Re: charcoal troubleshoot

[David Yarrow]

doug & jono,

 

need more info to offer a diagnosis.  most likely the inner barrel didn't get hot enough to start gasification full force.  could be three reasons:  too wet; not enough firewood to start charring & gasification; not enough air intake for firewood to burn hot and fast and thus generate adequate temperature.

 

first question: what was your feedstock?  leaves and sawdust might block the exit of gases down and out, especially if packed in too tight, leaving no opens spaces for gases to flow through the inner barrel. 

 

from your photo of feedstock in your smaller barrel, i believe it's loosely packed, with enough sticks and open spaces for gases to flow through and exit the barrel during pyrolysis.  however, you have a lot of leaves in the mix, which can pack down on the bottom to clog and restrict the exit passageways -- especially if leaves are damp.  it looks like some charring occurred, but not much -- as if your burn got near charring temperature, but either didn't get completely hot enough, or didn't stay hot enough long enough.

 

second question: how long did firewood burn?  at least 15 minutes seems a minimum time to get feedstock in the inner barrel over 250 degrees and initiate gasification, and many experimenters report 30-40 minutes.

 

we had similar trouble in a burn monday night.  woodchips were rolled in newspaper into half a dozen bundles, and put in the inner barrel bottom, which was then turned upside down, so woodchip bundles were at the top of the inner barrel.  at the burn's end, these bundles (and much of the newspaper) failed to char, even though other sticks and slats in the barrel nicely charred all through.  when opened, woodchip bundles were steaming.  before they were rolled up, i handled them and commented they felt wet -- probably from rain earlier in the week.  steam kept temperature low -- not above 250 degrees -- so charring and gasification never started inside the bundles.  further, steam was trapped at the top of the inner barrel, unable to go down and out of the barrel, affecting all material at the top of the inner barrel.

 

so the lesson is 2-fold.  first, feedstock must be very dry, or it will use up heat producing steam until the water is evaporated out.  damp or wet feedstock lowers temperature to retard, even prevent, charring and gasification.

 

second, steam was trapped at the top of the inner barrel.  since the 2-barrel retort forces heated gases to move down and out of the inner barrel, steam couldn't be released.  thus, ideally gases should exit the inner barrel at the top, not the bottom, to prevent this dead space for steam and gases to accumulate.  however, the simple 2-barrel retort will serve us well enough for the moment if we only use very dry feedstocks, but the 2-barrel equipment can be improved by adding an exhaust at the top of the retort.

 

i doubt the seal between inner barrel top and outer barrel bottom was too tight, and thus didn't allow gases to escape.  it shouldn't be necessary to engineer a gap between the inner barrel and large barrel bottom.  gasification generates enough gas, and thus pressure, to bust through any cracks and gaps between the two barrels.  however, if in doubt, drill three to six small holes (1 inch or less) at the top of the inner barrel to allow gas to jet out into the larger barrel.

 

martin kemple & david ludt observed if the inner barrel is too large relative to the outer, with too little space between barrels, the firewood won't burn hot or long eough to raise feedstock temperature and initiate gasification.  some experimentation is required to assure the two barrels are properly proportioned to offer enough space between for adequate firewood.  last night we used 30 and 55 gallon barrels -- the smaller barrel was tall and less wide, and -- if anything -- we had too much firewood stuffed in the barrel gap, so the firewood burned long, and produced more smoke than desireable.

 

looking at your photo, i am very sure you need more air holes at the bottom edge of the outer barrel.  to burn hot, the firewood needs lots of air sucking in the bottom and exiting the top.  the only air hole i see in your photo is the round bunghole -- clearly not enough to suck adequate air into and all around the burn chamber.  so, cut several horizontal slots along the very bottom edge of the outer barrel, distributed evenly all around the barrrel.  you can always cover these holes with dirt to choke the fire if you want to slow the burn.  but right now your fire is starved to air.

 

another strategy is to place a lid over the outer barrel after the fire is burning good -- but leave a small gap for smoke, flames and exhuast to escape.  if you completely close and seal the top of the outer barrel, flames will downdraft and shoot out airholes at the base of the barrel.  adding a lid will contain heat and increase burn temperature, allow more effective regulation of the rate of firewood burn rate, and reduce smoke.  david ludt added a lid to the outer barrel, and cutout a hole in the lid and inserted a stovepipe smokestack exhaust flue with a variable damper.

 

keep trying and learning.  and sharing successes and failures.  photos such as the two you sent help others to understand how your equipment works and how you conduct your burn.

 

for a green & peaceful planet,
David Yarrow
Turtle EyeLand Sanctuary
44 Gilligan Rd, East Greenbush, NY 12061
www.championtrees.org
www.OnondagaLakePeaceFestival.org
www.farmandfood.org
www.SeaAgri.com

----- Original Message -----

From: Jono Neiger

To: douglasFrances --

Cc: dya...@nycap.rr.com

Sent: Monday, October 06, 2008 9:04 PM

Subject: Re: charcoal troubleshoot

Its very possible the inner barrel was too packed. I've had good success with vertical material like sticks, and tubes with packable material in them. This seems to allow some gas flow inside the charcoal chamber.

 Was the material wet? That could be another problem. Gas escape is not an issue, I think as it can push out as needed. How much fuel did you use? Was it very hot? Not hot enough or long enough fire might be another prob.

My first guess would be too packed chamber.

Try it again. We did 3 burns this weekend and two worked. The third had too much wet material.

cheers

Jono

On Mon, Oct 6, 2008 at 11:54 AM, douglasFrances -- <pfk...@gmail.com> wrote:

hello, you two.

so.  yesterday was Burn Day.  the short is that the burn did not yield charcoal and am wondering if you had any advice on the matter.  the inner barrel is still full and i'll do another burn if i discover where my process left the charcoal path.

it seemed to me that the gas from the inner barrel that feeds the outer barrel fire, never appeared.

possible mis-steps:

-- inner barrel too full/compacted (though i would not at all describe it as tight)

-- the inner barrel was flush with the outer can -- there was no space for the gas to escape, if i was supposed to leave one.

-- not enough fuel in the outer barrel, or not a hot enough fire.

anyway, kindly yours.  thank you.  and thank you for sharing with me the wonders of charcoal.

Frances

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Jono Neiger
Regenerative Design
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