A 50L stockpot could be turned into a TLUD with some grinding, for a prefilled batch run of biomass to biochar. This is the same mainframe used for the 20L 'Tinkerer TLUD' (see the TLUD page) and 200L oil drum TLUDs but for an in between sized 50L batch of biochar. I imagine this will be good entry level system for testing different feedstocks and running small biochar experiments. The volume of biochar produced/feedstock availability/feedstock processing effort required is probably suitable for an urban setting. This apptech should be perfect for smaller biochar integrated systems such as water filtration (contaminated water/brackish water), sanitation, microgreens and fabric pot growing systems. There's also the potential of biochar used in an Atmospheric Water Harvesting (AWH) system (see page above).



  • 50L stainless stockpot
  • 1 metre of 1" galvanised square tube (or 304)
  • 2x Carbon steel oven trays 39cm x 28cm x 7cm
  • 1m x 6" 304 stainless chimney flue
  • 6" chimney wall bracket
  • 3 standard bricks



  • angle grinder with discs suitable for stainless



  • grind lots of small slots in concentric circles in the base of the stockpot
  • grind a circle slightly small than a 6" diameter circle in the centre of the stockpot lid
  • grind the square tube in half
  • grind 2/3 off a 1m chimney flue
  • assemble all parts according to the photo



A couple of bricks are placed at the base of the chimney providing a stable platform for windproofing and stabilising it while also locking the lid on.


The advantage of the large C steel oven trays at the base are:

  1. Insulates the base of the Stockpot for a hotter fire = more fuel efficient and higher surface area of the biochar
  2. Allows more primary airflow than a 3 brick system
  3. Can provide a stable platform for the TLUD - handy if only uneven ground is available
  4. Collects excess water from a burn quench for reuse in the next quench
  5. A safer system than tipping the biochar out of the stockpot into a water filled bucket/stockpot quenching system


The STBS could also be used as a firepit.


Overall system cost: AUD$230


User instructions (experimental)
  • Place a couple of large oven trays eg. C steel with 7cm depth (same depth as a standard clay brick), edge to edge in the centre, on the ground with a half brick in the centre of each tray
  • Place the stockpot in the centre of the tray footprint
  • Add the fuel to stockpot all the way to the top eg.wood pellets, rice husk pellets, nut shells eg.macadamia (perfect), almond; thin bamboo pieces, small sticks, ?kangaroo droppings, ?elephant dung, ?yak dung etc. or a combination of biomass/feedstock to get that little bit of airflow happening between the pieces for access to primary air flow
  • Squirt some firelighter gel on top in a couple of concentric circles
  • Light a scewer at one end or use a butane flame torch to light the gel
  • Add the 2 square tube pieces
  • Add the lid
  • Add the chimney 
  • Secure the chimney with a couple of bricks
  • Burn
  • End of burn

-An infrared laser thermometer/infrared camera (standalone/smartphone) could be used with the STBS to work out the outside temperatures of the stockpot to predict when a burn is over but would need to be calibrated to the feedstock. Another method is when the flame stops exiting the chimney, the burn is over but a little innacurate. Whatever works best for you - maybe you can work out a better way to do it - just don't burn yourself.

Put on the welder's gloves. For a quench/water-free method, the chimney can be removed with a steel '6" flue wall bracket' attached to the chimney half way down (used like a handle), the lid bricks removed, the lid removed (on the edges), the 2 square tubes removed (at the ends),  then place a few inches thick layer of premade biochar (preferably finely milled) on top of the top coals, lift the stockpot with the handles and place it on flat ground next to the oven trays - this will essentially starve the remaining biochar coals of Oxygen and avoid turning it to ash. There is a small risk of touching the outside of the stockpot while moving it and getting a nasty burn on your legs - wearing thick cotton pants would be advisable.

 -Alternatively, for a water-based quench after a burn, with welders gloves again, remove the chimney, remove the lid bricks, remove the lid, remove the square tubes then pour bucket(s) of water over the biochar and completely put out the hot biochar coals. There will be some steam - avoid it. Excess water will exit the base of the stockpot and collect in the oven trays for reuse. If the stockpot is reasonable quality, the metal shouldn't deform with the hot-cold shock of the cold water touching the hot stainless steel.

-The quenched biochar could be added to an incubator, such as half a PE barrel or even a 100L stainless stockpot which are easy to clean, good if you are doing microbial inoculation as you can clean the stockpot between each batch...


More information is available on the TLUD page above.

An integrated biochar system for water filtration, sanitation, inoculation; microgreens and fabric pot growing systems
An integrated biochar system for water filtration, sanitation, inoculation; microgreens and fabric pot growing systems
Round 1...Inertinite!
Round 1...Inertinite!