February 27, 2008

Letter to the Editor

Concrete correction to article on green cement-plant technology

Re: Greener Concrete Around the Corner, Feb. 8 by Korky Koroluk
An interesting article, surely. Those Kiwis are a resourceful bunch, as I read an article last month about them using crushed mussel shells as a substitute for cement.

Working in the cement/building materials business, such developments are promising. I do, however, notice a flagrant oversight, namely Korky’s following paragraph:

“So what they are now trying to do is develop a closed-loop system in which the kiln produces carbon dioxide, which is captured and fed to algae, which is harvested and used to produce biodiesel, which fuels the kiln, which produces more carbon dioxide — and around and around.”

Sounds like someone forgot the Second Law of Thermodynamics; the one describing increasing entropy and the irreversibility of heat-engine-type reactions. In the same way as you can’t burn a piece of paper, catch the gas and ashes, and turn them back into a piece of paper, the “around and around” cycle described above is physically and thermodynamically impossible.

Considering most cement plants I know of use powered PET Coke to fuel their kilns, I’m also not sure you can use biodiesel to fuel a cement kiln at 1450C.

Just pointing that out. It struck a chord with something I remembered from third-year engineering at university. Thanks.

Nicholas Cifelli, EIT
St Marys CBM

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