[Stoves] Stoves Digest, Vol 33, Issue 19

[Crispin Pemberton-Pigott]

Dear Dr Tom

Thanks for popping up.

>O Pyrolytic Gasification (TLUD and larger) which primarily  gasifies the
cellulose and pyrolyses the lignin to ~20% charcoal

Does the fact this is from lignin mean that there is something fundamentally
different about the structure of the char product compared with commercial
charcoal? Is it just a 'temperature thing'?

>The smoke from a TLUD stove will leave a deposit on a cold steel plate.  I
was interested in finding out how much "tar" was in the TLUD combustible gas
before it is burned.  

I have observed quite a lot of tar on the pots when the flames of TLUDs is
not given time to burn completely.

Another problem observed is that using wood (not pellets) in a TLUD with
fairly high moisture content (like 15-20%) seems to produce quite a lot of
fuel moisture-sourced condensation on the pots, probably because of the
strong thermal connection between the two ends of the chunks of wood. So far
it appears the wood dries early and completely, then pyrolyses as usual.

This provides several measurement problems for both volume-based (hood) and
chemically balanced test methods (sample+scale). 

It may be that the products I am seeing allow too much combustion, but there
does not seem to be an easy way to spread the evaporation over a longer
time. Ideas are welcome. To break the thermal connection means physically
separating the wood into smaller pieces, a task strongly opposed by users.

One conclusion I can draw is that pyrolytic combustion of wet wood (which is
already a problem to burn) is perhaps more difficult to start and manage
that other types of combustion. Tinkering with the air supply can produce
wonders but cooks may not be willing to do that when there are much lower
attention methods of burning the same fuel.

In some places people are pretty attentive to using waste heat from stoves
to dry the fuel for the next day but that is to get it down towards 15%, not
to really dry it.

Thanks
Crispin