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

[Anand Karve]

Dear Crispin,
We found out almost 10 years ago that the oven-and-retort system was ideal
for torrefaction. It is easy to control the process by restricting the
quantity of fuel burned outside the retort. The heated incline over which
barrels tumble down, as suggested by Ron was also tried by us. In our case
we had a long tube which was heated from outside. The barrels filled with
biomass did not move by gravity, but were manually pushed through the tube.
When a fresh barrel is pushed into the tube at one end, the barrel having
completed torrefaction would pop out of the tube from its other end.  The
residence time of the barrels inside the tube determined the degree of
torrefaction. However, we discontinued this system because it needed more
fuel than the simpler batch type oven-and-retort system. The question I
wish to ask you is about the quality of the gas when the biomass is heated
to just below 300 C. Theory says that the tar percentage is high at lower
temperature. So supposing we heated the biomass at less than 300 degrees C
and supposing we collected the volatiles, would it be predominently tar
that we would be getting?
Yours
A.D.Karve


On Fri, Feb 24, 2012 at 11:59 AM, Crispin Pemberton-Pigott <
crispinpigott at gmail.com> wrote:

> 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.
>
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