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smokeless biochar retort, start with alcohol or propane?  RSS feed

 
Gilbert Fritz
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Location: Denver, CO
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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?
 
Bryant RedHawk
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Location: Vilonia, Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5
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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
 
Gilbert Fritz
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Location: Denver, CO
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Thanks Bryant!
 
I agree. Here's the link: http://stoves2.com
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