[Stoves] Grates and chimneys

Crispin Pemberton-Pigott crispinpigott at gmail.com
Mon Feb 13 10:42:44 CST 2012


Dear Xavier

Please make sure they are actually giving the number you think they are: is
it on a wet weight basis or a dry weight basis?

50% moisture is no common if it was calculated on a wet weight basis (i.e.
50% of the total mass is water). 33% moisture is no uncommon, but calculated
on a dry weight basis, it is 50% (i.e the moisture mass is 50% of the mass
of the dry material).

That is why it is normal to put WWB after a number that means a % of the
total mass.

It is probably 33% WWB (=50% DWB).

That said, there is wood growing is Southern Africa with a 66% WWB moisture
content. It will not support combustion on its own. In other words it can't
burn hot enough to dry itself. Simon Mortimore found some when testing all
wood samples found at orphan feeding stations where institutional stoves
were being used. The average moisture content of all samples was pretty high
but not unreasonable, indicating a short time between collection and use. As
they were saving a lot with improved institutional stoves, some accumulation
was possible. Tons, in some cases, giving better fuel by the time it as
used.

Regards
Crispin


++++++

Xavier, I don't know of any study, but if you stick a moisture meter into a
living tree, you will get much higher moisture contents than 'only' 50%. and
a freshly  cut tree will not lose that much moisture in the one day before
it gets stuck into a stove. and you are right:  
it is nearly impossible to burn that type of moisture content cleanly...
do you have a moisture meter? if not, try to collect some wood and charcoal
samples and calculate the moisture through the weight loss after you have
dried the samples well in a kiln/oven. you will be surprised what you get.
regards christa





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