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?
This piece originally appeared in Climate Progress.