55/30 Gal Tinman TLUD needs your help!

Wow - what a great site!  I just built a two-can "tinman" TLUD kiln based on the Bob Wells (Living Web Farms) video for cooking biochar.  A 30 gallon drum inside a 55 gallon with air hole placements gleaned as best I could from the video and a 6” dia. 4' tall stack on top.  My feedstock is 1x1x4” very dry hardwood.  The annular space is packed with the same hardwood stock, just cut longer.  After running two batches, my char came out great!  100% cooked.  I clocked almost 850 degrees on the outer drum with the temp gun.  HOWEVER...  The kiln fired up great and burned hot, clear, and clean for the first 1hr 45min, then BAM – once the inner drum got hot enough and pyrolysis began, it started belching continuous large amounts dense yellow-ish smoke out the stack.  With the humid air, it made a cloud! This continued for about 45 minutes and then tapered off quickly as the process concluded – about 3 hours total.  I'm thrilled at the quality of the biochar but I gotta do something about the smoke!  I have lots of biochar to make to renovate my 3,000 sq. ft. garden.

I attached some photos of the primary and secondary air holes I started with.  Please help with your experience on how I should adjust the holes to get a much better syngas burn.  More/larger secondary holes?  Less/smaller primary holes?  The draw is really pretty strong so my first thought was shmaybe the syngas is being drawn thru too quickly and it is not in contact with the flame location for long enough to ignite?  I can hear the gas hissing from the bottom of the 30 gallon but I did not see any kind of blue flame I read about.  I also thought maybe the burn stock was packed to tightly between the drums and the flame was not getting enough air flow to burn the volume of syngas being generated. Two opposite thoughts though.   There was a breeze both days.  I braced a sheet of ply to cut that down somewhat.  Don't know if that was a factor.

Also read that it may help to remove the stack right before the smoke starts and drop some wood scraps in the hole on top of the drum (then replace the stack).  I guess this is done to insure ignition of the gas near the top of the drum.  What do you think?  Is it possible the wind stopped the syngas from burning?

that dense yellow smoke sounds like pyrolysis gases boiling off without enough secondary air to reburn. When I used to do this I would place a second 50 gallon barrel open top and bottom on top of the lower one propped up on two metal dowels to allow extra air in. The smoke would recombust in the upper chamber.  I ended up doing away with the inner barrel and made char directly in the lower barrel. you have to be able to starve it of oxygen at the end though...
hope that somewhat helps...
cheers,  David

Your char looks good.   I don't use a retort, because I think you get less char per wood.

I really like your idea of adding new wood later to help burn off the gases after awhile.  I have been doing that, but not specifically for that reason.  I am just trying to keep it burning well and make just the right amount of char for each step in my process.

There are others who use retorts here and  some who have extremely advanced experience in many types of biochar.  I hope they chime in.

John S
PDX OR

OK I have to ask, what is the quality of the smoke from the process?
Are pollutants being discharged to the atmosphere?
From /biochar-production-climate-change

"In many parts of the world, people are wiping out forests to make charcoal for fuel. When they cook with charcoal, they often use poorly designed indoor stoves that fill their houses with a deadly cloud of pollutants. (Indoor air pollution kills 1.6 million people every year.)
Moreover, when wood burns in an ordinary stove, it releases soot and carbon dioxide, both of which can trap heat in the atmosphere.
Biochar stoves could potentially knock out both threats with one proverbial stone.
Several inventors are designing cheap, efficient models that allow people to cook without generating a lot of smoke.
Instead of heating wood, these stoves use other plant material—even run-of-the-mill farm refuse.
"Rather than women having to trudge into the forest and bring out a big log, they can use brush or corn husks," says Lehmann.
They simply load the stove with fresh organic matter and light a conventional fire just long enough to get the material hot enough to release gases,
which the stove can then burn to release even more heat.
It takes conventional wood fire only a few minutes to get pyrolysis into a self-sustaining cycle.
And because a pyrolysis stove doesn't produce much smoke, it releases very little carbon dioxide or soot.
Instead, the carbon ends up in leftover lumps of biochar. And when farmers bury it in their fields, that carbon stays underground
—for an extraordinarily long time.
It's the kind of win-win that captures people's imaginations. Thanks to Lehmann and his fellow biochar advocates, terra preta has been transformed from
obscure patches of Amazonian dirt to the subject of some of the biggest debates in climate-policy circles. "

My concern is the fact that heat is being created and dumped to the atmosphere, can that process be improved to heat something? A home, water etc?

You've got a good point, John.

It would be way more efficient to use the heat to cook food, heat homes, etc, when making biochar to sequester carbon and improve plant growth.

I feel like we are on the cutting edge of using biochar. One of the great things about permies.com is that we can freely share ideas about what works and what doesn't, and present new and better ways of doing things.

I don't use the heat from my biochar burning in a very efficient manner.  I would love to hear models of how to use the heat constructively.  As H. Ross Perot used to say back in the day, "I'm all ears."

John S
PDX OR

I think some holes on the base of your chimney could clean up your burn.

William Bronson wrote: I think some holes on the base of your chimney could clean up your burn.

I believe William is correct.  A number of holes, probably 1" or so around the bottom of the chimney will allow enough air for the secondary burn of the gases.  I have used David's solution as well.  You just need to figure out a way to burn those gases, and extra air should do it.

I use a retort now set up just like yours except that I don't use any chimney at all and I have better results.  If you do it with no chimney as I do, it's important to keep a small fire burning on your retort to burn off the gases as the come up the sides.  When you start your fire, all is good, but the wood on top of the retort burns off and the wood around it starts burning down the sides.  Soon after that, your retort will start to out gas and if you don't put more small wood on the top of the retort, there is nothing to burn the gases and you'll get that same smoke.

John C Daley wrote:My concern is the fact that heat is being created and dumped to the atmosphere, can that process be improved to heat something? A home, water etc?

This is something I always think of as well.
Drying the incoming fuelstock is the obvious use.
I advocate distilling , because it creates a storable value added product , and the process involves moving heat, which opens up possibilities as to where the heat is used.
Almost any liquid could be purified this way, without concern of wasting energy.
Depending on what is being distilled, the dregs might have as much value as the part that is evaporated and condensed.