[Stoves] Calculating cooking costs and char costs ----Re: [biochar] Where to discuss STOVES AND CARBON offsets and drawdown

[Andrew Heggie]

On 17 September 2017 at 14:00, Paul Anderson <psanders at ilstu.edu> wrote:

> I really like the numbers that    1 kg of wood contains (or can yield) 4
> KWh.    That is a very useful figure.

But not entiorely accurate until you add that the moisture content is
about 20% by weight, bone dry wood gives about 5kWh
>
> One revision of your other comments.
> Pyrolysis releases about 70% of the energy (some might say 67%, about
> 2/3rds).   And 30 % resides in the charcoal.

And this is entirely dependant on the temperature at which pyrolysis
takes place (and to some extent the speed)
>
> At the same time, the remaining charcoal does have about 50% of the carbon
> atoms.

Tom Miles said there was a calculator on the IBI site which showed
what the carbon to hydrogen ratio in the char was, basically you need
to raise the temperature to about 900C to eliminate all the hydrogen,
by which time the almost pure carbon char  is only 15% of the original
dry wood weight (it varies between woods). From 400C on up to 3000C
the carbon turns from an amorphous mix of carbon in chain like
structures to graphite platelets and by 3000C I think it becomes
entirely graphite, so recalcitrant that it will only burn if heated
and dropped into liquid oxygen.

So from the above  the resultant char could be below  1/3rd of the
original carbon atoms. As the TLUD seems to work in the 500-700C range
I suspect the char will be variable between 50% to 30% of the original
carbon content. I do think the char from TLUD will have a higher
cation exchange  capacity than conventional charcoal but much less
adsorbtion capacity than activated carbon.

Andrew