As Greg Rau and I pointed out more than a decade ago, rather than kilning, power plant flue gases can be used to dissolve carbonate minerals in seawater. If it is placed in seawater dilutely, the time scale for reprecipitation of these minerals should be thousands of years.
Whether it is "better" to start with carbonates or silicates is not a simple question. In some absolute "environmental" sense, silicates are likely to be better. My guess is that in atmospheric CO2 reduction per dollar invested, dissolving carbonates in seawater using power plant flue gases is likely to be cheaper. Silicates provide "permanent" storage but unfavorable kinetics. Carbonates provide less of a degree of permanence (but still can be effectively thousands of years) but favorable kinetics and energetics. (McDermott Technologies estimated a 2% hit on a power plant output if such approaches were deployed.) A few citations here: http://dge.stanford.edu/labs/caldeiralab/Caldeira_research/Rau_Knauss.html http://dge.stanford.edu/labs/caldeiralab/Caldeira_research/Caldeira_Rau.html http://dge.stanford.edu/labs/caldeiralab/Caldeira_research/Rau_Caldeira.html Of course, all of these approaches have the fundamental problem that CO2 has a mass of 44 g / mol and CaCO3 has a mass of 100 g / mol, so you will need a minimum of ~2.5 ton CaCO3 per ton CO2. So, these approaches all involve substantial amounts of mass handling. (If you kiln off the CO2 from the CaCO3 and using "conventional" CCS to bury that carbon, then the mass handling gets cut in half but at substantial energetic expense.) On Sun, Sep 25, 2011 at 12:22 PM, Oliver Tickell <[email protected]>wrote: > Hi, I'm familiar with CQuestrate and Tim Kruger, but my understanding > is that this is all about kilning CaCO3 to CaO + CO2, then hydrating > CaO to Ca(OH)2, then putting that in ocean to react with CO2 to Ca++ + > 2(HCO3)- - a net gain of one CO2. The problems are that this is energy > intensive, and in alkaline conditions you get a high rate of CaCO3 > precipitation which just takes you back where you started, and in the > long term all the Ca / CO2 ends up as CaCO3 anyway. If CQuestrate is > now taking silicates as their starting point, I can only be glad that > colleagues such as Olaf Schuilling, and to some extent I, have managed > to convince him that Mg silicate is a much better starting point than > Ca carbonate. Oliver Tickell. > > On Sep 23, 3:20 pm, Chris <[email protected]> wrote: > > Oliver, > > > > In his reference to "Dumping lime or calcium or magnesium silicates > > into > > the sea...", George Monbiot was referring to the concept put forward > > by Tim Kruger of Cquestrate - seewww.cquestrate.com. > > > > Chris Vivian. > > > > On Sep 23, 12:40 pm, Oliver Tickell <[email protected]> wrote: > > > > > > > > > > > > > > > > > Monbiot's real mistake here is to swallow the conclusion of the Royal > > > Society report on the subject, whole and undigested, without critical > > > scrutiny or attention to other sources of information - in particular > > > as regards the weathering of magnesium silicate (not enough Ca > > > silicate to bother with): > > > > > Monbiot reports: "Dumping lime or calcium or magnesium silicates into > > > the sea, where they react with carbon dioxide. Fairly safe. Effective. > > > Expensive. Has > > > the advantage of potentially reversing ocean acidification, but the > > > amount of quarrying required to produce enough ground-up rock is > > > likely to be prohibitive. " > > > > > A) where does he get the idea that it's about dumping it in the sea? > > > It is about spreading the rock powder on land, and in intertidal > > > zones. > > > B) So it's "fairly safe". Why only "fairly"? This is just to > > > accelerate a natural process that is going on all the time anyway. > > > C) "Expensive" - how much? People who have done the sums > > > conservatively estimate $10-15 per tCO2. Making it one of the cheapest > > > options around. > > > D) It will only "potentially" reverse ocean acidification. Well, > > > insofar as the science of chemistry "potentially" applies. He seems to > > > be implying that maybe chemistry is "potentially" all wrong. George, > > > tell us more! > > > D) The amount of quarry is "likely to be prohibitive" - is it? Has he > > > done the sums? Has he asked anyone who has done the sums? Or is this > > > just his uniformed guess? For a start there are Gt of already mined > > > rock that can be used, in mine tailings around the world. From then > > > on, roughly 1t of rock sequesters 1t of CO2. So you need to mine an > > > amount of rock comparable to the amount of fossil fuel we are burning. > > > If it's not "prohibitive" to mine the coal, why's it "prohibitive" to > > > mine the rock? > > > > > Oliver Tickell. > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
