The results of the first attempted burn of the D.I.Y. charcoal retort were not as impressive as expected but seem to be on the right track.
Yesterday morning I picked up some nice cut-offs of spruce, cedar, and fir from Chris and his crew who were more than willing to assist with my experiment. I loaded the retort as tightly as I could and ended up putting in some other wood from the yard pile to fill it up.
I closed it up with the lid and angle iron braces, flipped it over, and used some cedar shavings, kindling, and deadfall to start the fire in the combustion chamber. Once the fuel wood caught, I put on the chimney and the smoke disappeared right away.
It burned for half an hour or so and then the wood gas started coming out around the bottom lid and getting sucked into the draft going into the air holes. I could also see a few drops of wood tar coming out around the bottom rim.
After another half hour or so, the fire seemed to be almost self-sustaining and the steel pipe started to glow red.
However, I think too much heat was lost because of moisture in the fuel wood, and some in the charcoal wood as well. It is also possible that the outside of the drum dissipated more heat than the reaction could counter. The fire died right down but there was still a lot of wood gas being produced so I added more fuel wood again. With the chimney in place it was roaring like a small jet engine and pulling all the wood gas into the combustion chamber again.
For the next hour I continued to feed it with fuel wood in small amounts, cleaning up most of the deadfall in the area. During this time, the steel pipe glowed red almost to the top of the barrel and it seemed like the best reaction conditions. The charcoal wood seemed to still be producing wood gas but as I began to run out of partially dry wood, finally I decided to call it a night and see what was in the retort the next day. I decided that if it was still brown it would still be a good head start on the next burn.
Based on watching this burn, changes I would make to the retort for next time are to place it up on a ring of blocks or stones to allow a larger burn area underneath, a cleanout access for ashes and fuel stoking, and more control over the airflow. I would also plan to keep the fuel wood fire as hot as possible for the first hour. I think insulating the drum on the outside would improve efficiency but do not have a satisfactory material to do it with yet.
My estimate is that half of the process was complete after yesterday’s burn. There were some very nice pieces of charcoal and many pieces of brown or partially heated wood. I decided to run the whole batch through again with some of the changes I came up with yesterday.
Find out about the construction and operation of our new and improved charcoal kiln: Charcoal Kiln V.3