I spent some time today making charcoal from apple tree trimmings using my Gilmore style double barrel “retort”. This is a video of the outside of the barrel setup. http://youtu.be/Js-cphoptuM I use the bottom 3 inches from a 5 gallon pail to set a 30 gallon metal garbage can on. The garbage can has maybe 20 to 30 1/2 inch holes in the bottom for air inlet. A 2 inch pipe lets in combustion air thru the outside barrel and into the space below the garbage can. As seen in the pictures below, the fire is lit at the top and burns downward using up the oxygen as it burns down so the charred wood above the burn does not have the oxygen to burn up. When the fire gets down to the bottom I can see the glow thru the 2 inch pipe and then I plug the pipe with a ball of aluminum foil (I’m too cheap to buy a 2 inch ball valve) , then remove the barrel cover/chimney and put the metal cover on the garbage can, then the solid cover and band on the outside barrel. As you can see in the video, there is very little smoke using this method. I know it is more work cutting the smaller pieces to make charcoal with but the whole process only takes a couple hours at most this way. I have not tried big pieces but I believe it would take longer. I had a feathered friend join me part way through as seen in the last picture.
Looks good! Those rounds are just about right for a regular wood gasifier. Here is a photo of what goes in my charcoal barrels. (I am using the method Gary first described, with the lower 55 gallon drum having holes around the bottom, and a second drum as a chimney. In operation, the two are separated by two horizontal rebar rods about 3 feet long.) My lower barrel is covered with an old wash tub (while waiting for the burn ban to lift), shown at the upper left portion of the photo, a drying rack on the right, and a stack of junk wood that will be turned into charcoal. I tightly pack the lower barrel with the wood shown, letting it extend 12" to 18" into the chimney. (I will split those rounds that are in the wheelbarrow.) I light a 5 gal bucket of crumpled paper balls on top of the wood, and feed it with the skinny branches and brush. There is no smoke! I use tree trimming loper shears to get the skinny stuff so I can stuff it into the chimney. If I get too much flame shooting out of the chimney, I toss in a large chunk…if the flames go down, I put in more paper balls. After 1 hour, when the glow is seen in the bottom holes, and the flames die down, I remove the chimney barrel and the three bricks under the edges of the lower barrel, and push dirt over the holes. I use an old steel fence post to poke around inside the barrel, and when the flames die down again, it is time for the lid. The charcoal level is about half-way in the barrel, so here is my latest twist. I take two five gallon buckets of those nice rounds like you have prepared and toss them in on top of the charcoal, and slap the lid on. The rounds effectively insulate the wood in the lower half of the barrel, and a generous amount of dirt and clay insulate the lower portion of the barrel. 23 hours later, open the barrel and remove the charred rounds. Save them for your wood gasifier. (Mine smell like mesquite BBQ!) Now dump out the charcoal onto old sheets of galvanized or tin roofing. Spread it out, make sure it is not going to burn up. (It turns white!) I have a good supply of dry charcoal, so I use 10 or 15 gallons of water to wash it down, and then the our sub-tropical sun will dry it out. After 12 hours or so, I can sift/sort/grade without getting charcoal dust in my lungs and all over everywhere. If you want to have it very dry, and ready to use immediately, you will obviously not use water, but may need to either leave it in the original barrel until it is dead cold, or transfer it to a container with a tight lid.
I might add that I trim large branches with the lopping shears, and the good clean wood goes to the chop saw table. I use the ugly stuff to make charcoal!
I got some charcoal made over the weekend also. Mostly for my base in my gasser, but also to test out a scaled down version of the double barrel retort. I used a 6in x 12in long pipe. Made several batches of pine charcoal. I also made a batch of 1/2in dia corn stalk pellets into charcoal. They turned out very nice. I was surprised how well the density stayed to them. Not sure what I will use them for yet. It took quite a while to do. I actually put the lid on them somewhat loosly and let them just cook overnight. I think due to the lack of void space between the pellets is why.