[Stoves] Re Alexis Belonio article

[AJH]

On Wed, 04 Apr 2007 16:51:46 -0300, Kevin Chisholm wrote:

>Certainly, splitting water in a hot fire, in the presence of carbon, is 
>real!! However, I do not know if the temperature of a "hot fire" would, 
>or would not, be sufficient to dissociate 2H2O into 2H2 and O2.

The presence of hot carbon is the key, I think dissociation of water
needs about 2500C in the absence of any catalysts but dissociating it
on the surface of hot carbon and forming CO rather than O atoms brings
it down to less than 1000C, bearing in mind its likely to be an
equilibrium action. I think the principle driver for this is that
entropy favours gases and small molecules at higher temperatures, so
moving the solid carbon to gaseous carbon monoxide overcomes the usual
better affinity hydrogen has for oxygen.
>
>I suspect that water reduction, or water dissociation, could have a 
>positive effect on biomass combustion processes, by permitting the 
>formation of intermediate compounds that would burn better, or more 
>completely.

We've talked about this a bit in the past and the suggestion was that
wood at 12% mc burned more cleanly than oven dry wood. The impression
I got, from comments by Tom Reed and Tami Bond, was that it more
likely the endothermy of the vapourisation of this small amount of
moisture in the primary combustion zone was just enough to reduce
temperatures in this zone to below the temperature that pyrolysis
offgas products may crack, producing sooty particulates. The
implication was that if these species did crack burning them out
cleanly in the secondary combustion was more difficult.

AJH