This video has been circulating on Faceborg content farms. The design works. A buddy has built several units.
Wood is loaded into a metal drum that is then sealed. The gap between the chimney and the drum can be packed with wet mud. A bolted flange and gasket is the better seal if the unit will be used more than a few times.
The fire is started in an internal rocket stove. Dry kindling or a small amount of cooking oil is the cleaner way to light it. Used motor oil will work, but it burns dirtier and leaves more residue.
The rocket stove heats the charge. As the wood carbonizes it gives off gas. Moisture plus those volatiles commonly account for 60 percent or more of the original weight, more if the wood is green.
A metal pipe returns the gases to the rocket firebox. Once that loop is established, the process is largely self-fueling until the volatiles are spent. What burns is a mix of tars, wood vinegar, carbon monoxide, and light hydrocarbons such as propane and butane. Combustion in a simple drum is not complete, but it is cleaner than venting the same gases to the air.
Clean, dry, untreated wood is the intended feedstock if the goal is charcoal or biochar. Other dry organics such as paper or chlorine-free plastics can be run in the same vessel; that is not the same as clean incineration. Do not use PVC, vinyl, or ABS. Food waste is high in moisture and is a poor charge for this design.
The same gas stream can supply heat to a boiler or a grain dryer. Tar and uneven gas quality remain practical problems for heat-exchange surfaces and for temperature control.
If you was planning on making large quantities of charcoal, you can roll some steel plate (or staineless steel) for a more durable machine.
Keep the drum sealed until it has cooled. Opening it while hot admits air, can ignite the charcoal, and releases carbon monoxide. Thin drums fatigue after repeated high-temperature cycles.
DIY High temp paint
This is a paintable sodium-silicate / red-iron-oxide coating. It is the closest homemade equivalent to a heat-stable red oxide film.
Dry mix (by volume)
- 2 parts red iron oxide powder (Fe₂O₃, rust pigment, or finely ground red oxide primer pigment if you can isolate it)
- 1 part fine silica flour, fireclay, or bentonite
Binder
- Liquid sodium silicate (water glass), about 37–42 °Bé, SiO₂:Na₂O ratio around 2.0–3.2
Mix
- Blend the powders dry.
- Add water glass until the mix is like thin cream. Typical starting point is about 1 part liquid silicate to 1–1.5 parts dry powder by volume.
- Thin with a little water only if it will not brush. Do not make it watery; a thick film flakes.
Use the batch the same day. Silicate mixes skin over and gel in the pot.
Application
- Wire-brush the drum. Remove loose scale, oil, and old flaking paint. A slightly rusted but sound surface is acceptable.
- Degrease (hot water and detergent, then rinse and dry).
- Brush or roll two to three thin coats. Let each coat dry to a hard film before the next. Total dry film should stay thin—roughly 0.1–0.3 mm. Thick coats crack and peel.
- Air-dry at least 24 hours.
- On the first firing, heat slowly. The silicate must lose water and begin to vitrify. A gentle first run is better than an immediate hard fire.
This film is a glassy silicate loaded with Fe₂O₃. It reduces scale growth. It is not a permanent enamel and will need touching up after hard thermal cycles.
Red iron oxide powder is sold as cement coloring powder. (Also works in thermite)