[Stoves] Adding value to charcoal from TLUD stoves

[Julien Winter]

Hello Rajan and all;

The point you raise about allowing for a few minutes of the char-burning
phase to heat the charred fuel and drive off any left over volatiles is a
good one.

The height of the TLUD combustion chamber is likely to be important,
because the top of a tall column of charcoal may not get hot enough to
drive off volatiles by char-burning. In addition, the top of a tall column
will have experienced a longer time for tars to condense during the
flaming-pyrolysis phases than a shorter column.  I have made some grimy
wood-pellet biochar in a stove pipe TLUD.

Not driving off the volatiles will result in fine pore space of the
biochar being occluded.  Perhaps that is what was going on with the
following research:

Peterson, S. 2013.  Comparison of gasification and pyrolysis methods for
preparing biochar from corn stover and wheat straw.

http://biochar.illinois.edu/Peterson.pdf

In this Powerpoint presentation, he shows that TLUD biochar had a lower
surface area than biochar made by pyrolysis.

I think there are some questions to answer:

1)  Is it commonly the case the a short period of char-burning will raise
the temperature of the bed of char sufficiently to drive off all condensed
volatiles?

2)  Is there any difference between forced and natural draft TLUDs?

3)  How recalcitrant to decomposition is tar in soil, and in particular,
tar embedded on biochar?  Is the occlusion of pore space long-term?

And a final comment.  Users of TLUDs will have to learn how to drive them
properly if they want to make good quality biochar.

Thanks, Rajan, for your observations.

Cheers,

Julien.


-- 
Julien Winter
Cobourg, ON, CANADA
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