retort

Here in Tallahassee, disposing of wood scraps from a home workshop is a problem. Except for a few winter days, the weather is too warm to burn wood for heat. Scraps from woodworking are mostly too large and well cured to shred for compost. The local trash collection people will pick up "yard debris", but refuse to pick up scraps from woodworking, on the grounds that they "construction debris". So, one is left with the choice of setting up a "burn barrel" or hauling them to the country landfill oneself. So, I looked for information on how to build a high-efficiency burn barrel, perhaps using forced air.

My search for burn-barrel designs led me to another alternative, in the form of a charcoal-making retort designed by James Hookway. Like a burn-barrel, it starts with a 55-gallon steel drum to hold the wood scraps. However, instead of drawing air into the barrel and burning the wood, you close the barrel up and cook the wood until nothing but charcoal remains. An L-shaped "rocket stove" runs through the middle of the drum, to heat the wood. Insulation around the outside of the drum retains heat to aid in getting the temperature up enough for pyrolisis. The Hookway design is very efficient, because it includes one additional element: a tube to carry the cooked-off wood gases (alcohol, creosote, etc.) back into the combustion chamber, where they burn to generate more heat, which greatly reduces the amount of wood one needs to burn in the rocket stove.

I bought the plans from James, and built one. The main difficulty I encountered was obtaining large-diameterstainless steel tubing for the combustion chamber. I finally found some at https://www.shapirosupply.com/, and had a local welder do the fabrication of that part. I did the rest of the fabrication myself, mostly using materials from the local Home Depot store. Since the only galvanized sheet metal they had was too narrow, I ended up using a lot of pop rivets! The insulation is "rock wool". James Hookway says Perlite or Vermiculite is better, but rock wool was easier to find, and is holding up pretty well so far.

The retort has now been fired several times. Some of the charcoal has gone into a "Big Green Egg" for cooking, some has gone to friends, and some has gone into compost after being pulverized in a chipper-shredder. The retort takes about the same space as a burn barrel, and making charcoal feels better than just disposing of wood by just burning it all up.

Here are links to some more photos of the retort, in construction and in use: