Here's a brief 'ible on burning sawdust. If you've ever tried to burn a pile of sawdust, you'll soon find a very smoky mess on your hands - and lots of unburned sawdust at the end of it.
For reasons which I can't quite fathom this method is also known as "The Boy Scout Candle". It will yield a very clean flame, because the operation is by "pyrolysis in excess air". The wood is strongly heated by the flame front, liberating burning gases into the flame. Convection through the stack forces lots of air into the reaction, and there is very little smoke, if any.
The example shown here burns for only about 15 minutes. The burn will scale up, but if you are very interested in advanced combustion, take a look for projects on "TLUD gasifiers"
Step 1: Equipment.
All you need for this demonstration version is
- A charcoal starter,
- Sawdust, or planer shavings
- A "packing tube" - I used a piece of 1.5", 38mm plastic tube, because it was what I had.
Step 2: Method.
Place the packing tube in the centre of the charcoal starter
Pack sawdust fairly tightly around the OUTSIDE of the tube.
Withdraw the tube slowly. I find a twisting action helps. You are aiming to leave a well defined core to the pack, with clear air holes at the base for the fresh air.
Step 3: Lighting
Well, you can cheat like me and use a blowtorch, or you can do it with some tissues at the bottom of the starter. If the wood is dry, you won't need any accelerant at all.
Step 4: More Work.
Experiment with scaling this up to a bigger unit. I'd love to try a 5 gallon metal bucket, because the demo version doesn't burn too long.
The flame is pretty clean, and you can cook on it.