Green Energy — February 7, 2010 at 11:50 am

Capturing carbon in cement?


This is probably going to look like a commercial for the Calera company but I’ll say right off the bat that I have no connection or financial interest in them.

What I do have is a scientist’s interest in them.

Here’s a statistic that shocked me: cement manufacturing is responsible for 5% of global CO2 emissions and in the U.S., cement production represents 2.9% of overall energy usage.

What Calera has figured out how to do is use CO2 from factory emissions to make concrete. And here’s the amazing part:

Calera estimates that each cubic yard of its concrete would soak up more than 1,000 lb of CO2. In contrast, producing a cubic yard of traditional concrete generates more than 500 lb of CO2.

Most of the info in this blog entry is from a recent article in Chemical & Engineering News (Amer. Chem. Soc. membership req’d) called “Seeking To Cement A Green Future”. In the article the talk about several new cement manufacturing start-up companies that are aiming to make “green” cement and wallboard. But the part about Calera was what really caught my interest.

From the article:

To make cement, manufacturers heat limestone in a kiln to 2,650°F. The process eliminates chemically bound water molecules, releases CO2, and produces a marble-sized material called clinker, which is then ground to a fine powder. Gypsum is added, and the resulting cement is mixed with water, sand, and aggregates to produce concrete. The rehydration causes an exothermic chemical reaction that hardens the mix.

Brent Constantz, Calera’s chief executive officer and an associate professor of geological and environmental sciences at Stanford University, plans to produce cement and aggregate that will enable the production of concrete with a negative CO2 footprint. In Calera’s process, CO2 from hot industrial flue gas is bubbled through mineral-rich seawater or hard water. Calcium and magnesium carbonates precipitate out of the solution and are transformed into two concrete ingredients: a synthetic limestone aggregate and an amorphous calcium carbonate with cementlike properties.

“Our process is akin to the skeletogenic process of corals and other marine organisms that precipitate carbonates from seawater,” Constantz says. Calera estimates that each cubic yard of its concrete would soak up more than 1,000 lb of CO2. In contrast, producing a cubic yard of traditional concrete generates more than 500 lb of CO2.

For the precipitation to occur, the solution must have a high pH. Depending on the water source, Constantz tells C&EN, the company can opt to use a proprietary, low-energy electrochemical process to add alkalinity. The full process is being tested at the company’s Moss Landing pilot plant near Monterey, Calif.

Will this eliminate all 5% of the CO2 generated from the manufacture of concrete? No. There are some conditions that must be met in order for a plant to be viable.

Given the mass-balance challenges of creating sufficient carbonates from flue gas and water, Constantz says Calera will have to carefully select its locations. The ideal site would include a power plant to supply CO2, a concrete ready-mix plant, and a water desalination plant. He says Calera’s wastewater, when stripped of its calcium and magnesium, could be inexpensively desalinated. And salt from the desalination could resupply Calera with raw material for the electrochemical plant.

So, of course not all cement can be made in this way. But, because of the negative carbon footprint of the process, every pound of concrete made using this process is the carbon equivalent of NOT making 2 pounds of cement in the conventional process. If one-third of all cement made used the Calera process, it would be the same as eliminating all CO2 emissions from current cement manufacturing. Put another way, founder of Calera, Brent Constantz, says “For every ton of cement we make, we are sequestering half a ton of CO2″.

It’s worth having a look at the video on Calera’s website. It features Carl Pope, the former Executive Director of the Sierra Club, speaking quite favorably about this exciting new technology.

It should be noted that there are some skeptics. You’ll find doubters HERE and HERE. However, if Calera’s claims turn out to be true and their pilot facility, now operational, proves their concept, this is just one more example demonstrating why we need to value and invest in science and scientific R&D in this country. The more resources we provide to smart, clever, capable entrepreneurs like the ones at Calera, the faster we will be able to solve the most vexing problems associated with carbon emissions. As Vinod Khosla, a technology investor who is backing this venture puts it, “this is so game-changing it could completely change the nature of the carbon problem this planet is currently dealing with.”

And that is cool.

I’m just sayin’…