link by my name and you’ll see what it did to my electric bill.

  36. 186
    Jerry Toman says:

    What is AVE–Atmospheric Vortex Engine

    (Ref: http://www.vortexengine.ca)

  37. 187
    Scott Hawley says:

    This topic brings up a question that I have been pondering for some time. Why can’t we build a power plant that acts like a carbon sink. If a bio-fuel, like ethanol, power plant were designed and used CO2 capture and carbon sequestration would it not be carbon negative. The concept is simple, let nature concentrate atmospheric CO2 then burn it for power and sequester the CO2. The technology all exists but I have never read anything actually discussing the possibility.

  38. 188
    David B. Benson says:

    Scott Hawley (187) — The concept of carbon-negative bioenergy has been frequently discussed here:

    http://biopact.com/

  39. 189
    Jerry Toman says:

    #187 Scott Hawley. This is a good question, Scott–I hope I have an answer that will satisfy you.

    First of all, be aware that in order to get 4 Btu (or kjoule) of ethanol, you need to spend, by most accounts, about 3 units worth of fossil fuels in the form of fertilizer, pesticides, and mostly diesel fuel for planting, harvesting and transportation.

    Distillation requiring either fuel or steam is also an important component of this. These inputs represents lot of “uncaptured” CO2 emitted to the atmosphere in the overall balance.

    In describing the combustion process, I’m going to use cellulose as an example of which ethanol is a slightly enriched derivative.

    Cellulose is a “carbohydrate” which means “hydrated” carbon (chain). It can be viewed as a chain of carbon atoms with H2O “ornaments” attached to each carbon. When you burn the cellulose (stover), essentially no energy is obtained as the H2O molecules are broken off. Energy is obtained by breaking both the the C-C bonds and O=O bonds in O2, and creating much stronger (double) O=C=O bonds. Nearly all the energy liberated by the combustion process is a result of this type of bond rearrangement.

    Now, you would like to sequester the CO2 after combustion. While you a right in saying that we know “how” to do this, it is somewhat energy intensive because an absorbent or adsorbent is generally used to separate CO2 fromt the flue gases, which later has to be regenerated using even more energy. Enough so that the 1 Btu margin you got from growing the corn and making ethanol out of it would essentially be annhialated. IMO, you would be better off partially oxidizing the cellulose, producing “char” for sequestration, and burning the modest amount of off gas for energy. You would have to count enriching the soil as part of the “benefit” in order to justify doing it this way.

    Hope that helped.

  40. 190
    Chris Dudley says:

    Frank,

    (#184) There are efforts to develop synthetic sieves but what is used on the space station is natural zeolite. The space station gets free vacuum so they don’t have to pump to get the CO2 back out. But, pumping seems to minimize energy requirements compared to the chemical methods you’ve been describing for application here below. Here is a report characterizing the material used on the space station: http://hdl.handle.net/2060/19980237902

    Chris

  41. 191
    Dylan says:

    Would air capture work well in road tunnels, I wonder? Presumably the CO2 concentration inside road tunnels is much higher than in the atmosphere generally.

    Just a thought…

  42. 192
    Harold Ford says:

    This is a follow up to #96.
    The main idea is to not find new ways of doing anything but to tweak the current processes. The advantage is that we experiment very little on our atmosphere while removing higher percentages of CO2 and natural gas, re-storing carbon in the ground, approximately as it had been before.
    Experimenting is done on a small scale then prototyping. If the prototype doesnt come out right, scrap it. You cannot scrap the Earth and get another, not now at any rate. Reckless I think is the word I’m looking for. Just the scale of the assumption that it would work perfectly and not add too much or take away too much of whatever gases is mind boggling. Keep experimenting, of course, on a small scale, just try it on Mars or Venus first, that way we can look at the results from a distance. If the Earth was really bad off, we needed personal oxygen supplies etc, then doing it here wouldnt be such a bad idea.
    I like the Moringa tree idea Lynn, not sure about the amount of Carbon it absorbs from the air but it sounds like it should be alot compared to other trees (doesn’t take it from the ground, where else would it get it from but the air?). Phil, the idea of ocean going plants and/or organisms eating the CO2 and then sinking after death is a good one, wish I’d thought of that lol. How would we control their growth, once the job was done?

  43. 193
    Andy Siebert says:

    There are so many wonderful posts already discussing possible solutions to this CO2 dilemma. I especially found value in comments 13 (thanks Jim) and 9 (thanks Bernie): planting more trees makes a lot of sense to me too, though I understand with their decay they release much of the C02 they stored. Many solutions have been discussed by people more articulate on the subject than me. However, I notice something relatively obvious to me isn’t being discussed.

    While we ponder solutions to the dilemma in so many ways, what about pondering the dilemma itself? Consumption is the source of the release of CO2. One of the easiest ways to PREVENT the release of CO2 is to reduce consumption. Unfortunately, we built the foundation of our industrial economy in such a way that consumption appears hardwired into the root of the equation. What if there’s another way?

    The cost prohibitive factors of CO2 re-sequestering (following release from a previously stable source) will always be less efficient than NOT RELEASING these gases in the first place. Alternative fuels, better/more efficient technology and processes merit continued focus, but what can be done to shift the trend of consumption?

    I realize this video is a bit simplistic but that’s part of what I like about it: http://www.storyofstuff.com/ is accessible/understandable to anyone. We must remove the incentive for planned obsolescence. Why mine, transport, manufacture, assemble, and again transport materials for entire new machines when only a fraction of parts are actually being upgraded? There’s waste at every step of this process. Even as “retro” becomes increasingly trendy, you don’t see an influx of “antique computer repair” shops opening up everywhere. A universal motherboard with upgradeable components isn’t hard to conceptualize: but the manufacturer can’t justify selling you a $1,000 processor unless it comes in a shiny new computer… The first cellphone I ever bought was the most reliable I’ve ever had, but I’ve been FORCED to buy 5 in 10 years due to the manufacturers no longer “supporting those devices”. This trend puts us on a crash course when we’re already in a tailspin.

    The irony is not lost on me that I say I’m forced to consume a product that hasn’t existed for the span of my life on this planet. But my point is that we need to shift the incentive away from encouraging companies to continually create waste by continually making products that are only slightly better, when it makes more sense to reward them for upgrading existing products. This doesn’t even touch on the e-waste issue, which is beyond the scope of this article but can’t escape mention.

    The first step in this process is with the consumer’s perception that “new = better”. This would create a consumer base that would support financial incentives for companies to provide upgrades instead of entirely new products, and we could substantially reduce emissions and also save costs which would otherwise be spent sequestering the waste of this production. The incentive has 2 components: STOP rewarding waste, and START rewarding expandable products.

  44. 194
    Hank Roberts says:

    I grew up repairing most anything and still try.
    But it’s amazing how hard it is nowadays.

    And — compare the insides of a lamp socket made a few decades ago, next time one fails, with what you can buy to replace it. The new stuff can’t last anywhere near as long as the old did; thinner, more fragile, cheaper. Always.

  45. 195
    Harold Ford says:

    Hi Andy 193
    I was curious to see if I had the last word on this topic and looked in. CO2 is released by the decay of trees. However, if you store the debris in a container that has no oxygen, you get CH4. That in mind, if you have CH4, you have another greenhouse gas but one that is burnable and stored in said container, the whole crux of the issue. So, everything is still stored and not released into the atmosphere until it is burned for such things as heating and/or electricity. The gas would change to H2O and CO2 as usual after burning however that means that other forms of fossil fuels were not used. A plus here is that it naturally scales itself to the size of the civilization that produced it. Whether or not it produces enough energy is a question that can only be answered through simulation or actually doing it. I’m in favor of doing it as we have nothing to lose and much to gain (in comparison to the current system).

  46. 196

    The dispersal of pulverized olivine I recommended here earlier is also recommended by Prof.dr. Olaf Schuiling,
    Universiteit Utrecht:

    19 June 2007

    Geochemical CO2 sequestration – to save the world (in case the world needs any saving)
    Outside the group of earth scientists it is rarely realized that chemical weathering is the major pathway by which CO2 is removed from the atmosphere. Enhanced weathering increases the rate of removal. This can be achieved by mining and crushing large quantities of olivine, and spreading the olivine powder over the land surface, or in the high energy zone of coastal waters…

    (http://www.gt.citg.tudelft.nl/live/pagina.jsp?id=0285f1d6-f442-4230-84e4-7e9cb4411a67&lang=en)

    It’s common knowledge that olivine is an extremely abundant mineral, but in case a specific instance is needed, here’s talk of a 200-gigatonne deposit in the state of Washington, USA: http://www.netl.doe.gov/publications/proceedings/01/minecarb/oconnor.pdf

  47. 197
    Hank Roberts says:

    And it’s been looked at for going on a decade now. Something about the spam filter won’t allow me to give you cites to the work done over the past decade on this, but look them up:
    olivine+chemical+carbon+dioxide

  48. 198
    Arch Stanton says:

    Hank (197),

    I have also heard encouraging things about olivine/serpentine CO2 sequestration. When I put “olivine+chemical+carbon+dioxide” into Google Scholar I find few hits within the last decade and few that are discouraging. Outside of the obviously significant problems of serpentine being found in geologically active areas, and the energy intensiveness of the process of sequestration, what other problems are there? Perhaps a name would help my search?

    Thanks, Arch

  49. 199
    Hank Roberts says:

    Dumping a slurry into the ‘active coastal waters’ where mixing would happen likely wipes out most of the base of the marine food chain, and the method is very slow at standard temperature and pressure.

    The work I found published, as you note mostly a decade or so ago, described olivine reactors efficient as closed systems with high temperature and high pressure. That’s expensive.

    Price of fuel has gone way up since then. Perhaps siting something like this where it could use waste heat from power plants makes sense.

  50. 200

    Dumping a slurry into the ‘active coastal waters’ where mixing would happen likely wipes out most of the base of the marine food chain

    That would not be the objective. As I said above, each 100 gigatonnes of legacy CO2 in the atmosphere would convert to a few hundred km^3 of dust. If this were deposited over tens of millions of km^2 of dry desert, or hundreds of millions of km^2 of a wet desert such as the southern ocean, it would be unobtrusive.

    Understand that the accumulation would be over a decade or so. It would not arrive all at once as a layer 1 cm thick on the tens of millions of km^2 of land, nor as a 1-mm layer on hundreds of millions of km^2 of sea.

    You’re the first to speak of a slurry. Per mole of legacy CO2, the creation of which mole yielded about 400 thermal kJ if it was in a coal furnace, 20 kJ would be needed for comminution. I had in mind that another 20 kJ/mol could be used to lift the olivine powder 10 km above ground level so that it would be well dispersed when it came down.

    … and the method is very slow at standard temperature and pressure.

    It’s quick enough — four years for forsterite grains of which 80 percent pass through a 100-micron screen, fewer years for olivine with a significant fayalite component. BTRO.

    (I believe fayalite does not sequester any CO2 itself, but its iron’s oxidation from II to III helps break up the rock. So a few parts in 20 is helpful, even if it increases the required amount of olivine, because it allows the same speed with less comminution energy input.)


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