[Stoves] Is there a role for combining torrefaction and char-making stoves?

[Crispin Pemberton-Pigott]

Dear Paul

" So, I raise the question:  Why go all the way to torrification unless
significant transportation or shape modifications are in the next steps?"

The issue seems to be raising the heat content per kg above the 0% moisture
content value. This is accomplished by removing some of the endothermic
volatiles between 100 C and perhaps 280 C.

After you pass 280 the volatiles that are removed result in an actual loss
net of heating value.
For this reason I suppose you could call for heating to 280 but not to 400.

The heat content per kg at 400 is higher, but the total heat content is
reduced.

Do you follow that? When biomass burns, between 100 and 280 you have to put
in heat. What comes out burns, but not with enough heat to drive that
process. Something else has to be burning to drive that initial portion of
the pyrolysis.

So be careful before jumping into or out of torrefaction - it is not as
simple as 'being a waste of heat', and certainly there is a strong argument
for the processing if there is a transport cost for the final product. The
farther you need to ship it, the higher the content per kg should be.

On the other hand, if you have to pay for the heating to 280 (using an
external heat source) that energy has to come from somewhere. It is comes
from the fuel itself, it needs to be run above 280 (say, 400) to get a net
heat result sufficient to drive the process.

A fairly simple formula would optimise all the elements to get the best
economic and energetic bargain.

Regards
Crispin