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I am trying to identify the plausible CO2-mitigation strategies that are scalable — that can comprise at least a half a wedge (see “How the world can stabilize at 350 to 450 ppm: The full global warming solution).
So when a new process gets this much hype — as in Scientific American’s, “Cement from CO2: A Concrete Cure for Global Warming?” — it deserves scrutiny. Wired magazine’s “The Top 10 Green-Tech Breakthroughs of 2008,” provides both a good summary of the process and more evidence of the hype:
1. CALERA’S GREEN CEMENT DEMO PLANT OPENS
Cement? With all the whiz bang technologies in green technology, cement seems like an odd pick for our top clean technology of the year. But here’s the reason: making cement — and many other materials — takes a lot of heat and that heat comes from fossil fuels.
Calera’s technology, like that of many green chemistry companies, works more like Jell-O setting. By employing catalysis instead of heat, it reduces the energy cost per ton of cement. And in this process, CO2 is an input, not an output. So, instead of producing a ton of carbon dioxide per ton of cement made — as is the case with old-school Portland cement — half a ton of carbon dioxide can be sequestered.
With more than 2.3 billion tons of cement produced each year, reversing the carbon-balance of the world’s cement would be a solution that’s the scale of the world’s climate change problem.
In August, the company opened its first demonstration site next to Dynegy’s Moss Landing power plant in California, pictured here.
As the sage once said, “Amazing, if true.”
Yet whether Calera’s process can actually sequester significant amounts of net CO2 and whether it is scalable has been called into question by some of the country’s leading climate scientists, including Ken Caldeira, a widely published expert on the carbon cycle whom I have known for many years.
Emails on this subject have been racing around the Internet, and I have communicated with both Calera and Caldeira (yes, I know, the kind of strange coincidence that makes reality so much less plausible than fiction).
While this is a long post with a lot of unavoidable chemistry it, the bottom line is that I think Caldeira has made a strong case that
- The scalability of the process is in doubt
- We won’t know if net CO2 is saved unless Calera is much more forthcoming on all of the inputs and outputs
Questions surrounding Calera’s process — and the too-hot e-mail exchange — became public when John Carey of Business Week wrote about the “Hot Debate over Green Concrete“:
The process is similar to the formation of coral reefs, the company says. It even arranged for an exhibit showing the process at the California Academy of Sciences.
Not so fast, says Ken Caldeira, climate scientist at the Carnegie Institution of Washington at Stanford University. “Their claim that they can put CO2 in sea water and create minerals makes no sense to me at all.” When coral does make reefs, Caldeira points out, CO2 is actually released to the atmosphere. Making concrete-like minerals through the process “is backwards to the chemistry the rest of the world is accustomed to,” Caldeira says.
So in an email message on March 22, Caldeira took on Calera, company founder and CEO Brent Constantz (also an earth sciences professor at Stanford), and the California Academy of Sciences.
He wrote: “From the publicly available information it seems that Calera’s process goes in the wrong direction and will tend to increase and not decrease atmospheric CO2 content. Furthermore, when I raised these concerns to Calera, they would not respond openly to my critique, asking me instead to sign a non-disclosure agreement.”
“I call upon the California Academy of Sciences to withdraw the Calera exhibit until such time that Calera demonstrates (i) that its process does not remove cations from the ocean in a way that will ultimately drive a CO2 flux from the ocean to the atmosphere that exceeds the amount of fossil fuel stored in the carbonate mineral and (ii) that its process does not acidify the ocean.”
I asked Calera for a response to what Caldeira (and other scientists) have said in emails. Brent Constantz replied with a forwarded email:
Dear Dr. Pope,
Brent Constantz informed me yesterday of the negative comments about the Calera Corporation made by Ken Caldeira on a blog site. I judge these comments to be fatuous and indeed insulting and question Caldeira’s motivation for writing them.
The credentials of Brent Constantz and those of the group of distinguished scientists who comprise his Scientific Advisory Board are beyond dispute. Let me assure you that the Calera process does not introduce carbon dioxide to the atmosphere! In stark contrast, the process is an extremely effective means of sequestering carbon dioxide that would otherwise go into the atmosphere from the stacks of power plants. The process described by Caldeira has nothing to do with the Calera process and he should know better than to suggest that it does.
The attached file is a brief explanation of how the Calera process sequesters carbon dioxide. If you have any questions, please do not hesitate to contact me.
Sincerely yours,
J. R. O’Neil, Chair
Scientific Advisory Board
Calera Corporation
Here is the attached file from Calera (see here for original with subscripts and superscripts) — my apologies for the chemistry, but it is unavoidable:
The Calera Process: An Effective Means of CO2 Sequestration
The Calera Process consists of reacting carbon dioxide (CO2) tapped from stacks of operating energy generating plants with treated seawater to produce solid carbonates of calcium (Ca) and magnesium (Mg). These solids are then used in various ways in the production of concrete. The process is a simple and effective means of sequestering CO2 that would otherwise pollute the atmosphere and contribute to global warming..
Seawater contains the following pertinent chemical species:
Ca2+, Mg2+, CO32-, HCO3-, (CO2)aq, H2CO3, H+ and OH-
At a given pH the relative amounts of the various carbonate species are all in rapidly attained chemical equilibrium. Carbonate precipitation can occur if the solubility products (Ksp) of the various possible carbonates are exceeded. The solubility product of a carbonate is given by the following expression:
[M2+][CO32] = Ksp
where [M2+] is the concentration (activity) of the metal cation and [CO32-] is the concentration of the carbonate ion. Precipitation of a solid carbonate from seawater will take place under one of two conditions.
1. The concentrations of the cation (M), in this case Ca2+ or. Mg2+ or both, are increased to the point where
[M2+][CO32-] > Ksp of MCO3.
2. The concentration of CO32- is increased to the point where
[M2+][CO32-] > Ksp of MCO3
In the Calera process the concentration of CO32- is raised (case 2) by the addition of CO2 and most or all of the Ca and Mg present in a given volume of seawater precipitates as a solid carbonate. The concentrations of Ca and Mg in seawater are relatively constant and fixed worldwide.
The concentration of CO32- in seawater is increased upon introduction of the stack CO2 because the pH of the seawater (normally around 8 ) has been raised to the point where CO32- is the dominant and stable species of dissolved carbonate. Alkaline solutions like this are very effective sinks for gaseous CO2. Calera methods for making seawater appropriately alkaline are proprietary, but it can be done simply by addition of a base like sodium hydroxide.
I then shared this document with Caldeira (who in turn shared it with others).
This was Caldeira’s reply:
The document you send gives away the piece of information missing from the museum exhibit. They need to add alkalinity to the system and that is not mentioned in their museum exhibit.
They need to add a base like sodium hydroxide. How much sodium hydroxide is available in the world? The answer is not much.
Kheshgi 1995 discussed the availability of alkaline resources in the world and his conclusion was that there was not enough to make a substantial dent in global emissions. (I sent this paper to the google discussion group.) For example, Kheshgi estimates that if you mined all of the available sodium hydroxide in the world, you would be able to offset about 5 GtC of CO2 emissions.
They claim publicly that their process requires only seawater and CO2, both of which are abundantly available, and then it turns out that their process depends on relatively rare alkali deposits.
Anybody can reduce net emissions with a good supply of alkali materials, so if that is their process, it is a non-event. They promised a scalable solution and provide a solution with very limited applicability.
So, they did misrepresent their process to schoolchildren. They neglected to mention their most important ingredient — relatively rare alkali materials.
By the way, if you do have alkali materials, it is much more effective to dissolve it in the ocean — reduce ocean acidification and store more CO2 in the ocean — than to make carbonate minerals. Dissolving it in the ocean would store about twice as much CO2.
So, they advertise to the world that they can store CO2 as cement using only seawater and CO2 as source materials, which would be a miraculously impressive invention. Then when pushed, they say they can store CO2 if you would give them an abundant supply of alkali minerals — but everyone knew this already. If they had said that from the outset, nobody would have found their process interesting.
So, it is clearly a case of public misrepresentation: They claimed they could sequester CO2 with seawater and they cannot. Now they are saying they can sequester CO2 using alkali minerals. They certainly can, but everyone knew that already … and this approach has been discounted as being unimportant to the climate-carbon problem because it is not scalable to the scale of the problem….
Best,
Ken Caldeira
Carnegie Institution Dept of Global Ecology
Caldeira adds in a separate email:
I am pretty sure that the magnesium hydroxide [Mg(OH)2] at Moss Landing was made through the process something like:
Mg2+ + CaMg(CO3)2 + 2H2O –> 2Mg(OH)2 + 2CO2 + Ca2+
If Calera is using this magnesium hydroxide in their process, they are just recovering the CO2 released during its manufacture.
And he adds:
I note that Calera still is not forthcoming in response to my question regarding what are the inputs to and outputs from their process, in a way that allows balances of mass, energy, and electric charge to be assessed.
They need to maintain acid-base balance and get the alkalinity from somewhere or dispose of acidity somewhere, and until they are forthcoming on this point there is no way their process can be assessed.
Their process can be proprietary but there is no need for secretiveness with respect to inputs and outputs.
Until such time as they present information that allows independent assessment, I will assume their process can make no quantitatively important contribution to addressing the climate-carbon problem.
I am not a chemist, but I have received emails supporting his analysis. Caldeira’s argument seems strong, especially as to scalability.
Ken sent me a further elaboration when I asked for something for a non-technical audience:
You need alkalinity from somewhere. Alkalinity is the net positive charge on the cations of the strong acids (HCl, etc) minus the net negative charge on the anions of the strong bases (NaOH, etc). This difference is available to bind with CO2 to form carbonates.
There are at least three approaches to getting alkalinity:
1. From carbonate minerals like CaCO3. Unfortunately, this comes with CO2 (CaO+CO2) so if you are trying to produce carbonates this is no help.
2. From strong bases available naturally. Unfortunately, there are no large pools of lye hanging around ready to react with CO2. Strong bases today are formed in factories, and are not generally mined. For example, most NaOH would have already reacted with CO2 to form Na2(CO3), but since they are forming carbonates they cannot afford to start with a carbonate. Also, its production, say by electrolosis of NaCl, also produces HCl, which you would need to get rid of somehow. Another example is the Mg(OH)2 at Moss Landing which was produced by heating the CO2 out of dolomite.
3. By disposing of acidity from seawater. You could, as above, electolyze seawater (with large energy input) and then make NaOH and HCl (again, cost is about $1000/ton NaOH). Then you need to do something with the HCl. If you return it to the ocean it will acidify the ocean and drive CO2 into the atmosphere. I suppose you could pump the HCl underground or something and sequester HCl instead of CO2. This is probably scalable, but unlikely to be economic.
4. By accelerating the weathering of silicate rocks. This is something that Klaus Lackner and others have been working on. The problem is that the kinetics are slow.
Recall that they will need 1 atom of Mg or Ca for each molecule of CO2. So for each ton of CO2, they will need approximately and equal mass of Mg or Ca from a strong base. These are not minor requirements that can be easily overlooked.
So, without them saying exactly what their inputs and outputs it is hard to evaluate their scheme. My guess is that they may be heading to option 3, but it is hard to see how that will be economically viable.
One way to get a handle on this is to look at prices of strong bases like NaOH, Mg(OH)2, etc. I think you will find that if you have to pay market prices for these strong bases (making sure that you are producing them by methods that do not release CO2 or acidity into the environment), their process will not be economic.
Best,
Ken
So I think at the least, Calera needs to prove the “inputs to and outputs from their process, in a way that allows balances of mass, energy, and electric charge to be assessed” independently.
Thoughts?
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Impressions from National Academies Climate Summit
http://www.huffingtonpost.com/ bill-chameides/ impressions-from-national_b_182401.html
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“We need to move [our focus] from the mean to the extremes.”
— Carter Roberts, President and CEO, World Wildlife Fund
I was at the re-opened Academy of Science in San Francisco over the weekend, and this product was on prominent display in the (otherwise well crafted) area of the floor devoted to AGW.
My first thought was: Doesn’t matter if this is a real product or not. A year from now you are going to see the Calera logo on everything made out of cement, the architectural version of Intel Inside. Developers will pay Calera a license fee and add “Calera Certified Green Cement” on all their construction proposals. Municipalities will give developers favorable treatment on condition they use Calera cement at some minimal percentage. Cement companies will license the Calera logo (and nothing more) to plaster all over their trucks, implying their commitment to green-ness.
You’ll know we’ve hit the bottom when an Escalade cruises by with a “Carbon Offsets by Calera” sticker on the bumper.
The same thing has already happened to organic farming and the labeling of organic foods. Does anyone seriously believe that food imported from overseas and labeled “organic” is in any significant way organic? How would you even verify that? And does the definition of “organic” mean the same there as here?
Seeing is deceiving, as they say.
cougar
I just wrote a research paper for my energy policy class on Mineral Sequestration. Using the Mg2+ and Ca2+ (from mined rocks) to form carbonates in solution has been an active area of research for the past 15 years, notably by Klaus Lackner (now of Columbia).
I wanted to offer a few comments:
1) From what I’ve seen with wollastonite (CaSiO3), a kind of rock containing roughly 40% Calcium– far beyond the concentration in salt water–, the cost to sequester CO2 is $90 per ton STORED. It would be much higher per ton SEQUESTERED, as the process of energy intensive. I highly doubt this would be commercially viable, given present prices.
2) If anyone can simply add CO2 into seawater to make cement, this would have been in the literature long ago.
3) Strong acids and bases (such as NaOH and HCl) are certainly not easily used to catalyze the reaction, though they do work in theory. This is very energy intensive and hard to recover from waste streams for recycling. I believe Caldiera is correct in identifying this “ingredient” as being where Calera’s analysis is faulty.
[JR: Thanks for the insight.]
As someone who has reported on Calera, I would suggest that they are following the Option 3 route (mentioned by Caldeira in his elaboration) based on the explanation I’ve had of the process. Setting economics aside for a moment, the environmental problem seems to be the acidic seawater left over at the end. Problematic to put back in the ocean as noted. But wait: it works better for desalinization plants! Of course, then you end up with problematic brines and desal is only really of interest in places like California at present… Plus, we’re talking large volumes of water to create one ton of sequestered CO2 cement so the economics are, to say the least, challenging. There are no free lunches. But that doesn’t mean it might not play a small role or even a large role if these challenges can be overcome. Remember, cement is a LARGE CO2 source so, at present, it’s this and carbon capture and storage, which has its own issues.
Things are about he heat up…the sun will soon starting to get warm again….what can this mean for temps here on earth??
Deep Solar Minimum
http://science.nasa.gov/ headlines/ y2009/ 01apr_deepsolarminimum.htm
Take a look at the article about cement in last Tuesday’s TNYT Scinece Times. It seems there is no some willingness on the part of engineers and contrators to consider materials other than just plain old ordinary Portland cement. Nonetheless this Calera product is likely to be treated with considerable suspeciion by the (Necessarily) conservatie engineers and contractors. While it seems that CalTrans seems ready to give it a try, I doubt you’ll see dams or bridges constructed out of it any time soon.
In my estimation, Calera is a niche player and whatever they are doing is unlikely to either hlep or hinder in any substantive way.
You should be promoting innovation. There is enormous potential in the building and construction sector.
[JR: I do. I couldn't agree more!]
As odd as it might sound, isn’t the building material called “wood” at least as functional for sequestration as “exotique” cement? Sure, wood burns and releases CO2 in the process, it also rots and does the same over a longer time. But there are structures 100s of years old made of wood, and they are sequestering fine looks to me. Then there is furniture, countertops, window treatments, wall treatments, floors. The stuff is beautiful, you can go nuts.. It seems to me that the technical problems of building from wood to last are compatible with — oh say for example — public safety. That is, sprinkler companies and fire departments have that covered.
Pretty lo-tech stuff.
And don’t start in with how hard it is to maintain wood floors and countertops. What is your life going to be about post-peak-oil if not maintaining things? What better use for our future masses of unemployed than massive mega-scale carpentry and converting the works of Man to wood?
I understand that wood is not as flexible as cement because the latter can be poured. Nor does it work in the ground (for foundations or sidewalks). Nor does it stack very high (what is the limit, 4 stories?) But if we accepted 1) boxy structures, 2) on treated pilings, that 3) were limited to a few floors at best — and assuming that structural and materials engineers never tried to solve the basic engineering issues with mega framing — we could just build everything on earth out of fast growing species of wood and see where that gets us.
Guys, we need to figure this out fast. I hear people talking about exotic batteries, exotic materials, exotic cement, exotic lighting, exotic solar panels, all kinds of blackboard theoretical solutions always a few years away that all boil down to “business as usual now and until a miracle happens”, and I want to hit something. WE HAVE NO TIME FOR THIS. I fear we’re going to burn the last barrel of oil perfecting cement, push atmospheric CO2 to 1200ppm building hybrid cars for all the soccer moms, and THEN WE WILL DIE EN MASS and take half the biodiversity on the planet with us on the way out.
So how painfully stupid and short sighted would that be? Is there a long enough string of invectives to adequately describe, in as long a sentence as you want, how painfully stupid that would be? How many orders of magnitude of “epic fail” would that be? We’d need a whole new branch of abstract mathematics to describe that level of failure.
cougar
One thing that is interesting to look at in the concrete world is the so called “bendable concrete” invented at UM. It’s interesting in that it is more crack resistant than normal concrete (and indeed has some self healing processes), and can be made in a normal concrete mixer, unlike other fibrous concrete. Will it sequester CO2? No, but it will reduce the amount of materials we use and the rate which they have to be replaced.
Amen to that, cougar_w: I’ve covered the green/cleantech sector for years now, and every new potential innovation that seems to work in the lab is hailed as the next “miracle” that will save us … once it can be made scalable and commercially viable, usually over a window of 3 to 5 to 7 years.
How many can you think of over the last few years that have been held up as the thing that will — FINALLY — save us?
Corn ethanol (well, that didn’t work out so well after all, did it?)
Cellulosic ethanol (still waiting for that to become commercially viable — some companies say they’re getting close, but time will tell if cellulosic eventually is proven the next corn)
Algae-based biofuels (even venture capitalist Vinod Khosla, who backs Calera, says it won’t be ready for prime time soon enough for him to invest in the near term)
Hydrogen (you all can ask Joe about that one — I know he’s had plenty to say)
Not to rain on the parade of technological advances, because I think they’re as swell as anyone does, but waiting for the technology miracle while we keep doing “business as usual” is, as you said, cougar_w “painfully stupid.”
Even PV solar, which I still believe holds tremendous potential, comes with limitations: many of the compounds and processes used to produce solar cells are toxic, some are in relatively short supply and — unless we put all our eggs in PV solar’s basket immediately — we could end up burning those last barrels of oil to make photovoltaics instead of “green” cement. (Because there’s nowhere yet where solar energy is used to power all the processes and manufacturing that goes into producing solar cells.)
For me, it borders on maddening when people keep tying their hopes to miracle solutions instead of focusing on the “easy” stuff that could make such a difference: energy efficiency and conservation, in particular. It all boils down, I think, to our unwillingness — still — to surrender that global “Ponzi scheme” of oil-driven consumption that both Joe and Tom Friedman have written about.
As the parent of a six-year-old, I worry about these things a lot. My husband and I have had a nice run during our lives, but the next few generations aren’t going to be as fortunate, I fear.
“Simple, Low-cost Carbon Filter Removes 90 Percent Of Carbon Dioxide From Smokestack Gases”:
http://www.sciencedaily.com/ releases/ 2008/ 05/ 080519092205.htm
Oh goody. And then what do you do with the filled sorbant? Bury it?
“first economical way to produce biodiesel from algae oil”-researcher:
http://www.icis.com/ blogs/ biofuels/ archives/ 2009/ 03/ first-economical-way-to-produc.html
Be sure to read the comments as well.
This is encouraging news.
Let’s not forget that the climate problem with cement is not just the fact that fossil fuels are used to generate the heat required during manufacture but also the fact that they are heating limestone which is a carbonate rock that releases CO2 when heated (correct me if I am wrong).
A blogger named gwashtracker writes that he read the patent, and Calera simply adds dolomitic lime to the seawater. Dolo lime is simply dolo limestone with the CO2 cooked off, so that would make the whole thing a cynical joke. Water would also want to react with and slake the dolo lime.
Further name irony: LaFarge Cement owns a cement plant in Calera, Alabama. The locals call it it “Calera Cement”. Talking about jokes, npr just did a great April Fool’s joke with a bogus but realistic (and gory) sounding report on whale farming in Indiana (or Illinois?)! The outraged comments received were a hoot.
Fascinating discussion, thanks for the info.
Ancient Roman concretes may have been roughly carbon neutral, because they hardened by carbonation, and so would slowly absorb most of the CO2 released during the calcination of the lime as they age. I believe that they would have had to be porous enough to let the CO2 into the interior of the concrete, and that achieving this reliably might be a problem.
Concretes are composed of a cement, though, and of an aggregate. In some European building codes, as much of 40 percent of a concrete can be limestone aggregate, either crushed or powdered.
If a carbon neutral cement like ancient Roman concrete was used as a binder to sequester calcium or magnesium carbonate aggregate, that process might actually be carbon negative, providing that the carbonate came from carbon sequestration by mineral carbonation, like Lackner proposed.
Anything similar to modern concrete might not be a very good choice for a sequestration material, because modern concretes release huge amounts of CO2 during their manufacture, but harden by hydration rather than carbonation, and tend to become rubble on fairly short time scales, on the order of centuries.
A better choice, but one that uses very alkaline components, are geopolymers, which may be durable enough to last for a very long time.
http://www.csiro.au/ science/ Geopolymers-Overview.html
One interesting material is carbon fiber reinforced geopolymer, which might combine desirable engineering properties with high carbon content, and longevity as a building material.
http://composite.about.com/library/weekly/aa030529.htm
If carbon fibers were made directly from biomass, and were used to reinforce geopolymers, this process would likely be carbon negative, very much like biochar.
Comments? Corrections?
Limits of wood structures?
The State of California built a four-story wood-frame office building in Long Beach, California, back in 1981. The structure is glu-lam timbers. It was originally designed to be a six-story building, but the state budget consequences of Prop 13 led to shaving two stories off the top. There was a twin, private sector office building designed by the same architects and built in Burbank. Both are still in use. The “structural” issues are not problematic.
Earthquake resistance is a major design issue in California and elsewhere. In other locations, wind resistance results in similar structural demands.
Wood structures are more flexible than concrete or steel structures and, flexibility is a key issue in building survival during a seismic event. Many wood frame structures survive earthquakes when masonry structures fail. Therefore, the code requires wood-frame structures to be capable of resisting only half the forces that concrete or steel structures must resist.
One issue for wood is fire resistance, but steel structures can fail under extreme heat (WTC – 9/11/2001) and, therefore, the steel must be coated with 3/4 to 1.5 inches of cementitious material to “protect” it from the heat during a fire. Massive timbers don’t fail immediately during a fire, and much of a wood structure will still be standing after a fire.
An issue for wood, and the real long-term hazard, is various forms of decay. Chemical treatments (wood preservation) in the Long Beach building were with Pentachlorophenol, no longer legally used indoors in part because of the Long Beach case which I investigated for the state while EPA was in the process of restricting its use. Wood preservatives are a challenge in terms of find long-lasting, non-toxic solutions. Paint works.
But they exist. Water is the enemy. There are well-preserved villages of old wood-frame structures more than 300 years old in Japan as well as major palaces, although fire has taken a toll there. There is a beautiful wood-frame church in Norway or Denmark built in the 13th Century. There are colonial houses in the U.S. that are still extant. But fire ravaged many of the gold rush towns in the California of the 1850s, sometimes more than once before they were rebuilt in brick or stone. But there are still many structures standing there from that era as well. The Court House in Mariposa was built around 1850 and is still functioning as a court house.
I have a 100-year old barn on my property, kind of old for California, but there still are many scattered around.
Bamboo is fast growing and can be very durable when harvested, processed, and used properly in structures. Today’s “green” bamboo products are gaining market share,some of them as veneers on composite bamboo or wood substrates. These products can be very strong and durable. Bamboo requires lots of water to grow but can generally be grown faster (mass per acre) than most commercial softwoods or hardwoods.
Fast-growing hardwoods (Eucalyptus, Tanoak, and many more) can be used for furniture, flooring, trim, etc. if harvested and processed properly (slowly dried rather than “flash” kiln-drying that dominates most hardwood curing processes. My floor is Tanoak which grows wild in the Santa Cruz Mountains, is usually harvested for firewood because of its abundance, and which can be dried properly and milled into beautiful, durable flooring.
I wrote about Calera several months ago on my web site. The title of the article was borrowed from the song title from “My Fair Lady,” — “Cement Sequesters CO2 – Wouldn’t it be lovely?”
- hal
I wonder also if a Roman cement could be made from calcium or magnesium carbonate, in which only the surface of the carbonate particles was calcined – a sort of “flash calcination” process. So the interior of the cement particles would be carbonate, but the exterior of the particles would be hydroxide (slaked lime). Mixed with silica particles and allowed to carbonate via exposure to the atmosphere, a carbon neutral cement might be the result. Roman concretes, while durable for thousands of years in a warm climate, suffer from freeze/thaw problems, although this might be alleviated by proper air entrainment design, like portland cement concretes designed for freeze/thaw resistance.
If this cement was then used to bind a carbonate aggregate, a true carbon negative concrete might result.
A better bet is a geopolymer carbon fiber composite, I think. A geopolymer carbon fiber composite could be as much as 50 percent carbon, perhaps, while carbonate sequestration materials are only a few percent carbon. If these carbon fibers came from biomass – perhaps by a rayon or cellulose acetate process – the result could be similar to a very tough and durable rock, capable of sequestering large amounts of carbon for a very long time.
Ken Caldeira has patented his own process for CO2 capture and sequestration by mineralization. See United States Patent 6890497 to Gregory H. Rau and Kenneth G. Caldeira (May 10. 2005). Those who would like further background on this subject can see that patent at http://www.freepatentsonline.com/6890497.html
Carbonatation (note spelling) is the reaction of CO2 with lime (calcium hydroxide) to make calcium carbonate (limestone). Roman cement is based on this reaction, which is slow. Roman cement got stronger over the centuries. http://en.wikipedia.org/wiki/Carbonatation
Producing the lime for this process of CO2 sequestration takes energy in the form of heat from burning fossil fuels, emitting CO2. Lime is made by heating calcium carbonate to drive off CO2 — yet another source of emissions.
The long time and high energy required, and the CO2 emissions in converting limestone to lime, would seem to rule out carbonatation. Calera must have some other process. Signing a nondisclosure agreement to find out what it is would not be an unreasonable request.
Thanks for the input, and the spelling correction.
I intend to work on calcination, in my garage, and see if there is a way to just convert the surface of particles of calcium carbonate into calcium oxide, and then hydrate this surface into calcium hydroxide – a sort of flash calcination process, likely to be less energy intensive than traditional calcination. Subsequent carbonatation of this sort of updated Roman cement would likely be quicker than that of traditional Roman cement. According to articles I have found on the web, it is also possible to accelerate at least the hardening of Roman cement, presumably by carbonatation, by adding salts.
I doubt myself that the Calera process is carbon negative. I do think it likely that a carbon negative cement is possible. I also think it likely that a carbon negative concrete is easier to achieve than a carbon negative cement, if you count the aggregate in the concrete as well as the cement, and use carbonate produced from captutured CO2 as aggregate.
It is apparently possible to use carbon itself as an admixture in concrete, and this has been done to produce electrically conductive concrete that can be heated by electrical resistance heating to keep it free from snow. Google this to confirm, if you like.
If the carbon (charcoal) admixture comes from biomass, and if this biomass is replanted, then this is a carbon negative process, similar to biochar.
Whether the whole block or mass of concrete could be made carbon negative and still retain reasonable structural properties and longevity including freeze/thaw resistance is a very good question. I doubt this can be done with traditional portland cement. It seems more likely that this can be done with Roman cement, flash calcined Roman cement, carbon filled Roman concrete, or carbon filled geopolymer.
Leland Palmer – good luck in your experiments. Men in sheds will save the world
I’m sure that you’ve looked for and found lots on pozzolans (this may be your definition of Roman Cement).
You may be interested in one of our little British companies
http://rktron.com/ major-c02-reductions-for-the-cement-industry
I have an open question – is anyone working on harnessing the proteins that shellfish use to produce their shells in order to capture CO2 ?
It appears that carbon or graphite can be made into a harder material, as is done with various grades of pencil lead, by the addition of clay and by then firing it at high temperatures.
Addition of geopolymer and or some other cement to carbon from biomass may be able to produce a high carbon material suitable as aggregate in concrete. If the biomass is replanted, this is a carbon negative process. Since this aggregate material could be perhaps 80 percent carbon, it may be that addition of this aggregate to ordinary portland cement concrete would make it carbon negative. To serve as aggregate, all something has to be is hard and fracture resistant, like the stone or sand aggregate now used in concrete.
So, it appears that if carbon from biomass in the form of biocarbon was mixed with clay, and fired at high temperatures using more biocarbon to fuel this process, a hard graphite material similar to very hard pencil lead could be produced, suitable for use as aggregate in concrete. So far, this is a carbon neutral process, if the harvesting equipment and so on is also run off of biomass in the forms of wood gas, pyrolysis oil, biocarbon, or electricity generated by burning biocarbon.
Add this biocarbon aggregate to any cement including traditional portland cement, and replant the biomass, and you’ve got a carbon negative concrete.
Calera’s process is total Greenwash – no wonder that Brent Constantz is hiding behind his Advisory board.
As for O’Neils response – a pathetic attempt to cover up their Greenwash.
An examination of Calera’s patent (application US 20090020044) clearly shows that they are using base, that their process generates far more CO2 than it releases, and that they are a scam.
The patent describes taking dolomite/dolomitic limestone and calcining it (releasing CO2) and then reacting this with seawater and CO2 to regenerate calcium/magnesium carbonate!!!
There is very little if any capture of CO2 by their process since the calcining step generates so much CO2, and there is CO2 generated from the processing operations – it is highly probable that the technology has a net positive carbon footprint.
Where is the biological process for capturing CO2? Calera is using decades old and very dirty and polluting chemistry for extracting magnesium/calcium from seawater – a very similar process was used by the magnesium factory which formerly occupied the Moss Landing site.
There is nothing Green about Calera’s process – basically, they are burning/calcining limestone, and using it to make artificial limestone from seawater. All smoke and mirrors.
And, Calera’s product is no cement – at best it is a poor mineral admixture. The patent shows that at a 20% replacement of Portland cement, the strength is only 50%(3000 psi) of that of 100% Portland cement – to get close to the strength development of Portland cement, the replacement level has to be reduced to 5%. Also, the drying shrinkage is doubled at 20% replacement of Portland cement.
Not only is Calera’s product not a cement, but its addition to Portland cement is very deleterious – it greatly reduces strength and increases shrinkage – and almost certainly decreases long-term durability, corrosion resistance, freeze-thaw resistance, etc..
This is very disappointing – first Calera said that it had a 100% replacement for Portland cement that would capture 1 ton of CO2 per ton of cement (impossible, unless the cement is pure CO2!)- they then amended this to a 50% replacement for Portland cement and a carbon neutral cement. Now what – 5% replacement for Portland cement?
Total Greenwash!
And note for comparison that (natural) limestone is commonly used as an aggregate for concrete, and is used as an admixture for cement in Europe at up to 45%.
Continuing the analysis of Calera’s claimed seawater cement process:
Assuming Calera captures calcium and magnesium from seawater as carbonates, one ton of carbonate cement would require at least 500 tons of seawater (> 80% capture efficiency) – or about 300 tons of desalination brine. So, to supply just US cement demand (over 120 million Mt per year), you would need to process 50 billion cubic meters of seawater!
The most economic method would be to piggyback the process onto desalination plants, but even with desalination capacity increases, desalination brines could supply at most 6% of US cement demand. And, processing seawater for cement production alone is neither economic (Portland cement sells at $100-120 per Mt in the US) nor environmentally friendly.
Also, such a process will generate a calcium/magnesium-stripped brine rich in sodium/potassium. Many, many studies have shown that such brines have severe environmental impacts when discharged into the ocean – the high salinity kills flora and fauna in the brine plume – so much so that regulations now dictate that such brines have to be diluted with seawater prior to discharge, or have to be landfilled.
Also, processing seawater produces large amounts of a toxic sludge containing copper, nickel and chromium (leached from metal piping and processing tanks) as well as cleaning agents and disinfectants (used in daily cleaning operations) – this sludge is highly hazardous and has to be landfilled.
It is puzzling that Calera does not appear to be talking about a biological process, and in fact their patent is a pure chemical process that essentially reprocesses natural limestone to make artificial limestone. Originally, Calera was talking about making calcium/magnesium carbonates via a biological path – ie. use carbonate-forming marine organisms to form magnesian calcite, and collect/process the resulting biomass/skeletons (the precursor to limestone).
Of course, the chemistry is such that this product could never be a cement (it does not undergo a hydraulic reacting with water and does not set) – this would explain why Calera has now given up on making a cement (as they had initially claimed). Similarly, this product would be a poor mineral admixture for cement due to its biomass content and the crystalline form of the magnesian calcite – this would explain the poor results reported in the Calera patent application.
Now, presumably as a last-ditch effort to salvage something, Calera is talking about making an aggregate. Well, if you want a strong, resilient and time-tested carbonate aggregate, you simply use limestone. You do not set up a limestone-to-calcined limestone-to artificial limestone process that is dirty and polluting and carries huge environmental consequences, makes a much inferior product to the natural material, and then claim it is Green!
Greenwash!
Sounds like Calera has serious problems.
But, carbon negative processes are all about sources and sinks.
So if the Calera process started with carbonate produced by mineral carbonatation from carbon capture, and if the carbon came ultimately from biomass, the end product of all their fooling around would be carbon negative, I think. But if you’ve got carbonate aggregate to begin with, why all the fooling around?
If the Calera process calcined just the surface of the particles of calcium carbonate derived ultimately from biomass, and resulted in an acceptable aggregate, it might be worth doing.
I don’t want to totally disregard Calera’s process – they may have solved some piece of the problem. At least they have tested their stuff as aggregate, and published the results in the patent application. But I can’t see much benefit from it, right now.
I’ve been thinking about this part of Caldiera’s opinion:
This part made me uneasy when I first read it, and it still makes me uneasy. Deposits of sodium hydroxide might be limited, but potassium hydroxide, another source of alkali, can be produced from wood ash, and used to be produced that way all the time.
Sodium hydroxide can also be produced by boiling sodium carbonate with calcium hydroxide, producing calcium carbonate, which precipitates, and sodium hydroxide, which remains in solution. Sodium carbonate and calcium hydroxide are both bases, and are present in very large deposits around the world. The heat required to run this metathesis reaction could come from biomass or solar, and could even possibly be waste heat from combustion of biomass.
It may be that Caldiera is getting his information from bad sources. He quotes Kheshgi, who works for ExxonMobil – an obvious conflict of interest. I’ve seen papers from these Exxon guys before, which very cleverly make alternative energy technologies sound extremely expensive and difficult.
http://www.google.com/ search?q=Kheshgi+exxon&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a
I’m not buying any horses from any of these guys, either Calera or Caldiera, and certainly not Kheshgi, until I count the legs, and make sure there is a leg on each and every corner.
Leyland
You err on several points:
1) Wood ash contains potassium carbonate – not potassium hydroxide. The latter, like all alkali and alkali earth hydroxides, is highly reactive and is not stable in air.
2) Obtaining potassium carbonate from wood ash, or any biomass ash for that matter, is not sustainable. Biomass ashes contain from 11 to 28% w/w of potassium carbonate, and ash yields from biomass are typically in the range of 0.4 to 9.0% w/w. So, you have to burn 40 to 2,300 tons of biomass to obtain just one ton of potassium carbonate. This is clearly non-scalable. Also, the carbon footprint would be huge – about 16 to 5,060 tons of CO2 per ton of potassium carbonate (assuming typical biomass carbon contents of 40-50% w/w)! Clearly, this process would be an environmental disaster to implement.
3) Yes – sodium hydroxide can indeed be produced by reacting sodium carbonate with calcium hydroxide. However, calcium hydroxide is very rare in nature – the mineral (portlandite) is very scarce and is formed only in certain high-temperature geologies. This is clear from its chemistry – calcium hydroxide is highly reactive and rapidly forms calcium carbonate in air. The only scalable route to calcium hydroxide is to calcine limestone to calcium oxide, then react this with water to form calcium hydroxide. This is what Calera is doing – with limestone/dolomitic limestone – this has a large carbon footprint, and this is what makes Calera’s process a Greenwash.
Hmm… I see your points.
I also see I need to research my comments more thoroughly.
The greenest concrete on the planet:
http://www.youtube.com/watch?v=nxfSbLPAW30
Mark Celebuski
Mark Celebuski
Yes – you have Portland cement concrete with recycled aggregate and supplementary materials.
This is nothing new – “Low-CO2/Recycled Content Concretes” have been in development for decades.
Your product is most certainly not “The Greenest Concrete on the Planet” – that is Greenwash.
And more to the point, this blog is not for self-promotion.
Sorry to disappoint you greenwash tracker but it is Portland cement free is most certainly the greenest concrete on the planet.
Any one can contact me with questions.
Mark
Just a question form a non-scientific Proletariat:
Just whay do we “need” cement? Why don’t we just stop doing the things that are wrecking the Bio-sphere?
If making cement stops being an option, we’ll just have to work it out! But for crying out loud – lets do STOP! ALL of the activities that are threatening to make the planet unliveable…
jeez…
Eric Karo – electrician at a cement plant &
President, Boilermakers Local Lodge D-46
(Representing CEMENT plant & limestone Quarry workers)