Calera Process Uses CO2 in Production of Cement
10 August 2008
SciAm. Calera, a California start-up, is developing a process to capture about 90% of CO2 from power plant flue gas to use in the production of cement.
It’s a twist that could make a polluting substance into a way to reduce greenhouse gases. Cement, which is mostly commonly composed of calcium silicates, requires heating limestone and other ingredients to 2,640 degrees F (1,450 degrees C) by burning fossil fuels and is the third largest source of greenhouse gas pollution in the US, according to the US Environmental Protection Agency. Making one ton of cement results in the emission of roughly one ton of CO2—and in some cases much more.
While Calera’s process of making calcium carbonate cement wouldn’t eliminate all CO2 emissions, it would reverse that equation. “For every ton of cement we make, we are sequestering half a ton of CO2,” says crystallographer Brent Constantz, founder of Calera. “We probably have the best carbon capture and storage technique there is by a long shot.&rduqo;
The Calera process seawater with the CO2 from the flue gas, and uses the wast heat from the power plant in spray dryers to dry the resulting slurry. Once dried, the Calera cement can be used as a replacement for Portland cement.
The US used more than 122 million metric tons of Portland cement in 2006 and China used at least 800 million metric tons.
(A hat-tip to Allen!)
China, with about 4x the USA's population uses over 7 times the cement. Does this make Chinese the front runner builders and Americans or a downward curve?
Are Big Macs a better indicator?
Posted by: HarveyD | 10 August 2008 at 01:04 PM
Sounds great, but I suspect even if all the old cement plants are replaced with this, there would still be excess flue gas.
Posted by: GdB | 10 August 2008 at 02:36 PM
Of course there would be excess flue gas. The difference here, is that the amount of flue gas would be drastically less, and the mitigation of said flue gas would be drastically easier.
What they don't use to make the cement, they could use to grow algae with. Hell, they could probably use the waste heat for the algae, as well...
Posted by: The Scoot | 10 August 2008 at 05:31 PM
Serious - what is the breakdown path of cement?
How is the seawater used in this process so as not to contaminate the product.
Not so serious,
Will we see more greener garden gnomes as a result of this?
Posted by: | 10 August 2008 at 08:47 PM
I suppose the process take Ca ions out of the seawater and turns it into CaCO3. While it takes CO2 out of the air, it also take Calcium out of the oceanwater.
So the actual equasion for the ocean is :
CaCl2 + H2CO3 -> 2 HCL + CaCO3. (Chloride-ions are the main negative ions in oceanwater)
Although the HCl is buffered in oceanwater, you still acidify the ocean, and take out Calcium. That's exactly what you don't want if you want to preserve coral reefs.
I would certainly not consider it long-time carbon sequestration, since it acidifies the ocean, and diminishes the long-term capacity of the ocean to absorb CO2. It could even be that some of the 'sequestered' CO2 will still be in the returned water and will just bubble-out of it when the partial pressure above it drops to natural levels. The acid water could also turn dissolved HCO3-ions (which was already present in the surrounding oceanwater) into H2CO3, which turns into CO2 + H2O.
If we would use ocean water on large scales to produce cement that way, I expect it would be disastrous for ocean fauna. I hope they do very good calculations before implementing this technique.
The only way I see to turn flue-gas CO2 into CaCO3 without unaxeptable side effects is by using basalt as a calcium source. That would truly sequester the CO2 for eons, while turning it into a useful product.
Posted by: Alain | 11 August 2008 at 03:24 AM
We should be suspicious of these new breakthrough inventions where the parties refuse to disclose many details of the actual process.
The energy/CO2 crisis is bringing out a lot of profiteers.
We want to believe they provide usable cement, negative CO2 emissions and waste heat reclamation all for almost nothing.
Making cement “… requires heating limestone and other ingredients to 2,640 degrees F”
They imply they will reduce the cement energy usage by using hot flue gas, but power plant exhaust can not be anywhere near this hot or the plant would be grossly inefficient.
Aha, but then they then say “ .. uses the waste heat from the power plant (again?) in spray dryers to dry the resulting slurry.” What slurry? The slurry they get by mixing the power plant (or the cement plant?) flue gas with sea water?
I think this technology is already in use – how does this process sequester more in sea water? Is their secret how they get the solids to precipitate?
Also the caveats “ … capture about 90% of CO2 from power plant flue gas ..”
And
: ,, While Calera’s process of making calcium carbonate cement wouldn’t eliminate all CO2 emissions, ..”
Seem at odds with the promises.
On the positive side, in regard to fears of acidifying the ocean; can we actually affect the ocean Ph this easily? I don;t know.
Posted by: ToppaTom | 11 August 2008 at 06:15 AM
Ocean pH is already being affected because of CO2 translocation from the atmosphere to the oceans. If substantial amounts of CO2 (or HCl) are additionally transfered to the ocean (while calling it carbon sequestration) it will certainly affect it even more.
But what is the problem of ocean acidification ?
The decrease in ocean pH is a problem because it would make it harder for aquatic organisms to produce shells and corals. If in addition of acidification, you also remove gigatons of calcium out of the water, it will produce an additional burden on the organisms.
Even if the influence on the total of all the ocean water would be (calculated) small, it would certainly have a big local impact where the trillions of gallons of decalcified and acidified water is dumped back into the ocean. The amount of oceanwater that you need to extract substantial amounts of calcium is that of a big river.
Calcium in seawater is about 410 ppm. So for each ton of calcium you remove, you need a thousand times more seawater (molecular weight of Ca is 10, that of water is 18). I can immagine that the energy needs of the pumps would be substantial.
Posted by: Alain | 11 August 2008 at 07:31 AM
This is one of the most promising developments in the past year.
The amount of greenhouse gases generated by cement production is huge - and to actually take two of the top ten sources, electricity production and cement production, combine them and turn them into a net GHG reduction, is simply incredible. Even if we can only do this across 5-10% of the electricity production, the WW GHG impact would be measurable and beneficial. Wow.
I understand the concern about ocean acidification. I would point out two mitigating points. The first is that currently electricity production is causing the oceans to acidify due to precipitation of the various exhaust gases, and if you could reduce the amount of the exhaust gases, you probably reduce the acidification from that source (Not a 1:1 relationship because it's not a closed system, but it does mitigate). The second is that if the problem is the altered seawater that exits the process, then some or all of that seawater could be processed through reverse osmosis and used as fresh water. Again, there are issues of energy usage with osmosis and questions about whether there is a demand for the fresh water, but it could mitigate the acidification in many oceanside scenarios.
Overall, this will take hundreds of millions of research dollars to determine 1) best ways to implement the process and 2) uses for the huge amount of calcium-based cement products (wallboard, anyone?). But this idea has truly enormous potential.
Posted by: dollared | 11 August 2008 at 11:51 AM
There are many upsides to this concept. These were well represented in the article.
There is demand for cement in construction reflected by the enormous usage which if it were cheaper could easily double.
As there is only so much land labor and associated raw materials to meaningfully consume the product, there are associated environmental costs and limits to be considered.
The useful life expectancy of concrete buildings may in theory be many hundreds of years but practically 100 - 50 often sees the buildings ripped down for a new one.
This suggests that a fair portion of any construction will need careful unconventional design to meet better than short term sequestration.
Hence the breakdown products can be (are) relevant.
The lime component in portland cement only 50%?
the clay component will require the usual calorie @ temperature.
One of the proponents is experienced in a range of manufactured cement products Without all details and process option or possibilities, we can only guess.
Temperature for portland clay firing @1450c sounds high. But lets not assume this process is a hot process as such. It may be the chemistry is (can) operates at ambient?
Deferring the technical chemistry to others.
As free calcium in sea water is in demand by atmospheric CO2 gases and marine organisms and reaching (or passing) the points of availability - the carbon sink full condition. (At which point the trajectory for acidification takes off.)
It is not clear that the process will be a benefit to the marine environment.
But that the resilience or buffering ability of the oceans is sounding alarm bells and considered as order(s) of magnitude larger indication of environmental stress than atmospheric indicators.
50 years ago or even 20 years ago no one would have asked the question.
Today careful consideration is appropriate.
Posted by: arnold | 12 August 2008 at 02:58 AM
Calera's cement is utter balderdash on so many levels - a couple of preliminary takes:
1) Where is the cement??? Calera appears to be making Ca/Mg carbonates via a biological path - ie. their cement is carbonate (magnesian calcite) skeletons - they are collecting the skeletons and drying the sludge. This will give a Ca/Mg carbonate powder akin to powdered chalk and limestone. None of these are cementitous (ie. preformed Ca/Mg carbonates will not set into a cement when combined with water) - unlike Portland cement.
2) Note that Calera is now saying that they will not offer a 100% replacement for Portland Cement, but rather a 50:50 blend. This clearly points to their "cement" simply being a filler - you can acheive the same (very poor results) by using powdered limestone or chalk.
3) Note that Calera has also emended their initial claim that their process captures one ton of CO2 for every ton of cement produced, to half a ton of CO2 capture. Stay tuned for more amendments.
4)Assuming (biological) capture of Ca and Mg from seawater as carbonates via Calera's technology, one ton of carbonate cement would equate to at least 500 tons of seawater (at > 80% Ca/Mg capture efficiency)- or ca. 250-300 tons of desalination brine. So, to supply just US cement demand (ca. 100 million MT pa), you would need to process 50 billion cubic meters of seawater. The most economic method would be to piggyback the process onto desalination capacity, but even with projected desalination capacity increases, desalination brines could supply at most 6% of US cement demand. And, processing seawater for cement production alone is neither economic (Note: Portland cement sells at $100-120 per MT in the US) nor environmentally friendly.
5) The Calera process will generate a Ca/Mg-stripped brine rich in Na/K. Many studies have indicated the severe environmental impacts that such brines have when discharged into the ocean - so much so that regulations now dictate dilution of such brines, remote discharge or landfill.
6) In summary - Calera's "cement" is a non-cementitous filler, whose production is non-scalable, uneconomic, carries huge environmental consequences.
Posted by: Ulu | 19 August 2008 at 05:42 PM
@Ulu,
My thoughts exactly.
I wrote a post on this for my blog.
"If we precipitate all of the Ca2+ and Mg2+ as carbonates (CaCO3 and MgCO3), sequestering 1 T of CO2 would require 360 T of sea water. Additionally, carbonate precipitation does not occur below a pH of ~10, whereas sea water has a pH of ~7.5-8.4 , which could be decreased by increasing the partial pressure of CO2. Increasing the pH of the solution to favor carbonate precipitation likely requires the use of a base, such as sodium hydroxide, NaOH."
On the issue of blending, I think that the current ASTM standard allows 5% limestone (CaCO3) blend in Portland cement.
I hope (and believe) that Calera has overcome the obstacle of using 100s of tons of sea water to capture 1 T of CO2. Rather, I think that the source of calcium comes from alkaline materials such as clinker kiln dust added to the water. A patent talks about a similar process .
Posted by: Pradeep | 20 November 2008 at 05:01 PM