[Stoves] Why doesn't charcoal burn in the Champion TLUD?

[Ray Menke]

Julien and Huck,
I have been using a Champion, a 9" copy of a Champion, and one of
Paul's Quad stoves for some time.  (Since they were introduced, in
fact.)  I do not burn pellets because they are not sold here in the
sub-tropics, and I have lots of junk wood slivers and chunks.  I also
have a good supply of torrefied wood, and other wood that has not been
completely converted to charcoal.  (1" cubes that contain some brown
or unconverted wood.)  When the fuel in the Champion burns down and
the flames no longer enter the short chimney, one can use a small
computer fan to fire up the charcoal, but doing so will burn out the
steel grate, and the lower part of the fuel container.  (This
basically turns your stove into a forge!) I line all my burn chambers
with sacrificial steel cylinders made from old stovepipe or water
heater tin, so if I use a fan, I can just replace the liner, rather
than constructing a whole new stove bottom.
Another method of conserving the gate and burn chamber is to carefully
load the stove, putting green chunks on the grate, followed with a
layer of half-done charcoal chunks, and then a thick layer of bone dry
hardwood slivers, followed by several inches of starter fuel.  Small
pieces of charcoal screened through two sizes of hardware cloth can be
layered with the starter fuel ( 1/8" and 1/4" screen/hardware cloth).
These pieces of charcoal will be less than 1/4" and greater than 1/8",
and when the starter fuel and char pieces are sprinkled with a few
drops of alcohol, they will quickly ignite.  The small pieces of char
will help form that glowing charcoal that consumes the smoke from the
wood below it.
The size of the holes in the grate, and the depth of the fuel in the
stove will control how much charcoal is left at the end.  I also use
dampers on my primary air tube at the bottom.  (Sometimes, I just put
a large stick in the primary air tube.)  My Anderson Quad came with
relatively large holes in the grate, and it does not leave me much
charcoal at the end.  My copy of Paul's Champion has smaller holes in
the grate, and it needs the fan toward the end of the burn, if I want
to use the heat from the charcoal.  (Like to finish a pot of rice, for
example.)  My 9" stove uses a fuel height of 14", and puts out about 2
or 3 times the power of the Champion.  I can regulate (reduce) the
output power by adding large chunks of half-done charcoal if the
flames get too high.  This stove is used for heating a large pot of
water (4 gallons), boiling tomatoes down to paste, or running my 14"
cast iron wok.  For water heating, I just light it, and go away.  It
does not smoke.  When standing over the wok, I do use quite a bit of
half charcoal chunks to regulate the power.  For a bit more flame, if
I have added too much charcoal, I can add more dry hardwood slivers.
This flame and the glowing charcoal is then directly on top of the
fuel load, and near the bottom of the pot.  This stove yields a large
amount of very high grade charcoal when it goes out.  I dump the
charcoal into a large steel bowl of water, pour it through a screen,
dry it, and then run it through my hand powered charcoal grinder.  The
end result is pure charcoal sized between 1/4" and 3/4" that is stored
in sealed 55 gallon drums.  I also save the charcoal measuring less
than 1/4" and greater than 1/8" in separate containers.  (The biochar
folks love this stuff.)  The charcoal fines and ash end up in my
compost piles, which I turn with a diesel powered front end loader.
I feel the key to using these TLUD stoves is to insure that you have
very dry properly sized wood, which takes hours and hours of simple
labor.  I am using wood now that was chopped and dried several years
ago.  Also, I use a ceramic wool insulation on the riser tubes.  It is
covered with aluminum foil with a wire wrap to hold the foil in place.
The insulation on the Quad is inside the riser.  The foil holds it in
place.
Ray, in South Texas  29.9N

On Tue, Oct 14, 2014 at 12:36 PM, Julien Winter <winter.julien at gmail.com> wrote:
> Dear Huck;
>
> Charcoal from pellets burn slowly in a Champion-type TLUD, because there is
> not enough primary air movement.  The resistance to gas movement in the
> charcoal bed is too high.  Also, there isn't the draft from a strong pyrogas
> flame.
>
> If you burn wood chips or sticks, the gas permeability of the char bed is
> high, and the charcoal will burn off quite well.
>
> It would be nice, however, if one can get the charcoal fire closer to the
> bottom of the pot so that there is better transmission of radiant heat.
> Paul has a TLUD for that which breaks in half when the pyrolysis phase is
> complete.  Otherwise the path between the char fire and the pot should be
> well insulated.
>
> Some people mention how good it is to have a fan to force the primary air.
> That is true for pellets, but not so much for sticks and chips, because
> their permeability is already high and their bulk density is low (so you
> will burn off your batch of fuel is 10 minutes if you force the air).
>
> (I should note that the gas permeability of a bed of fine wood chips (< 10
> mm)  is also low).
>
> I keep promising data to show this.  Its coming soon.
>
> Cheers,
> Julien.
>
> --
> Julien Winter
> Cobourg, ON, CANADA
>
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-- 
Ray  Menke