Build a simple TLUD to make your own charcoal

So you want to make some biochar? The only way to do that in countries like New Zealand at present, is to make your own "TLUD" stove. That can be very simple - and a fun project for a family or a school - once you understand the principles involved.

Pyrolysis in a TLUD

As it heats, wood "gasifies", i.e. it breaks down chemically into volatile gases (smoke) and solid, almost pure carbon (charcoal). If the two products can be separated at that point, it is possible to "pyrolyse" the wood, by burning the gases and retaining the carbon. In a "top-lit-up-draught" stove, or TLUD, the fuel is set alight from the top and begins to gasify as it heats up. This hot smoke rises, drawing air in through the secondary air supply above the fuel, and burns cleanly because it contains very little carbon (soot). Fresh secondary air cannot reach the fuel, and in this oxygen-starved atmosphere, the fuel pyrolyses from the top down. The primary air supply, drawn up through the bottom of the fuel chamber, is sufficient to light the stove and support pyrolysis, but not enough for full combustion of the fuel. Once all the fuel is pyrolysed and no more gas is being driven off, the stove goes out.

Flame in a single-can TLUD

A used vegetable can with holes punched in appropriate places will make a small TLUD, a simple BBQ stove for your emergency preparedness kit. It will cook a small meal with a handful of sticks, small pine cones or any other dry vegetable matter. The resulting charcoal could be used for longer, slower cooking in an emergency.

With a little more effort - and more fun! - you can make your stove more efficient, with some control over its heat output.


But why wait for an emergency? Make some now; experiment with can sizes and hole placement, different fuels, pot stands etc, and be really prepared when the unexpected happens! In the meantime, you can use your TLUD at any time to make some biochar for your home garden.

Different sized food cans

Different sized food cans

Holes in 450ml can

Ready to light

Suitable fuels

TLUD No.1

Simple stove made from one 450ml (15oz) can

Most of the tools and materials required to make a simple TLUD are commonplace around the house. The only two absolutely essential materials are:

  • a fuel container with holes to admit primary and secondary air;
  • a pot stand.

The tools required are:

  • hammer and a large nail;
  • a nail punch or similar tool to enlarge nail holes;
  • can openers - different types depending on the sophistication of the stove;
  • a can punch;
  • wood blocks for support while punching holes in cans.

Primary air holes in base
Secondary air holes


Punch a ring of holes in the base of the can, and evenly spaced holes round the side about one third of the way down from the top. The top holes should be larger than the bottom holes to admit plenty of secondary air. Experiment with hole sizes and different types of fuel - some fuels need more air to keep them burning.

Stand the stove on blocks to allow air to enter the primary air holes in the bottom of the can. Half-fill the stove with small chunky wood chips or similar fuel.

It helps in lighting the stove to have a small amount of fuel soaked in rubbing alcohol on top, to get the pyrolysis started quickly.

Tip: if using alcohol-soaked starter fuel, light the stove through the secondary air holes to avoid burnt fingers!

Lighting a single-can TLUD

For your safety!!

Never light a TLUD stove inside a confined space. The exhaust gas may contain carbon monoxide.

Pyrolysis in single-can TLUD


Once pyrolysis starts the flame will reduce to a little jet inside each air hole, and the fuel will glow red. It is now ready to cook on.

In windy conditions, stand the TLUD on blocks inside a larger can.

With sufficient air holes round the top, the large can may serve as a pot stand as well. You may need to prop the pot up a bit further to give enough space for the exhaust gases to escape - experiment!

TLUD No.2

Three or four cans and a little more effort ...

For a more sophisticated, longer-burning stove, you will need:

  • three cans of different sizes;
  • a concentrator lid with a large central hole;
  • a riser - a cylinder open at both ends;
  • handles.



Tools required

...and the following tools:

  • hammer and a large nail;
  • a nail punch or similar tool to enlarge nail holes;
  • can openers - different types depending on the sophistication of the stove;
  • a can punch;
  • wood blocks for support while punching holes in cans.
  • tin snips;
  • pliers;
  • file;
  • ruler and measuring tape;
  • a permanent marker;
  • paper and pen.

This TLUD consists of two cans one inside the other, and a lid. It also needs a pot stand, which could be made from another can. We have used a 480ml can (10.5cm high, 7.5cm diameter) for the inner fuel container; a 680ml can (14.5cm high, 8.5cm diameter) for the outer container, and a shallow fish can (5cm high, 10cm diameter) for the lid. Cans B, D and I in the photo above.

          Inner can

Punching primary air holes
Primary air holes in inner can
Inner can, lugs turned out


1. Mark the centre of the base of the can.



2. With the can supported on a piece of wood, use the hammer and nail to punch a hole at the centre, and small holes evenly spaced all over the bottom of the can. The centre hole will be used to screw the two cans together, and the other holes will admit the primary air supply



3. Measure the circumference of the can and mark 6 or 8 points evenly spaced around the top.

4. Punch holes at the marks, using the can punch from the inside of the can, so that the lugs are pushed outwards. They will serve as spacers when the two cans are fitted together.

5. Carefully turn the lugs up far enough that you can slide this can inside the larger can.


Outer can

6. Using the hammer and nail again, punch a small hole in the centre of the bottom of the outer can.

7. Punch 8 secondary air holes around the side near the bottom of the can, using the can punch on the outside, pushing the lugs into the can.

          Assemble the two cans

Centring two cans
Two cans centred

8. Screw the sheet metal screw into the hole in the centre of the base of the outer can until the tip is above the holes around the base of the can.

9. Push the smaller can inside, and screw into the centre hole in its base. The inner can must be securely fixed with its base above the holes in the outer can, so that air can enter the primary air holes in the base of the inner can.

10. Use a screwdriver to push the lugs on the inner can out until they touch the side of the outer can, keeping the two cans evenly spaced all round.



Concentrator lid

Lid, punched
Hole cut in lid

11.  Find and mark the centre of the shallow lid can.

12. The hole in the lid must be half the diameter of the inner stove can.

13. Measure one quarter (half the radius) of the inner can, out from the centre of the lid can, and mark a circle at this radius.

14. Punch nail holes at the centre, and 8 evenly spaced around the circle on the lid can.

15.Use tin snips (preferably), or a can ripper, to cut from the centre out to each hole.

16. Use pliers to bend the segments inside the can, and flatten them neatly.


Using your TLUD

Lighting a TLUD
Pyroysis, lid on
TLUD inside larger wind shield
Suitable fuels
Pyrolysis complete


This stove can be filled with fuel up to the secondary air holes (the top holes) in the inner can. A little fuel soaked in rubbing alcohol will help to light it.





Start the stove without the lid. Once pyrolysis has started (flame reduced to a jet inside each secondary air hole), put the lid on to concentrate the burning gases and increase the "draw".

Fuel may be added slowly during cooking. If you put the stove out with too much new fuel, quickly drop another lighted match in to re-start it.





As with the single-can stove, wind can put the fire out, and the stove should be shielded inside a larger can or some kind of fire-proof screen, which may double as a pot rest. The fire will go out if there is an insufficient gap between the stove and the pot for exhaust gases to escape.


Try different fuels. Any dry biomass will burn, some better than others. Pyrolysis is more even if the pieces of fuel are of fairly uniform size. Rough, broken edges catch more readily than smooth, rounded shapes. On the other hand, hard, solid woods usually burn longer than light porous fuels. You could try placing round hard seed pods at the bottom of the stove, then adding progressively lighter, rougher fuels. Once the fire is burning vigorously its heat will be sufficient to start harder fuels.

When the fuel is fully pyrolysed the flames will die down for a few minutes, then go out. As long as you have provided sufficient air supply, there should be no visible smoke. However, as noted above, if the pyrolysed fuel - charcoal - is left to burn, it is likely to produce deadly carbon monoxide.

Remember!!

Never light a TLUD inside a room!

Quench the hot charcoal with water, and it is then ready to use in your compost -

or, Bokashi.

This Japanese composting system uses a medium (bran) inoculated with micro-organisms to start the composting process anaerobically. The organic material breaks down very quickly once it is buried in soil.


The anaerobic process produces very microbe-rich liquid which collects in the bottom bucket. Charcoal, when added to this liquid, absorbs it, complete with nutrients and microbes, i.e. it becomes  biochar!

Food scraps in Bokashi bucket
Charcoal in Bokashi liquid


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