Calera – Using CO2 to make cement

This entry was posted by Thursday, 1 July, 2010
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Calera, a 3 year old California-based start up, has come out with an emerging technology which represents an innovative solution to advance our energy, environmental and economic goals, by recycling carbon dioxide into beneficial building products.

One of the few weak points is that the Calera process says that it captures “86% of the flue gases which is treated”, which seems to imply that not the whole of the emitted flue gas is by them treated.

The Calera Process imitates nature

The Calera process mimics how nature grows the hard, durable materials in teeth, bone and shells. Minerals in seawater attach to CO2 molecules in the air to create a limestone-like material.

The chemical composition of Calera cement is essentially limestone, a favorite material for cement, concrete, and pavements.

Because Calera’s process removes minerals and other constituents from seawater, it also acts as a freshening system to produce fresh water, which also gives it added value for clean water projects.

Moreover, unlike traditional sequestration, where CO2 threatens to break free and escape back into the atmosphere, in the Calera process, once the CO2 is converted into cement, only temperatures hotter than 700 degrees C, or sustained exposure to concentrated acid can release it again into the atmosphere, Calera says.

Critics of the technology are concerned with an acid byproduct from the reaction that must be neutralized and disposed of. Apparently, as yet they do not have a way to neutralize the acid without creating additional environmental hazards and raising costs.

The water requirements of the process are a bit dicey – seawater is required to produce cement. The Calera process must have a plentiful source of brine, so how will they implement their idea at inland and water starved power plants? And what are the energy requirements of the process? An answer to these questions is expected soon, since Calera has announced it will open its first commercial plant next year.

An economic alternative

Calera claims that its relatively low-cost cement-making process can surpass all other CCS techniques, cutting a plant’s energy drain to less than 15 percent, instead of the 30-40% for conventional chemical scrubbing, and reducing the cost of CCS technology to zero.

A smarter economy

CO2 is an essential raw ingredient in the Calera process, so the cost of capturing and storing it in materials would be more than offset by profits from the sale of those materials.

But if the Calera process immediately replaced 100 percent of conventional cement-making in the United States, the 15.5 billion tons in current CO2 emissions from fossil fuels would not even be enough to address the demand of the aggregate market, Constantz said.

Calera recently completed a demonstration project near Moss Landing, Calif. that is capable of capturing 30,000 tons per year of a CO2, equivalent to a 10MWe natural-gas power plant. In January, Calera began drawing 1 percent of the stack gas from a Dynegy power plant across the street through a massive pipe to its cement plant. Calera was hoping to capture 80 percent of the smokestack CO2, and sequester it in its patented cement mixture using the abundant stock of magnesium hydroxide (Mg(OH)2) available on site. Calera’s plant is capturing 86 percent of the CO2 in the flue gas from the Dynegy plant per a study by R.W. Beck, a consulting firm hired by Calera.

Calera has started work on a plant in Australia, and is getting ready to announce plans to build another plant in Southern California.

Just how unclean is cement?

Pollution occurs from the use of coal, natural gas or oil as fuel in a burn of aggregates, silica and lime at 2700 degrees F, in large cylindrical steel rotating kilns. Inside, extreme heat causes a chemical change to take place. The entire process uses an enormous amount of energy – 6 million Btus for every ton of cement produced. Thus, cement uses the most energy of all industrial manufacturing processes – as much as .6% of total US energy use.

Industry taking note

In March, Peabody Energy, the world’s largest private-sector coal company, led Calera’s latest investors by purchasing a $15 million equity interest.

But skeptics not as foolhardy

The skepticism of critics like Caldeira and Romm is fueled by Calera’s evasiveness when confronted with demands for factual information about how their process actually works, and that the fact that their replies tend to come in cartoon form.

“People have been looking for ways to do this for 15 years,” said Ken Caldeira, an expert on the carbon cycle who is a senior scientist with the Carnegie Institution for Science at Stanford. “The idea that they’re going to come up with something that’s both economic and scalable? I’m highly skeptical.”

In ClimateProgress, Romm notes that Caldeira 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

Romm summarizes it as “I see no evidence that they have found an affordable and scalable process, but it is impossible to say anything definitive because they are not being adequately forthcoming.”

Calera’s CO2 capture technology has given us hope that CO2 capture can be economical, and produce useful byproducts, but they still have to prove that it’s actually viable, and that too at a large scale.

ROSE RAGSDALE, Greeningfoil

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