[Stoves] Smoke-free biomass pellet fueled stove

[ajheggie at gmail.com]

[Default] On Mon, 12 Nov 2012 04:02:59 +0000,"Crispin
Pemberton-Pigott" <crispinpigott at gmail.com> wrote:

>Dear Paul
>
>The point I am making is not that there is more energy gained from the char water interaction in terms of splitting water

Crispin I think it unlikely any water is being split



>. It is that with say, 20% moisture, the loss of char is far more than the energy needed to boil off that water - several times more. 

Yes I reckoned from what Tom Reed posted way back that the difference
was a factor of six if the  oven dry wood yielded 25% char and the 25%
mc wwb yielded none. I could replicate the od figure but didn't
sustain a tlud burn at the 25% mc wwb. This is why it would be
interesting to run the experiment in a controlled way.
>
>Two things can be concluded from this: first that the total energy released from 1 g of raw fuel is higher with moisture than without, and that the water is somehow involved in this additional char burn. We are not clear on the mechanism, for sure, but that it yields more total heat from a given amount of raw fuel is clear.

Yes in that there is no residual char with energy still in it. 
>
>25% char produced from a kilo of 15% moisture fuel contains about 45-50% of the original fuel energy (considering the moisture). 
>
>0% char from the same raw fuel means that 45-50% energy is released because the char is burned. Only a small percentage of that char is needed to dry the fuel so the rest is a net gain as far as the forest is concerned. 
>
>So, what is the mechanism for pulling out that carbon and burning it?

I think that Jaakko and I tried to explain that but the proof would be
in measuring the temperature and volume of the offgas above the
pyrolysis front. Generally we expect to add more primary air in a
conventional fire as the mc increases so we should see either an
increase in offgas volume and/or a higher temperature as mc is
increased.
>
>If you redo the above calculation with 10% and 20% wood, yielding different amounts of char (you choose how much) what does the final comparison look like?

We can only do that calculation once we have empirical data of how
much char and at what peak temperature it has been exposed to remains
from samples of 0%, 5%,10%,15%20% and 25% samples.

AJH