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?
