The Oil Drum: Europe | Concentrating Solar Power

184 comments on Concentrating Solar Power

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ericy on May 31, 2007 - 9:46am

I was wondering whether CSP could be used to make concrete. Part of the process involves mixing up some common chemicals, and heating to about 1400C in a kiln:

http://en.wikipedia.org/wiki/Portland_cement

Typical design for a kiln given here:

http://en.wikipedia.org/wiki/Cement_kiln

So the question I have is whether it is possible to design a kiln that could directly use CSP instead of oil/natural gas.

It might or might not be possible to use the CSP directly - depends on whether you can design the kiln to get the material heated properly. It might be easier to replace the flame in an existing kiln with a hydrogen flame, but this would be clearly less efficient.

There are other industrial processes which require heat in one form or another that currently use gas or oil, and my guess is that people ought to be thinking of ways to use the light of the sun directly to provide this heat.

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half full on May 31, 2007 - 11:17am

I've given this some thought myself, and concluded that it is possible to make C3S clinker, but not by the same route used in conventional kilns. Remember that 75% of PC kiln feed is limestone, and the limestone produces CO2 as it is calcined, so that about 80% of the CO2 produced in cement-making comes from the limestone, not the fuel. (and cement accounts for 5-7% of man-made CO2 globally!)

An alternative process uses molten calcium chloride, and has been around for decades.
CaCl2.H2O -> CaO + 2HCl
3CaO + SiO2 -> Ca3SiO5 (at about 700C)

Hydrated calcium chloride melts at about 180C, so the whole process can take place in liquid phase, with the silica in slurry form.

If there is an ocean or brine reservoir nearby, the CaCl2 can be made from limestone and MgCl2 brine by exchange
CaCO3 + MgCl2 -> MgCO3 + CaCl2

You also need a market for the hydrochloric acid.

The challenge here is firstly materials, because molten chlorides + HCl at high temp are extremely corrosive (remember there is water present). The whole reactor loop, and especially the solar absorber will have to be ceramic (carbides?) and able to withstand day/night thermal cycling. If you can figure this out you will be a hero.

Second challenge is business. The cement companies are global semi-monopolies with billions invested in conventional kilns, and won't change until they absolutely have to. They will buy carbon credits for decades first.

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ericy on May 31, 2007 - 12:41pm

Hadn't considered this 2nd process. On the one hand it sounds easier, on the other there would be a hell of a lot of HCl that needs to be put to good use. Reminds me of the glycerine problem with biodiesel...

The global companies will just end up chasing fossil fuels all over the world. As time goes on that will get harder, or the plants may need to relocate (esp if they are using natural gas).

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Rib on June 1, 2007 - 7:27am

Rib
I think we will have to just make less Cement.Timber houses Etc.
See company below has promise of solving issue of what to do with waste glycerol from bio fuel
VIRENT ENERGT
Cellulose /Sugar conversion to Hydrogen /Methane/MethanolCan also use waste Glycerol from Biodiesel manufacture as fuel
http://www.virent.com/
http://www.ecw.org/biomass2power/index.html

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