[Terrapreta] Folke's retort kiln

[francoise precy]

Hi everyone,

http://www.holon.se/folke/carbon/simplechar/simplechar.shtml
Trying to piece things together and clear up my understanding. What got said so far: 

On 27 May 2008 22:51:33 -0700 "Philip Small" wrote:
“when the pyrolysis front advances "upwind", against the draft, and that draft comes from below, it corresponds to the same principles as both top lit updraft pyrolysis and reverse downdraft pyrolysis. The draft carries smoke, generated between the pyrolysis front and the charcoal, across the hot char to the flame.” This device is top-lit so we “get some of this effect.” “The more he controls his Superficial Velocity (Source - PDF http://www.woodgas.com/Superficial%20Velocity.pdf), the more benefit he can get from this effect.” “Only a toplit "stage 1" is a candidate (for that effect). 
“after the initial batch burns down, (...) the retort is still putting out woodgas”. When the fuel (is topped up), (the pyrolizing) does “not conform to the same effect.”  “Superficial Velocity effects (affects?) the pyrolysis gas temp as it closes in on the charcoal. ie slower SV cracks more CO2, until it's too slow to keep the flame above the charcoal burning red hot enough to radiate down (so as) to push the pyrolysis front (advancing upwind, away from the charcoal). OK my head hurts now. -philip 

This gets me confused b/c I imagine the draft going down (towards the only way out, so there is a downdraft inside that inner barrel), and the flame(s) being mostly up albeit outside. Assuming that the pyrolysis starts within at the top, is the pyrolysis front on top of the layer of charcoal or underneath it? 
If it's underneath, then the gases get 'filtered' mostly by the biomass / wood etc, not by the charcoal. If the pyrolysis front is on top, which doesn't make much sense to me so far, then the gases get filtered both by charcoal and by biomass. Was seeing it underneath but Philip ain't the only one who gets a headache from it, so by now I just can't work out anything further
The only sort of sensible thing I can think of is a system of 3 barrels of progressive sizes, the smallest (with a few small vents at the bottom maybe) filled with wood / biomass, sitting upstraight inside the largest; with the intermediary barrel turned over (bottom up) coming on top of the smallest barrel. So the smoke would have to go through the charcoal, come out by the top, go down the inner side of the intermediate barrel, and get burnt on the outside of it. 
One notable advantage as far as I am concerned: saves lugging full barrels about (can't see myself lifting – not dragging – on my own 2 metal bins with the smaller one full of wood). So allows for bigger batches than a poxy 20 litres-sized one. Don't know about any advantage re. elimination of gases.
Serious potential downfall: it'll probably take longer to heat up as the fire is not in direct contact with the container that holds the wood. Wonder if anyone's got any more precise idea on that point?

“Wok pan”:
2008/5/27 Ron Larson wrote: “enjira. This is a (delicious) thin sourdough flat bread cooked on a homemade thick ceramic disk (a "magogo"), of about 60 cm diameter.... this plate (disc) maybe sitting on top of the interior can (barrel).”
Folke answers: “when putting something flat on the stove, it easily starts smoking (=incomplete burning of the gasses).” So it's not the wok-pan-shape that's necessarily needed: if the 'plate / disc' is sitting on top of the inner barrel without overlapping (too much) the gap between the inner and outer barrel, the combustion of gases should still be effective. May also raise the disc on 3 stones so it leaves a gap between itself and the outer barrel's rim. 
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