Australian company joins race to make 'green' cement from CO2

LONDON -- An Australian cement and minerals company believes it has an answer to a problem that is vexing the experts -- how to safely and effectively capture the carbon from a power plant at very low energy cost and high efficiency.

Not only that, but the resulting byproducts may have uses in construction or farming.

Calix, based in Sydney, says its Endex Reactor can scrub 90 percent of the carbon dioxide from the fuel gas of a power plant -- burning either natural gas or gasified coal -- by using specially treated lime.

Calix is one of three companies rushing to perfect a clean coal technology that can also be used to make construction materials, such as cement, that can permanently store CO2 emissions from power plants. Two potential competitors include Calera, a California company that has received interest from Australia and China, and Novacem, a company based in the United Kingdom.

In his State of the Union speech Tuesday night, President Obama added some impetus to this race by saying clean coal should be part of a U.S. goal to develop clean energy including nuclear power, renewable energy and natural gas. "To meet this goal," he said, "we will need them all."

In the Calix pilot plant, the fuel stream turns to mostly hydrogen to be burned and fed to the turbines to make electricity. The carbon dioxide is removed as a pure stream for burial, and the lime goes back into the cycle again to repeat the process.

"It is very efficient," said Brian Sweeney, the company's European business development director. "Every kilogram of lime can extract 40 kilos of carbon dioxide, and you can use the lime 3,000 to 4,000 times before it becomes compromised. Even then it has industrial or agricultural uses." (Forty kilograms is equal to 88 pounds.)

Calix says the pre-combustion capture process is far more energy-efficient than post-combustion methods of capturing CO2, which are generally calculated to use about 20 percent more energy to obtain the same level of power output.

The so-called calcium cycle that the process uses is by no means new. It has been known since the 1950s. What is novel is the way the lime is treated to make it super-absorbent at moderate temperatures and very high speeds -- it is in the carbon capturing reactor chamber for just seconds at a time.


Potential marriage of 2 industries

"It is essentially a case of the cement industry suggesting to the power industry to try looking at the carbon emissions problem from a slightly different perspective -- combining the expertise of both to produce a novel solution to a serious problem," Sweeney told ClimateWire.

The Calix carbon capture process involves mixing the finely powdered treated lime with heated, gasified fuel as it enters the Endex Reactor. The carbon in the fuel instantly sticks to the lime, which precipitates out as limestone into Calix's patented "Calciner," which strips off the CO2 and in the process regenerates the lime for reinjection.

Part of what makes the technology work is the treatment of the lime using a process called Flash Calcination that was originally invented by Connor Horley. Horley died in 2008, three years after Calix acquired the intellectual property rights to the process and its products. He discovered that dropping fine particles of dolomite, a sedimentary, carbonate rock, down a tube full of superheated steam converted them to oxides within three seconds.

The reaction turned them, in effect, into minute sponges with a great chemical affinity for CO2 and vast surface area for absorption. Calix says 1 kilogram of the product emerging from the flash calcination process has a surface area of more than 100,000 square meters (or 1.07 million square feet).

The original goal was to create a product with the same properties as traditional portland cement but using carbon emissions as one input at a fraction of the energy cost of making conventional cement. Finding cost-effective ways to capture and use carbon is a pressing problem in a world faced with the daunting challenge of cutting its carbon emissions by at least half within the next 40 years.

Some three billion metric tons of portland cement are produced every year, and demand is booming as the major developing economies like China and India expand rapidly. But because it is made by a coal-fired process, every metric ton of portland cement produced also generates some 770 kilograms (1,694 pounds) of CO2 through the very high temperatures involved in turning limestone into calcium carbonate and then into calcium oxide.

That means that cement production on its own accounts for roughly 5 percent of the world's emissions of carbon dioxide -- the most plentiful of the so-called greenhouse gases deemed responsible for climate change.

Calix already has a demonstration calciner operating at Bacchus Marsh outside Melbourne in Australia producing carbon-containing dolomitic cement that has a capacity of 20,000 metric tons a year. The company says concrete made with its treated dolomite -- a substance it calls semidolime -- not only sets to the same strength as classic concrete in 20 minutes, but after a day or so achieves about three times the strength.

A 'technology that you can kick'

Referring to its competitors, Calix says its process is based on proven technology that can be seen working at scale. "This is no pie in the sky. Ours is technology that you can kick," said Sweeney.

Confident in its process and already backed by a group of Australian and European investors, Calix is planning an initial public offering of shares -- most likely a joint listing in Sydney and London this year.

As part of proving its processes to the public and attracting more investors, the company aims to set up a 10-megawatt demonstration Endex Reactor at its Australia site and a similar-sized one in the United Kingdom this year.

It says it aims to have a 50 MW prototype during 2012 and to be in a position to deliver fully developed Flexi-fuel Endex Reactors in 50 MW modules the following year. Sweeney said clusters of these modules could be retrofitted to existing natural gas and gasified coal-fired power plants with relatively few modifications -- notably the addition of hydrogen burners to the gas turbines.

In the United Kingdom, Calix has teamed up with mining and power company Powerfuel to build the 10 MW European demonstration plant next to the latter's colliery at Hatfield near Doncaster in northern England.

"This will be a showcase for our technology. There are 20 other power plants in England already using the same gas turbines that will go in at Hatfield. They will be our target market initially, because you can bolt our technology onto them very easily," Sweeney said.

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