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

[Huck Rorick]

Thank you all for these responses.

I noticed that some other gasifiers seem to burn the charcoal: the SilverFire Hunter and the Prime cookstove.
Do these do that effectively?  And if so, why does it work for them?

The initial thoughts for our project are that people would prefer to burn the charcoal immediately for the additional heat (but it seems that this may not be very effective) and less handling.



-----Original Message-----
From: Ray Menke [mailto:ray.menke at gmail.com] 
Sent: Tuesday, October 14, 2014 12:57 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Why doesn't charcoal burn in the Champion TLUD?

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