smokeless biochar retort, start with alcohol or propane?

I would like to make biochar on a mid size scale (30-40 gallons at a time.) I built a TLUD and got it nearly smokeless with a little tinkering, and it was a lot of fun, but most of my fuels are not suitable for a TLUD without a lot of work. A retort would do a lot better. However, most retorts get up to operating temperature by building an open fire around the container/ inner container. This is not a good option for me, since I live in a fairly densely populated area, and am often bothered by other folk's smokey fire pits. I'd rather not contribute to the problem.

Could I use an alcohol or propane flame to get a retort going? I was thinking of something along the lines of the following. An inner barrel contains the biomass to be charred, mostly sealed with just a few small holes at the bottom. It is propped off the ground on bricks, and is surrounded by an insulated barrel (using rockwood) with both ends removed and air vents at the bottom; maybe the top of the outer insulated barrel could be left in place, and a chimney installed. Under the propped up inner barrel is a propane or alcohol burner, which is lit to start the reaction. Once thing are hot enough to keep the reaction going, the propane would be turned off, or the alcohol would run out, and the burning wood gas would finish the process.

Questions: Would the propane cause an explosion hazard? (Let's say I was using an old propane fired grill for this, and that the propane tank, though not the grill burner, was removable once things got going.)

How long would it take before the wood gas reaction was strong enough for a smokeless burn by itself?

Would it help if I used more volatile materials (straw, paper) at the bottom of the barrel and more solid materials higher up?

Eventually, I'd like to use the heat for a masonry oven of some sort; how do you think this would work?

Could I get the same effect by simply adding some alcohol to the inside of the retort (in the inner barrel, near the bottom) and lighting a bit of paper under it? Would all the alcohol have evaporated before the heavier fuels were gasifying enough to sustain a clean burn? Remember that the outer container is insulated. Would it explode?

Is there a better way to get a smokeless retort cheaply?

hau Gilbert. For a TLUD to work well, the wood needs to be really dry to start with.

Instead of a true Retort (which is a distillation apparatus) why not use a "boiler" type setup where your wood is inside an inner container with gas vents and the fire surrounds the inner chamber.

This would make it safer and easier to do controlled burns I believe.

You would only need venting at the top of the inner chamber so the wood gasses have a way out, they would ignite just as they do in a TLUD and you would end up with nearly perfect charcoal if not perfect charcoal.

Using Alcohol to start a fire can be as dangerous as using gasoline to start a fire with, plus the flame will be nearly colorless which can be a hazard all by itself.
Propane, would be a better choice and if you use the burners from an old grill, you can position them around the inner chamber to get the best burn possible.
Pipe makes a perfect, safe method of getting the gas to the burners, leaving the rubber hose as far from the danger zone as possible.

This method means you can pack the inner chamber as tightly as possible with little worry and results in the most char possible per burn.



Redhawk

Thanks Bryant!

Old thread -- but I have a crazy notion that perhaps might fit. And I like the idea of the clean burn from one end to the other.

Charcoal is fuel in many places. And it burns mostly smokeless. If you took a portion of char from your first propane-fired burn and created a charcoal pre-heat burner, with oxygen pressed in by a small efficient fan, could you pre-heat and start the next burn? And then repeat the cycle? And come out ahead in total char production?

Yeah, crazy, but think of it as a jumpstart system. I wonder ...

I've has the same struggle as the OP, with tluds burning cleanly and without tending but requiring refined fuel,flame cap methods needing lots of attention to get the same result, and retorts needing external heat ro get them started.
This is why so many designs are tlud fired retorts, they use a little bit of refined fuel to fire a lot of unrefined feed stock.
Some of them even use blowers to feed the flames.

Douglass, I love  your idea of dipping into the refined end product to create more of the same.
There are lots of charcoal fired foundery designs that would do the job, just scale up, replace the crucible with a retort and you are good to go.
Mind you, there are also wood fired foundery designs that might work, but the fuel takes up more room in such a design, and we are already be upsizing the design to accommodate a retort instead of a crucible.
Plus, we are in the business of making charcoal anyway.

I  think forced combustion air might be actually be overkill.
My tlud firepit got hot enough that it melted through an aluminum tray sitting under it.
That might have been from coals that fell and sat right on on the aluminum,  but even so it it was without forced combustion air.
Thats plenty hot, so how much hotter would it get if they were filled with char from the get go?
I'm kinda afraid to try this for fear of destroying the firepit or even the retort!

This could be even simpler than heating a retort with finished char.
Maybe we could load a tlud 80% full with moist/irregular fuel but fill it the rest of the way with charcoal.
The top lit charcoal fire could do a lot of drying as the flame front moved downward.